Process optimization of Calophyllum inophyllum-waste cooking oil mixture for biodiesel production using Donax deltoides shells as heterogeneous catalyst

In the present work, the waste material Donax deltoides shells (DDS) was utilized as a heterogeneous base catalyst for biodiesel production from Calophyllum inophyllum oil (CIO)-waste cooking oil (WCO) mixture. Non-edible CIO possessing 65 mg of KOH g(-1) of acid value was mixed with WCO of low acid value in different proportions. The acid value was reduced to 33.3 mg of KOH g(-1) of oil by using a volumetric ratio of 1:1 and it was further reduced to 5.6 mg of KOH g(-1) of oil by acid catalyzed esterification process and used for biodiesel production. DDS was converted into active CaO catalyst by calcination and the catalyst characterization was performed using different instrumental techniques. The impact of calcined DDS (catalyst) concentration, reaction time and methanol to esterified oil volumetric ratio on biodiesel conversion was investigated to optimize the transesterification reaction using response surface methodology based central composite design. The biodiesel conversion was determined by proton nuclear magnetic resonance spectroscopy and a maximum biodiesel conversion of 96.5% was achieved with catalyst concentration of 7.5 wt%, methanol to oil volumetric ratio of 63.8%, reaction time of 129.3 min, stirrer speed of 450 rpm and reaction temperature of 65 degrees C.