Removal of sulfur compounds from LPG by heteropoly acid-modified Al–MCM-41 mesoporous molecular sieves

Abstract

Al–MCM-41(30) was synthesized using Al₂(SO₄)₃ as the aluminum source, Na₂SiO₃ as the silicon precursor and cetyltrimethylammonium bromide (CTAB) surfactant as the template. Heteropolyacid supported on the mesoporous sieves was prepared using the incipient wetness method. The heteropolyacid-modified Al–MCM-41 adsorbents significantly enhanced the desulfurization ability of LPG through a dynamic adsorption method in a fixed bed. Several factors that affect desulfurization, including PW₁₂ loading, calcination temperature and the type of heteropolyacid, were investigated. The adsorbents were characterized by power X-ray diffraction, nitrogen adsorption, FTIR spectroscopy, thermogravimetric analysis and Py-IR spectroscopy. Al–MCM-41 mesoporous molecular sieves, with a hexagonal phase and a large specific surface area (1265.033 m² g⁻¹), were obtained. The experimental results showed that the PW₁₂-modified Al–MCM-41 adsorbents with a 25 wt% PW₁₂ loading had an optimum desulfurization ability. Also, a higher calcination temperature better promoted the removal of sulfur compounds by improving the acid amount of adsorbents. In addition, PW₁₂-modified Al–MCM-41 is better than PMo₁₂ modified Al–MCM-41 adsorbents in removing sulfur compounds from LPG. A total acid site number within a certain range on the adsorbent surface facilitated the desulfurization, and these values were obtained via Py-IR analyses.