Enhanced biodiesel production from low-value acidic oils using ordered hierarchical macro–mesoporous MoAl@H-SiO2 catalyst

The current research investigated the feasibility of using hierarchical porous solid catalysts for ameliorating the mass transfer of larger oil molecules to efficiently catalyze the oil transesterification particularly with low-value acidic oils as feedstocks, in response to the demand for the durable and green production of biodiesel. For this purpose, a series of ordered macro-mesoporous hierarchical MoAl@H-SiO2 catalyst was synthesized in acidic solution by in-situ synthesis method using polymethyl methacrylate (PMMA) and Pluronic P123 as double templates. The structural and morphological features as well as the acidic properties were validated by several catalyst characterization techniques. It was shown that Mo and Al metals were uniformly dispersed on the H-SiO2 support, and the ordered macro–mesoporous hierarchical structure was remained hardly unchangeable even after these metals had been loaded. The so-prepared solid catalyst demonstrated both Lewis and Bronsted acid sites, thus displaying high catalytic activities for concurrently converting of triglycerides and free long-chain fatty acids (FFAs) to biodiesel. Such technical advantages could impart a one-pot process for the cost-effective biodiesel production from low-value acidic oils, without requirement for the pretreatment of removing these FFAs. By comparing with the similar catalysts without hierarchical porous structure or with single metal oxide, the macro-mesoporous hierarchical structure could obviously enhance the catalytic performance due to the intensification of mass transfer and diffusion, meanwhile the synergism between the double Al and Mo species was also shown for the fabricated solid catalyst to promote the oil transesterification. Further, this hierarchical porous MoAl@H-SiO2 catalyst owned high FFA- and water resistance capacity, and still had considerable activity after repeated use for five times, endowing its great potential to be used for the production of biodiesel especially from low-value oil feedstocks.