279133 Kinetics of Steam Gasification of Biomass Using Fluidizable Ni/La2O3-gAl2O3 Catalyst
Kinetics of Steam Gasification of Biomass Using Ni/La2O3-γAl2O3 Catalyst
Jahirul Mazumder and Hugo I. de Lasa
Chemical Reactor Engineering Centre (CREC), Department of Chemical & Biochemical Engineering, The University of Western Ontario, London, ON N6A 5B9 (Canada)
Steam gasification of biomass involves a complex network of heterogeneous reactions . Primary reactions break down the vaporized biomass molecules, forming permanent gases, higher hydrocarbons and coke. Secondary reactions crack the higher hydrocarbons into gases. Furthermore, permanent gases react to alter the gas composition depending on gasifier conditions.
A Ni-based catalyst supported on fluidizable γ-Al2O3 is one of the most promising catalysts due to its high surface area, high activity for tar conversion and affordability . Gasification of glucose (a model compound for cellulose) and 2-methoxy-4methylphenol (a model compound for lignin) was conducted using the La2O3 modified Ni/γAl2O3 catalyst at different steam/biomass ratios, temperatures and reaction times in a CREC fluidized riser simulator . Significant improvements in dry gas yield and carbon conversion compare to the non-catalytic and catalytic gasification using Ni/α-Al2O3 catalyst at the same operating conditions confirmed the high activity of the developed catalyst for reforming of tars compounds and coke combustion. The trends of gasification products (H2, CO, CO2, CH4, etc) with the variation of these parameters are in consistent with the thermodynamics predictions . With the increase in temperature, H2 and CO concentrations were increased while CO2 and CH4 concentrations were decreased. On the other hand, increasing CO2 and decreasing CO profiles were observed with the steam/biomass ratio and residence. TOC analysis of spent catalyst showed negligible coke deposition.
Glucose gasification results showed that H2, CO, CO2, CH4 and H2O are mainly present in the product gas with negligible C2+ species and coke deposited on catalyst surface. Thus, steam reforming of methane, CO methanation and water gas-shift reaction can be considered as the dominant reactions. Rates of these reactions can be modeled using a Langmuir-Hinshelwood type rate equation. This approach considers chemical species adsorption as well as intrinsic kinetics. After simplifications and linearization it results,
The overall rate of formation/disappearance of each chemical species can be written as:
Knowing that the CREC Riser Simulator is a well mixed batch reactor, a balance equation for each species “i” can be expressed as follows:
Thus, a set of differential equations representing the catalytic steam gasification of glucose can be obtained by substituting eq (1)-(4) into eq. (5). Adsorption constants for CO2 were calculated using experimental data from the CREC Riser Simulator. Intrinsic kinetic parameters were estimated from experimental glucose gasification results using a “nlinfit” subroutine from Matlab.
Key words: biomass gasification, La2O3 modified γ-Al2O3, Ni catalyst, Langmuir-Hinshelwood equation, CREC riser simulator
 E. Salaices, B. Serrano, H.I. de Lasa, Biomass Steam Gasification Thermodynamics Analysis and Reaction Experiments in a CREC Riser Simulator, Ind. Eng. Chem. Res. 49 (2010) 6834-6844.
 H.I. de Lasa, E. Salaices, J. Mazumder, R. Lucky, Catalytic Steam Gasification of Biomass: Catalysts, Thermodynamics and Kinetics, Chem. Rev. 111 (2011) 5404-5433.
 H.I. de Lasa, Riser Simulator for Catalytic Cracking Studies, US patent 5, 102, 628 (1992).