Fatty oil hydrogenation in supercritical solvents: Process design and safety issues

A simulation study of a SCF process is carried out using Aspen™ with previously available catalytic kinetics for the simulation of the reactor. Two supported catalysts were considered: a standard Pd/carbon, and an egg-shell Pd/alumina, in a vapour-phase process that uses propane as solvent. Best reactor-catalyst combination was selected using optimization. Optimal reactor-catalyst conditions were: Pd (0.5 wt%) on alumina catalyst in tubes, shell cooling, inlet temperature 170 °C, space-time 100 s, 4 mol% of H₂ in the feed, oil feed 1 mol%, propane 95 mol%, with pressure up to 20 MPa. Three SC solvents, were considered in the simulation. These were (i) SC propane, (ii) a cosolvent case with hexane-modified CO₂, and (iii) a case with pure liquid hexane. In plant simulation, three recycle streams (H₂, CO₂ and cosolvent) complicate the separations. In order to assess the safety differences between these options, a study was done using the Dow Fire and Explosion Index to roughly figure out process safety. It is shown that plant complexity increases with cosolvent use, but the hazard index is sensibly reduced, from F&EI = 150 (pure propane) to a low value (F&EI = 60) for a plant with CO₂ with 40 mol% of hexane as cosolvent.