Saccharification of steam-exploded poplar wood

Effects of time, temperature, and pH during the steam explosion of poplar wood were studied with the aim of optimize both pentoses recovery and enzymatic hydrolysis efficiency. Steam explosion of acid impregnated wood chips allowed the recovery of 70% of potential xylose as monomers (217 degrees C, 120 s) Enzymatic hydrolysis of pretreated fiber with Trichoderma reesei CL-847 cellulase system increased progressively with the severity of the steam treatment conditions. The best yield in term of glucose recovery after 24 h of enzymatic hydrolysis was 70% of potential glucose (225 degrees C, 120 s). Deactivation by adsorption on lignin of Trichoderma reesei cellulases and inhibition of these enzymes by low-molecular-weight phenols and trihydroxybutyric acids were noticed.     

Enzymatic digestion of liquid hot water pretreated hybrid poplar

Liquid hot (LHW) water pretreatment (LHW) of lignocellulosic material enhances enzymatic conversion of cellulose to glucose by solubilizing hemicellulose fraction of the biomass, while leaving the cellulose more reactive and accessible to cellulase enzymes. Within the range of pretreatment conditions tested in this study, the optimized LHW pretreatment conditions for a 15% (wt/vol) slurry of hybrid poplar were found to be 200^oC, 10 min, which resulted in the highest fermentable sugar yield with minimal formation of sugar decomposition products during the pretreatment. The LHW pretreatment solubilized 62% of hemicellulose as soluble oligomers. Hot‐washing of the pretreated poplar slurry increased the efficiency of hydrolysis by doubling the yield of glucose for a given enzyme dose. The 15% (wt/vol) slurry of hybrid poplar, pretreated at the optimal conditions and hot‐washed, resulted in 54% glucose yield by 15 FPU cellulase per gram glucan after 120 h. The hydrolysate contained 56 g/L glucose and 12 g/L xylose. The effect of cellulase loading on the enzymatic digestibility of the pretreated poplar is also reported. Total monomeric sugar yield (glucose and xylose) reached 67% after 72 h of hydrolysis when 40 FPU cellulase per gram glucan were used. An overall mass balance of the poplar‐to‐ethanol process was established based on the experimentally determined composition and hydrolysis efficiencies of the liquid hot water pretreated poplar. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

Biogas production and saccharification of Salix pretreated at different steam explosion conditions

Different steam explosion conditions were applied to Salix chips and the effect of this pretreatment was evaluated by running both enzymatic hydrolysis and biogas tests. Total enzymatic release of glucose and xylose increased with pretreatment harshness, with maximum values being obtained after pretreatment for 10 min at 210 °C. Harsher pretreatment conditions did not increase glucose release, led to degradation of xylose and to formation of furfurals. Samples pretreated at 220 and 230 °C initially showed low production of biogas, probably because of inhibitors produced during the pretreatment, but the microbial community was able to adapt and showed high final biogas production. Interestingly, final biogas yields correlated well with sugar yields after enzymatic hydrolysis, suggesting that at least in some cases a 24 h enzymatic assay may be developed as a quick method to predict the effects of pretreatment of lignocellulosic biomass on biogas yields.     

Hydrolysis of Miscanthus for bioethanol production using dilute acid presoaking combined with wet explosion pre-treatment and enzymatic treatment

Miscanthus is a high yielding bioenergy crop. In this study we used acid presoaking, wet explosion, and enzymatic hydrolysis to evaluate the combination of the different pre-treatment methods for bioethanol production with Miscanthus. Acid presoaking is primarily carried out in order to remove xylose prior to wet explosion. The acid presoaking extracted 63.2% xylose and 5.2% glucose. Direct enzymatic hydrolysis of the presoaked biomass was found to give only low sugar yields of 24-26% glucose. Wet explosion is a pre-treatment method that combines wet-oxidation and steam explosion. The effect of wet explosion on non-presoaked and presoaked Miscanthus was investigated using both atmospheric air and hydrogen peroxide as the oxidizing agent. All wet explosion pre-treatments showed to have a disrupting effect on the lignocellulosic biomass, making the sugars accessible for enzymatic hydrolysis. The combination of presoaking, wet explosion, and enzymatic hydrolysis was found to give the highest sugar yields. The use of atmospheric air gave the highest xylose yield (94.9% xylose, 61.3% glucose), while hydrogen peroxide gave the highest glucose yield (82.4% xylose, 63.7% glucose).     

Pretreatment efficiency and structural characterization of rice straw by an integrated process of dilute-acid and steam explosion for bioethanol production

The combined pretreatment of rice straw using dilute-acid and steam explosion followed by enzymatic hydrolysis was investigated and compared with acid-catalyzed steam explosion pretreatment. In addition to measuring the chemical composition, including glucan, xylan and lignin content, changes in rice straw features after pretreatment were investigated in terms of the straw's physical properties. These properties included crystallinity, surface area, mean particle size and scanning electron microscopy imagery. The effect of acid concentration on the acid-catalyzed steam explosion was studied in a range between 1% and 15% acid at 180°C for 2 min. We also investigated the influence of the residence time of the steam explosion in the combined pretreatment and the optimum conditions for the dilute-acid hydrolysis step in order to develop an integrated process for the dilute-acid and steam explosion. The optimum operational conditions for the first dilute-acid hydrolysis step were determined to be 165°C for 2 min with 2% H(2)SO(4) and for the second steam explosion step was to be carried out at 180°C for 20 min; this gave the most favorable combination in terms of an integrated process. We found that rice straw pretreated by the dilute-acid/steam explosions had a higher xylose yield, a lower level of inhibitor in the hydrolysate and a greater degree of enzymatic hydrolysis; this resulted in a 1.5-fold increase in the overall sugar yield when compared to the acid-catalyzed steam explosion.     

Production of 2,3-butanediol by Klebsiella pneumoniae grown on acid hydrolyzed wood hemicellulose

Summary Previously steam explosion had been used to enhance the enzymatic hydrolysis of lignocellulosic substrates to glucose. The conditions for pretreating aspen wood chips were optimized so that highest amounts of undegraded hemicellulose could be obtained after washing the steam exploded chips. The hemicellulose rich water soluble fractions showing highest pentosan yields were then acid hydrolysed to their composite sugars. Approximately 65–75% of the total reducing sugars detected in the wood hydrolysates were in the form of monosaccharides with D-xylose being the major component. Klebsiella pneumoniae was grown in media containing these wood hydrolysates as the substrate and 2,3-butanediol yields of 0.4–0.5 g per g of monosaccharide utilised were obtained.     

固定化纤维素酶对预处理纤维素原料水解效果的影响

以壳聚糖为载体用交联法制备固定化纤维素酶,考察固定化纤维素酶对蒸爆、球磨、超声波、喷淋、高温预处理玉米秸秆纤维素原料的酶解效果.结果表明:物料经蒸爆预处理后酶水解效率最高可以达到95%,球磨预处理水解效率次之,达到60%.用电镜和FT-IR对处理前后秸秆结构进行表征分析,证明预处理对物料的物理结构及化学组成有一定的影响.蒸爆法和球磨法可以使物料致密的天然结构彻底破坏,从而增加物料的比表面积;蒸爆预处理可以使纤维素内部氢键和官能团改变,使物料更易于酶解.     

Effects of cellulase and xylanase enzymes on the deconstruction of solids from pretreatment of poplar by leading technologies

Comparative data is presented on glucose and xylose release for enzymatic hydrolysis of solids produced by pretreatment of poplar wood by ammonia fiber expansion (AFEX), ammonia recycled percolation (ARP), controlled pH, dilute acid, flowthrough (FT), lime, and sulfur dioxide (SO₂) technologies. Sugar solubilization was measured for times of up to 72 h using cellulase supplemented with β‐glucosidase at an activity ratio of 1:2, respectively, at combined protein mass loadings of 5.8–116 mg/g of glucan in poplar wood prior to pretreatment. In addition, the enzyme cocktail was augmented with up to 11.0 g of xylanase protein per gram of cellulase protein at combined cellulase and β‐glucosidase mass loadings of 14.5 and 29.0 mg protein (about 7.5 and 15 FPU, respectively)/g of original potential glucose to evaluate cellulase–xylanase interactions. All pretreated poplar solids required high protein loadings to realize good sugar yields via enzymatic hydrolysis, and performance tended to be better for low pH pretreatments by dilute sulfuric acid and sulfur dioxide, possibly due to higher xylose removal. Glucose release increased nearly linearly with residual xylose removal by enzymes for all pretreatments, xylanase leverage on glucan removal decreased at high cellulase loadings. Washing the solids improved digestion for all pretreatments and was particularly beneficial for controlled pH pretreatment. Furthermore, incubation of pretreated solids with BSA, Tween 20, or PEG6000 prior to adding enzymes enhanced yields, but the effectiveness of these additives varied with the type of pretreatment. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

斑茅酶解转化可发酵单糖的液氨预处理及参数优化

斑茅(Saccharum arundinaceum Retz.)的生物产量高,对土壤条件要求低,可作为纤维素乙醇生产的原料作物在我国南方地区广泛种植.实验以斑茅为原料,采用液氨预处理法克服其水解顽抗性,并添加纤维素酶进行酶解,运用高效液相色谱(HPLC)测定了酶解液中的单糖含量.实验结果表明在纤维素酶添加量为15FPU/(g当量葡聚糖)、预处理原料含水率为80％、预处理温度为130℃、预处理驻留时间为10 min、液氨与生物质的质量比例为2∶1时,葡聚糖和木聚糖的总转化率分别为69.34％和82.60％,相比于未作预处理的原料分别提高了573％和1 056％,单糖产量提高8倍.实验结果表明液氨预处理对斑茅是一种有效的预处理方式,并优于稀酸或湿爆法预处理,与酸预处理和氨爆法(AFEX)处理效果接近.     

Synergistic effects of mixing hybrid poplar and wheat straw biomass for bioconversion processes

Background

Low cost of raw materials and good process yields are necessary for future lignocellulosic biomass biorefineries to be sustainable and profitable. A low cost feedstock will be diverse, changing as a function of seasonality and price and will most likely be available from multiple sources to the biorefinery. The efficacy of the bioconversion process using mixed biomass, however, has not been thoroughly investigated. Considering the seasonal availability of wheat straw and the year round availability of hybrid poplar in the Pacific Northwest, this study aims to determine the impact of mixing wheat straw and hybrid poplar biomass on the overall sugar production via steam pretreatment and enzymatic saccharification.

Results

Steam pretreatment proved to be effective for processing different mixtures of hybrid poplar and wheat straw. Following SO₂-catalyzed steam explosion pretreatment, on average 22 % more sugar monomers were recovered using mixed feedstock than either single biomass. Improved sugar recovery with mixtures of poplar and wheat straw continued through enzymatic hydrolysis. After steam pretreatment and saccharification, the mixtures showed 20 % higher sugar yields than that produced from hybrid poplar and wheat straw alone.

Conclusions

Blending hybrid poplar and wheat straw resulted in more monomeric sugar recovery and less sugar degradation. This synergistic effect is attributable to interaction of hybrid poplar’s high acetic acid content and the presence of ash supplied by wheat straw. As a consequence on average 20 % more sugar was yielded by using the different biomass mixtures. Combining hybrid poplar and wheat straw enables sourcing of the lowest cost biomass, reduces seasonal dependency, and results in increasing biofuels and chemicals productivity in a cellulosic biorefinery.

     

Steam-explosion pretreatment of wood: Effect of chip size, acid, moisture content and pressure drop

Material balances for pentosan, lignin, and hexosan, during steam-explosion pretreatment of aspenwood, showed almost quantitative recovery of cellulose in the water-insoluble fraction. Dilute acid impregnation resulted in more selective hydrolysis of pentosan relative to undesirable pyrolysis, and gave a more accessible substrate for enzymatic hydrolysis. Thermocouple probes, located inside simulated aspenwood chips heated in 240 degrees C-saturated steam, showed rapid heating of air-dry wood, whereas green or impregnated wood heated slowly. Small chips, 3.2 mm in the fiber direction, whether green or airdry gave approximately equal rates of pentosan destruction and solubilization, and similar yields of glucose and of total reducing sugars on enzymatic hydrolysis with Trichoderma harzianum. Partial pyrolysis, destroying one third of the pentosan of aspenwood at atmospheric pressure by dry steam at 276 degrees C, gave little increase in yield of reducing sugars on enzymatic hydrolysis. Treatment with saturated steam at 240 degrees C gave essentially the same yields of glucose and of total reducing sugars, and the same yields of butanediol and ethanol on fermentation with Klebsiella pneumoniae, whether or not 80% of the steam was bled off before explosion and even if the chips remained intact, showing that explosion was unnecessary.     

Effect of hemicellulose and lignin removal on enzymatic hydrolysis of steam pretreated corn stover

Ethanol can be produced from lignocellulosic biomass using steam pretreatment followed by enzymatic hydrolysis and fermentation. The sugar yields, from both hemicellulose and cellulose are critical parameters for an economically-feasible ethanol production process. This study shows that a near-theoretical glucose yield (96-104%) from acid-catalysed steam pretreated corn stover can be obtained if xylanases are used to supplement cellulases during hydrolysis. Xylanases hydrolyse residual hemicellulose, thereby improving the access of enzymes to cellulose. Under these conditions, xylose yields reached 70-74%. When pre-treatment severity was reduced by using autocatalysis instead of acid-catalysed steam pretreatment, xylose yields were increased to 80-86%. Partial delignification of pretreated material was also evaluated as a way to increase the overall sugar yield. The overall glucose yield increased slightly due to delignification but the overall xylose yield decreased due to hemicellulose loss in the delignification step. The data also demonstrate that steam pretreatment is a robust process: corn stover from Europe and North America showed only minor differences in behaviour.     

Novel Single-step Pretreatment of Steam Explosion and Choline Chloride to De-lignify Corn Stover for Enhancing Enzymatic Edibility

It is important to develop efficient and economically feasible pretreatment methods for lignocellulosic biomass, to increase annual biomass production. A number of pretreatment methods were introduced to promote subsequent enzymatic hydrolysis of biomass for green energy processes. Pretreatment with steam explosion removes the only xylan at high severity but increases lignin content. In this study, corn stover soaked in choline chloride solution before the steam explosion is economically feasible as it reduced cost. Enzymatic hydrolysis of de-lignified corn stover is enhanced by combinatorial pretreatments of steam explosion and choline chloride. Corn stover pretreated with choline chloride at the ratio of 1:2.2 (w/w), 1.0 MPa, 184 °C, for 15 min efficiently expelled 84.7% lignin and 78.9% xylan. The residual solid comprised of 74.59% glucan and 7.51% xylan was changed to 84.2% glucose and 78.3% xylose with enzyme stacking of 10FPU/g. This single-step pretreatment had ∼ 4.5 and 6.4 times higher glucose yield than SE-pretreated and untreated corn stover, respectively. Furthermore, SEM, XRD and FTIR indicated the porosity, crystalline changes, methoxy bond-cleavage respectively due to the lignin and hemicellulose expulsion. Thus, the released acetic acid during this process introduced this novel strategy, which significantly builds the viability of biomass in short pretreatment time.     

The effects of four different pretreatments on enzymatic hydrolysis of sweet sorghum bagasse

Four pretreatment processes including ionic liquids, steam explosion, lime, and dilute acid were used for enzymatic hydrolysis of sweet sorghum bagasse. Compared with the other three pretreatment approaches, steam-explosion pretreatment showed the greatest improvement on enzymatic hydrolysis of the bagasse. The maximum conversion of cellulose and the concentration of glucose obtained from enzymatic hydrolysis of steam explosion bagasse reached 70% and 25 g/L, respectively, which were both 2.5 times higher than those of the control (27% and 11 g/L). The results based on the analysis of SEM photos, FTIR, XRD and NMR detection suggested that both the reduction of crystallite size of cellulose and cellulose degradation from the Iα and Iβ to the Fibril surface cellulose and amorphous cellulose were critical for enzymatic hydrolysis. These pretreatments disrupted the crystal structure of cellulose and increased the available surface area, which made the cellulose better accessible for enzymatic hydrolysis.     

Enhanced enzymatic hydrolysis of lignocellulosic biomass pretreated by low-pressure steam autohydrolysis

Summary The use of low-pressure steam autohydrolysis in the pretreatment of corn stover and hybrid poplar has been assessed. In terms of yield of prehydrolyzed solids, minimal by-product formation and extent of subsequent enzymatic saccharification, the results of low-pressure steam pretreatment were found to be as good as or better than those reported for more severe pretreatment processes. Almost complete saccharification of the cellulose in the prehydrolyzed biomass solids was obtained within 24h with a commercial cellulase preparation — Celluclast. The presence of grinding elements (glass beads) during the enzymatic hydrolysis was found to increase the extent of saccharification by 40% to 50% over controls without any grinding elements.     

pH catalyzed pretreatment of corn bran for enhanced enzymatic arabinoxylan degradation

Corn bran is mainly made up of the pericarp of corn kernels and is a byproduct stream resulting from the wet milling step in corn starch processing. Through statistic modeling this study examined the optimization of pretreatment of corn bran for enzymatic hydrolysis. A low pH pretreatment (pH 2, 150 °C, 65 min) boosted the enzymatic release of xylose and glucose and maximized biomass solubilization. With more acidic pretreatment followed by enzymatic hydrolysis the total xylose release was maximized (at pH 1.3) reaching ～ 50% by weight of the original amount present in destarched corn bran, but the enzyme catalyzed xylose release was maximal after pretreatment at approx. pH 2. The total glucose release peaked after pretreatment of approx. pH 1.5 with an enzymatic release of approx. 68% by weight of the original amounts present in destarched corn bran. For arabinose the enzymatic release was negatively affected by the acidic pretreatment as labile arabinosyl-linkages were presumably hydrolysed directly during the pretreatment. A maximum of 60% arabinose release was achieved directly from the optimal (acidic) pretreatment. The total content of diferulic acids, supposedly involved in the cross-linking of the arabinoxylan polymers, decreased by both alkaline and acidic pretreatment pH, with the loss by alkaline pretreatments being highest. No direct correlation between the enzymatic release of xylose and the content of diferulic acids in the substrate could be verified. On the contrary the enzymatic release of xylose was significantly correlated to the total release of arabinose, indicating that the degree of arabinosyl-substitutions on the xylan backbone is an essential parameter for enzymatic hydrolysis of corn bran arabinoxylan.     

Mild pretreatment of yellow poplar biomass using sequential dilute acid and enzymatically-generated peracetic acid to enhance cellulase accessibility

Biomass contains cellulose, xylan and lignin in a complex interwoven structure that hinders enzymatic hydrolysis of the cellulose. To separate these components in yellow poplar biomass, we sequentially pretreated with dilute sulfuric acid and enzymatically-generated peracetic acid. In the first step, the dilute acid with microwave heating (140°C, 5 min) hydrolyzed 90% of xylan. The xylose yield in hydrolysate after dilute acid pretreatment was 83.1%. In the second step, peracetic acid (60°C, 6 h) removed up to 80% of lignin. This sequential pretreatment fractionated biomass into xylan and lignin, leaving a solid residue enriched in cellulose (~80%). The sequential pretreatment enhanced enzymatic digestibility of the cellulase by removal of the other components in biomass. The glucose yield after enzymatic hydrolysis was 90.5% at a low cellulase loading (5 FPU/g of glucan), which is 1.6 and 18 times higher than for dilute acid-pretreated biomass and raw biomass, respectively. This novel sequential pretreatment with dilute acid and peracetic acid efficiently separates the three major components of yellow poplar biomass, and reduces the amount of cellulase needed.     

Quantitative predictions of bioconversion of aspen by dilute acid and SPORL pretreatments using a unified combined hydrolysis factor (CHF)

A combined hydrolysis factor (CHF) was developed to predict xylan hydrolysis during pretreatments of native aspen (Populus tremuloides) wood chips. A natural extension of previously developed kinetic models allowed us to account for the effect of catalysts by dilute acid and two sulfite pretreatments at different pH values. When xylan is modeled as two fractions with different hydrolysis rates, previously identified as fast and slow xylan, the model closely matches the experimental data. Extent of xylan hydrolysis is strongly correlated with pretreatment solids yield, energy consumption for size reduction, and substrate enzymatic digestibility (SED). Composition of the pretreatment hydrolysate was less correlated with extent of hydrolysis due to carbohydrate decomposition reactions. Substrate cellulose enzymatic conversion and enzymatic hydrolysis glucose yield can be predicted to approximately 10% accuracy using CHF alone.     

Feasibility of Manufacturing Cellulose Nanocrystals from the Solid Residues of Second-Generation Ethanol Production from Sugarcane Bagasse

The reuse of the solid residues generated in the production of second-generation (2G) ethanol to obtain high-value products is a potential strategy for improving the economic and environmental viability of the overall process. This study evaluated the feasibility of using the residual solids remaining after the enzymatic hydrolysis of sugarcane bagasse for the production of cellulose nanocrystals (CNC), a valuable bionanomaterial. To this end, sugarcane bagasse subjected to steam explosion (SEB) or liquid hot water (LHWB) pretreatment was hydrolysed using different loadings of a commercial cellulase cocktail. Samples of SEB and LHWB were hydrolysed enzymatically, resulting in glucose releases close to 40 g/L, which would be suitable for producing 2G ethanol by microbial fermentation. The solid residues after the enzymatic hydrolysis step presented cellulose contents of up to 54 %, indicating that a significant amount of recalcitrant crystalline cellulose remained available for subsequent use. These solid residues were purified and submitted to acid hydrolysis, resulting in the successful formation of CNC with crystallinity close to 80 %, lengths of 193–246 nm and diameters of 14–18 nm. The CNC produced presented morphology, dimensions, physical-chemical characteristics, thermal stability and crystallinity within the ranges reported for this type of material. Moreover, the enzyme loading or the type of hydrothermal pretreatment process employed here showed no significant effects on the CNC obtained, indicating that these variables could be flexibly adjusted according to specific interests.     

Novel endophytic yeast Rhodotorula mucilaginosa strain PTD3 I: production of xylitol and ethanol

An endophytic yeast, Rhodotorula mucilaginosa strain PTD3, that was isolated from stems of hybrid poplar was found to be capable of production of xylitol from xylose, of ethanol from glucose, galactose, and mannose, and of arabitol from arabinose. The utilization of 30 g/L of each of the five sugars during fermentation by PTD3 was studied in liquid batch cultures. Glucose-acclimated PTD3 produced enhanced yields of xylitol (67% of theoretical yield) from xylose and of ethanol (84, 86, and 94% of theoretical yield, respectively) from glucose, galactose, and mannose. Additionally, this yeast was capable of metabolizing high concentrations of mixed sugars (150 g/L), with high yields of xylitol (61% of theoretical yield) and ethanol (83% of theoretical yield). A 1:1 glucose:xylose ratio with 30 g/L of each during double sugar fermentation did not affect PTD3's ability to produce high yields of xylitol (65% of theoretical yield) and ethanol (92% of theoretical yield). Surprisingly, the highest yields of xylitol (76% of theoretical yield) and ethanol (100% of theoretical yield) were observed during fermentation of sugars present in the lignocellulosic hydrolysate obtained after steam pretreatment of a mixture of hybrid poplar and Douglas fir. PTD3 demonstrated an exceptional ability to ferment the hydrolysate, overcome hexose repression of xylose utilization with a short lag period of 10 h, and tolerate sugar degradation products. In direct comparison, PTD3 had higher xylitol yields from the mixed sugar hydrolysate compared with the widely studied and used xylitol producer Candida guilliermondii.