Rectification technology for purifying and recovering dimethyl tetrahydrofuran and trimethyl tetrahydrofuran from tetrahydrofuran raffinate

Abstract

The invention relates to the technical field of permanent magnetic ferrite materials, in particular to a rectification technology for purifying and recovering dimethyl tetrahydrofuran and trimethyl tetrahydrofuran from tetrahydrofuran raffinate. The preparation method comprises the following steps: preliminary extractive distillation of tetrahydrofuran raffinate; preparing an extracting agent [Hemim] [Ac] and extracting; preparing a molecular sieve membrane separation tube; and tetrahydrofuran, dimethyl tetrahydrofuran and trimethyl tetrahydrofuran are separated by a rectifying tower. According to the invention, mordenite is used as a seed crystal liquid and is crystallized under the combined action of mordenite and calcined kaolin, and a crystallized product is used for preparing the molecular sieve membrane separation tube, so that the selectivity of tetrahydrofuran molecules is improved; according to the molecular sieve membrane separation tube, tetrahydrofuran, dimethyl tetrahydrofuran and trimethyl tetrahydrofuran can be obviously separated from water molecules and other impurity molecules, so that water is efficiently removed, and the recovery rate of the dimethyl tetrahydrofuran and the trimethyl tetrahydrofuran is increased.

Description

Technical Field

[0001] The invention relates to the technical field of waste liquid treatment, and in particular to a distillation technology for purifying tetrahydrofuran residue and recovering dimethyltetrahydrofuran and trimethyltetrahydrofuran. Background Art

[0002] BDO (1,4-butanediol) can be used to prepare tetrahydrofuran. This process is usually achieved through the dehydration cyclization reaction of BDO. BDO is converted into tetrahydrofuran through a dehydration reaction under the action of a catalyst. The waste liquid generated in the process of preparing tetrahydrofuran from BDO may contain incompletely reacted BDO, catalyst residues, by-products and possible impurities. There may still be a certain amount of tetrahydrofuran and other compounds in the waste liquid after the preparation. The residual liquid containing a large amount of tetrahydrofuran can be separated and purified through preliminary separation.

[0003] In the prior art, after separating a residual liquid containing a large amount of tetrahydrofuran, water is directly removed by distillation to obtain a tetrahydrofuran product with low purity. However, other impurity molecules such as dimethyltetrahydrofuran and trimethyltetrahydrofuran are also present in the residual liquid, which is also the reason for the low purity of tetrahydrofuran. Therefore, the present invention provides a distillation technology for purifying and recovering dimethyltetrahydrofuran and trimethyltetrahydrofuran from tetrahydrofuran residual liquid to solve the above-mentioned shortcomings of the prior art. Summary of the invention

[0004] In view of the shortcomings of the prior art, the object of the present invention is to provide a distillation technology for purifying tetrahydrofuran residue to recover dimethyltetrahydrofuran and trimethyltetrahydrofuran.

[0005] A distillation technology for purifying tetrahydrofuran residue to recover dimethyltetrahydrofuran and trimethyltetrahydrofuran comprises the following steps:

[0006] S1: Preliminary extractive distillation of tetrahydrofuran residue

[0007] Add THF waste liquid to the tower bottom tank, heat and reflux, obtain tower top distillate and primary bottom liquid after reflux, add primary bottom liquid to the tower bottom tank, heat and reflux, collect tower top distillate and secondary bottom liquid after reflux, heat the secondary bottom liquid, take the upper layer liquid, and cool to room temperature to obtain treated liquid, add treated liquid to the tower bottom tank, turn on the heating and insulation switches, heat until the liquid in the tower bottom tank is fully refluxed, collect the tower top liquid, and obtain distillate;

[0008] S2: Preparation of extractant [Hemim][Ac] and extraction

[0009] In a nitrogen atmosphere, N-methylimidazole and 2-bromoethanol are mixed and reacted to obtain intermediate I. Ethyl acetate solution and acetonitrile solution are mixed, and intermediate I is added thereto. After being fully dissolved, the mixture is refluxed. After the reflux is completed, the mixture is allowed to stand and cooled to room temperature. The mixture is recrystallized, filtered, and dried to obtain [Hemim][Br]. [Hemim][Br] is placed in a beaker, and deionized water is added thereto for dissolution. The solution is then poured into an OH-type anion exchange resin for reaction to obtain [Hemim][OH]. Acetic acid solution and [Hemim][OH] are mixed and added to a round-bottom flask for reaction to obtain intermediate II. Anhydrous ethanol and acetonitrile are mixed and added to an equal volume of intermediate II for reaction to obtain an extractant [Hemim][Ac]. The distillate is placed in a constant temperature water bath. After the layers are stabilized, the extractant [Hemim][Ac] is added thereto for extraction. The upper clear liquid is an alcohol phase, and the lower clear liquid is an aqueous phase. The lower clear liquid is collected to obtain a tetrahydrofuran aqueous solution.

[0010] S3: Preparation of molecular sieve membrane separation tube

[0011] Adding deionized water to mordenite with a particle size of 5 μm to prepare a large seed solution, grinding the mordenite to 700 nm and then adding deionized water to prepare a small seed solution, mixing the large seed solution and the small seed solution to obtain a mixed seed solution, mixing calcined kaolin, sodium hydroxide and deionized water, and then adding the mixed seed solution to a reaction solution, and obtaining a synthetic solution while maintaining room temperature, sealing both ends of a ceramic tube with polytetrafluoroethylene plugs, quickly placing it in the synthetic solution, taking it out after soaking and drying it, and then placing it in a microwave oven for microwave crystallization to obtain a crystallized product, washing, filtering and drying the crystallized product to obtain a molecular sieve membrane separation tube;

[0012] S4: Distillation tower to separate tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran

[0013] Both ends of the molecular sieve membrane separation tube are sealed and installed in a separator, which is placed in a tetrahydrofuran aqueous solution. The carrier side is connected to a vacuum pump through a cold trap to remove water to obtain a mixture of tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran. The mixture of tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran is added to a distillation tower system, and tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran are separated by gas chromatography separation technology.

[0014] Furthermore, step S1 of preliminary extractive distillation of tetrahydrofuran residue comprises the following steps:

[0015] S1.1: Add THF waste liquid to the bottom tank of the tower and heat it to 65°C. Pass the tetrahydrofuran residual liquid preheated to 65°C into the tower. Continue heating to make the liquid in the bottom tank reflux completely. After the reflux is completed, obtain the top distillate and the first bottom liquid;

[0016] S1.2: Add the primary kettle liquid to the tower kettle and heat it to 90°C. Pass the primary kettle liquid preheated to 90°C into the tower and continue heating to make the liquid in the tower kettle reflux completely. After the reflux is completed, collect the distillate from the top of the tower and the secondary kettle liquid.

[0017] S1.3: Heat the secondary kettle liquid to 80°C and keep it for 1 hour, take the upper layer of liquid, and cool it to room temperature to obtain the treated liquid;

[0018] S1.4: Add the treated liquid to the bottom tank of the tower, and turn on the heating and insulation switches to heat until the liquid in the bottom tank is fully refluxed. Add the treated liquid heated to 60°C into the tower and keep it for 2-3 hours. Collect the liquid at the top of the tower to obtain the distillate.

[0019] Further, step S2 prepares the extractant [Hemim][Ac] and extracts, comprising the following steps:

[0020] S2.1: Under nitrogen atmosphere, N-methylimidazole and 2-bromoethanol were mixed in a reaction bottle, and the mixture was stirred at 100-120°C for 44-48 hours. After the reaction, the product was washed three times with anhydrous ethanol to obtain intermediate I;

[0021] S2.2: Mix 7 parts by volume of ethyl acetate solution and 3 parts by volume of acetonitrile solution, add 6 parts by volume of intermediate I, and reflux in an oil bath at 60-80°C after sufficient dissolution. After reflux is completed, cool to room temperature by standing, seal and place at 0-4°C for recrystallization for 2-4h, filter and collect the solid product, and dry at 65-70°C for 24h to obtain [Hemim][Br];

[0022] S2.3: Place [Hemim][Br] in a beaker, add deionized water to dissolve, then pour the solution into an OH-type anion exchange resin to react for 2 h to obtain [Hemim][OH], mix the acetic acid solution and [Hemim][OH] and add them to a round-bottom flask, react for 45-48 h under stirring to obtain intermediate II;

[0023] S2.4: Anhydrous ethanol and acetonitrile are mixed in a volume ratio of 9:1, added to an equal volume of intermediate II, stirred for reaction for 4.5-5 hours, and after the reaction is completed, low-temperature cooling is performed to precipitate unreacted acetic acid, and then filtered. Finally, the resulting solution is vacuum dried at 55-60°C for 45-48 hours to obtain an extractant [Hemim][Ac];

[0024] S2.5: Place the distillate in a constant temperature water bath at 80°C. After the layers are stabilized, add the extractant [Hemim][Ac] for extraction. The upper clear liquid is the alcohol phase and the lower clear liquid is the water phase. Collect the lower clear liquid to obtain a tetrahydrofuran aqueous solution.

[0025] Furthermore, in step S2.3, the material-liquid ratio of [Hemim][Br] and deionized water is 1:(8-10).

[0026] Furthermore, in step S2.3, the mass ratio of the acetic acid solution to [Hemim][OH] is 2:(3-5).

[0027] Furthermore, in step S2.5, the amount of the extractant [Hemim][Ac] added is 10-15% of the total volume of the system.

[0028] Furthermore, step S3 of preparing a molecular sieve membrane separation tube comprises the following steps:

[0029] S3.1: Add deionized water to 5 μm mordenite to prepare a large seed solution of 0.2 g / L, grind the mordenite to 700 nm and add deionized water to prepare a small seed solution of 0.3 g / L, mix the large seed solution and the small seed solution to obtain a mixed seed solution;

[0030] S3.2: 15 parts by mass of calcined kaolin, 24 parts by mass of sodium hydroxide, 34 parts by mass of silica sol and 220 parts by mass of deionized water were mixed and stirred, and then 2% by mass of mixed seed solution was added to the reaction solution, and stirred at a speed of 600-800 r / min for 5 hours while maintaining room temperature to obtain a synthetic solution;

[0031] S3.3: Seal both ends of the ceramic tube with polytetrafluoroethylene stoppers, quickly put it into the synthetic liquid, soak for 20 seconds, take it out and dry it, then put it into the microwave oven for microwave crystallization for 80-90 minutes to obtain a crystallized product, wash and filter the crystallized product until the pH of the washing liquid is <11, and then dry the washed crystallized product at 105°C to obtain a molecular sieve membrane separation tube.

[0032] Furthermore, in step S3.1, the large seed crystal solution and the small seed crystal solution are mixed in a volume ratio of 1:1.

[0033] Furthermore, in step S3.3, the microwave oven power is set to 700w.

[0034] Further, step S4, the distillation tower separates tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran, comprising the following steps:

[0035] S4.1: Both ends of the molecular sieve membrane separation tube are sealed and placed in a separator, which is placed in a tetrahydrofuran aqueous solution. The carrier side is connected to a vacuum pump through a cold trap. The tetrahydrofuran aqueous solution directly contacts the permeation side of the mordenite membrane. Water molecules penetrate the zeolite membrane into the carrier side under the action of the pressure difference. The vacuum system promptly takes away the permeated water, which is condensed by liquid nitrogen and collected in a cold trap to obtain a mixture of tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran;

[0036] S4.2: Add a mixed liquid of tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran into a distillation tower system, and separate tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran by gas chromatography separation technology.

[0037] Compared with the prior art, the present invention has at least the following beneficial effects:

[0038] 1. The present invention uses mordenite as a seed liquid and crystallizes it together with calcined kaolin, and uses the crystallized product to prepare a molecular sieve membrane separation tube. Kaolin and mordenite themselves have certain pore structures. After the calcined kaolin changes its own crystal structure and increases the porosity and specific surface area, the two can be combined to form a typical tetrahedral structure with a large cage-like cavity and a twelve-membered ring or eight-membered ring window. Such a structure can screen molecules of a specific size, thereby improving the selectivity for tetrahydrofuran molecules, so that the molecular sieve membrane separation tube can clearly distinguish tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran from water molecules and other impurity molecules, thereby efficiently removing water and improving the recovery rate of dimethyltetrahydrofuran and trimethyltetrahydrofuran.

[0039] 2. The present invention uses [Hemim][Ac] to extract tetrahydrofuran residue. The [Hemim][Ac] extractant has good selectivity for tetrahydrofuran. The acetate and anion of [Hemim][Ac] interact with the groups of tetrahydrofuran, so that [Hemim][Ac] can specifically combine with tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran in the waste liquid. In the tetrahydrofuran residue prepared from tetrahydrofuran by BDO (1,4-butanediol), a small amount of unreacted BDO will still exist in the tetrahydrofuran residue due to the large amount of BDO added. [Hemim][Ac] not only has good selectivity for tetrahydrofuran, but also has good separation performance for alcohol substances. Using [Hemim][Ac] as an extractant can increase the content of tetrahydrofuran and its methyl compounds and reduce impurities, so that the subsequent separation of dimethyltetrahydrofuran and trimethyltetrahydrofuran will not be interfered by other impurities.

[0040] 3. The present invention prepares two mordenite seed solutions with different particle sizes, and prepares a mixed seed solution by adjusting the ratio of the two seed solutions. The smaller particle size of the mordenite can increase the surface area to volume ratio, shorten the diffusion path of the molecules inside the molecular sieve, and thus improve the adsorption rate of the prepared molecular sieve. However, too small a particle size will affect the crystallization rate and the uniformity of crystallization, thereby affecting the overall adsorption capacity of the molecular sieve membrane separation tube for tetrahydrofuran. Therefore, by compounding two mordenite seed solutions with different particle sizes, the adsorption rate of the molecular sieve can be improved without affecting the adsorption capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The accompanying drawings, which are incorporated herein and constitute a part of the specification, illustrate embodiments of the present disclosure and, together with the description, further serve to explain the principles of the present disclosure and to enable those skilled in the relevant art to make and use the present disclosure.

[0042] Figure 1 The present invention is a flow chart of a distillation technology for purifying and recovering dimethyltetrahydrofuran and trimethyltetrahydrofuran from tetrahydrofuran residue adopted in an embodiment of the present invention. DETAILED DESCRIPTION

[0043] The following is a detailed description of a distillation technology for purifying and recovering dimethyltetrahydrofuran and trimethyltetrahydrofuran from tetrahydrofuran residue provided by the present invention in conjunction with the accompanying drawings and specific embodiments. It is also explained here that, in order to make the embodiments more detailed, the following embodiments are the best and preferred embodiments, and those skilled in the art may also adopt other alternatives to implement some known technologies; and the accompanying drawings are only for more specific description of the embodiments, and are not intended to specifically limit the present invention.

[0044] Embodiment 1:

[0045] A distillation technology for purifying tetrahydrofuran residue to recover dimethyltetrahydrofuran and trimethyltetrahydrofuran, such as Figure 1 As shown, the following steps are included:

[0046] S1: Preliminary extractive distillation of tetrahydrofuran residue

[0047] S1.1: Add THF waste liquid to the bottom tank of the tower and heat it to 65°C. Pass the tetrahydrofuran residual liquid preheated to 65°C into the tower. Continue heating to make the liquid in the bottom tank reflux completely. After the reflux is completed, obtain the top distillate and the first bottom liquid;

[0048] S1.2: Add the primary kettle liquid to the tower kettle and heat it to 90°C. Pass the primary kettle liquid preheated to 90°C into the tower and continue heating to make the liquid in the tower kettle reflux completely. After the reflux is completed, collect the distillate from the top of the tower and the secondary kettle liquid.

[0049] S1.3: Heat the secondary kettle liquid to 80°C and keep it for 1 hour, take the upper layer of liquid, and cool it to room temperature to obtain the treated liquid;

[0050] S1.4: Add the treatment liquid to the tower kettle, turn on the heating and insulation switches, heat until the liquid in the tower kettle is fully refluxed, add the treatment liquid heated to 60℃ to the tower and keep it for 2h, collect the liquid at the top of the tower to obtain the distillate;

[0051] S2: Preparation of extractant [Hemim][Ac] and extraction

[0052] S2.1: Under nitrogen atmosphere, N-methylimidazole and 2-bromoethanol were mixed in a reaction bottle, and the mixture was stirred at 100°C for 48 h. After the reaction, the product was washed three times with anhydrous ethanol to obtain intermediate I.

[0053] S2.2: Mix 7 parts by volume of ethyl acetate solution and 3 parts by volume of acetonitrile solution, add 6 parts by volume of intermediate I, and reflux in an oil bath at 80°C after sufficient dissolution. After reflux is completed, cool to room temperature, seal and place at 0°C for recrystallization for 2 hours, filter out the solid product, and dry at 65°C for 24 hours to obtain [Hemim][Br];

[0054] S2.3: Place [Hemim][Br] in a beaker and add deionized water to dissolve it. The solid-liquid ratio of [Hemim][Br] to deionized water is 1:10. Then pour the solution into an OH-type anion exchange resin and react for 2 hours to obtain [Hemim][OH]. Mix the acetic acid solution and [Hemim][OH] and add them to a round-bottom flask. The mass ratio of the acetic acid solution to [Hemim][OH] is 2:5. Stir and react for 48 hours to obtain intermediate II.

[0055] S2.4: Anhydrous ethanol and acetonitrile were mixed in a volume ratio of 9:1 and added to an equal volume of intermediate II, and the mixture was stirred for reaction for 4.5 hours. After the reaction was completed, the mixture was cooled at low temperature to precipitate unreacted acetic acid, and then filtered. Finally, the obtained solution was vacuum dried at 60°C for 48 hours to obtain the extractant [Hemim][Ac];

[0056] S2.5: Place the distillate in a constant temperature water bath at 80°C. After the layers are stabilized, add the extractant [Hemim][Ac] for extraction. The amount of the extractant [Hemim][Ac] added is 15% of the total volume of the system. The upper clear liquid is the alcohol phase, and the lower clear liquid is the water phase. Collect the lower clear liquid to obtain a tetrahydrofuran aqueous solution.

[0057] S3: Preparation of molecular sieve membrane separation tube

[0058] S3.1: Add deionized water to 5 μm mordenite to prepare a large seed solution of 0.2 g / L, grind the mordenite to 700 nm and add deionized water to prepare a small seed solution of 0.3 g / L, mix the large seed solution and the small seed solution in a volume ratio of 1:1 to obtain a mixed seed solution;

[0059] S3.2: 15 parts by mass of calcined kaolin, 24 parts by mass of sodium hydroxide, 34 parts by mass of silica sol and 220 parts by mass of deionized water were mixed and stirred, and then 2% by mass of mixed seed solution was added to the reaction solution, and stirred at a speed of 800 r / min for 5 hours while maintaining room temperature to obtain a synthetic solution;

[0060] S3.3: Seal both ends of the ceramic tube with polytetrafluoroethylene stoppers, quickly put it into the synthetic liquid, soak it for 20 seconds, take it out and dry it, then put it into a microwave oven (700w) for microwave crystallization for 80 minutes to obtain a crystallized product, wash and filter the crystallized product until the pH of the washing liquid is <11, and then dry the washed crystallized product at 105°C to obtain a molecular sieve membrane separation tube.

[0061] S4: Distillation tower to separate tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran

[0062] S4.1: Both ends of the molecular sieve membrane separation tube are sealed and placed in a separator, which is placed in a tetrahydrofuran aqueous solution. The carrier side is connected to a vacuum pump through a cold trap. The tetrahydrofuran aqueous solution directly contacts the permeation side of the mordenite membrane. Water molecules penetrate the zeolite membrane into the carrier side under the action of the pressure difference. The vacuum system promptly takes away the permeated water, which is condensed by liquid nitrogen and collected in a cold trap to obtain a mixture of tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran;

[0063] S4.2: Add a mixed liquid of tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran into a distillation tower system, and separate tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran by gas chromatography separation technology.

[0064] Embodiment 2:

[0065] A distillation technology for purifying tetrahydrofuran residue to recover dimethyltetrahydrofuran and trimethyltetrahydrofuran, such as Figure 1 As shown, the following steps are included:

[0066] S1: Preliminary extractive distillation of tetrahydrofuran residue

[0067] S1.1: Add THF waste liquid to the bottom tank of the tower and heat it to 65°C. Pass the tetrahydrofuran residual liquid preheated to 65°C into the tower. Continue heating to make the liquid in the bottom tank reflux completely. After the reflux is completed, obtain the top distillate and the first bottom liquid;

[0068] S1.2: Add the primary kettle liquid to the tower kettle and heat it to 90°C. Pass the primary kettle liquid preheated to 90°C into the tower and continue heating to make the liquid in the tower kettle reflux completely. After the reflux is completed, collect the distillate from the top of the tower and the secondary kettle liquid.

[0069] S1.3: Heat the secondary kettle liquid to 80°C and keep it for 1 hour, take the upper layer of liquid, and cool it to room temperature to obtain the treated liquid;

[0070] S1.4: Add the treatment liquid to the tower kettle, turn on the heating and insulation switches, heat until the liquid in the tower kettle is fully refluxed, add the treatment liquid heated to 60°C to the tower and keep it for 3 hours, collect the liquid at the top of the tower to obtain the distillate;

[0071] S2: Preparation of extractant [Hemim][Ac] and extraction

[0072] S2.1: Under nitrogen atmosphere, N-methylimidazole and 2-bromoethanol were mixed in a reaction bottle, and the mixture was stirred at 120°C for 44 h. After the reaction, the product was washed three times with anhydrous ethanol to obtain intermediate I.

[0073] S2.2: Mix 7 parts by volume of ethyl acetate solution and 3 parts by volume of acetonitrile solution, add 6 parts by volume of intermediate I, and reflux in an oil bath at 60°C after sufficient dissolution. After reflux is completed, cool to room temperature, seal and place at 0°C for recrystallization for 4 hours, filter out the solid product, and dry at 70°C for 24 hours to obtain [Hemim][Br];

[0074] S2.3: Place [Hemim][Br] in a beaker and add deionized water to dissolve it. The solid-liquid ratio of [Hemim][Br] to deionized water is 1:10. Then pour the solution into an OH-type anion exchange resin and react for 2 hours to obtain [Hemim][OH]. Mix the acetic acid solution and [Hemim][OH] and add them to a round-bottom flask. The mass ratio of the acetic acid solution to [Hemim][OH] is 2:5. Stir and react for 48 hours to obtain intermediate II.

[0075] S2.4: Anhydrous ethanol and acetonitrile were mixed in a volume ratio of 9:1 and added to an equal volume of intermediate II, and stirred for reaction for 5 hours. After the reaction was completed, the solution was cooled at low temperature to precipitate unreacted acetic acid, and then filtered. Finally, the obtained solution was vacuum dried at 55°C for 48 hours to obtain the extractant [Hemim][Ac];

[0076] S2.5: Place the distillate in a constant temperature water bath at 80°C. After the layers are stabilized, add the extractant [Hemim][Ac] for extraction. The amount of the extractant [Hemim][Ac] added is 15% of the total volume of the system. The upper clear liquid is the alcohol phase, and the lower clear liquid is the water phase. Collect the lower clear liquid to obtain a tetrahydrofuran aqueous solution.

[0077] S3: Preparation of molecular sieve membrane separation tube

[0078] S3.1: Add deionized water to 5 μm mordenite to prepare a large seed solution of 0.2 g / L, grind the mordenite to 700 nm and add deionized water to prepare a small seed solution of 0.3 g / L, mix the large seed solution and the small seed solution in a volume ratio of 1:1 to obtain a mixed seed solution;

[0079] S3.2: 15 parts by mass of calcined kaolin, 24 parts by mass of sodium hydroxide, 34 parts by mass of silica sol and 220 parts by mass of deionized water were mixed and stirred, and then 2% by mass of mixed seed solution was added to the reaction solution, and stirred at a speed of 800 r / min for 5 hours while maintaining room temperature to obtain a synthetic solution;

[0080] S3.3: Seal both ends of the ceramic tube with polytetrafluoroethylene stoppers, quickly put it into the synthetic liquid, soak it for 20 seconds, take it out and dry it, then put it into a microwave oven (700w) for microwave crystallization for 90 minutes to obtain a crystallized product, wash and filter the crystallized product until the pH of the washing liquid is <11, and then dry the washed crystallized product at 105°C to obtain a molecular sieve membrane separation tube.

[0081] S4: Distillation tower to separate tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran

[0082] S4.1: Both ends of the molecular sieve membrane separation tube are sealed and placed in a separator, which is placed in a tetrahydrofuran aqueous solution. The carrier side is connected to a vacuum pump through a cold trap. The tetrahydrofuran aqueous solution directly contacts the permeation side of the mordenite membrane. Water molecules penetrate the zeolite membrane into the carrier side under the action of the pressure difference. The vacuum system promptly takes away the permeated water, which is condensed by liquid nitrogen and collected in a cold trap to obtain a mixture of tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran;

[0083] S4.2: Add a mixed liquid of tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran into a distillation tower system, and separate tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran by gas chromatography separation technology.

[0084] Embodiment 3:

[0085] A distillation technology for purifying tetrahydrofuran residue to recover dimethyltetrahydrofuran and trimethyltetrahydrofuran, such as Figure 1 As shown, the following steps are included:

[0086] S1: Preliminary extractive distillation of tetrahydrofuran residue

[0087] S1.1: Add THF waste liquid to the bottom tank of the tower and heat it to 65°C. Pass the tetrahydrofuran residual liquid preheated to 65°C into the tower. Continue heating to make the liquid in the bottom tank reflux completely. After the reflux is completed, obtain the top distillate and the first bottom liquid;

[0088] S1.2: Add the primary kettle liquid to the tower kettle and heat it to 90°C. Pass the primary kettle liquid preheated to 90°C into the tower and continue heating to make the liquid in the tower kettle reflux completely. After the reflux is completed, collect the distillate from the top of the tower and the secondary kettle liquid.

[0089] S1.3: Heat the secondary kettle liquid to 80°C and keep it for 1 hour, take the upper layer of liquid, and cool it to room temperature to obtain the treated liquid;

[0090] S1.4: Add the treatment liquid to the tower kettle, turn on the heating and insulation switches, heat until the liquid in the tower kettle is fully refluxed, add the treatment liquid heated to 60℃ to the tower and keep it for 2h, collect the liquid at the top of the tower to obtain the distillate;

[0091] S2: Preparation of extractant [Hemim][Ac] and extraction

[0092] S2.1: Under nitrogen atmosphere, N-methylimidazole and 2-bromoethanol were mixed in a reaction bottle, and the mixture was stirred at 100°C for 48 h. After the reaction, the product was washed three times with anhydrous ethanol to obtain intermediate I.

[0093] S2.2: Mix 7 parts by volume of ethyl acetate solution and 3 parts by volume of acetonitrile solution, add 6 parts by volume of intermediate I, and reflux in an oil bath at 80°C after sufficient dissolution. After reflux is completed, cool to room temperature, seal and place at 0°C for recrystallization for 2 hours, filter out the solid product, and dry at 65°C for 24 hours to obtain [Hemim][Br];

[0094] S2.3: Place [Hemim][Br] in a beaker and add deionized water to dissolve it. The solid-liquid ratio of [Hemim][Br] to deionized water is 1:8. Then pour the solution into an OH-type anion exchange resin and react for 2 hours to obtain [Hemim][OH]. Mix the acetic acid solution and [Hemim][OH] and add them to a round-bottom flask. The mass ratio of the acetic acid solution to [Hemim][OH] is 2:3. Stir and react for 48 hours to obtain intermediate II.

[0095] S2.4: Anhydrous ethanol and acetonitrile were mixed in a volume ratio of 9:1 and added to an equal volume of intermediate II, and the mixture was stirred for reaction for 4.5 hours. After the reaction was completed, the mixture was cooled at low temperature to precipitate unreacted acetic acid, and then filtered. Finally, the obtained solution was vacuum dried at 60°C for 48 hours to obtain the extractant [Hemim][Ac];

[0096] S2.5: Place the distillate in a constant temperature water bath at 80°C. After the layers are stabilized, add the extractant [Hemim][Ac] for extraction. The amount of the extractant [Hemim][Ac] added is 10% of the total volume of the system. The upper clear liquid is the alcohol phase, and the lower clear liquid is the water phase. Collect the lower clear liquid to obtain a tetrahydrofuran aqueous solution.

[0097] S3: Preparation of molecular sieve membrane separation tube

[0098] S3.1: Add deionized water to 5 μm mordenite to prepare a large seed solution of 0.2 g / L, grind the mordenite to 700 nm and add deionized water to prepare a small seed solution of 0.3 g / L, mix the large seed solution and the small seed solution in a volume ratio of 1:1 to obtain a mixed seed solution;

[0099] S3.2: 15 parts by mass of calcined kaolin, 24 parts by mass of sodium hydroxide, 34 parts by mass of silica sol and 220 parts by mass of deionized water were mixed and stirred, and then 2% by mass of mixed seed solution was added to the reaction solution, and stirred at a speed of 800 r / min for 5 hours while maintaining room temperature to obtain a synthetic solution;

[0100] S3.3: Seal both ends of the ceramic tube with polytetrafluoroethylene stoppers, quickly put it into the synthetic liquid, soak it for 20 seconds, take it out and dry it, then put it into a microwave oven (700w) for microwave crystallization for 80 minutes to obtain a crystallized product, wash and filter the crystallized product until the pH of the washing liquid is <11, and then dry the washed crystallized product at 105°C to obtain a molecular sieve membrane separation tube.

[0101] S4: Distillation tower to separate tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran

[0102] S4.1: Both ends of the molecular sieve membrane separation tube are sealed and placed in a separator, which is placed in a tetrahydrofuran aqueous solution. The carrier side is connected to a vacuum pump through a cold trap. The tetrahydrofuran aqueous solution directly contacts the permeation side of the mordenite membrane. Water molecules penetrate the zeolite membrane into the carrier side under the action of the pressure difference. The vacuum system promptly takes away the permeated water, which is condensed by liquid nitrogen and collected in a cold trap to obtain a mixture of tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran;

[0103] S4.2: Add a mixed liquid of tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran into a distillation tower system, and separate tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran by gas chromatography separation technology.

[0104] Comparative Example 1:

[0105] Compared with Example 1, the difference of Comparative Example 1 is that no calcined kaolin is added in step S3, specifically: "S3.1: adding deionized water to mordenite with a particle size of 5 um to prepare a large crystal seed solution of 0.2 g / L, grinding the mordenite to 700 nm and then adding deionized water to prepare a small crystal seed solution of 0.3 g / L, mixing the large crystal seed solution and the small crystal seed solution in a volume ratio of 1:1 to obtain a mixed crystal seed solution;

[0106] S3.2: 24 parts by mass of sodium hydroxide, 34 parts by mass of silica sol and 220 parts by mass of deionized water were mixed and stirred, and then 2% by mass of mixed seed solution was added to the reaction solution, and stirred at a speed of 800 r / min for 5 hours while maintaining room temperature to obtain a synthetic solution;

[0107] S3.3: Seal both ends of the ceramic tube with polytetrafluoroethylene stoppers, quickly put it into the synthetic liquid, soak it for 20 seconds, take it out and dry it, then put it into a microwave oven (700w) for microwave crystallization for 80 minutes to obtain a crystallized product, wash and filter the crystallized product until the pH of the washing liquid is <11, and then dry the washed crystallized product at 105℃ to obtain a molecular sieve membrane separation tube". Calculate the yields of dimethyltetrahydrofuran and trimethyltetrahydrofuran.

[0108] Comparative Example 2:

[0109] Compared with Example 1, the difference of Comparative Example 2 is that no large seed solution is added in step S3, specifically: "S3.1: grinding the mordenite to 700 nm and then adding deionized water to prepare a 0.3 g / L small seed solution;

[0110] S3.2: 15 parts by mass of calcined kaolin, 24 parts by mass of sodium hydroxide, 34 parts by mass of silica sol and 220 parts by mass of deionized water were mixed and stirred, and then 2% by mass of a small seed solution was added to the reaction solution, and the mixture was stirred at a speed of 800 r / min for 5 hours while maintaining room temperature to obtain a synthetic solution;

[0111] S3.3: Seal both ends of the ceramic tube with polytetrafluoroethylene stoppers, quickly put it into the synthetic liquid, soak it for 20 seconds, take it out and dry it, then put it into a microwave oven (700w) for microwave crystallization for 80 minutes to obtain a crystallized product, wash and filter the crystallized product until the pH of the washing liquid is <11, and then dry the washed crystallized product at 105℃ to obtain a molecular sieve membrane separation tube". Calculate the yields of dimethyltetrahydrofuran and trimethyltetrahydrofuran.

[0112] Comparative Example 3:

[0113] Compared with Example 1, the difference of Comparative Example 3 is that no small seed solution is added in step S3, specifically: "S3.1: adding deionized water to mordenite with a particle size of 5 μm to prepare a large seed solution of 0.2 g / L;

[0114] S3.2: 15 parts by mass of calcined kaolin, 24 parts by mass of sodium hydroxide, 34 parts by mass of silica sol and 220 parts by mass of deionized water were mixed and stirred, and then 2% by mass of large crystal seed solution was added to the reaction solution, and stirred at a speed of 800 r / min for 5 hours while maintaining room temperature to obtain a synthetic solution;

[0115] S3.3: Seal both ends of the ceramic tube with polytetrafluoroethylene stoppers, quickly put it into the synthetic liquid, soak it for 20 seconds, take it out and dry it, then put it into a microwave oven (700w) for microwave crystallization for 80 minutes to obtain a crystallized product, wash and filter the crystallized product until the pH of the washing liquid is <11, and then dry the washed crystallized product at 105℃ to obtain a molecular sieve membrane separation tube". Calculate the yields of dimethyltetrahydrofuran and trimethyltetrahydrofuran.

[0116] Comparative Example 4:

[0117] Compared with Example 1, the difference of Comparative Example 4 is that [Hemim][Ac] is not used for extraction, but conventional extractant ether is used, specifically: "Put the distillate into a constant temperature water bath at 80°C, and after the stratification is stable, add ether for extraction, the amount of ether added is 15% of the total volume of the system, the upper clear liquid is the alcohol phase, the lower clear liquid is the water phase, the lower clear liquid is collected to obtain a tetrahydrofuran aqueous solution" and the yields of dimethyltetrahydrofuran and trimethyltetrahydrofuran are calculated.

[0118] The yields of dimethyltetrahydrofuran and trimethyltetrahydrofuran of Examples 1-3 were calculated and are shown in Table 1 together with the comparative example data.

[0119] Table 1:

[0120]

[0121] In the table, the yields of dimethyltetrahydrofuran in Examples 1-3 are 43.12%, 42.56% and 42.89% respectively, while the yields of trimethyltetrahydrofuran are 22.64%, 21.98% and 20.65%. The proportion of dimethyltetrahydrofuran in the tetrahydrofuran residue is higher than that of trimethyltetrahydrofuran, so the yield is higher.

[0122] The yield of dimethyltetrahydrofuran in Comparative Example 1 is 33.67%, and the yield of trimethyltetrahydrofuran is 16.54%. It can be seen that the presence of calcined kaolin affects the selectivity of mordenite for preparing molecular sieves, thereby resulting in a decrease in the water removal capacity of the molecular sieve and a decrease in the recovery rates of dimethyltetrahydrofuran and trimethyltetrahydrofuran.

[0123] The yields of dimethyltetrahydrofuran and trimethyltetrahydrofuran in Comparative Examples 2 and 3 are not much different, and are both lower than those in Example 1. It can be seen that the mordenite seed solution of different particle sizes has an effect on the adsorption capacity of the molecular sieve, resulting in an impact on the recovery rate of dimethyltetrahydrofuran and trimethyltetrahydrofuran.

[0124] The yield of dimethyltetrahydrofuran in Comparative Example 4 is 22.45% and the yield of trimethyltetrahydrofuran is 15.46%, which shows that [Hemim][Ac] is more effective as an extractant than conventional extractants.

[0125] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical ideas disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A distillation technology for purifying and recovering dimethyltetrahydrofuran and trimethyltetrahydrofuran from tetrahydrofuran residue, characterized in that: The steps include: S1: Preliminary extractive distillation of tetrahydrofuran residue Add THF waste liquid to the tower bottom tank, heat and reflux, obtain tower top distillate and primary bottom liquid after reflux, add primary bottom liquid to the tower bottom tank, heat and reflux, collect tower top distillate and secondary bottom liquid after reflux, heat the secondary bottom liquid, take the upper layer liquid, and cool to room temperature to obtain treated liquid, add treated liquid to the tower bottom tank, turn on the heating and insulation switches, heat until the liquid in the tower bottom tank is fully refluxed, collect the tower top liquid, and obtain distillate; S2: Preparation of extractant [Hemim][Ac] and extraction In a nitrogen atmosphere, N-methylimidazole and 2-bromoethanol are mixed and reacted to obtain intermediate I. Ethyl acetate solution and acetonitrile solution are mixed, and intermediate I is added thereto. After being fully dissolved, the mixture is refluxed. After the reflux is completed, the mixture is allowed to stand and cooled to room temperature. The mixture is recrystallized, filtered, and dried to obtain [Hemim][Br]. [Hemim][Br] is placed in a beaker, and deionized water is added thereto for dissolution. The solution is then poured into an OH-type anion exchange resin for reaction to obtain [Hemim][OH]. Acetic acid solution and [Hemim][OH] are mixed and added to a round-bottom flask for reaction to obtain intermediate II. Anhydrous ethanol and acetonitrile are mixed and added to an equal volume of intermediate II for reaction to obtain an extractant [Hemim][Ac]. The distillate is placed in a constant temperature water bath. After the layers are stabilized, the extractant [Hemim][Ac] is added thereto for extraction. The upper clear liquid is an alcohol phase, and the lower clear liquid is an aqueous phase. The lower clear liquid is collected to obtain a tetrahydrofuran aqueous solution. S3: Preparation of molecular sieve membrane separation tube Adding deionized water to mordenite with a particle size of 5 μm to prepare a large seed solution, grinding the mordenite to 700 nm and then adding deionized water to prepare a small seed solution, mixing the large seed solution and the small seed solution to obtain a mixed seed solution, mixing calcined kaolin, sodium hydroxide and deionized water, and then adding the mixed seed solution to a reaction solution, and obtaining a synthetic solution while maintaining room temperature, sealing both ends of a ceramic tube with polytetrafluoroethylene plugs, quickly placing it in the synthetic solution, taking it out after soaking and drying it, and then placing it in a microwave oven for microwave crystallization to obtain a crystallized product, washing, filtering and drying the crystallized product to obtain a molecular sieve membrane separation tube; S4: Distillation tower to separate tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran Both ends of the molecular sieve membrane separation tube are sealed and installed in a separator, which is placed in a tetrahydrofuran aqueous solution. The carrier side is connected to a vacuum pump through a cold trap to remove water to obtain a mixture of tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran. The mixture of tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran is added to a distillation tower system, and tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran are separated by gas chromatography separation technology.

2. A distillation technology for purifying and recovering dimethyltetrahydrofuran and trimethyltetrahydrofuran from tetrahydrofuran residue according to claim 1, characterized in that: Step S1: batching and ball milling, comprising the following steps: S1.1: Add THF waste liquid to the bottom tank of the tower and heat it to 65°C. Pass the tetrahydrofuran residual liquid preheated to 65°C into the tower. Continue heating to make the liquid in the bottom tank reflux completely. After the reflux is completed, obtain the top distillate and the first bottom liquid; S1.2: Add the primary kettle liquid to the tower kettle and heat it to 90°C. Pass the primary kettle liquid preheated to 90°C into the tower and continue heating to make the liquid in the tower kettle reflux completely. After the reflux is completed, collect the distillate from the top of the tower and the secondary kettle liquid. S1.3: Heat the secondary kettle liquid to 80°C and keep it for 1 hour, take the upper layer of liquid, and cool it to room temperature to obtain the treated liquid; S1.4: Add the treated liquid to the bottom tank of the tower, and turn on the heating and insulation switches to heat until the liquid in the bottom tank is fully refluxed. Add the treated liquid heated to 60°C into the tower and keep it for 2-3 hours. Collect the liquid at the top of the tower to obtain the distillate.

3. A distillation technology for purifying and recovering dimethyltetrahydrofuran and trimethyltetrahydrofuran from a tetrahydrofuran residue according to claim 2, characterized in that: Step S2: preparing the extractant [Hemim][Ac] and extracting, comprising the following steps: S2.1: Under nitrogen atmosphere, N-methylimidazole and 2-bromoethanol were mixed in a reaction bottle, and the mixture was stirred at 100-120°C for 44-48 hours. After the reaction, the product was washed three times with anhydrous ethanol to obtain intermediate I; S2.2: Mix 7 parts by volume of ethyl acetate solution and 3 parts by volume of acetonitrile solution, add 6 parts by volume of intermediate I, and reflux in an oil bath at 60-80°C after sufficient dissolution. After reflux is completed, cool to room temperature by standing, seal and place at 0-4°C for recrystallization for 2-4h, filter and collect the solid product, and dry at 65-70°C for 24h to obtain [Hemim][Br]; S2.3: Place [Hemim][Br] in a beaker, add deionized water to dissolve, then pour the solution into an OH-type anion exchange resin to react for 2 h to obtain [Hemim][OH], mix the acetic acid solution and [Hemim][OH] and add them to a round-bottom flask, react for 45-48 h under stirring to obtain intermediate II; S2.4: Anhydrous ethanol and acetonitrile are mixed in a volume ratio of 9:1, added to an equal volume of intermediate II, stirred for reaction for 4.5-5 hours, and after the reaction is completed, low-temperature cooling is performed to precipitate unreacted acetic acid, and then filtered. Finally, the resulting solution is vacuum dried at 55-60°C for 45-48 hours to obtain an extractant [Hemim][Ac]; S2.5: Place the distillate in a constant temperature water bath at 80°C. After the layers are stabilized, add the extractant [Hemim][Ac] for extraction. The upper clear liquid is the alcohol phase and the lower clear liquid is the water phase. Collect the lower clear liquid to obtain a tetrahydrofuran aqueous solution.

4. A distillation technology for purifying and recovering dimethyltetrahydrofuran and trimethyltetrahydrofuran from tetrahydrofuran residue according to claim 3, characterized in that: In step S2.3, the material-liquid ratio of [Hemim][Br] to deionized water is 1:(8-10).

5. A distillation technology for purifying and recovering dimethyltetrahydrofuran and trimethyltetrahydrofuran from tetrahydrofuran residue according to claim 4, characterized in that: The mass ratio of acetic acid solution to [Hemim][OH] in step S2.3 is 2:(3-5).

6. A distillation technology for purifying and recovering dimethyltetrahydrofuran and trimethyltetrahydrofuran from tetrahydrofuran residue according to claim 5, characterized in that: In step S2.5, the amount of the extractant [Hemim][Ac] added is 10-15% of the total volume of the system.

7. A distillation technology for purifying and recovering dimethyltetrahydrofuran and trimethyltetrahydrofuran from tetrahydrofuran residue according to claim 6, characterized in that: Step S3 is to prepare a molecular sieve membrane separation tube, comprising the following steps: S3.1: Add deionized water to 5 μm mordenite to prepare a large seed solution of 0.2 g / L, grind the mordenite to 700 nm and add deionized water to prepare a small seed solution of 0.3 g / L, mix the large seed solution and the small seed solution to obtain a mixed seed solution; S3.2: 15 parts by mass of calcined kaolin, 24 parts by mass of sodium hydroxide, 34 parts by mass of silica sol and 220 parts by mass of deionized water were mixed and stirred, and then 2% by mass of mixed seed solution was added to the reaction solution, and stirred at a speed of 600-800 r / min for 5 hours while maintaining room temperature to obtain a synthetic solution; S3.3: Seal both ends of the ceramic tube with polytetrafluoroethylene stoppers, quickly put it into the synthetic liquid, soak for 20 seconds, take it out and dry it, then put it into the microwave oven for microwave crystallization for 80-90 minutes to obtain a crystallized product, wash and filter the crystallized product until the pH of the washing liquid is <11, and then dry the washed crystallized product at 105°C to obtain a molecular sieve membrane separation tube.

8. A distillation technology for purifying and recovering dimethyltetrahydrofuran and trimethyltetrahydrofuran from tetrahydrofuran residue according to claim 7, characterized in that: In step S3.1, the large seed solution and the small seed solution are mixed in a volume ratio of 1:

1.

9. A distillation technology for purifying and recovering dimethyltetrahydrofuran and trimethyltetrahydrofuran from tetrahydrofuran residue according to claim 8, characterized in that: In step S3.3, the microwave power is set to 700w.

10. A distillation technology for purifying and recovering dimethyltetrahydrofuran and trimethyltetrahydrofuran from tetrahydrofuran residue according to claim 9, characterized in that: Step S4: a distillation tower is used to separate tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran, comprising the following steps: S4.1: Both ends of the molecular sieve membrane separation tube are sealed and placed in a separator, which is placed in a tetrahydrofuran aqueous solution. The carrier side is connected to a vacuum pump through a cold trap. The tetrahydrofuran aqueous solution directly contacts the permeation side of the mordenite membrane. Water molecules penetrate the zeolite membrane into the carrier side under the action of the pressure difference. The vacuum system promptly takes away the permeated water, which is collected in a cold trap after condensation with liquid nitrogen to obtain a mixed solution of tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran; S4.2: Add a mixed liquid of tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran into a distillation tower system, and separate tetrahydrofuran, dimethyltetrahydrofuran and trimethyltetrahydrofuran by gas chromatography separation technology.

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