Primary Study On The Effect Of Pressure To Maximize Propylene Selectively In Fluid Catalytic Cracking

Unit capacity of TMP (two stage riser for maximizing propylene yield) ,whose propylene yield had achieved above 20% with Daqing atmospheric residue in Daqing refinery Corporation, is 12 kt per year now. To make it large scale further is the biggest task currently. To make a larger scale TMP set, pressure is one of the most important factors relating to unit capacity and energy consumption, especially the propylene yield. When the unit capacity is not well cooperating with the pressure at certain process conditions, product quality decreases or catalyst loss increases. The relation between the energy recovery and the pressure is positive that when pressure of the set boosts, energy using efficient increases. However, boosting pressure can result in the olefins' secondary side reaction such as hydrogen shifting and isomeration, leading to the distribution differences of the products (dry gas,LPG and gasoline), especially the propylene yield and its selectivity. So firstly study on the effect of boosting pressure on product distribution and corresponding resolving methods is top priority.According to particle fluiding principle, we revamp the pilot scale test riser to make it operate smoothly in the boosting pressure. And guiding by the knowledge of chemical reaction engineering, we replace atoming and prelifting steam with petroleum ether to increase partial hydrocarbon pressure(PHP) in the riser. Besides, we also debug a program to caculate the mixing temperature when we need to stratify the feeding. Finally, we design special experiment and make out the effect of partial pressure to maximize propylene in the process of fluid catalytic cracking and corresponding resolving methods.Result of the experiment shows that we can boost up the partial hydrocarbon pressure substantially when we replace the atoming and lifting steam with petroleum ether. When the partial hydrocarbon pressure rises, in case of LPG yield goes down and light oil(gasoline plus diesel) goes up, the liquid yield(LPG+gasoline+diesel)goes down, and coke yield increases, but dry gas yield changes slowly. In the range of partial hydrocarbon pressure changing from 0.095MPa to 0.233MPa, LPG yield decreases 6.91% in which the yield of propylene and butylene decreases 5.52% and 4.69% seperately and the selectivity decreases 5.67% and 4.71%. Compostions of gasoline varies from olefins to paraffins and aromatics. Otherwise, high temperature and big mass ratio of catalyst to feed and increasing butene feeding can revamp the restraining effect of the pressure to olefins. At last, It is proven that the law about pressure's effect above is universal when we use different characteristic feed. And we conclude in theory that when the reaction is determained by the route of monomolecular protolytic cracking, which can be achieved at the condition of high temperature or low feed conversion or low olefins concentration or low partial hydrocarbon pressure or low acid density and activity catalyst or selective catalyst and butene recycling, it is suitable for maximizing propylene,...