Biodiesel production with nanotubular sodium titanate as a catalyst

• Biodiesel synthesis from soybean oil and methanol with solid base catalyst.
• Nanotubular sodium titanate as a catalyst for biodiesel production.
• Studied effects: catalyst amount, methanol:oil ratio, reaction time and temperature.
• High biodiesel yields (up to 100%) obtained with sodium titanate nanotubes.

Sodium titanate nanotubes (STNT) with a chemical formula Na2Ti3O7·nH2O were synthesized and tested as a heterogeneous catalyst in the transesterification of soybean oil with methanol. The catalyst was characterized by N2 physisorption, powder XRD, scanning electron microscopy (SEM-EDX), transmission electron microscopy (TEM) and CO2 temperature-programmed desorption (CO2-TPD). It was found that the prepared catalyst had nanotubular structure, high sodium content (10.3 wt.%) and attractive textural characteristics (surface area around 200 m2/g and total pore volume of 0.61 cm3/g). The influence of the catalyst's loading, methanol to oil molar ratio, reaction time and temperature on the biodiesel yield was investigated. High biodiesel yields (97–100%) were obtained with the STNT catalyst at 8 h reaction time at methanol reflux temperature with 1–2 wt.% of the catalyst and 40:1 methanol:oil molar ratio. Increase in the reaction temperature to 100–120 °C had a positive effect on the biodiesel yield. In this case, 99–100% yields were obtained with a lower catalyst loading (∼1 wt.%) and methanol to oil molar ratio (20:1). In addition, it was found that the STNT catalyst does not require high temperature thermal pre-treatment (activation) before the transesterification reaction. The reuse of the same catalyst in the transesterification reaction three times showed a decrease of about 10% in the catalytic activity.

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