Synthesis of a modified heteropolyacid and evaluation as a phase-transfer catalyst for soybean oil epoxidation

• Published in: Chemical engineering research & design 2024-11, Vol.211, p.356-366
• Main Authors: Cárdenas, Juliana, Katryniok, Benjamin, Araque-Marin, Marcia C., Orjuela, Alvaro
• Format: Article
• Language: English
• Subjects: Heteropolyacids; Ion exchange resins; Phase-transfer catalyst; Soybean oil; Vegetable oil epoxidation
• ISSN: 0263-8762
• DOI: 10.1016/j.cherd.2024.10.010

Novel modified heteropolyacid (HPA) catalysts have been developed for the epoxidation of unsaturated vegetable oils. These were synthesized through hybridization of phosphotungstic acid (PTA) with cetyltrimethylammonium bromide (CTAB), tetrabutylammonium bromide (TBAB), and 1-dodecyl-3-methylimidazolium bromide (C12mimBr). Characterization of the modified HPAs was conducted using FT-IR, XRD, and TGA, and they were assessed as phase-transfer catalysts in the epoxidation of soybean oil (SO) with H2O2, in a two-phase system, without a percarboxylic acid intermediate. The performance of the epoxidation reaction was evaluated based on conversion (change of iodine value), selectivity (oxirane value), and productivity. The catalyst that exhibited superior performance was the phosphotungstic acid modified with CTAB corresponding to [C19H42N]3PW12O40 (CTA3PTA). Subsequently, it was found that the introduction of acidity to the reaction medium significantly enhanced the catalytic activity of CTA3PTA by promoting active peroxo forms. Different ion exchange resins (Dowex 50WX2, Amberlyst 15, and Amberlite IR-120) were explored as co-catalysts for reaction. Effective epoxidation conditions were achieved at a temperature of 60 ºC, a molar ratio of double bond to H2O2 of 1:2, and 2 g of Amberlite IR-120, resulting in a 4.6 % wt. oxirane value. Finally, the structure-performance relationship was discussed focusing on the influence of acidity in the epoxidation reaction. [Display omitted] •Modified heteropolyacid catalysts were assessed in epoxidation of soybean oil.•Phosphotungstic acid modified with cetyltrimethylammonium bromide was selected.•Amberlite IR-120 resin was required as co-catalyst to obtain high selectivity.•Catalytic pair had a Turn Over Frequency of ∼ 0.036 mol oxirane · (min · Eq H+)−1.•Oxirane oxygen content in epoxidized oil up to 5 % wt. in less that 5 h was obtained.