Sustainable biodiesel production from used cooking oil using dual-function silica catalysts (SO4/SiO2 and SiO2/CaO).

Abstract

Silica with high surface area and porosity is potentially used as a catalyst; its success decreases the free fatty acid value of used cooking oil and produces high-yield biodiesel. Modified SiO2 to enhance its catalytic activity was carried out by the sulfation process with H₂SO₄ solution 1, 2, and 3 M. The total acidity analysis concluded the SO4/SiO2 2 M as the catalyst with the optimum acidity value. The SO4/SiO2 2 M catalyst has a surface area of 296.39 m2/g, a mesopore and micropore structure, an increase in the amorphous structure, and a surface morphology with small granules and a rough texture. This catalyst reduces the free fatty acid value of used cooking oil by up to 84.6% under reaction conditions of 3% catalyst weight, a molar ratio of oil to methanol of 1:18, and a reaction time of 30 min. After esterification, used cooking oil is processed to produce biodiesel through transesterification with a base catalyst. This research uses SiO2 as a support for CaO to increase the porosity of CaO. Preparation of SiO2/CaO 10, 20, and 30 wt% catalyst shows the optimum basicity value at the SiO2/CaO 20% catalyst. Moreover, the SiO2/CaO 20% catalyst provides better basicity value and surface area compared to CaO. Additionally, hydrothermal treatment in the preparation of the SiO2/CaO 20% catalyst also affects the formation of high crystallinity and uniform surface structure morphology, thereby enhancing the thermal stability and distribution of active catalytic sites. These properties have a significant effect on the transesterification of used cooking oil, resulting in 100% biodiesel yield.

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