A method for removing coking substances from a dimethyl oxalate hydrogenation catalyst

Abstract

The present invention discloses a method for removing coking substances from a hydrogenation catalyst for dimethyl oxalate. The steps are as follows: First, a mixed reagent composed of 70% - 90% tetrahydrofuran, 5% - 20% ethylene glycol monomethyl ether, and 5% - 20% methanol is used as a solvent to dissolve and elute the coking substances aggregated on the hydrogenation catalyst; then, an inert atmosphere containing tetrahydrofuran, methanol, and water is used for purging to remove the high-boiling esters and organic acids adsorbed on the catalyst, and then an inert atmosphere containing tetrahydrofuran and methanol is used for purging to remove the high-boiling alcohols adsorbed on the catalyst, so as to achieve the removal of the coking substances. This method can remove the coking substances on the hydrogenation catalyst for dimethyl oxalate, restore the activity lost due to the catalyst being covered by the coking substances, thereby greatly extending the service life of the catalyst; the method is simple, the cost is low, and the effect is good.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical engineering, and particularly relates to a method for removing coking substances from a hydrogenation catalyst for dimethyl oxalate. Background Art

[0002] Ethylene glycol is an important chemical raw material with wide applications. It is mainly used in the synthesis of polyesters and also in fields such as antifreeze agents, surfactants, and plasticizers. Currently, the international method for preparing ethylene glycol mainly adopts the route of ethylene oxidation - ethylene oxide hydrolysis. In China, this process has problems such as dependence on petroleum resources, high water and energy consumption, and low economic efficiency. In recent years, the coal - based ethylene glycol route, which synthesizes dimethyl oxalate (DMO) from CO and methyl nitrite and then hydrogenates dimethyl oxalate to prepare ethylene glycol under the action of a hydrogenation catalyst, has been widely developed in China. This process utilizes China's relatively rich coal resources to replace the petroleum route for producing ethylene glycol, and at the same time greatly reduces water consumption, having good economic and environmental protection advantages.

[0003] Currently, copper - based catalysts are generally used for the hydrogenation of oxalate esters. The copper - based catalysts of US54112245, NL77 047 34 of ARCO Company in the United States and the series of copper - based catalysts for producing ethylene glycol (EG) of UCC Company, US4677 234, US4628128, US4649226, US4628129. Domestically, CN101474561B, CN101455976A, and CN1014111990B disclose different types of carriers, including MCM - 14, ZSM - 5, SiO2, SAB - 15, etc. In the above - mentioned disclosed patents, the reaction temperature for the hydrogenation of dimethyl oxalate (DMO) to synthesize ethylene glycol (EG) is usually around 200°C, the pressure is around 2.5 MPa, and the selectivity of ethylene glycol is over 90%. For the catalysts of US4551565 and US4585890 of Ube Industries, when using Cu / SiO 2 catalyst, at a reaction pressure of 3 Mpa, a reaction temperature of 215°C, and a hydrogen - to - ester ratio of 30, the conversion rate of diethyl oxalate is 100%, and the selectivity of ethylene glycol is 97.2%.

[0004] CN101856615B discloses a Cu / SiO 2 catalyst with ZrO 2 as the main promoter. CN102247847A discloses a preparation method of a Cu / SiO 2 catalyst. CN102336666A discloses a preparation method for producing ethylene glycol by hydrogenating oxalate esters.

[0005] Since 2009 in China, more than 30 sets of coal-to-ethylene glycol industrial plants have been put into production successively, and the total annual production capacity of polyester-grade ethylene glycol is nearly 10 million tons. At present, the synthesis, rectification of dimethyl oxalate, and the rectification process of crude ethylene glycol are relatively mature. However, the hydrogenation of dimethyl oxalate to ethylene glycol faces the problems of short catalyst service life (6 - 14 months for most plants) and frequent catalyst replacement, which has a greater impact on the production capacity and operating cost of the plant.

[0006] Currently, the main factor affecting the service life of the dimethyl oxalate hydrogenation catalyst is the accumulation of coke on the catalyst. During the hydrogenation of dimethyl oxalate, raw materials such as dimethyl oxalate, intermediate methyl glycolate (MG), product ethylene glycol (EG), and some hydrogenation by-products are prone to adsorb on the catalyst surface and undergo polymerization reactions to form polymers composed of alcohol ester monomers. These polymers are easily accumulated on the catalyst surface. Together with the adsorbed alcohol ester substances, under the action of the system temperature, coke is gradually formed. This not only reduces the catalyst activity but also causes adhesion between catalyst particles, catalyst bed plugging, and an increase in the resistance of the circulating gas. Eventually, a new catalyst has to be replaced. CN 216704307 discloses a system for preparing ethylene glycol by hydrogenating dimethyl oxalate with a long service life, which uses a hollow catalyst to reduce the influence of coke on the resistance drop of the circulating gas and extend the service time of the catalyst. For the dimethyl oxalate hydrogenation catalyst that has already coked, there is currently no patent or literature introducing relevant treatment methods to reduce the resistance, restore its activity, and extend its service life. Summary of the Invention

[0007] The purpose of the present invention is to propose a method for removing coke from the dimethyl oxalate hydrogenation catalyst. This method can remove the coke on the dimethyl oxalate hydrogenation catalyst, restore the activity lost due to the catalyst being covered by coke, and greatly extend the service life of the catalyst; the method is simple, low-cost, and has good effects.

[0008] To solve the above technical problems, the present invention adopts the following technical solutions:

[0009] Provide a method for removing coke from the dimethyl oxalate hydrogenation catalyst, specifically including the following steps:

[0010] 1) The first stage: Using a mixed reagent composed of 70% - 90% tetrahydrofuran, 5% - 20% ethylene glycol monomethyl ether, and 5% - 20% methanol by volume percentage as a solvent to submerge the catalyst, dissolve and discharge the accumulated coke on the catalyst.

[0011] 2) The second stage: Passing an inert atmosphere containing tetrahydrofuran, methanol, and water to purge the catalyst, using methanol for esterification reaction, and at the same time, using methanol for transesterification reaction under an aqueous medium.

[0012] 3) The third stage: Continuously purge the catalyst by introducing an inert atmosphere containing tetrahydrofuran and methanol, and carry out an etherification reaction using methanol until there are no impurities purged out in the recycle gas, i.e., the removal of the coking substances on the dimethyl oxalate hydrogenation catalyst is completed.

[0013] According to the above solution, in step 1), the coking substances have not formed carbonized solids, and the hydrogenation reactor is not completely blocked.

[0014] According to the above solution, in step 1), the soaking time of the catalyst in the solvent is 8 - 24 h.

[0015] According to the above solution, in step 1), the catalyst is immersed at a temperature of 30°C - 50°C.

[0016] According to the above solution, in step 1), the solvent is pressed into the bottom of the hydrogenation reactor, and after the coking substances are fully dissolved, the coking substance solution is discharged from the bottom of the hydrogenation reactor.

[0017] According to the above solution, in step 1), if the coking substances in the discharged coking substance solution are not completely dissolved, or the solution is viscous, secondary dissolution can be carried out according to the same steps.

[0018] According to the above solution, in step 2) or step 3), the inert atmosphere is nitrogen.

[0019] According to the above solution, in the inert atmosphere containing tetrahydrofuran, methanol and water in step 2), by volume percentage, methanol is 10% - 20%; preferably, tetrahydrofuran is 15% - 30%, and water is 0.1% - 1%. Among them, tetrahydrofuran, methanol and water are vaporized into gases.

[0020] According to the above solution, in the inert atmosphere containing tetrahydrofuran and methanol in step 3), by volume percentage, methanol is 15% - 30%; preferably, tetrahydrofuran is 5% - 15%. Among them, tetrahydrofuran and methanol are vaporized into gases.

[0021] According to the above solution, in step 2), the purging temperature is 140°C - 160°C.

[0022] According to the above solution, in step 3), the purging temperature is 210°C - 230°C.

[0023] According to the above solution, in step 2), the purging process is: space velocity 200 - 500 h -1 , time 2 - 4 hours.

[0024] According to the above solution, in step 3), the purging process is: space velocity 200 - 500 h -1 , time 2 - 4 hours.

[0025] A reaction process for preparing ethylene glycol by hydrogenating dimethyl oxalate is provided. During the reaction process, the state of the hydrogenation catalyst is monitored. When the coke deposits on the hydrogenation catalyst have not formed carbonized solids and the hydrogenation reactor is not completely blocked, the above method is used for removal to realize the recycling of the hydrogenation catalyst.

[0026] The present invention provides a method for removing coke deposits from a dimethyl oxalate hydrogenation catalyst, which is carried out in three stages. The specific principle is as follows:

[0027] First, a mixed solvent composed of tetrahydrofuran, ethylene glycol monomethyl ether, and methanol with a suitable ratio is configured to immerse the catalyst, dissolve and discharge the coke deposits accumulated on the catalyst. Secondly, an inert atmosphere containing tetrahydrofuran, methanol, and water is introduced. The esterification reaction of methanol and organic acids is carried out, and at the same time, in an aqueous medium, the transesterification reaction of methanol and high-boiling esters is carried out, both generating lower-boiling methyl esters. The generated methyl esters are purged out of the hydrogenation reactor with the purge gas to remove the high-boiling esters adsorbed on the catalyst and a small amount of organic acids generated by the hydrolysis of esters. Tetrahydrofuran serves as a dispersant to facilitate the penetration of methanol and water in the adsorbate. Water serves as an intermediary for the transesterification reaction. Finally, the catalyst is continuously purged with an inert atmosphere containing tetrahydrofuran and methanol. The high-boiling alcohols undergo methyl etherification reaction with methanol to generate lower-boiling ether substances, which are purged out of the reactor. By regulating different process conditions in three stages, the coke deposits on the catalyst are removed, the activity of the catalyst is restored, the resistance of the recycle gas is reduced, and the service life of the catalyst is prolonged.

[0028] This method can be used in the initial stage of coke formation on the dimethyl oxalate hydrogenation catalyst when alcohol esters are adsorbed on the catalyst surface and polymers are formed, or in the middle stage of coke formation when the polymers formed on the catalyst surface accumulate in large quantities and begin to affect the activity of the catalyst, the resistance of the reactor begins to increase, but the polymers have not been converted into carbonized solids and the reactor is not completely blocked. It is not applicable to the situation where the coke deposits have formed carbonized solids and the reactor is basically blocked. Its characteristics are high efficiency in removing coke deposits, short time for removing coke deposits, and no need to reload the catalyst.

[0029] The beneficial effects of the present invention are as follows:

[0030] 1. The present invention provides a method for removing coking substances from a dimethyl oxalate hydrogenation catalyst. In the first stage, the catalyst is immersed in a configured mixed solvent to fully dissolve and remove the coking substances. In the second stage, an inert atmosphere containing tetrahydrofuran, methanol, and water is introduced to remove high-boiling esters and organic acids. In the third stage, an inert atmosphere containing tetrahydrofuran and methanol is introduced to remove high-boiling alcohols adsorbed on the catalyst. Through process regulation in different stages, the coking substances are gradually removed, the activity lost due to the catalyst being covered by coking substances is restored, and the service life of the catalyst is significantly extended. This method has a high removal efficiency for coking substances, a short time for removing coking substances, and does not require reinstalling the catalyst, thus having a wide application prospect.

[0031] 2. The present invention provides a dimethyl oxalate hydrogenation reaction process. By removing coking substances from the catalyst with accumulated coking substances, the recycling of the catalyst is realized, the catalyst does not need to be frequently replaced, the production capacity of the device is significantly improved, and the operation cost is reduced. Description of the Drawings

[0032] Figure 1 It is a schematic diagram of the device for the embodiment; wherein:

[0033] 1 - Nitrogen pipeline, 2 - Purge solvent pipeline, 3 - Vaporized purge solvent pipeline, 4 - Purge gas pipeline, 5 - Purge gas outlet, 6 - Elution mixed solvent pipeline, 7 - Waste liquid discharge pipeline. Detailed Embodiments

[0034] For further detailed description of the present invention, specific implementation cases are given below, but the present invention is not limited to the given embodiments.

[0035] Figure 1 It is a schematic diagram of the device for the embodiment of the present invention. The specific process operation flow is as follows: In the first stage: The mixed solvent enters the reactor from the elution mixed solvent pipeline 6 below the reactor to dissolve the coking substances. After the coking substances are dissolved, the solution is discharged from the waste liquid discharge pipeline 7. In the second and third stages: Nitrogen is introduced from the nitrogen pipeline 1, and tetrahydrofuran, methanol, and water (tetrahydrofuran and methanol) enter the vaporizer from the purge solvent pipeline 2. After vaporization, it comes out from the vaporized purge solvent pipeline 3 and mixes with the nitrogen in the nitrogen pipeline 1 to form a purge gas, which enters the hydrogenation reactor through the purge gas pipeline 4. The purged gas is discharged from the purge gas outlet 5 of the hydrogenation reactor.

[0036] Example 1

[0037] In this example, a hydrogenation catalyst in the middle stage of coking (the coking substances on the catalyst account for about 15% by weight) is used as the treatment object. The specific removal method includes the following steps:

[0038] The solvent composed of tetrahydrofuran, ethylene glycol monomethyl ether and methanol (volume ratio of 90:5:5) is pumped into the hydrogenation reactor from below and slowly submerges the catalyst. The reactor temperature is set at 50 °C and maintained for 12 hours. Then the solution in the reactor is discharged from the bottom of the reactor to the recovery storage tank. Tetrahydrofuran, methanol and water are heated into gases by the DMO vaporizer and then mixed with nitrogen, with the ratio being 70% nitrogen, 19.8% tetrahydrofuran, 10% methanol, and 0.2% water. At atmospheric pressure and 150 °C, the hydrogenation reactor is purged for 2 hours at a space velocity of 500 h -1 . Then the reactor temperature is gradually raised to 220 °C. Meanwhile, the ratios of nitrogen, tetrahydrofuran and methanol are adjusted to 70%, 10% and 20%. Keeping the space velocity unchanged, it is purged for 3 hours, thus completing the removal of the coking substances.

[0039] Example 2

[0040] This example takes the hydrogenation catalyst in the middle stage of coking (the coking substances on the catalyst account for about 15% by weight) as the treatment object. The specific removal method includes the following steps:

[0041] The solvent composed of tetrahydrofuran, ethylene glycol monomethyl ether and methanol (75:15:10) is pumped into the reactor from below and slowly submerges the catalyst. The reactor temperature is set at 50 °C and maintained for 12 hours. Then the solution in the reactor is discharged from the bottom of the reactor to the recovery storage tank. Tetrahydrofuran, methanol and water are heated into gases by the DMO vaporizer and then mixed with nitrogen, with the ratio being 70% nitrogen, 19.8% tetrahydrofuran, 10% methanol, and 0.2% water. At atmospheric pressure and 150 °C, the hydrogenation reactor is purged for 2 hours at a space velocity of 500 h -1 . Then the reactor temperature is gradually raised to 220 °C. Meanwhile, the ratios of nitrogen, tetrahydrofuran and methanol are adjusted to 70%, 10% and 20%. Keeping the space velocity unchanged, it is purged for 2 hours.

[0042] Example 3

[0043] This example takes the hydrogenation catalyst in the middle stage of coking (the coking substances on the catalyst account for about 15% by weight) as the treatment object. The specific removal method includes the following steps:

[0044] The solvent composed of tetrahydrofuran, ethylene glycol monomethyl ether and methanol (75:15:10) is pumped into the reactor from below and slowly submerges the catalyst. The reactor temperature is set at 50 °C and maintained for 12 hours. Then the solution in the reactor is discharged from the bottom of the reactor to the recovery storage tank. Tetrahydrofuran, methanol and water are heated into gases by the DMO vaporizer and then mixed with nitrogen, with the ratio being 60% nitrogen, 25% tetrahydrofuran, 14.9% methanol, and 0.1% water. At atmospheric pressure and 150 °C, the hydrogenation reactor is purged for 2 hours at a space velocity of 500 h -1The hydrogenation reactor was purged for 2 hours at a certain airspeed. Then, the reactor was gradually heated to 220 °C. Meanwhile, the ratio of nitrogen, tetrahydrofuran, and methanol was adjusted to 70%, 10%, and 20%. Keeping the airspeed unchanged, it was purged for 2 hours.

[0045] Example 4

[0046] In this example, a hydrogenation catalyst in the middle stage of coking (the coke on the catalyst accounted for about 28% by weight) was used as the treatment object. The specific removal method included the following steps:

[0047] A mixed solvent composed of tetrahydrofuran, ethylene glycol monomethyl ether, and methanol (90:5:5) was pressed into the reactor from below the reactor and slowly submerged the catalyst. It was soaked at 50 °C for 24 hours, and the solution in the reactor was drained from the bottom of the reactor to the recovery storage tank. After soaking the catalyst again for 2 hours with the mixed solvent using the same steps and draining it, tetrahydrofuran, methanol, and water were heated into gases through a DMO vaporizer and mixed with nitrogen. The ratio was 70% nitrogen, 19.5% tetrahydrofuran, 10% methanol, and 0.5% water. At normal pressure and under the condition of 160 °C, at an airspeed of 500h -1 The hydrogenation reactor was purged for 2 hours. Then, the reactor was gradually heated to 230 °C. Meanwhile, the ratio of nitrogen, tetrahydrofuran, and methanol was adjusted to 70%, 5%, and 25%. Keeping the airspeed unchanged, it was purged for 4 hours.

[0048] Example 5

[0049] In this example, a hydrogenation catalyst in the middle stage of coking (the coke on the catalyst accounted for about 28% by weight) was used as the treatment object. The specific removal method included the following steps:

[0050] A solvent composed of tetrahydrofuran, ethylene glycol monomethyl ether, and methanol (80:15:5) was pressed into the reactor from below the reactor and slowly submerged the catalyst. The reactor temperature was set at 50 °C and maintained for 24 hours. The solution in the reactor was drained from the bottom of the reactor to the recovery storage tank. After soaking the catalyst again for 2 hours with the mixed solvent using the same steps and draining it, tetrahydrofuran, methanol, and water were heated into gases through a DMO vaporizer and mixed with nitrogen. The ratio was 70% nitrogen, 19.5% tetrahydrofuran, 10% methanol, and 0.5% water. At normal pressure and under the condition of 160 °C, at an airspeed of 500h -1 The hydrogenation reactor was purged for 2 hours. Then, the reactor was gradually heated to 230 °C. Meanwhile, the ratio of nitrogen, tetrahydrofuran, and methanol was adjusted to 65%, 10%, and 25%. Keeping the airspeed unchanged, it was purged for 4 hours.

[0051] Example 6

[0052] This example takes a hydrogenation catalyst in the middle stage of coking (the coking substance on the catalyst accounts for about 28% by weight) as the treatment object, and the specific removal method includes the following steps:

[0053] The solvent composed of tetrahydrofuran, ethylene glycol monomethyl ether and methanol (90:5:5) is pressed into the reactor from below the reactor and slowly submerges the catalyst. The reactor temperature is set at 50 °C and maintained for 24 hours. The solution in the reactor is discharged from the bottom of the reactor to the recovery storage tank. After soaking the catalyst again with the mixed solvent using the same steps for 2 hours and draining it, tetrahydrofuran, methanol and water are heated into gases through a DMO vaporizer and mixed with nitrogen, with the ratio of nitrogen 60%, tetrahydrofuran 20%, methanol 19%, and water 1.0%. Under normal pressure and at 160 °C, the hydrogenation reactor is purged at a space velocity of 500 h -1 for 2 hours. Then the reactor temperature is gradually raised to 230 °C. At the same time, the ratio of nitrogen, tetrahydrofuran and methanol is adjusted to 65%, 10%, 25%. Keeping the space velocity unchanged, purge for 4 hours.

[0054] Example 7

[0055] This example takes a hydrogenation catalyst in the middle stage of coking (the coking substance on the catalyst accounts for about 28% by weight) as the treatment object, and the specific removal method includes the following steps:

[0056] The solvent composed of tetrahydrofuran, ethylene glycol monomethyl ether and methanol (80:15:5) is pressed into the reactor from below the reactor and slowly submerges the catalyst. The reactor temperature is set at 50 °C and maintained for 24 hours. The solution in the reactor is discharged from the bottom of the reactor to the recovery storage tank. After soaking the catalyst again with the mixed solvent using the same steps for 2 hours and draining it, tetrahydrofuran, methanol and water are heated into gases through a DMO vaporizer and mixed with nitrogen, with the ratio of nitrogen 60%, tetrahydrofuran 20%, methanol 19%, and water 1.0%. Under normal pressure and at 160 °C, the hydrogenation reactor is purged at a space velocity of 500 h -1 for 2 hours. Then the reactor temperature is gradually raised to 230 °C. At the same time, the ratio of nitrogen, tetrahydrofuran and methanol is adjusted to 60%, 10%, 30%. Keeping the space velocity unchanged, purge for 2 hours.

[0057] Example 8

[0058] This example takes a hydrogenation catalyst in the initial stage of coking (the coking substance on the catalyst accounts for about 6% by weight) as the treatment object, and the specific removal method includes the following steps:

[0059] A solvent composed of tetrahydrofuran, ethylene glycol monomethyl ether, and methanol (70:10:20) is pressed into the reactor from below and slowly submerges the catalyst. The reactor temperature is set at 30 °C and maintained for 12 hours. Then the solution in the reactor is discharged from the bottom of the reactor to the recovery storage tank. Tetrahydrofuran, methanol, and water are heated into gases by a DMO vaporizer and then mixed with nitrogen, with the ratio being 74.9% nitrogen, 15% tetrahydrofuran, 10% methanol, and 0.1% water. Under normal pressure and at 140 °C, the hydrogenation reactor is purged at a space velocity of 500 h -1 for 2 hours. Then the reactor temperature is gradually increased to 210 °C. At the same time, the ratios of nitrogen, tetrahydrofuran, and methanol are adjusted to 70%, 5%, and 25%. Keeping the space velocity unchanged, it is purged for 2 hours.

[0060] Example 9

[0061] In this example, a hydrogenation catalyst at the initial stage of coking (the coking substance on the catalyst accounts for about 6% by weight) is taken as the treatment object. The specific removal method includes the following steps:

[0062] A solvent composed of tetrahydrofuran, ethylene glycol monomethyl ether, and methanol (70:10:20) is pressed into the reactor from below and slowly submerges the catalyst. The reactor temperature is set at 50 °C and maintained for 12 hours. Then the solution in the reactor is discharged from the bottom of the reactor to the recovery storage tank. Tetrahydrofuran, methanol, and water are heated into gases by a DMO vaporizer and then mixed with nitrogen, with the ratio being 74% nitrogen, 15% tetrahydrofuran, 10% methanol, and 1.0% water. Under normal pressure and at 140 °C, the hydrogenation reactor is purged at a space velocity of 500 h -1 for 2 hours. Then the reactor temperature is gradually increased to 210 °C. At the same time, the ratios of nitrogen, tetrahydrofuran, and methanol are adjusted to 70%, 5%, and 25%. Keeping the space velocity unchanged, it is purged for 2 hours.

[0063] Example 10

[0064] In this example, a hydrogenation catalyst at the initial stage of coking (the coking substance on the catalyst accounts for about 6% by weight) is taken as the treatment object. The specific removal method includes the following steps:

[0065] A solvent composed of tetrahydrofuran, ethylene glycol monomethyl ether, and methanol (80:10:10) is pressed into the reactor from below and slowly submerges the catalyst. The reactor temperature is set at 30 °C and maintained for 12 hours. Then the solution in the reactor is discharged from the bottom of the reactor to the recovery storage tank. Tetrahydrofuran, methanol, and water are heated into gases by a DMO vaporizer and then mixed with nitrogen, with the ratio being 74.9% nitrogen, 15% tetrahydrofuran, 10% methanol, and 0.1% water. Under normal pressure and at 140 °C, the hydrogenation reactor is purged at a space velocity of 200 h -1The hydrogenation reactor was purged for 2 hours at an airspeed. Then, the reactor was gradually heated to 210 °C. At the same time, the ratio of nitrogen, tetrahydrofuran, and methanol was adjusted to 70%, 5%, and 25%. Keeping the airspeed unchanged, it was purged for 2 hours.

[0066] The coke content before and after the removal of the coked product and the reaction temperature, DMO conversion rate, and EG selectivity in the dimethyl oxalate hydrogenation reaction were tested to verify the effect of removing the coked product from the hydrogenation catalyst in the example; where the feed rate of DMO was 0.5 h -1 , the hydrogen-to-ester ratio was 80. The specific results are shown in Table 1. Table 1 shows that the coked product on the catalyst was basically removed, the system reaction temperature decreased, and at the same time, the DMO conversion rate and EG selectivity increased, indicating that the activity of the catalyst after removing the coked product was significantly restored.

[0067] Table 1

[0068]

[0069] Example 11

[0070] The comparison of the operation data of the hydrogenation catalyst at the initial stage of operation and before and after the removal of the coked product is shown in Table 2, where the feed rate of DMO was 0.5 h -1 , and the hydrogen-to-ester ratio was 72. Table 2 shows that after the hydrogenation system had been operating for 250 days in total, it reached the mid-stage of coking, the bed resistance drop increased (the resistance drop of the hydrogenation reactor under 100% design load was 45 kPa), the system reaction temperature rose, and the activity and selectivity of the catalyst decreased to a certain extent. The hydrogenation catalyst was treated, and the specific method for removing the coked product included the following steps:

[0071] The solvent composed of tetrahydrofuran, ethylene glycol monomethyl ether, and methanol (85:10:5) was pressed into the reactor through the outlet at the bottom of the reactor and slowly submerged the catalyst. The reactor temperature was set at 50 °C and maintained for 24 hours, and the solution in the reactor was discharged from the bottom of the reactor to the recovery storage tank. After soaking the catalyst again with the mixed solvent using the same steps for 2 hours and draining it, tetrahydrofuran, methanol, and water were heated into gases through the DMO vaporizer and mixed with nitrogen, with the ratio of nitrogen being 74%, tetrahydrofuran being 15%, methanol being 10%, and water being 1.0%. At normal pressure and under the condition of 160 °C, at an airspeed of 500 h -1 The hydrogenation reactor was purged for 4 hours. Then, the reactor was gradually heated to 230 °C. At the same time, the ratio of nitrogen, tetrahydrofuran, and methanol was adjusted to 70%, 10%, and 20%. Keeping the airspeed unchanged, it was purged for 4 hours.

[0072] After removing the coke deposits according to the above method, the pressure drop of the reactor bed decreases, the reaction temperature drops, while the DMO conversion rate and EG selectivity increase, indicating that the activity of the catalyst is basically restored. After that, the system continues to operate for 60 days, and there is no obvious change in the catalyst activity and bed resistance, showing that this method has a good effect on removing the coke deposits of the oxalate hydrogenation catalyst and extending its service life.

[0073] Table 2

[0074]

Claims

1. A method for removing coke deposits from a dimethyl oxalate hydrogenation catalyst, characterized in that, it specifically includes the following steps: 1) The first stage: Using a mixed reagent composed of 70%-90% tetrahydrofuran, 5%-20% ethylene glycol monomethyl ether, and 5%-20% methanol by volume percentage as a solvent to immerse the catalyst, dissolving and discharging the coke deposits accumulated on the catalyst; 2) The second stage: Passing an inert atmosphere containing tetrahydrofuran, methanol, and water to purge the catalyst, carrying out an esterification reaction with methanol, and at the same time, carrying out a transesterification reaction with methanol under an aqueous medium; 3) The third stage: Continuing to purge the catalyst by passing an inert atmosphere containing tetrahydrofuran and methanol, carrying out an etherification reaction with methanol until there are no impurities purged out in the recycle gas, that is, the removal of coke deposits from the dimethyl oxalate hydrogenation catalyst is completed.

2. The method according to claim 1, characterized in that, in the step 1), the immersion temperature of the catalyst in the solvent is 30°C - 50°C, and the immersion time is 8 - 24 h.

3. The method according to claim 1, characterized in that, in the step 1), if the coke deposits in the discharged coke deposit solution are not completely dissolved, or the solution becomes viscous, secondary dissolution can be carried out according to the same steps.

4. The method according to claim 1, characterized in that, in the step 2), in the inert atmosphere containing tetrahydrofuran, methanol, and water, methanol is 10%-20% by volume percentage.

5. The method according to claim 4, characterized in that, in the inert atmosphere containing tetrahydrofuran, methanol, and water, tetrahydrofuran is 15%-30% by volume percentage, and water is 0.1%-1% by volume percentage.

6. The method according to claim 1, characterized in that, in the step 3), in the inert atmosphere containing tetrahydrofuran and methanol, methanol is 15%-30% by volume percentage.

7. The method according to claim 6, characterized in that, in the inert atmosphere containing tetrahydrofuran and methanol, tetrahydrofuran is 5%-15% by volume percentage.

8. The method according to claim 1, characterized in that, in the step 2), the purge temperature is 140°C - 160°C; in the step 3), the purge temperature is 210°C - 230°C.

9. The method according to claim 1, characterized in that, In the step 2) or 3), the purging process is as follows: the space velocity is 200 - 500 h -1 , and the time is 2 - 4 hours.

10. A reaction process for preparing ethylene glycol by hydrogenating dimethyl oxalate, characterized in that, during the reaction process, the state of the hydrogenation catalyst is monitored. When the coke deposits on the hydrogenation catalyst have not formed carbonized solids and the hydrogenation reactor has not been completely blocked, the method described in claim 1 is used for removal to achieve the recycled use of the hydrogenation catalyst.

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