Porous aluminium silicates

In a sorption pump, the gas is trapped within the adsorbing material (zeolites or active charcoal) called molecular sieve. Zeolites are porous aluminium silicates which adsorb large amount of gas when cooled to low temperature (usually 77K). The pump is filled with zeolite and put in a bucket containing liquid nitrogen (see Fig. 1.11). 

Table 3.2-7 Properties of porous aluminium silicates and magnesium silicates according to DIN EN 60672 [2.6]...

Enzyme acrylamide matrix system entrapped in porous aluminium silicate particles... 

Si 4H CP/MAS-NMR, 27A1 and 23Na MQ/MAS-NMR studies have been made of amorphous aluminium silicates, to determine local atomic struc-tures. A1 MAS-NMR (together with some other nuclei) studies have been carried out on novel porous sodium aluminophosphate-silicate and sodium ammonium fluorophosphates silicate 340 an ordered hexagonal mesoporous silica material (JLU-30) 341 mesoporous Al-MSU-X aluminosilicate 342 cubic mesoporous aluminosilicate A1MB48 343 and mesoporous Al-SBA-15.344... 

C.400 alkaline earth alumino-silicates. C.500 porous aluminium and magnesium silicate. 

The EDX spectrum (Fig. 11.8) shows the main surface scale impurity peaks of silica, aluminium, sodium, chloride and iron. If this EDX is compared to that of a new, clean membrane surface (Fig. 11.9), the clean surface shows sulphur, carbon and oxygen, which is typical of a porous polysulphone support. It was concluded that the scale is amorphous, composed of aluminosilicate and silicate. These compounds are normally found in trace amounts in brine solutions. Analysis showed that the surface could be cleaned with hydrochloric acid and analysis of the dissolved scale was similar to the EDX spectrum analysis. Review of the plant operation determined that the precipitation was the result of high pH in combination with high silica concentrations in the brine. 

As well as occurring naturally, alumino-silicates are manufactured. Their structure is that of a framework of silicon, aluminium and oxygen atoms. If the framework contains water, then this may be driven off by heating, leaving a porous structure, access to which is controlled by windows of precise molecular dimensions. Larger molecules are excluded, hence the description molecular sieve as discussed in Chapter 17. 

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