US2371644A - Degreasing process - Google Patents

Description

Patented Mar. 20, 1945 DEGREASING PROCESS Wilbur H. Petering, South Charleston, W. Va and Adam G. Aitchison, Westfleld,

N. 1., minors to Westvaoo Chlorine Products Corporation,

New York, N. Y.,

a corporationoi' Delaware No Drawing; Application October 1, 1942,

Serial No. 400,451 I 19 Claims.

This invention relates to an improvement in degreasing processesand other processes wherein chlorinated solvents are used as solvent media: and 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 solvent of a type normally subject to such decomposition, containing a minor amount of certain oxygen-containing organic compounds,

advantageously alcohols, which restrain such decomposition.

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

The removal of grease films 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 point and in communication with a chamber adapted to contain a large body of the solvent vapor. The article t 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 on, usually returning to the boiling body of the solvent. With it goes dirt, et cetera, adhering to the greasy surface. This dirt often includes metal chips, et cetera, 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 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 solvent,

so that the article brought into contact with the solvent vapor will have a sufliciently low temperature to cause the desired condensation of solvent on its surface in the vapor chamber.

As noted, numerous solvents have been employed in degreasing operations. Among these.

. solvents of. the chlorinated hydrocarbon type, in-

cluding 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 noninfiammable. 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 normall type of decomposition is promoted by light and oxygen, and their action is accelerated by heat.

Several stabilizers are available and commonly used for the purpose of inhibiting this decompo-.

sltion.

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 degreas'ed is aluminum or an aluminum alloy, or certain other metals not containing substantial quantities of aluminum, it has been found that a a different type of decomposition of, the solvent is encountered, and that this type of decomposi tion 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 metallicaluminum or other metals having a. specific decomposing eflect on the solvent 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.

This type of decomposition takes place principally when the solvent is in the liquid phase and at elevated temperatures. It is most commonly encountered in the boiling compartment of I a vapor-phase degreaser where, as previously noted, the solvent is maintained at the boiling point, and where thereis usually a collection of grease and finely divided metal chips, filings, bufiings, et cetera, removed from the metal surfaces during treatment. When this accumulation includes turnings, chips, or other particles of aluminum (and to some extent, certain other metals) the described metal-induced decomposition is quite pronounced, unless special precautions are taken. This may be attributable, for example, to the catalytic or dechlorinating action of aluminum and its compounds on the hot solvent Efforts have been made heretofore to eliminate or minimize 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-mentioned tarry and gummy masses from the solvent, for example. However, when such results have been obtained, they have been accompanied by undesirable 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 eliminating the special metal-induced type of decomposition encountered with the chlorinated solvents which are susceptible thereto. such as trichlorethylene, perchlorethylene, et cetera, when they are kept in contact with aluminum or other metals 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 completely prevented by the addition to the chlorinated hydrocarbon solvents of certain oxygen-containing organic compounds, such as organic oxides, oximes, ethers and alcohols. For instance, the aliphatic alcohols are particularly suitable for this purpose and various monohydric and polyhydric aliphatic alcohols may be advantageously employed as the stabilizer in the practice of this invention. Likewise, certain derivatives of these alcohols, such as amino-alcohols, mono-alkyl ethers of glycol, et cetera, may be employed with advantage in stabilizing chlorinated hydrocarbon solvents against metal-induced decomposition.

In particular. the monohydric aliphatic alcohols are very effective stabilizers for chlorinated hydrocarbon solvents. As a class, these alcohols have many advantageous properties which render them particularly suitable for the present purposes. For instance, trichlorethylene and other unsaturated chlorinated hydrocarbon solvents containing minor amounts of such alcohols are stable against auto-oxidation, as well as metalinduced decomposition. Many of these alcohols are volatile with the chlorinated hydrocarbons and protect the solvent in the vapor phase; the alcohol remaining with the solvent when distilled and condensed.

The monohydric aliphatic alcohols also have other advantages for the present purposes. First, as a class, they are readily soluble in chlorinated hydrocarbons and are completely compati ble with such solvents under service conditions. Under ordinary conditions they do not react with the chlorinated hydrocarbons to form, sludge or other deleterious lay-products. Likewise, aliphatic alcohols do not attack metals; they being neither alkaline nor acidic. In fact, the aliphatic alcohols are themselves substantially inert and stable under most conditions. In other words, the aliphatic alcohols effectively stabilize chlorinated hydrocarbons without any deleterious acboth during storage and under service conons.

Thus, in preventing metal-induced deteriorzi:

tlon of chlorinated solvents (both saturated and unsaturated chlorinated hydrocarbons), we usually employ aliphatic alcohols as the stabilizer.

In general, we have'found that the monohydric alcohols are more effective than the polyhydric alcohols for the purpose of this invention. Accordingly, we usually employ the monohydrlc alcohols in the practice of this invention. In doing so, we have used both straight-chain and branch-chain alcohols and obtained effective stabilization against metal-induced decomposition of the chlorinated solvents. With the primary aliphatic alcohols we have found that straightchain alcohols, such as ethanol, n-propanol, nbutanol, n-amyl alcohol, n-hexanol, n-octanol, n-decanol, lauryl alcohol and heptadecanol, are particularly effective as stabilizers. Also primary alcohols in which the aliphatic group is unsaturated, such as allyl alcohol, et cetera, are also effective. Likewise, we have found that branchchain alcohols are also effective stabilizers and that their effectiveness varies with the branching of the aliphatic chain. For instance, isobutanol, S-methylbutanol (isoamyl alcohol), 2- methylbutanol, Z-ethylhexanol and 2-ethylbutanol are all good stabilizers. Likewise, secondary alcohols, such as l-ethylpropanol, l-methylbutanol and 1,3-dimethylbutanol, are good stabilizers against metal-induced decomposition but are not as effective as the primary alcohols.

Tertiary aliphatic alcohols, such as tertiary amyl 46 propylene glycol, et cetera, are effective stabilizers. These dihydroxy aliphatic alcohols may be represented by the following general formula:

HO-R-OH 50 wherein R represents a divalent aliphatic group.

I the following generic formula wherein R represents an alkyl group, such as methyl, ethyl, propyl or butyl. As shown by the above formula, these stabilizers contain an alkoxy group attached to the aliphatic chain of a monohydric alcohol.

All of the stabilizers shown are aliphatic alco-' hols and as a class may be represented by the following generic formula X-R-OH wherein R represents a divalent aliphatic radical and X represents a substituent of the class consisting of alkyl, amino-alkyl, alkoxy and hydroxy groups, hydrogen and other substituents. That is, as the stabilizer, we may employ aliphatic alcoacme hols carrying other substituents attached to the aliphatic group. as well as the simple monohydric aliphatic alcohols.

However, our broad invention is not limited to the use 01 aliphatic alcohols as the stabilizer. We may also employ other oxygen-containing compounds which are capable of preventing metalinduced decomposition of chlorinated hydrocarbon solvents. For instance, various organic oxides, such as ethylene oxide, propylene oxide. dioxane, etc., are also effective stabilizers and have been used in certain embodiments 01' our invention. Further, oximes, such as dimethyl glyoxime, alpha-benzyl dioxime, acetaldoxime, acetoxime, et cetera, are also effective. oximes also contain a hydroxyl group but it is attached to the nitrogen atom of the oxime. They may be used as the stabilizer and in fact they have been successfully used in certain embodiments of our invention.

In the broad practice of our invention these oxygen-containing compounds are generally employed in minor amounts, advantageously in the order of 1 per cent of the amount of chlorinated solvent by weight. However, as the eflectiveness of these stabilizers varies to some extent with the type of compound employed, the particular percentage incorporated in the chlorinated hydrocarbon solvent maybe varied to obtain the stabilization desired. However, for purposes of the present invention, the more alcohol or other oxygen compound present, the more effective the composition in restraining this metal-induced" decomposition. This seemsto betrue because the oxygen compounds unite chemically with tie aluminum compounds that appear to cause 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 proportionately reater stabilization against metal-induced decomposition. If the solvent is used under condi-' tions where both metal induced decomposition and auto-oxidation are encountered, the alcohol or other oxygenated compound must be used in a balanced concentration -for optimum results.

That is, in the practice of our inventlommany and various embodiments 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 normal-decomposition, as previously mentioned, such as aralkyl ethers of hydroquinone, described in Pitman Patent 2,319,261.

In one useful embodiment of the invention, isoamyl alcohol is employed as the oxygen-com taining organic compound. This alcohol is especially suited for the purpose, because in small amounts it'forms a constant-boiling mixture with 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 of a vapor-phase degreaser to permit cleaning of this compartment, little, if any, of the alcohol is lost. The alcohol evaporates and recondenses' with the solvent. It has also been found that isoamyl alcohol is highly effective in preventing the metal-induced type of decomposition of trichlorethylene and similar chlorinated solvents,

These and its moderate cost is another favorable factor. Also, n-butanol, and n-hexanol are advantageous from the standpoint of, formation of these con-,

stant-boiling compositionaa't low concentrations 5 of alcohol, and, in preventing metal-induced decomposition 0! chlorinated solvents. In general, the primary alcohols are most effective in preventing the metal-induced'decomposition. Secondary alcohols also produce good results. The tertiary alcohols are less effective. The polyhydric alcohols,such as the ethylene glycols and glycerine, also have a substantial stabilizing effect, and are partlcularlyadapted for use with the less volatile chlorinated solvents. In general, when working with any specific chlorinated solvent, it is desirable to employ'an alcohol orother oxygen-containing compound forming a mixture which may be distilled without loss ofstabilizer.

Organic compounds having both alcoholic and amino characteristics may be employed. The

aliphatic alcohol amines maybe used for this purpose, although somewhat larger amounts are required than with the simpler and less expen-v sive alcohols. The compounds, 2-,aminoij2-methyl propane] and 2-aminoblitanol, are soluble enough in chlorinated solvents tobe useiul alone; ,suffi: cient of them can be" dissolved injthe solvent to give 1 the requireddeg'ree of stabilization Alcohols wit-bother substituentsthan the amino group may also be utilized. 1 j

- One specific advantage resulting from, theiaddltion or suitablealcohols antifs'ijrnilar compounds to? chlorinated degreasing olve n'ts," as described hereinabovel isllithat the: once one minor amountbfox'ygn T 1, .n 'mscuni wit e resulting 1 decrease n metal-induce decompose tion', pern its opration' of" the deer work durihg' thehegiieas the boiling point (or ife. boiling wmpamse" extent"thatreacti I rinated solvent and fine or other metal wine worlefi-ff lhis was liquid solvent h'asflarge ii whicharehighly reactive;"espe ejia lly v creased boiling temperature .01 f,th'e"jdirt so It may'be thatwtheflqi e meta ana;

the *boiling *eql iparimggntnt "frequent?intervals. This 1 involves additiona ab'onflo of production during the: cleaning These di fiicultiesf are ,1 ating' in accordance wi and it has-been foun ne' j q ii. ment for a lonser perlodwithou the ecessit r degreasin operations in which hot chlorinated solvents a e employed.

In a specific example illustrative of a useful embodiment of the present invention, a decreasing solvent was prepared containing 99.0 parts by weight of stabilized trichlorethylene, and 1.0 part by weight of n-butyl alcohol. .This solvent was used in a vapor-phase degreasing operation of the type previously described for degreasing aluminum surfaces. Naobiectionable decomposition was 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 alcohol, in accordance with this invention.

In the operation Just described, it was found that the alcohol vaporized with thetrichlorethylene, was condensed, and returned to the liquid compartments with the trichlorethylene.

These chlorinated solvents, such as trichlorethylene, containing minor amounts of alcohols or other suitable oxygen-containing organic compounds, are particularly adapted for use in degreasing aluminum and its alloys, and metals which tend to cause metal-induced decomposition, as described in our copending application, Serial Number 386,544. Such solvents are also useful in degreasing other metals, including zinc and magnesium and their alloys as well as iron. steel, copper, et cetera, under conditions causing normal decomposition.

What we claim is:

1. As an improvement in degreaslngsurfaces of aluminum and it 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 monohydric aliphatic alcohol suillcient to inhibit such metal-induced decomposition thereof.

2. An improved process of degreasing surfaces of metals of the class consisting of aluminum and its alloys having a decomposing 'eifect on chlorinated hydrocarbon grease solvents, which comprises contacting such surfaces with a chlorinated hydrocarbon grease solvent containing a minor amount of an aliphatic alcohol, said chlorinated hydrocarbon solvent being normally subject to decomposition in contact with such surfaces and said aliphatic alcohol having the property of restraining decomposition of such solvents in the presence of said metal surfaces, the amount of said alcohol being sufllcient to inhibit such metal-induced decomposition of said chlorinated admixture therewith a minor amount of a monofl hydric aliphatic alcohol suflicient to inhibit the said metal-induced decomposition thereof.

4. The improved process of degreasing surfaces of metals of the class consisting of aluminum and proportion of oxygen-containing organic com pound having the following formula K n-0H wherein R represents a divalent aliphatic radial and X represents a substituent of the class consisting of hydrogen, alkyl, amino-alkyl, alkoxy and hydroxygroups and 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 amount ofsaid oxygen-containing compound in said body of grease solvent being sufficient to inhibit metal-induced decomposition thereof.

5. The method of claim 4 wherein said chlorinated hydrocarbon solvent is trichlorethylene.

6. The method of claim 4 wherein said oxygencontaining compound is n-butyl alcohol.

7. An improved method of degreasing surfaces of aluminum and its alloys with chlorinated hydrocarbon solvents normally subject to decomposition in the presence of aluminum, which comprises contacting such metal surface with a solvent composition comprising a chlorinated hydrocarbon grease solvent containing a minor amount of a monohydric aliphatic alcohol, the amount of said alcohol being sufllcient to inhibit metalinduced decomposition of said chlorinated solvent.

8. The process of claim 7 wherein said alcohol is volatile with the chlorinated hydrocarbon solvent and the metal surfaces are contacted with the solvent composition in the vapor phase.

9. An improved process of degreasing surfaces of aluminum and its alloys, which comprises boiling a solvent mixture comprising a major amount 0 of a chlorinatedhydrocarbon grease solvent, norits 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 mctal surfaces, and a minor mally subject to decomposition in the presence of aluminum, and a minor amount of aliphatic alcohol having the property of preventing decomposition oi such solvent in contact with such surfaces, contacting said metal surfaces with the vapors from the boiling solvent mixture to cause partial condensation thereof, and returning solvent condensing on said metal surfaces to the boiling solvent mixture.

10. The method of claim 9 wherein said chlorinated solvent is trichlorethylene.

11. The method of cla m 9 wherein said alcohol is n-butyl alcohol.

12. The method of claim ,9 wherein said alcohol is isoamyl alcohol.

13. The method of claim 9 wherein said chlorinated solvent is perchlorethylene.

14. As an improvement in methods of degreesing surfaces of metals of theclas consisting of aluminum and its alloys having a decomposing effect on chlorinated hydrocarbon solvents, the improvement which comprises contacting such metal surfaces with a solvent composition comprising a chlorinated hydrocarbon grease solvent and a minor amount of an oxygen-containing compound having the following formula X-R-OH wherein R represents a divalent aliphatic radical and X represents a substituent of the class consisting of hydrogen, alkyl, amino-alkyl, alkoxy and hydroxy groups and having the property of restraining decomposition of chlorinated hydrocarbon in the presence of said metals, the chlorinated hydrocarbon grease solvent being normally subject to decomposition in contact with such metal surfaces during decreasing and the amount oi said oxygen-containing compound being suiflcient to prevent such metal-induced decomposition of the chlorinated solvent. I

15. The improved process of claim 14 wherein said oxygen-containing compound is a monohydric aliphatic alcohol which is volatile with the chlorinated hydrocarbon grease solvent.

16; An improved process of decreasing suri'aces of aluminum and its alloys, which comprises heating a solvent mixture containing a major amount of a chlorinated hydrocarbon grease solvent and a minor amount of an aliphatic alcohol, to a tem.

perature suflicient to evolve mixed vapors of chlorinated solvent and alcohol, contacting said vapors with said surfaces. condensing the mixed yapor in contact on said surface and returning cohol.

WILBUB H. PE'I'ERING. ADAM G. AI'iCi-IISON.