CATALYTIC-OXIDATION OF ETHYLBENZENE TO ACETOPHENONE USING ALUMINA-SUPPORTED DICHROMATE - PROCESS OPTIMIZATION AND DEVELOPMENT OF A CONTINUOUS PROCESS

Potassium dichromate supported on neutral alumina is a heterogeneous c atalyst for the liquid phase oxidation of hydrocarbons. The material h as been used to catalyse the oxidation of ethylbenzene to acetophenone using air as the consumable oxidant with high selectivity and is trul y catalytic in the metal, unlike homogeneous Cr(VI) systems. Optimisat ion of reaction conditions has been achieved in terms of air flow rate , agitator speed, and catalyst quantity. An induction period prior to achievement of maximum catalytic turnover, which is proportional to bo th temperature and the concentration of catalyst, may be reduced by do ping the substrate with 5-15% acetophenone (w/w) and eliminated by dop ing with 30% (w/w) acetophenone , A rate of conversion of ca. 3.8% h(- 1) (0.39 turnover s(-1)) may be achieved at a reaction temperature of 130 degrees C for a period of ca. 10 h before catalyst deactivation oc curs. However, this rate may be maintained for periods in excess of 24 h by continuous addition of substrate to the reaction vessel in order to maintain a constant molar ratio of substrate to product, It may th us be concluded that, at high agitator speeds, the rate-limiting facto r is adsorption/desorption at the catalyst surface (and is therefore a ffected by the overall polarity of the medium) rather than mass transf er between solid-liquid-gas interfaces, The catalyst has been successf ully recovered and reused with no induction period, and initial activi ty is comparable with that for fresh catalyst, although deactivation o ccurs readily thereafter.