A Kinetic Analysis of Wood Degradation in Supercritical Alcohols Jeeban Poudel and Sea Cheon Oh* Department of Environmental Engineering, Kongju National University, 275, Budae-dong, Cheonan, Chungnam, 330-717, Korea ABSTRACT: The kinetic analysis method for degradation of wood in supercritical ethanol and methanol was proposed in this work. This method was applied to predict the degradation of wood in supercritical ethanol and supercritical methanol by a nonisothermal weight loss technique with heating rates of 3.1, 9.8, and 14.5 °C/min for ethanol and 5.2, 11.3, 16.3 °C/min for methanol. To verify the effectiveness of the kinetic analysis proposed in this work, the experimental values were compared with those of the numerical integration results using kinetic parameters obtained in this work. The kinetic analysis method proposed in this work gave reliable values of kinetic parameter for wood degradation in supercritical ethanol and supercritical methanol. To understand the effectiveness of the solvents as supercritical fluid, the calculation results of wood weight loss using the kinetic parameters obtained from this work were studied at a heating rate of 7 °C/min for both supercritical ethanol (SCE) and supercritical methanol (SCM). From this work, it can be seen that SCE is better solvent than SCM for wood degradation in supercritical alcohols. 1. INTRODUCTION Owing to the limitations of homogeneous and heterogeneous catalytic reactions for biodiesel production from biomass, a sustainable and environmental friendly technology using supercritical alcohol (SCA) has been receiving considerable attention. SCA technology is a noncatalytic process which makes the separation and purification of biodiesel relatively easy and simple. It has also been shown that this process only requires a small amount of reaction time to achieve a significant yield of biodiesel. 11 Supercritical fluids have properties of both liquid and gas phases. Having a density close to that of a liquid, the supercritical fluid has the ability to dissolve many components, whereas the high diffusivity and low viscosity of the supercritical fluid also enables it to behave similar to gas. Such mobile properties of the supercritical fluid tend to maximize the yields of the product in the prescribed reaction time. Along with this major advantage of a supercritical fluid, others have been mentioned in the referred paper. 2,3 Water offers a remarkable solvent tenability with its wide range of dielectric constants; its applications and potential as a new reaction medium in chemistry have been reviewed. 4 The fact that the critical temperatures of alcohols (T c = 512.6 K, 513.9 K; P c = 80.9 bar, 61.4 bar; ρ c = 0.272 g/cm 3 , 0.276 g/cm 3 for methanol and ethanol, respectively) are quite low compared to that of water (T c = 647.1 K; P c = 220.6 bar; ρ c = 0.322 g/ cm 3 ) which suggests that hydrogen bonding is weaker in the alcohols than in water. 5 The alcohols may be alternatives to water as supercritical solvents considering their less corrosive and aggressive chemical nature, the lower critical temperatures and pressures, and their reasonably high dielectric constants. Because these alcohols have lower critical temperatures and pressures than those of water, they can offer milder conditions for reaction. In addition, these alcohols are expected to readily dissolve relatively high molecular weight products from cellulose, hemicelluloses, and lignin because of their low dielectric constants when compared with that of water. 6 However, there is sufficient literature which compared the effects of types of alcohol used in a noncatalytic SCA reaction, which is important as they influence the performance of the reaction significantly. 7 There is a plethora of reported articles focusing on the supercritical methanol (SCM) process, while there is limited research on the supercritical ethanol (SCE) process. Very few researches have been conducted for comparative study of methanol and ethanol. SCM and SCE reactions were carried out by utilizing a single-variable experimental design to investigate the effect of alcohols on the yield of biodiesel. 8 In this work, the degradation kinetics of wood using SCM and SCE has been studied. Wood and other forms of biomass can be used in various ways to provide energy through combustion, gasification, and pyrolysis, etc. 9 Pyrolysis which converts wastes to fuel or useful hydrocarbons is a promising and economical process to produce liquid fuels that can be readily stored and transported. 10 But it was never commercial- ized because of some problems to be tackled such as excessively long degradation time, tar formation, and the coking of reactants. So, new technologies using supercritical fluid are vital in the thermal treatment process of biomass. It is well known that a kinetic investigation is very important to get information for rationally designing the reactor for the degradation of wood in supercritical fluids. But unfortunately, such factors as hard reaction conditions, complicated compositions of degradation products, difficulty of continuous operation, etc. tend to limit the kinetic study on the degradation of wood in supercritical fluids. The overall target of this research is to generate the basic parameters for design of this system rather than developing the mechanism of operation. These parameters will help in further development of the system. The parameters are calculated using SCM and SCE which shows the comparative analysis of the two solvents too. The use of supercritical alcohols like ethanol and methanol shows some promising output for better Received: March 11, 2011 Revised: December 25, 2011 Accepted: January 2, 2012 Published: January 2, 2012 Article pubs.acs.org/IECR © 2012 American Chemical Society 4509 dx.doi.org/10.1021/ie200496b | Ind. Eng.Chem. Res. 2012, 51, 4509-4514