EP0231524B1 - Application of alkylbenzoylacrylic acids as corrosion inhibitors - Google Patents

Abstract

3-(4-alkylbenzoyl)-acrylic acids corresponding to formula (1) <IMAGE> (I) in which R is straight-chain or branched-chain C8-C18 alkyl, or mixtures thereof, are useful as corrosion inhibitors in lubricating oils and lubricating greases based on mineral oils.

Description

The invention relates to the use of 3- (p-alkylbenzoyl) acrylic acid as a corrosion inhibitor in lubricating oils and lubricating greases based on mineral oils.

In industrial processes in which metal surfaces, in particular surfaces made of iron and its alloys, come into contact with oils or oil-containing aqueous emulsions under extreme conditions of pressure and temperature, the problem of corrosion of the metal surfaces occurs. Such processes are, for example, large-scale industrial cooling processes, metal surface cleaning and processing processes of the metal surfaces, such as drilling, cutting, rolling, etc. In such processes, oils or oil-containing emulsions are used without the influence of water on the metal surface can be completely excluded. However, the successive corrosion of the metal parts coming into contact with the oils or oil-containing liquids leads to a significant reduction in the service life of such systems or to problems in the subsequent treatment of the Metal surface, for example when applying a corrosion-protective surface layer by phosphating or painting.

It has therefore been known for a long time to add corrosion inhibitors to the oil-based liquids which come into contact with the metal surfaces. As such, numerous compounds or mixtures of different compounds come into question in predominantly oil-containing liquids or pure oils. For example, DE-AS 11 49 843 discloses half-amides of saturated or unsaturated dicarboxylic acids and their salts with alphatic primary amines as additives for fuel oils and lubricating oils. Although these additives significantly improve corrosion protection, they have an extremely strong tendency to foam, which cannot be accepted in such additives. DE-AS 12 98 672 discloses alkali or amine salts of sulfonaminocarboxylic acids as corrosion inhibitors with good lubricating properties and little tendency to foam. However, compositions containing these compounds have the disadvantage that they can only be prepared in processes which are complex in terms of manufacturing technology, and because of the relatively high content of sulfonamide groups they sometimes have a toxic effect or at least allow toxic effects to be expected, which necessitates corresponding toxicological tests.

For corrosion inhibition in oil or oil-containing systems, Ullmann's Encyclopedia d. Technical Chem. Vol. 18, 4th edition (1979) p. 1/2; Winnacker, Küchler, Chem. Technologie, Vol. 4 Org. Technologie II, 3rd edition (1972) p. 475 also known synthetic sulfonates from the group of petroleum sulfonates.

The disadvantage of this class of compounds, however, is that they are not biodegradable and therefore cannot be used in processes in which environmental contact inevitably takes place, since leakage of such agents into wastewater or into the soil would cause ecological damage that is difficult to transmit.

The object of the present invention was to provide a new class of compounds which does not have the disadvantages of the prior art mentioned. The compounds should show a corrosion-inhibiting effect which is at least equivalent to the known corrosion inhibitors. They should also be ecologically and toxicologically safe. It has now been found that 3- (p-alkylbenzoyl) acrylic acids fully meet the requirements mentioned.

in der R für einen Alkylrest mit 8 bis 18 C-Atomen steht oder von Gemischen mehrerer Verbindungen der allgemeinen Formel (I) als Korrosionsschutzmittel in Schmierölen und Schmierfetten auf Mineralölbasis.The invention relates to the use of 3- (p-alkylbenzoyl) acrylic acids of the general formula (I)

in which R represents an alkyl radical having 8 to 18 carbon atoms or mixtures of several compounds of the general formula (I) as corrosion inhibitors in lubricating oils and lubricating greases based on mineral oils.

sind aus der DE-OS 33 38 953 bekannt. Die dort genannten Verbindungen haben Alkylreste R mit 1 bis 6 C-Atomen und dienen als Korrosionsinhibitoren in wässrigen Systemen.3- (p-alkylbenzoyl) acrylic acids of the general formula (I)

are known from DE-OS 33 38 953. The compounds mentioned there have alkyl radicals R with 1 to 6 carbon atoms and serve as corrosion inhibitors in aqueous systems.

in der R die oben genannten Bedeutungen hat, im Zuge einer Friedel-Crafts-Acylierung mit Maleinsäureanhydrid umgesetzt werden, wobei unmittelbar die erfindungsgemäß verwendeten Verbindungen der allgemeinen Formel (I) in guten Ausbeuten und hoher Reinheit entstehen.Such compounds are prepared by methods known per se. For example, alkylbenzenes of the general formula (II)

in which R has the meanings given above, are reacted with maleic anhydride in the course of a Friedel-Crafts acylation, the compounds of the general formula (I) used according to the invention being formed immediately in good yields and high purity.

According to the invention, 3- (p-alkylbenzoyl) acrylic acids of the general formula (I) are used as anti-corrosion agents, in which R represents an alkyl radical having 8 to 18 carbon atoms. Suitable alkyl radicals are therefore unbranched or branched radicals from the group octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl and octadecyl, with straight-chain or branched alkyl radicals having 8 to 12 carbon atoms, i.e. Octyl, nonyl, decyl, undecyl and dodecyl radicals are preferred.

The compounds of the general formula (I) mentioned can be used both individually and in a mixture with one another as corrosion inhibitors in lubricating oils and lubricating greases based on mineral oils, in mixtures two or more compounds of the general formula (I) can be mixed in anti-corrosion agents.

The compounds of general formula (I) mentioned or their mixtures can be used in aqueous solutions, dispersions or emulsions for corrosion protection agents. They are soluble in mineral oil at room temperature so that liquid concentrates can be produced. Their effectiveness is very high even in low concentrations. It has surprisingly been shown that amounts in the range between 0.005 and 10% by weight are sufficient to ensure excellent corrosion protection. The preferred application amounts are in the range from 0.01 to 1% by weight, based on the mineral oil base.

The invention is illustrated by the following examples.

example 1

Testing of compounds of general formula (I) as rust inhibitor in mineral oil according to DIN 51359 (humidity chamber)

The test procedure was carried out as follows: Steel sheets of quality 088 St-1405, which had been degreased and sanded, were immersed in mineral oil samples (mineral oil: Pioneer 4556 (naphthenic-based) from Hansen & Rosenthel, Hamburg)), which were a compound of the general Formula (I) contained as a corrosion inhibitor. The steel sheets were kept in brief contact with the mineral oil / anti-corrosion agent sample, then removed and after 24 hours of dripping or Suspended drying time in the humidity chamber according to DIN 51359, in which the relative air humidity was 100% with a continuous air supply of 875 l / h and a temperature of 50 ° C. After the prescribed test duration, the steel sheets were assessed for signs of corrosion.

0:

keine Korrosion;

1:

Spuren von Korrosion;

2:

leichte Korrosion (korrodierte Fläche ≦5 %);

3:

mäßige Korrosion (korrodierte Fläche im Bereich zwischen 5 und 20 %); und

4

: starke Korrosion (korrodierte Fläche >20 %).

The test duration in the humidity chamber and the concentration of the rust inhibitor in the mineral oil used are shown in Table 1 below. The evaluation was carried out as follows:

0:

no corrosion;

1:

Traces of corrosion;

2:

slight corrosion (corroded area ≦ 5%);

3:

moderate corrosion (corroded area in the range between 5 and 20%); and

4th

: severe corrosion (corroded area> 20%).

Comparative Example 1

According to the procedure described in Example 1, steel sheets were immersed in identical mineral oil which did not contain any compound of the general formula (I) which can be used as a corrosion inhibitor. The evaluation of signs of corrosion was carried out according to the same treatment method in accordance with the evaluation scale given in Example 1. The results are shown in Table 1 above.

Result:

While the steel sheets immersed in mineral oil with a compound of the general formula (I) predominantly showed no or at most slight corrosion (degree of corrosion up to 2), sheets which had been immersed in mineral oil without a corrosion inhibitor showed strong corrosion without exception. Significant signs of corrosion were observed even after a short test period.

Example 2

Steel bars of quality CK 15, which had been degreased and sanded, were subjected to a mineral oil / water stirring test in accordance with DIN 51585. For this purpose, they were immersed at 60 ° C. in a stirred mixture of mineral oil of the quality analogous to Example 1 and water (method A) or of mineral oil of the quality analogous to Example 1 and artificial seawater (method B) for 24 h, the mineral oil-water Mixture was stirred at a speed of 1000 rpm. The volume ratio oil / water was 10: 1.

After 24 hours, the rods were removed from the mineral oil-water mixture and assessed for signs of corrosion.

The concentration of the compounds of general formula (I) used as corrosion inhibitor in the mineral oil used is shown in Table 2 below. The evaluation was carried out on the evaluation scale given in Example 1.

Comparative Example 2

In accordance with the method given in Example 2, steel rods were immersed in mineral oil which did not contain a corrosion inhibitor of the general formula (I). Both a mixture of mineral oil the quality analogous to example 1 and water (method A) and a mixture of mineral oil of the quality analogous to example 1 and artificial seawater (method B). The results are also shown in Table 2 above.

Result:

In the corrosion test according to DIN 51585, the compounds of the general formula (I) show satisfactory to good corrosion protection in mineral oil, in particular at concentrations from 0.05% by weight, based on mineral oil. In contrast, identical steel rods are heavily corroded by mineral oil-water mixtures without a corrosion inhibitor.

Claims (3)

1. The use of 3-(p-alkylbenzoyl)-acrylic acids corresponding to the following general formula

   

   in which R is a straight-chain or branched-chain C₈-C₁₈ alkyl group, or of mixtures of several compounds corresponding to general formula (I) as corrosion inhibitors in lubricating oils and lubricating greases based on mineral oils.
2. The use of 3-(p-alkylbenzoyl)-acrylic acids corresponding to the general formula (I) as claimed in claim 1, in which R is a straight-chain or branched-chain C₈-C₁₂ alkyl group.
3. The use of 3-(p-alkylbenzoyl)-acrylic acids corresponding to the general formula (I) as claimed in claim 1 in quantities of from 0.005 to 10% by weight and preferably in quantities of from 0.01 to 1% by weight, based on mineral oil.