Deep Hydroisomerization of n-Hexadecane over NiWS/SAPO-11 Catalyst: Size Effect of the Support and Revelation of the Reaction Network

Abstract

SAPO-11 molecular sieves with different crystal sizes and particle sizes, especially nanosized small-crystal SAPO-11 molecular sieves, were successfully synthesized, and the corresponding NiWS-supported catalysts were prepared for the hydroisomerization of n-hexadecane. XRD, SEM, N2 adsorption–desorption, Py-IR, and HRTEM were used to analyze the effects of crystal size and particle size of the supports on their physicochemical properties, active phase properties, and catalytic performance of the catalysts. Through reaction evaluation and analysis of isomeric products, the effects of the size change of the support on the hydroisomerization performance of the catalyst and the hydroisomerization depth of n-hexadecane were determined. Through comprehensive analysis of the cracking products, it was determined that secondary cracking occurred when the conversion of n-hexadecane on the NiW/SAPO-11-S catalyst reached about 42.7%, and the secondary isomerization occurred when the conversion of n-hexadecane reached about 80%. The hydroisomerization reaction network of n-hexadecane over the NiWS/SAPO-11 catalyst was studied emphatically, and it was found for the first time that the secondary cracking of n-hexadecane during hydroisomerization followed the C3-β-scission mechanism.

Changing Template/Al2O3 Ratio in Reaction Gel—An Effective Way to Regulate Nature of Intermediate Phases and Properties of SAPO-11 Molecular Sieves during Crystallization

“…The highest activity and selectivity are shown by the sample Pt/SAPO-11-1.0, which is characterized by nanosized crystals with a low aspect ratio and a higher concentration of available acid sites ( Figure 12 ). Due to this porous structure, diffusion limitations for reacting molecules are reduced, leading to a decrease in their residence time inside the channels and the contribution of the secondary cracking reaction on the acid sites [ 46 , 47 , 48 ]. For the Pt/SAPO-11-1.8 sample, the lowest selectivity for the C 16 isomers is observed due to the presence of primary crystals with higher aspect ratios, in which the residence time of molecules in the channels is significantly increased, and the contribution of cracking reactions is increased.…”

Synthesis, Modification, and Performance Regulation of SAPO-11 Molecular Sieve and Development of n-Alkane Hydroisomerization Catalyst: A Mini-Review

“…SAPO-11 molecular sieves are the most widely used hydroisomerization catalyst support at present because of their mild acidity and unique one-dimensional pore structure. There are many reports about SAPO-11 molecular sieve-based hydroisomerization catalyst. ,− ,,,,,,− Yu et al used activated carbon and n -butanol as additives to adjust the pore structure and acidity of SAPO-11 molecular sieve (Figure ). The double additives promoted the formation of a high specific surface area and more mesoporous structures with suitable mesoporous distribution, and the total Brønsted acid sites of SAPO-11 samples were enhanced by the double additives.…”

“…The pore structure of SAPO-11 molecular sieve is one-dimensional ten-membered ring structure, and the pore size is about 0.39 × 0.61 nm 2 , which belongs to microporous molecular sieve. , The molecular size of n -hexadecane with 16 carbon atoms is about 0.56 nm, which is equivalent to the micropore size of SAPO-11 molecular sieve. , With the isomerization of n -alkanes to form branched isomers, the molecular size of alkanes will become larger, and the deeper the isomerization, the larger the molecular size of alkanes . The pore size of SAPO-11 molecular sieve will not allow n -alkane molecules with long carbon chains to enter its pore channel to react and will make branched isomers suffer greater diffusion resistance in the pore, thus reducing the activity and isomerization selectivity of the catalyst.…”