CA2435834A1 - Process for the selective isomerization of alpha-olefins in the presence of vinylidene olefins - Google Patents

Abstract

A process for the isomerization of alpha olefins to internal olefins is disclosed. The process is selective in that when both vinylidene olefins and alpha olefins are present in the feed or reaction mixture, only the alpha olefins are isomerized substantially in the absence of isomerization of the vinylidene olefins to trisubstituted olefins. The catalysts employed in the process are ruthenium trihalides, preferably RuCl3, RuBr3, and/or hydrated forms of these ruthenium trihalides.

Description

PROCESS FOR THE SELECTIVE ISOMERIZATION OF ALPHA-OLEFINS IN THE
PRESENCE OF VINYLIDENE OLEFINS
RELATIONSHIP TO PRIOR APPLICATIONS
s (Not Applicable) STATEMENT REGARDING FEDERALLY FUNDED RESEARCH
(Not Applicable) FIELD OF THE INVENTION
The invention generally relates to a process for isomerizing alpha-olefins to 1o internal olefins without significant concurrent isomerization of vinylidene olefins also present in the reaction mixture.
BACKGROUND OF THE INVENTION
In the catalytic isomerization of olefins, it is common that isomerization of a vinylidene olefin to a trisubstituted olefin (Reaction 1 below) proceeds more readily 15 than isomerization of an alpha-olefin to an internal olefin (Reaction 2 below) when both are present in the same reaction mixture.

CH --=r \C CH3 REACTION 1 - ISOMER(ZATION OF A VINYLIDENE
CH2~H-CH2-R -= CH3- CH=CH-R
REACTION 2 - ISOMERI7~ITfON OF AN ALPHA-OLEFIN
In Reactions 1 and 2, R and R' are rnonovalent groups such as straight or branched alkyl groups or aryl groups typically in the range of about 1-30 carbon atoms.
Some 2s of the hydrogen atoms in the R and R' groups may optionally be substituted with groups that do not interfere in the isomerization reaction.

Accordingly, when both vinylidenes and alpha-olefins are present, it has been difficult to selectively isomerize alpha-olefins to internal olefins without also isomerizing the vinylidene olefins. The present invention addresses this problem and provides a catalytic process for accomplishing the selective isomerization of alpha-s olefins to internal olefins in the presence of vinylidene olefins without substantial isomerization of the vinylidenes.
BRIEF DESCRIPTION OF THE INVENTION
This invention relates to a process for the conversion of olefins. More specifically it relates to the isomerization of alpha olefins to internal olefins wherein 1o vinyiidene olefins are also present in the alpha olefin feed or reaction mixture. (t has been found that the alpha olefins may be catalytical(y isomerized to internal olefins without significant concurrent isomerization of vinylidene olefins to trisubstituted olefins.
The selective isomerization process utilizes a metal-based homogeneous or i5 heterogeneous catalyst. The catalysts used in the process are ruthenium trihalides including ruthenium trihalide hydrates. The preferred catalysts are ruthenium trichloride and ruthenium tribromide including the various hydrated forms of either.
Investigators Jochem U. Koehler and Hans L. Krauss (Journal of Molecular Catalysis, 1997, Volume 123, Number 1, Pages 49-64) have reported the use of 2o RuCl3~3H20 as an active olefin isomerization catalyst. However, there is no disclosure what-so-ever in the reference regarding selective isomerization of alpha olefins in the presence of vinylidene olefins.
The ruthenium trihalide (RuX3) catalysts of this invention may be employed in homogeneous form, dissolved in neat liquid olefin or a mixture of olefin and a solvent.
2s Alcohols are effective solvents for the RuX3 compounds of this invention.
The selective alpha-olefin isomerization process of this invention using RuX3 compounds may be conducted at temperatures in the range of about 50°C to about 250°C. The isomerization process is typically conducted in an inert atmosphere e.g., under nitrogen or in the presence of other gases such as hydrogen at any manageable 3o pressure.

DETAILED DESCRIPTION OF THE INVENTION
For the sake of clarity, the term "comprising" as used in this application is defined as "specifying the presence of stated features, integers, steps, or components as recited, but not precluding the presence or addition of one or more other steps, components, or groups thereof'. Comprising is different from "consisting of which does preclude the presence or addition of one or more other steps, components, or groups thereof.
The alpha olefins to be converted to internal olefin are C4 to C3o straight or branched-chain monoolefinically unsaturated hydrocarbons in which the olefinic unsaturation occurs at the 1- or alpha-position of the carbon chain. Typically these compounds have the following formula RZ
I
R'-CHZ CHZ (CHZ)m C=CHZ
~5 where R' and R2 are the same or different and are hydrogen or alkyl, i.e., C, to C3o linear or branched alkyl, preferably C, to C2o linear or branched alkyl, most preferably C, to C6 linear or branched alkyl, e.g. methyl, ethyl and the like, and m is an integer from 0 to 26. Particularly preferred are compounds where R' is alkyl and RZ is hydrogen.
2o Such alpha-olefins are commercially available and can be made by the thermal cracking of paraffinic hydrocarbons, by conversion of the corresponding alcohol to an olefin or by the we(I-known Zieg(er ethylene chain growth and displacement from trialkylaluminum compounds. Individual olefins may be used as well as mixtures of such olefins. Examples of such olefins are 1-hexene, 1-heptene, 25 1-octene, 1-nonene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicocene, and the like. The more preferred normal-alpha-olefins are those containing about 6-30 carbon atoms. The most preferred normal-alpha-olefins are those containing about 10-30 carbon atoms. Some internal alpha olefins may also be present in the reaction mixture at the start of the reaction.
Obviously, the so amount of internal olefin present in the reaction mixture will increase at the conversion of alpha olefins _to internal olefins proceeds in accord with the process of this invention.
After conversion the internal olefins are useful, e.g., when oligomerized, as oils.
Depending on their viscosity, different applications for such oils are known, e.g., as lubricants. These materials are generally mixtures of different percentages of dimer, trimer, tetramer, pentamer and higher oligomers which oligomers are produced .in different proportions in an oiigomerization process. In order to increase the viscosity, processes are used which either produce more of the higher oligomers or, alternatively, some of the lower oligomers are removed typically by distillation. Most low viscosity dimer and trimer products are obtained as by-products of the production of higher viscosity synthetic oils. Due to 'the increasing use of dimers in applications such as low temperature lubricants and drilling fluids, methods for their preferential production from the isomerized alpha olefins are of interest.
Vinylidenes or vinylidene olefins may be represented by the formula ~C CH2 and "trisubstituted olefins" may be represented by the formula R
C\ H
wherein R3, R4, and R5 represent hydrocarbon groups. Reaction 1 above shows the isomerization of a vinylidene olefin to a trisubstituted olefin. Typically, the isomerization of a vinylidene olefin to a trisubstituted olefin occurs with greater facility than the internal isomerization of an alpha olefin to an internal olefin when both are present. Upon oligomerization of such an isomerization mixture, the oligomerization products of trisubstituted species will be present together with the oligomerization products of internal olefins in the oligomer oils produced. In commercial production, it may be difficult to obtain an oligomer product mix which, when fractionated, will produce the relative amounts of each viscosity product which correspond to market demand. Thus, the ability to selectively isomerize only the alpha olefin may offer a significant commercial advantage.

5 In this application, Applicants disclose a process which selectively isomerizes alpha olefins to internal olefins in a reaction mixture which also contains vinylidene olefins and without substantial isomerization of the vinylidene olefins to trisubstituted olefins. For the purpose of this invention, without substantial isomerization of the vinylidene is intended to denote that the conversion achieved in the desired reaction 1o is at least five times as great as the conversion of vinylidene olefins to trisubstituted olefins. For example in a feed containing both alpha olefins and vinylidene olefins where 5 % (mole or weight %) of the vinylidene olefins were converted to trisubstituted olefins by the method of this invention, a conversion of alpha olefins to internal olefins exceeding 25 % (mole or weight %) would be considered to have met T5 the condition without substantial isomerization of the vinylidene olefin to trisubstituted olefin.
The process utilizes a metal-based homogeneous or heterogeneous catalyst.
The catalysts used in the process are ruthenium trihalides including ruthenium trihalide hydrates. The preferred catalysts are ruthenium trichloride and ruthenium 2o tribromide including the various hydrated forms of either. The ruthenium trihalide (RuX3) catalysts of this invention are preferably employed in homogeneous form, dissolved in neat liquid olefin or a mixture of olefin and a solvent. Alcohols are effective solvents far the RuX3 compounds of this invention.
The selective alpha-olefin isomerization process of this invention using RuX3 25 compounds may be conducted at temperatures in the range of about 50°C to about 250°C, but preferably in the range of about 100°C to about 200°C. The isomerization process is typically conducted in an inert atmosphere e.g., under nitrogen or in the presence of other gases such as hydrogen. The process is typically conducted at atmospheric pressure (about 1.0 bars) but may be conducted at any manageable 3o pressure typically in the range of about 0.1 to about 25 bars, and preferably in the range of about 0.5 bars to about 5.0 bars.

Example To a glass reaction vessel was added 100 ml of an olefin mixture containing alpha, internal, vinylidene, and trisubstituted olefins of even carbon numbers from 18 through 30. To this was added 0.5 m( of a 0.0024 molar solution of ruthenium trichloride hydrate in hexanol, corresponding to a charge of about 1.2 ppm Ru in the reaction solution. The solution was vigorously stirred at room temperature and a small sample of the liquid was removed for analysis and designated as the "Before Reaction Sample". The reaction vessel was then immersed in an oil bath which had been pre-heated to 170°C. The reaction vessel was maintained at 170°C while.a flow of hydrogen gas at atmospheric pressure was sparged through the reaction solution at 0.1 SCFH. Afterward, another liquid sample was removed (4Hour Reaction Sample) from the vessel. The two samples were analyzed by NMR to determine the types of olefins present. The results obtained are as shown in Table 1 below.
Table 1 Olefin Mole % Olefin Type Mole % Olefin Type Type in in Before Reaction Sample4-Hour Reaction Sample Alpha 30.5 2.7 Internal 11.5 36.6 Vinylidene 55.3 55.2 Trisubstituted2.8 5.5 These results clearly indicate that isomerization of alpha-olefins to internal olefins predominated over isomerization of vinylidene olefins to trisubstituted species.
Comparative Example The data for the following comparative example was taken from US Patent No.
4,724,274. Table 2 below shows the feed composition prior to isomerization and the product mixture after isomerization. The feed was passed over a fixed bed catalyst consisting of 0.3 weight percent palladium deposited on gamma alumina. Sulfur (in the form of dimethyl sulfide) was added to the feed so as to be present at a level of 6 PPM. The reaction was conducted in the presence of hydrogen at a pressure of bars and a temperature of 80° C.
Table Species Weight % in Feed Weight Present Before IsomerizationAfter Isomerization 1-pentene 25 ~0 (alpha olefin) internal olefins~0 ~0 2-methyl-1 butene40 7.2 (vinylidene olefin) 2-methyl-2-butene~0 32.7 (trisubstituted) pentane 35 isopentane ~0 0.1 From this comparative example it is observed that 82 % of the vinylidene olefin present in the feed was converted to trisubstituted olefin while none of the alpha olefin present in the feed was converted to internal olefin. In fact, the alpha olefin was destroyed (hydrogenated to pentane). These results are in stark contrast to the working example of this invention where alpha olefin was selectively isomerized to internal olefin without substantial isomerization of the vinylidene olefin to trisubstitued olefin.

Claims (10)

We claim:

1. A process for the selective isomerization of alpha olefins to internal olefins comprising the use of ruthenium trihalide catalyst wherein vinylidene olefin is also present in the reaction mixture and wherein the selective isomerization of the alpha olefins to internal olefins occurs without significant concurrent isomerization of the vinylidine olefin also present in the reaction mixture.

2. The process of claim 1 wherein the alpha olefin has the formula where R1 and R2 are independently selected from the group consisting of hydrogen, C1 to C30 straight alkyl, and C1 to C30 branched alkyl and wherein m is an integer in the range of 0-26.

3. The process of claim 2 where R1 and R2 are independently selected from the group consisting of hydrogen, C1 to C20 straight alkyl, and C1 to C20 branched alkyl.

4. The process of claim 2 where R1 and R2 are independently selected from the group consisting of hydrogen, C1 to C6 straight alkyl, and C1 to C6 branched alkyl.

5. The process of claim 2 where R1 is C1 to C30 straight or branched alkyl and R2 is hydrogen.

6. The process of claim 1 wherein the ruthenium trihalide is selected from the group consisting of ruthenium trichloride, ruthenium trichloride hydrate;
ruthenium tribromide, ruthenium tribromide hydrate, and mixtures of the preceding.

7. The process of claim 1 wherein the selective isomerization is conducted at a temperature in the range of about 50°C to about 250°C.

8. The process of claim 1 wherein the selective isomerization is conducted at a temperature in the range of about 100°C to about 200°C.

9. The process of claim 1 wherein the selective isomerization is conducted at a pressure in the range of about 0.1 bars to about 25 bars.

10. The process of claim 1 wherein the selective isomerization is conducted at a pressure in the range of about 0.5 bars to about 5.0 bars.