Ultrasound-assisted biodiesel generation from waste edible oil using CoFe2O4@GO as a superior and reclaimable nanocatalyst: Optimization of two-step transesterification by RSM

Abstract

In current study, CoFe2O4@graphene oxide (GO) and CoFe2O4 heterogeneous nanocatalysts were successfully synthesized using the ultrasonic method and then used to generate biodiesel from waste edible oil (WEO) in a two-step transesterification process. To do so, the catalysts surface was characterized using CO2-TPD, SEM, EDX/Map, XRD, VSM, BET, FTIR, and DLS analyses. Also, central composite design (CCD) was utilized to optimize the impact of various factors on biodiesel generation. With the help of ultrasonication, the highest biodiesel yield using CoFe2O4 (91.64%) and CoFe2O4@GO (98.17%) was achieved at time of 55.75 min, temperature of 64.75 °C, methanol/oil ratio of 16.05:1 and catalyst concentration of 5.22 wt%. Also, the highest biodiesel yield without ultrasonication using CoFe2O4 and CoFe2O4@GO were gained as 58.96 and 67.13%, respectively. Moreover, the highest predicted biodiesel yield in the presence of CoFe2O4@GO by the RSM-CCD method is 98.95%, which is the maximum biodiesel yield ever achieved from WEO. The outcomes show that ultrasound-assisted transesterification is an efficient method for biodiesel generation, which can reduce costs and production time. After 5 reuse cycles, the CoFe2O4@GO nanocatalyst showed a yield of about 90%, which is due to its desirable magnetic attributes and easy separation. According to international standards and using FT-IR and HNMR analyses, the biodiesel produced can be used in diesel engines without further modification. Besides, kinetic and thermodynamics studies indicated that the generation reaction of biodiesel using both nanocatalysts is endothermic and non-spontaneous.