Continuous deoxygenation of triglycerides on solid catalysts

In times of declining oil reserves and rising fuel prices research focuses on new processes to produce chemicals and fuels from renewable resources (e.g. triglycerides). Biofuels are an alternative, with biodiesel (fatty acid methyl esters) being used most. Besides its ecological advantages, biodiesel has some drawbacks such as limited durability, corrosion and formation of deposits in car engines, and a lower specific energy content. This is due to the residual oxygen, and removal of oxygen could minimize the above-mentioned disadvantages and allow upgrading of biodiesel. One possible route for deoxygenation of triglycerides is the conversion to alkanes with hydrogen on noble metal catalysts [1]. However, an additional hydrogen supply reduces economical attractivity of the process. Experiments with autoclaves at LIKAT proved that a partial deoxygenation of triglycerides in the presence of basic oxides is possible. In the presented work, the continuous deoxygenation of sunflower oil in the presence of basic and acidic catalysts was investigated.
The catalysts used are basic and acidic oxides and basic carbonates. By pressing, crushing and sieving a particle size fraction from 400 to 500 µm was obtained, which was tested in a glass tube reactor together with SiO2 as inert diluent material. The catalyst screening was carried out with nitrogen in feed at 400 °C, a GHSV of 1200 h-1 and a test time of 5 hours. In further tests, the influence of temperature, contact time and the time of operation were investigated.
By means of GC-MS analysis mainly hexacosadien, decanoic acid, C17- and C18-hydrocarbons and other by-products were identified. The formation of hexacosadien, decanoic acid and C18-hydrocarbons runs via a radical mechanism [2]. The C17-hydrocarbons were formed per direct deoxygenation. The best results were obtained for K2CO3 and Cs2CO3. Applying these catalysts, GC-MS and NMR analyses proved the absence of organic acids and oxygenated compounds in the liquid products. It was found during the study of temperature dependence that the radical mechanism is being suppressed with increasing temperature. At the same time, an increase in the yield of C17-hydrocarbons was observed. A long-term experiment over 24 hours revealed that for catalyst K2CO3 no change in product distribution with time and particularly no formation of oxygen-containing molecules occurred.

[1] Mathias Snåre, Iva Kubiková, Päivi Mäki-Arvela, Kari Eränen, and Dmitry Yu. Murzin, Ind. Eng. Chem. Res. 2006 (45) 5708.
[2] A. K. Sen Gupta, Fette Seifen Anstrichmittel 1966 (68) 475.