610 / 2019-01-20 14:29:50

Investigation on thermal degradation of waste cooking oil through TG-FTIR and Py–GC/MS

waste cooking oil, thermal degradation, mechanism, decarboxylation

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Renewable energy sources are being considered as an effective solution for overcoming the energy needs and reducing environmental issues. Waste cooking oil has been considered as a type of a renewable energy resource. Highly corrosive waste cooking oil exhibits high viscosity and strong acidity, and it cannot be used directly as fuels or chemicals. Rapid pyrolysis provides an alternative way for converting waste cooking oil into renewable fuels and chemicals. In the present work, the thermal degradation properties of waste cooking oil were investigated by a combination of thermogravimetry-Fourier transform infrared spectroscopy (TG–FTIR) and pyrolysis-gas chromatography/mass spectrometry (Py–CG/MS) analyses. The multichannel pathways of waste cooking oil thermal degradation and radical-related evolution mechanisms of the pyrolysis products were speculated. TG-FTIR analysis was conducted to reveal the yield profiles of evolved gaseous species and functional groups, and Py-GC/MS analysis was employed to determine the components of the volatile products obtained from the rapid pyrolysis of waste cooking oil. The results revealed that the thermal degradation process of waste cooking oil is divided into three stages, viz. (a) the decomposition mainly focus on the fission of the C-O bond between the glycerol backbone and fatty acid chain of triglycerides in waste cooking oil in the temperature range of 200~360°C, associated with the production of RCOO·, esters and glycerol. (b) the decomposition of RCOO· radical with the fission of the α, β-C bond and decarboxylation, with CO2, alkanes, alkenes, and fatty acids as the main products, which are released between 380°C and 500°C; (c) at temperatures of greater than 500 °C, the main products involved in the thermal degradation process are CO2, aromatics, alkenes, and alkanes. The Py-GC/MS analysis of waste cooking oil under Helium atmosphere revealed the presence of >60 compounds that were classified as fatty acids, alkenes and alkanes. The major reactions occurring during the thermal degradation of waste cooking oil consist of the C-O bond fission, the decarboxylation of the RCOO· radical, elimination of ethylene, and Diels-Alder reaction.