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Renewable and Reviews 42 (2015) 1234–1244

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Renewable and Sustainable Energy Reviews

journal homepage: www.elsevier.com/locate/rser

Aviation from renewable resources: Routes, opportunities and challenges

Thushara Kandaramath Hari a, Zahira Yaakob a,n, Narayanan N. Binitha b a Department of Chemical and Process Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, Bangi 43600, Malaysia b Deparment of Chemistry, Sree Neelakanta Govt. Sanskrit College Pattambi, Kerala, India article info abstract

Article history: Air transport describes an inevitable part in the day to day life of the modern world. It is highly Received 16 October 2013 responsible for the worldwide social contacts and business developments. The use of petroleum fuels as Received in revised form energy source for air transport is not sustainable. Aviation is one of the leading contributors to the total 31 July 2014 emissions. Also, the prices are becoming more volatile day by day. Accepted 28 October 2014 So it is very essential to introduce and industrialize alternative aviation fuels generated from renewable Available online 18 November 2014 resources, especially . A number of industrial commitments and collaborations have emerged to Keywords: find alternative ways to reach bio aviation fuels. Research on the conversion of biomass based sources to Bio bio jet fuels is of current interest. The main concern is the production of biojet fuel, from renewable Aviation resources, with relatively low greenhouse gas life cycle and with affordable price. The Feedstock present paper overviews the opportunities and challenges in the development of alternative fuels for Production route Challenge aviation. The production process, feedstock used and the most promising global projects are also reviewed. & 2014 Elsevier Ltd. All rights reserved.

Contents

1. Introduction ...... 1235 2. Renewable resources ...... 1236 2.1. Camelina...... 1236 2.2. Jatropha ...... 1236 2.3. ...... 1236 2.4. Wastes...... 1236 2.5. Halophytes ...... 1236 3. Alternative fuels for air transport ...... 1237 3.1. Hydroprocessed renewable jet fuels ...... 1237 3.2. Fischer Tropsch fuels ...... 1237 3.3. ...... 1237 3.4. Liquid biohydrogen and biomethane ...... 1237 3.5. Bio alcohols ...... 1237 4. Production routes ...... 1238 4.1. Thermochemical process ...... 1238 4.1.1. Biomass to liquid process (BTL process) ...... 1238 4.1.2. Fischer Tropsch process (FT process) ...... 1238 4.2. Hydroprocessing ...... 1238 4.3. Biochemical process...... 1238 4.3.1. Direct to process (DHSC) and alcohol to jet process (ATJ) ...... 1238 4.3.2. Bio alcohol production...... 1238

n Corresponding author. Tel.: þ60 389216422; fax: þ60 389216148. E-mail address: [email protected] (Z. Yaakob). http://dx.doi.org/10.1016/j.rser.2014.10.095 1364-0321/& 2014 Elsevier Ltd. All rights reserved. T. Kandaramath Hari et al. / Renewable and Sustainable Energy Reviews 42 (2015) 1234–1244 1235

5. Other alternative fuels production routes ...... 1239 5.1. Liquid hydrogen and liquid methane ...... 1239 5.2. Transesterification of oils/fats ...... 1239 6. Industry commitments and collaborations...... 1239 7. Challenges...... 1241 7.1. Environmental challenges ...... 1241 7.2. Production issues...... 1241 7.3. Distribution problems ...... 1241 7.4. Feedstock availability and sustainability...... 1241 7.5. Compatibility with conventional fuel ...... 1242 8. Future outlook and recommendations ...... 1242 9. Conclusion ...... 1242 References...... 1242

1. Introduction attracted by the low greenhouse gas emissions while combustion, decrease in the dependence on fossil fuel sources and availability Combustion of fossil fuels and human activities disturb the of renewable resources [9]. The aviation transport sector requires environment by the emission of greenhouse gases like nitrous fuels with high energy density and so it depends mainly on liquid oxide, carbon dioxide, methane etc. [1]. The requirement of oils for hydrocarbon fuels. Alternative aviation fuels must possess some transport is growing day by day and it is expected to be increased specific qualities such as good cold flow properties, thermal by 1.3% per year up to 2030 [2]. There is no unique solution stability and low freezing point [10]. The fuel must be well suited available for these complications and so alternative ways are to be for the present design of the aircraft engine [11]. Sustainable found out such as modification in vehicle designs, development in aviation fuels must offer low carbon emission over their lifecycles. public transport and replacement of conventional fuels with The energy crops used as the production source should not alternative advanced fuels and fuel technologies [3]. It is expected challenge the food production and ecosystem and also do not that by 2030, the carbon emission from the transport sector and harm the environment and do not cause [12]. the energy requirement will increase up to 80% [4]. Air transport The feedstock used for the production of alternative aviation acquired a significant role in the everyday life of modern world. fuels are biological in origin and thus are renewable. Non edible oil The influence of air travel increased worldwide social contact, crops such as camelina, jatropha, algae, halophytes, municipal and especially in improving business and marketing. The total diesel sewage wastes, forest residues etc are the major available fuel and jet fuel consumption was in the range of 5 to 6 million resources for the energy production process [13]. Many technol- barrels per day in between 2005 and 2010 [5]. The average cost of ogies have emerged for the production of aviation bio fuel from jet fuels was $320/t in 2004 which is increased to an average of the biomass resources. The conversion routes include thermoche- $1005/t in 2011 [2]. Fig. 1 represents worldwide commercial jet mical and biochemical approaches [14]. The bright future of fuel prize and usage, world market: 2011–2021 [6]. According to alternative can be influenced by the co-operation the report from U.S. Energy Information Administration (IEA), for between national and international organizations, states and the next thirty years, the jet fuel cost will increase gradually and countries [15]. International Air Transport Association (IATA) the average price in the year of 2013 was ($2.82/gal) [7]. expects 30% contribution of Bio jet fuel for the jet fuel use by The production of alternative fuel for aviation is mainly 2030 [16]. The annual universal production of biomass is about inspired by increased petroleum costs and environmental concern 100 trillion kilograms. So obviously, biomass is a potential feed- [5]. Not only the increased cost and environmental effects, some stock having the ability to substitute fossil fuel resource [17,18]. other factors such as secured working of the aircraft engine, In addition to the reduction in the emission of greenhouse consistency etc. should also be considered [8]. Use of are gases, alternative aviation biofuels experiences several advantages

Fig. 1. Worldwide commercial jet fuel prize and usage, world market: 2011–2021 [6]. 1236 T. Kandaramath Hari et al. / Renewable and Sustainable Energy Reviews 42 (2015) 1234–1244 over conventional jet fuel. The fossil fuels are affected mainly by Otherwise the continuous mono cropping may cause decrease in cost fluctuation [19]. Since the sources used for the production of the yield and can destroy the soil. bio aviation fuel are renewable and of low cost, a well suited production route can reduce the cost of the fuel. Bio aviation fuel 2.2. Jatropha production can offer economic profits, especially in developing countries where there is unusable land available for the cultivation Jatropha is a non-edible energy crop which can grow in of non-food crops and thus can support the supply chain process marginal land and so it does not compete with food crops. The [20]. One of the major problems that related to fossil fuels is the jatropha plant is drought and pest resistant. The plant can grow difficulty in supply with increasing demand. Here the attraction of even in unproductive soil under unfavourable climatic conditions bio aviation fuels is that the feedstock is available worldwide and and grows quickly [33]. The plant has a permanent pattern of high the production process is not location limited [21]. Bio aviation yield oil production [34]. Jatropha plant can continue yielding for fuels can satisfy the fundamental properties of conventional 40 years once started when a small amount of moisture is aviation fuels such as low temperature performance, low flash available [35]. The meal left after the extraction of oil cannot be point, good thermal stability etc. [22]. In brief the aviation biofuels used since it is poisonous, but it is rich in N, K and P so can be used are ecologically, economically and socially sustainable [23]. as organic manure [34]. Jatropha cultivation is currently occurring Daggett et al. gave a well outline of the alternative aviation in South Africa, South and Central America and South East Asia fuels and their feasibility [24]. Bomani et al. provided a survey on [36]. The jatropha seed production also depends on location, biofuels as an alternative aviation energy source in which they management practices, varieties, etc. Information from current included application of fuel produced from , algae, plantation reveals that the plant requires irrigation for better halophytes and biomass for aviation and road transport purposes growing [37]. [25]. Nygren et al. investigated the scenarios in aviation fuel and future oil production [26]. Liu et al. investigated various jet fuel 2.3. Algae production processes and discussed each process in detail [27]. A recent review by Kallio et al. analyzed the application of microbial Algae is an attractive solution for the fuel scarcity issues biotechnology for the renewable production of jet fuel [28]. because of their high lipid content, high rate of carbon dioxide Even though bio jet fuels are excellent alternatives for conven- absorption, low land use and faster rate of growth [38–40]. The tional aviation fuels; there are many difficulties and challenges to most important benefit of algae is that algae do not affect crop overcome in order to achieve it. Collection of feedstock, the cultivation since it does not require land or water to survive, which production route, characteristic of the produced fuel and its help to reduce the food-fuel competition [41]. Algae can produce characterization are extremely challenging. The present paper large quantities of lipids and carbohydrate by using sunlight, waste deals with the opportunities and challenges in the production of water and carbon dioxide and thus can play a crucial role in from renewable feedstock. Discussions on the wastewater treatment [42,43]. The biomass left after the extrac- characteristics of feedstock, the methods used in the production tion of algal oil can be used as animal feed, for preparing bio process, a comparison of renewable hydrocarbon fuel with biohy- plastic and for nutrition and also the dried biomass can be further drogen, biodiesel, bioalcohol and biomethane as alternative fuels, processed for energy production [31]. Microalgae are widely used the industry commitments and collaborations and future outlook for fuel purpose. It is easy to cultivate and can be harvested all the and recommendations in this field are also included. year [2]. Compared to other energy crops, algae can produce 30 times more yields per acre [21]. Algae can be processed into a variety of renewable fuels [44]. 2. Renewable resources 2.4. Wastes Renewable feedstocks are better resources for the production of bio jet fuels. The important advantages of these feedstock are Wastes from different sources are dependable feedstock for (1) sustainability (2) carbon dioxide recycling (3) renewability (4) the production of alternative biofuels. Wastes of plant origin and eco-friendly technology and (5) less dependence on petroleum animal origin, such as foodstuffs, wood products, paper, forest supplying countries [29]. The feedstocks generally favoured are residues, industrial and agricultural residues, household wastes, non-food energy crops, algae, municipal and sewage wastes, waste bagasse, animal wastes and municipal wastes can be converted to wood, forest residues and halophytes. The characteristics of some biofuel through different potential routes [20]. These resources of the renewable feedstock are mentioned below. are of low cost and easily available. The use of waste materials for the production of energy will be an asset to the waste manage- 2.1. Camelina ment technology without the generation of any harmful pro- ducts. Municipal wastes and sewage sludge can contribute more Camelina is a non-food energy crop with high oil content. since they are widely available and are rich in lipids [45].Theuse The average oil content of the plant is about 30–40% and the plant of waste materials for the production of biofuels can overcome needs lesser amount of fertilizers for growth [30]. Camelina many difficulties such as need of fertilizer, irrigation, land and possesses many advantages. Camelina plant can grow on infertile labour [46]. soil or marginal land [31] and the plant is less susceptible to diseases and pets [20]. Camelina can be cultivated as a rotational 2.5. Halophytes crop for wheat and cereals and it needs minimum input [30]. The meal left after the extraction of oil can be used as animal feed. Halophytes are grasses that grow in salty water where plants The cost of the camelina oil is very less ($0.40–$0.70/gal) and the could not grow usually [20]. Halophytes are mostly found in current markets of the oil in US are Northwest US and Southern tropical and subtropical regions [47]. Halophytes are can grow in Canada; in 2012, 200 million gallons of camelina oil were pro- marshes, inland lakes, coastal shorelines, desert areas and in the duced only in US [22]. Since it can be cultivated as a rotational sea [48]. The speciality of halophytes feedstock is that they will crop, it can solve the problems related to mono cropping which not compete with agricultural crops for fresh water supply and will help farmers to find additional profits from the land [32]. land [49]. T. Kandaramath Hari et al. / Renewable and Sustainable Energy Reviews 42 (2015) 1234–1244 1237

3. Alternative fuels for air transport other problem with the fuel is low lubricity because of the absence of sulphur [62]. Solena is going to establish waste to bio jet fuel Alternative aviation fuels can be produced from all of the above plants having a capacity of 50,000 t/year by 2017. StoraEnso and renewable bioresources. The properties of alternative aviation fuels Oil, UPM and Carbona have formed consortia to develop BTL are (1) reduced greenhouse gas emission (2) renewable resources plants in Europe [57]. The ASTM international standard, D7566, (3) compatibility with conventional fuel (4) sustainability and has approved specification for aviation fuels, FT fuels in 2009 and clean burning. The currently developing alternative fuels includes HRJs in 2011 [63]. the following. 3.3. Biodiesel 3.1. Hydroprocessed renewable jet fuels Biodiesel is alkyl esters of , especially vegetable oils Hydroprocessed renewable jet fuels (HRJs or hydroprocessed and animal fats and it is produced by the process of transester- esters and fatty acids (HEFA) are generally paraffinic liquids having ification. Biodiesel fuel is biodegradable and possesses excellent chemical formula CnH2nþ 2. HRJs are produced by the hydrodeox- lubricity [8]. Biodiesel as fuel shows the advantages of renew- ygenation of vegetable oils, animal fats, waste grease, algal oil and ability in origin, high flash point, good energy balance and good bio oil and the major side products are water and propane [50]. miscibility with petroleum fuels. It contains no sulphur and show The hydroprocessed renewable jet fuels are high energy biofuels highly reduced greenhouse gas emissions [64]. It is also noted that that can be used as such as fuel even without blending. One of the the biodiesel fuels do not contain aromatic compounds, does not major advantages of hydroprocessed renewable jet fuels is reduc- cause any water, soil or and it is non-toxic [65–67]. tion in the emission of greenhouse gas such as carbon monoxide But the biodiesel fuel is not sufficient to use as an aviation fuel. The (CO), (HC), nitrogen oxides (NOx), and particulate energy density of biodiesel is very low compared to conventional matter (PM) [51]. The HRJs are free of aromatics and sulphur and jet fuels [68]. possess high cetane number, high thermal stability and low Use of biodiesel as aviation fuel does not need further engine tailpipe emissions [52]. These fuels are stable for storage and modification and infrastructure, but it does not show much resistant to microbial growth [53]. efficiency [69]. The biodegradability of biodiesel may cause biolo- The hydroprocessed renewable jet fuels are suitable for con- gical growth during storage which will affect the stability [8]. The ventional aircraft engines without further engine modification and freezing point of biodiesel is very high compared to petroleum do not raise any fuel quality issues. These fuels avoid the chance of based aviation fuel, which makes it insufficient for high altitude deposit formation in the engine and engine corrosion [54]. The flights. The presence of polyunsaturated and unsaturated fatty fuel combustion is completely ash free. Because of the better cold acids decreases the stability of the biodiesel due to the oxidation of flow properties, HRJs are highly fit for higher altitude flights [51]. the unsaturated sites [46]. Because of the presence of ester groups, Complete absence of oxygen and sulphur in the fuel decreases its biodiesel is polar to some extent which will cause the formation of lubricity [55]. The higher paraffin content in the fuel somehow emulsion and therefore water separation will be difficult [8]. adversely affects the cold flow properties like cold filter plugging Inadequate feedstock supply and deprived economics are the point and cloud point which in turn depend on the type of other problems of biodiesel fuel [64]. feedstock used [56]. The difference in the cetane numbers of hydroprocessed renewable jet fuels and conventional petroleum 3.4. Liquid biohydrogen and biomethane fuels affects the fuel ignition in the engine. These problems are better solved by blending HRJs with conventional fuels [55]. Liquid hydrogen is being established as alternative jet fuel. Bio The Nest Oil Company has established plants to produce hydrogen is produced from a wide range of biomass resources by hydrotreated renewable jet fuels. UOP Honeywell, ENI and Galp following both thermal and biochemical methods [70]. Liquid Energia have plans for to construct hydrotreating plants world- hydrogen produces more energy per weight compared to conven- wide [57]. Aeroméxico, Air China, Air France, , Iberia and tional aviation fuel, but requires high storage volume [71,72]. The Air France KLM, have performed commercial passen- combustion of liquid hydrogen fuels causes low emission of ger flights with hydroprocessed esters and fatty acids (HEFA) as greenhouse gases compared to petroleum based jet fuels [73]. fuels [58]. The major problem is that the liquid hydrogen fuel cannot be used as such in the conventional aircraft engine so the engine has to be 3.2. Fischer Tropsch fuels modified [74]. The production cost, formation of char and tar as side products are also to be faced [70]. The other problem Fischer Tropsch fuels (FT fuels) are hydrocarbon fuels, which associated with the use of liquid hydrogen is that upon mixing are produced by catalytic conversion of syn gas (CO and H2) [59]. with air, it can burn in low concentration which will cause safety A wide range of biomass feedstock can be used for the generation problems and the storage of hydrogen as liquid is also difficult of syn gas [60]. The FT fuels are usually clean burning, high value since it need low temperature [75]. The emission of comparatively fuels [61]. The FT fuels are characterized by non-toxicity, no high amount of water vapour is a problem associated with emission of nitrogen oxides, high cetane number, reduced parti- hydrogen aircrafts [46]. Liquid methane can be used as fuel in culate emission, low sulphur and aromatic content etc. Also the cryogenic aircrafts. The use of carbon dioxide emission can be fuel combustion is free of carbon dioxide and hydrocarbons [46]. decreased about 25% by the use of liquid methane fuel. Engine Unlike many other alternative fuels, FT fuels does not need special design is a difficulty that has to be faced for the commercialization distribution infrastructure and because of the quality of fuel and of the liquid methane fuels. The combustion of liquid methane fuel comfortable for distribution, FT fuels can be produced 2–3 million emits methane, which is a major greenhouse gas [46]. barrels per day [61]. The characteristics of FT fuels less depend on the nature of the feedstock used and the differences in fuel 3.5. Bio alcohols properties are mainly due to the operational conditions [62]. The FT process is expensive and the efficiency of the process ranges Bio alcohols are produced by the fermentation of starch and between 25 and 50% [59]. Due to less energy density, the Fischer sugar or catalytic conversion of biogas. and are Tropsch fuels offer low power and low fuel economy [61]. The generally used as alternative fuels. Ethanol cannot be used for 1238 T. Kandaramath Hari et al. / Renewable and Sustainable Energy Reviews 42 (2015) 1234–1244 aviation purposes because of its high volatility, low flash point, and 4.2. Hydroprocessing low energy density [52]. The case of butanol is almost similar. Alcohol as aviation fuel needs special delivery infrastructure and The method of hydroprocessing involves treatment of fats and storage system [8]. Use of alcohol as jet fuel needs engine oils (vegetable oils and bio oils) in the presence of hydrogen for modifications [59]. The high volatility of ethanol causes safety the removal of oxygen from the feedstock. The hydrodeoxygena- problems during high altitude travels [52]. Blending of alcohol tion step is followed by isomerization and cracking to get fuel of with conventional fuels is not feasible because of its poor fuel desired specifications like low temperature properties [83]. Hydro- properties which will cause aviation issues. processing results in the formation of clean paraffinic fuels with high thermal stability, no aromatics and suphur and they are generally mentioned as hydroprocessed renewable jet fuels (HRJs) 4. Production routes [84]. In the hydrodeoxygenation method, oxygen is most prefer- ably removed as water and propane is one of the byproducts [85]. The fuel production routes have much importance in determin- The most promising feedstock used for the production of HRJs are ing the fuel characters. The method adopted to produce the fuel plant oils like jatropha oil, camelina oil, algal oil, bio oil, animal fats will influence the product composition, fuel cost, fuel properties, and waste grease that can be made available in plenty [52]. The availability and environmental impact. The generally used meth- method is efficient and it can produce hydrocarbon fuel with ods for the production of hydrocarbon fuels involve two types. One improved cold flow behaviours and high cetane number [78]. is thermochemical process and the other is biochemical process Hydroprocessed renewable jet fuels are comparatively economical [14]. The other methods used for the production of alternative [23]. The low lubricity of HRJs can be improved by blending with fuels are also discussed below. conventional jet fuel or by the use of additives [52].

4.3. Biochemical process 4.1. Thermochemical process

Biochemical process is the conversion of biomass to carbohy- Thermochemical process is the conversion of biomass to fuel by drates that can be further transformed into alcohol by the method , gasification and upgrading. Pyrolysis is the process of of fermentation using enzymes or micro-organisms [86]. Studies thermal decomposition of biomass in the absence of air, which are going on to decrease the cost of the pretreatment and results in the formation of bio oil and methane with other side hydrolysis process by enzymes, and also trying to develop new products [76]. Gasification involves the treatment of pyrolysis microorganisms to carry out the process. The current processes products with air or steam to produce syn gas, which is a mixture used are: of hydrogen and carbon monoxide. can be upgraded by the FT process Instead gasification and the FT process bio oil can be subjected to hydroprocessing or hydrodeoxygenation which will 4.3.1. Direct sugar to hydrocarbon process (DHSC) and alcohol to jet result in hydrocarbon fuel same as that from the FT process [77]. process (ATJ) The method includes biochemical fermentation or catalytic conversion of from biomass hydrolysis or from direct sugar 4.1.1. Biomass to liquid process (BTL process) sources such as sugar cane to hydrocarbon fuels [87]. The process Biomass to liquid process comprises the conversion of biomass involves hydrolysis of biomass, carbohydrate fermentation, pur- to liquid hydrocarbon fuel. A wide range of feedstock can be ification and hydroprocessing [88]. Direct Sugar to Hydrocarbon subjected to this process, including municipal and agricultural process does not involve the intermediacy of alcohol. The advan- wastes, cellulose, wood, and algae [23]. The process involves the tages of the use of this method are plentifully available cost- fi following steps, namely pretreatment of biomass, gasi cation, effective feedstocks that not directly cause food crisis, sustain- fi syngas puri cation and FT synthesis or pyrolysis followed by ability and fuel with the reduction in greenhouse gas emission up hydroprocessing [78,79]. The method takes the advantages of to 82% [89]. sustainability, reduced greenhouse gas emissions and no food to Alcohol formed by the biochemical or thermochemical fermen- fuel competition [80]. tation of carbohydrates obtained from biomass or thermochemical and thermo biochemical combined conversion of syngas can be 4.1.2. Fischer Tropsch process (FT process) subjected to a series of steps to form hydrocarbon fuels [87]. The The Fischer Tropsch process comprises the catalytic conversion process mainly includes 4 steps-ethanol dehydration, oligomeriza- tion, distillation and hydrogenation [90]. A wide range of the of syngas (CO and H2) which is produced by the gasification of biomass to liquid straight chain hydrocarbon fuels [81]. The range potential feedstock can be used for the process, including starch, of hydrocarbons produced depends on the catalyst, pressure and cellulose, sugar and waste [23]. The method is very economical temperature conditions of the process [82]. Jet fuel produced by since the feedstocks are not much expensive and the process does the FT process from different feedstock exhibits similar properties not need large amounts of energy [20]. Sugar and starch can be and they are characterized by zero sulphur and aromatics [52]. The converted to alcohol by direct fermentation, but in the case of resulted FT fuels show clean burning. FT fuels are now recom- biomass it must be pretreated to get sugar, which is then directly fi mended to use in blending with conventional fuel to meet fermented to alcohol or subjected to gasi cation followed by gas requirement of specific lubricity in the absence of sulphur [81]. fermentation [91]. The method takes the advantage of the production of total negative greenhouse gas fuels [62]. Since the fuel is free of 4.3.2. Bio alcohol production aromatic compounds, it makes some fuel leakage problems in Bio alcohols are produced by thermal and biochemical fermen- the engine due to shrinkage of the engine while blending and it tation of carbohydrates resulted by the hydrolysis of biomass [52]. can be better minimized by the use of additives [8]. Even though a Biomass sources like corns and cellulose are first hydrolysed to wide range of feedstock like waste wood and agricultural residues extract sugars and then fermented followed by distillation to get can be upgraded using the FT process to fuel, the method is quite bio alcohol. Direct sugar sources are subjected to fermentation to expensive [23,68]. produce alcohol [92]. Bioalcohol can be produced from a wide T. Kandaramath Hari et al. / Renewable and Sustainable Energy Reviews 42 (2015) 1234–1244 1239 range of biomass feedstock such as wood, agricultural wastes, but it is not a suitable alternative for aviation fuels. Biodiesel forest residues and wastes [93]. Methanol, Ethanol and butanol possesses low energy density and poor cold flow properties of the have the potential to use as transportation fuels, but they are not fuel causes freezing of fuel in the aircraft engine at higher altitudes suitable to use as aviation fuel alternatives. The low flash point, [52]. Table 1 represents an overview of biojet fuel production low energy density and pure low temperature properties limit its routes, renewable sources and various alternative aviation fuels. use as aviation biofuel [94].

6. Industry commitments and collaborations 5. Other alternative fuels production routes With the increasing need for alternative aviation fuels, there are 5.1. Liquid hydrogen and liquid methane many projects and collaborations developing worldwide. There are many public and private programmes including universities, insti- Bio hydrogen can be generated from a variety of feedstock like tutes, companies and government organizations [102].Allthe municipal and sewage residues, cellulose forest waste materials projects aim to commercialize renewable aviation fuels through and crops [95]. Bio hydrogen can be produced by biomass different ways and from different sources. The important intentions fi gasi cation. At higher temperatures and pressures, biomass is behind the development of renewable aviation fuels are (1) decrease converted to hydrogen with CO and CO2 as side products. From the dependence on non-renewable fossilfuelsources(2)reduce this hydrogen can be separated by membrane method or chemical environmental impacts (3) use of cheaply available feedstocks methods. Hydrogen can also be produced from pyrolysed oil by (4) reduce the fuel cost. The current commitments and collaborations catalytic steam reforming [96]. Another method is the biological in this field are discussed here. route using algae and bacteria [97]. Introduction of liquid hydro- Private sector projects on aviation fuel developments are well gen for aviation decreases the greenhouse gas emissions [98]. emerged in United States, concentrating selection of feedstock, Biomethane is produced by anaerobic digestion or fermentation of conversion routes and scaling up [102]. Commercial Aviation a large number of renewable feedstocks like waste materials, crops Alternative Fuels Initiative (CAAFI) is a confederation of airlines, and biomass [99]. The major problem with the use of liquid gas airports, manufactures, fuel suppliers and government organiza- fi fuels is the requirement of modi cation of aircraft engine which tions Federal Aviation Administration (FAA) in the United States will make fuel system very complex [98]. [103]. IATA, American Society for Testing and Materials (ASTM), Coordinating Research Council (CRC), Department of Conservation 5.2. Transesterification of oils/fats (DOC), Defense Advanced Research Projects Agency (DARPA), Defense Energy Support Center (DESC), International Civil Aviation Transesterification is the process of the catalytic conversion of Organization (ICAO), original equipment manufacturer (OEM) are fats and oils into fatty acids of alkyl esters which are well known some of the members in the group. The association stands for as biodiesel [100]. The method biodiesel production is not much development, certification and verification of renewable jet fuel expensive and since it can be produced from non edible oils, it and to support energy safety, environmental security and aviation does not create a food-fuel crisis [101]. The biodiesel fuel produced capitals [104]. Brazilian Alliance is a collaborative group formed by by this method exhibits , reduced emission of airlines, biomass producers, biofuel researchers and manufac- greenhouse gases, non-toxicity and biodegradability [9]. Biodiesel turers. The purposes are (1) support the sustainable aviation fuel can be used in diesel engines without further engine modification, development (2) decrease the environmental impacts of aviation

Table 1 Overview of biojet fuel production routes, renewable sources and various alternative aviation fuels. 1240 T. Kandaramath Hari et al. / Renewable and Sustainable Energy Reviews 42 (2015) 1234–1244 industry and (3) commercialization and scaling up of bio jet fuels Singapore, Brazil, China, Canada and Australia [102]. Airlines [2]. Defence Energy Support Centre and US Military Services work have signed agreements with fuel producing companies, Alaska in co-operation for the development, commercialization and Airlines with Hawai’i Bio Energy, with Alt Air and certification of alternative jet fuels. They plan to reduce the Avianca Brasil with Byogy for the development of bio jet fuels. Alt dependence on petroleum fuels, exploitation of renewable Air plans for a hydroprocessing plant by 2014 having a capacity of resources and to produce advanced fuel with decreased green- 90 kt/year [109]. house gas emissions. Dynamotive Energy Systems Corporation (DESC) in partnership The US Air Force Research Laboratory is prepared to test the with Tecna SA and IFPen/Axens produces 1 gal of jet fuel at cost fuels produced by FT process and hydroprocessing of jatropha, between $1.82 and $3.25 from biomass by Dynamotive’s fast camelina, algae oils and animal fats [105]. Biojet Corporation (USA) pyrolysis and refining processes through two ways [59]. Imperium is a collaborative project including South Pole Carbon Asset Renewables, Inc. (IRI) with Pacific Northwest National Laboratory Management Ltd. of Zurich, Switzerland, Abundant Biofuels Cor- (PNNL) follow Alcohol to Jet process for the jet fuel production poration of Monterey, California, Mitch Hawkins & Co. Inc., of using waste materials from forests, municipalities and agriculture Santa Ynez, California. Biojet Corporation makes an association [113]. Altair Fuels (US) targets to supply 75 million gal/year of bio with algae developers and also uses jatropha and camelina oils as jet fuels using potential oil crops like Camelina [114]. Solena (US) resources [106]. Energy & Environmental Research Center(EERC), follows Fischer tropsch method for the conversion of agricultural USA with DARPA has industrialised a process called catalytic and municipal wastes to biojet fuels and it also takes the hydrodeoxygenation and isomerization (CHI process). The method advantages of a cleaning technology [115]. Virent (US) in partner- makes use of feedstocks such as camelina oil, algal oil, canola oil, ship with Shell and Cargill uses sugar cane, cone starch and sugar corn, and waste grease for the production of bio jet fuels beet as feedstock for the generation of biojet fuels [116]. They also that are highly compatible with conventional fuels [86]. Global plans to use corn stover, switch grass, wood and bagasse as Seawater Inc., (GSI) established in UK and USA is a project mainly potential feedstocks [117]. Air Force Certification Office (AFCO) is concerned with the production of alternative aviation fuels from a fuel certifying agency which has legalized the use of FT fuel seawater crops like halophytes. The work is primarily based on blends [118]. SkyNRG, Netherlands planned to start flights with Salicornia bigelovii, which is a native plant in Europe, United Thomson airlines, Fin Air and Alaska airlines powered by biojet States, South Asia and South Africa [107]. fuel produced from waste cooking oil [34]. Sapphire Energy aim to Rentech, Inc. is a USA based company concentrated on the produce 300–500 b/d algal aviation biofuel within three years [26]. production of hydrocarbon fuels from biomass sources. The project According to Solazyme Inc.USA, they will produce large amount works on Rentech Process the basic principle of which is FT of oil from microalgae which can be effectively converted to bio jet process and it converts biomass, green waste, municipal and solid fuel [2]. European Aerospace Defence System in 2010 and US Navy wastes to synthetic jet fuels. The hydrocarbon fuel produced by in 2011 tested flight with microalgae bio aviation fuel. European the company can be better blended with conventional fuel to use airlines has invested 2.7 billion euro to achieve 4% development by in military and commercial jet fuel [108]. UOP (USA) is a well- 2020 and IATA plans for 6% development in biofuel production known company in the fields of petroleum refining and proces- [34]. Alternative Fuels and Biofuels for Aircraft Development sing. They have resourcefully synthesized hydroprocessed renew- (ALFA-BIRD) is an assignment financed by European Union. The able jet fuels from various natural sources such as camelina oil, objectives of the projects are (1) production of new aviation bio algal oil, jatropha oil and tallow by the process of deoxygenation, fuels and their analysis, introduction of injection systems and isomerization and cracking [86]. Universal Oil Products, US mainly modelling, testing the compatibility of the newly developed fuel focused on hydrodeoxygenation of free fatty acids for fuel produc- [86]. Syntroleum Corporation produces FT fuels using natural gas tion [68]. Amyris, USA with Total Alternative Aviation Fuel aim to as the feedstock and USAF (US Air Force) tried flight with 50:50 produce renewable hydrocarbon fuels by Direct Sugar to Hydro- blend of the produced fuel with JP-8 [119]. Dynamic Fuels, USA is a carbon (DSHC) process with low greenhouse gas emissions and joint mission of Syntroleum Corporation and Tyson Foods, Inc. better fuel properties. They also plan to gain acceptance from OEM aiming the development of advanced feasible routes for the and to get ASTM and Def Stan authentication [88]. Tecbio, Brazil production of high quality aviation fuels and fuel technologies. tries to upraise their crop Babassu palm for biokerosene produc- Tyson foods supplies animal fats and it is hydroprocessed to clean tion with NASA [68]. The Midwest Aviation Sustainable Biofuels jet fuels. Their project targets to produce 284 million liters of fuel Initiative (MASBI) established in 2012 focused to promote mid- per year [86]. Avantium Chemicals in Netherlands (Europe) has western U.S. energy security. The Canadian company Applied established the method of catalytic conversion of sugar to 5- Research Associates, Inc (ARA) used hydroprocessed vegetable oil hydroxymethylfurfural. It could be used as a component in aviation on business jet flight [109]. fuel with good stability and blending properties [120].NesteOil International Air Transport Association (IATA) is an interna- Corporation is a worldwide Finland (Europe) based marketing tional trade industry. Their aviation plan is based on four main company focused on the production of good value transportation policies (1) development of fuel technology i.e., finding new fuels. They use the biomass to fuel process which is well known as energy sources, production of clean bio jet fuels and engine NExBTL process. The feedstocks used by them are vegetable oils compatibility (2) Aircraft processing with good efficiency (3) Infra- mainly jatropha and algae as well as animal fats [54,121].Swedish structure (4) favourable aviation economy [110]. , a multi- Biofuels AB (Sweden) company also makes efforts for the develop- national American aerospace company that is highly dynamic ment and industrialization of renewable alternative jet fuels. They in the field of development and testing of alternative aviation have secured patents in this field. With LanzaTech they produce jet fuel with Airbus aim to initiate innovative fuel technologies, to fuel mainly from wood, forest residues, agricultural wastes and improve life cycles, to advance international flight operations and grains. The method of synthesis involves production of sugar from reliable fuel distribution [111]. Aliança Brasileira para Biocombus- the biomass feedstock followed by fermentation. The resulted tiveis de Aviação, ABRABA (Brazilian Alliance for Aviation Biofuels), alcohols are then chemically converted into hydrocarbon [122]. Brazil is collaboration project of institutes, industries and govern- Airbus is a European aircraft manufacturing company. They ment for the generation of sustainable biojet fuels [112]. Many focus on the current situation of aviation fuels, development of private companies and organizations are on the road from differ- sustainable biojet fuels, development of technology and certifica- ent countries all over the world mainly U.S, Japan, Qatar, Mexico, tion of Bio SPK. They have also performed test flights with T. Kandaramath Hari et al. / Renewable and Sustainable Energy Reviews 42 (2015) 1234–1244 1241 renewable aviation fuels [123]. GE Aviation a part of General competition are the major obstacles come across. Sustainability Electric Company (GE) US uses bio oil hydroprocessing [68]. is a big obstacle to overcome which depends mainly on the Aviation Initiative for Renewable Energy in Germany (AIREG) work availability of feedstock and the fuel production route that bring for advanced research and development in aviation biofuels and out social, economic and environmental impacts [133]. combining experts in the field to achieve fuels with reduced emissions and sustainability [124]. The Sustainable Aviation Fuel 7.1. Environmental challenges Users Group (SAFUG) based in Europe involving Natural Resources Defence Council and the Roundtable for Sustainable Biofuels (RSB) One of the major issues that should be faced is the social and concentrated on production of advanced aviation fuels from environmental impact of fuel production and management. 2.5% renewable sources with minimum impacts on the environment of man-made carbon dioxide was from aviation sector in 2005 and ecosystems. They also decided to cultivate plants which can and it is expected to become 4–4.7% by 2050 [134]. The uprising fi nancially support undeveloped areas and communities [125]. demand for bio jet fuels creates afforestation issues which will Sustainable Way for Alternative Fuel and Energy in Aviation affect the fertility of soil and biodiversity and will cause increase (SWAFEA) mainly concerns with lifecycle analysis, compatibility of in atmospheric CO2 [72]. Use of agricultural land for crop fl alternative fuel, environmental in uences and fuel economics [12]. cultivation for biofuel production will cause food scarcity and it The Nordic Initiative for Sustainable Aviation, NISA is founded by will reduce soil quality and water availability in the soil. The use Nordic stakeholders for the development of a sustainable aviation of fertilizers and insecticides will result in soil destruction and fl fuel [109]. Lufthansa tested ights with biofuel in 2011 as a part of water pollution [135]. The fuel developed must not arise any burnFAIR research project between Hamburg and Frankfurt [126]. human health issues [136]. Initiative Towards sustainable Kerosene for Aviation, ITAKA is a collaborative initiative that targets to connect feedstock cultiva- 7.2. Production issues tors, biofuel producers, distributors and users in developing a large scale camelina bio jet supply chain [57]. Air France-KLM has set a Cost effectiveness of the process and feedstock flexibility are schedule for the development of next generation biofuels, new major hurdles related to production process [137]. Even though technologies, policies and legislation [127]. there are projects developing on the basis of algae as feedstock, (SA) is marketing company which is now functioning in there are many problems and difficulties related to algae. The Qatar and establishing a new branch in Nigeria. They adopted the selection and production of useful algal species and lipid extrac- Gas to liquid process (GTL) fuels through Fischer Tropsch synthesis tion is a puzzling process [138]. The production of bio jet fuel from for the synthesis and scaling up of hydrocarbon. They have algae needs optimization of the process, production cost, proper- certified the use of 50:50 blend of FT fuel with JET-A for aviation ties and its certification [139]. The suitable catalyst selection and purpose [68]. An Indo-Canadian programme involving Pratt, Uni- right designing of the process are important tasks to be faced by versities of Laval, Ryerson, Queens, Whitney, HPCL, Indian Institute the alternative fuel producers [140]. The production process is of Science Bangalore, IIP, Info Tech, Indian Oil, IIT (K) is signed for feedstock dependent and so varying [141]. Production process renewable fuel production, blending and applications [128]. Chi- must be consistent, competent and highly efficient. nese Academy of Sciences in partnership with Boeing has started Joint Research Laboratory for Sustainable Aviation Biofuels for the production of algal biojet fuels [112]. with Boeing 7.3. Distribution problems produces bio jet fuel from algae, jatropha and camelina oils and uses in aircraft engines with 50:50 blends with Jet-A [129]. Quality of product and suitable blending for effective function- , Australia’s second largest airlines company ing are problematic in the supply process [137]. The costs of HRJ – joined with government and other industries work for the devel- and BTL fuels are now in a range of $0.80 $2.00/L which is 3 times opment of renewable aviation fuel, fuel technologies and com- higher than that for petroleum based jet fuels [12]. Fuel infra- mercialization of alternative aviation fuels for affordable cost structure, fuel marketing, storage of feedstock and fuel, byproducts fi [130]. Sustainable Aviation Fuel Road Map (SAFRM), an enterprise marketing regulations and certi cations are also major tasks to of the SAFUG was launched targeting local supply chain develop- overcome [44]. The current production cost of biojet fuels should ment of bio jet fuels [112]. Queensland Sustainable Aviation Fuel be reduced; otherwise it will not be feasible and the increasing Initiative in Australia focuses on the production and lifecycle prize will affect the production investments [102]. The co- assessment of bio jet fuels from oil crops, sucrose and algae. They ordination of investors and biomass suppliers is also highly plan to develop sugar to bio aviation fuel process by yeast essential [124]. fermentation [131]. The Global Bioenergy Partnership (GBEP), The Roundtable for Sustainable Biofuels (RSB), International Sus- 7.4. Feedstock availability and sustainability tainability and Carbon Certification (ISCC), REDcert, The Renew- able Transportation Fuel Obligation Meta The feedstock which is cost effective that can grow with Standard (RTFO), Sustainable Biodiesel Alliance are the existing minimum water supply and fertilizers, with good yield, without sustainability evaluation programs [132]. affecting the food crops and thereby avoiding food to fuel issues, that possess low greenhouse gas emission and provides econom- ical benefits are largely favoured for the production of aviation 7. Challenges biofuels [20]. The challenges related to feedstock are availability of feedstock in bulk scale with comparatively low cost and restric- Even though the need of alternative aviation biofuels are tions for large scale applications [137]. The major problems exceeding, there are many challenges to overcome and to achieve associated with algae culture are temperature maintenance and the goals. The price gaps between bio and conventional jet fuels, energy requirement [139]. Large amount of fuel must be produced sustainability and financial problems in commercialization are to test in aircrafts and need large amount of feedstock [141]. While major concerns in the development of alternative jet fuels [127]. producing alternative aviation fuels, the feedstocks must be Economic and environmental issues including land-water usage, selected such as to minimize impact on the land use and water greenhouse gas (GHG) and particulate emissions, fuel-food intake [136]. Now the availability of biomass feedstock for the 1242 T. Kandaramath Hari et al. / Renewable and Sustainable Energy Reviews 42 (2015) 1234–1244 production of bio jet fuel is restricted due to competition with the and international organizations can help the scaling up, commer- current fuel requirements [142]. cialisation and supply chain infrastructure to large extent. 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