Importance of Irreversible Thermodynamics for Liquid Phase Ion Exchange Catalysis: Experimental Verification for MTBE-Synthesis

Abstract

The internal macrokinetics for the liquid phase synthesis of methyl tertiary buthyl ether (MTBE) from methanol and isobutene using a macroporous sulfonic acid ion exchange resin as catalyst were examined experimentally in a continuous stirred tank reactor in the temperature range 333–363 K at 2.1 MPa. The employed catalyst was the self-prepared CVT resin (7.5% DVB) shaped in Raschig-rings (6×6×1). The experimental data are used to verify a mathematical model for the macrokinetics of MTBE—synthesis, which is based on the principles of irreversible thermodynamics. The multicomponent diffusion in the macropore system of the catalyst is described by the generalized Maxwell—Stefan equations. The reaction microkinetics are formulated in chemical potentials starting from a Langmuir—Hinshelwood rate expression in liquid phase activities according to the extreme nonideal character of the reaction mixture. The stoichiometry and an eigenvalue analysis of the matrix of diffusion coefficients help to reduce the model to the Frank—Kamenetzki equation. which can be solved analytically for a Rasching—ring and numerically for a sphere as catalyst bodies. Experimental results concerning the effectiveness factor and the selectivity of the CVT-resin and Amberlyst 15 (20% DVB) are in good agreement with the presented model.