Analysis of operating variables on the performance of a reactor for total hydrogenation of olefins in a C 3C 4 stream

Abstract

The effect of process and operating variables in the catalytic hydrogenation of unsaturate traces in C 3C 4 streams, intended for aerosol propellant use, has been analysed. The results from catalytic tests carried out on a commercial Pd/Al 2O 3 catalyst have been used to estimate the kinetic parameters of rate expressions. The set of rate expressions is used in a mathematical model of a three-phase fixed-bed catalytic unit operated in up-flow mode. The mathematical model allowed studying the effect that variables such as temperature, pressure, hydrogen mass flow and feed composition will exert on the reactor performance. The volatility of the hydrocarbon mixture is found to be a paramount factor in the process, as H 2 becomes diluted in the vapour phase and, consequently, the amount of H 2 dissolved in the liquid stream and the hydrogenation rates decrease significantly. A temperature rise turned out to be detrimental for the reactor performance, as the increased hydrocarbon volatility overcomes the effect on the kinetic coefficients. This conclusion precludes the usual operating practice of rising temperature to compensate for catalytic activity decay. Instead, increasing the H 2 input and/or the operating pressure were shown to be effective alternatives for this purpose.