KINETIC CHARACTERIZATION OF HOT WATER AND DILUTE ACID PRETREATMENT OF LIGNOCELLULOSIC BIOMASS

Lishi Yan

Acidic aqueous-phase pretreatment is a promising approach that has been directed at maximizing intermediates yields (e.g. sugars, sugar degradation products, and lignin) from biomass for fuel and chemical production. This dissertation explores the kinetic fundamentals of biomass hydrolysis in acidic aqueous-phase with different catalysts (e.g. sulfuric acid, metal chlorides), operating conditions (e.g. temperature, time pressure), and equipment configurations (e.g. batch, flowthough). The kinetic analysis revealed that crystalline cellulose is insusceptible to hydrolysis compared with agarose at low temperature (e.g.140 oC), while it decomposed rapidly at elevated temperature (e.g. 220 oC). Higher temperature with reduced time was desirable for glucose production whereas lower temperature with prolonged time was preferred for xylose generation. In acidic conditions, furfural and levulinic acid were stable whereas 5-hydroxymethylfurfural was susceptible to decomposition with high rate constant. MgCl2 can promote the cleavage of C-O-C bond in polysaccharides (e.g. agarose) and enhance the subsequent dehydration reaction to 5-hydroxymethylfurfural. Unlike transition metal chlorides and H2SO4, MgCl2 has little ability to induce retro aldol and rehydration reactions to generate byproducts like lactic acid and levulinic acid. Mg2+ possessing hgiher activity than other alkali and alkaline earth metal chlorides (Na+ and Ca2+) resulted in 40.7% yield and 49.1% selectivity of 5-hydroxymethylfurfural. Dissolution of biomass was significantly enhance using acidic hot water flowthrough pretreatment at 200－280 oC. Significant cellulose removal accompanied with the transformation of cellulose I to cellulose II and amorphous cellulose were observed when temperature was above 240 oC for water-only and 220 oC for dilute acid. Approximately100% of the xylan and ~90% of the cellulose were solubilized and recovered. Up to 15% of the lignin was solubilized, while the remaining lignin was insoluble. Over 90% sugar yields were obtained from pretreated whole slurries using less than 10 FPU/g cellulase plus hemicellulase enzyme. A kinetic model was developed to depict the biomass degradation in flowthrough system. This model predicted the sugar generation more precisely than the conventional homogeneous first-order reaction models. Mass transfer limitations were minimized using 4mm biomass particle sizes with 4g biomass loading at 25mL/min flow rate, produced hydrolyzate slurries with 13g/L potential sugar concentrations.

KINETIC CHARACTERIZATION OF HOT WATER AND DILUTE ACID PRETREATMENT OF LIGNOCELLULOSIC BIOMASS

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