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Biochemical conversion of biomass to biofuels: pretreatment–detoxification–hydrolysis–fermentation
Umeå University, Faculty of Science and Technology, Department of Chemistry. Chalmers University of Technology.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The use of lignocellulosic materials to replace fossil resources for the industrial production of fuels, chemicals, and materials is increasing. The carbohydrate composition of lignocellulose (i.e. cellulose and hemicellulose) is an abundant source of sugars. However, due to the feedstock recalcitrance, rigid and compact structure of plant cell walls, access to polysaccharides is hindered and release of fermentable sugars has become a bottle-neck. Thus, to overcome the recalcitrant barriers, thermochemical pretreatment with an acid catalyst is usually employed for the physical or chemical disruption of plant cell wall. After pretreatment, enzymatic hydrolysis is the preferred option to produce sugars that can be further converted into liquid fuels (e.g. ethanol) via fermentation by microbial biocatalysts. However, during acid pretreatment, several inhibitory compounds namely furfural, 5-hydroxymethyl furfural, phenols, and aliphatic acids are released from the lignocellulose components. The presence of these compounds can greatly effect both enzymatic hydrolysis and microbial fermentation. For instance, when Avicel cellulose and acid treated spruce wood hydrolysate were mixed, 63% decrease in the enzymatic hydrolysis efficiency was observed compared to when Avicel was hydrolyzed in aqueous citrate buffer. In addition, the acid hydrolysates were essentially non-fermentable. Therefore, the associated problems of lignocellulose conversion can be addressed either by using feedstocks that are less recalcitrant or by developing efficient pretreatment techniques that do not cause formation of inhibitory byproducts and simultaneously give high sugar yields. A variety of lignocellulose materials including woody substrates (spruce, pine, and birch), agricultural residues (sugarcane bagasse and reed canary grass), bark (pine bark), and transgenic aspens were evaluated for their saccharification potential. Apparently, woody substrates were more recalcitrant than the rest of the species and bark was essentially amorphous. However, the saccharification efficiency of these substrates varied based on the pretreatment method used. For instance, untreated reed canary grass was more recalcitrant than woody materials whereas the acid treated reed canary grass gave a higher sugar yield (64%) than the woody substrates (max 34%). Genetic modification of plants was beneficial, since under similar pretreatment and enzymatic hydrolysis conditions, up to 28% higher sugar production was achieved from the transgenic plants compare to the wild type. As an alternative to the commonly used acid catalysed pretreatments (prior to enzymatic hydrolysis) lignocellulose materials were treated with four ionic liquid solvents (ILs): two switchable ILs (SILs) -SO2DBUMEASIL and CO2DBUMEASIL, and two other ILs [Amim][HCO2] and [AMMorp][OAc]. viii After enzymatic hydrolysis of IL treated substrates, a maximum amount of glucan to glucose conversion of between 75% and 97% and a maximum total sugar yields of between 71% and 94% were obtained. When using acid pretreatment these values varied between 13-77% for glucan to glucose conversion and 26-83% for total sugar yield. For woody substrates, the hemicellulose recovery (max 92%) was higher for the IL treated substrates than compared to acid treated samples. However, in case of reed canary grass and pine bark the hemicellulose recovery (90% and 88%, respectively) was significantly higher for the acid treated substrates than the IL treated samples. To overcome the inhibitory problems associated with the lignocellulose hydrolysates, three chemical conditioning methods were used 1. detoxification with ferrous sulfate (FeSO4) and hydrogen peroxide (H2O2) 2. application of reducing agents (sulfite, dithionite, or dithiothreitol) and 3. treatment with alkali: Ca(OH)2, NaOH, and NH4OH. The concentrations of inhibitory compounds were significantly lower after treatments with FeSO4 and H2O2 or alkali. Using reducing agents did not cause any decrease in the concentration of inhibitors, but detoxification of spruce acid hydrolysates resulted in up to 54% improvement of the hydrolysis efficiency (in terms of sugar release) compared to untreated samples. On the other hand, application of detoxification procedures to the aqueous buffer resulted in up to 39% decrease in hydrolysis efficiency, thus confirming that the positive effect of detoxification was due to the chemical alteration of inhibitory compounds. In addition, the fermentability of detoxified hydrolysates were investigated using the yeast Saccharomyces cerevisiae. The detoxified hydrolysates were readily fermented to ethanol yielding a maximum ethanol concentration of 8.3 g/l while the undetoxified hydrolysates were basically non-fermentable.

Place, publisher, year, edition, pages
Umeå: Umeå universitet , 2015. , 90 p.
Keyword [en]
Lignocellulosic materials, Ionic liquids, Pretreatment, Inhibitors, Detoxification, Ferrous sulfate and hydrogen peroxide, reducing agents, alkaline treatments, Hydrolysis, Fermentation, Biofuels
National Category
Environmental Biotechnology
Research subject
Biochemistry
Identifiers
URN: urn:nbn:se:umu:diva-102722ISBN: 978-91-7601-268-0 (print)OAI: oai:DiVA.org:umu-102722DiVA: diva2:809239
Public defence
2015-05-28, KB, Chalmers University of Technology, Göteborg, 13:30 (English)
Opponent
Supervisors
Available from: 2015-05-07 Created: 2015-04-30 Last updated: 2015-06-01Bibliographically approved
List of papers
1. Enzymatic hydrolysis of Norway spruce and sugarcane bagasse after treatment with 1-allyl-3-methylimidazolium formate
Open this publication in new window or tab >>Enzymatic hydrolysis of Norway spruce and sugarcane bagasse after treatment with 1-allyl-3-methylimidazolium formate
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2013 (English)In: Journal of chemical technology and biotechnology (1986), ISSN 0268-2575, E-ISSN 1097-4660, Vol. 88, no 12, 2209-2215 p.Article in journal (Refereed) Published
Abstract [en]

BACKGROUND Enzymatic hydrolysis of cellulose in lignocellulosic materials suffers from slow reaction rates due to limited access to enzyme adsorption sites and to the high crystallinity of the cellulose. In this study, an attempt was made to facilitate enzymatic hydrolysis by pretreatment of cellulosic materials using the ionic liquid (IL) 1-allyl-3-methylimidazolium formate ([Amim][HCO2]) under mild reaction conditions. The effect of the IL was compared with that of thermochemical pretreatment under acidic conditions.

RESULTS The lignocellulosic substrates investigated were native and thermochemically pretreated Norway spruce and sugarcane bagasse. Microcrystalline cellulose (Avicel) was included for comparison. The IL treatments were performed in the temperature range 45–120 °C and, after regeneration and washing of the cellulosic substrates, enzymatic saccharification was carried out at 45 °C for 72 h. After 12 h of hydrolysis, the glucose yields from regenerated native spruce and sugarcane bagasse were up to nine times higher than for the corresponding untreated substrates. The results also show positive effects of pretreatment using [Amim][HCO2] on the hydrolysis of xylan and mannan.

Conclusion The present work demonstrates that both native wood and agricultural residues are readily soluble in [Amim][HCO2] under gentle conditions, and that pretreatment with ionic liquids such as [Amim][HCO2] warrants further attention as a potential alternative to conventional pretreatment techniques. © 2013 Society of Chemical Industry

Place, publisher, year, edition, pages
Wiley-Blackwell, 2013
Keyword
ionic liquid; 1-allyl-3-methylimidazolium formate; lignocellulose; pretreatment; enzymatic hydrolysis
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-79641 (URN)10.1002/jctb.4089 (DOI)000326462900012 ()
Funder
Swedish Research Council Formas
Available from: 2013-08-27 Created: 2013-08-27 Last updated: 2017-12-06Bibliographically approved
2. Coupled Enzymatic Hydrolysis and Ethanol Fermentation: Ionic Liquid Pretreatment for Enhanced Yields
Open this publication in new window or tab >>Coupled Enzymatic Hydrolysis and Ethanol Fermentation: Ionic Liquid Pretreatment for Enhanced Yields
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2015 (English)In: Biotechnology for Biofuels, ISSN 1754-6834, E-ISSN 1754-6834, Vol. 8, 135Article in journal (Refereed) Published
Abstract [en]

Background

Pretreatment is a vital step upon biochemical conversion of lignocellulose materials into biofuels. An acid catalyzed thermochemical treatment is the most commonly employed method for this purpose. Alternatively, ionic liquids (ILs), a class of neoteric solvents, provide unique opportunities as solvents for the pretreatment of a wide range of lignocellulose materials. In the present study, four ionic liquid solvents (ILs), two switchable ILs (SILs) DBU–MEA–SO 2 and DBU–MEA–CO 2 , as well as two ‘classical’ ILs [Amim][HCO 2 ] and [AMMorp][OAc], were applied in the pretreatment of five different lignocellulosic materials: Spruce (Picea abies) wood, Pine (Pinus sylvestris) stem wood, Birch (Betula pendula) wood, Reed canary grass (RCG, Phalaris arundinacea), and Pine bark. Pure cellulosic substrate, Avicel, was also included in the study. The investigations were carried out in comparison to acid pretreatments. The efficiency of different pretreatments was then evaluated in terms of sugar release and ethanol fermentation.

Results

Excellent glucan-to-glucose conversion levels (between 75 and 97 %, depending on the biomass and pretreatment process applied) were obtained after the enzymatic hydrolysis of IL-treated substrates. This corresponded between 13 and 77 % for the combined acid treatment and enzymatic hydrolysis. With the exception of 77 % for pine bark, the glucan conversions for the non-treated lignocelluloses were much lower. Upon enzymatic hydrolysis of IL-treated lignocelluloses, a maximum of 92 % hemicelluloses were also released. As expected, the ethanol production upon fermentation of hydrolysates reflected their sugar concentrations, respectively.

Conclusions

Utilization of various ILs as pretreatment solvents for different lignocelluloses was explored. SIL DBU–MEA–SO 2 was found to be superior solvent for the pretreatment of lignocelluloses, especially in case of softwood substrates (i.e., spruce and pine). In case of birch and RCG, the hydrolysis efficiency of the SIL DBU–MEA–CO 2 was similar or even better than that of DBU–MEA–SO 2 . Further, the IL [AMMorp][OAc] was found as comparably efficient as DBU–MEA–CO 2. Pine bark was highly amorphous and none of the pretreatments applied resulted in clear benefits to improve the product yields.

Keyword
Lignocellulose, (Switchable) Ionic liquids, Pretreatment, Hydrolysis, Fermentation, Ethanol, Bio-fuels
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:umu:diva-102761 (URN)10.1186/s13068-015-0310-3 (DOI)000361713900001 ()
Note

Originally included in thesis in manuscript form.

Available from: 2015-05-04 Created: 2015-05-04 Last updated: 2017-12-04Bibliographically approved
3. Detoxification of acid pretreated spruce hydrolysates with ferrous sulfate and hydrogen peroxide improves enzymatic hydrolysis and fermentation
Open this publication in new window or tab >>Detoxification of acid pretreated spruce hydrolysates with ferrous sulfate and hydrogen peroxide improves enzymatic hydrolysis and fermentation
2014 (English)In: Bioresource Technology, ISSN 0960-8524, E-ISSN 1873-2976, Vol. 166, 559-565 p.Article in journal (Refereed) Published
Abstract [en]

The aim of the present work was to investigate whether a detoxification method already in use during waste water treatment could be functional also for ethanol production based on lignocellulosic substrates. Chemical conditioning of spruce hydrolysate with hydrogen peroxide (H2O2) and ferrous sulfate (FeSO4) was shown to be an efficient strategy to remove significant amounts of inhibitory compounds and, simultaneously, to enhance the enzymatic hydrolysis and fermentability of the substrates. Without treatment, the hydrolysates were hardly fermentable with maximum ethanol concentration below 0.4 g/l. In contrast, treatment by 2.5 mM FeSO4 and 150 mM H2O2 yielded a maximum ethanol concentration of 8.3 g/l.

Keyword
Lignocellulose hydrolysate, Detoxification, Enzymatic hydrolysis, Fermentation, Fenton’s reaction
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-91458 (URN)10.1016/j.biortech.2014.05.096 (DOI)000338711100072 ()
Available from: 2014-08-05 Created: 2014-08-05 Last updated: 2017-12-05Bibliographically approved
4. Reducing agents improve enzymatic hydrolysis of cellulosic substrates in the presence of pretreatment liquid
Open this publication in new window or tab >>Reducing agents improve enzymatic hydrolysis of cellulosic substrates in the presence of pretreatment liquid
2011 (English)In: Journal of Biotechnology, ISSN 0168-1656, E-ISSN 1873-4863, Vol. 155, no 2, 244-250 p.Article in journal (Refereed) Published
Abstract [en]

Enzymatic hydrolysis of pretreated lignocellulosic substrates has emerged as an interesting option to produce sugars that can be converted to liquid biofuels and other commodities using microbial biocatalysts. Lignocellulosic substrates are pretreated to make them more accessible to cellulolytic enzymes, but the pretreatment liquid partially inhibits subsequent enzymatic hydrolysis. The presence of pretreatment liquid from Norway spruce resulted in a 63% decrease in the enzymatic saccharification of Avicel compared to when the reaction was performed in a buffered aqueous solution. The addition of 15mM of a reducing agent (hydrogen sulfite, dithionite, or dithiothreitol) to reaction mixtures with the pretreatment liquid resulted in up to 54% improvement of the saccharification efficiency. When the reducing agents were added to reaction mixtures without pretreatment liquid, there was a 13-39% decrease in saccharification efficiency. In the presence of pretreatment liquid, the addition of 15mM dithionite to Avicel, α-cellulose or filter cake of pretreated spruce wood resulted in improvements between 25 and 33%. Positive effects (6-17%) of reducing agents were also observed in experiments with carboxymethyl cellulose and 2-hydroxyethyl cellulose. The approach to add reducing agents appears useful for facilitating the utilization of enzymes to convert cellulosic substrates in industrial processes.

Place, publisher, year, edition, pages
Elsevier, 2011
Keyword
Saccharification, Enzymatic hydrolysis, Cellulase; Cellulose, Reducing agents
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-45838 (URN)10.1016/j.jbiotec.2011.06.026 (DOI)000293777800016 ()21740934 (PubMedID)
Available from: 2011-08-17 Created: 2011-08-17 Last updated: 2017-12-08Bibliographically approved
5. Methods for improvement of enzymatic hydrolysis of lignocellulosic material
Open this publication in new window or tab >>Methods for improvement of enzymatic hydrolysis of lignocellulosic material
2013 (English)Patent (Other (popular science, discussion, etc.))
Abstract [en]

The present invention relates to a method of enzymatic hydrolysis of a lignocellulosic material, comprising the steps of: a) pretreating the lignocellulosic material to obtain a slurry having a pH of less than 6; b) adding NaOH, Ca(OH)2 and/or CaO to the slurry to increase its pH to at least 8, said addition being carried out at a slurry temperature of at least 60 °C; c) reducing the pH of the slurry to below 7; and optionally cooling the slurry from step b) to a temperature below 60 °C; and d) adding hydrolytic enzymes to the slurry from c) and allowing the slurry to hydrolyze wherein no washing of the slurry is performed prior to step d)

National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:umu:diva-102752 (URN)
Patent
WO 2013/000696 A1 (2013-01-03)
Note

WO 2013/000696 A1, PCT/EP2012/061021

Available from: 2015-05-04 Created: 2015-05-04 Last updated: 2015-05-05

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