Solid acid catalysts for hydrolyzing oligosaccharides derived from corn fiber
Abstract
Pretreatment of lignocellulosic biomass is a key step in the fuel ethanol production process. Liquid hot water pretreatment of plant biomass produces a liquid stream with dissolved oligosaccharides which are usually converted to fermentable sugars by enzymatic hydrolysis. The goals of this study are to use a solid acid catalyst, instead of liquid mineral acids or enzymes, to understand the mechanism of solid acid catalysis, and to study economical feasibility of using solid acid catalysts for saccharification of oligosaccharides. Strong cation exchange resins offer the advantages of continuous processing of pretreatment liquid, reusability, and short reaction times when compared with enzymes. The kinetic behavior of the cellobiose and oligosaccharide hydrolysis using different types of strong cation exchange resins in packed bed, plug flow reactor and batch reactor tubes was investigated at temperatures between 100 to 160°C. A pseudo first-order reaction model was developed to fit the hydrolysis data and has been shown to satisfactorily fit the experimental data. High temperature and short residence times were required to minimize formation of aldehydes and other fermentation inhibitors formation while achieving high glucose yield. The hydrolysis of oligosaccharides in liquid from a pilot-scale corn fiber pretreatment process was also investigated at different reaction conditions, as well as approaches that minimize fouling of the catalyst by proteins, phenolics and minerals. This study also reports the effects of particle size, degree of cross-linking, and temperature on hydrolysis of oligosaccharides and degradation of monosaccharides. Both gel type and macro-reticular type resins having different degree of cross-linking and ion exchange capacity were tested for hydrolysis of malto-oligosaccharides at various reaction conditions. Results show that low percentage cross-linked gel-type cation exchange resins give a higher glucose yield than macro-reticular type resins. 80% of total sugars were recovered as monosaccharides with 90% oligosaccharide conversion at 150°C by using a 2% cross-linked gel type resin. The hydrolysis was diffusion limited in both resin types. A mathematical model that quantifies diffusion and kinetic characteristics of this reaction is presented and potential application of plug flow reactors to hydrolysis of oligosaccharides obtained from pretreatment of cellulose is discussed.
Degree
Ph.D.
Advisors
Ladisch, Purdue University.
Subject Area
Agricultural engineering|Chemical engineering
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