Dissolution kinetics of corncob in lithium perchlorate solvent system

Abstract

To improve the economical use of lignocellulosic bio-waste (e.g. corn cob), an efficient pre-treatment route is required to make its content accessible to enzymatic hydrolysis to produce bio-products such as biofuels and bio-chemicals. The use of mineral acidic (H2SO4) and alkaline (NaOH) media for pre-treatment is very efficient but produces toxic effluents that are not environmental benign. However, studies have shown that the use of molten hydrate salts is very efficient and environmentally benign. This study presents results of the investigation of dissolution kinetics of corn cob in lithium perchlorate (LiClO4•2H2O), an environmentally friendly molten hydrate solvent system. Pre-screened milled corncob sample was fractionated in LiClO4•2H2O solvent system at solid to solvent ratio of 1:10 and the mixture was stirred continuously at stirring rate of 250 rpm for 10 hours. Samples of the mixture were taken for analysis after every 10-minute interval for the first hour and 1-hour intervals until the end of the experiment. Dissolution kinetic study was carried out at 120 oC-180 oC at 20 oC intervals to understand the effect of temperature on the kinetics. The samples obtained were filtered to separate the liquid and the solid fractions and analyzed with a pre-calibrated high-performance liquid chromatograph. The study reveals that dissolution kinetics of corn cob in the solvent system is fast with rate constant that is enhanced at increasing temperature and could be described by a pseudo-first order dissolution kinetics. The dissolution (activation) energy for the kinetics for glucose, xylose and lignin were 15.0 kJ/mol, 14.2 kJ/mol and 36.54 kJ/mol, respectively. It is apparent that the activation energy associated with lignin is higher than that of glucose and xylose, indicating that more energy will be required to release lignin from corn cob.