Abstract:
An improved heterogeneous catalyst effective to catalyze the oligomerization of ethylene is formed be depositing a bis(1,5-cyclooctadiene)Ni(O) compound onto an omega zeolite or type Y zeolite support. The catalyst is used to oligomerize olefins. The catalyst is particularly effective in terms of selectivity and reactivity in catalyzing the formation of 1-butene from ethylene.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to the oligomerization of olefins with a supported nickel catalyst, particularly a nickel-zeolite catalyst. 
     More particularly, the present invention relates to the formation of 1-butene by reacting ethylene in the presence of this nickel-zeolite catalyst. 
     The present invention further relates to a novel heterogeneous nickel-zeolite catalyst formed for bis(1,5-cycloocatdiene)Ni(O). 
     2. Description of the Prior Art 
     A variety of oligomerization catalysts are currently known. These include both homogeneous and heterogeneous catalysts. In particular nickel compounds have been used to catalyze the oligomerization of lower olefins to olefinic products of higher molecular weight, e.g., dimmers, trimers, tetramers or the like. 
     The selectivity towards particular products and the overall reactivity depend to a large extent upon the catalyst used as well as reaction conditions. Barnett U.S. Pat. No. 3,532,765 discloses an ethylene oligomerization process using cyclopentenyl(cyclopentadienyl) nickel supported on an inorganic oxide support. This catalyst exhibits a relatively low reactivity. Barnett U.S. Pat. No. 3,134,824 discloses bis (cyclopentadienyl) nickel deposited on a support such as silica, alumina, titania, zirconia, thoria, boria, and mixtures thereof. This catalyst exhibits a relatively low selectivity for 1-butene and an overall low reactivity. 
     Walker, et al, U.S. Pat. No. 3,134,824, describe a process using nickelocene [bis (η 5  -cyclopentadienyl) nickel]supported on silica-alumina as a catalyst for oligomerization of olefins. However, this catalyst is not selective nor is it active at temperatures below one hundred degrees Centigrade. 
     Other catalysts are disclosed in Beach et al U.S. Pat. Nos. 4,272,406, 4,272,407 and 4,293,725. The patents disclose tris(cyclopentadienyl) trinickel dicarbonyl catalysts. These catalyst exhibit a relatively low selectivity toward 1-butene relative to other C-4 compounds specifically in the range of 11-44% 1-butene, and further produce considerable quantities of higher molecular weight oligomers, e.g. hexenes, octenes, etc. 
     A nickel II salt derived from phosphinoacetate is currently used as a homogeneous catalyst for oligomerization of olefins. This produces a relatively high proportion of higher molecular weight olefins. In fact the product distribution of C 6  -C 20  olefins is relatively flat. 
     Triethylaluminum is also used as an oligomerization catalyst. The product distribution of C 4  -C 8  and higher olefins is weighted towards lower molecular weight olefins. 
     A particularly desirable product is 1-butene. It can be used in the formation of poly 1-butene a very useful polymer. However, the known oligomerization catalysts are unsuitable for production of a very high concentration of 1-butene from ethylene. 
     SUMMARY OF THE INVENTION 
     The present invention is premised upon the realization that a catalyst, formed by depositing bis(1,5-cyclooctadiene)Ni(O) (hereinafter (COD) 2  Ni) onto an omega zeolite support or Y type molecular sieve, acts to catalyze the oligomerization of ethylene to form 1-butene with extremely high selectivity towards 1-butene. Further the catalyst of the present invention is very reactive under mild conditions. Accordingly, it provides a catalyst uniquely suited for the production of 1-butene from ethylene. 
     DETAILED DESCRIPTION OF THE INVENTION 
     According to the present invention ethylene is reacted in the presence of a catalyst to form 1-butene. The catalyst is a heterogeneous catalyst formed from (COD) 2  Ni or alkyl substituted (COD) 2  Ni simply deposited onto an omega zeolite support or a Y-type zeolite support. 
     Catalyst Formation 
     The omega type zeolite support is a synthetic crystalline zeolite the production of which is described in U.S. Pat. No. 4,241,036 which is incorporated herein by reference. Omega zeolites are readily prepared by digesting and crystallizing an aqueous mixture having an overall composition expressed in terms of mole ratios of oxides falling within the following range: ##EQU1## A particularly preferred set of initial reacting compositions for producing the omega zeolites again expressed in terms of mole ratios is as follows: ##EQU2## 
     Representative reactants are silica gel, silicic acid, colloidal silica, alkali metal silicate and reactive amorphous solid silicas as a source of silicon and activated alumina, gamma alumina, alumina trihydrate or alkali metal aluminate as the source of aluminum. Sodium hydroxide and tetramethylammonium hydroxide or halide are typical convenient sources of sodium and tetramethyl ammonium ions. Preferred sources of silica are the reactive solid silicas which include materials known commercially as Hi-Sil, Cab-O-Sil, Zeosyl, QUSO, Arc silica and the aqueous colloidal silica soles which include such materials as Nalcoag, Ludox, Syton and Mertone. 
     The reaction system is formed by placing all the required reactants in the proportions hereinbefore defined in a reaction vessel and bringing the temperature of the system to a temperature of between 20° C. and 210° C., preferably between 80° C. and about 210° C. An initial aging of the reaction system at ambient temperature can be utilized if desired. Products of the highest purity have been obtained using temperatures of from about 90° C. to about 180° C. and are therefore preferred. Crystallization periods of from about 1-8 days at 80°-100° C. have been found satisfactory. 
     After the reaction period the zeolite crystals are filtered off. The mass of zeolite crystals is washed preferably with distilled water and conveniently on the filter, until the effluent wash water in equilibrium with the zeolite has a pH of between 9 and 12. Thereafter the crystals are dried, conveniently in a vented oven, at a temperature of between 25° C. and 150° C. 
     Preferred omega zeolites are obtained from Linde Division of Union Carbide and are referred to as ELZ-omega-5 zeolite and ELZ-omega-6 zeolite. As used herein and in the claims the ELZ-omega-5 zeolite refer to a zeolite, also called a molecular sieve, having the following chemical and physical properties. 
     
         ______________________________________(a) Chemical composition anhydrous basisAl.sub.2 O.sub.3         16.3 wt percentSiO.sub.2     75.7 wt percentNa.sub.2 O     6.5 wt percentSiO.sub.2 /Al.sub.2 O.sub.3         molar ratio 7.7Na.sub.2 O/Al.sub.2 O.sub.3         molar ratio 0.6(b) Physical propertiesForm - powderUnit cell constantsa.sub.o            18.20 angstromsc.sub.o            7.59 angstromsFree aperture 12 ring,              17.5 angstromsLargest molecule absorbed              (C.sub.4 F.sub.9).sub.3 NEffect of dehydration              Stable to 750° CentigradeSurface area (1 pt. BET)              240 square meters/gramsO.sub.2 capacity (at -183° C., 100 torr)              15.0%______________________________________ 
    
     As used herein and in the claims ELZ-omega-6 zeolite refers to a zeolite also called a molecular sieve having the following chemical and physical properties. 
     
         ______________________________________(a) Chemical Composition Anhydrous BasisAl.sub.2 O.sub.3     18.8 wt percentSiO.sub.2            78.9 wt percentNa.sub.2 O            0.68 wt percentSiO.sub.2 /Al.sub.2 O.sub.3                 7.1 molar ratioNa.sub.2 O/Al.sub.2 O.sub.3                 0.06 molar ratio(b) Physical PropertiesForm - powderUnit cell constantsa.sub.o             18.20 angstromsc.sub.o              7.57 angstromsSurface area (1 pt. BET)               300 square meters/gramsO.sub.2 capacity (at -183° C., 100 torr)               15.8%______________________________________ 
    
     The Y type molecular sieves or zeolites are Y-type crystalline aluminosilicates. These are discussed in U.S. Pat. No. 3,130,007, the disclosure of which is incorporated herein by reference. These can be prepared by preparing an aqueous sodium aluminosilicate mixture having a composition expressed in terms of oxide-mole-ratios falling within the following approximate ranges: 
     
         ______________________________________Na.sub.2 O/SiO.sub.2         0.20 to 0.40SiO.sub.2 /Al.sub.2 O.sub.3          5 to 40H.sub.2 O/Na.sub.2 O         25 to 60______________________________________ 
    
     wherein the major source of silica in the mixture is aqueous colloidol silica sol and/or amorphous solid silica. The aqueous mixture is maintained at a temperature in the range of from about 20° C. to about 125° C. until the crystalline type Y zeolite is formed. 
     Ammonium exchanged type Y zeolites are preferred and specifically LZ-Y82 zeolite sold by the Linde Division of Union Carbide. In the specification and claims LZ-Y82 zeolite refers to a type Y molecular sieve having the following chemical and physical properties: 
     
         ______________________________________a. Chemical Composition Anhydrous BasisSiO.sub.2          about 72.2 wt. percentAl.sub.2 O.sub.3   about 22.8 wt. percentNa.sub.2 O          about 0.2 wt. percent(NH.sub.4).sub.2 O  about 4.0 wt. percentSiO.sub.2 /Al.sub.2 O.sub.3               about 5.38 molar ratioNa.sub.2 O/Al.sub.2 O.sub.3               about 0.01 molar ratiob. Physical PropertiesLOI at 800° F.              23.1 wt. percentSurface Area, 1 point B.E.T.              770 square meters per gramUnit Cell Size     24.56 angstroms______________________________________ 
    
     LZ-Y82 is an ammonia exchanged powder form of Linde type Y molecular sieve LZ-Y72 and is also commonly referred to as low soda Diuternal-Y. 
     The bis(1,5-cyclooctadiene)Ni(0) compound used in the present invention includes (COD) 2  Ni and alkyl substituted (COD) 2  Ni specifically bis(R a  -1,5-cyclooctadiene)Ni(O) and (R a  -1,5-cyclooctadiene) (1,5-cyclooctadiene)Ni(O) wherein R represents C 1  -C 10  straight or branched alkyl and &#34;a&#34; represents 1-8. Alkyl substitution on the cyclooctadiene ring is not believed to enhance catalytic activity. Therefore preferably unsubstituted (COD) 2  Ni(O) is used. 
     Formation of Catalyst 
     The catalyst is formed by depositing the (COD) 2  Ni compound onto the omega zeolite or type Y zeolite support. Care must be taken to insure no water or oxygen is present because the (COD) 2  Ni(O) compound as well as the formed catalyst are very reactive with water and oxygen and can be easily deactivated. 
     In the reaction it is preferable to use from 0.1 to 10 weight percent of the (COD) 2  Ni compound based on weight of zeolite. 
     The (COD) 2  Ni is deposited on the zeolite in the presence of an inert diluent preferably an aliphatic hydrocarbon in a pressurized autoclave. Suitable inorganic diluents are those which can be easily removed from the product mixture and recycled such as heptane, decane, decalin, etc. The ratio of diluent to catalyst can be from 50 parts by weight to 15 parts by weight. 
     The catalyst is formed by flushing the reactor several times with nitrogen or other inert gas, charging the reactor with the (COD) 2  Ni(O) compound, zeolite, diluent and nitrogen to about 500 psig, and stirring these components for about one hour. The catalyst is then ready to use in slurry form. Alternately the diluent can be removed by evaporation to form a solid catalyst. 
     Oligomerization Reaction 
     Because the catalyst is so sensitive to moisture and oxygen it is preferred to use the catalyst in situ to eliminate the need for transferring the catalyst from one reactor to another. Accordingly, to use the catalyst in an oligomerization reaction, the nitrogen is vented off and the catalyst composition resulting from the reaction is used in the inert diluent. 
     The oligomerization reaction can be conducted in a batch or continuous reactor. In this reaction, ethylene is reacted with itself at elevated pressure with agitation to form preferably 1-butene. The reaction is exothermic accordingly cooling is required. 
     The ethylene supplied as a gas is charged into the reactor to increase the reactor pressure as desired. The ethylene can be in the form of reagent grade ethylene or alternately may be contained in low concentration as the byproduct of various petroleum distillation processes and may contain other olefins such as proplyene. In order to prevent deactivation of the catalyst water must be removed from the ethylene source prior to being contacted with the catalyst. Further in order to prevent hydrogenation of ethylene, hydrogen should be removed from the ethylene source. 
     The reaction temperature should be preferably about room temperature generally from about 20° to 70° C. Higher temperatures cause the equilibrium to shift towards formation of 2-butene as opposed to 1-butene. This is particularly so when the reaction temperature exceeds about 40° C. Further at higher temperatures higher molecular weight olefins such as C 6  and C 8  olefins are produced in higher quantities. Preferably the temperature should be from about 25 to about 40° C. 
     The amount of catalyst present relative to the amount of ethylene converted is relatively low. Generally about 4,000 moles of ethylene can be converted per mole of nickel per hour. Including the support this corresponds to 17 grams of product per gram of catalyst per hour. Optimum composition of the catalyst in the present form is about 1-5% of the (COD) 2  Ni(O) compound and the remainder support. 
     The reaction is conducted in the liquid phase for about 1 to about 60 minutes. The reaction pressure can be from about 150 pounds per square inch to about 1,000 pounds per square inch (10.3 to 68.9 bars). The preferred range is from about 400 to about 500 psi (27.6 to 34.5 bars). Preferably the reaction time will be maintained at from about 5 to about 20 minutes. 
    
    
     EXAMPLES 
     In the following examples the catalyst is prepared by first flushing a 300 milliliter autoclave with nitrogen gas. The autoclave is equipped with a stirrer and cooling coils. Under a blanket of nitrogen, 6.0 grams zeolite support, 0.5 grams of commercial grade (COD) 2  Ni(O), and 90 mls of dry nitrogen purged decane are charged into the 300 milliliter autoclave under the nitrogen blanket. The autoclave was closed, pressured with nitrogen, vented, repressured with nitrogen to 500 psig and the mixture stirred for one hour at room temperature. 
     The oligomerization reaction was conducted by pressurizing the reactor with 500 psig of ethylene. In Examples 1-4, a vigorous reaction began as evidenced by a rise in temperature and rapid pressure consumption. Repressurization was continued manually thereafter. Then the reactor was cooled and vented. Table I shows the results obtained following this procedure. The maximum temperature of the oligomerization reaction, the time of the oligomerization reaction, ethylene pressure are all provided. Further, the particular support is also provided Ω-6 designating omega 6 zeolite and Ω-5 designating omega 5 zeolite and LZ-Y82 representing the type Y zeolites. Example 5 is a comparative example. 
     To facilitate analysis of the product the gas phase was vented and the liquid product mixture is analyzed by gas chromatography. 
     
                                           TABLE I__________________________________________________________________________                                PercentEx Max.    Support     Sel Sel  Sel  1-ButeneNo.   Temp.  Time      Wt. Grams            g. product                  Butene                      Hexenes                           Octenes                                in C.sub.4 s__________________________________________________________________________1  84° C.  20 min.      Ω-6            100.3  51%                       38%  11% 282  90  20  Ω-6            97.8  53  36   11   303  36  60  Ω-5            37.9  77  19   3    584  42  60  LZY-82            38.9  74  25   1    515  32  60  Silicalite            Trace Trace                      Trace                           --   --__________________________________________________________________________ 
    
     Examples 1-4 demonstrate the present invention. Example 5 is a comparative example provided to demonstrate the effect of using supports other than type Y or omega zeolites. Specifically, silicalite was employed as a support. The catalyst formed on this support showed very little activity particularly in comparison to the catalysts used in Examples 1-4. 
     The present invention can also be conducted using a continuous reactor wherein the catalyst is in an extruded form, held in a wire mesh basket. In such a reactor the ethylene which may be provided at low concentrations such as in the off gas of petroleum processing, is injected into the high-pressure reactor containing the solvent such as decane, the catalyst and a stirrer. Cooling may also be provided. A portion of the produced oligomers are retained in the solvent and and the remainder of the product and the unreacted gases are vented off the top. The reaction can be stopped periodically and the oligomer/solvent solution removed. Alternately, the oligomer/solvent can be continuously drained from the reactor and new solvent added. In this process, the catalyst is the same with the exception that the catalyst may include a binder such as silica to facilitate the formation of pellitized catalysts. Further the catalyst may be retained in a powder form and simply removed with the formed oligomer, separated and returned to the reaction vessel. 
     The reaction can also be conducted in the vapor phase by passing fuel gas containing about 20% ethylene in an inert carrier over the dry catalyst. The ethylene is preferably diluted with nitrogen . 
     Although the invention has been described with reference to specific details of certain illustrative embodiments, it is not intended that it shall be limited thereby except insofar as such details appear in the following claims.