High-Yield and High-Titer Production of Levulinic Acid from Red Macroalgae via Sulfuric Acid-Catalyzed Hydrolysis: Optimization by Response Surface Methodology and Application to Actual Biomass

Abstract

Levulinic acid (LA) is a versatile bio-based platform chemical with wide-ranging applications in biofuels, solvents, and biodegradable materials. To establish an efficient LA production strategy, red macroalgae were selected as the biomass feedstock due to their high carbohydrate content—particularly galactan, which is rich in 3,6-anhydro-L-galactose (AHG), a sugar that readily converts to LA under acidic conditions. In this study, a response surface methodology (RSM) based on a Box–Behnken design was used to optimize LA production from agar, the primary polysaccharide in red algae. The RSM model predicted an optimum of 172.5°C, 67.4 min, 8% H2SO4, with a predicted LA yield of 32.45%, and independent experimental validation under these conditions resulted in an LA yield of 33.23%. The validated reaction conditions were subsequently applied to two species of red macroalgae, Gracilaria verrucosa and Gelidium amansii. At 1% (w/v) biomass loading, carbohydrate-based LA yields of 52.9% and 48.4% were obtained, with corresponding titers of 3.1 and 3.0 g/L, respectively. Increasing the biomass loading to 25% (w/v) increased the LA titers to 49.8 and 48.6 g/L, while the corresponding carbohydrate-based yields decreased to 34.6% and 31.3%, respectively. These findings highlight the potential of high-solids processing as a practical approach for LA production from marine biomass and provide a basis for further process development toward sustainable biorefinery applications.