EP0420931A1

EP0420931A1 - Synthetic lubricants containing polar groups

Info

Publication number: EP0420931A1
Application number: EP89907958A
Authority: EP
Inventors: Catherine Shuihua Hsia Chen
Original assignee: Mobil Oil Corp
Current assignee: ExxonMobil Oil Corp
Priority date: 1988-06-23
Filing date: 1989-06-21
Publication date: 1991-04-10
Also published as: WO1989012663A1; AU3854889A; JPH03505342A

Abstract

On a mis au point un nouveau fluide lubrifiant polaire comprenant le produit de la réaction d'un énopile et d'hydrocarbure oléfinique C20+ contenant des groupes allyliques. Le produit de la réaction hydrogénée polaire présente d'excellentes propriétés lubrifiantes et la capacité de former des mélanges homogènes avec des additifs. Le produit d'addition est formé par addition thermiquement induite d'énophile à de l'oléfine ou par addition catalysée d'acide Lewis.A new polar lubricating fluid has been developed comprising the reaction product of an enopile and C20 + olefinic hydrocarbon containing allylic groups. The product of the polar hydrogenated reaction has excellent lubricating properties and the ability to form homogeneous mixtures with additives. The adduct is formed by thermally induced addition of enophil to olefin or by catalyzed addition of Lewis acid.

Description

SYNTHETIC LUBRICANTS CONTAINING POLAR GROUPS

This invention relates to novel compositions useful as lubricants having polar functional groups. In particular, the invention relates to novel lubricant compositions and methods for their preparation from lubricant range olefins and enophiles.

The formulation of lubricants typically includes an additive package incorporating a variety of chemicals to improve or protect lubricant properties in application specific situations, particularly internal combustion engine and machinery applications. The more commonly used additives include oxidation inhibitors, rust inhibitors, antiwear agents, pour point depressants, detergent-dispersants, viscosity index (VI) improvers, foam inhibitors and the like. This aspect of the lubricant arts is specifically described in Kirk-Othmer "Encyclopedia of Chemical Technology", 3rd edition, Vol. 14, pp477-526. Considering the diversity of chemical structures represented by the plethora of additives incorporated in a typical lubricant formulation, and the quantity in which they are added, the artisan in the lubricant formulation arts faces a substantial challenge to provide a homogeneous formulation which will remain stable or in solution during inventory and during use. Lubricants, particularly synthetic lubricants of the type of interest in the instant invention, are usually hydrogenated olefins. Due to their hydrocarbon structure they are largely incompatible with polar additives such as antioxidants, antirust and antiwear agents,etc. Accordingly, in order to render the lubricants compatible with the polar additives large amounts of expensive polar organic esters must be added to the formulation. Useful commercial formulations may contain 20% percent or more of such esters as bis-tridecanol adipate for example, solely to provide a fully homogeneous lubricant blend of lubricant and additive. Modifying the solvent properties of lubricants with solubilizing agents such as organic esters, while solving the problem of how to prepare stable blends with lubricant additives, creates or accentuates other performance related problems beyond the added burden on cost of the product. The vulnerability of solubilizing agents to oxidative degradation promoting the formation of tars and gums must be taken into account. Seal swelling properties may be changed. Seal swell measures the ability of a lubricant to swell a seal, thus enhancing its sealing function. Solubilizing agents may effect viscometric properties such as viscosity and viscosity index of the material. When materials deficient in these properties are added in large amounts, the lubricant's effectiveness will be impaired. In view of these complications it is evident that novel approaches are called for in the modification or formulation of lubricants to incorporate additives without compromising properties or adding significantly to the cost of the product.

One approach to improve lubricant compatibility with additives is to add polar groups to the structure of the lubricant. Lubricants, in particular synthetic lubricants, are known to contain olefinic unsaturation and it has been determined in the present invention that such unsaturation can be effectively utilized to react with polar groups to add a polar functionality on to the lubricant molecule. The added polar group in the lubricant has sufficient solubilizing character to adequately dissolve additive packages without the addition of solubilizing agents such as adipate esters. It has been discovered in the instant invention that the necessary functionality i.e., functional group, can be added to the lubricant by reacting the lubricant olefinic group with an electronegative enophile.

It has been found that unsaturated C₂₀+ lubricant range hydrocarbons containing an allylic hydrogen will react thermally or catalytically by addition to an alkene which contains olefinic unsaturation in the alpha,beta position to an electronegative group when the C₂₀+ unsaturated lubricant has the following structure comprising one or more allylic hydrogens:

where R₁, R₂, R₃, R₄ and R₅ may be hydrogen,alkyl or alkenyl and at least 17 carbon atoms in total.

The alpha, beta unsaturated alkenes useful in the present invention include all those having the structure:

where at least one of R₆, R₇, R₈ and R₉ is an electronegative group and the remainder hydrogen,alkyl, alkenyl, alkynalkyl, aryl or aralkyl. These structures are referred to herein as in the art as enophiles.

More particularly, a polar lubricant liquid has been obtained which liquid includes the adduct of the above unsaturated lubricant and unsaturated alkene and having the structure:

where at least one of R₈ or R₉ is an electronegative group and the remainder R₆, R₇, R₈ and R₉ is an electronegative group or hydrogen, alkyl, alkenyl, alkynalkyl, aryl or aralkyl and R₁, R₂, R₃, R₄ and R₅ is hydrogen, alkyl or alkenyl at least one of which is C₁₇+ alkyl or alkenyl group. Where the unsaturated C₂₀+ lubricant molecule contains multiple allylic groups more than one mole of enophile will react with the lubricant to form an adduct containing more than one electronegative group or multiple polar sites. According to the invention, hydrogenation of the olefinic bonds of the adduct yields a polar lubricant with dispersant properties.

The formation of the adduct between C₂₀+ olefinic lubricant and an enophile is accomplished in the present invention by heating the mixture at elevated or by reaction catalyzed by a Lewis acid such as BF3 or A1Cl₃.

The olefinic lubricants useful in the present invention in the formation of adducts with enophiles include unsaturated lubricants having 20 to 5000 carbon atoms where one or more of the unsaturated groups is allylic unsaturation. These include natural lubricants from mineral oil as well as synthetic lubricants containing twenty to five thousand carbon atoms. To be useful in the present invention all such lubricant molecules must contain one or more olefinic group of the following structure:

where R₁, R₂ ,R₃, R₄ and R₅ may be hydrogen, alkyl or alkenyl and at least 17 carbon atoms in total for the sum of carbon atoms in R₁ , R₂,R₃ , R₄ and R₅. The olefinic bond may be in the alpha position, i.e., a vinyl structure where R₁, and R₂ are hydrogen, or the bond may be an internal olefin where R₁, R₂, R₃, R₄ and/or R₅ is an aliphatic hydrocarbon. Since lubricants comprise a mixture of molecules usually having a wide range of molecular weights certain molecules may contain more than one olefinic bond, including alpha olefins and internal olefins of allylic structures. It is to be expected then that certain lubricant molecules may be produced according to this invention containing multiple adducts with specific enophiles, following reaction at multiple olefinic sites in the unsaturated lubricant molecule. Methods well known in the lubricant art are employed to produce the unsaturated lubricants required as feedstock in the instant invention. The separation of mineral oil provides C₂₀+ lubricant basestock having native olefinic unsaturation, or other petroleum fractions may be cracked or dehydrogenated to provide a C₂₀+ lubricant basestock containing olefinic unsaturation. Of particular interest as feedstock in the present invention are the synthetic lubricants, especially those derived from C₃+ olefins or polyalphaolefins.

Synthetic polyalphaolefins (PAO) have found wide acceptability and commercial success in the lubricant field for their superiority to mineral oil based lubricants. The PAO's are prepared by the polymerization of C₆-C₂₀ 1-alkenes such as 1-decene using typically Lewis acid catalyst such as BF₃, aluminum chloride or Ziegler- Natta catalysts. Their preparation and properties are described by J. Brennan in Ind. Eng. Chem. Prod. Res. Dev. 1980, 19, pp 2-6. PAO incorporating improved lubricant properties are also described by J. A. Brennan in U.S. Patents 3,382,291, 3,742,082, and 3,769,363, and also in U.S. 4,041,098. According to these references, C₃-C₅ olefins are oligomerized in contact with an acidic, medium pore, shape selective metallosilicate catalyst such as aluminosilicate. The aluminosilicate catalyst may have its surface dectivated by a surface deactivating agent such as a bulky amine or phosphine. As oligomerized according to the above procedures, the PAO contains olefinic unsaturation reactive with enophiles.

A novel class of PAO lubricant compositions, herein referred to as HVI-PAO, exhibiting surprisingly high viscosity indices has been obtained. These novel HVI-PAO lubricants are particularly characterized by low ratio of methyl to methylene groups, i.e., low branch ratios, as further described hereinafter and low pour points below -15°C. HVI-PAO lubricant basestock, typically with a viscosity of 3 to 500 mm₂/s at 100ºC and a very high VI greater than 130, are produced from alphaolefins, 1-alkenes, of C₆ to C₂₀ , either alone or in mixture, over an activated chromium of reduced valence state catalyst supported on silica. The HVI-PAO is further characterized by having a branch ratio of less than 0.19. As produced from the oligomerization step, both PAO and HVI/PAO contain olefinic unsaturation and may be used in the instant invention.

The branch ratios referred to are defined as the ratios of CH₃ groups to CH₂ groups in the lube oil and are calculated from the weight fractions of methyl groups obtained by infrared methods, published in Analytical Chemistry, Vol. 25, No. 10, p. 1466 (1953).

Branch ratio = wt fraction of methyl group

1-(wt fraction of methyl group)

The preparation of HVI-PAO is described in the following examples but utilized in the instant invention without the hydrogenation of the oligomerization product:

Example 1

A commercial Cr on silica catalyst which contains 1% Cr on a large pore volume synthetic silica gel is used. The catalyst is first calcined with air at 700°C for 16 hours and reduced with CO at 350 °C for one to two hours. 1.0 part by weight of the activated catalyst is added to 1-decene of 200 parts by weight in a suitable reactor and heated to 185 °C. 1-Decene is continuously fed to the reactor at 2-3.5 parts/minute and 0.5 parts by weight of catalyst is added for every 100 parts of 1-decene feed. After 1200 parts of 1-decene and 6 parts of catalyst are charged, the slurry is stirred for 8 hours. The catalyst is filtered and light product boiled below 150 °C at 13 Pa (0.1mm Hg) is stripped. The residual product is hydrogenated with a Ni on Kieselguhr catalyst at 200 °C. The finished product has a viscosity at 100 °C of 18.5 mm²/s, VI 165 and pour point of -55 °C. Example 2

Similar as in Example 1, except reaction temperature is 185 °C. The finished product has a viscosity at 100°C of 145 mm²/s, VI of 214, and a pour point of -40°C.

Example 3

Similar as in Example 1, except reaction temperature is 100 °C. The finished product has a viscosity at 100°C of 298 mm²/s, VI of 246 and a pour point of -32°C.

Unsaturated lubricants containing allylic groups obtained from the oligomerization of lower olefins such as C₃-C₆ olefins in contact with an acidic, shape selective metallosilicate catalyst, such as ZSM-5, are also useful in the present invention. These lubricants generally have a viscosity between 2 and 12mm²/s at 100ºC. U.S. Patent 4,568,786 describes the oligomerization of propylene to produce a low molecular weight lube olefin which can be reacted according to the present invention to provide the novel adduct disclosed. Other zeolite catalyzed processes producing olefinic lubes useful in the present invention are described in the following U.S.Patents 4,520,221, 4,658,786 both to C.S.H.Chen.

The alpha,beta unsaturated alkenes useful in the present invention include all those having the structure:

where at least one of R₆, R₇, R₈ and R₉ is an electronegative group and the remaining groups are hydrogen, alkyl, alkenyl, aryl or aralkyl. These structures are referred to herein as enophiles. The electronegative groups useful in the enophiles of structure (II) include:

where A is 0, NH, NR where R is alkyl ; -C-Z where Z is H, OH,

NH₂, halogen, alkyl, aryl, benzyl; and groups such as -CN, -NO₂,

0-» aryl,benzyl, -CH₂CN, -CH₂X where X is halogen, -C-OQ where Q is alkyl, aryl or benzyl. Enophiles of particular use in the instant invention include maleic anhydride, maleimide, acrylonitrile, styrene, 4-carboethoxy styrene, ethylacrylate, acrylamide, acrolein, methyl vinyl ketone, phenyl vinyl ketone, cinnamyl chloride,

4-sulfamyl styrene, methacrylic acid, ethyl vinyl carbonate,

2-hydroxyethyl acryate and the like.

The novel lubricants of the present invention are prepared according to the well-known "Ene" reaction by reacting the unsaturated lubricants and enophiles described above thermally or in contact with a catalyst to form the unsaturated adduct. The "Ene" reaction is described in "Accounts of Chemical Research",

1980,13,426-432 by B.B. Snider. Upon completion of the "Ene" reaction and formation of the adduct, the adduct is hydrogenated to produce the polar lubricants of the invention. The adduct (III) and the polar saturated lubricant (IV) have the structure:

where,in (III) and (IV), R, through Rr may be hydrogen, alkyl or alkenyl and the sum of carbon atoms in all R₁ through R5 groups totals at least 17, where at least one of R₈, R₉ is an electronegative group with the remaining groups of R₆ through R₉ being an electronegative group or hydrogen, alkyl, alkenyl, alkynalkyl, aryl or aralkyl.

where the unsaturated lubricant feedstock contains molecules having multiple sites of allylic unsaturation, the Ene reaction will produce an adduct containing multiple enophile moieties comprising lubricant molecules of particularly enhanced polarity.

As noted above, the Ene reaction adduct formation between unsaturated lubricant molecules and enophiles may be conducted thermally at temperatures between 100°C and 400°C either neat or in a solvent. The process may be conducted as a batch process or continuous. Where catalysts are used, Lewis acid catalysts are preferred such as BF₃, AlCl₃, (CH₃)₂A1Cl, SnCl₄, C₂H₅A1C1₂ and the like.

The scope of the present invention includes the further reaction of the polar function of the hydrogenated adducts prepared by the process of the invention to provide further useful products, typically enhancing the properties of the lubricant. For example, the nitrile function of adducts prepared from acrylonitrile may be hydrolyzed to acid or amide or esterified by methods well known in the art. Hydrogenation of the adduct formed between an unsaturated lubricant and maleic anhydride produces the substituted succinic anhydride which may be further reacted with alcohol by known means to yield a diester of the structure (V) from the anhydride (VI):

where R in (V) and (VI) is hydrogen, alkyl or alkenyl and the total number of carbon atoms in all R groups is at least 17 and, preferably, with at least one R group a lubricant moiety of between

C₁₇ and C₁₀₀₀ carbon atoms, more preferably between

C₃₀-C₆₀. R₁ of (V) is C₁-C₃₀ alkyl such as methyl, ethyl, 2-hydroxyethyl, propyl, octyl, lauryl and the like.

In the following examples the process and products of the instant Invention are described together with the distinguishing characteristics of the novel lubricants.

Example 4

297g of an olefin mixture containing C₃₀ and C₄₀ olefins obtained according to the procedure of J. Brennan as referenced hereinbefore in U.S. patents 3,382,291 3,742,082 3,769,363 and 4,041,098 from oligomerization of decene-1, and 44.5g of maleic anhydride are charged into a 450 ml Parr reactor equipped with a stirrer, a gas inlet and a sampling outlet. After the reactor is closed, the charged mixture is purged with nitrogen and left with 294 kPa (28 psig) nitrogen pressure for convenient sampling during the reaction. The mixture is heated with stirring to 175 °C whereby the pressure increased to 793 kPa (100 psig) and kept at this temperature for 14 days. Samples are taken periodically during the reaction and analyzed by GC, FTIR, and proton NMR for the overall boiling range and structural changes of the reaction mixture. The GC results show a progressive decrease with time in the relative amounts of maleic anhydride and C₃0 and a corresponding increase in the amounts of higher boiling materials. Both the FTIR results and the proton NMR results showed progressive reaction between the olefins and maleic anhydride forming the corresponding succinic anhydride adducts. Although the reaction was carried out for 14 days at 175°C, analytical results showed that no significant change took place after 9 days.

After cooling the reaction mixture to room temperature, the reactor is opened and the reaction mixture is taken out and subjected to a short-path distillation to remove any unreacted maleic anhydride. IR and NMR spectra confirm the structure. The product has a significantly higher viscosity than the starting olefin mixture but still maintained a high viscosity index as indicated in Table I:

TABLE 1

Comparison of Viscosities and Viscosity Indices Between Starting Olefins and Product Succinic Anhydride Adducts

Viscosi ty Viscosity

Materials Temp. °F Kv, mm²/s Index

Starting Olefins 104 29.6 132

212 5.43

Products 104 75.19 122

212 10.35 Example 5

227g of the succinic anhydride adducts obtained in Example 4 is hydrogenated at 140°C over a nickel catalyst (Harshaw 5132-P) in a Parr reactor until no more hydrogen is taken up. After filtering off the nickel catalyst, the hydrogenated succinic anhydride adducts are refluxed overnight in excess ethanol over HZSM-5B catalyst as the esterification catalyst. After removing the catalyst and excess ethanol, the product is identified as diethyl succinic esters by IR and is shown to be soluble in a variety of polar organic compounds.

Example 6

The "Ene" reaction was carried out between 305g of the C₃0 -C₄0 mixture and 48g of maleic anhydride as described in Example 4, except that the reaction temperature is raised to 190°C. The reaction is essentially complete in 5 days.

Example 7

100g of the succinic anhydride adduct obtained in Example 6 in 100g of ethanol is hydrogenated over 1g of 10% palladium on charcoal at 50°C. After filtering off the hydrogenation catalyst the mixture esterified over HZSM-5B as described in Example II.

Example 8

100g of low molecular weight lube olefins obtained from oligomerization of propylene via a two-stage zeolite catalytic process as described in U.S. 4,568,786, and 20g of maleic anhydride are reacted according to Example 4 and the reaction is essentially complete in 30 hours. The increase in the boiling range from the starting material to the product is substantial as shown in Table II. TABLE II

Comparison of GC Retention Time Between Starting Olefins and Functionalized Products

Percent of Total

Retention Time,sec Starting Olefins Products

< 1515 (>c₁₈=) 99.8 98.2

<1785 (>C₂₀=) 89.4 92.4

<2160 (>C₂₅=) 6.0 40.0

Although the present invention has been described with preferred embodiments, it is to be understood that modifications and variations may be resorted to, without departing from the spirit and scope of this invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the appended claims.

Claims

What is claimed is:

1. A polar lubricating fluid comprising the adduct of an enophile and olefin hydrocarbon having at least 20 carbon atoms, the adduct having the structure:

where R₁, R₂, R₃, R₄ and R₅ are hydrogen, alkyl or alkenyl and the sum of carbon atoms of all R₁, R₂, R₃, R₄ and R₅ groups is at least 17, where at least one of R₈ and R₉ is an electronegative group selected from

0 where A is 0, N or NR where R is alkyl; -C-Z where Z is H, OH,

NH₂, halogen, alkyl, aryl, benzyl, -CN, -NO₂, -CH₂CN, -CH₂X where X is halogen ^OC-OQ where Q is alkyl, aryl or benzyl; R₆, R₇, R₈ and R₉ being selected from the electronegative group or hydrogen, alkyl, alkenyl, alkynalkyl, aryl or aralkyl.

2. The polar lubricating fluid of claim 1 wherein the adduct is hydrogenated.

3. The lubricating fluid of claim 1 wherein the enophile has the structure:

where at least one of R₆, R₇, R₈ and R₉ is the electronegative group and the remaining groups are hydrogen, alkyl, alkenyl, alkynalkyl, aryl or aralkyl.

4. The lubricating fluid of claim 1 wherein the olefin comprises C₂₀+ alpha olefins having a branch ratio less than 0.3 and a molecular weight between 280 and 20,000.

5. The lubricating fluid of claim 4 wherein the olefin comprises C₃₀-C₄₀ olefins.

6. The lubricating fluid of claim 2 having the structure:

and acidic or araido reaction products thereof with water, ammonia or amines and where R is hydrogen, alkyl or alkenyl and the total number of carbon atoms in all R groups is at least 17.

7. The lubricanting fluid of claim 2 having the structure:

where R is hydrogen, alkyl or alkenyl and the total number of carbon atoms in all R groups is at least 17 and R₁ is C₁-C₃₀ alkyl methyl, ethyl, 2-hydroxyethyl, propyl,octvl, lauryl or aryl.

8. The lubricating fluid of claim 1 wherein the olefin comprises the oligomerization product of C₆-C₂₀ alpha olefins in contact with a Lewis acid or Ziegler-Natta type catalyst, the oligomerization product having a VI greater than 80.

9. The lubricating fluid of claim 1 wherein the olefin comprises the product of C₃-C₅ olefin oligomerized in contact with an acidic, medium pore , shape selective metallosilicate catalyst.

10. The lubricating fluid of claim 9 wherein the metallosilicate is aluminosilicate.

11. The lubricating fluid of claim 10 wherein the aluminosilicate is surface deactivated by a surface deactivating agent comprising a bulky amine or phosphine.

12. The lubricating fluid of claim 2 wherein the hydrogenated adduct has a viscosity of 75 mm²/s at 104°C and a VI of 122.

13. The lubricating fluid of claim 6 comprising succinic acid having C₂₀+ hydrocarbon substituent in the alpha position.

14. The lubricating fluid according to claim 1 wherein the ratio of the enophile moiety to the olefin hydrocarbon moiety in the adduct is greater than one.

15. A process for the production of a polar lubricating fluid comprising the adduct of an enophile and a C₂₀+ olefin, comprising: reacting the enophile and the olefin at an elevated temperature in an enclosed reaction zone; and separating the effluent from the reaction zone whereby the adduct is produced.

16. The process of claim 15 wherein the olefin and the enophile are reacted in contact with a Lewis acid catalyst.

17. The process of claim 15 further comprising the step of hydrogenating the adduct in contact with a hydrogenating catalyst and hydrogen at a temperature between 20 and 300 ºC to produce a hydrogenated polar lubricating fluid.

18. The process of claim 15 wherein the elevated temperature is between 40 and 400 C.

19. The process of claim 15 wherein the enophile comprises maleic anhydride, the olefin comprises C₃₀-C₄₀ hydrocarbon obtained from oligomerization of 1-decene.

20. A process according to claim 15 wherein said enophile and the C₂₀+ olefin are reacted in a mole ratio of enophile to C₂₀+ olefin greater than one.