EP0323088A1

EP0323088A1 - Preparation of overbased magnesium sulphonate

Info

Publication number: EP0323088A1
Application number: EP88311968A
Authority: EP
Inventors: John Arthur Cleverley; John Frederick Marsh; Joseph Marian Swietlik
Original assignee: Exxon Chemical Patents Inc
Current assignee: ExxonMobil Chemical Patents Inc
Priority date: 1987-12-29
Filing date: 1988-12-16
Publication date: 1989-07-05
Also published as: BR8806939A; JPH01308820A

Abstract

Overbased magnesium sulphonates having increased resistance to interactions, to modifications to the manufacture of overbased magnesium sulphonates to reduce interactions and to compositions comprising overbased magnesium sulphonate, particularly in combination with high molecular weight dispersants and/or friction modifiers are prepared by introducing an ashless dispersant into the carbonation mixture. Stable sediment-free lubricating oil compositions (including lubricants and concentrates therefor) can be prepared from these sulphonates to meet the SG quality and the Tier II fuel economy requirements.

Description

This invention related to improved overbased magnesium sulphonates and to compositions containing them, particularly for use in lubricating oils for use in transport applications.
Magnesium sulphonates are well-known lubricant additives, and are described as "overbased" when they contain a stoichiometric excess of magnesium compared to that required to neutralize the sulphonic acid. Overbased magnesium sulphonates are commonly used as detergents in lubricating oils. They are generally prepared by carbonation of a reaction mixture comprising a sulphonic acid or sulphonate and an excess of a magnesium compound such as an alkoxide, oxide or hydroxide in oil, typically with a hydrocarbon solvent and usually in the presence of a promoter. Examples of preparations are found in US-A-3158009, GB-A-1166744, GB-A-1297150, GB-A-1399092, EP-A-0013808 and EP-A-0015341.
Lubricating oils for automobile are having to pass increasingly severe tests, usually engine tests, for approval by automobile manufacturers, and/or to meet industry standards. In particular, tests for sludge and varnish inhibition are becoming more severe requiring the use of more potent dispersants. The oils are also being required to be more resistant to thickening caused by oxidation, requiring the use of potent antioxidants. The SC quality level in the API Engine Service Categories for service station oils developed by API in conjunction with ASTM and SAE reflects this increased severity in requirements for passenger car applications.
Additionally, there is a desire to improve the effect of lubricating oils on fuel economy requiring the use of friction modifier. API in conjunction with ASTM and SAE has developed a more stringent engine test (Sequence 6 Test) for determining fuel economy performance, and a pass at the so-called "Tier II" level of fuel economy for a lubricating oil requires a 2.7 percent minimum improvement in fuel economy versus a standard lubricating oil run in the Sequence 6 engine test.
The use of overbased magnesium sulphonates in lubricating oils designed to meet these more stringent criteria can give rise to problems of interactions between the additives, either in concentrated form or in the finished lubricants, which may result in undesirable sediment or haze formation.
This invention relates to overbased magnesium sulphonates having increased resistance to interactions, to modifications to the manufacture of overbased magnesium sulphonates to reduce interactions and to compositions comprising overbased magnesium sulphonate, particularly in combination with high molecular weight dispersants and/or friction modifiers. The invention may provide stable sediment-free lubricating oil compositions (including lubricants and concentrates therefor) which can meet the proposals for SG quality and the Tier II fuel economy requirement (as defined hereinbefore).
The high molecular weight dispersants which may be used in the invention include those of number average molecular weight (M_n) of greater than 1300, e.g. those described in EP-A-0208560. Friction modifiers are well known and include polar materials such as partial esters of fatty acids such as glyceryl mono-oleate, various straight chain acids such as oleic acid and stearic acid and derivatives of linoleic acid dimers.
The overbased magnesium sulphonate is prepared by a process as described hereinbefore in which the reaction mixture for carbonation contains an effective amount, preferably 0.5 to 10 wt% (of the formed overbased magnesium sulphonate) of an ashless dispersant. The ashless dispersant is preferably a reaction product of:

(a) a hydrocarbyl-substituted C₄ to C₁₀ mono-unsaturated acid or anhydride; and
(b) an amine, alcohol, amino-alcohol or mixtures thereof,

As an alternative, an ashless dispersant comprising a hydrocarbyl-substituted C₄ to C₁₀ mono-unsaturated acid or anhydride may, without further reaction, be used in the reaction mixture in the preparation of an overbased magnesium sulphonate according to the invention.
The term "ashless" is used in connection with dispersants herein as it is used in the field of lubricating compositions - that is, to refer to dispersants which do not form any significant amounts of ash, sulphated ash- (as measured e.g. by ASTM D482 and 874) on combustion, and are not metal salts. The term does not exclude borated materials as described herein, or dispersants containing incidental amounts of metal salts, such as zinc salts, which are occasionally used in preparing ashless dispersants as catalysts and may be present in the product typically in an amount of 0.01 to 0.5 wt % of the dispersant.
The hydrocarbyl-substituted C₄ to C₁₀ mono-unsaturated acid or anhydride, whether used as such or as a reaction product with an amine, alcohol, amino-alcohol or mixtures thereof, is preferably a hydrocarbyl succinic acid or anhydride comprising a hydrocarbon group substituted with one or more moles, per mole of hydrocarbon, of maleic acid. The preferred hydrocarbon is a long chain hydrocarbon having at least 50 carbon atoms, and polyolefins having a molecular weight of at least 900 are more preferred. The preferred polyolefin is polyisobutylene, and for convenience hereinafter polyisobutenyl succinic anhydride or acid will be referred to as PIBSA. A preferred category of PIBSA has a number average molecular weight of from 900 to 5000, and more preferably also comprises at least 1 succinic moiety per polyisobutene.
When the ashless dispersant is a reaction product of PIBSA with component b), as defined hereinbefore, it is preferred that b) is a polyamine (hereinafter referred to as PAM). A preferred group of PAMs are polyalkyleneamines with alkylene groups containing 2 to 6 carbon atoms and with 2 to 8 nitrogen atoms per molecule. The polyamines used may comprise a single polyalkyleneamine, or a commercial mixture comprising two more more such amines.
Preferred PIBSA/PAM reaction products for use in the invention include those wherein the polyisobutene group has a number average weight (M_n) of 900 to 2500, and specific examples of such products contain a polyisobutene group of M_n = 950, 1300 and 2200. However, a wide range of ashless dispersant, and particularly PIBSA based dispersants, may be used in the invention. Each of these products may be used in a borated form or without boration.
The preferred process of the invention comprises carbonating a reaction mixture comprising:

a) an oil-soluble sulphonic acid or sulphonate;
b) a stoichiometric excess of a magnesium compound such as an alkoxide, oxide or hydroxide;
c) oil;
d) hydrocarbon solvent such as benzene, toluene or xylene, with toluene being a preferred solvent;
e) promoter such as ketones, amines, oil-soluble carboxylic acids, amine salts or diketones
f) 0.5 to 10 wt % (of the ultimately formed overbased magnesium sulphonate) of an ashless dispersant

The sulphonic acid or sulphonate may be natural or synthetic with synthetic alkylaryl sulphonic acids and sulphonates being preferred. The alkyl substituent in such alkylaryl moieties may have 15 or more carbon atoms and is typically a polyolefin formed from an olefin having 2 to 5 carbon atoms.
The magnesium compound provides the basicity to the formed overbased magnesium sulphonate and is therefore present in excess of the amount stoichiometrically required to react with the sulphonic acid, the amount in the product dictating the total base number (TBN) of the product. It may however be introduced in stages with intervening carbonation steps.
The solvent is typically present in an amount of from 0.1 to 10 parts by weight of solvent per part of magnesium in the reaction mixture. The promoter is typically present in an amount of from 0.01 to 5 parts by weight per part of magnesium in the reaction mixture. Water may be present in an amount of from 0 to 2 parts by weight per part of magnesium in the reaction mixture.
An additional surfactant such as an alkyl phenol may be present in an amount of from 0 to 1 part by weight per part of magnesium present in the reaction mixture.
The reaction mixture is carbonated by passing carbon dioxide gas through the mixture at a typical temperature of 25° to 200°C, with a preferred range being 50° to 150°C.
After carbonation the product may be stripped to remove volatiles, and filtered to remove solids, but these operations may be carried out in either order. Further carbonation may be carried out during stripping and further oil may be added to replace material lost in stripping.
The formed product may be post-treated with a carboxylic acid and/or a glycol to improve the water tolerance and/or stability and/or foaming performance and/or seal compatibility thereof.
The overbased magnesium sulphonate preferably has a total base number (TBN) as measured by ASTM D2896 of at least 300, more preferably 300 to 450, and most preferably about 400.
The overbased magnesium sulphonates may be used in oleaginous compositions, e.g. lubricants and concentrates therefor, and in particular those comprising:-

(i) high molecular weight ashless dispersant, and preferably an ashless dispersant of the type described hereinbefore for use in the carbonation, but having M_n of at least 1300, more preferably 1500-5000 and optionally
(ii) friction modifier, preferably even when used at the levels required to meet the Tier II fuel economy requirement (as defined hereinbefore) which may require levels of friction modifier in a concentrate of greater than 0.5 wt%, and/or
(iii) copper compound as antioxidant, and/or
(iv) a zinc dihydrocarbyl dithiophosphate (ZDDP), and/or
(v) other conventional additives.

The overbased magnesium sulphonate will typically comprise from 0.01 to 5 wt % of such compositions for use as crankcase lubricants, but concentrates may contain up to 50 wt % of the overbased magnesium sulphonate. The tendency for such compositions and concentrates to give interactions may be tested by blending the additives required for the composition or concentrate which are then stored at an elevated temperature, typically 54°C or 66°C and observing the appearance of haze/sediment.
A lubricating oil composition or concentrate may be regarded as being acceptably stable if it is clear and substantially free from haze and/or sediment after at least 3 months at 66°C. The compositions of the invention may provide a means of meeting more severe testing regimes with acceptably stable formulations and packages.
The compositions contain a major amount of a lubricating oil which may be a mineral lubricating oil, a synthetic lubricating oil or mixtures thereof. The synthetic oils include polyalpha olefins, diester oils, such as di(2-ethylhexyl) sebacate, azelate and adipate, complex ester oils such as those formed from dicarboxylic acids, glycols and either monobasic acids or monohydric alcohols and silicone oils.
In addition to the additives specifically listed above, the compositions may contain additives such as viscosity modifiers, corrosion inhibitors, other oxidation inhibitors, other friction modifiers, other dispersants, anti-foaming agents, anti-wear agents, pour point depressants, detergents, rust inhibitors and the like.
Viscosity modifiers impart high and low temperature operability to the lubricating oil and permit it to remain shear stable at elevated temperatures and also exhibit acceptable viscosity or fluidity at low temperatures.
Viscosity modifiers are generally high molecular weight hydrocarbon polymers including polyesters. The viscosity modifiers may also be derivatized to include other properties or functions, such as the addition of dispersancy properties.
These oil soluble viscosity modifying polymers will generally have number average molecular weights of from 10³ to 10⁶, preferably 10⁴ to 10⁶, e.g. 20,000 to 250,000, as determined by gel permeation chromatrography or membrane osmometry.
Representative examples of suitable viscosity modifiers are any of the types known to the art including polyisobutylene, copolymers of ethylene and propylene, polymethacrylates, methacrylate copolymers, copolymers of an unsaturated dicarboxylic acid and vinyl compound, interpolymers of styrene and acrylic esters, and styrene/isoprene copolymers.
Corrosion inhibitors, also known as anti-corrosive agents, reduce the degradation of the metallic parts contacted by the lubricating oil composition. Illustrative of corrosion inhibitors are phosphosulphurized hydrocarbons and the products obtained by reaction of a phosphosulphurized hydrocarbon with an alkaline earth metal oxide or hydroxide, preferably in the presence of an alkylated phenol or of an alkylphenol thioester, and also preferably in the presence of carbon dioxide. Phosphosulphurized hydrocarbons are prepared by reacting a suitable hydrocarbon such as terpene, a heavy petroleum fraction of a C₂ to C₆ olefin polymer such as polyisobutylene, with from 5 to 30 wt % of a sulfide of phosphorus for 1/2 to 15 hours, at a temperature in the range of 150°F to 600°F. Neutralization of the phosphosulphurized hydrocarbon may be effected in the manner taught in US Patent No. 1,969,324.
Oxidation inhibitors reduce the tendency of mineral oils to deteriorate in service which deterioration can be evidenced by the products of oxidation such as sludge and varnish-like deposits on the metal surfaces and by viscosity growth. Such oxidation inhibitors include ZDDP's, aromatic amines such alkylated diphenylamines and phenyl alpha naphthylamine, hindered phenols, copper compounds, alkaline earth metal salts of alkylphenolthioesters having preferably C₅ to C₁₂ alkyl side chains, eg, calcium nonylphenol sulphide, barium t-octylphenyl sulphide, dioctylphenyl-amine, phenylalphanaphthylamine and phosphosulphurized or sulphurized hydrocarbons.
Friction modifiers serve to impact the proper friction characteristics to lubricating oil compositions such as automatic transmission fluids.
Representative examples of suitable friction modifiers are found in US Patent No. 3,933,659 which discloses fatty acid esters and amides; US Patent No. 4,176,074 which describes molybdenum complexes of polyisobutenyl succinic anhydride-amino alkanols; US Patent No. 4,105,571 which discloses glycerol esters of dimerized fatty acids; US Patent No. 3,779,928 which discloses alkane phosphonic acid salts; US Patent No. 3,778,375 which discloses reaction products of a phosphonate with an oleamide; US Patent No. 3,852,205 which discloses S-carboxyalkylene hydrocarbyl succinimide, s-carboxyalkylene hydrocarbyl succinamic acid and mixtures thereof; US Patent No. 3,879,306 which discloses N-(hydroxyalkyl)alkenyl-succinamic acids or succinimides; US Patent No. 3,932, 290 which discloses reaction products of di-(lower alkyl) phosphites and epoxides; and US Patent No. 4,028,258 which discloses the alkylene oxide adduct of phosphosulphurized N-(hydroxyalkyl) alkenyl succinimides. The most preferred friction modifiers are succinate esters, or metal salts thereof, of hydrocarbyl substituted succinic acids or anhydrides and thiobis alkanols such as described in US Patent No. 4,344,853.
Dispersants maintain oil insolubles, resulting from oxidation during use, in suspension in the fluid thus preventing sludge flocculation and precipitation or deposition on metal parts. High molecular weight ashless dispersants for use in the invention have a number average molecular weight of at least 1300 and preferably comprise an alkenyl succinimide, the reaction product of oil-soluble polyisobutylene succinic anhydride with an amine such as an ethylene amine which may optionally be borated.
Pour point depressants lower the temperature at which the fluid will flow or can be poured. Such depressants are well known. Typically of those additives which usefully optimize the low temperature fluidity of the fluid are C₈-C₁₈ dialkylfumarate vinyl acetate copolymers, polymethacrylates, and wax naphthalene. Foam control can be provided by an antifoamant of the polysiloxane type, eg silicone oil and polydimethyl siloxane.
Additional detergents and metal rust inhibitors may be present including the metal salts of sulphonic acids, alkyl phenols, sulphurized alkyl phenols, alkyl saliscylates, naphthenates and other oil soluble mono- and di-carboxylic acids.
Highly basic (viz, overbased) metal salts, such as highly basic alkali and alkaline earth metal sulphonates (especially Na, Ca and Mg salts) are frequently used as detergents, alone and in combination. Mixtures of calcium and magnesium salts, and of calcium, magnesium and sodium salts are preferred.
Copper and lead corrosion inhibitors and antiwear agents include borate esters, thiadiazoles such as derivatives of 2, 5 dimercapto 1,3,4-thiadiazole and benzotriazoles.
Some of these numerous additives can provide a multiplicity of effects, eg a dispersant-oxidation inhibitor. This approach is well known and need not be further elaborated herein.

Compositions when containing these conventional additives are typically blended into the base oil in amounts which are effective to provide their normal attendant function. Representative effective amounts of such additives are illustrated as follows:

Additive	Vol %	Wt % a.i.
Viscosity Modifier	.01-4	.01-4
Corrosion Inhibitor	0.01-1	.01-1.5
Oxidation Inhibitor	0.01-1	.01-1.5
Dispersant	0.1-7	0.1-8
Pour Point Depressant	0.01-1	.01-1.5
Anti-Foaming Agents	0.001-0.1	.001-0.15
Anti-Wear Agents	0.001-1	.001-1.5
Friction Modifiers	0.01-1	.01-1.5
Detergents/Rust Inhibitors	.01-2.5	.01-3
Mineral Oil Base	Balance	Balance

When other additives are employed, it may be desirable, although not necessary, to prepare additive concentrates comprising concentrated solutions or dispersions of the dispersant (in concentrate amounts hereinabove described), together with one or more of said other additives (said concentrate when constituting an additive mixture being referred to herein as an additive-package) whereby several additives can be added simultaneously to the base oil to form the lubricating oil composition. Dissolution of the additive concentrate into the lubricating oil may be facilitated by solvents and by mixing accompanied with mild heating, but this is not essential. The concentrate or additive-package will typically be formulated to contain the dispersant additive and optional additional additives in proper amounts to provide the desired concentration in the final formulation when the additive-package is combined with a predetermined amount of base lubricant. Thus, the combination of additives of the present invention can be added to small amounts of base oil or other compatible solvents along with other desirable additives to form additive-packages containing active ingredients in collective amounts of typically from about 2.5 to about 90%, and preferably from about 5 to about 75%, and most preferably from about 8 to about 50% by weight additives in the appropriate proportions with the remainder being base oil.
The final formulations may employ typically about 10 wt % of the additive-package with the remainder being base oil.
When otherwise stated, all weight percents expressed herein are based on active ingredient (a.i.) content of the additive, and/or upon the total weight of any additive-package, or formulation, which will be the sum of the a.i. weight of each additive plus the weight of total oil or diluent.
The following Examples and Test Results are given, though only by way of illustration, to show certain aspects of the invention in more detail.

Examples 1-10 and Comparative Example A

An overbased magnesium sulphonate was prepared by carbonation at 40-70°C of a reaction mixture comprising:

a) an alkylbenzene sulphonic acid
b) excess magnesium oxide
c) ethylene diamine in an amount of 0.06 parts by weight per part of magnesium in b), the ethylene diamine being introduced as a carbamate solution prepared by reacting ethylene diamine, water, methanol and carbon dioxide
d) oil.

Carbonation was continued until breakthrough and the formed product after stripping and filtration was post-treated with 2 wt % (based on product) fumaric acid to form a nominal 400 TBN product. This product is Comparative Example A, and contains approximately 47 wt % active ingredient.
The procedure was repeated using various amounts of dispersant in the reaction mixture to give products which are examples of the invention as detailed in Table 1 below.

Test Results

The formed overbased magnesium sulphonates were blended into a typical service station oil additive package including in addition to other conventional additives 18.2% of a borated PIBSA/PAM dispersant in which the polyisobutene moiety has a number average molecular weight of about 2200, 120 ppm of added copper as antioxidant and 0.75 wt % of glyceryl monooleate as friction modifier. The overbased magnesium sulphonate comprised 9.85 wt % of this package.

The packages were evaluated by storing them at 150°F (66°C) and observing them at regular intervals. The results are given in Table 1 below as the number of days after which incompatibility manifested itself as haze and/or sediment. A '+' sign indicates the test was still running at the number of days given without sign of incompatibility.

TABLE 1

Example	Dispersant	%¹	Days
A	-	-	7²
1	950 M.W.³PIBSA/PAM	5%	17
2	1300 M.W. PIBSA/PAM	5%	45
3	2200 M.W. PIBSA/PAM	3%	12
4	2200 M.W. PIBSA	2.5%	52⁺
5	2200 M.W. PIBSA	1.0%	40⁺
6	2200 M.W. PIBSA	3.0%	40⁺
7	2200 M.W. PIBSA	5.0%	40⁺
8	900 M.W. PIBSA	2.5%	5
9	1300 M.W. PIBSA	2.5%	12
10	Borated 1300 M.W. PIBSA/PAM	5%	12

1. as wt. percentage of 400 TBN overbased magnesium sulphonate product
2. average of 10 repeats
3. M.W. = number average molecular weight.

Claims

1. A process for the preparation of overbased magnesium sulphonate in which a reaction mixture comprising a sulphonate or a sulphonic acid and a magnesium compound in oil, optionally with a hydrocarbon solvent and/or a promoter is carbonated characterized in that the reaction mixture for carbonation also comprises an effective amount of an ashless dispersant.

2. A process as claimed in claim 1, in which the reaction mixture comprises from 0.5 to 10 wt % (of the formed overbased magnesium sulphonate) of the ashless dispersant.

3. A process as claimed in claim 1 or claim 2, in which the ashless dispersant is a reaction product of:

a) a hydrocarbyl-substituted C₄ to C₁₀ mono-unsaturated acid or anhydride; and

(b) an amine, alcohol, amino-alcohol or mixtures thereof.

4. A process as claimed in claim 3, in which the reaction product is borated.

5. A process as claimed in claim 1 or claim 2, in which the ashless dispersant comprises a hydrocarbyl-substituted C₄ to C₁₀ mono-unsaturated acid or anhydride.

6. A process as claimed in any of claims 3 to 5, in which the hydrocarbyl-substituted C₄ to C₁₀ mono-unsaturated acid or anhydride is a hydrocarbyl succinic acid or anhydride comprising a hydrocarbon group substituted with one or more moles, per mole of hydrocarbon, of maleic acid.

7. A process as claimed in claim 6, in which the hydrocarbon has at least 50 carbon atoms.

8. A process as claimed in claim 7, in which the anhydride or acid is polyisobutenyl succinic anhydride or acid having a number average molecular weight of from 900 to 5000.

9. A process as claimed in claim 8, in which the ashless dispersant is a reaction product of polyisobutenyl succinic anhydride with a polyamine and the polyisobutene group has a number average weight (M_n) of 900 to 2500.

10. A process as claimed in any of claims 1 to 9, which comprises carbonating a reaction mixture comprising:

a) an oil-soluble sulphonic acid or sulphonate;

b) a stoichiometric excess of a magnesium compound, preferably an alkoxide, oxide or hydroxide;

c) oil;

d) hydrocarbon solvent, preferably benzene, toluene or xylene;

e) promoter preferably ketones, amines, oil-soluble carboxylic acids, amine salts or diketones;

f) 0.5 to 10 wt % (of the ultimately formed overbased magnesium sulphonate) of an ashless dispersant.

11. A process as claimed in any of claims 1 to 10, in which the sulphonic acid or sulphonate is an alkylaryl sulphonic acid or sulphonate in which the alkyl substituent in the alkylaryl moiety or moieties has 15 or more carbon atoms.

12. A process as claimed in claim 10 or claim 11, in which the solvent is present in an amount of from 0.1 to 10 parts by weight of solvent per part of magnesium in the reaction mixture and/or the promoter is present in an amount of from 0.01 to 5 parts by weight per part of magnesium in the reaction mixture and/or water is present in an amount of from 0 to 2 parts by weight per part of magnesium in the reaction mixture.

13. A process as claimed in any of claims 10 to 12, in which an additional surfactant is present in an amount of from 0 to 1 part by weight per part of magnesium present in the reaction mixture.

14. An oleaginous composition comprising an overbased magnesium sulphonate as prepared by a process as claimed in any of claims 1 to 13, and:

(i) high molecular weight ashless dispersant having a number average molecular weight of at least 1300 and optionally

(ii) friction modifier and/or

(iii) copper compound as antioxidant, and/or

(iv) a zinc dihydrocarbyl dithiophosphate.

15. A composition as claimed in claim 14, in which the dispersant (i) has a number average molecular weight of 1500-5000.

16. A crankcase lubricant composition comprising a major amount of oil and from 0.01 to 5 wt % of an overbased magnesium sulphonate prepared by a process as claimed in any of claims 1 to 13, an ashless dispersant having a number average molecular weight of 1500-5000 and a friction modifier at the level required to meet the Tier II fuel economy requirement by the API Sequence 6 test.

17. A concentrate for use in lubricating oils comprising up to 50 wt % of an overbased magnesium sulphonate as prepared by a process as claimed in any of claims 1 to 13 and an ashless dispersant having a number average molecular weight of 1500-5000.

18. A concentrate as claimed in claim 17, which contains at least 0.5 wt % of friction modifier.

19. A composition as claimed in claim 17 or a concentrate as claimed in claim 18, which further comprises a copper compound as an antioxidant.

20. A composition as claimed in claim 17, or a concentrate as claimed in claim 18, which contains calcium and magnesium.

21. A composition or concentrate as claimed in claim 20, which contains calcium, magnesium and sodium.

22. A stable, sediment-free lubricating oil composition meeting API requirements for SG quality and Tier II fuel economy which comprises an overbased magnesium sulphonate prepared by a process as claimed in any of claims 1 to 13.