FR2564478A1 - Aqueous corrosion inhibitor additives and process for their preparation - Google Patents

Abstract

Aqueous corrosion inhibitor additives characterised in that they contain as active substance in a quantity of 0.1-99.9 % an organic phosphate of general formula (I): where R1 denotes a hydrogen or a cyclohexyl group, R2 denotes a cyclohexyl group and n has a value between 0.5 and 3 and in relation to the organic phosphate not more than 10 % of zinc phosphate and the usual solvents for additives of this type, preferably water.

Description

et le phosphate de zinc. Dans la formule générale (I)
R1 représente un hydrogène ou un groupe cyclohexyle,
R2 représente un groupe cyclohexyle et n a une valeur comprise entre 0,5 et 3.The present invention relates to aqueous corrosion inhibiting additives and a process for their preparation. The aqueous additives according to the invention contain as active material organic phosphates of general formula (I)

and zinc phosphate. In the general formula (I)
R1 represents a hydrogen or a cyclohexyl group,
R2 represents a cyclohexyl group and has a value between 0.5 and 3.

 The aqueous additives according to the invention can be used in closed cycles of cooling with cold water and with hot water to reduce the rate of corrosion.

It is known that the corrosion of metals in aqueous solutions is in most cases essentially an electrochemical process whose speed depends on the speed of two reactions which take place on the surface of the metal and which are coupled one to the other. the other: that of the anodic reaction during which the ionic atoms of the metal leave the network and go into solution with the release of electrons, and that of the cathodic reaction, where a depolarizer fixes the electrons released in the reaction anodic (Rozenfeld: A korrózió inhibitorai, Müszaki Könyvkiadó,
Budapest 1981).

It is also known that in comparison with other methods of protection against corrosion, for example the application of corrosion-resistant materials, the modification of the incidence of corrosion, the application of protective layers and coatings, the methods active protectors (Kovacs Klara: Korrgziós alapfogalmak, Müszaki konyvkiado,
Budapest 1965), the protection against corrosion by means of inhibitors has the advantage of being simple and cheaper.

The cyclic corrosion process must, in order for it to occur, to be closed, i.e. which chemicals which - added to water - stop the anodic reaction, simultaneously stop corrosion, or according to agents that decrease the rate of the cathodic reaction also decrease the rate of corrosion. Correspondingly, a basic distinction is made between anodic inhibitors and cathodic inhibitors. The third group of inhibitors is formed by organic films which inhibit the two processes (zamier, Franc N .: The NALCO Water Handbook, McGraw
Hill, Inc., 1979).

 Among the anodic inhibitors, the most effective are chromate and orthophosphate. The application of chromate is limited by environmental protection considerations, and the use of orthophosphate is limited by the fact that eventually tricalcium phosphate can deposit and impair heat transfer. In the case of pure anodic inhibitors, the corrosion rate also depends on the concentration of the inhibitor: if the concentration falls below a critical value, the corrosion rate is not reduced, but increased by the inhibitor .

 With cathodic inhibitors - for example polyphosphonates, zinc - such problems do not appear, but their effect of lowering the corrosion rate is weaker than that of anodic inhibitors. Organic film-forming materials - usually long carbon amines form a film on the surface of the metal and thus between water and the metal a dynamic barrier which inhibits corrosion processes. The disadvantage of film-forming materials is that when a small crack is formed in the film, corrosion attacks in a concentrated manner in the unprotected area and quickly destroys the metal there (localized corrosion).

 To increase the effectiveness of the various inhibitors, combinations of inhibitors of different types have often been used for some time, and efforts have been made to obtain synergistic mixtures (Betz: Handbook of Industrial Water Conditioning, 1976 , as well as KURIZET S-207, Prospekt).

 The aqueous additives with inhibiting action according to the invention do not have the drawbacks of the various types of isolated inhibitors. They can be prepared from bodies which can easily be obtained by a simple and inexpensive process. Their anti-corrosion efficiency reaches or exceeds that of the known agents that are commercially available, that is to say that the inhibitors according to the invention are optimal from the point of view of cost / effectiveness !.

 By the application, carried out in a known manner, of aqueous additives with inhibiting action according to the invention in closed cycles of cooling with cold water and with hot water, it is possible to obtain a more secure protection against corrosion and to great efficiency.

 According to the invention, the organic phosphates of general formula (I) are prepared in a simple chemical reaction by adding to phosphoric acid at 5-85%, with stirring and constantly cooling, cyclohexylamine or dicyclohexylamine.

Depending on the concentration of phosphoric acid, organic phosphorus compounds of general formula (I) are obtained in the pure state or in the form of an aqueous solution. The remarkably effective aqueous additives according to the invention are obtained by adding to the organic phosphate of general formula (I) at most 10% of zinc phosphate. Zinc can also be supplied by dissolving zinc oxide in phosphoric acid in the first step and then adding cyclohexylamine or, as the case may be, dicyclohexylamine to the solution obtained.

 In contrast to known water treatment agents, the aqueous additives according to the invention contain cyclohexylamine or dicyclohexylamine phosphate. The application of these compounds in the field of corrosion protection is hitherto unknown. Their combination with zinc phosphate should also be considered new.

The aqueous corrosion inhibiting additives according to the invention have the following advantages: - they inhibit corrosion according to all three mechanisms
inhibitory nisms: anodic (phosphate), cathodic
(zinc) and by the formation of a film (cyclohexyl
or dicyclohexylamine) and thus offer the best
safety possible, - they inhibit the corrosion process even when
the water temperature is high, - they can be easily prepared using the
usual devices in the chemical industry (auto
clave), - given their simplicity of preparation, they are
cheaper than agents with
analogous protective effect, - they have a neutral or almost neutral character and
therefore hardly influence the pH of the treated water, - they do not contain a chromate dangerous for
the environment, - in comparison with agents containing phosphate
having a similar protective effect, it suffices
maintain a low phosphate concentration
in water, - in comparison with agents containing zinc
having a similar protective effect, a more
low concentration of zinc is needed in e-au
treated, - as opposed to known phosphorus-containing agents,
the addition of inhibitors inhibiting the deposition of phos
tricalcium phate is not necessary at all, or
only to a much lesser extent, possible contamination of the water with ions
copper (II) does not decrease the effectiveness of addi
aqueous tifs according to the invention.

 The invention is clarified with the aid of the following examples.

Example 1
474 liters of deionized water are placed in an enamelled double-walled autoclave fitted with a stirrer.

23.4 liters of 85% phosphoric acid are added thereto.

By constantly stirring and switching on the water cooling, 86.2 kg of dicyclohexylamine are added to the solution - for example at a speed of 90 kg / hour. After the end of the addition, the mixture is stirred for a further 10 minutes and then poured into barrels (in practice in plastic barrels).

Product characteristics: pH: 7-8.

Density: 1.04 g / cm3 at 20 C.

Composition: zinc 70-90 mg / kg
phosphate 52-56 g / kg
dicyclohexylamine 140-150 g / kg.

Example 2
0.01 g of zinc oxide is dissolved in 56.7 g of 85% phosphoric acid in a 100 cm3 beaker. 40.8 g of cyclohexylamine are dissolved in 903 g of distilled water in a beaker with a volume of 2 liters. The phosphoric acid containing the zinc oxide is then allowed to flow slowly, with constant stirring, for approximately 10 minutes in the amine solution.

Parameters of the product obtained:
Color: t colorless or slightly yellow pH: 4-5 density: 1.03 g / cm3 at 20-C composition:
zinc: 7-9 mg / l
phosphate: 45-50 g / l cyclohexylamine: 40-44 gtl.

Example 3
In 1.97 g of 85% phosphoric acid, 0.30 mg of zinc oxide is dissolved. This solution is poured with intensive stirring into 4.5 g of dicyclohexylamine.

Parameters of the product obtained: pH: 7-8, in aqueous solution at 20% appearance: white crystalline substance composition:
zinc: 0.0035-0.0040 X
phosphate: 25-27
dicyclohexylamine: 68-71
water: 4-6
Example 4
612 liters of deionized water are poured into an enamelled double-walled autoclave with a volume of 1 m3 fitted with an agitator. 47.8 liters of 85% phosphoric acid are added to the water. By switching on the water cooling and constantly stirring, 99 liters of dicyclohexylamine are poured into the autoclave. The product is poured into barrels.

Product parameters:
Color: colorless or slightly yellow pH: 3-4 density: 1.05 g / cm3 at 20 C composition:
zinc: 11-13 mg / kg
phosphate: 80-90 g / kg
dicyclohexylamine: 110-120 g / kg
The effect of inhibiting corrosion of the aqueous additives according to the invention is demonstrated with the following experiments.

Experiment 1
The action of a pretreatment with the agent prepared according to example 1 (called below-X-102) and a treatment with the agent prepared according to example 3 (called ci below X-100) with the action of a few known agents that are commercially available. Comparative experiments are carried out in the manner known in the specialized literature (Kemmer,
Frank N.: The NALCO Water Handbook, McGraw-Hill,
Inc. 1979, and Betz: Handbook of Industrial Water
Conditioning, 1976) by comparison of the values of the corrosion rate (mm / year) measured on the standard, or as the case may be by comparison of the relative inhibitory action (the value of the corrosion rate in percentage compared to the control no With known aqueous additives, we choose for the pre; treatment and for treatment the concentration indicated by the manufacturer.

Parameters of the experiments: duration of the corrosion experiment: 72 hours water temperature: 900C suspension: every 24 hours aeration: continuous pH: 7.5-8.5
Main parameters of the water used: total calcium hardness (in CaCO3): 80-100 mg / l conductivity: 500-600 pS alkalinity t in CaCO3): 40-60 mg / l total iron: 0.1-0.2 mg / l sulfate: 140-160 mg / l chloride: 20-30 mg / l silicon dioxide 3-5 mg / l.

 The results are summarized in Table I.

From the table it can be seen that the additives according to the invention reach or exceed, depending on the case, the action of the best commercial products.

Experiment 2
The agent according to Example 4 (called below X-10091 and its modified form (zinc content ten times greater and (below called X-1021)) is used for the pre-treatment for the continuous treatment. compare the results with those of known agents The parameters of the experiment and the water quality correspond to those indicated in experiment 1. The results are also seen from Table I.

The aqueous additives according to the invention reach or exceed in their action the known agents.

Experiment 3
In this experiment, the agent according to example 2 (below called X-103) is used for the pretreatment and for the continuous treatment and compared with the known agents according to experiment 1. The parameters of the experiment and the water quality are the same as in Experiment 1. From the values indicated in Table I it can be seen that the agent X-103 according to the invention offers better protection against corrosion than the agents usual commercial corrosion.

Experiment 4
The effect of a pre-treatment with agent X-102 according to the invention (example 1) and of continuous treatment with agent X-100 prepared according to example 3 is compared with the effect of the agent who presented the best action in the experiment (combination of I + II + III) (for the meaning of the symbols see under Table I). The examination also extends to low water temperatures, but the other parameters correspond to those which have already been given.

 The results are summarized in Table II.

It can be seen from this that the aqueous additive according to the invention achieves at least the corrosion inhibiting effect of the best usual agents on the market. Table I
Comparative examination of the anti-corrosion action of various aqueous additives
Experience Pre-Concentration Agent Processing Agent Concentration Speed of Action
N treatment mg / 1 mg / 1 erosion (mm / year) hibition (%) 1 - - - - 2.203 0 2 I 1000 III 150 0.069 97
II 200 3 IV 200 IV 150 0.726 67 4 V 200 V + VI 100 0.194 92
VI 100 5 VII 200 VII 150 1.90 14 6 VIII 100 VIII 30 1.76 20 7 X-102 5000 X-100 150 0.068 97 8 X-1021 5000 X-1001 150 0.032 99 9 X-103 2000 X-103 300 0.212 90
I: Polyphosphate, zinc salt (3% Zn), copper inhibitor (trade name: Kurizet S 207, manufacturer: KURITA)
II: Sodium polyacrylate copolymer (Kurizet T 225, Manufacturer: KURITA)
III: Polyphosphonate, zinc salt, copper inhibitor, phosphate (Kurizet S 611, KURITA)
IV: Inhibitory mixture of organic and inorganic components, zinc 34 mg / 1, copper 10 mg / 1, phosphate 20% (Kurizet S 113, KURITA)
V: Zinc-containing phosphonate inhibitor, zinc 13%, phosphate 17% (Tecpractor 657 M, TECPRO)
VI: Organic inhibitor (Tecpractor 2045, TECPRO)
VII: Inhibitor mixture containing phosphate, 7% phosphate (Betz 801, manufacturer: Betz)
VIII: Agent containing zinc, organic phosphates and phosphonic acids, 7.3% zinc, 10% phosphate (Drewgarde 187, manufacturer: Drew).

Table II
Comparative examination of the anti-corrosion action of various aqueous additives
Experience Pre-Concentration Agent Treatment Agent Concentration Temp. of Vit. from Action in
N treatment mg / 1 mg / 1 water 0 corrosion hibition,% mm / year mm / year 1 - - - - 30 0.814 0 2 I 1000 III 150 30 0.021 97
II 200 3 X-102 5000 X-100 150 30 0.021 97 4 - - - - 60 1.021 0 5 I 1000 III 150 60 0.024 98
II 200 6 X-102 5000 X-100 150 60 0.024 98
The meaning of the symbols I, II and III is given in the note at the bottom of the
Table I.

Claims (7)

1. Aqueous corrosion-inhibiting additives, characterized in that they contain, as active material in an amount of 0.1-99.9%, an organic phosphate of general formula (I)

 or R1 represents a hydrogen or a cyclohexyl group, R2 represents a cyclohexyl group and n has a value between 0.5 and 3 as well as with respect to organic phosphate at most 10% of zinc phosphate and the usual solvents for additives of this type, preferably water. 2. Aqueous additives according to claim 1, characterized in that they contain, as active material, organic phosphates of general formula (I) having, as substituents R1, a cyclohexyl group. 3. Aqueous additives according to claim 1, characterized in that they contain as active material organic phosphates of general formula (I) having as substituents R1 a hydrogen. 4. Process for the preparation of the aqueous corrosion-inhibiting additives according to one of claims 1-3, characterized in that phosphoric acid at 5-85X is reacted with cyclohexylamine or dicyclohexylamine. 5. Method according to claim 4, characterized in that one reagent flows continuously into the other by stirring and constantly cooling. 6. Method according to one of claims 4 and 5, characterized in that the reaction mixture is added before, during or after the reaction, with respect to the organic phosphate, at most 10% of zinc phosphate or a zinc compound forming with phosphoric acid zinc phosphate. 7. Method according to one of claims 4-6, characterized in that the reaction is carried out without solvent or in an inert solvent, preferably water.