Evaluation of Soxhlet extractor for one-step biodiesel production from Zanthoxylum bungeanum seeds

• One-step biodiesel production from plant seeds in the Soxhlet extractor was developed.
• The conversion of Z. bungeanum seed oil (ZSO) into biodiesel was almost complete.
• Biodiesel was produced by simultaneous oil extraction and acid-catalyzed reaction.
• Simultaneous esterification and transesterification of ZSO were monitored by 1H NMR.
• Biodiesel production in the Soxhlet extractor avoided solid–liquid separation.

Soxhlet extractor was applied for biodiesel production from Zanthoxylum bungeanum seeds containing high amount of free fatty acids (FFA) using methanol and ethanol as both extractants and reactants. The yields, fatty acid concentration and acid values of Z. bungeanum seed oil (ZSO) extracted with different solvents were determined. With a solvent-to-seed ratio of 6 (ml/g), extraction time of 4 h and water bath at 95 °C, the yields of ZSO with methanol and ethanol reached above 20%, which was almost as efficient as n-hexane, and the acid values of the corresponding ZSO were 56.9 and 41.9 mg KOH/g, respectively. The final acid values of ZSO were reduced to below 10 mg KOH/g when sulfuric acid was used as a catalyst presented in receiver flask in 4 h extraction and reaction. After 12 h of extraction and transesterification in a Soxhlet extractor with methanol and ethanol, the conversion of ZSO from Z. bungeanum seeds into ZSO biodiesel was almost complete as confirmed by 1H NMR. Application of the Soxhlet extractor for one-step biodiesel production from Z. bungeanum seeds containing high FFA avoided solid–liquid separation process and solvent wash, showing great potential of reducing the production cost of biodiesel.