Study On Dehydrogenation Of Isobutane To Isobutene Over K-Cu-Cr/Al₂O₃ Catalyst

With the development of petrochemical technology, isobutene has become an important basic raw material for petrochemical following ethene and propene, which was widely used for light industry, oil refining, pharmaceutical, perfume, building materials and other fine chemical department. Previously, various kinds of catalysts Cr/y-Al₂O₃ have been studies due to the high activity and low cost. In this thesis, the Cr/γ-Al₂O₃ catalyst was modified by joining metal additives and used in the procedure of catalytic dehydrogenation of isobutane to isobutene. The major results as follows:（1） After detailed analysis, the optimized conditions were K₂O:2%, CuO:1 %, CrO_x:10%, the best temperature was 853 K and GHSV was 1000 h"1. What’s more, under the optimized conditions, the K-Cu-Cr/γ-Al₂O₃ catalyst can obtain initial conversion of 64.76% for catalytic dehydrogenation of isobutane to isobutene, and the selectivity and yield of isobutene is 88.4% and 57.24%, respectively.（2） The stability of K-Cu-Cr/Al₂O₃ catalyst for catalytic dehydrogenation of isobutane to isobutene was tested under the optimized conditions. After continuous operation of accumulative 100 h total, it still obtained isobutane conversion of higher than 60% with the corresponding isobutene selectivity of 90% in initial activity. The catalytic activity could be recovered with the treatment of coke burning by O₂, which showed this catalyst exhibited excellent stability and regenerative performance.（3） The influence of the amount of carbon deposited on K-Cu-Cr/γ-Al₂O₃ catalysts on dehydrogenation of isobutane and catalytic activity was studied. The results showed that the catalyst activity was closely related to carbon deposition, the amout of carbon deposited on the catalyst surface increased with the prolonging reaction time, which caused the catalytic activity to decrease. Then, the experimental data were simulated to fit the relationship of carbon deposition and reaction time, and the carbon content and coking rate equations were:Cc=2.49 t^0.630 and rc=dCc/dt=1.57 t^-0.37.（4） The reaction intrinsic kinetics of isobutane dehydrogenation over K-Cu-Cr/Al₂O₃ catalyst was researched on the basis of the basic requirements of the industrial reactor design. According to the Langmuir-Hinshelwood mechanism and theories of rate-determining step, some models were put forward and the reaction rate equation of isobutane dehydrogenation was obtained. The results of parameter estimated values and model tested experiments showed the rate-determining step was surface reaction, and the model of which would be more suitable for describing the reaction of isobutane dehydrogenation over K-Cu-Cr/Al₂O₃ catalyst.