Synthetic polyolefin lubricant oil

The invention is directed to method of making a thermally and oxidatively stable lubricating oil having a high viscosity index and a low pour point by the thermal polymerization of 1-olefins containing 8 to 10 carbon atoms, the preferred 1-olefins are 1-decanes. The polymerization is conducted at temperatures ranging from 280.degree. C. to 350.degree. C. and low pressures, of less than about 280 psig, in a reactor which is free of catalytic material. Thereafter, the polyalphaolefin is hydrotreated over a nickel catalyst, preferably nickel on Kieselguhr. In an improved process the polyalphaolefin is separated from a low molecular weight product by distillation. The low molecular product contains unreacted 1-olefins which are recycled to the thermal polymerization zone to produce more of the lubricant base stock. The remaining lower molecular weight olefinic materials which include mixed olefins, paraffins, cracked olefins and olefin dimers are routed to a polymerization zone to make a second lubricant base stock.

FIELD OF THE INVENTION 
The invention is directed to a method of making a lubricating oil by 
thermal polymerization of olefins. The invention is also directed to an 
improved process for making a high performance polyolefin lubricating oil 
from linear olefins. 
BACKGROUND OF THE INVENTION 
Engines which are required to operate under severe conditions of high 
temperatures for extended periods of time need a high performance 
lubricant that can withstand the extreme conditions. High performance 
lubricants will not degrade under high temperatures and will have a 
relatively small change in viscosity over a wide temperature range; that 
is, a high viscosity index. 
Attempts to thermally polymerize various 1-olefins have been described. For 
example, U.S. Pat. No. 2,500,166 teaches a synthetic lubricating oil made 
from mixtures of normally liquid straight-chain 1-olefins containing from 
six to twelve carbon atoms by thermal treatment of the olefins. The 
thermal treatment includes polymerization of 1-decene at 
190.degree.-440.degree. C. for 1 to 40 hours and non-critical pressures of 
reaction ranging from less than 50 to over 1000 pounds per square inch of 
pressure. The patent identifies as conditions, for good yields of good 
products, polymerization at a range from 3 to 20 hours and at temperatures 
of from about 650.degree. F. (330.degree. C.) to about 600.degree. F. 
(300.degree. C.). The patent teaches that increased pressure is desirable 
to maximize the yield. Although a high yield is beneficial to refinery 
operation, the detriment of running a reactor at high pressures can 
outweigh the benefit of a greater yield. 
A 2-stage thermal polymerization of mixed mono-olefins is taught in U.S. 
Pat. No. 3,883,417. The product is first polymerized under pressure 
conditions ranging from atmospheric to 1000 psig at temperatures ranging 
from 300.degree. F. to 650.degree. F. The product is distilled to 
600.degree.-650.degree. F. to obtain a purified product which is treated 
in a second-stage polymerization at 600.degree.-800.degree. F. and at 0 to 
1000 psig. The unreacted olefins of the second stage polymerization can be 
distilled off and recycled to the second-stage polymerization. Although 
the products resulting from the 2-stage thermal process have a good VI, a 
higher VI product made by a one-stage thermal process would be desirable. 
In general, premium lubricating oils are finished by hydrogen finishing 
(hydrofinishing) units which eliminate the polar sites in the oil 
molecules and improve their thermal stability and oxidation stability and 
lighten their color. 
In the hydrofinishing unit the charge oil is first heated, mixed with 
hydrogen, and then heated again to a temperature sufficient to effectuate 
reaction. The heated charge is pumped into the reactor which contains a 
hydrotreating catalyst. The reaction destroys the molecular polarity and 
lightens the color of the oil. 
SUMMARY OF THE INVENTION 
The invention is directed to a process for making a finished synthetic 
lubricating oil base stock by thermal polymerization of linear long chain 
olefins in a one stage low pressure thermal polymerization, i.e., 
pressures ranging from 100-280 psig and temperatures ranging from 
280.degree.-400.degree. C. for 1 to 24 hours, recovering the high quality 
polyalphaolefin product by distilling to separate the high quality higher 
molecular weight polyalphaolefin from a lower molecular weight olefin 
product which includes a 1-olefin recycle component. The high quality 
higher molecular weight polyalphaolefin is subjected to hydrotreating to 
produce a thermally and oxidatively stable finished lubricating oil base 
stock having a high viscosity index and a low pour point. 
The 1-olefin recycle component of the low pressure thermal polymerization 
is separated from the lower molecular weight olefin product and recycled 
back to the low pressure thermal polymerization to produce more of the 
high quality higher molecular weight product. The remaining lower 
molecular weight olefin product which contains a plurality of cracked 
olefins including from 3 to 5 carbon atoms and 1-decene dimers is 
polymerized in a polymerization reaction under conditions of temperature 
ranging from 200.degree. C. to 400.degree. C. and pressure ranging from 
100 to 1000 psig.

DETAILED DESCRIPTION OF THE INVENTION 
A thermally and oxidatively stable synthetic polyalphaolefin lubricating 
oil has now been made in a 1-stage low pressure thermal polymerization 
process to produce a high quality, high viscosity index and low pour point 
product in commercially viable yields. 
An object of the invention is to increase the thermal and oxidative 
stability of a polyalphaolefinic lubricating oil base stock. 
A further object of the invention is to produce a high viscosity index, low 
pour point polyalphaolefin lubricating oil base stock without the 
processing costs associated with the catalytic manufacture of 
polyalphaolefinic base stocks. 
It is a feature of the invention to thermally polymerize relatively pure 
linear long chain olefins in a reactor which is substantially free of 
catalytic material under conditions which permit the polymerization of the 
olefins. 
It is an advantage of the invention that producing a finished lubricating 
oil base stock by hydrotreating thermally polymerized polyalphaolefins 
results in a water white product which has a high viscosity index and a 
low pour point. 
It is a further advantage of the invention to produce a very pure 
polyalphaolefin in a thermal polymerization process by utilizing an olefin 
recycle step. 
The properties of the synthetic lubricating oils of the invention present 
an improvement over the properties of the known polyalphaolefin 
lubricating oils in that the product can withstand more severe thermal 
conditions. Additionally, the thermal polymerization product of the 
invention has a lesser tendency to form deposits when exposed to the 
severe operating conditions found in a diesel engine. 
The starting materials are substantially pure linear long chain 
mono-olefins ranging from 8 to 10 carbon atoms, such as 1-octene, 1-nonene 
and 1-decene. The preferred olefin is 1-decene. Although charged stocks of 
mixed olefins produce a suitable product, it was a discovery of the 
invention that polymerization of 1-decene produced a product with superior 
performance properties. 
The process conditions are critical to the invention. The optimum 
polymerization conditions described herein have been found to produce a 
superior synthetic lubricating oil. It has been found that the pressure of 
reaction should not exceed 280 psig in order to produce a product having 
the necessary high viscosity index, low pour point and resistance to high 
temperatures. The temperature of reaction should be maintained in a range 
of 280.degree. to 400.degree. C., preferably from 300.degree. to 
350.degree. C. The polymerization reaction should be carried out for 1 to 
24 hours, preferably 3 to 20 hours. 
The pressure of reaction should be maintained between about 100 psig and 
280 psig. Preferably the pressure is maintained below 250 psig, and most 
preferably from about 110 to 240 psig. 
The finished lubricating oil is made by recovering the polyalphaolefin by 
distillation which removes the unreacted 1-olefins, cracked hydrocarbons 
and olefin dimers. Distillation is accomplished under a vacuum to remove 
the 1-olefins and olefin dimers. For example, 1-decene, having a boiling 
point above 170.degree. C. and the 20 carbon 1-decene dimers having a 
boiling point above 340.degree. C. are separated by making a final cut at 
170.degree. C./1.0 mm Hg. The separation can be accomplished by collecting 
the 1-olefin fraction individually; that is, separate from the dimer, or 
one cut can be made which contains both the 1-decene and the 1-decene 
dimer. The remaining product is the desired high quality polyalphaolefin. 
Thereafter the product is recovered and hydrotreated under very specific 
conditions which are necessary to maintain the high viscosity index and 
low pour point of the polymerization product. The hydrotreating is 
conducted to saturate the double bonds of the polymerization product and 
produce a commercially desirable water white synthetic lubricant. The 
preferred hydrotreating catalyst is a nickel on diatomaceous earth, or 
kieselguhr, catalyst such as 649D manufactured by United Catalysts, Inc. 
The conditions of hydrotreating include temperatures ranging from about 
50.degree. C. to 300.degree. C., preferably 100.degree. C. to 200.degree. 
C. Relatively high pressures are employed, i.e. ranging from 300 to 600 
psig of hydrogen. Most preferably, the conditions include temperatures of 
150.degree. C. and pressures of 600 psig of hydrogen. 
FIG. 1 presents a simplified schematic diagram of an improved process for 
making a finished polyalphaolefin lubricant base stock in accordance with 
the instant invention. A plurality of linear olefins containing 8 to 10 
carbon atoms, preferably pure 1-decenes, are fed to a first polymerization 
reactor 13 via line 11. The reactor is free of any catalytic material and 
is operated at temperatures ranging from 280.degree. C. to 400.degree. C., 
preferably from 300.degree. to 350.degree. C., and pressures of less than 
about 280 psig. The polymerization is carried out for 1 to 20 hours. The 
reaction product is conveyed through line 15 to a distillation zone 17 
which separates the polyalphaolefins from the low molecular weight 
olefins. The polyalphaolefins have a viscosity index (IV) of 140-160. The 
polyalphaolefins include long chain hydrocarbons containing more than 24 
carbon atoms from polymerization of the C.sub.8 olefins preferably more 
than 27 carbon atoms from the polymerization of the C.sub.9 olefins and 
most preferably, more than 30 carbon atoms from the polymerization of the 
C.sub.10 olefins. The low molecular weight olefins include unreacted 
olefins, cracked olefins and olefinic products of dimerization which 
contain at least 16 carbon atoms to at most 20 carbon atoms. 
Alternatively, the reaction can be carried out in a batch operation in 
which the reactor is set at the proper reaction temperature, loaded with 
the 1-olefin feed, sealed and subjected to an inert gas, i.e. nitrogen, 
flush. The reactor is heated to 280.degree.-400.degree. C. for 1-20 hours. 
The product is then transferred to a distillation unit. Alternatively, the 
product is distilled directly from the reactor. 
In the preferred method, the olefins are reacted at the elevated 
temperatures and under autogenous or externally imposed gaseous pressures 
maintained below 280 psig. Non-limiting examples of non-reactive gases 
include nitrogen, helium and argon. 
The polyalphaolefins are routed to hydrotreating unit 21 via line 23 
wherein the polyalphaolefins are purified to produce a lubricant base 
stock. The hydrotreating conditions are critical to avoid significantly 
reducing the viscosity index or raising the pour point properties of the 
base stock. The preferred hydrotreating unit is operated under mild 
conditions and employs a nickel on diatomaceous earth catalyst. The 
operating conditions of the hydrotreating unit include a reactor 
temperature of 150.degree. to 300.degree. C. and pressures ranging from 
300 to 600 psig. The finished lubricant base stock is then conveyed to a 
lubricant blending plant for blending with suitable additive packages to 
make the commercial lubricant product. 
The low molecular weight olefins are conveyed to separator 25 through line 
27. The unreacted olefins, i.e., 1-decenes, are separated and recycled to 
the first polymerization zone 13 via line 29. 
The instant invention is considered a one stage thermal polymerization 
reaction because a satisfactory final product is obtained after one 
thermal polymerization reaction. This is opposed to a two-stage thermal 
polymerization reaction which would require that the entire product of the 
first polymerization be again subjected to a polymerization reaction to 
obtain a suitable product. A second polymerization reaction is applied in 
the instant invention to only a portion of the product of the first 
polymerization reaction in order to obtain a second product. 
Thus, the remaining low molecular weight components, the cracked olefins 
and olefinic dimers, are conveyed via line 33 to a second polymerization 
zone 35 which is operated under conditions which can differ from the first 
polymerization zone because the olefinic feed covers a much broader 
molecular weight range. The operating conditions of the second 
polymerization zone 35 can be more severe to compensate for the higher 
molecular weight dimers which would be more difficult to polymerize. The 
temperatures of the reaction zone can range from 200.degree. to 
400.degree. C., preferably 300.degree. C. to 350.degree. C. and pressures 
can range from about 100 to 1000 psig. Since the purity of the feed to 
this second polymerization zone is not as important as that of the first 
polymerization zone, the feed can also include other feeds, a 
representative example is a cracked wax containing mixtures of C.sub.8 and 
C.sub.10 olefins as well as charge stocks containing hydrocarbons of 
broader molecular weight ranges such as olefinic hydrocarbons containing 5 
to 20 carbon atoms. The second polymerization reaction is conducted in the 
presence or absence of a conventional polymerization catalyst. Preferred 
polymerization catalysts include HCl, H.sub.2 SO.sub.4 and Lewis acid 
catalysts such as BF.sub.3 and AlCl.sub.3. The resulting polyalphaolefin 
is then conveyed via line 37 to distillation zone 39 to remove the low 
molecular weight olefins which include unreacted olefinic starting 
materials, cracked olefins C.sub.3 's to C.sub.5 's and olefinic dimers. 
Thereafter, the polyalphaolefin is hydrotreated in hydrotreating unit 41 
and transported to the lubricant blending plant for blending with suitable 
additive packages to make the commercial lubricant product. 
The thermal polymerization coupled with the olefin overhead recycle process 
is an advantage over the known polyalphaolefin processing techniques. The 
thermal polymerization facilitates the olefin recycle because there is no 
need for spent catalyst removal which is costly and time consuming. 
Additionally, there is no need for catalyst regeneration which is also 
costly and amounts to a separate process. The invention produces a very 
high quality product since the undesirable low molecular weight components 
are constantly removed with recycle. Additionally, greater quantities of 
the high quality thermally stable product are made without the addition of 
extra 1-olefin feed because of the 1-olefin recycle. 
The following examples present a more detailed description of the thermal 
polymerization process of the instant invention. 
EXAMPLE 1 
A reactor under a nitrogen atmosphere was loaded with 1500 grams of 
1-decene and stirred while being heated to 310.degree. C. Pressure was 
autogenous and maintained at or below 135 psig. The temperature was 
maintained for 16 hours, after which time the heating was stopped. The 
reaction mixture was distilled to remove any unreacted decene and volatile 
products. The conversion was 33.5%. 
EXAMPLE 2 
A reactor under a nitrogen atmosphere was loaded with 1500 grams of 
1-decene and stirred while being heated to 330.degree. C. pressure was 
autogenous and maintained at or below 250 psig. The temperature was 
maintained for 16 hours, after which time the heating was stopped. The 
reaction mixture was distilled to remove any unreacted decene and volatile 
products. The conversion was 58.1%. 
EXAMPLE 3 
A reactor under a nitrogen atmosphere was loaded with 1500 grams of 
1-decene and stirred while being heated to 350.degree. C. Pressure was 
autogenous and maintained at or below 250 psig. The temperature was 
maintained for 16 hours, after which time the heating was stopped. The 
reaction mixture was distilled to remove any unreacted decene and volatile 
products. The conversion was 74%. 
EXAMPLE 4 
A reactor under a nitrogen atmosphere was loaded with 1500 grams of 
1-decene and stirred while being heated to 350.degree. C. Pressure was 
maintained at 230 psig. The temperature was maintained for four hours, 
after which time the heating was stopped. The reaction mixture was 
distilled to remove any unreacted decene and volatile products. The 
conversion was 40.2%. 
EXAMPLE 5 
A reactor under a nitrogen atmosphere was loaded with 1500 grams of 
1-decene and stirred while being heated to 310.degree. C. Pressure was 
maintained at 135 psig. The temperature was maintained for 16 hours, after 
which time the heating was stopped. The reaction mixture was distilled to 
remove any unreacted decene and other volatiles. The product polyolefin 
was removed and hydrogenated using nickel on kieselguhr at 150.degree. 
C./600 psig H.sub.2 to provide a clear product. The conversion was 30%. 
EXAMPLE 6 
A reactor under a nitrogen atmosphere was loaded with 1500 grams of 
1-decene and stirred while being heated to 330.degree. C. Pressure was 
maintained at 250 psig. The temperature was maintained for 16 hours, after 
which time the heating was stopped. The reaction mixture was distilled to 
remove any unreacted decene and other volatiles. The product polyolefin 
was removed and hydrogenated using nickel on kieselguhr at 150.degree. 
C./600 psig H.sub.2 to provide a clear product. The conversion was 58%. 
EXAMPLE 7 
A reactor under a nitrogen atmosphere was loaded with 1500 grams of 
1-decene and stirred while being heated to 350.degree. C. Pressure was 
maintained at 250 psig. The temperature was maintained for 16 hours, after 
which time the heating was stopped. The reaction mixture was distilled to 
remove any unreacted decene and other volatile components such as 5 carbon 
olefins and 1-decene dimers. The product polyolefin was removed and 
hydrogenated using nickel on Kieselguhr at 150.degree. C./600 psig H.sub.2 
to provide a clear product. The conversion was 74%. 
EXAMPLE 8 
A reactor under a nitrogen atmosphere was loaded with 1500 grams of 
1-decene and stirred while being heated to 350.degree. C. Pressure was 
maintained at 230 psig. The temperature was maintained for 4 hours, after 
which time the heating was stopped. The reaction mixture was distilled to 
remove any unreacted decene and other volatiles. The product polyolefin 
was removed and hydrogenated using nickel on kieselguhr at 150.degree. 
C./600 psig H.sub.2 to provide a clear product. The conversion was 40%. 
EVALUATION OF THE PRODUCTS 
The kinematic viscosity, of the products of the examples both before and 
after hydrogenation, at 40.degree. C. and 100.degree. C. was evaluated as 
well as the viscosity index and pour point. The data collected before 
hydrogenation are presented in Table 1. The data collected after 
hydrogenation are presented in Table 2. 
TABLE 1 
__________________________________________________________________________ 
THERMAL POLYMERIZATION PRODUCT 
Pressure Pour 
Ex. 
Olefin 
Temp. (.degree.C.) 
(psig) 
KV @ 40.degree. C. 
KV @ 100.degree. C. 
VI Point .degree.F. 
__________________________________________________________________________ 
1 C.sub.10 
310.degree. C. 
at or less 
46.0 8.22 154 
-65 
than 135 
2 C.sub.10 
330.degree. C. 
at or less 
33.9 6.53 150 
-65 
than 250 
3 C.sub.10 
350 at or less 
32.3 6.14 146 
-30 
than 250 
4 C.sub.10 
350 at or less 
26.6 5.57 155 
-31 
than 230 
__________________________________________________________________________ 
The data of Table 1 show that the VI, viscosity, and pour point of the 
thermal polymerization products of pure 1-decene made in accordance with 
the invention are very good. 
TABLE 2 
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HYDROGENATED THERMAL POLYMERIZATION 
PRODUCT HYDROGENATION CARRIED OUT AT 
150.degree. C., 600 psig H.sub.2 
OVER Ni CATALYST 
Ex- Pour 
ample Olefin KV @ 40.degree. C. 
KV @ 100.degree. C. 
VI Point .degree.F. 
______________________________________ 
5 C.sub.10 
50.8 8.59 146.4 
-25 
6 C.sub.10 
40.8 7.38 147.7 
-20 
7 C.sub.10 
34.4 6.54 147.2 
-0 
______________________________________ 
The data of Table 2 show that hydrogenating the thermal polymerization 
product of 1-decene over a nickel on kielselguhr catalyst at 150.degree. 
C. and 600 psig H.sub.2 in accordance with the invention significantly 
improves the kinematic viscosity (KV) at 40.degree. C. and 100.degree. C. 
Hydrogenating the products does not significantly lower the viscosity 
index of the product. 
The products were tested for their thermal stability at elevated 
temperatures. The change in viscosity over time for the hydrogenated 
thermal polymerization product of Example 1 and a catalytically 
synthesized 1-decene polymer was evaluated and the data collected are 
presented in Table 3. The test procedure included placing a 1-inch test 
tube containing a sample of the test lubricant in an aluminum block. A 
nitrogen blanket was maintained over the sample to prevent oxidation. 
After 72 hours of exposure to 310.degree. C. the change in lubricant 
viscosity was measured using the formula 
##EQU1## 
where V.sub.i =initial lubricant viscosity and V.sub.f =final lubricant 
viscosity. The % viscosity change is reported as a negative number when 
the final viscosity is lower than the initial viscosity. 
TABLE 3 
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THERMAL STABILITY TEST RESULTS 
% Viscosity Change 
After 72 Hours 
______________________________________ 
Hydrogenated Thermal -4.4 (at 310.degree. C.) 
Oligomer (of Example 1) 
Commercial catalytically synthesized 
-23 (at 310.degree. C.) 
1-decene polyolefin: 
Sample 1 
______________________________________ 
Table 4 presents a comparison between the oxidative stability of the 
hydrogenated product of example 1 with the same catalytically synthesized 
1-decene polymer as shown in Table 3. The oxidative stability was measured 
in the hot tube test. 
The hot tube oxidation test measures the tendency of a sample to form 
deposits. These tests were run on a formulated diesel engine oil, the only 
difference being a change of base stock. The rating is from 0 to 9, a 
clean tube achieves a rating of 0, a heavy black carbonaceous deposit on 
the tube achieves a rating of 9. 
The results show that the thermal oligomer is significantly less prone to 
form deposits than the commercial catalytically synthesized 
polyalphaolefin sample. 
TABLE 4 
______________________________________ 
OXIDATIVE STABILITY TEST RESULTS 
Hot Tube Oxidation Test 
______________________________________ 
Thermal Oligomer of Example 1 
6 
Commercial Synthetic PAO 
9 
Made Using Catalysis 
______________________________________