Two-stage Pretreatment Process Research Articles

Two-Stage Pretreatment of Jerusalem Artichoke Stalks with Wastewater Recycling and Lignin Recovery for the Biorefinery of Lignocellulosic Biomass

Jerusalem artichoke (Helianthus tuberosus L.) is emerging as one of the energy plants considered for biofuel production. Alkali and alkali-involved pretreatment methods have been widely used for the bioconversion of cellulosic materials due to their high sugar yield and low inhibitor release. However, the recovery and treatment of wastewater (black liquor) have been poorly studied. Here, we present a novel two-stage pretreatment process design for recycling black liquor. Jerusalem artichoke stalk (JAS) was first treated with 2% (w/v) NaOH, after which lignin was recovered by H2SO4 at pH 2.0 from the black liquor. The recycled solutions were subsequently used to treat the NaOH-pretreated JAS for the second time to dissolve hemicellulose. CO-pretreated JAS, hydrolysates, and acid-insoluble lignin were obtained after the above-mentioned two-stage pretreatment. A reducing sugar yield of 809.98 mg/g Co-pretreated JAS was achieved after 48 h at 5% substrate concentration using a cellulase dosage of 25 FPU/g substrate. In addition, hydrolysates containing xylose and acid-insoluble lignin were obtained as byproducts. The pretreatment strategy described here using alkali and acid combined with wastewater recycling provides an alternative approach for cellulosic biorefinery.

Pilot scale demonstration of a two-stage pretreatment and bioethanol fermentation process for cotton gin trash

A two-stage dilute acid and steam explosion (SE) pretreatment process was developed and evaluated at pilot scale for ethanol production from cotton gin trash (CGT). Optimal conditions for CGT processing were defined as 1:6 solids to liquids ratio with 9% H2SO4 wt. on solids at 180 °C for 15 min. during stage 1 with ensuing pressed fibres successively exposed to SE at 200 °C for 5 min during stage 2. SE fibres were highly acquiescent to enzyme hydrolysis (76%) in the presence of PEG 6000, yielding 381 g glucose kg−1 fibre. Simultaneous saccharification and fermentation (SSF) trials validated the selected process option and additional fed-batch SSFs confirmed titres above the minimum 4% ww-1 benchmark for economically viable distillation. The practicality of converting CGT to ethanol was demonstrated at pilot scale with titres above 4% ww-1 and a conversion efficiency of 60% t−1 dry GCT.

A two-stage pretreatment using dilute sodium hydroxide solution followed by an ionic liquid at low temperatures: Toward construction of lignin-first biomass pretreatment

A two-stage pretreatment process is constructed to test the feasibility of lignin-first biomass pretreatment. It is expected that mild pretreatment conditions help to reduce structural alterations to lignin or minimize condensation reactions in lignin which are important for certain high value applications. The pretreatment process consists of a step using 1% sodium hydroxide solution to increase the porosity of biomass and a second step using a typical ionic liquid, 1-ethy-3-methylimidazolium acetate ([C2C1Im][OAc]), to transform native crystalline cellulose into amorphous cellulose and therefore enhance enzymatic hydrolysis efficiency. Both pretreatments are carried out at 60 °C for 3 h to lower the severity of the pretreatment. Lignin samples extracted from untreated biomass (Lignin 1), liquid phase after NaOH pretreatment (lignin 2), liquid phase after subsequent IL pretreatment (lignin 3) and the lignin remaining in pretreated biomass (lignin 4) were analyzed using FTIR and by measuring molecular weight and antioxidant properties.

Two-Stage Pretreatment Process Validation for Production of Ethanol from Cotton Gin Trash

This study reports on the evaluation of a two-stage pretreatment process for preparing cotton gin trash (CGT) for conversation to ethanol. During the first stage, CGT was mixed with acid at 12% H2SO4 on solids and heated to 180 °C for 15 min in a pressurised stirred reactor. Pressed first-stage pretreated fibres were heated to 200 °C for 5 min during the second stage. The two-stage process facilitated excellent sugar recovery from both cellulose (84%) and hemicellulose (78%) fractions of CGT. Recombinant yeast GSF335 propagated on first-stage liquors yielded 41.8 g kg−1 of dry CGT and was compared with the commercial yeast during separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentations (SSF). SHF of pretreated CGT fibre yielded the equivalent of 66.2 and 64.0 kg ethanol per tonne of unprocessed CGT with GSF335 and the commercial yeast, respectively. SSF ethanol yields for the commercial yeast were significantly lower (50.3 kg) while GSF335 correspondingly produced 63.8 kg ethanol per tonne of raw CGT.

Membrane distillation coupled with a novel two-stage pretreatment process for petrochemical wastewater treatment and reuse

A novel hybrid system was designed for petrochemical wastewater treatment and reuse by coupling membrane distillation (MD) with a two-stage pretreatment process comprising oil/water separation and photocatalytic organics degradation. The oil/water separation process removed oil emulsions from water, while the follow-up photocatalysis process degraded dissolved oil and volatile organic pollutants. The pretreated water was then introduced to the MD process to produce distilled water. A modified stainless steel mesh/glass microfiber filter was used for removal of oil emulsions and exhibited excellent performance and durability (92% oil rejection in the first cycle and 87% after 10 consecutive cycles). In the photocatalysis stage, TiO2 P25 was used as the photocatalyst to effectively decompose the remaining organic compounds and to inactivate microorganisms under UV light irradiation. The two-stage pretreatment reached 99.5% total organic degradation and 6.02 log bacteria removal. The advantages of the hybrid system are to prevent MD membrane fouling and produce high quality distillate with low TDS and minimal volatile organics that are difficult to remove by a conventional MD process.

New two-stage pretreatment for the fractionation of lignocellulosic components using hydrothermal pretreatment followed by imidazole delignification: Focus on the polysaccharide valorization

The combination of hydrothermal pretreatment followed by delignification with imidazole was evaluated for the first time as a potential selective two-stage fractionation for elephant grass, aiming at obtaining pure fractions susceptible to conversion to high value-added products. In addition, the recovery of cellulose and hemicelluloses and enzymatic hydrolysis yield of pretreated elephant grass were evaluated. Hydrothermal pretreatment at 180 °C under non-isothermal conditions allowed obtaining a liquor rich mainly in xylo- and glucooligosaccharides, as well as pentoses. Subsequent treatment of the recovered solid fraction with imidazole at 140 °C for 182.5 min resulted in 83.8 wt% delignification and cellulose enrichment of 97.7 wt%. The solids obtained from the two-stage pretreatment process also permitted high glucan to glucose conversion through enzymatic hydrolysis using Cellic CTec2 (99.0 mol%) or an enzymatic complex of Penicillium echinulatum (96.3 mol%).

Effect of xylanase-assisted pretreatment on the properties of cellulose and regenerated cellulose films from sugarcane bagasse

A two-stage pretreatment process using alkaline and xylanase-assisted pretreatments was studied and compared to one-step alkaline pretreatment to investigate the effect of xylanase-assisted pretreatments on the properties of fibers and regenerated cellulose films. The alkaline-xylanase bleached fibers (AXB-fibers) could reduce bleaching time from 6 to 4 times to obtain an 83.3% whiteness index. A substantial proportion of the cellulose content (83%) was successfully extracted from sugarcane bagasse using the two-step process. Moreover, the fiber had an increased crystallinity index and thermal stability. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) revealed that hemicellulose and lignin were removed from the sugarcane bagasse (SCB) structure during the cellulose extraction process. The alkaline bleached fibers (AB-fibers) and AXB-fibers were dissolved in 1-butyl-3-methylimidazolium chloride, and regenerated cellulose films, AB-films and AXB-films, respectively, were prepared from the solutions. SEM images showed that both cellulose films were homogeneous and had a smooth surface. FTIR and X-ray diffraction (XRD) analyses corroborated that the transition from cellulose I to cellulose II occurred during the dissolution and regeneration process. Furthermore, the AXB-films displayed higher thermal stability and mechanical properties (258 °C and 90.43 MPa for the onset temperature and tensile strength, respectively) than those of the AB-films.

Enhancement of sugar recovery and ethanol production from wheat straw through alkaline pre-extraction followed by steam pretreatment

To improve sugar recovery and ethanol production from wheat straw, a sequential two-stage pretreatment process combining alkaline pre-extraction and acid catalyzed steam treatment was investigated. The results showed that alkaline pre-extraction using 8% (w/w) sodium hydroxide at 80 °C for 90 min followed by steam pretreatment with 3% (w/w) sulfur dioxide at 151 °C for 16 min was sufficient to prepare a substrate that could be efficiently hydrolyzed at high solid loadings. Moreover, alkaline pre-extraction reduced the process severity of steam pretreatment and decreased the generation of inhibitory compounds. During enzymatic hydrolysis, increasing solid loading decreased the yield of monomeric sugars. Enzymatic hydrolysis at 25% (w/v) solid loading, the yields of approximately 80% of glucose and 65% of xylose could be reached with an enzyme dosage of 25 mg protein/g glucan. Following fermentation of hydrolysate with sugar concentration of approximately 120 g/L, an ethanol concentration of 54.5 g/L was achieved.

Evaluation of an organosolv-based biorefinery process to fractionate wheat straw into ethanol and co-products

In this study, organosolv pre-extraction of wheat straw (WS) was conducted to extract lignin for understanding the effect of silica on enzymatic hydrolysis of carbohydrates. The results showed that the presence of silica in the WS substrate was associated with a decreased conversion of carbohydrates into monomeric sugars during enzymatic hydrolysis. Then, a sequential two-stage pretreatment process comprising ethanol pre-extraction and alkaline pretreatment was investigated to convert WS carbohydrates into bioethanol and recover lignin and silica. The results demonstrated that the pre-extraction with ethanol at 160 °C for 50 min followed by alkaline treatment with 11% sodium carbonate (Na2CO3) was sufficient to generate a highly digestible substrate. 85.7% of the original sugars in the raw feedstock was recovered by two-stage pretreatment followed by enzymatic hydrolysis with an enzyme loading of 12 FPU/g glucan. Fermentation with Saccharomyces cerevisiae SR8 u strain consumed 97.8% sugars in the hydrolysate to reach 6.5% w/v ethanol titer. With this proposed process, about 89.1% silica and 62.5% lignin were recovered at high levels of purity.

Efficient conversion of wheat straw into methyl levulinate catalyzed by cheap metal sulfate in a biorefinery concept

Wheat straw can be converted into biofuel candidate-methyl levulinate with copper sulfate as the cheap catalyst. To take advantage of the whole components of wheat straw, a two-stage pretreatment process was developed in this study. In the first-stage process, the hemicellulose component in wheat straw can be converted into biosurfactant at the mild conditions, and the lignin component can be extracted as another value added by-product in the second stage. On the basis, the pretreated wheat straw was used as raw material for methyl levulinate production, and a yield of 20.2 wt% can be obtained under the optimum reaction conditions. Meanwhile, the catalyst recycling experiments showed that copper sulfate was stable and can be reused more than five times. The results of mass balances and preliminary economic analysis further indicated that the production of integrated biorefinery processes producing diversified products offers potential for the sustainable valorization of wheat straw.

Ethanol production from bamboo using mild alkaline pre-extraction followed by alkaline hydrogen peroxide pretreatment

A sequential two-stage pretreatment process comprising alkaline pre-extraction and alkaline hydrogen peroxide pretreatment (AHP) was investigated to convert bamboo carbohydrates into bioethanol. The results showed that mild alkaline pre-extraction using 8% (w/w) sodium hydroxide (NaOH) at 100°C for 180min followed by AHP pretreatment with 4% (w/w) hydrogen peroxide (H2O2) was sufficient to generate a substrate that could be efficiently digested with low enzyme loadings. Moreover, alkali pre-extraction enabled the use of lower H2O2 charges in AHP treatment. Two-stage pretreatment followed by enzymatic hydrolysis with only 9FPU/g cellulose led to the recovery of 87% of the original sugars in the raw feedstock. The use of the pentose-hexose fermenting Saccharomyces cerevisiae SR8u strain enabled the utilization of 95.7% sugars in the hydrolysate to reach 4.6%w/v ethanol titer. The overall process also enabled the recovery of 62.9% lignin and 93.8% silica at high levels of purity.

Algorithm of multi-criterion green process assessment for renewable raw materials bioconversion

Green Chemistry is one of the most important and practically used tools to integrate principles of sustainable development and green economy in the field of chemistry and the chemical industry in various countries. There is a number of metrics in the field of green chemistry. The research presented is an original algorithm of multi-criterion green process assessment for renewable raw materials bioconversion. The algorithm is used when the process of obtaining the same target substance N is possible to be carried out in many ways (or under different conditions). In this case, the researcher task is to choose the best process in compliance with the principles of green chemistry. The multiple-factor complex assessment is to be used to choose the optimum process conditions. The algorithm designed was tested for efficiency in choosing the optimal processes of acid hydrolysis of deproteinized meals. The deproteinized sunflower meal preprocessing efficiency analysis was carried out during the course of its microbiological conversion into a vegetable protein and carbohydrate feed supplement taking into account the principles of green chemistry. The methodology testing was based on the experimental data obtained by chemical hydrolysis of deproteinized residues, and two-stage pretreatment process of deproteinized residues processing comprising the steps of chemical and enzymatic hydrolysis. The combination of chemical and enzymatic hydrolysis in two-stage deproteinized sunflower meal processing was justified. The proposed algorithm allowed not only to determine the effective ranges of parameters of deproteinized sunflower meal processing, but also allowed to justify the possibility of its optimization due to the both processes combined.

Evaluation of an integrated process to fully utilize bamboo biomass during the production of bioethanol

Aiming for the complete utilization of bamboo biomass, an integrated process which combines ethanol production with the recovery of silica and lignin was proposed. To reduce chemical charge required for the fractionation of silica and lignin from bamboo and improve the digestibility of the obtained substrate, a sequentially two-stage pretreatment process of autohydrolysis and alkaline extraction was carried out. From the view of enhancing enzymatic hydrolysis and recovery of silica and lignin, a two-stage treatment of autohydrolysis at 180°C for 90min followed by alkaline extraction at 100°C with 6% NaOH (based on pretreated chips) for 120min was optimized. About 93.7% of original silica and 75.7% of original lignin could be recovered from bamboo. Enzymatic hydrolysis and fermentation of carbohydrates showed that an overall sugar yield of 88.6% of original sugar content and an ethanol recovery of 0.467g/g sugar were achieved based on the proposed scheme.

Green chemistry for the optimum technology of biological conversion of vegetable waste

Nowadays the development of low-waste and resource-saving technologies of food products based on renewable raw materials and waste products of their processing enriched with protein is one of the priority tasks to be solved in the framework of sustainable development of modern society. The method of assessing the effectiveness of waste pretreatment of deproteinized sunflower meal (DSFM), one of oil and fat industry waste products is proposed for its microbial conversion into vegetable carbohydrate and protein concentrates according to the principles of green chemistry. The methodology proposed includes an assessment of three factors: amount of wastes per unit of the desired product; the amount of hazardous substances used in the pretreatment process, and process efficiency. The methodology testing was based on the experimental data obtained by chemical hydrolysis of DSFM, and also two-stage pretreatment process of DSFM comprising the steps of chemical and enzymatic hydrolysis. The recommendations for selection of optimal DSFM pretreatment conditions based on the calculated assessments of the process efficiency are submitted.

Comparison of two-stage acid-alkali and alkali-acid pretreatments on enzymatic saccharification ability of the sweet sorghum fiber and their physicochemical characterizations

Two-stage acid/alkali pretreatment was used to enhance the saccharification efficiency of sweet sorghum fiber. The physicochemical characterizations of the pretreated fibers were evaluated by SEM, FTIR and XRD. The acid and alkali sequence in the two-stage pretreatment process was compared, and their dosage was optimized. The results indicated that the two-stage pretreatment showed better saccharification performance when compared with conventional single stage pretreatment. And compared with the acid-alkali sequence, the alkali-acid sequence achieved higher glucose yield (0.23g·g−1) under the optimized conditions, which was 1.64 and 1.21 times higher than that of the single stage and the acid-alkali pretreatments, respectively. Overall, the two-stage pretreatment process is a promising approach to achieve high fermentable glucose conversion rate of cellulosic material.

A two-stage pretreatment process using dilute hydrochloric acid followed by Fenton oxidation to improve sugar recovery from corn stover

A two-stage pretreatment process is proposed in this research in order to improve sugar recovery from corn stover. In the proposed process, corn stover is hydrolyzed by dilute hydrochloric acid to recover xylose, which is followed by a Fenton reagent oxidation to remove lignin. 0.7wt% dilute hydrochloric acid is applied in the first stage pretreatment at 120°C for 40min, resulting in 81.0% xylose removal. Fenton reagent oxidation (1g/L FeSO4·7H2O and 30g/L H2O2) is performed at room temperature (about 20°C) for 12 has a second stage which resulted in 32.9% lignin removal. The glucose yield in the subsequent enzymatic hydrolysis was 71.3% with a very low cellulase dosage (3FPU/g). This two-stage pretreatment is effective due to the hydrolysis of hemicelluloses in the first stage and the removal of lignin in the second stage, resulting in a very high sugar recovery with a low enzyme loading.

English

Microbial inhibitors including weak acids, furan derivatives and phenolic compounds are key problems of cellulosic bio-fuels production by fermentation. Most of these inhibitors are sugars and lignin degradation compounds, which are almost unavoidable during pretreatment processes. While, most of the one stage pretreatment has been conducted at high severity factors of 3.5 or more to get high sugar yield, with increase in severity factor, high concentration of microbial inhibitors were formed and significantly affected downstream biofuel yield. Thus, a two-stage pretreatment of corn stalk, hydrothermal followed by oxalic acid, under low severity factor and its enzymatic degradability was investigated in this study to identify fermentable sugar production and corresponding microbial inhibitors formation. Additionally, effect of equivalent severity factors of 2 to 3.5 and particle sizes of 1 to 35 mm were also studied systematically. Particle size of 15 mm was found as an optimum size at an equivalent severity factor of 2.5. Sugars 61.99 ± 0.03 g and inhibitors 5.12 ± 0.01 g from 100 g of corn stalk were obtained at the optimum particle size and pretreatment condition. The highest glucan conversion and recovery at the optimum conditions were 92.95± 0.08 and 78.42± 0.07%, respectively. Overall, the two-stage pretreatment process with the larger particle size and low equivalent severity factor could be an alternative to reduce microbial inhibitors formation and excessive biomass processing cost. Key words: Bio-fuel, corn stalk, pretreatment, particle size, microbial inhibitors, fermentable sugars.

Coupling alkaline pre-extraction with alkaline-oxidative post-treatment of corn stover to enhance enzymatic hydrolysis and fermentability.

BackgroundA two-stage chemical pretreatment of corn stover is investigated comprising an NaOH pre-extraction followed by an alkaline hydrogen peroxide (AHP) post-treatment. We propose that conventional one-stage AHP pretreatment can be improved using alkaline pre-extraction, which requires significantly less H2O2 and NaOH. To better understand the potential of this approach, this study investigates several components of this process including alkaline pre-extraction, alkaline and alkaline-oxidative post-treatment, fermentation, and the composition of alkali extracts.ResultsMild NaOH pre-extraction of corn stover uses less than 0.1 g NaOH per g corn stover at 80°C. The resulting substrates were highly digestible by cellulolytic enzymes at relatively low enzyme loadings and had a strong susceptibility to drying-induced hydrolysis yield losses. Alkaline pre-extraction was highly selective for lignin removal over xylan removal; xylan removal was relatively minimal (~20%). During alkaline pre-extraction, up to 0.10 g of alkali was consumed per g of corn stover. AHP post-treatment at low oxidant loading (25 mg H2O2 per g pre-extracted biomass) increased glucose hydrolysis yields by 5%, which approached near-theoretical yields. ELISA screening of alkali pre-extraction liquors and the AHP post-treatment liquors demonstrated that xyloglucan and β-glucans likely remained tightly bound in the biomass whereas the majority of the soluble polymeric xylans were glucurono (arabino) xylans and potentially homoxylans. Pectic polysaccharides were depleted in the AHP post-treatment liquor relative to the alkaline pre-extraction liquor. Because the already-low inhibitor content was further decreased in the alkaline pre-extraction, the hydrolysates generated by this two-stage pretreatment were highly fermentable by Saccharomyces cerevisiae strains that were metabolically engineered and evolved for xylose fermentation.ConclusionsThis work demonstrates that this two-stage pretreatment process is well suited for converting lignocellulose to fermentable sugars and biofuels, such as ethanol. This approach achieved high enzymatic sugars yields from pretreated corn stover using substantially lower oxidant loadings than have been reported previously in the literature. This pretreatment approach allows for many possible process configurations involving novel alkali recovery approaches and novel uses of alkaline pre-extraction liquors. Further work is required to identify the most economical configuration, including process designs using techno-economic analysis and investigating processing strategies that economize water use.

Efficient removal of lignin with the maintenance of hemicellulose from kenaf by two-stage pretreatment process

The enhancement of lignocellulose hydrolysis using enzyme complexes requires an efficient pretreatment process to obtain susceptible conditions for the enzyme attack. This study focuses on removing a major part of the lignin layer from kenaf (Hibiscus cannabinus) while simultaneously maintaining most of the hemicellulose. A two-stage pretreatment process is adopted using calcium hydroxide, Ca(OH)2, and peracetic acid, PPA, to break the recalcitrant lignin layer from other structural polysaccharides. An experimental screening of several pretreatment chemicals, concentrations, temperatures and solid–liquid ratios enabled the production of an optimally designed pretreatment process for kenaf. Our results showed that the pretreatment process has provide 59.25% lignin removal while maintaining 87.72% and 96.17% hemicellulose and cellulose, respectively, using 1g of Ca(OH)2/L and a 8:1 (mL:g) ratio of liquid–Ca(OH)2 at 50°C for 1.5h followed by 20% peracetic acid pretreatment at 75°C for 2h. These results validate this mild approach for aiding future enzymatic hydrolysis.

Acid-Alkaline Two-Stage Pretreatments of Corn Stover for Enhancing Enzymatic Saccharification

For the enzymatic saccharification of lignocellulosic biomass, single acid or alkaline pretreatment is not satisfactory because of the low sugar yields together with the neutralization of residual chemicals before enzymatic hydrolysis. Herein, an acid-alkaline two-stage pretreatment process was designed to treat corn stover. During the process, the pretreated liquid from the first stage and the solid residues from the second stage were mixed together for the subsequent simultaneous enzymatic hydrolysis, where a mixture of cellulase with an activity loading of 20 FPU/g substrate, cellobiase with an activity loading of 5 U/g substrate, and xylanase with an activity loading of 200 U/g substrate was used. Compared to the single acid or alkaline pretreatment, the acid-alkaline two-stage pretreatment could significantly improve the enzymatic saccharification, and 91.2% glucose yield with 52.56% of the theoretical total reducing sugar yield was achieved after the subsequent enzymatic hydrolysis.