METHOD AND DEVICE FOR SEPARATION OF A GAS MIXTURE

Description

[0001] The invention relates to a method for separating a gas mixture containing at least methane and carbon dioxide. The gas mixture is, in particular, a gas mixture produced by fermentation from biomass. Such gas mixtures are also referred to as biogas. Furthermore, the invention relates to a device for separating such a gas mixture.

[0002] Methods and devices of the type mentioned above are known in principle from practice and from the prior art in various embodiments. WO 2013 / 087046 A1 describes a method and a plant for separating carbon dioxide from methane-containing raw gases. DE 10 2008 060 310 A1 relates to a method and a plant for purifying raw gases, in particular biogas, for the production of methane. DE 10 2005 051 952 B3 discloses a method for producing methane and liquid carbon dioxide from refinery and / or biogas. DE 10 2008 025 971 A1 relates to a method and a plant for purifying biogas for the production of methane. The publication LAURA ANNAMARIA PELLEGRINI ET AL: "Biogas to liquefied biomethane via cryogenic upgrading technologies", RENEWABLE ENERGY, Vol. 124, August 31, 2018 (2018-08-31), pages 75-83, XP055711440, GB; ISSN: 0960-1481, DOI: 10.1016 / j.renene.2017.08.007 describes the production of biomethane from biogas.Biogas is typically produced by fermenting biomass under suitable fermentation conditions in biogas plants. This process yields gas mixtures containing at least methane and carbon dioxide, and, depending on the fermentation conditions, may also contain hydrogen and other components such as sulfur compounds. These gas mixtures can be used directly for electricity and heat generation. Alternatively, they can be used to produce biogenic methane. However, separation steps are necessary to extract methane from the biogas or gas mixture with a purity that meets the required standards.

[0003] Experience with existing methods and equipment has shown that the corresponding separation steps are very complex and, in particular, costly. Separating the gas mixtures produced by fermentation from biomass to obtain biogenic methane using established methods, such as pressure swing adsorption or amine scrubbing, is therefore not always economical. Furthermore, it has been shown that the reliability of gas separation in these known methods is sometimes unsatisfactory, or that achieving satisfactory purity of the product gases requires a very high level of separation effort. Gas separation using these methods is often uneconomical, especially for smaller biogas plants. Therefore, improvements are needed.

[0004] In contrast, the invention addresses the technical problem of providing a method of the type mentioned above that avoids the disadvantages described above and, in particular, enables the separation of a gas mixture—preferably produced by fermentation from biomass—containing at least methane and carbon dioxide, in a simple, reliable, and cost-effective manner. Furthermore, the invention addresses the technical problem of providing a device for separating a gas mixture, preferably produced by fermentation from biomass.

[0005] To solve the technical problem, the invention teaches a method for separating a gas mixture, in particular one produced by fermentation from biomass, which contains at least methane and carbon dioxide, wherein the gas mixture is brought into contact with a liquid phase in a pressure vessel in which a pressure in the range of 2 bar to 30 bar, preferably 5 bar to 25 bar, preferably 10 bar to 20 bar prevails, so that at least a part of the carbon dioxide dissolves in the liquid phase, wherein the dissolved carbon dioxide is at least partially separated from the liquid phase in a stripping device by at least one stripping agent as part of at least one stripping material stream, in particular continuously, and wherein the stripping agent is an alkane with two to five carbon atoms.

[0006] It is preferred that the carbon dioxide contained in the gas mixture dissolves completely or substantially completely in the liquid phase. It is further preferred that the dissolved carbon dioxide is completely or substantially completely separated from the liquid phase in the stripping device by the at least one stripping agent as part of at least one stripping material stream.

[0007] It is within the scope of the invention that the gas mixture contains minor components in addition to methane and carbon dioxide. These minor components may, for example, be ammonia and / or sulfur compounds, in particular hydrogen sulfide. Advantageously, the minor components contained in the gas mixture also dissolve at least partially, preferably completely or substantially completely, in the liquid phase and are preferably separated from the liquid phase at least partially, preferably completely or substantially completely, by the stripping agent as part of the stripping material stream, in particular continuously. According to a preferred embodiment of the invention, the (unseparated) gas mixture contains between 1 vol.% and 50 vol.%, preferably between 10 vol.% and 45 vol.%, and more preferably between 15 vol.% and 40 vol.% carbon dioxide. More preferably, the (unseparated) gas mixture contains between 45 vol.% and 95 vol.% carbon dioxide.-%, preferably between 50 vol.% and 85 vol.%, preferably between 55 vol.% and 80 vol.% methane.

[0008] In the context of the invention, the term "pressure" refers specifically to relative pressure or gauge pressure. It is preferred that a pressure in the range of 2 bar to 30 bar, preferably 5 bar to 25 bar, and more preferably 10 bar to 20 bar, prevails throughout the entire process or device according to the invention. It is recommended that a pressure in this range also prevails, at least in the stripping device. Most preferably, a pressure corresponding to, or substantially corresponding to, the pressure in the pressure vessel prevails throughout the entire process or device according to the invention.

[0009] The liquid phase with which the gas mixture is brought into contact in the process according to the invention is, in particular, an aqueous liquid phase. It is possible that the liquid phase consists of water or consists essentially of water. The stripping device is advantageously a stripping column. Within the scope of the invention, stripping refers in particular to a separation process for separating at least one substance from a liquid phase using a stripping agent, which is preferably gaseous, in which the at least one substance to be separated is transferred from the liquid phase into the gas phase and, most preferably, leaves the stripping device together with the stripping agent as a stripping stream.

[0010] A particularly preferred embodiment of the process according to the invention is characterized in that the pressure vessel is a pressure fermenter in which the gas mixture is preferably produced by fermentation from biomass, and wherein the liquid phase is expediently a liquid fermentation phase. In the pressure fermenter, the fermentation according to the invention can be carried out in batch or continuous operation. The liquid fermentation phase is expediently an aqueous liquid fermentation phase. It is possible that the liquid fermentation phase consists of water or essentially consists of water, with biomass particles being suspended in the liquid fermentation phase.

[0011] The invention recognizes that, through contact of the gas mixture with a liquid phase in a pressure vessel, at least a portion of the carbon dioxide and preferably at least a portion of any impurities present in the gas mixture dissolve in the liquid phase. The gases dissolved in the liquid phase are then at least partially separated from the liquid phase in the stripping device as part of at least one stripping stream. Advantageously, the liquid phase is subsequently returned to the pressure vessel. Thus, preferably, a carbon dioxide-rich liquid phase is fed from the pressure vessel to the stripping device, and more preferably, a carbon dioxide-poor liquid phase is returned from the stripping device to the pressure vessel. Preferably, the methane contained in the gas mixture remains in the pressure vessel, which can advantageously be removed and utilized as biogenic methane.

[0012] One embodiment of the process according to the invention is characterized in that the biomass is first pre-fermented in a pre-fermenter, whereby hydrogen is produced in particular. The pre-fermentation is advantageously performed upstream of the gas separation in the pressure vessel or the generation and separation of the gas mixture in the pressure fermenter. The pre-fermented biomass is then preferably transferred to the pressure fermenter for further fermentation. The hydrogen preferably remains in the pre-fermenter and is thus obtained as an additional valuable product in this embodiment of the process according to the invention.

[0013] A particularly preferred embodiment of the invention is characterized in that the liquid phase is circulated, and in particular continuously circulated, between the pressure vessel and the stripping device. This embodiment is based on the understanding that carbon dioxide dissolved in the liquid phase, and optionally other dissolved components, are at least partially separated from the liquid phase in the stripping device, and that the liquid phase can then be returned to the pressure vessel. If the pressure vessel is a pressure fermenter, the liquid fermentation phase is thus circulated, and in particular continuously circulated, between the pressure fermenter and the stripping device. Then, a gas mixture containing at least carbon dioxide and methane is continuously generated in the pressure fermenter through ongoing fermentation.The carbon dioxide dissolves in the liquid fermentation phase and is continuously separated from the liquid fermentation phase by stripping through the recirculation between the pressure fermenter and the stripping unit. In this way, methane is continuously supplied in the pressure fermenter.

[0014] It is preferred that the stripping agent is brought into contact with the liquid phase in the stripping device and preferably flows countercurrently to the liquid phase. In this context, countercurrent means in particular that the liquid phase and the stripping agent flow through the stripping device, at least section by section, in opposite directions. In this way, the transfer of the carbon dioxide dissolved in the liquid phase into the gas phase or into the stripping material stream can be carried out with particular reliability. For this purpose, the stripping agent is expediently supplied to the stripping device in a lower section, and the liquid phase is preferably supplied to the stripping device above the point where the stripping agent is added. The liquid phase is then expediently supplied to the stripping device in a lower section or...The liquid is extracted at the lower end and, in particular, returned to the pressure vessel. Within the scope of the invention, it is fundamentally possible for the stripping agent and the liquid phase to be conducted in the stripping device in a co-current flow.

[0015] According to a highly preferred embodiment of the invention, the stripping agent is gaseous, at least when introduced into the stripping device. Advantageously, the stripping stream exiting the stripping device is gaseous. The stripping stream preferably consists of the stripping agent and the gases separated from the liquid phase by stripping, such as carbon dioxide and optionally minor components. As already explained above, the stripping agent is advantageously added to the stripping device in a lower section. In this context, it is recommended that the stripping agent, or the gaseous stripping agent, be injected into the stripping device, particularly into a lower section of the stripping device, by means of at least one nozzle. The gaseous state of the stripping agent, at least when introduced into the stripping device, is advantageously maintained by the device or by means of therealized by the pressure conditions prevailing in the stripping device and / or by the temperature of the stripping agent.

[0016] According to the invention, the stripping agent is an alkane with two to five carbon atoms, particularly preferably at least one stripping agent selected from the group consisting of "ethane, propane, n-butane, isobutane," and most preferably isobutane. The use of isobutane as a stripping agent has proven particularly advantageous within the scope of the invention. The use of a hydrocarbon or an alkane with two to five carbon atoms as a stripping agent, and in particular the use of isobutane, is based primarily on the understanding that these stripping agents can be handled as gaseous stripping agents in the stripping device with relatively little effort. At the same time, liquefaction of these stripping agents, especially isobutane, for further processing of the stripped material stream is possible with relatively little effort.Furthermore, it has been shown that these stripping agents, and isobutane in particular, enable a very reliable separation of carbon dioxide and, if applicable, the impurities from the liquid phase. Moreover, the preferred stripping agents, and especially isobutane, are also advantageous from an environmental perspective.

[0017] As explained above, the stripping stream exiting the stripping device contains at least the stripping agent and at least carbon dioxide, as well as optionally additional components. A particularly preferred embodiment of the invention is characterized in that the stripping stream exiting the stripping device is fed to a separation device, preferably a rectification column. Advantageously, a carbon dioxide-containing stream is separated from the stripping stream in the separation device, in particular continuously. It is recommended that the stripping stream be fed to the separation device below an upper end of the separation device.According to one embodiment, the stripping material flow is fed to the separating device at a distance from the upper end of the separating device that corresponds to between 40% and 60%, preferably between 45% and 55%, of the length of the separating device. According to an alternative embodiment, the stripping material flow is fed to the separating device at a lower end of the separating device.

[0018] In the separation unit or rectification column, carbon dioxide is advantageously enriched towards the upper end of the separation unit. It is recommended that pure or substantially pure carbon dioxide is produced at the upper end of the separation unit. It is also preferred that the separation unit is cooled at least in the region of its upper end and / or that the separation unit is heated at least in the region of its lower end. In this way, the separation process in the separation unit can be controlled. Within the scope of the invention, the terms "upper end" and "lower end" of the separation unit refer in particular to a separation unit that is vertically or substantially vertically oriented in its operating state, for example, a rectification column. If the separation unit is horizontally oriented in its operating state, the terms "upper end" and "lower end" refer to a separation unit that is vertically or substantially vertically oriented in its operating state.In this invention, the term "separation device" refers to a substantially horizontally oriented device. The upper end refers specifically to the end where the carbon dioxide is collected after the separation process, and the lower end refers specifically to the end opposite the upper end. Within the scope of the invention, the term "length of the separation device" refers specifically to the greatest longitudinal extent between the lower and upper ends of the separation device.

[0019] It is recommended that the carbon dioxide-containing material stream be drawn off from the separation device at an upper end and preferably subsequently fed to a storage device. The storage device is preferably a pressurized gas cylinder. If, according to a preferred embodiment, the separation device is a rectification column, the upper end of the separation device is preferably the head of the rectification column. It is preferred that the carbon dioxide-containing material stream has carbon dioxide as its main component and, in particular, consists of at least 95 vol%, preferably at least 97 vol%, and most preferably at least 98 vol% carbon dioxide. According to one embodiment, the carbon dioxide-containing material stream consists entirely or substantially entirely of carbon dioxide. It is preferred that the carbon dioxide-containing material stream...The carbon dioxide contained therein is liquefied after being extracted from the separation device, preferably by means of a coolant. This embodiment is based on the understanding that the carbon dioxide contained in the carbon dioxide-containing material stream can be further isolated by liquefaction. In particular, residual methane that dissolves in the liquid phase in the pressure vessel and is introduced into the separation device with the stripping agent can be separated in this step and preferably returned to the pressure vessel. Furthermore, the liquefied carbon dioxide can be fed to a storage device, for example a compressed gas cylinder, particularly easily and reliably. The separation process according to the invention thus allows technically pure carbon dioxide to be separated from the gas mixture, which contains at least methane and carbon dioxide.Furthermore, it is within the scope of the invention that a portion of the liquefied carbon dioxide is used to cool the separation device, preferably at least in the area of ​​the upper end of the separation device.

[0020] It is also within the scope of the inventive process that the stripping agent accumulates in the separation device as a liquid stripping agent, preferably at a lower end of the separation device, and is preferably returned to the stripping device. The stripping agent is thus expediently liquefied in the separation device. If the separation device according to a preferred embodiment of the invention is a rectification column, the stripping agent preferably accumulates in the column sump, particularly as a liquid stripping agent, and is especially preferably returned to the stripping device. This embodiment is based on the understanding that a very efficient separation of a carbon dioxide-containing mass stream is possible in the separation device.The separation of carbon dioxide from the stripping material stream is possible, and the stripping agent and optionally by-products preferably accumulate at the lower end of the separation device. The liquid or liquefied stripping agent is advantageously returned to the stripping device, so that a recirculation, in particular a continuous recirculation, preferably takes place between the stripping device and the separation device, in which the stripping material stream exits the stripping device and is introduced into the separation device, and in which the stripping agent advantageously exits the separation device and is returned to the stripping device. The separation steps according to the invention thus enable a recirculation of the liquid phase between the pressure vessel and the stripping device and / or a recirculation of the stripping agent between the stripping device and the separation device.Using the separation steps according to the invention, methane and carbon dioxide can be separated with a very satisfactory degree of purity.

[0021] It is possible that the pressure in the separation device is in the range of 2 bar to 30 bar, preferably 5 bar to 25 bar, and more preferably 10 bar to 20 bar. Particularly preferably, the pressure in the separation device corresponds to, or substantially corresponds to, the pressure in the pressure vessel and / or in the stripping device, expediently including a pressure deviation to carry out the separation or rectification process.

[0022] Within the scope of the invention, it is possible that the pressure build-up in the pressure vessel is achieved through technical compression and / or through the production of the gas mixture from biomass by means of fermentation.

[0023] To solve the technical problem, the invention further teaches a device for separating a gas mixture, preferably produced by fermentation from biomass, for carrying out a process described above, wherein the device has a pressure vessel in which the gas mixture, which contains at least methane and carbon dioxide, can be brought into contact with a liquid phase under pressure, wherein the device has a stripping device connected to the pressure vessel, with which carbon dioxide dissolved in the liquid phase can be at least partially separated from the liquid phase by means of at least one stripping agent as part of at least one stripping material stream, in particular continuously, and wherein the stripping agent (5) is an alkane with two to five carbon atoms.

[0024] It is within the scope of the invention that the pressure vessel is a pressure fermenter in which the gas mixture is preferably produced by fermentation from biomass, and wherein the liquid phase is preferably a liquid fermentation phase. It is also possible that the device according to the invention has a pre-fermenter upstream of the pressure vessel in which the biomass can be pre-fermented.

[0025] A particularly preferred embodiment of the device according to the invention is characterized in that the pressure vessel is connected to the stripping device via at least two connecting lines such that the liquid phase can be circulated between the pressure vessel and the stripping device. Advantageously, a first connecting line, provided for a carbon dioxide-rich liquid phase, leads from the pressure vessel, and in particular from a lower section of the pressure vessel, to the stripping device. A carbon dioxide-rich liquid phase is supplied to the stripping device by means of the first connecting line. Preferably, a second connecting line leads from the stripping device, and in particular from a lower section of the stripping device, back to the pressure vessel.This second connecting line returns the carbon dioxide-depleted liquid phase from the stripping unit back into the pressure vessel. The liquid phase can thus be circulated between the pressure vessel and the stripping unit via these at least two connecting lines, and in particular, continuously circulated in such a loop.

[0026] It has proven advantageous for the device according to the invention to have at least one separation device downstream of the stripping unit, with which a carbon dioxide-containing mass stream can be separated from the stripping mass stream. According to a particularly preferred embodiment of the device according to the invention, the separation device is a rectification column, preferably a packed column and / or a bubble-cap column. Within the scope of the invention, a rectification column particularly comprises a column head forming the upper end and a column sump forming the lower end. The carbon dioxide-containing mass stream can be extracted from the separation device, particularly at the upper end. The stripping agent accumulates in the separation device, particularly as a liquid or liquefied stripping agent, preferably at the lower end of the separation device.

[0027] It is within the scope of the invention that the stripping device is connected to the separating device via at least two connecting lines such that the stripping agent can be circulated in a loop between the stripping device and the separating device. Advantageously, the stripping agent can be circulated continuously between the stripping device and the separating device. It is recommended that the stripping material stream containing the stripping agent is conveyed from the stripping device, in particular from an upper section of the stripping device, to the separating device and introduced into the separating device by means of at least a first connecting line. More preferably, the liquid or...The liquefied stripping agent is guided from the separation device, particularly from its lower end, back into the stripping device, specifically to a lower section of the stripping device, and returned to the stripping device. The stripping agent is advantageously heated so that it can be introduced into the stripping device as a gaseous agent. This embodiment is based on the understanding that the stripping agent can be circulated between the stripping device and the separation device, in particular continuously, and thus reused.

[0028] It is further preferred that the device includes a refrigeration unit for liquefying the separated carbon dioxide-containing material stream or the carbon dioxide contained therein. The refrigeration unit is preferably located at the upper end of the separation unit. If the separation unit, according to a preferred embodiment, is a rectification column, the refrigeration unit is expediently located at the column head. Within the scope of the invention, the arrangement of the refrigeration unit at the upper end of the separation unit particularly means that the carbon dioxide-containing material stream exiting the separation unit, or the carbon dioxide contained therein, can be liquefied by means of the refrigeration unit. It is preferred that a portion of the liquefied carbon dioxide is returned to the upper end of the separation unit for cooling purposes.The remaining liquefied carbon dioxide can be conveniently fed into a storage device, for example a pressurized gas cylinder.

[0029] The invention is based on the understanding that the inventive method or device enables a simple and reliable separation of gas mixtures, in particular gas mixtures produced by fermentation from biomass, which contain at least methane and carbon dioxide. Due to the pressure conditions in the pressure vessel, carbon dioxide is separated from the gas mixture by dissolving it in a liquid phase, so that methane remains in the pressure vessel with a purity that meets all requirements. According to the invention, the carbon dioxide dissolved in the liquid phase is separated from the liquid phase in a stripping device. In a separation device, a carbon dioxide-containing stream, containing carbon dioxide as the main component, is separated from the resulting stripping stream in a preferred embodiment.Using the inventive method and device, methane and carbon dioxide can be separated from the gas mixture with a high degree of purity. The inventive method and device are particularly characterized by their simple design, which nevertheless enables a surprisingly reliable separation of the gas mixture, thus ensuring a high purity of methane and carbon dioxide. Furthermore, it should be emphasized that the inventive measures are highly efficient, allowing the method and device to be used very economically for gas separation, regardless of the scale of the biogas plant.As a result, the measures according to the invention enable a reliable gas separation, so that gas products of high purity are obtained, and the separation process is very economical due to the highly efficient separation steps.

[0030] The invention is explained in more detail below with reference to a drawing that illustrates only one embodiment. The single figure shows a schematic flow diagram of a device according to the invention for carrying out the method according to the invention.

[0031] The device comprises a pressure vessel 2, which is preferably, and in the exemplary embodiment, designed as a pressure fermenter. Within the framework of the process according to the invention, a gas mixture 1 containing at least methane and carbon dioxide is produced from biomass in the pressure vessel 2, which is designed as a pressure fermenter. The gas mixture may additionally contain minor components such as hydrogen sulfide. According to the invention, the pressure in the pressure vessel 2, or in the pressure fermenter, is in the range of 2 bar to 30 bar, preferably 10 bar to 20 bar. According to a recommended embodiment of the invention and in the exemplary embodiment, the pressure build-up in the pressure vessel 2 is achieved by producing the gas mixture 1 from biomass by means of fermentation.

[0032] According to the invention, the gas mixture 1 is brought into contact with a liquid phase 3 in the pressure vessel 2, such that at least a portion of the carbon dioxide dissolves in the liquid phase 3 under the prevailing pressure conditions. Advantageously, and in the exemplary embodiment, the liquid phase 3 is an aqueous liquid phase, and in particular an aqueous liquid fermenter phase. Preferably, the carbon dioxide contained in the gas mixture 1 dissolves completely or substantially completely in the liquid phase 3. Furthermore, any minor components, such as hydrogen sulfide, that may be present in the gas mixture 1 also preferably dissolve at least partially, and more preferably completely or substantially completely, in the liquid phase 3.

[0033] In a stripping device 4, which is preferably designed as a stripping column in the exemplary embodiment, the dissolved carbon dioxide is at least partially, preferably completely or substantially completely, separated from the liquid phase 3 by at least one stripping agent 5 as part of at least one stripping stream 6, preferably continuously. The minor components that may be contained in the gas mixture 1 are also expediently, and in the exemplary embodiment, at least partially, preferably completely or substantially completely, separated from the liquid phase 3 by the stripping agent 5 as part of the stripping stream 6. Furthermore, and in the exemplary embodiment according to the single figure, the pressure in the stripping device 4 is preferably in the range of 2 bar to 30 bar, and more preferably from 10 bar to 20 bar.Advantageously, a pressure prevails in this area during the entire method according to the invention or in the entire device according to the invention, and particularly preferably a pressure that corresponds to the pressure in the pressure vessel 2 or that essentially corresponds to the pressure in the pressure vessel 2.

[0034] According to a particularly preferred embodiment, the liquid phase 3 is continuously circulated between the pressure vessel 2 and the stripping device 4. The liquid phase 3 thus advantageously circulates between the pressure vessel 2 and the stripping device 4. For this purpose, the device preferably has two connecting lines 12, 13, by means of which the pressure vessel 2 is connected to the stripping device 4. The first connecting line 12 is advantageously provided, and in the exemplary embodiment, for conveying a carbon dioxide-rich liquid phase 3 from the pressure vessel 2 to the stripping device 4. The second connecting line 13 is preferably provided, and in the exemplary embodiment, for conveying a carbon dioxide-poor liquid phase 3 from the stripping device 4 back into the pressure vessel 2.In the pressure vessel 2 designed as a pressure fermenter, a gas mixture 1 containing at least carbon dioxide and methane is preferably and continuously produced by continuous fermentation in the exemplary embodiment.

[0035] The carbon dioxide dissolves in the liquid phase 3, or the liquid fermenter phase, and is continuously separated from the liquid phase 3 by stripping through the recirculation between the pressure vessel 2 and the stripping unit 4. In this way, methane is continuously supplied to the pressure vessel 2.

[0036] In the stripping unit 4, which is designed as a stripping column, the stripping agent 5 is brought into contact with the liquid phase 3 or with the liquid fermenter phase and preferably, and in the exemplary embodiment, is carried in countercurrent flow to the liquid phase 3. Countercurrent flow means that the liquid phase 3 and the stripping agent 5 flow through the stripping unit 4 in opposite directions. Advantageously, and in the exemplary embodiment, the stripping agent 5 is fed into the stripping unit 4 in a lower section. The liquid phase 3 is preferably fed into the stripping unit 4 above the point where the stripping agent 5 is added. Advantageously, and in the exemplary embodiment, the liquid phase 3 is then withdrawn in a lower section of the stripping unit 4 and returned to the pressure vessel 2 via the second connecting line 13.

[0037] According to a preferred embodiment and in the exemplary embodiment, the stripping agent 5 is gaseous, at least when introduced into the stripping device 4. Advantageously, the stripping material stream 6 exiting the stripping device 4 is also gaseous. Preferably, and in the exemplary embodiment, the stripping agent 5, which is gaseous at least when introduced into the stripping device 4, is injected into the stripping device 4 by means of at least one nozzle, and in particular into a lower section of the stripping device 4.

[0038] The gaseous state of the stripping agent 5, at least upon introduction into the stripping device 4, is advantageously achieved by the pressure conditions prevailing in the device or in the stripping device 4 and / or by the temperature of the stripping agent 5. According to the invention, the stripping agent is an alkane with two to five carbon atoms. In the exemplary embodiment, the stripping agent 5 may be isobutane.

[0039] The stripping material stream 6 preferably consists, and in the exemplary embodiment at least, of the stripping agent 5 and the carbon dioxide separated from the liquid phase 3 by stripping, as well as optionally of minor components such as hydrogen sulfide. According to a particularly preferred embodiment of the invention and in the exemplary embodiment according to the single figure, the stripping material stream 6 exiting the stripping device 4 is fed to a separation device 7, which is preferably, and in the exemplary embodiment, designed as a rectification column.

[0040] In the separation device 7, a carbon dioxide-containing material stream 8 is preferably separated from the stripping material stream 6, preferably continuously. For this purpose, carbon dioxide is expediently concentrated in the separation device 7 on the path between a lower end 11 and an upper end 9 of the separation device 7. It is recommended that pure or substantially pure carbon dioxide is present at the upper end 9 of the separation device 7, i.e., at the column head of the rectification column. According to the invention and in the exemplary embodiment, the stripping agent 5 contained in the stripping material stream 6 is present in the separation device 7 as a liquid or liquefied stripping agent 5. Preferably, and in the exemplary embodiment according to the figure, the stripping agent 5 is present in the separation device 7 at the lower end 11 of the separation device 7, i.e., in the bottom of the rectification column, as a liquid or liquefied stripping agent 5.The stripping agent 5 is liquefied. Preferably, and in the exemplary embodiment, the liquid or liquefied stripping agent 5 is then returned to the stripping device 4. Furthermore, at the lower end of the separation device 11, any by-products such as hydrogen sulfide that may be contained in the stripping material stream 6 also collect according to the invention.

[0041] It is preferred that the separation device 7 is cooled at least in the region of its upper end 9 and / or that the separation device 7 is heated at least in the region of its lower end 11. In this way, the separation process in the separation device 7 can be controlled. It is further preferred that the pressure in the separation device 7 is in the range of 2 bar to 30 bar, preferably 10 bar to 20 bar, and that the pressure in the separation device 7 corresponds to, or substantially corresponds to, the pressure in the pressure vessel 2 and / or in the stripping device 4, including a slight pressure deviation to carry out the separation process or rectification in the separation device 7 or in the rectification column.

[0042] According to the recommended embodiment and in the exemplary embodiment, the stripping material stream 6 is fed to the separating device 7 below the upper end 9 of the separating device 7. Particularly preferably, the stripping material stream 6 is fed to the separating device 7 at a distance from the upper end 9 of the separating device 7, relative to the length L of the separating device 7, which corresponds to a distance of between 40% and 60%, and more preferably, and in the exemplary embodiment, between 45% and 55% of the length L of the separating device 7. Within the scope of the invention, the term length L of the separating device 7 refers in particular to the greatest longitudinal extent of the separating device 7 between the lower end 11 and the upper end 9.

[0043] Advantageously, and in the exemplary embodiment, the stripping device 4 is connected to the separating device 7 via at least two connecting lines 14, 15. In the inventive method and in the exemplary embodiment, the stripping agent 5 is circulated between the stripping device 4 and the separating device 7. Advantageously, the stripping material stream 6 containing the stripping agent 5 is conveyed from the stripping device 4, in particular from an upper section of the stripping device 4, to the separating device 7 by means of the first connecting line 14. More preferably, and in the exemplary embodiment, the liquid or...The liquefied stripping agent 5 is guided from the separating device 7, in particular from the lower end 11 of the separating device 7, back into the stripping device 4 and in particular to a lower section of the stripping device 4, and introduced or injected into the stripping device 4. The liquid or liquefied stripping agent 5 is preferably heated on its way from the separating device 7 to the stripping device 4 in order to transition into the gaseous state.

[0044] Particularly preferably, and in this exemplary embodiment, the carbon dioxide-containing material stream 8 is extracted from the separating device 7 at the upper end 9 and preferably subsequently fed to a storage device 10, preferably, and in this exemplary embodiment, a pressurized gas cylinder. Within the scope of the invention, it is preferred that the carbon dioxide-containing material stream 8 has carbon dioxide as its main component and, in particular, consists of at least 97% by volume, preferably at least 98% by volume, of carbon dioxide. Preferably, the carbon dioxide-containing material stream 8 consists entirely or substantially entirely of carbon dioxide.

[0045] As recommended and in the exemplary embodiment, the carbon dioxide-containing material stream 8, or the carbon dioxide contained therein, is liquefied after being extracted from the separation device 7, preferably by means of a refrigerant. For this purpose, the device according to the invention, in a preferred embodiment and in the exemplary embodiment, has at least one refrigeration unit 16, which is particularly preferably, and in the exemplary embodiment shown in the figure, located at the upper end 9 of the separation device 7. The carbon dioxide-containing material stream 8, or the carbon dioxide contained therein, can preferably be further isolated by liquefaction. The liquefied carbon dioxide can also be fed to the storage device 10 or the pressurized gas cylinder particularly easily and reliably. With the separation process according to the invention, technically pure carbon dioxide is thus separated and obtained.In the exemplary embodiment of the invention, a portion of the liquefied carbon dioxide is used to cool the separation device 7, at least in the region of the upper end 9 of the separation device 7.

[0046] By means of the method or device according to the invention, a simple and reliable separation of a gas mixture 1, in particular a gas mixture 1 produced by fermentation from biomass, which contains at least methane and carbon dioxide, is possible, so that at least methane and carbon dioxide are obtained as separated product gases in a purity that meets the requirements.

Claims

1. A method for separating a gas mixture (1) which is produced in particular by fermentation from biomass and contains at least methane and carbon dioxide, wherein the gas mixture (1) is brought into contact with a liquid phase (3) in a pressure vessel (2) in which a pressure in the range from 2 bar to 30 bar, preferably from 5 bar to 25 bar, preferably from 10 bar to 20 bar prevails, so that at least some of the carbon dioxide dissolves in the liquid phase (3), and wherein the dissolved carbon dioxide in a stripping device (4) is separated at least in part from the liquid phase (3) by at least one stripping agent (5) as part of at least one stripping mass flow (6), in particular is continuously separated, and wherein the stripping agent (5) is an alkane with two to five carbon atoms.

2. The method according to claim 1, wherein the pressure vessel (2) is a pressure fermenter in which preferably the gas mixture (1) is produced by fermentation from biomass, and wherein the liquid phase (3) is expediently a liquid fermenter phase.

3. The method according to any one of claims 1 or 2, wherein the liquid phase (3) is circulated between the pressure vessel (2) and the stripping device (4), in particular is circulated continuously.

4. The method according to any one of claims 1 to 3, wherein the stripping agent (5) is brought into contact with the liquid phase (3) in the stripping device (4) and is preferably guided in counterflow to the liquid phase (3).

5. The method according to any one of claims 1 to 4, wherein the stripping agent (5) is gaseous at least when introduced into the stripping device (4), and wherein the stripping mass flow (6) emerging from the stripping device (4) is preferably gaseous.

6. The method according to any one of claims 1 to 5, wherein the stripping agent (5) is at least one stripping agent (5) selected from the group: "ethane, propane, n-butane, iso-butane" and most preferably is iso-butane.

7. The method according to any one of claims 1 to 6, wherein the stripping mass flow (6) emerging from the stripping device (4) is fed to a separating device (7), preferably to a rectification column, wherein a carbon dioxide-containing mass flow (8) is separated from the stripping mass flow (6) in the separating device (7), in particular is separated continuously.

8. The method according to claim 7, wherein the carbon dioxide-containing mass flow (8) is removed from the separating device (7) at an upper end (9) and is preferably subsequently fed to a storage device (10).

9. The method according to any one of claims 7 or 8, wherein the carbon dioxide-containing mass flow (8) or the carbon dioxide contained therein is liquefied after removal from the separating device (7), preferably liquefied by means of a coolant.

10. The method according to any one of claims 7 to 9, wherein the stripping agent (5) accumulates in the separating device (7) as liquid stripping agent (5), preferably accumulates at a lower end (11) of the separating device (7), and is preferably returned to the stripping device (4).

11. The method according to any one of claims 1 to 10, wherein the pressure build-up in the pressure vessel (2) takes place by technical compression and / or by producing the gas mixture (1) from biomass by means of fermentation.

12. A device for separating a gas mixture (1) preferably produced from biomass by fermentation, for carrying out a method according to any one of claims 1 to 11, wherein the device has a pressure vessel (2) in which the gas mixture (1), which contains at least methane and carbon dioxide, can be brought into contact under pressure with a liquid phase (3), wherein the device has a stripping device (4) connected to the pressure vessel (2), with which carbon dioxide dissolved in the liquid phase (3) can be separated at least partially from the liquid phase (3) by at least one stripping agent (5) as part of at least one stripping mass flow (6), in particular can be separated continuously, and wherein the stripping agent (5) is an alkane with two to five carbon atoms.

13. The device according to claim 12, wherein the pressure vessel (2) is a pressure fermenter, in which preferably the gas mixture (1) can be produced by fermentation from biomass, and wherein the liquid phase (3) is preferably a liquid fermenter phase.

14. The device according to any one of claims 12 or 13, wherein the pressure vessel (2) is connected to the stripping device (4) via at least two connecting lines (12, 13) in such a way that the liquid phase (3) can be circulated between the pressure vessel (2) and the stripping device (4).

15. The device according to any one of claims 12 to 14, wherein the device comprises at least one separating device (7) downstream of the stripping device (4), with which a carbon dioxide-containing mass flow (8) can be separated from the stripping mass flow (6).

16. The device according to claim 15, wherein the separating device (7) is a rectification column, preferably a packed column and / or a bubble-cap column.

17. The device according to any one of claims 15 or 16, wherein the stripping device (4) is connected to the separating device (7) via at least two connecting lines (14, 15) in such a way that the stripping agent (5) can be circulated between the stripping device (4) and the separating device (7).

18. The device according to any one of claims 15 to 17, wherein the device comprises a cooling device (16) for liquefying the separated carbon dioxide-containing mass flow (8) or the carbon dioxide contained therein, wherein the cooling device (16) is preferably associated with an upper end (9) of the separating device (7).