Hydrocarbon hydroisomerization is crucial for petroleum refining processes. The branched isomers produced via hydroisomerization increase the octane number of gasoline. However, conventional Pt/SAPO-11 catalysts with micropores and large particles mainly produce mono-branched isomers with low octane numbers, limiting their application for improving the gasoline octane number. A novel route to synthesize SAPO-11 molecular sieve in ethylene glycol and supercritical carbon dioxide with smaller particles and larger external surface area is proposed. The addition of supercritical carbon dioxide to ethylene glycol decreases the solubility of SAPO-11 precursors in the ethylene glycol solvent. As a consequence, the gel reaches high supersaturation, accelerating the rate of the SAPO-11 nucleation and increasing the number of SAPO-11 crystal nuclei. Thus, SAPO-11 with smaller particles is obtained. The scanning electron microscopy (SEM), N2 xifutuofu and pyridine adsorbed infrared (Py-IR) experiments of the as-synthesized SAPO-11 sample are carried out. The as-synthesized SAPO-11 sample has small flaky particles with sizes ranging from 400 nm to 1μm. The external surface area and the mesopore volume of the as-synthesized SAPO-11 (Sexternal=122 m2g-1, Vmesopore=0.28 cm3g-1) are much larger than those of conventional SAPO-11 (Sexternal=65 m2g-1, Vmesopore=0.06 cm3g-1). In addition, compared with the conventional SAPO-11, the as-synthesized SAPO-11 has more total amount of Brönsted acid sites (77.6 μmolPy/g vs. 48.4 μmolPy/g) and higher amount of moderate and strong Brönsted acid sites (31.0 μmolPy/g vs. 18.1 μmolPy/g). Therefore, the as-synthesized corresponding Pt/SAPO-11 catalyst exhibits higher di-branched isomer selectivity (20.5% vs. 8.6%, at 62% conversion of 1-octene) and lower cracking selectivity (6.1% vs. 10.9%, at 62% conversion of 1-octene) during 1-octene hydroisomerization than those of conventional Pt/SAPO-11 catalyst.

Synthesis of SAPO-11 molecular sieve in ethylene glycol and supercritical carbon dioxide

255th National Meeting (2018)

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