Recent progress in separation strategies for upgrading bio-oil: mechanisms, challenges and a way forward

Due to the presence of high content of oxygenated compounds (aldehydes, alcohols, carboxylic acids, esters, ethers, furfurals, ketones, lignin-derived compounds, phenols, and sugars), bio-oil has inferior oil properties compared to petroleum-derived oils. This creates numerous technological challenges in downstream separation processes. The present study outlines recent research trends on various separation strategies for upgrading crude biogenic pyrolysis oil for the production of valuable commodities. The present study mainly focuses on the various separation strategies, such as column chromatography, distillation, membrane filtration, crystallization, solvent extraction, electrosorption, and fractional condensation with respect to principles of operation, efficiency, economy and environmental concerns. Phase separation using solvent and adsorbent was found to be the best separation strategy compared to others due to lower capital investment and energy expenditure. However, there are various technological challenges with separation strategies for scale-up in industries. A comparative analysis of various separation strategies with the application of various bio-oil fractions from aqueous phases of bio-oil is summarized to understand the possible pathways for utilization in various industries. A brief section on technoeconomic analysis with existing pilot and semi-pilot pyrolysis plants is presented to understand the economic feasibility of pyrolysis and upgrading strategies. In the end, a circular economy perspective of pyrolysis-separation and its integration with a machine learning model, are briefly outlined.