The process for producing sulfonic acid.

Abstract

DEPCT6429 / 04 / 2563 The subject of this invention is a process for producing sulfonic acid, which is corrosive. There is very little or no corrosion for stainless steel caused by such processes. This includes at least one step of adding nitrite to the sulfonic acid during curing. Containing sparge stirring of the mixture and recovery of sulfonic acid. Low corrosive properties obtained. The invention also involves a low-corrosion sulfonic acid obtained through a process. The invention, and also their use, are related to sulfonic acids which are low in corrosiveness. ----------------------------------------------------------- The subject of this invention is a process for producing sulfonic acid, which is corrosive. As needed, or even without corrosion in the stainless steel portion, the process... Which includes at least one step of adding nitrite to sulfonic acid. Aging involving sparge of the mixture and recovery of sulfonic acid. Low corrosive material obtained. The invention also involves a low-corrosive sulfonic acid obtained through a process of... They were invented and are also associated with the use of low-corrosive sulfonic acids.

Description

PROCESS FOR PREPARING SULFONIC ACID

[0001] The present invention relates to the field of corrosion protection of metals against acid attacks, and in particular a process for preparing a sulfonic acid that is slightly, or even not, corrosive to metals and in particular to stainless steels.

[0002] Sulfonic acids, and in particular so-called organic sulfonic acids, such as methanesulfonic acid (MSA), para-toluenesulfonic acid (PTSA), benzenesulfonic acid (BS), trifluoromethanesulfonic acid are strong acids widely used in many applications, particularly in catalysis and surface treatment, such as electroplating, pickling, cleaning, descaling, to name only the main ones, without being limited to them.

[0003] However, it has been observed that aqueous solutions of such sulfonic acids corrode metals, with corrosion rates depending on the acid concentration, temperature, and the nature of the metal. For example, at room temperature, 304L or 1.4307 stainless steel is corrodible at MSA concentrations exceeding 5 wt% in water. Such corrosion risks are unacceptable in many applications, particularly for the storage of these acids, especially when they are in aqueous solution.

[0004] To make sulfonic acids less corrosive, or even non-corrosive, towards metals, and particularly towards stainless steels, numerous studies have already been conducted. Among these, one technique that has shown satisfactory results involves adding nitrates to these acids. This method is described in particular by B. Gaur and HS Srinivasan ("British Corrosion Journal", 34(1), (1999), 63-66), who demonstrated that the addition of ferric or nitrate ions produces an inhibitory effect on AMS corrosion in various steels.

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

[0006] Therefore, there remains a need for a process for preparing a sulfonic acid that is not very, or even not, corrosive (called "low corrosion") towards metals, and stainless steels in particular, said process being less toxic and less harmful to operators, users and the environment, compared to the processes known in the prior art.

[0007] The Applicant has now discovered, surprisingly, that adding a corrosion inhibitor under specific and appropriate conditions overcomes the drawbacks described above. The Applicant has therefore implemented a process for preparing a sulfonic acid that meets these specific conditions, and the implementation of this process will be explained in the following description.

[0008] Thus, a first object of the invention relates to a process for preparing a low-corrosion sulfonic acid comprising at least the following steps: a) adding at least one nitrite to a conventional sulfonic acid; b) cooking 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 time 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) recover the weak sulfonic acid corrosion.

[0009] In the present invention, "weak corrosion sulfonic acid" means a sulfonic acid whose potential remains almost at the same level and does not rise after the application of a current of -800 μA.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 weakly corrosive sulfonic acid according to the present invention remains in a passive state after the application of a current of -800 μA.αττ 2 , for 1 minute, while a sulfonic acid not conforming to the present invention (corrosive), returns to the active state (corrosion) after depassivation by application of said quantity of current of -800 μA.αττ 2 for 1 minute.

[0010] In the present invention, the nitrite used as a corrosion inhibitor can be any nitrite known to those skilled in the art, and preferably is chosen from alkali metal or alkaline earth nitrites, or ammonium nitrite. Among the alkali nitrites, sodium nitrite and potassium nitrite are preferred. In a preferred embodiment of the invention, sodium nitrite is used. Other nitrites may be used; however, for obvious reasons of cost, availability, and environmental protection, the use of metal nitrites such as, for example, copper nitrite or other heavy metal nitrites should be avoided.

[0011] In the present invention, the term "conventional sulfonic acid" means, in particular, any sulfonic acid known to those skilled in the art that does not contain a corrosion inhibitor, especially a corrosion inhibitor as defined above. For example, it refers to a sulfonic acid that has not undergone any chemical and / or physical treatment intended to give it anti-corrosive properties towards metals, and stainless steels as mentioned above.In particular, "conventional sulfonic acids" means sulfonic acids of the formula R-SO3H, where R represents a saturated or unsaturated, linear, branched, or cyclic hydrocarbon chain of 1 to 12 carbon atoms, substituted or unsubstituted by one or more radicals and / or atoms selected from halogen atoms (such as fluorine, chlorine, bromine), alkyl radicals containing 1 to 6 carbon atoms, and aryl and heteroaryl radicals of 6 or 10 members, not comprising a corrosion inhibitor, in particular a corrosion inhibitor as defined above. In one embodiment, "conventional sulfonic acids" are not low-corrosion sulfonic acids as defined above.

[0012] In the present invention, sulfonic acid means any sulfonic acid known to those 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, containing 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 from 1 to 6 carbon atoms and aryl and heteroaryl radicals with 6 or 10 links.

[0013] By "alkyl" we mean a saturated hydrocarbon radical, linear or branched. By "aryl" we mean an aromatic radical, preferably phenyl or naphthyl, more preferably phenyl. By "heteroaryl" we mean an aromatic radical possessing one or more heteroatoms selected from oxygen, nitrogen, and sulfur.

[0014] Preferably R represents a hydrocarbon chain comprising 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 without limitation, the sulfonic acids included within the scope of the present invention are preferably chosen from methanesulfonic acid, ethanesulfonic acid, n-propanesulfonic acid, isopropanesulfonic acid, n-butanesulfonic acid, 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 any proportions.

[0016] According to a particularly preferred embodiment, the sulfonic acid used in the context of the present invention is methanesulfonic acid, ethanesulfonic acid, trifluoromethanesulfonic acid or para-toluenesulfonic acid, most preferably the sulfonic acid is methanesulfonic acid.

[0017] The sulfonic acid used in the context of the present invention may be sulfonic acid alone or a mixture of two or more sulfonic acids, possibly in a solvent medium and possibly mixed with one or more additives and / or fillers well known to those skilled in the art.

[0018] Thus, the sulfonic acid(s) may be in a solvent medium, said solvent being water, an organic solvent, a mixture of organic solvents, or water mixed with one or more other organic solvents. Generally, the concentration of sulfonic acid(s) in the solvent(s) is between 0.01% and 100% inclusive, expressed as a percentage of the total weight of sulfonic acid(s) in the solvent medium, it being understood that when the concentration is equal to 100%, the amount of solvent is zero, negligible, or undetectable. Preferably, this concentration is between 0.01% and 99.99%, preferably between 0.1% and 99.9%, preferably again between 0.5% and 75%, inclusive, in weight of sulfonic acid(s) relative to the total weight of sulfonic acid(s) in solvent medium.

[0019] The organic solvents indicated above and usable for dissolving sulfonic acid(s) can be of any type known to a person skilled in the art, and preferably water-soluble organic solvents, such as alcohols, sulfoxides, mineral or organic acids, more preferably methanol, ethanol, dimethyl sulfoxide, sulfuric acid, to name only the most common and well-known of them.

[0020] Additives and fillers that may be present in mixture with sulfonic acids may, for example, be, but not limited to, one or more additives and / or fillers selected from viscosity or rheology modifiers, foaming agents, antifoaming agents, surfactants, disinfectants, biocides, stabilizers, oxidizing agents, enzymes, pigments, dyes, flame retardants, flame retardants, perfumes, aromas, and others.

[0021] These various additives and fillers are present in quantities 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.

[0022] Step a) of the process according to the invention comprises adding at least one nitrite (or a solution comprising at least one nitrite) to a sulfonic acid (or a solution comprising at least one sulfonic acid). It is particularly preferred to add said at least one nitrite to the sulfonic acid and not the other way around. Indeed, the addition can be more or less exothermic, and the addition of acid Sulfonic acid in nitrite can lead to a very rapid and significant rise in temperature and consequently potentially cause decomposition of the nitrite and / or vaporization of said nitrite.

[0023] Said at least one nitrite is added to the 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.

[0024] Nitrite can be added in its pure form or in solution in water, or any organic or mineral solvent, and in particular an alcohol or sulfuric acid. When nitrite is in solution in an alcohol, the alcohol used can be any type of alcohol containing 1 to 6 carbon atoms, preferably methanol or ethanol.

[0025] The addition according to step a) of the process according to the present invention is generally carried out under stirring, more or less vigorous, depending on the viscosity of the reaction medium and the desired rate of addition and homogenization. It is indeed important to carry out the addition and homogenization sufficiently slowly to avoid any potential problems of decomposition and / or vaporization of the nitrite, as indicated above.

[0026] Without being bound by the theory, it has been 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 allowing to confer to the sulfonic acid its so-called "low corrosion" property as indicated above.

[0027] 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 about 3 h.

[0028] Step b) is advantageously carried out under agitation by any means known to a person skilled in the art, when it is a question of stirring a mixture comprising a strong acid heated to the cooking temperature set out above.

[0029] The cooking process carried out in step b) can lead to the formation of nitrogen oxides (hereafter referred to as "NOx"), which may escape from the reaction medium and may be visually observed as reddish-brown vapors emanating from the reaction medium. For obvious safety and security reasons, these NOx can advantageously be extracted and removed for treatment, for example by suppression, preferably suppression by a base aqueous such as a sodium hydroxide solution, which will be treated before release into the environment, according to conventional techniques known to those skilled in the art.

[0030] According to an advantageous embodiment of the process according to the present invention, the mixture obtained after cooking in step b), or during cooking in step b), or during and after cooking in step b), is subjected to a step enabling the removal of all or part of the NOx formed during the cooking of said step b).

[0031] The removal of all or part of the NOx formed can be achieved by any means known to those skilled in the art, for example by stripping, bubbling, or stirring. These latter methods consist of bubbling air and / or an inert gas, preferably an inert gas, into the reaction mixture during and / or after step b). According to a 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 numerous factors such as the quantity of reaction medium, the nitrite concentration, and the sulfonic acid concentration. Those skilled in the art will readily be able to adjust the quantity and flow rate of air and / or inert gas to be used.

[0032] For example, when NOx removal is carried out by bubbling with air or an inert gas, preferably an inert gas, bubbling is carried out on the mixture 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 time 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 about 6 hours.

[0033] The NOx removal step can be carried out in one or more stages, continuously, sequentially, alternately, or concurrently with step b) of cooking the mixture. It is preferred to carry out the NOx removal step, in whole or in part, in a single stage during step b) of cooking. According to another preferred embodiment, the NOx removal step, in whole or in part, is carried out in a single stage after step b) of cooking.

[0034] The process according to the invention can be carried out in batch or continuous operation. In the case of a continuous process, the sulfonic acid and nitrite are preferably added counter-currently. In the case of a batch process, the reactor can be equipped with any type of agitation such as anchor, impeller, and external loop agitation.

[0035] The process 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 does not in any way alter said sulfonic acid, which can thus be used like any conventional sulfonic acid, said acid having the advantage of not corroding and of corroding very little 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 pairs 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.

[0036] A second object of the present invention relates to a weakly corrosive sulfonic acid substantially obtained according to the process described above. This acid, according to the invention, exhibits remarkable properties in that it is only slightly, or not at all, corrosive towards metals, and in particular towards stainless steels such as, for example, ferritic, martensitic, austenitic, and duplex stainless steels. Among austenitic stainless steels, AISI 304L and AISI 316L are particularly noteworthy.

[0037] A third object of the present invention relates to the use of said low corrosion sulfonic acid prepared according to the process described above, to limit, or even avoid, the corrosion of metals by sulfonic acids.

[0038] The invention will be better understood with the aid of the following examples, said examples being in no way limiting and serving only to illustrate the invention. EXAMPLES

[0039] The sulfonic acid used in the following examples is 70% methanesulfonic acid (MSA), i.e., methanesulfonic acid diluted to 70% by weight in water. Example 1: Bubble-free process

[0040] 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 (KMnO4)), a nitrogen introduction tube and a neck for adding sodium nitrite (NaNO2), 135 g of AMS are introduced at 20°C and stirred (400 rotations per minute or rpm).

[0041] Next, over 1 minute, using an automatic pipette, 0.24 mL (0.30375 g) of a 40% wt. NaNO2 solution in water is added. The NaNO2 / AMS molar ratio is 1800 ppm. Alternatively, solid NaNO2 (0.1215 g) could be added.

[0042] The flask is immediately sealed with a stopper and stirred (400 rpm) for 60 minutes at 20°C. The low-corrosion AMS obtained is then collected. Example 2: Process according to the invention (with bubbling)

[0043] In a 250 mL three-necked flask connected to a water condenser (itself connected to a guard flask followed by a trap containing NaOH and then a trap containing KMnO4), a nitrogen introduction tube and a neck for adding NaNO2, 135 g of AMS are introduced at 20°C and stirred (400 rpm).

[0044] Next, over 1 minute and using an automatic pipette, 0.24 mL (or 0.30375 g) of a 40% wt% NaNO2 solution in water is added. The NaNO2 / AMS molar ratio is 1800 ppm.

[0045] The balloon is immediately closed with a stopper and stirred (400 rpm) for 60 min at 20°C.

[0046] 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 The reaction medium is prepared with a nitrogen flow rate of approximately 30 mL / minute. The resulting low-corrosion AMS is then collected. Example 3: NOx Measurement

[0047] NOx levels are measured on each of the 3 previously obtained low-corrosion AMS samples.

[0048] One hundred grams of low-corrosion AMS (a type of antioxidant) is weighed into a 500 ml two-necked flask, and a magnetic stir bar is added. The flask is sealed with a glass stopper. A Draeger NOx analysis tube is connected to the top of the flask, which is heated to 60°C for 30 minutes.

[0049] The sky is then aspirated with a number of pump strokes determined by the operating instructions provided with the Draeger company tubes, and the measurements are read.

[0050] The results are presented in Table 1 below. -- Table 1 --

[0051] It was observed that without a sparging step, the amount of NOx in the low-corrosion AMS is significantly higher than in the low-corrosion AMS formulations subjected to sparging. Furthermore, after 360 minutes of sparging, the amount of NOx present in the low-corrosion AMS formulation is three times lower than that present in the low-corrosion AMS formulation previously subjected to 240 minutes of sparging. This demonstrates the impact of the sparging step on NOx removal from the AMS, as well as the impact of sparging duration on NOx production. VALIDATION TEST PROTOCOL Sulfonic acid, low corrosion

[0052] In order to verify the "low corrosion" quality, within the meaning of the present invention, of a sulfonic acid, an electrochemical test is carried out using a 3-electrode setup connected to a BIOLOGIC VMP3 potentiostat: 1) Reference electrode: saturated calomel electrode or "ECS", 2) Working electrode: 1 cm diameter 304L stainless steel test specimen 2 , And 3) against a platinum electrode.

[0053] The test specimen is polished with P400 grit sandpaper and then passivated for 1 hour in a 10% nitric acid solution at room temperature. This ensures an identical starting state for all tests. The test temperature is thermostated to 20°C ± 2°C.

[0054] The protocol used comprises the following three steps: a) monitoring the abandonment potential of the working electrode (304L) in sulfonic acid added according to the process of the present invention, i.e. measuring the potential of the material in the solution as a function of time, for 30 minutes, b) immersion of the three-electrode system in a standard (i.e., non-additized) sulfonic acid solution, then application of a current of -800 μA.αττ to the working electrode 2 for 1 minute in order to artificially depassivate the material by fixing its potential in the corrosion range, c) immersion of the three-electrode system again in the sulfonic acid solution added according to the process of the present invention, and monitoring again of the abandonment potential of the working electrode, until it stabilizes. VALIDATION TEST RESULTS

[0055] In the case of a standard methanesulfonic acid, i.e., without additives, in a 70% by weight solution in water, after application of a current quantity of -800 μA.αττ 2 The potential of the working electrode (a 304L stainless steel specimen) drops to around -350 mV, which corresponds to the 304L stainless steel transitioning to its active state. When the current application is stopped, the material's potential remains almost at the same level and does not rise. The 304L stainless steel remains in its active state and corrodes.

[0056] The behavior is totally different in a 70% by weight solution in water of a methane-sulfonic acid added according to the process of the present invention (examples 1 and 2 above).

[0057] First, a discharge potential of approximately 750 mV is observed for the 304L stainless steel after 30 minutes. During the application of a current of -800 μA.αττ 2 , THE The material potential drops to around -200 mV (transition of 304L stainless steel to its active state). When the current is stopped, the material potential rises very rapidly. It reaches 780 mV after 2 hours of potential monitoring, and a complete absence of corrosion is observed.

[0058] In all cases (examples 1 and 2 above), methanesulfonic acid with sodium nitrite additive is a low-corrosion methanesulfonic acid within the meaning of the present invention.

Claims

DEPCT6429 / 04 / 25631. A process for the production of low-corrosion sulfonic acid comprising at least the following steps: a) addition of at least one type of nitrite to a general sulfonic acid; b) curing of the mixture obtained in step a) at temperatures between 0°C and 100°C, and ideally between 0°C and 80°C, particularly between 10°C and 60°C, even particularly between 10°C and 50°C for an interval between a few seconds and a few hours, ideally between 1 minute and 4 hours, particularly between 10 minutes and 2 hours, even more ideally between 10 minutes and 1 hour; c) Recovery of low corrosive sulfonic acid.

2. The process according to claim 1 in which nitrite is selected from alkali metal nitrite, alkaline-earth metal nitrite and ammonium nitrite, ideally from sodium nitrite and potassium nitrite, even more suitable nitrite is sodium nitrite. 3.The process according to claim 1 or claim 2 where sulfonic acid is the sulfonic acid of the formula R-SO3H, where R represents a chain of saturated or unsaturated hydrocarbons, straight, branched or cyclic, composed of 1 to 12 carbon atoms, either unsubstituted or substituted by one radical and / or one or more atoms chosen from halogen atoms, alkyl radicals of 1 to 6 carbon atoms, and aryl and heteroaryl radicals composed of 6 or 10 members in a 4-ring.The process according to one of the claims 1 through 3 in which a sulfonic acid is selected from methanesulfonic acid, ethanesulfonic acid, normal-propanesulfonic acid, iso-propanesulfonic acid, normal-butanesulfonic acid, iso-butanesulfonic acid, sec-butanesulfonic acid, tert-butanesulfonic acid, trifluoromethanesulfonic acid, para-toluenesulfonic acid, benzenesulfonic acid, naphthalenesulfonic acid, etc. And a mixture of two or more of them in any proportion, the appropriate being from methane sulfonic acid, egensulfonic acid, trifluoromethane sulfonic acid and para-toluene sulfonic acid, the appropriate of all being sulfonic acid is methane sulfonic acid5. The process according to one of the preceding claims in which the molar ratio of nitrite / sulfonic acid is between 200ppm and 6000ppm, the appropriate being between 400ppm and 2000ppm, specifically between 500ppm and 1900ppm6.The process under any of the preceding claims in which the mixture obtained after the curing of step b), or during the curing of step b), or during and after the curing of step b), is brought to a bubbling stage of air and / or inert gas, preferably inert gas 7. Low corrosive sulfonic acid obtained primarily by the process of any of the claims 1 through 6.

8. The use of low corrosive sulfonic acid under claim 7 or obtained under any of the preceding claims for limiting or even preventing corrosion of metals by sulfonic acid.The process for producing low-corrosive sulfonic acids comprises at least the following steps: a) the addition of at least one nitrite to a conventional sulfonic acid; b) the curing of the mixture obtained in step a) at temperatures between 0°C and 100°C, and ideally between 0°C and 80°C, particularly between 10°C and 60°C, even more so between 10°C and 50°C for a period of time. between a few seconds and a few hours, the optimal is between 1 minute and 4 hours, particularly between 10 minutes and 2 hours, even more particularly between 10 minutes and 1 hour; c) Low corrosive sulfonic acid recovery.

2. The process according to claim 1 in which nitrite is selected from alkali metal nitrite, alkaline-earth metal nitrite and ammonium nitrite, the optimal is from sodium nitrite and potassium nitrite, the more suitable nitrite is sodium nitrite. 3.The process according to claim 1 or claim 2 where sulfonic acid is a sulfonic acid of the formula R-SO3H, where R represents a chain based on a saturated or unsaturated hydrocarbon, straight, branched or cyclic, composed of 1 to 12 carbon atoms, which is either unsubstituted or substituted by one radical and / or one or more atoms chosen from halogen atoms, alkyl radicals of 1 to 6 carbon atoms, and aryl and heteroaryl radicals composed of 6 or 10 members of the ring 4.The process under one of the claims 1 through 3 in which a sulfonic acid is selected from methane sulfonic acid, ethane sulfonic acid, n-propane sulfonic acid, iso-propane sulfonic acid, n-butane sulfonic acid, iso-butane sulfonic acid, sec-butane sulfonic acid, tert-butane sulfonic acid, trifluoromethane sulfonic acid, para-toluene sulfonic acid, benzene sulfonic acid, naphthalene sulfonic acid and two or more mixtures of them. Furthermore, in any proportion, the optimal is from methane sulfonic acid, ethane sulfonic acid, trifluoromethane sulfonic acid and para-toluene sulfonic acid, of which the optimal sulfonic acid is methane sulfonic acid5. The process according to any of the preceding claims where the molar ratio of nitrite / sulfonic acid is between 200ppm and 6000ppm, the optimal is between 400ppm and 2000ppm, specifically between 500ppm and 1900ppm6.The process under any of the preceding claims in which the mixture obtained after the curing of step b), or during the curing of step b), or during and after the curing of step b), is brought to a bubbling stage of air and / or inert gas, the appropriate inert gas being 7. Low corrosive sulfonic acid obtained materially under the process of any of the claims 1 through 6.

8. The use of low corrosive sulfonic acid under claim 7 or obtained under any of the preceding claims for the limitation or even prevention of corrosion of metals by sulfonic acids;