Basic magnesium carbonate calcination

Recently, the influence of the preparation method of various MgO samples on their catalytic activity in the MPV reaction of cyclohexanone with 2-propanol has been reported 202). The oxides were prepared by various synthetic procedures including calcination of commercially available magnesium hydroxide and magnesium carbonate calcination of magnesium hydroxides obtained from magnesium nitrate and magnesium sulfate sol-gel synthesis and precipitation by decomposition of urea. It was concluded that the efficiency of the catalytic hydrogen transfer process was directly related to the number of basic sites in the solid. Thus, the MgO (MgO-2 sample in Table IV) prepared by hydration and subsequent calcination of a MgO sample that had been obtained from commercially available Mg(OH)2 was the most basic and the most active for the MPV process, and the MgO samples with similar populations of basic sites exhibited similar activities (Table IV). 

Fig. 2. Pseudomorphic MgO (550°C calcine) from A.R. basic magnesium carbonate showing lightly interjoined plate-like crystallites.

Fig. 3. MgO from A.R. basic magnesium carbonate (700°C calcine) showing two-dimensional moire pattern from overlapped crystallites.

Reference to Table I shows that while the A. R. basic magnesium carbonate has some reasonable claim to purity, the technical grade material is distinctly inferior on the basis of the limited data available, particularly in respect to the levels of lime, soda, and foreign anion species. Thus the A. R. basic carbonate has been used almost exclusively in the present investigation, but some earlier observations on the lightly calcined technical grade material are relevant to the issue of the influence of impurities. Figure 12 depicts a pseudomorph obtained by calcination at 550°C for 1 hr reminiscent of Fig. 2, which illustrated the pseudomorphed condition of the A. R. material when... 

After addition of the acetaldehyde solution is complete, the product is decomposed by pouring the reaction mixture on to 2 kg. of cracked ice. The excess magnesium may be removed conveniently by decantation at this point. The basic magnesium halide is dissolved by addition of about 11. of 15 per cent sulfuric acid. The ether solution is separated, and the aqueous layer is extracted with four 150-cc. portions of ether. The ether solutions are combined, dried over 25 g. of calcined potassium carbonate, filtered and fractionally distilled, using a short column. The methyl isopropyl carbinol distils at no-ni.50. The fraction boiling 37 -1090 should be dried and refractionated. The total yield is 210-215 g. (53-54 per cent of the theoretical amount) (Note 7). 

The quality of magnesium oxychloride cements is highly dependent on the reactivity of the magnesium oxide used in their preparation. Typically, such oxides are prepared by calcination of the basic carbonate (Eubank, 1951 Harper, 1967), but their reactivity varies according to the conditions under which such calcination is carried out. As the reactivity alters so does the amount of oxide that can be incorporated into a cement relative to the amount of aqueous MgClj (Harper, 1967). 

Fig. 1. MgO prepared from (a) buring magnesium ribbon and collecting the residue, (b) decomposition of magnesium hydroxide and calcining at 800°C, (c) decomposition of magnesium basic carbonate and calcining at 800°C, and (d) decomposition of magnesium basic carbonate and calcining at 1100°C. Reproduced from Ret (8).

Light Magnesia. A form of magnesium oxide normally made by extraction from sea-water (see sea-water magnesia) the precipitated hydrate is subsequently purified by conversion to the carbonate which is then calcined at approx. 800°C. The bulk density is 0.1. On exposure to the air it takes up water and COj to form a basic carbonate. Light magnesia finds use as a heat insulator and as a source of magnesia in various chemical processes. 

---