EP0206311B1 - Process for preventing corrosion of metallic materials - Google Patents

Description

It is known that additives to aqueous and non-aqueous solutions can reduce (inhibit) the rate of corrosion attack. In particular, organic compounds such as amines, imines, quaternary ammonium salts, unsaturated alcohols and other substances act as inhibitors in media which attack metallic materials, in particular unalloyed steels, by acid corrosion. (see Akstinat: Werkstoff und Korrosion 21, 273 (1970); Sanyal, B .: Progress in Organic Coatings 9, p 165 - 236 (1981); Rozenfeld, LL: Corrosion Inhibitors, McGraw Hill Inc., New York, 1981 A distinction is made between corrosion inhibitors according to their mode of action as adsorption inhibitors, passivators, film or top layer formers, neutralizers and others (cf. Dean, SW et al .: Materials Performance, p. 47-51 (1981)).

The group of amines, including aliphatic and aromatic, saturated and unsaturated amine compounds, and the quaternary ammonium compounds, are known as adsorption inhibitors for acid corrosion. According to the protective mechanism, these substances only work in acidic aqueous media in the absence of oxidizing agents, especially atmospheric oxygen (Risch, K .: VDI Report 365, 11 (1980)). On the other hand, it is known that the protective action of inhibitors for corrosion in neutral and alkaline oxygen-containing waters, that is, in particular phosphorus-containing products, for example phosphates and polyphosphates, depends on the formation of a film (film-forming inhibitors) or a barrier layer from precipitated solids, the corrosion protection effect of which strongly depends on the medium and the initial growth conditions. In particular, in the case of heat transfer from metallic material into the medium (heating elements, heat exchangers), layers can form form, which hinder the heat flow and which lead to overheating or local corrosion under the top layer formed.

It was surprising that special compounds from the groups of the quaternary ammonium compounds and the oxyalkylated quaternary ammonium compounds are able to effectively inhibit the corrosion of metallic materials, in particular unalloyed steels and copper, in the acidic, neutral and alkaline pH range, the protective effect, in particular in flowing and neutral aqueous media is independent of whether dissolved oxygen is present or not.

The invention thus relates to a method for avoiding the corrosion of metallic materials in flowing aqueous media with the characterizing features of claim 1.

The invention further relates to the use of these compounds as corrosion inhibitors.

für n= 12 bis 24 mit folgenden Benzoesäureanionen

• a) Salicylat oder m-Halogenbenzoat,
  
  mit R= Methyl oder Ethyl oder Propyl oder C_nH_2n+1O - mit n= 1 bis 4,
  vorzugsweise in den Stellungen 3 oder 4 oder 5 zur Carboxylgruppe,
  
  mit R= Methyl oder Ethyl oder Propyl oder C_nH_2n+1O - mit n= 1 bis 4,
  vorzugsweise in den Stellungen 4 oder 5 zur Carboxylgruppe,
  
  mit Hal= F, Cl, Br, J
  

mit den Anionen 2-hydroxy-1-naphthoat, 3-(oder 4)-hydroxy-2-naphthoat bzw. die entsprechenden Derivate der Naphthol-Sulfonsäuren.The salts of the following cations and anions are particularly preferred:

for n = 12 to 24 with the following benzoic acid anions

• a) salicylate or m-halobenzoate,
  
  with R = methyl or ethyl or propyl or C _n H _{2n + 1} O - with n = 1 to 4,
  preferably in positions 3 or 4 or 5 to the carboxyl group,
  
  with R = methyl or ethyl or propyl or C _n H _{2n + 1} O - with n = 1 to 4,
  preferably in positions 4 or 5 to the carboxyl group,
  
  with Hal = F, Cl, Br, J
  

with the anions 2-hydroxy-1-naphthoate, 3- (or 4) -hydroxy-2-naphthoate or the corresponding derivatives of naphthol sulfonic acids.

The compounds described above show a pronounced anticorrosive effect on metallic materials of all kinds, preferably for copper and unalloyed steel. This anti-corrosive effect extends from the strongly acidic to the strongly alkaline pH range and is independent of the presence or absence of oxygen. Of particular interest is the use of these compounds in flowing aqueous media, such as in cooling and heating circuits. The use concentrations for the compounds are 0.01 to 5% by weight, preferably 0.05 to 2% by weight and particularly preferably 0.1 to 1% by weight. For the preparation of the compounds, reference is made to DE-A-32 24 148.

For each of the compounds, depending on the temperature, there is a different lower critical concentration limit for a sufficient corrosion protection effect _, which, however, as described further below, can be determined by a simple preliminary test. The effect depends on the temperature. The compounds mentioned act overall in a temperature range from 0 ° C to 145 ° C; however, a single compound shows effectiveness only over a temperature interval of approx. 45 ° C (± 25 ° C). The lower temperature limit for all compounds is the solubility temperature (isotropic solution) or better the Krafft point. However, if the surfactant is in solution, the solubility temperature can in most cases fall below 5 to 25 ° C. for a few hours to weeks without loss of effectiveness. The use of those surfactants which remain in solution up to the melting point of the water is possible at temperatures below 0 ° C. if the melting point of the water is lowered by adding organic solvents, such as ethylene glycol or isopropanol. A lowering of the melting temperature of the water by adding electrolyte, such as NaCl, without loss of effectiveness is only possible to a limited extent.

Surprisingly, it has now been found that surfactants in aqueous solution are always effective as anti-corrosion agents if they form non-spherical, preferably rod-shaped micelles for concentrations greater than the CMC _II . Non-spherical, preferably rod-shaped micelles are present when the isotropic surfactant solution is examined using the electrical birefringence method with a pulsed, rectangular electrical field (E. Fredericq and C. Housier, Electric Dichroism and Electric Birefringence, Claredon Press, Oxford 1973 and H Hoffmann et al., Ber. Bunsenges. Phys. Chem. 85 (1981) 255) a measurement signal is found, from the drop of which a relaxation time of> 0.5 µs can be determined. The lower concentration limit above which a surfactant in aqueous solution is effective as a corrosion protection agent is therefore always determined by the CMC _II , preferably by 1.5 to 3 times the concentration value of the CMC _II . The CMC _II can be determined, for example, by measuring the electrical conductivity of the surfactant solution as a function of the surfactant concentration, as in H. Hoffmann et al. (Ber. Bunsenges. Phys. Chem. 85 (1981) 255). It was shown that the value of the CMC _{II is} temperature-dependent and shifts to higher surfactant concentrations with increasing temperature.

In the case of the salts of the formula, the minimum concentration required to achieve a sufficient corrosion protection effect in a certain temperature range can be determined by determining the CMC _II at the application temperature can be determined with the help of electrical conductivity.

wobei V die Abtragsrate ohne Inhibitor, V₁ die Abtragsrate mit Inhibitor bedeutet.In the following examples, the corrosion protection effect was tested in the usual way by determining the mass loss of samples of the metallic materials (sample coupons), in certain cases in which only acid corrosion predominated, also by determining the removal rates from the polarization resistance. The effectiveness ω of the individual inhibitor can be calculated by comparison with the removal rates in solutions without additives:

where V is the removal rate without inhibitor, V 1 is the removal rate with inhibitor.

example 1

The removal rates and the inhibitory activity of the compound hexadecyltrimethylammonium salicylate, C₁₆TA-Sal, were determined in concentrations of 0.075% by weight and 0.1% by weight in solutions with deionized water (DI water) by measuring the polarization resistance. For this purpose, a measuring device from Magnachem (Corrater model 1136) was used. The results are summarized in Table 1. Unalloyed steel (ST 37) and copper were examined.

Table 1

Material of unalloyed steel ST 37 . Final stationary value of the removal rates after 20h for C₁₆TA-Sal in non-aerated deionized water

Example 2

As described in Example 1, solutions of hexadecyltrimethylammonium-3-hydroxy-2-naphthoate (C₁₆TA-Bons) in demineralized water were examined for their inhibitory activity for copper and unalloyed steel (ST 37). The following concentrations were examined at a measuring temperature of 50 ° C:
0.01; 0.025; 0.05; 0.075 and 0.1% by weight
Table 2 summarizes the results.

Table 2

stationary final value of the removal rate after 20h for C₁₆TA-BONS deionized water

Example 3

The removal rates of unalloyed steel and copper in aerated and non-aerated demineralized water with the addition of 0.04, 0.05 and 0.075% by weight of C₁₆TA vouchers were determined in a flow-through apparatus by introducing test coupons and pipe samples. The results are shown in Table 3.

Table 3

Removal rates, determined by measuring the mass loss for C₁₆TA-BONS in demineralized water

Example 4

As described in Example 3, solutions of docosyltrimethylammonium-3-hydroxy-2-naphthoate in demineralized water at 100 and 120 ° C. were examined for their removal rates for unalloyed steel (ST37). At a concentration of 0.125% by weight, values less than 0.01 mm / year were measured.

Example 5

As described in Example 1, solutions of C₁₆TA-BONS in 0.1 N hydrochloric acid of 65 ° C were examined for their removal rates for unalloyed steel (ST37). The value for the concentration 0 is 6.3 mm / year, for 0.0075% by weight 1.5 mm / year and 0.075% by weight 1.2 mm / year, corresponding to 76% and 81% inhibitor activity.

Example 6

As described in Example 3, solutions of C₁₆TA-BONS in 0.1 N hydrochloric acid from 65 ° C were examined for the removal rate for unalloyed steel (ST37). The value for the concentration 0 is 16.2 mm / year, for 0.075% by weight 0.9 mm / year corresponding to 94% inhibitor activity.

Example 7

In a test stand to investigate the bursting behavior of plastic membranes, which consists of brass, unalloyed steel and galvanized steel pipes with a total volume of 200 l of aerated demineralized water (T = 80 ° C), strong abrasive corrosion was found. The addition of commercial phosphate-based inhibitors (DIANODIC II, Betz, Düsseldorf) only provided unsatisfactory corrosion protection, recognizable by the formation and discharge of corrosion products. The addition of 0.1 wt .-% C₁₆TA-BONS completely prevented the formation of corrosion products. The removal rates (test time 140 h) on additional coupons made of unalloyed steel (ST37) were less than 0.01 mm / year.

Claims (3)

1. A process for the avoidance of corrosion of metallic materials in flowing aqueous media, which comprises adding to the aqueous medium a compound of the formula

   

   in which
   R₁ denotes C₁₂-C₂₆-alkyl or C₁₂-C₂₆-alkenyl, n denotes a number from 0 to 5, R₂ denotes C₁-C₃-alkyl, R₃ denotes C₁-C₃-alkyl or a group of the formula -(C₂H₄O)_xH, x denotes a number from 1 to 3, A^(-) denotes an anion of the following formulae: SCN^(-) R₄SO3^(-) where R₄ is C₆-C₉-alkyl or C₈-C₉-alkenyl and the sum of the carbon atoms in R₁ and R₄ should be at least 21;

   

   where Hal is fluorine, chlorine, bromine or iodine, R₅ is C₁-C₅-alkyl, C₂-C₅-alkenyl or C₁-C₅-alkoxy in the 3, 4, 5 and 6 positions and R₆ is hydrogen or hydroxy in the 2 and 3 positions to the carboxyl group and

   

   where R7 is COO^(-) or SO₃^(-) and R₈ is hydrogen or methyl.
2. A process as claimed in claim 1, wherein the compounds of the formula are employed in an amount of 0.01 to 5% by weight.
3. Use of the compounds as claimed in claim 1 as corrosion inhibitors.