Process for synthesis of isophorone in liquid phase comprising recycling of basic catalyst by electrodialysis

Abstract

The 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) a condensation reaction of acetone in a reactor in an alkaline medium, followed by b) distillation of the reaction mixture from the reactor, optionally reactive distillation, then c) separating the stream recovered at the bottom of the distillation column, optionally a reactive distillation column, of step b) in order to separate the alkaline aqueous phase from the organic phase, and then d) extracting and / or purifying the organic phase in order to recover isophorone, characterized in that the separation of the stream recovered at the bottom of the distillation column, optionally the reactive distillation column, of step b) is carried out in order to recover isophorone. The process comprises the following successive steps: e) subjecting the alkaline aqueous phase recovered at the end of step c) to an electrodialysis treatment; f) recycling the aqueous phase from the electrodialysis into the reactor of step a), the alkaline hydroxide content of the aqueous phase being greater than the alkaline hydroxide content of the aqueous phase recovered at the end of step c).

Description

Technical Field

[0001] The present invention relates to a process for the liquid-phase synthesis of isophorone by the base-catalyzed self-condensation of acetone, which comprises treating the aqueous effluent generated during the synthesis by electrodialysis. Background Art

[0002] Isophorone (or 3,5,5-trimethylcyclohex-2-enone) is an α,β-unsaturated cyclic ketone which is increasingly used as a synthetic intermediate, in particular for the manufacture of isophorone diamine (which is used as a hardener for epoxy resins), isophorone diisocyanate (which is used as a polyurethane monomer), 3,5-dimethylphenol (which is used as a precursor for PCMX (an antibacterial agent)), ketoisophorone (a synthetic intermediate for vitamin E) and 3,5,5-trimethylcyclohexanol (which is used as a precursor for homosalate (an ultraviolet 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 agrochemistry for formulating emulsifiable pesticide concentrates.

[0003] Isophorone is usually obtained by the catalytic self-condensation of 3 molecules of acetone, according to the following reaction:

[0004]

[0005] This reaction is carried out in the liquid phase or in the gas phase.

[0006] The gas-phase processes described in the literature mainly use solid heterogeneous catalysts, while the liquid-phase processes use homogeneous or heterogeneous catalytic systems.

[0007] The synthesis of isophorone by the condensation of acetone in the liquid phase is carried out almost entirely under basic conditions at high temperature and under high pressure; basic catalysis is most often achieved by using an aqueous solution of sodium hydroxide or potassium hydroxide.

[0008] Since the solubility of inorganic bases in acetone is low, processes for promoting the contact between acetone and the catalyst have been sought. Thus, it is known from the literature US2,344,226 that the synthesis is carried out in a stirred reactor. The literature FR1238954 discloses a synthesis carried out using a tubular reactor with internal packing. The literature US2,399,976 discloses a synthesis carried out using a tubular reactor equipped with a recycling system. The literature CN102367223 and CN102516051 disclose a synthesis carried out using a premixing system (such as a static mixer). It is also known from the literature FR1042057 to use an alkaline alcohol solution instead of an alkaline aqueous solution.

[0009] The synthesis can be carried out continuously in a tubular reactor without special mixing equipment by using very low weight concentrations of sodium hydroxide or potassium hydroxide. Generally, the catalyst concentration is less than 1% (by weight), even on the order of about 0.1% (by weight) relative to the total weight of the reaction mixture. This low concentration allows for a single-phase mixture. These methods are described in the documents FR1316515, DD145096, EP2649032, EP2707352 and EP2837618.

[0010] The synthesis can also be carried out by reactive distillation as follows, by injecting acetone and an aqueous solution of sodium hydroxide or potassium hydroxide into a reactive distillation column 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 acetone countercurrently with sodium hydroxide or potassium hydroxide. This process is described in the documents FR1315788, FR2271191 and FR2328686.

[0011] The self-condensation reaction of acetone and / or the hydrolysis of reaction intermediates and polycondensation by-products give rise to an alkaline aqueous effluent. In addition to the initial alkaline aqueous solution used, this effluent contains the water produced by the self-condensation of acetone to form isophorone and contains small amounts of organic products (mainly isophorone). This effluent must be subjected to expensive special treatment to limit its environmental impact upon discharge.

[0012] A process is known from document US 8,889,914 B2 in which the aqueous phase of a hydrolysis column is treated by distillation and flash evaporation in order to recycle a portion of the organic compounds and water contained in this stream. This process is capable of recovering most of the organic matter and water, but not the catalyst. Thus, all of the catalyst injected into the reaction is lost. There remains the problem of treating the residual aqueous effluent: it must be neutralized and then the salts resulting from this neutralization must be removed before the water is discharged into the natural environment.

[0013] Accordingly, there is a need for a process for synthesizing isophorone that is more economical in terms of reagents, more economical in terms of energy and more environmentally friendly. The ideal process must produce less waste without losing selectivity or productivity. Summary of the Invention

[0014] The present invention relates to a process for the liquid-phase synthesis of isophorone by the alkaline self-condensation of acetone, preferably a continuous process, which comprises the following successive steps:

[0015] a) carrying out the condensation reaction of acetone in an alkaline medium in a reactor, and then

[0016] b) distilling the reaction mixture obtained from the reactor, optionally by reactive distillation, and then

[0017] c) Withdraw the stream taken at the bottom of the distillation column (optionally a reactive distillation column) of step b) in order to separate the alkaline aqueous phase from the organic phase, and then

[0018] d) Extract and / or purify the organic phase to recover isophorone,

[0019] Characterized in that the method comprises the following successive steps:

[0020] e) Subject the alkaline aqueous phase withdrawn at the end of step c) to continuous or batch electrodialysis treatment

[0021] f) Recycle the aqueous phase obtained from the electrodialysis to the reactor in step a), the aqueous phase having a higher alkali metal hydroxide content than the aqueous phase withdrawn at the end of step c).

[0022] Other advantageous characteristics of the process according to the invention are as follows:

[0023] - The electrodialysis device comprises at least one ion exchange membrane, the ion exchange membrane comprising a polymer-based matrix, the matrix comprising at least one fluoropolymer or copolymer, preferably PVDF;

[0024] - The total active exchange surface area 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 ;

[0025] - The current density applied to the electrodialysis device is 20 to 200 mA / cm 2 , preferably 30 to 100 mA / cm 2 ;

[0026] - The electrodialysis device includes a plurality of electrodialysis units in parallel or in series;

[0027] - The aqueous alkali metal hydroxide solution is an aqueous solution of sodium hydroxide or potassium hydroxide;

[0028] - The concentration of alkali metal hydroxide in the aqueous phase present in the reactor is greater than or equal to 50 g / l, preferably 50 to 200 g / l, more preferably 80 to 150 g / l and even more preferably 100 to 150 g / l;

[0029] - The ratio of the mass flow rate (Q alkali metal hydroxide) of the aqueous alkali metal hydroxide solution stream supplied to the mass flow rate (Q organic) of the organic stream supplied is 0.25 to 1.0, preferably 0.4 to 0.8 and more preferably 0.5 to 0.7;

[0030] - The concentration of alkali metal hydroxide in the aqueous solution at the feed zone is from 5 to 40 g / l, preferably from 10 to 40 g / l and more preferably from 15 to 35 g / l.

[0031] The invention also relates to the use of an electrodialysis device as defined above for treating at least one basic aqueous effluent obtained in a process for the synthesis of isophorone by basic self - condensation of acetone in the liquid phase. Description of the Drawings

[0032] Figure 1 is a schematic view of the device for implementing the claimed process. Detailed Description

[0033] After reading the following description, other characteristics, aspects, subjects and advantages of the invention will become more clearly apparent.

[0034] It should be clear that the expressions "(from)... to (to)..." and "between... and (to)..." used in this specification should be understood as including each of the mentioned endpoints.

[0035] The process according to the invention comprises the following successive steps:

[0036] Step a) carrying out the condensation reaction of acetone in a reactor in a basic medium

[0037] This synthesis can be carried out by injecting, preferably continuously, a stream of aqueous alkali metal hydroxide solution and a stream of organic solution containing acetone into the reactor R.

[0038] Advantageously, the ratio of the mass flow rate (Qalkali metal hydroxide) of the supplied aqueous alkali metal hydroxide solution stream to the mass flow rate (Qorganic) of the supplied organic stream is from 0.25 to 1.0, preferably between 0.4 and 0.8 and more preferably between 0.5 and 0.7.

[0039] The concentration of alkali metal hydroxide in the aqueous solution at the feed zone can be from 5 to 40 g / l, preferably 10 to 40 g / l and more preferably 15 to 35 g / l.

[0040] This stream can be pre - heated beforehand using a heat exchanger.

[0041] The reaction temperature in the reactor can be between 180 °C and 250 °C and preferably between 200 °C and 230 °C, and the absolute pressure is between 30 and 50 bar, preferably between 35 and 45 bar and even more preferably between 38 and 42 bar.

[0042] The reactor R is preferably a tubular reactor, and more specifically a tubular reactor in a vertical position. Additionally, where appropriate, it can consist of several tubular reactors fed in parallel.

[0043] 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 and more preferably between 100 and 150 g / l.

[0044] The reaction mixture is withdrawn at the reactor outlet and transferred to a distillation column.

[0045] Step b): Distillation

[0046] The reaction mixture withdrawn at the reactor outlet is distilled in a distillation column (optionally a reactive column).

[0047] According to one embodiment of the process of the present invention, the process comprises a hydrolytic reactive distillation so as to hydrolyze the heavy products. According to this possibility, the process may comprise two or three successive distillations in order to purify the fraction mainly containing isophorone at each distillation.

[0048] According to another embodiment of the process of the present invention, the process does not comprise a reactive distillation but a series of non-reactive distillations. Preferably, the process comprises four to six successive distillations in order to purify the fraction mainly containing isophorone at each distillation. The heavy products separated by these distillations can be recycled.

[0049] At the end of the first reactive or non-reactive distillation, the unreacted acetone is withdrawn at the top of the column and the concentrated crude reaction mixture is discharged at the bottom of the column. The acetone withdrawn at the top of the column can be recycled to the reactor R.

[0050] Step c): Separation

[0051] The concentrated crude reaction mixture discharged at the bottom of the first distillation column is separated, preferably by decantation. The basic aqueous phase can be separated from the organic phase rich in isophorone by means of a decanter.

[0052] Optional neutralization of the organic phase

[0053] Any alkali metal hydroxide present in the organic phase rich in isophorone withdrawn in separation step c) can be neutralized. This neutralization can be carried out by any technique known to those skilled in the art, but preferably by means of an inorganic acid providing a buffering action. Phosphoric acid is preferably used.

[0054] Step d): Extraction and / or purification

[0055] The organic phase rich in isophorone withdrawn in the separation step and then optionally neutralized is purified. It is preferably distilled, preferably under reduced pressure, in order to extract mainly the polycondensation by-products at the bottom of the column and to withdraw at the top of the column a stream consisting mainly of isophorone.

[0056] Subsequent distillation

[0057] The stream mainly composed of isophorone collected in the previous step can undergo multiple successive distillations to achieve a high degree of purification.

[0058] Step e): Electrodialysis treatment

[0059] The aqueous stream leaving separation step c), preferably the aqueous stream leaving the decanter, undergoes electrodialysis treatment.

[0060] This treatment step can be carried out batchwise or continuously.

[0061] This basic aqueous phase is treated by electrodialysis in order to collect:

[0062] - An aqueous phase with an alkali metal hydroxide content higher than that of the aqueous phase collected at the end of step c); and

[0063] - An aqueous phase with an alkali metal hydroxide content lower than that of the aqueous phase collected at the end of step c).

[0064] In other words, the electrodialysis equipment makes it possible to obtain a catalyst-rich phase and a catalyst-poor phase.

[0065] Electrodialysis is carried out in any equipment known to those skilled in the art, which allows the migration of ions through selective (anion or cation) ion exchange membranes under the action of an electric field applied perpendicular to the membranes. The electrodialysis equipment comprises at least one electrodialysis unit, which unit comprises at least 2 electrodes: an anode and a cathode, and alternately parallel arranged anion and cation membranes so as to form at least one concentration chamber and at least one dilution chamber. Advantageously, the electrodialysis equipment consists of a plurality of electrodialysis units arranged in parallel or in series.

[0066] In the case of a basic aqueous phase loaded with an alkali metal hydroxide, the alkali metal cations pass through the cation membrane (hereinafter denoted as MEC) and the OH − anions pass through the anion membrane (hereinafter denoted as MEA). Thus, in the case of a basic aqueous phase loaded with sodium hydroxide, Na + cations pass through the cation membrane (MEC) and the OH − anions pass through the anion membrane (MEA). In the case of a basic aqueous phase loaded with potassium hydroxide, K + cations pass through the cation membrane (MEC) and the OH − anions pass through the anion membrane (MEA). These ion exchange membranes comprise a polymer matrix on which functional groups are grafted, preferably sulfonic acid groups -(SO3) - or phosphoric acid groups -(PO3) 2- of the type and preferably alkylammonium groups -(NR3) for MEA+ 、 -(NHR2) + 、 -(NH2R) + or an alkylsulfonium group -(SR2) + type; the R groups can be the same or different and represent a saturated C1-C6 alkyl group.

[0067] Preferably, the ion exchange membrane comprises a polymer-based matrix which may in particular comprise a fluoropolymer or copolymer, in particular PVDF.

[0068] Preferably, the total active exchange surface area constituted by all the ion exchange membranes of the electrodialysis device is from 1 to 10 m² per ton of alkaline aqueous phase to be treated and preferably from 2 to 5 m² per ton of alkaline aqueous phase to be treated.

[0069] Preferably, a current density of 20 to 200 mA / cm² and in particular 30 to 100 mA / cm² is applied to the electrodialysis device.

[0070] According to one embodiment of the process of the invention, the total active exchange surface area of the electrodialysis device is from 1 to 10 m² per ton of alkaline aqueous phase to be treated and the current density is from 20 to 200 mA / cm².

[0071] According to a preferred embodiment of the process of the invention, the total active exchange surface area of the electrodialysis device is from 2 to 5 m² per ton of alkaline aqueous phase to be treated and a current density of 30 to 100 mA / cm² is applied to the electrodialysis device.

[0072] Electrodialysis treatment of the aqueous effluent enables the catalyst to be recycled, and thus avoids its loss in the wastewater and thus enables the wastewater to be treated. The treatment also enables the removal of excess water from the process.

[0073] The 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.

[0074] The aqueous stream poor in catalyst at the electrodialysis outlet can be sent to the sewage treatment plant S E .

[0075] Step f): Recycling

[0076] The catalyst-rich aqueous phase obtained from the electrodialysis device, i.e. the aqueous phase in which the alkali metal hydroxide content is greater than the alkali metal hydroxide content of the aqueous phase collected at the end of step c), is recycled to the reaction step.

[0077] Use

[0078] The invention also relates to the use of an electrodialysis device as defined above for treating at least one basic aqueous effluent obtained from a process for synthesizing isophorone by basic self-condensation of acetone in the liquid phase. The aqueous phase rich in basic catalyst thus obtained can be recycled to the reactor for the acetone self-condensation reaction.

[0079] For the purposes of the present invention, the term "aqueous effluent" is to be understood as meaning any basic aqueous solution produced by the isophorone synthesis process. Preferably, the synthesis process is as defined above, i.e. it comprises steps a) to d) as defined above.

[0080] The invention also relates to a process for treating at least one basic aqueous effluent as defined above, which is obtained from a process for synthesizing isophorone by basic self-condensation of acetone in the liquid phase as defined above, the process comprising a step of treatment using an electrodialysis device as defined above.

[0081] Description of the drawings

[0082] Figure 1 An embodiment of the process according to the invention is shown.

[0083] Acetone is introduced via line 1 into heat exchanger E1. An aqueous solution of alkali metal hydroxide is introduced via line 2 into heat exchanger E2. The preheated streams are collected in line 3 and introduced into tubular reactor R.

[0084] The reaction mixture obtained from tubular reactor R is introduced via line 4 into hydrolysis reactive distillation column D H . The hydrolysis of the reaction mixture is carried out under reduced pressure.

[0085] The acetone which has not reacted in tubular reactor R is collected at the top of column D H . This fraction is recycled via line 5 to line 1.

[0086] The concentrated crude reaction mixture is collected at the bottom of column D H and is conveyed via line 6 to decanter d1.

[0087] Decanter d1 separates the aqueous phase and the organic phase.

[0088] The basic aqueous phase is removed via line 8. This line 8 sends all or part of the aqueous phase to electrodialysis device E d . Any remaining aqueous phase not sent to the electrodialysis device is recycled as is via line 9 to line 10 to the reaction step.

[0089] The basic aqueous phase is treated in E d by electrodialysis in order to:

[0090] - The aqueous phase containing the rich catalyst (alkali metal hydroxide) is recycled through line 10 to the reaction step;

[0091] - The aqueous phase depleted of the catalyst is discharged and sent to the wastewater treatment unit S E .

[0092] The organic phase obtained from the decanter d1 is transported through line 7 to the neutralizer N. The neutralized organic phase is transported through line 11 to the distillation column D1.

[0093] Vacuum distillation using the distillation column D1 enables the collection of residual water and any light organic impurities at the top of the column D1, and the collection of a stream mainly containing isophorone at the bottom of the column. This stream is transported through line 12 to the distillation column D2.

[0094] The stream extracted from the top of the column D1 is transported through line 13 to the decanter d2 to separate the aqueous phase sent to the wastewater treatment S E and the organic phase that is sent back as reflux to the column D1 and, where appropriate, partially recycled through lines 14 to 15 to the hydrolysis column D H .

[0095] Vacuum distillation using the distillation column D2 allows the collection of isophorone with a purity greater than 99% at the top of the column D2, and the collection of C 3n H (4n+2) O polycondensation by-products at the bottom of the column. These by-products are recycled in whole or in part through line 15 to the reaction column D H . The un-recycled fraction containing the C 3n H (4n+2) O polycondensation by-products is collected (S L ).

[0096] Preferably, the weight concentration of isophorone in the stream at the inlet of D1 is greater than 70%, preferably greater than 75%.

[0097] Preferably, the weight concentration of isophorone in the stream at the inlet of D2 is greater than 75%, preferably greater than 80%.

[0098] The following examples illustrate the present invention but are not limiting in any way.

[0099] Examples

[0100] These examples illustrate the implementation process of collecting the catalyst using sodium hydroxide as the catalyst based on the unit production of 1 t / h of pure isophorone.

[0101] Hydrolysis column D HThe flow rate of the alkaline aqueous phase stream at the outlet of the decanter d1 at the bottom 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.

[0102] Example 1 (comparative, not within the scope of the present invention) : No recycling of the aqueous phase is carried out.

[0103] By discharging all the alkaline aqueous phase to wastewater treatment, the consumption at the feed of the reaction step of the isophorone synthesis process is 131 kg of sodium hydroxide and 4.3 m 3 of water per ton of pure isophorone produced, and the loss of isophorone contained in the alkaline aqueous phase is 39.7 kg per ton of pure isophorone.

[0104] Example 2 (comparative, not within the scope of the present invention) : Partial recycling of the alkaline aqueous phase, but the discharge is not concentrated.

[0105] To remove the excess water generated by the reaction, after discharging 0.24 t / h of the alkaline aqueous phase stream, the main remaining part of the stream (i.e., 4.43 t / h) is recycled to the reaction step and the discharge is discharged as it is to wastewater treatment.

[0106] At this time, the consumption during the feed of the reaction step of the isophorone synthesis process is 7 kg of sodium hydroxide (also considering the loss of sodium hydroxide dissolved in the crude isophorone stream and approximately 0.25 kg per ton of pure isophorone). Since the supplementary sodium hydroxide is added in the form of a sodium hydroxide aqueous solution with a weight concentration of 30.5%, the water consumption is 16 liters of water per ton of pure isophorone. And the loss of isophorone contained in the alkaline aqueous phase discharge is 2.0 kg per ton of pure isophorone.

[0107] Example 3 (according to the present invention) :

[0108] The 4.67 t / h alkaline aqueous phase stream leaving the decanter d1 is treated in an electrodialysis device (a constant direct current of 60 mA / cm 2 is supplied to the device to remove a lean sodium hydroxide aqueous stream with a flow rate of 0.23 t / h, and a 4.44 t / h alkaline aqueous phase stream rich in catalyst (sodium hydroxide) is collected), and is recycled as it is back to the feed of the reaction step. The electrodialysis device consists of 34 units, which provides an exchange surface area of 13.3 m 2 . The efficiency of the electrodialysis device is monitored by measuring the conductivity of various aqueous phase streams containing soda: the concentrated alkaline aqueous phase (2.9% sodium hydroxide) is approximately 140 mS / cm and the diluted alkaline aqueous phase (0.3% sodium hydroxide) is 16 mS / cm.

[0109] The weight composition of the lean catalyst aqueous stream is: 0.05% acetone, 0.85% isophorone, 0.3% sodium hydroxide, and 98.8% water. This stream is directed to wastewater treatment S E .

[0110] In the aqueous solution rich in catalyst, the weight concentrations of NaOH and isophorone are 2.9% and 0.85% respectively.

[0111] With the recycling of this catalyst, the consumption limit at the feed of the reaction step of the isophorone synthesis process is 0.95 kg of sodium hydroxide per ton of pure isophorone produced (corresponding to 0.7 kg discharged at the outlet of the electrodialysis equipment to S E and 0.25 kg of NaOH dissolved in the crude isophorone stream) and 2 liters of water. The loss of isophorone contained in the aqueous stream discharged to wastewater treatment is 2 kg per ton of pure isophorone.

[0112] Therefore, the present invention enables the following savings:

[0113] - Compared with a process without any aqueous phase recycling, per ton of isophorone, 130 kg of sodium hydroxide, 38 kg of isophorone, and 4.3 m 3 of water;

[0114] - Compared with a process with recycling by simply discharging the aqueous phase, per ton of isophorone, 6 kg of sodium hydroxide and 14 m 3 of water.

[0115] Therefore, the present invention enables the recycling of 99.2% of the catalyst used in the isophorone synthesis process and 95% of the isophorone contained in the alkaline aqueous phase at the outlet of the hydrolysis tower.

[0116] In addition, compared with a process that removes excess water (~230 kg) by a thermal evaporation process that requires 135 kWh, this process can save 129 kWh of energy; per ton of isophorone, electrodialysis only consumes 6 kWh.

[0117] More generally, the amount of water to be removed in the process according to the present invention depends on the amount of by-products formed, the degree of hydrolysis, and the amount of water entrained in the crude isophorone, and is 200 to 250 kg per ton of isophorone. Except for the residual catalyst, the weight concentration of water in the stream S E is greater than 98.5%, and the remaining part basically corresponds to isophorone and trace amounts of acetone.

[0118] Material balance of the entire process of Example 3: from feed to final isophorone

[0119] Introduce an acetone logistics with a flow rate of 1.4 t / h and an aqueous solution logistics containing 30% catalyst and 70% water with a flow rate of 0.003 t / h into the reactor. The reactor is also fed by two recycle logistics defined as follows.

[0120] The flow rate of the reaction medium logistics leaving the reactor is 14.8 t / h.

[0121] The flow rate of the organic phase logistics leaving the reaction column is 1.28 t / h. This organic phase contains more than 79% isophorone.

[0122] The flow rate of the purified isophorone fraction logistics leaving the distillation column is 1 t / h.

[0123] The flow rate of the light fraction logistics (recycling this fraction to the reactor) from the reaction column is 9 t / h.

[0124] The flow rate of the aqueous phase logistics leaving the reaction column and the decanter is 4.67 t / h. This aqueous phase contains 2.8% catalyst, 0.9% organic compound, and the rest is water. This aqueous phase is introduced into the electrodialysis equipment.

[0125] At the outlet of the electrodialysis equipment, the flow rate of the catalyst-lean phase logistics is 0.23 t / h. The catalyst-lean phase contains 0.9% organic compound, 0.3% catalyst, and the rest is water. The flow rate of the catalyst-rich phase logistics recycled to the reactor feed is 4.44 t / h. The catalyst-rich phase contains 2.9% catalyst, 0.9% organic compound, and the rest is water.

[0126] Therefore, using the electrodialysis equipment and recycling the catalyst-rich phase allows reducing the consumption of water and catalyst (0.003 t / h), minimizing the volume of the aqueous effluent (0.23 t / h), reducing the catalyst content in the effluent to one-tenth, and reducing energy consumption.

Claims

1. A process for the liquid-phase synthesis of isophorone by the base-catalyzed self-condensation of acetone, preferably a continuous process, which comprises the following successive steps: a) carrying out the condensation reaction of acetone in a reactor in a basic medium, and then b) distilling the reaction mixture obtained from the reactor, optionally by reactive distillation, and then c) separating the stream collected at the bottom of the distillation column in step b) so as to separate the basic aqueous phase from the organic phase, the distillation column being optionally a reactive distillation column, and then d) extracting and / or purifying the organic phase to recover isophorone, Characterized in that, The process comprises the following successive steps: e) subjecting the basic aqueous phase collected at the end of step c) to continuous or batch electrodialysis treatment f) recycling the aqueous phase obtained from the electrodialysis to the reactor in step a), the aqueous phase having a higher alkali metal hydroxide content than the aqueous phase collected at the end of step c).

2. The process according to claim 1, wherein The electrodialysis device comprises at least one ion-exchange membrane, the ion-exchange membrane comprising a polymer-based matrix, the matrix comprising at least one fluoropolymer or copolymer, preferably PVDF.

3. The process according to any one of the preceding claims, characterized in that, The total active exchange surface area of the electrodialysis device is 1 to 10 m per ton of the alkaline aqueous phase to be treated 2 , preferably 2 to 5 m per ton of the alkaline aqueous phase to be treated 2 .

4. The process according to any one of the preceding claims, characterized in that, Apply a current density of 20 to 200 mA / cm 2 to the electrodialysis device, preferably 30 to 100 mA / cm 2 .

5. The process according to any one of the preceding claims, characterized in that, The electrodialysis device comprises a plurality of electrodialysis units connected in parallel or in series.

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

7. The process according to any one of the preceding claims, 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 50 to 200 g / l, more preferably 80 to 150 g / l, and further preferably 100 to 150 g / l.

8. The process according to any one of the preceding claims, characterized in that, The ratio of the mass flow rate (Qalkali metal hydroxide) of the aqueous alkali metal hydroxide solution stream supplied to the mass flow rate (Qorganic) of the organic stream supplied is 0.25 to 1.0, preferably 0.4 to 0.8 and more preferably 0.5 to 0.

7.

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

10. Use of an electrodialysis device as defined in any one of claims 1 to 5 for treating at least one basic aqueous effluent obtained from a process for the synthesis of isophorone by the base-catalyzed self-condensation of acetone in the liquid phase.

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