The organosolv process for pretreatment and fractionation of lignocellulosic biomass for fermentation and lignin valorization 6th European Bioethanol Technology Meeting,
Detmold, Germany
Huijgen
W. J. J.; Reith
J. H. & den Uil, H
ECN-L--10-029 MAY 2010
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The Organosolv Process for Pretreatment and Fractionation of Lignocellulosic Biomass for Fermentation and Lignin Valorization
Wouter Huijgen, Hans Reith & Herman den Uil
Contents
Introduction organosolv • Biomass pretreatment for production second generation bioethanol • Organosolv
Organosolv fractionation at ECN • Experimental – Process conditions – Enzymatic cellulose hydrolysis – Lignin isolation & characterisation • Process evaluation
Conclusions
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Lignocellulose Pretreatment
Production second generation bioethanol from lignocellulose: 1. Pretreatment. 2. Enzymatic hydrolysis cellulose to glucose. 3. Fermentation sugars to bioethanol.
Direct enzymatic saccharification of lignocellulose not feasible: • Structural components strongly linked (physically & chemically). • Cellulose protected against decay by lignin. • Cellulose crystalline. • …
Æ Pretreatment required.
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Functions Pretreatment
Æ Pretreatment: overcoming nature’s protection (biomass ‘recalcitrance’).
Enhancement enzymatic digestibility of cellulose to fermentable sugars: • Removing hemicellulose and lignin to improve accessibility for hydrolytic enzymes. • Removing / altering lignin to reduce non- productive cellulase binding. • Reducing crystallinity of cellulose. • Creating specific surface area. • ….
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Pretreatment Processes
Several physical-chemical pretreatment routes under development.
Main pretreatment technologies at pilot/demo-scale: • (Dilute) acid pretreatment • Steam explosion
Routes effective for cellulose.
However: • Lignin ends up in residue (with unconverted sugars, process chemicals, ash, etc). • Residue generally only suitable for CHP.
Alternative: • Separation of lignin prior to enzymatic hydrolysis, while preserving the chemical structure of lignin Æ organosolv.
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Lignin
Lignin: • Polymeric network of aromatic compounds. • Potential feedstock for wide range of chemicals and performance products. • Renewable resource for aromatics!
Lignin (model)
Lignocellulose biorefinery: • No large-scale commercial market for lignin (derivatives) at the moment (in contrast to sugar derivatives). • Valorisation lignin improves carbon footprint & economics lignocellulose biorefinery.
Wood adhesives and resins
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Lignocellulose Biorefinery
Primary biorefinery Secondary biorefinery
Ethanol Fermentation Butanol Propanediol Lactic acid Cellulose Enzymatic hydrolysis Conversion Lignocellulosic Chemical derivatives, & biomass & PretreatmentPretreatment e.g. surfactants Hemi- synthesis && cellulose residual streams fractionationfractionation Platform chemicals, Thermochemical Lignin e.g. phenolics, styrene,… depolymerisation Performance products & conversion Fuel additives Electricity H/P Heat
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Organosolv Process
Solvent recycling
Lignocellulose Lignin Solvent Organic solvent Organosolv Hemicellulose separation separation (derivatives) Water (+ catalyst)
Cellulose (S) Lignin (S) (to enzymatic hydrolysis)
Many different organic solvents applied: • Alcohols (methanol, ethanol, phenol, ethylene glycol…) • Acetone • Organic acids (formic, acetic, …) • 1,4-Dioxane • ….
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History Organosolv
Begin 20th century (analytics): • Use organic solvent to separate wood components for analysis.
1970-90’s (organosolv pulping): • Organosolv as environmental-friendly alternative to Kraft pulping for paper making. • Many different processes up to pilot-scale: – Alcell, ethanol-water pulping of wood (Canada). – Organocell, soda pulping with methanol (Germany). – ASAM, alkaline sulphite-anthraquinone-methanol (Germany). – Acetosolv, acetic acid based cooking (Germany). – Milox, formic acid and peroxyformic acid (Finland). –…. • Extensive overview provided by E. Muurinen (2000), Organosolv pulping, PhD thesis, Oulu university, Finland.
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Organosolv Biorefinery Processes
Shift to organosolv as: • Pre-treatment for second generation bioethanol. • Primary biorefinery process.
Current developments: • Organosolv biorefinery processes on pilot-scale. • Lignol (Canada), solvent = ethanol, feedstock = hardwood + softwood. • Chempolis (Finland), solvent = formic acid, feedstock = non-wood lignocellulose. • CIMV (France), solvent = mixture of formic & acetic acid, feedstock = wheat straw. • …. • Many alternative routes under development at lab-scale.
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Contents √ Introduction on organosolv
Organosolv fractionation at ECN • Experimental – Process conditions – Enzymatic cellulose hydrolysis – Lignin isolation & characterisation • Process evaluation
Conclusions
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Process Parameters
Parametric studies performed: • Solvents: ethanol & acetone. • Various lignocellulose feedstocks incl cereal straw. Freshstraw wheat Studied variables: • Particle size • Solvent mixture : solid ratio • Solvent-water ratio • Pretreatment severity: – Temperature –Reaction time
– Acid catalysts such as H2SO4 After organosolv • Stirring rate
Æ Example: acetone-based organosolv on wheat straw (without catalyst).
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Experimental Set-up Organosolv Fractionation
Milling Analysis composition
Washing Enzymatic hydrolysis Lignocellulose Solid residue Analysis sugars Solvent / H O Filtration (monomeric + 2 oligomeric) Filtrate Analysis other Optional: compounds catalyst Volume: 0.5 / 2 ltr Lignin separation & Stirring analysis Temperature ↑ T reactor T jacket p p T
0 t t
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Acetone-Water Mixture
Fractionation: 100 • Organosolv fractionation effective. 80 • Cellulose recovery >90%. 60 Cellulose Hemicellulose Acetone:water ratio: 40 Lignin • Strong influence on hemicellulose hydrolysis & 20
delignification. Recovered in solid fraction (%) • Optimisation dependent on 0 product revenues. 0:100 25:75 40:60 50:50 60:40 Acetone-water (% w/w)
Huijgen et al. (2010), Pretreatment and fractionation of wheat straw by an acetone-based organosolv process, submitted.
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Pretreatment Severity
Fractionation improves with pretreatment severity (temperature & time).
100
Maximum severity limited by: 80 • Decrease cellulose recovery. 60 Cellulose • Degradation reactions Æ Hemicellulose product loss & inhibiting effect 40 Lignin on fermentation. 20 Recovered in solid fraction (%) fraction Recovered solid in
0 160 175 190 205 220 Temperature (ºC)
Huijgen et al. (2010), Pretreatment and fractionation of wheat straw by an acetone-based organosolv process, submitted.
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Enzymatic Cellulose Hydrolysis
Organosolv effective pretreatment process: • Strong enhancement enzymatic cellulose hydrolysis (>10x). • Enzymatic digestibility at optimised conditions Æ ~90%.
20 220 100 205 16 80
190 12 60
8 40 175 [Glucose] (g/L) [Glucose] 4 160 20 Enzymatic(%) digestibility Fresh 0 0 0244872 Fresh 160 175 190 205 220 Enzymatic hydrolysis time (h) Temperature (°C)
Huijgen et al. (2010), Pretreatment and fractionation of wheat straw by an acetone-based organosolv process, submitted.
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Feedstocks Fresh Pretreated
Effectiveness organosolv dependent on type of lignocellulosic biomass: Straw • Organosolv less effective for softwoods and (more dense) hardwoods. • More severe pretreatment conditions or use of catalyst required. • Organosolv especially suitable for straws. Willow
Biomass Xylan hydrolysis Delignification Enzymatic digestibility (%) (%) (% cellulose feedstock) Barley straw 80 57 92 Wheat straw 76 59 88 200 °C Willow 50 64 71 EtOH-H O 60:40% w/w Olive tree 44 50 53 2 Poplar 28 39 Spruce 33
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Lignin Isolation & Characterisation
Lignin isolation:
• Insoluble in H2O, soluble in ethanol & acetone. • Precipitation lignin from organosolv liquor. • Lignin isolation efficiency >90%. 160, 180, 200, 220 °C
Lignin appearance:
• Light brown to black (compacted) powder. 100 Ethanol Acetone • Colour and structure dependent on process conditions 80 Dioxane organosolv, biomass type and contaminants. 60
40 Lignin purity: • High purity (>90 wt%, up to 96% for wheat straw 20 Part [%] lignin dissolved derived lignin without additional processing). 0 -20406080100
• Main contaminant oligomeric xylose (hemicellulose). Solvent composition [wt% organic solvent] • Lignin sulphur and ash free (max 0.1 wt% S).
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Lignin Characterisation - II
Molecular weight: • Low mean molecular weight (2000-3500) compared to other types of lignins. • Relatively narrow distribution.
31P-NMR: • Identification of functional groups. • SGH type lignins in different ratios depending on feedstock.
Æ Organosolv lignin promising properties for valorisation (relative to other types of lignin).
Organosolv lignin
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Simulation Organosolv Process
Process design in ASPEN: • Determination of streams and energy consumption. C5 sugars • Feedstock: wheat straw. • Process: 200 °C, 60 min,
EtOH:H2O 60:40, 5 L/kg straw. • Preliminary results.
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Recycling Ethanol
Importance recycling: • 1 ton wheat straw Æ 0.32 ton EtOH (maximum). • Solvent: 2.7 ton EtOH/ton straw. • Recycling degree 99% Æ 8% EtOH production loss!
Simulations: • Recycling degree ethanol set at 99.9%. • Separation and recycling of ethanol present in moisture cellulose and lignin required!
Benefits using ethanol as solvent: • Solvent = product! • Ethanol in cellulose and hemicellulose streams not directly lost. • Recycling required to avoid product inhibition during fermentation. • Recycling degree might be slightly lowered to save costs.
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Energy Consumption
Major energy consumers: • Ethanol separation for 83 recycling. 78-102 • Large differences in process temperatures Æ heating. 200
41 Heat flows significant compared to energy content ethanol produced. 50 32
Æ Next step: • Improved process lay-out including direct recycling of liquor. Temperatures (°C)
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Recycling Organosolv Liquor
Wheat straw pulping in ethanol. 100 100
pH decrease due to recycling acetic 80 80 acid.
60 60 Benefits recycling: • Improvement hemicellulose 40 40 hydrolysis.
• Substantial increase enzymatic (%) yield Glucose 20 20 hydrolysis. Recovery in solid fraction (%) fraction solid Recovery in
On the other hand: 0 0 IIIIII • Increase degradation Recycling step hemicellulose sugars. • Slight decrease cellulose recovery. Cellulose Hemicellulose Lignin Enzymatic digestibility
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Conclusions
Conclusions: • Organosolv able to fractionate lignocellulose. • Enzymatic hydrolysis cellulose improved substantially (up to ~90% for wheat straw). • Organosolv particularly effective for straw. • Successful isolation of lignin with high purity (>90%). • Lignin promising properties for production of chemicals and performance products. • Recycling organic solvent crucial process element.
Future plans: • Development continuous organosolv reactor. • Lignin conversion tests. • Solvent integrity and recycling. • Investment and operating costs.
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Thank you for your attention!
More information: [email protected]
This work has been performed with subsidy of the Dutch ministry of Economic Affairs and the European Commission in the context of the projects (2007-2010):
Agentschap NL EOS-LT
http://www.biosynergy.eu/ http://www.lignovalue.nl/
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