GB1035644A - Improvements relating to the preparation of synthetic crystalline zeolites - Google Patents

Abstract

A zeolite of formula Na2O.Al2O3.2SiO2.nH2O (where n is 0-8) and pore size 4.5 <\>rA, designated Z-12L-Na, is prepared by ageing a reaction mixture, of composition such that Na2O/Al2O3 is 0.84 to 3.1, SiO2/Al2O3 is 0.88 to 1.8, and H2O/Na2O is 6.4 to 25, at 20-60 DEG C. for at least 2 hours (up to e.g. 72 hrs.), then heating at elevated temperatures, e.g. at 50-120 DEG C., until the zeolite crystallizes and is recovered. Material used may be a mixture of the oxides Na2O, Al2O3, SiO2 and H2O, or of materials whose compositions are mixtures of such, e.g. sodium silicate, sodium aluminate, or alumina; or may be clay, e.g. kaolin or halloysite, precalcined at 500-900 DEG C. for 2-18 hrs. and treated with NaOH solution containing 3.8 to 13.5% Na2O such that there are 0.7 to 2.6 parts calcined clay and 6.4 to 25 parts H2O per part Na2O. The wet zeolite may be activated by heating at 350 DEG C. for a few hours, or converted to Z-12L-Ca, of pore size 5.5 <\>rA, by treating with CaCl2. The preparation of Z-12-Na, of pore size 4 <\>rA, is also described, in which the ageing step is omitted. The two Na zeolites have similar X-ray diffraction patterns, but Z-12L-Na will absorb CHClF2 (molecular diameter 4.0 <\>rA) whereas Z-12-Na will not.