Study On The Adsorption Of Impurities From Coking Toluene

Aromatic hydrocarbons are important organic raw materials which play aconsiderable role in chemical industry. Toluene is one of the aromatic hydrocarbons.Coking toluene is one of the main sources of toluene, and it contains trace quantitiesof impurities, such as olefins and methylthiophene, which have bad effect on theequipment, adsorbents and catalysts. So trace quantities of impurities has to beremoved to meet the coking toluene purity standard.Molecular sieves Y were used to remove cyclic olefin (Dicyclopentadiene) fromtoluene. Batch experiments results show that USY zeolite has better absorptiveproperty for DCPD than HY zeolite. The equilibrium adsorption capacity of USY is305mg/g with the adsorption time is6h. The adsorption isotherm of USY zeolitebelongs to the type of H (high affinity), which means that USY has a very strongadsorption force with DCPD. The adsorption capacity of USY zeolite in fixed bedexperiments is lower than that in batch experiments. The bed utilization is only25.7%,which may be caused by a higher external diffusion resistance. ThermogravimeticAnalysis (TGA) reveals that USY has a stronger adsorption capacity for DCPDcompared with toluene. USY zeolite also has a good performance for the refining ofthe industrial coking toluene and exhibits a great potential for the practicalapplications.Molecular sieves Y(HY and USY)and HZSM-5（HZSM-5-I and HZSM-5-II）were used to remove2-methylthiophene and3-methylthiophene from toluene. Thebatch experiment result shows that the four zeolites have a better adsorption capacityfor2-MTP than3-MTP.The competitive adsorption of toluene becomes strongerwhen the solvent/adsorbent ratio increases, and the desulfurization ability of HY，HZSM-5-I and HZSM-5-II decreases, accordingly. USY zeolite has strongeradsorption sites, so the competitive adsorption of toluene has no effect on itsdesulfurization ability.Y zeolite shows better desulfurization ability than HZSM-5due to more amounts of surface acidity sites and larger diameter of the hole.