Experimental perspective for reactive separation of malonic acid using TBP in natural non-toxic solvents

Abstract Recent technological advancement allows the synthesis of malonic acid from the bio-fermentation route by using cost-effective raw material like biomass, which enhances its overall production. The dilute aqueous stream of malonic acid produced from the biological route needs to be recovered. Process intensification with precise operating conditions and low toxicity such as reactive separation is applied for extraction of malonic acid from the dilute aqueous stream by using non-toxic natural solvents like canola oil, sunflower oil, and soybean oil with the tributyl phosphate (TBP) extractant. An in-depth experimental analysis is performed in the present study to evaluate extraction complexation equilibrium constant (KE(MA)), extraction efficiency (E(MA)%), distribution coefficient (KD(MA)), and loading ratio (Z(MA)). The overall loading ratio is less than 0.5 for all solvents, which signifies the formation of 1:1 complexation. KD(MA) and E(MA)% with soybean oil are in range of 0.265 - 0.832, and 20.683 - 43.850, for sunflower oil is 0.208 - 0.763 and 17.227 to 42.340, for canola oil is 0.301 to 0.875 and 22.878 to 45.106. The behavior of TBP-malonic acid complexation equilibrium in the reactive separation process is predicted by comparing relative basicity model values with experimental outputs. The separation process requires a continuous column operation, and the number of transfer stages is evaluated to be 2. Furthermore, the diffusion coefficients (D(MA)) of malonic acid to the natural, non-toxic solvents with variable TBP concentrations are evaluated by employing various empirical correlations. The present study paves the way for future research in continuous in-situ product recovery of malonic acid produced via biological route.