CA1087961A

CA1087961A - Process for dispersing solid materials

Info

Publication number: CA1087961A
Application number: CA245,457A
Authority: CA
Inventors: Martyn G. Chapman; Brian Shaw
Original assignee: Albright and Wilson Ltd
Current assignee: Solvay Solutions UK Ltd
Priority date: 1975-02-11
Filing date: 1976-02-10
Publication date: 1980-10-21
Also published as: GB1548881A; FR2300609A1; IT1057165B; JPS51105987A; BE838447A; AU507756B2; NL7601386A; AU1097876A; DE2605340A1

Abstract

PROCESS FOR DISPERSING SOLID MATERIALS

A B B T R A C T
PolyphosPhate salt mixtures which have been obtained by the neutralization of a polyphosphate acid comprising from 82 to 86% by weight of P2O5 with a basic derivative of sodium or a mixture thereof with potassium have been found to be especially useful as dispersing agents for particulate inorganic solids in aqueous media. They are especially effective when used to disperse certain types of clay. The partially neutralized sodium salts of such polyphosphoric acids are surprisingly soluble in aqueous solution and the dispersants are preferably manufactured and transported in the form of such solutions.

Description

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This invention relates to a novel method for the dispersion and/or deflocculation of finely divided inorganic particulate solid material in an aqueous medium.
Dispersions of a variety of inorganic solids in 5 water which contain finely divided solid material, find use in a wide variety of industries, for example dispersions of clay and of pigment materials are used to the paper coating indus-try, dispersions of various raw materials are wide1y used in the cement industry and dispersing agents are added in large 10 quantities to water based oil well drilling muds to produce fluids of high solids content having specified flow properties.
A large number of other applications involving the dispersion of inorganic materials are constantly being developed.

Several chemicals have been developed which act as 15 dispersing agents and are widely used in industry as such. As the dispersing agent is purely additive and contributes little or nothing to the end use of the dispersed material, it is desirable to use an agent which is effective in as small a quantity as possible and it is preferably also readily avail-20 able at as low a price as possible.
Among the accepted dispersing agents are the saltsof the linear condensed phosphoric acids. Among those poly-phosphates of this type most commo~ly employed are those which are conveniently prepared by thermal methods such as the salts 25 of pyrophosphoric acid and tripolyphosphoric acid and the longer chain polyphosphate glasses. While the salts of polyphosphoric acids having a chain length of 2 or 3 can be prepared as homo-geneous species, salts of polyphosphoric acids havi~g an average chain length greater than three în fact comprise mixtures of a , , - 2 ~U~
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~0~79~1 spectrum of polyphosphate species the composition of which will vary with the average chain length and the method by which such compounds are prepared. We have now discovered that a parti-cular class o~ polyphosphate salts are especially effective as dispersing agents for inorganic solids in aqueous media.
The invention provides a process for dispersing a particulate inorganic solid in an aqueous medium which comprises ; adding to that medium a solution comprising the sodium salts or a mixture of the sodium and potassium salts of a plurality of polyphosphoric acids which solution has been obtained by reaction of a polyphosphori~ acid solution containg from 82 to 86% by weight of phospho~us pentoxide which a basic derivative of sodium or a mixture thereof with up to an equimolar quantity of a basic derivative of potassium in such a manner that no substantial hydrolysis of the polyphosphoric acid species present in a polyphosphoric acid solution takes place.
The salts of such polyphosphoric acid mixtures have ~` previously been proposed for use as fertilizer and as builders for liquid detergent compositions. Possibly because they con-tain some orthophosphate species they have not, in so far as we are aware, been recommended for use as dispersing agents. We have now discovered that the aqueous solutions of a plurality ~' of sodium salts derived ~rom such strong polyphosphoric acid solutions are especially useful as dispersing agents, parti-cularly in the case of clays, although the degree of advantage -~ ~or clays varies to some extent with the species of clay.
Such mixtures comprise species of the formula Mx Hy P 3n~1 where M may be sodium or a mixture thereof with potassium comprising at least 50 mole % of sodium ions, y is less than or equal to n-l the values of n, x and y satisfy .

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:10~'7~1 the equa-tion x~y=n-~2 and n is less -than 12. The sodium salts or mixtures thereof with potassium may be ~ully n~utralized, i.e. with y equal to 0 or may be obtained by partial neutrali-zation of the polyphosphoric acid species. The sodium salts are notably more effective than their potassium analogues in certain areas of application, most notably when used for the dispersion of clays. Furthermore, the salts of the particular polyphosphate anions employed are surprisingly stable to hydrolysis when present in an aqueous medium, this stabili~y being essential since the ultimate produc~ of such hydrolysis are orthophosphates which have no utility as dispersing agents.
Moreover we have discovered that the solubility of such sodium polyphosphate mixtures in water may be increasedif the pH of the solution is in the range 5 to 9, more notably in the range 6.0 to 8Ø This pH adjustment means that a greater proportion of partially neutralized acid salts are formed. It is therefore possible to prepare these solutions in a more con-centrated form which facilitates the handling and transport of the treatment solution. Accordingly the use of aqueous solu-tions of a mixture of the sodium polyphosphates as hereinbeforedefined having a pH in the range 5.0 to 9.0j more preferably 6.0 to 8.0, is preferred in the proces'ses of the invention.
The polyphosphate salts useful in the processes o~
the invention may be obtained by the controlled neutralization ~S of concentrated aqueous solutions of phosphorus pentoxide,with a basic derivative of sodium or a mixture thereof with a basic derivative of potassium according to the methods described in our published West German Patent Application 2359767. Thus the neutralization of the polyphosphoric acid will be carried out in a'reaction medium having a pH in the range 6 to 12, the - 3a -, 1/UI~979b;~L
temperature of which is below 70C. Preferably the pH of the reaction medium will be in the range 8 to lO. The temperature will conveniently be maintained in the range 15 to 70C, more preferably 15 to 40C. Where the final pH of the desired product falls outside the preferred pH limit - 3b -;`
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il79~i1 for the reaction mixture tlle majority of the reaction is preferably carried O-lt within these limits with the proportion of acid or base intro~luced being increased as appropriate at the end of a batch~ise procedure. Alternatively, the pH of the preformed product may be adjusted if desi~ed by a~dition of additional acid or base as required, The spectrum of the polyphosphoric acids species present in such solutions when at equilibrium is dependent upon the concentration of phosphorus pentoxide in the solution as is described for example in the Canadian Journal of Chemistry volume 34 (1956) page 790O It is characteristic of the polyphosphate salts useful according to the present invention that the spectrum of polyphosphate species present substantially corresponds to this SpeCtrUIn of polyphosphoric acidsO It is therefore necessary to ensure that the solution of phosphorus pentoxide in water has attained such an equilibrium before reaction with a basic compound takes placeO Equilibrium will be attained if the polyphosphoric acid solution is allowed to stancl at room lS temperature for a few minutes as will normally happen in the course of a conventional manufacturing procedureO
The solutions of phosphorus pentoxide in water may be produced by conventional means such as concentration of orthophosphoric acid solutions, dilution of polyphosphoric acid solu~ions having greater than the desired content of phosphorus pentoxide or dissolution of phosphorus pentoxide in water or in orthophosphoric acidO
Aqueous solutions derived from the dissolution of phosphorus pentoxide - in orthophosphoric acid are preferred for present useO The preferred solutions comprising some partially neutralized polyphosphate species may be prepared by neutrnlizlng with s~fficient base as to maintain the pH of the overall solution ., ,. '.
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in the deslred rsrlge, Thc dispersi.llg agents of tlie invention may be manufactured in any convenient concentration in aqueous solution and sufficient water to achieve this desired concentration, may be introduced into the reaction step as a heel 5 or as a solvent for the basic derivative, In general, solutions containing from 4 to 25% of the dispersing agent (expressed as percentage weight of pl~osphorus pentoxide on the total weight of solution) will be useful~
Preferably solutions containing from 15 to 22% by weight of phosphorus pentoxide are employedO
The solutions are then added to aqueous suspension of particulate~
inorganic materials in order to disperse those particlesO The processes of the invention find application in a wide variety of industries ~here the dispersion and : deflocculation /of inorganic materials in water is employedO The polyphosphate dispersing : agents of our inventi.on may be used in combination with other known dispersing de and/flocculating agentsO In particular they can be combined with ionic dispersants such as sodium hydroxide, sodium polyacrylate, sodium silicate~
sodium carbonate, sodium aluminate, ammonia, sodium oxalates and ammonium oxalates and dipole-dipole dispersants such as amino alcohols, polyamines and ar,lines. Such combined dispersing agents find particular use in the production of systems wherein close control of stability and ~iscosity of the suspension is required such as in the production of water based emulsion paints, Typically the processes will be applied to the dispersion of clays, limestones and pigments such as titaniaL The inorganic material may be present in aqueous suspension as solid particles of a size between 0005and 100,0 micronsO The solids will generally constitute from loO to 8000% by weight of the suspension, ', ' .
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79~1 the preferred range depending upon the particular ~pp]ication, for example, the processes of the invention will normally be applied to pigiment dispersions containing from 10 to 50~ by weight of pigment material and to clay suspensions containing 5 from 50 to 80%, preferably ~0 to 70% by weight of solid mater-ial.
The polyphosphates are added to the aqueous suspen-sion of solid material as aqueous solutions containing from 2 to 50% by weight of the polyphosphate salt. In general, it 10 will be preferred to employ solutions containing from 30 to ~0%
by weight of the polyphosphate salt. They are added to the suspension in a quantity so as to provide from 0.05 to 2.0%, preferably 0.05 to 1.0% by weight of phosphorus pentoxide on the weight of solid material. For the dïspersion of aqueous 15 clay suspensions, the polyphosphates are employed in a quan-tity of between 0.06 to 0.25% by weight of phosphorus pentoxide.
The use of the sodium polyphosphates of the invention is especiall~t advantageous when applied to processes of dispersing aqueous cla~ suspension. For the dispersion of pigments and ` 20 other simple inorganic solids, the solutions will be employed in a quantity so as to provide from 0.05 to 0.5% by weight of phosphorus pentoxide based on the weight of the solid material.
The discovery that the partially neutralized sodium salts of the polyphosphoric are surprisingly soluble represents 25 a further aspect of our invention. Thus our invention provides a solution having a pH in the range 5.0 to 9.0 of the sodium salts of a polyphosphoric acid which comprises from 82 to 86~ by weight of phosphorus pentoxide, which salts have been obtained by neutralizing the polyphosphoric acid with a basic derivative 30 of sodium in such a manner as to avoid any hydrolysis thereof.

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7~1 Such solutions will preferably comprise from 20 to 25%, more usually 22 to 25% by weight of phosphorus pentoxide.
The aqueous dispersing solution will be added to the suspension of inorganic material with suf~icient agitation to 5 ensure thorough mixing. A stable dispersion is produced.
The invention is illustrated by the following Examples:

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EXAM.'LL l A sodiulll polyphospllate solution useful according to this lnvcntion was prepared using the followillg procedure.
A heel of 426 parts by weight of water and 30 parts of a previously ; prepared product mix~ure was placed in a stainless steel vessel. The vessel was equipped with a blade stirrer and efficient cooling facilities and had provision for external recirculation of part of the liquor. 238 parts of a polyphosphoric acid solution comprising 84% by weight of P205 was fed into the tank under gravity at a temperature of 60C. Simultaneously 336 parts of a caustic soda ; solution comprising 46% w/w NaOH was pumped into the vessel at a point directly 10 opposite the acid inlet. The rate of addition of alkali was governed by a valve attached to a pH meter set so that the pH of the system rernained in the range 6 to 10, The temperature of the reaction mixture was maintained at less than 40C. The product was a clear colourless liquid having a pH of 7.0 and a specific gravity of 1.33 at 25C.

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The efficiency of the sodium polyphosphate solution as a dispersing agent was compared with that of other poly-phosphate dispersants by subjecting them to a comparative test 5 procedure. Each was gradually added to a 70% w/w solids ball clay and the viscosity of the resulting suspension was measured. The clay was composed o~ 30 parts by weight of quartz, 20 parts by weight of calcite and 50 parts by weight of kaolinite. The two components were thoroughly mixed during 10 the operation. The result of these tests were as follows:

DISPERSANT C~ION AVEE~AGE % P205 % MSPER- % AS VISCOS-C~N IN DIS- ~S~NT.ON P2Os ON ITY
LENG:rH PERSANT CEAY SOLIDS CLP~Y SOIIDS (POISE) . .
Sodium Tri- Na 3 57.9 0.15 0.087 1.2 15 polyphate Potassium Tri- K 3 47.5 0.40 0.190 2.6 polyphosphate Sodium Poly- Na 4 20.0 0.40 0.080 1.1 phosphate (as in 20 E~ple 1) ` Kalipol 25* Na /K 4 25.0 0-40 0.100 1.2 1: 1 , Kallpol 18 K 4 18.0 0.90 0.162 1.3 Ka~pol 35 AZ NH4 4 35.0 0.60 0.120 1.8 25 ~x~um Phosphate Na 5.5 62.7 0.20 0.125 1.4 Glass Sodium Phosphate Na 15.6 67.0 0.20 0.134 1.4 Glass * Kalipol is a registered Trade Mark.

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g~l Kalipo].~s 25~ 1.8 and 35~Z were ol>tained ~y ne~ltra].i~,lng a polyphosphoric acid solution with an eql~imolar mixture of bas:ic derivatives of potassium and sodium; with a basic derivative of potassium and a basic de~ivative of ammonium respectively in such a manner as to avoid any substantial hydrolsis of the poly~
S phosphate species.
The efEecti~eness of the various polyphosphates should be compared on the basis of the % weight of dispersant (expressed as weight.of P205) giving a minimum viscosityO It will be seen that the product of Example 1 performs substantially better than the majority of dispersants tested and measurably better than sodium tripolyphosphateO The difference between the last two is - sufficient to be significant to the commercial user `~

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for dispersing a particulate inorganic solid in an aqueous medium which comprises adding to that medium a solution comprising the sodium salts or a mixture of the sodium and potassium salts of a plurality of polyphosphor-ic acids of the formula Mx Hy Pn O3n+1 where M is sodium or a mixture thereof with potassium comprising at least 50 mole %
of sodium ions, y is less than or equal to n-1, the values of n,x and y satisfy the equation x+y=n+2 and n is less than 12, which solution has been obtained by reaction, at a pH of 6 to 12 and at a temperature of 15° to 70°C, of a polyphosphoric acid solution containing from 82 to 86% by weight of phos-phorus pentoxide with a basic derivative of sodium or a mix-ture thereof with up to an equimolar quantity of a basic derivative of potassium in such a manner that no substantial hydrolysis of the polyphosphate species present in the poly-phosphoric acid solution takes place.

2. The process of claim 1 wherein the polyphosphate salts present are the sodium salts.

3. The process of claim 1 wherein the poly-phosphate is added to the aqueous medium in an amount of from 0.5 to 2.0% by weight; expressed as weight of phosphorus pentoxide on the weight of solid material present.

4. The process of claim 3 wherein the polyphosphate is added in an amount of from 0.05 to 1.0% by weight.

5. The process of claim 1 wherein the particulate solid is a clay.

6. The process of claim 5 wherein the aqueous medium comprises from 50 to 80% by weight of solid material.