Primary Study On Two-Stage Riser Catalytic Pyrolysis Of Gas Oil

Ethylene and propylene are useful petro-chemical feedstocks which are usually produced by steam cracking now. Along with the development of economy, the conflict between demand and supply of propylene and ethylene becomes more and more acuity. On the other hand, the shortage of light oil resource in our country puts a strict to steam cracking, so it becomes more important to enhance the yield of light olefins on the FCC unit.Two-stage riser fluid catalytic cracking (TSRFCC) technology has four predominant characteristics, that are catalyst relay, high temperature, short residence time and large catalytic to oil ratio(C/O). C/O, residence time and temperature are three important factors which affect the result of the reaction. Research indicated that high temperature, large C/O and proper residence time between catalyst and oil vapor benefited the yield of light olefins. Comparing with other FCC technology, TSRFCC-â… exhibits great advantages on improving the yield of ethylene and propylene. In order to improve the yield of light olefins, we increased reaction temperature and C/O in this paper.Gas oil has less resins and asphaltenes but more saturates and aromatics than residue, which react easily and reduce the catalyst deactivation, so it has more potential for maximizing the yield of light olefins on catalyst with high content of ZSM-5. The first stage riser was fed Fushun VGO and the second was fed gasoline and heavy oil from the first stage. Along with improving the yield of ethylene and propylene, a great deal of butylene was produced, so recycled the butylene to produce ethylene and propylene in the first riser made great sense. Also the quantity of recycle butylene and the length of stratified injection nozzle were studied in this paper.A series of experiments on the TSRFCC showed that using the special catalyst LTB-2 the yield of propylene reached 25.24% and the yield of propylene+ethylene was up to 35.15% when the butylene was not recycled, also the product distribution was greatly improved. Recycling the butylene in the first riser could improve the yield of propylene by 4.6 percentage while not affect the yield of ethylene at all. So utilizing VGO to improve the yield of light olefins is available.