Ultrasonic-assisted catalytic transfer hydrogenation of cottonseed biodiesel using Raney-Ni catalyst in aqueous environment

Abstract

The amounts of methyl stearate (C18:0) and trans-methyl oleate (trans-C18:1) increase during the catalytic transfer hydrogenation (CTH) process of biodiesel. Although it could improve the oxidation stability of biodiesel, its low temperature performance would be worsened. As for it, ultrasonic was introduced in the CTH to control the generation of C18:0 and trans-C18:1. In this study, the ultrasonic-assisted CTH was performed using Raney-Ni as catalyst, isopropanol as hydrogen donor and water as solvent. The effect of operating parameters such as reaction temperature, stirring rate, catalyst dosage, isopropanol amount and water amount on hydrogenation process was investigated. It was revealed that the optimum reaction conditions were determined as reaction temperature 80 °C, stirring rate 600 rpm, catalyst dosage 10 wt%, isopropanol amount 32 g and water amount 100 g in the aspect of the iodine value of bioidesel and the yield of C18:0 and trans-C18:1. The process of the ultrasonic-assisted CTH for biodiesel could be well described by pseudo-first order kinetic model. The conversion rate constants from C18:2 to C18:1 (k1) and from C18:1 to C18:0 (k2) were 0.02649 min−1 and 0.00438 min−1, respectively. Ultrasonic field effectively repressed the selectivity of trans-C18:1 and further decreased the iodine value of biodiesel. On the basis of the same iodine value, the yield of C18:0 and hydrogenation time reduced with ultrasonic. Overall, ultrasonic is an effective intensification method for the CTH of biodiesel in the aspect of product selectivity and reaction rate.