GB2154603A - Catalytic oligomerization of liquid olefins - Google Patents

Abstract

A process for oligomerizing olefins in the liquid phase uses a nickel-containing silicaceous crystalline molecular sieve catalyst of intermediate pore size in the hydrogen form. The molecular sieve can be HZSM-5, HZSM-11, silicalite, or CZM. The catalyst may also contain zinc.

Description

SPECIFICATION Catalytic oligomerization of liquid olefins This invention relates to catalytic olefin oligomerization and is concerned with the oligomerization of olefins in the liquid phase with a nickel-containing silicaceous crystalline molecular sieve catalyst.

In accordance with the present invention, there is provided a process for oligomerizing alkenes comprising contacting a C2 to C20 olefin or a mixture of two or more thereof in the liquid phase with at least one nickel-containing silicaceous crystalline molecular sieve of intermediate pore size (as hereinafter defined) in the hydrogen form selected from HZSM-5, HZSM-1 1, crystalline admixtures of HZSM-5 and HZSM-1 1, silicalite, an RE 29,948 organosilicate (as hereinafter defined) and CZM, at a temperature in the range from 450to 450"F (7 to 232"C) to produce an effluent comprising oligomerized alkene.

It has been found that the process of the invention provides selective conversion of the olefin feed to oligomer products. The process effects the conversion of the olefin feed to dimer, trimer, tetramer, etc.

products with high selectivity. The product of the reaction thus contains primarilyolefin oligomer and little or no light cracked products, paraffins, etc.

The high selectivity is in part due to the surprisingly high oligomerization activity of the catalyst employed in the process, which permits high conversion at low temperatures where cracking reactions are minimized.

The oligomers which are the products of the process of this invention are medium to heavy olefins which are highly useful for both fuels and chemicals. These include olefinic gasoline, such as from propylene dimerization, and extremely high quality midbarrel fuels, such as jet fuel. Higher molecular weight compounds can be used without further reaction as components of functional fluids such as lubricants, as viscosity index improvers in lubricants, as hydraulic fluids, as transmission fluids, and as insulating oils, e.g., in transformers to replace PCB containing oils.These olefins can also undergo chemical reactions to produce surfactants which in turn can be used as additives to improve the operating characteristics of the compositions to which they are added (e.g., lubricating oils) or can be used as primary surfactants-in highly important activities such as enhanced oil recovery or as detergents. Among the most used surfactants prepared from the heavy olefins are alkyl sulfonates and alkyl aryl sulfonates.

A significant feature of the present process is the liquid phase contacting of the olefin feed and the nickel-containing silicaceous crystalline molecular sieves. It will be appreciated that the pressures and temperatures employed must be sufficient to maintain the system in the liquid phase. As is known to those in the art, the pressure will be a function of the number of carbon atoms of the feed olefin and the temperature.

The oligomerization process of the invention may be carried out as a batch type, semi-continuous or continuous operation utilizing a fixed or moving bed catalyst system.

The feeds used in the process of the invention contain alkenes which are liquids under the conditions in the oligomerization reaction zone. Under standard operating procedures it is normal both to know the chemical composition of feedstocks being introduced into a reaction zone and to set and control the temperature and pressure in the reaction zone. Once the chemical composition of a feedstock is known, the temperature and hydrocarbon partial pressures which will maintain all or part of the feed as liquids can be determined using standard tables or routine calculations. Conversely, once the desired temperature and pressure to be used in the reaction zone are set, it becomes a matter of routine to determine what feeds and feed components would or would not be liquids in the reactor. These calculations involve using critical temperatures and pressures.Critical temperatures and pressures for pure organic compounds can be found in standard reference works such as CRC Handbook of Chemistry and Physics, International Critical Tables, Handbook of Tables forApplied Engineering Science, and Kudchaker, Alani, and Zwolinski, Chemical Reviews 68, 659 (1968). The critical temperature for a pure compound is that temperature above which the compound cannot be liquefied regardless of pressure. The critical pressure is the vapor pressure of the pure compound at its critical temperature.These points for several pure alkenes are listed below: TCOC 5F} P,-atm lbarl ethene 9.21 ( 48.6 ) 49.66 (50.3) propene 91.8 (197.2 ) 45.6 (46.2) 1-butene 146.4 (295.5 ) 39.7 (40.2) 1-pentene 191.59 (376.9 ) 40 (40.5) iso-2-pentene 203 (397) 36 (36.5) 1-hexene 230.83 (447.49) 30.8 (31.2) 1-heptene 264.08 (507.34) 27.8 (28.2) 1-octene 293.4 (560.1 ) 25.6 (25.9) 1-decene 342 (648) 22.4 (22.7) It will be appreciated that at temperatures above about 205"C (401"F), pure C5 and lower alkenes must be gaseous, while pure C6 and higher alkenes can still be liquefied by applying pressure.Similarly, above about 2750C (527 F) pure C6 and higher alkenes can be maintained in the liquid state, while pure C7 and lower alkenes must be gaseous.

Typical feeds are mixtures of compounds. But even so, once the chemical composition of the feed is known, the critical temperature and pressure of the mixture can be determined from the ratios of the chemicals and the critical points of the pure compounds. See for example, the methods of Kay and Edmister in Perry's Chemical Engineers Handbook, 4th Edition, pages 3-214,3-215 (McGraw Hill, 1963).

Of course, the only constraint on the alkenes present in the feed and which are to react in the oligomerization reaction zone is that these alkenes be liquids under the conditions in the reaction zone (the conditions include a temperature of less than about 450"F (232"C)). The chemical composition of the alkenes can be varied to obtain any desired reaction mixture or product mix, so long as at least some of the alkene components of the feed are liquid.

The alkene chains can be branched. And, even though the nickel-containing silicaceous crystalline molecular sieve catalysts used in this invention are intermediate pore size molecular sieves, alkenes having quaternary carbons (two branches on the same carbon atom) can be used. But where quaternary carbons are present, it is preferred that the branches are methyl.

The preferred alkenes are straight chain, or n-alkenes, and the preferred n-alkenes are 1-alkenes. The alkenes have from 2 to 20 carbon atoms, and more preferably have from 2 to 6 carbon atoms.

One of the surprising discoveries of this invention is that under certain reaction conditions, longer chain alkenes can be polymerized instead of being cracked to short chain compounds. Additionally, the oligomers produced from long n-1-alkenes are very highly desirable for use as lubricants. The oligomers have surprisingly little branching so they have very high viscosity indices, yet they have enough branching to have very low pour points.

The feed alkenes can be prepared from any source by standard methods. Sources of such olefins can include FCC offgas, coker offgas, syngas (by use of CO reduction catalysts), low pressure, nonhydrogenative zeolite dewaxing, alkanols (using high silica zeolites), and dewaxing with crystalline silica polymorphs.

Highly suitable n-l -alkene feeds, especially for preparing lubricating oil basestocks, can be obtained by thermal cracking of hydrocarbonaceous compositions which contain normal paraffins or by Ziegler polymerization of ethene.

Often, suitable feeds are prepared from lower alkenes which themselves are polymerized. Such feeds include polymer gasoline from bulk H3PO4 polymerization, and propylene dimer, and other olefinic polymers in the C4-C20 range prepared by processes known to the art.

The nickel-containing silicaceous crystalline molecular sieves used in this invention are of intermediate pore size. By "intermediate pore size", as used herein, is meant an effective pore aperture in the range of from 5 to 6.5 Angstroms when the molecular sieve is in the H-form. Molecular sieves having pore apertures in this range tend to have unique molecular sieving characteristics. Unlike small pore zeolites such as erionite and chabazite, they will allow hydrocarbons having some branching into the molecular sieve void spaces. Unlike larger pore zeolites such as the faujasites and mordenites, they can differentiate between n-alkanes and slightly branched alkanes on the one hand and larger branched alkanes having, for example, quaternary carbon atoms.

The effective pore size of the molecuar sieves can be measured using standard adsorption techniques and hydrocarbonaceous compounds of known minimum kinetic diameters. See Breck, Zeolfte Molecular Sieves, 1974 (especially Chapter 8) and Anderson et al, J. Catalysis 58, 114(1979).

Intermediate pore size molecular sieves in the H-form will typically admit molecules having kinetic diameters of 5.0 to 6.5 Angstroms with little hindrance. Examples of such compounds (and their kinetic diameters in Angstroms) are: n-hexane (4.3), 3-methylpentane (5.5), benzene (5.85), and toluene (5.8).

Compounds having kinetic diameters of about 6 to 6.5 Angstroms can be admitted into the pores, depending on the particular sieve, but do not penetrate as quickly and in some cases are effectively excluded.

Compounds having kinetic diameters in the range of 6 to 6.5 Angstroms include: cyclohexane (6.0), 2,3-dimethylbutane (6.1), m-xylene (6.1), and 1,2,3,4-tetramethylbenzene (6.4). Generally, compounds having kinetic diameters of greater than about 6.5 Angstroms do not penetrate the pore apertures and thus are not absorbed into the interior of the molecular sieve lattice. Examples of such larger compounds include: o-xylene (6.8), hexamethylbenzene (7.1),1,3,5-trimethylbenzene (7.5), (7.5), and tributylamine (8.1).

The preferred effective pore size range is from 5.3 to 6.2. Angstroms.

In performing adsorption measurements to determine pore size, standard techniques are used. It is convenient to consider a particular molecule as excluded if it does not reach at least 95% of its equilibrium adsorption value on the zeolite in less than about 10 minutes (p/po=0.5; 25"C).

Nickel-containing HZSM-5 is described in U.S. Patent Nos. 3,702,886 and 3,770,614.

HZSM-1 1 is described in U.S. 3,709,979. "Crystalline admixtures" of ZSM-5 and ZSM-11 also exist, which are thought to be the result of faults occurring within the crystal or crystallite area during the synthesis of the zeolites. The "Crystalline admixtures" are themselves zeolites but have characteristics in common, in a uniform or nonuniform manner, to whatthe literature reports as distinct zeolites. Examples of crystalline admixtures of ZSM-5 and ZSM-11 are disclosed in U.S. 4,229,424. The crystalline admixtures are themselves intermediate pore size zeolites and are not to be confused with physical admixtures of zeolites in which distinct crystals or crystallites of different zeolites are physically present in the same catalyst composite or hydrothermal reaction mixture.

Silicalite is disclosed in U.S. 4,061,724; the "RE 28,948 organosilicates" are disclosed in U.S. Reissue Patent RE 29,948; and chromia silicates, CZM, are disclosed in UKApplication Serial No.2056961.

The so-called "RE 29,948 organosilicates" are defined in both this United States Re-issue Patent, and its original United States Patent 3,941,871 as a crystalline metal organosilicate having a composition, in its anhydrous state, in terms of mole ratios of oxides, as follows: 0.9 + 0.2 [xR2O + (l-x)M,,O]: < 0.005 A1203: > 1SiO2 where M is sodium, or sodium in combination with tin, calcium, nickel or zinc, n is the valence of the metal M, R is a tetraalkylammonium radical and xis a number greater than zero but not exceeding 1. Such organosilicates have an X-ray diffraction pattern characteristic of ZSM-5 type zeolites and Table 1 of the U.S.

specification shows the significant lines of the pattern. Table 1 includes some 16 lines for various interplanar spacings. The four main ones appear two be a very strong line for a spacing of 3.85 + 0.07A, and strong lines at 3.71 t 0.05A, 10.0 t 0.2A, and 11.1 + 0.2A.

The crystalline silica polymorphs, silicalite, and RE 29,948 organosilicates, and the chromia silicate, CZM are essentially alumina free.

"Essentially alumina free", as used herein, means that the product silica polymorph (or essentially alumina-free silicaceous crystalline molecular sieve) has a silica:alumina mole ratio of greater than 200:1, preferably greater than 500:1. The term "essentially alumina free" is used because it is difficult to prepare completely aluminum free reaction mixtures for synthesizing these materials. Especially when commercial silica sources are used, aluminum is almost always present to a greater or lesser degree. The hydrothermal reaction mixtures from which the essentially alumina free crystalline silicaceous molecular sieves are prepared can also be referred to as being substantially aluminum free.By this usage is meant that no aluminum is intentionally added to the reaction mixture, e.g., as an alumina or aluminate reagent, and that to the extent aluminum is present, it occurs only as a contaminant in the reagents.

The most preferred molecular sieve is the zeolite Ni-HZSM-5 and Ni containing hydrogen form of silicalite.

Of course, these and the other molecular sieves can be used in physical admixtures.

When synthesized in the alkali metal form, the zeolites may be conveniently converted to the hydrogen form by well known ion exchange reactions, for example, by intermediate formation of the ammonium form as a result of ammonium ion exchange and calcination of the ammonium form to yield the hydrogen form, as disclosed in U.S. Patent No. 4,211,640, or by treatment with an acid such as hydrochloric acid as disclosed in U.S. Patent No. 3,702,886.

Nickel is incorporated into these silicaceous crystalline molecular sieves according to techniques well known in the art such as impregnation and cation exchange. For example, typical ion exhange techniques would be to contact the hydrogen form of the particular sieve with an aqueous solution of a nickel salt.

Although a wide variety of salts can be employed, particular preference is given to chlorides, nitrates and su Ifates. The amount of nickel in the zeolites range from 0.5% to 10% by weight and preferably from 1 % to 5% by weight.

Representative ion exchange techniques are disclosed in a wide variety of patents including U.S. Patent Nos. 3,140,249; 3,140,251; 3,960,978 and 3,140,253.

Following contact with the salt solution, the zeolites are preferably washed with water and dried at a temperature ranging from 1 50"F (65"C) to 500"F (260"C) and thereafter heated in air at temperatures ranging from about 500"F (260"C) to 1000"F (538"C) for periods of time ranging from 1 to 48 hours or more.

The nickel-containing silicaceous crystalline molecular sieve catalysts can be made substantially more stable for oligomerization by including from about 0.2% to 3% by weight and preferably 0.5% to 2% by weight of the Group IIB metals zinc or cadmium, preferably zinc. A primary characteristic of these substitutents is that they are weak bases, and are not easily reduced. These metals can be incorporated into the catalysts using standard impregnation, ion exchange, etc., techniques. Strongly basic metals such as the alkali metals are unsatisfactory as they poison substantially all of the polymerization sites on the zeolite. For this reason, the alkali metal content of the zeolite is less than 1%, preferably less than 0.1%, and most preferably less than 0.01%.The feed should be low in water, i.e., less than 100 ppm, more preferably less than 10 ppm, in sulfur, i.e., less than 100 ppm and preferably less than 10 ppm, in diolefins, i.e., less than 0.5%, preferably less than 0.05% and most preferably less than 0.01%, and especially in nitrogen, i.e., less than 5 ppm, preferably less than 1 ppm and most preferably less than 0.2 ppm.

The polymerization processes of the present invention are surprisingly more efficient with small crystallite sieve particles than with larger crystalline particles. Preferably, the molecular sieve crystals or crystallites are less than about 10 microns, more preferably less than about 1 micron, and most preferably less than about 0.1 micron in the largest dimension. Methods for making molecular sieve crystals in different physical size ranges are known to the art.

The molecular sieves can be composited with inorganic matrix materials, or they can be used with an organic binder. It is preferred to use an inorganic matrix since the molecular sieves, because of their large internal pore volumes, tend to be fragile, and to be subject to physical collapse and attrition during normal loading and unloading of the reaction zones as well as during the oligomerization processes. Where an inorganic matrix is used, it is highly preferred that the matrix be substantially free of hydrocarbon conversion activity. It will be appreciated that if an inorganic matrix having hydrogen transfer activity is used, a significant portion of the oligomers which are produced by the molecular sieve may be converted to paraffins and aromatics and to a large degree the benefits of the invention wil be lost.

The reaction conditions under which the oligomerization reactions take place include hydrocarbon partial pressures sufficient to maintain the desired alkene reactants in the liquid state in the reaction zone. Of course, the largerthe alkene molecules, the lower the pressure required to maintain the liquid state at a given temperature. As described above, the operating pressure is intimately related to the chemical composition of the feed, but can be readily determined. Thus, the required hydrocarbon partial pressure can range from 31 bar at 450"F (232"C) for a pure n-1 -hexene feed to about atmospheric pressure for a n-1 -Cas-C20 alkene mixture.In the process of this invention, both reactant and product are liquids under the conditions in the reaction zone, thus leading to a relatively high residence time of each molecule in the catalyst.

The reaction zone is typically operated below about 450"F (232"C). Above that temperature not only significant cracking of reactants and loss of oligomer product take place, but also significant hydrogen transfer reactions causing loss of olefinic oligomers to paraffins and aromatics take place. An oligomerization temperature in the range from 90into 350"F(32 to 177"C) is preferred. Liquid hourly space velocities can range from 0.05 to 20, preferably from 0.1 to about 4.

The reaction zone will generally have a pressure in the range from 50 to 1600 psig (4.5 to 111 bar).

Once the effluent from the oligomerization reaction zone is recovered, a number of further processing steps can be performed.

If it is desired to use the long chain compounds which have been formed in middle distillate fuel such as jet or diesel or in lube oils as base stock, the alkene oligomers are preferably hydrogenated.

All or part of the effluent can be contacted with the molecular sieve catalyst in further reaction zones to further react unreacted alkenes and alkene oligomers with themselves and each other to form still longer chain materials. Of course, the longer the carbon chain, the more susceptible the compound is to being cracked. Therefore, where successive oligomerization zones are used, the conditions in each zone must not be so severe as to crack the oligomers. Operating with oligomerization zones in series can also make process control of the exothermicoligomerization reactions much easier.

One particularly desirable method of operation is to separate unreacted alkenes present in the effluent from the alkene oligomers present in the effluent and then to recycle the unreacted alkenes back into the feed.

In the accompanying drawings, Figure 1 is a graph showing the conversion of propylene to higher molecular weight products as a function of time at 130"F (540C), 1600 psig (111 bar) and 0.5 LHSV for two different catalysts; Figure 2 is a graph showing the carbon number selectivity for oligomerizing propylene at 130"F (54"C), 1600 psig (111 bar) and 0.5 LHSV for two different catalysts; Figure 3 is a graph showing a plot of temperature for 90% conversion of propylene to C5+ over Ni-Zn-HZSM-5 catalyst versus time under the conditions shown; Figure 4 is a graph showing a plot of temperature for 70% conversion of C6-Cg gasoline feed to higher boiling product versus time over Ni-Zn-HZSM-5 and Zn-HZSM-5 catalysts under the conditions shown.

Figure 5 is a gas chromatogram of the product of Example 19; and Figure 6 is a graph showing a plot of temperature for 70% conversion of C6-Cg gasoline feed to higher boiling product versus time over Ni-Zn-HZSM-5 under the conditions shown.

The following Examples illustrate the preparation of molecular sieves and their use in accordance with the invention.

EXAMPLES Example 1 HZSM-5 zeolite of 80 SiO2/AI203 mole ratio was mixed with peptized Catapal alumina at a 50/50 sieve/alumina weight ratio, extruded through a 1/16" (1.6 mm) die, dried overnight at 300"F (149"C) under N2, then calcined in air for 8 hours at 8500F (454"C). The catalyst was exchanged five times with a 1% aqueous ammonium acetate solution, then washed with water to give a final Na level of 100 ppm.

Example 2 The catalyst of Example 1 was impregnated by the porefill method with 1% Zn using an aqueous solution of zinc nitrate, then dried and calcined as in Example 1.

Example 3 The catalyst of Example 1 was exchanged with a 1% aqueous nickel acetate solution at 180"F (820C) for five hours, washed with water, then dried and calcined as in Example 1. The Ni content of the calcined catalyst was3wt%.

Example 4 The catalyst of Example 3 was impregnated with 1% Zn, dried, and calcined as in Example 1.

Example 5 The catalyst of Example 2 (Zn-HZSM-5) was tested for conversion of propylene to higher molecular weight products at 130"F (54"C), 1600 psig (111 bar), and 0.5 LHSV. At 40 hours on stream, conversion to C5 f was less than 20 wt % (Figure 1), with 32 wt % selectivity to dimer (Figure 2).

The propylene dimer distribution is given in Table I.

TABLE I C6 Olefin Composition From Propylene Oligomerization C6 Olefin Selectivity 4-m-2-C5= 14.6 3-,4-m-1-C5= 9.4 2-m-2-C5= 32.2 2-m-1-C5= 4.3 3-m-2-C5= 10.4 n-C6= 0.8 2,3-dm-C4= 28.3 Example 6 The catalyst of Example 4 (Ni-Zn-HZSM-5) was tested for propylene conversion at the same conditions as in Example 5. At 40 hours on stream, conversion to C5+ was over 98 wt % (Figure 1), with selectivity to dimer at 71 wt % (Figure 2). This shows the surprising benefit of Ni addition to HZSM-5 in terms of both activity and selectivity to dimer. The propylene dimer distribution is given in Table II.

TABLE li C6 Olefin Composition From Propylene Oligomerization C6 Olefin Selectivity 4-m-2-CS= 50.7 3-, 4-m-1-C5= 6.1 2-m-2-C5= 8.7 2-m-1-C5= 1.2 3-m-2-CS= 0.2 n-C6= 26.8 2,3-dm-C4= 6.3 Example 7 For comparison, a 5% Ni on amorphous SiO2-AI203 was prepared by pore-fill impregnation of a 40/60 SiO2-A12O3 cogel with an aqueous nickel acetate solution, drying at 3000F (149"C) overnight, then calcining in air for eight hours at 8500F (454"C). When tested for propylene conversion at the conditions of Example 5, conversion to C5+ at 40 hours on stream was 54 wt %, with 40 wt % selectivity to dimer.

Example 8 The catalyst of Example 3 (Ni-HZSM-5) was tested for propylene conversion at 1600 psig (111 bar) and 1.) LHSV. At 200 hours on stream, conversion to C5+ was 73 wt % at 120"F (49"C).

Example 9 The catalyst of Example 2 (Zn-HZSM-5) was tested for propylene conversion at 0 psig (1 bar), 5500F (288"C), and 2 LHSV under olefin gas phase conditions. After 90 hours on stream, conversion to C5+ was 80 wt %.

Example 10 The catalyst of Example 3 (Ni-HZSM-5) was tested for propylene conversion at the same conditions as in Example 9. At 70 hours on stream, conversion to C5+ was 30 wt %. This shows that the addition of Ni to HZSM-5 is only beneficial when oligomerization is carried out under substantially liquid phase conditions.

Example Ii The catalyst of Example 4 (Ni-Zn-HZSM-5) was tested for propylene conversion at 0.5 LHSV snf 16000 psig (111 bar). A plot of catalyst temperature for 90% conversion to C5+ versus time on stream is shown in Figure 3. At 430 hours on stream, the reactor pressure was reduced to 800 psig (56 bar). The catalyst operated 800 hours before requiring a temperature of 1800F (82"C) for 90% conversion to C5+. Product inspections are shown in Table Ill.

TABLE ill C5+ Product Inspections from Oligomerizing Propylene at 1000 psig (70 bar) and 0.5 LHSV Temperature "F 120 (49"C) Conversion to C5+, wt % 85 Gravity, API 74.0 Research Octane No., clear 94.0 Simulated TBP Distillation LV %, "F "C 10/20 136/139 58/59 30/50 141/154 60/68 70/90 161/283 721139 Paraffins,LV% 0 Olefins, LV% 100 Naphthenes, LV% 0 Aromatics, LV% 0 Examples 12-16 The catalyst of Example 1 was impregnated with transition metals known in the art to be active for promoting light olefin oligomerization. These include Co, Cu, Pd, V, and Cr. The results given in Table IV show these catalysts much less active than Ni-HZSM-5.

TABLE IV Conversion of Propylene to C5+ Products over Transition Metal- HZSM-5 Catalyst at 130-150'F (54-66'C), 0.5 LHSV, and 1600 psig (111 bar) Wt% Conversion Example Metal % Loading at40Hrs.

12 Co 2.4 12 13 Cu 0.5 < 5 14 Pd 2.5 < 10 15 V 1.6 < 10 16 Cr 5 < 5 6 Ni 3 98 Example 17 The catalyst of Example 2 (Zn-HZSM-5) was tested for conversion of an olefinic C6-Cg gasoline feed (Table V) to higher boiling product. The catalyst temperature for 70% conversion to 350 F+ (177'C+) as a function of time on stream at 800 psig (56 bar) and 0.5 LHSV is shown in Figure 4. The catalyst fouling rate at these conditions was about 0.17 F/hr (0.09 C/hr).

TABLE V Inspections of CrCg Olefinic Gasoline Gravity, API 69.8 Research Octane Number, Clear 95.5 D-86 Distillation, LV%, F "C 10/20 152/156 67/69 30/50 158/162 70/72 70/90 190/348 88/176 Paraffins, LV% 0 Olefins, LV% 99 Naphthenes, LV% o Aromatics, LV% 1 Example 18 The catalyst of Example 4 (Ni-Zn-HZSM-5) was tested with the same feed as in Example 17 and at the same pressure and LHSV.At 100 hours on stream, catalyst temperature was 260"F (127"C) (Figure 4), about 1 70'F (77'C) lower than needed with ZN-HZSM-6. Beyond 250 hours, the fouling rate was only < 0.04 F/hr ( < 0.02 C/hr), one-fourth or less than that for Zn-HZSM-5, showing the benefit of Ni addition to the catalyst with C6+ olefinic feeds. A gas chromatogram of the product is shown in Figure 5.

Example 19 The catalyst of Example 3 (Ni-HZSM-5) was tested with the same feed as in Example 17 and at the same pressure but at a higher feed rate (1 and 2 LHSV). Even at 2 LHSV, the fouling rate was only 0.10 F/hr (0.06 C/hr) (Figure 6), less than that for Zn-HZSM-5 at only 0.5 LHSV.

Example 20 A Zn-silicalite catalyst was prepared in the following manner. H-silicalite of 240 SiO2/AI203 mole ratio was mixed with peptized and neutralized Catapal alumina at a 67/33 sieve/alumina weight ratio, extruded through a 1/16"(1.6 mm) die, dried over night at 300 F (149"C) under N2, then calcined in air for 8 hours at 850"F (454 C). The catalyst was impregnated by the pore-fill method to 1 weight % Zn using an aqueous solution of Zn(NO3)2,then dried and calcined as done previously.

Example 21 The catalyst of Example 20 was impregnated to 3 weight % Ni by the pore-fill method using an aqueous soution of Ni(NO3)2.6H2O. The catalyst was dried overnight under N2 at 300 F (149 C), then calcined in air for 8 hours at 850 F (454 C).

Example 22 The Zn-silicalite catalyst of Example 20 was tested for converting propylene to higher molecular weight products at 150 F (66 C), 1000 psig (70 bar), and 0.5 LHSV. At 24 hours onstream conversion to C5+ was 3.2% with 38% selectivity to dimer.

Example 23 The Ni-Zn-silicalite catalyst of Example 21 was tested for converting propylene at the same conditions as in Example 22. At 40 hours onstream, conversion to C5+ was 72.7% with 77% selectivity to dimer.

Claims (16)

1. A process for oligomerizing alkenes which comprises contacting a feed comprising a C2 to C20 olefin or a mixture of two or more thereof in the liquid phase with at least one nickel-containing silicaceous crystalline molecular sieve of intermediate pore size (as hereinbefore defined) in the hydrogen form selected from HZSM-5, HZSM-1 1, crystalline admixtures of HZSMd and HZSM-1 1, silicalite, an RE 29,948 organosilicate (as hereinbefore defined) and CZM at a temperature in the range from 45"F to 450"F (7 to 232"C) to produce an effluent comprising oligomerized alkene.

2. A process according to Claim 1, wherein the nickel-containing silicaceous crystalline molecular sieve also contains zinc cation.

3. A process according to Claim 1 or 2, wherein said contacting is carried out at a LHSV in the range from 0.2 to 5.

4. A process according to Claim 1,2 or 3, wherein the contacting is effected under a pressure of from 50 to 1600 psig (4.5 to 111 bar).

5. A process of according to Claim 1, 2,3 or 4, wherein said nickel-containing silicaceous crystalline molecular sieve is HZSM-5.

6. A process according to Claim 1, 2, 3 or 4, wherein said nickel-containing silicaceous crystalline molecular sieve is HZSM-11.

7. A process according to Claim 1, 2,3 or 4, wherein said nickel-containing silicaceous crystalline molecular sieve is a crystalline or physical admixture of HZSM-5 and HZSM-11.

8. A process according to Claim 1, 2, 3 or 4, wherein said nickel-containing silicaceous crystalline molecular sieve is silicalite.

9. A process according to Claim 1,2,3 or 4, wherein said nickel-containing silicaceous crystalline molecular sieve is an RE 29,948 organosilicate.

10. A process according to Claim 1,2,3 or 4, wherein said nickel-containing silicaceous crystalline molecular sieve is CSM.

11. A process according to any preceding claim, wherein said feed comprises n-alkenes.

12. A process according to Claim 11, wherein said n-alkenes are 1 -alkenes.

13. A process according to any one of Claims 1 to 10, wherein said feed comprises branched chain alkenes and wherein the branches of said branched chain alkenes are methyl branches.

14. A process according to any preceding claim and further comprising the step of hydrogenating the oligomerized alkene of said effluent.

15. A process according to any one of Claims 1 to 13 and further comprising the steps of separating unreacted alkenes present in said effluent from oligomerized alkenes present in said effluent and recycling said unreacted alkenes into the feed for said contacting step.

16. A process in accordance with Claim 1 for oligomerizing alkenes, substantially as described in the foregoing Example 6,8, 11,18,19 or 23.