Synthesis of biodiesel via transesterification of tung oil catalyzed by new Brönsted acidic ionic liquid

•Two new Brönsted acidic ionic liquids (ILs) were prepared and characterized.•Synthesis of biodiesel from tung oil was proposed with Brønsted acidic ILs as catalyst.•[Ps-N-Ch(Me)2][p-TSA] exhibits better on its catalyst activity.•The maximum biodiesel yield of 98.98% was obtained.•The catalyst has excellent utility for repeated use.

Two new Brönsted acidic ionic liquids were prepared and characterized by NMR and FTIR. Their catalytic activities for the synthesis of biodiesel fuel via transesterification of tung oil with methanol were evaluated and compared to that of two imidazole-based ionic liquids for the first time. Among them, [Ps-N-Ch(Me)2][p-TSA] exhibited the highest catalytic activity and was chosen as catalyst for further research. A study on optimizing the reaction conditions was performed by orthogonal experiment based on the single factor experiment. It was found that the ranking of the significance of factors on the biodiesel yield is as follows: molar ratio of methanol to oil > reaction temperature > reaction time > catalyst dosage. The maximum biodiesel yield reaches 98.98% under the optimal reaction conditions at a molar ratio of methanol to oil of 21:1, a reaction temperature of 120 °C, a reaction time of 2 h and a catalyst dosage of 5.0 wt.%. Moreover, the reusability experiment exhibits that the catalyst can be reused five times with negligible loss of the activity. The refined biodiesel meets the biodiesel standard ASTM D6751-07, which can be used as fuel in diesel engines.

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