Synthesis and Scale-up of a Sulfonamide Catalyst for Mercaptan Removal from Light Oils: A Reaction Kinetics Investigation with Density Functional Theory Validation

The sweetening of lighter petroleum fractions such as liquefied petroleum gas (LPG) involves the extraction of lighter thiols (RSHs) by caustication to form mercaptides (NaSRs). Oxygen subsequently oxidizes these NaSRs to disulfides (RSSRs) in the presence of a catalyst typically – based on cobalt phthalocyanines (CoPc) and an alkali. The present study focuses on joint development and commercialization efforts for an LPG sweetening catalyst – Thoxcat ES – by CSIR-Indian Institute of Petroleum (IIP) and Bharat Petroleum Corporation Ltd. (BPCL) using a step-by-step approach toward elucidating mechanistic pathways, establishing applicable rate laws, laboratory reactor design, and determining kinetic parameters for the catalyst–substrate system. Gas–liquid (G-L) kinetics studies using oxygen were conducted in an agitated and sparged tank contactor (ASTC) equipped with a turbine impeller operated in the total recirculation regime (TRR) using 1-ethanethiol in the range of 400–700 ppm w at temperature (T) = 303–317 K and atmospheric pressure. The derived rate law, though similar to the Michaelis–Menten rate law, simplifies into a linear form for the usual industrial process conditions. The experimental activation energy (Ea) determined as 50.715 kJ mol–1 compared within a range of ±2.0% with density functional theory (DFT) predictions indicates adequate representation of intrinsic kinetics after discounting hydrodynamic and mass transfer limitations. During refinery runs, such kinetic models are helpful in optimization of catalyst makeup dosages and dosing frequency for achieving operating cost competitiveness in petroleum refineries.