CA1049679A - Aqueous portland cement precursors comprising salts or styrene-maleic anhydride copolymers - Google Patents

Abstract

ABSTRACT

The amount of water required for processing wet process portland cement slurries is sharply reduced by adding to the slurry from 0.01 to 0.2 weight per cent, based on slurry solids, of a water-soluble salt of a styrene-maleic anhydride copolymer having a mole-cular weight of 1000 to 5000. The copolymer contains from 33 to 50 mole per cent of maleic anhydride and from 50 to 67 mole percent of styrene. The sodium salt is the preferable salt for use in the process.

Description

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. .
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:~ 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 :~ , - 17,404-F ~_3_ :~ .
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, :~49~79 : -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:
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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 j 17,404~F -6-., . , ' .

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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 .
., 17,404-F -7-~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) .

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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Claims (12)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A kiln feed slurry useful in a wet process to produce portland cement, having a water content of between 25% and 35% based on the weight of the slurry, said slurry containing from 0.01 to 0.2 weight % of a water-soluble monovalent inorganic salt of a copolymer containing from 33 to 50 mole % of maleic anhydride and from 67 to 50 mole % styrene and a molecular weight of from 1000 to 5000.

2. The composition of Claim 1 in which the salt is a sodium salt.

3. The composition of Claim 1 in which the salt is an ammonium salt.

4. The composition of Claim 1 in which the salt is a potassium salt.

5. The composition of Claim 1 in which the copolymer has a molecular weight of from 1200 to 3000 and-the salt is a sodium salt which is present in the mixture in an amount from 0.02 to about 0.075% by weight.

6. A method of preparing a kiln feed water slurry in the wet process for producing portland cement which comprises adding to the kiln feed water slurry mixture from 0.01 to 0.2% by weight, based on slurry solids, of a water-soluble monovalent inorganic salt of a styrene maleic anhydride copolymer containing from 50 to 67 mole % of styrene and 33 to 50 mole of maleic anhydride and a molecular weight of from 1000 to 5000.

7. The method of Claim 6 in which the copoly-mer is an alternating copolymer of equimolar proportions of styrene and maleic anhydride.

8. The method of Claim 7 in which the salt is a sodium salt.

9. The method of Claim 7 in which the salt is an ammonium salt.

10. The method of Claim 7 in which the salt is a potassium salt.

11. The method of Claim 8 in which the amount of copolymer salt is 0.02 to 0.075 weight %.

12. The method of Claim 7 in which the slurry contains from 25 to 35% water, and from 0.02 to 0.075 weight % of a sodium salt of an equimolar copolymer of styrene and maleic anhydride having a molecular weight of 1600.