2
Ind. Eng. Chem. Prod. Res. Dev. 1980, 19, 2-6
SYMPOSIA SECTION
I.
Chemistry of Synthetic Lubricants and Additives H. V. Lowther 178th National Meeting of the American Chemical Society, Washington, D.C., September 1979
Wide-Temperature Range Synthetic Hydrocarbon Fluids James A. Brennan Mobil Research and Development Corporation, Paulsboro, New Jersey 08066
Normal adefins of 6-12 carbon atoms are preferred for the preparation of polyolefin lubricating oils. Boron trifluoride is the best catalyst when dimers through pentamers of these olefins are desired. This work compares the wide-temperature range fluidity of individual oligomers of normal a-olefins of the same degree of oligomerization (molecular weight effects)and individual oligomers of the same molecular weight (molecular structure effects). The BF, trimerization of ldecene yields the best wide-temperature range synthetic hydrocarbon fluid. This conclusion is at variance with an earlier study in which oligomerization of lactene using a modified Ziegler catalyst was preferred. Comparison of both processes shows a decided advantage for the ldecene-BF, system over that of l-octenemodified Ziegler catalyst for the preparation of the most desirable oligomers. The olefin oligomers are also compared in wide-temperature range fluidity with other synthetic hydrocarbon compositions.
Introduction It is generally recognized that normal a-olefins of 6 to 12 carbon atoms are preferred for the preparation of polyolefin lubricating oils (Hamilton and Seger, 1964; Duling et al., 1965). To identify the preferred starting materials, the olefins have been oligomerized at constant reaction conditions, and properties such as pour point and viscosity index of the total products were compared and related to the chain length of the starting olefin (Sullivan et al., 1931; Biritz, 1963). Others have oligomerized the olefins at several reaction conditions and compared pour points and temperature-viscosity relationships of the total product or dimer free polymer at a constant viscosity (Giannetti and Henke, 1963). In order to minimize the effect of molecular weight on physical properties, one study isolated a narrow boiling material representing approximately a Cm fraction and compared the pour points and viscosity indices of these oligomers (Antonsen et al., 1963). The present study compares the wide-temperature range fluidity of individual oligomers of the same degree of oligomerization (molecular weight effects) and individual oligomers of the same molecular weight (molecular structure effects). Normal cy-olefin oligomers are also compared in wide-temperature range fluidity with other synthetic hydrocarbon lubricant compositions. Experimental Section The even carbon number, a-olefins were supplied by Gulf Oil Corp. 1-Nonene and 1-hendecene were obtained from Humphrey-Wilkinson. Other organic chemicals (e.g., the promoters) were Eastman Reagent grade and were used as received. The BF, (CP grade) was purchased from Matheson Co., Inc. Conventional metal-supported catalysts were used to hydrogenate the oligomers. 0196-4321/80/1219-0002$01 .OO/O
The preferred oligomerization procedure (Brennan, 1968) involved saturation of the olefin with BF,. The promoter-BF, complex was preformed. The apparatus is shown schematicallyin Figure 1. The BF3-saturated olefin and the promotereBF, complex were metered, by means of syringe pumps, separately and simultaneously into the reaction vessel. The vessel was previously pressured with BF3 to 4 in. of Hg and maintained at the reaction temperature with a constant temperature bath. The oligomerization reaction was followed by gas-liquid chromatography (Figure 2). At completion of the reaction, the reactor was depressured and swept with N2. The mixture was quenched with NH3, heated at 80 "C for 1 h (N&, filtered to remove the BF,.NH3 complex, H20-washeduntil neutral, and dried over anhydrous Na2S04. Oligomers were separated by distillation at reduced pressure using a heated 12-in. Vigreux column. Hydrogenations were accomplished in a stirred autoclave at 170 "C and 500 psig. Results and Discussion A literature search was initiated for molecular structures associated with wide-temperature range fluidity. The most reliable source of data was the API Project 42 at Pennsylvania State University (American Petroleum Institute, 1966), where it was found that one of the structures associated with superior low-temperature fluidity is the concentration of atoms very close to the center of a chain of carbon atoms, as
P'
R-C-R,
I
R3
Where R and R2 are nearly identical in size, R1 is generally hydrogen but may be an alkyl group, and R3can vary from 0 1980 American Chemical Society
Ind. Eng. Chern. Prod. Res. Dev., Vol. 19, No. 1, 1980
Table 11. 1-Decene Oligomerizations-Various
3
Catalysts
catalyst
V i J
---,-In P ronioter Cornolexed i:ith B F j
-==7==7
bd
pz '
BF,. ROH
'11
temperature, "C time, h conversion, wt 96 degree of oligomerizationa selectivity, wt 96 dimer trimer tetramer
:it,
'iz,,/ ~
T h er -0 meter
Decene I n
A Pump
Figure 1. Apparatus used in the BF, polymerization of olefins. c:ILrP
-
?
5 i t 31 ? u t t
DiaiI'?r
l
Figure 2. Typical chromatogram of a BF, polydecene fluid. Table I. Melting Points of Model Symmetrical Zsoparaffinsa skeletal structure
ma. "C -28.3
c,-c-c:, I
C6
c,-c-c:,
-13.8
I
n
%
c ,,-c-c:
9
n
17
a
American Petroleum Institute (1966).
a methyl to a group larger than R and R2. The carbon atoms comprising R, Flz, and R3may be arranged in a chain or a ring. Compounds with carbon numbers up to 36 in which R1 is hydrogen and R, R2, and R3 are alkyl and nearly identical in size, exhibit very good wide-temperature range fluidity. The examples shown in Table I have surprisingly low melting points for hydrocarbons of this size. Also, the measured low-temperature viscosities of compounds of this structure are less than predicted from their high-temperature viscosities (standard ASTM D 341 form). Long chain linear a-olefins should yield trimer fractions structurally similar to that represented above. For example, 1-decene trimer would have the skeletal structure
c,-c-c-c-c I
1
c
cs
,
Thus, the trimerization of long-chain olefins is a one-step synthesis of a superior lubricant molecule. A reaction in which trimer is produced exclusively is not likely. Also, even at the most closely controlled reaction conditions, the
+
30
3 96 3.5 12 54 34
Al(C,H,); di-tertTiCl; butyl CHC1, weroxide 77 155 5.3 4.3 87 41 6.9 7.2 5 15 80
13 9 78
a Molecular weight of oligomer/molecular weight of monomer.
trimer will be a mixture of isomers. This, however, has the advantage of lowering the melting point of the trimer mixture relative to that of pure compounds of comparable molecular weight and structure. Pure hydrocarbons having molecular weight and structural features similar to tetramer and higher oligomers of normal a-olefins are not available for comparison. Long-chain a-olefins have been oligomerized to oils thermally (Seger et al., 1950) and catalytically using radical (Garwood, 1960), cationic (Sullivan et al., 193i; Giannetti and Henke, 1963; Hamilton and Seger, 1964), and Ziegler-type catalysts (Antonsen et al., 1963; Beynon et al., 1962). All of these methods yield fluids which are superior to conventional mineral oils in wide-temperature range fluidity. The oils prepared by the catalyzed oligomerization of olefins have received the most attention. These methods would not be expected to yield the same product, and significant differences in conversion rates and degree of oligomerization are found (Table 11). Among the methods shown in Table 11, the BF3 catalyzed oligomerization gives the highest rate of conversion and provides the lowest number of monomer units in the oligomer. For the preparation of wide-temperature range fluids with a degree of oligomerization from 2 to 5 , BF, is the preferred catalyst (Brennan, 1968, 1973). (Degree of oligomerization = mol wt of oligomer/mol wt of monomer.) Boron trifluoride oligomerizations require a promoter and an excess of BF, over that needed to form a 1:l molar adduct with the promoter. Promoters are Lewis bases with a hydrogen atom available for protonation of the olefin. An initiation step which accounts for the above stoichiometry may be represented by H HC
11 +
RC H
R' HOBF,
+
[Ri
H R' H C . . . H . . .OBF,
BF,
-+
:
BF,
]
+
However, no direct evidence for the initiation reaction has been obtained. The degree of oligomerization in BF3 !eactions can be varied by changes in promoter concentration or type, and reaction temperature. The molecular structures of oligomers obtained in olefin oligomerizations are not well characterized. In BF,-catalyzed oligomerizations appreciable double bond isomerization does occur. In studies with 1-decene the dimer recovered from the BF, reaction after hydrogenation has
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Ind. Eng. Chem. Prod. Res. Dev., Vol. 19, No. 1, 1980
Table 111. Comparison of Hydrogenated 1-Olefin Trimers kinematic viscositv. - , cSt olefin trimerized
carbon no.
hexene octene nonene decene hendecene dodecene tetradecene
18 24 27 30 33 36 42
pour point, "C --r ---, Hamilton, L. A,, Seger. F. M . , U.S.Patent 3 149 178 (1964). Seger, F. M., Doherty. H. G., Sachanen, A. N., Ind. Eng. Chem., 42, 2446 (1950). Sullivan, F. W., Voorhees, V., Neeley, A. W., Sharkland, R. V., Ind. Eng. Chem., 23, 604 (1931).
Received f o r review July 18, 1979 Accepted September 17, 1979 Presented at the "Symposium on Chemistry of Synthetic Lubricants and Additives" before the Division of Petroleum Chemistry, 178th National Meeting of the American Chemical Society, Washington, D.C., Sept 9-14, 1979.
Cluster' Fluids Robert N. Scott,' Karl 0. Knollmueller, Frank J. Mllnes, Thomas A. Knowles, and David F. Gavln Olin Research Center, 275 Winchester Avenue, New Haven, Connecticut 065 11
This paper describes the synthesis, properties, and potential applications of a new class of synthetic lubricants, the Silicate Cluster fluids. These new materials offer a unique combination of properties including low toxicity, good hydrolytic stability, low volatility, high temperature stability, exceptionally broad liquid range, excellent dielectric properties, and compatibility with common fluid additives and base stocks. Potential applications include high performance hydraulics, heat transfer, dielectric coolants, and as a formulating aid in combination with other fluids.
Introduction Silicate esters, long known as a class of compounds but only more recently industrially investigated, have been shown to have physical properties which would make them superior synthetic lubricants and functional fluids were it not for their hydrolytic instability (Hatton, 1962). 'Silicate Cluster is a trademark of Olin Corporation. 0196-4321/80/1219-0006$0 1.OO/O
Nevertheless, through careful selection of structure, this deficiency can be attenuated thus allowing their use in selected applications. Previously developed commercial silicates are based on ortho- and disilicate esters of 2-ethylhexanol or 2-ethylbutanol as shown in Figure 1. Excellent viscosity-temperature characteristics, good thermal stability combined with low volatility, fair oxidation stability, and satisfactory lubricating ability have led to the low volume (500M lb/ 0 1980 American Chemical Society
