Enhancing deoxygenation of waste cooking palm oil over CaO-MgO catalyst modified by K2O for green bio-fuel

Abstract

There are challenges to replacing traditional fossil fuels completely, so producing efficient green biofuels is crucial. In this work, waste cooking palm oil (WCPO) was used as raw material to produce biofuel through pyrolytic catalysis cracking (PCC) over alkaline catalysts as CaO-MgO with various dopants at 0, 3, 6 and 9 wt% K2O contents. The WCPO reacted under atmospheric pressure without purging gases at 500, 525 and 550 °C, respectively. Catalysts were characterized by various techniques in terms of physical and chemical properties. The pyrolytic oil (PO) was separated from the crude oil product. Then, PO was characterized by TGA/DTG, CHNO, FTIR and GC–MS. The PO was distilled following an ASTM D86 method. The properties of biofuels, such as density, kinematic viscosity and acidity, were measured. The basicity of the catalyst increased with increasing K2O contents. K2O not only enhanced the pyrolytic-liquid product yield but also significantly reduced the oxygenated compounds in biofuel through the deoxygenation process to improve biofuel quality. The different reaction temperatures were observed in which low-temperature reaction provided incompletely cracking heavy molecules, and more gas product occurred at the high reaction temperature. Surprisingly, the fatty acid compounds of WCPO were transferred to hydrocarbon compounds by deoxygenation reactions confirmed by GC–MS and FTIR results. The highest pyrolytic oil yield was approximately 92 vol% compared with crude oil product, obtained from 3 wt% K2O-MgO/CaO and 525 °C. The paraffinic and olefinic compounds were the main hydrocarbon products with K2O doping catalysts, while ketone compounds were found in all catalysts via the ketonic decarboxylation mechanism. In this condition, pyrolytic oil was completely distilled to get gasoline, kerosene and diesel. The kinematic viscosity and density were under ASTM standards except for acidity. Remarkably, the acidity of biofuel with K2O doping was reduced about 2–3 times compared to MgO/CaO alone.