Method and apparatus for treating methane-containing gas

Abstract

The invention relates to a method for treating a methane-containing gas comprising CO2 and at least one compound selected from the group of volatile organic compounds (VOCs) wherein the volatile organic compounds are selected from the group of ketones, sulfur-containing hydrocarbons and terpenes and the VOC concentration in the gas mixture is 10-10000 ppm. The methane-containing gas mixture is compressed and cooled and then supplied to an absorption device, where the absorption device comprises an absorbent that reversibly absorbs liquid VOCs. In an absorption device, at least a portion of the VOC and no more than 55% by volume of CO2 are absorbed from the methane-containing gas mixture, thereby producing a methane-containing VOC and CO2 reduced gas mixture and a VOC and CO2 loaded absorbent. Thereafter, the absorbent loaded with VOC and CO2 is conveyed from the absorption device to the desorption device. Further, a methane-containing and VOC-reduced gas mixture is supplied from the absorption device to a separation device in which CO2 is removed. In the desorption device, a regeneration gas stream comprising at least a portion of the CO2-rich gas stream is used for regeneration of an absorbent loaded with VOC and CO2. Thereafter, the exhaust gas stream is discharged from the desorption device and the at least partially regenerated absorbent is conveyed from the desorption device into the absorption device.

Description

[0001] The invention relates to a method for treating a methane-containing gas as claimed in claim 1 and to a device for carrying out said method.

[0002] In view of the gradual warming of the global climate, CO2-neutral energy carriers are becoming increasingly important for modern society. An effective method for obtaining such CO2-neutral energy carriers is to ferment food waste in a fermenter to produce biogas. Since foods such as fruits or vegetables combine CO2 from the atmosphere when they grow, the methane formed in the fermentation of these foods and present therein is CO2-neutral or climate-neutral. Biogas in this application refers to a methane-containing gas mixture of natural origin. In addition to biogas produced by fermentation, for example from a fermenter or landfill, biogas can also be of non-fermentative origin, for example in the form of natural gas, mine gas or coalbed methane.

[0003] In order to make such a methane-containing gas mixture or biogas 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, known as impurities. To this end, biogas produced, in particular by fermentation, is often purified to increase the methane content.

[0004] For the purification of gas mixtures, it is common knowledge to use suitable adsorbers, for example in industrial exhaust gas purification or in domestic ventilation (for example in the hoods of range hoods). Air pollutants, in particular hydrocarbons, are removed from the gas mixture to be purified by adsorption on the inner surface of the porous adsorber material. A distinction can be made between fixed-bed adsorbers, moving-bed adsorbers, rotor adsorbers, fluidized-bed adsorbers and inflow adsorbers. In multi-stage exhaust gas purification systems, adsorbers are often also used as final purification stages, such as "policing filters".

[0005] Impurities in biogas can now be separated out by various biological, chemical and physical methods, which is often referred to as "(bio)gas treatment" and constitutes an important field of application for gas purification. Compounds with high boiling points can be separated, for example, by adsorption (e.g. 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 that are 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 collective term for organic substances (i.e. carbon-containing substances) that are converted to the gas phase (i.e. volatile) by evaporation at room temperature or above. Examples of VOCs are terpenes, ketones, amines, aldehydes, sulfur-containing hydrocarbons (S-HC), etc. In the context of the present application, methane (CH4) is not a component of the VOC group.

[0007] In exhaust gas purification, the removal of VOCs is becoming increasingly important, since the reduction of VOC emissions in the industrial and commercial sectors is important for two reasons: Firstly, from a health point of view, VOCs in ambient air can cause specific symptoms in people, such as headaches, oversensitive reactions, tiredness, reduced physical ability, sleep disorders and respiratory irritation, which are also collectively referred to as the term "sick building syndrome". Secondly, the presence of VOCs in gas mixtures used industrially can lead to malfunctions, damage and reduced efficiency in processing or feeding plants, which can quickly cause economic effects. In membrane devices for gas purification, condensed terpenes impair the filtering capacity, while ketones damage the seals, which shortens the maintenance intervals, meaning that the membranes must be replaced earlier and more frequently. Therefore, in the field of exhaust gas purification and biogas treatment, specific methods for separating VOCs from gas mixtures at an early stage have been developed.

[0008] US2019 / 0001263A1 discloses a method for removing CO2, O2, N2 and VOC from biogas. In a first step, the gas is compressed and then VOCs are continuously removed by a first adsorber (preferably "pressure swing temperature adsorption", abbreviated as "PTSA"). Subsequently, CO2 is removed by a low-temperature membrane, and finally O2 and N2 are separated by a second adsorber (preferably PTSA) to obtain purified biogas. The method is relatively complex because it has three separate separation devices (two PTSAs and one membrane), and is therefore relatively expensive and maintenance-intensive. The two PTSAs running in parallel must in particular be heated to regenerate the adsorption medium and then cooled back to operating temperature to ensure a continuous process.

[0009] WO2017099581A2 discloses a method for purifying a feed gas. This includes compressing the feed gas and removing water from the compressed gas. Subsequently, VOCs, carbon dioxide and any water are removed from the gas by an absorber. One purpose of the method in WO 2017099581A2 is to extract the maximum amount of carbon dioxide from the feed gas for further use of the carbon dioxide. The method is optimized so that the absorber is reprocessed by two absorption devices connected in series, and the components extracted from the feed gas are partially fed back to the purification process to minimize carbon dioxide losses. One disadvantage of the method is that VOCs with a low boiling point cannot be removed, remain in the loop due to recycling, and therefore accumulate in the equipment. In this context, VOCs with a low boiling point refer to compounds with a boiling point below 50°C.

[0010] The object of the present invention is therefore to eliminate the above-mentioned disadvantages of the prior art and to provide an improved method for removing impurities, in particular CO2 and VOCs, from a methane-containing gas mixture, which method is able to effectively and efficiently reduce the content of CO2 and VOCs.

[0011] According to the invention, this object is achieved by a method as claimed in claim 1 and an apparatus as claimed in claim 16. Preferred embodiments of the invention are reflected in the dependent claims.

[0012] In the process of the present invention, in a first step a), a methane-containing gas mixture is provided, which contains CO2 and at least one compound selected from the group of volatile organic compounds (VOC). In the following, the expression "VOC" is also selectively used instead of the expression "compound selected from the group of volatile organic compounds (VOC)". According to the present invention, at least one VOC is selected from the group consisting of ketones, sulfur-containing hydrocarbons and terpenes. In addition, according to the present invention, the VOC concentration in the methane-containing gas mixture is 10-10000 ppm. In a second step b), the methane-containing gas mixture is compressed and cooled. In a third step c), the compressed and cooled methane-containing gas mixture is fed to an absorption device, wherein the absorption device contains a liquid absorbent that reversibly absorbs VOC. In a fourth step d), in the absorption device, at least a portion of the VOC and not more than 5% by volume of CO2 are absorbed from the methane-containing gas mixture by the absorbent, and a methane-containing gas mixture with reduced VOC and CO2 levels, as well as an absorbent loaded with VOC and CO2, is obtained. In a fifth step e), the absorbent loaded with VOC and CO2 is fed from the absorber to the desorber. In a sixth step f), the methane-containing gas mixture with reduced VOC and CO2 levels from the absorber is fed to a separation device comprising a membrane, in which the methane-containing gas mixture with reduced VOC and CO2 levels 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-rich gas stream from step f) is supplied to the desorber for regeneration of the absorbent loaded with VOC and CO2 to obtain an exhaust gas stream comprising CO2 and at least one VOC and an at least partially regenerated absorbent. In an eighth step h), the exhaust gas stream from the seventh step is removed from the desorber to a regeneration post-combustion device, and the at least partially regenerated absorbent from the desorber is fed to the absorber.

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

[0014] In the context of the present invention, the expression "reversibly absorbs" 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 it again. It is not excluded here that, for example, an absorbent that reversibly absorbs VOCs can also reversibly absorb other compounds (e.g. CO2).

[0015] In the context of the present invention, the term "absorbent" refers to a material which is able to at least temporarily bind the compound to be absorbed.

[0016] It is preferred to use an absorbent that can drip in the method of the present invention, that is, an absorbent that can form droplets or form small droplets. For example, for water, a droplet volume of about 50 μl (i.e., the volume of a typical droplet) is assumed. It should be clear to those skilled in the art that the droplet volume must be determined individually for each absorbent. Water is used as an example here for illustration only. The formation of droplets increases the surface area of ​​the absorbent, which in turn improves the efficiency of the absorbent. It is preferred to use a conventional liquid distributor to produce droplets. In addition, random fillers or structured fillers can also be used preferably to better distribute the gas and thus optimize the contact between the gas and the absorbent. The design of the absorbent is selected here to work below the overflow point of the filler or absorbent, thereby preventing the filler or absorbent from being squeezed out of the absorbent by the gas flow. Physical shielding plates can also be installed to prevent such entrainment. Droplet catchers and grids are also feasible.

[0017] In the context of the present invention, the expression "decompression" refers to reducing the pressure of a gas, for example by expanding the gas.

[0018] Furthermore, in the context of the present invention, the term "isobaric" means that there are only negligible changes, if any, in the pressure conditions. Negligible changes are changes of at most ±5%.

[0019] Even if the steps in the method of the present invention are numbered, it will be clear to those skilled in the art that certain steps can also be performed in parallel. For example, steps e) and f) can be performed in parallel.

[0020] The advantage of the method of the invention over the known prior art methods is that, as a result of the local separation of the absorption and desorption of VOCs, the equipment (particularly the containers in the equipment in which the above-mentioned absorption and desorption take place) is not subjected to any varying stresses, thus extending its lifetime.

[0021] Replacing a heavily loaded absorbent with a less loaded absorbent requires only a short time and allows a continuous purification of a methane-containing gas mixture. In addition, the process according to the invention reduces the production costs for purifying biogas, since the process requires only one absorption device, which can also be operated in a more inexpensive manner, since the absorbent is regenerated and not consumed, as is the case, for example, when using activated carbon as absorbent.

[0022] Another advantage of the method of the present invention over the prior art is the use of a liquid absorbent, which can therefore be pumped from a first container to a second container and is easier to handle than the absorbents disclosed in the prior art, which are usually in the form of bulk materials.

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

[0024] The advantage of using CO2 from the membrane as regeneration gas is that it is at almost ambient pressure and contains almost no VOCs. The costs incurred in providing a separate regeneration gas can therefore be reduced, since the regeneration gas is continuously consumed. When the VOCs are desorbed from the absorbent, the latter are loaded with CO2 in the desorber and leave the desorber as an absorbent loaded with CO2. The cooling of the absorbent before entering the absorber releases more absorption binding sites in the absorbent, as a result of which it can absorb CO2 again in the absorber.

[0025] However, it is clear to the person skilled in the art that the regeneration gas can also be provided separately, for example when the CO2 gas stream from the membrane is used in some other way, or the absorbent is preferably purged with a different regeneration gas (for example N2).

[0026] In a preferred embodiment of the process, a single absorption device is used in step d). One advantage of using only one absorption device instead of two absorption devices connected in series as disclosed in the prior art is that a process with only one absorption device is cheaper in terms of configuration and maintenance than a plant with more than two absorption devices.

[0027] In another preferred embodiment of the method, the absorption device in step d) comprises at least 4 stages. A stage in the context of this application refers to an intermediate tray in the absorption device, which divides the absorption process into separate sub-processes. Using at least 4 stages in the absorption device enables the absorption of the maximum concentration of VOCs, as shown later in Figures 3-11.

[0028] Preferably, in step h), the waste gas stream produced in step g) from the desorption unit is fed to a post-regeneration combustion unit for oxidation. This makes it possible to oxidize the VOCs and any methane components present, which results in the release of the waste gas stream into the environment. The destruction of the VOCs saves additional treatment costs, which increases the operating capacity of the entire facility for biogas treatment. Due to the use of CO2-rich permeate as regeneration gas, which is oxidized after use, the so-called methane slip in the CO2-rich permeate is also oxidized at the same time and emissions to the atmosphere are prevented.

[0029] A regenerative post-combustion device generally comprises a mixing device in which a gas mixture to be combusted is mixed with air as an oxygen source; a heat exchanger device in which the gas mixture to be combusted mixed with air is heated by the heat of the combusted gas mixture and simultaneously the combusted gas mixture is cooled; a combustion chamber in which the organic components of the gas mixture are completely oxidized; and a chimney through which the combusted 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 a methane-containing gas can be operated more efficiently and economically than when the gas is treated only in batches. Furthermore, continuous operation is less prone to failures than the cyclic conversions usually proposed in the prior art, since no accessories prone to failure are required to monitor the conversion.

[0031] In a preferred embodiment, in step c), 2-10 liters of absorbent / Bm are used in the absorption device. 3 The methane-containing gas mixture from step b).

[0032] In the context of this application, the unit Bm 3 Stands for working cubic meter, which defines the actual volume of the gas present in the working state. The working volume of a gas can be determined in a first approximation with sufficient accuracy with the aid of the ideal gas equation.

[0033] Preferably, in step g), 1Bm 3 The CO2-rich gas from step f) regenerates 1 to 3 liters of the VOC-loaded absorbent from step d).

[0034] In a preferred embodiment, the absorbent 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, preferably polyethylene glycol.

[0035] Absorbents having the above-mentioned properties are particularly suitable for the process of the invention because they can efficiently absorb and desorb VOCs under conditions of clear separation and these conditions can be achieved without any particular costs and inconveniences. This means that these absorbents can ensure an advantageous and efficient process.

[0036] The absorbent which reversibly absorbs VOCs preferably comprises a compound of formula (I):

[0037] I) R1-O-(CH2CH2O) n -R2,

[0038] Where n = 3 to 8, and

[0039] R1 and R2 are independently selected straight-chain C1-C 10 alkyl.

[0040] Based on formula (I), the absorbent that reversibly absorbs VOC is more preferably compound (Ia)

[0041] R1-O-(CH2CH2O) n -R2,

[0042] wherein n=11, and R1 and R2=CH3.

[0043] Therefore, the preferred compound (Ia) is CH3-O-(CH2CH2O) 11 -CH3.

[0044] Another preferred absorbent is known as Genosorb 300, CAS No. 24991-55-7.

[0045] It has surprisingly been found that, for the reasons stated above, absorbents of the formula (I) are particularly suitable for the process according to the invention.

[0046] A further preferred absorbent is the stable reaction product of 5,8,11,14-tetraoxahenoctane and 5,8,11,14,17-pentaoxaheneicosane (also known as Genosorb 1843).

[0047] 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.

[0048] In a preferred embodiment, 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-3-hexanone, 2-heptanone, 4-octanone, 3-octanone, 2-octanone, 2,9-decanedione, α-thujene, α-pinene, camphene, sabinene, β-pinene, myrcene, 3-carene, thujone, thujone, thujone, thymol, α-terpinene, β-caryophyllene, 1,4-cineole, eucalyptol, anisone, The group consisting of gamma-terpinene, terpinolene, limonene, tricyclopentane, linalool, menthone, nopinone, p-menth-2-one, p-menth-2-ol, camphor, carvone, 3,3-dimethyl-2-camphone, carbonyl sulfide, methyl mercaptan, ethyl mercaptan, dimethyl sulfide, carbon disulfide, 2-propanethiol, 2-methyl-2-propanethiol, 1-propanethiol, thiophene, 2-butyl mercaptan, isobutyl mercaptan, methyl allyl sulfide, methyl propyl sulfide, butyl mercaptan, dimethyl disulfide, 2-methylthiophene, 3-methylthiophene, tetrahydrothiophene, 1-pentanethiol, thiophenol, dimethyl trisulfide, diisopropyl disulfide, dimethyl tetrasulfide, methyl propyl disulfide and methyl isopropyl disulfide. Obviously, mixtures of the above compounds can also be used.

[0049] It has been found that the method of the invention is also suitable for treating gas mixtures comprising at least two VOCs. Thus, the gas mixture preferably comprises at least one other VOC selected from the group consisting of aldehydes, alcohols, amines, BTEX, esters, ethers, CFCs and siloxanes.

[0050] In a preferred embodiment, the at least one other VOC is selected from the group consisting of linear or branched C1-C5 alcohols, thioethers and terpenes.

[0051] At least one other VOC is preferably selected from the group consisting of 2-methylbutanal, acetaldehyde, decanal, formaldehyde, hexanal, isobutyraldehyde, isovaleraldehyde, n-butyraldehyde, propionaldehyde, 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-dimethyltetrahydropyran-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 valerate, methyl valerate, 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, ethyl chloride, methyl chloride, chloroform, dichloromethane , tetrachloroethylene, 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, dimethylcyclopentene, heptane, hexane, isobutane, methylcyclohexane, methylcyclohexene, methylcyclopentane, naphthalene, n-dodecane, nonane, nonene, n-tetradecane, n-tetradecane, n-Tridecane, n-tridecane, octane, pentane, propane, propylene, tetramethylbenzene, undecane, decamethylcyclopentasiloxane, decamethyltetrasiloxane, dodecamethylcyclohexasiloxane, dodecamethylpentasiloxane, ethoxytrimethylsilane, fluorotrimethylsilane, hexamethylcyclotrisiloxane, hexamethyldisiloxane, hydroxytrimethylsilane, octamethylcyclotetrasiloxane, octamethyltrisiloxane, 1-ethyl-1H-pyrrole, acetonitrile, isobutyric acid, methylpropionitrile, 1-(methylthio)-1-propylene, 2-ethyl-5-methylthiazole, 2-ethylthiophene, 2-propane 1-(Methylthio)pentane, 2-butyl propyl 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]-hept-2-one, 3,7-dimethyl-2,4-octadiene, alpha-phellandrene, alpha-terpineol, alpha- The group consisting of copaene, α-cubebene, α-gurjunene, α-carvone, α-terpineol acetate, β-elemene, carane, dihydromyrcene, dihydroumbellulone, isomenthol, myrtanol, p,α,α-trimethylbenzyl alcohol, p-cymene, phellandrene, pincamphor, p-menthen-3-ene, terpinen-4-ol, α-caryophyllene and γ-cadinene.

[0052] Preferably, the methane-containing gas mixture is compressed in step b) to 6 to 24 bar(g), preferably 10 to 20 bar(g), more preferably 14 to 18 bar(g), since within these pressure ranges the methane-containing gas can be processed particularly effectively.

[0053] In a preferred embodiment, the methane-containing gas mixture is cooled in step b) to 0°C to 20°C, preferably 2°C to 10°C, since within these temperature ranges VOCs are effectively absorbed by the absorbent.

[0054] Preferably, the VOC-loaded absorbent from step d) is heated to 30 to 90° C., more preferably to 50 to 70° C. before being sent to the desorption unit. Heating of the absorbent allows for easier and more efficient regeneration in the desorption unit.

[0055] In a preferred embodiment, the regenerated absorbent from step g) is cooled, preferably to 0 to 20°C, more preferably to 2 to 10°C, before being recycled into the absorption unit.

[0056] In a preferred embodiment, in step c), the liquid absorbent that reversibly absorbs VOCs is heated to at least 6 kg / Bm 3 , preferably at least 7kg / Bm 3 , more preferably at least 7.8 kg / Bm 3 The mass flow rate of the gas mixture fed to the absorber is at least 6 kg / Bm of the liquid absorbent for reversible absorption of VOCs. 3 , preferably at least 7kg / Bm 3 , more preferably at least 7.8 kg / Bm 3 The mass flow rate of the gas mixture also makes it possible to absorb VOCs with low boiling points (below 50°C) and thus remove them from the gas mixture. For example, it has been found that for the removal of dimethyl sulfide, a VOC substance with a boiling point of 37°C at standard pressure, a volume flow rate of 7.8 kg of absorbent per cubic meter of working gas mixture is ideal. The density of the absorbent in this embodiment is about 0.9-1.1 kg / l.

[0057] Another aspect of the present invention relates to an apparatus for treating methane-containing gas by the method of the present invention. The apparatus comprises the following components:

[0058] Gas source,

[0059] Cooling device,

[0060] compressor,

[0061] An absorption device having an upper end and a lower end,

[0062] A desorption device having an upper end and a lower end,

[0063] Separation device,

[0064] A first connecting conduit connecting the lower end of the desorption device to the upper end of the absorption device,

[0065] A second connecting conduit connecting the lower end of the absorption device to the upper end of the desorption device,

[0066] Connect the upper end of the absorption device to the third connecting conduit of the separation device,

[0067] A fourth connecting conduit connects the separation device to the lower end of the desorption device.

[0068] The invention is explained in detail below with reference to the described and attached working examples. The accompanying drawings show the following in purely schematic form:

[0069] Figure 1 is a schematic diagram of a preferred embodiment of the method of the present invention for purifying a methane-containing gas;

[0070] Figure 2 It is the configuration of the computer simulation model;

[0071] FIG3 is a step diagram of VOC methyl mercaptan;

[0072] FIG4 is a step diagram of VOC dimethyl sulfide;

[0073] FIG5 is a step diagram of VOC acetone;

[0074] FIG6 is a step diagram of the VOC 2-butanone;

[0075] FIG7 is a step diagram of VOC 1-propanol;

[0076] FIG8 is a step diagram of VOC toluene;

[0077] FIG9 is a step diagram of VOC limonene;

[0078] Fig.10 is a graph of VOC concentrations measured in a facility producing biogas from renewable feedstocks;

[0079] Fig.11 is a graph of VOC concentrations measured in facilities that produce biogas from waste;

[0080] Fig.12 It is the configuration of the computer simulation model.

[0081] exist Figure 1 In a preferred embodiment of the method of the invention, which is schematically shown in FIG. 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 selected 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 cooling device 107.

[0082] Subsequently, the methane-containing gas mixture 103 is fed to the absorption device 109. The methane-containing gas mixture 103 is introduced here at the lower end 111 of the absorption device 109 and rises to the upper end 113 of the absorption device 109.

[0083] The words “top” and “bottom” relate to the orientation of the respective device shown in the figures.

[0084] Furthermore, the absorption device 109 is supplied with a liquid absorbent 117 via a first connecting conduit 115, which opens into the absorption device 109 in the region of the upper end 113. This liquid absorbent 117 flows in the form of droplets from the upper end 113 to the lower end 111 of the absorption device 109 and comes into contact with the counter-flowing methane-containing gas mixture 103. The contact of the absorbent 117 with the methane-containing gas mixture 103 leads to a reversible binding of the VOCs present in the gas mixture in the absorbent 117, as a result of which a methane-containing gas mixture 119 with a reduced VOC level is obtained at the upper end 113 of the absorption device 109, while the absorbent 121 loaded with VOCs is collected at the lower end 111 of the absorption device 109. The methane-containing gas mixture 119 with a reduced VOC level is conveyed from the upper end 113 of the absorption device 109 to a separation device 125 via a second connecting conduit 123. The VOC-laden absorbent 121 is pumped from the lower end 111 of the absorber 109 to the heat exchanger 129 by means of a pump (not shown) via a third connecting conduit 127 and heated therein to 50-70° C. Subsequently, the VOC-laden absorbent 121 is further pumped to the upper end 133 of the desorber 135 and fed to the desorber 135. In the separation device 125, the methane-containing gas mixture 119 with a reduced VOC level is separated into a depressurized CO2-rich gas stream 137 (pressure of -0.5 to +0.5 bar (g)) and an isobaric methane-rich gas stream 139 (pressure of 14-18 bar (g)). The CO2-rich gas stream 137 is then introduced at the lower end 141 of the desorber 135 through a fourth connecting conduit 143 and rises to the upper end 133 of the desorber 135. When the liquid absorbent 121 loaded with VOC flows in the form of droplets from the upper end 133 to the lower end 141 of the desorber 135, it contacts the CO2-rich gas stream 137 flowing in the opposite direction. Due to the heating of the liquid absorbent 121 loaded with VOC, the bound VOC is reversibly released and flows to the upper end 133 of the desorber 135 together with the CO2-rich gas stream 137. This allows the purified absorbent 145 to be collected at the lower end 141 of the desorber 135. The fifth connecting conduit 147 conveys the purified absorbent 145 to the heat exchanger device 129 by means of a pump (not shown), where it is cooled to 2-10°C and then pumped to the upper end 113 of the absorber 109 via the feed conduit 115. The heat exchanger device 129 may comprise a plurality of individual heat exchangers 131 , 131 ′, 131 ″. At the upper end 133 of the desorption device 135 , a gas stream 149 rich in CO 2 and VOCs is removed and sent to a regeneration post-combustion device 151 in order to reduce environmental pollution by this method.

[0085] In order to use methane-containing gas as a natural gas substitute, the sulfur content in the product gas must be reduced to less than 6 mg / m 3 Limits for sulfur equivalent. This is specified, for example, in the specification manual G260 of the DVGW [German Technical and Scientific Association for the Gas and Water Industry].

[0086] For example, for other VOCs, restrictions apply to the use of gas permeable membranes. In this case, the total VOC concentration must be below 10 ppm in order to meet the conditions of use of Evonik (manufacturer of gas permeable membranes), for example.

[0087] Another reason for the discussion on limiting VOCs in biogas is the odor that may be caused by VOCs.

[0088] Figure 2A computer simulation model of a preferred embodiment of the method of the present invention is shown. The simulation model includes an absorber 201 and a desorber 203. The absorbent (PEG here) enters the absorber 201 as a liquid 205. The absorbent leaves the absorber 201 as a liquid 207 loaded with VOCs and is heated in a heat exchanger 209. The heated absorbent 211 loaded with VOCs obtained thereby is conveyed from the heat exchanger 209 to another heat exchanger 213 and further heated therein. The heat exchanger 213 is supplied with external heat 215 here. The significantly heated absorbent 217 loaded with VOCs leaves the heat exchanger 213 and expands in the control valve 219. The heated expanded absorbent 221 loaded with VOCs enters the desorber 203 and releases VOCs there. The mostly regenerated, heated and expanded absorbent 223 is compressed by a pump 225 and further conveyed to the heat exchanger 209 as a compressed, heated and mostly regenerated absorbent 227. In the heat exchanger 209, it releases some of its heat to the VOC-laden absorbent 207. The cooler, compressed and mostly regenerated absorbent 229 is then conveyed to another heat exchanger 231 and further cooled therein. For this purpose, the heat exchanger 231 is supplied with external cooling 233. The cooled, compressed and mostly regenerated absorbent 205 enters the absorption device 201 again, thus completing the absorbent circuit. The compressed biogas 235 to be purified is cooled in the heat exchanger 237 by external cooling 239, and the condensate is then removed in the condensate separator 241. The resulting cooled compressed biogas 243 is fed to the absorption device 201, where it comes into contact with the cooled, compressed and mostly regenerated absorbent 205 and releases its VOCs to the absorbent 205. The purified biogas 245 is discharged from the absorption device 201 and can then be used for further processing 247. The regeneration gas 249 (e.g. lean gas from biogas treatment 251) is fed to the heat exchanger 253 and heated therein. The heated regeneration gas 255 enters the desorber 203 and releases the VOCs therein from the heated expanded VOC-laden absorbent 221. The VOC-laden regeneration gas 257 then exits the desorber 203 and releases its heat to the regeneration gas 249 in the heat exchanger 253. The cooled VOC-laden regeneration gas 259 is conveyed to the post-treatment unit 263 by the suction blower 261.

[0089] In the above computer simulation, the solubility of a specific VOC in an absorbent (PEG here) is simulated by Henry's law. In the first step, an equilibrium line in which the gas phase and the liquid phase are in equilibrium is simulated; the slope of the equilibrium line corresponds to the Henry coefficient of the compound at the corresponding temperature. In the second step, a mass balance line generated by the mass balance of VOC in the absorber is simulated. The starting point of the mass balance line is the VOC concentration at the upper end of the absorber (purified biogas 245) and the liquid phase concentration at the upper end of the absorber (regenerated PEG 205). The end point of the mass balance line comes from the gas phase concentration at the lower end of the absorber (biogas 243 loaded with VOC) and the liquid phase concentration at the lower end of the absorber (PEG 207 loaded with VOC). The starting point and end point of the mass balance line are connected by a straight line (mass balance line). This is only applicable when the temperature in the absorber is assumed to be constant. In the case of a temperature gradient, both the mass balance line and the equilibrium line are displayed as a mass balance curve and an equilibrium curve. A step configuration can be drawn between the mass balance line and the equilibrium line. Each step represents a theoretical plate. 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. If the mass balance line is below the equilibrium line, the operation is desorption.

[0090] Figure 3a A similar step diagram is shown for the VOC methyl mercaptan (CAS 74-93-1) and PEG as absorbent in an absorption device. The mass balance line (dashed line) is arranged above the equilibrium line (dash-dot line) and the step configuration (solid line) is shown in between.

[0091] Figure 3b A step diagram similar to the step diagrams described above for the VOC methyl mercaptan (CAS 74-93-1) and PEG as absorbent in a desorption unit is shown. The equilibrium line (dash-dotted line) is arranged above the mass balance line (dashed line) and the step configuration (solid line) is shown in between. Figure 3a It can be clearly seen that for methyl mercaptan, a step configuration is not feasible, since if the absorbent flow is too small (in the simulation model), a large amount of methyl mercaptan residues remain in the cleaned biogas. Figure 3b It can be clearly seen that the absorbent is almost completely regenerated in the desorption unit to release methyl mercaptan.

[0092] Similar to the step diagram above, Figure 4a and 4b The results show that the VOC dimethyl sulfide (CAS 75-18-3) and PEG as absorbents in the absorption device ( Figure 4a ) and desorption device ( Figure 4b ). Figure 4a It is clear that multiple steps are required to purify the biogas, and residual dimethyl sulfide still remains in the biogas. Figure 4bIt can be clearly seen that the absorbent is almost completely regenerated in the desorption unit to release dimethyl sulfide.

[0093] Similar to the step diagram above, Figure 5a and 5b It is shown that VOC acetone (CAS 67-64-1) and PEG as absorbents in the absorption device ( Figure 5a ) and desorption device ( Figure 5b ). Figure 5a It can be clearly seen that multiple steps are required to purify the biogas, while very small amounts of acetone residues still remain in the biogas. Figure 5b It can be clearly seen that the absorbent is almost completely regenerated in the desorption unit to release acetone.

[0094] Similar to the step diagram above, Figure 6a and 6b It is shown that VOC2-butanone (CAS78-93-3) and PEG as absorbents in the absorption device ( Figure 6a ) and desorption device ( Figure 6b ). Figure 6a It can be clearly seen that only a few steps are required to purify the biogas and no 2-butanone remains in the biogas. Figure 6b It can be clearly seen that the absorbent is regenerated through multiple steps in the desorption unit to release 2-butanone, but a small amount of 2-butanone remains in the regenerated absorbent.

[0095] Similar to the step diagram above, Figure 7a and 7b The results show that VOC 1-propanol (CAS 71-23-8) and PEG as absorbents in the absorption device ( Figure 7a ) and desorption device ( Figure 7b ). From Figure 7a It can be clearly seen that only a few steps are required to purify the biogas and that very small amounts of 1-propanol residues remain in the biogas. Figure 7b It can be clearly seen that despite the multiple steps, the absorbent is not fully regenerated in the desorption unit to release 1-propanol.

[0096] Similar to the step diagram above, Figure 8a and 8b The results show that VOC toluene (CAS 108-88-3) and PEG as absorbents in the absorption device ( Figure 8a ) and desorption device ( Figure 8b ). Figure 8a It can be clearly seen that only a few steps are needed to purify the biogas, but toluene residues remain in the biogas because it has not been fully regenerated. Figure 8bIt is evident that despite the multiple steps, the absorbent is not fully regenerated in the desorber to release the toluene. Since the mass balance line and the equalization line run in parallel, full regeneration is not possible.

[0097] Similar to the step diagram above, Figure 9a and 9b The results show that the VOC limonene (CAS 7705-14-8) and PEG as absorbents in the absorption device ( Figure 9a ) and desorption device ( Figure 9b ). Figure 9a It can be clearly seen that only a few steps are needed to purify the biogas, but limonene residues remain in the biogas because it is not fully regenerated. Figure 9b It is evident from the plot that despite the multiple steps, the absorbent is not fully regenerated in the desorption unit to release limonene because the absorbent mass flow is too high (in the simulation model).

[0098] Based on Figure 2 From the simulations of 9 to 100°C, it can be pointed out that VOCs with a boiling point of 35°C to 100°C can be almost completely released from the biogas in the absorption unit and almost completely released from the absorbent in the desorption unit. VOCs with a boiling point above 100°C are almost completely removed from the biogas. However, the regeneration of the absorbent is incomplete. VOCs with a boiling point below 35°C are not completely removed from the biogas. The gas components CO2 and methane remain almost completely in the gas phase.

[0099] Fig.10 A graph based on 48 measured values ​​of VOC in biogas samples is shown, where the biogas is produced from renewable raw materials. The concentration of VOC in the biogas is between 5 and 20 ppm. Individual values ​​are higher. VOC in biogas from renewable raw materials does not present any problems in further processing.

[0100] Fig.11 A graph based on 138 measurements of VOCs in biogas samples is shown, where the biogas is produced from waste. The concentration of VOCs in the biogas is between 10 and 250 ppm. Higher concentrations are also achieved in many cases. VOCs in biogas from waste often present problems in further processing; therefore, there is a need to control the removal of VOCs.

[0101] Experimental data

[0102] Fig.12 It shows that Figure 2A computer simulation model of a preferred embodiment of the method of the present invention as described. Various parameters of biogas, absorbent and regeneration gas are added to the simulation model to show the amount of CO2 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 leaves heat exchanger 1201 as cooled compressed methane-containing gas BG2. Methane-containing gas BG2 is fed to absorption device 1203, wherein CO2 and VOC components present in methane-containing gas BG2 are absorbed. Methane-containing gas BG3 with reduced CO2 and VOC levels leaves absorption device 1203. In absorption device 1203, methane-containing gas BG2 contacts with cooled regeneration absorbent AB1. Cooled regeneration absorbent AB1 absorbs CO2 and VOC in absorption device 1203 and leaves absorption device 1203 as absorbent AB2 loaded with CO2 and VOC. The absorbent AB2 loaded with CO2 and VOC is heated in the heat exchanger 1205 and leaves as heated absorbent AB3 loaded with CO2 and VOC. The heated absorbent AB3 loaded with CO2 and VOC is further heated in another heat exchanger 1207 and leaves as heated absorbent AB4 loaded with CO2 and VOC. The heated absorbent AB4 loaded with CO2 and VOC is fed to the control valve 1209 and expanded and leaves as heated expanded absorbent AB5 loaded with CO2 and VOC. The heated expanded absorbent AB5 loaded with CO2 and VOC is fed to the desorption device 1211.

[0103] The regeneration gas RG1 is heated in the heat exchanger 1213 and leaves as heated regeneration gas RG2. The regeneration gas RG1 is a gas stream having CO2 as its main component. The heated regeneration gas RG2 is fed to the desorption device 1211 and contacts therein with the heated expanded absorbent AB5 loaded with CO2 and VOCs. The heated regeneration gas RG2 releases CO2 and VOCs from the absorbent AB5 to obtain the regeneration gas RG3 loaded with CO2 and VOCs and the mostly regenerated heated expanded absorbent AB6. The mostly regenerated, heated and expanded absorbent AB6 is compressed in the pump 1215 and fed to the heat exchanger 1205 as compressed, heated and mostly regenerated absorbent AB7. In the heat exchanger 1205, the compressed, heated and mostly regenerated absorbent AB7 releases its heat to the absorbent AB2 loaded with CO2 and VOCs and leaves the heat exchanger 1205 as cold, compressed and mostly regenerated absorbent AB8. The cold, compressed and mostly regenerated absorbent AB8 is fed to the heat exchanger 1217 and cooled and leaves as cooled regenerated absorbent AB1. The regeneration gas RG3 loaded with CO2 and VOC is fed to the heat exchanger 1213, releases its heat to the regeneration gas RG1 and leaves the heat exchanger 1213 as cooled regeneration gas RG4 loaded with CO2 and VOC. The cooled regeneration gas RG4 loaded with CO2 and VOC is conveyed in the suction blower 1219 as cooled regeneration gas RG5 loaded with CO2 and VOC to the post-treatment unit 1221.

[0104] Table 1 below shows the parameters of the simulation model for the absorbent PEG 1843. This absorbent absorbs only 2.5 kg / h of methane (0.4%), while 36.6 kg / h of CO2 (3.6%) and more than 98% of VOCs (dimethyl sulfide (DMS), acetone, 2-butanone and terpenes) are absorbed. It should be noted here 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 point 140-230° C.) are absorbed.

[0105] This is evident from the mass difference between BG2 and BG3. 36.6 kg / h of CO2 and VOC are released from the methane-containing gas BG2 to the absorbent AB1, which is evident from the increase in CO2 and VOC concentrations from AB1 to AB5. The absorbent loaded with VOC and CO2 then delivers 36.6 kg / h of CO2 and VOC to the regeneration gas RG1, which is evident from the increase in CO2 and VOC concentrations from RG1 to RG3.

[0106] Table 1

[0107] BG2 BG3 RG1 RG5 AB1 AB5 Mass flow [kg / h] 1585 1540 732 777 645 689 Volume flow <![CDATA[[m 3 / h]]]> 83.9 82.3 365.8 435.7 0.693 0.774 temperature [℃] 8 8 20 55 8 57 pressure [Bar(g)] 15 15 0.1 0.1 15 0.1 CH4 [kg / h] 557.5 555.0 2.1 4.6 0.00 2.51 CO2 [kg / h] 1022.0 985.4 730.0 766.6 0.14 36.76 DMS [kg / h] 0.04 0.00 0.00 0.03 0.00 0.03 acetone [kg / h] 0.34 0.00 0.00 0.34 0.00 0.34 2-Butanone [kg / h] 0.42 0.00 0.00 0.42 0.03 0.44 Terpenes [kg / h] 3.95 0.06 0.00 3.88 44.51 48.40 H2O [kg / h] 0.69 0.00 0.00 0.69 0.03 0.70 PEG [kg / h] 0.00 0.00 0.00 0.06 600.00 600.00

[0108] Tables 2 to 4 show parameter configurations similar to Table 1, and are different from Table 1 only in that the temperatures of the regeneration gases RG1 and RG3 and the absorbent AB5 and the mass flow rates of RG1, RG3, AB1, and AB5 are varied.

[0109] Tables 5 to 8 show the same parameter configuration as Tables 1 to 4; the only change in the simulation model is that the absorbent is changed from PEG1843 (Tables 1-4) to PEG300 (Tables 5-8).

[0110] Table 2

[0111] BG2 BG3 RG1 RG5 AB1 AB5 Mass flow [kg / h] 1585 1541 732 776 846 890 Volume flow <![CDATA[[m 3 / h]]]> 83.9 82.3 365.8 389.1 0.910 0.969 temperature [℃] 8 8 20 20 8 22 pressure [Bar(g)] 15 15 0.1 0.1 15 0.1 CH4 [kg / h] 557.5 555.0 2.1 4.6 0.00 2.51 CO2 [kg / h] 1022.0 985.5 730.0 766.5 0.22 36.76 DMS [kg / h] 0.04 0.00 0.00 0.03 0.00 0.04 acetone [kg / h] 0.34 0.00 0.00 0.33 0.01 0.35 2-Butanone [kg / h] 0.42 0.02 0.00 0.40 0.22 0.62 Terpenes [kg / h] 3.95 0.35 0.00 3.60 245.54 249.14 H2O [kg / h] 0.69 0.03 0.00 0.66 0.36 1.01 PEG [kg / h] 0.00 0.00 0.00 0.00 600.00 600.00

[0112] Table 3

[0113] BG2 BG3 RG1 RG5 AB1 AB5 Mass flow [kg / h] 1585 1540 732 777 638 682 Volume flow <![CDATA[[m 3 / h]]]> 83.9 82.3 403.3 435.7 0.686 0.767 temperature [℃] 8 8 50 55 8 57 pressure [Bar(g)] 15 15 0.1 0.1 15 0.1 CH4 [kg / h] 557.5 555.0 2.1 4.6 0.00 2.51 CO2 [kg / h] 1022.0 985.4 730.0 766.7 0.10 36.76 DMS [kg / h] 0.04 0.00 0.00 0.03 0.00 0.03 acetone [kg / h] 0.34 0.00 0.00 0.34 0.00 0.34 2-Butanone [kg / h] 0.42 0.00 0.00 0.42 0.01 0.42 Terpenes [kg / h] 3.95 0.05 0.00 3.89 37.64 41.54 H2O [kg / h] 0.69 0.00 0.00 0.69 0.00 0.68 PEG [kg / h] 0.00 0.00 0.00 0.06 600.00 600.00

[0114] Table 4

[0115] BG2 BG3 RG1 RG5 A81 AB5 Mass flow [kg / h] 1585 1540 732 777 638 682 Volume flow <![CDATA[[m 3 / h]]]> 83.9 82.3 365.8 399.8 0.685 0.766 temperature [℃] 8 8 20 27.96098 8 57 pressure [Bar(g)] 15 15 0.1 0.1 15 0.1 CH4 [kg / h] 557.5 555.0 2.1 4.6 0.00 2.51 CO2 [kg / h] 1022.0 985.4 730.0 766.7 0.09 36.76 DMS [kg / h] 0.04 0.00 0.00 0.03 0.00 0.03 acetone [kg / h] 0.34 0.00 0.00 0.34 0.00 0.34 2-Butanone [kg / h] 0.42 0.00 0.00 0.42 0.00 0.42 Terpenes [kg / h] 3.95 0.05 0.00 3.89 37.55 41.45 H2O [kg / h] 0.69 0.00 0.00 0.69 D.00 0.68 PEG [kg / h] 0.00 0.00 0.00 0.00 600.00 600.00

[0116] Table 5

[0117] BG2 BG3 RG1 RG5 AB1 AB5 Mass flow [kg / h] 1585 1542 732 775 646 689 Volume flow <![CDATA[[m 3 / h]]]> 83.9 82.5 365.8 433.7 0.612 0.689 temperature [℃] 8 8 20 55 8 57 pressure [Bar(g)] 15 15 0.1 0.1 15 0.1 CH4 [kg / h] 557.5 556.3 2.1 3.3 0.00 1.17 CO2 [kg / h] 1022.0 985.3 730.0 766.7 0.14 36.86 DMS [kg / h] 0.04 0.00 0.00 0.03 0.00 0.03 acetone [kg / h] 0.34 0.00 0.00 0.34 0.00 0.34 2-Butanone [kg / h] 0.42 0.00 0.00 0.42 0.03 0.45 Terpenes [kg / h] 3.95 0.07 0.00 3.88 45.31 49.20 H2O [kg / h] 0.69 0.01 0.00 0.69 0.24 1.17 PEG [kg / h] 0.00 0.00 0.00 0.00 600.00 600.00

[0118] Table 6

[0119] BG2 BG3 RG1 RG5 AB1 AB5 Mass flow [kg / h] 1585 1542 732 775 848 890 Volume flow <![CDATA[[m 3 / h]]]> 83.9 82.5 365.8 387.3 0.803 0.856 temperature [℃] 8 8 20 20 8 22 pressure [Bar(g)] 15 15 0.1 0.1 15 0.1 CH4 [kg / h] 557.5 556.3 2.1 3.3 0.00 1.17 CO2 [kg / h] 1022.0 985.4 730.0 766.6 0.22 36.86 DMS [kg / h] 0.04 0.00 0.00 0.03 0.00 0.04 acetone [kg / h] 0.34 0.01 0.00 0.33 0.04 0.37 2-Butanone [kg / h] 0.42 0.02 0.00 0.40 0.26 0.66 Terpenes [kg / h] 3.95 0.35 0.00 3.60 245.54 249.14 H2O [kg / h] 0.69 0.05 0.00 0.64 1.52 2.15 PEG [kg / h] 0.00 0.00 0.00 0.02 600.00 600.00

[0120] Table 7

[0121] BG2 BG3 RG1 RG5 AB1 AB5 Mass flow [kg / h] 1585 1542 732 776 638 681 Volume flow <![CDATA[[m 3 / h]]]> 83.9 82.4 403.3 433.9 0.604 0.681 temperature [℃] 8 8 50 55 8 57 pressure [Bar(g)] 15 15 0.1 0.1 15 0.1 CH4 [kg / h] 557.5 556.3 2.1 3.3 0.00 1.17 CO2 [kg / h] 1022.0 985.3 730.0 766.8 0.10 36.86 DMS [kg / h] 0.04 0.00 0.00 0.03 0.00 0.03 acetone [kg / h] 0.34 0.00 0.00 0.34 0.00 0.34 2-Butanone [kg / h] 0.42 0.00 0.00 0.42 0.01 0.43 Terpenes [kg / h] 3.95 0.05 0.00 3.89 37.64 41.54 H2O [kg / h] 0.69 0.00 0.00 0.69 0.06 0.73 PEG [kg / h] 0.00 0.00 0.00 0.37 600.00 600.00

[0122] Table 8

[0123] 8G2 8G3 RG1 RG5 AB1 AB5 Mass flow [kg / h] 1585 1540 732 777 638 682 Volume flow <![CDATA[[m 3 / h]]]> 83.9 82.3 365.8 399.8 0.604 0.682 temperature [℃] 8 8 20 28 8 57 pressure [Bar(g)] 15 15 0.1 0.1 15 0.1 CH4 [kg / h] 557.5 555.0 2.1 4.6 0.00 2.51 C02 [kg / h] 1022.0 985.4 730.0 766.7 0.09 36.76 DMS [kg / h] 0.04 0.00 0.00 0.03 0.00 0.03 acetone [kg / h] 0.34 0.00 0.00 0.34 0.00 0.34 2-Butanone [kg / h] 0.42 0.00 0.00 0.42 0.00 0.42 Terpenes [kg / h] 3.95 0.05 0.00 3.89 37.55 41.45 H2O [kg / h] 0.69 0.00 0.00 0.69 0.00 0.68 PEG [kg / h] 0.00 0.00 0.00 0.05 600.00 600.00

[0124] In all parameter configurations in the simulation model, it is clear that 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 terpene concentrations in AB1 and AB5 are higher than in Tables 1, 3-5 and 7-8. In all parameter configurations, terpenes could not be completely removed from the absorbent (see AB1). Surprisingly, however, terpenes present in the methane-containing biogas BG2 could be removed in large quantities therefrom (see BG3).

Claims

1. A method for treating a gas containing methane, comprising the following steps: a) providing a methane-containing gas mixture (103) comprising 20-60% by volume of CO2 and at least one compound selected from the group of volatile organic compounds (VOC), wherein at least one VOC is selected from the group consisting of ketones, sulfur-containing hydrocarbons and terpenes, wherein the VOC concentration in the gas mixture is 10-10000 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 absorption device (109), wherein the absorption device (109) contains a liquid absorbent (117) that reversibly absorbs VOCs; d) absorbing at least a portion of VOC and no more than 5% by volume of CO2 by the absorbent (117) to obtain a methane-containing gas mixture (119) with reduced VOC and CO2 levels, and an absorbent (121) loaded with VOC and CO2; e) feeding the absorbent (121) loaded with VOC and CO2 from the absorption device (109) to the desorption device (135); f) feeding the methane-containing gas mixture (119) with reduced VOC and CO2 levels from the absorption device (109) to a separation device (125) comprising a membrane, wherein the methane-containing gas mixture (119) with reduced VOC and CO2 levels is separated into a depressurized CO2-rich gas stream (137) and an isobaric methane-rich gas stream (139) in the separation device (125); g) feeding a regeneration gas stream (138) comprising at least a portion of the CO2-rich gas stream (137) from step f) to the desorption device (135) for regeneration of the absorbent (121) loaded with VOCs and CO2, to obtain an offgas stream (149) comprising CO2 and VOCs and at least partially regenerated absorbent (145); h) removing the waste gas stream (149) from the desorber (135) and recycling the at least partially regenerated absorbent (145) from the desorber (135) to the absorber (109).

2. The method according to claim 1, characterized in that In step h), the exhaust gas stream (149) is fed to a post-regeneration combustion device (151) for oxidation.

3. The method according to claim 1 or 2, characterized in that At least steps c) to h) are performed continuously.

4. The method according to any one of claims 1 to 3, characterized in that In step c), 2-10 liters of absorbent / Bm are used in the absorption device. 3 The methane-containing gas mixture from step b).

5. The method according to any one of claims 1 to 4, characterized in that In step g), 1Bm 3 The CO2-rich gas from step f) regenerates 1 to 3 liters of the VOC-loaded absorbent from step d).

6. The method according to any one of claims 1 to 5, characterized in that The VOC absorbing absorbent (117, 145) 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, preferably polyethylene glycol.

7. The method according to any one of claims 1 to 6, characterized in that The VOC absorbing agent (117, 145) comprises a compound of formula (I): I)R1-O-(CH2CH2O) n -R2, Where n = 3 to 11, and R1 and R2 are independently selected straight-chain C1-C 10 alkyl.

8. The method according to any one of claims 1 to 7, characterized in that 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.

9. The method according to any one of claims 1 to 8, characterized in that 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-3-hexanone, 2-heptanone, 4-octanone, 3-octanone, 2-octanone, 2,9-decanedione, α-thujene, α-pinene, camphene, sabinene, β-pinene, myrcene, 3-carene, thujone, thujone, thymol, α-terpinene, β-caryophyllene, 1,4-cineole, eucalyptol, anisone, γ-terpinene , terpinolene, limonene, tricyclopentaene, linalool, menthone, nopinone, p-menth-2-one, p-menth-2-ol, camphor, carvone, 3,3-dimethyl-2-benzophenone, carbonyl sulfide, methyl mercaptan, ethyl mercaptan, dimethyl sulfide, carbon disulfide, 2-propanethiol, 2-methyl-2-propanethiol, 1-propanethiol, thiophene, 2-butyl mercaptan, isobutyl mercaptan, methyl allyl sulfide, methyl propyl sulfide, butyl mercaptan, dimethyl disulfide, 2-methylthiophene, 3-methylthiophene, tetrahydrothiophene, 1-pentanethiol, thiophenol, dimethyl trisulfide, diisopropyl disulfide, dimethyl tetrasulfide, methyl propyl disulfide and methyl isopropyl disulfide.

10. The method according to any one of claims 1 to 9, characterized in that In step b) the methane-containing gas mixture (103) is compressed to 6 to 24 bar(g), preferably 10 to 20 bar(g), more preferably 14 to 18 bar(g).

11. The method according to any one of claims 1 to 9, characterized in that In step b) the methane-containing gas mixture (103) is cooled to 0°C to 20°C, preferably 2°C to 10°C.

12. The method according to any one of claims 1 to 10, characterized in that The VOC-loaded absorbent (121) from step d) is heated before being fed to the desorption device (135), preferably to 30 to 90°C, more preferably to 50 to 70°C.

13. The method according to any one of claims 1 to 11, characterized in that The regenerated absorbent (145) from step g) is cooled, preferably to 0 to 20°C, more preferably to 2 to 10°C, before being recycled into the absorption unit (109).

14. The method according to any one of claims 1 to 13, characterized in that In step c), the liquid absorbent (117) that reversibly absorbs VOCs is added at a concentration of at least 7.8 kg / Bm 3 The gas mixture (103) is fed to the absorption device (109) at a volume flow rate of .

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

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