Production of Renewable Hydrocarbons from Thermal Conversion of Abietic Acid and Tall Oil Fatty Acids

Abstract

The primary objective of this study was to investigate the pyrolytic conversion of crude tall oil, a byproduct from the Kraft process in the pulping industry, to hydrocarbon products for use as renewable hydrocarbons and fuels. Abietic acid, the main resin acid in crude tall oil, and tall oil fatty acids, the main distillate fraction of crude tall oil, were pyrolyzed separately using a batch micro reactor at 370, 410, and 450 °C for 2 h. The gas and liquid reaction products were identified and quantified using gas chromatography equipped with a flame ionization detector, a thermal conductivity detector, and mass spectrometry. At all temperature regimes, the pyrolysis of abietic acid resulted in the formation of aromatic compounds characterized by up to three benzene rings. While the pyrolysis of tall oil fatty acids at lower temperatures resulted in alkanes and alkenes and negligible amounts of aromatic compounds, higher temperatures promoted the formation of relatively shorter chain alkanes and alkenes and detectable amounts of aromatics. The presence of both CO and CO2 in the gas fractions suggested that deoxygenation of the initial compounds proceeded through decarbonylation and decarboxylation, but the favored mechanism is dependent upon the structure of the initial substance. This work demonstrates the feasibility of producing renewable hydrocarbons through the pyrolysis of the fatty-acid-rich distillate fraction of crude tall oil.