Lewis acid-catalyzed in situ transesterification/esterification of microalgae in supercritical ethanol

The activities of several Lewis acid catalysts such SnCl 2 , FeCl 3 , ZnCl 2 , AlCl 3 , and NbCl 5 for the in situ transesterification/esterification of lipid contained within a microalga ( Chlorella pyrenoidosa ) in ethanol at 350   °C were examined to identify the most suitable catalyst in term of crude biodiesel (CBD) yield. Of those catalysts tested, ZnCl 2 showed the highest performance toward the CBD production. Using ZnCl 2 as catalyst, effects of reaction temperature (200–370   °C), time (0–120   min), ethanol to microalga ratio (EtOH:MA) (5/5–40/5), catalyst loading (0–30   wt.%), and algae moisture (0–80   wt.%) on the yields of product fractions and the properties of CBD were studied. The presence of ZnCl 2 not only promoted the production of CBD but also showed activities toward the deoxygenation and denitrogenation of CBD. The moisture content in the starting material is the most influential factor affecting the yield and properties of CBD.