Process for the preparation of 1,2-propanediol from propane

Abstract

A process for making 1,2-propanediol includes the step of dehydrogenating propane to provide a product stream comprising propane, propylene, and hydrogen; a separation step of separating the product stream into a stream consisting essentially of hydrogen, a stream rich in propane, and a stream rich in propylene; a step of reacting the stream consisting essentially of hydrogen with oxygen to provide a stream comprising hydrogen peroxide; a step of reacting the stream rich in propylene with the stream comprising hydrogen peroxide in the presence of a catalyst mixture comprising a phase transfer catalyst and a heteropolytungstate in a reaction mixture having two liquid phases; and a step of separating the propylene-oxidized reaction mixture into an aqueous phase and an organic phase, recycling the organic phase to the propylene-oxidized step, and a step of isolating 1,2-propanediol from the aqueous phase.

Description

Technical Field

[0001] This invention relates to a method for preparing 1,2-propanediol from propane. Background Technology

[0002] In established methods used in the industry, 1,2-propanediol is prepared by reacting propylene oxide with water. Propylene oxide can be prepared industrially using the HPPO method, which involves reacting propylene with hydrogen peroxide in the presence of a titanium zeolite catalyst and an organic solvent. The 1,2-propanediol is then separated and purified prior to the step of reacting propylene oxide with water to prepare it.

[0003] WO 2017 / 089075 discloses a method for producing 1,2-propanediol from propylene and hydrogen peroxide, the method 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 and an organic phase having a maximum pH of 6; b) separating the two-phase 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-propanediol from the aqueous phase separated in step b).

[0004] Several methods for producing propylene by dehydrogenating propane are known and have been implemented on an industrial scale. An overview is provided in Process Economics Program (PEP) Report 267A, “Propane Dehydrogenation Process Technologies”, IHS Chemical, October 2015. Summary of the Invention

[0005] The inventors of this invention have now discovered that 1,2-propanediol can be prepared from propane using an integrated method that requires less equipment and consumes fewer raw materials compared to known methods for preparing propylene from propane and 1,2-propanediol from propylene. The novel integrated method provides 1,2-propanediol from propane in a stoichiometric ratio of propane + O₂ → 1,2-propanediol, thereby providing optimal atomic efficiency.

[0006] Therefore, the subject of this invention is a method for preparing 1,2-propanediol, the method comprising:

[0007] a) The step of dehydrogenating the feed stream S1 containing propane to provide a product stream S2 containing propane, propylene and hydrogen.

[0008] b) A first separation step of separating stream S2 into stream S3, which is essentially composed of hydrogen, and stream S4, which contains propane and propylene, with the total amount of propane and propylene being at least 95% by weight.

[0009] c) The step of reacting all or part of the stream S3 with oxygen to provide a stream S5 containing hydrogen peroxide;

[0010] d) A second separation step that separates stream S4 into a propane-rich stream S6 and a propylene-rich stream S7;

[0011] e) The step of reacting all or part of stream S7 with stream S5 in a liquid reaction mixture in the presence of a catalyst mixture comprising a phase transfer catalyst and a heteropolytungstate, wherein the liquid reaction mixture comprises an aqueous phase having a maximum apparent pH of 6 and an organic phase.

[0012] f) Separate the reaction mixture from step e) into an aqueous phase containing 1,2-propanediol (P a ) and organic phase (P o The third separation step;

[0013] g) The organic phase (P) separated in step f) o The process is repeated in step e); and...

[0014] h) The aqueous phase (P) separated from step f) a The fourth separation step for separating 1,2-propanediol in ) Attached Figure Description

[0015] The figure illustrates an embodiment of the method of the present invention, wherein hydrogen peroxide is prepared by the anthraquinone method. Detailed Implementation

[0016] The method of the present invention includes: step a) dehydrogenating a feed stream containing propane; step b) separating the product stream of step a) into a stream consisting essentially of hydrogen and a stream containing propane and propylene; step c) reacting the hydrogen provided in step b) with oxygen to provide hydrogen peroxide; step d) separating the stream containing propane and propylene provided in step b) into a propane-rich stream and a propylene-rich stream; step e) reacting the propylene-rich stream separated in step d) with the hydrogen peroxide provided in step c) in the presence of a catalyst mixture containing a phase transfer catalyst and a heteropolytungstate; step f) separating the reaction mixture of step e) into an aqueous phase and an organic phase containing 1,2-propanediol; step g) recycling the organic phase separated in step f) to reaction step e); and step h) separating 1,2-propanediol from the aqueous phase separated in step f).

[0017] In step a) of the method of the present invention, the feed stream S1 containing propane is dehydrogenated to provide a product stream S2 containing propane, propylene, and hydrogen. Suitable methods for dehydrogenating propane are known from the prior art (e.g., from Ullmann's Encyclopedia of Industrial Chemistry, online edition 2013, entry "Propylene", Chapter 3.3.1, DOI 10.1002 / 14356007.a22_211.pub3). Suitable methods for dehydrogenating propane are also licensed, for example, from UOP Oleflex from Honeywell UOP. TM Method, from CB&I Lummus Methods, STAR from ThyssenKrupp Industrial Solutions Alternatively, the PDH approach from Linde and BASF.

[0018] In step b) of the method of the present invention, stream S2 is separated into stream S3, which is essentially composed of hydrogen, and stream S4, which contains propane and propylene, with the total amount of propane and propylene being at least 95% by weight. Stream S2 can be separated from the dehydrogenation reaction mixture of step a) by separating hydrogen from hydrocarbons containing fewer than 3 carbon atoms via condensation and distillation using methods known in the art. Stream S3 can be further purified to remove impurities (such as carbon monoxide) that would be detrimental to the hydrogenation catalyst used in step c) of the method. Stream S3 can be purified by known methods (such as by pressure swing adsorption or by membrane separation using a hydrogen-permeable gas separation membrane).

[0019] In a preferred embodiment, steps a) and b) comprise passing a mixture of propane and hydrogen through a supported platinum catalyst bed in a series of moving bed reactors at a temperature of 500-700°C and a pressure of 0.1-0.2 MPa. The resulting reaction mixture is then cooled and compressed, and a liquid mixture containing propane and propylene is separated from stream S3 by condensation. This liquid mixture is subjected to selective partial hydrogenation using a palladium catalyst to convert propadiene and propyne into propylene, followed by distillation in a deethanizer to separate ethane and ethylene as overhead products and provide stream S4 as bottom products.

[0020] In step c) of the method of the present invention, all or part of the stream S3 separated in step b) is reacted with oxygen to provide a stream S5 containing hydrogen peroxide.

[0021] In the so-called direct synthesis of hydrogen peroxide, stream S3 can react with oxygen in a liquid reaction medium in the presence of a noble metal catalyst. The noble metal catalyst is preferably a supported catalyst, with alumina, silica, titanium dioxide, zirconium dioxide, zeolite, and activated carbon being preferred supports. The noble metal catalyst can be a suspended catalyst or preferably a fixed-bed catalyst. The noble metal catalyst preferably contains palladium as the noble metal, optionally in combination with platinum, gold, or silver; a palladium-platinum combination with a Pd:Pt weight ratio exceeding 4 is most preferred. Oxygen can be used in the form of pure oxygen, air, or oxygen-rich air. The direct synthesis is preferably carried out using a non-flammable gas composition. For this purpose, an inert gas (such as nitrogen or carbon dioxide) can be added. The direct synthesis is preferably carried out using a gas mixture containing at most 6 vol% hydrogen, most preferably 3-5 vol% hydrogen. The gas mixture preferably contains preferably 10-50 vol% oxygen, most preferably 15-45 vol% oxygen. Stream S3 and oxygen are preferably dispersed separately in the liquid reaction medium, and an inert gas can be added to stream S3 or the oxygen feed. The liquid reaction medium can be aqueous, aqueous-organic, or organic, and preferably consists substantially of an alcohol or a mixture of alcohol and water, with methanol being the most preferred alcohol. The liquid reaction medium preferably contains a halide, more preferably an iodide or bromide, and most preferably a bromide, in an amount of 10. -6 Up to 10 -2 mol / L, preferably 10 -5 Up to 10 -3 mol / L, most preferably 10 -5 Up to 5.10 - 4 The concentration of pK is mol / L to suppress the decomposition of hydrogen peroxide on the noble metal catalyst. The liquid reaction medium preferably also contains 0.0001-0.5 mol / L, preferably 0.001-0.1 mol / L of pK. a Strong acids with a strength less than 3 are preferred to enhance the selectivity for hydrogen peroxide formation, among which sulfuric acid, phosphoric acid, nitric acid, and methanesulfonic acid are preferred. Direct synthesis of hydrogen peroxide is preferably carried out in a fixed-bed reactor operating as a bubble-cap tower, wherein stream S3, oxygen, and optionally present inert gases are dispersed below the catalyst fixed bed.

[0022] In a preferred embodiment, all or part of stream S3 is reacted with oxygen in an anthraquinone process to provide stream S5 as a 15-50% by weight aqueous solution of hydrogen peroxide. Then, step c) includes the following steps:

[0023] c1) The working solution is hydrogenated with stream S3 in the presence of a hydrogenation catalyst to provide a hydrogenated working solution comprising alkylanthraquinone and / or alkyltetrahydroanthraquinone and at least one solvent for said alkylanthraquinone and / or alkyltetrahydroanthraquinone.

[0024] c2) Oxidize the hydrogenated working solution of step c1) with a gas containing molecular oxygen to provide an oxidized working solution containing dissolved hydrogen peroxide; and

[0025] c3) Extract the oxidized working solution from step c2) with an aqueous extractant to provide a stream S5 containing water and 15-50% by weight hydrogen peroxide as the extractant.

[0026] The anthraquinone process preferably uses a working solution comprising at least one 2-alkylanthraquinone, 2-alkyltetrahydroanthraquinone, or a mixture of both (hereinafter referred to as quinone) and at least one solvent for dissolving the quinone and hydroquinone. The 2-alkylanthraquinone is preferably 2-ethylanthraquinone (EAQ), 2-pentylanthraquinone (AAQ), or 2-(4-methylpentyl)-anthraquinone IHAQ, more preferably a mixture of EAQ with AAQ and / or IHAQ, wherein the molar fraction of the ethyl-containing quinone is 0.05-0.95. The working solution preferably also comprises the corresponding 2-alkyltetrahydroanthraquinone, and the ratio of 2-alkyltetrahydroanthraquinone plus 2-alkyltetrahydroanthraquinone to 2-alkylanthraquinone plus 2-alkylhydroanthraquinone is preferably maintained in the range of 1-20 by adjusting the conditions of the hydrogenation and regeneration steps used in the anthraquinone process. The working solution preferably comprises a mixture of an alkylbenzene having 9 or 10 carbon atoms (as a solvent for anthraquinone) and at least one polar solvent (as a solvent for anthraquinone), said polar solvent being selected from diisobutylmethanol (DiBC), methyl cyclohexyl acetate (MCA), trioctyl phosphate (TOP), tetrabutylurea (TBU), and N-octylcaprolactam, with DiBC, MCA, and TOP being preferred, and TOP being the most preferred.

[0027] The anthraquinone process is a cyclical process comprising a hydrogenation stage, a subsequent oxidation stage, and an extraction stage. In the hydrogenation stage, stream S3 reacts with the working solution in the presence of a hydrogenation catalyst to convert at least a portion of the quinone into the corresponding hydroquinone. In the oxidation stage, the hydrogenated working solution containing hydroquinone reacts with oxygen to form hydrogen peroxide and quinone. In the extraction stage, hydrogen peroxide is extracted from the oxidized working solution with water to provide stream S5 as an aqueous hydrogen peroxide solution. The extracted working solution is then returned to the hydrogenation stage to complete the reaction cycle.

[0028] In the hydrogenation stage of the anthraquinone process, the working solution reacts with all or part of the S3 stream in the presence of a heterogeneous hydrogenation catalyst. During the reaction, all or part of the quinone is converted to the corresponding hydroquinone. All hydrogenation catalysts known from the prior art for anthraquinone recycling processes can be used as catalysts in the hydrogenation stage. Noble metal catalysts containing palladium as the main component are preferred. The catalyst can be used in the form of a fixed-bed catalyst or a suspended catalyst, and the suspended catalyst can be an unsupported catalyst (such as palladium black) or a supported catalyst, wherein a suspended supported catalyst is preferred. SiO2, TiO2, Al2O3 and their mixed oxides, as well as zeolites, BaSO4, or polysiloxanes can be used as support materials for fixed-bed catalysts or supported suspended catalysts, wherein TiO2 and SiO2 / TiO2 mixed oxides are preferred. Catalysts in the form of integral or honeycomb structures with a surface coated with a noble metal can also be used. Hydrogenation can be carried out in stirred tank reactors, tubular reactors, fixed-bed reactors, circulating reactors, or airlift reactors, which may be equipped with devices (such as static mixers or injection nozzles) for distributing stream S3 in the working solution. Preferably, a tubular reactor with recirculation and Venturi nozzles, as known from WO 02 / 34668, is used to inject stream S3 into the reactor feed. Hydrogenation is carried out at a temperature of 20-100°C, preferably 45-75°C, and a pressure of 0.1 MPa to 1 MPa, preferably 0.2 MPa to 0.5 MPa. Hydrogenation is preferably carried out in such a manner that substantially all the hydrogen introduced into the hydrogenation reactor with stream S3 is consumed in a single pass through the reactor. The ratio between stream S3 fed into the hydrogenation reactor and the working solution is preferably selected such that 30-80% of the quinone is converted to the corresponding hydroquinone. If a mixture of 2-alkylanthraquinone and 2-alkyltetrahydroanthraquinone is used, the ratio between flow S3 and the working solution is preferably selected such that only 2-alkyltetrahydroanthraquinone is converted to hydroquinone, while 2-alkylanthraquinone remains in quinone form.

[0029] In the oxidation stage of the anthraquinone process, the hydrogenated working solution from the hydrogenation stage reacts with an oxygen-containing gas, preferably air or oxygen-rich air. All oxidation reactors known in the art for the anthraquinone process can be used for oxidation, with bubble cap towers operating in parallel flow being preferred. The bubble cap tower may be without internal devices, but preferably includes a distribution device in the form of packing or sieve plates, most preferably a combination of sieve plates and an internal cooler. Oxidation is carried out at a temperature of 30-70°C, preferably 40-60°C. Oxidation is preferably carried out with excess oxygen so that more than 90%, preferably more than 95%, of the hydroquinone is converted to the quinone form.

[0030] In the extraction stage of the anthraquinone process, the oxidized working solution containing dissolved hydrogen peroxide is extracted with an aqueous extractant to provide an aqueous hydrogen peroxide solution and an extracted oxidized working solution that is substantially free of hydrogen peroxide. Deionized water is preferably used for the extraction of hydrogen peroxide, and the deionized water may optionally contain additives for stabilizing hydrogen peroxide, adjusting pH, and / or protecting against corrosion. Extraction is preferably carried out in a countercurrent continuous extraction column, with a sieve plate column being most preferred. The aqueous hydrogen peroxide solution obtained by extraction can be used directly as stream S5, or it can be concentrated by distilling off water under reduced pressure to provide stream S5. The aqueous hydrogen peroxide solution obtained by extraction can also be purified, preferably by washing with a solvent (preferably a solvent contained in the working solution). The extracted working solution is preferably dried in a desiccator to reduce its water content before recycling it to the hydrogenation stage.

[0031] The anthraquinone process typically also includes a step of drying the extracted working solution to reduce its water content before recycling it to the hydrogenation stage. Any type of dryer known from the prior art for removing water from the working solution in the anthraquinone process can be used.

[0032] The anthraquinone process preferably includes at least one additional stage for regenerating the working solution, wherein byproducts formed during the process are converted back into quinone. Regeneration is performed by treating the hydrogenated working solution with alumina or sodium hydroxide, preferably using a side stream of a circulating process. In addition to the regeneration of the hydrogenated working solution, the extracted and oxidized working solution can be regenerated in a side stream using alumina, sodium hydroxide, or an organic amine. Suitable methods for regenerating the working solution in the anthraquinone process are known from the prior art.

[0033] In step d) of the method of the present invention, the stream S4 separated in step b) is separated into a propane-rich stream S6 and a propylene-rich stream S7. The separation in step d) is preferably carried out in at least one distillation column to provide stream S7 as the overhead stream and stream S6 as the bottom stream. One or more distillation columns may include discrete trays (such as sieve trays or bubble cap trays) to provide the necessary number of separation stages. Alternatively, the distillation column may contain one or more packing materials, which may be random packing or structured packing, with structured packing being preferred. C3 separation columns known from the prior art for separating propylene and propane can be used for the separation in step d). One or more distillation columns are preferably operated at a pressure of 1.5-2.5 MPa to utilize water cooling for vapor condensation. Stream S6 is preferably recycled to step a).

[0034] If the propane dehydrogenation in step a) is carried out on a scale that provides more propylene than required in reaction step e), then the separation of stream S4 in step d) is preferably carried out in at least one distillation column to provide a polymer-grade propylene stream containing 99.5-99.8% by weight of propylene as the top product stream, a side stream containing 90-98% by weight of propylene as the propylene-rich stream S7, and a bottom product stream as stream S6, which is rich in propane relative to stream S4, preferably containing more than 90% by weight of propane. The term "side stream" here refers to the stream discharged from a withdrawal point in the distillation column between the bottom and the top, preferably from a point at least 10 separation trays below the top and at least 10 separation trays above the bottom. The side stream can be discharged as a liquid stream or as a vapor stream. Preferably, the side stream is discharged as a vapor stream and condensed in a separate condenser after discharge. The necessary separation efficiency to provide polymer-grade propylene and the compositions of streams S6 and S7 can be achieved by adjusting the number of separation plates and the reflux ratio in the distillation column. A higher number of separation plates and a higher reflux ratio provide better separation efficiency with a higher propylene concentration in the polymer-grade propylene and a higher propane concentration in stream S6. In a preferred embodiment, step d) is carried out in two thermally integrated distillation columns, wherein the first column operates at a higher pressure than the second column, and the overhead vapor from the first column is used to heat the bottom evaporator of the second column. Stream S4 is then fed into the first column, and stream S7 is discharged from the first column as a side stream. The bottom product of the first column is fed into the second column, the bottom product of the second column is discharged as stream S6, and the overhead products of the first and second columns are combined to provide the polymer-grade propylene stream. Stream S7 is preferably discharged as a vapor stream and used to heat the bottom evaporator of the second column. In this implementation scheme, the bottom evaporator of the second tower is equipped with at least two heat exchangers, one heated by steam from the top of the first tower and the other heated by steam stream S7.

[0035] In step e) of the method of the present invention, all or part of stream S7 is reacted with stream S5 in the presence of a catalyst mixture comprising a phase transfer catalyst and a heteropolytungstate. This reaction is carried out in a liquid reaction mixture comprising an aqueous phase with a maximum apparent pH of 6 and an organic phase.

[0036] The catalyst mixture used in step e) comprises a heteropolytungstate. The heteroatom is preferably phosphorus or arsenic, and particularly preferably phosphorus (i.e., the heteropolytungstate is particularly preferably polytungstophosphate). Heteropolytungstates are well known to those skilled in the art. The preferred polytungstophosphate has a phosphorus to tungsten molar ratio in the range of 1:2 to 1:12. The polytungstophosphate can be 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 phosphorus to tungsten molar ratio of 1:2 to 10:1, preferably 4:1 to 8:1. The polytungstophosphate 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 a catalytically active species for the oxidation of propylene.

[0037] The catalyst mixture used in step e) further comprises a phase transfer catalyst. The phase transfer catalyst comprises a cation or a compound that forms a cation in the aqueous phase, whereby the cation can form a salt with peroxytungstate or heteropolyperoxytungstate, the salt being soluble in the organic phase of the liquid reaction mixture. The phase transfer catalyst preferably comprises a monovalent cation or a compound that forms a monovalent cation in the aqueous phase. Suitable phase transfer catalysts are tertiary amines, tertiary ammonium salts, quaternary ammonium salts, and quaternary phosphonium salts. Suitable counterions for tertiary and quaternary ammonium salts are the following anions: chloride, bromide, nitrate, sulfate, hydrogen phosphate, dihydrogen phosphate, methanesulfonate, methyl sulfate, and ethyl sulfate. The amount of phase transfer catalyst used is preferably such that the molar ratio of the phase transfer catalyst to tungsten in the liquid mixture is in the range of 0.2:1 to 3:1, particularly preferably 0.4:1 to 1:1, where the molar ratio refers to the amount of cation or cation-forming compound in the phase transfer catalyst used relative to the amount of tungsten used.

[0038] In a preferred embodiment, the phase transfer catalyst is a tertiary amine or tertiary ammonium salt or quaternary ammonium salt comprising a total of at least 12 carbon atoms, preferably 12-60 carbon atoms. Tetraalkylammonium salts are preferred. Suitable tertiary amines include, for example, dodecyl dimethylamine, hexadecyl dimethylamine, octadecyl dimethylamine, tributylamine, and trioctylamine. Suitable tertiary ammonium salts are protonated products of these tertiary amines. Suitable quaternary ammonium salts include, for example, dodecyl trimethylammonium salt, hexadecyl trimethylammonium salt, octadecyl trimethylammonium salt, methyl tributylammonium salt, and methyl trioctylammonium salt. More preferably, the phase transfer catalyst comprises a structure R... 1 R 2 R 3 NR4+ Tertiary or quaternary ammonium ions, wherein R 1 R 2 and R 3 They are the same or different, and each is selected from alkyl groups having 8-10 carbon atoms, and R 4 It is hydrogen or methyl. Most preferably, the phase transfer catalyst comprises methyltris(octyl / decyl)methylammonium sulfate (CAS No. 2387913-24-6).

[0039] In another preferred embodiment, the phase transfer catalyst comprises at least one having a structure of R 1 R 2 R 3 R 4 N + Salts of tertiary or quaternary ammonium ions, wherein R 1 is YO(C=O)R 5 Group, wherein Y is CH2CH2, CH(CH3)CH2 or CH2CH(CH3), and R 5 It is an alkyl or alkenyl group having 11-21 carbon atoms, R 2 It is hydrogen or an alkyl group having 1-4 carbon atoms, and R 3 and R 4 Each independently as R 1 Alkyl groups or γ-OH having 1-4 carbon atoms. Preferably, it is a quaternary ammonium salt with methyl sulfate as the counterion, wherein R... 2 It is methyl, and R 5 It is a straight-chain alkyl or alkenyl group. Particularly preferred are the following salts: (CH3)3N + CH2CH2O(C=O)R 5 CH3OSO3 - (CH3)2N + (CH2CH2OH)(CH2CH2O(C=O)R 5 CH3OSO3 - (CH3)2N + (CH2CH2O(C=O)R 5 )2CH3OSO3 - CH3N + (CH2CH2OH)2(CH2CH2O(C=O)R 5 CH3OSO3 - CH3N + (CH2CH2OH)(CH2CH2O(C=O)R 5 )2CH3OSO3 - CH3N + (CH2CH2O(C=O)R5 )3CH3OSO3 - (CH3)3N + CH2CH(CH3)O(C=O)R 5 CH3OSO3 - (CH3)2N + (CH2CH(CH3)OH)(CH2CH(CH3)O(C=O)R 5 CH3OSO3 - and (CH3)2N + (CH2CH(CH3)O(C=O)R 5 )2CH3OSO3 - , where R 5 In each case, it is a straight-chain alkyl or alkenyl group having 11-21 carbon atoms. The 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 having 11-17 carbon atoms. The phase transfer catalyst of this embodiment can be prepared by esterifying ethanolamine, isopropanolamine, diethanolamine, diisopropanolamine, triethanolamine, or triisopropanolamine with fatty acids, followed by quaternization with dimethyl sulfate. These phase transfer catalysts have the advantages that they are readily biodegradable (unlike tetraalkylammonium salts) and can be introduced into biological treatment facilities without further pretreatment. Salts with methyl sulfate as the anion are also less corrosive than tetraalkylammonium halides.

[0040] The reaction in step e) 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" here refers to the value determined by measurement with a glass electrode using a commercially available pH meter calibrated with a known pH buffer solution for measuring dilute aqueous solutions. This apparent pH differs by a constant value from the theoretical pH (i.e., the negative logarithm of hydrogen ion activity) because the standard potential of the glass electrode in the aqueous phase of the reaction mixture (containing hydrogen peroxide and glycol) differs from its standard potential in pure water. The apparent pH of the aqueous phase is preferably maintained in the range of 1.0 to 3.5, particularly preferably in the range of 2.0 to 3.0. The apparent pH can be maintained within this range by adding an acid, preferably sulfuric acid or phosphoric acid, or by adding a base, preferably an aqueous solution of sodium hydroxide. Adjusting the apparent pH within this preferred range provides high selectivity for 1,2-propanediol and prevents enrichment of propylene oxide in the aqueous phase, which simplifies the subsequent separation of propylene glycol from the aqueous phase.

[0041] The reaction is preferably carried out at a temperature in the range of 50-110°C, more preferably 60-100°C, and particularly preferably 70-90°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.

[0042] The reaction in step e) 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 with a boiling point exceeding 100°C, preferably exceeding 120°C, and said organic solvent 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. Adding a solvent can improve the extraction of the salt formed by the heteropolytungstate and 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, ranging from 10% to 90% by weight.

[0043] In a preferred embodiment, the solvent comprises an alkylated aromatic hydrocarbon having 8-12 carbon atoms. Suitable alkylated aromatic hydrocarbons include, for example, 1,2-xylene (o-xylene), 1,3-xylene (m-xylene), 1,4-xylene (p-xylene), ethylbenzene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene (mesotrimethylbenzene), 1-ethyl-2-toluene, 1-ethyl-3-toluene, and 1-ethyl-4-toluene, and n-propylbenzene. Preferably, a hydrocarbon mixture comprising more than 50% by weight, particularly preferably more than 80% by weight, of alkylated aromatic hydrocarbons having 8-12 carbon atoms is used as the solvent. The use of these solvents allows for the extraction and recycling of most of the peroxytungstate into the organic phase of the reaction mixture, enabling the operation of the method without the need to recover the heteropolytungstate from the aqueous phase of the reaction mixture in step e). Then, the phase transfer catalyst, the molar ratio of the phase transfer catalyst to the heteropolytungstate, the molar ratio of heteroatoms in the heteropolytungstate to tungsten, the molar ratio of propylene to hydrogen peroxide, and the amount of solvent are preferably selected to transfer as much tungsten as possible from the liquid reaction mixture into the organic phase. If step c) is carried out using a working solution containing a mixture of alkylbenzenes via the anthraquinone process, it is preferable to also use the same mixture of alkylbenzenes as the solvent in step e), which reduces the number of solvent storage containers required to operate the method.

[0044] The phase transfer catalyst, heteropolytungstate, and optionally a solvent may be added in step e) individually or as a mixture containing two or all three of these components. Preferably, a solvent is used in step e), and the phase transfer catalyst and heteropolytungstate are added and dissolved in an organic phase containing the solvent.

[0045] The reaction in step e) can be carried out intermittently or continuously, with continuous reaction being preferred. The concentration of hydrogen peroxide in the aqueous phase is preferably maintained in the range of 0.1-5% by weight, particularly preferably 0.5-3% by weight. The concentration of hydrogen peroxide can be adjusted within this range by appropriately selecting the reaction temperature, the molar ratio of propylene to hydrogen peroxide, and the residence time of the liquid mixture in the reactor where the reaction occurs. The residence time of the reaction mixture is preferably adjusted to maintain the hydrogen peroxide conversion in the range of 80-99%.

[0046] During the reaction, the liquid mixture is preferably mixed to create a large phase interface between the aqueous and organic phases. For this purpose, the reaction is preferably carried out continuously in a circulating reactor with fixed internal components, and the liquid mixture flows through the circulating reactor at a velocity that generates turbulence at the internal components. For this purpose, baffles, static mixing elements, structured packing, or random packing can be used as internal components. In combination with or as an alternative to these internal components, heat exchangers (such as plate heat exchangers or tube bundle heat exchangers) can be used, wherein, for example, turbulence is generated between the plates of a plate heat exchanger or in the tubes of a tube bundle heat exchanger.

[0047] Preferably, all or part of the heat of reaction generated in step e) is removed during the reaction, preferably by cooling the reaction mixture in a heat exchanger. More preferably, the reaction is carried out continuously in a circulating reactor that includes a heat exchanger within the reactor loop to cool the reaction mixture.

[0048] In step f) of the method of the present invention, the reaction mixture of step e) is separated into an aqueous phase (P) containing 1,2-propanediol. a ) and organic phase (P o The separation of the two-phase reaction mixture provided by step e) is preferably carried out in a settling tank. It is preferable to pass the two-phase reaction mixture through a coalescing element for more complete separation, the coalescing element comprising ordered or random packing material whose surfaces are wetted by the dispersed phase of the two-phase mixture.

[0049] Step f) preferably further includes separating a stream S8 containing propane and propylene, wherein the total amount of propane and propylene is at least 70% by weight, from the reaction mixture, and recycling stream S8 to step d). Preferably, the stream is from the organic phase (P). o Stream S8 is separated from the organic phase (P) by means of reduced pressure. The separation of stream S8 preferably includes the separation of oxygen, preferably by means of separation from the organic phase (P) by means of reduced pressure. oIn the step of desorbing propylene and propane, nitrogen is added, followed by compression of the resulting gas mixture and condensation of propylene and propane to provide stream S8. Stream S8 is preferably combined with stream S4 before being recycled to step d). This allows for control of propane accumulation in the organic phase of the reaction mixture in step e) for continuous reactions.

[0050] In step g) of the method of the present invention, the organic phase (P) separated in step f) is... o The organic phase (P) is recycled to reaction step e). o The propylene oxide present in the organic phase (P) is recycled to step a) to achieve complete conversion of propylene to 1,2-propanediol, dipropylenediol, and tripropylenediol. Preferably, the organic phase (P) is recycled to step a). o The heteropolytungstate present in the organic phase is recycled to step a), and particularly preferably, substantially all of the catalyst mixture present in the organic phase is recycled to step a). The organic phase (P) recycled to step a) is... o Preferably, it contains at least a portion of the propylene that has not yet reacted in step e) and preferably all of the unreacted propylene (except for the portion contained in the purge stream, which is necessary to remove propane to control the accumulation of propane in the organic phase of the reaction mixture in step e). Preferably, along with stream S7 and along with the recycled organic phase (P... o The molar ratio of the total amount of propylene fed to step e) to the amount of hydrogen peroxide fed to step e) along with stream S5 is in the range of 1.1:1 to 10:1.

[0051] In step h) of the method of the present invention, the aqueous phase (P) separated from step f) a 1,2-Propanediol is separated from the propylene glycol. Preferably, 1,2-Propanediol is separated by a series of distillation steps. Preferably, a series of distillation steps described in Ullmann's Encyclopedia of Industrial Chemistry, online version, entry "Propanediol", page 4, DOI 10.1002 / 14356007.a22_163.pub2 is used, wherein a water-containing overhead product is separated from a bottom product containing 1,2-propanediol and dipropylene glycol in a series of 2-4 thermally integrated distillation steps, followed by successive vacuum distillation steps that provide 1,2-propanediol 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.

[0052] In a preferred embodiment, before separating 1,2-propanediol by distillation, the aqueous phase (P...) is... aThe hydrogenation process is performed. Hydrogenation is preferably carried out using a supported hydrogenation catalyst containing one or more metals selected from Ru, Rh, Pd, Pt, Ag, Ir, Fe, Cu, Ni, and Co on a support, preferably using activated carbon, SiO2, TiO2, ZrO2, Al2O3, and aluminosilicate as the support material. A hydrogenation catalyst containing ruthenium as the active metal is preferred. 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 a temperature of 80-140°C, preferably 90-120°C. The hydrogenation catalyst can be used in the form of a suspension or a fixed bed; trickle-bed hydrogenation using a fixed-bed catalyst is preferred. Hydrogenation can prevent problems in step d) of the recovery of 1,2-propanediol and dipropanediol caused by the decomposition of hydrogen peroxide that has not yet reacted in step a). Hydrogenation also converts the byproducts formed in step a)—1-hydroperoxy-2-propanol, 2-hydroperoxy-1-propanol, and hydroxyacetone—into 1,2-propanediol, thereby increasing the yield of 1,2-propanediol.

[0053] The figures illustrate how the steps of the method of the present invention are combined in a preferred embodiment.

[0054] Feed stream S1 is fed into propane dehydrogenation reactor (1), where the propane contained in stream S1 is dehydrogenated to provide product stream S2 containing propane, propylene, and hydrogen. Stream S2 is separated in a first separation step in a hydrogen separator (2) into stream S3, which is essentially composed of hydrogen, and stream S4, which contains propane and propylene, preferably essentially composed of propane and propylene. Stream S4 is then separated in a second separation step in a C3 splitter (3) into a propane-rich stream S6 and a propylene-rich stream S7. The propane-rich stream S6 is recycled back to propane dehydrogenation reactor (1).

[0055] Most of the stream S3 is passed to the hydrogenator (5) of unit (4) to prepare hydrogen peroxide via the anthraquinone process, in which the hydrogen in stream S3 reacts with oxygen to obtain hydrogen peroxide. In the hydrogenator (5), the working solution of the anthraquinone process is hydrogenated with the hydrogen in stream S3. Then, the hydrogenated working solution is oxidized with air in the anthraquinone oxidizer (6) to provide an oxidized working solution containing dissolved hydrogen peroxide. Hydrogen peroxide is extracted from the oxidized working solution with water in the extraction column (7) to provide a hydrogen peroxide-containing stream S5 in the form of an aqueous hydrogen peroxide solution. The extracted working solution of the anthraquinone process is dried in the dryer (8) and recycled back to the hydrogenator (5).

[0056] A propylene-rich stream S7 and a hydrogen peroxide-containing stream S5 are fed into a propylene oxidation reactor (9), where propylene and hydrogen peroxide react in a liquid reaction mixture comprising two liquid phases (an aqueous phase and an organic phase with a maximum apparent pH of 6) in the presence of a catalyst mixture containing a phase transfer catalyst and a heteropolytungstate. The propylene oxidation reaction mixture is then separated in a phase separator (10) into an aqueous phase (P) containing 1,2-propanediol. a ) and an organic phase (P) containing unreacted propylene, unhydrolyzed propylene oxide intermediates, phase transfer catalysts, heteropolytungstates, and solvent (if a solvent is used in propylene oxidation). o The stream S8, comprising propylene and propane, and preferably substantially composed of propylene and propane, is removed from the organic phase (P) in the propane removal unit (11). o Separate from the organic phase (P) and recycle it to the C3 splitter (3). The organic phase (P) from which some dissolved propylene and propane have been removed will be separated. o The aqueous phase (P) is recycled to the propylene oxidation reactor (9). a The aqueous phase (P) is transferred to the hydrogenation reactor (12), where it is subjected to hydrogenation. a Hydrogenation removes unreacted hydrogen peroxide and converts the byproducts hydroxyacetone and hydroperoxypropanol into 1,2-propanediol. Hydrogenation can be carried out using hydrogen supplied by a hydrogen separator (2). In the separation unit (13), hydrogenated aqueous phase (P...)... a 1,2-Propanediol is separated from the aqueous phase (P), and the separation unit (13) preferably includes a distillation column. The distillation column can separate 1,2-propanediol from the hydrogenated aqueous phase (P). a The water separated in the process is transferred as an extractant to the extraction tower (7) of unit (4) to prepare hydrogen peroxide via the anthraquinone process.

[0057] Since the total stoichiometry of the method of the present invention is propane + O2 → 1,2-propanediol, the method can convert propane into 1,2-propanediol with optimal atomic efficiency.

[0058] List of reference numerals in the attached diagram:

[0059] 1. Propane dehydrogenation reactor

[0060] 2. Hydrogen Separator

[0061] 3 C3 splitter

[0062] 4. Units for the preparation of hydrogen peroxide via the anthraquinone process

[0063] 5. Hydrogenator

[0064] 6. Oxidizer

[0065] 7 Extraction Tower

[0066] 8. Dryer

[0067] 9. Propylene Oxidation Reactor

[0068] 10-phase separator

[0069] 11 Propane Removal Unit

[0070] 12 Hydrogenation Reactor

[0071] 13 1,2-Propanediol Separation Unit

[0072] 14. Air

[0073] 15 1,2-Propanediol

[0074] 16. Water.

Claims

1. Process for the preparation of 1,2-propanediol, the process comprising: a) a step of dehydrogenating a feed stream S1 comprising propane to provide a product stream S2 comprising propane, propene and hydrogen; b) a first separation step of separating stream S2 into a stream S4 comprising propane and propene in a total amount of at least 95 wt.% of propane and propene and a stream S3 comprising the remaining components of stream S2; c) a step of reacting all or part of stream S3 with oxygen to provide a stream S5 comprising hydrogen peroxide, step c) comprises the steps of: cl) hydrogenating a working solution with stream S3 in the presence of a hydrogenation catalyst to provide a hydrogenated working solution, the working solution comprising an alkylanthraquinone and / or an alkyltetrahydroanthraquinone and at least one solvent for the alkylanthraquinone and / or alkyltetrahydroanthraquinone, c2) oxidizing the hydrogenated working solution of step cl) with a gas comprising molecular oxygen to provide an oxidized working solution containing dissolved hydrogen peroxide; and c3) extracting the oxidized working solution of step c2) with an aqueous extractant to provide a stream S5 comprising water and 15-50 wt.% hydrogen peroxide as extract; d) a second separation step of separating stream S4 into a stream S6 rich in propane and a stream S7 rich in propene; e) a step of reacting all or part of stream S7 with stream S5 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, wherein the term apparent pH refers to a value determined by measurement with a glass electrode using a commercial pH meter calibrated with a pH known aqueous buffer solution for measuring dilute aqueous solutions; f) separating the reaction mixture of step e) into an aqueous phase P a containing 1,2-propanediol and an organic phase P o of a third separation step; g) isolating the organic phase P from step f) o recycled to the step of recycling to the reaction step e); and h) the aqueous phase P isolated from step f) a a fourth separation step for isolating 1,2-propanediol.

2. The process of claim 1, wherein stream S6 separated in step d) is recycled to step a).

3. The process of claim 1 or 2, wherein step f) comprises separating from the reaction mixture a stream S8 comprising propane and propene in a total amount of at least 70 wt.% of propane and propene and recycling stream S8 to the second separation step d).

4. The method of claim 3, wherein, Before recycling stream S8 to step d), stream S8 is combined with stream S4.

4. The process of claim 1, wherein step c) is carried out 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, wherein the term apparent pH refers to a value determined by measurement with a glass electrode using a commercial pH meter calibrated with a pH known aqueous buffer solution for measuring dilute aqueous solutions.

5. The process of claim 1, wherein step c) is carried out 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, wherein the term apparent pH refers to a value determined by measurement with a glass electrode using a commercial pH meter calibrated with a pH known aqueous buffer solution for measuring dilute aqueous solutions.

6. The process of claim 1, wherein step c) is carried out 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, wherein the term apparent pH refers to a value determined by measurement with a glass electrode using a commercial pH meter calibrated with a pH known aqueous buffer solution for measuring dilute aqueous solutions.

7. The process of claim 1, wherein step c) is carried out 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, wherein the term apparent pH refers to a value determined by measurement with a glass electrode using a commercial pH meter calibrated with a pH known aqueous buffer solution for measuring dilute aqueous solutions.

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