Chemistry of hydrocarbon compounds – Unsaturated compound synthesis – By addition of entire unsaturated molecules – e.g.,...
Reexamination Certificate
1999-02-17
2001-02-06
Griffin, Walter D. (Department: 1764)
Chemistry of hydrocarbon compounds
Unsaturated compound synthesis
By addition of entire unsaturated molecules, e.g.,...
C585S525000, C585S527000, C585S528000, C585S529000, C585S531000, C502S155000, C502S162000
Reexamination Certificate
active
06184428
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to ethylene oligomerization to produce alpha-olefins, and in particular, to a heterogeneous catalyst and a process for ethylene oligomerization.
2. Description of the Related Art
An oligomer is a multiple unit of a monomer, and in this case the monomer of interest is ethylene. Oligomers include dimers, trimers, tetramers, and so on, but the resulting molecule is smaller than a polymer. Oligomers of ethylene are linear alpha-olefins which typically contain between 4 and 20 carbon atoms. Linear alpha-olefins are commercially important, and thus, improvements in the production of linear alpha-olefins are highly desirable.
In U.S. Pat. No. 3,676,523, issued to Mason on Jul. 11, 1972, Mason discloses a process of oligomerizing ethylene to linear alpha-olefins by reacting ethylene in a liquid phase solution in the presence of a nickel catalyst. Mason describes reacting nickel chloride hexahydrate, sodium borohydride and a potassium salt of a dihydrocarbylphosphinobenzoic acid, such as o-diphenylphosphinobenzoic acid, in a reaction medium of 1,4-butanediol and ethylene. Thus, Mason discloses a homogeneous catalyst and a process of oligomerizing ethylene in the presence of the catalyst in a polar organic solvent. The process is characterized by ethylene conversion to a linear alpha olefin product mixture of relatively high proportion of olefinic products in a higher molecular range including C
12
-C
20
alpha-olefins.
Lutz, the inventor of U.S. Pat. No. 4,528,416 issued Jul. 9, 1985, disclosed a process for producing ethylene oligomers in a polar organic solvent in the presence of a catalyst which is a chelate of nickel with a bidentate ligand. The solvent mixture contained between about 40 and 82% by weight of an aliphatic dihydric alcohol and between about 18 and 60% by weight of an aliphatic monohydric alcohol. It is critical to the Lutz process that the ethylene partial pressure be at least about 800 psig. Lutz stated that the use of the described reaction solvent mixture resulted in improvement in the rate of ethylene oligomerization and/or modification of the carbon number distribution of the product oligomer mixture. Lutz states that it is essential that the catalyst composition be prepared in the presence of ethylene, and the ethylene should be at a substantially elevated pressure, preferably in the range from 400 to 1,500 psig. The catalyst of Lutz is homogeneous, and it is necessary to carry out the oligomerization process in the solvent described above.
Wu in U.S. Pat. No. 5,286,696, issued Feb. 15, 1994, describes a heterogeneous catalyst. Wu states that homogeneous catalyst systems, such as described above, are not suitable for continuous processes or are relatively expensive. Wu further states that the ethylene oligomerization processes known at that time had not always achieved high catalyst productivity and good product selectivity. Wu discloses an ethylene oligomerization process comprising: (1) combining a nickel compound and a phosphine compound and a solvent to form a mixture; (2) combining this mixture with a phosphated alumina under an ethylene pressure to form a catalyst system; (3) contacting ethylene with the catalyst system under oligomerization conditions to produce higher olefins having more than 2 carbon atoms; and (4) recovering the higher olefins. Wu states that an advantage of his invention is the use of a heterogeneous composition that is easily employed in a continuous process for ethylene oligomerization.
Thus, a heterogeneous catalyst system, such as where the catalyst is a solid suspended in a liquid diluent, is advantageous for a continuous process, which can have a higher production rate than a batch process. Further, it remains true that even slight improvements in the process and/or catalyst for making ethylene oligomers is highly desirable because there is a significant commercial demand for linear alpha-olefins, such as produced by ethylene oligomerization.
SUMMARY OF THE INVENTION
The present invention provides a catalyst on a solid support slurried in a diluent to provide a heterogeneous catalyst system. Thus, the present invention is advantageous for a continuous process. The catalyst system of the present invention is highly active for ethylene oligomerization and is capable of selectively producing a desirable distribution of linear alpha-olefins. For product produced using the present invention, the product distribution is generally narrower than a product distribution obtained from a homogeneous catalyst system. Further, the catalyst system of the present invention is stable in air and can be stored for a period of time before use.
In one aspect, the present invention provides a process for ethylene oligomerization. A supported nickel catalyst is maintained as a slurry in a liquid material. The preferred catalyst is a reaction product of 2-diphenylphosphino benzoic acid (DPPBA), nickel chloride hexahydrate (NiCl
2
.6H
2
O) and sodium tetraphenylborate, which is deposited upon silica particles by freeze-dry evaporation of an alcohol solvent. Ethylene feed is dissolved into the liquid material, and catalyst slurry temperature is controlled from about 80° C. to about 120° C. for a time sufficient to oligomerize the ethylene to produce lower alpha-olefins.
In another aspect, the present invention provides the catalyst for the ethylene oligomerization process. DPPBA, NiCl
2
.6H
2
O and sodium tetraphenylborate are reacted together in a solvent to form a complex in a solution. Preferably, an alcohol is used as the solvent. A support material, preferably silica, is added to the solution, which is then fed into freeze-drying equipment. At a low temperature, the solvent is evaporated, and the catalyst reaction product is deposited onto the support material, thus forming the heterogeneous catalyst.
DETAILED DESCRIPTION OF THE INVENTION
The ethylene oligomers produced by the process of the present invention are addition products that contain two or more ethylene units, but not as many as ethylene units as in the relatively high molecular weight addition product referred to as polyethylene. The present invention is particularly adapted for production of linear mono-olefinic oligomers, particularly alpha-olefins having from 4 to about 20 carbon atoms. For all that they teach about the oligomerization process in general, including catalyst therefor, U.S. Pat. Nos. 3,676,523; 4,528,416; and 5,286,696, the patents described in the background section, are incorporated by reference in their entirety.
The catalyst system of the present invention is based on the following four components: (1) a chelating ligand; (2) a nickel precursor; (3) an activator; and (4) a support, preferably silica. Generally, the chelating ligand is a dihydrocarbylphosphinobenzoic acid such as described in U.S. Pat. No. 3,676,523. However, in a preferred catalyst system, the chelating ligand is 2-diphenyl phosphino benzoic acid (DPPBA). DPPBA is commercially available from Institute of Petroleum Chemistry, Aachen, Germany.
The nickel precursor can, in general, be prepared from many nickel salts including both inorganic and organic nickel salts. Simple divalent nickel salts are employed for preparing the catalyst composition of the present invention. Simple divalent nickel salts contain water of crystallization, a hydrate, in addition to bondingly coordinated anionic groups. Although, it is believed that any one of numerous nickel salts can be used, a complex must be formed between the catalyst components. The nickel precursor presently preferred is nickel chloride hexahydrate (NiCl
2
.6H
2
O).
The activator can be any compound that sufficiently activates the catalyst to provide the desired oligomerization. Various catalyst activators have been used in the past. Suitable activators are generally capable of transferring a hydride or an alkyl, alkenyl, alkynyl, or aryl group from itself to the metal/ligand complex formed by the reactio
Abdillahi Mohammed M.
Al-Sherehy Fahad
Olabisi Olagoke
Saeed Mian Rahat
Zahoor Mohammad Akhtar
Akin Gump Strauss Hauer & Feld & LLP
Griffin Walter D.
Saudi Basic Industries Corporation
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