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Oxalic acid as a catalyst for the hydrolysis of sisal pulp

Lacerda, Talita M., Zambon, Márcia D., Frollini, Elisabete
Industrial crops and products 2015 v.71 pp. 163-172
acid hydrolysis, activation energy, biomass, catalysts, cellulose, crystal structure, energy, glucose, high performance liquid chromatography, kinetics, mercerization, molecular weight, oxalic acid, petroleum, pulp, scanning electron microscopy, sisal, temperature
The possible shortage of crude oil has led to the search for alternative sources of chemicals and energy producers from biomass.The current results are related to the analysis of the unreacted cellulosic material and the liquor, from the acid hydrolysis of an industrial Kraft sisal pulp. An important characteristic involving the acid hydrolysis of biomass is the possibility to utilize different acids because the only requirement for the reaction to occur is the presence of a proton source in the media. In this context, a series of acid hydrolysis reactions of a prior mercerized sisal pulp was performed with 4.6molL−1 oxalic acid at varying temperatures (from 80 to 100°C), and aliquots were withdrawn from the reaction media.The liquor composition was analyzed by HPLC and the unreacted pulps (e.g., the material that was not decomposed to sugars) were characterized by SEM, average molar mass, crystallinity index, and their size distribution was determined using a fiber analyzer. The kinetic model developed by Saeman was applied to calculate the activation energy for the acid hydrolysis of sisal pulp. A higher glucose concentration (approximately, 8gL−1) was detected at 100°C, after 16h. The percentage of hydrolyzed cellulose under these conditions was 50.4%, and the amount of glucose recovered as a percentage of the amount in the raw sisal pulp was 22.3%. Unreacted cellulose was isolated at a low average molar mass (approximately 6000gmol−1) and high crystallinity (approximately 88%), at 100°C. Oxalic acid is a promising catalyst for the hydrolysis of cellulose for the production of sugars and for pretreatment of the fibers prior to other processes (e.g., enzymatic hydrolyses).