Application of ionic liquid in extraction of trioxymethylene

Abstract

The invention discloses an application of an ionic liquid in extraction of trioxymethylene, in the process of generating trioxymethylene by acid-catalyzed condensation of a formaldehyde aqueous solution, the ionic liquid is added as an extraction agent to extract and separate the trioxymethylene generated by reaction, and the ionic liquid is methyl tributyl phosphonium bis (trifluoromethanesulfonyl) imide salt; when the ionic liquid is used for extracting trioxymethylene, a ternary azeotropic system of trioxymethylene, water and methylene glycol can be broken, the ionic liquid and trioxymethylene are subjected to nonpolar Van der Waals' force interaction so as to realize extraction, and methylene glycol and water are left in a water phase through hydrogen-bond interaction, so that high-purity trioxymethylene with the purity of more than or equal to 99.5 wt.% is obtained.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of trioxane separation and purification, and relates to application of an ionic liquid in extraction of trioxane. BACKGROUND

[0002] Trioxane is a cyclic trimer, which is polymerized by three formaldehyde molecules, and its molecular formula is (CH2O)3. It is the main raw material for producing polyformaldehyde and polymethoxy dimethyl ether, and can also be used as a raw material for other chemicals such as disinfectants. In industry, the synthesis process of trioxane is usually to use a 50-70 wt.% concentrated formaldehyde solution as raw material, and after catalysis by an acid catalyst, trioxane is obtained. However, the reaction conversion rate of this process is low, so the product is preliminarily concentrated, and the separated formaldehyde solution is recycled to the reactor, and then trioxane is separated and refined. In the synthesized product, there is an azeotrope of trioxane, water and formaldehyde, and ordinary separation technology cannot achieve separation.

[0003] At present, various methods and devices are used in the prior art to prepare and process trioxane. For example, patent publication CN116832731A discloses a device and method for preparing trioxane, which uses a crystallization method to obtain concentrated trioxane crystals. However, the energy consumption of the crystallization method is too high, and scaling and plugging phenomena are prone to occur. Patent publication CN214361096U discloses a trioxane production device based on formaldehyde recycling, which separates formaldehyde and trioxane through a membrane assembly to realize recycling of formaldehyde. However, the membrane assembly has high cost, short service life, fast permeation flux decay and complex maintenance. In addition, the existing extractants mostly use benzene solvents. For example, patent publication CN103420974A discloses a trioxane refining system and method, which uses a benzene vapor-liquid extraction tower, a benzene recovery tower and a trioxane rectification tower in series, extracts impurities in trioxane raw gas through a benzene solvent, and separates benzene-water phases through a delayer. However, the benzene used in this technology has strong toxicity, poor operability, high residual risk and great environmental post-processing risk. In addition to benzene, the commonly used extractants also include dichloroethane, dichloromethane and dichlorobenzene, but the extraction efficiency is not high, and the extractants are generally organic substances with high toxicity, which can harm the health of operators or have adverse effects on subsequent processes if they are leaked or mixed into subsequent production.

[0004] The complex characteristics of formaldehyde aqueous solution make separation difficult. Studies have shown that when the concentration of formaldehyde solution is low, formaldehyde mainly exists in the form of methyl glycol (HOCH2OH, MG) in the aqueous solution, followed by a binary alcohol polycondensate. Therefore, the trioxane-water-formaldehyde ternary azeotropic system can be changed to a trioxane-water-methyl glycol system for molecular-level research.

[0005] Based on this, the application provides a separation process of ionic liquid extraction rectification of trioxane, which is used for solving the separation and purification problem of trioxane. SUMMARY

[0006] In order to solve the above technical problems, the application provides an application of ionic liquid in extraction of trioxane, wherein ionic liquid is added as an extractant to extract trioxane generated in a reaction in a process of generating trioxane by acid catalysis condensation of formaldehyde aqueous solution, the ionic liquid is methyl tributyl phosphonium bis-trifluoromethanesulfonimide salt, the ionic liquid can break the ternary azeotropic system of trioxane, water and methyl glycol when extracting trioxane, the ionic liquid and trioxane interact with each other through non-polar van der Waals force to realize extraction, methyl glycol and water are left in the water phase through hydrogen bond interaction, and high-purity trioxane with purity of 99.5wt.% or more is obtained.

[0007] In order to achieve the above object, the technical scheme adopted by the application is as follows:

[0008] An application of ionic liquid in extraction of trioxane, wherein ionic liquid is added as an extractant to extract trioxane generated in a reaction in a process of generating trioxane (TOX) by acid catalysis condensation of formaldehyde aqueous solution, the ionic liquid is methyl tributyl phosphonium bis-trifluoromethanesulfonimide salt [P 4441 ][TF2N], wherein: the cation is methyl tributyl phosphonium ion [P 4441 ] + , and the anion is bis-trifluoromethanesulfonimide ion [TF2N] - .

[0009] As a limitation of the application, the method for generating trioxane by acid catalysis condensation of formaldehyde aqueous solution is sequentially performed according to the following steps:

[0010] S1, passing 50-60wt.% formaldehyde aqueous solution into a fixed-bed reactor with a solid acid catalyst, and reacting at 100-102℃ and 0.09-0.11MPa for 2.5-4h to generate a synthesis liquid containing trioxane;

[0011] S2, passing the synthesis liquid containing trioxane into an extraction tower, injecting ionic liquid at 0.09-0.11MPa, 50-65℃ of tower top temperature and 70-85℃ of tower bottom temperature, and collecting ionic liquid phase containing trioxane from the tower bottom;

[0012] S3, the above trioxane-containing ionic liquid phase is introduced into a recovery column, and is separated under the conditions of a pressure of 0.09-0.11 MPa, a column top temperature of 80-120℃, and a column bottom temperature of 150-200℃, to obtain 93-96 wt.% trioxane crude product at the column top, and 99.5 wt.% ionic liquid is recovered at the column bottom and recycled to step S2;

[0013] S4, the trioxane crude product of step S3 is introduced into a rectification column, and is refined under the conditions of a pressure of 0.5-0.8 MPa, a column top temperature of 80-120℃, and a column bottom temperature of 65-80℃, to obtain trioxane-water-formaldehyde azeotrope at the column top and recycled to the raw material feed inlet of the extraction column, and ≥99.5 wt.% high-purity trioxane is obtained at the column bottom.

[0014] As a further limitation of the present application, in step S1, the solid acid catalyst is Amberlyst-15.

[0015] As a further second limitation of the present application, in step S2, the extraction column has a column height of 10-28 m, a column diameter of 0.5-3.0 m, a number of plates of 28-44, and a plate spacing of 0.3-0.6 m, and the feed inlet of the trioxane-containing synthesis liquid is located at the 4th-7th plate from the bottom.

[0016] As a further third limitation of the present application, in step S2, the mass flow ratio of the ionic liquid to the trioxane-containing synthesis liquid is (1-2):1, and the feed inlet of the ionic liquid is located at the 2nd-5th plate from the top.

[0017] As a further fourth limitation of the present application, in step S3, the recovery column has a column height of 8-20 m, a column diameter of 0.8-2.5 m, a number of plates of 16-31, and a plate spacing of 0.4-0.6 m, and the feed inlet of the trioxane-containing ionic liquid phase is located at the 3rd-5th plate from the bottom.

[0018] As a further fifth limitation of the present application, in step S3, the recovered ionic liquid is dehydrated under reduced pressure at 80℃ and 0.001-0.01 MPa for 2 h, and then recycled to step S2.

[0019] As a further sixth limitation of the present application, in step S4, the rectification column has a column height of 12-25 m, a column diameter of 1.0-3.0 m, a number of plates of 26-39, and a plate spacing of 0.4-0.6 m, and the feed inlet of the trioxane crude product is located at the 4th-7th plate from the bottom.

[0020] For the ternary azeotrope of trioxane (TOX), water (H2O), and methyl glycol (MG), water and methyl glycol interact through hydrogen bonding, and the three oxygen atoms of trioxane act as hydrogen bond acceptors, forming weak hydrogen bonds with the oxygen atoms of water and methyl glycol. The present application uses methyl tributyl phosphonium bistrifluoromethanesulfonimide salt as an extractant for extracting trioxane. When methyl tributyl phosphonium bistrifluoromethanesulfonimide salt extracts trioxane, the ternary azeotrope of trioxane, water, and methyl glycol is broken, and methyl tributyl phosphonium bistrifluoromethanesulfonimide salt and trioxane interact through nonpolar van der Waals forces to achieve extraction, while methyl glycol and water interact through hydrogen bonds to remain in the aqueous phase. Methyl tributyl phosphonium bistrifluoromethanesulfonimide salt preferentially interacts with trioxane through van der Waals forces, breaking the azeotrope of trioxane, water, and methyl glycol. In addition, methyl tributyl phosphonium bistrifluoromethanesulfonimide salt is strongly nonpolar and immiscible with strongly polar water. At the same time, since methyl glycol is strongly polar, it will be tightly bound to water through strong hydrogen bonds, thus remaining in the aqueous phase and not being extracted. This reflects that there is almost no water and methyl glycol in the extraction phase except for trioxane, and the extractant has a high extraction rate for trioxane. Therefore, in the subsequent separation process, only simple rectification is needed to obtain high-purity trioxane.

[0021] As shown by σ-profile analysis (such as Figure 2 and Figure 3 ), it can be concluded that the σ distribution widths of water and methyl glycol are very similar, and there are significant peaks in the hydrogen bond donor region (σ<-0.0082e / Å 2 ) and the hydrogen bond acceptor region (σ>0.0082e / Å 2 ), which indicates that water and methyl glycol can act as both hydrogen bond donors and hydrogen bond acceptors. The σ distribution range of trioxane is relatively narrow, and it is mainly distributed in the nonpolar region (-0.0082<σ<0.0082e / Å 2 ) with a relatively strong peak. Due to the influence of the three oxygen atoms, part of the peak area appears in the hydrogen bond acceptor region, but the peak is close to the nonpolar region, and there is a small part of the distribution in the hydrogen bond donor region, which indicates that trioxane is only a weak hydrogen bond donor and acceptor. Obviously, the reason why trioxane, water, and methyl glycol are difficult to separate is that trioxane forms weak hydrogen bonds with water and methyl glycol. The difference in the σ distribution of trioxane, water, and methyl glycol in the nonpolar region provides a basis for the extraction separation of trioxane. For [P 4441 ][TF2N], [P 4441 ] + , the σ distribution peaks of [P 4441 ] + cation are located in the nonpolar region, and only a small amount of peaks are located in the hydrogen bond donor region, which indicates that [P + cation has weak hydrogen bond donor ability. [TF2N] +The σ distribution peak is also located in the nonpolar region, with a strong peak in the hydrogen bond acceptor region near the nonpolar region, indicating that [TF2N] + Anions have hydrogen bond acceptor capabilities. It is obvious that [P] 4441 ] + and [TF2N] - They are bonded together by van der Waals forces and weak hydrogen bonds. [P] 4441 The high selectivity of [TF2N] for trioxymethylene stems from the high matching of the σ peak, which enhances the solubility of trioxymethylene. Simultaneously, it exhibits almost no overlap with the strongly polar peaks of water and methyl glycol, resulting in better solubility of water and methyl glycol in [P... 4441 The solubility of [TF2N] is extremely low, and the strong hydrogen bonds formed between water and methyl glycol further retain methyl glycol in the aqueous phase.

[0022] A molecular model was constructed using Gauss View, optimized in Gaussian, and the optimal interaction configuration between the anions and cations and trioxymethylene was calculated. Figure 4 As shown, from Figure 4 This shows the lowest and most stable energy configuration for the interaction between the trioxymethylene molecule and the extractant's cations and anions. The interaction energy is expressed as ΔE = E AB -E A -E B +E BSSE The calculations and specific results are shown in the table below:

[0023]

[0024] As can be seen from the table above, the interaction energy between cations and trioxymethylene is greater than that between anions and trioxymethylene. Therefore, cations play a major role in the extraction process.

[0025] The contributions of different physical components are obtained through energy decomposition. Energy decomposition breaks down the total intermolecular interaction energy (ΔEint) into electrostatic interaction energy (ΔEels), exchange-repulsion interaction energy (ΔExrep), orbital overlap interaction energy (ΔEorb), and dispersion interaction energy (ΔEdisp). The weak interaction energy is decomposed using SobEDAw. The dispersion correction term in SobEDAw is calculated using the DFT-D3(BJ) dispersion correction method, and basis set superposition error correction is incorporated. The specific results are as follows:

[0026] ΔEint ΔEels ΔExrep ΔEorb ΔEdisp [[P 4441 ] + +TOX]]> -75.04 -31.51 66.54 -30.33 -79.74 [[TF2N] - +TOX]]> -47.40 -19.29 27.35 -12.24 -43.22

[0027] As can be seen from the energy decomposition table above, the dispersive interaction, also known as van der Waals interaction, is the strongest, indicating that the interaction between ionic liquid and trioxymethylene is mainly due to van der Waals forces, with hydrogen bonding being secondary.

[0028] Molecular dynamics simulation was performed on the extraction process, and the simulation molecule number was placed according to the azeotropic composition of trioxane-water-methylene glycol (methylene glycol). The extraction process was simulated using Gromacs software based on the GAFF force field, as shown in Figure 5 , which is the system after extraction is completed, wherein the blue molecules are water, the red molecules are methylene glycol, the green molecules are trioxane, and the orange molecules are [P 4441 ][TF2N]. As can be seen from the figure, most of the trioxane enters the ionic liquid, and the methylene glycol remains in the water. Radial distribution function analysis was performed on the simulation results, as shown in Figure 6 and Figure 7 , it can be seen from Figure 6 that the longitudinal coordinates of the first peaks of MG-M and W-W are both greater than 1, indicating that water forms clusters, and methylene glycol is surrounded by water, proving that methylene glycol remains in the water phase; it can be seen from Figure 7 that the abscissa of the first peak of the cation is smaller than that of the anion, thereby proving that the cation has a greater force on trioxane.

[0029] The above technical solutions of the present application are as a whole, each step is closely related to each other, and they jointly determine the morphology characteristics and performance of the product.

[0030] The above technical solutions have the following advantages or beneficial effects:

[0031] 1. When the ionic liquid extractant described in the present application is used to extract and rectify trioxane, the ternary azeotropic system of trioxane, water and methylene glycol can be broken, methylene glycol and water can be left in the water phase through hydrogen bonding, and ionic liquid and trioxane can interact with each other through non-polar van der Waals force, thereby realizing efficient extraction of trioxane, with an extraction rate of 96.55wt.%, and a purification degree of trioxane ≥99.5wt.%;

[0032] 2. The ionic liquid extractant described in the present application can be recycled, and after 5 cycles, the purification degree of trioxane can still reach more than 99wt.%;

[0033] 3. The ionic liquid extractant described in the present application can directly interact with trioxane, avoiding the problem of interaction between the extractant and the complex polymers contained in the formaldehyde solution, thereby reducing the difficulty of subsequent rectification and purification operation of trioxane, making the rectification and purification process easier to control and more efficient;

[0034] 4. The present application breaks through the limitations of traditional processes, and does not need to pre-concentrate the trioxane synthesis liquid, omits the whole set of concentration device and the corresponding energy consumption, and shortens the process flow.

[0035] The technical solutions of the present application will be further described in detail below in combination with the drawings in the specification and specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 The process flow chart for preparing trioxane in the embodiments of the present application, wherein: E1 is a formaldehyde evaporator, R1 is a trioxane reactor, T1 is a trioxane extraction column, T2 is an extractant recovery column, T3 is a trioxane rectification column, E2 is a first total condenser, E6 is a second total condenser, E4 is a partial condenser, E3 is a first reboiler, E5 is a second reboiler, and E7 is a third reboiler;

[0037] Figure 2 The σ-profile chart of trioxane, water, and methyl glycol, wherein: the left side is a hydrogen bond donor zone, the middle is a nonpolar zone, and the right side is a hydrogen bond acceptor zone;

[0038] Figure 3 The σ-profile chart of the anion and cation of methyl tributyl phosphonium bistrifluoromethanesulfonimide, trioxane, water, and methyl glycol, wherein: the left side is a hydrogen bond donor zone, the middle is a nonpolar zone, and the right side is a hydrogen bond acceptor zone;

[0039] Figure 4 The optimal interaction configuration chart of the anion and cation of methyl tributyl phosphonium bistrifluoromethanesulfonimide and trioxane, wherein: (a) is the optimal interaction configuration chart of the methyl tributyl phosphonium cation and trioxane, and (b) is the optimal interaction configuration chart of the bistrifluoromethanesulfonimide anion and trioxane;

[0040] Figure 5 The molecular dynamics simulation chart of water, methyl glycol, trioxane, and [P 4441 ][TF2N], wherein: the blue molecules are water, the red molecules are methyl glycol, the green molecules are trioxane, and the orange molecules are [P 4441 ][TF2N];

[0041] Figure 6 The radial distribution function chart of the molecular dynamics simulation results, wherein: MG-W refers to the radial distribution function curve of water around methyl glycol, and W-W refers to the radial distribution function curve of water around water;

[0042] Figure 7 The radial distribution function chart of the molecular dynamics simulation results, wherein: [P 4441 ] + -TOX refers to the radial distribution function curve of trioxane around [P 4441 ] + -TOX refers to the radial distribution function curve of trioxane around [TF2N] - -TOX refers to the radial distribution function curve of trioxane around [TF2N] - -TOX refers to the radial distribution function curve of trioxane around [TF2N]. DETAILED DESCRIPTION

[0043] The following examples are merely illustrative of the present application and are not intended to limit the scope of the application. Therefore, the detailed description of the present application provided below is not intended to limit the scope of the application, but merely to represent selected embodiments of the application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0044] In the present application, all the equipment and raw materials, etc. can be purchased from the market or commonly used in the industry, unless otherwise specified. The methods in the following examples are conventional methods in the art, unless otherwise specified.

[0045] The present application utilizes the acid-catalyzed condensation of aqueous formaldehyde solution to generate trioxane, which is purified by extraction with an ionic liquid, and the specific process is as follows: Figure 1 The system is implemented according to the following pipeline connection sequence: a formaldehyde evaporator E1, a trioxane reactor R1, a trioxane extraction column T1, an extractant recovery column T2, and a trioxane rectifying column T3. The top of the trioxane extraction column T1 is connected to a first total condenser E2 through a pipeline, and the outlet of the first total condenser E2 is connected to the top of the trioxane extraction column T1 through a pipeline. The bottom of the trioxane extraction column T1 is connected to a first reboiler E3 through a pipeline, and the outlet of the first reboiler E3 is connected to the bottom of the trioxane extraction column T1. The top of the extractant recovery column T2 is connected to a partial condenser E4 through a pipeline, and the outlet of the partial condenser E4 is connected to the inlet of the trioxane reactor R1 through a pipeline, to the top of the extractant recovery column T2 through a pipeline, and to the inlet of the trioxane rectifying column T3 through another pipeline. The bottom of the extractant recovery column T2 is connected to the top of the trioxane extraction column T1 through a pipeline, and to a second reboiler E5 through a pipeline, and the outlet of the second reboiler E5 is connected to the bottom of the extractant recovery column T2. The top of the trioxane rectifying column T3 is connected to a second total condenser E6 through a pipeline, and the outlet of the second total condenser E6 is connected to the bottom of the trioxane extraction column T1 through a pipeline and to the top of the trioxane rectifying column T3 through a pipeline. The bottom of the trioxane rectifying column T3 is connected to a third reboiler E7 through a pipeline, and the outlet of the third reboiler E7 is connected to the bottom of the trioxane rectifying column T3.

[0046] The following examples 1-3 are implemented by the system.

[0047] Example 1

[0048] The present example provides an application of ionic liquid in the extraction of trioxane, in which trioxane is first generated by acid-catalyzed condensation of aqueous formaldehyde solution, and then purified by extraction with an ionic liquid, and the specific process is as follows:

[0049] S1, 60wt.% formaldehyde aqueous solution was fed into a fixed tube reactor with Amberlyst-15 at a flow rate of 1000 kg / h (space velocity 0.8 h -1 ), and reacted for 2.5 h at 100°C and 0.1 MPa to produce 1000 kg / h of a synthesis solution containing trioxane, wherein the synthesis solution contained 480 kg / h of trioxane;

[0050] S2, the synthesis solution containing trioxane was fed into an extraction column, which was a plate column with float valve trays, 10 m in height, 0.5 m in diameter, 0.3 m in tray spacing, 28 trays in total, the feed position of the synthesis solution containing trioxane was the 4th tray from the bottom, at 0.1 MPa, 60°C at the top of the column and 85°C at the bottom of the column, methyltributylphosphonium bistrifluoromethanesulfonimide was injected into the 2nd tray from the top of the column at a flow rate of 1000 kg / h, the mass flow ratio of methyltributylphosphonium bistrifluoromethanesulfonimide to the synthesis solution containing trioxane was controlled to be 1:1, the formaldehyde solution at the top of the column was recycled to a formaldehyde evaporator, and the ionic liquid phase containing trioxane was collected at the bottom of the column, wherein the ionic liquid phase contained 456 kg / h of trioxane;

[0051] S3, the ionic liquid phase containing trioxane was fed into a recovery column, which was a plate column with float valve trays, 8 m in height, 0.8 m in diameter, 0.4 m in tray spacing, 16 trays in total, the feed position of the ionic liquid phase containing trioxane was the 3rd tray from the bottom, and the column was separated at 0.1 MPa, 80°C at the top of the column and 180°C at the bottom of the column, 93wt.% crude trioxane was obtained at the top of the column, and 99.5wt.% ionic liquid was recovered at the bottom of the column, the ionic liquid was dehydrated at 80°C and 0.005 MPa for 2 h under reduced pressure, and then recycled to step S2 as the injected ionic liquid;

[0052] S4, the crude trioxane of step S3 was fed into a rectification column, which was a plate column with float valve trays, 12 m in height, 1.0 m in diameter, 0.4 m in tray spacing, 26 trays in total, the feed position of the crude trioxane was the 4th tray from the bottom, and the column was refined at 0.6 MPa, 80°C at the top of the column and 70°C at the bottom of the column, trioxane-water-formaldehyde azeotrope was collected at the top of the column and recycled to the feed inlet of the extraction column, and 99.5wt.% high-purity trioxane was collected at the bottom of the column at a flow rate of 396.4 kg / h.

[0053] Example 2

[0054] The present embodiment provides an application of ionic liquid in the extraction of trioxane, in which trioxane is first generated from formaldehyde aqueous solution by acid-catalyzed condensation, and then purified by ionic liquid extraction, and the specific process is as follows:

[0055] S1, 55wt.% formaldehyde aqueous solution was fed into a fixed tube reactor with Amberlyst-15 at a flow rate of 1000 kg / h (space velocity 0.8 h -1 ), and reacted for 3.5 h at 101 °C and 0.11 MPa to produce 1000 kg / h of a synthesis solution containing trioxane, wherein the trioxane content was 440 kg / h;

[0056] S2, the synthesis solution containing trioxane was fed into an extraction column, which was a plate column with float valve trays, 20 m in height, 1.7 m in diameter, 0.45 m in tray spacing, 41 trays in total, the feed position of the synthesis solution containing trioxane was the 6th tray from the bottom, at 0.11 MPa, 50 °C at the top and 70 °C at the bottom, methyltributylphosphonium bistrifluoromethanesulfonimide was injected into the 4th tray from the top at a flow rate of 1500 kg / h, the mass flow ratio of methyltributylphosphonium bistrifluoromethanesulfonimide to the synthesis solution containing trioxane was controlled at 1.5:1, the formaldehyde solution at the top was recycled to a formaldehyde evaporator, and the ionic liquid phase containing trioxane at the bottom was collected, wherein the trioxane content was 418 kg / h;

[0057] S3, the ionic liquid phase containing trioxane was fed into a recovery column, which was a plate column with float valve trays, 16 m in height, 1.6 m in diameter, 0.5 m in tray spacing, 29 trays in total, the feed position of the ionic liquid phase containing trioxane was the 4th tray from the bottom, at 0.11 MPa, 90 °C at the top and 150 °C at the bottom, 94wt.% trioxane crude was obtained at the top, and 99.5wt.% ionic liquid was recovered at the bottom, which was dehydrated at 80 °C and 0.001 MPa for 2 h under reduced pressure, and then recycled to step S2 as the injected ionic liquid;

[0058] S4, the trioxane crude from step S3 was fed into a rectification column, which was a plate column with float valve trays, 20 m in height, 2.0 m in diameter, 0.5 m in tray spacing, 37 trays in total, the feed position of the trioxane crude was the 5th tray from the bottom, at 0.5 MPa, 90 °C at the top and 65 °C at the bottom, trioxane-water-formaldehyde azeotrope was collected at the top and recycled to the feed inlet of the extraction column, and 99.6wt.% high-purity trioxane was collected at the bottom at a flow rate of 366 kg / h.

[0059] Example 3

[0060] The present embodiment provides an application of ionic liquid in the extraction of trioxane, in which trioxane is first generated from formaldehyde aqueous solution through acid-catalyzed condensation, and then purified by ionic liquid extraction, the specific process is as follows:

[0061] S1, pass 1000 kg / h of 50 wt.% formaldehyde aqueous solution into a fixed bed reactor with Amberlyst-15 (space velocity is 0.8 h -1 ), under the conditions of 102℃ and 0.09 MPa for 4 h, to generate 1000 kg / h of a synthesis solution containing trioxane, wherein the synthesis solution contains 400 kg / h of trioxane;

[0062] S2, pass the synthesis solution containing trioxane into an extraction column, which is a plate column with float valve trays, with a column height of 28 m, a column diameter of 3.0 m, a tray spacing of 0.6 m, and 44 trays, and the synthesis solution containing trioxane is fed at the 7th tray from the bottom, under the conditions of 0.09 MPa, 65℃ at the top of the column, and 80℃ at the bottom of the column, inject methyl tributyl phosphonium bistrifluoromethanesulfonimide at the 5th tray from the top of the column at a rate of 2000 kg / h, control the mass flow ratio of methyl tributyl phosphonium bistrifluoromethanesulfonimide to the synthesis solution containing trioxane to be 2:1, and take the formaldehyde solution at the top of the column to a formaldehyde evaporator, and take the ionic liquid phase containing trioxane at the bottom of the column, wherein the ionic liquid phase contains 320 kg / h of trioxane;

[0063] S3, pass the ionic liquid phase containing trioxane into a recovery column, which is a plate column with float valve trays, with a column height of 20 m, a column diameter of 2.5 m, a tray spacing of 0.6 m, and 31 trays, and the ionic liquid phase containing trioxane is fed at the 5th tray from the bottom, under the conditions of 0.09 MPa, 120℃ at the top of the column, and 200℃ at the bottom of the column, to separate, obtain 96 wt.% crude trioxane at the top of the column, and recover 99.5 wt.% ionic liquid at the bottom of the column, and the ionic liquid is dehydrated under reduced pressure at 80℃ and 0.01 MPa for 2 h, and then recycled to step S2;

[0064] S4, pass the crude trioxane into a rectification column, which is a plate column with float valve trays, with a column height of 25 m, a column diameter of 3.0 m, a tray spacing of 0.6 m, and 39 trays, and the crude trioxane is fed at the 7th tray from the bottom, under the conditions of 0.8 MPa, 120℃ at the top of the column, and 80℃ at the bottom of the column, to refine, take the trioxane-water-formaldehyde azeotrope at the top of the column and recycle it to the feed inlet of the extraction column, and take 99.5 wt.% high-purity trioxane at the bottom of the column at a rate of 278.4 kg / h.

[0065] Comparative Example

[0066] In order to explore the effects of different ionic liquids and the mass flow ratio of ionic liquid to formaldehyde aqueous solution on the extraction of trioxane, the following comparative experiments were conducted, as follows:

[0067] Comparative Example 1

[0068] The comparative examples respectively use different ionic liquids as extractant to extract trioxane, the synthesis and extraction process of trioxane is similar to example 1, the difference is only that the methyl tributyl phosphonium bis-trifluoromethanesulfonimide salt is replaced by the following substances, as follows:

[0069] Group A: the methyl tributyl phosphonium bis-trifluoromethanesulfonimide salt is replaced by 1-octyl-3-methyl imidazole bis-trifluoromethanesulfonimide salt;

[0070] Group B: the methyl tributyl phosphonium bis-trifluoromethanesulfonimide salt is replaced by 1-ethyl-3-methyl imidazole bis-trifluoromethanesulfonimide salt;

[0071] Group C: the methyl tributyl phosphonium bis-trifluoromethanesulfonimide salt is replaced by 1-butyl-3-methyl imidazole bis-trifluoromethanesulfonimide salt;

[0072] Group D: the methyl tributyl phosphonium bis-trifluoromethanesulfonimide salt is replaced by 1-hexyl-3-methyl imidazole bis-trifluoromethanesulfonimide salt.

[0073] Comparative example 2

[0074] The comparative example provides an application of ionic liquid in extracting trioxane, the synthesis and extraction process of trioxane is similar to example 1, the difference is only that in step S2, the mass flow ratio of methyl tributyl phosphonium bis-trifluoromethanesulfonimide salt to the synthesis liquid containing trioxane is different, as follows:

[0075] Group A: the mass flow ratio of methyl tributyl phosphonium bis-trifluoromethanesulfonimide salt to the synthesis liquid containing trioxane is controlled to be 0.5:1;

[0076] Group B: the mass flow ratio of methyl tributyl phosphonium bis-trifluoromethanesulfonimide salt to the synthesis liquid containing trioxane is controlled to be 3:1.

[0077]

[0078]

[0079] Finally, it should be noted that the above only for the preferred embodiments of the present application, and is not intended to limit the present application, although the foregoing embodiments of the present application have been described in detail, for those skilled in the art, it still can be modified, or the equivalent replacement of part of the technical features recorded in the foregoing embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application, shall be included in the scope of protection of the claims of the present application.

Claims

1. Use of an ionic liquid in the extraction of trioxane, characterized in that, In a process of preparing trioxane by acid catalyzed condensation of formaldehyde aqueous solution, an ionic liquid is added as an extractant to extract trioxane from the reaction system; the ionic liquid is methyltributylphosphonium bis(trifluoromethylsulfonyl)imide, wherein the cation is methyltributylphosphonium ion and the anion is bis(trifluoromethylsulfonyl)imide ion.

2. Use of an ionic liquid according to claim 1 for the extraction of trioxane, characterized in that, The process of preparing trioxane by acid catalyzed condensation of formaldehyde aqueous solution is carried out in the following order: S1, passing 50-60 wt.% formaldehyde aqueous solution into a fixed-bed reactor with a solid acid catalyst at 100-102 ℃ and 0.09-0.11 MPa for 2.5-4 h to produce a synthesis solution containing trioxane; S2, passing the synthesis solution containing trioxane into an extraction column at 0.09-0.11 MPa, 50-65 ℃ at the top and 70-85 ℃ at the bottom, injecting the ionic liquid, and collecting the ionic liquid phase containing trioxane at the bottom of the column; S3, passing the ionic liquid phase containing trioxane into a recovery column at 0.09-0.11 MPa, 80-120 ℃ at the top and 150-200 ℃ at the bottom to separate the crude trioxane at the top and the ionic liquid at the bottom, which is recycled to step S2; S4, passing the crude trioxane of step S3 into a rectifying column at 0.5-0.8 MPa, 80-120 ℃ at the top and 65-80 ℃ at the bottom to collect the trioxane-water-formaldehyde azeotrope at the top and recycle it to the extraction column, and collect the high-purity trioxane at the bottom.

3. Use of an ionic liquid according to claim 2 for the extraction of trioxane, characterized in that, In step S1, the solid acid catalyst is Amberlyst-15.

4. Use of an ionic liquid according to claim 2 for the extraction of trioxane, characterized in that, In step S2, the extraction column has a height of 10-28 m, a diameter of 0.5-3.0 m, 28-44 plates, and a plate spacing of 0.3-0.6 m, and the feed inlet of the synthesis solution containing trioxane is located at the 4th-7th plate from the bottom.

5. Use of an ionic liquid according to claim 2 for the extraction of trioxane, characterized in that, In step S2, the mass flow ratio of the ionic liquid to the synthesis solution containing trioxane is (1-2):1, and the feed inlet of the ionic liquid is located at the 2nd-5th plate from the top.

6. Use of an ionic liquid according to claim 2 for the extraction of trioxane, characterized in that, In step S3, the recovery column has a height of 8-20 m, a diameter of 0.8-2.5 m, 16-31 plates, and a plate spacing of 0.4-0.6 m, and the feed inlet of the ionic liquid phase containing trioxane is located at the 3rd-5th plate from the bottom.

7. Use of an ionic liquid according to claim 2 for the extraction of trioxane, characterized in that, In step S3, the recovered ionic liquid is dehydrated at 80 ℃ and 0.001-0.01 MPa for 2 h, and then recycled to step S2.

8. Use of an ionic liquid according to claim 2 for the extraction of trioxane, characterized in that, In step S4, the rectifying column has a height of 12-25 m, a diameter of 1.0-3.0 m, 26-39 plates, and a plate spacing of 0.4-0.6 m, and the feed inlet of the crude trioxane is located at the 4th-7th plate from the bottom.

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