Production of fermentable sugars from corn fiber using soaking in aqueous ammonia (SAA) pretreatment and fermentation to succinic acid using <Emphasis Type="Italic">Escherichia coli</Emphasis> AFP184

Conversion of corn fiber (CF), a by-product from the corn-to-ethanol conversion process, into fermentable sugar and succinic acid was investigated using soaking in aqueous ammonia (SAA) pretreatment followed by biological conversions, including enzymatic hydrolysis and fermentation using genetically engineered E. coli (AFP184). The SAA pretreatment (using a 15% w/w NH₄OH solution at a solid-to-liquid ratio of 1: 10 at 60 °C for 24 h) removed 20-38% of lignin and significantly improved the digestibility of the treated solid (85-99% of glucan digestibility). Following the enzymatic hydrolysis, the sugar-rich hydrolysate was subjected to dilute sulfuric acid treatment (1 wt% sulfuric acid and 120 °C for 1 h), which hydrolyzed the oligosaccharides in the hydrolysate into fermentable monomeric sugars. The mixed sugar hydrolysates containing hexose and pentose obtained from the two-step hydrolysis and SAA pretreatment were fermented to succinic acid using a genetically engineered microorganism, Escherichia coli AFP184, for evaluating the fermentability. Engineered E. coli AFP184 effectively converted soluble sugars in the hydrolysate to succinic acid (20.7 g/L), and the production rate and yield were further enhanced with additional nutrients; the highest concentration of succinic acid was 26.3 g/L for 48 h of fermentation.     

Switchgrass pretreatment and hydrolysis using low concentrations of formic acid

BACKGROUND: Acid hydrolysis using organic acids is a promising approach for liquefying biomass without introducing any additional inorganic salt species into the reaction media. Formic acid may be a very useful acid catalyst for biomass pre‐treatment because (i) it is an effective, strong acid catalyst, (ii) it is no more corrosive than sulfuric acid, (iii) it is an organic acid, so it adds noinorganic salt species that might negatively impact downstream catalysis, and (iv) it can be produced from biomass, making ita green reagent. RESULTS: At pH_{25 °C} = 1.65, formic acid yielded high dissolution of switchgrass (52 wt%) at a high temperature (200 °C), comparable with the dissolution yield achieved using sulfuric acid. When treated 9/1 wt/wt with an 8 wt% aqueous solution of formic acid at 150 °C for 1 h, 44 wt% of switchgrass was dissolved, yielding 63 wt% of the carbohydrates from switchgrass. CONCLUSIONS: The efficiency of formic acid for the hydrolysis and dissolution of the carbohydrate fraction of switchgrass was proved and compared with other organic and mineral acids. The liquid product of pretreatment of switchgrass using formic acid at both 150 °C and 200 °C showed that 24 wt% and 28 wt%, respectively, of soluble monosaccharides after enzymatic hydrolysis consisted of glucose. Copyright © 2011 Society of Chemical Industry     

EFFECT OF PRETREATMENT CONDITIONS ON STRUCTURAL CHARACTERISTICS OF WHEAT STRAW

Structural characteristics of lignocellulosic biomass such as surface area, pore volume, crystallinity, hemicellulose, and lignin content significantly affect the yield of fermentable sugars for bioethanol production. In the present work, the effect of dilute acid pretreatment was studied on structural characteristics of wheat straw, using different combinations of process variables (temperature, time, and acid concentration). Pretreated wheat straw (PWS) exhibited higher available surface area and pore volume along with low hemicellulose and lignin content. Crystallinity index (CrI) of biomass at different pretreatment conditions showed an increased trend followed by sharp decrease at high temperature (190°C) conditions. Maximum increase in surface area (7.1 m²/g compared to 4.0 m²/g for untreated wheat straw) was obtained at pretreatment conditions of 180°C temperature, 0.5% (v/v) acid, and 7 min time. SEM imaging of biomass revealed that pore breaking, compression of pores, and partial pore blocking in the case of high temperature (190°C) pretreatment conditions may be the reason behind decreased surface area of biomass. FT-IR analysis showed almost complete hemicellulose removal and acid-soluble lignin removal after dilute acid pretreatment but insufficient removal of acid insoluble lignin.

[Supplementary material is available for this article. Go to the publisher's online edition of Chemical Engineering Communications for the following free supplemental resource: figure showing XRD pattern of biomass with respect to different pretreatment conditions.]     

Statistical methodology for optimizing the dilute acid hydrolysis of sugarcane bagasse

In converting advanced biomass to fuel, one pretreatment that has been extensively explored is a high temperature, dilute-sulfuric acid (H₂SO₄) process. This effectively hydrolyzes the hemicellulosic portion of the lignocellulosic biomass to fermentable sugars. Our aim was to optimize the concentration of sulfuric acid and residence time to release xylose from the hemicellulose of sugarcane bagasse. According to response surface methodology (RSM), the optimum concentrations and residence time were determined. The experimental maximum yield for xylose production was found to be 78.9% at 170 °C, 0.24% acid, for 15 min, and 76.4% at 200 °C, 0.22% acid, for 6 min. The predicted maximum yield obtained for the fitted model was found to be 80.3% and 78.1% for the conditions stated above, respectively. The experimental yield was around 1.5% lower than that of the predicted yield. It was confirmed in this study that pentose sugars (xylose and arabinose) derived from hemicellulose fraction were further degraded. The statistical optimization method, which incorporates reaction time, temperature and acid concentration, did prove to provide a useful means of trading off the combined effects of these three variables on total xylose recovery yields.     

Reaction mechanisms and kinetics of xylo‐oligosaccharide hydrolysis by dicarboxylic acids

Hydrothermal pretreatment of lignocellulosic materials generates a liquid stream rich in pentose sugar oligomers. Cost‐effective hydrolysis and utilization of these soluble sugar oligomers is an integral process of biofuel production. We report integrated rate equations for hydrolysis of xylo‐oligomers derived from pretreated hardwood by dicarboxylic maleic and oxalic acids. The highest xylose yield observed with dicarboxylic acids was 96%, and compared to sulfuric acid, was 5–15% higher with less xylose degradation. Dicarboxylic acids showed an inverse correlation between xylose degradation rates and acid loadings unlike sulfuric acid for which less acid results in less xylose degradation to aldehydes and humic substances. A combination of high acid and low‐temperature leads to xylose yield improvement. Hydrolysis time course data at three different acid concentrations and three temperatures between 140 and 180°C were used to develop a reaction model for the hydrolysis of xylo‐oligosaccharides to xylose by dicarboxylic acids. © 2012 American Institute of Chemical Engineers AIChE J, 59: 188–199, 2013     

Sequential hydrolysis of hemicellulose and lignin in lignocellulosic biomass by two-stage percolation process using dilute sulfuric acid and ammonium hydroxide

To obtain the total fractionation and pretreatment of the corn stover, two-stage percolation process was investigated. This process consists of two steps: use of 0.07 wt% sulfuric acid for hemicellulose recovery in first stage and ARP (ammonia recycled percolation) in the following stage for lignin recovery. Among tested conditions, the best conditions of two-stage process were as follows: 1^st stage; 170 °C, 2.5 ml/min, 30 minutes using 0.07 wt% sulfuric acid and 2^nd stage; 170 °C, 5.0 ml/min, 60minutes using 15 wt% ammonium hydroxide. At above two-stage treatment conditions, the hemicellulose in corn stover was easily hydrolyzed (95%) and recovered with high yields (86%) and the extent of the lignin removal was 81%. After two-stage process, the treated biomass contained nearly pure glucan (85%). Two-stage treatment brought about enzymatic digestibility of 90% and 89% with 60 and 15 FPU/g glucan cellulase enzyme loadings, respectively.     

Evaluation of the effects of operational parameters in the pretreatment of sugarcane bagasse with diluted sulfuric acid using analysis of variance

The pretreatment of lignocellulosic residues has been extensively studied as a method to disrupt the cellulose–hemicelluloses–lignin complex in biomass to access the sugars in their respective components. In this work, we carried out a study using sulfuric acid pretreatment of sugarcane bagasse by varying the following operational parameters: solid loading (10–30% of bagasse relative to the volume of the sulfuric acid solution), sulfuric acid concentration (0.5–2.5% relative to the dry mass of bagasse), reaction time (5–25?min), and temperature (135–195°C). The obtained solids from each pretreatment condition were submitted to enzymatic hydrolysis under the same process conditions: 0.232?g of Celluclast 1.5?L and 0.052?g of Novozym 188 per g of pretreated sugarcane bagasse, 72?h of hydrolysis, and 200?rpm of agitation at 50°C. Using central composite rotational design configuration in the experiments and analysis of variance, the results indicate that the conditions that produced larger quantities of glucose by enzymatic hydrolysis (0.35?g glucose/g pulp) with minimum amounts of degradation products were as follows: 20% solids loading, 15?min of reaction time, 1.5% sulfuric acid, and a minimum temperature of reaction of 170°C.     

Comparative analysis of the effect of pretreating aspen wood with aqueous and aqueous-organic solutions of sulfuric and nitric acid on its reactivity during enzymatic hydrolysis

The effect of aspen wood pretreatment methods with the use of both aqueous solutions of sulfuric and nitric acids and aqueous-organic solutions (ethanol, butanol) of sulfuric acid (organosolv) on the limiting degree of conversion of this type of raw material into simple sugars during enzymatic hydrolysis are compared. The effects of temperature, acid concentration, composition of organic phase (for sulfuric acid), and pressure (for nitric acid) on the effectiveness of pretreatment were analyzed. It is shown that the use of organosolv with 0.5% sulfuric acid allows us to increase the reactivity of ground wood by 300–400%, compared to the initial raw material. Pretreatment with a 4.8% aqueous solution of nitric acid (125°C, 1.8 MPa, 10 min) is shown to be most effective, as it increases the reactivity of the ground aspen wood by more than 500%.     

Increase in bioethanol production yield from triticale by simultaneous saccharification and fermentation with application of ultrasound

BACKGROUND: Bioethanol produced from renewable biomass, such as sugar, starch or lignocellulosic materials, is one of the alternative energy resources that is environmentally friendly. Triticale crops have a high yield as well as a high starch content and amylolytic enzyme activity and are therefore considered to be ideal for bioethanol production. RESULTS: This study examined the feasibility of ultrasound pretreatment to enhance the release of fermentable sugars from triticale meal during pretreatment and consequently increase bioethanol yield in the simultaneous saccharification and fermentation (SSF) process by Saccharomyces cerevisiae yeast. Ultrasonic pretreatment effectively increased the glucose and maltose content after liquefaction by 15.71% and 52.57%, respectively, compared with the untreated control sample under determined optimal conditions of sonication (5 min, 60 °C). The ultrasound pretreatment consequently improved bioethanol production during SSF processing since the bioethanol content was increased by 10.89%. CONCLUSION: Taking into consideration significant process parameters obtained in the SSF process of triticale meal with ultrasound pretreatment at 60 °C, the process time may be reduced from 72 to 48 h. At that point of the SSF, maximum bioethanol content of 9.55% (w/v), bioethanol yield of 0.43 g g^?1 of triticale starch, and percentage of the theoretical bioethanol yield of 84.56% were achieved. Copyright © 2011 Society of Chemical Industry     

Influence of pretreatment conditions on composition of liquid hydrolysate and subsequent enzymatic saccharification of remaining solids

In the present work, the effect of dilute acid pretreatment was studied on the composition of liquid hydrolysate obtained after pretreatment by employing different combinations of process variables (temperature, time and acid concentration). The effect of pretreatment was also studied on subsequent enzymatic saccharification of remaining solids to obtain maximum yield of sugars. The efficiency of pretreatment was measured in terms of high‐xylose and low‐glucose yields, which was found most suitable at pretreatment conditions of 120°C, 120 min and 2% (v/v) acid concentration. With increased severity of pretreatment, xylose yield decreased with concomitant increase in glucose yield. The decrease in xylose yield was attributed to conversion into degradation products such as 5‐hydroxylmethyl furfural (HMF) and acetic acid. The percentage of enzymatic saccharification increased with increased pretreatment severity. Saccharification of biomass pretreated at 180°C, 7 min and 0.5% (v/v) acid concentration produced the maximum glucose yield of saccharification of 352 g/kg dry matter, compared to just 97 g glucose/kg dry matter in the case of untreated biomass. The same pretreatment conditions resulted in maximum total sugar yield of pretreatment and saccharification of 459 g/kg dry matter, which was more than 67% of the total potential sugars in biomass. © 2012 Canadian Society for Chemical Engineering     

蔗渣预水解液酸催化制备糠醛及其萃取分离（急）

以蔗渣为原料,在高温低酸浓度（H2SO4添加量占蔗渣绝干质量的0.176%）条件下预水解得到富含木糖的预水解糖液,再进一步深度酸解得到糠醛,并以混合有机溶剂实现了糠醛从水相中高效萃取分离。对蔗渣预水解条件、糠醛的有机溶剂萃取条件进行了探索,并采用FT-IR、XRD、SEM、TGA对蔗渣及预水解渣的形貌和结构进行了表征,利用紫外分光光度计对预水解过程中的木糖及深度酸解过程中的糠醛进行了定量检测。结果表明,在160 °C,液固比6：1,浓硫酸/蔗渣绝干质量为0.176%条件下,预水解液中木糖浓度最高（41.72 g/L）;该预水解液直接在170 °C条件下深度酸解90 min,溶液中糠醛浓度最高可达15.91 g/L,糠醛摩尔得率最高为59.60%。以v(1,2-二氯乙烷):v(正丁醇) = 9:1的比例混合有机溶剂对水溶液中糠醛进行萃取,萃取相体积比为v(有机相):v(水相) = 2:1,糠醛的萃取率可达93.53%。     

Liquefaction of Red Pine Wood,Pinus densiflora,Biomass Using Peg-400-Blended Crude Glycerol for Biopolyol and Biopolyurethane Production

Red pine wood, Pinus densiflora, biomass was liquefied through liquefaction using a solvent mixture of crude glycerol and PEG-400 with a sulfuric acid catalyst. The liquefaction process parameters of crude glycerol/PEG-400 blending ratio, biomass loading, acid loading, reaction temperature, and reaction time were optimized. Biopolyol with 61.9% biomass conversion was produced at 170°C within 1 h using a co-solvent of crude glycerol and PEG-400 (5/5, w/w), 15% biomass loading, and 3% sulfuric acid loading. The biopolyol possessed a 4.2 mg KOH/g acid number and 892.4 mg KOH/g hydroxyl number. Polyurethane foam was successfully synthesized from the liquefied red pine wood biomass with toluene diisocyanate. The synthesis of biopolyurethane derived from red pine wood biopolyol was confirmed with FT-IR.     

Evaluation of enzymatic hydrolysis of wheat straw pretreated by atmospheric glycerol autocatalysis

BACKGROUND: Because ethanol organosolv pulping requires high pressure and is highly volatile, an atmospheric autocatalytic glycerol organosolv pretreatment process has been investigated. Enzymatic hydrolysis of wheat straw pretreated using this method was evaluated to explore a novel, economically competitive and environmentally friendly pretreatment technology for bioconversion of lignocellulosic biomass. The method also provides economical utilization of industrial glycerol, helping to cope with the challenge of the excess production of glycerol and to further defray the cost of biodiesel production. RESULTS: With preliminary optimization of the parameters in the pretreatment process, pretreatment performed at 240 °C for 4 h with the glycerol addition of 15 g g^?1 dry feedstock and wash at 80 °C led to high recovery of cellulose (95%) and good removal of lignin (>70%), which formed, respectively, 80% and 10% of the pulp. The enzymatic hydrolysis of the pretreated wheat straw yielded 90% of theoretically achievable sugar after 24 h and 92% after 48 h. CONCLUSION: Atmospheric autocatalytic glycerol organosolv pretreatment removed significant amounts of hemicellulose and lignin without affecting good cellulose recovery. The proposed novel strategy increased the susceptible of wheat straw to enzyme attack and led to enzymatic hydrolysis that was comparable with that achieved using ethanol organosolv pretreatment. Copyright © 2007 Society of Chemical Industry     

Characterization of electropolymerized graphite fiber–polyacrylamide composites

The synthesis of a series of graphite fiber-polyacrylamide composites was performed electrochemically in dilute sulfuric acid (0.125M)-acrylamide (2M) solution, 1 : 1 sulfuric acid (0.25M) : acetone-acrylamide (2M) solution, and 1 : 1 sulfuric acid (0.25M) : 2-propanol-acrylamide (2M) solution, respectively, using graphite fiber bundles as the working electrode. The graphite fiber-polyacrylamide composites, synthesized in a 1 : 1 2-propanol : sulfuric acid-acrylamide solution, were more easily characterized than those synthesized from the sulfuric acid-acrylamide solution that contained no alcohol. Composites that were synthesized in a dilute sulfuric acid solution were, however, more readily crosslinked. (Fourier transform infrared spectroscopy, FTIR, confirmed the formation of inter-chain and intrachain imide functional groups after the resin was cured at ≈ 200°C.) Polymer weight gain analysis, coupled with surface morphology studies using scanning electron microscopy, showed that the thickness of the coatings, and hence the volume fraction of the resin in the composites, varied linearly with the time of electropolymerization. Scanning electron microscopy revealed an open and folded chain surface structure, which permitted unrestricted permeation of the monomer onto the electrode surface. Differential scanning calorimetry of the electropolymerized resins confirmed a glass transition temperature of between 180 and 207°C. © 1994 John Wiley & Sons, Inc.     

An integrated process for continuous cellulosic bioethanol production

A high-efficiency, integrated bioethanol production process was developed in this study, using Miscanthus as lignocellulosic biomass. The continuous process involved a twin-screw extruder, a pretreated biomass washing/dewatering process, and a saccharification/fermentation process. In addition, the integration process was designed for the reuse of pretreatment solution and the production of highly concentrated bioethanol. Pretreatment was performed with 0.72 M NaOH solution at 95 °C using an 80 rpm twin-screw speed and a flow rate of 90mL/min (18 g/min of raw biomass feeding). Following washing and dewatering steps, the pretreated biomass was subjected to simultaneous saccharification and bioethanol fermentation processes. The maximum ethanol concentration, yield from biomass, and total volume obtained were 59.3 g/L, 89.9%, and 60 L, respectively, using a pretreated biomass loading of 23.1% (w/v) and an enzyme dosage of 30 FPU/g cellulose. The results presented here constitute an important contribution toward the production of bioethanol from Miscanthus.     

氨预处理对大豆秸秆纤维素酶解产糖影响的研究

为了提高大豆秸秆酶解产糖能力, 以利于从大豆秸秆中提取生物降解性塑料的原料 ?? 乳酸, 对大豆秸秆纤维素预处理过程的影响因素进行了探索,对预处理前后大豆秸秆的物理结构变化、化学成分变化及预处理条件对大豆秸秆酶水解产糖的影响进行了研究。研究结果表明,粉碎结合氨处理对大豆秸秆酶水解影响较大,较适宜的预处理条件为大豆秸秆粉碎至 140 目,10%氨水处理 24h。经过预处理后大豆秸秆纤维素含量提高 70.27%, 半纤维素含量下降 41.45%, 木质素含量下降 30.16%, 有利于大豆秸秆酶解产糖。     

Production of high purity biodiesel through direct saponification of wet biomass of <Emphasis Type="Italic">Chlorella protothecoides</Emphasis> in a low cost microwave reactor: Kinetic and thermodynamic studies

We studied production of biodiesel from microalga Chlorella protothecoides (SAG 211-10 C) through direct saponification of its wet biomass (70% moisture) in a microwave reactor using ethanolic potassium hydroxide. The resulting soap was precipitated by “common ion effect” using saturated solution of potassium chloride and subjected to simultaneous acidulation and esterification to form biodiesel. The optimum parameters for saponification were: Temperaure- 60 °C, Ethanol to dry biomass ratio (ml/g)-80 : 1, concentration of KOH-0.5%, microwave power-450W; and for esterification they were Temperature-60 °C, wt% of sulfuric acid-2.5%, molar ratio of methanol to fatty acids-70 : 1, microwave power-450W. The kinetics and thermodynamics of saponification and esterification were investigated. Both reactions were found to follow pseudo-first-order kinetics. Activation energies were determined as 14.177 kJ/mol and 17.234 kJ/mol for saponification and esterification, respectively. The final biodiesel yield and purity were 98.74% and 94.83%, respectively.     

Modeling and optimization of dilute nitric acid hydrolysis on corn stover

BACKGROUND: Because of its high cost, nitric acid has not been widely employed as the catalyst for hydrolysis of lignocellulosic biomass to obtain fermentable sugars. However, recently more and more research results have reported that nitric acid was more effective than other acids for the hydrolysis of lignocellulose. Therefore, it is necessary to find an optimum condition for nitric acid pretreatment and a means of reducing the cost. RESULTS: In this work, low concentrations of nitric acid and short reaction times were considered to optimize the pretreatment process. The kinetic parameters of models to predict the concentrations of xylose, glucose, arabinose, acetic acid and furfural in the hydrolysates were obtained. Applying the kinetic models, the optimum conditions were: 150 °C, 0.6% HNO₃ and 1 min, which yielded a solution containing up to 22.01 g L^?1 xylose, 1.91 g L^?1 glucose, 2.90 g L^?1 arabinose, 2.42 g L^?1 acetic acid and 0.21 g L^?1 furfural, which were consistent with the predicted values. The influence of temperature was also studied using the Arrhenius equation. CONCLUSIONS: A combination of experimental data and model analysis suggested that 96% xylose yield can be achieved by using low concentration nitric acid for a short reaction time, which could greatly reduce the pretreatment cost. Therefore, dilute nitric acid could be considered a good choice for the hydrolysis of corn stover. Copyright © 2010 Society of Chemical Industry     

Low-Temperature Dilute Acid Hydrolysis of Oil Palm Frond

Oil palm frond (OPF) fiber, a lignocellulosic waste from the palm oil industry, contains high cellulose and hemicellulose content, thus it is a potential feedstock for simple sugars production. This paper describes the two-stage hydrolysis process focusing on the use of low-temperature dilute acid hydrolysis to convert the hemicellulose in OPF fiber to simple sugars (xylose, arabinose, and glucose). The objective of the present study was to evaluate the effect of operating conditions of dilute sulfuric acid hydrolysis undertaken in a 1 L self-built batch reactor on xylose production from OPF fiber. The reaction conditions were temperatures (100–140°C), acid concentrations (2–6%), and reaction times (30–240 min). The mass ratio of solid/liquid was kept at 1:30. Analysis of the three main sugars glucose, xylose, and arabinose were determined using high-pressure liquid chromatography. The optimum reaction temperature, reaction time, and acid concentration were found to be 120°C, 120 min, and 2% acid, respectively. Based on the potential amount of xylose (10.8 mg/mL), 94% conversion (10.15 mg/mL) was obtained under the optimum conditions with small amount of furfural (0.016 mg/mL). To enhance the effectiveness of dilute acid hydrolysis, the hydrolysis of OPF fiber was also performed using ultrasonic-pretreated OPF fiber. The effects of ultrasonic parameters power (40–80%) and ultrasonication times (20–60 min) were determined on sugar yields under optimum hydrolysis conditions (2% acid sulfuric, 120°C and 120 min). However, the use of ultrasonication was found to have detrimental effect on the yield of simple sugars due to the 10-fold increase in the formation of furfural.     

Enzymatic Hydrolysis of Corn Stover after Pretreatment with Dilute Sulfuric Acid

Although many previous studies have been carried on the enzymatic hydrolysis of corn stover after pretreatment with dilute sulfuric acid, this paper emphasizes the use of different conditions to attain the highest yields of two sugars, xylose and glucose, from both stages. The pretreatment was performed at a range of sulfuric acid concentrations of 2, 4 and 6 % at 80, 100 and 120 °C. Up to 77 % xylose yield was obtained while the glucose yield was only 8.4 %. The corresponding solid phase was hydrolyzed by cellulase and the influences of five factors and their interactions on enzyme hydrolysis were evaluated by response surface methodology based on one‐factor‐at‐a‐time experiments. The optimal levels for each variable to obtain the highest reducing sugar yield were as follows: enzyme concentration of 22 FPU/g substrate, substrate concentration of 77 g/L, temperature of 49 °C, pH 4.8 and reaction time of 38 h. A reducing sugar yield of 42.11 g/100 g substrate was achieved, which was consistent with the predicted value of 42.13 g/100 g substrate. Compared with the one‐factor‐at‐a‐time experiments, there was a 9.4 % increase in reducing sugar yield when the enzyme concentration was decreased to 3 FPU/g substrate, the substrate concentration increased to 17 g/L and the reaction time dropped to 22 h. The total sugar released from the two stages was 62.81 g/100 g substrate.