CA1114595A - Corrosion inhibitor treatment for boiler water - Google Patents

Abstract

ABSTRACT OF DISCLOSURE

An improvement in a coordinated phosphate/pH corrosion control treatment for boiler water is disclosed, which improvement comprises supplementing the treatment with an alpha amine-neutral-ized organic acid. An alpha amine is one which has a distribution ratio of 0.01 or greater and a pKb of 8.0 or less.

Description

TREATMENT FOR BOILER WATER

Technical F~eld ~, ~
Boilers using demineralized makeup water are known to be prone to caustic attack. High pressure boilers are particularly suscept~ble to this type of metal corros~on.

The inside surfaces of the boiler are typically protected with magnet~te. Hydrox~de ion, being the predominant anion in high purity boiler water, can dissolve the magnet~te when highly concen-trated. Even though high purity water is being used, caustic cannonetheless become highly concentrated, primarily due to the pre-sence of iron oxide deposits on rad~ant wall tubes. Wh~le the bulk water may contain only 5-10 ppm of caustic, it is quite possible to have localized caustic concentrations of up to 100,000 ppm. The iron oxide deposits are extremely porous so that water ~s drawn thereinto. Due to heat being applied from beneath, steam is gen-erated and passes out of the porous deposit, while fresh water is again drawn thereinto. The result ~s the noted high concentrations of caustic whlch must be dealt with ~f the bo~ler is to properly be protected.

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A widely used method for controlling caustic corrosion in boilers using demineralized (high purity) makeup water, particularly in high pressure boilers, is the coordinated phosphate/pH control treatment. This method of treatment is detailed in an article by George Gibson entitled "The Basics of Phosphate-pH Boiler Water Treatment", Power Engineering, February, 1978, p. 66.
In any event, portions are excerpted below for purposes of explanation.
The coordinated phosphate/pH corrosion control treatment is based on two principles: first, that sodium phosphates are a pH buffer; and second, that disodium hydrogen phosphate converts potentially corrosive caustic into re-latively harmless trisodium phosphate according to the following equation:

' '''' (1) disodium caustic trisodium water hydrogen phosphate phosphate Accordingly, general corrosion is prevented through the control of boiler water pH, and adherent deposits with concomitant caustic corrosion are prevented by maintaining a disodium hydrogen phosphate residual in the boiler water to react with caustic according to equation (1).

IN THE DRAWINGS
Figure 1 is a control chsrt showing the desirable pH/phosphate parameter control used to insure maintenance of the proper level of disodium hydrogen phosphate in the boiler;
Figure 2 is a graphical representation fihowing the relationship between solution pH~ phosphate concentration, and Na:P04 molar ratios; and Figure 3 is a schematic illustration of a research boiler, utilized in performing the tests herein reported.

B

~, . . ~ .. , . . ,. ... .. . .... ., .. .. . .. ~ ... .....
., .. ~ . . . j . .,.. ;.... ... ; .. .. . ..

', - ' ' .. . . ' . - ' ', ': : ' ` . ' :" ' ' ' .: ' .. , , ~ ' ' " ~ ' .:,, '.. ' ' .. ' : ' r -The program is implemented with a control chart such as in Figure 1.
Disodium hydrogen phosphate is present if the coordinate of pH and phosphate lies within the control boundary.

B 2a -., .. . ,: . . ..... .... . . .... . ..

~ ~ 14S r~

Many sodium phosphates are used in boiler water treatment.
Of these, orthophosphates are preferred. Complex phosphates, in the form of polymer chains, break down into orthophosphates at boiler water temperatures by a process known as reversion. Th~ ortho- ~ -phosphates are monosodium dihydrogen phosphate (MSP), disodium hydrogen phosphate (DSP) and trisodium phosphate ~TSP).

Orthophosphates can be ~dentified by name, formula or sodium-to-phosphate rat~o which can be expressed with the notation "Na:P04", read as sodium-to-phosphate rat10.

Monosodium dihydrogen phosphate has one mole ~f sodium per mole of phosphate. Therefore, the sodium-to-phosphate r~tio is one-to-one (Na:P04 = 1:1 ) . Disodium hydrogen phosphate, with two moles of sodium per mole of phosphate, has a Na:P04 = 2:1, and tr~sodium phosphate has a Na:P04 = 3:1.

Sod~um-to-phosphate ratios are useful to describe mixtures of phosphates in solut~on. For example, solut~ons of DSP and TSP
have a Na:P04 between 2:1 and 3:1. The Na:P04 ~s falrly propor-tional to the m1x rat~o. For Instance, a solut~on of half DSP and half TSP has a rat~o of about 2.5~ t ~s actually 2.~6:1 because DSP and TSP have d~fferent molecular we~ghts).

F1gure 2 shows the relat10n between solution pH and phos-phate concentrat10n for various sodium-to-phosphate molar ratlos.
Examlnation of the f~gure reveals pH ~ncreases w~th ~ncreasing Na:P04 (at equal phosphate concentrations). Accordingly, solution pH and phosphate concentration ~dentify phosphate form, it being kept in m~nd that disodium hydrogen phospha~e is the species which 1$~

neutralizes caustic according to equation (1).

A trisodium phosphate solution exists if the phosphate/pH
coordinate falls on the Na:P04 = 3:1 line; disodium hydrogen phos-phate solution if the coordinate falls on the 2:1 line; and a mix-ture of DSP and TSP if the coordinate falls between the 2:1 and 3:1lines. As the coordinate approaches the 3:1 line, there is more and more TSP and less and less DSP in the solution.

The solution is a mixture of TSP and caustic if the coord-inate falls above the 3:1 line. In this "free caustic" region there is no DSP to tie up the caustic.

It is seen that the phosphate/pH coordinate must be below the Na:P04 = 3:1 line to ensure that there is DSP in solution to tie up the caustic. The further the phosphate/pH coordinate is kept below the line the greater the caustic-absorbing capacity of the water and the less chance of drifting into the region above the 3:1 line.

F~gure 2 is based on pure sodium phosphate solution. The pure solution theory can be used with impure boiler water because the concentration of other species is low and their solubility high.
Complex chemistry is avoided by using pH as a varlable. It is de-sirable to keep the Na:P04 between 2.8:1 and 2.2:1. The phosphate-pH control chart, Figure 1, is a refinement of Figure 2 with a control boundary in the appropriate range to prevent caustic cor-rosion. The control chart is the heart of phosphate-pH control.

There has been some confusion in applying sodium-to-. . .

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phosphate ratios. The Na:P04 used in phosphate-pH control is determined only from boiler water pH and phosphate concentration, not by measuring sodium and phosphate concentrations of the boiler water.

This information can be used to make a phosphate-pH
control chart by first setting phosphate limits. Maximum allowable phosphate decreases with increasing boiler pressure because of carryover and phosphate "hideout." The latter term, incidentally, refers to the phenomenon of dim~nishing bo~ler water phosphate levels with increased firing rate (everything else held constant) and the reappearance of boiler wa~er phosphate level when the firing rate is reduced. Hideout phosphate is believed to be caused by precipitating the phosphates under high heat flux condit~ons.

Individual plants have set their own phosphate limits, based on what works for them and on results at similar installa-tions. The limits chosen for the control chart shown in Figure 1 are consistent with industry practice and have proved to be satis-factory in practical applicatlons.

Note that the residual phosphate limits contained ~n the control chart (Figure 1) are the maximum levels recommended for sat-isfactory bo~ler operation. Whatever the allowable residual phos-phate concentration, it is prudent to operate with as little phos-phate as practicable.

There should be an upper Na:P04 limit of 2.85:1 to pre-vent caust~c corrosion and a lower Na:P04 l~mit of 2.13:1 to pre-vent acid attack. But, it would be prudent to include a safety factor into these numbers,which safety factor depends on in-dividual boiler characteristics and system water tightness.
Lower pressure boilers have less trouble with caustic corrosion than higher pressure boilers and generally can be run with Na:P04 close to the 2.85:1 line. Of course, if caustic corrosion is occurring, a lower maximum limit should be set for the boilers involved. High pressure boilers tend to be more susceptible to caustic corrosion, and a maximum Na:P04 line of 2.6:1 usually is chosen. This has proved to be an effective limit.

It should be understood from the foregoing that the coordinated phosphate/pH control treatment consists primarily of two basic steps as follows:

(1) maintenance of an appropriate level of residual ortho-phosphate in the bo~ler water; and

(2) maintenance of the proper Na:P04 ratio in the water.

The residual orthophosphate level wlll depend on such known factors as the nature and severity of the problem and boiler pressure. Since it is considered best to operate with as little phosphate as possible, amounts as low as about 1 ppm could be used, with about 2 ppm being the preferred minimum. While amounts as high as about 50 ppm residual orthophosphate could be used, about 30 ppm is the preferred maximum.

While the coordinated phosphate/pH corrosion control trea~ment is w~dely used, it is not without its drawbacks and limi-tations. Often, it is desirable to supplement the treatment with addîtional corrosion inhibitor; however, this is not always practicable. It has been customary for many years to use the sodium -salt of a polymeric dispersant, such as sodium polymethacrylate, as the supplement. When the sodium salt form is used, the Na:P04 in the boiler water is often significantly altered and the solids level of the boiler water rises. If the Na:P04 is allowed to rise over the 3:1 line of Figure 2, caustic attack again becomes a problem, and, particularly in high pressure boiler systems, increased solids levels can lead to undesirable foaming in the water. Thus, the use of supplemental treatment has been severely limited. In fact, when the Na:P04 is near the control limit, the supplemental treatment has been completely omitted.

Description of the Invention The present invention relates to an improvement fn the coordinated phosphate/pH corrosion control treatment for boiler water. According to the present invention, a supplemental corrosion inhibitor is provided which neither significantly alters the sodium burden of the boiler nor significantly increases the sol~ds level therein.

The present invention is drawn to the use, in con~unction with a coordinated phosphate/pH corrosion control treatment, of an aqueous solution of an organic acid dispersant which has been neu-tralized with any one of a class of specific amines, hereinafter referred to as "alpha" amines. More specifically, according to the present invention, the organic acid dispersant is neutralized with , ~ . - , .. . . . . . -a suitable amine (or NH3) which is volatile under the conditions of the boiler water to be treated and has a basicity constant of 8.0 or less. A detailed description of how to determine suitable amines is presented below.

The invention offers certain advantages as follows:

(1) the sodium burden in the boiler is limited, thus limiting caustic gouging and other forms of boiler metal corrosion;

(2) advantage (1) is accomplished with volatile materials that do not concentrate in the boiler and, thereby, do not contri-bute to either corrosion or deposition processes; and (3~ the supplemental material will aid in corrosion con-trol in both the boiler and in the steam distr~bution system (due to volatile neutralizing agents).

The utility of the present invention is considered to be greatest for those high pressure (above about 900-1200 psig) boiler systems exper~encing difficulty in maintaining a ~a:P04 less than 2.8:1. The use of a low sodium supplement under these conditions does not contribute to the sodium burden of the boiler, thereby simplifying the maintenance of a coordinated phosphate/pH control treatment, i.e., supplemental feed to the boiler feedwater can be made without disrupting the sodium to phosphate ratio.

According to the present invention~ a supplemental cor-rosion inhibitor is provided in which a volatile organic base has replaced caustic as a neutralizing agent. This resulting alkaline " . ~ r ~

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product ~s considered to be preferable to an acidic product. Fur-thermore, the volatile organic base finds utility as a condensate corrosion inhibitor, neutralizing carbonic acid at steam conden-sation sites.

The Organic Acid Any reference hereinafter to the polymers used in accord-ance with the present invention is intended to include the polymers individually as well as any combination of homopolymer, copolymer and mixtures thereof. The term "polymeric acid" is intended to in-clude any polymer containing acid functional group(s), as well asacid precursor compounds (e.g., anhydrides).

As already noted, the compounds which are considered to be useful ~n practicing the present inventlon are any of the well known organic acid dispersants, such as polymeric sulfonic acids, poly-meric phosphonic acids, polymeric carboxylic acids and poly phos-phonic acids.

Illustrative examples of polymeric carboxylic acids would be as follows: ;~

polyacrylic acid : -polymethacrylic acid polymaleic anhydride acrylic acid/hydroxypropylacrylate copolymer sulfonated styrene/male k anhydride copolymer methylvinyl ether/maleic anhydride copolymer acrylic acid/methacrylic acid copolymer . .

Illustrative examples of polymeric sulfonic acids would be as follows:

sulfonated polystyrene polyvinylsulfuric acid sulfonated styrene/maleic anhydride copolymer polyvinylsulfonic acid poly[~-acrylamido-2-methylpropanesulfonic acid]
Illustrative examples of poly phosphonic acids would be:

ethylenediamine tetra(methylene phosphonic acid) l-hydroxyethylidene-1,1-diphosphonic acid nitrilotri(methylene phosphonic acid) These compounds are believed to be useful in boilers of up to about 1500 psig.
.
The polymeric phosphonic acids are believed to be suitable for use at pressures up to well above 1500 ps~g; however, few are presently commercially ava~lable. Illustrative examples of these compounds are polyvinyl phosphonic acid and its substituted analogs.

As is well known in the art, the amount of supplemental corrosion inh~bitor would depend on such factors as the nature and severity of the problem to be treated and could vary over a wide range. The amount of organic acid could, accordingly, be as low as about 1 part polymer per million parts of boiler water (ppm). The preferred minimum is considered to be about 5 ppm. Based on economic .. j .

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considerations, the upper limit for the organic acid dosage is con-sidered to be about 150 ppm; while 50 ppm represents the preferred maximum.

With respect to the polymeric organic acids, it is we11 known that molecular weight is not critical. In any event, a mole-cular welght of from about 1000 to about 200,000 is believed to be operable.

The Neutralizing Agent Suitable amines for use as neutralizing agents in accord-ance with the present invention have already been described as alpha amines. The important properties of these amines are, first, that they are volatile under the operating conditions of the boiler and, second, that they have sufffcient basicity to neutralize the organic acid dispersant. Defining the first property In terms of distri-bution ratio and the second in terms of basicity constant, pKb, a1pha amines are those having a distr1bution ratio of 0.01 or greater under the operating conditions of the boiler and a PKb of 8.0 or less.

The distribution ratio, DR, is defined as the quantity of voltile amine found in the steam phase over the quantity found in the bulk flu~d and is represented by:

DR = ppm amine in steam ppm am ne n wn (I) The values for this ratio, of course, are easily obtained by draw-, ", 1 ," ,., ,, , " , ~ " "

~$~a~ ~

ing a condensed steam sample and a blowdown sample from the boiler and analyzing for respective amine contents.

The basicity constant is a well known comparison for bas-icities of amines in terms of the~r respectiYe abilities to accepthydronium ion from water. Using the reaction:

RNH2+H20 ~ RNH3+ + OH-, the basicity constant, pKb, is defined by:

pKb = - log [RNH~+NR~

Each amlne has its own pKb, and, the lower the value, the stronger the base. As is well known to the artisan, tabulated values for pKb's are readily obtainable from numerous chemical reference }5 books. For example, a table of such values can be found in the "Handbook of Chemistry and Physics", The Chemical Rubber Co., 45th Edition (1964-1965), p. D-76.

Following ls an exemplary list of alpha amines believed to be sultable for use in accordance with the present invention:

morpholine am~nomethylpropanol (AMP) dimethylamlnomethylpropanol (DMAMP) cyclohexylamine dimethylpropanolamine (DMPA) ~ . .
''' . .. , , ., . , .. ,, , . , ., .. , . ,. . . . . .. . , .; " "., , ,, .. ,, .... . ~ . , - -. . .

diethylaminoethanol N-hexylamine methoxypropylamine ~MPA) ben ylamine ammonia monolsopropanolamine 1,6 hexanediamlne 1,3 dlamlnopropane trlbutylamine trlethylam~ne n-amylamine n-methylmorpholine .~^k ;; N,N-dimethyl-1,3 propanediamine.
.
EXAMPLES

; 15 Determinlng Distrlbut~on Rat~os Example 1 A f~rst ser~es of tests were conducted to determlne the DR's of varlous amlnes uslng a research bo~ler slm~lar to the one schemat1cally 111ustrated ln F~gure 3. Two f~berglass feed tanks were filled w~th a total of 600 l~ters of de1Onized water wh~ch was deaerated by n~trogen sparg~ng for two hours. At the end of the deaeration per1Od one tank was charged w~th 50 ppm amine, while the other was charged w~th various chem~cals to prov~de boiler test water as follows:

"P" alkalinity = 200 ppm residual silica = 20 ppm, added as sodium metasilicate residual phosphate = 20 ppm, added as sodium dihydrogen phosphate res~dual sulfite = 20 ppm, added as sodium sulfite calcium hardness = 10 ppm, added as calcium chloride magnesium hardness = 5 ppm, added as magnesium sulfate cycles of concentrat~on = 15 ppm 2 level after N2 sparg~ng = 0.25-0.5 ppm The boiler was energized and allowed to come to equilibrium over-night at 100 psig. On the second through fifth days two sets of samples (each set consisted of a steam sample and a blowdGwn sample) were taken per pressure step at a minimum of one hour and a maximum of one and a half hours between sets (at a given pressure). The samples, refrigerated during the accumulation stage in glass containers, were then analyzed using standard gas chromatographic procedures under the following conditions:

G.C. unlt: Perk~n Elmer~Model 990 Detector(s): Thermal conduct~v~ty or flame ~onization Column Size: 6' x 2 mm ~d Pyrex Packing: 14% Carbowaxi~20 M/2~ KOH on 80/100 mesh Supelcoport~
Oven Temperature: 110C
Carr~er Gas: N2 at 20 ml/min at 40 psig Sample S~ze: 1Jll Inject~on Temperature: 105C.

The resulting distribution ratios, calculated according to equation (I), are reported below in Table 1. Also reported are the dissociat~on constants, pKb, for the materials tested.

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DR YALUES AT VARIOUS PRESSURES

Compound Pressure (psig) DR _ pKh Morpholine 0 0.4 5.7 100 1.0 200 1.6 .
300 1.4 400 1.2 500 1.2 600 1.3 700 1.2 -900 1.3 --; 1100 1.3 1300 1.3 1450 1.2 :~ aminomethylpropanol 0 0.1 4.18 100 0.5 200 1.0 300 0.8 400 0.8 500 O.g 600 0.8 700 0.8 900 0.9 1100 0.9 1300 o.g 1450 0.9 - , . . , .. - , ,, : ~ , , , - ,- , ~

TABLE 1 (Continued) Compound __ _ Pressure (Psi~g) DR pKh cyclohexylamine 0 2 3.4 100 9.3 400 8.0 500 6.7 600 6.6 5 700 6.1 : 900 : 5.3 1100 4.7 : ~
:~ 1300 4.4 ~:
~ 1450 4.1 : :
~: 15 ammon~a 0 10.0 4.75 lO0 7.1 : : 200 7.1 : 300 6.3 .
400 5.0 :
500 5.3 600 4.2 700 4.2 900 3.9 "
1100 3.6 1300 3.4 1450 1.6 ~ .
~: :

, , Exam~le 2 An investigation was undertaken to determine the possible effects, if any, of boiler chemicals or water quality on DR. The *
testing method used was slmilar to that reported in Example 1. In 5 the present test, however, water "P" alkalinity was increased by a factor of two; and in the comparative "without chemical" tests, the hardness, phosphates and silicates were re ved comple~ely. Some results of these tests are reported below in Table 2 in terms of comparative average DR values with chemicals and without chemicals.
10 All DR's reported are averages of at least two to nine separate data points.

.
EFFECT OF BOILER CHEMICALS OR WATER
QUALITY ON DISTRIBUTION RATIO
. _ . .
Average DR Average DR
Compound Pressure With Chemicals Without Chemicals morphol~ne 400 1.3 1.0 700 1.2 1.2 1450 1.2 1.4 cyclohexylamine 400 7.9 8.3 700 5.8 7.1 1450 3.8 5.0 aminomethylpropanol 400 0.9 0.7 700 0.8 0.8 1450 0.9 1.1 .

,, .. .. ~ - , , , - , . :
- . ~ :

The results of Table 2 are seen to indicate that over the pressure range of interest, with respect to practicing the present invention, no sign~ficant effect on DR was noted due to either the absence of boiler chemicals or an increase in alkalinity.

Example 3 Also investigated was the effect, if any, of increased neutralizing amine concentration on the various DR's. This was accomplished by simply doubling the amine concentration from 50 ppm to 100 ppm and comparing the results. A testing method similar to that reported in Example 1 was used. The amines tested were morph-oline and cyclohexylamine. The results of these tests are reported below in Table 3 in terms of comparative average DR at 50 ppm and lOO ppm.
.
.

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1:~L145~5 -19- -:*~

EFFECT OF AMINE CONCENTRATION ON DR
.
Average DR Average DR
Compound Pressure (psig) at 50 Pe~__ at 100 ppm-_ -5morpholine400 1.2 1.2 500 1.2 1.2 600 1.3 1.4 700 1.2 1.3 900 1.3 1.3 1100 1.3 1.3 1300 1.3 1.2 - -1450 1.3 1.2 .
cyclohexylam1ne 400 8.2 7.3 500 6.6 7.0 600 6.4 7.2 700 5.9 6.6 900 5.2 5.6 1100 4.7 4.7 1300 4.6 4.0 1450 4.1 4.3 5~5 Based on the results from Table 3, there is seen to be no significant effect of amine concentration on the DR. Of course, the individual values for quantity of amine present in the steam and blowdown samples increased significantly, but the magnitude of the DR still remained about the same.

MAKING AMINE-NEUTRALIZED ORGANIC ACID

Example 4 This example is seen to illustrate the preparation of an aqueous solution of alpha amine-neutralized organic acid to be used -~
in accordance with the present invention. The starting material was polymethacrylic acid (PMA) having the formula:

CH2--f --O = C - OH I n 15 which polymer had a molecular weight average of 6,000 to 12,000 as determined by gel permeation chromatography, using as reference a commercial sodium polymethacrylate of advertised molecular weight of 8,000-10,000.

A stock solution is made by the following procedure:

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:
5~ - -*

-21- ~ -1. weigh out 250 9 of tap water (pH = 8.2) 2. add 65 9 of PMA (30.8X actives)

3. mix well

4. record pH and neutralize to des~red pH wl~h amine At this point, the 4~ PMA solution is reweighed and the amount of amine used is recorded. The solution is brought to a final we~ght of 500 9 and a final pH reading is taken. The tap water added ~ncreased the pH by about .2 un~ts.
.~ ;
The weights of the amine used to reach various pH's for numerous solutions actual1y made were as follows:

Solution 1: 4~ PMA stock solution, 500 9 total weight, pH about 2.5 Solution 2: Solution 1 neutralized to pH = 7 with 17.5 9 of morpholine; final pH = 7.2 :
Solution 3: Solution 1 neutral1zed to pH 3 7 with 18.0 9 of AMP; f~nal pH ~ 7.1 Solutlon 4: Solution 1 neutral~zed to pH z 7 with 17.2 9 of cyclohexylamine; final pH = 7.0 Solution 5: Solut1On 1 neutralized to pH = 9.5 with ~11.3 9 of morphol~ne; final pH = 9.7 (this solution less than 4X PMA) Solution 6: Solution 1 neutralized ~o pH = 10 with 25.5 9 of AMP; f~nal pH = 10.0 L r Solution 7: Solut~on 1 neutralized to pH = 7 with 15.5 9 of morpholine, then to pH = 10.8 with 59.7 9 of AMP;
final pH = 10.9 Solution 8: Solution 1 neutralized to pH = 7 with 18~2 9 of morpholine, then to pH = 10.9 with 53.7 9 of cyclohexylamine; final pH ~

Solution 9: Solution 1 neutralized to pH = 7 with 18~4 9 of : .
morpholine, then to pH = 9.8 wlth 46~8 9 of AMP;
final pH = 10~1 -~
Solution 10: Solution 1 neutralized to pH = 7 with 19.0 9 of morpholine to pH = 9 w~th 11.1 9 of AMP, then to pH = 11 with 37.9 9 of cyclohexylamine; final pH = 11.0 .
Solution 11: Solut~on 1 neutralized to pH = 7 with 24~1 9 of morphol~ne, to pH = 9 w~th 15.3 9 of AMP, then to pH = 11 with 8.9 9 of sod~um hydrox~de anhydrous;
flnal pH ~ 5 Solution 12: Solution 1 neutral1zed to pH = 8 wlth 21~2 9 of morpholine; final pH = 8.0 Solut~on 13: Solut~on 1 neutral~zed to pH = 7.5 with 22 9 of AMP; final pH = 8.0 Solution 14: Solution 1 neutralized 1:o pH = 8 with 20~9 9 o1 cyclohexylamine; final pH = 8.1 .~, .. , ., . . ,. ,, . ,, ~ , . .. , ., . ., .. ,. , .~ .. , . .... ., . ., .~ ., .. ......... , . . .,. :

:

45~

Example 5 This example is seen to further illustrate the preparation of an aqueous solution of alpha amine-neutralized organic acid to be B used in accordance with the present invention. The starting S material was Acrysol~A - 41, commercially available from Rohm and Haas. It is a copolymer of methacrylic and acrylic acid, having a molecular weight average of about 10,000-12,000 and a mole ratio of methacrylic ac~d to acrylic acid of about 9:1. :

A stock solution is made according to the same procedural 10 steps set forth in the preceding example, however, (71.5 9 of) ~ -Acrysol A-41 (28% actives) was used instead of the PMA.

The weights of the amine used to reach various pH's for numerous solutions actually made were as follows:

Solution 1: 4% copolymer stock solution, S00 9 total weight, pH about 2.65 Solution 2: Solution 1 neutral k ed to pH = 7 with 19.3 g of morpholine; final pH = 7.2 Solution 3: Solution 1 neutralized to pH = 7 with 20.2 9 of AMP; flnal pH = 7.2 Solution 4: Solution 1 neutralized ko pH = 7 with 23 9 of cyclohexylamine; final pH = 7.6 * ~ ~ P~

., .. , .-....... . , . .. , . ",, - - . . - ~ - .. ,, -.. .. . .. . ,, ~

~ 3 Solution 5: Solution 1 neutralized to pH = 9.2 with 129.6 g of morpholinej final pH = 9.4 (not stable at this pH) Solution 6: Solution 1 neutralized to pH = 10 with 43.6 9 of AMP; final pH = 10.2 Solu~ion 7: Solution 1 neutralized to pH = 10 with 35.5 9 of cyclohexylamine; final pH = 10.1 Solution 8: Solutlon 1 neutralized to pH = 7 with 21.7 9 of morpholine, then to pH = 9 with 13.6 9 of AMP, then to pH = 10.8 with 114 g of cyclohexylamine, final pH = 11.1 .

EFFICACY OF TREATMENT IN BOILER

Example 6 A series of tests were conducted to determine the efficacy of alpha amlne-neutral~zed organic acids as boiler water treatments.
The tests were conducted in the research boiler descrlbed in Example 1 and schematically illustrated in Figure 3. As already noted, certain boilers are highly susceptible to caustlc corrosion as a result of lron oxide deposits formed on interior surfaces. Thus, any treatment which will prevent the formation of iron oxide deposits is cons~dered to be a highly desirable supplement for a coordinated phosphate/pH control program.

Since the research boiler was electrically powered using immersion heating probes, deposits formed directly on probe sur-faces. On completion of the tests, the deposits formed on the heat-3-~

ing probes were analyzed to determ~ne the quantity of iron oxide present and the total amount of deposit.

Dur~ng the tests performed, boiler condit~ons ~ncluded a coordinated phosphate/pH control program, 15 cycles of concen-tration, operat~ng pressure of 1450 ps~g, 3.4 ppm Fe~2 contamin-ated feedwater, and bo~ler probes of differing heat flux values.
One probe had a heat flux value of 240,000 BTU/ft2/hr; while the other had a heat flux of 185,000 BTU/ft2/hr. Test durations were 2 days.

The feedwater had the following composition:

7.5 ppm NaHC03 0.04 ppm Silica 8.2 ppm Tr~-sodium phosphate 0.2 ppm antifoam (polyalkylene glycol) 6 ppm NaN03 (for conductivity) 16.7 ppm FeS04 (3.4 ppm Fe) The tests ~ncluded comparat1ve studles of alpha amlne-neutral~zed polymer~c ac~d d~spersants wlth commonly used polymeric ac1d d~spersants as sodium salts. The mater~als tested were as follows:

ComparatlYe Product X: Commercial sodium polymethacrylate, reported molecular we~ght = 6,000-8,000 Comparat~ve Product Y: Commercial sodium polymethacrylate, reported molecular weight = 8,000-10,000 i . : , ' ': ' ~ : - .. ,:: .. ','; " ': '::, ~ , . . .. . -

5~

Product A: Polymer~c ac~d starting material of Example 5, neutralized with AMP, pH = 10.0, stored at 120F
for three months before testing Product B: Polymeric acid starting material of Example 5, neutral~zed w~th morpholine, pH = 8.0, stored at 120F for three months before testing Product C: Polymeric acid starting material of Example 4, neutralized with morpholine and AMP, pH = 10.3, stored at 120F for three months before testing Product D: Polymeric acid starting material of Example 4, neutralized with morpholine, pH = 8.1, stored at : 120F for three months before testing The results of these tests are reported below in Table 4 in terms of amount of iron deposition (in g/ft2) on the probes.

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Based on the results reported in Table 4, not only are treatments according to the present invention considered to be efficacious for boiler water, but they are seen to compare favorably with treatments containing the sodium salts of the organic acids.
Accordingly, the coordinated phosphate/pH corrosion control treat-ment can be supplemented with an organic acid treatment in a form which will neither adversely affect the critical Na:P04 nor in-crease the solids level in the boiler water.

It should be kept in mind that the stronger the basicity of the alpha amine neutralizing agent, the less amine required to neutralize the polymeric acid dispersant. To avoid problems related to fungi growth, higher pH formulations, e.g., above 8.5, are preferred.

A preferred supplemental treatment composition for use with the coordinated phosphate/pH corrosion control treatment is Solut~on 1 of Example 5 neutralized to pH = 8.5 with 27.3 grams of morpholine.

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Claims (18)

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

1. In a coordinated phosphate/pH caustic corrosion control treatment for boiler water according to which residual orthophosphate is maintained in the water in an amount of from about 1 to about 50 ppm and a Na:PO4 ratio of from about 2:1 to less than 3:1 is maintained in the water, the improvement comprising supplementing the treatment with an effective amount for the purpose of preventing the formation of iron oxide deposits on boiler surfaces of an aqueous solution of alpha amine-neutralized organic acid, said amine being characterized by having a distribution ratio of 0.01 or greater.

2. A method according to claim 1, wherein the organic acid is at least one member selected from the group consisting of carboxylic acid polymer, sulfonic acid polymer, phosphonic acid polymer and poly phosphonic acid.

3. A method according to claim 2, wherein the organic acid is carboxylic acid polymer.

4. A method according to claim 3, wherein the organic acid is selected from the group consisting of acrylic acid polymer and methacrylic acid polymer.

5. A method according to claim 1, wherein the Na:PO4 is maintained at from about 2.13:1 to about 2.85:1.

6. A method according to claim 5, wherein the residual orthophosphate level is maintained at from about 2 to about 33 ppm.

7. A method according to claim 6, wherein the organic acid is at least one member selected from the group consisting of carboxylic acid polymer, sulfonic acid polymer, phosphonic acid polymer and poly phosphonic acid.

8. A method according to claim 7, wherein the organic acid is carboxylic acid polymer.

9. A method according to claim 8, wherein the organic acid is selected from the group consisting of acrylic acid polymer and methacrylic acid polymer.

10. A method according to claim 1, wherein the organic acid is added in an amount of from about 1 to about 150 ppm.

11. A method according to claim 10, wherein the organic acid is added in an amount of from about 5 to about 50 ppm.

12. A method according to claim 11, wherein the Na:PO4 is maintained at from about 2.2:1 to about 2.6:1.

13. A method according to claim 12, wherein the organic acid is at least one member selected from the group consisting of carboxylic acid polymer, sulfonic acid polymer, phosphonic acid polymer, and poly phosphonic acid.

14. A method according to claim 11, wherein the organic acid is carboxylic acid polymer.

15. A method according to claim 11, wherein the organic acid is selected from the group consisting of acrylic acid polymer and methacrylic acid polymer.

16. A method according to claim 15, wherein the organic acid is copolymer of acrylic acid and methacrylic acid.

17. A method according to claim 15, wherein the organic acid is polymethacrylic acid.

18. A method according to claim 16 or 17, wherein the "alpha" amine is at least one member selected from the group con-sisting of morpholine, cyclohexylamine and aminomethylpropanol.