A process for the preparation of glycolic acid methyl ester and / or ethylene glycol by hydro genation of dimethyl oxalate

Abstract

The application discloses a method for preparing glycol and / or methyl glycolate by dimethyl oxalate hydrogenation, which comprises the following steps: (1) mixing methanol with hydrogen and then feeding into a heat exchanger for preheating to obtain a mixed material; (2) mixing the mixed material obtained in step (1) with dimethyl oxalate, heating through a feeding heater and then performing hydrogenation reaction to generate a reaction product comprising methyl glycolate and / or glycol. The method can greatly improve the heat exchange efficiency of the heat exchanger, reduce the heat load of the subsequent feeding heater, reduce steam consumption, thereby saving energy consumption, and avoiding the crystallization problem of dimethyl oxalate after being mixed with low-temperature hydrogen.

Description

Technical Field

[0001] This invention belongs to the field of methyl glycolate and ethylene glycol production technology, specifically relating to a method for preparing methyl glycolate and / or ethylene glycol by hydrogenation of dimethyl oxalate. Background Technology

[0002] Methyl glycolate is an important chemical product and intermediate. Because it has both hydroxyl and ester functional groups, it combines the chemical properties of alcohols and esters. It can undergo carbonylation, hydrolysis, oxidation and other reactions, and is widely used in many fields such as chemical industry, pharmaceuticals, pesticides, feed, fuel and fragrance.

[0003] In recent years, with the continuous maturation of the technology for producing ethylene glycol from syngas via oxalate esters, further developing the downstream product chain of the intermediate oxalate ester has become a research hotspot and focus in this catalysis field. Among these, the production of methyl glycolate via the hydrogenation of dimethyl oxalate, followed by the development of downstream products to form a high-end coal chemical product chain, is a promising technological route. The main reactions for the hydrogenation of dimethyl oxalate to methyl glycolate are as follows:

[0004] Main reaction: CH3OOCCOOCH3 + 2H2 → HOCH2COOCH3 + CH3OH

[0005] Side reaction: HOCH2COOCH3 + 2H2 → HOCH2CH2OH + CH3OH.

[0006] Chinese patent CN104109095B discloses a method for producing glycolate by hydrogenation of oxalate. The method uses a staged feeding method of reaction raw materials to improve the conversion rate of oxalate and the selectivity of glycolate. A solvent, usually methanol, is added to the oxalate raw material.

[0007] Chinese patent CN104262152A discloses a method for producing glycolate by hydrogenation of oxalate ester. The method involves mixing a methanol solution of dimethyl oxalate and a feed gas containing hydrogen and feeding them into a reactor to react with a silver-containing catalyst. This method mainly solves the problems of low conversion rate of dimethyl oxalate and low selectivity of methyl glycolate in the prior art.

[0008] According to existing technology, adding methanol to the reaction feedstock can improve reaction performance and solve the problems of low conversion rate of dimethyl oxalate and low selectivity of methyl glycolate. However, the addition of methanol significantly increases the energy consumption of the reaction process, mainly due to the heating of methanol after it enters the reactor and the separation of methanol. Therefore, solving the energy consumption problem caused by adding methanol to the reaction feedstock is of great significance. Summary of the Invention

[0009] To address the problems existing in the prior art, this invention provides a method for the hydrogenation of dimethyl oxalate to prepare methyl glycolate and / or ethylene glycol. This method involves first mixing methanol and hydrogen, preheating the mixture in a heat exchanger, and then mixing it with dimethyl oxalate for the hydrogenation reaction. This significantly improves the heat exchanger's efficiency, reduces the heat load on the subsequent feed heater, and lowers steam consumption, thereby saving energy. Specifically, by separating the liquid-phase reaction products obtained during the hydrogenation of dimethyl oxalate to prepare methyl glycolate and / or ethylene glycol in a methanol recovery tower and collecting the methanol from the side stream as recycled methanol for use as a reaction feedstock, impurities in the recycled methanol can be separated more efficiently, heat from the reaction products can be recovered, and the selectivity of the reaction can be improved.

[0010] This invention provides a method for preparing methyl glycolate and / or ethylene glycol by hydrogenation of dimethyl oxalate, comprising the following steps:

[0011] (1) Methanol and hydrogen are mixed and then passed into a heat exchanger for preheating to obtain a mixture;

[0012] (2) The mixture obtained in step (1) is mixed with dimethyl oxalate and then heated by a feed heater to carry out a hydrogenation reaction to generate reaction products including methyl glycolate and / or ethylene glycol.

[0013] According to some embodiments of the present invention, the methanol is recovered methanol obtained during the hydrogenation of dimethyl oxalate to prepare methyl glycolate and / or ethylene glycol.

[0014] According to some embodiments of the present invention, the purity of the recovered methanol is 95%-99.99%, preferably 98%-99.9%.

[0015] According to some embodiments of the present invention, the water content in the recovered methanol is 0-0.5% by mass, preferably 0.005-0.05%.

[0016] According to some embodiments of the present invention, the mass content of methyl acetate in the recovered methanol is 0-1%, preferably 0.02-0.1%.

[0017] According to some embodiments of the present invention, the hydrogen includes recycled hydrogen used in the process of hydrogenating dimethyl oxalate to prepare methyl glycolate and / or ethylene glycol.

[0018] According to the present invention, the recovered methanol may include impurities such as methyl formate, methyl acetate, ethanol, and water. Since over-hydrogenation during the reaction generates water and ethanol, the water content in the recycled methanol must be controlled; excessively high water content will reduce reaction performance. Simultaneously, the content of the byproduct methyl acetate must also be controlled; excessively high methyl acetate content will reduce reaction selectivity. The present invention improves the reaction performance and selectivity by controlling the content of water and methyl acetate in the recovered methanol. Theoretically, the lower the content of water and methyl acetate in the recovered methanol, the better, but considering the cost of methanol recovery, it is preferable to control the mass content of water in the recovered methanol to 0.005-0.05% and the mass content of methyl acetate to 0.02-0.1%, which improves the reaction performance and selectivity while saving energy, making it the most economical choice.

[0019] According to some embodiments of the present invention, the weight ratio of methanol to dimethyl oxalate added in the hydrogenation reaction is (0.1:1)-(9:1), preferably (0.5:1)-(3:1).

[0020] According to some embodiments of the present invention, the hot end temperature difference of the heat exchanger is 10-50°C, preferably 15-35°C.

[0021] According to some embodiments of the present invention, the mixing of methanol and hydrogen can be carried out in the heat exchanger.

[0022] According to some embodiments of the present invention, the heat exchanger includes a liquid distributor.

[0023] According to the present invention, mixing methanol with hydrogen before preheating it in a heat exchanger can significantly improve the heat exchange efficiency of the heat exchanger, which is beneficial to maximizing the temperature of the feed heater, reducing the heat load of the feed heater, and reducing steam consumption.

[0024] According to some embodiments of the present invention, the recovered methanol is obtained by a method comprising the following steps:

[0025] S1. Separate the reaction products obtained in the process of hydrogenating dimethyl oxalate to prepare methyl glycolate and / or ethylene glycol to obtain the hydrogenated liquid phase product;

[0026] S2. The resulting hydrogenated liquid product is passed into a distillation column for separation, and the recovered methanol is collected from the side stream of the distillation column.

[0027] According to the present invention, light components such as methyl acetate are generated during the hydrogenation reaction. Using side-stream methanol extraction for recycling can effectively reduce the light components in the methanol and improve the purity of the recycled methanol.

[0028] According to some embodiments of the present invention, the location where the side stream of the distillation column is drawn is at least 10 theoretical plates away from the feed location where the hydrogenated liquid phase product enters the distillation column.

[0029] According to some embodiments of the present invention, the distillation column has 20-80 theoretical plates, the feed position is located on the 15th-70th theoretical plate from top to bottom, and the methanol recovery side stream is located on the 2nd-20th theoretical plate from top to bottom.

[0030] According to some embodiments of the present invention, the distillation column has 30-60 theoretical plates, the feed position is located on the 20th-50th theoretical plate from top to bottom, and the methanol recovery side stream is located on the 5th-10th theoretical plate from top to bottom.

[0031] According to some embodiments of the present invention, the operating pressure of the distillation column is -0.08 to 0.1 MPa.

[0032] According to some embodiments of the present invention, the operating temperature at the top of the distillation column is 40-80°C, and the operating temperature at the bottom of the column is 100-180°C.

[0033] According to some embodiments of the present invention, the operating pressure of the distillation column is -0.06 to -0.03 MPa.

[0034] According to some embodiments of the present invention, the operating temperature at the top of the distillation column is 45-60°C, and the operating temperature at the bottom of the column is 110-150°C.

[0035] According to the present invention, controlling the operating temperature of the top of the distillation column to be greater than 40°C allows the top of the column to be cooled by conventional circulating water, and controlling the operating temperature of the bottom of the distillation column to be lower than 150°C can reduce the polymerization loss of methyl glycol and ethylene glycol.

[0036] According to some embodiments of the present invention, the weight ratio of reflux liquid to side stream product during the operation of the distillation column is (1.2:1)-(3:1), preferably (1.6:1)-(2.2:1).

[0037] According to some embodiments of the present invention, the molar ratio of hydrogen to dimethyl oxalate in the hydrogenation reaction is (40-150):1, preferably (60-100):1.

[0038] According to some embodiments of the present invention, the reaction pressure of the hydrogenation reaction is 2.0-4.0 MPag.

[0039] According to some embodiments of the present invention, the temperature of the hydrogenation reaction is 160-250°C, preferably 180-240°C.

[0040] According to some embodiments of the present invention, the hydrogenation reaction is carried out in a hydrogenation reactor, which is a tubular fixed-bed reactor.

[0041] Compared with the prior art, the present invention has the following advantages:

[0042] (1) Methanol and dimethyl oxalate are fed separately. Methanol enters the heat exchanger, which can greatly improve the heat exchange efficiency of the heat exchanger, increase the recovered heat, and help to maximize the temperature of the feed heater to the reaction, reduce the heat load of the feed heater, and reduce steam consumption.

[0043] (2) Dimethyl oxalate is mixed with the material after heat exchange in the heat exchanger, thus avoiding the problem of crystallization when mixed with low-temperature hydrogen.

[0044] (3) The process is simple, and high-purity recovered methanol can be obtained by side-stream extraction, which can improve the performance and selectivity of the reaction. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the system used in an embodiment of the present invention.

[0046] Reference numerals: 1. Feed heater; 2. Hydrogenation reactor; 3. Feed and discharge heat exchangers; 4. Discharge cooler; 5. Gas-liquid separator; 6. Compressor; 7. Methanol recovery tower; 8. Dimethyl oxalate; 9. Make-up hydrogen; 10. Release hydrogen; 11. Methanol recovery; 12. Produced methanol; 13. Methyl glycolate and glycolic acid mixture; 14. Hydrogenation liquid phase product. Detailed Implementation

[0047] To make the present invention easier to understand, it will be described in detail below with reference to embodiments and accompanying drawings. These embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply.

[0048] The following examples utilize Figure 1The system shown is used for the hydrogenation of dimethyl oxalate to prepare methyl glycolate and / or ethylene glycol. Methanol and hydrogen are mixed and preheated in a feed heat exchanger 3. The preheated material is then mixed with dimethyl oxalate 8 and heated by a feed heater 1 before being fed into a hydrogenation reactor 2 to produce the reaction product. The resulting reaction product is cooled by the feed heat exchanger 3 and further cooled by a discharge cooler 4, then separated by a gas-liquid separator 5 to obtain a hydrogenated liquid product 14. The hydrogenated liquid product 14 is then mixed with recycled hydrogen. The hydrogenated liquid product 14 is fed into a methanol recovery tower 7 (distillation tower) for separation. The recycled hydrogen, after being discharged as purge hydrogen 10, is mixed with supplementary hydrogen 9 by a compressor 6 and used as feedstock for the hydrogenation of dimethyl oxalate to prepare methyl glycolate and / or ethylene glycol.

[0049] Recovered methanol for recycling is collected from the side stream of the rectification section of methanol recovery tower 7. Methanol 12 is collected from the top of the tower, and a mixture 13 containing methyl glycol and ethylene glycol is obtained from the bottom of the tower. The recovered methanol 11 collected from the side stream of the rectification section of methanol recovery tower can be used as a feedstock for the hydrogenation of dimethyl oxalate to produce methyl glycol and / or ethylene glycol. It is mixed with circulating hydrogen and then preheated in the feed and discharge heat exchanger 3. The methanol recovery tower 7 includes a top condenser and a bottom reboiler, and the condensation temperature of the top reflux liquid is uniformly 40°C.

[0050] Example 1

[0051] use Figure 1 The system shown involves mixing recovered methanol with recycled hydrogen, which is then heated to 180°C in a feed heat exchanger. This mixture is then mixed with dimethyl oxalate and heated to 210°C in a feed heater before being sent to a hydrogenation reactor to produce the reaction products. The hydrogenation reactor is a tubular fixed-bed reactor with an outlet temperature controlled at 210°C. The weight ratio of recovered methanol to dimethyl oxalate is 1.5:1, the dimethyl oxalate feed rate is 5 t / h, the molar ratio of hydrogen to dimethyl formate at the reactor inlet is controlled at 100 mol / 1 mol, and the reaction pressure is 3.0 MPag.

[0052] The resulting reaction product is then cooled to 80°C via an inlet / outlet heat exchanger, and further cooled to 40°C via an outlet cooler. After passing through a gas-liquid separator, the product is separated into hydrogenated liquid phase and recycled hydrogen. The recycled hydrogen is partially discharged, then pressurized by a compressor and mixed with fresh hydrogen as a reaction feedstock.

[0053] The distillation column has 50 theoretical plates. The feed is located on the 40th theoretical plate from the top, and the recovered methanol is collected on the 5th theoretical plate from the top. The operating pressure of the distillation column is -0.03 MPa, the top temperature is 48°C, and the bottom temperature is 130°C. The reflux / sidestream weight ratio is 1.70.

[0054] The recovered methanol has a purity of 99.5% wt, with a water content of 0.01% and a methyl acetate content of 0.05%. The heat load of the feed heater is 1.95 MW, the heat load of the discharge cooler is 3.40 MW, and the load of the methanol removal tower reboiler is 4.53 MW. The results of the reaction using the recovered methanol as raw material are: a dimethyl oxalate conversion rate of 99.9% and a methyl glycolate selectivity of 85.0%.

[0055] Example 2

[0056] The method is the same as in Example 1, except that the molar ratio of hydrogen to dimethyl formate at the hydrogenation reactor inlet is controlled at 60 mol / 1 mol, and the weight ratio of methanol to dimethyl oxalate is 1:1.

[0057] The distillation column has 30 theoretical plates, with the feed point located on the 25th theoretical plate from the top, and the methanol recovery point located on the 10th theoretical plate from the top. The operating pressure of the purification column is -0.05 MPa, the top temperature is 58°C, and the bottom temperature is 150°C.

[0058] The recovered methanol had a purity of 98.4% wt, with a water content of 0.05% and a methyl acetate content of 0.1%. The heat load of the feed heater was 1.32 MW, the heat load of the discharge cooler was 2.46 MW, and the load of the methanol removal tower reboiler was 3.91 MW. The results of the reaction using the recovered methanol as raw material were: a dimethyl oxalate conversion rate of 99.5% and a methyl glycolate selectivity of 82.2%.

[0059] Example 3

[0060] The method is the same as in Example 1, except that the weight ratio of reflux liquid to side stream produced liquid is increased to 2.0 to improve the purity of the recovered methanol. The purity of the recovered methanol is 99.91% wt, with a water content of 0.005% and a methyl acetate content of 0.02%. The heat load of the feed heater is 1.95 MW, the heat load of the discharge cooler is 3.91 MW, and the load of the methanol removal tower reboiler is increased to 5.51 MW. The results of the reaction of the raw materials are: the conversion rate of dimethyl oxalate is 99.92%, and the selectivity of methyl glycolate is 85.1%.

[0061] Example 4

[0062] The method is the same as in Example 2, except that the weight ratio of reflux liquid to side stream product is reduced to 1.1 to decrease separation energy consumption. Simultaneously, the purity of the recovered methanol is also reduced accordingly, reaching 97.80% wt, with a water content of 0.16% and a methyl acetate content of 0.12%. The heat load of the feed heater is 1.32 MW, the heat load of the discharge cooler is 2.46 MW, and the reboiler load of the methanol removal tower is 3.54 MW. Results show that increasing the water content inhibits catalyst performance, reducing the DMO conversion rate from greater than 99.5% to less than 99%. The results of the feedstock reaction are: a dimethyl oxalate conversion rate of 98.5% and a methyl glycolate selectivity of 78.0%.

[0063] Comparative Example 1

[0064] The method is the same as in Example 1, except that methanol recovery does not use a side-stream sampling scheme. Instead, methanol is directly sampled from the top of the tower and recycled back to the reactor. As a result, the methyl acetate content in the recycled methanol will continue to accumulate and rise to more than 1%. The purity of the recycled methanol will decrease to below 98%. The excessively high methyl acetate content will further promote the formation of side reactions and reduce the selectivity of the reaction. This will cause the selectivity of ethylene glycol monoethyl ester to increase from less than 0.01% to more than 0.1%. Since ethylene glycol monoethyl ester and ethylene glycol have an azeotropic relationship, it will increase the difficulty of separation in subsequent equipment.

[0065] Comparative Example 2

[0066] The method is the same as in Example 1, except that the recovered methanol and dimethyl oxalate are directly mixed and then mixed with hydrogen that has been heated by the inlet and outlet heat exchangers. As a result, the load of the feed heater will increase to 3.6MW, and the energy consumption will increase significantly.

[0067] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for preparing methyl glycolate and / or ethylene glycol by hydrogenation of dimethyl oxalate, comprising the following steps: (1) Methanol and hydrogen are mixed and then passed through a heat exchanger for preheating to obtain a mixture; the methanol is recovered methanol obtained in the process of hydrogenating dimethyl oxalate to prepare methyl glycolate and / or ethylene glycol, and the mass content of methyl acetate in the recovered methanol is less than 1%; the mass content of water in the recovered methanol is 0-0.5%; (2) The mixture obtained in step (1) is mixed with dimethyl oxalate, heated by a feed heater, and then subjected to a hydrogenation reaction to generate reaction products including methyl glycolate and / or ethylene glycol. The recovered methanol is obtained through a method comprising the following steps: S1. Separate the reaction products obtained in the process of hydrogenating dimethyl oxalate to prepare methyl glycolate and / or ethylene glycol to obtain the hydrogenated liquid phase product; S2. The obtained hydrogenated liquid product is fed into a distillation column for separation. The recovered methanol is collected from the side stream of the distillation column, and methanol is collected from the top of the column. The weight ratio of reflux liquid to side stream produced liquid during the operation of the distillation column is (1.2:1) to (3:1).

2. The method according to claim 1, characterized in that, The purity of the recovered methanol is 95%-99.99%; and / or the mass content of methyl acetate in the recovered methanol is 0.02-0.1%; And / or the hydrogen gas includes recycled hydrogen gas used in the process of hydrogenating dimethyl oxalate to prepare methyl glycolate and / or ethylene glycol.

3. The method according to claim 2, characterized in that, The purity of the recovered methanol is 98%-99.9%; and / or The water content in the recovered methanol is 0.005-0.05% by mass.

4. The method according to any one of claims 1-3, characterized in that, The weight ratio of methanol to dimethyl oxalate added in the hydrogenation reaction is (0.1:1) to (9:1).

5. The method according to claim 4, characterized in that, The weight ratio of methanol to dimethyl oxalate added in the hydrogenation reaction is (0.5:1) to (3:1).

6. The method according to any one of claims 1-3, characterized in that, The hot end temperature difference of the heat exchanger is 10-50℃.

7. The method according to claim 6, characterized in that, The temperature difference at the hot end of the heat exchanger is 15-35℃.

8. The method according to any one of claims 1-3, characterized in that, The heat exchanger includes a liquid distributor.

9. The method according to claim 1, characterized in that, The location where the side stream of the distillation column is drawn is at least 10 theoretical plates away from the feed location where the hydrogenated liquid phase product enters the distillation column.

10. The method according to claim 9, characterized in that, The distillation column has 20-80 theoretical plates, the feed position is located on the 15th-70th theoretical plate from top to bottom, and the side stream is located on the 2nd-20th theoretical plate from top to bottom.

11. The method according to claim 9, characterized in that, The distillation column has 30-60 theoretical plates, the feed position is located on the 20th-50th theoretical plate from top to bottom, and the side stream is located on the 5th-10th theoretical plate from top to bottom.

12. The method according to claim 1, characterized in that, The operating pressure of the distillation column is -0.08-0.1 MPa, and / or the operating temperature at the top of the distillation column is 40-80℃, and the operating temperature at the bottom of the column is 100-180℃.

13. The method according to claim 12, characterized in that, The operating pressure of the distillation column is -0.06 to -0.03 MPa, and / or the operating temperature at the top of the distillation column is 45-60°C, and the operating temperature at the bottom of the column is 110-150°C.

14. The method according to claim 1, characterized in that, The weight ratio of reflux liquid to side stream produced liquid during the operation of the distillation column is (1.6:1) - (2.2:1).

15. The method according to any one of claims 1-3, characterized in that, In the hydrogenation reaction, the molar ratio of hydrogen to dimethyl oxalate is (40-150):

1.

16. The method according to claim 15, characterized in that, In the hydrogenation reaction, the molar ratio of hydrogen to dimethyl oxalate is (60-100):

1.

17. The method according to any one of claims 1-3, characterized in that, The hydrogenation reaction is carried out at a pressure of 2.0-4.0 MPag and / or at a temperature of 160-250°C.

18. The method according to claim 17, characterized in that, The hydrogenation reaction is carried out at a temperature of 180℃-240℃.

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