Use of stirred batch reactors for the assessment of adsorption constants in porous solid catalysts with simultaneous diffusion and reaction. Theoretical analysis.

BIDABEHERE, C. M.; SEDRAN, U. A.

CHEMICAL ENGINEERING SCIENCE

ELSEVIER

Año: 2006 vol. 61 p. 2048 - 2055

0009-2509

A simple, pseudo-equilibrium model was derived to represent a catalytic system where a first order chemical reaction is conducted under the simultaneous consideration of diffusive and adsorptive processes, in order to assess the corresponding kinetics and Henry law’s-type adsorption parameters. Solutions from this model were compared to exact solutions from a more detailed, general model. It was shown that under most of the experimental conditions normally used in stirred batch reactors and the usual model considerations, it is only possible to assess apparent adsorption parameters, and that a stable relation between the concentrations in the gas and solid phases (a pseudo-steady state) is reached. The error produced in assuming that the apparent adsorption constant is the real one was calculated to be very important. The value of the apparent constant depends on various system properties and experimental conditions, such as the Thiele modulus, the amount of catalyst and the contact time. The relation between the apparent and real adsorption constants was shown to be the transient effectiveness factor for a first order reaction at any moment. That relationship between constants is always larger than the steady state effectiveness factor, becoming closer as long as the system’s adsorption capacity is smaller. A new experimental methodology was proposed to assess kinetics and adsorption parameters in stirred batch reactors by means of a very simple algebraic expression. Keywords: Adsorption, Catalysis, Kinetics, Chemical reactors, Diffusion, Reaction Engineering