GB1595688A

GB1595688A - Treatment of aqueous systems

Info

Publication number: GB1595688A
Application number: GB23434/78A
Authority: GB
Original assignee: Ciba Geigy UK Ltd
Current assignee: Ciba Geigy UK Ltd
Priority date: 1978-05-26
Filing date: 1978-05-26
Publication date: 1981-08-12
Also published as: FR2426648A2; FR2426648B2; DE2921374C2; DE2921374A1; IT1207199B; IT7922996A0; JPS5511092A

Description

(54) TREATMENT OF AQUEOUS SYSTEMS (71) We, CIBA-GEIGY (UK) LIMITED, a British Company, whose registered address is: 30 Buckingham Gate, London SWIE 6LH do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a method of treating an aqueous system.

In our British Patent Specification No. 1458235, there is described and claimed a method of inhibiting the precipitation of the scale forming salts of calcium, magnesium, barium and strontium from aqueous systems over a wide temperature range, comprising adding to the aqueous system a minor proportion of a product comprising a telomeric compound of the formula:

and salts thereof, wherein R" is hydrogen or a methyl or ethyl residue, R is hydrogen, a straight- or branched alkyl residue, having from 1 to 18 carbon atoms, a cycloalkyl residue having from 5 to 12 carbon atoms, an aryl residue, an aralkyl residue, a residue of formula:

wherein R" has its previous significance and the sum n + m is an integer of at the most 100, or a residue-OX wherein X is hydrogen or a straight- or branched alkyl residue having from 1 to 4 carbon atoms and R' is a residue-OX wherein X has its previous significance.

There are a substantial number of commercial applications such as industrial boilers, cooling water systems, gas scrubbing plants, slurries e.g. china clayslurries, wherein it is important to maintain various solid materials that are found in waters in a suspended or dispersed state. If such solids cease to be suspended in the liquid, fouling of equipment may occur. This is true, for example, in so-called "oncethrough" cooling systems. If there is a plentiful supply of water in close proximity to an industrial plant, cooling is often accomplished by passing the water through heat transfer equipment and then discharging the water back to its source. Because of the large quantities of water that are employed in this system it is not feasible from an economic standpoint to filter the water in a conventional manner. For this reason deposit formation, within the plant, readily occurs and it is normally necessary to stop the operation periodically for cleaning purposes. Similarly corrosion of the plant leads to the deposition of iron oxides, which, if not carefully controlled, leads to mechanical failure of the plant.

In a modification of the method of British Patent Specification No. 1458235, we have now found that products comprising telomers of formula I also function as dispersing agents and/or antifoulants towards common deposits e.g. iron oxides, calcium and magnesium deposits, e.g. their carbonates, sulphates, oxalates and phosphates, and silt, alumina, silicates and clays found in such waters.

It is also known that polyacrylates and partially hydrolysed polyacrylamides having a molecular weight of at least 8000 are effective dispersants for use in aqueous systems. However, such dispersants generally have a low calcium tolerance, viz. they react with calcium cation to form a precipitate which, in turn, creates a deposition problem. In most practical situations, the aqueous system to be treated is high in hardness so that the known polyacrylates and polyacrylamides cannot be used effectively. Similar disadvantages are associated with other known dispersants e.g. phosphate and lignosulphonate dispersants.

In contradistinction thereto, we have found that the treatment of aqueous systems in hard water environments with products comprising telomers of formula I provides a very effective means of dispersing deposits, and potential deposits, in the system.

Accordingly, the present invention provides a method of treating an aqueous system having a calcium ion content of 5-1500 ppm'by weight and containing suspended solids, comprising adding to the aqueous system a minor proportion of a product comprising a telomeric compound of formula I, as hereinbefore defined, but modified to include substituents X which are water-solubilizing cations or a salt thereof.

Salts of the telomeric compounds of formula I are for example compounds in which some or all of the acidic hydrogens in the acidic compounds of formula I have been replaced by alkali metal - or alkaline earth metal ions, ammonium ions or quaternised amine radicals.

These salts also are effective in dispersing suspended solids in the hard water system treated and maintaining deposited matter in dispersion.

Preferably R" is hydrogen and it is preferred that the sum of m and n is an integer less than 60.

Preferred examples of substituent R include hydrogen, or a residue of formula:

wherein R" and m have their previous significance.

Particularly preferred compounds of formula I are those wherein R is hydrogen or a residue of formula:

wherein R' is OX wherein X is hydrogen or a water-solubilising cation, R" is hydrogen and m and n are integers up to 30.

Examples of the bases with which compounds of formula I may be reacted in order to form partial or complete salts are the hydroxides and carbonates of sodium, potassium and ammonium. Similarly organic bases may be employed, for instance primary, secondary and tertiary alkyl amines and substituted alkyl amines in which the total carbon number does not exceed twelve, such as triethanolamine.

The compounds of formula I are not new; the compounds and their process of manufacture are described in U.S. Patent Specification No. 2,957,931.

Thus the compounds of formula I may be prepared in a convenient manner by reacting various molar ratios of a compound of formula: CH2=CR"-CO2H II wherein R" has its previous significance, with a compound of formula:

wherein R' has its previous significance and R"' is hydrogen, a straight or branched chain alkyl residue having from 1 to 18 carbon atoms, a cycloalkyl residue having from 5 to 12 carbon atoms, a phenyl, a benzyl residue or OX wherein X has Its previous significance.

Alternatively a salt of the compound of formula III may be employed in which the acidic hydrogens have been partially or completely replaced by cations derived from the salt forming bases hereinbefore described.

The reaction is carried out in a solvent inert under the reaction conditions and in the presence of a reaction initiator. Suitable reaction solvents are for instance, water, aqueous ethanol or dioxan. Suitable reaction initiators include materials which decompose under the reaction conditions to yield free radicals. Examples of such materials are bisazoisobutyronitrile, organic peroxides such as benzoyl peroxide, methyl ethyl ketone peroxide, ditertiary butyl peroxide and monobutyl hydroperoxide, and oxidising agents such as hydrogen peroxide, sodium perborate and sodium persulphate.

The products of this process are obtained as solutions. These may be subjected to partial or complete evaporation under reduced pressure. The unpurified reaction products may be used as the telomeric products in the method of the invention. The reaction products may also be purified. The purification procedure may be: i) by evaporation of reaction solvent, dissolving the residue in water, washing with a water immiscible organic solvent e.g. ether and evaporation of the aqueous solution ii) by evaporation of reaction solvent, dissolving the residue in e.g. methanol, filtration and reprecipitation e.g. by addition of ether.

When the reaction products are employed without purification the ratio of reactants is important in that the activity of the product for a specific application can vary accordingly.

Salts of the compounds of formula I in which some or all of the acidic hydrogens in the compounds of formula I have been replaced by the cations derived from the salt forming bases hereinbefore defined, may be prepared by mixing an aqueous or alcoholic solution of the compound of formula I with an aqueous or alcoholic solution containing an amount of the requisite base in excess of, equal to or less than the stoichiometric requirement. The solvent may then be removed by evaporation. In many of the water-containing systems where inhibitors used in the method of this invention would prove useful, the water is sufficiently alkaline to effect neutralisation and only the product of formula I need be added.

The precise composition of the products of this preparative process has not been fully defined. Nuclear magnetic resonance examination has shown; however, that in addition to unreacted compound of formula III and polymerised compounds derived from formula II, the reaction product of the process hereinbefore described contains a compound of the formula I as hereinbefore defined.

For most relatively dilute aqueous dispersions treated, the amount of the product comprising a compound of formula I to be used in the method of the invention when used as a dispersant, may be, for example, 1 part per million up to 200 parts per million, preferably 2 to 20 parts per million by weight. However, aqueous slurries to be treated may require much higher levels of the product comprising a compound of formula I e.g. from 0.1 to 5% by weight on total solids, which can be as high as 70% by weight of the total aqueous system.

The product used according to the method of the invention may be incorporated into the aqueous system to be treated in conjunction with other compounds known to be useful in water treatment.

Further dispersing and/or threshold agents and/or anti foam agents may be used, together with a product comprising a compound of formula I, such as for example polymerised acrylic acid and its salts, hydrolysed polyacrylonitrile, polymerised methacrylic acid and its salts, polyacrylamide and co-polymers of acrylamide with acrylic and methacrylic acids, lignin sulophonic acid and its salts, tannin, naphthalene sulphonic acid/formaldehyde condensation 'products, starch gnd its derivatives, and cellulose. Specific threshold agents such as for example, hydrolysed polymaleic anhydride and its salts, alkyl phosphonic acids, 1aminoalkyl- I,l-diphosphonic acids and their salts and alkali metal phosphates, may also be used. Antifoaming agents which may be used include distearyl sebacamide, distearyl adipamide and ethylene oxide condensates thereof; in addition to fatty alcohols, such as capryl alcohols and their ethylene oxide condensates.

The method of the present invention finds particular use in the china clay industry. In this industry, it is most important to obtain slurries which will not appreciably separate out during transportation from the clay pits to the user. At the high concentrations of suspended solids in these slurries, the telomers of formula I have been found to exhibit dispersion of china clay and to be of value as "in- process" dispersants and as grinding aids.

The following Examples 7 to 11 further illustrate the present invention.

Examples 1 to 5 describe the production of various products containing compounds of formula I the use of which, as dispersing agents, is shown in Examples 7 to 11.

Example 6 is a comparative Example. Parts and percentages shown therein are by weight.

Example 1 Reaction of acrylic acid and sodium hypophosphite in a 2:1 molar ratio.

To a solution of 44 g (0.5 mole) sodium hypophosphite in 100 g water at 750C is added a solution of 14.4 sodium persulphate in 100 g of water dropwise over a period of 2.5 hours. 5 minutes after the start of this addition the addition of 72 g (1 mole) acrylic acid is commenced, the acrylic acid being added over a period of 2 hours. On the completion of the additions, the reaction mixture is heated to 850C and maintained thus for a period of 2 hours.

There is obtained an aqueous solution having a solids content of 25.2%.

A sample of the telomer was isolated by evaporating 100 g of the solution to dryness. The residue was treated with 200 mls hot methanol. The solution was filtered to remove unreacted sodium hypophosphite and sodium persulphate decomposition products. The filtrate was concentrated to a volume of 100 mls and the telomer precipitated by the addition of 1 litre diethyl ether. The telomer of formula I so obtained after drying under vacuum at 500C had a phosphorous content of 12.7% and molecular weight of 440, determined by osmometry in water.

Example 2 Reaction of acrylic acid and sodium hypophosphite in a 4:1 molar ratio.

The telomer was prepared by the method described above excepting that 144 g (2.0 moles) acrylic acid was used instead of 72 g.

The telomer of formula I isolated as described in Example 1 had a phosphorus content of 8.0% and a molecular weight of 665 determined by osmometry in water.

Example 3 Reaction of acrylic acid and sodium hypophosphite in a 6:1 molar ratio.

The telomer was prepared by the method described above in Example 1 excepting that 216 g (3.0 moles) acid were used instead of 72 g.

The telomer of formula I isolated as in Example I had a phosphorus content df 5.2% and molecular weight of 696, determined by osmometry in water.

Example 4 Reaction of acrylic acid and sodium hypophosphite in a 8:1 molar ratio The telomer of formula I was prepared by the method described above in Example 1, excepting that 288 g (4.0 moles) acrylic acid were used instead of 72 g.

The telomer isolated as in Examplel had a phosphorus content of 4.9% and molecular weight of 750, determined by osmometry in water.

Example 5 Reaction of acrylic acid and sodium hypophosphite in a 16:1 molar ratio The telomer was prepared by the method described above in Example 1 excepting that 576 g (8.0 moles) acrylic acid were used instead of 72 g.

The telomer of formula I had a phosphorus content of 2.0% and molecular weight of 1,130, determined by osmometry in water.

Examples 6-11 Demonstration of dispersion activity of the product from Examples 1--5 for calcium phosphate at an additive concentration of s ppm.

Test method A small circulating rig was set up as shown in the accompanying drawing and filled with 18 1. tap water (Manchester Town Mains) and recirculated at 550/l/hr.

18.4 g CaCl2.6H2O and 32.2 g Na3PO4.12H2O were added, the temperature of the water adjusted to 40 C and the pH to 8.0 (with N.HCl). After allowing the rig to recirculate for 1 day, samples of the calcium phosphate dispersion were removed and sufficient of a 1000 ppm solution was added to give 5 ppm of the additive in solution. The dispersions were then allowed to cool to ambient temperature (25 C), stirred well, poured into 4 cm, glass cells and readings of the absorbance of these dispersions were taken at various times at a wavelength of 400 nm using a Unicam SP 1800 Spectrophotometer. The higher the reading obtained the greater the amount of calcium phosphate suspended in solution.

The results are shown in Table 1, and demonstrate the superior dispersion activity of products of Examples 1 to 5 relative to a control experiment.

TABLE I

Additive Optical density after Products Example from 0 mins 10 mins 20 mins 30 mins 40 mins 50 mins 60 mins 70 min 80 mins 90 mins 6 - 1.7 1.14 0.56 0.45 0.38 0.34 0.30 0.27 0.25 0.23 7 Example 1 1.7 1.6 0.78 0.60 0.46 0.40 0.35 0.31 0.29 0.27 8 Example 2 1.7 1.69 1.53 1.17 0.82 0.65 0.60 0.54 0.49 0.47 9 Example 3 1.7 1.69 1.63 1.58 1.25 0.85 0.75 0.68 0.64 0.60 10 Example 4 1.7 1.69 1.64 1.60 1.32 1.05 0.86 0.78 0.73 0.68 11 Example 5 1.7 1.7 1.69 1.65 1.58 1.45 1.26 1.12 1.0 0.98 Similar results were obtained using the products of Examples A to K of British Patent Specification No. 1458235.

Claims

WHAT WE CLAIM IS:1. A method of treating an aqueous system having a calcium ion content of 5-1500 ppm by weight and containing suspended solids, comprising adding to the aqueous system a minor proportion of a product comprising a telomeric compound of formula I:

or a salt thereof, wherein R" is hydrogen or a methyl or ethyl residuie, R is hydrogen, a straight- or branched- alkyl residue having t'rom 1 to 18 carbon atoms, a cycloalkyl residue having from 5 to 12 carbon atoms, an aryl residue, an aralkyl residue, a residue of formula:

wherein R" has its previous significance and the sum n + m is an integer of at the most 100, or a residue-OX wherein X is hydrogen, a water-solubilising cation or a straight- or branched- alkyl residue having from I to 4 carbon atoms and R' is a residue-OX wherein X has its previous significance.
2. A method as claimed in claim I wherein R" is hydrogen and the sum of m and n is an integer less than 60.
3. A method as claimed in claim I or 2 wherein R is hydrogen or a residue of formula:

wherein R" and m are as defined in claim 1.
4. A method as claimed in claim 3 wherein R is hydrogen or residue of formula:

R' is -OX wherein X is hydrogen or a water-solubilising cation, R" is hydrogen and m an n are integers up to 30.
5. A method as claimed in any of the preceding claims wherein the dispersion treated is dilute and the amount of the product comprising a compound of formula I added is from I to 200 ppm, by weight.
6. A method as claimed in claim 5 wherein the amount of the product comprising a compound of formula I added is 2 to 20 ppm, by weight.
7. A method as claimed in any of claims 1 to 4 wherein an aqueous slurry is treated and the amount of the product comprising a compound of formula I added is from 0.1 to 5% by weight on total solids.
8. A method as claimed in any of the preceding claims wherein the compound of formula I is used in conjunction with other compounds known to be useful in water treatment.
9. A method as claimed in claim 8 wherein in addition to the telomeric compound a dispersing agent and/or threshold agent is added.
10. A method as claimed in claim 9 wherein the dispersing agent is polymerised acrylic acid or a salt thereof, hydrolysed polyacrylonitrile, polymerised methacrylic acid or a salt thereof, polyacrylamide or a copolymer of acrylamide with acrylic acid or methacrylic acid, lignin sulphonic acid or a salt thereof, tannin, a naphthalene sulphonic acid/formaldehyde condensation product, starch or a derivative thereof or cellulose.
II. A method as claimed in claim 9 wherein the threshold agent is hydrolysed polymaleic anhydride or a salt thereof, an alkyl phosphonic acid, a l-aminoalkyl- l,l-diphosphonic acid or a salt thereof, or an alkali metal phosphate.
12. A method as claimed in any of the preceding claims wherein an antifoam agent is also added.
13. A method as claimed in claim 12, wherein the antifoam agent is distearyl sebacamide, distearyl adipamide or an ethylene oxide condensate thereof; or a fatty alcohol or an ethylene oxide condensate thereof.
14. A method of treating an aqueous system substantially as described with reference to any of Examples 7 to 11.
15. An aqueous system when treated by a method claimed in any of the preceding claims.