Patent Publication Number: US-2010107481-A1

Title: Antioxidant blends for fatty acid methyl esters (biodiesel)

Description:
BACKGROUND 
     As worldwide energy demand continues to increase and reserves of fossil fuels shrink, the diversification of energy sources becomes increasingly important. Biodiesel is one way to achieve diversification. Biodiesel is a generic name for mono-alkyl esters of long-chain fatty acids derived from renewable lipid sources such as vegetable oils, animal fats, or used cooking oils and fats. Biodiesel fuels have many names, depending on the feedstocks used to produce them, for example, fatty acid methyl ester (FAME), rapeseed methyl ester (RME), used vegetable oil methyl ester (UVOME), soybean oil methyl ester (SOME) or palm oil methyl ester (POME). Biodiesel feedstocks vary widely in their fatty acid compositions (chain length and saturation). 
     Biodiesel is typically produced by the reaction of a vegetable oil or an animal fat with an alcohol, such as methanol, in the presence of a catalyst to yield methyl esters (the biodiesel) and glycerine. The most commonly used catalyst, potassium hydroxide, is used in transesterification of a wide range of oils and fats, from vegetable to animal, from virgin to used, including those with the highest acid contents. The thus produced biodiesel can be distilled to remove excess alcohols and other impurities. Other methods for production of biodiesel are known. 
     Freshly produced vegetable oils are protected from oxidation by the presence of naturally occurring antioxidants (for example, tocopherols). However, the manufacturing process for biodiesel tends to remove some of the natural antioxidants, leaving the fuel less protected from oxidative degradation. In addition, distillation of the biodiesel tends to remove essentially all the natural antioxidants leaving the fuel even further unprotected from oxidative degradation. Oxidation of biodiesel by contact with air and metal surfaces results in the formation of hydroperoxides. These induce free-radical chain reactions that lead to decomposition into low-molecular-weight, highly oxidized species (aldehydes, ketones, acids) and high-molecular-weight polymeric materials (gums). These gums tend to cause poor combustion and other engine problems such as deposits on injectors and pistons. The presence of high-molecular weight, insoluble gums generally leads to fuel-filter plugging. 
     The RANCIMAT test is a widely accepted method for measuring the oxidation stability of biodiesel. This test consists of bubbling air through biodiesel that has been heated to 110° C. The amount of short-chain acids present in the distillate (the cleavage products of the fatty acid oxidation) is a direct indication of the oxidation stability of the biodiesel. In Europe and Brazil, biodiesel has to fulfill a six-hour RANCIMAT test requirement at the production plant and at the pump when refueling vehicles, irrespective of the age of the biodiesel. Other countries may institute similar requirements. Although freshly produced biodiesel may show an oxidation stability (measured by the RANCIMAT method) of more than six hours, this value will decrease over time under common storage conditions if no antioxidants are present. 
     Antioxidants are used in hydrocarbon fuels to increase oxidation stability. The oxidation stability of biodiesel can also be increased by the addition of antioxidants. However, given the relative youth of biodiesel fuels as compared to hydrocarbon fuels, antioxidant technology for biodiesel is not as well-developed. 
     Thus, there is a need for improved antioxidant compositions for use in biodiesel fuels and for biodiesel compositions comprising such antioxidant compositions that are economically suited for commercial use. 
     THE INVENTION 
     This invention meets the above-described needs by providing compositions derived from biodiesel, mono- or bis-hindered phenolic derived from 2,6-di-tert-butylphenol, and N,N′-di-substituted para-phenylene diamine, wherein the combined amount of the mono- or bis-hindered phenolic and the N,N′-di-substituted para-phenylene diamine is from about 50 ppm to about 5000 ppm based on the biodiesel. Further, such compositions are provided wherein the biodiesel is crude biodiesel, and wherein the crude biodiesel is derived from soybean oil, canola oil, palm oil, coconut oil, rapeseed oil, corn oil, or used vegetable oil, and wherein the crude biodiesel is a fatty acid methyl ester. Such compositions are provided wherein the biodiesel is distilled biodiesel, and wherein the distilled biodiesel is derived from soybean oil, canola oil, palm oil, coconut oil, rapeseed oil, corn oil, or used vegetable oil. Also, such compositions are provided wherein the combined amount of the mono- or bis-hindered phenolic and the N,N′-di-substituted para-phenylene diamine is from about 100 ppm to 2500 ppm based on the biodiesel. Further, such compositions are provided wherein the ratio of the mono- or bis-hindered phenolic to N′N-di-substituted para-phenylene diamine varies from about 10:1 to about 1:10 by weight, in particular varies from about 5:1 to about 1:5 by weight. Also provided are compositions derived from biodiesel, 2,4,6-tri-tert-butylphenol, and N,N′-di-substituted para-phenylene diamine, wherein the ratio of the 2,4,6-tri-tert-butylphenol to the N,N′-di-substituted para-phenylene diamine varies from about 10:1 to about 1:10 by weight. This invention also provides compositions prepared by combining, or comprising, biodiesel, mono- or bis-hindered phenolic derived from 2,6-di-tert-butylphenol, and N,N′-di-substituted para-phenylene diamine, wherein the combined amount of the mono- or bis-hindered phenolic and the N,N′-di-substituted para-phenylene diamine is from about 50 ppm to about 5000 ppm based on the biodiesel. 
     This invention also provides methods of improving oxidation stability of a composition comprising biodiesel by combining the composition and mono- or bis-hindered phenolic derived from 2,6-di-tert-butylphenol, and N,N′-di-substituted para-phenylene diamine such that the combined amount of the mono- or bis-hindered phenolic and the N,N′-di-substituted para-phenylene diamine is from about 50 ppm to 5000 ppm based on the biodiesel. Also provided are such methods wherein the biodiesel is crude biodiesel, and wherein the crude biodiesel is derived from soybean oil, canola oil, palm oil, coconut oil, rapeseed oil, corn oil, or used vegetable oil, and wherein the crude biodiesel is a fatty acid methyl ester. Also provided are such methods wherein the biodiesel is distilled biodiesel, and wherein the distilled biodiesel is derived from soybean oil, canola oil, palm oil, coconut oil, rapeseed oil, corn oil, or used vegetable oil. Also, such methods are provided wherein the combined amount of the mono- or bis-hindered phenolic and the N,N′-di-substituted para-phenylene diamine is from about 100 ppm to 2500 ppm based on the biodiesel. Further, such methods are provided wherein the ratio of the mono- or bis-hindered phenolic to N′N-di-substituted para-phenylene diamine is varies from about 10:1 to about 1:10 by weight, in particular varies from about 5:1 to about 1:5 by weight. Also provided are methods of improving oxidation stability of a composition comprising biodiesel by combining the composition, 2,4,6-tri-tert-butylphenol, and N,N′-di-substituted para-phenylene diamine, wherein the ratio of the 2,4,6-tri-tert-butylphenol to the N,N′-di-substituted para-phenylene diamine varies from about 5:1 to about 1:5 by weight. 
     In this invention, the mono- or bis-hindered phenolic derived from 2,6-di-tert-butylphenol can comprise ortho-tert-butylphenol, 2,6-di-tert-butylphenol, 2,4,6-tri-tert-butylphenol, 4,4′-methylenebis(2,6-di-tert-butylphenol), 3,5-di-tert-butyl-4-hydroxyphenylhydrocinnamicacid, methyl ester, 3,5-di-tert-butyl-4-hydroxyphenylhydrocinnamicacid, C7-C9 branched alkyl esters, 2,6-di-tert-butyl-alpha-dimethylamino-p-cresol; butylated hydroxytoluene, or 2,4,6-tri-tert-butylphenol; and the N,N′-di-substituted para-phenylene diamine can comprise N,N′-di-sec-butyl-p-phenylenediamine, N,N′-diisopropyl-p-phenylenediamine, or N,N′-bis-(1,4-dimethylpentyl)-p-phenylenediamine. 
     In some of the compositions and/or methods of the present invention, the weight ratio of the 2,4,6-tri-tert-butylphenol to the N,N′-di-substituted para-phenylene diamine is greater than about 1, in some embodiments, greater than about 1.25, and in other embodiments, greater than about 1.5. 
     A glossary of terms is provided prior to the claims. 
     We were surprised to discover the substantial increase in oxidation stability of biodiesel provided by this invention. We did not have reason to expect that the combinations of biodiesels and antioxidants as described and claimed herein would provide the benefits shown by the examples provided herein. 
     Mono or Bis-Hindered Phenolics Derived from 2,6-Di-Tert-Butylphenol 
     Suitable mono or bis-hindered phenolics derived from 2,6-di-tert-butylphenols can comprise 2,6-di-tert-butylphenol (e.g., the product comprising 2,6-di-tert-butylphenol sold under the trademark ETHANOX 4701); 2,4,6-tri-tert-butylphenol; combinations of ortho-tert-butylphenol, 2,6-di-tert-butylphenol, and 2,4,6-tri-tert-butylphenol (e.g., the product comprising ortho-tert-butylphenol, 2,6-di-tert-butylphenol, and 2,4,6-tri-tert-butylphenol sold under the trademark ETHANOX 4733); combinations of 2,6-di-tert-butylphenol and 2,4,6-tri-tert-butylphenol (e.g., the product comprising 2,6-di-tert-butylphenol and 2,4,6-tri-tert-butylphenol sold under the trademark ETHANOX 4735); 4,4′-methylenebis(2,6-di-tert-butylphenol) (e.g., the product comprising 4,4′-methylenebis(2,6-di-tert-butylphenol) sold under the trademark ETHANOX 4702); 3,5-di-tert-butyl-4-hydroxyphenylhydrocinnamicacid, methyl ester (e.g., the product comprising 3,5-di-tert-butyl-4-hydroxyphenylhydrocinnamicacid, methyl ester sold under the trademark ETHANOX 4750); 3,5-di-tert-butyl-4-hydroxyphenylhydrocinnamicacid, C7-C9 branched alkyl esters (e.g., the product comprising 3,5-di-tert-butyl-4-hydroxyphenylhydrocinnamicacid, C7-C9 branched alkyl esters sold under the trademark ETHANOX 4716); 2,6-di-tert-butyl-alpha-dimethylamino-p-cresol (e.g., the product comprising 2,6-di-tert-butyl-alpha-dimethylamino-p-cresol sold under the trademark ETHANOX 4703); butylated hydroxytoluene (BHT); essentially 100% 2,4,6-tri-tert-butylphenol (TTBP), or combinations thereof. In this invention, concentration of the mono or bis-hindered phenolic derived from 2,6-di-tert-butylphenol can be from about 0.0025 wt % to about 0.25 wt % of the total biodiesel. 
     N,N′-Di-Substituted Para-Phenylene Diamines 
     Suitable N,N′-di-substituted para-phenylene diamines can comprise N,N′-di-sec-butyl-p-phenylenediamine (PDA), N,N′-diisopropyl-p-phenylenediamine, N,N′-bis-(1,4-dimethylpentyl)-p-phenylenediamine, or combinations thereof. In this invention, concentration of the N,N′-dis-substituted para-phenylene diamine can be from about 0.0025 wt % to about 0.25 wt % of the total biodiesel. 
     Biodiesels 
     As used herein, unless otherwise distinguished, the term biodiesel comprises crude biodiesel, distilled biodiesel, or any individual chemical component of either. Crude biodiesel comprises 8 carbon to 22 carbon saturated, mono-unsaturated, di-unsaturated, or tri-unsaturated methyl ester, or fatty acid methyl ester derived from a vegetable or animal source. Processes for producing crude biodiesel are well know to those skilled in the art. Example individual chemical components of fatty acid methyl ester include methyl stearate (n-octadecanoic acid, methyl ester), methyl oleate (9-octadecenoic acid, methyl ester), methyl vaccenate (11-octadecenoic acid methyl ester), methyl linoleate (9,12-octadecadienoic acid, methyl ester), or methyl linoleniate (9,12,15-octadecatrienoic acid, methyl ester), caprylic acid methyl ester, capric acid methyl ester, lauric acid methyl ester, myristic acid methyl ester, palmitic acid methyl ester, arachidic acid methyl ester, behenic acid methyl ester, lauroleic acid methyl ester, myristoleic acid methyl ester, palmitoleic acid methyl ester, elaidic acid methyl ester, gadoleic acid methyl ester, arachidonic acid methyl ester, erucic acid methyl ester, and the like. 
     Distilled biodiesel comprises crude biodiesel that has been subjected to at least one distillation step, e.g., to remove excess alcohols, residual glycerine, and other impurities, and includes biodiesel obtained as a specific cut or fraction produced during the distillation of crude biodiesel. Methods of distilling crude biodiesel are well known to those skilled in the art. 
     Crude biodiesel can be derived from any suitable vegetable or animal source, including for example soybean oil, low erucic acid rapeseed oil (Canola Oil), high erucic acid rapeseed oil, palm oil, used cooking oil, vegetable oil, coconut oil, corn oil, cottonseed oil, safflower oil, sunflower oil, peanut oil, sugar cane oil, lard, tallow, poultry fat, yellow grease, and the like. Fatty acid methyl ester in crude biodiesel can be produced, e.g., by a transesterification reaction between a vegetable or animal based triglyceride and methanol using a catalyst, as is familiar to those skilled in the art. 
     Crude biodiesel or distilled biodiesel can be subjected to additional chemical treatment, e.g., to reduce unsaturation. 
     Combinations 
     Compositions according to this invention comprising, or prepared by combining, biodiesel, mono or bis-hindered phenolic derived from 2,6-di-tert-butylphenol (component (2)), and N,N′-di-substituted para-phenylene diamine (component (3)), can comprise, or be prepared by combining, from about 50 ppm to about 5000 ppm of components (2) and (3), based on the amount of the biodiesel, and can comprise, or be prepared by combining, from about 100 ppm to about 2500 ppm of components (2) and (3), based on the amount of the biodiesel. 
     Methods of improving oxidation stability of biodiesel according to this invention can comprise combining the biodiesel and from about 50 ppm to about 5000 ppm of antioxidant component comprising mono or bis-hindered phenolic derived from 2,6-di-tert-butylphenol and N,N′-di-substituted para-phenylene diamine. Such methods can also comprising combining the biodiesel component and from about 100 ppm to about 2500 ppm of antioxidant component comprising mono or bis-hindered phenolic derived from 2,6-di-tert-butylphenol and N,N′-di-substituted para-phenylene diamine. 
    
    
     EXAMPLES 
     The following examples are illustrative of the principles of this invention. It is understood that this invention is not limited to any one specific embodiment exemplified herein, whether in the examples or the remainder of this patent application. 
     In each example summarized in Table 1, the identified biodiesel sample and antioxidant composition were combined. In some of the comparative examples, no antioxidant composition was added to the identified biodiesel. In the examples in which the biodiesel was distilled, the biodiesel was distilled using standard techniques known to those skilled in the art. In each example, the oxidation stability of the combination (or of just the biodiesel in certain of the comparative examples) was tested with the RANCIMAT test using RANCIMAT test method (DIN EN 14112). In each instance the sample size was 3 grams, the temperature was 110° C., the air source was purified dry air, and the flow rate was 10 L/hr. The data in Table 1 clearly shows the benefits of this invention. For example, for soybean oil methyl ester, distilled, with no antioxidant added, the highest RANCIMAT result was 1.7 hour (see comparative example nos. 33-39); whereas, for soybean oil methyl ester, distilled, with antioxidant added in accordance with this invention, the RANCIMAT results ranged from 3.87 hours to 11.19 hours (see example nos. 1-22). For soybean oil methyl ester, not distilled, with no antioxidant added, the highest RANCIMAT result was 4.63 hours (see comparative example nos. 40 and 41); whereas, for soybean oil methyl ester, not distilled, with antioxidant added in accordance with this invention, the RANCIMAT results ranged from 6.46 hours to 9.28 hours (see example nos. 23-32). Comparing comparative example nos. 42 and 44, both of which show results of combining soybean oil methyl ester, distilled and antioxidant composition of 300 ppm ETHANOX 4733 and 100 ppm of a component not of this invention, to example nos. 1, 3, 5, and 6 of this invention, each of which shows results of combining soybean oil methyl ester, distilled and antioxidant composition of less than 300 ppm ETHANOX 4733 and PDA, shows that each of example nos. 1, 3, 5, and 6 has a better RANCIMAT result (8.76 hrs, 9.53 hrs, 6.91 hrs, and 5.89 hrs, respectively) than either of comparative example nos. 42 and 44 (2.94 hrs and 2.88 hrs, respectively). Comparing comparative example nos. 43, 45, and 46, each of which shows results of combining soybean oil methyl ester, distilled and antioxidant composition of 300 ppm ETHANOX 4702 and 100 ppm of a component not of this invention, to example 2 of this invention, which shows results of combining soybean oil methyl ester, distilled and antioxidant composition of 200 ppm ETHANOX 4702 and 200 ppm PDA, shows that example no. 2 has a better RANCIMAT result (10.52 hrs) than any of example nos. 43, 45, and 46 (3.6 hrs, 3.87 hrs, and 4.06 hrs, respectively). Comparing comparative example nos. 50, 51, and 52, each of which shows results of combining soybean oil methyl ester, not distilled and antioxidant composition of varying amounts (200 ppm to 600 ppm) of TTBP, to example nos. 27-32 of this invention, each of which shows results of combining soybean oil methyl ester, not distilled and antioxidant composition of 200 ppm or less of TTBP and PDA, shows that each of example nos. 27-32 has a better RANCIMAT result (8.1 hrs, 9.28 hrs, 8.38 hrs, 7.77 hrs, 6.95 hrs, and 6.46 hrs, respectively) than any of comparative example nos. 50, 51, or 52 (5.28 hrs, 5.53 hrs, and 5.84 hrs, respectively). In particular, comparing comparative example no. 50 (with an antioxidant composition of 200 ppm TTBP, and a RANCIMAT result of 5.28 hrs.) with example no. 28 of this invention (with an antioxidant composition of 200 ppm TTBP and 200 ppm PDA, and a RANCIMAT result of 9.28 hrs) it can be seen that this invention provides a substantial benefit. A similar comparison, based on antioxidant composition of ETHANOX 4703 compared to antioxidant compositions of this invention including ETHANOX 4703, can be made between comparative example no. 48 and example nos. 3, 7, 8, and 9 of this invention. Comparative example no. 47 shows use of 381 ppm PDA as an antioxidant with distilled biodiesel gives a RANCIMAT result of 6.39 hrs. While some of the examples of this invention using a distilled biodiesel and an antioxidant of PDA with a mono or bis-hindered phenolic show a lower RANCIMAT result, none of these examples use near 381 ppm PDA. The relatively high cost of PDA, and relatively low cost of phenolics, makes it beneficial to be able to use smaller amounts of PDA with a phenolic, in accordance with this invention, and yet obtain acceptable RANCIMAT results. See, e.g., examples nos. 2 and 3 of this invention where, with a distilled biodiesel, only 200 ppm PDA is used with a phenolic and RANCIMAT results of 8.76 hrs and 10.52 hrs are obtained. Also, in each of the examples of this invention using a distilled biodiesel and an antioxidant of PDA and phenolic that shows a RANCIMAT result lower than 6.39 hrs, the phenolic in the antioxidant is ETHANOX 4733; the lowest such RANCIMAT result being 3.87 hrs. Comparing this to comparative example nos. 42 and 44 (RANCIMAT results of 2.94 hrs and 2.88 hrs), where ETHANOX 4733 is used with amines not of this invention, shows improved results with antioxidant compositions of this invention. Comparative example no. 49 shows use of 200 ppm PDA as an antioxidant with biodiesel (not distilled) gives a RANCIMAT result of 9.01 hrs. Comparative example no. 50 shows use of 200 ppm TTBP as an antioxidant with biodiesel (not distilled) gives a RANCIMAT result of 5.28 hrs. When a combination of 100 ppm TTBP and 100 ppm PDA of this invention is used as an antioxidant with biodiesel (not distilled) a RANCIMAT result of 8.1 hrs is obtained (example no. 27). The result of 8.1 hrs with the TTBP/PDA combination is significantly better than the 5.28 hrs obtained with the TTBP alone. Also, the result of 8.1 hrs with the TTBP/PDA combination is only slightly lower than the 9.01 hrs obtained with the PDA alone and yet provides a commercially significant cost advantage. While some of the examples of this invention using a biodiesel (not distilled) and an antioxidant of PDA with a mono or bis-hindered phenolic show a lower RANCIMAT result, none of these examples use near 200 ppm PDA. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 Antioxidant 
                   
               
               
                   
                   
                 Composition (ppm 
                 Result 
               
               
                 Example No. 
                 Biodiesel Sample 
                 based on Biodiesel) 
                 (Hrs) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                  1 
                 soybean oil methyl 
                 200 ppm ETHANOX 
                 8.76 
               
               
                   
                 ester, distilled 
                 4733, 200 ppm PDA 
               
               
                  2 
                 soybean oil methyl 
                 200 ppm PDA, 200 
                 10.52 
               
               
                   
                 ester, distilled 
                 ppm ETHANOX 4702 
               
               
                  3 
                 soybean oil methyl 
                 200 ppm PDA, 200 
                 9.53 
               
               
                   
                 ester, distilled 
                 ppm ETHANOX 4703 
               
               
                  4 
                 soybean oil methyl 
                 85 ppm ETHANOX 
                 5.85 
               
               
                   
                 ester, distilled 
                 4733, 295 ppm PDA 
               
               
                  5 
                 soybean oil methyl 
                 183 ppm ETHANOX 
                 6.91 
               
               
                   
                 ester, distilled 
                 4733, 206 ppm PDA 
               
               
                  6 
                 soybean oil methyl 
                 296 ppm ETHANOX 
                 5.89 
               
               
                   
                 ester, distilled 
                 4733, 98 ppm PDA 
               
               
                  7 
                 soybean oil methyl 
                 318 ppm PDA, 104 
                 9.3 
               
               
                   
                 ester, distilled 
                 ppm ETHANOX 4703 
               
               
                  8 
                 soybean oil methyl 
                 204 ppm PDA, 202 
                 7.88 
               
               
                   
                 ester, distilled 
                 ppm ETHANOX 4703 
               
               
                  9 
                 soybean oil methyl 
                 105 ppm PDA, 297 
                 6.56 
               
               
                   
                 ester, distilled 
                 ppm ETHANOX 4703 
               
               
                 10 
                 soybean oil methyl 
                 100 ppm ETHANOX 
                 4.45 
               
               
                   
                 ester, distilled 
                 4733, 100 ppm PDA 
               
               
                 11 
                 soybean oil methyl 
                 200 ppm ETHANOX 
                 6.5 
               
               
                   
                 ester, distilled 
                 4733, 200 ppm PDA 
               
               
                 12 
                 soybean oil methyl 
                 300 ppm ETHANOX 
                 8.35 
               
               
                   
                 ester, distilled 
                 4733, 300 ppm PDA 
               
               
                 13 
                 soybean oil methyl 
                 150 ppm ETHANOX 
                 3.87 
               
               
                   
                 ester, distilled 
                 4733, 50 ppm PDA 
               
               
                 14 
                 soybean oil methyl 
                 300 ppm ETHANOX 
                 5.47 
               
               
                   
                 ester, distilled 
                 4733, 100 ppm PDA 
               
               
                 15 
                 soybean oil methyl 
                 450 ppm ETHANOX 
                 6.78 
               
               
                   
                 ester, distilled 
                 4733, 150 ppm PDA 
               
               
                 16 
                 soybean oil methyl 
                 100 ppm ETHANOX 
                 4.34 
               
               
                   
                 ester, distilled 
                 4733, 100 ppm PDA 
               
               
                 17 
                 soybean oil methyl 
                 200 ppm ETHANOX 
                 6.54 
               
               
                   
                 ester, distilled 
                 4733, 200 ppm PDA 
               
               
                 18 
                 soybean oil methyl 
                 300 ppm ETHANOX 
                 8.42 
               
               
                   
                 ester, distilled 
                 4733, 300 ppm PDA 
               
               
                 19 
                 soybean oil methyl 
                 400 ppm ETHANOX 
                 9.69 
               
               
                   
                 ester, distilled 
                 4733, 400 ppm PDA 
               
               
                 20 
                 soybean oil methyl 
                 500 ppm ETHANOX 
                 11.19 
               
               
                   
                 ester, distilled 
                 4733, 500 ppm PDA 
               
               
                 21 
                 soybean oil methyl 
                 375 ppm ETHANOX 
                 6.15 
               
               
                   
                 ester, distilled 
                 4733, 125 ppm PDA 
               
               
                 22 
                 soybean oil methyl 
                 375 ppm ETHANOX 
                 6.07 
               
               
                   
                 ester, distilled 
                 4733, 125 ppm PDA 
               
               
                 23 
                 soybean oil methyl 
                 100 ppm ETHANOX 
                 7.74 
               
               
                   
                 ester, not distilled 
                 4733, 100 ppm PDA 
               
               
                 24 
                 soybean oil methyl 
                 200 ppm ETHANOX 
                 9.04 
               
               
                   
                 ester, not distilled 
                 4733, 200 ppm PDA 
               
               
                 25 
                 soybean oil methyl 
                 150 ppm ETHANOX 
                 6.82 
               
               
                   
                 ester, not distilled 
                 4733, 50 ppm PDA 
               
               
                 26 
                 soybean oil methyl 
                 300 ppm ETHANOX 
                 8.3 
               
               
                   
                 ester, not distilled 
                 4733, 100 ppm PDA 
               
               
                 27 
                 soybean oil methyl 
                 100 ppm PDA, 100 
                 8.1 
               
               
                   
                 ester, not distilled 
                 ppm TTBP 
               
               
                 28 
                 soybean oil methyl 
                 200 ppm PDA, 200 
                 9.28 
               
               
                   
                 ester, not distilled 
                 ppm TTBP 
               
               
                 29 
                 soybean oil methyl 
                 100 ppm PDA, 300 
                 8.38 
               
               
                   
                 ester, not distilled 
                 ppm TTBP 
               
               
                 30 
                 soybean oil methyl 
                 100 ppm PDA, 100 
                 7.77 
               
               
                   
                 ester, not distilled 
                 ppm TTBP 
               
               
                 31 
                 soybean oil methyl 
                 75 ppm PDA, 75 ppm 
                 6.95 
               
               
                   
                 ester, not distilled 
                 TTBP 
               
               
                 32 
                 soybean oil methyl 
                 50 ppm PDA, 50 ppm 
                 6.46 
               
               
                   
                 ester, not distilled 
                 TTBP 
               
               
                 33 
                 soybean oil methyl 
                 none 
                 1.57 
               
               
                 (comparative) 
                 ester, distilled 
               
               
                 34 
                 soybean oil methyl 
                 none 
                 1.58 
               
               
                 (comparative) 
                 ester, distilled 
               
               
                 35 
                 soybean oil methyl 
                 none 
                 1.7 
               
               
                 (comparative) 
                 ester, distilled 
               
               
                 36 
                 soybean oil methyl 
                 none 
                 1.58 
               
               
                 (comparative) 
                 ester, distilled 
               
               
                 37 
                 soybean oil methyl 
                 none 
                 1.56 
               
               
                 (comparative) 
                 ester, distilled 
               
               
                 38 
                 soybean oil methyl 
                 none 
                 1.59 
               
               
                 (comparative) 
                 ester, distilled 
               
               
                 39 
                 soybean oil methyl 
                 none 
                 1.61 
               
               
                 (comparative) 
                 ester, distilled 
               
               
                 40 
                 soybean oil methyl 
                 none 
                 4.63 
               
               
                 (comparative) 
                 ester, not distilled 
               
               
                 41 
                 soybean oil methyl 
                 none 
                 4.49 
               
               
                 (comparative) 
                 ester, not distilled 
               
               
                 42 
                 soybean oil methyl 
                 300 ppm ETHANOX 
                 2.94 
               
               
                 (comparative) 
                 ester, distilled 
                 4733, 100 ppm 
               
               
                   
                   
                 didecylmethylamine 
               
               
                 43 
                 soybean oil methyl 
                 300 ppm ETHANOX 
                 3.6 
               
               
                 (comparative) 
                 ester, distilled 
                 4702, 100 ppm 
               
               
                   
                   
                 didecylmethylamine 
               
               
                 44 
                 soybean oil methyl 
                 300 ppm ETHANOX 
                 2.88 
               
               
                 (comparative) 
                 ester, distilled 
                 4733, 100 ppm 
               
               
                   
                   
                 dilauryl 
               
               
                   
                   
                 thiodipropionate 
               
               
                 45 
                 soybean oil methyl 
                 300 ppm ETHANOX 
                 3.87 
               
               
                 (comparative) 
                 ester, distilled 
                 4702, 100 ppm 
               
               
                   
                   
                 dilauryl 
               
               
                   
                   
                 thiodipropionate 
               
               
                 46 
                 soybean oil methyl 
                 300 ppm ETHANOX 
                 4.06 
               
               
                 (comparative) 
                 ester, distilled 
                 4702, 100 ppm N,N′ 
               
               
                   
                   
                 disalicylidene 
               
               
                   
                   
                 propylenediamine 
               
               
                 47 
                 soybean oil methyl 
                 381 ppm PDA 
                 6.39 
               
               
                 (comparative) 
                 ester, distilled 
               
               
                 48 
                 soybean oil methyl 
                 471 ppm ETHANOX 
                 3.14 
               
               
                 (comparative) 
                 ester, distilled 
                 4703 
               
               
                 49 
                 soybean oil methyl 
                 200 ppm PDA 
                 9.01 
               
               
                 (comparative) 
                 ester, not distilled 
               
               
                 50 
                 soybean oil methyl 
                 200 ppm TTBP 
                 5.28 
               
               
                 (comparative) 
                 ester, not distilled 
               
               
                 51 
                 soybean oil methyl 
                 400 ppm TTBP 
                 5.53 
               
               
                 (comparative) 
                 ester, not distilled 
               
               
                 52 
                 soybean oil methyl 
                 600 ppm TTBP 
                 5.84 
               
               
                 (comparative) 
                 ester, not distilled 
               
               
                   
               
            
           
         
       
     
     It is to be understood that the reactants and components referred to by chemical name or formula anywhere in the specification or claims hereof, whether referred to in the singular or plural, are identified as they exist prior to being combined with or coming into contact with another substance referred to by chemical name or chemical type (e.g., another reactant, a solvent, or etc.). It matters not what chemical changes, transformations and/or reactions, if any, take place in the resulting combination or solution or reaction medium as such changes, transformations and/or reactions are the natural result of bringing the specified reactants and/or components together under the conditions called for pursuant to this disclosure. Thus the reactants and components are identified as ingredients to be brought together in connection with performing a desired chemical reaction or in forming a combination to be used in conducting a desired reaction. Accordingly, even though the claims hereinafter may refer to substances, components and/or ingredients in the present tense (“comprises”, “is”, etc.), the reference is to the substance, component or ingredient as it existed at the time just before it was first contacted, combined, blended or mixed with one or more other substances, components and/or ingredients in accordance with the present disclosure. Whatever transformations, if any, which occur in situ as a reaction is conducted is what the claim is intended to cover. Thus the fact that a substance, component or ingredient may have lost its original identity through a chemical reaction or transformation during the course of contacting, combining, blending or mixing operations, if conducted in accordance with this disclosure and with the application of common sense and the ordinary skill of a chemist, is thus wholly immaterial for an accurate understanding and appreciation of the true meaning and substance of this disclosure and the claims thereof. 
     While the present invention has been described in terms of one or more preferred embodiments, it is to be understood that other modifications may be made without departing from the scope of the invention, which is set forth in the claims below. 
     GLOSSARY 
     Biodiesel comprises crude biodiesel, distilled biodiesel, or any individual chemical component of either. 
     Crude biodiesel comprises 8 carbon to 22 carbon saturated, mono-unsaturated, di-unsaturated, or tri-unsaturated methyl ester, or fatty acid methyl ester derived from a vegetable or animal source. 
     Distilled biodiesel comprises crude biodiesel that has been subjected to at least one distillation step, e.g., to remove excess alcohols, residual glycerine, and other impurities, and includes biodiesel obtained as a specific cut or fraction produced during the distillation of crude biodiesel. 
     TTBP comprises essentially 100% 2,4,6-tri-tert-butylphenol.