Method for cleaning gas mixtures by adding ozone - Patent Application 20070122997

Abstract

The present invention describes a method for cleaning a gas mixture. In a first step (a), a gas mixture is provided, containing a gas selected from the group consisting of methane-containing biogas (3, 7) obtained by fermentation of organic matter and having a methane concentration of at least 40% by volume, pyrolysis gas obtained by thermal treatment of organic matter and having a carbon monoxide concentration of at least 2% by volume, or a combination thereof. The gas mixture also contains impurities from the group of volatile organic compounds (VOCs), and the gas mixture has a VOC concentration of 0.0001 to 0.2% by volume. In a second step (b), 0.0001 to 12% by volume of ozone is added to the gas mixture, and the ozone oxidizes at least a portion of the VOCs in the gas mixture. In a third step (d), the gas mixture from the second step is contacted with a VOC-adsorbent selected from the group consisting of activated carbon, activated coke, silica gel, aluminum oxide, molecular sieves, and mixtures thereof to clean the gas mixture.

Description

[Technical Field]

[0001] The present invention relates generally to a method for cleaning gas mixtures obtained by pyrolysis or fermentation of organic matter, in particular by removing harmful components such as volatile organic compounds (VOCs) by oxidation with ozone and adsorption onto an adsorbent. [Background technology]

[0002] Cleaning of gas mixtures by using suitable adsorbents is a known practice not only in industrial off-gas cleaning but also in domestic technology, e.g., in ventilation hoods. Air pollutants, especially hydrocarbons, are removed from the off-gas to be cleaned by accumulation on the inner surface of porous adsorbent materials. There are various types: fixed-bed, moving-bed, rotor-type, fluidized-bed, and entrained-flow adsorbers. In multi-stage off-gas cleaning plants, adsorbents are often also used as the final cleaning stage, in the form of so-called polishing filters.

[0003] One important field of application of gas cleaning is the cleaning of methane-containing gas mixtures ("biogas"). Methane-containing gas mixtures usually contain, in addition to the available methane, a number of further gaseous compounds. Methane-containing biogas originates, for example, from fermenters or landfills, or may also have a non-fermentable origin, for example in the form of natural gas, pit gas or seam gas. In order to utilize such methane-containing gas mixtures (hereinafter referred to as biogas) for energy recovery, it is necessary to remove as much as possible all other compounds (also known as impurities) to increase the methane concentration in the gas mixture.

[0004] A further important field of application for gas cleaning is the cleaning of gas mixtures obtained by pyrolysis, which generally contain a significant proportion of carbon monoxide.

[0005] Examples of impurities or components typically present in biogas or pyrolysis gases are, for example, hydrogen sulfide (H2S), ammonia (NH3), and volatile organic compounds (abbreviated VOCs), such as sulfur-hydrocarbons (S-HC). These impurities can nowadays be removed using a variety of biological, chemical, and physical processes, commonly referred to as "(bio)gas treatment". High boiling point compounds can be removed, for example, by adsorption on activated carbon filters, low boiling point compounds can be removed, for example, by condensation, and water-soluble compounds can be removed by scrubbers.

[0006] EP 1979446 B1 discloses a method for recovering methane from landfill gas and other gases from anaerobic fermenters, which includes the following steps: removal of H2S, compression, followed by removal of VOCs and water, and finally removal of further impurities.

[0007] Depending on the number and nature of the impurities, the stages of biogas treatment can be more or less costly and complex, focusing in particular on the removal of sulfur compounds and so-called VOCs, as well as the separation of condensates such as ammonia.

[0008] Desulfurization of biogas or pyrolysis gas, i.e., removal of HS and S-HCs, is often essential for industrial use, for example, as fuel gas, because sulfur compounds react to form sulfuric acid, which can corrode pipes, for example. Corrosion-sensitive systems such as fuel cells therefore impose much stricter requirements on the sulfur content of fuel gas compared to engines and turbines. Depending on the application, the sulfur content of fuel gas must be reduced to a few ppmv (parts per million by volume), or all trace components must be removed to 100 ppbv (parts per billion by volume). In this desulfurization context, HS is typically removed first, followed by sulfur-containing hydrocarbons (S-HCs) in a second stage. HS removal is typically achieved by adsorption onto specifically doped activated carbon, although biological or chemical methods are also possible. An additional activated carbon filter may be placed downstream for a process known as precision desulfurization. Subsequent S-HC removal is typically achieved using a standard activated carbon filter.

[0009] In addition to the removal of sulfur components, the removal of VOCs is also an important factor in the gas treatment of gas mixtures resulting from the pyrolysis or fermentation of organic matter. VOCs are a general term for organic substances (and therefore carbon-containing substances) that migrate to the gas phase by evaporation (or "vaporization") at room temperature or higher and are therefore volatile. Examples of VOCs include terpenes, ketones, amines, aldehydes, and sulfur-containing hydrocarbons. Methane (CH4) is not a component of VOCs. The exact definition of VOCs varies by country and region; the WHO defines VOCs as "all organic compounds, excluding pesticides, with a boiling point between 50 and 260°C." In Switzerland, the "Act on Preferential Taxation of Volatile Organic Compounds (VOCV)" of November 12, 1997, defines VOCs as "organic compounds with a vapor pressure of at least 0.1 mbar at 20°C or a boiling point of at most 240°C at 1013.25 mbar." In Europe, VOCs are defined according to Directives 1999 / 13 / EC, 2001 / 81 / EC, 2004 / 42 / EC, and 2008 / 50 / EC. DIN EN ISO 16000-6 defines VOCs as "all substances that appear in a gas chromatogram between and including n-hexane and n-hexadecane." Substances that appear early in a gas chromatogram are considered VVOCs (very volatile organic compounds), while substances that appear later are considered SVOCs (semi-volatile organic compounds).

[0010] Reducing VOC emissions in industrial and commercial applications is important for two reasons. First, for health reasons, VOCs in ambient air can cause certain symptoms in humans, including headaches, irritability, fatigue, reduced performance, sleep disorders, and respiratory irritation, collectively referred to as "sick building syndrome." Second, VOCs in industrial gas mixtures can cause breakdowns, damage, and reduced efficiency in treatment or distribution plants, resulting in rapid economic impacts. For example, terpenes condense on membrane systems, reducing their performance, while ketones damage seals, shortening maintenance intervals and requiring earlier and more frequent membrane replacement. Therefore, specific methods for removing VOCs from gas mixtures have been developed, both in the field of air pollution control and in biogas processing.

[0011] For example, a method is known from DE 101 58 970 A1, which allows for the removal of oxidizing substances or VOC components from an air stream, in particular the air in a vehicle compartment. For air stream cleaning, a specific layer structure is used, in which an adsorbent, an electrode and a barrier layer between them are embodied as structural units. With this layer structure, two spaced apart electrodes and a barrier between them form a plasma source that leads to a dielectric barrier discharge.

[0012] In the field of exhaust cleaning, attempts have also been made to achieve improved VOC removal by utilizing UV light to generate free radicals and / or by using certain catalytically active adsorbent materials doped with metal nanoparticles.

[0013] There are various methods known in the prior art that employ the addition of ozone and that employ adsorbent materials for the purpose of cleaning VOC-containing gas mixtures.

[0014] EP 3332862 A1 discloses a method for oxidative decomposition of gases containing VOCs. In this case, the gas to be treated is, more specifically, methane-free exhaust gas. For treatment, the gas is mixed with ozone, which oxidizes the VOCs. The gas is then contacted with the oxidized VOCs, and the residual ozone is contacted with a filler. The filler adsorbs the oxidized VOCs and residual ozone. The substrate it contains is an adsorbent with a high silicon dioxide content, and further contains 80 ml of silicon dioxide. 2 The adsorbent includes a powdered transition metal oxide having a BET specific surface area of ​​1 / g or more, the oxide being a composite oxide of Co, Mn, and Cu. One drawback of the method disclosed in EP 3332862 A1 is that the composite filler must be coated with the transition metal oxide, which is costly and complicated. This type of adsorbent is relatively expensive, and therefore the method cannot be profitably implemented.

[0015] Chinese Patent Publication No. 101391177 discloses a gas cleaning method for treating low-concentration organic compounds, more specifically, a gas cleaning method targeting malodorous compounds. This method comprises a catalytic adsorption unit and an ozone generation unit that supplies ozone to the catalytic adsorption unit. In this method, compounds such as dimethyl sulfide (DMS), dimethyl disulfide (DMDS), hydrogen sulfide (HS), formaldehyde, acetic acid, isopropyl alcohol, or acetone are oxidized. Oxidation by ozone enhances the adsorption capacity of the catalyst, extending its life and improving the efficiency of the method. However, the method from Chinese Patent Publication No. 101391177 (B) requires a relatively expensive catalyst compared to conventional adsorbents, reducing its profitability. As with the method from European Patent Publication No. 3332862 (A1), the gas in Chinese Patent Publication No. 101391177 is, more specifically, methane-free exhaust gas.

[0016] Japanese Patent Application Laid-Open No. 11-342313 discloses adding ozone to a pollutant-containing gas, mixing the gas, and then passing the gas through an adsorption bed filled with an adsorbent having a high silicon dioxide content, whereby both the ozone and pollutants present in the gas are adsorbed.

[0017] German Patent Application Publication No. 102014212914 A1 discloses the use of bottom products and fly ash obtained from biomass gasification for the purpose of adsorbing VOCs in the treatment of gaseous or liquid compositions obtained in the pretreatment of biomass. These fly ash and bottom products are hydrophobic compared to other adsorbents, such as silica gel, and are particularly suitable for adsorbing VOCs in moist gaseous compositions (exhaust gas, for example) or even in water. A disadvantage of the method disclosed in German Patent Application Publication No. 102014212914 A1 is that the fly ash and bottom products can only adsorb a very limited amount of VOCs.

[0018] German Patent Application Publication No. 102008058114 A1 discloses a method for cleaning biogas, which contains at least hydrogen sulfide and ammonia as impurities, and possibly also carbon dioxide. These impurities are removed from the biogas in a cleaning and / or separation step. For this purpose, the biogas is mixed with a defined amount of hydrogen peroxide and an alkaline solution containing at least one alkali metal hydroxide. The method disclosed in German Patent Application Publication No. 102008058114 A1 has the disadvantage that unreacted hydrogen peroxide residues, water, and the alkaline solution containing alkali metal hydroxide must be removed from the treated biogas accordingly, making it costly and complicated, and the chemicals used are relatively expensive.

[0019] EP 1997549 A1 discloses a method for catalytic cleaning of biogenic or anthropogenic methane-containing gases, in which the gas is heated to a temperature in the range of 200°C to 450°C and the heated gas is subjected to a combination of catalytic oxidation and hydrolysis (in which all minor components present in the gas are decomposed to form carbon dioxide, water and acidic reaction products), which are then removed. The method disclosed in EP 1 997 549 A1 has the drawback that an unprofitably large amount of energy is consumed for heating the gas in order to clean it.

[0020] European Patent Application Publication No. 0947233 (A1) discloses a method for treating gas contaminated with pollutants. In this case, the gas is mixed with ozone and then passed through an adsorption unit. The adsorption unit includes a first adsorption layer located on the inlet side and comprising mesoporous silicate, and a second adsorption layer located on the outlet side and comprising aluminized faujasite. In the adsorption unit, both ozone and the pollutants are adsorbed, and the pollutants are detoxified by exposure to ozone within the adsorption layer. However, this adsorption unit is relatively expensive and cannot be operated profitably.

[0021] WO 2012 / 006729 A1 discloses a biogas cleaning method in which hydrogen gas is mixed with biogas to remove VOCs from the biogas. The hydrogen is then catalytically combusted with oxygen contained in the biogas using a deoxygenation catalyst bed, thereby substantially completely removing the oxygen contained in the biogas and heating the biogas stream. In a further step, VOCs are removed from the biogas together with water in a pre-condenser. The method of WO 2012 / 006729 A1 has the disadvantage that biogas cleaning requires the use of relatively large amounts of energy for hydrogen production and gas cooling.

[0022] A common problem with VOC adsorbents is their limited adsorption capacity or charging level. Particularly in the case of "heavy" VOCs, these compounds preferably adhere to the outermost or externally easily accessible adsorbent surfaces, making it more difficult for additional VOCs to penetrate into the adsorbent pores and / or be adsorbed onto the surfaces within the pores. As a result, the theoretical adsorption capacity, depending on the VOC composition, is sometimes almost completely unused, being only 10-30%. Summary of the Invention [Problem to be solved by the invention]

[0023] Therefore, in the present invention, the shortcomings of the prior art are addressed and a cost-effective method for the efficient removal of VOCs from gas mixtures obtained by fermentation is provided. [Means for solving the problem]

[0024] This object is achieved according to the invention by a method as defined in claim 1. Preferred embodiments of the invention are reproduced in the dependent claims.

[0025] In the method of the present invention, in the first step (a), a gas mixture is provided, which includes a methane-containing biogas obtained by fermentation of organic matter and having a methane concentration of at least 40% by volume, a pyrolysis gas obtained by thermal treatment of organic matter and having a carbon monoxide concentration of at least 2% by volume, or a combination thereof. The gas mixture further includes at least one impurity from the group of volatile organic compounds (VOCs), and the VOC concentration of the gas mixture is 0.0001 to 0.2% by volume. In the second step (b), the gas mixture is mixed with 0.0001 to 12% by volume of ozone, based on the gas mixture, so that the ozone oxidizes at least a portion of the VOCs in the gas mixture. In the third step (c), the gas mixture from the second step is contacted with a VOC-adsorbing adsorbent selected from the group consisting of activated carbon, activated coke, silica gel, molecular sieves, and mixtures thereof to clean the gas mixture.

[0026] The method of the present invention is particularly suitable for cleaning fermentation products, such as those produced in biogas plants, e.g., methane-containing gases (hereinafter referred to as "methane-containing biogas" or "biogas"). In the case of such biogas, the gas mixture according to the present invention has a methane content of at least 40%, preferably at least 50% (percentages in the gas mixture are always based on volume percentages, as described above). In a preferred embodiment, the biogas originates from a fermenter.

[0027] Pyrolysis gas (also called synthesis gas) is defined in the present invention as the gas formed during the thermal treatment of organic matter. In this case, oxygen is excluded, resulting in the breaking of intramolecular bonds at high temperatures (typically 250-500 °C), which prevents combustion. The pyrolysis gas produced in this process contains carbon monoxide (CO) and is subsequently used preferentially in steam reforming to produce hydrogen.

[0028] In the present invention, an adsorbent is defined as a substance capable of binding (adsorbing) VOCs from a gas mixture. "Adsorption" in this context is understood as a process in which a substance (generally a molecule) remains attached to the surface of another substance and accumulates on that surface. In the present invention, this attachment to the adsorbent surface can occur both based on chemical bonding (chemisorption) and physical attraction (physisorption). As adsorbents, activated carbon, activated coke, silica gel, or molecular sieves (zeolites), among others, can be used.

[0029] Surprisingly, it has been found that the addition of ozone to a gas mixture can significantly improve the adsorption capacity of the adsorbent. In particular, it has been confirmed that pretreatment with ozone has the overall effect of more efficiently loading the adsorbent with VOCs and facilitating the removal of VOCs from the gas mixture. This effect is believed to be due to the fact that the VOCs are partially oxidized by the addition of ozone before they impinge on the adsorbent. [ka]

[0030] The method of the present invention has the advantage over the prior art in that the VOCs contained in the gas mixture are pretreated with ozone, resulting in more efficient adsorption of the VOCs onto the adsorbent, which results in less frequent treatment or replacement of the adsorbent, making the method more efficient and cost-effective.

[0031] Oxygen and ozone are generally known to promote fires and explosions. However, contrary to expectations, it has been found that mixing ozone with methane- or carbon monoxide-containing gases is easily manageable. This is believed to be at least in part due to the fact that ozone preferentially reacts with, and is therefore very rapidly converted by, VOCs present in the gas mixture.

[0032] In the present invention, an adsorbent that adsorbs VOCs is ideally used, but other gas components, particularly methane, can pass through the adsorbent unadsorbed, or at least with minimal adsorption, so that by definition the relative concentration of methane in the gas mixture after passing through the adsorbent is higher than before impinging on the adsorbent.

[0033] Those skilled in the art recognize that adsorbents can only adsorb a certain amount of VOCs before becoming saturated. As soon as the adsorption capacity of an adsorbent drops to a certain threshold, the adsorbent must be regenerated, reprocessed, or replaced to re-establish its original adsorption capacity. Many methods are known for desorbing or desorbing substances (mainly VOCs in this case) bound to an adsorbent. For example, a so-called regeneration gas is passed through the adsorbent, separating the bound substances from the adsorbent surface and carrying them along with the regeneration gas.

[0034] In a preferred embodiment, the gas mixture from step a) contains a VOC concentration of 0.001 to 0.01% by volume. Those skilled in the art will recognize that the method of the present invention will continue to function without problems at higher concentrations, particularly at VOC concentrations above about 0.2% by volume, but will nevertheless no longer be usefully practiced.

[0035] Preferably, the at least one impurity selected from the group of volatile organic compounds (VOCs) is selected from the group consisting of linear or branched C1-C5 alcohols, sulfides, and unsaturated terpenes. Molecules of these substance groups can be particularly effectively oxidized by ozone, which promotes their adsorption onto the adsorbent.

[0036] In a further preferred embodiment of the method, the at least one impurity selected from the group of volatile organic compounds (VOCs) is 1-butanol, 1-pentanol, 2-butanol, 2-methyl-1-butanol, 2-methyl-1-propanol, 2-methyl-2-butanol, 2-methyl-2-propanol, 2-pentanol, 3-methyl-1-butanol, 3-methyl-2-butanol, 3-pentanol, ethanol, 2-propanol, methanol, propanol, 1-pentanethiol, 1-propanethiol, 2-butanethiol, 2-methyl-2-propanethiol, 2-propanethiol, butanethiol, carbonyl sulfide, dimethyl disulfide, , dimethyl sulfide, dimethyl trisulfide, ethyl mercaptan, methyl mercaptan, methyl propyl disulfide, tetrahydrothiophene, thiophene, thiophenol, 1,4-cineole, 3-carene, α-pinene, α-thujene, β-pinene, limonene, eucalyptol, fenchone, limonene, linalool, myrcene, p-cymene, sabinene, α-caryophyllene, α-terpinene, γ-terpinene, 2-methylthiophene, 3-methylthiophene, diisopropyl disulfide, dimethyl tetrasulfide, isobutyl mercaptan, methyl allyl sulfide, methyl isopropyl disulfide, methyl propyl sulfide, 3,The methyl methyl ether is selected from the group consisting of 3-dimethyl-2-bornanone, nopinone, phellandrene, p-menthan-2-ol, p-menthan-2-one, santhene, terpinolene, thujanone and tricyclene, more preferably 1-butanol, 1-pentanol, 2-butanol, 2-methyl-1-butanol, 2-methyl-1-propanol, 2-methyl-2-butanol, 2-methyl-2-propanol, 2-pentanol, 3-methyl-1-butanol, 3-methyl-2-butanol, 3-pentanol, ethanol, 2-propanol, methanol, propanol, 1-pentanethiol, 1- The adsorbents are selected from the group consisting of propanethiol, 2-butanethiol, 2-methyl-2-propanethiol, 2-propanethiol, butanethiol, carbonyl sulfide, dimethyl disulfide, dimethyl sulfide, dimethyl trisulfide, ethyl mercaptan, methyl mercaptan, methylpropyl disulfide, tetrahydrothiophene, thiophene, thiophenol, 1,4-cineole, 3-carene, α-pinene, α-thujene, β-pinene, limonene, eucalyptol, fenchone, limonene, linalool, myrcene, p-cymene, sabinene, α-caryophyllene, α-terpinene, and γ-terpinene. The adsorption capacity of the adsorbent was improved by the oxidation of these molecules by ozone.

[0037] Particularly preferably, the at least one impurity from the group of volatile organic compounds (VOCs) is selected from the group consisting of 1,4-cineole, 3-carene, α-pinene, α-thujene, β-pinene, limonene, eucalyptol, fenchone, limonene, linalool, myrcene, p-cymene, sabinene, α-caryophyllene, α-terpinene and γ-terpinene. Through oxidation of molecules from the group of terpenes, it has been possible to achieve a sharp increase in the adsorption capacity of the adsorbent.

[0038] As a preferred definition, in the present invention, a compound is included in the group of VOCs if it has a vapor pressure of at least 0.1 mbar at 20° C. or a boiling point of at most 240° C. at 1013.25 mbar.

[0039] However, in the method of the present invention, VOCs are preferably oxidized by ozone without the concomitant effect of a catalyst, more particularly, without the concomitant effect of a catalyst comprising a material selected from the group consisting of manganese, iron, cobalt, nickel, copper, silver, lead, zinc, vanadium, titanium, chromium, aluminum, silicon, acid-activated bentonite, and mixtures thereof. Discarding the catalyst reduces the need for periodic treatment of the catalyst, which leads to maintenance costs.

[0040] In an alternative embodiment, the VOCs in the method of the present invention are oxidized by ozone and under irradiation with UV light (ultraviolet light). The effect of UV light irradiation is that the ozone reduced to elemental oxygen (O2) reacts again to form ozone, and the UV light converts elemental oxygen (O2) to oxygen radicals (O * ), and the oxygen radical subsequently reacts with elemental oxygen (O2) to form ozone.

[0041] The reaction described in the previous section can be represented using the following equation: [ka]

[0042] In one preferred embodiment, the at least one impurity is from the group of volatile organic compounds VOCs selected from the group consisting of the following compounds: propane, n-butane, n-pentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, n-undecane, n-dodecane, n-tridecane, n-tetradecane, n-pentadecane, nC 16 , nC 17 , nC 18 , nC 19 , nC 20 , nC 21 , nC 22, isobutane, neopentane, isopentane, 2,2-dimethylbutane, 2,3-dimethylbutane, 2-methylpentane, 3-methylpentane, 2,2,3-trimethylbutane, 2,2-dimethylpentane, 2,3-dimethylpentane, 2,4-dimethylpentane, 2-methylhexane, 3,3-dimethylpentane, 3-methylhexane, 2,2,3,3-tetramethylbutane, 2,2,4-trimethylpentane, 2,2-dimethylhexane , 2,3,4-trimethylpentane, 2,3-dimethylhexane, 2,4-dimethylhexane, 2,5-dimethylhexane, 2-methylheptane, 3-methylheptane, 4-methylheptane, 2,2,5-trimethylhexane, 2,3,5-trimethylhexane, 2,4-dimethylheptane, 2-methyloctane, 3,3-diethylpentane, 3,5-dimethylheptane, 4-ethylheptane, 4-methyloctane, 2,4-dimethyloctane hexane, 2,6-dimethyloctane, 2-methylnonane, 3,4-diethylhexane, 3-methylnonane, 4-methylnonane, 4-propylheptane, 2,6-dimethylnonane, 3,5-diethylheptane, 3-methyldecane, 4-methyldecane, 2,6-diethyloctane, 3,6-dimethyldecane, 3-methylundecane, 5-methylundecane, 3,6-dimethylundecane, 3,7-diethylnonane, 3-methyldodecane, 5-methyldodecane Decane, 3,7-dimethyldodecane, 3,8-diethyldecane, 3-methyltridecane, 6-methyltridecane, 3,7-dimethyltridecane, 3,9-diethylundecane, 3-methyltetradecane, 6-methyltetradecane, 3-methylpentadecane, 4,8-dimethyltetradecane, 7-methylpentadecane, cyclopropane, cyclobutane, cyclopentane, cyclohexane, isopropylcyclopropane, methylcyclopentane,

[0043] 1,3-dimethylcyclopentane, cycloheptane, ethylcyclopentane, methylcyclohexane, 1,3-dimethylcyclohexane, cyclooctane, ethylcyclohexane, propylcyclopentane, 1,1,3-trimethylcyclohexane, 1-ethyl-4-methylcyclohexane, propylcyclohexane, 1,3-diethylcyclohexane, 1,4-diethylcyclohexane, 1-methyl-3-isopropylcyclohexane, butylcyclohexane, 1,3-diethyl-5-methylcyclohexane, 1-ethyl-2-propylcyclohexane Cyclohexane, pentylcyclohexane, 1,3,5-triethylcyclohexane, 1-methyl-4-pentylcyclohexane, hexylcyclohexane, 1,3-diethyl-5-pentylcyclohexane, 1-methyl-2-hexylcyclohexane, heptylcyclohexane, 1,3-dipropyl-5-ethylcyclohexane, 1-methyl-4-heptylcyclohexane, octylcyclohexane, 1,3,5-tripropylcyclohexane, 1-methyl-2-octylcyclohexane, nonylcyclohexane, 1,3-propyl-5-butyl Cyclohexane, 1-methyl-4-nonylcyclohexane, decylcyclohexane, ethene, propene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3,3-dimethyl-1-butene, 3-methyl-1-pentene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, isobutene, 2-methyl-1-butene, 2,3-dimethyl-1-butene, 2-ethyl-1-butene, 2-methyl-1-pentene , 2,3,3-trimethyl-1-butene, 3-methyl-2-isopropyl-1-butene, cis-2-butene, trans-2-butene, 2-pentene, 2-methyl-2-butene, cis-2-pentene, trans-2-pentene, 2,3-dimethyl-2-butene, 2-hexene, 2-methyl-2-pentene, cis-2-hexene, cis-3-hexene, cis-3-methyl-2-hexene, trans-2-hexene, trans-3-hexene, trans-3-methyl-2-hexene, trans-4-methyl-2-hexene, 2,3-dimethyl-2-hexene, 2-heptene, cis-3-heptene, trans-2-heptene, trans-3-heptene, trans-4,4-dimethyl-2-pentene, 3-octene, cis-4-octene, trans-2,2-dimethyl-3-hexene, trans-2,5-dimethyl-3-hexene, trans-3-octene, trans-4-octene, 2,4,4-trimethyl-2-pentene, 3-nonene, trans-4-nonene, 3,4-diethyl-2-hexene, cis-5-decene, trans-4-decene, trans-5-undecene, trans-5-dodecene, trans-5-tridecene, trans-5-tetradecene, trans-5-pentecene, cyclopentene, 1-methylcyclopentene, cyclohexene, 1-methylcyclohexene, 4-methylcyclohexene, 1,2-dimethylcyclohexene, 1,3-butadiene, isoprene, C6 cyclic olefins, C7 cyclic olefins, C8 cyclic olefins, C9 cyclic olefins, C, 10 Cyclic olefin, C 11 Cyclic olefin, C 12 Cyclic olefin, C 13 Cyclic olefin, C 14 Cyclic olefin, C 15 Cyclic olefins, cyclopentadiene, α-pinene, β-pinene, 3-carene, D-limonene, terpenes, α-methylstyrene, C9 styrene, C 10 Styrene, benzene, toluene, ethylbenzene, isopropylbenzene, n-propylbenzene, n-butylbenzene, s-butylbenzene, m-xylene, o-xylene, p-xylene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, indan, naphthalene, tetralin, 1-methylnaphthalene, 2-methylnaphthalene, 2,3-dimethylnaphthalene,

[0044] C 12 Monosubstituted naphthalenes, C 12 Disubstituted naphthalenes, C 13 Monosubstituted naphthalenes, C 13 Disubstituted naphthalenes, C 13Trisubstituted naphthalenes, acetylene, methyl acetylene, 2-butyne, ethyl acetylene, methanol, ethanol, isopropyl alcohol, n-propyl alcohol, isobutyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, cyclopentanol, 2-pentanol, 3-pentanol, pentyl alcohol, cyclohexanol, 1-hexanol, 2-hexanol, 1-heptanol, 1-octanol, 2-octanol, 2-ethyl-1-hexanol, 3-octanol, 4-octanol, 8-methyl-1-nonanol, ethylene glycol, propylene glycol, 1,2-butanediol, glycerol, 2-methyl-2,4-pentanediol, 1,2-dihydroxyhexane, dimethyl ether, trimethylene oxide, tetrahydrofuran, diethyl ether, dimethoxymethane, α-methyltetrahydrofuran, tetrahydropyran, ethyl isopropyl ether, methyl n-butyl ether, methyl tert-butyl ether, ethyl n-butyl ether, ethyl tert-butyl ether, methyl tert-amyl ether, di-n-propyl ether, 2-butyltetrahydrofuran, di-n-butyl ether, diisobutyl ether, di-n-pentyl ether, 2-methoxyethanol, 2-methoxy-1-propanol, 2-ethoxyethanol, 1-methoxy-2-propanol, 2-propoxyethanol, 3-ethoxy-1-propanol, 3-methoxy-1-butanol, 1-ethoxy-2-propanol, diethylene glycol, 3-methoxy-3-methylbutanol, 2-butoxyethanol, 1-propoxy-2-propanol, 2-(2-methoxyethoxy)ethanol, n-butoxy-2-propanol, 1-tert-butoxy-2-propanol, 2-tert-butoxy-1-propanol, 2-(2-ethoxyethoxy)ethanol, dipropylene glycol, dipropylene glycol methyl ether, 2-(2-butoxyethoxy)ethanol, methyl formate, ethyl formate, propyl formate, ethyl acetate, methyl propionate, n-butyl formate, ethyl propionate, isopropyl acetate, methyl butyrate, methyl isobutyrate, n-propyl acetate, n-butyl acetate, ethyl butyrate, isobutyl acetate, pivalic acid Methyl, n-propyl propionate, sec-butyl acetate, tert-butyl acetate, butyl propionate, amyl acetate, n-propyl butyrate, n-butyl butyrate, isobutyl isobutyrate, n-hexyl acetate, 2-methylpentyl acetate, 3-methylpentyl acetate, 4-methylpentyl acetate, 2,3-dimethylbutyl acetate, n-heptyl acetate, 2-methylhexyl acetate, 3-methylhexyl acetate, 4-methylhexyl acetate, 5-methylhexyl acetate, 3-ethylpentyl acetate, 2,4-dimethylpentyl acetate,

[0045] Isoamyl isobutyrate, n-octyl acetate, 2-ethylhexyl acetate, 3,4-dimethylhexyl acetate, 3,5-dimethylhexyl acetate, 3-ethylhexyl acetate, 4-methylheptyl acetate, 4,5-dimethylhexyl acetate, 5-methylheptyl acetate, 3-methylheptyl acetate, 2,4-dimethylhexyl acetate, n-nonyl acetate, 2-methyloctyl acetate, 4-methyloctyl acetate, 5-methyloctyl acetate, 3-ethylheptyl acetate, 3,6-dimethylheptyl acetate, 3,5-dimethyl acetate ethylheptyl acetate, 4,5-dimethylheptyl acetate, 4,6-dimethylheptyl acetate, 2,4-dimethylheptyl acetate, 2,3-dimethylheptyl acetate, 2,5-dimethylheptyl acetate, 2,3,5-trimethylhexyl acetate, 3,6-dimethyloctyl acetate, 4,6-dimethyloctyl acetate, 3-isopropylheptyl acetate, 4,7-dimethylnonyl acetate, 3,5,7-trimethyloctyl acetate, 3-ethyl-6-methyloctyl acetate, 3,6,8-trimethylnonyl acetate, 3,5, 7-Trimethylnonyl acetate, 2,3,5,7-tetramethyloctyl acetate, 2,4,6,8-tetramethylnonyl acetate, 4,7,9-trimethyldecyl acetate, 3-ethyl-6,7-dimethylnonyl acetate, 5-ethyl-3,6,8-trimethylnonyl acetate, 2,3,5,6,8-pentamethylnonyl acetate, dimethyl carbonate, propylene carbonate, methyl lactate, ethyl lactate, 2-methoxyethyl acetate, methyl isopropyl carbonate, 2-methoxy-1-propyl acetate, 2-ethoxyethyl acetate, 1-methyl acetate 2-propyl hydroxyl, dimethyl succinate, ethylene glycol diacetate, ethyl 3-ethoxypropionate, diisopropyl carbonate, dimethyl glutarate, 2-butoxyethyl acetate, dimethyl adipate, 3-hydroxy-2,2,4-trimethylpentyl 1-isobutyrate, 1-hydroxy-2,2,4-trimethylpentyl 3-isobutyrate, ethylene oxide, propylene oxide, 1,2-epoxybutane, formic acid, acetic acid, acrylic acid, propionic acid, methyl acrylate,

[0046] Vinyl acetate, 2-methyl-2-buten-3-ol, ethyl acrylate, methyl methacrylate, butyl methacrylate, isobutyl methacrylate, furan, formaldehyde, acetaldehyde, propionaldehyde, butanal, 2-methylpropanal, pentanal, 2,2-dimethylpropanal, 3-methylbutanal, glutaraldehyde, hexanal, heptanal, octanal, glyoxal, methylglyoxal, acrolein, crotonaldehyde, methacrolein, hydroxymethacrolein, cyclobutanone, methyl ethyl ketone, cyclopentanone, 3-pentanone, 2-pentanone, cyclohexanone, 4-methyl-2-pentanone, methyl n-butyl ketone, methyl tert-butyl ketone, 2-methyl-3-hexanone, 2-heptanone ethanolamine, dimethylaminoethanol, diethanolamine, triethanolamine, n-methyl-2-pyrrolidone, oxohexyl acetate, oxoheptyl acetate, oxooctyl acetate, oxononyl acetate, oxodecyl acetate, oxododecyl acetate, oxotridecyl acetate, dimethyl sulfide, and hexamethylcyclotrisiloxane.

[0047] Preferably, the gas mixture in the second step b) is mixed with ozone at a concentration of 0.0001-3% by volume, preferably 0.0001-0.5% by volume, more particularly 0.0001-0.1% by volume, and very preferably 0.0002-0.05% by volume, relative to the gas mixture in step a). This means that the gas mixture after ozone addition preferably has an ozone concentration of 0.0001-3% by volume. Alternatively, it can be expressed that in step b), preferably 0.0001-3% by volume of ozone is preferably mixed with 97-99.9999% by volume of the gas mixture. It is clear to those skilled in the art that ozone instantly begins to react upon addition. Therefore, the maximum concentration of ozone in the gas mixture exists only theoretically. The upper limit of 12% by volume is determined by the maximum allowable oxygen concentration (O2) in the cleaned gas in step c). In the case of gas mixtures with biogas, this concentration should not exceed 12% by volume to avoid the formation of explosive gas mixtures. For simplicity, we will assume that one molecule of ozone (O3) reacts with one molecule of VOC to form one molecule of oxygen (O2) and one molecule of oxidized VOC. Those skilled in the art will understand that one molecule of VOC may be repeatedly oxidized, i.e., may react with more than one molecule of ozone. The minimum ozone concentration of 0.0001% by volume is determined by the minimum VOC concentration of 0.0001% by volume, or by the fact that VOC concentrations exceeding the allowable limit of 0.0001% by volume are oxidized.

[0048] This method would work with just a few molecules of ozone, or even just one molecule. However, in that case, the economic benefits of improved purification would no longer justify the operating costs. The gas mixture may be mixed with oxygen (O2), from which ozone (O3) is formed only in the reaction space, for example by UV light.

[0049] The methane-containing biogas may in particular be gas from a biogas plant, or alternatively may be natural gas or landfill gas. The methane-containing biogas preferably contains a methane concentration of at least 50% by volume, more preferably at least 60% by volume.

[0050] In the case of methane-containing biogas, it is preferably present at a temperature between 10° C. and 30° C., preferably at room temperature, and at a pressure between 50 and 200 mbar, preferably about 100 mbar.

[0051] After cleaning, the gas mixture may preferably be used to operate a combustion system such as a heater, a vehicle gas engine or a gas turbine, or, in the case of upgraded methane-containing biogas, may be supplied to the gas network as biomethane.

[0052] When the method of the present invention is used to clean pyrolysis gases, the pyrolysis gases preferably contain at least 5% by volume of carbon monoxide.

[0053] The pyrolysis gas may further comprise at least one component from the group consisting of hydrogen, carbon dioxide, methane, ethane, propane, ethene, higher hydrocarbons, acetylene, ammonia, and propylene.

[0054] In the case of pyrolysis gases, this method has proven to be particularly efficient at preferred temperatures between 5° C. and 60° C. Particularly preferred in this case is a temperature of about 40° C.

[0055] In a preferred embodiment, hydrogen sulfide is removed from the gas mixture before mixing with ozone. As mentioned above, hydrogen sulfide can react in gas processing plants to form sulfuric acid, which can cause corrosion of conduits, so removal of hydrogen sulfide is preferred as soon as it is present in the gas mixture in significant concentrations. Prior to the addition of ozone, the hydrogen sulfide concentration is preferably reduced to less than 5 ppm. Depending on the type of plant, hydrogen sulfide is not required in liquefaction plants, so it is even more preferred that hydrogen sulfide be removed prior to any liquefaction of the product gas.

[0056] Preferably, CO2 is also removed from the gas mixture before or after VOC adsorption. In particular, in the case of cleaning methane-containing gas mixtures in the present invention, it is preferable to maximize the proportion of methane as a combustible component in the cleaned gas mixture (product gas) in order to utilize the cleaned product gas as a combustible energy carrier, rather than just removing contaminants from the gas mixture. Biogas typically contains a variable proportion of CO2. Since CO2 is not combustible, it is preferably removed from the gas mixture to increase the energy density of the gas mixture, for example, for supply to a natural gas network. In the present invention, desulfurized biogas after CO2 removal is also referred to as biomethane. Such biomethane may still contain VOCs, which can be removed by the method of the present invention. As with hydrogen sulfide, CO2 is preferably removed before liquefaction. Removal after liquefaction is more expensive and complicated because CO2 freezes faster than product gas, potentially clogging or damaging cooling equipment.

[0057] In a preferred embodiment, the gas mixture after ozone addition and before contacting the VOCs with the adsorbent is subjected to a post-treatment step, preferably using a scrubber, a cooling scrubber or a gas condenser equipped with a condensate separator, in which water-soluble VOCs and any ammonia present can be removed in advance, thereby reducing the load on the adsorbent.

[0058] The adsorbent preferably comprises activated carbon, activated coke, silica gel, aluminum oxide, and / or molecular sieves (zeolites), with activated carbon being preferred. More preferably, the adsorbent (19) is selected from the group consisting of activated carbon, activated coke, molecular sieves, and mixtures thereof. Highly preferably, the adsorbent (19) is at least 90% activated carbon. Activated carbon is often used as an adsorbent to remove unwanted colorants, flavors, and odorants from gases, vapors, and liquids. One major advantage of activated carbon is its thermal reactivatability, low cost, low manufacturing complexity, and universal availability. However, in practice, activated carbon is preferably not reprocessed but instead replaced and then incinerated as waste. Activated carbon has also proven to be an excellent adsorbent for VOCs. Depending on environmental standards, activated carbon containing VOCs can be used as fertilizer.

[0059] In a preferred embodiment, ozone is mixed into the gas mixture as an ozone-oxygen mixture, since this type of mixture has been proven to be efficient in oxidizing VOCs. The ozone-oxygen mixture preferably comprises 1%-15% ozone and 85%-99% oxygen, more preferably 3%-13% ozone and 87%-97% oxygen, and most preferably 5%-10% ozone and 90%-95% oxygen. In the present invention, oxygen is always defined as O2 molecules, which is also commonly known as molecular oxygen. In contrast, O · Or O * Oxygen radicals, also known as ozone radicals, are also referred to as such in the present invention to distinguish them from ozone and oxygen.

[0060] In the above ozone-oxygen mixtures, a relatively high ozone content is generally preferred. In the present invention, 20% ozone at 80% oxygen is the preferred upper limit. Higher concentrations of ozone in the ozone-oxygen mixture are technically possible, but are currently not economically preferred due to the increased cost and complexity.

[0061] It has been found that optimal oxidation is achieved with a final ozone concentration in the range of 0.0001-0.1% by volume, and more preferably 0.0002-0.05% by volume. Higher concentrations are feasible but less economically desirable. The term "final concentration" refers to the ozone concentration at the time of addition to the gas mixture, i.e., after complete addition, under the theoretical assumption that the ozone has not yet reacted with the components of the gas mixture.

[0062] If the composition of the gas mixture is known, the ozone concentration can optionally be specifically adapted to the concentration of VOCs in the gas mixture. Therefore, the amount of ozone added is preferably stoichiometric relative to the expected or present VOC concentration in the gas mixture. On the one hand, this prevents unnecessary accumulation of ozone and oxygen in the gas mixture, which could result in an increased risk of explosion. On the other hand, the adsorbent is prevented from contacting ozone as much as possible. The oxidation reaction between ozone and the components of the gas mixture typically occurs within a few seconds or a few tenths of a second. In oxidation, ozone is reduced to molecular oxygen, and the liberated oxygen radicals combine with oxidizable substances, preferably VOCs, and in the process, oxidize the oxidizable substances, preferably VOCs. If there is an excess of ozone, not all of the ozone will be consumed by the reaction before the gas mixture reaches the adsorbent. Therefore, the remaining ozone may reach the adsorbent together with the oxidized VOCs, where it may dissociate the VOCs already adsorbed on the adsorbent. For this reason, the ozone concentration is preferably adapted to the amount of VOCs contained or expected in the gas mixture, and is preferably adjusted so that ozone is no longer present in the gas mixture when it impinges on the adsorbent. The amount of VOCs often depends on the origin of the gas mixture. However, for fermentation-produced gases and naturally occurring methane-containing gases, average VOC concentrations are known. In the case of fermentation-produced gases, these average VOC concentrations are further specified based on the properties of the fermentation raw materials used. Therefore, the amount of ozone to be added can be determined based on such known average VOC concentration values. However, preferably, the VOC concentrations present and the amount of ozone to be added based thereon are determined based on a reference sample of the gas mixture before it is cleaned.

[0063] In a preferred embodiment, the time from the time of mixing of ozone to the time of impingement of the gas mixture on the adsorbent is at least 1 second, preferably at least 4 seconds, more preferably 6 to 10 seconds. As mentioned above, it is desirable that all of the ozone has reacted with the VOCs before the gas mixture impinges on the adsorbent. To prevent the ozone from reaching the adsorbent before it has reacted with the VOCs present in the gas mixture, the reaction space for VOC oxidation or ozone addition is preferably separated from the adsorbent, or the VOCs are injected together with the ozone at one end of the reaction space, and the adsorbent is located at the opposite end. In the last-mentioned variant, the dimensions of the reaction space are therefore such that the ozone reacts as completely as possible with the components in the gas mixture before reaching the adsorbent.

[0064] In a further preferred embodiment, ozone is generated in situ from air in an ozone generator. For autonomous production plants, it is highly advantageous if ozone can be obtained from ambient air and does not require pure oxygen as a precursor. This reduces plant maintenance efforts and allows remote production without the need for a pure oxygen source. For this purpose, an oxygen concentrator is preferably installed on-site, which can filter oxygen from the air and pass it to the ozone generator.

[0065] Preferably, ozone is alternatively generated from oxygen in an ozone generator. Ozone generation using very high purity oxygen (preferably 90-95% oxygen concentration) as a precursor allows ozone to be generated more efficiently and at higher concentrations. The use of pure oxygen is particularly reasonable in established sites where a supply of pure oxygen is not an issue.

[0066] In a further aspect, the present invention relates to an apparatus for cleaning a gas mixture by the above-described method. The apparatus comprises at least one gas supply conduit, at least one reaction space, at least one adsorbent for VOCs, an ozone source with an ozone supply conduit, and a gas outlet conduit. The reaction space can be any space, container, or housing in which VOCs can react with ozone. The reaction space does not necessarily have to be enclosed on all sides; for example, a tubular section is also conceivable. In the present invention, the adsorbent may be contained within the reaction space, but is preferably separated from the reaction space. Compared to known cleaning apparatuses of the prior art, the apparatus of the present invention has the advantage that, as a result of pretreatment of VOCs with ozone, VOCs are more efficiently adsorbed by the adsorbent, and therefore the adsorbent needs to be treated or replaced less frequently. Overall, therefore, the apparatus can operate more efficiently and cost-effectively.

[0067] The reaction space of the device is preferably equipped with packing elements, which allow efficient mixing or flow routing of gases or different gas streams in the reaction space, and thus efficient oxidation of VOCs by ozone.

[0068] The device preferably has a modular structure and is suitable for retrofitting existing gas cleaning plants. In this context, a modular device is defined as a device in which the components of the device described above can be pre-assembled or on-site and installed in an existing plant. This has the advantage that defective modules can be replaced cost-effectively and without complex works. Furthermore, a modular device has the advantage that existing plants can be retrofitted cost-effectively instead of having to be rebuilt or replaced, which is costly. The modular structure of the device therefore increases its profitability.

[0069] In a preferred embodiment, the ozone source is an ozone generator that communicates with the reaction space via an ozone supply conduit. If necessary, the ozone generator may be installed remotely from the device. Such a separate location of the ozone generator is particularly reasonable when space problems or other reasons preclude the possibility of direct installation in the plant.

[0070] In an alternative method, in a first step a), a gas mixture containing gas is provided. The gas is selected from the group consisting of pyrolysis gas obtained by pyrolysis of organic matter and methane-containing biogas obtained by fermentation of organic matter, or a mixture thereof. The pyrolysis gas has a carbon monoxide concentration of at least 2% by volume, and the biogas has a methane concentration of at least 40% by volume. The gas mixture further contains at least one impurity from the group of volatile organic compounds (VOCs). In a second step b), the gas mixture is mixed with ozone, which oxidizes at least a portion of the VOCs in the gas mixture. In a third step c), the gas mixture from the second step is contacted with a VOC-adsorbing adsorbent to clean the gas mixture.

[0071] The invention will be explained in more detail below with reference to exemplary embodiments represented in the accompanying drawings, in which: Figure 1 is a block diagram of a microprocessor according to an embodiment of the present invention; [Brief explanation of the drawings]

[0072] [Figure 1] FIG. 1 shows a schematic representation of a preferred embodiment of the method of the invention for cleaning a gas mixture comprising methane-containing biogas. [Figure 2] FIG. 2 shows a schematic diagram of an alternative, simplified embodiment of the method of the present invention for purifying a gas mixture including methane-containing biogas. DETAILED DESCRIPTION OF THE INVENTION

[0073] In a preferred embodiment of the method of the present invention, as shown diagrammatically in FIG. 1, a raw gas 3 is extracted from a gas source 1 and introduced into a gas processing plant 2. In the gas processing plant 2, the raw gas 3 is first passed through a pretreatment chamber 5, where it is cooled for pretreatment purposes, ie, for the removal of condensates and ammonia. The raw gas 3 is then compressed to 0.1 bar (g) and desulfurized using specially doped activated carbon (usually KI, K2CO3, KMnO4) or further pretreated by removal of hydrogen sulfide (HS). Alternatively, desulfurization can be carried out by biological or chemical methods. Furthermore, a downstream activated carbon filter (not shown) can be used to perform more sophisticated desulfurization.

[0074] After pretreatment, a pretreated desulfurized gas 7 is obtained. However, this does not mean that the pretreated gas 7 is completely free of sulfur compounds, and in particular does not exclude the presence of sulfur-containing VOCs in the desulfurized gas. At this point, the desulfurized gas 7 still contains at least VOCs and CO2 as impurities. To obtain a usable product gas in the form of biomethane, at least the VOCs, and preferably also CO2, are removed from the gas mixture. Depending on the operating sequence, CO2 may be removed before, during, or after the removal of VOCs (dashed arrow). Removal of CO2 is also referred to as "upgrading," as it typically significantly increases the relative methane concentration in the gas mixture. Upgrading can be achieved by membrane separation, amine scrubbing, and / or the use of PTSA, using methods well known to those skilled in the art. The CO2 content is preferably reduced to less than 2%.

[0075] In the preferred embodiment shown, CO2 is removed prior to VOC removal. After CO2 removal, gas 9 is now called methane-rich gas and can generally be utilized as an energy carrier or combustion material. The fact that this gas 9 still contains VOCs is not relevant in the case of combustion, unless energy conversion takes place in a sensitive system, such as a fuel cell. If the feed gas 3 is raw biogas, the methane-rich gas 9 is also called biomethane.

[0076] In the illustrated embodiment, the methane-rich gas 9 is introduced into a reaction space 11, where it is mixed with ozone (O3) from an ozone source 13, to remove VOCs. The reaction space 11 contains a filler 15 that promotes mixing of the gas 9 with the ozone. As soon as the ozone comes into contact with the VOCs in the gas 9, an oxidation reaction occurs, reducing the ozone and oxidizing the VOCs, forming oxygen (O2) in the process. The oxidation reaction typically lasts for less than 10 seconds. During the oxidation of the VOCs, the VOCs are at least partially split into "smaller" VOC components. This also changes the physical and chemical properties of the VOCs. Based on these properties, the VOC components obtained after oxidation can be classified into groups, e.g., water-soluble VOCs (abbreviated as "water-soluble VOCs"). WS VOC) and water-insoluble VOC (abbreviated NWS can be divided into different fractions called VOCs.

[0077] It is important to note that the change in the physical and chemical properties of VOCs can occur due to oxidation itself, i.e., the attachment of oxygen atoms, and not necessarily as a result of their splitting into smaller components. Furthermore, a single VOC molecule can be multiply oxidized. After oxidation, an oxidized gas 14 is obtained.

[0078] The oxidation gas 14 containing the various VOC fractions is cleaned after oxidation by a scrubber, by a cooling scrubber or by a gas condenser with a condensate separator 17, WS VOCs and easily condensable gases are removed to produce scrub gas 16. Scrub gas 16 is then passed to an adsorbent 19 (preferably activated carbon), which NWS The VOCs are adsorbed and the cleaned methane-enriched product gas 21 is passed through. The methane-enriched product gas 21 can then be passed to a gas liquefaction plant 23 where it is liquefied to make it transportable and / or storable. Depending on the composition of the feed gas 3, the nature and / or sequence of the cleaning steps in the gas processing plant 2 can be varied and therefore other impurities can also be removed.

[0079] The dashed arrows starting from the scrub gas 16 and the product gas 21 respectively indicate that the removal of CO2 may take place only at these points and not before the introduction of the desulfurization gas 7 into the reaction space 11.

[0080] In the simplified alternative embodiment shown in FIG. 2, only the main steps of the method of the present invention are illustrated. Similar to the embodiment shown in FIG. 1, a feed gas 3 containing methane and VOCs is supplied from a feed gas source 1 to a gas processing plant 2 and may optionally be pretreated in a pretreatment chamber 5. The feed gas 3 (or, in the case of pretreatment, a desulfurized feed gas 7 or a gas with reduced CO content 9) is passed through a reaction space 25, which has a packing 15 at its front end 10. At the front end 10 of the reaction space 25, ozone (O3) is injected from an ozone source 13 and mixes with gas 3 (or 7 / 9). In the region of the packing 15, the ozone reacts with the VOCs present in gas 3 (7 / 9) and oxidizes them. Meanwhile, the gas-ozone mixture 14 flows from the front end to the rear end 12 of the reaction space 25, in which an adsorbent 19 is located. The VOCs are adsorbed in the adsorbent 19, resulting in a cleaned, methane-enriched product gas 21.

[0081] Similar to FIG. 1, removal of CO2 can occur before entering the reaction space 25 or after leaving the reaction space 25 (dashed arrow).

[0082] The methane-enriched product gas 21 obtained after cleaning may, if desired, be at least partially utilized directly in the plant itself as an energy carrier. For example, the methane-enriched product gas can be introduced into an integrated heat engine or heat engine separate from the gas processing plant, where energy is generated and can be utilized to operate individual components. In particular, compressor units that are typically used in various parts of a gas processing plant for cooling and compressing gases require energy.

[0083] Finally, it should be mentioned that although the ozone source 13 in the illustrated embodiment is represented as an external source, it is nevertheless open to different solutions. For example, the ozone source can be an ozone generator that is retroactively installed in an existing gas treatment plant in the sense of an add-on module. In the case of newly built plants, such an ozone source can also be integrated into the treatment plant from the start.

[0084] The method described above can be applied according to the invention not only to methane-containing biogas, but also to pyrolysis gases, ie gas mixtures obtained from the pyrolysis of organic matter. [Example]

[0085] Testing Data: Ozone and UV light treatments were investigated to remove VOCs and sulfur-containing compounds from biogas. For these studies, each substance listed in Table 1 below was evaporated in an evaporator and mixed with N2 carrier gas. In this way, concentrations of substances corresponding to those normally present in biogas could be achieved. N2 carrier gas was chosen instead of biogas because N2 exhibits similar reaction behavior to ozone. This is supported by data from the NIST Standard Reference Database, which allowed the calculation of the following equilibrium constants: [ka]

[0086] It is therefore clear that compounds such as CO or CH4 react significantly less well with ozone than terpenes such as 3-carene, α-pinene or d-limonene.

[0087] The resulting gas mixture was then treated with ozone and / or UV light. Here, Sample 1 refers to the concentration of the sample substance before treatment, and Sample 2 refers to the concentration of the sample substance after treatment. "nd" means "not detected" if the sample concentration was below the detection limit of the gas chromatograph for that substance.

[0088] [Table 1]

[0089] Additionally, gas chromatography was used to analyze the degradation products of the substances in Table 1 (Table 2). In the "Conversion" column, each entry reports the percentage of the sample oxidized by UV, ozone, or ozone + UV in the treatment, where "nC" represents no conversion, i.e., no oxidation of VOCs, and "nco" represents "not performed."

[0090] [Table 2]

[0091] All experiments have shown that UV light alone does not cause the reaction / decomposition of compounds in the gas stream. In certain cases, such as with ethyl acetate, isopropanol, limonene, and DMDS, UV light may actually activate ozone, resulting in an increased rate of decomposition.

[0092] As is evident from the above data, quantitative conversion of isopropanol, ethyl acetate, hydrogen sulfide, and hexamethylcyclotrisiloxane (D3) can be achieved using ozone. Acetone and limonene react slowly, requiring superstoichiometric amounts of ozone for acceptable conversion. Dimethyl disulfide, free of a second component, was converted slowly (similar to acetone). However, if a co-reactant, such as ethyl acetate, is present in the gas phase, it is almost completely consumed by the reaction.

[0093] Cyclohexene, a model compound for terpenes such as limonene, reacts with ozone at a high rate, but deposits in the reactor suggest polymerization.

[0094] When we look at the composition of VOCs, including sulfur-containing compounds, sulfur-containing compounds mainly react with ozone, and the resulting sulfoxide radicals react partially with VOCs.

[0095] Therefore, one reason why the conversion rate is higher with UV + ozone than with ozone alone is thought to be that the ozone oxidized to O2 reacts again with UV light to produce ozone and is reactivated.

[0096] In further experiments, biogas compositions from three different fermentation plants were treated with and without ozone (250 ppm) in each case, then contacted with a VOC-adsorbing adsorbent, and finally the amount of unadsorbed VOCs in the biogas compositions was measured. The results are shown in Tables 3 to 5 below, where "nd" stands for "not detected" and corresponds to a concentration below the detection limit.

[0097] [Table 3]

[0098] [Table 4]

[0099] [Table 5]

[0100] The reacted ozone refers to the amount of ozone that reacted with VOC. For example, in the case of Composition 1, a gas mixture containing VOC was mixed with 250 ppm of ozone, and 23 ppm of ozone reacted with the VOC.

[0101] The experimental data in Tables 3-5 clearly show that ozone treatment reduces VOC concentrations and alters VOC composition. The resulting oxidized VOCs are more efficiently adsorbed by the adsorbent, resulting in greater removal of VOCs from the gas mixture. Some of the embodiments of the invention related to the present invention are shown below. [Embodiment 1] A method for cleaning a gas mixture, comprising the steps of: (a) providing a gas mixture containing a gas selected from the group consisting of the following i. to iii. and at least one impurity from the group of volatile organic compounds (VOCs), the gas mixture having a VOC concentration of 0.0001 to 0.2% by volume: i. methane-containing biogas obtained by fermentation of organic matter and having a methane concentration of at least 40% by volume (3, 7); ii. Pyrolysis gas obtained by thermal treatment of organic matter and having a carbon monoxide concentration of at least 2% by volume; or iii. combinations thereof; (b) Add ozone (O) to the gas mixture of step a) at a concentration of 0.0001 to 12% by volume based on the gas mixture. 3 ), wherein the ozone oxidizes at least a portion of the VOCs in the gas mixture; (c) contacting the gas mixture from step b) with a VOC adsorptive adsorbent (19) selected from the group consisting of activated carbon, activated coke, silica gel, aluminum oxide, molecular sieves, and mixtures thereof to clean the gas mixture. [Embodiment 2] The at least one impurity is selected from the group of volatile organic compounds (VOCs) and is a linear or branched C 1 ~C 5 2. The method of embodiment 1, wherein the hydroxybenzoate is selected from the group consisting of alcohols, sulfides, and unsaturated terpenes. [Embodiment 3] The at least one impurity is selected from the group of volatile organic compounds (VOCs) and is selected from the group consisting of 1-butanol, 1-pentanol, 2-butanol, 2-methyl-1-butanol, 2-methyl-1-propanol, 2-methyl-2-butanol, 2-methyl-2-propanol, 2-pentanol, 3-methyl-1-butanol, 3-methyl-2-butanol, 3-pentanol, ethanol, 2-propanol, methanol, propanol, 1-pentanethiol, 1-propanethiol, 2-butanethiol, 2-methyl-2-propanethiol, 2-propanethiol, butanethiol, carbonyl sulfide, dimethyl disulfide, dimethyl Sulfide, dimethyl trisulfide, ethyl mercaptan, methyl mercaptan, methyl propyl disulfide, tetrahydrothiophene, thiophene, thiophenol, 1,4-cineole, 3-carene, α-pinene, α-thujene, β-pinene, limonene, eucalyptol, fenchone, limonene, linalool, myrcene, p-cymene, sabinene, α-caryophyllene, α-terpinene, γ-terpinene, 2-methylthiophene, 3-methylthiophene, diisopropyl disulfide, dimethyl tetrasulfide, isobutyl mercaptan, methyl allyl sulfide, methyl isopropyl disulfide, methyl propyl sulfide, 3,The alkyl esters are selected from the group consisting of 3-dimethyl-2-bornanone, nopinone, phellandrene, p-menthan-2-ol, p-menthan-2-one, santhene, terpinolene, thujanone and tricyclene, and preferably 1-butanol, 1-pentanol, 2-butanol, 2-methyl-1-butanol, 2-methyl-1-propanol, 2-methyl-2-butanol, 2-methyl-2-propanol, 2-pentanol, 3-methyl-1-butanol, 3-methyl-2-butanol, 3-pentanol, ethanol, 2-propanol, methanol, propanol, 1-pentanethiol, 1-propanethiol, 2-butanethiol, 2-methyl-2-propanethiol, 2-propanethiol, butanethiol, carbonyl sulfide, dimethyl disulfide, dimethyl methyl 2. The method according to claim 1, wherein the hydroxybenzoate is selected from the group consisting of methyl disulfide, dimethyl trisulfide, ethyl mercaptan, methyl mercaptan, methyl propyl disulfide, tetrahydrothiophene, thiophene, thiophenol, 1,4-cineole, 3-carene, α-pinene, α-thujene, β-pinene, limonene, eucalyptol, fenchone, limonene, linalool, myrcene, p-cymene, sabinene, α-caryophyllene, α-terpinene, and γ-terpinene, more preferably selected from the group consisting of 1,4-cineole, 3-carene, α-pinene, α-thujene, β-pinene, limonene, eucalyptol, fenchone, limonene, linalool, myrcene, p-cymene, sabinene, α-caryophyllene, α-terpinene, and γ-terpinene. [Embodiment 4] 2. The method of claim 1, wherein the at least one impurity from the group of volatile organic compounds (VOCs) has a vapor pressure of at least 0.1 mbar at 20°C or a boiling point of at most 240°C at 1013.25 mbar. [Embodiment 5] The at least one impurity is selected from the group of volatile organic compounds (VOCs) and is selected from the group consisting of propane, n-butane, n-pentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, n-undecane, n-dodecane, n-tridecane, n-tetradecane, n-pentadecane, n-C 16 , nC 17 , nC 18 , nC 19 , nC 20 , nC 21 , nC 22 , isobutane, neopentane, isopentane, 2,2-dimethylbutane, 2,3-dimethylbutane, 2-methylpentane, 3-methylpentane, 2,2,3-trimethylbutane, 2,2-dimethylpentane, 2,3-dimethylpentane, 2,4-dimethylpentane, 2-methylhexane, 3,3-dimethylpentane, 3-methylhexane, 2,2,3,3-tetramethylbutane, 2,2,4-trimethylpentane, 2,2-dimethylhexane, 2,3,4-trimethylpentane, 2,3-dimethylhexane, 2,4-dimethylhexane San, 2,5-dimethylhexane, 2-methylheptane, 3-methylheptane, 4-methylheptane, 2,2,5-trimethylhexane, 2,3,5-trimethylhexane, 2,4-dimethylheptane, 2-methyloctane, 3,3-diethylpentane, 3,5-dimethylheptane, 4-ethylheptane, 4-methyloctane, 2,4-dimethyloctane, 2,6-dimethyloctane, 2-methylnonane, 3,4-diethylhexane, 3-methylnonane, 4-methylnonane, 4-propylheptane, 2,6-dimethylnonane, 3, 5-Diethylheptane, 3-methyldecane, 4-methyldecane, 2,6-diethyloctane, 3,6-dimethyldecane, 3-methylundecane, 5-methylundecane, 3,6-dimethylundecane, 3,7-diethylnonane, 3-methyldodecane, 5-methyldodecane, 3,7-dimethyldodecane, 3,8-diethyldecane, 3-methyltridecane, 6-methyltridecane, 3,7-dimethyltridecane, 3,9-diethylundecane, 3-methyltetradecane, 6-methyltetradecane, 3-methylpentadecane, 4,8-di Methyltetradecane, 7-methylpentadecane, cyclopropane, cyclobutane, cyclopentane, cyclohexane, isopropylcyclopropane, methylcyclopentane, 1,3-dimethylcyclopentane, cycloheptane, ethylcyclopentane, methylcyclohexane, 1,3-dimethylcyclohexane, cyclooctane, ethylcyclohexane, propylcyclopentane, 1,1,3-trimethylcyclohexane, 1-ethyl-4-methylcyclohexane, propylcyclohexane, 1,3-diethylcyclohexane, 1,4-Diethylcyclohexane, 1-methyl-3-isopropylcyclohexane, butylcyclohexane, 1,3-diethyl-5-methylcyclohexane, 1-ethyl-2-propylcyclohexane, pentylcyclohexane, 1,3,5-triethylcyclohexane, 1-methyl-4-pentylcyclohexane, hexylcyclohexane, 1,3-diethyl-5-pentylcyclohexane, 1-methyl-2-hexylcyclohexane, heptylcyclohexane, 1,3-dipropyl-5-ethylcyclohexane, 1-methyl-4-heptylcyclohexane San, octylcyclohexane, 1,3,5-tripropylcyclohexane, 1-methyl-2-octylcyclohexane, nonylcyclohexane, 1,3-propyl-5-butylcyclohexane, 1-methyl-4-nonylcyclohexane, decylcyclohexane, ethene, propene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3,3-dimethyl-1-butene, 3-methyl-1-pentene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene 1-tetradecene, 1-pentadecene, isobutene, 2-methyl-1-butene, 2,3-dimethyl-1-butene, 2-ethyl-1-butene, 2-methyl-1-pentene, 2,3,3-trimethyl-1-butene, 3-methyl-2-isopropyl-1-butene, cis-2-butene, trans-2-butene, 2-pentene, 2-methyl-2-butene, cis-2-pentene, trans-2-pentene, 2,3-dimethyl-2-butene, 2-hexene, 2-methyl-2-pentene, cis-2-hexene, cis-3-hexene, cis-3-methyl trans-2-hexene, trans-2-hexene, trans-3-hexene, trans-3-methyl-2-hexene, trans-4-methyl-2-hexene, 2,3-dimethyl-2-hexene, 2-heptene, cis-3-heptene, trans-2-heptene, trans-3-heptene, trans-4,4-dimethyl-2-pentene, 3-octene, cis-4-octene, trans-2,2-dimethyl-3-hexene, trans-2,5-dimethyl-3-hexene, trans-3-octene, trans-4-octene, 2,4,4-trimethyl-2-pentene, 3-nonene, trans-4-nonene, 3,4-diethyl-2-hexene, cis-5-decene, trans-4-decene, trans-5-undecene, trans-5-dodecene, trans-5-tridecene, trans-5-tetradecene, trans-5-pentecene, cyclopentene, 1-methylcyclopentene, cyclohexene, 1-methylcyclohexene, 4-methylcyclohexene, 1,2-dimethylcyclohexene, 1,3-butadiene, isoprene, C, 6 Cyclic olefin, C 7 Cyclic olefin, C 8 Cyclic olefin, C 9 Cyclic olefin, C 10 Cyclic olefin, C 11 Cyclic olefin, C 12 Cyclic olefin, C 13 Cyclic olefin, C 14 Cyclic olefin, C 15Cyclic olefins, cyclopentadiene, α-pinene, β-pinene, 3-carene, D-limonene, terpenes, α-methylstyrene, C 9 Styrene, C 10 Styrene, benzene, toluene, ethylbenzene, isopropylbenzene, n-propylbenzene, n-butylbenzene, s-butylbenzene, m-xylene, o-xylene, p-xylene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, indan, naphthalene, tetralin, 1-methylnaphthalene, 2-methylnaphthalene, 2,3-dimethylnaphthalene, C 12 Monosubstituted naphthalenes, C 12 Disubstituted naphthalenes, C 13 Monosubstituted naphthalenes, C 13 Disubstituted naphthalenes, C 13 Trisubstituted naphthalene, acetylene, methylacetylene, 2-butyne, ethylacetylene, methanol, ethanol, isopropyl Phenyl alcohol, n-propyl alcohol, isobutyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, cyclopentanol, 2-pentanol, 3-pentanol, pentyl alcohol, cyclohexanol, 1-hexanol, 2-hexanol, 1-heptanol, 1-octanol, 2-octanol, 2-ethyl-1-hexanol, 3-octanol, 4-octanol, 8-methyl-1-nonanol, ethylene glycol, propylene glycol, 1,2-butanediol, glycerol, 2-methyl-2,4-pentanediol, 1,2-Dihydroxyhexane, dimethyl ether, trimethylene oxide, tetrahydrofuran, diethyl ether, dimethoxymethane, α-methyltetrahydrofuran, tetrahydropyran, ethyl isopropyl ether, methyl n-butyl ether, methyl tert-butyl ether, ethyl n-butyl ether, ethyl tert-butyl ether, methyl tert-amyl ether, di-n-propyl ether, 2-butyltetrahydrofuran, di-n-butyl ether, diisobutyl ether, di-n-pentyl ether, 2-methoxyethane Alcohol, 2-methoxy-1-propanol, 2-ethoxyethanol, 1-methoxy-2-propanol, 2-propoxyethanol, 3-ethoxy-1-propanol, 3-methoxy-1-butanol, 1-ethoxy-2-propanol, diethylene glycol, 3-methoxy-3-methylbutanol, 2-butoxyethanol, 1-propoxy-2-propanol, 2-(2-methoxyethoxy)ethanol, n-butoxy-2-propanol, 1-tert-butoxy-2-propanol, 2-tert-butoxy-1-propanol, 2- (2-Ethoxyethoxy)ethanol, dipropylene glycol, dipropylene glycol methyl ether, 2-(2-butoxyethoxy)ethanol, methyl formate, ethyl formate, propyl formate, ethyl acetate, methyl propionate, n-butyl formate, ethyl propionate, isopropyl acetate, methyl butyrate, methyl isobutyrate, n-propyl acetate, n-butyl acetate, ethyl butyrate, isobutyl acetate, methyl pivalate, n-propyl propionate, sec-butyl acetate, tert-butyl acetate, butyl propionate, amyl acetate, n-propyl butyrate, n-butyrate -butyl, isobutyl isobutyrate, n-hexyl acetate, 2-methylpentyl acetate, 3-methylpentyl acetate, 4-methylpentyl acetate, 2,3-dimethylbutyl acetate, n-heptyl acetate, 2-methylhexyl acetate, 3-methylhexyl acetate, 4-methylhexyl acetate, 5-methylhexyl acetate, 3-ethylpentyl acetate, 2,4-dimethylpentyl acetate, isoamyl isobutyrate, n-octyl acetate, 2-ethylhexyl acetate, 3,4-dimethylhexyl acetate, 3,5-dimethylhexyl acetate, 3-ethylhexyl acetate, 4-methylheptyl acetate, 4,5-Dimethylhexyl acetate, 5-methylheptyl acetate, 3-methylheptyl acetate, 2,4-dimethylhexyl acetate, n-nonyl acetate, 2-methyloctyl acetate, 4-methyloctyl acetate, 5-methyloctyl acetate, 3-ethylheptyl acetate, 3,6-dimethylheptyl acetate, 3,5-dimethylheptyl acetate, 4,5-dimethylheptyl acetate, 4,6-dimethylheptyl acetate, 2,4-dimethylheptyl acetate, 2,3-dimethylheptyl acetate, 2,5-dimethylheptyl acetate, 2,3,5-trimethylhexyl acetate 3,6-dimethyloctyl acetate, 4,6-dimethyloctyl acetate, 3-isopropylheptyl acetate, 4,7-dimethylnonyl acetate, 3,5,7-trimethyloctyl acetate, 3-ethyl-6-methyloctyl acetate, 3,6,8-trimethylnonyl acetate, 3,5,7-trimethylnonyl acetate, 2,3,5,7-tetramethyloctyl acetate, 2,4,6,8-tetramethylnonyl acetate, 4,7,9-trimethyldecyl acetate, 3-ethyl-6,7-dimethylnonyl acetate, 5-ethyl-3,6,8-trimethylnonyl acetate Nonyl, 2,3,5,6,8-pentamethylnonyl acetate, dimethyl carbonate, propylene carbonate, methyl lactate, ethyl lactate, 2-methoxyethyl acetate, methyl isopropyl carbonate, 2-methoxy-1-propyl acetate, 2-ethoxyethyl acetate, 1-methoxy-2-propyl acetate, dimethyl succinate, ethylene glycol diacetate, ethyl 3-ethoxypropionate, diisopropyl carbonate, dimethyl glutarate, 2-butoxyethyl acetate, dimethyl adipate, 3-hydroxy-2,2,4-trimethylpentyl 1-Hydroxy-2,2,4-trimethylpentyl 3-isobutyrate, ethylene oxide, propylene oxide, 1,2-epoxybutane, formic acid, acetic acid, acrylic acid, propionic acid, methyl acrylate, vinyl acetate, 2-methyl-2-buten-3-ol, ethyl acrylate, methyl methacrylate, butyl methacrylate, isobutyl methacrylate, furan, formaldehyde, acetaldehyde, propionaldehyde, butanal, 2-methylpropanal, pentanal, 2,2-Dimethylpropanal, 3-methylbutanal, glutaraldehyde, hexanal, heptanal, octanal, glyoxal, methylglyoxal, acrolein, crotonaldehyde, methacrolein, hydroxymethacrolein, cyclobutanone, methyl ethyl ketone, cyclopentanone, 3-pentanone, 2-pentanone, cyclohexanone, 4-methyl-2-pentanone, methyl n-butyl ketone, methyl tert-butyl ketone, 2-methyl-3-hexanone, 2-heptanone, diisopropyl ketone, 2-octanone, 2-nonanone, diisobutyl ketone, 2-decanone, biacetyl, methyl vinyl ketone, hydroxyacetone, methoxyacetone 2. The method of claim 1, wherein the alkyl group is selected from the group consisting of acetone, diacetone alcohol, phenol, alkylphenol, m-cresol, o-cresol, p-cresol, nitrobenzene, p-toluene isocyanate, methylene diphenylene diisocyanate, dimethylamine, ethylamine, trimethylamine, ethanolamine, dimethylaminoethanol, diethanolamine, triethanolamine, n-methyl-2-pyrrolidone, oxohexyl acetate, oxoheptyl acetate, oxooctyl acetate, oxononyl acetate, oxodecyl acetate, oxododecyl acetate, oxotridecyl acetate, dimethyl sulfide, and hexamethylcyclotrisiloxane. [Embodiment 6] 3. The method of claim 1 or 2, wherein the gas mixture of step a) has a VOC concentration of 0.001 to 0.1% by volume. [Embodiment 7] 7. The method according to any one of the preceding embodiments, wherein the biogas (3, 7) originates from a fermenter and preferably has a methane concentration of at least 50% by volume, more preferably at least 60% by volume. [Embodiment 8] 8. The method according to any one of the preceding embodiments, wherein the biogas (3, 7) is present at a temperature between 10°C and 30°C, preferably at room temperature, and at a pressure between 50 and 200 mbar, preferably about 100 mbar. [Embodiment 9] 7. The method according to any one of the preceding claims, wherein the pyrolysis gas further comprises at least one component from the group consisting of hydrogen, carbon dioxide, methane, ethane, propane, ethene, higher hydrocarbons, acetylene, ammonia, and propylene. [Embodiment 10] Before or after the adsorption of the VOC, CO 2 10. The method of any one of the preceding embodiments, wherein the is removed from the gas mixture. [Embodiment 11] 11. The method according to any one of the preceding claims, characterized in that the gas mixture before contact of the VOCs with the adsorbent (19) is subjected to a post-treatment step (17), preferably using a scrubber, a cooling scrubber, or a gas condenser equipped with a condensate separator. [Embodiment 12] 12. The method according to any one of the preceding claims, wherein the adsorbent (19) is selected from the group consisting of activated carbon, activated coke, molecular sieves, and mixtures thereof, more preferably the adsorbent (19) consists of at least 90% activated carbon. [Embodiment 13] 13. The method according to any one of the preceding claims, wherein the ozone is mixed into the gas mixture as an ozone-oxygen mixture. [Embodiment 14] 14. The method according to any one of embodiments 1 to 13, wherein the final concentration of ozone in the gas mixture (3, 7, 9) is between 0.0001% and 3% by volume, preferably between 0.0001% and 0.5% by volume, more particularly between 0.0001 and 0.1% by volume, and more preferably between 0.0002 and 0.05% by volume. [Embodiment 15] 15. The method according to any one of the preceding claims, characterized in that the ozone is generated in situ in an ozone generator (13) from air or from oxygen, preferably from concentrated atmospheric oxygen in an ozone generator (13).

Claims

1. A method for cleaning a gas mixture, comprising the steps of: (a) providing a gas mixture containing a gas selected from the group consisting of i. to iii. below and at least one impurity from the group of volatile organic compounds (VOCs) selected from the group consisting of linear or branched C1 to C5 alcohols, sulfides, and unsaturated terpenes, the gas mixture having a VOC concentration of 0.0001 to 0.2% by volume: i. methane-containing biogas obtained by fermentation of organic matter and having a methane concentration of at least 40% by volume (3, 7); ii. Pyrolysis gas obtained by thermal treatment of organic matter and having a carbon monoxide concentration of at least 2% by volume; or iii. combinations thereof; (b) adding ozone (O ) to the gas mixture of step a) at a concentration of 0.0001 to 12% by volume based on the gas mixture; ３ ), wherein the ozone oxidizes at least a portion of the VOCs in the gas mixture; (c) contacting the gas mixture from step b) with a VOC adsorbent (19) selected from the group consisting of activated carbon, activated coke, silica gel, aluminum oxide, molecular sieves, and mixtures thereof to clean the gas mixture.

2. 2. The method according to claim 1, characterized in that the at least one impurity from the group of volatile organic compounds (VOC) has a vapor pressure of at least 0.1 mbar at 20°C or a boiling point of at most 240°C at 1013.25 mbar.

3. 2. The method of claim 1, wherein the gas mixture of step a) has a VOC concentration of 0.001 to 0.1% by volume.

4. 4. The method according to any one of claims 1 to 3, characterized in that the biogas (3, 7) originates from a fermenter.

5. 5. The method according to any one of claims 1 to 4, characterized in that the biogas (3, 7) is present at a temperature between 10°C and 30°C and at a pressure between 50 and 200 mbar.

6. 3. The method according to claim 1, wherein the pyrolysis gas further comprises at least one component selected from the group consisting of hydrogen, carbon dioxide, methane, ethane, propane, ethene, higher hydrocarbons, acetylene, ammonia, and propylene.

7. Before or after the adsorption of the VOCs, further ２ 7. The method according to claim 1, wherein the gas mixture is removed from the mixture.

8. 8. The method according to any one of claims 1 to 7, characterized in that the gas mixture before contact of the VOCs with the adsorbent (19) is subjected to a post-treatment step (17).

9. A method according to any one of claims 1 to 8, characterized in that the adsorbent (19) is selected from the group consisting of activated carbon, activated coke, molecular sieves and mixtures thereof.

10. A method according to any one of claims 1 to 9, characterized in that the ozone is mixed into the gas mixture as an ozone-oxygen mixture.

11. 11. The method according to any one of claims 1 to 10, characterized in that the final concentration of ozone in the gas mixture (3, 7, 9) is between 0.0001% and 3% by volume.

12. Method according to any one of the preceding claims, characterized in that the ozone is generated in situ from air in an ozone generator (13) or from oxygen in an ozone generator (13).

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