Enzymatic hydrolysis of cellulosic fiber

Abstract

Low cost cellulosic wastes like paper sludge, municipal wastes, solid wastes from food, packing etc. contain a high amount of cellulose which can be converted to bioethanol by two steps: (1) solubilization of cellulosic fibers to monosaccharides (2) conversion of monosachharides to bioethanol via fermentation. At present the implementation of this technology has been deterred by high cost for enzymes. Enzymatic hydrolysis of cellulosic fibers shows a biphasic behavior with an initial fast step followed by a slow step leading to low cellulose conversion rates. Low hydrolytic conversion rates necessitate the use of a high enzyme dosage to obtain meaningful cellulose conversion rates which make the implementation of this entire technology economically infeasible. The objective of this study is to get a better understanding of the mechanism of enzymatic hydrolysis of fibers to glucose and to investigate the effect of cationic polymers on enzymatic hydrolysis rates. To achieve the first objective, we performed experiments so as to study changes in morphological and physiochemical properties like fiber length, percentage of fines, crystallinity index, kink angle, kink index, mean curl, total organic carbon and glucose production with time. We used bleached kraft softwood, hardwood, and unbleached softwood fiber as cellulosic substrate and pergalase as cellulase enzyme. All of the experiments were carried out at experimental conditions of a temperature of 50 .C and a pH of 5.0 which maximize enzymatic activity. We studied the impact of recycling and refining on hydrolysis rates by measuring total organic carbon and glucose production. We found that refining increases enzymatic conversion rates by about as much as 20 %, however refining being energy intensive makes its implementation economically unfavorable. We found a novel way of enhancing hydrolysis rates by the use of cationic polyacrylamides. The effect of cationic polacrylamides was studied on both hardwood and softwood fibers at similar experimental conditions. Cationic polyacrylamides produced a maximum rate increase of 20 % in hydrolytic conversion rates for hardwood fibers. Even though, the increase in hydrolysis rates for softwood fibers was smaller than hardwood fibers, it was still significant. We further studied the effect of parameters like polymer concentration, cationicity and molecular weight to find a relation between properties of polymers and the increase in enzymatic hydrolysis.