US2517894A - Metal degreasing composition - Google Patents

Description

Patented Aug. 8, 1950 METAL DEGREASING COMPOSITION Arthur W. Lax-char, MendenhallQPag assignor to E. I. du Pont de Nemours &' Company, Wilmington, DeL, a corporation of Delaware No Drawing. Application May 13, 1946,- Serial No. 669,459.

This invention relates to'the stabilization of chlorinated hydrocarbons against decomposition and their use as cleaning compositions, such as in the degreasing of metals. More particularly this invention relates to a method for preventing or retarding the metal-induced decomposition of volatile chlorohydrocarbon solvents and to compositions containing volatile chlorohydrocarbon solvents stabilized against decomposition, such as is encountered in the degreasing of metals.

Although volatile chlorohydrocarbons are excellent cleaning and degreasing agents, they possess certain disadvantages when used. in contact with metals. The use of volatile chlorinated hydrocarbons, such as trichloroethylene', for degreasing metals or in metallic apparatus, has the disadvantage that metals, such as aluminum or iron, tend to induce and catalyze certain condensation reactions involving the chlorine atoms of the chlorinated hydrocarbons, As a result, the solvent may decompose, sometimes vigorously, with the evolution of products such as hydrochloric acid or phosgene and the formation of a gummy mass. Thus metallic apparatus, in which the solvent is used, is subject to severe corrosion and dangerous fumes are given off. It is therefore of great industrial importance to prevent or retard. metal-induced decomposition of volatile chlorinated hydrocarbon solvents. Since cleaning treatments of metals or other objects are in practice carried out in the vapor as well as in the liquid phase, it is necessary to prevent decomposition of the volatile hydrocarbon solvent in both the vapor and liquid phases.

An object of this invention is to provide a method for preventing or substantially retarding the decomposition of volatile chlorinated hydrocarbon solvents in the presence of metals, such as iron or aluminum. A further object of this invention is to provide a cleaning composition comprising a volatile chlorohydrocarbon solvent which is stabilized against metal-induced decomposition. A still further object is to provide a cleaning composition comprising a stabilized volatile chlorohydrocarbon solvent in which the stabilizer is sufficiently volatile to be present in effective amounts in the vapor of the chlorohydrocarbon. Another object is to provide a stabilizer for volatile chlorohydrocarbons which is effective in low concentration in both the liquid and vapor phase. An important object is to provide \a stabilized chlorinated hydrocarbon solvent for the degreasing of metals. An additional object is to provide a practical and safe method of degreasing metals with a volatile chlorohy- 1 Claim. (01. 252-171) carbon solvent.

2 drocarbon solvent. Other objects will appear hereinafter.

These objects are accomplished by adding to the volatile chlorinated hydrocarbon an effective amount of cyclohexene. It has now been discovered that volatile chlorohydrocarbon solvents containing cyclohexene are stabilized toward metal decomposition.

For eiiective results, the cyclohexene should be used in amounts of at least 0.02 based on the weight of the chlorohydrocarbon. It is in general unnecessary to use more than a small amount, such as 1% of cyclohexene, a concentration of about 0.05 to 0.25% based on the chlorohydrocarbon being preferred in most instances.

In order to be eiiective in the vapor phase as Well as in the liquid phase, the stabilizer must be volatile with the vapor of the chlorinated hydro- In practice this requires that the stabilizer should have a boiling point below 175 0., at the most and much preferably below 100 C. for use with the lower boiling chlorohydrocarbons. Cyclohexene, having a boiling point of 833 C. under atmospheric pressure, is not only effective in low concentrations, but is sufliciently volatile to be present in efiective amounts in the vapor of the chlorohydrocarbon.

The chlorinated hydrocarbons to which this invention is chiefly applicable are the volatile chlorohydrocarbon solvents boiling below about 150 0., particularly the volatile aliphatic chlorohydrocarbon solvents, examples of which are chloroform, carbon tetrachloride, and the lower alkyl chlorides, such as butyl, amyl and hexyl chlorides, dichloroethane, trichloroethylene, tetrachloroethane. However, this invention is generally applicable to volatile chlorohydrocarbons and includes cyclic chlorohydrocarbons, such as chlorobenzene and chlorocyclohexane.

One of the most important of the volatile chlorohydrocarbon solvents is trichloroethylene, and the invention will be further illustrated with reference to this particular solvent. In the following examples, parts are by weight, unless otherwise stated.

Example I In comparative tests, two mixtures of parts of trichloroethylene and 0.2 part of mesh aluminum powder were held at C. for 24 hours in sealed glass tubes from which substantially all oxygen had been removed. One sample contained 0.1% by weight of cyclohexene, the other was an unstabilized control. At the end of the test, each vessel and its contents was washed thoroughly with 100 parts of 5% nitric acid, and the chloride content of the wash liquor was determined by adding excess 0.02 N silver nitrate solution and back titrating with 0.02 N potassium thiocyanate solution, using ferric alum indicator. It was found that 100 parts of the unstabilized control contained 0.389 part of chloride ion, whereas 100 parts of the sample stabilized with cyclohexene contained only 0.012 part of chloride ion. Thus, in the presence of cyclohexene, the

extent of trichloroethylene decomposition in this accelerated test was only about 3% of what it was in the absence of cyclohexene. The inhibitory power of cy-clohexene towardmetal-induced decomposition of chlorohydrocarbons is all the more remarkable when it is compared to that of such a closely related compound as cyclohexane. Under identical conditions cyclohexene is seventeen times more effective than cyclohexane.

. Eaiample II The effectiveness of cyclohexene in conjunction with known oxidation inhibitors for chlorinated hydrocarbon solvents such as aniline, isshown by the following tests. Five hundred and forty (540) parts of trichloroethylene containing 0.04% by weight of aniline was boiledunder total reflux with 5 parts of 100 mesh aluminum powder and 0.5 part of iron powder. Samples were withdrawn periodically and acidity was determined by titrating with 0.01 N sodium hydroxide. After 13 days, 28 cc. were required to neutralize the acid in a 25 cc. sample. In an exactly similar test except that the trichloroethylene contained 0.04% aniline and 0.04% vcyclohexene, a 25 cc. sample taken after 18 days required only 8 cc. of 0.01 N sodium hydroxide. Thus, the presence of cyclohexene had brought about a more than threefold improvement in stabilizing action over aniline alone. When no stabilizer at all is used in the above-described test, the acidity developed in a 25 cc. samplecorrespondsto 68 cc. of 0.01 N sodium hydroxide after only 24 hours refluxing.

If desired, other stabilizers may be used in conjunction with cyclohexene and other beneficial adjuvants, such as known antioxidants, may be added.

The stabilized chlorohydrocarbons made available by this invention find their chief use in the cleaning and degreasing of metals or alloys such as iron, steel, aluminum, nickel, chromiumm, copper, brass, and the like or of articles made therefrom. However, they are also useful whenever a chlorinated solvent is to be used in metallic apparatus as in the textile cleaning industry or in solvent extraction processes. The volatile stabilizer of this invention, cyclohexene, has the further advantage that it can be recovered with the solvent when the latter is distilled from the oil, grease and dirt left in it after a cleaning operation, thus avoiding unnecessary waste and economic loss.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiments thereof except as defined in the appended claim.

I claim: I i

A metal degreasing composition stabilized against aluminum-induced decomposition in the liquid and vapor phases consisting essentially of trichloroethylene and from .02% to 25% of cyclohexene based on the weight of said trichloroethylene.

ARTHUR W. LARCHAR.

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

UNITED STATES PATENTS Number Name Date 1,949,857 Braun Mar. 6, 1934 2,371,645 Aitchison et a1 Mar. 20, 1945 OTHER REFERENCES Mellan: Industrial Solvents, Reinhold Pub. Co., N..Y., 1939, pages 154, 156, 179 and 181.