MXPA00004690A - Biodegradable oleic estolide ester base stocks and lubricants - Google Patents

Abstract

Esters of estolides derived from oleic acids are characterized by superior properties for use as lubricant base stocks. These estolides may also be used as lubricants without the need for fortifying additives normally required to improve the lubricating properties of base stocks.

Description

RAW MATERIALS AND LUBRICANTS BASED ON OLEIC BIODEGRADABLE ESTERS OF STOLVES Field of the Invention This invention relates to oleic acid ester solvents and their use as raw materials and basic biodegradable lubricants.

BACKGROUND OF THE INVENTION Synthetic esters, such as polyol esters and adipates, polyalpha olefins (PAO) of low viscosity, such as PAO 2, vegetable oils, especially canola oil and oleates are used industrially as basic and biodegradable raw materials for the formulation of lubricants. Lubricants usually contain 80-100% by weight of basic raw material and 0-20% by weight of additives to adjust their viscometric properties, low temperature behavior, oxidation stability, corrosion protection, de-emulsification and water rejection, friction coefficients, lubricities, wear protection, air release, color and other properties. Biodegradability can not be improved by using additives. In the prior art, scant attention has been given to the styolides as possessing power for basic raw material and lubricants. A stolide is a unique oligomeric fatty acid containing secondary ester bonds in the alkyl backbone of the molecule. Stolides have typically been synthesized by the homopolymerization of fatty acids from castor oil [Modak et al., JAOCS 42: 428 (1985); Neissner et al., Fette Seifen Anstrichm82: 183 (1990)] or 12-hydroxystearic acid [Raynor et al., J. Chromatogr. 505: 179 (1990); Delafield et al., J. Bacteriol. 90: 1455 (1965) under conditions catalyzed by heat or acid. Yamaguchi et al., [Japanese Patent 213,387, (1990)] recently described a process for the enzymatic production of stolides from hydro fatty acids (particularly ricinoleic acid) present in castor oil using lipase.

The styolides derived from these sources are composed of esters in carbon 12 of the fatty acids and have a residual hydroxyl group in the backbone of the stolide. In addition, the level of unsaturation in the produced stolides (expressed through, for example, iodine value) is not significantly lower than that in raw materials, ie, hydroxy fatty acids. Erhan et al. [JAOCS 70: 461 (1993)] reported the production of styolides from unsaturated fatty acids using a high temperature condensation and pressure on clay catalysts. The conversion of the fatty acid double bond into an ester function is an impressively different method to the hydroxy esterification process.

Objectives of the Invention We have now discovered a new family of styolide compounds derived from oleic acids and characterized by superior properties for use as a raw material for lubricants. These stolides can also be used as lubricants without the need for fortifying additives that are normally required to improve the lubricating properties of basic raw materials. The estolide esters of this invention are generally characterized by Formula (I): R3-C (i) CH3 (CH2) 3 (CH2) and CH (CH2) x (CH2) 2C00R where x and y are each equal to 1 or greater than 1; where x + y = 10; where n is 0, 1 or greater than 1; wherein R is CHR.R2; wherein R. and R2 are independently selected from hydrogen and C1 to C36 hydrocarbons, which may be saturated or unsaturated, branched or straight chain, and substituted or unsubstituted; wherein R3 is a residual fragment of an oleic, stearic or other fatty acid chain; and wherein the predominant species of the secondary ester bond is in the 9 or 10 position; that is, where x = 5 or 6 and y = 5 or 4, respectively. According to this discovery, it is an object of this invention to provide new styolide compounds which have utility as a basic raw material for lubricants and also as lubricants without the need for the inclusion of conventional additives. It is a further object of the present invention to provide a family of stolides that are biodegradable and which have superior properties of oxidation stability, low temperature and viscometric. Other objects and advantages of this invention will become clearer from the following description.

Detailed Description of the Invention For purposes of this invention, the term "monoestolides" is used generically to refer to the acid form of compounds having the structure of Formula I, wherein n = 0. The term "polystyrenes" is used herein to refer to the acid form of compounds having the structure of Formula I, wherein n is greater than 0. The terms "ester," "ester of styrene" and the like are generally used here to refer to products produced by esterification of the residual fatty acid (binding to the R group in Formula I) in the stolide or blends of styolides as described below. Of course, the stolides are esters that result from the secondary ester bonds between fatty acid chains, and the effort will be made here to distinguish the real ester from the latter ester. The production of monoestolides and polystyrenes by several routes is completely described in Isbell et al (I) [JAOCS, Vol. 71, No. 1, pp. 169-174 (February 1994)], Erhan et al., [JAOCS, Vol. 74, No. 3, pp 249-254 (1997)] and Isbell et al. (II) [JAOCS, Vol. 74, No. 4, pp 473-476 (1997)], all of which are incorporated herein by reference. Although not required, it is preferred for quality control purposes that the starting material be as pure in oleic acid as practical. Isbell et al., (III) [JAOCS, Vol. 71, No. 1, pp 379-383 (April 1994)], characterizes oleic stolides produced by acid catalysis as being a mixture of polystyrene and monoestolide oligomers of up to eight or more interesterified fatty acid molecules through secondary ester linkages in the alkyl backbone. This publication also describes that the positions of these secondary ester linkages were centered around the original position of the C9 double bond, with links actually varying from positions C-5 to C-13 and more abundantly at positions C-9 and C-10 in approximately equal amounts. Similarly, the remaining unsaturation in the terminal fatty acid was distributed along the fatty acid backbone, presumably also from C-5 to C-13. The linkages of the styolides of this invention would have the same or about the same distribution of bonds reported by Isbell et al., 1994. Therefore, it should be understood that Formula I, supra, is a generalization of the structure of the spinal column. of the compounds contemplated herein, and that the formula is intended to encompass normal distributions of reaction products resulting from the various reaction processes referred to herein. Applicants believe that the superior properties of the present stolide esters are dictated not so much by the positions of the bonds and the site of unsaturation, but rather by the combination of the degree of oligomerization, decrease in the level of unsaturation, the virtual absence of hydroxyl functionalities in the stolide backbone, and the nature of the specific ester fraction (R). However, the process inherently introduces a distribution of secondary bond positions in the stolide, which in general affects very favorably low temperature and viscometric behavior. Minor components other than oleic acid, such as linoleic acid or stearic acid can lead to variations in the basic structure of stolide shown in Formula I. The oleic acid stylosides to be used in the preparation of esters of this invention can be recovered by any conventional method. Typically, the preponderance of low boiling point monomer fraction (unsaturated fatty acids and saturated fatty acids) and also dimer acids that can be formed are removed. In a preferred embodiment, the reaction conditions will be selected such that in the course of the reaction nothing occurs, or substantially none, of dimer acids, only stolides being formed and the residue fraction substantially comprising pure stolides. The oleic stolides are esterified by normal procedures, such as acid catalyzed reduction and with an appropriate alcohol. In the preferred embodiment of the invention R. and R2 are not both hydrogen and, more preferably, neither Ri nor R2 are hydrogen. Tis, it is preferred tthe reactant alcohol be branched. In the most preferred embodiment of the invention, the oleic stolide esters are selected from the group of isopropyl ester, 2-ethylhexyl ester and isostearyl ester. It is also preferred tthe average value of n in Formula I be greater than about 0.5 and more preferably greater than about 1.0. Particularly contemplated within the scope of the invention are those esters which are characterized by: a viscosity at 40 ° C of at least 20 cSt and preferably at least about 32 cSt; a viscosity at 100 ° C of at least 5 cSt and preferably at least about 8 cSt; a viscosity index of at least 150; a pour point of less than -21 ° C and preferably at least -30 ° C; a volatility of less than 10% at 175 ° C; an insignificant oxypolymerization (<10%) in 30 minutes at 150 ° C in the microoxidation test [Cevitkovic et al., ASLE Trans, 22: 395 (1979); Asadauskas, PhD Thesis, Pennsylvania State Univ. P. 88 (1997)]; and a biodegradability in the OECD test greater than 70%. The determination of these properties by conventional test procedures are routine. Therefore, the identification of oleic stolide esters within the scope of Formula I will be fully within the knowledge of ordinary persons of the art. As previously indicated and demonstrated in the Examples below, the oleic stolide esters of this invention have superior properties which make them useful as raw materials for biodegradable lubricant applications, such as crankcase oils, hydraulic fluids, perforation, oils of two-cycle engines and the like. Some of these esters meet or exceed many, if not all, of the specifications for some applications of terminal use lubricants without the inclusion of conventional additives. When used as raw material, the present esters can be mixed with an effective amount of other lubricating agents such as mineral or vegetable oils, other styolides, polyalphaolefins, polyol esters, oleates, diesters and other natural or synthetic fluids. In the preparation of lubricants, any of a variety of conventional lubricant additives can optionally be incorporated into the raw material in an effective amount. Illustrative examples of these additives are detergents, antiwear agents, antioxidants, viscosity index improvers, pour point depressants, corrosion protectors, coefficient of friction modifiers, dyes, defoaming agents, demulsifiers and the like. The term "effective amount" as used herein, is defined as meaning any amount that produces an measurable effect, for the intended purpose. For example, an effective amount of an anti-wear agent used in a lubricant composition is an amount that reduces the wear on a machine by a measurable amount, when compared to a control composition that does not include said agent.

EXAMPLE 1 Preparation of 2-Ethylhexyl Oleic Stolide (Laboratory) To 1 000 ml of commercial grade oleic acid (70% oleic) in a 3,000 ml 3-neck flask, at a vacuum of 27 in. (686 mm) of Hg 50 ml of sulfuric acid are added in the course of 4 min. The temperature was maintained at 55 ° C for 24 hours and the agitation speed was 300 rpm. After breaking the vacuum with nitrogen, 373 ml (2.39 moles, 1.1 molar equivalents) of 2-ethylhexyl alcohol were added to the flask for 5 min and subsequently the vacuum was restored. After mixing for 2 hours at 55 ° C, 190 g of Na2HP? 4 in 2 L of water were added with vigorous stirring. The mixture was allowed to stand overnight and the water layer was removed. The product was recovered by removing the alcohol using vacuum distillation at 0.1-0.5 torr at 100 ° C. During the course of three runs, the overall production of the product varied from 82-84%, and the average value of n in Formula I was 1.2.

Example 2 Preparation of 2-Ethylhexyl Oleic Stolide (Pilot) A pilot scale production of 2-ethylhexyl oleic stolide was carried out as follows: Two hundred fifty pounds (113 kg) of oleic acid (commercial grade) were added to a drum covered with plastic and degassed with a nitrogen sprayer for 15 minutes. Twenty-three pounds (10 kg) of concentrated sulfuric acid were added slowly with stirring, maintaining the temperature below 55 ° C by the rate of addition. The temperature of the drum was maintained after all the sulfuric acid was added by storage in a warm space at 55 ° C. After 24 hours, a sample of forty pounds (18 kg) was removed and the acid value and iodine value were checked. Sixty-eight pounds (31 kg) of e-ethylhexanol were then added and after 2 hours it was confirmed that the hydroxyl value was less than 10.0, signaling completion of the reaction. The reaction mixture was washed by mixing with a 10% solution of potassium acid phosphate [50 Ibs (23 kg) of K2HP0 in 500 Ibs (227 kg) of city water]. After the separation for 1 hour by sedimentation, it was verified that the pH in both layers was 5-6 and the water layer was decanted. After separation, the ester of stolide was transferred to a kettle and dried under vacuum at 105 ° C and 29 inches of Hg to remove excess water and 2-ethylhexanol. Vacuum drying was followed by filtration under pressure using 0.5% filtration aid. The value of n in the Formula was 0.5.

Example 3 Characterization of the Physical Properties of the 2-Ethylhexyl Oleic Stolide of Example 2. Biodegradation is usually tested using the modified Sturm test, measuring the degradation percentage in 28 days (OECD 301 B). The biodegradabilities in the main raw materials are compared with those of unsterified oleic stolide in Table I. It is expected that the 2-ethylhexyl ester of the oleic stolides does not have biodegradability substantially different from that of the non-esterified stolides. The viscometric properties determine the flow characteristics of the lubricants, their film thickness, and their ability to maintain a film of lubricant under varying temperatures. In the lubricant industry these properties are determined by measuring kinematic viscosities using Canno Fenske viscometers and subsequently assigning viscosity grades. ISO 32 and ISO 46 are the most popular. The key viscometric properties of most of the raw materials used industrially to prepare biodegradable lubricants are compared in Table II with 2-ethylhexyl ester (2EH) of oleic stolide.

The advantage of the stolide is its high viscosity index (VI) and viscosity grade of ISO 46. This compares to the viscometric properties of oleates and vegetable oils. This stolide would not require thickeners that are necessary for tridecyl adipate or PAO2. The presence of polymer-based thickeners or viscosity modifiers can cause problems of cutting stability in formulated lubricants. The low temperature properties are important for the ease of pumping lubricants, the capacity of filtration, the fluidity, as well as for the rotation and cold start. The point of runoff is the most common indicator of low temperature behavior. Raw materials derived from vegetable oils usually can not remain liquid in cold storage tests for more than 1 day, therefore, in addition to the point of runoff, the cold storage test is being developed by ASTM D02 to evaluate the stability of lubricants. The key properties of low temperature are compared in Table III. The stolide has significantly better low temperature properties than trioleates, vegetable oils or polyol esters of higher viscosities. Volatility is very important for the vapor pressure of the lubricant, the flammability, burning of volatiles and emissions. Volatility is related to the flash point, which is measured using the Cleveland Open Cup test method. The micro-oxidation data allows to quantify the volatility at particular temperatures, in this case 150 ° C (same range as the hydraulic system or crankcase of the engine crankshaft). The key properties of volatility are compared in Table IV. Stolides are much less volatile than PAOs or low viscosity adipates. Oxidative stability defines the durability of lubricants and their ability to maintain functional properties during use. Lubricants based on vegetable oils and oleates usually suffer from poor oxidative stability. Microoxidation is recognized in the lubricant industry as a technique for cataloging oxidative stabilities by quantifying oxypolymerization tendencies. The microoxidation information is compared in Table V. The oxidative stability of the stolides is comparable to that of fully saturated materials such as PAOs, polyol esters and adipates. Vegetable oils and most of the fluids derived from them are clearly inferior to the stolides. In general, the ester of 2-ethylhexyl ester has advantages over vegetable oils and oleates in their oxidative stability and low temperature properties, on PAOs and adipates of low viscosity, in volatility, viscometric properties and biodegradability.

EXAMPLE 4 Substances of methyl, butyl, decyl, oleyl, isopropyl, isostearyl and branched C24 of oleic stolide for the 2-ethylhexyl ester were prepared substantially as described in Example 1. These esters were evaluated in terms of their melting point, viscosity index and viscosity at each of the temperatures of 100 ° F (38 ° C), 40 ° C and 100 ° C compared to known vegetable oils, fatty acids and other styolides and vegetable oil derivatives. The results are presented in Table VI.

EXAMPLE 5 The pour points of 12-hydroxystearic acid esters (Guerbet) and 2-ethylhexyl ester of ricinoleic stolide and oleic stolide were compared (Table VII). It is understood that the foregoing detailed description is provided only by way of illustration and that modifications and variations may be made thereto without departing from the spirit and scope of the invention.

Table 1 Properties, units (TMP Estoluro method, PAO 2 Adipate Ester test oil) trioleate cañola tridecyl polyol Modified Sturn Test,% in 28 days > 80% 70% > 85% > 70% < 40% < 30% (OECD 301 B) Table II Table Properties, units (method of Estoluro 1 TMP Oil of II PAO 2 l Ester of I Adipato test) 2EH | Trioleato cañola | I polyol || tridecil Drain point, ° C (ASTM D 97) -27 -24 -18 I -72 I -21 -54 Cold storage (at -25 ° C), 7+ days < 1 < 1 I 7+ I < 1 I 7+ Table IV Table V Table VI Formula I Viscosity index point (cSt) | SAMPLE Fusion weight (° C) viscosity (g / mol) | 100 ° F 40 ° C 100 ° C | Cranberry oil 1042 6 205 54.2 50.7 10.6 Pradofoam oil 1020 1 207 53.2 48.9 10.4 Rape seed oil 1024 6 203 50.0 46.5 9.8 Soybean oil 924 -9 * 217 35.0 33.3 7.8 Erucic oil 338 35 186 36.9 34.3 7.3 Fatty acids of meadowfoam 310 204 24.6 22.9 5.6 Miter Esters of meadowfoam 324 -13 201 6.3 6.0 2.2 Butyl esters from meadowfoam 366 -16 209 8.0 7.6 2.6 Decor Esters from meadowfoam 450 - 2 117 12.3 11.5 3.0 Pradofoam oleyl esters 560 meadowfoam isopropyl esters 352 9.1 200 11.7 11.2 3.4 2-ethylhexyl esters from meadowfoam 422 -19.6 197 10.5 9.9 3.1 meadowfoam isostearyl esters 566 -5.6 200 21.6 20.1 5.1 C24 ester branched meadowfoam 622 Oleic acid 282 13 185 20.0 19.2 4.8 Ester methyl oleic acid 296 -23 t 4.9 4.7 1.8 Oleic acid butyl ester 338 -24 226 6.7 6.3 2.3 Ester decyl of oleic acid 422 2 198 11.4 10.8 3.3 Oleic acid oleic ester 532 -10 241 18.6 17.5 5.0 Isopropyl ester of oleic acid 324 -37 192 9.5 9.1 2.9 2-ethylhexyl ester of oleic acid 394 -39 178 9.7 9.1 2.8 Isostearyl ester of oleic acid 538 -30 353 19.6 18.2 4.8 Branched C24 ester of oleic acid 622 - 5 193 25.3 23.4 5.6 'Stippling point between the two can not be determined for oils with low viscosity < 2.0 cSt @ 100 ° C

Claims (1)

1. (CH2) x (CH_) 2 e that 1; 5 of hydrogen and h unsaturated, of 10-chain oleic fatty acid, where the predominant species of the secondary ester bond is in the Table VII Runoff Point (° C) Ester Guerbet Ester 2-EH Ricinoleic stolide -12 Not available Oleic stolide -43 -27 to -35 7. The stolide compound of claim 1, wherein R is 2-ethylhexyl. 8. The stolide compound of claim 1, wherein R is isostearyl. 9. A lubricant composition comprising (1): a stolide compound of the Formula: R, -C (i) CH3 (CHa) j (CHj) and CH (CH,) x (CH2) 2C00R where x and y are each equal to 1 or greater than 1; where x + y = 10; where n is 0, 1 or greater than 1; wherein R is CHR.R2; wherein R. and R2 are independently selected from hydrogen and hydrocarbons d to C36, which may be saturated or unsaturated, branched or straight chain, and substituted or unsubstituted; wherein R3 is a residual fragment of an oleic, stearic or other fatty acid chain; and wherein the predominant species of the secondary ester bond is in the 9 or 10 position; that is, where x = 5 or 6 and y = 5 or 4, respectively. and (2), an effective amount of a lubricating agent. The lubricating composition of claim 9, wherein said lubricating agent is selected from the group consisting of mineral oil, vegetable oil, other styolide than that defined in Formula I, polyalphaolefin, polyol ester, oleate and diester. The lubricant composition of claim 9, and further comprising an effective amount of a lubricant additive selected from the group consisting of detergent, antiwear agent, antioxidant, viscosity index improver, pour point depressant, corrosion protector, modifier coefficient of friction, dyes, antifoaming agents and demulsifiers.