A system and method for hydrogenating dimethyl oxalate to ethylene glycol

Abstract

The present invention belongs to the technical field of hydrogenation of dimethyl oxalate to ethylene glycol, and specifically relates to a system and method for hydrogenation of dimethyl oxalate to ethylene glycol. By providing two serially connected ethylene glycol synthesis reactors to form a primary reactor and a secondary reactor, after the primary reactor shares part of the load, the catalyst load on the upper layer of the secondary reactor is reduced, the severity of the reaction is decreased, the reaction temperature is lowered, the catalyst is not prone to coking and activity decline, ensuring the long-term operation of the secondary reactor; when the activity of the catalyst in the secondary reactor declines to the point where it cannot completely convert dimethyl oxalate, the secondary reactor is switched to the primary to act as the primary reactor, and the catalyst can continue to be used, extending the service life of the catalyst, making full use of the catalyst, thereby reducing the catalyst usage cost, and at the same time reducing the catalyst replacement frequency, ensuring the long-term operation of the ethylene glycol production unit.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogenation of dimethyl oxalate to ethylene glycol, and specifically relates to a system and method for hydrogenation of dimethyl oxalate to ethylene glycol. Background Art

[0002] Ethylene glycol, as a basic chemical raw material widely used in the polyester industry and industrial production fields, can be used to produce chemical products such as polyester fibers, lubricants, antifreeze agents, and nonionic surfactants. The technology of producing ethylene glycol from coal-based syngas is an important green and atom-economic ethylene glycol production technology. Compared with the traditional ethylene glycol production route, coal-based ethylene glycol production uses the rich domestic coal resources to replace the petroleum resources that need to be imported in large quantities for ethylene glycol production, which conforms to the current energy structure situation of "poor in oil, rich in coal, and scarce in gas" in China. This technology can not only reduce China's dependence on oil, but also enable the clean and efficient utilization of coal resources. Some domestic research institutions such as Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Tianjin University, East China University of Science and Technology, etc. have conducted in-depth research. Among them, the chemical reaction equations for the hydrogenation of dimethyl oxalate to ethylene glycol are CH3OCOCOOCH3 + 2H2 = CH3OCOCH2OH + CH3OH, and CH3OCOCH2OH + 2H2 = CH2OHCH2OH + CH3OH. The commonly used process route is the one-step hydrogenation method of oxalate to produce ethylene glycol. The catalysts used include the Cu-Cr catalyst of Fujian Institute of Research on the Structure of Matter. The results of the pilot test conducted under the conditions of 208 - 230 °C and 2.5 - 3.0 MPa show that the conversion rate of oxalate is 99.8%, the average selectivity of ethylene glycol is 95.3%, and the catalyst can operate for 1134 hours; the CuSi and CuAgSi series catalysts developed by Tianjin University. The tests conducted under the conditions of 240 °C, 1.0 MPa, and a hydrogen-to-ester molar ratio of 200:1 show that the conversion rate of oxalate is about 95%, and the yield of ethylene glycol is about 80%.

[0003] Although great research progress has been made in the hydrogenation of oxalate to ethylene glycol, there are still some problems in the large-scale industrial production of hydrogenation of dimethyl oxalate to ethylene glycol. The hydrogenation of dimethyl oxalate to ethylene glycol uses a fixed-bed reactor filled with a catalyst, with multiple units in parallel at the first stage. After mixing dimethyl oxalate and hydrogen, they enter from the top of the fixed-bed reactor. The catalytic hydrogenation reaction occurs in the upper part of the catalyst bed, resulting in a heavy load on the upper-layer catalyst of the fixed-bed reactor, intense reaction, high temperature, and thus easy coking of the upper-layer catalyst and rapid decline in activity. As some of the tubes become blocked by coking, the resistance of the tubes increases, and the gas flow rate distributed to each tube varies more. In the tubes with a large flow rate, the reaction is intense, and the catalyst decays faster. In severe cases, the catalyst in the tubes becomes deactivated, and dimethyl oxalate cannot be completely converted, leading to the forced shutdown of the production system to replace the catalyst. In the tubes with a small flow rate, the catalyst decays slowly, resulting in underutilization of the catalyst in the lower part of the bed. The service life of the entire reactor is short, the catalyst needs to be replaced frequently, and the production cost is high. Summary of the Invention

[0004] In order to overcome the defects of the prior art, the present invention provides a system and method for hydrogenating dimethyl oxalate to ethylene glycol. This invention avoids the defects of heavy load on the upper-layer catalyst of the first-stage fixed-bed reactor, intense reaction, high temperature, easy coking, and rapid decline in activity. At the same time, it can make full use of the activity of the catalyst in the lower layer of the fixed-bed, improve the utilization rate of the catalyst, and reduce the frequency of shutdowns.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] A system for hydrogenating dimethyl oxalate to ethylene glycol includes two or more ethylene glycol synthesis reactors and a number of control valves. Any two of the two or more ethylene glycol synthesis reactors are connected in series through valves and pipelines. The two ethylene glycol synthesis reactors connected in series form a first-stage reactor and a second-stage reactor, and the first-stage reactor and the second-stage reactor constitute a production process system. Catalysts are loaded in all of the two or more ethylene glycol synthesis reactors.

[0007] A method for hydrogenating dimethyl oxalate to ethylene glycol: After mixing dimethyl oxalate and hydrogen, they enter the first-stage reactor for a pre-reaction. In the first-stage reactor, part of the dimethyl oxalate is hydrogenated and converted into ethylene glycol. The material flowing out of the first-stage reactor enters the second-stage reactor, where dimethyl oxalate is completely converted into ethylene glycol and by-products.

[0008] Further, when the activity of the catalyst in the second-stage reactor drops to a level where dimethyl oxalate cannot be completely converted, by switching the valves, the second-stage reactor acts as the first-stage reactor, and after the first-stage reactor replaces the catalyst, it acts as the second-stage reactor.

[0009] Furthermore, a spare reactor is provided. When the activity of the catalyst in the secondary reactor drops to a level where it cannot completely convert all the dimethyl oxalate, the spare reactor replaces the secondary reactor by switching the valves, and the secondary reactor replaces the primary reactor to form a new series system. The primary reactor is removed from the production system for catalyst replacement, and the primary catalyst is kept in reserve after the replacement is completed.

[0010] Furthermore, the activity of the catalyst filled in the secondary reactor is higher than that of the catalyst in the primary reactor.

[0011] Furthermore, the catalyst is a Cu / SiO2 catalyst.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0013] 1. By providing a series of ethylene glycol synthesis reactors, the dimethyl oxalate and hydrogen pass through two series-connected ethylene glycol synthesis reactors successively. In the primary reactor, part of the dimethyl oxalate is hydrogenated and converted into ethylene glycol, reducing the concentrations of hydrogen and dimethyl oxalate entering the secondary reactor. As a result, the load on the catalyst in the secondary reactor is reduced, the load on the catalyst in the upper layer of the secondary reactor is alleviated, the severity of the reaction is reduced, the reaction temperature is decreased, the catalyst is not easily coked and its activity does not decline, avoiding the penetration of dimethyl oxalate through the catalyst bed layer and the entry of dimethyl oxalate into the distillation system to corrode the equipment, ensuring that all the dimethyl oxalate is converted and guaranteeing the long-term operation of the secondary reactor.

[0014] 2. When the activity of the catalyst in the secondary reactor declines to a level where it cannot completely convert the dimethyl oxalate, by switching the valves, the secondary reactor is switched to the primary position to act as the primary reactor, and the catalyst can continue to be used, extending the service life of the catalyst, making full use of the catalyst, thus reducing the procurement cost of the catalyst. At the same time, the frequency of catalyst replacement is also reduced, saving the time for catalyst replacement.

[0015] 3. The present invention also provides a spare reactor. Without shutting down the production system, the reactors can be switched, enabling the replacement of the catalyst without stopping the production, avoiding system shutdown and ensuring the continuous operation of the ethylene glycol production unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is the structural schematic diagram a of the present invention;

[0017] Figure 2 is the structural schematic diagram b of the present invention;

[0018] In the figure: 1 - Reactor a; 2 - Reactor b; 3 - Reactor c; 11 - Valve a; 12 - Valve b; 13 - Valve c; 14 - Valve d; 15 - Valve e; 16 - Valve f; 17 - Valve g; 18 - Valve h; 19 - Valve i; 20 - Valve j; 21 - Valve k; 22 - Valve m; 23 - Valve n; 24 - Valve o; 25 - Valve p; 26 - Valve q; 27 - Valve r; 28 - Valve s. Detailed implementation mode

[0019] Example 1

[0020] Refer to Figure 1 In order to avoid the phenomenon that only the upper-layer catalyst of the first-stage ethylene glycol synthesis reactor reacts violently, has a high temperature, is prone to coking, and is prone to activity decline, avoid the penetration of dimethyl oxalate through the catalyst bed, while increasing the service time of the catalyst, reducing production costs, reducing the frequency of shutdowns and reducing the frequency of catalyst replacement, and at the same time ensuring that all the dimethyl oxalate flowing out of the ethylene glycol synthesis device is hydrogenated and converted. The present invention provides a system for hydrogenating dimethyl oxalate to ethylene glycol, including two ethylene glycol synthesis reactors and several control valves. The two ethylene glycol synthesis reactors are respectively Reactor a1 and Reactor b2. Reactor a1 and Reactor b2 are connected in series through valves and pipelines. The two ethylene glycol synthesis reactors connected in series constitute a first-stage reactor and a second-stage reactor. The first-stage reactor and the second-stage reactor constitute a production process system. The valves include Valve a11, Valve b12, Valve c13, Valve d14, Valve e15, Valve f16, Valve g17, Valve h18; Catalysts are filled in both Reactor a1 and Reactor b2.

[0021] A method for hydrogenating dimethyl oxalate to ethylene glycol. Open Valve a11, Valve e15, Valve c13, Valve h18, and keep Valve b12, Valve d14, Valve g17, Valve f16 closed. Reactor a1 is the first-stage reactor, and Reactor b2 is the second-stage reactor. After dimethyl oxalate and hydrogen are mixed, they enter Reactor a1 for pre-reaction. In Reactor a1, part of the dimethyl oxalate is hydrogenated and converted into ethylene glycol. The material flowing out of Reactor a1 enters Reactor b2. In Reactor b2, the dimethyl oxalate is completely converted into ethylene glycol and by-products. The main by-products are ethanol, methyl glycolate, 1,2-butanediol, and 1,2-propanediol. The reaction temperatures of Reactor a1 and Reactor b2 are 180°C to 195°C.

[0022] The catalysts filled in both Reactor a1 and Reactor b2 are Cu / SiO2 catalysts, and the activity of the catalyst filled in Reactor b2 is higher than that of the catalyst in Reactor a1.

[0023] When the activity of the catalyst in reactor b2 drops to the point where it cannot completely convert dimethyl oxalate, close valves a11, e15, c13, and h18, and open valves b12, d14, g17, and f16. Make reactor b2 serve as the primary reactor, and after replacing the catalyst in reactor a1, make it serve as the secondary reactor; after dimethyl oxalate and hydrogen are mixed, they enter reactor b2 for pre-reaction. In reactor b2, part of the dimethyl oxalate is hydrogenated and converted into ethylene glycol. The material flowing out of reactor b2 enters reactor a1, where dimethyl oxalate is completely converted into ethylene glycol and by-products. The main by-products are ethanol, methyl glycolate, 1,2-butanediol, and 1,2-propanediol. The reaction temperatures of reactor b2 and reactor a1 are 180°C to 195°C.

[0024] Example 2

[0025] Refer to Figure 2 , in order to avoid the phenomenon that only the upper-layer catalyst of the primary ethylene glycol synthesis reactor reacts violently, has a high temperature, is prone to coking, and is prone to activity decline, avoid dimethyl oxalate from penetrating the catalyst bed, improve the service time of the catalyst, reduce production costs, reduce the frequency of shutdowns and the frequency of catalyst replacement, and ensure that all the dimethyl oxalate flowing out of the ethylene glycol synthesis device is hydrogenated and converted. The present invention provides a system for hydrogenating dimethyl oxalate to ethylene glycol, which includes three ethylene glycol synthesis reactors and several control valves. The valves include valves a11, b12, c13, d14, e15, f16, g17, h18, i19, j20, k21, m22, n23, o24, p25, q26, r27, s28; the three ethylene glycol synthesis reactors are reactor a1, reactor b2, and reactor c3 respectively. By regulating the valves, reactor a1 and reactor b2 are connected in series, and reactor c3 is in standby. The series-connected reactor a1 and reactor b2 constitute a primary reactor and a secondary reactor, and the primary reactor and the secondary reactor constitute a production process system. Catalysts are loaded in all three ethylene glycol synthesis reactors.

[0026] A method for hydrogenating dimethyl oxalate to ethylene glycol. Open valves b12, k21, d14, and r27, and keep valves a11, c13, e15, f16, g17, h18, i19, j20, q26, m22, n23, o24, p25, and s28 closed. Reactor a1 and reactor b2 are connected in series. Reactor a1 is a primary reactor, and reactor b2 is a secondary reactor. The catalysts filled in reactors a1 and b2 are Cu / SiO2 catalysts, and the activity of the catalyst filled in reactor b2 is higher than that of the catalyst in ethylene glycol synthesis reactor a1.

[0027] After mixing dimethyl oxalate and hydrogen, they enter reactor a1 for pre-reaction. In reactor a1, part of the dimethyl oxalate is hydrogenated and converted into ethylene glycol. The material flowing out of reactor a1 enters reactor b2, and in reactor b2, the dimethyl oxalate is completely converted into ethylene glycol and by-products. The main by-products are ethanol, methyl glycolate, 1,2-butanediol, and 1,2-propanediol. The reaction temperatures of reactor b2 and reactor a1 are 180°C to 195°C.

[0028] When the activity of the catalyst in reactor b2 drops to the point where dimethyl oxalate cannot be completely converted, by switching the valves, open valves e15, n23, g17, and s28, and close valves a11, b12, c13, d14, f16, h18, i19, j20, k21, m22, o24, p25, q26, and r27, so that reactor b2 is connected in series with reactor c3. Reactor b2 serves as the primary reactor, and reactor c3 serves as the secondary reactor to form a new series system. Reactor a1 is removed from the production system for catalyst replacement. After the catalyst replacement of reactor a1 is completed, it is reserved. After mixing dimethyl oxalate and hydrogen, they enter reactor b2 for pre-reaction. In reactor b2, part of the dimethyl oxalate is hydrogenated and converted into ethylene glycol. The material flowing out of reactor b2 enters reactor c3, and in reactor c3, the dimethyl oxalate is completely converted into ethylene glycol and by-products. The main by-products are ethanol, methyl glycolate, 1,2-butanediol, and 1,2-propanediol. The reaction temperatures of reactor b2 and reactor c3 are 180°C to 195°C.

[0029] When the activity of the catalyst in reactor C3 drops to a level where not all dimethyl oxalate can be converted, by switching the valves, valves H18, P25, A11, and Q26 are opened, and valves B12, C13, D14, E15, F16, G17, I19, J20, K21, M22, N23, O24, R27, and S28 are closed, so that reactor C3 is connected in series with reactor A1. Reactor C3 serves as the primary reactor and reactor A1 serves as the secondary reactor, forming a new series system. Reactor B2 is removed from the production system for catalyst replacement and is kept in reserve after the catalyst replacement is completed. After dimethyl oxalate and hydrogen are mixed, they enter reactor C3 for a pre-reaction. In reactor C3, part of the dimethyl oxalate is hydrogenated and converted into ethylene glycol. The material flowing out of reactor C3 enters reactor A1, where all the dimethyl oxalate is converted into ethylene glycol and by-products. The main by-products are ethanol, methyl glycolate, 1,2-butanediol, and 1,2-propanediol. After dimethyl oxalate and hydrogen are mixed, they enter reactor C3 for a pre-reaction. In reactor C3, part of the dimethyl oxalate is hydrogenated and converted into ethylene glycol. The material flowing out of reactor C3 enters reactor A1, where all the dimethyl oxalate is converted into ethylene glycol and by-products. The main by-products are ethanol, methyl glycolate, 1,2-butanediol, and 1,2-propanediol. The reaction temperature of reactor C3 and reactor A1 is 180°C to 195°C.

[0030] The working principle of the present invention is as follows: The present invention connects ethylene glycol synthesis reactors in series, and a new catalyst is loaded into the secondary reactor. The new catalyst has strong activity, ensuring that all the dimethyl oxalate flowing out of the secondary reactor is converted. When the activity of the catalyst in the secondary reactor decreases with the increase of the usage time and cannot convert all the dimethyl oxalate into ethylene glycol and by-products, by switching the valves, the secondary reactor acts as the primary reactor. In the primary reactor, the catalyst continues to be used. Since the activity of the catalyst in the primary reactor is relatively weaker than that in the secondary reactor, part of the dimethyl oxalate entering the primary reactor undergoes a hydrogenation reaction to form ethylene glycol. Since part of the dimethyl oxalate undergoes a hydrogenation reaction in the primary reactor, the concentration of dimethyl oxalate entering the secondary reactor decreases, reducing the catalyst load on the upper layer of the secondary reactor, lowering the intensity of the reaction, reducing the reaction temperature, making the catalyst less likely to coke and less likely to experience activity decline, thus ensuring the long-term operation of the secondary reactor. By connecting the ethylene glycol synthesis reactors in series, the overall usage time of the catalyst is extended, the catalyst is fully utilized, the cost of catalyst use is reduced, and the frequency of catalyst replacement is reduced. By setting up a standby ethylene glycol synthesis reactor, the production system can also operate continuously, avoiding shutdown for catalyst replacement.

[0031] As described in the above specific embodiments, they are only examples of the content of the present invention. Any modifications and changes made by those familiar with the present invention to this creation fall within the scope of the patent of the present invention, not limited to only the embodiments described.

Claims

1. A method for preparing ethylene glycol by hydrogenating dimethyl oxalate, characterized in that: A system for producing ethylene glycol by hydrogenating dimethyl oxalate, the system for producing ethylene glycol by hydrogenating dimethyl oxalate includes two or more ethylene glycol synthesis reactors and a number of control valves. Any two of the two or more ethylene glycol synthesis reactors are connected in series through valves and pipelines. The two ethylene glycol synthesis reactors connected in series constitute a primary reactor and a secondary reactor. The primary reactor and the secondary reactor constitute a production process system. Catalysts are filled in all of the two or more ethylene glycol synthesis reactors; the system for producing ethylene glycol by hydrogenating dimethyl oxalate is used to implement the method for producing ethylene glycol by hydrogenating dimethyl oxalate. The method for producing ethylene glycol by hydrogenating dimethyl oxalate includes that dimethyl oxalate and hydrogen are mixed and then enter the primary reactor for pre-reaction. In the primary reactor, part of the dimethyl oxalate is hydrogenated and converted into ethylene glycol. The material flowing out of the primary reactor enters the secondary reactor. In the secondary reactor, the dimethyl oxalate is completely converted into ethylene glycol and by-products; the activity of the catalyst filled in the secondary reactor is higher than that of the catalyst in the primary reactor; When the activity of the catalyst in the secondary reactor drops to a level where it cannot completely convert dimethyl oxalate, by switching the valves, the secondary reactor acts as the primary reactor, and after the catalyst in the primary reactor is replaced, it acts as the secondary reactor.

2. The method for preparing ethylene glycol by hydrogenating dimethyl oxalate according to claim 1, characterized in that: A spare reactor is also provided. When the activity of the catalyst in the secondary reactor drops to a level where it cannot completely convert dimethyl oxalate, by switching the valves, the spare reactor replaces the secondary reactor, and the secondary reactor replaces the primary reactor to form a new series system. The primary reactor is removed from the production system for catalyst replacement, and after the catalyst replacement of the primary reactor is completed, it is reserved.

3. A method for preparing ethylene glycol by hydrogenating dimethyl oxalate according to claim 1 or 2, characterized in that: The catalyst is a Cu / SiO2 catalyst.

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