US3079348A - Surfactants - Google Patents

Description

Edited rates i atent: @hfice 356749348 Patented Feb. 26, 1953 This invention relates to improvements in the art of cleaning objects, particularly those made of metal, glass, etc.

Broadly stated, the invention pertains to alkaline cleaning and, more particularly, to surfactants for use in alkaline metal cleaning baths.

An object of the invention is to improve the cleaning efficiency of alkaline metal cleaners.

Other objects of the invention will in part be obvious and will in part be disclosed hereinafter.

Alkaline cleaners are the most widely used means in industry for cleaning metal, glass, certain plastics, etc. They are primarily used to prepare metals such as steel, brass, and copper for plating, painting, enameling, rust proofing, pickling, and other operations. Such preparation includes the removal of various types of soil such as cutting oils, grinding, buffing, stamping, and drawing compounds used in various metal-forming operations, as well as rust preventatives, lubricating greases, and various forms of dirt. The alkaline cleaning solutions may be used for soaking, spraying, or electrolytic types of cleanmg. Of these, the soaking or tank cleaning technique is most important because of its widespread use in industry.

In the soaking method of cleaning, the metal article to be cleaned usually is dipped in or slowly transported through a hot alkaline solution with little or no agitation present. The cleaning solutions employed generally are made of materials consisting of between about 88 to 99 percent by weight of various alkalies, such as caustic soda, sodium metasilicate, soda ash, trisodium phosphate, and tetrasodium pyrophosphate, and from about 1 to 12 percent by weight of a surfactant. Previously, the most widely used surfactants for this purpose have been alkylaryl sulfonates and rosin soaps. Usually, the concentration of the cleaning materials (alkali plus surfactant) in the tank or bath is maintained between 2 and percent of the cleaning solution.

As oil, grease, and other soils are caused to be separated from the part being cleaned in the tank, a scumlike layer collects at the top of the bath. If the surfactant employed is not thoroughly soluble in the hot alkaline solution, it also will tend to accumulate in this surface layer. When the accumulation of scum in the surface layer becomes so great that it tends to coat the otherwise clean part as it is withdrawn from the bath, it becomes necessary to skim the soil and undissolved surfactant from the top of the tank. Each time this is done, a considerable amount of the surfactant is removed and, of course, this tends to lower the concentration of the effective cleaning agents in the bath to a point where the operation of the bath becomes unsatisfactory much sooner than it otherwise would if such losses could be minimized or eliminated. One obvious solution to this problem is to employ only surfactants that are soluble in hot alkaline solutions.

There are available polyoxyalkylated tert.-carbinamines which are known to have a detergent effect on metal surfaces and would appear to have other requisite characteristics for alkaline cleaning purposes. These compositions, which have been disclosed in copending US. application Serial No. 632,648, now US. Patent No.

2,871,266, have a structure which may be generally represented by the following formula:

in which R R and R are alkyl groups Whose total carbon atom content ranges from 7 to 23, and m is an integer of 6 to 101.

The difficulty with compounds of the above-mentioned formulas is that they lack the requisite solubility property in hot alkaline solutions, such as, for example, 5 percent sodium hydroxide. It was thought that this lack of desired solubility could be overcome by completely (or essentially so) sulfating the compound so as to obtain a product having the following formula:

in which the values for R R R and m are the same as indicated above, and X is a monovalent cation such as an alkali metal or hydrogen. However, When a number of these compounds were sulfated, they were found to have a materially decreased cleaning efiiciency notwithstanding the fact that the product Was quite soluble in hot alkaline solutions. This effect appeared difiicult to explain or otherwise account for, and so efforts were made to determine the mechanism of this change in cleaning performance.

in the course of the investigation which ensued, it was discovered that not all of the polyoxyalkylated tert.-carbinamines would function efliciently as metal cleaners after they had been sulfated. Specifically, the sulfated amine-s which proved to be useful were those having the following formula:

R1 R -$-NH(o H,o)ms0 X+ in which R +R +R =11 to 14, m is an integer of 6 to 101, and X is a monovalent cation such as an alkali metal or hydrogen.

A further discovery was that, of these sulfated amines which had been demonstrated to possess utility as metal cleaners, only those having a certain narrow range of ethylene oxide units, namely between 12.5 and 17.5, gave metal cleaning results which are substantially as good as the results obtained with the non-sulfated compositions. At the same time, these compounds containing the indicated narrow range of ethylene oxide units also had the added advantage of complete solubility in the hot alkaline solution and thereby eliminated the objec tion described above, namely, the excessive losses caused when the surface of the cleaning baths had to be skimmed to remove the scum-like layer.

The foregoing discovery, which was based on the use of amines that were believed to have been completely those otherwise excellent compositions. When less than 75 percent sulfated, the compositions are not compatible with strong alkali, such as a 5 percent sodium hydroxide solution. When more than 85 percent sulfated, the cleaning efiiciency of the compositions is considerably diminished. Thus, it is essential, for maximum performance, that the polyoxyalkylated tert.-carbinamines be sulfated between about 75 to 85 percent.

In actual practice, our preferred composition is an alkali metal salt, generally sodium salt, of the tert.-carbinamine ethylene oxide sulfate. Such compounds are completely soluble in 5 percent sodium hydroxide at temperatures of 100 C. They are also soluble in concentrations such as 10 percent caustic, although not throughout this entire temperature range.

Example 1 describesin detail the alkaline metal cleaning test which was employed to establish the utility of the present invention. Following Example 1, Table I lists a series of tert.-carbinamine ethylene oxide compounds which have been sulfated in varying amounts from 0 to 100 percent. Also indicated for each of these compounds is the cleaning emciency index as determined by the method described below. In this series, the ethylene oxide content has been maintained at 15.0 units, this being the amount present in one of the best of the completely sulfated compositions in accordance with the invention disclosed in our above-mentioned copending application. The actual conditions of test were made more severe than the ones which were employed in our other case in order to more sharply delineate the differences in cleaning effectiveness. This was done primarily by using less of the surfactant in the cleaning solution than the concentrations described in the examples in our other application.

EXAMPLE 1 The following test method was used for evaluating the comparative efiiciencies of various alkaline metal cleanem. The method was adapted from a procedure used throughout the industry and which is described by S. Spring, H. Porman and L. Peale in Method of Evaluating Metal Cleaners, Ind. & Eng. Chem, Analytical Edition, vol. 18, No. 3, pp. 201-204 (1946). Briefly, the test consists of carefully cleaning thin SAE 1010 steel panels (3 x 3") and uniformly coating them with a thin film of brightstock mineral oil, which is drained for one hour at 35 C. The coated panel is then rotated'for 5 minutes at 30 rpm. in a 1000 ml. beaker of the solution being tested. That solution, which is maintained at a temperature of 82i2 C. in an oil bath, contains 0.07 percent active surfactant and 5 percent of a heavy duty alkaline cleaner consisting of 30 parts caustic soda, 35 parts sodaash and 30 parts sodium metasilicate pentahydrate.

' Following this period of alkaline cleansing, the panel is rinsed in an overflowing beaker of warm water which is approximately 40 C., allowed to drain in air for 20 seconds, and then subjected to a light spray of deionized water for approximately seconds on each side. Any area on the panel which is still coated with residual oil will exhibit readily visible droplets which are termed water breaks. On clean areas, a continuous water film will be observed. By means of a transparent plastic sheet which is the size of the test panel, and which has been ruled off into 100 squares of uniform dimensions, itis possible to determine the percentage of surface area which does not show any water breaks. This value represents an index of the cleaning efficiency of the alkaline cleaner which has been used. Three such panels are run, readings taken for each side of each panel, and the average of the six sides is considered to represent the cleaning efficiency index for the particular cleaner composition being tested. For the particular oil and concentration of surfactant used, etc., the minimum limit of-acceptability has arbitrarily been set at 70 percent,

Table I t-Alkyl Amine (E O)1s Percent Sulfated Cleaning Efficiency (percent) 50 Insoluble in 5% 62.5 NaOH.

1 NorE.The surfactants employed were sulfated, polyethoxylated t-alkyl amines, the amines being a commercially available mixture in the ranges t-Cm-1sH2s a1NI'-I2. The surfactants were all in the sodium form and the number of ethylene oxide units was 15. Their formulas, therefore, were t-C'i -isl-Tes-arNH(czHrOhsSosNil.

Similar data is obtained with the compounds which are exactly the same except for the ethylene oxide content which is varied from 12.5 to 17.5 units. Corresponding data is also obtained with compounds which are the same except that, instead of using the mixture of amines, the amine which is polyethoxylated and sulfated is one in the range Of t=C12H25NHz Q t C15H31NH2.

It is readily apparent from the data in the table that the polyoxyalkylated t-carbinamines which, priorto sulfation, have excellent metal cleaning abilities when used incombination with strong alkalies are: (1) not compatible with strong alkali (and therefore unsatisfactory products) when sulfated below 75 percent, because their incompatibility with the alkali causes surface loading and resultant excessive losses of the cleaner; (2) satisfactory cleaners (in combination with strong alkali) when sulfated between 75 and 85 percent; and (3) unsatisfactory cleaners (with strong alkali) when sulfated over 85 percent and only a relatively small percentage of the surfactant is employed. A further indication of the comparative efiectiveness of the present invention may be had from the fact that a commercially available alkyl aryl sulfonate, which heretofore had been considered to be among the finest surfactants known for alkaline metal cleaning applications, only rated a 13 percent cleaning efficiency index under identical test conditions.

The variousamines described above can be prepared by procedures similar to that disclosed in U.S. application Serial No. 632,648 and may be sulfated by any of several well-known methods, using sulfuric acid, sulfur trioxide, chlorosulfonic acid, or other suitable sulfating agents. In Examples 2 and 3 are described preparations of two amines by a suitable process (the latter being the polyoxyethylene adduct of the amine produced inthe former example). In Examples 4 and 5 are described typical preparations of a sulfated amine in accordance with the present invention.

EXAMPLE 2 In a suitable reaction vessel, there were combined 500 g. (2.54 mols.) t-dodecylamine, 45.8 g. (2.54 mols.) water and g. methanol. This mixture was heated to 80 C. and 139 g. (3.05 mols.) of ethylene oxide was added at 8085 C. over a period of 2 to 8 hours. At the end of this time, the product was isolated by distillation to remove the methanol and water. The yield, of product (N-(t-dodecyl)ethanol amine) amounted to 618.2 g. and had a neutral equivalent of 246.8. This was equivalent to N- (t-dodecyl)amine combined with 1.18 rnols. of ethylene oxide. This neutral equivalent indicated that the product contained a small amount of the diethanol amine.

5 EXAMPLE 3 In an appropriate reaction vessel, there Were combined 402.3 g. N-(t-dodecyDethanol amine (from above), having a neutral equivalent of 246.8, with 989.7 g. ethyleneoxide in the presence of 1.6 g. powdered potassium hydroxide at 140-180 C. When the reaction was complete, the catalyst was neutralized by the addition of a strong acid. The isolated product amounted to 1392.2 g. of a light yellow liquid which tended to solidify on standing at room temperature. This product (t-dodecylamineethyleneoxide had a neutral equivalent of 855.5 which was equivalent to t-dodecylamine combined with 15 mols. of ethylene oxide.

EXAMPLE 4 In a suitable reaction vessel, there were combined 213.5 g. (0.25 mol.) t-alkylaminopolyoxyethyiene (from Example 3 above) with 62.5 g. (0.625 mol.) 98% sulfuric acid, at a temperature of 60 -65 C. over a 2-hour period. At the end of this time, there was mixed with this reaction mixture 51 g. (1.27 mols.) NaOI-I dissolved in 600 cc. of water. After separation of the excess sodium sulfate the product (237 g. of t-alkylamino-polyxyethylene sulfate) was isolated as a pale amber, viscous liquid (viscosity 5,120 cps). Analysis of this product gave results indicating that the material was 77.0% sulfated.

This product was soluble in boiling sodium hydroxide and soluble up to 62 in 7% sodium hydroxide.

EXAMPLE 5 This preparation was carried out exactly as in Example 4 using 449.6 g. t-alkylarnino-polyoxyethylene (0.5 mol.) 138 g. (1.375 mols.) 97.6% H 89 and 90 g. (2.25 mols.) NaOi-i dissolved in 475 g. water. The yield of the product (t-alkylamino-polyoxyethylene sulfate), a pale amber viscous liquid, was 475 g. (viscosity=5,860 cps). Analysis of this product indicated that it Was 85% sulfated.

This product was soluble in boiling 5% NaOH and soluble up to 75 C. in 7% aqueous NaOH.

It will be apparent to anyone skilled in the alkaline cleaner art that certain variations from the compositions and methods set forth above by way of illustration are readily feasible without departing from the scope of the present invention. For example, any of the sulfated poiyoxyalkylated tert.-carbinamines described in our previously mentioned copending application will certainly be suitable. Further, although the specific examples described a typical alkaline cleaning composition made with sodium hydroxide, other alkalies of high pH may be employed. Nor must the percentages of the alkali and surfactant be limited to the 5 percent and 0.07 percent, respectively, that were employed by way of illustration in the examples. The surfactant which is the subject of the present invention is readily soluble in lower or higher concentrations of alkali and will, within the stipulated ranges of ethylene oxide content and degree of sulfation, perform with comparable efiiciency in the cleaning of metal and other surfaces. Moreover, the amounts of surfactant may be varied with a proportionate effect on cleaning etiiciency. Still other modifications are possible, all obviously within the scope of the following claims.

We claim:

1. A surfactant composition consisting essentially of a mixture of at least one sulfated and one unsulfated tcarbinamine polyoxyethylene compounds, the unsulfated compounds having the Formula I R2t NH OiHi o)mH and the sulfated compounds having the Formula 11 R1 RPNH(C2H4O)m K in which formulas R R and R are alkyl groups having a total of 11 to 14 carbon atoms, In is a value of from 12.5 to 17.5, and X is a monovalent cation from the class consisting of hydrogen and the alkali metals, the amounts of the respective compounds in the mixture being from about to about percent of the sulfated compound and from about 25 to about 15 percent of the unsulfated compound.

2. The composition of claim 1 in which X is sodium. 3. The composition of claim 1 in which X is hydrogen. 4. The composition of claim 1 in which X is potas- Slllfi'l.

References tilted in the file of this patent UNITED STATES PATENTS 1,970,578 Schoeller et al Aug. 21, 1934 2,746,932 Vitale May 22, 1956 2,755,296 Kirkpatrick July 17, 1956 2,768,956 Scott Oct. 30, 1956 2,871,266 Riley Jan. 27, 1959

Claims (1)

1. A SURFACTANT COMPOSITION CONSISTING ESSENTIALLY OF A MIXTURE OF AT LEAST ONE SULFATED AND ONE UNSULFATED TCARBINAMINE POLYOXYETHYLENE COMPOUNDS, THE UNSULFATED COMPOUNDS HAVING THE FORMULA I