WO2006131308A1

WO2006131308A1 - Method for the oligomerization of olefins

Info

Publication number: WO2006131308A1
Application number: PCT/EP2006/005377
Authority: WO
Inventors: Thomas Heidemann; Andreas Brodhagen
Original assignee: Basf Aktiengesellschaft
Priority date: 2005-06-07
Filing date: 2006-06-06
Publication date: 2006-12-14
Also published as: DE102005026213A1

Abstract

The invention relates to a method for oligomerizing C2-C8 mono-olefins in the presence of an oligomerization catalyst. According to said method, a) the C2-C8 mono-olefins are contacted with at least one adsorbing agent in at least one adsorption zone in order to eliminate components that affect oligomerization, and b) the product discharged from step a) is oligomerized in at least one reaction zone. The inventive method is characterized in that the adsorbing agent contains at least one component which can be used as an oligomerization catalyst. The invention further relates to the use of an adsorbing agent containing nickel in an oxidized form in order to reduce the concentration of polyunsaturated hydrocarbons and/or impurities containing oxygen, nitrogen, sulfur, phosphorus, and/or halogen in a hydrocarbon mixture by contacting the hydrocarbon mixture with the adsorbing agent containing nickel in an oxidized form.

Description

Process for the oligomerization of olefins

The present invention relates to a process for the oligomerization of C ₂ -C ₈ monoolefins in the presence of an oligomerization catalyst, wherein the C ₂ -C ₈ monoolefins are brought into contact with an adsorbent to remove components which impair the oligomerization before it reacts in a catalytic Oligomerisieruπgsreaktion.

Mixtures of longer chain linear oligomers, e.g. B. with 8 or more carbon atoms, are of economic importance, since they are z. As suitable as diesel fuel components and as intermediates for the preparation of functionalized, predominantly linear hydrocarbons. So you get z. B. by hydroformylation and subsequent hydrogenation of the longer-chain linear olefin oligomers, the corresponding alcohols, which in turn are used inter alia as starting materials for detergents and as a plasticizer.

For use as plasticizer alcohols, a low degree of branching of the olefins is crucial. The degree of branching is described by the ISO index, which indicates the average number of methyl branches of the respective olefin fraction. To wear z. For example, in the case of a C ₈ fraction, the n-octenes have 0, methylheptenes have 1 and dimethylhexenes have 2 to the ISO index of the fraction. The lower the ISO index, the greater the linearity of the molecules in each fraction. Higher linearity generally results in higher hydroformylation yields and better properties of the plasticizers made therefrom.

The above-mentioned mixtures of relatively long-chain linear oligomers are in turn obtainable from olefin mixtures with predominantly linear short-chain starting olefins. Such hydrocarbon mixtures containing short chain olefins, e.g. B. containing 2 to 8 carbon atoms, are available on a large scale. So you get z. For example, in the workup of petroleum by steam cracking or fluidized catalyst cracking (FCC) a hydrocarbon mixture referred to as C _{4 cut} having a high total content of olefins, especially of olefins having 4 carbon atoms. Such C ₄ cuts are essentially mixtures of isomeric butenes and butanes and are suitable, if appropriate after prior separation of isobutene, especially for the preparation of relatively long-chain oligomers, in particular of octenes and dodecenes.

On an industrial scale, both homogeneous and heterogeneously catalyzed processes are used for the oligomerization. Due in part to the technically complicated separation of the catalyst from the reaction mixture in homogeneous catalysis, heterogeneous catalysis is to be preferred here. The known heterogeneous catalyst Systems are based essentially on nickel- and silicon-containing catalysts, which often additionally contain aluminum and / or other active components. Methods for preparing such catalysts and their use for the oligomerization of olefins are known and z. In DE 43 39 713 A1, WO 01/37989 A2, EP 0 272 970 A1, US Pat. No. 5,169,824, DE-A-2051 402, DD 273 055 A1 and US Pat. No. 5,113,034.

The mixtures of short-chain olefins, which can be obtained on a large scale, used for the oligomerization, such as. For example, C ₄ cuts often contain compounds which act as catalyst ore and deactivate the aforementioned oligomerization catalysts. These catalyst poisons include, for. As alkynes and polyunsaturated hydrocarbons such as butadiene, further oxygen-containing compounds such as alcohols, aldehydes, ketones and ethers, and nitrogen-containing, sulfur-containing and halogen-containing compounds. The presence of such catalyst poisons in the oligomerization leads over time to a decrease in catalyst activity, which is often irreversible.

Methods are known in the art for removing individual oligomerization-impairing components from a hydrocarbon mixture. Here, the hydrocarbon mixtures are usually brought into contact with more or less easily regenerable adsorbents.

It is Z. For example, it is known to remove sulfur compounds by alkali washing and nitrogen compounds by water washing from olefin-containing hydrocarbon mixtures used for oligomerization. However, this results in only a rough separation of the compounds in question.

DE-A-39 14 817 describes a process for the oligomerization of olefins on a heterogeneous nickel-containing fixed bed catalyst, wherein the hydrocarbon mixture to be used is passed before the oligomerization through a molecular sieve having a pore diameter of greater than 4 Angstroms to 15 Angstroms and the contained polyunsaturated hydrocarbons removed by selective hydrogenation. The molecular sieves used are natural and synthetic aluminum silicates, ie zeolites. However, the use of aluminum silicates for the adsorption of catalyst poison effective impurities from olefin mixtures for the catalytic oligomerization is associated with disadvantages. Thus, the surface of molecular sieves available for adsorption irreversibly decreases in the presence of water vapor. In addition, zeolites under thermal stress tend to form Lewis acidic groups which undesirably catalyze the oligomerization of olefins, e.g. B. a decrease in the selectivity, a broadening the molecular weight distribution or a high degree of branching (ISO index) of the obtained oligomers cause. Furthermore, describe z. For example, DE-A-20 57 269, EP 0 081 041 A1 and DE-A-1 568 542 disclose the removal of polyunsaturated olefins by selective catalytic hydrogenation to the corresponding monoolefins. Depending on the boundary conditions, a residual content of dienes of less than 50 ppm or less than 5 ppm can be achieved.

The process for the catalytic oligomerization of short-chain monoolefins described in DE 198 45 857 A1 uses an adsorbent which is selected from aluminum oxides, aluminum oxide-containing solids, aluminum phosphates, silicon dioxides, kieselguhr, titanium dioxides, zirconium dioxides, phosphates, carbonaceous adsorbents, polymer adsorbents and mixtures thereof.

However, the processes mentioned are only of limited use for the removal of compounds which act as catalyst poisons. On the one hand, many catalyst poisons already in trace amounts can reduce the lifetime of an oligomerization catalyst, on the other hand, the adsorbents used hitherto are not able to safely retain all potential catalyst poisons. Therefore, the known methods for the removal of catalyst poisons are generally not sufficient to win olefin suitable for the oligomerization olefin mixtures that allow good service life of the catalysts used.

Thus, even in the case of polyunsaturated olefins such as dienes, even contents as low as less than 50 ppm or less than 5 ppm can permanently lead to deactivation of the catalyst. A further depletion, z. B. to less than 1 ppm, is not feasible in practice by means of the above-mentioned selective hydrogenation, as this leads to a significant overhydration, d. H. lead to the formation of alkanes, and thus the loss of valuable feedstock.

It is an object of the present invention to provide a process for the catalytic oligomerization of C ₂ -C ₈ monoolefins, in which the olefin mixture used is brought into contact with an adsorbent which can be regenerated easily and substantially without decreasing the adsorption capacity, that the catalyst poisons contained therein are removed as far as possible before the oligomerization. In particular, the process of the invention should allow the most complete removal of polyunsaturated hydrocarbons. Surprisingly, it has been found that this object is achieved if the adsorbent used is a component which is capable of being used as an oligomerization catalyst.

The present invention therefore provides a process for the oligomerization of C ₂ -C ₈ monoolefins in the presence of an oligomerization catalyst in which

a) bringing the C ₂ -C ₈ monoolefins into contact with at least one adsorbent in at least one adsorption zone to remove components which impair the oligomerization, and

b) oligomerizing the effluent from step a) in at least one reaction zone,

characterized in that the adsorbent contains at least one component capable of being used as an oligomerization catalyst.

For the purposes of the present invention, an oligomerization catalyst is generally understood to mean a component which undergoes an oligomerization reaction of monoolefins, such as C ₂ -C ₈ -monoolefins, to form longer-chain monoolefins, eg. B. C ₈ -, Cio, Ci ₂ -Monoolefine or monoolefins having more than 12 carbon atoms, catalyze.

For the catalytic oligomerization of monoolefin-containing hydrocarbon mixtures, it is possible to use all customary processes known to the person skilled in the art, and in particular oligomerization catalysts, as described, for example, in US Pat. For example, in DE-A-43 39 713, WO 01/37989 A2, EP 0 272 970 A1, US Pat. No. 5,169,824, DE-A-2051 402, DD 273 055 A1 and US Pat. No. 5,113,034. The oligomerization catalysts described in this prior art generally have a proportion of nickel in oxidized form as the catalytically active component. Usually, the nickel in oxidized form is present as nickel oxide (NiO), optionally as nickel aluminosilicate. In principle, however, all catalysts useful for catalyzing oligomerization reactions of C ₂ -C ₈ monoolefins are suitable as oligomerization catalysts for the process according to the invention.

Components which can be used as oligomerization catalyst generally have a content of nickel in oxidized form, calculated as NiO, of at least 0.5% by weight and in particular in the range from 0.5 to 90% by weight, especially in the range from 0, 5 to 80% by weight, more particularly in the range of 2 to 70% by weight, more particularly in the range of 10 to 70% by weight, and more particularly in the range of 40 to 60% by weight, based on the total weight of the oligomerization catalyst. The oligomerization catalysts can be supported or used in the form of unsupported catalysts. Suitable support materials on which the oligomerization catalysts may be applied or with which they may be present are described below in connection with support materials for the adsorbents to be used according to the invention. The support materials described there are in principle also useful for the oligomerization catalysts to be used according to the invention.

The components which can be used as oligomerization catalyst may further comprise one or more further metal oxides as active components and / or as support materials. These include in particular TiO ₂ , ZrO ₂ , SiO ₂ , Al ₂ O ₃ , Ga ₂ O ₃ , In ₂ O ₃ and the mixed oxides and mixtures thereof. In particular, an oligomerization catalyst is used which has a content of TiO ₂ and / or ZrO ₂ in the range of 5 to 30 wt .-%, especially in the range of 10 to 20 wt .-%; a content of Al ₂ O ₃ in the range of 0 to 20 wt .-%, especially in the range of 0 to 10 wt .-%; and a content of SiO ₂ in the range of 0 to 60 wt .-%, especially in the range of 10 to 50 wt .-%, each based on the total weight of the oligomerization catalyst having.

The components which can be used as oligomerization catalyst optionally contain sulfur in oxidized form, the molar ratio of sulfur atoms to nickel atoms in the relevant oligomerization catalyst usually being less than 1.

The oligomerization catalysts described in WO 95/14647 are preferably used to carry out the process according to the invention.

It will be understood by those skilled in the art that combinations of the aforementioned oligomerization catalysts may also be used. For example, several identical oligomerization catalysts can be used in reactors connected in parallel or in series. One of the advantages of a parallel connection is that temporary power drops or failures can be absorbed or compensated in a reactor without switching off the reaction current. A combination of different oligomerization catalysts is possible.

For the purposes of the method according to the invention several different adsorbents can be used in combination. In this case, according to the invention, it is only necessary that at least one of the adsorbents used has a component which is capable of being used as an oligomerization catalyst, eg. B. one of the above oligomerization catalysts contains. In a first embodiment of the invention, an adsorbent which contains a component which is capable of being used as an oligomerization catalyst is employed without further adsorbents which are different therefrom. In this case, the component contained in the adsorbent and capable of use as an oligomerization catalyst and the oligomerization catalyst used for the olefin oligomerization may be identical, ie in each case the same component is used both as adsorbent and as oligomerization catalyst. Furthermore, the component contained in the adsorbent and suitable for use as an oligomerization catalyst and the oligomerization catalyst used can be different. As the component capable of being used as the oligomerization catalyst, especially the above-mentioned oligomerization catalysts are suitable.

In a further embodiment, an adsorbent which contains a component which is capable of being used as an oligomerization catalyst is used together with further adsorbents. Again, the component contained in the adsorbent and capable of being used as an oligomerization catalyst and the oligomerization catalyst used for the olefin oligomerization may be the same or different. The other adsorbents can be other components which are capable of being used as oligomerization catalyst as well as conventional adsorbents, as described below, without catalytic activity for olefin oligomerization. As the component capable of being used as the oligomerization catalyst, especially the above-mentioned oligomerization catalysts are suitable. If conventional adsorbents are used, it has proved advantageous to first contact the monoolefins to be oligomerized with them before they are brought into contact with the components or adsorbents which are suitable for use as oligomerization catalysts.

In a preferred embodiment of the invention, the same component is used as adsorbent and as oligomerization catalyst. Optionally, one or more further conventional adsorbents other than the oligomerization catalyst are used here, as described below.

Suitable adsorbents which are the same as the oligomerization catalyst used are, in principle, all components mentioned above as employable oligomerization catalysts. In particular, those adsorbents which are capable of being used as oligomerization catalysts are suitable for carrying out the process according to the invention which comprise nickel in oxidized form. These adsorbents containing nickel in oxidized form generally have a content of nickel in oxidized form, calculated as NiO, of at least 0.5% by weight and in particular in the range from 0.5 to 90% by weight, especially in the range from 0.5 to 80% by weight, more particularly in the range from 2 to 70% by weight, more particularly in the range from 10 to 70% by weight, and more particularly in the range from 40 to 60% by weight, in each case based on the total weight of the nickel in oxidized form containing adsorbent on. In addition, such adsorbents may comprise the same additional active components or support materials previously mentioned for the components to be used as the oligomerization catalyst. These additional active components or support materials are in this case in the same amounts in the adsorbent in nickel in oxidized form, which were previously given for the components mentioned as Oligomerisierungskatalysator.

In a preferred embodiment, an adsorbent containing nickel in oxidized form is used, which consists essentially of

(i) the nickel in oxidized form, in particular in an amount in the range from 0.5 to 90% by weight, especially in the range from 10 to 70% by weight and especially in the range from 40 to 60% by weight , each calculated as NiO;

(Ii) one or more metal oxide (s), preferably selected from TiO ₂ , ZrO ₂ , SiO ₂ , Al ₂ O ₃ , Ga ₂ O ₃ , In ₂ O ₃ and the mixed oxides and mixtures thereof, more preferably selected from TiO ₂ , ZrO ₂ , SiO ₂ , Al ₂ O ₃ ; in particular TiO ₂ and / or ZrO ₂ in an amount in the range from 5 to 30% by weight, especially in the range from 10 to 20% by weight; SiO ₂ in an amount ranging from 0 to 60% by weight, especially in the range of 10 to 50% by weight; Al ₂ O ₃ in an amount ranging from 0 to 20% by weight, especially in the range of 0 to 10% by weight;

(iii) optionally, sulfur in oxidized form, wherein the molar ratio of sulfur atoms to nickel atoms is preferably less than 1, more preferably in the range of 0.25: 1 to 0.38: 1;

consists. The proportions of the individual components complement each other to 100 wt .-%. The term "essentially" here means that the proportion of other components is usually not more than 0.5% by weight. In general, this proportion will not be more than 0.1% by weight.

To carry out the process according to the invention, it has proved to be advantageous to select the component of the adsorbent which is capable of being used as oligomerization catalyst from those components which contain nickel in oxidized form. In particular, it will be used in this case, the aforementioned nickel in oxidized form containing adsorbent. Preferably, the nickel-containing oligos described in WO 95/14647 and WO 01/37989 are used. merisierungskatalysatoren as nickel in oxidized form containing adsorbent.

Particular preference is given to using an adsorbent which consists essentially of nickel oxide, silicon dioxide, titanium dioxide and / or zirconium dioxide and, if appropriate, aluminum oxide. The content of nickel oxide after deduction of the loss on ignition after tempering at 900 ⁰ C, calculated as NiO, is 10 to 70 wt .-%. Furthermore, the adsorbent 5 to 30 wt .-% titanium dioxide and / or zirconia, 0 to 20 wt .-% alumina, 20 to 40 wt .-% silica, and 0.01 to 1 wt .-% of an alkali metal oxide, with with the proviso that the proportions of the individual components add up to 100% by weight. The adsorbent is obtainable by precipitating an aluminum-free or a dissolved aluminum salt-containing nickel salt solution at a pH of 5 to 9 by adding this nickel salt solution to an alkali water glass solution containing solid titania and / or zirconia. The precipitation is preferably carried out at a temperature of 30 to 90 ^° C. The drying and heat treatment of the precipitate obtained are preferably carried out at 350 to 650 ^° C. and in particular at 400 to 600 ^° C.

It is also particularly preferred to use an adsorbent which is prepared by a process in which aluminum oxide is charged with a nickel compound and a sulfur compound. This is done simultaneously or first with the nickel compound and then with the sulfur compound. The resulting adsorbent is then dried and calcined, thereby adjusting a molar ratio of sulfur to nickel of 0.25: 1 to 0.38: 1 in the finished adsorbent.

The abovementioned adsorbents generally have a BET specific surface area in the range from about 10 to 2000 m ² / g, in particular in the range from 10 to 1500 m ² / g, especially in the range from 20 to 600 m ² / g and especially in the range of 100 to 500 m ² / g.

It is understood by those skilled in the art that the component contained in the aforementioned adsorbents and capable of being used as oligomerization catalyst can be used both in their active form and in the form of a precursor. Such precursors are usually obtained by thermal treatment at temperatures of a few hundred degrees, e.g. Example in the range of 200 to 800 "C ₁ transferred to the respective active form. Preferable to add the used qualified as oligomerization catalyst component in its active form thereof. In order to remove possibly present moisture can be the catalyst or its active form before performing the oligomerization reaction of a treatment in a stream of nitrogen at a sufficiently high temperature, for. B. in the range of 150 to 200 ⁰ C, subject. This drying is preferably carried out in situ.

In a specific embodiment, at least one further, essentially nickel-free adsorbent is additionally used. For this purpose, in particular all those adsorbents are contemplated which have already been proposed or used in the prior art for the removal of impurities from hydrocarbon mixtures which are used for the oligomerization of olefins. "Substantially nickel-free" here and in the following means that the particular adsorption agent generally contains nickel only in minor amounts, eg in traces. For the purposes of the present invention, an adsorption agent is "essentially nickel-free" if its content of nickel is less than 0.5% by weight, based on the total weight of the adsorbent.

Such essentially nickel-free adsorbents which are suitable for the process according to the invention are generally customary and known to those skilled in the so-called active aluminas. Their preparation takes place for. B. starting from aluminum hydroxide, which is obtainable by conventional precipitation of aluminum salt solutions. This includes z. For example, the commercially available Bayer aluminum hydroxide. These aluminum hydroxides can then directly by heating to temperatures of about 700 to 2100 ⁰ C in suitable furnaces, such as. As rotary or fluidized bed calcination, are converted to active aluminum oxides. To produce spherical activated alumina, aluminum hydroxide may be subjected to flash heating in vacuum or in the presence of a high temperature resistant gas. In this case, the aluminum hydroxide is heated for a short time, generally a few seconds, to temperatures of about 1100 to 1600 ^° C. Active aluminas suitable for the process according to the invention are also obtainable starting from aluminum hydroxide gels. For the preparation of such gels z. Example, precipitated aluminum hydroxide after conventional work-up steps, such as filtering, washing and drying, activated and then optionally ground or agglomerated. If desired, the resulting alumina may then be subjected to a shaping process such as extrusion, granulation, tabletting, etc. Suitable adsorbents are preferably the Selexsorb ™ types from Alcoa.

Further, suitable for the process according to the invention, essentially nickel-free adsorbent are still alumina-containing solids. These include z. As the so-called clays, which also have aluminum oxides as the main component, and mixtures of at least one alumina and at least one other of the aforementioned adsorbent. If desired, the aluminum oxides or aluminum oxide-containing solids used according to the invention may additionally comprise at least one alkali metal and / or alkaline earth metal compound. For this purpose, the alumina or the alumina-containing solid z. B. a soaking step with an appropriate solution and optionally further conventional process steps, such as drying and / or calcination, are subjected. Preferably, this modification of the adsorbent takes place after molding. Preferably, the alumina or the alumina-containing solid has an alkali metal and / or alkaline earth metal content of at most 1 wt .-%, z. In a range of about 0.0001 to 1.0% by weight, based on the total weight of the substantially nickel-free adsorbent. The aluminum oxides or aluminum oxide-containing solids used according to the invention preferably contain the alkali metals and / or alkaline earth metals in the form of their oxides.

Further suitable for the inventive method, essentially nickel-free adsorbents are aluminum phosphates.

Furthermore, suitable for the inventive method, essentially nickel-free adsorbents are silicas, z. B. by dehydration and activation of silica gels are available. Another method for the production of silicon dioxide is the flame hydrolysis of silicon tetrachloride, wherein by suitable variations of the reaction parameters, such. As the stoichiometric composition of the educt mixture and the temperature, the desired surface properties of the resulting silica can be varied within wide ranges.

Further suitable, essentially nickel-free adsorbents are diatomaceous earth, which also has silicas as its main constituent. This includes z. As the diatomaceous earth obtained from silica sediments.

Further suitable, essentially nickel-free adsorbents are titanium dioxides and zirconium dioxides, as z. In Römpp, Chemie Lexikon, 9th edition (paperback), Vol. 6, p. 4629f. and pp. 5156f. and the literature cited therein. This is hereby fully incorporated by reference.

Further suitable, essentially nickel-free adsorbents are phosphates, in particular condensed phosphates, such. As melting or annealing phosphates, which have a large active surface area. Suitable phosphates are, for. B. in Römpp, Chemie Lexikon, 9th ed. (Paperback), Vol 4, p 3376f. and the literature cited therein. This is hereby fully incorporated by reference. Further suitable, essentially nickel-free adsorbents are carbonaceous adsorbents, preferably activated carbon. Activated carbon is generally understood to mean carbon with a porous structure and a high internal surface area. For the production of activated carbon are plant, animal and / or mineral carbonaceous raw materials, eg. B. with dehydrating agents such as zinc chloride or phosphoric acid, heated or charred by dry distillation and then activated by oxidation. This can be z. B. treat the charred material at elevated temperatures of about 700 to 1000 ⁰ C with water vapor, carbon dioxide and / or mixtures thereof.

The substantially nickel-free adsorbents are preferably selected from titanium dioxides, zirconium dioxides, silicon dioxides, kieselguhr, aluminum oxides, aluminum oxide-containing solids, aluminum phosphates, natural and synthetic aluminum silicates, phosphates, carbonaceous adsorbents and mixtures thereof, more preferably alumina and alumina-containing solids , Very particular preference is given to aluminas and alumina-containing solids which comprise at least one alkali metal and / or alkaline earth metal. Preferably, the alkali metal and / or alkaline earth metal content is at most 1% by weight, for. In the range of 0.0001 to 1% by weight, based on the total weight of the substantially nickel-free adsorbent.

The essentially nickel-free adsorbents generally have a BET specific surface area in the range from about 10 to 2000 m ² / g, in particular in the range from 10 to 1500 m ² / g and especially in the range from 20 to 600 m ² / g, up.

The inventively used, essentially nickel-free adsorbents generally have no catalytic activity for the oligomerization of olefins. An oligomer formation of at most 0.2% by weight, in particular not more than 0.1% by weight, based on the total amount of monoolefin in the amine used in the process according to the invention for the first time (so-called 1st cycle) is observed Oligomerization used hydrocarbon mixture. Advantageously, this tendency to oligomer formation substantially does not increase even with regenerated adsorbents (2nd to nth cycle). Furthermore, the essentially nickel-free adsorbents used according to the invention advantageously show no tendency to significantly isomerize unbranched monoolefins.

If conventional adsorbents are used in addition to adsorbents which contain a component which is suitable for use as an oligomerization catalyst, the weight ratio of the former to the latter is usually in the range from 10:90 to 90:10 and in particular in the range from 30 : 70 to 70: 30. It is preferable to use one of the above-mentioned nickel-containing oligomerization catalysts as an adsorbent containing a component capable of being used as an oligomerization catalyst. As conventional adsorbents, the above-described nickel-free adsorbents are preferably used. Thus, in one particular embodiment, nickel-containing and nickel-free adsorbents are used, with the weight ratio of nickel-containing to nickel-free adsorbents being in the range of 10:90 to 90:10 and especially in the range of 30:70 to 70:30.

The adsorbents to be used according to the invention can be subjected to a conventional shaping process such as pelleting, tableting or extrusion prior to their use. In particular, the adsorbents are in the form of extrudates, e.g. B. strands, in particular cylindrical strands, or balls used. Strand-shaped adsorbents preferably have a length in the range of 0.1 to 2 mm and more preferably in the range of 0.2 to 1 mm and a diameter in the range of about 0.5 to 10 mm and more preferably in the range of 1 to 5 mm on. Spherical adsorbents preferably have a diameter in the range of about 0.1 to 5 mm, and more preferably in the range of 1 to 5 mm.

Furthermore, before being used, the adsorbents can be applied to optionally inert and / or non-porous carrier materials, as known from the prior art. These include, for example, quartz (SiO ₂ ), porcelain, magnesium oxide, silicon carbide, titanium dioxide, alumina (Al ₂ O ₃ ), aluminum silicate, steatite (magnesium silicate), zirconium silicate or mixtures of these support materials. The shape of the support material is generally not critical. For example, carrier materials in the form of spheres, rings, tablets, spirals, tubes, extrudates or chippings can be used. The dimensions of these support materials correspond to the dimensions usually set in the production of adsorbents used as solid phase and overflowed by a gas phase. The abovementioned carrier materials can also be mixed into the adsorbents in powder form.

For the cup-shaped coating of the carrier materials with the adsorbents used according to the invention, known methods of the prior art can be used. For example, the adsorbent-containing suspensions can be sprayed onto the substrates in a coating drum or in a fluid bed coater, optionally at elevated temperature. In a suspension or slurry of a powder of the adsorption used according to the invention in water or in an organic solvent, for. B. higher alcohols, polyhydric alcohols, eg. As ethylene glycol, 1, 4-butanediol or glycerol, di- methylformamide, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone or cyclic ureas, eg. As N, N'-dimethylethyleneurea or N, N'-dimethylpropyleneurea, or mixtures of these organic solvents with water, organic binders such as copolymers can be dissolved or such binders can be advantageously added in the form of an aqueous dispersion. In general, binder contents in the range from 10 to 20% by weight, if appropriate in the range from 1 to 10% by weight, based on the solids content of the suspension or slurry, are set here. Suitable binders are z. As vinyl acetate / vinyl laurate, vinyl acetate / acrylate, styrene / acrylate, vinyl acetate / maleate or vinyl acetate / ethylene copolymers.

In the coating of the carrier materials with the adsorbents used in the invention can be applied generally temperatures in the range of 20 to 500 ⁰ C, wherein the coating rend or jerk in the coating apparatus under atmos- can be carried out under reduced pressure. When using binders for coating they should be removed from the applied layer by thermal treatment at temperatures above 200 to 500 ° C, at which the binders decompose and / or burn, z. B. as part of a conditioning pretreatment.

The abovementioned carrier materials and coating methods are also suitable in principle for the oligomerization catalysts which can be used according to the invention.

According to the invention, the C ₂ -C ₈ -monoolefins to be oligomerized are brought into contact with the adsorbent (s) in at least one adsorption zone and are oligomerized in at least one reaction zone. An adsorption zone is understood here to mean the spatial area which is claimed by one or more usually solid adsorbents and can be passed through by the educt mixture, usually a gaseous mixture with a high content of C ₂ -C ₈ monoolefins. A reaction zone is understood here to mean the spatial area which is claimed by one or more usually solid oligomerization catalysts and can be flowed through by the educt mixture after it has been discharged from the adsorption zone.

It will be understood by those skilled in the art that the specific configuration and arrangement of the adsorption and reaction zone (s) may be in any known manner. It is preferable to arrange the adsorption and reaction zone (s) spatially separated from one another, ie to structurally separate from one another by the apparatus design. For this you can z. Example, a relatively small-sized apparatus (eg., In the order of magnitude of some m ³ , usually in the range of 1 to 20 m ³ and often not more than 25 m ³ ) provide as an adsorption zone and a larger compared in comparison te apparatus (for example in the order of about 100 m ³ , usually in the range of 50 to 250 m ³ and often more than 25 m ³ ) as a reaction zone. It has proved to be advantageous for carrying out the process according to the invention if the volume ratio of adsorption to reaction zone is chosen such that it is in the range from 1: 1 to 1: 500 and in particular in the range from 1: 2 to 1: 100. If available, in each case the total adsorption zones or reaction zones are to be calculated together and then related to one another.

If one uses different adsorbents, z. B. provide a first adsorption zone in a first reactor containing a first adsorbent, and separately, so separated by equipment, z. B. in a second reactor, a second adsorption zone containing a second adsorbent. In this case, the first and / or the second adsorbent may contain at least one component which is suitable for use as an ON gomerization catalyst.

Advantageously, at least two adsorption zones will be arranged so that the C ₂ -C ₈ monoolefins to be oligomerized in the first adsorption zone are treated with a conventional adsorbent, e.g. A substantially nickel-free adsorbent as described above, and in the second adsorption zone are contacted with an adsorbent containing at least one component capable of use as an oligomerization catalyst. The latter can z. Example, a nickel in oxidized form containing adsorbent, as described above, be.

In another embodiment, a substantially nickel-free adsorbent is used together with an adsorbent containing nickel in oxidized form in a single adsorption zone, e.g. In layered form, mixed in the form of a random distribution or in the form of a gradient coating. The use in mixed form optionally allows a better control of the temperature. In the case of a gradient bed, linear and nonlinear gradients can be used. It may be advantageous in this case to carry out the distribution within the bed in such a way that the C ₂ -C ₈ monoolefins to be oligomerized are first brought into contact with the essentially nickel-free adsorbent before they are adsorbed with the nickel in oxidized form Contact us.

It is understood by those skilled in the art that the illustrated different variants for the design of the adsorption and reaction zones can each be applied in such a way that two or more identically designed adsorption and / or reaction zones are arranged in parallel and / or behind one another , In particular, an embodiment is advantageous in which at least two separate identical ge adsorption zones are provided which can be operated in parallel. As a result, temporary power losses or failures can be absorbed or compensated in a reactor without switching off the reaction current. This is z. B. achieved by operating the adsorption zones so that both are loaded with mutually different amounts of catalyst poisons. It is preferable to arrange two adsorption zones in parallel and operate them alternately, for. B. alternately during a given time period. With such a procedure, it is particularly preferable to switch from one to the other adsorption zone after a loading of the adsorbent with a predetermined maximum amount of catalyst poisons has been achieved. This maximum amount can be z. B. result from a specific product specification. In particular, this maximum amount will be such that the catalytic activity of the oligomerization catalyst is at an economically acceptable level. It has z. B. proven advantageous to make such an aforementioned switching in each case when in the emerging from the adsorbent stream, a content of potential catalyst poisons, as described below, of 0.001 wt .-% (10 ppm by weight) reached or exceeded becomes.

In the process according to the invention, generally customary monoolefin-containing hydrocarbon mixtures which contain C ₂ -C ₈ -monoolefins can be used as starting materials. Such hydrocarbon mixtures have one or more types of monoolefins having 2 to 8 carbon atoms, in particular having 2 to 6 carbon atoms. In particular, mixtures with a high proportion of monoolefins, z. B. in the range of 10 to 90 wt .-%, based on the total weight of the mixture suitable. Of these, especially suitable are those which contain, in particular, aliphatic and / or cycloaliphatic C ₄ -monoolefins and / or Cs-C ₆ -monoolefins. The hydrocarbon mixtures used advantageously contain a high proportion of unbranched monoolefins, z. Example, in the range of 10 to 90 wt .-%, based on the total weight of the mixture., The use of an oligomerization catalyst which leads to low branched oligomers in good yield, thus allows according to the invention oligomers with high linearity, ie with a low ISO Index, to get.

For the process according to the invention can be z. B. use an industrially occurring hydrocarbon mixture. These include z. As obtained in the workup of petroleum by steam cracking or fluidized catalyst cracking (FCC)

C ₄ cuts. In a specific embodiment, a so-called raffinate II is used. In a further specific embodiment, a C ₂ -C ₈ monoolefins containing hydrocarbon mixture consisting of a z. B. carried out according to the DE 198 59 911 olefin metathesis used. In a further specific embodiment, a large-scale C _{4 cut is} used which contains essentially 10 to 90% by weight of butenes and 10 to 90% by weight of butanes, the butene fraction containing the following hydrocarbons: 1 to 99 Wt% trans-2-butene; 1 to 50% by weight of 1-butene; From 1 to 50% by weight of cis-2-butene; and 1 to 5% by weight of isobutene; and wherein the proportion of the butene and the butane fraction add up to 100 wt .-%. The term "essentially" here means that the proportion of further components is generally not more than 1% by weight and in particular not more than 0.1% by weight.

Usually, the aforementioned hydrocarbon mixtures contain catalyst poisons, d. H. Components which interfere with oligomerization by deactivating the oligomerization catalyst. These include oxygen-containing compounds such as water, alcohols, eg. For example, methanol, ethanol, isopropanol, n-propanol, n-butanol, sec-butanol, isobutanol, tert-butanol, ethers, eg. As diethyl ether, methyl tert-butyl ether, aldehydes, z. As formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, ketones, z. As acetone, methyl ethyl ketone, etc. Other frequently used catalyst poisons are nitrogen-containing compounds such as amines and sulfur-containing compounds such as hydrogen sulfide, thio alcohols, thioethers, z. B. dimethyl sulfide and dimethyl disulfide, carbon dioxide sulfide, etc. Optionally, hydrocarbon mixtures used industrially for olefin oligomerization contain further production-related catalyst poisons. These include z. As halogen compounds, traces of common extraction agents, eg. As acetonitrile or N-methylpyrrolidone, etc., and optionally organic phosphorus and arsenic compounds.

The content of the above-mentioned catalyst poisons in the hydrocarbon mixtures used in the process according to the invention is not a limiting factor in principle for the use of the adsorbents described above to be used according to the invention. With increasing content of the catalyst poison, however, the required volume of adsorbent used per unit time and hydrocarbon throughput increases. Therefore, it may be more economical to use the hydrocarbon mixtures used for olefin oligomerization prior to contacting with the adsorbents described above, in particular prior to contacting with the previously described substantially nickel-free adsorbents of a coarse purification method known in the art to undergo. So it is generally favorable, the content of the aforementioned catalyst poisons in the hydrocarbon mixtures before contacting with the adsorbents used in the invention, if necessary, by conventional methods to at most about 0.5 wt .-% (5000 ppm by weight ), preferably at most 0.2 wt .-% (2000 wt ppm), in particular at most 0.1 wt .-% (1000 wt ppm) to reduce. Suitable methods for such a rough purification of hydrocarbon mixtures are z. For example, in DE-A-39 14 817 and the literature cited therein, which is incorporated herein by reference in its entirety.

In a preferred embodiment, a hydrocarbon mixture containing the C ₂ -C ₈ monoolefins is contacted with nickel-free adsorbent prior to contacting with adsorbents containing nickel in oxidized form such that the content of oxygen, Nitrogen, sulfur, phosphorus and / or halogen-containing impurities in the hydrocarbon mixture to at most 0.001 wt .-% and in particular to at most 0.0001 wt .-%, based on the total weight of the hydrocarbon mixture is reduced.

The hydrocarbon mixtures used for the oligomerization further usually contain multiple monoethylenically unsaturated hydrocarbons and / or alkynes. So z. For example, a typical raffinate II has a content of butadiene of the order of several thousand ppm by weight. It has proved to be advantageous for carrying out the process according to the invention to reduce the content of such impurities prior to oligomerization by selective hydrogenation to the corresponding monoolefins. Suitable methods for selective hydrogenation are, for. In DE-A-20 57 269, EP-A-0 081 041 and DE-A-15 68 542, to which reference is hereby made in their entirety. In particular, hydrogenation is carried out in such a way that the resulting hydrocarbon mixture obtained in the process according to the invention has a content of polyunsaturated hydrocarbons and / or alkynes of at most 0.01% by weight (100 ppm by weight), especially 0.005% by weight ( 50 wt. Ppm) and especially 0.001 wt.% (10 wt. Ppm). Optionally, this selective hydrogenation may also be effected after contacting the hydrocarbon mixture with a substantially nickel-free adsorbent, but prior to contacting with the adsorbent containing the nickel in oxidized form.

In a preferred embodiment, the discharge from step a), d. H. after exiting the adsorption zone and before entering the reaction zone, a content of polyunsaturated hydrocarbons of less than 0.001 wt .-%, based on the total weight of the discharge, on.

According to the invention, an adsorbent is used in at least one adsorption zone, which contains at least one component capable of being used as an oligomerization catalyst. While the essentially nickel-free adsorbents, as stated above, usually have no significant catalytic activity for the oligomerization of olefins, this naturally does not apply to the adsorbent component which contains the component which is capable of being used as an oligomerization catalyst. In particular, this relates to nickel containing in oxidized form Adsorbent or components. In this connection, it is advantageous to use an identical or similar component both as an oligomerization catalyst and as an adsorbent which contains the component which is capable of being used as oligomerization catalyst, since in this case the olefin already formed in the adsorption zone by oligomerization. Products correspond to the olefin products formed in the reaction zone in terms of selectivity and quality. It has been found that this also applies if the adsorption is carried out under conditions in which generally only a small amount, for. B. less than 20 wt .-% of the C ₂ -C ₈ monoolefins used to be oligomerized. Conditions for controlling the conversion of the oligomerization reaction are known in principle to the person skilled in the art and can easily be determined by him in routine experiments. It has also been found that by using lower temperatures than are commonly used for the oligomerization reaction, e.g. B. setting temperatures below 50 ⁰ C and in particular below 30 ⁰ C, the catalytic oligomerization activity of the adsorbent, which contain the capable of use as oligomerization catalyst component, can be greatly reduced; on the other hand, the adsorption capacity for potential catalyst poisons is essentially retained.

In general, the process according to the invention is carried out under reaction conditions (temperature, pressure, throughput, etc.) in which less than 50% by weight, in particular less than 20% by weight and especially less than 10% by weight of C ₂ -C ₈ monoolefins, in each case based on the total weight of the C ₂ -C ₈ monoolefins used, are oligomerized in step a). To achieve this purpose, in particular a control of the temperature of the adsorption zone (s) into consideration. Usually, the adsorption is carried out at a temperature of less than 50 ⁰ C, in particular less than 40 ⁰ C and especially less than 30 ⁰ C. At a temperature of less than 30 ^° C. in the adsorption zone, only slight oligomerization usually occurs (for example in the order of from 0.1 to 5% by weight of the C ₂ -C ₈ monoolefins used), However, their absolute extent is influenced, inter alia, by the olefin concentration and the state and the load of the catalyst. Here and hereinafter, the term "space velocity" is defined as related by set reactant mixture used to reactor volume and time, that is expressed as kg _Ra ffinat / (l catalyst or Adsorbervoiumen * h). At a temperature of fewer than 10 ⁰ C in the It is possible to carry out the adsorption at a temperature higher than 50 ^° C. In this case, however, the heat of reaction caused by the significantly occurring oligomerization reaction is reliably removed from the adsorption zone, ie from the catalyst bed so as to give a qualitatively comparable olefin product as in the oligomerization reaction carried out in the reaction zone. The process according to the invention is preferably carried out in such a way that the temperature in the adsorption zone containing nickel-free adsorbents is in the range from 0 to 150 ^° C., more preferably in the range from 5 to 100 ^° C. and most preferably in the range from 10 to 50 ⁰ C is. The temperature in the adsorption zone containing nickel-containing adsorbent is preferably in the range of 0 to 50 ⁰ C, more preferably in the range of 5 to 40 ⁰ C and most preferably in the range of 10 to 30 ⁰ C. Substituting nickel-free and nickel-containing Adsorbent in combination in the same adsorption zone, it is advantageous to choose the previously mentioned for the nickel-containing adsorbent temperatures.

Typically, the C ₂ -C ₈ -lvlonoolefins or a hydrocarbon mixture containing them at a pressure in the range of about 1 to 200 bar, in particular in the range of about 1 to 100 bar, especially in the range of about 1 to 50 bar and very specifically in the range of about 10 to 30 bar, brought into contact with the adsorbent.

Suitable for the contacting of the C ₂ -C ₈ -lv1onoolefins or of a hydrocarbon mixture containing them with the adsorbents described above, which may be pressure-resistant, are known to the person skilled in the art. These include the commonly used reactors for gas / solid reactions and liquid / solid reactions. Preferably, a fixed bed reactor or a moving bed reactor is used. The adsorbent may, as stated above, be used in the form of a single or in the form of multiple adsorption zones (also referred to as contact zones). Here, each of these zones may comprise one or more of the adsorbents described above. Adsorption and oligomerization can be carried out in different reactors or in successive zones in one reactor. In this case, if appropriate, the zones for the adsorption and the zones for the oligomerization are operated at different reaction conditions, in particular at different temperatures.

The bringing into contact of the hydrocarbon mixture containing the C ₂ -C ₈ -lv1onoolefines with the adsorbents is generally carried out by passing over. Here, the hydrocarbon mixture z. B. in gaseous, liquid or supercritical phase are brought into contact with the adsorbents. The linear velocity is preferably in a range of about 1 to 200 cm / min.

The regeneration of the adsorbents used according to the invention, in particular of the essentially nickel-free adsorbents, is usually carried out by treatment with oxygen, oxygen-containing gas mixtures, eg. As air, oxygen supplying compounds, nitrogen oxides or mixtures thereof. The temperature at the Regeneration is usually in the range of about 100 to 800 ⁰ C and in particular in the range of 200 to 600 ⁰ C.

The regeneration of the nickel-containing adsorbents used according to the invention is preferably carried out by substantially regenerating the nickel used in oxidized form adsorbents whose adsorptivity has been reduced as a result of use in one of the above-described methods by using the nickel-containing adsorbent with an oxygen-containing gas , Air, nitrogen oxides or a mixture thereof at a temperature of at least 300 ⁰ C, z. B. in the range of 300 to 600 ⁰ C, treated.

Advantageously, the adsorbents used according to the invention can be regenerated frequently, without the adsorption capacity decreasing significantly. They are suitable for a simple and economical oxidative thermal regeneration, as described above. Here, even after a plurality of regeneration cycles, substantially no increase in the oligomerization catalyzed by the adsorbent is observed. In general, cycle numbers of at least 2, in particular at least 20, especially at least 200, and especially at least 2000, can be achieved.

The adsorbents described above are suitable not only for use in a process for the catalytic oligomerization of monoolefinic hydrocarbon mixtures, but more generally for the treatment of olefins or olefin mixtures for reducing the content of potential catalyst poisons. The invention therefore also relates to a process for the preparation of pure olefins or olefin mixtures, eg. Example of C ₂ -C ₃₀ monoolefins or olefin mixtures containing them, which is characterized in that olefins or olefin mixtures, for. B. C ₂ -C ₃ o-monoolefins or olefin mixtures containing them, with at least one of the previously described adsorbent containing at least one ready for use as Oligome- risierungskatalysator component brings into contact.

Another object of the invention is the use of an adsorbent containing nickel in oxidized form, as described above, for reducing the content of polyunsaturated hydrocarbons and / or oxygen, nitrogen, sulfur, phosphorus and / or halogen-containing impurities in a hydrocarbon mixture by contacting the hydrocarbon mixture with the adsorbent containing the nickel in oxidized form.

The invention will be explained in more detail by means of the following non-limiting examples. Examples

The starting material mixture containing the olefins to be oligomerized was a raffinate II. The reactions were carried out continuously using a thermostated fixed bed reactor (30 mm clear width) under elevated compared to the autogenous pressure of the raffinate Il pressure (20 bar). The adsorption of catalyst poisons was carried out in an analogous reactor (30 mm clear width), which was switched before the reactor with the oligomerization catalyst and was present in A / B design. In such an A / B design, two similar reactors are connected in parallel so that during operation of one reactor the other can be removed, regenerated ex situ, and then reinstalled without interrupting the ongoing process. The pressure was generated via a reactor feed pump in front of the first reactor and controlled in accordance with a pressure holding device behind the second reactor.

In each case, a similar pretreatment of the catalyst and the adsorbent was carried out. For this purpose, each 250 ml of catalyst or 500 ml of adsorbent were charged into the reactor and 24 h at 160 ⁰ C and under normal pressure in a dry stream of N ₂ (1500 Nl / h) conditioned. It was then cooled to 20 ° C. There was a metered addition of raffinate II and an increase in the pressure to 20 bar by means of the pump or pressure holding device. Subsequently, an increase in temperature in the reaction zone was optionally carried out.

I. butadiene adsorption on a Ni-containing adsorbent

A raffinate II was used, consisting of 3.1% i-butane, 15.3% n-butane, 29.8% 1-butene, 2.1% i-butene, 31.7% trans-2-butene , 17.8% cis-2-butene, 0.2% i-pentane and 100 ppm of 1, 3-butadiene. At a catalyst loading of 2 kg / (l ^* h), the butadiene-containing feed raffinate II at 20 ⁰ C over a period of 20 days via a nickel-containing oligomerization catalyst, as described in Ex. 2 of DE-A-43 39 713, passed. By means of off-line GC analysis, the butadiene content in the effluent was regularly examined. Based on the specified period of 20 days, the butene conversion was less than 5% by weight of the butene used. No butadiene could be detected at the reactor outlet (<1 ppm or <0.0001 wt .-%, based on the total weight of the discharge). This shows that the Ni-containing oligomerization catalyst used as adsorbent effectively causes a retention of olefins such as butadiene.

II. Long-term test with adsorbent according to DE-A-198 45 857 and regeneration of Ni-containing catalysts (comparative experiment) A raffinate II was used, which comprises on average 3% of i-butane, 23% of n-butane, 26% of 1-butene, 1% of i-butene, 31% of trans-2-butene, 16% of cis-2-butene, and as trace components 10 ppm dienes, 30 ppm water, 20 ppm alcohols, 5 ppm aldehyde and 20 ppm ketones (all data as ppm by weight). At a catalyst loading of 2 kg / (l * h), this butadiene-lean feedstock raffinate II was first passed over a first fixed bed reactor thermostated at 20 ° C. over a period of 180 days. This first reactor was filled with 500 ml of active Al ₂ O ₃ (3 mm spheres, Selexsorb CD from Alcoa) and was available in duplicate for driving in A / B mode. Subsequently, the discharge from the first reactor was passed through a second thermostated fixed bed reactor. This second reactor was filled with 250 ml of nickel-containing oligomerization catalyst, as described in Ex. 2 of DE-A-43 39 713. The purified olefin stream discharged from the adsorber was examined regularly for trace components by GC analysis. After reaching the breakthrough capacity (defined here as more than 10 ppm by weight or 0.001% by weight of catalyst poisons), switching was made to the other adsorber. The spent adsorbent was blown dry by flushing the adsorbent with N ₂ , then removed and replaced with ex situ regenerated adsorber. The ex situ regeneration was carried out by burning in air at 400 to 500 ⁰ C and cooling under N ₂ , with a flow of 500 NI _gas / (kg _adsorber * h) was set The reaction temperature was adjusted so that over the period considered a butene Conversion between 40 and 50% of the butenes used was achieved.

At the beginning of the long-term test, the temperature was at 60 ⁰ C, after 180 days at

100 ⁰ C. The teildesaktivierte after this period the catalyst was removed and subjected to extensive analysis. It was found that the catalyst located at the reactor inlet significant amounts of nitrogen and halogen-containing residues (100-500 ppm nitrogen or 30-40 ppm halogen), while these components are virtually undetectable at the reactor outlet. The carbon content is about 2% by weight over the total catalyst bed, with a tendency to decrease towards the reactor outlet. Rapid tests were performed to verify the performance of the degraded catalysts in a thermostated micro bed reactor 10 mm in diameter and 20 cm in length. For this purpose, in each case 10 g of the removed catalyst were conditioned in accordance with the above catalyst pretreatment. Subsequently, the catalysts were regenerated in situ for 2 h at 400 to 500 ⁰ C by passage of air (5 Nl / h) and cooling under N ₂ . Again, "rapid tests" were carried out over a period of 3 days, the results are given in Table 1. Table 1: Rapid test (catalyst loading 1 kg / (1 _R on _n a _t ii * h), reactor temperature 60 ^° C., pressure 20 bar)

It can be seen clearly that the expansion catalyst was deactivated in comparison to the fresh catalyst. In addition, the significantly greater deactivation of the expansion catalyst at the reactor inlet, presumably caused by the additional adsorption of nitrogen- and halogen-containing catalyst poisons, can be seen. Finally, the treatment in the hot air stream shows that the deactivation is reversible.

Example 1 (according to the invention)

Adsorber and Ni-based catalyst according to DE-A-43 39 713

The procedure was as in the experiment described under II., However, where fresh nickel-containing oligomerization catalyst, as described in Ex. 2 of DE-A-43 39 713, was also used as an adsorbent. The reaction temperature was adjusted so that again a butene conversion between 40 and 50 wt .-% of the butenes used was achieved over the period considered. At the beginning of the long-term test, the temperature was 60 ^° C., after 180 days only 75 ^° C. Compared to the use of Al ₂ O ₃ as adsorbent, the deactivation is thus significantly reduced.

Example 2 (according to the invention)

Ni-based adsorber according to WO 01/37989 and Ni-based catalyst according to DE-A-43 39 713

The procedure was as in the experiment described under II., However, being used as an adsorber fresh nickel-containing oligomerization catalyst, as in Ex. EK4 of WO 01/37989. The reaction temperature was adjusted so that again a butene conversion between 40 and 50 wt .-% of the butenes used was achieved over the period considered. At the beginning of the long-term test, the temperature was 60 ⁰ C, after 180 days at only 80 ⁰ C. Compared to the use of Al ₂ O ₃ as adsorbent, the deactivation is thus again significantly reduced.

Claims

claims

1. A process for the oligomerization of C ₂ -C ₈ monoolefins in the presence of an oligomerization catalyst in which

b) oligomerizing the effluent from step a) in at least one reaction zone,

2. The method according to claim 1, characterized in that the adsorbent contained in the capable of use as an oligomerization catalyst component and the oligomerization catalyst used are the same.

3. The method according to any one of the preceding claims, characterized in that at least one of the adsorbent contains nickel in oxidized form.

4. The method according to claim 3, characterized in that the nickel in oxidized form containing adsorbent consists essentially of

(i) the nickel in oxidized form;

(ii) one or more metal oxide (s), preferably selected from TiO ₂ , ZrO ₂ , SiO ₂ , Al ₂ O ₃ , Ga ₂ O ₃ , In ₂ O ₃ and the mixed oxides and mixtures thereof;

(iii) optionally sulfur in oxidized form, the molar ratio of

Sulfur atoms to nickel atoms is preferably less than 1;

wherein the proportions of the individual components add up to 100 wt .-%.

5. The method according to claim 4, characterized in that the adsorbent containing nickel in oxidized form contains at least 0.5 wt .-%, based on the total weight of the nickel in oxidized form containing adsorbent, of nickel oxide.

6. The method according to any one of claims 3 to 5, characterized in that at least one further, nickel-free adsorbent is used.

7. The method according to claim 6, characterized in that the nickel-free adsorbent is selected from titanium dioxides, zirconium dioxides, silicas, diatomaceous earth, alumina, alumina-containing solids, Aluminiumphos- phaten, natural and synthetic aluminosilicates, phosphates, carbonaceous adsorbents, Polymeradsorbentien and mixtures thereof.

8. The method according to any one of the preceding claims, characterized in that the adsorption and the reaction zone (s) are arranged spatially separated from each other.

9. The method according to any one of the preceding claims, characterized in that the volume ratio of adsorption to reaction zone in the range of 1: 1 to 1: 500.

10. The method according to any one of claims 6 to 9, characterized in that the nickel-free adsorbent is used together with the nickel in oxidized form containing adsorbent in a single adsorption zone in the form of a gradientenschüttung.

11. The method according to any one of the preceding claims, characterized in that the components which impair the oligomerization comprise polyunsaturated hydrocarbons and / or oxygen, nitrogen, sulfur, phosphorus and / or halogen-containing impurities.

12. The method according to claim 11, characterized in that the C ₂ -C ₈ monoolefins are present in a hydrocarbon mixture having a content of polyunsaturated hydrocarbons of at most 0.01 wt .-%, based on the total weight of the hydrocarbon mixture.

13. The method according to claim 12, characterized in that the hydrocarbon mixture comprises substantially aliphatic and / or cycloaliphatic C ₄ monoolefins and / or C ₅ -C _β -Monoolefϊne.

14. The method according to any one of claims 6 to 13, characterized in that one brings the C ₂ -C ₈ monoolefins containing hydrocarbon mixture before contacting with adsorbents containing nickel in oxidized form so with nickel-free adsorbent, in that the content of oxygen, nitrogen, sulfur, phosphorus and / or halogen-containing impurities in the hydrocarbon mixture is not more than 0.001% by weight, based on the

Total weight of the hydrocarbon mixture is reduced.

15. The method according to any one of the preceding claims, characterized in that the adsorption is carried out at a temperature of less than 50 ⁰ C.

16. The method according to any one of the preceding claims, characterized in that less than 50 wt .-%, based on the total weight of the C ₂ -C ₈ monoolefins used, are oligomerized in step a).

17. The method according to any one of the preceding claims, characterized in that the discharge from step a) has a content of polyunsaturated hydrocarbons of less than 0.001 wt .-%, based on the total weight of the contract, has.

18. The method according to any one of claims 3 to 17, characterized in that the used, nickel in oxidized form containing adsorbent whose

Has adsorptivity as a result of the use in a method according to claim 3 is reduced to 17, essentially in regenerated completely, that the nickel-containing adsorbent with an oxygen-containing gas, air, nitrogen oxides, or a mixture thereof at a temperature of at least 300 ⁰ C treated.

19. Use of an adsorbent containing nickel in oxidized form as defined in any one of claims 3 to 18 for reducing the content of polyunsaturated hydrocarbons and / or oxygen, nitrogen, sulfur, phosphorus and / or halogen. containing contaminants in a hydrocarbon mixture by contacting the hydrocarbon mixture with the nickel in oxidized form containing adsorbent.