Reaction mechanisms of thioetherification for mercaptans and olefins over sulfided Mo-Ni/Al2O3 catalysts

Abstract

The thioetherification reaction of 1-butanethiol and 1-hexene dissolved in n-hexane was investigated over sulfided Mo-Ni/Al2O3 catalysts. The experimental results showed the catalysts have good catalytic performance for thioetherification reaction, but the isomerization and hydrogenation reactions of olefins over the catalysts can inhibit thioetherification reaction. As reaction temperature increases, the isomerization and hydrogenation reactions of olefins increase rapidly, however, the inhibition of thioetherification reaction also increases. The sulfur distribution and molecular structures of sulfur compounds in the products were analyzed by the gas chromatograph with sulfur chemiluminescence detector (GC-SCD) and the gas chromatograph/mass spectra spectrometry (GC/MS). Two possible routes of thioetherification reaction could be observed. At low temperature, the major pathway involves a direct addition of 1-butanethiol to the terminal carbon of double bond of 1-hexene. In this mechanism, the main product is anti-Markovnikov adduct. At a higher temperature, the CS bond of 1-butanethiol can be subsequently cleaved, and the adsorbed -SH species can be formed on the catalysts. On the same time, abundant 1-hexene can be absorbed on the catalysts, as well. Therefore, the adsorbed SH species can then recombine with adsorbed 1-hexene to form new hexyl-mercaptans, which can continue to produce another kind of thioether (di-hexyl sulfide) with adsorbed 1-hexene. Similar with the first reaction route, the thioether of the anti-Markonikov adduct still dominates in the product.