SULPHONIC ACID PREPARATION PROCESS

The present invention relates to the field of the protection of the corrosion of metals against attack by acids, and in particular a process for preparing a sulphonic acid which is little, or even not, corrosive to metals and in particularly stainless steels.

[0002] Sulfonic acids, and in particular so-called organic sulfonic acids, such as, for example, methanesulfonic acid (AMS), para-toluenesulfonic acid (APTS), benzenesulfonic acid (BS ), trifluoro-methane-sulfonic acid are strong acids widely used in many applications, especially in catalysis and surface treatment, such as electroplating, pickling, cleaning, descaling, to name only the main of them, limit themselves to them.

[0003] However, it has been observed that aqueous solutions of such sulphonic acids corrode metals, the corrosion rates depending both on the acid concentration, on the temperature and on the nature of the metal. For example, at room temperature, type 304L or 1.4307 stainless steel is corrodible at AMS concentrations greater than 5% by weight in water. Such corrosion risks are unacceptable in many applications, and particularly for the storage of these acids mainly when they are in aqueous solution.

To make sulphonic acids little, if not not, corrosive towards metals, and particularly towards stainless steels, many works have already been carried out, among which a technique which has shown satisfactory results consists in the addition of nitrates in said acids. This method is in particular described by B. Gaur and HS Srinivasan (“British Corrosion Journal”, 34 (1), (1999), 63-66) who have shown that the addition of ferric ions or nitrates makes it possible to produce a corrosion inhibiting effect by AMS on various steels.

[0005] Other solutions have been studied, among which one can for example cite that described in application EP0931854, which proposes to inhibit the corrosion of stainless steels in organosulfonic acid medium, by adding at least one oxidant chosen from among salts or oxides of cerium (IV), iron (III), molybdenum (VI) or vanadium (V), nitrites and persulphates. However, the addition of some of these inhibitors, such as nitrites, generally leads to the release of nitrogen oxides (NOx) which may prove to be dangerous or at least harmful and toxic both for operators and operators. users, as well as the environment. This patent application is in particular silent on the manner of preparing nitrite / sulphonic acid mixtures, without causing the release of NOx.

[0006] Thus, there consequently remains a need for a process for preparing a sulphonic acid which is little, or even not, corrosive (called "low corrosion") with respect to metals, and stainless steels in particular, said process being less toxic and less harmful for the operators, the users and for the environment, compared to the known processes of the prior art.

[0007] The Applicant has now surprisingly discovered that the addition of a corrosion inhibitor under specific and suitable conditions makes it possible to overcome the drawbacks described above. The Applicant has therefore implemented a process for preparing a sulfonic acid meeting these precise conditions and whose implementation will appear in the light of the description which follows.

[0008] Thus a first object of the invention relates to a process for preparing a weak corrosion sulfonic acid comprising at least the following steps: a) addition of at least one nitrite in a conventional sulfonic acid;

b) baking the mixture obtained in step a) at a temperature between 0 ° C and 100 ° C, preferably between 0 ° C and 80 ° C, more particularly between 10 ° C and 60 ° C, even more particularly between 10 ° C and 50 ° C, for a period of between a few seconds and a few hours, preferably between 1 min and 4 h, more particularly between 10 min and 2 h, even more particularly between 10 min and 1 h;

c) recovering weak corrosion sulfonic acid.

In the present invention, the term "weak corrosion sulfonic acid" is understood to mean a sulfonic acid whose potential remains almost at the same level and does not rise after application of a quantity of current of -800 μΑ.αττ 2 , for 1 minute, then stop the application of this current, as explained later in the “low corrosion” validation test protocol. In other words, a weak corrosion sulfonic acid according to the present invention remains in the passive state after application of a current of -800 μΑ.αττ 2 , for 1 minute, while a sulfonic acid not in accordance with the present invention (corrosive), returns to the active state (corrosion) after depassivation by application of said quantity of current of -800 μΑ.αττ 2, for 1 minute.

In the present invention, the nitrite, used as a corrosion inhibitor, can be any nitrite known to those skilled in the art, and is preferably chosen from alkali metal or alkaline earth metal nitrites, or else ammonium nitrite. Among the alkali nitrites, sodium nitrite and potassium nitrite are preferred. According to a preferred embodiment of the invention, sodium nitrite is used. Other nitrites can be used; however, for obvious reasons of cost, availability, environmental protection, the use of metal nitrites such as, for example, copper nitrite or other heavy metal nitrites, will be avoided.

In the present invention, the term "conventional sulfonic acid" is understood to mean in particular any sulfonic acid known to a person skilled in the art not comprising any corrosion inhibitor, in particular a corrosion inhibitor as defined above. . For example, it is a sulphonic acid which has not undergone chemical and / or physical treatment aimed at giving it anticorrosive properties with respect to metals, and stainless steels as mentioned above. In particular, the term “conventional sulphonic acids” is understood to mean sulphonic acids of formula R-SO3H, where R represents a saturated or unsaturated, linear, branched or cyclic hydrocarbon chain, comprising from 1 to 12 carbon atoms, substituted or unsubstituted. by one or more radicals and / or atoms chosen from the atoms of halogen (such as fluorine, chlorine, bromine), alkyl radicals containing from 1 to 6 carbon atoms and 6 or 10-membered aryl and heteroaryl radicals not comprising any corrosion inhibitor, in particular corrosion inhibitor such as defined above. According to one embodiment, the “conventional sulphonic acids” are not low corrosion sulphonic acids as defined above.

In the present invention, by sulfonic acid is meant any sulfonic acid known to a person skilled in the art and more particularly sulfonic acids of formula R-SO3H, where R represents a hydrocarbon chain

saturated or unsaturated, linear, branched or cyclic, comprising from 1 to 12 carbon atoms, substituted or unsubstituted by one or more radicals and / or atoms chosen from halogen atoms (such as fluorine, chlorine, bromine), alkyl radicals containing 1 to 6 carbon atoms and 6 or 10 membered aryl and heteroaryl radicals.

By "alkyl" is meant a saturated, linear or branched hydrocarbon radical. The term “aryl” is understood to mean an aromatic radical, preferably phenyl or naphthyl, more preferably phenyl. By “heteroaryl” is meant an aromatic radical having one or more heteroatoms chosen from oxygen, nitrogen and sulfur.

Preferably R represents a hydrocarbon chain comprising from 1 to 6 carbon atoms, more particularly chosen from methyl, ethyl, n-propyl, / ' so-propyl, n-butyl, / ' so-butyl, sec-butyl , terf-butyl, linear or branched pentyl radicals, linear or branched hexyl radicals, and phenyl and naphthyl radicals.

[0015] Thus, and in a nonlimiting manner, the sulfonic acids included in the context of the present invention are preferably chosen from methane-sulfonic acid, ethanesulfonic acid, n-propane-sulfonic acid, iso-propane-sulfonic acid, n-butane-sulfonic acid, / ' n-butane-sulfonic acid, sec-butane-sulphonic acid, tert-butane-sulphonic acid, trifluoro-methanesulfonic acid, para-toluenesulfonic acid, benzenesulfonic acid, naphthalenesulfonic acid and mixtures of two or more of them in all proportions.

According to a very particularly preferred embodiment, the sulfonic acid used in the context of the present invention is methane-sulfonic acid, ethanesulfonic acid, trifluoromethanesulfonic acid or para-toluenesulfonic acid , most preferably the sulfonic acid is methanesulfonic acid.

The sulfonic acid used in the context of the present invention can be sulfonic acid alone or a mixture of two or more sulfonic acids, optionally in a solvent medium and optionally mixed with one or more additives and / or fillers well known to those skilled in the art.

Thus, the sulfonic acid (s) peuv (en) t be in a solvent medium, said solvent possibly being water or an organic solvent or a mixture of organic solvents, or else water mixed with one or more other organic solvents. As a general rule, the concentration of sulfonic acid (s) in the solvent (s) is between 0.01% and 100%, limits included, by weight of sulfonic acid (s). relative to the total weight of sulfonic acid (s) in a solvent medium, it being understood that when the concentration is equal to 100%, the amount of solvent is zero or negligible or not detectable. Preferably, this concentration is between 0.01% and 99.99%, preferably between 0.1% and 99.9%, more preferably between 0.5% and 75%, limits included, by weight of

The organic solvents indicated above and which can be used to solvent the sulfonic acid (s) can be of any type known to those skilled in the art, and preferably the organic solvents soluble in water. , such as alcohols, sulfoxides, inorganic or organic acids, more preferably methanol, ethanol, dimethylsulfoxide, sulfuric acid, to name only the most common and the best known of them.

The additives and fillers which may be present as a mixture with the sulfonic acids can for example be, without limitation, one or more additives and / or fillers chosen from viscosity or rheology modifiers, foaming agents, anti-foaming agents, surfactants, disinfectants, biocides, stabilizers, oxidizing agents, enzymes, pigments, colorants, flame retardants, flame retardants, fragrances, flavors, and the like.

These various additives and fillers are present in amounts well known to those skilled in the art, which may vary depending on the desired effect, the nature of the sulfonic acid used and the application considered for said sulfonic acid used.

Step a) of the process according to the invention comprises the addition of at least one nitrite (or a solution comprising at least one nitrite) in a sulfonic acid (or a solution comprising at least one sulfonic acid). It is particularly preferred to add said at least one nitrite in the sulfonic acid and not vice versa. Indeed, the addition can be more or less exothermic, and the addition of sulphonic acid in the nitrite can lead to a very rapid and significant rise in temperature and therefore potentially cause a decomposition of the nitrite and / or a vaporization of said nitrite.

Said at least one nitrite is added in sulfonic acid such that the nitrite / sulfonic acid molar ratio is between 200 ppm and 6000 ppm, preferably between 400 ppm and 2000 ppm, in particular between 500 ppm and 1900 ppm.

The nitrite can be added in pure form or in solution in water, or any organic or inorganic solvent medium, and in particular an alcohol or sulfuric acid. When the nitrite is in solution in an alcohol, the alcohol used can be any type of alcohol comprising from 1 to 6 carbon atoms, preferably methanol or ethanol.

The addition according to step a) of the process according to the present invention is generally carried out with stirring, more or less vigorous, according to the viscosity of the reaction medium, and according to the desired rate of addition and homogenization. It is indeed important to carry out the addition and the homogenization in a sufficiently slow manner to avoid possible problems of decomposition and / or vaporization of the nitrite, as indicated above.

Without being bound by theory, it was discovered that the necessary step b) of "cooking" allows the perfect homogenization of the nitrite in the sulfonic acid and "the activation" of said nitrite to give the acid sulfonic its so-called “low corrosion” property as indicated above.

According to one embodiment, step b) of cooking is carried out for a period of between 1 h and 5 h, preferably between 1 h and 4 h, for example approximately 3 h.

Step b) is advantageously carried out with stirring according to any means known to those skilled in the art, when it comes to stirring a mixture comprising a strong acid heated to the cooking temperature set out above.

The cooking carried out in step b) can lead to the formation of nitrogen oxides (denoted "NOx" below), which can escape from the reaction medium and possibly be visually observed in the form of vapors red hairs emerging from the reaction medium. For obvious reasons of safety and security, these NOx can advantageously be sucked in and evacuated for treatment, for example by slaughter, preferably slaughter by a base.

aqueous such as a sodium hydroxide solution, which will be treated before discharge into the environment, according to conventional techniques known to those skilled in the art.

According to an advantageous embodiment of the method according to the present invention, the mixture obtained after cooking of step b) is subjected, or even during the cooking of step b), or even during and after the cooking of step b), to a step making it possible to facilitate and / or accelerate the elimination of all or part of the NOx formed during the cooking of said step b).

The elimination of all or part of the NOx formed can be carried out by any means known to those skilled in the art, and for example by "stripping", bubbling or bubbling. These latter methods consist in bubbling air and / or an inert gas, preferably an inert gas, in the reaction mixture during and / or after step b). According to a very particularly preferred embodiment of the process of the present invention, the inert gas used is nitrogen. The quantity and flow rate of air and / or inert gas used depend on many factors such as the quantity of reaction medium, on the concentration of nitrite and of sulphonic acid. Those skilled in the art will easily know how to adapt said quantity and the flow rate of air and / or inert gas to be implemented.

For example, when the removal of NOx is carried out by bubbling with air or an inert gas, preferably an inert gas, the bubbling is carried out on the mixture resulting from step b), for example at a temperature between 0 ° C and 100 ° C, preferably between 0 ° C and 80 ° C, more particularly between 10 ° C and 60 ° C, even more particularly between 10 ° C and 50 ° C, for a period of between a few minutes and a few hours, preferably between 10 minutes and 12 hours, more particularly between 15 minutes and 8 hours, even more particularly between 30 minutes and 7 hours, for example between 30 minutes and approximately 6 hours.

One can operate the step of removing NOx in one or more times, continuously, sequenced, or alternately or concomitantly ave step b) of cooking the mixture. It is preferred to carry out the step of eliminating all or part of the NOx at one time during step b) of cooking. According to another preferred embodiment the step of removing all or part of the NOx is carried out all at once after the cooking step b).

The method according to the invention can be carried out in batch or continuously. In the case of a continuous process, the sulfonic acid and the nitrite are preferably added against the current. In the case of a batch process, the reactor can be equipped with any type of agitation such as anchoring, impeller and agitation by external loop.

The method according to the invention thus makes it possible to obtain a low corrosion sulfonic acid, said sulfonic acid comprising only a small amount of nitrites, which in no way affects said sulfonic acid which can thus be used as any conventional sulphonic acid, said acid having the advantage of not corroding and of very slightly corroding metals and in particular passivable metals and alloys, in particular based on iron, nickel, titanium, copper, aluminum, molybdenum, manganese, lead , and their alloys, as well as the torques of these metals or alloys obtained by contact (crimping, riveting, bolting, welding, brazing), in particular stainless steels, and in particular common stainless steels (for example of type AISI 304L and AISI 316L),but also more generally any stainless steel as defined in standard NF EN 10088-1.

A second object of the present invention relates to a low corrosion sulfonic acid substantially obtained according to the process described above. Said acid according to the invention shows quite remarkable properties in that it is little, or even not, corrosive with respect to metals, and in particular stainless steels such as, for example, ferritic or martensitic stainless steels, austenitic and duplex. Among the austenitic stainless steels, we will more particularly retain AISI 304L steel and AISI 316L steel.

A third object of the present invention relates to the use of said weak corrosion sulfonic acid prepared according to the method described above, to limit, or even avoid, the corrosion of metals by sulfonic acids.

The invention will be better understood with the aid of the examples which follow, said examples not being in any way limiting and serving only to illustrate the invention.

EXAMPLES

The sulfonic acid used in the following examples is 70% methane sulfonic acid (AMS), that is to say methanesulfonic acid diluted to 70% by weight in water .

Example 1: Process without bubbling

In a 250 mL three-necked flask connected to a water condenser (itself connected to a guard flask followed by a trap containing sodium hydroxide (NaOH), then a trap containing potassium permanganate (KMnO 4 )), a nitrogen introduction tube and a neck for adding sodium nitrite (NaNO2), 135 g of AMS are introduced at 20 ° C which are stirred (400 rotations per minute or rpm).

Then added, over 1 minute and via an automatic pipette, 0.24 mL (or 0.30375 g) of a solution of NaNO2 at 40% by weight in water. The NaNO2 / AMS molar ratio is 1800 ppm. One could also add the NaNO2 in solid form (0.1215 g).

The flask is immediately closed with a stopper and stirred (400 rpm) for 60 min at 20 ° C. The resulting low corrosion AMS is then recovered.

Example 2: process according to the invention (with bubbling)

In a 250 mL three-necked flask connected to a water condenser (itself connected to a guard flask followed by a trap containing NaOH then a trap containing KMnO 4 ), a nitrogen introduction tube and a neck for adding NaNO2, 135 g of AMS are introduced at 20 ° C., which are stirred (400 rpm).

Then added, over 1 minute and via an automatic pipette, either 0.24 mL (or 0.30375 g) of a solution of NaNO2 at 40% by weight in water. The NaNO2 / AMS molar ratio of 1800 ppm.

The flask is immediately closed with a stopper and stirred (400 rpm) for 60 min at 20 ° C.

A part of the mixture is subjected to a bubbling step for 240 min at 20 ° C and the second part of the mixture is subjected to a bubbling step for 360 min at 20 ° C. Bubbling is the bubbling of nitrogen into the

reaction medium with a nitrogen flow rate of about 30 mL / minute. The low corrosion AMS obtained is then recovered.

Example 3: NOx measurement

A NOx assay is performed on each of the 3 low corrosion AMS previously obtained.

Is weighed in a two-necked flask of 500 ml_, 100 g of low corrosion AMS to be assayed and a magnetic bar is added. The flask is closed with a glass stopper. A tube for NOx analysis, from the company Draeger, is connected to the top of the flask which is heated at 60 ° C. for 30 minutes.

The sky is then sucked up with a number of pump strokes determined by the operating mode supplied with the tubes from the Draeger company, and the measurements are read.

The results are shown in Table 1 below.

- Table 1 -

It is found that without a bubbling step, the amount of NOx in the low corrosion AMS is much greater than in the low corrosion AMS formulations subjected to the bubbling. In addition, it is observed that after a 360 min bubbling, the quantity of NOx present in the formulation of low corrosion AMS is 3 times lower than that present in the formulation of low corrosion AMS previously subjected to a bubbling of 240 min. This demonstrates the impact of the bubbling step on NOx removal from AMS as well as the impact of the bubbling time on NOx production.

VALIDATION TEST PROTOCOL

LOW CORROSION SULPHONIC ACID

In order to check the "low corrosion" quality, within the meaning of the present invention, of a sulfonic acid, an electrochemistry test is carried out using an assembly with 3 electrodes connected to a BIOLOGIC VMP3 potentiostat. :

1) reference electrode: saturated calomel electrode or "ECS",

2) working electrode: 304L stainless steel test tube of size 1 cm 2 , and

3) against platinum electrode.

The test piece of the material to be tested is polished with P400 abrasive paper and then passivated for 1 hour in a 10% nitric acid solution at room temperature. This allows an identical starting state for all tests. The temperature of the test is thermostatically controlled at 20 ° C ± 2 ° C.

The protocol applied comprises the following three steps:

a) monitoring of the abandonment potential of the working electrode (304L) in the additivated sulfonic acid according to the method of the present invention, that is to say measurement of the potential of the material in the solution as a function of time , during 30 minutes,

b) immersion of the three-electrode system in a standard sulphonic acid solution (ie without additives), then application to the working electrode of a current of -800 μΑ.αττ 2 for 1 minute in order to depassivate the material of artificially by fixing the potential thereof in the corrosion range, c) immersing the three-electrode system again in the solution of additivated sulfonic acid according to the process of the present invention, and again monitoring the potential of abandonment of the working electrode, until stabilization thereof.

VALIDATION TEST RESULTS

In the case of a standard methanesulfonic acid, that is to say without additives, in solution at 70% by weight in water, after application of an amount of current of -800 μΑ. αττ 2 , the potential of the working electrode (304L stainless steel test tube) drops to around -350 mV, which corresponds to the passage of 304L stainless steel in the active state. When the application of the current is stopped, the potential of the material remains almost at the same level and does not rise again. 304L stainless steel remains in the active state and corrodes.

The behavior is totally different in a 70% solution by weight in water of a methanesulfonic acid with additives according to the process of the present invention (examples 1 and 2 above).

We first note a potential for abandonment of stainless steel 304L of the order of 750 mV after 30 minutes. When applying the current of -800 μΑ.αττ 2 , the

potential of the material drops to around -200 mV (change from 304L stainless steel to the active state). When the application of the current is stopped, the potential of the material rises very quickly. It is 780 mV after 2 hours of potential monitoring and a total absence of corrosion is noted.

In all cases (Examples 1 and 2 above), the methane-sulfonic acid additivated with sodium nitrite is a low corrosion methane-sulfonic acid within the meaning of the present invention.
CLAIMS

1. Process for preparing a weak corrosion sulfonic acid comprising at least the following steps:

a) addition of at least one nitrite in a conventional sulfonic acid;

b) baking the mixture obtained in step a) at a temperature between 0 ° C and 100 ° C, preferably between 0 ° C and 80 ° C, more particularly between 10 ° C and 60 ° C, even more particularly between 10 ° C and 50 ° C, for a period of between a few seconds and a few hours, preferably between 1 min and 4 h, more particularly between 10 min and 2 h, even more particularly between 10 min and 1 h;

c) recovering weak corrosion sulfonic acid.

2. The method of claim 1, wherein the nitrite is chosen from alkali metal nitrites, alkaline earth nitrites and ammonium nitrite, preferably from sodium nitrite and potassium nitrite, more preferably. , nitrite is sodium nitrite.

3. The method of claim 1 or claim 2, wherein the sulfonic acid is a sulfonic acid of formula R-SO3H, where R represents a saturated or unsaturated, linear, branched or cyclic hydrocarbon chain, comprising from 1 to 12 carbon atoms. , substituted or unsubstituted by one or more radicals and / or atoms chosen from halogen atoms, alkyl radicals containing from 1 to 6 carbon atoms and aryl and heteroaryl radicals with 6 or 10 members.

4. Method according to any one of claims 1 to 3, wherein the sulfonic acid is selected from methane-sulfonic acid, ethanesulfonic acid, n-propane-sulfonic acid, acid / ' so-propanesulfonic acid, n-butane-sulfonic acid, / ' so-butanesulfonic acid, sec-butanesulfonic acid, terf-butanesulfonic acid, trifluoromethanesulfonic acid, para-toluenesulfonic acid, benzenesulfonic acid, naphthalenesulfonic acid and mixtures of two or more of them in all proportions, preferably from methanesulfonic acid, ethanesulfonic acid, trifluoromethanesulfonic acid and para-toluenesulfonic acid,most preferably the sulfonic acid is methanesulfonic acid.

5. Method according to any one of the preceding claims, in which the nitrite / sulfonic acid molar ratio is between 200 ppm and 6000 ppm, preferably between 400 ppm and 2000 ppm, particularly between 500 ppm and 1900 ppm.

6. Method according to any one of the preceding claims, in which the mixture obtained after cooking in step b), or even during cooking in step b), or else during and after cooking in step b ), is subjected to a stage of bubbling air and / or inert gas, preferably inert gas.

7. Low corrosion sulfonic acid substantially obtained according to the process of any one of claims 1 to 6.

8. Use of low corrosion sulfonic acid according to claim 7 or obtained according to any one of the preceding claims, to limit, or even avoid, the corrosion of metals by sulfonic acids.