Pretreatment Liquor Research Articles

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.

Deep eutectic solvent pretreatment enabling full utilization of switchgrass

In this study, an acidified, aqueous DES comprising choline chloride: glycerol (ChCl:Gly) was used to fractionate switchgrass into three major streams under a relatively mild condition: cellulose-rich pulp, lignin, and xylose-rich liquor. The pulp showed good digestibility with about 89% glucose yield. The solvent can be recycled successfully and reused for at least four more pretreatment cycles while maintaining its pretreatment capability. The solvent recycling also improved the lignin recovery from the pretreatment liquor. Lignin recovered from different pretreatment cycles had the β–O–4 bonds preserved, and shared similar structures with native lignin. Using the pretreatment liquor as a substrate, the oleaginous yeast Rhodotorula toruloides produced 18.7 g/L biomass with lipid and carotenoid titers of 8.1 g/L and 15.0 mg/L, respectively. Overall, this study demonstrated a green process integrating chemical and biological methods toward full utilization of lignocellulosic biomass.

Aqueous Choline Chloride: A Novel Solvent for Switchgrass Fractionation and Subsequent Hemicellulose Conversion into Furfural

The performance of aqueous choline chloride (ChCl) solution on switchgrass fractionation and further utilization was evaluated. Under a relatively mild pretreatment condition (120 °C, 25 min), acidified ChCl solution efficiently removed 76% xylan and 51% lignin from switchgrass. The solvent was recycled and reused with similar performance for at least four pretreatment cycles when an acidic condition was maintained. The solvent recycling and reuse led to an increase in cumulative lignin yield with increased pretreatment cycles, reaching 93% at the fifth cycle. Two-dimensional heteronuclear single quantum coherence (HSQC) NMR analysis revealed that lignin recovered from the fifth cycle had a similar β-O-4 linkage abundance to native lignin. Such lignin would be well-suited for aromatic monomer production via depolymerization. The solvent recycling also resulted in xylose-rich pretreatment liquor, which was a good substrate and reaction medium for furfural production. The pretreated switchgrass showed good ...

Optimising conditions for bioethanol production from rice husk and rice straw: effects of pre-treatment on liquor composition and fermentation inhibitors

BackgroundRice straw and husk are globally significant sources of cellulose-rich biomass and there is great interest in converting them to bioethanol. However, rice husk is reportedly much more recalcitrant than rice straw and produces larger quantities of fermentation inhibitors. The aim of this study was to explore the underlying differences between rice straw and rice husk with reference to the composition of the pre-treatment liquors and their impacts on saccharification and fermentation. This has been carried out by developing quantitative NMR screening methods.ResultsAir-dried rice husk and rice straw from the same cultivar were used as substrates. Carbohydrate compositions were similar, whereas lignin contents differed significantly (husk: 35.3% w/w of raw material; straw 22.1% w/w of raw material). Substrates were hydrothermally pre-treated with high-pressure microwave processing across a wide range of severities. 25 compounds were identified from the liquors of both pre-treated rice husk and rice straw. However, the quantities of compounds differed between the two substrates. Fermentation inhibitors such as 5-HMF and 2-FA were highest in husk liquors, and formic acid was higher in straw liquors. At a pre-treatment severity of 3.65, twice as much ethanol was produced from rice straw (14.22% dry weight of substrate) compared with the yield from rice husk (7.55% dry weight of substrate). Above severities of 5, fermentation was inhibited in both straw and husk. In addition to inhibitors, high levels of cellulase-inhibiting xylo-oligomers and xylose were found and at much higher concentrations in rice husk liquor. At low severities, organic acids and related intracellular metabolites were released into the liquor.ConclusionsRice husk recalcitrance to saccharification is probably due to the much higher levels of lignin and, from other studies, likely high levels of silica. Therefore, if highly polluting chemical pre-treatments and multi-step biorefining processes are to be avoided, rice husk may need to be improved through selective breeding strategies, although more careful control of pre-treatment may be sufficient to reduce the levels of fermentation inhibitors, e.g. through steam explosion-induced volatilisation. For rice straw, pre-treating at severities of between 3.65 and 4.25 would give a glucose yield of between 37.5 and 40% (w/DW, dry weight of the substrate) close to the theoretical yield of 44.1% w/DW, and an insignificant yield of total inhibitors.

Effects of Green Liquor (GL) and Sodium Carbonate (SC) Pretreatment on Structural Characteristics of Wheat Stem Lignin

The content and structure of lignin have been considered as important factors that affect both pretreatment and enzymatic hydrolysis of lignocellulosic biomass. In this work, wheat stems (WS) were pretreated using mild alkali including green liquor (GL) and sodium carbonate (SC). The results indicate that GL pretreatment exhibits better delignification selectivity and higher enzymatic digestibility than SC pretreatment. Analysis of 1H–13C HSQC NMR and FTIR on cellulolytic enzyme lignin (CEL) preparations isolated from untreated and pretreated WS also proves that a certain amount of lignin degrades which leads to a decrease of β-O-4′ linkages. Under mild alkaline conditions, more guaiacyl units in lignin are removed than syringyl units, which results in a higher condensation degree and S/G ratio of CELs isolated from GL- and SC-pretreated stems. Compared with p-coumarate structures, ferulates in lignin are more stable under mild alkaline conditions.

Sugarcane Bagasse Hydrothermal Pretreatment Liquors as Suitable Carbon Sources for Hemicellulase Production by Aspergillus niger

The aim of this study was to valorize the hemicellulose-rich liquid fraction (liquor) arising from hydrothermal pretreatment of sugarcane bagasse (SCB) through its utilization as an unconventional, soluble carbon source for the production of hemicellulases, namely xylanases and α-L-arabinofuranosidases (ABFases), by Aspergillus niger DCFS11. Through the use of factorial design, pretreatment conditions producing liquors optimized for either early- or late-phase enzyme production were identified. Subsequent deep characterization of liquor components using liquid chromatography and mass spectrometry was performed to identify compounds likely responsible for hemicellulase induction. SCB liquors arising from various pretreatment configurations induced up to 2- and 8.6-fold higher xylanase and ABFase production, respectively, by A. niger DCFS11 than raw SCB substrate owing to the strong inducing potential of arabinosylated xylooligosaccharides and free arabinose solubilized during pretreatment. Notably, unlike the severe pretreatment conditions required for maximum cellulose saccharification and ethanol yields during biomass conversion, low severity and low biomass loading are required if enzyme production from liquor is desired at early-phase growth with no additional detoxification steps. This suggests that for effective application in biorefineries, separate or multi-step processes would be required to optimize both hemicellulase production by A. niger DCFS11 and cellulose digestion. This work demonstrates the potential of hydrothermal pretreatment of lignocellulosic substrates as a tool to increase the production of enzymes by filamentous fungi.

Improving the Efficiency of Biomass Pretreatment and Enzymatic Saccharification Process by Metal Chlorides

A series of metal chlorides with different valences were used during biomass pretreatment and enzymatic saccharification. After pretreatment, the solid substrate (SS), pretreatment liquor (PL), and conversion yield of cellulose (CYC) were characterized. The results showed that the monovalent salts, NaCl and KCl, as well as the divalent salts, MgCl2 and FeCl2, could promote the enzymatic saccharification to a certain extent, while CaCl2 had little influence on the enzymatic saccharification and cellulase activity, and ZnCl2 had an inhibitor effect on them. For a trivalent salt, FeCl3, the removal rate of hemicellulose and the CYC could come up to a high value. The hemicellulose degradation was mainly related to the valences of metal ions. The cellulose models, the enzymatic saccharification, and the enzyme activity assay results showed that most of the metal chlorides had promoter action toward the enzymatic hydrolysis and cellulase activity, with the exception of ZnCl2. Moreover, the metal ions, especially with high valences, had local effects, which could intensify the potentiation or inhibition impacts on the cellulase activities.

Bioethanol potential of Eucalyptus obliqua sawdust using gamma-valerolactone fractionation

Optimisation of conditions for gamma-valerolactone (GVL) pretreatment of Australian eucalyptus sawdust for high cellulose biomass and bioethanol production was demonstrated. Pretreatment parameters investigated included GVL concentrations of 35–50% w/w, temperatures of 120–180 °C and reaction durations of 0.5–2.0 h. Optimum conditions were determined using the response surface method (RSM) and central composite face-centred design. Cellulose content increased from 39.9% to a maximum of 89.3% w/w using treatments with 50% GVL at 156 °C for 0.5 h. Temperature had the most significant effect (RSM p < .05) on cellulose content of residual biomass and reducing operational duration of < 0.5 h may be viable according to RSM. PSSF fermentations of optimised pretreated eucalyptus sawdust produced up to 94% theoretical ethanol yield, which corresponded to approximately 181 kg of ethanol per dry ton of eucalyptus sawdust. The compositions of both the residual biomass and pretreatment liquors show that GVL pretreatment is a promising solvent for lignocellulosic biorefining.

Ultrafast fractionation of lignocellulosic biomass by microwave-assisted deep eutectic solvent pretreatment

Deep eutectic solvents (DESs) have received increasing attention in recent years as designer solvents for bioprocessing. In this study, ultrafast microwave-assisted DES pretreatment was developed for lignocellulose fractionation. The pretreatment was conducted for 45 s with microwave irradiation at 800 W using a DES composed of choline chloride and lactic acid (ChCl: LA). The results indicated that such pretreatment was highly effective in removing lignin and xylan while retaining most of cellulose in the pretreated solids. The ultrafast fractionation increased the cellulose digestibility by 2–5 folds. Switchgrass gave a similar glucose yield to corn stover but experienced less cellulose loss during the pretreatment. Miscanthus was also substantially fractionated but showed lower digestibility than switchgrass and corn stover. Lignin was readily recoverable with relatively high purity from all the pretreatment liquor. Our study demonstrated an innovative ultrafast pretreatment process with superior effectiveness for biomass fractionation and cellulose digestibility improvement as well as lignin extraction.

Feasibility of high-concentration cellulosic bioethanol production from undetoxified whole Monterey pine slurry

The economic feasibility of high-concentration cellulosic bioethanol production remains challenging because it requires easily available feedstock and low energy consumption process. Simultaneous saccharification and fermentation (SSF) of sulfite pretreated Momentary pine slurry at 20% (w/w) loadings increased ethanol concentration from 59.3 g/L to 68.5 g/L by washing strategy. Effects of inhibitors in pretreatment liquor were further investigated. Besides HMF, furfural and acetic acid, other inhibitors and/or their synergistic effects proved to be responsible for a lower fermentability. To bypass the inhibition and achieve high-efficient bioethanol concentration, a fermentation temperature of 28 °C was optimized for both cell growth and ethanol production. Under the optimal conditions with prehydrolyzed 25% (w/w) whole undetoxified slurry, a high ethanol concentration (up to 82.1 g/L) were produced with a yield of 205 kg/ton Monterey pine in the SSF. Thus, this high cellulosic bioethanol production from Monterey pine makes it a potential strategy for biofuel production.

Comparison of sodium hydroxide and calcium hydroxide pretreatments on the enzymatic hydrolysis and lignin recovery of sugarcane bagasse

Sodium hydroxide (NaOH) and calcium hydroxide (Ca(OH)2) respectively dissolved in water and 70% glycerol were applied to treat sugarcane bagasse (SCB) under the condition of 80°C for 2h. NaOH solutions could remove more lignin and obtain higher enzymatic hydrolysis efficiency of SCB than Ca(OH)2 solutions. Compared with the alkali-water solutions, the enzymatic hydrolysis of SCB treated in NaOH-glycerol solution decreased, while that in Ca(OH)2-glycerol solution increased. The lignin in NaOH-water pretreatment liquor could be easily recovered by calcium chloride (CaCl2) at room temperature, but that in Ca(OH)2-water pretreatment liquor couldn’t. NaOH pretreatment is more suitable for facilitating enzymatic hydrolysis and lignin recovery of SCB than Ca(OH)2 pretreatment.

Adsorptive detoxification of fermentation inhibitors in acid pretreated liquor using functionalized polymer designed by molecular simulation.

Acid pretreatment is the most common method employed in the lignocellulosic biorefinery leading to the separation of pentose and hexose sugar. The liquor obtained after pretreatment (acid pretreatment liquor or APL) needs to be detoxified prior to fermentation. The aim of this study was to design functional groups on a polymer matrix which are selective in their interaction to inhibitors with little or no specificity to sugars. Molecular modeling was used as a tool to design a suitable adsorbent for selective adsorption of inhibitors from a complex mixture of APL. Phenyl glycine-p-sulfonic acid loaded on chloromethylated polystyrene polymer was designed as an adsorbent for selective interaction with inhibitors. Experimental verification of the selectivity was successfully achieved. The current study provides insights on the adsorptive separation processes at the molecular level by design of specific adsorbent which can be tailor made for the better selectivity of the desired component.

High gravity enzymatic hydrolysis of hydrothermal and ultrasonic pretreated big bluestem with recycling prehydrolysate water

Enhancing sugar concentration and minimizing water consumption are key objectives for future cellulosic biofuel economics. To achieve those objectives, high-solids loading pretreatment and enzymatic hydrolysis (up to 20%, w/v) were studied. Big bluestem was selected and combined hydrothermal and ultrasonic treatment without chemicals addition was carried out in this study. Optimal high-solids loading pretreatment (16%, w/v) was identified in the ultrasonic reactor at 200 °C for 30 min. High-solids enzymatic hydrolysis (12%, w/v) was inefficient in the laboratory rotary shaker. However, using a horizontal reactor with good mixing is effective for high solids loading (20%, w/v), yielding 75 g/L of glucose. Minimum water to detoxify pretreated biomass while maintaining high sugar yields was 10 mL/g, which reduced by 50% as compared to the conventional washing process for steam-treated wheat straw. Recycling pretreatment liquor to treat the next batch of biomass was proved to be feasible without affecting the sugar yields.

Lactic acid production from Sophora flavescens residues pretreated with sodium hydroxide: Reutilization of the pretreated liquor during fermentation

The feasibility of lactic acid production from Sophora flavescens residues (SFRs) pretreated with sodium hydroxide with the reutilization of the pretreated liquor during fermentation was investigated. After sodium hydroxide pretreatment, 67.5% of the lignin was removed, and hydrolysis efficiency increased from 37.3% to 79.2%. The reutilization of pretreated liquor at 50% loading during open fermentation of unwashed SFR increased lactic acid production by 34.1%. The pretreated liquor acted as pH buffer and resulted in stable pH and high cellulase activity during fermentation. Inhibitors in the pretreated liquor did not affect the growth of lactic acid bacteria but severely inhibited the growth of ethanol-producing yeast. Consequently, lactic acid production increased and ethanol production was zero at 50% loading. Water consumption during pretreatment and fermentation with 50% pretreated liquor was 1.341L per 100g SFR, which was 67.6% lower than that during fermentation with washed SFR.

Enhancement of enzymatic hydrolysis of sugarcane bagasse by pretreatment combined green liquor and sulfite

Green liquor (GL) is readily available in any pulp mills which could be recycled. Alkaline sulfite pretreatment process was developed for non-woody biomass biorefinery. In this study, GL combined with sulfite was effectively utilized to improve the enzymatic hydrolysis of sugarcane bagasse by selectively removing lignin. Compare to conventional alkaline sulfite pretreatment, the solid yield could be higher with low degradation of polysaccharide. With the increment of the pretreatment temperature from 100 to 140°C, the enzymatic hydrolysis efficiency was improved. And a higher glucose yield was achieved under pretreatment condition of 0.4g/g-DS Na2SO3 and 1.5mL/g-DS GL due to the higher degradation of xylan. The highest glucose yield of 96.8% could be reached with 3.36g/(L·h) of initial rate after Kraft GL-sulfite pretreatment at 140°C. The superior performance of Kraft GL allows conversion of cellulose to glucose more significantly than Soda GL. In addition, surface tension test indicated that a part of lignin was dissolved in the pretreatment liquor as lignosulfonate. The results showed that GL combined with sulfite is a promising way for sugarcane bagasse pretreatment.

Research on the Dissolution of Pentosans during Eucalyptus Hydrolysate Pretreatment

Hydrolysate pretreatment (HP) uses hot water pre-hydrolysis liquor (HWPL) as partial or full pretreatment medium for biomass. Pentosan dissolution during Eucalyptus HP was studied under holding times between 0 min and 160 min, holding temperatures between 150 °C and 190 °C, a hot water pre-hydrolysate ratio (HWPR) from 20% to 100%, and a fixed liquid to wood ratio of 1:6. Both the pentosan removals in the hydrolysate pretreated solid (HPS) and the hydrolysate pretreatment liquor (HPL) pento-saccharides contents were determined and compared with those of hot water pre-hydrolysis (HWP). When compared to HWP, the HP enhanced pentosan removal from the solid phase, and enriched the saccharides or promoted the in-situ conversion of saccharides into other chemicals in the liquid phase. Pentosan removal in the HPS increased when holding time and temperature were increased. Increasing holding time first increased the pento-saccharide content in the HPL, and then decreased it after reaching the maximum. Elevating the holding temperature increased the pento-saccharide content in the HPL, except for arabino-oligosaccharide. Different HWPR had varying influences on pentosan removal in the HPS and on the saccharides concentration in the HPL. When controlled, HP positively influenced hemicellulose removal from biomass, and increased utilization value of the liquid phase obtained post pretreatment.

Pentose rich acid pretreated liquor as co-substrate for 1,3-propanediol production

Abstract Lignocellulosic biomass is considered to be a potential raw material for production of renewable fuels like bioethanol and biodiesel. Cellulose and hemicelluloses constitute major portion of the lignocellulosic biomass. Cellulose can be converted to glucose by hydrolysis and subsequently to ethanol by fermentation. The hemicellulosic portion mostly contains pentose sugars which cannot be utilized by many microorganisms for ethanol production. Acid pretreatment results in separation of a pentose-rich fraction which can be utilized for the production of various high value chemicals. The present study evaluates the utilization of pentose sugars as co-substrate, along with biodiesel industry-generated crude glycerol, for the production of 1,3-propanediol (1,3-PDO). Bioconversion of these low value byproducts into a high value chemical would be an economically advantageous strategy in terms of waste disposal for biorefineries. In this study, the production of 1,3-propanediol from the acid pretreated liquor obtained from rice straw was evaluated using Klebsiella pneumonia. Different carbon sources like pure hexose and pentose sugars, mixed pentose sugar containing acid pretreated liquor (APL) from rice straw and different concentrations of pentose sugars and acid pretreated liquor were evaluated. There is 65% increase in titers from 9.55 g/L to 15.75 g/L using APL as co-substrate. With addition of 0.5% (v/v) APL, 1,3-propanediol production reached 20.88 g/L with 0.69 g/g yield and 0.87 g/L/h productivity. The study comprehensively explains the behavior of Klebsiella pneumoniae strain utilizing pentose rich APL and crude glycerol which enroute to an integrated biorefinery approach.

Multi-objective regulation in autohydrolysis process of corn stover by liquid hot water pretreatment

Increasing reducing sugars (xylose and glucose) yield for bioethanol from corn stover depends strongly on optimization of pretreatment conditions. The optimum reaction conditions of two-stage liquid hot water (LHW) pretreatment based on total sugars yield were investigated. Under optimal conditions, the recovery of glucose of corn stover after two-stage LHW pretreatment and 72h enzymatic digestion, reached 89.55%. In addition, acetic acid-rich spent liquor pretreatment and one-stage LHW pretreatment have been carried out to make comparisons with two-stage LHW treatment. Glucose yield 89.55% is superior to the recovery 83.38% using acetic acid-rich spent liquor pretreatment or 80.58% using one-stage LHW pretreatment. The production of total sugars was increased by 7.8% when compared with one-stage pretreatment. Moreover, the structural features of the treated corn stover solid residues were also investigated by XRD and SEM technology in order to clarify the effects of the reaction on corn stover. The results indicated that the two-stage LHW pretreatment was an effective pretreatment method of corn stover to get most massive resource utilization, and it could be successfully applied to corn stover.

New degradation compounds from lignocellulosic biomass pretreatment: routes for formation of potent oligophenolic enzyme inhibitors

In this study 26 new oligophenol cellulase inhibitors were discovered from wheat straw pretreatment liquors.

Structural characteristics of milled wood lignin (MWL) isolated from green liquor (GL) pretreated poplar (Populus deltoides)

Abstract Pretreatment is one of the key steps for the utilization of lignocellulosic biomasses via biorefinery. Green liquor (GL) pretreatment has been considered as an effective approach to improve the subsequent enzymatic saccharification. For the better understanding of the structural changes of lignin in GL pretreatment, milled wood lignin (MWL) samples isolated from untreated and GL-pretreated poplar by the Björkman method were characterized by means of gel permeation chromatography (GPC), alkaline nitrobenzene oxidation (NBO), Fourier transform-infrared (FT-IR) spectroscopy, and quantitative 13C and 2D heteronuclear single quantum coherence nuclear magnetic resonance (HSQC NMR). The results indicate that the average molecular weight of MWLs decreased after GL pretreatment. Surprisingly, more guaiacyl-propane units are extracted under mild alkaline conditions than syringyl-propane units, which results in a higher condensation degree and higher S/G ratios of MWLs isolated from GL-pretreated poplars. The amount of β–O–4 structures decreased, while the β–β and β-5 structures increased after GL pretreatment. The structure of esterified p-hydroxybenzoic acid was detected in poplar MWL sample and it degraded obviously after GL pretreatment.