Copper and copper alloy corrosion inhibitors

The use of alkoxybenzotriazoles to inhibit the corrosion of metallic surfaces in contact with an aqueous system. Systems and compositions containing alkoxybenzotriazole are also claimed.

BACKGROUND OF THE INVENTION 
Benzotriazole, mercaptobenzothiazole and tolyltriazole are well known 
copper corrosion inhibitors. For example, see U.S. Pat. No. 4,675,158 and 
the references cited therein. Also, see U.S. Pat. No. 4,744,950, which 
discloses the use of alkoxybenzotriazoles as corrosion inhibitors and U.S. 
Pat. No. 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; Dec. 14, 1984; Chem. Abst. 102:153153b.), the 
use of alkoxybenzotriazoles is not known in the water treatment art. 
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: 
##STR1## 
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. 
Compositions comprising water, particularly cooling water, and an 
alkoxybenzotriazole are also claimed. 
The inventors have discovered that alkoxybenzotrizoles 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-alkoxybenzotriazoles 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. 
Substituted alkoxybenzotriazoles and their isomers can also be used. Thus, 
one or more of the CH.sub.2 groups in R of structure I when R is an 
unsubstituted alkoxy group of 3-18 carbons may be replaced by an O or NH. 
Specific examples include, but are not limited to, the oxapentyl group 
(CH.sub.3 CH.sub.2 OCH.sub.2 CH.sub.2 --), the azapentyl group (CH.sub.3 
CH.sub.2 NHCH.sub.2 CH.sub.2 --) and the 6-oxa-3-aza-octyl group (CH.sub.3 
CH.sub.2 OCH.sub.2 CH.sub.2 NHCH.sub.2 CH.sub.2 --). As used herein, the 
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 I 
contains halogenomethylene group, CH.sub.y X.sub.z, 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: 
##STR2## 
wherein n is 1-9 and X is H, halageno, nitro, carboxy, cyano, amido, 
substituted amino or C.sub.1 -C.sub.3 alkoxy; and compounds where R is: 
##STR3## 
wherein n is 1-8, and x is as above. 
An effective amount of an instant alkoxybenzotriazole 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. 
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 alkoxybenzotriazoles 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 
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 and/or 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. Pat. No. 
4,744,950), these alkoxybenzotriazoles are relatively hard to produce and 
therefore only find limited application for economic reasons. Another 
disadvantage is their relatively slow rate of passivation of copper alloys 
in some waters, their failure to passivate 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 alkoxybenzotriazoles and isomers of these compounds 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 nonyloxybenzotriazole. The most preferred 
compounds are butyloxybenzotriazole, pentoxybenzotriazole and 
hexyloxybenzotriazole.

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 7.5.degree. and 50.degree. C. 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". 
The maximum duration of any test was 15 days at which time the experiment 
was terminated. 
TABLE I 
______________________________________ 
Composition of Pretreatment Water 
pH = 7.5 
Concentration 
Ion (mg/L) 
______________________________________ 
Ca 88 
Mg 24 
Cl 70 
SO.sub.4 
325 
______________________________________ 
TABLE II 
______________________________________ 
Composition of Aggressive Water 
pH = 7.5 
Ion Concentration (mg/L) 
______________________________________ 
Ca 750 as Ca.sup.+2 
Mg 130 as Mg.sup.+2 
Cl 2400 
SO.sub.4 3200 
______________________________________ 
TABLE III 
__________________________________________________________________________ 
Passivation and Persistency Tests 
mpy mpy 
Corrosion Rate 
Corrosion Rate 
No. of days 
Concentration 
after in inhibitor-free 
in inhibitor-free 
Inhibitor (mg/L) 24 hrs. pretreatment 
Aggressive Water 
Aggressive Water 
__________________________________________________________________________ 
None 0 1.1 2.5-3.0 15 
5-ethyloxybenzotriazole 
5 0.01 3.2 2 
Tolyltriazole 
5 0.01 5-6 1 
5-pentyloxybenzotriazole 
3 0.005 0.03 15 
__________________________________________________________________________ 
Table III shows that 5-pentyloxybenzotriazole provided 99% 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.degree. F. The system was entirely enclosed to minimize 
evaporation. The linear velocity through the heated tubes was 2.2 fps, 
which gave a N.sub.Re of approximately 9350. Heat fluxes of 8,000-10,000 
Btu/hr-ft.sup.2 were chosen as being representative of industrial 
practices. 
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. 
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. 
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, pentyloxybenzotriazole gave over 90 
percent corrosion protection and the hexyloxybenzotriazole gave over 85 
percent corrosion protection. 
TABLE IV 
______________________________________ 
WATER COMPOSITION USED IN THE CHLORINE 
CHEMICAL RESISTANCE EXAMPLES 6-9 
Concentration 
Ion (mg/L) 
______________________________________ 
Ca 88 
Mg 24 
Cl 70 
SO.sub.4 
325 
pH 7.5 
______________________________________ 
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. 
TABLE V 
__________________________________________________________________________ 
EFFECT OF CHLORINATION ON CORROSION RATES OF HEAT-TRANSFER 
ADMIRALTY BRASS TUBES AND IMMERSED COPPER PROBES 
Corrosion Rates (mpy) 
Corrosion Protection 
Copper-Probe Corrosion 
Recovery 
of Admiralty Rates during Cl.sub.2 Contact 
Corrosion Rate 
Ex. Conc. 
Brass Tubes 
% for the Final Chlorination 
After the Final 
No. 
Inhibitor 
mg/L 
(wt. loss) Protection* 
5 min. 
15 min. 
30 min. 
60 min. 
Chlorination 
__________________________________________________________________________ 
5 None 0 3.45 0 -- 5.5 5.0 3.0 1.5 
6 Hexyloxy 
10 0.50 86 0.005 
0.005 
0.01 
0.02 
0.005 
Benzotriazole 
7 Pentyloxy 
5 0.30 91 0.02 
0.02 
0.02 
0.03 
0.005 
Benzotriazole 
8 Tolyltriazole 
5 2.2 36 0.9 2.0 2.0 2.0 1.0 
__________________________________________________________________________ 
##STR4## 
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 Exchanger. 
Instrumentation for monitoring and control of test variables included a pH 
and conductivity indicator/controller, PAIR corrosion rate indicators, a 
temperature indicator/controller, and rotometers for air and water flows. 
PAIR probes for continuous monitoring of 90/10 copper/nickel corrosion 
rates 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 
G1-81. 
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 days, less than 
one-eighth of the original inhibitor concentration was present, and after 
five days, practically no inhibitor remained. 
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 0.5 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 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 9-10 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 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 weeks only due to practical limitations of time and expense. 
TABLE VI 
______________________________________ 
PILOT COOLING TOWER TEST WITH CHLORINATION: 
EFFECTIVENESS OF PENTYLOXYBENZOTRIAZOLE 
Corrosion Rates (mpy) on Cu/Ni 90/10 
Example 10 
Example 9 5 mg/L Pentyloxy BT 
Control (No Inhibitor) 
Initial Charge 
Rate Max. Rate Rate Max. Rate 
Prior to In Presence 
Prior to In Presence 
Day Chlorination 
of Cl.sub.2 
Chlorination 
of Cl.sub.2 
______________________________________ 
1 2.0 No Cl.sub.2 
0.05 No Cl.sub.2 
Added Added 
2 2.0 No Cl.sub.2 
0.05 No Cl.sub.2 
Added Added 
3* 1.5 7.8 0.05 0.05 
4* 0.9 5.8 0.05 0.05 
5* 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 
Bright, very slight tarnish 
darkened after Day 7 
______________________________________ 
*Chlorine was added to the system on the indicated days. 
TABLE VII 
______________________________________ 
Inhibition Persistency of Pentyloxybenzotriazole 
In the Pilot Cooling Tower 
Example 11 Example 12 
Blank Pentyloxybenzotriazole 
Day (no inhibitor) 
5 mg/L Initial Charge 
______________________________________ 
0 13 7 
1 5 0.1 
2 3.5 0.05 
3 2.5 0.03 
4 2.5 0.03 
5 2.5 0.03 
6 2.0 0.03 
7 2.0 0.03 
8 2.0 0.03 
9 2.0 0.03 
10 2.0 0.03 
11 1.8 0.03 
12 2.0 0.05 
13 1.5 0.05 
14 1.4 0.05 
______________________________________