Production of a gas mixture of hydrogen and carbon dioxide

Abstract

Production of a gas mixture of hydrogen and carbon dioxide The present invention provides a method for producing a hydrogen-carbon dioxide gas mixture, comprising the following process steps: (I) isolating CO2 from a gas mixture having a CO2 volume fraction in the range of 0.01% to 20% using an adsorption device; (II) desorbing CO2 using a heated hydrogen-containing gas stream in a desorber; and (III) adjusting the CO2 volume fraction of the hydrogen-containing gas stream to a target content using a recycle gas system, where the heated hydrogen-CO2 gas mixture passes through the desorber, thereby increasing the CO2 volume fraction in the hydrogen-CO2 gas mixture. Process step III may be followed by process step IV, in which the hydrogen-carbon dioxide gas mixture is used to produce methanol after the required CO2 volume fraction has been adjusted.

Description

[Technical Field]

[0001] The present invention relates to a process for obtaining a hydrogen-carbon dioxide mixture and its use for the production of methanol. [Background technology]

[0002] prior art The isolation of CO2 from process off-gases is an important aspect for the climate-neutral industrial production of raw materials or energy. Prior art techniques employ so-called amine scrubbing, in which CO2 is reversibly isolated from gas streams by passing it through an aqueous amine solution to form carbamates. The drawbacks of this technique include, among other things, the relatively high CO2 partial pressure required for effective CO2 separation. In other words, this process is not suitable for process off-gases with low CO2 content or for CO2 isolation directly from the atmosphere (direct air capture, or DAC). This problem can be solved by adsorbing CO2 onto a solid adsorbent. The key issue is desorption of CO2 from the adsorbent. This requires a significant increase in the adsorbent temperature, for example, in a temperature swing process, typically by introducing superheated steam. This means that CO2 requires energy-intensive drying after desorption. It would be better if there were a gas mixture that could be further processed immediately after desorption without expensive and inconvenient treatment. The invention proposed here makes this possible. By using hydrogen gas as a desorber gas and simultaneously as a heat carrier, it is possible to efficiently obtain a hydrogen-carbon dioxide gas mixture that can subsequently be used, for example, for methanol production without expensive and complex processing.

[0003] The use of hydrogen for carbon dioxide desorption is not new. Thus, German Patent No. DE 10 2013 022 021 B4 claims a method for isolating CO2 from a gas mixture in which the CO2-rich gas mixture is passed through a gas chromatography column, with CO2 physically diffusing more slowly than the tail gas. After loading the column, the column is backwashed "isothermally" with hydrogen, i.e., the column is not heated during the desorption step. This method is disadvantageous, especially in the case of chemical adsorbents, because desorption is an endothermic process and desorption occurs only incompletely without a temperature increase.

[0004] European Patent Application Publication No. EP 3530640A discloses a method for the reductive production of methane from CO2 and hydrogen. CO2 is desorbed from an adsorbent with preheated hydrogen, which is heated by waste heat from the reduction reactor. The desorbed H2 / CO2 mixture is also mixed with fresh hydrogen to establish the required H2 / CO2 ratio. A drawback of this method is that for low CO2 mixtures, there is no way to increase the CO2 partial pressure of the gas mixture.

[0005] The object of the present invention is therefore to overcome the drawbacks of the prior art and in particular to find a simple and cost-effective method for adapting the CO2 content in a hydrogen-carbon dioxide mixture to a wide range. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] German Patent No. DE 10 2013 022 021 B4 Specification [Patent Document 2] European Patent Application Publication No. EP3530640A DETAILED DESCRIPTION OF THE INVENTION

[0007] The present invention relates to a method for producing a hydrogen-carbon dioxide gas mixture, comprising the following process steps: (I) isolating CO2 from a gas mixture having a CO2 volume fraction in the range of 0.01% to 20% using an adsorption device; (II) using the heated hydrogen-containing gas stream in a desorber to desorb CO; (III) adjusting the CO volume fraction of the hydrogen-containing gas stream to a target content using a recycle gas system by passing the heated hydrogen-CO gas mixture through the desorber, thereby increasing the CO volume fraction in the hydrogen-CO gas mixture; The present invention provides a method of manufacturing a semiconductor device, comprising:

[0008] Description of individual process steps (I) Isolation: Carbon dioxide is preferably isolated from process off-gases or mixtures of other industrial or natural gases. The gas mixture preferably has a CO volume fraction of 0.01% to 20%, particularly 0.04% to 15%. The gas mixture is preferably purified of harmful components, such as reactive secondary gases like sulfur dioxide and nitrogen oxides, and / or finely divided solids like dust, before the adsorption step. This isolation can be achieved using established technologies, such as wet scrubbers, deNOx systems (catalytic nitrogen oxide reduction systems, nitrogen oxide removal systems), electrofilters, cyclones, and dust filters. Adsorption is preferably carried out in the chemisorption mode (i.e., a chemical reaction between carbon dioxide and the adsorbent that occurs during adsorption). Therefore, the water content of the gas mixture is adjusted before entering the adsorption device. The optimal water content of the gas mixture depends on the chemical reaction in the chemisorption step. Carbon dioxide isolation is preferably carried out in an adsorption device equipped with a solid adsorbent. The adsorption step may be carried out in a gas-borne or stirred fluidized bed, or in a fixed bed, but a fixed-bed adsorption apparatus is preferred. The number of adsorption apparatuses is preferably 2 to 10, particularly 2 to 5. The adsorption temperature is preferably in the range of 0 to 150°C, particularly preferably 20 to 100°C. That is, the process gas temperature upon entering the adsorption apparatus is preferably in the range of 0 to 150°C, particularly preferably 20 to 100°C. The pressure in the adsorption apparatus is preferably in the range of 0 to 50 bar (absolute), particularly preferably 0.5 to 10 bar (absolute).

[0009] (II) Desorption: The absorbed CO2 adsorber is then preferably separated from the CO2-rich process gas stream and connected as a desorber. The desorber is thus an adsorber undergoing regeneration. Preheated hydrogen-rich gas is used for desorption. The hydrogen volume fraction in the desorber gas can be in the range of 100% to 0.1%. Therefore, pure hydrogen or a gas mixture can be used. In this case, the second gas component is carbon dioxide with a volume fraction of 99.1% to 0%. Passing through the desorber increases the CO2 content in the desorber gas. This applies particularly to partial pressure-independent adsorption and desorption. That is, capacity is defined solely or primarily by temperature conditions, as in typical chemisorption. If physisorption plays a significant role, a high CO2 content in the desorbed gas would be detrimental or require overcompensation by further temperature increase. In addition to heating with the CO2-rich process gas, the adsorber can be heated, for example, via a heating jacket using a heat transfer liquid or gas, or externally electrically. The adsorption device may also be heated, if desired, by heatable internal structures within the adsorption device, such as heating coils, heating plates, or heating fingers.

[0010] Heating of the CO2-rich process gas is preferably carried out by a gas heater, such as, for example, a plate heat exchanger, a shell-and-tube heat exchanger, a finned heater, a heating register, or an electric resistance heater. Suitable energy sources for operating the gas heater include electrical energy (resistance heating) or fluid heat transfer media (preferably from a heat recovery system), such as thermal oil, hot / pressurized water, and steam. Energy coupling for heat recovery is possible when heat is generated in a spatially adjacent process at least 20 K above the adsorption temperature, for example, a heat stream from a combustion plant upstream of the CO2 capture plant, or else in a downstream process step for CO2 utilization (e.g., exothermic methanol synthesis, optional process step IV).

[0011] (III) Adjustment of CO2 volume fraction: The adjustment of the CO volume fraction according to the present invention is preferably carried out via a recycle gas circuit, in which the desorber gas is passed completely or partially through one or more desorbers until the CO content in the desorber gas reaches the target value required for a subsequent process step, e.g., methanol synthesis. In a first embodiment (IIIa) of the present invention, the recycle gas circuit is configured so that the desorber that releases the recycle gas is identical to the desorber that receives the recycle gas. In the operating mode of the recycle gas system of the present invention, the absorber that has taken up CO is purged with cold fresh hydrogen in a first step to replace the residual amount of process off-gas from the absorber. This amount of purge gas can either be discarded or recycled into the CO2-rich process gas stream. When the purge gas purity downstream of the absorber preferably reaches a value of at least 99% by volume, in particular at least 99.5% by volume, the desorption step begins by starting the recycle gas process. For this purpose, the regenerated adsorber (which will then become the desorber) is purged with heated recycle gas. The cycle gas can be pure hydrogen or a hydrogen-carbon dioxide gas mixture. The cycle gas is circulated through the desorber until the gas composition corresponds to at least the target value, i.e., at least the target value of the CO volume fraction. Once the target value is reached, at least one substream is removed from the cycle gas and, if desired, sent to further processing, for example, reductive methanol synthesis. The subamount removed from the cycle gas is preferably replaced by adding pure hydrogen to the cycle gas circuit. The desorption step ends when the CO content of the cycle gas does not substantially change during passage through the desorber. The cycle gas process then ends. The remaining amount of cycle gas in the desorber is then replaced with cold hydrogen gas or process gas, preferably process gas, while the desorber is simultaneously cooled. This purge gas amount can either be discarded or fed into the cycle gas stream or process gas stream.When the CO2 content in the purge gas becomes equal to or less than the CO2 content in the process gas and / or the temperature inside the desorber becomes equal to or less than the process gas temperature before entering the adsorber, the purge process ends and the desorber can be used again as an adsorber.

[0012] In a particularly preferred embodiment, the process according to the invention comprises at least two independent recycle gas systems for producing a hydrogen-carbon dioxide gas mixture, in order to allow continuous operation with subsequent optional utilization of the gas mixture, for example in reductive methanol synthesis.

[0013] In a further embodiment (IIIb) according to the invention, the desorber releasing the cycle gas and the desorber receiving the cycle gas are at least partially separate. That is, the desorber fully loaded with CO2 is connected to a cycle gas process in which at least one further desorber is already in the desorption step. Here, the desorbers may be connected in series or in parallel, preferably in parallel. As in embodiment IIIa, the connection of the desorber fully loaded with CO2 is carried out after the remaining amount of process gas is replaced by a purge with fresh hydrogen or cycle gas, preferably cycle gas. The amount of purge gas can be either discarded or recycled to the CO2-rich process gas stream. When the purity of the purge gas downstream of the absorber reaches a value of at least 99% by volume, in particular at least 99.5% by volume, in the case where fresh hydrogen is used as the purge gas, or when the purity of the purge gas downstream of the absorber reaches the composition of the cycle gas in the case where cycle gas is used as the purge gas, the desorption step begins by starting the cycle gas process. For this purpose, the regenerated adsorber (which then becomes the desorber) is purged with heated circulating gas. The circulating gas can be pure hydrogen or a hydrogen-carbon dioxide gas mixture. The circulating gas is circulated through the desorber until the gas composition reaches at least the target value, i.e., the target CO volume fraction. Once the target value is reached, at least one side stream is removed from the circulating gas and, if desired, sent to further processing, for example, reductive methanol synthesis. The side stream removed from the circulating gas is preferably replaced by adding pure hydrogen to the circulating gas circuit. The desorption step, which involves at least one desorption, ends when the CO content of the circulating gas does not substantially change during its passage through the desorber. The corresponding desorber is isolated from the circulating gas system. The remaining amount of circulating gas in the desorber is then replaced with cold hydrogen gas or process gas, preferably process gas, while the desorber is cooled. This purge gas amount can be either discarded or fed to the circulating gas stream or process gas stream.When the CO2 content in the purge gas becomes equal to or less than the CO2 content in the process gas and / or the temperature inside the desorber becomes equal to or less than the process gas temperature before entering the adsorber, the purge process ends and the desorber can be used again as an adsorber.

[0014] The aforementioned circulation gas system preferably comprises suitable pipe conduits with connection options to different adsorption / desorption devices, as well as suitable ventilation / compression equipment for transporting the gas and a suitable heating system for adjusting the required temperature of the circulation gas. The circulation gas system preferably also comprises suitable gas supply and discharge systems, as well as measurement and control technologies, such as CO concentration measurement equipment (e.g., mass spectrometry, process gas chromatography, Raman spectroscopy), and conventional measurement equipment for pressure, temperature, and flow rate, for process control.

[0015] The temperature of the desorber gas is preferably in the range of 20 to 250°C, particularly preferably in the range of 50 to 200°C. The pressure is preferably in the range of 0 to 50 bar (absolute), particularly preferably in the range of 0.5 to 10 bar (absolute). The temperature of the desorber gas in step II is preferably at least 5°C higher, particularly preferably at least 10°C higher, particularly preferably at least 20°C higher than the temperature of the mixed gas in step I. In addition to heating with the desorber gas, the desorber may be heated, for example, via a heating jacket, for example, via a heating jacket with a heat transfer liquid or gas, or externally electrically. The desorber may also be heated, if desired, by heatable internal structures within the desorber, such as heating coils, heating plates, or heating fingers.

[0016] Heating of the desorber gas is preferably carried out by a gas heater, such as a plate heat exchanger, a shell-and-tube heat exchanger, a finned heater, a heating register, or an electrical resistance heater. A gas heater is preferably employed in the circulation gas system so that the inlet temperature of the desorber gas to the desorber can be repeatedly readjusted to the desired value. Suitable energy sources for operating the gas heater include electrical energy (resistance heating) or fluid heat transfer media (preferably from a heat recovery system), such as thermal oil, hot / pressurized water, and steam. Energy coupling for heat recovery is possible when heat is generated in a spatially adjacent process at a temperature at least 20 K above the desorption temperature, such as a heat stream from a combustion plant upstream of the CO2 capture plant or a downstream process step for CO2 utilization (e.g., exothermic methanol synthesis, optional process step IV).

[0017] The number of desorbers preferably corresponds to the number of adsorber devices. This is understood to mean that while one adsorber device is in operation, another adsorber device that has reached its CO2 absorption capacity is regenerated by purging with desorber gas and functions as a desorber during this time. This is understood to mean that the process according to the invention preferably comprises at least two adsorber devices. However, taking into account the total process capacity, it is advantageous to increase the number of adsorber devices. The number of adsorber devices is preferably in the range of 2 to 10, particularly preferably in the range of 2 to 5. This is understood to mean that at least one adsorber device is in operation, at least one adsorber device is regenerated and functions as a desorber, and the remaining adsorber devices can be maintained in a regenerated state, i.e., without a CO2 load, in standby mode.

[0018] In a preferred embodiment, following step III, the hydrogen-carbon dioxide gas mixture removed from the recycle gas circuit is used for methanol production. In a preferred embodiment, the hydrogen-carbon dioxide gas mixture may be mixed with additional fresh hydrogen after being removed from the recycle gas circuit and before being introduced into the methanol production process, in order to be able to adjust the CO volume fraction of the hydrogen-carbon dioxide gas mixture to the correct target value for methanol synthesis, in particular if the CO volume fraction of the hydrogen-carbon dioxide gas mixture is too high.

[0019] (IV) Optional Use of Hydrogen-Carbon Dioxide Gas Mixtures: The gas mixture with the adjusted carbon dioxide volume fraction can then be used for methanol production in the same manner as synthesis gas. It is preferred that the hydrogen content in this gas mixture be 75 mol%, i.e., the CO content be 25 mol%. The reduction of CO with hydrogen in the gas mixture is carried out in a reactor of established design (e.g., a catalytic fixed-bed reactor) using a suitable catalyst. The hydrogen-carbon dioxide gas mixture may optionally be preheated to the required reaction temperature before the reaction. The exact temperature and pressure depend on the catalyst selected. The reduction of CO with hydrogen to give methanol is exothermic, at -49.6 kJ / mol (at 300 K). The released heat of reaction may be used, for example, to heat the hydrogen-carbon dioxide gas mixture using a heat exchanger, or alternatively, to heat the desorber gas for the purpose of releasing carbon dioxide in desorption step II.

Claims

1. 1. A method for producing a hydrogen-carbon dioxide gas mixture, comprising the following process steps: (I) Using an adsorption device, CO ２ from a mixed gas in which the volume fraction of CO is in the range of 0.01% to 20% ２ isolating (II) A heated hydrogen-containing gas stream is used in a desorber to remove CO ２ and (III) Using a recycle gas system to remove CO from a hydrogen-containing gas stream ２ adjusting the volume fraction of the heated hydrogen-CO ２ The gas mixture passes through the desorber to form the hydrogen-CO ２ CO in the gas mixture ２ Adjustment by increasing the volume fraction, A manufacturing method comprising:

2. In step I, the mixed gas preferably contains CO in the range of 0.04% to 15%. ２ The method of claim 1 having a volume fraction.

3. 3. The method according to claim 1, wherein in step I, the adsorption apparatus is a fixed-bed adsorption apparatus.

4. In step I, CO ２ In step II, the adsorption device ２ 4. The method according to claim 1, wherein the desorbent is separated from the rich process gas stream and connected as a desorber.

5. 5. The method of claim 1, wherein the temperature of the desorber gas in step II is at least 5° C. higher than the temperature of the mixed gas in step I.

6. The method according to any one of claims 1 to 5, wherein in step III, the circulating gas system is configured such that the desorber that discharges the circulating gas is the same as the desorber that receives the circulating gas.

7. In step III, the desorber that discharges the circulating gas and the desorber that receives the circulating gas are separate, ２ The method according to any one of claims 1 to 6, wherein the desorber fully loaded with is connected to a cycle gas process in which at least one further desorber is already in a desorption process.

8. After process step III, the required CO ２ 8. The method according to any one of claims 1 to 7, wherein after the volume fraction has been adjusted, there follows process step IV in which the hydrogen-carbon dioxide mixture is used for the production of methanol.

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