Micelle effect on the conversion of microporous to mesoporous molecular sieves and biodiesel synthesis

Abstract

Tetrabutylammonium bromide (TBAB) is used as a template for the preparation of AlPO₄ and AlSiO₄ materials by the hydrothermal method. TBAB is acting as an individual template molecule due to the high temperature and pressure and it creates only microporous materials. But in the present investigation, the same template produces mesoporous AlPO₄ and AlSiO₄ at room temperature and atmospheric pressure by the sol–gel method. During this method, TBAB molecules are combined to produce a TBAB micelle template. The pore expansion property of the TBAB micelle template on AlPO₄ and AlSiO₄ synthesis is observed by BET. The surface areas of AlPO₄ and AlSiO₄ are 17.23 and 42.52 m² g⁻¹, respectively. The XRD pattern of AlPO₄ and AlSiO₄ confirms the strong single reflections with d spacing values of AlPO₄ (11.6 nm) and AlSiO₄ (12.7 nm). FT-IR confirms the tetrahedral framework vibrations of AlPO₄ and AlSiO₄ at 1133 and 1128 cm⁻¹ respectively. TGA spectra for both catalysts show that the decomposition of the template is observed at 200–450 °C. SEM and HR-TEM characterization were used to verify the morphology of the synthesized materials. BJH pore size distribution analysis proves that the TBAB micelle template acts as a pore size expander for both AlPO₄ (18 nm) and AlSiO₄ (41 nm). Herein, we introduce the newly expanded pores of mesoporous AlPO₄ and AlSiO₄ as catalysts that are effectively applied in transesterification reactions to produce biodiesel from waste cooking oil (WCO). The biodiesel conversion efficiency achieved was 78% for aluminosilicate and 64% for aluminophosphate. The biodiesel selectivity of aluminosilicate is 98% and that of aluminophosphate is 87%. The synthesized catalysts are recycled 10 times. The high conversion and selectivity of biodiesel are achieved easily due to the expanded pore micelle effect. This will reduce the biodiesel synthesis time, temperature, molar ratio and catalyst dosage when compared to the conventional method.