Note: Descriptions are shown in the official language in which they were submitted.
P
c-148s
TITLE OF THE INVENTION
"NOVEL COPPER AND COPPER ALLOY CORROSION INHTBITORS"
BACKGROUND OF THE INVENTION
Benzotriazole, mercaptobenzothiazole and
tolyltriazole are well known copper corrosion
inhibitors. For example, see U.S. patent 4,675,158
and the references cited therein. Also, see U.S.
patent 4,744,950, which discloses the use of
alkoxybenzotriazoles as corrosion inhibitors and U.S.
patent 4,406,811, which discloses the use of
benzotriazole/tolyltriazole blends in water treatment
compositions for multimetal corrosion inhibition.
Aside from the known use of 5-methoxybenzotriazole
(anisotriazole) in corrosion inhibition compositions
(see Japan Kokai Tokkyo Koho, JP 59,222,589; 14 Dec.
1984; Chem. Abst. 102:153153b.), the use of
alkoxybenzotriazoles is not known in the water
treatment art.
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The instant invention .relates to the use of
alkoxybenzotriazoles as corrosion inhibitors,
particularly copper and copper alloy corrosion
inhibitors. These compounds from long-lasting
protective films on metallic surfaces, particularly
copper and copper alloy surfaces, in contact with
aqueous systems.
DESCRIPTION OF THE INVENTION
The instant invention is directed to a method of
inhibiting the corrosion of metallic surfaces,
particularly copper and copper alloy surfaces, in
contact with an aqueous system, comprising adding to
the aqueous system being treated an effective amount
of a compound having the following structure:
4 3
0
~ H
wherein R is any straight or branched, substituted or
unsubstituted alkoxy group having 3-18 carbons, and
isomers of such compounds.
The instant invention is also directed to an
aqueous system which is in contact with a metallic
surface, particularly a copper or copper alloy
surface, and which contains an alkoxybenzotriazole.
- 3 - C-1486
Compositions comprising water) particularly
cooling water, and an alkoxybenzotriazole are also
claimed.
The inventors have discovered that alkoxybenzo-
trizoles are effective corrosion inhibitors. These
compounds form durable, long-lasting films on metallic
surfaces, including but not limited to copper~and
copper alloy surfaces. Alkoxybenzotriazoles are
especially effective inhibitors of copper and copper
alloy corrosion, and can be used to protect multimetal
systems, especially those containing copper or a
copper alloy and one or more other metals.
The instant inventors have also found that
alkoxybenzotriazoles de-activate soluble copper ions,
which prevents the galvanic deposition of copper which
concomminantly occurs with the galvanic dissolution of
iron or aluminum in the presence of copper ions. This
minimizes aluminum and iron corrosion. These
compounds also indirectly limit the above galvanic
reaction by preventing the formation of soluble copper
ions due to the corrosion of copper and copper alloys.
Isomers of the above described 5-alkoxybenzo-
triazoles can also be used. The 5 and 6 isomers are
interchangeable by a simple prototropic shift of the 1
position hydrogen to the 3 position and are believed
to be functionally equivalent. The 4 and 7 isomers
are believed to function as well as or better than the
5 or 6 isomers, though they are more difficult and
expensive to manufacture. As used herein, the term
"alkoxybenzotriazoles" is intended to mean
5-alkoxybenzotriazoles and 4, 6 and 7 position isomers
thereof.
- C-14a6
Substituted alkoxybenzotriazoles and their isomers
can also be used. Thus, one or more of the CH2
groups in R of structure I when R is an unsubstituted
alkoxy group of 3-la carbons may ~e replaced by an 0
or NH. Specific examples include, but are not limited
to, the oxapentyl group (CH3CH20CH2CH2-), the
azapentyl group (CH3CH2NHCH2CH2-) and the
6-oxa-3-aza-octyl group (CH3CH20CH~CH2
NHCH2CH2-). As used herein, ther term
''substituted alkoxybenzotriazoles°' includes compounds
wherein R of structure I is any oxa and/or aza alkoxy
group. Substituted alkoxybenzotriazoles also include
compounds wherein R of structure T contains halogeno
methylene group, CHyXz, where y is 1 or 0 and z is
1 or 2) x is a group VII element, and x can be either
the same or a different halogen. Also, one or more of
the methylene groups may be substituted with oxygen or
sulfur resulting in for example an alcohol,
thioalcohol) keto or thioketo group. The carbon of
the ether linkage should be unsubstituted. Also one
or more pairs of methylene groups may be unsaturated,
resulting in an ethylene or acetylene unit.
Substituted alkoxybenzotriazoles also include
compounds wherein R of structure I contains an
aromatic group. Particular examples include, but are
not limited to, compounds wherein R is:
H ~ CH2) n
X
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wherein n is 1-9 and X is H, halageno, vitro, carboxy,
cyano, amido, substituted amino or Cl-C~ alkoxy;
and compounds where R is:
X , -(CH2)ri
, wherein n is 1-8, and x is as above.
An effective amount of an instant alkoxy-
benzotriazole should be used. As used herein, the
term ~~effective amount~~ refers to that amount of an
alkoxybenzotriazole which effectively inhibits
corrosion in a given aqueous system.
More particularly, the alkoxybenzotriazoles,
substituted alkoxybenzotriazoles and isomers thereof
of the present invention effectively inhibit the
corrosion of metallic surfaces, especially copper and
copper alloy surfaces, when added to an aqueous system
in contact with such surfaces at a concentration of at
least about 0.1 ppm, preferably about 0.5 to 100 ppm
and most preferably about 1-10 ppm. Maximum
concentrations are determined by the economic
considerations of the particular application, while
minimum concentrations are determined by operating
conditions such as pH, dissolved solids and
temperature.
- s - c-148s
The instant alkoxybenzotriazoles may be prepared
by any known method. For example, the instant alkoxy
benzotriazoles may be prepared by contacting a
4-alkoxy-1, 2-diaminobenzene with an aqueous solution
of sodium nitrite in the presence of an acid, e.g.,
sulfuric acid, and then separating the resultant oily
product from the aqueous solution. The 4-alkoxy-1,
2-diaminobenzene may be obtained from any number of
sources.
The instant compounds can be used as water
treatment additives for industrial cooling water
systems, gas scrubber systems or any water system
which is in contact with a metallic surface,
particularly surfaces containing copper and/or copper
alloys. They can be fed alone or as part of a
treatment package which includes, but is not limited
to) biocides, scale inhibitors, dispersants, defoamers
and other corrosion inhibitors. The instant
alkoxybenzotriazoles and substituted alkoxybenzo-
triazoles can be fed intermittantly or continuously.
Treatment of cooling water which contacts copper
or copper alloy surfaces, such as admiralty brass or
90/10 copper-nickel, requires the use of specific
copper inhibitors. These inhibitors:
1. minimize the corrosion of the copper or copper
alloy surfaces, including general corrosion,
dealloying and galvanic corrosion; and
- 7 - C-1486
2. minimize problems of galvanic "plating out!' of
soluble copper ions onto iron or aluminum. Thus,
soluble copper ions can enhance the corrosion of
iron andlor aluminum components in contact with
aqueous systems. This occurs through the
reduction of copper ions by iron or aluminum
metal, which is concommitantly oxidized, resulting
in the "plating-out" of copper metal onto the iron
surface. This chemical reaction not only destroys
the iron or aluminum protective film but creates
local galvanic cells which can cause pitting
corrosion of iron or aluminum.
Conventional copper inhibitors such as
tolyltriazole, benzotriazole, and
2-mercaptobenzothiazole are commonly used as copper
inhibitors in aqueous systems. They are generally fed
continuously because of the limited durability of
their protective films.
Continuous feed of an inhibitor generally makes it
uneconomical to apply these conventional inhibitors to
once-through systems or systems with high blowdown
rates. Additionally, conventional inhibitors provide
only limited protection against chlorine induced
corrosion.
While 5-alkoxybenzotriazoles are known which do
not require continuous feeding in order to inhibit
copper corrosion (See U.S. Patent 4,744,950), these
alkoxybenzotriazoles are relatively hard to produce
and therefore only find limited application for
economic reasons. Another disadvantage is their
relatively
- 8 - C-1486
slow rate of passivation of copper alloys in some
waters, their failure to pass:ivate copper in high
dissolved-solids waters, and their limited chemical
resistance to chlorine.
An object of the instant :invention is to provide
inhibitors which produce durable protective films, and
which overcome the above-described limitations.
These objects are achieved through the use of
alkoxybenzotriazoles, substituted alkoxybenzo-
triazoles and isomers of these compunds to minimize
corrosion and/or to provide protective, durable
hydrophobic films on metallic surfaces) especially
copper and copper alloy surfaces.
The instant alkoxybenzotriazoles allow
intermittent feed to cooling water systems. Depending
on water aggressiveness, the time between feedings may
range from several days to months. This results in an
average lower inhibitor requirement and provides
advantages relative to waste treatment and
environmental impact.
The preferred alkoxybenzotriazoles are within the
range of propyloxybenzotriazole to nonyl-
oxybenzotriazole. The most preferred compounds are
butyloxybenzotriazole, pentoxybenzotriazole and
hexyloxybenzotriazole.
- C-1486
EXAMPLES
The following examples demonstrate the
effectiveness of the instant compounds as copper and -
copper alloy corrosion inhibitors. They are not,
however, intended to limit the scope of the invention
in any way.
EXAMPLES 1-4 - FILM PERSISTENCY
In these examples, copper specimens were
pretreated by immersing them in aerated water at pH
IO 7.5 and 50oC. This water contained a specified
concentration of inhibitor, which formed a protective
film on the specimens)
After 24 hours, the specimens were transferred to
inhibitor-free water of a highly corrosive nature to
determine film persistency. Corrosion rates were
measured using linear polarization to determine
passivation.
The characteristics of the pretreatment water and
the aggressive water are given in Tables I and II)
respectively.
Corrosion results are given in Table III. The
results are reported as "Corrosion Rates After
Passivation" for the passivation step and as
"Corrosion Rates In Inhibitor-Free Agressive Water".
~~.~~.~c~~
C-1486
The maximum duration or any test was 15 days at
which time the experiment was terminated.
- zl - c-1486
TABLE I .
Composition of Pretreatment Water
pH = 7.5
Ion Concentration (mg/L)
Ca gg
M9 24
C1 70
S04 325
- 12 - C-148b
TABLE II
Composition of Aggressive Water
pH = 7.5
Ion Concentration (mg/L)
Ca 750 as Ca~2
Mg 130 as Mg+2
C1 2400
S04 3200
CA 02016147 1999-04-08
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- 14 - C-1486
Table. III shows that 5-pentyloxybenzotriazole
provided 9996 inhibition, even after 15 days exposure
to aggressive water, while the ethyloxybenzotriazole
film lasted less than 2 days) and tolyltriazole, a
conventional inhibitor, failed within one day.
EXAMPLES 5-8 - Chlorine Resistence
These examples, which were run in a dynamic test
unit, demonstrate the resistance of protective films
formed by alkoxybenzotriazoles to corrosiveness caused
by chlorine on heat-transfer brass tubes and on
immersed copper coupons.
The dynamic test unit for these examples consisted
of an 8L reservoir, a heater-circulator and a coil
heater to provide the desired heat flux. The coil
heater was designed to fit securely around the 3/8" OD
tubes used in the tests. Flow through the tube was
monitored by an in-line rotameter having a flow
capacity of 400 ml/min. The power input to the heater
was controlled by a rheostat, which made it possible
to vary temperature differences across the tubes. The
tube inlet and outlet temperatures were monitored by
thermocouples attached to a digital readout having an
accuracy of 0.1°F. The system was entirely enclosed
to minimize evaporation. The linear velocity through .
the heated tubes was 2.2 fps, which gave a NRe of
approximately 9350. Heat fluxes of 8,000-10,000
Btu/hr-ft2 were chosen as being representative of
industrial practices.
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- 15 ° C-1486
The corrosion rates of the heated tubes were
determined by the weight loss method described in
"Standard Practice for Preparing, Cleaning and
Evaluating Corrosion Test Specimens"; ASTM designation
G1-81. The corrosion rates of immersed specimens were
determined by linear-polarization using a Petrolite
Model M1010 Corrosion Data Acquisition System. This
method measures the corrosion rate at a particular
time, and is thus useful for following the immediate
effects of chlorine concentration on corrosion rates.
The following procedure was followed relative to
the test specimens:
1. Cleaned specimens were placed in the test
unit described above, and a specified amount
of inhibitor was added.
The specimens were then allowed to passivate
for 24 hours at which time they were placed
in inhibitor-free water.
2. Chlorine was added to give an initial
concentration of 1 mg/L free chlorine. The
corrosion rate of each specimen was monitored
for one hour. The chlorine concentration
normally decreased from 1 mg/L to about 0.7
mg/L during this time.
3. After one hour, each specimen was placed in
fresh inhibitor-free, chlorine-free water.
The decrease in corrosion rate, i.e. the
recovery corrosion rate, was then measured
for each specimen.
- 16 - C-1486
4, .Steps 2 and 3 were repeated in 24 hour cycles
for a total of four cycles, with one
additional cycle following a weekend period.
5. After a seven day period, the weight loss of
the heated tube was .determined.
The composition of the water used in these tests
is given in Table IV.
to The results are shown in Table V. The corrosion
rates of the heat-transfer Admiralty brass tubes show
the cumulative corrosion which occurred during the
7-day test period. As can be seen, pentyloxy-
benzotriazole gave over 90 percent corrosion
protection and the hexyloxybenzotriazole gave over 85
percent corrosion protection.
CA 02016147 1999-04-08
- 17 -
TABLE I4'
WATER COMPOSITION USED IN THE CHLORINE
CHEMICAL RESISTANCE EXAMPLES 6-9
Ion Concentration (mg/L)
Ca 88
Mg 24
C1
S04 325
pH 7.5
- 18 - G-1486
By contrast, tolyltriazole, which is a widely used
inhibitor, gave only 36 percent corrosion protection.
Also, the immersed copper probes treated with either
pentyloxybenzotriazole or hexyloxyl benzotriazole were
not significantly affected by exposure to chlorine
over the 1 hour contact time while the copper probes
treated with tolyltriazole or the blank experienced
dramatically higher corrosion rates in the presence of
chlorine.
CA 02016147 1999-04-08
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- 20 - c-l4ss
EXAMPLES 9-10 - Dynamic Pilot Cooling Tower Tests
These examples illustrate the outstanding chlorine
resistance and film persistency of
pentyloxybenzotriazole in a dynamic system which
simulate the operational variations commonly found in
industrial cooling towers. Operational factors
simulated include blow-down, heat transfer surfaces,
dynamic flow, evaporative-cooling, cycles of
concentration, and customary chlorination practices.
The pilot cooling tower system used contained two
single tube heat exchangers. Cooling water flowed in
series through the shell side (annular space) of the
heat exchangers and hot water was circulated through
the tubes in series, counterflow. In addition to the
main recirculation circuit through the cooling tower,
the system also contained a recycle loop from the
outlet of the No. 2 Heat Exchanger to the inlet of the
No. 1 Heat Exchanger for the purpose of maintaining
cooling water linear velocity in the heat exchangers.
The heat exchanger shells were fabricated of
Plexiglass to permit observation of the heat exchanger
surfaces during the test run. For these tests, a
90/10 copper/nickel tube was placed in the No. 2 Heat
z5 Exchanger.
Instrumentation for monitoring and control of test
variables included a pH and conductivity indicator/
controller, PATR corrosion rate indicators, a
temperature :indicator/controller, and rotometers for
air and watex flows.
i~~ _ )
- 21 - C-1486
PAIR_probes for continuous monitoring of 90/10
copper/nickel corrosion gates were installed after the
outlet of the No. 2 Heat Exchanger. A corrosion test
coupon of 90/10 copper/nickel was installed in the
recycle loop. The PAIR cells and the corrosion test
loop were fabricated of Plexiglass to permit
observation of the Corrater electrodes and the
corrosion coupons.
The cleaning procedures employed to prepare tubes,
corrosion coupons and PAIR electrodes for use in these
tests are described in ASTM standard Gl-81.
In preparation for these tests, stainless steel
tubes were installed in the heat exchangers and the
system was filled with makeup water. The system
required three days for the recirculating water to
concentrate to the target cycles of concentration.
The target water composition was the same for Examples
5-8. After the target cycles were reached) the
stainless steel tubes were removed and the test
specimens installed (tubes, coupons, and PAIR
electrodes). At this time, blowdown commenced and the
desired copper inhibitor was added. The inhibitor was
allowed to deplete by gradually replacing the cooling
water. Thus, after three (3) days, less than
one-eighth of the original inhibitor concentration was
present, and after five (5) days, practically no
inhibitor remained.
e~~r ~~l~.~c~~
- 22 - C-148b
Table VI shows the corrosion rate just prior to
the addition of chlorine to the system and the maximum
corrosion rate recorded while chlorine was present.
Chlorine was added so that between 0.2 mg/L to O.S
mg/L free residual of chlorine was present. The
chlorine concentration was then allowed to dissipate
through blow-down, evaporation, and reaction.
As can be seen in Table VI, pentoxybenzotriazole
effectively passivated the 90/10 copper/nickel
to specimens and dramtically reduced the aggressiveness
of chlorine even, surprisingly, when all of the
inhibitor had depleted.
EXAMPLES 11 - 12 - Film Persistency
The experimental procedure of Examples 9-ZO was
used. However, no chlorine was added to the system.
The purpose of this test was to determine the
persistency of the protective film formed by the
inhibitor after the inhibitor had been exhausted from
the system due to replacement of the original water.
The results are shown in Table VII, which shows
that pentoxybenzotriazole provided durable protection
throughout the two (2) week, test. This is especially
surprising in view of the practically complete
depletion of original inhibitor concentration by the
fifth day. The test was terminated after two (2)
weeks only due to practical limitations of time and
expense.
CA 02016147 1999-04-08
- 23 -
TABLE VI
PILOT COOLING TOWER TEST WITH CHLORINATION:
EFFECTIVENESS OF PENT'YLOXYBENZOTRIAZOLE
Corrosion Rates (mpy) on Cu/Ni 90/10
Example 9 Example 10
S mg/L Pentyloxy BT
Control (No Inhibitor) Initial Charge
Rate Max. Rate Rate Max. Rate
Prior to In Presence Prior to In Presence
Chlorination of C12_ Chlorination of C12-
1 2.0 No C12 Added 0.05 No C12 Added
2 2.0 No C12 Added 0.05 No C12 Added
3* 1.5 7.8 0.05 0.05
4* 0.9 5.8 0.05 0.05
S* 0.7 2.8 0.05 0.08
6* 0.5 2.3 0.07 0.30
7* 0.7 1.7 0.10 0.70
Tube appearance uniformly darkened Bright) very slight tarnish
after Day 7
* Chlorine vas added to the system on the indicated days.
CA 02016147 1999-04-08
- 24 -
TABLE VII
Inhibition Persistency of Pentylo:Kybenzotriazole
In the Pilot Cooling 'Tower
Example 11 Example 12
Blank Pentyloxybenzotriazole
Day (no inhibitor) 5 mg/L Initial Charge
0 I3
1 5 0.1
2 3,5 0.05
3 2.5 0.03
4 y_5 0.03
2.5 0.03
2.0 0.03
7 2.0 0.03
g 2.0 0.03
2.0 0.03
2.0 0.03
11 1.8 0.03
12 2.0 0.05
13 1.5 0.05
14 1.4 0.05
