Levulinic acid production from wheat straw

Studies were carried out on the effects of temperature, acid concentration, liquid:solid ratio and reaction time on levulinic acid production from wheat straw using response surface methodology. The P-value of the coefficient for acid concentration was 0.0002, suggesting that this was highly significant. The quadratic effects of temperature and liquid:solid ratio were also significant and their P-values were <0.0001 and 0.0027, respectively. The coefficient determination (R(2)) was good for the second-order model. The optimal conditions for levulinic acid production from wheat straw were 209.3 degrees C, 3.5% acid concentration, 15.6 liquid:solid ratio and 37.6 min of reaction time resulted 19.86% yield.     

Organosolv pulping of wheat straw by use of phenol

A central composite design was used to investigate the influence of the cooking conditions (time, temperature and phenol concentration) for wheat straw with phenol-water mixtures on the properties of the pulp obtained (yield and holocellulose, -cellulose, lignin and ethanol-benzene extractable contents) and the pH of the resulting wastewater. A second-order polynomial model consisting of three independent process variables was found to accurately describe the organosolv pulping of wheat straw. The equations derived predict the yield, the holocellulose, -cellulose, lignin and ethanol-benzene extractable contents of the pulp, and the pH of the wastewater with multiple-R, R² and adjusted-R² high values. The process variables must be set at low variables in order to ensure a high yield and pH. Conversely, if high holocellulose and -cellulose contents, and low lignin and ethanol-benzene extractable contents are desired, then a high temperature (200°C), long cooking time (120 min), and intermediate phenol concentration (65%) must be used.     

Optimization of dilute sulfuric acid pretreatment of corn stover for enhanced xylose recovery and xylitol production

Pretreatment steps are necessary for the bioconversion of corn stover (CS) to xylitol. In order to optimize the pretreatment parameters, the sulfuric acid concentration, sulfuric acid residence time, and solid slurry concentration were evaluated, based on the glucose and xylose recovered from CS at the relatively low temperature of 120°C. The optimum conditions were found to be pretreatment with 2.5% (w/v) sulfuric acid for 1.5 h, with a solid slurry concentration of 90 g/L. Under these conditions, the hydrolysis rates of glucan and xylan were approximately 26.0 and 82.8%, respectively. High xylitol production (10.9 g/L) and conversion yield (0.97 g/g) were attained from corn stover hydrolysate (CSH) without detoxification and any nutrient addition. Our results were similar for xylitol production in synthetic medium under the same conditions. The non-necessity of both the hydrolysate detoxification step and nutrient addition to the CSH is undoubtedly promising for scale-up application on an industrial scale, because this medium-based manufacturing process is expected to reduce the production cost of xylitol. The present study demonstrates that value-added xylitol could be effectively produced from CS under optimized pretreatment conditions, especially with CSH as the substrate material.     

超临界下有机酸对稻秆水解糖化的影响

采用间歇式反应器在超临界条件下,以有机酸（甲酸、乙酸和丙酸）为催化剂对稻秆进行水解糖化研究,重点考察反应温度、反应时间、固液比对还原糖产率的影响。实验表明：有机酸的加入有利于稻秆的水解糖化,稻秆水解速率和还原糖产量都有所提高,这种趋势在加入甲酸时最为明显;随着反应时间的延长,还原糖产量会逐渐减少;适当提高固液比有助于增加还原糖产量。稻秆超临界水解糖化的最佳条件：甲酸体积分数3％、固液比4：60（g／mL）、反应温度410℃、反应时间5min,在此条件下,还原糖产量最高,达6．65g／L。     

Production of xylooligosaccharides by controlled acid hydrolysis of lignocellulosic materials

Different agricultural wastes, namely tobacco stalk (TS), cotton stalk (CS), sunflower stalk (SS), and wheat straw (WS), were used for the production of xylooligosaccharide (XO). XO production was performed by acid hydrolysis of xylan, which was obtained by alkali extraction from these agricultural wastes. The major component of these agricultural wastes was determined as cellulose (30-42%), followed by xylan (20%) and lignin (20-27%). Xylans from these wastes had mainly xylose (85-96%) with small amount of glucose, while wheat straw xylan contained also arabinose. The best xylan conversion into XOs was achieved with 0.25 M H₂SO₄ with 30-min reaction time. Under these conditions, the XO yield was between 8% and 13%. The yield of XOs depends on both acid concentration and hydrolysis time, but the yield of monosaccharide depends on the structure and composition of xylan besides acid concentration and the time. The more branched xylan, WSX, gave the highest monosaccharide (∼16%) and furfural (∼49 mg/100 g xylan) yield. This research showed that all xylans from selected agricultural wastes generated XOs with similar profiles, and these oligosaccharides could be used as functional food ingredients or soluble substrates for xylanases.     

Monosaccharide yields and lignin removal from wheat straw in response to catalyst type and pH during mild thermal pretreatment

The influence of various low temperature (140 °C) pretreatments, using different acid and alkaline catalysts and different pH values, was studied for enzymatic hydrolysis of wheat straw. The pretreated wheat straw was treated by a standard blend of Celluclast 1.5L and Novozym 188. While pretreatment at pH 1 gave the highest yield of saccharides in the liquid fraction, the solid fraction was more susceptible to enzymatic attack when pretreated at pH 13. The highest yields were obtained after pretreatment with hydrochloric acid at pH 1, and with sodium hydroxide at pH 13 when enzymatic hydrolysis was employed. A two-step pretreatment strategy at pH 1 (hydrochloric acid) and subsequently at pH 13 (sodium hydroxide) released 69% and 95% of the theoretical maximal amounts of glucose and xylose, respectively. Furthermore, this two-step pretreatment removed 68% of the lignin from the straw with only minor losses of monosaccharides and production of only low amounts of inhibitors. Type of catalyst and pH indeed influenced the monosaccharide yields and lignin removal from wheat straw, and need more attention in the choice of pretreatment strategy.     

Hydrolysis of wheat straw hemicellulose with trifluoroacetic acid. Fermentation of xylose with Pachysolen tannophilus

Treatment of wheat straw with 1N trifluoroacetic acid (TFA) for 7 h at reflux temperature yielded 23% xylose based upon initial straw weight. This corresponds to about an 80% xylose yield based on the xylan content of the hemicellulose. The cellulose component of wheat straw was largely unaffected, as evidenced by low glucose yields. Decomposition of xylose by prolonged refluxing (23 h) was minimal in 1N TFA compared to 1N HCl. Treatment of wheat straw with refluxing 1N TFA converts about 10% of the lignin initially present in straw into water-soluble lignin fragments. Fermentation of the xylose-rich wheat straw hydrolyzate to ethanol with Pachysolen tannophilus was comparable to the fermentation of reagent grade xylose, indicating that furfural and toxic lignin by-products were not produced by 1N TFA in sufficient amounts to impair cell growth and ethanol production. Cellulase treatment of the wheat straw residue after TFA hydrolysis resulted in a 70-75% conversion of the cellulose into glucose.     

Acidogenic and methanogenic fermentation of causticized straw

The effects of pretreatment process variables [straw concentration between 20 and 90 kg volatile solids (VS)/m(3), temperature between 30 and 85 degrees C, and alkaline dosage between 0 and 80 g NaOH/kg VS] on acidogenesis and methanogenesis were investigated. Rates of acidogenesis and methanogenesis were determined using firstorder kinetics, and ultimate acid and methane yields were measured. The acid yield was not affected by pretreatment concentration or temperature, but increased as alkaline dosage increased. The acidogenesis rate was not affected by pretreatment temperature or alkaline dosage, but decreased as the substrate concentration increased. This decrease in the acidogenesis rate was attributed to a decrease in the inoculum: substrate ratio as the substrate concentration increased. The methane yield and methanogenesis rate were not affected by pretreatment substrate concentration or temperature, and both increased with alkaline dosage up to about 40 g NaOH/kg VS, then remained relatively constant above 40 g NaOH/kg VS.     

Optimization of the pretreatment of rice straw hemicellulosic hydrolyzates for microbial production of xylitol

Hemicellulosic hydrolyzate obtained from rice straw was evaluated to determine if it was a suitable fementation medium for the production of xylitol byCandida mogii ATCC 18364. To obtain xylose selectively from rice straw, it is important to establish rapid hydrolysis conditions that yield xylose-rich substrates. The results of hydrolysis experiments indicated that the optimal reaction conditions for the recovery of xylose from rice straw hemicellulose were obtained using a sulfuric acid concentration of 1.5%, a reaction temperature of 130°C, a reaction time of 20 min and a solid to liquid ratio of 1∶10. Because the fermentation of concentrated acid hydrolyzates can be inhibited by compounds present in the raw material or produced during the hydrolysis process, various methods were tested to determine if they could detoxify the hydrolyzates and thus improve xylitol production. The greatest xylitol yield (0.53 g/g) and volumetric productivity (0.38 g/L·h) were obtained when an overlimed hydrolyzate was treated with activated charcoal.     

Optimization of processing conditions for the fractionation of triticale straw using pressurized low polarity water

Pressurized low polarity water (PLPW) fractionation of triticale straw was optimized to maximize hemicellulose and lignin yield, and to produce a cellulose rich fraction for biofuels production. The optimum PLPW conditions for hemicellulose yield was determined to be 165 °C, with a flow rate of 115 mL/min, and a solvent-to-solid ratio of 60 mL/g. Hemicellulose and lignin yield generally increased with increasing temperature and solvent-to-solid ratio. There was a small decrease in hemicellulose yield with an increase in flow rate. Minimum lignin content of the triticale straw residue after extraction was predicted to occur at a processing condition of 206 °C, 160 mL/min, and 67 mL/g. PLPW was successful in removing 73-78% of the hemicellulose, leaving a cellulose rich fraction (65% glucose concentration). Lignin was equally distributed between the solid residues and the extracts and most of the hemicellulose was extracted in oligomer form. Remaining solid residues after fractionation were highly digestible by cellulase enzymes.     

Wheat as a dual crop for biorefining: Straw quality parameters and their interactions with nitrogen supply in modern elite cultivars

Agricultural residues, such as straw, offer an opportunity to produce biofuels and chemicals in biorefineries without compromising food production. The ideal “dual‐purpose cultivar” would have high yield of grain and straw. In addition, the straw should be easy to process in a biorefinery: It should have good degradability, high concentration of carbohydrates, and low concentration of ash. Nitrogen (N) is an essential nutrient important for plant growth, crop yield and grain quality. However, N production and application comes with a high cost and high environmental footprint. The N application should consequently be based on an economical optimum. Limited knowledge exists on how N application affects the potential of straw for biorefining, for example, straw yield and quality. This study, conducted over three cropping seasons, investigated the effect of N supply on the biorefining potential and included 14 wheat cultivars and one triticale cultivar. The N supply directly affected the yield of straw and grain. In addition, the protein concentration in grain and straw increased, but the composition of the straw with respect to carbohydrates and lignin was largely unaffected by N supply. The only significant change was a lower silicon concentration at increasing N application rate, which could be beneficial for lignin valorization in biorefineries. Likely due to the negligible changes in cell wall composition, the effect of N application rate on straw degradability was not significant. N application should therefore primarily be optimized with respect to grain quality and overall yield of grain and straw. Differences between cultivars were also minor with respect to their performance in a biorefinery process. From a breeding and agronomic perspective, focus should therefore be put on maximizing the biomass output from the field, that is, selecting the cultivar with highest grain and straw yield and optimizing the application of fertilizer to get optimum N use efficiency.     

Dilute acid pretreatment, enzymatic saccharification and fermentation of wheat straw to ethanol

Wheat straw consists of 48.57 ± 0.30% cellulose and 27.70 ± 0.12% hemicellulose on dry solid (DS) basis and has the potential to serve as a low cost feedstock for production of ethanol. Dilute acid pretreatment at varied temperature and enzymatic saccharification were evaluated for conversion of wheat straw cellulose and hemicellulose to monomeric sugars. The maximum yield of monomeric sugars from wheat straw (7.83%, w/v, DS) by dilute H₂SO₄ (0.75%, v/v) pretreatment and enzymatic saccharification (45 °C, pH 5.0, 72 h) using cellulase, β-glucosidase, xylanase and esterase was 565 ± 10 mg/g. Under this condition, no measurable quantities of furfural and hydroxymethyl furfural were produced. The yield of ethanol (per litre) from acid pretreated enzyme saccharified wheat straw (78.3 g) hydrolyzate by recombinant Escherichia coli strain FBR5 was 19 ± 1 g with a yield of 0.24 g/g DS. Detoxification of the acid and enzyme treated wheat straw hydrolyzate by overliming reduced the fermentation time from 118 to 39 h in the case of separate hydrolysis and fermentation (35 °C, pH 6.5), and increased the ethanol yield from 13 ± 2 to 17 ± 0 g/l and decreased the fermentation time from 136 to 112 h in the case of simultaneous saccharification and fermentation (35 °C, pH 6.0).     

Bioconversion of wheat straw to ethanol: Chemical modification,enzymatic hydrolysis,and fermentation

Native wheat straw (WS) was pretreated with various concentrations of H₂SO₄ and NaOH followed by secondary treatments with ethylene diamine (EDA) and NH₄OH prior to enzymatic saccharification. Conversion of the cellulosic component to sugar varied with the chemical modification steps. Treatment solely with alkali yield 51–75% conversion, depending on temperature. Acid treatment at elevated tempeatures showed a substantial decrease in the hemicellulose component, whereas EDA-treated WS (acid pretreated) showed a 69–75% decrease in the lignin component. Acid-pretreated EDA-treated straw yielded a 98% conversion rate, followed by 83% for alkali–NH₄OH treated straws. In other experiments, WS was pretreated with varying concentration of H₂SO₄ or NaOh followed by NH₄OH treatment prior to enzymatic hydrolysis. Pretreatment of straw with 2% NaOH for 4 h coupled to enzymatic hydrolysis yield a 76% conversion of the cellulosic component. Acid–base combination pretreatment yielded only 43% conversions. A reactor column was subsequently used to measure modification–saccharification–fermentation for wheat straw conversion on a larger scale. Thirty percent conversions of wheat straw cellulosics to sugar were observed with subsequent fermentation to alcohol. The crude cellulase preparation yielded considerable quantities of xylose in addition to the glucose. Saccharified materials were fermented directly with actively proliferating proliferating yeast cells without concentration of the sugars.     

Effect of inhibitors formed during wheat straw pretreatment on ethanol fermentation by Pichia stipitis

The inhibitory effect of the main inhibitors (acetic acid, furfural and 5-hydroxymethylfurfural) formed during steam explosion of wheat straw was studied through ethanol fermentations of model substrates and hydrolysates from wheat straw by Pichia stipitis. Experimental results showed that an increase in acetic acid concentration led to a reduction in ethanol productivity and complete inhibition was observed at 3.5 g/L. Furfural produced a delay on sugar consumption rates with increasing concentration and HMF did not exert a significant effect. Fermentations of the whole slurry from steam exploded wheat straw were completely inhibited by a synergistic effect due to the presence of 1.5 g/L acetic acid, 0.15 g/L furfural and 0.05 g/L HMF together with solid fraction. When using only the solid fraction from steam explosion, hydrolysates presented 0.5 g/L of acetic acid, whose fermentations have submitted promising results, providing an ethanol yield of 0.45 g ethanol/g sugars and the final ethanol concentration reached was 12.2 g/L (10.9 g ethanol/100 g DM).     

Experimental studies for levulinic acid production from whole kernel grain sorghum.

Levulinic acid has potential as an important basic chemical material. This study proposed a method of making levulinic acid using abundant and low cost whole kernel sorghum grain as the raw material. Flour made from grinding whole kernel sorghum grains was blended with 2%, 5% and 8% aqueous solutions of sulfuric acid. Mixtures were heated to 160 or 200 degrees C in a pressurized reactor. A stepwise heating scheme helped improve the yield of levulinic acid. Levulinic acid yield was determined based on sorghum flour content, as opposed to total sorghum mass. Levulinic acid yield increased as reaction temperature increased. Higher sulfuric acid concentration also significantly increased the levulinic acid yield. However, flour loading had an adverse effect on levulinic acid yield. A maximum yield of 32.6% levulinic acid was achieved at 200 degrees C, 8% sulfuric acid concentration and 10% flour loading. A linear regression model was capable of predicting the levulinic acid yield with respect to effects of reaction temperature, mineral acid concentration and flour loading (R2 = 0.88).     

Alkaline pre-treatment of oilseed rape straw for bioethanol production: evaluation of glucose yield and pre-treatment energy consumption

The objective of the research was to investigate the effect of biomass loading, alkali (NaOH) concentration and pre-treatment time on the yield of glucose obtained following alkaline pre-treatment and enzymatic hydrolysis of oilseed rape (OSR) straw. A maximum glucose yield of (440.6 ± 14.9) g glucose kg⁻¹ biomass was obtained when OSR straw was pre-treated at a biomass loading of 50 g kg⁻¹ and an alkali concentration of 0.63 mol dm⁻³ NaOH for 30 min. The energy efficiency of glucose extraction (0.39 kg glucose MJ⁻¹ consumed) was highest when OSR straw was pre-treated at a biomass loading of 50 g kg⁻¹ and an alkali concentration of 0.63 or 0.75 mol dm⁻³ for 30 min. The study demonstrated alkaline pre-treatment of OSR straw is superior to acid pre-treatment in terms of glucose yield and energy efficiency.     

Biogas Production by Co-Digestion of Goat Manure with Three Crop Residues

Goat manure (GM) is an excellent raw material for anaerobic digestion because of its high total nitrogen content and fermentation stability. Several comparative assays were conducted on the anaerobic co-digestion of GM with three crop residues (CRs), namely, wheat straw (WS), corn stalks (CS) and rice straw (RS), under different mixing ratios. All digesters were implemented simultaneously under mesophilic temperature at 35±1 °C with a total solid concentration of 8%. Result showed that the combination of GM with CS or RS significantly improved biogas production at all carbon-to-nitrogen (C/N) ratios. GM/CS (30:70), GM/CS (70:30), GM/RS (30:70) and GM/RS (50:50) produced the highest biogas yields from different co-substrates (14840, 16023, 15608 and 15698 mL, respectively) after 55 d of fermentation. Biogas yields of GM/WS 30:70 (C/N 35.61), GM/CS 70:30 (C/N 21.19) and GM/RS 50:50 (C/N 26.23) were 1.62, 2.11 and 1.83 times higher than that of CRs, respectively. These values were determined to be the optimal C/N ratios for co-digestion. However, compared with treatments of GM/CS and GM/RS treatments, biogas generated from GM/WS was only slightly higher than the single digestion of GM or WS. This result was caused by the high total carbon content (35.83%) and lignin content (24.34%) in WS, which inhibited biodegradation.     

Hydrolysis of sorghum straw using phosphoric acid: evaluation of furfural production

Sorghum straw is a waste that has been studied scarcely. The main application is its use as raw material for xylose production. Xylose is a hemicellulosic sugar mainly used for its bioconversion toward xylitol. An alternative use could be its conversion toward furfural. The objective of this work was to study the furfural production by hydrolysis of sorghum straw with phosphoric acid at 134 degrees C. Several concentrations of H(3)PO(4) in the range 2-6% and reaction time (range 0-300 min) were evaluated. Kinetic parameters of mathematical models for predicting the concentration of xylose, glucose, arabinose, acetic acid and furfural in the hydrolysates were found. Optimal conditions for furfural production by acid hydrolysis were 6% H(3)PO(4) at 134 degrees C for 300 min, which yielded a solution with 13.7 g furfural/L, 4.0 g xylose/L, 2.9 g glucose/L, 1.1g arabinose/L and 1.2g acetic acid/L. The furfural yield of the process was 0.1336 g furfural/g initial dry matter was obtained. The results confirmed that sorghum straw can be used for furfural production when it is hydrolyzed using phosphoric acid.     

On the concentration of acetic acid in straw and soil

Summary Freshly harvested wheat straw contained 0.096 g water g^–1 dry straw and 180 mM acetic acid. The straw absorbed water more rapidly from wet soil. The concentration of acetic acid fell to about 10 mM within 6 h of incorporation of straw in the soil and then remained relatively constant for a period of 12 days, irrespective of soil moisture content. In soil at its maximum water holding capacity after gravitational drainage, the decline in acetic acid concentration (c) with distance (d) from wheat or barley straw was exponential, with c=c_o e^–nd where c_o is the concentration of acetic acid at the straw surface and n is a constant (0.46 for barley and 0.42 for wheat straw). The presence of acetic acid seems to be a major cause of poor establishment and growth when seeds and seedling roots come into contact with straw.     

采用玉米秸秆水解糖和玉米浆发酵生产丁二酸

研究了以玉米秸秆水解糖为碳源,不同氮源条件下琥珀酸放线杆菌Actinobacillus succinogenesSF-9的丁二酸发酵产酸能力。结果表明玉米浆可以替代酵母膏作为丁二酸发酵的廉价氮源。厌氧摇瓶丁二酸发酵单因素试验,得到在初糖浓度50 g/L时,玉米浆的较佳用量为20 g/L。在5 L搅拌罐上,考察了不同初始玉米秸秆水解糖浓度对A.succinogenes SF-9发酵生产丁二酸的影响,结果显示高初始秸秆糖浓度对琥珀酸放线杆菌的生长有抑制作用。采用补料分批发酵,发酵60 h丁二酸的产量达到42.7g/L,丁二酸产率82.7%,生产强度0.81 g/(L·h)。丁二酸的产量和生产强度较分批发酵有明显提高。