PARTIAL LIQUID-PHASE HYDROGENATION OF BENZENE TO CYCLOHEXENE OVER RUTHENIUM CATALYSTS IN THE PRESENCE OF AN AQUEOUS SALT SOLUTION .1. PREPARATION, CHARACTERIZATION OF THE CATALYST AND STUDY OF A NUMBER OF PROCESS VARIABLES

A study has been made of the batch-wise partial hydrogenation of benzene to cyclohexene over ruthenium catalysts in the presence of an aqueous zinc sulphate solution. The reaction was performed at 423 K and at a pressure of 5.0 MPa in a stirred autoclave. The influence of a number of process variables on the performance of the catalyst, like the presence of water, the presence of salt-additives, the stirring speed, the temperature, the hydrogen pressure, the amount of catalyst, the catalyst particle size and the benzene/water ratio have been studied. It was found that it is extremely important that the catalyst is hydrophilic and therefore surrounded by a stagnant water layer; the presence of a stagnant water layer results in the suppression of the reaction rate and in a strong increase of the cyclohexene selectivity and yield. The high yield of the intermediate product, cyclohexene, which is of the order of 40 to 50 mol-%, is attributed to a physical effect, in casu severe mass transport limitation. Mass transfer calculations strongly support this conclusion.