Process for the synthesis of isophorone in liquid phase with recycling of alkaline catalyst by electrodialysis.

Abstract

The present invention comprises the following consecutive steps: a) condensation reaction of acetone in an alkaline medium in a reactor, followed by b) distilling, optionally reactively distilling, the reaction mixture obtained from the reactor, and then c) separating the stream recovered at the bottom of the distillation column of step b), optionally the reactive distillation column, in order to separate the alkaline aqueous phase from the organic phase, and then d) extracting and / or purifying the organic phase to recover isophorone; 1. A process for the liquid phase synthesis of isophorone by alkaline self-condensation of acetone, comprising the following successive steps: e) electrodialyzing the alkaline aqueous phase recovered at the end of step c); f) recycling the aqueous phase obtained from the electrodialysis, which has an alkali metal hydroxide content greater than the alkali metal hydroxide content of the aqueous phase recovered at the end of step c), to the reactor of step a); The present invention relates to a process comprising:

Description

[Technical Field]

[0001] The present invention relates to a process for the liquid phase synthesis of isophorone by alkaline self-condensation of acetone, comprising electrodialytic treatment of the aqueous effluent produced during said synthesis. [Background technology]

[0002] Isophorone (or 3,5,5-trimethylcyclohex-2-enone) is an α,β-unsaturated cyclic ketone that is increasingly used as a synthetic intermediate, particularly for the production of isophorone diamine, used as a curing agent for epoxy resins; isophorone diisocyanate, used as a polyurethane monomer; 3,5-xylenol, used as a precursor to PCMX (an antibacterial agent); keto-isophorone, a synthetic intermediate for 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 in pesticides for the formulation of emulsifiable pesticide concentrates.

[0003] Isophorone is conventionally obtained by catalytic self-condensation of three molecules of acetone according to the following reaction: [ka]

[0004] The reaction is carried out in the liquid phase or the gas phase.

[0005] The gas phase processes described in the literature essentially use solid heterogeneous catalysts, whereas the liquid phase processes use homogeneous or heterogeneous catalyst systems.

[0006] The synthesis of isophorone by condensation of acetone in the liquid phase is carried out almost exclusively under alkaline conditions at high temperature and pressure, with alkaline catalysis most often achieved by using aqueous solutions of sodium hydroxide or potassium hydroxide.

[0007] Due to the low solubility of inorganic bases in acetone, a process aimed at promoting the contact of acetone with a catalyst is needed. Thus, from US 2,344,226, it is known to carry out the synthesis in a stirred reactor. FR 1,238,954 discloses the synthesis using a tubular reactor with internal packing. US 2,399,976 discloses the synthesis using a tubular reactor equipped with a recirculation system. CN 102367223 and CN 102516051 disclose the synthesis using a premixing system such as a static mixer. FR 1,042,057 also discloses the replacement of the aqueous alkaline solution with an alkaline alcohol solution.

[0008] The synthesis can be carried out continuously in a tubular reactor without special mixing equipment by using very low concentrations (by weight) of sodium hydroxide or potassium hydroxide. Typically, the catalyst concentration is less than 1 wt. % or even as low as 0.1 wt. % based on the total weight of the reaction mixture. This low concentration allows for single-phase mixing. These processes are described in documents FR1316515, DD145096, EP2649032, EP2707352, and EP2837618.

[0009] The synthesis can also be carried out by reactive distillation by injecting acetone and an aqueous solution of sodium hydroxide or potassium hydroxide into a reactive distillation column, maintaining a low concentration of sodium hydroxide or potassium hydroxide (less than 0.1% by weight relative to the total weight of the reaction mixture) and reacting the acetone countercurrent with the sodium hydroxide or potassium hydroxide. This process is described in documents FR1315788, FR2271191, and FR2328686.

[0010] The acetone self-condensation reaction and / or hydrolysis of the reaction intermediates and polycondensation by-products produces an alkaline aqueous effluent. In addition to the initial alkaline aqueous solution used, this effluent contains water resulting from the self-condensation reaction of acetone with isophorone and small amounts of organic products (mainly isophorone). This effluent must be subjected to specific and expensive treatments to limit the environmental impact upon discharge.

[0011] Document US 8,889,914 discloses a process for treating the aqueous phase of a hydrolysis column by distillation and flash evaporation in order to recycle part of the organic compounds and water contained in this stream. This process allows for the recovery of most of the organic matter and water, but not the catalyst. Therefore, all of the catalyst injected into the reaction is lost. The problem of managing the residual aqueous effluent still arises, which must be neutralized and then the salts resulting from this neutralization must be removed before the water is discharged into the natural environment. Summary of the Invention [Problem to be solved by the invention]

[0012] Therefore, there is a need for a process for the synthesis of isophorone that is more economical in terms of reagents, more economical in terms of energy, and more environmentally friendly. Any process should produce less waste without losing selectivity or productivity. [Means for solving the problem]

[0013] The present invention comprises the following consecutive steps: a) condensation reaction of acetone in an alkaline medium in a reactor, followed by b) distilling, optionally reactively distilling, the reaction mixture obtained from the reactor, and then c) separating the stream recovered at the bottom of the distillation column of step b), optionally the reactive distillation column, in order to separate the alkaline aqueous phase from the organic phase, and then d) extracting and / or purifying the organic phase to recover isophorone; 1. A process, preferably a continuous process, for the liquid phase synthesis of isophorone by alkaline self-condensation of acetone, comprising the following successive steps: e) subjecting the alkaline aqueous phase recovered at the end of step c) to electrodialysis, either continuously or batchwise; f) recycling the aqueous phase obtained from the electrodialysis, which has an alkali metal hydroxide content greater than the alkali metal hydroxide content of the aqueous phase recovered at the end of step c), to the reactor of step a); The present invention relates to a process comprising:

[0014] Other advantageous features of the process according to the invention are specified below:

[0015] said electrodialysis device comprises at least one ion exchange membrane comprising a polymer-based matrix comprising at least one fluorinated polymer or copolymer, preferably PVDF;

[0016] - The electrodialysis device has a capacity of 1 to 10 m per ton of alkaline aqueous phase to be treated. 2 , preferably 2 to 5 m per ton of alkaline aqueous phase to be treated 2 having a total active exchange surface area of

[0017] -20~200mA / cm 2 , preferably 30 to 100 mA / cm 2 is applied to the electrodialysis device.

[0018] the electrodialysis device comprises several electrodialysis units in parallel or in series,

[0019] the aqueous alkali metal hydroxide solution is an aqueous solution of sodium hydroxide or potassium hydroxide,

[0020] the concentration of alkali metal hydroxide in the aqueous phase present in 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 preferentially between 100 and 150 g / l;

[0021] the ratio of the mass flow rate of the aqueous alkali metal hydroxide stream fed (Q alkali metal hydroxide) to the mass flow rate of the organic stream fed (Q organic) is between 0.25 and 1.0, preferably between 0.4 and 0.8, more preferentially between 0.5 and 0.7,

[0022] The concentration of alkali metal hydroxide in the aqueous solution in the feeding zone is between 5 and 40 g / l, preferably between 10 and 40 g / l, more preferentially between 15 and 35 g / l.

[0023] The present invention also relates to the use of an electrodialysis device as described above for treating at least one alkaline aqueous effluent obtained from the process for the synthesis of isophorone by alkaline self-condensation of acetone in the liquid phase. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 shows a schematic diagram of an apparatus for carrying out the claimed process. DETAILED DESCRIPTION OF THE INVENTION

[0025] Other features, aspects, subjects and advantages of the present invention will become even more clearly apparent upon reading the following description.

[0026] It is expressly stated that the expressions "from to" and "between and" used herein are to be understood as including each of the limitations mentioned.

[0027] The process according to the invention comprises the following successive steps:

[0028] Step a) Condensation reaction of acetone in an alkaline medium in a reactor

[0029] The synthesis can be carried out by injecting, preferably continuously injecting, through reactor R a stream of aqueous alkali metal hydroxide and a stream of an organic solution comprising acetone.

[0030] Advantageously, the ratio of the mass flow rate of the aqueous alkali metal hydroxide stream fed (Q alkali metal hydroxide) to the mass flow rate of the organic stream fed (Q organic) is between 0.25 and 1.0, preferably between 0.4 and 0.8, more preferentially between 0.5 and 0.7.

[0031] The concentration of alkali metal hydroxide in said aqueous solution in the feeding zone may be between 5 and 40 g / l, preferably between 10 and 40 g / l, more preferentially between 15 and 35 g / l.

[0032] The stream may be preheated beforehand using a heat exchanger.

[0033] The reaction temperature in the reactor may be 180°C to 250°C, preferably 200°C to 230°C, and the reaction may be carried out under an absolute pressure of 30 to 50 bar, preferably 35 to 45 bar, and even more preferentially 38 to 42 bar.

[0034] The reactor R is preferably a tubular reactor, more particularly a tubular reactor in a vertical position. Furthermore, it may, if appropriate, consist of several tubular reactors fed in parallel.

[0035] Preferably, the concentration of alkali metal hydroxide in the aqueous phase present in 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, more preferentially between 100 and 150 g / l.

[0036] The reaction mixture is collected at the outlet of the reactor and conveyed to a distillation column.

[0037] Step b): Distillation

[0038] The reaction mixture recovered at the reactor outlet is distilled through a column, optionally a reaction column.

[0039] According to one embodiment of the process according to the invention, the process comprises a hydrolysis reactive distillation making it possible to hydrolyze the heavy product, and according to this result, the process may comprise two or three successive distillations in order to purify the fractions containing mainly isophorone in each distillation.

[0040] In another embodiment of the process according to the invention, the process does not involve a reactive distillation but a series of non-reactive distillations. Preferably, the process comprises 4 to 6 successive distillations in each of which the fraction containing mainly isophorone is purified. The heavy products isolated by these distillations can be recycled.

[0041] At the end of the first reaction or non-reaction distillation, unconverted acetone is recovered at the top of the column and a concentrated crude reaction mixture is withdrawn at the bottom of the column. The acetone recovered at the top of the column can be recycled to reactor R.

[0042] Step c): Separation

[0043] The concentrated crude reaction mixture withdrawn from the bottom of the first distillation column is preferably separated by decantation, and the alkaline aqueous phase can be separated from the isophorone-rich organic phase by a decanter.

[0044] Optional neutralization of the organic phase

[0045] The alkali metal hydroxide present in the isophorone-enriched organic phase recovered in separation step c) may be neutralized. This neutralization can be carried out by any technique known to those skilled in the art, but preferably by a mineral acid that provides a buffering effect. Preferably, phosphoric acid is used.

[0046] Step d): Extraction and / or purification

[0047] After recovery from the separation step, the optionally neutralized isophorone-rich organic phase is purified, preferably by distillation under reduced pressure, to extract primarily polycondensation by-products at the bottom of the column and recover a stream consisting primarily of isophorone at the top of the column.

[0048] Subsequent distillation

[0049] The stream consisting mainly of isophorone recovered in the preceding step may be subjected to several successive distillations to obtain a high degree of purification.

[0050] Step e): Electrodialysis treatment

[0051] The aqueous stream leaving separation step c), preferably leaving the decanter, is subjected to an electrodialysis treatment.

[0052] This process can be carried out batchwise or continuously.

[0053] This alkaline aqueous phase is an aqueous phase having an alkali metal hydroxide content greater than the alkali metal hydroxide content of the aqueous phase recovered at the end of step c), and - an aqueous phase having an alkali metal hydroxide content lower than the alkali metal hydroxide content of the aqueous phase recovered at the end of step c). The resulting product is treated by electrodialysis to recover the

[0054] In other words, the electrodialysis device makes it possible to obtain a catalyst-rich phase and a catalyst-depleted phase.

[0055] The electrodialysis is carried out in any device known to those skilled in the art that allows the migration of ions through a selective (anionic or cationic) ion exchange membrane under the action of an electric field applied perpendicular to the membrane. The electrodialysis device 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 to form at least one concentrate compartment and at least one dilute compartment. Advantageously, the electrodialysis device consists of several electrodialysis units in parallel or in series.

[0056] In the case of an alkaline aqueous phase loaded with alkali metal hydroxides, alkali metal cations pass through the cationic membrane, hereinafter referred to as MEC, and OH - Anions pass through the anionic membrane, hereafter referred to as MEA. Thus, in the case of an alkaline aqueous phase loaded with sodium hydroxide, Na + Cations pass through the cationic membrane (MEC) and react with OH - Anions pass through the anionic membrane (MEA). In the case of an alkaline aqueous phase filled with potassium hydroxide, K + Cations pass through the cationic membrane (MEC) and react with OH - The anions pass through the anionic membrane (MEA). These ion exchange membranes are preferably sulfone-(SO3) for MEC. - or phosphorus (PO3) 2- of the type, preferentially alkylammonium-(NR3) for MEA + , -(NHR2) + , -(NH2R) + or alkylsulfonium-(SR2) + It comprises a polymer matrix grafted with functional groups of the type R, the R groups being the same or different and representing saturated C1-C6 alkyl groups.

[0057] Preferably, the ion exchange membrane comprises a polymer-based matrix which may in particular comprise a fluorinated polymer or copolymer, including in particular PVDF.

[0058] Preferably, the total active exchange surface area formed by all the ion exchange membranes of the electrodialysis device is 1 to 10 m per ton of alkaline aqueous phase to be treated. 2 , preferably 2 to 5 m per ton of alkaline aqueous phase to be treated 2 is.

[0059] Preferably, 20 to 200 mA / cm 2 , especially 30 to 100 mA / cm 2 is applied to the electrodialysis device.

[0060] According to one embodiment of the process according to the invention, the electrodialysis device is operated at a rate of 1 to 10 m per tonne of alkaline aqueous phase to be treated. 2 of total active exchange surface area, and 20-200 mA / cm 2 has a current density of

[0061] According to a preferred embodiment of the process according to the invention, the electrodialysis device is operated at a rate of 2 to 5 m per tonne of alkaline aqueous phase to be treated. 2 and a total active exchange surface area of ​​30-100 mA / cm 2 is applied to the electrodialysis device.

[0062] The electrodialysis treatment of the aqueous effluent makes it possible to recycle the catalyst, thus avoiding its loss in the wastewater, and consequently allows the treatment of this wastewater, which also makes it possible to remove excess water from the process.

[0063] This excess water corresponds to the water formed in the reactor minus the water consumed in the hydrolysis column minus the water dissolved in the crude isophorone removed at the top of one of the subsequent distillation columns.

[0064] The catalyst-depleted aqueous stream at the outlet of the electrodialysis is passed through a wastewater treatment plant S E can be sent to.

[0065] Process f): Recirculation

[0066] The catalyst-rich aqueous phase obtained from the electrodialysis apparatus, i.e. having an alkali metal hydroxide content higher than the alkali metal hydroxide content of the aqueous phase recovered at the end of step c), is recycled to the reaction step.

[0067] use

[0068] The present invention also relates to the use of an electrodialysis apparatus as described above for treating at least one alkaline aqueous effluent obtained from the process for the synthesis of isophorone by alkaline self-condensation of acetone in the liquid phase, wherein the aqueous phase obtained, rich in alkaline catalyst, can be recycled to the reactor of the acetone self-condensation reaction.

[0069] For the purposes of the present invention, the term "aqueous effluent" is understood to mean any aqueous alkaline solution produced by said isophorone synthesis process. Preferably, said synthesis process is as defined above, i.e. comprises steps a) to d) as defined above.

[0070] The present invention also relates to a process for the treatment of at least one alkaline aqueous effluent, as defined above, obtained from a process for the synthesis of isophorone by alkaline self-condensation of acetone in the liquid phase, as defined above, which process comprises a treatment step with an electrodialysis apparatus, as defined above.

[0071] BRIEF DESCRIPTION OF THE DRAWINGS

[0072] FIG. 1 depicts one embodiment of the process according to the present invention.

[0073] Acetone is introduced into heat exchanger E1 via line 1. The aqueous alkali metal hydroxide solution is introduced into heat exchanger E2 via line 2. The preheated stream is recovered in line 3 and introduced into tubular reactor R.

[0074] The reaction mixture obtained from the tubular reactor R is fed via line 4 to the hydrolysis reaction-distillation column D HThe hydrolysis of the reaction mixture is carried out under reduced pressure.

[0075] The acetone not converted in the tubular reactor is transferred to column D H This fraction is recycled via line 5 to line 1.

[0076] The concentrated crude reaction mixture is then passed through column D H and is conveyed via line 6 to decanter d1.

[0077] Decanter d1 separates the aqueous phase from the organic phase.

[0078] The alkaline aqueous phase is removed via line 8. This line 8 transfers all or part of the aqueous phase to an electrodialysis unit E d The remaining aqueous phase that has not been brought into the electrodialysis device is recycled directly to the reaction step via lines 9 and 10.

[0079] The alkaline aqueous phase is - to recover the aqueous phase rich in catalyst (alkali metal hydroxide) and recycle it to the reaction step via line 10; -Remove the catalyst-depleted aqueous phase and treat the wastewater E To send to E d The water is treated by electrodialysis within the facility.

[0080] The organic phase obtained from the decanter d1 is conveyed via line 7 to the neutralizer N. The neutralized organic phase is conveyed via line 11 to the distillation column D1.

[0081] Distillation under reduced pressure using distillation column D1 makes it possible to recover the residual water and any light organic impurities at the top of column D1 and to recover at the bottom a stream comprising mainly isophorone which is transferred via line 12 to distillation column D2.

[0082] The stream extracted at the top of column D1 is sent to wastewater treatment SE via line 13 to a decanter d2, and, if appropriate, via lines 14 and 15 to separate the aqueous phase, which is sent to the hydrolysis column D1, and the organic phase, which is returned to the reflux of the column D1. H is partially recycled to

[0083] By distillation under reduced pressure using distillation column D2, isophorone can be recovered at the top of column D2 with a purity of more than 99%, 3n H (4n+2) Polycondensation by-products can be recovered at the bottom of the column. These by-products are passed through line 15 to reactor D H C 3n H (4n+2) A portion of the recovered fraction containing polycondensation by-products is recovered (S L ).

[0084] Preferably, the concentration of isophorone in the stream at the feed of D1 is greater than 70% by weight, preferably greater than 75% by weight.

[0085] Preferably, the concentration of isophorone in the stream at the feed of D2 is greater than 75% by weight, preferably greater than 80% by weight.

[0086] The following examples illustrate the present invention but do not limit it in any way.

[0087] (Example) These examples demonstrate the implementation of catalyst recovery based on a unit production of 1 t / h of pure isophorone using sodium hydroxide as catalyst.

[0088] Hydrolysis tower D H The flow rate of the alkaline aqueous phase at the outlet of the bottom decanter d1 is 4.67 t / h, and the concentrations of sodium hydroxide (catalyst) and isophorone in this aqueous phase are 2.8% by weight and 0.85% by weight, respectively.

[0089] Example 1 (comparison, outside the invention): No recirculation of the aqueous phase.

[0090] By removing all of the alkaline aqueous phase to wastewater treatment, the feed consumption of the reaction step of the isophorone synthesis process is 131 kg of sodium hydroxide and 4.3 m of water per tonne of pure isophorone produced. 3 and the loss of isophorone contained in the alkaline aqueous phase is 39.7 kg per tonne of pure isophorone.

[0091] Example 2 (comparison, outside the invention): with partial recycle of the alkaline aqueous phase but without concentration treatment of the purge.

[0092] After subjecting the alkaline aqueous phase stream to a 0.24 t / h purge to remove excess water produced by the reaction, the majority of the remaining stream, i.e., 4.43 t / h, is recycled to the reaction step, and the purge is directly removed for wastewater treatment.

[0093] The feed consumption of the reaction step of the isophorone synthesis process is then 7 kg of sodium hydroxide (and, taking into account the loss of NaOH dissolved in the crude isophorone stream, corresponds to about 0.25 kg per ton of pure isophorone). Since the make-up sodium hydroxide is added in the form of an aqueous sodium hydroxide solution having a concentration of 30.5 wt.%, the water consumption is 16 liters of water per ton of pure isophorone. Also, the loss of isophorone contained in the alkaline aqueous phase purge corresponds to 2.0 kg per ton of pure isophorone.

[0094] Example 3 (according to the invention):

[0095] The flow of the alkaline aqueous phase of 4.67 t / h leaving decanter d1 is 60 mA / cm 2 The electrodialysis equipment is supplied with a constant direct current of 13.3 m, which removes an aqueous stream depleted in NaOH at a flow rate of 0.23 t / h and recovers an alkaline aqueous stream rich in catalyst (NaOH) at a flow rate of 4.44 t / h, which is recycled directly to the feed of the reaction step. The electrodialysis equipment consists of 34 cells and has a capacity of 13.3 m 2The efficiency of the electrodialysis device is monitored by measuring the conductivity of the various soda-containing aqueous phases: approximately 140 mS / cm for concentrated alkaline aqueous phase (2.9% NaOH) and 16 mS / cm for diluted alkaline aqueous phase (0.3% NaOH).

[0096] The catalyst-depleted aqueous stream has a composition of 0.05 wt. % acetone, 0.85 wt. % isophorone, 0.3 wt. % NaOH, and 98.8 wt. % water. This stream is passed through the wastewater treatment plant S E It is directed towards.

[0097] The concentrations of NaOH and isophorone in the catalyst-rich aqueous solution are 2.9 wt % and 0.85 wt %, respectively.

[0098] By recycling the catalyst in this way, the consumption of the feed in the reaction step of the isophorone synthesis process is reduced to 0.95 kg of NaOH (S at the outlet of the electrodialysis device) per ton of pure isophorone produced. E The isophorone loss in the aqueous stream and removed in the wastewater treatment is limited to 2 kg per tonne of pure isophorone (corresponding to 0.7 kg removed in the aqueous stream and 0.25 kg of NaOH dissolved in the crude isophorone stream) and 2 liters of water.

[0099] Therefore, according to the present invention, - Compared to a process without any aqueous phase recycle, 130 kg of sodium hydroxide, 38 kg of isophorone and 4.3 m per ton of isophorone 3 Water, - 6 kg of sodium hydroxide and 14 liters of water per ton of isophorone compared to a process with simple purging and recycling of the aqueous phase It will be possible to save on

[0100] The invention therefore makes it possible to recycle, at the outlet of the hydrolysis column, 99.2% of the catalyst used in the isophorone synthesis process and 95% of the isophorone contained in the alkaline aqueous phase.

[0101] Furthermore, this process allows saving 129 kWh of energy compared to removing excess water (approximately 230 kg) by a thermal evaporation process, which requires 135 kWh, while the electrodialysis consumes only 6 kWh per ton of isophorone.

[0102] More typically, the amount of water removed in the process according to the invention is between 200 and 250 kg per ton of isophorone, depending on the amount of by-products formed, the degree of hydrolysis and the amount of water entrained in the crude isophorone. E The concentration of water in the filtrate is greater than 98.5% by weight, the remainder essentially corresponding to isophorone and traces of acetone, in addition to residual catalyst.

[0103] Overall Process: Example 3 Balance from Feed to Final Isophorone

[0104] A stream of acetone with a flow rate of 1.4 t / h and a stream of an aqueous solution with a flow rate of 0.003 t / h containing 30% of catalyst and 70% of water are introduced into the reactor, which is also fed with two recycle streams defined below.

[0105] The flow rate of the reaction medium stream leaving the reactor is 14.8 t / h.

[0106] The flow rate of the organic phase stream leaving the reactor is 1.28 t / h, and this organic phase contains more than 79% isophorone.

[0107] The flow rate of the purified isophorone fraction stream leaving the distillation column is 1 t / h.

[0108] The flow rate of the light fraction stream from the reaction tower is 9 t / h, and the reaction tower recycles this fraction to the reactor.

[0109] The aqueous phase leaving the reactor and decanter has a flow rate of 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 electrodialysis device.

[0110] At the outlet of the electrodialysis device, the catalyst-depleted phase stream has a flow rate of 0.23 t / h. The catalyst-depleted phase contains 0.9% organic compounds, 0.3% catalyst, and the remainder is water. The catalyst-rich phase stream recycled to the reactor feed has a flow rate of 4.44 t / h. The catalyst-rich phase contains 2.9% catalyst, 0.9% organic compounds, and the remainder is water.

[0111] The use of the electrodialysis device and the recycling of the catalyst-rich phase therefore allows for a reduced consumption of water and catalyst (0.003 t / h), a minimal volume of aqueous effluent (0.23 t / h), a tenth lower catalyst content in the effluent, and a reduced energy consumption.

Claims

1. The following consecutive steps: a) condensation reaction of acetone in an alkaline medium in a reactor, followed by b) distilling, optionally reactively distilling, the reaction mixture obtained from the reactor, followed by c) separating the stream recovered at the bottom of the distillation column of step b), optionally the reactive distillation column, in order to separate the alkaline aqueous phase from the organic phase, and then d) extracting and / or purifying the organic phase to recover isophorone; 1. A process, preferably a continuous process, for the liquid phase synthesis of isophorone by alkaline self-condensation of acetone, comprising the following successive steps: e) subjecting the alkaline aqueous phase recovered at the end of step c) to electrodialysis, either continuously or batchwise; f) recycling the aqueous phase obtained from the electrodialysis, the aqueous phase having an alkali metal hydroxide content greater than the alkali metal hydroxide content of the aqueous phase recovered at the end of step c), to the reactor of step a); A process comprising:

2. 2. Process according to claim 1, characterized in that the electrodialysis device comprises at least one ion exchange membrane with a polymer-based matrix comprising at least one fluorinated polymer or copolymer, preferably PVDF.

3. The electrodialysis device is configured to treat 1 to 10 m per ton of alkaline aqueous phase. ２ , preferably 2 to 5 m per tonne of alkaline aqueous phase to be treated ２ 3. The process according to claim 1 or 2, characterized in that the total active exchange surface area is

4. 20~200mA / cm ２ , preferably 30 to 100 mA / cm ２ The process according to any one of claims 1 to 3, characterized in that a current density of

5. Process according to any one of claims 1 to 4, characterized in that the electrodialysis device comprises several electrodialysis units in parallel or in series.

6. The process according to any one of claims 1 to 5, characterized in that the aqueous alkali metal hydroxide solution is an aqueous solution of sodium hydroxide or potassium hydroxide.

7. 7. The process according to any one of claims 1 to 6, characterized in that the concentration of alkali metal hydroxide in the aqueous phase present in 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, more preferentially between 100 and 150 g / l.

8. 8. A process according to any one of claims 1 to 7, characterized in that the ratio of the mass flow rate of the aqueous alkali metal hydroxide stream fed (Q alkali metal hydroxide) to the mass flow rate of the organic stream fed (Q organic) is between 0.25 and 1.0, preferably between 0.4 and 0.8, more preferentially between 0.5 and 0.

7.

9. 9. The process according to any one of claims 1 to 8, characterized in that the concentration of alkali metal hydroxide in the aqueous solution in the feeding zone is between 5 and 40 g / l, preferably between 10 and 40 g / l, more preferentially between 15 and 35 g / l.

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

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