Synthesis of heterogenized polyoxometalate-based ionic liquids with Brönsted-Lewis acid sites: A magnetically recyclable catalyst for biodiesel production from low-quality oils

Abstract

The aim of this study is to develop a magnetically recyclable acid catalyst for biodiesel production from low-quality acidic oils. To achieve this, polyoxometalate (POM)-based sulfonated ionic liquids (ILs) bearing Brönsted-Lewis acid sites, namely (Py-Ps)PMo, were firstly prepared by reaction of pyridine with 1,3-propanesultone, followed by anion exchange with phosphomolybdic acid (HPMo). Thereafter, the so-prepared ILs were loaded on the amino-functionalized metal–organic framework (CoFe2O4/MIL-88B(Fe)-NH2) to synthesize the recoverable solid catalyst. The obtained CoFe2O4/MIL-88B(Fe)-NH2/(Py-Ps)PMo catalyst was characterized by several techniques, which provided an evidence that the acidic ILs were loaded on the magnetic support by strong charge interaction effect. This catalyst showed highly catalytic activities toward the transesterification of soybean oil and esterification of free fatty acids (FFAs), making it to be applicable for one-pot production of biodiesel from low-quality acidic oils. The catalytic performance was originated from the combination of the characteristics of Brönsted-Lewis acid sites and porous structure of the support. Moreover, the catalyst could be simply recovered by a permanent magnet and reutilized for several times with no remarkable attenuation of catalytic activity. Thus, the IL based solid catalyst possessed the potential of efficient and environmentally benign production of biodiesel practically from the low-quality oils.