The Electrochemical hydrogenation of reutealis trisperma oil as non-edible biodiesel feedstock

Abstract

Nowadays various vegetable, especially non-edible, oils are considered as the most promising source of biofuel for future generations. Among these, oil obtained from a highly productive tree locally known as kemiri sunan (Reutealis trisperma) is now being developed as one of the non-edible oil feedstocks for biodiesel production. However, the oil possesses a relatively high Iodine value, typically about 120 g-I2 / 100 g oil. Such oil will produce biodiesel with not only poor thermal as well as oxidative stability, but also insufficient cetane number. In the present work, electrochemical hydrogenation was the chosen technique to lower the Iodine value of the oil, since it was not only simple and safe to operate, but also required very low capital cost. The system used stainless steel coil as the anode, whereas the cathode were nickel screen or copper raschig rings. An electrolyte solution of potassium formate or cuprous ammonium formate was utilized. The unsaturation level of the oil was measured by Wijs method (AOCS Cd 1-25). The Iodine value of the original oil, which was initially around 115, could be significantly lowered to 55 – 95 at various KCOOH concentrations and reaction times. However, excessively low Iodine value would result in biodiesel with high cloud point (maximum 18 oC according to SNI standard). Thus, the process conditions had to be carefully chosen, and the use of 2.5 M KCOOH solution within 6 hours was sufficient to bring down the Iodine value to the desired (ideal from the cetane number and cloud point requirements) level of 85 g-I2/100 g (equivalent to methyl oleate). Even more promising results using cuprous ammonium formate were obtained, among which similar Iodine value decrease could be achieved using 0.6 M electrolyte solution within 6 hours. In addition, the use of cuprous ammonium formate could significantly save the electricity energy consumption. However, the benefit had to be compensated by the more tedious purification of the processed oil using EDTA solution.