EP4225471A1

EP4225471A1 - Method for cleaning a gas mixture by adding ozone

Info

Publication number: EP4225471A1
Application number: EP21790214.7A
Authority: EP
Inventors: Uwe Jordan; Gamuret HACK; Lukas VÖLLMY
Original assignee: Hitachi Zosen Innova AG
Current assignee: Hitachi Zosen Innova AG
Priority date: 2020-10-12
Filing date: 2021-10-12
Publication date: 2023-08-16
Also published as: JP2023545148A; AU2021359761A1; WO2022079004A1; EP3981498A1

Abstract

The invention describes methods for cleaning a gas mixture. In a first step a) a gas mixture is provided, the gas mixture comprising a gas selected from the group consisting of a methane-containing biogas (3, 7) which is obtained by fermentation of organic material and which has a methane concentration of at least 40 vol.% and a pyrolysis gas which is obtained by thermal treatment of organic material and which has a carbon monoxide concentration of at least 2 vol.% or a combination thereof. The gas mixture also comprises an impurity from the group of volatile organic compounds (VOC), the gas mixture having a VOC concentration of 0.0001 to 0.2 vol.%. In a second step b), 0.0001 to 12 vol.% ozone is added to the gas mixture, which ozone oxidizes at least part of the VOC in the gas mixture. In a third step d), the gas mixture from the second step is brought into contact with a VOC-adsorbing adsorber selected from the group consisting of activated carbon, activated coke, silica gel, aluminum oxide, molecular sieve and mixtures thereof, in order to clean the gas mixture.

Description

Process for cleaning a gas mixture by adding ozone

The present invention generally relates to a

Process for cleaning a gas mixture obtained by pyrolysis or fermentation of organic material, in particular by removing harmful components such as volatile organic compounds (VOC), by oxidation with ozone and by adsorption on an adsorber.

The cleaning of gas mixtures by using suitable

Adsorbers is used both in the cleaning of industrial exhaust gases and in building services, for example in

extractor hoods, known . By attachment to the inner

Air pollutants, especially hydrocarbons, are removed from the exhaust gas to be cleaned on the surface of porous adsorber materials. A distinction can be made between fixed bed, moving bed, rotor, fluidized bed and entrained flow adsorbers. In multi-level

Exhaust gas cleaning systems are often used as final adsorbers

Cleaning stage, used as a so-called police filter.

An important area of application for gas cleaning is

Purification of methane-containing gas mixtures ("biogas"), which usually include a large number of other gaseous compounds in addition to the usable methane. Biogas containing methane can come from fermenters or landfills, for example, or it can be of non-fermentative origin, for example in the form of

Natural gas, mine gas or CBM. To such methane-containing

Gas mixtures hereinafter referred to as biogas for the

To make energy production usable, the

Methane concentration in the gas mixture by removal as possible of all other compounds (so-called impurities) are increased.

Another important area of application for gas purification is the purification of gas mixtures obtained by pyrolysis, which usually contain a significant proportion of carbon monoxide.

Commonly contained in biogas or pyrolysis gas

Components or impurities are, for example,

Hydrogen sulfide (H ₂ S), ammonia (NH ₃ ) and volatile organic compounds (VOC for short), such as e.g. sulfuric hydrocarbons (S-

KW) . Nowadays, contaminants can be identified using a variety of biological, chemical and physical sources

processes can be separated, which is generally referred to as " (bio-

) Gas processing". Connections with high

Boiling point can be separated about by adsorption, for example on an activated carbon filter, while

For example, compounds with a low boiling point

Condensation and water-soluble compounds using a

washer can be removed.

EP 1979446 B1 discloses a method for obtaining

Methane from a landfill gas and gas from another anaerobic

fermenters. The procedure includes the following

Steps : H ₂ S removal, compression, then

Removal of VOC and water and finally removal of other contaminants.

Depending on the number and type of impurities, the individual steps of biogas processing are more or less complex. In addition to the separation of condensates such as e.g. B. Ammonia stand in particular the removal of

Sulfur compounds and so-called VOC in the foreground.

A desulfurization d . H . the removal of H ₂ S and S-KW from biogas or pyrolysis gas is in terms of industrial use, z. B. as fuel gas, often unavoidable, since sulfur compounds react to sulfuric acid and e.g. B.

can cause corrosion on the lines.

Corrosion-sensitive systems such as fuel cells are therefore significantly higher compared to engines and turbines

Requirements for sulfur content in fuel gas. Depending on

area of application, the sulfur content in the fuel gas must be reduced to a few ppmv (parts per million by volume) or even all trace components must be reduced to 100 ppbv

(parts per billion by volume) are separated from the gas stream. As part of the desulfurization is usually first H ₂ S removed and in a second step takes place

Separation of sulfuric hydrocarbons (S-KW) . The H ₂ S

Removal usually takes place by means of adsorption on specially doped activated carbon, although the use of biological or chemical processes is also possible. Another activated carbon filter can be used for the purpose of the so-called

Fine desulfurization are downstream. A normal activated carbon filter is usually used for the subsequent separation of S-KW.

In addition to the removal of sulfur components is also the

Removal of VOC an important part of

Gas treatment of gas mixtures from pyrolysis or

fermentation of organic matter. VOC is one

Collective term for organic, i.e. carbonaceous

Substances - those at room temperature or higher temperatures through Evaporate (colloquially "evaporate") into the gas phase, i.e. are volatile. Examples of VOCs are terpenes, ketones, amines, aldehydes, sulphurous hydrocarbons and others. Methane (CH ₄ ) is not a component of the VOC. The precise definition of VOC is varies depending on the country and region: The WHO defines VOC as "all organic compounds with boiling points in the range of 50 to 260°C, with the exception of pesticides”. In Switzerland, according to the Ordinance on the Incentive Tax on Volatile Organic Compounds (VOCV) from November 12, 1997 as VOC "organic compounds with a vapor pressure of at least 0.1 mbar at 20°C or with a boiling point of not more than 240°C at 1013.25 mbar". Europe, on the other hand, defines VOC according to Directive 1999/13/ EG, Directive 2001/81/EG, Directive 2004/42/EG and Directive 2008/50/EG DIN EN ISO 16000-6 defines VOC as "all substances between and including n-hexane and n-hexadecane in the gas chromatogram appear. Substances appearing earlier in the gas chromatogram are considered WOC (very volatile organic compounds) and substances appearing later are considered SVOC (semi-volatile organic compounds)".

Reducing VOC emissions from industry and commerce is important for two reasons. On the one hand from health aspects, because VOCs in the ambient air can develop certain symptoms in people such as headaches, hypersensitivity reactions, tiredness, reduced performance, sleep disorders and irritation of the respiratory tract, which are also summarized under the term "sick building syndrome". On the other hand, VOCs in industrially used gas mixtures can lead to failures, damage and reduced efficiency in processing or feed-in systems lead, which quickly have a financial impact. For example, terpenes condense on membrane equipment and reduce capacity, while ketones damage seals, reducing service intervals and requiring membrane replacement sooner and more frequently. For this reason, special processes have been developed both in the field of exhaust air purification and in biogas treatment in order to separate VOC from gas mixtures.

A method is known from DE 10158970 A1, for example, with which oxidizable substances or VOC components can be removed from an air flow, in particular from aircraft cabin air. A special layer structure is used for air flow cleaning, in which an adsorber, electrodes and a barrier layer in between are designed as a structural unit. With said layer structure, two spaced electrodes and a barrier lying between them form a plasma source with a dielectric barrier discharge.

In the field of exhaust air purification, attempts were also made to achieve improved VOC removal by using UV light to generate free radicals and/or by using special catalytically active adsorber materials doped with metallic nanoparticles.

Various methods are known in the prior art in which the addition of ozone and an adsorber substance are used to clean VOC-containing gas mixtures.

EP 3332862 A1 discloses a method for carrying out an oxidative decomposition treatment of a gas comprising VOC. The treated gas is in particular an exhaust gas that contains no methane. The gas becomes

Treatment mixed with ozone, which oxidizes the VOC, and then the gas with the oxidized VOC and the residual ozone are brought into contact with a packing material. That

Packing material adsorbs the oxidized VOC and the rest

Ozone. As a base material, it contains an adsorbent with high

Silica content and includes ffeerrnneerr a powder

Transition metal oxide with a BET specific surface area of

80 m ² /g or more that is a complex oxide of Co, Mn and Cu. A disadvantage of the method disclosed in EP 3332862 A1 is that the complex packaging material is expensive to use

Transition metal oxide must be coated. Such a

Adsorber is relatively expensive and the process is therefore not economical to operate.

The Chinese patent no. 101391177 discloses a

Gas purification process for the treatment of organic

Low concentration compounds, in particular a

Gas purification process targeting malodorous compounds. The process includes a catalyst

Adsorption unit and an ozone generation unit, the

Catalyst adsorption unit supplies ozone. be there

Compounds such as dimethyl sulfide (DMS), dimethyl disulfide

(DMDS) , hydrogen sulfide (H ₂ S ) , formaldehyde, acetic acid,

Isopropyl alcohol or acetone oxidizes. Oxidation with ozone enhances the adsorption capacity of the catalyst, prolongs its life and improves accordingly

efficiency of the procedure. However, that is also required

Process from CN 101391177 B compared to a conventional adsorber relatively expensive catalyst, whereby the

The economics of the process is reduced. As with According to the method from EP 3332862 A1, the gas from CN 101391177 is in particular an exhaust air gas which contains no methane.

JP H11342313 A discloses the addition and mixing of ozone to a pollutant-containing gas, followed by passage through an adsorption layer filled with a high-silica adsorbent. In the process, both the ozone and the pollutants contained in the gas are adsorbed.

DE 102014212914 A1 discloses the use of a bottom product as well as fly ash from the gasification of biomass for the adsorption of VOC for the treatment of gaseous or liquid compositions which occur during the pretreatment of the biomass. The fly ash and the bottom product are hydrophobic and compared to other adsorbers such as e.g. B. Silica gel, particularly well suited for the adsorption of VOCs in a wet gaseous composition, e.g. B. exhaust air or even in the water. The disadvantage of the method disclosed in DE 102014212914 A1 is that fly ash and the bottom product can only adsorb a very limited amount of VOC.

DE 102008058114 A1 discloses a method for cleaning biogas which comprises at least hydrogen sulphide and ammonia and optionally carbon dioxide as an impurity. These impurities are separated from the biogas in a single cleaning and/or separation stage. For this purpose, a defined amount of hydrogen peroxide and at least one alkali metal hydroxide is added to the biogas alkaline solution added. The method disclosed in DE 102008058114 A1 has the disadvantage that the residues of unreacted hydrogen peroxide, water and the biogas from the correspondingly treated

Alkaline solution containing alkali metal hydroxide must be removed in a complex manner and the chemicals used are relatively expensive.

EP 1997549 A1 discloses a method for catalytic

Purification of biogenic or anthropogenic methaniferous

gases. The gases are heated to temperatures in the range of

200 ° C to 450 ° C heated, the heated gases subjected to a combined catalytic oxidation and hydrolysis in which all minor components contained in the gas

Carbon dioxide, water and acidic reaction products are degraded and then separated the acidic reaction products. The method from EP 1997549 A1 has the

The disadvantage is that an uneconomically high amount of energy is used to heat the gas in order to clean it.

EP 0947233 A1 discloses a method for treating a gas contaminated with pollutants. We take the gas with us

Ozone mixed and then passed through an adsorption unit. The adsorption unit includes a first

Adsorption layer, which is located on the upstream side and has a mesoporous silicate, and a second

Adsorption layer located on the downstream side and an aluminized faujasite. In the

Adsorption unit both ozone and the pollutants are absorbed, with the pollutants within the Adsorption layer are rendered harmless by the action of ozone. However, the adsorption unit is relatively expensive and therefore not economical to operate.

WO 2012/006729 A1 discloses a method for cleaning biogas, in which a hydrogen gas is added to remove VOC from the biogas. The hydrogen is then burned catalytically by means of a deoxidation catalyst bed with the oxygen contained in the biogas, so that the oxygen contained is essentially completely removed from the biogas and the biogas stream is heated. In a further step, the VOC are removed from the biogas together with water via a pre-cooler. The method of WO 2012/006729 A1 has the disadvantage that a relatively large amount of energy has to be used for the production of hydrogen and for the cooling of the gas to clean the biogas.

A general problem with VOC adsorbers is their limited adsorption capacity or loading level. In the case of "heavier" VOCs in particular, they tend to adhere to the outermost or adsorber surface that is easily accessible from the outside and thus make it difficult for further VOCs to penetrate into the pores or their adsorption on the surface within the pores of the adsorber: This means that the theoretical adsorption capacity, depending on the composition of the VOC, cannot be nearly exhausted and is only 10 - 30%.

It is therefore the object of the invention to eliminate the disadvantages of the prior art and to provide a cost-effective one Provide a method for the efficient separation of VOC from a gas mixture obtained by fermentation.

The object is achieved according to the invention with a method according to claim 1 . Preferred embodiments of the invention are given in the dependent claims.

In the inventive method, in a first step a), a gas mixture containing a methane-containing biogas obtained by fermentation of organic material with a methane concentration of at least 40 vol. -%, a pyrolysis gas obtained by thermal treatment of organic material with a carbon monoxide concentration of at least 2 vol. -% or a combination thereof provided. Furthermore, the gas mixture comprises at least one impurity from the group of volatile organic compounds (VOC), the gas mixture having a VOC concentration of 0. 0001 - 0 . 2 vol. -% having . In a second step b), the gas mixture is 0. 0001 - 12vol. -% ozone added based on the gas mixture, the ozone oxidizing at least part of the VOC in the gas mixture. In a third step c), the gas mixture from the second step for cleaning the gas mixture is brought into contact with a VOC-adsorbing adsorber selected from the group consisting of activated carbon, activated coke, silica gel, molecular sieves and mixtures thereof.

The method of the present invention is particularly suitable for cleaning methane-containing gas produced by fermentation—for example in biogas plants—which is referred to below as “methane-containing biogas” or “biogas”. In the case of such biogas, the gas mixture according to the invention Methane content of at least 40%, and preferably at least 50% (percentages in the gas mixture refer - as mentioned above - always to volume percentages). In a preferred embodiment, the biogas comes from a fermenter.

In the context of the invention, pyrolysis gas (also called synthesis gas) is defined as a gas which is produced during the thermal treatment of organic material. At high temperatures (usually 250 - 500°C) the bonds within the molecules are broken and combustion is prevented by the exclusion of oxygen. The carbon monoxide (CO)-comprising pyrolysis gas produced in this way is later preferably used in steam reforming to produce hydrogen.

Within the meaning of the invention, an adsorber is defined as a substance which can bind (adsorb) VOC from the gas mixture. "Adsorption" is understood to mean a process in which substances (usually molecules) adhere to the surface of another substance and accumulate on its surface. For the purposes of the present invention, this adhesion to the adsorber surface can be due to chemical bonding (chemisorption) as well as due to physical forces of attraction (physisorption). Activated charcoal, activated coke, silica gel or molecular sieves (zeolites) can in particular serve as adsorbers.

Surprisingly, it was found that the adsorption capacity of the adsorber can be significantly increased by adding ozone to the gas mixture. Specifically, it was found that pretreatment with ozone allows more efficient loading of the adsorber with VOC and overall removal of VOC relieved from the gas mixture. It is assumed that this effect is due to the fact that the VOC are partially oxidized by the addition of ozone before they hit the adsorber.

VOC + O ₃ → VOC ( ox ) + O ₂

The method according to the invention has the advantage over the prior art that the adsorption of the VOC on the adsorber takes place more efficiently as a result of the pretreatment of the VOC contained in the gas mixture with ozone. This in turn means that the adsorber does not have to be refurbished or replaced as often, making the process more efficient and cost-effective.

Oxygen and ozone are well known to be flammable and explosive. Contrary to expectations, however, it was found that adding ozone to gases containing methane or carbon monoxide is also easy to handle. It is assumed that this is at least partly due to the fact that ozone reacts preferentially with the VOC contained in the gas mixture and is therefore converted very quickly.

For the purpose of the present invention, an adsorber is ideally used which adsorbs VOC while other gas components, in particular methane, can pass through the adsorber without being adsorbed—or at least only slightly so. By definition, the relative concentration of methane in the gas mixture after passing through the adsorber is higher than before hitting the adsorber.

Those skilled in the art know that an adsorber can only adsorb a certain amount of VOC before it is saturated. As soon the adsorption capacity of the adsorber has decreased to a predefined threshold, the adsorber must be regenerated, refurbished or replaced in order to restore its original adsorption capacity. Several methods are known for dissolving or desorption of the substances bound to the adsorber - here predominantly VOC. For example, a so-called regeneration gas is passed through the adsorber, which releases the bound substances from the adsorber surface and takes them with it.

In a preferred embodiment, the gas mixture from step a) has a VOC concentration of 0.001-0.01% by volume. The person skilled in the art is aware that the method according to the invention would function without problems even at higher VOC concentrations, and in particular also at VOC concentrations above 0.2% by volume, but it could no longer be operated economically.

Preferably, the at least one impurity is selected from the group of volatile organic compounds (VOC), selected from the group consisting of linear or branched C ₁ -C ₅ alcohols, sulfides and unsaturated terpenes. The molecules of these groups of substances can be oxidized particularly well using ozone, which facilitates their adsorption on the adsorber.

In another preferred embodiment of the process, the at least one impurity selected from the group of volatile organic compounds (VOC) 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, Carbonylsulfide, dimethyldisulfide, dimethylsulfide, dimethyltrisulfide, ethylmercaptan, methylmercaptan, methylpropyldisulfide, tetrahydrothiophene, thiophene, thiophenol, 1,4-cineol, 3- Carene, α-pinene, α-thujene, ß-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, 3,3-dimethyl-2- bornanone, nopinone, phellandrene, p-menthan-2-ol, p-menthan-2- one, Santen, terpinoia, thujanone and tricyclics; and particularly preferably 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, methylpropyl disulfide, tetrahydrothiophene, thiophene, thiophenol, 1,4-cineole, 3- carene, α-pinene, α- Thujen, ß-pinene, limonene, eucalyptol, fenchone, limonene, linalool, myrcene, p-cymene, sabinene, α-caryophyllene, α-terpinene and γ ^_ terpinene. The adsorption capacity of the adsorber could be increased by the oxidation of these molecules by means of ozone. The at least one impurity from the group of volatile organic compounds (VOC) is very particularly preferably selected from the group consisting of 1,4-cineole, 3-carene, α-pinene, α-thujene, ß-pinene, limonene, eucalyptol, Fenchone, limonene, linalool, myrcene, p-cymene, sabinene, α-caryophyllene, α-terpinene and γ ^_ terpinene. By oxidizing molecules from the terpene group, the adsorption capacity of the adsorber could be greatly increased.

According to the preferred definition, a compound belongs to 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.

In the process according to the invention, the VOC are preferably oxidized by means of ozone but without the involvement of a catalyst, in particular without the involvement of a catalyst containing a material selected from the group consisting of manganese, iron, cobalt, nickel, copper, silver, lead, zinc, vanadium, titanium, Chromium, aluminum, silicon, acid-activated bentonites and mixtures thereof. By doing without a catalytic converter, it is avoided that it has to be conditioned periodically, which leads to maintenance costs.

In an alternative embodiment, in the process according to the invention, the VOC are oxidized by means of ozone and exposure to UV light. Irradiation with UV light causes the ozone, which has been reduced to elementary oxygen (O ₂ ), to react again to form ozone, in that the UV radiation splits the elementary oxygen (O ₂ ) into oxygen radicals (O*), which then react with elemental oxygen Oxygen (O ₂ ) react to ozone. The reactions described in the previous paragraph can be represented using the following reaction equations:

VOC + O ₃ → VOC ( ox ) + O ₂ O ₂ + UV → 2 O*

2O* + _2O2 → _2O3

In a preferred embodiment, the at least one impurity from the group of volatile organic compounds VOC 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, nC ₁₆ , nC ₁₇ , nC ₁₈ , nC ₁₉ , nC ₂₀ , n- C 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, 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-dimethyltetradecane, 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-diethyl cyclohexane, 1,4-diethylcyclohexane, l-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, l-methyl-4-heptylcyclohexane, octylcyclohexane, 1, 3, 5-tripropylcyclohexane, l-methyl-2-octylcyclohexane, nonylcyclohexane, 1, 3-propyl-5-butylcyclohexane, l-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-dimethyl3-hexene, trans-2, 5-dimethyl3-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-pentadecene, 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 ₁₅ cyclic olefin, cyclopentadiene , α-pinene, ß-pinene, 3-carene, D-limonene, terpene, α-methyl-styrene, 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, inda n, naphthalene, tetralin, 1 - methylnaphthalene, 2-methylnaphthalene, 2 ,3-dimethylnaphthalene, C ₁₂ monosubstituted naphthalene, C ₁₂ disubstituted naphthalene, C ₁₃ monosubstituted naphthalene, C ₁₃ disubstituted naphthalene, C ₁₃ trisubstituted naphthalene, acetylene, methylacetylene, 2 -Butyne, ethylacetylene, methanol, ethanol, isopropyl alcohol, n-propyl alcohol, isobutyl alcohol, n-butyl alcohol, s-butyl alcohol, t-butyl alcohol, cyclopentanol, 2-pentanol, 3-pentanol, pentyl alcohol, cyclohexanol, 1-hexanol, 2-hexanol , 1-heptanol , 1-octanol , 2-octanol , 2-ethyl-l-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 t-butyl ether, Ethyl n-butyl ether, Ethyl t-butyl ether,

methyl t-amyl ether, di-n-propyl ether, 2-butyltetrahydrofuran,

Di-n-butyl ether, di-isobutyl ether, di-n-pentyl ether, 2-methoxyethanol, 2-methoxy-l-propanol, 2-ethoxyethanol, 1-methoxy-2-propanol, 2-propoxyethanol, 3-ethoxy-l -propanol , 3-Methoxy-l-butanol , 1-Ethoxy-2-propanol , Diethylene glycol , 3-Methoxy-3 methyl-butanol , 2-Butoxyethanol , l-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 ester, ethyl butyrate, isobutyl acetate, methyl pivalate, n-propyl propionate, s-butyl acetate, t-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 , isoamyl isobutyrate , n-octyl acetate , 2-ethylhexyl acetate , 3 , 4-dimethylhexyl acetate , 3 ,5-dimethylhexyl acetate , 3-ethylhexyl acetate , 4-methylheptylace tat , 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, 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, l-methoxy-2-propyl acetate, dimethyl succinate, ethylene glycol diacetate, ethyl 3-ethoxypropionate, diisopropyl carbonate, dimethyl glutarate, 2-butoxyethyl acetate, dimethyla dipat, 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, 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 t-butyl ketone, 2-methyl-3-hexanone, 2- Heptanone, diisopropyl ketone, 2-octanone, 2-nonanone, diisobutyl ketone, 2-decanone, biacetyl, methyl vinyl ketone, hydroxyacetone, methoxyacetone, diacetone alcohol, phenol, alkylphenol, m-cresol, o-cresol, p-cresol, nitrobenzene, para-toluene isocyanate , methylenediphenylenediisocyanate, dimethylamine, ethylamine, trimethylamine, ethanolamine, dimethylaminoethanol, diethanolamine, triethanolamine, n-methyl-2-pyrrolidone, oxo-hexyl acetate, oxo-heptyl acetate, oxo-octyl acetate, oxo-nonyl acetate, oxo-decyl acetate, oxo-dodecyl acetate, oxo -Tridecyl acetate, dimethyl sulfide and hexamethylcyclotrisiloxane.

Preference is given to the gas mixture in the second step b) ozone in a concentration of 0.0001 - 3% by volume, preferably 0.0001 - 0.5% by volume, in particular 0.0001 - 0.1% by volume and particularly preferably 0.0002 - 0.05% by volume. in relation to the gas mixture according to step a) - added. This means that the gas mixture after the ozone addition preferably has an ozone concentration of 0.0001-3% by volume ozone - or to put it another way: in step b) preferably 0.0001-3% by volume ozone with 97-99.9999% by volume gas mixture mixed. It is clear to the person skilled in the art that the ozone starts to react immediately when it is added. Therefore, the maximum concentration of ozone in the gas mixture will only theoretically exist. The upper limit of 12 vol .-% is defined by the maximum tolerable oxygen concentration (O ₂ ) in the cleaned gas in step c). When mixed with biogas, this should not exceed a value of 12% by volume so that no explosive gas mixture is formed. For simplicity, assume that one molecule of ozone (O ₃ ) with one molecule of VOC converts to one molecule of oxygen (O ₂ ) and one molecule of oxidized VOC reacted. It is clear to the person skilled in the art that a molecule of VOC can also be oxidized several times, ie it can react with several molecules of ozone. The minimum concentration of 0.0001% by volume ozone is defined by the minimum concentration of 0.0001% by volume VOC, or that a VOC concentration above the tolerance limit of greater than or equal to 0.0001% by volume should be oxidized.

The process would also work with a few molecules of ozone, or even just a single molecule. However, the economic benefit of the improved purification would then no longer be in proportion to the operating costs. Oxygen (O ₂ ) can also be added to the gas mixture, from which ozone (O ₃ ) is only formed in the reaction space, for example by means of UV light.

The methane-containing biogas can in particular be gas from biogas plants, but also natural gas or landfill gas. It preferably contains a methane concentration of at least 50% by volume and particularly preferably at least 60% by volume.

In the case of a methane-containing biogas, this is preferably present at a temperature of 10° C. to 30° C., preferably at room temperature, at a pressure of 50-200 mbar, preferably approximately 100 mbar.

After cleaning, the gas mixture can preferably be used to operate combustion systems such as heaters, gas engines in vehicles or gas turbines, or in the case of upgraded methane-containing biogas can be fed into a gas network as biomethane. If the process according to the invention is used for cleaning pyrolysis gas, the latter preferably contains at least 5% by volume of carbon monoxide.

The pyrolysis gas can also contain at least one component from the group consisting of hydrogen, carbon dioxide, methane, ethane, propane, ethene, higher hydrocarbons, acetylene, ammonia and propylene.

In the case of pyrolysis gas, the process has been shown to be particularly efficient at a preferred temperature of 5°C to 60°C. A temperature of approx. 40° C. is specifically preferred here

In a preferred embodiment, hydrogen sulfide is removed from the gas mixture before ozone is admixed. Removal of hydrogen sulfide is preferred once it is present in the gas mixture in appreciable concentration because, as discussed above, hydrogen sulfide can react to form sulfuric acid in gas treatment plants and cause corrosion of the piping. The hydrogen sulfide concentration is preferably reduced to below 5 ppm before the ozone is added. It is also preferred that the hydrogen sulfides are removed before any liquefaction of the product gas, since hydrogen sulfide is undesirable in a liquefaction plant, depending on the type of plant.

CO ₂ is preferably additionally separated off from the gas mixture before or after the adsorption of the VOC. In particular, in the purification of methane-containing gas mixtures according to the invention, not only pollutants are preferably removed from the gas mixture, but with regard to the use of the cleaned product gas as a combustible energy carrier, the proportion of methane as a combustible component in the cleaned gas mixture (product gas) is preferably increased as much as possible. Biogas normally contains a variable amount of CO ₂ . Since CO ₂ is non-flammable, it is preferably removed from the gas mixture in order to reduce its energy density, e.g. B. for feeding into the natural gas network. Within the meaning of the invention, a desulfurized biogas is also referred to as biomethane after the CO ₂ has been separated off. However, such biomethane can still contain VOC, which can then be separated using the method according to the invention. As with the hydrogen sulfides, it is also preferred for CO ₂ to be removed prior to any liquefaction. Removal after liquefaction is more cumbersome as the CO ₂ freezes out before the product gas and as a result may damage or block the refrigeration unit.

In a preferred embodiment, after the addition of ozone and before the VOC is brought into contact with the adsorber, the gas mixture is subjected to an after-treatment step, preferably using a scrubber, a cooling scrubber or a gas cooler with a condensate separator. This step removes the water-soluble VOC and any ammonia that may be present beforehand, thereby relieving the load on the adsorber.

The adsorber preferably comprises activated charcoal, activated charcoal, silica gel, aluminum oxide and/or molecular sieves (zeolites), with activated charcoal being preferred. The adsorber ( 19 ) is particularly preferably selected from the group consisting of activated carbon, activated coke, molecular sieves and mixtures thereof. Very particularly preferably, the adsorber (19) consists of at least 90% activated carbon. Activated charcoal is sometimes called Adsorbents are used to remove undesirable colour, flavor and odor substances from gases, vapors and liquids. A great advantage of activated carbon is its thermal reactivability, the low price, the low complexity in production and the universal availability. In practice, however, this is preferably not recycled but replaced and later incinerated as waste. Activated carbon has also proven to be an excellent adsorber for VOCs. The activated carbon containing VOC can be used as a fertilizer depending on the environmental standard.

In a preferred embodiment, the ozone is admixed to the gas mixture as an ozone-oxygen mixture, which has been found to be efficient for oxidizing VOCs. The ozone-oxygen mixture preferably contains 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. For the purposes of the present invention, an O 2 molecule is always defined as oxygen, which is generally also known as molecular oxygen. In contrast to this, oxygen radicals - also known as O ^· or O* - are also referred to as such within the meaning of the invention in order to distinguish them from ozone and oxygen.

In general, a higher ozone content is preferable in the ozone-oxygen mixture mentioned above. For the present invention, 20% ozone with 80% oxygen is the preferred upper limit. Although higher concentrations of ozone in the ozone-oxygen mixture are technically possible, they are currently not preferred from an economic point of view due to the increasing complexity. It has been shown that optimal oxidation occurs with a final ozone concentration in the range of 0. 0001 - 0 . 1 vol. -% and more preferably between 0 . 0002 - 0 . 05 vol. -% is reached. Higher concentrations would certainly be conceivable, but less preferred from an economic point of view. The final concentration here is defined as the concentration of ozone at the time it was added to the gas mixture, ie after the addition is complete, but under the theoretical assumption that no ozone has reacted with components of the gas mixture up to that point.

If the composition of the gas mixture is known, the ozone concentration can be adjusted specifically to the concentration of the VOC in the gas mixture. In this respect, it is preferred that the amount of ozone added is added in a stoichiometric ratio in relation to the VOC concentration present or expected in the gas mixture. On the one hand, this prevents the gas mixture from being unnecessarily enriched with ozone and oxygen, which would increase the risk of explosion. On the other hand, the adsorber should not come into contact with ozone if possible. The oxidation reactions of ozone and components of the gas mixture normally take place within seconds or even fractions of a second. During the oxidation, the ozone is reduced to molecular oxygen, with the oxygen released binding substances that can be oxidized by free radicals—preferably VOC—and oxidizing them in the process. If there was an excess of ozone, not all of the ozone would react before the gas mixture reached the adsorber. The remaining ozone would then reach the adsorber with the oxidized VOC and could there dissolve the VOC already adsorbed by the adsorber. For this reason the Ozone concentration preferred to that contained or expected

VOC amount tuned in the gas mixture and preferably dimensioned so that when the gas mixture hits the adsorber no

Ozone is more present in the gas mixture. The amount of VOC sometimes depends on the origin of the gas mixture. For gases produced by fermentation or natural gases containing methane

However, the origin are average values for VOC

known concentrations. In the case of gases produced by fermentation, these average VOC concentrations are also specified based on the type of fermentation material used. The amount of ozone to be added can thus be known based on such

VOC average concentration values are determined.

However, the VOC concentration contained and, based on this, the amount of ozone to be added is preferably determined using

Reference samples of the gas mixture defined before its purification.

In a preferred embodiment, the period of time between the time the ozone is added and the

Impact of the gas mixture on the adsorber at least 1

second, preferably at least 4 seconds, and most preferably 6-10 seconds. As described above, it is desirable that all of the ozone has reacted with the VOC before the

Gas mixture meets the adsorber. To prevent that

Ozone that reaches the adsorber before it has reacted with the VOC contained in the gas mixture is the reaction space of the VOC

Oxidation or the addition of ozone is preferably separated from the adsorber or the VOC are combined with the ozone at one end

Reaction space injected while the adsorber is placed at the opposite end. In the latter

Variant, the dimension of the reaction space is consequently like this measured so that the ozone has reacted as completely as possible with the components in the gas mixture before it would reach the adsorber.

Furthermore, in a preferred embodiment, the ozone is generated from air in an on-site ozone generator. In the case of a self-sufficient production plant, it is very advantageous if the ozone can be obtained from the outside air and does not require pure oxygen as a preliminary stage. This reduces plant maintenance and allows production in remote locations without providing a source of pure oxygen. For this purpose, an oxygen concentrator is preferably installed on site, which filters the oxygen from the air and then passes it on to the ozone generator.

Alternatively, the ozone is preferably generated from oxygen in an ozone generator. Ozone production with oxygen that is as pure as possible as a precursor (oxygen concentration of 90-95% is preferred) makes it possible to produce ozone more efficiently and in higher concentrations. The use of pure oxygen makes particular sense in well-developed locations where the provision of pure oxygen is unproblematic.

In a further aspect, the invention relates to a device for cleaning a gas mixture with the aid of the method described above. According to the invention, said device comprises at least one gas supply line, at least one reaction chamber, at least one adsorber for VOC, an ozone source with an ozone supply line and a gas discharge line. Any space, container or housing can serve as the reaction space. in which the VOC can react with the ozone. The reaction space does not necessarily have to be separated on all sides—for example, a tube section would also be conceivable as the reaction space. The adsorber can be accommodated in the reaction space, but is preferably separated from it. The device according to the invention has the advantage over known cleaning devices from the prior art that the adsorption of the VOC on the adsorber takes place more efficiently due to the prior treatment of the VOC with ozone and the latter therefore has to be processed or replaced less often. As a result, the device can be operated more efficiently and cost-effectively overall.

The reaction chamber of the device is preferably equipped with packing elements. This enables efficient mixing or flow control of the gas or different gas flows in the reaction space and thus enables efficient oxidation of the VOC by the ozone.

The device preferably has a modular structure and is suitable for retrofitting existing gas cleaning systems. In this context, a modular device is defined as a device in which the components of the device described above can be assembled in advance or on site and upgraded to existing systems. This has the advantage that a defective module can be replaced inexpensively and easily. Furthermore, a modular device has the advantage that existing systems can be retrofitted inexpensively instead of being rebuilt or replaced at great expense. The modular design of the device thus increases its cost-effectiveness. In a preferred embodiment, the ozone source is an ozone generator, which is connected to the reaction chamber via the ozone supply line. The ozone generator can also be placed at a distance from the device if required. Such a separate positioning of the ozone generator makes particular sense when space problems or other reasons make it impossible to mount it directly on the system.

In an alternative method, a gas mixture containing a gas is provided in a first step a), the gas being selected from the group consisting of a pyrolysis gas obtained by pyrolysis of organic material and a methane-containing biogas obtained by fermentation of organic material or a mixture thereof . The pyrolysis gas has a carbon monoxide concentration of at least 2 vol. -% and the biogas has a methane concentration of at least 40 vol. -% . The gas mixture also includes at least one impurity from the group of volatile organic compounds (VOC). In a second step b), ozone is added to the gas mixture, the ozone oxidizing at least part of the VOC in the gas mixture. In a third step c), the gas mixture from the second step for cleaning the gas mixture is brought into contact with a VOC-adsorbing adsorber.

The invention is explained in more detail below using an exemplary embodiment illustrated in the attached figures. They each show purely schematically:

Fig. 1 is a schematic representation of a preferred one

Embodiment of the inventive method for Purification of a gas mixture comprising a methane-containing biogas; and

Fig. 2 shows a schematic representation of an alternative simplified embodiment of the method according to the invention for the purification of a gas mixture comprising a methane-containing biogas.

In the case of FIG. 1 schematically illustrated preferred embodiment of the method according to the invention is taken from a gas source 1 raw gas 3 and introduced into a gas treatment plant 2. In the gas treatment plant 2, the raw gas 3 is first passed into a pre-treatment chamber 5, where the raw gas 3 is cooled in order to remove condensates and ammonia in the sense of a pre-treatment. The raw gas 3 is then set to 0 . 1 bar (g) and further pre-treated by desulfurizing with specially doped activated carbon (usually KI, K ₂ CO ₃ , KMnO ₄ ) or Hydrogen sulfide (H ₂ S) are removed. Alternatively, desulfurization can also be carried out using biological or chemical processes. An additional fine desulfurization can also be carried out with a downstream activated carbon filter (not shown).

After the pre-treatment, a pre-treated, desulfurized gas 7 is obtained, although this does not mean that the pre-treated gas 7 is completely free of sulfur compounds and in particular does not rule out that the desulfurized gas still contains VOCs containing sulfur. At this point in time, the desulfurized gas 7 still contains at least VOC and CO ₂ as impurities, with at least the VOC and preferably also the CO ₂ being extracted as product gas to obtain usable biomethane be removed from the gas mixture. Depending on the course of the process, the CO ₂ can be separated before, during or after the removal of the VOC (dashed arrows). The removal of CO ₂ is also referred to as "upgrading" since the relative methane concentration in the gas mixture normally increases significantly as a result. The upgrading can take place in a manner known to those skilled in the art by means of membrane separation, amine washing and/or use of a PTSA. The CO ₂ content is preferably reduced to below 2%.

In the preferred embodiment shown, the CO ₂ is separated before the VOC removal. After the removal of CO ₂ is presently spoken of a methane-enriched gas 9, which is usually used as an energy source or. can be used as fuel. The fact that this gas 9 still contains VOC is irrelevant in the event of combustion, provided that said energy conversion does not take place in sensitive systems, such as fuel cells. If the raw gas 3 is raw biogas, the methane-enriched gas 9 is also referred to as biomethane.

In the embodiment shown, the methane-enriched gas 9 is introduced into a reaction chamber 11 to separate the VOC, where it is mixed with ozone (O ₃ ) from an ozone source 13 . The reaction chamber 11 includes filling bodies 15 which promote mixing of the gas 9 with the ozone. As soon as the ozone comes into contact with the VOC in the gas 9, oxidation reactions take place, in which the ozone is reduced and the VOC is oxidized, and in the course of which oxygen (O ₂ ) is produced. The oxidation reaction usually lasts less than 10 seconds. In the course of the oxidation of the VOC, these are at least partially broken down into "smaller" VOC components on split . This also changes the physical and chemical properties of the VOC. The VOC parts obtained after the oxidation can be divided into different fractions on the basis of these properties, for example into water-soluble VOC (water-soluble VOC, wsVOC for short) and non-water-soluble VOC (non-water-soluble VOC, NWSVOC for short).

For the sake of completeness it should be mentioned that the change in the physical and chemical properties of the VOC can already occur as a result of the oxidation itself - ie due to the binding of an oxygen atom and not just necessarily due to the splitting into smaller components. It is also possible for a VOC molecule to be oxidized several times. After the oxidation has taken place, an oxidized gas 14 is obtained.

The oxidized gas 14 with the various VOC fractions is cleaned after the oxidation by means of a scrubber, cooling scrubber or gas cooler with a condensate separator 17, whereby the wsVOC and easily condensing gases are removed and a scrubbed gas 16 is obtained. The washed gas 16 is then conducted to an adsorber 19 (preferably activated carbon), which adsorbs the _NWS VOC and allows cleaned, methane-enriched product gas 21 to pass through. The methane-enriched product gas 21 can then be routed to a gas liquefaction plant 23, where it is liquefied in order to make it transportable and/or storable. Depending on the composition of the raw gas 3, the type and/or sequence of the cleaning steps in the gas treatment plant 2 can be changed so that other impurities can also be removed. The dashed arrows starting from the scrubbed gas 16 and Product gas 21 indicate that the CO ₂ removal can also only take place at these points—instead of before the desulfurized gas 7 is introduced into the reaction space 11 .

In the case of FIG. 2 schematically illustrated alternative, simplified embodiment, only the core steps of the method according to the invention are shown. Analogous to that in FIG. 1 embodiment, the raw gas 3 containing methane and VOC can be fed from a raw gas source 1 into a gas treatment plant 2 and optionally pretreated in a pretreatment chamber 5 . The raw gas 3 (or, in the case of a pretreatment, the desulfurized raw gas 7 or gas 9 with a reduced CO ₂ content) is conducted into a reaction chamber 25 which is equipped with packing elements 15 at a front end 10 . Ozone (O ₃ ) is injected from an ozone source 13 at the front end 10 of the reaction chamber 25 and mixes with the gas 3 (or 7/9). In the area of the packing 15, the ozone reacts with the VOC contained in the gas 3 (FIGS. 7/9), as a result of which the latter are oxidized. Meanwhile, the gas-ozone mixture 14 flows from the front end to a rear end 12 of the reaction chamber 25 in which an adsorber 19 is located. The VOC are adsorbed at the adsorber 19 , as a result of which a cleaned, methane-enriched product gas 21 is obtained.

Analogous to Fig. 1, any CO ₂ removal that may take place can take place before entry into the reaction space 25 or after exit from the reaction space 25 (dashed arrows). The methane-enriched product gas 21 obtained after cleaning can, if required—at least partially—also be used directly as an energy carrier in the plant itself. For example, it can be fed into a heat engine that is integrated or separate from the gas treatment plant, where energy is generated that can in turn be used to operate the individual components. Energy is required in particular by compressor units which are used as standard for cooling and/or compressing the gas at various points in the gas treatment plant.

Finally, it should be mentioned that although the ozone source 13 is shown as an external source in the embodiments shown, this can also be solved differently. The ozone source can be an ozone generator, for example, which is subsequently connected to existing gas treatment plants in the sense of an additional module. In the case of newly built plants, such an ozone source can also be integrated into the treatment plant right from the start.

According to the invention, the method described above can be applied not only to methane-containing biogas but also to pyrolysis gas—that is, a gas mixture obtained from the pyrolysis of organic material.

Experimental Data :

Treatment with ozone and UV light has been investigated to remove VOC and sulphur-containing compounds from biogas. For this purpose, the respective substances were evaporated using an evaporator according to Table 1 below and mixed with an N ₂ carrier gas. In this way, concentrations of the substances could be achieved that correspond to the concentrations usually present in biogas. The N ₂ carrier gas was chosen as a replacement for biogas, since N ₂ has a comparable reaction behavior with ozone. This is supported by the data from the NIST Standard Reference Database, with which the following equilibrium constants can be calculated: O ₃ → O ₂ + O* 1.51*10 ^-26

CO ₊ O3 → CO2 ₊ O2 4.00* ₁₀ ^-25

CH ₄ + O ₃ → products 1.37*10 ^-24

3-carene + O ₃ → products 3.70*10 ^-17 α-pinene+ O ₃ → products 4.80*10 ^-16 d-limonene + O ₃ → products 2.01*10 ^-16

It is thus clearly evident that components such as CO or CH ₄ react much less well with ozone than terpenes such as 3-carene, α-pinene or d-limonene.

The gas mixture thus obtained was then treated with ozone and/or UV light. Sample 1 defines the concentration of the sample material before the treatment and sample 2 the concentration of the sample material after the treatment, "nd" stands for "not detectable" if the concentration of the sample was below the detection limit of the gas chromatograph for the respective substance.

Table 1

Next were using a gas chromatograph

Decomposition products of the substances from Table 1 analyzed (Table 2). In the "Sales" column, the percentage of the sample that is UV, ozone or

Ozone + UV was oxidized in the treatment. "kU" stands for no conversion, i.e. no oxidation of the VOC and "ndf" stands for "not carried out".

Table 2

All tests showed that UV light alone does not cause any reaction/degradation of the compounds in the gas flow. In some cases, e.g. with ethyl acetate, isopropanol, limonene and DMDS, the UV radiation activates the ozone, so that an increased degradation rate is observed.

As can be seen from the above data, isopropanol, ethyl acetate, hydrogen sulfide and hexamethylcyclotrisiloxane (D3) can be reacted quantitatively with ozone. acetone and Limonene are inert and require over-stoichiometric amounts of ozone for a reasonable conversion. Dimethyldisulfide without a second component is slowly (comparable to acetone) implemented. However, if a reaction partner such. B. Ethyl acetate present in the gas phase reacts almost completely.

Cyclohexene is a model substance for terpenes such as e.g. B. Limonene and reacts with ozone at a high reaction rate. However, the deposits in the reactor indicated polymerization.

If you look at substance mixtures of VOCs with sulphur-containing compounds, the sulphur-containing compounds react primarily with the ozone. The resulting sulfoxide radicals partially react with the VOC.

The increased conversion of UV + ozone in contrast to ozone alone can be explained by the fact that the ozone oxidized to O ₂ reacts again to ozone through the UV radiation and is thus reactivated.

In a further experiment, biogas compositions from three different fermentation plants were each treated with and without ozone (250 ppm), then brought into contact with a VOC-adsorbing adsorber and finally the non-adsorbed amount of VOC in the biogas composition was measured. The results are shown in Tables 3 to 5 below. The term "nd" stands for undetectable and corresponds to a concentration below the detection limit. Table 3

S-KW = sulfuric hydrocarbons

HC = hydrocarbons Table 4 Table 5

The amount of ozone that has reacted with the VOC is given as reacted ozone. For example, for composition 1, a gas mixture containing VOC was mixed with 250 ppm ozone, with 23 ppm ozone having reacted with the VOC.

From the experimental data shown in Tables 3 to 5 it is clear that treatment with ozone reduces the VOC concentration and changes the VOC composition. The resulting oxidized VOC can be more efficiently adsorbed by the adsorber and thus more VOC can be removed from the gas mixture.

Claims

patent claims

1. A method for cleaning a gas mixture comprising the following steps:

(a) providing a gas mixture containing a gas selected from the group consisting of i. a methane-containing biogas (3, 7) obtained by fermentation of organic material with a methane concentration of at least 40% by volume and ii. a pyrolysis gas obtained by thermal treatment of organic material with a carbon monoxide concentration of at least 2 vol. iii. or a combination thereof; and at least one impurity from the group of volatile organic compounds (VOC), the gas mixture having a VOC concentration of 0.0001-0.2% by volume;

(b) admixing ozone (O ₃ ) to the gas mixture according to step a) at a concentration of 0.0001-12% by volume, based on the gas mixture, the ozone oxidizing at least part of the VOC in the gas mixture;

(c) contacting the gas mixture from step b) with a VOC-adsorbing adsorbent (19) selected from the group consisting of activated carbon, activated coke, silica gel, alumina, molecular sieves and mixtures thereof to purify the gas mixture.

2. The method according to claim 1, characterized in that the at least one impurity is selected from the group of volatile organic compounds (VOC), which is selected from the group consisting of linear or branched C ₁ - C ₅ alcohols, sulfides and unsaturated terpenes. Process according to Claim 1, characterized in that the at least one impurity is selected from the group of volatile organic compounds (VOC), which 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-cineol, 3- carene, α-pinene, α-thujene, ß-pinene, limonene, eucalyptol, fenchone, limonene, linalool, Myrcene, p-cymene, sabinene, a- caryophyllene, α-terpinene, γ ^_ terpinene, 2-methylthiophene,

3-Methylthiophene, Diisopropyldisulfide, dimethyltetrasulfide, isobutyl mercaptan, methyl allyl sulfide, methylisopropyldisulfide, methylpropylsulfide, 3,3-dimethyl-2-bornanone, nopinone, phellandrene, p-menthan-2-ol, p-menthan-2-one , Santen, Terpinoiene, Thujanon and Tricyclen; and preferably 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, methylpropyl disulfide, tetrahydrothiophene, thiophene, thiophenol, 1,4-cineol , 3-carene, α-pinene, α-thujene, ß-pinene, limonene, eucalyptol, fenchone, limonene, linalool, myrcene, p-cymene, sabinene, a- caryophyllene, α-terpinene and γ ^_ terpinene; and particularly preferably from the group consisting of 1,4-cineole, 3-carene, α-pinene, α-thujene, ß-pinene, limonene, eucalyptol, fenchone, limonene, linalool, myrcene, p-cymene, sabinene, α- Caryophyllene, α-terpinene and γ ^_ terpinene is selected. Process 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. Process according to Claim 1, characterized in that the at least one impurity is selected from the group of volatile organic compounds VOC, which 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, 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, 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-dimethyltetradecane, 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-diethyl -cyclohexane, 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 1-5-ethylcyclohexane, 1-methyl-4-heptylcyclohexane , 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-l-butene, 3-methyl-

1-pentene, 4-methyl-l-pentene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, isobutene, 2-methyl-l-butene, 2,3-dimethyl-

1-butene, 2-ethyl-l-butene, 2-methyl-l-pentene, 2,3,3-trimethyl-l-butene, 3-methyl-2-isopropyl-l-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-dimethyl3-hexene, trans-2,5-dimethyl3-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-tridec, trans-5-tetradecene, trans-5-pentadecene, 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 ₁₅ cyclic olefin, cyclopentadiene, α-pinene, ß- Pinene, 3-carene, D-limonene, terpene, α-methyl styrene, C ₉ -styrene, Cio-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, Indane, Naphthalene, Tetralin, 1-Methylnaphthalene, 2-Methylnaphthalene, 2,3-dimethylnaphthalene, C ₁₂ Monosubstituted naphthalene, C ₁₂ Disubstituted naphthalene, C ₁₃ Monosubstituted naphthalene, C ₁₃ Disubstituted naphthalene, C ₁₃ Trisubstituted naphthalene, Acetylene, Methylacetylene ,

2-butyne, ethylacetylene, methanol, ethanol, isopropyl alcohol, n-propyl alcohol, isobutyl alcohol, n-butyl alcohol, s-butyl alcohol, t-butyl alcohol, cyclopentanol, 2-pentanol, 3-pentanol, pentyl alcohol, cyclohexanol, 1-hexanol, 2- Hexanol, 1-Heptanol, 1- Octanol, 2-0ctanol, 2-Ethyl-1-hexanol, 3-0ctanol, 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 t-butyl ether, ethyl n- butyl ether, ethyl t-butyl ether, methyl t-amyl ether, di-n-propyl ether, 2-butyltetrahydrofuran, di-n-butyl ether, di-isobutyl ether, di-n-pentyl ether, 2-methoxyethanol, 2-methoxy-1 -propanol, 2-ethoxyethanol, l-methoxy-2-propanol, 2-propoxyethanol, 3-ethoxy-1-propanol, 3-methoxy-1-butanol, 1-ethoxy-2-propanol, diethylene glycol,

3-Methoxy-3-methyl-butanol, 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, s-butyl acetate, t-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, Isoamyl Isobutyrate, n-Octyl Acetate, 2-Ethyl Hexyl 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, 2,3,5,6,8-pentamethylnonyl acetate, dimethyl carbonate, propylene carbonate, methyl lactate, ethyl lactate, 2-methoxy ethyl acetate, methyl isopropyl carbonate, 2-methoxy-1-propyl acetate , 2-ethoxyethyl acetate , 1 -methoxy-2 -propyl acetate , dimethyl succinate , ethylene glycol diacetate , ethyl3- ethoxypropionate , diisopropyl carbonate , dimethyl glutarate , 2-butoxyethyl acetate , dimethyl adipate , 3-hydroxy-2 , 2 , 4- trimethylpentyl-1-isobutyrate , l- 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 d, 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 t-butyl ketone, 2-methyl-3-hexanone, 2-heptanone, diisopropyl ketone, 2-octanone, 2-nonanone, diisobutyl ketone, 2-decanone, biacetyl, methyl vinyl ketone, hydroxyacetone, methoxyacetone, diacetone alcohol, phenol, alkylphenol, m-cresol, o-cresol, p-cresol, nitrobenzene, para-

Toluene Isocyanate , Methylenediphenylenediisocyanate , dimethylamine, ethylamine, trimethylamine, ethanolamine, dimethylaminoethanol, diethanolamine, triethanolamine, n-methyl-2-pyrrolidone, oxo-hexyl acetate, oxo-heptyl acetate, oxo-octyl acetate, oxo-nonyl acetate, oxo-decyl acetate, oxo-dodecyl acetate, oxo-tridecyl acetate, dimethyl sulfide and hexamethylcyclotrisiloxane. Process according to one of Claims 1 or 2, characterized in that the gas mixture according to step a) has a VOC concentration of 0.001 - 0.1% by volume. Method according to one of Claims 1 to 6, characterized in that the biogas (3, 7) originates from a fermenter and preferably has a methane concentration of at least 50% by volume, preferably at least 60% by volume. The method according to any one of claims 1 to 7, characterized in that the biogas (3, 7) with a

Temperature of 10°C - 30°C, preferably at room temperature, and at a pressure of 50 - 200 mbar, preferably about 100 mbar. Process according to any one of Claims 1 to 6, characterized in that 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. Process according to one of Claims 1 to 9, characterized in that CO ₂ is additionally separated from the gas mixture before or after the adsorption of the VOC. Process according to one of Claims 1 to 10, characterized in that the gas mixture is subjected to an after-treatment step (17) before the VOC is brought into contact with the adsorber (19), preferably using a scrubber, a cooling scrubber or a gas cooler with a condensate separator. Process according to one of Claims 1 to 11, characterized in that the adsorber (19) is selected from the group consisting of activated carbon, activated coke, molecular sieves and mixtures thereof, the adsorber (19) particularly preferably consisting of at least 90% activated carbon. Process according to one of Claims 1 to 12, characterized in that the ozone is added to the gas mixture as an ozone-oxygen mixture. Method according to one of Claims 1 to 13, characterized in that the final concentration of the ozone in the gas mixture (3, 7, 9) is 0.0001% by volume to 3% by volume, preferably 0.0001% by volume to 0.5% by volume. -%, in particular 0.0001-0.1% by volume, particularly preferably 0.0002-0.05% by volume. Method according to one of Claims 1 to 14, characterized in that the ozone is produced in an ozone generator (13) on site from air or in an ozone generator (13) from oxygen, preferably from concentrated

atmospheric oxygen is generated.