WORKING PAPER 2019-13

Advanced alternative fuel pathways: Technology overview and status

Authors: Chelsea Baldino, Rosalie Berg, Nikita Pavlenko, Stephanie Searle Date: July 19, 2019 Keywords: Thermochemical conversion; biochemical conversion; non-food feedstock; lignocellulosic biomass; biofuels; renewable fuel; electrofuels

Introduction and summarized in this paper. For Fischer-Tropsch (FT) synthesis and this figure, as well for all the follow- methanation, before it can be used as Policymakers recognize the signifi- ing figures in this paper that illustrate a transportation fuel. Hydrothermal cant greenhouse gas (GHG) savings the individual conversion technology liquefaction and fast pyrolysis are that are possible by transitioning from pathways in more detail, yellow boxes other primary conversion technolo- first-generation, food-based biofuels indicate processes and green boxes gies that process biomass into crude to alternative, non-food based fuels, represent an input to the process. oils, which are then fed into hydropro- i.e., advanced alternative fuels. First- Blue boxes represent the desired cessing or other upgrading technolo- generation biofuels are produced by fuel output, whereas gray boxes are gies to produce drop-in fuel. converting readily available biomass intermediary products. Bold arrows chemicals—sugars, starch or oils—into indicate primary steps in the conver- This paper synthesizes the best avail- transportation fuels such as ethanol sion process; narrow arrows indicate able information on the feedstocks and fatty acid methyl esters (FAME). less common, or less important, steps. that are or could be suitable for each Advanced biofuels, on the other hand, The black, dashed box groups pro- pathway. Overall, these feedstocks are those produced by converting cesses that can be applied to the include materials such as lignocel- additional chemicals contained in oxygen and hydrogen that is produced lulosic biomass, municipal or indus- the biomass feedstocks, specifically in the PtX pathway. PtX refers to elec- trial waste streams, and waste oils hemicellulose and cellulose, which are trolysis followed by upgrading. and fats. Lignocellulosic biomass is more difficult to extract and convert organic material with a high cellulose into transport-grade liquid fuels. For This paper reviews primary conver- and lignin content. It includes agri- this reason, more complex, advanced sion technology pathways, such as cultural residues such as wheat straw conversion techniques are required. electrolysis and gasification, which and corn stover, forestry residues, Advanced fuels also can include non- convert water and biomass, respec- and purpose-grown energy crops biological pathways, such as power- tively, into gases, as well as cellulosic such as switchgrass and poplar. In to-liquid or power-to-gas, which are ethanol conversion. In some cases, the case of PtX, the feedstocks are such as in the production of cellulosic generically referred to as PtX fuels or electricity and carbon dioxide (CO2). electrofuels. This paper provides an ethanol, the finished product from Also described is any pretreatment, overview of some of the most promis- the pathways addressed in this paper chemical or physical, necessary to ing advanced alternative fuels produc- can be used directly as transporta- prepare the feedstock for the conver- tion pathways. tion fuel. In most cases, however, the sion processes. liquid or gas carrier that is produced Figure 1 presents the conversion tech- from the pathway requires further Although technical assessments for nology pathways that are assessed processing and upgrading, such as each of these conversion technology

Acknowledgements: This work was generously supported by the David and Lucile Packard Foundation. Thanks to helpful reviews from Nic Lutsey, Jacopo Giuntoli, Adam Christensen, Bruno Miller, Rob Conrado, Dave Newport, Arne Roth, Alex Menotti, and Steven Gust.

© INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION, 2019 WWW.THEICCT.ORG ADVANCED ALTERNATIVE FUEL PATHWAYS: TECHNOLOGY OVERVIEW AND STATUS

CO2 or CO Legend

Process Oxygen Methanol Methanol Synthesis Water Electrolysis Input or Intermediary Hydrogen Methanation Methane Product or Wax Desired FT Product Synthesis Biomass Other Gasification Syngas or Wastes Hydro-carbons Gas Fermentation Cellulosic Ethanol Ethanol Conversion

Hydro- thermal Bio-Crude Liquefaction

Hydro-processing Fast Drop-in Bio-Oil and Other Pyrolysis Fuels Upgrading

Waste Oils & Fats

Figure 1: Simplified overview of the conversion pathways reviewed in this paper. Primary steps are highlighted with bold arrows. The black, dashed box groups processes that can be applied to the oxygen and hydrogen that is produced in the PtX pathway. pathways are available in the litera- Cellulosic Ethanol polymer chains that form the physical ture, there is no study that the authors Conversion structure of plants. The process of know of that includes all of these converting lignocellulosic biomass pathways together. This overarching to ethanol is called cellulosic ethanol OVERVIEW OF CONVERSION study summarizes how these tech- conversion. Cellulose is trapped inside PROCESS nologies convert biomass and wastes the lignin, making it more difficult into fuel and assesses their com- Ethanol is conventionally made primar- to convert to ethanol compared to mercial potential, citing examples, ily from sugars and starches obtained first-generation ethanol production if they exist. It also addresses the from food crops, such as corn, wheat, from starches or sugars. Cellulose and major costs associated with these sugarcane, and sugar beet. These hemi-cellulose are first broken down pathways, when information is avail- sugars and starches can be easily into monomeric sugars by enzymes, able. Obstacles that might inhibit converted into ethanol by microbes, and the sugars are then fermented commercialization are reviewed for such as yeast. Lignin and cellulose, to ethanol by yeasts. Lignin is a by- each of the technologies. in contrast, consist of long organic product of this process that is typically

2 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION WORKING PAPER 2019-13 ADVANCED ALTERNATIVE FUEL PATHWAYS: TECHNOLOGY OVERVIEW AND STATUS

combusted on-site for electricity gen- There are different feasible pretreat- route, and is described in the sections eration, although the use of lignin to ment methods for various kinds of on Gasification and Gas Fermentation. extract chemical products with higher biomass due to differences in physical The biochemical route uses a com- added-value is being explored in bio- structure, lignin content, and other bination of either enzymes or acids refinery concepts. considerations (Maurya, Singla, & Negi, to convert the pretreated cellulosic 2015). In particular, the pretreatment biomass to ethanol; this pathway Feedstocks utilized process for woody biomass differs includes three steps: hydrolysis, fer- substantially from that for agricultural mentation, and distillation. Within lignocellulosic biomass, the cel- biomass (Limayem & Ricke, 2012). lulose is bundled into structures, called Figure 2 illustrates the steps neces- Various pretreatment techniques have microfibrils, that are surrounded by sary to convert biomass inputs into been developed, each with its own lignin and attached to each other by cellulosic ethanol combustion fuel: benefits and drawbacks, as addressed hemicellulose. Typical proportions are pretreatment, hydrolysis, fermen- in the Obstacles to Commercialization 40%–50% cellulose, 25%–30% hemi- tation, distillation and drying, and section below. These include the cellulose, and 15%–20% lignin (Menon separation of distillation. Cellulosic application of physical processes & Rao, 2012). Cellulose is a polymer ethanol production requires external (e.g., particle size reduction through of glucose, which means it is made heat and energy, but in this figure grinding or steam explosion), chemi- of many glucose molecules bound we show only where there is poten- cals (e.g., sulfuric acid), physicochemi- tightly into chains. Hemicellulose also tial for recycling or export of energy. cals (e.g., liquid hot water combined is a polymer of sugars, but a mixture As shown, along with the primary with ammonium fiber explosion, of sugars, including six-carbon sugars product of ethanol, a secondary, where high-pressure, liquid ammonia (such as glucose) and five-carbon desired product—biogas, which is is applied and then the pressure is sugars (such as xylose). shown in blue—can also be produced. explosively released), and biological Pretreatment agents (e.g. white-rot or brown-rot Hydrolysis breaks down cellulose fungi and bacteria), or combinations into free sugars in order to make the Pretreatment is the first step in the of these (Bensah & Mensah, 2013). glucose within the cellulose acces- conversion of lignocellulosic biomass sible for fermentation (see Figure 2). into cellulosic ethanol (see Figure 2). Chemistry of the conversion This process is also called sacchari- Pretreatment alters the lignin and fication or cellulolysis. Hemicellulose Lignocellulosic biomass can be con- hemicellulose structures, exposing has more complex sugar polymers as verted into ethanol through either the cellulose to the action of enzymes well, but the use of enzymes to cleave thermochemical or biochemical and reducing particle size to maximize these sugar polymers has been found pathways. In both routes, the recal- surface area to mass ratio; this mini- to be cost-prohibitive (Limayem & citrant structure of lignocellulose is mizes energy consumption and allows Ricke, 2012). for maximal sugar recovery (Tong, broken down into fragments of lignin, Pullammanappallil, & Teixeira, 2012; hemicellulose, and cellulose; the hemi- Breaking down cellulose through Limayem & Ricke, 2012). Further, agri- cellulose and cellulose are then con- hydrolysis can be done using either cultural and forestry residues often are verted into sugars and then ethanol. sulfuric acid or enzymes. Sulfuric collected from the ground and there- The thermochemical route, in which acid can be used in either diluted fore contain soil and other unwanted the biomass is gasified into syngas—a or concentrated form; concentrated materials that must be removed, mixture of gases, primarily hydrogen acid hydrolysis is more common and usually by washing, so that they do not and carbon monoxide, that also can considered to be more practical. One interfere with the conversion process include carbon dioxide and methane— drawback is that undesirable degrada- (U.S. Government Accountability and then converted into ethanol, is far tion products, such as aldehyde, form Office, 2016). less common than the biochemical during acid hydrolysis.

WORKING PAPER 2019-13 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION 3 ADVANCED ALTERNATIVE FUEL PATHWAYS: TECHNOLOGY OVERVIEW AND STATUS

Cellulase Micro-organisms Ligno-cellulosic Enzymes & (e.g. Brewer’s Ethanol Co-products Biomass Water, or yeast) Sulfuric Acid

Pretreatment: Separation of Mechanical, Distillation & Distillate; Hydrolysis Fermentation Chemical Drying Recovery of and/or Fungal Residue

Legend

Process

Input Heat & Lignin Waste-water Energy Residue By-Product

Internal Energy Anaerobic Desired Biogas Combustion Digestion Product

Figure 2: Simplified overview of cellulosic ethanol conversion. Primary steps are highlighted with bold arrows. Dashed arrows indicate optional processes. Adapted from from Limayem & Ricke (2012), Baeyens et al. (2015), and Humbird et al. (2011).

In the enzymatic hydrolysis process, consumed as soon as it is produced, in regions where ethanol is used as cellulases, usually a mixture of several allowing cellulolysis to proceed unin- a blend it is impractical because enzymes belonging to three different hibited. SSF also has the advantage of the water content inhibits blending groups (endoglucanase, exogluca- requiring a single reaction vessel for with gasoline (Volpato Filho, 2008). nase or cellobiohydrolase, and b-glu- the two processes, instead of one for To remove the remaining water, pro- cosidase), are used to break down each. However, saccharification and ducers use more energy intensive the cellulose. Once the cellulose fermentation have different optimal distillation methods or adsorption has been broken down into glucose temperatures, so for this factor a com- columns (Vane, 2008). In an adsorp- molecules, the fermentation process promise must be made. tion column, the ethanol is passed uses microorganisms to consume across a material called a molecu- glucose and produce ethanol as an After fermentation, the ethanol is sep- lar sieve, which selectively attracts end product (see Figure 2). These arated from the yeast solids and most water, leaving dehydrated ethanol. microorganisms include brewer’s of the water by distillation (University The molecular sieve is then regener- yeast (Saccharomyces cerevisiae) and of Illinois Extension, 2009). To do this, ated, which is to say dried, resulting in Escherichia coli. the broth that comes from fermen- a cyclic operating scheme. tation is heated, and ethanol, which The accumulation of the sugar end evaporates more readily than water, It is also worth noting that one of the products in the enzymatic hydrolysis is collected and cooled. However, it is end products of the biochemical con- process inhibits the activity of the impossible to achieve perfect separa- version of lignocellulosic biomass into cellulase enzymes and slows down tion using standard distillation; there- ethanol, whether acid or enzymatic, is the reaction. To counter this, in some fore, the product of distillation, called lignin, which can be combusted and systems, the hydrolysis and fermen- hydrous ethanol, still contains about converted to electricity and heat. The tation steps are done together in 5% water. economics of cellulosic ethanol pro- simultaneous saccharification and duction could also be improved were fermentation (SSF) processes (Sun & Hydrous ethanol is sometimes used lignin to become a higher-value end Cheng, 2002). This way the glucose is as a fuel in Brazil (E100), although product.

4 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION WORKING PAPER 2019-13 ADVANCED ALTERNATIVE FUEL PATHWAYS: TECHNOLOGY OVERVIEW AND STATUS

COMMERCIAL POTENTIAL least one has been shut down. These (Ethanol Producer Magazine, n.d.-b). facilities use agricultural waste, energy Woodland Biofuels has a demonstra- Commercial cellulosic ethanol produc- crops, woody biomass, or a combina- tion plant in Sarnia, Ontario, using tion generally falls into two categories: tion of all three. POET-DSM Advanced woody biomass with a nameplate smaller, add-ons to existing, first-gen- Biofuels operates a cellulosic ethanol capacity of 2 million liters per year eration ethanol facilities using starch plant in Emmetsburg, IA, with a name- (Ethanol Producer Magazine, n.d.-a). or sugar crops, or larger, stand-alone plate capacity of approximately 76 American Process Inc. Biorefinery has projects. Add-on facilities are some- million liters per year using corn cobs a facility in Thomaston, GA, with a times called “bolt-on” facilities, pri- and corn stover as feedstock (Ethanol nameplate capacity of approximately 1 marily using cellulosic waste from the Producer Magazine, n.d.-b). Recently, million liters per year using sugarcane conventional ethanol facility. Bolt-on POET filed suit against an engineering bagasse and woody biomass (Ethanol facilities have generally had more company for building an unsatisfactory Producer Magazine, n.d.-b). The facility success ramping up production than pretreatment process; in 2010 POET also is manufacturing nanocellulose stand-alone facilities. Quad County contracted with Andritz, Inc. to build a for use as a material in tires and other Corn Processors is an ethanol plant in biomass pretreatment unit, but POET consumer products (Lane, 2017a). Galva, Iowa, with a bolt-on cellulosic claims that the process never worked Production of co-products such as ethanol process that uses corn kernel at commercial scale, despite one and these may improve the economic fea- fiber sourced from an adjacent first- a half years of redesigns and multiple sibility of cellulosic ethanol production. generation ethanol facility (Ethanol plant shutdowns (Ellis, 2017; Sapp, Producer Magazine, n.d.-b). The Quad 2017). DuPont operated a plant in In Europe, Beta Renewables operated County facility’s nameplate capacity Nevada, IA, with a nameplate capacity a plant in Crescentino, Italy, until its is approximately 8 million liters per of 114 million liters per year using corn closure in late 2017. It has a name- year of cellulosic ethanol, which is far stover until the plant was shut down in plate capacity of 50 million gallons less than the 130 million-liters-per-year late 2017 (Ethanol Producer Magazine, per year and came online in 2012, capacity of the adjacent corn ethanol n.d.-b). DuPont cited its merger with but it was never able to reach this facility (Lane, 2014b). ICM Inc. is oper- Dow as the reason for the decision capacity. Beta Renewables utilized ating a pilot bolt-on facility at a con- and is seeking a buyer for the facility wheat straw, rice straw, and Arundo ventional ethanol plant in St. Joseph, (Scott, 2017). POET and DuPont were donax (ETIP Bioenergy, n.d.-a; Schill, MO, with a nameplate capacity of both operating well below capacity as 2016). Clariant has a plant in Germany nearly 1 million liters per year (Rivers, of April 2016 (Rapier, 2016). producing ethanol from agricultural 2015). The operators claim to have wastes (Clariant, 2017). The nameplate successfully run their unit with corn At a smaller scale, several U.S. pro- capacity of the plant is approximately kernel fiber and switchgrass. Ethanol ducers also have developed demon- 1 million liters per year (Clariant, n.d.). producer Raízen Energia Participacoes stration projects for cellulosic ethanol SA, using Iogen Energy cellulosic conversion at stand-alone facilities. biofuel technology, has a $100 million Fiberight planned to convert post- OBSTACLES TO ethanol production plant utilizing sug- recycling municipal solid waste (MSW) COMMERCIALIZATION into cellulosic ethanol, but after seven arcane bagasse located adjacent to a Cost sugarcane mill in São Paulo. In 2016, years of research and development, the plant produced 7 million liters of the company decided to instead The conversion process for cellulosic next-generation ethanol. The facility focus on producing biogas in lieu of ethanol remains costly. Limayem and is slated to produce 40 million liters cellulosic ethanol. Statements from Ricke (2012) emphasizes that while per year of cellulosic ethanol using Fiberight suggest that securing invest- technology continues to improve, sugarcane bagasse and straw (Iogen ment for MSW-to-ethanol is very dif- advanced fuels still require “the most Corporation, n.d.). ficult (Lane, 2015b). ZeaChem has a advanced systems analysis and eco- demonstration plant in Boardman, OR, nomical techniques designed to cope Several large, stand-alone cellulosic using poplar, straw, and corn stover. with feedstock versatility and com- ethanol facilities are in development, The Boardman facility has a nameplate modity.” Some research suggests that in early operational phases, and at capacity of 946,000 liters per year cellulosic ethanol production may

WORKING PAPER 2019-13 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION 5 ADVANCED ALTERNATIVE FUEL PATHWAYS: TECHNOLOGY OVERVIEW AND STATUS

be cheaper than other production and does not produce inhibitory com- during SSF, and actively removing it processes using lignocellulosic feed- pounds but requires 4 to 6 weeks and improved the economics of high-solids stocks. For example, Peters, Alberici, thus incurs costs related to storage loading processes. Passmore, and Malins (2015) estimated space for that time period (Sun & the costs for cellulosic ethanol to be Cheng, 2002). Cost of enzymes and other lower than for the gasification/Fischer- chemicals Tropsch process and hydrotreated There is also potentially promising Both acid and enzyme hydrolysis pyrolysis oil process, although the research on genetically modifying require expensive materials. Acid authors emphasize that this finding is plants to reduce the difficulties of pro- hydrolysis requires large quantities of indicative and not absolute. cessing lignin, either through modify- ing the lignin’s chemical structure or acid, which can be costly to purchase or recycle within the process. For reducing the lignin content. This could Recalcitrance of lignin and these reasons, research and develop- be achieved, for example, through hemicellulose ment has focused mainly on enzy- down-regulating lignin biosynthesis matic hydrolysis for the commercial Pretreatment is the most expensive enzymes in the plant or shifting the production of cellulosic ethanol, step in cellulosic ethanol production plant’s energy from lignin biosynthesis but cellulase enzymes also can con- because lignocellulosic biomass is to the synthesis of polysaccharides tribute significantly to the ongoing highly recalcitrant, which is to say, hard such as sugars and starches (Mood et operating cost of a plant (Tong, to break down. Many lignocellulosic al., 2013). feedstocks also are heterogenous and Pullammanappallil, & Teixeira, 2012). Enzyme costs fall in the range of $5 their characteristics can change over High-solids loading time, so it is important for pretreat- to $20 per kilogram (Johnson, 2016; ment methods to be flexible and effec- Solids loading refers to the ratio at Liu, Zhang & Bao, 2015). tive across a range of physical and which solids (i.e., biomass) are added To minimize enzyme consumption, chemical characteristics (Limayem & to the system, relative to the water that manufacturers have options such as Ricke, 2012). However, all of the avail- is needed for the fermentation broth. A recycling enzymes for use in subse- able pretreatment options have limita- higher ratio of solids to liquid trans- quent cycles (Lu, Yang, Gregg, Saddler, tions related to cost, effectiveness, or lates to reduced water needs, smaller & Mansfield, 2002). One study reports other problems. tank sizes, and lower distillation costs. However, increasing solids loading that this technique can reduce enzyme Mechanical means of pretreatment results in decreased sugar yields in costs by 50% (Du, Su, Zhang, Qi, & can be prohibitively energy intensive. the hydrolysis step and decreased He, 2014). Another solution is to use Using heat or chemicals to remove ethanol yields in the fermentation step. additives, such as proteins called car- lignin and break down biomass can Kristensen, Felby, & Jørgensen (2009) bohydrate binding modules (CBMs), be effective and is a common method. found that there is a linear, inverse cor- that can enhance the enzyme activity Chemical pretreatment of lignocel- relation between conversion efficiency (Chundawat et. al., 2011). lulosic biomass forms the basis of and solids concentrations between several proprietary cellulosic ethanol 5% and 30% initial total solids content C5 sugar content production configurations and tech- by weight (w/w). Ongoing research is Most yeasts and microbes metabolize nologies (Bensah & Mensah, 2013). attempting to determine the drivers of glucose and other six-carbon sugars; However, chemical pretreatment tends this relationship with an aim to identi- however, hemicellulose is mostly made to produce compounds such as furfural fying solutions to increase sugar and of five-carbon (or C5) sugars. C5 that are toxic and inhibit microbial fer- ethanol yields. For example, Kristensen sugars, such as xylose and arabinose, mentation. Organic solvents such as et al. (2009) found that hydrolysis are not digested by many organisms; ammonia can avoid this problem but products, such as glucose, inhibit the consequently, enzymes that hydro- are relatively expensive and require adsorption of cellulase at higher loads. lyze these sugars are less common. solvent recovery systems. Biological In addition, Jin et al. (2017) found that Low-cost enzymes that can hydrolyze pretreatment using white rot or other the presence of ethanol was the major C5 sugars have not been identified, fungi has low energy requirements cause of decreased sugar conversion and thus hemicellulose is currently

6 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION WORKING PAPER 2019-13 ADVANCED ALTERNATIVE FUEL PATHWAYS: TECHNOLOGY OVERVIEW AND STATUS

cost-prohibitive to process into ethanol. It also can be used to make liquid and particle size and the additional energy Additionally, research has shown that gaseous hydrocarbon fuels, such as required to achieve that particle size. the presence of some of the C5 sugars, diesel, methane, and ethanol. Some gasifiers require a consistent such as xylose, can inhibit the efficacy energy density of the feedstock, while of cellulase enzymes. These issues are Feedstocks utilized others can tolerate variation. For those seen with all lignocellulosic feedstocks that require consistent energy density, Gasification can use a wide variety (Limayem & Ricke, 2012). Research in torrefaction is another pretreatment of feedstocks, including agricultural this area focuses mainly on developing option that processes solid biomass at residues, organic fractions of MSW, genetically modified microbes that can low temperatures (ca. 250°C–300°C) forest residues, lignocellulosic energy digest xylose and arabinose (Agbogbo in the absence of oxygen. Torrefied crops, glycerin, tall oil pitch, and black biomass is dry, has higher and more & Coward-Kelly, 2008). Taurus Energy and brown liquor that are residues of consistent energy density and is easier has developed a strain of yeast called pulp-making. Wood and lignocellulosic to grind than untreated biomass, XyloFerm that is being tested at the residues from forestry and agricul- thus behaving similarly to lignite coal Quad County facility in Iowa (Lane, ture are the main feedstocks currently (Phanphanich & Mani, 2011). 2017c). Inbicon also developed a C5 fer- used by 80% of the commercial and mentation technology (Ørsted, 2013). operating biomass gasification plants MSW is inherently heterogeneous, as (Bermudez & Fidalgo, 2016). both household and commercial waste Gasification streams contain a variety of waste Pretreatment products including paper products, OVERVIEW OF CONVERSION All feedstocks must be processed into food waste, and yard trimmings. For a PROCESS a dry, more uniform material through feedstock like MSW, feed handling at pretreatment. The objective of pre- a conversion facility must be flexible Gasification of coal is already widely treatment is to produce input materials and able to accommodate a set of het- used as a power generation technol- for the gasifier with uniform physical erogeneous feedstocks. Depending on ogy. Increasingly, biomass is also being properties, high energy density, and the gasification process selected, the gasified for power, either alone or low moisture content. Biomass also fraction of non-organic components in co-fed with coal. In the presence of can be perishable, and some of these the MSW such as metal and glass will oxygen, but less than what is needed pretreatment steps stabilize the need to be sorted out and minimized for combustion, gasification converts biomass so it can be stored or trans- in the feed to the reactor. biomass or organic wastes—for ported more easily. The ideal moisture example, the organic fraction of MSW— content for feedstocks for gasification Chemistry of the conversion into syngas. This syngas is a mixture of is between 10% and 15% by weight hydrogen (H ), carbon monoxide (CO), Figure 3 illustrates the steps neces- 2 (Bermudez & Fidalgo, 2016). Besides and CO . Simply, gasification is sary to convert biomass inputs into 2 drying, other preprocessing steps may syngas using gasification. Gasification include particle size reduction and requires external heat and energy, but Biomass+ O + Heat à H + CO + CO + 2 2 2 compaction of the feedstock; these in this figure we only show where there Hydrocarbons + H O + CH + Tar + Char 2 4 are dependent on the specific type is potential for recycling or export of of gasification technology employed. energy. After the feedstock has been Tar is the unconverted organic Research suggests that gasification pretreated, it is gasified and then material produced after biomass has of solids works better with smaller cleaned; the primary output of this been devolatilized during gasification. particle sizes, so, depending on the process is syngas, some of which can During devolatilization, tar is released specific gasification technology, the be combusted on-site for energy. in gaseous form but is condensable biomass must be ground, milled, at lower temperatures. Char is a high- or shredded to an appropriate size There are two basic categories of carbon solid by-product of pyrolysis, (Gaston et al., 2011). At the same gasifiers: partial oxidation and steam gasification, and incomplete combus- time, size reduction takes energy, and reforming. For partial oxidation gasifi- tion of biomass. Syngas can be com- there is a trade-off between improved cation, the biomass enters the gasifier busted for electrical power generation. gasification efficiency with smaller along with an oxidizing gas, typically

WORKING PAPER 2019-13 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION 7 ADVANCED ALTERNATIVE FUEL PATHWAYS: TECHNOLOGY OVERVIEW AND STATUS

Legend Water, Tar, Biomass or Oxidizing Gas Sulfur or Process Wastes or Steam Nitrogen-Containing Compounds Input

By-Product

Internal Energy Cleaning Pretreatment Gasification Syngas (Hot or Cold) Desired Product

On-Site Ash Energy Combustion Recovery

Figure 3: Simplified overview of gasification. oxygen, air, steam, or a combina- which are devices that transfer heat to heat up, carbon-containing mol- tion thereof. The choice of oxidizing between mediums by conduction. ecules (i.e., lignin, cellulose, and agent depends on the quality required their decomposition products) for the syngas and on the operating There is a fundamental trade-off break down into gaseous compo- between using oxygen or air as the conditions. The quantity of oxygen nents (i.e., CO2, oxygenated vapor introduced is insufficient to combust gasifying agent. Purifying oxygen from species) and condensable vapors the biomass. Complete oxidation (i.e., air requires additional expense, but air (i.e., char, primary oxygenated combustion) occurs if there is a perfect has a very large fraction of nitrogen, liquids, and water). match between (a) the ratio of the an inert gas. Bermudez and Fidalgo 3. Gasification: The remaining char actual amount of oxygen and carbon (2016) report that for partial oxidation reacts with CO , water, and oxygen from the biomass in the reactor and gasification reactions, oxygen gasifica- 2 in the presence of heat to form CO, (b) the stoichiometric ratio between tion is more favorable than air gasifi- H , and methane (CH ). The vola- oxygen and carbon that is necessary cation because it allows for smaller 2 4 tiles from the previous step may for complete oxidation. This match downstream equipment and facilitates the removal of CO from the syngas be converted into fuel gases by is expressed in an equivalence ratio, 2 product, which is required for proper the secondary reactions of com- which divides the first factor by the synthesis in a Fischer-Tropsch reaction. bustion and reforming (Bermudez second. The equivalence ratio is there- & Fidalgo, 2016). fore approximately 1 for complete Several distinct reactions occur in oxidation. Gasification usually is con- the gasifier, throughout either steam The gasifier output is a mixture of ducted with an equivalence ratio reforming or partial oxidation (see hydrogen and carbon monoxide, the two primary energy carriers, along between 0.2 and 0.4 (Bermudez & Figure 3): Fidalgo, 2016). The reaction usually with some combination of water, occurs at temperatures between 800 1. Dehydration: The high heat of the methane, carbon dioxide, ash, tar, and and 1300°C. process evaporates any moisture sulfur- or nitrogen-containing com- still present in the feedstock. This pounds (National Energy Technology In steam reforming, the feedstock steam serves a purpose in subse- Laboratory, n.d.). Ash composition enters the gasifier along with steam, quent reactions. varies depending on the feedstock, but and the endothermic energy required it usually contains some trace elements, for the reaction is provided directly 2. Pyrolysis (also known as devolatil- such as potassium, calcium, and phos- or indirectly through heat exchangers, ization): As the biomass continues phorus. The ratio of CO and H2 depends

8 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION WORKING PAPER 2019-13 ADVANCED ALTERNATIVE FUEL PATHWAYS: TECHNOLOGY OVERVIEW AND STATUS

on the type of substrate and gasifica- whereas disadvantages include sen- of solids; complex operation; and a tion conditions (Du et al., 2016). sitivity to the quality and size of the medium amount of tar yield compared feedstock; feedstock size limits; low to other reactors. Circulating fluidized A gasification reaction is endother- energy efficiency; inability to scale bed gasifiers are also best for medium- mic, which is to say it requires heat up; and risks of corrosion, explosions, to large-scale gasification processes, inputs from outside the system, but and fuel blockages. Minimizing tar are flexible across varying feedstock the process can be designed so that production is important for minimiz- characteristics, and can be constructed the required energy is provided com- ing impacts on gasifier machinery and compactly. Compared to bubbling pletely by the recirculation of syn- for increasing product yield, because fluidized bed reactors, they have thesis gas, the recirculation of tail tar is essentially unconverted carbon. several advantages, such as greater gas from the Fischer-Tropsch process Updraft reactors’ advantages include gas-solid contact. Their disadvantages downstream, or the partial combus- their simple design; suitability for include medium tar yield and complex tion of the solid fuel (Bermudez & biomass with high moisture content, operation, as well as the potential for Fidalgo, 2016). low volatility, high ash content, and damages due to corrosion and attri- a variety of particle sizes; low char tion (Bermudez & Fidalgo, 2016). Gasification technology formation; and high energy efficiency. Disadvantages include risk of explo- In an entrained flow reactor, very finely Several different reactor configurations sions, fuel blockages, and corrosion, dispersed feed is added together with can be used for gasification. The main as well as high tar yield (Bermudez & the oxidizing gas. The small particle types are fixed bed, entrained flow, Fidalgo, 2016). size allows the reactions to occur much and fluidized bed gasifiers (Bermudez more quickly and allows high conver- & Fidalgo, 2016). Except for fluidized In fluidized bed reactors, the biomass sion efficiency with low tar production. beds, which are essentially isothermal, is either directly injected into the hot An entrained flow reactor operates there are different zones with varying fluidized bed or mixed with inert (or at very high temperatures, higher temperatures and material composi- sometimes catalytic) bed material than those in a fluidized bed reactor, tions where the conversion reactions such as quartz sand or dolomite, which causing ash to melt into slag that is described above take place. The fosters heat transfer so that there is then collected from the bottom of the reactor types differ in how and where a uniform temperature in the conver- reactor. Of the three primary gasifier the feedstock and gasifying agents are sion zone. This gasifier configuration configurations, an entrained flow introduced and in how ash is handled. is therefore able to process feedstocks reactor is the most expensive reactor with varying qualities. Contrary to to operate, requiring high amounts of Fixed bed reactors, also called moving the different zones in the fixed bed oxidizing gas and high temperatures. It bed reactors, follow the same basic reactor, drying, devolatilization, oxida- also requires a biomass feedstock that configuration as common blast tion, and gasification occur simultane- is brittle enough to be broken down furnaces. Feedstock is introduced at ously and homogenously, producing to the necessary particle size, such as the top and moves down through the a synthesis gas with relatively high torrefied biomass. Despite these draw- vessel through four primary zones: (1) heating value. These kinds of reactors backs, the clean syngas it produces drying, (2) carbonization, (3) gasifi- generally perform better than fixed makes this technology promising cation, and (4) combustion. Feed is bed gasifiers. There are two main con- for use with biomass (Bermudez & added to the top of the reactor in gen- figurations of fluidized bed reactors: Fidalgo, 2016). erally large pieces, i.e., coarse particle bubbling fluidized beds and circulating size, forming a bed inside the reactor. fluidized beds. Before the syngas can be used for The oxidizing gas can be added from fuel production, it must be purified below the bed (updraft reactor), from Bubbling fluidized bed gasifiers are and upgraded in order to prepare the the side (cross draft reactor), or from among the most popular for biomass proper gaseous mixture for the down- just below the top (downdraft reactor). gasification. Their advantages include stream synthesis. Syngas cleaning can The oxidation reaction occurs nearest flexibility regarding feedstock charac- occur via two routes, known as hot to where the oxidizer is added, with teristics (e.g., ash content and particle and cold (see Figure 3). The cold route the heat from that reaction powering size) and feed rate, and they can be is more developed, but the hot route the others. Downdraft reactors’ advan- constructed compactly. Disadvantages offers better energy efficiency if the tages include their simple design and include potential back-mixing, which syngas will be used downstream at a low tar and particulate formation, limits the conversion efficiency high temperature. Current research

WORKING PAPER 2019-13 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION 9 ADVANCED ALTERNATIVE FUEL PATHWAYS: TECHNOLOGY OVERVIEW AND STATUS

focuses on how to better implement to produce hydrogen and carbon a range of equipment costs that fall this route. Cleaning removes tar, sulfur dioxide. Catalysts are used, typi- between $2,540 and $3,860 per kW.

(in the form of H2S), hydrochloric acid cally an iron oxide-based catalyst For circulating fluidized bed reactors,

(HCl), ammonia (NH3), and fly ashes. followed by a copper-based cata- equipment costs fall between $1,440 There are various processes that can lyst. Researchers are still working and $3,000 per kW. Because these be applied downstream of the gasifica- to improve this process. cost figures are at least six years old, tion process to produce usable trans- however, it is possible that in recent portation fuels (Bermudez & Fidalgo, years gasification technology has COMMERCIAL POTENTIAL 2016). These include: become less expensive. Unlike gasification of coal, gasification • Methanation: At temperatures of biomass and waste feedstocks for Fulcrum BioEnergy, which is devel- of 700°C–1,000°C and with a transportation fuel production is still oping several commercial-scale MSW nickel catalyst, carbon monoxide in its relatively early stages of devel- gasification facilities across the United and hydrogen are converted to opment. However, the extensive expe- States, is using steam-reforming methane and water. rience gathered from its application bubbling fluid bed reactors (Fulcrum to coal could help the development BioEnergy, 2018). In Europe, most • Methanol production: At temper- of the biomass gasification industry. existing commercial plants that gasify atures of 220°C–300°C, a pressure biomass are dedicated to the produc- between 50 and 100 bar, and with There are major differences between coal and biomass gasification and tion of power or combined heat and a catalyst of copper-zinc oxide many of the coal gasifier technolo- power, although there are some pilot supported on alumina, methanol gies cannot be directly applied to projects using gasification for further synthesis occurs through the reac- biomass. For example, entrained flow processing into biofuels for transport tion of both carbon monoxide and technology is the most widely used (IEA Bioenergy, n.d.). For example, the carbon dioxide with hydrogen. gasifier type for fossil fuel gasifica- bioliq project in Karlsruhe, Germany, • Fischer-Tropsch synthesis: In the tion, but entrained flow gasifiers are uses an entrained flow reactor to presence of a catalyst, the hydro- not available on a commercial scale gasify the bio-crude being produced gen and carbon monoxide from for biomass. Current research is trying from fast pyrolysis (bioliq, n.d.-b). syngas are combined into liquid to address the challenge of how to hydrocarbons, the composition enhance the production of syngas Almost all of the facilities that produce of which can be modified accord- liquid biofuel from biomass gasifica- with high H2 content where impurities ing to the desired specifications such as tar are minimized and capital tion at a commercial level are in the for the finished fuel, such as and operating costs are also reduced United States and Canada. Enerkem, a renewable diesel. See the Fischer- (Bermudez & Fidalgo, 2016). Montreal, Quebec-based company with Tropsch Synthesis section for a long history of working with bubbling more information. Gasification has higher capital costs fluidized bed biomass gasifiers, is now than pyrolysis and biochemical pro- converting MSW containing mixed • Gas fermentation: In the presence cesses (Wang & Tao, 2016). Currently, textiles, plastics, fibers, wood and of catalysts, syngas can be fed to around 75% of commercial biomass other non-recyclable waste materials acetogenic microorganisms, such gasifiers are fixed bed reactors into chemical-grade syngas, which is as Clostridium ljungdahli, which (Bermudez & Fidalgo, 2016). A study then converted into methanol, ethanol then produce ethanol (Limayem by the Internation Renewable Energy and other chemicals. At its Westbury, & Ricke, 2012). See the Gas Agency (IRENA, 2012) found that fixed Quebec, facility Enerkem processes Fermentation section for more bed gasifiers have equipment costs 17,500 tonnes per year of treated information. that fall between $1,730 and $5,074 wood (e.g., electric utility poles), wood • Hydrogen production: In order to per kilowatt (kW). Bermudez and waste, and MSW into syngas. At its maximize hydrogen production, Fidalgo (2016) suggest that bubbling facility in Edmonton, Alberta, Enerkem for example for use in hydrogen fluid bed reactors are a promising processes 100,000 tonnes per year fuel cell vehicles, the hydrogen technology for biofuels because this of MSW (IEA Bioenergy, n.d.). In the concentration can be increased reactor type already has been demon- United Kingdom, BioSNG built a com- with a water-gas shift reaction. In strated across a wide range of condi- mercial facility that will process 10,000 the water-gas shift process, steam tions. The 2012 IRENA study found that tonnes per year of waste wood and

(H2O) reacts with carbon monoxide bubbling fluidized bed reactors have other wastes to produce 22 gigawatt

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hours (GWh) per year of grid quality increase product yield and selectivity used as a carbon and energy source methane through thermal gasification and produce non-native products. by microorganisms suspended in a and methanation (Gogreengas, n.d.). liquid nutrient solution. If hydrogen LanzaTech is the best-known company is present, it also can be used as an that has developed and commercial- energy source. The microbes secrete OBSTACLES TO ized a gas fermentation process, con- fermentation products, such as COMMERCIALIZATION verting waste gas from industrial pro- ethanol, 2,3-butanediol, and acetic There are several technological issues cesses into fuels, such as ethanol, and acid into the broth. Modifications related to cleaning the syngas so it chemicals, such as 2,3‑butanediol (Wu to the process can change both the can be used for downstream con- & Tu, 2016). The waste gases used by nature of the reaction products as well versions. For example, gasification LanzaTech include gaseous streams as the ratio between products and co- produces tar, which can degrade con- from steel mills that would otherwise products. The selectivity and yield of version equipment over time. Tar pro- be combusted for electricity and biofuel depend not only on the type duction can be handled on the front process heat or be flared. This tech- of bacteria used, but also on process nology also reportedly can convert end by pretreating biomass via tor- conditions such as temperature, pH, gaseous streams from other indus- and syngas composition. refaction or conducting pyrolysis first trial processes, such as oil refining and (Phanphanich & Mani, 2011). Both of chemical plants, as well as syngas from There are also different designs and those technologies are under devel- gasification of forestry and agricul- configurations of bioreactors, and opment for use in this application, but tural residues, unsorted unrecyclable each type has its advantages and dis- neither has been proven cost-effec- municipal waste, natural gas, and coal advantages. The bioreactor design is tive at a commercial scale. Tar, along (Handler, Shonnard, Griffing, Lai, & critical for gas fermentation because it with other syngas contaminants, also Palou-Rivera, 2015). influences the gas-liquid interface and can be handled on the back end, via the gas-liquid mass transfer rate (Wu & syngas cleaning processes. These are Tu, 2016). The continuous stirred-tank Chemistry of the conversion proven technologies, used in coal gas- reactor (CSTR) is a common design: ification facilities, but they do add Hydrocarbons such as tar inhibit fer- Syngas is continuously injected into additional steps, and thus costs. mentation and adversely affect cell the reactor through a diffuser and growth; it is thus necessary to clean mechanical agitation breaks the large the syngas first, as described in the bubbles into smaller ones. However, Gas Fermentation previous section on Gasification. After CSTR is not economically feasible at a the syngas is cleaned, it is compressed commercial scale because of its high OVERVIEW OF CONVERSION and delivered to the reactor, where energy cost, so significant research PROCESS fermentation is carried out by micro- efforts have been undertaken to organisms. The steps necessary for improve the design of this kind of Gas fermentation is a hybrid biochemi- fermenting gas into ethanol combus- reactor. Bubble column reactors do cal/thermochemical process where tion fuel are shown in Figure 4. Gas fer- not require the same mechanical agi- biocatalysts convert gases composed mentation requires external heat and tation as CSTRs and they have higher of hydrogen, carbon monoxide, and energy, but in this figure we show only mass transfer rates, but they can have carbon dioxide into liquid fuels (Griffin where there is potential for recycling problems with mixing and coalescence. & Schultz, 2012). Biocatalysts can be or export of energy. Product recovery In a trickle-bed reactor, liquid flows acetogenic microorganisms, such as comes after fermentation and includes down through a packing medium, with bacteria in the Clostridium genus that distillation and other techniques. As the syngas moving either downward use the Wood-Ljungdahl pathway in the case of cellulosic ethanol con- (co-current) or upward (counter- for gas fixation into several fuel version, a secondary desired product, current). These reactors also do not products, primarily ethanol, butanol biogas (shown in blue), can also be require mechanical agitation and have and methanol (Wu & Tu, 2016). Value- produced by anaerobically digesting been shown to have higher gas conver- added co-products can include a waste organic solids. sion rates as well as higher produc- range of chemical products including tivity compared to CSTR and bubble acetone, isopropanol, 2,3‑butanediol, In the LanzaTech process, carbon mon- column reactors. Finally, there are and isoprene (Liew et al., 2016). The oxide-containing gas is first deoxygen- hollow fiber membranes (HFMs), where bacteria can be genetically modified to ated and then the carbon monoxide is syngas is diffused through micro-size

WORKING PAPER 2019-13 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION 11 ADVANCED ALTERNATIVE FUEL PATHWAYS: TECHNOLOGY OVERVIEW AND STATUS

Other Product Syngas or Micro- Recovery Ethanol waste gas organisms Techniques

or

Cleaning & Fermentation Distillation Co-products Compression

Legend

Process

Organic Input solids

By-Product

Internal Energy On-Site Anaerobic Biogas Combustion Energy Digestion Desired Recovery Product

Figure 4: Simplified overview of gas fermentation to ethanol. pores without forming bubbles. This • Adsorption: Product fuels from operate continuously at an indus- system offers the highest volumetric gas fermentation, such as butanol, trial scale, does not harm the fer- mass transfer coefficient, followed by first are adsorbed by certain mentation culture, and does not trickle-bed reactors and CSTR (Wu & adsorbent materials, such as resin, require a membrane, making it one Tu, 2016). and then desorbed, creating a of the most attractive techniques concentrated product. for product recovery (Strods & Wu and Tu (2016) describe several Mezule, 2017; Wu & Tu, 2016). • Pervaporation: In this membrane- techniques for recovering the desired based technique, a membrane Another technique is the LanzaTech fuel and other co-products from the selectively separates volatile fermentation broth, which is the mix conversion process, in which fer- compounds such as ethanol and mentation products are continuously of fermentation products. These tech- butanol; these compounds diffuse withdrawn from the reactor and sent niques include: through the membrane, evaporate, through a distillation-based separation and then are recovered through A dis- system for product and co-product • Liquid-liquid extraction: condensation. solved compound is extracted recovery (see Figure 4). Waste streams from a liquid mixture using a • Gas stripping: In this process, an are minimized and recycled internally; oxygen-free gas, such as nitrogen for example, organic solids such as solvent. (N2), circulates in the fermenta- spent microbial biomass can be filtered • Pertraction: This is a liquid-liq- tion broth in bubbles that then out and digested anaerobically, and uid extraction process in which break, inducing vibration of the with the resulting biogas, can be mixed a membrane is placed between liquid and the removal of vola- with some of the vented gas from the the extracting liquid and the tile compounds (Ezeji, Karcher, reactor for on-site energy recovery extractant. Qureshi, & Blaschek, 2005). It can (Handler et al., 2015).

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COMMERCIAL POTENTIAL INEOS Bio converts several types of as distillation, or instead to geneti- waste biomass including wood waste, cally engineer or breed strains that are Compared to other technologies, gas vegetative waste, and yard waste into tolerant of more concentrated product. fermentation has several advantages: bioethanol (Wu & Tu, 2016). In 2013, Bacterial activity is also inhibited by high product selectivity, low reaction INEOS Bio started its first commer- acetic acid produced as a by-product, temperature, high tolerance to sulfur, cial gas fermentation plant in Florida; thereby reducing ethanol yield. It is and the biocatalyst is much cheaper however, a few years later there were possible that genetically engineering than the heterogenous catalyst used reports that the facility was not pro- or breeding more selective bacteria in the Fischer-Tropsch synthesis ducing much fermentation-derived strains could mitigate this problem process. Gas fermentation also can ethanol, primarily due to the sensi- (IRENA, 2016). handle a wider range of H :CO ratios 2­ tivity of the microorganisms to high in the input syngas than FT synthesis levels of hydrogen cyanide in the Bacterial contamination is another (Wu & Tu, 2016). syngas. Recently, INEOS Bio sold this barrier that can have a substantial impact on final yields. To mitigate this, To date, the developers exploring this facility, citing changes in the market operators must use resilient bacterial conversion pathway have focused on for ethanol as one of the reasons for strains and reactor systems that are maintaining stable microbial popula- this decision (Voegele, 2016). less susceptible to contamination and tions and setting up new reactor tech- As of 2018, the Shougang-LanzaTech improve the removal of trace species nologies. Reactor design still must be Joint Venture is operating LanzaTech’s that can cause population loss (Daniell, optimized to improve pass-through gas fermentation technology at the Köpke, & Simpson, 2012). rates, downsize equipment, and inte- Shougang Group’s Jingtang Steel Mill grate energy by using unreacted gases in Caofeidian, China. This 60 million- (e.g., unused H from the syngas) for 2 liter-per-year facility is converting steel Fischer-Tropsch Synthesis process energy recovery (IRENA, mill waste gas to ethanol. Four further 2016). Further, Wu and Tu (2016) high- commercial projects are expected OVERVIEW OF CONVERSION light that mass transfer of gas-to-liquid to start up in 2019–2020 producing PROCESS in a bioreactor is the largest rate-lim- ethanol from refinery and ferroalloy Fischer-Tropsch (FT) synthesis, illus- iting parameter, posing a major chal- off-gases in India and South Africa; trated in Figure 5, is used in conjunc- lenge to gas fermentation. biomass syngas in California; and steel tion with other conversion technol- Researchers also are working on select- mill off-gases in Belgium. In Japan, ogies that produce syngas, such as ing desirable traits in the microbes SEKISUI has demonstrated ethanol gasification and power-to-X, which and blocking out particular metabolic production using LanzaTech’s gas fer- are addressed in other sections of this pathways in order to improve primary mentation technology on syngas from paper. After the syngas is cleaned, FT product yields. Specifically, there are gasified unsorted unrecyclable MSW synthesis catalytically converts syngas efforts to genetically modify the fer- that would otherwise be incinerated to produce liquid hydrocarbons, which mentation bacteria to improve yields, (Burton, 2017). include waxes, drop-in fuel, and other reduce product inhibition, and make hydrocarbons, as well as tail gas. Tail gas usually is recycled if it is made them more tolerant to operating con- OBSTACLES TO up mainly of syngas, and it usually is ditions that are uninhabitable to other COMMERCIALIZATION bacteria strains. Capital costs also combusted if it is made up mainly of can be reduced by using new product Continuous input of the feedstock and other off-gases. FT synthesis requires recovery technologies, such as mem- removal of the product is necessary energy, but in this figure we show only branes (IRENA, 2016). to maintain the activity rate of the where there is potential for recycling microorganisms, but this increases the or export of energy. This product may INEOS Bio, Synata Bio, and LanzaTech energy necessary for product separa- require further refining before use in are the three major companies that tion. It is therefore critical to identify the transport sector but in some cases have, or have had, precommercial or methods to either reduce energy includes fuels that ready to use (see commercial gas fermentation facilities. demand for product separation, such Figure 5).

WORKING PAPER 2019-13 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION 13 ADVANCED ALTERNATIVE FUEL PATHWAYS: TECHNOLOGY OVERVIEW AND STATUS

Legend

Syngas Catalyst Wax Process

Input

By-Product Other Cleaning & Hydrocarbons Fischer-Tropsch Water-Gas Energy Synthesis Shift Desired Product Drop-in Fuel

On-Site Tail Gas Combustion Energy Recovery

Figure 5: Simplified overview of Fischer-Tropsch synthesis.

Chemistry of the conversion be applied to the syngas to adjust the each of the interfaces of solids (cat- H :CO ratio if required for FT synthesis. alysts), liquids (hydrocarbons), and FT synthesis converts a mixture of 2 Ideally, the final concentration of inert gases (carbon monoxide, hydrogen, hydrogen gas and carbon monoxide gases (CO , N , CH etc.) should make steam, and hydrocarbons). Finally, into hydrocarbons and water accord- 2 2 4, up less than 15% of the gas volume because this is a capital-intensive ing to the following equation: (Bergman et al., 2004). process, reactors must scale up effec- tively. Three reactor types are con- (2n+1) H + n CO à C H + n H O 2 n (2n+2) 2 Fischer-Tropsch synthesis sidered viable for commercial scale catalysts production: multitubular fixed bed The n in this equation indicates that reactors, fluidized bed reactors, and the reaction can be manipulated to Several kinds of metals can be used three-phase slurry reactors. produce hydrocarbons with a range to catalyze Fischer-Tropsch synthe- of carbon chain lengths. The hydro- sis: iron, cobalt, nickel, and ruthenium. Multi-tubular fixed bed reactors are carbon distribution is determined by In practice, ruthenium is prohibitively easy to operate and scale up, but they operating conditions, such as tempera- expensive, and nickel catalyzes some are expensive to construct and have ture, pressure, type of catalyst, etc. other undesired reactions, so only iron high gas compression costs for the Conditions can be chosen to maximize and cobalt are industrially relevant. recycled gas feed.1 They also require the yield of a particular cut with a They have different prices, sensitivities long downtimes during replacement higher market value, such as middle to contaminants, life spans, ideal gas of catalysts. distillates (National Energy Technology compositions, and ideal operating con- Laboratory, n.d.). ditions (National Energy Technology Fluidized bed reactors have higher Laboratory, n.d.). efficiency in heat exchange and better Prior to the catalytic reaction, the temperature control. They also require gaseous inputs for the FT synthesis The FT reaction is exothermic, which smaller heat exchange area and lower process require cleaning and upgrad- is to say it releases heat, so an impor- gas compression costs. In addition ing. The process is very sensitive to tant consideration for the reactors is they are easier to construct than contaminants, especially substances their capacity to quickly dispel heat fixed beds. Fluidized bed reactors containing sulfur or metals because from the catalysts to avoid overheat- also allow for online catalyst removal, they can poison the catalysts (Peters ing and catalyst deactivation, while at so there is no downtime for catalyst et al., 2015). Syngas cleaning is the same time maintaining steady tem- addressed in the Gasification section perature control. Reactors also must 1 Fixed and fluidized bed reactors are described of this paper. The water-gas shift can facilitate effective mass transfer across in more detail in the Gasification section.

14 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION WORKING PAPER 2019-13 ADVANCED ALTERNATIVE FUEL PATHWAYS: TECHNOLOGY OVERVIEW AND STATUS

replacement. They also are more molecules, although it also can be sold usually are less costly to produce when complicated to operate, have erosion for its material value for candles and electricity is generated as a major co- problems, and pose some difficulty in other products (Envia Energy, 2015). product rather than when only liquid separating the fine catalyst particles Hydrocracking is addressed in the fuels are produced. In general, studies from the exhaust gas. Hydroprocessing section. on the technology status and eco- nomics of FT synthesis suggest that Three-phase slurry reactors are a type The output from an FT reactor is distinct research and development should from bio-oil or bio-crude derived from of fluidized bed reactor wherein the focus on gasifier designs, syngas fast pyrolysis or hydrothermal lique- catalyst is suspended in a liquid and quality, product selectivity in chemical faction, which are addressed in other the feed gas is bubbled through. They synthesis, and process integration and sections of this paper. FT liquids and have many of the same advantages as scale (Lappas & Heracleous, 2016). other fluidized bed reactors, including waxes are hydrocarbons, containing no downtime for catalyst replacement only hydrogen and carbon. FT syn- Choren attempted the world’s first com- and excellent heat transfer, but it is thesis also generates some tail gas, mercial gasification-FT plant in 2008 difficult to separate catalysts and wax a mixture of the light hydrocarbons partnering with Shell, Volkswagen, and (Lappas & Heracleous, 2016). that are either generally too small Daimler using Choren’s Carbo-V gas- to be sold as fuel, unreacted syngas, ification process and Shell’s Middle For small-scale FT systems, mono- or include any inert gases that were Distillate Synthesis Fischer-Tropsch lithic/microstructured reactors are contained in the process stream. process. Due to “uncontrollable costs,” becoming increasingly popular. In Depending on the composition of insolvency was announced in 2011 a monolithic reactor, there is a thin the tail gas, it may be economical to and the plant was never completed. layer of catalyst on the channel recycle it through the FT reactor or to There were also several plants in other walls, which helps control diffusion burn it for power generation. areas of Europe that failed, such as the of the gas as it flows through the Finland Bioenergy Ajos BTL, launched reactor (Holmen, Venvik, Myrstad, by Vapo Oy and Metsäliitto, and the Zhu, & Chen, 2013). These reactors COMMERCIAL POTENTIAL UPM Stracel BTL in France, both of are compact, lightweight, and safe, FT synthesis is a well-established tech- which had received EU funding in 2010 and given their small size, allow for nology and has been used for decades through NER 300, a large funding process intensification and capital to produce liquid fuels from coal and program for innovative energy dem- cost reductions compared to conven- natural gas. Sasol and Shell are com- onstration projects. In both cases, tional reactors (Arias Pinto, 2016). panies that currently operate com- mercial scale coal-to-liquid (CTL) or the companies cited uncertainty in the regulatory outlook for advanced Product separation and upgrading gas-to-liquid (GTL) FT plants (National Energy Technology Laboratory, n.d.). fuels beyond 2020 as the reason The straight-chain hydrocarbons FT However, gasification of biomass and the projects fell through (Lappas & synthesis produces include waxes, liquid waste feedstocks is still in its early Heracleous, 2016). hydrocarbons, and light gases, which stages. There are several examples Fulcrum BioEnergy and ThermoChem are virtually free of oxygenates, sulfur, of gasification-FT synthesis facilities Recovery International, Inc. (TRI), a metals, and other heteroatoms, which are using biomass and waste feedstocks in gasification technology company, have atoms other than carbon and hydrogen operation around the world, although operated a gasification-FT demo plant (e.g., oxygen, nitrogen). Generally, when many are still at the demonstration or in North Carolina converting MSW the iron catalyst operates in a high pilot scale. temperature range, usually in fluidized into jet fuel and diesel. Fulcrum is now bed reactors, it produces gaseous and In general, the gasification-FT process developing a commercial scale plant in gasoline-range products, whereas in the is capital intensive compared to Reno, NV, that is planned to produce low-temperature range, both iron and other methods for producing cellu- approximately 42 million liters of jet cobalt produce more waxy products and losic biofuel (Peters et al., 2015). De and road fuel from 181,400 tonnes straight-run diesel and naphtha (Lappas Jong et al. (2015) report the minimum of garbage per year (Tepper, 2017). & Heracleous, 2016). The heaviest hydro- fuel selling point to be $1.50 per liter Fulcrum has agreements with United carbon fraction, wax, is usually hydro- for FT fuel produced from forestry Airlines, Cathay Pacific, and BP to cracked to break the larger molecules residues. Liu, Larson, Williams, Kreutz, produce a combined 662 million liters into smaller diesel- or naphtha-sized & Guo (2011) find that FT-derived fuels of jet fuel over 10 years. Fulcrum has

WORKING PAPER 2019-13 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION 15 ADVANCED ALTERNATIVE FUEL PATHWAYS: TECHNOLOGY OVERVIEW AND STATUS

seven more plants planned around the France (Total, n.d.). The goal is to open Catalyst selectivity United States. a commercial scale plant by 2020. Fischer-Tropsch catalysts have low Velocys designs and builds FT reactors The Güssing Renewable Energy dem- product selectivity. The FT reaction for partnerships, rather than running onstration plant in Güssing, Austria, produces a mixture of hydrocarbons, its own plants. Its process uses cobalt has the world’s first functioning fast and although there is some ability to control output, the fraction of desir- catalysts, which Velocys claims offer internally circulating fluidized bed able fuels is usually less than 40% better yields and stability compared gasification plant, producing syngas (IRENA, 2016). The remainder of the to other catalysts. Velocys operates that has low nitrogen and a suitable output needs to be upgraded through a pilot plant in Ohio for technology H2:CO ratio for downstream FT syn- hydrocracking, sold as lower-value development and participates in two thesis. Its FT pilot plant, which has product, or burned for electricity. This joint projects (Velocys, n.d.). Envia been in operation since 2005, represents either an added expense Energy is a joint venture commercial produces 5 to 10 kilograms per day or a loss. Possible solutions include plant in Oklahoma City among Velocys, of raw product when it is in operation improving catalyst technology—for Waste Management, Ventech, and (Lappas & Heracleous, 2016). example, through improving catalyst NRG, using a gasification-FT process selectivity—or optimizing downstream at its 17 million-liters-per-year facility, OBSTACLES TO upgrading processes. (Envia Energy, n.d.). The plant just COMMERCIALIZATION came online in 2017 and is not yet up to capacity. Gasification technology Fast Pyrolysis Further research is needed to optimize Red Rock Biofuels is another Velocys the choice of gasification technol- OVERVIEW OF CONVERSION joint venture that appears to be in an ogy, for example the reactor type, to PROCESS earlier stage of development after be used with FT synthesis in order In fast pyrolysis, feedstock is heated in receiving a $70 million grant (Lappas to meet the stringent syngas quality the absence of oxygen so that cellu- & Heracleous, 2016). The company’s requirements for FT while minimizing lose and other structures break down. stated goal is to make aviation fuel thermal efficiency losses (Lappas & This process is related to gasification, from woody biomass for the military, Heracleous, 2016). Most biomass tends which occurs at much higher temper- FedEx Express, and Southwest Airlines. to produce a syngas that is relatively atures with partial oxidation of the Its plant in Lake County, OR, which was low in hydrogen, requiring water-gas biomass and produces mostly gas, and approved for state funding in January shift to increase hydrogen content, torrefaction, which occurs at much 2018, is slated to use 159,000 dry tons which can further increase costs. The lower temperatures with much lower of residual woody biomass to produce barriers to gasification are addressed in heating rates and aims at maximizing approximately 61 million liters per year more detail in the Gasification section solid products. of finished product (Sapp, 2018). of this paper. Gasification accounts for the bulk (60%–75%) of the capital There are three main stages of fast BioTfueL is a joint project among cost of the combined gasification-FT pyrolysis. First, the feedstock is six French partners (IFP Energies process (van Steen & Claeys, 2008). prepared for the conversion process. Nouvelles, Total, Axens, CEA [a public Second, the conversion process occurs research organization], Sofiprotéol, Syngas cleanup by heating the feedstock in an anoxic and ThyssenKrupp) to convert cellu- Biomass contains low concentrations environment at very high heating losic biomass and coal into drop-in of sulfur, which can deactivate the FT rates. The conversion process gener- diesel through gasification-FT.2 This catalysts (IRENA, 2016). Sulfur can ates three products: heavier, condens- project has a total budget of $120 be removed, but that removal poses able gases (tar); off-gases; and a solid million (Lappas & Heracleous, 2016). another cost trade-off; potential char residue (Banks & Bridgwater, BioTfueL operates two demonstra- remedies may include cheaper cleanup 2016). Finally, the tar is condensed tion plants in in Venette and Dunkirk, processes or more resilient catalyst to produce bio-oil, which is then pro- formulations. Low-sulfur feedstocks, cessed, refined, or otherwise upgraded 2 A drop-in fuel is made up of hydrocarbons that have no blending limit, such as synthetic such as white woody biomass, could to an end product that can be sold as gasoline and diesel. also be used. fuel for transport, electricity, or heat,

16 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION WORKING PAPER 2019-13 ADVANCED ALTERNATIVE FUEL PATHWAYS: TECHNOLOGY OVERVIEW AND STATUS

or as a feedstock for chemical produc- upgrading process later on (Banks There are several possible reactor con- tion (Bridgwater, 2012). & Bridgwater, 2016). Pretreatment figurations. All reactors rely on hot is critical to the process because it sand or a catalyst to transfer heat to Feedstocks utilized improves the yields and the quality of the biomass and to facilitate cracking. the bio-oil. Improving the quality of the Some of the most common reactors Fast pyrolysis can use a wide variety feedstock input into the process also are fluidized bed reactors, which are of feedstocks, including cellulosic reviewed in the Gasification section. biomass such as woody material, agri- reduces the impurities downstream. The reaction speed is critical to fast cultural residues, and energy crops. pyrolysis; at slower speeds, less liquid The technology also can be applied to Chemistry of the conversion is produced. Consequently, the typical industrial waste or by-product materi- Fast pyrolysis, which is illustrated step- residence time of the feedstock in the als such as glycerin and black liquor by-step in Figure 6, is an endother- reactor is about 1–2 seconds. In order (IRENA, 2016). mic reaction requiring temperatures to minimize secondary cracking, which between 475 and 525 C. Following ° generates increased quantities of Pretreatment pretreatment, the biomass or waste undesired products like water, off-gas, material is fed into a reactor that yields During pretreatment, the feedstock and tar, the char by-product must be is dried to less than 10% moisture 40%-70% phase organic compounds removed and vapors must be cooled content by weight to reduce the water (often refered to as pyrolysis oil or quickly (Banks & Bridgwater, 2016). content in the resulting bio-oil. It also is bio-oil) and 12%-40% char, water, and ground or milled into particles smaller gas including light hydrocarbons, Depending on the reactor type, the than 5 mm to ensure sufficiently small carbon monoxide, and carbon dioxide off-gases, which generally consist of particles for rapid heat transfer and (bioliq, n.d.-a) (see Figure 6). These light hydrocarbons such as methane reaction (Mohan, Pittman, & Steele, proportions can vary by adjusting the and ethane, as well as carbon dioxide 2006). Additionally, washing the feed- temperature, feedstock, and reactor and carbon monoxide, are burned to stock prior to the drying process can residence times. This figure also shows supply heat or power for the process. reduce the share of unwanted com- where there is potential for recycling In some cases, the gas could also pounds in the bio-oil and ease the gas for the reactor or exporting energy. be used as the fluidizing vector in a

Biomass or Wastes Drop-in Fuel

or

Bio-oil Pretreatment Fast Pyrolysis

and Legend On-Site Process Char Combustion Energy Recovery Input

By-Product Fluidization for fluidized O -Gases Internal reactors Energy

Desired Product Water

Figure 6: Simplified overview of fast pyrolysis.

WORKING PAPER 2019-13 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION 17 ADVANCED ALTERNATIVE FUEL PATHWAYS: TECHNOLOGY OVERVIEW AND STATUS

fluidized bed, thereby increasing the difficult. A certain amount of organic and selectivity (i.e., narrowing the

H2:CO ratio and therefore the hydro- material dissolves in the water, con- molecular weight range of the liquid carbon content in the bio-oil. In some sisting mostly of light acids, such as products so that they are consistent processes, the char produced in the acetic acid. These organic compounds with fossil fuels) to a better extent pyrolysis reactor is burned to reheat in the water phase are essentially “lost” than other processes. In some cases, the sand or catalyst to provide heat for product. Technology developments to the vapor output from the process the pyrolysis reaction. In other cases, it collect and upgrade these compounds can be directly upgraded to drop-in is combined with the oil. would improve the efficiency of the liquid fuel; hydroprocessing is thus fast pyrolysis process. BTG Empyro unnecessary. If hydroprocessing is The primary product of the pyroly- is researching recovery of light acids, used for upgrading bio-oil produced sis pathway, the bio-oil, generally although it is unclear whether that is from catalytic pyrolysis, less light has an oxygen content between for improved fuel yields or to sell as off-gases are produced compared to 15 and 40% (Czernik & Bridgwater, co-products. Despite these drawbacks, conventional bio-oil because of the 2004). Its composition depends on water contamination has the advan- lower oxygen content of the catalytic a variety of factors, including feed- tage of making the oil less viscous so pyrolysis bio-oil. Catalytic pyrolysis stock material composition, pyroly- that it flows more easily (Czernik & requires potentially simpler pretreat- sis temperature, residence time in Bridgwater, 2004). ment processes. Lastly, the reaction the reactor, heating rate, collection temperature can be lower than system, and storage conditions. The The physical and chemical properties non-catalytic fast pyrolysis, thereby bio-oil is composed of hydrocar- of the bio-oil make it unusable except reducing energy consumption and bons, water, and a small amount of in lower-value uses such as station- cost (Thilakaratne, 2016). ash. The bio-oil retains between 50 ary combustion, for example, station- and 70% of the energy of the input ary heat and steam generation. For One commonly discussed option biomass feedstock. The remaining the liquid to be used in the transport is to co-process bio-oil with petro- energy is contained in the char and sector, it needs further upgrading to leum oils in refineries. Bio-oil could off-gases (Banks & Bridgwater, 2016). remove oxygen, water, ash, and other be co-processed in fluid catalytic The energy density of the bio-oil is contaminants, and to reduce its vis- cracking (FCC) units together with 50% that of petroleum due to the bio- cosity. There are a number of upgrad- the heavier fractions of fossil crude; oil’s relatively high oxygen content ing technologies that can be used and many refineries in the United States (Czernik & Bridgwater, 2004). Oxygen are being tested. Simple physical pro- and Europe are equipped with this content increases the corrosivity of cesses such as filtration and adding equipment (California Air Resources the bio-oil as a fuel. In addition, many solvents can remove solids and ash Board, 2017). For example, the CRI of the oxygen-containing molecules in and reduce viscosity, respectively Catalyst Company, owned by Shell, bio-oil are very reactive compounds (Bridgwater, 2012). has a license to scale up the new that react with each other, making catalytic thermochemical process IH2. the mixture unstable and susceptible An alternative to conventional fast Hydrotreatment also can be applied to degradation over time. Bio-oil is pyrolysis is catalytic pyrolysis, which to bio-oil co-fed with petroleum oils in therefore impractical to store and produces a better quality bio-oil refineries; this is further covered in the challenging to process downstream that requires less upgrading (Banks Hydroprocessing section. At the same (IRENA, 2016). & Bridgwater, 2016). Several kinds time, the oxygen content of bio-oil of catalysts can be used, depending may need to be reduced before it can The high oxygen content in bio-oil also on the desired product; naturally- be processed in petroleum refineries means that greater quantities of water occurring catalysts such as dolomite (IRENA, 2016). can be mixed in the oil compared to are the cheapest. There are several conventional petroleum. Dissolved reported advantages of catalytic water further decreases the energy upgrading compared to other conver- COMMERCIAL POTENTIAL content of the bio-oil and makes sion processes. This process has been Since the fast pyrolysis technology further processing of the oil more shown to control product distribution emerged in the 1980s, much of the

18 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION WORKING PAPER 2019-13 ADVANCED ALTERNATIVE FUEL PATHWAYS: TECHNOLOGY OVERVIEW AND STATUS

focus has been on scaling up reactor operational fast pyrolysis facilities, pri- commercial pyrolysis plant in Quebec technologies, reducing product marily in the United States, Canada, that is slated to produce almost 40 moisture content, improving bio-oil and the EU (Germany, the Netherlands, million liters per year from a mix of forest oxidative stability, and decreasing the Sweden, and Finland). Four more residues. Some of the bio-oil produced amount of solids produced. IRENA facilities are under construction in will be used for heating, and some will (2016) found that some of the greatest Canada, and one more in Germany. be used for refining into transportation opportunities for improving this tech- There are three facilities in the United fuels, although the split has not been nology involve introducing catalysts States and one in Finland that are shared publicly (Ensyn, 2016). The joint that promote higher selectivity of non-operational. Companies with venture claims it can use existing oil desirable alkanes in the bio-oil and multiple operating facilities include refining technology, which would rep- thereby improve yields. BTG (Netherlands), Ensyn (Brazil and resent a major development in making Canada), Fortum (Finland), Karlsruhe pyrolysis a practical technology for There are no commercial examples Institute of Technology (Germany), transportation fuel production. of bio-oil from pyrolysis or upgraded and Red Arrow (United States) (IEA bio-oil being used as a transport fuel. A In 2013, a consortium of VTT of Finland, Bioenergy, 2018). 2015 study estimated that commercial Metso (now Valmet), UPM, and Fortum hydrotreated bio-oil would cost $1,758 BTG BioLiquid, part of the BTG Biomass built a commercial plant with a capacity per tonne, far higher than the current Technology Group, specializes in of 50,000 tonnes per year of bio-oil that price of petroleum (Peters et al., optimizing pyrolysis technology. The is integrated into Fortum’s combined 3 2015). However, the study also found company’s first-of-a-kind commer- heat and power plant in Joensuu, that producers reduced hydrotreated cial plant in Hengelo, Netherlands, Finland. The plant uses forest residue, bio-oil conversion costs threefold has been designed to process 40,000 wood chips, and sawdust (Perkins, between 2009 and 2014; therefore, it tonnes of biomass per year, and the 2018). The primary focus has been on is possible this downward trend could company believes that the success of thermal pyrolysis but various catalysts continue. Most of these cost reductions this plant bodes well for full-scale fast also have been tested. have come from reducing the cost of pyrolysis technology commercializa- The bioliq pilot plant at the Karlsruhe upgrading the bio-oil to a transport tion (Banks & Bridgwater, 2016).4 BTG Institute of Technology in Germany fuel. Famously, the company KiOR per- BioLiquid also opened a pilot plant can process up to 500 kilogram per formed pyrolysis using wood as a feed- in Enschede, Netherlands, in 2015 hour of biomass, although it is not run stock at its facility in Columbus, MS. that generates heat, electricity, and at full capacity (bioliq, n.d.-a). Bioliq KiOR, recently renamed Inaeirs, filed bio-oil, which is intended for boiler sends its bio-oil and char to a gasifier for bankruptcy in 2014 after a scandal and furnace applications. emerged in which the company had to make syngas, which is then used to misrepresented the technology and Ensyn is known to have some of the make transportation fuels. production costs to shareholders most competitive costs of production (Lane, 2016). in the industry, with reported capital OBSTACLES TO costs in the range of $1.32–$1.59 per Many existing facilities generate bio-oil COMMERCIALIZATION liter and production costs around $0.33 for stationary combustion only. IEA There are some obstacles relating per liter for a prototypical 76 million- Bioenergy maintains a global database to the feedstock and pretreatment liter-per-year plant (Lane, 2015a). As of biomass conversion facilities, and process. Grinding, milling, and drying of 2017, Ensyn, Arbec Forest Products, as of January 2018, it contained 27 the feedstock represent a substantial Groupe Rémabec, and Honeywell UOP cost. In addition, particle shape and were constructing a first-of-a-kind 3 Calculated from 1,647 € per tonne using size distribution affect processing. the average exchange rate in 2015 of 0.937 EUR/USD from the U.S. Internal Revenue 4 Based on the original statistic that this plant IRENA (2016) reports that low yields Service (https://www.irs.gov/individuals/ can produce 5 tonnes per hour and assuming international-taxpayers/yearly-average- 90% uptime, i.e., that the plant runs for 8000 are one of the greatest technology currency-exchange-rates). hours per year. barriers to commercialization of

WORKING PAPER 2019-13 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION 19 ADVANCED ALTERNATIVE FUEL PATHWAYS: TECHNOLOGY OVERVIEW AND STATUS

fast pyrolysis. Pyrolysis is an endo- Hydrothermal Liquefaction step, as with other thermochemical thermic reaction, and ensuring suf- processes described above. ficient heat transfer into the system OVERVIEW OF CONVERSION can be a substantial economic PROCESS Pretreatment barrier, as systems for external heat Hydrothermal liquefaction (HTL), also The feedstock for HTL usually contains transfer can add substantially to the known as hydrothermal upgrading, is 5%–35% dry solids. For algal feedstocks, overall cost of the process (IRENA, a process that converts high-water this could mean that some water needs 2016). The Bioeconomy Institute at content biomass, or biomass slurries, to be removed, whereas for woody Iowa State University claims that into liquid fuel, as illustrated in Figure biomass, this means adding water to autothermal pyrolysis improves the 7. Following pretreatment, the biomass create a slurry (IRENA, 2016). HTL of pyrolysis process because the energy slurry is heated and pressurized to woody biomass would require pre- demand of the endothermic reaction convert it to bio-crude. Bio-crude is an treatment, such as size reduction and is balanced with the energy released intermediary product that has a higher alkaline treatment—which is a means from exothermic reactions; this is energy density than the original form of using acids to remove lignin without common in gasification and steam of the biomass, making it easier to degrading the other carbohydrates—in reforming. Autothermal pyrolysis elim- transport to a facility where it can be order to obtain a pumpable and stable inates the need for heat exchange and hydroprocessed in a manner similar to slurry (Kim, Lee, & Kim, 2016). ancillary equipment and results in a conventional crude to produce drop-in higher feedstock throughput that does fuels (IRENA, 2016). The HTL process Chemistry of the conversion also generates aqueous phase (i.e, not degrade product yield or quality During HTL, the biomass is subjected carbon oxygenates and other organic (IRENA, 2016). to a temperature in the range of materials suspended in water), solid 250°C–375°C and a pressure between 5 residue (mainly char), and gaseous Additionally, it is challenging and and 28 megapascals, with water acting by-products (primarily carbon dioxide expensive to upgrade bio-oil. For both as a solvent and reaction medium and carbon monoxide) (see Figure 7). example, the high water content of (Tian, Li, Liu, Zhang, & Lu, 2014). At this The aqueous phase can be recycled, bio-oil is harmful to hydrotreating temperature and pressure, the water reducing requirements for fresh water catalysts. Because bio-oil is very cor- remains in a liquid state. As reported and potentially enhancing the total rosive, it requires that refineries use by Biller and Ross (2016), three main yield. This process water also can metal equipment resistant to corro- steps occur: be treated anaerobically to produce sion, usually stainless steel. This is biogas (shown in blue) or via catalytic 1. Hydrolysis of macromolecules into more expensive than the carbon steel hydrothermal gasification to produce smaller fragments; generally used in petroleum refining. syngas (also in blue), although anaero- In order for this bio-oil to be co-fed bic digestion of process water has not 2. Conversion into smaller com- into conventional refinery units, which been demonstrated experimentally pounds by dehydration and would bring significant cost savings, (Biller & Ross, 2016). decarboxylation; it has been reported that the high oxygen content would first need to Feedstocks utilized 3. Rearrangement into larger, hydro- phobic macromolecules via be reduced (IRENA, 2016). Catalysts A variety of feedstocks can be pro- condensation, cyclization, and also can rapidly deactivate due to cessed through HTL, including MSW, polymerization (i.e., producing oxygen content (Banks & Bridgwater, algae, manure, distillers’ grains with bio-crude). 2016). More robust and selective cata- solubles (DGS), and food wastes. HTL lysts need further development, and is particularly desirable for converting HTL does not require a catalyst, the cost of this process needs to be feedstocks with high water content especially if the feedstock is high in reduced for it to be commercially because the process does not require nitrogen, but adding a catalyst could applied (Du et al., 2016). an additional pretreatment drying theoretically improve the process’s

20 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION WORKING PAPER 2019-13 ADVANCED ALTERNATIVE FUEL PATHWAYS: TECHNOLOGY OVERVIEW AND STATUS

O-Gases Optional Biomass Catalyst

Char

On-Site Combustion Energy Hydrothermal Recovery Pretreatment Bio-Crude Anaerobic Liquefaction Biogas Digestion

Legend Aqueous Or Process Phase

Input Catalytic Hydrothermal Syngas By-Product Gasification

Internal Energy

Desired Product

Figure 7: Simplified overview of hydrothermal liquefaction. efficiency and suppress the formation molecular weights, influenced largely COMMERCIAL POTENTIAL of some undesirable products (IRENA, by feedstock composition and oper- While it has some potential advantages 2016). In particular, alkali catalysts have ating conditions. Before it can be used relative to other conversion pathways, been beneficial for improving yield and as a transport fuel, it requires deoxy- HTL is not a mature technology; there bio-crude quality from lignocellulosic genation and denitrogenation (Tian are no commercial-scale projects cur- feedstocks. et al., 2014). This can be achieved rently in operation. Techno-economic through hydrotreating, which is analyses have found that feedstock Reactor system addressed in the Hydroprocessing price and product yield are two impor- Currently, research has focused on section. Hydrotreating is also nec- tant factors for the minimum fuel selling price (Biller & Ross, 2016). batch reactors, but continuous reactor essary for the bio-oil resulting from systems have higher throughput and pyrolysis, but pyrolysis bio-oil and Research suggests that biowaste, lig- lower residence times than batch HTL bio-crude are two very differ- nocellulosic wood, and MSW all can be operation, increasing total reactor ent products. Bio-crude from HTL converted to bio-crude oil using the output and reducing energy require- HTL process. HTL could be a particu- ments. An important consideration contains less water and oxygen, larly attractive technology to convert for commercial HTL producers will making it more viscous but less dense algae to bio-crude, given the ability of be how to balance operating at lower (Biller & Ross, 2016). Bio-crude could the process to handle feedstocks with residence times while still achieving also be used as a feedstock for co- very high water content, such as algal the desired chemical energy recovery refining in an existing fossil refinery streams. Further, HTL produces higher (Biller & Ross, 2016). to produce energy and chemicals yields of fuel given the same amount (Tian et al., 2014). Further research of feedstock, compared to other tech- Final product and upgrading and development would be needed nologies that process only the lipid The bio-crude from HTL contains for using continuous upgrading facili- fraction of algal biomass to produce organic compounds with a variety of ties (Biller & Ross, 2016). biofuels, such as hydroprocessing and

WORKING PAPER 2019-13 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION 21 ADVANCED ALTERNATIVE FUEL PATHWAYS: TECHNOLOGY OVERVIEW AND STATUS

transesterification. However, because plug-flow reactors, are the most wastewater for anaerobic digestion the upstream barriers for microal- promising type for HTL at the com- or catalytic hydrothermal gasification, gae mass cultivation remain steep, at mercial scale. The authors report an optimal solution has not yet been the moment hydrothermal process- that since 2010, there have been five identified (IRENA, 2016). ing of other feedstocks, particularly continuous reactors reported in the biowaste, is more promising (Biller & literature, ranging in maximum poten- Ross, 2016). tial capacity from 13 liters per day at Hydroprocessing a pilot project at Aarhus University Feedstocks utilized and chemistry HTL has several unique advantages. up to 700 liters per day, with 10% of the conversion Using pressurized, non-vapor water by weight slurry, at the University of as a reaction medium enhances mass Sydney. Other institutions, such as the Hydroprocessing is an overarch- transfer, and because the water is Pacific Northwest National Laboratory ing term for a refining process with not converted to steam, this greatly (PNNL) and the University of Illinois, several separate chemical processes— reduces the latent loss of energy, thus are evaluating the suitability of a hydrotreating, hydroisomerization, increasing the energy efficiency of the variety of other feedstocks, includ- and hydrocracking—that can be reaction. Further, it is possible that by ing algae, manure, and lignocelluosic used to prepare biofuels for use as manipulating operating conditions, the biomass at the research scale. “drop-in” fuels, with characteristics process could self-regulate product similar to their fossil fuel counterparts. separation, whereas in other conver- Although hydroprocessing as a means sion processes additional rectification OBSTACLES TO of treating crude oil is an established or extraction is usually necessary (Tian COMMERCIALIZATION technology within the conventional et al., 2014). Another major advan- IRENA (2016) highlights several dif- refining industry, its use for treatment tage for HTL is its potential flexibil- ficulties facing HTL: (a) expensive of biofuels is a relatively recent devel- ity, as the process can use feedstocks alloy materials are necessary for the opment. This process can be applied with qualities that can be difficult for process equipment necessary to avoid to fast pyrolysis bio-oil, hydrothermal other technologies to handle, such as corrosion; (b) high pressures can liquefaction bio-crude, and heavier moisture content, heterogeneity, and damage system components; and (c) hydrocarbons from Fischer-Tropsch ash content (Biller & Ross, 2016). moving and stirring large volume of synthesis, all of which are addressed biomass slurry may create technical in previous sections, as well as to raw There are several demonstration- problems. There may be potential for vegetable or waste oils and fats. scale HTL projects around the world. improvements through better catalyst In Denmark, a small pilot project can performance. Hydrotreatment removes atoms other process 20 liters per hour with SCF’s than carbon and hydrogen (e.g., catalytic liquefaction technology. In HTL consumes high volumes of water; oxygen, nitrogen) and saturates double 2011, Licella, in partnership with Virgin while generally this is not a problem bonds by reacting fuel streams with Australia and Air New Zealand, estab- on the input end, it produces similar hydrogen in the presence of a catalyst. lished a demonstration plant producing volumes of wastewater, which often The hydrogen combines with these jet fuels using a catalytic hydrothermal contain a large amount of organic heteroatoms and they are removed reactor processing wood and other matter, leading to high wastewa- as volatile hydrogenated compounds. biomass (Tian et al., 2014). Additionally, ter treatment or processing costs These non-hydrocarbons (e.g., water Sapphire Energy Inc., based in the (IRENA, 2016). Some researchers have and off-gases) are then separated United States, and Muradel Pty Ltd., proposed a system where an algal from the upgraded hydrocarbon oil. based in Australia, are two compa- biorefinery reuses and recycles nutri- The light gases go to the hydrogen nies working on HTL from microal- ents, wastewater and chemicals; i.e., plant as feed, and the oil is fed into a gae. Muradel began operating a $10.7 the HTL wastewater is cleaned and fractionator column to obtain gasoline million, 30,000 liter-per-year plant to reused in algae cultivation (IRENA, and diesel (Thilakaratne, 2016). demonstrate its technology converting 2016). However, some of the wastewa- algae to crude oil at an industrial scale ter contains oxidative and toxic com- Hydrocracking is used to break down in 2014 (ETIP Bioenergy, n.d.-b). pounds that inhibit algae regrowth and low-value heavy oil fractions, which is thus cannot be recycled (Tian et al., to say those with longer carbon chains, Biller and Ross (2016) suggest that 2014). Although research is ongoing into higher value products with shorter continuous reactors, particularly to assess the potential for HTL carbon chains, such as gasoline, by

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applying hydrogen to the crude fuel alternative jet fuel that is also nearing of its product slate, making it the mix at high temperatures and pres- ASTM certification at a lower blend world’s first HVO facility to regularly sures in the presence of a catalyst. For rate than standard HEFA, but may be produce renewable jet fuel at scale. example, waxes from Fischer-Tropsch cheaper to produce than conventional United Airlines agreed to purchase synthesis can be hydrocracked into HEFA (Pavlenko & Kharina, 2018). up to 5 million liters of alternative jet lighter hydrocarbon fractions, such as fuel a year for three years, starting in gasoline and diesel, to increase the Neste, which is headquartered in Espoo, 2016 (Kharina & Pavlenko, 2017). To final yield of valuable products. Finland, is the largest renewable diesel minimize capital costs, AltAir repur- producer in the world. It also was the posed a former asphalt plant. The ret- Waste oils, vegetable oils, and fats, first company to successfully develop rofitting process cost several hundred such as tallow, can be converted into a commercial-scale HVO production million dollars, some of which was paid drop-in diesel or jet fuel substitutes process, using its NEXBTL technol- for by government grants. using a combination of both hydro- ogy. In total, Neste facilities have about processing technologies. These 2.6 million tonnes capacity, costing finished fuels are typically referred roughly $1.7 billion in total investment OBSTACLES TO to as renewable diesel, hydrogena- (Lindfors, n.d.). Neste operates two COMMERCIALIZATION tion derived renewable diesel (HDRD), plants in Finland processing 200,000 For HVO and HEFA specifically, or hydrotreated vegetable oil (HVO). tonnes per year that each cost around because the production methods are A similar middle distillate, hydro- $115 million to construct. In Singapore already commercialized, there are no processed esters and fatty acids and Rotterdam, Neste operates facili- major technology barriers to expand- (HEFA) fuel, can be produced for ties that cost around $630 million and ing hydroprocessing capacity. Relative use in aviation. The resulting hydro- $770 million, respectively, to construct, to production capacity, the capital carbons can be further hydrocracked which both process 1.1 million tonnes costs for hydroprocessing facilities into shorter chains depending on the per year (Neste, personal communica- are substantially lower than for other desired outputs for the process. tion, June 15, 2018). advanced fuel conversion pathways and there is much greater certainty In Italy, Eni SpA was the first company on product yields ((S&T)2 Consultants, COMMERCIAL POTENTIAL in the world to transform an existing oil Inc., 2018) Hydroprocessing-derived renew- refining plant into a biorefinery, which able diesel from fats and oils already it says required a capital expenditure of Techno-economic assessment esti- is considered a mature pathway that $123 million, compared to $638 million mates that feedstock costs are the is produced at a commercial scale, for a greenfield project (Mawhood, single biggest contributor to the prices showing that there is potential for Gazis, de Jong, & Hoefnagels, 2016). It of HEFA fuels from waste oils (Seber et hydroprocessed fuels from other feed- uses Ecofining technology. al., 2014). Thus, it is unlikely that pro- stocks to reach this level of commer- duction costs can decline much further cial maturity. Because of the potential Diamond Green Diesel, in Norco, (Pearlson, Wollersheim, & Hileman, for integrating hydroprocessing with LA, operates the largest commercial 2013). Although vegetable oils are an conventional petroleum refining, co- advanced biofuel facility in the United expensive feedstock, waste oil and refining is considered to be a promising States. For that facility, Honeywell UOP fat prices are not much lower (U.S. route for advanced fuels production. and Eni SpA have developed the hydro- Department of Agriculture Economic processing method called Ecofining Research Service, n.d.). However, Neste At least 10 plants worldwide produce that converts nonedible natural oils has indicated that future research renewable diesel using hydropro- and animal fats to drop-in diesel (Lane, and development efforts will target cessing, which together produced 2014a). In 2017, Diamond Green Diesel expanding the feedstock base for its around 4.5 billion liters in 2014 (IEA reported it would be expanding from process in order to both expand pro- Bioenergy, 2018). HEFA fuel for 10,000 barrels per day (bpd) to 18,000 duction and bring down feedstock aviation already has been ASTM- bpd, producing 1 billion liters per year. prices. It is important that these feed- certified as a drop-in alternative jet In 2017, this project was slated for stocks include low-carbon, sustain- fuel and is being produced at commer- completion in 2018 (Lane, 2017b). able feedstocks such as agricultural cial scales (Kharina & Pavlenko, 2017). residues, municipal or industrial waste High-freeze point HEFA, or HEFA+, AltAir uses Honeywell UOP’s tech- streams, lignocellulosic energy crops, is another hydroprocessing-derived nology to produce HEFA fuel as part and forestry residues. Additionally, if

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the conversion pathways that require combine the energy from renewable be recovered at very high purity levels. hydroprocessing to create drop-in electricity with captured carbon to SOECs operate at higher temperatures fuels reach commercialization, e.g., create synthetic fuels. than the other technologies, 600°C– Fischer-Tropsch and fast pyrolysis, the 800°C, and the waste heat can be used need for hydroprocessing finishing for steam generation and reducing CHEMISTRY OF THE facilities also will increase. total electricity consumption relative CONVERSION to other options (Schmidt, Weindorf, Figure 8 shows the primary steps in the Power-to-X Roth, Batteiger, & Riegel, 2016). Only PtX process: electrolysis and combin- SOECs produce enough heat to make ing the hydrogen with carbon, through steam, which can be used as an energy OVERVIEW OF CONVERSION either methanol synthesis, methanation, source for electrolysis (see Figure 8). PROCESS or reverse water-gas shift. PtX requires Power-to-X (PtX), which includes external heat and energy, but this figure After electrolysis, the hydrogen must be power-to-liquids (PtL) and power-to- shows only where there is potential for combined with carbon in order to create gas (PtG), is a set of processes that recycling or exporting energy. a hydrocarbon fuel, such as methane, or convert electrical energy to liquid or a liquid fuel, such as drop-in diesel or Electrolysis splits water into its elemen- gaseous fuels using either CO2 or CO gasoline, methanol, or dimethyl ether as a feedstock. To achieve climate tal components, hydrogen gas and (DME) (Schmidt et al., 2016). Typically, benefits through PtX, the electricity oxygen gas. There are several electro- the carbon in a PtX process comes for the process must come from low- lyzing technologies currently in various from carbon dioxide collected from the carbon, renewable sources such as states of development or deployment, atmosphere or from a point source. In solar or wind power, and use carbon including alkaline electrolysis, proton some cases, the process may also use captured from either industrial flue exchange membrane (PEM) electroly- carbon monoxide captured from steel gases or stack emissions or directly sis, and solid-oxide electrolyzer cells mills or other industrial processes. from the atmosphere. The PtX process, (SOECs), also known as steam and rather than one discrete technology, co-electrolysis. All three technologies There are two main chemical technolo- uses a series of separate processes to allow for the oxygen and hydrogen to gies for CO2 capture: (a) CO2 is absorbed

Legend Carbon Dioxide Catalyst Process Water or Carbon Monoxide Input

By-Product

Internal Oxygen Methanol Synthesis Methanol Energy

Electrolysis or Desired Product

Hydrogen Methanation Methane

or

Reverse Fischer-Tropsch Syngas Heat Water-Gas Shift Synthesis

Steam (for electricity)

Figure 8: Simplified overview of PtX. Primary steps are highlighted with bold arrows.

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onto amines, then recovered by heating COMMERCIAL POTENTIAL In addition, Inerate’s Soletair operates a pilot-sized unit, using direct air the saturated amines, which can then All of the stages of the power-to-liq- capture, at Lappeenranta University of be used again; or (b) calcium hydroxide uid process have been demonstrated, Technology in Finland (“Finnish demo solution binds CO2, forming calcium although no existing facilities produce plant,” 2017). In October 2016, Carbon carbonate (CaCO3), which is then drop-in transportation fuels via this Engineering and Greyrock announced heated to high temperatures to release technology (Malins, 2017). These tech- that they were developing a demon- the CO , and the residual calcium oxide nologies are only now being assem- 2 stration plant in British Columbia, which is returned to the capture solution. bled together into a single process to will use CO from direct air capture to Both systems can be used with either produce fuels (Schmidt et al., 2016). 2 produce liquid transportation fuels. It point sources of CO , such as industrial 2 Alkaline electrolysis is the most devel- is still in its early stages, and project flue gases (carbon capture) or with CO 2 oped and commercially ready step in funding comes from the British recovered from the atmosphere (direct PtX technology. It has been used in Columbia Innovative Clean Energy air capture), but the technological industry for many years and provides Fund. Carbon Engineering already has readiness of carbon capture at a con- a very high degree of hydrogen purity; a 1 tonne-CO2 ­ per day air capture pilot centrated source is higher than direct however, it requires high maintenance. plant (Greyrock, n.d.). air capture technology (Schmidt et al., PEM is more reliable and more flexible 2016). The main differences between but also more expensive, and it still OBSTACLES TO carbon capture at a point source and requires further development. SOEC COMMERCIALIZATION direct air capture are the gas tempera- has lower electricity needs to produce High production cost is a major barrier tures and the concentration of CO . In hydrogen (Badwal, Giddey, & Munnings, 2 to commercialization of PtX (Searle & particular, flue gases are hotter than 2013). This technology promises the Christensen, 2018). The primary cost air and have a higher concentration of highest electrolysis efficiency and low driver for PtX production is the cost of CO than the atmosphere (Jones, 2012). capital costs, but it still is in the proof- 2 of-concept phase of development renewable electricity production. The These differences necessitate different (Grond & Holstein, 2014). German Umweltbundesamt (Federal operational implementations, but the Environment Agency) wrote that PtG underlying chemistry is similar. Carbon Recycling International has been and PtL plants are not currently eco- operating the George Olah Renewable nomically viable in Germany because Once the CO has been collected, the 2 Methanol plant in Iceland since 2012. It of the lack of investment, high operat- specific chemical process it undergoes is a power-to-liquid process that uses ing costs, transformation losses, and with the hydrogen depends on the type framework conditions (e.g., taxes and power and CO2 from a geothermal of fuel desired. For example, hydrogen plant. It appears to be commercially charges) (Purr, et al., 2016). could be reacted with carbon dioxide operational, producing 4,000 tonnes of to produce methane or methanol. methanol a year, with plans for expan- Methanol can be used in low blends with sion (Gale, 2016; Extance, 2016). Conclusions gasoline (Malins, 2017). As described in The commercial statuses and obsta- There are several PtL demonstra- Schmidt et al. (2016), there are several cles facing the conversion technology tion plants around the world. Sunfire processes by which to further convert pathways and upgrading processes has a demonstration-scale facility in methanol to drop-in transport fuels: reviewed in this paper are summarized Dresden, Germany, using SOEC tech- in Table 1. Advanced alternative fuels DME synthesis, olefin synthesis, oligo- nology and producing synthetic crude pathways are at varying stages of devel- merization, and hydrotreating. oil (Beckman, 2014). Recently the opment, with some having been dem- company announced achieving 1,500 Alternatively, the mixture of CO and onstrated only at the pilot project scale 2 continuous hours on-stream, producing hydrogen could be converted into a mix and others having reached commercial 3 tonnes of electrofuels (Sunfire, 2017). maturity. Finishing processes such as of CO, water, and hydrogen through a The facility is part of a project funded hydroprocessing and FT synthesis are reverse water-gas shift reaction. The by Germany’s Ministry for Economic already largely commercialized. resulting syngas can then be used as an Affairs and Energy. Sunfire also is in a input for Fischer-Tropsch synthesis and partnership with Nordic Blue Crude, For each pathway assessed here, a converted to liquid hydrocarbons, a which is planning a facility in Herøya, number of obstacles to commercializa- process addressed in an earlier section. Norway (Nordic Blue Crude, n.d.). tion have been identified. The largest

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barriers may be political and economic, be a capital-intensive, expensive, and as these can be executed efficiently. For but there are several technological complex process, making the overall example, some FT facilities use tail gas barriers as well. A critical barrier is conversion process more difficult. recycling, and process water can also the issue of scaling: Across pathways, be recycled during hydrothermal lique- Several of these obstacles could be the literature suggests that reactors faction. An example of co-processing overcome in the near future through for larger-scale facilities may need to would be co-refining the bio-oil from the deployment of systems that allow adopt different designs than what has fast pyrolysis along with conventional for material and energy recovery or oth- been done already at a demonstration oil in fluid catalytic cracking units. For erwise take advantage of economies of scale. Another common obstacle is the production of cellulosic ethanol, scale. For example, the chemical cata- some bolt-on facilities are located next related to the supply of raw materials, lysts common in many processes can be which may be dispersed, leading to high expensive to purchase and maintain, but to conventional corn ethanol facilities, transportation costs, or highly heterog- this barrier can be overcome through converting the waste that is left over enous, potentially requiring complex the use of robust catalysts with longer from the conventional facility. By over- and expensive collection. Finally, lifetimes and reactor designs that facili- coming these obstacles during the next pretreatment is a significant cost in tate more efficient catalyst recovery. decade, advanced alternative fuels pro- advanced alternative fuels production. Recycling energy and other inputs, as ducers will demonstrate that promising Although many waste and lignocel- well as co-processing of bio-oil and bio- results at demonstration-scale projects lulosic feedstocks are cheap to acquire, crude along with conventional petro- are scalable with the right financial and preparing them for conversion can leum, could also reduce costs, as long political incentives in place.

Table 1: Summary of the current status and obstacles facing the conversion technology pathways and upgrading processes addressed in this paper

Status in 2019 for Technology producing advanced fuels Obstacles to commercialization

Pretreatment Conversion Upgrading

Recalcitrance High-solids loading; cost of enzymes and Cellulosic Early commercial of lignin and other chemicals; ethanol hemicellulose C5 sugar content Early commercial, but demonstration for Grinding, milling, and Syngas Gasification Tar production transport fuels production drying the feedstock cleaning

Maintaining activity rate of microorganisms is Gas Demonstration energy intensive; bacterial activity is inhibited fermentation by by-products; bacterial contamination Commercial, but demonstration for low- Optimization of gasification technology for Fischer-Tropsch carbon fuels production use with FT; low catalyst selectivity

Early commercial for High water on-site combustion, Grinding, milling, and Heating the feedstock to an appropriate and oxygen Fast pyrolysis but demonstration for drying the feedstock temperature is expensive content; bio-oil transport fuels production is corrosive

Expensive alloy materials are necessary to prevent corrosion of system components; high pressure can damage system Hydrothermal Demonstration components; moving and stirring large liquefaction volume of biomass slurry may create technical problems and creates high volumes of wastewater Commercial (using fats Hydroprocessing and oils) Power-to-X Demonstration High electricity input costs in many regions

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