Device and method for improving conversion of carbon dioxide to methanol

Abstract

The present application relates to a kind of device and method for improving the conversion rate of carbon dioxide methanol conversion, comprising first reactor, second reactor first gas gas heat exchanger, first cooler, first separator, second gas gas heat exchanger, second cooler, second separator.The present application uses two-stage reactor series process, byproduct different specification steam, the first reactor outlet increases cooling and liquid separation device, reduce the alcohol partial pressure and water partial pressure of second reactor inlet, it is favorable to improve the methanol conversion rate of second reactor, carbon dioxide and hydrogen are reacted in stages and added to interstage liquid separation device, it is favorable to maximize the conversion rate of the whole device, the unreacted gas of reactor is separated and recycled into synthesis reactor, it is useful to improve the total carbon conversion rate of carbon dioxide, fresh synthesis gas is introduced into second reactor by bypass, when the activity of first reactor catalyst is reduced in the late stage of reaction, the reaction is moved to second reactor, so as to ensure the conversion rate and yield of the whole device.

Description

Technical Field

[0001] This invention relates to the field of chemical production technology, specifically to an apparatus and method for improving the conversion rate of carbon dioxide to methanol. Background Technology

[0002] Carbon dioxide is a common greenhouse gas. In my country's industrial sector, especially in industries that rely on coal resources, a large amount of CO2 is produced every year.

[0003] In 2005, Nobel laureate in Chemistry George Andrew Euler proposed the concept of a "methanol economy," which he sees as a potential solution to energy problems after the oil and gas era. He argued that using renewable energy to produce hydrogen, and then synthesizing methanol from carbon dioxide, allows methanol to be used directly as fuel, or synthesized into fuels or chemicals through processes such as methanol-to-gasoline (MTG), methanol-to-aromatics (MTA), methanol-to-olefins (MTO), and methanol-to-propylene (MTP). He considered this a promising technology.

[0004] Currently, numerous research institutes and universities in China are developing CO2-to-methanol catalysts and technologies, which have reached a mature stage and are playing a positive role in promoting the national goals of carbon peaking and carbon neutrality. Compared to methanol production from carbon monoxide, methanol production from carbon dioxide mainly relies on the use of catalysts and the control of reaction temperature.

[0005] Existing catalyst preparation technologies can already meet the industrial requirements for methanol production from carbon dioxide. For example, patent application CN110975938A discloses a catalyst and its preparation method for the hydrogenation of carbon dioxide to methanol. It uses a framework-modified metal-organic framework material MIL-101(Cr)-NH2 as a support, utilizing the shape-selective properties of the pore structure of MIL-101(Cr) to improve methanol selectivity. Simultaneously, MIL-101(Cr) has a high specific surface area and a high adsorption capacity for CO2, effectively improving the catalytic selectivity for CO2. Chinese invention patent CN110833843B discloses a catalyst for the hydrogenation of carbon dioxide to methanol, using molybdenum disulfide as the main component. This catalyst is characterized by low cost, simple operation, high carbon dioxide conversion rate, high methanol selectivity in the product, and good stability.

[0006] Patent application CN105622344A discloses a carbon dioxide-to-methanol process using a single-stage reactor with a hydrogen-to-carbon ratio (H2 / CO2) of 2.0–3.0. It employs a CO2 reverse water-gas shift reaction, a methanol synthesis reaction, and a gas recirculation process. Patent application CN113045383A also uses a single-stage reactor with a hydrogen-to-carbon ratio (H2+CO) / (CO+CO2) of 3.05–3.1. This process introduces CO, thus approaching the traditional methanol production process. Existing carbon dioxide-to-methanol processes mostly use a single-stage reactor with cooling and separation processes, resulting in low total carbon conversion, high energy consumption, low methanol content in the product, and a large load on subsequent distillation, leading to high overall energy consumption. Summary of the Invention

[0007] The first technical problem to be solved by the present invention is to provide a device for improving the conversion rate of carbon dioxide to methanol, which has a high total carbon conversion rate and low total energy consumption, in light of the current state of the prior art.

[0008] The second technical problem to be solved by the present invention is to provide a method for improving the conversion rate of carbon dioxide to methanol with high total carbon conversion rate and low total energy consumption of the device, in view of the current situation of the prior art.

[0009] The technical solution adopted by the present invention to solve at least one of the above-mentioned technical problems is as follows:

[0010] An apparatus for improving the conversion rate of carbon dioxide to methanol includes:

[0011] The first reactor is used for the reaction of carbon dioxide to produce methanol; the top of the first reactor has an inlet for the input of raw material gas and the bottom has an outlet for the output of the first reaction product.

[0012] The second reactor is used for further reaction of carbon dioxide to produce methanol; the top of the second reactor has an inlet for inputting the reaction raw materials and the bottom has an outlet for outputting the second reaction product;

[0013] A first gas-to-gas heat exchanger is connected to the outlet of the first reactor;

[0014] The first cooler is connected to the first outlet of the first gas-to-gas heat exchanger;

[0015] The first separator, connected downstream of the first cooler, is used to separate the first reaction product output from the first reactor into gas and liquid components; the top outlet of the first separator is connected to the inlet of the first gas-to-gas heat exchanger, and the second outlet of the first gas-to-gas heat exchanger is connected to the inlet of the second reactor.

[0016] The second gas-to-gas heat exchanger is connected to the outlet of the second reactor;

[0017] The second cooler is connected to the third outlet of the second gas-to-gas heat exchanger; and

[0018] The second separator, connected downstream of the second cooler, is used to separate the second reaction product output from the second reactor into gas and liquid components. The top outlet of the second separator is connected to the inlet of the second gas-to-gas heat exchanger, and the fourth outlet of the second gas-to-gas heat exchanger is connected to the inlet of the first reactor.

[0019] Preferably, a feed line is connected to the inlet of the second gas-to-gas heat exchanger, and the gas phase produced at the top of the second separator is fed into the feed line as circulating gas through the first contact, while fresh synthesis gas is fed into the feed line through the second contact.

[0020] Preferably, a reflux line is connected between the second outlet of the first gas-to-gas heat exchanger and the inlet of the second reactor, and a bypass line is connected between the feed line and the reflux line, and a valve for controlling the opening degree of the bypass line according to the temperature is provided.

[0021] As can be seen from the following reaction formula, the production of methanol from carbon dioxide is an exothermic reaction. Compared with the traditional production of methanol from carbon monoxide, the production of methanol from carbon dioxide consumes more hydrogen and produces more water. For every unit of methanol produced, a unit of water is also produced. According to the characteristics of chemical reaction kinetics, an excess of water will inhibit the forward reaction of methanol. Therefore, if water and methanol are drained in time during the reaction process, and the reaction temperature is lowered and the concentrations of carbon dioxide and hydrogen are increased, the entire reaction can be effectively promoted in the direction of methanol production, thereby increasing the methanol yield.

[0022] CO2 + 3H2 → CH3OH + H2O

[0023] CO + 2H₂ → CH₃OH

[0024] This invention introduces a portion of fresh gas directly into the inlet of the second reactor, reducing the inlet temperature of the second reactor and increasing the partial pressure of carbon dioxide and hydrogen, which helps to increase the driving force at the inlet of the second reactor, thereby further improving the methanol conversion rate in the second reactor.

[0025] Preferably, the connection between the bypass line and the feed line is located between the first contact point and the second contact point.

[0026] Preferably, a first compressor is provided at the input of the fresh synthesis gas, and a second compressor is provided at the input of the recirculated gas.

[0027] Preferably, the top of the first reactor is connected to a No. 1 steam drum, and the bottom of the second reactor is connected to a No. 2 steam drum. The No. 1 steam drum and the No. 2 steam drum are interconnected and are provided with a pipe for supplying boiler water.

[0028] A method for improving the conversion rate of carbon dioxide to methanol includes the following steps:

[0029] Fresh syngas reacts at high temperature in the first reactor in the presence of a catalyst to produce a first reaction product containing methanol. The first reaction product contains a large amount of unreacted carbon dioxide and hydrogen.

[0030] After the first reaction product is cooled, it undergoes a first separation, which separates it into a gas phase and a liquid phase in the first separator. The liquid phase consists of methanol and water, which enter the downstream distillation system. The gas phase mainly consists of unreacted carbon dioxide and hydrogen, which enters the second reactor to continue the reaction and obtain the second reaction product. The methanol concentration of the second reaction product is greater than that of the first reaction product.

[0031] After the first reaction product is cooled, it undergoes a first separation, separating into a gas phase and a liquid phase in the first separator. The methanol content in the process gas decreases from 2-6% (mol) to 1-2.5% (mol), and the water content decreases from 2-6% (mol) to 0.5-2% (mol). At the inlet of the second reactor, the partial pressure of alcohol decreases from 2-6% (mol) to 1-2.5% (mol), and the partial pressure of water decreases from 2-6% (mol) to 0.5-2% (mol). The driving force of the reaction in the second reactor increases, and unreacted carbon dioxide and hydrogen continue to participate in the reaction, generating a second reaction product containing methanol, thereby improving the carbon dioxide conversion rate and methanol yield of the entire methanol synthesis system.

[0032] This invention employs a two-stage methanol process to increase the single-pass CO2 conversion rate of the methanol synthesis system from the traditional 10-20% to 15-35%, and uses a pressurized circulation process of unreacted process gas to increase the total CO2 conversion rate from 10-20% to 80-95%.

[0033] Preferably, the inlet temperature of the first reactor is 230~280℃, used to generate high-grade steam; the outlet temperature of the first reactor is 250~300℃, used to preheat the inlet temperature of the second reactor.

[0034] Preferably, the reaction liquid at the outlet of the first reactor is cooled to 90-150°C by a first gas-to-gas heat exchanger and a first cooler, and the liquid phase fraction is 5%wt-15%wt.

[0035] Preferably, the gas phase exiting the first separator is preheated to 220-250°C by a first gas-to-gas heat exchanger before entering the second reactor. The outlet temperature of the second reactor is 230-280°C, which is used to preheat the inlet temperature of the first reactor.

[0036] Preferably, the gas phase at the outlet of the second separator is pressurized by the second compressor and used as circulating gas to enter the reaction system for further reaction, with a circulation ratio of 5-8.

[0037] Preferably, a reflux line is connected between the second outlet of the first gas-to-gas heat exchanger and the inlet of the second reactor, and a bypass line is connected between the feed line and the reflux line. The bypass line is equipped with a valve for controlling its opening degree according to the temperature, and the valve opening degree is 0%-30% of the total amount of fresh synthesis gas.

[0038] Preferably, the alcohol content at the inlet of the first reactor is 0.2-1% (mol); and the alcohol content at the inlet of the second reactor is 1-2.5% (mol).

[0039] Preferably, the alcohol content at the outlet of the first reactor is 2-6% (mol); and the alcohol content at the outlet of the second reactor is 3-7% (mol).

[0040] In this invention, a gas-to-gas heat exchanger is installed between the first reactor and the second reactor. The high-temperature gas at the outlet of the first reactor is used to preheat the gas at the inlet of the second reactor, and the high-temperature gas at the outlet of the second reactor is used to preheat the gas at the inlet of the first reactor, thus making reasonable use of the heat of reaction.

[0041] Compared with the prior art, the advantages of this invention are as follows: This invention adopts a two-stage reactor series process, and simultaneously produces steam of different specifications as by-products. This invention adds a cooling and liquid separation device at the outlet of the first reactor to reduce the alcohol partial pressure and water pressure at the inlet of the second reactor, which is beneficial to improving the methanol conversion rate of the second reactor. This invention incorporates the carbon dioxide and hydrogen in a stepwise reaction into the interstage liquid separation device, which is beneficial to maximizing the conversion rate of the entire device. This invention separates the unreacted gas from the reactor and recycles it into the synthesis reactor, which is beneficial to improving the total carbon conversion rate of carbon dioxide. This invention introduces fresh synthesis gas into the second reactor through a bypass. When the catalyst activity in the first reactor decreases at the end of the reaction, the reaction is moved to the second reactor, thereby ensuring the conversion rate and yield of the entire device. Attached Figure Description

[0042] Figure 1 This is a process flow diagram of an embodiment of the present invention. Detailed Implementation

[0043] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0044] like Figure 1 As shown, the apparatus for improving the conversion rate of carbon dioxide to methanol in this embodiment includes:

[0045] The first reactor 1 is used for the reaction of carbon dioxide to produce methanol; the top of the first reactor 1 has an inlet for the input of raw material gas and the bottom has an outlet for the output of the first reaction product.

[0046] The second reactor 2 is used for the reaction of carbon dioxide to produce methanol; the top of the second reactor 2 has an inlet for the input of the reaction raw materials and the bottom has an outlet for the output of the second reaction product.

[0047] The first gas-to-gas heat exchanger 10 is connected to the outlet of the first reactor 1;

[0048] The first cooler 100 is connected to the first outlet of the first gas-to-gas heat exchanger 10;

[0049] The first separator 01 is connected downstream of the first cooler 100 and is used to separate the first reaction product output from the first reactor 1 into gas and liquid. The top outlet of the first separator 01 is connected to the inlet of the first gas-to-gas heat exchanger 10, and the second outlet of the first gas-to-gas heat exchanger 10 is connected to the inlet of the second reactor 2.

[0050] The second gas-to-gas heat exchanger 20 is connected to the outlet of the second reactor 2;

[0051] The second cooler 200 is connected to the third outlet of the second gas-to-gas heat exchanger 20; and

[0052] The second separator 02 is connected downstream of the second cooler 200 and is used to separate the second reaction product output from the second reactor 2 into gas and liquid components. The top outlet of the second separator 02 is connected to the inlet of the second gas-to-gas heat exchanger 20, and the fourth outlet of the second gas-to-gas heat exchanger 20 is connected to the inlet of the first reactor 1.

[0053] In the above scheme, a feed line 201 is connected to the inlet of the second gas-gas heat exchanger 20. The gas phase produced at the top of the second separator 02 is fed into the feed line 201 as circulating gas through the first contact, and fresh synthesis gas is fed into the feed line 201 through the second contact.

[0054] A reflux line 101 connects the second outlet of the first gas-to-gas heat exchanger 10 to the inlet of the second reactor 2. A bypass line 003 connects the feed line 201 to the reflux line 101, and a valve 031 is installed on the bypass line 003 to control its opening degree according to the temperature. The connection between the bypass line 003 and the feed line 201 is located between the first contact and the second contact. A first compressor 04 is installed at the input of fresh synthesis gas, and a second compressor 05 is installed at the input of recirculated gas.

[0055] As can be seen from the following reaction formula, the production of methanol from carbon dioxide is an exothermic reaction. Compared with the traditional production of methanol from carbon monoxide, the production of methanol from carbon dioxide consumes more hydrogen and produces more water. For every unit of methanol produced, a unit of water is also produced. According to the characteristics of chemical reaction kinetics, an excess of water will inhibit the forward reaction of methanol. Therefore, if water and methanol are drained in time during the reaction process, and the reaction temperature is lowered and the concentrations of carbon dioxide and hydrogen are increased, the entire reaction can be effectively promoted in the direction of methanol production, thereby increasing the methanol yield.

[0056] CO2 + 3H2 → CH3OH + H2O

[0057] CO + 2H₂ → CH₃OH

[0058] In this embodiment, some fresh gas is directly introduced into the inlet of the second reactor 2, which reduces the inlet temperature of the second reactor 2 and increases the partial pressure of carbon dioxide and hydrogen, which helps to increase the inlet driving force of the second reactor 2, thereby further improving the methanol conversion rate in the second reactor 2.

[0059] In this embodiment, the top of the first reactor 1 is connected to a No. 1 steam drum, and the bottom of the second reactor 2 is connected to a No. 2 steam drum. The No. 1 steam drum and the No. 2 steam drum are interconnected and are provided with a pipe for boiler water input.

[0060] Taking a 200,000-ton-scale carbon dioxide to methanol process technology as an example, the method for improving the conversion rate of carbon dioxide to methanol in this embodiment includes the following steps:

[0061] Fresh syngas composed of CO2 and hydrogen in a 3:1 ratio ~74100 Nm 3 / h, pressurized to 8 MPaG, and combined with the pressurized methanol unit recirculation gas of 444600 Nm³. 3 After being mixed at / h, the mixture is preheated to 240℃ via a second gas-gas heat exchanger and then enters the primary reactor, where it reacts in the presence of a catalyst to undergo a methanol synthesis reaction that is exothermic.

[0062] CO2 + 3H2 → CH3OH + H2O

[0063] The outlet temperature of the first-stage reactor is 280℃. The first reaction product contains 2.6% (mol) CH3OH and 2.3% (mol) water. The first reaction product enters the first gas-to-gas heat exchanger and is cooled to 90℃. The liquid phase is 7% wt. It then enters the first separator, where it is separated into gas and liquid phases. The liquid phase consists of 35% (mol) methanol and 63% (mol) water. The gas phase mainly consists of 11% (mol) unreacted carbon dioxide and 86% (mol) hydrogen. After separation, the gas phase contains 1.8% (mol) CH3OH and 0.8% (mol) water. The gas phase exiting the first separator is preheated to 220℃ by the first gas-to-gas heat exchanger and then enters the second reactor to continue the reaction, yielding the second reaction product. The outlet temperature of the second reactor is 250℃. The second reactant contains 3.2% (mol) CH3OH and 2.1% (mol) water, with a higher methanol concentration than the first reaction product.

[0064] The reaction product temperature at the outlet of the second reactor is 250°C. It enters the second gas-gas heat exchanger and the downstream cooler. The second reactant is cooled to ~40°C after the cooler and enters the second separator. The separated liquid phase contains 58% methanol (mol) and 41% water (mol).

[0065] The liquid products from the primary and secondary separators are mixed and then enter the downstream distillation system. The methanol content is 49% (mol). The single-pass carbon dioxide conversion rate of the entire methanol synthesis system is 25%, and the total carbon dioxide conversion rate is 90%.

[0066] In this example, after the second reactant is cooled and separated, the unreacted process gas is recycled into the synthesis system at a recycling ratio of 6. The methanol content in the recycled gas is 0.38% (mol), and a small amount of inert gas is discharged as purge gas.

[0067] In this example, the fresh syngas is provided with a bypass line that directly enters the inlet of the second reactor. The bypass line is equipped with a valve to control its opening degree according to the inlet temperature of the second reactor. When the reactor inlet temperature is 220 ℃, the valve is closed. In order to ensure that the inlet temperature of the second reactor is stable at 220 ℃, the valve flow rate is approximately 10% of the total fresh syngas for every 5 ℃ increase in temperature during operation.

[0068] In this embodiment, a gas-to-gas heat exchanger is installed between the first reactor and the second reactor. The high-temperature gas at the outlet of the first reactor is used to preheat the gas at the inlet of the second reactor, and the high-temperature gas at the outlet of the second reactor is used to preheat the gas at the inlet of the first reactor. The heat load of the first gas-to-gas heat exchanger is ~38MW, and the heat load of the second gas-to-gas heat exchanger is ~22MW, so the heat of reaction is rationally utilized.

Claims

1. An apparatus for improving the conversion rate of carbon dioxide to methanol, characterized in that... include: The first reactor is used for the reaction of carbon dioxide to produce methanol; the top of the first reactor has an inlet for the input of raw material gas and the bottom has an outlet for the output of the first reaction product. The second reactor is used for the reaction of carbon dioxide to produce methanol; the top of the second reactor has an inlet for the input of the reaction raw materials and the bottom has an outlet for the output of the second reaction product. A first gas-to-gas heat exchanger is connected to the outlet of the first reactor; The first cooler is connected to the first outlet of the first gas-to-gas heat exchanger; The first separator, connected downstream of the first cooler, is used to separate the reaction liquid output from the first reactor into gas and liquid components; the top outlet of the first separator is connected to the inlet of the first gas-to-gas heat exchanger, and the second outlet of the first gas-to-gas heat exchanger is connected to the inlet of the second reactor. The second gas-to-gas heat exchanger is connected to the outlet of the second reactor; The second cooler is connected to the third outlet of the second gas-to-gas heat exchanger; as well as The second separator, connected downstream of the second cooler, is used to separate the reaction liquid output from the second reactor into gas and liquid components; the top outlet of the second separator is connected to the inlet of the second gas-to-gas heat exchanger, and the fourth outlet of the second gas-to-gas heat exchanger is connected to the inlet of the first reactor. A feed line is connected to the inlet of the second gas-to-gas heat exchanger. The gas phase produced at the top of the second separator is fed into the feed line as circulating gas through the first contact, and fresh synthesis gas is fed into the feed line through the second contact. A return line is connected between the second outlet of the first gas-to-gas heat exchanger and the inlet of the second reactor. A bypass line is connected between the feed line and the return line, and a valve is installed on the bypass line to control its opening degree according to the temperature. A first compressor is installed at the input of the fresh synthesis gas, and a second compressor is installed at the input of the recirculated gas.

2. The apparatus for improving the conversion rate of carbon dioxide to methanol according to claim 1, characterized in that: The connection between the bypass line and the feed line is located between the first contact point and the second contact point.

3. The apparatus for improving the conversion rate of carbon dioxide to methanol according to claim 1 or 2, characterized in that: The top of the first reactor is connected to a No. 1 steam drum, and the bottom of the second reactor is connected to a No. 2 steam drum. The No. 1 steam drum and the No. 2 steam drum are interconnected and are provided with a pipe for supplying boiler water.

4. A method for improving the conversion rate of carbon dioxide to methanol, characterized in that, Using the apparatus according to any one of claims 1 to 3, the method comprises the following steps: Fresh syngas reacts at high temperature in the first reactor in the presence of a catalyst to produce a first reaction product containing methanol. The first reaction product contains a large amount of unreacted carbon dioxide and hydrogen. After the first reaction product is cooled, it undergoes a first separation, which separates it into a gas phase and a liquid phase in the first separator. The liquid phase consists of methanol and water, which enter the downstream distillation system. The gas phase mainly consists of unreacted carbon dioxide and hydrogen, which enters the second reactor to continue the reaction and obtain the second reaction product. The methanol concentration of the second reaction product is greater than that of the first reaction product. After the first reaction product is cooled, it undergoes a first separation, separating into a gas phase and a liquid phase in the first separator. The methanol content in the process gas decreases from 2-6% mol to 1-2.5% mol, and the water content decreases from 2-6% mol to 0.5-2% mol. At the inlet of the second reactor, the alcohol partial pressure in the process gas decreases from 2-6% mol to 1-2.5% mol, and the water partial pressure decreases from 2-6% mol to 0.5-2% mol. The driving force of the reaction in the second reactor increases, and unreacted carbon dioxide and hydrogen continue to participate in the reaction, generating a second reaction product containing methanol, thereby improving the carbon dioxide conversion rate and methanol yield of the entire methanol synthesis system.

5. The method for improving the conversion rate of carbon dioxide to methanol according to claim 4, characterized in that: The reaction temperature in the first reactor is 230 ~ 280℃, used to generate high-grade steam; the outlet temperature of the first reactor is 250 ~ 300℃, used to preheat the inlet temperature of the second reactor.

6. The method for improving the conversion rate of carbon dioxide to methanol according to claim 4, characterized in that: The reaction liquid at the outlet of the first reactor is cooled to 90 ~ 150°C by the first gas-to-gas heat exchanger and the first cooler, with a liquid phase fraction of 5%wt ~ 15%wt.

7. The method for improving the conversion rate of carbon dioxide to methanol according to claim 4, characterized in that: The gas phase at the outlet of the first separator is preheated to 220-250°C by the first gas-to-gas heat exchanger and then enters the second reactor. The outlet temperature of the second reactor is 230-280°C.

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