Olefin oligomerization process

Abstract

 A process is described for producing a synthetic hydrocarbon especially useful as a base for high performance motor oils. The material is an α-olefin monomer having a uniquely selective product distribution emphasizing tetramers and pentamers. This distribution is achieved by using a catalyst comprising boron trifluoride and a long, straight-chain alcohol promoter, such as 1-hexanol.

Description

[0001] The present invention relates to a process of producing a higher degree of olefin oligomerization.

BACKGROUND OF THE INVENTION

[0002] Synthetic lubricants produced by the oligomerization of alpha-olefins are well-known. The nature of the alpha-olefin from which these oligomers are produced prescribes the properties of the resultant lubricant.

[0003] While it has been reported that even fairly large amounts of internal or branched-chain olefins may be present without extremely adverse effect on the alpha-olefin oligomerization, the resultant lubricants have restricted utility and do not justify their usage as a replacement for naturally occurring petroleum fluids.

[0004] In general, linear olefins of from eight to twelve carbons have proven most effective. Normal alpha-olefins are generally preferred.

[0005] Oligomerization may be achieved with a wide variety of catalysts. Representative catalyst include such Friedel-Crafts agents as AlCl₃, AlBr₃, BF₃, BCl₃, GaCl₄, and the like. Although each such agent facilitates oligomerization, the activity of the catalyst will differ widely. The very active catalyst, such as AlCl₃, will produce extremely high molecular weight polymers in conjunction with use of appropriate promoters. Other Friedel-Craft catalysts, such as SnCl₄ or GaCl₃ may present disposal problems after use. Moreover, solid catalysts present difficulties with respect to control of the exothermic oligomerization reaction due to the heterogeneous nature of the reaction system.

[0006] A preferred catalyst has been boron trifluoride (BF₃), which forms a liquid complex with the necessary promoters, and thus lends itself to conventional reaction systems.

[0007] Boron trifluoride and the other catalysts must be used in combination with a promoter. The promoter complexes with the BF₃ and, in so doing, provides an activated system needed for initiation of the oligomerization reaction. Among the most widely used promoters are the alkanoic and/or inorganic acids which are suitable for selective formation of oligomers ranging from two to four monomeric units.

[0008] Conventional practice for conducting the oligomerization reaction has been to admix the promoter with the monomeric olefin in the presence of an imposed atmosphere of BF₃, which is normally gaseous. The presence of excess BF₃ necessary for the reaction is delineated by the observed pressure of BF₃ in the reaction vessel.

[0009] The rate of oligomerization is related to some degree to the BF₃ pressure, since the probability of excess BF₃ in the liquid reactants is directly related to its pressure.

[0010] The use of a variety of alcohols as promoters is disclosed by Shubkin in U.S. Patent No. 3,780,128 entitled "Synthetic Lubricants by Oligomerization and Hydrogenation." There is no discussion on the pros and cons of the various alcohols, but the preferred alcohol is propanol.

[0011] The use of variety of alcohols as promoters is also disclosed by Cupples et al. in U.S. Patent No. 4,045,508 entitled "Method of Making Alpha-Olefin Oligomers," but that reference does not discuss the relative advantages and disadvantages of each promoter.

[0012] A two-step process using a mixture propanol and hexanol is disclosed by Pratt in U.S. Patent No. 4,587,368 entitled "Process for Producing Lubricant Material," where an aliquot of monomer is added to an intermediate oligomer. Example 2 shows that a 75:25 mixture of hexanol and propanol leads to a heavier product than a 50:50 mixture of hexanol and propanol

[0013] U.S. Patent Nos. 3,780,128; 4,045,508; and 4,587,368 are hereby incorporated by reference for all purposes.

[0014] The subsequent refining processes can be modified to yield particular product compositions. Where, for example, a lubricant consisting chiefly of higher oligomers is desired, one may remove unreacted monomer and low boiling dimer by distillation at atmospheric pressure. Trimer has also been removed in this manner, but through conditions of high vacuum distillation.

[0015] After hydrogenation, the substantially saturated lubricant material is then ready for compounding. Depending upon its composition and properties, it may be used directly in a wide variety of known applications. Alternatively, known lubricant additives may be incorporated. The material may be mixed with other available lubricants, to achieve the characteristics necessary for given conventional utilities.

[0016] Products of many of these known oligomerization reactions have been primarily designed for specialized applications. Aircraft hydraulic or turbine oils, for example, possess low viscosity requirements requiring oligomerization limited to dimers, trimers and tetramers (with emphasis on the trimer). Polymers resulting from such a procedure, however, have limited application as conventional lubricants. Lubricants for higher temperature, e.g., motor oils and industrial lubricants use, require considerably higher viscosities.

[0017] In general, higher viscosity fluids can only be made with a severe production rate penalty, since longer residence times are required to achieve the target viscosity with current technology.

SUMMARY OF THE INVENTION

[0018] The present invention provides a process for producing a high degree of olefin oligomerization. We have found that the oligomer distribution can be affected by the size of the primary alcohol that is used as promoter. A higher degree of oligomerization can be achieved by increasing the carbon to hydroxyl ratio for alcohol promoters. Moreover, we have also found that by using longer straight chain alcohols, we can produce a heavier product viscosity with greater BF₃ efficiency.

[0019] In our process, a synthetic lubricant material is produced by oligomerizing a C_8-16 α-olefin monomer in the presence of a boron trifluoride catalyst and a straight-chain alcohol promoter, wherein substantially all of the alcohol promoter has a carbon number of at least four, and at least 80 wt.% of the alcohol promoter has a carbon number of at least five.

[0020] Preferably, the olefinic monomer contains predominately 10 to 12 carbon atoms.

[0021] Preferably, substantially all of the alcohol promoter has a carbon number of at least five, and least 80 wt.% of the alcohol promoter has a carbon number of at least six. Most preferably, the alcohol promoter is 1-hexanol.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to assist the understanding of this invention, reference will now be made to the appended drawings. The drawings are exemplary only, and should not be construed as limiting the invention.

[0023] The Figure shows the effect of longer chain alcohols on the oligomer distribution of the product. It shows the data from Examples 6 through 8 and Comparative Example B.

DETAILED DESCRIPTION OF THE INVENTION

[0024] In its broadest aspect, the present invention involves the oligomerization of an olefinic monomer by contacting that monomer with boron trifluoride and a straight-chain alcohol promoter. Substantially all of the alcohol promoter has a carbon number of at least four, at least 80 wt.% of the alcohol promoter has a carbon number of at least five.

OLEFINIC MONOMER

[0025] The olefins used in making the oligomer are predominately (at least 50 mole %) C₈-C₁₆ straight-chain, mono-olefinically unsaturated hydrocarbons in which the olefinic unsaturation occurs at the 1- or α-position of the straight carbon chain. Straight-chain α-olefins are used because they are more reactive and commercially available. Such α-olefins can be made by the thermal cracking of paraffinic hydrocarbons or by the well known Ziegler ethylene chain growth and displacement on triethyl aluminum. Individual olefins may be used, as well as mixtures of such olefins. Examples of such olefins are 1-octene, 1-decene, 1-dodecene, 1-hexadecene and 1-tetradecene. The preferred normal α-olefin monomers are those containing about 10 to 12 carbon atoms. The olefin monomers can also contain minor amounts of up to about 50 mole %, and usually less than 25 mole %, of internal olefins and vinylidene olefins.

OLIGOMERIZATION REACTION

[0026] The alcohol promoter can be either a single straight-chain alcohol or a mixture of straight-chain alcohols. Examples of preferable single alcohols are 1-pentanol, 1-hexanol, 1-octanol, 1-decanol, 1-dodecanol, and 1-tetradecanol. Most preferably, the alcohol promoter is 1-hexanol.

[0027] Substantially all of the alcohol promoter has a carbon number of at least four, and at least 80 wt.% of the alcohol promoter should have a carbon number of at least five. In other words, the promoter should have no ethanol or propanol, and should have no more than 20% butanol.

[0028] Preferably, substantially all of the alcohol promoter has a carbon number of at five, and at least 80 wt.% of the alcohol promoter should have a carbon number of at least six. In other words, the promoter preferably should have no ethanol, propanol, or butanol and should have no more than 20% pentanol.

[0029] The alcohol promoter is used in minor but effective amounts. For example, the total amount of alcohol promoter used can be from about 0.001 to 0.04 moles per mole of monomer (0.1 to 4.0 mole percent). In general, the boron trifluoride is used in molar excess to the amount of promoter. This can be accomplished by using a closed reactor and maintaining a positive boron trifluoride pressure over the reaction mixture.

[0030] The alcohol can be mixed with the olefin feed and the reaction can be carried out in a batch or continuous process at temperatures of about 0° to 200° C and pressures ranging from atmospheric up to, for example, 1,000 psig. The reaction temperature will change the oligomer distribution, with increasing temperatures favoring the production of dimers. Preferred reaction temperatures and pressures are about 20° to 90° C and 5 to 100 psig.

[0031] When a desired oligomer distribution is reached, the reaction is terminated by venting off excess boron trifluoride gas and purging with nitrogen gas to replace all boron trifluoride gaseous residue. The reaction product, unreacted monomer, and boron trifluoride-promoter complex residue are removed from the reactor for further processing. The reactor product is then washed with an aqueous caustic solution and followed by several water washes to ensure neutralization.

[0032] The oligomer mixture from the reaction contains monomer, which can be removed by distillation. The monomer has been found to contain appreciable amounts of less reactive, isomerized material. However, this monomer can be recycled because it will react to form oligomers in the presence of fresh α-olefin monomer. For example, portions of up to about 25 wt. %, and preferably 5 to 15 wt. % recycled monomer, based on total monomer, can be mixed with fresh monomer. The product mixture can be further separated by distillation to provide one or more product fractions having the desired viscosities for use in various lubricant applications such as drilling, hydraulic or metal working fluids, gear oils and crankcase lubricants.

[0033] The oligomer product can be hydrogenated by conventional methods to increase the oxidation stability of the product. Supported nickel catalysts are useful. For example, nickel on a Kieselguhr support gives good results. Batch or continuous processes can be used. For example, the catalyst can be added to the liquid and stirred under hydrogen pressure or the liquid may be trickled through a fixed bed of the supported catalyst under hydrogen pressure. Hydrogen pressures of about 100 to 1,000 psig at temperatures of about 150° to 300° C are especially useful.

EXAMPLES

[0034] The invention will be further illustrated by following examples, which set forth particularly advantageous method embodiments. While the Examples are provided to illustrate the present invention, they are not intended to limit it.

COMPARATIVE EXAMPLE A

BF₃:1-BUTANOL BATCH PROCESS

[0035] The oligomerization reaction was carried out in an autoclave reactor equipped with a packless stirrer; and all wetted surfaces were made of 316 stainless steel. The reactor had an external electrical heater and an internal cooling coil for temperature control. The reactor was equipped with a dip tube, gas inlet and vent valves, and a pressure relief rupture disc. Prior to the monomer charge, the reactor was cleaned, purged with nitrogen and tested for leaks.

[0036] One thousand grams of 1-decene was charged into the reactor. The promoter, 1-butanol, was added to a concentration of 3.2 mole % based on feed. The entire reactor content was under vacuum. Boron trifluoride gas was then sparged slowly with agitation and controlled at 30° C via a cooling coil to avoid reactor temperature overrun. Additional boron trifluoride was added as necessary to maintain a reactor pressure of 60 psig. The reaction was terminated after two hours by venting off excess boron trifluoride gas and purging with nitrogen. The reaction product was then washed with a 4 wt. % aqueous sodium hydroxide solution followed by several water washes to ensure neutralization. The product was saved for further treatments such as hydrogenation and fractionation.

EXAMPLES 1 THROUGH 5

EFFECT OF LONGER CHAIN ALCOHOLS IN BATCH MODE

[0037] In these examples the following alcohols are substituted one at a time for the n-butanol promoter employed in Comparative Example A and the rest of the procedure of Comparative Example A was carried through in the same manner.

(1) n-hexanol

(2) n-octanol

(3) n-decanol

(4) n-dodecanol

(5) n-tetradecanol

Table 1.

Effects of Longer Chain Alcohols on 100°C Kinematic Viscosity (1 Hour Batch Reactions)
Example	Type of Promoter	Percent Monomer	Percent Dimer	Trimer+ Calculated Viscosity
A	n-butanol	2.67	6.74	5.66
1	n-hexanol	3.30	12.36	5.83
2	n-octanol	1.58	14.12	6.21
3	n-decanol	2.85	13.82	6.40
4	n-dodecanol	3.41	13.51	6.30
5	n-tetradecanol	2.91	12.06	6.46

COMPARATIVE EXAMPLE B

BF3:1-BUTANOL IN CONTINUOUS PRODUCTION MODE

[0038] The continuous monomer feed reactor was equipped with monomer, promoter and gas inlet ports, vent valves, and a pressure relief rupture disc. At the onset of oligomerization reaction, the reactor was cleaned, purged with nitrogen and tested for leaks. A 1-dodecene monomer flow rate of 2000 grams per hour, a reactor temperature of 30°C and a reactor pressure of 60 psig were controlled throughout the reaction period. The reactor had a gas cap and its liquid volume was controlled through a level control device and approximately one half of the reactor volume. A preformed BF₃:n-butanol complex was added at a concentration of 0.3 mole % based on feed. The reaction product was discharged to a low pressure flash tank to remove the gaseous reactant. The liquid product stream was then subjected to neutralization and washing steps. The product was saved for further treatments such as hydrogenation and fractionation.

EXAMPLES 6 THROUGH 8

EFFECT OF LONGER CHAIN ALCOHOLS IN CONTINUOUS MODE

[0039] In these examples the following alcohols are substituted one at a time for the n-butanol promoter employed in Comparative Example B and the rest of the procedure of Comparative Example B was carried through in the same manner.

(6) n-hexanol

(7) n-octanol

(8) n-decanol

Table 2.

Effects of Longer Chain Alcohols on 100°C Kinematic Viscosity for Continuous Production
Example	% Monomer	% Dimer	Trimer+ Calculated Viscosity
B	0.3	1.0	6.88
6	1.3	2.1	7.76
7	4.0	5.0	8.12
8	6.6	6.9	8.19

COMPARATIVE EXAMPLES C THROUGH G

EFFECT OF MIXED ALCOHOLS

[0040] In these examples the following alcohols are substituted one at a time for the n-butanol promoter employed in Comparative Example A and the rest of the procedure of Comparative Example A carried through in the same manner.

(C) n-propanol

(D) 2.30 mole % n-propanol and 0.77 mole % n-hexanol

(E) 0.77 mole % n-propanol and 2.30 mole % n-hexanol

(F) 2.30 mole % n-butanol and 0.77 mole % n-hexanol

(G) 0.77 mole % n-butanol and 2.30 mole % n-hexanol

Table 3

Mixed Alcohols with n-Hexanol (1 Hour Batch Reactions)
Example	Type of Lighter Alcohol	Ratio Lighter Alcohol to Hexanol	Percent Monomer	Percent Dimer	Trimer+ Calculated Viscosity
C	n-propanol1	-	1.84	9.71	5.37
D	n-propanol	75:25	2.83	11.98	5.26
E	n-propanol	25:75	3.81	12.91	5.39
A	n-butanol1	-	2.67	6.74	5.66
F	n-butanol	75:25	2.58	12.82	5.20
G	n-butanol	25:75	2.56	12.75	5.44
1	n-hexanol	-	3.30	12.36	5.83

1no hexanol used

[0041] Table 3 shows the results of mixtures of alcohols as promotors on the calculated 100° C kinematic viscosity of the trimer and higher oligomers. As this invention teaches, n-hexanol gives a heavier product than n-butanol, which in turn produces a heavier product than n-propanol. One would expect that mixtures would produce products with viscosities bounded by that which is produced from the pure alcohols (i.e., propanol and hexanol). However, this data shows that mixtures produce lower viscosities than that produced by the lighter of the two alcohols. For example, a 25:75 mixture of propanol:hexanol gives a product viscosity of less than that produced by propanol alone. Butanol and hexanol mixtures behave in a similar manner.

COMPARATIVE EXAMPLE H AND EXAMPLES 9 AND 10

EFFECT OF LONGER CHAINED ALCOHOLS ON BF₃ CONSUMPTION

[0042] In Comparative Example H, n-butanol was substituted as the promoter for the promoter complex employed in Comparative Example B. Furthermore, the feed was 1-decene instead of 1-dodecene, the BF₃ pressure was 80 psig and the mole % promoter was 2.21. The rest of the procedure was carried through in the same manner as Comparative Example B.

[0043] In Examples 9 and 10, n-hexanol was substituted for the n-butanol promoter used in Comparative Example H. In Example 9, 1.63 mole % of n-hexanol was used and in Example 10, 2.24 mole % of n-hexanol was used. The rest of the procedure was carried through in the same manner as Comparative Example H.

Table 4

BF3 Consumption
Example	Type of Promoter	Mole % Promoter of Feed	Trimer+ Calculated Viscosity cSt	BF3 wt% of Feed
H	n-butanol	2.21	8.5	1.16
9	n-hexanol	1.63	8.3	0.92
10	n-hexanol	2.24	9.6	1.17

[0044] Table 4 shows the effect of n-hexanol as compared to n-butanol in producing near equivalent product viscosity with a savings of the amount of BF₃ consumed. Comparative Example H and Example 9 show that if n-hexanol is used instead of n-butanol, a 8.3 cSt product can be produced with about 20% savings in BF₃. Conversely, a 9.5 cSt can be produced with near equivalent use of BF₃ by using n-hexanol instead of n-butanol at equivalent mole % of the promoter.

[0045] While the present invention has been described with reference to specific embodiments, this application is intended to cover those various changes and substitutions that may be made by those skilled in the art without departing from the spirit and scope of the appended claims.

Claims

1. A process for producing a synthetic lubricant material comprising oligomerizing a C_8-16 α-olefin monomer in the presence of a boron trifluoride catalyst and a straight-chain alcohol promoter:

(a) wherein substantially all of the alcohol promoter has a carbon number of at least four, and

(b) wherein at least 80 wt.% of the alcohol promoter has a carbon number of at least five.

2. A process according to Claim 1 wherein substantially all of the alcohol promoter has a carbon number of at least five, and wherein at least 80 wt.% of the alcohol promoter has a carbon number of at least six.

3. A process according to Claim 2 wherein the alcohol promoter is 1-hexanol.

4. A process according to Claim 1 wherein the olefinic monomer contains predominately 10 to 12 carbon atoms.

Drawing