US2371647A - Degreasing process - Google Patents

Description

Patented Mar. 20, 1945 nnoaansmc PROCESS Wilbur H. Petering, Metuchen, and Adam G. Aitchison, Westfield, N. J., assignors to West--, vaco Chlorine Products Corporation, New York, N. Y. a corporation of Delaware No Drawing. Application December 28-, 1943,

Serial No. 515,990

9 Claims. ('01. 134-31 solvent, so that the article brought into contact H with thesolvent vapor will have a suificiently low temperature to cause the desired condensation of This invention relates to an improvement in degreasing processes and other processes wherein chlorinated solvents are used as solvent media. It comprises particularly a method of degreasing articles with surfaces of a metal having a decomposing efiect on chlorinated grease solvents, such as aluminum goods, wherein grease is removed from such a metal surface by a chic-.

rinatedsolvent of a type normally subject to,

such decomposition, containing a minor amount of certain oxygen-containing organic compounds, advantageously esters, which restrain such decomposition.

This application is a continuation-in-part of our co-pending application,

386,544 filed April 2. 1941.

.The removal of grease films from metal sur- Serial Number solventon itsfsurface in the vapor. chamber.

, As'noted, numerous solvents have, been em ployed in degreasing operations. .nmongthese, solventsofv thechlorinated hydrocarbon type,

including both saturated, compounds such as carbon tetrachloride, ethylenedichloride, et cetera,

and unsaturated compounds such astrichlorethylene, perchlorethylene, et cetera, have been widely employed because of their high greasesolvent capacity and their low inflammability.

' Several of these chlorinated compounds are confaces by the application of grease solvents has been widely practiced during recent years. Numerous solvents have been employed, and numerous variations of the degreasing procedure have been suggested. In one method of operating, the metal article to be degreased is brought into contact with the solvent in the liquid phase. This may be accomplished by immersing the article in a large body of the solvent, or by spray- ,ing the solvent on the surface of the article. In

another common method of degreasing, known generally as vapor-phase degreasing, a body of solvent is maintained atthe boiling point and in 1 communication with a chamber adapted to contain a large body of the solvent vapor. The

article to be degreased is brought into contact with this body of vapor, and causes condensation of the solvent on the greasymetal surface. The condensed solvent removes grease and oil from the metal surface and drips off, usually returningto the boiling body of the solvent. With it goes dirt, adheringto the greasy surface. This dirt often includes metal chips. In vapor-phase degr easers of this type, it is conventional to provide cooling coils or some equivalent arrangement near the top of the solvent vapor chamber to prevent or minimize the escape of vapors and loss of solvent from the system. Solvent condensed by such cooling coils is generally substantially uncontaminated by either grease or dirt, and is usually returned to a clean solvent.

reservoir, which, in many cases. is arranged to overflow into the "solvent boiling compartment.

In some cases, even when employing vapor-phase degreasing, the article to be degreased is preliminarily dipped in a body of liquid solvent. When hot solvent is employed for-this purpose. there is sometimes a subsequent dip in cooler sidered non-inflammable. Of the available solvents of this type, trichlorethylene-is probably most widely used in degreasing. However, it is seldom used without the addition of some (stabilizer, adapted to prevent or retard its decomposition during storage and normal use. This so-called normal type of decomposition is promoted by light and oxygen. The actionof light and oxygen is accelerated by heat. Several stabilizers are available and commonly usedfor the purpose of inhibiting this decomposition.

These previously known stabilizers are, efiective when present in minute amounts in preventing decomposition "of trichlorethyleneand other degreasing solvents during storage and during the usual degreasing operations applied to, ferrous metals and several other metals. However.

when the metal to be degreased is aluminum or analuminum alloy, it has been found that a different type of decomposition of the solvent is encountered, and that this type of decomposition may occur even in the presence of stabilizers which are effective in all other cases. This form of decomposition. of chlorinated solvents in contact with metallic aluminum ,or its alloys is evidenced by a rapid rise in acidity (largely hydrochloric acid by pronounced discoloration of the solvent, and, in the advanced stages of decomposition, by the formation of a tarry or gummy mass in the solvent.

Efforts have been made heretofore to eliminate or minimize this type of decomposition by various special practices. these practices have been partially successful, in that they have reduced formation of the abovementioned tarry and gummymasses, in the solvent. However. when such results have been obtained, they have been accompanied by dudesirable'results of other types. such as increased It does not appear that prior, to this invention there has been any satisfactory,

acid development.

In some instances,

' acid and otherdeleterious decomposition products, is prevented by. the addition to the chlorinated hydrocarbon solvents of certain oxygencontaining organic compounds such as organic esters.

The organic esters have many advantages for the present purposes. First, as a class, they are usually soluble in chlorinated hydrocarbons and are compatible with such solvents under service conditions. Under ordinary'conditions they do not react with the chlorinated hydrocarbons to form sludge or other deleterious by-products'. Likewise, the esters do not attack metals. They are inexpensive and have boiling points covering a wide range which permits selection 01' an ester having a boiling point near that or the solvent to be stabilized.- In other words, the esters efl'ectivelystabilize chlorinated hydrocarbons against "metal-induced decomposition without any deleterious'actio'n, both during storage and under service conditions. The following esters are illustrative oi the types that are efl'ective in the practice of our invention:

Ester Formula 1. N-hutyliormatc H oicnmcm .2. Ethyl acetate CHIC I I V. 0cm

' l o :i. Isopropylsostate CHIC ocmcnm 4. Amylsoetatc 0E|O\ I 00:31.

OCH! 6. Dlmethylcarbonste 0=='C\ OCH:

7 001K! 6. Trlethylortho iormaie HC-Othm 0 0 7. Dimethyl oxalate GHQ-EL-PL-OCH:

OCH:

8. Trimothylotthoaostate CHE-OCH:

0 I 9. Diethyl oxalate H;C:OECOCQH| 0 H H g 10. Ethylmaloneie C-g- -0C;H|

alls solution to the problem of decomposition en- Ester Formula II C-O CsHl 11. Ethyl benzoste ll C0 CHSCHCHI l2. p-Amino isobutyl benzoate Ha v o is. n-Butyl enz me en orsin -00in.

where B: may be hydrogen or an organic radical such as an aliphatic, aryl, heterocyclic or alicyclic group and R: may be an organic radical such as 'an aliphatic, aryl, heterocyclic or alicyclic group.

These radicals may contain other substituents. The esters of ortho acids, esters of carbonic acid and esters of diand multi carboxylic acids may also be used.

In the case of esters prepared from aliphatic employ a wide variety of esters as noted above.

These oxygen-containing compounds are generally employed in minor amounts, advantageously in the order 01' 1 per cent of the amount of chlorinated solvent by weight. However, as the efl'ectiveness 01 these stabilizers varies to some extent with the type of compound employed, the particular percentage incorporated in the chlorinated hydrocarbon solvent may be varied to obtain the stabilization desired. Ordinarily it is advantageous to add definite molar percentages of the esters to the chlorinated hydrocarbon solvents. Howevenfor purposes of the present invention, the more ester present, the most eilective the composition in restraining this "metalinduced" decomposition. This seems to be true because these oxygen compounds unite chemically with the aluminum compounds that appear to cause the metal-induced decomposition and thus the more ester present the more stabilization obtained. For "metal-induced decomposition claimed in this application it is generally advantageousto use about 1 mol of oxygen compound per 99 mole oi' chlorhydrocarbon. However, this amount may be increased with proportionately greater stabilization against metal-induced decomposition.

Inthe practice of our invention, many and variousembodiments thereof may be employed. For instance, the chlorinated hydrocarbon solvent, in addition to the stabilizers described, may also contain one of the known stabilizers against norchlorinated solvent and the finely divided mal decomposition, as previously mentioned, such as aralkyl ethers of hydroquinone, described in Pitman Patent 2,319,261.

One specific advantage resulting from the addition of suitable esters to chlorinated de greasing solvents, as described hereinabove, is that the presence of a minor amount of the ester with the resulting decrease in metal-induced decomposition, permits operation of the degreasing equipment for a. longer period without the necessity of shutting down to clean out accumulations in the boiling compartment. As previously noted, the reactions involved in this metalinduced decomposition are somewhat obscure. One explanation of these reactions is that the accumulation of non-volatile oils removed from the work during the degreasing operation, may raise the boiling point (or range) of the liquid in the boiling compartment of the degreaser to such an extent that reaction sets in between the aluminum or other metal which has also been washed off the work. This waste metal accumulating in the liquid solvent has large effective surface areas which are highly reactive, especially at the increased boiling temperature of the dirty solvent. It may be that the large metal surface catalyzes the decomposition, or it is possible that aluminum chloride forms at the surface of the metaland that this compound is the active decomposing agent.

Whatever the mechanism of the metal-induced decomposition, it has been necessary to remove the accumulation of oily material and finely divided metal and metal compounds from the boiling compartment at frequent intervals. This involves additional labor, loss of production during the cleaning period, and loss of solvent. These diificulties are largely eliminated by operating in accordance with the present invention, and it has been found that a vapor-phase degreasing unit can be kept in operation when degreasing aluminum, for example, up to at least three times fore, when suitable oxygen-containing organic compounds are added to the solvent, as described hereinabove.

Similar advantages are obtained in liquidphase degreasing operations in which hot chlorinated solvents are employed.

In a specific example illustrative of a useful embodiment of the present invention, a degreasing solvent was prepared containing 99.0 parts by weight of stabilized trichlorethylene, and 1 part by weight of isopropyl acetate. This solvent was used in a vapor-phase degreasing operation of the type previously described for degreasing aluminum surfaces. No objectionable decompositionwas encountered, even after continuing the operations without cleaning out the boiling compartment of the degreaser for considerably longer than had been possible before the use of the ester in accordance with this invention.

These chlorinated solvents, such as trichlorethylene, containing minor amounts of organic in the, past as long as was permissible heretoesters, are particularly adapted for use in degreasing aluminumand its alloys. Such solvents are also useful in degreasing other metals, including zinc and magnesium and their alloys as well as iron, steel, copper, et cetera.

- While we have particularly described our invention hereinabove with respect to certain organic esters, it will be obvious to the skilled in the art that the invention is not limited to the specific examples shown, but may be practiced and embodied within the scope of the claims hereinafter made. I

What we claim is:

1. As an improvement in degreasing surfaces 1 of aluminum and its alloys with chlorinated hydrocarbon solvents normally subject to deterioration in the presence of aluminum, the improvement which comprises maintaining, in admixture with such chlorinated solvents, a minor amount of a carboxylic acid ester to inhibit such metal-induced decomposition thereof.

2. The method of claim 1, wherein said chlorinated hydrocarbon solvent is trichlorethylene.

3. The method of claim 1,wherein said chlorinated hydrocarbon solvent is perchlorethylene.

4. The method of claim 1, wherein the ester ,is an aliphatic ester prepared from an aliphatic carboxylic acid having less than six carbon atoms and an aliphatic alcohol having less than six carbon atoms.

5. The improved process for degreasing surfaces of metals of the class consisting of aluminum and its alloys having a decomposing effect on chlorinated hydrocarbon grease solvents, which comprises establishing a body of grease solvent in communication with a space adapted to receive vapors therefrom, said solvent comprising a major proportion of chlorinated hydrocarbon solvent, normally subject to decomposition in the presence of such metal surfaces,

and a minor proportion of a carboxylic ester.

having the property of restraining decomposition of such solvents in the presence of said metal surfaces, boiling said body of grease solvent and thereby maintaining a body of vapors thereof in said vapor space, contacting the metal surface to be degreased with said body of vapors and returning the solvent condensed by said metal to said boiling body of solvent, the amountof said' ester in said body of grease solvent being sufflclent to inhibit metal-induced decomposition thereof.

6. The method of claim 5, wherein the chlorinated hydrocarbon solvent is trlchlorethylene.

7. The method of claim 5, wherein the chlorinated hydrocarbon solvent is perchlorethylenc.

8. The method of claim 5, wherein the ester is isopropyl acetate.

9. The method ofclaim 5, wherein the ester is an aliphatic ester prepared from an aliphatic carboxylic acid having less than six carbon atoms andan aliphatic alcohol having less than sit carbon atoms.

- WILBUR H. PETERING.

ADAM G. AI'I'CBIBON.