Microcrystalline cellulose production by acid hydrolysis of hydrotropic rice straw pulp

Abstract

Rice straw is a by-product of the production of rice. Most of this material is considered as agricultural waste, used only for fodder, left or burned on the fields after harvest. Rice straw contains 35-50% cellulose, making it promising as raw material for microcrystalline cellulose production. The production of microcrystalline cellulose consists of three stages, namely delignification, bleaching, and hydrolysis. Those processes can be conducted at relatively high temperatures by both oven or microwave irradiation. The objective of this study was to compare the performances of those processes (oven and microwave irradiation) by evaluating the cellulose content and the crystallinity index of the microcrystal cellulose. The rice straw pulp was successively pre-treated with hydrotropic delignification and was bleached. Those pretreatments are intended to significantly remove unwanted substances such as lignin, coloring materials, and hemicellulose before the hydrolysis. The hydrotropic delignification was performed using a 20% urea solution with a liquid solids ratio of 1:10 at 80°C for 60 minutes. The bleaching process was carried out at 70°C for 60 minutes using hydrogen peroxide, an environmentally friendly bleaching agent. The hydrolysis was performed using hydrochloric acid and sulphuric acid in an oven for 10 to 50 minutes. The product was analyzed using Chesson-Datta method and FTIR. The FTIR analysis result shows that the highest crystalline cellulose fraction was 63,23%, which was obtained from hydrolysis using 1,5 M sulfuric acid for 50 minutes, the yield content is 55,91%. The same condition using hydrochloric acid resulted in a crystalline cellulose fraction of 60,70% with 59,16% yield content.