Grafting copolymerization of dual acidic ionic liquid on core-shell structured magnetic silica: A magnetically recyclable Brönsted acid catalyst for biodiesel production by one-pot transformation of low-quality oils

[Display omitted] •A magnetically recyclable Brönsted acid catalyst was prepared.•The catalyst was effective for one-pot biodiesel production from low-quality oils.•The catalyst could be used for five times with no significant loss of activity.•The catalyst could be readily recovered by using a magnetic field.•The catalyst possessed showed high catalytic activity with 94.2% of oil conversion. The objective of the current research is to prepare an efficient and magnetically separable Brönsted acid catalyst for one-pot transformation of low-quality oils to biodiesel. In this premise, the core–shell structured magnetic composites were firstly prepared by coating of silica shells on magnetic Fe3O4 nanoparticles. Thereafter, the grafting copolymerization of dual acidic ionic liquids (ILs, 1-vinyl-3-(3-sulfopropyl)imidazolium hydrogen sulfate as an monomer and 1.4-butanediyl-3,3′-bis-1-vinylimidazoliu hydrogen sulfate as a cross-linker agent) on the magnetic silica composite was conducted to impart the richer Brönsted acidic functionality on the support. The detailed catalyst characterization results showed that the magnetic silica support was really formed, and moreover the polymeric acidic ILs were successfully grafted on the magnetic support. The so-prepared solid catalyst had a large surface acidity (3.93 meq H+/g) and strong magnetism (27.5 emu/g). Benefiting from the synergism between the polymeric ILs and magnetic porous support, this developed catalyst displayed good catalytic activities toward both the transesterification of soybean oil and esterification of free fatty acids (FFAs), which endowed it to be a robust solid acid catalyst for one-pot biodiesel production from low-quality acidic oils. The solid catalyst could be simply recovered by an external magnet with minor loss of catalytic activity within five cycles, and further showed insensitivities to moisture and FFAs present in the feedstocks, possessing both economic and environmental advantages for the application in biodiesel production especially from the low-quality oils.