Preparation of crystalline 4A zeolites
AssigneeLaviosa Rhone-Poulenc
InventorsDominique Bretaudeau, Francois Delprato, Marc Malassis
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Abstract
Crystalline 4A zeolites having high calcium ion exchange capacity, well adapted as builder materials for detergent compositions, are prepared by directly admixing an aqueous sodium silicate solution with a first aqueous sodium aluminate solution in a first reaction vessel to form a hydrogel therefrom, and transferring the hydrogel thus formed to a discrete crystallization zone and therein contacting such hydrogel with a crystallization-effecting amount of a second aqueous sodium aluminate solution to convert same into a crystalline 4A zeolite, and, advantageously, filtering, washing and optionally drying such crystalline 4A zeolite.
Claims23
A continuous process for the preparation of a crystalline 4A zeolite having a high exchange capacity for calcium ions, comprising directly mixing an aqueous sodium silicate solution at a temperature greater than ambient with a first volume of an aqueous sodium aluminate solution at a temperature greater than ambient into a non-stirred reactor, to form a hydrogel therefrom within about 60 seconds of mixing, and transferring said hydrogel to an open, stirred reactor into which has been introduced a second volume of said aqueous sodium aluminate solution at a temperature greater than ambient, to convert said hydrogel into said crystalline 4A zeolite;
- wherein the aqueous solutions of sodium silicate and sodium aluminate are continuously introduced into said non-stirred reactor at respective flow rates such that the ratio of the flow rate of aluminate solution to the flow rate of silicate solution ranges from about 4 to 8;
- and wherein said crystalline 4A zeolite has the following formula, expressed in molar fractions:
- x' SiO.sub.2 ;
- y' Al.sub.2 O.sub.3 ;
- z' Na.sub.2 O;
- t' H.sub.2 O
- where 1.5<x'/y'<3, 0.5<z'/y'<1.5, 3<t'/y'<6.
A continuous process for the preparation of a crystalline 4A zeolite having a high exchange capacity for calcium ions, comprising directly mixing an aqueous sodium silicate solution at a temperature greater than ambient with a first volume of an aqueous sodium aluminate solution at a temperature greater than ambient into a non-stirred reactor, to form a hydrogel therefrom, and transferring said hydrogel to an open, stirred reactor into which has been introduced a second volume of said aqueous sodium aluminate solution at a temperature greater than ambient, to convert said hydrogel into said crystalline 4A zeolite;
- wherein the aqueous solutions of sodium silicate and sodium aluminate are continuously introduced into said non-stirred reactor at respective flow rates such that the ratio of the flow rate of aluminate solution to the flow rate of silicate solution ranges from about 4 to 8;
- and wherein said crystalline 4A zeolite has the following formula, expressed in molar fractions:
- x' SiO.sub.2 ;
- y' Al.sub.2 O.sub.3 ;
- z' Na.sub.2 O;
- t' H.sub.2 O
- where 1.5<x'/y'<3, 0.5<z'/y'<1.5, 3<t'/y'<6.
Dependencies are inferred from the claim text.