Super Acid Catalysts In SCF Media For Production Of Linear Alkyl Benzenes

The advantages of supercritical fluid (SCF) solvents relate to the density dependence properties (solubility, diffusivity, viscosity, heat capacity) which can be tuned by changing temperature and pressure over a relatively small range. Polar solvents have the added feature of a tunable dielectric constant. For catalytic applications, these tunable features can be manipulated to affect kinetics, selectivity, yield, mass transfer etc as well as facilitating separation of products and catalyst recovery. In the production of linear alkylbenzenes (which when sulphonated are the key products in the detergents industry) the current catalysts are AlCl₃ and HF both of which suffer from waste-handling and process safety issues. The use of perfluoro octane sulphonic acid in SCF CHF₃, however, allows the reaction to be run homogeneously and excellent yield and selectivity are obtained. In contrast in SC CO₂, low conversions and much isomerisation occur. The authors of the paper (from DuPont) speculate that CHF₃ disrupts diesters of acid end groups - this does not appear to occur in CO₂ (Harmer M A et al, Chem Comm, 2002, 18).