April 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY
491
coYcLusIoss
ACKNOWLEDGMENT
A rlumber of diester fluids have been found with a combination of properties desirable in lubricants for use a t low temperatures. T h e most suitable compounds are long-chain diesters with two or more short aliphatic side chains suitably positioned. Although these compounds contain two ester groups (and in some cases also ether-oxygen linkages), they are dominantly hydrocarbon in composition. They are found t o resemble in viscometric, thermometric, and volatility properties the geometrically analogous hydrocarbons, particularly a t high molecular weights. T h e most promising fluids have molecular weights ranging from 300 t o 600 and freezing and pour points from -40" t o lese than - 100" F. They have maximum evaporation rates at 150" F. of 0.5% by weight, decreasing t o values of less than 0 . 1 5 for those of t h e higher molecular weights. T h e flash and fire points ranged from 300" t o 500" F., t h e spontaneous ignition temperature from 700" t o 800" F., and t h e spray flammability from 13 t o 45% oxygen, increasing with t h e viscosity of the fluid. T h e fluids can be grouped in four classes according t o their viscosities a t 100" and -40" F., respectively: ( a ) 5 t o 10 and 300 t o 1300 centistokes: ( b ) 10 t o 14 and 1200 t o 3000 centistokes: (c) 15 t o 25 and 6700 t o 8300 centistokes: ((1) 30 t o 60 and 7000 t o G6,OOO centistokes. The best combination of viscometric properties are found for several types of diesters: (1) glutarates, adipates, azelates, and sebacates made with sec-amy1 alcohol, 3-methylbutanol, 2-ethylbutanol, 2-ethylhexanol, and the branched-chain secondary alcohols, undecanol and tetradecanol; (2) those made by reacting the above acids with 2-(2'-ethylbutoxy) ethanol; (3) those made by reacting hexamethylene glycol or decamethylene glycol with a branched-chain acid such as 2-ethylhexanoic acid: and (4)those made by reacting triethylene glycol or a polyethylene glycol with 2-ethylhexanoic acid. The somewhat inferior viscometric properties of type 3 diesters, as compared t o type 1, coupled n.ith their lesser availability make t h e type 3 fluids of little present interest for lubrication. T h e higher specific gravities and the ability of class 2 and 4 diesters to dissolve more water than those of class 1 of t h e same molecular weight makes them less desirable for some applications. It is concluded t h a t specially selected diesters of classes 1, 2, and 4 are good base fluids for the development of lnbricant compositions, those of cl 1 being most suitable for the greatest variety of uses. Also a comparative study is decirable of the oxidation stabilities and t,he effectiveness with which these fluids can he inhibited agiinst oxidation and rusting hy tlir nction of chemical addition agents.
T h e authors gratefully acknowledge the cooperation received from their co-workers, especially from Charles Saunders who supplied t'he d a t a relating to solubility and hydrolysis, Miles V. Sullivan who made the measurements of spontaneous ignition temperature and spray flammabilit'y, and Paula Taylor and Charles Saundcrs who obtained the data on flash and fire points. LlTERATURE CITED
Aepli, 0 . T., and McCarter, I T , S.,ISD. ENQ.CHEM.,AX. I . R . , and eo--workers. 0 . S . R . D . R ~ p t 1894 . 1943). Fischer, Karl, A n g e w . Chem., 48, 394 (1933), Helmore, W., in "Science of Petroleum" (Dunstan rt ( I ! . ) , Val. IT, p. 297'0, Oxford Univ. Press. 1938. Hickman, K. C., J . Franklin Inst., 221, 215 (1%36). I b i d . , 221, 383 (1938). Hickman, K. C., and Sanford, C. It,, Ret. Sci. I m t i , m i p r r / a . 1, 140~~~~, 11930).
Mikeska, L. A , , IND.ESG.CHEM.,28, 97'0 (1936~. Natl. Bur. of Standards, Supplement to C'irc. C410 (1937). Nissan, -1.H., Clark, L. V. W., and Nash, A. IT., J . I m / . F'-I, phenosyphenyl, xenyl, and dodecylphenyl), of phenylhendecThe pure diesters resemble highly refined petroleum oils in anoic acid, and of the available naphthenic and petroleum their inahility t o prevent the displacement of the oil from iron or steel surfaces hy drops of mater: hence they do not have rust sulfonic acids having molecular weights from 300 t o 600, were all able to inhibit the rusting of steel in this test when used in conpreventive properties. .I few samples of commercially availcentrations of 0.2 t o 0.5% b y m i g h t . T h e salts of t h e acids able diesters were found t o have some rust preventive value, having the highest molecular n-eights Tere those required in the b u t this was found t o tie due t o the presence of an adsorbable lowest concentration. Thus, zinc di-(phenylhendecanoate), impuritv. -1common and often adequatelv effective met,hod of imparting rust, preventive propertie? t o oils is by dissolving or zinc di-(phenyletearate), and zinc di-(dodecylphenylstearate) dispersing in them a small amount of a polar and hydrophilic \\-ere needed in weight concentrations of 0.5, 0.35, and 0 . 2 5 5 , compound of suitahle itruetiire. .in investipation on the mode respectively. Sorbitan mono-oleate and also any one of the of action o f such additives, the relation of organic structure t o animoniuni compounds made from cyclohexylamine or dicyclorust inhilitive value, and the significance of the various empirical hexylamine and either lauric or sylylstearic acid !yere satisfactory in inhibiting rusting a t neight concentration of 0.5$. test methods was completed during the war, and a preliminary For many applications a greater degree of rust inhibition was report rvas made (1). This background n ' a ~used as a guide i n the t election of riiqt in hi hi to^ and of the niethods of testing the desired than could be made evident n-ith the turbine oil rusting oils for rust preventive value. I t n-ne concluded t h a t the rust teat. The various inhibited oils found satisfactory in the turinhibitor5 found efcectire in hydrocarbons should also be effecbine oil corroqion test r e r e therefore esposed t o the static water drop t e 4 ( 1 ) using distilled 11-ater a t 140' F. .I11 of the inhihitors Ithough differences in the solubilities of the compounds in the two types of fluids might affect their relative by iveight, were mentioned, in coiicentrntions of 0.2 t o 0.5', ratings as rust inhibitors. wtkfactory after 168 hour3 of esposure except the sortlitan Since the most promising application of diehters is in the mono-oleate and the ammonium compounds ~ l i i c hirere required del-elopnient of l o n temperature luhricants, only tho.se rust inin :i concentration of 1.OC;. 0
T ~ B L111. E
EFFECT
Intioxidant
- ........
.
diphenyl;^ II i i ii e S - ( p - f e r / - a i r i v l p h e i i v l ) ethanolamine
O F VARIOCS I X H I B I T O R S O N OXID.\TIOS
10
:1 10 o-Cyclohesyiphenof 10 p-Cyclohex?li)henol 20 p-Phenylphennl 0 20 4-te~.t-Ruty1-2-phenylphenol 0 10 4-teri-Butyl-o-crerol 0 10 p-lert-hniylpheiiol 0 10 6-Isoprop?l-ni-cresol 0.10 4-id-Butylcatechol 0 10 a Using oxygen a t 125 pounds jnitial pressure b n.c. = no change,
OF
DI-(z-ETHYLHEXYL) S E B i C i T E
Appearance after Oaida-ion Te-t h .___ T'iscositp at 100" F. yellIra1iza2481' Initial, tinn S o I)ur?lcentistokes Increase Increase Fluid C w ~ p ~ r uniin Steel 12.6 0.8 16 6 Cloudy Clxidized. c n r r oded 11.r. 11.c. 12 6 -0 8 0 21 nr. 11'. .\mber, -light sedinient Oxidized 1 0 12 6 0.0 2 6 n a r k green Oxidized iic. ii.(?. 2 5 12.6 0 0 0 33 Clear, slightly yellow Oxidized n.c. 11 r . 0 5 12 6 0 0 0.07 n.r III'. Clear, slightly yellow Oxidized 0 5 12 6 -0.8 2.6 I.ight green Xnne present I1.C 1I.C. 0 12.6 0.0 2 6 Zieht e r w n Oxidized n.r. 11 c . 0 12.6 0.0 0 07 Clk.r,':lightly yellow n . r . n.c. i1.c. 0 12.6 0.0 0.10 Clear Oridized n.c. n c. 0 5 12 6 0 0 0 20 Clear, slightly yello\v Oxidized 11.c 11.1'. 0 12.6 0.0 0.07 Clear. pale yellow (Ixidized n,r. i1.c. 12.6 0.5 0 0 0.32 Clear, slightly green Oxidized 11.r. 11.c. a n d bomb maintained a t 212" F. for 168 hours.
C'oncn . W t . no 0 0 0 0 0
3T.IBILITY"
AP, 1.h. 33 0
INDUSTRIAL AND ENGINEERING CHEMISTRY
494
Vol. 39, No. 4
limitation of the available rust-inhitititig compounds. \\
r
POLYIIER THlCKENERS A N D V . 1 . IIlPROVERS
I.e.210' to -40'
1'. E'.
740 1,060 2.1 Ill1
8.700
.540
liil(1
1X i
I1
1,:35[1
:3+5(J
2240
182 li3 I5fi 1:i4
0 60' IJ S O '
-,nlJ -
,.>'i
:311 460b 1.470h 43,100 5
68 8 . . . 80
0 71' CJ 6 7 ' 0 6 1' 0 5i' I1 4 8 " 0 41'
445 540
187 217
li
3
. . .
...
12 15 21 29 38 179
..
1.52
181
42!l 826 ,504
6.15 829
666
116 , ,
.. ... ... ...
($7'
050' 0 SI'' 0 77' 0 64,1 0.69d 0.68d
0.63d 0.61J
INDUSTRIAL AND ENGINEERING CHEMISTRY
April 1947
1.ubricant C'oniposition Rust Inhibitorb
IXeater"
.\dipate 3 r o l adipate & 2 r o l sebacate .Izelate Sebacate Sebacate Sebacate Sebacate Sebacate Yebacate Sebacate Sebacate Sebacate Sebaca te Pebacate
1
'&%(ZnPhj
.Izelated debacatea
L;i%(CaPh) '/r'"''o(CaPh)
S e u t . K O . of Finished Oil
? l o o F.
0.32
2.38
0 35
2.85 3.06
0 0 0 0 0 0 0 1
53 45 06 08 28 28 46 42 3 74 0 94 1 23 1 88
3.31 3 35 3.43 3.56 3.77 3 31 3 44 3.69 3 31 3.32 .i41
130° F.
looo F.
Viscosity, Centistoke- . 77O I?. 3 2 O F. O D F. -20'
L-srsr, ~-F:TBTLHESTL DIESTERS 5.35 8.22 12.5 371
~
F. - 4 0 ' F. -60'
108
262
46 I 52.0 60 9 61.0 72 8 83 1 105 61.6 63.3 68.1' 62f 62 1 63:
146 158 187 190 230 300 400 190f 189 205 194 198 202
:3:351 400 450f 460
1-ETHYLPROPl-L I ) I E * T E R S C 9.41 13.5 20 2 51 4 9.4 14.3 211 56.2
13% 150
2951
6.51 7 20 7.98 8.03 8.51 9.2 10 3 1 8.01 8 31 8 51 8.01 8.11 8 31
9.90 11.4 12.6 12.8 13.5 15.0 16.8 12.7 13.0 13., 12 9 13 0 13 2
15.5
17 1 19 5 19 6 22 5 1 24.6 27.8 19 51 20 3 21 0 1 19.6~' 19.61'
20f
...
495
4601 500 4601 4651'
4681
Kineniatir
\.I.
.\.S.'r..\I. Slope
810
121
0 77,
1090 1200 1420 1450
153 146 154 154 149 138 132 154 162 178 146 145 1.53
0 7:3'
0 0 0 0 0 0 0 0 0 0 0 0
259 217
0 64)
U U J !
4501
P.
1420 148:1 1634 148'2 1510 1.5.50
72L 701 711 71h 73h i4n
701 691 691 71 71 70.
t.3ISC
0.05 0.06
4.25
4.33
Inhibited n i t h 0.20% 4-terl-buty1-2-pheiiyl phenol. 6 ZnPh = zinc di-(phenylstearate), C a P h = calcium di-(phenylstearate), XIgPh = magnesium di-(xylysteara t e ) , M g X y = nragnesiuni di-(xylylstearaIe). 'I
M a d e from Sharples diethylcarbinol. f Thickened a i t h 3.0% Acryloid HF-880 Thickened with 2.5y0 Arryloid HF-880. 1 Interpolated.
F-10, HF-845, HF-860, arid HF-880); these alao had the advantage of not being precipitated from diester oils when contaminated accidentally by either petroleum oils or the commoil volatile solvents used t o clean lubricated systems. Table V shows the effect of increasing concentrations of some of these Acryloids on the viscosity-temperature characteristics o f di-(2-ethylhesyl) sebacate. -1cryloid HF-880 was the most effective as evidenced hy increased V.I. and decreased A.S.T.31. slope. The apparent anomaly of the decrease in V.I. with incre:ising polymer concentration is due in greater part t o the well known peculiarity of the V.I. scale. ;\t the higher concentrations several of the solutions eshibited non-Sen.tonian behavior. This may be attributed t o the orientation of the linear polymeric molecules with the direction of Ron- and the anomolous viscometric hehavior increases with increasing rates of shear. Graphs of the results in Table V, plotted on -1.S.T.M. viscosity-temperature paper, show a progressive deviation from linearity n i t h increasing polymer concentrations. This curvature of the thickened diesters makes it necessary (as do the footnotes of Table V) t o specify the temperature range over which the A.S.T.11. slope was calculated. The thickening effects of tlie .icryloids in di-(1-ethylpropyl) azelate and sehacate are also given in Table V. These d a t a exemplify the generalization that the viscosity-temperature characteristics are improved hy increasing t h e concentration of polymer and t h a t the fluids made h y thickening the less v i s o u s diester, cli-(l-ethyli)ropyl) sebncate, had better viecosity-temperatiire characteristics than fluids made by thickeiiing the more vim)iis diehtrr, di-(2-ethylhesyl) seh:icate. DIESTER INSTRUJIENT LUBRICAlTS
For inany years there has been a need for nonvolatile, nongumming, low temperature instrument oils capable of performing effectively over the temperature range 250' t o -100" F. Conferences n-ith manufacturers and users of a variety of naval and industrial instrument and control devices indicated that such oils should have viscosities of 10 t o 15 centistokes a t 100" F. and not over 2000 centistokes a t -40' F. Six of the diesters already discussed were selected as particularly suitable for the preparation of two classes of oils. Di-(2-ethylhesyl) sehactite, di-(2-ethylhesyl) azelate, di-(2-ethylhesyl) adipate, and a mixture of three volumes of di-(2-ethylhexyl) adipate n-ith two volumes of the corresponding sebacate a-ere used to prepare instrument oils. XI1 of these fluids were suitable for ship and shore
340
810 90s
2690 ,3130
0.641
u Sun-Sewtonian behavior.
A.B.T,\I. slope, 210' to 0' I.'. i .1.S.T.M. slope, 210" t e -40' F. i A.S.T.1LI. slope, 210' t o -60' F.
h
iiistallations, and all but the first could satisfy niost nvi:ition needs. Where still lower viscosities were needed for the extremely lo^ temperature applications, either di-( l-ethylpropyl) azelate or di-(1-ethylpropyl) sehacate thickened with 2.5 to 3c', of .h-yloid HF-880 may he wed. In all cases 0.2c; by weight \vas employed a i antioxidant. The of 4-tert-butyl-2-phenylplie1i~~l rust inhibitors were c:irefully purified magnesium, calcium, o r zinc soaps of phen- earic, sylylste:iric, or, preferably, senylstearic acids in cone ration. of 0.25 t o 3.0' i,depending on the application. Concentrations greater than 1c ; were avoided tvherever possible, especially where it wis importiint t o have Freedom from clouding :it loa temperatures and during long term storage. The high-molerulwr-n.eight petroleum su1fon:ites and riaphthenates of these and other metals were :ilm used with equal success. T h e viscometric properties of some diester luhricant compositions are listed in Table VI. ('omparison of Table VI with Table I11 of the first paper ( 2 ) shows t h a t the addition of antiosidant and as much as 0 . 3 3 5 of the rust inhihitor httd a negligible effect on viscosity. Concentrations of the rust inhibitor of 1% or more increased the viscosity, decreased the V.I., and caused t h e appearance of non-Sewtonim behavior. T h e magnesium and zinc aryl stearates were more readily dissolved in the diester fluids than the corresponding cilcium soaps. The fluids prepared from di-(a-ethylhesyl) sehacnte were free from precipitates or clouding after storage for 96 hours a t -60" F., nnd the other fluids of Table VI Tvere satisfactor>-:it -75' F. The diester used for there compositions h a d ;I neutra1iz;ition number of 0.03 or less, The :intiosid:int had :I negligible effect on the neutralization number. Holyever, wine of the rust inhibitors, such :i3 zinc :itid m:ignesium so:!ps, c2iused $! coriidernhle increase {vhich i5 attrit)nted t o alkiiliIit~hydrolysis of the soap during titratioli. The rieutl,:\liz~itiolliiwnljer of tlie oils containing zinc, magnesium, :ind calcium so:tps tvere c:ilrul:tted :iwumiiig complete hydrolysi.. From the esperimentd tlrterminations of the neutralizatio numherr of these solutions it was calcnlnted t h a t hydrolysis xva looc; for the .ciIic, 80 t o 85'; for tlie magnesium, and 10 t o 30" for the calciuni soaps a t the inolal concentration used (4.6 x 10-4). Since some of the oil compositions containing or more rust inhihitor had mther high neutralization numbers, their corrosiveness t o copper was determined by Federal Specification Board Xethod 530.31. .It the end of the 3-hoW test period each copper test strip h:id tieveloped a faint brown color. At the end of 21 hours the color became only slighly darker, but there \v:~< n o evidence ( i f the
INDUSTRIAL AND ENGINEERING CHEMISTRY
496
Rust Inhibitor Zn di-(phenylstearate) Ca di-(phenylstearate)
I l g di-(phenylstearate)
a b
Concn , n - t 7c 1 1 1 3
1 2 3 1 2 3
0 0 0 0 0 0
Pressure Decrease. I.b./Sq. In 0 4 1 2 2 0 0 0
Visco-ity at 100' F. Initial, Increase, n centistokes
Seutralization 1 - o . Initial Increase 0 30 0.43 0.Oi 0 40 0.02 1 31 0 28 0.31 0 28 0.48 1 23 0 37 2 23 -0.12 3 18 -0.05
Vol. 39, No. 4
.ippearance after Oxidation Teat Fluid CopperC Faint green cast, clear Oxidized Yellow, clear Oxidized Light brown, clear Darkened Light brown. clear Darkened Light brown, clear Darkened Pale yellow. clear Darkened Pale yellow. clear Darkened Pale yelloa, clear Darkened
Csing osxgen a t 125 pounds initial pressure and 212' 17. Stabilized with 0.207c 4-te,.t-butyl-Z-phenylphenoi. ?io change in appearance of the duralumin and cold-rolled >reel s t r i p s
TABLE VIII.
DYNI\IIC
OXXD.iTIOS
TESTS* O S DIC>TER ISSTRULIEST S eur
r
Lubricant Coniposition Viscosity a t 100' Rust Initial, Increase. Diesterb InhibitorC centistokes C; azeiateDi- (2-ethylheayl) sebacate
Di-(1-ethg-lpropyl I sebacated
0 9
1,/3%(CaPh1 1 O&G, "(CaPh) 2.0 /,(CaPh) 3.0Tc (CaPhi l.O"L(l1gPh) 3 . 0 R~(lld'h)
12 8 13.5 15.0 16.8 13.1) 13. I
l's%(CaPh)
14 3
-0 0 0 -0 0 1
Seutralization s o Initial Increase 0.42
8 7 0 6 8 5
0 07
0 0
006
0 19
0 0 -0 -0
0 20 0 51 0 56 12:1 3 18
43
54 41 43
0.62
so.of Volatile .4r,id.;
OILS
;\ppearance after 0sid:ition 're-t 24ST DuralFluid C (inner 11111111 ..
~~
~
6 OS
Light green, clear Slight corro-ion
0.60 6 40 6.80 5 50 5 2 i 3 40
'ielloa., clear l e l l o w , clear Rron-n. clear Brown, clear
6.96
n.c n c
n,r
Oxidized Oxidized Oxidized Oxidlzed Oxidized 0yi di zed
Light yelloiv
Osidized
11
11.c.
*
dreel
n c.
11.1'
I1
c.
XI,I.. Kidder, H. F.. Murphy, C. M., : m i l Zisman, W. .k., ISD. EXG.C H E J I . , 39, 484 (1947). (3) Dornte, K.IT., Ibid., 28, 26 (1930). (4) Dornte, R. W ,and Ferguson, C. V.,Ibid., 28, 883 (1‘336). ( 5 ) Dornte. R. W., Ferguson. C. T., and Haskiw, C. P., Ibid., 28, 1342 (1936). (6) Egloff, G., in Gilrnan’s “Organic Chemistry”. Vol. 1, p. 54, New York, John Wiley & Sons, Inc., 1943. (7) Egloff, G., Morrell, J . C., Lowry, C. D., and Dryer, C. G., Proc. W o r l d Petroleum Congr., 2, 50 (1933). (8) Ellis, C., “Chemistry of Petroleum Derivatives”, Vol. I, New York, Chemical Catalog Co., 1934. (9) I b i d . , Vol. 11, 1937. (10) Evans, H. C.. and Young, D. If-.,IXD.E N G . C H m r . , to be published.
(11) Lowry, C. D., Trans. EZectrochern. Soc., 69, 185 (1936).
(12) Staudinger, H., “Hochrnolekularen organisidle Verbindungen”, Berlin, Julius Springer, 1932.
T K Eopinions or assertions contained in this paper arc the authors’ and are not t o be construed as official or reflecting t h e views of the Navy
Department.
