Adsorption and reaction over HFAU zeolites of thiophene in liquid hydrocarbon solutions Original Research Article

Thiophene adsorption from liquid solutions containing hydrocarbons which are representative of a light gasoline cut: heptane, hexene, toluene as well as the reactions which can occur during this adsorption over HFAU zeolites were investigated in a stirred batch system at room temperature. With a diluted solution of thiophene (0.3 wt.%) in n-heptane, essentially adsorption was found to occur; the maximum number of thiophene molecules adsorbed per gram of zeolites with framework Si/Al ratios of 5, 17, and 47 was equal to their concentration of acidic sites. These sites can therefore be considered as the adsorption sites. However, with a very rich thiophene solution (27.7 wt.%), essentially acid catalyzed condensation of thiophene occurs with production of dimers, trimers, and tetramers which remain trapped on the zeolite. The adding of 20 wt.% toluene or hexene or both to the diluted thiophene solution in n-heptane causes a large decrease in the removal of thiophene from the solution. This decrease was shown to be related to different phenomena: competition between thiophene and toluene for adsorption on the acidic sites, acid catalyzed alkylation by hexene of thiophene and/or toluene molecules with trapping on the zeolite of the related products. From these observations, it can be concluded that thiophene removal by adsorption on acidic zeolites can only be carried out from diluted solutions containing no olefinic compounds.