Estolide esters and use thereof as a base oil in lubricants

Abstract

Estolide esters obtainable by esterification of —hydroxycarboxylic acids having 12 to 24 carbon atoms, the hydroxycarboxylic acids comprising unsaturated hydroxycarboxylic acids having a) —monocarboxylic acids with 6 to 22 carbon atoms and —polyols with at least two hydroxy groups or b) —monoalcohols having 8 to 22 carbon atoms and —linear carboxylic acids having at least two carboxyl groups or c) —monocarboxylic acids having 6 to 22 carbon atoms and —monoalcohols having 8 to 22 carbon atoms.

Claims

1. An estolide ester obtainable by the esterification of hydroxycarboxylic acids with 12 to 24 carbon atoms, said hydroxycarboxylic acids including unsaturated hydroxycarboxylic acids, wherein the esterification comprises: a) reacting the unsaturated hydroxycarboxylic acids with monocarboxylic acids having 6 to 22 carbon atoms to form an estolide; and reacting the estolide with polyols having at least two hydroxy groups to form an estolide ester comprising linked estolides; or b) reacting the unsaturated hydroxycarboxylic acids with monoalcohols having 8 to 22 carbon atoms to form an estolide; and reacting the estolide with linear carboxylic acids having at least two carboxy groups to form an estolide ester comprising linked estolides; or c) reacting the unsaturated hydroxycarboxylic acids with monocarboxylic acids having 6 to 22 carbon atoms to form an estolide; and reacting the estolide with monoalcohols having 8 to 22 carbon atoms to form an estolide ester wherein hydroxyl groups and carboxylic acid groups esterify to form the estolide ester with unsaturated bonds.

2. The estolide ester according to claim 1, wherein said unsaturated hydroxycarboxylic acids contain one or more double bonds.

3. The estolide ester according to claim 1, wherein said hydroxycarboxylic acids contain one or more hydroxy groups.

4. The estolide ester according to claim 1, wherein said monocarboxylic acids or said carboxylic acids with at least two carboxy groups are saturated or unsaturated monocarboxylic acids.

5. The estolide esters according to claim 1, wherein said hydroxycarboxylic acids have 12 to 18 carbon atoms.

6. The estolide ester according to claim 1, wherein the molar ratio of hydroxycarboxylic acids to polyols or carboxylic acids with at least two carboxy groups is within a range of from 12:1 to 2:1.

7. The estolide ester according to claim 1, wherein the molar ratio of hydroxycarboxylic acids to monocarboxylic acids or monoalcohols is within a range of from 3:1 to 1.1.

8. The estolide ester according to claim 1, wherein said polyols are polyhydric alcohols without any β-hydrogen atoms.

9. The estolide ester according to claim 1, wherein said polyols are selected from trimethylolpropane, di(trimethylol)propane, neopentyl glycol, pentaerythritol, dipentaerythritol, isotridecanol, 2-alkyl-alcohols (Guerbet alcohols), and mixtures thereof.

10. The estolide ester according to claim 1, wherein said unsaturated hydroxycarboxylic acids are selected from ricinoleic acid, lesquerolic acid, 15-hydroxylinoleic acid, auricolic acid, or hydroxypalmitoleic acid, or mixtures thereof.

11. The estolide ester according to claim 1, wherein said monocarboxylic acids are selected from hexanoic acid, caprylic acid, caprinic acid, pelargonic acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linolic acid, linolenic acid, arachidonic acid, behenic acid, isostearic acids, monomer acids, and mixtures thereof.

12. The estolide ester according to claim 1, wherein said carboxylic acids with at least two carboxy groups are selected from 1,4-butanedioic acid (succinic acid), 1,6-hexanedioic acid (adipic acid), 1,9-nonanedioic acid (azelaic acid), and 1,10-decanedioic acid (sebacic acid), and mixtures thereof.

13. The estolide ester according to claim 1, wherein said monoalcohols are selected from octanol, decanol, isotridecyl alcohol, 2-alkyl-alcohols obtained by the Guerbet reaction, and mixtures thereof.

14. The estolide ester according to claim 1, wherein the viscosity is at least 40 mm.sup.2/s at 40° C., or at least 100 mm.sup.2/s at 25° C.

15. A process for preparing estolide esters according to claim 1, comprising a) reacting hydroxycarboxylic acids with 12 to 24 carbon atoms, said hydroxycarboxylic acids including unsaturated hydroxycarboxylic acids, with monocarboxylic acids having 6 to 22 carbon atoms to form an estolide; and reacting the estolide with polyols having at least two hydroxy groups to form an estolide ester comprising linked estolides; or b) reacting hydroxycarboxylic acids with 12 to 24 carbon atoms, said hydroxycarboxylic acids including unsaturated hydroxycarboxylic acids, with monoalcohols having 8 to 22 carbon atoms to form an estolide; and reacting the estolide with linear carboxylic acids having at least two carboxy groups to form an estolide ester comprising linked estolides; or c) reacting hydroxycarboxylic acids with 12 to 24 carbon atoms, said hydroxycarboxylic acids including unsaturated hydroxycarboxylic acids, with monocarboxylic acids having 6 to 22 carbon atoms to form an estolide; and reacting the estolide with monoalcohols having 8 to 22 carbon atoms to form an estolide ester, wherein hydroxyl groups and carboxylic acid groups esterify to form the estolide ester with unsaturated bonds.

16. A lubricant comprising an estolide ester according to claim 1.

17. The estolide ester according to claim 1, wherein reacting the unsaturated hydroxycarboyxlic acids is performed at a selected temperature range between about 150° C. and about 300° C., reacting hydroxycarboxylic acids with monoalcohols proceeds until the hydroxyl number is less than about 50 mg of KOH/g, and reacting the estolide is performed in the presence of a catalyst.

18. The estolide ester according to claim 1, wherein the pour point is from −20° C. to −55° C.

19. The process according to claim 15, wherein reacting the unsaturated hydroxycarboxylic acids is performed at a selected temperature range between about 150° C. and about 300° C., reacting hydroxycarboxylic acids with monoalcohols proceeds until the hydroxyl number is less than about 50 mg of KOH/g, and reacting the estolide is performed in the presence of a catalyst.

Description

EXAMPLE 1: SYNTHESIS OF AN ESTOLIDE TMP ESTER WITH A C8/C10 FATTY ACID (ISO-VG 150)

(1) 105.4 g of a C8/C10 fatty acid mixture (58:42% by weight) and 200 g of ricinoleic acid are charged in a three-necked flask with an intensive cooler and thermometer, and esterified at 180-250° C. under 100-250 mbar, until the hydroxyl number of the reaction mixture is <30 mg of KOH/g. The mixture is cooled down, and 30.0 g of 1,1,1-trimethylolpropane and 0.1 g of SnO as a catalyst are metered in. Subsequently, the product is esterified at 185-220° C. and under 100-250 mbar until the acid number is <2 mg of KOH/g. After removing the catalyst, the ester is obtained with a viscosity of about 150 mm.sup.2/s.

EXAMPLE 2: SYNTHESIS OF AN ESTOLIDE NPG ESTER WITH A C8/C10 FATTY ACID (ISO-VG 68)

(2) 105.8 g of a C8/C10 fatty acid mixture (58:42% by weight) and 333.1 g of ricinoleic acid are charged in a three-necked flask with an intensive cooler and thermometer, and esterified at 180-200° C. under 100-250 mbar, until the hydroxyl number of the reaction mixture is <30 mg of KOH/g. The mixture is cooled down, and 54.1 g of 2,2-dimethylolpropane and 0.1 g of SnO as a catalyst are metered in. Subsequently, the product is esterified at 185-220° C. and under 100-250 mbar until the acid number is <2 mg of KOH/g. After removing the catalyst, an ester is obtained with a viscosity of about 70 mm.sup.2/s.

EXAMPLE 3: SYNTHESIS OF AN ESTOLIDE TMP ESTER WITH A C8/C10 FATTY ACID (ISO-VG 320)

(3) 75.4 g of a C8/C10 fatty acid mixture (58:42% by weight) and 333.1 g of ricinoleic acid are charged in a three-necked flask with an intensive cooler and thermometer, and esterified at 180-200° C. under 100-250 mbar, until the hydroxyl number of the reaction mixture is <30 mg of KOH/g. The mixture is cooled down, and 28.5 g of 2,2-dimethylolpropane and 0.1 g of SnO as a catalyst are metered in. Subsequently, the product is esterified at 180-220° C. and under 10-100 mbar until the acid number is <2 mg of KOH/g. After removing the catalyst, the ester is obtained with a viscosity of about 320 mm.sup.2/s.

EXAMPLE 4: SYNTHESIS OF AN ESTOLIDE ITD ESTER WITH ADIPIC ACID (ISO-VG 100)

(4) 233.9 g of isotridecyl alcohol and 333.1 g of ricinoleic acid are charged in a three-necked flask with an intensive cooler and thermometer, and esterified at 180-200° C. under 100-250 mbar, until the hydroxyl number of the reaction mixture is <30 mg of KOH/g. The mixture is cooled down, and 62.5 g of adipic acid (1,6-hexanedioic acid) and 0.1 g of SnO as a catalyst are metered in. Subsequently, the product is esterified at 180-220° C. and under 10-100 mbar until the acid number is <2 mg of KOH/g. After removing the catalyst, an ester is obtained with a viscosity of about 100 mm.sup.2/s.

EXAMPLE 5: SYNTHESIS OF AN ESTOLIDE MEG ESTER WITH ISOSTEARIC ACID (ISO-VG 100)

(5) 399.7 g of isostearic acid and 333.1 g of ricinoleic acid are charged in a three-necked flask with an intensive cooler and thermometer, and esterified at 180-200° C. under 100-250 mbar, until the hydroxyl number of the reaction mixture is <30 mg of KOH/g. The mixture is cooled down, and 50.3 g of monoethylene glycol and 0.1 g of SnO as a catalyst are metered in. Subsequently, the product is esterified at 180-220° C. and under 10-100 mbar until the acid number is <2 mg of KOH/g. After removing the catalyst, an ester is obtained with a viscosity of about 100 mm.sup.2/s.

EXAMPLE 6: SYNTHESIS OF AN ESTOLIDE ITD ESTER WITH ISOSTEARIC ACID (ISO-VG 46)

(6) 399.7 g of isostearic acid and 333.1 g of ricinoleic acid are charged in a three-necked flask with an intensive cooler and thermometer, and esterified at 180-200° C. under 100-250 mbar, until the hydroxyl number of the reaction mixture is <30 mg of KOH/g. The mixture is cooled down, and 285.9 g of isotridecyl alcohol and 0.1 g of SnO as a catalyst are metered in. Subsequently, the product is esterified at 180-220° C. and under 10-100 mbar until the acid number is <2 mg of KOH/g. After removing the catalyst, an ester is obtained with a viscosity of about 46 mm.sup.2/s.

EXAMPLE 7: SYNTHESIS OF AN ESTOLIDE TMP ESTER WITH ISOSTEARIC ACID (ISO-VG 220)

(7) 399.7 g of isostearic acid and 333.1 g of ricinoleic acid are charged in a three-necked flask with an intensive cooler and thermometer, and esterified at 180-200° C. under 100-250 mbar, until the hydroxyl number of the reaction mixture is <30 mg of KOH/g. The mixture is cooled down, and 66.8 g of TMP and 0.1 g of SnO as a catalyst are metered in. Subsequently, the product is esterified at 180-220° C. and under 10-100 mbar until the acid number is <2 mg of KOH/g. After removing the catalyst, an ester is obtained with a viscosity of about 225 mm.sup.2/s.

(8) Determination of the Hydrolytic Stability According to ASTM D2619

(9) The determination of the hydrolytic stability of the estolides was effected according to ASTM D2619. The difference of the acid numbers before and after the test was used as the measured quantity. The values for the estolides according to Examples 1 to 3 were compared with complex esters of the respective ISO VG classes.

(10) The values stated in Table 1 were obtained.

(11) Determination of the Pour Point

(12) The pour point of the estolides was determined in accordance with ISO 3016:1994. Estolides according to the invention and those of adipic and dimer fatty acids were compared. Here too, the values for the estolides according to Examples 1 to 3 were compared with complex esters of the respective ISO VG classes.

(13) The values stated in Table 1 were obtained.

(14) TABLE-US-00001 Viscosity Hydrolytic Pour class Carboxylic Fatty stability [mg point (ISO VG) Polyol acid acids of KOH/g] [° C.] 150 TMP caprylic/ ricinoleic 0.04 −36 (Example 1) caprinic acid acid 150 TMP adipic acid oleic fatty  0.2 −30 (Comparative acid Example) 68 NPG caprylic/ ricinoleic 0.05 −51 (Example 2) caprinic acid acid 320 TMP caprylic/ ricinoleic 0.22 −36 (Example 3) caprinic acid acid 320 TMP dimer fatty oleic fatty 0.21 −30 (Comparative acid acid Example) 100 ITD adipic acid ricinoleic 0.32 −45 (Example 4) acid 100 MEG isostearine ricinoleic 0.06 −24 (Example 5) acid 46 ITD isostearine ricinoleic 0.01 −36 (Example 6) acid 220 TMP isostearine ricinoleic 0.05 −42 (Example 7) acid