OXIDATION INHIBITOR FOR DIESEL, AND DIESEL FUEL COMPOSITION

Abstract

The present invention provides an oxidation inhibitor for diesel that improves the oxidative stability thereof and a diesel fuel composition having an excellent oxidative stability. A diesel fuel composition excellent in oxidative stability and low-temperature fluidity is obtained by adding an oxidation inhibitor that contains a fatty acid methyl ester derived from palm, rapeseed or soybean oil and in which the contents of polyunsaturated and saturated fatty acid methyl esters are each specified.

Claims

1. A method of inhibiting oxidation of diesel comprising adding to diesel an oxidation inhibitor for diesel which comprises a palm oil-derived fatty acid methyl ester, wherein said oxidation inhibitor contains 0.5 mass %-7.0 mass % of polyunsaturated fatty acid methyl ester and 50 mass %-84 mass % of saturated fatty acid methyl ester.

2. A method of inhibiting oxidation of diesel comprising adding to diesel an oxidation inhibitor for diesel which comprises a rapeseed oil-derived fatty acid methyl ester, wherein said oxidation inhibitor contains 0.5 mass %-24.5 mass % of polyunsaturated fatty acid methyl ester and 7 mass %-50 mass % of saturated fatty acid methyl ester.

3. A method of inhibiting oxidation of diesel comprising adding to diesel an oxidation inhibitor for diesel which comprises a soybean oil-derived fatty acid methyl ester, wherein said oxidation inhibitor contains 0.8 mass %-32 mass % of polyunsaturated fatty acid methyl ester and 15 mass %-56 mass % of saturated fatty acid methyl ester.

4. A diesel fuel composition, which comprises an oxidation inhibitor for diesel comprising at least one selected from the group consisting of a palm oil-derived fatty acid methyl ester, a rapeseed oil-derived fatty acid methyl ester, and a soybean oil-derived fatty acid methyl ester, in an amount of 1.0 mass % or more and 70 mass % or less, wherein said palm oil-derived fatty acid methyl ester contains 0.5 mass %-7.0 mass % of polyunsaturated fatty acid methyl ester and 50 mass %-84 mass % of saturated fatty acid methyl ester, wherein said rapeseed oil-derived fatty acid methyl ester contains 0.5 mass %-24.5 mass % of polyunsaturated fatty acid methyl ester and 7 mass %-50 mass % of saturated fatty acid methyl ester, and wherein said soybean oil-derived fatty acid methyl ester contains 0.8 mass %-32 mass % of polyunsaturated fatty acid methyl ester and 15 mass %-56 mass % of saturated fatty acid methyl ester.

5. The diesel fuel composition of claim 4, which comprises an oxidation inhibitor for diesel comprising at least one selected from the group consisting of the palm oil-derived fatty acid methyl ester, the rapeseed oil-derived fatty acid methyl ester, and the soybean oil-derived fatty acid methyl ester, in an amount of 1.0 mass % or more and 20 mass % or less.

6. The diesel fuel composition of claim 4, which comprises an oxidation inhibitor for diesel comprising at least one selected from the group consisting of the palm oil-derived fatty acid methyl ester, the rapeseed oil-derived fatty acid methyl ester, and the soybean oil-derived fatty acid methyl ester, in an amount of more than 20 mass % and 50 mass % or less.

7. The diesel fuel composition of claim 4, which comprises an oxidation inhibitor for diesel comprising at least one selected from the group consisting of the palm oil-derived fatty acid methyl ester, the rapeseed oil-derived fatty acid methyl ester, and the soybean oil-derived fatty acid methyl ester, in an amount of more than 50 mass % and 70 mass % or less.

8. The diesel fuel composition of claim 4, which satisfies all the following conditions (a), (b), and (c): (a) the pour point is 9 C. or less; (b) the oxidative stability by PetroOxy method is 65 minutes or more; and, (c) no sludge is formed after forced-oxidation test performed by supplying pure oxygen at 115 C. for 16 hours.

9. The diesel fuel composition of claim 5, which satisfies all the following conditions (a-1), (b), and (c): (a-1) a pour point is 8 C. or less; (b) an oxidative stability by PetroOxy method is 65 minutes or more; and, (c) no sludge is formed after forced-oxidation test performed by supplying pure oxygen at 115 C. for 16 hours.

10. The diesel fuel composition of claim 6, which satisfies all the following conditions (a-2), (b), and (c): (a-2) a pour point is 4 C. or less; (b) an oxidative stability by PetroOxy method is 65 minutes or more; and, (c) no sludge is formed after forced-oxidation test performed by supplying pure oxygen at 115 C. for 16 hours.

11. The diesel fuel composition of claim 7, which satisfies all the following conditions (a), (b), and (c): (a) a pour point is 9 C. or less; (b) an oxidative stability by PetroOxy method is 65 minutes or more; and, (c) no sludge is formed after forced-oxidation test performed by supplying pure oxygen at 115 C. for 16 hours.

Description

EXAMPLES

[0088] The present invention will be described below based on Examples and Comparative Examples, but the present invention is not limited thereto. First, measurement methods of pour point and oxidative stability, and composition of fatty acid methyl esters in stock oil used in the examples are described.

Measurement of Pour Point

[0089] Pour points were measured using an automatic pour/cloud point tester (type MPC-102A, manufactured by Tanaka Scientific Limited) in compliance with US standard ASTM D 6749.

Measurement of Oxidative Stability

[0090] Oxidative stabilities were measured by the PetroOxy method. In this method, 5 ml of a sample is placed in the sample chamber, oxygen is injected into the chamber to 700 kPa5 kPa, and then the temperature is raised to 140.0 C.0.5 C. and held.

[0091] Oxygen is consumed due to oxidative deterioration of the sample with the lapse of time and the pressure inside the sample chamber drops. The oxidative stability means the time elapsed from the start of the temperature rise to the pressure drop point (the point at which the pressure inside the sample chamber dropped by 10% from the maximum pressure) during continuous pressure change measurement.

[0092] Sludge formation test was carried out by former forced-oxidation method. In the method, 20 g of a sample was placed in a reaction vessel, heated to 115 C. while feeding pure oxygen into the reaction vessel at 100 ml/min and allowed to oxidize for 16 hours. Acid values before and after the oxidation were measured and the difference therebetween was calculated to obtain the increase in acid value. The acid values were measured using an automatic titrator (type Titrand, manufactured by Metrome). When the sample was held at room temperature after forced oxidation, presence of sludge formation and change in oil color were also investigated.

Stock Oil

[0093] Fatty acid methyl esters (FAME) used as oxidation inhibitors in the present invention were palm oil FAME, rapeseed oil FAME and soybean oil FAME. Palm oil FAME used was obtained from Thailand. The other FAME was prepared by ourselves from stock oil by the alkali catalyst method. Into a glass autoclave 150 g of these FAME were added together with 1.2 g of a commercially available hydrogenation catalyst and hydrogenated at a hydrogen pressure of 0.5 MPa and 80 C., and then samples were taken at the specific times, thereby changing the FAME composition. The FAME composition and pour point of each sample are shown in Tables 1 to 3. Methyl stearate (purity: 99% or more) and methyl oleate (purity: 99% or more) as reagents were added to palm oil FAME-1 to adjust the amount of polyunsaturated FAME. The FAME composition and pour point obtained by the adjustment are shown in Table 4.

TABLE-US-00001 TABLE 1 FAME palm oil FAME composition (%) FAME-1 FAME-2 FAME-3 FAME-4 FAME-5 FAME-6 FAME-7 FAME-8 saturated FAME 50.0 50.0 50.7 54.2 59.4 72.0 77.6 84.0 monoenoic acid ME 40.5 42.2 45.4 42.7 39.0 26.7 21.0 14.7 polyunsaturated FAME 9.2 7.0 3.1 2.1 1.0 0.7 0.5 0.5 pour point ( C.) 13 13 13 13 14 15 17 19

TABLE-US-00002 TABLE 2 FAME rapeseed oil FAME composition (%) FAME-9 FAME-10 FAME-11 FAME-12 FAME-13 EAME-14 FAME-15 saturated FAME 7.0 7.0 8.1 13.6 23.3 36.5 49.8 monoenoic acid ME 63.3 67.1 78.8 81.2 73.6 61.5 48.7 polyunsaturated FAME 28.6 24.5 11.9 3.4 1.5 0.9 0.5 pour point ( C.) 13 12 6 5 13 20 25

TABLE-US-00003 TABLE 3 FAME soybean oil FAME composition (%) FAME-16 FAME-17 FAME-18 FAME-19 FAME-20 FAME-21 saturated FAME 15.1 15.9 17.8 27.0 39.3 55.9 monoenoic acid ME 24.7 51.9 76.4 70.8 59.0 42.5 polyunsaturated FAME 59.2 34.7 4.4 1.4 1.2 0.8 pour point ( C.) 0 0 3 12 18 24

TABLE-US-00004 TABLE 4 palm oil FAME + reagent FAME-22 FAME-23 FAME-24 FAME composition (%) saturated FAME 60.0 60.0 60.0 monoenoic acid 45.0 47.0 49.0 ME polyunsaturated 5.0 3.0 1.0 FAME pour point ( C.) 16 15 14

Examples 1 to 3

[0094] The palm oil FAMEs 2, 3 and 5 shown in Table 1 were mixed into a commercially available diesel so as to be 20 mass % (bended diesel), and the increases in acid value, oxidation stabilities and pour points of the bended diesel were measured. The measurement results are shown in Table 5. From the results shown in Table 5, when palm oil FAME was used, there was no large difference in the increases in acid value, but when palm oil FAME having less polyunsaturated component was used, oxidative stability was improved and sludge formation and oil color change were not observed.

TABLE-US-00005 TABLE 5 pour point increase in acid precipi- oxidative of mixed value(mgKOH/g) tation oil color stability (min) diesel ( C.) Example 1 FAME-2 0.04 no pale yellow 107.8 8 Example 2 FAME-3 0.02 no pale yellow 123.7 8 Example 3 FAME-5 0.02 no pale yellow 145.6 8 Comparative 3.85 yes orange 70.3 14 Example 1 Comparative FAME-1 3.98 yes orange 78.5 8 Example 2

Comparative Examples 1 to 2

[0095] As Comparative Example 1, the same measurements as in Example 1 were carried out except that a diesel alone with no fatty acid methyl ester oil mixed was used. As Comparative Example 2, the same measurements as in Example 1 were carried out except that palm oil FAME-1 shown in Table 1 was used. The measurement results are shown in Table 5. From the results shown in Table 5, when a commercially available diesel alone was subjected to the forced oxidation test, the increase in acid value was as high as 3.85 mg KOH/g. On the other hand, by mixing 20% of FAME-1, the increase in acid value was slightly increased to 3.98 mg KOH/g. By forced oxidation, the sample oil was gradually oxidized and its color became deeper from pale yellow to yellow, and further to orange. When the sample oil after forced oxidation showed orange, formation of sludge was also confirmed. On the other hand, oxidative stability was 65 minutes or more in either case.

Examples 4 to 7 and Comparative Examples 3 to 5

[0096] As Examples 4 to 7, the palm oil FAME-7 shown in Table 1 was mixed into a commercially available diesel so as to be 1, 5, 10 or 20 mass %, and the increases in acid value and pour points of the mixed diesels were measured. As Comparative Examples 3 to 5, the same measurements as in Example 4 were carried out except that palm oil FAME-1 shown in Table 1 was mixed into a commercially available diesel so as to be 1, 5 or 10 mass %. The measurement results are shown in Table 6. From the results shown in Table 6, when FAME-1 with a large content of polyunsaturated component was mixed, the increase in acid value was enhanced with increase in the mixing ratio, and sludge formation was also observed at 10 mass % or more. On the other hand, when FAME-7 with a less content of polyunsaturated component was mixed, no increase in acid value was observed even when the mixing ratio of the FAME was increased, and also no sludge formation was observed.

TABLE-US-00006 TABLE 6 FAME pour point mixing increase in acid precipi- of mixed FAME ratio (%) value (mgKOH/g) tation oil color diesel ( C.) Example 4 FAME-7 1 0.01 No pale yellow 13 Example 5 FAME-7 5 0.03 No pale yellow 12 Example 6 FAME-7 10 0.02 No pale yellow 10 Example 7 FAME-7 20 0.02 No pale yellow 8 Comparative FAME-1 1 0.62 No yellow 13 Example 3 Comparative FAME-1 5 0.85 No yellow 12 Example 4 Comparative FAME-1 10 1.65 yes orange 11 Example 5

Examples 8 to 15 and Comparative Examples 6 to 16

[0097] As Examples 8 to 15, the palm oil FAME-7 shown in Table 1 was mixed into a commercially available diesel so as to be 1, 5, 10, 20, 30, 40, 50, or 70 mass %, and their oxidative stabilities and pour points were measured. In order to make the difference due to the difference in oil composition more obvious, the accelerated test was carried out with the forced oxidation temperature set at 125 C. As Comparative Examples 6 to 14, the same measurements as in Example 8 were carried out except that palm oil FAME-1 shown in Table 1 was mixed into a commercially available diesel so as to be 1, 5, 10, 20, 30, 40, 50, 70, or 80 mass %. As Comparative Example 15, the same measurements as in Example 8 were carried out except that palm oil FAME-7 shown in Table 1 was mixed into a commercially available diesel so as to be 80 mass %. As Comparative Example 16, the same measurements as in Example 8 were carried out except that a diesel alone with no fatty acid methyl ester oil mixed was used. The measurement results are shown in Table 7. From the results in Table 7, the forced-oxidation at 125 C. resulted in a significantly enhanced increase in acid value and an increased sludge formation even in a diesel alone. When FAME-1 with a large content of polyunsaturated component was used, the increase in acid value gradually increased with the increase in the mixing ratio to diesel, but the oxidative stability was slightly improved inversely. On the other hand, when FAME-7 with a less content of polyunsaturated component was used, the increase in acid value significantly decreased with the increase in the mixing ratio, and sludge formation was not observed at any mixing ratio. On the other hand, when FAME-7 was mixed into a commercially available diesel so as to be 80 mass % (Comparative Example 15), the increase in oxidation was very small, but the pour point of the mixed diesel showed a significantly increased value of 11 C. exceeding 10 C.

TABLE-US-00007 TABLE 7 FAME pour point mixing increase in acid precipi- oxidative of mixed FAME ratio (%) value (mgKOH/g) tation oil color stability (min) diesel ( C.) Example 8 FAME-7 1 6.32 no yellow 123.6 13 Example 9 FAME-7 5 3.35 no pale yellow 156.4 12 Example 10 FAME-7 10 1.31 no pale yellow 172.7 10 Example 11 FAME-7 20 1.09 no pale yellow 186.2 8 Example 12 FAME-7 30 0.76 no pale yellow 198.6 5 Example 13 FAME-7 40 0.45 no pale yellow 201.3 2 Example 14 FAME-7 50 0.12 no pale yellow 215.0 1 Example 15 FAME-7 70 0.08 no pale yellow 218.2 8 Comparative FAME-1 1 16.03 yes orange 71.3 13 Example 6 Comparative FAME-1 5 18.04 yes orange 72.1 12 Example 7 Comparative FAME-1 10 21.19 yes orange 76.7 11 Example 8 Comparative FAME-1 20 34.37 yes orange 78.5 8 Example 9 Comparative FAME-1 30 35.29 yes orange 78.7 5 Example 10 Comparative FAME-1 40 37.80 yes orange 79.0 3 Example 11 Comparative FAME-1 50 38.92 yes orange 79.5 1 Example 12 Comparative FAME-1 70 40.06 yes orange 79.8 5 Example 13 Comparative FAME-1 80 41.23 yes orange 79.9 8 Example 14 Comparative FAME-7 80 0.06 no pale yellow 222.6 11 Example 15 Comparative 0 11.62 yes orange 70.3 14 Example 16

Examples 16 to 21

[0098] The same measurements as in Example 8 were carried out except that palm oil FAMEs-2 to 6 and 8 shown in Table 1 were mixed into a commercially available diesel so as to be 20 mass %. The measurement results are shown in Table 8. From the results shown in Table 8, when FAMEs with a larger content of polyunsaturated component were mixed, inhibitory effects on the increase in acid value were observed, and also no sludge formation was observed. On the other hand, when FAME-8 with a large content of polyunsaturated component was used, the pour point of the mixed diesel increased to 7 C.

TABLE-US-00008 TABLE 8 pour increase point of in acid mixed value oil diesel FAME (mgKOH/g) precipitation color ( C.) Example FAME-2 28.08 yes orange 8 16 Example FAME-3 16.08 yes orange 8 17 Example FAME-4 14.20 yes orange 8 18 Example FAME-5 5.95 no yellow 8 19 Example FAME-6 2.31 no yellow 8 20 Example FAME-8 0.09 no pale 7 21 yellow

Examples 22 to 27 and Comparative Example 17

[0099] As Examples 22 to 27, the same measurements as in Example 1 were carried out except that rapeseed oil FAMEs-10 to 15 were mixed into a commercially available diesel so as to be 20 mass %. As Comparative Example 17, the same measurements as in Example 1 were carried out except that rapeseed oil FAME-9 shown in Table 2 was mixed into a commercially available diesel so as to be 20 mass %. The measurement results are shown in Table 9. From the results shown in Table 9, even when a rapeseed oil FAME was mixed, use of FAMEs with a less content of polyunsaturated component showed inhibitory effects on the increase in acid value and sludge formation and also resulted in increased oxidative stabilities. On the other hand, when FAMEs with higher depth of hydrogenation were used, the pour point of the mixed diesel increased.

TABLE-US-00009 TABLE 9 pour point increase in acid precipi- oxidative of mixed FAME value (mgKOH/g) tation oil color stability (min) diesel ( C.) Example 22 FAME-10 21.68 yes orange 44.9 13 Example 23 FAME-11 10.80 no yellow 68.8 12 Example 24 FAME-12 0.01 no pale yellow 100.2 10 Example 35 FAME-13 0.05 no pale yellow 114.8 8 Example 26 FAME-14 0.03 no pale yellow 117.9 8 Example 27 FAME-15 0.01 no pale yellow 124.5 6 Comparative FAME-9 24.93 yes orange 26.6 13 Example 17

Examples 28 to 32 and Comparative Example 18

[0100] As Examples 28 to 32, the same measurements as in Example 1 were carried out except that soybean oil FAMEs-17 to 21 were mixed into a commercially available diesel so as to be 20 mass %. As Comparative Example 18, the same measurements as in Example 1 were carried out except that soybean oil FAME-16 shown in Table 3 was mixed into a commercially available diesel so as to be 20 mass %. The measurement results are shown in Table 10. From the results shown in Table 10, even when a soybean oil FAME was mixed, use of FAMEs with a less content of polyunsaturated component showed inhibitory effects on the increase in acid value and sludge formation and also resulted in increased oxidative stabilities. On the other hand, when FAMEs with higher depth of hydrogenation were used, the pour point of the mixed diesel increased.

TABLE-US-00010 TABLE 10 pour point increase in acid precipi- oxidative of mixed FAME value (mgKOH/g) tation oil color stability (min) diesel ( C.) Example 28 FAME-17 27.56 yes orange 40.2 11 Example 29 FAME-18 1.49 no yellow 87.3 10 Example 30 FAME-19 0.04 no pale yellow 121.7 9 Example 31 FAME-20 0.00 no pale yellow 125.0 8 Example 32 FAME-21 0.00 no pale yellow 132.2 6 Comparative FAME-16 29.02 yes orange 17.2 11 Example 18

Examples 33 to 35

[0101] As Examples 33 to 35, the same measurements as in Example 1 were carried out except that FAMEs-22 to 24 whose compositions were adjusted by adding methyl stearate and methyl oleate as reagents to palm oil FAME-1 were mixed into a commercially available diesel so as to be 20 mass %. The measurement results are shown in Table 11. From the results shown in Table 11, even when palm oil FAMEs whose compositions were adjusted by adding the reagents were mixed, use of FAMEs with a less content of saturated component showed inhibitory effects on the increase in acid value and sludge formation and also resulted in increased oxidative stabilities.

TABLE-US-00011 TABLE 11 pour point increase in acid precipi- oxidative of mixed FAME value (mgKOH/g) tation oil color stability (min) diesel ( C.) Example 33 FAME-22 0.08 no pale yellow 100.7 8 Example 34 FAME-23 0.06 no pale yellow 121.6 8 Example 35 FAME-24 0.05 no pale yellow 130.2 8

[0102] Thus, the oxidation inhibitor for diesel comprising fatty acid methyl esters of the present invention is effective for improving the oxidative stability of diesel and suppressing sludge formation, and a diesel fuel comprising the oxidation inhibitor is a diesel fuel composition excellent in oxidative stability and low-temperature fluidity.

INDUSTRIAL AVAILABILITY

[0103] The oxidation inhibitor of the present invention can be used as an oxidation inhibitor for diesel.