Enzymatic Digestibility Of Lignocellulosic Biomass Research Articles

Effects of Pulverization Forces on Structural Features and Enzymatic Digestibility of Lignocellulosic Biomass

Effects of Pulverization Forces on Structural Features and Enzymatic Digestibility of Lignocellulosic Biomass

Two‐Step Autohydrolysis Pretreatment: Towards High Selective Full Fractionation of Wheat Straw

AbstractPretreatment is necessary to increase the enzymatic digestibility of lignocellulosic biomass. Here, degradation reactions of solubilized pentoses to furfural and others are undesired regarding the reduced product yield and increasing downstream processing efforts. In this work, the use of the unit operation configuration was successfully shown to reduce degradation reactions. In the used two‐step autohydrolysis pretreatment, the reaction is stopped before degradation takes place. The pentoses are removed by water leaching to make them unavailable for degradation in a second autohydrolysis treatment. The overall sugars yield is increased, and the furfural formation is decreasing while maintaining the high lignin purity using the two‐step autohydrolysis pretreatment.

Investigation of Alkaline Hydrogen Peroxide in Aqueous Organic Solvent to Enhance Enzymatic Hydrolysis of Rice Straw

Alkaline hydrogen peroxide (AHP) pretreatment is a promising process for enhancing enzymatic digestibility of lignocellulosic biomass in biorefineries. In the present work, the effects of organic bases (NH4OH and tri-ethylamine) and co-solvents (ethanol, isopropanol, tert-butyl alcohol, water) on AHP pretreatment efficiency of rice straw were studied and compared to the typical aqueous reaction with NaOH. It was found that the glucose recovery from enzymatic hydrolysis of the biomass pretreated by AHP at 35 °C for 24 h using NH4OH in aqueous/tert-butyl alcohol (73.6%) was higher than that achieved using ethanol and isopropanol (31.6–48.6%) and water (71.2%) under the same experimental conditions. Increasing H2O2 concentration from 1 to 10% v/v in the aqueous/tert-butyl alcohol with NH4OH led to enhancing sugar yield to from 349 to 623 mg/g pretreated rice straw, equivalent to the highest glucose recovery of 83.0%. Formation of highly porous structures in pretreated rice straw by removals of hemicelluloses and lignin was revealed by Fourier transform infrared spectroscopy and scanning electron microscopy while the increased crystallinity index was shown by X-ray diffraction. This modified low-temperature AHP pretreatment using organic solvent system is advantageous on recyclability potential of the reagents and potent for further implementation in lignocellulosic biorefineries.

EFFECT OF COMBINATION OF LIQUID HOT WATER SYSTEM AND HYDROGEN PEROXIDE PRETREATMENT ON ENZYMATIC SACCHARIFICATION OF CORN COB

Alkaline hydrogen peroxide pretreatment is an effectively enhance the increasing enzymatic digestibility of lignocellulosic biomass for conversion to fuels and chemicals in the biorefinery processes. In this study, effects of H2O2 on monomeric sugar in the liquid fraction during hydrogen peroxide pretreatment and sugar after enzymatic hydrolysis from corncobs were studied under varying reaction conditions. The temperature (30-120oC) and H2O2 concentration (2.5-10%) efficiently promoted sugar yield in the piqued fraction and improved enzymatic hydrolysis of pretreated solids. The optimal condition for H2O2 pretreatment of corncob (H2O2 concentration of 5% using 60 oC for 2 h) increased hemicellulose solubilization into the aqueous phase, resulting into the maximized pentose yield of 61.88% (xylose + arabinose) in the aqueous phase. H2O2 pretreatment under the optimal conditions at 60oC for 2 h, leading to the enhance glucose yield from enzymatic hydrolysis of the pretreated biomass using 10 FPU/g CelluclastTM (85.66 %) and small amount of formation of inhibitory by-products. Combined with glucose in the aqueous phase, this resulted in the maxima 95.61% glucose recovery from the native corncob. This was related to changes in crystallinity and surface area of the pretreated biomass. Scanning electron microscopy (SEM) showed disruption of the intact biomass structure resulting increasing enzyme’s accessibility to the cellulose microfibers which showed higher crystallinity index compared to the native biomass as shown by X-ray diffraction with a marked increase in surface area as revealed by BET measurement. The results provided efficiency of H2O2 pretreatment on increasing sugar recovery and an efficient approach for its processing in biorefinery industry.

Effect of Mechanical Refining Energy on the Enzymatic Digestibility of Lignocellulosic Biomass

Mechanical refining of lignocellulosic biomass has emerged as a promising technology for the improvement of enzymatic hydrolysis yields. Further research is necessary to understand the effects of mechanical refining at different conditions to allow for further optimization of the process. In this research, the impact of refining intensity (specific edge load; kWh/m) is investigated by the use of multiple refining passes to reach equivalent total specific refining energy (SRE) using a 12-in. disk refiner. In addition, the effect of adjusting gap-width vs adjusting consistency to increase refining energy is explored. Results show that enzymatic carbohydrate conversion is a function of SRE, independent of refining intensity. At lower enzyme loadings, gap-width adjustments were observed to be most effective at improving enzymatic digestibility. At higher enzyme loadings carbohydrate conversions leveled-off slightly as SRE increased, implying that there may be an economically optimum degree of refining.

Lignocellulosic biomass to biofuels and biochemicals: A comprehensive review with a focus on ethanol organosolv pretreatment technology.

Lignocellulosic biomass is one of the potential feedstocks to produce second-generation cellulosic ethanol and biochemicals. To enhance the enzymatic digestibility of lignocellulosic biomass for efficient enzymatic saccharification, a variety of pretreatment methods have been studied. Among these, organosolv pretreatment using ethanol is a promising pretreatment method owing to its inherent advantages, such as low solvent cost, lack of toxicity, the ability to retain most cellulose fraction in substrates for enzymatic hydrolysis, coproduction of high-purity lignin and hemicellulosic sugars, easy solvent recovery, and reuse. In this review, the research progress regarding different types of ethanol organosolv pretreatment processes has been summarized in terms of methods, substrate properties, reaction mechanisms, delignification kinetic as well as the impact of pretreatment methods on the enzymatic digestibility. Attempts are also made to provide insights into the complete utilization of lignocellulosic biomass to achieve high potential revenues. Though some ethanol organosolv processes have been studied or are being developed towards commercialization, ethanol organosolv pretreatment is still facing some challenges. Finally, the direction for future work is given to develop a proper ethanol organosolv pretreatment for commercialization.

Effects of Liquid Hot Water Pretreatment on Enzymatic Hydrolysis and Physicochemical Changes of Corncobs.

Liquid hot water (LHW) pretreatment is an efficient chemical-free strategy for enhancing enzymatic digestibility of lignocellulosic biomass for conversion to fuels and chemicals in biorefinery. In this study, effects of LHW on removals of hemicelluloses and lignin from corncobs were studied under varying reaction conditions. LHW pretreatment at 160°C for 10min promoted the highest levels of hemicellulose solubilization into the liquid phase, resulting into the maximized pentose yield of 58.8% in the liquid and more than 60% removal of lignin from the solid, with 73.1% glucose recovery from enzymatic hydrolysis of the pretreated biomass using 10FPU/g Celluclast™. This led to the maximal glucose and pentose recoveries of 81.9 and 71.2%, respectively, when combining sugars from the liquid phase from LHW and hydrolysis of the solid. Scanning electron microscopy revealed disruption of the intact biomass structure allowing increasing enzyme's accessibility to the cellulose microfibers which showed higher crystallinity index compared to the native biomass as shown by x-ray diffraction with a marked increase in surface area as revealed by BET measurement. The work provides an insight into effects of LHW on modification of physicochemical properties of corncobs and an efficient approach for its processing in biorefinery industry.

Pilot-scale steam explosion pretreatment with 2-naphthol to overcome high softwood recalcitrance

BackgroundSteam explosion pretreatment has been examined in many studies for enhancing the enzymatic digestibility of lignocellulosic biomass and is currently the most common pretreatment method in commercial biorefineries. It is however not effective for overcoming the extremely high recalcitrance of softwood to biochemical conversion. Recent fundamental research in small-scale liquid hot water pretreatment has shown, though, that the addition of a carbocation scavenger like 2-naphthol can prevent lignin repolymerization and thus enhance the enzymatic digestibility of softwood cellulose. This work studies the technical application potential of this approach in a larger steam explosion pilot plant for surmounting softwood recalcitrance.ResultsThe addition of 35.36 g 2-naphthol to the steam explosion pretreatment of 1.5 kg spruce wood chips allowed to considerably enhance the enzymatic cellulose digestibility. Different ways of adding the solid 2-naphthol to steam pretreatment were tested. Mixing with the biomass before pretreatment could enhance digestibility by up to 55% compared to control experiments. Impregnation of the biomass with 2-naphthol was yet more effective. Acetone and ethanol were tested to dissolve 2-naphthol and impregnate the biomass. The solvents were then removed again by evaporation before the pretreatment. The impregnation allowed to enhance digestibility by up to 179 and 192%, respectively. A comparison to prevalent acid-catalyzed steam explosion pretreatments for softwood revealed that the scavenger approach allows for obtaining exceptionally high yields in enzymatic hydrolysis. The biomass impregnation with 2-naphthol even renders a complete enzymatic cellulose conversion possible, which is remarkable for a softwood pretreatment not removing lignin. Steam pretreatment experiments without explosive decompression revealed that the enhancing effects of the explosion and the scavenger complement each other well. The explosion enhances the accessibility of the cellulose while the use of the scavenger reduces particularly the deactivation of enzymes.ConclusionsThis is the first study to show that a carbocation scavenger in steam pretreatment can enhance the enzymatic digestibility of lignocellulosic biomass. The approach opens up a novel possibility for overcoming the high softwood recalcitrance in a process that does not require an acid catalyst or the removal of lignin from the biomass.

Steam explosion pretreatment of softwood: the effect of the explosive decompression on enzymatic digestibility.

BackgroundSteam explosion pretreatment has been examined in many studies for enhancing the enzymatic digestibility of lignocellulosic biomass and is currently the most common pretreatment method in commercial biorefineries. The information available about the effect of the explosive decompression on the biochemical conversion is, however, very limited, and no studies prove that the latter is actually enhanced by the explosion. Hence, it is of great value to discern between the effect of the explosion on the one hand and the steaming on the other hand, to identify their particular influences on enzymatic digestibility.ResultsThe effect of the explosive decompression in the steam explosion pretreatment of spruce wood chips on their enzymatic cellulose digestibility was studied systematically. The explosion had a high influence on digestibility, improving it by up to 90 % compared to a steam pretreatment without explosion. Two factors were identified to be essentially responsible for the effect of the explosion on enzymatic digestibility: pretreatment severity and pressure difference of the explosion. A higher pretreatment severity can soften up and weaken the lignocellulose structure more, so that the explosion can better break up the biomass and decrease its particle size, which enhances its digestibility. In particular, increasing the pressure difference of the explosion leads to more defibration, a smaller particle size and a better digestibility. Though differences were found in the micro- and nanostructure of exploded and non-exploded biomass, the only influence of the explosion on digestibility was found to be the macroscopic particle size reduction. Steam explosion treatments with a high severity and a high pressure difference of the explosion lead to a comparatively high cellulose digestibility of the—typically very recalcitrant—softwood biomass.ConclusionsThis is the first study to show that explosion can enhance the enzymatic digestibility of lignocellulosic biomass. If the enhancing effect of the explosion is thoroughly exploited, even very recalcitrant biomass like softwood can be made enzymatically digestible.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0567-1) contains supplementary material, which is available to authorized users.

Ethylenediamine pretreatment changes cellulose allomorph and lignin structure of lignocellulose at ambient pressure.

BackgroundPretreatment of lignocellulosic biomass is essential to increase the cellulase accessibility for bioconversion of lignocelluloses by breaking down the biomass recalcitrance. In this work, a novel pretreatment method using ethylenediamine (EDA) was presented as a simple process to achieve high enzymatic digestibility of corn stover (CS) by heating the biomass–EDA mixture with high solid-to-liquid ratio at ambient pressure. The effect of EDA pretreatment on lignocellulose was further studied.ResultsHigh enzymatic digestibility of CS was achieved at broad pretreatment temperature range (40–180 °C) during EDA pretreatment. Herein, X-ray diffractogram analysis indicated that cellulose I changed to cellulose III and amorphous cellulose after EDA pretreatment, and cellulose III content increased along with the decrease of drying temperature and the increase of EDA loading. Lignin degradation was also affected by drying temperature and EDA loading. Images from scanning electron microscope and transmission electron microscope indicated that lignin coalesced and deposited on the biomass surface during EDA pretreatment, which led to the delamination of cell wall. HSQC NMR analysis showed that ester bonds of p-coumarate and ferulate units in lignin were partially ammonolyzed and ether bonds linking the phenolic monomers were broken during pretreatment. In addition, EDA-pretreated CS exhibited good fermentability for simultaneous saccharification and co-fermentation process.ConclusionsEDA pretreatment improves the enzymatic digestibility of lignocellulosic biomass significantly, and the improvement was caused by the transformation of cellulose allomorph, lignin degradation and relocalization in EDA pretreatment.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0359-z) contains supplementary material, which is available to authorized users.

Enhancement of Enzymatic Saccharification of Poplar by Green Liquor Pretreatment

Green liquor (Na2S + Na2CO3, GL) pretreatment is an effective pathway for improving the enzymatic digestibility of lignocellulosic biomass for the production of bioethanol. In this work, GL was employed as a pretreatment to enhance the enzymatic saccharification of poplar. During pretreatment, the increase of H-factor and TTA charge resulted in enhanced delignification and increased degradation of polysaccharides. The sugar yield of enzymatic hydrolysis increased rapidly with increasing TTA charge in GL pretreatment, while the effect of different H-factors (from 400 to 800) on sugar yield was unnoticeable. The pretreated solid recovery was 75.5% at a lignin removal rate of 29.2% under optimized conditions of total titratable alkali (TTA) charge 20%, sulfidity 25%, and H-factor 400. The sugar yield of glucan, xylan, and total sugar of GL-pretreated poplar in enzymatic hydrolysis reached up to 89.9%, 65.5%, and 82.8%, respectively, at a cellulase loading of 40 FPU/g-cellulose.

Biomass recalcitrance. Part I: the chemical compositions and physical structures affecting the enzymatic hydrolysis of lignocellulose

AbstractLignocellulosic biomass is recalcitrant to biodegradation due to the rigid and compact structure of plant cell wall. The recalcitrance of biomass is mainly constructed by its chemical compositions that build a spatial network as a protective bulwark. Generally, the factors affecting the accessibility of biomass cellulose can be divided into direct and indirect factors. The direct factors refer to the accessible surface area, and the indirect factors include biomass structure‐relevant factors (pore size and volume, particle size, and specific surface area), chemical compositions (lignin, hemicelluloses, and acetyl group), and cellulose structure‐relevant factors (cellulose crystallinity and degree of polymerization). Pre‐treatment is actually the process to alter indirect factors and improve direct factors thus enhancing the accessibility of cellulose. In this review, we summarize the effects of chemical compositions and physical structures on the enzymatic digestibility of lignocellulosic biomass. We suggest that future work should be focused on but not limited to the molecular mechanisms of biomass recalcitrance by investigating the microscale and nanoscale features as well as hydrogen bonds network of lignocellulosic biomass. © 2012 Society of Chemical Industry and John Wiley & Sons, Ltd

Oxidative Lime Pretreatment of Dacotah Switchgrass

Oxidative lime pretreatment increases the enzymatic digestibility of lignocellulosic biomass primarily by removing lignin. In this study, recommended pretreatment conditions (reaction temperature, oxygen pressure, lime loading, and time) were determined for Dacotah switchgrass. Glucan and xylan overall hydrolysis yields (72h, 15FPU/g raw glucan) were measured for 105 different reaction conditions involving three different reactor configurations (very short term, short term, and long term). The short-term reactor was the most productive. At the recommended pretreatment condition (120°C, 6.89bar O(2), 240min), it achieved an overall glucan hydrolysis yield of 85.2g glucan hydrolyzed/100g raw glucan and an overall xylan yield of 50.1g xylan hydrolyzed/100g raw xylan. At this condition, glucan oligomers (1.80g glucan recovered/100g glucan in raw biomass) and xylan oligomers (25.20g xylan recovered/100g xylan in raw biomass) were recovered from the pretreatment liquor, which compensate for low pretreatment yields.

Redistribution of xylan in maize cell walls during dilute acid pretreatment

Developing processes for the conversion of biomass for use in transportation fuels production is becoming a critically important economic and engineering challenge. Dilute acid pretreatment is a promising technology for increasing the enzymatic digestibility of lignocellulosic biomass. However, a deeper understanding of the pretreatability of biomass is needed so that the rate of formation and yields of sugars can be increased. Xylan is an important hemicellulosic component of the plant cell wall and acts as a barrier to cellulose, essentially blocking cellulase action. To better understand xylan hydrolysis in corn stover, we have studied changes in the distribution of xylan caused by dilute acid pretreatment using correlative microscopy. A dramatic loss of xylan antibody signal from the center of the cell wall and an increase or retention of xylan at the plasma membrane interface and middle lamella of the cell were observed by confocal laser scanning microscopy (CLSM). We also observed a reduction in xylan fluorescence signal by CLSM that is generally consistent with the decrease in xylan content measured experimentally in the bulk sample, however, the compartmentalization of this xylan retention was not anticipated.