Methods for collecting CO2 and testing membrane materials

Abstract

The invention relates to a method for transferring a gas component from a sample gas, in which the gas component present in the sample gas is collected through at least one membrane permeable to the gas component in a liquid that absorbs or binds the gas component.

Description

[0001] The invention relates to a method for transferring a gas component from a sample gas, in which the gas component present in the sample gas is collected through at least one membrane permeable to the gas component in a liquid absorbing or binding the gas component, and wherein the sample gas is introduced into a container in which a container region carrying the sample gas is separated from a container region containing the liquid by means of at least one membrane permeable to the gas component.

[0002] In a preferred application, the gas component is CO2, especially CO2 with the isotopes 12 C and / or 13 C and / or 14 C. In one possible application, the sample gas comes from the exhaust gas of combustion plants. The liquid used for CO2 is preferably sodium hydroxide.

[0003] Such a method can be used, for example, to determine the proportions of fossil or biogenic components in a combustion process, since it is known that fossil and biogenic starting components have different proportions of carbon isotopes. Based on the isotope ratios, the respective proportions of fossil and biogenic starting components can be determined.

[0004] There are known methods that can perform such a task. One of these is the process of contacting the sample gas with soda lime. This has some disadvantages.

[0005] Filling and emptying the containers containing the soda lime powder must be done while wearing protective suits and using compressed air breathing apparatus; there is a high risk that CO2 from the laboratory technicians' breathing air will enter the sample and falsify the results.

[0006] Furthermore, it is questionable whether the entire amount of CO2 reaches and is bound by the soda lime; for this to happen, the contact surface would have to be very large. Used soda lime is considered waste requiring special monitoring; documentation is required to ensure proper disposal.

[0007] In another known method, the sample gas is bubbled into a CO2-absorbing liquid, such as sodium hydroxide, creating direct contact between the CO2 bubbles and the liquid. Whether this effectively binds the entire amount of CO2 in the solution is questionable, particularly because the bubble surface shields gas deeper within the bubble. The residence time of the bubbles in the liquid remains uncertain and uncontrollable.

[0008] To generate bubbles, a sintered glass element, such as a Nutsche filter, can be used. The problem is that when caustic soda is used as the CO2 gas-binding or CO2-absorbing liquid, the sintered glass does not last long, as the sintered glass, particularly the contact points between the fine glass beads, are dissolved by the caustic solution and the gas flowing through it. Such a bubble-generating element therefore does not have a long service life.

[0009] A further disadvantage of the aforementioned methods is that the sample gas supply and discharge are not separated from the liquid absorbing or binding the gas. Therefore, all materials, especially those supplying and / or removing the liquid, must be made of alkali-resistant material. The risk of leakage of the liquid reacting with the gas or binding the gas, e.g., caustic soda, at the connectors for the sample gas supply and discharge cannot be effectively prevented.

[0010] Another disadvantage is that leaks in pipes or connections caused by liquid contact can lead to dilution of the sample gas with the ambient or outside air. The sample gas may therefore contain CO2 gas components from the ambient air.

[0011] Furthermore, it is known, for example from patent application DE 10 2020 005 098 A1 of the same applicant, to allow the sample gas to diffuse through a membrane into a liquid and thus collect it in the liquid.

[0012] The sample gas from a combustion plant, for example, originating from an exhaust pipe or chimney, is naturally at a high temperature and contains a high water vapor or water content. Such components in the sample gas can also distort the CO2 measurement from the sample gas.

[0013] In other applications, the gas component to be transferred may be different, e.g., ammonia. In this case, the liquid may be water.

[0014] The following pairings can also be used as gas components to be transferred and suitable liquids: Furthermore, the following liquids can be used for collecting CO2: ionic liquids, potassium hydroxide solution, sodium hydroxide solution, calcium hydroxide solution, barium hydroxide solution. If hydrogen sulfide is to be collected, a potassium hydroxide solution or sodium hydroxide solution is also used. If ammonia is to be collected, water is used.

[0015] When using a potassium hydroxide solution or sodium hydroxide solution, the CO2 dissolves in the liquid. The CO2 can first be precipitated and dried in the laboratory, e.g., using barium chloride, and then analyzed using mass spectrometry.

[0016] However, if calcium hydroxide or barium hydroxide solution is used, the CO2 compound precipitates with the solution in the container. It then only needs to be filtered out, dried, and analyzed using mass spectrometry.

[0017] The invention has set itself the task of developing a process with which gas components, e.g. CO2, in particular CO2 with the isotopes 12 C and / or 13 C and / or 14 C from a sample gas into a liquid, preferably such that the entire portion of the gas component is collected from the portion of sample gas supplied to the liquid.

[0018] Preferably, the invention is intended to enable the method to collect gas components from a sample gas, in particular to enable further analysis of the gas components. Further preferably, the invention is intended to enable the method to be used to test membranes that are permeable to a predetermined gas component.

[0019] This object is achieved according to the invention in that the container area carrying the sample gas is filled until a predetermined pressure measured in the container area is reached, wherein after reaching the predetermined pressure, further filling is stopped, e.g. by closing an inflow valve, and the sample gas remains in the container area for the transfer of the gas component, preferably until the pressure falls below a predetermined pressure value or pressure gradient measured in the same container area or until a predetermined period of time has elapsed or until a conductivity value measured in the liquid is exceeded and is then released from the container area, preferably, wherein the respective measured pressure value represents a differential pressure compared to the atmospheric ambient pressure or a partial pressure of the gas component

[0020] This procedure ensures that a certain amount of sample gas enters the container and the gas component from the sample gas passes into the liquid via the membrane.

[0021] By measuring the pressure in the container area containing the sample gas, the decrease in the gas component content in the sample gas can be determined. As soon as the pressure no longer decreases and / or falls below a predetermined pressure value or pressure gradient, in particular when the temporal gradient of the measured pressure becomes zero, which indicates in particular that the pressure is no longer falling, or the time period has elapsed, or the conductance is no longer changing, the container is opened again to release the sample gas. Depending on the application, the sample gas can, for example, only be released when there is no further transfer of the gas component or at least no significant transfer from the sample gas into the liquid. In this case, the transfer of the gas component into the liquid is complete, at least essentially complete.

[0022] Depending on the application, it may not be necessary to wait for the end of the transfer of the gas component into the liquid, especially if the application does not entail the later use of the transferred gas component.

[0023] The duration may be determined based on experience or previous measurements.

[0024] In one possible embodiment, the invention can use the method, for example, in such a way that the gas component, in particular CO2, is transferred from the sample gas through the at least one membrane into the liquid in order to collect the gas component in the liquid and to determine the relative ratios of isotopes in the collected gas component by analyzing the liquid or a product made from the liquid.

[0025] In another possible embodiment, the method can also be used in such a way that the gas component, in particular CO2, is transferred from the sample gas through the at least one membrane into the liquid in order to test the permeability of the membrane used for the transferred gas component.

[0026] For example, in the second use mentioned, the method can test the suitability of a membrane to be used for the first use mentioned.

[0027] For example, by analyzing the pressure drop after filling the vessel, conclusions can be drawn about the permeability or, more generally, the appropriate function of the membrane. For example, the absolute magnitude of the temporal pressure gradient or the time period during which the pressure falls below a certain limit pressure, starting from the initial pressure, can be evaluated. Depending on the test criteria, these parameters can indicate whether the membrane is intact and / or suitable for the process described in the first application.

[0028] Particularly in the first-mentioned use, the invention can preferably ensure that essentially the entire content of gas component from the sample gas has been transferred into the liquid, so that the sample gas is now released from the container. For example, an outlet valve can be opened for this purpose.

[0029] With this method implementation, the invention realizes a batchwise treatment of sample gas, whereby the complete elimination of the gas component, e.g. CO2, from the sample gas is checked or ensured for each batch by pressure measurement.

[0030] Preferably, such a membrane is formed by a tube made of a material permeable to the gas component, in particular silicone, wherein the container region conducting the sample gas encompasses the inner volume of the at least one tube, and the container region containing the liquid is formed around the at least one tube. The tubular membrane can thus simultaneously assume the function of a conduit element by means of which the sample gas is conducted through the container. The sample gas can be conducted simultaneously within the container through several tubes made of a material permeable to the gas component.

[0031] Due to the filling process according to the invention, the preferably tubular membrane acts like an expandable balloon. It is preferably provided that liquid from the area around the membrane can be displaced when the membrane is pressurized with sample gas, e.g., into a compensation vessel.

[0032] Preferably, the invention provides that the content of gas components in the sample gas that has undergone the method according to the invention reaches zero due to the batchwise treatment, i.e., that all gas components from the sample gas have been collected in the liquid. This ensures that, in a preferred application of the method, for example, the isotopic ratios of carbon can be measured correctly. This would not be the case if the permeation rates for CO2 of different isotopes were different, and CO2 were to remain in the sample gas.

[0033] The invention preferably provides that the sample gas is extracted by means of a pump as a portion from an exhaust gas-carrying exhaust line of an exhaust gas-producing plant, in particular an incineration plant. This is particularly the case in the first-mentioned application. The invention takes advantage of the fact that CO2 is usually evenly distributed in the sample gas, so that collecting CO2 from a portion of the exhaust gas is sufficient.

[0034] In the second use, the invention can also provide for the sample gas to be obtained from a commercially available gas source, e.g., a gas cylinder. In this use, it can preferably be provided that the sample gas is formed entirely by the gas component to be transferred.

[0035] To carry out the method with particularly high quality, the invention preferably provides that the sample gas is first passed through a cold trap before being introduced into the container and thereby dried. The gas component present in the dried sample gas is collected through at least one membrane permeable to the gas component in a liquid that absorbs or binds the gas component, in particular in sodium hydroxide solution. Dried sample gas is understood to mean a sample gas that has a lower water content than the undried sample gas; preferably, dried sample gas no longer contains any water components.

[0036] A cold trap is a section of pipe through which the sample gas is passed and cooled at least to the point where water components condense out of the sample gas, thus making the dried sample gas exiting the cold trap drier than the sample gas entering it. The drying process is more effective the colder the cold trap is, especially the lower it is cooled below zero degrees Celsius.

[0037] By drying the sample gas, the invention ensures that water components from the sample gas cannot deposit on the permeable membrane, or at least that they can deposit less water than in non-dried sample gas, so that diffusion through the membrane is not impaired, or at least less impaired, by water deposits. This ensures better than the prior art that the gas component from the sample gas can pass into the liquid and be collected there, e.g., by chemical bonding to the liquid or dissolving in the liquid.

[0038] The invention can preferably provide for drying the sample gas in the cold trap to such an extent that the dried sample gas no longer contains any water components, or these are at least negligible.

[0039] It is particularly preferred that the gas component contained in the condensate from the cold trap be collected in the same liquid in which the gas component from the dried sample gas is collected. In this case, only this one liquid needs to be analyzed, for example, with regard to isotope ratios, which simplifies the analysis.

[0040] According to the invention, it is provided in a further development that the condensate from the cold trap is passed at least partially, preferably completely, through the same container as the dried sample gas, in particular the dried sample gas is passed through at least one first tube made of a material permeable to the gas component and the condensate is passed at least partially, preferably completely, through at least one second tube made of a material permeable to the gas component.

[0041] According to the invention, the different portions of the gas component from dried sample gas and condensate pass through different pipe sections / tube membranes in the container, but are transferred into the same liquid.

[0042] In a further development, the invention can also provide that downstream of the container, the gas component content of the condensate flowing away from the container is determined by means of a sensor in a line section leading away from the container and the residence time of the condensate in the container is regulated as a function of the measured content, in particular if the content is greater than zero, the residence time is extended, in particular by changing the outflow cross-section in the line section leading away or by guiding the condensate in a circuit through the container.

[0043] In one possible embodiment, the invention can provide that the container region containing the condensate is also operated in batches, in particular that it is filled until a predetermined pressure measured in this container region is reached. In particular, after the predetermined pressure is reached, further filling is stopped. The condensate remains in the container region for the transfer of the gas component, in particular until a predetermined pressure value or pressure gradient measured in the same container region is undershot or a predetermined time has elapsed, and is then released from the container region. In this embodiment, the container is filled with condensate in batches.

[0044] Based on the undershoot of a pressure measurement value and / or the temporal gradient of this measurement value in the respective container area, which includes the sample gas, preferably dried sample gas and / or the condensate, or based on the elapse of a predetermined time, it can be determined or ensured, for example, whether or that all of the gas component in the liquid has been collected, in particular because after this state has been reached the pressure value and / or the gradient no longer falls or the selected time period ensures complete collection, e.g. based on empirical values.

[0045] The gradient in particular can be used to determine whether the liquid is exhausted in terms of its ability to collect the gas component, particularly to chemically bind it or dissolve it in solution. This is primarily because with increasing exhaustion, the rate of collection per unit time and thus the gradient decreases. If the gradient falls below a minimum required value, this can indicate that the liquid is approaching exhaustion and needs to be replaced. The magnitude of the gradient can also be used to test the function of the membrane. If, for example, the temporal gradient exceeds a predetermined limit, it can be concluded that the membrane is defective and is also allowing gas to pass through convection.

[0046] The invention can thus provide for monitoring this gradient in order to indicate the need to replace the fluid and / or the membrane.

[0047] The measured pressure value can preferably represent a differential pressure compared to the atmospheric ambient pressure or a partial pressure of the gas component, in particular in the dried sample gas and / or in the (preferably again gaseous) condensate.

[0048] In the first mentioned use, the invention preferably provides that the liquid used to collect the gas component, in particular the CO2 gas, in particular sodium hydroxide solution, after removal from the container or a product produced from the liquid is analyzed by means of mass spectrometry for the proportions, in particular relative proportions, of isotopes in the gas component, e.g. carbon isotopes.

[0049] For example, the liquid can be thickened, in particular dried, before the mass spectrometric analysis, preferably with a remaining powder being analyzed by mass spectrometry.

[0050] The invention can provide that the sample gas, which is initially conveyed via a heated line and is therefore still hot, is fed to a cold trap and dried therein.

[0051] An embodiment of the invention for the second use mentioned is described below. List of reference symbols 1 pressure gauge, preferably electronic pressure gauge. 2 Gas to be used 3 Conductivity meter 4 Gas outlet 5 membranes, here e.g. tubular membranes 6 Gas absorbing or gas binding liquid 7 Vessel for holding the gas-absorbing liquid 8 Conductivity sensor 9 Valve 10 Pump or storage tank, here hand pump with gas supply (2). 11 Device for clamping a surface membrane 12 Tightly clamped surface membrane. 13 Cavity to accommodate the gas to be used (2).

[0052] The gas supply (2) is introduced into the membrane (5) or the cavity (13).

[0053] For this purpose, the valves (9) are opened. After the gas (2) has been added, the valves (9) are closed.

[0054] The gas (2) permeates through the membrane (5) or (12) into the gas-absorbing or gas-binding liquid (6). The resulting negative pressure is displayed on the pressure gauge (1). The signal from the pressure gauge (1) is stored over time and displayed using a suitable program.

[0055] The conductivity measurement with (3) can indicate its increase during the measurement or serves to control the saturation of the liquid (6). QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2020 005 098 A1

[0011]

Claims

[1] Method for transferring a gas component from a sample gas, in which the gas component present in the sample gas is transferred through at least one membrane permeable to the gas component into a liquid absorbing or binding the gas component, and wherein the sample gas is introduced into a container in which a container region carrying the sample gas is separated from a container region containing the liquid by means of at least one membrane permeable to the gas component, characterized bythat the container area carrying the sample gas is filled until a predetermined pressure measured in the container area is reached, wherein after the predetermined pressure is reached, further filling is stopped and the sample gas remains in the container area for the transfer of the gas component, preferably until a predetermined pressure value or pressure gradient measured in the same container area is undershot or until a predetermined period of time has elapsed or until a conductivity measurement value measured in the liquid is exceeded, and is then released from the container area, preferably, wherein the respectively measured pressure value represents a differential pressure compared to the atmospheric ambient pressure or a partial pressure of the gas component. [2] Method according to claim 1, characterized bythat the at least one membrane is formed by a tube made of a material permeable to the gas component, in particular silicone, and the container region carrying the sample gas comprises the inner volume of the at least one tube and the container region containing the liquid is formed around the at least one tube. [3] Method according to one of the preceding claims, characterized by that the sample gas is taken as a portion from an exhaust gas-carrying exhaust gas line of an exhaust gas-producing plant, in particular an incineration plant, by means of a pump. [4] Method according to one of the preceding claims, characterized bythat the sample gas is first passed through a cold trap and dried in the process, and the gas component present in the dried sample gas is collected through at least one membrane permeable to the gas component into a liquid absorbing or binding the gas component, in particular in sodium hydroxide solution. [5] Method according to claim 4, characterized by that the gas component contained in the condensate of the cold trap is also collected through at least one membrane permeable to the gas component in a liquid absorbing or binding the gas component, in particular in sodium hydroxide solution. [6] Method according to claim 5, characterized bythat the gas component contained in the condensate is collected in the same liquid in which the gas component from the dried sample gas is also collected, in particular for which purpose the condensate from the cold trap is at least partially, in particular completely, passed through the same container as the dried sample gas, in particular the dried sample gas is passed through at least one first tube made of a material permeable to the gas component and the condensate is at least partially passed through at least one second tube made of a material permeable to the gas component. [7] Method according to one of the preceding claims, characterized bythat the container area carrying the condensate is also filled until a predetermined pressure measured in the container area is reached, in particular after the predetermined pressure is reached, further filling is stopped and the condensate remains in the container area for the gas component to collect, preferably until a predetermined pressure value or pressure gradient measured in the same container area is undershot in the container area or until a predetermined period of time has elapsed until a conductivity limit value measured in the liquid is exceeded, and is then released from the container area, preferably, wherein the respectively measured pressure value represents a differential pressure compared to the atmospheric ambient pressure or a partial pressure of the gas component. [8] Method according to one of the preceding claims, characterized bythat the liquid used to collect the gas component, in particular sodium hydroxide solution, after removal from the container or a product made from the liquid is examined by means of mass spectrometry for the proportions, in particular relative proportions, of isotopes in the gas component, in particular carbon isotopes. [9] Method according to claim 8, characterized by that the liquid is thickened, in particular dried, before the mass spectrometric analysis, preferably with a remaining powder being analyzed by mass spectrometry. [10] Use of the method according to one of the preceding claims, characterized by that the gas component, in particular CO2, is transferred from the sample gas through the at least one membrane into the liquid in order to a. to collect the gas component in the liquid and to determine the relative ratios of isotopes in the collected gas component by analyzing the liquid or a product made from the liquid, or b. to test the permeability of the membrane used for the transferred gas component.

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