An Efficient, Solvent-Free Process for Synthesizing Anhydrous MgCl2

A new efficient and solvent-free method for the synthesis of anhydrous MgCl 2 from its hexahydrate is presented. Fluidized dehydration of MgCl 2 ·6H 2 O feedstock at 200 °C in a porous bed reactor yields MgCl 2 ·nH 2 O (0 < n < 1), which has a similar diffraction pattern as activated MgCl 2 . The MgCl 2 ·nH 2 O is then ammoniated directly using liquefied NH 3 in the absence of solvent to form MgCl 2 ·6NH 3 . Calcination of the hexammoniate complex at 300 °C then yields anhydrous MgCl 2 . Both dehydration and deammoniation were thoroughly studied using in situ as well as ex situ characterization techniques. Specifically, a detailed understanding of the dehydration process was monitored by in situ PXRD and in situ FTIR techniques where formation of salt with nH 2 O (n = 4, 2, 1, <1) was characterized. Given the reduction in thermal energy required to produce dehydrated feedstock with this method compared with current strategies, significant cost benefits are expected. Overall, the combined effect of activation, macroporosity, and coordinated water depletion allows the formation of hexammoniate without using solvent, thus minimizing waste formation.