Process for the recovery of organotin catalysts

Abstract

The invention relates to a new process for the recovery of dialkyl tin oxide after the synthesis process of aminoalkyl (meth) acrylates.

Description

TECHNICAL FIELD

[0001] The present invention relates to a brand new process for the recovery of organotin catalysts after the synthesis process of aminoalkyl (meth)acrylates. BACKGROUND

[0002] Aminoalkyl (meth)acrylates, such as 2-dimethylaminoethyl (meth)acrylate and its quaternary ammonium derivatives, are common monomers used in the preparation of polymers in many industries, such as water treatment, papermaking, home and personal care, or the oil and gas industry, for example, to enhance oil recovery, hydraulic fracturing, water shutoff, etc.

[0003] These monomers are obtained from the transesterification reaction of (meth)acrylic alkyl esters with aminoalcohols, catalyzed by organometallic derivatives. The choice of catalyst depends on various criteria, such as the nature of the aminoalkyl (meth)acrylate or the alcohol used, or the nature of the synthesis process.

[0004] For 2-dimethylaminoethyl (meth)acrylate, the use of organotin derivatives as catalysts is well known, in particular dialkyl tin oxides, such as dibutyl tin oxide (DBTO). The role of the catalyst is to shift the equilibrium to produce more 2-dimethylaminoethyl (meth)acrylate and to reduce the formation of impurities. After the reaction, the catalyst can be recovered for use in new synthesis processes, but in these recoveries, the DBTO catalyst tends to deactivate and needs to be replaced periodically, which is costly and generates toxic waste that is difficult to manage and dispose of.

[0005] When the DBTO starts to deactivate, the reaction product contains more impurities. These impurities are Michael addition products of the alcohol, such as methanol or dimethylaminoethanol, which react with (meth)acrylic acid methyl ester, (meth)acrylic acid dimethylaminoethyl ester or (meth)acrylic acid. These impurities, produced as by-products, reduce the quality of the 2-dimethylaminoethyl (meth)acrylate product. The reduction in the quality of the monomer affects the performance of the polymers prepared from these monomers.

[0006] Many attempts have been made to recover the catalyst as efficiently as possible.

[0007] Document JP2008-231003 describes the synthesis of multifunctional acrylates and the recovery of the catalyst by adding a strong acid.

[0008] Document WO03 / 028888 describes the recovery of transesterification catalysts by extraction with water.

[0009] Document WO2019 / 196048 describes a process for the production of 2-dimethylaminoethyl (meth)acrylate using a mixture of fresh catalyst and recovered catalyst.

[0010] As an alternative to organotin catalysts, as described in US 7,268,251, tetraisopropyl titanate catalysts have been used to synthesize 2-dimethylaminoethyl (meth)acrylate. These titanium catalysts require an activation step, first reacting tetraisopropyl titanate with dimethylaminoethanol to undergo ligand exchange, thereby generating an isopropanol side stream that must be further processed. This activation step is very energy-intensive and produces waste side streams.

[0011] Despite all these more or less successful attempts, a better catalyst recovery method is still needed to recycle the catalyst more times, thereby reducing the environmental impact of aminoalkyl (meth)acrylate synthesis.

[0012] The recycling method according to the present invention aligns with environmentally conscious principles and addresses the impact of industry and humanity on the planet. This recycling method allows for better catalyst recovery and improves performance in subsequent aminoalkyl (meth)acrylate synthesis processes, resulting in an overall reduction in greenhouse gas emissions such as CO2. Invention Overview

[0013] This invention relates to a novel method for recovering organotin catalysts after an aminoalkyl (meth)acrylate synthesis process (e.g., 2-dimethylaminoethyl (meth)acrylate).

[0014] More specifically, the organotin catalyst recovery method includes the following continuous (i.e., sequential or continuous) steps:

[0015] 1) Preparation of a mixture comprising: selected from water, at least one C1-C 12 Alcohols, and water with at least one C1-C 12 A mixture of alcohols in a polar solvent (i), an organotin catalyst residue solution S1 (ii) produced by the synthesis of aminoalkyl (meth)acrylate compounds, and at least one organic extraction solvent ES1 (iii), the mixture is subjected to liquid-liquid extraction LLE1 using the organic extraction solvent ES1 to obtain an organic solution OS1 and an aqueous solution AS1.

[0016] 2) At temperature T1 and pressure P1, distill the organic solution D1 into OS1 to obtain the organic solution OS. 1' and organic distillate OD1;

[0017] 3) Distilling organic solution D2 OS at temperature T2 and pressure P2. 1’ To obtain organic solution OS 1” and organic distillate OD2, wherein the organic solution OS 1” Contains 2-40 wt% organotin catalyst residues;

[0018] Said temperature T2 is greater than temperature T1 and / or pressure P2 is less than pressure P1 ;

[0019] wherein, in step 1), said organic tin catalyst residue solution S1 (ii) and said at least one organic extraction solvent ES1 (iii) are mixed when said polar solvent (i) is added, or said polar solvent (i), organic tin catalyst residue solution S1 (ii) and said at least one organic extraction solvent ES1 (iii) are added simultaneously.

[0020] Another object of the present application relates to a process for the synthesis of aminoalkyl (meth)acrylates using at least part of the recovered organic tin catalyst, wherein said organic tin catalyst is obtained according to the recovery process of the present application.

[0021] Another object of the present application relates to a polymer obtained from a process for the synthesis of aminoalkyl (meth)acrylates using at least part of the recovered organic tin catalyst obtained according to the recovery process of the present application.

[0022] Description of the present application

[0023] As used herein, the expression "A and / or B" means "A, or B, or A and B".

[0024] As used herein, the expression "heavy" corresponds to a Michael adduct of an alcohol, such as methanol or dimethylaminoethanol, with methyl (meth)acrylate, dimethylaminoethyl (meth)acrylate or (meth)acrylic acid.

[0025] The present application also includes all possible combinations of the various embodiments disclosed, whether they are preferred or exemplary embodiments, when they are not mutually exclusive. Furthermore, in the case of indicating a range of values, the end values are part of these ranges. The present disclosure also includes all combinations between the end values of these ranges. For example, the range "1-20, preferably 5-15" implies the disclosure of the ranges "1-5", "1-15", "5-20" and "15-20".

[0026] Liquid-liquid extraction LLE1 of the organic tin catalyst residue solution S1

[0027] The recovery process can be carried out after any of the processes for the synthesis of aminoalkyl (meth) acrylates in the state of the art which use (meth) alkyl acrylate and 2-dimethylaminoethanol as starting materials. Advantageously, the (meth) alkyl acrylate has an alkyl chain of 1 to 6 carbon atoms, preferably a linear alkyl chain, more preferably the (meth) alkyl acrylate is (meth) acrylate methyl ester. Preferably, the recovery process is carried out after a process for the synthesis of 2-dimethylaminoethyl (meth) acrylate which involves an organotin catalyst. Thus, the organotin catalyst residual solution S1 is preferably the one resulting from the synthesis of 2-dimethylaminoethyl (meth) acrylate.

[0028] In the process for the synthesis of aminoalkyl (meth) acrylates, the reaction is carried out in the presence of a reaction solvent which forms an azeotrope with the lower alcohol formed as a by-product during the synthesis. This azeotrope is distilled during the synthesis to shift the reaction towards the formation of the aminoalkyl (meth) acrylate.

[0029] Advantageously, the reaction solvent is selected from saturated or unsaturated linear, branched or cyclic hydrocarbons containing 3 to 16 carbon atoms. Preferably, the solvent is selected from n-hexane, isomers of n-hexane and mixtures thereof.

[0030] At the end of the process for the synthesis of aminoalkyl (meth) acrylates, as a result of the distillation of the azeotrope mixture, the resulting reaction mixture usually contains the aminoalkyl (meth) acrylate, residues of the catalyst (organotin catalyst) and traces of starting materials such as (meth) alkyl acrylate, 2-dimethylaminoethanol, alcohol and reaction solvent. Usually, the different compounds are separated by a distillation step. After such a distillation step, an organotin catalyst residue solution S1 containing the catalyst and high-boiling compounds (such as Michael adducts) is obtained.

[0031] According to a preferred embodiment, the organotin catalyst residue solution S1 results from the synthesis of an aminoalkyl (meth) acrylate, preferably 2-dimethylaminoethyl (meth) acrylate, in the presence of a dialkyl tin oxide, preferably dibutyl tin oxide.

[0032] According to the present application, in a first step (liquid-liquid extraction LLE1 step), the organotin catalyst residue solution S1 (ii) is mixed with at least one extraction solvent ES1 (iii) and a polar solvent (i) selected from water or at least one C1-C12 alcohol or a mixture of water and at least one C1-C12 alcohol.

[0033] Usually, the organotin catalyst residue solution S1 contains Michael adducts, high-boiling compounds, organotin catalyst and possibly traces of starting materials and aminoalkyl (meth) acrylate.

[0034] The organotin catalyst residue solution S1 advantageously contains 1-40% by weight of organotin catalyst, preferably 3-30% by weight, more preferably 5-20% by weight.

[0035] Advantageously, the organic extraction solvent ES1 is selected from straight-chain and saturated hydrocarbons containing 3 to 16 carbons, straight-chain and unsaturated hydrocarbons containing 3 to 16 carbons, branched and saturated hydrocarbons containing 3 to 16 carbons, branched and unsaturated hydrocarbons containing 3 to 16 carbons, cyclic saturated hydrocarbons containing 3 to 16 carbons, cyclic unsaturated hydrocarbons containing 3 to 16 carbons, or combinations thereof. Preferably, the extraction organic solvent ES1 has a carbon chain range of C3 to C4. 12 Saturated alkanes. It can be C3 to C4. 12 A mixture of alkanes.

[0036] Examples of organic extraction solvents ES1 used in this invention include n-propane, n-butane, n-pentane, n-hexane, n-heptane, n-decane, toluene, benzene, xylene, cyclohexane, isooctane, C3-C6 and C46. 10 Isomers of n-alkanes, and mixtures thereof.

[0037] Preferably, the organic extraction solvent ES1 is selected from n-propane, n-butane, n-pentane, n-hexane, n-heptane, n-decane, their isomers, and mixtures thereof. More preferably, the organic extraction solvent ES1 contains at least 50% by weight of n-hexane; even more preferably, at least 60% by weight; even more preferably, at least 70% by weight; even more preferably, at least 80% by weight; and even more preferably, at least 85% by weight of n-hexane.

[0038] As described above, step 1) involves a mixture of water, lower alcohols (C1-C4), and other similar substances. 12 Polar solvents for ), and mixtures thereof. Lower alcohols (C1-C12 ... 12 The polar solvent includes methanol, ethanol, and mixtures thereof. Preferably, the polar solvent contains at least 70% by weight of water, more preferably at least 80% by weight, and even more preferably at least 90% by weight.

[0039] In step 1), advantageously, the weight ratio between the organic extraction solvent ES1 and the polar solvent is between 20:1 and 2:1, preferably between 15:1 and 2.5:1, more preferably between 12:1 and 3:1, and even more preferably between 9:1 and 4:1.

[0040] The liquid-liquid extraction (LLE1) can be performed in any manner known to those skilled in the art.

[0041] Advantageously, the liquid-liquid extraction LLE1 includes at least: a mixing step and a separation step.

[0042] Said liquid-liquid extraction LLE1 is advantageously carried out at a temperature between 1 and 90°C, preferably between 10 and 80°C, more preferably between 20 and 70°C.

[0043] In a particular embodiment, said LLE1 is carried out using a continuous extraction column.

[0044] Said mixing step (polar solvent + ES1 + S1) can be carried out using any mixing device, for example, with a combination of stirring blades, centrifugal pumps, static mixers, rotor / stator. Preferably, said mixing step is carried out using stirring blades. It involves mixing a polar solvent (i) chosen from water, at least one Ci-Ci2alcohol, a mixture of water and at least one Ci-Ci2alcohol, an organic tin catalyst residual solution S1 (ii) resulting from the synthesis of aminoalkyl (meth)acrylate compounds and at least one organic extraction solvent ES1 (iii).

[0045] Said mixing time (polar solvent + ES1 + S1) is advantageously continued between 5 seconds and 60 minutes, preferably between 1 minute and 30 minutes, more preferably between 90 seconds and 10 minutes.

[0046] The rotational speed for mixing (polar solvent + ES1 + S1) is advantageously comprised between 10 and 10000 rpm, preferably between 100 and 5000 rpm, more preferably between 200 and 1000 rpm (rpm = rotations per minute).

[0047] Said mixing time and rotational speed (polar solvent + ES1 + S1) depend on (1) the stirrer design and the mixing vessel volume, (2) the amount of organic tin catalyst in the organic tin catalyst residual solution S1, (3) the ratio of solvents (polar + ES1) to the organic tin catalyst residual solution S1. The person skilled in the art is able to determine these parameters without any difficulty, as they correspond to conventional settings.

[0048] Said separation step can form two separate phases, namely an aqueous phase and an organic phase. Said separation step can be achieved by any one of the following methods: centrifuge, coalescer, cyclone, column, gravity settling, and combinations thereof. Preferably, said separation step is achieved by gravity settling.

[0049] Preferably, said separation step lasts between 10 seconds and 60 minutes, preferably between 30 seconds and 30 minutes, more preferably between 1 minute and 10 minutes.

[0050] At the end of the liquid-liquid extraction LLE1, an organic solution OS1 and an aqueous suspension AS1 are obtained.

[0051] Generally, said organic solution OS1 comprises Michael adducts, organic tin catalyst residues, an organic extraction solvent ES1 and possibly traces of aminoalkyl (meth)acrylate,

[0052] Advantageously, said organic solution OS1 comprises from 1 to 40% by weight of organic tin catalyst residues, preferably from 2 to 30%, more preferably from 3 to 20%.

[0053] Generally, said aqueous suspension AS1 contains some organic tin catalyst and starting material (meth)acrylate aminoalkyl ester.

[0054] Said aqueous suspension AS1 advantageously comprises from 0,1 to 10% by weight of organic tin catalyst residues, preferably from 0.15 to 5%, more preferably from 0.5 to 2%.

[0055] Liquid-liquid extraction LLE2 of aqueous suspension AS1

[0056] In a particular embodiment, said aqueous suspension AS1 is treated by liquid-liquid extraction LLE2 with an extraction solvent ES2.

[0057] This liquid-liquid extraction LLE2 can be performed with the same equipment as described for liquid-liquid extraction LLE1.

[0058] Advantageously, said organic extraction solvent ES2 is an organic solvent.

[0059] Advantageously, said organic extraction solvent ES2 is selected from linear saturated hydrocarbons containing from 3 to 16 carbons, linear unsaturated hydrocarbons containing from 3 to 16 carbons, branched saturated hydrocarbons containing from 3 to 16 carbons, branched unsaturated hydrocarbons containing from 3 to 16 carbons, cyclic saturated hydrocarbons containing from 3 to 16 carbons, cyclic unsaturated hydrocarbons containing from 3 to 16 carbons, and mixtures thereof. Preferably, said organic extraction solvent ES2 is a saturated alkane having a carbon chain from C3 to C 12 . It can be a mixture of C3 to C 12 alkanes.

[0060] Organic extraction solvent ES n Examples of (n is an integer greater than or equal to 1) are n-propane, n-butane, n-pentane, n-hexane, hexanes, n-heptane, n-decane, toluene, benzene, xylene, cyclohexane, iso-octane, their isomers, and mixtures thereof, preferably said organic extraction solvent ES n is n-hexane and its isomers.

[0061] The ratio between the extraction solvent ES2 and the aqueous suspension AS1 is advantageously comprised between 20:1 and 2:1, preferably between 15:1 and 2.5:1, more preferably between 12:1 and 3:1, even more preferably between 9:1 and 4:1.

[0062] There is no specific order of addition of the extraction solvent ES2 and the aqueous suspension AS1. The addition of the extraction solvent can be done in several steps. The extraction solvent ES2 can be added first, or the aqueous suspension AS1 can be added first, they can be added alternately (i.e. first the first component of the extraction solvent ES2, then the first component of the aqueous suspension AS1, then the second component of the extraction solvent ES2, then the second component of the aqueous suspension AS1, or vice versa), or they can be added simultaneously. Preferably, the extraction solvent ES2 is added first.

[0063] The liquid-liquid extraction LLE2 can be performed by any means known to the person skilled in the art. Advantageously, the liquid-liquid extraction LLE2 comprises at least one mixing step and one separation step.

[0064] The liquid-liquid extraction LLE2 is advantageously performed at a temperature comprised between 1 and 90°C, preferably between 10 and 80°C, more preferably between 20 and 70°C.

[0065] The mixing time is advantageously comprised between 5 seconds and 30 minutes, preferably between 1 minute and 10 minutes, more preferably between 90 seconds and 5 minutes.

[0066] The rotation speed for mixing is advantageously comprised between 50 and 10000 rpm, preferably between 100 and 5000 rpm, more preferably between 200 and 1000 rpm.

[0067] The mixing time and the rotation speed depend on (1 ) the mixer design, the mixing vessel volume, (2) the amount of organotin catalyst residues in the aqueous suspension AS1 and (3) the ratio between the extraction solvent ES2 and the aqueous suspension AS1. The person skilled in the art is able to determine these parameters without any difficulty as they are routine settings.

[0068] The second separation step enables the formation of two separate phases, i.e. an aqueous phase and an organic phase. The separation step is advantageously a gravitational settling.

[0069] The separation step is advantageously comprised between 10 seconds and 60 minutes, preferably between 30 seconds and 10 minutes, more preferably between 1 minute and 5 minutes.

[0070] At the end of the liquid-liquid extraction LLE2, an organic solution OS2 and an aqueous suspension AS2 are obtained.

[0071] In a preferred embodiment, said organic solution OS2 is partially or totally recovered so as to form or complete the organic extractant solvent ES1 in the first liquid-liquid extraction LLE1.

[0072] In a particular embodiment, said aqueous suspension AS2 is discarded.

[0073] In a preferred embodiment, the aqueous suspension AS2 is distilled and the resulting aqueous distillation phase is partially or totally recovered in the first liquid-liquid extraction LLE1 or in the second liquid-liquid extraction LLE2.

[0074] In a particular embodiment, at least one carboxylic acid is added to the aqueous suspension AS1 prior to performing the liquid-liquid extraction LLE2. Said carboxylic acid is advantageously selected from the group consisting of acrylic acid, methacrylic acid, acetic acid, formic acid, itaconic acid, maleic acid, citric acid, fumaric acid, tartaric acid and mixtures thereof. Preferably, said carboxylic acid is acrylic acid.

[0075] The weight ratio between the carboxylic acid and the organic tin catalyst residue in said aqueous suspension AS1 is advantageously comprised between 0.005 and 0.2, preferably between 0.01 and 0.15, more preferably between 0.02 and 0.1.

[0076] Said liquid-liquid extraction LLE2 is advantageously performed at a temperature comprised between 1 and 200°C, preferably between 5 and 120°C, more preferably between 5 and 80°C, more preferably between 10 and 70°C.

[0077] Said liquid-liquid extraction step is advantageously performed at an absolute pressure comprised between 0.1 and 20 bar, preferably between 0.5 and 5 bar, more preferably between 0.8 and 2 bar, more preferably between 0.9 and 1.1 bar, more preferably at atmospheric pressure.

[0078] Optionally, after LLE1, a distillation step of AS1 is performed to obtain an aqueous phase having a water content higher than or equal to 90 wt%, advantageously said aqueous phase is recovered for the liquid-liquid extraction.

[0079] Distillation D1

[0080] In a second step, distillation D1 is performed on the organic solution OS1 to obtain an organic solution OS 1' .

[0081] Distillation D1 can be performed in any distillation equipment known by the person skilled in the art, for example: a flash evaporator, a thin film evaporator, a wiped film evaporator, a short path distillation equipment, a falling film, a stirred reactor, or a kettle. Preferably, distillation D1 is performed in a flash evaporator.

[0082] Distillation D1 is advantageously carried out at a temperature T1 comprised between 5 and 180°C, preferably between 10 and 150°C, more preferably between 15 and 80°C.

[0083] Distillation D1 is advantageously carried out at an absolute pressure P1 comprised between 0.01 and 1 bar, preferably between 0.05 and 0.8 bar, more preferably between 0.3 and 0.6 bar.

[0084] At the end of distillation D1, an organic solution OS 1' .

[0085] Said organic solution OS 1' advantageously comprises between 1 and 40% by weight of organotin catalyst residues, preferably between 2 and 35%, more preferably between 3 and 30%.

[0086] Distillation D1 produces a distillate (fraction DF1) and an organic solution OS 1' .

[0087] In a particular embodiment, said distillation fraction DF1 can be partially or totally recovered for the first and / or second liquid-liquid extraction LLE2 (as shown in Figure 2 .

[0088] In a particular embodiment, at least one carboxylic acid is added to the organic solution OS1 before carrying out distillation D1. Said carboxylic acid is advantageously selected from the group consisting of acrylic acid, methacrylic acid, acetic acid, formic acid, itaconic acid, maleic acid, citric acid, fumaric acid, tartaric acid, and mixtures thereof. Preferably, said carboxylic acid is acrylic acid.

[0089] The weight ratio between carboxylic acid and organotin catalyst residues in said organic solution OS1 is advantageously comprised between 0.005 and 0.2, preferably between 0.01 and 0.15, more preferably between 0.02 and 0.1.

[0090] Distillation D2

[0091] In a third step, the organic solution OS 1' is subjected to a distillation D2 to obtain an organic solution OS 1” .

[0092] Distillation D2 can be carried out in any distillation apparatus known to the person skilled in the art, such as for example: a flash evaporator, a thin film evaporator, a wiped film evaporator, a short path distillation apparatus, a falling film, a stirred reactor, or a kettle. Preferably, distillation D2 is carried out in a flash evaporator.

[0093] Distillation D2 is advantageously carried out at a temperature T2 comprised between 20 and 220°C, preferably between 30 and 200°C, more preferably between 50 and 190°C.

[0094] The distillation D2 is advantageously performed at an absolute pressure P2 comprised between 0.001 and 1 bar, preferably between 0.01 and 0.5 bar, more preferably between 0.02 and 0.2 bar.

[0095] The temperature T2 of the distillation D2 is greater than the temperature T1 of the distillation D1 and / or the pressure P2 of the distillation D2 is lower than the pressure P1 of the distillation D1.

[0096] At the end of the distillation D2, an organic solution OS 1” and a distillate fraction DF2.

[0097] The organic solution OS 1” advantageously comprises between 2 and 40 wt% of organotin catalyst residues, preferably between 3 and 40 wt%, more preferably between 5 and 40 wt%.

[0098] The distillate fraction DF2 is typically composed of Michael adducts and of the organic extraction solvent ES n (n is an integer greater than or equal to 1) and of aminoalkyl (meth)acrylates. The distillate fraction DF2 can be removed or further treated according to the method described in document WO2016 / 124837 which describes a thermal treatment of high-boiling compounds to recover and recycle 2-dimethylaminoethanol and / or alkyl (meth)acrylates and / or 2-dimethylaminoethyl (meth)acrylates.

[0099] In a particular embodiment, at least one carboxylic acid is added to the organic solution OS 1' before performing the distillation D2. The carboxylic acid is advantageously selected from the group consisting of acrylic acid, methacrylic acid, acetic acid, formic acid, itaconic acid, maleic acid, citric acid, fumaric acid, tartaric acid, and mixtures thereof. Preferably, the carboxylic acid is acrylic acid.

[0100] The weight ratio between the carboxylic acid and the organotin catalyst residues in the organic solution OS 1' is advantageously comprised between 0.005 and 0.2, preferably between 0.01 and 0.15, more preferably between 0.02 and 0.1.

[0101] In the aminoalkyl (meth)acrylate synthesis process, at least a portion of the resulting organic solution OS 1” can be recycled as catalyst. Advantageously, 100 wt% of the catalyst for the new aminoalkyl (meth)acrylate synthesis process comes from the recycled organic solution OS 1” , preferably not more than 90 wt%, more preferably not more than 80 wt%, more preferably not more than 70 wt%, more preferably not more than 60 wt%, more preferably not more than 50 wt%. Advantageously, the remaining catalyst is fresh organotin catalyst.

[0102] By "fresh", it is meant not recycled organotin catalyst.

[0103] Optional step 4)

[0104] In a particular embodiment according to the application, the organotin catalyst recycling process comprises an optional step 4).

[0105] Optional step 4) comprises at least one additional aqueous suspension AS n-1 liquid-liquid extraction LLE n with an extraction solvent ES n to obtain an organic solution OS n and an aqueous suspension AS n where n is a non-zero integer > 1.

[0106] More particularly, the recycling process can comprise one or more of the following additional liquid-liquid extractions LLE n+1 where n is an integer > 1:

[0107] - preparation of a mixture comprising an aqueous suspension AS n (i), at least one extraction solvent ES n (ii),

[0108] liquid-liquid extraction LLE n+1 of this mixture to obtain an organic solution OS n+1 and an aqueous suspension AS n+1 .

[0109] In this particular embodiment, at least part of the organic solution OS n+1 is distilled according to steps 2) and 3) of claim 1 to obtain respectively an organic solution OS' n+1 and then an organic solution OS" n+1 .

[0110] At least part of the resulting organic solution OS" n+1' can be used as catalyst for an aminoalkyl (meth)acrylate synthesis process. Advantageously, 100% by weight of the catalyst of the synthesis process comes from the recycled organic solution OS" n+1 , preferably no more than 90% by weight, more preferably no more than 80% by weight, more preferably no more than 70% by weight, more preferably no more than 60% by weight, more preferably no more than 50% by weight, based on the total amount of catalyst. Advantageously, the remaining catalyst is a fresh organotin catalyst.

[0111] In this particular embodiment, part or all of the aqueous suspension AS n+1for liquid-liquid extraction LLE with or without a pre-treatment step n+2 and the organic solvent OS n+1 for liquid-liquid extraction LLE with or without a pre-treatment step n is partially or totally recovered.

[0112] In this particular embodiment, the extraction solvent ES n advantageously consists of at least one organic solvent, advantageously selected from saturated or unsaturated linear, branched or cyclic hydrocarbons containing from 3 to 16 carbon atoms, preferably selected from saturated alkanes with a carbon chain ranging from C3 to C 12 and mixtures thereof, wherein the total amount of polar solvent and organic solvent corresponds to 100% by weight of the extraction solvent ES n .

[0113] Examples of organic extraction solvents for the extraction solvent ES n include n-propane, n-butane, n-pentane, n-hexane, n-heptane, n-decane, toluene, benzene, xylene, cyclohexane, iso-octane, their isomers, and mixtures thereof.

[0114] In a particular embodiment, advantageously, the aqueous suspension AS n+1 is distilled (D3) to obtain an aqueous suspension AS n+1’ and an organic solution OS n+1’ .

[0115] The distillation D3 can be carried out in any distillation equipment known to the person skilled in the art, such as: flash evaporator, thin-film evaporator, wiped-film evaporator, short-path distillation equipment, falling film, stirred reactor, or kettle. Preferably, the distillation D3 is carried out in a flash evaporator.

[0116] Advantageously, the distillation D3 is carried out at a temperature T3 comprised between 10 and 100°C, preferably between 30 and 100°C, more preferably between 50 and 100°C.

[0117] Advantageously, the distillation D3 is carried out at an absolute pressure P3 comprised between 0.001 and 1 bar, preferably between 0.05 and 1 bar, more preferably between 0.1 and 1 bar.

[0118] In a particular embodiment, advantageously, the organic solution OS n+1 is partially or totally recovered for LLE with or without a pre-treatment step n . DETAILED DESCRIPTION

[0119] In a particular embodiment, the distillation D1 and the distillation D2 are carried out in the same distillation apparatus.

[0120] In a particular embodiment, at least one carboxylic acid and / or one alcohol is added to the organic solution OS 1” and then it is recovered for the aminoalkyl (meth)acrylate synthesis.

[0121] Said carboxylic acid is advantageously selected from acrylic acid, methacrylic acid, acetic acid, formic acid, itaconic acid, maleic acid, citric acid, fumaric acid, tartaric acid and mixtures thereof. Preferably, said carboxylic acid is acrylic acid.

[0122] Said alcohol is advantageously selected from lower alcohols (Ci-C 12 , such as methanol, ethanol, propanol, butanol and mixtures thereof. Preferably, said alcohol is methanol.

[0123] In the organic solution OS 1” , the molar ratio between carboxylic acid and / or alcohol (1) and organotin catalyst residue (2) is advantageously comprised between 1 :50 and 1 :2, preferably between 1 :30 and 1 :5, more preferably between 1 :20 and 1 :10.

[0124] Said recovery process can be carried out in batch, or in a semi-continuous or continuous process. Preferably, said recovery process is carried out as a continuous process.

[0125] In a particular embodiment, the recovery process according to the present application is carried out as a continuous process. By "continuous process" according to the present application, it is understood that in this process at least one stream continuously enters (ES n , advantageously said organotin catalyst residue solution S1, and at least two streams continuously leave the process, advantageously one corresponding to the aqueous phase AS n , and one corresponding to the organic phase OS n (n is an integer greater than or equal to 1). The continuous process according to the present application can be operated for several days to several months without interruption.

[0126] In this particular embodiment, the residence time (D1+D2) within the distillation device is comprised between 30 seconds and 60 minutes, preferably between 1 minute and 30 minutes, more preferably between 5 minutes and 20 minutes.

[0127] In this particular embodiment, the weight ratio between LS1 and LS2 is advantageously comprised between 0.01 and 1, preferably between 0.1 and 1, more preferably between 0.15 and 1 (n is an integer greater than or equal to 1).

[0128] Another object of the present invention relates to a process for the synthesis of aminoalkyl (meth)acrylates using at least part of the recovered organotin catalyst obtained according to the recovery process of the present invention.

[0129] Advantageously, at least 70% by weight of the catalyst used in the synthesis, based on the total amount of catalyst, comes from the recovery process of the organotin catalyst of the present invention, preferably 60% by weight, more preferably 50% by weight. Advantageously, the remaining catalyst is fresh organotin catalyst.

[0130] Another object of the present invention relates to a polymer obtained from a process for the synthesis of aminoalkyl (meth)acrylates using at least part of the recovered organotin catalyst obtained according to the recovery process of the present invention.

[0131] The present invention and its advantages will be better understood and its advantages will be better illustrated by, but not limited to, the following examples. BRIEF DESCRIPTION OF DRAWINGS

[0132] [ Figure 1 ] Figure 1 represents a continuous mode with 1 liquid-liquid extraction LLE.

[0133] [ Figure 2 ] Figure 2 represents a continuous mode with 2 liquid-liquid extractions LLE.

[0134] [ Figure 3 ] Figure 3 represents a continuous mode with n liquid-liquid extractions LLE.

[0135] List of abbreviations:

[0136] ADAME: 2-dimethylaminoethyl acrylate

[0137] MA: methyl acrylate

[0138] DMOH: dimethylaminoethanol

[0139] Hx: n-hexane

[0140] DBTO: dibutyl tin oxide

[0141] Ptz: phenothiazine

[0142] GC-FID: gas chromatography flame ionization detector

[0143] Hv: heavy fraction

[0144] MeOH: methanol

[0145] ICP-OES: inductively coupled plasma-optical emission spectroscopy

[0146] AZDN: azobisisobutyronitrile

[0147] Example

[0148] Example 1 - ADAME synthesis

[0149] In a 250 mL three-necked round bottom flask, 89 g of MA, 46 g of DMOH, 13 g of Hx, 1.84 g of DBTO and 0.11 g of Ptz were added. A magnetic stirrer was started at 500 RPM. On one neck, a 50 cm high, 20 mm internal diameter column was installed, equipped with a 3 mm Dixon ring, topped with a cooling condenser filled with -10°C glycol water. The head temperature was monitored and adjusted by varying the reflux ratio, using a metering valve to control the collection of distillate.

[0150] The round bottom flask was heated with a heating plate, the external temperature was set to 110°C. The head temperature was maintained between 48 and 53°C by using a reflux ratio control valve, the distillate was continuously collected at the top of the column.

[0151] The reaction medium was recharged with 7 mL of Hx every 10 mL of distillate collected.

[0152] The reaction was continued, increasing the reflux ratio to full value, until the temperature at the top of the temperature column could not be maintained below 53.5°C.

[0153] The reaction mixture was analyzed by GC-FID.

[0154] A GC Agilent 7820A was used with a DB-WAX UI chromatographic column 30 m long and 0.50 pm internal diameter.

[0155] The temperature was set at 80°C for 5 min, then increased at 4°C / min to 122°C and set at 122°C for 2 min, then again increased at 35°C / min to 240°C and set at 240°C for 9 min. The injector was set at 250°C, helium was used as phase carrier. 1 pL was injected with a split ratio of 1 : 100.

[0156] Detection was performed using a flame ionization detector.

[0157] ADAME, DMOH, MA, MeOH, Hx were injected in 5 sample standards of different composition to establish a calibration curve. After 16 min of retention time, the ADAME response factor was used for the quantification of the heavier components.

[0158] The concentration of ADAME was measured at 64.6 wt%, DMOH at 0.9 wt%, and the high molecular weight heavier components at 0.35%.

[0159] The ADAME conversion was calculated as ((%ADAME / (%ADAME + %DMOH + %Heavies))*100) = 98.2%.

[0160] The reaction mixture was then distilled under vacuum using the same apparatus to recover the ADAME monomer. Subsequently, different fractions were collected together with the final ADAME fraction when the top column temperature reached 78°C at 40 mbar until an absolute value of 10 mbar.

[0161] The composition of the ADAME component was 99.5%wt ADAME, 1500 ppm DMOH, 100 ppm MeOH, 1500 ppm MA and 505 ppm Hv measured by GC-FID.

[0162] The concentrated solution in a round bottom flask corresponds to the catalyst residue solution S1.

[0163] The tin concentration was measured by ICP-OES with an ICP E-5800 Agilent. 0.1 g of S1 was weighted in 8 mL of concentrated chloro-acid and 2 mL of nitric acid. The sample was placed in a closed crucible. The crucible was heated in a microwave at 600 W for 90 min to reach 150°C. The obtained solution was diluted 100 times and nebulized at 0.7 L / min. The emission intensity was measured at 189,925 nm wavelength based on a tin standard solution to be quantified.

[0164] The tin concentration was corrected by the molecular weight assuming a pure DBTO structure. 2.87%wt of Sn corresponds to 6%wt of DBTO measured.

[0165] Example 2 (invention)

[0166] In a 1 L reactor equipped with a mechanical stirrer, which is a 4-blade 90° impeller, 500 g of Hx and 250 g of catalyst residue solution S1 prepared in example 1 were added.

[0167] The stirrer was set to 500 RPM, 50 g of water was added after 30 seconds.

[0168] After 1 min, the stirring was stopped and the solution was left to rest for 1 min.

[0169] The top and bottom phases were collected, which correspond to OS1 and AS1 respectively.

[0170] In a 1 L batch distillation apparatus, OS1 was distilled at 60°C for 30 min; the Hx phase was collected in a distillate DF1 at 300 mbar, the bottom phase corresponds to OS1 1’ .

[0171] Then a distillation was performed at 120°C; 5 mbar until no distillate could be collected.

[0172] 55 g of bottom concentrate corresponding to OS 1” was obtained.

[0173] OS 1” contained 3.80 wt% of tin composition measured per ICP-OES, corresponding to 8.0 wt% of DBTO.

[0174] Example 3 (counter example)

[0175] In a 1 L reactor equipped with a mechanical stirrer, which was a 4-blade 90° impeller, 500 g of Hx and 250 g of the catalyst residue solution S1 prepared in example 1 were added.

[0176] The stirrer was set to 500 RPM and 50 g of water were added after 30 seconds.

[0177] After 1 minute, the stirring was stopped and the solution was left to rest for 1 minute.

[0178] The top and bottom phases were collected, which corresponded to OS1 and AS1, respectively.

[0179] In a 1 L batch distillation apparatus, OS1 was distilled at 60 °C for 30 min; the Hx phase in the distillate DF1 was collected at 300 mbar.

[0180] 55 g of bottom concentrate corresponding to OS 1' was obtained.

[0181] OS 1' contained 3.80 wt% of tin composition measured per ICP-OES, corresponding to 8.0 wt% of DBTO.

[0182] Example 3-2 (counter example)

[0183] In a 1 L reactor equipped with a mechanical stirrer, which was a 4-blade 90° impeller, 50 g of water and 250 g of the catalyst residue solution S1 prepared in example 1 were added.

[0184] The stirrer was set to 500 RPM and 500 g of Hx were added after 30 seconds.

[0185] After 1 minute, the stirring was stopped and the solution was left to rest for 1 minute.

[0186] The top and bottom phases were collected, which corresponded to OS1 and AS1, respectively. In a 1 L batch distillation apparatus, OS1 was distilled at 60 °C for 30 min; the Hx phase in the distillate DF1 was collected at 300 mbar. Then a distillation was performed at 120 °C; 5 mbar until no distillate could be collected. 45 g of bottom concentrate corresponding to OS 1” was obtained.

[0187] OS 1” The tin composition in the OS was 0.5 wt% as measured per ICP-OES, which corresponds to 1.05 wt% of DBTO.

[0188] Example 3-3 (counter example)

[0189] In a 1 L reactor equipped with a mechanical stirrer, which is a 4-blade 90° impeller. Add 500 g Hx and 250 g of the catalyst residue solution S1 prepared in example 1.

[0190] Set the stirrer to 500 RPM, after 30 seconds add 300 g water.

[0191] After 1 minute, stop stirring and let the solution rest for 1 minute.

[0192] A stable emulsion is obtained. The bottom and top phases cannot be separated.

[0193] Example 4 (invention)

[0194] In a 1 L reactor equipped with a mechanical stirrer, which is a 4-blade 90° impeller. Add 500 g Hx and 250 g of the catalyst residue solution S1 prepared in example 1.

[0195] Set the stirrer to 500 RPM, after 30 seconds add 50 g water.

[0196] After 1 minute, stop stirring and let the solution rest for 1 minute.

[0197] Collect the top phase, which corresponds to OS1.

[0198] The bottom phase, which corresponds to AS1, remains in the reactor, then add 500 g Hx and then stir every 1 minute at 500 RPM, then let it settle for 1 minute.

[0199] Collect the top and bottom phase, which correspond to OS2 and AS2, respectively.

[0200] In a 1 L batch distillation setup, distill OS2 at 60 °C for 30 min; collect the Hx phase in distillate DF1 at 300 mbar, the bottom phase corresponds to OS 2' .

[0201] Then distill at 120 °C; 5 mbar until no distillate can be collected.

[0202] Obtain 40 g of the bottom concentrate OS 2” .

[0203] In OS 2”The tin composition in the sample was measured at 7.3 wt% per ICP-OES, corresponding to 15.4 wt% recovered DBTO.

[0204] Example 5 (Invention)

[0205] This embodiment corresponds to Figure 3 A specific pattern.

[0206] A 7L kühni stirring column, consisting of a 10-stage 4-blade 90° impeller, was loaded with 6L Hx.

[0207] The stirrer was set to 100 RPM. The catalyst residue solution S1 prepared in Example 1 was continuously added to the first tray of the column at a rate of 250 g / h.

[0208] A homogeneous mixture of Hx / water (50:50) was continuously added at a rate of 100 g / h to the second tray near the top of the column.

[0209] Hx was continuously added at a rate of 200 g / h at the last tray of the tower.

[0210] Organic phase OS1 and aqueous phase AS1 were collected at the top and bottom of the column, respectively.

[0211] In a rotary evaporator, OS1 was distilled at 60°C for 30 min; the Hx phase in the distillate DF1 was collected at 300 mbar, and the organic phase OS was collected at the bottom. 1' .

[0212] Then OS is performed at 120°C. 1' Single distillation; 5 mbar until no more distillate can be collected.

[0213] Obtain 45g / h of bottom concentrate OS 1” .

[0214] In OS 1” The tin composition in the sample was determined to be 8.1 wt% by ICP-OES, corresponding to 17 wt% recovered DBTO.

[0215] Example 6 - ADAME using DBTO recovered in Examples 2-5

[0216] The recovered DBTO produced in Examples 2 through 5 was used in the new ADAME synthesis process as described in Example 1, except that the amount of catalyst was adjusted to start with the same DBTO concentration.

[0217] Table 1 shows the final composition of ADAME components.

[0218] The composition of the ADAME component was 99.5%wt ADAME, 1500 ppm DMOH, 100 ppm MeOH, 1500 ppm MA and 505 ppm Hv, measured by GC-FID.

[0219]

[0220] Table 1

[0221] Example 7 - ADAME polymer synthesis and application test

[0222] In the following example, the ADAME material synthesized in Example 6 was quaternized with chloromethane.

[0223] In a 2L autoclave reactor equipped with a 4-bladed impeller and double jacket, the reactor was degassed for 30 minutes with a nitrogen flow, then closed.

[0224] ADAME was added at a rate of 236 g / h for 3h using a gear pump. When 200 mL was reached, the reactor was started to stir and chloromethane was added at a rate of 128 g / h for 2h. The temperature was regulated to a maximum of 45°C using the double jacket.

[0225] After 1 hour, water was started at a rate of 216 g / h for 1h.

[0226] The mixture was stirred at 40°C for 1 hour, then cooled and degassed to reach atmospheric pressure.

[0227] The chloromethylated ADAME (ADC80) was then diluted with 10 g of water.

[0228] 1190 g of finished product was obtained at an activity concentration of 80% by weight. The finished product was then polymerized according to the following process:

[0229] In a 2L beaker, 137 g of acrylamide solution (50%wt in water), 437 g of water and 926 g of ADC80 were added.

[0230] The mixture was cooled to 0°C under stirring and the pH was adjusted to 3.6 with phosphoric acid.

[0231] The solution was transferred into a dewar and degassed with nitrogen for 15 min. Then 1 mg of AZDN was added in 1 ml of water.

[0232] Nitrogen degassing was maintained for 15 min and the temperature was monitored.

[0233] At the end of the degassing, 2 mg of sodium hypophosphite were added in 1 ml of water to the dewar, then 6 mg of sodium persulfate in 1 ml of water and 4 mg of Mohr salt dissolved in 1 ml of water. The polymerization reaction was started.

[0234] The reaction is then left adiabatic until the temperature reaches a plateau of 80 to 85°C.

[0235] The obtained gel is then left at plateau temperature for 30 min, then it is ground into small pieces.

[0236] The ground material is dried in an oven at 70°C for 2h. The polymer granules are then pulverized into a powder with a particle size ranging from 1.5 to 2.5mm.

[0237] The UL viscosity is measured using a Brookfield viscometer equipped with a UL adapter at 23 to 25°C at 60 turns per minute (1M saline sodium chloride solution at 0.1% by weight of polymer content).

[0238] The insolubility is measured by transferring 1 g of polymer solution into 200 ml of water at 20°C, stirring for 2h, then filtering the dissolved solution with a filter having a porosity of 200 pm and a diameter of 4 cm, and draining the solution.

[0239] The number of insoluble corresponds to the number of aggregates on the filter, which is visually counted after the entire solution has passed through the filter. The results are shown in Table 2.

[0240]

[0241] Table 2

[0242] Example 8 - ADAME synthesis in example 1

[0243] The catalyst residue solution SI produced in example 1 is directly reused in the ADAME synthesis process as described in example 1 without any treatment. The dimethylaminoethanol is adjusted with reference to the residual monomers in the catalyst residue solution SI in addition to the raw material methyl acrylate. The operation is repeated 10 times. The results are shown in Table 3.

[0244]

[0245] Table 3

[0246] Example 9 - ADAME synthesis with recycling method of example 4 between each cycle

[0247] Organic solution OS prepared in example 4 1” For the new method as described in example 1, the dimethylaminoethanol is adjusted with reference to the residual monomers in the organic solution OS in addition to the raw material methyl acrylate. The operation is repeated 10 times. The results are shown in Table 4. 1”

[0248]

[0249] ​Table 4

[0250] Example 10 - ADAME synthesis of the recycling process of Example 4 mixed with 50% fresh catalyst between each cycle

[0251] Organic solution OS prepared in Example 4 1” For the new process described in Example 1, in addition to the raw material methyl acrylate, the residual monomer in the reference organic solution OS 1” was adjusted with dimethylaminoethanol and half of OS was replaced with fresh DBTO based on the Sn content in its equivalent 1” . The operation was repeated 10 times. The results are shown in Table 5.

[0252]

[0253] Table 5

[0254] Example 11 - ADAME polymer synthesis and application tests

[0255]

[0256] Table 6

[0257] The ADAME monomers in Examples 8, 9 and 10 have been quaternized and polymers were prepared according to Example 7. The UL viscosity and the number of insolubles were compared to observe the effect of the different recycling processes according to the application. The results are summarized in Tables 6, 7 and 8.

[0258]

[0259]

[0260] Table 7

[0261]

[0262] Table 8

Claims

1. A process for the recovery of organotin catalyst residues, said recovery process comprising the following successive steps: 1) preparation of a mixture comprising a polar solvent (i) selected from water, at least one Ci-C4alcohol, and a mixture of water and at least one Ci-C4alcohol, a solution S1 (ii) of organic tin catalyst residues resulting from the synthesis of aminoalkyl (meth)acrylate compounds, and at least one organic extraction solvent ES1 (iii), subjecting the mixture to a liquid-liquid extraction LLE1 using the organic extraction solvent ES1 to obtain an organic solution OS1 and an aqueous solution AS1 ; 12 12 1) preparation of a mixture comprising a polar solvent (i) selected from water, at least one Ci-C4alcohol, and a mixture of water and at least one Ci-C4alcohol, a solution S1 (ii) of organic tin catalyst residues resulting from the synthesis of aminoalkyl (meth)acrylate compounds, and at least one organic extraction solvent ES1 (iii), subjecting the mixture to a liquid-liquid extraction LLE1 using the organic extraction solvent ES1 to obtain an organic solution OS1 and an aqueous solution AS1 ; 1) preparation of a mixture comprising a polar solvent (i) selected from water, at least one Ci-C 12 alcohol, and a mixture of water and at least one Ci-C4alcohol, a solution S1 (ii) of organic tin catalyst residues 2) distilling D1 the organic solution OS1 at a temperature T1 and a pressure P1 to obtain an organic solution OS 1' and an organic distillate OD1; 3) distilling D2 the organic solution OS1' at a temperature T2 and a pressure P2, to obtain an organic solution OS1" and an organic distillate OD2, wherein, said organic solution OS1" contains 2-40 wt% of organotin catalyst residues; said temperature T2 is greater than temperature T1 and / or said pressure P2 is less than pressure P1 ; wherein, in step 1), said organotin catalyst residues solution S1 (ii) and said at least one organic extraction solvent ES1 (iii) are mixed when said polar solvent (i) is added, or said polar solvent (i), organotin catalyst residues solution S1 (ii) and said at least one organic extraction solvent ES1 (iii) are added simultaneously; said organic extraction solvent ES1 and said polar solvent have a weight ratio ES1 : polar solvent comprised between 20:1 and 2:

1.

2. The recycling method of claim 1, wherein, said organotin catalyst residues solution S1 is produced from the synthesis of 2- dimethylaminoethyl (meth)acrylate.

3. The recycling method of claim 2, wherein, said organotin catalyst residues solution S1 is produced from the synthesis of 2- dimethylaminoethyl (meth)acrylate in the presence of dialkyltin oxide.

4. The recycling method of claim 3, wherein, said dialkyltin oxide is dibutyltin oxide.

5. The recycling method of claim 1, wherein, said organic extraction solvent ES1 is selected from linear saturated hydrocarbons containing 3 to 16 carbons, linear unsaturated hydrocarbons containing 3 to 16 carbons, branched saturated hydrocarbons containing 3 to 16 carbons, branched unsaturated hydrocarbons containing 3 to 16 carbons, cyclic saturated hydrocarbons containing 3 to 16 carbons, cyclic unsaturated hydrocarbons containing 3 to 16 carbons, and mixtures thereof.

6. The recycling method of claim 1, wherein, said organic extraction solvent ES1 contains at least 50 wt% of n-hexane.

7. The recycling method of claim 1, wherein, said polar solvent contains at least 80 wt% of water.

8. The recycling method of claim 1, wherein, said liquid-liquid extraction LLE1 comprises at least one mixing step and one separation step.

9. The recycling method of claim 8, wherein, said mixing step lasts from 5 seconds to 60 minutes and involves mechanical stirring at a rotation speed comprised between 10 and 10000 rpm.

10. The recycling method of claim 8, wherein, said separation step is carried out by gravitational sedimentation.

11. The recycling method of claim 8, wherein, said separation lasts from 10 seconds to 60 minutes.

12. The recycling method of claim 1, wherein, distillation D1 is carried out at a temperature T1 comprised between 5-180 °C.

13. The recycling method of claim 1, wherein, distillation D1 is carried out at an absolute pressure P1 comprised between 0.01 and 1 bar.

14. The recycling method of claim 1, wherein, distillation D2 is carried out at a temperature T2 comprised between 20-220 °C.

15. The recycling method of claim 1, wherein, distillation D2 is carried out at an absolute pressure P2 comprised between 0.001 and 1 bar.

16. The recycling method of claim 1, wherein, The recovery method includes one or more of the following additional liquid-liquid extractions LLE n+1 wherein n is an integer greater than or equal to 1 : - preparation of a mixture comprising: an aqueous suspension AS n (i), and at least one extraction solvent ES n (iii), Liquid-liquid extraction LLE of the mixture n+1 to obtain an organic solution OS n+1 and an aqueous suspension AS n+1 .

17. The recycling method of claim 16, wherein, distilling steps 2) and 3) of claim 1 at least partially the organic solution OS n+1 to obtain an organic solution OS' n+1 and then obtaining an organic solution OS" n+1 .

18. The recycling method of claim 16, wherein, said aqueous solution AS n partly or totally in liquid-liquid extraction LLE n+1 with or without a pre-treatment step n+1 in liquid-liquid extraction LLE n partly or totally with or without a pre-treatment step.

19. The recycling method of claim 1, wherein, distillations D1 and D2 are carried out in the same distillation apparatus.

20. The recycling method of claim 1, wherein, said process is carried out as a continuous process.

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