CRYSTALLINE TYPE-A ZEOLITE MOLECULAR SIEVE AND A PROCESS FOR THE PRODUCTION THEREOF

摘要

The present invention provides a process of producing a crystalline type-A zeolite molecular sieve having the stoichiometric formula 1.0 : 0.2 M2.nO :Al2O3 : 1.85 : 0.5 SiO2 . y M2O, wherein M represents a metal cation, n represents the valency of the metal cation and y represents a number of up to 6, the molecular sieve being in the form of particles, at least 99.5% by weight of the particles having diameters smaller than 30 .mu.m and at least 90% by weight of the particles having diameters smaller than 10 .mu.m and 50% by weight of the particles having diameters below a value not exceeding 6.5 .mu.m, comprises admixing an aqueous alkali-silicate solution and a first aqueous alkali-aluminate liquor containing no more than 75% by weight of soluble Al2O3 . H2O to form a presynthesis mixture, allowing the presynthesis mixture to congeal so as to form a gel, adding a second aqueous alkali-aluminate liquor having a higher concentration of soluble Al2O3 . H2O than the first aqueous alkalialuminate liquor to said gel at a temperature between 10 and 100.degree.C while stirring to obtain a synthesis mixture and allowing the synthesis mixture to crystallize at a temperature between 20 and 175.degree.C, for at least 15 minutes.