Study Of Modified Low Temperature Isomerization Catalyst Pt/Al₂O₃ For Light Paraffins

China's gasoline have the drawbacks that aromatics,benzene and sulfur content is high and the octane number distribution is not uniform,which is also something that the standard upgrade must be overcome.The isomerization oil is a high octane number,low sulfur,benzene-free,aromatic and non-olefin products which is an ideal gasoline blending components.Therefore,it is of great significance to study the low temperature isomerization catalyst.In this paper,two series of supports were prepared under different calcination temperatures with two kinds of materials.And the carriers were characterized by BET,XRD and other methods.Characterization result showed that with the increase of calcination temperature,specific surface area decreases,pore size increases and pore volume remains unchanged.Calcination temperatures of the supports have little effect on the dispersion degree of Pt on Pt/Al₂O₃ catalysts and the activity of the catalysts.However,the selectivity of the catalysts decreased with the increase of calcination temperature.Z-1cat.has the best isomerization performance.N-hexane isomerization rate is 74.5%,the selectivity of 2,2-DMB is 15.2%.And the corresponding Z-1 carrier's most probable aperture is 8 nm and the pore diameter is mainly distributed from 5 to 10 nm.The influences of the impregnation liquid pH value on the performance of the Pt/Al₂O₃catalysts were investigated.The catalysts were characterized by XRD,TEM,TPR,H₂-O₂ cycle titration and other methods.The results show that when pH=2,the dispersion degree of Pt on Pt/Al₂O₃ catalysts reaches the maximum value,the average particle diameter of Pt crystal gets the minimal value and the activity and selectivity of the catalysts obtains the best value.N-hexane isomerization rate is 78.3%,2,2-DMB selectivity is 20.5%.Respectively,3.8%and 5.3%more than that of no adjust the pH value.Whereas,when pH<2 those parameters almost unchanged with the pH value continuing to reduce.A series of Pt-Sn/?-Al₂O₃ catalysts with different tin-platinum molar ratio were prepared by co-impregnation method with anhydrous tin tetrachloride as the precursor of Sn.The effects of the loading of metal additives Sn on the isomerization performance of the catalysts were investigated.The catalysts were characterized by BET,XRD,TPR,NH₃-TPD,Py-IR and TEM.The results show that the diameter of Pt crystal on Pt-Sn/?-Al₂O₃ catalyst increases with the increase of tin-platinum molar ratio,the isomerization rate of n-hexane and the selectivity of2,2-DMB decreases with the increase of the molar ratio of tin-platinum on Pt-Sn/?-Al₂O₃catalyst.The effects of reduction pressure,reduction temperature,reaction pressure,reaction temperature,space velocity and volume ratio of hydrogen to oil on reaction isomerization rate and selectivity were investigated.It was found that the reduction pressure had the greatest influence on the isomerization performance of the catalyst.The reaction temperature was lower.Within the scope of the study,the reaction pressure,reaction pressure,space velocity and hydrogen/oil volume ratio were less affected the isomerization rate and selectivity.The optimum reaction conditions were as follows:atmospheric pressure reduction,reduction temperature 350?,reaction pressure 2MPa,reaction temperature 140?¹60?,space velocity1.0h^-11.2h^-1,hydrogen oil volume ratio 150.The isomerization rate and selectivity are 80%and 20%respectively under the optimum technological conditions.