A method for co-producing hydrogen and liquid carbon dioxide by methanol cracking

Abstract

This invention discloses a method for producing hydrogen and co-producing liquid carbon dioxide by methanol cracking. Methanol and demineralized water are pressurized and then vaporized into gaseous methanol and water vapor via heat exchange. This vapor is sent to a conversion tower to convert methanol and water into carbon dioxide, hydrogen, a small amount of methane, and a small amount of carbon monoxide. Excess steam is then cooled via heat exchange and sent to a temperature swing adsorption separation unit to remove liquid. The high-pressure liquid is pressurized and returned to the raw material methanol system. The dried gas is directly sent to carbon dioxide liquefaction. The liquefied gas is then purified by Fischer-Tropsch purification of carbon monoxide and carbon dioxide before being sent to a pressure swing adsorption hydrogen production unit to produce hydrogen with a concentration of over 99.9%. The regenerated gas-liquid mixture is heated during the methanol-water vaporization process using catalytic combustion.

Description

[0001] This invention relates to the field of hydrogen production technology, and in particular to a method for producing hydrogen from methanol and co-producing liquid carbon dioxide. Background Technology

[0002] Methanol-to-hydrogen (MHH) refers to the production of hydrogen gas with wide applications through the cracking of methanol. Methanol-to-hydrogen typically uses methanol and deionized water as raw materials, undergoing catalytic cracking and shift reactions at 220-280℃ and 0.8-1.8 MPa. The resulting converted gas contains approximately 74% hydrogen and 24% carbon dioxide. After condensation, the converted gas enters a water washing tower. Unconverted methanol and water are collected in the bottom of the tower for recycling. The top gas is sent to a pressure swing adsorption (PSA) unit to separate and extract hydrogen at a pressure of 0.75-1.75 MPa. The remaining gas is carbon dioxide-rich. Recovering carbon dioxide from this carbon-rich gas can reduce the concentration of carbon dioxide in the atmosphere, which is beneficial for maintaining the balance of the global ecosystem. The collected carbon dioxide can then be used in oil extraction, food processing, and organic synthesis, possessing significant social and economic value.

[0003] CN201911032731.3 discloses a high-pressure methanol-water hydrogen production system, including a reformer, a hydrogen separation unit, and a carbon dioxide separator. A liquid pump delivers methanol-water into a methanol-water vapor pipe at a pressure of 18–50 MPa. The mixed gas is separated into pure hydrogen and a residual carbon dioxide mixture. The pure hydrogen is collected through heat exchange, while the residual carbon dioxide mixture is liquefied and separated at 18–30.8 °C through heat exchange. The residual hydrogen mixture is then mixed with water to form a reformed mixed gas. The entire system produces hydrogen under high pressure (18–50 MPa), achieving high hydrogen production efficiency and enabling the circulation and purification of gases within the system. The theoretical yield can reach 100%, and the hydrogen yield is ≥95%.

[0004] CN202310102622.4 discloses a method for producing hydrogen from methanol. The method involves heating and vaporizing methanol-water to obtain methanol-water vapor; reforming methanol to obtain a hydrogen mixture; cooling the hydrogen mixture and then passing it through a water washing tower to absorb unreacted methanol-water; subsequently, adjusting the relative humidity and temperature of the hydrogen mixture; feeding the hydrogen mixture into a carbon dioxide absorption tower to remove carbon dioxide; after carbon dioxide removal, product hydrogen is obtained and stored in a hydrogen tank for supply to end users. This method, through the reforming of methanol-water vapor to produce a hydrogen mixture, further purifies the hydrogen mixture to obtain product hydrogen with very low carbon monoxide content. It offers advantages such as easy transportation of raw materials, high purity of produced hydrogen, low equipment construction costs, and low energy consumption, thereby expanding the application range of hydrogen. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for producing liquid carbon dioxide from methanol to hydrogen.

[0006] The technical solution adopted by the present invention to solve its technical problem is as follows: (1) Methanol and demineralized water are mixed in a ratio of 1:1.1~1.3, pressurized to 4.5~5.5MPa, and vaporized into gaseous methanol and water vapor by heat exchange. The vapor is sent to the conversion tower to convert methanol and water into carbon dioxide, hydrogen, a small amount of methane, and a small amount of carbon monoxide. The excess steam is heat exchanged, cooled, and sent to the temperature swing adsorption separation device to remove the liquid. The high-pressure liquid is returned to the raw material methanol system by pressure boosting. The liquid content in the dry gas is ≤10ppm and is directly sent to carbon dioxide liquefaction. After liquefaction, the carbon dioxide concentration in the gas reaches below 50ppm. Fischer-Tropsch purification of carbon monoxide and carbon dioxide is carried out to below 1ppm. The gas pressure is 4.3~5.3MPa and sent to the pressure swing adsorption hydrogen production device to produce hydrogen with a concentration of more than 99.9%, of which the carbon monoxide + carbon dioxide content is ≤0.1ppm, the hydrogen pressure is 4.2~5.2MPa, and the regenerated gas-liquid is 0.02~0.05MPa. Catalytic combustion is used for heating in the vaporization process of methanol-water solution.

[0007] (2) The temperature-switching adsorption device described in step (1) uses low temperature isobaric adsorption of methanol and water, heats up to desorb methanol and water, then liquefies and separates methanol and water, and obtains liquid under high pressure.

[0008] (3) The regenerated gas-liquid of the hydrogen production device described in step (1) contains carbon monoxide, carbon dioxide, methane, and Fischer-Tropsch liquid products.

[0009] Compared with the prior art, the beneficial effects of the present invention are: 1. The conventional method achieves a methanol conversion rate of 97-98% in a single step; the present invention achieves a methanol conversion rate of 90-92% in a single step, but the amount of catalyst used is less than 50% of that in the conventional method, and the total methanol conversion rate reaches over 99.5%.

[0010] 2. The energy exchange between the Fischer-Tropsch purification process and the methanol cracking process can reduce the system's energy consumption.

[0011] 3. High-pressure conversion can reduce the energy consumption of hydrogen repressurization process and greatly help to improve hydrogen yield.

[0012] 4. The gas after high-pressure conversion is liquefied into carbon dioxide in the pre-treatment stage, which saves more energy. Moreover, separating carbon dioxide before producing hydrogen by pressure swing adsorption helps to reduce the investment in adsorption equipment and the energy consumption of separation. Attached Figure Description

[0013] Figure 1 This is a flowchart of the methanol-to-hydrogen method of the present invention. Implementation

[0014] The following embodiments are used to illustrate the present invention, but should not be used to limit the scope of protection of the present invention. The conditions in the embodiments can be further adjusted according to specific conditions, and simple improvements to the method of the present invention under the premise of the concept of the present invention are all within the scope of protection claimed by the present invention.

[0015] Example 1: Methanol and demineralized water were mixed in a 1:1.1 ratio, pressurized to 4.5 MPa, and vaporized into gaseous methanol and water vapor through heat exchange. The vapor was then sent to a conversion tower to convert methanol and water into carbon dioxide, hydrogen, a small amount of methane, and a small amount of carbon monoxide. Excess steam was then cooled through heat exchange and sent to a temperature swing adsorption separation unit to remove liquid. The high-pressure liquid was pressurized and returned to the raw material methanol system. The liquid content in the dried gas was 10 ppm, which was then directly sent to carbon dioxide liquefaction. After liquefaction, the carbon dioxide concentration in the gas reached 40 ppm. Fischer-Tropsch purification reduced carbon monoxide and carbon dioxide to 0.8 ppm, and the gas pressure was 4.3 MPa. The gas was then sent to a pressure swing adsorption hydrogen production unit to produce hydrogen with a concentration of over 99.9%, of which the carbon monoxide + carbon dioxide content was 0.1 ppm. The hydrogen pressure was 4.2 MPa, and the regenerated gas-liquid mixture was 0.02 MPa. Catalytic combustion was used to heat the methanol-water vaporization process.

[0016] Example 2: Methanol and demineralized water were mixed in a 1:12 ratio, pressurized to 5.0 MPa, and vaporized into gaseous methanol and water vapor through heat exchange. This vapor was then sent to a conversion tower to convert methanol and water into carbon dioxide, hydrogen, a small amount of methane, and a small amount of carbon monoxide. Excess steam was then cooled through heat exchange and sent to a temperature swing adsorption separation unit to remove liquid. The high-pressure liquid was pressurized and returned to the raw material methanol system. The liquid content in the dried gas was 8 ppm, which was then directly sent to carbon dioxide liquefaction. After liquefaction, the carbon dioxide concentration in the gas reached 35 ppm. Fischer-Tropsch purification reduced carbon monoxide and carbon dioxide to 0.6 ppm, and the gas pressure was 4.5 MPa. This gas was then sent to a pressure swing adsorption hydrogen production unit to produce hydrogen with a concentration of over 99.9%, of which the carbon monoxide + carbon dioxide content was 0.08 ppm. The hydrogen pressure was 4.5 MPa, and the regenerated gas-liquid mixture was 0.035 MPa. Catalytic combustion was used to heat the methanol-water vaporization process.

[0017] Example 3: Methanol and demineralized water were mixed in a 1:1.3 ratio, pressurized to 5.5 MPa, and vaporized into gaseous methanol and water vapor through heat exchange. This vapor was then sent to a conversion tower to convert methanol and water into carbon dioxide, hydrogen, a small amount of methane, and a small amount of carbon monoxide. Excess steam was then cooled through heat exchange and sent to a temperature swing adsorption separation unit to remove liquid. The high-pressure liquid was pressurized and returned to the raw material methanol system. The liquid content in the dried gas was 5 ppm, and it was directly sent to carbon dioxide liquefaction. After liquefaction, the carbon dioxide concentration in the gas reached 20 ppm. Fischer-Tropsch purification reduced carbon monoxide and carbon dioxide to 0.5 ppm, and the gas pressure was 5.0 MPa. This gas was then sent to a pressure swing adsorption hydrogen production unit to produce hydrogen with a concentration of over 99.9%, of which the carbon monoxide + carbon dioxide content was 0.05 ppm. The hydrogen pressure was 5.0 MPa, and the regenerated gas-liquid mixture was 0.05 MPa. Catalytic combustion was used to heat the methanol-water vaporization process.

Claims

1. A method for methanol cracking to produce hydrogen and co-produce liquid carbon dioxide, characterized in that... Methanol and demineralized water are mixed in a ratio of 1:1.1~1.3, pressurized to 4.5~5.5 MPa, and vaporized into gaseous methanol and water vapor through heat exchange. This vapor is then sent to a conversion tower to convert methanol and water into carbon dioxide, hydrogen, a small amount of methane, and a small amount of carbon monoxide. Excess steam is then cooled through heat exchange and sent to a temperature swing adsorption separation unit to remove liquid. The high-pressure liquid is pressurized and returned to the raw material methanol system. The liquid content in the dried gas is ≤10 ppm, and it is directly sent to carbon dioxide liquefaction. After liquefaction, the carbon dioxide concentration in the gas reaches below 50 ppm. Fischer-Tropsch purification reduces carbon monoxide and carbon dioxide to below 1 ppm. The gas pressure is 4.3~5.3 MPa, and it is sent to a pressure swing adsorption hydrogen production unit to produce hydrogen with a concentration of over 99.9%, of which the carbon monoxide + carbon dioxide content is ≤0.1 ppm. The hydrogen pressure is 4.2~5.2 MPa, and the regenerated gas-liquid mixture is 0.02~0.05 MPa. Catalytic combustion is used to heat the methanol-water vaporization process.

2. The method for methanol cracking to produce hydrogen and co-produce liquid carbon dioxide according to claim 1, characterized in that... The aforementioned temperature-switching adsorption separation device employs low-temperature isobaric adsorption of methanol and water, followed by heating to desorb methanol and water, then liquefaction to separate methanol and water, and finally high-pressure to obtain the liquid.

3. The method for methanol cracking to produce hydrogen and co-produce liquid carbon dioxide according to claim 1, characterized in that... The regenerated gas-liquid of the pressure swing adsorption hydrogen production device contains carbon monoxide, carbon dioxide, methane, and Fischer-Tropsch liquid products.

Images