Biodiesel production using Chlor-alkali brine sludge waste as a heterogeneous catalyst: optimisation using response surface methodology

Chlor-alkali process industries produce a million tonnes of brine sludge which are dumped in landfills. Brine sludge waste can be thermally modified and applied as a heterogeneous basic catalyst to synthesise biodiesel from waste cooking oil (WCO). In this work, an experimental design obtained by response surface methodology was used to study the effects of process parameters and hence, optimise the transesterification process. A quadratic model was generated to estimate the yield of biodiesel to its process variables. A biodiesel yield of value 97.8 wt % was optimally achieved using numerical optimisation method at a reaction period; methanol to oil weight ratio, a catalyst to oil weight ratio, and temperature of 1.53 hr, 29.8 wt %, 2.47 wt %, and 60.31 degrees C, respectively. The brine sludge waste catalyst was reutilised up to four times without being deactivated. Morphological modifications of the brine sludge after calcination and transesterification were characterised using a scanning electron microscope (SEM) and X-ray diffraction (XRD). From the basic fuel properties specifications stipulated in the ASTM standard, it was found WCO biodiesel properties were within the acceptable range.