Novel binuclear acidic ionic liquid as efficient and reusable catalyst for green biodiesel synthesis

Abstract

Inorganic acids/bases as catalysts in traditional biodiesel production pose problems (e.g., poor recyclability, equipment corrosion), urging the development of novel green catalysts. This study synthesized precursor salts (DPPP‐PS) using 1,3‐bis (diphenylphosphine) propane (DPPP) and 1,3‐propanesultone (PS). Furthermore, two novel green binuclear acidic ionic liquids, [DPPP‐PS][HSO ₄ ] ₂ and [DPPP‐PS] ₃ [PW ₁₂ O ₄₀ ] ₂ , were prepared and applied in the catalytic preparation of biodiesel. Both ionic liquids can be dissolved in alcohols and precipitated from esters, which is beneficial for recycling. Characterization analysis was conducted using FT‐IR, XPS and TGA. Comparisons were conducted through catalyst screening experiments. The process conditions were optimized by combining the single‐factor method and response surface methodology (RSM). Finally, experiments on the generality and reusability of the catalyst were carried out. Both catalysts are soluble in alcohols and precipitable in esters. Comparative studies indicate that Catalyst [DPPP‐PS][HSO ₄ ] ₂ exhibits superior catalytic performance. The optimized reaction conditions were established with the following parameters: reaction duration of 4.2 h, operating temperature of 71°C, catalyst concentration of 5%, and a molar ratio of methanol to oleic acid of 14.5:1. Under the aforementioned optimized reaction conditions, the conversion rate of oleic acid reaches 97.74%. For other fatty acids, the catalyst retains over 95% conversion; after 15 cycles, it still maintains over 95% conversion with unchanged structure. When catalyst [DPPP‐PS][HSO ₄ ] ₂ was employed to catalyze biodiesel production from waste fried oil, the transesterification conversion rate was 71.68%, which reveals that catalyst [DPPP‐PS][HSO ₄ ] ₂ possesses outstanding catalytic stability and compatibility with complex feedstock systems.