Ethanol Organosolv Research Articles

Investigation on the production of formic and acetic acids from lignin by ethanol organosolv treatment at mild conditions.

Cellulose and hemicellulose are usually considered the sources of formic and acetic acids that are obtained during ethanol pulping process, while our research reveals that lignin is another critical source of acids in the process. In this research, the sample lignin was purified and treated under ethanol pulping conditions and the factors that influence the yields of acids including: ethanol ratio (0-100%), residence time (30-210 min), reaction temperature (150-200 °C) and the effect of residual oxygen in the vessel, were tested separately. The yields of acids were identified using UPLC, the volatile products were characterized by GC-MS and the residual lignin was characterized by 13C NMR. The results indicated that the residual oxygen in the reaction vessel acted as an oxidant and the maximum yields of formic and acetic acid are 5.5% and 4.8% (g/g-lignin) from reed and aspen lignin, respectively. For understanding mechanism of the reaction, six lignin model compounds (LMCs) were treated and analyzed in the same reaction conditions; the subsequent results showed that both formic and acetic acid could be detected for all the LMCs tested. On the bases of the experimental results, the reaction pathways have been proposed and discussed.

Hydrothermal conversion of wood, organosolv, and chlorite pulps

In this work, beech wood has been submitted to fractionation and hydrothermal liquefaction in order to produce fermentable carbohydrates. Fractionation either by ethanol organosolv or by sodium chlorite/acetic acid (SC/AA) treatment allowed obtaining delignification yields of 50 and 91 wt.% respectively. The recovered pulps were then submitted to liquefaction in hot-compressed water (HCW). Three temperatures were studied: 180, 200, and 220 °C during 2 h. The same experiments were conducted on untreated beech and model cellulose (Avicel PH-101). Product yields and total carbohydrates were determined. The liquefaction products, i.e., solid residue, water-soluble compounds, and permanent gas, were analyzed respectively by X-ray diffraction (XRD), high-performance anion-exchange chromatography with pulsed amperometric detector (HPAEC-PAD), and gas chromatography (GC). SC/AA treatment allowed a high recovery of hemicelluloses and for this reason, xylose content was significantly higher than for the organosolv pulp. The maximum yields of total carbohydrates (based on the initial carbohydrates in wood), found when the liquefaction temperature was 220 °C, increased from 9.0 wt.% for the raw beech to 13.5 and 33.7 wt.% for the organosolv and SC/AA pulps respectively.

The structural characterization and antioxidant properties of oil palm fronds lignin incorporated with p-hydroxyacetophenone.

This study reports on the effects of unmodified autohydrolyzed ethanol organosolv lignin (AH EOL) and modified autohydrolyzed ethanol organosolv lignin on the structural characteristics and antioxidant properties upon incorporation of p-hydroxyacetophenone (AHP EOL). The lignin samples isolated from black liquor of oil palm fronds (OPF) were evaluated and compared using various complementary analyses; FTIR, 1H and 13C NMR spectroscopy, 2D-NMR spectroscopy (HMBC and HSQC), CHN, GPC, HPLC and thermal analyses (TGA and DSC). Chemically modified organosolv lignin (AHP EOL) provided lignin with lower molecular weight (Mw), which has smaller fragments that leads to higher solubility rate in water in comparison to unmodified organosolv lignin, AH EOL (DAHP EOL: 19.8% > DAH EOL: 14.0%). It was evident that the antioxidant properties of modified organosolv lignin has better reducing power in comparison to the unmodified organosolv lignin. Therefore, the functionalization of lignin polymers enhanced their antioxidant properties and structural features towards a various alternative approach in lignin-based applications.

Functionality study of lignin as a tyrosinase inhibitor: Influence of lignin heterogeneity on anti-tyrosinase activity.

Valorization of lignin based on its biological activities is always suffering the restriction from lignin heterogeneity, including wide molecular weight distributions and variable functional group contents. In this work, organosolv ethanol lignin (OEL) from corn stalk was divided into four fractions by multiple organic solvent successive extraction and the anti-tyrosinase activities of four obtained fractions were compared to evaluate the effect of lignin heterogeneity on the anti-tyrosinase activity. The characterization revealed that the successive extraction realized the fractionation of the heterogeneous OEL into four relatively homogeneous parts with gradually increasing molecular weight and decreasing phenolic OH content. The enzymatic inhibition study showed that the four fractions exhibited obviously different anti-tyrosinase activities and the dichloromethane fraction had the highest tyrosinase inhibition rate (75.12%, 0.5 mg/mL), whose value was comparable to the positive control p-hydroxybenzaldehyde. Besides, the relationships between the anti-tyrosinase activity and the lignin properties (purity, molecular weight and phenolic OH) were discussed to elucidate the possible formation mechanism of differences among the four lignin fractions in anti-tyrosinase activity. Consequently, these results suggest that lignin heterogeneity has a significant effect on the tyrosinase inhibition rate, and lignin fractionation is an effective way to screen lignin fractions with high anti-tyrosinase activity.

Enhanced Biogas Production from Rice Husk Through Solid-State Chemical Pretreatments

Solid-state chemical pretreatment was carried out on rice husk (RH) for biogas production with hydrochloric acid (HCl), sodium hydroxide (NaOH) and ethanol (C2H5OH), at three concentrations i.e., 1, 3 and 5% at 100 and 120 °C for 60 min. Ethanol (organosolv) pretreated sample with 3% concentration and pretreatment temperature of 100 °C (3E100) had the highest biogas production of 5545 mL followed by NaOH pretreated substrate (3N100) with 4705 mL while acid pretreated sample (5H100) produced 700 mL which was lower than the control (raw RH) which was 2500 mL. The biogas yields values were 67.32, 60.89, 32.26 and 9.32 mL/gVS for 3E100, 3N100, RH and 5H100 respectively. Alkaline and organosolv pretreatments improved biogas quality with methane contents of 50.27 and 50.68%. A confirmation that solid state chemical pretreatment of RH with NaOH and C2H5OH could significantly enhance biogas production. The viability of the digestates as biofertilizer was evaluated with the conclusion that they could be used as low grade fertilizers based on their mineral contents and heavy metal concentrations.

Characterization and evaluation of antioxidation of lignin from bamboo powder using a formic acid-catalyzed ethanol organosolv process

The antioxidant activity of lignin for producing biochemicals has attracted attention. In this paper, a separation method for lignin is proposed, with high-yield and high-antioxidant activity by using a formic acid-catalyzed subcritical ethanol process. The formic acid-catalyzed ethanol lignin (EOL/FA) and ethanol organosolv lignin (EOL) were first prepared using a high-pressure autoclave at different formic acid dosages. Then, the antioxidant activity and the structural and thermal properties of EOL/FA, EOL, alkali lignin, and sodium lignosulfonate were analyzed using antioxidant analysis, Fourier transform infrared (FTIR) spectroscopy analysis, and thermogravimetric analysis (TGA). The phenolic hydroxyl content of the four lignins was also determined by the Folin–Ciocalteau colorimetric method. Results showed EOL/FA had a higher radical scavenging ability and higher total phenolic hydroxyl content than industrial lignin. It indicated that the formic acid-catalyzed subcritical ethanol process was effective for enhancing the antioxidant activity of lignin.

Relationship of thermal degradation behavior and chemical structure of lignin isolated from palm kernel shell under different process severities

Lignin has been considered to be a potential feedstock to produce phenols chemicals by fast pyrolysis technology because of its aromaticity. In this work, four types of lignin were isolated from palm kernel shell with different severities: milled wood lignin (MWL), alkali lignin (AL), Klason lignin (KL), and organosolv ethanol lignin (OEL). A deep investigation of the relevance of the pyrolysis behaviors and chemical structure was carried out by FTIR, GPC, 2D-HSQC-NMR, TGA-FTIR and Py-GC/MS. AL contained highest content of β-O-4 aryl ether bond (53.9/100 Ar) and highest value of S/G ratio (1.68). MWL showed the widest temperature range (126–536 °C) of thermal degradation because of its inhomogeneous distribution of molecular weight. Highest content of oxygen-containing non-condensable gas components (H2O, CO2, CO) was observed in AL. The dominant organic components from lignin pyrolysis were S-type phenols, G-type phenols, P-type phenols, and C-type phenols. G-type (9.74–26.01%) was the dominant phenols products in AL, while P-type (44.23–56.01%) for KL, P-type (29.38–56.07%) for OEL, and G-type (9.08–25.81%) and P-type (22.60–29.04%) in MWL. Higher pyrolysis temperature promoted the formation of aromatics. As the conversion rate increased from 0.1 to 0.8, the activation energy estimated from DAEM model of four types of lignin, all gradually increased.

Combined Ball Milling and Ethanol Organosolv Pretreatment to Improve the Enzymatic Digestibility of Three Types of Herbaceous Biomass

A combined ball milling and ethanol organosolv process is proposed for the pretreatment of three types of herbaceous biomass, giant miscanthus, corn stover, and wheat straw. The combined pretreatment was effective at both removing lignin and increasing the glucan content. After 120 min pretreatment, the glucan content increased to 63.09%, and 55.89% of the acid-insoluble lignin was removed from the giant miscanthus sample. The removal of cellulose, hemicellulose, and acetyl groups were correlated with the removal of lignin. The pretreatment of corn stover showed the highest removal of cellulose, but this was dependent on the removal of acid-insoluble lignin. The slope of the regression lines, which shows the correlation between the removal of lignin and cellulose, was lower than other correlations. The changes in biomass size were analyzed using size distribution graphs. With increasing pretreatment time, the particle size reduction improved in the three types of herbaceous biomass. Because of the combined physicochemical pretreatment, the enzymatic digestibility improved, and a maximum of 91% glucan digestibility was obtained from the pretreated corn stover when 30 FPU/g-glucan enzyme was added. Finally, compositional analysis of the recovered lignin from the remaining black liquor was investigated.

Lignocellulosic biomass to biofuels and biochemicals: A comprehensive review with a focus on ethanol organosolv pretreatment technology.

Lignocellulosic biomass is one of the potential feedstocks to produce second-generation cellulosic ethanol and biochemicals. To enhance the enzymatic digestibility of lignocellulosic biomass for efficient enzymatic saccharification, a variety of pretreatment methods have been studied. Among these, organosolv pretreatment using ethanol is a promising pretreatment method owing to its inherent advantages, such as low solvent cost, lack of toxicity, the ability to retain most cellulose fraction in substrates for enzymatic hydrolysis, coproduction of high-purity lignin and hemicellulosic sugars, easy solvent recovery, and reuse. In this review, the research progress regarding different types of ethanol organosolv pretreatment processes has been summarized in terms of methods, substrate properties, reaction mechanisms, delignification kinetic as well as the impact of pretreatment methods on the enzymatic digestibility. Attempts are also made to provide insights into the complete utilization of lignocellulosic biomass to achieve high potential revenues. Though some ethanol organosolv processes have been studied or are being developed towards commercialization, ethanol organosolv pretreatment is still facing some challenges. Finally, the direction for future work is given to develop a proper ethanol organosolv pretreatment for commercialization.

Insights of Ethanol Organosolv Pretreatment on Lignin Properties of Broussonetia papyrifera

Delignification of Broussonetia papyrifera during ethanol organosolv pretreatment was studied. Milled wood lignin (MWL), the ethanol organosolv lignin recovered at 5 min (PL5), 10 min (PL10), and 60 min (PL60) during the pretreatment, and the residual lignin (RL60) after the pretreatment were characterized and compared. GPC results demonstrated that the weight-average molecular weights (Mw) of the ethanol organosolv lignin fractions increased as the pretreatment time extended from 5 to 60 min. 31P NMR analysis revealed that the content of aliphatic OH decreased in the following order: RL60 < PL60 < PL5 < PL10 < MWL. HSQC NMR results suggested that the contents of syringyl, guaiacyl, p-hydroxybenzoate unit, phenylcoumaran, and resinol in the solubilized lignin fractions were significantly changed during the pretreatment. In addition, a significant portion of β-O-4 interunit linkages of lignin was cleaved during the pretreatment, leading to the formation of stilbene structures in lignin samples such as PL60.

Lignin from an integrated process consisting of liquid hot water and ethanol organosolv: Physicochemical and antioxidant properties

Corncob was successively pretreated by liquid hot water (LHW) and ethanol organosolv (EO) in an integrated process. LHW was performed at 200 °C for 30 min, and EO was performed using uncatalyzed ethanol–water solutions, according to a design of experiments. The effects of the most influential operational variables (ethanol concentration, temperature and time) on yield and chemical composition of the fractions were assessed. Results showed the factor with the greatest effect was ethanol concentration (p < 0.05), leading to a high-purity lignin (86.7%–93.1%) with a total phenolic content of around 25 mg GAE/g. Moreover, the solids recovered from the high ethanol concentration conditions presented the lowest lignin contents (15.4%–17.2%) with good preservation of cellulose (82.5%–88.6% of glucans). The lignin antioxidant capacity showed that all lignin samples presented radical scavenging activity (IC50 of 0.17 mg/mL and 0.016 mg/mL on DPPH (2,2‑diphenyl‑1‑picrylhydrazyl) and ABTS (2,2′‑azino‑bis(3‑ethylbenzothiazoline‑6‑sulphonic acid) assays, respectively) with values close to the commercial antioxidant BHT. Moreover, the chemical (FTIR) and thermal (DSC and TGA) characterization showed lignins with similar properties that were compared with lignin from direct ethanol organosolv process. Results showed that the integrated process of LHW-EO was the most effective way to obtain lignin with high purity and antioxidant capacity.

Deconstruction of hybrid poplar to monomeric sugars and aromatics using ethanol organosolv fractionation

Acidic ethanol organosolv fractionation of hybrid poplar was investigated to determine the impact of pretreatment conditions on the resulting biomass and lignin properties and to assess the subsequent deconstruction of the cell wall biopolymers to monomeric sugars and aromatics. It was found that increasing reaction severity (i.e., time and temperature) during the organosolv fractionation increased the rate of delignification and xylan solubilization while the lignins recovered from the liquors were found to exhibit lower degrees of polymerization. Glucose hydrolysis yields > 75% at moderate enzyme loadings (30 mg/g glucan) could be obtained for the more severe pretreatment conditions. The lignins recovered from the pretreatment liquors were subjected to fractionation using a sequential extraction with solvents of increasing polarity. It was found that the low molar mass, low polydispersity lignins increased in pretreatment liquors with increasing time and temperature and were concentrated in the methanol fraction while a high molar mass fraction was extracted with the diethyl ether. We hypothesize that the extraction of the high molar mass fraction with diethyl ether is due to partial ethyl O-alkylation of lignin hydroxyl groups during pretreatment, rendering lignins more soluble in the non-polar solvent. Finally, depolymerization of unfractionated lignins by thioacidolysis resulted in mass yields of aromatic monomers ranging from 80 to 157 mg monomer per gram of lignin and that these yields exhibited strong positive correlations to the lignin β-O-4 content, molar mass, and strong negative correlations to the pretreatment temperature.

Oxygen-assisted ethanol organosolv pretreatment of sugarcane bagasse for efficient removal of hemicellulose and lignin

Hemicellulose and lignin act as physical barriers impeding the hydrolysis of lignocellulosic biomass by cellulases. To develop a process which could simultaneously remove most hemicellulose and lignin in biomass, in this study, oxygen-assisted ethanol organosolv pretreatment (O2-EOP) of sugarcane bagasse (SCB) was carried out. The effects of temperature, time, oxygen pressure and ethanol concentration on the pH of the hydrolysate, the solubilization and the chemical composition of SCB were investigated. Compared with autocatalytic EOP and acid-catalyzed EOP, O2-EOP could remove most xylan and lignin from SCB at much milder conditions. At optimized conditions (40/60 ethanol/water (v/v), 1.5 MPa O2, 160 °C and 80 min), 82.9% xylan and 83.3% lignin were removed. Glucan content in the residue reached 86.3%, much higher than results obtained by autocatalytic EOP and acid-catalyzed EOP. In subsequent enzymatic hydrolysis (1% solid loading, 4.96 mg protein/g cellulose, 72 h), O2-EOP pretreated SCB produced 3.97 and 1.90 times more glucose than untreated material and N2-EOP pretreated SCB, respectively. O2-EOP also produced abundant organic acids, total amounts of formic acid and acetic acid in the hemicellulose hydrolysate reached 5.42 g/L. In conclusion, O2-assisted EOP was an effective process for the production of pulp with high cellulose purity and good accessibility to cellulases.

Comparative characterization of ethanol organosolv lignin polymer from bamboo green, timber and yellow

In order to make better use of bamboo resources in industrial processes, it is necessary to understand its recalcitrant morphological stem structure and unique chemical composition. In the present work, microspectroscopic imaging approaches were used to reveal the heterogeneous distribution of lignin at cellular and subcellular level. Results showed the higher lignin concentration in the narrow layer of fiber and parenchyma secondary cell walls. Furthermore, ethanol organosolv lignin, isolated from different zones of the bamboo vascular tissue [outer (green), middle (timber) and inner (yellow)], was subjected to extensive structural characterization, including chemical component analysis, Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric/differential thermal analysis (TGA/DTA), and nuclear magnetic resonance (NMR). Main chemical differences among the green, timber and yellow zone were sugar content and S/G/H ratios. Since bamboo green had higher density, hardness and lignin content than bamboo timber and bamboo yellow, the mass transfer during the organosolv process was limited and resulted in the reduced removal/dissolution of polysaccharides at the same acidic conditions. Because bamboo green exhibited the highest content of G units in the vascular tissue, it was more condensed and thus had increased thermal stability compared to bamboo timber and bamboo yellow.

Pretreatment of Corn Stover Using Organosolv with Hydrogen Peroxide for Effective Enzymatic Saccharification

In this study, the chemical pretreatment method using ethanol organosolv with hydrogen peroxide was investigated to improve enzymatic saccharification of corn stover. The pretreatment method using ethanol with hydrogen peroxide in a flow-through reaction was proposed to lower the reaction severity such as the pretreatment temperature. With the same reaction time, the pretreatment process using organosolv (30 wt.% ethanol) containing 1 wt.% hydrogen peroxide at 150 °C resulted in a similar conversion yield as the result of the alkali pretreatment method using 15 wt.% aqueous ammonia at 170 °C. When corn stover was pretreated with 30 wt.% ethanol solution containing 5 wt.% hydrogen peroxide, a glucose conversion yield of 69.7 wt.% and glucose production of 23.8 g were achieved.

Simultaneous production of glucose, furfural, and ethanol organosolv lignin for total utilization of high recalcitrant biomass by organosolv pretreatment

Abstract The main purpose of this study was simultaneous production of glucose, ethanol organosolv lignin (EOL), and furfural for total utilization of lignocellulosic biomass to improve economics of biorefinery. The glucose production (37.1 g, under conditions of 160 °C with 1% sulfuric acid) was significantly increased after organosolv pretreatment, dissolving 11.4 g of the initial hemicellulose-derived sugars and 22.6 g of the initial lignin. Progressively, organosolv lignin precipitation and furfural production processes were conducted using the liquid hydrolysates obtained after organosolv pretreatment. 12 g of EOL (at 160 °C, 1% sulfuric acid) was yielded with the remaining residues of soluble lignin-derived compounds in the liquid hydrolysates. Also, 7.9 g of furfural (at 160 °C, 1% sulfuric acid) was observed after additional acid-catalyzed treatment from the liquid hydrolysates. Consequently, a high yield of glucose, EOL and furfural can be obtained simultaneously using ethanol organosolv pretreatment.

Ethanol Organosolv Lignin Depolymerization with Hydrogen over a Pd/C Catalyst

AbstractThe effect of a 3% Pd/C catalyst on the depolymerization of the ethanol organosolv lignin (EOL) was studied in ethanol at 300–400 °C and 10–50 bar H2 pressure. The EOL depolymerized to monoaromatic compounds, oligomers and larger lignin fragments in both catalytic and non‐catalytic experiments. In addition, char was formed simultaneously due to repolymerization. The commercial Pd/C catalyst influenced the content of the bio‐oil and gas fraction through the secondary reactions of the smaller product molecules. However, the EOL decomposition occurred mainly thermally and possibly autocatalytically due to the inert nature of the catalyst support. The effect of the catalyst on the monoaromatic product distribution was remarkable. With the catalyst, most of the identified products contained a saturated side chain produced by hydrogenation, whereas without the catalyst, the product distribution was wider, with a large portion of products exhibiting unsaturated and carbonyl side chains. Additionally, the monoaromatic compounds formed in the presence of the catalyst had longer side chains than the components formed in non‐catalytic experiments.

Synergistic effects of pH and organosolv lignin addition on the enzymatic hydrolysis of organosolv-pretreated loblolly pine.

The effect of ethanol organosolv lignin (EOL) on enzymatic hydrolysis was examined at pH 4.8–6.0. The addition of EOL prepared from sweetgum enhanced the enzymatic hydrolysis of organosolv-pretreated loblolly pine (OPLP) by 38.8% and 88.0% at pH 4.8 and 5.6, respectively. The addition of EOL prepared from loblolly pine inhibited the enzymatic hydrolysis of OPLP at pH 4.8 but improved it by 43.0% at pH 5.6. This suggests that the addition of EOL and increase in pH act synergistically to improve the enzymatic hydrolysis of OPLP. The effect of EOL addition on cellulase adsorption onto residual lignins was examined. The results revealed that increasing the pH intensified the suppression of non-productive binding between enzymes and residual lignins by EOL. The potential stabilization effects of EOL on enzymes can contribute to the improvement of enzymatic hydrolysis with EOL at higher pH.

Membrane separation and characterisation of lignin and its derived products obtained by a mild ethanol organosolv treatment of rice straw

Abstract An organosolv process using ethanol-water was optimized in order to recover high quality lignin from rice-straw previously pre-treated by autohydrolysis at 210 °C. The results showed a selective and appreciable removal of lignin under very mild conditions and the highest delignification yield occurred at 30 °C. The lignin extracts were characterised using capillary zone electrophoresis (CZE), size exclusion chromatography (SEC), Fourier transform infrared spectroscopy (FT-IR) and 31P-NMR, and two-dimensional heteronuclear single quantum correlation NMR spectroscopy (2D-HSQC NMR), which enabled the identification of low molecular weight lignins with a syringyl/guaiacyl ratio of about 0.74 containing phenolic compounds with potential bioactive properties. In order to separate the target compounds, membrane technology has been used and an enriched extract containing value-added phenolic compounds such as tricin, vanillin, ferulic acid and p-coumaric acid was obtained. High membrane efficiency (around 80%) was obtained for target compounds.

Impact of lignin extraction methods on microstructure and mechanical properties of lignin‐based carbon fibers

ABSTRACTIn order to optimize the use of residues of enzymatic hydrolysis of corn stalk (REHCS) and explore the low‐cost and sustainable raw material substitute for carbon fibers, three types of lignin samples were extracted from REHCS by various extraction methods, and then they were converted into carbon fibers (CFs) by electrospinning, thermostabilization, and carbonization under the same process conditions. The microstructure and mechanical properties of the three types of carbonized fibers were different. The CFs from the ethanol organosolv lignin were actually smooth and brittle carbon films. The CFs from the formic acid/acetic acid organosolv lignin had microscopic pores, causing poor mechanical properties. Comparatively, the CFs from the alkaline lignin demonstrated preferable microstructure and mechanical properties. The reasons for the differences were analyzed by characterizing the lignin samples, precursor fibers, and resultant CFs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45580.