WO2013098509A1

WO2013098509A1 - Method for extracting metals present in hydrocarbon fractions

Info

Publication number: WO2013098509A1
Application number: PCT/FR2012/053015
Authority: WO
Inventors: Joëlle NOKERMAN; Vincent RIETSCH; Romain RUPPERT
Original assignee: Total Raffinage Marketing
Priority date: 2011-12-27
Filing date: 2012-12-20
Publication date: 2013-07-04
Also published as: FR2984912A1

Abstract

The invention relates to a method for extracting metals from a hydrocarbon fraction containing coordinated metals, comprising the following steps of: demetallation of the coordinated metals by (i) bringing said hydrocarbon fraction into reaction, in an inert atmosphere, with a solution having a pH of between 1 and 5, said solution comprising at least one C1-C4 carboxylic acid, the reaction medium thus obtained further comprising a reducing metal having a standard potential, E0, of between -0.7 and -0.9 V, present in an amount of at least 6 equivalents per 1 equivalent of coordinated metal, (ii) reflux heating the reaction medium to a temperature matching the boiling temperature of said carboxylic acid, until discolouration of the reaction medium, and extraction of the metal salts by adding a lipophilic solvent and an aqueous solution, said metals being recovered in the aqueous phase.

Description

Process for extracting metals present in hydrocarbon fractions

The invention relates to a process for extracting metals present in hydrocarbon fractions containing coordinated metals.

Heavy oils usually have a significant share of different petrophorphyrins or coordinated metals, from a few particles per million to a few hundred ppm. These, difficult to separate from crude oil, are metallated, mainly by vanadium (IV) and nickel (II). Of the petroporphyrins, vanadium porphyrins are typical of marine sediments, while those of nickel are mainly present in a continental environment. The high thermodynamic stability of these compounds explains their predominance in sediments vis-à-vis other metalloporphyrins.

The nickel and vanadium contained in the petroleum residues are mainly concentrated in the asphaltene fraction of the latter. In the particular case of Athabasca bitumens, metals were also found in significant quantities in the Maltene fraction. The metal compounds present in the residues are in the form of soluble organometallic complexes such as porphyrins. Nickel and Vanadium may also be present in non-porphyrinic structures, which are currently poorly defined. In the particular case of vanadium, it seems that porphyrins are largely in the majority compared to other metallic structures.

On the other hand, it appears that the vanadium present in heavy oils is essentially in the form of vanadylporphyrins. The most common forms of vanadylporphyrins have been identified as ETIO (etioporphyrin), which derives directly from Theme, and DPEP (deoxophylloerythropetioporphy), which is derived from different types of chlorophylls. The presence of vanadium in heavy oil comes from the slow degradation of these systems.

The removal of these metals as early as possible in the crude treatments is a necessity, as these metals reduce the service life of the catalysts that are used in downstream refining operations, such as catalytic cracking, hydrocracking, hydrodesulfurization (EP 1939270 A1). Indeed, some metals such as vanadium poison the catalyst by depositing on its surface, tending to reduce the activity, which requires the premature replacement of it. Other metals, such as nickel, generate side reactions such as dehydrogenation. In the refining industry, if necessary, the metals present in petroleum hydrocarbons are removed by hydrotreating, and more particularly by hydrodemetallization, or by coking. These processes, however, lead to a significant loss of raw material and lead to the formation of vanadium pentoxide V ₂ O ₅ , which poses problems of toxicity (L. Zychlinski et al., Arch., Environ Tox 1991, 20, 295 -298) and corrosion (LF Drbal et al, Power Plant Engineering by Black & Veatch, Springer, New York, 1996).

The catalysts are based on noble metals, and therefore expensive, it is advisable to preserve and save them by demetalling the porphyrins contained in the crude oil. However, these metalloporphyrins are often contained in asphaltenes, a portion of these oils soluble in toluene and insoluble in alkanes. In heavy oils, there are colloidal aggregates, which can be very stable, and thus prevent easy extraction of these metalloporphyrins.

However, several patents have been published to provide methods for extracting metalloporphyrins using polar solvents such as 2-pyrrolidone (US 3,052,627) or 2-butyrolactone (US 2,913,394). US Pat. No. 4,643,821 describes the best specific solvents for extracting vanadylporphynes in asphaltenes. It is by employing a mixture of aromatic and polar solvents that the best results have been obtained insofar as this mixture makes it possible both to solubilize the heavy oils and to extract the metalloporphyrins.

One of the objectives of the inventors is to achieve this demetallation reaction with high yields and using the mildest possible conditions to preserve the crude oil. For this purpose, numerous methods for the demetallation of various metalloporphyrins have been described in the literature or patents, for example oxidation demetallation (US Pat. (US 5,726,056; PM Fedorak et al., Enzyme Microb., Tech., 1993, 15, 429-437), electrolytic demetallation (US 5,529,684, C. Ovalles et al, Fuel Processing Technology, 1996, 48, 241-247). or photolysis (Kunkely, H. et al, Inorganic Chemistry Communications, 2007, 10, 479-481). However, two main methods emerge: an electrochemical route and a chemical route. The two approaches have been envisaged and are described in the literature, in particular by MF Ali et al, Fuel Processing Technology, 2006, 32, 573-584.

Mr. F. Ali et al lists a large quantity of proposed chemical reagents for the demetallation of petroporphyrins. Several of the studies described have been carried out by manufacturers (Exxon, Shell, China Petrochemical Corp., etc.). While some of the proposed reagents appear to be relatively non-destructive of organic matter, others, such as hydrofluoric acid, sulfuric acid, nitric acid and sodium hypochlorite, are not very selective towards demetallation of porphyrins. In addition to the demetallation reactions, deterioration of unmetallated molecules is observed by different side reactions, such as oxidation, polymerization of unsaturated compounds and incorporation of chlorine. This explains the reason why the development of these demetallation processes was not a priori led to the stage of industrialization.

The patent application cited above, EP 1 939 270 A1, discloses a process for the selective metalloporphyrin oxidation demetallation of a real charge and removal of the metal in a single step. The oxidant used is a hydroperoxide and the oxidation is catalyzed by Fe (III). However, the use of such conditions is not without consequences, since they lead to the deterioration of heavy oil by oxidation and the formation of free radicals. Despite high demetallation rates on real load, this method is therefore not entirely satisfactory economically.

The Applicant has focused his research on chemical demetallation using acidic and / or reducing conditions. This method is generally represented in the literature by a general equation

PM (II) + 2 HX <→ PH ₂ + MX ₂ The use of acidic conditions is valid for many metal ions, such as zinc-octaethylporphyrin (Zn (II) OEP), which requires hydrochloric acid (HCl) or the Ni (II) OEP for which sulfuric acid (H ₂ SO ₄ ) is essential for the demetallation reaction. However, the use of a strong acid, even little destructive vis-à-vis oils, is not recommended in engineering because of corrosion problems. In the case of vanadylporphyrins (O = V (IV)), both reductive and acidic conditions are required (JW Buchler, The Porphyrins, Ed D. Dolphin, 1978). Vanadium being paramagnetic, in order to determine the structure of vanadylporphyrins by NMR, geochemists have developed a demetallation reaction under very stringent conditions, such as treatment with methanesulfonic acid at 110 ° C. for 1 h 30 (US 3190829). Then, the bases thus obtained, are metallized with nickel (II) to obtain nickelporphyrins analysable by NMR because diamagnetic. However, this method causes the degradation of 60 to 70% porphyrins.

The SU 1403082 A1 patent describes conditions that are much milder at temperatures and pressures, and more selective, with the use of zinc as a reducing agent and acetic acid as a source of protons. This document describes the possibility of demetalling Vanadium metalloporphyrins by reduction in the presence of H ⁺ ions. Zinc powder is used as a reducing agent and glacial acetic acid is used as a protic solvent (ie proton donor). The demetallation tests were carried out at a pressure close to atmospheric pressure and at a relatively low temperature, namely the boiling point of acetic acid (ie 1 18.1 ° C. to 1013 mbar). The Russian patent discloses the recovery of demetallated porphyrins, using diethyl ether, with a yield of between 60 and 85% by weight as a function of the proportion acetic acid / zinc powder. One of the aims described in this document is the search for a shortest reaction time possible (20 to 30 min) while avoiding the implementation of an inert atmosphere. This method therefore uses a reagent and inexpensive and non-toxic solvents.

On the basis of this document, the Applicant has attempted to implement a demetallation of porphyrins based on Ni and V, and more generally on a hydrocarbon fraction comprising such porphyrins or of coordinated metals. However, the strict implementation of this process, as described in this document, did not provide the expected results in terms of yields and reaction times.

In order to overcome the drawbacks of the prior art, the Applicant has set a goal of implementing a process for the demetallation of porphyrins and derivatives, which is simple, under non-corrosive conditions, at relatively low temperatures. order of a hundred degrees, and at pressures close to atmospheric ones. Accordingly, the invention relates to a process for extracting metals from a hydrocarbon fraction containing coordinated metals, comprising the following steps of:

1) demetallation of the metals coordinated by (i) reacting, under an inert atmosphere, said hydrocarbon fraction with a solution of pH between 1 and 5, which solution comprises at least one C ₁ -C ₄ carboxylic acid, the reaction medium thus obtained further comprising a reducing metal having a standard potential, E ₀ , between -0.7 and -0.9 V, present in an amount of at least 6 equivalents for 1 equivalent of coordinated metal, ( ii) refluxing the reaction medium at a temperature corresponding to the boiling point of said carboxylic acid, until the reaction medium is decoloured, and

2) extraction of the metal salts by adding a lipophilic solvent and an aqueous solution, said metals being recovered in the aqueous phase.

The applicant has thus shown that the implementation of the method allows a recovery of the coordinated metals from this hydrocarbon fraction, which metals advantageously represent nickel and vanadium, with a rate of between 10% and 30% for vanadium. preferably between 10% and 20%, and between 2% and 6% nickel. In addition, the extraction of metals has the advantages of avoiding, on the one hand, the poisoning of the catalysts used in the treatment of these hydrocarbon fractions and, on the other hand, the degradation of this fraction.

The implementation and the optimization of the process to achieve such levels have been carried out by the Applicant by considering model porphyrins containing vanadium and nickel.

Such model porphyrins are vanadyloctaethylporphyrin (O = VOEP), vanadyletioporphyrin (O = VETIO) existing in four isomers (O = VETIO I, O = VETIO II, O = VETIO III, O = VETIO IV), nickeloctaethylporphyrin (NiOEP ), nickeletioporphyrin (NiETIO) existing in four isomers (NiETIO I, NiETIO II, NiETIO III, NiETIO IV), because representative of petroforphyrins and others, in petroleum fractions.

This method, when used on these model porphyrins, makes it possible to obtain metal recovery rates (V and Ni) of between 10% and 96%, the levels of the lower limit being usually obtained for nickel. . Indeed, the Applicant has therefore shown that, without being bound by any theory, nickel porphyrins have the lowest recovery rates, which can be explained by the fact that they are less reducible in the medium. due to their standard potential, E ₀ , of about -1.2 V, whereas that of vanadium porphyrins has a value of about -1.0 V.

In addition to the yields obtained, defined as being the material balance of the metals present in the aqueous phase and in the organic phase by the lipophilic solvent and the solid residue, the method of the invention has the advantage of being implemented in a controlled manner. simple in particular on an industrial scale, by using mild conditions, in particular at pressures close to those of atmospheric pressure, and operating conditions allowing the non-degradation of the starting hydrocarbon fraction and conventional setting devices to be avoided; implemented. The solid residue represents, for example, the salts resulting from the oxidation of the reducing metal and / or the insoluble or poorly soluble salts of the metals of interest during the extraction of these salts, and which are in particular recovered by filtration.

The hydrocarbon fraction to be treated contains coordinated metals in particular in the form of metal-based petrophorphyrines essentially representing vanadium and nickel, which does not exclude other complex structures also coordinated by these metals. Such fractions are advantageously crude and have very variable levels of these metals depending on the origin thereof. By way of example, the average metal contents extracted from the 375 ° C + section (equivalent to an atmospheric residue) are between 1, 2 and 135 ppm Ni and between 1 and 2300 ppm vanadium, in the 375 ° section. C-550 ° C (equivalent to a vacuum distillate), the average contents of these metals are between 0 and 0.3 ppm and between 0 and 0.8 ppm, and in the 550 ° C + cut (equivalent to a residual under vacuum), the respective average contents are from 5 to 175 ppm and from 4 to 3000 ppm.

The first step of the process (step 1) concerns a demetallation reaction of the coordinated metals present in the forms indicated above of the hydrocarbon fraction.

This reaction is carried out by contacting the hydrocarbon fraction with a solution comprising at least one C ₁ -C ₄ carboxylic acid (step 1) (i)), protic solvent, which is chosen from preferably in the group consisting of formic acid, acetic acid, propanoic acid, butanoic acid and mixtures thereof.

The pH of this solution should be between 1 and 5, and is preferably fixed by the carboxylic acid as such. If necessary, the pH can be adjusted by adding an acidic or basic compound to obtain these values. Preferably, the pH is between 1.5 and 4.

The reaction medium is obtained by mixing the hydrocarbon fraction, C ₁ -C ₄ carboxylic acid and reducing metal, the latter having a standard potential, E ₀ , between -0.7 and -0.9 V .

In order for the reaction to be quantitative with regard to the standard potentials of vanadylporphyrins (E ₀ of approximately -1 V) and nickelporphyrins (E ₀ of approximately -1.2 V), the choice of reducing metal is governed by its E ₀ . Such reducing metals are advantageously chromium (E ₀ = - 0.74 V (Cr ³ 7 Cr)) and zinc (E ₀ = -0.76 V (Zn ² 7 Zn)), zinc being the preferred.

The demetallation reaction involves maintaining the reaction medium under an inert atmosphere, such as under argon or nitrogen or other rare gas.

The reaction under an inert atmosphere promotes the kinetics of demetallation and improves the extraction efficiencies of the metals.

The starting quantities of hydrocarbon fraction relative to those of carboxylic acid are advantageously between 1/20 and 1/40, w / v.

The amounts of reducing metal present in the reaction medium is at least 6 equivalents for 1 equivalent of coordinated metal. Indeed, considering the model porphyrins, O = VOEP, O = VETIO, NiOEP and NiETIO, the stoichiometry of the reaction involves 3 moles of metal to reduce 1 mole of porphyrin, with exchange of 6 electrons. For example, 200-400 mg of reducing metal can be considered for the laboratory scale for approximately 2-4.5 mg of metals (sum of Ni and V), in a ratio by weight of the amount of reducing metal on the quantity of metals between 20 and 100. It is possible to extrapolate these quantities for implementation on a pilot or industrial scale, provided that the respective proportions are respected. The reducing metal is usually in the form of powder or filings.

The amount of reducing metal present in the reaction medium and necessary for the demetallation reaction can be added all at once, or very advantageously several times during the reaction. Indeed, an addition several times, preferably at least twice or even three times, of the amount necessary over the entire duration of the reaction improves substantially the kinetics of the reaction, which decreases the reaction time by about 50%.

The reaction medium is obtained by mixing the hydrocarbon fraction, C ₁ -C ₄ carboxylic acid and reducing metal, and is refluxed (stage 1) (ii) at the boiling point of said carboxylic acid. , until discoloration of the reaction medium.

The purpose of the demetallation reaction is to extract metal ions from petroporphyrins or the like.

Without being bound by any theory and on the basis of model porphyrin demetallation reactions described above, the first step of this reaction would correspond to the dielectronic reduction of the coordinated metals, for example from O = VOEP to a reaction intermediate, vanadyloctaethylchlorin. (O = VOEC), leading to color changes of the compounds obtained, in particular by passing from an initial blue-violet color to a green color in the case of O = VOEP. In a second step, a further reduction by four electrons is observed, resulting in a porphyrinogenic compound (s). The porphyrinogenic compound is subsequently degraded, this degradation being accompanied by the release of metal ions in the reaction medium which is noted by a loss of color, the reaction medium thus becoming colorless. In the presence of C ₁ -C ₄ carboxylic acids, these metal ions stabilize in the form of salts, such as acetate salts. According to this second step, the loss of color is explained by a loss of aromaticity of the porphyrin-type macrocycle.

The duration of the demetallation step is usually between

3 and 7h. After completion of this step, the temperature of the reaction medium is preferably lowered to room temperature.

It is thus essential to implement the process under inert atmosphere because the presence of oxygen in all likelihood leads to one or reoxidation of the various intermediate compounds. We can observe a gain in metal recovery rate by a factor of two, especially for vanadium.

The second step of the process (step 2) consists of an extraction of the metal salts, which are obtained by reactions with the at least one C ₁ -C ₄ carboxylic acid, by addition of a lipophilic solvent and a solution aqueous, said metals being present in the aqueous phase. Once step 1) has been completed, the lipophilic solvent is added to the reaction medium, very advantageously chosen from the group consisting of chlorinated solvents, for example chloroform, trichlorethylene, tetrachlorethylene and / or methylene chloride, and benzene derivatives. such as toluene, xylene and / or ethylbenzene, toluene being the preferred, a reformate cut and their mixture.

Then, an aqueous solution is added, the added volumes of lipophilic solvent and aqueous solution being preferably in the ratio of 0.5 to 3, and in any case adapted to the volume of the reaction medium and, according to embodiments, the sum of the solvent / aqueous solution volumes being preferably between 0.4 and 1 volume of the reaction medium. The addition of the aqueous solution can be carried out at the same time as the addition of solvent.

Preferably, the aqueous solution is water or an aqueous saline solution containing salts in a concentration which does not have a detrimental effect on the effects of the invention, in particular to avoid the precipitation of the metal salts obtained by the upstream step (Step 1 )). This aqueous saline solution may therefore comprise inorganic salts, such as sodium chloride, phosphate, nitrate or sulfate salts, or appropriate organic salts, the solution having a concentration of, for example, between 10 ^-3 and 10 ^-2. Mr.

This step of adding solvent and aqueous solution is carried out as a liquid-liquid extraction step in order firstly to wash the organic phase obtained with the lipophilic solvent, and secondly to extract the metal salts and thereby concentrate the enriched aqueous phase in these metal salts. According to this implementation, the yield is maximum. The organic phase is preferably washed at least two more times with water or the aqueous solution which is recovered and combined with the aqueous phase. The organic phase is enriched in coordinated metals that have not been demetallated.

The method may also advantageously comprise a filtration step of the reaction medium at the end of the demetallation step (step 1)).

This filtration step is carried out in order to eliminate particles of powder or filings of unreacted reducing metal. However, the filtration may cause a deposit on the filter of insoluble metal salts in the reaction medium. This recovery may, according to embodiments, not be negligible, for example at least 30% of metal salt, and thus affect the material balance and the recovery rate of metals. The recovery rates and material balance (yield) take this aspect into account. Thus, depending on the case, a cleaning of the filter for the recovery of insoluble salts can be carried out, typically by washing with a strong acid, such as nitric acid in a concentration sufficient to effect the mineralization, and then by microwave treatment especially during 0.5-2h at a temperature between 150 ° C and 170 ° C.

The process may comprise an additional step, carried out after step 2), of treating the aqueous phase enriched in metal salts with a strong acid, such as nitric acid, under heat (T ° = 70 ° C. -90 ° C), the mineralized material, obtained after removal of the acidic liquid medium, in particular by evaporation, preferably under reduced pressure, is then preferably recovered and for example analyzed by ICP-AES to determine the content of the metals.

According to embodiments, the method further comprises after step 1), after an optional filtration step, a step of removal of the carboxylic acid C ₁ -C ₄ , especially by evaporation, preferably under reduced pressure.

The mineralized material obtained after evaporation of the acid undergoes the treatment of step 2) described above. Although the yields are satisfactory, this implementation is however less preferred than the previous one.

The percentage of demetallation or the metal recovery rate is defined as the ratio between the content of metals in the aqueous phase, and optionally that in the filter, and the sum of the metal contents in the aqueous phase, in the organic phase and possibly the one in the filter.

The process may comprise a separation step, in particular by electrolysis, and recycling of the reducing metal present in the aqueous phase and which has been oxidized to step 1), and also a step of separation and recycling of the solvents used, implemented after step 2).

A treatment of the aqueous phase containing the metal salts is also possible in order to separate and recycle, for example, zinc oxidized to Zn ²⁺ during the reduction of the coordinated metals at the end of step 2). This step can be carried out in particular by electrolysis. To do this, a prior elimination of most of the solubilized salts in it must be implemented. One possibility is to promote the precipitation of salts by varying the pH of the aqueous phase. The precipitated salts can then be recovered by filtration, which makes it possible to limit their presence in the aqueous effluents. The zinc metal can then be introduced in step 1) of the process.

Moreover, after step 2), the process may include a step of separating and recycling the solvents used during the demetallation (step 1) and / or the extraction (step 2), especially after their recovery. during the various operations. This is implemented by techniques known to those skilled in the art. The invention is now described in more detail with reference to the following nonlimiting examples and to the drawings in which:

- Figure 1 shows the structures of the various model porphyrins vanadyloctaethylporphyrin (O = VOEP), vanadyletioporphyrin (O = VETIO) existing under four isomers (O = VETIO I, O = VETIO II, O = VETIO III, O = VETIO IV) , nickeloctaethylporphyrin (NiOEP), nickeletioporphyrin (NiETIO) existing in four isomers (NiETIO I, NiETIO II, NiETIO III, NiETIO IV),

- Figure 2 shows a diagram of the demetallation reaction of O = VOEP.

Example 1

General procedure for the demetallation reaction of O = VOEP in the presence of acetic acid

At room temperature, vanadyloctaethylporphyrin (50 mg, 0.08 mmol, 1 eq) in the form of purple crystals and zinc (200 mg, 3.06 mmol, 38 eq.) Are added to 200 mL of glacial acetic acid, previously degassed for 10 minutes with argon. The reaction medium is then heated under reflux for 3h30, still under argon. Zinc (200 mg, 3.06 mmol, 38 eq.) Is added and the reaction medium is then refluxed for a further 30 minutes. After returning to ambient temperature, the resulting colorless solution is filtered on filter paper. After adding of dichloromethane (50 mL) and water (50 mL), the two liquid phases obtained are separated using a separating funnel. The organic phase is then washed with water (2 × 15 mL) and then concentrated under reduced pressure (25 ° C., 15 mmHg). The combined aqueous phases are also evaporated under reduced pressure (25 ° C., 15 mm Hg).

The residue from the organic phase is taken up in 10 ml of nitric acid of sufficient concentration to effect mineralization, then this solution is placed for 1 hour in microwaves (800 W, 50 bar, 150-170 ° C). In an identical manner, the filter is placed in 10 ml of nitric acid and then treated with microwaves (800 W, 50 bar, 150-170 ° C.). The aqueous phase is taken up in 10 ml of nitric acid of sufficient concentration to carry out the mineralization for 1 hour in a sand bath at 80 ° C. The mineralizates are then assayed at the ICP-AES, which allows the vanadium to be isolated:

for the organic phase: 950 g, recovery rate = 26%,

the filter: 30 g, yield = 1%, and

the aqueous phase: 2700 g, yield = 73%.

Initial vanadium in the sample: 4.25 mg

Vanadium recovered: 3.68 mg

Example 2

General procedure for the demetallation reaction of NiOEP in the presence of acetic acid

The protocol of Example 1 is repeated under the same conditions but replacing the O = VOEP with NiOEP.

Initial nickel: 4.96 mg.

Organic phase: recovery rate = 90%,

Aqueous phase: recovery rate = 10%.

This example shows that the demetallation of the NiOEP is performed with a yield well below that of the O = VOEP, which is explained by the different standard potentials.

Example 3

The protocol of Example 1 is carried out with a crude oil sample (10 g) containing 3.60 mg of vanadium and 0.8 mg of nickel (sample A). Vanadium recovery rate

Organic phase: 88%

Aqueous phase: 12%

Nickel recovery rate

Organic phase: 100%

Aqueous phase: 0%

These results show a satisfactory vanadium recovery rate, but, on the other hand, the nickel recovered is below the detection limit.

Claims

1. A method of extracting metals from a hydrocarbon fraction containing coordinated metals, comprising the steps of:

The process according to claim 1, wherein the C ₁ -C ₄ carboxylic acid is selected from the group consisting of formic acid, acetic acid, propanoic acid, butanoic acid and mixtures thereof.

The process of claim 1 or 2, wherein the reducing metal is chromium or zinc, with zinc being the preferred.

4. Method according to one of claims 1 to 3, wherein the reducing metal present in the reaction medium is added in one go or in several times during the reaction.

5. Method according to one of claims 1 to 4, wherein the duration of the demetallation step is usually between 3 and 7h.

6. Method according to one of claims 1 to 5, wherein the lipophilic solvent is selected from the group consisting of chlorinated solvents, for example chloroform, trichlorethylene, tetrachlorethylene and / or methylene chloride, benzene derivatives such as toluene, xylene and / or ethylbenzene, with toluene being the preferred, a reformate cut and mixtures thereof.

7. Method according to one of claims 1 to 6, further comprising a filtration step of the reaction medium at the end of the demetallation step (step 1)).

8. Method according to one of claims 1 to 7, comprising an additional step, implemented after step 2), treatment of the aqueous phase enriched in metal salts with a strong acid, followed by elimination of the liquid medium by evaporation.

9. Method according to one of claims 1 to 8, further comprising, after step 1), after an optional filtration step, a step of removing the carboxylic acid C ₁ -C ₄ .

10. Method according to one of claims 1 to 9, comprising a step of separating and recycling the reducing metal, which has been oxidized, present in the aqueous phase, to step 1), said step being implemented after step 2).

1 1. Process according to one of Claims 1 to 10, comprising a step of separating and recycling the solvents used during the demetallation

(step 1)) and / or extraction (step 2), implemented after step 2).