A coal-based ethylene glycol byproduct mixed alcohol separation system and method based on selective reactive distillation

Abstract

The application discloses a coal-based ethylene glycol byproduct mixed alcohol separation system and method based on selective reaction rectification, and belongs to the field of chemical separation technology. The system comprises an ester exchange reaction rectification tower, a pressurized azeotropic rectification tower, an alcoholysis reaction rectification tower, a dihydric alcohol azeotropic rectification tower and an alcohol-ester vacuum rectification tower which are connected in sequence. The core of the application is to utilize the intrinsic kinetic difference between butylene carbonate and ethylene carbonate in the alcoholysis reaction, to overcome the separation difficulty caused by the close boiling point of ethylene glycol and 1,2-butanediol by constructing a two-stage reaction rectification coupling process. By accurately controlling the alcoholysis reaction conditions, the separation effect of preferentially reacting butylene carbonate to generate 1,2-butanediol and selectively retaining ethylene carbonate is realized. The azeotrope at the top of the pressurized azeotropic rectification tower is directly used in the alcoholysis section, which significantly reduces the energy consumption of high-purity separation, and finally synchronously outputs high-purity 1,2-butanediol, ethylene carbonate, methanol and recovered ethylene glycol.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gas purification, in particular to a coal-based ethylene glycol byproduct mixed alcohol separation method and system based on selective reaction rectification, and in particular to a high-selectivity reaction rectification separation technology based on reaction kinetics difference driving for efficient separation. BACKGROUND

[0002] Coal-based ethylene glycol technology is an important path to realize clean and efficient utilization of coal, but about 1-5% of binary alcohol mixture mainly composed of ethylene glycol and 1,2-butanediol is by-produced in the production process. Among them, the boiling points of ethylene glycol and 1,2-butanediol are very close (the difference is only about 5℃ at normal pressure), and the system may form azeotrope. The use of conventional rectification for separation faces the severe challenges of high theoretical tray number, large reflux ratio, high energy consumption and high equipment investment, and poor economic efficiency. In addition, the high theoretical tray number also causes high total column pressure drop, which in turn increases the column bottom temperature, thereby affecting the product quality of ethylene glycol.

[0003] The prior art has made some explorations to solve this problem. For example, special solvents are introduced by using extractive rectification (such as CN 106866369B, 110357763B), but there are problems of solvent loss and recovery energy consumption; another technology (such as CN112079688B) proposes to react butanediol with aldehyde ketone to generate acetals / ketones with large boiling point difference, but introduces new reactants, increasing the complexity of the process and the burden of by-product separation; there is also a technology aimed at producing high-purity chemicals (such as CN120554229A), which proposes to use ester exchange reaction, pressurized azeotropic rectification and continuous falling film crystallization to realize complete reaction and efficient separation of products, but there are problems of long process flow, poor coordination between steps, and high energy consumption.

[0004] In addition, existing patents (such as CN114478187B, CN107417534B) mainly focus on process optimization for co-production of dimethyl carbonate and ethylene glycol through ethylene carbonate route, and the technical goal is to improve the conversion rate of the main reaction and the purity of the main product, and does not involve how to utilize the reaction characteristic difference between by-product components to realize their own efficient separation.

[0005] Therefore, there is an urgent need in the art for an innovative method that can efficiently, energy-efficiently and greenly separate high-purity butanediol from mixed alcohol, in order to improve the overall economic efficiency and resource utilization rate of the coal-based ethylene glycol industry chain. SUMMARY

[0006] The purpose of the present application is to overcome the shortcomings of the prior art and provide a coal-based ethylene glycol byproduct mixed alcohol separation system and method based on selective reaction rectification.

[0007] To achieve the above object, the present application adopts the following technical solutions to achieve the above object: A coal-based ethylene glycol by-product mixed alcohol separation system based on selective reaction rectification, comprising:

[0008] An ester exchange reaction rectification tower is used for ester exchange reaction of mixed dihydric alcohol and dimethyl carbonate, and a light component sampling outlet is arranged at the top of the tower, and a heavy component sampling outlet is arranged at the tower bottom;

[0009] A pressurized azeotropic rectification tower, whose feed inlet is connected with the light component sampling outlet at the top of the ester exchange reaction rectification tower through a pressurized azeotropic rectification tower feed pump;

[0010] A low-pressure azeotropic rectification tower, whose feed inlet is connected with the top sampling outlet of the pressurized azeotropic rectification tower;

[0011] An ethylene glycol vacuum rectification tower, whose feed inlet is connected with the heavy component sampling outlet at the tower bottom of the ester exchange reaction rectification tower;

[0012] An alcoholysis reaction rectification tower, whose upper feed inlet is connected with the tower bottom sampling outlet of the ethylene glycol vacuum rectification tower through an alcoholysis reaction rectification tower feed pump, and whose lower feed inlet is directly connected with the top sampling outlet of the pressurized azeotropic rectification tower;

[0013] A dihydric alcohol azeotropic rectification tower, whose feed inlet is connected with the tower bottom sampling outlet of the alcoholysis reaction rectification tower through a dihydric alcohol azeotropic rectification tower feed pump;

[0014] An alcohol ester vacuum rectification tower, whose feed inlet is connected with the tower bottom sampling outlet of the dihydric alcohol azeotropic rectification tower through an alcohol ester vacuum rectification tower feed pump.

[0015] Further, the tower bottom sampling outlet of the pressurized azeotropic rectification tower is connected with the lower feed inlet of the ester exchange reaction rectification tower through a pipeline; the top sampling outlet of the low-pressure azeotropic rectification tower is connected with the feed inlet of the pressurized azeotropic rectification tower through a pressurized azeotropic rectification tower back feed pump; the top sampling outlet of the alcoholysis reaction rectification tower is connected with the lower feed inlet of the ester exchange reaction rectification tower through an ester exchange reaction rectification tower back feed pump; and the top sampling outlet of the dihydric alcohol azeotropic rectification tower is connected with the upper feed inlet of the ester exchange reaction rectification tower through a dihydric alcohol pressurization pump.

[0016] The coal-based ethylene glycol by-product mixed alcohol separation method based on selective reaction rectification is as follows:

[0017] Step 1, ester exchange and preliminary separation: the mixed dihydric alcohol and dimethyl carbonate are respectively fed into the ester exchange reaction rectification tower to perform ester exchange reaction, to generate vinyl carbonate, butene carbonate and methanol; the azeotrope of methanol and dimethyl carbonate is sampled out at the top of the tower, and the mixture containing ethylene glycol, vinyl carbonate and butene carbonate is sampled out at the tower bottom;

[0018] Step 2, azeotrope gradient separation and energy integration: the overhead azeotrope of step 1 is sent to a pressurized azeotrope rectifying column for separation, and the carbonic dimethyl ester is obtained at the column bottom; the methanol-rich azeotrope partially taken from the column top is directly sent to the alcoholysis reaction rectifying column as the reaction raw material, and the other part is sent to a low-pressure azeotrope rectifying column for further purification;

[0019] Step 3, ethylene glycol vacuum separation and purification: the mixture at the column bottom of step 1 is sent to an ethylene glycol vacuum rectifying column for separation, and the high-purity ethylene glycol product is taken from the column top, and the mixture of ethylene carbonate and butylene carbonate is obtained at the column bottom;

[0020] Step 4, selective alcoholysis separation: the mixture at the column bottom of step 3 is sent to the alcoholysis reaction rectifying column together with the methanol-rich azeotrope taken from the overhead of the pressurized azeotrope rectifying column in step 2, and by controlling the reaction conditions, the butylene carbonate is almost completely alcoholized to generate 1,2-butylene glycol, while the alcoholysis reaction of ethylene carbonate is inhibited;

[0021] Step 5, product fine separation and recycling: the column bottom product of the alcoholysis reaction rectifying column in step 4 is sent to a diol azeotrope rectifying column, and the residual ethylene glycol is taken away by the overhead azeotrope and recycled back to the ester exchange reaction rectifying column; the column bottom product is sent to an alcohol-ester vacuum rectifying column, and the high-purity 1,2-butylene glycol product is taken from the column top, and the ethylene carbonate product is taken from the column bottom.

[0022] Preferably, the methanol raw material of the alcoholysis reaction rectifying column in step 2 is the azeotrope of methanol and carbonic dimethyl ester taken from the overhead of the pressurized azeotrope rectifying column, which is directly used for alcoholysis reaction with the mixture of ethylene carbonate and butylene carbonate obtained at the column bottom of the ethylene glycol vacuum rectifying column in step 3, without the need to purify the part of material into high-purity methanol, so that the energy consumption of the low-pressure azeotrope rectifying column is reduced by 45-90%.

[0023] Preferably, the carbonic dimethyl ester taken from the column bottom of the pressurized azeotrope rectifying column and the overhead of the alcoholysis reaction rectifying column in steps 2 and 4 is returned to the ester exchange reaction rectifying column for recycling; the ethylene glycol and 1,2-butylene glycol azeotrope taken from the overhead of the diol azeotrope rectifying column in step 5 is returned to the ester exchange reaction rectifying column for recycling, so as to construct multiple material closed-loop circulation loops including carbonic dimethyl ester and the ethylene glycol and 1,2-butylene glycol azeotrope; thus, while ensuring high separation efficiency, the process energy consumption is reduced by 23-56%, and the material consumption due to the loss of heat-sensitive material in the column is reduced by 8-24%.

[0024] Preferably, the reaction section temperature of the ester exchange reaction rectifying tower in step 2 is 80-150 DEG C, the pressure is 0.04-0.20 MPa, the reflux ratio is 0.05-4.15, the conversion rate of 1,2-butanediol in the mixed dihydric alcohol raw material is higher than 98.1%, and the conversion rate of ethylene glycol is lower than 50.8%; 1,2-butanediol is the raw material in step 2, and 1,2-butanediol is the product in step 4, which are the positive reaction and the reverse reaction respectively.

[0025] Preferably, the selective alcoholysis reaction in step 4 is carried out in an alcoholysis reaction rectifying tower, and the reaction section temperature is controlled to be 75-135 DEG C, the pressure is 0.05-0.21 MPa, the reflux ratio is 0.04-3.52, and the reaction residence time is 10-120 min, so as to ensure that the butylene carbonate is almost completely reacted, and the conversion of the ethylene carbonate is maximally inhibited, so that the conversion rate of butylene carbonate is higher than 98.5%, and the conversion rate of ethylene carbonate is lower than 10%.

[0026] Preferably, the operating pressure of the pressurized azeotropic rectifying tower in step 2 is 0.5-1.7 MPa, and the operating pressure of the low-pressure azeotropic rectifying tower is 0.1-0.3 MPa.

[0027] Preferably, the operating pressure of the ethylene glycol vacuum rectifying tower in step 3 and the alcohol-ester vacuum rectifying tower in step 5 is 0.001-0.010 MPa.

[0028] The present application provides a coal-based ethylene glycol byproduct mixed alcohol separation system and method based on selective reaction rectification.

[0029] 1、The present application is based on the significant kinetic difference between butylene carbonate and ethylene carbonate in the methanol alcoholysis reaction, that is, the reaction rate constant of butylene carbonate is significantly greater than that of ethylene carbonate, and through the Arrhenius formula and transition state theory, it is known that the transition state steric hindrance effect and intramolecular tension of butylene carbonate with an ethyl side chain are different from those of ethylene carbonate, resulting in lower reaction activation energy and easier reaction. Based on the theoretical basis, by accurately controlling the conditions of the alcoholysis reaction rectifying tower, a reaction and separation environment maximizing the kinetic difference can be created, and the high-selectivity separation of 1,2-butanediol and ethylene glycol can be finally realized.

[0030] 2、Because the alcoholysis reaction has no high requirement on the purity of methanol, the non-high-purity methanol-dimethyl carbonate azeotrope collected from the top of the pressurized azeotropic rectification tower is directly used for the alcoholysis reaction, avoiding the energy consumption of purifying the part of materials to high-purity methanol, greatly reducing the load and total energy consumption of the low-pressure azeotropic rectification tower, realizing the use of energy according to quality, and constructing multiple material closed-loop circulation loops including dimethyl carbonate, methanol and ethylene glycol azeotrope, so that the process has high separation efficiency, and the energy consumption and material consumption are greatly reduced.

[0031] 3、The present application realizes the intensification of reaction and separation, and the in-vivo circulation of materials through two-stage reaction rectification coupling, and can obtain high-purity 1,2-butanediol product, high-purity ethylene carbonate product and recovered ethylene glycol product, realizes the full-component high-value utilization of by-product mixed alcohol, has significant economic benefits, avoids the high energy consumption of traditional high-pressure differential precision rectification and dynamic crystallization, and the closed-loop circulation of dimethyl carbonate and methanol greatly reduces the raw material consumption and three-waste emissions, and meets the requirements of green chemical industry.

[0032] 4、The whole system organically couples the processes of reaction, rectification, azeotropic separation and vacuum separation, breaks the reaction equilibrium limitation, improves the atomic utilization rate, realizes the in-situ separation of products, has compact and reasonable process, and has mature and reliable operation conditions, the whole process has no odor and no introduction of toxic and harmful substances, and has strong industrial amplification and popularization and application potential. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without any creative effort.

[0034] Figure 1 It is a process flow diagram of the system of the present application.

[0035] In the figure, 1 is an ester exchange reaction rectification tower, 2 is a pressurized azeotropic rectification tower feed pump, 3 is a pressurized azeotropic rectification tower, 4 is a low-pressure azeotropic rectification tower, 5 is a pressurized azeotropic rectification tower return pump, 6 is a methanol booster pump, 7 is an alcohol-ester vacuum rectification tower, 8 is a butanediol booster pump, 9 is an ethylene carbonate booster pump, 10 is an ethylene glycol vacuum rectification tower, 11 is an ethylene glycol booster pump, 12 is an alcoholysis reaction rectification tower feed pump, 13 is an alcoholysis reaction rectification tower, 14 is an ester exchange reaction rectification tower return pump, 15 is a dihydric alcohol azeotropic rectification tower feed pump, 16 is a dihydric alcohol azeotropic rectification tower, 17 is an alcohol-ester vacuum rectification tower feed pump, and 18 is a dihydric alcohol booster pump. DETAILED DESCRIPTION

[0036] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application. The embodiments described below and the features in the embodiments can be combined with each other without conflict.

[0037] Reference is made to Figure 1 , Figure 1 The structural schematic diagram of the present application is a coal-based ethylene glycol byproduct mixed alcohol separation system based on selective reaction rectification, mainly comprising: an ester exchange reaction rectification tower 1, a pressurized azeotropic rectification tower feed pump 2, a pressurized azeotropic rectification tower 3, a low-pressure azeotropic rectification tower 4, a pressurized azeotropic rectification tower back feed pump 5, a methanol booster pump 6, an alcohol ester vacuum rectification tower 7, a butanediol booster pump 8, an ethylene carbonate booster pump 9, an ethylene glycol vacuum rectification tower 10, an ethylene glycol booster pump 11, an alcoholysis reaction rectification tower feed pump 12, an alcoholysis reaction rectification tower 13, an ester exchange reaction rectification tower back feed pump 14, a dihydric alcohol azeotropic rectification tower feed pump 15, a dihydric alcohol azeotropic rectification tower 16, an alcohol ester vacuum rectification tower feed pump 17, and a dihydric alcohol booster pump 18.

[0038] The ester exchange reaction rectification tower 1 has a rectification section, a reaction section and a stripping section arranged in the tower from top to bottom. The mixed dihydric alcohol raw material from the coal-based ethylene glycol process enters the tower through the feed port at the bottom of the rectification section, and the dimethyl carbonate raw material enters the tower through the feed port at the top of the stripping section. In the presence of a catalyst, in the reaction section, all 1,2-butylene glycol and part of the ethylene glycol in the mixed dihydric alcohol raw material react with dimethyl carbonate to form butylene carbonate and ethylene carbonate, respectively. In this process, the light components taken out from the top of the tower are the azeotrope of methanol and dimethyl carbonate; the heavy components taken out from the bottom of the tower contain unreacted ethylene glycol, reaction-generated ethylene carbonate and butylene carbonate.

[0039] The overhead light component material of the transesterification reaction distillation column 1 is fed to the pressurized azeotropic distillation column 3 after being pressurized by the pressurized azeotropic distillation column feed pump 2. After the pressurized azeotropic distillation, high-purity dimethyl carbonate is obtained in the column bottom, and this part of dimethyl carbonate is returned to the feed inlet of the lower part of the transesterification reaction distillation column 1 to realize recycling; the light component collected from the column top is an azeotrope with a higher methanol content and a lower dimethyl carbonate content. This column top material is divided into two routes: one is directly fed to the feed inlet of the lower part of the alcoholysis reaction distillation column 13 to be used as the methanol raw material for alcoholysis reaction; the other is fed to the low-pressure azeotropic distillation column 4 for further decompression azeotropic distillation purification. In the low-pressure azeotropic distillation column 4, an azeotrope with a higher dimethyl carbonate content is obtained at the column top, and this material is pressurized by the pressurized azeotropic distillation column return pump 5 and then returned to the pressurized azeotropic distillation column 3 for reprocessing; high-purity methanol product is obtained in the column bottom, which is pressurized by the methanol pressurizing pump 6 and then sent out of the system boundary.

[0040] In the above process, the direct use of the pressurized azeotropic distillation column 3 overhead azeotrope for alcoholysis reaction is a key energy-saving design, and its scientificity lies in that the alcoholysis reaction itself does not require high purity of the methanol raw material, thereby avoiding the deep purification of this part of azeotrope with high energy consumption, which can significantly reduce the load of the low-pressure azeotropic distillation column 4 and the overall energy consumption of the system.

[0041] The heavy component material collected from the column bottom of the transesterification reaction distillation column 1 is introduced into the ethylene glycol vacuum distillation column 10 for separation. Under vacuum conditions, the unreacted ethylene glycol product is collected at the column top, which is pressurized by the ethylene glycol pressurizing pump 11 and then sent out of the system boundary; the mixture rich in ethylene carbonate and butylene carbonate collected from the column bottom is pressurized by the alcoholysis reaction distillation column feed pump 12 and then fed to the feed inlet of the upper part of the alcoholysis reaction distillation column 13.

[0042] The alcoholysis reaction rectification column 13 also has rectification section, reaction section and stripping section inside. The mixture of ethylene carbonate and butylene carbonate from the previous step is delivered to the feed inlet at the bottom of the rectification section of the alcoholysis reaction rectification column via the alcoholysis reaction rectification column feed pump 12; and the methanol-rich azeotrope from the top of the pressurized azeotropic rectification column 3 is delivered to the feed inlet at the top of the stripping section. In the reaction section of the alcoholysis reaction rectification column 13, by using the higher alcoholysis reaction activity of butylene carbonate than that of ethylene carbonate and by precisely controlling the reaction conditions (such as temperature, pressure and residence time), selective reaction is achieved: that is, nearly all of the butylene carbonate and a small part of the ethylene carbonate react with methanol to generate 1,2-butanediol, dimethyl carbonate and a small amount of ethylene glycol. After the reaction, the mixture of unreacted methanol and generated dimethyl carbonate is taken out from the top of the column, and the mixture is pressurized by the ester exchange reaction rectification column return pump 14 and then returned to the ester exchange reaction rectification column 1 for recycling; the heavy components taken out from the column bottom include 1,2-butanediol, unreacted ethylene carbonate and a small amount of ethylene glycol generated in the reaction.

[0043] The heavy components of the column bottom of the alcoholysis reaction rectification column 13 are pressurized by the diol azeotropic rectification column feed pump 15 and then sent to the diol azeotropic rectification column 16 for vacuum azeotropic rectification, and the azeotrope at the top of the column is used to take out all the residual ethylene glycol in the system. The material is pressurized by the diol pressurizing pump 18 and then returned to the ester exchange reaction rectification column 1 for reprocessing; the column bottom obtains a mixture of 1,2-butanediol and ethylene carbonate.

[0044] The column bottom mixture is delivered to the alcohol-ester vacuum rectification column 7 via the alcohol-ester vacuum rectification column feed pump 17 for final separation. Under the action of vacuum rectification, high-purity 1,2-butanediol product is taken out from the top of the column, pressurized by the butanediol pressurizing pump 8 and then sent out of the system; high-purity ethylene carbonate product is taken out from the column bottom, pressurized by the ethylene carbonate pressurizing pump 9 and then sent out of the system.

[0045] From the above analysis, it can be concluded that a coal-based ethylene glycol byproduct mixed alcohol separation system based on selective reaction rectification is designed ingeniously, the separation system driven by the difference in reaction kinetics is creatively coupled with the two-stage core processes of "ester exchange reaction rectification" and "selective alcoholysis reaction rectification", and is deeply synergized with multi-stage azeotropic rectification and energy integration network. Moreover, by accurately controlling the operating conditions of the alcoholysis reaction section, the significant difference in intrinsic reaction activity between butylene carbonate and ethylene carbonate is utilized to realize the high selectivity conversion and separation of 1,2-butanediol. At the same time, high-purity 1,2-butanediol product, ethylene carbonate and ethylene glycol product can be simultaneously produced, realizing the full-component high-value and resource utilization of byproduct mixed alcohol, and supporting the continuous and automated operation of the whole process. The technical scheme has novel separation path, high resource utilization rate and outstanding economic efficiency, and is particularly suitable for energy saving and efficiency improvement of coal-based ethylene glycol process and product structure upgrading, and has broad application prospect in the field of coal chemical separation technology.

[0046] The above content only illustrates the technical idea of the present application and cannot limit the protection scope of the present application. Any modification made according to the technical idea of the present application on the basis of the technical scheme falls within the protection scope of the claims of the present application.

[0047] Hereinafter, the technical scheme of the present application will be further illustrated in combination with specific examples.

[0048] Example 1

[0049] The raw material used in this example has the following mass composition: the mass fraction of ethylene glycol is 75.5%, the mass fraction of 1,2-butanediol is 24.5%, and the flow rate is 12158 kg / h.

[0050] A coal-based ethylene glycol byproduct mixed alcohol separation method based on selective reaction rectification, specifically comprising the following steps:

[0051] 1. The ester exchange reaction rectification column 1 is internally provided with a rectification section, a reaction section and a stripping section from top to bottom in turn, wherein the temperature of the reaction section is 86-130℃, the operating pressure is 0.12 MPa, and the reflux ratio of the column is 0.15. The mixed dihydric alcohol raw material from the coal-to-ethylene glycol process enters the column through the feed port located at the bottom of the rectification section, while the dimethyl carbonate raw material enters the column through the feed port located at the top of the stripping section. In the presence of catalyst, in the reaction section, all 1,2-butanediol and part of the ethylene glycol contained in the mixed dihydric alcohol raw material react with dimethyl carbonate to generate butylene carbonate and ethylene carbonate, respectively, wherein the conversion rate of 1,2-butanediol is 99.52%, and the conversion rate of ethylene glycol is 42.3%. In this process, the light components taken out from the top of the column are azeotropes formed by methanol and dimethyl carbonate; the heavy components taken out from the column bottom contain unreacted ethylene glycol, reaction-generated ethylene carbonate and butylene carbonate.

[0052] 2. The light component material taken out from the top of the ester exchange reaction rectification column 1 is pressurized by the pressurized azeotropic rectification column feed pump 2, and then transported to the pressurized azeotropic rectification column 3 for separation, with an operating pressure of 1.6 MPa. After pressurized azeotropic rectification, high-purity dimethyl carbonate is obtained from the column bottom, and this part of dimethyl carbonate is returned to the feed port at the lower part of the ester exchange reaction rectification column 1 for recycling; the light component taken out from the top of the column is an azeotrope with a higher content of methanol and a lower content of dimethyl carbonate, wherein the mass fraction of methanol is 91.2%. This column top material is divided into two streams: one is directly transported to the feed port at the lower part of the alcoholysis reaction rectification column 13 for use as the methanol raw material for alcoholysis reaction; the other is introduced into the low-pressure azeotropic rectification column 4 for further decompression azeotropic rectification purification, with an operating pressure of 0.1 MPa. In the low-pressure azeotropic rectification column 4, the top obtains an azeotrope with a higher content of dimethyl carbonate, which is pressurized by the pressurized azeotropic rectification column return pump 5 and returned to the pressurized azeotropic rectification column 3 for reprocessing; the column bottom obtains high-purity methanol product, which is pressurized by the methanol pressurizing pump 6 and sent out of the system boundary.

[0053] 3. The heavy component material taken out from the column bottom of the ester exchange reaction rectification column 1 is introduced into the ethylene glycol vacuum rectification column 10 for separation. Under vacuum conditions, the top takes out the unreacted ethylene glycol product, which is pressurized by the ethylene glycol pressurizing pump 11 and sent out of the system boundary; the column bottom takes out a mixture rich in ethylene carbonate and butylene carbonate, which is pressurized by the alcoholysis reaction rectification column feed pump 12 and transported to the feed port at the upper part of the alcoholysis reaction rectification column 13.

[0054] 4、The alcoholysis reaction rectification column 13 is also provided with rectification section, reaction section and stripping section inside, wherein the temperature of the reaction section is 78-112 ℃, the reaction residence time is 32 min, the operating pressure is 0.11 MPa, and the reflux ratio of the column is 0.21. The mixture of ethylene carbonate and butylene carbonate from the previous step is delivered to the feed inlet at the bottom of the rectification section of the alcoholysis reaction rectification column through the alcoholysis reaction rectification column feed pump 12; and the methanol-rich azeotrope from the top of the pressurized azeotropic rectification column 3 is fed into the feed inlet at the top of the stripping section. In the reaction section of the alcoholysis reaction rectification column 13, by utilizing the higher alcoholysis reaction activity of butylene carbonate than that of ethylene carbonate and by precisely controlling the reaction conditions (such as temperature, pressure and residence time), selective reaction is realized: that is, nearly all of the butylene carbonate and a small part of the ethylene carbonate react with methanol to generate 1,2-butanediol, dimethyl carbonate and a small amount of ethylene glycol, wherein the conversion rate of butylene carbonate is 99.71%, and the conversion rate of ethylene carbonate is 8%. After the reaction, the mixture of unreacted methanol and generated dimethyl carbonate is taken out from the top of the column, and the mixture is pressurized by the ester exchange reaction rectification column feed pump 14 and then returned to the ester exchange reaction rectification column 1 for recycling; the heavy components taken out from the column bottom include 1,2-butanediol, unreacted ethylene carbonate and a small amount of ethylene glycol generated in the reaction.

[0055] 5、The heavy components taken out from the column bottom of the alcoholysis reaction rectification column 13 are pressurized by the diol azeotropic rectification column feed pump 15 and then sent to the diol azeotropic rectification column 16 for vacuum azeotropic rectification, and the remaining ethylene glycol in the system is taken out by the column top azeotrope, and the material is pressurized by the diol pressurizing pump 18 and then returned to the ester exchange reaction rectification column 1 for reprocessing; the column bottom obtains a mixture of 1,2-butanediol and ethylene carbonate.

[0056] The column bottom mixture is delivered to the alcohol-ester vacuum rectification column 7 through the alcohol-ester vacuum rectification column feed pump 17 for final separation. Under the action of vacuum rectification, high-purity 1,2-butanediol product is taken out from the column top and pressurized by the butanediol pressurizing pump 8 and then sent out of the system; high-purity ethylene carbonate product is taken out from the column bottom and pressurized by the ethylene carbonate pressurizing pump 9 and then sent out of the system.

[0057] In this embodiment, the chemical purity of the obtained ethylene glycol and ethylene carbonate is 99.59% and 99.65% respectively, and the chemical purity of 1,2-butanediol and methanol is greater than 99.99%, the energy consumption of the low-pressure azeotropic rectification column 4 is reduced by 52.8%, the total material loss is 24.3 kg / h, and the total steam consumption is 21.6 t / h.

[0058] Example 2

[0059] A coal-based ethylene glycol byproduct mixed alcohol separation method and system based on selective reaction rectification, the raw material mass composition used in the embodiment is: the mass fraction of ethylene glycol is 63.8%, the mass fraction of 1,2-butanediol is 36.2%, and the flow rate is 12158 kg / h.

[0060] In addition, the temperature of the reaction section of the transesterification reaction rectification tower 1 is 88-134℃, the operating pressure is 0.13 MPa, the reflux ratio of the tower is 0.11, the conversion rate of 1,2-butanediol in the tower is 99.68%, and the conversion rate of ethylene glycol is 43.8%; the operating pressure of the pressurized azeotropic rectification tower 3 is 1.7 MPa, the mass composition of methanol in the azeotrope collected from the top of the tower is 92.8%; the operating pressure of the low-pressure azeotropic rectification tower 4 is 0.11 MPa; the temperature of the reaction section of the alcoholysis reaction rectification tower 13 is 81-118℃, the reaction residence time is 40 min, the operating pressure is 0.11 MPa, the reflux ratio of the tower is 0.28, the conversion rate of butylene carbonate in the tower is 99.82%, and the conversion rate of ethylene carbonate is 9.1%; the remaining conditions are the same as in Example 1.

[0061] In the embodiment, the chemical purity of the obtained ethylene glycol and ethylene carbonate is 99.95% and 99.97% respectively, the chemical purity of 1,2-butanediol and methanol is both greater than 99.99%, the energy consumption of the low-pressure azeotropic rectification tower 4 is reduced by 92.4%, the total material loss is 30.2 kg / h, and the total steam consumption is 24.7 t / h.

[0062] Example 3

[0063] A coal-based ethylene glycol byproduct mixed alcohol separation system and method based on selective reaction rectification, the raw material mass composition used in the embodiment is: the mass fraction of ethylene glycol is 84.9%, the mass fraction of 1,2-butanediol is 15.1%, and the flow rate is 12158 kg / h.

[0064] In addition, the temperature of the reaction section of the transesterification reaction rectification tower 1 is 84-128℃, the operating pressure is 0.13 MPa, the reflux ratio of the tower is 0.20, the conversion rate of 1,2-butanediol in the tower is 99.48%, and the conversion rate of ethylene glycol is 45.3%; the operating pressure of the pressurized azeotropic rectification tower 3 is 1.8 MPa, the mass composition of methanol in the azeotrope collected from the top of the tower is 93.4%; the operating pressure of the low-pressure azeotropic rectification tower 4 is 0.10 MPa; the temperature of the reaction section of the alcoholysis reaction rectification tower 13 is 76-110℃, the reaction residence time is 26 min, the operating pressure is 0.12 MPa, the reflux ratio of the tower is 0.32, the conversion rate of butylene carbonate in the tower is 99.70%, and the conversion rate of ethylene carbonate is 9.8%; the remaining conditions are the same as in Example 1.

[0065] In the present embodiment, the chemical purity of the obtained ethylene glycol and 1,2-butanediol is 99.60% and 99.79% respectively, the chemical purity of the obtained ethylene carbonate and methanol is both greater than 99.99%, the energy consumption of the low-pressure azeotropic rectification tower 4 is reduced by 29.0%, the total material loss is 21.2 kg / h, and the total steam consumption is 20.8 t / h.

[0066] It should be understood, however, that the scope of the present application is not limited to the specific embodiments described herein, but encompasses any and all embodiments within the scope of the claims. Numerous modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the claims, the application can be practiced otherwise than as specifically described, and that this application includes all modifications and equivalents of the subject matter recited in the claims included herein.

Claims

1. A coal-based ethylene glycol by-product mixed alcohol separation system based on selective reactive distillation, characterized in that, include: The transesterification distillation column (1) is used to perform transesterification reaction between mixed diols and dimethyl carbonate. The top of the column is provided with a light component outlet and the bottom of the column is provided with a heavy component outlet. The feed inlet of the pressurized azeotropic distillation column (3) is connected to the light component outlet at the top of the transesterification reaction distillation column (1) via the pressurized azeotropic distillation column feed pump (2); The inlet of the low-pressure azeotropic distillation column (4) is connected to the top outlet of the pressurized azeotropic distillation column (3); The inlet of the ethylene glycol vacuum distillation column (10) is connected to the bottom recombinant fractionation outlet of the transesterification reaction distillation column (1); The upper feed port of the alcoholysis reaction distillation column (13) is connected to the bottom outlet of the ethylene glycol vacuum distillation column (10) through the alcoholysis reaction distillation column feed pump (12), and the lower feed port is directly connected to the top outlet of the pressurized azeotropic distillation column (3). The feed inlet of the diol azeotropic distillation column (16) is connected to the bottom outlet of the alcoholysis reaction distillation column (13) via the diol azeotropic distillation column feed pump (15). The inlet of the alcohol ester vacuum distillation column (7) is connected to the bottom outlet of the diol azeotropic distillation column (16) via the alcohol ester vacuum distillation column feed pump (17).

2. The system according to claim 1, characterized in that, The bottom outlet of the pressurized azeotropic distillation column (3) is connected to the lower feed inlet of the transesterification distillation column (1) via a pipeline; the top outlet of the low-pressure azeotropic distillation column (4) is connected to the feed inlet of the pressurized azeotropic distillation column (3) via a pressurized azeotropic distillation column return pump (5); the top outlet of the alcoholysis distillation column (13) is connected to the lower feed inlet of the transesterification distillation column (1) via a transesterification distillation column return pump (14); and the top outlet of the diol azeotropic distillation column (16) is connected to the upper feed inlet of the transesterification distillation column (1) via a diol booster pump (18).

3. A method for separating mixed diols byproducts of coal-based ethylene glycol using the system described in claim 1 or 2, characterized in that, Includes the following steps: Step 1, transesterification and preliminary separation: The mixed diol and dimethyl carbonate are fed into the transesterification reaction distillation column (1) to carry out the transesterification reaction, generating ethylene carbonate, butene carbonate and methanol; the azeotrope of methanol and dimethyl carbonate is collected from the top of the column, and the mixture containing ethylene glycol, ethylene carbonate and butene carbonate is collected from the bottom of the column. Step 2, Azeotropic Step-by-Step Separation and Energy Integration: The azeotrope from the top of the column in Step 1 is sent to a pressurized azeotropic distillation column (3) for separation, and dimethyl carbonate is obtained from the bottom of the column; a portion of the azeotrope of methanol and dimethyl carbonate collected from the top of the column is directly sent to an alcoholysis reaction distillation column (13) as methanol feedstock, and a portion is sent to a low-pressure azeotropic distillation column (4) for further purification; Step 3, Ethylene glycol vacuum separation and purification: The mixture from the bottom of the column in Step 1 is fed into the ethylene glycol vacuum distillation column (10) for separation. High-purity ethylene glycol product is collected from the top of the column, and a mixture of ethylene carbonate and butene carbonate is obtained from the bottom of the column. Step 4, Selective alcoholysis separation: The mixture from the bottom of the column in step 3 and the azeotrope of methanol and dimethyl carbonate from the top of the pressurized azeotropic distillation column (3) in step 2 are fed into the alcoholysis reaction distillation column (13). By controlling the reaction conditions, butene carbonate is alcoholyzed to generate 1,2-butanediol, while the alcoholysis reaction of ethylene carbonate is inhibited. Step 5, fine separation and recycling of products: The bottom product of the alcoholysis reaction distillation column (13) in step 4 is sent to the diol azeotropic distillation column (16). The ethylene glycol and 1,2-butanediol azeotrope at the top of the column carries away the residual ethylene glycol and is recycled to the transesterification reaction distillation column (1). The bottom product is sent to the alcohol-ester vacuum distillation column (7). High-purity 1,2-butanediol product is collected at the top of the column, and ethylene carbonate product is collected at the bottom of the column.

4. The method according to claim 3, characterized in that, The methanol feedstock of the alcoholysis distillation column (13) in step 2 is an azeotrope of methanol and dimethyl carbonate taken from the top of the pressurized azeotropic distillation column (3). It is directly used to carry out alcoholysis reaction with the mixture of ethylene carbonate and butene carbonate obtained from the bottom of the ethylene glycol vacuum distillation column (10) in step 3, without the need to purify all of this material into high-purity methanol, thereby reducing the energy consumption of the low-pressure azeotropic distillation column (4) by 45-90%.

5. The method according to claim 3, characterized in that, The dimethyl carbonate collected from the bottom of the pressurized azeotropic distillation column (3) and the top of the alcoholysis reaction distillation column (13) in steps 2 and 4 is returned to the transesterification reaction distillation column (1) for recycling; the ethylene glycol and 1,2-butanediol azeotrope collected from the top of the diol azeotropic distillation column (16) in step 5 is returned to the transesterification reaction distillation column (1) for recycling, so as to construct multiple material closed-loop circulation loops including dimethyl carbonate and ethylene glycol and 1,2-butanediol azeotrope.

6. The method according to claim 3, characterized in that, In step 2, the temperature of the reaction section of the transesterification distillation column (1) is 80~150℃, the pressure is 0.04~0.20 MPa, the reflux ratio is 0.05~4.15, the conversion rate of 1,2-butanediol in the mixed diol feedstock is higher than 98.1%, while the conversion rate of ethylene glycol is lower than 50.8%; in step 2, 1,2-butanediol is the feedstock, and in step 4, 1,2-butanediol is the product.

7. The method according to claim 3, characterized in that, The selective alcoholysis separation described in step 4 is carried out in an alcoholysis reaction distillation column (13), with the reaction section temperature controlled at 75~135℃, the pressure at 0.05~0.21MPa, the reflux ratio at 0.04~3.52, and the reaction residence time at 10~120min, so as to ensure that while the butene carbonate reacts, the conversion of ethylene carbonate is suppressed to the maximum extent, so that the conversion rate of butene carbonate is higher than 98.5%, while the conversion rate of ethylene carbonate is lower than 10%.

8. The method according to claim 3, characterized in that, The operating pressure of the pressurized azeotropic distillation column (3) in step 2 is 0.5~1.7 MPa, and the operating pressure of the low-pressure azeotropic distillation column (4) is 0.1~0.3 MPa.

9. The method according to claim 3, characterized in that, The operating pressure of the ethylene glycol vacuum distillation column (10) in step 3 and the alcohol ester vacuum distillation column (7) in step 5 is 0.001~0.010 MPa.

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