Process for the preparation of 1,2-propylene glycol and dipropylene glycol

Abstract

The method for preparing 1,2-propylene glycol and dipropylene glycol comprises the steps of a) continuously reacting propylene with hydrogen peroxide in the presence of a catalyst mixture in a liquid reaction mixture to obtain 1,2-propylene glycol and dipropylene glycol, wherein the catalyst mixture comprises a phase transfer catalyst and a heteropolytungstate, and the liquid reaction mixture comprises an aqueous phase having a maximum apparent pH of 6 and an organic phase; and b) separating the reaction mixture into an aqueous phase (P a ) and the organic phase (P o ); Step c) the separated organic phase (P o ) is recycled to the reaction step a); and step d) from the separated aqueous phase (P a ) to recover 1,2-propylene glycol and dipropylene glycol; wherein the heat of reaction generated in step a) is at least partially removed, and the ratio of 1,2-propylene glycol to dipropylene glycol is controlled by adjusting the weight ratio of hydrogen peroxide to water fed to step a).

Description

Technical Field

[0001] The present invention relates to a process for preparing 1,2-propylene glycol and dipropylene glycol by reacting propylene with hydrogen peroxide, wherein the ratio of 1,2-propylene glycol to dipropylene glycol can be controlled. 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 the reaction of propylene with hydrogen peroxide in the presence of a titanium zeolite catalyst and an organic solvent. Before the propylene oxide reacts with water to produce 1,2-propylene glycol, it is separated and purified. A small amount of dipropylene glycol is obtained as a valuable byproduct. The second step, hydrolyzing propylene oxide to 1,2-propylene glycol, is typically performed under adiabatic conditions, making it difficult to increase the amount of dipropylene glycol because adiabatic hydrolysis requires a minimum amount of water to absorb the heat of reaction.

[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 with 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). Furthermore, the document teaches reducing the amount of dipropylene glycol and tripropylene glycol by subjecting the aqueous phase separated in step b) to a nanofiltration step, in which a retentate enriched in heteropolytungstate is obtained and recycled to the reaction in step a). Sufficient water is thereby recycled to step a) to maintain the 1,2-propylene glycol concentration in the aqueous phase within the range of 10-30 wt%.

[0004] Both 1,2-propylene glycol and dipropylene glycol are valuable products, but the demand for these products in the market fluctuates. Therefore, it is desirable in the industry to have a process for producing 1,2-propylene glycol and dipropylene glycol in which the ratio of 1,2-propylene glycol to dipropylene glycol produced can be easily controlled and varied to suit market needs. Summary of the Invention

[0005] The inventors of the present invention have now found that in the two-phase oxidation process of WO 2017 / 089075, the ratio of 1,2-propanediol to dipropylene glycol can be adjusted by adjusting the weight ratio of hydrogen peroxide to water fed to the reaction step, which allows obtaining a higher dipropylene glycol ratio than is possible for the adiabatic hydrolysis of propylene oxide.

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

[0007] a) reacting propylene with hydrogen peroxide in the presence of a catalyst mixture comprising a phase transfer catalyst and a heteropolytungstate in a liquid reaction mixture comprising an aqueous phase having a maximum apparent pH of 6 and an organic phase to obtain 1,2-propylene glycol and dipropylene glycol;

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

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

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

[0011] The heat of reaction generated in step a) is at least partially removed, and the ratio of 1,2-propylene glycol to dipropylene glycol is controlled by adjusting the weight ratio of hydrogen peroxide to water fed to step a). DETAILED DESCRIPTION

[0012] 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 heteropolytungstate. The reaction is carried out in a liquid reaction mixture comprising an aqueous phase having a maximum apparent pH of 6 and an organic phase.

[0013] 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.

[0014] 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.

[0015] 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 well known to those skilled in the art. The molar ratio of phosphorus to tungsten of the preferred polytungstophosphate is in the range of 1:2 to 1:12. The polytungstophosphate is preferably generated in situ by combining phosphoric acid and 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 molar ratio of phosphorus to tungsten 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 peroxytungstate and peroxytungstophosphate such as PO4[WO(O2)2]4 3- and HPO4[WO(O2)2]2 2- and its partially protonated form, which is presumably the catalytically active species for propylene oxidation.

[0016] 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 heteropolyperoxytungstate, 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.

[0017] 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).

[0018] 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.

[0019] 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.

[0020] In the reaction of 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.

[0021] The concentration of hydrogen peroxide in the aqueous phase of step a) is preferably kept in the range of 0.1 to 5% by weight, preferably 0.12 to 1.0% by weight.

[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 include 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 from the heteropolytungstate 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, suitable alkylated aromatic hydrocarbons 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 to extract most of the peroxytungstate into the organic phase of the reaction mixture and recycle it, which allows the method to be operated without recovering heteropolytungstate in the aqueous phase of the reaction mixture of step a). Then, the phase transfer catalyst, the molar ratio of the phase transfer catalyst to the heteropolytungstate, the molar ratio of the heteroatoms of the heteropolytungstate 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] Phase transfer catalyst, heteropolytungstate and optionally used solvent can be added in step a) of the method of the present invention individually or in the form of a mixture containing two or all three of these components. Preferably, in step a), a solvent is used, and the phase transfer catalyst and heteropolytungstate are added and dissolved in the organic phase comprising the solvent.

[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, preferably mixed liquid mixture, to produce large phase interface between aqueous phase and organic phase.For this reason, reaction is preferably carried out continuously in the loop reactor with fixed internals (internal), and liquid mixture passes through the loop reactor with the flow velocity that produces turbulence at the internals place.For this reason, baffle, static mixing element, structured packing or random packing can be used as internals.With these internals combination or as an alternative, heat exchanger (such as plate heat exchanger or tube bundle heat exchanger) can be used, wherein turbulence for example produces between the plate of plate heat exchanger or in the pipe of tube bundle heat exchanger.

[0029] In step a) of the process according to the present invention, the heat of reaction generated by the oxidation of propylene is at least partially removed. Preferably, all or part of the generated heat of reaction is removed by cooling the reaction mixture in a heat exchanger. More preferably, the reaction is carried out continuously in a loop reactor comprising a heat exchanger within the reactor loop for cooling the reaction mixture.

[0030] In step b) of the process of the present invention, the liquid reaction mixture provided by step a) is separated into an aqueous phase (P) comprising 1,2-propylene glycol and dipropylene glycol. a ) and the 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 comprising a structured or random packing whose surface is wetted by the dispersed phase of the biphasic mixture.

[0031] Water phase (P a ) typically comprises water, unreacted hydrogen peroxide, and the reaction products 1,2-propylene glycol and dipropylene glycol. The aqueous phase typically also contains tripropylene glycol and 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 hydroxyacetone formed by further oxidation of 1,2-propylene glycol). The aqueous phase may also typically comprise phosphoric acid and a sodium salt of phosphoric acid (if a polytungstate phosphate generated in situ by combining phosphoric acid with sodium tungstate is used in step a). The organic phase (P o ) contains unreacted propylene and propylene oxide which is formed as an intermediate when propylene reacts with hydrogen peroxide and has not yet been hydrolyzed to 1,2-propylene glycol. o ) usually also contains one or more salts formed from heteropolytungstates and cations of a phase transfer catalyst. o It will also include propane (if the propylene starting material contains propane) and an 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 invention, 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 a preferred embodiment, the aqueous phase (P a ) is subjected to a hydrogenation treatment before being transferred to step d). 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, with activated carbon, SiO2, TiO2, ZrO2, Al2O3, and aluminum silicate being preferred 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, and even more preferably 8-25 bar, and at 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, with trickle bed hydrogenation using a fixed bed catalyst being preferred. Hydrogenation can prevent problems caused by the decomposition of unreacted hydrogen peroxide from step a) in step d) for recovering 1,2-propylene glycol 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-propylene glycol and thereby increases the yield of 1,2-propylene glycol.

[0036] In step d) of the process of the present invention, 1,2-propylene glycol and dipropylene glycol are recovered from the optionally hydrogenated aqueous phase of step b). 1,2-propylene glycol and dipropylene glycol are preferably recovered by a series of distillation steps. Preferably, the series of distillation steps 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 an overhead product comprising water is separated from a bottom product comprising 1,2-propylene glycol and dipropylene glycol in a series of 2-4 heat-integrated distillation steps, followed by successive vacuum distillation steps, which provide 1,2-propylene glycol and dipropylene glycol as overhead products and a bottom product containing high-boiling organic compounds and salts. From this bottom product, tripropylene glycol can be recovered as an overhead product in a further vacuum distillation step.

[0037] The present invention will now be explained in more detail with reference to Examples.

[0038] Example

[0039] Preparation of initial epoxidation catalyst solution

[0040] A mixture of 100 g of 70 wt% hydrogen peroxide, 155 g of demineralized water, 160 g of 85 wt% phosphoric acid, and 100 g of sodium tungstate dihydrate was stirred at room temperature for 2 hours. A solution of 150 g of methyltri(octyl / decyl)ammonium methylsulfate (CAS No. 2387913-24-6) in 1020 g of Hydrosol A200ND (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 1230 g of the organic phase as the initial epoxidation catalyst solution.

[0041] Reaction of propylene with hydrogen peroxide

[0042] 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 -1The reactor was operated at a circulation rate of 1000 kg / min. 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 a mixture of 100 g of 70 wt% hydrogen peroxide, 155 g of demineralized water, 160 g of 85 wt% phosphoric acid, and 20 g of sodium tungstate dihydrate was charged to the organic phase collection vessel. The loop initially contained the reaction mixture from a previous experiment. The circulation was started and maintained at 130 kg / min. -1 , and the circulating mixture was heated to 80°C. Then, 80 g h -1 Propylene, 50g h -1 Propane, aqueous hydrogen peroxide solution containing 0.1 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 concentration and feed rate of the hydrogen peroxide solution were varied in the three examples to the values ​​given in Table 1. 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 phase and aqueous phase 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 for 5 minutes, the phases were separated by sedimentation, and the organic phase was transferred to a catalyst feed reservoir, wherein the aqueous phase remained in the organic phase collection container. After approximately 11 hours of operation, the feed of the reactants and the circulation in the loop reactor were stopped, and 0.33 g of sodium tungstate dihydrate was loaded into the organic phase collection container to compensate for the loss. The next day, the circulation in the loop reactor was restarted, and the dosing of the reactants was resumed after the reaction temperature had been established in the loop reactor, and the reaction was allowed to continue for another 11 hours. 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., a ramp rate of 10 K / min to 220° C. and a ramp rate of 5 K / min to 235° C., FID detector) and 1 The organic products of the aqueous phase separated from the oxidation reaction mixture were analyzed by H-NMR. Table 2 shows the analytical data obtained after steady-state operation was achieved.

[0043] Table 1 Concentration and feed rate of hydrogen peroxide solution and weight ratio of hydrogen peroxide to water fed to the reactor

[0044] Example <![CDATA[H2O2 concentration (wt%)]]> <![CDATA[H2O2 feed rate (g / h)]]> <![CDATA[Weight ratio of H2O2 to water]]> 1 30,0 116 0.429 2 25,0 139 0.334 3 15,0 210 0.177

[0045] Table 2 Composition of the aqueous phase (all values ​​are in weight %, except the MPG / DPG ratio)

[0046] Example <![CDATA[H2O2]]> <![CDATA[MPG 1 ]]> <![CDATA[DPG 2 ]]> <![CDATA[TPG 3 ]]> Hydroxyacetone Acetic acid MPG / DPG ratio 1 0.4 27.1 6.2 1.0 0.6 0.2 4.37 2 0.3 24.2 5.0 1.0 0.6 0.2 4.84 3 0.2 18.3 2.3 0.2 0.3 0.1 7.96

[0047] 1 1,2-Propanediol

[0048] 2 Dipropylene glycol

[0049] 3 Tripropylene glycol

[0050] From the data in Table 2, it is apparent that the ratio of 1,2-propylene glycol to dipropylene glycol increases as the weight ratio of hydrogen peroxide to water fed to the reactor decreases. Acetic acid formation increases only slightly with increasing hydrogen peroxide concentration, resulting in slightly reduced selectivity. Thus, it is apparent that the weight ratio of 1,2-propylene glycol to dipropylene glycol can be controlled by adjusting the weight ratio of hydrogen peroxide to water fed to the reactor without compromising the selectivity of the reaction.

Claims

1. A method for preparing 1,2-propylene glycol and dipropylene glycol, the method comprising: a) reacting propylene with hydrogen peroxide in the presence of a catalyst mixture comprising a phase transfer catalyst and a heteropolytungstate in a liquid reaction mixture comprising an aqueous phase having a maximum apparent pH of 6 and an organic phase to obtain 1,2-propylene glycol and dipropylene glycol; b) separating the reaction mixture into an aqueous phase comprising 1,2-propylene glycol and dipropylene glycol and an organic phase; c) recycling at least a portion of the separated organic phase to reaction step a); and d) recovering 1,2-propylene glycol and dipropylene glycol from the separated aqueous phase; wherein the heat of reaction generated in step a) is at least partially removed, and the ratio of 1,2-propylene glycol to dipropylene glycol is controlled by adjusting the weight ratio of hydrogen peroxide to water fed to step a), wherein the weight ratio of hydrogen peroxide to water varies within the range of 0.05 to 1.5, wherein the ratio of 1,2-propylene glycol to dipropylene glycol is reduced by increasing the weight ratio of hydrogen peroxide to water fed to step a), or the ratio of 1,2-propylene glycol to dipropylene glycol is increased by reducing the weight ratio of hydrogen peroxide to water fed to step a).

2. The process of claim 1 , wherein 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.

3. The process of claim 2, wherein the molar ratio of propylene to hydrogen peroxide fed to step a) is from 1.1:1 to 10:

1.

4. The process of claim 3, wherein the molar ratio of propylene to hydrogen peroxide fed to step a) is from 1.2:1 to 4:

1.

5. The method of any one of claims 1 to 4, wherein the weight ratio of hydrogen peroxide to water ranges from 0.10 to 0.

7.

6. The method of claim 5, wherein the weight ratio of hydrogen peroxide to water ranges from 0.15 to 0.

45.

7. The method according to any one of claims 1 to 4, wherein the concentration of hydrogen peroxide in the aqueous phase in step a) is 0.1 to 5% by weight.

8. The method of claim 7, wherein the concentration of hydrogen peroxide in the aqueous phase in step a) is 0.12-1.0 wt%.

9. The process according to any one of claims 1 to 4, wherein the residence time of the reaction mixture in step a) is adjusted so that the hydrogen peroxide conversion is maintained in the range of 80-99%.

10. The process according to any one of claims 1 to 4, wherein step a) is carried out in a loop reactor and the heat of reaction generated in step a) is at least partially removed by circulating the reaction mixture through a heat exchanger.

11. The process according to any one of claims 1 to 4, wherein the aqueous phase obtained in step b) is further processed without recycling any part of the aqueous phase directly or indirectly to step a).

12. The method according to any one of claims 1 to 4, wherein In step d), the aqueous phase is subjected to catalytic hydrogenation.

13. The method of any one of claims 1 to 4, wherein step a) is carried out in the presence of phosphoric acid, and the heteropolytungstate is a polytungstate phosphate.

14. The process of any one of claims 1 to 4, 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.

15. The method of claim 14, wherein the organic solvent is selected from alkylated aromatic hydrocarbons having 8 to 12 carbon atoms.

16. The process of any one of claims 1 to 4, wherein the phase transfer catalyst is selected from tertiary amines and tertiary or quaternary ammonium salts and contains at least 12 carbon atoms in total.

17. The method of claim 16, 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.

18. The method of any one of claims 1 to 4, wherein step b), step c) and step d) are performed continuously.