Solar-Heated Sustainable Biodiesel Production from Waste Cooking Oil Using a Sonochemically Deposited SrO Catalyst on Microporous Activated Carbon

A novel catalyst, SrO on microporous activated carbon (SrO/C), was synthesized by sonochemical deposition of SrO on carbon. The SrO/C demonstrated high catalytic performance in solar-heated transesterification reactions of canola oil, soybean oil, and waste cooking oil (WCO). The catalytic activity increased more than 5-fold (corresponding to 81% less catalyst compared to pristine SrO), using soybean oil as a feedstock. Similar enhancement was also observed with canola oil and WCO, where the catalytic activity improved more than 4-fold, corresponding to 76% less catalyst compared to pristine SrO. A yield of 98.5 wt % fatty acid methyl esters (FAME) was obtained from WCO in 60 min using a 1:6 oil:methanol molar ratio and 7.1 wt % SrO/C catalyst (24% SrO loading) at 46°C (solar heating). The SrO/C catalyst was used for four consecutive transesterification reactions of WCO without any significant decrease in its catalytic activity (only 3% decrease in FAME yield and less than 5 ppm leaching). The results confirm the stability and sustained activity of the SrO/C catalyst, which is of great importance for industrial applications. The proposed method can significantly minimize the cost of biodiesel production by harnessing solar thermal energy. Performing the reaction without any additional energy consumption for heating, using a carbon-supported catalyst and low-cost feedstock, make the current biodiesel production a simple, economically worthwhile, environmentally-friendly, and industrially appealing process.