Method of increasing the oxidation stability of biodiesel

Abstract

The invention relates to a method of increasing the oxidation stability of biodiesel, which comprises adding a primary antioxidant having a melting point of less than or equal to 40° C. to the biodiesel to be stabilized in an amount of from 10 to 20 000 ppm (w/w), where the primary antioxidant comprises at least one compound having the structure where: R 1 , R 2 =hydrogen, a linear alkyl group having from 1 to 20 carbon atoms or where * is a carbon atom of the aromatic ring system, R 3 , R 5 =hydrogen, a linear alkyl group having from 1 to 20 carbon atoms, R 4 =hydrogen, a linear alkyl group having from 1 to 40 carbon atoms, where both the substituents of the type R 1 and R 2 and those of the type R 3 and R 5 are in each case identical or different.

1 . A method of increasing the oxidation stability of biodiesel, comprising: adding a primary antioxidant having a melting point of less than or equal to 40° C. to a biodiesel in an amount of from 10 to 20 000 ppm (w/w), wherein the primary antioxidant comprises at least one compound having the structure  
     
       
         
         
             
             
         
       
     
     wherein 
 R 1 , R 2 =hydrogen, a linear alkyl group having from 1 to 20 carbon atoms or  
                     
 wherein * is a carbon atom of the aromatic ring system,  
 R 3 , R 5 =hydrogen, a linear alkyl group having from 1 to 20 carbon atoms,  
 R 4 =hydrogen, a linear alkyl group having from 1 to 40 carbon atoms,  
 wherein both R 1  and R 2  and R 3  and R 5  are in each case identical or different.  
 
   
   
       2 . The method as claimed in  claim 1 , wherein the primary antioxidant comprising from 0.1 to 99.9% by weight of one or more compounds having the structure I is used as primary antioxidant.  
   
   
       3 . The method as claimed in  claim 1 , wherein a mixture comprising exclusively compounds having the structure I is used as the primary antioxidant.  
   
   
       4 . The method as claimed in  claim 1 , wherein the primary antioxidant comprises at least one compound having the structure  
     
       
         
         
             
             
         
       
     
   
   
       5 . The method as claimed in  claim 1 , wherein the primary antioxidant comprises at least one compound having the structure  
     
       
         
         
             
             
         
       
     
   
   
       6 . The method as claimed in  claim 1 , wherein the compound represented by structure I is added in the form of a liquid.  
   
   
       7 . The method as claimed in  claim 1 , wherein the primary antioxidant comprises at least one member selected from the group consisting of tri-tert-butylphenols, di-tert-butylphenols, di-tert-butylmethylphenols, tert-butylmethylphenols, tert-butyldimethylphenols, tert-butylphenols, di-sec-butylphenols, sec-butylphenols, tert-amylphenols and di-tert-amylphenols.  
   
   
       8 . The method as claimed in  claim 1 , wherein the primary antioxidant comprises at least one member selected from the group consisting of 2,4,6-tri-tert-butylphenol, 2,4-di-tert-butylphenol, 2,5-di-tert-butylphenol, 2,6-di-tert-butylphenol, 2,5-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-methylphenol, 4,6-di-tert-butyl-2-methylphenol, di-tert-butyl-3-methylphenol, 2-tert-butyl-4-methylphenol, 6-tert-butyl -2-methylphenol, 4-tert-butyl-2-methylphenol, 6-tert-butyl-3-methylphenol, 4-tert -butyl-2,6-dimethylphenol, 6-tert-butyl-2,4-dimethylphenol, tert-butyl-2,5-dimethylphenol, 2-tert-butylphenol, 4-tert-butylphenol, 2-sec-butylphenol, 2-sec -butyl-4-tert-butylphenol, 4-sec-butyl-2,6-di-tert-butylphenol, 2-tert-amylphenol, 2,4-di-tert-amylphenol, 2-isopropylphenol, 4-octylphenol, 4-nonylphenol, 2,6-di-tert -butyl-4-nonylphenol, 4-dodecylphenol and octadecylphenol.  
   
   
       9 . The method as claimed in  claim 1 , in which a secondary antioxidant is added to the biodiesel.  
   
   
       10 . The method as claimed in  claim 9 , wherein the secondary antioxidant comprises at least one member selected from the group consisting of alkylthiomethylphenols, hydroxylated diphenyl thioethers, phosphates and phosphonites and peroxide-destroying compounds  
   
   
       11 . The method as claimed in  claim 9 , wherein the secondary antioxidant comprises at least one member selected from the group consisting of 2,4-di((octylthio)methyl)-6-tert-butylphenol, 2,4-di((octylthio)methyl)-6-methylphenol, 2,4-di((octylthio)methyl)-6-ethylphenol, 2,6-di((dodecylthio)methyl)-4-nonylphenol, 2,2′-thiobis[6-tert-butyl-4-methylphenol], 2,2′-thiobis[4-octylphenol], 4,4′-thiobis[6-tert-butyl-3-methylphenol], 4,4′-thiobis[6-tert-butyl-2-methylphenol], 4,4′-thiobis[3,6-di-sec-amylphenol], 4,4′-bis[2,6-dimethyl-4-hydroxyphenyl]disulfide, triphenyl phosphite, diphenyl alkyl phosphites, phenyl dialkyl phosphites, tris[nonylphenyl] phosphite, trilauryl phosphite, trioctadecyl phosphite, distearyl pentaerythrityl diphosphite, tris[2,4-di-tert-butylphenyl] phosphite, diisodecyl pentaerythrityl diphosphite, bis[2,4-di-tert-butylphenyl] pentaerythrityl diphosphite, bis[2,6-di-tert-butyl-4-methylphenyl] pentaerythrityl diphosphite, bis[isodecyloxy] pentaerythrityl diphosphite, bis[2,4-di-tert-butyl-6-methylphenyl] pentaerythrityl diphosphite, bis[2,4,6-tri-tert-butylphenyl] pentaerythrityl diphosphite, tristearyl sorbitol triphosphite, tetrakis[2,4-di-tert-butylphenyl] 4,4′-biphenylenediphosphonite, 6-isooctyloxy-2,4,8,10-tetra-tert-butyl-12H-dibenzo[d,g]-1,3,2-dioxaphosphocine, 6-fluoro-2,4,8,10-tetra-tert-butyl-12-methyldibenzo[d,g]-1,3,2-dioxaphosphocine, bis[2,4-di-tert-butyl-6-methylphenyl] methyl phosphate, bis[2,4-di-tert-butyl-6-methylphenyl] ethyl phosphite, esters of β-thiodipropionic acid, mercaptobenzimidazole, the zinc salt of 2-mercaptobenzimidazole, zinc dibutyldithiocarbamate, dioctadecyl disulfide and pentaerythrityl tetrakis[β-dodecylmercapto]propionate.  
   
   
       12 . The method as claimed in  claim 1 , wherein the biodiesel comprises a saturated and/or unsaturated alkyl ester of a fatty acid.  
   
   
       13 . The method as claimed in  claim 1 , wherein the biodiesel comprises a mixture of a saturated and/or unsaturated fatty acid alkyl ester with a liquid energy carrier.  
   
   
       14 . The method as claimed in  claim 1 , wherein the primary antioxidant is added in an amount of from 50 to 12 000 ppm (w/w).  
   
   
       15 . The method as claimed in  claim 1 , wherein the primary antioxidant is added in an amount of from 100 to 8000 ppm (w/w).  
   
   
       16 . The method as claimed in  claim 1 , wherein the primary antioxidant is added to the biodiesel at a temperature of from 18° C. to 60° C.  
   
   
       17 . The method as claimed in  claim 1 , wherein the primary antioxidant is added to the biodiesel at a temperature of from 20° C. to 40° C.  
   
   
       18 . An oxidation-stabilized biodiesel, comprising: 
 from 10 to 20 000 ppm (w/w) of a primary antioxidant which has a melting point of less than or equal to 40° C. and comprises at least one compound having the structure                          wherein    R 1 , R 2 =hydrogen, a linear alkyl group having from 1 to 20 carbon atoms or                          wherein * is a carbon atom of the aromatic ring system,    R 3 , R 5 =hydrogen, a linear alkyl group having from 1 to 20 carbon atoms,    R 4 =hydrogen, a linear alkyl group having from 1 to 40 carbon atoms,    wherein both R 1  and R 2  and R 3  and R 5  are in each case identical or different.    
   
   
       19 . The method as claimed in  claim 1 , wherein the primary antioxidant comprising from 0.1 to 99.9% by weight of one or more compounds having the structure I is used as primary antioxidant.  
   
   
       20 . The biodiesel as claimed in  claim 18 , wherein a mixture comprising exclusively compounds having the structure I is used as the primary antioxidant.  
   
   
       21 . The biodiesel as claimed in  claim 18 , wherein the primary antioxidant comprises at least one compound having the structure  
     
       
         
         
             
             
         
       
     
   
   
       22 . The biodiesel as claimed in  claim 18 , wherein the primary antioxidant comprises at least one compound having the structure  
     
       
         
         
             
             
         
       
     
   
   
       23 . The biodiesel as claimed in  claim 18 , wherein the primary antioxidant comprises at least one member selected from the group consisting of tri-tert -butylphenols, di-tert-butylphenols, di-tert-butylmethylphenols, tert -butylmethylphenols, tert-butyldimethylphenols, tert-butylphenols, di-sec -butylphenols, sec-butylphenols, tert-amylphenols and di-tert-amylphenols.  
   
   
       24 . The biodiesel as claimed in  claim 18 , wherein the primary antioxidant comprises at least one member selected from the group consisting of 2,4,6-tri-tert -butylphenol, 2,4-di-tert-butylphenol, 2,5-di-tert-butylphenol, 2,6-di-tert-butylphenol, 2,5-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-methylphenol, 4,6-di-tert-butyl -2-methylphenol, di-tert-butyl-3-methylphenol, 2-tert-butyl-4-methylphenol, 6-tert -butyl-2-methylphenol, 4-tert-butyl-2-methylphenol, 6-tert-butyl-3-methylphenol, 4-tert-butyl-2,6-dimethylphenol, 6-tert-butyl-2,4-dimethylphenol, tert-butyl-2,5-dimethylphenol, 2-tert-butylphenol, 4-tert-butylphenol, 2-sec-butylphenol, 2-sec -butyl-4-tert-butylphenol, 4-sec-butyl-2,6-di-tert-butylphenol, 2-tert-amylphenol, 2,4-di-tert-amylphenol, 2-isopropylphenol, 4-octylphenol, 4-nonylphenol, 2,6-di-tert -butyl-4-nonylphenol and 4-dodecylphenol and octadecylphenol.  
   
   
       25 . The biodiesel as claimed in  claim 18 , further comprising a secondary antioxidant.  
   
   
       26 . The biodiesel as claimed in  claim 25 , wherein the secondary antioxidant comprises at least one member selected from the group consisting of alkylthiomethylphenols, hydroxylated diphenyl thioethers, phosphates, phosphonites and peroxide-destroying compounds  
   
   
       27 . The biodiesel as claimed in  claim 25 , wherein the secondary antioxidant comprises at least one member selected from the group consisting of 2,4-di((octylthio)methyl)-6-tert-butylphenol, 2,4-di((octylthio)methyl)-6-methylphenol, 2,4-di((octylthio)methyl)-6-ethylphenol, 2,6-di((dodecylthio)methyl)-4-nonylphenol, 2,2′-thiobis[6-tert-butyl-4-methylphenol], 2,2′-thiobis[4-octylphenol], 4,4′-thiobis[6-tert-butyl-3-methylphenol], 4,4′-thiobis[6-tert-butyl-2-methylphenol], 4,4′-thiobis[3,6-di-sec-amylphenol], 4,4′-bis[2,6-dimethyl-4-hydroxyphenyl]disulfide, triphenyl phosphite, diphenyl alkyl phosphites, phenyl dialkyl phosphites, tris[nonylphenyl] phosphite, trilauryl phosphite, trioctadecyl phosphite, distearyl pentaerythrityl diphosphite, tris[2,4-di-tert-butylphenyl] phosphite, diisodecyl pentaerythrityl diphosphite, bis[2,4-di-tert-butylphenyl] pentaerythrityl diphosphite, bis[2,6-di-tert-butyl-4-methylphenyl] pentaerythrityl diphosphite, bis[isodecyloxy] pentaerythrityl diphosphite, bis[2,4-di-tert-butyl-6-methylphenyl] pentaerythrityl diphosphite, bis[2,4,6-tri-tert-butylphenyl] pentaerythrityl diphosphite, tristearyl sorbitol triphosphite, tetrakis[2,4-di-tert-butylphenyl] 4,4′-biphenylenediphosphonite, 6-isooctyloxy-2,4,8,10-tetra-tert-butyl-12H-dibenzo[d,g]-1,3,2-dioxaphosphocine, 6-fluoro-2,4,8,10-tetra-tert-butyl-12-methyldibenzo[d,g]-1,3,2-dioxaphosphocine, bis[2,4-di-tert-butyl-6-methylphenyl] methyl phosphate, bis[2,4-di-tert-butyl-6-methylphenyl] ethyl phosphite, esters of β-thiodipropionic acid, mercaptobenzimidazole, the zinc salt of 2-mercaptobenzimidazole, zinc dibutyldithiocarbamate, dioctadecyl disulfide and pentaerythrityl tetrakis[β-dodecylmercapto]propionate.  
   
   
       28 . The biodiesel as claimed in  claim 18 , which comprises a saturated and/or unsaturated alkyl ester of a fatty acid.  
   
   
       29 . The biodiesel as claimed in  claim 18 , which comprises a saturated and/or unsaturated fatty acid alkyl ester and a liquid energy carrier.  
   
   
       30 . The biodiesel as claimed in  claim 18 , which comprises the primary antioxidant in an amount of from 50 to 12 000 ppm (w/w).  
   
   
       31 . The biodiesel as claimed in  claim 18 , which comprises the primary antioxidant in an amount of from 100 to 8000 ppm (w/w).