Production of Sugars and Levulinic Acid from Marine Biomass Gelidium amansii

This study focused on optimization of reaction conditions for formation of sugars and levulinic acid from marine algal biomass Gelidium amansii using acid catalyst and by using statistical approach. By this approach, optimal conditions for production of sugars and levulinic acid were found as follows: glucose (reaction temperature of 139.4°C, reaction time of 15.0 min, and catalyst concentration of 3.0%), galactose (108.2°C, 45.0 min, and 3.0%), and levulinic acid (160.0°C, 43.1 min, and 3.0%). While trying to optimize the conditions for the production of glucose and galactose, levulinic acid production was found to be minimum. Similarly, the production of glucose and galactose were found to be minimum while optimizing the conditions for the production of levulinic acid. In addition, optimized production of glucose required a higher reaction temperature and shorter reaction time than that of galactose. Levulinic acid was formed at a high reaction temperature, long reaction time, and high catalyst concentration. The combined results of this study may provide useful information to develop more economical and efficient systems for production of sugars and chemicals from marine biomass.     

Novel hybrid process for the conversion of microcrystalline cellulose to value-added chemicals: part 1: process optimization

In this paper, a novel hybrid process for the treatment of microcrystalline cellulose (MCC) under hot-compressed water was investigated by applying constant direct current on the reaction medium. Constant current range from 1A to 2A was applied through a cylindrical anode made of titanium to the reactor wall. Reactions were conducted using a specially designed batch reactor (450 mL) made of SUS 316 stainless steel for 30–120 min of reaction time at temperature range of 170–230 °C. As a proton donor H₂SO₄ was used at concentrations of 1–50 mM. Main hydrolysis products of MCC degradation in HCW were detected as glucose, fructose, levulinic acid, 5-HMF, and furfural. For the quantification of these products, High Performance Liquid Chromatography (HPLC) and Gas Chromatography with Mass Spectroscopy (GC–MS) were used. A ½ fractional factorial design with 2-level of four factors; reaction time, temperature, H₂SO₄ concentration and applied current with 3 center points were built and responses were statistically analyzed. Response surface methodology was used for process optimization and it was found that introduction of 1A current at 200 °C to the reaction medium increased Total Organic Carbon (TOC) and cellulose conversions to 62 and 81 %, respectively. Moreover, application of current diminished the necessary reaction temperature and time to obtain high TOC and cellulose conversion values and hence decreased the energy required for cellulose hydrolysis to value added chemicals. Applied current had diverse effect on levulinic acid concentration (29.9 %) in the liquid product (230 °C, 120 min., 2 A, 50 mM H₂SO₄).     

Enzymatic Pretreatment Coupled with the Addition of <Emphasis Type="Italic">p</Emphasis>-Hydroxyanisole Increased Levulinic Acid Production from Steam-Exploded Rice Straw Short Fiber

Levulinic acid production, directly from lignocellulosic biomass, resulted in low yields due to the poor substrate accessibility and occurrence of side reactions. The effects of reaction conditions, enzymatic pretreatment, and inhibitor addition on the conversion of steam-exploded rice straw (SERS) short fiber to levulinic acid catalyzed by solid superacid were investigated systematically. The results indicated that the optimal reaction conditions were temperature, time, and solid superacid concentration combinations of 200 °C, 15 min, and 7.5 %. Enzymatic pretreatment improved the substrate accessibility to solid superacid catalyst, and p-hydroxyanisole inhibitor reduced the side reactions during reaction processes, which helped to increase levulinic acid yield. The levulinic acid yield reached 25.2 % under the optimal conditions, which was 61.5 % higher than that without enzymatic pretreatment and inhibitor addition. Therefore, enzymatic pretreatment coupled with the addition of p-hydroxyanisole increased levulinic acid production effectively, which contributed to the value-added utilization of lignocellulosic biomass.     

Fast preparation of nanocrystalline cellulose by microwave-assisted hydrolysis

In this work we report on the procedure for fast and controlled preparation of nanocrystalline cellulose (NCC) from commercially available microcrystalline cellulose using microwave-assisted hydrolysis. By varying the sulfuric acid concentration and hydrolysis temperature, an average hydrodynamic diameter of NCC between 126 and 1,310 nm with corresponding yields between 16 and 82 %, respectively, was obtained in a very short reaction time of 10 min. An additional advantage of the described procedure is its high reproducibility and ability to fine-tune the average NCC particle size by adjusting the reaction conditions, i.e., the sulfuric acid concentration and/or reaction temperature.     

Production of Xylose from Meranti Wood Sawdust by Dilute Acid Hydrolysis

Xylitol production by bioconversion of xylose can be economically interesting if the raw material can be recovered from a cheap lignocellulosic biomass (LCB). Meranti wood sawdust (MWS) is a renewable and low-cost LCB that can be used as a promising and economic source of xylose, a starting raw material for the manufacture of several specialty chemicals, especially xylitol. This study aimed to optimize the hydrolysis process of MWS and to determine the influence of temperature, H₂SO₄ concentration, and residence time on xylose release and on by-product formation (glucose, arabinose, acetic acid, furfural, hydroxymethylfurfural (HMF), and lignin degradation products (LDPs)). Batch hydrolysis was conducted under various operating conditions, and response surface methodology was adopted to achieve the highest xylose yield. Xylose production was highly affected by temperature, acid concentration, and residence time. The optimum temperature, acid concentration, and time were determined to be 124 °C, 3.26 %, and 80 min, respectively. Under these optimum conditions, xylose yield and selectivity were attained at 90.6 % and 4.05 g/g, respectively.     

Comparison of changes in cellulose ultrastructure during different pretreatments of poplar

One commonly cited factor that contributes to the recalcitrance of biomass is cellulose crystallinity. The present study aims to establish the effect of several pretreatment technologies on cellulose crystallinity, crystalline allomorph distribution, and cellulose ultrastructure. The observed changes in the cellulose ultrastructure of poplar were also related to changes in enzymatic hydrolysis, a measure of biomass recalcitrance. Hot-water, organo-solv, lime, lime-oxidant, dilute acid, and dilute acid-oxidant pretreatments were compared in terms of changes in enzymatic sugar release and then changes in cellulose ultrastructure measured by ¹³C cross polarization magic angle spinning nuclear magnetic resonance and wide-angle X-ray diffraction. Pretreatment severity and relative chemical depolymerization/degradation were assessed through compositional analysis and high-performance anion-exchange chromatography with pulsed amperometric detection. Results showed minimal cellulose ultrastructural changes occurred due to lime and lime-oxidant pretreatments, which at short residence time displayed relatively high enzymatic glucose yield. Hot water pretreatment moderately changed cellulose crystallinity and crystalline allomorph distribution, yet produced the lowest enzymatic glucose yield. Dilute acid and dilute acid-oxidant pretreatments resulted in the largest increase in cellulose crystallinity, para-crystalline, and cellulose-I_β allomorph content as well as the largest increase in cellulose microfibril or crystallite size. Perhaps related, compositional analysis and Klason lignin contents for samples that underwent dilute acid and dilute acid-oxidant pretreatments indicated the most significant polysaccharide depolymerization/degradation also ensued. Organo-solv pretreatment generated the highest glucose yield, which was accompanied by the most significant increase in cellulose microfibril or crystallite size and decrease in relatively lignin contents. Hot-water, dilute acid, dilute acid-oxidant, and organo-solv pretreatments all showed evidence of cellulose microfibril coalescence.     

Effect of alkaline ultrasonic pretreatment on crystalline morphology and enzymatic hydrolysis of cellulose

In this study, ultrasound-assisted alkaline pretreatment is developed to evaluate the morphological and structural changes that occur during pretreatment of cellulose, and its effect on glucose production via enzymatic hydrolysis. The pretreated samples were characterized using scanning electron microscopy, infrared spectroscopy, and X-ray diffraction to understand the change in surface morphology, crystallinity and the fraction of cellulose Iβ and cellulose II. The combined pretreatment led to a great disruption of cellulose particles along with the formation of large pores and partial fibrillation. The effects of ultrasound irradiation time (2, 4 h), NaOH concentration (1–10 wt%), initial particle size (20–180 μm) and initial degree of polymerization (DP) of cellulose on structural changes and glucose yields were evaluated. The alkaline ultrasonic pretreatment resulted in a significant decrease in particle size of cellulose, besides significantly reducing the treatment time and NaOH concentration required to achieve a low crystallinity of cellulose. More than 2.5 times improvement in glucose yield was observed with 10 wt% NaOH and 4 h of sonication, compared to untreated samples. The glucose yields increased with increase in initial particle size of cellulose, while DP had no effect on glucose yields. The glucose yields exhibited an increasing tendency with increase in cellulose II fraction as a result of combined pretreatment.     

Optimizing Dilute-Acid Pretreatment of Rapeseed Straw for Extraction of Hemicellulose

Biological conversion of biomass into fuels and chemicals requires hydrolysis of the polysaccharide fraction into monomeric sugars prior to fermentation. Hydrolysis can be performed enzymatically or with mineral acids. In this study, dilute sulfuric acid was used as a catalyst for the pretreatment of rapeseed straw. The purpose of this study is to optimize the pretreatment process in a 15-mL bomb tube reactor and investigate the effects of the acid concentration, temperature, and reaction time. These parameters influence hemicellulose removal and production of sugars (xylose, glucose, and arabinose) in the hydrolyzate as well as the formation of by-products (furfural, 5-hydroxymethylfurfural, and acetic acid). Statistical analysis was based on a model composition corresponding to a 3³ orthogonal factorial design and employed the response surface methodology to optimize the pretreatment conditions, aiming to attain maximum xylan, mannan, and galactan (XMG) extraction from hemicellulose of rapeseed straw. The obtained optimum conditions were: H₂SO₄ concentration of 1.76% and temperature of 152.6 °C with a reaction time of 21 min. Under these optimal conditions, 85.5% of the total sugar was recovered after acid hydrolysis (78.9% XMG and 6.6% glucan). The hydrolyzate contained 1.60 g/L glucose, 0.61 g/L arabinose, 10.49 g/L xylose, mannose, and galactose, 0.39 g/L cellobiose, 0.94 g/L fructose, 0.02 g/L 1,6-anhydro-glucose, 1.17 g/L formic acid, 2.94 g/L acetic acid, 0.04 g/L levulinic acid, 0.04 g/L 5-hydroxymethylfurfural, and 0.98 g/L furfural.     

Selective hydrolysis of cellulose for the preparation of microcrystalline cellulose by phosphotungstic acid

Microcrystalline cellulose (MCC), prepared from natural cellulose through acid hydrolysis, has been widely used in the food, chemical and pharmaceutical industries because of its high degree of crystallinity, small particle size and other characteristics. Being different from conventional mineral acids, phosphotungstic acid (H₃PW₁₂O₄₀, HPW) was explored for hydrolyzing cellulose selectively for the preparation of MCC in this study. Various reaction parameters, such as the acid concentration, reaction time, temperature and solid-liquid ratio, were optimized. Rod-like MCC was obtained with a high yield of 93.62 % and also exhibited higher crystallinity and narrower particle diameter distribution (76.37 %, 13.77–26.17 μm) compared with the raw material (56.47 %, 32.41–49.74 μm) at 90 °C for 2 h with 58 % (w/w) HPW catalyst and a solid-liquid radio of 1:40. Furthermore, HPW can easily be extracted and recycled with diethyl ether for four runs without affecting the quality of the MCC products. The technology of protecting the crystalline region while selectively hydrolyzing the amorphous region of cellulose as much as possible by using HPW is of great significance. Due to the strong Brønsted acid sites and highest activity in solid heteropoly acid, the use of effective homogeneous HPW may offer an eco-friendly and sustainable way to selectively convert fiber resources into chemicals in the future.     

Cellulose nano-particles from Pandanus: viscometric and crystallographic studies

Pandanus utilis a plant abundant throughout Kerala, India has been used as a source to isolate nano-particles. The fibres were extracted from Pandanus plant by biological natural retting. Extracted fibres were dried, ground and treated with 5 % NaOH followed by bleaching using 5 wt % hypochlorite solution. Bleached cellulose was hydrolysed using sulphuric acid. After centrifugation, suspension was freeze dried. Effect of Acid concentration, temperature and time of hydrolysis on the isolation of cellulose nanoparticles was studied. FESEM images of cellulose showed the presence of spherical nano-particles. Dynamic light scattering revealed homogeneous dispersion of nano-particles. Degree of polymerisation of cellulose was determined viscometrically using cupriethylene-diamine as solvent. Removal of lignin and hemicelluloses was confirmed from FTIR spectra. X-Ray diffractograms of powdered fibre, bleached cellulose and nano-cellulose were compared. Using peak height method and peak de-convolution method, crystallinity indices were determined. Using Scherrer equation crystallite size was calculated and it further confirmed that particles are of nanometre size.     

Preparation and characterization of nanocrystalline cellulose via low-intensity ultrasonic-assisted sulfuric acid hydrolysis

Nanocrystalline cellulose (NCC) was extracted from microcrystalline cellulose via low-intensity ultrasonic-assisted sulfuric acid hydrolysis process. NCC samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), particle size distribution (PSD) analysis, Fourier-transformed infrared spectra (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and rheological measurement. It was found that NCC yield reached 40.4 % under the optimum process of low-intensity ultrasonic-assisted sulfuric acid hydrolysis, while it was only 33.0 % in the absence of ultrasonic treatment. Furthermore, the results showed that the two NCC samples obtained from ultrasonic-assisted hydrolysis and conventional hydrolysis were very similar in morphology, both exhibiting rod-like structures with widths and lengths of 10–20 and 50–150 nm, respectively. XRD result revealed that the NCC sample from ultrasonic-assisted hydrolysis contained a small amount of cellulose II and possessed a Segal Crystallinity Index of 90.38 % and a crystallite size of 58.99 Å, higher than those of the NCC sample from conventional hydrolysis. Moreover, PSD analysis demonstrated that the former exhibited a smaller value in average particle size than the latter. In addition, rheological measurements showed that the NCC suspensions from the ultrasonic-assisted process exhibited a lower viscosity over the range of shear rate from 0.1 to 100 s^?1 in comparison with that prepared in the absence of ultrasonic treatment.     

Enzymatic Hydrolysis and Succinic Acid Fermentation from Steam-Exploded Corn Stalk at High Solid Concentration by Recombinant Escherichia coli

Steam-exploded corn stalk biomass was used as the substrate for succinic acid production via lignocellulose enzymatic hydrolysis and fermentation. Succinic acid fermentation was investigated in Escherichia coli strains overexpressing cyanobacterium Anabaena sp. 7120 ecaA gene encoding carbonic anhydrase (CA). For the washed steam-exploded corn stalk at 30 % substrate concentration, i.e., 30 % water-insoluble solids (WIS), enzymatic hydrolysis yielded 97.5 g/l glucose solution and a cellulose conversion of 73.6 %, thus a high succinic acid level up to 38.6 g/l. With the unwashed steam-exploded corn stalk, though a cellulose conversion of 71.2 % was obtained in hydrolysis at 30 % solid concentration (27.9 % WIS), its hydrolysate did not ferment at all, and the hydrolysate of 25 % solid loading containing 3.8 g/l acetic acid and 168.2 mg/l furfural exerted a strong inhibition on succinic acid production.     

Utilization of waste cellulose—I. Gamma irradiation and hydrolysis with dilute sulphuric acid

The yield of glucose, levulinic acid and furaldehyde derivatives as a function of the time of hydrolysis have been determined at 190° in 1 or 0.1% H₂SO₄ for non-irradiated and irradiated cellulose samples. Various additives, swelling agents and decrystallization techniques were used to improve either the accessibility or the yield of irradiation-induced chain scission. Results at lower temperatures of hydrolysis and with phosphoric acid as hydrolysing medium are also reported.     

Enzymatic Hydrolysis of Cellulose Using Mixes of Mutant Forms of Cellulases from <Emphasis Type="Italic">Penicillium verruculosum</Emphasis>

Cellulases are the major components of multienzyme systems applied in processes of bioconversion of renewable lignocellulosic feedstocks to various useful products. The hydrolytic efficiency of enzyme mixes based on recombinant wild-type endoglucanase II, cellobiohydrolases I and II from the Penicillium verruculosum fungus (in the presence of Aspergillus niger β-glucosidase) with mixes of mutant forms of these enzymes in the hydrolysis of cellulosic materials is compared, and the influence of temperature and substrate concentration on the glucose yield is studied. The mutant cellulases represented proteins, in which N-linked glycans were partially removed using site-directed mutagenesis. In the hydrolysis of microcrystalline cellulose and milled aspen wood by mixes of mutant cellulases, the yields of glucose after 24–72 h of an enzymatic reaction were higher by 31–38% and 11–27%, respectively, than those for the compositions based on the wild-type enzymes. The highest product concentrations, using mutant enzyme compositions, are achieved at 50°С when the hydrolysis temperature is varied in the range of 40 to 60°С. Increasing the substrate concentration in the reaction system from 5 to 50 g/L (while maintaining the enzyme dosage at the same level) led to a 2.6–2.8-fold increase in the glucose yield, accompanied by a decrease in the cellulose conversion degree.     

Optimizing Phosphoric Acid plus Hydrogen Peroxide (PHP) Pretreatment on Wheat Straw by Response Surface Method for Enzymatic Saccharification

Wheat straw was pretreated by phosphoric acid plus hydrogen peroxide (PHP), in which temperature, time, and H₃PO₄ proportion for pretreatment were investigated by using response surface method. Results indicated that hemicellulose and lignin removal positively responded to the increase of pretreatment temperature, H₃PO₄ proportion, and time. H₃PO₄ proportion was the most important variable to control cellulose recovery, followed by pretreatment temperature and time. Moreover, these three variables all negatively related to cellulose recovery. Increasing H₃PO₄ proportion can improve enzymatic hydrolysis; however, reduction on cellulose recovery results in decrease of glucose yield. Extra high temperature or long time for pretreatment was not beneficial to enzymatic hydrolysis and glucose yield. Based on the criterion for minimizing H₃PO₄ usage and maximizing glucose yield, the optimized pretreatment conditions was 40 °C, 2.0 h, and H₃PO₄ proportion of 70.2 % (H₂O₂ proportion of 5.2 %), by which glucose yielded 299 mg/g wheat straw (946.2 mg/g cellulose) after 72-h enzymatic hydrolysis.     

Selective conversion of cellulose to levulinic acid and furfural in sulfolane/water solvent

Direct conversion of cellulose into levulinic acid and furfural in sulfolane media with the aid of water and H₂SO₄ was performed at 140–220 °C under the pressures of 0–1.5 MPa. This approach could obtain 72.5 mol% levulinic acid and 11.5 mol% furfural formation under an optimal condition in which the mass ratio of sulfolane, water and H₂SO₄ was 90:10:1. It was found that the decrease of water content led to an increasing yield of furfural and that the maximum furfural yield (51.1 mol%) could be obtained in the absence of water. The synergism of sulfolane and water in the selective liquefied system was demonstrated to be responsible for not only reinforced effect of optimizing and isolating the target products but also for reducing re-polymerization and side reactions. Furthermore, sulfolane in our case could be recycled and re-used for the conversion of cellulose with the same yield, which shed light on the remarkable potential for future industrial application.     

Hydrolysis of cellulose by the heteropoly acid H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript>

The potential of heteropoly acid H₃PW₁₂O₄₀ to catalyze the hydrolysis of cellulose to glucose under hydrothermal conditions was explored. This technology could contribute to sustainable societies in the future by using cellulose biomass. A study to optimize the reaction conditions, such as the amount of catalyst, reaction time, temperature, and the amount of cellulose used, was performed. A remarkably high yield of glucose (50.5%) and selectivity higher than 90% at 453 K for 2 h with a mass ratio of cellulose to H₃PW₁₂O₄₀ of 0.42 were achieved. This was attributed to the high hydrothermal stability and the excellent catalytic properties, such as the strong Brønsted acid sites. This homogeneous catalyst can be recycled for reuse by extraction with diethyl ether. The results illustrate that H₃PW₁₂O₄₀ is an environmentally benign acid catalyst for the hydrolysis of cellulose.     

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.     

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.     

Thermophilic Bacillus coagulans Requires Less Cellulases for Simultaneous Saccharification and Fermentation of Cellulose to Products than Mesophilic Microbial Biocatalysts

Ethanol production from lignocellulosic biomass depends on simultaneous saccharification of cellulose to glucose by fungal cellulases and fermentation of glucose to ethanol by microbial biocatalysts (SSF). The cost of cellulase enzymes represents a significant challenge for the commercial conversion of lignocellulosic biomass into renewable chemicals such as ethanol and monomers for plastics. The cellulase concentration for optimum SSF of crystalline cellulose with fungal enzymes and a moderate thermophile, Bacillus coagulans, was determined to be about 7.5 FPU g^?1 cellulose. This is about three times lower than the amount of cellulase required for SSF with Saccharomyces cerevisiae, Zymomonas mobilis, or Lactococcus lactis subsp. lactis whose growth and fermentation temperature optimum is significantly lower than that of the fungal cellulase activity. In addition, B. coagulans also converted about 80% of the theoretical yield of products from 40 g/L of crystalline cellulose in about 48 h of SSF with 10 FPU g^?1 cellulose while yeast, during the same period, only produced about 50% of the highest yield produced at end of 7 days of SSF. These results show that a match in the temperature optima for cellulase activity and fermentation is essential for decreasing the cost of cellulase in cellulosic ethanol production.