Preparation Of AlCl₃Loaded Catalyst And Its Catalytic Removal Of Thiophene And Olefins In Coking Benzene

Coking crude benzene is the main byproducts in coking industry and also a major source of benzene, which is an important chemical raw material. The coking is one of the main techniques to utilization coal and the total output of coking benzene is big in China. But its composition is very complex, especially the thiophenic sulfur in it, has limited the using range of coking benzene by corroding the equipment and poisoning to the catalyst in the process of benzene conversion. With the lower and lower for the sulfur content required by downstream products and the more and more attention for environmental protection by our government, the research to find a method with the advantages of high desulfurization efficiency, little environmental pollution and good economic returns for the removal of thiophene from coking benzene is of a great theoretical significance and application value. The method to remove thiophene using solid acid catalyst by alkyl reaction is become popular in recent years and its development potential is great, because it has the advantages of low investment cost, mild reaction conditions, clean process, large treatment capacity, high efficiency desulfurization. The preparation of the solid acid catalyst with good reaction activity and stability, high mechanical strength, mild reaction conditions is the focus needed to concern. So, the optimization of preparation method, support and operating conditions of A1C13supported catalyst were investigated, and the alkyl reaction mechanism of thiophene with olefins in coking benzene was also discussed.Firstly, AlCl3/γ-Al203catalyst was prepared by a gas-phase loaded method under ambient pressure and the effects of support size, preparation temperature and time, AlCl3addition amount and carrier gas flow rate on catalyst activity were investigated. The fresh and used catalysts were analyzed by a variety of characterization methods. The results show that the gas-phase loaded method can make the AICI3uniformly load on the γ-Al2O3, and the existence of AICl3on γ-Al2O3support surface is mainly bonded by hydroxyl groups. Not only chemical reaction but also physical adsorption exist in the combination of AICl3and y-Al2O3at low temperature. Carrier particle size, preparation temperature and time, AlCl3addition amount and carrier gas flow rate can affect the catalyst’s surface area, the content of the active component and distribution on the surface of catalyst, and then change the ability of removal of thiophene from benzene on the catalyst. Based on the evaluation results of the catalyst, the optimum preparation conditions of AICl3/γ-Al2O3are that3g AlCl3was loaded on10g y-Al2O3support with the particle size of0.198-0.246mm under N2atmosphere and flow rate of100ml/min for5h at200℃, in which the removal efficiency of thiophene can reach62.11%when the ratio of liquid to catalyst is20ml/g. Taking silica gel as the support, the active component or AlCl3/silica gel catalyst prepared under the optimum preparation conditions is similar to that of the AICl3/γ-Al2O3catalyst, their capacity of thiophene removal in benzene is similar.Secondly, the activity of AlC13loaded catalyst using y-A12O3and silica gel as support prepared by high-pressure gas-phase loaded method was compared with the catalyst from ambient pressure loaded method. The results indicate that the loading of AlC13under high-pressure is better than ambient pressure and the activity of prepared catalyst is also higher than the catalyst from ambient pressure loaded method. The catalyst loaded on silica gel support presents a better desulfurization capacity than the catalyst prepared γ-Al2O3support, so it is considered that the silica gel is more suitable for using as the support in the high-pressure loaded method. Taking AlCl3/silica gel catalysts as experimental sample, the effects of preparation temperature, preparation time, AICl3addition amount and heat treatment temperature on the catalyst activity were investigated and the fresh and used samples were characterized. The results show that the AICI3can be uniformly loaded on the silica gel, the load process of AlCl3is mainly achieved by hydroxyl groups on the surface of silica gel, which is combined in the form of the’Si-O-Al’. The preparation temperature, preparation time and heat treatment temperature can affect the catalytic activity by changing the surface area of catalyst, the active component content and distribution on the its surface. When the silica gel was heated for4h at180℃, the catalyst prepared by loading2g AICl3on10g support at200℃for4h has the highest activity. This catalyst possesses the desulfurization efficiency of94.23%when the liquid to catalyst ratio is20ml/g.Finally, the catalytic mechanism of alkylation reaction for AlCl/silica gel catalyst is also studied. The results of products composition after alkylation reaction in benzene analyzed by GC-MS show that the AlCl3/silica gel catalyst can promote the reaction of thiophene with1-hexene and mainly produce2-Butyl-5-ethylthiophene,2-hexylthiophene,2-propylthiophene,2-isohexylthiophene and2,4-dimethylthiophene. In the temperature range of40-80℃, thiophene is mainly removed by alkylation reaction with olefin, and the rate of alkylation reaction increases with the rise of reaction temperature. The conversion rate of thiophene remains unchanged after olefin in benzene is completely consumed and the conversion rate of thiophene accordingly increases with the increase of the ratio of1-hexene to thiophene in the system.