February, 1925 ~~
INDUSTRIAL A N D ENGINEERING CHEMISTRY
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Chemical Treatment of Refrigeration Brines to Prevent Corrosion' By Emerson P. Poste THEPFAUDLER Co., ELYRIA, OHIO
It is necessary to realize what takes place when these reagents are added to calcium chloride brines free from magnesium chloride. The determining point is the solubility of calcium oxychloride, resulting from a reaction between the brine and the treatment material. The limiting factor is the precipitation of an excess of this basic salt. If lime is used as the reagent, a reaction probably takes place between the Alkaline Brine CaO-Ca(0H)z particles and the calcium chloride to form the Previously published data2 and various private communi- basic salt. This, in turn, reacts with additional brine to raise the alkalinity. When cations from engineers inthe brine becomes saturated terestedinthepr'blemfrom The chemistry of the treatment of brines with lime and with the oxyc~oride, the the points Of view Of sodium hydroxide is discussed and a chart showing the limit of d k a b i t y is manupossible maximum alkalinities under varying conditions If calcium &loride brine is suppliers of of dairy and reof brine strength and temperature is presented. The treated withso~iurnhy&,oxfrigeration equipment, and use of a bag of lime, either t o produce or maintain alkaide, the basic salt is formed Of a' agree linity, is shown to be wrong. The addition of lime as a as before and its on certain slurry has proved practicable. Encouraging results have in the brine determines the which may be been obtained with sodium hydroxide in a bag, but not possible summarized as follows : enough data have been available to cover this point fully. In the treatment of soIts use as a solution would be satisfactory. Thesegeneral dium &loride brine with brines are less statements apply to both calcium and sodium chloride lime the situation is again corrosive than acid brines. ( 2 ) Strong brines are less brines' controlled by the formacorrosive than dilute brines. tion of the basic salt. The (3) Calcium chloride brines turn acid on contact with air. oxychloride resulting from the reaction with the lime goes (4) Calcium chloride brines free from magnesium chloride may into solution and establishes a certain definite alkalinity bebe rendered alkaline by chemical treatment. yond which the excess precipitates. When sodium chloride (5) Sodium chloride brines may be rendered alkaline. brine is treated with sodium hydroxide there is no limiting There seems to be some difference of opinion as to the relative factor. Aside from possibilities resulting from impurities in corrosive action of sodium and calcium chloride brines of like the brine, no basic salt separates and, as sodium hydroxide gravity and reaction, although data indicating a greater cor- is very soluble in sodium chloride solution, very high alkarosive action from sodium chloride brines are on record. The linities may be produced. Concerning the nature of this obvious conclusion from these statements is that it is neces- basic salt. Thor~e3savs: sary to maintain alkalinity in a brine to reduce corrosion. When calcium chloride solution is hoiled with slaked lime, and This fact forms the starting point of the investigations covthe liquid filtered, white needle-shaped crystals of calcium oxyered herein. chloride separate out on cooling of the composition C1.CaO.Ca-
HERE is a growing appreciation on the part of refrigeration engineers and milk-plant operators that brine control is an important means of inhibiting corroPion. The fact that certain experimental and commercial observations have been made in connection with this problem warrants the publication of another paper on the subject.
T
Methods of Producing Alkalinity
The method generally recommended has been to hang a bag of lime in a brine tank, using 10 pounds of quicklime per 1000 gallons (1.2 kg.per 1000 liters) of brine. A less frequent suggestion is a similar use of sodium hydroxide t o the amount of 13 pounds per 1000 gallons (1.6 kg. per 1000 liters). Occasionally, the use of soda ash has been advised. Of these three methods of producing alkalinity only the first two have practical possibilities. Sodium chloride brines contain some calcium salt as an impurity, and this calcium would be precipitated as carbonate before alkalinity from sodium carbonate could be realized. The addition of sodium carbonate to a calcium chloride brine would result in the precipitation of an equivalent amount of calcium carbonate without the production of alkalinity. In view of the action on the calcium salts in sodium chloride brine and the impossibility of getting results in calcium chloride brine, the use of soda ash should not be considered. The problem is thus reduced to the treatment of brines with lime and sodium hydroxide. Received November 12. 1924. Poste and Donauer. The M i l k Dealer, February, 1923; Hull, Ice and Refvigeration, March, 1929.
(OH). 7Hz0 or 3CaO.CaC12.15H20. The salt is stable out of contact with air, loses part of its water of crystallization over sulfuric acid or caustic lime, and absorbs carbon dioxide from the atmosphere. It is decomposed by water or alcohol.
According to another authority, quoted by Thorpe, the composition is CaC12.3Ca0.16Hz0, and on drying in a vacuum it becomes converted into CaC12.3Ca0.3HzO. Other considerations determining the possible alkalinity are the effect of the gravity and temperature of the brine upon the solubility of calcium oxychloride. The solubility in calcium chloride brines increases with increase of temperature and changes but slightly with difference in gravity of brine. With sodium chloride brine the solubility decreases with increase in temperature and is greater in weak than in strong brines. These various points have been observed in the literature4 and checked in the laboratory on brines made from pure and commercial raw materials. The various possibilities involving treatment of both types of brine of different strengths and at different temperatures are summarized in Figure 1. Alkalinity is expressed in per cent of normal solution and in
1
f
4
''Dictionary of Applied Chemistry," Vol. I, p. 737. Lunge, "Sulphuric Acid and Alkali," Vol. 111, p. 419
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grams CaO per liter. It so happens that the first figure also represents the number of cubic centimeters of tenth normal acid necessary to neutralize 10 cc. of the brine. The recommended treatment of 10 pounds of quicklime per 1000 gallons of brine (1.2 kg. per 1000 liters) represents an alkalinity of 4.5 per cent, assuming that the lime is pure and all goes into solution. Figure 1 indicates that it is theoretically possible to get this amount of lime into solution in a calcium chloride brine with a gravity of 1.2 at a temperature of 70' F. (21' C.), but under no other conditions of strength or temperature. If the brine were treated to saturation at atmospheric temperature, followed by cooling to refrigeration temperature, the amount of alkalinity would be reduced by the precipitation of the basic salt. On the other hand, if sodium chloride brine were treated a t atmospheric temperature and cooled to refrigeration temperature, the alkalinity would increase. The weaker brine would finally take all the lime into solution, but not so with the stronger brine. If the lime used were of commercial grade, falling well short of 100 per cent calcium oxide, the excess present in any case would be accordingly less.
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of calcium chloride brine with a gravity of 1.10. The temperature was about 70' F. (21" C . ) . The brine was gently agitated with compressed air during the day. The test was continued for 40 days. Under the most favorable conditions of treatment, involving pure calcium hydroxide in a coarse mesh cheesecloth bag, there resulted a 2 per cent norma1 alkalinity as a maximum and well under that as an average. I n considering these results it should be kept in mind that at the temperature and concentration involved the brine shoul& theoretically take on an alkalinity of 4 per cent normal. I n the belief that the carbon dioxide in the air used for agitation might have been a determining factor in the formation of a hard crust that had closed the meshes of the bag, the test was repeated using an excess of quicklime in a burlap bag with frequent mechanical agitation. The resulting alkalinity did not exceed 1 per cent normal and the meshes of the bag became clogged essentially as before. In both cases the material in the meshes contained some carbonate. Carbonation due to air agitation was apparently not a controlling factor, however, the second alkalinity being lower than the first. Direct addition of the same amounts of the two types of lime to like quantities of brine produced the expected alkalinity in each case. A bag test with sodium chloride brine, gravity 1.1, gave as a maximum alkalinity only 0.3 per cent normal, and the theoretical figure is 4 per cent normal, The bag again became clogged. The condition of the bags suggested the formation of 8 mixture of calcium carbonate and a material which may be analogous to the oxychloride cements that are used for floors and stucco. A trial with an excess of sodium hydroxide in a burlap bag hung in a jar of calcium chloride brine, specific gravity 1.1, gave a maximum alkalinity of 3.4per cent normal, approaching the theoretical of 4 per cent normal. The bag was empty when examined, the test having been continued for 50 days. Apparently, under these conditions some of the sodium hydroxide had gone into reactions other than those producing alkalinity. These laboratory tests suggested the possibility of treating brine with lime by direct addition but not by placing it in a bag. The use of sodium hydroxide by the latter method was promising. Obviously, the addition of this material in solution would produce results. Commercial Brine Treatment
O°F 10 Figure I-Possible
Alkalinity of Commercial Brines-CaCt, Calcium chloride Sodium chloride A-Per cent normal alkalinity B-Grams CaO per liter
------
NaCl
It is concluded, therefore, that with strong brines and refrigeration temperature of 10' F. (-12' C.), calcium chloride brine may be treated to produce a 1.0 per cent normal alkalinity, while that possible in sodium chloride brine is 3.0 per cent normal. I n terms of corrosion either of these alkalinities should be sufficient greatly to inhibit action on metal. Experimental Brine Treatment
Following these theoretical considerations as to the possibilities of alkalinity, it will be well to see how nearly these results can be realized by various methods. Several laboratory studies will be covered, followed with records of commercial cases. The first tests involved placing an excess of slaked lime in a small cloth bag hung in a jar containing 3 gallons (11 liters)
Several different cases of brine treatment on a commercial scale were studied. Those having to do with calcium chloride brine will be discussed first, and then.sodium chloride brines will receive attention. CALCIUMCHLORIDE BRINE-The first test with calcium chloride brine involved a small installation using only 300 gallons (1140 liters) of brine. The log of the observations is given in Table I. Table - . . -I-Effect ~~ ~
Time Days
Start
1 2
of Treatment of CaC1z Brine
Alkalinity Gravity Per cent N N o treatment. Freshly made wfi brine 1.18 0.90 1.17
1.17
0.64 0.64
Bag- of. lime hung i n tank after sample was taken 0.56 1.17 7 0.45 1.14 I9 0.28 90 1.13 Bag oj$ake sodium hydroxide hung in lank 1.12 0.90 100 1.10 I08 1.20 118 1.10
...
The lime was a commercial grade containing considerable magnesia. The amount used was 10 pounds (4.5kg.). It did not even maintain the alkalinity existing when it was introduced. When removed the contents of the bag were in
February, 1925
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
a hard mass. The treatment with sodium hydroxide involving 7 pounds (3.2 kg.) of flake material was more promising, producing an alkalinity that should be satisfactory in inhibiting corrosion, but much less than the theoretical. The average temperature of the brine was about 18" F. (-8" C.), at which a brine with a gravity of 1.1 could reach an alkalinity of 2.5 per cent normal. It is unfortunate that this case could not be studied to a final conclusion. The data obtained may be taken to indicate a commercial possibility with sodium hydroxide, however. A second commercial case coming under observation involved the treatment of a brine that had become slightly acid. Quicklime in the amount of 10 pounds per 1000 gallons (1.2 kg. per 1000 liters) of brine was put in a bag and hung in the tank. Several weeks later the brine showed an alkalinity of only 0.15 per cent normal. Another case has afforded valuable data. The brine, initially quite weak and about neutral, was strengthened by adding fresh calcium chloride. This was followed by treatments with quicklime in accordance with the data in Table 11. Table 11-Effect of Adding Fresh CaCla Followed by Lime Treatment Time Ah;;t& Days Gravity N o treatment 0 1.07 0.10 15 Fresh chloride added 0.25 1.12 31 0.20 1.12 37 Treated with lime slurry, 10 pounds per 1000 gallons (1.2 k g . per 1000 liters) after taking above sample 1.12 1.85 38 1.12 1.90 39 1.12 1.90 40 1.12 2.00 41 1.10 1.70 43 1.70 1.10 44 1.50 1.10 45 Fresh chloride added 1.70 1.11 46 1.70 1.11 47 1.70 1.11 48 1.40 1.11 53 Treated with lime slurry, 5 pounds per 1000 gallons (0.6 kg. per 1000 liters) 2.50 54 1.11 2.50 55 1.11 2.30 1.11 57 2.30 1.11 59 2.30 61 1.11 1.90 75 1.11 1.40 93 1.10 1.00 95 1.10 Treated with lime slurry, 5 pounds per 1000 gallons (0.6 kg. per 1000 liters) ; bag of lime i n tank 96 1.10 2.50 97 1.10 2.30 107 1.09 2.40 114 1.09 2.10 Fresh chlortdc added 121 1.13 1.50
The theoretical maximum alkalinity for the brine involved is 2.5 per cent normal. The rather impure commercial quicklime initially added did not bring the maximum results, and so another treatment involving half the previous amount of lime was made. The brine responded to this promptly, but after a few days the alkalinity dropped off. When it had reached 1.0 per cent normal, another treatment was made and, in addition, a bag of lime was hung in the tar$. The alkalinity again came up to the maximum, but it dropped off in substantially the same manner as previous to the use of the bag of lime. These studies indicate that the desired alkalinity can be reached by the use of lime as a slurry, but that the treatment with the bag of lime will not even maintain previously established alkalinity, to say nothing of producing alkalinity. SODIUMCHLORIDE BRINE-several cases involving sodium chloride brine have been noted. I n the first the brine was initially practically neutral. Lime hung in bags over the side of the tank produced only a very slight alkalinity. I n another case brine with a gravity of 1.16 was treated by
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direct addition of slaked lime in water suspensioh. An alkalinity of 3.5 per cent normal resulted, approaching the theoretical for the brine involved. It was found impossible to maintain this alkalinity by means of lime in a bag hung in the tank, but direct additions made from time to time accomplished the desired results. The cases that have been cited are typical of a larger number on record. The conclusions to be drawn from the various studies are substantiated by all the data at hand. The data in the tables are presented graphically in Figure 2.
0
10
20
30
-40
60
60
70
80
90
100
110
Time D c ~ Figure 2-Commercial T r e a t m e n t of Calcium Chloride Brine I-Data from Table I: 0-Freshly prepared brine 2-Bag of slaked lime hung in tank 90-Bag of flake sodium hydroxide hung in tank 11-Data from Table 11: 0-Initial weak brine 15-Fresh chloride added 37-Treated with lime slurry, 10 lbs./1000 gals. 45-Fresh chloride added 53-Treated with lime slurry 5 lbs./IOOO gals. 9 k T r e a t e d with lime slurry' 5 lbs./1000 gals., and bag of lime hung in tank
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Recommendations The author's present knowledge concerning the prevention of corrosion by brine, based in part on previously published work not included herein, leads to certain very definite statements. 1-For making calcium chloride brine, a chloride free from magnesium chloride should be used. 2-The gravity of the brine should be kept in the neighborhood of 1.20. 3-Either calcium or sodium chloride brine should be treated with pure quicklime on the basis of 10 pounds of lime per 1000 gallons (1.2 kg. per 1000 liters) of brine, or with sodium hydroxide on the basis of 13 pounds per 1000 gallons (1.6 kg. per 1000 liters). 4-The reagents should be added as a slurry or solution at a point of rapid brine circulation, though the introduction of sodium hydroxide in a bag is reasonably effective. 5-Additional reagent should be added from time to time by the foregoing method as may be necessary to maintain an alkalinity approaching the maximum for the brine involved as indicated in Figure 1. 6-Undue contact between brine and air should be avoided.
Acknowledgment The author wishes to acknowledge the valuable criticisms and suggestions made by J. H. Kaiser, Technical Service Dept., The Solvay Process Co., Syracuse, N. Y.; F. N. Speller, Metallurgical Engineer, The National Tube Co., Pittsburgh, Pa.; and A. C. White, Technical Research Dept., Dow Chemical Co., Midland, Mich.
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