Solubility and antisolvent crystallization of lithium hydroxide monohydrate in various organic solvents

Abstract

The effect of various organic antisolvents on the solubility of lithium hydroxide monohydrate (LiOH·H₂O) in water was systematically determined in order to obtain composition data for lithium hydroxide – water – antisolvent ternary systems. Based on these data, antisolvent crystallization of LiOH·H₂O from a synthetic aqueous feed solution was investigated. A total of nine antisolvents were studied, including methanol, ethanol, acetone, 1-propanol, 2-propanol, 1,4-dioxane, 1,2-dimethoxyethane, acetonitrile and tetrahydrofuran (THF). LiOH·H₂O showed high solubility in methanol and ethanol, and low solubility in 2-propanol, 1,4-dioxane and 1,2-dimethoxyethane aqueous solutions. The use of THF resulted in the formation of two liquid phases in all cases, while acetonitrile and 1-propanol also led to liquid phase separation at lower antisolvent mole fractions. In the acetone system, solvent decomposition was confirmed by ¹H NMR, revealing aldol condensation. Crystallization of LiOH·H₂O was confirmed for all antisolvents by X-ray diffraction (XRD) and thermogravimetric analysis (TGA). Among the tested solvents, 2-propanol was selected as the most promising antisolvent due to its favorable solubility behavior, environmental and human health profile, safety, and lower cost compared to 1,4-dioxane and 1,2-dimethoxyethane.