CA1128402A

CA1128402A - Water treatment

Info

Publication number: CA1128402A
Application number: CA316,871A
Authority: CA
Inventors: Kenneth G. Cooper
Original assignee: Albright and Wilson Ltd
Current assignee: Solvay Solutions UK Ltd
Priority date: 1977-11-25
Filing date: 1978-11-24
Publication date: 1982-07-27
Also published as: ES475398A1; AU4187078A; MX150586A; DE2850925A1; FR2409964B1; IT1109096B; FR2409964A1; JPS6017830B2; SG34883G; IT7869694A0; AU528091B2; JPS5499746A; HK59183A; AR217882A1; DE2850925C2

Abstract

WATER TREATMENT

A B S T R A C T

Potentially scale forming corrosive water systems are treated with threshold amounts of cyclic dimer of 1-hydroxyethan-1, 1-diphosphonic acid or its homologs. Dimer comprises a single 6 membered ring including 2 C-O-P bonds and is particularly effective in conjunction with other threshold agents, anti-corrosive agents, threshold synergist, polyelectrolytes and dispersants, and for treating water systems containing strong oxidising agents such as chromate.

Description

4~2 The present invention re1ates to water treatment, and in particular to the treatment of scale forming or corrosive water systems, such as the threshold treatment of evaporators, cooling systems or oil wells, in order to inhibit scale formation and/or corrosion.

The evaporation of sea water and other brackish or non-potable waters in order to provide drinking water entails problems of scale deposition on the heat exchange surfaces of the evaporator. It is theoretically possible to prevent scale formation by use of sequestering agents such as phosphates or citrates, capable of forming soluble complexes with the metal ions of the scale forming salts (usually calcium and magnesium ions). However, sequestration of the ions would require the presence of a substantially stoichiometric amount of complexant based on the scale forming ions, which would be prohibitively expensive.

However, there exists a small class of compounds which, when dissol-ved in water in proportions as low as 0.1 to 100 ppm have the power to inhibit the fouling of heat exchange surfaces by scale. Such concentrations are of a ver~ much smaller order of magnitude than those which would be required to sequester the ions (of the order of several percent by weight).
The mechanism of this phenomenon, which is called the threshold effect, is obscure, but it clearly differs from sequestration both because of the very much smaller concentrations of agent required and because many common seq-uestrants such as citrates do not exhibit threshold properties. Unlike sequestrants, threshold agen~s may be effective in very small concentrations, even when they do not prevent deposition of solids, by inhibiting the tendency of the deposited solids to form a tenaceous scale on the heat exchange surfaces.

Another scaling problem can arise when water is injected in bulk through boreholes into partially exhausted oil bearing strata in order to facilita~e the enhanced recovery of residual mineral oil. The water may tend to deposit barium sulphate, barium carbonate, calcium sulphate and/or calcium carbonate scale causing blockage of the boreholes.

' ~.~z~

Another problem in connection with water treatment is corrosion oF metal equipment exposed to water in, for example, cooling water systems. It is known ~hat certain compounds usual1y in concentrations s1ight1y greater ~han those required for thresho1d treatment ~e.g. 10 to 500 typically 50 to 200 ppm) tend to inhibit corrosion, especial1y of iron, steel, copper and their alloys.

It is known that l-hydroxyethane-l, l-diphosphonic acid, herein-after referred to as "HEDP" and its salts exhibit a useful threshold effect, and they have been used successfully to treat evaporators. They are also effectjve corrosion inhibitors. As used herein, the term HEDP
includes homo10gs of HEDP containing up to 20 carbons e.g. l-hydroxy-butane-l,l-diphosphonic acid or l-hydroxy-3-phenylpropane-1,1diphosphonic acid.

We have now discovered that certain dimeric condensates o~ HEDP
exhibit powerful thresho1d and corrosion inhibiting properties, and are effective at 1cwer dosage rates thatn HEDP itself and retain effective-ness for longer periods, in certain kinds of water system. They are particularly useful in the treatment of oi1 wells or water syste~s which contain traces of strong oxidising agents such as chromate and bromine, which are sometimes present in water systems.

The 1itera~ure concerning the chemistry of the dimeric condensates of the diphosphonic acids is contradictory. The ear1y work of Prentice, Quimby, Grabenstetter and Nicholson reported in JACS August 1972, pp 6119 to 6124, which formed the basis of a series of Patent App1ications, granted or assigned, to Procter and Gamb1e, indicated that the reaction of acetic anhydride with phosphorous acid in a non-aqueous solvent cou1d be made to yie1d a cyc1ic dimer joined by a P-O-P and a C-0-C bond. The aforesaid workers denied the existence of a dimer containing a C-0-P
C-0-P ring. However, subsequent work by Co11ins, Frazer Perkin and Russe1 reported in JACS 1974 c1ear1y indicated that the a11eged P-O-P, C-O-C cyc1ic dimer was identica1 with a product obtained by heating HEDP under vacuum.

~;Z84¢~2 -- 3 ~

They presented strong evidence to show that this product is in fact a condensate of the for~ula:

\C/ \O
R ~ ¦ / R
~ I / \ PO H

FOR~
, where R is methyl.
The products which we have now found to be of particular value as threshold agents and corrosion inhibitors are dimeric condensates of HEDP
wh;ch were obtained by heating anhydrous HEDP at 170 - 180C under vacuum to remove 1 mole of water per mole of HEDP The products have been identi-fied as having the formula 1 above where each R is an alkyl, aryl, aralkyl or aliphatic ether group having 1 to 20 carbon atoms and will be referred to hereinafter as HEDP dimer". We believe that the same products may be obtained from the react;on of for example acetic anhydrides with phosp-horous acid as described, for example, in B.P. 1,079,340, and is also formed when a tetra metal salt o~ HEDP jS heated as described in B.P.
1,345,518. The term HEDP dimer" as used herein is not therefore to be construed as limited to HEDP dimer produced by any particular process.
The preferred HEDP dimer is the dimer of l-hydroxyethane-l,l-diphosphonic acid itself. It will be apparent that the water soluble and sparingly atersoluble salts and esters of HEDP dimer are equivalent to the dimer forthe purposes of this invention. For convenience, the term HEDP dimer"
will be used herein, where the context so permits, to include such salts and esters.

', . ' .

~ ~z~z Our invention accordingly provitles a method for the inhibition of scale formation or of corrosion, in aqueous systems which have a tendency or potential to deposit scale or to corrode meta1 surfaces, which method comprises adding thereto, respectively, a threshold or corrosion inhibiting amount of HEDP dimRr as herein defined.

Preferably HEDP dimer is used according to the invention as its alkali metal (e.g. sodium or potassium) or ammonium salts, e.g. its di, tri, or tetra sodium salts or hexammonium salt. Other water soluble salts, including salts of organic bases such as methylamine or trimethylamine are also operative. It is also possible to employ water soluble esters, such as polyoxyethylene esters, or partial esters or their salts, such as the sodium salt of the dimethyl ester. Sparingly soluble derivatives are also operative to give a controlled solubility additive.

The HEDP dimer is preferably used in the proportions conventional in threshold treatment or corrosion inhibition i.e. at concentrations of 0~1 to 100 ppm, preferably 1 to SO ppm e.g. 2 to 20 ppm for threshold treatment or ~ to 500 ppm, preferably 10 to 200 ppm for corrosion inhibition.

The invention is particulary applicable to the treatment of the sea water which is fed to the evaporators used for making drinking water in ships and arid coastal or island localities, especially chlorinated sea water and most particularly sea water which is subject to continous chlorin-ation. The HEDP dimer is also of particular use ;n the treatment of water injected into o;l wells during secondary recovery of oil, in order to ;nhibit the formation of barium or calcium conta;n;ng scales. The HEDP d;mer ;s most effective in neutral or alkal;ne solut;ons.

We have discovered HEDP d;mer may be used, according to a further aspect of the present ;nvent;on ;n conjunction with other threshold or corrosion ;nhib;t;ng agents or ingredients of commercial threshold active compositions or corrosion inhibitors such as condensed phosphates e.g.
threshold agents such as sodium tr;polyphosphate,sodium or potass;um hexa-metaphos?hate, H~DP itself,aminomethylene phosphonic acids e.g.~amino tris (methylene phosphon;c) acid or ethylenediamine tetra (methylenephosphon;c) acid; threshold synergists such as d;carboxylic or hydroxycarboxyl;c acids, ~Z8~2 5 .
eOg. malonic, maleic, malic, tartaric, lactic, citric, adipic, succinic, pimelic, sebacic or suberic acids; dispersants, e.gO l;gnin sulphonates, tannin or ~ethylene b;s naphthalene sulphonates, polyelectrolytes such as polymaleic acid, polyacrylic acid and polymethacrylic acid; corrosion inhibitors such as water soluble zinc salts, molybdates, nitrites, chromates, silicates, triazoles, substituted thiazoles orthophosphates, polyol esters; biocides, and antifoams~ References in the foregoing to acids are to be construed as importing references to the corresponding water soluble or sparingly water soluble salts and esters which are equivalent to the acids for the purposes of this invention. It is within the scope of the present invention that HEDP dim~r may also be used in aqueous systems which contain various other inorganic and/or organic materials, particularly all ingredients or substances used by the water treating industry with the proviso that such materials do not render HEDP dimer substantially ineffective for the desired purpose of scale or corrosion inhibition.
Accord;ng to a further aspect, therefore, our invention provides compositions for threshold treatment which contain from 5 to 95% by weight of the total active material, of HEDP dimer, the balance of the active material consisting essentially of at least one other threshold agent or anti-corrosive agent, and/or at least one dispersent, polyelectrolyte and/or threshold synergist.
By "active material" is meant those ingredients which have threshold~anti-corrosive, dispersive, synergistic, or surface activity, and excluding any inert diluent, or any solvent, such as water, which may, optionally be present in the composition.
Threshold synergists are substances, such as maleic or adipic acid which are not in themselves threshold agents, but which enhance the threshold activity of HEDP di~er. Preferably the HEDP dimer is present in a proportion of from 10 to 80% by weight of the total active material, e.g. 30 to 70% most preferably 40 to 60%.

EXA~IPLE 1 - TIIRESHOLD ACTIVITY OF ~IEDP CYCLIC DIMER

The ability of sub-stoichiome-tric amounts of HEDP dimer to inhibit the precipitation of calcium carbonate has been demonstrated in a labora-tory simulation of an evaporative cooling water system. In this, a natur-al1y hard water from the town supply was recirculated around a system where the flow was alternately heated to about 70C by a nickel sheathed immersion heater and then cooled ko about 40C in a forced draught cooling column.
Scale, formed by the thermal breakdown of calcium bicarbonate, was deposited on the heater sheath and the quantity determined by dissolution methods. A
typical analysis of the water used in these experiments was as follows:-Total Hardness = 149 ppm CaC03Temporary Hardness = 78 ppm CaC03 Chloride = 40 ppm Cl pH = 6.9 The effectiveness of HEDP Dimer as a threshold agent for calcium carbonate is sho~m by the following results (Table 1):-T A B L E
.. . . _ _ __ Scale deposited % Inhibition Inhibitor Concn ppm expressed as mg w.r.t. the - CaC03 b~ank . . ... _ ... _ .... . . . _ .. _ Blank 0 403 0 HEDP Cyclic Dimer 2 83 79.4 . . . _ . _ The structure of the dimer was confimed by the following tests:-112B~Z

A. ELEMENTAL ANALYSIS
1.1 ~ Total P.

Breakdown Procedure % P Found (a) Wet oxidation + persulphat:e 28.63; 28.65 (b) Acid persulphate oxidation28.66; 28.76 (c) Peroxide fusion - Parr bomb28.75; 28.92 Mean ~ Total P = 28.73 = ~ , = . _ .
1.2 Ortho P,_C, H; Moisture Ortho P 50 ppm p % C 11. 1%
% H 4.1%
% Moisture 12.6%
(1 hour at 120C) . .

B. MOLECULAR FORMULA
Molecular Formula Atom Ratio % Found Theory Found Theory P 28.7 28.84 4.00 ~ 4 C 11.1 11.2 4.00 4 H 4.1 4.19 17.7 18 (diff) O 55.3 55.8 14.9 15 H20 12.6 12.56 On the results obtained the molecular formula is:-4 12 4 12 3H2; Mol. Wt. 430.

C. STRUCTURAL FORMULA

(i) X-ray The X-ray powder photograph of the sample was substantially .
.

1~284~;2 i identical with that of the hydrated cyclic dimer prepared by Collins, Frazer, Perkins and Russell(JCS-Dalton, 1974, 960) as:-OCH O
Ill3 ll OH ~ P C - P OH
OH
O O OH

FORMU~A 2 HO - P - C - P - OH
(ii) N.M.R.

lH NMR
The spectrum consists of an 'OH' and a ' - P - C - P -' triplet absorption. The chemical shift of the 'CH3' is 2ppmorandis consistent with this 'CH3l being in a more strained environment than the corres-ponding 'CH3' in HEDP monomer (chemical shift 1.8 ppmor).

31p NMR

The spectrum consists of two complex absorptions of equal intensity, one at -5.2 ppm and the other at -16.0 ppm (from external 85% H3P04 refer-ence), i.e. two magnetically different p nuclei are present in equal abundance.

3y preparing the methyl ester~ other works (JACS 1972, 94, 6119) have shown that the -16.0 ppm absorption is due to the 'P03 units attached to the ring.

8~2 The NMR data given above cou1d be accounted for by either of the following structures:-O CH O O CH O
~ ~3 ~ 3 HO - P C P - OH HO - P C - P OH
1H I I bH
o o o ~
fH ~ OH
HO P C P - OH HO - P - C - P OH
Il I ~ 11 I' 11 (A) (B) FOR~IULA 3 -El;minating the proton coupling gave a 31p spectrum consisting of two triplets centred at -5.2 ppm and -16 ppm. This result favours struc-ture B, since structure A should give rise to a more complex spectrum showing both P-C-P and P-O-P coupling, whilst s~ructure B would give P-C-P
only.
D. POTENTIOMETRIC TITRATION
_ . _ _ _ . . . .. ...
Using 0.5 - 1.09 sample in 100 ml water a potentiometric titration with l.ON HaOH shows two end-points. The 1st end-point at approxi-mately pH 5.5 corresponds to 4 replaceable H and the second end-point at pH 10.7 to a total of 6 replaceable H.

~10-The high stability of the dimer compared with -the monomer in the presence of strong oxidising agents, was demonstrated as follows:

A. STABILITY TO OXIDATION
(i) Br2/NaHC03 HEDP monomer was added at a level of 10 ppm to a solution containing 100 ppm NaHCO3 and 10 ppm Br2. The resulting solu-tion (pH 7.8) was maintained lat 30C. and 20 ml aliquots removed for analysis. The results were as follows:

TABLE_2 Time PO4 Found Per Cent (Secs? (Mlcrograms) Decomposition O lo9 9.4 4.1 15235 14.8 7.0 357 19.9 9.8 533 25.6 12.8 827 31.2 15.8 12~0 39.7 20.S

2~ 1470 46.0 23.9 1785 S4.2 28.3 The experiment was repeated using 10 ppm HEDP dimer. The results were as follows:

25 Time PO4 Found Per Cent (Secs) (Micrograms)Decomposition _ . _ . .... . _ O 1.1 320 1.3 0.10 910 1.7 0.30 1845 2.1 0.49 ~Z84`~2 This example clearly shows that HEDP dimer is s-table under the test conditions, whereas HEDP monomer is attacked wnder these conditions.
(ii) Sea Water containing bromine - pH 8.3 The cyclic dimer was added to artificial bromine-containing sea water at a level of 10 ppm. The mixture was split into two portions, one of which was allowed to stand at room temperature and the other was hea-ted on a steam bath. The analytical results were as follows:

ppm Br2 Present Overnight at room Steam bath for 1 temperature hour ppm PO4 ppm PO4 found found 0 0.31 0.29 2.9 0.32 0.30 156.1 0.35 - ~
0 30 0.28 11.0 0.50 0-34 15.1 0.30 0.20 The artificial sea water used in this experiment had the composition.
NaCl KCl M~C126H20 CaC126H20 NaBr NaHC03 MgSO43H2O Town Water 265g 7.3g 6.3g 21.7g 2.9g 2.0g 46.9g to 10 litres pH adjusted to 8.5 Compared to results obtained for HEDP monomer in 25 bromine containing water at 30C (See Example 2A(i)), the sample of dimer tested shows no evidence for oxidative breakdown in the presence of bromine.

~28~V2 B. ACID AND ALKALINE_~IYDROLYSIS
(i) 0.5g samples of the dimer hydrate were heated under reflux 4N.H2S04 for 1 hour, (B) 100 ml 4N.H2S04 for ~ hours and (C) 100 ml N.NaOH for 2 hours.
After hydrolysis, each solution was neutralised to pH 8.5 and made up to 200 ml with distilled water.
A 20 ml aliquot was then taken for the determination of HEDP
monomer. The results are given in Table 5.

T A B L E S

Hydrolysis¦ Dimer Hydrolysed Expt. P w/w BLANK _ (A) - acid 1 hour15 + 1 -(B) - acid 4 hour49 + 1 (C) - alkali 2 hour _ _ *under the conditions used this result is at the limit of reproducibility of the method.

The results obtained show that the dimer is hydrolysed to monomer in strongly acid solution but is unaffected by N. sodium hydroxide over a similar time scale.
- 20 (ii) The possibility of orthophosphate formation by hydrolysis was checked by refluxing 50 mg samples of the dimer for 20 hours with N.NaOH and 9N.H2S04. Each solution was neutralised and made up to 250 ml with distilled water. No orthophosphate ( O.S ppm ortho P) was found in either of these solutions.

i3 -i The following compositions were prepared and tested by the method of Example 1. All percentages are weight.

6% HEDP d;mer potassium salt 14% Potassium polyacrylate Balance Water . .
50% HEDP dimer 50% Adipic acid 50~ HEDP dimer 50% Sodium lignin sulphonate 50% HEDP dimer 50X Sodium tripolyphosphate 80% HEDP dimer 20% HEDP

Z~

40% HEDP dimer 60% Zinc sulphate 75% HEDP dimer 25% sod;um chromate 60% HEDP dimer 40% sodium molybdate /

70% HEDP dimer 30% sodium nitrite In each case the composition of the example provided satisfactory inhibition of scale formation.

Claims

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

1. A method for the inhibition of scale formation or of corrosion, in aqueous systems which have a tendency or potential to deposit scale or to corrode metal surfaces, which method comprises adding thereto, respectively, a threshold or corrosion inhibiting amount of a dimeric condensate of 1-hydroxyalkyl-1,1-diphosphonic acid having the formula:

( I ) wherein R is a C1 to C20 hydrocarbon group, or a water soluble or sparingly water soluble salt or ester thereof.

2. A method according to claim 1, wherein the water system contains a strong oxidizing agent.

3. A method according to claim 2, wherein the strong oxidizing agent is bromine.

4. A method according to claim 2, wherein the strong oxidizing agent is chromate.

5. A method according to any of claims 1, 2 and 3, wherein said dimeric condensate is added as its sodium, potassium and/or ammonium salt.

6. A method according to any of claims 1, 2 and 3, wherein said dimeric condensate is added in a concentration of from 0.1 to 100 ppm.

7. A method according to claim 1 wherein the aqueous system is a sea water evaporator.

8. A method according to claim 7, wherein the sea water is subjected to chlorination.

9. A method according to any of claims 1, 2 and 7, wherein the aqueous system is neutral or alkaline.

10. A threshold treatment or anti-corrosive composition containing from 5 to 95% by weight of the total active material of a dimeric condensate of 1-hydroxyalkyl-1,1-diphosphonic acid having the formula:

(I) wherein R is a C1 to C20 hydrocarbon group, or a water soluble or sparingly water soluble salt or ester thereof, the balance of the active material consisting substantially of at least one other threshold treatment and/or anti-corrosive agent, and/or at least one dispersant, and/or at least one threshold synergist and/or at least one biocide and/or antifoam.

11. A composition according to claim 10, wherein the proportion of said dimeric condensate is 10 to 80 by weight of the total active material.

12. A composition according to claim 11, wherein the proportion of said dimeric condensate is 30 to 70 by weight of the total active material.

13. A composition according to claim 10 wherein the active material comprises a polyelectrolyte.

14. A composition according to claim 10 wherein the active material comprises a threshold synergist.

15. A composition according to claim 14, wherein the threshold synergist is a dicarboxylic acid having from 3 to 10 carbon atoms, or a water soluble or sparingly water soluble salt or ester thereof.

16. A composition according to claim 15, wherein the dicarboxylic acid is adipic acid.

17. A composition according to claim 10 wherein the active material comprises a lignin sulphonate.

18. A composition according to claim 10, wherein the active material comprises a condensed phosphate.

19. A composition according to claim 18, wherein the condensed phosphate is an alkali metal tripolyphosphate.

20. A composition according to claim 18, wherein the condensed phosphate is an alkali metal hexametaphosphate.

21. A composition according to any of claims 10 to 20, wherein the active material comprises 1-hydroxyethane-1,1-diphosphonic or a water soluble or sparingly water soluble salt or ester thereof.

22. A composition according to any of claims 10 to 21, wherein the active material comprises a zinc salt.

23. A composition according to claims 10 to 22 wherein the active material comprises a chromate.

24. A composition according to claims 10 to 23 wherein the active material comprises a molybdate.

25. A composition according to any of claims 10 to 24, wherein the active material comprises a nitrite.

26. A composition according to claims 10 to 25, wherein the active material comprises an anti-foam and/or biocide.

27. A method for the treatment of aqueous systems comprising adding thereto a threshold or corrosion inhibiting amount of a composition according to any of claims 10 to 12.

28. A method for the treatment of aqueous systems comprising adding thereto a threshold or corrosion inhibiting amount of a composition according to any of claims 13 to 15.

29. A method for the treatment of aqueous systems comprising adding thereto a threshold or corrosion inhibiting amount of a composition according to any of claims 16 to 18.

30. A method for the treatment of aqueous systems comprising adding thereto a threshold or corrosion inhibiting amount of a composition according to any of claims 19 to 21.

31. A method for the treatment of aqueous systems comprising adding thereto a threshold or corrosion inhibiting amount of a composition according to any of claims 22 to 24.

32. A method for the treatment of aqueous systems comprising adding thereto a threshold or corrosion inhibiting amount of a composition according to either claim 25 or 26.