Study On The Shaping Of Pt/SO₄^2-/ZrO₂ Catalyst And Its Isomerization Performances

The skeletal isomerization of n-alkanes to iso-alkanes was one of the important technologies for improvement of the octane number in clean gasoline. Due to no corruption and high isomerization activity at low reaction temperature, Pt/SO42-/ZrO2 was considered as a good low temperature catalyst and possessed good application prospect. The catalyst shaping was one of the key factors influencing its industrial application. It was of great significance to study the shaping of Pt/SO42-/ZrO2.In this dissertation, this kind of Pt-modified sulfated zirconia catalyst (PSZ) was shaped by extrusion method. Isomerization of n-hexane acted as model reaction. The influences of binder type on the isomerization performance and mechanical strength of catalyst were studied. The suitable binder was determined. On this base, the influences of binder content, the addition order of binder and catalyst post-processing on the isomerization performance and mechanical strength of catalyst were studied. Finally, the suitable extrusion process of PSZ was determined.The experimental results demonstrated that when the binder was added into sulfated Zr(OH)4 powder, the PSZA(a) catalyst prepared with pseudo boehmite powder as the binder showed higher catalytic activity and higher mechanical strength than that with aluminum sol and silica sol as binder. The increase of Al2O3 content from 5 wt% to 30 wt% led to an obvious reduction of n-hexane conversion from 85% to 43%. However, the effect of Al2O3 content on n-hexane conversion over PSZA(b) catalyst was negligible, when the catalyst was prepared by the addition of pseudo boehmite to Zr(OH)4 powder before sulfation of Zr(OH)4. But, the yield of dimethyl butane (DMB) decreased obviously from 28% to 20%.For this decrease of activity due to the increment of binder usage, two treatment technologies were explored to improve this case. One was solvent treatment and the other was the enhancement of calcination temperature. The conversion of n-hexane and the yield of DMB could be improved significantly when PSZA(a) and PSZA(b) were treated by solvent. The isomerization activity of latter was better. The conversion of n-hexane and the yield of DMB over PSZA(b)-30 after treatment with solvent two times, reached maximum, i.e.90% and 32%, respectively. Besides, the isomerization activity of the catalyst could be also improved obviously by the enhancement of calcination temperature of PSZA(b)-30 to 700℃. Meantime, the conversion of n-hexane and the yield of DMB were up to 88% and 30%, respectively.Both mechanical strength and sulfur content of catalyst were improved with the increasing content of Al2O3 whatever the addition orders of pseudo boehmite. But, the isomerization activity of catalyst decreased obviously. The solvent treatment or calcination at higher temperature removed the part of sulfur species on catalyst, which should be the main reason for the increase of activity. The moderate sulfur content was essential to obtain a catalyst with high isomerization activity. The good catalyst with high isomerization activity and high mechanical strength could be prepared by the above two methods.