US2436772A - Solvent for degreasing iron and aluminum - Google Patents

Description

iatented Feb. 24, 948

UNITED STATES PATENT- OFFICE SOLVENT FOR nii fiit isnve TRON AND V Walter Klabunde, Niagara Falls, N. Y., assignor to E. I. du Pont deNemours & Company, Wilmington, Del., a corporation of Delaware 'No Drawing. Application August 24, 1945,

a Serial No. 012,552 a This invention relates to the Prevention of trichlorethylene decomposition as catalyzed by the presence of aluminum or iron, particularly as is encountered in the metal vapor de reasing.

It is known that trichlorethylene when exposed to air, light, and heat decomposes by oxidation with the formationoi dichloracetyl chloride, hydrochlorie acid, and phosgene. Several types oi stabilizersare commonlyused to inhibit the decomposition ,of trichlorethylene by oxidation. However, in. metal degreasing where the solvent often is subjected to higher temperatures, trichlorethylene can'undergo a condensation type decomposition to form hydrochloric acid, together with a resinous material.- .In the presence of aluminum or iron, the hydrochloric acid formed by either type decomposition reacts with these metals to form the chloride salts which act as catalysts for the condensation reaction. Thus, when the condensation reaction takes place in a metal degreaser, where the chips of these metals are often heaped in the boiling solvent, it often becomes autocatalytic, i. e., where aluminum is present, the hydrochloric acid forms aluminum chloride which decomposes more trichlorethylene to form more catalyst. When this occurs, the solvent decomposes very vigorously with the evolution of large quantities of hydrochloric acid and the formation of a tarry or gummy mass in the solvent.

Eflorts have been made in the past to combat this type of decomposition of the trichlorethylene by the addition of water to the solvent. This practice has only been partially successful, primarily due to the low solubility of water in trichlorethylene. Certain alcohols have also been used in this connection. However, the addition of alcohols increases the solubility of hydrochloric acid in trichlorethylene, and this is undesirable in metal degreasing because of corrosion difficulties encountered.

The object of the present invention is to provide a stabilizer for trichlorethylene which will inhibit the condensation type of decomposition which is catalyzed by the presence of aluminum or iron. Another object of this invention is to provide a condensation inhibitor for trichlorethylene which is neutral to the solvent and can be readily recovered with the solvent and need only be present in relatively small concentration. A further object is to degrease iron and aluminum articles with chemically stable trichlorethylene. Still other objects will be apparent from the ensuing description.

The present invention is based on my discovery 3 clai s" (01. 252-171) that certain alkylesters of nitrogen acids inhibit the decomposition of trichlorethylene exposed to higher temperatures and which is catalyzed by the presenceof aluminum or iron. These esters are alkyl. nitrates in which the alkyl group contains from 2 to 4 carbon atomsand the alkyl nitrites in which the alkyl group contains 3 to 6 carbon atoms. In other words, the stabilizers of my-invention are those having the formulas CnH2n+1NO3, where n is a whole number from 2 to 4; and CnH2n+1NO2, where n is a whole number from3 to The high volatility of these compounds is advantageous, inasmuch as they can be readily recovered with the trichlorethylene in a distillation step as in metal degreasing. Examples of these compounds, which are especially suited to this purpose because of their boiling points, are ethyl nitrate, B. P. 88 C., and isoamyl nitrite, B. P. 99 C.

Examples of alkyl nitrates and nitrites suitable for the practice of my invention are: ethyl nitrate, propyl nitrate, isopropyl nitrate, n-butyl nitrate, sec-butyl nitrate, ter-butyl nitrate, propyl nitrite, isobutyl nitrite, n-butyl'nitrite, n-amyl nitrite, isopropyl nitrite, and n-hexyl nitrite.

These esters of nitric and nitrous acids are efiective for the purposes described in concentrations of about 0.02 to 1 per cent by weight. Generally, excellent results are obtained at a concentration of around 0.1 per cent by weight.

Especially well suited for operations wherein it is desired to recover stabilized trichlorethylene by distillation are ethyl nitrate (B. P. 88 C.)'

and isoamyl nitrite (B. P. 99 C.) as these readily distill over with the trichlorethylene. The other nitrates and nitrites above described have boiling points within the range of 57 to 129 C. and are, therefore, distillable with trichlorethylene to a considerable extent.

Generally the solvent is used under conditions where decomposition by oxidation can also occur, and for this reason an antioxidant may also be incorporated in the solvent for optimum results.

I have demonstrated the stabilizing effect of the alkyl nitrates and nitrites by the following test. Separate portions of trichlorethylene were stored in the absence of air in closed glass containers under identical storage time and condi-- tions. Certain portions, as shown by the following table, contained 0.04 g. per 100 cc. of hydrogen reduced iron powder (about 200 mesh size) and 0.2 g. per 100 cc. of 40 mesh size aluminum powder, respectively, with and without the addition of 0.1 per cent by weight of the nitrate 3 2,436,772 or nitrite, and one portion consisted of the triapparatus may be used for this purpose, in which chlorethylene alone. Other portions consisted the solvent temperature may vary from room of trichlorethylene and 0.1 per cent by weight temperature to the boiling point. The stabilized of alkyl nitrate or nitrite. At the end of the trichlorethylene may be applied to the metal storage period, the samples were analyzed for 5 articles, for example, by dipping, spraying, or chloride ion, "thereby todetern'iine the degree of tibndensaition' of vapor an-the articles.

decomposition which occurred. The"following Tclai'm: results were obtained: 1. A solvent for degreasing iron and aluminum cbmprising trichlorethylene containing 0.02 to Tri mor. 151033 'rby weig ht otan alkyl ester of a nitrogen e y e e SubstancesAdded Content acid selected from the group consisting of alkyl (fngmolm) nitrates containing 2 to 4 carbon atoms and alkyl -'-nitrites*iconta g 3 to 6 carbon atoms, said None v fester servnrg to inhibit the condensation reac- Iron and1soamyln1tritc.---

*ftions' oftrichlorethylene catalyzed by the afore- Alummum 60D i V Aluminum andisoamyl nit! 2157 w d fi. %ggnglirgttlrll;fgi.tfi.fi.e 1, 'lrhe solvent of claim 1 wherein said alkyl 8 u: A luminum and ethyl iiiiiii,--- jljl 17 f; iSBt y nitrate- 9 hthylmtrate -'-3.'The-'so1vent of claim 1 wherein said alkyl 7 t v g 220 ester is isoamyl nitrite. In the practiceof thisi inverition'iniany-and various embodiments thereof may 'be employed. v For instance, the trichlorethyleire' in:addition to CES EITED the alkyl nitrate or 'nitritezmaymlso -:contain one r l of the known .stabilizer agains' t1heoxidation mi -2 ifigggig record in the decomposition reactions.

While trichlorethylene stabiliied i by theZa'd- UNITED STATES PATENTS dition of thealkyl nitrat'e'sf' and' nitrites is"well m Name Date suited for the various'u'ses of' thisHch'omrohy- -;99* ;q1r1 -:Ca- 1is1e A 1 1 935 drocarbon solvent, theupresent invention is:espe- 2129 7 3666 Wachter -JSep't. 29, 1942 ial1y us ul in m ta "d er asin bp ra s i-253715646 -'-Peter-ing=et a1. Mar. 20 1945 'wherein iron 'or :aluminum' farticleseare washed with trichlorethylene rto remove-inland sgrease, FOREIGN PATENTS particularly "after machining operations. Number Country -Date warious known metal idegreas'ingtprocesses fiand 188,373 eGreat' Britain -..:Apr. 20, .1922