Alkylation Of Coking Benzene To Ethylbenzene Over Nanosized HZSM-5

Gas-phase alkylation of benzene with ethene is an important technology for ethylbenzene production. With the shortage of petroleum, researchers try to find alternatives of benzene and ethylene. Coking benzene is main by-product of coke oven gas. Ethylation of coking benzene provides another feedstock to ethylbenzene production. However, two chanlleges concerning with high sulfur content in coking benzene exit in this work. One is to develop a sulfur-tolerant catalyst, while the other is to effectively remove the sulfur in the formed ethylbenzene. The development of nanosized ZSM-5 zeolites provides a chance to solve the above challenges. A new sulfur-tolerant catalyst, La-HT-HZSM-5, was obtained by hydrothermal treatment at 400℃and loading of 3wt% La2O3 in series over nanosized HZSM-5 zeolites. We scaled up this catalyst for 1000 kg and put them into application in 10000 ton/y ethylbenzene production uint in Danhua Group. Based on their feed-back information, La-C-HT-HZSM-5 was developed by adding calcination at 540℃between hydrothermal treatment and loading La2O3. Over this catalyst, the yield of ethylbenzene was about 14%. Besides, the coking benzene conversion maintained stable during 1500 h of time on stream under the conditions of industrial ethylation of coking benzene with pure ethylene. Furthermore, Y-C-HT-HZSM-5 was developed by loading Y2O3 instead of La2O3 on C-HT-HZSM-5 catalyst. Both the decrease in acidity, B/L and formation of larger micropore over nanosized HZSM-5 were key factors in extention of catalyst lifetime in the ethylation of coking benzene. Besides, co-feding water extended catalyst lifetime and improved catalyst selectivity by the dilution of ethanol around the active sites. From the point view of theoretical investigation, the role of different acidic sites in the ethylation of coking benzene with ethanol was clarified by selectively poisoning them with 2,6-dimethylpyridine. The acidity-activity correlation indicated that acid sites with pKa<-3.0 were responsible for the ethylation of coking benzene and sites with pKa<2.27 for the thiophene conversion, while sites with pKa<4.8 was active centres for ethanol conversion. The possible reaction pathway was proposed on the results of both experiments and chemical calculation from ONIOM method. Ethanol dehydrated firstly to ethene, then ethylation of coking benzene with ethene occurred. Besides, ethylbenzene from the ethylation of coking benzene contained high sulfur content (mainly ethylthiophene). CeY zeolites removed selectively ethylthiophene when it coexisted with ethylbenzene, consequently obtained sulfur-free ethylbenzene. This was contributed to formation ofσ-πbetween thiophenic sulfur with CeY.