US2981685A

US2981685A - Lubricating oil thickened to a grease with asphaltene absorbed clay

Info

Publication number: US2981685A
Application number: US805715A
Authority: US
Inventors: Donald E Loeffler
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1959-04-13
Filing date: 1959-04-13
Publication date: 1961-04-25
Anticipated expiration: 1978-04-25
Also published as: GB879896A; NL250416A; DE1101673B

Description

United States Patent LUBRICATING OIL THICKENED TO A GREASE WITH ASPHALTENE ABSORBED CLAY Donald E. Loeffler, Walnut Creek, Calif., assignor to Shell 011 Company, a corporation of Delaware No Drawing. Filed Apr. 13, 1959, Ser. No. 805,715

5 Claims. (Cl. 252-28) This invention relates to an improvement in grease compositions. More particularly, it relates to grease compositions having improved water resistance and resistance to deterioration in the presence of ionizing radiation.

Grease compositions normally comprise a gelling agent dispersed in colloidal form in a lubricating oil base. Many types of gelling agents and of oil bases have been investigated. and utilized. The most widely employed greases are gelled with soaps of high molecular weight fatty acids and mineral lubricants are the most generally utilized oil base. However, greases gelled with soaps have certain inherent disadvantages which cannot be overcome by the use of additives or by other means than substitution of-the soaps. The soap-base greases, for example, exhibit softening points at relatively moderate temperatures which are normally substantially below the decomposition temperature of either the soap or of the oil. This is due in large part to the relatively low melting point of the soap fibers dispersed in the oil.

The problem of softening or even fiuidizing at relatively low temperatures has been cured in a substantial measure by substituting for the soaps gelling agents which may be broadly referred to as microgels. These comprise a large variety of colloidal substances which are either inorganic colloids or are organic derivatives of these colloids. Typical materials include silica, clays and the so-called onium clays as well as surface esterified colloids, such as butylated silica and the like. Unless the colloids are protected by the presence of hydrophobingagents or surface treatment, the greases prepared therefrom exhibit water sensitivity which limits their field of use. The onium clays and the surface esterified silica are waterproofed by surface treatments. In these cases the ester groups or the onium radicals perform a hydrophobing function, providing the colloids with an oleophilic surface which enables them to maintain their grease structure even in the presence of water.

The hydrophobic surfactants normally utilized for improving the water resistance of greases gelled with inorganic colloids include particularly the cationic surfactants which may be amines and amino amides, preferably aliphatic in character and of relatively high molecular weight. While these improve the Water resistance of the colloidal gelled greases containing them, they do not prevent (in fact, they even accelerate) sensitivity of ice 2 the grease is made up of the cost of the individual ingredients. Consequently, any reduction in the cost of an essential ingredient correspondingly lowers the cost of the total grease composition and thereby improves the possible applicability of the grease to additional indus trial usage. Ordinarily, the most expensive ingredient utilized in the microgel grease systems is the hydrophobing additive, since the gelling agent and the lubricant are in most instances relatively less costly. Th ehydrophobic surfactants are utilized for the sole reason that they are essential for the promotion of Water resistance of the 'grease compositions containing them.

It is an object of the present invention to improve greasecompositions. It is another object of the invention to improve the resistance of grease compositions to degradation in the presence of ionizing radiation. It is a further object of the invention to provide microgel grease compositions exhibiting not only high water resistance but also resistance to degradation caused by ionizing radiation. It is a further object to provide the foregoing benefits while at the same time decreasing the cost of the grease compositions. Other objects Willbecome apparent in the following description of the invention.

Now, in accordance with the present invention, grease composition are provided which exhibit excellent water resistance, have no dropping point and are stable in the presence of ionizing radiation while at the same time the cost of the composition is reduced. These compositions comprise a lubricating oil gelled to a grease consistency with an inorganic colloidal gelling agent, the agent bearing on the surface of the colloidally dispersed particles asphaltenes, as more fully defined hereinafter, in an of the grease to ionizing radiation. Thus, when many greases are subjected to the influence of ionizing radiation, they exhibit their sensitivity in one of two directions. First, many greases will fiuidize and lose their grease" structure. On the other hand, other greases will become rubbery in texture and lose their lubricating propertiesflfl In either case'an unsatisfactory resultlhas been obtained. In the case of soap-base greases it is the universal experience that such greases fiuidize upon exposure to ionizing radiation. a

i always be considered i cations due to their cost. Of course, the total cost of amount sufficient to provide the grease composition with water resistance and stability against degradation due to ionizing radiation. More particularly, preferred compositions comprise mineral oil bright stocks gelled to a grease consistency with colloidally dispersed clay, the clay bearing 25-100% by weight (based on. the clay) of oxidized asphaltenes.

, While the asphaltenes which are employed for the present purpose may be naturally occurring components obtained from petroleum residues as more fully described hereinafter, much better results are obtained if they have been subjected to an oxidizing treatment, preferably air blowing or other oxidation by means of oxygen-contain-. ing gas.

The term asphaltenes is defined in Abraham, Asphalts and Allied Substances, Fifth Edition, pages 1165-6, as being the non-mineral constituents remaining insoluble in petroleum naphtha, thus differentiating them from the maltenes (petrolenes) which dissolve in the same medium and under the same conditions. As the test is run at room temperature (6 5-75 R), this latter constitutes a part of the definition. A still further limitation is the proportion of petroleum naphtha employed for the purpose of causing separation. I According to the standardized method, 50 volumes of petroleum naphtha are employed,;the test temperature normally being ambient room temperature. While this standard procedure defines the term, it will be understood that the asphaltic fraction insoluble at room temperature in any aliphatic hydrocarbon having 5-12 carbon atoms per molecule may be regarded as asphaltene for the purpose of the present invention.

Asphaltenes may be isolated from other asphaltic constituents by preferential precipitation. For example, asphalts may be introduced into an aliphatic hydrocarbon precipitant (C alkanes) by several alternative methods, dependent upon their physical characteristics. For example, hard asphalts (especially cracked or blown) having penetrations at 77 F. less than about 10 are preferably introduced by first dissolving them in a minimum amount,

of an aromatic hydrocarbon solvent. In order to minimize the effect of the aromatic solvent upon the precipitation of the asphaltene, it is preferred that the proportion of solvent be restricted to between about 0.5 and 2 volumes for each volume of the asphaltic residue. The aromatic solvent is preferably one predominating in aromatic hydrocarbons having less than 10 carbon atoms per molecule, of which benzene, toluene and xylene are suitable members. Softer asphalts may be dispersed by refluxing in the presence of a limited proportion of the precipitating aliphatic hydrocarbon, although the aromatic solvent may be used in addition to or in place of the aliphatic medium. The maltene solution and precipitated particles are separated by any suitable means, including filtration, centrifuging, sedimentation, decanting or similar treatment. Following separation of the asphaltene particles, they may then be dissolved in an aromatic volatile solvent for use in the modification of microgel grease compositions. They may be added to such compositions under a variety of circumstances, such as by addition to an aqueous gel of the gelling agent or by dispersal in the lubricating oil prior to or subsequent to incorporation of the gelling agent in the oil. Preferably, asphaltenes-are incorporated in the oil subsequent to addition of the colloidal gelling agent thereto and removal of any volatile solvents initially introduced together with the gelling agent. The table which follows gives an analysis of typical asphaltenes:

Asphaltene analysis It has been determined that asphaltenes are polycyclic, contain numerous hetero atoms, particularly nitrogen, sulfur and oxygen, and usually contain between 1 and 13 hetero atoms, usually 4-10, per asphaltene molecule on the average. The metallic content of asphaltenes is in the order of 0.1-0.3%, the major constituents being iron, vanadium, sodium and nickel. About A of the nitrogen atoms are weakly basic and only about 1% of the nitrogen atoms are strongly basic. Approximately of the sulfur groups exist as aliphatic or alicyclic sulfides, 1% as disulfides and 57% of the sulfur as thiophenes or polythiophenes. In the average asphalt molecule, there are believed to be about 150 carbon atoms, 18 hydroxyl groups, 3.4 nitrogen atoms, 1.5 sulfur atoms and 2.1 oxygen atoms, although this analysis will depend upon the molecular weight selected as being nearest actuality. Moreover, there are understood to be about methyl radicals in the average asphaltene molecule. The molecular weights of asphaltenes vary widely dependent upon the method by which the molecular Weight determination is made. The table which follows shows that these vary all the way from about 2000 to 100,000 depending upon the method.

The asphaltenes may be oxidized either prior to or subsequent to their separation from other asphaltic components such as maltenes and the like. Oxidation results in the conversion of maltenes to asphaltenes, and the further polymerization of asphaltenes. Oxidation may be carried out by means well known in the asphalt art. For the most part, such operations are conducted by simply blowing the asphaltic body with air at an elevated temperature (450-550 F.) for an extended period of between about 1-15 hours. The oxidation may be carried out in the presence of oxidizing catalysts if desired, such as phosphoric acid, phosphorus pentoxide, ferric chloride, Friedel-Crafts catalyst, and the like'although this is not an essential feature of this invention. The isolated asphaltenes have been found to be especially sensitive to oxidation especially in the presence of ultraviolet light, such as sun light.

The other constituents of the grease compositions of this invention are well known in the art. They comprise lubricating oils which may be mineral lubricants, especially petroleum lubricating oils, as Well as synthetic lubricants, including esters, ethers, silicone fluids, and other well known materials. Specific lubricants include mineral oil bright stocks, methyl phenyl silicone fluids, dimethyl silicone fluids, polyphenyl ethers,-diesters of aliphatic dicarboxylic acids with monohydric alcohols, such as bis- (2-ethylhexyl)sebacate, polyesters, such as'pentaerythritol esters of C aliphatic monohydric alcohols, complex esters formed between polybasic aliphatic acids and polyhydric alcohols, and other materials well known for their lubricating properties.

While these grease compositions are not intended to be restricted to lubrication in the presence of radiation, this constitutes one of the environments in which the properties of these greases show up to greatest advantage. For this purpose residual lubricating oils commonly known as bright stocks are preferred. The term bright stock is one which is well recognized in the art of refining mineral oils. To obtain the desired fraction, crude oils are usually subjected to distillation under ordinary pressures in order to obtain a long residue comprising the fraction which does not distill under these conditions without substantial decomposition. The long residue is than subjected to steam distillation, usually under a vacuum, or simply to vacuum distillation. Under these conditions, gas oil and waxy lubricant fractions distill over, leaving what is normally termed a short residue or a steam refined stock, also known as cylinder stock. The steam refined stock is then deasphalted (if an asphaltic crude is employed) and subjected to dewaxing operations to remove microcrystalline or macrocrystalline waxes. Following this, the oil is treated with a solvent for the purpose of reducing or removing the aromatic fractions. Clay contact treatment or percolation may be employed to clean up the oil following any one or all of these separate operations. The raflinate which remains after deasphalting, dewaxing, extraction, and clay treatment is generally called bright stock.

The bright stocks suitable for use in the present compositions should have the following ranges of properties:

TABLE I Properties of bright stocks Viscosity, S.U.S., at F., 1250, usually 1250-11,000,

preferably 1500-3500 Viscosity, S.U.S., at 210 F, 75, usually -325, preferably -250 Viscosity index 60, preferably 85-110 Aniline point 100, preferably 115 Flash, F., 475, preferably 500 Fire, F., 550, preferably 600 Pour point, F., maximum 25, preferably lower than 15 Percent aromatics, 15, preferably 1 Percent naphthenes, 35

Percent paraifins, at least 60 The tables which follow give the properties of typical bright stocks which are useful in the compositions of this invention.

capable of maximum thickening of the lubricating oil as opposed to aerogels which are not suitable for grease formation. Aerogels are normally prepared by forming TABLE II Examplesof typical bright stocks SUS Ring Analysis Aver- Vis- Average age cosity Rings 100 210 Index Aro- Naph- Paraf- Weight per matic thenes fins Mol Mid-Continent Bright Stock:

Conventional o Extraction..-" 3,650 164 77 13 17 70 685 3.7 Mild Extraction- 2,569 141 85 9 19 72 685 3.4 Deep Extraction. 2, 049 131 93 3 21 76 675 2.9 Perms lvania Bri id Stock 2,109 144 102 5 16 79 730 3.0 CoastalBright Stock. 1, 251 85 63 4 35 61 515 3.4

TABLE III a hydrogel, displacing the water. therefrom with a relatively volatile miscible solvent such as acetone heating zd-Contment brz ht stocks Speclficatlons for typlcalM g the organo gel so formed under pressure to a hlgh temd 25 perature and thereafter flashing the solvent by release of Unfiltered F We pressure to form a dry powdery gel having a highly ex- 7 O l 25 5 panded structure. Alternatively, the gels may be in- 81 Dark fg f; corporated into oil in the form of an organo gel from Pour izomtfir. ,maximum 10 10 ig which most or all of the water has been eliminated and ,2 3 f ggfigf it; 322 610 30 thereafter stripping ed the volatile solvent. Finally, the 8118210 F 0- 200-215 88 gels may be transferred into oil by the so-called direct Vlscoslty Index mmlmum' 90 9O transfer process wherein the hydrogel and oil are com- It will be understood from the above analyses that the source or treatment of a particular mineral oil is not as important for the present purpose as the final properties of the mineral oil constituent to be used in these compositions. For example, it is possible to vary theextent of solvent extraction dependent upon the original aromatic content and the requirements of the specific use of the final product, as well as upon the necessity or desirability of deasphalting, clay treating, acid treating, and the like. Hence, it will be recognized that the present invention is predicated upon the use of a mineral oil fraction having the above defined ranges of properties and not upon the source or treatment of such oil.

The two most important properties of a mineral oil suitable for the present use comprise the aromatic content and the viscosity characteristics. The aromatic content has a large influence upon the sensitivity of the oil to thermal changes and the viscosity of the oils defines their suitability for their present purpose. Hence, the best definition with respect to essential characteristics of mineral oil suitable for the present compositions comprises those having a saturate molecule hydrocarbon content between about 15-65% and having a viscosity of between about 1250 and about 11,000 SUS at 100 F. Having defined these particular properties, the other properties such as flash, fire, aniline point, and viscosity index usually are largely dependent upon them.

The gelling agents to be utilized in accordance with this invention include particularly the clays having relatively high base-exchange capacity, i.e., greater than milliequivalents per gram and preferably about 75-100 milliequivalents per gram. Bentonites, such as Wyoming bentonite and hectorite as well as other montmorillonites are preferred. In addition to the naturally occurring clays, other inorganic colloids may be utilized, such as silica, magnesia, magnesia-silica, silica-alumina and other amorphous colloidal gels. They may be used in combination with clays or may constitute the sole gelling agent. Means are known for incorporating these classes of inorganic colloidal gels in lubricating oils for grease formation. Two of the favorite means comprise preparing the gels as aerogels which are low density gels bined, preferably in the presence of the asphaltenes, thus, causing separation of a major proportion of water from the gel, milling the remaining composition sufiiciently to disperse the gel throughout the oil and thereafter raising the temperature sufiiciently to eliminate the water remaining by evaporation.

The greases ofthis invention are especially useful where the compositions are to be subjected to ionizing radiation since the asphaltenes absorbed on the surface of the gelling agent .act in some undetermined manner to maintain the consistency and properties of the grease. Thus, the greases are particularly useful for the lubrication of bearings and other relatively moving metallic surfaces which are exposed in atomic piles, atomic reactors, atomic powered machinery, such as in submarines and aircraft and for lubrication purposes generally where radiation is encountered. However, this special virtue does notrestrict the use of the grease to such locations since the greases are also highly satisfactory and effective for lubrication of bearings and other metallic surfaces where greases are generally required.

Due to the relatively low cost of the stabilizing component, namely, the asphaltenes, the field of use of these greases is substantially broadened beyond that to which.

microgel greases can normally be applied. Hence, they are especially useful for lubrication sites where high temperature or exposure to water will be encountered as well as in positions where ordinary operating conditions prevail.

The following examples illustrate the advantages to be gained by the use of these greases: A grease composition was prepared by dispersing hectorite clay in a bright stock lubricating oil. The hectorite clay was modified by the presence of 60% by weight thereof of an amino amide hydrophobing agent. The grease contained 5% by weight of the clay. A second grease was prepared using the same bright stock lubricating oil to which was added a hectorite clay alcogel. After mixing, the alcohol was evaporated by heating, leaving the clay dispersed throughout the oil, A xylene solution of blown asphaltene was then added to the mixture and xylene evaporated, the components being milled thereafter to a. grease consistency. The grease contained 4% by weight of hectorite and 3% by weight of blown asphaltenes. These two greases were subjected to a high temperature and high speed bearing test using the Standard Federal Test Meth od No. 331 which requires a temperature of 300 F. and 10,000 r.p.m. The grease containing the amino amide ran for 562 hours until it failed, while the grease containing blown asphaltenes ran 378 hours until failure.

Other samples of the grease were then subjected to irradiation in a Van de Graafi accelerator until rads. of radiation had been absorbed. The irradiated greases were then subjected to the same test conditions. The irradiated grease containing the amino amide ran only 36 hours to failure while the grease containing blown asphaltenes ran 148 hours to failure. These comparative data illustrate the stabilizing effect 8f the asphaltene as compared with amino amides which are a usual type of hydrophobing agent employed in microgel greases.

The blown asphaltenes employed in the above comparative tests were obtained by air blowing a heavy crude lube residue having a 250 F. softening point and thereafter precipitating the asphalt with propane and extracting the asphaltenes by precipitation in isopentane. The asphaltenes had an average molecular weight (ebullioscopic) of 28,000.

The stability of greases to irradiation and the effect of unblown asphaltenes thereon was studied by determining the penetration of the greases before and after irradiation thereof to the extent of 10 rads. radiation absorption. Sample A in the table below is the same clay grease modified with amino amide hydrophobing agent as was used in the test described above. Sample B was the same as the second clay grease described above containing asphaltenes. Table IV which follows shows the greater stability of the greases containing the I claim as my invention:

1. A grease composition consisting essentially of a lubricating oil gelled to a grease consistency with a grease forming proportion of a colloidally dispersed clay, said clay having absorbed on the surfaces thereof a hydrophobing amount of asphaltenes.

2. A grease composition consisting essentially of a major proportion of a mineral lubricating oil and a minor proportion sufficient to thicken the oil to a grease consistency of a colloidally dispersed clay, said clay bearing on the surfaces thereof a minor amount, sufficient to increase the radiationand water-resistance of the grease, of asphaltenes.

3. A grease composition consisting essentially of a major proportion of a mineral lubricating oil and a minor proportion, sufficient to impart a grease consistency to the composition of a colloidally dispersed bentonetic clay, said gel bearing on the surfaces thereof a minor amount, sufficient to increase the radiationand waterresistance of the grease, of oxidized asphaltenes.

4. A' grease composition consisting essentially of a major proportion of a bright stock mineral oil gelled to a grease consistency with 1-15% by weight, based on the grease,of colloidally dispersed hectorite clay, said clay having adsorbed on the surfaces thereof 25-l00% by weight, based on the clay, of airblown asphaltenes.

5. A grease composition consisting essentially of a major proportion of a polyphen-yl ether oil gelled to a grease consistency with 1-15 by weight of colloidally dispersed hectorite clay, said clay having absorbed on the surfaces thereof 25100% by weight, based on the clay, of airblown asphaltenes.

References Cited in the file of this patent UNITED STATES PATENTS 2,773,031 Tailleur Dec. 4, 1956 2,860,104 Peterson et al Nov. 11, 1958 2,885,360 Haden et al. May 5, 1959

Claims

1. A GREASE COMPOSITION CONSISTING ESSENTIALLY OF A LUBRICATING OIL GELLED TO A GREASE CONSISTENCY WITH A GREASEFORMING PROPORTION OF A COLLOIDALLY DISPERSED CLAY, SAID CLAY HAVING ABSORBED ON THE SURFACES THEREOF A HYDROPHOBING AMOUNT OF ASPHALTENES.