Integrated two-stage chemically processing of rice straw cellulose to butyl levulinate

Abstract

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.

Keywords: 5-hydroxymethylfurfural; Butyl levulinate; Glucose; Levulinic acid; Rice straw.