The invention relates to the treatment of fatty acids, especially the esterification of fatty acids. Esters of fatty acids obtained can thus be used as raw materials in various fields such as cosmetics or biofuel production. In particular, the invention relates to a composition of acid may in particular be a catalyst in the esterification of fatty acids.

[0002] During the esterification of fatty acids, it is often necessary to use a catalyst, for example acid. Among the acid catalysts used, particularly discloses the use of sulfuric acid.

[0003] For example, the patent EP1951852 B1 provides a process for producing alkyl esters of fatty acids from "tall oil" containing sulfur compounds in the presence of a strong acid catalyst such as especially sulfuric acid.

[0004] Sulfuric acid is known for its oxidizing power and dehydrating causing secondary reactions that may compete with the main esterification reaction.

[0005] It is also known the use of alkanesulfonic acid as an acid catalyst esterification reactions of fatty acids. Thus, documents

WO2006081644 and WO2015134495 describe the use of methane sulphonic acid in the esterification of fatty acids.

[0006] However, the alkane sulfonic acids are relatively expensive compounds, we seek to optimize their use. Moreover, it may be useful to further improve the efficiency of esterification catalysts.

[0007] It is therefore necessary to find an acid catalyst that is more efficient, both in terms of the degree of conversion fatty acid esters from the point of view of the kinetics of the esterification, and is inexpensive. For this, we have shown that a catalyst comprising at least one particular acid composition makes it possible, inter alia, to alleviate these drawbacks.

[0008] Thus, according to a first aspect, the present invention relates to a composition comprising:

- at least one alkanesulfonic acid of formula R-SO3H wherein R is a saturated hydrocarbon chain, linear or branched, having from 1 to 4 carbon atoms, which may or may not be substituted by at least one halogen atom;

- sulfuric acid;

- and optionally at least one solvent;

in which :

- the proportion by weight of alkanesulfonic acid based on the total weight of alkanesulfonic acid and sulfuric acid is between 40% and 90%, preferably between 44% and 89%;

- the sulfuric acid by weight in proportion to the total of alkanesulfonic acid and sulfuric acid weight is between 10% and 60%, preferably between 1 1% and 56%.

[0009] The solvent may be of any type known to those skilled in the art and for example water, an organic solvent, a mixture of organic solvents or a mixture of water and one or more organic solvents.

[0010] In one embodiment, the solvent is selected from water, an alcohol and an ether, preferably water and an alcohol in Ci to C3, and more particularly water and methanol, alone or in combination. The proportion by weight of solvent based on the total weight of the composition is generally between 0% and 50%, preferably between 5% and 35%.

[0011] When the hydrocarbon chain of the R group above is substituted with at least one halogen atom, said halogen atom is preferably selected from fluorine, chlorine and bromine, preferably fluorine.

[0012] The alkane-sulfonic acid, R-SO3H formula defined above, used in the context of the present invention is advantageously chosen from methanesulfonic acid, ethanesulfonic acid, n-propane acid sulfonic acid, / ' n-propane-sulfonic acid, n-butane-sulfonic acid, / ' n-butane-sulfonic acid, sec-butane-sulphonic acid, tert-butane acid sulfonic acid, trifluoro methane sulfonic acid (also known as triflic acid), and mixtures of two or more of them in any ratio, and so

most preferably, the alkanesulfonic acid is methanesulfonic acid.

[0013] In addition, the acid composition of the present invention may comprise one or more additive (s) and / or filler (s), well known to those skilled in the art, such as those selected, for example, from inhibitors corrosion, fragrances, odorants, and others.

[0014] The present invention also relates to the use of said composition as an esterification catalyst, more particularly of acid esterification (s) fat.

[0015] Finally, the invention relates to a method for producing fatty acid esters comprising the steps of:

a / introducing at least one fatty acid in a reactor;

b / adding at least one alcohol;

c / heating the reaction medium;

d / introduce acid composition defined above as a catalyst; e / optionally, removing the water formed during the esterification reaction; and f / recover the fatty acid ester;

step d may be performed simultaneously with step a and / or b, preferably at the same time as steps a and / or b.

[0016] In said process, the molar ratio catalyst / fatty acid is between 0.001 and 1, preferably between 0.01 and 0.5 and more particularly between 0.02 and 0.2.

[0017] The invention will be better understood in light of the description, the figures and the following examples but is in no way limited to the said figures and examples.

[0018] Figure 1 shows the percentage of residual fatty acids (ordinate) in the organic phase after the esterification reaction depending upon the nature of the acid catalyst.

[0019] Figure 2 shows the conversion kinetics of residual fatty acids in the esterification step according to the nature of the acid catalyst.

[0020] In the said Figures 1 and 2:

- AMS 100 means that the catalyst used contains 70% pure methanesulfonic acid and 30% water,

- AMS 70/30 H 2 SO 4 means that the catalyst used is a catalyst according to the invention and it comprises:

o 49% by weight pure methanesulfonic acid relative to the total weight of the mixture,

o 29.1 wt% pure sulfuric acid weight relative to the total weight of the mixture and,

o 21, 9% water.

- AMS 60/40 H 2 SO 4 means that the catalyst used is a catalyst according to the invention and it comprises:

o 42% by weight pure methanesulfonic acid relative to the total weight of mixture,

o 38.8 wt% pure sulfuric acid weight relative to the total weight of the mixture and,

o 19.2% of water.

- 100 H 2 SO 4 means that the catalyst used comprises 97% pure sulfuric acid and 3% water.

[0021] The AMS AMS used is diluted to 70% by weight in water and sulfuric acid used is a sulfuric acid diluted to 97% by weight in water.

[0022] More specifically, the invention relates to a composition comprising:

- at least one alkanesulfonic acid of formula R-SO3H wherein R is a saturated hydrocarbon chain, linear or branched, having from 1 to 4 carbon atoms, which may or may not be substituted by at least one halogen atom, and

- sulfuric acid.

[0023] In the composition according to the invention:

- the proportion by weight of acid pure alkanesulfonic relative to the total weight of alkanesulfonic acid and sulfuric acid is between 40% and 90%;

- the proportion by weight in pure sulfuric acid relative to the total weight of alkanesulfonic acid and sulfuric acid is between 10% and 60%.

[0024] Preferably:

- the proportion by weight of acid pure alkanesulfonic relative to the total weight of alkanesulfonic acid and sulfuric acid is between 44% and 89%; - the proportion by weight in pure sulfuric acid relative to the total weight of alkanesulfonic acid and sulfuric acid is between 1 1% and 56%.

[0025] By "pure" is meant a non-diluted compound in water or a solvent.

[0026] With the composition according to the invention, the Applicant has demonstrated surprising results, such as those exemplified in the present application.

[0027] It should be noted that said composition may also comprise one or more solvents, and optionally one or more additives.

[0028] The term "solvent" is meant aqueous, organic or water-soluble. Preferably, the solvent may be water, an alcohol or an ether, used alone or in combination. Preferably, the solvent is water and / or a C1 to C3. And more preferably, the solvent is water, methanol or a water / methanol mixture. The solvent content by weight relative to the total weight of the composition is between 0 and 50%, and most preferably between 5% and 35%.

[0029] When the hydrocarbon chain of the R group above is substituted with at least one halogen atom, said halogen atom is selected from fluorine, chlorine and bromine, preferably fluorine.

[0030] Preferably, the alkane sulfonic acid included in the composition according to the invention is selected from methanesulfonic acid, ethanesulfonic acid, n-propane-sulfonic acid, / ' n-propane-sulfonic acid, n-butane-sulfonic acid, / ' n-butane-sulfonic acid, sec-butane-sulphonic acid, tert-butane-sulphonic acid, trifluoro-methanesulfonic acid sulfonic acid (also known as triflic acid), and mixtures of two or more of them in all proportions. Preferably, the alkanesulfonic acid is methanesulfonic acid.

[0031] Said alkanesulfonic acid can be used as such, or in combination with one or more other components, that is to say in formulation. Any type of formulation comprising at least one alkanesulfonic acid is suitable. Generally, the formulation comprises 0.01% to 100% by weight of alkanesulfonic acid, more typically 0.05% to 90% by weight, in particular from 0.5% to 75% by weight, inclusive, acid (s) alkanesulfonic (s), relative to the total weight of said formulation of alkanesulfonic acid.

[0032] The formulation is an aqueous formulation for example, organic or aqueous-organic. The formulation may be prepared as a concentrated mixture, said concentrated mixture can be diluted before use. Finally, within the meaning of the present invention, the formulation may be a pure alkanesulfonic acid, or a mixture of pure alkanesulfonic acids, that is to say, the formulation may contain only one or more acid (s) alkanesulfonic (s), without other formulation additive or other solvent or diluent.

[0033] According to one embodiment of the invention, the alkane sulfonic acid may be diluted to 70% in a solvent, preferably in water. Preferably, the alkanesulfonic acid is methanesulfonic acid diluted to 70% by weight in water, such as found in commerce. One can for example use of anhydrous methane sulfonic acid or AMSA (acronym for "anhydrous methane sulphonic acid" in English) or of methane sulfonic acid in aqueous solution such as a methane-sulfonic acid solution 70% by weight in water and marketed by Arkema under the name Scaleva ® . One can also use the

[0034] Use may also be of methanesulfonic acid in aqueous solution, such as sold by BASF under the name Lutropur ® MSA ready for use or diluted with water in the proportions indicated above.

[0035] Concerning the formulation of sulfuric acid, any type of formulation may be suitable. Generally, the formulation comprises 0.01% to 100% by weight of sulfuric acid, more typically 0.05% to 98% by weight, in particular from 74% to 97% by weight, inclusive, of sulfuric acid, based on the total weight of said formulation.

[0036] The formulation is an aqueous formulation for example, organic or aqueous-organic. The formulation may be a concentrated mixture. Alternatively, the formulation can also be a ready-to-use formulation, that is to say, it does not need to be diluted. Finally, within the meaning of the present invention, the formulation may be pure sulfuric acid without other formulation additive or other solvent or diluent. Preferably, sulfuric acid is diluted to 97% by weight in water, such as that sold by Arkema or dilute sulfuric to 96% by weight acid in water marketed by BASF.

[0037] According to a preferred embodiment, the composition according to the invention is used as the acidic esterification catalyst, preferably as an acidic esterification catalyst of fatty acids.

[0038] The present invention also relates to an acidic esterification catalyst, preferably fatty acid esterification comprising, preferably consisting of, the acidic composition as defined above.

[0039] The composition according to the invention finds a particularly advantageous use as a catalyst, for example as pure fatty acid esterification catalyst or as a mixture in oils or fats, which is then denominated "fatty acids free ", as opposed to fatty acids present in the form of mono-, di- and / or tri-glycerides present in said oils and / or fats.

[0040] The esterification reaction of fatty acids allows, from the condensation of an alcohol with a fatty carboxylic acid, to obtain a fatty ester and a water molecule. By fatty acid means a carboxylic acid with an aliphatic chain including C 4 -C36. Natural fatty acids generally have a carbon chain of 4 to 36 carbon atoms, said carbon chain possibly being saturated or unsaturated, linear or branched.

[0041] According to the invention, the fatty acids may preferably be of the fatty acids present in the oils. In this case, the esterification reaction may be followed by a transesterification reaction in the presence of a lower alcohol, typically comprising 1 to 4 carbon atoms, to obtain esters of fatty acids and glycerol, said fatty acid esters may then be used as fuel, known as "biodiesel".

[0042] Typically, in the preparation of biodiesel, if the level of residual fatty acids in the oil or fat is greater than 1%, there is a risk of hydrolysis of said residual fatty acids by reaction with the catalysts of transesterification. This can particularly be a disadvantage in the production of biodiesel, the trainees know that can create an emulsion and make the separation of biodiesel and glycerol difficult or impossible.

[0043] The Applicant has thus demonstrated that, compared with an alkane sulfonic acid used alone as catalyst or with respect to the only sulfuric acid used as catalyst, the mixture of at least one alkanesulfonic acid with the acid sulfuric acid in the claimed proportions, makes it possible, after an esterification step to lower the rate of residual fatty acids in the organic phase below 1, 1% by weight, preferably 1% by weight, more particularly 0.95% by weight; which is very difficult to achieve with a alkanesulfonic acid used alone or sulfuric acid alone.

[0044] This low level of residual fatty acids in particular has an advantage over the final purity of the ester or in the transesterification step, often subsequently performed, since the latter will consume less catalyst, generally basic catalyst, often expensive and limit the formation of soaps which disturb the reaction.

[0045] It has also been shown that the use of the acid composition according to the invention as esterification catalyst provides an amount of lower residual catalyst in the organic phase than that obtained with the acid catalyst alkane- sulfonic alone or the sulfuric acid catalyst alone. This reduces the consumption of basic catalyst during any step subsequent transesterification in order to prepare for example biodiesel.

[0046] Surprisingly, it was further demonstrated that the use of the composition according to the invention improves the conversion kinetics of the fatty acids with respect to the use of an alkane sulfonic acid used alone used alone or sulfuric acid.

[0047] According to one embodiment of the invention, the composition according to the invention is an esterification and transesterification catalyst thus achieving, in a single step, the esterification and transesterification of the free fatty acids and fatty acids present in the form of mono-, di- and / or tri-glycerides.

[0048] Optionally, the composition according to the invention may comprise one or more additives well known to those skilled in the art, such as those selected from corrosion inhibitors, fragrances, odorants, and other well-known additives of the art.

[0049] According to a preferred embodiment, the composition according to the invention comprises at least one corrosion inhibitor. According to another preferred embodiment, the composition comprises at least one perfume and / or an odorant.

[0050] The composition of the invention may be prepared by mixing the alkanesulfonic acid (s) and sulfuric acid, according to any method known to those skilled in the art such as, for example, the method described herein, said method not being limiting.

[0051] Into a vessel cooled to approximately 10 ° C, introducing the alkane sulfonic acid. Sulfuric acid is then added by any technique known to those skilled in the art, so as to minimize the potential of the reaction exotherm. Generally, the addition of sulfuric acid will be carried out so that the temperature did not exceed 90 ° C, preferably 80 ° C and more particularly 60 ° C. In the case where a solvent and optional additives are used, it is preferable to pre-mix with the alkane sulphonic acid before slowly adding sulfuric acid. Depending on the solvent and additives used, the rate of addition of sulfuric acid will be carried out so as not to reach a temperature of above 90 ° C mixture,

[0052] The present application also relates to a method for producing fatty acid esters wherein the fatty acids are esterified in the presence of the composition according to the invention.

[0053] The esterification process involves introducing a fatty acid or a fatty acid mixture in a reactor. The alcohol is then added and the medium is heated to a temperature generally between 50 ° C and 200 ° C, more usually between 60 ° C and 120 ° C, preferably between 60 ° C and 80 ° C. The introduction of the composition according to the invention is preferably to the esterification temperature. According to another embodiment of the invention said composition may be added prior to heating.

[0054] According to yet another embodiment of the invention, the alcohol and said composition can be added continuously, together or separately, when the medium has reached the esterification temperature. According to one embodiment of the invention, said composition can be added with the fatty acid or fatty acid mixture.

[0055] According to a preferred embodiment of the invention, the fatty acid or mixture of fatty acids, alcohol and said composition are added together prior to heating. The esterification reaction is then carried out in the temperature range indicated above.

[0056] During the esterification process, the composition of the invention acts as a catalyst.

[0057] The fatty acids may be of any type selected from fatty acids and mixtures of fatty acids known to the skilled person including fatty acids from vegetable or animal community, including algae, and more generally the plant kingdom. These said acids generally and advantageously include at least one olefinic unsaturation.

[0058] The said acids are usually present in vegetable oils from various oil plants such as, but not limited to, peanuts, sunflower, rapeseed, castor bean, lesquerella, olive, soybean, oil palm, avocado, walnuts, hazelnuts, almonds, sesame seeds, sea buckthorn and limanthe, including algae.

[0059] They can also be derived from terrestrial or marine animal world, and in the latter case, they can come from fat fish or mammalian fats, such as, for example and without limitation, the fat from cattle, cod, whales and seals. Finally, said acids can come from recycled waste oils such as, but not limited to, frying oils ( "used cooking oil" in English).

[0060] As described above, the acids in these oils are put in the presence of an alcohol. Alcohol can be of any type known to the art such as monoalcohols, diols, triols, tetrols, and others, used alone or in combination. Preferably, the alcohol used has a molar mass of 30 to 200 g. mol "1 .

[0061] According to one embodiment of the invention the alcohol is of type R 1 -OH where R 1 is an alkyl or aromatic chain, linear or branched, saturated or unsaturated, comprising from 1 to 20 carbon atoms. Preferably, R 1 is an alkyl chain containing from 1 to 10 carbon (s), in particular from 1 to 4. According to another embodiment of the invention, the alcohol has more than one -OH functional group, such as by

example two or three -OH functional groups, and, for example, the alcohol may be glycerol (propane-1, 2,3-triol).

[0062] In one embodiment of the invention wherein the amino acid composition is used as reaction catalyst of esterification of fatty acids, especially of free fatty acids in oils, the molar ratio catalyst of the invention / fatty acid is between 0.001 and 1, preferably between 0.01 and 0.5 and more particularly between 0.02 to 0.2. The number of moles of fatty acids is measured by acid-base potentiometry assay and is expressed as moles per gram of fatty acids present in the starting material. This value is then multiplied by the molar ratio catalyst / fatty acids, to determine the amount of catalyst to be added.

[0063] According to one embodiment of the esterification process of the invention, the molar ratio alcohol / fatty acids is between 1 and 20, preferably between 4 and 10.

[0064] According to one embodiment of the invention, the esterification reaction of fatty acids can be carried out at any temperature, but preferably at temperatures between 50 ° C and 200 ° C, more usually at temperatures between 60 ° C and 120 ° C, preferably between 60 ° C and 80 ° C.

[0065] According to one embodiment of the invention, the esterification reaction of fatty acids can be carried out at any pressure but preferably under a pressure of between 10 3 Pa (0.01 bar absolute) and 2.10 6 Pa ( 20 bar absolute), more generally between atmospheric pressure and 10 6 Pa (10 bar absolute) and most preferably at atmospheric pressure basis.

[0066] The reaction time for the esterification of fatty acids may vary within wide limits and is generally between a few minutes and a few hours, for example between 10 minutes and 6 hours, typically between 30 minutes and 180 minutes.

[0067] The esterification reaction can be carried out batchwise or continuously. The catalyst of the invention is added to the mixture or separately into the reaction medium. It can be added alone or in co-feed with the source of fatty acids (oil, animal fat, etc ..) and / or alcohol. The reaction may be carried out in one or more reactors, between 2 and 15, more generally 2-10 reactors, more usually 2 to 5 reactors, arranged in parallel or in cascade. In a particular, preferred batch process with multiple reactors arranged in cascade.

[0068] It may be advantageous to operate separations of organic and aqueous phases between two reactors. To improve the yield of the reaction, the water formed can be removed according to any method well known to those skilled in the art, for example as and when it is formed, for example by heating. In one embodiment of the invention, the removal of water may result in elimination of all or part of the solvent, particularly when the solvent is an alcohol.

[0069] In an embodiment of the invention, the free fatty acids from used vegetable oil to obtain biofuels, especially biodiesel. In this case, biodiesel is obtained after transesterification step as described above. If this biodiesel neutralization step is necessary, it is possible to use the acidic aqueous phase obtained at the end of the esterification reaction of free fatty acids. According to one embodiment of the invention, the alcohol is removed before using said acid phase.

[0070] The esterification reaction of the fatty acids according to the invention also allows to obtain products that can be used in various fields such as cosmetics, lubricants, agrochemicals, pharmaceuticals, cleaning, etc.

Examples

[0071] The following examples illustrate the present invention but are by no means limiting.

Method of preparing a composition according to the invention:

[0072] A composition is prepared comprising:

• 60% by weight of methanesulfonic acid diluted to 70% in water (42% by weight of pure methanesulfonic acid);

• 40% by weight of sulfuric acid diluted to 97% in water (39% by weight of pure sulfuric acid).

[0073] The above composition is prepared from an aqueous solution at 70% by weight of AMS LC from Arkema introduced into a jacketed reactor cooled by a water bath controlled at 10 ° C. Sulfuric acid 97% by weight is added dropwise with a dropping funnel attached to the cap jacketed reactor being careful not to exceed 60 ° C.

[0074] The composition thus obtained contains, per 100 g of composition, 0.8355 moles acid (42/96 + 39/98 (96 being the molecular weight of AMS and 98 being the molecular weight of H 2 SO 4 ) ). The molecular weight of the acid mixture is from 1 19.7 g / mole (= 100 / 0.8355).

[0075] The thus prepared composition is used as the esterification catalyst in Example below.

Example of an oil esterification:

[0076] Use an industrial mixture comprising an oil comprising triglycerides and 94% by weight of free fatty acids (FFA to "Free Fatty Acids") with an average molecular weight of fatty acids 268 ± 1 g / mol.

[0077] The molar ratio methanol / FFA is 8. The molar ratio catalyst / FFA is equal to 0.175.

[0078] In a jacketed reactor preheated to 50 ° C and equipped with a mechanical stirrer, a temperature probe and a condenser was charged with 451 g of said industrial mixture comprising triglycerides and 94 wt% FFA or 1, 582 moles of fatty acid. The amount of methanol introduced is determined as follows: 1, 582 x 8 x 32 = 405 g of methanol (8 molar equivalents / FAA).

[0079] The reaction mixture is heated to 70 ° C and then introduced the catalyst prepared above. The amount of catalyst to be added is calculated as follows: 1, 582 x 0.175 x 1 = 33.14 19.7 g of composition (0.175 molar equivalent / FFA). The reaction medium is stirred for 2 hours at 70 ° C, then decanted and left overnight at 70 ° C. The aqueous and organic phases were analyzed using the methods described below.

Analytical Methods:

[0080] The FFA and the catalyst in the organic phase, are assayed potentiometrically as follows: in a beaker were introduced about 1, 5 g of organic phase, is then completed to 50 mL with toluene mixture / isopropanol / water in the proportions 500/495/5 by volume.

[0081] The potentiometric titration is performed with KOH 0.1 mol L "1 in ethanol with 13 DG1 electrode-SC # 2 and a titrator T50, both from Mettler Toledo.

[0082] The dosage can be determined accurately, on the one hand the amount of residual catalyst in the organic phase mole per gram and, secondly, the residual fatty acid content in the organic phase in% by weight.

[0083] The acid-base dosing provides potential 2 breaks: the first jump is the catalyst and the second jump corresponds to the residual fatty acids.

Results:

[0084] The above-described assays to measure the percentage of residual FFA in the organic phase.

[0085] These results, shown in Figure 1, show that the weight percentage of residual FFA is 1, 2 with the only AMS, 1, 05 with the H 2 SO 4 alone, with the composition of 0.89 AMS 70 / 30 H 2 SO 4 according to the invention and with the composition 0.9 AMS 60/40 H 2 SO 4 according to the invention.

[0086] With the composition according to the invention, we obtain a percentage of residual FFA lower than those obtained with the other compositions.

[0087] Furthermore, the conversion of FFA kinetics are improved compared with the use of each acid alone, as shown in Figure 2. Indeed, it is noted, with the composition according to the invention kinetics ester conversion faster and, after a same given time (1 h), a higher conversion of FFA (98% with the composition according to the invention and 97% with only AMS and h 2 SO only) .

WE CLAIMS

1. A composition comprising:
- at least one alkanesulfonic acid of formula R-SO3H wherein R is a saturated hydrocarbon chain, linear or branched, having from 1 to 4 carbon atoms, which may or may not be substituted by at least one halogen atom;
- sulfuric acid;
- and optionally at least one solvent;
in which :

- the proportion by weight of alkanesulfonic acid based on the total weight of alkanesulfonic acid and sulfuric acid is between 40% and 90%, preferably between 44% and 89%;

- the sulfuric acid by weight in proportion to the total of alkanesulfonic acid and sulfuric acid weight is between 10% and 60%, preferably between 1 1% and 56%.

2. Composition according to claim 1 wherein the solvent is selected from water, an alcohol and an ether, alone or in combination.

3. Composition according to one of the preceding claims wherein the solvent is water or an alcohol -C 3, taken alone or in combination.

4. Composition according to one of the preceding claims wherein the solvent is water or methanol, alone or in combination.

5. Composition according to one of the preceding claims wherein the proportion by weight of solvent based on the total weight of the composition is between 0% and 50%, preferably between 5% and 35%.

6. Composition according to one of the preceding claims wherein the alkane sulfonic acid is selected from methanesulfonic acid, ethanesulfonic acid, n-propane-sulfonic acid, / ' N -propane-sulphonic acid, n-butane-sulfonic acid, / ' n-butane-sulfonic acid, sec-butane-sulphonic acid, tert-butane-sulfonic acid, trifluoro methane sulfonic acid and mixtures of two or more of them in any proportion.

7. Composition according to one of the preceding claims wherein the alkanesulfonic acid is methanesulfonic acid.

8. Composition according to one of the preceding claims comprising at least one corrosion inhibitor.

9. Composition according to one of the preceding claims comprising at least one perfume or fragrant agent, alone or in combination.

10. Use of the composition according to one of claims 1 to 9 as an esterification catalyst, preferably fatty acid esterification.

11. A method of making fatty acid esters comprising the steps of: a / introducing at least one fatty acid in a reactor;

b / adding at least one alcohol;

c / heating the reaction medium;

d / introducing the composition according to any one of claims 1 to 9 as catalyst;

e / optionally, removing the water formed during the esterification reaction; f / recover the fatty acid esters;

step d may be performed simultaneously with step a and / or b, preferably at the same time as steps a and / or b.

12. The method of claim 1 1 wherein the molar ratio catalyst / fatty acid is between 0.001 and 1, preferably between 0.01 and 0.5 and more particularly between 0.02 to 0.2.