Sustainable valorization of sour gas: Optimized synthesis of Bis-(p-chlorobenzyl) sulfide using liquid-liquid-solid catalysis

Abstract

A protocol to utilize sour gas H₂S by the synthesis of value-added fine chemicals, i.e., Bis-(p-chlorobenzyl) sulfide (BPCBS), has been developed, and the conditions for the reaction have also been optimized. This technique of synthesis of aromatic thioether is challenging because of the formation of the by-product p-chlorobenzyl mercaptan (p-CBM). This makes the selective synthesis of thioether-like Bis-(p-chlorobenzyl) sulfide complex. For this investigation, H₂S absorbed in aqueous N-methyl diethanolamine was used to synthesize Bis-(p-chlorobenzyl) sulfide using Tributylmethyl phosphonium chloride polymer-bound catalyst as phase transfer catalyst in the liquid-liquid-solid mode of catalysis. Response surface methodology accompanied by a central composite design was used to study reaction kinetics, model development, and the optimization of reaction conditions. There are two products of the reaction Bis-(p-chlorobenzyl) sulfide (BPCBS) and p-chlorobenzyl mercaptan, so the dual response, i.e., conversion of p-CBC and selectivity of BPCBS, has been studied and optimized. The optimum values of the different variables for the maximum p-CBC conversion and BPCBS selectivity are as follows: temperature: 327.37 K, Catalyst concentration: 2.8 × 10⁻⁵ kmol/m³, reactant concentration: 2.468 × 10⁻³ kmol/m³, MDEA/Sulfide ratio: 2.033. The results demonstrate the feasibility of using H₂S as a reactant in fine chemical synthesis, offering an environmentally benign solution to industrial H₂S emissions.