Reaction Rate and Its Pressure Dependence in Heterogeneous Liquid Phase Isomerization of Diethyl Maleate over a CaO Catalyst

Abstract

The isomerization of diethyl maleate (A) to diethyl furnarate (B) over a CaO. catalyst suspended in heptane proceeds rapidly in the initial stage but very, slowly in the latter stage. Original basic sites [s]e on the CaO surface mainly promote the reaction in the initial stage, in which the adsorption of A onto [S] limits the reaction rate. A strong adsorption of the product (B) results in a decrease in the surface concentration of [S]e and, when the adsOrption, reaches, the saturation, the initial stage finishes. Only weak basic sites [B_**S]c promote the reaction in the latter. stage, in which the adsorption of A onto. [B_**S]Q limits the rate. The rate of the latter stage obeys the zero-th order kinetics. These characteristic features of the reaction are observed in every one of the other solvents including pentane, hexane, and octane. Furthermore the rate of the latter stage is little affected by the viscosity of the solvent.
In the range between 0 and 150 11413ath e increase in pressure results in a decrease in the reaction rate of the 'latter stage; the experimental activation volume ΔV_exp, is 20±2ml·mol^-1(in heptane). The positive activation volume is explained in terms of a desolvation caused by the formation of transition state with a highly dispersed ionic charge:, A linear relationship between the apparent activation volume and the molar volume of solvent is utilized to estimate the intrinsic activation volume for adsorption ΔV_ads; The negative value of ΔV_ads(-21ml·mol^-1) well conforms to the physical picture of adsorption.