Direct conversion of wet microalgae to levulinic acid via water-organic biphasic reaction system

Abstract

This work addresses the conversion of wet microalgae to levulinic acid (LA) using a one-pot reaction system. By utilizing moisture in microalgae, a biphasic system with an organic solvent of 1, 2-dichloroethane (DCE) is formed. This system enhances the LA yield by making an acidic environment through the decomposition of DCE in a small quantity and the recovery of products in each aqueous and organic phase. With lipid-rich Nannochloropsis gaditana and carbohydrate-rich Chlorella species, the effects of reaction variables of temperature, water content, and DCE dosage on the LA production were investigated. The LA yield of 30.13 wt% and 28.15 wt% based on mass of total hexose (43-47 w/w% of convertible carbohydrates) for the two types of microalgae at $160^\circ C$ while the yield of free fatty acids reaches 90.13 w/w% at $180^\circ C$ based on the esterifiable lipid. This biphasic system facilitates the forward reaction and the product recovery for concurrent reaction and separation.