Xylose Yield Research Articles

Subcritical Water-Carbon Dioxide Pretreatment of Oil Palm Mesocarp Fiber for Xylooligosaccharide and Glucose Production.

The present work aimed to investigate the pretreatment of oil palm mesocarp fiber (OPMF) in subcritical H2O-CO2 at a temperature range from 150–200 °C and 20–180 min with CO2 pressure from 3–5 MPa. The pretreated solids and liquids from this process were separated by filtration and characterized. Xylooligosaccharides (XOs), sugar monomers, acids, furans and phenols in the pretreated liquids were analyzed by using HPLC. XOs with a degree of polymerization X2–X4 comprising xylobiose, xylotriose, xylotetraose were analyzed by using HPAEC-PAD. Enzymatic hydrolysis was performed on cellulose-rich pretreated solids to observe xylose and glucose production. An optimal condition for XOs production was achieved at 180 °C, 60 min, 3 MPa and the highest XOs obtained was 81.60 mg/g which corresponded to 36.59% of XOs yield from total xylan of OPMF. The highest xylose and glucose yields obtained from pretreated solids were 29.96% and 84.65%, respectively at cellulase loading of 10 FPU/g-substrate.

Integrated production of cellulosic bioethanol and succinic acid from rapeseed straw after dilute-acid pretreatment

The aim of this study was to develop an integrated biofuel (cellulosic bioethanol) and biochemical (succinic acid) production process from rapeseed straw after dilute-acid pretreatment. Rapeseed straw pretreatment at 20% (w/v) solid loading and subsequent hydrolysis with Cellic® CTec2 resulted in high glucose yield (80%) and ethanol output (122–125 kg of EtOH/Mg of rapeseed straw). Supplementation the enzymatic process with 10% dosage of endoxylanases (Cellic® HTec2) reduced the hydrolysis time required to achieve the maximum glucan conversion by 44–46% and increased the xylose yield by 10% compared to the process with Cellic® CTec2. Significantly higher amounts of succinic acid were produced after fermentation of pretreatment liquor (48 kg/Mg of rapeseed straw, succinic acid yield: 60%) compared to fermentation of xylose-rich residue after ethanol production (35–37 kg/Mg of rapeseed straw, succinic yield: 68–71%). Results obtained in this study clearly proved the biorefinery potential of rapeseed straw.

Disintegration of the agricultural by-product wheat bran under subcritical conditions.

The disintegration of destarched wheat bran in water and sulfuric acid (pH 3) under subcritical conditions (275-300 °C) and at short reaction times (1-4 min) was investigated. A cascade process comprising a stepwise separation of the liquid was applied to reduce the formation of undesired degradation products. The highest degree of biomass disintegration (67% dry mass solubilization) was achieved by application of a cascade process at 275 °C (pH 3). Regarding the dissolution of carbohydrates (monomeric and oligomeric form), the total glucose yields remained below 60%, while the total xylose and arabinose yields were about 76% and 67%. Approximately 74% of the protein and 95% of the mineral fraction could be extracted. The application of the cascade process enabled a substantially reduced formation of degradation products. When operating hydrothermally and subcritically in order to avoid some problematic aspects of a biorefinery, an extensive disintegration and monomerization of wheat bran and its constituents remains difficult even under the tested conditions (300 °C, pH 3). However, the applied cascade process proved to be useful to increase the yields and to substantially reduce the formation of undesired degradation products. Despite this fact, increased water consumption has to be conceded. © 2018 Society of Chemical Industry.

Impact of blending on hydrolysis and ethanol fermentation of garden wastes

Abstract Mixed biomass has the characteristics of stable supply and low cost of collection, and its bio-refinery could provide an effective contribution to the sustainable development of fuel ethanol production. Compared to traditional single energy crops, the key challenge of mixed biomass conversion lies in overcoming the non-uniformity of blended materials. In this study, the influence of blending on hydrolysis and ethanol fermentation of garden wastes was investigated. There was an unexpected result in that the total xylose yield during a liquid hot water process was enhanced when different garden biomasses were mixed. The peak of total xylose recovery appeared at the value of ∼0.5 for the ratio of xylan to lignin, which was further confirmed by blending multiple biomasses. Moreover, the non-uniformity of physio-chemical characteristics in mixed garden wastes restricted the co-hydrolysis of cellulose, particularly in the mixed-five-biomass. In spite of this disadvantage, blended feedstocks showed a better flow behavior, which could make them more suitable for enzymatic hydrolysis and ethanol fermentation with high substrate loading. The 72 h enzymatic digestibility and glucose concentration of treated mixed-three-biomass reached 100 ± 5% and 52.3 ± 2.6 g/l under the conditions of 15% (w/v) substrate loading, with the addition of 1% (v/v) Tween 20, which gave a maximum ethanol concentration of 16.9 ± 0.8 g/l. Overall, these results have shown that the complementary or synergistic effects of different individual biomasses make it feasible to produce ethanol from mixed biomass.

Microwave-Assisted Oxalic Acid Pretreatment for the Enhancing of Enzyme Hydrolysis in the Production of Xylose and Arabinose from Bagasse.

In this study, highly-efficient hydrolysis of bagasse into xylose and arabinose sugars (C5 sugars) was developed by microwave-assisted oxalic acid pretreatment under mild reaction conditions. The effects of acid and hydrolysis conditions on the C5 sugar yields were discussed. The results showed that oxalic acid performed better than hydrochloric acid and maleic acid, and was a promising alternative to sulfuric acid for xylose production at the same acid concentration. The maximum yields of xylose (95.7%) and arabinose (91.5%) were achieved via the microwave-assisted oxalic acid pretreatment (120 °C, 10 min, 0.4 mol/L, solid–liquid ratio of 1:50 g/mL), indicating that almost all xylan-type hemicelluloses were released from the cell wall and hydrolyzed into C5 sugars. After pretreatment, more than 90% of the cellulose in the residual bagasse was converted to glucose (92.2%) by enzymatic hydrolysis. This approach could realize the highly-efficient hydrolysis of xylan from bagasse into C5 sugars, which would enhance the enzyme hydrolysis of treated bagasse into glucose.

Impact of activation on properties of carbon-based solid acid catalysts for the hydrothermal conversion of xylose and hemicelluloses

Activation plays an important role in improving the pore structure of the carbon materials preparation. For carbon-based solid catalysts, activation could provide the high specific surface area and porosity. In this work, non-activated, KOH-activated, ZnCl2-activated treatments were comparatively discussed to prepare carbon-based solid acid catalysts for furfural production from xylose and hemicelluloses. These prepared catalysts were characterized by SEM, FT-IR, elemental analysis, Raman, N2 adsorption-desorption and Boehm titration. The results showed that the chemical activated treatment could significantly improve the specific surface area of carbon-based solid catalysts, but also had an important influence on the distribution of surface functional groups especially for decreasing of the SO3H density and the enhancement of the phenolic OH and COOH density. For the highest SO3H density of non-activated carbon-based catalyst, it displayed higher catalytic activity in the conversion of xylose to furfural than other catalysts. Meanwhile, using non-activated carbon-based catalyst in the aqueous solution, the maximum furfural yield of 50% was obtained from hemicelluloses at 200 °C for 2.5 h, the maximum xylose yield of 55% was achieved at 200 °C for 1.5 h. While KOH-activated carbon-based catalyst exhibited the excellent catalytic performance to produce xylooligosaccharide with the highest yield of 62% at 180 °C for 1.5 h.

Metabolic engineering of a xylose pathway for biotechnological production of glycolate in Escherichia coli

BackgroundGlycolate is a valuable chemical with extensive applications in many different fields. The traditional methods to synthesize glycolate are quite expensive and toxic. So, the biotechnological production of glycolate from sustainable feedstocks is of interest for its potential economic and environmental advantages. d-Xylose is the second most abundant sugar in nature and accounts for 18–30% of sugar in lignocellulose. New routes for the conversion of xylose to glycolate were explored.ResultsOverexpression of aceA and ghrA and deletion of aceB in Escherichia coli were examined for glycolate production from xylose, but the conversion was initially ineffective. Then, a new route for glycolate production was established in E. coli by introducing NAD+-dependent xylose dehydrogenase (xdh) and xylonolactonase (xylC) from Caulobacter crescentus. The constructed engineered strain Q2562 produced 28.82 ± 0.56 g/L glycolate from xylose with 0.60 ± 0.01 g/L/h productivity and 0.38 ± 0.07 g/g xylose yield. However, 27.18 ± 2.13 g/L acetate was accumulated after fermentation. Deletions of iclR and ackA were used to overcome the acetate excretion. An ackA knockout resulted in about 66% decrease in acetate formation. The final engineered strain Q2742 produced 43.60 ± 1.22 g/L glycolate, with 0.91 ± 0.02 g/L/h productivity and 0.46 ± 0.03 g/g xylose yield.ConclusionsA new route for glycolate production from xylose was established, and an engineered strain Q2742 was constructed from this new explored pathway. The engineering strain showed the highest reported productivity of glycolate to date. This research opened up a new prospect for bio-refinery of xylose and an alternative choice for industrial production of glycolate.

High-solid pretreatment of corn stover using urea for enzymatic saccharification

The aim of this research was to study a high-solid pretreatment of corn stover using urea. Effects of solid loading (30–70%), temperature (60–80 °C), time (2–14 d), ratio of urea to corn stover (1:10–1:1), and ratio of soybean flour to corn stover (1:40–1:10) on enzymatic saccharification were investigated. Generally, the glucose and xylose yield increased as the reaction temperature, time, and ratio of urea to corn stover increased. Urea enhanced enzymatic saccharification at a relatively high-solid loading and low temperature. The results showed that 80 °C for 10 d with urea to corn stover ratio of 1:1 and 50% solid loading are optimum treatment condition to achieve high glucose recovery and enzymatic saccharification efficiency. Under optimum condition, 97.24% glucan and 61.63% xylan were preserved in the treated corn stover, and the maximum enzymatic saccharification efficiencies of 84.11% and 78.54% were achieved for glucose and xylose, respectively.

Birch wood pre-hydrolysis vs pulp post-hydrolysis for the production of xylan-based compounds and cellulose for viscose application

Hydrothermal treatments of birch wood and kraft pulp were compared for their ability to extract the xylan and produce viscose-grade pulp. Water post-hydrolysis of kraft pulp produced a high-purity cellulosic pulp with lower viscosity but higher cellulose yield than traditional pre-hydrolysis kraft pulping of wood. Post-hydrolysis of pulp also increased the crystallite dimensions and degree of crystallinity in cellulose, and promoted a higher extent of fibril aggregation. The lower specific surface area in post-hydrolyzed pulps, derived from their larger fibril aggregates, decreased the accessibility of OH groups. However, this lower accessibility did not seem to decrease the pulp reactivity to derivatizing chemicals. In the aqueous side-stream, the xylose yield was similar in both pre- and post-hydrolysates, although conducting post-hydrolysis of pulp in a flow-through system enabled the recovery of high purity and molar mass (∼10 kDa) xylan for high-value applications.

Comprehensive evaluation of combining hydrothermal pretreatment (autohydrolysis) with enzymatic hydrolysis for efficient release of monosaccharides and ferulic acid from corn bran

The combination of hydrothermal pretreatment (autohydrolysis) and enzymatic hydrolysis was comprehensively evaluated for the efficient release of monosaccharides and ferulic acid from corn bran. Arabinan was depolymerized and solubilized more easily during autohydrolysis compared to xylan, esterified ferulic acid, and the acetyl group. Also, the enzymatic xylose yield showed strong linear correlation with arabinan, ferulic acid, and acetic acid content in autohydrolysis residues while correlations between enzymatic glucose yield and hemicellulose contents were separated into two stages with different slopes. The addition of a few debranching enzymes to commercial cellulase and xylanase only slightly enhanced enzymatic hydrolysis of autohydrolysis residues, whereas an enzyme blend from Aspergillus oryzae and Eupenicillium parvum showed a significant synergistic effect. Desirable combined hydrolysis yields of glucose (72.26%), xylose (75.87%), arabinose (76.95%), and ferulic acid (74.13%) were obtained after autohydrolysis at 165 °C for 40 min and subsequent hydrolysis by an equal mixture blend produced by A. oryzae and E. parvum at an enzyme loading dosage of 14.1 mg protein/g dry destarched corn bran.

Integrated approach for extraction of xylose, cellulose, lignin and silica from rice straw

In this paper, a novel process for xylose production was developed and discovered with simultaneous extraction of other product like cellulose, silica, and lignin. The study explored the effect of chemicals on xylose yield, and the xylose production process was optimized as followings: After pre-impregnation with nitric acid at 140°C for 15min, rice straw was treated at 1bar with 0.5% (v/v) nitric acid, followed by second hydrolysis by using 2.5%(w/v) sodium hydroxide with 2%(w/v) sodium hypochlorite at 121°C for 1h, decoloration and ionic impurities were removed by ion exchange. Using this process, 13.8g of crystal xylose was produced from 100g rice straw, simultaneously 26.01% (w/w) of cellulose, 10.11% (w/w) silica, and 6.21% (w/w) lignin were also extracted from rice straw respectively. All results indicated that this process is a more effective than the traditional method sulphuric acid hydrolysis process for lignocellulose biorefinery.

Mild and efficient extraction of hardwood hemicellulose using recyclable formic acid/water binary solvent

Formic acid/water binary solvent extraction with formic acid fraction lower than 77.5% (w/w) of azeotrope was used to extract hemicellulose-derived saccharides from poplar wood at various levels of severity. The highest xylose yield of 77.8% and arabinose yield of 93.5% were obtained at 120 °C and 1 h. To reduce cellulose hydrolysis and facilitate downstream xylose crystallization, mild conditions at 90 °C and 4 h was chosen as optimum severity, which led to the highest xylose fraction of 81.7% in all saccharides extracted, with a remarkable xylose yield of 73.1%. Mass balance analysis showed that 5.84% of xylan was degraded, but only 0.25% of xylan ended up as furfural at optimum severity. The proposed extraction process has high feasibility for industrial application since the low formic acid fraction in solvent allows simple recovery and concentration of used solvent.

Moderate pretreatment of oil palm empty fruit bunches for optimal production of xylitol via enzymatic hydrolysis and fermentation

Moderate pretreatment methods were evaluated on oil palm empty fruit bunches (OPEFB) in order to obtain xylose-rich hydrolysate for xylitol production via enzymatic hydrolysis and fermentation. Assessments on the effects of catalysts (autohydrolysis/water, acetic acid, or ammonia) and the corresponding concentration and pretreatment time at moderate pressure/temperature were conducted while the process performance was evaluated by enzymatic hydrolysis. Most hemicellulose was still retained in the pretreated solid at the evaluated pretreatment conditions, hydrolysis of both the pretreated solid and spent liquor are necessary to obtain most of xylose from OPEFB. Pretreatment using 5% ammonia gave the highest xylose yield; however, great amount of acid would be needed for pH adjustment for the following enzymatic hydrolysis process and thereby autohydrolysis was preferred. The optimum yield was obtained from autohydrolysis at 1.5 barg/127.9 °C for 60 min, which gave xylose yield of 0.085 g xylose/g OPEFB (or 39.1% of hemicellulose). The obtained hydrolysate could be directly used as substrate for fermentation.

Sodium Chloride-Assisted Depolymerization of Xylo-oligomers to Xylose

The depolymerization of hemicellulose is essential in the downstream processing of biomass within a biorefinery, with the search for energy efficient selective pathways for its conversion presenting a significant challenge. Herein, the process of NaCl promoted depolymerization of xylo-oligomers to xylose through use of seawater and NaCl, under microwave hydrolytic conditions, is investigated by systematic kinetic study assisted by deuterated agents. It was found that NaCl shortened the reaction time (10 min in NaCl–H2O vs 60 min in H2O at 180 °C) to obtain the maximum yield of xylose (about 90 wt %) without significant secondary reaction products formed. NaCl was observed to generate acidic products from residual xylose structure, rate limiting the process, but providing acids that simultaneously catalyzed the depolymerization of xylose-oligomers. It was also found that Cl– cleaved the hydrogen bonding in xylo-oligomers, releasing separated xylo-oligomer chains and enhancing the interaction of H+ with xyl...

Optimizing xylose production from pinewood sawdust through dilute-phosphoric-acid hydrolysis by response surface methodology

Abstract Response surface methodology was used to optimize the xylose production from pinewood sawdust through dilute-phosphoric-acid hydrolysis. The effects of independent variables on xylose yield were investigated, including reaction temperature (75–175 °C), reaction time (0–7.2 h), solution-to-feed ratio (4–20 mL/g), and phosphoric-acid concentration (0–6.67 wt%). Results indicated that the individual factor H3PO4 concentration and the interacting factors including temperature × time, temperature × H3PO4 concentration, and solution-to-feed ratio × H3PO4 concentration were all significant factors. Long reaction time (>5.4 h) and high phosphoric-acid concentration (>5%) showed little effect. Xylose yield increased with increasing temperature up to 125 °C. Higher phosphoric-acid concentration and larger solution-to-feed ratio also increased xylose yield. The coefficient of determination, corresponding analysis of variance, and parity plot indicated that the fitted model was appropriate for the acid-hydrolysis process. The maximum xylose production of 90.95% could be obtained with the reaction temperature of 106.7 °C, reaction time of 4.57 h, phosphoric-acid concentration 4.49 wt%, and solution-to-feed ratio of 12.51 mL/g.

Upgrading of Postconsumer Absorbent Hygiene Products for Bioethanol Production

Postconsumer absorbent hygiene products (AHPs), one of the most intractable municipal solid waste (MSW) streams, are generally subjected to landfills, causing urban waste management difficulties and environmental pollution. This study investigated the viability of recycling the cellulose component from postconsumer AHPs, demonstrated the fermentability of obtained cellulosic sugars for bioethanol production, and evaluated the technical feasibility of the process through scale-up. A set of integrated unit operations was developed to effectively upcycle the recovered AHPs into bioproducts. The processes were further optimized and scaled up 50-fold. Up to 83.5% glucose and 46.0% xylose yields were achieved during enzymatic saccharification. The sugars were readily fermentable through separate hydrolysis and fermentation (SHF) as well as simultaneous saccharification and fermentation (SSF) with maximum 89.9% ethanol theoretical yield.

Production of Xylitol from Agricultural Waste by Enzymatic Methods

Enzyme catalyzed production of xylose from autoclaved and non-autoclaved wheat straw was conducted followed by bioconversion of xylose to xylitol using a Crude preparation of Xylose Reductase (CXR) from Candida guillermondii. Ground wheat straw (autoclaved and non autoclaved) was treated at 40 and 50°C for up to 9 h at pH 4.5 with various concentrations of xylanase (12.4 to 37.2 U) and the reactions were assayed for reducing sugars. Hydrolysis of autoclaved wheat straw at 50°C for 3 h with 24.8 U of xylanase at pH 4.5 resulted in the highest yield of xylose (9.8% of total xylose). Overall, the autoclave pre-treatment resulted in a 22% higher yield of reducing sugars compared to the non pre-treated samples. The xylose hydrolysed wheat straw was adjusted to pH 7 and the effects of temperature, pH, time and CXR concentration were investigated to determine optimum conditions for xylitol production with NADPH. The optimal conditions for the synthesis of xylitol were 30°C at pH 7 for 8 h with 7.92 U of CXR and 10 mM NADPH with 23.9 g xylose. This research shows that xylitol synthesis using only an enzymatic system is feasible.

Effect of Moisture Content and Inoculum Size on Cell Wall Composition and Ethanol Yield from Switchgrass after Solid-State Pleurotus ostreatus Treatment

Abstract. The white-rot fungus is capable of selectively degrading lignin over polymeric sugars. Solid-state cultivation and subsequent simultaneous saccharification and fermentation for ethanol production were performed. Effects of moisture content (MC) and fungus inoculum on biomass degradation, ligninolytic enzyme, and ethanol production were evaluated. First, fungal pretreatment was performed with varied MC and inoculum levels and sampled every 20 days. The highest xylose yield observed was 15.6% for samples with 75% MC and 5 mL inoculum at fungal pretreatment of 40 days. The highest lignin degradation of 52% and highest ethanol yield of 31% (based on the glucan present in the raw switchgrass) were achieved for 80-day fungal-treated samples with 75% MC and 5 mL inoculum. Keywords: KLywords. Bioenergy, Fungal pretreatment, Oyster mushroom, Perennial grass.

Phase-Exchange Solvent Pretreatment Improves the Enzymatic Digestibility of Cellulose and Total Sugar Recovery from Energy Sorghum

Traditional liquid hot water pretreatment (LHWP) has a high water consumption, a high reaction temperature, and low lignin removal, making it unsuitable for industrial applications of biomass conversion. In this study, we developed a new phase-exchange solvent pretreatment (PESP) based on the varied phase composition of furfural (FF)-water at different temperatures. Substitution of water with FF had no significant influence on xylan hydrolysis, but it improved the mass transfer performance. At the optimum conditions of 180 °C, an FF:water ratio of 30:70 (v/v), a solid:liquid ratio of 1:8 (w/v), and 0.2 wt % sulfuric acid for 30 min, the PESP of energy sorghum achieved a 74.98% total xylose yield and removed 85.08% of the lignin, while there was a selective distribution of sugar and lignin in the aqueous and organic phases, respectively. Moreover, 99.58% of the cellulase enzyme digestibility and 94.02% of the total sugar recovery were achieved after 72 h. This unusually high enzymatic digestibility could b...

Comparative study of three optimized acid-based pretreatments for sugar recovery from sugarcane leaf waste: A sustainable feedstock for biohydrogen production

This paper reports the development and comparison of three optimized pretreatment models for xylose and glucose recovery from sugarcane leaf waste (SLW) using HCl, H2SO4 and HNO3. The input variables for each model consisted of acid concentration, temperature, solid to liquid ratio and heating time in the range of 0.5–5.0% (v/v), 60–100 °C, 30–50% (w/v) and 60–240 min respectively. All models showed high coefficients of determination (R2) above 0.78. Process optimization gave xylose and glucose yields of 78 and 11.48 g/L, 50.75 and 7.15 g/L, 30.82 and 3.99 g/L for HCl, H2SO4 and HNO3 pretreatments respectively. The HCl-based model gave up to 160% more sugar while simultaneously requiring a 2.5-fold lower heating time compared to H2SO4 and HNO3. The highest hemicellulose removal (93.15%) was also observed with the HCl model. Preliminary assessment of sugars from the optimized HCl pretreatment on dark fermentation gave a peak hydrogen fraction of 40.11% and a yield of 18.6 ml H2 g−1 fermentable sugar. The optimized pretreatments showed high efficiency at releasing xylose and glucose from SLW. In addition, the recovered sugars are excellent substrates for various fermentation bioprocesses and biofuel generation.