Process for preparing zeolite powder of type A (IV)

摘要

There are produced crystalline zeolite powders of Type A with the composition 1.0+/-0.2 M2/nO:Al2O3:1.85+/-0.5 SiO2.y H2O where M is a metal cation, n is its valence and y has a value up to 6 with 50 weight % of the particles not over 4.9 mu and with a particle spectrum -Fraction ( mu ) Portion (weight %) - <3 10 to 60 - <5 55 to 95 -<10 93 to 99 -<15 96 to 100 - by hydrothermally crystallizing a SiO2, Al2O3, Na2O and water containing alkali aluminate, water, silicate synthesis mixture with an optional tempering step wherein in a given case during the crystallization or tempering step instead of stirring shearing forces are employed. The process comprises mixing with stirring (1) an aqueous alkali silicate solution and (2) an aqueous sodium hydroxide with a NaOH content of 0.1 to 500 grams/l and/or (3) aqueous sodium aluminate liquor which contains 0.1 to 100 grams/l of Al2O3 and 1 to 200 grams/l of Na2O, one of components (1) and (2) or (3) being present in a container and the other being added thereto while preventing for a time of 10 to 30 minutes the formation of an insoluble gel having an SiO2/Al2O3 ratio of from 2 to 50:1, adding with stirring an aqueous sodium aluminate which contains 10 to 200 grams/l of Al2O3 and 10 to 250 grams/l of Na2O and having a temperature of 10 DEG to 100 DEG C. and allowing the thus obtained synthesis mixture to crystallize at a temperature within between 20 DEG and 175 DEG C. inside at least 15 minutes.