Liquid-phase thiophene adsorption on MCM-22 zeolite and activated carbon

Abstract The liquid-phase adsorption of thiophene from thiophene/ iso -octane and toluene-rich thiophene/toluene/ iso -octane solutions has been investigated in batch conditions at room temperature and atmospheric pressure on MCM-22 zeolite and activated carbon. The adsorption of toluene from toluene/ iso -octane solutions has also been investigated on both the adsorbents. These were characterised by X-ray diffraction, nitrogen physisorption, scanning electron microscopy and adsorption microcalorimetry of ammonia. Both MCM-22 and activated carbon were able to adsorb thiophene and toluene from the corresponding single-adsorptive iso -octane solutions. MCM-22 appeared superior to activated carbon for the adsorption of thiophene from toluene-rich thiophene/toluene/ iso -octane mixtures. The adsorption data for MCM-22 were correlated with the acid sites and silanol groups concentrations, as determined by microcalorimetric experiments. No such correlation was found for activated carbon. Apparently, on MCM-22 thiophene adsorption occurs first on the acid sites until they are saturated and then continues on the silanol groups. Toluene adsorption also occurs on the acid sites of MCM-22 until saturation, but no further adsorption by interaction of toluene with the silanol groups takes place. GC/MS investigation of the nature of the organosulphur material retained by the adsorbent revealed that the tiophene adsorbed on MCM-22 undergoes transformation into heavy products. Besides thiophene trimers and tetramers, these include other compounds formed by two and three thiophenic rings linked by alkyl groups, as well as a rather high molecular weight product where a trimer is linked to thiophenic ring by a cyclohexadienic ring. Reaction pathways leading to these products have been tentatively outlined.