Reaction kinetics of cellulose hydrolysis in subcritical and supercritical water

Abstract

The uncertainties in the continuous supply of fossil fuels from the crisis-ridden oil-rich region of the world is fast shifting focus on the need to utilize cellulosic biomass and develop more efficient technologies for its conversion to fuels and chemicals. One such technology is the rapid degradation of cellulose in supercritical water without the need for an enzyme or inorganic catalyst such as acid. This project focused on the study of reaction kinetics of cellulose hydrolysis in subcritical and supercritical water. Cellulose reactions at hydrothermal conditions can proceed via the homogeneous route involving dissolution and hydrolysis or the heterogeneous path of surface hydrolysis. The work is divided into three main parts. First, the detailed kinetic analysis of cellulose reactions in micro-and tubular reactors was conducted. Reaction kinetics models were applied, and kinetics parameters at both subcritical and supercritical conditions were evaluated. The second major task was the evaluation of yields of water soluble hydrolysates obtained from the hydrolysis of cellulose and starch in hydrothermal reactors. Lastly, changes in molecular weight distribution due to hydrothermolytic degradation of cellulose were investigated. These changes were also simulated based on different modes of scission, and the pattern generated from simulation was compared with the distribution pattern from experiments. For a better understanding of the reaction kinetics of cellulose in subcritical and supercritical water, a series of reactions was conducted in the microreactor. Hydrolysis of cellulose was performed at subcritical temperatures ranging from 270 to 340 °C (τ = 0.40-0.88 s). For the dissolution of cellulose, the reaction was conducted at supercritical temperatures ranging from 375 to 395 °C (τ = 0.27-0.44 s). The operating pressure for vii TABLE OF CONTENTS LIST OF TABLES .

Hydrothermal decomposition of various crystalline celluloses as treated by semi-flow hot-compressed water

“…At 270 ˚C/10 MPa/15 min, cell II was shown to be totally decomposed to WS portions as compared with other celluloses. The overall results from Fig.4-1 illustrated that higher yields were obtainable for group II celluloses than group I. hydrolysis is classically defined by a pseudo-homogeneous kinetics model, a term that in reality reflects that the hydrolysis process is heterogeneous (Olanrewaju 2012). Every parameter used such as time, pressure and DP on the celluloses were kept constant, satisfying the assumption that the Arrhenius-plot is temperature dependent.…”

Effect of water of crystallization on the dissolution efficiency of molten zinc chloride hydrate salts during the pre‐treatment of corncob biomass

“…Pre‐treatment directly results in an improvement of overall polymer deconstructions and efficiency of the bioconversion of resulting sugars to several value‐added products . Proven pre‐treatment techniques in the literature include chemical treatments such as organosolv, SO 2 and CO 2 impregnation, and dilute acid/alkaline solvation systems. In addition, non‐aqueous methods such as microwave treatment have been found to effectively increase the susceptibility of biomass to digestion .…”

Noncatalyzed Liquefaction of Celluloses in Hydrothermal Conditions: Influence of Reactant Physicochemical Characteristics and Modeling Studies

“…34 Olanrewaju has obtained a value of 99 kJ mol −1 for microcrystalline cellulose hydrolysis in water using a shrinking-core model. 60 Some other studies have founded higher value but generally experiments were conducted at higher temperature leading to a significant change of H 3 O + concentration reaching near-critical state. For example, Cantero et al obtained an activation energy of 154 kJ mol −1 for a temperature between 280 and 370 °C.…”