A purification method, purification system and application of crude ethylene glycol

Abstract

In order to solve the problems of high energy consumption and high equipment cost in the prior art of purifying crude ethylene glycol produced by the alcoholysis process of ethylene carbonate, the present invention discloses a purification method, purification system and application of crude ethylene glycol. The method comprises: subjecting the crude ethylene glycol to vacuum distillation, collecting the materials in the bottom of the tower to obtain ethylene glycol product I, and subjecting the materials at the top of the tower to vacuum distillation to obtain ethylene glycol product II. The present invention adopts a combined process of a vacuum continuous distillation tower and a vacuum intermittent distillation tower, and utilizes the characteristics that ethylene glycol and ethylene carbonate will form azeotropes within a certain pressure range. A small part of ethylene glycol in the feed is used as an entrainer to entrain the heavy component impurity ethylene carbonate that is difficult to separate from the top of the tower. Most of the high-purity polyester-grade ethylene glycol can be obtained at the bottom of the vacuum distillation tower. Through the pretreatment in the previous step, the processing capacity of the subsequent intermittent distillation tower can be greatly reduced, thereby reducing operating costs and equipment investment.

Description

Technical Field

[0001] The invention relates to ethylene glycol purification, and in particular to a purification method, a purification system and application of ethylene glycol crude product. Background Art

[0002] Ethylene glycol is a very important basic chemical raw material with a wide range of uses in various industries, such as antifreeze, plasticizers, lubricants, non-ionic surfactants, etc., especially high-purity polyester-grade ethylene glycol, which can be used to produce high-value-added fine chemicals such as polyester fibers and unsaturated polyester resins.

[0003] There are many methods for preparing ethylene glycol, including direct hydration, pressurized hydration, catalytic hydration, and alcoholysis of ethylene carbonate. Among them, the preparation of ethylene glycol from ethylene carbonate has great advantages in terms of conversion rate, selectivity, energy conservation and environmental protection, and is currently a more advanced method for preparing ethylene glycol. However, it is still impossible to directly obtain high-purity polyester-grade ethylene glycol, and only crude ethylene glycol can be obtained. The impurities in the obtained crude ethylene glycol mainly include unreacted ethylene carbonate and methanol, as well as by-product dimethyl carbonate. Although ethylene carbonate is a heavy component, it is easy to form azeotrope-like components with ethylene glycol under many pressures and is difficult to separate. According to the physical property analysis of the binary system of ethylene carbonate and ethylene glycol, the two do not form azeotrope-like components only when the pressure is close to vacuum or is twice that of atmospheric pressure. Ethylene carbonate and ethylene glycol have high boiling points, and the energy consumption of pressurized distillation is too large. Therefore, the conventional method generally performs vacuum distillation to separate ethylene glycol and ethylene carbonate. However, for alcoholysis products, in which ethylene glycol accounts for the vast majority, it is energy-intensive to perform vacuum distillation and purification. Summary of the invention

[0004] In order to overcome the problems existing in the prior art, the present invention provides a method for purifying crude ethylene glycol, a purification system and application, in particular, purifying crude ethylene glycol containing ethylene carbonate, wherein the characteristic that ethylene glycol and ethylene carbonate form azeotrope-like products within certain pressure and / or temperature ranges is utilized, a small portion of ethylene glycol in the feed is used as an entrainer, and the heavy component impurity ethylene carbonate is entrained out from the top of the tower, and most of the high-purity ethylene glycol can be obtained at the bottom of the distillation tower, which greatly reduces the processing capacity of the subsequent intermittent distillation tower, thereby reducing operating costs and equipment investment.

[0005] One of the purposes of the present invention is to provide a method for purifying a crude ethylene glycol product, wherein the crude ethylene glycol product contains ethylene carbonate (and preferably the purity of the crude ethylene glycol product is higher than 90wt% and lower than 100wt%), and the method comprises: subjecting the crude ethylene glycol product to vacuum distillation, collecting the bottom material to obtain an ethylene glycol product I, and subjecting the top material to vacuum distillation to obtain an ethylene glycol product II (preferably the heavy components in the bottom of the vacuum distillation tower are discharged).

[0006] Among them, a small part of ethylene glycol in the vacuum distillation feed acts as an entrainer to entrain the heavy component ethylene carbonate and enter the subsequent vacuum distillation. In this way, not only is the ethylene glycol purified in the vacuum distillation (high-purity polyester-grade ethylene glycol is obtained at the bottom of the vacuum distillation kettle), but the processing capacity of the subsequent vacuum distillation is also greatly reduced.

[0007] In a preferred embodiment, the crude ethylene glycol is derived from the alcoholysis reaction product of ethylene carbonate.

[0008] In a further preferred embodiment, the purity of the crude ethylene glycol is 90 wt% to 99.8 wt%, preferably 95 wt% to 99.8 wt%.

[0009] For example, the purity of the crude ethylene glycol is 90wt%, 91wt%, 92wt%, 93wt%, 94wt%, 95wt%, 96wt%, 97wt%, 98wt%, 99wt% or 99.8wt%.

[0010] In a preferred embodiment, the vacuum distillation is continuous vacuum distillation.

[0011] In a further preferred embodiment, the vacuum distillation is carried out in a vacuum distillation tower, and the top operating pressure is 8KPa to 70KPa; and / or the top operating temperature is 60°C to 180°C (e.g., 65°C to 180°C or 70°C to 180°C); and / or the bottom operating pressure is 8.5KPa to 80KPa (e.g., 25 to 80KPa); and / or the bottom operating temperature is 120°C to 205°C (e.g., 155 to 205°C).

[0012] In a further preferred embodiment, the vacuum distillation is carried out in a vacuum distillation tower, the top operating pressure is 15KPa~60KPa (e.g. 25KPa~60KPa), preferably 25KPa~45KPa, the top operating temperature is 70℃~140℃; and / or, the bottom operating pressure is 16KPa~65KPa (e.g. 30~65KPa); and / or, the bottom operating temperature is 140℃~185℃ (e.g. 155~185℃).

[0013] For example, the vacuum distillation is carried out in a vacuum distillation tower, and the tower top operating pressure is 15KPa, 20KPa, 25KPa, 30KPa, 35KPa, 40KPa, 45KPa, 50KPa, 55KPa or 60KPa, and the tower top operating temperature is 70°C, 75°C, 80°C, 90°C, 100°C, 110°C, 120°C or 130°C; and / or, the tower bottom operating pressure is 16KPa, 20KPa, 25KPa, 30KPa, 35KPa, 40KPa, 45KPa, 50KPa, 55KPa, 60KPa or 65KPa; and / or, the tower bottom operating temperature is 140°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C or 185°C.

[0014] Among them, the crude ethylene glycol enters the vacuum continuous distillation tower, and the pressure at the top of the distillation tower is controlled. By utilizing the characteristic that ethylene glycol and ethylene carbonate will form azeotrope-like products within certain pressure ranges, part of the ethylene glycol is allowed to act as an entrainer in the vacuum continuous distillation tower to entrain the heavy component impurity ethylene carbonate. Most of the high-purity polyester-grade ethylene glycol products are obtained at the bottom of the vacuum continuous distillation tower, and a small amount of ethylene glycol, heavy component ethylene carbonate and light component impurities are obtained at the top of the tower.

[0015] In a preferred embodiment, the vacuum distillation is carried out in a vacuum distillation tower, the number of plates of the vacuum distillation tower is 20 to 50; and / or the feed position of the distillation tower is the 8th to 35th plate; and / or the top reflux ratio of the distillation tower is 1 to 50.

[0016] In a further preferred embodiment, the vacuum distillation is carried out in a vacuum distillation tower, the number of plates of the vacuum distillation tower is 20 to 45; and / or the feed position of the distillation tower is the 9th to 21st plate; and / or the top reflux ratio of the distillation tower is 5 to 20.

[0017] For example, the number of plates of the distillation tower is 20, 25, 30, 35, 40, 45 or 50; and / or the feed position of the distillation tower is the 8th, 10th, 15th, 20th, 25th, 30th or 35th plate; and / or the top reflux ratio of the distillation tower is 1, 5, 10, 15, 20, 25, 30, 35, 40, 45 or 50.

[0018] In the present invention, the mass ratio of the output from the top of the vacuum distillation tower to the crude ethylene glycol feed is 0.01-0.4, preferably 0.02-0.2; and / or the mass ratio of the polyester-grade ethylene glycol product output from the bottom of the vacuum distillation tower to the crude ethylene glycol feed is 0.6-0.99, preferably 0.8-0.98.

[0019] For example, the ratio of the quality of the output from the top of the distillation tower to the quality of the crude ethylene glycol fed is 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08, 0.1, 0.15, 0.2, 0.3 or 0.4; and / or the ratio of the quality of the polyester-grade ethylene glycol product output from the bottom of the distillation tower to the quality of the crude ethylene glycol fed is 0.8, 0.85, 0.9, 0.95 or 0.99.

[0020] In a preferred embodiment, the vacuum distillation is carried out using a vacuum intermittent distillation tower, wherein the vacuum intermittent distillation tower first performs total reflux to enrich the light components, then removes the light components, and then produces the ethylene glycol product II after the light components are removed.

[0021] In a further preferred embodiment, in the vacuum intermittent distillation tower, when the obtained ethylene glycol product II is lower than the required standard (the product standard is the national standard GB_T 4649-2018), the production of ethylene glycol product II is stopped and the recombinant residual liquid in the bottom of the vacuum intermittent distillation tower is discharged.

[0022] Among them, full reflux is first carried out in the vacuum intermittent distillation tower to enrich the light component impurities to the top of the tower, and the light component impurities are first removed at the top of the tower, and then the ethylene glycol product II is started to be produced; when the ethylene glycol product II is lower than the standard, the production is stopped and the heavy component residual liquid in the bottom of the kettle is discharged.

[0023] The light component impurities are mainly dimethyl carbonate and methanol. The required standard can be any standard defined by oneself, or can be a national standard, such as national standard GB_T 4649-2018.

[0024] In a preferred embodiment, the vacuum distillation is carried out using a vacuum intermittent distillation tower with 5 to 100 plates; and / or the tower top operating pressure is 0 to 20 KPa; and / or the tower bottom operating temperature is 80°C to 200°C; and / or the tower top reflux ratio is 0.5 to 100.

[0025] In a further preferred embodiment, the vacuum distillation is carried out using a vacuum intermittent distillation tower with 10 to 50 plates; and / or the top operating pressure is 0 to 10 KPa; and / or the bottom operating temperature is 100° C. to 150° C.; and / or the top reflux ratio is 1 to 30.

[0026] For example, the vacuum distillation is carried out using a vacuum intermittent distillation tower having 10, 20, 30, 40 or 50 plates; and / or, the tower top operating pressure is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 KPa; and / or, the tower bottom operating temperature is 100°C, 110°C, 120°C, 130°C, 140°C or 150°C; and / or, the tower top reflux ratio is 1, 5, 10, 15, 20, 25 or 30.

[0027] In the present invention, the obtained ethylene glycol product I and ethylene glycol product II are both polymerization-grade ethylene glycol, and their purity is 99.9% to 99.99%, wherein the polyester-grade ethylene glycol product standard is the national standard GB_T4649-2018.

[0028] In a preferred embodiment, the tower top material of the vacuum distillation enters the vacuum distillation after buffer storage, and preferably, enters the vacuum distillation after a certain amount is accumulated.

[0029] The second object of the present invention is to provide a purification system for crude ethylene glycol, preferably for carrying out the method described in one of the objects of the present invention, wherein the system comprises a vacuum distillation tower, a buffer device and a vacuum distillation tower.

[0030] In a preferred embodiment, the vacuum distillation tower is a vacuum continuous distillation tower.

[0031] In a further preferred embodiment, a condensing device is provided at the top of the vacuum distillation tower; and / or a reboiler is provided at the bottom of the vacuum distillation tower.

[0032] In a preferred embodiment, the vacuum distillation tower has 20 to 50 plates; and / or the feed position of the distillation tower is the 8th to 35th plate; and / or the top reflux ratio of the distillation tower is 1 to 50.

[0033] In a further preferred embodiment, the number of plates of the vacuum distillation tower is 20-45; and / or the feed position of the distillation tower is the 9th to 21st plate; and / or the top reflux ratio of the distillation tower is 5-20.

[0034] In a preferred embodiment, the vacuum distillation is carried out in a vacuum distillation tower, and the top operating pressure is 8KPa to 70KPa; and / or the top operating temperature is 60°C to 180°C; and / or the bottom operating pressure is 8.5KPa to 80KPa; and / or the bottom operating temperature is 120°C to 205°C.

[0035] In a further preferred embodiment, the vacuum distillation is carried out in a vacuum distillation tower, the top operating pressure is 15KPa~60KPa, preferably 25KPa~45KPa, the top operating temperature is 70℃~140℃; and / or, the bottom operating pressure is 16KPa~65KPa; and / or, the bottom operating temperature is 140℃~185℃.

[0036] In a preferred embodiment, the buffer device is a buffer tank, which is connected to the top of the vacuum distillation tower and the feed position of the vacuum distillation tower respectively.

[0037] In a preferred embodiment, the vacuum distillation tower is a vacuum batch distillation tower.

[0038] In a further preferred embodiment, a cooling device is provided at the top of the vacuum distillation tower; and / or a reboiler is provided at the bottom of the vacuum distillation tower.

[0039] In a further preferred embodiment, a light component recovery device and an ethylene glycol product II recovery device which are arranged in parallel with each other are arranged at the top of the vacuum distillation tower and behind its cooling device (along the material flow direction).

[0040] In a preferred embodiment, the vacuum distillation is carried out using a vacuum intermittent distillation tower, the number of plates of the vacuum intermittent distillation tower is 5 to 100; and / or the top operating pressure is 0 to 20 KPa; and / or the bottom operating temperature is 80°C to 200°C; and / or the top reflux ratio is 0.5 to 100.

[0041] In a further preferred embodiment, the vacuum distillation is carried out using a vacuum intermittent distillation tower with 10 to 50 plates; and / or the top operating pressure is 0 to 10 KPa; and / or the bottom operating temperature is 100° C. to 150° C.; and / or the top reflux ratio is 1 to 30.

[0042] In the present invention, a vacuum continuous distillation tower is combined with a vacuum intermittent distillation tower, and the characteristic that ethylene glycol and ethylene carbonate form azeotrope-like products within a certain pressure range is utilized. A small portion of ethylene glycol in the feed of the vacuum continuous distillation tower is used as an entrainer to entrain the heavy component impurity ethylene carbonate from the top of the vacuum continuous distillation tower, and most of the high-purity ethylene glycol can be obtained at the bottom of the vacuum continuous distillation tower, which greatly reduces the processing capacity of the subsequent vacuum intermittent distillation tower, better solves the technical problem, and can be used in various industrial productions of purifying high-purity ethylene glycol.

[0043] The third object of the present invention is to provide an ethylene glycol product obtained by the treatment method described in the first object of the present invention or the treatment system described in the second object of the present invention, preferably, it is a polyester-grade ethylene glycol product with a purity of 99.9% to 99.99%.

[0044] Among them, the polyester-grade ethylene glycol product standard is the national standard GB_T 4649-2018.

[0045] A fourth object of the present invention is to provide an application of the purification method described in the first object of the present invention or the purification system described in the second object of the present invention for purifying ethylene glycol from the alcoholysis reaction product of ethylene carbonate.

[0046] The alcoholysis reaction product of ethylene carbonate contains unreacted ethylene carbonate and methanol, and byproduct dimethyl carbonate. Preferably, the ethylene carbonate alcoholysis reaction product has an ethylene glycol content of 90 wt % or more, preferably 95% to 99.8%, and more preferably 96 to 99.8%.

[0047] The endpoints and any values ​​of the scope disclosed in the present invention are not limited to the precise scope or value, and these scopes or values ​​should be understood to include values ​​close to these scopes or values. For numerical ranges, the endpoint values ​​of each scope, the endpoint values ​​of each scope and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this article. Hereinafter, in principle, each technical solution can be combined with each other to obtain a new technical solution, which should also be regarded as specifically disclosed in this article.

[0048] Compared with the prior art, the present invention has the following beneficial effects: utilizing the characteristic that ethylene glycol and ethylene carbonate can form azeotrope-like products within certain pressure and / or temperature ranges, a small portion of ethylene glycol in the vacuum distillation feed is used as an entrainer to entrain the heavy component impurity ethylene carbonate from the top of the vacuum distillation tower, and most of the high-purity ethylene glycol can be obtained at the bottom of the distillation tower, thereby greatly reducing the processing capacity of the subsequent intermittent distillation tower, thereby reducing operating costs and equipment investment. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 A schematic diagram of the structure of the system of the present invention is shown.

[0050] T101 is a vacuum continuous distillation tower, B101 is a buffer storage tank, and T102 is a vacuum intermittent distillation tower.

[0051] 1-ethylene glycol crude product, 2-venting, 3-vacuum pump, 4-logistics containing ethylene glycol, ethylene carbonate, and light component impurities, 5-ethylene glycol product I, 6-light component, 7-ethylene glycol product II, 8-heavy component residual liquid.

[0052] The crude ethylene glycol raw material enters the vacuum continuous distillation tower, and part of the ethylene glycol acts as an entrainer to entrain the heavy component impurity ethylene carbonate, and the light component impurities are all discharged from the top of the vacuum continuous distillation tower T101 and sent to the buffer storage tank. After a certain amount is collected, it is sent to the vacuum intermittent distillation tower. A high-purity polyester-grade ethylene glycol product is obtained at the bottom of the vacuum continuous distillation tower T101. A small amount of ethylene glycol, heavy component ethylene carbonate, and light component impurities are sent to the vacuum intermittent distillation tower T102, and the light component impurities are first removed, and then the ethylene glycol product is started to be produced. When the obtained ethylene glycol product II is lower than the standard (the product standard is the national standard GB_T 4649-2018), the production of ethylene glycol product II is stopped, and the heavy component residual liquid in the vacuum intermittent distillation tower kettle is discharged. DETAILED DESCRIPTION

[0053] The present invention is described in detail below in conjunction with specific embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the contents of the present invention still fall within the scope of protection of the present invention.

[0054] It should also be noted that the various specific technical features described in the following specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0055] In addition, the various embodiments of the present invention may be arbitrarily combined as long as they do not violate the concept of the present invention. The technical solutions thus formed belong to part of the original disclosure of this specification and also fall within the protection scope of the present invention.

[0056] Example 1

[0057] According to the above process flow, a raw material of ethylene carbonate alcoholysis reaction product (ethylene glycol mass fraction 99.52%, ethylene carbonate mass fraction 0.4%, dimethyl carbonate mass fraction 0.03%, methanol mass fraction 0.05%) is fed from the 9th plate in the middle of the continuous vacuum distillation tower, with a flow rate of 1000kg / h. The continuous vacuum distillation tower comprises 20 plates, the tower top operating pressure is 50KPa, the tower bottom pressure is 52KPa, the tower top temperature is 145.47℃, the tower bottom temperature is 175.96℃, the reflux ratio is 10, the tower top extraction volume is 50kg / h, and 950kg / h of ethylene glycol product with a purity of 99.97% is obtained at the bottom of the tower. The tower top extraction stream consists of ethylene glycol mass fraction 91.02%, ethylene carbonate mass fraction 7.379%, dimethyl carbonate mass fraction 0.6%, and methanol mass fraction 1%. This stream is sent to the buffer storage tank, and after it is filled with 1000kg, it is sent to the vacuum intermittent distillation tower. The top pressure of the vacuum intermittent distillation tower is 0.2KPa, it contains 20 trays, the operating temperature of the tower bottom is 112℃, the reflux ratio is 4, and finally 850kg of ethylene glycol product with a purity of 99.98% is obtained.

[0058] The energy consumption of the tower top and tower bottom in Example 1 is shown in Table 1, wherein, since intermittent distillation is a dynamic process, the tower top cold load and the reboiler heat load of the vacuum intermittent distillation tower in Example 1 are converted into average values.

[0059] Example 2

[0060] According to the above process flow, a raw material of ethylene carbonate alcoholysis reaction product (ethylene glycol mass fraction 99.71%, ethylene carbonate mass fraction 0.22%, dimethyl carbonate mass fraction 0.03%, methanol mass fraction 0.04%) is fed from the 10th plate in the middle of the continuous vacuum distillation tower, with a flow rate of 1000kg / h. The continuous vacuum distillation tower comprises 22 plates, the tower top operating pressure is 47KPa, the tower bottom pressure is 49KPa, the tower top temperature is 82.95℃, the tower bottom temperature is 169.67℃, the reflux ratio is 12, the tower top extraction volume is 35kg / h, and the tower bottom obtains ethylene glycol product with a purity of 99.97%, with a flow rate of 965kg / h. The tower top extraction stream consists of ethylene glycol mass fraction 92.66%, ethylene carbonate mass fraction 5.34%, dimethyl carbonate mass fraction 0.86%, and methanol mass fraction 1.14%. This stream is sent to the buffer storage tank, and after it is filled with 1000kg, it is sent to the vacuum intermittent distillation tower. The top pressure of the vacuum intermittent distillation tower is 0.43KPa, it contains 31 trays, the operating temperature of the tower bottom is 110℃, the reflux ratio is 8.5, and finally 860kg of ethylene glycol product with a purity of 99.97% is obtained.

[0061] Example 3

[0062] According to the above process flow, a raw material of ethylene carbonate alcoholysis reaction product (ethylene glycol mass fraction 99.09%, ethylene carbonate mass fraction 0.5%, dimethyl carbonate mass fraction 0.05%, methanol mass fraction 0.36%) is fed from the 12th plate in the middle of the continuous vacuum distillation tower, with a flow rate of 1000kg / h. The continuous vacuum distillation tower contains 25 plates, the tower top operating pressure is 30KPa, the tower bottom pressure is 32KPa, the tower top temperature is 72.69℃, the tower bottom temperature is 161.95℃, the reflux ratio is 12, the tower top production is 60kg / h, and the tower bottom obtains ethylene glycol product with a purity of 99.98%, with a flow rate of 940kg / h. The tower top production stream consists of ethylene glycol mass fraction 85.04%, ethylene carbonate mass fraction 8.13%, dimethyl carbonate mass fraction 0.83%, and methanol mass fraction 6%. This stream is sent to the buffer storage tank, and after it is filled with 1000kg, it is sent to the vacuum intermittent distillation tower. The top pressure of the vacuum intermittent distillation tower is 0.9KPa, it contains 25 trays, the operating temperature of the tower bottom is 115℃, the reflux ratio is 3, and finally 780kg of ethylene glycol product with a purity of 99.97% is obtained.

[0063] Example 4

[0064] According to the above process flow, a raw material of ethylene carbonate alcoholysis reaction product (ethylene glycol mass fraction 98.50%, ethylene carbonate mass fraction 1%, dimethyl carbonate mass fraction 0.03%, methanol mass fraction 0.47%) is fed from the 14th plate in the middle of the continuous vacuum distillation tower, with a flow rate of 1000kg / h. The continuous vacuum distillation tower comprises 30 plates, the tower top operating pressure is 40Kpa, the tower bottom pressure is 41.5KPa, the tower top temperature is 81.33℃, the tower bottom temperature is 166.03℃, the reflux ratio is 10, the tower top extraction volume is 80kg / h, and the tower bottom obtains ethylene glycol product with a purity of 99.99%, with a flow rate of 920kg / h. The tower top extraction stream consists of ethylene glycol mass fraction 81.26%, ethylene carbonate mass fraction 12.487%, dimethyl carbonate mass fraction 0.375%, and methanol mass fraction 0.47%. This stream is sent to the buffer storage tank, and after it is filled with 1000kg, it is sent to the vacuum intermittent distillation tower. The top pressure of the vacuum intermittent distillation tower is 0.8KPa, it contains 30 trays, the operating temperature of the tower bottom is 118℃, the reflux ratio is 5, and finally 750kg of ethylene glycol product with a purity of 99.96% is obtained.

[0065] Example 5

[0066] According to the above process flow, a raw material of ethylene carbonate alcoholysis reaction product (ethylene glycol mass fraction 98.20%, ethylene carbonate mass fraction 1.06%, dimethyl carbonate mass fraction 0.22%, methanol mass fraction 0.52%) is fed from the 17th plate in the middle of the continuous vacuum distillation tower, with a flow rate of 1000kg / h. The continuous vacuum distillation tower comprises 37 plates, the tower top operating pressure is 37KPa, the tower bottom pressure is 38.8KPa, the tower top temperature is 72.40℃, the tower bottom temperature is 166.03℃, the reflux ratio is 8, the tower top production volume is 90kg / h, and the tower bottom obtains ethylene glycol product with a purity of 99.99%, with a flow rate of 910kg / h. The tower top production stream consists of ethylene glycol mass fraction 80.02%, ethylene carbonate mass fraction 11.75%, dimethyl carbonate mass fraction 2.44%, and methanol mass fraction 5.78%. This stream is sent to the buffer storage tank, and after it is filled with 1000kg, it is sent to the vacuum intermittent distillation tower. The top pressure of the vacuum intermittent distillation tower is 0.7KPa, it contains 42 trays, the operating temperature of the tower bottom is 126℃, the reflux ratio is 9, and finally 713kg of ethylene glycol product with a purity of 99.94% is obtained.

[0067] Example 6

[0068] According to the above process flow, a raw material of ethylene carbonate alcoholysis reaction product (ethylene glycol mass fraction 97.80%, ethylene carbonate mass fraction 1.42%, dimethyl carbonate mass fraction 0.27%, methanol mass fraction 0.51%) is fed from the 16th plate in the middle of the continuous vacuum distillation tower, with a flow rate of 1000kg / h. The continuous vacuum distillation tower comprises 39 plates, the tower top operating pressure is 41KPa, the tower bottom pressure is 43KPa, the tower top temperature is 84.12℃, the tower bottom temperature is 167.25℃, the reflux ratio is 8.5, the tower top production is 115kg / h, and the tower bottom obtains ethylene glycol product with a purity of 99.99%, with a flow rate of 885kg / h. The tower top production stream consists of ethylene glycol mass fraction 80.87%, ethylene carbonate mass fraction 12.35%, dimethyl carbonate mass fraction 2.35%, and methanol mass fraction 4.43%. This stream is sent to the buffer storage tank, and after it is filled with 1000kg, it is sent to the vacuum intermittent distillation tower. The top pressure of the vacuum intermittent distillation tower is 0.43KPa, it contains 46 trays, the operating temperature of the tower bottom is 126℃, the reflux ratio is 7.5, and finally 723kg of ethylene glycol product with a purity of 99.95% is obtained.

[0069] Example 7

[0070] According to the above process flow, a raw material of ethylene carbonate alcoholysis reaction product (ethylene glycol mass fraction 97.50%, ethylene carbonate mass fraction 1.76%, dimethyl carbonate mass fraction 0.18%, methanol mass fraction 0.56%) is fed from the 17th plate in the middle of the continuous vacuum distillation tower, with a flow rate of 1000kg / h. The continuous vacuum distillation tower comprises 42 plates, the tower top operating pressure is 47KPa, the tower bottom pressure is 49KPa, the tower top temperature is 136.01℃, the tower bottom temperature is 174.19℃, the reflux ratio is 5, the tower top production is 125kg / h, and the tower bottom obtains ethylene glycol product with a purity of 99.99%, with a flow rate of 875kg / h. The tower top production stream consists of ethylene glycol mass fraction 80.02%, ethylene carbonate mass fraction 14.05%, dimethyl carbonate mass fraction 1.44%, and methanol mass fraction 4.48%. This stream is sent to the buffer storage tank, and after it is filled with 1000kg, it is sent to the vacuum intermittent distillation tower. The top pressure of the vacuum intermittent distillation tower is 0.85KPa, it contains 40 trays, the operating temperature of the tower bottom is 128℃, the reflux ratio is 6, and finally 705kg of ethylene glycol product with a purity of 99.93% is obtained.

[0071] Comparative Example 1

[0072] Purify the alcoholysis product of ethylene carbonate according to the continuous process flow (the mass fraction of ethylene glycol in the raw material is 99.52%, the mass fraction of ethylene carbonate is 0.4%, the mass fraction of dimethyl carbonate is 0.03%, and the mass fraction of methanol is 0.05%), and the feed rate of crude ethylene glycol is 1000kg / h. The process includes a vacuum continuous distillation tower and a vacuum continuous distillation tower. The vacuum continuous distillation tower includes 20 plates, a reflux ratio of 2, a top extraction of 20kg / h, a top pressure of 20KPa, a bottom pressure of 22KPa, a top temperature of 66°C, and a bottom temperature of 151.81°C. The raw material is fed from the 9th plate, and the light component impurities dimethyl carbonate and methanol are discharged from the top of the tower. Ethylene glycol and heavy component impurity ethylene carbonate are discharged from the bottom of the tower and enter the vacuum continuous distillation tower T2 from the middle section. The vacuum distillation tower contains 20 plates, a reflux ratio of 3, a top pressure of 0.5 KPa, a bottom pressure of 0.8 KPa, a top temperature of 74.88°C, a bottom temperature of 76.20°C, and high-purity ethylene glycol flows out from the top of the tower at a flow rate of 960 kg / h.

[0073] The energy consumption of the tower top and tower kettle in Comparative Example 1 is shown in Table 1.

[0074] Comparative Example 2

[0075] If the alcoholysis reaction product of ethylene carbonate is purified by intermittent distillation according to the traditional method (the mass fraction of ethylene glycol in the raw materials is 99.52%, the mass fraction of ethylene carbonate is 0.4%, the mass fraction of dimethyl carbonate is 0.03%, and the mass fraction of methanol is 0.05%), the feed amount of crude ethylene glycol is 1000 kg / h. The process comprises a vacuum intermittent distillation tower, which comprises 50 plates, a reflux ratio of 3, a tower top pressure of 0.5 KPa, a tower bottom pressure of 1 KPa, a tower top temperature of 75°C, a tower bottom temperature of 100°C, and light components of methanol and dimethyl carbonate are first discharged from the tower top, and high-purity ethylene glycol is then discharged after the light components are completely removed.

[0076] The energy consumption of the tower top and tower bottom of Comparative Example 2 is shown in Table 1, wherein, since intermittent distillation is a dynamic process, the tower top cooling load and the reboiler heat load of the intermittent distillation tower of Comparative Example 2 are converted into average values.

[0077] Table 1: Energy consumption comparison

[0078]

[0079] It can be seen from Table 1 that the energy consumption of the method or system of the present invention is much less than that of Comparative Example 1 and Comparative Example 2.

[0080] Comparative Example 3

[0081] The process of Example 1 was repeated, except that the vacuum distillation conditions were as follows and the others remained unchanged.

[0082] According to the process of the present invention, a raw material of ethylene carbonate alcoholysis reaction product (ethylene glycol mass fraction 99.52%, ethylene carbonate mass fraction 0.4%, dimethyl carbonate mass fraction 0.03%, methanol mass fraction 0.05%) is fed from the 9th tower plate in the middle of a continuous vacuum distillation tower, with a flow rate of 1000kg / h. The continuous vacuum distillation tower comprises 20 tower plates, a tower top operating pressure of 50KPa, a tower bottom pressure of 52KPa, a tower top temperature of 67.14°C, a tower bottom temperature of 175.96°C, and a reflux ratio of 10. If the tower top extraction amount is 5kg / h, 995kg / h of ethylene glycol product with a purity of 99.64% is obtained at the tower bottom.

[0083] Comparative Example 4

[0084] According to the process of the present invention, a raw material of ethylene carbonate alcoholysis reaction product (ethylene glycol mass fraction 99.52%, ethylene carbonate mass fraction 0.4%, dimethyl carbonate mass fraction 0.03%, methanol mass fraction 0.05%) is fed from the 9th tower plate in the middle of a continuous vacuum distillation tower, with a flow rate of 1000kg / h. The continuous vacuum distillation tower comprises 20 tower plates, a tower top operating pressure of 100KPa, a tower bottom pressure of 102KPa, a tower top temperature of 175.1°C, a tower bottom temperature of 197.4°C, a reflux ratio of 10, and if the tower top extraction amount is 50kg / h, 950kg / h of ethylene glycol product with a purity of 99.87% is obtained at the tower bottom.

[0085] In this comparative example, the operating pressures at the tower top and tower bottom are relatively high, resulting in unsatisfactory entrainment effect and unqualified products.

[0086] The present invention has been described in detail above in conjunction with specific implementations and exemplary examples, but these descriptions cannot be understood as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, a variety of equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its implementation methods, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be subject to the attached claims.

Claims

1. A method for purifying crude ethylene glycol, wherein the crude ethylene glycol contains ethylene carbonate, the method comprising: The crude ethylene glycol product is subjected to vacuum distillation, the bottom material is collected to obtain ethylene glycol product I, and the top material is subjected to vacuum distillation to obtain ethylene glycol product II; the vacuum distillation is continuous vacuum distillation, the vacuum distillation is carried out in a vacuum distillation tower, the top operating pressure is 8KPa~70KPa, the top operating temperature is 60℃~180℃, the bottom operating pressure is 8.5KPa~80KPa, and the bottom operating temperature is 120℃~205℃; the vacuum distillation is carried out using a vacuum intermittent distillation tower, the number of its plates is 5~100, the top operating pressure is 0~20KPa, the bottom operating temperature is 80℃~200℃, and the top reflux ratio is 0.5~100.

2. The purification method according to claim 1, characterized in that The crude ethylene glycol is derived from the alcoholysis reaction product of ethylene carbonate.

3. The purification method according to claim 1, characterized in that The purity of the crude ethylene glycol is 90wt%~99.8wt%.

4. The purification method according to claim 1, characterized in that The purity of the crude ethylene glycol is 95wt%~99.8wt%.

5. The purification method according to claim 1, characterized in that The vacuum distillation is carried out in a vacuum distillation tower, the number of plates of the vacuum distillation tower is 20 to 50; and / or the feed position of the distillation tower is the 8th to 35th plate; and / or the top reflux ratio of the distillation tower is 1 to 50.

6. The purification method according to claim 1, characterized in that The top material of the vacuum distillation tower is buffered and stored before entering the vacuum distillation.

7. The purification method according to any one of claims 1 to 6, characterized in that: The vacuum intermittent distillation tower first performs total reflux to enrich the light components, then removes the light components, and then produces ethylene glycol product II after the light components are completely removed.

8. The purification method according to claim 7, characterized in that In the vacuum intermittent distillation tower, when the obtained ethylene glycol product II is lower than the required standard, the extraction of ethylene glycol product II is stopped and the recombinant residual liquid in the bottom of the vacuum intermittent distillation tower is discharged.

9. Use of the purification method according to any one of claims 1 to 8 for purifying ethylene glycol from an alcoholysis reaction product of ethylene carbonate.

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