Typical Acid Catalysts And Their Complexes In 1-Hexene Study On Catalytic Performance In Isomerization Reaction

Olefin,as a major gasoline blending component with high octane number,occupies a large part in FCC gasoline(FCC gasoline).However,due to the active nature and thermal instability of olefin,it is extremely volatile,which causes serious environmental pollution and easily leads to the formation of carbon deposition in the engine during use.Moreover,the upgrading of national gasoline quality standard requires more and more stringent olefin content in gasoline.It is the joint research direction of a large number of scholars to reduce the olefin content in gasoline and protect octane number without loss.Compared with existing olefin reduction technologies,it is found that olefin isomerization technology has obvious advantages both in terms of technology and development prospect.Therefore,starting from the study of the skeleton isomerization reaction of 1-hexene,this paper tries to understand the reactive sites and reaction rules of the skeleton isomerization reaction,and then develops catalytic materials with high skeleton isomerization rate and good selectivity of isomerized alkane products,so as to achieve the purpose of reducing olefin and preserving octane number.Firstly,the physical properties and isomerization properties of different acidic materials were analyzed,and the results showed that the ZSM-35 T with more medium and strong acid center acid content and less strong acid center acid content,and the medium and strong B acid center with larger strength ZSM-35 T had better catalytic performance,its skeletal isomerization selectivity can reach 83%.As an acidic material,amorphous silica-alumina SA33 has milder acidity than molecular sieves.The weak acid center and some medium strong acid centers catalyze the cis-trans isomerization reaction,while the remaining medium and strong acid centers and strong acid centers jointly catalyze the skeletal isomerization reaction.Then,ZSM-35 with different silicon-alumina ratios was studied,and it was found that a smaller pore size in the skeletal isomerization reaction would increase the occurrence of side reactions;a larger amount of medium and strong acid and acid strength were conducive to the skeletal isomerization reaction.Higher strength of strong acid promotes the occurrence of side reactions,while the amount of acid is not the main factor;the appropriate L/B acid ratio is conducive to the occurrence of hydrogen transfer reaction(hydrogenation of skeletal isoolefins to isoparaffins).On the basis of further research on ZSM-35 with different silicon-alumina ratios and amorphous silicon-alumina with different silicon contents,isomerization catalysts were prepared by the composite of ZSM-35-40 and SA33,two different acidic materials.The proportion of SA33 in the sample keeps increasing,the micropore surface area and pore volume in the sample gradually decrease,and the outer surface area and mesopore volume continue to increase.The composite material characterization data combined with the isomerization reaction performance found that the B acid center can promote the reaction in the sample.At a lower temperature,the acid content of medium-strong acid centers and the synergistic effect of L acid centers and B acid centers are necessary conditions to improve the yield of isoparaffins.The composite catalyst overcomes the shortcomings of higher cracking activity of ZSM-35-40 and higher reaction temperature of SA33,among which AZ-3/2 can achieve 84% skeletal isomerization rate and 29% skeletal isomerization rate at the reaction temperature of 270 ℃.Isoparaffin selectivity,while the cracked product selectivity is only 2%.By adjusting the calcination temperature of SA33 catalyst,it was found that the acid content of the catalyst changed significantly.With the increase of calcination temperature,the acid content further decreased,especially at 350℃ and 450℃.The skeletal isomerization rate of SA33-350 can reach 81%,which is significantly higher than 49% of SA33-450 and 63% of SA33-550,and the isoparaffin selectivity of SA33-350 is as high as 29%.Comparing the acid properties and isomerization selectivity results,it is concluded that the selectivity of the product is not only related to the amount of acid in the center of the required acid strength,but also has a certain relationship with the ratio of the amount of acid in the center of each acid strength.are competing reactions.Finally,the SA33-350 catalyst was modified by doping with different elements.The doping modification of 6% P and 6% La was beneficial to the skeletal isomerization reaction.The addition of P contributes to the improvement of the skeletal isomerization performance of the catalyst,but due to the reduction of the acid content of the strong acid center,the isoparaffin selectivity is reduced.The addition of La increases the strength of the catalyst in the strong acid,while the acid sites that contribute to the hydrogen transfer require a lower strength of the medium and strong acid,thus causing the hydrogen transfer reaction to be weakened with a slight increase in the rate of skeletal isomerization.Compared with 350-SA33-0.8,the intensity of medium and strong acid centers of the catalyst after double element doping of P and La is enhanced,and the skeletal isomerization reaction requires stronger medium and strong acid centers,so the rate of skeletal isomerization after double element doping has seen an increase.The hydrogen transfer reaction of skeletal isoolefins is the main way to generate isoparaffin products,and the hydrogen transfer reaction requires lower medium-strong acid strength,so the increase of strong acid strength in the catalyst leads to the decrease of isoparaffin products.