Biodiesel production from waste cooking oil using a waste diaper derived heterogeneous magnetic catalyst

A series of waste diaper-derived heterogeneous magnetic catalysts for the synthesis of biodiesel was developed through the two-step method, i.e., first wet-impregnation in nickel nitrate solution and then calcination at 700 °C. The structure and catalytic ability of the catalyst were characterized by SEM, FTIR, XRD, BET, VSM, and acid–base titration techniques. The investigation results indicated that WDHMCs were mainly composed of Ni, Na2CO3, and carbon. With the increase in the ratio of nickel nitrate to waste diapers, the magnetization of the prepared catalysts increased, while the catalytic activity decreased. When the ratio of nickel nitrate to waste diaper was 2 mmol/g, the obtained catalyst exhibited relatively high catalytic activity with the biodiesel yield of 96.4% and high magnetic separation property in the transesterification reaction of waste cooking oil with methanol. Moreover, the prepared waste diaper-derived heterogeneous magnetic catalyst could be easily reused by simple magnetic separation and maintain high catalytic activity after being reused four times.