EP1694801A1

EP1694801A1 - Odorisation of fuel gas with low-sulphur content odorisers

Info

Publication number: EP1694801A1
Application number: EP04804632A
Authority: EP
Inventors: Gerd Mansfeld; Jörg Eilers
Original assignee: Symrise AG
Current assignee: Symrise AG
Priority date: 2003-12-19
Filing date: 2004-12-01
Publication date: 2006-08-30
Anticipated expiration: 2024-12-01
Also published as: DE502004012336D1; DE10359743A1; MXPA06006895A; JP2007515520A; US20090064585A1; WO2005061680A1; CA2550273A1; RU2006126094A; EP1694801B1; CN1898366A; ATE502994T1; AU2004303520A1

Abstract

The use is described of a mixture containing A) at least two different acrylic acid C1-C6 alkyl esters; B) at least one compound from the group comprising C1-C8 mercaptans, C4-C12 thiophenes, C2-C8 sulfides or C2-C8 disulfides; C) at least one compound from the group comprising norbornenes, C1-C5 carboxylic acids, C1-C8 aldehydes, C6-C14 phenols, C7-C14 anisoles or C4-C14 pyrazines; D) optionally an antioxidant for the odorisation of fuel gas having a methane content of at least 60 wt. %. Corresponding fuel gases and processes for the odorisation of fuel gases are also described.

Description

Symrise GmbH & Co. KG Mühlenfeldstrasse 1, 37603 Holzminden

Odorization of fuel gas with low sulfur odorants

The present invention relates to the use of an acrylic acid alkyl ester containing a small proportion of a sulfur-containing compound and a further component for the odorization of fuel gas, a process for the odorization of fuel gas and fuel gas containing this mixture.

The city and coke oven gases formerly used for public gas supply contained intensely smelling components and therefore had a strong smell, so that escaping gas could easily be perceived. Gas odorization means the addition of odor-intensive substances (odorants) that act as warning or alarm substances to gases that do not have a significant intrinsic odor, ie to gases that are otherwise essentially or completely odorless.

Natural gas mainly consists of methane (typical methane contents are in the

Range 50 to 99 wt .-%, mostly in the range 60 to 99 wt .-% and usually 80 to 99 wt .-%) and, depending on the origin, can also contain different proportions of ethane, propane and higher molecular weight hydrocarbons. Natural gas H (H = high) has a methane content of 87 to 99.1 vol%, natural gas L (L = low) generally contains 79.8 to 87 vol%

Methane.

Due to its high degree of purity, the gas normally used in the public network today, which is usually obtained from natural gas, is virtually odorless.

If leaks are not noticed in time, explosive gas / air mixtures with a high risk potential quickly build up.

For safety reasons, gas is therefore odorized by adding 'odor-intensive substances. In Germany, for example, it is mandatory that all gases that do not have a sufficient odor and are distributed in the public gas supply, according to the DVGW worksheet

G 280 can be odorized (DVGW = German Association of Gas and Water Specialists). These odorants can also be perceived in great dilution and, due to their exceptionally unpleasant smell, can cause an alarm association in humans as desired. The odorant must not only smell unpleasant and unmistakable, but above all must clearly represent a warning smell. Therefore, the smell of the odorized gas must not be familiar to people from everyday life, e.g. from the kitchen and household. In Germany about 90% of the process gas is currently odorized with tetrahydrothiophene (THT) (12 - 25 mg / m ³ ); in addition, odorization with mercaptans is also common. It may make sense to add a larger amount of odorant to the gas over a longer period of time. In so-called shock odorization, up to three times the amount of odorant is added to the gas compared to conventional odorization. Shock odorization is used, for example, when new networks or line sections are put into operation to quickly reach the minimum odorant concentration or to detect small leaks in the gas installation.

THT alone is ideal for reliable gas odorization. In the course of a more sensitive handling of the environment, however, it should be noted that the gases odorized in this way burn to a greater extent

Sulfur oxides are produced as combustion products.

Since the aim is to reduce or avoid sulfur compounds, attempts have already been made to develop low-sulfur or sulfur-free odorants.

JP-B-51-007481 mentions that acrylic acid alkyl esters such as methyl acrylate, ethyl acrylate and butyl acrylate are known to have weak odorization properties for fuel gases and are of practically no significance in this regard. The document describes and claims allyl acrylate as an effective odor component.

JP-A 55-104393 describes that odorant containing an alkyne and at least 2 compounds selected from a group consisting of methyl acrylate, ethyl acrylate, methyl methacrylate, allyl methacrylate, ethyl propionate, methyl n-butyrate, methyl isobutyrate and prenyl acrylate , and optionally tert-butyl mercaptan, are suitable for the odorization of fuel gases. The amount of odorant is 50 ppm by weight (mg / kg gas), preferably greater than or equal to 100 ppm. The best results with LPG (liquefied petroleum gas) were obtained with mixtures including TBM. A better odor effect was achieved by adding 2-butyne (50 ppm) to a mixture of methyl acrylate (50 ppm), allyl acrylate (100 ppm) and TBM (5 ppm). The best result showed a mixture of 2-butyne (50 ppm), allyl methacrylic lat (20 ppm), methyl acrylate (20 ppm), methyl n-butyrate (20 ppm), methyl isobutyrate (20 ppm), ethyl propionate (20 ppm) and TBM (5 ppm).

JP-B-51-034841 found "odor threshold values" of various substances, n-valeric acid, n-butyric acid, isobutyraldehyde and various methylamines having low odor "odor threshold values". Ethyl acrylate or n-valeric acid used alone, due to their olfactory properties, were not sufficiently odorant. The optimized mixture comprised 50-90% by weight of ethyl acrylate, 10-50% by weight of n-valeric acid and optionally triethylamine. The optimized mixture comprised ethyl acrylate, n-valeric acid and triethylamine, this mixture containing equal parts by weight of n-valeric acid and triethylamine and 30 to 80% by weight of ethyl acrylate. A mixture consisting of 60% by weight of ethyl acrylate and 20% by weight of n-valeric acid and triethylamine was added to a gaseous fuel gas at 10 mg / m ³ .

Odorants for fuel gases consisting of ethyl acrylate (70% by weight) and tert-butyl mercaptan (30% by weight) are known from JP-B 51-021402. This mixture was added to a gaseous fuel gas in an amount of 5 mg / m ³ .

Odorants for the odorization of heating gases consisting of a) 30-70% by weight of CrC-alkyl mercaptans, b) 10-30% by weight of n-valeraldehyde and / or isovaleralaldehyde, n-butyric acid and / or isobutyric acid and optionally c ) up to 60 wt .-% tetrahydrothiophene are described in DE-A 31 51 215. These odorants were added to heating gas in amounts of 5-40 mg / m ³ .

Mixtures containing a) 1 part by weight of dimethyl sulfide, b) 0.8-3 parts by weight of tert-butyl mercaptan and c) 0.1-0.2 parts by weight of tert-heptyl mercaptan or 0.05-0.3 parts by weight of tert. ~ Hexyl mercaptan to the O - Dorierung of fuel gases are known from JP-A 61-223094. These mixtures had an odor of teit-butyl mercaptan, which is associated with the odor of city gas. The use of norbornene derivatives for fuel gas odorization is known from JP-A 55056190. LPG was obtained at 40 mg / kg with a mixture of equal parts of 5-ethylidene-2-norbornene and 5-vinyl-2-norbornene or at 50 mg / kg with a mixture of 80% by weight of 5-ethylidene-2 norbornene and 20% by weight of ethyl acrylate.

Mixtures for the odorization of town gas containing norbornene or a norornene derivative and a diluent are described in DE-A 100 58 805.

Mixtures of C ₄ -C aldehydes and sulfur compounds are described as odorants in JP-A 50-126004. The 1 kg of propane was odorized with 50 mg of a mixture of 60% by weight of valeraldehyde and 40% by weight of n-butyl mercaptan. Valeraldehyde enhances the smell of n-butyl mercaptan. Similarly, 2-methylvaleraldehyde was used.

DE-A 19837066 solved the problem of sulfur-free gas odorization by means of mixtures comprising at least one C ₁ -C ₂ -alkyl acrylate and a nitrogen compound with a boiling point in the range from 90 to 210 ° C. and a molecular weight from 80 to 160, mixtures containing at least two various acrylic acid alkyl esters are preferred. Alkyl-substituted 1,4-pyrazines are described as particularly suitable nitrogen compounds.

That antioxidants, especially phenol derivatives, to stabilize

Mercaptan-containing or alkyl acrylate-containing gas odorants are suitable, is known from US-A 2,430,050 and DE-A 19837066.

Alternative low-sulfur odorants for the odorization of natural gas or fuel gases consisting mainly of methane were sought, the properties of which are preferably superior to those of the odorants known hitherto, in particular with regard to their warning odor, both the quality of the warning odor and the storage stability of the odorant is important so that the quality of the warning smell can also be guaranteed over a longer (storage) period.

The present invention relates to the use of a mixture containing

A) at least two different acrylic acid CrC ₆ alkyl esters;

B) at least one compound from the group of the C ₄ -C ₂ thiophene, the C ₂ -C ₈ sulfide or the C ₂ -C ₈ disulfide;

C) at least one compound from the group of the norbornenes, the Ci-Cβ-carboxylic acids, the CrC ₈ aldehydes, the C ₆ -Cι phenols, the C ₇ -C ₄ anisoles or the C ₄ -C _M pyrazines;

D) optionally an antioxidant

for odorising fuel gases with a methane content of at least 60% by weight.

The invention also relates to a corresponding process for the odorization of fuel gases with a methane content of at least 60% by weight with mixtures to be used according to the invention. Here, a mixture to be used according to the invention is added to the fuel gas. With regard to preferred configurations, compare the information on the preferred uses, which apply accordingly.

Another object of the present invention are fuel gases with a methane content of at least 60% by weight containing the mixtures to be used according to the invention.

The fuel gas to be odorized has a methane content of at least 60% by weight, preferably at least 70% by weight and particularly preferably at least 75% by weight.

The acrylic acid CrC ₆ alkyl esters are advantageously selected from the group comprising acrylic acid methyl ester, acrylic acid ethyl ester, acrylic acid n-propyl ester, acrylic acid isopropyl ester, acrylic acid n-butyl ester, acrylic acid isobutyl ester, acrylic acid tert-butyl ester, acrylic acid n-pentyl ester, acrylic acid iso-pentyl ester and acrylic acid n-hexyl ester.

CrC ₄ -alkyl acrylates, in particular methyl acrylates, ethyl acrylates, n-propyl acrylates, isopropyl acrylates, n-butyl acrylates and isobutyl acrylate are preferred. Very particularly preferred acrylic acid CrC ₄ alkyl esters are acrylic acid methyl ester, acrylic acid ethyl ester and acrylic acid n-butyl ester.

If the mixtures to be used according to the invention comprise two acrylic acid-dC-alkyl esters from the group of acrylic acid methyl ester, acrylic acid ethyl ester and acrylic acid n-butyl ester, the preferred weight ratio of low molecular weight acrylic acid alkyl ester to higher molecular weight acrylic acid alkyl ester is in the range 9: 1 - 1: 9, preferably in the range 7 : 3 - 3: 7, in particular in the range 3: 1 - 1: 4. The weight ratio of low molecular weight acrylic acid alkyl ester to higher molecular weight acrylic acid alkyl ester is very particularly preferably in the range 1: 1 - 1: 3.

The compounds from group A) are advantageously contained in the mixtures to be used according to the invention to 60-97% by weight, preferably to 70-95% by weight and particularly preferably to 80-95% by weight.

The mercaptans can be, for example, ethyl mercaptan, n-

Propyl mercaptan, isopropyl mercaptan, n-butyl mercaptan, sec.-butyl mercaptan, isobutyl mercaptan, tert.-butyl mercaptan, n-pentyl mercaptan, isopentyl mercaptan, neopentyl mercaptan, n-hexyl mercaptan, isohexylmer-captan, sec.-hexylhexaptaptan, neo-hexyl mercaptan, Heptyl mercaptan, isoheptyl mercaptan, sec.-heptyl mercaptan, tert-

Act heptyl mercaptan, n-octyl mercaptan, isooctyl mercaptan, sec-octyl mercaptan or tert-octyl mercaptan.

The thiophenes are advantageously thiophenes which are substituted by 1 to 4, preferably by one or two, dC ₄ alkyl and / or alkoxy groups. The thiophenes can also be hydrogenated thiophenes, with tetrahydrothiophene being preferred. The sulfides can be, for example, dimethyl sulfide, diethyl sulfide, di-n-propyl sulfide, diisopropyl sulfide, di-n-butyl sulfide, diisobutyl sulfide, ethyl methyl sulfide, methyl n-propyl sulfide, methyl isopropyl sulfide, methyl isobutyl sulfide, ethyl isopropyl sulfide, or ethyl isopropyl sulfide. Dimethyl sulfide, diethyl sulfide, di-n-propyl sulfide, diisopropyl sulfide, di-n-butyl sulfide and diisobutyl sulfide are preferred.

The disulphides can be, for example, dimethyl disulphide, diethyl disulphide, di-n-propyl disulphide, diisopropyl disulphide, di-n-butyl disulphide, diisobutyl disulphide, ethyl methyl disulphide, methyl n-propyl disulphide, methyl isopropyl disulphide, methyl disulphyl disulphyl disulphyl disulphide or disulfide act.

Dimethyl disulfide, diethyl disulfide, di-n-propyl disulfide, diisopropyl disulfide, di-n-butyl disulfide and diisobutyl disulfide are preferred.

The compounds from group B) in the mixtures to be used according to the invention are typically 1-30% by weight, advantageously 2-25% by weight, preferably 3-15% by weight, and particularly preferably 5-10

% By weight.

The norbornenes are advantageously those with a molecular weight of less than or equal to 130, preference is given to norbornene, 2,5-norbornadiene, 5-ethylidene-2-norbornene and 5-vinylI-2-norbornene.

The carboxylic acids are advantageously acetic acid, propionic acid, n-butyric acid, isobutyric acid, n-valeric acid, isovaleric acid, n-caproic acid, isocaproic acid or 2-methylvaleric acid.

The aldehydes are advantageously acetaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde, n-valeraldehyde, isovaleraldehyde, n-capronaldehyde, isocapronaldehyde or 2-methylvaleraldehyde.

The phenols are advantageously substituted phenols with a total of one or two dC ₄ alkyl and / or CC ₄ alkoxy groups. Preferred phenols are 3-methylphenol, 2-ethylphenol, 4-ethylphenol, 2-isopropylphenol, 2-tert-butylphenol, 2-tert-butyl-4-methylphenol, 2- Methoxyphenol, 2-methoxy-4-methylphenol and 2-methyl-5-isopropylphenol. C 1 -C 4 -monoalkylated phenols are particularly preferred.

Advantageous anisoles are anisole, 2-methylanisole, 4-allylanisole or 4-methylanisole.

The pyrazines are advantageously alkylated and / or acylated pyrazines. Examples of advantageous pyrazines are 2-methylpyrazine, 2-ethylpyrazine, 2,3-dimethylpyrazine, 2,3-diethylpyrazine, 2,6-dimethylpyrazine, 2,3-methylethylpyrazine, 5,2-methylethylpyrazine, 2,3,5-trimethylpyrazine, 3,5,2-dimethylethylpyrazine, 3,6,2-dimethylethylpyrazine, 5,2,3-methyldiethylpyrazine, tetramethylpyrazine, 2,3-methylacetylpyrazine or 2-acetylpyrazine. Preferred are pyrazines with a total of one to three, particularly preferably with a total of one or two, dC ₄ alkyl and / or C 1 -C 8 acyl groups.

The acylated pyrazines are preferably monoacylated and particularly preferably have an acetyl or propionyl group, preference being given to monoacetylated pyrazines, in particular 2-acetylpyrazine.

The compounds from group C) are typically contained in the mixtures to be used according to the invention to 0.5-20% by weight, advantageously to 1-10% by weight, preferably to 1-5% by weight.

A weight ratio of components B) to components C) in the range from 6: 1 to 1: 3, preferably in the range 5: 1 to 1: 2 and particularly preferably 4: 1 - 1: 1 is advantageous.

The odorant to be used according to the invention can, for example, have antioxidants used as component D) to increase stability. Examples include vitamin C and derivatives (e.g. ascorbyl palmitate, ascorbyl acetate), tocopherols and derivatives (e.g. vitamin E, vitamin E acetate), vitamin A and derivatives (vitamin A palmitate) phenolic benzylamines, formic acid, acetic acid, benzoic acid, sorbic acid, Hexamethylenetetramine, tert-butylated hydroxytoluene, tert.-butylated hydroxyanisole, α-hydroxy acids (eg citric acid, lactic acid, malic acid), hydroquinone monomethyl ether. Preferred antioxidants are tert-butyl hy- droxytoluene (BHT, Jonol), tert-butylated hydroxyanisole and hydroquinone monomethyl ether.

The addition of antioxidants in particular ensures a high storage stability of the mixtures to be used according to the invention, as well as of the odorized ones

Natural gas reached. Storage stability tests have shown that the warning smell of the mixtures to be used according to the invention remains largely the same over a period of more than 5 months at 40 ° C. (incubator). For the odorants according to the invention, tert-butylhydroxy toluene and hydroquinone monomethyl ether have proven to be particularly effective and stabilizing well.

Several antioxidants can also be added to an odorant. The odorants advantageously contain one, two or three antioxidants, and one or two antioxidants are preferred.

The total amount of antioxidants (component D) in the odorant is usually in the range 0.01-2% by weight, preferably in the range 0.02-1% by weight, particularly preferably in the range 0.03-0.6% by weight. -%.

The amount of odorant based on the fuel gas to be odorized is typically in the range 5-100 mg / m ³ , preferably 5-50 mg / m ³ , particularly preferably 10-40 mg / m ³ and very particularly preferably 12-30 mg / m ^3rd

The warning smell of a natural gas odorized according to the invention was from a

Group of testers clearly perceived even with a dilution of natural gas in air in the range 1: 200 - 1: 2000.

Due to the presence of component C) in the mixtures to be used according to the invention, a better warning smell was achieved compared to mixtures which only contained components A) and B), see also the examples below.

The use of mixtures comprising is preferred according to the invention A) at least two different acrylic acid CrC ^ alkyl esters;

B) at least one compound from the group of the C ₈ -C mercaptans, the C ₄ -C ₈ thiophene, the C ₂ -C ₈ sulfide or the C ₂ -C ₈ disulfide;

C) at least one compound from the group of Norbomene, the C ₂ - C ₅ carboxylic acids, C ₂ -C ₅ aldehydes, C ₆ -C ₁₀ -F'henole, the C ₇ - Cio-anisoles or C -Cι ₀ -Pyrazine as well

D) at least one antioxidant.

The use of mixtures comprising is particularly preferred according to the invention

A) methyl acrylate and ethyl acrylate;

B) at least one compound from the group of thiophene, tetrahydrothiophene, dimethyl sulfide, diethyl sulfide, di-n-propyl sulfide, diisopropyl sulfide, dimethyl disulfide, diethyl disulfide, di-n-propyl disulfide, diisopropyl disulfide or the mercaptans of the formula (I)

in which

R ^{1 is} hydrogen, methyl or ethyl, preferably methyl, and

R ^{2 represents} an alkyl group with 1 to 4 carbon atoms, preferably methyl, ethyl, iso-propyl, iso-butyl or tert-butyl;

C) at least one compound from the group of C ₂ -C ₅ carboxylic acids, the C ₃ -C ₅ aldehydes, the C ₁ -C 4 -monoalkylated phenols;

D) at least one antioxidant. Preferred components B) are the mercaptans of the formula (I).

The use of mixtures comprising or consisting of is very particularly preferred

A) methyl acrylate and ethyl acrylate;

B) tert-butyl mercaptan;

C) at least one compound from the group propionaldehyde, isovaleraldehyde, isovaleric acid, 2-ethylphenol, 4-ethylphenol;

D) one or two antioxidants.

The best odorization of the gas was achieved with these mixtures, the warning smell was strongest and was clearly perceived.

The most preferred group C) compound is isovaleric acid, the most preferred group D) antioxidants are hydroquinone monomethyl ether and tert-butylated hydroxytoluene.

The methods according to the invention correspond to the uses according to the invention, in particular with regard to the preferred configurations. Further aspects of the invention emerge from the appended claims.

The following examples illustrate the invention:

Unless otherwise stated, all information is based on weight.

It means:

MeAc: methyl acrylate; EtAc: ethyl acrylate; TBM: tert-butyl mercaptan; IVS: isovaleric acid; BHT: tert-butylated hydroxytoluene. example 1

Components A), B) and C) odorants to be used according to the invention became odorless as individual substances in concentrations of 10, 25 and 50 mg / m ³ natural gas (natural gas L; methane content: approx. 85% by volume) with regard to their warning - Odor and their warning intensity against unodorized natural gas (blank value). These concentrations correspond to the typical concentrations of odorant in natural gas under normal conditions or with shock odorization. Odorized natural gas containing the same concentrations of THT was used as a reference. The experiment was carried out at room temperature (about 20 ° C.) in such a way that the odorant was metered into a gas stream in a tube. At the end of this 2 m long tube (homogenization takes place inside the tube), the escaping odorized gas is assessed by a group of trained examiners (8 to 12 people). The evaluation was carried out on a scale from 1 (very weak / very little warning) to 10 (very strong / very warning), the values given are mean values. The industrial standard THT was given the value 10.

The results were essentially the same for the 3 concentrations examined (10, 25 and 50 mg / m ³ gas). Table 1 shows THT and components A), B) or C) to be used according to the invention as individual substances (ie not in the form of the mixture to be used according to the invention) in comparison.

Table 1 :

It can be seen from Table 1 that the individual components A), B) or C) do not have a good odorizing effect.

Example 2

Table 2 shows the evaluations for mixtures of two compounds of component type A) with TBM = tert-butyl mercaptan (methylpropanthiol-2,2) as component B); the procedure was as described in Example 1.

Table 2:

From Table 2 it can be seen that the addition of TBM resulted in an improved odorization performance, although very good odorization was still not possible.

Example 3

Table 3 shows the evaluations for mixtures of two compounds of component type A) with IVS = isovaleric acid as component C); the procedure was as described in Example 1.

Table 3:

It can be seen from Table 3 that the addition of IVS brought about an improved odorization performance, although very good odorization was still not possible.

Example 4

Table 4 shows the evaluations for mixtures of two compounds of component type A) with TBM = tert-butyl mercaptan as component B) and IVS = isovaleric acid as component C); the procedure was as described in Example 1.

Table 4:

Table 4 shows that the use of mixtures of components A), B) and C) brings about excellent odorization performance.

Example 5

To investigate the storage stability, odorants with various antioxidants, natural gas L, were added and the odorized natural gas was tested for odor after certain periods at 40 ° C. storage, as described in Example 1. The criterion for storage stability was the significant odor correspondence of the odorant or gas stored with the original warning odor.

The amount of odorant added to the natural gas was 20 mg / m ³ . The odorant consisted of 60% EtAc minus y% antioxidant, 31% MeAc, 7% TBM, 2% IVS and y% antioxidant. Table 5 shows the results in comparison.

Classification of storage stability: a = less than 6 weeks; b = maximum 3 months; c = maximum 5 months; d = more than 5 months

Table 5:

With a suitable choice and dosage of the antioxidant, even after a storage period of more than 5 months at 40 ° C, the warning smell was still clearly perceptible, both of the odorant itself and the odorized natural gas.

Claims

Expectations

1. Using a mixture containing

A) at least two different acrylic acid CrC ₆ alkyl esters;

B) at least one compound from the group of the CC ₈ mercaptans, the C -Ci ₂ thiophene, the C ₂ -C ₈ sulfide or the C ₂ -C ₈ disulfide;

C) at least one compound from the group of the norbornenes, the CC ₆ carboxylic acids, the CrC ₈ aldehydes, the C ₆ -C ₄ phenols, the C ₇ -C ₄ anisoles or the C -C ₄ pyrazines;

D) optionally an antioxidant

for odorization of fuel gas with a methane content of at least 60% by weight.

2. Use according to claim 1, wherein the mixture

A) at least two different acrylic acid-C C -alkyl esters;

B) at least one compound from the group of the CrC ₈ mercaptans, the C ₄ -C ₈ thiophene, the C ₂ -C ₆ sulfide or the C ₂ -C ₈ disulfide;

C) at least one compound selected from the group consisting of norbornenes, the C ₂ - C ₅ carboxylic acids, C ₂ -C ₅ aldehydes, C ₆ -C ₁₀ -phenols, C ₇ -Cι ₀ - anisoles or C ₄ -Cι ₀ -Pyrazine as well

D) at least one antioxidant

contains.

3. Use according to claim 1, wherein the mixture

A) methyl acrylate and ethyl acrylate; B) at least one compound from the group of thiophene, tetrahydrothiophene, dimethyl sulfide, diethyl sulfide, di-n-propyl sulfide, diisopropyl sulfide, dimethyl disulfide, diethyl disulfide, di-n-propyl disulfide, diisopropyl disulfide or the mercaptans of the formula (I)

in which

R is hydrogen, methyl or ethyl, preferably methyl, and R ^{2 is} an alkyl group having 1 to 4 carbon atoms, preferably methyl, ethyl, isopropyl, isobutyl or tert-butyl;

C) at least one compound from the group of C ₂ -C ₅ carboxylic acids, C -C ₅ aldehydes, C ₁ -C ₄ monoalkylated phenols and

D) at least one antioxidant

contains.

4. Use according to claim 1, wherein the mixture

A) methyl acrylate and ethyl acrylate;

B) tert-butyl mercaptan;

C) at least one compound from the group propionaldehyde, isovaleraldehyde, isovaleric acid, 2-ethylphenol, 4-ethylphenol and D) one or two antioxidants

comprises or consists of these components.

5. Use according to any one of claims 1 to 4, characterized in that the mixture contains tert-butylhydroxytoluene or hydroquinone monomethyl ether as an antioxidant.

6. Use according to one of claims 1 to 5, characterized in that the mixture contains:

60-97% by weight of component A) and / or

1 - 30% by weight of component B) and / or

0.5-20% by weight of component C) and / or

0.01-2% by weight of component D).

7. Use according to one of claims 1 to 5, characterized in that the mixture contains:

70-95% by weight of components A) and / or

2-25% by weight of components B) and / or

1 - 10% by weight of components C) and / or

0.02-1% by weight of components D).

8. Use according to at least one of claims 1 to 7, characterized in that the weight ratio of component B) to de component C) is in the range from 6: 1 to 1: 3.

9. fuel gas with a methane content of at least 60 wt .-%, containing a mixture as defined in any one of claims 1 to 8.

10. Fuel gas according to claim 9, characterized in that the fuel gas is natural gas.

11. A method for odorizing fuel gas with a methane content of at least 60% by weight, characterized in that a mixture is added to the fuel gas as defined in one of claims 1-8.

12. The method according to claim 11, characterized in that the mixture is added to the fuel gas in an amount of 5 - 100 mg / m ³ gas.