Study On Inferior Heavy Oil Catalytic Pyrolysis Process For Maximizing Yield Of Propylene

With the rapid development of polypropylene application, the demand for propylene isincreasing. Restricted by the energy consumption and the lack of raw materials, conventionalsteam cracking process cannot meet the market demand. Because there are a large amount ofheavy oil,in China, it is beneficial to develop heavy oil catalytic cracking technology formaximizing propylene.The feedstock used in this study were provided by the Dongyouliqing company.According to the characteristics of the feedstock, the cracking property of resins was firstlyinvestigated. It was found that the resin was converted mainly to gases and coke. With theincrease of resin content, the conversion of the feed did not change much, while the yield ofolefins, dry gas and coke increased continually together with a decrease of light oil yield. Inorder to satisfy the industrial requirement of less than10wt%coke yield, the resin content inFCC feedstocks should be controlled no more than35wt%.The temperature of the regenerated catalyst were studied for different feedstocks, whichare Jihua feed, Qilu hydrogenation tail oil, and Dongyouliqing feed, respectively. It indicatedthat lower regeneration temperatures could increase the conversion of feed and decrease theyield of dry gas. The difference was that for Jihua feed and Qilu hydrogenation tail oil, theyield and selectivity of propylene increased with the decreasing regeneration temperautures,while for Dongyouliqing feed, the tendency went down after a peak for the yield andselectivity of propylene. If the temperature of the regenerated catalyst is too low, theDongyouliqing feed could not be completely gasified and the coke yield increased intensivelydue to the high content of higher boiling point components in the feed. When the inferiorfeeds are treated, properly decreasing the temperature of the regenerated catalyst could optimize the product distribution and increase the yield and selectivity of propylene. Besides,the temperature of the regenerated catalyst in a stratified injection process was also studied.Although the propylene selectivity increased when decreasing the regenerated catalysttemperature, the dry gas and coke yield together with the gasoline and diesel yields decreasedsharply. So, it is not a good choice to decrease the regenerated catalyst temperature when thestratified injection was applied.In terms of the investigation of reaction temperature and residence time for theDongyouliqing feed, it was confirmed that both of the increased temperature and a longerresidence time could enhance the feed conversion and increase the propylene yield. Theutilization efficiency of hydrogen underwent a tendency of decrease after a peak at thereaction temperature of540℃together with a residence time of1.9s. When treated by theTMP process, the Dongyouliqing feed could be converted with a conversion of97.46wt%and the propylene yield and selectivity were22.61wt%and60.63wt%, respectively. Itindicated that the inferior Dongyouliqing feedstock with high carbon residue and high contentof heavy metals could also be used to produce propylene. Besides, the feasibility to variousfeedstocks of the TMP technoloty was also proved.