Process for the preparation of 1,2-propanediol

Abstract

1,2-propanediol is prepared by a process comprising the steps of: step a) reacting propene with hydrogen peroxide in the presence of a catalyst mixture comprising a phase transfer catalyst and a polytungstophosphate at 50-110°C in a liquid reaction mixture comprising an aqueous phase having a maximum apparent pH of 6 and an organic phase; step b) separating the reaction mixture into an aqueous phase (P a ) and an organic phase (P o ) comprising 1,2-propanediol; step c) recycling at least a portion of the separated organic phase (P o ) to step a); step d) recovering 1,2-propanediol from the aqueous phase (P a ); and step e) reacting a tungstate with hydrogen peroxide and phosphoric acid in the presence of a phase transfer catalyst in a liquid mixture comprising an aqueous phase and an organic phase at 5-40°C, followed by passing at least a portion of the resulting organic phase comprising polytungstophosphate and phase transfer catalyst to reaction step a).

Description

Technical Field

[0001] The present invention relates to a process for preparing 1,2-propylene glycol by reacting propylene with hydrogen peroxide. Background Art

[0002] In a long-established process used in the industry, 1,2-propylene glycol is produced by reacting propylene oxide with water. Propylene oxide can be produced industrially using the HPPO process, which involves reacting propylene with hydrogen peroxide in the presence of a titanium zeolite catalyst and an organic solvent. The propylene oxide is then isolated and purified before reacting it with water to produce 1,2-propylene glycol.

[0003] WO 2017 / 089075 discloses a method for producing 1,2-propylene glycol from propylene and hydrogen peroxide, comprising: 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 having a maximum pH of 6 and an organic phase; b) separating the biphasic mixture from step a) into an aqueous phase and an organic phase containing propylene oxide; c) returning the propylene oxide contained in the separated organic phase to the reaction in step a); and d) separating 1,2-propylene glycol from the aqueous phase separated in step b). The heteropolytungstate and the phase transfer catalyst may be provided to step a) as a mixture, but as further shown in the Examples, it is preferred that the heteropolytungstate and the phase transfer catalyst be fed separately to step a).

[0004] The embodiment of WO 2017 / 089075 uses polytungstophosphate and the separate feed of hydrogen peroxide and aqueous solution (comprising alkali metal tungstate and phosphoric acid) to step a).Then, catalytically active peroxy polytungstophosphate (peroxopolytungstophosphate) is formed in situ in the reaction mixture of step a). Summary of the Invention

[0005] The inventors of the present invention have now discovered that, in the process described in WO 2017 / 089075, the in situ generation of peroxypolytungstophosphate with high catalytic activity requires a relatively high phosphoric acid concentration in the aqueous phase of step a), and that the catalytic activity of the catalyst mixture of WO 2017 / 089075 deteriorates over time when the phosphoric acid concentration in the aqueous phase of step a) is low. The inventors have also discovered that if an organic phase containing peroxypolytungstophosphate is provided by a separate step of reacting tungstate with hydrogen peroxide and phosphoric acid in the presence of a phase transfer catalyst, and this organic phase is then transferred to step a) of reacting propylene with hydrogen peroxide, high and sustained catalytic activity for the oxidation of propylene can be achieved even at low phosphoric acid concentrations in the aqueous phase of step a). It is also possible to subject the organic phase separated in step b) to a separate step of catalyst activation before recycling it to step a).

[0006] The present invention therefore provides a process for preparing 1,2-propylene glycol, comprising:

[0007] a) reacting propylene with hydrogen peroxide at a temperature of 50-110° C. in the presence of a catalyst mixture comprising a phase transfer catalyst and a polytungstophosphate in a liquid reaction mixture comprising an aqueous phase having a maximum apparent pH of 6 and an organic phase;

[0008] b) separating the reaction mixture into an aqueous phase (P) containing 1,2-propylene glycol a ) and organic phase (P o );

[0009] c) separating the organic phase (P o ) is recycled to reaction step a); and

[0010] d) From the aqueous phase (P a ) to recover 1,2-propylene glycol;

[0011] The method comprises at least one step:

[0012] e) reacting the tungstate with hydrogen peroxide and phosphoric acid at a temperature of 5-40° C. in the presence of a phase transfer catalyst in a liquid mixture comprising an aqueous phase and an organic phase, and subsequently removing the resulting organic phase (P oc ) is passed to reaction step a). DETAILED DESCRIPTION

[0013] In the process 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 polytungstophosphate. The reaction is carried out in a liquid reaction mixture comprising an aqueous phase and an organic phase having a maximum apparent pH of 6.

[0014] Propylene can be used in pure form or in 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 propene to hydrogen peroxide of 1.1:1 to 10:1.

[0015] The hydrogen peroxide is preferably used in the form of an aqueous solution, preferably having a hydrogen peroxide content of 10 to 80% by weight, particularly preferably 30 to 70% by weight. Any commercially available grade of aqueous hydrogen peroxide solution can be used. The crude hydrogen peroxide obtained in the extraction stage of the anthraquinone process for producing hydrogen peroxide can also be used.

[0016] The catalyst mixture used in step a) comprises polytungstophosphate. Polytungstophosphate is well known to those skilled in the art. The molar ratio of phosphorus to tungsten of the preferred polytungstophosphate is within the range of 1:2 to 1:12.

[0017] The catalyst mixture used in step a) also includes a phase-transfer catalyst. The phase-transfer catalyst includes a cation or a compound that forms a cation in the aqueous phase, whereby the cation can form a salt with peroxytungstate or peroxypolytungstate phosphate, and the salt is soluble in the organic phase of the liquid reaction mixture. The phase-transfer catalyst preferably includes a single-charge cation or a compound that forms a single-charge cation in the aqueous phase. Suitable phase-transfer catalysts are tertiary amines, tertiary ammonium salts, quaternary ammonium salts, and quaternary phosphonium salts. Counterions suitable for tertiary ammonium salts and quaternary ammonium salts are the following anions: chloride, bromide, nitrate, sulfate, hydrogen phosphate, dihydrogen phosphate, methanesulfonate, methylsulfate, and ethylsulfate. The amount of the phase-transfer catalyst preferably provides a molar ratio of the phase-transfer catalyst to tungsten in the liquid mixture within the range of 0.2:1 to 3:1, particularly preferably within the range of 0.4:1 to 1:1, wherein the molar ratio refers to the amount of tungsten in the phase-transfer catalyst used or the compound that forms the cation to the amount of tungsten used.

[0018] In a preferred embodiment, the phase transfer catalyst is a tertiary amine or a tertiary ammonium salt or a quaternary ammonium salt containing 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 tertiary amine having structure R 1 R 2 R 3 NR 4+ tertiary ammonium ion or quaternary ammonium ion, wherein R 1 、R 2 and R 3 are the same or different and are each selected from an alkyl group having 8 to 10 carbon atoms, and R 4 is hydrogen or methyl.Most preferably, the phase transfer catalyst comprises methyltri(octyl / decyl)ammonium methylsulfate (CAS No. 2387913-24-6).

[0019] In another preferred embodiment, the phase transfer catalyst comprises at least one compound having the structure R 1 R 2 R 3 R 4 N + A salt of a tertiary ammonium ion or a quaternary ammonium ion, wherein R 1 is YO(C=O)R 5 A group wherein 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 Each independently is R 1 , an alkyl group having 1 to 4 carbon atoms or Y-OH. Preferred is a quaternary ammonium salt with methyl sulfate as the counter ion, wherein R 2 is a methyl group, and R 5 is a straight chain alkyl or alkenyl. 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)R 5 )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 acid, and then carrying out quaternization with dimethyl sulfate. These phase-transfer catalysts have the following advantages: they are easily biodegradable (being different from tetraalkylammonium salts), and can be introduced into biological treatment equipment without the need for further pretreatment. Compared to tetraalkylammonium halides, the corrosiveness of salts with methylsulfate as anion is also less.

[0020] The reaction in step a) is carried out in a liquid reaction mixture comprising two liquid phases: an aqueous phase with a maximum apparent pH of 6 and an organic phase. The term "apparent pH" herein refers to the value determined by measurement with a glass electrode using a commercial pH meter calibrated with a buffered aqueous solution of known pH for measuring dilute aqueous solutions. This apparent pH differs from the theoretical pH (i.e., the negative logarithm of the hydrogen ion activity) by a constant value because the standard potential of the glass electrode in the aqueous phase of the reaction mixture (containing hydrogen peroxide and diol) differs from its standard potential in pure water. The apparent pH of the aqueous phase is preferably maintained within a range of 1.0 to 3.5, particularly preferably within a range of 2.0 to 3.0. The apparent pH can be maintained within this range by adding an acid, preferably sulfuric acid or phosphoric acid, or by adding a base, preferably aqueous sodium hydroxide. Adjusting the apparent pH within this preferred range provides 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.

[0021] In reaction step a), the weight ratio of hydrogen peroxide to water fed to step a) is preferably adjusted while maintaining a molar excess of propylene fed to step a) relative to hydrogen peroxide. The weight ratio of hydrogen peroxide to water is preferably 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 in the range of 1.1:1 to 10:1, more preferably 1.2:1 to 4:1.

[0022] The reaction is preferably carried out at a temperature in the range of 50 to 110° C., more preferably 60 to 100° C., 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.

[0023] The reaction in step a) can be carried out with or without the addition of an organic solvent. The reaction is preferably carried out in the presence of at least one organic solvent having a boiling point exceeding 100° C., preferably exceeding 120° C., and having a solubility in water of less than 250 mg / kg at 20° C. Suitable solvents are alcohols, ethers, esters, ketones, and alkylated aromatic hydrocarbons having one or more hydroxyl groups. The addition of a solvent can improve the extraction of the salt formed by the polytungstophosphate and the phase transfer catalyst into the organic phase. Preferably, the amount of organic solvent is selected to provide a proportion of organic solvent in the organic phase during the reaction in the range of 10-90% by weight.

[0024] In a preferred embodiment, the organic solvent comprises epoxidized fatty acid methyl esters. Epoxidized fatty acid methyl esters can be formed in situ in the reaction mixture of step a) by using fatty acid methyl esters having unsaturated fatty acid groups, which are reacted with hydrogen peroxide to form the epoxidized fatty acid methyl esters. Particularly preferred are epoxidized fatty acid methyl esters containing fatty acid groups derived from vegetable oils, particularly soybean oil. Epoxidized fatty acid methyl esters have the advantage that they have low solubility in aqueous phases.

[0025] In another preferred embodiment, the solvent comprises an alkylated aromatic hydrocarbon with 8-12 carbon atoms. For example, the alkylated aromatic hydrocarbons suitable for are 1,2-dimethylbenzene (o-xylene), 1,3-dimethylbenzene (m-xylene), 1,4-dimethylbenzene (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 comprising an alkylated aromatic hydrocarbon with 8-12 carbon atoms exceeding 50 % by weight, particularly preferably exceeding 80 % by weight, is used as a solvent. The use of these solvents makes it possible for most peroxytungstate to be extracted into the organic phase of the reaction mixture and to be recycled, which allows the method to be operated without the need to reclaim polytungstophosphate from the aqueous phase of the reaction mixture of step a). Then, the phase transfer catalyst, the molar ratio of phase transfer catalyst to polytungstophosphate, the molar ratio of phosphorus to tungsten, the molar ratio of propylene to hydrogen peroxide, and the amount of solvent are preferably selected to transfer as much of the tungsten present in the liquid reaction mixture as possible to the organic phase.

[0026] The reaction of step a) is usually carried out in the presence of phosphoric acid. The amount of phosphoric acid used is preferably such that the aqueous phase (P a ) apparent pH. The aqueous phase of the reaction mixture (P a ) is preferably 0.02-2.0 wt %, more preferably 0.2-0.8 wt % (relative to the mass of the aqueous phase according to PO4 3- calculate).

[0027] The reaction in step a) can be carried out batchwise or continuously, with continuous reaction being preferred. The concentration of hydrogen peroxide in the aqueous phase is preferably maintained within the range of 0.1-5 wt. %, particularly preferably 0.5-3 wt. 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 where the reaction occurs. The residence time of the reaction mixture is preferably adjusted so that the hydrogen peroxide conversion remains within the range of 80-99%.

[0028] During the reaction, the liquid mixture is preferably mixed to create a large phase interface between the aqueous and the organic phase. To this end, the reaction is preferably carried out continuously in a loop reactor having fixed internals in the tubular section and the liquid mixture is passed through the loop reactor at a flow rate that creates turbulent flow at the internals. To this end, baffle plates, static mixing elements, structured or random packings can be used as internals. In combination with these internals or as an alternative, heat exchangers, such as plate heat exchangers or tube bundle heat exchangers, can be used, in which turbulent flow is created, for example, between the plates of a plate heat exchanger or in the tubes of a tube bundle heat exchanger.

[0029] Preferably, the entire or part of the heat of reaction generated in step a) is removed while the reaction is ongoing, 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.

[0030] In step b) of the process of the present application, the liquid reaction mixture provided by step a) is separated into an aqueous phase (P a ) comprising 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 coalescer elements comprising structured or random packings whose surface is wetted by the dispersed phase of the biphasic mixture to achieve a more complete separation.

[0031] The aqueous phase (P a ) generally comprises 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 from the reaction of propene oxide with hydrogen peroxide, and formic acid, acetic acid and hydroxyacetone formed from the further oxidation of 1,2-propanediol. The aqueous phase usually also comprises phosphoric acid and, if sodium tungstate is added in step e), also sodium salts of phosphoric acid. The organic phase (P o ) comprises unreacted propene, and propene oxide formed as an intermediate in the reaction of propene with hydrogen peroxide and which has not yet been hydrolyzed to 1,2-propanediol. The organic phase (P o ) usually also comprises one or more salts formed from the polytungstophosphate and the cations of the phase transfer catalyst. The organic phase P o will also contain propane, if the propene raw material contains propane, and the organic solvent, if an organic solvent with low water solubility is used as described further above.

[0032] In step c) of the process of the present application, the separated organic phase (Po ) is recycled to reaction step a). Thus, the organic phase (P o ) is recycled to step a) to achieve complete conversion of propylene to 1,2-propylene glycol, dipropylene glycol and tripropylene glycol. Preferably, the propylene oxide present in the organic phase (P o ) is recycled to step a), and particularly preferably substantially the entire catalyst mixture present in the organic phase is recycled to step a).

[0033] The organic phase (P) separated from the liquid reaction mixture provided in step a) may be o ) is recycled to step a) without further treatment. If the propylene fed to step a) contains propane, then preferably a stream of unreacted propylene is separated from the organic phase in step c) before the organic phase is recycled to step a), wherein the stream of separated unreacted propylene contains as much propane as the impure propylene fed to step a). In this way, for a continuous reaction, accumulation of propane in the organic phase of the reaction mixture in step a) can be avoided. The stream of separated unreacted propylene can be passed to a C3 splitter to separate propylene and propane, and the recovered propylene can be recycled to step a).

[0034] The aqueous phase (P) obtained in step b) a ) is preferably further processed without directly or indirectly recycling any part thereof to step a).

[0035] In step d) of the process of the present invention, from the aqueous phase (P aThe 1,2-propanediol is preferably recovered by distillation. Preferably, 1,2-propanediol and higher propylene glycols (such as dipropylene glycol and tripropylene glycol) are recovered by a series of distillation steps, such as a multi-step distillation comprising a first distillation step providing a column top product comprising water and a column bottom product which is passed to the next distillation step and optionally further distillation steps, and a distillation step providing a column top product comprising 1,2-propanediol and a residual column bottom product which is preferably subjected to at least one further distillation step. Most preferably, a series of distillation steps as described in Ullmann’s Encyclopedia of Industrial Chemistry, online version, entry “Propylene glycol”, page 4, DOI 10.1002 / 14356007.a22_163.pub2 is used, wherein the column top product comprising water is separated from the column bottom product comprising 1,2-propanediol and higher propylene glycols in a series of 2-4 thermally integrated distillation steps, followed by a vacuum distillation step providing 1,2-propanediol as column top product and a column bottom product containing high-boiling organic compounds and salts. From this column bottom product, dipropylene glycol and tripropylene glycol can be recovered as column top product in a further vacuum distillation step.

[0036] In a preferred embodiment, at least part of and preferably all of the aqueous phase (P a ) obtained in step b) is subjected to catalytic hydrogenation in step d) prior to the recovery of 1,2-propanediol, preferably by distillation. The catalytic hydrogenation is preferably performed using a supported hydrogenation catalyst comprising one or more metals selected from the group consisting of Ru, Rh, Pd, Pt, Ag, Ir, Fe, Cu, Ni and Co on a support, wherein activated carbon, Si02, Ti02, Zr02, AI2O3 and aluminosilicates are preferred as support materials. Preferred is a hydrogenation catalyst comprising ruthenium as active metal. The catalytic hydrogenation is preferably performed at a temperature of 80 °C to 140 °C, preferably 90 °C to 120 °C, and preferably at a hydrogen partial pressure of 5-50 bar, more preferably 5-35 bar, even more preferably 7-30 bar, most preferably 8-25 bar. The hydrogenation catalyst can be used in the form of a suspension or in a fixed bed, with trickle bed hydrogenation using a fixed bed catalyst being preferred. The hydrogenation prevents problems caused by the decomposition of hydrogen peroxide which has not reacted in step a) upon recovery of 1,2-propanediol by distillation. 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 thereby improves the yield of 1,2-propanediol.

[0037] The method of the present invention further comprises at least one step e) reacting tungstate with hydrogen peroxide and phosphoric acid at a temperature of 5-40° C. in the presence of a phase transfer catalyst in a liquid mixture comprising an aqueous phase and an organic phase. Then, the resulting organic phase (P oc ) is transferred to the reaction step a). Preferably, the aqueous phase (P ac ) is passed to reaction step a).

[0038] Phosphoric acid and tungstate are preferably used in step e) in a molar ratio of phosphorus to tungsten of 1:2 to 10:1, preferably 4:1 to 8:1. The aqueous phase of the liquid mixture of step e) preferably contains 10-40% by weight, more preferably 15-38% by weight, and most preferably 18-35% by weight of phosphoric acid. The amount of hydrogen peroxide used is preferably such that at least 2 mol of hydrogen peroxide is provided 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, as well as the preferred concentration of phosphoric acid in the aqueous phase, convert the majority of the tungstate to the formula PO4[WO(O2)2]4 3- and HPO4[WO(O2)2]2 2- The peroxytungstophosphate and its partially protonated form are presumably the most catalytically active species for propylene oxidation. The temperature of 5-40°C used in step e) prevents these species from decomposing and forming molecular oxygen before being transferred to reaction step a). Preferably, step e) is carried out at a temperature of 10-35°C, more preferably 15-30°C.

[0039] The reaction time in step e) is generally 1 to 200 minutes, preferably 1 to 20 minutes, more preferably 2 to 10 minutes, wherein if the liquid mixture of step e) contains propylene, the reaction time is preferably less than 20 minutes at the upper limit of the temperature range of 5 to 40° C. Then, only a small portion of the propylene present in the liquid mixture of step e) will be oxidized, step e) can be carried out in the absence of cooling, and substantially all of the peroxytungstophosphate produced in step e) can be transferred to step a).

[0040] In step e), the tungstate is preferably reacted with hydrogen peroxide and phosphoric acid in the presence of an organic solvent having a boiling point exceeding 100° C. at atmospheric pressure and a solubility in water of less than 250 mg / kg at 20° C. In step e), the same organic solvent as described above for reacting propylene with hydrogen peroxide in step a) can be used. The organic solvent preferably contains more than 50% by weight, more preferably more than 80% by weight, of an alkylated aromatic hydrocarbon having 8 to 12 carbon atoms.

[0041] Step e) can be carried out in any type of reactor known to be suitable for mixing the two liquid phases present in step e). Suitable reactors for carrying out step e) are stirred vessels and the reactor types described further above for providing a large phase interface between the aqueous and organic phases in step a). For short reaction times in step e), tubular reactors with fixed internals for generating turbulent flow can also be used.

[0042] Preferably, the organic phase (P o ) is used as a tungstate source in step e), and the resulting organic phase (P oc ) is transferred to the reaction step a) to supply the recycle of step c). More preferably, step a), step b), step c) and step e) are carried out continuously, and 5-50%, preferably 10-25% of the organic phase (P) separated in step b) is transferred to the reaction step a) to supply the recycle of step c). o ) is transferred to step e), wherein the remainder is directly recycled to step a). In this way, the most catalytically active peroxytungstophosphate species can be continuously regenerated, and step a) can be operated continuously for a long time without loss of catalytic activity (i.e., with a constant hydrogen peroxide conversion rate), even when the concentration of phosphoric acid in the aqueous phase of reaction step a) is low. If the organic phase (P o ) contains unreacted propylene, the reaction of step e) is preferably carried out for a short reaction time as described further above, in order to avoid o ) is oxidized by the propylene introduced, so that there will be no need to cool the liquid mixture in step e). For this reason, it is also preferred that no propylene is added in step e).

[0043] In a preferred embodiment, the organic phase (P o ) is used as a tungstate source for step e), and step e) is operated with a volume ratio of organic phase to aqueous phase of 50:1 to 1:1, preferably 20:1 to 5:1, more preferably 14:1 to 8:1. In this embodiment, it is preferred that the entire aqueous phase (P ac ) is transferred to reaction step a), and the organic phase (P) produced in step e) is then not required oc ) and aqueous phase (P ac ) of the phase separation. When the entire aqueous phase (P ac ) is transferred to reaction step a), preferably all of the phosphoric acid used in reaction step a) is introduced in step e).

[0044] In another preferred embodiment, the organic phase (P o) is used as a tungstate source for step e), and step e) is operated with a volume ratio of organic phase to aqueous phase of less than 10:1, preferably 7:1 to 0.1:1. In this embodiment, the aqueous phase (P) produced in step e) is separated ac ) and organic phase (P oc ), and a portion of the separated aqueous phase (P ac ) is reused as a source of phosphoric acid in step e). ac ) is transferred to the reaction step a) of the portion not reused as a source of phosphoric acid in step e). When steps a) and e) are carried out continuously, it is preferred to adjust the separated aqueous phase (P ac ) is reused as part of the phosphoric acid source of step e) to maintain a constant volume of the aqueous phase of the liquid mixture of step e), i.e., the separated aqueous phase (P ac The portion of the aqueous phase (P) not reused but discharged from step e) will discharge the water introduced with the hydrogen peroxide and phosphoric acid used in step e). ac ) and organic phase (P oc ) can be carried out as described above for step b).

[0045] For both preferred embodiments and the continuous operation of step a), step b), step c) and step e), it is preferred that the additional tungstate and preferably the phase transfer catalyst be added to the aqueous phase (P) in step b). a ) are introduced into step e) at the same rate at which they exit, in order to maintain a constant amount of phase transfer catalyst and polytungstophosphate in the liquid reaction mixture of step a).

[0046] The present invention will now be explained in more detail with reference to Examples.

[0047] Example

[0048] Example 1

[0049] Preparation of initial epoxidation catalyst solution

[0050] A mixture of 29 g of 70 wt% hydrogen peroxide, 94 g of demineralized water, 78 g of 85 wt% phosphoric acid, and 48 g of sodium tungstate dihydrate was stirred at room temperature for 2 hours. A solution of 82 g of methyltri(octyl / decyl)ammonium methylsulfate (CAS No. 2387913-24-6) in 884 g of Hydrosol A 200ND (a mixture of C10 alkylbenzenes) was then added, and the mixture was stirred at room temperature for a further 2 hours. The aqueous and organic phases were then separated to provide 995 g of the organic phase as the initial epoxidation catalyst solution.

[0051] Reaction of propylene with hydrogen peroxide

[0052] The reaction of propene with hydrogen peroxide was carried out at a temperature of 80° C. and a pressure of 30 bar in a loop reactor having a loop volume of 0.45 l, a circulation pump and a heat exchanger for regulating the reaction temperature. The loop reactor was heated at a rate of 130 kg h -1 The reactor was operated at a circulation rate of 1000 rpm. The reactor was equipped with a catalyst feed reservoir, an organic phase collection vessel equipped with an agitator, and a feed pump for feeding liquid propylene, liquid propane, aqueous hydrogen peroxide, and liquid from the catalyst feed reservoir. The initial epoxidation catalyst solution was charged to the catalyst feed reservoir, and the aqueous phase separated from the initial epoxidation catalyst solution was charged to the organic phase collection vessel. The loop initially contained the reaction mixture from the previous experiment. The circulation was started and maintained at 130 kg h -1 , and the circulating mixture was heated to 80 ° C. Then, 80g h -1 Propylene, 50g h -1 Propane, 210gh -1 15 wt% aqueous hydrogen peroxide solution containing 0.05 wt% phosphoric acid, and 320 g h -1 The organic catalyst solution from the catalyst feed reservoir was introduced into the loop reactor, and the circulating mixture was cooled to maintain a reaction temperature of 80° C. The biphasic oxidation reaction mixture was withdrawn from the loop reactor in an amount corresponding to the added amount, and 18 g h -1 9 wt % aqueous solution of disodium sulfate was added to accelerate phase separation. The organic and aqueous phases of the resulting mixture were separated, and the organic phase was transferred to an organic phase collection container after decompression and cooling to 25°C. When 500 g of the organic phase had accumulated in the organic phase collection container, the contents of the container were thoroughly mixed by stirring at 25°C for 5 minutes, the phases were separated by sedimentation, and the organic phase was transferred to a catalyst feed reservoir, with the aqueous phase remaining in the organic phase collection container. After approximately 7 hours of operation, the feed of reactants and circulation in the loop reactor were stopped, and 0.33 g of sodium tungstate dihydrate was added to the organic phase collection container to compensate for the loss. The next day, circulation in the loop reactor was restarted, and after the reaction temperature had been established in the loop reactor, the dosing of reactants was resumed, and the reaction was allowed to continue for approximately another 7 hours, operating the process for a total of 32.4 hours over a 5-day period. After different time periods, the aqueous phase separated from the oxidation reaction mixture was analyzed for hydrogen peroxide by redox titration and by capillary GC (25 m CP-WAX-52CB column from Agilent, He carrier gas, temperature program starting from 50° C. with a ramp rate of 20 K / min to 90° C., with a ramp rate of 10 K / min to 220° C. and with a ramp rate of 5 K / min to 235° C., FID detector) and1 The aqueous phase separated from the oxidation reaction mixture was analyzed for 1,2-propylene glycol (MPG) by H-NMR. The data are summarized in Table 1.

[0053] Example 2 (comparison)

[0054] Example 1 was repeated, but the aqueous phase separated from the initial epoxidation catalyst solution was not charged to the organic phase collection vessel (ie, step e) of the process according to the invention was not performed). The data from this example are also summarized in Table 1.

[0055] Table 1

[0056] Concentrations of hydrogen peroxide and 1,2-propylene glycol in the aqueous phase separated from the oxidation reaction mixture

[0057] (All values ​​are in weight %)

[0058]

[0059] 1 1,2-Propanediol

[0060] The results in Table 1 show that in Example 1 (in which step e) of the process according to the invention is carried out), the catalyst activity can be maintained for a longer period of time than in Comparative Example 2 without step e), as indicated by a higher and constant hydrogen peroxide conversion and a higher amount of the product 1,2-propylene glycol (MPG).

Claims

1. A method for preparing 1,2-propylene glycol, comprising: a) reacting propylene with hydrogen peroxide at a temperature of 50-110° C. in the presence of a catalyst mixture comprising a phase transfer catalyst and a polytungstophosphate in a liquid reaction mixture comprising an aqueous phase having a maximum apparent pH of 6 and an organic phase, wherein the term apparent pH refers to the value determined by measurement with a glass electrode using a commercial pH meter calibrated with a buffered aqueous solution of known pH for measuring dilute aqueous solutions; b) separating the reaction mixture into an aqueous phase P containing 1,2-propylene glycol a and organic phase P o ; c) the separated organic phase P o at least a portion of which is recycled to reaction step a); and d) from the aqueous phase P a Recover 1,2-propylene glycol; The method comprises at least one step e) reacting the tungstate with hydrogen peroxide and phosphoric acid at a temperature of 5-40° C. in the presence of a phase transfer catalyst in a liquid mixture comprising an aqueous phase and an organic phase, and subsequently separating the resulting organic phase P comprising the polytungstophosphate and the phase transfer catalyst. oc at least a portion of which is transferred to reaction step a), The phase transfer catalyst is a tertiary amine or a tertiary ammonium salt or a quaternary ammonium salt containing 12 to 60 carbon atoms in total, Phosphoric acid and tungstate are used in step e) in a molar ratio of phosphorus to tungsten of 1:2 to 10:1, The hydrogen peroxide is used in step e) in an amount that provides at least 2 mol of hydrogen peroxide per mol of tungsten.

2. The method according to claim 1, wherein In step e), the tungstate is reacted with hydrogen peroxide and phosphoric acid in the presence of an organic solvent having a boiling point exceeding 100° C. at atmospheric pressure and a solubility in water at 20° C. of less than 250 mg / kg.

3. The process of claim 2, wherein the organic solvent comprises more than 50% by weight of an alkylated aromatic hydrocarbon having 8 to 12 carbon atoms.

4. The process according to claim 1 , wherein the organic phase P separated in step b) is o At least a portion of the organic phase P is used as a tungstate source in step e), and the organic phase P is then oc is passed to reaction step a) to supply said recycle of step c).

5. The method of claim 4, wherein the volume ratio of the organic phase to the aqueous phase in step e) is 50:1 to 1:

1.

6. The method of claim 5, wherein the volume ratio of the organic phase to the aqueous phase in step e) is 20:1 to 5:

1.

7. The method of claim 5, wherein the volume ratio of the organic phase to the aqueous phase in step e) is 14:1 to 8:

1.

8. The method of claim 4, wherein in step e), the volume ratio of the organic phase to the aqueous phase is less than 10:1, and the aqueous phase P is ac With organic phase P oc Separate, and a portion of the separated aqueous phase P ac Reuse as the phosphoric acid source in step e).

9. The method of claim 8, wherein the volume ratio of the organic phase to the aqueous phase is 7:1 to 0.1:

1.

10. The process according to any one of claims 1 to 3, wherein the aqueous phase P produced in step e) is ac At least a portion of the precipitate is passed to reaction step a).

11. The process according to any one of claims 1 to 3, wherein hydrogen peroxide is used in step e) in an amount providing 2 to 10 mol of hydrogen peroxide per mol of tungsten.

12. The method according to any one of claims 1 to 3, wherein In step e), the aqueous phase of the liquid mixture comprises 10-40 wt% of phosphoric acid.

13. The method of claim 12, wherein: In step e), the aqueous phase of the liquid mixture comprises 15-38 wt% of phosphoric acid.

14. The method of claim 12, wherein: In step e), the aqueous phase of the liquid mixture comprises 18-35 wt% of phosphoric acid.

15. The process of any one of claims 1 to 3, wherein no propylene is added in step e).

16. The method according to any one of claims 1 to 3, wherein In step d), before recovering 1,2-propylene glycol by distillation, the aqueous phase P a Subjected to catalytic hydrogenation.

17. The method according to any one of claims 1 to 3, wherein step a) is performed continuously, and the concentration of hydrogen peroxide in the aqueous phase of step a) is 0.1 to 5% by weight.

18. The process of any one of claims 1 to 3, wherein step a) is performed continuously in a loop reactor comprising fixed internals in a tubular section and wherein the liquid reaction mixture is passed through the reactor at a flow rate sufficient to provide turbulence at the internals.

19. The process of any one of claims 1 to 3, wherein the organic phase in step a) comprises an organic solvent having a boiling point exceeding 100°C at atmospheric pressure and a solubility in water at 20°C of less than 250 mg / kg.

20. The method of claim 19, wherein the organic solvent is a mixture of alkylated aromatic hydrocarbons having 8 to 12 carbon atoms.

21. The method of any one of claims 1 to 3, wherein the phase transfer catalyst comprises a catalyst having structure R 1 R 2 R 3 NR 4+ tertiary ammonium ion or quaternary ammonium ion, wherein R 1 、R 2 and R 3 are the same or different and are each selected from an alkyl group having 8 to 10 carbon atoms, and R 4 is hydrogen or methyl.

Images