Process for the synthesis of isophorone in the liquid phase, including recycling of the alkaline catalyst by electrodialysis

Abstract

The present invention relates to a process for the synthesis of isophorone in the liquid phase by alkaline self-condensation of acetone, comprising the following successive steps: a) condensation reaction of the acetone in a reactor in an alkaline medium, followed by b) distillation, optionally reactive distillation, of the reaction mixture from the reactor, then c) separation of the stream recovered at the bottom of the optionally reactive distillation column from step b) so as to separate the alkaline aqueous phase from the organic phase, then d) extraction and / or purification of the organic phase so as to recover isophorone, characterized in that the process comprises the following successive steps: e) treatment, by electrodialysis, of the alkaline aqueous phase recovered at the end of step c), f) recycling, to the reactor used in step a), the aqueous phase from the electrodialysis, which has an alkali hydroxide content that is greater than the alkali hydroxide content of the aqueous phase recovered at the end of step c).

Description

[0001] Liquid-phase isophorone synthesis process with recycling of the alkaline catalyst by electrodialysis

[0002] Technical field

[0003] The present invention relates to a process for the liquid phase synthesis of isophorone by alkaline self-condensation of acetone comprising the treatment by electrodialysis of an aqueous effluent generated during the synthesis.

[0004] Technical background

[0005] Isophorone (or 3,5,5-trimethylcyclohex-2-enone) is an a,p-unsaturated cyclic ketone that is increasingly used as a synthesis intermediate, notably for the manufacture of isophorone diamine used as a hardener for epoxy resins, isophorone diisocyanate used as a polyurethane monomer, 3,5-xylenol used as a precursor to PCMX (an antimicrobial agent), keto-isophorone, which is an intermediate in the synthesis of vitamin E, and 3,5,5-trimethylcyclohexanol used as a precursor to homosalate (a UV absorber). Isophorone is also an excellent high-boiling solvent for many natural and synthetic resins. It is also used as a solvent in the paint, ink, and varnish industries, and also in agrochemicals for the formulation of emulsifiable concentrates of pesticides.

[0006] Isophorone is classically obtained by catalytic self-condensation of 3 acetone molecules, according to the following reaction:

[0007] The reaction is carried out in the liquid phase or in the gas phase.

[0008] The gas phase processes described in the literature mainly use solid heterogeneous catalysts, whereas the liquid phase processes use homogeneous or heterogeneous catalytic systems.

[0009] The synthesis of isophorone by condensation of acetone in the liquid phase is carried out almost exclusively under alkaline conditions at high temperature and under high pressure; alkaline catalysis is most often carried out by using an aqueous solution of sodium hydroxide or potassium hydroxide.

[0010] Due to the low solubility of the mineral base in acetone, processes are being sought to promote contact between the acetone and the catalyst. Thus, it is known from document US 2,344,226 to carry out the synthesis in a stirred reactor. Document FR 1 238954 discloses a synthesis using a tubular reactor with internal packing. Document US 2,399,976 discloses a synthesis using a tubular reactor equipped with a recirculation system. Documents CN 102367223 and CN 102516051 disclose a synthesis using a premixing system, such as a static mixer. It is also known from document FR 1042057 to replace the alkaline aqueous solution with an alkaline alcoholic solution. The synthesis can be carried out continuously in a tubular reactor without special mixing equipment via the use of very low weight concentrations of sodium hydroxide or potassium hydroxide.Generally, catalyst concentrations are less than 1% by weight, or even around 0.1% by weight relative to the total weight of the reaction mixture. This low concentration allows for single-phase mixing. These processes are described in documents FR 1 316 515, DD145096, EP 2 649 032, EP 2 707 352, EP 2 837 618.

[0011] The synthesis can also be carried out by reactive distillation via the injection of acetone and an aqueous solution of sodium hydroxide or potassium hydroxide into a reactive distillation column so as to maintain a low concentration of sodium hydroxide or potassium hydroxide (< 0.1% by weight relative to the total weight of the reaction mixture) and to react the acetone countercurrently with the sodium hydroxide or potassium hydroxide. This process is described in documents FR 1 315 788, FR 2 271 191 and FR 2 328 686.

[0012] The self-condensation reaction of acetone and / or the hydrolysis of reaction intermediates and polycondensation by-products generates an alkaline aqueous effluent. In addition to the initial alkaline aqueous solution used, this effluent includes the water resulting from the self-condensation reaction of acetone to isophorone and contains small amounts of organic products (mainly isophorone). This effluent must undergo specific, costly treatment to limit its environmental impact upon discharge.

[0013] Document US 8,889,914 B2 discloses a process in which the aqueous phase of the hydrolysis column is treated by distillation and flash evaporation, in order to recycle part of the organic compounds and water contained in this flow. This process makes it possible to recover most of the organic compounds and water, but not the catalyst. Thus, all of the catalyst injected into the reaction is lost. The problem of managing the residual aqueous effluent still arises: it must be neutralized, then the salts resulting from this neutralization must be eliminated before releasing the water into the natural environment.

[0014] There is therefore a need for a more reagent-efficient, energy-efficient, and environmentally friendly isophorone synthesis process. The desired process must generate less waste without compromising selectivity or productivity.

[0015] Brief description of the invention

[0016] The present invention relates to a process, preferably continuous, for the liquid phase synthesis of isophorone by alkaline self-condensation of acetone comprising the following successive steps: a) condensation reaction of acetone within a reactor in an alkaline medium then b) distillation, optionally reactive, of the reaction mixture from the reactor, then c) separation of the flow recovered at the bottom of the distillation column, optionally reactive, from step b) so as to separate the alkaline aqueous phase from the organic phase, then d) extraction and / or purification of the organic phase so as to recover the isophorone, characterized in that the process comprises the following successive steps: e) treatment by electrodialysis, continuously or in batch,of the alkaline aqueous phase recovered at the end of step c) f) recycling to the reactor of step a) of the aqueous phase resulting from the electrodialysis which has an alkali hydroxide content greater than the alkali hydroxide content of the aqueous phase recovered at the end of step c). Other advantageous characteristics of the process according to the invention are specified below:,

[0017] -the electrodialyzer comprises at least one ion exchange membrane comprising a polymer-based matrix comprising at least one fluorinated polymer or copolymer, preferably PVDF,

[0018] -the electrodialyzer has a total active exchange surface area of ​​between 1 and 10 m 2 per tonne of alkaline aqueous phase to be treated, and preferably between 2 and 5 m 2 per tonne of alkaline aqueous phase to be treated,

[0019] - a current density between 20 and 200 mA / cm 2and preferably between 30 and 100 mA / cm 2 is applied to the electrodialyzer,

[0020] -the electrodialyzer includes several electrodialysis units in parallel or in series,

[0021] -aqueous alkali hydroxide solution is an aqueous solution of sodium hydroxide or potassium hydroxide,

[0022] -the alkali hydroxide concentration of the aqueous phase present within the reactor is greater than or equal to 50 g / L, preferably between 50 and 200 g / L, preferably between 80 and 150 g / L and more preferably between 100 and 150 g / L,

[0023] -the ratio of the weight flow rate of the flow of aqueous alkali hydroxide solution supplied (Qalkali hydroxide) and the weight flow rate of the organic flow supplied (Qorga) is between 0.25 and 1.0, preferably between 0.4 and 0.8 and more preferably between 0.5 and 0.7,

[0024] -the concentration of the aqueous alkali hydroxide solution in the feed is between 5 and 40 g / L, preferably between 10 and 40 g / L, and more preferably between 15 and 35 g / L.

[0025] The invention also relates to the use of an electrodialyzer as defined above, for treating at least one aqueous alkaline effluent from a process for the synthesis of isophorone by alkaline self-condensation of acetone in the liquid phase.

[0026] Brief description of the figure

[0027] Figure 1 is a diagram of the device implementing the claimed method.

[0028] Detailed description

[0029] Other features, aspects, objects and advantages of the present invention will become even more apparent from the following description.

[0030] It is specified that the expressions “from ... to ...” and “between ... and ....” used in this description must be understood as including each of the limits mentioned.

[0031] The method according to the invention comprises the following consecutive steps.

[0032] Step a) Condensation reaction of acetone within a reactor in an alkaline medium

[0033] The synthesis can be carried out by injection, preferably continuously, of a flow of an aqueous solution of alkali hydroxide and a flow of an organic solution comprising acetone through a reactor R. Advantageously, the ratio of the weight flow rate of the flow of aqueous solution of alkali hydroxide supplied (Qalkali hydroxide) and the weight flow rate of the organic flow supplied (Qorga) is between 0.25 and 1.0, preferably between 0.4 and 0.8 and more preferably between 0.5 and 0.7.

[0034] The concentration of the aqueous alkali hydroxide solution in the feed may be between 5 and 40 g / L, preferably between 10 and 40 g / L, and more preferably between 15 and 35 g / L.

[0035] The streams can be preheated beforehand using heat exchangers.

[0036] The reaction temperature within the reactor may be between 180 and 250°C, and preferably between 200 and 230°C, and under an absolute pressure of between 30 and 50 bars, preferably between 35 and 45 bars, and even more preferably between 38 and 42 bars.

[0037] The reactor R is preferably a tubular reactor, and more particularly a tubular reactor in a vertical position. In addition, it may, if necessary, consist of several tubular reactors supplied in parallel.

[0038] Preferably, the alkali hydroxide concentration of the aqueous phase present within the reactor is greater than or equal to 50 g / L, preferably between 50 and 200 g / L, preferably between 80 and 150 g / L and more preferably between 100 and 150 g / L.

[0039] The reaction mixture is recovered at the outlet of the reactor and directed to a distillation column.

[0040] Step b): Distillation

[0041] The reaction mixture recovered at the outlet of the reactor is distilled through a column, possibly reactive.

[0042] According to one embodiment of the process according to the invention, the process comprises a reactive hydrolysis distillation, making it possible to hydrolyze the heavy products. According to this possibility, the process can comprise two or three successive distillations, so as to purify at each distillation the fraction mainly comprising isophorone.

[0043] According to another embodiment of the process according to the invention, the process does not involve reactive distillation, but a succession of non-reactive distillations. Preferably, the process comprises four to six successive distillations, so as to purify at each distillation the fraction mainly comprising isophorone. The heavy products isolated by these distillations can be recycled.

[0044] At the end of the first distillation, reactive or not, the unconverted acetone is recovered at the top of the column and the concentrated reaction crude is withdrawn at the bottom of the column. The acetone recovered at the top of the column can be recycled to reactor R.

[0045] Step c): Separation

[0046] The concentrated reaction crude drawn off at the bottom of the first distillation column is separated, preferably by decantation. The alkaline aqueous phase can be separated from the isophorone-rich organic phase using a decanter.

[0047] Optional neutralization of the organic phase. Any alkali hydroxide present in the isophorone-rich organic phase recovered in separation step c) may be neutralized. This neutralization may be carried out by any technique known to those skilled in the art, but preferably by means of a mineral acid providing a buffer effect. Preferably, phosphoric acid is used.

[0048] Step d): Extraction and / or purification

[0049] The isophorone-rich organic phase recovered in the separation step, then optionally neutralized, is purified. Preferably, it is distilled, preferably under reduced pressure in order to extract mainly the polycondensation by-products at the bottom of the column and to recover at the top of the column a stream consisting mainly of isophorone.

[0050] Further distillation(s)

[0051] The stream consisting mainly of isophorone recovered in the previous step can undergo several successive distillations in order to obtain a high degree of purification.

[0052] Step e): Electrodialysis treatment

[0053] The aqueous stream leaving separation step c), preferably leaving a decanter, undergoes electrodialysis treatment.

[0054] This processing step can be performed in batch or continuous mode.

[0055] This alkaline aqueous phase is treated by electrodialysis in order to recover: - an aqueous phase having an alkali hydroxide content greater than the alkali hydroxide content of the aqueous phase recovered at the end of step c); and - an aqueous phase having an alkali hydroxide content lower than the alkali hydroxide content of the aqueous phase recovered at the end of step c).

[0056] In other words, the electrodialyzer allows the production of a catalyst-enriched phase and a catalyst-depleted phase.

[0057] Electrodialysis is carried out in any equipment known to those skilled in the art allowing the migration of ions through selective ion exchange membranes (anionic or cationic) under the action of an electric field applied perpendicular to the membranes. The electrodialyzer comprises at least one electrodialysis unit comprising at least two electrodes: an anode and a cathode, and anionic and cationic membranes arranged alternately in parallel so as to constitute at least one concentration compartment and at least one dilution compartment. Advantageously, the electrodialyzer consists of several electrodialysis units in parallel or in series.

[0058] In the case of the alkaline aqueous phase charged with alkali hydroxide, the alkali cations cross the cationic membranes, noted MEC hereinafter and the OH" anions cross the anionic membranes, noted MEA hereinafter. Thus, in the case of the alkaline aqueous phase charged with sodium hydroxide, the Na cations + cross the cationic membranes (ECM), and the OH" anions cross the anionic membranes (AEM). In the case of the alkaline aqueous phase loaded with potassium hydroxide, the K cations + cross cationic membranes (MEC) and OH" anions cross anionic membranes (MEA). These ion exchange membranes comprise a polymer matrix onto which functional groups are grafted, preferably of the sulfonic type -(SO3) _ or phosphoric - (PO3) 2- for MEC and preferably of the alkyl ammonium type -(NR3) +, -(NHRîf, -(NHzRf or alkylsulfonium -(SRîf for MEAs; the R group(s), identical or different, designating a saturated C1-Cg alkyl group.

[0059] Preferably, the ion exchange membranes comprise polymer-based matrices which may in particular comprise fluorinated polymers or copolymers, including in particular PVDF.

[0060] Preferably, the total active exchange surface area constituted by all the ion exchange membranes of the electrodialyzer is between 1 and 10 m 2 per tonne of alkaline aqueous phase to be treated, and preferably between 2 and 5 m 2 per tonne of alkaline aqueous phase to be treated.

[0061] Preferably a current density between 20 and 200 mA / cm 2 and in particular between 30 and 100 mA / cm 2 is applied to the electrodialyzer.

[0062] According to one embodiment of the method according to the invention, the electrodialyzer has a total active exchange surface area of ​​between 1 and 10 m 2 per tonne of alkaline aqueous phase to be treated and a current density between 20 and 200 mA / cm 2 .

[0063] According to a preferred embodiment of the method according to the invention, the electrodialyzer has a total active exchange surface area of ​​between 2 and 5 m 2 per tonne of alkaline aqueous phase to be treated and a current density between 30 and 100 mA / cm 2 is applied to the electrodialyzer.

[0064] Electrodialysis treatment of aqueous effluents allows the catalyst to be recycled and thus prevents its loss in wastewater, and consequently the treatment of this wastewater. This treatment also allows excess water to be removed from the process.

[0065] This quantity of excess water corresponds to the water formed in the reactor less the water consumed in the hydrolysis column, less the water solubilized in the crude isophorone which is eliminated at the top of one of the subsequent distillation columns.

[0066] The catalyst-depleted aqueous stream at the outlet of the electrodialysis can be sent to a SE wastewater treatment plant.

[0067] Step ): Recycling

[0068] The catalyst-enriched aqueous phase from the electrodialyzer, i.e. having an alkali hydroxide content greater than the alkali hydroxide content of the aqueous phase recovered at the end of step c), is recycled to the reaction step.

[0069] Use

[0070] The invention also relates to a use of an electrodialyzer as defined above for treating at least one alkaline aqueous effluent from a process for the synthesis of isophorone by alkaline self-condensation of acetone in the liquid phase. The aqueous phase enriched with alkaline catalyst obtained can be recycled to the reactor for the acetone self-condensation reaction.

[0071] For the purposes of the present invention, the term “aqueous effluent” means any alkaline aqueous solution produced by the isophorone synthesis process. Preferably, the synthesis process is as defined above, i.e. it comprises steps a) to d) defined above. The invention also relates to a process for treating at least one alkaline aqueous effluent as defined above from a process for synthesizing isophorone by alkaline autocondensation of acetone in the liquid phase as defined above, comprising a step of treatment by an electrodialyzer as defined above.

[0072] Description of the figure

[0073] Figure 1 represents an embodiment of the method according to the invention.

[0074] Acetone is introduced via line 1 into heat exchanger E1. The aqueous alkali hydroxide solution is introduced via line 2 into heat exchanger E2. The preheated streams are recovered in line 3 and introduced into tubular reactor R.

[0075] The reaction mixture from the tubular reactor R is introduced into the reactive hydrolysis distillation column D H via line 4. The hydrolysis of the reaction mixture is carried out under reduced pressure.

[0076] The acetone that has not been converted in the tubular reactor R is recovered at the top of the DH column. This fraction is recycled via line 5 to line 1.

[0077] The concentrated reaction crude is recovered at the bottom of the DH column and is brought to the decanter dl via line 6.

[0078] The decanter dl separates the aqueous phase from the organic phase.

[0079] The alkaline aqueous phase is removed via line 8. This line 8 brings all or part of the aqueous phase to the electrodialyser Ed. Any remaining aqueous phase, which is not brought to the electrodialyser, is recycled as is to the reaction stage via line 9 to line 10.

[0080] The alkaline aqueous phase is treated by electrodialysis within E in order to:

[0081] - to recover an aqueous phase enriched in catalyst (alkali hydroxide), recycled to the reaction stage via line 10, and

[0082] - to eliminate an aqueous phase depleted in catalyst, sent to a wastewater treatment S E .

[0083] The organic phase from decanter dl is brought to neutralizer N via line 7. The neutralized organic phase is brought to distillation column Dl via line 11.

[0084] Distillation under reduced pressure using distillation column D1 makes it possible to recover residual water and any light organic impurities at the top of column D1 and a flow comprising mainly isophorone at the bottom of the column, which is transferred via line 12 to distillation column D2.

[0085] The flow extracted at the top of column D1 is conducted via a pipe 13 to a decanter d2 in order to separate an aqueous phase sent to a wastewater treatment S E and an organic phase returned to the reflux of column D1 and, where appropriate, partly recycled into the hydrolysis column Dnvia line 14 to line 15.

[0086] Distillation under reduced pressure using distillation column D2 makes it possible to recover isophorone with a purity greater than 99% at the top of column D2 and polycondensation by-products C3nH(4n+2)O at the bottom of the column. These by-products are recycled, in whole or in part, via line 15 to the reactive column DH. The part of the recovered fraction comprising the polycondensation by-products C3nH(4n+2)O, which is not recycled, is recovered (S L ).

[0087] Preferably, the weight concentration of isophorone in the feed stream of Di is greater than 70%, preferably greater than 75%.

[0088] Preferably, the weight concentration of isophorone in the feed stream of D2 is greater than 75%, preferably greater than 80%.

[0089] The following examples illustrate the present invention, but are in no way limiting.

[0090] Examples

[0091] These examples illustrate the implementation of catalyst recovery based on a unit production of pure isophorone of 1 t / h, using sodium hydroxide as catalyst.

[0092] The flow rate of the alkaline aqueous phase at the outlet of the decanter di at the bottom of the DH hydrolysis column is 4.67 t / h and the weight concentrations of sodium hydroxide (catalyst) and isophorone in this aqueous phase are 2.8% and 0.85% respectively.

[0093] Ex.l (comparative, outside the invention): Without any recycling of the aqueous phase.

[0094] By removing the entire alkaline aqueous phase to wastewater treatment, the feed consumption of the reaction stage of the isophorone synthesis process is 131 kg of sodium hydroxide and 4.3 m 3of water per tonne of pure isophorone produced, and the loss of isophorone contained in the alkaline aqueous phase is 39.7 kg per tonne of pure isophorone.

[0095] Ex.2 (comparative, outside the invention): With partial recycling of the alkaline aqueous phase but without purge concentration treatment.

[0096] After carrying out a purge of 0.24 t / h on the alkaline aqueous phase flow in order to eliminate the excess water generated by the reaction, the majority of the remaining part of the flow, i.e. 4.43 t / h, is recycled to the reaction stage and the purge is eliminated as is to a wastewater treatment.

[0097] The feed consumption of the reaction stage of the isophorone synthesis process is then 7 kg of sodium hydroxide (also taking into account the loss of NaOH solubilized in the flow of crude isophorone and representing approximately 0.25 kg per tonne of pure isophorone). The sodium hydroxide addition being carried out in the form of an aqueous sodium hydroxide solution with a weight concentration of 30.5%, the water consumption is then 16 liters of water per tonne of pure isophorone. And the loss of isophorone contained in the purge of the alkaline aqueous phase represents 2.0 kg per tonne of pure isophorone.

[0098] Ex.3 (in accordance with the invention):

[0099] The alkaline aqueous phase flow of 4.67 t / h leaving the decanter dl is treated in an electrodialyzer powered by a constant direct electric current of 60 mA / cm 2in order to eliminate an aqueous flow with a flow rate of 0.23 t / h depleted in NaOH and to recover a flow of 4.44 t / h of alkaline aqueous phase enriched in catalyst (NaOH) and recycled as is to the feed of the reaction stage. The electrodialyzer consists of 34 cells providing an exchange surface of 13.3m 2 The efficiency of the electrodialyzer is monitored by measuring the conductivity of the different sodium aqueous phase flows: approximately 140 mS / cm for the concentrated alkaline aqueous phase (2.9% NaOH) and 16 mS / cm for the dilute alkaline aqueous phase (0.3% NaOH).

[0100] The weight composition of the catalyst-depleted aqueous stream is 0.05% acetone, 0.85% isophorone, 0.3% NaOH and 98.8% water. This stream is directed towards SE wastewater treatment.

[0101] The weight concentrations of NaOH and isophorone in the catalyst-enriched aqueous solution are 2.9% and 0.85%, respectively.

[0102] With such catalyst recycling, the feed consumption of the reaction stage of the isophorone synthesis process is limited to 0.95 kg of NaOH (corresponding to 0.7 kg eliminated towards S E at the outlet of electrodialysis and 0.25 kg of NaOH solubilized in the flow of crude isophorone) and 2 liters of water per ton of pure isophorone produced. The loss of isophorone contained in the aqueous flow eliminated towards the wastewater treatment is 2 kg per ton of pure isophorone.

[0103] The invention therefore makes it possible to save:

[0104] -130 kg of soda, 38 kg of isophorone and 4.3 m 3 of water per tonne of isophorone, compared to a process without any recycling of the aqueous phase;

[0105] -6 kg of soda and 14 liters of water per ton of isophorone compared to a process with recycling via a simple purge of the aqueous phase.

[0106] The invention thus makes it possible to recycle 99.2% of the catalyst used in the isophorone synthesis process and 95% of the isophorone contained in the alkaline aqueous phase leaving the hydrolysis column.

[0107] In addition, this process saves an amount of energy of 129 kWh compared to a process that would eliminate excess water (~230 kg) by a thermal evaporation process which would require 135 kWh; electrodialysis only consumes 6 kWh per ton of isophorone.

[0108] More generally, the quantity of water to be eliminated in the process according to the invention is between 200 and 250 kg per tonne of isophorone, depending on the quantity of by-products formed, the hydrolysis rate and the quantity of water entrained with the crude isophorone. The water weight concentration of the stream S Eis greater than 98.5%, apart from the residual catalyst, the remainder essentially consists of isophorone and traces of acetone.

[0109] Summary of Example 3 on the entire process: from feed to final isophorone

[0110] A flow of acetone with a flow rate of 1.4 t / h and a flow of an aqueous solution comprising 30% catalyst and 70% water with a flow rate of 0.003 t / h are introduced into the reactor. The reactor is also fed by two recycle flows, defined below.

[0111] The flow rate of the reaction medium at the reactor outlet is 14.8t / h.

[0112] The flow rate of the organic phase at the outlet of the reactive column and decanter is 1.28 t / h. This organic phase contains more than 79% isophorone.

[0113] The flow rate of the purified isophorone fraction at the outlet of the distillation column is lt / h.

[0114] The flow rate of the light fraction from the reactive column, which recycles this fraction to the reactor, is 9 t / h. The flow rate of the aqueous phase at the outlet of the reactive column and decanter is 4.67 t / h. This aqueous phase contains 2.8% catalyst, 0.9% organic compounds, and the remainder is water. This aqueous phase is introduced into the electrodialyzer.

[0115] At the electrodialyzer outlet, the flow rate of the catalyst-depleted phase is 0.23 t / h. The catalyst-depleted phase contains 0.9% organic compounds, 0.3% catalyst, and the remainder is water. The flow rate of the catalyst-enriched phase recycled to the reactor feed is 4.44 t / h. The catalyst-enriched phase contains 2.9% catalyst, 0.9% organic compounds, and the remainder is water.

[0116] Thus, the use of the electrodialyzer and the recycling of the catalyst-enriched phase allows reduced water and catalyst consumption (0.003t / h), a minimized aqueous effluent volume (0.23t / h), a catalyst content in the effluent divided by 10 and reduced energy consumption.

Claims

Claims 1. A process, preferably continuous, for the liquid phase synthesis of isophorone by alkaline self-condensation of acetone comprising the following successive steps: a) condensation reaction of acetone within a reactor in an alkaline medium then b) distillation, optionally reactive, of the reaction mixture from the reactor, then c) separation of the flow recovered at the bottom of the distillation column, optionally reactive, from step b) so as to separate the alkaline aqueous phase from the organic phase, then d) extraction and / or purification of the organic phase so as to recover the isophorone, characterized in that the process comprises the following successive steps: e) treatment by electrodialysis, continuously or in batch,of the alkaline aqueous phase recovered at the end of step c) f) recycling to the reactor of step a) of the aqueous phase resulting from the electrodialysis which has an alkali hydroxide content greater than the alkali hydroxide content of the aqueous phase recovered at the end of step c)., 2. Method according to claim 1, characterized in that the electrodialyzer comprises at least one ion exchange membrane comprising a polymer-based matrix comprising at least one fluorinated polymer or copolymer, preferably PVDF.

3. Method according to any one of the preceding claims, characterized in that the electrodialyzer has a total active exchange surface area of ​​between 1 and 10 m 2 per tonne of alkaline aqueous phase to be treated, and preferably between 2 and 5 m 2 per tonne of alkaline aqueous phase to be treated.

4. Method according to any one of the preceding claims, characterized in that a current density of between 20 and 200 mA / cm 2 and preferably between 30 and 100 mA / cm 2 is applied to the electrodialyzer.

5. Method according to any one of the preceding claims, characterized in that the electrodialyzer comprises several electrodialysis units in parallel or in series.

6. Method according to any one of the preceding claims, characterized in that the aqueous solution of alkali hydroxide is an aqueous solution of sodium hydroxide or potassium hydroxide.

7. Method according to any one of the preceding claims, characterized in that the concentration of alkali hydroxide in the aqueous phase present within the reactor is greater than or equal to 50 g / L, preferably between 50 and 200 g / L, preferably between 80 and 150 g / L and more preferably between 100 and 150 g / L.

8. Method according to any one of the preceding claims, characterized in that the ratio of the weight flow rate of the flow of aqueous alkali hydroxide solution supplied (Qalkali hydroxide) and the weight flow rate of the organic flow supplied (Qorga) is between 0.25 and 1.0, preferably between 0.4 and 0.8 and more preferably between 0.5 and 0.

7.

9. Method according to any one of the preceding claims, characterized in that the concentration of the aqueous alkali hydroxide solution at the feed is between 5 and 40 g / L, preferably between 10 and 40 g / L, and more preferably between 15 and 35 g / L.

10. Use of an electrodialyzer, as defined in any one of claims 1 to 5, for treating at least one aqueous alkaline effluent from a process for the synthesis of isophorone by alkaline self-condensation of acetone in the liquid phase.

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