Sasol has been engaged in the production of high-purity aluminas and alumina hydrates with customised physical characteristics for more than five decades.
The development of doped aluminas and mixed oxides led to a further diversification of our product portfolio with an even higher level of optimization for final use.
The combination of dopants and doping technologies is another important step towards support materials with well-defined phase composition leading to improved properties like thermostability and acidity.
Silica-aluminas exhibit a higher degree of acidity than pure aluminas. The hydrates are sold under the trade name SIRAL and the corresponding oxides as SIRALOX.
Mg / Al mixed hydroxides and oxides exhibiting more basic surface sites are indispensable support materials for diverse applications. These materials are sold as PURAL MG and PURALOX MG.
Besides the formation of mixed oxides, also the addition of other elements to the pure alumina, silica-alumina or mixed Al / Mg oxides and hydroxides is a facile way to further improve the properties of the corresponding starting materials for several applications.
For example, lanthanum-doped aluminas exhibit a much higher thermostability in comparison to the non-doped counterparts.
SIRAL / SIRALOX
Silica-alumina hydrates (SIRAL) and the corresponding oxides (SIRALOX) exhibit characteristics which differ significantly from pure aluminas.
One of the key properties of silica-aluminas is their comparatively high level of surface acidity, making them useful catalyst support materials, for example in the field of refinery catalyst or in diesel-engine applications.
The concentration and type of acidic sites (Lewis-acidic sites versus Bronsted-acidic sites) present in the materials strongly depends on Al2O3 / SiO2 ratio.
In general, the total acidity is governed by the Lewis-acidic sites. The highest concentration of Lewis-acidic sites is observed for SIRAL 5, while the highest amount of Bronsted-acidic sites is found in SIRAL 30 and SIRAL 40.
The more recently developed SIRAL HPV series provides even higher acidity and exhibits a larger pore volume.
PURAL MG / PURALOX MG
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 also 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.
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. Additionally, it is now possible to obtain hydrotalcites with a purity and controlled anion content that were previously unavailable.
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