The collected and refined know-how to produce alumina hydrates via the sol-gel technique is used by Sasol to prepare other inorganic oxides or mixed oxides. The properties of these inorganic specialty materials are leading Sasol into new, interesting fields of research and application. One of these specialties is the hydrotalcite family (aluminium-magnesium compounds) which is obtained by hydrolysis of mixed alcoholates.
Compared to alumina hydrates, hydrotalcites are even more alkaline in nature. Basicity is adjustable by increasing the Mg/Al ratio and/or incorporating anions other than OH-. Hydrotalcites have a double-layered metal hydroxide structure. The layers consist of magnesium and aluminium hydroxide octahedra sharing edges. Additional interstitial anions between the layers compensate the charge of the crystal and determine the size of the interlayer distance (basal spacing).
While hydrotalcites are accessible through the corresponding metal salts, the metal alcoholate route, patented by Sasol, has advantages over other synthesis routes. Most important is that the Al/Mg ratio can be varied over a wide range. In addition, it is now possible to obtain hydrotalcites with a purity and a controlled anion content that have to date been unavailable.
The calcined version PURALOX MG 28 consists of the spinel phase MgAl2O4. This oxide is another attractive catalyst support material for applications which require a lower degree of surface acidity than obtained in pure alumina. The advantage of PURALOX MG 28 is its high surface area of 100 m2/g in combination with its high phase purity. Also versions with an excess of Al2O3 (PURALOX MG 20) or MgO (PURALOX MG 30) are available.