Production of levulinic acid from wet microalgae in a biphasic one-pot reaction process
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pISSN: 0256-1115 eISSN: 1975-7220
INVITED REVIEW PAPER
INVITED REVIEW PAPER
Production of levulinic acid from wet microalgae in a biphasic one-pot reaction process Minji Kim, Jeongwoo Yang, Bora Kim, and Jae W. Lee† Department of Chemical and Biomolecular Engineering, KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Korea (Received 8 April 2020 • Revised 15 June 2020 • Accepted 30 June 2020) AbstractThis work addresses the conversion of wet microalgae to levulinic acid (LA) using a one-pot reaction system. Utilizing moisture in microalgae forms 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 was 30.13 wt% and 28.15 wt% based on the mass of total hexoses (43-47 wt% of convertible hexoses) for the two types of microalgae at 160 oC, while the yield of free fatty acids reached 90.13 w/w% at 180 oC based on the esterifiable lipid. This biphasic system facilitates the forward reaction and the product recovery for concurrent reaction and separation. Keywords: Microalgae, Levulinic Acid (LA), Biphasic System, One-pot Reaction
hydrolysis of carbohydrates. Therefore, a pretreatment step is required for weakening bonds between hemicellulose and lignin or removing lignin, for making easier hydrolysis of hemicellulose to monomers [24,25]. However, this step inevitably employs a solvent and an acid catalyst, thereby increasing costs [26,27]. Marine biomass has an advantage of a negligible portion of lignin and thus a pretreatment step is unnecessary for the LA production [28]. Several articles have reported conversion of LA from macroalgae utilizing this advantage [29,30]. However, even if a chemical conversion route from microalgae was proposed for the production of ethyl levulinate, an ethanol-esterified form of LA, as a byproduct in biodiesel production [31-32], LA production utilizing microalgae which has both lipid and carbohydrate has rarely been studied. A well-known mechanism of LA production is acid hydrolysis of carbohydrates. C6 sugars, mainly glucose, are isomerized to fructose which is converted to 5-hydroxymethylfurfural (5-HMF), a dehydrated intermediate product. The intermediate is converted to LA by rehydration. Theoretically, the maximum yield of LA from totally converted glucose is 64.5 wt% [33]. However, the LA yield commonly reaches about 66% of the theoretical yield because of a side reaction causing the formation of humin [34,35]. Therefore, many studies have been carried out to obtain a high yield of LA by using various types of catalysts. Mineral acid catalysts such as hydrochloric acid, sulfuric acid, and phosphoric acid have high catalytic activity and thus are conventional
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