US2550425A

US2550425A - Suppression of corrosion

Info

Publication number: US2550425A
Application number: US756111A
Authority: US
Inventors: Jr Cecil Phillips
Original assignee: Standard Oil Development Co
Current assignee: Standard Oil Development Co
Priority date: 1947-06-20
Filing date: 1947-06-20
Publication date: 1951-04-24
Anticipated expiration: 1968-04-24

Description

Patented Apr. 24, 1951 SUPPRESSION OF CORROSION Cecil Phillips, Jr., Baytown, Tex., assignor to Standard Oil Development Company, Elizabeth, N. 3., a corporation of Delaware No Drawing. Application June 20, 1947, Serial No. 756,111

Claims. 1

This invention is directed to a method for suppressing the corrosion of copper-containing alloys in the presence of ammonia. Specifically, it is directed to the prevention of corrosion of copper alloys in aqueous solutions containing ammonia.

In many operations it is often desirable to use various types of equipment (tanks, heat exchanger and condenser tubes, valves, lines, etc.) constructed of or containing copper alloys for handling solutions or gases containing ammonia. Such equipment usually suffers from severe corrosion of the copper alloys due to the chemical dissolution of the copper by the ammonia. The rapid destruction of the copper alloys in contact with solutions or vapors containing ammonia is believed to be due to the formation of highly soluble copper-ammonium complex ions. The presence of oxygen is necessary for the formation of the soluble copper-ammonium ions.

As a result of the corrosive action of ammoniacal solutions on copper, the employers of ammonia, such as the petroleum refiner, must exercise extreme care in selection of suitable alloys for his processing equipment. Thus, where ammonia is to be used, copper alloys are avoided. However, as mentioned before, various services require the-use of copper alloys on account of other corrosive fluids being encountered. Thus, the corrosive action of carbon dioxide in steam makes nearly mandatory the employment of copper alloys such as alloys of copper, zinc, and tin in heat exchange equipment using corrosive steam as the heat transfer medium. Thus, when ammonia is employed in this type of equipment, rapid attack of the copper alioy may be sufiered even though the ammonia may prevent attack of ferrous metals by other components travelling through the equipment. Ammoniacal solutions are also widely used in solvent extraction of hydrocarbons. Here, again the petroleum refiner must guard against allowing the solutions to contact copper bearing surfaces. The aforementioned corrosion reaction generally occurs at atmospheric temperature and pressure. It is believed that higher temperatures and pressures may accelerate this reaction.

It is, therefore, the main object of the present invention to provide a process whereby the deterioration of copper alloys in the presence of ammonia is substantially eliminated.

Another object of the invention is to provide a method whereby copper alloys may be employed in services where they are exposed to ammoniacal solutions.

' ammoniacal solutions.

The objects of the present invention are achieved by maintaining in corrosive ammoniacal solutions in contact with copper and its alloys a corrosion inhibiting amount of a halogen acid.

Briefly, the present invention involves the addition to corrosive ammoniacal solutions in contact with copper-containing metals of a quantity of a halogen acid in the range between 0.05 and 5% by weight of the ammoniacal solution. The halogen acid may be hydrochloric acid, hydrobr-omic acid, hydroiodic acid, or hydrofluoric acid.

The mechanism by which the halogen acid is effective in preventing the corrosion of copper alloys by ammonia is not understood, but it is believed to involve the formation of a very thin protective film on the metal. This hypothesis is based on the fact that the halogen acid is employed in amounts insuflicient to neutralize the Therefore, some other explanation of the beneficial aspects of the invention is necessary. It is understood, of course, that I do not wish to bind myself to any theory offered as an explanation of the benefiicial effect.

An advantage of the process of the present invention, irrespective of the prevention of corrosion of copper and its alloys, is the ability to use existing equipment in which copper and its alloys are present in processes involving the use of ammonia.

In order to illustrate the beneficial aspects of this invention, copper-containing metal copper, 29% zinc, and 1% tin) was immersed in aqueous solutions of ammonia. These tests were in progress for 24 hours at room temperature and atmospheric pressure. Air was bubbled through the ammonia solutions throughout the tests. These tests were repeated under identical conditions with small amounts of hydrofluoric acid added to the aqueous solutions of ammonia. Results obtained in these tests are shown in the following table:

It will be observed from the data presented in the foregoing table that the addition of a small amount of hydrofluoric acid effects a marked reduction in the tendencies of aqueous solutions of ammonia to corrode copper-bearin alloys.

The present invention has utility in inhibiting the corrosive eflects of solutions of ammonia in water in the presence of oxygen but is also applicable to inhibiting the corrosive effects of other ammoniacal solutions. For example, solutions of ammonium acetate readily dissolve copper and copper bearing metals. Maintenance of the required amount of halogen acid will effec.- tively inhibit the corrosiveness of such solutions to copper surfaces.

The nature and objects of the present invention having been fully described and illustrated, what I wish to claim as new and useful and to secure by Letters Patent is:

1. A method for reducing the corrosive action of a corrosive basic solution including ammonia, water and oxygen to apparatus adapted to contain corrosive fluids and having a corrodible copper-containing surface in contact with said solution which comprises introducing into said solu tion an amount of a halogen acid sufiicient to'inhibit the corrosion thereof but insufficient to neutralize the solution.

2. A method in accordance with claim 1 in.

which the amount of halogen acid is in the range between 0.05% and 5% by weight of the corrosive solution.

3. A method in accordance with claim 1 in which the halogen acid is hydrofluoric acid.

4. A method in accordance with claim 1 in which the halogen acid is hydrochloric acid.

5. A method in accordance with claim 1 in which the halogen acid. is hydrobromic acid.

CECIL PHILLIPS, JR.

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

UNITED STATES PATENTS Number Name Date 1,994,702 Harris Mar. 19, 1935 2,024,680

Curtis Dec. 17, 1935 OTHER REFERENCES

Claims

1. A METHOD FOR REDUCING THE CORROSIVE ACTION OF A CORROSIVE BASIC SOLUTION INCLUDING AMMONIA, WATER AND OXYGEN TO APPARATUS ADAPTED TO CONTAIN CORROSIVE FLUIDS AND HAVING A CORRODIBLE COPPER-CONTAINING SURFACE IN CONTACT WITH SAID SOLUTION WHICH COMPRISES INTRODUCING INTO SAID SOLUTION AN AMOUNT OF A HALOGEN ACID SUFFICIENT TO INHIBIT THE CORROSION THEREOF BUT INSUFFICIENT TO NEUTRALIZE THE SOLUTION.