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(11) | EP 0 083 871 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Arylamine-aldehyde lubricant antioxidants |
| (57) Oils of lubricating viscosity exhibit improved resistance to oxidative degradation
when additive amounts of an arylamine-aldehyde additive are incorporated therein. |
BACKGROUND OF THE INVENTION
Field of the Invention:
[0001] The present invention relates to arylamines such as alkylated diphenylamine and alkylated phenyl-alpha-napthylamine which undergo condensation reactions with an aldehyde to produce an additive which imparts non-sludging characteristics as well as high temperature antioxidation characteristics to lubricant compositions.
Description of the Prior Art:
[0002] Antioxidants or oxidation inhibitors are used to minimize the effects of oil deterioration which occurs whenever hot oil is contacted with air. The proper operation of engine parts and efficiency of mechanical systems is oftentimes hampered due to the detrimental effect of oxidation in changing the viscosity of the oil. Similarly, it is known that the oxidation of fuels, particularly during storage, causes'gum formation and layer deposits which tend to cause ooerating malfunctions. Lubricating oils are subject to oxidative deterioration under conditions of use such as in modern internal combustion engines. Oxidation products are formed in the oil which are acidic in nature and can exert an erosive effect on metal parts with which the oil comes into contact. Furthermore, these oxidation products produce formations and deposits of varnish and sludge on the engine surfaces and, in various channels, galleries, ports and orifices. This tends to interfere with lubricating and may eventuate in the breakdown of the engine.
[0003] The degree and rate of the oxidation will depend on temperature, air and oil flow rates, and, of particular importance, on the presence of metals that may catalytically promote oxidation.
[0004] Antioxiaants generally function by prevention of chain peroxide reaction and/or metal catalyst deactivation. Such materials prevent the formation of acid sluoges, darkening of the oil ana increase in viscosity of the oil due to the formation of polymeric materials.
[0005] Typical prior art lubricant antioxidants include hindered phenolic compounds such as 2,6-di-tert-butyl-4-methyl phenol, commonly known as DBPC in lubricants, and BHT in foods. It has been suggested in the prior art that such phenolic compounds may be combined with amine antioxidants for optimum activity. However, amines generally cannot be used alone as lubricant antioxidants due to their tendency to decompose and form sludge.
[0006] In accordance with the present invention, additives are provided for lubricants and fuel compositions which are capable of inhibiting the oxioative aeterioration of sucn materials as well as the tendency towards sludge formation when such lubricants are in use. Of particular significance in accordance with the present invention is the ability of the additives to improve the anti-oxidant properties of oleagenous materials such as lubricating media which may comprise either a mineral oil or a synthetic oil, or a grease tnerefrom. In general, mineral oils, both paraffinic, naphthenic and mixtures thereof, employed as the lubricant or grease vehicle, may be of any suitable lubricating viscosity range, as for example, from adout 45 SSU at 100°F to about 600 SSU at 100°F, and preferably, from about 50 to about 250 SSU at 100°F. These oils may have viscosity indexes ranging to about 100 or higher. Viscosity indexes from about 70 to about 95 are preferred. The average molecular weights of these oils may range from about 250 to about 800.
[0007] In instances where synthetic oils are desired in preference to mineral oils, or in combination therewith, various compounds of this type may be successfully utilized. Typical synthetic vehicles include polyisobutylene, polybutenes, hydrogenated polyolefins, polypropylene glycol, polyethylene glycol, trimethylol propane esters, neooentyl and pentaerythritol esters, di(2-ethylhexyl) sebacate,dialkylbenzenes such as di-dodecylbenzene, di(2-ethylhexyl) acioate, dibutyl phthalate, fluorocarbons, silicate esters, silanes, esters of phosphorus-containing acids, liquid ureas, ferrocene derivatives, hydrogenated mineral oils, chain-type polyphenyls, siloxanes and silicones (polysiloxanes), alkyl-substituted diphenyl ethers typified by a butyl-substituted bis(p-ohenoxy phenol) ether, phenoxy phenylethers. It is to be understood, however, that the compositions contemplated herein can also contain other materials. For example, corrosion inhibitors, extreme pressure agents, viscosity index improvers, co-antioxidants, anti-wear agents and the like can be used. These materials do not detract from the value of the compositions of this invention, but rather they serve to impart their customary properties to the particular compositions in which they are incorporated.
SUMMARY OF THE INVENTION
[0008] In accordance with the present invention, it has now been discovered that condensation reaction products obtained when arylamines are reacted with formaldehyde are exceptional antioxidant additive materials. The novel antioxidant additives of the present invention are produced when an aldehyde such as formaldehyde is reacted with arylamine. Water is given off and it is postulated that a dimer is formed which, unlike conventional amines, not only reduces sludge in oxioation testing reactions but also provides an excellent antioxidant additive. It is theorized that the arylamine-formaldehyde reaction product which forms the novel compositions of the present invention comprises two or more moles of arylamine coupled by a methylene bridge. The molar ratio of arylamine to formaldehyde used in the process of the present invention may range from about 1:2 up to about 2:1 with the preferred ratio being about 1:1. The reaction temperatures may range from about 50°C to about 250°C, with the preferrea range being from about 80°C to about 200°C. The operable reaction times may range from about 0.5 hours to about 10 hours. The preferred reaction times range from about 2 hours to about 6 hours.
[0009] The reaction may also be carried out in the presence of non-reactive solvents such as hexane, cyclohexane, toluene and the like.
[0010] It has been founa, in accordance with the present invention, that the preferred arylamines which may be employed in accordance with the oresent invention may include those with the following structural formulas:
(or)
wherein R and R' may be the same or different and may include hydrogen, alkyl, cycloalkyl, aralkyl and the like. Preferred R and R' moieties are hydrogen and alkyl groups containing up to about 30 carbon atoms.
[0011] Alcehyde reactants which are suitable to form the additive compounds of the present invention may be represented by the following structural formula:
wherein R may be hydrogen, alkyl, alkaryl, aralkyl, cycloalkyl and the like. Preferred R moieties are lower alkyl having up to about five carbon atoms.
[0012] Arylamines such as alkylated diphenylamines and alkylated phenyl-alpha-naphthylamine are particularly preferred amine reactants. Even more particularly preferred arylamines are those which are described in the following soecific examples and include di-t-octyl-diphenyl amine and t-octyl-phenyl-alpha-naphthylamine. Such arylamines when reacted with formaldehyde result in additive materials which exhibit excellent oxidation resistance and low sludge formation.
DESCRIPTION OF SPECIFIC EMBODIMENTS
[0013] The anti-oxidation properties of the novel additive comoositions of the present invention, the arylamines/formaldehyde reaction products, are shown by the data contained in the following Table I and the tests procedures employed to obtain this data are summarized hereinbelow:
Oxidation Test Techniques
1. Rotary Bomb Oxidation Test (RBOT ASTM D2272)
[0014] This test represents a rapid means of estimating the oxidation stability of turbine oils. In this method, the test oil, water and copper catalyst coil contained in a glass receptacle are placed in a copper bomb equipped with a pressure gauge. The bomb which is charged with oxygen to a pressure of 90 psi is placed in a constant temperature oil bath set at 150CC and rotated axially at 100 rpm at an angle of 30 degrees from the horizontal. The time for test oil to react with a given volume of oxygen is measured and reported in minutes. Low RBOT values ( 100 minutes) are indicative of low or poor oxidation stability.
2. Turbine Oil Stability Test (TOST) for Sludge Formation
[0015] The tendency of a lubricant to form sludge under oxidizing conditions for 1000 hours is determined gravimetrically by filtration of the oxidation lube contents and reported as % sludge.
[0016] Lubricants which are stable to oxidation and resistant to sludge formation give typical values of 0.1% sludge and are suitaole for use as circulating oils designed to cool turbine oil journal oearincs.
Additive A Preparation
[0017] A mixture of 200 grams (0.56 mol) of di tertiary octyl diphenylamine and 17 grams (0.56 mol) paraformaldehyde was stirred to about 175°C over a period of about four hours using a stream of nitrogen to remove water of reaction.
ADditive 8 Preoaration
[0018] A mixture of 252 grams (0.76 mol) of monotertiary octyl phenyl 1-naphthylamine and 23 grams (0.76 mol) paraformaldehyde was stirred to about 180°C over a period of about four hours using a stream of nitrogen to remove water of reaction.
[0019] It will be apparent from the data presented in the preceding Taole 1 that both mineral oil anc mineral oil plus antirust agent, as shown in Examples 1 and 2, have poor oxidation stability as indicated by the short time, less than 100 minutes, required for a 25 psi oxygen pressure crop in the RBOT test. These oils also form excessive sludge, in excess of 0.1%, in the 1000 hour TOST test.
[0020] The addition of a standard, highly effective antioxidant (i.e. DBPC) as shown in Example 3 of Table 1 results in an increase in RBOT values to 2-5 minutes; however, use of the same concentration of the arylamine/formaldehyde compounds of the present invention (as shown in Examples 4 and 6) prepared from alkylated diphenyl amine and alkylated phenyl-alpha-naphthylamine respectively provides a suostantial RBOT increase over the DBPC antioxidant; i.e., 300-600 plus minutes depending upon the specific amine structure used.
[0021] As mignt oe expected, a reduction in concentration of the novel amine/formaldehyde composition of the present invention result in an RBOT loss. However, 0.4% amine/aldehyde reaction product (Example 8) is still more active (RBOT value 315) than the reference antioxioant DEFC at 0.8% in a paraffinic oil. It is also pointed out as shown in the precedine Tacle that these novel amine additives prevent (Examoles 6-8) sludge formation during the 1000 hour TOST oxidation tests in the presence of water, steel and copper catalyst.
1. A lubricant or liquid hydrocarbon fuel composition comprising a major proportion
of a lubricant or liquid hydrocarbon fuel and an antioxidant amount of the compound
produced by the reaction of an aryl amine with an aldehyde.
2. The composition of claim 1 wherein said compound is produced by the reaction of
an aryl amine with formaldehyde.
3. The composition of claim 1 wherein said compound is produced by the reaction of
an alkylated aryl amine with formaldehyde.
4. The composition of claim 1 wherein said composition contains a compound produced
by the reaction of an alkylated phenyl-alpha-naphthalene with formaldehyde.
5. The composition of claim 1 wherein said compound is produced by the reaction of
an alkylated diphenyl amine with formaldehyde.
6. The composition of claim 1 wherein said compound is produced by the reaction of
di-tertiary-octyl-diphenyl amine with formaldehyde.
7. The composition of claim 1 wherein said compound is produced by the reaction of
monotertiary octyl phenyl 1-naphthyl-amine with paraformaldehyde.
8. The composition of claim 1 wherein said aryl amine is a diaryl amine.