Catalytic aqueous hydrodeoxygenation of palmitic acid with in-situ hydrogen donor

Abstract

Algal bio-oil obtained from hydrothermal liquefaction of algae contains a large amount of water and long-chain fatty acids. High acidity and corrosiveness seriously restrict the application of algal bio-oil. The aqueous-phase catalytic upgrading was a promising approach to solve this problem, and the hydrogen donor was one of the most important parameters to the conversion of the algal bio-oil and the quality of the products. Catalytic transfer hydrogenation (CTH) reaction was an efficient, economical and green method for hydrogenation reaction, which can directly transfer hydrogen from the hydrogen donor to the reaction substrate. In this work, the CTH reaction of algal bio-oil model compound palmitic acid was investigated to deal with the problem of high oxygen content in the algal bio-oil. Several common hydrogen donors, included methanol, ethanol, formic acid, and isopropanol, as well as different reaction conditions were experimented to study the CTH process of palmitic acid. The results showed that, with the reaction conditions of 350 °C and 10 h, formic acid achieved the best oxygen removal, carbon retention and energy efficiency, the C16 selectivity reached the highest at 33.3 % as the formic acid addition ratio was 1:2, and the C15 selectivity reached the highest at 48.3 % as the formic acid addition ratio was 1:3. In general, the best ratio of formic acid added was 1:3, which showed the highest yield of C15 and above alkanes of 79.6 %. This result indicates that the catalytic transfer hydrogenation reaction of formic acid has practical value in improving the combustion performance of algal bio-oil.