CA1205348A - Method of inhibiting scale - Google Patents
Method of inhibiting scaleInfo
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- CA1205348A CA1205348A CA000432384A CA432384A CA1205348A CA 1205348 A CA1205348 A CA 1205348A CA 000432384 A CA000432384 A CA 000432384A CA 432384 A CA432384 A CA 432384A CA 1205348 A CA1205348 A CA 1205348A
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- maleic anhydride
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Abstract
ABSTRACT OF THE INVENTION
The present invention provides a method or process by which the deposit of scale is inhibited or prevented, particularly alkaline earth metal scales such as magnesium hydroxide, which is a particular problem in desalina-tion units where brine temperatures exceed 90°C. In the method, a copolymer of maleic anhydride and certain olefins is introduced into the aqueous medium of the system, preferably in amounts of from about 0.01 ppm to about 100 ppm based on aqueous medium. The preferred copolymer is based on maleic anhydride and di-iso butylene, which has been found extremely effective in multi-stage flash desalination units.
The present invention provides a method or process by which the deposit of scale is inhibited or prevented, particularly alkaline earth metal scales such as magnesium hydroxide, which is a particular problem in desalina-tion units where brine temperatures exceed 90°C. In the method, a copolymer of maleic anhydride and certain olefins is introduced into the aqueous medium of the system, preferably in amounts of from about 0.01 ppm to about 100 ppm based on aqueous medium. The preferred copolymer is based on maleic anhydride and di-iso butylene, which has been found extremely effective in multi-stage flash desalination units.
Description
53~
The present invention is in the technical field of processes for controlling the formation of scale deposits in desalination processes, particular-ly those desalination processes known as multi-stage flash processes.
There is a shortage of fresh water in the world which is becoming increasingly more serious, particularly in arid and semi-arid regions. Sea water, as a source of fresh water, is being given greater consideration. Sea water, however, contains significant salt levels which must be eliminated or at least reduced for not only drinking purposes, but also for most industrial uses.
Of the desalting processes currently available, the multi-stage flash process ~"MSF") is generally considered the most reliable and economic method of fresh water production from sea water. It accounts for the majority of the total production capacity now existent. The principle of MSF desalination is the separation of vaporized fresh water from the brine accomplished through the use of many stage effects.
Without any treatmentl however, sea water MSF units rapidly accumulate scale deposits in the brine heater section. These deposits reduce heat transfer efficiency and lead to loss of fresh water production. Acid cleaning ~iill restore the unit to its original efficiency, but only at the loss of production time and cost of such cleaning. To avoid such scale deposits in the past, acid has been added on a continuous basis. Such continuous use of acid, however, requires an extremely precise control of pH. Too little acid does not prevent scale, and too much induces corrosion. Because of such corrosion problems, and problems inherent in handling acids, alternative methods were deemed desirable.
In the past, polyphosphates were also used but the needs of present MSF units make them undesirable. The backbone structures of polyphosphate additives are readily hydrolysed at high temperatures, such as the excess of 90C. brine temperatures reached in present day high production MSF units. Upon ,., 34~
hydrolysis in MSF units, thc polyphosphatcs combine with calciunl and magnesium ions to form deposits on the hcat exchangc surfaces.
United States Patent ~o. 3,715,307 discloscs the addition of vinyl acetate/maleic anhydride copolymer to alleviate hard film deposits of scale, and that the resultant scale precipitate was more easily removed than that formed with use of polyacrylamide, polyelectrolyte, sodium polyphosphate, or l-hydroxy ethylidene-l,l-diphosphonic acid additives. United States Patent No. 3,810,834 discloses the use of hydrolysed polymaleic anhydride having a molecular weight of 300 to 5,000 for controlling scale formation when salt containing waters are subjected to heating, giving an example of a flash evaporator process, and further comparing its activity with that of sodium tripolyphosphate, polyacrylic acid (molecular weight of 20,000), and polymethacrylate. (A hydroly~ed poly-maleic anhydride, under the trademark of Belgard EV by Ciba Geigy Corporation, Ardsley, N.Y., has been marketed and used as a scale controlling additive in MSF
units). United States Patent No. 4,001,134 discloses that copolymers of maleic anhydride and allylacetate have scale inhibiting properties for calcium carbonate and magnesium hydroxide scales, and compares the activity to that of a maleic anhydride/ethylene oxide copolymer (molecular weight of 1,500 - 2,000) and a maleic/methyl vinyl ether copolymer. United States Patent No. 4,048,066 dis-closes copolymers of styrene sulfonic acid with acrylic or methacrylic acid or mixtures of the homopolymers as scale control additives for steam generating boilers, and that they are more active than polystyrene sulfonate, polymaleic acid, or polyacrylates alone. United States Patent No. 4,288,327 discloses that copolymers of sulfonated styrene and maleic anhydride control scale formation and sludge deposits in boilers and desalination systems be-tter than polymeth-acrylate, sulfonated polystyrenes, etlIylene/maleic anhydride polymers, maleic anhydride telomers, or styrene maleic anhydride polymers.
~ 2 -~' s~
In the field of scale control additives for MFS units, an additive more effective and less costly than the presently used polymaleic anhydride acid is desirable. (Polymaleic anhydride hydrolysis readily in water to the acid form, and readily forms the salt form. Although such hydrolysis may possibly not be complete or may entail some decarboxylation, the terms hydrolysed poly-maleic anhydride or polymaleic acid, or in the salt form polymaleate, are under-stood in the art, and used herein, as equivalent species).
This desirability of more effective and less costly scale control additives is demanded by the extremely high production capacity of commercial MSF units. Fresh water production can exceed 9,000,000 gallons per day in a commercial MSF unit. Thus the potential for scale fouling, and the level of lost production due to unit shut down for cleaning is tremendous. Further, even if acceptable additive usage is on the order of a number of parts per million based on sea water intake, the additive usage over a day, a week, or a month's time is clearly very significant. Thus the additive's cost is a significant factor, and the cost of many of the above noted additives may well preclude their use in commercial MSF units.
Further, MSF units operate in temperature environments typically in excess of 90C., and it has been found that scale deposits from sea water formed in temperatures of up to 90C. are predominantly calcium carbonate, while at the higher temperatures of MSF units, the scale deposit is mainly magnesium hydroxide. This is believed due to the temperature dependent route of bicarbon-ate ion decomposition, and the inverse solubility characteristics of calcium carbonate and magnesium hydroxide. Operating conditions of MSF units are such that the nonalkaline scale, such as calcium sulfate, are not generally formed.
The mechanism of scale control by polymer additives is not precisely known, but it is believed that they tend to stabilize dispersions of precipitated scale-~S;348 forming compositions. Thus, given the dependency of the scale species on the temperature environment, the extrapolation of scale control effectiveness of an additive -from one temperature environment to another is not generally possible.
It is an object of the present invention to provide a scale control-ling process using a scale control composition that is effective in controlling scale under conditions present in commercial MSF units, where temperature environments may range from 90C. to 110C., and even up to 120C.
The present invention is a method for inhibiting or preventing the deposit of scale, particularly alkaline earth metal scale such as magnesium hydroxide, on structural surfaces of aqueous medium systems in which such scale would normally be deposited, particularly heat exchange surfaces of commercial multi-stage flash ~"MSF") units for producing fresh water from sea water, comprising introducing into the aqueous medium of such systems an effective amount for the purpose of a water soluble copolymer or salt thereof, wherein the polymer chain of such copolymer is comprised of maleic anhydride (maleic acid) units and comonomer units having the following formula:
Rl- C - R2 wherein Rl and R2 are selected independently from the group consisting of H, methyl, and ethyl, and R3 is selected from the group consisting of trimethyl substituted methyl, trimethyl substituted ethyl, tetramethyl substituted ethyl, and pentamethyl substituted ethyl. Preferably, both Rl and R2 are methyl and R3 is trimethyl substituted methyl, tetramethyl substituted ethyl or pentamethyl substituted ethyl.
The present invention is also a process for inhibiting scale fouling in the brine heater section of desalination units, particularly those operating at temperatures in excess of 90C, comprising introducing into the brine feed ~s~
an cffective amount of aforesaid copolymer.
In preferred embodiment, such copolymer or water soluble salt thereof is introduced into the aqueous medium in an amount of from about 0.01 ppm to about 100 ppm ~parts per million based on aqueous medium), depending upon the particular additive, concentration of scale forming species in the aqueous medium, and the temperature environment in the area of scale deposit. In pre-ferred embodimentl wherein the scale normally formed is substantially alkaline earth metal scale, e.g. magnesium hydroxide, such copolymer or water soluble salt thereof is introduced into the aqueous medium in an amount of from about 0.1 ppm to about 50 ppm, and more preferably~ in an amount of from about 1 ppm to about 20 ppm.
In further preferred embodiment, the molar ratio of maleic anhydride to other comonomer in the polymer of the present invention is from about 0.5 :
1.0 to about 2.0 : 1Ø ~s to molecular weight, the polymer additive of the present invention should be within suitable molecular weight range so as to be water soluble at least at use level and under use conditions. Preferred mole-cular weight range for the polyrner additive of the present invention is from about 500 to about 10,000 by gel permeation chromatography ("GPC"), and more preferably from about 1,000 to about 5,000 by GPC.
The polymer additives useful in the present invention include those derived from maleic anhydride and the comonomer di-iso butylene (also known as
The present invention is in the technical field of processes for controlling the formation of scale deposits in desalination processes, particular-ly those desalination processes known as multi-stage flash processes.
There is a shortage of fresh water in the world which is becoming increasingly more serious, particularly in arid and semi-arid regions. Sea water, as a source of fresh water, is being given greater consideration. Sea water, however, contains significant salt levels which must be eliminated or at least reduced for not only drinking purposes, but also for most industrial uses.
Of the desalting processes currently available, the multi-stage flash process ~"MSF") is generally considered the most reliable and economic method of fresh water production from sea water. It accounts for the majority of the total production capacity now existent. The principle of MSF desalination is the separation of vaporized fresh water from the brine accomplished through the use of many stage effects.
Without any treatmentl however, sea water MSF units rapidly accumulate scale deposits in the brine heater section. These deposits reduce heat transfer efficiency and lead to loss of fresh water production. Acid cleaning ~iill restore the unit to its original efficiency, but only at the loss of production time and cost of such cleaning. To avoid such scale deposits in the past, acid has been added on a continuous basis. Such continuous use of acid, however, requires an extremely precise control of pH. Too little acid does not prevent scale, and too much induces corrosion. Because of such corrosion problems, and problems inherent in handling acids, alternative methods were deemed desirable.
In the past, polyphosphates were also used but the needs of present MSF units make them undesirable. The backbone structures of polyphosphate additives are readily hydrolysed at high temperatures, such as the excess of 90C. brine temperatures reached in present day high production MSF units. Upon ,., 34~
hydrolysis in MSF units, thc polyphosphatcs combine with calciunl and magnesium ions to form deposits on the hcat exchangc surfaces.
United States Patent ~o. 3,715,307 discloscs the addition of vinyl acetate/maleic anhydride copolymer to alleviate hard film deposits of scale, and that the resultant scale precipitate was more easily removed than that formed with use of polyacrylamide, polyelectrolyte, sodium polyphosphate, or l-hydroxy ethylidene-l,l-diphosphonic acid additives. United States Patent No. 3,810,834 discloses the use of hydrolysed polymaleic anhydride having a molecular weight of 300 to 5,000 for controlling scale formation when salt containing waters are subjected to heating, giving an example of a flash evaporator process, and further comparing its activity with that of sodium tripolyphosphate, polyacrylic acid (molecular weight of 20,000), and polymethacrylate. (A hydroly~ed poly-maleic anhydride, under the trademark of Belgard EV by Ciba Geigy Corporation, Ardsley, N.Y., has been marketed and used as a scale controlling additive in MSF
units). United States Patent No. 4,001,134 discloses that copolymers of maleic anhydride and allylacetate have scale inhibiting properties for calcium carbonate and magnesium hydroxide scales, and compares the activity to that of a maleic anhydride/ethylene oxide copolymer (molecular weight of 1,500 - 2,000) and a maleic/methyl vinyl ether copolymer. United States Patent No. 4,048,066 dis-closes copolymers of styrene sulfonic acid with acrylic or methacrylic acid or mixtures of the homopolymers as scale control additives for steam generating boilers, and that they are more active than polystyrene sulfonate, polymaleic acid, or polyacrylates alone. United States Patent No. 4,288,327 discloses that copolymers of sulfonated styrene and maleic anhydride control scale formation and sludge deposits in boilers and desalination systems be-tter than polymeth-acrylate, sulfonated polystyrenes, etlIylene/maleic anhydride polymers, maleic anhydride telomers, or styrene maleic anhydride polymers.
~ 2 -~' s~
In the field of scale control additives for MFS units, an additive more effective and less costly than the presently used polymaleic anhydride acid is desirable. (Polymaleic anhydride hydrolysis readily in water to the acid form, and readily forms the salt form. Although such hydrolysis may possibly not be complete or may entail some decarboxylation, the terms hydrolysed poly-maleic anhydride or polymaleic acid, or in the salt form polymaleate, are under-stood in the art, and used herein, as equivalent species).
This desirability of more effective and less costly scale control additives is demanded by the extremely high production capacity of commercial MSF units. Fresh water production can exceed 9,000,000 gallons per day in a commercial MSF unit. Thus the potential for scale fouling, and the level of lost production due to unit shut down for cleaning is tremendous. Further, even if acceptable additive usage is on the order of a number of parts per million based on sea water intake, the additive usage over a day, a week, or a month's time is clearly very significant. Thus the additive's cost is a significant factor, and the cost of many of the above noted additives may well preclude their use in commercial MSF units.
Further, MSF units operate in temperature environments typically in excess of 90C., and it has been found that scale deposits from sea water formed in temperatures of up to 90C. are predominantly calcium carbonate, while at the higher temperatures of MSF units, the scale deposit is mainly magnesium hydroxide. This is believed due to the temperature dependent route of bicarbon-ate ion decomposition, and the inverse solubility characteristics of calcium carbonate and magnesium hydroxide. Operating conditions of MSF units are such that the nonalkaline scale, such as calcium sulfate, are not generally formed.
The mechanism of scale control by polymer additives is not precisely known, but it is believed that they tend to stabilize dispersions of precipitated scale-~S;348 forming compositions. Thus, given the dependency of the scale species on the temperature environment, the extrapolation of scale control effectiveness of an additive -from one temperature environment to another is not generally possible.
It is an object of the present invention to provide a scale control-ling process using a scale control composition that is effective in controlling scale under conditions present in commercial MSF units, where temperature environments may range from 90C. to 110C., and even up to 120C.
The present invention is a method for inhibiting or preventing the deposit of scale, particularly alkaline earth metal scale such as magnesium hydroxide, on structural surfaces of aqueous medium systems in which such scale would normally be deposited, particularly heat exchange surfaces of commercial multi-stage flash ~"MSF") units for producing fresh water from sea water, comprising introducing into the aqueous medium of such systems an effective amount for the purpose of a water soluble copolymer or salt thereof, wherein the polymer chain of such copolymer is comprised of maleic anhydride (maleic acid) units and comonomer units having the following formula:
Rl- C - R2 wherein Rl and R2 are selected independently from the group consisting of H, methyl, and ethyl, and R3 is selected from the group consisting of trimethyl substituted methyl, trimethyl substituted ethyl, tetramethyl substituted ethyl, and pentamethyl substituted ethyl. Preferably, both Rl and R2 are methyl and R3 is trimethyl substituted methyl, tetramethyl substituted ethyl or pentamethyl substituted ethyl.
The present invention is also a process for inhibiting scale fouling in the brine heater section of desalination units, particularly those operating at temperatures in excess of 90C, comprising introducing into the brine feed ~s~
an cffective amount of aforesaid copolymer.
In preferred embodiment, such copolymer or water soluble salt thereof is introduced into the aqueous medium in an amount of from about 0.01 ppm to about 100 ppm ~parts per million based on aqueous medium), depending upon the particular additive, concentration of scale forming species in the aqueous medium, and the temperature environment in the area of scale deposit. In pre-ferred embodimentl wherein the scale normally formed is substantially alkaline earth metal scale, e.g. magnesium hydroxide, such copolymer or water soluble salt thereof is introduced into the aqueous medium in an amount of from about 0.1 ppm to about 50 ppm, and more preferably~ in an amount of from about 1 ppm to about 20 ppm.
In further preferred embodiment, the molar ratio of maleic anhydride to other comonomer in the polymer of the present invention is from about 0.5 :
1.0 to about 2.0 : 1Ø ~s to molecular weight, the polymer additive of the present invention should be within suitable molecular weight range so as to be water soluble at least at use level and under use conditions. Preferred mole-cular weight range for the polyrner additive of the present invention is from about 500 to about 10,000 by gel permeation chromatography ("GPC"), and more preferably from about 1,000 to about 5,000 by GPC.
The polymer additives useful in the present invention include those derived from maleic anhydride and the comonomer di-iso butylene (also known as
2,4,4-trimethyl pentene-2, which gives rise to comonomer units wherein in the above formula Rl and R2 are both methyl, and R3 is trimethyl substituted methyl).
Such copolymers are commercially available, for instance the copolymer available under the trademark TAMOL 731 from the Rohm ~1 Haas Company.
The polymer additives of the present invention can be produced by methods known in the art for copolymerizing maleic anhydride with other copoly-~L~2~S3~l~
mcrizable unsaturated monomers. For instance, United States Patent No.
2,938,061 describes the production of low molecular weight olefin/maleic anhy-dride polymers.
The sea water used in the examples below has the following analysis as to its most pertinent components, as shown below in Table I.
Table Sea Water Analysis Bicarbonate alkalinity (CaC03) 130 ppm Chloride (Cl) 17000 ppm Sulfate (S0~) 2300 ppm Alkalinity (CaC03) - total130 ppm Alkalinity (CaC03) - phenolphthalein **
Total dissolved solids a~ 180C. 31000 ppm Calcium (CaC03) - sol. and insol. 820 ppm Magnesium (CaC03) - sol. and insol. ~600 ppm Total organic carbon (C)11 ppm pH 6.9 pH units _ ** Not detected - below 2 ppm limit of detection For such sea water, which is used herein as representative of sea water generally unless specified otherwise, it has been found that the addition of sodium hydroxide in an amount that raises the sea water's pH to about 9.85 induces the precipitation of 354 ppm magnesium as CaC03. This magnesium is precipitated in the form of magnesium hydroxide. Thus in inducing magnesium hydroxide such treatment simulates r~SF units to the extent that in MSF units operated at temperature environments in excess of 90C. magnesium hydroxide scale is formed. The concentration of magnesium hydroxide precipitation in MSF
units is, however, generally less severe than 35~ ppm.
S3~15 COMPARATIVE EXAM~LE 1 A polymer additive of the present invention and several other polymers, including a commercial MFS scale preventive additive (the hydrolysed polymaleic anhydride indicated below) were tested to determine their relative abilities to stabili~e a caustic-induced magnesium hydroxide dispersion as follows. 200 ml.
of sea water was poured into a black 250 ml. beaker, a magnetic stirring bar was added, and the sea water was stirred at a setting of 3.8 on a Fisher Thermix.
The desired ppm of additive was added to the sea water using a lO,O00 ppm additive actives solution adjusted to pH of 7. Then 2 ml. of lN NaOH solution were added to bring the pH of the sea water to approximately 9.85, whereupon a visible white precipitate is formed ~magnesium hydroxide as noted above). A
fiber optic encased in a black cover was placed in the beaker and stirring continued for lO minutes, at which time the stirring was stopped and the change in turbidity was recorded on a strip chart to determine dispersion stability and the duration of dispersion stability.
The tracking of dispersion stability was discontinued if stable for up to 27 minutes at a given additive concentration. Where stability of some duration was noted or a given additive at 500 ppm concentration, the test was repeated for that additive at lower concentration levels.
The polymer of the present invention that was tested was a maleic anhydride/di-iso butylene copolymer of 1 to 1 molar ratio of comonomers having a molecular weight of 1,680 by GPC.
The results of this testing are shown below in Table II.
Also indicated in Table II, where available or applicable, are the molar ratios of comonomers in the given copolymer, followed by the molecular weight of the given polymer. In each instance, the given molecular weight is by GPC.
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o ,.
:~ o ~ o ~d ~
V~
o o a~
o R
~1 h C~
~> E '~-~
~ ~ ~ ~ ~ _1 h C~
a) co1~ ~ O$-1 ~ O P~ E :~
R `C)O ~ O~ 4 0 :~ ~
h ~ ~ o ~ ~, ~ O ~ o ~ o ~ ~
O ~ d ~ O~ O ~ O U) u~ h ~ h~ ~I h o ~,1 0 ~rl o o ~ nh `D
h ~~ h ~ h ~ ~ ~ a) ~ h r~
a) 6 ~ ~3 6 ,s: 6 ~ O ~ O ~ `
h - O* ~ o ~, ~ ~\ h o h a~ h ~
,s~ O h~H h ~d h ~rl F: h ~ a) h .rl h ~ ~d ~1 td e ~ O
~1~ ~ h ') 6 6)~ e e ~1 ~o o o ~~
a) oh ~ L~l o ~ O~ _1 ~ ~) h ~1 O
~d O~ ~ ~ oa~ o~
6 ~ 6 ~ I' 5~415 As shown in Table II above, any magnesium hydroxide dispersion stabilization activity of polymers such as methyl vinyl ether/maleic anhydride or vinyl sulfonate/acrylic acid copolymers is not detected by this test which demonstrates significant stabilization activity of maleic anhydride/di-iso butylene copolymer within the present invention not only at 500 ppm concentra-tion, but at the low 50 ppm concentration. Surprisingly, the maleic anhydride/
di-iso butylene copolymer's activity is shown to be greater than that of the commercial polymaleic anhydride and the sulfonated styrene/maleic anhydride copolymer. Further, this test detected li~tle activity for the rather highly carboxylated acrylic acid/ethyl acrylate copolymer, and the styrene/maleic anhydride copolymer.
The test of Comparative Example 1, although conducted at ambient room temperature, should correspond to an MSF unit environment in that magnesium hydroxide precipitation is induced, and further tests, shown in the examples below which are conducted in a~simulated MSF unit, demonstrate this correspon-dence .
In the simulated MSF unit, the sea water is processed as follows.
The sea water is filtered through a Millipore ~Trade mark) 0.~5 micron filter and then admixed with the desired concentration of additive solution which has been adjusted to pH 7. The treated sea water is then added to several feed water burrettes and therein sparged continuously with nitrogen. After the first hour of nitrogen sparging, the treated sea water is dosed with 2.5 ml. per liter of sea water of a ~ gram Na2S03 per liter solution. The desalination processing then is begun, wherein the sea water is pumped from the feed water burrettes through a rotameter and recirculation pump, through a filter, and then through a first and second preheater, where the temperature is raised to 105C. The preheated sea water then is pumped through a brine heater coil _ g _ which is sealed in an autoclave where the sea water in the coil is heated up an additiona] 10C. to a temperature of 115C., and then is pumped to an evaporator chamber having an upper distillate collector line and lower line to a blow down collector and pump, which recirculates undistilled sea water back to the line forward of the rotameter.
This laboratory scale simulated MSF unit has been determined to be comparable to commercial MSF units as to all important parameters as indicated by the comparison shown below in Table III.
Table Ill **
CommercialSimulated Parameter MSF unitMSF unit Brine heater inlet Temp. 110.6C 105C.
Brine heater oulet Temp. 120C 115C
Brine velocity 6.6 ft/sec. 6.0 ft/sec.
Tube length 22 ft 18 ft Sea water concentration 1.7 1.5 ** as given in Sea water and Sea water Distillation, Fichtner Handboo~
Vulkan-Verlag, Essen, 197~
The processing of sea water in the simulated MSF unit is run continu-ously in -the tests below until the test is terminated, i.e., when the brine heater coil inlet pressure rises to about 160 psig, indicating substantial scale deposits, at which point the unit is shut down for scale removal from the coil.
The performance of an additive in the simulated MSF unit is measured in terms of brine heater coil inlet pressure rise per unit time, being an indicator of scale deposit build-up per unit time. The lesser the pressure rise, the lesser the scale deposit in the brine heater coil.
;i39~8 COMPA~ATIVE EXAMPLE 2 The simulated MSF unit was run in separate tests using as additives a commercial scale preventive, a hydrolyzed polymaleic anhydrideJ and then a sulfonated styrene/maleic anhydride copolymer, and then a polymer within the present invention, a maleic anhydride/di-iso butylene copolymer. All of these additives are described above in Comparative Example 1. In these tests, the level of additive (ppm based on sea water) is lower than what would be normally chosen for commercial use so that the distinctions, if any, between activity, would be seen in a relatively short period of time. The change in brine heater coil inlet pressure at two day time intervals is shown below for each additive test and for a blank (no additive), in Table IV.
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V~
oo oo o~
~ In oo ~
V _1 C~
U~ o o ~1 ~U~ ~ O
,~
O
Ul O`D
h ~ Ul ~ 00 ~d ~C
.~ Il~ ~D N C~
h )~
H
a~
E~
h O~
Q>
h O '--¢ ~ ~ ~:S
t~ N
~r~ 1 As shown in Table IV above, after six days time the polymer within the present invention held pressure rise down to 3 psig, as compared to 118 psig for the blank, 49 psig for the commercial polymaleic anhydride, and 12 psig for the sulfonated styrene/maleic anhydride copolymer. After 8 days, the com-parison still remains, the polymaleic anhydride run increasing another 15 psig, and the sulfonated styrene/maleic anhydride increasing another 4 psig, while the maleic anhydride di-iso butylene copolymer test increased 5 psig.
After the above run for the blank, the brine heater coil scale deposit was analyzed and determined to be 99% magnesium hydroxide and 1% calcium car-bonate.
Not only is the maleic anhydride/di-iso butylene copolymer more effective as shown in Comparative Example 2, but its commercial price is less than that of hydrolyzed polymaleic anhydride or the sulfonated styrene/maleic anhydride copolymer. A significant cost savings is provided by the process of the present invention, particularly in large scale use. ~Cost comparison here based on cost per weight unit actives.) Another test as described above in ~omparative Example 2 was run using 4.25 ppm actives of the maleic anhydride/di-iso butylene copolymer. Be-ginning at an initial brine heater coil pressure of 47 psig, there was no rise in pressure, and in fact a drop in pressure of 3 psig over a 9 day period occurred, at which time the test was terminated.
For a comparable actives level (4.8 ppm) of the sulfonated styrene maleic anhydride copolymer, beginning with an initial brine heater coil pressure of 42 psig, after 9 days the pressure had increased to 62 psig, a 20 psig rise.
In a second run with the sulfonated styrene maleic anhydride copolymer, at actives level of 50 ppm~ it again failed to achieve a level pressure, rising ~IL~ 3~
from 52 psig to 65 psig in 5 days time.
In these tests, the additives are the same as those used in Com-parative F.xamples 1 and 2.
Maleic anhydride/di-iso butylene copolymers used in the process of the present invention constitute a preferred embodiment of the present inven-tion, particularly when such copolymers are within the preferred ranges of molar ratios of comonomers and molecular weights as given above. Even more preferrPd are such copolymers having molar ratio of comonomers of from about 1.0 to 1.5 to about 1.5 to 1.0, and preferably a molecular weight by GPC of from about 1,000 to about 2,000.
In the above description of the invention, all molecular weights are determined by Gel Pe~meation Chromatography, designated GPC, unless specified otherwise, and all pressures that were tracked on the simulated MSF unit are the brine heater coil inlet pressure unless speci~ied otherwise.
Such copolymers are commercially available, for instance the copolymer available under the trademark TAMOL 731 from the Rohm ~1 Haas Company.
The polymer additives of the present invention can be produced by methods known in the art for copolymerizing maleic anhydride with other copoly-~L~2~S3~l~
mcrizable unsaturated monomers. For instance, United States Patent No.
2,938,061 describes the production of low molecular weight olefin/maleic anhy-dride polymers.
The sea water used in the examples below has the following analysis as to its most pertinent components, as shown below in Table I.
Table Sea Water Analysis Bicarbonate alkalinity (CaC03) 130 ppm Chloride (Cl) 17000 ppm Sulfate (S0~) 2300 ppm Alkalinity (CaC03) - total130 ppm Alkalinity (CaC03) - phenolphthalein **
Total dissolved solids a~ 180C. 31000 ppm Calcium (CaC03) - sol. and insol. 820 ppm Magnesium (CaC03) - sol. and insol. ~600 ppm Total organic carbon (C)11 ppm pH 6.9 pH units _ ** Not detected - below 2 ppm limit of detection For such sea water, which is used herein as representative of sea water generally unless specified otherwise, it has been found that the addition of sodium hydroxide in an amount that raises the sea water's pH to about 9.85 induces the precipitation of 354 ppm magnesium as CaC03. This magnesium is precipitated in the form of magnesium hydroxide. Thus in inducing magnesium hydroxide such treatment simulates r~SF units to the extent that in MSF units operated at temperature environments in excess of 90C. magnesium hydroxide scale is formed. The concentration of magnesium hydroxide precipitation in MSF
units is, however, generally less severe than 35~ ppm.
S3~15 COMPARATIVE EXAM~LE 1 A polymer additive of the present invention and several other polymers, including a commercial MFS scale preventive additive (the hydrolysed polymaleic anhydride indicated below) were tested to determine their relative abilities to stabili~e a caustic-induced magnesium hydroxide dispersion as follows. 200 ml.
of sea water was poured into a black 250 ml. beaker, a magnetic stirring bar was added, and the sea water was stirred at a setting of 3.8 on a Fisher Thermix.
The desired ppm of additive was added to the sea water using a lO,O00 ppm additive actives solution adjusted to pH of 7. Then 2 ml. of lN NaOH solution were added to bring the pH of the sea water to approximately 9.85, whereupon a visible white precipitate is formed ~magnesium hydroxide as noted above). A
fiber optic encased in a black cover was placed in the beaker and stirring continued for lO minutes, at which time the stirring was stopped and the change in turbidity was recorded on a strip chart to determine dispersion stability and the duration of dispersion stability.
The tracking of dispersion stability was discontinued if stable for up to 27 minutes at a given additive concentration. Where stability of some duration was noted or a given additive at 500 ppm concentration, the test was repeated for that additive at lower concentration levels.
The polymer of the present invention that was tested was a maleic anhydride/di-iso butylene copolymer of 1 to 1 molar ratio of comonomers having a molecular weight of 1,680 by GPC.
The results of this testing are shown below in Table II.
Also indicated in Table II, where available or applicable, are the molar ratios of comonomers in the given copolymer, followed by the molecular weight of the given polymer. In each instance, the given molecular weight is by GPC.
~ f~p~~
~39~1!3 E3 a~
o ,~
o ,.
:~ o ~ o ~d ~
V~
o o a~
o R
~1 h C~
~> E '~-~
~ ~ ~ ~ ~ _1 h C~
a) co1~ ~ O$-1 ~ O P~ E :~
R `C)O ~ O~ 4 0 :~ ~
h ~ ~ o ~ ~, ~ O ~ o ~ o ~ ~
O ~ d ~ O~ O ~ O U) u~ h ~ h~ ~I h o ~,1 0 ~rl o o ~ nh `D
h ~~ h ~ h ~ ~ ~ a) ~ h r~
a) 6 ~ ~3 6 ,s: 6 ~ O ~ O ~ `
h - O* ~ o ~, ~ ~\ h o h a~ h ~
,s~ O h~H h ~d h ~rl F: h ~ a) h .rl h ~ ~d ~1 td e ~ O
~1~ ~ h ') 6 6)~ e e ~1 ~o o o ~~
a) oh ~ L~l o ~ O~ _1 ~ ~) h ~1 O
~d O~ ~ ~ oa~ o~
6 ~ 6 ~ I' 5~415 As shown in Table II above, any magnesium hydroxide dispersion stabilization activity of polymers such as methyl vinyl ether/maleic anhydride or vinyl sulfonate/acrylic acid copolymers is not detected by this test which demonstrates significant stabilization activity of maleic anhydride/di-iso butylene copolymer within the present invention not only at 500 ppm concentra-tion, but at the low 50 ppm concentration. Surprisingly, the maleic anhydride/
di-iso butylene copolymer's activity is shown to be greater than that of the commercial polymaleic anhydride and the sulfonated styrene/maleic anhydride copolymer. Further, this test detected li~tle activity for the rather highly carboxylated acrylic acid/ethyl acrylate copolymer, and the styrene/maleic anhydride copolymer.
The test of Comparative Example 1, although conducted at ambient room temperature, should correspond to an MSF unit environment in that magnesium hydroxide precipitation is induced, and further tests, shown in the examples below which are conducted in a~simulated MSF unit, demonstrate this correspon-dence .
In the simulated MSF unit, the sea water is processed as follows.
The sea water is filtered through a Millipore ~Trade mark) 0.~5 micron filter and then admixed with the desired concentration of additive solution which has been adjusted to pH 7. The treated sea water is then added to several feed water burrettes and therein sparged continuously with nitrogen. After the first hour of nitrogen sparging, the treated sea water is dosed with 2.5 ml. per liter of sea water of a ~ gram Na2S03 per liter solution. The desalination processing then is begun, wherein the sea water is pumped from the feed water burrettes through a rotameter and recirculation pump, through a filter, and then through a first and second preheater, where the temperature is raised to 105C. The preheated sea water then is pumped through a brine heater coil _ g _ which is sealed in an autoclave where the sea water in the coil is heated up an additiona] 10C. to a temperature of 115C., and then is pumped to an evaporator chamber having an upper distillate collector line and lower line to a blow down collector and pump, which recirculates undistilled sea water back to the line forward of the rotameter.
This laboratory scale simulated MSF unit has been determined to be comparable to commercial MSF units as to all important parameters as indicated by the comparison shown below in Table III.
Table Ill **
CommercialSimulated Parameter MSF unitMSF unit Brine heater inlet Temp. 110.6C 105C.
Brine heater oulet Temp. 120C 115C
Brine velocity 6.6 ft/sec. 6.0 ft/sec.
Tube length 22 ft 18 ft Sea water concentration 1.7 1.5 ** as given in Sea water and Sea water Distillation, Fichtner Handboo~
Vulkan-Verlag, Essen, 197~
The processing of sea water in the simulated MSF unit is run continu-ously in -the tests below until the test is terminated, i.e., when the brine heater coil inlet pressure rises to about 160 psig, indicating substantial scale deposits, at which point the unit is shut down for scale removal from the coil.
The performance of an additive in the simulated MSF unit is measured in terms of brine heater coil inlet pressure rise per unit time, being an indicator of scale deposit build-up per unit time. The lesser the pressure rise, the lesser the scale deposit in the brine heater coil.
;i39~8 COMPA~ATIVE EXAMPLE 2 The simulated MSF unit was run in separate tests using as additives a commercial scale preventive, a hydrolyzed polymaleic anhydrideJ and then a sulfonated styrene/maleic anhydride copolymer, and then a polymer within the present invention, a maleic anhydride/di-iso butylene copolymer. All of these additives are described above in Comparative Example 1. In these tests, the level of additive (ppm based on sea water) is lower than what would be normally chosen for commercial use so that the distinctions, if any, between activity, would be seen in a relatively short period of time. The change in brine heater coil inlet pressure at two day time intervals is shown below for each additive test and for a blank (no additive), in Table IV.
h ~¦
V~
oo oo o~
~ In oo ~
V _1 C~
U~ o o ~1 ~U~ ~ O
,~
O
Ul O`D
h ~ Ul ~ 00 ~d ~C
.~ Il~ ~D N C~
h )~
H
a~
E~
h O~
Q>
h O '--¢ ~ ~ ~:S
t~ N
~r~ 1 As shown in Table IV above, after six days time the polymer within the present invention held pressure rise down to 3 psig, as compared to 118 psig for the blank, 49 psig for the commercial polymaleic anhydride, and 12 psig for the sulfonated styrene/maleic anhydride copolymer. After 8 days, the com-parison still remains, the polymaleic anhydride run increasing another 15 psig, and the sulfonated styrene/maleic anhydride increasing another 4 psig, while the maleic anhydride di-iso butylene copolymer test increased 5 psig.
After the above run for the blank, the brine heater coil scale deposit was analyzed and determined to be 99% magnesium hydroxide and 1% calcium car-bonate.
Not only is the maleic anhydride/di-iso butylene copolymer more effective as shown in Comparative Example 2, but its commercial price is less than that of hydrolyzed polymaleic anhydride or the sulfonated styrene/maleic anhydride copolymer. A significant cost savings is provided by the process of the present invention, particularly in large scale use. ~Cost comparison here based on cost per weight unit actives.) Another test as described above in ~omparative Example 2 was run using 4.25 ppm actives of the maleic anhydride/di-iso butylene copolymer. Be-ginning at an initial brine heater coil pressure of 47 psig, there was no rise in pressure, and in fact a drop in pressure of 3 psig over a 9 day period occurred, at which time the test was terminated.
For a comparable actives level (4.8 ppm) of the sulfonated styrene maleic anhydride copolymer, beginning with an initial brine heater coil pressure of 42 psig, after 9 days the pressure had increased to 62 psig, a 20 psig rise.
In a second run with the sulfonated styrene maleic anhydride copolymer, at actives level of 50 ppm~ it again failed to achieve a level pressure, rising ~IL~ 3~
from 52 psig to 65 psig in 5 days time.
In these tests, the additives are the same as those used in Com-parative F.xamples 1 and 2.
Maleic anhydride/di-iso butylene copolymers used in the process of the present invention constitute a preferred embodiment of the present inven-tion, particularly when such copolymers are within the preferred ranges of molar ratios of comonomers and molecular weights as given above. Even more preferrPd are such copolymers having molar ratio of comonomers of from about 1.0 to 1.5 to about 1.5 to 1.0, and preferably a molecular weight by GPC of from about 1,000 to about 2,000.
In the above description of the invention, all molecular weights are determined by Gel Pe~meation Chromatography, designated GPC, unless specified otherwise, and all pressures that were tracked on the simulated MSF unit are the brine heater coil inlet pressure unless speci~ied otherwise.
Claims (22)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of inhibiting the deposit of scale on structural surfaces of aqueous medium systems in which such scale would normally be deposited, comprising:
introducing into the aqueous medium of said systems an effective amount for said purpose of a water soluble copolymer or salt thereof, wherein the polymer chain of said copolymer is comprised of maleic anhydride units and comonomer units having the formula wherein R1 and R2 are selected independently from the group consisting of H, methyl, and ethyl, and R3 is selected from the group consisting of trimethyl substituted methyl, trimethyl substituted ethyl, tetramethyl substituted ethyl, and pentamethyl substituted ethyl.
introducing into the aqueous medium of said systems an effective amount for said purpose of a water soluble copolymer or salt thereof, wherein the polymer chain of said copolymer is comprised of maleic anhydride units and comonomer units having the formula wherein R1 and R2 are selected independently from the group consisting of H, methyl, and ethyl, and R3 is selected from the group consisting of trimethyl substituted methyl, trimethyl substituted ethyl, tetramethyl substituted ethyl, and pentamethyl substituted ethyl.
2. The method of Claim 1 wherein said aqueous medium contains such ions that in said system said scale which would normally be deposited would be sub-stantially alkaline earth metal scale.
3 The method of Claim 2 wherein said alkaline earth metal scale is substantially magnesium hydroxide.
4. The method of Claim 1, 2 or 3 wherein said copolymer is introduced at a level of from about 0.01 ppm to about 100 ppm based on aqueous medium.
5. The method of Claim 2 wherein said copolymer is introduced at a level of from about 0.1 ppm to about 50 ppm based on aqueous medium.
6. The method of Claim 1, 2 or 5 wherein said copolymer has a molar ratio of maleic anhydride to said other comonomer of from about 0.5 : 1.0 :
to about 2.0 : 1Ø
to about 2.0 : 1Ø
7. A method of inhibiting the deposit of alkaline earth metal scale on heat exchange surfaces of aqueous medium systems in which such scale would normally be deposited on said heat exchange surfaces, comprising:
introducing into the aqueous medium of said system an effective amount for said purpose of a water soluble copolymer or salt thereof, wherein the polymer chain of said copolymer is comprised substantially of maleic anhydride units and comonomer units having the formula wherein R1 and R2 are independently selected from the group consisting of H, methyl, and ethyl, and R3 is selected from the group consisting of trimethyl substituted methyl, trimethyl substituted ethyl, tetramethyl substituted ethyl, and pentamethyl substituted ethyl; and wherein said copolymer has a molar ratio of maleic anhydride units to said comonomer units of from about 0.5 : 1.0 to about 2.0 : 1Ø
introducing into the aqueous medium of said system an effective amount for said purpose of a water soluble copolymer or salt thereof, wherein the polymer chain of said copolymer is comprised substantially of maleic anhydride units and comonomer units having the formula wherein R1 and R2 are independently selected from the group consisting of H, methyl, and ethyl, and R3 is selected from the group consisting of trimethyl substituted methyl, trimethyl substituted ethyl, tetramethyl substituted ethyl, and pentamethyl substituted ethyl; and wherein said copolymer has a molar ratio of maleic anhydride units to said comonomer units of from about 0.5 : 1.0 to about 2.0 : 1Ø
8. The method of Claim 7 wherein said copolymer has a molecular weight of from about 500 to about 10,000 by gel permeation chromatography.
9. The method of Claim 8 wherein said copolymer is a maleic anhydride/
di-iso butylene copolymer.
di-iso butylene copolymer.
10. The method of Claim 9 wherein said copolymer has a molar ratio of maleic anhydride units to said comonomer units of from about 1.0 : 1.5 to about 1.5 : 1.0, and a molecular weight of from about 1,000 to about 5,000 by gel permeation chromatography.
11. The method of Claim 7, 9 or 10 wherein said copolymer is introduced at a level of from about 0.1 ppm to about 50 ppm based on aqueous medium.
12. A method of inhibiting the deposit of scale on heat exchange surfaces of sea water desalination systems in which the sea water medium in said system is heated to temperatures in excess of 90°C, comprising:
introducing into the sea water medium of said system an effective amount for said purpose of a water soluble copolymer or salt thereof, wherein the polymer chain of said copolymer is comprised substantially of maleic an-hydride units and comonomer units having the formula wherein R1 and R2 are independently selected from the group consisting of H, methyl, and ethyl, and R3 is selected from the group consisting of trimethyl substituted methyl, trimethyl substituted ethyl, tetramethyl substituted ethyl, and pentamethyl substituted ethyl; and wherein said copolymer has a molar ratio of maleic anhydride units to said comonomer units of from about 0.5 : 1.0 to about 2.0 : 1Ø
introducing into the sea water medium of said system an effective amount for said purpose of a water soluble copolymer or salt thereof, wherein the polymer chain of said copolymer is comprised substantially of maleic an-hydride units and comonomer units having the formula wherein R1 and R2 are independently selected from the group consisting of H, methyl, and ethyl, and R3 is selected from the group consisting of trimethyl substituted methyl, trimethyl substituted ethyl, tetramethyl substituted ethyl, and pentamethyl substituted ethyl; and wherein said copolymer has a molar ratio of maleic anhydride units to said comonomer units of from about 0.5 : 1.0 to about 2.0 : 1Ø
13. The method of Claim 12 wherein said copolymer has a molecular weight of from about 500 to about 10,000 by gel permeation chromatography and is introduced at a level of from about 0.1 ppm to about 50 ppm based on sea water medium.
14. The method of Claim 13 wherein said copolymer is a maleic anhydride/
di-iso butylene copolymer.
di-iso butylene copolymer.
15. The method of Claim 14 wherein said copolymer has a molecular weight of from about 1,000 to about 5,000 by gel permeation chromatography and is introduced at a level of from about 1.0 ppm to about 20 ppm based on sea water medium.
16. The method of Claim 15 wherein said copolymer has a molecular weight of from about 1,000 to about 2,000 by gel permeation chromatography.
17. The method of Claim 12, 15 or 16 wherein said copolymer has a molar ratio of maleic anhydride units to said comonomer units of from about 1.0:
1.5 to about 1.5 : 1Ø
1.5 to about 1.5 : 1Ø
18. A method of inhibiting the deposit of scale in the brine heater of a multi-stage flash desalination unit in which such deposit would normally occur, comprising:
introducing into the aqueous medium of a multi-stage flash desalina-tion unit a water soluble copolymer of maleic anhydride and di-iso butylene in an amount of from about 0.1 to about 100 ppm based on aqueous medium, where-in said copolymer has a molar ratio of maleic anhydride units to di-iso butylene units of from about 0.5 : 1.0 to about 2.0 : 1Ø
introducing into the aqueous medium of a multi-stage flash desalina-tion unit a water soluble copolymer of maleic anhydride and di-iso butylene in an amount of from about 0.1 to about 100 ppm based on aqueous medium, where-in said copolymer has a molar ratio of maleic anhydride units to di-iso butylene units of from about 0.5 : 1.0 to about 2.0 : 1Ø
19. The method of Claim 18 wherein said copolymer has a molecular weight of from about 1,000 to about 5,000 by gel permeation chromatography and is introduced at a level of from about 1.0 ppm to about 20 ppm based on sea water medium.
20. The method of Claim 19 wherein said copolymer has a molecular weight of from about 1,000 to about 2,000 by gel permeation chromatography.
21. The method of Claim 18, 19 or 20 wherein said copolymer has a molar ratio of maleic anhydride units to di-iso butylene units of from about 1.0 :
1.5 to about 1.5 : 1Ø
1.5 to about 1.5 : 1Ø
22. The method of Claim 18, 19 or 20 wherein said copolymer has a molar ratio of maleic anhydride units to di-iso butylene units of about 1 : 1.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US39826282A | 1982-07-14 | 1982-07-14 | |
| US398,262 | 1982-07-14 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1205348A true CA1205348A (en) | 1986-06-03 |
Family
ID=23574688
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000432384A Expired CA1205348A (en) | 1982-07-14 | 1983-07-13 | Method of inhibiting scale |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1205348A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2021117134A1 (en) * | 2019-12-10 | 2021-06-17 | Kurita Water Industries Ltd. | Copolymers suitable for reducing the formation of magnesium hydroxide containing scale |
-
1983
- 1983-07-13 CA CA000432384A patent/CA1205348A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2021117134A1 (en) * | 2019-12-10 | 2021-06-17 | Kurita Water Industries Ltd. | Copolymers suitable for reducing the formation of magnesium hydroxide containing scale |
| WO2021117727A1 (en) | 2019-12-10 | 2021-06-17 | Kurita Water Industries Ltd. | Copolymers suitable for reducing the formation of magnesium hydroxide containing scale |
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