Production of molecular sieve adsorbents from kaolin minerals

摘要

Zeolites A, X or Y (see below) are produced by an improved process wherein the major source of aluminium oxides for zeolites X and Y, and the major sources of both aluminium and silicon oxides for zeolite A is provided by inclusion in the aqueous reaction mixture of a reactive kaolin-type clay rendered amorphous to X-ray diffraction by calcining for a period of at least 45 minutes at 600 DEG to 850 DEG C., digesting said aqueous reaction mixture for at least two hours and thereafter thermally treating at elevated temperature and under at least autogenous pressure until the crystals form. Additional silicon oxide may be provided by the inclusion of reactive silica, i.e. a soluble silicate or colloidial silica. Preferred digestion temperatures are in the range of 20 DEG to 55 DEG C. and crystallization temperatures from 75 DEG to 120 DEG C. Between 0.1 to 5 moles per mole of alumina, of a soluble alkali metal sulphate, phosphate, fluoride or chloride may be added to the reactant mixture, e.g. as in an example by the neutralization of excess sodium hydroxide by an appropriate acid or by the actual addition of the salt. A list of suitable kaolin-type minerals and their oxide compositions are provided. The Specification also contains novel oxide ratios. The examples also contain comparative data on the effect of varying the digestion period, outside the scope of the invention, on the product purity and an example wherein the digestion and crystallization are effected at identical temperatures. Specifications referred to in respect of Zeolites A, X and Y are 777,232, 777,233, 909,266, 972,831. Reference has been directed by the Comptroller to Specification 924,938.