Pyrolysis of polyunsaturated fatty acids

• Thermal cracking of linoleic acid was used to produce renewable hydrocarbons.
• Deoxygenation proceeded through both decarbonylation and decarboxylation.
• Presence of double bonds in linoleic acid promoted cracking at the beta position.
• There was predominance of C6 to C10 hydrocarbon and C9 to C10 fatty acids.
• Two new cycloalkanes and alkenes series were observed for the first time.

The primary goal of this work was to study the thermal conversion of polyunsaturated fatty acids to hydrocarbon for use as renewable chemicals and fuels. Linoleic acid (cis,cis-9,12-octadecedienoic acid) was selected as a model polyunsaturated fatty acid. Batch pyrolysis reactions were conducted at temperatures from 350 to 450 °C for 0.5 to 8 h reaction times. Gas chromatography and mass spectrometry were used to analyze and identify products in the gas and liquid product fractions. Analysis of the gas phase showed concurrent production of CO and CO2, indicating that deoxygenation reaction proceeded through both decarbonylation and decarboxylation mechanisms. The gas product encompassed alkanes and alkenes with carbon numbers ranging C1–C5 with ethane and propane as the major products. Analysis of the liquid fraction revealed series of n-alkanes, alkenes, cyclic alkanes and alkenes, and fatty acids. The presence of the unsaturation resulted in cracking at the allylic CC and predominance of C6 to C10 hydrocarbons and C9 and C10 fatty acids. This work uncovers the dominant reaction pathways in the pyrolysis of free polyunsaturated fatty acids and demonstrates the viability of this pyrolysis to produce renewable hydrocarbons immediately compatible with the existing petrochemical infrastructure.