Efficient hydrolyzation of cellulose in ionic liquid by novel sulfonated biomass-based catalysts

A green and effective approach for comprehensive hydrolyzation of cellulose has been described. Several carbon-based solid acids were successfully prepared using various biomass (glucose, microcrystalline cellulose, bamboo, and rice husk) and used to catalyze cellulose hydrolysis. The acid groups (–SO₃H and –COOH) were successfully introduced onto the surface of the carbon-based solid acid catalysts as evidenced by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The structure of the prepared catalysts was characterized by scanning electron microscope and X-ray diffraction. The catalysts showed excellent catalytic performance for hydrolysis of cellulose. To improve the reaction efficiency, ball-milling and solubilization in ionic liquids of cellulose were adopted. A maximum total reducing sugar yield of 81.8 % was obtained in ionic liquid 1-butyl-3-methyl imidazolium chloride at 125 °C for 90 min when the water addition was 10 % of ionic liquid. This study provided a promising strategy to synthesize solid acids from lignocelluloses, which were further used to convert biomass into biofuels and platform chemicals.     

Effect of alkaline pretreatment on delignification of wheat straw

This study was conducted to analyse structural changes through scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) after alkaline pretreatment of wheat straw for optimum steaming period. During the study, 2 mm size of substrate was soaked in 2.5% NaOH for 1 h at room temperature and then autoclaved at 121°C for various steaming time (30, 60, 90 and 120 min). Results revealed that residence time of 90 min at 121°C has strong effect on substrate, achieving a maximum cellulose content of 83%, delignification of 81% and hemicellulose content of 10.5%. Further SEM and FTIR spectroscopy confirmed structural modification caused by alkaline pretreatment in substrate. Maximum saccharification yield of 52.93% was achieved with 0.5% enzyme concentration using 2.5% substrate concentration for 8 h of incubation at 50°C. This result indicates that the above-mentioned pretreatment conditions create accessible areas for enzymatic hydrolysis.     

Evaluation and Optimization of Organic Acid Pretreatment of Cotton Gin Waste for Enzymatic Hydrolysis and Bioethanol Production

This paper investigates the efficiency of the organic acids on the pretreatment of an industrially generated cotton gin waste for the removal of lignin, thereby releasing cellulose and hemicellulose as fermentable sugar components. Cotton gin waste was pretreated with various organic acids namely lactic acid, oxalic acid, citric acid, and maleic acid. Among these, maleic acid was found to be the most efficient producing maximum xylose sugar (126.05?±?0.74 g/g) at the optimum pretreatment condition of 150 °C, 500 mM, and 45 min. The pretreatment efficiency was comparable to the conventional dilute sulfuric acid pretreatment. A lignin removal of 88% was achieved by treating maleic acid pretreated biomass in a mixture of sodium sulfite and sodium chlorite. The pretreated biomass was further evaluated for the release of sugar by enzymatic hydrolysis and subsequently bioethanol production from hydrolysates. The maximum 686.13 g/g saccharification yield was achieved with maleic acid pretreated biomass which was slightly higher than the sulfuric acid (675.26 g/g) pretreated waste. The fermentation of mixed hydrolysates(41.75 g/l) produced 18.74 g/l bioethanol concentration with 2.25 g/l/h ethanol productivity and 0.48 g/g ethanol yield using sequential use of Saccharomyces cerevisiae and Pichia stipitis yeast strains. The production of bioethanol was higher than the ethanol produced using co-culture in comparison to sequential culture. Thus, it has been demonstrated that the maleic acid pretreatment and fermentation using sequential use of yeast strains are efficient for bioethanol production from cotton gin waste.     

The Influence of Different Strategies for the Saccharification of the Banana Plant Pseudostem and the Detoxification of Concentrated Broth on Bioethanol Production

Pseudostem of the Musa cavendishii banana plant was submitted to chemical pretreatments with acid (H₂SO₄ 2%, 120 °C, 15 min) and with alkali (NaOH 3%, 120 °C, 15 min), saccharified by commercial enzymes Novozymes® (Cellic CTec2 and HTec2). The influences of the pretreatments on the degradation of the lignin, cellulose and hemicellulose, porosity of the surface, particle crystallinity, and yield in reducing sugars after saccharification (Y _RS), were established. Different concentrations of biomass (70 and 100 g/L in dry matter (dm)), with different physical differences (dry granulated, crushed wet bagasse, and whole pseudostem), were used. The broth with the highest Y _RS among the different strategies tested was evaporated until the concentration of reducing sugars (RS) was to the order of 100 g/L and fermented, with and without prior detoxification with active carbon. Fermentation was carried out in Erlenmeyer flasks, at 30 °C, initial pH 5.0, and 120 rpm. In comparison to the biomass without chemical pretreatment and to the biomass pretreated with NaOH, the acid pretreatment of 70 g/L of dry granulated biomass enabled greater digestion of hemicellulose, lower index of cellulose crystallinity, and higher Y _RS (45.8 ± 0.7%). The RS increase in fermentation broth to 100 g/L, with posterior detoxification, presented higher productivity ethanol (Q _P = 1.44 ± 0.02 g/L/h) with ethanol yield (Y _P/RS) of 0.41 ± 0.02 g/g. The value of Q _P was to the order of 75% higher than Q _P obtained with the same broth without prior detoxification.     

Ethanol production from steam-explosion pretreated wheat straw

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

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

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

Hydrothermal saccharification of cotton cellulose in dilute aqueous formic acid solution

Cotton cellulose subjected to a dilute aqueous formic acid solution, at acid concentrations up to 1% (w/w), under hydrothermal conditions in a semi-batch reactor was converted into glucose and oligomers with lower degrees of polymerizations (DP). After heating at 250 °C for 60 min in 0.1% (w/w) aqueous formic acid solution, yields of glucose and total sugar with DP = 1 to 9 were 36.6 and 83.8% (100 × gC/gC of initial cotton sample), respectively, and 5-hydroxymethylfurfural was almost as low as 1%. The yields of glucose and oligomers were significantly improved by adding the acid. The reaction was represented by first-order reaction kinetics with regard to (1 ?C x) where x is the conversion based on the total sugar or glucose yield. At 250 °C, the differences in the rate constants (k ? k _water) were proportional to the square root of formic acid concentration.     

NiO@CuO@Cu bilayered electrode: two-step electrochemical synthesis supercapacitor properties

Present work deals with a two-step synthesis and electrochemical properties of nickel oxide @copper oxide@copper (NiO@CuO@Cu) bilayered electrode. In the first step, anodization (40 V for 25 min) of Cu foil has been carried out for forming Cu-hydroxide@Cu which when annealed at 300 °C for 1 h produces CuO@Cu. In the second step, Ni-hydroxide is deposited onto CuO@Cu by applying current density of 0.03 A/cm² for 3 min which when re-annealed at 300 °C for 1 h gives out NiO@CuO@Cu bilayered electrode. Obtained NiO@CuO@Cu bilayered electrode demonstrates separate CuO and NiO phases. The electrochemical properties have obtained using cyclic voltammetry, galvonostatic charge-discharge, and Nyquist plot measurements that reveal an importance of NiO@CuO@Cu as a potential electrode material in the electrochemical supercapacitor application with 58.14, 51.25, and 4.73 F g^?1 values in 0.5 M, NaOH, KOH, and Na₂SO₄ electrolytes, respectively, measured at 2 mVs^?1 scan rate.     

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

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

The Effect of Alkaline Addition in Hydrothermal Pretreatment of Empty Fruit Bunches on Enzymatic Hydrolysis Efficiencies

In general, lignocellulosic biomass contains three major components, namely lignin, hemicellulose and cellulose which are the polymers of C5 and C6 sugars. Thus, there is potential to utilize of this biomass for bioethanol production. The hydrolysis of cellulose into glucose was difficult due to the more fibrous nature and thus inhibit enzyme penetration into the cellulose. In order to solve this problem, hydrothermal pretreatment can be used for breaking the bonds within the lignin structure and increase the accessibility of enzyme into the cellulose. In this study, the effect of chemical addition, sodium hydroxide (NaOH) and calcium oxide (CaO) in hydrothermal pretreatment at 180 °C and 30 minutes reaction time of palm oil empty fruit bunches (EFB) on the enzymatic hydrolysis efficiencies was investigated. The enzymatic hydrolysis of hydrothermally pretreated EFB give the highest concentration of glucose at 0.67 g/L while the hydrothermally pretreated of EFB in the presence of NaOH gives the lowest glucose concentration 0.45 g/L.     

Improved two-step hydrothermal process for acetic acid production from carbohydrate biomass

An improved two-step process for converting carbohydrate biomass to acetic acid under hydrothermal conditions is proposed. The first step consists of the production of lactic acid from carbohydrate biomass, and the second step consists of conversion of the lactic acid obtained in the first step to acetic acid using CuO as an oxidant. The results indicated that CuO as an oxidant in the second step can significantly improve the production of high-purity acetic acid from lactic acid, and the maximum yield of acetic acid was 61%, with a purity of 90%. The yield of acetic acid obtained using the improved two-step hydrothermal process from carbohydrate biomass, such as glucose, cellulose and starch, was greater than that obtained using traditional two-step process with H2O2 orO2. In addition, a proposed pathway for the production of acetic acid from lactic acid in the second step with CuO was also discussed. The present study provides a useful two-step process for the production of acetic acid from carbohydrate biomass.     

Structural coarsening of aspen wood by hydrothermal pretreatment monitored by small- and wide-angle scattering of X-rays and neutrons on oriented specimens

Structural changes across multiple length scales associated with hydrothermal pretreatments of biomass were investigated by using small- and wide-angle X-ray and neutron scattering on oriented specimens. Isotropic and anisotropic scattering components were numerically separated and then interpreted as contributions from matrix and cellulose components, respectively. Equatorial diffraction peaks present in the isotropic component became sharper after hydrothermal treatments or ammonia treatment. Before pretreatment the wet cell wall was found to be homogeneous in the 10–100 nm range and scattering below Q = 0.5 (nm^?1) was dominated by surface scattering from the lumen. After pretreatment with acid or steam at 160 or 180 °C, density fluctuation developed in the cell wall at length scales above 10 nm, most likely due to lateral coalescence of microfibrils that partially co-crystallize to give larger apparent crystal sizes. A density fluctuation up to about 100 nm appeared in the isotropic component after acid and steam pretreatments due to morphological changes in the hemicellulose and lignin matrix.     

Bioethanol Production from Ipomoea Carnea Biomass Using a Potential Hybrid Yeast Strain

The paper deals with the exploitation of Ipomoea carnea as a feedstock for the production of bioethanol. Dilute acid pretreatment under optimum conditions (3 %H₂SO₄, 120 °C for 45 min) produced 17.68 g L^?1 sugars along with 1.02 g L^?1 phenolics and 1.13 g L^?1 furans. A combination of overliming and activated charcoal adsorption facilitated the removal of 91.9 % furans and 94.7 % phenolics from acid hydrolysate. The pretreated biomass was further treated with a mixture of sodium sulphite and sodium chlorite and, a maximum lignin removal of 81.6 % was achieved. The enzymatic saccharification of delignified biomass resulted in 79.4 % saccharification with a corresponding sugar yield of 753.21 mg g^?1. Equal volume of enzymatic hydrolysate and acid hydrolysate were mixed and used for fermentation with a hybrid yeast strain RPRT90. Fermentation of mixed detoxified hydrolysate at 30 °C for 28 h produced ethanol with a yield of 0.461 g g^?1. A comparable ethanol yield (0.414 g g^?1) was achieved using a mixture of enzymatic hydrolysate and undetoxified acid hydrolysate. Thus, I. carnea biomass has been demonstrated to be a potential feedstock for bioethanol production, and the use of hybrid yeast may pave the way to produce bioethanol from this biomass.     

Hydrothermal pretreatment conditions to enhance ethanol production from poplar biomass

Pretreatment has been recognized as a key step in enzyme-based conversion processes of lignocellulose biomass to ethanol. The aim of this study is to evaluate two hydrothermal pretreatments (steam explosion and liquid hot water) to enhance ethanol production from poplar (Populus nigra) biomass by a simultaneous saccharification and fermentation (SSF) process. The composition of liquid and solid fractions obtained after pretreatment, enzymatic digestibility, and ethanol production of poplar biomass pretreated at different experimental conditions was analyzed. The best results were obtained in steam explosion pretreatment at 210°C and 4 min, taking into account cellulose recovery above 95%, enzymatic hydrolysis yield of about 60%, SSF yield of 60% of theoretical, and 41% xylose recovery in the liquid fraction. Large particles can be used for poplar biomass in both pretreatments, since no significant effect of particle size on enzymatic hydrolysis and SSF was obtained.     

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

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

Microbial Lipid Production from Enzymatic Hydrolysate of Pecan Nutshell Pretreated by Combined Pretreatment

Biodiesel is a fuel composed of monoalkyl esters of long-chain fatty acids derived from renewable biomass sources. In this study, biomass waste pecan nutshell (PS) was attempted to be converted into microbial oil. For effective utilization of PS, sequential pretreatment with ethylene glycol–H₂SO₄–water (78:2:20, wt:wt:wt) at 130 °C for 30 min and aqueous ammonia (25 wt%) at 50 °C for 24 h was used to enhance its enzymatic saccharification. Significant linear correlation was obtained about delignification-saccharification (R ² = 0.9507). SEM and FTIR results indicated that combination pretreatment could effectively remove lignin and xylan in PS for promoting its enzymatic saccharification. After 72 h, the reducing sugars from the hydrolysis of 50 g/L pretreated PS by combination pretreatment could be obtained at 73.6% yield. Using the recovered PS hydrolysates containing 20 g/L glucose as carbon source, microbial lipids produced from the PS hydrolysates by Rhodococcus opacus ACCC41043. Four fatty acids including palmitic acid (C16:0; 23.1%), palmitoleic acid (C16:1; 22.4%), stearic acid (C18:0; 15.3%), and oleic acid (C18:1; 23.9%) were distributed in total fatty acids. In conclusion, this strategy has potential application in the future.     

A novel transesterification system to rapidly synthesize cellulose aliphatic esters

Cellulose aliphatic esters (CEs) are important cellulose derivatives that have been widely used in many fields such as plastics, textiles, membranes, etc. However, in traditional methods, long pretreatment and reaction times limit the manufacture of CEs and their widespread application. Herein, a very efficient method for the preparation of CEs in a heterogeneous system was developed. This method involved the transesterification of cellulose with vinyl esters (from C4 to C14) in dimethylsulfoxide under the catalysis of aqueous NaOH. For better understanding of this new reaction system, factors such as the water content, amount of catalyst, reaction temperature and molar ratio of vinyl acetate to the anhydroglucose unit were explored. Results obtained from FT-IR, ¹H and ¹³C NMR spectroscopies confirmed that CEs could be synthesized at 100 °C within 5 min. High water content or excessive amounts of NaOH were detrimental to the synthesis of CEs. Results from small-angle X-ray diffraction showed that the interplanar spacings of these CEs showed an increasing trend with the length of the aliphatic chain. Thermogravimetric analysis and derivative thermogravimetric analysis showed that CEs had higher thermal stability than cellulose. This work provides a new and highly efficient method to synthesize various CEs.     

Cellulose hydrolysis catalyzed by highly acidic lignin-derived carbonaceous catalyst synthesized via hydrothermal carbonization

Acidic carbonaceous solids were synthesized from mass pine alkali lignin via hydrothermal carbonization followed by sulfonation. Hydrothermal carbonization of lignin in the presence of acrylic acid (LAHC-SO₃H) provided many more carboxylic groups than that in the absence of acrylic acid, allowing subsequent sulfonation to produce a highly active and stable catalyst for cellulose hydrolysis in the [BMIM]Cl-H₂O solvent system. The hydrochar and catalyst were characterized using field emission scanning electron microscopy, X-ray diffractometer, X-ray photoelectron spectroscopy, thermal gravimetric analysis, Fourier transform infrared spectrometer, Brunauer–Emmett–Teller and acid–base titration. Results showed that a high acid content of 5.48 mmol/g, including carboxylic group (2.85 mmol/g), phenolic hydroxyl group (1.05 mmol/g) and sulfonic acid group (1.58 mmol/g), contributed significantly to the highly efficient hydrolysis of cellulose. Further, it was found that addition of trace water in [BMIM]Cl was favorable to cellulose hydrolysis. The highest yield (75.4%) of total reducing sugar (TRS) obtained in [BMIM]Cl-H₂O at a mass ratio of 100:1 was more than twice that (36.1%) achieved in [BMIM]Cl without water; the corresponding reaction conditions were 50 mg of microcrystalline cellulose, 30 mg of catalyst, 1.0 g of [BMIM]Cl, 10 mg of H₂O, reaction temperature of 130 °C and reaction time of 2 h. Furthermore, the TRS yield with 5 cycles for LAHC-SO₃H was higher than 68.1%, and the catalytic activity of catalyst could be fully recovered (74.0% of TRS yield) easily by regeneration.     

Potential of Potassium Hydroxide Pretreatment of Switchgrass for Fermentable Sugar Production

Chemical pretreatment of lignocellulosic biomass has been extensively investigated for sugar generation and subsequent fuel production. Alkaline pretreatment has emerged as one of the popular chemical pretreatment methods, but most attempts thus far have utilized NaOH for the pretreatment process. This study aimed at investigating the potential of potassium hydroxide (KOH) as a viable alternative alkaline reagent for lignocellulosic pretreatment based on its different reactivity patterns compared to NaOH. Performer switchgrass was pretreated at KOH concentrations of 0.5–2 % for varying treatment times of 6–48 h, 6–24 h, and 0.25–1 h at 21, 50, and 121 °C, respectively. The pretreatments resulted in the highest percent sugar retention of 99.26 % at 0.5 %, 21 °C, 12 h while delignification up to 55.4 % was observed with 2 % KOH, 121 °C, 1 h. Six pretreatment conditions were selected for subsequent enzymatic hydrolysis with Cellic CTec2® for sugar generation. The pretreatment condition of 0.5 % KOH, 24 h, 21 °C was determined to be the most effective as it utilized the least amount of KOH while generating 582.4 mg sugar/g raw biomass for a corresponding percent carbohydrate conversion of 91.8 %.     

Electron beam combined with hydrothermal treatment for enhancing the enzymatic convertibility of sugarcane bagasse

The use of microbial cellulolytic enzymes is the most efficient process to liberate glucose from cellulose in biomass without the formation of fermentation inhibitors. A combination of pretreatment technologies is an alternative way to increase the access of enzymes to cellulose, and consequently, the conversion yield. In this way, the present study reports on the enzymatic hydrolysis of SCB submitted to three kinds of pretreatment: electron beam processing (EBP), and EBP followed by hydrothermal (TH) and diluted acid (AH) treatment. SCB samples were irradiated using a radiation dynamics electron beam accelerator, and then submitted to thermal and acid (0.1% sulfuric acid) hydrolysis for 40 and 60 min at 180 °C. These samples were submitted to enzymatic hydrolysis (EH) using commercial preparations, including Celluclast 1.5 L and beta-glycosidase. The addition of diluted acid improved TH treatment allowing for a shorter application time. EBP with 50 kGy increased the enzymatic hydrolysis yield of cellulose by 20% after TH and 30% after AH.