Chemistry of inorganic compounds – Zeolite – Seed used
Reexamination Certificate
1994-08-10
2002-07-02
Griffin, Walter D. (Department: 1764)
Chemistry of inorganic compounds
Zeolite
Seed used
C423S710000, C423S328100, C423S332000, C423S333000, C423S334000, C502S064000
Reexamination Certificate
active
06413493
ABSTRACT:
FIELD OF THE INVENTION
The invention describes the preparation of alkali metal aluminosilicates, in particular crystalline aluminosilicates having,the P-structure. These materials are of value as a component in detergent formulations in which they remove calcium and magnesium hardness ions by ion exchange. They also have other properties which provide additional benefits when used in detergent formulations. These aluminosilicates will be referred to as zeolite P in this description.
BACKGROUND OF THE INVENTION
While the utility of zeolite P in detergent formulations has been acknowledged, for example in European Patent Application 0384070 (Unilever), they must be manufactured by a commercially effective process in order to become available on the market place. Thus, while the properties of a material may make it a useful commercial commodity, its manufacture has to be optimised for large scale production.
The zeolite P class includes a series of synthetic zeolite phases which may be in cubic configuration (also termed B or P
c
) or tetragonal configuration (also termed P
1
) but is not limited to these forms. The structure and characteristics of the zeolite P class are given in “Zeolite Molecular Sieves” of Donald W Breck (published 1974 and 1984 by Robert E Krieger of Fla. USA). The zeolite P class has the typical oxide formula:
M
2
n
O
·
Al
2
O
3
·
1.80
-
5.00
SiO
2
·
5
H
2
O
The present invention provides a process for preparing crystalline P-zeolites having Si:A1 ratios from 0.9 to 1.33, which are particularly effective as detergent builders, preferably ratios of 1.15:1 and below and more preferably 1.07:1 and below.
M is an n-valent cation which for this invention is an alkali-metal, that is lithium, potassium, sodium, caesium or rubidium with sodium and potassium being preferred and sodium being the cation normally used in commercial processes.
Thus sodium may be present as the major cation with another alkali metal present in a minor proportion to provide a specific benefit.
The process of the present invention allows the production of P-zeolite with the above defined ratios at economic yield. During the formation of the crystalline zeolite the reacted medium passes through a gel stage. A preferred embodiment of the invention is the production of P-zeolites at a silicon:aluminium molar ratio of 1.00±0.05 from a synthesis gel with the same compositional ratio.
This feature results in the desired product and a filtrate liquor containing essentially only sodium hydroxide. This liquor can be recirculated, after optional concentration, e.g. by evaporation, to the preparation of the initial reactant solutions. Another advantage of producing P-zeolites from a synthesis gel with the same silicon:aliminium ratio is that all the sodium silicate and the sodium aluminate are used thus optimising the consumption of the starting material.
Moreover, for detergents applications there is a need for a product with high oil absorption.
GENERAL DESCRIPTION OF THE INVENTION
It is a first object of the present invention to provide a process for the preparation of P zeolite having the oxide formula
M
2
n
O
·
Al
2
O
3
·
(
1.80
-
2.66
)
SiO
2
·
y
H
2
O
wherein y is the water content,
i. a sodium aluminate solution at a temperature of at least 25° C. is mixed with a sodium silicate solution and a temperature of at least 25° C. in an adequately vigorously stirred vessel in the presence of an effective amount of a slurry of P zeolite seed to form a gel having the composition,
Al
2
0
3
: (1.00-3.5)SiO
2
: (1.2-7.5)Na
3
O.
(25 to 450) (preferably 40 to 150) H
2
O
ii. ageing the gel at a temperature above about 25° C. with adequate vigorous stirring to maintain solids in suspension for a period of at least about 0.1 hours, and
iii. separating the P zeolite product, washing and drying.
The product is washed in order to remove excess electrolytes such as caustic.
The sources of the seed zeolite P is not critical, although preferably it is added to the reactants as a previously prepared slurry. Alternatively a crystallised slurry from a previous reaction may be used. Additionally the ratio of the P-zeolite seed is not critical and a P-zeolite having a Si:Al ratio above 1.33 can be used.
That is to say the seed crystalline form drives the reaction to the P-form and the product ratio is attained from the gel ratio of the reactants. The processes of the invention can be operated at the scale required for commercial activities.
The ratios and concentrations of the aluminates and silicates used are not critical, but must be known to allow calculation of the gel and product compositions. The temperatures used will usually be well above the minimum temperature of 25° C. and are preferably above about 60° C. The gel composition will preferably contain about 40 to 150 moles of water per mole alumina.
The range of the silicon:aluminium ratio of the gel is wider than the corresponding ratio of the product since the silicon:aluminium ratio of the product is always between 2 and the corresponding ratio of the gel.
The period for ageing the gel to form the product zeolite is dependent on composition and temperature and will preferably be complete in about 10 hours, although the process will more preferably be completed within 5 hours for a commercial process.
Since it is particularly advantageous to produce P-zeolites at a silicon:aluminium molar ratio of 1.00±0.05 from a synthesis gel with the same compositional ratio, it is a second object of the present invention to provide a process for the preparation of P zeolite having the oxide formula
M
2
n
O
·
Al
2
O
3
·
(
1.90
-
2.10
)
SiO
2
·
y
H
2
O
wherein y is the water content, comprising the steps of:
i. a sodium aluminate solution having a temperature of at least 60° C. is mixed with a sodium silicate solution at a temperature of at least 60° C. in a stirred vessel in the presence of an effective amount of a slurry of P zeolite seed to form a gel having the composition,
Al
2
O
3
:(1.80-2.2)SiO
2
:(1.5-5)Na
2
O: (40 to 150) H
2
O
ii. ageing the gel at a temperature above about 60° C. with stirring to maintain solids in suspension for a period of least about 0.1 hour, and
iii. separating the P zeolite product, washing and drying.
The process described is a particularly favourable route for preparing P zeolites having improved properties for use as detergent builders. These P zeolites have effective binding capacities for calcium of above 150, preferably above 160 mg/g, good rate of calcium uptake i.e. below 25 seconds, preferably below 10 secs and effective oil absorption i.e. at least 50 g/100 g zeolite and in the range to 100 g/100 g zeolite. Their d
50
was in the range of about 0.85 to about 2.00 micron and was therefore particularly suitable as detergent builders.
It is therefore a third object of the present invention to provide a P zeolite having the oxide formula
M
2
n
O
·
Al
2
O
3
·
(
1.90
-
2.10
)
SiO
2
·
y
H
2
O
wherein y is the water content
and having a calcium effective binding capacity of above 150 mg/g,an oil absorption of above 80 g of oil per 100 g of zeolite and a calcium uptake rate of below 10 seconds.
Standard Procedures
In the characterisation of the zeolite-P materials prepared by the present process the following methods were used.
i. Particle size: The average particle size (microns) was measured by a Malvern Mastersizer (Trade Mark) obtainable from Malvern Instruments, England and expressed as the d
50
, i.e. 50% by weight of the particles have a diameter smaller than the diameter quoted. The definitions d
80
and d
90
may also be used in association with the appropriate figure. Prior to measuring the particle size, the sample is dried as a thin layer (about 1.5 mm) at 110° C. for two hours in a fan oven.
ii. Calcium uptake rate (CUR):
Griffin Walter D.
Pillsbury & Winthrop LLP
Unilever Patent Holdings B.V.
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