Note: Descriptions are shown in the official language in which they were submitted.
31 5;~L~L9~79
The present invention relates to the use of
monovalent salts of styrene-maleic anhydride copolymers
having molecular weight rangP of from about 1000 to
about 5000 to reduce the amount of water required for
preparing a slurry of ingredients used in producing
portland cement.
It i5 known that polyelectrolytes such as
polyacrylic acid salts, copolymers of acrylic acid
and acrylamide, and hydrolyzed polyacrylonitrile which
are flocculants at higher molecular weights show
different properties and act as dispersants at lower
molecular weights~ Such polymers having molecular
weights from a few thoùsand up to about 50,000, for
example, have been recommended for use in various dis~
persant applications.
In the wet grinding process for making port-
land cement, limestone and clay and optionally a small
amount of iron oxide are ground in the presence of
water to obtain a uniform slurry of very fine particles.
This slurry is then fed into a high temperature kiln
where it is dried and calcined to form the clinker
that is then dry ground to make portland cement. The
water demand of the finely ground limestone-clay slurry
is fairly high and requires a relatively large propor-
tion of water, for example, about 35-50% by weight~
to obtain a fluid, pumpable slurry. This limits the
rate at which the slurry can be processed and fed to
the kiln and it also increases the fuel re~irement
to dry and calcine a given quantity of solids to the
clinker stage.
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Many substances with dispersant activity
are available and have beén tried in order to decrease
the water demand of suspended inorganic solids in
various high solids water suspensions or slurries for
various applications, particularly in the wet grinding
step of the wet process for making portland cement.
Most of these have proven relatively ineffective or
undesirable ~or one reason or another. Complex phos-
phates are undesirable because they tend to hydrolyze
at the warm temperatures developed during grinding
and in storage of the slurry, and because of the adverse
effect of residual phosphate on the properties o~ the
inal portland cement product. Lignosulonates have
been tried for this use, but these require high addition
levels for only marginal improvement~ They also lose
their activity rapidly during storage of the slurry.
It has now been found that water-soluble
inorganic salts of copolymers of styrene and maleic
anhydride o molecular weight from about 1000 to about
5000 are unexpectedly effective for reducing the water
demand to maintain the fluidity of high solids content
of ingredients used for ~he aqueous suspensions in
the wet process for making portland cement. These
copolymers are further characterized by a ratio of
from about 50-67 mole p~rcent of styrene and 50-33
mole percent of maleic anhydride. The preferred co-
polymer molecules have a molecular weight of from about
I200 to about 3000 with a mole ratio of styrene to
maleic anhydride of 1:1. These are particularly effec
tive dispersing agents for limestone-clay suspensions
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~L~49~79
used in wet ~rinding process for making cement. Copolymer
amounts of about 0.01 to 0.2 percent by weight of solids
are operable and about 0.02 to 0.1 percent is preferred
and most pre~erred is a range of 0.02 to 0.075 percent,
based on the slurry solids.
Accordingly, the present invention is directed :~
to a kiln feed slurry useful in a wet process to produce
portland cement, having a water content of between 25
percent and 35 percent based on the weight of the slurry,
said slurry containing ~rom 0.01 to 0.2 weight percent of
a water-soluble monovalent inorganic salt of a copolymer
containing from 33 to 50 mole percent of maleic anhydride
and from 67 to 50 mole percent styrene and a molecular .
weight of from 1000 to 5000. .
. .
:~ 15 The present invention is also directed to a
~ method of preparing a kiln feed water slurry in the wet
proeess for producing portland cement which comprises
. adding to the kiln feed water slurry mixture from 0.01 to
0.2 pereent by weight, based on slurry solids, of a water- .
-soluble monovalent inorganic salt of a styrene-maleic
anhydride eopolymer containing from 50 to 67 mole pereent ~ ~:
of styrene and 33 to 50 mole percent of maleie anhydride ~ ;
~j and a moleeular weight of from 1000 to 5000.
.~ The eopolymers which are useful in the present
invention ean be made by known proeesses. U.S. Patent
I
.~ 2,606,891, issued to Rowland, August 12, 1952, discloses
~ a process in which styrene and maleie anhydride are
dissolved in an inert organic solvent, such as acetone,
dioxane or a liquid ester. One to 40 percent of a soluble
mereaptan of 5 to 22 carbon atoms, and .25 to 5 percent
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o~ a known or~anic peroxide catalyst are added. The mix-
ture is then heated to 50 to 150C.
U.S. Patent 2,640,819, issued to Barrett, June
2, 1953, discloses a process in which a mixture of styrene
; 5 and maleic anhydride is mass copolymerized in the pre~
sence of .01 to 2 weight percent of 2,5-ditertiary butyl
parabenzoquinone. The polymerization can be effected by
heating or by a combination of heat and a known organic
peroxide catalyst.
A third method is disclosed in U.S. Patent
3,085,994, issued to Muskat, April 16, 1963. The styrene,
maleic anhydride and an organic peroxide catalyst are dis-
solved in an alkyl benzene in which the alkyl group has
at least two carbon atoms, sUch as ethylbenzene, cumene
or P-cymene, and the mixture is heated to 85 to 120C.
The alkyl aromatic is a solvent for the monomers, but
a non-solvent for the low molecular weight copolymer.
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It is to be understood, however~ that the
process of making the styrene-maleic anhydride copolymer
is not critical to this invention. Any water-soluble
salt of a styrene-maleic anhydride copolymer, within
the 1000-5000 molecular weight ranye and the mole ratio
specified above can be used, without regard to its method
of preparation. The water content of the finished slurry
can be as low as 25~ and as high as 35% by weight. ;
In the wet process for making portland cement,
the raw materials, including ingredients such as lime-
stone, dolomite, oyster shells, blas~ furnace ~lag or
other well known high calcium-containing products, are
mixed with silicious materials, including slag, clay,
shale or any other silica containing ingredient in amounts
such that the calcium and silica materials constitute
about 85% by weight of the clinker ~ormed after heating
in a kiln. The remaining ingredients include aluminum-
-containing and iron-containing ingredients. The mixture
of raw ingredients, using well-known process steps,
is ground with the addition of water to prepare an ~queous
slurry, which is then screened and pumped into storage
silos preparatory to further ~lending with other slurries
or feeding into a clinkering kiln. Usually, the portion
;~ which passes a 200 mesh screen is used for preparing
the clinker. Such slurries contain ~rom 30-50~ water
by weight.
On an emperical basis, the cements made by
grinding the resulting clinker will contain
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SiO 19-23%
A12~3 4- 8%
Fe23 1.5- 6%
CaO 62-67%
MgO .6- 5%
The ~tyrene-maleic anhydride copolymer product
is used in the form of a water-soluble salt, usually
the sodium salt. Other such salts, for example, the
potassium and ammonium salts will also serve, but not
as well as the sodium salt. Surprisingly; these copoly-
meric salts are very ef~ective in maintaining fluidity
of the aqueous high solids mineral suspensions.
These copolymeric salts are extremely efective
for reducing water demand and promoting fluidity in vari-
ous kinds of high solids raw cement slurries consisting
largely of limestone and clay, usually with a small
amount of iron oxide. In this application the above-
-described copolymeric salts have a unique combination
of efficiency, stability and compatability in the wet -
grinding process slurries together with a lack o any
;20 adverse effects in the calcining process. A reduction
of up to 30 percent of the water content can be achieved,
80 that with the same volume feed to the cement kiln,
up to 30-35 percent increases in production can be
obtained with lower fuel costs. Increasing the feed
rate to the kiln while operating at normal fuel input
results in even further increases in clinker production.
The following examples illustrate the inven-
tion. Parts and percentages are given by weight unless
stated otherwise.
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Exam~le 1
A wet portland cement slurry obtained from a
commercial source contained 37% water. The viscosity
was measured by a Brookfield LTV viscometer employing
a #3 spindle at 12 RPM. A reading on the 100 scale was
converted and recorded as the control viscosity. As
received, this slurry had a viscosity of 4150 centipoise
tthe reading was the maximum during the first two revo-
lutions of the viscometer cup). A portion o~ the slurry
was evaporated down to 31.4% water. The viscosity of
the slurry at this water content was 9000 centipoise.
An aqueous solution containing 30 per cent by weight
of the sodium salt of a 1:1 mole ratio styrene-maleic
anhydride copolymer having a molecular weight of about
1600 was added in varying small amounts to samples of
this concentrated slurry and the viscosity was measured
by the procedure de~cribed above. ~he following results
were recorded:
'~
Wt~ % Copolymer
Salt Add~d Vi~cosity
(Based on Slurry~Solids) Centipoise
.01 6300
3500 ;~
.03 2100
.04 800
From these data it is apparent that addition
of only .02 weight ~ of the sodium salt of the copolymer
provides a slurry with a somewhat lower viscosity than
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it had prior to concentration, even though the slurry
contained 5.6~ less water. Further/ the viscosity of
the slurry containing only 31.4% water was reduced from
9000 centipoise to a readily pumpable slurry of 3500
centipoise viscosity.
Example 2
A wet process cement slurry different from
that of example 2 had a water content o 33.4% and a ~ :
viscosity of 3300 centipoise as measured by the Brook-
field viscometer procedure described above, u~ing a No. ~-
3 spindle and a rotation rate of 12 RPM.
The water content of the slurry was reduced
to 28% by evaporation of water at room temperature.
At 28% water the slurry had a viscosity of 5300 centi-
poise.
The aqueous soIution of the sodium salt of
styrene-maleic anhydride copolymer described in Example
l was added to the aqueous (28%) slurry and the following
data were recorded:
Wt. % Copolymer
5alt Added Viscosity
(Based on Slurry Solids) Centip _ e
.01 4550
.02 4400
03 4000 :
.04 3500 ~:.
.05 2800
~06 2500
07 . 1700
- 30 .10 600
.
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~49679
From these da~a it is apparent that .04~ of
the polymeric salt was sufficient to reduce the vis-
cosity of the slurry to approximately that of the ori-
ginal sample which contained 33.4% water.
Example 3
In this example sodium salts of (1) a styrene-
-maleic anhydride copolymer of a molecular weight approxi-
mately 1600 made from equimolar proportions of styrene
and maleic anhydride (2) a copolymer of a molecular weight
approximately 4000 made from a monomeric mixture of about
38 mole % maleic anhydride and 62 mole ~ styrene, and
(3) copolymer of about 20000 molecular weight made from
equimolar proportions of styrene and maleic anhydride
were tested using a wet process cement slurry containing
31% water. Sodium salts of the 1600 and 4000 molecular
weight copolymers were prepared in 30 weight % aqueous
- solution and the salt of the 20000 molecular weight
copolymer was prepared as a 15 weight % solution for
mixing with the slurry. The initial viscosity, as deter-
mined with the Brookfield viscometer using a No. 3 spindle
and 12 RPM, was 8300-8400. Data recorded in these runs
are tabulated below:
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Weight Percent Viscosity
Copolymer Salt Added Centipoi~e
tBased Oil Slurry Solids) (1)(~) (3)
.
1600 4000 20000
0.01 5100 6000 7~00
0~02 3400 ~650 7100
0~03 1750 2900 7600
0.04 750 2200 7800
0.05 -- 1500 7300
These data show that as lit~le as .02% by weight
of the 1600 molecular weight copolymer salt is sufficient
to reduce viscosity to a pumpable range. Slightly more,
.02-.03, % of the copolymer salt is needed with the 4000
molecular weight product. A molecular weight of 20~00,
however, is too high for use in ~he process, because
it does not reduce viscosity of the slurry uniformly
nor to the degree where it is readily pumpable even at
.05% concentration.
-~ 20 In commercial operation, the preferred proceduxe
is to meter or proportion a relatively concentrated
aqueous solution of the water-soluble copolymer salt
and water into the grinding mill. The proportions o~
water and copolymer salt are readily adju~table to
give the desired concentration of the salt in the mixture.
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