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Two distinct pretreatment technologies, autohydrolysis and AFEX, have been applied to coastal Bermuda grass (CBG) followed by enzymatic hydrolysis in order to compare the effects of pretreatment on the subsequent sugar generation. Furthermore, the influence of structural features from each pretreatment on biomass digestibility was characterized with SEM, ATR-FTIR, and XRD. Enzymatic conversion of pretreated solids from the pretreatments increased with elevated temperature and longer residence times. AFEX pretreatment at 100 degrees C for 30 min produced a sugar yield of 94.8% of theoretical possible with 30 FPU/g enzymatic loading, the maximum achieved with AFEX. It was also shown that with autohydrolysis at 170 degrees C for 60 min that 55.4% sugar yield of the theoretical possible was produced with a 30 FPU/g enzymatic loading, the maximum with autohydrolysis. AFEX pretreatment does not change the chemical composition of CBG but autohydrolysis reduces hemicellulose content in the pretreated solids. Both pretreatments cause re-localization of lignin components. There was no observed correlation between crystallinity and enzyme digestibility of the pretreated solids. AFEX pretreatment developed more enzymatic accessibility to pretreated solids of CBG than did autohydrolysis pretreatment, leading to more sugar generation through the whole process. The total amount of sugars accounted for with autohydrolysis decreases with increasing temperature, consistent with increased byproduct generation via thermal degradation reactions., (Published by Elsevier Ltd.)

Phenolation can effectively improve the reactivity of lignin by directly increasing the phenolic hydroxyl groups and reactive sites for adhesive applications. Wheat straw residue isolated from an autohydrolysis/refining/enzymatic hydrolysis process was phenolated to improve the reactivity of lignin. The optimum phenolation conditions were determined to be a lignin/phenol (L/P) ratio of 1/3 with a 10% acid charge at 120 °C for 2 hours. Phenolated lignin resulted in 32 wt% of phenol incorporated onto lignin and a significant decrease in molecular weight. A comprehensive characterization indicated that all lignin substructures (β-O-4′, β-5′/α-O-4′, β-β′, ferulate, p-coumarate and p-benzoate) were reacted along with a hydrolysis of over 50% of polysaccharides during phenolation, resulting in a decrease in aliphatic hydroxyl groups and an increase in the phenolic hydroxyl groups. Phenol was incorporated onto both the sidechains and aromatic nuclei. These improvements in lignin reactivity will enable it to be used in adhesives with higher substitution rates. [ABSTRACT FROM AUTHOR]

Mechanical refining has potential application for overcoming lignocellulosic biomass recalcitrance to enzyme hydrolysis and improving biomass digestibility. This study highlighted the ability for a pilot scale disc refiner to improve the total carbohydrate conversion to sugars from 39% (unrefined hardwood sodium carbonate biomass) to 90% (0.13 mm gap, 20% consistency, ambient temperature) by optimizing the refining variables. The different biomass properties that changed with refining indicated the expected increase in sugar conversion. Controlling the refining parameters to narrower gaps and higher consistencies increased the resulting refined biomass hydrolysis. Positive correlations that increases in net specific energy (NSE) input and refining intensity (SEL) improved the enzymatic hydrolysis. In some severe cases, over-refining occurred when smaller gaps, higher consistencies, and more energy input reached a point of diminished return. The energy input in these scenarios, however, was much greater than realistically feasible for industrial application. Although well-established in the pulp and paper industry, gaps in understanding the fundamentals of refining remain. The observations and results herein provide the justification and opportunity for further mechanical refining optimization to maximize and adapt the mechanical refining technology for maximum efficiency within the process of biochemical conversion to sugar. [ABSTRACT FROM AUTHOR]

A two-step hydrolysis method was evaluated as a potential means of obtaining high yields of furfural and levulinic acid from corn stover using sulfuric acid as catalyst in a water/gamma-valerolactone (GVL) system. The corn stover underwent a high-temperature hydrolysis process to produce levulinic acid, followed by a low-temperature hydrolysis process to produce furfural. A series of experiments were conducted to explore the relationship between the different reaction parameters and the final yields of furfural and levulinic acid. Scanning electron microscopy (SEM) pictures together with X-ray diffraction (XRD) analysis were used to further elaborate on the hydrolysis results. Molar yields of about 70.65% furfural and 57.7% levulinic acid were obtained by applying this method with a low temperature of 140 °C and a high temperature of 190 °C, together with 0.2 M of sulfuric acid used as the catalyst. These results indicated that this was an effective way to obtain satisfactory yields of furfural and levulinic acid from corn stover. [ABSTRACT FROM AUTHOR]

Recovered papers are suitable biomass sources for conversion into sugars that can be used in bioethanol production. However, paper materials with a high lignin content have been found to be recalcitrant to enzymatic hydrolysis. To address this issue, several biomass pretreatment methods were employed to evaluate their efficiency on the conversion of newspaper with high lignin content to sugar. Autohydrolysis, a hot water treatment, was identified to adversely affect sugar conversion, presumably as a result of pore collapse under high-temperature pretreatment. Flexo ink, used in newspaper printing, had no effect on the enzymatic hydrolysis, with or without autohydrolysis. The ink was still detachable after autohydrolysis, as measured by hyperwashing. Compared to untreated newspaper, separate treatments of either mechanical refining or a non-ionic surfactant (sorbitan polyoxyethylene monooleate) improved the sugar conversion by 10% at enzyme dosages of 2 and 8 FPU/g substrate. The combination of both refining and surfactant resulted in the highest sugar conversions, i.e., 46.3%, 56.7%, and 64.1% at 2, 4, and 8 FPU/g enzyme dosages, respectively. Oxidative pretreatment (oxygen, 100 °C) marginally increased the sugar conversion, whereas alkaline and green liquor (NaCO3 and Na2S) pretreatments (at 160 °C) had either no effect or decreased the sugar conversion. Based on the results of the pretreatments, higher pretreatment temperatures of newsprint negatively impacted subsequent enzyme hydrolysis. [ABSTRACT FROM AUTHOR]

Kraft pulping is one possible pretreatment for softwood to economically produce bioethanol. This work evaluates the techno-economic potential of using the kraft process for producing bioethanol from softwoods in a repurposed or co-located kraft mill. Pretreated loblolly pine was enzymatically hydrolyzed at low enzyme dosages of 5 and 10 FPU/g of substrate. Pretreated residue with 13% lignin content had the highest sugar recovery, 32.7% and 47.7% at 5 and 10 FPU/g, respectively. The pretreated residues were oxygen delignified and refined. In all cases, oxygen delignification improved sugar recovery, while refining was mostly effective for pulps with high lignin content. At 5 FPU/g, the sugar recovery for all kraft pulps was 51 to 53% with oxygen delignification and refining. Increasing the enzyme dosage to 10 FPU/g increased the sugar recovery for these pulps to greater than 60%. Economic analysis for the pulps with different initial lignin content showed that kraft pulps with an initial lignin content of 6.7% with oxygen delignification had an ethanol yield of 285 L/ODt wood and the lowest total production cost of $0.55/L. Pulps with initial lignin content of 18.6% had a total production cost of $0.64/L with an ethanol yield of 264 L/ODt wood. [ABSTRACT FROM AUTHOR]

Dilute sulfuric acid pre-treatment followed by enzymatic hydrolysis and fermentation is a technology widely studied as a potential pathway for conversion of lignocellulosic biomass to ethanol. Six feedstocks were evaluated in process and financial simulations. The woody feedstocks include natural hardwood, Eucalyptus, and loblolly pine while the non-woody feedstocks include corn stover, switchgrass, and sweet sorghum. Based on experimental and literature data, ethanol yields for the non-woody biomasses range from 315 to 328 liters per bone dry metric ton (L/BDt). Sweet sorghum that is pressed and washed to remove soluble sugars prior to dilute acid processing can have an ethanol yield of approximately 470 L/BDt. Natural hardwood and Eucalyptus produce ethanol yields of 336 and 309 L/BDt, respectively. When processing 700 000 bone dry metric tons per year, the non-woody biomasses have lower minimum ethanol revenues to achieve a 12% internal rate of return (MER@12%) than the woody biomasses. The non-wood MER@12% ranged from $0.70 to $080/liter while the MER@12% for natural hardwood and Eucalyptus was $0.84-$0.85/liter. The impact of feedstock composition variability on the net present value at 12% (NPV@12%) discount was estimated for corn stover, switchgrass, and loblolly pine. One standard deviation in the sample carbohydrate content for corn stover, switchgrass, and loblolly pine will impact the NPV@12% by approximately $40 M, $72 M, and $24 M, respectively. If recent historical cost and revenue variability continues for the life of the project the most attractive feedstock is squeezed sweet sorghum where the probability of achieving at least a 12% internal rate of return is 64%. [ABSTRACT FROM AUTHOR]

The impact of lignin-derived inhibition on enzymatic hydrolysis is investigated by using lignins isolated from untreated woods and pretreated wood pulps. A new method, biomass reconstruction, for which isolated lignins are precipitated onto bleached pulps to mimic lignocellulosic biomass, is introduced, for the first time, to decouple the lignin distribution issue from lignin chemistry. Isolated lignins are physically mixed and reconstructed with bleached pulps. Lignins obtained from pretreated woods adsorb two to six times more cellulase than lignins obtained from untreated woods. The higher adsorption of enzymes on lignin correlates with decreased carbohydrate conversion in enzymatic hydrolysis. In addition, the reconstructed softwood substrate has a lower carbohydrate conversion than the reconstructed hardwood substrate. The degree of condensation of lignin increases significantly after pretreatment, especially with softwood lignins. In this study, the degree of condensation of lignin (0.02 to 0.64) and total OH groups in lignin (1.7 to 1.1) have a critical impact on cellulase adsorption (9 to 70 %) and enzymatic hydrolysis (83.2 to 58.2 %); this may provide insights into the more recalcitrant nature of softwood substrates. [ABSTRACT FROM AUTHOR]

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 GLpretreated poplar in enzymatic hydrolysis reached up to 89.9%, 65.5%, and 82.8%, respectively, at a cellulase loading of 40 FPU/g-cellulose. [ABSTRACT FROM AUTHOR]

Highlights: [•] Bound enzymes are primarily responsible for enzymatic hydrolysis. [•] Free enzymes become insignificant for enzyme hydrolysis after a certain time. [•] The loss of synergistic effect in free enzymes limits digestibility of free enzymes. [•] Tween 80 assists releasing CBH I into free enzymes. [•] With surfactant, the digestibility of free enzymes on Avicel was greatly enhanced. [Copyright &y& Elsevier]

Autohydrolysis is a hot water pretreatment to extract soluble components from wood that can be used prior to converting the woody residuals into paper, wood products, fuel, or other goods. In this study, mixed softwood chips were autohydrolyzed in hot water at 150, 160, 170, and 180 °C for 1 and 2 h residence times. The objective was to understand the tradeoff between the extraction of fermentable sugar and the residual solid total energy of combustion quantitatively. This process strategy will be referred to as 'value prior to combustion'. High-performance liquid chromatography was used to determine chemical compositions (sugars and byproducts such as acetic acid, furfural, and hydroxymethylfurfural) of the extracted liquid and residuals; a bomb calorimeter was used to measure the heating value of original wood and solid residue. As the autohydrolysis temperature increased, material balances of the system indicated higher volatile byproducts loss. More hemicelluloses were solubilized by the hot water extraction process at higher temperatures and longer residence times, and a greater degree of sugar degradation was also observed. The maximum sugar yield was determined to occur at conditions of 170 °C for 2 h, during which 13 g of sugar was recovered from the extract out of 100 g of oven-dried wood. The heating value of the solid residues after extraction was greater than the original wood. The total energy content of the solid residual after extraction ranged from 85 to 98 % of the original energy content of the feed with higher temperatures reducing the total energy content. [ABSTRACT FROM AUTHOR]

The cleavage of lignin bonds in a wood matrix is an important step in the processes employed in both the biorefinery and pulp and paper industries. β-O-4 ether linkages are susceptible to both acidic and alkaline hydrolysis. The cleavage of α-ether linkages rapidly occurs under mildly acidic reaction conditions, resulting in lower molecular weight lignin fragments. Acidic reactions are typically employed in the biorefinery industries, while alkaline reactions are more typically employed in the pulp and paper industries, especially in the kraft pulping process. By better understanding lignin reactions and reaction conditions, it may be possible to improve silvicultural and breeding programs to enhance the formation of easily removable lignin, as opposed to more chemically resistant lignin structures. In hardwood species, the S/G ratio has been successfully correlated to the amount of β-O-4 ether linkages present in the lignin and the ease of pulping reactions. [ABSTRACT FROM AUTHOR]

In order to improve polysaccharide retention during pretreatment and increase enzymatic hydrolysis efficiency, green liquor (GL) pretreatment was performed at: (1) higher GL sulfidity; (2) higher sulfidity with the addition of sodium polysulfide; (3) higher sulfidity with the addition of sodium borohydride; or (4) higher sulfudity with the addition of sodium tetraborate. The results indicate that green liquor pretreatment with the higher sulfidity, with the addition of polysulfide and with the addition of sodium borohydride, is effective in increasing enzymatic conversion of the pretreated pulps. The addition of sodium tetraborate, on the other hand, is not effective. These measures can be combined with oxygen delignification and/or mechanical refining to further improve the enzymatic hydrolysis efficiency. Up to 80% of the polysaccharides in softwood can be converted to fermentable sugars, but only with the addition of 40 FPU enzyme dose. [ABSTRACT FROM PUBLISHER]

Red maple, sweet gum, trembling aspen, red alder, and Eucalyptus globulus samples were pretreated with dilute sulfuric acid and green liquor before enzymatic saccharification. Substrates showed different levels of delignification and sugar recovery, depending on the applied pretreatments and the syringaldehyde/vanillin ratio (S/V). Three major conclusions were drawn in this research. First, lignin is the greatest contributor to recalcitrance of hardwood to enzymatic saccharification. Second, a high S/V ratio is a useful indicator of high delignification during a pretreatment process. Third, green liquor pretreatment is a promising pretreatment method because of a high delignification degree and sugar recovery. In addition, xylan also contributes to the recalcitrance of hardwoods toward enzymatic saccharification. [ABSTRACT FROM AUTHOR]

Enzymes still exhibit activities after hydrolysis of biomass according to previous studies. Recycling the enzymes and use them in subsequent hydrolysis cycles can further utilize their remaining activities. Previous studies have mainly discussed enzyme recycling processes up to three cycles, in which the processes did not reach steady state. Steady state investigation is essential for the guidance of the real life process. Four cycles of processing have usually been considered enough to bring the system to steady state in process engineering. In this work, hydrolysate was used as the source of recycled enzymes to fresh substrate for five cycles. Because a large amount of enzymes remained on the pulp, surfactant was introduced to recycle the enzymes that remained with the residue. Recycled hydrolysate from previous enzymatic hydrolysis usually carries a high concentration of sugars, which can inhibit the new round of hydrolysis. To remove sugar from the recycling stream, a wash with fresh buffer was performed. Sugars were removed, while enzymes still remain on the fresh substrates. Six recycling strategies were evaluated for enzyme recycling percentage and enzymatic hydrolysis efficiency with both green-liquor pretreated softwood and hardwood in this investigation. Hydrolysis efficiency increased by about 40% for softwood at 30 mg/g enzyme dosage and about 25% for hardwood at 7.5 mg/g when a washing stage was applied with addition of surfactant. [ABSTRACT FROM AUTHOR]

Biomass pretreatment by autohydrolysis uses hot-water to extract soluble components from wood prior to converting the woody residuals into paper, wood products, or fuel, etc. Mixed hardwood chips were autohydrolyzed in hot-water at 150, 160, 170, and 180 ºC, for 1 and 2 h. The tradeoff between fermentable sugar yield and caloric value of the residual solids was studied for a process that will be referred to as "value prior to combustion". The extracted liquid was treated with dilute sulfuric acid to break down sugar oligomers into fermentable monomers. Material balances were performed around autohydrolysis to evaluate the role of temperature and residence time on sugar production and residual solid heating value. The composition (sugars and byproducts) of the extracted liquid was determined. As the autohydrolysis temperature increased, the material balance became less precise, presumably due to more volatile byproducts being formed that were not quantified. More hemicelluloses were extracted from the wood by the hot water extraction process under higher temperature and longer residence time, but a greater degree of sugar degradation was also observed. After hot-water extraction the heating value of the solid residues was higher than the original wood. The total energy content of the residual solid after extraction ranged from 74 to 95% of the original energy content of the feed. [ABSTRACT FROM AUTHOR]

Abstract: The effect of delignification methods on enzymatic hydrolysis of forest biomass was investigated using softwood and hardwood that were pretreated at an alkaline condition followed by sodium chlorite or ozone delignification. Both delignifications improved enzymatic hydrolysis especially for softwood, while pretreatment alone was found effective for hardwood. High enzymatic conversion was achieved by sodium chlorite delignification when the lignin content was reduced to 15%, which is corresponding to 0.30–0.35g/g accessible pore volume, and further delignification showed a marginal effect. Sample crystallinity index increased with lignin removal, but it did not show a correlation with the overall carbohydrate conversion of enzymatic hydrolysis. [Copyright &y& Elsevier]

Green liquor pretreatment, a technology presently used worldwide in hundreds of kraft pulp mills, is proposed in this work as a potential pretreatment pathway for the efficient conversion of lignocellulosic biomass into ethanol. Mixed southern hardwood, eucalyptus, and loblolly pine were evaluated through process simulations in two investment scenarios: a greenfield mill scenario and a repurposing scenario, using existing kraft pulp mill assets for cellulosic ethanol production. Several advantages come with this concept: i) proven technology (both process and equipment), ii) chemical and energy recovery in place, iii) existing fiber supply chain, and iv) experienced labor force around the mill. Ethanol yields through enzymatic hydrolysis of pretreated fibers were highest in natural mixed hardwood and eucalyptus (280-285 liters of ethanol per dry ton of biomass) and lowest in loblolly pine (273 liters per dry ton of biomass). Natural hardwood and eucalyptus in the repurposing scenario form the most profitable combinations with an IRR of about 19%, mainly due to low capital expenditure (CAPEX) (per liter of ethanol), low enzyme costs, and higher ethanol yield (compared to loblolly pine). Production cost (in the repurposing scenario) was estimated at $2.51 per gallon of ethanol (or $0.66 per liter), cash cost at $2.14 gallon-1 (or $0.57 per liter), and CAPEX at $3.15 gallon-1 (or $0.83 per liter). Repurposing existing closed mills creates a potential alternative to ramp up in the task of producing alternative lignocellulosic biofuels. [ABSTRACT FROM AUTHOR]

Coastal Bermuda grass (CBG) is an agricultural residue with considerable potential as a feedstock for lignocellulosic-based ethanol. The treatment of biomass with water at high temperature, termed autohydrolysis, can be used to recover sugars in the filtrate and to improve enzyme digestibility of the pretreated solids. The effect of a twostage autohydrolysis process with respect to total sugar recovery relative to a one stage process was investigated. CBG was subjected to lab scale one-stage (150, 160, and 170°C) and two-stage (150/170°C and 160/170°C) isothermal autohydrolysis processes followed by enzyme hydrolysis on the residual solids with different loadings (5 to 30 FPU/g). Two-stage autohydrolysis (160/170°C) solubilized 94.2% of the hemicellulose based on the original CBG material but only 17.7% of the cellulose and 30.4% of the lignin. Increases in the severity factor (a combination of time and temperature) of autohydrolysis pretreatments decreased the recoverable carbohydrates and total solids. Two-stage autohydrolysis enhanced enzyme digestibility of the cellulose in pretreated solids relative to one-stage autohydrolysis, especially at higher values of FPU/g. The overall total theoretical sugar recovery achievable by the two stage process was 57.8% and for the one stage process only 51.6% with 30 FPU/g. This marginal increase would have to be considered relative to increased complexity of operations when deciding whether to implement one or two stage autohydrolysis. [ABSTRACT FROM AUTHOR]

Softwood species generally have been found very recalcitrant to enzymatic hydrolysis of the carbohydrate fractions to monomeric sugars. To solve this problem, loblolly pine chips were pretreated with green liquor at 12-20% Total Titratable Alkali (TTA) (as Na2O on wood) at 170°C for 800 H-factor. The yield of resulting pulp was 76.5-78.6% and the lignin content decreased from 29.2 to 20.2-22.4% and the total polysaccharide decreased from 62.6 to 53.8-55.0%, all based on the weight of original wood. When the pulp was subjected to enzymatic hydrolysis using 40 Filter Paper Unit (FPU)/g pulp, only 41% of the polysaccharides in wood were converted to monomeric sugars. This conversion figure is much lower than that of mixed southern hardwoods (80%) treated under similar conditions. If the green liquor treated pulp was further subjected to either oxygen delignification or mechanical refining prior to the enzymatic hydrolysis, the conversion rate increased to around 55% and 60%, respectively. Furthermore, combination of oxygen delignification and refining further increased the total sugar conversion to 78% of the total sugar in wood, approximately equal to that of the mixed southern hardwoods. [ABSTRACT FROM AUTHOR]

Coastal Bermuda grass (CBG) has been shown to have potential as a biomass feedstock for sugar production. In this study, the effectiveness of ozone pretreatment for CBG to improve the sugar recovery via enzyme hydrolysis was investigated. Raw CBG and autohydrolysistreated CBG were pretreated with ozone at ozone consumption of 1.8 to 26.4 % (w/w) at room temperature. Lignin degradation and hemicellulose solubilization increased with increased ozone consumption. At 26.4% ozone consumption by weight on CBG the amount of lignin in the CBG was reduced by 34%. Autohydrolysis of CBG increased the reactivity of cellulose, hemicellulose, and lignin with ozone. The maximum total sugar recovery after enzymatic hydrolysis was 32% for a 14.0% consumption of ozone on raw CBG. For CBG samples pretreated with autohydrolysis followed by a 3.1% ozone consumption pretreatment the maximum total sugar recovery after enzyme hydrolysis was 40.1%. Autohydrolysis pretreatment followed by enzyme hydrolysis yielded a 36.4% sugar recovery, indicating that the application and benefits of ozone after autohydrolysis with the conditions studied herein are marginally better than autohydrolysis alone. [ABSTRACT FROM AUTHOR]

Three strategies were presented to achieve high solids loading while maximizing carbohydrate conversion, which are fed-batch, splitting/thickening, and clarifier processes. Enzymatic hydrolysis was performed at water insoluble solids (WIS) of 15% using washed dilute-acid pretreated corn stover. The carbohydrate concentration increased from 31.8 to 99.3 g/L when the insoluble solids content increased from 5% to 15% WIS, while the final carbohydrate conversion was decreased from 78.4% to 73.2%. For the fed-batch process, a carbohydrate conversion efficiency of 76.8% was achieved when solid was split into 60:20:20 ratio, with all enzymes added first. For the splitting/thickening process, a carbohydrate conversion of 76.5% was realized when the filtrate was recycled to simulate a steady-state process. Lastly, the clarifier process was evaluated and the highest carbohydrate conversion of 81.4% was achieved. All of these results suggests the possibility of enzymatic hydrolysis at high solids to make the overall conversion cost-competitive. [ABSTRACT FROM AUTHOR]

The autohydrolysis process has been considered a simple, low-cost and environmental friendly technology for generation of sugars from biomass. In order to improve accessibility of enzymes during enzymatic hydrolysis as well as to allow the recovery of hemicellulose in the filtrate, the sugarcane bagasse was pretreated using autohydrolysis followed by a mechanical refining process. The autohydrolysis was carried out in three different conditions. Autohydrolysis at 190 °C for 10 min provided the highest overall sugar (19.2/100 g raw bagasse) in prehydrolyzate. The enzymatic hydrolysis step was performed for all the post-treated solids with and without refining at enzyme loadings of 5 and 10 FPU/g for 96 h. A total of 84.4% of sugar can be recovered from sugarcane bagasse at 180 °C for 20 min with 5 FPU/g enzyme charge. The economic analysis for the proposed method showed that the bioethanol production can have a financial return larger than 12%. [ABSTRACT FROM AUTHOR]

A comparison study of autohydrolysis and acid-catalyzed autohydrolysis of wheat straw was performed to understand the impact of acid addition on overall sugar recovery. Autohydrolysis combined with refining is capable of achieving sugar recoveries in the mid 70s. If the addition of a small amount of acid is capable of increasing the sugar recovery even higher it may be economically attractive. Acetic, sulfuric, hydrochloric and sulfurous acids were selected for acid-catalyzed autohydrolysis pretreatments. Autohydrolysis with no acid at 190 °C showed the highest total sugar in the prehydrolyzate. Enzymatic hydrolysis was performed for all the post-treated solids with and without refining at enzyme loadings of 4 and 10 FPU/g for 96 h. Acid-catalyzed autohydrolysis at 190 °C with sulfurous acid showed the highest total sugar recovery of 81.2% at 4 FPU/g enzyme charge compared with 64.3% at 190 °C autohydrolysis without acid. [ABSTRACT FROM AUTHOR]

Highlights: [•] Autohydrolysis severity affects the chemical composition of pretreated wheat straw. [•] The enzymatic hydrolysis efficiency was strongly related to pretreatment severity. [•] Mechanical refining improved enzymatic hydrolysis efficiency of wheat straw. [•] The levels of sugar recovery are comparable to other pretreatment methods. [ABSTRACT FROM AUTHOR]

Abstract: In this work, mixed hardwoods were pretreated by sodium sulfite–formaldehyde (SF). The effects of SF pretreatment on the chemical compositions and enzymatic hydrolysis of mixed hardwoods were investigated. SF pretreatment temperature had a significant effect on pulp yield and delignification, resulting in an increased efficiency of enzymatic hydrolysis. After 96h of enzymatic hydrolysis at the cellulase loading of 40FPU/g substrate, the yields of glucan and xylan on the basis of original wood were 37% and 11% for the pulp produced with 12% sulfite charge at 170°C for 2h. The total sugar recovery based on the sugar in original wood was 74%. These results indicate that sulfite–formaldehyde cooking is of great potential to be a pretreatment method for a greenfield mill to produce fuel ethanol from hardwood. [Copyright &y& Elsevier]

Abstract: The novel low xylan content transgenic cottonwood (P. trichocarpa) was used to elucidate recalcitrance of enzymatic saccharification with or without four different pretreatment methods. The xylan contents of two transgenic samples (8Di3 and 8Di5) were 11.4% and 11.7%, respectively, as compared with the wild type (16.0%). Contrarily, the lignin contents of two transgenic samples were 23.1% and 24.5%, respectively, as compared with the wild type (20.8%). The four pretreatments were dilute acid (0.1% sulfuric acid, 185 °C, 30 min), green liquor (6% total titratable alkali (TTA), 25% sulfidity based on TTA, 185 °C and 15 min), auto hydrolysis (185 °C, 30 min) and ozone delignification (25 °C, 30 min). Following the pretreatment, enzymatic saccharification was carried out using three enzyme charges of 10, 20 and 30 FPU per gram of substrate. The removal of lignin and hemicelluloses varied with the type of pretreatment and with the lignin content of the transgenic trees. High lignin content implied low enzymatic saccharification. Low xylan content native substrates lead to high enzymatic saccharification. High S to V (sryingaldehyde to vanillin) ratio substrates had high delignification during pretreatment. Compared to the wild type, the transgenics were better choice as feed stocks due to higher enzymatic saccharification without pretreatment which mean low the cost of bio-ethanol. Compared to three pretreatment methods, the green liquor pretreatment greatly improves the conversion of polysaccharides in general. [Copyright &y& Elsevier]

Abstract: Autohydrolysis is a simple, green method of recovering sugars from biomass, using only hot water. One potential drawback is that byproducts are formed during the autohydrolysis process that could interfere with subsequent hydrolysis and fermentation to ethanol. In the present work, autohydrolysis prehydrolyzate from mixed hardwood chips was detoxified with activated carbon and the removal efficiency of byproducts as well as the loss of sugars determined. The resulting detoxified prehydrolyzate was evaluated for the fermentation to ethanol with a thermophilic anaerobic bacterium. Activated carbon at a 2.5 wt % level on the prehydrolyzate was able to remove 42% of formic acid, 14% of acetic acid, 96% of hydroxymethylfurfural (HMF) and 93% of the furfural. However, 8.9% of sugars were also removed. The removal of HMF and furfural follow expected adsorption isotherms but formic acid, acetic acid, and sugars did not. Autohydrolysis prehydrolyzates from mixed hardwood detoxified with activated carbon can be fermented with Thermoanaerobacterium saccharolyticum strain MO1442 with an essentially 100% yield. T. saccharolyticum strain MO1442 is able to metabolize the glucose, xylose, and arabinose in the hydrolyzate. The results showed the detoxification process with activated carbon improved the ethanol yields by the removal of toxic compounds, mainly HMF and furfural, with moderate loss of fermentable sugars. [ABSTRACT FROM AUTHOR]

Highlights • Sweet sorghum bagasse has much of free sugars after squeezing juice. • Single stage autohydrolysis causes degradation of free sugars. • Two-stage autohydrolysis pretreat bagasse minimizing free sugars degradation. • Two-stage autohydrolysis is effective for sugar recovery from Sweet sorghum bagasse. Abstract Modified autohydrolysis combined with mechanical refining has been suggested to recover free sugars from sweet sorghum bagasse and facilitates enzyme access to cellulose in bagasse for enhancing its conversion to fermentable sugars. The amount of total available sugars in sweet sorghum bagasse was found to be 76.1% and this value was used to evaluate the efficiency of the process suggested. Total sugar recovery was achieved up to 68.1% through the single-stage autohydrolysis at 170 °C for 60 min, followed by mechanical refining and enzymatic hydrolysis; however, the sugar recovery through partial degradation of free sugars induced by high-temperature autohydrolysis was lower than expected. A modified two-stage autohydrolysis was suggested to prevent sugar degradation and the total sugar recovery using this process reached 83.9% of total available sugars in sweet sorghum bagasse. [ABSTRACT FROM AUTHOR]

[Display omitted] • Enzymatic hydrolysis is a potential method to upcycle textile wastes. • Mechanical refining promotes high-yield enzymatic hydrolysis of textiles. • Dyes inhibit the enzymatic hydrolysis of textile wastes. • Chlorine-free oxidation removes dyes and whitens textiles with low chemical dosage. • Mechanical refining + oxidation processes boost enzyme conversion of dyed textiles. Given the increasing concern over textile waste management and the proliferation of textile landfills, enzymatic hydrolysis of cotton represents a potential pathway to upcycle textile waste into valuable chemical building blocks. However, this pathway is challenged by the presence of persistent dyes, hindering enzyme performance. To overcome this issue, environmentally friendly and total chlorine free oxidation methods such as ozone and alkaline hydrogen peroxide were used in combination with mechanical refining pretreatment. The results showed that the enzymatic conversion of black-dyed cotton, without oxidation, resulted in a glucose yield of only 60% as compared to 95% for undyed cotton fibers. On the other hand, the inclusion of oxidation processes in the pretreatment stage resulted in a glucose yield of 90% via enzymatic hydrolysis at expense of using low oxidation chemicals and low enzyme charges. This work highlights the potential of oxidation methods, enzymatic hydrolysis, and mechanical refining as an ecofriendly pathway for generating value-added chemicals from cotton textile waste while promoting economic circularity. [ABSTRACT FROM AUTHOR]

A biologically-based lignocellulosic biorefinery process for obtaining carbohydrates from raw biomass was investigated across six diverse biomasses (three hardwoods & three nonwoods) for the purpose of decoding lignin’s influence on sugar production. Acknowledging that lignin could positively alter the economics of an entire process if valorized appropriately, we sought to correlate the chemical properties of lignin within the process to the traditional metrics associated with carbohydrate production-cellulolytic digestibility and total sugar recovery. Based on raw carbohydrate, enzymatic recovery ranged from 40 to 64% w/w and total recovery ranged from 70 to 87% w/w. Using nitrobenzene oxidation to quantify non-condensed lignin structures, it was found that raw hardwoods bearing increasing non-condensed S/V ratios (2.5–5.1) render increasing total carbohydrate recovery from hardwood biomasses. This finding indicates that the chemical structure of hardwood lignin influences the investigated biorefinery process’ ability to generate carbohydrates from a given raw hardwood feedstock. [ABSTRACT FROM AUTHOR]

The role of solvent extractable lignin in enzymatic hydrolysis of hydrothermally pretreated sweetgum was investigated. Lignin extraction with acetone, methanol or acetone/methanol removed 27–33% of lignin in hydrothermally pretreated sweetgum pulp, resulting in total sugar yield reduction. Comprehensive characterization indicated that the extractable lignin is highly degraded with low molecular weight, high phenolic hydroxyls, and low native lignin interunit linkages and exhibited neither stimulation nor inhibition effects on enzymatic hydrolysis of filter paper, Avicel, and bleached eucalyptus kraft pulp. The extractable lignin was mainly deposited on the surface of the fibers and pores, which removal caused significant morphological change and collapse of the mesopores and macropores. Thus, the reduction in enzymatic digestion efficiency was more likely caused by the pore collapse in fiber and decreased accessible area, rather than the stimulative action of the extractable lignin. [Display omitted] • Lignin extraction with organic solvents from hydrothermally pretreated sweetgum pulp resulting in total sugar yield reduction. • Extractable lignin exhibited neither stimulation nor inhibition effects on enzymatic hydrolysis of cellulose. • Lignin extraction caused significant morphological change and collapse of the mesopores and macropores. • Reduction in enzymatic digestion was caused by the pore collapse rather than the stimulative action of the extractable lignin. [ABSTRACT FROM AUTHOR]

The valorization of paper sludge is a high-potential process to develop renewable fuels and chemicals, which can be integrated with pulp and paper mills. Calcium carbonate is the main ash component in sludge, which plays a role in buffering pH and potentially lowering the conversion during enzymatic hydrolysis. Therefore, it is important to investigate the effect of ash on sugar yields and examine pH change to introduce efficient and economical enzymatic hydrolysis of sludge. Carbohydrate conversion was enhanced when the ash was removed by fractionation. On the other hand, the highest sugar recovery was obtained when the sludge contained 20% ash content. The pH change during enzymatic hydrolysis was influenced by ash and explained why sludge-derived hydrolysate showed lower carbohydrate conversion. Therefore, a high shear process with the increased acid amount is suggested to prohibit the negative effect of ash and enhance the accessibility of cellulase to fibers. This study highlights the feasibility of using wet waste streams generated by the paper industry. • Enhanced carbohydrate conversion of sludge containing low ash after fractionation. • Enhanced carbohydrate conversion by lowering the starting pH environment. • Observed pH change during hydrolysis to understand the adverse effect of ash. • Obtained maximum sugar recovery when paper sludge contained 20% ash. • Provided the efficiency of enzymatic hydrolysis depending on the ash content. [ABSTRACT FROM AUTHOR]

Understanding enzyme-substrate interactions is critical in designing strategies for bioconversion of lignocellulosic biomass. In this study we monitored molecular events, in situ and in real time, including the adsorption and desorption of cellulolytic enzymes on lignins and cellulose, by using quartz crystal microgravimetry and surface plasmon resonance. The effect of a nonionic surface active molecule was also elucidated. Three lignin substrates relevant to the sugar platform in biorefinery efforts were considered, namely, hardwood autohydrolysis cellulolytic (HWAH), hardwood native cellulolytic (MPCEL), and nonwood native cellulolytic (WSCEL) lignin. In addition, Kraft lignins derived from softwoods (SWK) and hardwoods (HWK) were used as references. The results indicated a high affinity between the lignins with both, monocomponent and multicomponent enzymes. More importantly, the addition of nonionic surfactants at concentrations above their critical micelle concentration reduced remarkably (by over 90%) the nonproductive interactions between the cellulolytic enzymes and the lignins. This effect was hypothesized to be a consequence of the balance of hydrophobic and hydrogen bonding interactions. Moreover, the reduction of surface roughness and increased wettability of lignin surfaces upon surfactant treatment contributed to a lower affinity with the enzymes. Conformational changes of cellulases were observed upon their adsorption on lignin carrying preadsorbed surfactant. Weak electrostatic interactions were determined in aqueous media at pH between 4.8 and 5.5 for the native cellulolytic lignins (MPCEL and WSCEL), whereby a ~20% reduction in the enzyme affinity was observed. This was mainly explained by electrostatic interactions (osmotic pressure effects) between charged lignins and cellulases. Noteworthy, adsorption of nonionic surfactants onto cellulose, in the form cellulose nanofibrils, did not affect its hydrolytic conversion. Overall, our results highlight the benefit of nonionic surfactant pretreatment to reduce nonproductive enzyme binding while maintaining the reactivity of the cellulosic substrate. [ABSTRACT FROM AUTHOR]

Mechanical refining has been shown to improve biomass enzymatic digestibility. In this study industrial high-yield sodium carbonate hardwood pulp was subjected to lab, pilot and industrial refining to determine if the mechanical refining improves the enzymatic hydrolysis sugar conversion efficiency differently at different refining scales. Lab, pilot and industrial refining increased the biomass digestibility for lignocellulosic biomass relative to the unrefined material. The sugar conversion was increased from 36% to 65% at 5 FPU/g of biomass with industrial refining at 67.0 kWh/t, which was more energy efficient than lab and pilot scale refining. There is a maximum in the sugar conversion with respect to the amount of refining energy. Water retention value is a good predictor of improvements in sugar conversion for a given fiber source and composition. Improvements in biomass digestibility with refining due to lab, pilot plant and industrial refining were similar with respect to water retention value. [ABSTRACT FROM AUTHOR]

Highlights: [•] Na2CO3–O2 and NaOH–O2 was used as pretreatment on wheat straw. [•] Most carbohydrates were kept in the pretreated solids with a high delignification. [•] NaOH–O2 pretreatment showed better performance on improving enzymatic hydrolysis. [•] About 72% of the original polysaccharides were converted into fermentable sugars. [Copyright &y& Elsevier]

Efficiently producing second-generation biofuels from biomass is of strategic significance and meets sustainability targets, but it remains a long-term challenge due to the existence of biomass recalcitrance. Lignin contributes significantly to biomass recalcitrance by physically limiting the access of enzymes to carbohydrates, and this could be partially overcome by applying a pretreatment step to directly target lignin. However, lignin typically cannot be completely removed, and its structure is also significantly altered during the pretreatment. As a result, lignin residue in the pretreated materials still significantly hindered a complete conversion of carbohydrate to its monosugars by interacting with cellulase enzymes. The non-productive adsorption driven by hydrophobic, electrostatic, and/or hydrogen bonding interactions is widely considered as the major mechanism of action governing the unfavored lignin-enzyme interaction. One could argue this type of interaction between lignin residue and the activated enzymes is the major roadblock for efficient enzymatic hydrolysis of pretreated lignocellulosics. To alleviate the negative effects of lignin on enzyme performance, a deep understanding of lignin structural transformation upon different types of pretreatments as well as how and where does lignin bind to enzymes are prerequisites. In the last decade, the progress toward a fundamental understanding of lignin-enzyme interaction, structural characterization of lignin during pretreatment and/or conformation change of enzyme during hydrolysis is resulting in advances in the development of methodologies to mitigate the negative effect of lignin. Here in this review, the lignin structural transformation upon different types of pretreatments and the inhibition mechanism of lignin in the bioconversion of lignocellulose to bioethanol are summarized. Some technologies to minimize the adverse impact of lignin on the enzymatic hydrolysis, including chemical modification of lignin, adding blocking additives, and post-treatment to remove lignin were also introduced. The production of liquid biofuels from lignocellulosic biomass has shown great environmental benefits such as reducing greenhouse gas emissions and mitigate climate change. By addressing the root causes of lignin-enzyme interaction and how to retard this interaction, it is our hope that this comprehensive review will pave the way for significantly reducing the high cost associated with the enzymatic hydrolysis process, and ultimately achieving a cost-effective and sustainable biorefinery system. [Display omitted] • Structure changes of lignin under different pretreatments are proposed. • Up-to-date review the mechanism/role of lignin in enzymatic hydrolysis. • How to minimize adverse impact of lignin on enzymatic hydrolysis is emphasized. [ABSTRACT FROM AUTHOR]

Abstract: Coastal Bermuda grass (GBG) was pretreated using an autohydrolysis process with different temperatures and times, and the pretreated materials were enzymatically hydrolyzed using a mixture of cellulase, xylanase and β-glucosidase with different enzyme loadings to evaluate sugar yields. Compared with untreated CBG, autohydrolysis pretreatments at all elevated temperatures and residence times tested enhanced enzymatic digestibility of both cellulose and hemicellulose. Increasing the temperature and residence time also helps to solubilize hemicelluloses, with 83.3% of the hemicelluloses solubilized at 170°C for 60min treatment. However, higher temperatures and longer times resulted in an overall lower sugar recovery when considering monosaccharides in the prehydrolyzate combined with the enzyme hydrolyzate. Autohydrolysis at 150°C for 60min provided the highest overall sugar yield for the entire process. A total of 43.3g of sugars, 70% of the theoretical sugar yield, can be generated from 100g CBG, 15.0g of monosaccharide in the prehydrolyzate and 28.3g in the enzyme hydrolyzate. The conversion efficiency could be further improved by optimizing enzyme dosages and xylanases:cellulases ratio and pretreatment conditions to minimize sugar degradation. [Copyright &y& Elsevier]

P-toluene sulfonic acid (PTSA) was utilized to pretreat corn stover. Changes in morphology and structure of untreated and pretreated samples were analyzed by ESEM, TEM, BET, XRD and SXT. The characterization results demonstrated that PTSA pretreatment could markedly improve cellulase accessibility to cellulose because of the removal of lignin and hemicellulose simultaneously. The maximum glucose yield (67.2%) with an enzyme loading of 5FPU•g−1 substrate was achieved after the sample was the pretreated at 80 °C for 10 min with 71.0 wt% PTSA. P-toluene sulfonic acid pretreatment was a valid method to improve the enzymatic hydrolysis performance of cellulose in corn stover at low reaction temperature with a short reaction time. • PTSA pretreatment can remove lignin and hemicellulose simultaneously under mild condition. • P-toluene sulfonic acid pretreatment was an effective pretreatment process. • 67.2% of glucose yield was achieved at a low enzyme loading of 5FPU·g−1 substrate. [ABSTRACT FROM AUTHOR]