• Energy Research

A two-stage reaction system was developed to synthesize butyl levulinate (BL), a derivative chemical of levulinic acid, from agricultural residue (rice straw). A single reactor was employed during the first processing stage for the conversion of rice straw cellulose to levulinic acid (LA) in a novel co-solvent system consisting of dilute phosphoric acid and tetrahydrofuran. The highest yield of 10.8% wt. LA concentration (i.e., ∼42% of theoretical LA yield) with intermediate residuals concentration of 1.5% wt. glucose and 0.5% wt. 5-hydroxymethylfurfural (5-HMF) on dry weight basis of biomass was obtained at modest reaction conditions. During subsequent esterification reaction, approximately 7.8% wt. BL yield (at 89% conversion yield) was achieved from the solvent extracted precipitate containing majorly LA and residual 5-HMF in the presence of 0.5M sulfuric acid using n-butanol. Based on comparative esterification results obtained using commercial chemicals (LA and 5-HMF), apparently 5-HMF exhibited ∼8% wt. BL yield through direct synthesis in the presence of sulfuric acid using n-butanol under the same specified reaction conditions. Alongside, effectiveness of co-solvent treatment on rice straw for potential fermentable sugar release (glucose) was investigated by subjecting the respective post-reaction solid residues to enzymatic digestion using cellulase and yielded highest of 11% wt. per wt. solids (27% wt. glucose conversion efficiency), amongst solid residues underwent different processing conditions.

The present work refers to a process involving the use of dilute nitric acid pretreatment and enzymatic hydrolysis for the transformation of rice straw into simple sugars. Acid pre-treated rice straw was separated into the pulp and supernatant through centrifugation and filtration. The two fractions are then converted into simple sugars by combined action of microbes producing cellulase and laccase enzymes. These microbes were isolated from soil samples which were collected from different locations with varying altitudes, expected to harbour microbes with high-hydrolysing activity. The nitric acid pretreatment was carried out at 30 °C, 200 rpm for 72 h. After 72 h, the culture supernatants were analysed for the presence of glucose with the help of HPLC. The supernatant fraction separated after the acid pre-treated rice straw produced highest amount of glucose (205 mg/g of rice straw) upon subsequent hydrolysis with synergistic action of cellulase and laccase-producing microbes.

In this study, levulinic acid (LA) was produced from rice straw biomass in co-solvent biphasic reactor system consisting of hydrochloric acid and dichloromethane organic solvent. The modified protocol achieved a 15% wt LA yield through the synergistic effect of acid and acidic products (auto-catalysis) and the designed system allowed facile recovery of LA to the organic phase. Further purification of the resulting extractant was achieved through traditional column chromatography, which yielded a high purity LA product while recovering ∼85% wt. Upon charcoal treatment of the resultant fraction generated an industrial grade target molecule of ∼99% purity with ∼95% wt recovery. The system allows the solvent to be easily recovered, in excess of 90%, which was shown to be able to be recycled up to 5 runs without significant loss of final product concentrations. Overall, this system points to a method to significantly reduce manufacturing cost during large-scale LA preparation.

Abstract 5-Hydroxymethylfurfural (HMF) belongs to the group of “drop-in biofuels” and platform molecule of prime importance. Synthesis of HMF from various sugar sources has traversed a long span of time and has witnessed various modifications viz., use of heterogeneous catalysts over homogeneous catalysts, employment of organic phase over aqueous, introduction of biphasic systems to overcome side reaction limitations and still counting. Every modification has been carried out with the objective of improved selectivity and product synthesis, cost and energy optimization, and a shift towards greener process over existing methods. Use of lignocellulosic biomass instead of commercial sugars also finds applicability in direct HMF synthesis along with levulinic acid, furfural etc. However, low yields from these abundant, cheap and readily available sugar sources are still ideal for scale-up of the process strategies. Among large pool of studies available in this area, current review presents the advantages imparted towards HMF synthesis with the advent of heterogeneous catalysis over the course of time and various reaction systems evolved to meet the steeping demand of HMF, specifically from common carbohydrate sources. Special attention has been paid to understand the mechanism of modifications imparted to various solid catalysts for improved HMF synthesis.

Most of the chemical and biochemical processes used for the de-polymerization of structural polymers of lignocellulosic biomass are environment unfriendly and costly. Here an efficient process based on xylanase, produced by Acinetobacter pittii MASK25 (MTCC 25132), hydrolysis of only physically treated rice straw and corn cob has been developed for the production of xylooligosaccharides. Bacterial strain isolated from soil was found to produce maximum xylanase at 30°C and pH 7. While the optimum temperature and pH of xylanase were characterized as 40°C and 5. Process was further improved by developing magnetic-xylanase CLEA. Crude xylanase and magnetic-xylanase CLEA could convert respectively more than 45% and 60% xylan of the powdered rice straw and corn cob into xylooligosaccharides. Interestingly, hydrolysis by both types of enzymatic forms was found to produce predominantly xylopentose and xylohexose. Hence, the process is environment friendly and the predominant production of xylopentose and xylohexose could find unique prebiotic applications.

Hot springs are geothermally heated underground water that create a natural habitat for diverse thermophilic microorganisms. The study presents a comprehensive investigation of microbial diversity and functional potential of four thermal water reservoirs of 55 to 98 °C temperature range, located in Tattapani geothermal field of Chhattisgarh, India, by using culture-independent metagenome sequencing approach. The MG-RAST taxonomic profiling of metagenome samples revealed the predominance of bacterial domains (94.8 to 98.2%), followed by archaea (1.1 to 4.8%), eukaryota (0.1 to 0.5%), and viruses (0.04 to 0.09%). The quality filtered reads (42.1 to 68.1 million) were assembled into 66 to 330 thousand non-redundant contigs (>200 bp length) in the four metagenome samples. The functional annotation using CAZy database identified a total of 4083 putative genes with functional domains involved in catalysis of carbohydrate degradation or modification or synthesis of glycosidic bonds. The study detected many novel biocatalysts associated with hydrolysis of lignocellulosic biomass polymers- cellulose, hemicellulose, lignin, and pectin. Metagenome assembly and catalytic functions of two metagenomic contigs, encoding β-glucosidase, and xylanase, were experimentally validated. The findings emphasized these geothermal water reservoir sites as the repository of biocatalyst-encoding genes of carbohydrate-related and lignocellulosic biomass processing significance.

Lignocellulosic biomass is an important renewable resource that could substitute fossil feedstocks as a raw material for high value chemicals production.