Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
ll.~ S~I
INTRoDucrrIoN
It is well known that metal surfaces in contact ~lith
industrial cooling waters are susceptible to corrosion. It is
customary to treat these waters with various types of corrosion
inhibitors and scale inhibitors as well as dispersants to prevent
corrosion and fouling of heat exchange surfaces.
In order -to reduce corrosion, it is not unco~non that
industrial cooling waters be treated to adjust their pH to wit~Ln
alkaline range, e g. 7.5 or greater. As the pH o~ most industrial
cooling waters is increased, the tendency of ~hese waters to
precipitate hardness-~orming compounds increases. Also, as the
pH is increased in certain instances, non-ferrous metals tend to
corrode at a greater ra e.
A common inhibitor and scale preventative ~or treating
alkaline cooling waters resides in the use of organo phosphorous-
containing material in conjunction with water-soluble zinc salts.
The zinc salt which provides zinc ion is primarily an alkaline
corxosion inhibitor. When organic phosphorous compounds are
combined t;1erewith, improved corrosion protection is aforded
and, also, scale inhibition is achie~ed In certain instances,
it is also comlnon to use a chelating agent to prevent the zinc
from prematurely precipitating in these systems. Sometimes with
the inhibitors are used polymeric dispersants such as the lo~
molecular weight sodium polyacrylates. Another common practice
in treating industrial cooling systems is to initially treat the
system with high dosayes of corrosion and scale inhibitor compos~-
tions ancl then, a~ter initial protection is estab~ishecd, to lo~er
the dosage to provide what is known as a maintenance level
-treatment
-2-
7~
In the case of corrosion and scale inhibiting formulas, the zinc
maintenance level to stabilize the corrosiveness of the system is usually
between 3 - 5 ppm of zinc ion (Zn ). It frequently is increased when the
pH is between 8 - 9.
When these high maintenance levels of zinc are required, another
problem exists, e.g. these high zinc levels exceed the standards establish-
ed for adding such waters into sewage systems, lakes, streams, and the
like.
It would be of benefit to the art if it were possible to provide
a method of treating industrial cooling waters which would utilize zinc
salts at a low maintenance dosage yet allow these systems to be relatively
free of corrosion and scale and yet, at the same time, be capable of
operating at a high alkaline pH.
THE IN~ENTION
An improved method for preventing corrosion of metals in contact
with alkaline pH industrial cooling waters which contain as a corrosion
inhibitor:
(a) an organic phosphorous inhibitor in combination with
(b) a water-soluble zinc compound,
which comprises treating such waters with a zinc chelating amount of the
phosphorous- containingchelant of ~ormula (I)
H-- f -CH CH2 t I ~ 2 ~ t H
I CO I O CO
~ OH /n OH /
where n plus m equal about 6.
~, -3-
5~
The Organic Phosphorous Inhibitors
These materials, as indicated, act as both corrosion and scale
inhibitors when used at an alkaline pH. They may be selected from one or
more of the following:
Amino Phosphonic Acids
Certain organophosphorous compounds including aminomethyl-
enephosphonic acid, N-substituted aminomethylenephosphonic acids, and both
~- and C-substituted aminomethylenephosphonic acids may be employed as
scale inhibitors in the practice of our invention. These compounds may be
prepared according to the teaching of U.S. Patent 3,288,84~.
Generally, these compounds can be characterized as containing at
least one N-C-P linkage in their molecules, and as having the formula:
r 3
N - C - P ~ O
R2 ~4 OH
wherein R3 and R4 can be like or unlike, and are either hydrogen or organic
radicals; and Rl and R2 can be like or unlike, and can by hydrogen, hydroxyl,
amino, organic radicals, or alkylene phosphonic acid radicals (such as that
within the bracketed portion of Formula 1.) Salts of the above compo~mds
may also be employed. An especially useful organophosphorous compound is
aminotri (methylene phosphonic acid) and the potassium salt of hexamethyl-
enediamine tetra (methylene phosphonic acid.)
Diphosphonic Acids
Certain hydroxyalkane-l, l-diphosphonic acids such as those
described in U.S. Re. 28,553 have been found to be useful scale inhibitors
in the practice of our invention. These compounds may be obtained by
reacting phosphorous acid with acid anhydrides and/or acid chlorides,
especially those of acetic, propionic,
-4-
-~ 7~ D~
butyric, valeric and caproic acid ~hen both the anhydride and
the chloride are used simultaneously, they mus-t he derived from
the same acid, e.y. the anhydride and the chloride of acetic acid
can be used sirnultaneously, but no-t acetic anhydride together with
propionic chloride. In lieu of phosphorous acid and one of the
acid chlorides named above, phosphorous trichloride can be reacted
with one of the carboxylic acids themselves. Paxticularly, readil
available are the reaction products of phosphorous acid with ac~ti~
anhydride, with acetyl chloride or with a mixture thereof. The
xeactions opportunely are carried out at eleva-ted temperatureS,
preferably between 50 and 200C.
The acylation products of phosphorous acid, depending upon
the process whereby they are manufactured, are obtained in pure
form, but frequently in the form of mixtures. As has been ascer-
tained by the reactions described above, all products obtained
contain at least two phosphorous atoms in their molecules. Of
the products whose constitution is established, the following
representative formula is of especial importance as a scale
inhibi-tor in the practice of the invention:
~ R
HO - P - C - P - OE
OH OH OH
wherein R denotes a low alkyl radical having 1 - 5 carbon atoms.
When mixtures are obtained, the products ~lso have the above
forrnula wherein the OH groups are partially es-terified. The acyl
groups, in that case, correspond to the carboxylic acid componen~
used in the reaction~ Furthermore, -two or more molecules o~ the
above Eormula may convert into the corresponding intermolecule
anhydrides while splitting off water ana thus may be present
toyether with the compound conforminc~ to -the formula ~iven. Pure
ore refined compounds as well as the above described mixtures can
be em?loyed. An especially useful diphosphonic acid is l-hydroxy-
ethylidene 1,1 diphosphonic acid.
-5
7~
Phosphonotricarboxylic: Acids
Certain 2-phosphono-butane-1, 2, 4-tricarboxylic acids such as
those described in U.S. Patent 3,886,205 can be advantageously employed as
scale inhibitors in the practice of our invention. These compounds are
generally described by the formula:
R R
O CH - CH - -CO- - -CH
HO ¦¦ l
~P C--CO --CH
HO CH2 - -CO -OH
in which R is hydrogen9 lower alkyl or a carboxyl group, and Rl is hydrogen
or methyl, as well as their alkali metal, ammonium or amine salts, which
compounds have been found to exhibit a strong complex-forming effect on
alkaline earth metal ions. ~n especially effective 2-phosphono-butane-1
2, 4-tricarboxylic acid is represented by the formula:
O CH2- - CH CO OH
HO \ 11 i 2
~ P_ f co CH
HO CH2 - CO - OH
Polyol Phosphate Esters
Scale inhibiting compounds comprising certain phosphate esters
of polyols containing one or more 2-hydroxyethyl groups and one or more of
the groups
O O
Il 11
- O - -P OH and - O P - O
OH OH
and salts thereof, are used to inhibit scale deposits by adding them to
water containing scale-forming chemicals. These compounds and their
preparation are described in more detail in U.S. Patents 3,462,365 and
. -6-
:3L.ll7~5~
3,4?37,018. Preferred polyol phosphate esters are the gylcerine phosphate
esters. Closely related to the above-described scale inhibitors are the
phosphated mixed esters of non-surface active polyols containing at least
one hydroxyethyl group and monohydric surface active compounds containing
oxyethylene groups described in ~.S. Patent No. 3,72~,420. Preferred
among these compolmds are phosphated mixed esters of:
(A) either oxyethylated or oxypropylated-terminally
oxyethylated polyols, e.g. polyoxyethylated glycerol,
ethylene glycol, hexylene glycol, sorbitol, mannitol,
or trimethylolpropane, or oxyethylated or oxypropylated-
terminally oxyethylated erythritol, arabitol, xylitol,
quercitol, inositol, and mono-, di-, or tripentaerythritol,
and
(B) oxyalkylated monohydroxy surface active compounds, e.g.
oxyethylated nonyl phenol, oxyethylated tridecyl alcohol,
and oxyethylated normal alcohol mixtures containing six
or more carbon atoms.
This group of materials represents a preferred species of organic phos-
phorous inhibitors. A most preferred material is a phosphated glycerine
which has been pre~iously reacted with 50 weight percent ethylene oxide.
A o Phosphonates
Certain amino phosphonates useful as scale inhibitors in the
practice of our invention are described by the formula:
p" N ~
R'
where R is
e
- C~13- - -- p ~ -0~1
OM
--7--
11'74g5~
¦R' is R or - CH2CM2)H, and X" is R, ~ C~l2C~i~O~-I7 or
¦ R
- (CH 2 ~ n - N /
¦ \ R
where M is H, NHL" alkali metal~ or combination thereof, and "n"
is 1 to 6. These compounds are described in U.S. Patent No.
3,336,221. Preferably compounds from among those described in the
general formula include (OEI2)6N2~CH2PO(OM)2~4, NlCH2PO(OM~2~3 an~
¦(CH2CH2OH)2NCH2PO(OM~Z where M is H, NH~, alkali metal or combina-
tion thereof.
Other useful amino phosphonates are described in U.S.
Patent No. 3,434,969. These are of the following general formula:
\ N - ~ CH~ - CHz - W ~ - R
wherein each R is independently selected from the group consis~ing
of hydrogen and D
CH~ - P - OM
OM
provided, however, that at least half of the radicals rep~esen~ed
IbY R are D
CH 2 - ~OM
I OM
¦and n is an integer of 2 to 14 and M indicates that the inhibitor
¦is in water-soluble form. Typically, M will be îndependently
¦selected from the group consisting of hydrogen, alkali metalsr
¦ar~monium, alkaline ear-th metals, and zinc. Preferred scale inhi-
¦bitors of this group are N~methylene phosphona-ted dlethylene
¦triamines of the general formula:
I X ~X
~ X/ ~ \ X
wherein each X is independently selected from the group consisting of
hydrogen and
O
CH2 - -P - -OH
OH
and at least four of the radicals represented by X are
1l
- CH2 IP OH
OH
and water-soluble salts thereoE.
The Water-Soluble Zinc Compounds
These may be selected from any compound of zinc that is water-
soluble. Useful are the zinc salts of strong mineral acids such as zinc
sulphate or zinc chloride with the latter being preferred. The zinc is,
preferably, in the plus 2 form.
The Phosphorous Containing Chelant--Formula ~
These materials are effective at high pE~Is and chelate zinc icn
effectively. They do not interfere with the scale forming properties of
the formulas in which they are used nor do they aggravate corrosion pro-
tection afforded by the zinc ion and the organic phosphorous inhibitor.
These compounds may be prepared by using the synthetic tech-
niques generally disclosed in U.S. 4,088,678.
The ratio of phosphorous containing chelant to zinc material
contained in the water-treated may vary between 0.5:1 to 2:1 with a ratio
of about 1:1 being preferred.
_g_
~ ~J , ~.
~ ~.7~4~9~
The Maleic Anhydride Styrene
Sulfonate Copolymer Dlspersants
Materials of this type are described in U.S. 4,0~8,066. Polymers
used in the practice of this invention have a molecular weight within the
range of 800 to about 5 million. While they are primarily dispersants or
scale inhibitors, they may, in certain instances, impart additional cor-
rosion protection. In a preferred practice of the invention, the weight
ratio of the styrene sulfonate to maleic anhydride is abou~
As previously pointed out, the composition of the invention allows
relatively low maintenance levels of zinc to be effective as corrosion
inh;h:itors yet, at the same time, allows the cooling water to be utilized
at a pH of between 8 - 9 and, preferably, between 8.5 - 9.
Evaluation of the Invention
In the following evaluations, the following materials have the
following identifications:
Comp. I
Ingredients % by weight
Sodium lignosulfate 20.4
Zinc chloride 28.2
Ethoxylated glycerine (50~ EØ) 19.75
reacted with P205 per U.S.
3,487~01~.
Propanol 2.26
Soft water 29.48
Comp. II
Formula I
Comp. III
Glycerine reacted with 50 weight percent ethylene oxide and
phosphated per U.S. 3,487,018.
--10--
~,
Comp. IV
l-hydroxyethylidene l,l-diphosphonic acid
Comp. V
2-phosphono-butane-1,2,4-tricarboxylic acid
Comp. VI
Maleic anhydride styrene sulphonate copolymer
Test Method 1
The laboratory tests of solubility limits of scaling
species were carried out in laboratory pilot cooling towers such
as that described in a paper by D. T. Reed and R. Nass entitled
"Small-Scale Short-Term Methods of Evaluating Cooling Tower
Treatments. . .Are They Worthwhile?" presented at the 36th
~nmual Meeting of the INTERNATIONAL WATER CONFERENCE, Pittsburgh,
Pennsylvania, November 4 - 6, 1975, available from ~alco Chemical
Company - Reprint 233.
Test Method 2
The same test method as the Pilot Cooling Tower except that
it is essentially a closed system withou~ water evaporation being
used.
To illustrate the various facets of the invention, the
~ollowing data is provided. Using the Pilot Cooling Tower test,
~i various res 5 are presented in Table I.
TABLE I
~ormulation Coupon Test Results*,MPY
~ pH 8
1. Comp. I 0.426.2 14.3
2. Comp. I with 6.7% Comp. II0.0 2.8 2~5
3. 45% Water 0.5 9.5 8.1
35% Comp. II
20% ZnC12
4. 10% Waker 0.6 1.1 9.4
35% Comp. III
20~ znC12
35~ Comp. II
5. 35% Comp. IV 0.6 4.1 8.4
35~ Comp. II
20% znC12
10~ vlater
~Csupons were run for two days at 100F; they were treated
with a high level dose the first day and a maintenance
dose the second day.
-12-
~ s~ l
From the above, the addition oE a sm~ll amount of Comp. II
to Comp. I greatly improves corrosion inhibition at high pEI.
Formula 3 shows Comp. II and ~inc alone do not perform as well.
The tertiary combination of zinc, Comp. II, and Cornp. III seer.
in formula 4 does very well (by mistake, this product was run at
half the level of the other formulas on -this sheet.) Formula 5
proved unstable, but we have a stable form we will test in the
future. These tests demonstrate that Comp. II can b~ used to
improve the performance of zinc-based corrosion inhibitors.
Using heat transfer tests, additional data was generated
with respect to additional organic phosphorous inhibitors. The
results are presented in Table II.
~4~
TABLE I I
HTU TESTS OF LO~ ZINC PRODUC'rS
These tests w~re performed at 110F using Chicclgo tap water at the
indicated pH range. All tests ran 7 days: treated with 2,500
ppm of a commercial chelant-cleaner composition at room temperature,
with 150 ppm of product the second day at llO~F, and with 50 ppm of
product for the remainder of the test. The water typically reached
1.2 cycles by the conclusion of the test.
Product Tested ppm Zn @ Corrosion ~ate, ~py (Deposit, mg~
5~3~ Product Sa~plepH 6~5-7.0 pH 7~5-8.0pH 8.5-~,0
1. Comp. I 4.8 MS tube7.S7~848) 0.84~149~1.42[1593
MS coupon12.50(56) 0.47t2)0.73(4
~DM coupon 0.98(5)Q.04~0) 0 ~1
2. Comp. I ~ith 2 MS tube 0.69(4~)
lower Zn level MS coupon 0.15(8)
ADM coupon O
3. 35% Comp. II, 2 MS tube 6.34(777)1.17(121) 1.67~138
19~8% Comp. IV, MS coupon 5.89(41)0.33~4) 3.26(32)
4% Z~ AD~ coupon 0.99(6)0.77(5)
!
4. 20.5% Co~p. II, 2 MS tube 2.20(26B)0 79(11~) l.Oltll5)
67~ Comp. III7 MS coupon 2.76~19) 0.61(2~ 1.00(4)
4% Zn ADM coupon 0.64(3~ 0 9~6) 0 50)
5. 20% Comp. II~ 1 MS tube 2.32~220)* 0~68(51) 0.65~8)
67% Comp. III, ~s coupon 3.13(17) 0.5~t3)1.36tl2)
2% Zn ADM col~pon 0.74(5) 0 tO) 0 ~0)
6. 20% Comp. II, 1 MS tube 3 27~229)~ 0.56t39) 0.90~54)
34% Comp. III, MS coupon 3.51t21~ 0.68~3) 1.20(6)
207 Comp. V, ~DM coupon 0.85t5) 0.11(1) 0 ~0)
2% Zn
7. 207 Comp. LI 1 MS tube 3.72~353) 2.01(183)0.92t66
43.77 Comp. III, MS coup~n 4.10~23)2.86(12) 1.20~8)
30~ Co~p. VI, ~D~ coupon 0 al(5) 0.62(3) 0 (0)
2% Zn
MS -- ~Lild Steel
A~M -- Admira:Lty Bron%e
*Saople was pittèd.
-14-
:~'7'~5~
In a final series of experiments, a commercial type composition
was prepared which had the following composition:
Comp. VII
Ingredients % by weight
Soft water 73.1
Comp. II 7.0
Comp. VI 7.5
Comp. III 5.7
~nC12 6.7
Using this formula in Test Method 1, the following data is
generated in Table III.
-15-
~ .
~4'~
TABLE III
Comparison of Comp. VII
and Comp . I Corrosion Da ta
A. Corrosion Rates
COMP . VI I COMP . I
M/S tube ,j S 4 . O mpy 3 . 2 mpy
M/S tube ,r 5 2 . 9 mpy 3 .1 mpy
Cu tube ,s4' 0. 25 mpy 0.07 mpy
~dmiral~y Coupon 0 . 41 mpy 0 . 30 mpy
M/S Coupon 2 . 2 mpy 2 . 8 mpy
~osages 200/50 lppm 200f~0 ppm
pH Range 8 . 0/8 . 5 7. 6/8. 0
.
B. Average Zn~ Values During Main~enance I.evel
~ve. Total Zn ~2 Ave. Soluble æn~2 96 Zn 2 in Solu~`on
.
Comp. I3 . 2-1. 8 ppm 2 . 2-û . 8 ppm 70-45%
Comp. VII 1. 0-0 . 5 ppm 0, 8-D . 3 ppm 80-60%
~16-
