Extraction solvents, their use and methods for separating propylene oxide from alkane mixtures by liquid-liquid extraction

Abstract

This invention provides an extractant, its preparation method, and its application. The extractant contains an alkylpyrrole cation, a proline anion, and an acetate anion. The alkylpyrrole cation has the general structural formula [formula omitted], wherein the R1 group is any one of the n-alkyl groups. Preferably, the molar ratio of the alkylpyrrole cation, proline anion, and acetate anion is 10:0.5–4:6–9.5. This invention preferably utilizes a liquid-liquid extraction and flash evaporation process, combined with operating conditions and structural parameters such as feed location and theoretical plate number, to improve separation efficiency and obtain high-purity propylene oxide. The propylene oxide content in the obtained alkane impurities is less than 0.02 wt%, and the purity of the target product propylene oxide reaches 99.99 wt% or higher.

Description

Technical Field

[0001] This invention relates to an extractant and its application, and a method for liquid-liquid extraction to separate a mixture of propylene oxide and alkanes. Background Technology

[0002] Propylene oxide (PO) is the third largest propylene derivative after polypropylene and acrylonitrile. It is an important basic organic chemical synthesis raw material, mainly used in the production of polyether polyols, propylene glycol, etc. Propylene oxide is highly reactive and readily undergoes ring-opening polymerization. It can react with various extractants such as water, ammonia, alcohols, and carbon dioxide to produce corresponding compounds or polymers.

[0003] Propylene oxide is an important propylene derivative, with approximately 7% of propylene used in its production annually. In the propylene epoxidation reaction, besides the main reaction that produces the target products PO and dimethylbenzyl alcohol (DMBA), several side reactions occur: trace amounts of propylene undergo dimerization and further isomerization to produce C6 hydrocarbons such as 2-methylpentene and methylcyclopentane. The formation of these byproducts increases propylene consumption. Furthermore, because the boiling points of C6 hydrocarbons are very close to those of PO and their relative volatility is very low, they are difficult to remove using conventional distillation methods and can only be removed through extractive distillation.

[0004]

[0005] CH3-CH=CH2+CH3-CH=CH2→CH3CH2CH2CH=CHCH3

[0006] The literature "Research on the Process of Producing High-Purity Propylene Oxide by Extractive Distillation" (Hu Song, Li Jinlong, Li Mujin, et al. Research on the Process of Producing High-Purity Propylene Oxide by Extractive Distillation [J]. Journal of Chemical Industry and Engineering (China), 2019, 70(2):670-677.) reports the separation of impurities such as water, acetaldehyde, methanol, methyl formate, and C5-C6 light hydrocarbons from crude propylene oxide solution using nC8 as the extractant through extractive distillation and liquid-liquid extraction. Furthermore, considering the hydrolysis reaction of propylene oxide and the removal of 1,2-propanediol via side-stream extraction, the purification of propylene oxide is achieved while effectively removing impurities, with the final propylene oxide product achieving a purity of 99.99 wt%.

[0007] The paper "Design, Simulation, and Pilot Verification of a Coupled Azeotropic and Extractive Distillation Process for the Production of Propylene Oxide with High Purity" (Industrial & Engineering Chemistry Research, Ind.Eng.Chem.Res., 2021, 60(19):7385–7396) uses n-octane as the extractant to remove C5–C6 light hydrocarbons and propionaldehyde impurities. The theoretical plate number of the extractive distillation column is 92, the theoretical plate number of the solvent recovery column is 22, and the heat load of the reboiler is 5302.1 kW and 1063.7 kW, respectively, which obviously results in high energy consumption.

[0008] CN200910188103.4 discloses a method for purifying organic waste gas containing propylene oxide. The organic waste gas containing propylene oxide is washed with acidic washing liquid in a waste scrubbing tower and then catalytically oxidized to remove harmful substances to meet emission standards. However, this process is carried out under high temperature and high pressure, which poses significant safety hazards and consumes a lot of energy.

[0009] US20120077996A1 discloses a method for reducing the impurity content in propylene oxide using solvent-liquid extraction. The method removes C6 light hydrocarbons by contacting an impure propylene oxide stream with a glycol and C7 alkanes or higher alkanes. The glycols are preferably ethylene glycol, propylene glycol, glycerol, and mixtures thereof. The C7 alkanes or higher alkanes are preferably C8-C9 alkanes, more preferably branched or straight-chain octanes. The purified propylene oxide contains less than 0.1 wt% impurities. The C6 removal column is preferably an extractive distillation column, with a top operating pressure of 0-69 kPa, a top temperature of 20-55°C, a bottom temperature of 140-180°C, and a theoretical plate number of 20-50.

[0010] The methods reported so far are all extractive distillation methods, mostly using C7 to C8. 20 Straight-chain or branched alkanes, propylene glycol, water, or methanol are used as extractants to purify propylene oxide. However, organic extractants are used in large quantities, are not environmentally friendly, and are difficult to recycle. Currently, there is still a need for an extractant that can achieve high propylene oxide yield, low energy consumption, and easy recycling for propylene oxide purification. Summary of the Invention

[0011] To overcome the difficulties in the prior art, the present invention provides a method for separating a mixture of propylene oxide and alkanes by liquid-liquid extraction, using a compound solvent with anionic and cation composition having a high partition coefficient and high selectivity as the extractant to achieve the recovery of propylene oxide.

[0012] Compared with existing technologies, this invention innovatively uses an extractant composed of ionic liquids, and can utilize a flash evaporator to replace the traditional extractant recovery tower based on the easy separation advantage of ionic liquids, simplifying the process and saving energy and production costs.

[0013] According to a first aspect of the present invention, an extractant is provided, the extractant comprising: an alkylpyrrole cation, a proline anion, and an acetate anion, wherein the alkylpyrrole cation has the general structural formula as follows: Wherein, the R1 group is any one of the n-alkyl groups; preferably, the molar ratio of alkylpyrrole cation, proline anion and acetate anion is 10:0.5-4:6-9.5.

[0014] In this invention, the extractant only needs to contain the aforementioned ions to achieve the purpose of this invention, for example, it can be one or more ionic liquids containing the aforementioned ions. Ionic liquids are salts that are liquid at or near room temperature and are composed entirely of cations and anions. Common cations include quaternary ammonium salts and imidazole salts, while anions include halide ions and tetrafluoroborate ions. In this invention, ionic liquids can be designed and synthesized according to different combinations of cations and anions; this invention does not have special requirements in this regard and will not be described in detail here.

[0015] In this invention, the range of alkylpyrrole cations that can be selected is relatively wide. For this invention, it is preferred that the R1 group is any one of the C1 to C4 n-alkyl groups, and preferably R1 is methyl, ethyl, propyl or n-butyl.

[0016] In this invention, the range of proline anions that can be selected is relatively wide. For this invention, the general structural formula of the proline anion is:

[0017] In this invention, preferably, the general structural formula of the acetate anion is:

[0018] In this invention, preferably, the extractant is an ionic liquid extractant containing alkylpyrrole cations, proline anions, and acetate anions.

[0019] According to a second aspect of the invention, the present invention provides the application of the extractant described herein in the separation of mixtures of epoxides and alkanes.

[0020] The present invention allows for a wide range of selectable mass ratios of alkylene oxide to alkylene hydrocarbons. Preferably, the alkylene oxide content in the mixture of alkylene oxide and alkylene hydrocarbons is 0.01-30 wt%, and more preferably 0.5-10 wt%.

[0021] The present invention allows for a wide range of choices for epoxides, with C3-C6 epoxides being preferred, and one or more of propylene oxide and butane oxide being particularly preferred.

[0022] The present invention allows for a wide range of alkanes, preferably C5-C6 alkanes, and more preferably one or more of 2-methylpentane and cyclohexane.

[0023] According to a third aspect of the present invention, the present invention provides a method for separating a mixture of propylene oxide and alkanes by liquid-liquid extraction, the method comprising the following steps:

[0024] a) A mixture containing propylene oxide and alkanes is contacted with an extractant for liquid-liquid extraction to separate alkanes and a mixture containing the extractant and propylene oxide.

[0025] b) Separate the mixture containing the extractant and propylene oxide to obtain the extractant and the target product propylene oxide;

[0026] c) Optionally, the separated extractant may be returned as an extractant feedstock for recycling;

[0027] The extractant is the extractant described in this invention.

[0028] The objective of this invention can be achieved by following the aforementioned steps. There are no special requirements for the equipment or apparatus used in each step. Preferably, the method includes:

[0029] a) The mixture of propylene oxide and alkanes fed into the extractive distillation column is separated into alkanes at the top of the column by liquid-liquid extraction under the action of the extractant, and the bottom of the column contains a mixture of extractant and propylene oxide.

[0030] b) The mixture containing the extractant and propylene oxide is flash-distilled in a flash tank to obtain the extractant and the target product propylene oxide;

[0031] c) Optionally, the separated extractant may be recycled after being mixed with fresh extractant.

[0032] The present invention does not have any special requirements for the selection of the mass ratio of propylene oxide to alkanes. Preferably, in the mixture containing propylene oxide and alkanes, the alkanes content is 0.01-30 wt%, and more preferably 0.5-10 wt%.

[0033] The present invention does not have any special requirements for the type of alkane. Preferably, the alkane is a C5-C6 alkane, and more preferably one or more of 2-methylpentane and cyclohexane.

[0034] In this invention, the extractant and the mixture containing propylene oxide and alkanes can be in any proportion, specifically adjusted according to the process conditions. Preferably, the mass ratio of the extractant to the mixture containing propylene oxide and alkanes is 5 to 10.

[0035] The present invention does not have any special requirements for the contact method between the mixture containing propylene oxide and alkanes and the extractant. Preferably, the mixture containing propylene oxide and alkanes is contacted countercurrently with the extractant for liquid-liquid extraction and separation.

[0036] The present invention does not have any special requirements for the conditions of each step, and the specific conditions are adjusted according to the process conditions. The following are examples, but do not limit the scope of the present invention.

[0037] In this invention, preferably, in step a), the operating temperature is 40-85°C, the operating pressure is 0.1-0.3 MPaG, and the number of theoretical plates is 20-60.

[0038] In this invention, preferably, in step b), the operating temperature is 50-70°C and the operating pressure is 0.02MPa-0.04MPaG.

[0039] In this invention, preferably, the extraction process is carried out based on a liquid-liquid extraction tower, wherein the theoretical number of plates of the liquid-liquid extraction tower is 20 to 60, but this does not limit the scope of the invention.

[0040] The present invention does not have special requirements for the feed location of the circulating extractant. Preferably, the separated extractant is introduced into the extractant feed location of the extraction tower for recycling.

[0041] The present invention does not have any special requirements for the feed location of the mixture containing propylene oxide and alkanes. Preferably, the mixture containing propylene oxide and alkanes is fed into the liquid-liquid extraction tower from the middle or lower part of the extraction tower.

[0042] The present invention does not have special requirements for the feed location of fresh or recycled extractant. Preferably, the extractant is fed into the liquid-liquid extraction tower from the upper part of the extraction tower, such as the first theoretical plate at the top.

[0043] All pressures mentioned in this invention are absolute pressures. Unless otherwise specified, all unspecified components or contents refer to mass composition or content.

[0044] Compared with the prior art, the present invention has the following advantages:

[0045] (1) The extractant used in this invention, which is a compound of alkylpyrrole cation, proline anion and acetate anion, has strong chemical stability, high thermal stability, safety and good effect, and all three are indispensable.

[0046] (2) According to a preferred embodiment of the present invention, the present invention can improve the separation efficiency by using liquid-liquid extraction and flash evaporation processes, combined with operating conditions and structural parameters, such as feed location and theoretical plate number, and can obtain high-purity propylene oxide. The propylene oxide content in the obtained alkane impurities is less than 0.02 wt%, and the purity of the target product propylene oxide reaches 99.99 wt% or above.

[0047] (3) According to a preferred embodiment of the present invention, the present invention utilizes a flash tank instead of an extractant recovery tower based on the advantage of easy separation of ionic liquids, which simplifies the process flow, reduces extractant loss, and saves energy consumption and production costs. Attached Figure Description

[0048] Figure 1 The diagram shows a flowchart of liquid-liquid extraction-flash evaporation according to one embodiment of the present invention. Detailed Implementation

[0049] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0050] According to a preferred embodiment of the present invention, the present invention provides a method for separating a mixture of propylene oxide and alkanes by liquid-liquid extraction, comprising the following steps:

[0051] The mixture of propylene oxide and alkanes fed into the extractive distillation column undergoes liquid-liquid extraction with the help of the extractant. The alkanes are separated at the top of the column, while the bottom of the column contains a mixture of extractant and propylene oxide. After flash evaporation in a flash tank, the extractant and the target product, high-purity propylene oxide, are obtained. The separated extractant is mixed with fresh extractant for recycling.

[0052] The mass composition of the propylene oxide to be separated in the mixture of propylene oxide and alkane is in any proportion, and the extractant is a mixed ionic liquid extractant composed of alkylpyrrole cations, proline anions and acetate anions in a molar ratio of 10:0.5 to 4:6 to 9.5.

[0053] Specifically, the general structural formula of the alkylpyrrole cation is as follows: The general structural formula of the proline anion is: The general structural formula of the acetate anion is: The R1 group is any one of the n-alkyl groups containing 1 to 4 carbon atoms.

[0054] Furthermore, in the liquid-liquid extraction process, the operating temperature of the liquid-liquid extraction tower is 40–85°C, the operating pressure is 0.1–0.3 MPaG, and the theoretical plate number is 20–60; in the flash evaporation process, the operating temperature of the flash tank is 50–70°C, and the operating pressure is 0.02 MPa–0.04 MPaG. The temperature and pressure in this invention can be conventionally selected, and those skilled in the art can make reasonable selections based on the method of this invention. This is not a focus of the discussion in this invention and will not be described in detail.

[0055] Preferably, the extraction process is carried out using a liquid-liquid extraction tower with a theoretical plate number of 20 to 60. The extraction agent recycling refers to the extraction agent separated from the bottom of the flash tank being pressurized and circulated back to the extraction agent feed position of the liquid-liquid extraction tower.

[0056] Preferably, the mixture of propylene oxide and alkane is introduced into the liquid-liquid extraction tower from the middle or lower part of the tower.

[0057] Preferably, the extractant is introduced into the liquid-liquid extraction column from the top or slightly below, specifically, for example, from the first theoretical plate number from the top down.

[0058] In the above method, the mass concentration of the target product, high-purity propylene oxide, obtained from the top of the flash tank is not less than 99.99%.

[0059] In this invention, the overall mass loss rate of the extractant is less than 0.01%. The ionic liquid of this invention is difficult to decompose and is not easily lost.

[0060] The extractant in this invention is a salt composed entirely of cations and anions, which is liquid at or near room temperature. It consists of alkylpyrrole cations, thiocyanate anions, and amino acid anions. This extractant exhibits good thermal and chemical stability, is non-volatile, non-flammable, and non-toxic, making it a green solvent with a wide operating temperature range and good solubility for both organic and inorganic substances.

[0061] Furthermore, the interaction mechanism between the compound extractant and propylene oxide described in this invention was explained from a molecular perspective. The Dmol3 module in Materials Studio software was used to optimize and analyze the molecular / ionic and molecular cluster structures, ultimately obtaining the intermolecular interaction energies. GGA / VWN-BP density functional theory and DNP were employed in the calculations. + The basis set, the interaction energies between different molecules / ions are calculated using the following formula:

[0062] ΔE binding =E AB -E A -E B

[0063] In the formula, E AB E is the intermolecular interaction energy. A and E B Let represent the energies of molecules A and B. Some calculation results are shown below:

[0064]

[0065]

[0066] As can be seen from the above molecular formula, the anions and cations in the extractant of this invention exhibit a strong mutual attraction with the propylene oxide in the tail gas to be absorbed. This demonstrates the feasibility of the compound solvent described in this invention as a propylene oxide extractant.

[0067] In particular, the extractant in this invention can also effectively separate propylene oxide from C5-C6 light hydrocarbons in alkanes, such as the separation of propylene oxide from its binary azeotrope 2-methylpentane. From a molecular perspective, the fact that ionic liquids and alkanes are almost immiscible, as mentioned earlier, indicates a strong mutual repulsion between the ionic liquid cations and anions and alkane molecules.

[0068] This invention combines experimental data with molecular evidence to demonstrate that the extractant of this invention can effectively separate propylene oxide from alkanes, while obtaining high-purity propylene oxide products.

[0069] Figure 1 This is a flowchart of one embodiment of the present invention. In the specific process, the mixture of propylene oxide and alkane fed into the liquid-liquid extraction tower is subjected to liquid-liquid extraction under the action of the extractant. After the extraction, alkane impurities are separated at the top of the tower, and the bottom of the tower contains a mixture of extractant and propylene oxide. After flash evaporation in a flash tank, the extractant and high-purity propylene oxide product are obtained. The separated extractant is mixed with fresh extractant for reuse.

[0070] Figure 1 Only the most basic processes of liquid-liquid extraction and flash evaporation are given, without mentioning valves, pumps, reboilers, condensers, etc., but these are well known to those skilled in the art.

[0071] In this invention, changes in conditions, such as variations in feed composition and extractant structure, in different embodiments will affect the number of trays and thus the theoretical tray number. To avoid unnecessary repetition below, the feed will be consistently defined as the middle theoretical tray (middle of the extraction column), for example, the feed tray in Example 1 is the 15th theoretical tray. If further improvement in separation efficiency is desired, feed can also be introduced into the lower or middle section; however, since the separation effect in this paper is already very good, this will not be discussed further.

[0072] In this invention, feeding the extractant at the top or slightly below the top position yields better results. In the following embodiments, the extractant feed plate is fixed as the first theoretical plate for illustrative purposes to demonstrate the advantages of this invention.

[0073] Example 1

[0074] An ionic liquid extractant with a molar ratio of 1-ethyl-1-methylpyrrole cation, proline anion, and acetate anion of 10:4:6 was used to achieve a liquid-liquid extraction solvent-to-oil ratio of 9:1. Figure 1 The process for separating a mixture of propylene oxide and alkane (2-methylpentane) is as follows:

[0075] a) A mixture of propylene oxide and alkanes with an alkane content of 0.5% by mass is fed into the middle of the liquid-liquid extraction tower;

[0076] b) The extractant returned from the flash tank is mixed with the fresh extractant and introduced into the top of the liquid-liquid extraction tower, i.e., the position of the first theoretical plate; the ratio of the total mass of the circulating extractant and the fresh supplemental extractant to the total mass of the mixture containing propylene oxide and alkanes is 9:1;

[0077] c) The separated alkane impurities can be obtained from the top of the liquid-liquid extraction column after extraction;

[0078] d) The mixture of extractant and propylene oxide is obtained at the bottom of the liquid-liquid extraction tower and then introduced into a flash tank;

[0079] e) Obtain high-purity propylene oxide product from the top of the flash tank;

[0080] f) The extractant drawn from the bottom of the flash tank is returned to the liquid-liquid extraction tower;

[0081] The operating conditions, raw material composition, agent-to-oil ratio, circulating solvent solubility, and propylene oxide product indicators mentioned above are listed in Table 1.

[0082] Example 2

[0083] This embodiment is basically the same as Embodiment 1, except that:

[0084] The alkane content in the propylene oxide and alkane mixture feed is 1.0%. Due to the increased alkane content in the feedstock, while maintaining a liquid-liquid extraction solvent-to-oil ratio of 9:1, the propylene oxide product is guaranteed to be qualified by increasing the theoretical plate number of the liquid-liquid extraction tower. The operating conditions and product indicators for this example are listed in Table 1.

[0085] Example 3

[0086] This embodiment is basically the same as Embodiment 1, except that:

[0087] The alkane content in the propylene oxide and alkane mixture feed is 1.0%. Since the alkane content in the feedstock increases while the theoretical plate number of the liquid-liquid extraction column remains constant, the propylene oxide product is guaranteed to be qualified by increasing the agent-to-oil ratio to 10:1. The operating conditions and product indicators for this example are listed in Table 1.

[0088] Example 4

[0089] This embodiment is basically the same as Embodiment 1, except that:

[0090] The alkane content in the propylene oxide and alkane mixture feed is 3.0%. Due to the increased alkane content in the feedstock, while maintaining a liquid-liquid extraction solvent-to-oil ratio of 9:1, the relative density of propylene oxide to alkanes is increased by increasing the theoretical plate number of the liquid-liquid extraction column and decreasing the operating pressure to 0.1 MPaG. This ensures thorough separation of alkanes from the liquid-liquid extraction column, guaranteeing the quality of the propylene oxide product. The operating conditions and product indicators for this example are listed in Table 1.

[0091] Example 5

[0092] This embodiment is basically the same as Embodiment 1, except that:

[0093] The feed mixture of propylene oxide and alkanes contains 3.0% alkane, specifically 2-methylpentane. Due to the increased alkane content in the feedstock, the liquid-liquid extraction solvent-to-oil ratio is increased to 10:1, the theoretical plate number of the liquid-liquid extraction tower is increased, and the operating pressure of the liquid-liquid extraction tower is decreased to 0.1 MPaG. This increases the relative abundance of propylene oxide to 2-methylpentane, ensuring complete separation of 2-methylpentane in the liquid-liquid extraction tower and guaranteeing the quality of the propylene oxide product. The operating conditions and product indicators for this embodiment are listed in Table 1.

[0094] Example 6

[0095] This embodiment is basically the same as Embodiment 1, except that:

[0096] An extractant with a molar ratio of 1-propyl-1-methylpyrrole cation, proline anion, and acetate anion of 10:3:7 was used. The alkane content in the propylene oxide and alkane mixture feed was 5.0%. Because the alkane content in the feedstock increased while the theoretical plate number of the liquid-liquid extraction column remained constant, the extractant-to-oil ratio was increased to 10:1, and the operating pressure of the liquid-liquid extraction column was reduced to 0.1 MPaG. This ensured that the alkane was fully separated in the liquid-liquid extraction column, guaranteeing the quality of the propylene oxide product. The operating conditions and product indicators for this example are listed in Table 1.

[0097] Example 7

[0098] This embodiment is basically the same as Embodiment 1, except that:

[0099] An extractant with a molar ratio of 1-butyl-1-methylpyrrole cation, proline anion, and acetate anion of 10:1:9 was used. The alkane content in the propylene oxide and alkane mixture feed was 10.0%. Due to the increased alkane content in the feedstock, the theoretical plate number of the liquid-liquid extraction column was increased, the extractant-to-oil ratio was increased to 10:1, and the operating pressure of the liquid-liquid extraction column was reduced to 0.1 MPaG. This ensured that the alkane was fully separated in the liquid-liquid extraction column, guaranteeing the quality of the propylene oxide product. The operating conditions and product indicators of this example are listed in Table 1.

[0100] Example 8

[0101] This embodiment is basically the same as Embodiment 1, except that:

[0102] An extractant with a molar ratio of 1-isobutyl-1-methylpyrrole cation, proline anion, and acetate anion of 10:4:6 was used. Due to the change in the extractant structure, the extraction effect deteriorated, and increasing the theoretical plate number or adjusting the extractant-to-oil ratio could not achieve the separation effect of the extractant described in this invention.

[0103] Comparative Example 1

[0104] This embodiment is basically the same as Embodiment 1, except that:

[0105] An extractive distillation column was used, employing an extractant consisting of a 1:1 molar mixture of propanol and n-heptane. With the column top operation identical to that in Example 1, the top temperature was 55°C, the bottom temperature was 180°C, and the theoretical plate number was 50. This method resulted in poor extraction efficiency, significantly higher energy consumption, and greater extractant loss. Compared to traditional organic solvent extraction and separation, this invention is more environmentally friendly.

[0106] Comparative Example 2

[0107] This embodiment is basically the same as Embodiment 1, except that:

[0108] An ionic liquid extractant with a 1:1 molar ratio of 1-ethyl-1-methylpyrrole cation to acetate anion was used. Due to the change in the extractant structure, the extraction effect deteriorated, and increasing the theoretical plate number or adjusting the extractant-to-oil ratio could not achieve the separation effect of the extractant described in this invention.

[0109] Comparative Example 3

[0110] This embodiment is basically the same as Embodiment 1, except that:

[0111] An ionic liquid extractant with a 1:1 molar ratio of 1-ethyl-1-methylpyrrole cation to proline anion was used. Due to the change in the extractant structure, the extraction effect deteriorated, and increasing the theoretical plate number or adjusting the extractant-to-oil ratio could not achieve the separation effect of the extractant described in this invention.

[0112] Comparative Example 4

[0113] This embodiment is basically the same as Embodiment 1, except that:

[0114] An ionic liquid extractant with a molar ratio of 1-n-butyl-3-methylimidazolium cation, proline anion, and acetate anion of 10:4:6 was used. Due to the change in the extractant structure, the extraction effect deteriorated, and increasing the theoretical plate number or adjusting the extractant-to-oil ratio could not achieve the separation effect of the extractant described in this invention.

[0115] As can be seen from the table data, using the method of this invention, the separated extractant and propylene oxide can both reach a purity of 99.99%, and the alkanes can reach a purity of 99.98%, while the comparative ratio cannot achieve this at all.

[0116] Table 1

[0117]

[0118] In this invention, the propylene oxide concentration refers to the mass concentration of propylene oxide in the propylene oxide product separated from the flash evaporator. In case of any discrepancy between the data in the table and those described in the preceding embodiments, the data in the table shall prevail.

[0119] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. An extractant, characterized in that, The extractant contains: an alkylpyrrole cation, a proline anion, and an acetate anion, wherein the general structural formula of the alkylpyrrole cation is as follows: The R1 group is any one of the C1-C4 normal alkyl groups; the molar ratio of alkylpyrrole cation, proline anion and acetate anion is 10:0.5-4:6-9.5; the extractant is an ionic liquid extractant containing alkylpyrrole cation, proline anion and acetate anion.

2. The use of the extractant according to claim 1 in the separation of mixtures of alkylene oxides and alkanes; The mixture of epoxide and alkane contains 0.5-10 wt% alkane, wherein the epoxide is a C3-C6 epoxide and the alkane is a C5-C6 alkane.

3. The application according to claim 2, wherein, The epoxide is one or more of propylene oxide and butyl oxide; and / or The alkane is one or more of 2-methylpentane and cyclohexane.

4. A method for separating a mixture of propylene oxide and alkanes by liquid-liquid extraction, characterized in that: The method includes the following steps: a) A mixture containing propylene oxide and alkanes is contacted with an extractant for liquid-liquid extraction to separate alkanes and a mixture containing the extractant and propylene oxide. b) Separate the mixture containing the extractant and propylene oxide to obtain the extractant and the target product propylene oxide; c) Optionally, the separated extractant may be returned to step a) as an extractant feedstock for recycling. The extractant is the extractant according to claim 1. The mixture containing propylene oxide and alkanes has an alkane content of 0.5-10 wt%, wherein the alkanes are C5-C6 alkanes.

5. The method according to claim 4, wherein, The method includes: a) The mixture of propylene oxide and alkanes fed into the extractive distillation column is separated into alkanes at the top of the column by liquid-liquid extraction under the action of the extractant, and the bottom of the column contains a mixture of extractant and propylene oxide. b) The mixture containing the extractant and propylene oxide is flash-distilled in a flash tank to obtain the extractant and the target product, propylene oxide.

6. The method according to claim 5, wherein, The method includes: c) the separated extractant is optionally mixed with a replenishment of fresh extractant and then recycled.

7. The method according to claim 4 or 5, wherein, The alkane is one or more selected from 2-methylpentane and cyclohexane; and / or The mass ratio of the extractant to the oil containing propylene oxide and alkanes is 5-10; and / or A mixture containing propylene oxide and alkanes is subjected to countercurrent contact with an extractant for liquid-liquid extraction separation.

8. The method according to claim 4 or 5, wherein, In step a), the operating temperature is 40~85℃, the operating pressure is 0.1~0.3MPaG, and the theoretical plate number is 20-60; and / or In step b), the operating temperature is 50~70℃ and the operating pressure is 0.02MPa~0.04MPaG.

9. The method according to claim 4 or 5, wherein, The extraction process is carried out using a liquid-liquid extraction column, wherein the theoretical plate number of the liquid-liquid extraction column is 20-60; and / or The separated extractant is introduced into the extractant feed point of the extraction tower for recycling.

10. The method according to claim 4 or 5, wherein, A mixture containing propylene oxide and alkanes is introduced into the liquid-liquid extraction tower from the middle or lower part of the extraction tower.

11. The method according to claim 4 or 5, wherein, The extractant is introduced into the liquid-liquid extraction tower from the top of the extraction tower.

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