Understanding and Managing Phase Instability and Aging Reactions of Coalgae Pyrolysis Oils

South Africa greatly suffers from the accumulation of waste coal fines due to its heavy reliance on coal mining. The processing of pyrolysis oil ensures the beneficiation of waste coal fines to provide alternative sustainable fuels. However, phase separation and aging reactions affect the stability of the pyrolysis oils negatively, affecting their processing and the product yields and quality. Understanding and managing the stability of Coalgae pyrolysis oil remain gaps to resolving this issue, and as such, systematic time-course monitoring of Coalgae pyrolysis oils was considered. Phase separation by decanting, nitrogen purging to eliminate the oxidative environment, hydrogen purging to investigate a reducing protic environment, and adsorptive treatment to eliminate coordinating species were used to distinguish possible reactions. The rate and extent of aging reactions were reduced by bubbling the separated phases of pyrolysis oil with nitrogen gas, thereby limiting the interphase and autoxidation reactions. Furthermore, a 22.7% reduction in water content and over 9 MPa·s in P2 viscosity were observed. The use of hydrogen in pyrolysis oils resulted in gum formation and increased viscosity via promotion of condensation reactions. FT-IR, GC-MS, and NMR analyses hinted that oxygenates (phenols and carbonyls) play a major role in phase separation and aging of pyrolysis oil. The use of the in-house adsorbent prevented phase separation by removing oxygenates and resulted in a 62.4% decrease in the water content. The study revealed that removing reactive compounds, such as oxygenates, has a greater effect on managing phase separation and aging in coal-based pyrolysis oil, allowing better handling for further processing.