Hydrogen Sulfide Capture and Utilization: Multiphase Catalysis in Synthesis of Symmetrical Aromatic Sulfides

Abstract

The selective synthesis of symmetrical organic sulfide using industrial waste gas hydrogen sulfide (H2S) is a bit challenging. The present kinetic investigation is based on H2S gas released from refineries is chemisorbed in an industrially important alkanolamine,N-methyldiethanolamine (MDEA) followed by a biphasic reaction between the two immiscible reactants H2S–laden MDEA and p-chlorobenzyl chloride in solvent free condition to yield bis(p-chlorobenzyl sulphide) (BPCBS) using an ionic liquid as a phase transfer catalyst. Phosphonium-based ionic liquid was found to be an efficient biphasic catalyst as a significant amount of desired product was obtained in just 5 min of reaction. The selectivity of the desired product BPCBS was achieved as 100% at the optimized level of various process parameters. A Suitable mechanism has been proposed to explain the course of the reaction. A kinetic model was developed and validated successfully. The solvent-free condition is a ―green‖ approach which eliminates the use of harmful solvents. Another work was also carried for the determination of the numerical value of distribution coefficient and dissociation constant for Tetrabutylammonium bromide (TBAB) and Trihexyltetradecyl phosphonium chloride (ionic liquid). The value of distribution coefficient is determined by the UV-spectrometry method for four systems viz. toluene-water system, benzene-water system, chlorobenzene-water system and p-CBC-water. The estimated distribution coefficient was highest for benzene-water for both the catalyst studied. The value of dissociation constant was investigated to be same irrespective of the change in concentration of the catalyst. In the last study, an easy-preparation procedure was adopted for the synthesis of Multi-site phase transfer catalyst. The dual-site MPTC viz. 1,4- bis(triethylmethylammonium)benzene dichloride (DC-X) and 4,4‘-bis- (Triethylmethylammonium)-1, 1‘-biphenyl Dichloride (4, 4‘-B(TEMA)-1,1‘-BP DC). A polymer-bound N-ethyl-N-di-isopropyl ammonium chloride phase transfer catalyst was also synthesized and characterized. The formation of all the catalysts was evident from the FT-IR, NMR and elemental analysis. The catalytic activity of one of the prepared MPTC viz. bis- Quaternary Ammonium Salts 4,4‘-bis (triethylmethylammonium)-1,1‘-biphenyl dichloride (4,4‘- B(TEMA)-1,1‘-BP DC) was investigated by utilizing it for the sulfidation of different type of alkyl halides, which results in various types of thioethers.