TREATMENT OF AQUEOUS SYSTEMS

TRAITEMENT DE SYSTEMES AQUEUX

English Abstract

ABSTRACT
THE TREATMENT OF AQUEOUS SYSTEMS

A method of treating an aqueous system is
disclosed which comprises adding thereto a water-soluble
zinc salt, a chelant and either a product containing at
least one phosphorus-containing acid group and at least one
carboxylic acid group or an acrylic, vinyl or allyl
carboxylic acid polymer.

Claims

- 14 -
THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of treating an aqueous system which
comprises adding thereto a water soluble zinc salt, a chelant
which possesses the formula:

Image

wherein R1 is hydrogen, hydroxyethyl or carboxymethyl, R2 is
hydrogen, hydroxyphenyl, which is optionally methyl or
sulfonic acid substituted, or carboxyl, R4 is hydrogen or
carboxyl, R3 is
Image, -CH2CH2OH, - CH2C6H3(OH) (SO3H) or
Image
wherein R1, R2 and R4 are as above defined and X is -(CH2)2- or
-(CH2)3-, the phenyl groups being optionally further
substituted by one or more halogen atoms with the proviso that
at least one of R2 and R3 contains a hydroxyphenyl group and
either a product containing at least one carboxylic acid group
or an acrylic, vinyl or allyl carboxylic acid polymer.


- 14(a) -
2. A method according to Claim 1 in which the
chelant possesses the formula

Image
where R1 is hydrogen, hydroxyethyl or carboxymethyl, R2 is
hydrogen, hydroxyphenyl, which is optionally methyl or
sulphonic acid substituted, or carboxyl, R4 is hydrogen or
carboxyl, R3 is Image, -CH2CH2OH,
-CH2C6H3(OH)(SO3H) or Image
wherein R1, R2 and R4 are as defined above and X is
-(CH2)2- or -(CH2)3-; the phenyl groups being otionally
further substituted by one or more halogen atoms.

3. A method according to Claim 2 in which 1 to 10
parts by weight of chelant are added per part by weight of
zinc salt.

4. A method according to Claim 3 in which 4 to 6
parts by weight of the phosphorus-containing compound are
added per part by weight of the zinc salt.

- 15 -

5. A method according to Claim 2, 3 or 4 in which
the zinc salt is zinc sulphate, zinc chloride, zinc
nitrate or zinc acetate.

6. A method according to Claim 2, 3 or 4 in which
the phosphonate has the general formula

Image
wherein R is hydrogen, alkyl, alkenyl or alkynyl having up
to 4 carbon atoms; phenyl; cycloalkyl having 3 to 6 carbon
atoms; benzyl; phenethyl or

Image
wherein R' is hydrogen, alkyl having 1 to 4 carbon atoms
or carboxyl, R" is hydrogen or methyl and R''' is carboxyl
or phosphonate.

7. A method according to Claim 2, 3 or 4 in which
the phosphonate is hydroxy-phosphonoacetic acid or
2-phosphonobutane-1,2,4-tricarboxylic acid.

8. A method according to Claim 2, 3 or 4 in which
the product containing at least one phosphorus-containing
acid group and at least one carboxylic acid group is a
phosphino polycarboxylic acid having the formula

Image
where N + M = 4 to 20.


- 16 -
9. A method according to Claim 1, 2 or 3 in which
the polymer is a copolymer of acrylic, methacrylic,
maleic, fumaric, itaconic, crotonic or cinnamic acid with
acrylamide, an acrylate or methacrylate ester or hydroxy
ester, vinyl pyrrolidone, vinyl acetate, acrylonitrile,
vinyl methyl ether, 2-acrylamido-2-methyl-propane
sulphonic acid, vinyl, allyl or styrene sulphonic acid, or
diallyldimethyl ammonium chloride or dimethylamino ethyl
acrylate or methacrylate, optionally quaternised with
dimethyl sulphate or methyl chloride.

10. A method according to Claim 1, 2 or 3 in which
the polymer is a polymer of acrylic acid, methacrylic
acid, maleic acid, fumaric acid, itaconic acid or crotonic
acid, having a molecular weight from 1000 to 5000.

11. A method according to Claim 2, 3 or 4 in which
the zinc salt is added in an amount to provide up to 5 ppm
zinc.

12. A method according to Claim 2, 3 or 4 in which
the zinc salt is added to provide up to 2 ppm zinc.

13. A method according to Claim 2, 3 or 4 in which
the system water attains a temperature of at least 40°C.

14. A method according to Claim 2, 3 or 4 in which
the system water attains a pH of 8.2.

15. A method according to Claim 1 in which the
chelant is N,N'-di(2-hydroxyethyl) glycine.

16. A method according to Claim 1 or Claim 15 in
which the zinc salt is zinc sulphate, zinc chloride, zinc
nitrate or zinc acetate.


- 17 -
17. A method according to Claim 1 in which the
chelant is N,N'-di(2-hydroxybenzyl)-trimethylenediamine-
N,N'-diacetic acid, N,N'-ethylenebis-[2-(2-hydroxy-4-
methyl-phenyl)-glycine], ethylenediamine N,N'-bis-[2-
hydroxyphenylacetic acid] or N,N-di(2-hydroxy-5-sulphonic
acid benzyl) glycine.

18. A method according to Claim 17 in which 1 to 10
parts by weight of chelant are added per part by weight of
zinc salt.

19. A method according to Claim 18 in which the zinc
salt is zinc chloride, zinc nitrate or zinc acetate.

20. A method according to Claim 17, 18 or 19 in
which 4 to 6 parts by weight of the phosphorus-containing
compound are added per part by weight of the zinc salt.

21. A method according to Claim 15, 17 or 18 in
which the phosphonate has the general formula

Image
wherein R is hydrogen, alkyl, alkenyl or alkynyl having up
to 4 carbon atoms; phenyl; cycloalkyl having 3 to 6 carbon
atoms; benzyl; phenethyl or

Image
wherein R' is hydrogen, alkyl having 1 to 4 carbon atoms
or carboxyl, R" is hydrogen or methyl and R''' is carboxyl
or phosphonate.


- 18 -

22 A method according to Claim 15, 17 or 18 in
which the phosphonate is hydroxy-phosphonoacetic acid or
2-phosphonobutane-1,2,4-tricarboxylic acid.

23. A method according to Claim 15, 17 or 18 in
which the product containing at least one phosphorus-
containing acid group and at least one carboxylic acid
group is a phosphino polycarboxylic acid having the
formula

Image
where N + M = 4 to 20.

24. A method according to Claim 15, 17 or 18 in
which the polymer is a copolymer of acrylic, methacrylic,
maleic, fumaric, itaconic, crotonic or cinnamic acid with
acrylamide, an acrylate or methacrylate ester or hydroxy
ester, vinyl pyrrolidone, vinyl acetate, acrylonitrile,
vinyl methyl ether, 2-acrylamido-2-methyl-propane
sulphonic acid, vinyl, allyl or styrene sulphonic acid, or
diallyldimethyl ammonium chloxide or dimethylamino ethyl
acrylate or methacrylate, optionally quaternised with
dimethyl sulphate or methyl chloride.

25. A method according to Claim 15, 17 or 18 in
which the polymer is a polymer of acrylic acid,
methacrylic acid, maleic acid, fumaric acid, itaconic acid
or crotonic acid, having a molecular weight from 1000 to
5000.

26. A method according to Claim 15, 17 or 18 in
which the zinc salt is added in an amount to provide up to
5 ppm zinc.


- 19 -
27. A method according to Claim 15, 17 or 18 in
which the zinc salt is added to provide up to 2 ppm zinc.

28. A method according to Claim 15, 17 or 18 in
which the system water attains a temperature of at least
40°C.

29. A method according to Claim 15, 17 or 18 in
which the system water attains a pH of 8.2.

30. A method according to Claim 1, 3 or 18 in which
the product containing at least one phosphorus-containing
acid group is a phosphonate containing at least two acid
groups one of which is a phosphonate and the other is a
carboxylic acid group, at least the two said acid groups
being attached to carbon atoms.

31. A composition suitable for addition to an
aqueous system which comprises a water-soluble zinc salt,
a chelant, and a product containing at least one
phosphorus-containing acid group and at least one
carboxylic acid group or an acrylic, vinyl or allyl
carboxylic acid polymer.

32. A composition according to Claim 31 in which the
chelant possesses the formula

Image
wherein R1 is hydrogen, hydroxyethyl or carboxymethyl, R2
is hydrogen, hydroxyphenyl, which is optionally methyl or


-20-
sulphonic acid substituted, or carboxyl, R4 is hydrogen or
carboxyl, R3 is Image, -CH2CH2OH,
-CH2C6H3(OH)(SO3H) or Image
wherein R1, R2 and R3 are as defined above and X is
-(CH2)2- or -(CH2)3-; the phenyl groups being otionally
further substituted by one or more halogen atoms.

33. A composition according to Claim 32 which
contains 1 to 10 parts by weight of chelant per part by
weight of zinc salt.

34. A composition according to Claim 33 which
contains 4 to 6 parts by weight of the phosphorus-
containing compound per part by weight of the zinc salt.

35. A composition according to Claim 32, 33 or 34 in
which the zinc salt is zinc sulphate, zinc chloride, zinc
nitrate or zinc acetate.

36. A composition according to Claim 32, 33 or 34 in
which the phosphonate has the general formula

Image
wherein R is hydrogen, alkyl, alkenyl or alkynyl having up
to 4 carbon atoms; phenyl; cycloalkyl having 3 to 6 carbon
atoms; benzyl; phenethyl or

Image


-21-
wherein R' is hydrogen, alkyl having 1 to 4 carbon atoms
or carboxyl, R" is hydrogen or methyl and R''' is carboxyl
or phosphonate.

37. A composition according to Claim 32, 33 or 34 in
which the phosphonate is hydroxy-phosphonoacetic acid or
2-phosphonobutane-1,2,4-tricarboxylic acid.

38. A composition according to Claim 32, 33 or 34 in
which the product containing at least one phosphorus-
containing acid group and at least one carboxylic acid
group is a phosphino polycarboxylic acid having the
formula

Image
where N + M = 4 to 20.

39. A composition according to Claim 31, 32 or 33 in
which the polymer is a copolymer of acrylic, methacrylic,
maleic, fumaric, itaconic, crotonic or cinnamic acid with
acrylamide, an acrylate or methacrylate ester or hydroxy
ester, vinyl pyrrolidone, vinyl acetate, acrylonitrile,
vinyl methyl ether, 2-acrylamido-2-methyl-propane
sulphonic acid, vinyl, allyl or styrene sulphonic acid, or
diallyldimethyl ammonium chloride or dimethylamino ethyl
acrylate or methacrylate, optionally quaternised with
dimethyl sulphate or methyl chloride.

40. A composition according to Claim 31, 32 or 33 in
which the polymer is a polymer of acrylic acid, metha-
crylic acid, maleic acid, fumaric acid, itaconic acid or
crotonic acid, having a molecular weight from 1000 to
5000.


-22-
41. A composition according to Claim 31, 32 or 33
which is aqueous.

42. A composition according to Claim 31, 32 or 33
which is aqueous and contains from 1 to 2 percent by
weight of zinc salt (as zinc), from 4 to 10 percent by
weight of the phosphorus and carboxylic acid group-
containing material or polymer and from 1 to 25 percent by
weight of the chelant.

43. A composition according to Claim 31, 32 or 33
which further comprises a phosphate, biocide, yellow metal
corrosion inhibitor or dispersant.

44. A composition according to Claim 31, 32 or 33
which further comprises a dispersant which is a copolymer
of methacrylic acid and acrylamide.

45. A composition according to Claim 31 in which the
chelant is N,N'-di(2-hydroxyethyl) glycine.

46. A composition according to Claim 45 which
contains 1 to 10 percent by weight of chelant per part by
weight of zinc salt.

47. A composition according to Claim 31 in which the
chelant is N,N'-di(2-hydroxybenzyl)-trimethylenediamine-
N,N'-diacetic acid, N,N'-ethylenebis-[2-(2-hydroxy-4-
methyl-phenyl)-glycine], ethylenediamine N,N'-bis-[2-
hydroxyphenylacetic acid] or N,N-di(2-hydroxy-5-sulphonic
acid benzyl) glycine.

48. A composition according to Claim 47 which
contains 1 to 10 parts by weight of chelant per part by
weight of zinc salt.


-23-
49. A composition according to Claim 1, 46 or 48 in which
the zinc salt is zinc chloride, zinc nitrate or zinc
acetate.

50. A composition according to Claim 46, 47 or 48
which contains 4 to 6 parts by weight of the phosphorus-
containing compound per part by weight of the zinc salt.

51. A composition according to Claim 45, 47 or 48 in
which the phosphonate has the general formula

Image
wherein R is hydrogen, alkyl, alkenyl or alkynyl having up
to 4 carbon atoms; phenyl; cycloalkyl having 3 to 6 carbon
atoms; benzyl; phenethyl or

Image
wherein R' is hydrogen, alkyl having 1 to 4 carbon atoms
or carboxyl, R" is hydrogen or methyl and R''' is carboxyl
or phosphonate.

52. A composition according to Claim 45, 47 or 48 in
which the phosphonate is hydroxy-phosphonoacetic acid or
2-phosphonobutane-1,2,4-tricarboxylic acid.

53. A composition according to Claim 45, 47 or 48 in
which the product containing at least one phosphorus-
containing acid group and at least one carboxylic acid

-24-
group is a phosphino polycarboxylic acid having the
formula

Image
where N + M = 4 to 20.

54. A composition according to Claim 45, 47 or 48 in
which the polymer is a copolymer of acrylic, methacrylic,
maleic, fumaric, itaconic, crotonic or cinnamic acid with
acrylamide, an acrylate or methacrylate ester or hydroxy
ester, vinyl pyrrolidone, vinyl acetate, acrylonitrile,
vinyl methyl ether, 2-acrylamido-2 methyl-propane
sulphonic acid, vinyl, allyl or styrene sulphonic acid, or
diallyldimethyl ammonium chloride or dimethylamino ethyl
acrylate or methacrylate, optionally quaternised with
dimethyl sulphate or methyl chloride.

55. A composition according to Claim 45, 47 or 48 in
which the polymer is a polymer of acrylic acid,
methacrylic acid, maleic acid, fumaric acid, itaconic acid
or crotonic acid, having a molecular weight from 1000 to
5000.

56. A composition according to Claim 45, 47 or 48
which is aqueous.

57. A composition according to Claim 45, 47 or 48
which is aqueous and contains from 1 to 2 percent by
weight of zinc salt (as zinc), from 4 to 10 percent by
weight of the phosphorus and carboxylic acid group-
containing material or polymer and from 1 to 25 percent by
weight of the chelant.


-25-
58. A composition according to Claim 45, 47 or 48
which further comprises a phosphate, biocide, yellow metal
corrosion inhibitor or dispersant.

59. A composition according to Claim 45, 47 or 48
which further comprises a dispersant which is a copolymer
of methacrylic acid and acrylamide.

60. A composition according to Claim 33, 46 or 48 in
which the product containing at least one phosphorous-
containing acid group is a phosphonate containing at least
two acid groups one of which is a phosphonate and the
other is a carboxylic acid group, at least the two said
acid groups being attached to carbon atoms.

Description

~332~3,3 ~ -


THE TREATMENT OF AQUEOUS SYSTEMS

The present invention relates to the treatment of aqueous
systems and, more particularly, to reducing or eliminating
corrosion in asueous systems.

Many different types of material have been employed to
prevent or inhibit corrosion in aqueous systems. These
include inorganic salts such as nitrites and chromates,
inorganic mono and polyphosphates, certain water soluble
polymers including naturally occurring materials such as
lignins and starches as well as synthetic materials such
as polyacrylates, as well as organic phosphonates. In
addition, it is well known to use zinc salts for this -~
purpose. Indeed, it is known to use zinc salts in
combination with organic type corrosion inhibitors,
principally organic phosphonates and polyacrylates.
: ~ :
The u~e of zinc salts enables one to passivate corrosion
of the metal in contact with the system. It is generally ~;,,;
believed that localised high concentrations of hydroxide
ions arise at sites of corrosion on the metal surface
because, due to the galvanic cell effect, oxygen present -~
in the water is reduced to hydroxide ions at the ca hodic
sites. These hydroxide ions then react with zinc ions of - -
~ the zinc salt to give zinc hydroxide which in turn yields
- a protective film on the metal surface.

While this pas6ivation system works reasonably
sati8factorily in some aqueous media it is known that the
use of zinc salt~, with or wlthout the organic type
corrosion inhibitor, is ineffective when the pH of the
system is high, for example at pH from 8.2 to 9Ø Such a -~
pH can be pre~ent when the water is hard, or is otherwise

~ \
- ~ 332:~ 3~

alkaline ie of low hardness and high alkalinity as can be
the case with base exchanged water. Under such
circumstances, the zinc hydroxide precipitates prematurely
in the system water and therefore does not form a
protective film over the metal. Thus in such systems the
zinc actually becomes a foulant of the system. Similar
problems arise when th~ temperature of the aqueous system
i5 raised, for example to at least 40C as can occur when
the aqueous system is used as cooling water which comes
into contact with hot metal surfaces.

It has now surprisingly been found, according to the
present invention, that ~ore effective corrosion
inhibition can be obtained when a zinc salt is used
together with a class of phosphonate or similar material
and, in addition, a chelant. It has been found that this
combination is capable of being effective under a
combination of severe pH and temperature conditions. It
is considerably more effective than existing zinc/organic
products on pre-corroded mild steel surfaces since the
combination is capable of stifling existing corrosion as
;~ well as enabling much faster passivation of the rusty
surface to be brought about. Thus the combination, as
well as inhibiting corrosion, also acts as an on line
cleaning agent by removing old rust.
,
According to the present invention there is provided a
method of treating an aqueous system which comprises
adding thereto a zinc salt, a chelant and either a product
containing ~t least one phosphorus-containing acid group
and at least one carboxylic acid group or an acrylic,
vinyl or allyl carboxylic acid polymer.

Generally, any water soluble zinc salt can be used in the
present invention. Typical salts which can be used

..... .

1 332 138

- 3 -
include zinc sulphate, zinc chloride, zinc nitrate and
zinc acetate, zinc sulphate monohydrate and zinc chloride
being particularly preferred. -

The third component used in the present invention will, in
S general, be a phosphonate. Preferably, the materials used
contain at least two acid groups, one of which is a
phoæphonate group and the other is a carboxylic acid
group, at least the two said acid groups being attached to ~
carbon atoms. ,

10 Preferred phosphonates include hydroxy phosphonoacetic ~,~
;~ acid and 2-phosphono butane-1,2,4-tricarboxylic acid, the ~ h
latter being particularly preferred. Thus these preferred
; ~ phosphonates possess the general formula
O R
~ 0 ) 2P f COOH
~ H2 - COOH
, " . ~ ,
.,,:
~ 15 wherein R is hydrogen, alkyl, alkenyl or alkynyl having up
.~ to 4 carbon atoms; phenyl; cycloalkyl having 3 to 6 carbon ~`
atoms; benzyl; phenethyl or
~ -
R' ~"
CH ~ R
wherein R' is hydrogen, alkyl having 1 to 4 carbon atoms
or carboxyl, Ra is hydrogen or methyl and R''' is carboxyl
or phosphonate. ~
, , ,:



'.:., ''' :'`'
.
.

-
:
~ 3321:~
- 4 -
It is also possible to employ as the third component in
the method a polymeric material and, in particular,
carboxylic acid polymers which contain a chain phosphorus
atom which forms part of an acid group. Thus these
polymeric materials are preferably phosphino
polycarboxylic acids, typically those having the formula

Hf -- CH~p~/H2 -- I H~ :~
~ HOOC J ~H ~ COOH

where N + M = 4 to 20

The molecular weight of such polymers is relatively low,
generally below 5,000, the preferred molecular weight
being from 250 to 750, especially about 500. A
particularly suitable polymer is that sold as ~Belclene
500" by Ciba-Geigy.
~'
It has also been found that a synergistic effect, although
most pronounced when the phosphorus containing materials
` are used, can also be obtained when a polycarboxylic acid
- ~; is uæed, typically one having a molecular weight from
1,000 to 5,000. Such polymers may be derived from
acrylic, vinyl or allyl carboxylic monomers, typically
acrylic, methacrylic, maleic, fumaric, itaconic, crotonic
or ~innamic acid alone or with a suitable comonomer. Such
comonomers include acrylamide, (meth)acrylate esters or
hydroxy esters e.g. hydroxypropyl esters, vinyl
pyrrolidone, vinyl acetate, acrylonitrine, ~inyl methyl
ether, 2-acrylamido-2-methyl-propane sulphonic acid, vinyl
or allyl ~ulphonic acid and styrene sulphonic acid as well
as cationic monomers such as diallyl dimethyl ammonium
chloride, dimethylamino ethylacrylate or methacrylate,
optionally quaternised with, for example, dimethyl

J ~ :
,''''~`~.


``` ' ~33~13g
- 5 -
' s~lphate or methyl chloride.
i The chelants which can be used in the method of the
present invention are generally compounds with a nitrogen
ligand which are effective chelants for iron Usually,
these chelants will also possess a carboxylic acid group.
A preferred group of chelants possesses the formula ;

R3 - ~ - CH - R2
where Rl is hydrogen, hydroxyethyl or carboxymethyl,
preferably carboxymethyl, R2 ~s hydrogen, hydroxyphenyl, ~-~
preferably ortho-hydroxyphenyl, which is optionally methyl
or sulphonic acid substituted, or carboxyl, R4 is hydrogen
or carboxyl, ~
Rl R4 -
R is - X - N - CH - R , -CH2CH20H, R1~4
-CH2C6H~(OH)(S03H) or -CH2C6H2(OH)~CH3)CH2~-N-R
where R , R2 and R4 are as defined above and
X is -(CH2)2- or - ~CH2)3 -~ The phenyl groups may be
substituted, if desired, preferably by one or more halogen
atoms. `~
: ~ ' , ~-`,'
If the chelant is to be used in aqueous systems which
20 possess a high pH and a relatively high temperature it is ~
preferred that at least one of Rl, R2 and R3 contains a -~`
`~ hydroxyl group. Thus the most preferred chelants possess
a nitrogen ligand, a carboxylic acid group and a hydroxyl
~ group~

; ~ 25l Preferred chelants for use in t~e present invention
include N~N'-di(-2-hydroxybenzyl-)trimethylened1amine-N,
N'-diacetic acid, N,N'ethylene-bis-[2-
(2-hydroxy-4-methyl-phenyl)-glycine], ethylenediamine N,
N'-bis-[2-hydroxyphenylacetic acid] and N,
30 N-di(2-hydroxy-5-sulphonic acid benzyl~glycine which is


A ;~

~;
~ 3~2i~8

- 6 -
especially preferred not only on account of its
effectiveness but also on account of its excellent
solubility properties which faciliate the formulation of
compositions, as well as N,N-di(2-hydroxyethyl) glycine,
S N-hydroxyethyl N,N',N'-ethylenediamine triacetic acid and
2-hydroxyethyl iminodiacetic acid. Ethylenediamine
tetraacetic acid and diethylene triamine pentaacetic acid
can also be mentioned although they are less preferred
since they do not contain a hydroxyl group (other than as
part of the carboxylic acid groups).

In general, from 1 to 10 parts by weight of chelant and
from 4 to 6 parts by weight of the phosphorus containing
compound are employed to 1 part of the zinc salt. While
in certain circumstances it may be desirable to add the
individual components separately, in other situations it
will be convenient to add the components together in the
form of a composition. Accordingly, the present
invention also provides a composition suitable for
addition to an aqueous system which comprises a water ~-
soluble zinc salt, a product containing at least one
phosphorus containing acid group and at least one
carboxylic acid group or an acrylic, vinyl or allyl
carboxylic acid polymer, and a chelant. In such a
situation, it may be desirable to add further quantities
of chelant as required~ Typically, the composition will
be an aqueous formulation containing, generally, 1% to 2%
by weight Qf zinc salt (as zinc), 4~ to 10% by weight of
the phosphorus containing material or polymer and 1~ to
' 25~ by weight, especially about 5% by weight, of the ;~
; 30 chelant.

A further surprising feature of the present invention is
that the presence of the combination of chelant and
phosphorus conta~ning compound and/or acrylic vinyl or

~332~
- 7 - ~-
allyl carboxylic acid polymer enables one to reduce the
amount of zinc salt. It is usual in the art to employ
amounts of the order of 2 to 5ppm zinc. However, with
ever increasing restrictions on concentrations of zinc in
discharges there is a constant demand to reduce the
amounts of zinc used. It has been found that by using the
additional ingredients it is possible to reduce the amount
of zinc to, say, about lppm for comparable effectiveness.
In such circumstances it is preferred to employ about 4ppm
of the phosphorus compound and about 2.5 to 5ppm of
chelant. If, on the other hand, one usès 2.5ppm of zinc
then it is preferred to use about lOppm of phosphorus
compound and about 5ppm of chelant.
.
It is also possible to use the combination of the present
invention together with other ingredients including
phosphates, biocides, yellow metal corrosion inhibitors
such as benzotriazole and tolyltriazole as well as other ;
;~ polymers which act as dispersants such as polyacrylic
1~ acid, polymaleic acid and copolymers of maleic acid with
l 20 styrene sulphonic acid. In particular, it has been found
¦~ that the use of certain disper~ants, especially a ~ ;~
¦~ copolymer of methacrylic acid and acrylamide is
particularly advantageous, especially one in which the
mole ratio is about 1:3, and further enhances the
corrosion protection given by the three component system.
In general the molecular weight of the homopolymers will
be 1,000 to lO,000 while that of the copolymers will be
l,000 to 50,000.

The use of a phosphate is particularly noteworthy since
zinc phosphate i9 effective in low water hardness systems
because the zinc phosphate itself gives protection. By
using the chelant and phosphorus containing compound as -~
well it is possible, as previously discussed, to use

.,

~ ~ 33~ 3~

,
significantly lower quantities of zinc.

The following Examples further illustrate the present
invention.

Examples 1 to 34

In these Examples tests were carried out on a laboratory
scale recirculating rig consisting of a plastic vessel
holding 8 litres of water and connected by tubing to a
¦~; circulating pump the water passing from the pump through a
glass rack holding the metal test coupons ('line') and
returning to the plastic vessel. Any evaporation was made
~ up by the addition of de-ionised water. Metal test
I coupons were also suspended in the plastic vessel
('Pond'). ~he corrosion rate was calculated from the -
weight of metal lost during test. The water temperature
was maintained by means of a heater/thermostat
arrangement. The conditions of the test were as follows:

System Water : 150ppm Ca hardness/150ppm 'M'
Alkalinity
Water pH : 8.8
~; 20 ~Water Temperature : 54 C or 40C ~as stated)
Flow Rate : Line : 2 ft/sec `~
Pond : 0.2 ft/sec
Duration of Test : 3 days
Tnitial Passivation : 1 day at 3 times normal
; 25~ maintenance dose.

Examples No. 1 - 14 were carried out at 40C.


'"';''.:`


. ''' '' '.~

133~1~8

Example Additive Dose, ppm Corrosion of -
No. Mild Steel in
mils per year
(mpy) :
Line Pond
No addition
:~ 2 Zinc/Chelant 1/~ - 2.2/5/--- 5.7 12.9
3 Zinc/Chelant l/Phosphonate 1 2.2/5/8.8 1.0 0.9
4 zinc,~ /Phosphonate 1 2.2/-/8.8 7.8 3.3
~; 10 5 Zinc/Chelant 2/------- 2.2/5/---1.1 8.8
~: 6 Zinc/Chelant 2/Phosphonate 1 2.2/5/8.8 0.2 0.3 --
. ~: 7 Zinc/Chelant 3/~ -- 2.2/5/--- 1.5 2.4 . -:
8 Zinc/Chelant 3/Phosphonate 1 2.2/5/8.8 1.1 1.6
9 Zinc/Chelant 4/------- 2.2/5/---9.0 . 7.3 -~.~
Zinc/Chelant 4/Phosphonate 1 2.2/5/8.8 0.3 0.7 .` ;
11 Zinc/Chelant 5/------- 2.2/5/---10.7 12.9
12 Zinc/Chelant 5/Phosphonate 1 2.2/5/8.8 1.9 8.6 :~
;13 Zinc/Chelant 2/Phosphonate 2 2.2/5/8.8 4.5 4.8 ;:
14 Zinc/Chelant 9/Phosphonate 1 2.2/5/8.8 0.2 0.2 .

20~ ~;Examples 1 - 14 illustrate:
he blend of z`i~n~/chelant/phosphonate is superior to
zinc/phosphonate or zinc/chelant.
The~prefer;red ~chelants are Chelants 1, 2,3 and 9.
$ii~ Phosphonate l :gives significantly better results ~-
25 :~ than~comparative Phosphonate 2.

Examples l5 - 34 were carried out at 54C.

15 Zinc/Chelant 2/Phosphino 1 2.2/5/8.82.9 5.3
16~::Z:inc,~Chelant 2/Phosphino 1 2.5/5/10.0 1.2 3.1 `; 17 ~Zinc/~ Phosphino 1 2.2/-/8.810.5 11.7 ~:
: 30 18 Zinc/Chelant 2/Phosphonate 1 2.2/5/5 0.5 1.6 ~ `~
19 Zinc/Chelant 2/Phosphonate 1 2.2/5/8.8 0.5 1.4 .::


., , :',; .
' " ~
~','

13~2~3

-- 10 --
Zinc/Chelant 2/Phosphonate 1/
Polymer 1 2.2/5/8.8/2.5 0.4 0.9
21 Zinc/Chelant 2/Phosphonate 3 2.2/5/8.8 0.4 0.5
22 Zinc/Chelant l/Phosphonate 1 2.2/5/8.8 1.2 5.0
23 Zinc/Chelant 4/Phosphonate 1 2.2/5/8.8 2.3 5.6
24 Zinc/Chelant 3/Phosphonate 1 2.2/5/8.8 1.6 2.4
Zinc/Chelant 3/Phosphonate 1 1/5/4.4 2.1 5.2
26 Zinc/Chelant 2/Polymer 22.2/5/10 5.2 9.1
27 Zinc/~ /Polymer 2 2.2/-/10 21.4 21.3
28 Zinc/Chelant 2/Polymer 32.2/5/107.2 9.7
29 Zinc/-~ /Polymer 3 2.2/-/10 17.7 32.2
Zinc/Chelant 6/Phosphonate 1 2.2/5/8.8 3.1 3.4
31 Zinc/Chelant 7/Phosphonate 1 2.2/5/8.8 3.2 2.1
32 Zinc/Chelant 8/Phosphonate 1 2.2/5/8.8 3.6 6.8
33 Zinc/------ /Phosphonate 12.2/-/8.8 9.6 7.4
34 Zinc/Chelant 9/Phosphonate 1 2.2/5/8.8 1.0 0.8
- .;
~ Chelant 1 = N, N'-di(-2 hydroxybenzyl
-~ trimethylenediamine-N,N'-diacetic acid
Chelant 2 = N,N' Ethylene-bis- [2~2-hydroxy-4
methyl-phenyl) - glycine]
Chelant 3 = Ethylenediamine N, N'bis-[2 hydroxyl phenyl
~- acetic acid]
Chelant 4 = Ethylenediamine tetraacetic acid.
Chelant S s NIN-di (2 hydroxy ethyl) glycine.
- 25 helant 6 - N-Hydroxyethyl,N,N' Ethylenediamine triacetic
acid.
Chelant 7 - 2-hydroxyethyl iminodiacetic acid.
Chelant 8 - Diethylene triamine penta acetic acid.
helant 9 ~ N,N-di~2 hydroxy -5-sulphonic acid benzyl)
30 glyclne ~--
Pho~phonate 1 = 2-Phosphonobutane 1,2,4 tricarboxylic
acid.
Phosphonate 2 - Rydroxy ethylidene di-phosphonic acid.
Phosphonate 3 ~ ~ydroxy phosphonoacetic acid. ~

','';~,. ':
,~

', . ~

~33~ 3~ :

-- 11 --
Phosphino l = Phosphino polyacrylic acid, M.Wt. approx
500 (sold commercially as "Belclene S00" ~;
Ciba Geigy).

Polymer l = Copolymer of methacrylic acid/acrylamide,
mole ratio 1:3, M.Wt. 35,000.
Polymer 2 = Polyacrylic acid, M.Wt.1000.
Polymer 3 = Polyacrylic acid, M.Wt.4500.

Examples 15 - 34 indicate:
i) The excellent corrosion inhibiting properties of the ~-
zinc/chelant/phosphonate combinations are maintained
at the higher test temperature; this is less marked
with Chelant 8 which does not contain a hydroxy;group -~
(Example 32). The excellent corrosion inhibition is -~
also maintained when the phosphonate is replaced by
the phosphino-polycarboxylic acid in the 3 component
combination.
ii) The presence of Polymer l, (Example 20), enhances the
corrosion protection conferred by the 4 component
blend over that given by the cvrresponding 3
; 20 component blend, (Example l9), without polymer.
iii) The improvement brought about by the presen~e of the
chelant with the zinc/polyacrylic acid combination. -~

Examples 35 to 43

These Examples illustrate the effect of longer term tests. i~
25j~These were~carried out on a laboratory scale simulated
~;~ open, evaporative, recirculating cooling water system
inoorporating mild ~teel heat exchanger together with feed
a~nd bleed facilities which enable the system to run at a
given concentration factor throughout the 14 day test.
The est conditions were as follows~

,, ,~


~: '

~1332~3~
- 12 -

System Water : 160ppm C31cium hardness
50ppm Magnesium hardness
200ppm 'M' Alkalinity
Water Temperature (Pond) : 50C
5 pH : 8.8
Flow Rate through heat
exchanger : 0.3 ft/sec ;~-
Plow Rate through coupon
chamber : 1.5 ftJsec
10 Heat flux on exchanger 75 kj/ -2/
Duration of test : 14 days ~ ;
Initial passivation : 3 x normal maintenance
dose, allowed to decay from
start of test.
15 Example ~ Additive Dose,ppm Corrosion Rate
~ No. mpy ~-
`~ Heat Coupon
Exchanger in line
Zinc/Chelant 2/Phosphonate 1 2.2/2.5/8.8 7.8 1.0 ``~
36 Zinc/Chelant 2/Phosphonate 1 2.2/5/8.8 3.5 0.5 ;
37~ Zinc/Chelant 2/Phosphonate 1 2.2/7.5/8.8 5.6 1.1
38 Zinc/Chelant 2/Phosphonate 1 2.2/10/8.8 6.9 1.2 ;~
39~ zinc/Chelant 4/Phosphonate 1 2.2/5/8.8 63.6 38.7
4Q Zinc/~ /Phosphonate 1 2.2/--/8.8 9.5 1.0
25 ~ 41 Zinc/~helant 5/Pho~phonate 1 2.2/5/8.8 4.6 1.8
42 Zin~/0-phosphate/Chelant 2/ 1.1/1.5/5/5 2.6 1.0
Phosphonate 1
`,- ,43 Zinc/0-phosphate/ 2.2/3.0/-/5 4.2 ~ 6.~8
Phosphonate 1
30 0-phosphate ~i disodium ortho-phosphate --

It was noticed that when Chelant 2 was in use (Examples 35
to 38), the corrosion which initiated on the heat
exchanger was rapidly st~1ed whereas in Example 40

~ . ~
' ~ , ' ;, . ~`,

~3~213~
- 13 -
corrosion spread throughout the test. Chelant 4 was
largely ineffective; in fact, the results indicate
aggresSion. This shows that this chelant is unsuitable
where there is a heat exchanger giving a high surface
temperature.

Example 42 in relation to Example 43 shows the effect of
using Chelant 2 in enabling one to reduce the
concentration of zinc/phosphate.




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