A system and method for producing methanol by CO2 hydrogenation

Abstract

The present invention discloses a system and method for producing methanol by hydrogenation of CO2, and relates to the field of chemical technology. The present invention specifically includes a first reactor, a second reactor, a first cooler and a first gas-liquid separator, the output end of the first reactor is connected to the first cooler, the output end of the first cooler is connected to the first gas-liquid separator, the gas phase outlet of the first gas-liquid separator is connected to the second reactor, a high-temperature catalyst Zn-Zr-O is provided in the first reactor, a low-temperature catalyst Cu-Zn / Al2O3 is provided in the second reactor, and the reaction temperature in the first reactor is higher than the reaction temperature in the second reactor. The present invention is provided with a first reactor to first convert a portion of the raw materials into methanol, so that the amount of water produced in the second reactor is reduced, thereby reducing the effect of the hydrothermal reaction on the activity of the low-temperature catalyst Cu-Zn / Al2O3 in the second reactor, improving the service life of the low-temperature catalyst Cu-Zn / Al2O3, and reducing production costs.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical industry, and specifically provides a system and method for producing methanol by hydrogenating CO2. Background Art

[0002] In the existing methanol production process, the technical route of using CO2 and hydrogen to produce methanol is constantly developing. The use of CO2 and hydrogen to produce methanol can not only consume greenhouse gases and reduce greenhouse gas emissions, but also realize the carbon-hydrogen cycle and promote the development of new energy. When CO2 and hydrogen are used to produce methanol, it is necessary to place CO2 and hydrogen in a high-temperature and high-pressure environment, and add a catalyst to react CO2 and hydrogen to form methanol. Copper-based and Zn-Zr solid solutions are commonly used as catalysts in the existing technology. The active reaction temperature of copper-based catalysts is low and the equilibrium conversion rate is high, while the Zn-Zr solid solution catalyst has good hydrothermal stability. Therefore, they have become the main research directions at present.

[0003] However, simultaneously improving the service life and equilibrium conversion rate of the catalyst has become an important issue that needs to be urgently addressed in current industrialization. Summary of the Invention

[0004] The present invention provides a system and method for producing methanol by CO2 hydrogenation, which are used to solve the problems of CO2 conversion rate and long-term stability of catalyst in methanol production.

[0005] The technical solutions of the present invention are as follows:

[0006] A CO2 hydrogenation system for producing methanol includes a first reactor, a second reactor, a first cooler, and a first gas-liquid separator. The output end of the first reactor is connected to the first cooler, the output end of the first cooler is connected to the first gas-liquid separator, the gas phase outlet of the first gas-liquid separator is connected to the second reactor, a high-temperature catalyst Zn-Zr-O is provided in the first reactor, a low-temperature catalyst Cu-Zn / Al2O3 is provided in the second reactor, and the reaction temperature in the first reactor is higher than the reaction temperature in the second reactor.

[0007] In this scheme, the raw materials, CO2, and hydrogen, first react in the first reactor, which is equipped with a high-temperature Zn-Zr-O catalyst. The high-temperature Zn-Zr-O catalyst has a higher reaction temperature than the low-temperature Cu-Zn / Al2O3 catalyst and is more stable. Under the catalytic action of the high-temperature Zn-Zr-O catalyst, CO2 and hydrogen react with high efficiency. The gas discharged from the first reactor is cooled to liquefy methanol and water, which are then separated in the first gas-liquid separator. The remaining gas is then fed into the second reactor. Since the raw materials, CO2 and hydrogen, have already partially reacted in the first reactor, and the generated water and methanol have been discharged, the CO2 and hydrogen content entering the second reactor is reduced. Under the catalytic action of the low-temperature Cu-Zn / Al2O3 catalyst, the unreacted raw material gas reacts at a lower temperature. The reaction temperature in the second reactor is low, which allows the equilibrium conversion rate to be improved. The low-temperature catalyst Cu-Zn / Al2O3 in the second reactor ensures that the equilibrium conversion rate is maintained at a high level. Because the CO2 and hydrogen content that need to react in the second reactor is reduced, the amount of water produced in the second reactor is low, and the impact of the hydrothermal reaction on the low-temperature catalyst Cu-Zn / Al2O3 is also reduced. The present application sets up a first reactor and a second reactor, and uses different catalysts to catalyze the reaction of the raw gas, reducing the water production in the second reactor, thereby extending the service life of the low-temperature catalyst Cu-Zn / Al2O3.

[0008] A second cooler and a second gas-liquid separator are provided downstream of the second reactor. The output end of the second reactor is communicated with the second cooler, and the second cooler is communicated with the second gas-liquid separator.

[0009] In this solution, the gas discharged from the second reactor is cooled by the second cooler, so that the methanol can be liquefied, and then the methanol can be separated by the second gas-liquid separator.

[0010] The conversion rate of the first reactor is higher than 15%, and the total conversion rate of the first reactor (1) and the second reactor (5) is higher than 25%.

[0011] In this solution, since the conversion rate in the first reactor is higher than 15%, the amount of raw gas input into the second reactor can be greatly reduced, the amount of water generated in the second reactor can be reduced, and the service life of the catalyst can be extended.

[0012] It also includes an alcohol washing tower, and the gas phase outlet of the second gas-liquid separator is connected to the alcohol washing tower.

[0013] In this solution, an alcohol scrubber separates the alcohols from the gas, preventing them from being released into the environment. The gas treated by the alcohol scrubber contains unreacted hydrogen and may also contain impurities such as CO generated during the reaction. Therefore, the discharged gas can be released as fuel, avoiding the waste of raw materials.

[0014] The first reactor and the second reactor are respectively provided with valves at their input ends, a cold shock line and a first temperature sensor are provided in the first reactor, and a cold shock line and a second temperature sensor are provided in the second reactor. The first reactor also includes a controller, and the valve, the first temperature sensor, the second temperature sensor and the cold shock line are electrically connected to the controller. The controller controls the valve at the input end of the first reactor and the cold shock line in the first reactor according to the first temperature sensor, and controls the valve at the input end of the second reactor and the cold shock line in the second reactor according to the second temperature sensor.

[0015] In this solution, valves are installed at the inputs of the first and second reactors. If the temperature in the first or second reactor rises rapidly, the valves can be closed to reduce the input of raw materials, thereby reducing the heat generated by the reaction and achieving the purpose of cooling. If the temperature in the first or second reactor rises slowly, the temperature in the first and second reactors can be lowered through a cold shock line to achieve temperature control.

[0016] The reaction temperature in the first reactor is 300°C-360°C, and the reaction temperature in the second reactor is 200°C-250°C.

[0017] In this scheme, the reaction temperature in the first reactor is high, and the reaction can be rapid under the action of the high-temperature catalyst Zn-Zr-O, thereby improving the reaction efficiency; while the second reactor can make the unreacted raw materials react at a lower temperature under the catalytic action of the low-temperature catalyst Cu-Zn / Al2O3, thereby improving the conversion rate of the raw materials.

[0018] The cooling temperature of the first cooler and the second cooler is lower than the boiling point of methanol.

[0019] In this solution, both the first cooler and the second cooler are used to liquefy methanol, thereby facilitating the separation of methanol.

[0020] The present invention also provides a method for producing methanol by hydrogenating CO2, which can be applied to the above system.

[0021] The method comprises the following steps:

[0022] S1, using a high-temperature catalyst Zn-Zr-O to catalyze the reaction of CO2 and hydrogen at a first temperature environment to obtain a first mixed gas containing methanol;

[0023] S2, cooling the first mixed gas to liquefy the methanol in the first mixed gas, obtaining a liquefied methanol solution and exhaust gas after the first tower;

[0024] S3, using a low-temperature catalyst Cu-Zn / Al2O3 to catalyze the reaction of CO2 and hydrogen in the first exhaust gas at a second temperature to obtain a second mixed gas containing methanol, wherein the first temperature is higher than the second temperature;

[0025] S4. Cooling the second mixed gas to liquefy the methanol in the second mixed gas, thereby obtaining a liquefied methanol solution and a second exhaust gas from the gas tower.

[0026] In this solution, the raw gas is catalyzed twice using a high-temperature catalyst, Zn-Zr-O, and a low-temperature catalyst, Cu-Zn / Al2O3, respectively, so that the raw gas reacts under different catalysts and temperatures. Since the CO2 and hydrogen content of the gas after the first exhaust tower catalyzed by the low-temperature catalyst, Cu-Zn / Al2O3, is much lower than that in step S1, the raw gas content in the gas after the first exhaust tower is low, and the amount of water produced during the reaction is small, which has a smaller impact on the activity of the low-temperature catalyst, Cu-Zn / Al2O3, thereby ensuring the service life of the low-temperature catalyst, Cu-Zn / Al2O3. The low-temperature catalyst, Cu-Zn / Al2O3, is a copper-based catalyst. The second temperature is lower than the first temperature, and the reaction is an exothermic reaction with a higher equilibrium conversion rate. Step S3 ensures the conversion rate of the raw gas. Therefore, the combined action of the two catalysis steps can improve the conversion rate of the raw gas while ensuring the reaction efficiency. At the same time, the reduction of the second-stage production load can reduce the influence of the hydrothermal reaction on the low-temperature catalyst Cu-Zn / Al2O3 and extend the service life of the low-temperature catalyst Cu-Zn / Al2O3.

[0027] The carbon-hydrogen ratio of CO2 and hydrogen input in step S1 is 1:2.8~3.

[0028] The first temperature is 300°C-360°C, and the second temperature is 200°C-250°C.

[0029] In this scheme, the high-temperature catalyst Zn-Zr-O can maintain a reaction rate much higher than that of the low-temperature catalyst Cu-Zn / Al2O3 in the range of 300℃-360℃, while Cu-Zn / Al2O3 can maintain a conversion rate much higher than that of the high-temperature catalyst in the range of 200℃-250℃.

[0030] Beneficial effects of the present invention:

[0031] The present invention utilizes a first reactor to convert a portion of the feed gas into methanol, reducing the load on the second reactor. This reduces the impact of narrow hydrothermal conditions on the activity of the low-temperature Cu-Zn / Al2O3 catalyst in the second reactor, thereby increasing the service life of the catalyst and lowering production costs. Furthermore, the low reaction temperature in the second reactor ensures the conversion rate of the feed gas, thereby increasing the single-pass conversion rate of the entire system and saving cycle power. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 This is a system diagram of Example 1.

[0034] In the above drawings, the corresponding reference numerals are as follows:

[0035] 1. First reactor; 2. First cooler; 3. First gas-liquid separator; 4. Heat exchanger; 5. Second reactor; 6. Second cooler; 7. Second gas-liquid separator; 8. Alcohol wash tower. DETAILED DESCRIPTION

[0036] In conjunction with the accompanying drawings, the technical solution of the present invention is clearly and completely explained through the specific implementation methods of the embodiments of the present invention. Example

[0037] like Figure 1As shown, this embodiment 1 provides a CO hydrogenation methanol production system, comprising a first reactor 1, a first cooler 2, a first gas-liquid separator 3, a second reactor 5, a second cooler 6, and a second gas-liquid separator 7. The first reactor 1 is provided with an input and an output. The input is used to input raw materials, which are CO and hydrogen. The output of the first reactor 1 is connected to the first cooler 2. The cooling temperature of the first cooler 2 is lower than the boiling point of methanol, which is used to liquefy the methanol. The output of the first cooler 2 is connected to the first gas-liquid separator 3. The first gas-liquid separator 3 is provided with a gas phase outlet and a liquid phase outlet. The gas-liquid separator is used to separate the methanol solution, which is discharged through the liquid phase outlet. The gas phase outlet of the first gas-liquid separator 3 is connected to the second reactor 5. The output of the second reactor 5 is connected to the second cooling zone. The cooling temperature of the second cooler 6 is lower than the boiling point of methanol. The second cooler 6 is connected to the second gas-liquid separator 7, which is also used to separate the methanol solution. The first reactor 1 is equipped with a high-temperature Zn-Zr-O catalyst, and the reaction temperature within the first reactor 1 is 300°C-360°C. The second reactor 5 is equipped with a low-temperature Cu-Zn / AlO catalyst, and the reaction temperature within the second reactor 5 is 200°C-250°C. The conversion rate of the raw material in the first reactor 1 is 15%, and the total conversion rate of the first and second reactors 5 is 25%. The combination of the first and second reactors 5 can increase the conversion rate of the raw material to 25%, maintaining a high conversion rate while ensuring the service life of the low-temperature catalyst in the second reactor 5.

[0038] The pressure inside the first reactor 1 and the second reactor 5 is higher than atmospheric pressure and is 5.0-9 MPa.

[0039] A buffer tank 8 is provided between the first gas-liquid separator 3 and the second reactor 5 . The buffer tank 8 is used to contain gas and plays a buffering role to prevent the output fluctuation of the first reactor 1 from affecting the second reactor 5 .

[0040] A heat exchanger 4 is provided between the first reactor 1 and the first cooler 2, and a heat exchanger 4 is also provided between the second reactor 5 and the second cooler 6. The input end of the first reactor 1 is connected to the heat exchanger 4, and the raw materials are input into the first reactor 1 after heat exchange in the heat exchanger 4. The output end of the first reactor 1 is also connected to the heat exchanger 4, and the mixture discharged from the first reactor 1 is heat exchanged before entering the first cooler 2. During this process, the heat of the mixture output from the first reactor 1 is exchanged with the raw materials, so that the raw materials are preheated before being input into the first reactor 1. In other words, during this process, the heat of the mixture output from the first reactor 1 is recovered by the heat exchanger 4, making full use of energy.

[0041] A valve is installed at the input end of the first reactor 1, and a temperature sensor and a cold shock line are installed within the first reactor 1. The valve is used to control the connection or disconnection of the input end of the first reactor 1. When the valve is closed, raw materials cannot enter the first reactor 1. As the reaction progresses, the raw materials in the first reactor 1 gradually decrease, the reaction intensity decreases, and the heat generated in the first reactor 1 decreases accordingly. When the valve is open, raw materials can enter the first reactor 1. By controlling the opening or closing of the valve, the flow of materials into and out of the first reactor 1 is controlled, as well as the amount of materials flowing in and out, thereby achieving the temperature within the first reactor 1. The cold shock line can also cool the first reactor 1 and control the temperature within the first reactor 1. The valve and cold shock line can be controlled by a controller. When a controller is used to control the valve and cold shock line, a first temperature sensor is installed within the first reactor 1. The first temperature sensor, valve, and cold shock line are electrically connected to the controller. The controller controls the valve and cold shock line based on the temperature signal from the first temperature sensor. For example, when the temperature within the first reactor 1 rises to a certain level, the cold shock line is controlled to cool down, thereby lowering the temperature within the first reactor 1. If the cold shock line cannot achieve the cooling effect and the temperature continues to rise to another level, the controller closes the valve. In the absence of raw material replenishment, the temperature in the first reactor 1 will continue to drop. When the temperature drops to a certain value, the controller reopens the valve to allow the raw materials to enter the first reactor 1 for reaction.

[0042] Similarly, a valve is also provided at the input end of the second reactor 5, and a cold shock line is also provided within the second reactor 5. A second temperature sensor is also provided within the second reactor 5. The second temperature sensor is electrically connected to the controller, which controls the valve at the input end of the second reactor 5 and the cold shock line within the second reactor 5.

[0043] The controller can be a PLC, a single chip microcomputer or a PC.

[0044] The valve may be a stop valve.

[0045] The valve may also be a throttle valve, which reduces the input speed of the raw materials, reduces the reaction intensity in the first reactor 1 or the second reactor 5, reduces the heat generation in the first reactor 1 or the second reactor 5, and achieves the purpose of controlling the temperature.

[0046] It should be noted that although the reaction of the raw materials in the first reactor 1 and the second reactor 5 is exothermic, heating elements can still be installed in the first reactor 1 and the second reactor 5, and the controller is connected to the heating elements. When the life of the catalyst in the first reactor 1 and the second reactor 5 is significantly reduced, the heating elements can be used to increase the temperature to maintain the reaction temperature in the first reactor 1 and the second reactor 5.

[0047] The second gas-liquid separator 7 is provided with a gas phase outlet and a liquid phase outlet for separating the methanol solution. The methanol solution is discharged from the liquid phase outlet of the second gas-liquid separator 7, while the gas phase outlet of the second gas-liquid separator 7 is used to discharge the remaining gas. The system is also provided with an alcohol scrubber 8, and the gas phase outlet of the second gas-liquid separator 7 is connected to the alcohol scrubber 8. The alcohol scrubber 8 can separate the residual alcohol in the exhaust gas from the gas. The separated gas includes unreacted hydrogen, so the separated gas can be discharged as fuel gas for other equipment. Example

[0048] This second embodiment provides a method for producing methanol by hydrogenating CO2, which can be applied to the system described in the first embodiment.

[0049] The method of the second embodiment includes the following steps:

[0050] S1. Using a high-temperature catalyst Zn-Zr-O to catalyze the reaction of CO2 and hydrogen at a first temperature, wherein the carbon-hydrogen ratio of CO2 to hydrogen is 3-4, to obtain a first mixed gas containing methanol; the first temperature is 300°C-360°C, and the high-temperature catalyst Zn-Zr-O can cause the CO2 and hydrogen to react at a high speed under the first temperature;

[0051] S2. Cooling the first mixed gas to liquefy the methanol in the first mixed gas to obtain a liquefied methanol solution and a first exhaust gas; the first exhaust gas contains not only unreacted CO2 and hydrogen but also impurity gases such as CO generated during the reaction. Therefore, the content of CO2 and hydrogen in the first exhaust gas is relatively low.

[0052] S3. Using a low-temperature catalyst Cu-Zn / Al2O3 to catalyze the reaction of CO2 and hydrogen in the first exhaust gas under a second temperature environment to obtain a second mixed gas containing methanol, wherein the first temperature is higher than the second temperature; the second temperature is 200°C-250°C, and the low-temperature catalyst Cu-Zn / Al2O3 can maintain a high conversion rate of CO2 and hydrogen under the second temperature environment; at the same time, step S1 consumes a large amount of CO2 and hydrogen. At this time, using the low-temperature catalyst Cu-Zn / Al2O3 to catalyze the reaction of CO2 and hydrogen in the first exhaust gas under the second temperature environment, a small amount of water is generated during the reaction process, which can reduce the effect of the hydrothermal reaction on the activity of the low-temperature catalyst Cu-Zn / Al2O3, extend the service life of the low-temperature catalyst Cu-Zn / Al2O3, and reduce the production cost of methanol;

[0053] S4, cooling the second mixed gas to liquefy the methanol in the second mixed gas to obtain a liquefied methanol solution and a second exhaust gas. The second exhaust gas can be treated with an alcohol washing tower to wash away the alcohols in the second exhaust gas, and then the remaining gas can be released as fuel gas for other equipment.

[0054] By making CO2 and hydrogen react quickly in step S1 and then converting CO2 and hydrogen in the residual gas in step S3, it is possible to ensure high-speed reaction while ensuring conversion rate, thereby improving methanol production efficiency without increasing costs.

[0055] It should be noted that, in the reaction environment of CO2 and hydrogen, the reaction rate when the high-temperature Zn-Zr-O catalyst is catalyzed in the first temperature environment is greater than the reaction rate when the low-temperature Cu-Zn / Al2O3 catalyst is catalyzed in the second temperature environment. Furthermore, the conversion rate when the high-temperature Zn-Zr-O catalyst is catalyzed in the first temperature environment is lower than the conversion rate when the low-temperature Cu-Zn / Al2O3 catalyst is catalyzed in the second temperature environment.

Claims

1. A CO2 hydrogenation system for producing methanol, characterized in that: The invention comprises a first reactor (1), a second reactor (5), a first cooler (2) and a first gas-liquid separator (3), wherein the output end of the first reactor (1) is communicated with the first cooler (2), the output end of the first cooler (2) is communicated with the first gas-liquid separator (3), the gas phase outlet of the first gas-liquid separator (3) is communicated with the second reactor (5), a high-temperature catalyst Zn-Zr-O is provided in the first reactor (1), a low-temperature catalyst Cu-Zn / Al2O3 is provided in the second reactor (5), the reaction temperature in the first reactor (1) is higher than the reaction temperature in the second reactor (5), the equilibrium conversion rate of the first reactor (1) is higher than 15%, the amount of raw gas input into the second reactor (5) is reduced, the amount of water generated in the second reactor (5) is reduced, and the service life of the catalyst is extended, the reaction temperature in the first reactor (1) is 300°C-360°C, and the reaction temperature in the second reactor (5) is 200°C-250°C.

2. A CO2 hydrogenation methanol production system according to claim 1, characterized in that: A second cooler (6) and a second gas-liquid separator (7) are provided downstream of the second reactor (5); the output end of the second reactor (5) is communicated with the second cooler (6), and the second cooler (6) is communicated with the second gas-liquid separator (7).

3. A CO2 hydrogenation methanol production system according to claim 1, characterized in that: The total conversion rate of the first reactor (1) and the second reactor (5) is higher than 25%.

4. A CO2 hydrogenation methanol production system according to claim 2, characterized in that: It also includes an alcohol washing tower, and the gas phase outlet of the second gas-liquid separator is connected to the alcohol washing tower.

5. A CO2 hydrogenation methanol production system according to claim 1, characterized in that: The input ends of the first reactor (1) and the second reactor (5) are respectively provided with valves, a cold shock line and a first temperature sensor are provided in the first reactor (1), and a cold shock line and a second temperature sensor are provided in the second reactor (5), and a controller is also included. The valve, the first temperature sensor, the second temperature sensor and the cold shock line are electrically connected to the controller. The controller controls the valve at the input end of the first reactor (1) and the cold shock line in the first reactor (1) according to the first temperature sensor, and controls the valve at the input end of the second reactor (5) and the cold shock line in the second reactor (5) according to the second temperature sensor.

6. A system and method for producing methanol by CO2 hydrogenation according to claim 2, characterized in that: The cooling temperature of the first cooler (2) and the second cooler (6) is lower than the boiling point of methanol.

7. A method for producing methanol by hydrogenating CO2, characterized in that: The system according to any one of claims 1 to 6 comprises the following steps: S1, using a high-temperature catalyst Zn-Zr-O to catalyze the reaction of CO2 and hydrogen at a first temperature environment to obtain a first mixed gas containing methanol; S2. Cooling the first mixed gas to liquefy the methanol in the first mixed gas to obtain a liquefied methanol solution and a first exhaust gas; S3, using a low-temperature catalyst Cu-Zn / Al2O3 to catalyze the reaction of CO2 and hydrogen in the first exhaust gas at a second temperature to obtain a second mixed gas containing methanol, wherein the first temperature is higher than the second temperature; S4. Cooling the second mixed gas to liquefy the methanol in the second mixed gas to obtain a liquefied methanol solution and a second exhaust gas.

8. The method for producing methanol by CO2 hydrogenation according to claim 7, characterized in that: The carbon-hydrogen ratio of CO2 and hydrogen input in step S1 is 1:2.8~3.

2.

9. The method for producing methanol by hydrogenating CO2 according to claim 7, characterized in that: The first temperature is 300°C-360°C, and the second temperature is 200°C-250°C.

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