Study On Increasing Butene Production In Catalytic Cracking

With increasingly stringent environmental protection requirements,the production of clean gasoline components is extremely necessary based on the excessive proportion of catalytic cracking gasoline in the current gasoline composition of China.Alkylated gasoline has the best comprehensive development prospect among these kinds of gasoline,and butene is the main raw material for the production of alkylated gasoline.In order to ensure adequate supply of alkylated gasoline,it is of great significance to increase the production of butene in the fluid catalytic process of heavy oil.On the basis of this background,this paper studies the process of catalytic cracking to increase the production of butene.First,thermodynamic analysis of the catalytic cracking process for increasing the production of butenes is carried out.The results show that yield of butene increases before decreasing with the increase of temperature,and reaches its maximum at 873 K.Yield decreases with the increase of pressure and when the temperature is low,pressure has a great influence on yield.The effect of raw materials on the yield of butene has been investigated and results show that long-chain olefin is ideal raw materials.Also,this paper has studied product distribution of olefin and get the idea of catalyst design that the catalyst needs not only macropores zeolite that promote macromolecular cracking to produce olefins,but also mesopores zeolite that promote secondary cracking of olefins.And acid density needs to ensure the cracking activity as well as the lower hydrogen transfer activity to inhibit the production of by-products.And the reaction performance for increasing butene of different types of model compounds is investigated.The results show that yield is the highest when using olefin as raw materials.Therefore,the study of the reaction behavior of olefin in catalytic cracking is of great significance for increasing the production of butene.And analyzing the source of olefins and their product distribution,it is concluded that catalysts must have lower hydrogen transfer properties and can promote secondary cracking and inhibit cyclization.In summary,the catalyst for increasing the production of butene must have both mesoporous molecular sieves and macroporous molecular sieves,appropriate acid density and B/L acid ratio.And so silicon-aluminum ratio and phosphorus loading of a series of catalysts are changed to modulate catalyst performance.They are marked as MB-1 to MB-22 cocatalyst.Molecular sieves used in the synthesis of catalysts are characterized and the reaction performances are examined on a small confined fluidized bed reactor.The active component of MB-1~MB-5 is ZSM-5 molecular sieve and the ratio of silicon to aluminum increase in turn.The results show that the silica-alumina ratio of the zeolite has an effect on both acidity and pore size.The acid density and B/L acid ratio of zeolite gradually decreases in the order of MB-1~MB-5.The yield of liquefied gas was higher than that of the blank experiment after addition of these cocatalysts,and the yield decrease sequentially.Also,the yield of gasoline increased in turn.On the other hand,the hydrogen transfer coefficient decreases as silica-alumina ratio increases.MB-2cocatalyst with a silica-alumina ratio of 50 has significant effect on increasing yield of butene.And the yield increased from 2.06 wt% in the blank experiment to 2.58 wt%.And then phosphorus modification was performed on MB-2 cocatalyst to obtain MB-6~MB-9 cocatalyst with different phosphorus loadings(1.0 wt%,1.5 wt%,2.0 wt%,3.0 wt%).When the loading content of P is low,the acid density and the yield of LPG increases with the increase of phosphorus content.When the content reaches 3%,the presence of polymerized phosphorus leads to a decrease in acid density.The hydrogen transfer coefficient is the result of a combination of acid density and pore size.MB-7cocatalyst with a silica-alumina ratio of 50 and the phosphorus loading content of 1.5wt% has significant effect of increasing butene production.And the yield of MB-7increases from 2.06 wt% in the blank experiment to 3.21 wt%.ZSM-5/REY and ZSM-5/REUSY composite zeolite cocatalyst were prepared and labeled as MB-19 and MB-20.Butene yield of composite zeolite additive is inferior to MB-1~MB-9 cocatalyst,but yield of heavy oil is reduced and the conversion rate is improved.The active component of MB-10~MB-14 is beta molecular sieve and the ratio of silicon to aluminum increase in turn.The results show that the acidity of beta zeolite is the result of its hydrothermal stability and silica-alumina ratio.The acid density ofzeolite gradually decreases in the order of MB-11>MB-12>MB-10>MB-13>MB-14.Compared with the blank experiment,the yield of LPG is all increased,and yields of gasoline,diesel and heavy oil are decreased.It's worth noting that the change in diesel yield is the most obvious.MB-13 cocatalyst has significant effect on increasing yield of butene and the yield increased from 2.06 wt% in the blank experiment to 2.61 wt%.And then phosphorus modification was performed on MB-13 cocatalyst to obtain MB-15~MB-18 cocatalyst with different phosphorus loadings(0.5 wt%?1 wt%?1.5wt%?2.0 wt%).MB-16 cocatalyst with a silica-alumina ratio of 70 and the phosphorus loading content of 1.0 wt% has significant effect of increasing butene production.And the yield of MB-16 increases from 2.06 wt% in the blank experiment to 2.68 wt%.?/REY and ?/REUSY composite zeolite cocatalyst were prepared and labeled as MB-21 and MB-22.Yield of heavy oil of composite zeolite cocatalyst is reduced and the conversion rate is improved,but butene yield is inferior to MB-10~MB-18 cocatalyst.Considering factors such as liquefied gas yield,butene yield and coke yield,MB-7cocatalyst with a silica-alumina ratio of 50 and the phosphorus loading content of 1.5wt% has optimal effect of increasing butene production.And liquefied gas yield increases by 2.79 percentage points and the butene yield increases by 1.15 percentage points.