Fatty ester compositions with improved oxidative stability

Abstract

Compositions containing unsaturated fatty esters may be stabilized against atmospheric oxidation by the addition of an antioxidant package containing at least one nitroxide free-radical scavenger and at least one alkylalkanolamine. Compositions treated in this manner show good resistance to atmospheric oxidation and resultant viscosity increase. An advantage of the nitroxide free-radical scavenger is that it stops the oxidation of the unsaturated fatty esters already during the initiation stage. Moreover, it is much less volatile than for example the known alkylhydroxylamine oxygen scavengers. By the use of a nitroxide free-radical scavenger, the composition can thus be stabilized for a longer period of time. The stability period is moreover less affected by the supply of oxygen to the composition. The solubility problem of the nitroxide in the fatty ester component can be solved by dissolving the nitroxide first in the alkylalkanolamine.

1 . A composition comprising:
 a fatty ester component constituting at least 50 wt % of the composition and comprising unsaturated fatty esters; and   at least one alkylalkanolamine,   
       characterised in that 
       the composition further comprises at least one nitroxide free-radical scavenger or a precursor thereof. 
     
     
         2 . The composition as claimed in  claim 1 , which comprises at least one alkylalkanolamine selected from the group consisting of N-alkylalkanolamines, N-alkyldialkanolamines and N-dialkylalkanolamines. 
     
     
         3 . The composition as claimed in  claim 2 , wherein said alkylalkanolamine has the formula (II):
   R 1 R 2 NCH 2 CH 2 OH   
       wherein R 1  is an alkyl group or an isoalkyl group of 3 to 24 carbon atoms and R 2  is —H, —CH 2 , —CH 2 CH 2 OH or —R 1 . 
     
     
         4 . The composition as claimed in  claim 2 , wherein said alkylalkanolamine is selected from the group comprising butyldiethanolamine (BDEA), butylaminoethanol (BAE), dibutylaminoethanol (DBAE), diisopropylaminoethanol (DIPAE), octylaminoethanol (OAE) and octyldiethanolamine (ODEA). 
     
     
         5 . The composition as claimed in  claim 1 , wherein the nitroxide free-radical scavenger has the formula (I): 
       
         
           
           
               
               
           
         
         wherein each of R 1 , R 2  and R 3  and R 4  is an alkyl group or heteroatom substituted alkyl group having 1 to 15 carbon atoms, and wherein 
         R 5  and R 6  (a) each being an alkyl group having 1 to 15 carbon atoms, or a substituted alkyl group having 1 to 15 carbon atoms wherein the substituent is halogen, cyano, —CONH 2 , —SC 6 H 5 , —S—COCH 3 , —OCOCH 3 , —OCOC 2 H 5 , carbonyl, alkenyl wherein the double bond is not conjugated with the nitroxide moiety, or —COOR wherein R of the —COOR group is alkyl or aryl, or (b) together forming part of a ring that contains 4 or 5 carbon atoms and up to two heteratoms of O, N or S. 
       
     
     
         6 . The composition as claimed in  claim 5 , wherein the R 1 , R 2 , R 3  and R 4  groups in formula (I) are each methyl, ethyl or propyl groups. 
     
     
         7 . The composition as claimed in  claim 5 , wherein R 5  and R 6  in formula (I) are each methyl, ethyl or propyl groups. 
     
     
         8 . The composition as claimed in  claim 1 , wherein the nitroxide is a piperidino-1-oxyl, a pyrrolidino-1-oxyl or a pyrrolin-1-oxyl. 
     
     
         9 . The composition as claimed in  claim 8 , wherein the nitroxide is selected from the group consisting of 4-hydroxy-2,2,6,6-tetramethylpiperidino-1-oxy (4-hydroxy TEMPO), 4-oxo-2,2,6,6-tetramethylpiperidino-1-oxy and 2,2,6,6-tetramethylpiperidino-1-oxy (TEMPO), the nitroxide comprising preferably 4-hydroxy-2,2,6,6-tetramethylpiperidino-1-oxy. 
     
     
         10 . The composition as claimed in  claim 1 , wherein the nitroxide is di-tert-butyl-nitroxide. 
     
     
         11 . The composition as claimed in  claim 1 , which contains at least 1 ppm, preferably at least 5 ppm and more preferably at least 10 ppm of said nitroxide. 
     
     
         12 . The composition as claimed in  claim 1 , which contains less than 200 ppm, preferably less than 100 ppm and more preferably less than 50 ppm of said nitroxide. 
     
     
         13 . The composition as claimed in  claim 1 , which contains at least 50 ppm, preferably at least 100 ppm and more preferably at least 200 ppm of said alkylalkanolamine, but preferably less than 10 000 ppm thereof. 
     
     
         14 . The composition as claimed in  claim 1 , wherein the fatty ester component comprises a biodiesel. 
     
     
         15 . The composition as claimed in  4 , wherein the fatty ester component contains at least 10 wt %, preferably at least 25 wt % and more preferably at least 40 wt % of said unsaturated fatty esters. 
     
     
         16 . A method of making a stabilized composition as claimed in  claim 1 , comprising blending together:
 a fatty ester component comprising an unsaturated fatty ester;   at least one alkylalkanolamine; and   a nitroxide free-radical scavenger or precursor thereof.   
     
     
         17 . The method as claimed in  claim 16 , wherein said nitroxide free-radical scavenger is dissolved in said alkylalkanolamine before being blended with said fatty ester component. 
     
     
         18 . The method as claimed in  claim 16 , wherein said nitroxide free-radical scavenger is dissolved in a hydroxylamine, or in a mixture of a hydroxylamine and said alkylalkanolamine, before being blended with said fatty ester component.