Preparation of biopolyols by pyrrolidone ionic liquid-catalyzed ring-opening of epoxidized soybean oils

The effects of N-methyl pyrrolidone hydrogen sulfate ([Hnmp]HSO4), α-pyrrolidone hydrogen sulfate ([Hnhp]HSO4), and dinucleated pyrrolidone hydrogen sulfate ([[Hnhp]HSO4]2) on ring-opening of epoxidized soybean oils (ESO) was comparatively investigated. Results showed that [Hnhp]HSO4 had stronger catalytic activity than the other two. Under the optimal conditions ([Hnhp]HSO4 loading of 6%, water-epoxy group ratio of 9:1 (mol/mol), reaction temperature of 45 °C, and reaction time of 4 h), the resulting di-hydroxylated soybean oils (DSO) with an epoxy content of 0.87% and hydroxyl value (OHV) of 213.41 mg KOH/g was achieved, which corresponded to a conversion rate of OHV of 57.98%. In-situ Fourier transform infrared spectroscopy (In-situ FTIR) and FTIR analyses indicated that the rapid ring-opening of ESO and formation of DSO mainly occurred at 2–3.5 h. The increase of polarity and molecular weight after ring-opening and the formation of hydrogen bonds resulted in the higher viscosity of DSO than ESO. ESO and DSO were thermally stable at up to 350 °C. The effectiveness of [Hnhp]HSO4 in catalyzing the ring-opening of ESO was comparable to that of inorganic acids. Almost complete ring-opening of epoxy groups with much less etherification leads biopolyols to have more available hydroxyl groups. Thus, the resulting biopolyols can be processed as chemical intermediates under more flexible parameter conditions.