Optimizing Dilute-Acid Pretreatment of Rapeseed Straw for Extraction of Hemicellulose

Biological conversion of biomass into fuels and chemicals requires hydrolysis of the polysaccharide fraction into monomeric sugars prior to fermentation. Hydrolysis can be performed enzymatically or with mineral acids. In this study, dilute sulfuric acid was used as a catalyst for the pretreatment of rapeseed straw. The purpose of this study is to optimize the pretreatment process in a 15-mL bomb tube reactor and investigate the effects of the acid concentration, temperature, and reaction time. These parameters influence hemicellulose removal and production of sugars (xylose, glucose, and arabinose) in the hydrolyzate as well as the formation of by-products (furfural, 5-hydroxymethylfurfural, and acetic acid). Statistical analysis was based on a model composition corresponding to a 3³ orthogonal factorial design and employed the response surface methodology to optimize the pretreatment conditions, aiming to attain maximum xylan, mannan, and galactan (XMG) extraction from hemicellulose of rapeseed straw. The obtained optimum conditions were: H₂SO₄ concentration of 1.76% and temperature of 152.6 °C with a reaction time of 21 min. Under these optimal conditions, 85.5% of the total sugar was recovered after acid hydrolysis (78.9% XMG and 6.6% glucan). The hydrolyzate contained 1.60 g/L glucose, 0.61 g/L arabinose, 10.49 g/L xylose, mannose, and galactose, 0.39 g/L cellobiose, 0.94 g/L fructose, 0.02 g/L 1,6-anhydro-glucose, 1.17 g/L formic acid, 2.94 g/L acetic acid, 0.04 g/L levulinic acid, 0.04 g/L 5-hydroxymethylfurfural, and 0.98 g/L furfural.     

Enzymatic Pretreatment Coupled with the Addition of <Emphasis Type="Italic">p</Emphasis>-Hydroxyanisole Increased Levulinic Acid Production from Steam-Exploded Rice Straw Short Fiber

Levulinic acid production, directly from lignocellulosic biomass, resulted in low yields due to the poor substrate accessibility and occurrence of side reactions. The effects of reaction conditions, enzymatic pretreatment, and inhibitor addition on the conversion of steam-exploded rice straw (SERS) short fiber to levulinic acid catalyzed by solid superacid were investigated systematically. The results indicated that the optimal reaction conditions were temperature, time, and solid superacid concentration combinations of 200 °C, 15 min, and 7.5 %. Enzymatic pretreatment improved the substrate accessibility to solid superacid catalyst, and p-hydroxyanisole inhibitor reduced the side reactions during reaction processes, which helped to increase levulinic acid yield. The levulinic acid yield reached 25.2 % under the optimal conditions, which was 61.5 % higher than that without enzymatic pretreatment and inhibitor addition. Therefore, enzymatic pretreatment coupled with the addition of p-hydroxyanisole increased levulinic acid production effectively, which contributed to the value-added utilization of lignocellulosic biomass.     

Tailoring Wet Explosion Process Parameters for the Pretreatment of Cocksfoot Grass for High Sugar Yields

The pretreatment of lignocellulosic biomass is crucial for efficient subsequent enzymatic hydrolysis and ethanol fermentation. In this study, wet explosion (WEx) pretreatment was applied to cocksfoot grass and pretreatment conditions were tailored for maximizing the sugar yields using response surface methodology. The WEx process parameters studied were temperature (160–210 °C), retention time (5–20 min), and dilute sulfuric acid concentration (0.2–0.5 %). The pretreatment parameter set E, applying 210 °C for 5 min and 0.5 % dilute sulfuric acid, was found most suitable for achieving a high glucose release with low formation of by-products. Under these conditions, the cellulose and hemicellulose sugar recovery was 94 % and 70 %, respectively. The efficiency of the enzymatic hydrolysis of cellulose under these conditions was 91 %. On the other hand, the release of pentose sugars was higher when applying less severe pretreatment conditions C (160 °C, 5 min, 0.2 % dilute sulfuric acid). Therefore, the choice of the most suitable pretreatment conditions is depending on the main target product, i.e., hexose or pentose sugars.     

Conversion of Sago (<Emphasis Type="Italic">Metroxylon sagu</Emphasis>) Pith Waste to Fermentable Sugars via a Facile Depolymerization Process

The conversion of starchy sago (Metroxylon sagu) pith waste (SPW), a lignocellulosic biomass waste, to fermentable sugars under mild conditions had been successfully demonstrated. The optimum depolymerization of SPW was achieved at 2 wt% sample loading which was catalyzed by 100 mM of oxalic acid in the presence of 25 wt% NaCl solution at 110 °C for 3 h. Up to 97% SPW sample was being converted into fermentable sugars with limited formation of by-products after two sequential depolymerization cycles. Both reaction temperature and concentration of oxalic acid were crucial parameters for the depolymerization of SPW which exhibited a high selectivity for the production of glucose over other reducing sugars.     

Optimization of the process of chemical hydrolysis of cellulose to glucose

We studied the acid hydrolysis of cellulose in an aqueous medium with the aim of maximizing glucose yield and minimizing the formation of by-products. The influence of reaction parameters such as temperature, acid concentration, acid strength and type of cellulose precursor on glucose yield was investigated. We observed that moderate reaction temperature and low acid concentration resulted in the highest glucose yield with little formation of levulinic acid. Strong acid (pKa < 0) is required to achieve high glucose yield. The crystallite size of the cellulose also affects its reactivity; cellulose with higher crystallite size is more resistant to hydrolysis catalyzed by acid. The highest selectivity for glucose over levulinic acid was recorded at a reaction temperature of 413 K and a sulfuric acid concentration in the range of 0.2–0.5 mol/L. Under these reaction conditions, no levulinic acid was detected, but the glucose yield reached 20 % in only 2 h.     

Acid Hydrolysis of Hemicellulose in Green Liquor Pre-Pulping Extract of Mixed Northern Hardwoods

Forest biomass is a promising resource for future biofuels and bioproducts. Pre-pulping extraction of hemicellulose by alkaline (Green Liquor) pretreatment produces a neutral-pH extract containing hemicellulose-derived oligomers. A near-term option for use of this extract is to hydrolyze the oligomers to fermentable monomer sugars. Chips of mixed northern hardwoods were cooked in a rocking digester at 160 °C for 110 min in Green Liquor at a concentration of 3% Na₂O equivalent salts on dry wood. The mass of wood extracted into the Green Liquor extract was approximately 11.4% of the debarked wood mass, which resulted in a dilute solution of oligomeric hemicelluloses sugars. The concentration of the extract was increased through partial evaporation prior to hydrolysis. Dilute sulfuric acid hydrolysis was applied at conditions ranging from 100 to 160 °C, 2% to 6% (w/v) H₂SO₄, and 2- to 258-min residence time. The maximum fermentable sugar concentration achieved from evaporated extract was 10.7 g/L, representing 90.7% of the maximum possible yield. Application of the biomass pretreatment severity function to the hydrolysis results proved to offer a relatively poor prediction of temperature and reaction time interaction. The combined severity function, 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 sugar yields.     

Recovery of Algal Oil from Marine Green Macro-algae Enteromorpha intestinalis by Acidic–Hydrothermal Process

In this study, the recovery of algal oil from Enteromorpha intestinalis based on an acidic–hydrothermal reaction was investigated. Overall, the algal oil yield after the acidic–hydrothermal reaction was increased under the conditions of high reaction temperature, high catalyst concentration, and long reaction time within the tested ranges. Significantly, catalyst concentration, compared with reaction temperature and time, less affected algal oil recovery. The optimal acidic–hydrothermal reaction conditions for production of algal oil from E. intestinalis were as follows—200 °C reaction temperature, 2.92 % catalyst concentration, 54 min reaction time. Under these conditions, an 18.6 % algal oil yield was obtained. By increasing the combined severity factor, the algae oil recovery yield linearly increased.     

Novel hybrid process for the conversion of microcrystalline cellulose to value-added chemicals: part 1: process optimization

In this paper, a novel hybrid process for the treatment of microcrystalline cellulose (MCC) under hot-compressed water was investigated by applying constant direct current on the reaction medium. Constant current range from 1A to 2A was applied through a cylindrical anode made of titanium to the reactor wall. Reactions were conducted using a specially designed batch reactor (450 mL) made of SUS 316 stainless steel for 30–120 min of reaction time at temperature range of 170–230 °C. As a proton donor H₂SO₄ was used at concentrations of 1–50 mM. Main hydrolysis products of MCC degradation in HCW were detected as glucose, fructose, levulinic acid, 5-HMF, and furfural. For the quantification of these products, High Performance Liquid Chromatography (HPLC) and Gas Chromatography with Mass Spectroscopy (GC–MS) were used. A ½ fractional factorial design with 2-level of four factors; reaction time, temperature, H₂SO₄ concentration and applied current with 3 center points were built and responses were statistically analyzed. Response surface methodology was used for process optimization and it was found that introduction of 1A current at 200 °C to the reaction medium increased Total Organic Carbon (TOC) and cellulose conversions to 62 and 81 %, respectively. Moreover, application of current diminished the necessary reaction temperature and time to obtain high TOC and cellulose conversion values and hence decreased the energy required for cellulose hydrolysis to value added chemicals. Applied current had diverse effect on levulinic acid concentration (29.9 %) in the liquid product (230 °C, 120 min., 2 A, 50 mM H₂SO₄).     

The catalytic effect of Al-KIT-5 and KIT-5-SO<Subscript>3</Subscript>H on the conversion of fructose to 5-hydroxymethylfurfural

The aim of this work is to study the production of hydroxymethylfurfural (HMF) from fructose using heterogenous catalysts based on KIT-5. For this propose, Al-KIT-5 and KIT-5-SO₃H as the Lewis and Bronsted catalysts were prepared and were characterized using different techniques such as FT-IR, SEM, EDS, TEM, BET, TGA and elemental analysis. With the use of Al-KIT-5 as the catalyst, the appropriate reaction temperature and time were 135 °C and 60 min, respectively. Moreover, with the use of KIT-5-SO₃H as the catalyst, the proper reaction conditions were found to be 125 °C and 45 min, respectively. In addition, the corresponding amounts of catalyst weight were 40 and 50 mg for KIT-5-SO₃H and Al-KIT-5, respectively. Under these conditions, the conversion of fructose was 93.9 and 88.3%, respectively. These results indicated that, due to its Bronsted acid nature, the KIT-5-SO₃H catalyst showed better results when 40 mg catalyst was used at 125 °C for 45 min in DMSO as the solvent. Both catalysts could be recycled and reused several times.     

Dehydration of glucose into 5-hydroxymethylfurfural in SO_3H-functionalized ionic liquids

The continuous dehydration of D-glucose into 5-hydroxymethylfurfural（HMF） was carried out under mild conditions,using SO3H-functionalized acidic ionic liquids as catalysts and H2O-4-methyl-2-pentanone（MIBK） biphasic system as solvent.High glucose conversion of 97.4% with HMF yield of 75.1%was obtained at 120 8C for 360 min,also,small amounts of levulinic acid（LA） and formic acid were generated.Generally,the dosage of catalyst and the initial content of glucose influenced the reaction significantly; the HMF selectivity decreased with the excessive elevation of temperature and prolonging of time; and water content in the system had a negative effect on the reaction.The ionic liquid catalyst could be recycled and exhibited constant activity for five successful runs.This paper provided a new strategy for HMF production from glucose.     

Two-Stage Acidic–Alkaline Hydrothermal Pretreatment of Lignocellulose for the High Recovery of Cellulose and Hemicellulose Sugars

The focus of this work was to develop a combined acid and alkaline hydrothermal pretreatment of lignocellulose that ensures high recovery of both hexose and pentose. Dilute sulfuric acid and lime pretreatments were employed sequentially. Process performance was optimized in terms of catalyst concentration, retention time, and temperature using response surface methodology. Medium operational conditions in the acid stage and harsh conditions in the alkaline stage were desirable with optimal performance at 0.73 wt% H₂SO₄, 150 °C, 6.1 min in the first stage, and 0.024 g lime/g biomass, 202 °C, 30 min in the second stage. In comparison to single-stage pretreatments with high recovery of either glucose or xylose, two-stage process showed great promises with >80 % glucose and >70 % xylose recovery. In addition, the method greatly improved ethanol fermentation with yields up to 0.145 g/g Miscanthus, due to significantly reduced formation of inhibitory by-products such as weak acids, furans, and phenols. Supplementing biomimetic acids would further increase glucose yield by up to 15 % and xylose yield by 25 %.     

Hydrothermal conversion of cellulose into lactic acid with nickel catalyst

Utilization of biomass has become a major topic of research around the world. One promising aspect of utilization is production of lactic acid from carbohydrate biomass. Our previous study showed that lactic acid can be formed from glucose and cellulose by alkaline hydrothermal reactions, but the yield of lactic acid was low, particular for cellulose. In this study, an efficient method for producing lactic acid from cellulose under hydrothermal conditions with NaOH in the presence of nickel was developed. Experiments were conducted in a batch reactor at 300 °C for 1?C4 min. Results showed that nickel could promote the yield of lactic acid from cellulose. The highest yield of 34.07% was obtained by adding 0.5 mmol nickel using 2.5 M NaOH solution at 300 °C for 1 min.     

Ethanol production from steam-explosion pretreated wheat straw

Bioconversion of cereal straw to bioethanol is becoming an attractive alternative to conventional fuel ethanol production from grains. In this work, the best operational conditions for steam-explosion pretreatment of wheat straw for ethanol production by a simultaneous saccharification and fermentation process were studied, using diluted acid [H₂SO₄ 0.9% (w/w)] and water as preimpregnation agents. Acid-or water-impregnated biomass was steam-exploded at different temperatures (160–200°C) and residence times (5, 10, and 20 min). Composition of solid and filtrate obtained after pretreatment, enzymatic digestibility and ethanol production of pretreated wheat straw at different experimental conditions was analyzed. The best pretreatment conditions to obtain high conversion yield to ethanol (approx 80% of theoretical) of cellulose-rich residue after steam-explosion were 190°C and 10 min or 200°C and 5 min, in acid-impregnated straw. However, 180°C for 10 min in acid-impregnated biomass provided the highest ethanol yield referred to raw material (140 L/t wheat straw), and sugars recovery yield in the filtrate (300 g/kg wheat straw).     

Sulfonated porous biomass-derived carbon with superior recyclability for synthesizing ethyl levulinate biofuel

The synthesis of ethyl levulinate (EL) via esterification of levulinic acid (LA) with ethanol, which can be derived from biomass, has become an attractive topic since EL can be applied in many fields, such as fuel additives for petroleum and biodiesel, food additives and fragrance. Herein, the sulfonated porous carbon catalysts derived from the rinds of corn stalk biomass wastes were prepared by using sulfuric acid and phosphoric acid as the sulfonating agent and activator, respectively. The preparation parameters were optimized based on the catalytic activity for LA esterification with ethanol and the acid density of the corresponding catalysts. Also, various reaction factors were optimized to improve the catalytic efficiency over the optimal sulfonated corn stalk-derived carbon (s-CSC). Under the conditions of reaction temperature 80 °C, catalyst dosage 5 wt%, ethanol-to-LA molar ratio 5.0:1 and reaction time 8 h, the LA conversion reached 94% and 93% catalyzed by s-CSC and the optimal porous catalyst (s-p-CSC), respectively. Noticeably, benefitting from the hierarchical porous structure with large surface area, s-p-CSC exhibited much better recyclability than s-CSC. This work offers a highly effective solid acid catalyst for the synthesis of biofuel.

     

Production of Xylose from Meranti Wood Sawdust by Dilute Acid Hydrolysis

Xylitol production by bioconversion of xylose can be economically interesting if the raw material can be recovered from a cheap lignocellulosic biomass (LCB). Meranti wood sawdust (MWS) is a renewable and low-cost LCB that can be used as a promising and economic source of xylose, a starting raw material for the manufacture of several specialty chemicals, especially xylitol. This study aimed to optimize the hydrolysis process of MWS and to determine the influence of temperature, H₂SO₄ concentration, and residence time on xylose release and on by-product formation (glucose, arabinose, acetic acid, furfural, hydroxymethylfurfural (HMF), and lignin degradation products (LDPs)). Batch hydrolysis was conducted under various operating conditions, and response surface methodology was adopted to achieve the highest xylose yield. Xylose production was highly affected by temperature, acid concentration, and residence time. The optimum temperature, acid concentration, and time were determined to be 124 °C, 3.26 %, and 80 min, respectively. Under these optimum conditions, xylose yield and selectivity were attained at 90.6 % and 4.05 g/g, respectively.     

Pretreatment of Rice Straw by a Hot-Compressed Water Process for Enzymatic Hydrolysis

Hot-compressed water (HCW) is among several cost-effective pretreatment processes of lignocellulosic biomass for enzymatic hydrolysis. The present work investigated the characteristics of HCW pretreatment of rice straw including sugar production and inhibitor formation in the liquid fraction and enzymatic hydrolysis of pretreated material. Pretreatment was carried out at a temperature ranging from 140 to 240 °C for 10 or 30 min. Soluble oligosaccharides were found to constitute almost all the components of total sugars in the liquid fraction. The maximal production of total glucose at 180 °C and below accounted for 4.4–4.9% of glucan in raw material. Total xylose production peaked at 180 °C, accounting for 43.3% of xylan in raw material for 10-min pretreatment and 29.8% for 30-min pretreatment. The production of acetic acid increased at higher temperatures and longer treatment time, indicating more significant disruption of lignocellulosic structure, and furfural production achieved the maximum (2.8 mg/ml) at 200 °C for both 10-min and 30-min processes. The glucose yield by enzymatic hydrolysis of pretreated rice straw was no less than 85% at 180 °C and above for 30-min pretreatment and at 200 °C and above for 10-min pretreatment. Considering sugar recovery, inhibitor formation, and process severity, it is recommended that a temperature of 180 °C for a time of 30 min can be the most efficient process for HCW pretreatment of rice straw.     

Kinetic study of oxalic acid pretreatment of moso bamboo for textile fiber

In this study, samples of moso bamboo were hydrolyzed for textile fiber with oxalic acid under various process conditions. Saeman hydrolysis models were applied to predict the percentage of xylan remained in the substrate after pretreatment and the net xylose yield in the liquid stream. Kinetic constants for Saeman hydrolysis models were analyzed by an Arrhenius-type expansion which include activation energy and catalyst concentration factors. The result showed that the degradation activation energies of xylan and xylose were 97.27 and 136.38 kJ/mol, respectively. Then the kinetic of mathematical models were obtained. Furthermore, the reaction parameters of oxalic acid concentration (1–4 % w/w), reaction temperature (150–180 °C), and reaction time (5–60 min) were handled as a single parameter, combined severity, which ranged in the present study from 0.86 to 1.62. Using combined severity parameters, an optimal condition was achieved which was as the followings: oxalic acid 2.0 % w/w, 170 °C, and 20 min. Under these conditions, 2.3 g glucose/L and 13.65 g xylose/L were produced in the hydrolysate fraction, 54.1 % glucan and 10.8 % xylan were produced in the residue fraction.     

Comparative potentiality of Kans grass (Saccharum spontaneum) and Giant reed (Arundo donax) as lignocellulosic feedstocks for the release of monomeric sugars by microwave/chemical pretreatment

Two-stage microwave (microwave/NaOH pretreatment followed by microwave/H₂SO₄ pretreatment) was used to release monomeric sugars from Kans grass (Saccharum spontaneum) and Giant reed (Arundo donax). The optimum pretreatment conditions were investigated, and the maximum monomeric sugar yields were compared. The microwave-assisted NaOH and H₂SO₄ pretreatments with a 15:1 liquid-to-solid ratio were studied by varying the chemical concentration, reaction temperature, and reaction time to optimize the amount of monomeric sugars. The maximum amounts of monomeric sugars released from microwave-assisted NaOH pretreatment were 6.8 g/100 g of biomass [at 80 °C/5 min, 5 % (w/v) NaOH for S. spontaneum and at 120 °C/5 min, 5 % (w/v) NaOH for A. donax]. Furthermore, the maximum amounts of monomeric sugars released from microwave-assisted H₂SO₄ pretreatment of S. spontaneum and A. donax were 33.8 [at 200 °C/10 min, 0.5 % (w/v) H₂SO₄] and 31.9 [at 180 °C/30 min, 0.5 % (w/v) H₂SO₄] g/100 g of biomass, respectively. The structural changes of S. spontaneum and A. donax were characterized using Fourier transform infrared spectroscopy and scanning electron microscopy.     

Hydrothermal treatment of microcrystalline cellulose under mild conditions: characterization of solid and liquid-phase products

Microcrystalline cellulose (MCC) particles were subjected to hydrothermal treatment using an autoclave with temperatures ranging from 200 to 250 °C and reaction times ranging from 20 to 100 min. The structure and chemical composition of the reacted solid phase was analyzed by X-ray diffraction, thermo-gravimetric analysis, FTIR spectroscopy and ¹³C-NMR spectroscopy. The relative composition of the water-soluble products was determined by one-dimensional ¹H-NMR and two-dimensional homo and hetero-nuclear NMR spectroscopy. Within the experimental temperature and treatment time ranges, the crystallinity of the reacted solid phase was found to be mostly dependent on the treatment temperature while the aqueous solution was found to change with both temperature and treatment time. At the maximum temperature employed in this study (250 °C), the solid products are similar to amorphous oxidized carbon with glucose as the main water-soluble product. At lower temperatures the particles are unconverted MCC and the liquid products are primarily levulinic acid, formic acid and acetic acid with smaller quantities of 5-hydroxymethyl-furfural and glucose. Heterogeneous and liquid phase reaction-schemes are proposed to explain the observed solid and water-soluble products as a function of temperature and treatment time.     

The Optimization of Dilute Acid Hydrolysis of Cotton Stalk in Xylose Production

Cotton stalk, a lignocellulosic waste material, is composed of xylose that can be used as a raw material for production of xylitol, a high-value product. There is a growing interest in the use of lignocellulosic wastes for conversion into various chemicals because of their low cost and the fact that they are renewable and abundant. The objective of the study was to determine the effects of H₂SO₄ concentration, temperature, and reaction time on the production of sugars (xylose, glucose, and arabinose) and on the reaction by-products (furfural and acetic acid). Response surface methodology was used to optimize the hydrolysis process in order to obtain high xylose yield and selectivity. The optimum reaction temperature, reaction time, and acid concentration were 140 °C, 15 min, and 6%, respectively. Under these conditions, xylose yield and selectivity were found to be 47.88% and 2.26 g g⁻¹, respectively.