| 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 SiO2xy 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 4.0 mu and with a particle spectrum -Fraction ( mu ) Portion (weight %) -<3 35 to 60 -<5 82 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 optionally a tempering step wherein in a given case during the crystallization or tempering step instead of stirring shearing forces are employed. The process comprises providing an aqueous alkali silicate soluton, heating it to a temperature between 30 DEG and 80 DEG C., adding to the alkali silicate solution with stirring aqueous sodium aluminate having a content of 0.1 to 100 grams Al2O3/l and 1 to 200 grams Na2O/l and which had been pre-warmed to from 30 DEG to 100 DEG C. until the turbidity point of the reaction mixture within 10 to 60 minutes, adding with stirring to the turbid reaction mixture which had the composition SiO2/Al2O3=2 to 50:1, Na2O/SiO2=0.2 to 20:1 and H2O/Na2O=4 to 300:1 an aqueous sodium aluminate which contains 10 to 200 grams/l of Al2O3 and 10 to 250 grams/l of Na2O 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. in at least 15 minutes.
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