Biodiesel Production from Acidic Oils Using Polyoxometalate-Based Sulfonated Ionic Liquids Functionalized Metal–Organic Frameworks

Abstract

An efficient and recyclable catalyst, namely phosphomolybdenum-based sulfonated ionic liquids (ILs) functionalized MIL-100(Fe) metal–organic framework (AIL/HPMo/MIL-100(Fe)), was developed for the production of biodiesel via the transesterification-esterifications of acidic oils. For this goal, the MIL-100(Fe) metal–organic framework (MOF) was initially modified with phosphomolybdic acid (HPMo), and then the acidic ionic liquid (AIL) was immobilized on the prepared HPMo/MIL-100(Fe) composite through ion-exchange of 1-(propyl-3-sulfonate)imidazolium hydrogen sulfate with HPMo. The as-developed AIL/HPMo/MIL-100(Fe) catalyst possessed enhanced surface acidities, endowing the merits of Lewis and Bronsted acids with a heterogeneous microreactor of MOFs and favoring the better catalytic performance. The characterization results corroborated that the polyoxometalate-based ILs were incorporated into the MIL-100(Fe), and the porous structure of the MIL-100(Fe) maintained nearly unchangeable after the synthesis processes. The AIL/HPMo/MIL-100(Fe) catalyst could perform simultaneous transesterification of soybean oil and esterification of free fatty acids (FFAs) with long-term catalytic durability. The conversion of acidic oils using this solid catalyst gave 92.3% oil conversion for the transesterification of soybean oil and full FFA conversion for the esterification of FFAs with the methanol/oil molar ratio of 30:1 at 120 °C, showing potential applications for the production of biodiesel particularly from acidic oil feedstocks. Synopsis: Phosphomolybdenum-based sulfonated ionic liquids (ILs) functionalized MIL-100(Fe) metal–organic framework composites are fabricated and then utilized as efficient and recyclable catalysts for the production of biodiesel via one-pot transesterification-esterifications of acidic oils.