Fractionation and characterization of multi-feedstock lignocellulosic biomass via two-stage pretreatment

Abstract

Abstract A two-stage pretreatment toward lignocellulosic biomass fractionation was devised. The process consisted of dilute acid hydrolysis using oxalic acid, followed by oxalic acid–assisted ethanol organosolv pretreatment. A biomass mixture consisting of four regional lignocellulosic materials, namely, brewer’s spent grain, tomato waste biomass, cucumber waste biomass, and spent coffee grounds, was used. In the first stage, the optimum mixture composition was determined using a full factorial design coupled with a simplex-centroid design. The interactive effects of the solid-to-liquid ratio, holding time, acid type, and concentration were also considered. In the attempt to lower solid yields and increase hemicellulose dissolution, elevated levels of furfural (15.73 g/L) and 5-hydroxymethylfurfural (8.56 g/L) were formed, due to increased pretreatment severity (180 min, 135C, 83.15 mg oxalic acid/g biomass, and 100 g biomass/L). The solid yield achieved was 50.53%. In the second stage, the effect of ethanol-to-water solvent ratio, holding time, and temperature were investigated using a central composite experimental design. Solid yields ranged between 72.57 and 85.20% (w/w), mainly due to lignin removal. Pretreatment with 75% (v/v) ethanol at 120 min and 190 °C resulted in the highest lignin recovery (44.69%). Post-experimental verification runs were performed to evaluate the validity of the response surface models with a maximum error of 15.17%. Characterization by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and heteronuclear single quantum coherence spectroscopy (HSQC) were conducted to assess biomass fraction integrity and structural changes during pretreatment. Graphical abstract

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