Study On Preparation And Performance Of Catalyst For Hydroisomerization Of Long-Chain N-Alkanes

Hydroisomerization is an important process to produce low pour point diesel oil and lube base oil,and catalyst is the key of hydroisomerization process.In this paper,in order to prepare SAPO-11 molecular sieve-based non-noble metal supported bifunctional catalyst with excellent isomerization performance,in-depth research has been carried out from two aspects of support and metal components.In order to explore the effects of synthesis process conditions on the properties of SAPO-11 molecular sieve,firstly,the effects of medium system,feed silicon-aluminum ratio,crystallization temperature,crystallization time and water content of the system on the physicochemical properties of SAPO-11 molecular sieve were investigated,and the best synthesis process conditions of SAPO-11 molecular sieve were determined.Based on the analysis results of Ni W/SAPO-11 catalyst on the distribution of hydroisomerization products of n-hexadecane,it was determined that hydroisomerization of n-hexadecane followed the pore-mouth mechanism.In order to solve the problems of high hydrogenolysis activity,easy to agglomerate and difficult to be reduced of non-noble metal Ni in hydroisomerization catalyst,the Ni Me/SAPO-11 catalysts were prepared by adding different metal additives(La,Ga,Ce and Zr)into the impregnation solution of catalysts.The results showed that the introduction of metal additives weakened the metal-support interaction and improved the reducibility and dispersion degree of metals.XPS analysis showed that the different metal additives were alloyed with Ni,which increased the yield of i-hexadecane by41%.In order to further improve the performance of SAPO-11 molecular sieve,the effects of Ni content on the performance of SAPO-11 molecular sieves and catalysts were investigated by the in-situ modification method,and it was found that the performance of SAPO-11 molecular sieve and catalyst modified by 3% Ni content was the best.The effects of the different modification methods on the performance of SAPO-11 molecular sieves and catalysts were also investigated.The results showed that compared with the ion-exchange method and the in-situ modification method,the i-hexadecane yield of catalyst modified by the complexation-excessive impregnation modification method was the highest,which was 39.3% higher than that of the unmodified SAPO-11 molecular sieve catalyst.Aiming at the large crystal-size,small specific surface area and low acidity of conventional SAPO-11 molecular sieve,it was proposed that the small-crystal and hierarchical SAPO-11 molecular sieve was successfully synthesized with L-Lysine as the crystal growth inhibitor,and the formation mechanism of the molecular sieve was proposed.The results showed that the reduction of crystal-size greatly increased the mesoporous volume and the amount of medium and strong Br?nsted acid of SAPO-11 molecular sieve,and increased the dispersibility and stacking number of the Ni WS active phase on the catalyst,and the i-hexadecane yield of the small-crystal and hierarchical SAPO-11 molecular sieve Ni W supported catalyst was increased by 45.3%compared with the corresponding catalyst of conventional SAPO-11 molecular sieve.