Highly efficient crystallization for sustainable azeotrope separation of formic acid-Water

Abstract

The cost-effective separation of azeotropes poses a shared challenge. In this work, we utilized a green technique: layer melt crystallization (LMC), to separate the formic acid and water. Characterized by the lower energy consumption and high selectivity, LMC is welcome in high-purity production preparation. Firstly, we discussed the effects of temperature, cooling and heat rates, and time on the separation performance. We discovered that temperatures were important in the solute distribution and impurity migration. Then, the stirring technique is coupled to optimize the separation performance. Under the optimal trajectory, the product purity exceeds 99.7%. Next, to better understand the crystallization process, several theoretical models are established to clarify the intrinsic correlations of process variables and target parameters. Kinetic models are established to clarify the crystal layer growth, and sweating melt flow with the temperature difference-based driving force. Interfacial solute distribution factor and mass transfer coefficient are introduced to give the solute distribution rule and impurity migration mechanisms. At last, a dimensionless number is used to evaluate the sweating intensity, and we also correlated this coefficient with the separation performance of LMC qualitatively. In conclusion, LMC provides a viable approach for separating azeotropes, and the proposed theoretical models can offer valuable support for crystallization design.