Synthesis And Catalytic Activity Of SAPO-11 With Different Si/Al For Isomerization

The isomerization of n-alkanes in the distillate oil obtained in petroleum refining was one of the effective ways to produce high quality oil. But the use of acid catalysts for isomerization would cause n-alkanes to crack. So the preparation of efficient isomerization catalysts was the key factor to improve the isomerization selectivity of the n-alkanes.Silicoaluminophosphate molecular sieve (SAPO) has special characterizations of excellent regioselectivity, ion exchange performance, acid adjustability, thermal and heat stability etc. And it can be widely used in reactions like cracking reaction, alkylation reaction, polymerization reaction, reforming reaction, hydrogenation reaction, dehydrogenation reaction and hydration reaction. SAPO supported catalysts showed higher isomerization catalytic activities than traditional supports supported catalysts. Non-noble metal catalyst supported by SAPO received increasingly attention in the field of isomerization catalyst.because of its high surface area, high activity for isomerization, high stability and tolerant ability for poisoning.In this paper, SAPO-11 was hydrothermally synthesized from an aqueous medium using a conventional method. Crystallization time, crystallization temperature, template agent, PH, silica source and silica content were studied. Results showed that when crystallization time was 6 h, crystallization temperature were 180 oC, template agent was the mixture of DPA and DIPA, PH was 5.5, silica source was acidic silica sol, and Si/Al was 0.4, the preparation conditions were optimal. Mo/SAPO-11 and Co/SAPO-11 catalysts were prepared with the best SAPO-11 by the impregnation method. The catalysts were characterized by X-ray diffraction (XRD) and N2 adsorption-desorption specific surface area measurements (BET). The catalysts were evaluated using a lab-scale continuous flow fixed-bed reactor for isomerization of n-heptane. The catalytic activity of the Mo/SAPO-11 catalyst reduced at 500 oC for 6 h with a Mo loading of 4% (wt), H₂ flow rate of 30 ml/min, was found to be optimal. The conversion of n-heptane and isomerization selectivity were 14.23% and 86.74%, respectively, for Mo/SAPO-11 at a reaction temperature of 320 oC, and a normal atmosphere. The catalytic activity of the Co/SAPO-11 catalyst reduced at 400 oC for 6 h with a Co loading of 2% (wt), H2 flow rate of 30 ml/min, was found to be optimal. The conversion of n-heptane and isomerization selectivity were 33.24% and 62.47%, respectively, for Co/SAPO-11 at a reaction temperature of 280 oC, and a normal atmosphere.