In situ transesterification of Chlorella alga was investigated at 60 and 100 °C using sulfuric acid as a catalyst under excess of methanol. The FAME yield, 96–98% of theoretical level was obtained with 20 wt% sulfuric acid within 4 h, whereas lower sulfuric concentrations gave much lower FAME yields. It should, however, be pointed out, that the large amount of sulfuric acid used in in situ transesterification is not economically feasible and more research is required for further process optimization. Since Chlorella alga contained also substantial amounts of free fatty acids, acid catalyzed transesterification is preferred instead of base catalysts causing soap formation. The ester content of biodiesel was adequate for the biodiesel standard. The biodiesel was purified via adsorption of chlorophylls and carotenoids onto a clay. The purified biodiesel was characterized by several methods. The biodiesel contained 54% polyunsaturated FAMEs as well as 33 wt% saturated and 9.5 wt% monounsaturated FAMEs. Due to high content of polyunsaturated FAMEs the oxidative stability was lower than that for soybean biodiesel. The residual biomass after transesterification contained sugars and proteins. The former one could be transformed to furanic compounds.
Due to the fact that biodiesel is not fully compatible with current motor technology, the hydrodeoxygenation of biodiesel was also demonstrated over Pd/C and Ni–HY-80 catalyst. The main products were fatty acids over Pd/C catalyst giving only 40% conversion within 390 min. Nickel based catalyst was superior to produce hydrocarbons compared the Pd/C catalyst, since more than 95% yield of hydrocarbons was achieved within 250 min at 300 °C under 30 bar.