EP1694801B1 - Odorisation of fuel gas with low-sulphur content odorisers - Google Patents

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

The present invention relates to the use of an alkyl acrylate mixture containing a small proportion of a sulfur-containing compound and a further component for odorizing fuel gas, a method for odorizing fuel gas and fuel gas containing this mixture.

The city and coke oven gas previously used for public gas supply contained intensely smelling components and therefore had a strong odor, so that escaping gas could be easily perceived.

By gas odorization is meant the addition of odorous, acting as warning or alarm substances (odorants) to gases that have no significant odor, i. to otherwise substantially or completely odorless gases.

Natural gas consists mainly of methane (typical methane contents are in the range 50 to 99 wt .-%, usually in the range 60 to 99 wt .-% and usually 80 to 99 wt .-%) and may, depending on the origin, besides different shares Containing ethane, propane and higher molecular weight hydrocarbons. Natural gas H (H = high) has a methane content of 87 to 99.1% by volume, natural gas L (L = low) generally contains 79.8 to 87% by volume of methane.

Due to its high degree of purity, the gas currently used in the public grid, usually made from natural gas, is virtually odorless in itself.

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

For safety reasons, gas is therefore odorized by the addition of odorous substances. For example, in Germany it is mandatory that all gases that do not have a sufficient odor and are distributed in the public gas supply are odorized according to the DVGW Code of Practice G 280 (DVGW = German Association of Gas and Water). These odorants are also perceptible in high dilution and call due to their exceptionally unpleasant odor as desired, an alarm association in humans. The odorant must not only smell unpleasant and unmistakable, but above all clearly represent a warning smell. Therefore, the odor of the odorized gas must not be familiar to people from everyday life, eg from the kitchen and household. In Germany, about 90% of the service gas is currently odorized with tetrahydrothiophene (THT) (12-25 mg / m ³ ); In addition, the odorization with mercaptans is also common.

It may be useful to add a higher 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 as compared to conventional odorization. The shock odorization is used, for example, when commissioning new networks or line sections for faster achievement of minimum odorant concentration or to detect small leaks in the gas installation.

THT alone is ideal for reliable odorization of gas. In the course of a more sensitive approach to the environment, however, it should be noted that in the combustion of such odorized gases to a greater extent incurred sulfur oxides as combustion products.

Since a reduction or avoidance of sulfur compounds is sought, 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 odorant properties for fuel gases and have practically no significance in this respect. The document describes and claims allyl acrylate as an effective odorizing component.

US 4,487,613 discloses the use of a blend containing methyl acrylate, mertaptans and, for example, acetaldehyde as the odorant.

In JP-A 55-104393 is described 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-butylmercaptan, to Odoration of fuel gases are suitable. The amount of odorant is 50 ppm by weight (mg / kg gas), preferably greater than or equal to 100 ppm. The best results for LPG were obtained with mixtures comprising TBM. By adding 2-butyne (50 ppm) to a mixture of methyl acrylate (50 ppm), allyl acrylate (100 ppm) and TBM (5 ppm), a better odor effect was achieved. The best result was a mixture of 2-butyne (50 ppm), allyl methacrylate (20 ppm), methyl acrylate (20 ppm), methyl n-butyrate (20 ppm), methyl isobutyrate (20 ppm), ethyl propionate (20 ppm) and TBM (5 ppm).

In JP-B-51-034841 "odor thresholds" of various substances were determined, with n-valeric acid, n-butyric acid, isobutyraldehyde and various methylamines having low odor odor thresholds. Ethyl acrylate or n-valeric acid used alone, due to their odor properties, did not have sufficient odor. 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 wt .-%) and tert-butyl mercaptan (30 wt .-%) are made JP-B 51-021402 known. This mixture was added to a gaseous fuel gas in an amount of 5 mg / m ³ .

Odorants for the odorization of hot gases consisting of a) 30-70 wt .-% C ₁ -C ₄ -Alkylmercaptanen, b) 10-30 wt .-% n-valeraldehyde and / or isovaleraldehyde, n-butyric acid and / or isobutyric acid and optionally c) up to 60% by weight of tetrahydrothiophene are in DE-A 31 51 215 described. These odorants were added to heating gas in amounts of 5-40 mg / m ³ .

Mixtures comprising 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 for odorization of fuel gases are out JP-A 61-223094 known. These mixtures had a smell of tertiary butyl mercaptan associated with the smell of city gas.

The use of norbornene derivatives for fuel gas odorization is out JP-A 55056190 known. LPG was mixed at 40 mg / kg with a mixture of equal parts of 5-ethylidene-2-norbornene and 5-vinyl-2-norbornene and 50 mg / kg with a mixture of 80% by weight of 5-ethylidene-2 norbornene and 20 wt .-% ethyl acrylate.

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

Mixtures of C ₄ -C ₇ aldehydes and sulfur compounds are used as odorants in JP-A 50-126004 described. The odorization of 1 kg of propane was carried out with 50 mg of a mixture of 60% by weight of valeraldehyde and 40% by weight of n-butylmercaptan. Valeraldehyde intensifies the smell of n-butylmercaptan. Similarly, 2-methylvaleraldehyde was used.

In DE-A 19837066 the problem of sulfur-free gas odorization has been solved by means of mixtures containing at least one acrylic acid C ₁ -C ₁₂ -alkyl ester and a nitrogen compound having a boiling point in the range 90 to 210 ° C and a molecular weight of 80 to 160, mixtures containing at least two different alkyl acrylates, are preferred. Particularly suitable nitrogen compounds are described as being alkyl-substituted 1,4-pyrazines.

The fact that antioxidants, in particular phenol derivatives, are suitable for stabilizing mercaptan-containing or alkyl acrylate-containing gas odorants, is lacking US-A 2,430,050 respectively. DE-A 198 37 066 known.

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

The present invention is the use of a mixture for the odorization of fuel gases with a methane content of at least 60 wt .-%, according to claim 1.

The invention also relates to a corresponding method for the odorization of fuel gases with a methane content of at least 60 wt .-% with he inventively used mixtures. Here, a mixture to be used according to the invention is added to the fuel gas. With regard to preferred embodiments, compare the details of the preferred uses, which apply accordingly.

Another object of the present invention are fuel gases with a methane content of at least 60 wt .-% 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 of at least 70% by weight and more preferably of at least 75% by weight.

The preferred weight ratio of low molecular weight alkyl acrylate to relatively high molecular weight alkyl acrylate 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. Most preferably, the weight ratio of low molecular weight alkyl acrylate to higher molecular weight alkyl acrylate in the range 1: 1 -1: 3.

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

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, isohexyl mercaptan, sec-hexyl mercaptan , Neohexyl mercaptan, tert-hexyl mercaptan, n-heptyl mercaptan, isoheptyl mercaptan, sec-heptyl mercaptan, tert-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, C ₁ -C ₄ alkyl and / or alkoxy groups. The thiophenes may also be hydrogenated thiophenes, with tetrahydrothiophene being preferred.

The sulfides may 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 isobutyl isopropyl sulfide. Preferred are dimethylsulfide, diethylsulfide, di-n-propylsulfide, diisopropylsulfide, di-n-butylsulfide and diisobutylsulfide.

The disulfides may be, for example, dimethyl disulfide, diethyl disulfide, di-n-propyl disulfide, diisopropyl disulfide, di-n-butyl disulfide, diisobutyl disulfide, ethyl methyl disulfide, methyl n-propyl disulfide, methyl isopropyl disulfide, methyl isobutyl disulfide, ethyl isopropyl disulfide or isobutyl isopropyl disulfide. Preferred are dimethyl disulfide, diethyl disulfide, di-n-propyl disulfide, diisopropyl disulfide, di-n-butyl disulfide and diisobutyl disulfide.

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 Wt .-%, contained.

The norbornenes are advantageously those having a molecular weight of less than or equal to 130, preferred are norbornene, 2,5-norbornadiene, 5-ethylidene-2-norbornene and 5-vinyl-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, isocaproic aldehyde or 2-methylvaleraldehyde.

The phenols are advantageously substituted phenols having a total of one or two C ₁ -C ₄ -alkyl and / or C ₁ -C 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. Particularly preferred are C ₁ -C ₄ -monoalkylated phenols.

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. Preference is given to pyrazines having a total of one to three, particularly preferably a total of one or two, C ₁ -C ₄ -alkyl and / or C ₁ -C ₄ -acyl groups.

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

The compounds from group C) are typically present in the mixtures to be used according to the invention at 0.5-20% by weight, advantageously at 1-10% by weight, preferably at 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 from 5: 1 to 1: 2 and particularly preferably 4: 1 to 1: 1, is advantageous.

The odorants to be used according to the invention may be added to or added to conventional antioxidants as component D), for example to increase the stability. Examples include vitamin C and derivatives (eg ascorbyl palmitate, ascorbyl acetate), tocopherols and derivatives (eg vitamin E, vitamin E acetate), vitamin A and derivatives (vitamin A - palmitate) phenolic benzylamines, formic acid, acetic acid, benzoic acid, sorbic acid, Hexamethylenetetramine, tert-butylhydroxytoluene, tert-butylhydroxyanisole, α-hydroxy acids (eg, citric acid, lactic acid, malic acid), hydroquinone monomethyl ether. Preferred antioxidants are tert-butylhydroxytoluene (BHT, Jonol), tert-butylhydroxyanisole and hydroquinone monomethyl ether.

By adding antioxidants, in particular a high storage stability of the mixtures according to the invention to be used as well as the odorized natural gas is achieved. Storage stability tests have shown that the warning odor 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 odorizing agents according to the invention, tert-butylhydroxytoluene and hydroquinone monomethyl ether have proven to be particularly effective and readily stabilizing.

It can be added to an odorant also several antioxidants. Advantageously, the odorants contain one, two or three antioxidants, preferably one or two antioxidants.

The total amount of antioxidants (component D) in the odorant is usually in the range from 0.01 to 2% by weight, preferably in the range from 0.02 to 1% by weight, more preferably in the range from 0.03 to 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 , more preferably 10-40 mg / m ³ and most preferably 12-30 mg / m ³ .

The warning smell of an odorized natural gas according to the invention was clearly perceived by a panel of investigators 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 odor was achieved in comparison to mixtures which contained only components A) and B), see also the examples below.

1. A) Acrylsäuremethylester und Acrylsäureethylester;
2. B) mindestens eine Verbindung aus der Gruppe Thiophen, Tetrahydrothiophen, Dimethylsulfid, Diethylsulfid, Di-n-propylsulfid, Diisopropylsulfid, Dimethyldisulfid, Diethyldisulfid, Di-n-propyldisulfid, Diisopropyldisulfid oder der Mercaptane der Formel (I)
   
   wobei
   R¹ Wasserstoff, Methyl oder Ethyl, bevorzugt Methyl, und
   R² eine Alkylgruppe mit 1 bis 4 Kohlenstoffatomen, bevorzugt Methyl, Ethyl, iso-Propyl, iso-Butyl oder tert.-Butyl bedeutet;
3. C) mindestens eine Verbindung aus der Gruppe der C₂-C₅-Carbonsäuren, der C₃-C₅-Aldehyde, der C₁-C₄-monoalkylierten Phenole;
4. D) mindestens ein Antioxidans.

The present invention is the use of mixtures containing

1. A) methyl acrylate and ethyl acrylate;
2. 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 is} an alkyl group having 1 to 4 carbon atoms, preferably methyl, ethyl, iso-propyl, iso-butyl or tert-butyl;
3. C) at least one compound selected from the group consisting of C ₂ -C ₅ -carboxylic acids, C ₃ -C ₅ -aldehydes, C ₁ -C ₄ -monoalkylated phenols;
4. D) at least one antioxidant.

Preferred components B) here are the mercaptans of the formula (I).

1. A) Acrylsäuremethylester und Acrylsäureethylester;
2. B) tert.-Butylmercaptan;
3. C) mindestens einer Verbindung aus der Gruppe Propionaldehyd, Isovaleraldehyd, Isovaleriansäure, 2-Ethylphenol, 4-Ethylphenol;
4. D) ein oder zwei Antioxidantien.

Very particularly preferred is the use of mixtures containing or consisting of

1. A) methyl acrylate and ethyl acrylate;
2. B) tert-butylmercaptan;
3. C) at least one compound selected from the group consisting of propionaldehyde, isovaleraldehyde, isovaleric acid, 2-ethylphenol, 4-ethylphenol;
4. D) one or two antioxidants.

With these mixtures, the best odorization of the gas was achieved, the warning smell was most pronounced and was clearly perceived.

The most preferred compound of group C) is isovaleric acid, the most preferred antioxidants of group D) are hydroquinone monomethyl ether and tertiary butyl hydroxytoluene.

The processes according to the invention correspond to the uses according to the invention, in particular with regard to the preferred embodiments. Other aspects of the invention will be apparent from the appended claims.

The following examples illustrate the invention:

Unless otherwise indicated, all data are by weight.

It means:

MeAc: methyl acrylate; EtAc: ethyl acrylate; TBM: tert-butylmercaptan; IVS: isovaleric acid; BHT: tert-butylhydroxytoluene.

example 1

Components A), B) and C) odorants to be used according to the invention were odorous as individual substances in concentrations of 10, 25 and 50 mg / m ³ natural gas (natural gas L, methane content: about 85% by volume) with respect to their warning odor and their warning intensity against unodorated natural gas (blank value). These concentrations correspond to the typical concentrations of odorant in natural gas under normal conditions or in shock odorization. Odorated natural gas containing the same concentrations of THT was used as a reference.

The experiment was carried out at room temperature (about 20 ° C) such that in a gas stream in a tube, the odorant is metered. At the end of this 2 m long tube (within the tube is the homogenization), the exiting odorized gas is evaluated by a group of trained examiners (8 to 12 people) odor. The rating was on a scale from 1 (very weak / very little warning) to 10 (very strong / very warning), the values given are mean values. The industry standard THT was given the value 10.

The results were essentially the same for the 3 concentrations tested (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: material material MeAc EtAc rating tetrahydrothiophene 100 - - 10 ethyl acrylate - 100 5 methyl acrylate 100 - 4.5 Acrylic acid-n-butyl ester 100 - - 3.5 tert-butyl 100 - - 7 propionaldehyde 100 - - 3 isovaleric 100 - - 3.5 isovaleraldehyde 100 - - 3.5 2-ethylphenol 100 - - 3 4-ethylphenol 100 - - 3

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

Example 2

Table 2 shows the evaluations for mixtures of two compounds of the component type A) with TBM = tert-butylmercaptan (methylpropanethiol-2,2) as component B); the procedure was carried out as described in Example 1. Table 2: EtAc MeAc TBM rating 60.0 40.0 - 6 60.0 39.0 1.0 7 60.0 37.5 2.5 7 60.0 35.0 5.0 7 60.0 32.5 7.5 8th 60.0 30.0 10.0 8th 55.0 30.0 15.0 7 55.0 25.0 20.0 7 50.0 25.0 25.0 7

From Table 2 it can be seen that the addition of TBM caused an improved odorizing performance, although still no very good odorization was possible.

Example 3

Table 3 shows the evaluations for mixtures of two compounds of the component type A) with IVS = isovaleric acid as component C); the procedure was carried out as described in Example 1. Table 3: EtAc MeAc IVS rating 60.0 39.0 1.0 7 60.0 37.5 2.5 8th 60.0 35.0 5.0 8th 60.0 32.5 7.5 7 60.0 30.0 10.0 7 55.0 30.0 15.0 7 55.0 25.0 20.0 6 50.0 25.0 25.0 6

From Table 3 it can be seen that the addition of IVS caused an improved odorizing performance, although still no very good odorization was possible.

Example 4

Table 4 shows the evaluations for mixtures of two compounds of the component type A) with TBM = tert-butylmercaptan as component B) and IVS = isovaleric acid as component C); the procedure was carried out as described in Example 1. Table 4: EtAc MeAc TBM IVS rating 60.0 36.5 2.5 1.0 8th 60.0 32.5 2.5 5.0 8.5 60.0 34.0 5.0 1.0 8.5 60.0 31.0 5.0 4.0 9 60.0 30.0 5.0 5.0 9 60.0 29.0 5.0 6.0 8.5 60.0 33,0 6.0 1.0 9 60.0 31.0 6.0 3.0 10 60.0 29.0 6.0 5.0 9 55.0 31.0 6.0 8.0 8.5 60.0 32.0 7.0 1.0 9 60.0 31.0 7.0 2.0 10 60.0 30.0 7.0 3.0 10 60.0 29.0 7.0 4.0 10 60.0 28.0 7.0 5.0 9 60.0 31.0 8.0 1.0 8.5 60.0 29.0 8.0 3.0 9 60.0 28.0 8.0 4.0 9.5 55.0 30.0 8.0 7.0 8.5 60.0 30.0 9.0 1.0 8.5 60.0 28.0 9.0 3.0 9 60.0 27.0 9.0 4.0 9 60.0 26.0 9.0 5.0 9 55.0 29.0 9.0 7.0 8.5 60.0 29.0 10.0 1.0 8th 60.0 26.0 10.0 4.0 8.5 60.0 25.0 10.0 5.0 9 55.0 29.0 10.0 6.0 9 60.0 26.0 12.0 2.0 8.5 55.0 29.0 12.0 4.0 9 55.0 28.0 12.0 5.0 9 55.0 27.0 12.0 6.0 8.5

Table 4 shows that the use of mixtures of components A), B) and C) causes excellent odorizing performance.

Example 5

To assess storage stability, odorants containing various antioxidants were added to natural gas L and the odorized natural gas was odourously tested after certain periods of time at 40 ° C. storage as described in Example 1. The criterion for storage stability was the significant odor match of the stored odorant or stored odorized gas 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: antioxidant y% storage stability no antioxidant - a BHT 0.05 b BHT 0.10 d BHT 0.30 d BHT 0.50 d BHT 1.00 b hydroquinone 0.05 d hydroquinone 0.10 d hydroquinone 0.30 c hydroquinone 0.50 c hydroquinone 1.00 c

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

Claims (10)

1. Use of a mixture containing

   A) acrylic acid methyl ester and acrylic acid ethyl ester;

   B) at least one compound from the group 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 formula (I)

   

   wherein
   R¹ denotes hydrogen, methyl or ethyl, preferably methyl, and
   R² denotes an alkyl group having from 1 to 4 carbon atoms, preferably methyl, ethyl, isopropyl, isobutyl or tert-butyl;

   C) at least one compound from the group of the C₂-C₅-carboxylic acids, C₃-C₅-aldehydes, C₁-C₄-monoalkylated phenols, and

   D) at least one antioxidant
   for the odorisation of fuel gas having a methane content of at least 60 wt.%.
2. Use according to claim 1, wherein the mixture comprises

   A) acrylic acid methyl ester and acrylic acid ethyl ester;

   B) tert-butylmercaptan;

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

   D) one or two antioxidants

   or consists of these components.
3. Use according to either claim 1 or claim 2, characterised in that the mixture contains tert-butyl-hydroxytoluene or hydroquinone monomethyl ether as antioxidant.
4. Use according to any one of claims 1 to 3, characterised in that the mixture contains:

   from 60 to 97 wt.% of component A) and/or

   from 1 to 30 wt.% of component B) and/or

   from 0.5 to 20 wt.% of component C) and/or

   from 0.01 to 2 wt.% of component D).
5. Use according to any one of claims 1 to 3, characterised in that the mixture contains:

   from 70 to 95 wt.% of component A) and/or

   from 2 to 25 wt.% of component B) and/or

   from 1 to 10 wt.% of component C) and/or

   from 0.02 to 1 wt.% of component D).
6. Use according to at least one of claims 1 to 5, characterised in that the ratio by weight of component B) to component C) is in the range from 6:1 to 1:3.
7. Fuel gas having a methane content of at least 60 wt.%, containing a mixture as defined in any one of claims 1 to 6.
8. Fuel gas according to claim 7, characterised in that the fuel gas is natural gas.
9. Process for the odorisation of fuel gas having a methane content of at least 60 wt.%, characterised in that a mixture as defined in any one of claims 1 to 6 is added to the fuel gas.
10. Process according to claim 9, characterised in that the mixture is added to the fuel gas in a quantity of from 5 to 100 mg/m³ of gas.