Biomimetic catalysis for hemicellulose hydrolysis in corn stover

Efficient and economical hydrolysis of plant cell wall polysaccharides into monomeric sugars is a significant technical hurdle in biomass processing for renewable fuels and chemicals. One possible approach to overcoming this hurdle is a biomimetic approach with dicarboxylic acid catalyst mimicking the catalytic core microenvironment in natural enzymes. This paper reports developments in the use of a dicarboxylic acid catalyst, maleic acid, for hemicellulose hydrolysis in corn stover. Hemicellulose hydrolysis and xylose degradation kinetics in the presence of maleic acid was compared to sulfuric acid. At optimized reaction conditions for each acid, maleic acid hydrolysis results in minimal xylose degradation, whereas sulfuric acid causes 3-10 times more xylose degradation. These results formed the basis for optimizing the hydrolysis of hemicellulose from corn stover using maleic acid. At 40 g/L dry corn stover solid-loading, both acid catalysts can achieve near-quantitative monomeric xylose yield. At higher solids loadings (150-200 g dry stover per liter), sulfuric acid catalyzed hydrolysis results in more than 30% degradation of the xylose, even under the previously reported optimal condition. However, as a result of minimized xylose degradation, optimized biomimetic hydrolysis of hemicellulose by maleic acid can reach approximately 95% monomeric xylose yields with trace amounts of furfural. Fermentation of the resulting unconditioned hydrolysate by recombinant S. cerevisiae results in 87% of theoretical ethanol yield. Enzyme digestibility experiments on the residual corn stover solids show that >90% yields of glucose can be produced in 160 h from the remaining cellulose with cellulases (15 FPU/g-glucan).     

Optimization of furfural production from hemicellulose extracted from delignified palm pressed fiber using a two-stage process

This study aims to optimize the conditions for furfural production from hemicellulose extracted from delignified palm pressed fiber (dPPF) via two-stage process: acid hydrolysis followed by dehydration, using response surface methodology (RSM). The extracted hemicellulose contained 80.8% xylose. In order to convert hemicellulose to xylose in the acid hydrolysis step, there were four important parameters consisting of reaction temperature (100–150 °C), sulfuric acid concentration (1–10% v/v), ratio of sulfuric acid to hemicellulose (L/S ratio) (10, 9, and 8 v/w), and reaction time (30–120 min). The maximum xylose production (12.58 g/L) was achieved at 125 °C, 5.5% sulfuric acid, L/S ratio of 9 mL/g for 30 min with the determination coefficient (R²) value of 0.90. For the dehydration process, two parameters; reaction temperature (120–160 °C) and reaction time (30–150 min), were optimized. The maximum furfural production (8.67 g/L) was achieved at a reaction temperature of 140 °C for 90 min with the determination coefficient (R²) value of 0.93.     

Two-stage pretreatment of rice straw using aqueous ammonia and dilute acid

Liberation of fermentable sugars from recalcitrant lignocellulosic biomass is one of the key challenges in production of cellulosic ethanol. Here we developed a two-stage pretreatment process using aqueous ammonia and dilute sulfuric acid in a percolation mode to improve production of fermentable sugars from rice straw. Aqueous NH? was used in the first stage which removed lignin selectively but left most of cellulose (97%) and hemicellulose (77%). Dilute acid was applied in the second stage which removed most of hemicellulose, partially disrupted the crystalline structure of cellulose, and thus enhanced enzymatic digestibility of cellulose in the solids remaining. Under the optimal pretreatment conditions, the enzymatic hydrolysis yields of the two-stage treated samples were 96.9% and 90.8% with enzyme loadings of 60 and 15FPU/g of glucan, respectively. The overall sugar conversions of cellulose and hemicellulose into glucose and xylose by enzymatic and acid hydrolysis reached 89.0% and 71.7%, respectively.     

Optimization of acid hydrolysis from the hemicellulosic fraction of Eucalyptus grandis residue using response surface methodology

Biotechnological conversion of biomass into fuels and chemicals requires hydrolysis of the polysaccharide fraction into monomeric sugars. Hydrolysis can be performed enzymatically and with dilute or concentrate mineral acids. The present study used dilute sulfuric acid as a catalyst for hydrolysis of Eucalyptus grandis residue. The purpose of this paper was to optimize the hydrolysis process in a 1.4 l pilot-scale reactor and investigate the effects of the acid concentration, temperature and residue/acid solution ratio on the hemicellulose removal and consequently on the production of sugars (xylose, glucose and arabinose) as well as on the formation of by-products (furfural, 5-hydroxymethylfurfural and acetic acid). This study was based on a model composition corresponding to a 2(3) orthogonal factorial design and employed the response surface methodology (RSM) to optimize the hydrolysis conditions, aiming to attain maximum xylose extraction from hemicellulose of residue. The considered optimum conditions were: H(2)SO(4) concentration of 0.65%, temperature of 157 degrees C and residue/acid solution ratio of 1/8.6 with a reaction time of 20 min. Under these conditions, 79.6% of the total xylose was removed and the hydrolysate contained 1.65 g/l glucose, 13.65 g/l xylose, 1.55 g/l arabinose, 3.10 g/l acetic acid, 1.23 g/l furfural and 0.20 g/l 5-hydroxymethylfurfural.     

Comparative material balances around pretreatment technologies for the conversion of switchgrass to soluble sugars

For this project, six chemical pretreatments were compared for the Consortium for Applied Fundamentals and Innovation (CAFI): ammonia fiber expansion (AFEX), dilute sulfuric acid (DA), lime, liquid hot water (LHW), soaking in aqueous ammonia (SAA), and sulfur dioxide (SO₂). For each pretreatment, a material balance was analyzed around the pretreatment, optional post-washing step, and enzymatic hydrolysis of Dacotah switchgrass.All pretreatments + enzymatic hydrolysis solubilized over two-thirds of the available glucan and xylan. Lime, post-washed LHW, and SO₂ achieved >83% total glucose yields. Lime, post-washed AFEX, and DA achieved >83% total xylose yields. Alkaline pretreatments, except AFEX, solubilized the most lignin and a portion of the xylan as xylo-oligomers. As pretreatment pH decreased, total solubilized xylan and released monomeric xylose increased. Low temperature-long time or high temperature-short time pretreatments are necessary for high glucose release from late-harvest Dacotah switchgrass but high temperatures may cause xylose degradation.     

Dilute-acid hydrolysis for fermentation of the Bolivian straw material Paja Brava

Hydrolysis of the straw material Paja Brava, a sturdy grass characteristic for the high plains of Bolivia, was studied in order to find suitable conditions for hydrolysis of the hemicellulose and cellulose parts. Dried Paja Brava material was pre-steamed, impregnated with dilute sulfuric acid (0.5% or 1.0% by wt), and subsequently hydrolyzed in a reactor at temperatures between 170 and 230 degrees C for a reaction time between 3 and 10 min. The highest yield of xylose (indicating efficient hydrolysis of hemicellulose) were found at a temperature of 190 degrees C, and a reaction time of 5-10 min, whereas considerably higher temperatures (230 degrees C) were needed for hydrolysis of cellulose. Fermentability of hemicellulose hydrolyzates was tested using the xylose-fermenting yeast species Pichia stipitis, Candida shehatae and Pachysolen tannophilus. The fermentability of hydrolyzates decreased strongly for hydrolyzates produced at temperatures higher than 200 degrees C.     

Dilute acid pretreatment of rye straw and bermudagrass for ethanol production

Ethanol production from lignocellulosic materials provides an alternative energy production system. Rye and bermudagrass that are used in hog farms for nutrient uptake from swine wastewater have the potential for fuel ethanol production because they have a relative high cellulose and hemicellulose content. Dilute sulfuric acid pretreatment of rye straw and bermudagrass before enzymatic hydrolysis of cellulose was investigated in this study. The biomass at a solid loading rate of 10% was pretreated at 121 degrees C with different sulfuric acid concentrations (0.6, 0.9, 1.2 and 1.5%, w/w) and residence times (30, 60, and 90 min). Total reducing sugars, arabinose, galactose, glucose, and xylose in the prehydrolyzate were analyzed. In addition, the solid residues were hydrolyzed by cellulases to investigate the enzymatic digestibility. With the increasing acid concentration and residence time, the amount of arabinose and galactose in the filtrates increased. The glucose concentration in the prehydrolyzate of rye straw was not significantly influenced by the sulfuric acid concentration and residence time, but it increased in the prehydrolyzate of bermudagrass with the increase of pretreatment severity. The xylose concentration in the filtrates increased with the increase of sulfuric acid concentration and residence time. Most of the arabinan, galactan and xylan in the biomass were hydrolyzed during the acid pretreatment. Cellulose remaining in the pretreated feedstock was highly digestible by cellulases from Trichoderma reesei.     

酵母发酵蔗渣半纤维素水解物生产木糖酶

采用二次正交旋转组合设计研究了蔗渣半纤维素水解过程中硫酸浓度与液 固比对木糖收率的影响。回归分析表明 ,这两个因素与木糖的收率之间存在显著的回归关系。通过回归方程优化水解条件 ,当硫酸浓度 2 .4g L ,液 固 =6 .2 ,在蒸汽压力 2 .5× 10 4Pa的条件下水解 2 .5h ,10 0g蔗渣可水解生成木糖约 2 4g。大孔树脂吸附层析处理蔗渣半纤维素水解物 ,能有效地减少其中的酵母生长抑制物含量 ,显著改善水解物的发酵性能。用大孔树脂在pH 2条件下处理过的蔗渣半纤维素水解物作基质 ,含木糖 2 0 0g L ,产木糖醇酵母菌株CandidatropicalisAS2 .1776发酵 110h耗完基质中的木糖 ,生成木糖醇 12 7g L ,产物转化率 0 .6 4(木糖醇g 木糖g) ,产物生成速率 1.15g L·h .     

A study on the pretreatment of a sugarcane bagasse sample with dilute sulfuric acid

Experiments based on a 2³ central composite full factorial design were carried out in 200-ml stainless-steel containers to study the pretreatment, with dilute sulfuric acid, of a sugarcane bagasse sample obtained from a local sugar–alcohol mill. The independent variables selected for study were temperature, varied from 112.5°C to 157.5°C, residence time, varied from 5.0 to 35.0 min, and sulfuric acid concentration, varied from 0.0% to 3.0% (w/v). Bagasse loading of 15% (w/w) was used in all experiments. Statistical analysis of the experimental results showed that all three independent variables significantly influenced the response variables, namely the bagasse solubilization, efficiency of xylose recovery in the hemicellulosic hydrolysate, efficiency of cellulose enzymatic saccharification, and percentages of cellulose, hemicellulose, and lignin in the pretreated solids. Temperature was the factor that influenced the response variables the most, followed by acid concentration and residence time, in that order. Although harsher pretreatment conditions promoted almost complete removal of the hemicellulosic fraction, the amount of xylose recovered in the hemicellulosic hydrolysate did not exceed 61.8% of the maximum theoretical value. Cellulose enzymatic saccharification was favored by more efficient removal of hemicellulose during the pretreatment. However, detoxification of the hemicellulosic hydrolysate was necessary for better bioconversion of the sugars to ethanol.     

青贮对柳枝稷制取燃料乙醇转化过程的影响

青贮是一种传统的生物质原料保存方法,广泛应用于纤维素乙醇炼制领域尚需要考察其对原料品质和下游乙醇转化过程的影响。文中以秋季(初、中和末)收割的柳枝稷为原料,通过青贮、高温水热(LHW)预处理、纤维素酶水解和同步糖化与发酵(SSF)实验对上述问题予以回答。结果显示,秋季初收割的柳枝稷以不同湿度青贮后pH均小于4.0,干重损失小于2%,各主要成分与青贮前相比无明显变化;LHW预处理中青贮样品半纤维素水解率普遍高于未贮存样品,但青贮同样使原料获得了更高的发酵抑制物产生水平;青贮柳枝稷葡萄糖、木糖和半乳糖产量(预处理+酶水解)高于未贮存柳枝稷;经过168 h的SSF,青贮样品乙醇浓度为12.1 g/L,未贮存的秋季初、秋季中和秋季末柳枝稷为底物的浓度分别为10.3 g/L、9.7 g/L和10.6 g/L。综上,青贮有助于提高柳枝稷LHW预处理效率、酶水解率和乙醇产量。     

Kinetic modeling analysis of maleic acid-catalyzed hemicellulose hydrolysis in corn stover

Maleic acid-catalyzed hemicellulose hydrolysis reaction in corn stover was analyzed by kinetic modeling. Kinetic constants for Saeman and biphasic hydrolysis models were analyzed by an Arrhenius-type expansion which include activation energy and catalyst concentration factors. The activation energy for hemicellulose hydrolysis by maleic acid was determined to be 83.3 +/- 10.3 kJ/mol, which is significantly lower than the reported E(a) values for sulfuric acid catalyzed hemicellulose hydrolysis reaction. Model analysis suggest that increasing maleic acid concentrations from 0.05 to 0.2 M facilitate improvement in xylose yields from 40% to 85%, while the extent of improvement flattens to near-quantitative by increasing catalyst loading from 0.2 to 1 M. The model was confirmed for the hydrolysis of corn stover at 1 M maleic acid concentrations at 150 degrees C, resulting in a xylose yield of 96% of theoretical. The refined Saeman model was used to evaluate the optimal condition for monomeric xylose yield in the maleic acid-catalyzed reaction: low temperature reaction conditions were suggested, however, experimental results indicated that bi-phasic behavior dominated at low temperatures, which may be due to the insufficient removal of acetyl groups. A combination of experimental data and model analysis suggests that around 80-90% xylose yields can be achieved at reaction temperatures between 100 and 150 degrees C with 0.2 M maleic acid.     

A novel cleaning process for industrial production of xylose in pilot scale from corncob by using screw-steam-explosive extruder

Steam explosion is the most promising technology to replace conventional acid hydrolysis of lignocellulose for biomass pretreatment. In this paper, a new screw-steam-explosive extruder was designed and explored for xylose production and lignocellulose biorefinery at the pilot scale. We investigated the effect of different chemicals on xylose yield in the screw-steam-explosive extrusion process, and the xylose production process was optimized as followings: After pre-impregnation with sulfuric acid at 80 °C for 3 h, corncob was treated at 1.55 MPa with 9 mg sulfuric acid/g dry corncob (DC) for 5.5 min, followed by countercurrent extraction (3 recycles), decoloration (activated carbon dosage 0.07 g/g sugar, 75 °C for 40 min), and ion exchange (2 batches). Using this process, 3.575 kg of crystal xylose was produced from 22 kg corncob, almost 90 % of hemicellulose was released as monomeric sugar, and only a small amount of by-products was released (formic acid, acetic acid, fural, 5-hydroxymethylfurfural, and phenolic compounds were 0.17, 1.14, 0.53, 0.19, and 1.75 g/100 g DC, respectively). All results indicated that the screw-steam-explosive extrusion provides a more effective way to convert hemicellulose into xylose and could be an alternative method to traditional sulfuric acid hydrolysis process for lignocellulose biorefinery.     

The effect of metal salts on the decomposition of sweet sorghum bagasse in flow-through liquid hot water

The impact of the metal salts NaCl, KCl, CaCl(2), MgCl(2), FeCl(3), FeCl(2), and CuCl(2), particularly the latter, on the decomposition of hemicellulose and lignin from sweet sorghum bagasse in liquid hot water pretreatment processing was studied in an attempt to enhance the recovery of sugars. Transition metal chlorides significantly enhanced the hemicellulose removal compared to the alkaline earth metal chlorides and alkaline metal chlorides, contributing to the formation of a saccharide-metal cation intermediate complex. FeCl(2) greatly increased xylose degradation and about 60% xylan was converted into non-saccharide products. In contrast, an excellent total and monomeric xylose recovery was obtained after the CuCl(2) pretreatment. Most of the lignin was deposited on the surface of the residual solid with droplet morphologies after this pretreatment, and about 20% was degraded into monomeric products. The total recovery of sugars from sweet sorghum bagasse with 0.1% CuCl(2) solution pretreatment and 48 h enzymatic digestibility, reached 90.4%, which is superior to the recovery using hot water pretreatment only.     

Optimizing dilute acid hydrolysis of hemicellulose in a nitrogen-rich cellulosic material--dairy manure

Effective dilute acid hydrolysis of dairy manure which contains roughly 12% hemicellulose on a dry matter basis can produce a variety of mono-sugars such as arabinose, xylose and galactose, as well as to further benefit utilization of cellulose in the manure. To enhance the effectiveness of this dilute acid hydrolysis, the effect of manure nitrogen content was studied because some reactions such as the browning reaction between amino acids and reducing sugars and acid-base reactions involving ammonia and acid interfere with the hydrolysis. Two dairy manure samples were used to study this nitrogen effect; the original manure and the pretreated manure derived from a solid/liquid separation pretreatment. The pretreated manure had a total nitrogen content of 1.3% dry matter (DM) while the original dairy manure had twice that amount with a total nitrogen content of 2.6% DM. Results found that the optimal conditions for hydrolysis of manure hemicellulose were 2 h reaction time, 1% sulfuric acid concentration, 135 degrees C, and 10% sample concentration using the pretreated dairy manure as raw material. Under these conditions the corresponding sugar yield from hemicellulose was 111% and sugar concentration in the solution reached 16.5 g/l. At the same time, the hydrolyzed solid had 43% DM of cellulose, which was much higher than both the original manure containing 22% and the pretreated manure with 32%.     

Combination of dilute acid and ionic liquid pretreatments of sugarcane bagasse for glucose by enzymatic hydrolysis

Loss of hemicellulose and inability to effectively decrystallize cellulose, result in low yield and high cost of sugars derived from biomass. In this work, dilute sulfuric acid pretreatment could easily remove most of hemicellulose as sugars. The sugars were successfully used for 2,3-butanediol production with relative high yield (36.1%). Then, the remained solid residue after acid-pretreatment was further pretreated by ionic liquid (IL) to decrease its crystallinity for subsequent enzymatic saccharification. The combination of dilute acid- and IL-pretreatments resulted in significant higher glucose yield (95.5%) in enzymatic saccharification, which was more effective than using dilute acid- or IL-pretreatment alone. This strategy seems a promising route to achieve high yield of sugars from both hemicellulose and cellulose for biorefinery.     

Structure of hemicelluloses isolated from Canavalia ensiformis and Triticum aestivum straws

Hemicellulose was extracted from horse bean and wheat straws in a yield of 5 and 9% respectively. The whole hemicellulose was hydrolysed and the molar ratio of the component monosaccharides was determined. Uronic acid, galactose, glucose, arabinose and xylose were found in both hemicelluloses. The molar ratio of the monosaccharides was determined in each of 4 fractions derived from the saccharide. The main fractions (B and C) were partially hydrolysed and an oligosaccharide containing arabinose and xylose (1:1) was isolated from both hemicelluloses. Another oligosaccharide containing xylose and glucose (2:1) was also isolated from wheat straw hemicellulose. Periodate oxidation was carried out on fractions B and C. The formic acid and the consumed periodate were determined. Each hemicellulose was subjected to Smith's degradation. Glycerol, erythrytol and compounds containing xylose and glycerol (1:1), and xylose and erythrytol (1:1) were isolated.     

Degradation of Perennial Ryegrass Leaf and Stem Cell Walls by the Anaerobic Fungus Neocallimastix sp. Strain CS3b

The degradation of cell walls isolated from stems and leaves of perennial ryegrass by the anaerobic fungus Neocallimastix sp. strain CS3b was studied in a defined medium. The combined cellulose and hemicellulose fraction represented 53.1 (wt/wt) and 63.3% (wt/wt) of the dry weight of control grass leaf and stem cell walls, respectively. In both leaf and stem cell walls, glucose was the major neutral monosaccharide, followed by xylose, arabinose, and galactose. After 2 days of fermentation with Neocallimastix sp. strain CS3b, treated cell walls contained smaller amounts of neutral sugars compared with those of undigested cell walls. These results were more evident for glucose, xylose, and arabinose than for galactose. Furthermore, the sugar content of leaf cell walls decreased before a decline in the sugar content of stem cell walls was observed. Data from formate and hydrogen production indicated that the growth of Neocallimastix sp. strain CS3b was completed in 4 days in the culture system used. During this period, the fungus liberated about 95% of the fermentable sugars in untreated material. On a percentage basis, no significant differences were found in final extent of degradation of glucose, xylose, and arabinose. Galactose, however, was degraded to a lesser extent.     

Fermentation of lignocellulosic sugars to acetic acid by <Emphasis Type="Italic">Moorella thermoacetica</Emphasis>

A systematic study of bioconversion of lignocellulosic sugars to acetic acid by Moorella thermoacetica (strain ATCC 39073) was conducted. Four different water-soluble fractions (hydrolysates) obtained after steam pretreatment of lignocellulosic biomass were selected and fermented to acetic acid in batch fermentations. M. thermoacetica can effectively ferment xylose and glucose in hydrolysates from wheat straw, forest residues, switchgrass, and sugarcane straw to acetic acid. Xylose and glucose were completely utilized, with xylose being consumed first. M. thermoacetica consumed up to 62 % of arabinose, 49 % galactose and 66 % of mannose within 72 h of fermentation in the mixture of lignocellulosic sugars. The highest acetic acid yield was obtained from sugarcane straw hydrolysate, with 71 % of theoretical yield based on total sugars (17 g/L acetic acid from 24 g/L total sugars). The lowest acetic acid yield was observed in forest residues hydrolysate, with 39 % of theoretical yield based on total sugars (18 g/L acetic acid from 49 g/L total sugars). Process derived compounds from steam explosion pretreatment, including 5-hydroxymethylfurfural (0.4 g/L), furfural (0.1 g/L) and total phenolics (3 g/L), did not inhibit microbial growth and acetic acid production yield. This research identified two major factors that adversely affected acetic acid yield in all hydrolysates, especially in forest residues: (i) glucose to xylose ratio and (ii) incomplete consumption of arabinose, galactose and mannose. For efficient bioconversion of lignocellulosic sugars to acetic acid, it is imperative to have an appropriate balance of sugars in a hydrolysate. Hence, the choice of lignocellulosic biomass and steam pretreatment design are fundamental steps for the industrial application of this process.     

Dilute acid hydrolysis of wheat straw hemicellulose at moderate temperature: a simplified kinetic model

Wheat straw has been hydrolized with sulfuric acid at 34 and 90 degrees C. The treatment at 90 degrees C yields complete solubilization of hemicellulose to xylose and arabinose without significant amounts of furfural. The influence of acid concentration was studied and the kinetics of the acid-catalyzed hydrolysis has been modeled suggesting a two-consecutive reactions mechanism. This model is useful to explain the different behavior of the concentration of the two main sugars produced. The enhanced cellulose accessibility to enzymatic attack is also reported.     

Hydrothermal treatment of wheat straw at pilot plant scale using a three-step reactor system aiming at high hemicellulose recovery, high cellulose digestibility and low lignin hydrolysis

A pilot plant (IBUS) consisting of three reactors was used for hydrothermal treatment of wheat straw (120-150 kg/h) aiming at co-production of bioethanol (from sugars) and electricity (from lignin). The first reactor step was pre-soaking at 80 degrees C, the second extraction of hemicellulose at 170-180 degrees C and the third improvement of the enzymatic cellulose convertibility at 195 degrees C. Water added to the third reactor passed countercurrent to straw. The highest water addition (600 kg/h) gave the highest hemicellulose recovery (83%). With no water addition xylose degradation occurred resulting in low hemicellulose recovery (33%) but also in high glucose yield in the enzymatic hydrolysis (72 g/100g glucose in straw). Under these conditions most of the lignin was retained in the fibre fraction, which resulted in a lignin rich residue with high combustion energy (up to 31 MJ/kg) after enzymatic hydrolysis of cellulose and hemicellulose.