Method for separating dimethyl carbonate from methanol

Abstract

The invention discloses a method for separating dimethyl carbonate and methanol, which comprises the following steps: feeding a material containing dimethyl carbonate and methanol into a double-tower consisting of an atmospheric tower and a pressurized tower for separation to obtain methanol in the tower kettle of the atmospheric tower and obtain a crude dimethyl carbonate material in the tower kettle of the pressurized tower; wherein the pressurized tower top material is introduced into the atmospheric tower, and the atmospheric tower top material is introduced into the pressurized tower; the crude dimethyl carbonate material is rectified, the material flow at the bottom of the rectifying tower is a dimethyl carbonate product, and the material flow at the top of the rectifying tower is circulated back to the atmospheric tower or the pressurizing tower. The method provided by the invention not only reduces the separation energy consumption, but also prevents the blockage of the dimethyl carbonate polymer in the tower kettle, and has the advantages of simple process flow, high-efficiency separation of dimethyl carbonate and methanol, and the like.

Description

Technical Field

[0001] The invention relates to a method for separating dimethyl carbonate and methanol. Background Art

[0002] Dimethyl carbonate is an important organic chemical intermediate that can be used in organic synthesis reactions such as carbonylation, methylation, methoxylation and carbon-based methylation. It is widely used in gasoline additives and lithium battery electrolytes for new energy vehicles.

[0003] In the process of preparing dimethyl carbonate, the product dimethyl carbonate and methanol form a minimum binary azeotrope under low pressure conditions. The conventional method for separating dimethyl carbonate and methanol is mainly double-tower pressure swing separation. Double-tower pressure swing separation can usually only obtain crude dimethyl carbonate, which will have problems such as low purity of dimethyl carbonate, greatly reducing the economic value of the by-product dimethyl carbonate.

[0004] CN116159330A discloses a method for continuously purifying electronic grade dimethyl carbonate. The method comprises the following steps: DMC raw material (DMC content is 20wt% to 50wt%) is introduced into the atmospheric pressure tower of the first distillation tower, water and heavy components are discharged from the bottom of the tower to the outside of the system, the material with DMC content of 50wt% to 85wt% obtained at the top of the tower enters the pressure tower of the second distillation tower, and the crude DMC with DMC content of 920wt% to 97wt% obtained at the bottom of the tower; the crude DMC obtained is separated by crystallization to obtain a DMC product. However, the bottom temperature of the pressure tower of this method is relatively high, within the range of 180 to 200°C, which is easy to cause polymerization of dimethyl carbonate and blockage. Moreover, this method adopts a double tower plus crystallization method, and the crystallization temperature needs to be controlled at -2°C. The utility price is expensive, and a combination of multiple groups of crystallization devices is required. The process flow is complicated and the energy consumption is relatively high. Summary of the invention

[0005] The technical problem to be solved by the present invention is that the existing technology has the problem of high energy consumption for separation of dimethyl carbonate and methanol and easy polymerization of dimethyl carbonate. The present invention provides a method for separation of dimethyl carbonate and methanol. The method not only reduces separation energy consumption, but also prevents the blockage of dimethyl carbonate polymer in the tower bottom, and also has the advantages of simple process flow and high efficiency for separation of dimethyl carbonate and methanol.

[0006] The inventor has found through research that when a double-tower pressure-swing separation process is used, in order to reduce separation energy consumption, the tower pressure of the pressurized tower needs to be increased. However, when the tower pressure is high, it is easy to cause the tower bottom temperature to be too high, which in turn causes polymer blockage in the tower bottom. In order to prevent the pressure tower bottom temperature from being too high, low-pressure operation will cause a significant increase in separation energy consumption. Based on this, the inventor can effectively improve the purity of dimethyl carbonate in the dimethyl carbonate product while reducing energy consumption by controlling the operating conditions of the pressurized tower and combining the method of distillation.

[0007] The invention provides a method for separating dimethyl carbonate and methanol, comprising: sending materials containing dimethyl carbonate and methanol to a double tower consisting of an atmospheric tower and a pressure tower for separation, obtaining methanol in the atmospheric tower kettle, and obtaining crude dimethyl carbonate materials in the pressure tower kettle; wherein materials at the top of the pressure tower are introduced into the atmospheric tower, and materials at the top of the atmospheric tower are introduced into the pressure tower; the crude dimethyl carbonate materials are distilled, the bottom stream of the distillation tower is the dimethyl carbonate product, and the top stream of the distillation tower is circulated back to the atmospheric tower or the pressure tower.

[0008] Furthermore, when the mass concentration of dimethyl carbonate in the material containing dimethyl carbonate and methanol is lower than 25%, the material is first passed into the atmospheric pressure tower; when the mass concentration of dimethyl carbonate in the material containing dimethyl carbonate and methanol is higher than 25%, the material is first passed into the pressure tower.

[0009] Furthermore, the number of theoretical plates of the atmospheric pressure tower is 35 to 70, the operating pressure at the top of the tower is 0 to 0.1 MPaG, the operating temperature at the top of the tower is 40 to 81°C, and the operating temperature at the bottom of the tower is 50 to 88°C.

[0010] Furthermore, the operating conditions of the pressurized tower are as follows: the tower top operating pressure is 0.8-1.4 MPaG, preferably 0.9-1.3 MPaG; the tower top operating temperature is 125-155°C; the tower bottom operating temperature is 130-175°C, preferably 150-170°C.

[0011] Furthermore, the number of theoretical plates of the pressure tower is 25 to 65.

[0012] Furthermore, the number of theoretical plates for the dimethyl carbonate distillation is 10 to 50, the top operating pressure of the distillation tower is -0.1 to 0.75 MPaG and does not include -0.1 MPaG, the top operating temperature is 40 to 140°C, preferably 70 to 135°C, and the bottom operating temperature is 50 to 175°C, preferably 95 to 175°C.

[0013] Furthermore, in the dimethyl carbonate product, the mass purity of dimethyl carbonate reaches above 99.9%.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] The method of the invention adopts a three-tower separation mode, namely, normal pressure-pressurization-rectification. In this mode, the pressurization tower kettle releases more light components, which can reduce the energy consumption of the pressurization tower and the dimethyl carbonate refining tower. Moreover, the purity of the separated dimethyl carbonate reaches more than 99.9%, and the product index can reach or exceed the national standard first-grade product index (the national standard first-grade product purity is 99.5wt%, the national standard premium product purity is 99.9wt%, and the national standard electronic grade purity is 99.99wt%), thereby effectively improving the economic value of the dimethyl carbonate product and preventing the risk of high-temperature polymerization of dimethyl carbonate in the process of separating dimethyl carbonate from methanol. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 One of the flow diagrams of the method of the present invention;

[0017] Figure 2 The second schematic diagram of the process of the present invention;

[0018] Description of reference numerals:

[0019] A: atmospheric pressure tower; B: pressure tower; C: dimethyl carbonate refining tower;

[0020] 1: material containing dimethyl carbonate and methanol; 2: atmospheric pressure tower top stream; 3: methanol; 4: pressurized tower top stream; 5: crude dimethyl carbonate material; 6: dimethyl carbonate; 7: dimethyl carbonate refining tower top stream;

[0021] Figure 3 This is one of the comparative example process schematics. DETAILED DESCRIPTION

[0022] 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.

[0023] In the present invention, according to conventional applications, all of the tower bottom temperatures are higher than the tower top temperature.

[0024] The present invention provides a method for separating dimethyl carbonate and methanol. Figure 1 , including: passing material 1 containing dimethyl carbonate and methanol into atmospheric tower A, the tower top stream 2 is a stream containing methanol and dimethyl carbonate, and the tower bottom obtains high-purity methanol 3. Passing atmospheric tower top stream 2 into pressure tower B, and returning tower top stream 4 to atmospheric tower A, the tower bottom obtains crude dimethyl carbonate material 5. The crude dimethyl carbonate material 5 in the pressure tower bottom is introduced into a dimethyl carbonate refining tower C, the tower top stream 7 is returned to the atmospheric tower or the pressure tower, and the tower bottom obtains high-purity dimethyl carbonate 6.

[0025] The present invention also provides a method for separating dimethyl carbonate and methanol, such as Figure 2 , including: introducing material 1 containing dimethyl carbonate and methanol into a pressure tower B, introducing the top stream 4 into a normal pressure tower, and obtaining a crude dimethyl carbonate material 5 containing a certain concentration of methanol in the tower bottom. Introducing the top stream 4 of the pressure tower into a normal pressure tower A, obtaining a stream 2 containing methanol and dimethyl carbonate at the top of the tower and returning it to the pressure tower B, and obtaining high-purity methanol 3 in the tower bottom. Introducing the crude dimethyl carbonate material 5 in the pressure tower bottom into a dimethyl carbonate refining tower C, returning the top stream 7 to the normal pressure tower or the pressure tower, and obtaining high-purity dimethyl carbonate 6 in the tower bottom.

[0026] One of the conventional methods for separating dimethyl carbonate and methanol is as follows: Figure 3 , including: passing material 1 containing dimethyl carbonate and methanol into an atmospheric pressure tower A, the tower top stream 2 is a stream containing methanol and dimethyl carbonate, and high-purity methanol 3 is obtained in the tower bottom; the atmospheric pressure tower top stream 2 is passed into a pressurized tower B, and the tower top stream 4 is returned to the atmospheric pressure tower A, and dimethyl carbonate 6 is obtained in the tower bottom.

[0027] [Example 1]

[0028] like Figure 1 As shown, in feed stream 1, by weight percentage, dimethyl carbonate is 20% and methanol is 80%.

[0029] The atmospheric pressure tower (A) has 60 theoretical plates, a top operating pressure of 0.05 MPaG, a top operating temperature of 74°C, and a bottom operating temperature of 81°C.

[0030] The pressure tower (B) had a theoretical plate number of 40, a top operating pressure of 1.0 MPaG, a top operating temperature of 141° C., and a bottom operating temperature of 170° C. No polymer appeared in the bottom of the pressure tower.

[0031] The dimethyl carbonate refining tower (C) has a theoretical plate number of 20, a tower top operating pressure of 0.05 MPaG, a tower top operating temperature of 75°C, and a tower bottom operating temperature of 105°C.

[0032] In this embodiment, the methanol concentration in the bottom of the atmospheric tower (A) is 99.5%, the dimethyl carbonate concentration in the bottom of the pressure tower (B) is 95.55%, and the dimethyl carbonate concentration in the bottom of the dimethyl carbonate refining tower (C) is 99.9%. The sum of the reboiler loads of the pressure tower (B) and the dimethyl carbonate refining tower (C) per ton of feed is 0.7386MW.

[0033] [Example 2]

[0034] like Figure 1As shown, in feed stream 1, by weight percentage, dimethyl carbonate is 20% and methanol is 80%.

[0035] The atmospheric pressure tower (A) has 45 theoretical plates, a top operating pressure of 0.09 MPaG, a top operating temperature of 81°C, and a bottom operating temperature of 85°C.

[0036] The pressure tower (B) had a theoretical plate number of 35, a tower top operating pressure of 1.3 MPaG, a tower top operating temperature of 151° C., and a tower bottom operating temperature of 170° C. No polymer appeared in the tower bottom of the pressure tower.

[0037] The dimethyl carbonate refining tower (C) has 40 theoretical plates, a top operating pressure of 0.7 MPaG, a top operating temperature of 129°C, and a bottom operating temperature of 173°C.

[0038] In this embodiment, by weight percentage, the methanol concentration in the bottom of the atmospheric tower (A) is 99.5%, the dimethyl carbonate concentration in the bottom of the pressure tower (B) is 89.65%, and the dimethyl carbonate concentration in the bottom of the dimethyl carbonate refining tower (C) is 99.9%. The sum of the reboiler loads of the pressure tower (B) and the dimethyl carbonate refining tower (C) per ton of feed is 0.7707MW.

[0039] [Example 3]

[0040] like Figure 1 As shown, in feed stream 1, by weight percentage, dimethyl carbonate is 10% and methanol is 90%.

[0041] The atmospheric pressure tower (A) has 55 theoretical plates, a top operating pressure of 0.09 MPaG, a top operating temperature of 81°C, and a bottom operating temperature of 86°C.

[0042] The pressure tower (B) had a theoretical plate number of 35, a tower top operating pressure of 1.3 MPaG, a tower top operating temperature of 151° C., and a tower bottom operating temperature of 170° C. No polymer appeared in the tower bottom of the pressure tower.

[0043] The dimethyl carbonate refining tower (C) has 40 theoretical plates, a top operating pressure of 0.05 MPaG, a top operating temperature of 74°C, and a bottom operating temperature of 108°C.

[0044] In this embodiment, by weight percentage, the methanol concentration in the bottom of the atmospheric tower (A) is 99.5%, the dimethyl carbonate concentration in the bottom of the pressure tower (B) is 89.65%, and the dimethyl carbonate concentration in the bottom of the dimethyl carbonate refining tower (C) is 99.9%. The sum of the reboiler loads of the pressure tower (B) and the dimethyl carbonate refining tower (C) per ton of feed is 0.3736MW.

[0045] [Example 4]

[0046] like Figure 2 As shown, in feed stream 1, by weight percentage, dimethyl carbonate is 35% and methanol is 65%.

[0047] The atmospheric pressure tower (A) has 55 theoretical plates, a top operating pressure of 0.09 MPaG, a top operating temperature of 81°C, and a bottom operating temperature of 86°C.

[0048] The pressure tower (B) had a theoretical plate number of 40, a top operating pressure of 1.0 MPaG, a top operating temperature of 141° C., and a bottom operating temperature of 170° C. No polymer appeared in the bottom of the pressure tower.

[0049] The dimethyl carbonate refining tower (C) has a theoretical plate number of 40, a tower top operating pressure of 0.05 MPaG, a tower top operating temperature of 75°C, and a tower bottom operating temperature of 108°C.

[0050] In this embodiment, the methanol concentration in the bottom of the atmospheric tower (A) is 99.5%, the dimethyl carbonate concentration in the bottom of the pressure tower (B) is 95.55%, and the dimethyl carbonate concentration in the bottom of the dimethyl carbonate refining tower (C) is 99.9%. The sum of the reboiler loads of the pressure tower (B) and the dimethyl carbonate refining tower (C) per ton of feed is 1.0422MW.

[0051] [Example 5]

[0052] like Figure 1 As shown, in feed stream 1, by weight percentage, dimethyl carbonate is 22% and methanol is 78%.

[0053] The atmospheric pressure tower (A) has 45 theoretical plates, a top operating pressure of 0.09 MPaG, a top operating temperature of 81°C, and a bottom operating temperature of 85°C.

[0054] The pressure tower (B) had a theoretical plate number of 30, a top operating pressure of 1.3 MPaG, a top operating temperature of 151° C., and a bottom operating temperature of 155° C. No polymer appeared in the bottom of the pressure tower.

[0055] The dimethyl carbonate refining tower (C) has 40 theoretical plates, a top operating pressure of 0.7 MPaG, a top operating temperature of 129°C, and a bottom operating temperature of 173°C.

[0056] In this embodiment, by weight percentage, the methanol concentration in the bottom of the atmospheric tower (A) is 99.5%, the dimethyl carbonate concentration in the bottom of the pressure tower (B) is 60.58%, and the dimethyl carbonate concentration in the bottom of the dimethyl carbonate refining tower (C) is 99.9%. The sum of the reboiler loads of the pressure tower (B) and the dimethyl carbonate refining tower (C) per ton of feed is 0.8680 MW.

[0057] [Comparative Example 1]

[0058] The process of Example 1 was repeated, except that a dimethyl carbonate treating tower (C) was not provided. Figure 3 shown.

[0059] The atmospheric pressure tower (A) has 60 theoretical plates, a top operating pressure of 0.05 MPaG, a top operating temperature of 74°C, and a bottom operating temperature of 81°C.

[0060] The pressure tower (B) had 40 theoretical plates, a top operating pressure of 1.0 MPaG, a top operating temperature of 141°C, a bottom operating temperature of 189°C, and polymer appeared in the bottom of the pressure tower.

[0061] In this comparative example, by weight percentage, the concentration of methanol in the atmospheric tower (A) was 99.5%, and the concentration of dimethyl carbonate in the pressure tower (B) was 99.9%. The reboiler load of the pressure tower (B) was 0.6593MW per ton of feed. Although the energy consumption of comparative example 1 was lower than that of embodiment 1, polymer appeared in the pressure tower, and the tower reboiler was prone to scaling, which easily led to the tower being unable to operate normally, and the comprehensive industrial application effect was poor.

[0062] [Comparative Example 2]

[0063] The process of Example 1 was repeated, except that a dimethyl carbonate treating tower (C) was not provided. Figure 3 shown.

[0064] The atmospheric pressure tower (A) has 60 theoretical plates, a top operating pressure of 0.05 MPaG, a top operating temperature of 74°C, and a bottom operating temperature of 81°C.

[0065] The pressure tower (B) had 40 theoretical plates, a top operating pressure of 0.68 MPaG, a top operating temperature of 127°C, a bottom operating temperature of 172°C, and no polymer appeared in the bottom of the pressure tower.

[0066] In this comparative example, the methanol concentration in the bottom of the atmospheric tower (A) is 99.5%, and the dimethyl carbonate concentration in the bottom of the pressure tower (B) is 99.9% by weight. The reboiler load of the pressure tower (B) is 0.8515MW per ton of feed, which is 15.29% higher than the sum of the reboiler loads of the pressure tower (B) and the dimethyl carbonate refining tower (C) in Example 1, and the energy consumption is greatly increased.

[0067] [Comparative Example 3]

[0068] The process of Example 4 was repeated, except that no dimethyl carbonate refining tower (C) was provided.

[0069] The atmospheric pressure tower (A) has 55 theoretical plates, a top operating pressure of 0.09 MPaG, a top operating temperature of 81°C, and a bottom operating temperature of 86°C.

[0070] The pressure tower (B) had 40 theoretical plates, a top operating pressure of 1.0 MPaG, a top operating temperature of 141°C, a bottom operating temperature of 189°C, and polymer appeared in the bottom of the pressure tower.

[0071] In this comparative example, the concentration of methanol in the bottom of the atmospheric tower (A) is 99.5%, and the concentration of dimethyl carbonate in the bottom of the pressure tower (B) is 99.9% by weight. The reboiler load of the pressure tower (B) is 0.9727MW per ton of feed. Polymers appear in the bottom of the pressure tower, and the reboiler of the bottom is prone to scaling, which can easily lead to the bottom of the tower being unable to operate normally, and the comprehensive industrial application effect is poor.

[0072] [Comparative Example 4]

[0073] The process of Example 4 was repeated, except that no dimethyl carbonate refining tower (C) was provided.

[0074] The atmospheric pressure tower (A) has 55 theoretical plates, a top operating pressure of 0.09 MPaG, a top operating temperature of 81°C, and a bottom operating temperature of 86°C.

[0075] The pressure tower (B) had 40 theoretical plates, a top operating pressure of 0.65 MPaG, a top operating temperature of 126°C, a bottom operating temperature of 170°C, and no polymer appeared in the bottom of the pressure tower.

[0076] In this comparative example, the methanol concentration in the bottom of the atmospheric tower (A) is 99.5%, and the dimethyl carbonate concentration in the bottom of the pressure tower (B) is 99.9% by weight. The reboiler load of the pressure tower (B) is 1.2810MW per ton of feed, which is 22.90% higher than the sum of the reboiler loads of the pressure tower (B) and the dimethyl carbonate refining tower (C) in Example 4, and the energy consumption is greatly increased.

[0077] 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 separating dimethyl carbonate and methanol, comprising: The material containing dimethyl carbonate and methanol is sent to a double tower consisting of an atmospheric tower and a pressure tower for separation, methanol is obtained in the atmospheric tower kettle, and crude dimethyl carbonate material is obtained in the pressure tower kettle; wherein, the material at the top of the pressure tower is introduced into the atmospheric tower, and the material at the top of the atmospheric tower is introduced into the pressure tower; the crude dimethyl carbonate material is distilled, the bottom stream of the distillation tower is the dimethyl carbonate product, and the top stream of the distillation tower is circulated back to the atmospheric tower or the pressure tower.

2. The method according to claim 1, characterized in that When the mass concentration of dimethyl carbonate in the material containing dimethyl carbonate and methanol is lower than 25%, the material is first passed into the atmospheric pressure tower; when the mass concentration of dimethyl carbonate in the material containing dimethyl carbonate and methanol is higher than 25%, the material is first passed into the pressure tower.

3. The method according to claim 1, characterized in that The number of theoretical plates of the atmospheric pressure tower is 35 to 70, and the operating pressure at the top of the tower is 0 to 0.1 MPaG.

4. The method according to claim 1, characterized in that: The top operating temperature of the atmospheric pressure tower is 40-81°C, and the bottom operating temperature is 50-88°C.

5. The method according to claim 1, characterized in that The operating conditions of the pressurized tower are as follows: the operating pressure at the top of the tower is 0.8-1.4 MPaG; the operating temperature at the top of the tower is 125-155°C; and the operating temperature at the bottom of the tower is 130-175°C.

6. The method according to claim 1, characterized in that The operating conditions of the pressurized tower are as follows: the operating pressure at the top of the tower is 0.9-1.3 MPaG; the operating temperature at the bottom of the tower is 150-170°C.

7. The method according to claim 1, characterized in that The number of theoretical plates of the pressure tower is 25 to 65.

8. The method according to claim 1, characterized in that The number of theoretical plates for the dimethyl carbonate distillation is 10 to 50.

9. The method according to claim 1, characterized in that: The top operating pressure of the distillation tower for dimethyl carbonate distillation is -0.1 to 0.75 MPaG, excluding -0.1 MPaG.

10. The method according to claim 1, characterized in that The operating temperature of the tower top of the dimethyl carbonate distillation is 40-140°C, and the operating temperature of the tower bottom is 50-175°C.

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