Advisor: Professor Rayford G. Anthony
CoAdvisor: Professor Gilbert F. Froment

Aromatic thiols are used as intermediates in the manufacturing of pharmaceuticals, agrochemicals, pigments, polymers. These compounds have been produced through reduction of sulfonyl chloride or thiolation. The reagent of choice for the reduction process was typically zinc or tin in dilute acid. However, harmful byproducts in the form of metal salts (ZnCl2) were produced.

DuPont developed the catalytic hydrogenation of sulfonyl chloride to produce the desired aromatic thiols. This technology leads to a higher yield, a lower catalyst usage and little toxic heavy metals byproducts compared to the reduction method. A slurry reactor was used to carry out the hydrogenation reaction.

My research focuses on determining the kinetic rate of the three-phase (gas/liquid/solid) catalytic hydrogenation of 2,5-dimethylbenzenesulfonyl chloride into aromatic thiol. Palladium will be used as the catalyst (solid Phase).

A Robinson-Mahoney stationary catalyst basket reactor with a volume of 300 cm3 has been strategically selected to carry out this hydrogenation reaction. This type of reactor is far different from the reactor used by DuPont.

As hydrochloric acid is a by-product of the reaction, a corrosion study has been performed before buying the reactor. Considering the cost and the performance of different materials (stainless steel, Hastelloy alloy, tantalum, titanium...) in corrosive media, Hastelloy alloy C-276 has been selected as the material of construction for the reactor and the hydrogenation unit.

Design of the hydrogenation unit has been of primarily importance. A flow diagram including all the necessary equipment (valves, fittings, pumps, mass flow controllers etc) has been drawn. Apart from the catalytic reactor, a coalescer centrifuge-type gas/liquid separator and a scrubber unit are needed to perform the experiments.

Part of the experiments would be first to secure mass transfer resistance between phases (G/L and L/S). Thereafter, intrinsic reaction at the surface of the reactor can be determined experimentally and related to Hougen-Watson reaction rates. Several kinetic models have been established considering all the chemicals involved and the behavior of hydrogen on the catalyst surface (dissociation or non-dissociation of hydrogen). Parameter estimation and statistical methods would allow us to determine the best kinetic model for the hydrogenation reaction.