n-Nonane hydroisomerization over hierarchical SAPO-11-based catalysts with sodium dodecylbenzene sulfonate as a dispersant

Abstract

Abstract To enhance the gasoline octane number, low-octane linear n-alkanes should be converted into their high-octane di-branched isomers via n-alkane hydroisomerization. Therefore, hierarchical SAPO-11-based catalysts are prepared by adding different contents of sodium dodecylbenzene sulfonate (SDBS), and they are applied in n -nonane hydroisomerization. When n (SDBS)/ n (SiO 2 ) is less than or equal to 0.125, the synthesized hierarchical molecular sieves are all pure SAPO-11, and as the SDBS content increases, the submicron particle size decreases, and the external surface area (ESA) increases. Additionally, these hierarchical SAPO-11 have smaller submicron particles and higher ESA values than conventional SAPO-11. When n (SDBS)/ n (SiO 2 ) is greater than 0.125, with increasing SDBS content ( n (SDBS)/ n (SiO 2 ) = 0.25), the synthesized SAPO-11 contains amorphous materials, which leads to a decline in the ESA; with the further increase in SDBS content ( n (SDBS)/ n (SiO 2 ) = 0.5), the products are all amorphous materials. These results indicate that in the case of n (SDBS)/ n (SiO 2 ) = 0.125, the synthesized SAPO-11 molecular sieve (S–S 3 ) has the most external Brønsted acid centers and the highest ESA of these SAPO-11, and these advantages favor generation of the di-branched isomers in hydrocarbon hydroisomerization. Among these Pt/SAPO-11 catalysts, Pt/S–S 3 displays the highest selectivity to entire isomers (83.4%), the highest selectivity to di-branched isomers (28.1%) and the minimum hydrocracking selectivity (15.7%) in n -nonane hydroisomerization.