Preparation Of Hydroxylated SAPO - 31 Molecular Sieve Catalyst And Study On Hydrogenation Isomerization

A series of SAPO-31 molecular sieves were synthesized by hydrothermal method using different aluminum source and silicon source. The structure and acidic property were characterized by XRD, N2 physical adsorption, SEM, NH3-TPD and Py-IR. And then the influence of different aluminum source and silicon source were investigated. On this basis, the final choice intends to psedoboehmite as aluminum source, silica sol as silicon source, and di-n-butylamine as template, respectively. Different silicon content of SAPO-31 molecular sieves were synthesised by hydrothermal system and alcohol-water system of ethylene glycol and ethanol as solvent, and its catalytic performance were carried out on n-decane hydroisomerization reaction. In the hydrothermal system, Pd/SAPO-31 bifunctional catalyst synthesized with SiO2/Al2O3 molar ratio of 0.6 has a higher catalytic activity and isomerization selectivity in the hydroisomerization of n-decane. When SAPO-31 molecular sieves were synthesized using ethylene glycol and ethanol as solvent, the influence of different alcohol and alcohol-water ratio have great effect on the structure, acidity and catalytic performance. The samples synthesized with ethylene glycol as solvent not only have larger grain size and surface area, but also have a relatively mild acidity. Compared to hydrothermal method, the SAPO-31 samples synthesized with ethylene glycol-water at a molar ratio of 1:4 in the alcohol-water system loaded with Pd metal have significantly higher catalytic activity and isomerization selectivity.By hydrothermal synthesis method, hierarchical SAPO-31 molecular sieves with micropores-mesoporous form were synthesized with [3-(trimethoxysilyl)propyl] hexadecyldimethylammonium chloride(TPHAC) and PEO-PPO-PEO(P123) as mesoporous template, respectively. And the effect of mesoporous template form and dosage on the as-synthesized SAPO-31 molecular sieves structure and acidic were systematically investigated. As hierarchical SAPO-31 molecular sieves with increasing pore volume, and it improved the generate and diffusion of the product in hydroisomerization of n-decane. The n-decane conversion and dibranched isomers selectivity were significantly improved over Pd/hierarchical SAPO-31 molecular sieves.The influence of noble metal Pd content were studied in the hydroisomerization of n-decane. With increasing Pd content, it is help to transform monobranched isomers into the dibranched isomers. We also studied the content of non-noble metal Ni or Sn in the Ni-Pd(Sn-Pd)/SAPO-31 bimetallic catalyst of n-decane hydroisomerization. When introducting the non-noble metal Ni and Sn, it can significantly increasing the dispersion of Pd in the surface of the support. And it realized the match between acid center and metal center that achieving the synergy effect. It is not only improving the conversion and isomerization selectivity, but also help to transform monobranched isomers into the dibranched isomers.