US2459119A - Corrosion retarder - Google Patents

Description

Patented Jan. 11, 1049 CORROSION BETARDER John T. Ruclrer, Lewlston, N. Y., assignor to Hooker Electrochemical Company,

Nia ara Falls, N. Y., a corporation of New York No Drawing. Application September 27, 1946,

' Serial No. 699,840

3 Claims.

My invention relates more particularly to retarders of corrosion of metals by acids.

It is known that certain substances exert 'a protective effect upon metals, against attack of acids thereon, by rendering the metal passive with respect to the acid, i. e., as anti-catalysts. I will refer to these hereinafter as inhibitors. It is also known that certain other substances exert a protective effect by interposing a fllm between the metal and the acid. These are of the nature of detergents, or dispersing or wetting agents, characterized by low surface tension. I will refer to these hereinafter as "surface active materials.

Among the agents of the inhibitor category are the aralkyl thio-cyanates, such as benzyl and cymene thiocyanates. These are typical 'examples of aralkyl thio-cyanates, each 'having a methyl group, to which the thio-cyanate group is attached, and the cymene having, in addition, a propyl group. However, these compounds are of low solubility in acid pickling baths. Also, benzyl thio-cyanate has not only an exceedingly disagreeable odor, but toxic and lachrymatory properties, the efiects of which are aggravated by its low solubility and consequent tendency to collect at the surface of the bath and spatter into the atmosphere. For these reasons, these compounds have heretofore had little importance, except under conditions permitting of vigorous agitation.

Among the agents of the surface active category are the quaternary ammonium compounds, such as lauryl pyridinium chloride and lauryl dimethyl benzyl ammonium chloride. These are selected examples of quaternary ammonium compounds in which the nitrogen is in the ring and.

Example I Metal, steel Acid, sulphuric. 25% Temperature, 20 C. Corrosion retardcr... None LPG LPG LDBAC LDBAC Per cent retarder by m. p.hr.,g .0034 .0000057 .00019 .00011 .00018 Protection, percent 99.84 94.4 96.7 94.5

Example II Metal steel Acid, hydrochloric 20% Temperature, 20

Corrosion retarder... LPC LDBAC LDBAC LPG None

Per cent retarder by 1 p. hr., g 0043 Protection, per cent Example III respectively LDBAC LDBAC LPC LPC

. None Example IV Metal, steel Acid, sulphuric 15% Temperature, C.

Corrosion retarder Per cent retarder by wt Wt. Loss per sq. c. m. p. hr., 2.. Protection, per cent Lauryl pyridinium chloride and lauryl dimethyl benzyl ammonium chloride are partically odorless. They are water soluble and also quite soluble in oils. I have now found that, when these compounds are used in combination with benzyl or cymene thio-cyanates they act as dispersing agents for the thio-cyanates, besides increasing their solubility. Moreover, the foam layer formed by the surface active agents suppresses the tendency of the thio-cyanate to spatter and renders its use unobjectionable. In substantially equal proportions by weight lauryl pyridinium chloride forms with benzyl thiocyanate a eutectic melting at 15 C. In the same proportions it forms with cymene thio-cyanate a composition that is liquid at room temperature. I have found these compositions to be exceptional corrosion retarders.

This is illustrated by the following example:

Example V Metal, steel Acid, sulphuric, 15%

Temperature, 75 C.

Corrosion retarder LDBAC 50% LPC 510% LPC 50% B'IC 50% CIC 50% BTC 50% Per cent retarder by wt .02 .02 .02 Wt. loss per sq. c. m. p. lir., g. .0011 .001 .00076 l rotection, per cent 99.1 99.2 99.4

It will be seen by comparison of Example with Examples III and IV that these compositions are extremely effective. They are not in every case more efiective than thio-cyanate by itself. but itmust be remembered that these compositions are entirely practicable, whereas the thiocyanates are generally impracticable. However, the LPC-BTC eutectic is more efiective than either of its constituents.

When added to acid pickling baths, these corrosion retarders have in general a selective protective effect upon the metal, as compared with its oxide. This is illustrated by the following:

Example VI Mew], steel, hezlvilv coated with brown rust Acid, sulphuric. 15% Temperature, 75 C. Corrosion returdcr. None L PC 50% B'iO (WI, Per cont rctarder 0. 1 Time of cleaning, minutes Ii. ti

Example VII Metal, steel heavilv coated with blue scale Acid, sulphuric, 15% 'icmneruturc. 75 C. Corrosion retarrlcr None LlC 50% BIC 50% Per cent retardorn 0 Tim: of cleaning, minutes 0.5 0.7

It will be seen from Examples VI and VII that the addition of a relatively large quantity of one of my preferred corrosion retarders to the pickling bath increased the time of pickling only very slightly,

In order to show that my corrosion retarders have exceptional properties, I present herewith a table showing the percentage of protection afforded to ferrous metals by a considerable number of the best known corrosion retarders, against 4 per cent sulphuric acid at 71 C. This table is taken from Chemical Industries, 1935, vol. 37, page 124. The first part of this table is a comparison of certain retarders on the-basis of an equal percentage by weight. The second part is a comparison of certain other retarders on the basis of an equal molecular percentage. To each part I have added lauryl pyridinium chloride, lauryl pyridinium thio-cyanate and my LPC-CTC and LPC-BTC compositions, on the appropriate basis.

Mols Per Wt. Per Protection Remrder Liter Cent Per Cent Sulionated oiL., 0.1 Nitrogen base oil. 0. 1 30 Paper waste liquor. 0. 1 1:3 Sulfonated animal mattcL 0.1 63 Low grade wheat flour 0. l 85 Nitrogen bases. 0.1 88 Cool 'lnr nitrogen hoses 0.1 05 Lnuryl pyridinium LhlOl 0. 1 85 LPG- TC .l 0.1 90.4

LPC BlC eutectic l 0. l 0!). 00 Trietliylamine .01 10.5 Aniiine .01 .09 14.5 Pyridine 01 .08 19.0 Quinoiine 01 .13 49,4 Acridine .01 .18 82.4 2 me-quinolme l 01 .15 53. 0 xnc-ncridine 01 81. 8 Phenyl acridinc 01 .29 90. 2 Dimrthyl-diethyl-d[amino ucridino hydrochloride... .01 .33 09, 8 Lauryl pyridinium chlorid .01 .20 81. 8 LPC-CTC l 01 99. 5 LIC-B'IC eutectic .01 .22 09. 99+

It will be seen from the above that lauryl pyridinium chloride and lauryl pyridinium thiocyanate rank high among corrosion retarders, and when it is remembered that they have the advantage over most of them of high water solubility and freedom from offensive odor their importance as corrosion retarders will be manifest. It will also be seen that my LPCBTC eutectic tops all of 'the list, since in equal weight or molecular proportion it has a higher protective value, and for a given protective value much less of it need be used. It should be noted that while the difference between protective values of 99.8 and 99.99+ is not mathematically great, itssignificance is enormously important, for it means that in the latter case the corrosion rate is less than one twentieth. In other words, steel subjected to 4 per cent sulphuric acid at 71 C. will last more than twenty-times as lon if protected by my eutectic as if protected by the best of the previously known corrosion retarders.

Corrosion retarders are useful wherever acids are handled in metal equipment, of which pickling of metal is only one of many illustrations, acid treatment of oil wells being another, Another use for such retarders is in lubricants, which are liable to develop acidity through oxidation, by contact with the air. Organic acids developed in lubricating oils, such as those used in automotive crank cases, are mild compared with pickling acids, but the time factor is measured in months instead of hours, and in the long run the corrosive effect of such acids may be very serious, especially upon bearing alloys, such as those composed of lead, tin. copper and less commonmetals. It is difilcult to give a quantitative measure of the eifect of corrosion retarders in lubricating oils, as the matter is complicated by wear. Nevertheless, visual comparison of the effects of lubricating oils upon bearings, with and Without my retarders, indicates that my retarders have a useful efiect in such oils.

While I have given examples of the results obtained with my compositions only in equal proportions by weight, I do not wish to be limited to such proportions, as.any small addition, such as 10 per cent, of these and other analogous aralkyl thio-cyanates, of low solubility, to the quaternary ammonium compounds mentioned and other analogous compounds, of good solubility and having the property of dispersing, and increasing the solubility of, the thio-cyanate, will improve the corrosion retarding properties of the quaternary ammonium compounds, and the addition of as little as 20 per cent of the latter to the thio-cyana-te is useful in suppressing its spattering tendency. Also, while in the examples the proportion of corrosion retarder ranges from 0.02 to 0.1 per cent by weight, I do not wish to be held to these limits, as my retarders are useful in proportions as low as .005 per cent, and there is no objection to using up to 5 per cent of the retarder.

In the foregoing examples I have given tests only of compositions of benzyl and cymene thiocyanates with lauryl pyridinium chloride and lauryl dimethyl benzyl ammonium chloride, but these are given as typical only. Besides these, many combinations of other aralkyl thio-cyanates, such as xylyl thio-cyanate, and mesityl thio-cyanate, etc., with other quaternary ammonium compounds, such as lauryl pyridinium sulphonate, trimethyl cetyl ammonium chloride, amido benzyl pyridinium chloride, etc., form compositions which are superior retarders of corrosion of metals by acids. In short, any aralkyl thiocyanate in combination with a quaternary ammonium compound, and in particular those having an acid radical and an a kyl group of at least 10 carbon atoms attached to the nitrogen atom, the remaining nitrogen valences being satisfied by carbon members of one or more hydrocarbon rad- 1. As a new composition of matter, useful as a' retarder of corrosion of metals by acids, a substantially eutectic mixture consisting of lauryl pyridinium chloride and benzyl thiocyanate in substantiall equal proportions by weight.

2. The method of eliminating at least 99.99 per cent of the corrosion of ferrous metals by be benzyl and the others I acid pickling baths, such as 4 per cent sulphuric acid at 71 0., which comprises incorporating in the acid substantially 0.1 per cent of its weight of a substantially eutectic mixture consisting of lauryl pyridinium chloride and benzyl thiocyanate.

3. The method of protecting bearing metals in automobile crankcases veioped in lubricatingoils during use therein, which comprises incorporating in the oil 0.005 to 0.1 per cent of a substantially eutectic mixture of lauryl pyridinium chloride and benzyl thiocyanate.

JOHN T. RUCKER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED s'ra'ms PATENTS 15 Number 1 Name Date 2,006,218 MacArthur et a1. June 25, 1935 2,016,035 Downing et al Oct. 1, 1935 2,203,849 Felkers June 4, 1940 2,298,483 Frey et a1. Sept. 22, 1942 against organic acids de- I