Method and apparatus for treating methane-containing gases

Abstract

The present invention relates to a method for treating a methane-containing gas comprising CO2 and at least one compound from the group of volatile organic compounds (VOCs), the latter being selected from the group consisting of ketones, sulfur-containing hydrocarbons and terpenes, and the method is such that the VOC concentration in the gas mixture is 10 to 10,000 ppm. The methane-containing gas mixture is compressed, cooled and then fed to an absorption apparatus comprising a liquid reversible VOC-absorbing absorption means. In the absorption apparatus, at least a part of the VOCs and up to 55% by volume of the CO2 are absorbed from the methane-containing gas mixture, thereby obtaining a methane-containing VOC- and CO2-reduced gas mixture and a VOC- and CO2-loaded absorption means. Thereafter, the VOC- and CO2-loaded absorption means are transported from the absorption apparatus to a desorption apparatus. Further, the methane-containing VOC- and CO2-reduced gas mixture is fed from the absorption apparatus to a separation apparatus where the CO2 is removed. A regeneration gas stream containing at least a part of the CO2-enriched gas stream is used in the desorption apparatus for the regeneration of the VOC- and CO2-loaded absorption means. Thereafter, an exhaust gas stream is discharged from the desorption apparatus and at least partially regenerated absorption means are transported from the desorption apparatus to the absorption apparatus.

Description

[Technical Field]

[0001] The present invention relates to a method for treating a methane-containing gas according to claim 1 and to an apparatus for carrying out said method. [Background technology]

[0002] Given the ongoing global warming, CO₂-neutral energy carriers are becoming increasingly important for modern society. One proven method of obtaining such CO₂-neutral energy carriers is the fermentation of food waste in fermenters to produce biogas. Because foods such as fruits or vegetables combine CO₂ from the atmosphere as they grow, the biogas formed during the fermentation of these foods and the methane present therein are CO₂-neutral or climate-neutral. Biogas in this application refers to methane-containing gas mixtures of natural origin. In addition to biogas produced by fermentation, for example, from fermenters or landfills, biogas can also be of non-fermentative origin, for example, in the form of natural gas, pit gas, or coal seam gas.

[0003] In order for such methane-containing gas mixtures, or biogas, to be usable for energy production, the methane concentration in the gas mixture must be increased by removing or at least reducing the levels of substantially all other compounds (called impurities). Therefore, biogas, especially that produced by fermentation, is usually purified to increase its methane content.

[0004] The use of suitable adsorbents for the purification of gas mixtures is generally known, for example in industrial off-gas purification or in domestic ventilation, for example in extractor hoods. Air pollutants, in particular hydrocarbons, are removed from the gas mixture to be purified by adsorption on the inner surface of porous adsorbent materials. A distinction can be made between fixed-bed adsorbents, moving-bed adsorbents, rotor adsorbents, fluidized-bed adsorbents, and entrained-flow adsorbents. In multi-stage off-gas purification systems, adsorbents are often also used as "polishing filters" as the final purification stage.

[0005] Nowadays, it is possible to separate impurities in biogas by various biological, chemical, and physical processes, which is commonly called "(bio)gas treatment" and constitutes an important field of use for gas purification. Compounds with high boiling points can be separated, for example, by adsorption on activated carbon filters, while compounds with low boiling points can be removed, for example, by condensation, and water-soluble compounds can be removed by scrubbers. Impurities typically present in biogas are, for example, carbon dioxide (CO2), hydrogen sulfide (H2S), ammonia (NH3), and volatile organic compounds (VOCs for short).

[0006] VOC is a general term for organic or carbonaceous substances that evaporate into the gas phase at room temperature or higher, i.e., are volatile. Examples of VOCs are terpenes, ketones, amines, aldehydes, sulfur-containing hydrocarbons (S-HC), etc. Methane (CH4) is not a member of the group of VOCs in the context of this application.

[0007] In off-gas purification, the removal of VOCs is becoming increasingly important, as reducing VOC emissions in industrial and commercial fields is crucial for two reasons: First, from a health perspective, VOCs in ambient air can cause certain symptoms in humans, such as headaches, irritability, fatigue, reduced physical performance, sleep disorders, and respiratory irritation, collectively referred to as "sick building syndrome." Second, the presence of VOCs in industrially utilized gas mixtures can lead to breakdowns, damage, and reduced efficiency in treatment or supply plants, which can have rapid financial impacts. In membrane plants used for gas purification, filter capacity can be impaired by condensed terpenes, while ketones can damage seals, shortening maintenance intervals and requiring membranes to be replaced earlier and more frequently. Therefore, specific methods have been developed to separate VOCs from gas mixtures at an early stage, both in the field of exhaust gas purification and in biogas processing.

[0008] U.S. Patent Application Publication No. 2019 / 0001263(A1) discloses a method for removing CO2, O2, N2, and VOCs from biogas. In the first step, the gas is compressed, and then VOCs are continuously removed by a first adsorber (preferably "pressure temperature swing adsorption," or "PTSA" for short). Subsequently, CO2 is removed by a cryogenic membrane. Finally, O2 and N2 are separated by a second adsorber (preferably a PTSA) to obtain purified biogas. This method is relatively complex in that it involves three separate separation means (two PTSAs and one membrane), and is therefore relatively expensive and requires heavy maintenance. The two parallel-flowing PTSAs must be heated, particularly for regeneration of the adsorption media, and then cooled back down to operating temperature to ensure a continuous process.

[0009] WO2017099581(A2) discloses a method for purifying a feed gas. This method involves compressing the feed gas and removing water from the compressed gas. Subsequently, VOCs, carbon dioxide, and any water are removed from the gas using an absorber. One objective of the method in WO2017099581(A2) is to extract the maximum amount of carbon dioxide from the feed gas for further use. This method is optimized so that the absorber is reprocessed using two series-connected absorbers, and the components extracted from the feed gas are partially returned to the purification process, minimizing carbon dioxide loss. One drawback of the described method is that it cannot remove VOCs with low boiling points, which remain in the circuit due to recirculation and therefore accumulate in the plant. In this context, VOCs with low boiling points refer to compounds with a boiling point below 50°C. Summary of the Invention [Problem to be solved by the invention]

[0010] It is therefore an object of the present invention to overcome the above-mentioned drawbacks of the prior art and to provide an improved method for removing impurities, in particular CO2 and VOCs, from methane-containing gas mixtures, which allows for an efficient and effective reduction of the CO2 and VOC content. [Means for solving the problem]

[0011] This object is achieved according to the invention by a method according to claim 1 and an apparatus according to claim 16. Preferred embodiments of the invention are reflected in the dependent claims.

[0012] In the method of the present invention, in the first step a), a methane-containing gas mixture containing CO2 and at least one compound from the group of volatile organic compounds (VOCs) is provided. Hereinafter, the term "VOC" is used preferentially instead of the term "compound from the group of volatile organic compounds (VOCs)." According to the present invention, the at least one VOC is selected from the group consisting of ketones, sulfur-containing hydrocarbons, and terpenes. Furthermore, according to the present invention, the VOC concentration in the methane-containing gas mixture is 10 to 10,000 ppm. In the second step b), the methane-containing gas mixture is compressed and cooled. In the third step c), the compressed and cooled methane-containing gas mixture is supplied to an absorber containing a liquid absorbent that reversibly absorbs VOCs. In a fourth step d), at least a portion of the VOCs and up to 5% by volume of CO2 from the methane-containing gas mixture are absorbed by an absorbent in the absorber to obtain a methane-containing gas mixture having reduced levels of VOCs and CO2 and an absorbent loaded with VOCs and CO2. In a fifth step e), the absorbent loaded with VOCs and CO2 from the absorber is supplied to a desorber. In a sixth step f), the methane-containing gas mixture having reduced levels of VOCs and CO2 is supplied from the absorber to a separator including a membrane, where the methane-containing gas mixture having reduced levels of VOCs and CO2 is separated into a reduced pressure CO2-rich gas stream and an isobaric methane-rich gas stream. In a seventh step g), a regeneration gas stream comprising at least a portion of the CO2-enriched gas stream from step f) is supplied to the desorber for regeneration of the VOC- and CO2-loaded absorbent to obtain an off-gas stream comprising CO2 and at least one VOC and at least partially regenerated absorbent. In an eighth step h), the off-gas stream from the seventh step is removed from the desorber to a regenerative post-combustion device, and the at least partially regenerated absorbent from the desorber is supplied to the absorber.

[0013] In the context of the present invention, the term "liquid" means the liquid state of a substance under standard conditions, ie at ambient pressure of 1 bar and 20°C.

[0014] In the context of the present invention, the expression "reversibly absorb" refers to a reversible interaction between the absorbent and the compound to be absorbed, whereby the compound can be reversibly bound to the absorbent and can also be separated from the absorbent again. Here, it is not excluded that an absorbent that reversibly absorbs VOCs, for example, can also reversibly absorb further compounds, such as CO.

[0015] In the context of the present invention, the term "absorbent" means a material capable of at least temporarily binding the compound to be absorbed.

[0016] In the method of the present invention, it is preferable to use a drip-capable absorbent, i.e., an absorbent capable of forming droplets or small droplets. For example, in the case of water, a droplet volume (i.e., a typical droplet volume) of approximately 50 μL is assumed. It will be clear to those skilled in the art that the droplet volume must be determined individually for each absorbent. The example of water serves merely as a guide here. The droplet formation increases the surface area of ​​the absorbent and thus its efficiency. It is preferable to generate droplets using a conventional liquid distributor. Furthermore, it is also possible to use random or structured packings, preferably to better distribute the gas and thereby optimize contact between the gas and the absorbent. Here, the design of the absorber is selected to operate below the flooding point of the packing or absorbent to prevent the packing or absorbent from being pushed out of the absorber by the gas flow. Physical barriers can also be installed to prevent this entrainment. Droplet traps and meshes are considered.

[0017] In the context of the present invention, the expression "decompression" means that the pressure of a gas is reduced, for example by expanding the gas.

[0018] Furthermore, in the context of the present invention, the term "isobaric" means little, if any, variation in pressure conditions, whereby little variation means a variation of up to ±5%.

[0019] Although the steps in the methods of the present invention are numbered, it will be apparent to one of skill in the art that certain steps may proceed in parallel, for example steps e) and f) may be performed in parallel.

[0020] The advantage of the method of the present invention over known prior art methods is that, as a result of the local separation of VOC absorption and desorption, the equipment, in particular the containers in the equipment in which said absorption and desorption take place, are not subjected to any fluctuating stresses and therefore their lifespan is extended.

[0021] Replacing a loaded absorbent with a less loaded one takes only a short time and allows for continuous purification of methane-containing gas mixtures. Furthermore, the method of the present invention reduces the production costs of purified biogas because the method requires only one absorber, and furthermore, the absorber can be operated more inexpensively because the absorbent is regenerated and not consumed, as is the case, for example, with activated carbon as the absorbent.

[0022] One further advantage of the method of the present invention over the prior art is that a liquid absorbent is used, which can therefore be pumped from the first vessel to the second vessel and is easier to handle than the adsorbents disclosed in the prior art, which are typically in the form of bulk materials.

[0023] The use of membranes in the process of the present invention has the further advantage that CO2 can be separated continuously and the maintenance costs of the membranes are lower as opposed to other separation devices such as PTSA.

[0024] The use of CO2 from the membrane as the regeneration gas has the advantage that it is substantially at ambient pressure and substantially VOC-free. Therefore, the cost of providing a separate regeneration gas can be reduced because it is constantly consumed. In desorbing VOCs from the absorbent, the absorbent is loaded with CO2 in the desorber, and the CO2-loaded absorbent exits the desorber. Cooling the absorbent before entering the absorber frees up additional absorption binding sites in the absorbent, allowing it to absorb CO2 again in the absorber.

[0025] However, it will be clear to one skilled in the art that the regeneration gas can also be provided separately, or that it may be preferable to purge the absorbent with a different regeneration gas, e.g., N, for example, if the CO gas stream from the membrane is to be used in some other way.

[0026] In a preferred embodiment of the process, a single absorber is used in step d). One advantage of using just one absorber rather than two series-connected absorbers as disclosed in the prior art is that a process using just one absorber is less expensive to build and maintain than a plant using two or more absorbers.

[0027] In a further preferred embodiment of the method, the absorber in step d) comprises at least four stages. Stages in the context of this application refer to intermediate plates in the absorber that divide the absorption process into separate sub-processes. The use of at least four stages in the absorber allows for the absorption of maximum concentrations of VOCs, as will be shown later in Figures 3 to 11.

[0028] Preferably, in step h), the off-gas stream from the desorber generated in step g) is fed to a regenerative post-combustion unit for oxidation. This can oxidize both VOCs and any methane components present, allowing the off-gas stream to be released into the environment. Destruction of VOCs saves additional disposal costs and increases the overall viability of the plant for biogas processing. By using the CO2-enriched permeate as a regeneration gas that is subsequently subjected to oxidation, the so-called methane slip in the CO2-enriched permeate is also simultaneously subjected to oxidation and prevented from being released into the atmosphere.

[0029] A regenerative post-combustion device generally consists of a mixing device in which the gas mixture to be combusted is mixed with air as an oxygen source, a heat exchange device in which the gas mixture to be combusted mixed with air is heated by the heat of the combustion gas mixture and the combustion gas mixture is cooled, a combustion chamber in which the organic components of the gas mixture are completely oxidized, and a chimney in which the combustion gas mixture is released into the atmosphere.

[0030] In a preferred embodiment, at least steps f) and h), more preferably steps c) to h), are carried out continuously. This has the advantage that the method for treating methane-containing gas is carried out more efficiently and economically than if the gas were simply treated batchwise. Furthermore, continuous operation is less prone to malfunction, as malfunction-prone fixtures are not required to monitor the changeover, as opposed to periodic changeover as typically proposed in the prior art.

[0031] In a preferred embodiment, in step c), 1Bm of the methane-containing gas mixture from step b) is 3 2 to 10 liters of absorbent per unit of volume are used in the absorber.

[0032] In the context of this application, the unit Bm denotes the working cubic meter. 3 defines the actual volume of gas present in the working state. The working volume of a gas can be ascertained to a first approximation with sufficient accuracy using the ideal gas equation of state:

[0033] Preferably, in step g), 1 to 3 liters of VOC-loaded absorbent from step d) is mixed with 1 Bm from step f) in a desorber. 3 It is regenerated by CO2-rich gas.

[0034] In a preferred embodiment, the absorbent for absorbing VOCs has a boiling point of >250°C at 1013.25 mbar and comprises a compound selected from the group consisting of polyethylene glycol (PEG), mineral oil, esters, or combinations thereof, more preferably polyethylene glycol.

[0035] Absorbents with the above-mentioned properties are particularly well suited for the method of the present invention, since they efficiently absorb and desorb VOCs under well-defined conditions without any special cost or inconvenience to achieve those conditions, which means that these absorbents can ensure a good and efficient treatment method.

[0036] The absorbent that reversibly absorbs VOCs preferably has the formula (I): I) R1-O-(CH2CH2O) n -R2 and In the formula, n=3 to 8, R1 and R2 are straight-chain C1-C 10 alkyl.

[0037] The absorbent for reversibly absorbing VOCs based on formula (I) is more preferably compound (Ia) R1-O-(CH2CH2O) n -R2 and where n=11 and R1 and R2 are CH3.

[0038] Therefore, preferred compounds (Ia) are CH3-O-(CH2CH2O) 11 -CH3 is.

[0039] A more preferred absorbent is known under the name Genosorb 300, CAS No. 24991-55-7.

[0040] Surprisingly, it has been found that absorbents of formula (I) are particularly well suited for the process of the invention for the reasons stated above.

[0041] A more preferred absorbent is the stabilized reaction product of 5,8,11,14-tetraoxaoctadecane and 5,8,11,14,17-pentaoxaheneicosane, also known as Genosorb 1843.

[0042] In a preferred embodiment, the at least one VOC has a vapor pressure of at least 0.1 mbar at 20°C and / or a boiling point of at most 240°C at 1013.25 mbar.

[0043] In one preferred embodiment, the at least one VOC is selected from the group consisting of acetone, 2-butanone, 3-methyl-2-butanone, 2-pentanone, 3-pentanone, 3,3-dimethyl-2-butanone, 2-methyl-3-pentanone, 4-methyl-2-pentanone, 3-methyl-2-pentanone, 3-hexanone, 2-hexanone, 5-methyl-3-hexanone, 3-methyl-2-hexanone, 2-heptanone, 4-octanone, 3-octanone, 2-octanone, 2,9-decanedione, α-thujene, α-pinene, camphene, sabinene, β-pinene, myrcene, 3-carene, thujanone, thujopsene, thymol, α-terpinene, β-caryophyllene, 1,4-cineole, eucalyptol, fenchone, γ-terpinene, terpinolene, limonene, tricyclene, linalool, menthone, nopi The preferred thiol compounds are selected from the group consisting of methyl mercaptan, p-menthan-2-one, p-menthan-2-ol, camphor, carbomenthone, 3,3-dimethyl-2-bornanone, carbonyl sulfide, methyl mercaptan, ethyl mercaptan, dimethyl sulfide, carbon disulfide, 2-propanethiol, 2-methyl-2-propanethiol, 1-propanethiol, thiophene, 2-butanethiol, isobutyl mercaptan, methyl allyl sulfide, methyl propyl sulfide, butanethiol, dimethyl disulfide, 2-methylthiophene, 3-methylthiophene, tetrahydrothiophene, 1-pentanethiol, thiophenol, dimethyl trisulfide, diisopropyl disulfide, dimethyl tetrasulfide, methyl propyl disulfide, and methyl isopropyl disulfide. It will be apparent that mixtures of the compounds mentioned may also be used.

[0044] The method of the present invention has also been found to be suitable for treating gas mixtures containing at least two VOCs, preferably at least one further VOC selected from the group consisting of aldehydes, alcohols, amines, BTEX, esters, ethers, CFCs, and siloxanes.

[0045] In a preferred embodiment, the at least one additional VOC is selected from the group consisting of linear or branched C1-C5 alcohols, sulfides, and terpenes.

[0046] The at least one further VOC is preferably 2-methylbutyraldehyde, acetaldehyde, decanal, formaldehyde, hexanal, isobutyraldehyde, isopentanal, n-butyraldehyde, propylaldehyde, 1-butanol, 1-propanol, 2-butanol, 2-ethylhexanol, 2-methyl-1-butanol, 2-methyl-1-propanol, 2-methyl-2-butanol, 2-methyl-3-pentanol, 3-methyl-1-butanol, 3-pentanol, ethanol, isopropanol, methanol. , 4,4-dimethyloxazolidine, 1,4-dimethylpiperazine, 1-methylpiperazine, 1-methylpyrrole, 4-methylpiperazine-1-ethanol, dimethylaminoethanol, dimethylpiperazine, methyldiethanolamine, N-aminoethanolpiperazine, piperazine, pyridine, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, benzene, ethylbenzene, ethyltoluene, m-xylene, o-xylene, propylbenzene, p-xylene, styrene, toluene, 6,6-dimethyl n-tetrahydropyran-2-one, ethyl butyrate, methyl butyrate, propyl butyrate, dimethyl carbonate, ethyl acetate, ethyl heptanoate, methyl hexanoate, ethyl isobutyrate, methyl isobutyrate, isopropyl acetate, methyl acetate, methyl formate, n-butyl acetate, n-propyl acetate, n-propyl propionate, ethyl pentanoate, methyl pentanoate, ethyl propionate, methyl propionate, sec-butyl acetate, 1,3-dioxane, 1,3-dioxolane, 2,4,5-trimethyl-1,3-dioxolane, 2-butylfuran, 2-ethyl-2-methyl-1,3 -dioxolane, 2-ethyl-4-methyl-1,3-dioxolane, 2-ethyl-5-methylfuran, 2-ethylfuran, 5,6-dihydro-2-methyl-2H-pyran, 2-methylfuran, 2-propylfuran, 3-methylfuran, diethyl ether, dimethylfuran, methyl-1,3-dioxane, pentylfuran, tetrahydrofuran, trimethyldioxolane, 1,1,2,2-tetrachloroethane, 1,1,2-trichloroethane, 1,2-dibromoethane, 1,2-dichlorobenzene, 1,2-dichloroethane, 1,2-dichloropropane, 1,3-Dichlorobenzene, 1,4-dichlorobenzene, benzyl chloride, chloroethane, chloromethane, chloroform, dichloromethane, tetrachloroethene, trichlorofluoromethane, trichlorofluoromethane, vinyl chloride, 2,3-butanedione, 2,4-dimethylpentan-3-one, 2-methylhexan-3-one, 3,3-dimethyl-2-butanone, 3-ethylcyclopentanone, 3-heptanone, 4-ethylcyclohexanone, 4-methylhexan-3-one, 6-methylheptan-2-one, cyclohexanone, cyclopentanone, 2-methylcyclopentanone, 3-methylcyclopentanone, hydroxybutanone , 1,4-pentadiene, 2-methyl-1-butene, 1,1-dimethylcyclopropane, 1,3-butadiene, 1-nonene, 1-octene, 1-pentene, 2,2,4-trimethylpentane, 2,2-dimethylbutane, 2,3-dimethyloctane, 2,4-hexadiene, 2,6-dimethyloctane, 2-methyl-2-butene, 2-methylbutane, 2-methylhexane, 2-methylpentane, 2-nonene, 2-octene, 3-methyl-1-butene, 3-methylhexane, 3-methyloctane, 3-methylpentane, 4-methyloctane, 4-octene, butane, butene, cumene, cyclohexane, cyclopentene, trans-1,2-dimethylcyclopropane, decane, dimethyloctene, heptane, hexane, isobutane, methylcyclohexane, methylcyclohexene, methylcyclopentane, naphthalene, n-dodecane, nonane, nonene, n-tetradecane, n-tetradecane, n-tridecane, n-tridecane, octane, pentane, propane, propene, tetramethylbenzene, undecane, decamethylcyclopentasiloxane, decamethyltetrasiloxane, dodecamethylcyclohexasiloxane, dodeca Methylpentasiloxane, ethoxytrimethylsilane, fluorotrimethylsilane, hexamethylcyclotrisiloxane, hexamethyldisiloxane, hydroxytrimethylsilane, octamethylcyclotetrasiloxane, octamethyltrisiloxane, 1-ethyl-1H-pyrrole, acetonitrile, isobutyric acid, methylpropanenitrile, 1-(methylthio)-1-propene, 2-ethyl-5-methylthiazole, 2-ethylthiophene, 2-propylthiophene, 3-pentanethiol, Dipropyl disulfide, dipropyl trisulfide, methyl ethyl disulfide, methyl propyl disulfide, methyl thiirane, methylthiopropane, 1-(methylthio)pentane, sec-butylpropyl disulfide, 2,6-dimethyl-2,6-octadiene, 2,6-dimethyl-4-octene, 2-carene, 3,3,5-trimethyl-1,5-heptadiene, 3,6,6-trimethylbicyclo-[3.1.1]-heptan-2-one, 3,7-dimethyl-2,4-octadiene , alloaromadendrene, α-phellandrene, α-terpineol, α-copaene, α-cubebene, α-gurjunene, α-pinocarvone, α-terpineol acetate, β-elemene, carane, dihydromyrcene, dihydroumbellolone, isomenthol, myrtanol, p,α,α-trimethylbenzyl alcohol, p-cymene, phellandrene, pinocamphone, p-menth-3-ene, terpinen-4-ol, α-caryophyllene, and γ-cadinene.

[0047] Preferably, the methane-containing gas mixture is compressed in step b) to a pressure of 6 to 24 bar(g), preferably 10 to 20 bar(g), more preferably 14 to 18 bar(g), since in these pressure ranges the methane-containing gas can be processed particularly efficiently.

[0048] In a preferred embodiment, the methane-containing gas mixture is cooled in step b) to a temperature between 0°C and 20°C, preferably between 2°C and 10°C, since in these temperature ranges VOCs are efficiently absorbed by the absorbent.

[0049] Preferably, the VOC-loaded absorbent from step d) is heated to between 30° C. and 90° C., more preferably between 50° C. and 70° C., before being transported to the desorber. Heating the absorbent allows for easier and more efficient regeneration of the absorbent in the desorber.

[0050] In a preferred embodiment, the regenerated absorbent from step g) is cooled, preferably to between 0°C and 20°C, more preferably between 2°C and 10°C, before being recycled to the absorber.

[0051] In a preferred embodiment, in step c), the liquid reversibly VOC absorbing absorbent is 3 at least 6 kg per Bm of gas mixture, preferably 3 per Bm of gas mixture, more preferably at least 7 kg per Bm 3 The gas mixture is fed to the absorber at a mass flow rate of at least 7.8 kg per 1 Bm of the liquid reversibly VOC absorbent. 3 at least 6 kg per Bm of gas mixture, preferably 3 per Bm of gas mixture, more preferably at least 7 kg per Bm 3A mass flow rate of at least 7.8 kg per cubic meter of gas mixture also allows for the absorption of VOCs with low boiling points (below 50°C) and therefore their removal from the gas mixture. For example, to remove the VOC substance dimethyl sulfide, which has a boiling point of 37°C at standard pressure, a volumetric flow rate of 7.8 kg of absorbent per operating cubic meter of gas mixture has been found to be ideal. The density of the absorbent in this embodiment is approximately 0.9-1.1 kg / liter.

[0052] A further aspect of the invention relates to an apparatus for treating a methane-containing gas by the method of the invention, said apparatus comprising the following components: gas source, cooling device, Compressor, an absorber having an upper end and a lower end; a detachment device having an upper end and a lower end; separation equipment, a first connecting pipe connecting the lower end of the desorber to the upper end of the absorber; a second connecting pipe connecting the lower end of the absorber to the upper end of the desorber; a third connecting pipe connecting the upper end of the absorber to the separator; and a fourth connecting pipe connecting the separation device to the lower end of the desorber;

[0053] The invention will now be explained in more detail with reference to the following embodiments, the drawings being purely exemplary. [Brief explanation of the drawings]

[0054] [Figure 1] FIG. 1 is a schematic diagram of a preferred embodiment of the process of the present invention for the purification of methane-containing gases. [Figure 2] FIG. 2 shows the configuration of the in silico simulation model. [Figure 3] Figure 3 is a process diagram for the VOC methyl mercaptan. [Figure 4] Figure 4 is a process diagram for the VOC dimethyl sulfide. [Figure 5]Figure 5 is a process diagram for the VOC acetone. [Figure 6] Figure 6 is a process diagram for the VOC 2-butanone. [Figure 7] Figure 7 is a process diagram for the VOC 1-propanol. [Figure 8] Figure 8 is a process diagram for the VOC toluene. [Figure 9] Figure 9 is a process diagram for the VOC limonene. [Figure 10] FIG. 10 is a diagram of VOC concentrations measured in a plant producing biogas from renewable feedstocks. [Figure 11] FIG. 11 shows the VOC concentrations measured in a waste-to-biogas production plant. [Figure 12] FIG. 12 shows the configuration of the in silico simulation model. DETAILED DESCRIPTION OF THE INVENTION

[0055] In a preferred embodiment of the method of the present invention, which is shown schematically in Figure 1, in a first step a methane-containing gas mixture is provided from a gas source 101. The gas mixture 103 comprises CO2 and at least one compound from the group of volatile organic compounds (VOCs). The methane-containing gas mixture 103 is compressed to 14-18 bar(g) in a compressor 105 and then cooled to 2-10°C in a chiller 107.

[0056] The methane-containing gas mixture 103 is then fed to an absorber 109 where the methane-containing gas mixture 103 is introduced at a lower end 111 of the absorber 109 and rises to an upper end 113 of the absorber 109.

[0057] The terms "top" and "bottom" refer to the respective device orientations shown in the figures.

[0058] The absorber 109 is further supplied with a liquid absorbent 117 via a first connecting pipe 115 leading to the absorber 109 in the region of its upper end 113. The liquid absorbent 117 flows in the form of droplets from the upper end 113 to the lower end 111 of the absorber 109 and contacts the countercurrent flow of the methane-containing gas mixture 103. Contact of the absorbent 117 with the methane-containing gas mixture 103 results in reversible binding of VOCs present in the gas mixture in the absorbent 117, resulting in a methane-containing gas mixture 119 having a reduced VOC level at the upper end 113 of the absorber 109, and VOC-loaded absorbent 121 being collected at the lower end 111 of the absorber 109. The methane-containing gas mixture 119 having a reduced VOC level is passed from the upper end 113 of the absorber 109 to a separator 125 via a second connecting pipe 123. The VOC-loaded absorbent 121 is pumped by a pump (not shown) from the lower end 111 of the absorber 109 through a third manifold 127 to a heat exchanger 129 where it is heated to 50-70°C. The VOC-loaded absorbent 121 is then pumped further to the upper end 133 of a desorber 135 and fed to the desorber 135. In the separator 125, the methane-containing gas mixture 119 with reduced VOC levels is separated into a reduced pressure CO2-enriched gas stream 137 (pressure -0.5 to +0.5 bar(g)) and an isobaric methane-enriched gas stream 139 (pressure 14-18 bar(g)). The CO2-enriched gas stream 137 is then introduced through a fourth manifold 143 at the lower end 141 of the desorber 135 and flows up to the upper end 133 of the desorber 135. The liquid VOC-loaded absorbent 121 flows in droplet form from the upper end 133 to the lower end 141 of the desorber 135, where it contacts the counterflow of the CO2-enriched gas stream 137. As a result of heating the liquid VOC-loaded absorbent 121, the bound VOCs are reversibly released and flow with the CO2-enriched gas stream 137 to the upper end 133 of the desorber 135. This produces purified absorbent 145, which collects at the lower end 141 of the desorber 135. A fifth connecting pipe 147 carries the purified absorbent 145 via a pump (not shown) to the heat exchanger 129, where it is cooled to 2-10°C and then pumped via the feed pipe 115 to the upper end 113 of the absorber 109.The heat exchanger 129 may comprise multiple separate heat exchangers 131, 131', 131''. By this method, at the upper end 133 of the desorber 135, a CO2 and VOC-enriched gas stream 149 is removed and sent to a regenerative post-combustion unit 151 to reduce environmental pollution.

[0059] To use methane-containing gas as a natural gas substitute, the sulfur-containing components in the produced gas must be kept below 6 mg / m 3 The sulfur equivalent must be reduced below the limit, which is set out, for example, in the rulebook G260 of the DVGW [German Technical and Scientific Association for Gas and Water].

[0060] For example, restrictions on the use of gas-permeable membranes for other VOCs may apply, such as requiring total VOC concentrations to be less than 10 ppm to meet Evonik (a manufacturer of gas-permeable membranes) application requirements.

[0061] A further reason for the debate regarding the limitation of VOCs in biogas is the off-putting odor that VOCs can cause.

[0062] 2 shows an in silico simulation model of a preferred embodiment of the method of the present invention. The simulation model includes an absorber 201 and a desorber 203. An absorbent, here PEG, enters absorber 201 as liquid 205. The absorbent exits absorber 201 as VOC-laden liquid 207 and is heated in heat exchanger 209. The resulting heated VOC-laden absorbent 211 is conveyed from heat exchanger 209 to a further heat exchanger 213 where it is further heated. Here, external heat 215 is supplied to heat exchanger 213. The significantly heated VOC-laden absorbent 217 exits heat exchanger 213 and is expanded in control valve 219. The heated and expanded VOC-laden absorbent 221 enters desorber 203 where it releases VOCs. The heated, expanded, largely regenerated absorbent 223 is compressed by pump 225 and then further transported to heat exchanger 209 as heated, largely regenerated, compressed absorbent 227. In heat exchanger 209, absorbent 227 releases part of its heat to VOC-loaded absorbent 207. The cooler, largely regenerated, compressed absorbent 229 is then transported to a further heat exchanger 231 where it is further cooled. For this purpose, heat exchanger 231 is supplied with external cooling 233. The largely regenerated, compressed, cooled absorbent 205 enters absorber 201 again, thus completing the absorbent circuit. The compressed biogas 235 to be purified is cooled by external cooling 239 in heat exchanger 237, and the condensate is then removed in condensate separator 241. The resulting cooled compressed biogas 243 is fed to absorber 201 where it contacts the largely regenerated, compressed, and cooled absorbent 205 and releases its VOCs to the absorbent 205. The purified biogas 245 exits absorber 201 and can then be used for further processing 247. Regeneration gas 249, e.g., lean gas from biogas processing 251, is fed to heat exchanger 253 where it is heated. The heated regeneration gas 255 enters desorber 203 where it releases VOCs from the heated and expanded VOC-loaded absorbent 221.The VOC-laden regeneration gas 257 then exits the desorber 203 and gives up its heat to the regeneration gas 249 in heat exchanger 253. The cooled VOC-laden regeneration gas 259 is conveyed by suction blower 261 to post-treatment unit 263.

[0063] In the computer simulation described above, the solubility of a specific VOC in an absorbent, in this case PEG, was simulated using Henry's law. In the first step, an equilibrium line where the gas and liquid phases are in equilibrium is simulated. The slope of the equilibrium line corresponds to the Henry's coefficient of the compound at each temperature. In the second step, a mass balance line resulting from the mass balance of the VOCs in the absorber is simulated. The starting point of the mass balance line is the VOC concentration at the top of the absorber (cleaned biogas 245) and the liquid phase concentration at the top of the absorber (regenerated PEG 205). The end point of the mass balance line is found from the gas phase concentration at the bottom of the absorber (VOC-containing biogas 243) and the liquid phase concentration at the bottom of the absorber (VOC-loaded PEG 207). A straight line (mass balance line) connects the starting point and the end point of the mass balance line. This is only applicable under the assumption that the temperature in the absorber is constant. In the case of a temperature gradient, both the mass balance line and the equilibrium line are shown as mass balance curves and equilibrium curves. A step structure can be drawn between the mass balance line and the equilibrium line. Each step represents one theoretical plate of the column. The number of steps is a measure of the required height of the absorber. In absorption, the mass balance line is always above the equilibrium line. When the mass balance line is below the equilibrium line, the operation is desorption.

[0064] Figure 3a shows a similar process diagram for the VOC methyl mercaptan (CAS 74-93-1) in an absorber with PEG as the absorbent. The mass balance line (dashed line) is placed above the equilibrium line (dash-dotted line), and a staircase structure (solid line) is shown in between.

[0065] Figure 3b shows a similar process diagram to the one described above for the VOC methyl mercaptan (CAS 74-93-1) in the desorber and PEG as the absorbent. The equilibrium line (dash-dotted line) is located above the mass balance line (dashed line), and the staircase structure (solid line) is shown in between. From Figure 3a, it is clear that the staircase structure is not feasible for methyl mercaptan because if the absorbent flow is too low (in the simulation model), a large residue of methyl mercaptan remains in the purified biogas. From Figure 3b, it is clear that the absorbent is virtually completely regenerated in the desorber, resulting in the removal of methyl mercaptan.

[0066] Figures 4a and 4b show process diagrams similar to those described above for the VOC dimethyl sulfide (CAS 75-18-3) and PEG as the absorbent in an absorber (Figure 4a) and a desorber (Figure 4b). From Figure 4a, it is clear that biogas purification requires multiple steps, but that residual dimethyl sulfide remains in the biogas. From Figure 4b, it is clear that the absorbent is substantially completely regenerated in the desorber, resulting in the removal of dimethyl sulfide.

[0067] Figures 5a and 5b show exactly such process diagrams for the VOC acetone (CAS 67-64-1) and PEG as the absorbent in an absorber (Figure 5a) and a desorber (Figure 5b), similar to the process diagrams described above. From Figure 5a, it is clear that although biogas purification requires multiple steps, very little acetone residue remains in the biogas. From Figure 5b, it is clear that the absorbent is virtually completely regenerated in the desorber, resulting in the removal of acetone.

[0068] Figures 6a and 6b show exactly such process diagrams for the VOC 2-butanone (CAS 78-93-3) and PEG as the absorbent in an absorber (Figure 6a) and a desorber (Figure 6b), similar to the process diagrams described above. From Figure 6a, it is clear that only a few steps are required to purify the biogas, and no residual 2-butanone remains in the biogas. From Figure 6b, it is clear that the absorbent is regenerated in the desorber, and multiple steps are required to remove the 2-butanone, but small amounts of 2-butanone remain in the regenerated absorbent.

[0069] Figures 7a and 7b show process diagrams for the VOC 1-propanol (CAS 71-23-8) and PEG as absorbent in an absorber (Figure 7a) and a desorber (Figure 7b), similar to those shown above. From Figure 7a, it is clear that only a few steps are required for biogas purification, with very little residue of 1-propanol remaining in the biogas. From Figure 7b, it is clear that despite the multiple steps, the absorbent for 1-propanol removal is not completely regenerated in the desorber.

[0070] Figures 8a and 8b show process diagrams constructed similarly to those described above for the VOC toluene (CAS 108-88-3) and PEG as the absorbent in an absorber (Figure 8a) and a desorber (Figure 8b). From Figure 8a, it is clear that only a few steps are required to purify the biogas, but that residual toluene remains in the biogas because the biogas was incompletely regenerated. From Figure 8b, it is clear that despite the numerous steps, the absorbent for removing toluene is not fully regenerated in the desorber. Since the mass balance and equilibrium lines run parallel, complete regeneration is impossible.

[0071] Figures 9a and 9b show similarly constructed process diagrams for the VOC limonene (CAS 7705-14-8) and PEG as the absorbent in the absorber (Figure 9a) and desorber (Figure 9b). From Figure 9a, it is clear that only a few steps are required to purify the biogas, but that residual limonene remains in the biogas because the biogas was incompletely regenerated. From Figure 9b, it is clear that despite the large number of steps, the absorbent is not fully regenerated in the desorber to remove limonene because the absorbent mass flow rate (in the simulation model) is too high.

[0072] Based on the simulations shown in Figures 2 to 9, it can be concluded that VOCs with boiling points between 35°C and 100°C can be substantially completely released from the biogas in the absorber and substantially completely released from the absorbent in the desorber. VOCs with boiling points higher than 100°C are substantially completely removed from the biogas. However, the regeneration of the absorbent is incomplete. VOCs with boiling points below 35°C are incompletely removed from the biogas. The gas components CO2 and methane remain almost completely in the gas phase.

[0073] Figure 10 shows a diagram based on 48 measurements of VOCs in biogas samples, where the biogas was produced from renewable raw materials. The concentration of VOCs in biogas ranges from 5 to 20 ppm. Individual values ​​are higher. VOCs in biogas from renewable raw materials do not present any problems in further processing.

[0074] Figure 11 shows a diagram based on 138 measurements of VOCs in biogas samples. Here, biogas was produced from waste. The concentration of VOCs in biogas ranges from 10 to 250 ppm. In many cases, higher concentrations have been achieved. VOCs in biogas from waste often present problems in further processing. Therefore, controlled removal of VOCs is necessary. [Example]

[0075] Experimental data FIG. 12 shows an in silico simulation model of a preferred embodiment of the method of the present invention described in FIG. 2. Various parameters for the biogas, absorbent, and regeneration gas were added to the simulation model to determine the amount of CO and VOC absorbed. The simulation model includes three gas streams at different stages. Compressed methane-containing gas BG1 is fed to heat exchanger 1201 and exits the heat exchanger as compressed and cooled methane-containing gas BG2. Methane-containing gas BG2 is fed to absorber 1203, where CO and VOC components present in methane-containing gas BG2 are absorbed. Methane-containing gas BG3 with reduced levels of CO and VOC exits absorber 1203. In absorber 1203, methane-containing gas BG2 contacts regenerated and cooled absorbent AB1. The regenerated and cooled absorbent AB1 absorbs CO2 and VOCs in absorber 1203 and exits as CO2- and VOC-loaded absorbent AB2. The CO2- and VOC-loaded absorbent AB2 is heated in heat exchanger 1205 and exits as heated CO2- and VOC-loaded absorbent AB3. The heated CO2- and VOC-loaded absorbent AB3 is further heated in further heat exchanger 1207 and exits as heated CO2- and VOC-loaded absorbent AB4. The heated CO2- and VOC-loaded absorbent AB4 is fed to control valve 1209 where it expands and exits as heated and expanded CO2- and VOC-loaded absorbent AB5. The heated and expanded CO2- and VOC-loaded absorbent AB5 is fed to desorber 1211.

[0076] Regeneration gas RG1 is heated in heat exchanger 1213 and exits the heat exchanger as heated regeneration gas RG2. Regeneration gas RG1 is a gas stream having CO2 as its primary component. The heated regeneration gas RG2 is supplied to desorber 1211, where it contacts heated, expanded CO2- and VOC-loaded absorbent AB5. The heated regeneration gas RG2 releases the CO2 and VOCs from absorbent AB5 to produce regeneration gas RG3 containing CO2 and VOCs and heated, expanded, largely regenerated absorbent AB6. The heated, expanded, largely regenerated absorbent AB6 is compressed in pump 1215 and then supplied to heat exchanger 1205 as heated, largely regenerated, compressed absorbent AB7. In heat exchanger 1205, the heated, mostly regenerated, compressed absorbent AB7 loses its heat to CO2- and VOC-loaded absorbent AB2 and exits heat exchanger 1205 as mostly regenerated, compressed, cooled absorbent AB8. The mostly regenerated, compressed, cooled absorbent AB8 is supplied to heat exchanger 1217 where it is cooled and exits the heat exchanger as cooled regenerated absorbent AB1. Regeneration gas RG3 containing CO2 and VOCs is supplied to heat exchanger 1213 where it loses its heat to regeneration gas RG1 and exits heat exchanger 1213 as cooled regeneration gas RG4 containing CO2 and VOCs. The cooled regeneration gas RG4 containing CO2 and VOCs is conveyed by suction blower 1219 to post-treatment unit 1221 as cooled regeneration gas RG5 containing CO2 and VOCs.

[0077] Table 1 below shows the parameters of the simulation model using the absorbent PEG1843. This absorbent absorbs only 2.5 kg / h (0.4%) of methane, but 36.6 kg / h of CO2 (3.6%) and over 98% of the VOCs (dimethyl sulfide (DMS), acetone, 2-butanone, and terpenes) are absorbed. Note that VOCs with low boiling points, such as DMS (boiling point 37°C), VOCs with medium boiling points, such as acetone (boiling point 56°C) and 2-butanone (boiling point 79.6°C), and VOCs with high boiling points, such as terpenes (boiling points 140-230°C), are absorbed.

[0078] This is evident from the difference in mass between BG2 and BG3. 36.6 kg / h of CO2 and VOCs are released from the methane-containing gas BG2 to the absorbent AB1, which is reflected in the increase in CO2 and VOC concentrations from AB1 to AB5. The VOC- and CO2-containing absorbent then passes 36.6 kg / h of CO2 and VOCs to the regeneration gas RG1, which is reflected in the increase in CO2 and VOC concentrations from RG1 to RG3.

[0079] [Table 1]

[0080] Tables 2 to 4 show the same parameter configuration as Table 1, and differ from Table 1 only in that the temperatures of regeneration gases RG1 and RG3, the temperature of absorbent AB5, and the mass flow rates of RG1, RG3, AB1, and AB5 are changed.

[0081] Tables 5 to 8 show the same parameter configuration as Tables 1 to 4, and the only change in the simulation model was the change of absorbent from PEG1843 (Tables 1 to 4) to PEG300 (Tables 5 to 8).

[0082] [Table 2]

[0083] [Table 3]

[0084] [Table 4]

[0085] [Table 5]

[0086] [Table 6]

[0087] [Table 7]

[0088] [Table 8]

[0089] It is clear that in all parameter configurations in the above simulation model, only about 3.6% by volume of the CO2 present in BG1 is absorbed by the absorbent. It should be noted that in Tables 2 and 6, the concentrations of terpenes in AB1 and AB5 are higher than in Tables 1, 3-5, and 7-8. In all parameter configurations, terpenes were not completely removable from the absorbent (see AB1). Nevertheless, surprisingly, it was possible to remove most of the terpenes present in the methane-containing biogas BG2 from it (see BG3). The present disclosure also discloses the following exemplary embodiments. [Embodiment 1] 1. A method for treating a methane-containing gas, comprising: a) 20-60% by volume of CO 2 and at least one compound from the group of volatile organic compounds (VOCs), the at least one VOC is selected from the group consisting of ketones, sulfur-containing hydrocarbons, and terpenes; a VOC concentration in the gas mixture is 10 to 10,000 ppm; b) compressing and cooling the methane-containing gas mixture (103) from step a); c) feeding the compressed and cooled methane-containing gas mixture to an absorber (109), said absorber (109) comprising a liquid reversible VOC absorbent (117); d) removing at least a portion of the VOCs and 5% by volume or less of the CO by the absorbent (117). 2 Absorbs and reduces levels of VOCs and CO 2 a methane-containing gas mixture (119) having VOCs and CO 2 obtaining an absorbent (121) carrying the e) the VOC and CO from the absorber (109) 2 supplying the absorbent (121) carrying the f) said reduced levels of VOCs and CO 2 and feeding the methane-containing gas mixture (119) from the absorber (109) to a separator (125) including a membrane, wherein the reduced levels of VOCs and CO 2 A methane-containing gas mixture (119) having a reduced pressure of CO 2 separating the enriched gas stream (137) and an isobaric methane-enriched gas stream (139); g) the VOCs and CO 2 for regeneration of the absorbent (121) loaded with CO 2 A regeneration gas stream (138) comprising at least a portion of the enriched gas stream (137) is fed to the desorber (135) to produce CO 2 and obtaining an off-gas stream (149) containing said VOCs and an at least partially regenerated absorbent (145); h) removing the off-gas stream (149) from the desorber (135) and recycling the at least partially regenerated absorbent (145) from the desorber (135) to the absorber (109); A method comprising: [Embodiment 2] 2. The method of claim 1, wherein in step h), the off-gas stream (149) is fed to a regenerative post-combustion unit (151) for oxidation. [Embodiment 3] 3. The method according to embodiment 1 or 2, wherein at least steps c) to h) are carried out consecutively. [Embodiment 4] In step c), 1Bm of the methane-containing gas mixture from step b) 3 4. The method of any one of the preceding claims, wherein 2 to 10 liters of absorbent per 100 ml of water are used in the absorber. [Embodiment 5] In step g), 1 to 3 liters of VOC-loaded absorbent from step d) is mixed with 1 Bm from step f) in a desorber. 3 CO 2 5. The method according to any one of the preceding embodiments, characterized in that it is regenerated with enriched gas. [Embodiment 6] 6. The method according to any one of the preceding claims, wherein the absorbent (117, 145) for absorbing VOCs comprises a compound having a boiling point above 250°C at 1013.25 mbar and selected from the group consisting of polyethylene glycol (PEG), mineral oil, esters, or combinations thereof, preferably polyethylene glycol. [Embodiment 7] The absorbent (117, 145) for absorbing VOCs is represented by the formula (I): I) R 1 -O-(CH 2 CH 2 O) n -R 2 (wherein n=3 to 11, R 1 and R 2 But linear C 1 ~C 10 alkyl.) 7. The method of any one of embodiments 1 to 6, comprising the compound of formula: [Embodiment 8] 8. The method according to any one of the preceding claims, wherein the VOC has a vapor pressure of at least 0.1 mbar at 20°C and / or a boiling point of at most 240°C at 1013.25 mbar. [Embodiment 9] The at least one VOC is selected from the group consisting of acetone, 2-butanone, 3-methyl-2-butanone, 2-pentanone, 3-pentanone, 3,3-dimethyl-2-butanone, 2-methyl-3-pentanone, 4-methyl-2-pentanone, 3-methyl-2-pentanone, 3-hexanone, 2-hexanone, 5-methyl-3-hexanone, 3-methyl-2-hexanone, 2-heptanone, 4-octanone, and 3-octanone. , 2-octanone, 2,9-decanedione, α-thujene, α-pinene, camphene, sabinene, β-pinene, myrcene, 3-carene, thujanone, thujopsene, thymol, α-terpinene, β-caryophyllene, 1,4-cineole, eucalyptol, fenchone, γ-terpinene, terpinolene, limonene, tricyclene, linalool, menthone, nopinone, p-menthan-2-one, p-mentha 9. The method according to any one of the preceding claims, wherein the carboxylic acid is selected from the group consisting of benzophenone-2-ol, camphor, carbomenthone, 3,3-dimethyl-2-bornanone, carbonyl sulfide, methyl mercaptan, ethyl mercaptan, dimethyl sulfide, carbon disulfide, 2-propanethiol, 2-methyl-2-propanethiol, 1-propanethiol, thiophene, 2-butanethiol, isobutyl mercaptan, methyl allyl sulfide, methyl propyl sulfide, butanethiol, dimethyl disulfide, 2-methylthiophene, 3-methylthiophene, tetrahydrothiophene, 1-pentanethiol, thiophenol, dimethyl trisulfide, diisopropyl disulfide, dimethyl tetrasulfide, methyl propyl disulfide, and methyl isopropyl disulfide. [Embodiment 10] 10. The method according to any one of the preceding claims, wherein the methane-containing gas mixture (103) is compressed in step b) to a pressure between 6 and 24 bar(g), preferably between 10 and 20 bar(g), more preferably between 14 and 18 bar(g). [Embodiment 11] 10. The method according to any one of the preceding embodiments, wherein the methane-containing gas mixture (103) is cooled in step b) to a temperature between 0°C and 20°C, preferably between 2°C and 10°C. [Embodiment 12] 11. The method according to any one of the preceding embodiments, wherein the VOC-loaded absorbent (121) from step d) is heated, preferably to a temperature between 30°C and 90°C, more preferably between 50°C and 70°C, before being transported to the desorber (135). [Embodiment 13] 12. The method according to any one of the preceding embodiments, wherein the regenerated absorbent (145) from step g) is cooled, preferably to between 0°C and 20°C, more preferably to between 2°C and 10°C, before being recycled to the absorber (109). [Embodiment 14] In step c), the liquid reversibly VOC absorbing absorbent (117) is added to the gas mixture (103) 1Bm 3 14. The method according to any one of the preceding embodiments, characterized in that the absorber (109) is supplied with a volumetric flow rate of at least 7.8 kg per 100 ml of water. [Embodiment 15] 15. An apparatus (100) for treating a methane-containing gas (103) by the method of any one of embodiments 1 to 14, comprising: a gas source (101); a cooling device (107); a compressor (105); an absorber (109) having an upper end (113) and a lower end (111); a detachment device (135) having an upper end (133) and a lower end (141); a separation device (125) comprising a membrane; a first connecting pipe (115, 147) connecting the lower end (141) of the desorber (135) to the upper end (113) of the absorber (109); a second connecting pipe (127) connecting the lower end (111) of the absorber (109) to the upper end (133) of the desorber (135); a third connecting pipe (123) connecting the upper end of the absorber (109) to the separator (125); a fourth connecting pipe (143) connecting the separating device (125) to the lower end (141) of the desorbing device (135); An apparatus (100) comprising:

Claims

1. 1. A method for treating a methane-containing gas, comprising: a) 20 to 60% by volume of CO ２ and at least one compound from the group of volatile organic compounds (VOCs), the at least one VOC is selected from the group consisting of ketones, sulfur-containing hydrocarbons, and terpenes; a VOC concentration in the gas mixture is 10 to 10,000 ppm; b) compressing and cooling the methane-containing gas mixture (103) from step a); c) feeding the compressed and cooled methane-containing gas mixture to an absorber (109), said absorber (109) comprising a liquid reversibly VOC absorbing absorbent (117); d) removing at least a portion of the VOCs and 5% by volume or less of the CO by the absorbent (117). ２ to absorb reduced levels of VOCs and CO ２ a methane-containing gas mixture (119) having VOCs and CO ２ obtaining an absorbent (121) carrying the e) the VOCs and CO from the absorber (109) ２ supplying the absorbent (121) loaded with the f) the reduced levels of VOCs and CO ２ and feeding the methane-containing gas mixture (119) from the absorber (109) to a membrane-containing separator (125), wherein the reduced levels of VOCs and CO ２ A methane-containing gas mixture (119) having a reduced pressure CO ２ separating the enriched gas stream (137) and an isobaric methane-enriched gas stream (139); g) the VOCs and CO ２ for regeneration of the absorbent (121) loaded with CO ２ A regeneration gas stream (138) comprising at least a portion of the enriched gas stream (137) is fed to the desorber (135) to produce a CO ２ and obtaining an off-gas stream (149) containing said VOCs and an at least partially regenerated absorbent (145); h) removing the off-gas stream (149) from the desorber (135) and recycling the at least partially regenerated absorbent (145) from the desorber (135) to the absorber (109); A method comprising:

2. 2. The method of claim 1, wherein in step h) the off-gas stream (149) is fed to a regenerative post-combustion unit (151) for oxidation.

3. 2. The method of claim 1, wherein at least steps c) to h) are performed sequentially.

4. In step c), 1 Bm of the methane-containing gas mixture from step b) ３ 2. The method of claim 1, wherein 2 to 10 liters of absorbent per 100 ml of water are used in the absorber.

5. In step g), 1 to 3 liters of VOC-loaded absorbent from step d) is mixed with 1 Bm from step f) in a desorber. ３ CO ２ 2. The method of claim 1, wherein the regeneration is carried out with enriched gas.

6. 10. The method of claim 1, wherein the absorbent (117, 145) for absorbing VOCs has a boiling point greater than 250°C at 1013.25 mbar and comprises a compound selected from the group consisting of polyethylene glycol (PEG), mineral oil, ester, or a combination thereof.

7. The absorbent (117, 145) for absorbing VOCs is represented by the formula (I): I) R １ -O-(CH ２ CH ２ O) ｎ -R ２ (Wherein n=3 to 11, R １ and R ２ But linear C １ ~C １０ alkyl.) 2. The method of claim 1, comprising the compound of formula:

8. 2. The method of claim 1, wherein the VOCs have a vapor pressure of at least 0.1 mbar at 20°C and / or a boiling point of at most 240°C at 1013.25 mbar.

9. The at least one VOC is selected from the group consisting of acetone, 2-butanone, 3-methyl-2-butanone, 2-pentanone, 3-pentanone, 3,3-dimethyl-2-butanone, 2-methyl-3-pentanone, 4-methyl-2-pentanone, 3-methyl-2-pentanone, 3-hexanone, 2-hexanone, 5-methyl-3-hexanone, 3-methyl-2-hexanone, 2-heptanone, 4-octanone, 3-octanone, 2-hexanone, 5-methyl-3-hexanone, 2-hexanone, 4 ... Qutanone, 2-octanone, 2,9-decanedione, α-thujene, α-pinene, camphene, sabinene, β-pinene, myrcene, 3-carene, thujanone, thujopsene, thymol, α-terpinene, β-caryophyllene, 1,4-cineole, eucalyptol, fenchone, γ-terpinene, terpinolene, limonene, tricyclene, linalool, menthone, nopinone, p-menthan-2- 2. The method of claim 1, wherein the alkyl group is selected from the group consisting of methyl methyl mercaptan, methyl mercaptan, ethyl mercaptan, dimethyl sulfide, 2-propanethiol, 2-methyl-2-propanethiol, 1-propanethiol, thiophene, 2-butanethiol, isobutyl mercaptan, methyl allyl sulfide, methyl propyl sulfide, butanethiol, dimethyl disulfide, 2-methylthiophene, 3-methylthiophene, tetrahydrothiophene, 1-pentanethiol, thiophenol, dimethyl trisulfide, diisopropyl disulfide, dimethyl tetrasulfide, methyl propyl disulfide, and methyl isopropyl disulfide.

10. 2. The method of claim 1, wherein the methane-containing gas mixture (103) is compressed in step b) to 6-24 bar(g).

11. 2. The method of claim 1, wherein the methane-containing gas mixture (103) is cooled in step b) to between 0°C and 20°C.

12. 2. The method of claim 1, wherein the VOC-loaded absorbent (121) from step d) is heated before being transported to the desorber (135).

13. 2. The method of claim 1, wherein the regenerated absorbent (145) from step g) is cooled before being recycled to the absorber (109).

14. In step c), the liquid reversibly VOC absorbing agent (117) is added to the gas mixture (103) 1Bm ３ 2. The method of claim 1, wherein the absorber (109) is supplied with a volumetric flow rate of at least 7.8 kg per 1000 ml of water.

15. An apparatus (100) for treating a methane-containing gas (103) by the method of any one of claims 1 to 14, comprising: a gas source (101); a cooling device (107); A compressor (105); an absorber (109) having an upper end (113) and a lower end (111); a detachment device (135) having an upper end (133) and a lower end (141); a separation device (125) comprising a membrane; a first connecting pipe (115, 147) connecting the lower end (141) of the desorber (135) to the upper end (113) of the absorber (109); a third connecting pipe (127) connecting the lower end (111) of the absorber (109) to the upper end (133) of the desorber (135); a second connecting pipe (123) connecting the upper end of the absorber (109) to the separator (125); a fourth connecting pipe (143) for transporting permeate, connecting the separation device (125) to the lower end (141) of the desorber (135); An apparatus (100) comprising:

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