US2371645A - Degreasing process - Google Patents

Description

Patented Mar. 20, 1945 DEGBEASING PROCESS Adam G. 'Aitehison, Westfleld, and Wilbur H.

Peterlng, Metuchen, N. 1., assignors to Westvaco Chlorine Products Corporation, New York, N. Y.. a corporation of Delaware No Drawing. Application September 16, 1943,

Serial No. 502,648

11 Glalms.

This invention relates to animprovement 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 chlorinated sol- I vent of a type normally subject to such decomposition, containing a minor amount of certain oxygen-containing organic compounds, advantageously ethers and oxides, which restrain such decomposition.

This application is a continuation-in-part of our copending application, Serial Number 386,544, filed April 2, 1941.

. Theremoval of grease iilms from metal surfaces 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 spraying 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 at the boiling oint andin 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 greasy metal surface. The condensed solvent removes grease and oil from the metal surface and drips oii, usually returning to the boiling body of the solvent. With it goes dirt, adhering to the greasy surface. This dirt often includes metal chips. In vapor-phase degreasers 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 vaporphase 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 sometimesa subsequent dip in in degreasing operations. Among these, solvents of the chlorinated hydrocarbon type, including I .both saturated compounds such as carbon tetrachloride, ethylene dichloride. et cetera, and unsaturated compounds such as trichlorethylene, 'perchlorethylene, et cetera, have been widely employed because of their high grease-solvent capacity and their low inflammability. Several of these chlorinated compounds are considered noninflammable. Of the available solvents of this type, trichlorethylene is probably most widely used in degreasing. However, it is seldom used v without the addition of some stabilizer, adaptused for the purpose of inhibiting this decomposition. I

These previously known stabilizers are effective when present in minute amounts in preventing decomposition of trichlorethylene, for example during storage and during the usual degreasin operations applied to ferrous metals and several other metals. However, when the metal to be degreased is aluminum or an aluminum 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,jin 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 this type of decomposition by various special practices. In some instances, these practices have been partially successful, in that they have reduced formation of the above-men tioned tarry and gummy masses from the solvent, for example. However, when such results have been obtained, they have been accompanied by-undeslrable results of other types, such as increased acid development. It does not appear that prior to this invention there has been any satisfactory solution to the problem of decomposition encountered with the chlorinated solvents which are susceptible thereto, such as trichlorethylene, perchlorethylene, et cetera, when they ar kept in contact with aluminum ,or its alloys having a decomposing influence at high temperatures.

The present invention is based on our discovery that this metal-induced decomposition of chlorinated solvents, with production of hydrochloric acid and other deleterious decomposition products, is p v nt y t addition to the group, or a substituted ali hatic or aryl group. chlorinated hydrocarbon solvents of certain oxy- As noted below R and B may be substituted with gen-containing organic compoun Such as hydroxy, alkoxy. or with other substitutes such ganic oxides and ethers. For instance, that. all? as amino groups.

hatio ethers or oxides are particular y sui a e 5 For this purpose. Likewise, certain derivatives of complex and 03nd these ethers and oxides, such as amino-ethers, Ethyl Cellosolve hydroxy ethers, et cetera, may be employed with advantage in stabilizing chlorinated hydrocarbon HJFOH solvents against metal-induced decomposition. l a

The ethers and oxides also have other advan- Butyl 99110501 tages for the present purposes. First, as a class, r othey are readily soluble in chlorinated hydrocarmake}! bons and are completely compatible with such awe-idol solvents under service conditions. Under ordi- 5 nary conditions they do not react with the chlorinated hydrocarbons to form sludge or other deleterious by-products. Likewise, the ethers and G 1 d oxides do not attack metals since they are neither lycer he methyl ether alkaline nor acidic. In fact, the aliphatic ethers o CH'OCHI and oxides are themselves substantially inert and HOB stable under most conditions. In other words, HOCH,

the aliphatic ethers and oxides effectively stabmze chlorinated hydrocarbons against metal Glycerineamonomethyl ether induced decomposition without any deleterious x mon action, both during storage and under. service conditions. mocm We have used both straight chain and branched-chain ethers and oxides and obtained y r yl a cohol effective stabilization against metal-induced de- 30 '0 composition of the chlorinated solvents; The following ethers are illustrative of the types or ethers 1 that are eflective in the practice of our invention: PC3103 simple ethers Glycerine formal 36 0 Diethyl ether DialLvl ether onion Di-n-propyl ether Di-n-butyl ether l Di-isopropyl ether Diphenyl ether Hon on, or CH Ethers may be-used which have the general CH 0 type formula ROR where R and R mag be an aliphatic radical, either saturated or unsa ated, or an aryl group, or a substituted aliphatic or Glycenne Mural aryl radical. R and B may be the same or may 3K 0 be different radicals. 0 no on 5-0 1] II 1 no on Inner ethers or oaiides or CH ii a Propylene oxide o Ha I Hr-O moxane In the broad practice of our invention, we may 0 employ a wide variety of ethers and oxides as Q noted above. The simple symmetrical and the C CH? unsymmetrical ethers, the inner ethers or oxides,v m m substituted ethers and oxides particularly those containing hydroxy and-alkoxy, amino groups, Isobutylene oxide and the complex ethers having a number or sub- 0 on; stltuents but all containing the ether linkage are 1126/ all efiective. These oxygen-containing compgund: are gesalnerglltylemplioyedfili minor avanageouy eorero perceno e mphenylene oxide 0 amount of chlorinated solvent by weight. However, as the efiectiveness or these stabilizers varies to someextent with the type of compopnd employed, the particular percentage incorporated in the chlorinated hydrocarbon solvent may be 66 These ethers have the generic type formula varied to obtain the stabilization desired. Ordinarily it-is advantageous to add definite molar 0 Q percentages ofthe ether or oxides to the chlorior nated hydrocarbon solvents. However, for puro 10 poses oi the present invention, the more ether or oxide compound present, the more efiective the \o/ composition in restraining this metal-induced decomposition, This seems tobe true .because where R. and R may be a divalent aliphatic radi these oxygen compounds unite chemically with cal, either saturated or unsaturated, or an aryl (I the aluminum compounds that appear to cause asvaocs the metal-induced decomposition and thus the more oxygen compound present the more stabilization obtained; For "metal induced" decomposition claimed in this application it is generally advantageous to use about 1 mol of oxygen compound per 99 mols of chlorhydrocarbon. However, this amount may be increased with propdrtionately greater stabilization againstinetalinduced decomposition.

In the practice of our invention, many and various embodimentsthereof may be employed.

For instance, the chlorinated hydrocarbon. solvent, in addition to the stabilizers described, may also contain oneof the known stabilizers against normal decomposition, as previously mentioned,

such as aralkyl ethers of hydroquinone, described I in Pitman Patent 2,319,261.

'In one useful embodiment of the invention, propyl ether is employed as the oxygen-containing'organic compound. This ether is especially suited for the purpose, because in small amounts it tends to vaporize with the trichlorethylene, and therefore tends to remain with the solvent,

both as liquid and as vapor, during degreasing operations and purification of the solvent in solvent-extraction, dry-cleaning, and similar operations. For example, on distilling the solvent out of the boiling compartment, little, if any of this volatile ether is lost. The etherevaporates and rec'ondenses with the solvent. The propyl ether is highly effective in preventing the metal-induced type of decomposition of trichlorethylene and similar chlorinated solvents, and its moderate cost is another favorable factor. In general,

when working with any specific chlorinated solvent,- it is desirable to employ an ether or oxide forming a mixture which may be distilled with out loss of stabilizer.

One specific advantage resulting from the addition of suitable ethers and oxides to chlorinated embodiment of the present invention, a degreesing solvent was prepared containing 99.0 parts by weight of stabilized trichlorethylene, and 1 part by weight of propyl other. This solvent was used in a vapor-phase degreasing operation of the type previously described for degreasing aluminum surdegreasing solvent, as described hereinabove, is

that thepresence of a minor amount of the ether .or'oxide, with the resulting decrease in metalinduced 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 metal-induced decomposition are somewhat ob-' scure. One explanation of these reactions is that th 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 chlorinated solvent and the finely divided 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 thedirty 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 metal and that this compound is the active decomposing agent.

Whatever the mechanism of the metal-induced decomposition, it has been necessary in the past 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 difiiculties are largely eliminated by operface's. No objectionable decomposition was en-' countered, ,even after continuing the operations without cleaning out the boiling compartment of the degreaser for considerably longer than had beenpossible before the use of the ether in accordance with this invention.

In the operation justdescribed, it was found that the ether vaporized with the trichlorethylene, was condensed, and returned to the liquid compartments with the trichlorethylene.

These chlorinated solvents, such as trichlorethylene, containing minor amounts of ethers or oxides,*are particularly adapted'for use in degreasing aluminum and 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 ethers and oxides, 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.

What weclaim is:

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

2'. As an improvement in degreasing surfaces of aluminum and its alloys with chlorinated hydrocarbon solvents normally subject to deterioration in the presence of aluminum,.the improve-t ment which comprises maintaining, in admixture with such chlorinated solvents, a minor amount of an organic inner ether to inhibit such metal-"1 induced decomposition thereof.

3. As an improvement in degreasing surfaces is propyl ether.

oi 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 maior proportion of chlorinated hydrocarbon solvent, i normally subjectto decomposition in the presence of such metal surfaces, and a minor proportion of an organic ether having the property of restraining decomposition of such solvents in the presence of saidmetal 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 decreased with said body of vapors and returning the solvent condensed ADAM G. AITCHISON. wmaon H. PE'IERING.