Study On Performance Control Of Catalyst Support And Coke Formation Mechanism Of Propane Dehydrogenation

Propylene an important organic raw material(used in the production of Polypropylene,acrylonitrile,propylene oxide and acrylic acid)nainly produced through naphtha cracking and cracking catalysis.Statistical analysis shows that the demand of propylene is exponentially increased in the recent years.In 2017,China produced 28.36 million tons of propylene which was 13.6%more than in the year 2016 but still 5.6%less than the actual need,as the demand was about 32 million tons.The tight supply and the highly annual demand situations convinced the China to import propylene.Owing the disadvantages(high energy consumption and low olefin yield)in the traditional propylene production processes and particularly the insufficient production to meet the present demand,propane dehydrogenation to propylene became the most efficient and active area in petrochemical industry to overcome these challenges.In this thesis,mesoporous alumina was prepared by template method.Simultaneous one-step synthesis was used to modify mesoporous alumina by adding three kinds of materials:Sn,Zn and Ti,and finally modified mesoporous alumina was obtained.The catalyst was loaded by impregnation method with 19%Cr loading.The reactor at 610?and the propane was allowed to flow at a rate of 4.8mL/mint for 3h.The catalysts were characterized by physical adsorption-desorption,chemical adsorption-desorption(NH3-TPD)(H2-TPR),X-ray diffraction(XRD),XPS,scanning electron microscopy(SEM)and thermogravimetry(TG).The experimental results show that for the Sn modified mesoporous alumina catalyst,the catalytic performance is optimal when the Sn content is 1%and we observed 66%conversion with 83%selectivity and 54%yield.The uniform dispersion of the active sites on the surface of the catalyst has a certain inhibitory effect on the carbon deposition.For Zn modified ruesoporous alumina catalysts,the catalytic performance is optimal when the Zn content is 1%with 64%conversion,87%selectivity and 57%yield.The addition of Zn reduces the amount of strong acid and total acid and therefore inhibits the coke formation.For the Ti-modified mesoporous alumina catalyst,when the Ti content of 0.5%in the first 60 min of the reaction exhibited best catalytic performance,and the conversion,selectivity and yield are 62%,88%and 56%,respectively.After 60 min,the catalytic performance of the catalyst with Ti content of 1%is optimal.The addition of Ti increases the amount of coke formation which may be attributed to the production of the strong acid amount of the catalyst and the total acid amount.