Improved process for the preparation of 1,2-alkanediols from the corresponding alkenes and hydrogen peroxide

Abstract

The present invention relates to a process for the preparation of 1,2-alkanediols from the corresponding alkenes and hydrogen peroxide without the need for isolation and purification of the intermediate alkene oxide.

Description

[Technical field]

[0001] The present invention relates to a process for the production of 1,2-alkanediols from the corresponding alkenes and hydrogen peroxide without the need for isolation and purification of the intermediate alkene oxide. [Background technology]

[0002] 1,2-alkanediols, such as propylene glycol, are conventionally prepared on an industrial scale by first oxidizing an alkene to the corresponding alkene oxide, which is then isolated, purified, and then converted to the corresponding 1,2-alkanediol by hydrolysis.

[0003] US Patent 10,214,471 B2 relates to a method for the direct production of 1,2-propanediol from propene and hydrogen peroxide using a combination of a phase transfer catalyst and a heteropolytungstate in a two-phase reaction mixture, which does not require isolation and purification of the intermediate propene oxide, resulting in reduced equipment costs. In the first step of the described continuous process, an alkene is reacted with hydrogen peroxide in a liquid two-phase system containing an aqueous phase and an organic phase with a pH of up to 6 in the presence of a catalyst mixture containing a phase transfer catalyst and a heteropolytungstate. In the second step, the organic phase containing the propene oxide is separated from the aqueous phase and recycled to the reaction mixture of the first step, and 1,2-propanediol is separated from the aqueous phase obtained in the second step. Various phase transfer catalysts, including tertiary amines, and tetraalkylammonium salts, such as trimethylamine, and dodecyltrimethylammonium salts, are described in US Patent 10,214,471 B2. For example, Example 9 of US Pat. No. 10,214,471 describes a continuous process for the preparation of 1,2-propanediol from propene and hydrogen peroxide using trioctylamine in an aqueous phase in 52% yield.

[0004] J. Kaur et al. reported that in the presence of methyltrioctylammonium chloride as a surfactant, 2 WO4 , H 2 O 2 and H 3 PO 4 describe the epoxidation of propene with hydrogen peroxide in microemulsions or biphasic solvent mixtures, catalyzed by peroxopolytungstophosphates prepared by interaction with tungstophosphate (Catal. Commun. 2004, 5, 709-713, DOI: 10.1016 / J.catcom.2004.09.004).

[0005] C. Venturello et al. describe a method for epoxidizing olefins such as 1-octene and cyclohexene using hydrogen peroxide in the presence of a polytungstophosphate catalyst and a tetraalkylammonium phase transfer catalyst (e.g., methyltrioctylammonium chloride) in a two-phase solvent mixture (J. Org. Chem., 1983, 48, 3831-3833).

[0006] The formation of stable emulsions is sometimes observed in the two-phase processes described above, making the step of separating the aqueous and organic phases time- and energy-consuming.

[0007] It is therefore an object of the present invention to provide an improved two-phase process for the production of 1,2-alkanediols, such as 1,2-propanediol, from the corresponding alkenes, which avoids the above-mentioned disadvantages of the prior art processes.

[0008] Surprisingly, it has been found that the use of certain tetraalkylammonium cations in a biphasic reaction mixture avoids the formation of stable emulsions without compromising the efficiency, yield or selectivity of the epoxidation process. The tetraalkylammonium cations have the general formula N + R 1 R 2 R 3 R 4 R 1 , R 2 , R 3 and R 4may be independently the same or different, R 1 , R 2 , R 3 and R 4 are all the same, the tetraalkylammonium cation has a total of at least 32 carbon atoms in the alkyl groups, or 1 , R 2 , R 3 and R 4 When at least one of is different from the others, the tetraalkylammonium cation has a total of at least 37 carbon atoms in the alkyl groups. Summary of the Invention

[0009] The present invention therefore relates to a process for preparing 1,2-alkanediols from the corresponding alkenes and hydrogen peroxide, the process comprising: a) reacting an alkene with hydrogen peroxide in the presence of catalytic amounts of at least one tungsten trioxometalate and at least one tetraalkylammonium cation; wherein the reaction is carried out in a biphasic reaction mixture comprising an aqueous phase having a pH of up to 6 and an organic phase, and the tetraalkylammonium cation is of the general formula N + R 1 R 2 R 3 R 4 R 1 , R 2 , R 3 and R 4 are each independently the same or different alkyl groups, R 1 , R 2 , R 3 and R 4 are all the same, the tetraalkylammonium cation has a total of at least 32 carbon atoms in the alkyl groups, or 1 , R 2 , R 3 and R 4When at least one of the groups is different from the others, the tetraalkylammonium cation has a total of at least 37 carbon atoms in the alkyl group. b) separating the biphasic mixture from step a) into an aqueous phase P1 and an organic phase P2; c) optionally recycling any alkene oxides that may be present in the separated organic phase P2 to reaction step a), d) separating 1,2-alkanediols from the aqueous phase P1 separated in step b); Includes. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 shows phase separation of a two-phase mixture according to the invention using tetraoctylammonium as the tetraalkyl cation and mesitylene as the organic solvent at ambient temperature, recording the interfacial level (mL) of the organic phase (upper curve) and the aqueous phase (lower curve) over time (min) (Example 1).

[0011] [Diagram 2] FIG. 2 shows the phase separation of a two-phase mixture according to the invention using tetraoctylammonium as the tetraalkyl cation and Hydrosol A200ND as the organic solvent at ambient temperature, recording the interfacial level (mL) of the organic phase (upper curve) and the aqueous phase (lower curve) over time (min) (Example 2).

[0012] [Diagram 3] FIG. 3 shows phase separation of a two-phase mixture according to the invention using tetradecylammonium as the tetraalkyl cation and mesitylene as the organic solvent at ambient temperature, recording the interfacial level (mL) of the organic phase (upper curve) and the aqueous phase (lower curve) over time (min) (Example 3).

[0013] [Figure 4]FIG. 4 shows phase separation of a two-phase mixture according to the invention using tridodecylmethylammonium as the tetraalkyl cation and mesitylene as the organic solvent at ambient temperature, recording the interfacial level (mL) of the organic phase (upper curve) and the aqueous phase (lower curve) over time (min) (Example 4).

[0014] [Diagram 5] FIG. 5 shows phase separation of a comparative two-phase mixture using methyltrialkyl(C8-C10)ammonium as the tetraalkyl cation and mesitylene as the organic solvent at ambient temperature, recording the interfacial level (mL) of the organic phase (top curve) and aqueous phase (bottom curve) over time (min) (Comparative Example 5).

[0015] [Figure 6] FIG. 6 shows phase separation of a comparative two-phase mixture using methyltrialkyl(C8-C10)ammonium as the tetraalkyl cation and mesitylene as the organic solvent at 50° C., recording the interfacial level (mL) of the organic phase (top curve) and aqueous phase (bottom curve) over time (min) (Comparative Example 6).

[0016] [Figure 7] FIG. 7 shows phase separation of a comparative two-phase mixture using methyltrialkyl(C8-C10)ammonium as the tetraalkyl cation and Hydrosol A200ND as the organic solvent at ambient temperature, recording the interfacial level (mL) of the organic phase (upper curve) and aqueous phase (lower curve) over time (min) (Comparative Example 7).

[0017] [Figure 8] FIG. 8 shows the molar % yield of 1,2-propanediol obtained in the epoxidation / hydrolysis process according to the invention (Example 8) as a function of reaction time (min).

[0018] [Figure 9]FIG. 9 shows the molar % yield of 1,2-propanediol obtained in the epoxidation / hydrolysis process according to the invention (Example 9) as a function of reaction time (min).

[0019] [Figure 10] FIG. 10 shows the molar % yield of 1,2-propanediol obtained in the epoxidation / hydrolysis process according to the invention (Example 10) as a function of reaction time (min). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] As used herein, the term "comprising" and variations thereof are used synonymously with the terms "including", "containing" and variations thereof, and are understood to be open-ended, non-limiting terms that do not exclude the presence of additional unrecited or unlisted elements, compounds, ingredients, or method steps. As used herein, the term "consisting of" is understood to exclude the presence of unspecified elements, compounds, ingredients, or method steps. When the open-ended terms "comprising", "including" or "containing" are used herein, the term "consisting of" is included. For example, a method described as "comprising" or "including" a particular step can consist of the explicitly recited step or can further include one or more unrecited steps. The same can be applied, for example, to compositions and their corresponding explicitly recited or unrecited ingredients.

[0021] As used herein, the term “alkene” refers to an alkene having the general formula C n H 2n or an unsaturated (having a carbon-carbon double bond) acyclic branched or unbranched hydrocarbon of the general formula C n H 2n-2It is understood that the alkene is a cyclic hydrocarbon of the formula: Suitable alkenes include, but are not limited to, propene, butene, hexene, octene, and cyclohexene. The alkene may preferably be propene.

[0022] As used herein, the term “alkyl” refers to a group having the general formula C n H 2n+1 and is understood to mean an acyclic, saturated, branched or unbranched, preferably unbranched, group consisting of hydrogen and carbon. The alkyl group may be substituted or unsubstituted, but is preferably unsubstituted.

[0023] Unless otherwise specified, ambient temperature means room temperature (23° C.).

[0024] In step a) of the process of the present invention, an alkene is reacted with hydrogen peroxide in the presence of catalytic amounts of at least one tungsten trioxometalate and at least one tetraalkylammonium cation. The reaction is carried out in a liquid mixture comprising two liquid phases, an aqueous phase having a pH of up to 6, and an organic phase.

[0025] The alkene can be used in pure form or in a mixture with the corresponding alkane, where the proportion of alkane can be up to 20 mol %, but is preferably less than 5 mol %, based on the total amount of alkene and alkane.

[0026] Hydrogen peroxide can be preferably used in the form of an aqueous solution, and the hydrogen peroxide content is preferably 10-80% by weight, particularly preferably 30-70% by weight, based on the total weight of the aqueous hydrogen peroxide solution. Hydrogen peroxide can be prepared by any conceivable method, including, but not limited to, the anthraquinone method. For example, the crude hydrogen peroxide product obtained in the extraction stage of the anthraquinone method for producing hydrogen peroxide can be used.

[0027] During the course of the reaction, the aqueous phase contains water, unreacted hydrogen peroxide, and 1,2-alkanediol formed during the reaction. The organic phase contains the alkene and the alkene oxide formed as an intermediate. When a mixture of an alkene and its corresponding alkane, such as propene and propane, is used, the organic phase can further contain an alkane. Additionally, the organic phase may contain at least one solvent that is immiscible with water.

[0028] The reaction mixture of the present invention comprises a tungsten polyoxometalate, preferably a heteropolytungstate. The heteroatom of the heteropolytungstate may preferably be phosphorus or arsenic, particularly preferably phosphorus, i.e. the heteropolytungstate may particularly preferably be a polytungstophosphate. Particularly preferred are polytungstophosphates having a molar ratio of phosphorus to tungsten in the range of 1:2 to 1:12. A preformed tungsten polyoxometalate may be added to the reaction of step a) or the tungsten polyoxometalate may be generated in situ in the liquid reaction mixture of step a). For example, the polytungstophosphate may be generated in situ from preferably phosphoric acid and a water-soluble alkaline tungstate, preferably sodium tungstate, where the phosphoric acid and the alkaline tungstate may preferably be used in a molar ratio of phosphorus to tungsten in the range of 1:2 to 10:1, particularly 3:1 to 8:1. Peroxotungstates and peroxotungstophosphates, such as PO 4 [WO(O 2 ) 2 ] 4 3- and H.P.O. 4 [WO(O 2 ) 2 ] 2 2- as well as their partially protonated forms are formed from polytungstophosphates combined with hydrogen peroxide in the aqueous phase.

[0029] The reaction mixture used in the process according to the invention further comprises at least one tetraalkylammonium cation. The tetraalkylammonium cation has the general formula N + R 1 R 2 R 3 R 4 R 1 , R 2 , R 3 and R 4 are each independently the same or different alkyl groups, R 1 , R 2 , R 3 and R 4 are all the same, the tetraalkylammonium cation has a total of at least 32 carbon atoms in the alkyl groups, or 1 , R 2 , R 3 and R 4 When at least one of R is different from the others, the tetraalkylammonium cation has a total of at least 37 carbon atoms in the alkyl group. When a mixture of different tetraalkylammonium cations is used, the average number of total carbon atoms is also preferably at least 37 carbon atoms in the alkyl group. 1 , R 2 , R 3 and R 4 is at least 32 for the tetraalkylammonium cations where all of R 1 , R 2 , R 3 and R 4 is at least 37 for tetraalkylammonium cations where at least one of them is different from the others.

[0030] R 1 , R 2 , R 3 and R 4 If at least one of is different from the others, then R 1 is preferably CH 3 and R 2 , R 3 and R 4 are identical, preferably identical C 12 -C18 R is an alkyl group. 1 , R 2 , R 3 and R 4 If all of are identical, then R 1 , R 2 , R 3 and R 4 Each of the preferably identical C 8 -C 18 The tetraalkylammonium cation may include a tetraalkylammonium cation including at least one of tetraoctylammonium, tetradodecylammonium, tridodecylmethylammonium, or a mixture thereof.

[0031] Tetraalkylammonium cations are capable of forming organic phase soluble salts with tungsten trioxometalates.

[0032] The tetraalkylammonium cation may be added to the reaction in the form of a quaternary tetraalkylammonium salt having an anion different from the tungsten trioxometalate, such as, but not limited to, a tetraalkylammonium halide (e.g., chloride, bromide or iodide), sulfate or methyl sulfate. When using a salt having methyl sulfate as the anion, the corrosivity of the reaction mixture can be reduced compared to tetraalkylammonium halides. The tungsten trioxometalate and the tetraalkylammonium salt can be fed to the reaction in step a) as a mixture or separately from each other, with separate feeding being preferred. However, it is also possible to add a preformed quaternary tetraalkylammonium tungsten trioxometalate, where the tungsten trioxometalate represents the counterion of the quaternary tetraalkylammonium cation.

[0033] The tetraalkylammonium cation may be used in an amount that preferably results in a molar ratio of tetraalkylammonium cation to tungsten in the liquid mixture in the range of 1:1 to 3:1.

[0034] The reaction of the alkene with hydrogen peroxide is carried out under an aqueous phase pH of up to 6. The pH of the aqueous phase can be preferably maintained in the range of 1.0 to 3.5, particularly preferably in the range of 2.0 to 3.0, measured at room temperature. The pH can be maintained in this range by the addition of an acid, preferably sulfuric acid or phosphoric acid, or by the addition of a base, preferably aqueous sodium hydroxide. Here, the term pH refers to the apparent pH measured with a glass electrode, which is calibrated with an aqueous buffer solution. By adjusting the pH to the preferred range, a high selectivity for 1,2-alkanediols can be achieved and the concentration of the corresponding alkene oxide in the aqueous phase can be prevented, which simplifies the subsequent separation of the 1,2-alkanediols from the aqueous phase.

[0035] The reaction of the alkene with hydrogen peroxide is preferably carried out using a molar excess of the alkene, and the alkene is preferably used in a molar ratio of alkene to hydrogen peroxide of from 1.1:1 to 10:1.

[0036] The reaction can be carried out at a temperature preferably in the range of 30 to 100° C., particularly preferably 70 to 90° C. The reaction can be carried out at a pressure higher than the saturated vapor pressure of the alkene at the temperature of the reaction, such that the majority of the alkene is present in the organic phase of the liquid mixture.

[0037] The reaction of the alkene with hydrogen peroxide can be carried out with or without the addition of a solvent. The reaction can be carried out in the presence of at least one solvent, preferably with a boiling point above 100° C., preferably above 120° C., and a water solubility at 20° C. of less than 0.5 g / kg, preferably less than 250 mg / kg. The solvent used can be a halogenated hydrocarbon, such as 1,2-dichloroethane, and / or an aromatic hydrocarbon, such as an alkylated aromatic hydrocarbon. It may be preferred that neither the solvent nor any other compound present in the reaction mixture of step a) contains an ester functional group. The solvent can comprise or be an aromatic hydrocarbon, such as an alkylated aromatic hydrocarbon, preferably having 7 to 12 carbon atoms, or a mixture of such alkylated aromatic hydrocarbons. Suitable alkylated aromatic hydrocarbons are, for example, toluene, 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-methylbenzene, 1-ethyl-3-methylbenzene, 1-ethyl-4-methylbenzene, n-propylbenzene, and 1,2,3,4-tetrahydronaphthalene, as well as mixtures thereof. Preferably, as solvent, a mixture of hydrocarbons can be used, which comprises more than 50% by weight, preferably more than 80% by weight, of alkylated aromatic hydrocarbons having 7 to 12 carbon atoms, based on the total weight of the solvent mixture. By using a solvent containing an alkylated aromatic hydrocarbon having 7 to 12 carbon atoms, the heteropolytungstate can be extracted in large quantities into the organic phase of the reaction mixture in the form of a tetraalkylammonium complex, so that the recycling of the heteropolytungstate together with the organic phase in the reaction of the alkene with hydrogen peroxide can be improved, and the heteropolytungstate can be easily recovered from the aqueous phase.

[0038] The proportion of the solvent may be selected such that the proportion of the solvent in the organic phase during the reaction is preferably in the range of 10 to 90% by weight based on the total weight of the organic phase.

[0039] The reaction of the alkene with hydrogen peroxide can be carried out batchwise or continuously, with a continuous process being preferred. In a continuous process, the concentration of hydrogen peroxide in the aqueous phase can be in the range of 0.1 to 5% by weight, particularly preferably 0.5 to 3% by weight, based on the total weight of the aqueous phase. Such a concentration of hydrogen peroxide can be adjusted by the selection of the reaction temperature, the molar ratio of alkene to hydrogen peroxide, and the residence time of the liquid mixture in the reactor in which the reaction is carried out.

[0040] During the reaction, it is preferable to mix the liquid mixture in order to generate many phase interfaces between the aqueous phase and the organic phase. For this purpose, the reaction is preferably carried out continuously in a loop reactor having a fixed internal structure, the liquid mixture being led through the loop reactor at a flow rate that generates turbulence on the internal structure. A loop reactor suitable for continuously carrying out the process of the present invention is described in detail in US Pat. No. 10,214,471, specification B2, in particular in figures 1-4 and column 9, line 42 to column 10, line 51.

[0041] In step b) of the process of the invention, the biphasic reaction mixture from step a) is separated into an aqueous phase P1 and an organic phase P2. Separation may be preferably carried out in a settling tube and may be assisted by passing the biphasic mixture through a coalescer element comprising structured or random packing having a surface wetted by the phase dispersed in the biphasic mixture.

[0042] The liquid phase can preferably be separated in the presence of a gas phase in step b). The reaction in step a) can result in the decomposition of hydrogen peroxide with the formation of oxygen, so that in step b) the gas phase can contain oxygen. Therefore, in order to avoid the formation of a flammable gas phase, the oxygen content of this gas phase is preferably maintained below 7% by volume in step b), preferably by feeding an inert gas and withdrawing a gas stream. The inert gas used can be nitrogen, argon, carbon dioxide or methane, preferably nitrogen.

[0043] If present, in optional step c) of the process of the invention, the alkene oxide present in the organic phase P2 is recycled to the reaction of step a) in order to achieve as complete a conversion of the alkene to 1,2-alkanediol as possible. If the steps of the invention are carried out continuously, step c) is preferably present. Preferably, the tungsten trioxometallate present in the organic phase P2 can be further recycled to the reaction of step a). Similarly, the alkene present in the organic phase P2 can preferably be recycled to the reaction of step a). If the alkene is used as a mixture with the corresponding alkane, the same amount of alkane is preferably separated from the organic phase P2 in the recycle to step a) and is fed to step a) together with the mixture of alkene and alkane. In this way, if the reaction in step a) is carried out continuously, the concentration of the alkane in the organic phase in step a) can be avoided.

[0044] In a preferred embodiment of the process according to the invention, the organic phase P2 separated in step b) can be fully or partially recycled to the reaction in step a).

[0045] The organic phase P2 may be separated, completely or partially, preferably by nanofiltration in step c), into a retentate enriched in tungsten trioxometallates and a permeate depleted in tungsten trioxometallates, the retentate being recycled to the reaction in step a). Preferably, the total organic phase P2 may be separated into a retentate and a permeate by nanofiltration. For the nanofiltration in step c), a nanofiltration membrane may be used that retains the tungsten trioxometallates and tetraalkylammonium cations in the retentate and allows the alkene to pass with the permeate. The nanofiltration may then be preferably operated such that the concentration of the tungsten trioxometallates and tetraalkylammonium cations in the retentate does not increase above the saturation concentration. As used herein, the term "nanofiltration" refers to pressure-driven separation at a membrane, where the membrane retains particles and dissolved molecules with a diameter of less than 2 nm. Membranes based on the polymers polyimide, polyethersulfone, polyamide and polydimethylsiloxane may be used for nanofiltration. Suitable nanofiltration membranes are commercially available, for example, from Evonik Membrane Extraction Technology MET under the name PuraMem® S600, from GMT Membrantechnik under the names ONF-2, from SolSep under the numbers 010306, 030306, 030705 and 030306F, and from AMS Technologies under the name NanoPro™ SX. It is preferable to use one of the composite membranes known from DE 19507584 A1, EP 1741481 A1 and WO 2011 / 067054 A1.

[0046] Nanofiltration can preferably be carried out as cross-flow filtration, preferably at temperatures in the range from 20 to 90° C., particularly preferably from 40 to 80° C. The transmembrane pressure can preferably be in the range from 2 to 5 MPa. The retentate side pressure can be up to 10 MPa. The permeate side pressure can preferably be chosen to be higher than the minimum pressure in steps a) and b) of the process, in order to prevent outgassing of dissolved components on the permeate side.

[0047] The organic phase P2 may also be separated by nanofiltration into a retentate enriched in tungsten trioxometallate and a permeate depleted in tungsten trioxometallate, and a stream S1 containing unreacted alkenes and alkene oxides formed as intermediates may be separated from the permeate by distillation, and this stream may be recycled to the reaction of step a). The distillation may be carried out at a pressure that allows the alkene to be condensed with the distillate, preferably by cooling with water. Alternatively, the distillation may be carried out at a low pressure, allowing only the alkene oxides and a portion of the alkenes to be condensed with the distillate, and the remaining vapors to be compressed to condense the alkenes. In this embodiment, the high-boiling by-products and decomposition products of the phase transfer catalyst may be discharged with the bottom product of the distillation, avoiding the concentration of poorly water-soluble by-products and impurities in the organic phase in step a) when the reaction in step a) is carried out continuously. The removal of stream S1 by distillation after nanofiltration prevents further reaction of the alkene oxides formed as intermediates with the catalyst system by heating, which would result in by-products.

[0048] In step a) of the process, if the reaction is carried out in the presence of a solvent, the bottom product of this distillation, following the distillation to separate stream S1, is preferably fed to a further distillation, in which the solvent is separated by distillation. The separated solvent can be recycled to step a). If an alkene is used as a mixture with the corresponding alkane, the distillation can preferably be carried out so that, in addition to stream S1, a further stream is obtained which essentially consists of alkenes and alkanes, from which the alkene oxide is separated. The alkane can be completely or partially separated from this further stream, and the resulting alkene obtained, separated or depleted of alkanes, can preferably be recycled to step a). In this case, it is preferred to remove the same amount of alkane and feed it to step a) together with the mixture of alkene and alkane. The distillation of the permeate can be carried out for this purpose in two stages, in a first distillation stage a further stream consisting mostly of alkenes and alkanes is separated, and then stream S1 is separated in a second distillation stage. However, it is preferred that the distillation is carried out in only one column equipped with a side draw, with stream S1 being removed as a side stream and a further stream consisting essentially of alkenes and alkanes being removed as the overhead product of the column.

[0049] The organic phase P2 may also be separated by distillation into a stream S1 containing unreacted alkenes and alkene oxides formed as intermediates and a stream S2 depleted in alkenes and alkene oxides, which may be separated by nanofiltration into a retentate enriched in heteropolytungstates and a permeate depleted in tungsten trioxometallates, and stream S1 may be recycled to the reaction of step a). This embodiment is preferably used when the reaction in step a) of the method is carried out in the presence of a solvent and then a distillation is carried out so that the solvent remains in stream S2. The solvent may then be removed from the permeate of the nanofiltration, preferably by distillation, and then recycled to the reaction of step a).

[0050] Compared to the above-mentioned embodiment, the embodiment of separating stream S1 before nanofiltration has the advantage that a considerably smaller stream is separated by nanofiltration, which reduces the size of the apparatus and the energy consumption of nanofiltration. If an alkene is used as a mixture with an alkane, in this embodiment, preferably before stream S1 is recycled to step a), a further stream may be separated by distillation from stream S1, which essentially consists of an alkene and an alkane and from which an alkene oxide is separated. The alkane may be completely or partially separated from this further stream, and the resulting alkene obtained, separated or depleted of the alkane is preferably recycled to step a). In this case, it is preferable to separate the same amount of alkane and feed it to step a) together with the mixture of the alkene and the alkane. For a continuous process including step c), reference is made to US Pat. No. 10,214,471 B2, in particular the figures and passages already cited above.

[0051] In step d) of the process of the invention, 1,2-alkanediols are separated from the aqueous phase P1 separated in step b). The 1,2-alkanediols can be separated from the aqueous phase by distillation, preferably by a two-stage distillation, in which water is distilled off in a first stage and the 1,2-alkanediols are distilled off in a second stage from the bottom product of the first stage.

[0052] Prior to the separation of the 1,2-alkanediol, the hydrogen peroxide can be preferably removed by catalytic hydrogenation. The hydrogenation can be preferably carried out 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, where the support can be activated carbon, SiO 2 , TiO 2 , ZrO 2 , Al 2 O 3and aluminum silicate may be preferred. Hydrogenation catalysts containing ruthenium as active metal are preferred. Catalytic hydrogenation can be carried out preferably at hydrogen partial pressures of 5 to 300 bar and at temperatures of 80°C to 180°C, preferably 90°C to 150°C. The hydrogenation catalyst can be used as a suspension or as a fixed bed, trickle-bed hydrogenation with a fixed-bed catalyst being preferred. Hydrogenation can prevent problems due to decomposition of hydrogen peroxide in the separation of 1,2-alkanediols by distillation and reduce the by-products 1-hydroperoxy-2-alkanol, 2-hydroperoxy-1-alkanol and 1-hydroxy-2-alkanone formed in step a) to 1,2-alkanediols, thereby improving the yield of 1,2-alkanediols.

[0053] In step d) of the method of the invention, the aqueous phase P1 may be separated, preferably by nanofiltration, into a tungsten trioxometalate-enriched retentate and a tungsten trioxometalate-depleted permeate, where the retentate may be recycled to the reaction in step a) and the 1,2-alkanediol is separated from the permeate. For the nanofiltration in step d), a nanofiltration membrane may be used that retains the tungsten trioxometalate in the retentate and allows water and 1,2-propanediol to pass through with the permeate. The nanofiltration may be operated such that the solubility limit of the tungsten trioxometalate in the retentate is not exceeded. For the continuous reaction in step a), preferably most of the water together with the retentate is recycled to step a) and the concentration of the 1,2-alkanediol in the aqueous phase P1 is in the range of 10-30% by weight. By suitable recycling of water, on the one hand the formation of 1,1'-oxydi-2-alkanols and trialkylene glycols in step a) can be prevented and, on the other hand, the amount of water which has to be separated from the 1,2-alkanediols by distillation can be kept low.

[0054] In addition to or as an alternative to nanofiltration, the tungsten trioxometalate can be removed from the aqueous phase P1 by adsorption onto a support material. For such adsorption, it is preferable to use a cationized inorganic support material as described on page 7, line 1 to page 8, line 29 of WO 2009 / 133053 A1. The adsorption onto the support material and the recovery of the tungsten trioxometalate adsorbed onto the support material can preferably be carried out using the methods described in WO 2009 / 133053 A1 and WO 2013 / 110419 A1. If adsorption is used in addition to nanofiltration in step d), in order to keep the demand for support material low, the adsorption can preferably be carried out after the nanofiltration.

[0055] In order to avoid deactivation of the hydrogenation catalyst by the tungsten trioxometallates, nanofiltration and adsorption onto a support material may preferably be carried out prior to said hydrogenation.

[0056] In a preferred embodiment of the process according to the invention, the aqueous phase P1 separated in step b) can be contacted in step d) with a liquid alkene to obtain an aqueous phase P3 and an organic phase P4, the organic phase P4 can be recycled to the reaction in step a) and the 1,2-alkanediol is separated from the aqueous phase P3. In this embodiment, preferably no separation of tungsten from the aqueous phase P1 is performed, preferably tungsten is separated from the aqueous phase P3 by nanofiltration and / or adsorption, as described above for the aqueous phase P1. The aqueous phase P1 is contacted with the alkene, preferably in an additional mixing reactor, with a residence time in the reactor, which results in a conversion of the hydrogen peroxide present in the aqueous phase of at least 50%, preferably at least 80%. The contacting in the additional reactor is preferably carried out at a temperature of 60 to 100 ° C and at a pressure above the saturated vapor pressure of the alkene at the selected temperature. The aqueous phase P1 can be contacted with the alkene, preferably in a continuously operated reactor, particularly preferably in a loop reactor. By using additional reactors operated in series, high conversions of hydrogen peroxide can be achieved with lower overall reactor volumes.

[0057] Here, the alkene is preferably fed to the process only in step d) and is brought into the reaction of step a) together with the organic phase P4. If tetraalkylammonium cations are used in the process to transfer more than half of the tungsten from the aqueous phase to the liquid alkene in the presence of hydrogen peroxide, the aqueous phase P1 can also be contacted with the liquid alkene in a countercurrent extraction, preferably in a countercurrent extraction column, and the tungsten present in the aqueous phase P1 is then recycled to step a) together with the organic phase P4. EXAMPLES

[0058] I. Phase separation experiments: Examples 1 to 4 and Comparative Examples 5 to 7: To study the phase separation behavior of the two-phase epoxidation reaction mixture, an aqueous solution A containing a 1,2-alkanediol and an organic solution D containing an epoxidation catalyst and a tetraalkylammonium salt were prepared and mixed as described below. Phase separation after mixing was observed by recording the volumes of the separated organic and aqueous layers over time. The results are shown in Table 1 and Figures 1 to 7.

[0059] Preparation of aqueous solution A: A solution of 1,2-propanediol (20 wt %) and phosphoric acid (0.06 wt %) in HPLC grade demineralized water was prepared by mixing.

[0060] Preparation of POM catalyst solution B: Sodium tungstate dihydrate (13.0 g, 39.4 mmol) was dissolved in HPLC grade demineralized water (62.4 g). The solution was stirred at ambient temperature with a PFTE coated magnetic stir bar and 85% phosphoric acid (20.8 g, 0.181 mol) was slowly added.

[0061] Preparation of tetraalkylammonium solution C: Each tetraalkylammonium salt (see Table 1) (10 mmol) was dissolved in an organic solvent (60 g).

[0062] Preparation of Tetraalkylammonium / POM Catalyst Solution D: The total tetraalkylammonium solution C was combined with 22.2 g of POM catalyst solution B. The resulting two-phase solution was mixed at ambient temperature for 15 minutes using a PFTE coated magnetic stir bar. The phases were allowed to separate and the organic phase was collected and used in the phase separation experiments described below.

[0063] Experimental procedure for phase separation experiments: Equal volumes of tetraalkylammonium / POM catalyst solution D and aqueous solution A were placed in a 100 mL graduated cylinder with a 29 / 42 ground glass joint on top. The contents were mixed at ambient temperature by manually inverting the cylinder and returning it to an upright position five times.

[0064] [Table 1]

[0065] When methyltrialkylammonium salts having a total of less than 32 carbon atoms in the alkyl group are used as phase transfer catalysts, the formation of stable emulsions is observed (Comparative Examples 5-7). The aqueous and organic phases separate slowly, regardless of the temperature and organic solvent used. Surprisingly, the general formula N + R 1 R 2 R 3 R 4 The formation of stable emulsions can be avoided and the time required to achieve complete phase separation can be significantly reduced when using a tetraalkylammonium salt having the formula: 1 , R 2 , R 3 and R 4 are the same, the tetraalkylammonium cation has at least 32 carbon atoms in total in the alkyl group, such as tetraoctylammonium or tetradecylammonium (Examples 1-3), or 1 , R 2 , R 3 and R 4When at least one of is different from the others, the tetraalkylammonium cation has a total of at least 37 carbon atoms in the alkyl group, such as tridodecylmethylammonium (Example 4).

[0066] II. Epoxidation / Hydrolysis Experiments: Example 8: A 1 L jacketed glass reactor containing a dual pitched blade impeller agitator, bottom drain, thermoprobe, temperature controlled heater / cooler bath, and nitrogen purge was used for the catalyst preparation procedure.

[0067] Preparation of POM catalyst solution E: Sodium tungstate dihydrate (13.85 g) and 66.35 g of HPLC grade demineralized water were added to a glass vessel to form a clear solution. Next, 85% phosphoric acid (22.1 g) was added with stirring. Finally, 50 wt% aqueous hydrogen peroxide solution (19.4 g) was added with stirring.

[0068] Preparation of tetraoctylammonium solution F: Tetraoctylammonium bromide (25.0 g) and mesitylene (253.6 g) were added to a separate bottle and the mixture was heated while stirring until the tetraoctylammonium bromide was completely dissolved. The solution was charged into a 1 L glass reactor and kept at 50-60 °C. The solution was washed five times with 50 wt% sulfuric acid solution and then with water to ion-exchange the bromide to sulfate. The masses of the washing solutions were recorded in Table 2.

[0069] [Table 2]

[0070] The ion-exchanged tetraalkylammonium solution F remained in the reactor and was added with POM catalyst solution E (120.5 g). The mixture was stirred at 55° C. for 30 minutes. The stirring was stopped and the phases were allowed to separate. The aqueous phase was removed (136 g) and the organic solution (278.5 g) was collected and stored in the refrigerator until further use.

[0071] Epoxidation / Hydrolysis Reaction Procedure: A 1 L stainless steel reactor containing a bottom drain, internal thermoprobe, heating mantle, internal cooling coil, pitch-blade impeller and sampling lines was used for the epoxidation / hydrolysis reactions. A D1000 Isco pump was used to load the propene.

[0072] The epoxidation / hydrolysis catalyst solution (78.9 g) was diluted with mesitylene (11.1 g) and then charged to a 1 L stainless steel reactor. Next, a 15 wt% aqueous hydrogen peroxide solution containing phosphoric acid was charged to the reactor (the solution was prepared by mixing 93.8 g of 30 wt% hydrogen peroxide, 93.8 g of demineralized water, and 0.123 g of 85% phosphoric acid). The reactor was sealed, pressurized with nitrogen (100 psig (689 kPa)) and vented for two cycles, and the charging and venting were repeated while the reactor was filled with nitrogen (100 psig (689 kPa)). Liquid propene (139 mL) was then volumetrically charged to the reactor. The reactor was heated to 70° C. using an electric heating jacket, and the reaction mixture was stirred at 500 rpm. Liquid samples were taken throughout the 300 min experiment, and the concentration of 1,2-propanediol in the aqueous phase was measured by gas chromatography. The 1,2-propanediol yield (mol %) was calculated according to the following formula.

[0073] 1,2-propanediol yield (mol%) = total amount of 1,2-propanediol (mol) / total amount of hydrogen peroxide added (mol) * 100

[0074] In the formula, total amount of 1,2-propanediol (moles) = [1,2-propanediol concentration (wt%) * reactor aqueous phase solution mass (g)] / molecular weight of 1,2-propanediol (g / mol).

[0075] The results are summarized in Figure 8. The first sample was taken when the reactor temperature reached the desired set point of 2 °C, the first sample was labeled as 0 min, and all subsequent samples were labeled chronologically from the first sample. As shown in Figure 8, the catalyst composition produces a high yield (87.2%) of 1,2-propanediol.

[0076] Example 9: A 1 L jacketed glass reactor containing a dual pitched blade impeller agitator, bottom drain, thermoprobe, temperature controlled heater / cooler bath, and nitrogen purge was used for the catalyst preparation procedure.

[0077] Preparation of POM catalyst solution G: Sodium tungstate dihydrate (13.8 g) and 66.4 g of HPLC grade demineralized water were added to a glass vessel to form a clear solution. Next, 85% phosphoric acid (22.1 g) was added with stirring. Finally, 50 wt% aqueous hydrogen peroxide solution (19.4 g) was added with stirring.

[0078] Preparation of tetraoctylammonium solution H: Tetraoctylammonium bromide (25.15 g) and mixed xylenes (254 g, reagent grade, Sigma-Aldrich, St. Louis, MO, USA) were added to a separate bottle and the mixture was heated with stirring until the tetraoctylammonium bromide was completely dissolved. The solution was charged into a 1 L glass reactor and kept at 55 °C. The solution was washed five times with 50 wt% sulfuric acid solution and then with water to ion-exchange the bromide to sulfate. The masses of the washing solutions were recorded in Table 3.

[0079] [Table 3]

[0080] The ion-exchanged tetraalkylammonium solution G was left in the reactor and POM catalyst solution H (121.0 g) was added. The mixture was stirred at 55° C. for 30 minutes. The stirring was stopped and the phases were allowed to separate. The aqueous phase was removed (112 g) and the organic solution (282 g) was collected and stored in the refrigerator until further use.

[0081] Epoxidation / Hydrolysis Reaction Procedure: A 1 L stainless steel reactor containing a bottom drain, internal thermoprobe, heating mantle, internal cooling coil, pitch-blade impeller and sampling lines was used for the epoxidation / hydrolysis reactor. A D1000 Isco pump was used to load the propene.

[0082] The epoxidation / hydrolysis catalyst solution (80.0 g) was diluted with mixed xylenes (10.1 g) and then charged to a 1 L stainless steel reactor. A 15 wt% aqueous hydrogen peroxide solution containing phosphoric acid was then charged to the reactor (the solution was prepared by mixing 93.8 g of 30 wt% hydrogen peroxide, 93.8 g of demineralized water, and 0.110 g of 85% phosphoric acid). The reactor was sealed, pressurized with nitrogen (100 psig) and vented for two cycles, and the charging and venting were repeated while the reactor was filled with nitrogen (100 psig). Liquid propene (139 mL) was then volumetrically charged to the reactor. The reactor was heated to 70° C. using an electric heating jacket, and the reaction mixture was stirred at 500 rpm. Liquid samples were taken throughout the 300 min run, and the concentration of 1,2-propanediol in the aqueous phase was measured by gas chromatography. The yield of 1,2-propanediol was calculated as above.

[0083] The results are summarized in Figure 9. The first sample was taken when the reactor temperature reached the desired set point of 2 °C, the first sample was labeled as 0 min, and all subsequent samples were labeled chronologically from the first sample. As shown in Figure 9, the catalyst composition produced a high yield (80.6%) of 1,2-propanediol.

[0084] Example 10: A 1 L jacketed glass reactor containing a dual pitched blade impeller agitator, bottom drain, thermoprobe, temperature controlled heater / cooler bath, and nitrogen purge was used for the catalyst preparation procedure.

[0085] Preparation of POM catalyst solution I: Sodium tungstate dihydrate (13.8 g) and 66.5 g of HPLC grade demineralized water were added to a glass vessel to form a clear solution. Next, 85% phosphoric acid (22.1 g) was added with stirring. Finally, 50% by weight aqueous hydrogen peroxide solution (19.4 g) was added with stirring.

[0086] Preparation of tetraoctylammonium solution H: Tetraoctylammonium bromide (25.22 g) and toluene (254 g, HPLC grade, Fisher Scientific) were added to a separate bottle and the mixture was stirred at 50° C. until the tetraoctylammonium bromide was completely dissolved. The solution was charged into a 1 L glass reactor and kept at 50° C. The solution was washed seven times with 50 wt % sulfuric acid solution and then twice with water to ion-exchange the bromide to sulfate. The masses of the washing solutions were recorded in Table 4.

[0087] [Table 4]

[0088] The ion-exchanged tetraalkylammonium solution I was left in the reactor and POM catalyst solution J (121.5 g) was added. The mixture was stirred at 55° C. for 30 minutes. The stirring was stopped and the phases were allowed to separate. The aqueous phase was removed (121 g) and the organic solution (278.5 g) was recovered and stored in the refrigerator until further use.

[0089] Epoxidation / Hydrolysis Reaction Procedure: A 1 L stainless steel reactor containing a bottom drain, internal thermoprobe, heating mantle, internal cooling coil, pitch-blade impeller and sampling lines was used for the epoxidation / hydrolysis reactor. A D1000 Isco pump was used to load the propene.

[0090] The epoxidation / hydrolysis catalyst solution (79 g) was diluted with toluene (11.1 g) and then charged to a 1 L stainless steel reactor. Next, a 15 wt% aqueous hydrogen peroxide solution containing phosphoric acid was charged to the reactor (this solution was prepared by mixing 93.8 g of 30 wt% hydrogen peroxide, 93.8 g of demineralized water, and 0.109 g of 85% phosphoric acid). The reactor was sealed, pressurized with nitrogen (100 psig) and vented for two cycles, and the charging and venting were repeated while the reactor was filled with nitrogen (100 psig). Liquid propene (139 mL) was then volumetrically charged to the reactor. The reactor was heated to 70° C. using an electric heating jacket, and the reaction mixture was stirred at 500 rpm. Liquid samples were taken throughout the 300 min run, the concentration of 1,2-propanediol in the aqueous phase was measured by gas chromatography, and the yield of 1,2-propanediol was calculated as above.

[0091] The results are summarized in Figure 10. The first sample was taken when the reactor temperature reached the desired set point of 2 °C, the first sample was labeled as 0 min, and all subsequent samples were labeled chronologically from the first sample. As shown in Figure 10, the catalyst composition produced a high yield (87.2%) of 1,2-propanediol.

[0092] As demonstrated in Examples 8-10, the use of the above-described catalyst system surprisingly allows the production of 1,2-propanediol in a significantly improved yield of 80% or more.

Claims

1. 1. A process for preparing 1,2-alkanediols from the corresponding alkenes and hydrogen peroxide, comprising: a) reacting an alkene with hydrogen peroxide in the presence of catalytic amounts of at least one tungsten trioxometalate and at least one tetraalkylammonium cation; wherein the reaction is carried out in a two-phase reaction mixture comprising an aqueous phase having a pH of up to 6 and an organic phase, and the tetraalkylammonium cation is of the general formula N ＋ R １ R ２ R ３ R ４ and R １ , R ２ , R ３ and R ４ are each independently the same or different alkyl groups, and R １ , R ２ , R ３ and R ４ are all the same, the tetraalkylammonium cation has a total of at least 32 carbon atoms in the alkyl groups, or １ , R ２ , R ３ and R ４ where at least one of the alkyl groups is different from the others, the tetraalkylammonium cation has a total of at least 37 carbon atoms in the alkyl groups. b) separating the biphasic mixture from step a) into an aqueous phase P1 and an organic phase P2; c) optionally recycling any alkene oxides that may be present in the separated organic phase P2 to reaction step a); d) separating the 1,2-alkanediols from the aqueous phase P1 separated in step b); A method comprising:

2. 2. The method of claim 1, wherein the 1,2-alkanediol is 1,2-propanediol and the corresponding alkene is propene.

3. 3. The method of claim 1 or 2, wherein the tungsten trioxometalate is a heteropolytungstate.

4. 4. The method of claim 3, wherein the polytungstophosphate is generated in situ from phosphoric acid and a water-soluble alkaline tungstate.

5. R １ is CH ３ and R ２ , R ３ and R ４ are the same, or R １ , R ２ , R ３ and R ４ Each of the same C ８ -C １８ 3. The method of claim 1 or 2, wherein the alkyl is alkyl.

6. 3. The method of claim 1 or 2, wherein the tetraalkylammonium cation comprises at least one of tetraoctylammonium, tetradecylammonium, tetradodecylammonium, tridodecylmethylammonium, or mixtures thereof.

7. 3. The method of claim 1 or 2, wherein at least one tetraalkylammonium cation is provided in the form of a quaternary tetraalkylammonium salt having an anion different from the tungsten trioxometalate.

8. 8. The method of claim 7, wherein the molar ratio of tetraalkylammonium cation to tungsten ranges from 1:1 to 3:

1.

9. 3. The process according to claim 1 or 2, wherein the reaction in step a) is carried out in the presence of at least one solvent comprising an aromatic hydrocarbon.

10. 3. The method according to claim 1 or 2, wherein the pH of the aqueous phase in step a) is maintained in the range of 1.0 to 3.

5.

11. 3. The method of claim 1 or 2, wherein the reaction mixture of step a) does not contain any compound having an ester functional group.

12. 3. The process according to claim 1 or 2, wherein the process is a continuous process and step a) is carried out in a loop reactor.

13. 3. The method according to claim 1 or 2, wherein the tungsten trioxometalate present in the organic phase P2 separated in step b) is recycled to the reaction in step a).

14. 3. The method of claim 1 or 2, wherein step b) is carried out in a settling tube and the two-phase mixture is passed through a coalescer element comprising structured or random packing.

15. 3. The method according to claim 1 or 2, wherein the aqueous phase P1 is separated by nanofiltration in step d) into a polyoxometallate-enriched retentate and a polyoxometallate-depleted permeate, the retentate being recycled to the reaction in step a) and the 1,2-alkanediol being separated from the permeate.

Images