Dilute Acid Pretreatment Conditions Research Articles

Impact of dilute acid pretreatment conditions on p-coumarate removal in diverse maize lines

Prior work has identified that lignins recovered from dilute acid-pretreated corn stover exhibit superior performance in phenol–formaldehyde resins used in wood adhesive applications when compared to diverse process-modified lignins derived from other sources. This improved performance is hypothesized to be due to the higher content of unsubstituted phenolic groups specifically p-coumarate lignin esters. In this work, a diverse set of corn stover samples are employed that exhibit diversity in p-coumarate content and total lignin content to explore the relationship between dilute acid pretreatment conditions, p-coumarate ester hydrolysis, xylan solubilization, and the resulting glucose enzymatic hydrolysis yields. The goal of this study is to identify pretreatment conditions that preserve a significant fraction of the p-coumarate esters while simultaneously achieving high enzymatic hydrolysis yields. Kinetic parameters for p-coumarate ester hydrolysis were quantified and pretreatment-biomass combinations were identified that result in glucose hydrolysis yields of more than 90% while retaining nearly 50 mg p-coumarate/g lignin.

Optimization of dilute acid pretreatment of barley husk and oat husk and determination of their chemical composition

The pretreatment of renewable resources is the first step to make them metabolically available for microorganisms for generation of value-added products by fermentation. In this research, barley husk (BH) and oat husk (OH) were used as renewable resources to study the optimization of dilute acid pretreatment conditions by using Response Surface Methodology (RSM). Temperature (T, 110–130 °C), solid-to-liquid ratio (S:L, 1:8–1:16 w/v), dilute sulfuric acid concentration (DSA, 1–5%, v/v), and pretreatment time (t, 30–90 min) were selected as independent variables. Their levels were specified by one-factor-at-a-time (OFAT) method according to statistically significance level (p = 0.05). OFAT results indicated that the independent variables for optimization of acid pretreatment conditions of the renewable resources were T (120–130 °C), S:L (1:8–1:12 w/v), and DSA (1–3% v/v) for BH; T (120–130 °C), S:L (1:8–1:12 w/v), and t (10–30 min) for OH. Optimum pretreatment values were 130 °C, 1:8 (w/v), 1.86% (v/v), and 30 min for BH and 130 °C, 1:8 (w/v), 1% (v/v), and 19 min for OH by using Box-Behnken RSM. Under optimal conditions, fermentable sugar concentration, total phenolics, and extract yield were determined to be 76.28, 1.12 g/L, and 55% for BH and 59.63 g/L, 0.70 g/L, and 56% for OH, respectively. Additionally, the chemical composition of hydrolysates was also evaluated in terms of maltose, glucose, xylose, arabinose, mannose, galactose, phenolics, 5-hydroxymthylfurfural, 2-furaldehyde (2-F), formic acid, and acetic acid. Catalytic efficiency values of sulfuric acid for BH and OH were 21.58 and 8.35 g/g, respectively. Consequently, this study clearly indicates that the hydrolysates from the renewable resources can be used as feedstocks for the production of value-added products by biotechnological processes.

Efficiency of dilute sulfuric acid pretreatment of distillery stillage in the production of cellulosic ethanol

The aim of this study was to examine suitability of distillery stillage of various origins subjected to dilute sulfuric acidic pretreatment for production of cellulosic ethanol. Optimal conditions for dilute acid pretreatment of: rye and wheat distillery stillage 121 °C, 0.2 M H2SO4, 60 min; maize stillage 131 °C, 0.2 M H2SO4, 60 min. The highest efficiency of enzymatic hydrolysis was achieved for rye and wheat stillage using 1 g of DW and the concentration of cellulolytic enzyme of 24% w/w, and for maize stillage 3 g of DW and enzyme concentration of 24% w/w. The use of rye and wheat stillage for production of ethanol does not require a detoxification process and enables full attenuation of glucose after 48 h of the process. However, the use of maize stillage as a raw material must be preceded by a detoxification process that guarantees a reduction of 5-hydroxymethylfurfural concentration in the fermentation medium.

Dilute acid and alkaline pretreatment of spent tea leaves to determine the potential of carbon sources

Tea is one of the most commonly consumed beverages in the worldwide. Therefore, spent tea leaves (STL) are abundant low-cost lignocellulosic materials and can be evaluated as a carbon source for the production of value-added products by fermentation. The aim of this study was to optimize the dilute acid and alkaline pretreatment conditions of STL. The optimal conditions were determined by response surface method (RSM) in terms of fermentable sugars concentration (FSC) and total phenolics concentration (PHC). Independent variables were selected as temperature (115–135 °C), pretreatment time (20–60 min), solid-to-liquid ratio (1:8–1:16 w/v), and dilute acid (1–5% v/v) or alkaline (1–3 N) ratio. It was found that the optimum conditions for dilute acid pretreatment were 131.67 °C, 20 min, 1:10.26 w/v, and 1.58% v/v, which yielded as 21.56 g/L, 0.228 g/g, and 1.53 g/L for FSC, FSY, and PHC, respectively. Nevertheless, the best dilute alkaline pretreatment conditions were 116.42 °C, 20 min, 1:11.23 w/v, and 1.68 N, which achieved as 28.18 g/L, 0.316 g/g, and 5.26 g/L for FSC, FSY, and PHC, respectively. Nevertheless, based on the statistical evaluation, it was found that RSM models victoriously fitted the experimental data related to the pretreatment of STL. Consequently, acid and alkaline pretreated-STL can be considered as suitable carbon source for value-added products’ production by fermentation.

Investigation of conditions for dilute acid pretreatment for improving xylose solubilization and glucose production by supercritical water hydrolysis from Quercus mongolica

Abstract The objective of this study was to prepare a feedstock, which xylose should be highly solubilized and most of the glucose remained in the solid fraction, for supercritical water hydrolysis (SCWH). Response surface methodology (RSM) with two independent variables (reaction time and sulfuric acid concentration) was adopted to find suitable conditions for pretreatment using a simple apparatus an autoclave for massive production. Based on the results of the RSM experiments, higher xylose contents were obtained in the liquid fraction after dilute acid pretreatment at 121 °C for 60 min with 6.82% H2SO4 (condition #8 (18.0%)) and at 121 °C for 102.3 min with 4% H2SO4 (condition #6 (16.0%)). To preventing corrosion of the apparatus, condition #6 was modified by prolonging the reaction time to 105 min, which led to a xylose content of 17.6% in the liquid fraction. Furthermore, structural degradation of the solid fraction was observed, indicating a positive effect for sugar production via SCWH.

Study of the influence of dilute acid pre-treatment conditions on glucose recovery from Moringa oleifera Lam for fuel-ethanol production

ABSTRACTThe influence of temperature (175 to 195°C), residence time (5 to 15 min), and sulfuric acid concentration in high (2 to 4% w/w) and low (0.5 to 1.5% w/w) levels in dilute acid pretreatment of Moringa oleifera Lam is studied. Glucose recoveries in the liquid fraction and in the hydrolyzed insoluble fraction as well as the presence of inhibitors in the liquid fraction are determined. Best experimental results are achieved at 185°C, 2% w/w acid concentration, and 5 min reaction time obtaining a glucose recovery of 83.68%. An increment in 48.81% in glucose yield compared with the one of not pretreated Moringa is obtained. 0.13 g ethanol/g Moringa from fermentation of pre-hydrolysate and hydrolysate obtained at the optimal pre-treatment conditions are obtained.

Bench scale dilute acid pretreatment optimization for producing fermentable sugars from cotton stalk and physicochemical characterization

Cotton stalk is a holocellulose rich, inexpensive agricultural residue available in surplus without any competitive uses neither as food nor as animal fodder. These aspectshold high potential for cotton stalk as a biomass to be suitable for ethanol production. Dilute acid pretreatment conditions on bench scale have been optimized for cotton stalk by Response Surface Methodology (RSM) using Central Composite Design (CCD). Effect of four pretreatment process variables viz. temperature, acid concentration, time of reaction and stirring speed has been optimized for maximum enzymatic sugar release during the subsequent enzymatic saccharification. Under the optimized pretreatment conditions, i.e., temperature: 157°C, acid concentration: 1.07% (w/w),and time: 20min, enzymatic sugar releasewas found to be 684mg/g of dry pretreated biomass. A correlation of hemicellulose removal and inhibitor formation with combined severity factor (CSF) was drawn. Mass balance carried out for the pretreatment step under optimized conditions resulted in 68.35 and 8.31% of xylose and glucose saccharificationyieldsrespectively.Subsequent enzymatic saccharification yieldsofglucose and xylose were 93.56 and 19.93% respectively. The overall saccharification yield integrating pretreatment and enzymatic hydrolysis of cotton stalk was 91.06%. Physicochemical characterization of native and pretreated biomass was carried out by compositional analysis, FT-IR and XRD revealing significant changes in biomassproperties responsible for improved saccharification efficiency.

Effect of dilute acid pretreatment conditions and washing on the production of inhibitors and on recovery of sugars during wheat straw enzymatic hydrolysis

Pretreatment is an essential process to break down recalcitrant biomass and dilute acid hydrolysis is one of the most efficient and cost effective pretreatment technologies available today. However there are potential disadvantages in using dilute acid as a pretreatment, such as the production of degradation products, which inhibits the ensuing processing chain and limits its adoption. In this work, wheat straw was pretreated under varying dilute acid conditions; the resulting degradation products were determined and the quality of sugar stream generated via enzymatic saccharification was monitored. The dilute acid pretreatment conditions were: temperatures of 140 and 160 °C, sulfuric acid concentrations of 5, 10 and 20 dm3 m−3 and reaction times of 10, 20, 30, 45 and 60 min. Pretreated wheat straw was washed with six dilutions of water and hydrolyzed with commercial cellulase enzymes for 24–48 h. Optimal conditions for pretreating wheat straw were determined as: 140 °C, 10 dm3 m−3 sulfuric acid concentration and a 30 min reaction time. At these conditions, the glucose yield from wheat straw was maximized at 89% of the theoretical maximum, while the concentrations of formic acid, furfural, acetic acid and 5-hydroxymethylfurfural were 32.37 ± 4.91, 12.08 ± 1.69, 7.98 ± 1.02 and 1.14 ± 0.22 g kg−1, respectively. Increases in pretreatment severity led to increases in inhibitor generation, as well as a 27% reduction in monosaccharide yield. Rinsing with deionized water was effective in removing inhibitors, such as 86% of furfural. The formation of inhibitors was thus observed to depend on dilute acid pretreatment conditions.

Suppression of pseudo-lignin formation under dilute acid pretreatment conditions

Pseudo-lignin is formed during dilute acid pretreatment (DAP), particularly under high-severity conditions, and has been shown to significantly inhibit enzymatic hydrolysis of cellulose. To suppress its formation, DAP was modified by performing it under O2 or N2; adding surfactant (Tween-80) to the reaction mixture; or using a water–dimethyl sulfoxide (DMSO) mixture as reaction medium. Pseudo-lignin analysis showed that only the addition of DMSO to DAP reaction medium can effectively suppress pseudo-lignin formation. This was attributed to DMSO preferentially solvating and stabilizing 5-hydroxymethyl furfural (HMF) which is the key intermediate to form pseudo-lignin, thereby reducing the overall yield of pseudo-lignin. Furthermore, the addition of DMSO was shown not to reduce pseudo-lignin molecular weight or change any of its structural features significantly. Therefore, pseudo-lignin generated from aqueous DMSO DAP had similar inhibition properties as compared to that acquired from routine DAP at equal mass dosages. This study is the first demonstration that the amount of pseudo-lignin formed during DAP can be reduced, which contributes to further optimization of DAP technology.

PRETREATMENT OF MOSO BAMBOO WITH DILUTE PHOSPHORIC ACID

Dilute phosphoric acid pretreatment of moso bamboo materials was studied for producing high quality dissolving pulp for textile applications. The dynamics of dilute acid pretreatment were considered. The Saeman model was found to describe well the acid hydrolysis of moso bamboo hemicelluloses to their monomers under different temperatures and different dilute phosphoric acid concentrations. The initial degradation rate of hemicelluloses was much higher than its subsequent degradation rate, and the xylose generation rate increased with increasing temperature. The change rule of the pentose extraction rate was considered along with the pretreatment factor (P factor). Optimum dilute acid pretreatment conditions were 170 °C and 45 minutes. Based on the optimum conditions and a mass balance of sugars, a weight loss of 26.5% of the solid and liquid fractions combined was observed after the pretreatment. SEM results revealed that the moso bamboo fibers surfaces and cell wall were damaged. With the surface area increasing, the accessible pore areas also increased. At the same time, the crystallinity of the cellulose was reduced, which created a favorable environment for chemical penetration in the subsequent treatment.

Evaluation of triticale bran as raw material for bioethanol production

The present work addresses the introduction of second generation biofuels from agricultural by-products generated from low input cereal crops such as triticale. The main purpose was to investigate whether the overall ethanol yield in a triticale dry-mill ethanol plant could be increased by combination of pretreatment and enzymatic hydrolysis of the bran obtained by fractionation of the grain to separate from starch. Different dilute acid pretreatment conditions were studied using starch-free triticale bran (SFTB) as substrate at a fixed loading of 10% (dry weight/volume). A statistically experimental design approach, based on previous studies, was used to evaluate the sugar recovery so as to maximize the enzyme digestibility of the pretreated material. The highest overall sugar yield was attained by using 0.1% (w/v) of sulphuric acid at 160°C for 22.5min. At these conditions, it could be possible to obtain up to 245L of ethanol per dry ton of SFTB considering hexose and pentose sugars fermentation, which would increase by 14% the theoretical ethanol yield in a dry-mill ethanol plant.

The influence of dilute acid pretreatment conditions on the enzymatic saccharification of Erica spp. for bioethanol production

Production of bioethanol from biomass is one way to reduce both consumption and depletion of fossil fuels and environmental pollution. The conversion of lignocellulosic biomass-to-ethanol comprehends three major steps: thermochemical pretreatment, enzymatic saccharification and fermentation. The aim of this work is to study the influence of dilute acid pretreatment conditions in sugars removal and in enzymatic saccharification of Erica spp. for bioethanol production as well as the influence of poly(ethylene)glycol addition to the enzymatic saccharification step. Pretreatment of Erica spp. with dilute sulfuric acid was studied at different conditions of reaction time, temperature and acid concentration. The influence of supplementation of enzymatic saccharification with poly(ethylene)glycol 4000 and concentration of polymer were tested, using as response the release of glucose and the adsorption of cellulase to biomass by protein content in supernatant and by SDS-PAGE. The addition of PEG 4000 affects the adsorption of cellulase and influences the yield of enzymatic saccharification, leading to an improvement of 13–74% depending on the pretreatment applied to biomass. A maximum of 440 mg glucose/g dry biomass was obtained by enzymatic saccharification when pretreated Erica spp. at 180 °C with 2.75% of sulfuric acid for 75 min, supplemented with 0.25 g/g dry biomass of PEG 4000, was used. The observation of biomass structure by scanning electron microscopy after pretreatment reveals visible breaks in the structure, which could be related to the improvement of enzymatic process.

Effects of dilute acid pretreatment conditions on enzymatic hydrolysis monomer and oligomer sugar yields for aspen, balsam, and switchgrass

The effects of dilute acid hydrolysis conditions were investigated on total sugar (glucose and xylose) yields after enzymatic hydrolysis with additional analyses on glucose and xylose monomer and oligomer yields from the individual hydrolysis steps for aspen (a hardwood), balsam (a softwood), and switchgrass (a herbaceous energy crop). The results of this study, in the form of measured versus theoretical yields and a severity analysis, show that for aspen and balsam, high dilute acid hydrolysis xylose yields were obtainable at all acid concentrations (0.25–0.75 wt.%) and temperatures (150–175 °C) studied as long as reaction time was optimized. Switchgrass shows a relatively stronger dependence on dilute acid hydrolysis acid concentration due to its higher neutralizing mineral content. Maximum total sugar (xylose and glucose; monomer plus oligomer) yields post-enzymatic hydrolysis for aspen, balsam, and switchgrass, were 88.3%, 21.2%, and 97.6%, respectively. In general, highest yields of total sugars (xylose and glucose; monomer plus oligomer) were achieved at combined severity parameter values (log CS) between 2.20 and 2.40 for the biomass species studied.

Enzymatic saccharification of dilute acid pretreated saline crops for fermentable sugar production

Four saline crops [athel ( Tamarix aphylla L), eucalyptus ( Eucalyptus camaldulensis), Jose Tall Wheatgrass ( Agropyron elongatum), and Creeping Wild Ryegrass ( Leymus triticoides)] that are used in farms for salt uptake from soil and drainage irrigation water have the potential for fuel ethanol production because they don’t take a large number of arable lands. Dilute sulfuric acid pretreatment and enzymatic hydrolysis were conducted to select the optimum pretreatment conditions and the best saline crop for further enzymatic hydrolysis research. The optimum dilute acid pretreatment conditions included T = 165 °C, t = 8 min, and sulfuric acid concentration = 1.4% (w/w). Creeping Wild Ryegrass was decided to be the best saline crop. Solid loading, cellulase and β-glucosidase concentrations had significant effects on the enzymatic hydrolysis of dilute acid pretreated Creeping Wild Ryegrass. Glucose concentration increased by 36 mg/mL and enzymatic digestibility decreased by 20% when the solid loading increased from 4 to 12%. With 8% solid loading, enzymatic digestibility increased by over 30% with the increase of cellulase concentration from 5 to 15 FPU/g-cellulose. Under given cellulase concentration of 15 FPU/g-cellulose, 60% increase of enzymatic digestibility of pretreated Creeping Wild Ryegrass was obtained with the increase of β-glucosidase concentration up to 15 CBU/g-cellulose. With a high solid loading of 10%, fed-batch operation generated 12% and 18% higher enzymatic digestibility and glucose concentration, respectively, than batch process.

Combined sugar yields for dilute sulfuric acid pretreatment of corn stover followed by enzymatic hydrolysis of the remaining solids

A number of previous studies determined dilute acid pretreatment conditions that maximize xylose yields from pretreatment or glucose yields from subsequent digestion of the pretreated cellulose, but our emphasis was on identifying conditions to realize the highest yields of both sugars from both stages. Thus, individual xylose and glucose yields are reported as a percentage of the total potential yield of both sugars over a range of sulfuric acid concentrations of 0.22%, 0.49% and 0.98% w/w at 140, 160, 180 and 200 °C. Up to 15% of the total potential sugar in the substrate could be released as glucose during pretreatment and between 15% and 90+% of the xylose remaining in the solid residue could be recovered in subsequent enzymatic hydrolysis, depending on the enzyme loading. Glucose yields increased from as high as 56% of total maximum potential glucose plus xylose for just enzymatic digestion to 60% when glucose released in pretreatment was included. Xylose yields similarly increased from as high as 34% of total potential sugars for pretreatment alone to between 35% and 37% when credit was taken for xylose released in digestion. Yields were shown to be much lower if no acid was used. Conditions that maximized individual sugar yields were often not the same as those that maximized total sugar yields, demonstrating the importance of clearly defining pretreatment goals when optimizing the process. Overall, up to about 92.5% of the total sugars originally available in the corn stover used could be recovered for coupled dilute acid pretreatment and enzymatic hydrolysis. These results also suggest that enhanced hemicellulase activity could further improve xylose yields, particularly for low cellulase loadings.