Lubricating
Oil Addition
Agents
Application of Phenolic Compounds and Their M e t a l Derivatives 0. M. REIFF Socony-Vacuum Oil Company, Inc., Paulsboro, N. J.
of oils, the practice has been to add a separate ingredient for each of the improvements to be effected. The purpose of the present paper is to describe the application of certain phenolic compounds and their metal derivatives as lubricating oil addition agents; some of them have multifunctional value in the respect that the lubricating oil may be improved in more than one important property by the addition of a single compound. The application of these compounds as lubricating oil addition agents will be treated from the standpoint of observations made largely in the chemistry laboratory, rather than from those of the automotive engineer. Wax-substituted hydroxy aromatic hydrocarbons formed by the condensation of hydroxy aromatic hydrocarbons with chlorinated paraffin wax by the Friedel and Crafts reaction are the starting materials used in the synthesis of the multifunctional lubricating oil addition agents (Figure 1). Although alkylated hydroxy aromatic hydrocarbons containing alkyl substituents from paraffis of lower molecular weight than the wax range cannot be used in the synthesis of the desired type of multifunctional lubricating oil addition agent, they are important in the synthesis of mineral-oil-soluble metal derivatives which are valuable antioxidants.
New types of metal salt addition agents for lubricating oils have been developed from alkylated phenolic compounds. By the introduction of alkyl substituents derived from petroleum wax, multifunctional addition agents are formed which are capable of imparting combined properties such as pour-point depressant action, improved viscosity index, and antioxidant value to lubricating oils. The effectiveness of the multifunctional addition agents is improved by the introduction of metal substituents, particularly in respect to antioxidant value. Attention is directed to the importance of the type of solubilizing radical ae well as the kind of metal substituent in the formation of metal salt addition agents having antioxidant value.
Preparation of Alkylated Hydroxy Aromatic Hydrocarbons
HE advent of the high-speed automotive engine has necessitated research on the production of improved lubricating oils. In order to be acceptable under con-
T
Various well-known procedures (1) can be used in the synthesis of alkylated hydroxy aromatic hydrocarbons, but only the Friedel and Crafts reaction is applicable to the preparation of alkylated hydroxy a-romatic hydrocarbons containing alkyl substituents derived from high-molecular-weight paraffins (9).
ditions of use in the modern automotive engine, a lubricating oil must not only possess improved lubricating properties, but have greater stability against the oxidizing action of air. The lubricating quality of finished oils is indicated by characteristics such as oiliness, pour point, and viscosity index. The quality of oiliness is directly related to the wear-reducing action of mineral oil lubricants; the pour point and viscosity index of a lubricating oil are important to lubrication from the standpoint of controlling the temperature range of proper lubrication. The refiner seems to have a fair control of these lubricating properties, at least to the extent of producing an oil which is acceptable for use in an automotive engine. The most serious problem of the refiner lies in the production of a lubricating oil of sufficient stability to withstand the formation of sludge and acidic oxidation products; the latter result in ring sticking and the corrosion of hard alloy metal bearings, and thereby cause loss in efficiency and life of the automotive engine. The layman believes generally that lubricating oils are strictly mineral oil fractions, but the importance of incorporating addition agents to oils as a means of correcting certain deficiencies of the lubricant is well known to the petroleum technologist. In the use of addition agents as a means of improving the lubricating qualities and oxidation stability
In the preparation of wax-substituted phenol, for instance, a paraffin wax melting at about 125' F., with an average molecular weight of about 350,is melted and heated to about 200' F.; then chlorine is introduced until the wax has absorbed about 16 per cent, and the product has an average composition between a monochloro- and a dichlorowax. A quantity of this chlorowax, containing three atomic pro ortions of chlorine, is heated to about 150' F., and one mole of pfenol is added. At this temperature a quantity of anhydrous aluminum chloride corresponding to about 3 per cent by weight of chlorowax in the mixture, is slowly added with active stirring. After the aluminum chloride has been stirred in the temperature of the reaction mixture is increased slowly to about 350" F. and held there about one hour to complete the reaction, which is indicated by completion of the evolution of hydrogen ahloride gas. The product at this stage is in the form of an aluminum salt of the alkylated phenol, apparently of the aluminum phenate type. The roduct is clear rather than opaque or even cloudy, and can be &solved in mineral oils to give clear solutions. In order to decompose the aluminum salt, the reaction product is washed with water in the resence of butyl alcohol to break emulsions, and the ash-free alfylated hydroxy aromatic hydrocarbon is thus obtained. It is important that all unreaoted hydroxy aromatic material 351
352
INDUSTRIAL AND ENGINEERING CHEMISTRY
be removed. In the case of hydroxy aromatic hydrocarbons which are not readily removed by water washing, it is preferable to treat the water-washed product with superheated steam to ensure complete removal of any unreacted material.
A wax phenol prepared by chlorinating wax to 16 per cent chlorine content and reacting a quantity of this chlorowax containing three atomic proportions of chlorine with a mole of phenol will be designated “wax phenol (3-16)”. Parenthetical expressions of this type (A-B) will be used here in connection with the alkylated hydroxy aromatic compounds to designate ( A )the number of atomic proportions of chlorine in the chlorowax material reacted with one mole of hydroxy aromatic hydrocarbon in the Friedel-Crafts reaction, and ( B ) the chlorine content of the chlorowax. Thus, in the above example A = 3 and B = 16. Wax phenol (3-16) has a combined phenol content of about 13.5 per cent. By varying the chlorine content ( B ) of the chlorowax and the degree of alkylation ( A ) of the aromatic nucleus, the phenol content can be varied.
Structure of Alkylated Hydroxy Aromatic Hydrocarbons The simplest type of hydroxy aromatic hydrocarbon substituted with alkyl groups derived from low- or high-molecular-weight paraffins may be represented by the formula, R*[T(OH),l where R” represents at least one alkyl group of valence v attached to a mono- or polycyclic nucleus, T, and OH is the hydroxyl substituent; n represents the number of T(OH) groups attached to the aliphatic group and is numerically equal to I. Alkylated hydroxy aromatic hydrocarbons whose valence v is equal to 1 would be formed from monovalent aliphatic compounds such as mono-olefins, monohalides of paraffins, and aliphatic monohydric alcohols. Since in the chlorination of paraffin wax a mixture of monoand polyhalides is formed, the chlorowax is considered as a mixture of mono- and polyvalent alkyl halides in which v of R” is 1or more than 1,and would not be expected to exceed 4 in the preparation of mineral-oil-soluble wax-substituted hydroxy aromatic hydrocarbons. The molecular structure of alkylated hydroxy aromatic hydrocarbons may be more clearly indicated by the accompanying graphic formulas representing monoalkylated and polyalkylated phenols. p-tert-Amylphenol is an example of an alkylated hydroxy aromatic hydrocarbon in which the aliphatic group is derived from a low-molecular-weight paraffin and from which lubricating oil addition agents of the unifunctional type can be made. The remaining examples represent alkylated phenols in which the aliphatic group is derived from paraffin wax, and from which multifunctional addition agents are obtained. With the exception of the last example, the wax-substituted phenols are simple, unit molecules, the molecular weights of which would be determined directly by the degree of chlorination of the wax and the degree of alkylation of the aromatio nucleus. There is some tendency, however, for larger molecules to occur by chain formation in the case of polychlorinated wax, as found by molecular weight determinations by freezing point and boiling point methods. The last example represents a chain molecule of this type, which may be formed by the reaction of phenol with polychlorinated wax, the unsatisfied bonds of the formula representing a continuity of the chain reaction. The attachment of the alkyl group of the aryl nucleus is represented by a primary, secondary, or tertiary carbon linkage, but this is not an attempt to give an exact representation of the alkylated phenols. No doubt mixtures of primary,
Vol. 33, No. 3
fi v
v
CHa-C-CHzCHs AH3
p-tert-Amylphenol
CHa-C-CHa-CHs
I
CHa Monowax phenol (from monochlorowax)
v
CHI-CH CH-CHa Monosubstituted wax phenol (from dichlorowax) OH ()CH%-CH3
v
CHa--OH Y-CH. Disubstituted wax phenol (from mixed mono- and dichlorowaxes) CHa-CH
CH-
@OH CHs-CH
CHa
O O H
CHCHa Disubstituted wax phenol (from dichlorowax)
-CH-CHa
CHI-CH
CH-CHs
@OH CHa-CH Disubstituted wax phenol of chain type (from dichlorowax) FIGURE 1. WAX-SUBSTITUTED HYDROXY AROMATIC HYDROCARBONS
secondary, and tertiary chlorides are formed in the chlorination of petroleum wax, from which similar linkages result upon reacting the chlorowax with phenols by the Friedel and Crafts reaction. The degree of isomerization resulting in the alkylation of phenols by reaction with chlorowax would be expected to be comparable to products formed by the alkylation of aromatic hydrocarbons by reaction with alkyl halides of low molecular weight. The formation of alkylated aromatic hydrocarbons of low molecular weight along with discussions of theories of the types of alkylated compounds which result under various conditions is capably handled in the chemical literature (5,7).
Properties of Wax-Substituted Hydroxy Aromatic Hydrocarbons The physical properties of wax-substituted hydroxy aromatic hydrocarbons can be varied over a wide range by varying the degree of chlorination of the wax and the degree of alkylation of the aromatic nucleus in the preparation of the compounds, the viscosity of the compounds being increased particularly with increase in the chlorine content of the chlorowax used in the alkylation procedure. Wax phenol (3-16) may be taken as an important example of the wax-substituted hydroxy aromatic compounds; its physical properties are as follows:
March, 1941
INDUSTRIAL AND ENGINEERING CHEMISTRY 7 105
A. S. T. Id.color at 150° F. Pour point ' F. Saybolt vi&osity at 210' F.. seo. Conradson carbon, 70 Ash Mean mol. weight by freesing point method (cyclohexane as solvent)
307.4 0.6 Nil 1000
Wax phenol (3-16) represented above contains about 18 per cent of unreacted wax as determined by distillation under reduced pressure. The physical properties of wax phenol (3-16) after removal of unreacted wax by distillation to 350' C. under a pressure of 5 mm. are as follows: a
A. 8. T. M. color at 150° F. Pour y i n t , F. Saybo t viscosity at 210° F., sec. Conradson carbon 70 Mean mol. weight'by freezing point method (cyclohexane as solvent)
SO
516 1.1 1300
The effectiveness of wax-substituted hydroxy aromatic hydrocarbons as pour-point depressants for wax-bearing motor oils is illustrated in Table I. The pour tests were conducted with a mineral oil lubricating fraction having a Saybolt viscosity of 67 seconds a t 210' F. and an A. s. T. M. pour point a t 20" F. With the exception of the last five agents listed in Table I, the evaluation of all compounds described in this paper was made on wax-substituted hydroxy aromatic hydrocarbons containing unreaoted wax remaining after the Friedel and Crafts reaction. The presence of unreacted wax in the amounts left in the product does not detract appreciably from the value of the wax-substituted hydroxy aromatic compounds as lubricating oil addition agents.
+
353
from the deserving place of top rank in the field of plastics. Resins prepared from alkylated phenols vary in physical p r o p erties, according to the type of alkyl substituent and the degree of alkylation of the phenol nucleus, from hard resins to tough rubbery compositions. It has been found possible to convert wax phenols into improved motor oil addition agents by reaction with resinifying agents (8) such as aldehydes, polyhalides, sulfur halides, polyalcohols, and polybasic acids ( I S ); the resulting products have a higher viscosity, which imparts greater pour-point depressant action when added to motor oils. By reaction with polybasic acid chlorides, the wax phenols are converted into ester products having not only improved pour-point depressant activity, but also markedly improved heat stability; this is desirable in service conditions encountered in the operation of automotive engines. The improvement that can be produced on the pour-point depressant action of wax phenol by reaction with resinifying agents is shown in Table 11. The compounds were evaluated in a solvent-refined motor oil of 67-second Saybolt viscosity 20" F. a t 210" F. and a pour test value of
+
TABLE11. EFFECTOF RESINIFYING AGENTSON POUR-POINT ACTIONOF WAXPHENOL (4-14) DEPRESSANT Resinifying Agent None Phthalyl ohloride Formaldehyde
A. 9. T. M. Pour Point, O F. '/a%
'/le%
.. --20 15
- 10 -20 20
-
I/sa
%
..
- 10
..
TABLE^ I. EFFECTOF WAX-SUBSTITUTED HYDROXY AROMATIC HYDROCARBONS AS POUR-POINT DEPRESSANTS A. S. T. ,M.Pour Points on Oil Blends, Improving Agent
114%
1/8%
15 -- 20 20 5 -- 15 5 - 10
+ 5 10 0 15 + 5 10
-
+ +
l/sa%
.. .. 'd 0
a
+15 l/ia%
..
2,;
-20
1/~%
..0 -10 --20 20
1/2
F.
%
*... .. .. -..20 - 20 - 6 '/4%
0 -10 -25 - 25 25
-
Dewaxed agent,
The data of Table I show that the pour-point depressant action is dependent on the degree of chlorination of the wax and the degree of alkylation of the aromatic nucleus; greater pour-point depressant action is obtained from the more complex and more viscous compounds. The monocyclic phenols are also shown to be superior to the polycyclic or condensed nuclei type of hydroxy aromatic hydrocarbon in the formation of pour-point depressants. The chemical properties of phenols and naphthols are well known to the chemist. The chemical derivatives that can be prepared because of the reactivity of the phenolic OH group are numerous. It has been found that the same chemical reactions can be carried out with the alkylated hydroxy aromatic compounds, but with formation of products of different properties, particularly in the case of the wax-substituted compounds. Resinifying reactions, the formation of metal derivatives, and the Kolbe synthesis are highly important when applied to the alkylated phenols. These reactions and the properties of derived compounds will be briefly described. Resinification The large amount of research on resins and plastics has failed to displace Bakelite compositions prepared from phenol
M e t a l o x y D e r i v a t i v e s of A l k y l a t e d H y d r o x y Aromatic H y d r o c a r b o n s
It was pointed out in the preparation of alkylated phenols that the hydroxyl value could be adjusted by varying the chlorine content of the chloro-paraffin and by varying the degree of alkylation of the aromatic compound. The carbon chain length of the alkyl substituent also serves as a means of adjusting the phenol content. I n the preparation of mineraloil-soluble metaloxy derivatives of alkylated phenols ( I I ) , alkyl substituents of the more branched-chain type have been found to have a greater solubilizing action whereby alkylated phenols of higher phenol content can be used in the preparation of metal derivatives. Wax phenols prepared from peT. M. melting point must not troleum wax of 125" F. A. exceed a combined phenol content of 15 per cent in the preparation of mineral-oil-soluble metal derivatives, whereas mineral-oil-soluble metal derivatives can be prepared from tert-diamylphenol of about 40 per cent phenol content. The type of aryl nucleus has a slight effect on the degree of solubility of metal derivatives, monocyclic compounds favoring solubility more than the condensed-nuclei or polycyclic type of compound. This is explained by the greater complexity of the condensed-nuclei or polycyclic groups, such compounds being more resinous compositions than monocyclic derivatives of the same hydroxyl or metal content. The metaloxy derivatives of the alkylated hydroxyaromatic hydrocarbons may be represented by the general formula,
s.
R"[T(OM),I where R" represents the alkyl solubiliaing groups attached to the nucleus T,and M represents one equivalent of a metal substituted for hydroxyl hydrogen of the general formula R"[T(OH),I. The introduction of metal substituents into wax-substituted hydroxy aromatic hydrocarbons results in the formation of compounds of improved value as lubricating oil addition agents. An improvement is obtained in respect to
354
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 33, No. 3
pour-point depressant value and a highly effective antioxidant action is imparted. The effectiveness of the metaloxy derivatives as pour-point depressants is shown in Table 111.
Salicylic acid is known to have antioxidant action as a mineral oil addition agent, and is generally considered superior to the meta and equal to the para derivative in effectiveness. Of these phenolic acids, salicylic has fair solubility in mineral oils; but for the synthesis of phenolic acids with TAELE111. EFFECTOF METALOXY DERIVATIVES AS POURadequate mineral oil solubility, it is desirable to carboxylate POINTDEPRESSANTS tert-butyl- or tert-amylphenol. These alkylated phenolic Improving Agente A. S. T. hl. Pour Point, F. acids are effective antioxidants as motor oil addition agents. None +20 By carboxylating wax hydroxy aromatic hydrocarbons, Wax phenol (3-16) 0 Wax stannous phenate (3-16) - 15 however, multifunctional products are formed having imWax aluminum phenate (3-16) - 10 proved effectiveness as pour-point depressants and viscosity Wax zinc phenate (3-16) - 10 Wax ferric phenate (3-16) - 10 index agents as well as effective antioxidant action when used Wax cobaltous phenate (3-16) - 15 Wax calcium pbenate (3-lG) - 5 as additives for lubricating oils. Wax magnesium phenate (3-16) - 15 Since the alkylated phenolic acids are mixtures of the ortho, Wax sodium phenate (3-1G) 20 Wax potassium phenate (3-16) - 20 meta, and para derivatives, the following formula is repreWax @-naphthol (3-14) 10 Wax sodium naphtholate (3-14) - 15 sentative of these compounds, a '/s% of each agent used. OH A TABLE IV. EFFECTOF METALOXY DERIVATIVES AS OXIDATION INHIBITORS IN A CFR ENGINE
+
O A B A C
Ring Condition Degrees stuck i l 1 2 3 4 5 360 360 380 360 360 1 5 O O O O 360 270 360 360 0 240 360 0 0 0
3'% slots filled
3 60 O
20 0
4 40 O 60 0
-_
5 20 O 5 0
Carbon Deposit, Grams
19.53
9.90 16.2 7.13
The value of the compounds described in this paper as inhibitors of the formation of oxidation products in lubricating oils was determined under actual operating conditions of automotive engines. As one method of testing the compounds were evaluated in a single-cylinder CFR engine cooled with a diethylene glycol-water mixture held at about 390" F. The engine was operated continuously over a period of 28 hours a t a speed of 1200 r. p. m. which is equivalent to a road speed of 25 miles per hour. The oil temperature was held at about 150" F.during the test. The conditions observed a t the end of the test were the extent to which the piston rings were stuck, the extent to which the slots in the oil rings were Mled with deposits, the amount of carbonaceous deposits in the oil, and the neutralization number of the oil. The effectiveness of metaloxy derivatives as inhibitors of the formation of oxidation products in this kind of engine operation is shown Table IV. Oil A is the uninhibited oil of 120-second Saybolt viscosity a t 210" F. Oil B is the same oil to which per cent of wax cobaltous phenate (3-16) was added. Oil C contained '/B per cent diamyl cobaltous phenate.
Alkylated Phenolic Acids Formed by Bolbe Synthesis
Neutraliaation Number 1.6
where R represents one or more alkyl substituents. T h e e f f e c t i v e n e s s of alkylated 1.1 phenolic acids as lubricating oil addition agents is illustrated in the data of TaGes V, VI, and VII. A striking improvement is noted in respect to the action as pourpoint depressants, viscosity index agents, and antioxidants when the alkylated phenols are converted to the corresponding phenolic acids. 0.4 2.2
TABLE
B
V. EFFECTOF ALKYLATEDPHENOLIC ACIDS AS POINT DEPRESSANTSO
Improving agenta Wax phenol (3-16) Wax phenol carboxylic acid (3-16) Wax @-naphthol (3-14) Wax pnaphtholic acid (3-14) Wax a-naphthol (3-14) Wax a-naphtholic acid (3-14) '/S% by weight added in each case.
POUR-
A. 8. T. M. Pour Point, O F. 0
+--101015
+l5
-
5
TABLE VI. EFFECTO F ALKYLATEDPHENOLIC ACIDSON VISCOSITYINDEX Saybolt Viscosity, Sea. Improving Agents None Wax phenol (3-20) Wax phenolic acid (3-20) Wax phenol (4-20) Wax phenolic acid (4-20) Wax @-naphthol (3-18) Wax pnaphtholic acid (3-18)
100' F. 142.3 159.6 179.4 160.7 178.5
167.5 216.2
210' F.
41.8 43.6 45.3
43.7 45.2 44.4
viscosity
Index
76.1
94.0 101.2 94.6 1 0 0 . F, 99.4 127.3
50.5 When the alkylated aryl metal oxides of the alkali metals a 2 1 / ~ %by weight of each agent added. are reacted with carbon dioxide as in the Kolbe synthesis, the corresponding salts of the alkylated phenolic PHENOLIC ACIDSA s OXIDATION INHIBITORS IN A TABLEVII. EFFECTOF ALKYLATED CFR ENGINE acids are formed. The alkali derirative can then be converted to the free Ring Condition Carbon Degrees stuck % slots filled Deposit, Neutralization acid by neutralization with mineral O i l 1 2 3 4 5 3 4 5 Grams Number acid (1.2). When monoalkylatcd A 0 0 360 360 360 35 80 10 15.67 2.1 phenols are converted to phenolic B 0 0 0 0 0 0 0 0 4.92 0.8 A 180 0 360 360 360 SO 90 80 15.50 2.0 acids, presumably the carboxyl subC 0 0 0 0 0 3 0 1 0 0 7.20 1 2 stituent is introduced into the ortho Dosition t o give the alkylated salicylic acid derivative. However, wax I n Table V I 1 oil A is the uninhibited oil of 120-second phenols for use as mineral oil additives are polyalkylated, Saybolt viscosity at 210" F. Oil B is the same oil to which and when carboxylated a mixture of phenolic acids is formed 2l/2 per cent of wax phenolic acid (3-16) was added. Oil C which is used as such without any effort to separate the contained 21/* per cent of wax phenol (3-16). mixture into its constituents.
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
March, 1941
Metal Derivatives of Alkylated Phenolic Acids (10, 14) The alkylated hydroxy aromatic hydrocarbons of the hydroxyl content described under the preparation of alkylated aryl metal oxides are likewise the most suitable for the preparation of alkylated phenolic acids and their metal derivatives, By double decomposition of an alkali metal salt of alkylated phenolic acids, as formed in the Kolbe synthesis, with a chloride of the desired metal in alcohol solution, the alkali metal salt can be converted into any desired metal salt. When the metal salts of the wax phenolic acids are prepared by reaction of the sodium salt of the phenolic acid and a halide of the desired metal (with the latter in slight deficiency), sodium and chlorine are peculiarly combined in the molecule along with the substituted metal; in this state the compounds with the combined sodium and chlorine can be dissolved in mineral oil to give clear solutions. By adding the metal halide in stoichiometric proportions or in slight excess, the sodium and chlorine are precipitated to a considerable extent as sodium chloride. It has been found somewhat difficult, however, to precipitate the sodium chloride completely without resorting to contacting the reaction product with water. The precipitated sodium chloride can be removed by filtration in the presence of a filter aid such as Hi-Flo. Metal salts formed by this procedure may be represented as follows:
the aryl metal oxide-metal carboxylate type' may be due to the formation of the chelate type of metal salt, which is known to have improved solubility in organic solvents. The properties of metal salts of alkylated phenolic acids as oil addition agents are illustrated in the data of Tables ~~
TABLE VIII.
EFFECT OF METAL SALTSOF ALKYLATED PHENOLIC ACIDSAS POUR-POINT DEPRESSANTS A. 8. T.M. Pour Points on Oil Blends, F.
Improving Agent Wax phenol carboxylic acid (3-16) Stannous carboxylate Aluminum carboxylate Chromic carboxylate Zinc carboxvlate Manganous"carboxy1ate Ferric carboxylate Cobaltous carboxylate Calcium carboxylate Magnesium carboxylate Sodium carboxylate Stannous phenate-stannous carboxylate Cobaltous phenate-cobaltous carboxylate Sodium phenate-sodium carbox late Sodium carboxylate of wax a-napzthclic acid (3-14) Sodium carboxylate of wax B-naphtholic acid (3-14)
i/a%
' 0 0
- 5 - 5 0 0 - 5 0 0 - 5 - 10 10 10 10 +10
-.
.
1/8%
-- 15 15 -- 20 -- 15 15 15 -- 10 15 20 - 15 --20 25 - 20 - 20 10 --15
TABLE IX. EFFECT OF METALSALTS OF ALKYLATED PHENOLIC ACIDSON VISCOSITY INDEX
OH
Improving Agenta
where R represents one or more alkyl substituents and M represents one equivalent of metal. It has also been found possible to form metal salts, OM
355
None Wax phenol Carboxylic acid (4-20) Sodium carboxylate Salts of wax phenol oarboxylic acid (3-20) Sodium carboxylate Aluminum carhox late ' Stannous carboxy%te Sodium carboxylate of wax phenol carboxylic acid 3 1s). Wax$-naphthhia acid (3-18) So ium carboxylate . a 21/z%
Saybolt Viscosity, Sec. 1OOOF. 210" F. 540 66.9 633 72.1 677 76.1
Viscosity Index 101.6 101.6 105.6
720 688 603
81.7 79 71.7
111.7 110.4 104.2
672 666 706
75.8 76.8 82.6
105.6 108.7 114.6
by weight of each agent added.
TABLEX. EFFECT OF METAL SALTS OF ALKYLATED PHENOLIC ACIDS AS OXIDATION INHIBITORS IN A CFR ENGINE Ring Condition Degrees stuck
%
Carbon Deposit,
Neutralization
which may be termed "alkylated aryl Oil' 1 2 3 4 5 3 4 5 Grams Number metal oxide-metal carboxylate" salts. A 270 0 360 360 0 20 20 5 12.5 1.7 B 180 0 0 0 0 0 0 0 6 . 1 0.7 They are formed by introducing a 270 360 10 50 5 14.22 1.7 A 30 360 360 7.19 0.3 0 0 0 0 0 0 0 C 100 second equivalent of alkali metal in 360 360 20 80 5 18.1 2.0 A 80 360 360 the phenolic acid formed in the Kolbe D 60 0 4 5 0 0 0 0 0 5.39 0.3 360 360 80 75 85 17.0 1.5 A 360 360 360 synthesis, followed by double decomE 360 0 0 0 0 0 0 0 4.35 0.2 360 360 30 90 75 18.7 3.1 A 360 270 360 position with a chloride of the de0 0 0 0 0 5.0 0.2 F 0 0 0 sired metal in alcohol solution as A 30 0 360 360 360 85 80 75 11.56 1.5 8 0 0 0 0 0 0 0 0 6.2 0.7 previously described. The precipita360 360 25 70 10 16.2 1.6 A 360 120 360 H 360 90 0 0 0 10 26 5 9.2 0.6 tion of sodium chloride is controlled A 360 360 360 360 360 60 60 20 15.16 1.8 by the conditions outlined above. In 15 0 5 0 0 8.0 0.9 I 120 60 0 A 360 360 360 360 360 70 60 80 15.0 2.8 contactiqg with water, however, as a 0 0 0 0 0 5.3 0.3 J 60 0 0 means of completely precipitating the A is the uninhibited lubricating oil of 120-seconds Saybolt viscosity at 210' F. Oil B C etc the sodium chloride, the use of a limited same oil to which metal salts of alkylated phenolic acids were added as follows: B 1/4% cdbait?us'c&rboxylate of wax phenolic acid (3-19). C 1 / 8 7 cobaltous carboxylate of o-amylphknol carboxylic acid; amount of water is desirable to avoid D , I/,% cobaltous phenate-cobaltoudca;boxyflate of wax henolic acid (3-16); E l / a % vanadyl pheloss of metal from the metaloxy group. nate-vanadyl carboxylate of wax phenolic acid j3-16),: $', I/n% molybdenum phenate-molybdenum carboxylate of wax phenolic acid (3-16). 8 1 9% titanium henatetitanium carboxylate of wax Desalting can be accomplished by ppenolic acid (3-16); H , I/& cadmium bhedate-cadmium car%orylate of wax phenolic acid (3-16). I/*% stannous phenate-stannous carboxylate of wax phenolic acid (3-19) ; J , 1% sodium p h e n a t d refluxing the reaction product with sodium carboxylate of wax phenolic acid (3-16). about 2 ver cent of water, added in the f o k of a 10 per cent solution of water in butyl-alcohol. The VIII, IX, and X. The pour-point depressant action and butyl alcohol serves as an aid in contacting the water with the reaction twoduct. therebv facilitating the desalting viscositv index value are improved bv the introduction of metal kbstituents in the wax-substkuted phenolic acid. procedure. Alihough 'the meti1 content is-increased, thesi Improved antioxidant action is obtained by the introduction metal salts can be solubilized in motor oils by the same oomof metal substituents whether high- or low-molecular-weight position of phenolic acid that is used in solubilizing the alkyl substituents are introduced as solubilizing groups. metal carboxylate type of salt, This surprising solubility of (1
356
INDUSTRIAL AND ENGINEERING CHEMISTRY
Oxidation Inhibiting Value i n Dynamometer Tests The improvement in the performance of the CFR engine which results from the addition of a small percentage of a metal salt of a wax phenolic acid to the lubricant is striking. I n the absence of the addition agent the engine soon failed as a result of ring sticking, with subsequent cylinder wall damage; this condition was completely prevented by the presence of the addition agent. The test conditions in the CFR engine are exceedingly severe. It might be questioned whether these data are comparable to the improvements that would be obtained in the operation of an automotive engine under service conditions. To this end a series of careful Chevrolet engine dynamometer tests were run under high speed and high crankcase temperature conditions on a solvent-refined motor oil of 46second Saybolt viscosity a t 210" F. (SAE 10). The dynamometer tests were carried out under sustained operation of a six-cylinder Chevrolet engine a t 3100 r. p. m., with average road load a t the equivalent speed of 60 miles per hour, The water jacket temperature was held a t 200" F. throughout the test, giving a crankcase oil temperature of 280" F. These temperatures are considerably in excess of those normally encountered in passenger car operation.
Vol. 33, No. 3
77 seconds. The same oil treated with a small amount of the addition agent did not show any substantial increase in viscosity. While the ability to control the rate of development of acid is a striking example of the inhibiting action of metal salt addition agents against the formation of oxidation products, the control of engine sludge, which is far more difficult, is of even greater importance. This effect is illustrated by the third graph of Figure 2. After 32 hours of the engine run, the amount of insolubles present in the crankcase oil was about 2.8 per cent without the addition agent. I n the presence of the addition agent the sludge content was only 0.25 per cent a t the 32-hour point and reached 0.65 per cent a t the completion of the 64-hour run.
Mechanism of the Antioxidant Action of Metal Salts The mechanism by which metal salts inhibit the formation of sludge and acidic oxidation products in lubricating oils in actual operation in an automotive engine is not well understood. Various factors which appear worthy of consideration are the following: 1. Decarboxylation of organic carboxylic acids, known to be formed in the oxidation of a mineral oil and thereby retarding the formation of iron salts of aliphatic acids which are pro-oxidants. 2. Capacity of metal salts for removing carbon deposits by aiding combustion and thereby retarding ring sticking. 3. Capacity of metal salts for removing carbon and sludge deposits from rings by detergent action. 4. Capacity of metal salts in directing oxidation to the formation of oxidation products other than acids and sludge. 5. Tendency of metal salts t o inhibit the absorption of oxygen by lubricating oils.
FIGURE 2. EFFECTOF ADDITION AGENT ON RATE OF DETERIORATION OF MOTOR OIL S A E 10 IN DYNAMOMETER TEST
The results are summarized briefly in Figure 2. I n the absence of an addition agent the neutralization number rose so rapidly that after only 32 hours of service, which is equivalent to some 2Q00 miles of road operation, a number of 20 had been reached, I n a similar engine run on the same base oil, containing 1per cent of the cobaltous salt. of wax phenolic acid (3-16), the neutralization number was held throughout the test to a maximum of 0.6. The influence of the additive upon the rate of Viscosity increase is equally striking. After 32 hours of engine operation, the untreated oil had increased in viscosity from 46 to
Apparently any one or all of the above factors can occur in the oxidation of a mineral oil in the presence of metal salts. The fact that positive oxidation catalysts such as cobalt salts of aliphatic acids will act in some lubricating oils as inhibitors of the formation of oxidation products indicates that a combination of factors such as the first four can operate efficiently under some conditions of automotive engine tests. Factor 1 could give the appearance of oxidationinhibiting action by retarding the start of autocatalytic oxidation even when oxygen absorption methods of testing are used. I n the CFR ring test data given in this paper, the metals generally known as promoters of oxidation are shown to give the best results as inhibitors of the formation of carbonaceous material and acidic oxidation products. This appears to verify claims made in the literature for the efficiency of cobalt salts in maintaining clean metallic surfaces in engine tests on lubricating oils ( 3 ) . The metals tin, chromium, nickel, thallium, and titanium have also been claimed in the literature as inhibitors of the oxidation of lubricating oils when added to the oil in the form of metallic salts (8, 4, 6). Of these metals, titanium and tin are shown in Table X to be quite effective as inhibitors of the formation of oxidation products when added to the oil as salts of the alkylated phenolic acids. In some preliminary work a t the Socony-Vacuum laboratories on the action of metal salts in inhibiting the absorption of oxygen by lubricating oils, i t has been found that not only the kind of metal but also the type of solubilizing radical is important. By the use of alkylated phenolic acids as the solubilizing group, even cobalt salts will give effective antioxidant action. On the other hand, cobalt salts of aliphatic acids have been identified by the same test conditions as strong pro-oxidants.
March, 1941
INDUSTRIAL AND ENGINEERING CHEMISTRY
Apparently the oxidation characteristics of lubricating oils in the presence of metalsaltsare dependent on the of motor 0% the kind of eng;ne test, and the type Of salt used as an addition agent. This study of the mechanism of oxidation of lubricating oils in the presence of organometallic compounds will be continued.
Literature Cited (1) Dryer, C. G., Brooks, Walter, Morrell, J. C., and Egloff,Guetav, Universal Oil Products Co., Booklet 211, 1937. (2) Evans, E. A., and Kelman, A. L.,Znst. Mech. E ~ L B TLubrica~., tion discussion, Oct., 1937,Group IV,90-9. (3) Gilbert, W. V., Brit. Patent 455,097 (Oct. 14, 1936).
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(4) Griffith, A. A., and Helmore, W., Ibid., 423,441 (Aug, 1, 1933). Louis, J . Ow. Chenz., 5 , No. 3,253 (1940). (6) Mardles, E. W. J., Tech. Pub. Intern. Tin Research and Dmelopment Council C,No. 2 (1934). (7) Nightingale, D. V., Chem. Rev., 25,329 (1939). (8) Reiff, 0. M. (to Socony-Vacuum Oil C o . ) , U. 9. Patent 2,062,676 (Dec. 1. 1936). (9) Ib&.. 2.191.498'(Feb. 27, 1940). (id, Ibid.; 2,197,832(April 23, 1940). (11)Ibid., 2,197,833(April 23, 1940). (12) Ibid., 2,197,837(April 23, 1940). (13) Reiff, 0.M., and Badertacher, D. E., Ibid., 2,048,466(July 21, 1936). (14) Reiff, 0. M., Giammaria, J. J., and Redman, H. E., Ibid., 2,197,834 (April 23, 1940). (5) Ipatieff, V. N., Pines, Herman, and Schmerling,
Spontaneous Ignition of Hydrocarbons Zones of Nonignition CHARLES W. SORTMAN, HAROLD A. BEATTY, AND S. D. HERON Ethyl Gasoline Corporation, Detroit, Mich.
Spontaneous ignition temperatures in air, and the corresponding time lags, have been determined for a variety of hydrocarbons at atmospheric pressure by the oil-drop or Moore method, using a steel crucible and different air flow rates and liquid drop sizes, Under some conditions of air and liquid feed the readily ignited hydrocarbons, such as cetane and heptane, show two separate temperature zones of nonignition above the minimum ignition temperature, a behavior heretofore unobserved; under other conditions one or both of these zones are eliminated. The conditions of air and liquid feed also have a marked effect on the ignition time lag, especially at low temperatures. Addition of tetraethyllead completely inhibits ignition up to about 850-1000° F. (454-538' C.).
HE so-called spontaneous-ignition temperature of a T combustible liquid is not a definite property but varies according to the method of test. However, the application of one suitable test method to different combustibles will give comparative results which may be of considerable significance. For evaluating the fire hazard arising from the contact of liquids or vapors with a hot surface, the Moore oil-drop or crucible method of test is undoubtedly the simplest to apply in the laboratory, and may be expected to correlate with the actual behavior found in practice on a larger scale. In the Moore test of a given liquid, the principal variables
are: the amount of liquid taken (for a crucible of given size), the nature of the surface material of the crucible, the use of air or of oxygen, and the use of stagnant or of flowing air. It is assumed that the pressure is held a t one atmosphere, and that the liquid is charged in drops and not atomized; these two provisions are in accord with the conditions normally involved in consideration of the fire hazard of a liquid (although a t the same time they prevent the test from showing good correlation with the behavior of the liquid as a fuel in internal-combustion engines). For the same reason the use of air rather than of oxygen is desirable; in the present work a few tests were also made on a 50 per cent oxygen-nitrogen mixture, in order to demonstrate that the concentration rather than the total amount of oxygen is the important variable. The present work is an outgrowth of a series of tests (6) made on different liquids, in connection with their fire hazard when used in aircraft. On this account it was decided to adhere t o the use of a stainless steel crucible and of flowing air, rather than to follow the A. S. T. M. specification (designation D-286-30) of a glass crucible (flask) and of stagnant air. The steel surface gave good reproducibility, without requiring any unusual care in cleaning; while it normally gives somewhat higher ignition temperatures than glass does, the difference is not important. The air flow rate was varied one hundred fold, the lowest rate being practically the equivalent of stagnant air. The existence of one or two well-defined temperature zones of nonignition above the h s t or minimum ignition temperature was noted in the previous report (2) for some of the paraffinic fuels. This type of behavior is familiar in vaporphase oxidations studied by both the flow and static methods, but has not heretofore been reported for the Moore method; and the appearance of two zones of nonignition a t atmospheric pressure is novel in any case. Accordingly, this phenomenon was studied in some detail for cetane as a function of air flow rate and liquid drop size, and for heptane as a function of liquid drop size. For comparison, a number of other hydrocarbons were tested a t one or two liquid drop sizes.
