Method for recovering dimethyl ether from dimethyl ether purge gas

Abstract

The invention discloses a method for recovering dimethyl ether from dimethyl ether purge gas, and belongs to the technical field of dimethyl ether recovery, the method for recovering dimethyl ether from dimethyl ether purge gas comprises the following steps: cooling the dimethyl ether purge gas to 8-10 DEG C through heat exchange of a heat exchanger, and then discharging to obtain low-temperature purge gas, the low-temperature purge gas enters the bottom of the inner side of an absorption tower filled with composite filler and is absorbed by absorption liquid which flows from top to bottom and has the temperature of 10-15 DEG C, and enriched liquid is formed at the bottom of the absorption tower; according to the method, the composition and the adsorption temperature of the adsorption liquid are optimized, and the composite filler is modified, so that the recovery purity of the dimethyl ether is effectively improved, and the recovery rate of the dimethyl ether in the purge gas is also improved.

Description

Technical Field

[0001] The invention relates to the technical field of dimethyl ether recovery, and in particular to a method for recovering dimethyl ether from dimethyl ether purge gas. Background Art

[0002] Dimethyl ether (DME) is an important basic organic chemical raw material. It can replace chlorofluorocarbons as aerosols, refrigerants and foaming agents, and can be used to synthesize ethanol and low-carbon olefins. It can also replace diesel and liquefied gas. It is known as the clean fuel of the 21st century. However, due to the low boiling point of DME, the DME tail gas discharged from the top of the separation tower reflux tank still contains a considerable proportion of DME (about 43% of the total amount of purge gas). This part of the purge gas is mainly directly burned after being merged into the gas pipeline network through the tail gas heater, which is bound to cause waste of resources and increase CO2 emissions.

[0003] The components of the purge gas after condensation of the top material of the dimethyl ether separation tower mainly include dimethyl ether, methanol, CO2, H2, CH4 and trace amounts of C2H4 and C3H6. At present, the treatment methods of purge gas in industrial production processes mainly include absorption, adsorption and membrane separation. The absorption method has the advantages of high selectivity, low cost and simple operation. However, when the absorption method is used to absorb and regenerate dimethyl ether, due to the low boiling point of dimethyl ether, it is easy to produce azeotropy with the absorption liquid, resulting in reduced solubility of dimethyl ether, and the recovered dimethyl ether has poor purity. At the same time, the poor solubility of the absorption liquid in dimethyl ether also makes it impossible to absorb the dimethyl ether in the dimethyl ether purge gas, resulting in the recovery rate of dimethyl ether to be further improved.

[0004] In view of the technical defects in this aspect, a solution is now proposed. Summary of the invention

[0005] The object of the present invention is to provide a method for recovering dimethyl ether from dimethyl ether purge gas, so as to solve the technical problem in the prior art that the purity and recovery rate of dimethyl ether recovered from dimethyl ether purge gas need to be further improved.

[0006] The object of the present invention can be achieved by the following technical scheme: A method for recovering dimethyl ether from dimethyl ether purge gas, comprising the following steps:

[0007] S1, dimethyl ether purge gas is cooled to 8~10℃ by heat exchanger and then discharged to obtain low-temperature purge gas;

[0008] S2, the low-temperature purge gas enters the inner bottom of the absorption tower filled with composite fillers, and is absorbed by the absorption liquid with a temperature of 10-15°C flowing from top to bottom, forming an enriched liquid at the bottom of the absorption tower, and the absorbed waste gas is discharged from the waste gas discharge pipe at the top of the absorption tower;

[0009] S3. The temperature of the desorption tower filled with volcanic rock biological filler is increased to 47-52°C, and the enriched liquid is transferred to the inner top of the desorption tower. The enriched liquid flows from top to bottom and desorbs. The desorbed dimethyl ether is discharged from the top of the desorption tower to obtain crude dimethyl ether. The crude dimethyl ether is condensed and separated to obtain dimethyl ether product.

[0010] Furthermore, the number of plates of the absorption tower and the desorption tower are both 80, an air inlet pipe for guiding the low-temperature purge gas to enter is installed at the outer bottom of the absorption tower, one end of the air inlet pipe extending to the inside of the absorption tower is located at the top of the 5th tower plate from bottom to top, a low-temperature heat exchanger 1 is installed on the air inlet pipe, an exhaust gas discharge pipe is installed on the top of the absorption tower, an air supply pipe is installed on the top of the desorption tower, and a condenser is installed on the air supply pipe, a transfer pump 1 and a transfer pump 2 are arranged between the absorption tower and the desorption tower, the liquid inlet end of the transfer pump 1 is connected to the bottom of the absorption tower through a pipeline, and the output end of the transfer pump 1 is connected to the bottom of the absorption tower through a connecting pipe One is fixedly connected to the outer top of the desorption tower, a high-temperature heat exchanger is installed on the connecting pipe one, and one end of the connecting pipe one extending to the inside of the desorption tower is located at the top of the 72nd tower plate from bottom to top, the output end of the transfer pump two is fixedly connected to the outer top of the absorption tower through the connecting pipe two, a low-temperature heat exchanger two is installed on the connecting pipe two, and one end of the connecting pipe two extending to the inside of the absorption tower is located at the top of the 80th tower plate from bottom to top, an absorption liquid storage tank is provided between the transfer pump two and the desorption tower, the input end of the transfer pump two is connected to the bottom of the absorption liquid storage tank through a pipeline, and the bottom of the desorption tower is connected to the top of the absorption liquid storage tank through a pipeline.

[0011] Furthermore, in step S2, the temperature of the low-temperature purge gas input into the absorption tower is 20~25°C, the input ratio of the low-temperature purge gas to the absorption liquid is 1mL:8~10mL, and the absorption liquid is composed of anhydrous ethanol, ethylene glycol dimethyl ether and deionized water in a volume ratio of 7:2~3:5; in step S3, the condensation separation temperature of the crude dimethyl ether to prepare the dimethyl ether product is -15~-20°C.

[0012] Further, the composite filler is processed by the following steps:

[0013] A1, mixing the porous microspheres and fumed silica uniformly to obtain mixed silicon;

[0014] A2, stirring and mixing sodium hydroxide, sodium aluminate and deionized water until the system is dissolved, adding n-butylamine to the reaction system, stirring at room temperature for 15 to 20 minutes, adding mixed silicon to the reaction system, and stirring at this temperature for 90 to 120 minutes to obtain a mixed gel;

[0015] A3, transferring the mixed gel to a high pressure reactor at a temperature of 150-160°C and a pressure of 0.15-0.25 MPa, homogeneously crystallizing for 2 days, washing and calcining to obtain a porous material precursor, and performing ammonium exchange on the porous filler to obtain a porous filler;

[0016] The synthetic reaction mechanism of porous fillers is:

[0017] During the reaction, under alkaline conditions, the porous microspheres and the fumed silica undergo a dissolution-reprecipitation process, react with the sodium aluminate in the solution, and form a mixture of silicates and aluminates. As the reaction proceeds, these substances gradually cross-link to form a gel network structure. Under high temperature and high pressure, the silicates and aluminates in the gel network structure further undergo hydrolysis, condensation and rearrangement reactions, and the gel is gradually converted into a crystalline material with a porous structure. The moisture and organic template in the gel are removed by programmed calcination while the material is further solidified. The high-temperature heat preservation calcination further promotes the crystallization and perfection of the material, the stability of the pore structure, and the removal of residual organic matter and inorganic impurities to prepare a porous material precursor. Ammonium chloride undergoes an ion exchange reaction with part of the sodium ions or other impurity ions in the porous material precursor to further purify the material. The material is then calcined at high temperature to remove the moisture and ammonium chloride introduced during the ammonium chloride treatment to prepare a porous filler.

[0018] A4. Activate and modify the porous filler to obtain a composite filler.

[0019] Furthermore, in step A1, the weight ratio of the porous microspheres to the fumed silica is 1:2; in step A2, the amount ratio of the sodium hydroxide, sodium aluminate, deionized water, n-butylamine, and mixed silicon is 1g:3g:60mL:5g:20g; in step A3, the washing and roasting treatment includes: after the homogeneous crystallization is completed, filtration is performed, the filter cake is washed with purified water for 5 times and then dried, the filter cake is transferred to a muffle furnace, the temperature of the muffle furnace is increased to 90-100°C, and roasted for 40-60min, the muffle furnace is increased to 550-600°C at a heating rate of 3-5°C / min, and the temperature is kept and roasted for 5-6h, and the temperature is naturally cooled to room temperature, and the material is discharged to obtain a porous filler precursor.

[0020] Furthermore, in step A1, the preparation method of the porous microspheres is: mix the porogen and deionized water, ultrasonically disperse the system until it is dissolved, add the silicon source solution to the reaction system, increase the temperature of the reaction system to 70-75°C, keep the reaction warm for 10-12 hours, post-treat, separate and obtain solid particles, and calcine the solid particles to obtain porous microspheres.

[0021] The synthetic reaction mechanism of porous microspheres is:

[0022] During the reaction, ethyl orthosilicate and tetrabutyl titanate are hydrolyzed in deionized water containing a porogen to form silicate and titanate monomers, which then undergo polycondensation to form a sol of a silicate and titanate polymer network. As the hydrolysis and polycondensation reactions proceed, the sol gradually transforms into a gel. In the sol-gel process, urea undergoes a hydrolysis reaction to generate gases such as ammonia and carbon dioxide, and bubbles are formed in the gel, providing a template for the formation of a porous structure. 1-vinyl-3-dodecyl imidazolium bromide forms an ionic liquid in the solution. The cations and anions in the ionic liquid interact with the silicate and titanate networks through electrostatic interactions or coordination effects, further affecting the porous structure and stability of the product. After the gel is centrifuged, washed and dried, excess solvents and unreacted precursors are removed to obtain solid particles. The solid particles are calcined at a high temperature to further remove organic matter, improve the crystallinity and stability of the product, and promote further polycondensation and rearrangement of the silicate and titanate networks in the porous structure to form a more stable porous structure, thereby preparing porous microspheres.

[0023] Furthermore, the dosage ratio of the porogen, deionized water and silicon source solution is 8g:50mL:15g, the porogen is composed of 1-vinyl-3-dodecyl imidazole bromide and urea in a weight ratio of 5:3, the silicon source solution is composed of tetraethyl orthosilicate, tetrabutyl titanate and isopropanol in a weight ratio of 5:2:10, and the post-treatment includes: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, centrifuged, the bottom solid is washed with deionized water for 3 times and then dried, the filter cake is transferred to a drying oven at a temperature of 70-80°C, and vacuum dried to constant weight to obtain solid particles, and the calcination treatment temperature is 550-600°C, and the calcination time is 4-6h.

[0024] Furthermore, in step A3, the ammonium exchange method is: mixing the porous filler precursor and the ammonium chloride solution, raising the temperature of the reaction system to 85-95° C., keeping the temperature for 2-3 hours, washing and calcining to obtain the porous filler.

[0025] Furthermore, the amount ratio of the porous filler precursor and the ammonium chloride solution is 1g:10mL, the ammonium chloride solution is composed of ammonium chloride and deionized water in a ratio of 1g:10mL, and the washing and roasting include: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, filtered, the filter cake is washed with purified water for 3 times and then dried, the filter cake is transferred to a muffle furnace at a temperature of 550~600℃ and roasted for 5~6h, naturally cooled to room temperature, and discharged to obtain a porous filler.

[0026] Further, in step A4, the activation modification comprises the following steps:

[0027] B1. Mix the porous filler, tetrahydrofuran and KH-560, and disperse them by ultrasonic for 20-30 minutes. Add ammonia water to the reaction system, raise the temperature of the reaction system to 50-60°C, keep the temperature for 60-80 minutes, and perform post-treatment to obtain the activated filler.

[0028] B2. Mix polyethyleneimine, activated filler, deionized water and sodium hydroxide, increase the temperature of the reaction system to 60-70°C, perform ultrasonic dispersion for 80-90 minutes, and post-treat to obtain a composite filler.

[0029] The synthetic reaction mechanism of composite fillers is:

[0030] During the reaction, the porous filler is modified by KH-560 to form an epoxy modification on the porous filler. In an alkaline environment, the amino or imine group on the polyethyleneimine molecular chain undergoes a ring-opening condensation reaction with the epoxy group on the surface of the activated filler to form a polyethyleneimine modification on the activated filler particles, thereby preparing a composite filler.

[0031] Furthermore, in step B1, the amount ratio of the porous filler, tetrahydrofuran, KH-560 and ammonia water is 5g:50mL:3g:10mL, the mass fraction of the ammonia water is 5~8wt%, and the post-treatment includes: after the reaction is completed, the temperature of the reaction system is reduced to room temperature, suction filtration, the filter cake is washed with purified water until neutral and then dried, the filter cake is transferred to a drying oven at a temperature of 60~70°C, and vacuum dried to constant weight to obtain an activated filler; in step B2, the amount ratio of the polyethyleneimine, activated filler, deionized water, and sodium hydroxide is 3g:7g:20mL:2g, and the post-treatment includes: after the reaction is completed, the temperature of the reaction system is reduced to room temperature, suction filtration, the filter cake is washed with purified water 5 times and then dried, the filter cake is transferred to a drying oven at a temperature of 65~75°C, and vacuum dried to constant weight to obtain a composite filler.

[0032] The present invention has the following beneficial effects:

[0033] 1. The present invention uses an absorption liquid composed of anhydrous ethanol, ethylene glycol dimethyl ether and deionized water to absorb dimethyl ether, optimizes the ratio of each component and the absorption temperature, improves the selective absorption of dimethyl ether by the absorption liquid, and in the process of preparing the composite filler, introduces materials with high thermal conductivity such as titanium and fumed silica into the composite filler to make it have good thermal conductivity, avoids obstruction of the flow of gas and liquid phases in the composite filler, causes the fluid resistance in the local area to increase, causes the local temperature to rise, maintains good temperature stability inside the absorption tower, avoids the gasification of dimethyl ether caused by the temperature rise, increases the absorption amount of dimethyl ether, and then promotes the desorption and release of dimethyl ether absorbed by the absorption liquid through temperature increase heat treatment, and performs low-temperature separation of the high-boiling point absorption liquid through low-temperature treatment to avoid the absorption liquid from overflowing with gas, thereby further improving the purity of dimethyl ether.

[0034] 2. The present invention introduces metallic titanium into porous microspheres, and then mixes it with fumed silica having good thermal conductivity as mixed silicon and sodium aluminate to form a mixed gel in an alkaline environment. After homogeneous crystallization in a high-pressure reactor, the structure of the filler particles is promoted to be more uniform and dense, so that it has good heat transfer performance, thereby reducing the temperature runaway phenomenon in the filler layer and maintaining the internal temperature of the absorption tower relatively uniform and stable. The titanium element introduced into the filler particles has a certain electrophilicity and can interact with the negatively charged part of the acidic molecules to improve the absorption performance of the filler particles for the acidic molecules. By modifying the outside of the porous microspheres with strongly alkaline polyethyleneimine, the polyethyleneimine molecular chain is rich in amines or imines that can interact electrostatically, react acid-base or hydrogen bond with the acidic particles, thereby enhancing the adsorption capacity of the porous particles for the acidic particles.

[0035] 3. The present invention is to absorb dimethyl ether at low temperature by selecting an absorption liquid composed of anhydrous ethanol, ethylene glycol dimethyl ether and deionized water. The components of the absorption liquid are relatively safe at room temperature and are not easy to cause dangerous situations such as fire or explosion. Dimethyl ether has a certain solubility in anhydrous ethanol and ethylene glycol dimethyl ether, which enables the absorption liquid to effectively absorb dimethyl ether. At the same time, since dimethyl ether has a low boiling point, it can form an azeotrope with volatile anhydrous ethanol and ethylene glycol dimethyl ether, thereby facilitating the separation of dimethyl ether and the absorption liquid by heating. In addition, ethanol and ethylene glycol dimethyl ether have high boiling points and can be separated from dimethyl ether by simple low-temperature treatment, thereby effectively ensuring the purity of dimethyl ether. Deionized water helps to adjust the viscosity and fluidity of the absorption liquid and optimize the absorption effect. It can also increase the restraint on hydrophilic substances, avoid the impurity components in the dimethyl ether purge gas from overflowing in the azeotropic system of the desorption tower, and further improve the purity of dimethyl ether. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0037] Figure 1 It is a schematic diagram of the overall three-dimensional structure of the present invention.

[0038] In the figure: 100, absorption tower; 101, air inlet pipe; 102, low-temperature heat exchanger 1; 103, exhaust gas discharge pipe; 104, transfer pump 1; 105, connecting pipe 1; 106, high-temperature heat exchanger; 200, desorption tower; 201, air supply pipe; 202, condenser; 300, absorption liquid storage tank; 301, transfer pump 2; 302, connecting pipe 2; 303, low-temperature heat exchanger 2. DETAILED DESCRIPTION

[0039] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] In the present application, the fumed silica is selected from the EVONIK brand, has a pH value of 3.7-4.7, and an average primary particle size of 9 nm;

[0041] In this application, the CAS number of polyethyleneimine is 9002-98-6 and the molecular weight is 3500;

[0042] In this application, the density of the volcanic rock biofiller is 1.5 g / m³, the particle size is 2-3 mm, and the specific surface area is 3.5 m³ / g;

[0043] In the present application, the name of KH-560 is γ-glycidyloxypropyltrimethoxysilane, and the CAS number is 2530-83-8.

[0044] Example 1

[0045] This embodiment provides a method for preparing a composite filler for recovering dimethyl ether from dimethyl ether purge gas, comprising the following steps:

[0046] S1. Preparation of porous microspheres

[0047] Ethyl orthosilicate, tetrabutyl titanate and isopropyl alcohol are mixed uniformly in a weight ratio of 5:2:10 to obtain a silicon source solution for later use;

[0048] Weigh: 50 g of 1-vinyl-3-dodecyl imidazole bromide, 30 g of urea and 500 mL of deionized water are added to a three-necked flask and mixed, and ultrasonically dispersed until the system is dissolved. The three-necked flask is fixed on an iron stand with a mechanical stirrer for stirring, and 150 g of silicon source solution is added to the three-necked flask. The temperature of the three-necked flask is increased to 70°C, and the reaction is kept warm for 10 hours. The temperature of the three-necked flask is lowered to room temperature and centrifuged. The bottom solid is washed 3 times with deionized water and then dried. The filter cake is transferred to a drying oven at a temperature of 70°C and vacuum dried to constant weight to obtain solid particles, which are then transferred to a tubular furnace at a temperature of 550°C, kept warm and calcined for 4 hours, and naturally cooled to room temperature to obtain porous microspheres.

[0049] S2. Preparation of mixed gel

[0050] The porous microspheres and fumed silica are uniformly mixed in a weight ratio of 1:2 to obtain mixed silicon for later use;

[0051] Weigh: 10 g of sodium hydroxide, 30 g of sodium aluminate, and 600 mL of deionized water, add into a three-necked flask and stir until the system is dissolved; add 50 g of n-butylamine into the three-necked flask, stir at room temperature for 15 min; add 200 g of mixed silicon into the three-necked flask, and stir at this temperature for 90 min to obtain a mixed gel.

[0052] S3. Preparation of porous filler

[0053] The mixed gel was transferred to a high-pressure reactor at a temperature of 150°C and a pressure of 0.15MPa, and homogeneously crystallized for 2 days. The high-pressure reactor was cooled and depressurized to room temperature and atmospheric pressure, and filtered. The filter cake was washed with purified water for 5 times and then dried. The filter cake was transferred to a muffle furnace, and the temperature of the muffle furnace was increased to 90°C and calcined for 40min. The temperature of the muffle furnace was increased to 550°C at a heating rate of 3°C / min, and the mixture was kept warm and calcined for 5h. The mixture was naturally cooled to room temperature and discharged to obtain a porous filler precursor.

[0054] Mix ammonium chloride and deionized water at a ratio of 1 g:10 mL to obtain an ammonium chloride solution for later use;

[0055] The porous filler precursor and ammonium chloride solution were added into a beaker at a ratio of 1 g:10 mL and mixed. The temperature of the beaker was raised to 85°C and kept warm for 2 hours. The temperature of the beaker was lowered to room temperature and filtered. The filter cake was washed with purified water for 3 times and then dried. The filter cake was transferred to a muffle furnace at 550°C and calcined for 5 hours. The mixture was naturally cooled to room temperature and discharged to obtain a porous filler.

[0056] S4. Preparation of composite fillers

[0057] Weigh: 50 g of porous filler, 500 mL of tetrahydrofuran and 30 g of KH-560, add them into a three-necked flask, ultrasonically disperse for 20 min, fix the three-necked flask on an iron stand with a mechanical stirrer for stirring, add 100 mL of 5 wt% ammonia water into the three-necked flask, raise the temperature of the three-necked flask to 50°C, keep the temperature for 60 min, lower the temperature of the three-necked flask to room temperature, filter, wash the filter cake with purified water until it is neutral and then drain, transfer the filter cake to a drying oven at a temperature of 60°C, and vacuum dry it to constant weight to obtain an activated filler;

[0058] Weigh: 30 g of polyethyleneimine, 70 g of activated filler, 200 mL of deionized water and 20 g of sodium hydroxide, add them into a three-necked flask and mix, raise the temperature of the three-necked flask to 60°C, ultrasonically disperse for 80 minutes, lower the temperature of the reaction system to room temperature, filter, wash the filter cake with purified water 5 times and then dry it, transfer the filter cake to a drying oven at a temperature of 65°C, and vacuum dry it to constant weight to obtain a composite filler.

[0059] Example 2

[0060] This embodiment provides a method for preparing a composite filler for recovering dimethyl ether from dimethyl ether purge gas, comprising the following steps:

[0061] S1. Preparation of porous microspheres

[0062] Ethyl orthosilicate, tetrabutyl titanate and isopropyl alcohol are mixed uniformly in a weight ratio of 5:2:10 to obtain a silicon source solution for later use;

[0063] Weigh: 50 g of 1-vinyl-3-dodecyl imidazole bromide, 30 g of urea and 500 mL of deionized water are added to a three-necked flask and mixed, and ultrasonically dispersed until the system is dissolved. The three-necked flask is fixed on an iron stand with a mechanical stirrer for stirring, and 150 g of silicon source solution is added to the three-necked flask. The temperature of the three-necked flask is raised to 73° C. and the reaction is kept warm for 11 hours. The temperature of the three-necked flask is lowered to room temperature and centrifuged. The bottom solid is washed 3 times with deionized water and then dried. The filter cake is transferred to a drying oven at a temperature of 75° C. and vacuum dried to constant weight to obtain solid particles, which are then transferred to a tubular furnace at a temperature of 570° C. and calcined for 5 hours. The temperature is naturally lowered to room temperature to obtain porous microspheres.

[0064] S2. Preparation of mixed gel

[0065] The porous microspheres and fumed silica are uniformly mixed in a weight ratio of 1:2 to obtain mixed silicon for later use;

[0066] Weigh: 10 g of sodium hydroxide, 30 g of sodium aluminate, and 600 mL of deionized water, add into a three-necked flask and stir until the system is dissolved, add 50 g of n-butylamine into the three-necked flask, stir at room temperature for 17 min, add 200 g of mixed silicon into the three-necked flask, keep warm and stir for 105 min to obtain a mixed gel.

[0067] S3. Preparation of porous filler

[0068] The mixed gel was transferred to a high-pressure reactor at a temperature of 155°C and a pressure of 0.20 MPa, and homogeneously crystallized for 2 days. The high-pressure reactor was cooled and depressurized to room temperature and atmospheric pressure, and filtered. The filter cake was washed with purified water for 5 times and then dried. The filter cake was transferred to a muffle furnace, and the temperature of the muffle furnace was increased to 95°C and calcined for 50 minutes. The temperature of the muffle furnace was increased to 570°C at a heating rate of 4°C / min, and the temperature was kept and calcined for 5.5 hours. The temperature was naturally reduced to room temperature, and the material was discharged to obtain a porous filler precursor.

[0069] Mix ammonium chloride and deionized water at a ratio of 1 g:10 mL to obtain an ammonium chloride solution for later use;

[0070] The porous filler precursor and ammonium chloride solution were added to a beaker at a ratio of 1g:10mL and mixed. The temperature of the beaker was raised to 90°C and kept warm for 2.5 hours. The temperature of the beaker was lowered to room temperature and filtered. The filter cake was washed with purified water three times and then dried. The filter cake was transferred to a muffle furnace at a temperature of 570°C and calcined for 5.5 hours. The mixture was naturally cooled to room temperature and discharged to obtain a porous filler.

[0071] S4. Preparation of composite fillers

[0072] Weigh: 50 g of porous filler, 500 mL of tetrahydrofuran and 30 g of KH-560, add them into a three-necked flask, ultrasonically disperse for 25 min, fix the three-necked flask on an iron stand with mechanical stirring and stir, add 100 mL of 6 wt% ammonia water into the three-necked flask, raise the temperature of the three-necked flask to 55°C, keep the temperature for 70 min, lower the temperature of the three-necked flask to room temperature, filter, wash the filter cake with purified water until it is neutral and then drain, transfer the filter cake to a drying oven at a temperature of 65°C, and vacuum dry it to constant weight to obtain an activated filler;

[0073] Weigh: 30 g of polyethyleneimine, 70 g of activated filler, 200 mL of deionized water and 20 g of sodium hydroxide, add them into a three-necked flask and mix, raise the temperature of the three-necked flask to 65°C, ultrasonically disperse for 85 minutes, lower the temperature of the reaction system to room temperature, filter, wash the filter cake with purified water 5 times and then dry it, transfer the filter cake to a drying oven at a temperature of 70°C, and vacuum dry it to constant weight to obtain a composite filler.

[0074] Example 3

[0075] This embodiment provides a method for preparing a composite filler for recovering dimethyl ether from dimethyl ether purge gas, comprising the following steps:

[0076] S1. Preparation of porous microspheres

[0077] Ethyl orthosilicate, tetrabutyl titanate and isopropyl alcohol are mixed uniformly in a weight ratio of 5:2:10 to obtain a silicon source solution for later use;

[0078] Weigh: 50 g of 1-vinyl-3-dodecyl imidazole bromide, 30 g of urea and 500 mL of deionized water are added to a three-necked flask and mixed, and ultrasonically dispersed until the system is dissolved. The three-necked flask is fixed on an iron stand with a mechanical stirrer for stirring, and 150 g of silicon source solution is added to the three-necked flask. The temperature of the three-necked flask is increased to 75° C. and kept warm for 12 hours. The temperature of the three-necked flask is lowered to room temperature and centrifuged. The bottom solid is washed 3 times with deionized water and then dried. The filter cake is transferred to a drying oven at a temperature of 80° C. and vacuum dried to constant weight to obtain solid particles, which are then transferred to a tubular furnace at a temperature of 600° C. and calcined for 6 hours. The mixture is naturally cooled to room temperature to obtain porous microspheres.

[0079] S2. Preparation of mixed gel

[0080] The porous microspheres and fumed silica are uniformly mixed in a weight ratio of 1:2 to obtain mixed silicon for later use;

[0081] Weigh: 10 g of sodium hydroxide, 30 g of sodium aluminate, and 600 mL of deionized water, add into a three-necked flask and stir until the system is dissolved, add 50 g of n-butylamine into the three-necked flask, stir at room temperature for 20 min, add 200 g of mixed silicon into the three-necked flask, keep warm and stir for 120 min to obtain a mixed gel.

[0082] S3. Preparation of porous filler

[0083] The mixed gel was transferred to a high-pressure reactor at a temperature of 160°C and a pressure of 0.25MPa, and homogeneously crystallized for 2 days. The high-pressure reactor was cooled and depressurized to room temperature and atmospheric pressure, and filtered. The filter cake was washed with purified water for 5 times and then dried. The filter cake was transferred to a muffle furnace, and the temperature of the muffle furnace was increased to 100°C and calcined for 60min. The temperature of the muffle furnace was increased to 600°C at a heating rate of 5°C / min, and the temperature was kept and calcined for 6h, and the temperature was naturally reduced to room temperature, and the material was discharged to obtain a porous filler precursor;

[0084] Mix ammonium chloride and deionized water at a ratio of 1 g:10 mL to obtain an ammonium chloride solution for later use;

[0085] The porous filler precursor and ammonium chloride solution were added into a beaker at a ratio of 1 g:10 mL and mixed. The temperature of the beaker was raised to 95°C and kept warm for 3 hours. The temperature of the beaker was lowered to room temperature and filtered. The filter cake was washed with purified water for 3 times and then dried. The filter cake was transferred to a muffle furnace at 600°C and calcined for 6 hours. The mixture was naturally cooled to room temperature and discharged to obtain a porous filler.

[0086] S4. Preparation of composite fillers

[0087] Weigh: 50 g of porous filler, 500 mL of tetrahydrofuran and 30 g of KH-560, add them into a three-necked flask, ultrasonically disperse for 30 min, fix the three-necked flask on an iron stand with a mechanical stirrer for stirring, add 100 mL of 8 wt % ammonia water into the three-necked flask, raise the temperature of the three-necked flask to 60° C., keep the temperature for 80 min, lower the temperature of the three-necked flask to room temperature, filter, wash the filter cake with purified water until it is neutral and then drain, transfer the filter cake to a drying oven at a temperature of 70° C., and vacuum dry it to constant weight to obtain an activated filler;

[0088] Weigh: 30 g of polyethyleneimine, 70 g of activated filler, 200 mL of deionized water and 20 g of sodium hydroxide, add them into a three-necked flask and mix, raise the temperature of the three-necked flask to 70°C, ultrasonically disperse for 90 minutes, lower the temperature of the reaction system to room temperature, filter, wash the filter cake with purified water 5 times and then dry it, transfer the filter cake to a drying oven at a temperature of 75°C, and vacuum dry it to constant weight to obtain a composite filler.

[0089] Example 4

[0090] See also Figure 1 This embodiment provides a method for recovering dimethyl ether from dimethyl ether purge gas, comprising the following steps:

[0091] Step 1: Evenly mix anhydrous ethanol, ethylene glycol dimethyl ether and deionized water in a volume ratio of 7:2:5 to obtain an absorption liquid, and store the absorption liquid in an absorption liquid storage tank 300; fill the composite filler prepared in Example 1 into the absorption tower 100; fill the desorption tower 200 with volcanic rock biological filler; start the transfer pump 2 301; cool the absorption liquid to 20° C. through the low-temperature heat exchanger 2 303 on the connecting pipe 2 302; and flow out from the top of the 80th tower plate inside the absorption tower 100, and flow from top to bottom along each tower plate;

[0092] Step 2, dimethyl ether purge gas enters the air inlet pipe 101, and is cooled to 8°C by heat exchange in the low-temperature heat exchanger 102. After gas-liquid separation, the low-temperature purge gas enters the top of the 5th tower plate of the absorption tower 100 through the air inlet pipe 101, and the input ratio of the low-temperature purge gas to the absorption liquid is controlled to be 1mL:8mL. The low-temperature purge gas entering the absorption tower 100 floats upward and repeatedly contacts the absorption liquid flowing from top to bottom on the composite filler layer, and an enriched liquid absorbing dimethyl ether is formed at the bottom of the absorption tower 100. The gas not absorbed by the absorption liquid is discharged from the flying discharge pipe 103 at the top of the absorption tower 100;

[0093] Step 3: The temperature of the desorption tower 200 is raised to 47° C. The transfer pump 104 is started to transport the enriched liquid collected at the bottom of the inner side of the absorption tower 100 to the top of the 72nd tower plate inside the desorption tower 200 through the connecting pipe 105. During the transportation process, the high-temperature heat exchanger 106 on the connecting pipe 105 gradually heats the fluid inside the connecting pipe 105 to a temperature of about 47° C., and the dimethyl ether in the liquid is desorbed and released;

[0094] Step 4: The desorbed dimethyl ether gas floats upward, passes through the gas pipe 201 on the top of the desorption tower 200, and is condensed and cooled to -15°C by the condenser 202 installed on the gas pipe 201. The low-temperature gas overflows naturally to obtain the dimethyl ether product; after the enriched liquid in the desorption tower is desorbed, it naturally flows downward and is transported to the absorption liquid storage tank 300 through a pipeline for recycling.

[0095] Example 5

[0096] See also Figure 1 This embodiment provides a method for recovering dimethyl ether from dimethyl ether purge gas, comprising the following steps:

[0097] Step 1: Evenly mix anhydrous ethanol, ethylene glycol dimethyl ether and deionized water in a volume ratio of 7:2.5:5 to obtain an absorption liquid, and store the absorption liquid in an absorption liquid storage tank 300; fill the composite filler prepared in Example 2 into the absorption tower 100; fill the desorption tower 200 with volcanic rock biological filler; start the transfer pump 2 301; cool the absorption liquid to 23° C. through the low-temperature heat exchanger 2 303 on the connecting pipe 2 302; and flow out from the top of the 80th tower plate inside the absorption tower 100, and flow from top to bottom along each tower plate;

[0098] Step 2, dimethyl ether purge gas enters the air inlet pipe 101, is cooled to 9°C by heat exchange in the low-temperature heat exchanger 102, and after gas-liquid separation, the low-temperature purge gas enters the top of the 5th tray of the absorption tower 100 through the air inlet pipe 101, and the input ratio of the low-temperature purge gas to the absorption liquid is controlled to be 1mL:9mL. The low-temperature purge gas entering the absorption tower 100 floats upward and repeatedly contacts the absorption liquid flowing from top to bottom on the composite filler layer, and an enriched liquid absorbing dimethyl ether is formed at the bottom of the absorption tower 100. The gas not absorbed by the absorption liquid is discharged from the flying discharge pipe 103 at the top of the absorption tower 100;

[0099] Step 3: The temperature of the desorption tower 200 is raised to 50° C., and the transfer pump 104 is started to transport the enriched liquid collected at the bottom of the inner side of the absorption tower 100 to the top of the 72nd tower plate inside the desorption tower 200 through the connecting pipe 105. During the transportation process, the high-temperature heat exchanger 106 on the connecting pipe 105 gradually heats the fluid inside the connecting pipe 105 to a temperature of about 50° C., and the dimethyl ether in the liquid is desorbed and released;

[0100] Step 4: The desorbed dimethyl ether gas floats upward, and after being discharged through the gas pipe 201 on the top of the desorption tower 200, it is condensed and reduced to -17°C by the condenser 202 installed on the gas pipe 201. The low-temperature gas naturally overflows to obtain the dimethyl ether product; after the enriched liquid in the desorption tower is desorbed, it naturally flows downward, and is transported to the absorption liquid storage tank 300 through a pipeline for recycling.

[0101] Example 6

[0102] See also Figure 1 This embodiment provides a method for recovering dimethyl ether from dimethyl ether purge gas, comprising the following steps:

[0103] Step 1: Evenly mix anhydrous ethanol, ethylene glycol dimethyl ether and deionized water in a volume ratio of 7:3:5 to obtain an absorption liquid, and store the absorption liquid in an absorption liquid storage tank 300; fill the composite filler prepared in Example 3 into the absorption tower 100; fill the desorption tower 200 with volcanic rock biological filler; start the transfer pump 2 301; cool the absorption liquid to 25° C. through the low-temperature heat exchanger 2 303 on the connecting pipe 2 302; and flow out from the top of the 80th tower plate inside the absorption tower 100, and flow from top to bottom along each tower plate;

[0104] Step 2, dimethyl ether purge gas enters the air inlet pipe 101, is cooled to 10°C by heat exchange in the low-temperature heat exchanger 102, and after gas-liquid separation, the low-temperature purge gas enters the top of the 5th tower plate of the absorption tower 100 through the air inlet pipe 101, and the input ratio of the low-temperature purge gas to the absorption liquid is controlled to be 1mL:10mL. The low-temperature purge gas entering the absorption tower 100 floats upward and repeatedly contacts the absorption liquid flowing from top to bottom on the composite filler layer, and an enriched liquid absorbing dimethyl ether is formed at the bottom of the absorption tower 100. The gas not absorbed by the absorption liquid is discharged from the flying discharge pipe 103 at the top of the absorption tower 100;

[0105] Step 3: The temperature of the desorption tower 200 is raised to 52° C. The transfer pump 104 is started to transport the enriched liquid collected at the bottom of the inner side of the absorption tower 100 to the top of the 72nd tower plate inside the desorption tower 200 through the connecting pipe 105. During the transportation process, the high-temperature heat exchanger 106 on the connecting pipe 105 gradually heats the fluid inside the connecting pipe 105 to a temperature of about 52° C., and the dimethyl ether in the liquid is desorbed and released;

[0106] Step 4: The desorbed dimethyl ether gas floats upward, and after being discharged through the gas pipe 201 on the top of the desorption tower 200, it is condensed and reduced to -20°C by the condenser 202 installed on the gas pipe 201. The low-temperature gas naturally overflows to obtain the dimethyl ether product; after the enriched liquid in the desorption tower is desorbed, it naturally flows downward, and is transported to the absorption liquid storage tank 300 through a pipeline for recycling.

[0107] Comparative Example 1

[0108] The difference between this comparative example and Example 6 is that when preparing the composite filler used, no tetrabutyl titanate is added to the silicon source solution in step S1.

[0109] Comparative Example 2

[0110] The difference between this comparative example and Example 6 is that, when preparing the composite filler used, step S4 is omitted, and the porous filler in step S3 is used as the composite filler.

[0111] Comparative Example 3

[0112] The difference between this comparative example and Example 6 is that, in step 1, no deionized water is added to the absorption liquid.

[0113] Comparative Example 4

[0114] The difference between this comparative example and Example 6 is that, in step 1, the temperature of the absorption liquid is 35°C.

[0115] Example 5

[0116] The difference between this comparative example and Example 6 is that, in step 3, the temperature of the enriched liquid in the desorption tower and input into the analysis tower is 60°C.

[0117] Performance Test:

[0118] The mass fractions of dimethyl ether and methanol in the dimethyl ether samples prepared in Examples 4-6 and Comparative Examples 1-5 and the acidity of the samples were determined with reference to the standard HG / T 3934-2007 "Dimethyl Ether";

[0119] Reference formula The recovery rate of dimethyl ether in the dimethyl ether purge gas during the preparation of dimethyl ether in Examples 4-6 and Comparative Examples 1-5 was determined, where V DME The volume of dimethyl ether recovered is W DME is the volume fraction of recovered dimethyl ether, V 驰放气 is the volume fraction of dimethyl ether purge gas entering the absorption tower, W 驰放气-DME is the volume fraction of dimethyl ether in the dimethyl ether purge gas entering the absorption tower. The specific test results are shown in Table 1 below.

[0120] Table 1-Performance test data of the sample

[0121]

[0122] Data Analysis:

[0123] A comparative analysis of the data in Table 1 above shows that the mass fraction of dimethyl ether prepared by the present invention reaches 99.96%, the content of methanol is reduced to 0.01%, the acidity is reduced to 0.00011%, and the recovery rate of dimethyl ether in dimethyl ether purge gas reaches 90.3%. All performance parameters are better than those of the comparative example. The present invention optimizes the composition and adsorption temperature of the adsorption liquid and modifies the composite filler, thereby effectively improving not only the recovery purity of dimethyl ether, but also the recovery rate of dimethyl ether in the purge gas.

[0124] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to only specific implementation methods. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for recovering dimethyl ether from dimethyl ether purge gas, characterized in that: The following steps are involved: S1, dimethyl ether purge gas is cooled to 8~10℃ by heat exchanger and then discharged to obtain low-temperature purge gas; S2, the low-temperature purge gas enters the inner bottom of an absorption tower (100) filled with a composite filler, is absorbed by an absorption liquid having a temperature of 10 to 15° C. flowing from top to bottom, and forms an enriched liquid at the bottom of the absorption tower (100). The absorbed waste gas is discharged from a waste gas discharge pipe (103) at the top of the absorption tower (100); S3. The temperature of the desorption tower (200) filled with volcanic rock biological filler is increased to 47-52° C. The enriched liquid is transferred to the inner top of the desorption tower (200). The enriched liquid flows from top to bottom and desorbs. The desorbed dimethyl ether is discharged from the top of the desorption tower (200) to obtain crude dimethyl ether. The crude dimethyl ether is condensed and separated to obtain a dimethyl ether product.

2. A method for recovering dimethyl ether from dimethyl ether purge gas according to claim 1, characterized in that: In step S2, the temperature of the low-temperature purge gas input into the absorption tower (100) is 20-25°C, the input ratio of the low-temperature purge gas to the absorption liquid is 1 mL:8-10 mL, and the absorption liquid is composed of anhydrous ethanol, ethylene glycol dimethyl ether and deionized water in a volume ratio of 7:2-3:5; in step S3, the condensation separation temperature of the crude dimethyl ether to prepare the dimethyl ether product is -15--20°C.

3. A method for recovering dimethyl ether from dimethyl ether purge gas according to claim 1, characterized in that: The composite filler is processed by the following steps: A1, mixing the porous microspheres and fumed silica uniformly to obtain mixed silicon; A2, stirring and mixing sodium hydroxide, sodium aluminate and deionized water until the system is dissolved, adding n-butylamine to the reaction system, stirring at room temperature for 15 to 20 minutes, adding mixed silicon to the reaction system, and stirring at this temperature for 90 to 120 minutes to obtain a mixed gel; A3, transferring the mixed gel to a high pressure reactor at a temperature of 150-160°C and a pressure of 0.15-0.25 MPa, homogeneously crystallizing for 2 days, washing and calcining to obtain a porous material precursor, and performing ammonium exchange on the porous filler to obtain a porous filler; A4. Activate and modify the porous filler to obtain a composite filler.

4. A method for recovering dimethyl ether from dimethyl ether purge gas according to claim 3, characterized in that: In step A1, the weight ratio of porous microspheres to fumed silica is 1:2; in step A2, the amount ratio of sodium hydroxide, sodium aluminate, deionized water, n-butylamine, and mixed silicon is 1g:3g:60mL:5g:20g; in step A3, the washing and roasting treatment includes: after homogeneous crystallization is completed, suction filtration, the filter cake is washed with purified water 5 times and then dried, the filter cake is transferred to a muffle furnace, the temperature of the muffle furnace is increased to 90-100°C, roasted for 40-60min, the muffle furnace is increased to 550-600°C at a heating rate of 3-5°C / min, kept warm and roasted for 5-6h, naturally cooled to room temperature, and discharged to obtain a porous filler precursor.

5. A method for recovering dimethyl ether from dimethyl ether purge gas according to claim 3, characterized in that: In step A1, the preparation method of porous microspheres is: mix the porogen and deionized water, ultrasonically disperse until the system is dissolved, add silicon source solution to the reaction system, increase the temperature of the reaction system to 70-75°C, keep the reaction warm for 10-12 hours, post-treat, separate to obtain solid particles, and calcine the solid particles to obtain porous microspheres.

6. A method for recovering dimethyl ether from dimethyl ether purge gas according to claim 5, characterized in that: The dosage ratio of the porogen, deionized water and silicon source liquid is 8g:50mL:15g, the porogen is composed of 1-vinyl-3-dodecyl imidazole bromide and urea in a weight ratio of 5:3, the silicon source liquid is composed of tetraethyl orthosilicate, tetrabutyl titanate and isopropanol in a weight ratio of 5:2:10, the calcination treatment temperature is 550-600°C, and the calcination time is 4-6h.

7. A method for recovering dimethyl ether from dimethyl ether purge gas according to claim 3, characterized in that: In step A3, the ammonium exchange method is: mixing the porous filler precursor and the ammonium chloride solution, raising the temperature of the reaction system to 85-95° C., keeping the temperature for 2-3 hours, washing and calcining to obtain the porous filler.

8. A method for recovering dimethyl ether from dimethyl ether purge gas according to claim 7, characterized in that: The porous filler precursor and the ammonium chloride solution are used in a ratio of 1 g:10 mL, and the ammonium chloride solution is composed of ammonium chloride and deionized water in a ratio of 1 g:10 mL.

9. A method for recovering dimethyl ether from dimethyl ether purge gas according to claim 3, characterized in that: In step A4, the activation modification comprises the following steps: B1. Mix the porous filler, tetrahydrofuran and KH-560, and disperse them by ultrasonic for 20-30 minutes. Add ammonia water to the reaction system, raise the temperature of the reaction system to 50-60°C, keep the temperature for 60-80 minutes, and perform post-treatment to obtain the activated filler. B2. Mix polyethyleneimine, activated filler, deionized water and sodium hydroxide, increase the temperature of the reaction system to 60-70°C, perform ultrasonic dispersion for 80-90 minutes, and post-treat to obtain a composite filler.

10. A method for recovering dimethyl ether from dimethyl ether purge gas according to claim 9, characterized in that: In step B1, the amount ratio of the porous filler, tetrahydrofuran, KH-560 and ammonia water is 5g:50mL:3g:10mL, and the mass fraction of ammonia water is 5-8wt%; in step B2, the amount ratio of polyethyleneimine, activated filler, deionized water and sodium hydroxide is 3g:7g:20mL:2g.

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