An Efficient, Solvent-Free Process for Synthesizing Anhydrous MgCl₂

Abstract

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.

Molten Chloride Thermophysical Properties, Chemical Optimization, and Purification

“…1-4) and hydrolysis of anhydrous MgCl2 with the released H2O (Eqs. 5 and 6) form MgOHCl which have been reported by the literature [3,15,[49][50][51]16,17,29,31,39,41,42,48]. The temperature range after each reaction is a compilation of various reported values from the literature.…”

“…The insoluble particles were vacuum filtered through a 450-nm filter and weighed to calculate the mass fraction. 50 Based on similar mass measurements of insoluble particles in the entire volume of purified salt, including the sludge phase. 51 Investigation of MgO particle size and distribution seems to indicate that there is no significant difference in size distribution between particles in the sludge phase and the ones that can be present in the "clean" salt phase.…”

Synthesis, characterization and thermal behaviour of solid phases in the quasi-ternary system Mg(SCN)2–H2O–THF

“…Magnesium halides and pseudo-halides exhibit a great variety of chemical and structural properties and are used in many different applications, which is why they were extensively studied. [1][2][3][4][5] However, in the row of magnesium pseudo-halides, i.e. cyanides, cyanates, azides etc., the thiocyanates were often overseen, and only little chemical and structural knowledge is available for magnesium thiocyanates and their derivatives.…”

“…1,2,[26][27][28] The hexahydrate MgCl2 ⋅ 6 H2O is a commonly occurring mineral named bischofite and finds a diverse industrial usage. [1][2][3][4]29 Upon heating of MgCl2 hydrates different dehydration stages occur, however, the anhydrous state cannot simply be reached as the formation of oxychloride species prevails. 2,3,27 Solvent based methods or rather tedious thermochemical procedures are necessary to produce pure, anhydrous MgCl2.…”

“…[1][2][3][4]29 Upon heating of MgCl2 hydrates different dehydration stages occur, however, the anhydrous state cannot simply be reached as the formation of oxychloride species prevails. 2,3,27 Solvent based methods or rather tedious thermochemical procedures are necessary to produce pure, anhydrous MgCl2. 3 Besides the rich hydrate chemistry of MgCl2, it also forms different organometallic complexes, which are of great importance in organic chemistry (such as Grignard reagents or for Ziegler-Natta catalysis) [30][31][32][33] and have more recently even sparked interest in the battery community.…”