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Description  |
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TECHNICAL FIELD OF INVENTION
The present invention relates to a process for the preparation of granular
detergent compositions containing a porous crystal-growth-modified
carbonate salt, as described and claimed in EP No. 221 776A (Unilever).
The invention is of especial applicability to the production of detergent
powders containing reduced or zero levels of inorganic phosphate.
BACKGROUND AND INTRODUCTION
Conventional detergent powders contain relatively large quantities of
sodium tripolyphosphate (STP). This material is an excellent detergency
builder because of its calcium binding power, and in spray-dried powders
it also plays another important role: the intermeshing small needle-like
crystals of STP hexahydrate provide an excellent matrix for the powder,
capable of holding labile ingredients and forming the basis of a powder
having excellent flow properties, low compressibility and low tendency to
cake. In recent years environmental objections to inorganic phosphates in
waste waters have prompted detergent manufacturers to replace STP wholly
or partially by non-phosphate builders such as sodium carbonate, sodium
nitrilotriacetate or sodium aluminosilicate, but these materials do not,
in general, possess an ability comparable to that of STP to contribute to
the structure of a spray-dried powder.
EP No. 221 776A (Unilever), published on May 13, 1987, describes and claims
novel porous materials consisting of small crystals, comparable to those
of STP, interspersed with small pores. One such material,
crystal-growth-modified Burkeite, is prepared by drying (preferably
spray-drying) a slurry containing sodium carbonate and sodium sulphate in
an appropriate ratio and a crystal growth modifier, added to the slurry
not later than the sodium carbonate so as to influence the growth of
crystals of the double salt Burkeite. The use of crystal-growth-modified
Burkeite as the base for a spray-dried detergent powder is described, for
example, in Examples 16-23 of the aforementioned European specification.
Example 23 describes a powder containing STP as the principal builder and
structurant. The powder of Example 23 was prepared by slurrying together
all ingredients and spray-drying.
It has now been discovered that spray-dried detergent powders containing
crystal-growth-modified Burkeite or similar materials display better
particle structure if produced by a method involving the preparation of
two separate slurries. Powders containing STP show an additional benefit
in that breakdown of STP during spray-drying is also reduced when the
method of the present invention is used.
PRIOR ART
GB No. 2 013 707B (Unilever) discloses a process for preparing a powdered
detergent composition comprising the steps of forming a detergent slurry
in a mixing vessel, passing the slurry in a stream to a spray-nozzle and
spray-drying the slurry, wherein an aqueous solution or suspension of
sodium silicate is admixed with the stream of detergent slurry after it
leaves the slurry mixing vessel and before spray-dried particles leave the
spray nozzle. The detergent slurry contains sodium aluminosilicate
detergency builder and the process reduces the adverse reaction between
aluminosilicate and silicate to form insoluble siliceous species.
DEFINITION OF THE INVENTION
The present invention provides a process for the preparation of a granular
detergent composition, which comprises the steps of:
(i) preparing a first aqueous slurry in a first vessel, the slurry
comprising sodium carbonate, optionally together with sodium sulphate
and/or sodium bicarbonate, and an effective amount of a crystal growth
modifier which is an organic material having at least three carboxyl
groups in the molecule, the crystal growth modifier being incorporated in
the slurry not later than the sodium carbonate;
(ii) preparing a second aqueous slurry in a second vessel, the slurry
comprising one or more anionic and/or nonionic surfactants, optionally one
or more detergency builders and optionally one or more further
heat-insensitive detergent components,
(iii) mixing the first and second slurries and spray-drying the resulting
mixed slurry to form a powder including a crystal-growth-modified
carbonate-based salt.
For convenience, the first slurry will be referred to hereinafter as the
carbonate slurry, and the second slurry as the base powder slurry.
DESCRIPTION OF THE INVENTION
The present invention is directed to a preferred method for preparing
detergent powders which contain a porous carbonate-based
crystal-growth-modified salt, as described and claimed in the
aforementioned EP No. 221 776A (Unilever).
Three different porous carbonate-based crystal-growth-modified salts are of
especial interest: sodium carbonate itself, mainly in monohydrate form but
containing some anhydrous material; sodium sesquicarbonate, which is a
hydrated carbonate/bicarbonate double salt of the formula
Na.sub.2 CO.sub.3.NaHCO.sub.3.2H.sub.2 O;
and Burkeite, an anhydrous carbonate/sulphate double salt of the formula
2Na.sub.2 SO.sub.4.Na.sub.2 CO.sub.3.
All three salts exhibit crystal growth modification, when prepared by
drying a slurry containing the appropriate salt(s) and a crystal growth
modifier added to the slurry not later than the sodium carbonate. The
crystal growth modified materials are characterised by small needle-like
crystals interspersed with very small pores, and are very useful
structurants in detergent powders.
The sodium carbonate/sodium sulphate double salt Burkeite represents an
especially preferred embodiment of the invention. This material forms
small crystals (about 10 .mu.m) but in the normal block-like crystal form
these are packed together in dense aggregates and the material has a low
absorptivity for liquids. As explained in the aforementioned EP No. 221
776A (Unilever), Burkeite can be converted to a more desirable
needle-shaped crystal form in the slurry by the addition of a low level of
a polycarboxylate material at a particular stage in the slurry-making
process. Crystal-growth-modified spray-dried Burkeite contains small
needle-shaped crystals similar to those of sodium tripolyphosphate
hexahydrate, and can be shown by mercury porosimetry to be interspersed to
a large extent with very small (<3.5 .mu.m) pores. This material is
capable of absorbing and retaining substantial quantities of mobile
organic detergent components as a direct result both of a change in
crystal form and of a less dense form of crystal packing, giving particles
of greater porosity than those produced in the absence of a crystal growth
modifier. The modified crystal structure can be recognised by optical or
electron microscopy.
In the process of the invention, the modified crystals are allowed to grow
in the first slurry, and need not encounter the base powder components
until shortly before spray-drying. Similarly the crystal structures of the
materials in the base powder slurry, notably STP, are allowed to develop
separately. Different slurry-making conditions for each slurry can be
chosen without the need to compromise.
The two slurries are prepared in separate vessels, and then mixed before
they are conveyed to the spray nozzle of a spray-drying tower. Suitably
they are fed simultaneously to a holding vessel where mixing takes place,
and the mixture is then conveyed in the normal manner, via low-pressure
and high-pressure lines, to the distribution manifold of the tower, and
thence to the spray nozzle for atomisation and drying. If desired, the
slurries may be kept separate until they reach the distribution manifold.
The relative quantities of the two slurries used may easily be chosen such
that the resulting spray-dried powder contains the various ingredients in
the desired proportions. A carbonate-based structurant salt content in the
spray-dried powder of from 5 to 75% by weight, preferably from 10 to 50%
by weight, is suitable having regard to the amount of other structurants
present in the powder.
THE CARBONATE SLURRY
The carbonate slurry contains, as essential ingredients, sodium carbonate,
water and a polycarboxylate crystal growth modifier. Optionally sodium
sulphate and/or sodium bicarbonate may be present depending on the porous
salt desired. Minor amounts of other materials may also be included as
explained below.
It is essential that the polycarboxylate crystal growth modifier be present
in the slurry at a sufficiently early stage to influence the crystal
growth of the carbonate salt. It must accordingly be incorporated in the
slurry not later than the time at which the sodium carbonate is added. If
sodium sulphate and/or sodium bicarbonate is or are present, the crystal
growth modifier is preferably incorporated not later than the addition of
both the sodium carbonate and the other salt(s).
In batch slurry-making, there is no difficulty in arranging for the
ingredients to be added in the appropriate order. In continuous
slurry-making processes all components are added substantially
simultaneously, but once the start-up period is over the inorganic salts
will in practice always encounter a slurry containing some crystal growth
modifier.
The water used to prepare the carbonate slurry is preferably relatively
soft. Desirably water of hardness not exceeding 15.degree. (French) is
used.
The sodium carbonate used in the carbonate slurry may be of any type.
Synthetic light soda ash has been found to be especially preferred;
natural heavy soda ash is intermediate, while synthetic granular soda ash
is the least preferred raw material. All grades of sodium sulphate are
suitable for use in the invention, provided that they are not heavily
contaminated with other salts such as salts of calcium or magnesium.
If the porous salt is Burkeite, the extent of its formation in the slurry
will of course depend on the ratio of sodium carbonate and sodium sulphate
present. This must be at least 0.03:1 (by weight) in order for the
resulting spray-dried material to have a useful level of porosity; and it
is preferably at least 0.1:1 and more preferably at least 0.37:1, this
latter figure representing the stoichiometric ratio for Burkeite
formation. Thus it is preferred that as much as possible of the sodium
sulphate present be in the form of Burkeite. Any excess sodium carbonate
present will itself be in a crystal-growth-modified form.
The stoichiometric weight ratio for sodium sesquicarbonate formation
(sodium carbonate:sodium bicarbonate) is 1.26:1. During spray-drying some
dehydration of sesquicarbonate occurs, to produce bicarbonate and
carbonate; and some decomposition of bicarbonate to carbonate occurs.
Furthermore crystallisation in the slurry may not always be complete, so
the yield of sesquicarbonate may be as low as 50% of theoretical.
Preferably the weight ratio of sodium carbonate to sodium bicarbonate used
in preparing a sesquicarbonate slurry is within the range of from 1.5:1 to
1:1.
The preferred order of addition of the salts to a Burkeite slurry is for
sodium sulphate to be added before sodium carbonate. This has been found
to give a higher yield of Burkeite and the Burkeite thus formed appears to
have a higher useful porosity. In this preferred method, the crystal
growth modifier should be added to the slurry either before the addition
of both salts, or after the addition of the sodium sulphate and before the
addition of the sodium carbonate.
Similar considerations apply to the use of crystal-growth-modified sodium
sesquicarbonate.
The polycarboxylate crystal growth modifier is an organic material
containing at least three carboxyl groups in the molecule but we have
found that it cannot be generically defined further in purely structural
terms; it is also difficult to predict how much will be required. It can,
however, be defined functionally with reference to Burkeite crystal growth
modification, as an organic material having three or more carboxyl groups
in the molecule, which, when incorporated at a suitable level in a slurry
to which sodium carbonate and sodium sulphate in a weight ratio of at
least 0.03:1 are subsequently or simultaneously added, gives on drying a
powder having a pore size distribution, as measured by mercury
porosimetry, of at least 300 cm.sup.3 of pores <3.5 .mu.m per kg of
powder.
This porosity figure, measured by the recognised technique of mercury
porosimetry, has been found to correlate well with the capacity to take up
and retain mobile detergent components and to provide powder structuring.
For the purposes of selecting a crystal growth modifier on the basis of
pore size distribution, it is necessary to use a simple slurry containing
only sodium sulphate, sodium carbonate, the crystal growth modifier and
water, because the presence of other materials will influence the
porosity. This model system can then be used to select a crystal growth
modifier for use in more complex slurries where other materials may be
present, and/or for use in modifying the crystal growth of other carbonate
salts, for example, sodium carbonate itself or sodium sesquicarbonate.
As hinted above, the carbonate slurry for use in the process of the present
invention may advantageously contain minor amounts of other components. A
small amount of anionic surfactant, for example, increases slurry
stability, and a small amount of nonionic surfactant improves slurry
pumpability.
The crystal growth modifier is a polycarboxylate. Monomeric
polycarboxylates, for example, salts of ethylenediaminetetraacetic acid,
nitrilotriacetic acid and citric acid, may be used but the levels required
are rather high, for example, 5 to 10% weight based on the total amount of
sodium carbonate and, if present, sodium sulphate and/or sodium
bicarbonate. Preferred polycarboxylate crystal growth modifiers used in
the invention are polymeric polycarboxylates. Amounts of from 0.1 to 20%
by weight, preferably from 0.2 to 5% by weight, based on the total amount
of sodium carbonate and, if present, sodium sulphate and/or sodium
bicarbonate, are generally sufficient.
the polycarboxylate crystal growth modifier preferably has a molecular
weight of at least 1000, advantageously from 1000 to 300 000, especially
from 1000 to 250 000. Powders having especially good dynamic flow rates
may be prepared if the carbonate slurry incorporates polycarboxylate
crystal growth modifiers having molecular weights in the 3000 to 100 000
range, especially 3500 to 70 000 and more especially 10 000 to 70 000. All
molecular weights quoted herein are those provided by the manufacturers.
Preferred crystal growth modifiers are homopolymers and copolymers of
acrylic acid or maleic acid. Of especial interest are polyacrylates,
acrylic acid/maleic acid copolymers, and acrylic phosphinates.
Suitable polymers, which may be used alone or in combination, include the
following:
salts of polyacrylic acid such as sodium polyacrylate, for example Versicol
(Trade Mark ) E5 E7 and E9 ex Allied Colloids, average molecular weights
3500, 27 000 and 70 000; Narlex (Trade Mark) LD 30 and 34 ex National
Adhesives and Resins Ltd, average molecular weights 5000 and 25 000
respectively; Acrysol (Trade Mark) LMW-10, LMW-20, LMW-45 and A-IN ex Rohm
& Haas, average molecular weights 1000, 2000, 4500 and 60 000; and Sokalan
(Trade Mark) PAS ex BASF, average molecular weight 250 000;
ethylene/maleic acid copolymers, for example, the EMA (Trade Mark) series
ex Monsanto;
methyl vinyl ether/maleic acid copolymers, for example, Gantrez (Trade
Mark) AN119 ex GAF Corporation;
acrylic acid/maleic acid copolymers, for example, Sokalan (Trade Mark) CP5
and CP7 ex BASF; and
acrylic phosphinates, for example, the DKW range ex National Adhesives and
Resins Ltd or the Belsperse (Trade Mark) range ex Ciba-Geigy AG, as
disclosed in EP No. 182 411 A (Unilever).
Mixtures of any two or more crystal growth modifiers may if desired be used
in the compositions of the invention.
The carbonate slurry will generally contain from 45 to 60% by weight of
water.
As indicated previously, slurry-making conditions may be chosen to maximise
the yield of modified crystals obtained. Sodium carbonate and Burkeite
slurries are best prepared at relatively high temperatures, preferably
above 80.degree. C., more preferably from 85.degree. to 95.degree. C.;
while a sodium sesquicarbonate slurry is best prepared at a temperature
not exceeding 65.degree. C., preferably from 50.degree. to 60.degree. C.,
in order to minimise decomposition of the sodium bicarbonate present.
A high pH can be detrimental to good crystal formation of sodium
sesquicarbonate, and the process of the invention has the further
advantage when this structurant is used that any sodium alkaline silicate
or other strongly alkaline components of the powder can be included in the
base powder slurry and will not be encountered by the sesquicarbonate
until the crystal growth of the latter in the slurry is complete.
On drying a slurry containing crystal-growth-modified Burkeite, which is an
anhydrous material, the double salt survives unchanged in the dried
powder. Crystal-growth-modified sodium carbonate monohydrate and sodium
sesquicarbonate will generally lose some water of crystallisation on
drying, depending on the drying conditions, but this does not adversely
affect the structurant properties.
THE BASE POWDER SLURRY
The base powder slurry will generally contain all ingredients desired in
the final product that are sufficiently heat-stable to undergo
spray-drying. It will always contain one or more anionic and/or nonionic
surfactants, and will generally include one or more detergency builders.
Anionic surfactants are well known to those skilled in the detergents art.
Examples include alkylbenzene sulphonates, particularly sodium linear
C.sub.8 -C.sub.15 alkylbenzene sulphonates having an average chain length
of C.sub.11 -C.sub.13 ; primary and secondary alcohol sulphates,
particularly sodium C.sub.12 -C.sub.15 primary alcohol sulphates; olefin
sulphonates; alkane sulphonates; and fatty acid ester sulphonates.
It may also be desirable to include one or more soaps of fatty acids. The
soaps which can be used are preferably sodium soaps derived from naturally
occurring fatty acids, for example the fatty acids from coconut oil, beef
tallow, sunflower or hardened rapeseed oil.
The base powder slurry may also include one or more nonionic surfactants.
Examples of suitable nonionic surfactants are the primary and secondary
alcohol ethoxylates, especially the C.sub.12 -C.sub.15 primary and
secondary alcohols ethoxylated with an average of from 5 to 20 moles of
ethylene oxide per mole of alcohol.
The sodium carbonate present in the carbonate-based structurant material
acts as a detergency builder, but may not be present in a sufficient
amount to provide adequate building. Preferred builders for inclusion in
the base powder slurry include phosphates, for example, orthophosphates,
pyrophosphates and (most preferably) tripolyphosphates. Non-P builders
that may be present include, but are not restricted to, sodium carbonate,
crystalline and amorphous aluminosilicates, soaps, sulphonated fatty acid
salts, citrates, nitrilotriacetates and carboxymethyloxsuccinates.
Polymeric builders, for example, polycarboxylates such as polyacrylates,
acrylic/maleic copolymers and acrylic phosphinates, may also be present,
generally but not exclusively to supplement the effect of another builder
such as sodium tripolyphosphate or sodium aluminosilicate. The polymers
listed previously as crystal growth modifiers generally have builder
efficacy and any of these may with advantage also be included in the base
powder slurry.
Other ingredients that may be present in the base powder slurry include
alkali metal silicates, antiredeposition agents, antiincrustation agents
and fluorescers.
The water content of the base powder slurry will typically be in the range
of from 30 to 55% by weight, preferably from 35 to 50% by weight.
PREFERRED EMBODIMENTS OF THE INVENTION
According to the preferred embodiment of the invention, the base powder
slurry contains sodium tripolyphosphate (STP), preferably in an amount of
from 5 to 30% by weight, more preferably from 10 to 30% by weight, based
on the spray-dried powder.
The sodium tripolyphosphate may be the only builder present apart from the
sodium carbonate contributed by the porous structurant salt, or it may
form part of a mixed builder system with, for example, sodium
aluminosilicate, sodium nitrilotriacetate or a polymeric builder. The
invention is of especial interest for the production of powders containing
relatively low levels (25% or less) of STP, in which additional
structuring is especially important.
Since the carbonate and base powder slurries are prepared separately, a
base powder slurry containing STP can be prepared under conditions that
favour the growth of small, fully hydrated STP hexahydrate crystals,
without any need to consider whether or not the crystal growth of the
carbonate-based structurant salt is equally favoured. The preferred
temperature for optimum STP crystal development is below 90.degree. C.,
preferably from 60.degree. to 80.degree. C.: it will be seen that this is
lower than the preferred temperature for processing Burkeite or sodium
carbonate slurries but higher than the preferred temperature for
processing sodium sesquicarbonate slurries, so the preparation of separate
slurries avoids the need for a compromise or temperature.
It is also advantageous for a base powder slurry containing STP to contain
a relatively low level of other inorganic salts, preferably less than 15%,
more preferably less than 10%, based on the spray-dried powder.
In this embodiment of the invention, a further benefit has been found: the
amount of breakdown of STP to orthophosphate and pyrophosphate during
spray-drying is reduced, as compared with powders of identical composition
prepared from a single slurry. Reduced STP breakdown leads to decreased
deposition of calcium pyrophosphate ash on washed fabrics, descreased soil
redeposition during the wash, and improved enzyme efficacy.
In a second preferred embodiment of the invention, the base powder slurry
includes crystalline or amorphous aluminosilicate builder. This second
embodiment is especially applicable to the preparation of zero-phosphate
detergent powders. Aluminosilicates are not good structurants, and the use
of a supplementary structurant is very beneficial.
OPTIONAL POST-TREATMENTS
The spray-dried powder produced by the process of the invention may be
useful in its own right as a detergent powder. Alternatively, various
additional ingredients that are unsuitable for slurry-making and
spray-drying may be added subsequently.
Since the crystal-growth-modified structurant salts are highly absorbent
and have excellent carrier properties for mobile liquid detergent
components, such components that are unsuitable for spray-drying may
advantageously be sprayed onto the spray-dried powder. The term "liquid
detergent component" includes components that require liquefaction by
melting or dissolving in a solvent, as well as materials liquid at room
temperature. The liquid component is preferably applied to the spray-dried
powder by spraying while the powder is agitated in apparatus, for example,
a rotating drum, that continually provides a changing surface of powder to
the sprayed liquid. The spray nozzle is advantageously angled so that
liquid that penetrates the powder curtain falls on further powder rather
than the shell of the drum itself.
During the spraying process the temperature of the powder may range, for
example, from 30.degree. to 95.degree. C. The powder generally leaves the
spray-drying tower at an elevated temperature, and this may be
advantageous when the component to be sprayed on has to be melted.
Components that may be sprayed on to the spray-dried powder include in
particular nonionic surfactants having an average degree of ethoxylation
of 10 or below, which are generally liquid at room temperature and often
cannot be spray-dried because they give rise to unacceptable levels of
tower emission ("blue smoke" or "pluming").
Other ingredients that may be sprayed on include lather suppressors and
perfumes.
It will also generally be desirable to add to the spray-dried powder
various further ingredients that are not suitable for spray-drying or that
interfere with the spray-drying process. Examples of such ingredients are
enzymes; bleaches, bleach precursors, or bleach activators; inorganic
salts such as sodium sulphate, as described and claimed in EP No. 219 328A
(Unilever); or sodium silicate as described and claimed in our copending
Applications Nos. 86 08291 filed on Apr. 4, 1986 and 86 09042 and 86 09043
filed on Apr. 14, 1986; lather suppressors; perfumes; dyes; coloured
noodles or speckles. Further examples of ingredients best incorporated by
postdosing will readily suggest themselves to the skilled detergent
formulator.
PRODUCTS OF THE INVENTION
Phosphate-built powders prepared in accordance with the invention may
typically contain the following amounts of the following ingredients:
______________________________________
weight %
______________________________________
Surfactants (anionic, nonionic,
5-40
cationic, zwitterionic)
Sodium tripolyphosphate
5-40
Sodium carbonate (in structurant salt)
1-25
Sodium carbonate (other)
0-10
Sodium sulphate or sodium bicarbonate
0-25
(in structurant salt)
Sodium sulphate (other)
0-30
Crystal growth modifier
0.05-5
(polymeric polycarboxylate)
Sodium silicate 0-15
Bleach ingredients 0-30
Enzyme, lather suppressor etc
0-10
______________________________________
Low or zero-phosphate aluminosilicate-built powders prepared in accordance
with the invention may typically contain the following amounts of the
following ingredients:
______________________________________
weight %
______________________________________
Surfactants (anionic, nonionic,
5-40
cationic, zwitterionic)
Sodium aluminosilicate
10-60
Sodium tripolyphosphate
0-25
Sodium orthophosphate 0-20
Sodium nitrilotriacetate
0-20
Sodium carbonate (in structurant salt)
1-25
Sodium carbonate (other)
0-10
Sodium sulphate or sodium
0-25
bicarbonate (in structurant salt)
Sodium sulphate (other)
0-30
Crystal growth modifier
0.05-10
(polymeric polycarboxylate)
Sodium silicate 0-10
Bleach ingredients 0-30
Enzyme, lather suppressor etc
0-10
______________________________________
EXAMPLES
The invention is illustrated by the following non-limiting Examples, in
which parts and percentages are by weight unless otherwise stated.
EXAMPLE 1
In this experiment, a 1000 kg batch of slurry was prepared by the method of
the invention, and spray-dried to form a powder (Example 1); and a 500 kg
batch of slurry of the same composition was prepared by a single-slurry
method and spray-dried to form a powder (Comparative Example A).
To prepare the powder of Example 1, a Burkeite slurry was first prepared
from the following ingredients in the order listed:
______________________________________
kg
______________________________________
Softened water 250.0
Sodium polyacrylate solution (25% w/w)
27.0
Sodium sulphate 162.0
Sodium carbonate (light soda
61.0
ash ex ICI)
500.0
______________________________________
The percentage of sodium polyacrylate, based on the total amount of sodium
carbonate and sodium sulphate, was 3%; the ratio of sodium carbonate to
sodium sulphate was 0.37:1 (stoichiometric for Burkeite formation).
The slurry was heated to 90.degree. C. after the addition of the sodium
sulphate but before the addition of the sodium carbonate. When all
ingredients had been added, the slurry was stirred thoroughly.
In a second vessel, a base powder slurry was prepared from the following
ingredients in the order listed:
______________________________________
kg
______________________________________
Softened water at 65.degree. C.
270.0
Sodium alkylbenzene sulphonate
63.0
(48% w/w)
Sodium alkaline (2.0r) silicate solution
59.0
(48% w/w)
Sodium EDTA solution (40% w/w)
1.2
Fluorescer slurry (32% w/w)
4.4
Sodium carboxymethyl cellulose
2.1
Nonionic surfactant 4.8
Sodium tripolyphosphate (35% Phase I)
95.0
500.0
______________________________________
When all the ingredients had been added, the base powder slurry was stirred
for a further 5 minutes.
The Burkeite slurry and the base powder slurry were dropped successively
into a stirred holding vessel and the mixture was stirred for 10 minutes.
The mixed slurry was then spray-dried at a pressure of 45 bar through a 3
mm hollow cone swirl nozzle into a spray-drying tower. Hot air at
390.degree. C. was used to dry the slurry to give a powder having a
moisture content of about 10%. The compositions of the final slurry and of
the powder are shown in Table 1.
The control powder A was prepared by spray-drying a single slurry prepared
from the following ingredients in the order listed:
______________________________________
kg
______________________________________
Softened water at 90.degree. C.
130.0
Sodium polyacrylate solution (25% w/w)
13.5
Sodium sulphate 81.0
Sodium carbonate 30.5
Softened water at 15.degree. C.
130.0
Sodium ABS (45% w/w) 31.5
Sodium alkaline silicate (48% w/w)
29.5
EDTA (40% w/w) 0.6
Fluorescer (32% w/w) 2.2
Nonionic surfactant 2.4
Sodium tripolyphosphate 47.5
500.0
______________________________________
The ingredients were identical to those used to prepare the powder of
Example 1. The slurry was spray-dried under identical conditions, to give
a powder of the same composition, as shown in Table 1.
TABLE 1
______________________________________
1 A
Total Total 1, A
slurry slurry Powder
(kg) (kg) (% w/w)
______________________________________
Sodium polyacrylate
6.75 3.38 1.56
Sodium sulphate
162.00 81.00 37.36
Sodium carbonate
61.00 30.50 14.07
Sodium ABS 28.35 14.18 6.54
Sodium silicate
28.32 14.16 6.53
EDTA 0.48 0.24 0.11
Fluorescer 1.41 0.70 0.33
SCMC 2.10 1.05 0.48
Nonionic surfactant
4.80 2.40 1.11
STP 95.00 47.50 21.91
Water, moisture
to 1000 to 500 10.00
100.00
______________________________________
The dynamic flow rates of the powders were as follows:
______________________________________
Example 1 112 ml/s
Comparative Example A
101 ml/s
______________________________________
Analysis of both powders showed STP breakdown as follows:
______________________________________
1 A
______________________________________
Tripolyphosphate (%)
91.0 83.6
Pyrophosphate (%) 6.4 13.2
Orthophosphate (%) 2.6 3.2
100.0 100.0
______________________________________
Thus the powder prepared according to the invention showed better flow
properties, reflecting its superior structure, and reduced STP breakdown.
EXAMPLES 2-4
These examples illustrate the use of the process of the invention in the
preparation of zero-P powders built with zeolite.
A Burkeite slurry was prepared from the following ingredients in the order
listed, at a temperature of 90.degree. C.:
______________________________________
Parts
______________________________________
Softened water 22.0
Sodium polyacrylate
0.37
Sodium sulphate 11.4
Sodium carbonate 6.9
40.67
______________________________________
The percentage of sodium polyacrylate, based on the total amount of sodium
carbonate and sodium sulphate, was 2%; the ratio of sodium carbonate to
sodium sulphate was 0.60, greater than that required for Burkeite
formation, so that the eventual product contained both polymer-modified
Burkeite and polymer-modified sodium carbonate monohydrate.
In a second vessel, a base powder slurry was prepared from the following
ingredients in the order listed and at a temperature of 85.degree. C.:
______________________________________
Parts
______________________________________
Water 66.0
Sodium alkylbenzene sulphonate
12.0
Nonionic surfactant 3.0
Soap 2.0
Zeolite HAB A40 30.0
Polymer* 2.7
Sodium sulphate 19.2
SCMC 0.35
135.25
______________________________________
*Acrylic/maleic copolymer; Sokalan (Trade Mark) CP5 ex BASF
The first and second slurries were mixed for 10 minutes, then transferred
to a stirred mixing vessel and the mixture stirred for a further 10
minutes.
Batches of the combined slurry were spray-dried under conditions similar to
those in the previous Example, the conditions being adjusted to produce
powders having a range of moisture contents. The composition of the spray
dried powder was as follows:
______________________________________
Parts
______________________________________
Sodium alkylbenzene sulphonate
12.0
Nonionic surfactant 3.0
Soap 2.0
Zeolite HAB A40 30.0
Polymer (Sokalan CP5) 2.7
Sodium polyacrylate 0.37
Sodium sulphate 30.6
Sodium carbonate 6.9
SCMC 0.35
Water (nominal) 9.08
97.0
______________________________________
Control powders were prepared by spray drying batches of a single slurry in
which the ingredients of the base powder slurry were first mixed, followed
by addition of the ingredients of the Burkeite slurry.
The properties of the powders at different moisture contents were as
follows:
______________________________________
2 3 4 B C D
Moisture content (%)
5% 8% 10% 5% 8% 10%
______________________________________
Bulk density (g/l)
450 410 430 380 380 400
Dynamic flow rate (ml/s)
86 92 86 83 86 80
Compressibility (%)
12 20 25 28 36 45
Unconfined compression
0.1 1.1 1.4 1.3 2.8 3.5
test (kg) (UCT)
______________________________________
The powder properties, particularly the compressibility and UCT values, of
the powders of Examples 2-4 were better that those of the corresponding
control powders, and were less sensitive to changes in moisture content.
This makes control of the spray drying operation simpler and provides
greater processing flexibility.
EXAMPLES 5-7
These Examples relate to the preparation of a different zeolite-built
detergent powder.
A sodium carbonate/Burkeite slurry was prepared from the following
ingredients in the order listed, at a temperature of 90.degree. C.:
______________________________________
Parts
______________________________________
Softened water 34.0
Sodium polyacrylate
0.2
Sodium sulphate 18.2
Sodium carbonate 10.0
62.4
______________________________________
The percentage of sodium polyacrylate, based on the total amount of sodium
carbonate and sodium sulphate, was 0.7%. The ratio of sodium carbonate to
sodium sulphate was 0.55, so that, as in Examples 2-4, the slurry
composition was such as to produce a mixture of polymer-modified Burkeite
and polymer-modified sodium carbonate monohydrate.
In a second vessel, a base powder slurry was prepared from the following
ingredients in the order listed and at a temperature of 85.degree. C.:
______________________________________
Parts
______________________________________
Water 39.0
Sodium alkylbenzene sulphonate
9.0
Nonionic surfactant 1.0
Zeolite HAB A40 24.0
Polymer (Sokalon CP5) 4.0
Minor ingredients 0.83
77.83
______________________________________
The first and second slurries were mixed for 10 minutes, then transferred
to a stirred mixing vessel and the mixture stirred for a further 10
minutes.
Batches of the combined slurry were spray dried under conditions similar to
those in previous Examples. The composition of the spray dried powder was
as follows:
______________________________________
Parts
______________________________________
Sodium alkylbenzene sulphonate
9.0
Nonionic surfactant 1.0
Zeolite HAB A40 24.0
Polymer (Sokalan CP5) 4.0
Sodium polyacrylate 0.2
Sodium sulphate 18.2
Sodium carbonate 10.0
Minor ingredients 0.83
Water (nominal) 7.0
74.23
______________________________________
Batches of control powder of similar composition were prepared by
spray-drying a single slurry produced by mixing all the ingredients.
The properties of the powders at different moisture contents were as
follows:
______________________________________
5 6 7 E F G
Moisture content (%)
6.0 10.0 13.0 6.0 10.0 13.0
______________________________________
Bulk density (g/l)
412 400 426 350 360 375
Dynamic flow rate (ml/s)
96 96 83 83 83 75
Compressibility (5)
7 27 37 15 43 45
Unconfined Compression
0.2 1.0 2.3 0.2 2.3 3.0
Test (UCT) (Kg)
______________________________________
The powder properties, particularly the compressibility and UCT values, of
the powders of Examples 5, 6 and 7 were better that thos of the
corresponding control powders, and the properties were less sensitive to
variations in powder moisture content.
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