Study Of N-Butane Isomerization Over Sopported Heteropoly Acid Catalysts

With the ever-rising requirement of the environment protection, the demand of qualified gasoline is up day and day. The importance of C4-alkyllation gasoline is becoming more and more great. I-butane is one of the main feedstock of the C4-alkyllation gasoline. In order to convert the cheap n-butane to the needed i-butane, isomerization of n-butane shows its importance. But the existing process for n-butane isomerization can't avoid corrosion and pollution. So, exploration of environment friendly process is in need. Using Heteropoly acid (HPA) catalyst system, this article studied the n-butane isomerization performance of supported HPA catalysts and conditions required for keeping their acidity. NH3-TPD-MS, XRD, TG-DTA, and Hammett Index test were adopted to characterize the HPA catalysts.This dissertation investigated the catalytic performance of n-butane isomerization over supported HPA catalysts with different Keggin structure heteropolyacids, carriers and loading. We investigated the relation between acid strength and amount of supported HPA catalysts and catalytic performance of n-butane isomerization. The dispersion of HPW on the carriers was also studied. It was found that the HPW/SiO2 catalyst has a good performance of the studied reaction possessing a n-butane conversion of 38% which approaches thermodynamic equilibrium and i-butane selectivity above 90% under following reaction conditions: 300, 3.7MPa, hydrogen present.The influence of H2 on reaction performance of supported HPA catalysts was studied. It was found that the difference between coke on catalysts after reaction with H2 present or absent is not obvious by TG-DTA, acidity measurement etc. on HPW/SiO2 catalysts reacted for 8 hours. The decrease of catalytic activity without H2 is due to reduction of strong acid sites. The presence of H2 improved the stability ofstrong acid sites on the catalysts and reaction selectivity.The n-butane isomerization performance and acid properties of supported HPW catalysts added with metal ion were studied, which discovered that for supported HPA catalysts, only the acid sites with Ho<-13.75 exhibit good n-butane isomerization activity.As the acidity of HPA varies greatly with the quantity of water content, and losing of the water is difficult to control, their catalytic performance is difficult to keep stable. We traversed the water losing process of HPW/SiO2 and found the proper water pressure to keep the strength of supported HPA catalysts at definite temperature, application of which increase the activity and stability of HPA catalysts in n-butane isomerization.