CA2085433A1 - Process for oligomerizing olefins using titanium salts or zirconium salts deposited on silicon dioxide - Google Patents

Abstract

ABSTRACT
(D# 81,064-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 silica gels having certain titanium or zirconium salts deposited thereon.

Description

20~5433 PROCESS FOR OLIGOMERIZING OLE~INS USING TITANIUM SALTS
OR ZIRCONIUM SALTS DEPOSITED ON SILICON DIOXIDE
(D# 81,064 -F) Background 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 oligomeriæing linear olefins.
Description of Related Methods Synthetic lubricants are prepared from man-made base stocks having uniform molecular structures and, therefore, well-defined properties that can be tailored to specific applications.
Mineral oil base stocks, on 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 more 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 stocXs may be prepared by oligomerizing internal and alpha-olefin monomers to form a mixture of dimers, 20~?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 degree 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 100 C. 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 a base stock 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 20~5~33 oligomerization reaction. The length of the carbon chain of the monomer starting material also has a direct influence on the properties of the oligomer products. Fluids prepared from 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.
10One known approach to oligomerizing long-chain olefins to prepare synthetic lubricant base stocks is to contact the olefin with boron trifluoride together with a promotor at a reaction temperature sufficient to effect oligomerization of the olefin.
See, for example, co-assigned U.S. Patent Nos. 4,400,565;
154,420,646; 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 hazards preferably avoided. Additionally, the disposal/neutralization of BF3 raises environmental concerns.
Thus, a method for oligomerizing long-chain olefins using a less - hazardous catalyst would be a substantial improvement in the art.
Kuliev et al. attempted to prepare synthetic lubricants by oligomerizing long-chain (Cg-Cl4) olefins using non-hazardous and non-polluting acidic silica gels comprising sulfuric and hydrochloric acid-activated bentonites from the Azerbaidzhan SSR.
See Kuliev, Abasova, Gasanova, Xotlyarevskaya, and Valiev, 2 0 ~ 3 "Preparation of High-Viscosity Synthetic Lubricants Using an Aluminosilicate Catalyst," Institute of Petrochemical Processes of the Academy of Sciences of the Azerbaidzhan SSR, Azer. Neft. Khoz., 1983, No. 4, pages 40-43. However, Kuliev et al. concluded that "it was not possible to prepare viscous or high-viscosity oils by olefin polymerization over an aluminosilicate catalyst" and that "hydrogen redistribution reactions predominate with formation of aromatic hydrocarbon, coke, and paraffinic hydrocarbon." Gregory et al., on the other hand, used Wyoming bentonite to oligomerize shorter-chain olefins. (See U.S. Patent No. 4,531,014.) However, like Kuliev et al., they also were unable to obtain a product high in dimer, trimer and tetramer, and low in disproportionation products.
Applicants have discovered, surprisingly, that a high conversion of olefin to oligomer may be obtained by contacting the olefin with a catalyst prepared by depositing a non-halogenated, non-polymeric, non-organometallic titanium salt or non-halogenated, non-polymeric, non-organometallic zirconium salt on a substrate of silicon dioxide. Catalysts so prepared are as active as, yet less expensive than, the corresponding unsupported, essentially pure titanium or zirconium oxide. Additionally, the process of the present invention results in a high percentage of dimers, i.e., a high dimer to trimer ratio. A high proportion of dimers is often desirable when preparing a synthetic lubricant base stock from olefins having about 14 or more carbon atoms. In the absence of the high dimer to trimer ratio obtained using the present 208~433 invention, a synthetic lubricant base stock prepared from olefins having about 14 or more carbon atoms would contain a higher percentage of high molecular weight oligomers and may have too great a viscosity for some applications. In addition to being excellent catalysts, the silicon dioxide-supported titanium or zirconium salts used in the present invention are less hazardous and more easily handled than BF3.
Summary of the Invention The invention relates to a process for the preparation of oligomers, comprising contacting at elevated temperature (1) linear olefins containing from 10 to 24 carbon atoms with (2) a catalyst prepared by (a) depositing on a substrate of silicon dioxide a compound selected from the group consisting of non-halogenated, non-polymeric, non-organometallic titanium salts and non-halogenated, non-polvmeric, non-organometallic zirconium salts, and (b) calcining at a temperature of about 400 C or greater said silicon dioxide having said compound deposited thereon.
The invention also relates to a process for the preparation of oligomers, comprising the steps of (1) oligomerizing linear olefins containing from 14 to 24 carbon atoms in the presence of a catalyst prepared by (a) depositing on a silicon dioxide substrate a non-halogenated, non-polvmeric, non-organometallic zirconium salt, and then (b) calcining at a temperature of about 500 C or greater said silicon dioxide substrate having said zirconium salt deposited thereon, wherein said olefins are oligomerized at a temperature of about 120 to 20~5~33 about 250 C and at a pressure of about atmospheric to about 1000 psig, and (2) recovering oligomers of said linear olefins.
The invention further relates to a process for the preparation of oligomers, comprising the steps of ~1) oligomerizing alpha-olefins containing from 14 to 24 carbon atoms in the presence of a catalyst prepared by (a) depositing on a silica gel substrate a compound selected from the group consisting of zirconium sulfate, zirconium citrate, zirconium nitrate, and zirconium acetate, and then (b) calcining at a temperature of about 500 C or greater said silica gel substrate having said compound deposited thereon, wherein said olefins are oligomerized at a temperature of about 120 to about 250 C and at a pressure of about atmospheric to about 1000 psig, and (2) recovering oligomers of said alpha-olefins.
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 R' 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 range of 10 to 24, inclusive. However, alpha-olefins are preferred. 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 2085~3 may be used, as w~ll as mixtures of olefins having different numbers of carbon atoms, provided that the total number of carbon atoms in any one olefin shall be ~ithin the range of 10 to 24, inclusive. The alpha and internal-olefins that may be oligomerized according to the present 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 ----~~~~~~~> CmnH2mn where n represents moles of monomer and m represents the number of carbon atoms in the monomer. Thus, the oligomerization of l-tetradecene may be represented as follows:
catalyst s ~~~~~~~~~~~> C14nH28n The reaction occurs sequentially. Initially, olefin monomer reacts with olefin monomer to form dimers. Some of the dimers 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. An advantage of the present inventive process, particularly when oligomerizing olefins having about 14 or more carbon atoms, is that a high percentage of trimer (relative to dimer) is observed. Generally, each resulting oligomer contains one double bond.

208~433 According to the present invention, oligomers of long-chain olefins may be prepared using catalysts easily and economically prepared by the following steps: (a) depositing a non-halogenated, non-polymeric, non-organometallic titanium or zirconium salt on a silicon dioxide substrate, and then (b) calcining said silicon dioxide substrate. The silicon dioxide substrate may be any of the various - primarily amorphous - forms of sio2. See Kirk-Othmer, EncycloPedia of Chemical Technology, 3d.
ed., vol. 20, pp. 748-764 (1981), incorporated herein by reference.
Silica gels, which contain three-dimensional networks of aggregated silica particles of colloidal dimensions, are preferred. Silica gels are commercially available in at least the following mesh sizes: 3-8; 6-16; 14-20; 14-42; and 28-200 and greater. A
suitable commercially available silica gel is the grade 12, 28-200 mesh, silica gel available from Aldrich Chemical Co., Inc.
The silica gel should bè added to a solution of about 0.05 to about 25 wt.%, preferably from about 10 to about 20 wt.%, non-halogenated, non-polymeric, non-organometallic titanium salt or non-halogenated, non-polymeric, non-organometallic zirconium salt in water. The ratio of silica gel to titanium salt or zirconium salt solution should be sufficient to provide a catalyst having a quantity of titanium salt or zirconium salt deposited thereon ranging from about 0.05 to about 15 wt.%, preferably from about 0.05 to about 5.0 wt.%. The silica gel should remain in the titanium salt or zirconium salt solution for a period of time and under agitation to the extent necessary to meet these requirements, 208a~3 and then filtered and dried. Optionally, after filtration, the silica gel may be washed with distilled water before being dried, preferably under mild conditions.
Preferably, the non-halogenated, non-polymeric, non-organometallic titanium or zirconium salt is a simple, two-component salt. If a titanium salt is chosen, it is preferred that it be selected from the group consisting of titanium sulfate, titanium citrate, titanium nitrate, and titanium phosphate. Of these titanium salts, titanium sulfate is preferred. Non-halogenated, non-polymeric, non-organometallic titanyl compounds also are acceptable titanium salts for purposes of this invention.
Of the suitable zirconium salts, those selected from the group consisting of zirconium sulfate, zirconium citrate, zirconium nitrate, and zirconium acetate are preferred. Non-halogenated, non-polymeric, non-organometallic zirconyl compounds also are acceptable zirconium salts for purposes of this invention. Of the zirconium salts, zirconium sulfate is especially preferred.
Zirconium salts are preferred over titanium salts.
The silicon dioxide substrate having the titanium or zirconium salt deposited thereon should be calcined prior to use as an oligomerization catalyst. Calcination in air or in an inert gas environment, such as nitrogen, may be conducted at a temperature of at least 100C, but below the temperature at which thermal destruction leads to catalyst deactivation. Typically, the silicon dioxide substrates are calcined for about 1 to 24 hours, preferably from about 15 to about 20 hours, at a temperature of from about 208a433 400 to 800 C, preferably from about 500 to about 800 C. Good results were obtained after calcination at a temperature of about 650 C for 18 hours. Temperatures above 900 C should be avoided.
The oligomerization reaction may be carried out either batchwise, in a stirred slurry reactor, or continuously, in a fixed bed continuous flow reactor. The catalyst concentration should be sufficient to provide the desired catalytic effect. The temperatures at which the oligomerization may be performed are between about 50 and 300 C, with the preferred range being about 120 to 250 C, and the especially preferred range being about 140 to 180 C, for optimum conversion. At temperatures of about 200 C
or greater, the amount of unsaturation remaining in the products of the oligomerization reaction may decrease, thus reducing the degree of hydrogenation necessary to remove unsaturation from the base stocks. However, at temperatures above 200 C, the olefin conversion may decrease. Applicants have found that the addition of a hydrocarbon containing a tertiary hydrogen, such as methylcyclohexane, may further reduce the amount of unsaturation present in the base stocks. One skilled in the art may choose the reaction conditions most suited to the results desired for a particular application. 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 oxidative degradation during their use as 20854~3 lubricants~ The hydrogenation reaction for 1-t~tradecene oligomers may be represented as follows:
catalyst C14nH28n + H2 ~ -----> C14nH(28n+2) where n represents moles of monomer used to form the oligomer.
Hydrogenation processes known to those skilled in the art may be used to hydrogenate the oligomers. A number of metal catalysts are suitable for promoting the hydrogenation reaction, including nickel, platinum, 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 3,997,621.
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 fashion 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 100 C
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-stripped, hydrogenated bottoms are the desired synthetic lubricant components. Thus, the method of this invention does not require the costly, 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 sXilled 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 of illustration and not as limitations on the scope of this invention.
EXAMPLES
In the examples detailed below, the following procedures were used:
Preparation of Catalvsts Cat. #1: Silica gel (grade-12, 28 - 200 mesh, 200 g) was placed in a beaker and covered with 10 % zirconium sulfate solution. This was mixed well, and let stand for an hour. The beaker was then placed in an oven, which was heated to 400 C, and 20~5~33 held at this temperature for 18 hours. The white solid was cooled under nitrogen and placed in a stoppered bottle.
Cat. ~2: Silica gel (gracle-12, 28 - 200 mesh, 400 g) in a crucible was covered with 500 g 20 % zirconium sulfate solution.
This was mixed well, and let stand for an hour. The crucible was then placed in an oven and heated to 650 C for 18 hours. The solid was cooled under nitrogen and placed in a stoppered bottle.
Oligomerization of Olefins Olefin and catalyst were charged to a flask equipped with an overhead stirrer, thermometer, heating mantle, and a water-cooled condenser (N2 purge). The mixture was vigorously stirred and heated to the desired temperature for the desired time. The mixture was then cooled to ambient temperature and filtered with suction. The liquid was analyzed by liquid chromatography. The results obtained are detailed in the table below.

208a~33 OLEFIN OLIGOM~RIZATION
._ _-- _ _ . __ . _ _ ¦~-- Olefin(~) (g) of Ca~ly~l Arnounlr~m~/Temp OlcGn hl D T+ DIT+
No ~by c~rbon Olcfin of (Hr)l(oC) Con. (%) (~) (~) Ratio ¦_ number) C~laly ('~ _ ~ C 14 a 100 ZrO,-SiO2 (CaL 1/1) 105/16026.1 73.9 23.j 2.60 9.04 ~ C-10 ~ 100 ZrO2~5iO2 (CaL 111) 104114031.9 68 1 29.0 294 9.86 ¦~ C-14 s 100 ZrO2-5iO2 (Cal. ~1) 105116045.5 5-15 38 6 6.84 5.64 4 C-10 1~ 100 ZrO2-SiO, (C~t. ~1) 104114034.4 65.6 31.2 3.13 9.87 I -__ ¦~ C-14 a 100 ZrO2-SiO2 (Cat. b2) 106114052 1 48 0 43 6 8.51 5.12 ¦~ C-14 1 100 ZrO2-SiO2 (Cat, n? 10 51160 58 9 41.1 48.7 10.2 4.77 10¦~ C-14 a 100 ZrO2 5iO2 (Cat n) 10 41180 67.1 32.9 54.2 i2 8 4.23 ¦~ C-14 a 100 ZrO2-SiO2 (CAt. ~2) 205/16074.9 25.1 55.5 19.4 2.86 C-14 a 100 ZrO2-SiO2 (Cat. 112) 5 5/16035.1 64 9 30.8 4.27 7.21 C-13,14 1 100 ZrO2-5iO2 (Cat. A12)10 4/180 5.71 94.3 5.71 _ ¦~ C-15,18 1 100 ZrO2-SiO2 (Cat. 1~2)10 4/180 16.3 83.7 16.3 _ 15¦~ C-14,16 a 100 ZrO2~5iO2 (Cat. ~2)10 41180 63.0 37.0 52.2 10 8 4.83 ¦~ C 10 a 100 ZrO2~SiO2 (Cat. ~2) 105116079 8 20.2 57.3 22.5 2.55 ¦~ C-12 a 100 ZrO2-5iO2 (Cat. ~2) 105116062.5 32.5 51.0 16.4 3.11 ¦~ C-14 a 100 ZrO2~5iOt (Cat. #'2) 105116057.7 42.3 48.0 9 69 4.95 ~ C 14 a 100 ZrO2~SiO2 (Cat. ~7) 105/16062.2 37.8 50 0 10.6 4.n 2 0 ~ C-10 a 100 ZrO2~SiO2 (Cat. A~2) 10 5/160 75.1 24.9 56.6 18.4 3.08 L~ C 10 a 100 ZrO.-SiO (Cat. ~) 10 4/180 80.2 19.8 59.2 21 1 2.81 ¦~ C 10 a 100 ZrO,-SiO2 (Cat A12) 205116079.8 20.2 56.9 22.9 2.48 ¦~ G 10 100 ZrO~-SiO2 (Cat. ~2) 55/16058.4 41 6 49.5 8.9 5.56 ¦~ C 10 a 100 ZrO. SiO2 (Cat. Ii2) 54/18063.5 36.5 52.0 11 6 4.48 25l~ C-10 ~ 100 _ SiO2 10 4/180 -o~100 _ I -_ I = Internal: Con. = Conv~raion; M = Monomer: D = Dimer"md Trimer+ = Triln~r + T.:lramer + Pentamer, ~tc.

Claims (19)

1. A process for the preparation of oligomers, comprising contacting at elevated temperature (1) linear olefins containing from 10 to 24 carbon atoms with (2) a catalyst prepared by (a) depositing on a substrate of silicon dioxide a compound selected from the group consisting of non-halogenated, non-polymeric, non-organometallic titanium salts and non-halogenated, non-polymeric, non-organometallic zirconium salts, and (b) calcining, at a temperature of about 400° C or greater, said silicon dioxide having said compound deposited thereon.

2. The process of Claim 1, wherein the olefins contain from 14 to 16 carbon atoms.

3. The process of Claim 1, wherein the silicon dioxide substrate is silica gel.

4. The process of Claim 1, wherein the compound deposited on the silicon dioxide substrate is selected from the group consisting of non-halogenated, non-polymeric, non-organometallic zirconium salts.

5. The process of Claim 1, wherein the compound deposited on the silicon dioxide substrate is selected from the group consisting of titanium sulfate, titanium citrate, titanium nitrate, and titanium phosphate.

6. The process of Claim 1, wherein the compound deposited on the silicon dioxide substrate is selected from the group consisting of zirconium sulfate, zirconium citrate, zirconium nitrate, and zirconium acetate.

7. The process of Claim 1, wherein the compound deposited on the silicon dioxide substrate is titanium sulfate or zirconium sulfate.

8. The process of Claim 1, wherein the silicon dioxide substrate having said compound deposited thereon is calcined at a temperature greater than about 500° C.

9. A process for the preparation of oligomers, comprising the steps of (1) oligomerizing linear olefins containing from 14 to 24 carbon atoms in the presence of a catalyst prepared by (a) depositing on a silicon dioxide substrate a non-halogenated, non-polymeric, non-organometallic zirconium salt, and then (b) calcining at a temperature of about 500° C or greater said silicon dioxide substrate having said zirconium salt deposited thereon, wherein said olefins are oligomerized at a temperature of about 120° to about 250° C and at a pressure of about atmospheric to about 1000 psig, and (2) recovering oligomers of said linear olefins.

10. The process of Claim 9, wherein the silicon dioxide substrate is silica gel.

11. The process of Claim 9, wherein the zirconium salt deposited on the silicon dioxide substrate is selected from the group consisting of zirconium sulfate, zirconium citrate, zirconium nitrate, and zirconium acetate.

12. The process of Claim 9, wherein the zirconium salt deposited on the silicon dioxide substrate is zirconium sulfate.

13. The process of Claim 9, wherein the silicon dioxide substrate having said compound deposited thereon is calcined at a temperature of about 650° C or greater.

14. The process of Claim 9, wherein the silicon dioxide substrate is silica gel and the non-halogenated, non-polymeric, non-organometallic zirconium salt is a two-component zirconium salt.

15. The process of Claim 9, wherein the olefins are oligomerized at a temperature of from about 140° C to about 180° C.

16. A process for the preparation of oligomers, comprising the steps of (1) oligomerizing alpha-olefins containing from 14 to 24 carbon atoms in the presence of a catalyst prepared by (a) depositing on a silica gel substrate a compound selected from the group consisting of zirconium sulfate, zirconium citrate, zirconium nitrate, and zirconium acetate, and then (b) calcining at a temperature of about 500° C or greater said silica gel substrate having said compound deposited thereon, wherein said olefins are oligomerized at a temperature of about 120° to about 250° C and at a pressure of about atmospheric to about 1000 psig, and (2) recovering oligomers of said alpha-olefins.

17. The process of Claim 16, wherein the compound is zirconium sulfate.

18. The process of Claim 16, wherein the silicon dioxide substrate having said compound deposited thereon is calcined at a temperature of about 650° C or greater.

19. The process of Claim 16, wherein the olefins are oligomerized at a temperature of from about 140° C to about 180° C.