CATALYTIC-HYDROGENATION IN SUPERCRITICAL CO2 - KINETIC MEASUREMENTS IN A GRADIENTLESS INTERNAL-RECYCLE REACTOR

Catalytic hydrogenation in supercritical carbon dioxide has been studi ed. Experimental results and theoretical calculations are presented, a ttempting to elucidate the effects of temperature, pressure, and CO2 c oncentration on the rate of reaction. An effort has been made to devel op a procedure to test catalytic reactions in supercritical fluids in view of future industrial applications. Hydrogenation rates of the two double bonds of an unsaturated ketone on a commercial alumina-support ed palladium catalyst were measured in a continuous gradientless inter nal-recycle reactor at different temperatures, pressures, and CO2-to-f eed ratios. A Berty-type reactor has been suitably modified for use wi th supercritical solvents. The accurate control of the organic, carbon dioxide, and hydrogen feed flow rates and of the temperature and pres sure inside the reactor provided reproducible values of the product st ream compositions, which were measured on-line after separation of the gaseous components. In order to develop a kinetic model, vapor-liquid equilibrium calculations were carried out through a Peng-Robinson equ ation of state, tuned on binary high-pressure vapor-liquid equilibrium data. Compositions in the liquid phase inside the reactor were predic ted, starting from the on-line analysis after depressurization. A simp lified power law kinetic equation is shown to provide a good descripti on of the experimental data.