Liquid phase oligomerization of 1-hexene over different mesoporous aluminosilicates (Al-MTS, Al-MCM-41 and Al-SBA-15) and micrometer/nanometer HZSM-5 zeolites
The liquid phase oligomerization of 1-hexene at 200 °C and 5 MPa using n-octane as solvent towards hydrocarbon mixtures useful as fuels (gasoline and diesel) was tested over several acid catalysts: micrometer (μ-) and nanocrystalline (n-) HZSM-5 zeolites, mesoporous hydrothermal Al-MCM-41, and sol–gel Al-MTS and Al-SBA-15 catalysts. The conversion was always above 75% except for μ-HZSM-5 (just 8.4%) due to its low external surface area (5 m2 g−1) and the fast deactivation in the reaction conditions used in this work. The total selectivity towards oligomers was around 95% and the highest share of C9–C12 dimers (47%), C13–C18 trimers (33%) and heavy C19–C30 compounds (33%) were yielded over Al-SBA-15, n-HZSM-5 and sol–gel Al-MTS, respectively. The remarkable oligomerization performance of n-HZSM-5 was ascribed to its high external surface area (102 m2 g−1) and for the mesoporous catalysts, to their large BET surface area. In particular, Al-MTS showed the best behaviour due to its higher BET surface area and slightly weaker acidity. All the catalysts exhibited steady-state performance with time on stream (TOS) without drastic changes in activity up to 180 min. Simulated distillation analyses proved that the lighter fuel (gasoline + diesel) was obtained over Al-MTS (final distillation temperature = 463 °C; C26–C32 = 8.4%) while the heaviest was obtained over n-HZSM-5 zeolite (final distillation temperature = 524 °C; C28–C40 = 11.7%), probably related to its stronger acidity and microporous nature. The similar nature of hydrocarbons compounds retained over the catalysts after reaction proved by FTIR spectroscopy together with the thermogravimetric analyses results, showed the stronger adsorption of the reaction products promoted by the microporous nature of zeolites.
Journal: Applied Catalysis A: General - Volume 305, Issue 2, 24 May 2006, Pages 176–188