OLIGOMERIZATION OF ETHYLENE IN METHANOL AND WATER

Abstract: A process for oligomerizing ethylene using a nickel ylide catalyst substituted with a sulfonato group wherein the oligomerization is carried out in the presence of methanol and water.

Description: The present invention relates to the use of nickel ylides to oligomerize ethylene in a solvent medium containing methanol. It is well known in the art to use a variety of catalysts to oligomerize ethylene to higher molecular weight olefins. The term "oligomerize" has been employed, and is employed herein to describe the conversion of lower olefins such as ethylene to olefinic products of higher molecular weight, e.g., to dimer, trimer, tetramer and the like. The reaction rate and product distribution obtained are highly dependent on the exact catalyst composition and the reaction conditions employed. Two such general classes of catalysts are the "Ziegler" types consisting of aluminum trialkyls and the "Ziegler-Natta" types consisting of aluminum alkyls or alkyl halides and titanium halides. Major disadvantages of aluminum alkyl catalysts are their highly reactive and pyrophoric nature and the fact that they must be used at relatively high temperatures, e.g., 200°C to 275°C and pressures, e.g., 13790 to 27580 kPa (2000 to 4000 psig). Although much milder reaction conditions are used when the aluminum alkyls are used in conjunction with titanium halides, product quality and ease of catalyst separation from products of both of these prior art types of catalysts are not as high as desired. An article by W. Keim, F. H. Kowaldt, R. Goddard and C. Kruger entitled "Novel Coordination of (Benzoylmethylene) triphenylphosphorane in a Nickel Oligomerization Catalyst", in Angew. Chem. Int. Ed. Engl. (1978) No. 6, page 466, discloses that a nickel ylide having the structure: converts ethylene into alpha olefins or polyethylene. According to the present invention, a process is provided for oligomerizing ethylene to normal alpha olefins, that is, straight chain alpha olefins, which process comprises reacting ethylene in a methanol-water mixture containing 0.5 to 20 wt % water under oligomerization conditions in contact with a nickel ylide defined by the following formula: wherein R₁, R₂, R₃, R₄, R₅, R₆, R₇ and R₈ are either alike or different members selected from the group consisting of hydrogen, alkyl radicals having from 1 to 24 carbon atoms, aryl radicals having from 6 to 20 carbon atoms, alkenyl radicals having from 2 to 30 carbon atoms, cycloalkyl radicals having from 3 to 40 carbon atoms, aralkyl and alkaryl radicals having from 6 to 40 carbon atoms, halogen radicals, hydroxyl, alkoxy and aryloxy groups, and hydrocarbyl groups carrying halogen, hydroxyl, alkoxy or aryloxy groups, provided that at least one of each R₁ to R₈ radicals is a sulfonato group or an alkyl, aryl, alkenyl, cycloalkyl, aralkyl or alkaryl carrying a sulfonato group, M is sulfur or oxygen, E is phosphorus, arsenic, antimony or nitrogen and F is phosphorus, arsenic or antimony, to obtain a reaction product containing (A) a methanol-water phase having dissolved therein said nickel ylide and (B) an alpha olefin phase and then separating said phases from each other to recover said alpha olefin phase. Preferred amounts of water used in the process of the present invention are between 2 and 15 wt % more preferably between 7 and 13 wt %. The weight percent water is calculated as a percent of the combined methanol and water which is fed to the reaction zone in the oligomerization process of the present invention. Among other factors, the present invention is based on our finding that the addition of water to the reaction zone does not ruin the catalyst or its activity, particularly when the wt % water is controlled to below about 20 wt % of the combined methanol-water solvent. In addition, we have found that the water has an unexpectedly marked affect in improving the phase separation of the catalyst-rich phase from the product olefin-rich phase. Also we have found that the inclusion of water in the reaction zone results in a surprising increase in the purity of the alpha olefin product, and in a shift in product distribution toward lighter alpha olefin product. Typically, in the process of the present invention, the ethylene, methanol, water and nickel ylide catalyst are fed to a reaction zone or a reactor, such as a continuous stirred tank reactor, wherein the oligomerization reaction is controlled by reaction conditions such as temperature, pressure, residence time and catalyst concentration. The reaction effluent is passed to a separation zone wherein a methanol-water catalyst phase is separated for recycle to the reaction zone, also ethylene is separated for recycle, and product alpha olefins are separated. The separation may be carried out in two steps. First, a gas/liquid separation wherein recycle ethylene gas is removed. In a second step, the liquid from the first step may be passed to a liquid/liquid separator where a methanol, water and catalyst phase are separated as a lower liquid phase for recycle to the reaction zone and an organic liquid phase is separated as a top or lighter phase. The organic phase, consisting of minor amounts of ethylene, but mainly of the product normal alpha olefins, is preferably passed to a recovery zone to recover additional ethylene for recycle to the reaction zone and to recover the product normal alpha olefins. The product alpha olefins will typically be primarily in the C₄ to C₃₀ range, but may range from C₄ to as high as C₁₀₀. The catalysts used in the reaction zone are the nickel ylides as set forth in our prior patents, particularly including U.S. Patent No. 4,310,716 and U.S Patent No. 4,293,502, the disclosures of which patents are incorporated herein by reference. The same catalysts which are preferred in those cited patents are preferred herein. Likewise, preferred catalyst preparation procedures including methods of including a sulfonate group in the catalyst, and preferred reaction conditions such as temperatures, pressures, catalyst concentration and residence time, are as described in the cited patents, especially U.S. Patent No. 4,310,716 and U.S Patent No. 4,293,502. Such preferred reaction conditions include a temperature between 20°C and 100°C, oligomerization reaction zone residence time between 10 minutes and 24 hours, and pressures between 69 and 20685 kPa (10 and 3000 psig), more preferably between 689 and 13790 kPa (100 and 2000 psig). The drawing is a graph showing the effect of 10 wt % water on product C₁₄ alpha olefin. EXAMPLES Ethylene oligomerization reactions were carried out using a sulfonated nickel ylide (SUNY) catalyst. The SUNY catalyst used was Compound 9 of U.S. Patent No. 4,310,716 which has the following structure: The SUNY catalyst was prepared in accordance with the Example III preparation of U.S. Patent No. 4,310,716. Results for experiments at various water levels are set forth in Table I below. The experiments were performed using freshly prepared solutions of SUNY catalyst in methanol or a methanol/water mixture. Dilution of a 1000 mg/kg (ppm) water standard in methanol or gravimetric mixing of anhydrous methanol in distilled water gave the desired mixtures. The nominal concentration of SUNY catalyst was 2.5 x 10⁻³ grain moles per liter of the methanol or methanol-water mixture. Ethylene was chemically scrubbed to remove oxygen using a copper on alumina catalyst/adsorbent giving less than 1 ppm oxygen content in the feed ethylene. The experiments used the same reaction conditions, namely 50°C, 3447 kPa (500 psig) and 2 hours residence time. Results for runs at various amounts of water in methanol are given in Table I below. Example No. Water, (ppm) mg/kg Catalyst Activity 1 15 7971 2 452 7658 3 52979 7500 4 60115 6203 5 105904 5148 6 105944 4834 Table I shows that water was found not to ruin the catalyst activity when the water is used in amounts up to about 10.5% water. Our further data indicates the catalyst activity would likely not drop off too steeply up to water concentrations of about 20 wt %. The Activity column in Table I relates to moles of ethylene reacted per moles of SUNY catalyst in the reaction zone. Table II below is a summary of data on product distribution by weight percent from runs including those in Table I. The Table II data illustrates a large shift in product distribution, toward lighter oligomers, which we discovered occurred using water in the reaction system. Example No. Water, % C₆ C₈ C₁₀ C₁₂ C₁₄ C₁₆ C₁₈ C₂₀+ 7 ∼0 15.18 18.39 16.53 13.54 10.29 7.67 5.28 13.12 8 5 18.70 19.75 17.17 13.21 9.75 6.94 4.72 9.76 9 10 24.26 23.35 18.25 12.48 8.40 5.26 3.04 4.96 Runs were also made with oxygen injected into the reaction zone. We discovered that, unlike water, oxygen was ruinous to the catalyst activity even at low mg/kg (ppm) levels. The oxygen mg/kg (ppm) amounts are based on the parts by weight of ethylene fed to the reaction zone. The data from several runs where oxygen was injected are summarized in Table III below. Example No. Oxygen, (ppm) mg/kg Catalyst Activity 10 <1 8124 11 10 6607 12 10 7040 13 20 6421 14 20 5146 15 30 4826 16 30 4493 17 40 2609 18 40 3385 19 50 699 20 50 1044 In our initial work, careful measures were taken to exclude water from the reaction zone, such as the purchase of anhydrous methanol and the distillation of the methanol in the presence of sodium to reduce water to a very low level. After we discovered that water was not ruinous to catalyst activity, we explored other variables, such as the effect of pressure. We found surprisingly clean separation of unreacted ethylene from product alpha olefin, even at pressures as high as 3447 kPa (500 psig). Table IV below lists results of these runs in Examples 21, 22, 23 and 24. The catalyst solution consisted of the SUNY catalyst (at a concentration of 2.5 x 10⁻³ gram moles per liter of methanol-water solution fed to the reaction zone), methanol and water. Example No. 21 22 23 24 Run Conditions Reactor Temperature, °C 50 50 50 40 Reactor Pressure, (psig) kPa (700) 4826 (600) 4137 (600) 4137 (700) 4826 Separator Pressure, (psig) kPa (25) 172 (200) 1379 (500) 3447 (500-300) 3447-2068 Catalyst Concentration, Gm/L Initial Charge 2.0 2.0 2.0 2.0 Continuous Addition - - - 20.0 Water Content of Catalyst Solution, Wt % 10.0 10.0 10.0 10.0 Experimental Results Overall Length of Run, Hr 21 16 16 40 Catalyst Productivity, Gm Product/Gm Catalyst 836 N/A N/A 1127-770 Product Purity, Wt % Alpha-C₁₄ 94.4 91.1 91.6 92.7-94.6 Product Distribution, Epsilon 0.49 0.71 0.56 0.42-0.31 Referring in more detail now to the drawing (graph), the ordinate or "Y" axis relates to product purity, in particular C₁₄ linear alpha olefin purity. Impurities in the alpha olefin include branch chain olefins and internal (as opposed to alpha) olefins. The abscissa or "X" axis relates to the product distribution or "epsilon" value. Epsilon is a measure of the extent of reaction and is effectively a ratio of the chain termination rate to the growth rate. It is directly related to the mole fraction, X, of a given carbon number olefin by the following equation: where r is the number of ethylene units. The graph shows the data points, in terms of C₁₄ alpha olefin product purity and product distribution, for a number of oligomerization runs made with the above-described SUNY catalyst both with no water (only methanol as a solvent) in the reaction zone and with 10% water in the methanol solvent. As can be noted from the graph, approximately 2% greater C₁₄ alpha olefin product purity was achieved with 10% water versus that achieved without water in the methanol. Thus the runs represented by three data points at .57 epsilon can be considered. These runs were made at essentially identical conditions except that the run indicated by X had 10% water in the methanol solvent whereas the two runs indicated by the dots had no water in the methanol. The X data point shows about 90.8% purity for the C₁₄ alpha olefin whereas the dot data points show about 87.5 to 88% purity for the C₁₄ alpha olefin. The run conditions for the various epsilon values shown on the graph were varied similar to the conditions shown in Examples 21 through 24, except that for the runs indicated by dots, no water was included in the methanol.

Claims: A process for oligomerizing ethylene to normal alpha olefins and recovering said olefins from the reaction product which comprises reacting ethylene in a methanol-water mixture containing 0.5 to 20 wt % water under oligomerization conditions in contact with a nickel ylide defined by the following formula: wherein R₁, R₂, R₃, R₄, R₅, R₆, R₇ and R₈ are either alike or different members selected from the group consisting of hydrogen, alkyl radicals having from 1 to 24 carbon atoms, aryl radicals having from 6 to 20 carbon atoms, alkenyl radicals having from 2 to 30 carbon atoms, cycloalkyl radicals having from 3 to 40 carbon atoms, aralkyl and alkaryl radicals having from 6 to 40 carbon atoms, halogen radicals, hydroxyl, alkoxy and aryloxy groups, and hydrocarbyl groups carrying halogen, hydroxyl, alkoxy or aryloxy groups, provided that at least one of each R₁ to R₈ radicals is a sulfonato group or an alkyl, aryl, alkenyl, cycloalkyl, aralkyl or alkaryl carrying a sulfonato group, M is sulfur or oxygen, E is phosphorus, arsenic, antimony or nitrogen and F is phosphorus, arsenic or antimony, to obtain a reaction product containing (A) a methanol-water phase having dissolved therein said nickel ylide and (B) an alpha olefin phase and then separating said phases from each other to recover said alpha olefin phase. A process as defined in Claim 1 wherein the percent water is 2 to 15. A process a defined in Claim 1 wherein the percent water is 7 to 13. A process a defined in Claim 1 wherein the sulfonato group is in R₄, R₅ and/or R₆ and at least one of R₄, R₅ and R₆ is aryl. A process as defined in Claim 1 wherein the sulfonato group is in R₁, R₂ and or R₃. A process as defined in Claim 1 wherein R₇ comprises a sulfonato group. A process as defined in Claim 1 wherein E and F are both phosphorus and M is oxygen. A process as defined in Claim 4 wherein E and F are both phosphorus and M is oxygen. A process as defined in Claim 5 wherein E and F are both phosphorus and M is oxygen. A process as defined in Claim 6 wherein E and F are both phosphorus and M is oxygen. A process as defined in Claim 8 wherein each of R₄, R₅, and R₆ is phenyl, one of which is substituted with a sulfonato group. A process as defined in Claim 11 wherein each of R₁, R₂, R₃ and R₈ is phenyl and R₇ is hydrogen. A process as defined in Claim 9 wherein each of R₁, R₂ and R₃ is phenyl, one of which is substituted with a sulfonato group. A process as defined in Claim 13 wherein each of R₄, R₅, R₆ and R₈ is phenyl and R₇ is hydrogen. A process as defined in Claim 10 wherein each of R₁, R₂, R₃, R₄, R₅, R₆ and R₈ is phenyl and R₇ is a sulfonato group. A process as defined in Claim 15 wherein said ylide is in the form of its sodium salt. A process as defined in Claim 1 wherein said ethylene and said nickel ylide are contacted at a temperature of from about -20°C to about 200°C for about 1 minute to 72 hours. A process as defined in Claim 1 wherein said ethylene and said nickel ylide are contacted at a temperature of from about 20°C to about 100°C for about 10 minutes to about 24 hours. A process as defined in Claim 15 wherein said ethylene and said nickel ylide are contacted at a temperature of from about -20°C to about 200°C for about 1 minute to 72 hours. A process as defined in Claim 15 wherein said ethylene and said nickel ylide are contacted at a temperature of from about 20°C to about 100°C for about 10 minutes to about 24 hours. A process as defined in Claim 16 wherein said ethylene and said nickel ylide are contacted at a temperature of from about -20°C to about 200°C for about 1 minute to 72 hours. A process as defined in Claim 16 wherein said ethylene and said nickel ylide are contacted at a temperature of from about 20°C to about 100°C for about 10 minutes to about 24 hours. A process as defined in Claim 1 wherein the ethylene pressure is maintained in the range of about 689 kPa (100) to about 13790 kPa (2000 psig) throughout the reaction. A process as defined in Claim 1 wherein the ethylene pressure is maintained in the range of about 2413 kPa (350) to about 5860 kPa (850 psig) throughout the reaction. A process as defined in Claim 16 wherein the ethylene pressure is maintained in the range of about 689 kPa (100) to about 13790 kPa (2000 psig) throughout the reaction. A process as defined in Claim 1 wherein the methanol-water phase is recycled to the reaction zone for use therein. A process as defined in Claim 13 wherein the methanol-water phase is recycled to the reaction zone for use therein. A process as defined in Claim 14 wherein the methanol-water phase is recycled to the reaction zone for use therein.

Inventors: BEACH, DAVID L., HARRISON, JAMES S.
Applicants: CHEVRON RESEARCH AND TECHNOLOGY COMPANY
Application year: 1987
Main classification: C07C2
IPC codes: C07C1, B01J23, B01J31, C07C67, C07B61, C07C2, C08F10, C08F4, C07C11, C08F8