U.S. patent number RE30,714 [Application Number 05/942,208] was granted by the patent office on 1981-08-18 for removal of copper containing incrustations from ferrous surfaces.
This patent grant is currently assigned to The Dow Chemical Company. Invention is credited to Lester W. Harriman, Paul E. Muehlberg, Fred N. Teumac.
United States Patent |
RE30,714 |
Harriman , et al. |
August 18, 1981 |
**Please see images for:
( Certificate of Correction ) ** |
Removal of copper containing incrustations from ferrous
surfaces
Abstract
.Iadd.The invention concerns a method of removing copper from a
ferrous metal surface without excessive corrosion of the ferrous
metal surface. In the method, the copper is dissolved with an
aqueous alkaline solution containing a ferric chelate of an
alkylene polyamine polyacetic acid chelating agent. .Iaddend.
Inventors: |
Harriman; Lester W. (Angleton,
TX), Muehlberg; Paul E. (Jackson, TX), Teumac; Fred
N. (Charlotte, SC) |
Assignee: |
The Dow Chemical Company
(Midland, MI)
|
Family
ID: |
27052535 |
Appl.
No.: |
05/942,208 |
Filed: |
September 14, 1978 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
387481 |
Aug 4, 1964 |
|
|
|
Reissue of: |
497530 |
Oct 18, 1965 |
03438811 |
Apr 15, 1969 |
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Current U.S.
Class: |
134/2;
134/29 |
Current CPC
Class: |
C23G
1/19 (20130101) |
Current International
Class: |
C23G
1/19 (20060101); C23G 1/14 (20060101); C23G
001/14 () |
Field of
Search: |
;134/2,29
;252/80,82,156 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Alfano et al., Proceedings Intnl. Water Conf., "Chemical Removal of
Magnetite and Copper", 1961, pp. 41-51. .
Narcus, Metal Finishing, 1952, pp. 54-61. .
Geigy, Sequestrene Tech. Bull., 1952, pp. 2, 3, 27, 50. .
Loucks, Power, "Sequestrants Play Vital Role in Modern Chemical
Cleaning", vol. 105-No. 12, 12-1961, pp. 186-189. .
Viacova et al., Teploenorgetika, "Investigation of Solution of
Boiler Deposits with Complex Forming Reagents", No. 11, 1962, pp.
69-74. .
Loucks, Chem. Engnr., "Chemistry Tackles Plant Maintenance",
3-5-62, pp. 103-120. .
Bersworth Chem. Co., Versene Tech. Bull., 1954..
|
Primary Examiner: Caroff; Marc L.
Attorney, Agent or Firm: Kanuch; Bruce M.
Parent Case Text
This application is a continuation-in-part of U.S. patent
application Ser. No. 387,481, now abandoned.
Claims
What is claimed is:
1. A process for removing copper from a ferrous metal surface
containing copper thereon by contacting said surface with an
aqueous alkaline solution wherein the solution employed contains as
an essential constituent at least one member of the group
consisting of ferric chelates of .[.polycarboxylic.].
.Iadd.alkylene polyamine polyacetic .Iaddend.acid chelating agents
and mixtures of ferric and ferrous chelates of .[.polycarboxylic.].
.Iadd.alkylene polyamine polyacetic .Iaddend.acid chelating agents
in amount sufficient and for a time sufficient at a reaction
temperature above about 68.degree. F. and up to about 300.degree.
F., to dissolve said copper.Iadd., wherein said solution may also
contain a salt of the group consisting of ammonium, amine, and
hydroxyalkylamine salts of alkylene polyamine polyacetic acid
chelating agents.Iaddend.. .[.
2. A process as claimed in claim 1 wherein the said solution may
also contain a salt of the group consisting of ammonium, amine and
hydroxyalkylamine salts of polycarboxylic acid chelating
agents..].
3. A process as claimed in claim .[.2.]. .Iadd.1 .Iaddend.wherein
the total iron chelate originally present ranges between about 60
and about 100 weight percent of total salt form and iron chelate
and the solution originally contains a total of between ca. 0.5
weight percent and up to a saturated solution of salt form and iron
chelated chelating agent.
4. A process as claimed in claim 3 wherein some iron chelate is
maintained in the ferric form by the addition of a water-soluble
compatible oxidizing agent.
5. A process as claimed in claim 3 wherein some iron chelate is
maintained in the ferric form by bubbling air through said aqueous
alkaline solution. .[.6. A process as claimed in claim 3 wherein
the iron chelate and
chelating agent salt are those of ethylenediaminetetraacetic
acid..]. 7. A process as claimed in claim 3 wherein the reacted
ferrous surface is
rinsed with rinse water containing a water-soluble oxidant. 8. A
process as claimed in claim 3 wherein the reacted ferrous surface
is rinsed with
rinse water while air is bubbled therethrough. 9. A process for
removing copper from a ferrous metal surface containing copper
thereon by contacting said surface with an aqueous alkaline
solution wherein the solution contains as an essential constituent
ammoniated ethylenediaminetetraacetic acid adjusted to a pH of
about 9 with free ammonia and iron chelate thereof wherein the iron
chelate originally present ranges between about 60 and ca. 100
weight percent of total salt form ethylenediaminetetraacetic acid
and iron chelate thereof and the solution originally contains
between about 0.5 weight percent and up to a saturated solution of
total salt form and iron chelate of ethylenediaminetetraacetic acid
while air is being bubbled therethrough at a reaction temperature
above about 68.degree. F. and up to about 300.degree. F. in amount
sufficient and for a time sufficient to dissolve said copper,
removing said solution from said ferrous metal surface, contacting
said surface with rinse water while bubbling air therethrough and
removing said rinse water. .Iadd.10. A process for removing copper
from a ferrous metal surface containing copper thereon by
contacting said surface with an aqueous alkaline solution wherein
the solution employed contains as an essential constituent at least
one member of the group consisting of ferric chelates of
ethylenediaminetetraacetic acid and mixtures of ferric and ferrous
chelates of ethylenediaminetetraacetic acid in amount sufficient
and for a time sufficient at a reaction temperature above about
68.degree. F. and up to about 300.degree. F. to dissolve said
copper, wherein said solution may also contain a salt of the group
consisting of ammonium, amine and hydroxyalkylamine salts of
ethylenediaminetetraacetic acid and wherein the total iron chelate
originally present ranges between about 60 and about 100 weight
percent of total salt form and iron chelate and the solution
originally contains a total of between ca. 0.5 weight percent and
up to a saturated solution of salt form and iron chelated chelating
agent. .Iaddend. .Iadd.11. The process of claim 10, wherein the
reaction temperature ranges from about 140.degree. to about
180.degree. F. .Iaddend. .Iadd.12. The process of claim 11, wherein
at least 67 percent of the chelating agent is complexed
with iron. .Iaddend. .Iadd.13. The process of claims 11 or 12
wherein the salt consists of the ammonium salt of
ethylenediaminetetraacetic acid. .Iaddend. .Iadd.14. The process of
claim 13 wherein the pH of the solution is in excess of 7 and up to
about 10. .Iaddend. .Iadd.15. The process of claim 10 wherein the
pH of the solution is in excess of 7 and up to about 10. .Iaddend.
.Iadd.16. The process of claim 1 wherein said reaction temperature
ranges from about 140.degree. F. to about 180.degree. F. .Iaddend.
.Iadd.17. The process of claim 16 wherein at least 67 percent of
the chelating agent is complexed with iron. .Iaddend. .Iadd.18. The
process of claim 16 or 17 wherein the salt consists of an ammonium
salt of alkylene polyamine polyacetic acid chelating agent.
.Iaddend. .Iadd.19. The process of claim 17 wherein the pH of the
solution is in excess of 7 and up to about 10. .Iaddend. .Iadd.20.
The process of claim 16 wherein the pH of the solution is in excess
of 7 and up to about 10. .Iaddend. .Iadd.21. The process of claim 1
wherein the chelate is a compound corresponding to the formula
(HOOCCH.sub.2).sub.2 N[(CH.sub.2).sub.n NCH.sub.2 COOH].sub.m
CH.sub.2 COOH
wherein n and m are each independently 1, 2, 3 or 4 and up to two
of the carboxymethyl groups may be replaced with a
.beta.-hydroxyethyl group and one or more of the carboxymethyl
groups may be replaced with a carboxyethyl group. .Iaddend.
.Iadd.22. The process of claim 21 wherein the solution may also
contain an ammonium salt of said chelate. .Iaddend.
.Iadd.23. The process of claim 10 wherein said salt consists of the
ammonium salt of ethylene diaminetetraacetic acid said reaction
temperature ranging between about 140.degree. F. to 180.degree. F.
and wherein some iron chelate is maintained in the ferric form by
the addition of a water soluble compatible oxidizing agent.
.Iaddend. .Iadd.24. The process of claim 23 wherein the solution
also contains some chelating agent which is not chelated with iron.
.Iaddend. .Iadd.25. The process of claims 23 or 24 wherein air is
employed as the oxidant. .Iaddend. .Iadd.26. The process of claims
23 or 24 wherein an alkali metal nitrite is employed as the
oxidant. .Iaddend. .Iadd.27. The process of claim 10 wherein said
ferrous metal surface also contains iron oxide scale wherein said
iron oxide is first dissolved with an alkaline solution of the
ammonium salt of ethylene diaminetetraacetic acid, and the
copper-containing metal surface is then contacted with the solution
obtained from the removal of the iron oxide at a temperature of
about 140.degree. F. to 180.degree. F., said solution containing
from 60 to 100 percent of the ammonium salt in the form of iron
chelate while adding to such solution a water soluble compatible
oxidizing agent to maintain some of said iron chelate in the ferric
form said solution having a pH within the range in excess of 7 and
up to about 10. .Iaddend. .Iadd.28. The process of claim 27 wherein
the oxidant comprises at least air which is bubbled through the
copper-dissolving solution. .Iaddend.
Description
This invention concerns the removal of plated copper from a ferrous
surface.
It has long been desired to be able to remove plated copper from a
ferrous surface, e.g., steel, without also oxidizing excessively
the iron thereof. This problem has been especially difficult and
economically costly in the removal of plated copper from the
internal metal surfaces of steam generating equipment, particularly
high pressure steam generating equipment, which is operated in
connection with a condenser, the condensing surfaces of which are
of copper alloy.
In the operation of high pressure steam generating equipment (over
600 pounds per square inch steam pressure) in which the feed water
is largely returned condensate from a copper alloy condenser,
incrustations are usually produced upon the steam generating
surfaces of the steam generator despite the fact that the feed
water is substantially pure. These incrustations oftentimes contain
copper, both in metallic form and combined with oxygen, corroded
from the copper alloy condenser by the action of the condensed
steam which carries the copper to the steam generator.
Attempts to remove such incrustations, as by the use of
conventional acidizing procedures, are not wholly successful. Tests
have shown that by acidizing incrusted steam generating surfaces of
the usual high pressure steam generator, having copper in the
incrustations, some of the copper is removed from the incrustations
and some of the copper so-removed is redeposited elsewhere on the
surfaces of the steam generating equipment during the acidization
so that only a partial net removal of copper from the incrusted
surfaces results. Insofar as is known, there is no completely
satisfactory method commercially available for treating the
internal ferrous metal surfaces of high pressure steam generating
equipment subject to deposition of copper-containing incrustations
so as to free the surfaces of the incrustations and the copper.
Accordingly, it is an object of the invention to provide a method
fulfilling this need. Other objects and advantages will become
apparent as the description of the invention proceeds.
It has now been discovered that an aqueous solution of a ferric
chelate of a polycarboxylic acid chelating agent alone or together
with some free polycarboxylic acid chelating agent when adjusted to
an alkaline pH, i.e., in excess of 7 and up to about 10, by
combination with ammonia, an amine or a hydroxyalkylamine or one or
more of the preceding in amount of at least 50 mole percent in
combination with up to 50 mole percent of an alkali metal
hydroxide, is quite effective in dissolving plated copper from
ferrous surfaces, e.g., of high pressure steam boiler surfaces.
The chelating agents used in the practice of this invention as
their ferric chelates and, if desired, in combination with ammonium
and amine salts of the aforementioned polycarboxylic acid chelating
agents are those of alkylene polyamine polyacetic acid (APAPAA),
e.g., ethylenediaminetetraacetic acid (EDTA),
N-hydoxyethylethylenediaminetriacetic acid (NHEDTA);
nitrilotriacetic acid (NTA) and N-2-hydroxyethyliminodiacetic acid
(OHEtIDA); diethylenetriaminepentaacetic acid (DTPA); and mixtures
thereof, hereinafter referred to broadly as polycarboxylic acid
chelating agents.
In practice, a ferrous metal surface on which copper has plated
out, e.g., that of a high pressure boiler, is heated at a
temperature above room temperature and up to about 300.degree. F.
in the presence of an aqueous solution of a ferric chelate of a
polycarboxylic acid chelating agent, if desired also containing
free chelating agent, which solution is adjusted to an alkaline pH
up to about 10 with ammonia and/or an amine or alkanolamine and
with up to a 50 mole percent proportion of an alkali metal
hydroxide, if desired. The resulting salts will hereinafter be
referred to as ammonium and amine salts of said chelating agents. A
solution containing a total of about 0.5 weight percent
polycarboxylic acid as iron chelate and, if desired, as ammonium
and/or amine salt of said polycarboxylic acid up to a saturated
solution thereof can be used. The weight proportion of iron chelate
of the total of free and chelated chelating agent, i.e., degree or
percent spentness, can be varied from between about 60 to about 100
percent.
It appears that the solution containing ferric chelate oxidizes the
copper metal to copper ions (Cu.sup.++ and Cu.sup.+) which react
with the resulting ferrous chelate or with the free, i.e.,
uncomplexed or salt-form, chelating agent therein to form a copper
chelate, and after a sufficient reaction time, as determined by
analysis of the treating solution, the plated copper is dissolved.
However, we do not wish to be bound by this theory. As reaction
proceeds, the ferric chelate is reduced to a ferrous chelate. This
"reduction" would progressively slow the copper-dissolving
reaction. In order to maintain a useful level of ferric chelate,
i.e., some of the iron chelate must be in the ferric form, it has
been found necessary to add an oxidizing agent to the
copper-dissolving ferric chelate-containing solution so that
ferrous chelate formed when the plated copper is oxidized to copper
ions is reoxidized to ferric chelate for continued oxidation and
subsequent dissolution of copper. This may be done by continuously
or periodically monitoring or analyzing the copper-dissolving
solution and adding an oxidant such as hydrogen peroxide,
water-soluble salts such as alkali metal or ammonium nitrites,
permanganates, persulfates, or perchlorates; or such gaseous
oxidants as nitrogen tetraoxide, oxygen or air, advantageously by a
sparger, in amount sufficient to maintain some of the iron chelate
in the ferric chelate form. Of these oxidants, air is preferred,
since it does not substantially affect pH and it introduces no
extraneous matter.
The ferric chelates of polycarboxylic acid chelating agents useful
in the practice of the present method are advantageously made by
reacting iron, iron oxide or hydroxide or magnetite with a
polycarboxylic acid chelating agent which has been adjusted to an
alkaline pH up to about 10 with ammonia and/or an amine as stated
above or with a mixture of ammonia and/or an amine and an alakali
metal hydroxide, in proportions as specified, so than an average of
not more than one free carboxylic acid group remains per mole of
chelating agent, at least about half of the carboxylic acid groups
of the chelating agent are in the ammonium or amine salt form and
provided that an average of not more than half of the carboxylic
groups are in the alkali metal salt form. Alternatively, the
corresponding ferrous chelates are made and oxidized, at least
partially to the ferric chelate form in the manner previously
described, advantageously in use. It is not required that pure
ferric and/or ferrous chelates be used. On the contrary, a
commercially attractive iron chelate-chelating agent solution can
be prepared by dissolving iron-containing scale from ferrous
surfaces, e.g., those of oxide scaled ferrous boiler tubes, by the
reaction with an aqueous solution of a polycarboxylic acid
chelating agent adjusted to an alkaline pH with ammonia and/or an
amine or mixture thereof or with ammonia and/or an amine and with
an alkali metal hydroxide, thereby forming iron chelate containing
both ferrous and ferric chelate. Such a method is described in
copending U.S. patent application Ser. No. 296,464, filed July 22,
1963 now U.S. Pat. No. 3,308,065.
The more preferred ammonium and/or amine salts whose ferric
chelates are used in the process of this invention are those of the
APAPAAs of the formula
(HOOCCH.sub.2).sub.2 N[(CH.sub.2).sub.n NCH.sub.2 COOH].sub.m
CH.sub.2 COOH
where n and m may each independently be 1, 2, 3 or 4, up to two of
the carboxymethyl groups may be replaced with a .beta.-hydroxyethyl
group and one or more of the carboxymethyl groups may be replaced
by carboxyethyl groups.
Since no two ferrous surfaces are likely to have the same amount of
copper plated out thereon, it is advantageous that the
copper-dissolving ferric chelate-containing solutions can be varied
in concentration. The stoichiometry of polycarboxylic chelating
agents is well-known and can be used to calculate the requirements
for copper solution. In the case of EDTA, for instance, one mole is
required to solvate one mole of copper. Thus, as the plated copper
is oxidized to copper ions, it reacts with free chelating agent
present as a salt or as an iron chelate.
The degree or precent of "spentness of iron chelate-chelating agent
solution is defined by: ##EQU1## Free chelating agent is determined
analytically by a standard colorimetric or visual titration with
strontium chloride to a constant turbidity after first filtering
the sample solution. From this analysis, the percent by weight of
unchelated chelating agent can be determined. Dissolved copper is
analytical determined by a chlorimetric or visual determination
using diethyldithiocarbamate sodium salt as follows. Transfer 5 ml.
of sample solution to a 250 ml. volume flask and dilute to volume
with water. Mix solution and transfer 5 ml. thereof to a beaker or
flask. Add 1 ml. of aqueous one percent diethyldithiocarbamate
sodium salt and dilute to exactly 200 ml. volume with 2B ethanol.
Mix solution thoroughly and take a reading on a colorimeter or take
frequent samples and use the previous sample as a comparative blank
to a constant visual end point. Total dissolved iron and copper can
be determined by X-ray emission spectroscopy.
Most generally, optimum conditions for the removal of plated copper
from ferrous surfaces involve (1) a temperature of about
140.degree.-150.degree. F.; (2) a ca. 70-90 percent spent solution,
i.e., ca. 70-90 percent of the total chelating agent is complexed
with iron; (3) air at an average rate of 0.004 c.f.m./gal. of
copper-dissolving solution bubbled through the copper-dissolving
solution for about two hours, or, if at a lower rate, then for a
proportionately longer time.
It is necessary that magnetite be completely removed from the
ferrous metal surfaces, e.g., of boiler tubes, according to a
procedure previously indicated.
Degree of spentness determines the corrosion rate at any given
temperature. The rate can be modified with iron-oxidation
inhibitors. At each temperature, there is a degree of spentness
above which there is no further corrosion. At about 140.degree. F.,
it is about 85 percent spentness, and at about 180.degree. F., it
is about 88 weight percent spentness, in the latter case, if ca.
0.05 weight percent thioethylamine iron-oxidation inhibitor is
present. At 140.degree. F., the degree of spentness can be reduced
to 67 percent without any practical difference in corrosion rate.
Theoretically, a solution containing more ferrous EDTA should
require more oxygen. The efficiency of copper oxidation is
increased, however, and the same amount or less air is required to
oxidize the copper in a more highly spent solution.
If the solution is 67 percent spent or more, no iron oxidation
inhibitor is required at 140.degree. F. At 160.degree. or
170.degree. F., the solution should be 91 percent or more spent if
no iron inhibitor or only an inhibitor as disclosed in U.S. Patent
3,077,454, is used.
The solubilized copper appears to be stabilized by the formation of
cupric chelate. Therefore, in highly spent solutions, the stripping
of copper is accompanied by a reduction in the dissolved iron to
give a colloidal ferric hydroxide precipitate.
After plated copper and iron oxide are removed from the treated
ferrous surfaces, rising is accomplished, e.g., by draining the
boiler and refilling with water, all with air agitation. This
facilitates the removal of suspended undissolved solids and causes
better rinsing. Finally, the rinse water is drained off. If the
magnetite is not completely removed, small areas of copper are
protected from oxidation. In contact with air and water, these
areas develop tiny "ant hills" of corrosion products, i.e., red
rust.
The following examples describe completely representative specific
embodiments and the best mode contemplated by the inventors of
practicing the invention. They are not to be taken as limiting the
invention other than as defined in the claims. Parts and
percentages therein are given by weight.
EXAMPLE 1
A formulated spent solution of ammoniated EDTA was prepared by
adding iron powder, in amount sufficient to saturate, to an aqueous
7.6 weight percent solution of ammoniated EDTA originally adjusted
to a pH of about 9 with free ammonia and maintained at a reaction
temperature of about 95.degree. C. for 30 minutes in the presence
of a nitrogen atmosphere so that the ferrous chelate of EDTA was
formed. This solution was used to prepare a series of 3.8 percent
total EDTA solutions having various percentages of spentness, e.g.,
by mixing with ammoniated EDTA adjusted to a pH of about 9 with
free ammonia and with water, the percent of spentness being
measured as described above. About one-half gallon of such
solutions, some of them modified with a small percentage, up to ca.
0.1 weight percent of an iron-oxidation inhibitor, were then placed
in a simulated high pressure boiler containing 2.3-2.5 grams of
plated copper on a square foot of inside surface. Simulated boiler
heaters were turned on to give various operating temperatures.
Until a temperature equilibrium was reached, a constant flow of
nitrogen through the simulated boiler was maintained to get
circulation and exclude air. The nitrogen purge was then changed to
air, using a pressure regulator and a valve to meter air through a
coarse frit at the bottom of the boiler tubes. Time and rate of air
flow were measured. The solutions were sampled for subsequent iron
analysis, total iron and copper being determined by X-ray emission
spectroscopy. One or more steel coupons were suspended in the
boiler tubes for corrosion data.
At pre-determined times, the steel coupons were removed and dried
for determination of corrosion data and limited samples of the
aqueous solutions were taken. At the completion of each run, heat
was discontinued and the solution was drained from the bottom of
the boiler. Distilled water was then added and the boiler tubes
were air agitated for several minutes. The rinse water was drained
and the boiler tubes removed and examined. Operational data and
results are summarized in the following table.
TABLE I
__________________________________________________________________________
SUMMARY OF AIR-BLOWING DATA
__________________________________________________________________________
Percent Air-Blow Copper A. EDTA Temp., Total, Required Avg.,
Percent Run No.: Inhibitor.sup.1 Spent.sup.2 .degree.F. min. C.F.M.
Mins..sup.3 mils Stripped
__________________________________________________________________________
1 A-124 plus ThEA 88 180 40 .07 9 .29 100 2 " 89.5 180 40 .035 18
.18 100 3 " 98.5 180 40 .035 19 .29 100 4 " 91 180 65 .004 191 .19
100 5 " 83 140 125 .004 156 .27 100 6 A-124 70 140 180 .004 162 .29
100 7 A-124 67 140 180 .004 162 .24 100 8 A-124 67 140 210 .004 181
.47 100 9 A-124 85 140 40 .035 21 .47 100 10 A-124 90 140 40 .035
18 .30 100 11 A-124 91.0 180 40 .035 22 .27 100 12 A-124 90 160 40
.035 23 .25 100 13 A-124 79 80 80 .035 .25 100 14 A-124 68.5 140
240 .004 100 15 No inhibitor 67.0 140 30 .035 100 16 " 70.0 140 40
.035 .30 99+ 17 " 86.0 180 40 .035 .30 100 18 " 70.0 140 30 .035
100 19 " 82.0 180 40 .035 100 20 " 90.2 180 40 .035 100 21 " 86.5
180 40 .035 100 22 " 81.2 145 120 .035 100
__________________________________________________________________________
(Theoretical) O.sup.2 Corrosion Final Conc. in Solution Required
Rate, Run No.: Percent Cu Percent Fe (lb. moles) Used Percent
lbs./ft..sup.2 /day
__________________________________________________________________________
1 .13 .75 .00035 .00148 422 None 2 .11 .78 .00034 .00074 217 None 3
.16 .73 .00035 .00074 212 None 4 .10 .92 .00041 .00014 34 None 5
.12 .72 .00034 .00027 80 .0005 6 .14 .66 .00031 .00038 122 .00034 7
.14 .66 .00031 .00038 122 .00013 8 .22 .52 .00037 .00044 116 .00005
9 .18 .63 .00038 .00074 188 .0002 10 .12 .81 .00033 .00074 224 None
11 .13 .77 .00040 .00074 185 .0054 12 .10 .88 .00043 .00074 172
None 13 .072 .63 .00029 .00148 510 None 14 None 15 .59 16 None 17
.0189 18 None 19 .0330 20 .0089 21 .0403 22 .21 .62 .0233
__________________________________________________________________________
.sup.1 A124, an ironoxidation inhibitor disclosed in U.S. Pat. No.
3,077,454, is used in amount of 0.1%. ThEA is thioethylamine used
in amount of 0.05%. .sup.2 Ammoniated EDTA, pH ca. 9. .sup.3 The
calculated theoretical no. of mins. at the designated flow rat to
convert the ferrous EDTA to ferric EDTA and Cu.degree. to Cu
ion.
Elemental analysis of the solutions in runs 1, 2 and 3 indicated
that the copper was being complexed by the EDTA. In the case of
highly spent solvent (98.5 percent) the formation of ferric
hydroxide was obvious. In other runs, the colloidal sediment could
only be detected by the difference in iron analysis in filtered and
unfiltered solutions.
Free ammonia content is not critical. At the completion of run 3,
for example, the pH was almost neutral.
Runs 9 and 10 established the corrosion rate at 140.degree. F. when
A-124 was the only inhibitor employed. The data indicate that a
spentness of 67 percent gave a negligible iron corrosion rate.
Run 13 indicated that, although there was no iron corrosion at
80.degree. F. and 79 percent spentness, the copper stripping rate
was slow.
EXAMPLE 2
In accordance with the method described in Example 1, the following
named polycarboxylic acid chelating agents were prepared as 80
percent spent solutions and at about pH 9.3. The solutions (each
containing 3.8 percent chelating agent on an unreacted basis) were
tested at 140.degree. F. to remove copper-containing scale from
ferrous surfaces. The scale was about 0.25 mil in thickness. Air
was bubbled through the "solvent" at the rate of 0.035 c.f.m./gal.
during the cleaning. The following data show the comparative times
required in each instance to attain complete removal of the scale
from the ferrous surfaces. Analytical procedures were the same as
in Example 1.
______________________________________ Time to Strip Off Run No.:
Polycarboxylic Acid 100% of Scale, mins.
______________________________________ 1 DTPA 7 2 NHEDTA 20 3 NTA
15 4 EDTA 10 5 Diammonium disodium EDTA 6
______________________________________
EXAMPLE 3
The effect of EDTA concentration on the copper-stripping efficiency
of the system was tested by preparing, as 80 percent spent, a 38
percent ammoniated EDTA solution at pH 9.3. Several dilutions of
this solution were prepared and maintained at 140.degree. F. while
air was bubbled through the solution in contact with a 0.25 mil
copper-scale on a ferrous surface.
______________________________________ Conc. EDTA, percent:
Copper-strip ______________________________________ 38 Yes. 4 Yes.
2 Yes. 0.5 Yes. 0.25 Partial.
______________________________________
At the 0.25 percent level, corrosion of the substrate was
accelerated at stress areas.
EXAMPLE 4
The following listed amines have been found to be operable in the
practice of this invention for the purpose of adjusting the pH to
the proper range and thereby forming the salts or partial salts of
polycarboxylic acids and/or their partial salts, thereafter
"spending" at least a portion of the so-formed solution of
chelating agent by adding iron to form iron chelate. These highly
spent solutions are operable in removing copper-containing scale
from ferrous surfaces while having little or no corrosive effect on
the substrate, they also gave a passivated ferrous surface.
______________________________________ Amines: Used with:
polycarboxylic acid ______________________________________
Ethanolamine EDTA. Ethylamine EDTA. Ethylenediamine EDTA.
Diethylenetriamine EDTA. Pentaethylenehexamine EDTA. Dimethylamine
EDTA. Trimethylamine EDTA. Ethyleneimine EDTA. Ethanolamine
Ethylenediaminetetra- propionic acid. Ethylenediamine
N,N-di-(.beta.-hydroxyethyl) glycine. Ammonia
Tetramethylenediamine- N,N,N',N'-tetraacetic acid. Ammonia
(2-hydroxyethylimino) diacetic acid.
______________________________________
* * * * *