US2580923A - Prevention of corrosion in steam generation - Google Patents

Description

trines.

Patented Jan. 1, 1952 s 1 PREVENTION OF CORROSION IN STEAM GENERATION Arthur L. Jacoby, Western Springs, Ill., assignor to National Aluminate Corporation, Chicago, 111., a corporation of Delaware No Drawing. Application June 19, 1947, Serial No. 755,739

This invention relates to the art of treating water in boilers, steam generators, evaporators and the like, and the treatment of the steam and the condensate produced therefrom to reduce or prevent the corrosion of steam lines, traps, condensers and other pieces of equipment carrying the steam and the condensate. The invention also relates to the preparation of new and improved water treating compositions.

It has heretofore been suggested that certain amines may be added to boiler water from which they will volatilize with the steam and condense and dissolve in the condensed steam to inhibit corrosion occurring in the condensate lines. These amines may also be added directly to the steam lines. The amines proposed for this purpose are liquids boiling within the range from degrees C. to 171 degrees C. at atmospheric pressure. These liquid amines are, in general. highly caustic and present a serious hazard in their handling. Furthermore, they are quite volatile even under ordinary temperature conditions and the toxicity of their fumes in high concentrations presents a further hazard in their use. -Moreover, the addition of liquid to a boiler or to the steam lines is attended with many mechanical and practical difliculties.

One of the objects of the present invention is to provide a composition for the treatment of boiler water, steam and steam condensates, which composition is in substantially dry form that is readily soluble or dispersible in water, and from which suitable amines are liberated by the action of alkaline boiler water. v

Another object of the invention is to prepare corrosion inhibiting compositions of the type described in the form of briquettes which are gradually and uniformly dissolved in the feed water to a steam boiler, evaporator or the like. Other objects will appear hereinafter.

r In accomplishing these objects in accordance with the invention it has been found that corrosion inhibiting amines suitable for use in steam generating systems can be prepared in the form of crystalline non-hygroscopic water soluble salts. These amine salts are solids which are capable of liberating the free amines when added to the feed water of a steam boiler containing suilicient alkali to decompose the amine salts into free amines at steam generating temperatures. These solid amine salts can also be incorporated with other water treating chemicals either by mixing them together to produce a dry, free flowing powder or by briquetting them with a suitable binder, preferably one which is water soluble. The preferred compositions consist of the amine salts briquettedwith other water treating chemicals, e. g., tannins. lignin sulfonates, sodium sulfite, or the like, by means of binders such as dex- Claims. (Cl. 252--180)' Assuming that the alkali added to the boiler water' is sodium hydroxide, the general reaction which occurs between the amine salt and the alkali with the liberatirn of the amine may 'be described by the following equation:

Amine salt+NaOH (boiler water) Amine (volatile) +Na-salt (boiler water) Generally speaking, the quantities of amine salt required for the purpose of the invention are so small that the quantities of alkali employed in the boiler water will be sufficientto react with the amine salt and liberate the free amine while still maintaining an alkaline condition in the boiler water. In some cases, however, where the amine saltis made up with an'excess of acid or acid salt, it may be desirable to ,add larger amounts of alkali to the boiler feed water to compensate for the alkali which is utilized inthe reaction with the amine salt. The quantity of alkali required for this purpose can readily be calculated by any one skilled in the art.

The amines which are useful for the prepara tion of amine salts in accordance with the prac? tice of the invention are, in general, aliphatic,

alicyclic', cycloaliphatic, aromatic, and, heterofrom 5 to 250 pounds per square inch or at higher pressures if such pressures are employed, v H h 2. The amine should not cause foaming and carryover.

3. It should not decompose appreciably under boiler conditions of alkalinity, pH, pressure and temperature. 4; The boiling point of the amine should preferably be above degreesC. so that appreciable. amounts of the amine are not lost in venting or preheating of the feed water and so most of the amine will be in the liquid phase in the portions of the system handling hot condensate. It should be pointed out that boilingpoin't alone is not the factor which determines the relative volatility of the amine with steam, as the. tendency to form stable hydrates and other factors also influence this behavior.

5. The amine should not form stable carbonic acid addition products which will not decompose to the amine and carbon dioxide at preheater temperatures. v p

6. The carbonic acid addition products'of the amine should be reasonably water soluble.

7. The amine should have a low' 'equivalent weight. The lower the weight of thegamine for each. neutralizing amino group the lessi'the 'quan inhibit corrosion in Specific examples of suitable amines for most steam systems are: morpholine (B. P. 126-130 degrees C.) monoethanolamine (B. P. 171 degrees C.), cyclohexylamine (B. P. 134 degrees C), benzylamine (B. P. 184 degrees C.) and dimethylethanolamine (B. P. 133.5 degrees C.). These amines are miscible with water in all proportions. Other amines, such as aniline, which is only partially soluble in water, are unsatisfactory for the purpose of the invention. Amines which are soluble in water but have relatively high boiling points, e. g., triethanolamine, which boils around 280 degrees C. under a partial vacuum are not adapted for steam generation under pressures within the preferred range from to 250 pounds per square inch but might be used in steam generation under higher pressures and the correspondingtemperatures. It will be observed that the above described amines are illustrative of primary, secondary and tertiary amines.

The amine salts of mineral acids and organic carboxylic and/or sulfonic acids can be prepared .by dissolving the acid in a solvent, e. .g., water, diethyl ether or methanol, and adding the equivalent quantity of amine with stirring at arate such as to avoid overheating. Cooling may be resorted to in some cases. The salt is then recovered by filtration and, if necessary, evaporation. In cases where the corresponding amide is water insoluble care must be taken in the preparation of the salt to avoid dehydration to the amide. Another way in which the amine salts may be conveniently prepared consists in conducting the neutralization of the amine in the presence of a solid material capable of absorbing the water of reaction,

thereby yielding a dry appearing product withare suitable for the practice of the invention, for}. example, cyclohe'xylamine, sodium sulfate (i. a, the sodium ammonium sulfate), the mixed morpholine salts of lignin sulfonic acid and sulfuric acid, morpholine sodium sulfate. In reacting the amines with the alkali metal acid salts, an excess of the acid salt was used and hence the amine groups were neutralized.

The above mentioned amine salts or mixed fame salts are substantially non-hygroscopic solid water soluble salts, but it will be understood that not all amine salts have satisfactory properties for the purpose of the invention even though. the amine itself may be suitable in other respects for inhibiting corrosion in a steam system. Thus, the orthophosphite, the metaphosphate, the arsenate, the bor-ate, the sulfite, the

benzene sulfonate and the paratoluene sulfonate .of morpholine were all found to be too hygroscopic for the purpose of the invention. Similarly, the hydrochloride, the nitrate, the sulfate,

out the addition of anhydrous sodium sulfate.

The amine will then be converted to a mixed amine salt, namely, sodium amine sulfate, and the water will be absorbed by the excess of salt or salts producing a dry appearing powder.

The following amine salts or mixed salts have been prepared in accordance with the invention and have been found to be suitable for the practics of the invention:

A. The hydrochloride, the hydrobromide, the nitrate, the sulfate, the orthophosphate, the acetate, the phenyl acetate, and the '2-n-aphthalene sulfonate of morpholine;

. B. The hydrochloride, the hydrobromide, the nitrate, the sulfate, the orthophosphate, the acetate, the phenyl acetate, the pyrophosphate salt of cyclohexylamine and the 2-naphtha-lene sulfonate of cyclohexylamine;

C. The hydrochloride, the hydrobromide, the orthophosphate, the phenyl acetate, the acid oxalate of monoethanolamine, and the 2-naphthalene sulfonate of vmonoethanolamine;

D. The nitrate, the sulfate, the orthophosphate, the acetate, the phenyl acetate and the Z-napthalene sulfonateof henzylamine; and

E. The acid oxalate of dimethylethanolamine.

Additionally, mixed alkali metatamine salts the orthophosp'hate, the acetate, the phenyl acetate and the 2-napthalene sulfonate of dimethylethanolamine were too hygroscopic to be isolated. The nitrate, the sulfate and the acetate of monoethanolamine were all too hygroscopic,

The following examples are given to show methods of preparing amine salts suitable for the practice of the invention and also to illustrate the preparation of compositions containing such salts, it being understood, however, that these examples are not intended to limit the scope of the invention.

Example I To 8? parts by weight of morpholine was added 85.? parts by weight of 70% nitric acid. The addition was made with thorough mixing and at a rate such that the temperature was maintained at degrees C. to degrees C. When the addition was complete the temperature was permitted to drop and the mixture became a heavy mass of damp crystals which were useful in that state if mixed with sufficient other water soluble portions of a water treating composition, or were readily dried to a point where they were free flowing by themselves or compatible with other chemicals to give a powdered product containing a greater amine salt content than would be possible in the compositions containing the moist salt.

Example II Morpholine sulfate was prepared in the manner described in Example I except that equivalent amounts of concentrated sulfuric acid were employed instead of the nitric acid. It was found that by keeping the temperature of neutralization at 50 C. or below, the amine salt was much less prone to absorb moisture and gave a better product. The resultant product was a white granular powder of very faint morpholine odor. Similarly, the hydrochloride, the orthophosphate and the hydrobromide of morpholine were prepared using the appropriate acid instead of the nitric acid of Example I.

'In a like manner, by substituting equivalent amounts of the amine and/or the acid, the following amine salts were prepared; thenitrate, the sulfate and the orthophosphate of cyclohexylamine; the hydrochloride and the orthophosphate of monoethanolamine; and the sulfate,

the nitrate and the orthophosphate of benzylamine to the solid components, omitting the binder (dextrin) and water until last. The mix-i ing was conveniently done in a putty chaser.

The materials shown were made into briquettes;

Example III Parts Alkali soluble humic acids.- 10 Cyclohexylamine v 5- Sodium sulfate, anhydr 3.5- Ground nitre cake 4 Dextrin 2 Water 1 Example IV 'Per cent Morpholine nitrate 65 Monosodium phosphate, anhydr 12 Sodium acid pyrophosphate a. 15 Ammonium sulfate .5 Water (trace used during briquetting) Dextrin {3 Example V Per cent. Morpholine nitrate 66 Ammonium sulfate ;5 Chestnut tannin, dry 13- Sodium sulfite 5- Dextrin 9 Water (used in briquetting) 2 Example VI Per cent Morpholine nitrate .25 Sodium sulfate 31 Sodium sulfite 31 Dextrin 8 Water -5 Example VII There was first prepared a mixture of morpholine salts of lignin sulfonic acid and sulfuric acid in the following manner. One part of morpholine and 2.2 parts of lignin sulfonic'acid (obtained from waste sulfite liquors) were mixed and suflicient dilute sulfuric acid added to bring the pH down to about 4.7. This material was then dried on a drum drier to a moisture con-. tent of about- 6% to 7%, whereupon it was found tube a dry, water soluble powder. The amine As previously stated, in order to introduce the {amine saltinto the steam system it is preferable -to prepare it in the form of a briquette with other 'water treating chemicals and to cause it .-to be dissolved uniformly and gradually by :the -feed water-to the boiler. This is conveniently accomplished by preparing the .briquette and intro'ducing it into 'a by-pass feeder which isconf- -nected in the boiler feed water line. The boiler feed water circulates through the feeder, grad: ually dissolving the briquette and carrying the amine salt into the boiler where the amine is liberated by the action of the heat and inorganic alkali present. The liberated amine is then "in suflicient amount-to produce a pH preferably volatilized at a uniform rate' such that little change occurs in the water 'to amine ratio. The manner in which the aminevolatilizes will, of course, depend upon the chemical and physical characteristics of the amine. The volatilized amine should serve to provide a. nearly constant alkalinity in the boiling water and should redissolve in the steam condensate to provide the desired alkalinity in the latter at the point where condensation occurs.

The quantity of the amine salt initially added to the water from which the steam is generated should preferably be approximately 0.015 pound for each neutralizing amino group per grain of methyl orange alkalinity per thousand gallons of water. This means that if the methyl orange alkalinity of the feed water were 10 the quantity of amine salt would be that quantity'capable of liberating 0.15 pound of said amine per thousand gallons of feed water. If the methyl orange alkalinity were 20 the recommended dosage of amine salt would be the equivalent of 0.30 pound of said amine per thousand gallons of water. In a similar manner the dosage can be calculated for waters of different alkalinities. These dosages are based upon a pressure of 250 p. s. i. and the corresponding steam temperatures with adequate venting of the preheater.

The dosage can also be established by observation of the pH obtained in the condensate. In general, it is preferable to maintain a pH in the steamcondensate of about 7.0, although ithas been observed that substantial corrosionprotection has been obtained at a lower pH, as low as o 6.3. The preferred pH range in the steam condensate is about 6.5 to about 7.5.

' The treatment described herein can be employed in steam generation where the steam generators are operated at operating pressures from a high vacuum to rather high super-atmospheric pressures. It will be understood, however, that of the amines suggested some would be better than others for different pressure operations. Thus, for treatments involving vacuum evaporation the amine salts of cyclohexylamine' are recommended. For corrosion prevention or inhibition in steam generating systems "operating at superatrncspheric pressures within the range of to 250 pounds per squareinch and the cor.-

responding temperatures degrees C. to 210 degrees C.) excellent'results have been obtained with the amine salts of morpholine. Having thus described the invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. In a system wherein steam is generated from a boiler 'water containing an alkali and condensed, the process which comprises introduc- 'ing into said 'boiler'water-containing an alkali a quantity 'of' a substantially non-hygroscopic water'soluble salt of a mono-amine miscible with water in all proportions and volatile with steam at the boiler temperatures and pressures, the .quantity of alkali in said boiler water being in excess of the amount required to hydrolyze said amine salt to the free amine, and the quantity of. amine salt being'efiective to liberate. a corros'ion' inhibiting quantity" of said volatile amine in the steam condensate of at least 6.3. f

- 2. In a system wherein steam -isgenerated -irom a boiler water containing an alkali and condensed, the process which comprises introducing into said boiler water containing an ,alkali: a quantity of, a substantially nonz -hy rosoopic water soluble salt of a mono-amine miscible with water in all proportions and volatile with steam at the boiler temperatures and pressures, the quantity of alkali in said boiler water being in excess of the amount required to hydrolyze said amine salt to the free amine, and the quantity of amine salt being efiective to liberate a corrosion inhibiting quantity of said volatile amine in sufiicient amount to produce a pH in the steam condensate within the range of about 6.5 to about 7.5.

3. In a system wherein steam is generated from a boiler water containing an alkali and condensed, the process which comprises introducing into said boiler water containing an alkali a quantity of a substantially non-hygroscopic water soluble salt of a mono-amine miscible with water in all proportions and volatile with steam at the boiler temperatures and pressures, the quantity of alkali in said boiler water being in excess of the amount required to hydrolyze said amine salt to the free amine, and the quantity of amine salt corresponding to that quantity capable of liberating approximately 0.015 pound of amine per grain of methyl orange alkalinity per thousand gallons of boiler feed water.

4. In a system wherein steam is generated and condensed the method of protecting metal parts of the system against corrosion which comprises incorporating into boiler feed water, from which the steam is generated, and which contains an alkali, a quantity of a substantially non-hygroscopio morpholine salt, the quantity of alkali in said boilerwater being in excess of the amount required to hydrolyze said morpholine salt to free morpholine, and the quantity of morpholine salt being effective to liberate a corrosion inhibiting quantity of morpholine in sufiicient amount to produce a pH in the steam condensate of at least 6.3. Y

5. In a process of generating steam the method which comprises generating steam from an alkaline boiler water at pressures within the range of 100-250 pounds per square inch and the corresponding temperatures while incorporating into the feed water to the boiler a quantity of nonhygroscopic water soluble salt of morpholine, the quantity of alkali in the alkaline boiler water being in excess of the amount required to hydrolyze said morpholine salt and the quantity of the morpholine salt being sufficient to liberate a corrosion inhibiting quantity of morpholine upon said hydrolysis in suflicient amount to produce a pH in the steam condensate of at least 6.3.

6. In a process of generating steam the method which comprises generating steam from an alkaline boiler water at a pressure approximating 250 pounds per square inch, and the corresponding temperature while incorporating with the boiler feed water a quantity of a water soluble substantially non-hygroscopic morpholine salt capable of liberating approximately 0.015 pound of morpholine per grain of methyl orange alkalinity per thousand gallons of boiler feed water, the quantity of alkali in said boiler water being in excess of the amount required to hydrolyze said morpholine salt, and the quantity of morpholine salt being suflicient to maintain a pH in the steam condensate within the range of about 6.5 to 7.5.

'7. In a process or generating steam the method which comprises generating steam from an alkaline boiler water at pressures within the range of 100 to 250 pounds per square inch, and the corresponding temperatures, while incorporating into the boiler feed water a quantity of morpholine nitrate, the quantity of alkali in in the alkaline boiler water being in excess of the amount required to hydrolyze said morpholine nitrate, and the quantity of morpholine nitrate being effective to liberate a quantity of morpholine sufficient to produce a pI-I in. the steam condensate within the range of 6.5 to 7.5.

8. In a process of generating steam the method which comprises generating steam from an alkaline boiler water at pressures within the range of to 250 pounds per square inch, and the corresponding temperatures, while incorporating into the boiler feed water a quantity of morpholine sulfate, the quantity of alkali in the alkaline boiler water being in excess of the amount required to hydrolyze said morpholine sulfate, and the quantity of morpholine sulfate being effective to liberate a quantity of morpholine sufficient to produce a pH in the steam condensate within the range of 5.5 to 7.5.

9. In a process of generating steam the method which comprises generating steam from an alkaline boiler water at pressures within the range of 100 to 250 pounds per square inch, and the corresponding temperatures, while incorporating into the boiler feed water a quantity of cyclohexylamine sulfate, the quantity of alkali in the alkaline boiler water being in excess of the amount required to hydrolyze said cyclohexylamine sulfate, and the quantity of cyclohexylamine sulfate being effective to liberate a quantity of cyclohexylamine sufiicient to produce a pH in the steam condensate within the range of 6.5 to 7.5.

10. In the process of generating steam the method which comprises generating steam from an alkaline boiler water at pressures within the range of 100 to 250 pounds per square inch, and the corresponding temperatures, while incorporating into the boiler feed water a quantity of a mixed aminesalt oi morpholine lignin sulfonate and morpholine sulfate, the quantity of alkali in the alkaline boiler water being in excess of the amount required to hydrolyze said mixed amine salt of morpholine lignin sulfonate and morpholine sulfate, and the quantity of mixed amine salt of morpholine lignin sulfonate and morpholine sulfate being effective to liberate a quantity of morpholine suilicient to produce a pH in the steam condensate within the range of 6.5 to 7.5.

ARTHUR L. JACOBY.

REFERENCES CITED The following references are of record in the file of this patent:

OTHER REFERENCES Dictionary of Organic Compounds; Heilbron,

OxfordPress, N. Y., vol. 2 (19 3), p. 840.

Claims (1)

1. IN A SYSTEM WHEREIN STEAM IS GENERAGED FROM A BOILER WATER CONTAINING AN ALKALI AND CONDENSED, THE PROCESS WHICH COMPRISES INTRODUCING INTO SAID BOILER WATER CONTAINING AN ALKALI A QUANTITY OF A SUBSTANTIALLY NON-HYGROSCOPIC WATER SOLUBLE SALT OF A MONO-AMINE MISCIBLE WITH WATER IN ALL PROPORTIONS AND VOLATILE WITH STEAM AT THE BOILER TEMPERATURES AND PRESSURES, THE QUANTITY OF ALKALI IN SAID BOILER WATER BEING IN EXCESS OF THE AMOUNT REQUIRED TO HYDROLYZE SAID AMINE SALT TO THE FREE AMINE, AND THE QUANTITY OF AMINE SALT BEING EFFECTIVE TO LIBERATE A CORROSION INHIBITING QUANTITY OF SAID VOLATILE AMINE IN SUFFICIENT AMOUNT TO PRODUCE A PH IN THE STEAM CONDENSATE OF AT LEAST 6.3.