CA2046374A1 - Process for oligomerizing olefins using heteropoly acids on inert supports - Google Patents

Abstract

ABSTRACT
(D# 80,963-F) An improved process is disclosed for preparing synthetic lubricant base stocks. Synthetic lubricant base stocks are prepared in good yield by oligomerizing linear olefins using a catalyst comprising a heteropoly acid on an inert support.

Description

3 l ii~
D# 80,963-F
RRS

PROCESS FOR OLIGOMERIZING OLEFINS USING
HETEROPOLY ACIDS ON INERT SUPPORTS
(D# 80, ~63 -F) Backqround of the Invention Field of the Invention The invention relates to the preparation of synthetic lubricant base stocks, and more particularly to synthetic lubricant base stocks made by oligomerizing long-chain linear olefins.
Descri~tion of Related Methods Synthetic lubricants are prepared from man-made basa stocks having uniform molecular structures and, therefore, well-defined properties that can be tailored to specific applications.
Mineral oil base stocks, o~ the other hand, are prepared from crude oil and consist of complex mixtures of naturally occurring hydrocarbons. The higher degree of uniformity found in synthetic lubricants generally results in superior performance properties.
For example, synthetic lubricants are characterized by excellent thermal stability. As automobile engines are reduced in size to save weight and fuel, they run at higher temperatures, therefore requiring a mor~ thermally stable oil. Because lubricants made from synthetic base stocks have such properties as excellent oxidative/thermal stability, very low volatility, and good viscosity indices over a wide range of temperatures, they offer better lubrication and permit longer drain intervals, with less oil vaporization loss between oil changes.
Synthetic base stocks may be prepared hy oligomerizing internal and alpha-olefin monomers to form a mixture of dimers, ,j; , . :.
~ . . ' ! ,: ':
1,' `' : -' , ' 'i, , , : - ~:

~ 3~

trimers, tetramers, and pentamers, with minimal amounts of higher oligomers. The unsaturated oligomer products are then hydrogenated to improve their oxidative stability. The resulting synthetic base stocks have uniform isoparaffinic hydrocarbon structures similar to high quality paraffinic mineral base stocks, but have the superior properties mentioned due to their higher deqree of uniformity.
Synthetic base stocks are produced in a broad range of viscosity grades~ It is common practice to classify the base stocks by their viscosities, measured in centistokes (cSt) at 100C. Those base stocks with viscosities less than or equal to about 4 cSt are commonly referred to as "low viscosity" base stocks, whereas base stocks having a viscosity in the range of around 40 to 100 cSt are commonly referred to as "high viscosity"
base stocks. Base stocks having a viscosity of about 4 to about 8 cSt are referred to as "medium viscosity" base stocks. The low viscosity base stocks generally are recommended for low temperature applications. Higher temperature applications, such as motor oils, automatic transmission fluids, turbine lubricants, and other industrial lubricants, generally require higher viscosities, such as those provided by medium viscosity base stocks (i.e. 4 to 8 cSt grades). High viscosity base stocks are used in gear oils and as blending stocks.
The viscosity of the base stocks is determined by the length of the oligomer molecules formed during the oligomerization reaction. The degree of oligomerization is affected by the catalyst and reaction conditions employed during the :
':
' ' . ' :

, ~ :
: :

oligomerization reaction. The length of the carbon chain o~ the monomer starting material also has a direct influence on the properties of the oligomer products. Fluids prepared ~rom short-chain monomers tend to have low pour points and moderately low viscosity indices, whereas fluids prepared from long-chain monomers tend to have moderately low pour points and higher viscosity indices. Oligomers prepared from long-chain monomers generally are more suitable than those prepared from shorter-chain monomers for use as medium viscosity synthetic lubricant base stocks.
one known approach to ollgomerlzing long-chain ole~lns to prepare synthetic lubricant base stocks is to contact the olefin with boron trifluoride together with a promotor at a reaction temperature sufficient to e~fect oliyomerization of the olefin.
See, for example, co-assigned U.S. Patent Nos. 4,400,565;
4,420,646; 4,420,647; and 4,434,308. However, boron trifluoride gas (BF3) is a pulmonary irritant, and breathing the gas or fumes formed by hydration of the gas with atmospheric moisture poses ha2ard-~ preferably avoided. Thus, a method for oligomerizing long-chain olefins using a less hazardous catalyst would be an improvement in the art.
Applicants have discovered, surprisingly, that a high conversion of long-chain olefin to oligomer may be obtained by contacting the olefin with a catalyst comprising a heteropoly acid on an inert support. In addition to being excellent catalysts, these heteropoly acids on inert supports are less hazardous and more easily handled than boron triflouride.

.

,. .

; , ,.~ . . ~ , : .

Summary of the Invantion The invention relates to a process for the preparation of oligomers, comprising contacting a linear olefin containing from 10 to 24 carbon atoms with a heteropoly acid on an inert support.
Description of the Preferred Embodiments The olefin monomer feed stocks used in the present invention may be selected from compounds comprising (1) alpha-olefins having the formula R"CH=CH2, where R" is an alkyl radical of 8 to 22 carbon atoms, and ~2) internal olefins having the formula RCH=CHR', where R and Rl are the same or different alkyl radicals of 1 to 21 carbon atoms, provided that the total number of carbon atoms in any one olefin shall be within the ranye of 10 to 24, inclusive. A preferred range for the total number of carbon atoms in any one olefin molecule is 12 to 18, inclusive, with an especially preferred range being 14 to 16, inclusive. Mixtures of internal and alpha-olefins may be used, as well as mixtures of olefins having different numbers of carbon atoms, provided that the total number of carbon atoms in any one olefin shall be within the range of 10 to 24, inclusive. The alpha and internal-olefins to be oligomerized in this invention may be obtained by processes well-known to those skilled in the art and are commercially available.
The oligomerization reaction may be represented by the following general equation:
catalyst nCmH2m ----~ ~~~~~~> CmnH2w~

;

~, ~3 A ~ ~ i''1 ,J
where n represents moles of monomer and m represents the number of carbon atoms in the monomer. Thus, the ol1gomerization of l-decene may be represented as follows:
catalyst nC10H20 ----~ ~~~~~~> ClOnH20n The reaction occurs sequentially. Initially, ole~in monomer reacts with olefin monomer to form dimer~. The ~imers that are formed then react with additional olefin monomer to form trimers, and so on. This results in an oligomer product distribution that varies with reaction time. As the reaction time increases, the olefin monomer conversion increases, and the selectivities for the heavier oligomers increase. Generally, each resulting oligomer contains one double bond.
The heteropoly acid component of the catalysts used in the subject reaction may be selected from a class of acids formed by the condensation of two or more inorganic oxyacids. For example, phosphate and tungstate ions, when reacted in an acidic medium, are condensed to form 12-tungstophosphor$c acid, a typical heteropoly acid ~HPA), as demonstrated in the following equation:
Po43 ~ 12 W042 ~ 27 H ---- > H3PW12040 ~ 12 H20 The central atom of the HPA anion, also called the heteroatom (P in the equation above), may be selected from a wide variety of elements ranging from Group I to Group VIII. The nature of the heteroatom is a factor which determines both the condensation structure and the physical properties of the HPA. Atoms coordinated to the heteroatom via oxygen atoms are called polyatoms (W in the equation above), and in most cases are any one of such - ~ .

. .
' species as molybdenum, tungsten, niobium and vanadium. The nature of the heteroatoms, condensation ratios and chemical formulas for typical heteropoly acids are exempli~ied ~y the heteromolybdate anions described in Table I, below~

TABLe I
Heleromolybdate Anions Condens~tion R~tios Heten:)atoms (X) Chem;cal Fo~mulas 1:12 K~Rgin slructure p~t As~+. Si4~, Gc~ [X Mol20 Sih~ on stmcture ceJ~, Th~ tX:~ Mol~O,~
1:11 Ke~gin structure P~, As5~, Si~+, Ge4~ lxn~Mollo39] ~12. ~) (decomposition) 2:18 Dn~son slructure Ps~ MolaO
1:9 Waugh structure Mn~, Ni~ IX~M~
1:6 t~ndelson stNcture pe) Te~, 171' 1Xn~Mo~sO2~1-(12n) (~ Iype) Co~' A13~ C~ XI~M~02~H6~ s' ) ~:12 As5~ 54M01~~21'~' 2:5 p5~ IP2Mo~ul -Anions containing the Keggin structure have a condensation ratio of 1:12. The synthesis of these HPA's is well documented in the literature (see, for example, U.S. Pat. No. 3,947,332 (1976), incorporated herein by reference).
To oligomerize 10 to 24 carbon atom olefins, suitable heteropoly acid catalysts may contain polyatoms selected from the group molybdenum, tungsten, niobium and vanadium, while tha heteroatom may be selected from phosphorus, silicon, germanium, and arsenic. Preferably, the polyatoms are tungsten or molybdenum and the heteroatom is phosphorus or silicon. These heteropoly acids would likely have the Xeggin structure H8ntXM12040], were X = P or Si, M = Mo or W, and n is an i~teger of 4 or 5.
The preferred heteropoly acids for the practice of this invention include 12-molybdophosphoric acid (H3PMol2040), 12-tungstophosphoric acid (H3Pwl2o4o)~ molybdosilicic acid . : :
, (H4SiMo12040), and tungstosilicic acid (H3SiW12o4o). It is especially preferred that the heteropoly acid be 12-tungstophosphoric acid.
Preferably, the heteropoly acids are bound to an lnert support. Compounds which may be employed are those containing an element of Groups III or IV of the periodic table. Suitable compounds include the oxides of Al, Si, Ti and Zr, e.g. alumina, silica (silicon dioxide), titania (titanium dioxide) and zirconia, as well as combinations thereof. Also suitable are carbon, ion-exchange resins, and carbon-containing supports. It is preferred that the inert support be sioz or Tio2.
The inert support may be in the form of powders, pellets, spheres, shapes, and extrudates, and may have a surface area of from about lo to about looo m2/g. As demonstrated in the examples, the supports preferably are of high purity and high surface area.
Applicants have discovered that a greater conversion of olefin to oligomer is achieved where the support has a high surface area.
Preferably, the surface area of the support is greater than about 30 m2/g. Where the support is a silica support, it is more preferred that the surface area of the support be greater than about 100 m2/g, and especially preferred that the surface area of the support be about 300 m2/g or greater. Where the support is a titania support, it is especially preferred that the surface area of the support be from about 50 to about 60 m2/g. An extrudate which works well is an HSA titania carrier extrudate fro~ Norton Company: 1/8" extrudate with a sur~ace area o~ 51 m2/g. Another ..
,' useful titania extrudate is Norton Company's 1/8" extrudate with a surface area of 60 m2/g.
The weight percent of heteropoly acid to inert support should be such that the concentration of the polyatom (Mo, W, Nb or V) in the formulated catalyst preferably is in the range of about 0.1 to about 30 wt.%. However, one skilled in the art may find other weight percentages to be useful in the practice of this invention. Where the heteropoly acid is, for example, 12-molybdophosphoric acid, supported on titania, a suitable quantity of molybdenum is about 1 to about 10 wt.%~ In the preparation of a tungstophosphoric acid-on-titania catalyst, on the other hand, the tungsten content may be from about 1 to about 30 wt.~.
The oligomerization reaction may be carried out in either a stirred slurry reactor or in a fixed bed continuous flow reactor.
The catalyst concentration should be sufficient to provida the desired catalytic effect. The temperatures at which the oligomerization may be performed are between about 50 and 300C, with the preferred range being about 150 to 180C. The reaction may be run at pressures of from 0 to 1000 psig.
Following the oligomerization reaction, the unsaturated oligomers may be hydrogenated to improve their thermal stability and to guard against oxidiative degradation during their use as lubricants. The hydrogenation reaction for l-decene oligomers may be represented as follows:

catalyst onH20n + ~2 ~~~~~~~~~~~ Clon~20~2 ? ~ '' J~
( ~ , -~,. .. ..

where n represents moles of monomer used to form the oligomer.
Hydrogenation processes Xnown to those skilled in the art may be used to hydxogenate the oligomers. A number of metal catalysts are suitable for promoting the hydrogenation reaction, including nickel, plati~um, palladium, copper, and Raney nickel. These metals may be supported on a variety of porous materials such as kieselguhr, alumina, or charcoal, or they may be formulated into a bulk metal catalyst. A particularly preferred catalyst for this hydrogenation is a nickel-copper-chromia catalyst described in U.S.
Patent No. 3,152,998, incorporated by reference herein. Other U.S.
patents disclosing known hydrogenation procedures include U.S.
Patent Nos. 4,045,508; 4,013,736; 3,997,622; and 3,g97,621.
Unreacted monomer may be removed either prior to or after the hydrogenation step. Optionally, unreacted monomer may be stripped from the oligomers prior to hydrogenation and recycled to the catalyst bed for oligomerization. The removal or recycle of unreacted monomer or, if after hydrogenation, the removal of non-oligomerized alkane, should be conducted under mild conditions using vacuum distillation procedures known to those skilled in the art. Distillation at temperatures exceeding 250 C may cause the oligomers to break down in some ~ashion and come off as volatiles.
Preferably, therefore, the reboiler or pot temperature should be kept at or under about 225 C when stripping out the monomer.
Procedures known by those skilled in the art to be alternatives to vacuum distillation also may be employed to separate unreacted components from the oligomer.

.

~`?~

While it is known to include a distillation step after the hydrogenation procedure to obtain products of various 100C
viscosities, it is preferred in the method of the present invention that no further distillation (beyond monomer flashing) be conducted. In other words, the monomer-s~ripped, hydrogenated bottoms are the desired synthetic lubricant components. Thus, the method of this invention does not reqUire the c03tly, customary distillation step, yet, sUrprisingly, produces a synthetic lubricant component that has excellent properties and that performs in a superior fashion. However, in some contexts, one skilled in the art may find subsequent distillation useful in the practice of this invention.
The invention will be further illustrated by the following examples, which are given by way o~ illustration and not as limitations on the scope of this invention. The entire text of every patent, patent application or other reference mentioned above is hereby incorporated herein by reference.
EXAMPLES
In the examples detailed below, the following procedures were used:
Preparation of 12-Tungstophosphoric Acid~on Titania To a flask containing 250 cc of titania 1/8" diameter extrudates (from The Norton Company) was added a solution of 12-tungstophosphoric acid (80 g) dissolved in 300 ml of distilled water. The mixture was stirred for 1-2 hours, the exc~ss liquid was removed by rotary evaporation under vacuum, and the solids were .
, -- ~ ' ,;:

calcined at 150 C for 1 hour, and then 350 'C for 2 hours in a stream of nitrogen.
The recovered extrudates were found to contain:
% Tungsten - 9.5 - % Phosphorus - 0.27 PreParation of a 12-Tunqstophosphoric Acid on Silica To a flask containing 125 cc of silica gel (from MC/B
Man~facturing) was added a solution of 12-tungstophosphoric acid (40 g) dissolved in 150 ml of distilled water. The mixture was stirred for 1-2 hours, the excess liquid was recovered by rotary evaporation under vacuum, and the solids were calcined at 150 ~C
for 1 hours, then 350 C for 2 hours in a stream of nitrogen.
The recovered powder was ~ound to contain:
% Phosphorus - 0.5 Oligomerization of Olefins Olefin and finely ground catalyst were charged to a three-necked flask equipped with an overhead stirrer, thermom~ter, heatinq mantle, and a water-cooled condenser tN2 purge). The mixture was vigorously stirred and heated to the desired temperature for the desired time. ~he mixture was then cooled to ambient tamperature and filtered wlth suction. The liquid was analyzed by liquid chromatography. The results are detailed in the table that ~ollows.

.

` 11 : .

~ if OLEFIN OLIGOMERIZATION USlrlG HETEROPOLY ACIDS ON INERT SUPPORTS
r ~ =
Ex. ¦ fint~) C~ly,t (g3 Tim~/Temp Con. (Ib) Resull~ from Liquid Chrom~togr~phy No. I ~Dy c~rbon (Hr)1(C) M(%) D~%)T+(%) D/T+
numbcr) _ Rd(jo ¦ C-14A TPA on TiO2 10 5.0/160 8S.614.4 63.4 22.2 2.86 l _ .
2 ¦ C-14A TPA on SiO2 10 5.0/160 86.613.4 49.6 37.1 1.34 _ .

3 ¦ C-14A TPA on TiO2 10 5.0/160 _o ~ 100 -- --_ lW=4.11 4 C-14A TPA on TiO2 10 5.0/140 69.730.3 55.0 13.7 3.74 C-14A TPA on TiO2 10 5.0/160 83.816.2 61.t 22.7 2.69 6 ¦ C-14A TPA on TiO2 10 4.0/180 76.523.5 58.4 18.1 3.23 _ 7 ¦ C-14A TPA on Al2O~ 10 5.0/160 68.9 31.1 S3.4 14.9 3.63 l lW = 25,31 8 ¦ C-14A TPA on TiO2 10 5.01160 791 20.9 61 .4 17.6 3.49 l lW- 17,01 9 I C-14A TPA on S1O2 10 5.0/160 62.437.6 50.0 12.3 4.07 .. . . .
¦ C-14A TPA on TiO~ 10 5.0/160 62.4 37.6 51.8 8.48 6.11 l lW = 3 01 1 l l C-14A TPA on TiO2 10 5.0/160 32.0 68.1 25.8 1.38 4.ao IW=6.01 -12 C-14A TPA on SiO2 5.0 5.0/160 84.8 15.2 55.5 28.7 1.93 1~ ¦ C-12A TPA on SiO2 10 5.0/160 89.1 10.9 48.6 39.5 1.23 _ _ 14 C-131,141 TPA on SiO2 10 5.0/160 86.4 13.6 51.0 35.3 1.44 C-16A TPA on SiO2 10 5.0/160 81.9 18.1 54.4 27.4 1.98 I _ 16 1 C-1$1,181 TP.~ on SiO2 10 5.0/160 74.3 25.7 52.1 22.2 2.35 _ 17 ¦ C-14A TPA on TiO2 10 5.0/160 84.4 15.6 60.1 23.8 2.53 , .
18 C-16A TPA on TiO2 10 5.0/160 76.0 24.0 62.0 14.0 4.43 19 C-151,181 TPA on r~O2 10 5.0/160 61.338.7 52.7 8.62 6.11 ¦ C-12A TPA on TiO2 10 5.0/160 85.2 14.8 59.4 25.8 2.3 _ ... ___ , .. _ - . .__. _ 21 C-12A TPA on TiO2 10 5.0/140 83.1 16.9 60.7 22.4 2.71 22 ¦ C-12A TPA on TiO2 10 4.0/180 85.1 14.4 60.0 25.0 2.40 - . . __ ___ . . __ _ . . .

23 1 C-14A TSA on SiO2 9.7 5.0/160 --0 ~ 100 _ _ _ ....
24 C-14A TSA on SiO2 10 5.0/160 18.7 81.3 17.6 -O
C~ISA TSA on rlo2 10 5.0/160 15.2 83.8 12.1 1.41 8.01 26 C-14A TSA on rlo2 10 5.0/160 49.1 50~9 __ 40.9 8.21 4.98 _ _ .
27 C-14A MPA on TiO2 10 5.0/160 ~3 ~97 ~3 28 C-14A MPA on rl2 10 5.0/160 ~6 ~94 ~6 -- --_ 29 ¦ C-14A TPA on Low 10 5.0/160 19.3 80.7 16.7 2.68 6.23 _ S/Area SiO2_ _ ~ _ ¦ C-14A TPA on High 10 5.0/160 80.6 19.4 55.8 24.8 2.25 S/Are~ SiO2 _ _ 31 ¦ C-14A Anunonium 10 5.0/160 ~o ~ 100 -- --Tung~tale on I TiO2 Con.--:onvenion; h --Moromer; D = Dimer-, T = Trimer + Tetr~n :r ~ elc.; A - Alphn; I--Lnl~ n~l; TPA a Tungsto,ohosp lorlc ~cid;
TS~ ~ Tung-to~i1icic llc;d; MPA ~ Molybdopho~phoric ~cid; S/Are~ a Surr~ce Are~.

a ~x ~ _ - _ _ ¦ Ex. Olefin(~) Cat~l~nt ~g) Time/T~mp Con. (%) M(%) D(%) T-~(%) DIT+
o. (by c~rbon (Hr)l( C) R~tio number) _ 32 C-14A MPA on TiO2 10 4.0/180 28.6 71.4_ 23.6 2.5 9.44 33 C-14A MPA on TiO2 10 5.0/160 14.2 85.8 11.4 ~o Con. = Conv~r~ion; M = Monomer; t~ = Dimer; T+ ~= ~rTncr + T~tr~m~r + ~ic.~ A ~ I Alph~ I = ,nt~n~l, MPA = Molybdopho}pho-ic ~cid.
The SiO2 used as the catalyst support in examples 2, 12, 13~ 14, 15, and 16 had a surface area greater than 100 m2/g.
The sio2 used as the catalyst support in examples 23 and 24 had a surface area o~ >50 m2/g. The low surface area SiO2 used in example 29 had a surface area of 30 mZ/g. The high surface area sio2 used in example 30 had a surface area of 300 m2/g.

Claims (28)

1. A process for the preparation of oligomers, comprising contacting a linear olefin containing from 10 to 24 carbon atoms with a catalyst comprising a heteropoly acid on an inert support.

2. The process of Claim 1, wherein the heteropoly acid contains (1) a polyatom selected from the group consisting of tungsten, molybdenum, niobium, and vanadium, and (2) a heteroatom selected from the group consisting of phosphorous, silicon, germanium, and arsenic.

3. The process of Claim 1, wherein the heteropoly acid contains (1) a polyatom of tungsten and (2) a heteroatom of phosphorous,

4. The process of Claim 1, wherein the inert support comprises an oxide of Al, Ti, Si, or Zr.

5. The process of Claim 1, wherein the inert support is SiO2 or TiO2.

6. The process of Claim 1, wherein the catalyst is 12-tungstophosphoric acid on a support of TiO2.

7. The process of Claim 1, wherein the linear olefin contains from 12 to 18 carbon atoms.

8. The process of Claim 1, wherein the linear olefin contains from 14 to 16 carbon atoms.

9. The process of Claim 1, wherein the inert support has a high surface area.

10. A process for the preparation of oligomers, comprising contacting a linear olefin containing from 10 to 24 carbon atoms with a heteropoly acid on an inert support, wherein the heteropoly acid has the Keggin structure represented by the formula H8n[XM12O40], where X = P or Si, M = Mo or W, and n is an integer which is 4 or 5.

11. The process of Claim 10, wherein the heteropoly acid is 12-tungstophosphoric acid, 12-molybdophosphoric acid,

12-tungstosilicic acid, or 12-molybdosilicic acid.
12. The process of Claim 10, wherein the heteropoly acid is 12-tungstophosphoric acid.

13. The process of Claim 10, wherein the inert support comprises an oxide of Al, Ti, Si, or Zr.

14. The process of Claim 10, wherein the inert support is SiO2 or TiO2.

15. The process of Claim 10, wherein the olefin contains from 14 to 16 carbon atoms.

16. The process of Claim 10, wherein the heteropoly acid is 12-tungstophosphoric acid and the inert support is TiO2.

17. The process of Claim 10, wherein the linear olefin contains from 12 to 18 carbon atoms.

18. The process of Claim 10, wherein the inert support has a high surface area.

19. A process for the preparation of a synthetic lubricant base stock, comprising the following steps:
(a) contacting a linear olefin containing from 10 to 24 carbon atoms with a catalyst comprising a heteropoly acid on an inert support; (b) separating out any remaining un-oligomerized olefin;
and (c) hydrogenating the oligomer fraction resulting from step (b) to produce a synthetic lubricant base stock.

20. The process of Claim 19, wherein the heteropoly acid contains (1) a polyatom selected from the group consisting of tungsten, molybdenum, niobium, and vanadium, and (2) a heteroatom selected from the group consisting of phosphorous, silicon, germanium, and arsenic.

21. The process of Claim 19, wherein the heteropoly acid contains (1) a polyatom of tungsten and (2) a heteroatom of phosphorous.

22. The process of Claim 19, wherein the inert support comprises an oxide of Al, Ti, Si, or Zr.

23. The process of Claim 19, wherein the inert support is SiO2 or TiO2.

24. The process of Claim 19, wherein the olefin contains from 14 to 16 carbon atoms.

25. The process of Claim 19, wherein the catalyst is 12-tungstophosphoric acid on a support of TiO2.

26. The process of Claim 19, wherein the inert support has a high surface area.

27. The process of Claim 19, wherein the linear olefin contains from 12 to 18 carbon atoms.

28. The process of Claim 19, wherein the inert support has a high surface area.