Optimization and characterization studies on ecopolyol production from solvothermal acid-catalyzed liquefaction of sugar beet pulp using response surface methodology

The valorization of biomass has become extremely important for the polymer industry to struggle with the depletion of oil. Solvothermal liquefaction is one method where the biomass can be converted to a useful ecopolyol. However, the conventional liquefaction process causes losses of time, material, and energy. This study aims at optimizing the liquefaction process of sugar beet pulp (SBP) using a response surface methodology (RSM) based on central composite design (CCD), as well as giving detailed insights into the physicochemical properties of the obtained ecopolyols. The synthesized ecopolyols were analyzed in terms of hydroxyl number, acid number, viscosity, and water content, and their structural properties characterized using infrared spectroscopy and thermogravimetric analysis. It was determined that the reaction temperature and catalyst loading were more important parameters than the reaction time on the liquefaction yield (LY) according to the ANOVA results (95% confidence level). The optimum conditions of solvothermal liquefaction for SBP, confirming through validation experiments, were 4.25% catalyst loading, a reaction time of 70 min, and a reaction temperature of 170 degrees C, resulting in a LY of 95%. The results show that the effect of reaction temperature and catalyst loading on hydroxyl number is more dominant than the reaction time, the most determinant parameter of acid number is catalyst loading, and the most determinant parameter of viscosity is the reaction temperature. The ecopolyols produced under optimal conditions display similar characteristic features (a 29.9 +/- 1.1 mg KOH/g acid number, a 299.8 +/- 3.6 mg KOH/g hydroxyl number, a 643.8 +/- 23.7 cP viscosity at 25 degrees C, and a 2.1 +/- 0.5% water content) to those of petroleum-based polyols widely preferred in the industry of polyurethane foam.