Dry‐gel conversion synthesis of SAPO‐11 molecular sieves and their use in hydroisodewaxing of hydrocracking recycle oil

Abstract

AbstractSilicoaluminophosphate (SAPO‐11) molecular sieves were synthesized by the dry‐gel conversion [i.e. steam‐assisted conversion and vapor‐phase transport (VPT)] method using di‐n‐propylamine as a structure‐directing agent. The influence of the bottom water content, the crystallization time, the drying time and the pH value was investigated. The properties of the as‐synthesized samples were characterized by X‐ray powder diffraction, scanning electron microscopy, N2‐adsorption and NH3‐temperature‐programmed desorption. The results show that the crystallization process of SAPO‐11 was closely related to the pH value and the drying time of the gel; the amount of water in the wet gel plays an important role for SAPO‐11 formation. It can be observed that when the crystal time is within 48 h, and the pH value of the gel is between 0 and 5, the longer the crystal time and the higher the pH value, the higher the crystallinity of the samples. The presence of NH4+ leads to the formation of an amorphous phase in the samples synthesized by the VPT method. Of these two methods, the steam‐assisted conversion method exhibits better Si incorporation into the AlPO4 framework than the VPT method. The results from hydroisodewaxing of hydrocracking recycle oil show that the Pt/SAPO‐11 catalysts synthesized by these methods possess high activity and selectivity of isomerization. The pour point of the lubricating base oils can be lowered to below −15 from 42 °C. Copyright © 2016 Curtin University of Technology and John Wiley & Sons, Ltd.