Immobilized tetrabutylammonium amino acid ionic liquids as heterogeneous catalyst in biodiesel production from Chlorella vulgaris

Ionic liquids (ILs) are molten salts below 100 °C with the ability to be used as a catalyst for biodiesel production. However, to this date, the implementation of ILs as catalysts remains an enigma due to their practicability. Immobilizing ILs onto waste biomass solid support may improve the sustainability of its implementation. This study is focused on synthesizing immobilized tetrabutylammonium amino acid ionic liquids (TBA AAILs) onto bamboo activated carbon (BAC) as catalysts in transesterification of fatty acids extracted from Chlorella vulgaris. Three AAILs, consisting of tetrabutylammonium paired with arginine, histidine, and lysine, were synthesized via neutralization reaction and immobilized onto BAC through wet impregnation method. Thereafter, microwave-assisted transesterification was performed with C. vulgaris as a feedstock. Impregnation of TBA AAILs caused modifications on morphology, chemical composition, and surface area of the BAC. [TBA][His]/BAC had greater impact compared to [TBA][Arg]/BAC and [TBA][Lys]/BAC, where it reduced the surface area up to 35 m²/g and pore volume to 0.020 cm³/g, initially BAC's surface area are 842 m²/g and pore volume of 0.387 cm³/g. Optimization with the Box-Behnken method achieved the highest yield 81.9 % FAME using 20 % [TBA][His]/BAC with 3 % of catalyst dosage and 21 gs of methanol at 80 °C for 48 mins with three times reusability. The immobilized TBA AAILs/BAC reduced IL consumption by 10 times and obtained comparatively higher yield than TBA AAILs, providing a sustainable alternative to conventional ILs catalyst.