Abstract:
A mixture of acrylic acid and nitrogen compounds is particularly adapted to achieve a sulfur-free odorization of a gas.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the odorization of gas. 
     Town and coke-oven gases obtained by thermal processes contained intensely odoriferous components and therefore had a strong intrinsic odor, so that escaping gas could be readily detected. 
     BACKGROUND OF THE INVENTION 
     Because of its origin (natural gas) and a relatively high degree of purity, the gas used nowadays in the public network is in itself virtually odorless; if leakages are not noticed in good time, explosive gas/air mixtures with a high hazard potential quickly form. For safety reasons, gas is therefore odorized by adding odorants. For example, in Germany it is stipulated that all gases which do not have sufficient intrinsic odor and are distributed in the public gas supply (DVGW-Arbeitsblatt [Worksheet] G 260) are odorized in accordance with DVGW-Arbeitsblatt [Worksheet] G 280; DVGW=Deutscher Verein des Gas-und Wasserfaches e.V. [German Association on Gas and Water], Eschborn. These odorizing compositions are detectable even when highly diluted and, because of their extremely unpleasant odor, act, as is desired, as a warning signal for people. In Germany, approximately 90% of service gas is currently odorized with tetrahydrothiophene (THT) (12–25 mg/m 3 ); in addition, odorization using mercaptans or thioethers is also customary. 
     THT and mercaptans are highly suitable for reliable odorization of gas. However, in the context of treating the environment with more respect, it is to be noted that during the combustion of such odorized gases, sulfur dioxide forms as combustion product—only in small amounts at each individual combustion site, but, viewed on a countrywide scale, in amounts of a few hundred tons per year. It would be desirable to overcome this disadvantage; however, a number of requirements have to be satisfied:
     1. The odor must be unpleasant and unmistakable (odors from kitchens and homes are excluded). It must act as a warning signal for people who smell escaped gas.   2. Everybody with an average sense of smell and average physiological condition must be able to detect the odor.   3. The warning odor stage (=average odor intensity) must be achieved before the ignition limit or a kinetic carbon monoxide content is reached.   4. The odorizing composition must be as nontoxic as possible and must not form any toxic combustion products.   5. The odorizing composition must have high volatility and evaporate leaving as little residue as possible.   6. A suitable odorizing composition must not condense at winter temperatures, nor separate, nor adhere to metallic pipes.   7. The odorizing composition must combust without leaving a residue.   8. The odorizing composition must be storage-stable and chemically resistant to the gas and to the plants. It must not promote corrosion, nor attack customary seals.   

     Attempts have already been undertaken to provide new gas odorizing compositions. Thus, the following, for example, have been proposed:
         alkyl acrylates, vinyl or alkyl ethers and mixtures thereof (JP 76-7481),   n-valeric acid, optionally in combination with ethyl acrylate and/or triethylamine (JP 76-34 841),   mixtures of sulfur compounds and aliphatic aldehyde (JP 78-35 562),   cycohexene (JP 83-42 235),   norbornene derivatives (JP 87-1998) and   saturated ethers, saturated esters, and mixtures thereof with mercaptans.       

     SUMMARY OF THE INVENTION 
     It has now been found that, by additions of 
     A. acrylic C 1 –C 12 -, preferably C 1 –C 8 -alkyl, esters, 
     B. nitrogen compounds and optionally 
     C. antioxidants 
     progressively odorized gas is obtained which largely combines the desired properties. The novel odorizing composition can be added to the gas in the same order of magnitude as sulfur-containing compounds and does not produce corrosion-promoting products upon combustion. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The acrylic esters A include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate and dodecyl acrylate. In a preferred embodiment, mixtures of acrylic C 1 –C 6 -alkyl esters are used as component A; a particularly preferred combination comprises methyl acrylate and ethyl acrylate alongside one another. The acrylate mixtures can contain the lower and the higher esters in each case in the weight ratio of from 9:1 to 1:9, preferably 7:3 to 3:7. 
     Preferred nitrogen compounds B include primarily compounds
         with a flash point above 20° C., preferably above 40° C. (measured in accordance with ISO 2719),   with a molecular weight of from 80 to 160, preferably 110 to 145,   with a boiling point of from 90 to 210, preferably 110 to 165° C.       

     The nitrogen compounds B include, for example, 
     lactones, such as caprolactone 
     nitriles, such as 2-nonenenitrile and compounds of the formula 
                                
where
     R 1  to R 4 , independently of one another, are hydrogen or C 1 –C 4 -alkyl, preferably methyl or ethyl.   
     Preferred compounds (I) are e.g. 2-methylpyrazine, 2,3-dimethylpyrazine, 2,6-dimethylpyrazine, 2,3,5-trimethylpyrazine, tetramethylpyrazine, 2-ethylpyrazine, 2,3-diethylpyrazine, 5,2-methylethylpyrazine, 2,3-methylethylpyrazine, 5,2,3-methyldiethylpyrazine and 3,5,2- and 3,6,2-dimethylethylpyrazine, 2,3-methylethylpyrazine and tetramethylpyrazine are preferred. 
     The nitrogen compounds B can be used in amounts of from 1 to 100, preferably 30 to 100, in particular 10 to 50, parts by weight per 1 000 parts by weight of A. 
     To protect against undesired oxidation, the odorizing compositions may comprise antioxidants, as are described, for example, in Römpp-Lexikon Chemie Version 1.3. Preferred antioxidants include butylhydroxyanisole, ionol=tert-butylhydroxytoluene, hydroquinone monomethyl ether and α-tocopherol. 
     The antioxidants C are preferably used in amounts of from 0.01 to 5, in particular 0.05 to 2, especially 0.1 to 1, parts by weight per 1 000 parts by weight of A. 
     Preferred gas odorizing compositions can, for example, have the following compositions: 
     EXAMPLE 1 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Ethyl acrylate 
                 600 g 
               
               
                   
                 Methyl acrylate 
                 360 g 
               
               
                   
                 5,2,3-Methyldiethylpyrazine 
                  39 g 
               
               
                   
                 Ionol 
                  1 g 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE 2 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Ethyl acrylate 
                 535 g 
               
               
                   
                 Methyl acrylate 
                 400 g 
               
               
                   
                 2-Methylpyrazine 
                  64 g 
               
               
                   
                 Ionol 
                  1 g 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE 3 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Ethyl acrylate 
                 320 g 
               
               
                   
                 Methyl acrylate 
                 637 g 
               
               
                   
                 3,5(6),2-Dimethylethylpyrazine 
                  42 g 
               
               
                   
                 Ionol 
                  1 g 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE 4 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Ethyl acrylate 
                 460 g 
               
               
                   
                 Methyl acrylate 
                 460 g 
               
               
                   
                 2,6-Dimethylpyrazine 
                  79 g 
               
               
                   
                 Ionol 
                  1 g 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE 5 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Ethyl acrylate 
                 520 g 
               
               
                   
                 Methyl acrylate 
                 459 g 
               
               
                   
                 2,3,5-Trimethylpyrazine 
                  20 g 
               
               
                   
                 Ionol 
                  1 g 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE 6 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Ethyl acrylate 
                 885 g 
               
               
                   
                 Methyl acrylate 
                 100 g 
               
               
                   
                 2,3-Methylethylpyrazine 
                  14 g 
               
               
                   
                 Ionol 
                  1 g 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE 7 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Ethyl acrylate 
                 700 g 
               
               
                   
                 Methyl acrylate 
                 274 g 
               
               
                   
                 2,3-Dimethylpyrazine 
                  25 g 
               
               
                   
                 Ionol 
                  1 g 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE 8 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Ethyl acrylate 
                 350 g 
               
               
                   
                 Methyl acrylate 
                 600 g 
               
               
                   
                 Tetramethylpyrazine 
                  49 g 
               
               
                   
                 Ionol 
                  1 g 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE 9 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Ethyl acrylate 
                 144 g 
               
               
                   
                 Methyl acrylate 
                 800 g 
               
               
                   
                 2-Ethylpyrazine 
                  56 g 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE 10 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Ethyl acrylate 
                 615 g 
               
               
                   
                 Methyl acrylate 
                 300 g 
               
               
                   
                 5,2-Methylethylpyrazine 
                  85 g 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE 11 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Ethyl acrylate 
                 320 g 
               
               
                   
                 Methyl acrylate 
                 649 g 
               
               
                   
                 3,5(6),2-Dimethylethylpyrazine 
                  15 g 
               
               
                   
                 2,3-Dimethylethylpyrazine 
                  15 g 
               
               
                   
                 Ionol 
                  1 g 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE 12 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Ethyl acrylate 
                 120 g 
               
               
                   
                 Methyl acrylate 
                 807 g 
               
               
                   
                 2-Ethylpyrazine 
                  30 g 
               
               
                   
                 5,2-Methylethylpyrazine 
                  42 g 
               
               
                   
                 Ionol 
                  1 g 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE 13 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Ethyl acrylate 
                 520 g 
               
               
                   
                 Methyl acrylate 
                 434 g 
               
               
                   
                 2,6-Dimethylpyrazine 
                  20 g 
               
               
                   
                 2,3-Methylethylpyrazine 
                  25 g 
               
               
                   
                 Ionol 
                  1 g 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE 14 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Ethyl acrylate 
                 320 g 
               
               
                   
                 Methyl acrylate 
                 633 g 
               
               
                   
                 2,3-Diethylpyrazine 
                  34 g 
               
               
                   
                 2,3-Methylethylpyrazine 
                  12 g 
               
               
                   
                 Ionol 
                  1 g 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE 15 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Ethyl acrylate 
                 759 g 
               
               
                   
                 Methyl acrylate 
                 200 g 
               
               
                   
                 2-Methylpyrazine 
                  30 g 
               
               
                   
                 Tetramethylpyrazine 
                  10 g 
               
               
                   
                 Ionol 
                  1 g