Method for preparing 1,2-propanediol

Abstract

A process for preparing 1,2-propanediol comprises the following steps: (a) reacting propylene with hydrogen peroxide in a liquid reaction mixture in the presence of a phase transfer catalyst and a heteropolytungstate, the liquid reaction mixture comprising an aqueous phase and an organic phase having a maximum apparent pH of 6, the organic phase comprising a solvent having a solubility in water at 20 °C of less than 500 mg / kg; (b) separating the liquid reaction mixture of step (a) into an aqueous phase and an organic phase comprising 1,2-propanediol; (c) recycling at least a portion of the separated organic phase to step (a); (d) extracting the separated aqueous phase with an extractant solution to provide an extracted aqueous phase and an extract phase, the extractant solution comprising the same phase transfer catalyst and solvent as used in step (a); (e) recycling at least a portion of the extract phase to step (a); and (f) recovering 1,2-propanediol from the extracted aqueous phase.

Description

TECHNICAL FIELD

[0001] The present invention relates to a process for preparing 1,2 - propanediol by reacting propylene with hydrogen peroxide. BACKGROUND ART

[0002] In established processes used in the industry, 1,2 - propanediol is prepared by reacting propylene oxide with water. Propylene oxide can be prepared on an industrial basis using the HPPO process, which involves the reaction of propylene with hydrogen peroxide in the presence of a titanium zeolite catalyst and an organic solvent. Then, it is separated and purified before the step of reacting propylene oxide with water to prepare 1,2 - propanediol.

[0003] WO 2017 / 089075 discloses a process for producing 1,2 - propanediol from propylene and hydrogen peroxide, which comprises: a) reacting propylene with hydrogen peroxide in the presence of a catalyst mixture comprising a phase - transfer catalyst and a heteropolytungstate, wherein the reaction is carried out in a liquid mixture comprising an aqueous phase and an organic phase with a maximum pH of 6; b) separating the biphasic mixture from step a) into an aqueous phase and an organic phase containing propylene oxide; c) recycling the propylene oxide contained in the separated organic phase back to the reaction of step a); and d) separating 1,2 - propanediol from the aqueous phase separated in step b).

[0004] In the process of WO 2017 / 089075, the tungstate contained in the aqueous phase of the reaction mixture will ultimately be in the residual bottoms obtained from the distillation recovery of 1,2 - propanediol from the aqueous phase and will be lost with the bottoms or must be recovered from the bottoms. SUMMARY OF THE INVENTION

[0005] The inventors of the present invention have now found that extracting the aqueous phase resulting from the propylene oxidation reaction with an extractant solution comprising the phase - transfer catalyst and the solvent used in the oxidation reaction and recycling all or part of the extract phase to the oxidation reaction can significantly reduce the loss of tungstate with the aqueous phase of the propylene oxidation reaction mixture without having to recover the tungstate from the bottoms of the distillation for the recovery of 1,2 - propanediol.

[0006] Accordingly, the subject matter of the present invention is a process for preparing 1,2 - propanediol, said process comprising:

[0007] a) reacting propylene with hydrogen peroxide in a liquid reaction mixture in the presence of a catalyst mixture comprising a phase - transfer catalyst and a heteropolytungstate, said liquid reaction mixture comprising an aqueous phase and an organic phase with a maximum apparent pH of 6, said organic phase comprising a solvent (S) having a solubility in water at 20°C of less than 500 mg / kg;

[0008] b) Separate the liquid reaction mixture from step a) into an aqueous phase (P a ) containing 1,2 - propanediol and an organic phase (P o );

[0009] c) Recycle at least a portion of the separated organic phase (P o ) to reaction step a);

[0010] d) Extract the separated aqueous phase (P a ) with an extractant solution to provide an extracted aqueous phase (P ae ) and an extract phase (P e ), wherein the extractant solution contains the same phase - transfer catalyst and the same solvent (S) used in step a), and the extract phase (P e ) contains a salt of the phase - transfer catalyst and a heteropolytungstate or tungstate;

[0011] e) Recycle at least a portion of the extract phase (P e ) to step a); and

[0012] f) Recover 1,2 - propanediol from the extracted aqueous phase (P ae ).

[0013] Another subject of the present invention is a facility for preparing 1,2 - propanediol, the facility comprising:

[0014] a) A cooled loop reactor comprising an inlet for hydrogen peroxide, an inlet for propylene, an outlet for the reaction mixture, and at least one recycle stream inlet;

[0015] b) A phase separator comprising an inlet, a first outlet for the separated aqueous phase, and a second outlet for the separated organic phase, the inlet being connected to the outlet of the loop reactor by a conduit to receive the reaction mixture;

[0016] c) A membrane nanofiltration unit having an inlet, a first outlet for the retentate, and a second outlet for the permeate, the inlet being connected to the second outlet of the phase separator by a conduit to receive all or part of the separated organic phase, and the first outlet being connected to the recycle stream inlet of the loop reactor by a conduit;

[0017] d) An extraction unit having a feed port, an extractant inlet, an extract liquid outlet, and a raffinate outlet, the feed port being connected to the first outlet of the phase separator by a conduit to receive the separated aqueous phase, and the extractant inlet being connected to the second outlet of the membrane nanofiltration unit by a conduit to receive the permeate;

[0018] e) A first recirculation conduit that connects the extract outlet of the extraction unit to the inlet of the membrane nanofiltration unit and / or the recirculation flow inlet of the circulation reactor;

[0019] f) Optionally present, a second recirculation conduit that connects the second outlet of the phase separator to the inlet of the circulation reactor for receiving as a recirculation flow a portion of the separated organic phase that has not been transferred to the membrane nanofiltration unit; and

[0020] g) A separation unit having an inlet connected to the raffinate outlet of the extraction unit, an outlet for the separated water, an outlet for the separated 1,2 - propanediol, and an outlet for the by - products. Description of the Drawings

[0021] The figure shows an embodiment of the facility of the present invention, which has a counter - current extraction column in the extraction unit, a hydrogenation unit, and two distillation columns in the separation unit, as well as an additional catalyst re - activation unit. Detailed Description

[0022] In the method of the present invention, in step a), propylene is reacted with hydrogen peroxide in the presence of a catalyst mixture comprising a phase - transfer catalyst and a heteropolytungstate. The reaction is carried out in a liquid reaction mixture comprising an aqueous phase and an organic phase with a maximum apparent pH of 6, and the organic phase comprises a solvent (S) having a solubility in water at 20 °C of less than 500 mg / kg.

[0023] Propylene can be used in pure form or in the form of a mixture with propane, where the proportion of propane can be up to 20 mol%. The proportion of propane in the propylene used is preferably less than 5 mol%. Propylene is preferably used in a molar excess relative to hydrogen peroxide, preferably in a molar ratio of propylene to hydrogen peroxide of 1.1:1 to 10:1.

[0024] Hydrogen peroxide is preferably used in the form of an aqueous solution, which preferably has a hydrogen peroxide content of 10 - 80 wt%, particularly preferably 30 - 70 wt%. Any commercially available grade of hydrogen peroxide aqueous solution can be used. It is also possible to use the crude hydrogen peroxide product obtained in the extraction stage of the anthraquinone process for producing hydrogen peroxide.

[0025] The catalyst mixture used in step a) comprises a heteropolytungstate. The heteroatom is preferably phosphorus or arsenic, and particularly preferably phosphorus (i.e., the heteropolytungstate is particularly preferably a polytungstophosphate). Heteropolytungstates are known to those skilled in the art. The molar ratio of phosphorus to tungsten in the preferred polytungstophosphate is in the range of 1:2 to 1:12. The polytungstophosphate is preferably generated in-situ by combining phosphoric acid with sodium tungstate, which can be carried out in the liquid reaction mixture itself or before adding the polytungstophosphate to the liquid reaction mixture. Phosphoric acid and sodium tungstate are preferably used in a phosphorus to tungsten molar ratio of 1:2 to 10:1, preferably 4:1 to 8:1. The heteropolytungstate reacts with hydrogen peroxide in the liquid reaction mixture to form peroxotungstate and peroxotungstophosphate such as PO4[WO(O2)2]4 3- and HPO4[WO(O2)2]2 2- and their partially protonated forms, which are presumably the catalytically active species for the oxidation of propylene.

[0026] The catalyst mixture used in step a) further comprises a phase transfer catalyst. The phase transfer catalyst comprises a cation or a compound that forms a cation in the aqueous phase, whereby the cation can form a salt with peroxotungstate or heteropolyperoxotungstate, and the salt is soluble in the organic phase of the liquid reaction mixture. The phase transfer catalyst preferably comprises a monovalent cation or a compound that forms a monovalent cation in the aqueous phase. Suitable as phase transfer catalysts are tertiary amines, tertiary ammonium salts and quaternary ammonium salts, as well as quaternary phosphonium salts. The counterions suitable for tertiary ammonium salts and quaternary ammonium salts are the following anions: chloride, bromide, nitrate, sulfate, hydrogen phosphate, dihydrogen phosphate, methanesulfonate, methyl sulfate and ethyl sulfate. The amount of the phase transfer catalyst is preferably such that the molar ratio of the phase transfer catalyst to tungsten in the liquid mixture is in the range of 0.2:1 to 3:1, particularly preferably 0.4:1 to 1:1, where the molar ratio refers to the cation or the compound forming the cation in the phase transfer catalyst used compared to the amount of tungsten used.

[0027] In a preferred embodiment, the phase transfer catalyst is a tertiary amine or a tertiary ammonium salt or a quaternary ammonium salt that in total comprises at least 12 carbon atoms, preferably 12 - 60 carbon atoms. Preferred are tetraalkylammonium salts. For example, suitable tertiary amines are dodecyldimethylamine, hexadecyldimethylamine, octadecyldimethylamine, tributylamine and trioctylamine. Suitable tertiary ammonium salts are the protonated products of these tertiary amines. For example, suitable quaternary ammonium salts are dodecyltrimethylammonium salt, hexadecyltrimethylammonium salt, octadecyltrimethylammonium salt, methyltributylammonium salt and methyltrioctylammonium salt. More preferably, the phase transfer catalyst comprises a structure with R 1 R 2 R 3 NR4+ tertiary ammonium ions or quaternary ammonium ions, where R 1 , R 2 and R 3 are the same or different and are each independently selected from alkyl groups having 8 to 10 carbon atoms, and R 4 is hydrogen or methyl. Most preferably, the phase transfer catalyst comprises methyl tris(octyl / decyl)ammonium methyl sulfate (CAS No. 2387913-24-6).

[0028] In another preferred embodiment, the phase transfer catalyst comprises at least one salt having a tertiary ammonium ion or quaternary ammonium ion of the structure R 1 R 2 R 3 R 4 N + where R 1 is a Y-O(C=O)R 5 group, where Y is CH2CH2, CH(CH3)CH2 or CH2CH(CH3), and R 5 is an alkyl or alkenyl group having 11 to 21 carbon atoms, R 2 is hydrogen or an alkyl group having 1 to 4 carbon atoms, and R 3 and R 4 are each independently R 1 , an alkyl group having 1 to 4 carbon atoms or Y-OH. Preferred is a quaternary ammonium salt with a methyl sulfate counterion, where R 2 is methyl, and R 5 is a straight-chain alkyl or alkenyl group. Particularly preferred are the following salts: (CH3)3N + CH2CH2O(C=O)R 5 CH3OSO3 - , (CH3)2N + (CH2CH2OH)(CH2CH2O(C=O)R 5 )CH3OSO3 - , (CH3)2N + (CH2CH2O(C=O)R 5 )2CH3OSO3 - , CH3N + (CH2CH2OH)2(CH2CH2O(C=O)R 5 )CH3OSO3 - , CH3N + (CH2CH2OH)(CH2CH2O(C=O)R 5 )2CH3OSO3 - , CH3N + (CH2CH2O(C=O)R5 )3CH3OSO3 - 、(CH3)3N + CH2CH(CH3)O(C=O)R 5 CH3OSO3 - 、(CH3)2N + (CH2CH(CH3)OH)(CH2CH(CH3)O(C=O)R 5 )CH3OSO3 - and (CH3)2N + (CH2CH(CH3)O(C=O)R 5 )2CH3OSO3 - , where R 5 In each case it is a straight-chain alkyl or alkenyl radical having 11 to 21 carbon atoms. Most preferred is the salt (CH3)2N + (CH2CH(CH3)O(C=O)R 5 )2CH3OSO3 - , where R 5 It is an alkyl or alkenyl group with 11-17 carbon atoms. The phase transfer catalyst of this embodiment can be prepared by esterifying ethanolamine, isopropanolamine, diethanolamine, diisopropanolamine, triethanolamine or triisopropanolamine with fatty acids, and then quaternizing with dimethyl sulfate. These phase transfer catalysts have the following advantages: they are biodegradable (different from tetraalkylammonium salts) and can be introduced into biological treatment equipment without further pretreatment. Compared to tetraalkylammonium halides, the corrosivity of salts with methylsulfate as anions is also less.

[0029] The reaction of step a) is carried out in a liquid reaction mixture comprising two liquid phases, an aqueous phase having a maximum apparent pH of 6 and an organic phase comprising a solvent (S) having a solubility in water of less than 500 mg / kg at 20°C. The term "apparent pH" herein refers to a value determined by measuring with a glass electrode using a commercial pH meter calibrated with a buffered aqueous solution of known pH for measuring dilute aqueous solutions. The apparent pH differs from the notional pH (i.e., the negative logarithm of the activity of hydrogen ions) by a constant value because the standard potential of the glass electrode in the aqueous phase of the reaction mixture (comprising hydrogen peroxide and diol) is different from the standard potential in pure water. The apparent pH of the aqueous phase is preferably maintained in the range of 1.0 to 3.5, particularly preferably in the range of 2.0 to 3.0. The apparent pH can be maintained in this range by adding an acid, preferably sulfuric acid or phosphoric acid, or by adding a base, preferably an aqueous sodium hydroxide solution. Adjusting the apparent pH in this preferred range provides a high selectivity for 1,2-propylene glycol and prevents enrichment of propylene oxide in the aqueous phase, which simplifies the subsequent separation of propylene glycol from the aqueous phase.

[0030] In reaction step a), preferably, the weight ratio of hydrogen peroxide to water fed to step a) is adjusted while maintaining a molar excess of propylene fed to step a) relative to hydrogen peroxide. The weight ratio of hydrogen peroxide to water preferably varies in the range of 0.05 to 1.5, more preferably 0.10 to 0.7, and most preferably 0.15 to 0.45. The molar ratio of propylene to hydrogen peroxide fed to step a) is preferably from 1.1:1 to 10:1, more preferably 1.2:1 to 4:1.

[0031] The reaction is preferably carried out at a temperature in the range of 50 to 110 °C, more preferably 60 to 100 °C, and particularly preferably 70 to 90 °C. The reaction pressure is preferably higher than the vapor pressure of propylene at the reaction temperature to ensure that most of the propylene is present in the liquid organic phase of the liquid mixture.

[0032] The reaction of step a) is carried out in a liquid reaction mixture having an organic phase, and the organic phase contains a solvent (S) having a solubility in water at 20 °C of less than 500 mg / kg, preferably less than 250 mg / kg in water at 20 °C. The solvent preferably has a boiling point above 100 °C, preferably above 120 °C. Suitable as the solvent are alcohols, ethers, esters, ketones, and alkylated aromatic hydrocarbons having one or more hydroxyl groups. The solvent improves the extraction of the salt formed from the heteropolytungstate and the phase transfer catalyst into the organic phase present in step a). Preferably, the amount of the solvent (S) is selected to provide a proportion of the solvent (S) in the organic phase during the reaction in the range of 10-90% by weight.

[0033] The solvent preferably contains at least one alkylated aromatic hydrocarbon having 7-12 carbon atoms. For example, suitable alkylated aromatic hydrocarbons are toluene, 1,2-xylene (o-xylene), 1,3-xylene (m-xylene), 1,4-xylene (p-xylene), ethylbenzene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene (mesitylene), 1-ethyl-2-toluene, 1-ethyl-3-toluene, and 1-ethyl-4-toluene, and n-propylbenzene. Preferably, a hydrocarbon mixture containing more than 50% by weight, particularly preferably more than 80% by weight, of an alkylated aromatic hydrocarbon having 7-12 carbon atoms is used as the solvent. The use of these solvents enables most of the peroxotungstate to be extracted into the organic phase of the reaction mixture and recycled to step a) together with the organic phase of the reaction mixture. Then, preferably, the phase transfer catalyst, the molar ratio of the phase transfer catalyst to the heteropolytungstate, the molar ratio of the heteroatom of the heteropolytungstate to tungsten, the molar ratio of propylene to hydrogen peroxide, and the amount of the solvent are selected to transfer as much tungsten as possible present in the liquid reaction mixture into the organic phase.

[0034] The phase transfer catalyst, the heteropolytungstate, and the solvent (S) can be added in step a) of the process according to the invention either individually or in the form of a mixture containing two or all three of these components. Preferably, the phase transfer catalyst and the heteropolytungstate are added and dissolved in the organic phase containing the solvent (S).

[0035] The reaction of step a) can be carried out batchwise or continuously, with the continuous reaction being preferred. The concentration of hydrogen peroxide in the aqueous phase is preferably maintained in the range of 0.1 - 5% by weight, particularly preferably 0.5 - 3% by weight. The concentration of hydrogen peroxide can be adjusted within this range by appropriately selecting the reaction temperature, the molar ratio of propylene to hydrogen peroxide, and the residence time of the liquid mixture in the reactor in which the reaction takes place. The residence time of the reaction mixture is preferably adjusted such that the conversion of hydrogen peroxide is maintained in the range of 80 - 99%.

[0036] During the reaction, the liquid mixture is preferably mixed to create a large phase interface between the aqueous phase and the organic phase. For this purpose, the reaction is preferably carried out continuously in a loop reactor that has fixed internal components in the tubular section, and the liquid mixture passes through the loop reactor at a flow rate that creates turbulence at the internal components. For this purpose, baffles, static mixing elements, structured packings, or random packings can be used as internal components. In combination with or as an alternative to these internal components, heat exchangers (such as plate heat exchangers or shell-and-tube heat exchangers) can be used, where turbulence is generated, for example, between the plates of a plate heat exchanger or in the tubes of a shell-and-tube heat exchanger.

[0037] Preferably, all or part of the reaction heat generated in step a) is removed while the reaction is in progress, preferably by cooling the reaction mixture in a heat exchanger. More preferably, the reaction is carried out continuously in a loop reactor that contains a heat exchanger within the reactor loop to cool the reaction mixture.

[0038] In step b) of the process according to the invention, the liquid reaction mixture provided by step a) is separated into an aqueous phase (P a ) containing 1,2 - propanediol and an organic phase (P o ). The separation of the biphasic reaction mixture provided by step a) is preferably carried out in a settler vessel. The biphasic reaction mixture is preferably passed through a coalescer element to achieve a more complete separation, the coalescer element containing structured packings or random packings whose surfaces are wetted by the dispersed phase of the biphasic mixture.

[0039] The aqueous phase (P a) usually contains water, unreacted hydrogen peroxide, and the reaction product 1,2 - propanediol. The aqueous phase usually also contains dipropylene glycol and tripropylene glycol, as well as reaction by - products (such as 1 - hydroperoxy - 2 - propanol and 2 - hydroperoxy - 1 - propanol formed by the reaction of propylene oxide with hydrogen peroxide, and formic acid, acetic acid, and hydroxyacetone formed by the further oxidation of 1,2 - propanediol). The aqueous phase may also usually contain phosphoric acid and sodium salts of phosphoric acid (if polyoxotungstate formed in - situ by combining phosphoric acid with sodium tungstate is used in step a)). The organic phase (P o ) contains the solvent (S), unreacted propylene, and propylene oxide that forms as an intermediate during the reaction of propylene with hydrogen peroxide and has not yet been hydrolyzed to 1,2 - propanediol. The organic phase (P o ) usually also contains one or more salts formed from the cations of heteropolyoxotungstate and the phase - transfer catalyst. If the propylene raw material contains propane, the organic phase P o will also contain propane.

[0040] In step c) of the process of the present invention, at least a part of the separated organic phase (P o ) is recycled to reaction step a). Thus, the propylene oxide present in the organic phase (P o ) is recycled to step a) to achieve complete conversion of propylene to 1,2 - propanediol, dipropylene glycol, and tripropylene glycol. Preferably, the heteropolyoxotungstate present in the organic phase (P o ) is recycled to step a), and particularly preferably, substantially all of the catalyst mixture present in the organic phase is recycled to step a).

[0041] In a preferred embodiment, step c) includes the step of contacting part or all of the separated organic phase (P o ) with an aqueous reactivation solution containing hydrogen peroxide and phosphoric acid at a temperature of 5 - 40 °C. In this catalyst reactivation step, phosphoric acid is preferably used at a molar ratio of phosphorus to tungsten in the organic phase (P o ) in the range of 1:2 to 10:1, preferably 4:1 to 8:1. The aqueous phase of the liquid mixture formed in the catalyst reactivation step preferably contains 10 - 40 wt%, more preferably 15 - 38 wt%, most preferably 18 - 35 wt% of phosphoric acid. The amount of hydrogen peroxide used is preferably at least 2 mol of hydrogen peroxide per mol of tungsten, preferably 2 - 10 mol of hydrogen peroxide per mol of tungsten. It is believed that the preferred molar ratios of phosphorus to tungsten and hydrogen peroxide to tungsten and the preferred concentration of phosphoric acid in the aqueous phase convert most of the tungstate to the formulas PO4[WO(O2)2]4 3- and HPO4[WO(O2)2]2 2-Peroxotungstophosphate and its partially protonated forms, which are presumably the most catalytically active species for the oxidation of propylene. The temperature of 5 - 40 °C used in the catalyst reactivation step prevents these species from decomposing and forming molecular oxygen before being transferred to reaction step a). Preferably, the catalyst reactivation step is carried out at a temperature of 10 - 35 °C, more preferably 15 - 30 °C. The reaction time in the catalyst reactivation step is generally 1 - 200 minutes, preferably 1 - 20 minutes, more preferably 2 - 10 minutes, where if the organic phase (P o ) contains propylene, a reaction time of less than 20 minutes is preferred at the upper limit of the temperature range of 5 - 40 °C. Then, only a small portion of the propylene present in the liquid mixture of the oxidation catalyst reactivation step is oxidized. The catalyst reactivation step can be carried out without cooling, and substantially all of the peroxotungstophosphate produced in the catalyst reactivation step can be transferred to step a). Preferably, the organic phase produced by the catalyst reactivation step is transferred to reaction step a) without any intermediate steps.

[0042] The organic phase (P o ) separated from the liquid reaction mixture provided from step a) can be recycled to step a) without further treatment. If the propylene fed to step a) contains propane, it is preferred to separate a stream of unreacted propylene from the organic phase in step c) before recycling the organic phase to step a), where the separated stream of unreacted propylene contains as much propane as the impure propylene fed to step a). Thus, for a continuous reaction, the accumulation of propane in the organic phase of the reaction mixture in step a) can be avoided. The separated stream of unreacted propylene can be transferred to a C3 splitter to separate propylene and propane, and the recovered propylene can be recycled to step a).

[0043] In step d) of the process of the present invention, the separated aqueous phase (P a ) is extracted with an extractant solution comprising the same phase transfer catalyst and the same solvent (S) as used in step a). This extraction provides an extracted aqueous phase (P ae ) and an extract phase (P e ), where the extract phase (P e ) contains a salt of the phase transfer catalyst and a heteropolytungstate or tungstate. The extraction can be carried out in an extraction unit (comprising a mixer and a settler in series), or in a series of 2 - 5 consecutive extraction units (each comprising a mixer and a settler in series). Alternatively, the extraction can be carried out in an extraction column. The extraction is preferably carried out with the aqueous phase (P a) and the countercurrent flow mode of the extractant solution, preferably carried out in a countercurrent extraction column or in a series of extraction units (each comprising a mixer and a settler) in a countercurrent flow mode along the series of extraction units. Preferably, the amount of the phase transfer catalyst contained in the extractant solution provides a molar ratio of the phase transfer catalyst contained in the extractant solution to tungsten contained in the aqueous phase (P a ) within the range of 1:1 to 100:1. The amounts of the extractant solution and the phase transfer catalyst, and the number of extraction stages or theoretical stages in the extraction column (if multi-stage extraction is used) are selected to extract 25-90% of the tungsten contained in the aqueous phase (P a ) into the extract phase (P e ). By increasing the volume ratio between the extractant solution and the aqueous phase (P a ), increasing the concentration of the phase transfer catalyst in the extractant solution, increasing the number of extraction stages in the countercurrent extraction or any combination thereof, the percentage of tungsten extracted into the extract phase (P e ) can be increased. The extracted aqueous phase (P ae ) can be passed through a coalescer to coalesce the droplets of the extractant solution dispersed in the extracted aqueous phase (P ae ). Preferably, the organic phase formed by coalescing these droplets is combined with the extract phase (P e ).

[0044] In step e) of the method of the present invention, at least a part of the extract phase (P e ) obtained in step d) is recycled to step a). Preferably, before recycling the extract phase (P e ) to step a), it is combined with all or part of the organic phase (P o ) separated in step b). When the method of the present invention includes the catalyst reactivation step as described above, preferably the extract phase (P e ) is combined with the organic phase (P o ) before the catalyst reactivation step.

[0045] In step f) of the method of the present invention, from the extracted aqueous phase provided in step d) (P ae) Recover 1,2 - propanediol and dipropylene glycol. The 1,2 - propanediol and dipropylene glycol are preferably recovered by a series of distillation steps. Preferably, a series of distillation steps as described in Ullmann’s Encyclopedia of Industrial Chemistry, online version, entry “Propylene Glycols”, page 4, DOI 10.1002 / 14356007.a22_163.pub2 are used, in which the overhead product containing water is separated from the bottom product containing 1,2 - propanediol and dipropylene glycol in a series of 2 - 4 thermally integrated distillation steps, followed by successive vacuum distillation steps which provide 1,2 - propanediol and dipropylene glycol as the overhead product and a bottom product containing high - boiling organic compounds and salts. From this bottom product, tripropylene glycol can be recovered as the overhead product in an additional vacuum distillation step. The extraction step d) allows the content of tungsten in the extracted aqueous phase (P ae ) to be reduced to a level at which it is no longer necessary to recover tungsten in step f) or from the by - product stream of step f) for a resource - efficient and economic operation of the method.

[0046] In a preferred embodiment, step f) includes an additional step of subjecting the extracted aqueous phase (P ae ) to a hydrogenation treatment before recovering 1,2 - propanediol. The hydrogenation is preferably carried out using a supported hydrogenation catalyst comprising one or more metals selected from Ru, Rh, Pd, Pt, Ag, Ir, Fe, Cu, Ni, and Co on a support, where activated carbon, SiO2, TiO2, ZrO2, Al2O3, and aluminosilicate are preferably used as support materials. A hydrogenation catalyst comprising ruthenium as the active metal is preferred. The catalytic hydrogenation is preferably carried out at a hydrogen partial pressure of 5 - 50 bar, preferably 5 - 35 bar, more preferably 7 - 30 bar, even more preferably 8 - 25 bar and a temperature of 80 °C to 140 °C, preferably 90 °C to 120 °C. The hydrogenation catalyst can be used in the form of a suspension or a fixed bed, and trickle - bed hydrogenation using a fixed - bed catalyst is preferred. The hydrogenation can prevent problems caused by the decomposition of unreacted hydrogen peroxide in step a) during the distillation steps for recovering 1,2 - propanediol and dipropylene glycol. The hydrogenation also converts the by - products 1 - hydroperoxy - 2 - propanol, 2 - hydroperoxy - 1 - propanol, and hydroxyacetone formed in step a) into 1,2 - propanediol, and thus increases the yield of 1,2 - propanediol.

[0047] Steps a) to e) of the method of the present invention are preferably carried out continuously. Steps d) and e) for extracting and recycling tungsten allow the method to be operated continuously in a way that reduces tungsten consumption (i.e., the reduced need to feed tungsten compounds to step a) to maintain the catalytic activity of the catalyst mixture).

[0048] In a preferred embodiment of the process of the present invention, the recycling step c) comprises subjecting at least a portion of the separated organic phase (P o ) to nanofiltration, which provides a retentate rich in heteropolytungstate and a permeate poor in heteropolytungstate. The retentate provided by the nanofiltration is recycled to the reaction step a), and the permeate provided by the nanofiltration is passed to step d) to provide at least a portion of the extractant solution. Corresponding to the nomenclature recommendations of IUPAC, the term nanofiltration herein refers to pressure-driven solution separation, where a portion of the solvent permeates through the membrane to produce a permeate, and the membrane retains particles and dissolved molecules with a diameter less than 2 nm in the non-permeated portion of the solution and forms a retentate. The following nanofiltration membranes are used for this nanofiltration: the nanofiltration membrane retains salts of peroxotungstate or heteroperoxotungstate with the cations of the phase transfer catalyst in the retentate and allows the solvent (S) to pass through the membrane and into the permeate. The nanofiltration is preferably operated such that the concentration of the salts of peroxotungstate or heteropolytungstate with the cations of the phase transfer catalyst in the retentate does not increase above the saturation concentration. Preferably, before passing the portion of the organic phase (P o ) to be subjected to nanofiltration to the nanofiltration, it is combined with the extraction phase (P e ). This can be used to reduce the concentration of peroxotungstate or heteropolytungstate in the feed to the nanofiltration, which allows for the production of more permeate without exceeding the saturation limit on the retentate side.

[0049] Membranes based on the polymers polyimide, polyethersulfone, polyamide, and polydimethylsiloxane can be used for the nanofiltration. Suitable nanofiltration membranes can be commercially obtained, for example, under the name S600 from Evonik Membrane Extraction Technology MET, under the name ONF-2 from GMT Membrantechnik, under the names 010306, 030306, 030705, and 030306F from SolSep, and under the name NanoPro TM SX from AMS Technologies. Preferably, composite membranes known from DE 195 07 584, EP 1 741 481, and WO 2011 / 067054 are used for the nanofiltration.

[0050] The nanofiltration is preferably carried out in a cross-flow filtration mode, preferably at a temperature in the range of 20 - 90 °C, particularly preferably 40 - 80 °C. The transmembrane pressure is preferably 2 - 5 MPa. The pressure on the retentate side can be as high as 10 MPa. The pressure on the permeate side is preferably adjusted to be high enough to prevent entry on the permeate side of the nanofiltration membrane and dissolution in the organic phase (P o) desorption of propylene or oxygen. When step c) includes a nanofiltration step, it may also include a step of desorbing propylene and oxygen from the portion of the organic phase (P o ) that is subjected to nanofiltration. Such desorption prior to nanofiltration allows the nanofiltration to be operated at a lower permeate side pressure. In an alternative, propylene and oxygen can also be desorbed from the permeate prior to delivering the permeate to the extraction step to prevent desorption of gaseous propylene and oxygen in the extraction step. In another alternative, the extraction of step d) can be carried out at a pressure that prevents desorption of propylene and oxygen dissolved in the permeate delivered to the extraction step. Preferably, prior to delivering the nanofiltration permeate to extraction step d), a phase transfer catalyst is added to the nanofiltration permeate, preferably in an amount to provide the molar ratio of the phase transfer catalyst contained in the extractant solution as further specified above to tungsten contained in the aqueous phase (P a ). Preferably, the nanofiltration permeate added with the phase transfer catalyst is used as the extractant solution in extraction step d).

[0051] The process of the present invention can be carried out in the facility of the present invention.

[0052] The facility of the present invention includes a cooled loop reactor (1), and the loop reactor (1) includes an inlet (2) for hydrogen peroxide, an inlet (3) for propylene, an outlet (4) for the reaction mixture, and at least one recycle stream inlet (5). The loop reactor may include any type of heat exchanger (27) for achieving cooling, and preferably includes a plate heat exchanger or a tube bundle heat exchanger, which is preferably configured to pass the reaction mixture through the tubes. The loop reactor generally also includes a circulation pump (26) and a circulation conduit (28), as well as inlets for hydrogen peroxide, propylene feedstock, and heteropolytungstate. When polyphosphotungstate is used as the heteropolytungstate, the loop reactor may include an inlet (21) for phosphoric acid and an inlet (29) for tungstate (such as sodium tungstate). The outlet (4) for the reaction mixture is preferably located at the highest point of the loop, which allows the loop reactor (1) filled with the liquid reaction mixture to be operated (i.e., there is no continuous gas phase inside the loop reactor (1)).

[0053] The installation of the present invention further comprises a phase separator (6), which includes an inlet, a first outlet for the separated aqueous phase, and a second outlet for the separated organic phase. The inlet of the phase separator (6) is connected to the outlet (4) of the circulation reactor (1) via a conduit (7) to receive the reaction mixture. The outlet for the separated organic phase is preferably located at the highest point of the phase separator (6), which allows the operation of the phase separator (6) filled with a liquid reaction mixture (i.e., there is no continuous gas phase inside the phase separator (6)). The phase separator (6) preferably comprises a settler vessel. A coalescer element (not shown in the figures) comprising structured or random packing whose surface is wetted by the dispersed phase of the two-phase mixture can be arranged in the phase separator (6) or upstream of the phase separator (6). The phase separator (6) may further comprise an inlet for an aqueous sulfate solution (not shown in the figures), which is preferably located on the upstream conduit (7) and, if a coalescer is present, preferably upstream of the coalescer.

[0054] The installation of the present invention further comprises a membrane nanofiltration unit (8), which has an inlet, a first outlet for the retentate, and a second outlet for the permeate. The inlet is connected to the second outlet of the phase separator (6) via a conduit (9) to receive all or part of the separated organic phase. The first outlet is connected to the recycle stream inlet of the circulation reactor via a conduit (10). The membrane nanofiltration unit is preferably configured to perform cross-flow filtration on the retentate side of the membrane. The membrane nanofiltration unit may include several nanofiltration modules arranged in parallel, preferably spiral-wound nanofiltration modules.

[0055] The installation of the present invention includes an extraction unit (11), which has a feed inlet, an extractant inlet, an extract outlet, and a raffinate outlet. The feed inlet is connected to the first outlet of the phase separator (6) via a conduit (12) to receive the separated aqueous phase. The extractant inlet is connected to the second outlet of the membrane nanofiltration unit (8) via a conduit (13) to receive the permeate. The extraction unit (11) may include a combination of a mixer and a downstream settler, where the feed inlet and the extractant inlet are on the mixer, and the extract outlet and the raffinate outlet are on the settler. In a preferred alternative, the extraction unit (11) includes a countercurrent extraction column. In order to use a solvent (S) with a density lower than that of water, the extraction column preferably has a feed inlet near the top of the extraction column, an extractant inlet below the feed inlet and near the bottom of the extraction column, an extract outlet at the top of the extraction column, and a raffinate outlet at the bottom of the extraction column. Preferably, there is also an inlet for a phase transfer catalyst on the conduit (13), and the conduit (13) connects the second outlet of the membrane nanofiltration unit (8) to the extractant inlet of the extraction unit (11).

[0056] The facility of the present invention further includes a first recirculation conduit (14) that connects the extract outlet of the extraction unit (11) to the inlet of the membrane nanofiltration unit (8) or to the recirculation flow inlet of the circulation reactor (1) or to both of these inlets. The first recirculation conduit (14) is preferably connected to the inlet of the membrane nanofiltration unit (8). The facility preferably includes a second recirculation conduit (15) that connects the second outlet of the phase separator (6) to the inlet of the circulation reactor (1) for receiving, as a recirculation flow, the portion of the separated organic phase that is not transferred to the membrane nanofiltration unit (8). The facility will generally also include a controller and control valves (not shown in the figure) to regulate and control the portion of the separated organic phase that is transferred to the membrane nanofiltration unit (8).

[0057] The facility of the present invention further includes a separation unit (16) having an inlet connected to the raffinate outlet of the extraction unit (11), an outlet for the separated water, an outlet for the separated 1,2 - propanediol, and an outlet for by - products. The separation unit (16) preferably includes a series of at least two distillation columns having a first distillation column (17) and a second distillation column (18). The first distillation column (17) has a bottom product outlet and an inlet that provides the inlet of the separation unit (16). The second distillation column (18) has an inlet connected to the bottom product outlet of the first distillation column (17), a top product outlet for the separated 1,2 - propanediol, and a bottom product outlet for by - products.

[0058] The facility of the present invention preferably includes an additional hydrogenation unit (19) arranged between the raffinate outlet of the extraction unit (11) and the inlet of the separation unit (16). The hydrogenation unit (19) preferably includes a fixed - bed reactor (which is preferably configured for trickle - bed operation) to hydrogenate the separated aqueous phase with hydrogen in the presence of a heterogeneous hydrogenation catalyst.

[0059] In a preferred embodiment, the installation of the present invention further comprises a catalyst reactivation unit (20), the catalyst reactivation unit (20) comprising an inlet (21) for phosphoric acid and an inlet (22) for hydrogen peroxide, an inlet (23) connected to the second outlet of the phase separator (6) for receiving a portion of the separated organic phase, a mixing device (24) downstream of the inlet, and an outlet downstream of the mixing device (24). The outlet of the catalyst reactivation unit (20) is connected via a conduit (25) to an inlet of the loop reactor (1) for receiving the organic phase formed in the catalyst reactivation unit (20) as a recycle stream. The mixing device may be a stirred vessel or may be the loop reactor further described above. The outlet of the catalyst reactivation unit (20) may be configured to receive the entire biphasic mixture formed in the catalyst reactivation unit (20) or may comprise a settler for receiving only the organic phase of the mixture formed in the catalyst reactivation unit (20). When such a settler is present, it will typically also have an outlet for the aqueous phase, the outlet for the aqueous phase being connected to an inlet of the catalyst reactivation unit (20) for recycling a portion of the aqueous phase to the catalyst reactivation and to an inlet of the cooled loop reactor (1) for transferring a portion of the aqueous phase to the propylene epoxidation reaction.

[0060] The present invention will now be explained in more detail with reference to the examples.

[0061] Examples

[0062] Examples

[0063] Preparation of the initial epoxidation catalyst solution

[0064] 324 g of an aqueous solution containing 7.2 wt% sodium tungstate dihydrate, 23.1 wt% phosphoric acid and 7.1 wt% hydrogen peroxide was stirred at room temperature for 12 hours. Then, 122 g of a solution of methyltris(octyl / decyl)methylammonium sulfate (CAS No. 2387913-24-6) in 990 g of Hydrosol A 200ND (a mixture of C10 alkylbenzenes) was added and the mixture was stirred at room temperature for a further 2 hours. Then, the aqueous and organic phases were separated to provide 1148 g of an organic phase as the initial epoxidation catalyst solution.

[0065] Reaction of propylene with hydrogen peroxide

[0066] The reaction of propylene with hydrogen peroxide was carried out in a loop reactor at a temperature of 80 °C and a pressure of 3.3 MPa, the loop reactor having a loop volume of 0.5 l, a circulation pump and a heat exchanger for regulating the reaction temperature, the loop reactor operating at 70 kg h -1Cycling rate operation. The reactor is equipped with a catalyst feed reservoir and a feed pump for feeding liquid propylene, liquid propane, aqueous hydrogen peroxide solution, and liquid feed from the catalyst feed reservoir. The initial epoxidation catalyst solution is charged to the catalyst feed reservoir. The loop initially contains the reaction mixture from a previous experiment. The circulation is started and maintained at 70 kg h -1 , and the circulating mixture is heated to 80 °C. Then, 80 g h -1 propylene, 50 g h -1 propane, 210 g h -1 of a 15 wt% aqueous hydrogen peroxide solution containing 0.4 wt% phosphoric acid, and 320 g h -1 of the organic catalyst solution from the catalyst feed reservoir are introduced into the circulating reactor, and the circulating mixture is cooled to maintain the reaction temperature at 80 °C. The biphasic oxidation reaction mixture is withdrawn from the circulating reactor in an amount corresponding to the addition. The phases are separated, and the depressurized and cooled aqueous phase is allowed to stand for additional phase separation, and the organic phases from the first and second phase separations are combined. The combined organic phase is transferred to the catalyst feed reservoir after depressurization and cooling to 25 °C. After about 9 hours of operation, the feed of reactants and the circulation in the circulating reactor are stopped. The next day, the circulation in the circulating reactor is restarted, the dosing of reactants is resumed after the reaction temperature has been established in the circulating reactor, and the reaction is continued for another 11 hours.

[0067] The aqueous phase for the last 10 hours of the operating reaction is collected, and hydrogen peroxide is analyzed by redox titration, and the organic products are analyzed by capillary GC (25 m CP-WAX-52CB column from Agilent, He carrier gas, temperature program starting from 50 °C with a slope of 20 K / min to 90 °C, with a slope of 10 K / min to 220 °C and with a slope of 5 K / min to 235 °C, FID detector). The analysis shows a 96% conversion of hydrogen peroxide, where the stream of the aqueous phase provided by the reaction contains 630 mmol / h 1,2-propanediol, 95 mmol / h dipropylene glycol, 11 mmol / h tripropylene glycol, and 12 mmol / h hydroxyacetone.

[0068] Extraction of the separated aqueous phase

[0069] 800 g of the collected aqueous phase is extracted by mixing for 2 hours and allowing the mixture to stand until the phases have separated, using a solution of 160 g of 1.2 wt% methyltri(octyl / decyl)methylammonium sulfate in Hydrosol A 200ND. Before and after extraction, the tungsten content of the aqueous phase is analyzed by ICP-OES, which shows a tungsten content of 63 mg / kg before extraction and 46 mg / kg after extraction.

[0070] The aqueous phase collected, 800 g, was extracted with a solution of 160 g of 8.2 wt% methyltri(octyl / decyl)methylammonium sulfate in Hydrosol A200ND, and the extraction was repeated. Analysis showed that the tungsten content after extraction was 16 mg / kg.

[0071] List of reference numerals:

[0072] 1 Cooled loop reactor

[0073] 2 Inlet for hydrogen peroxide

[0074] 3 Inlet for propylene

[0075] 4 Outlet for reaction mixture

[0076] 5 Recirculation flow inlet

[0077] 6 Phase separator

[0078] 7 Pipe connecting the loop reactor (1) to the phase separator (6)

[0079] 8 Membrane nanofiltration unit

[0080] 9 Pipe connecting the phase separator (6) to the membrane nanofiltration unit (8)

[0081] 10 Pipe connecting the membrane nanofiltration unit (8) to the loop reactor (1)

[0082] 11 Extraction unit

[0083] 12 Pipe connecting the phase separator (6) to the extraction unit (11)

[0084] 13 Pipe connecting the membrane nanofiltration unit (8) to the extraction unit (11)

[0085] 14 Pipe connecting the extraction unit (11) to the membrane nanofiltration unit (8)

[0086] 15 Pipe connecting the phase separator (6) to the loop reactor (1)

[0087] 16 Separation unit

[0088] 17 First distillation column

[0089] 18 Second distillation column

[0090] 19 Hydrogenation unit

[0091] 20 Catalyst reactivation unit

[0092] 21 Inlet for phosphoric acid

[0093] 22 Inlet for hydrogen peroxide

[0094] 23 Inlet of the catalyst reactivation unit (20) connected to the phase separator (6)

[0095] 24 Mixing device

[0096] 25 Conduit connecting the catalyst reactivation unit (20) to the loop reactor (1)

[0097] 26 Circulation pump

[0098] 27 Heat exchanger

[0099] 28 Circulation conduit

[0100] 29 Inlet for tungstate

Claims

1. A process for preparing 1,2 - propanediol, the process comprising: a) reacting propylene with hydrogen peroxide in a liquid reaction mixture in the presence of a catalyst mixture, the catalyst mixture comprising a phase - transfer catalyst and a heteropolytungstate, the liquid reaction mixture comprising an aqueous phase and an organic phase with a maximum apparent pH of 6, the organic phase comprising a solvent S having a solubility in water of less than 500 mg / kg at 20 °C, where the term apparent pH herein refers to the value determined by measurement with a glass electrode using a commercial pH meter calibrated with a buffer aqueous solution of known pH for measuring dilute aqueous solutions; b) Separate the liquid reaction mixture from step a) into an aqueous phase P a and an organic phase P o ; wherein the aqueous phase P a contains 1,2 - propanediol; c) Recycle at least a portion of the separated organic phase P o to reaction step a); d) Extract the separated aqueous phase P with an extractant solution a to provide an extracted aqueous phase P ae and an extraction phase P e , wherein the extractant solution contains the same phase transfer catalyst and the same solvent S as used in step a), and the extraction phase P e contains a salt of the phase transfer catalyst and a heteropolytungstate or tungstate; e) Recycling at least a portion of the extraction phase P e to step a); and f) Recover 1,2 - propanediol from the extracted aqueous phase P ae ​ 2. The method according to claim 1, wherein step c) comprises the steps of: subjecting at least a portion of the separated organic phase P o to nanofiltration to provide a retentate rich in heteropolytungstate and a permeate poor in heteropolytungstate, recycling the retentate to reaction step a), and passing the permeate to step d) to provide at least a portion of the extractant solution.

3. The method according to claim 2, wherein, Before the nanofiltration, the separated organic phase P to be subjected to nanofiltration o is combined with the extraction phase P e to be combined.

4. The method according to claim 2 or 3, wherein Before transferring the permeate to step d), adding a phase - transfer catalyst to the permeate.

5. The process according to any one of claims 1 - 3, wherein the extraction in step d) is carried out in a counter - current extraction column.

6. The process according to any one of claims 1 - 3, wherein the extraction in step d) is carried out in an extraction unit or a series of 2 - 5 consecutive extraction units, each extraction unit comprising a mixer and a settler in series.

7. The process according to claim 1, wherein steps a) to e) are carried out continuously.

8. The method according to claim 7, wherein In step a), the concentration of hydrogen peroxide in the aqueous phase is 0.1 - 5 wt%.

9. The process according to claim 7 or 8, wherein step a) is carried out in a loop reactor, the loop reactor comprising fixed internal members in a tubular section, and the liquid reaction mixture passes through the reactor at a flow rate sufficient to provide turbulence at the internal members.

10. The process according to any one of claims 1 - 3, wherein the solvent S comprises an alkylated aromatic hydrocarbon having 7 - 12 carbon atoms.

11. The process according to any one of claims 1 - 3, wherein the phase - transfer catalyst is selected from tertiary amines and tertiary ammonium salts or quaternary ammonium salts and in total comprises at least 12 carbon atoms.

12. The method according to claim 11, wherein the phase transfer catalyst comprises a tertiary ammonium ion or a quaternary ammonium ion having the structure R 1 R 2 R 3 NR 4+ , wherein R 1 , R 2 and R 3 are the same or different and are each independently selected from alkyl groups having 8 to 10 carbon atoms, and R 4 is hydrogen or methyl.

13. The method according to claim 1, wherein step c) comprises contacting at least a portion of the separated organic phase P o with an aqueous reactivation solution comprising hydrogen peroxide and phosphoric acid at a temperature of 5 - 40 °C.

14. The process according to claim 13, wherein the organic phase produced by contact with the aqueous reactivation solution is transferred to reaction step a) without any intermediate steps.

15. The method according to claim 13 or 14, wherein Before the step of contacting with the aqueous reactivation solution, the separated organic phase P o is combined with the extraction phase P e to form a combined phase.

16. A facility for preparing 1,2 - propanediol, the facility comprising: a) a cooled loop reactor (1), the loop reactor (1) comprising an inlet (2) for hydrogen peroxide, an inlet (3) for propylene, an outlet (4) for the reaction mixture, and at least one recycle - flow inlet (5); b) a phase separator (6), the phase separator (6) comprising an inlet, a first outlet for the separated aqueous phase, and a second outlet for the separated organic phase, the inlet being connected by a conduit (7) to the outlet of the loop reactor (1) to receive the reaction mixture; c) a membrane nanofiltration unit (8), the membrane nanofiltration unit (8) having an inlet, a first outlet for the retentate, and a second outlet for the permeate, the inlet being connected by a conduit (9) to the second outlet of the phase separator (6) to receive all or part of the separated organic phase, and the first outlet being connected by a conduit (10) to the recycle - flow inlet of the loop reactor; d) An extraction unit (11) having a feed inlet, an extractant inlet, an extract outlet, and a raffinate outlet, wherein the feed inlet is connected via a conduit (12) to the first outlet of the phase separator (6) to receive the separated aqueous phase, and the extractant inlet is connected via a conduit (13) to the second outlet of the membrane nanofiltration unit (8) to receive the permeate; e) A first recirculation conduit (14) that connects the extract outlet of the extraction unit (11) to the inlet of the membrane nanofiltration unit (8) and / or the recirculation flow inlet of the circulation reactor (1); f) Optionally present, a second recirculation conduit (15) that connects the second outlet of the phase separator (6) to the inlet of the circulation reactor (1) for receiving as a recirculation flow a portion of the separated organic phase that is not transferred to the membrane nanofiltration unit (8); and g) A separation unit (16) having an inlet connected to the raffinate outlet of the extraction unit (11), an outlet for separated water, an outlet for separated 1,2 - propanediol, and an outlet for by - products.

17. The facility according to claim 16, wherein the extraction unit (11) comprises a counter - current extraction column or a combination of a mixer and a downstream settler.

18. The facility according to claim 16 or 17, comprising an inlet for a phase - transfer catalyst on the conduit (13) that connects the second outlet of the membrane nanofiltration unit (8) to the extractant inlet of the extraction unit (11).

19. The facility according to claim 16 or 17, wherein the separation unit (16) comprises a first distillation column (17) and a second distillation column (18), the first distillation column (17) having an inlet connected to the raffinate outlet of the extraction unit (11) and a bottoms product outlet, and the second distillation column (18) having an inlet connected to the bottoms product outlet of the first distillation column (17), a tops product outlet for separated 1,2 - propanediol, and a bottoms product outlet for by - products.

20. The facility according to claim 19, further comprising a hydrogenation unit (19) arranged between the raffinate outlet of the extraction unit (11) and the inlet of the separation unit (16).

21. The facility according to claim 16 or 17, further comprising a catalyst reactivation unit (20), the catalyst reactivation unit (20) comprising an inlet (21) for phosphoric acid and an inlet (22) for hydrogen peroxide, an inlet (23) connected to the second outlet of the phase separator (6) for receiving a portion of the separated organic phase, a mixing device (24) downstream of the inlet, and an outlet downstream of the mixing device (24), the outlet being connected via a conduit (25) to an inlet of the loop reactor (1) for receiving the organic phase formed in the catalyst reactivation unit (20) as a recycle stream.

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