Research Of The Reaction Of C9 Aromatics Over Nanosized HZSM-5

The reactions of C9 Aromatics (A9) over nanosized HZSM-5 were studied. The reactions included the dealkylation of individual A9 component as well as the transalkylation of benzene-1,2,4-trimethylbenzene(1,2,4-TMB) and benzene-A9. The effect of various modifications on the activity and stability of nanosized HZSM-5 in A9 reaction was also studied. Hβ, HMOR zeolite with 12-MR and microsized HZSM-5 were employed in the same reaction for comparison. The results were shown as follows:Compared with microsized HZSM-5, the acidic amount of nanosized HZSM-5 is higher while the strength of the strong acid sites is lower. The external acid sites on nanosized HZSM-5 is about 30% of the total acidic amount while that of microsized HZSM-5 is about 10%. The specific surface and pore volume of nanosized HZSM-5 is the same as that of microsized HZSM-5. The external area of nanosized HZSM-5 is 25% of the total specific area while that of microsized HZSM-5 is 5%.On the zeolite catalysts, with the increased temperature, the reaction of A9 is isomerization, disproportionation and dealkylation. The reaction activity is ordered as iso-propylbenzene>o-ethylbenzene>trimethylbenzene, which is in accordance with the stability of carbonium that the abovementioned A9 formed. The conversion of propylbenzene as well as ethylbenzene on nanosized HZSM-5 and microsized HZSM-5 is same because the reactivity propylbenzene and ethylbenzene is high. The acitive sites in the reaction of 1,2,4-TMB were located on external and pore mouth of HZSM-5. Therefore, nanosized HZSM-5 was more active than microsized HZSM-5.In the reaction of A9, ZSM-5 has higher ability of dealkylation while the disproportionation reaction is inhibited. Hβand HMOR zeolite has good ability of transalkylation and disproportionation. The stability of nanosized HZSM-5 is better than that of microsized HZSM-5, Hβand HMOR zeolite. The coke amount on nanosized HZSM-5 is higher than that on microsized HZSM-5 but the abundant secondary pores on nanosized HZSM-5 accommodate the coke.In the reaction of benzene-1,2,4-TMB, acid treatment does not change the acidity of nanosized HZSM-5 but ameliorated the diffusivity of nanosized HZSM-5 and then improves the activity of the catalyst. The steaming decreases both the activity and stability of nanosized HZSM-5. Loading metal oxides also decreases the activity of the catalyst. The results of long life run showes that the multi-modification of steaming followed by acid treatment improves the stability of nanosized HZSM-5 without decreasing its activity. Therefore, the multi-modification is a suitable method in this reaction system. In the reaction of benzene-A9, when the abovementioned multi-modified catalyst is loaded with Mo oxide, the amount of ethylbenzene and indan in the product decreases and the stability of the catalyst improved.On the acid catalysts indan mainly condenses to form polyaromatics or proceeds five member ring opening reactions. Larger pore size is favorable to the ring opening reaction. High concentration and high temperature is favorable to the condensation of indan. Because indan is preferentially adsorbed on the catalyst, indan decreases the initial conversion of TMB and the stability of the catalyst.