Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C2/00—Preparation of hydrocarbons from hydrocarbons containing a smaller number of carbon atoms
  • C07C2/02—Preparation of hydrocarbons from hydrocarbons containing a smaller number of carbon atoms by addition between unsaturated hydrocarbons
  • C07C2/04—Preparation of hydrocarbons from hydrocarbons containing a smaller number of carbon atoms by addition between unsaturated hydrocarbons by oligomerisation of well-defined unsaturated hydrocarbons without ring formation
  • C07C2/06—Preparation of hydrocarbons from hydrocarbons containing a smaller number of carbon atoms by addition between unsaturated hydrocarbons by oligomerisation of well-defined unsaturated hydrocarbons without ring formation of alkenes, i.e. acyclic hydrocarbons having only one carbon-to-carbon double bond
  • C07C2/08—Catalytic processes
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C11/00—Aliphatic unsaturated hydrocarbons
  • C07C11/02—Alkenes
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C2/00—Preparation of hydrocarbons from hydrocarbons containing a smaller number of carbon atoms
  • C07C2/02—Preparation of hydrocarbons from hydrocarbons containing a smaller number of carbon atoms by addition between unsaturated hydrocarbons
  • C07C2/04—Preparation of hydrocarbons from hydrocarbons containing a smaller number of carbon atoms by addition between unsaturated hydrocarbons by oligomerisation of well-defined unsaturated hydrocarbons without ring formation
  • C07C2/06—Preparation of hydrocarbons from hydrocarbons containing a smaller number of carbon atoms by addition between unsaturated hydrocarbons by oligomerisation of well-defined unsaturated hydrocarbons without ring formation of alkenes, i.e. acyclic hydrocarbons having only one carbon-to-carbon double bond
  • C07C2/08—Catalytic processes
  • C07C2/10—Catalytic processes with metal oxides
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C2521/00—Catalysts comprising the elements, oxides or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium or hafnium
  • C07C2521/02—Boron or aluminium; Oxides or hydroxides thereof
  • C07C2521/04—Alumina
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C2521/00—Catalysts comprising the elements, oxides or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium or hafnium
  • C07C2521/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C2521/00—Catalysts comprising the elements, oxides or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium or hafnium
  • C07C2521/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
  • C07C2521/08—Silica
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C2523/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group C07C2521/00
  • C07C2523/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group C07C2521/00 of the iron group metals or copper
  • C07C2523/74—Iron group metals
  • C07C2523/755—Nickel
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C2527/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
  • C07C2527/02—Sulfur, selenium or tellurium; Compounds thereof
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P20/00—Technologies relating to chemical industry
  • Y02P20/50—Improvements relating to the production of bulk chemicals
  • Y02P20/582—Recycling of unreacted starting or intermediate materials

Definitions

• the present invention relates to a process for the oligomerization of alkenes, which comprises providing an alkene-containing feed and subjecting it to oligomerization in two successive reaction zones.
• Hydrocarbon mixtures containing short-chain alkenes are available on a large scale. So falls z.
• a hydrocarbon mixture having a high total olefin content referred to as C4 cut, which is essentially alkenes of 4 carbon atoms.
• C4 cuts d.
• H. Mixtures of isomeric butenes and butanes, are suitable, optionally after a previous separation of the isobutene and hydrogenation of the butadiene contained, very well for the preparation of oligomers, in particular of octenes and dodecenes. The octenes and dodecenes can be converted by hydroformylation and subsequent hydrogenation to the corresponding alcohols, the z.
• the degree of branching plays a crucial role in the properties of the plasticizer.
• the degree of branching is described by the iso index, which indicates the average number of methyl branches in each fraction.
• the iso index indicates the average number of methyl branches in each fraction.
• the lower the iso-index the more linear the molecules are built up in the respective fraction.
• the higher the linearity, d. H. the lower the iso-index the higher the yields in the oxification and the better the properties of the plasticizer produced therewith.
• a lower iso index results in reduced volatility for phthalate plasticizers and improved cold crack behavior for plasticized PVC grades containing these plasticizers.
• nickel or other catalytically active metals such as ruthenium, palladium, copper, cobalt, iron, chromium or titanium.
• nickel-containing catalysts have gained technical importance.
• Homogeneous catalysts have the disadvantage over heterogeneous that the catalyst must be separated from the reactor effluent in an additional step.
• the catalyst costs per tonne of product in the homogeneous mode of driving are usually much higher than in the heterogeneous driving style.
• Important for large-scale use of heterogeneous Catalysts are as long as possible catalyst life, to minimize production losses, as they are associated with a catalyst regeneration and / or a catalyst exchange.
• No. 5,113,034 describes a process for the dimerization of C3- or C4-olefins over a catalyst which has a sulfate or tungstate as anion. Due to the high activity of the support material used are with these catalysts, as well as with other known catalysts, eg. B. based on zeolites, highly branched oligomers.
• WO 99/25668 describes a process for the preparation of substantially unbranched octenes and dodecenes by oligomerization of butene-1 and / or butene-2 and butane-containing hydrocarbon streams over a nickel-containing heterogeneous catalyst, wherein such amounts of the separated from the reaction mixture Butans and unreacted butene in the oligomerization reaction leads back that the maximum content of oligomers in the reaction mixture at any point of the reactor or the reactors exceeds 25%.
• WO 00/53546 describes a process for the oligomerization of C ⁇ -olefins on a nickel-containing fixed bed catalyst, wherein the reaction takes place in such a way that the conversion of oligomerized C ⁇ -olefins is at most 30% by weight, based on the reaction mixture.
• WO 01/72670 proposes an oligomerization process in which the reactor effluent is separated into two substreams, only one of the substreams subjected to a work-up to obtain the oligomerization product and the other recycled directly to the oligomerization reaction.
• EP 1 457 475 A2 describes a process for the preparation of oligomers of alkenes having 4 to 8 carbon atoms on a nickel-containing, heterogeneous catalyst in at least 2 successive adiabatically operated reactors.
• WO 2006/1 11415 describes a process for the oligomerization of olefins having 2 to 6 carbon atoms, in which an olefin-containing feed is reacted in the presence of a nickel-containing heterogeneous catalyst to a partial conversion, separates the discharge into a first and a second substream, the first Partial stream of a work-up to obtain a fraction containing substantially the oligomerization product subjected to the fraction and the second part in the oligomerization.
• WO 2004/005224 describes a process for the oligomerization of an alkene stream in two or more than two successive catalyst zones, wherein in the first catalyst zone, a catalyst is used which has a molar ratio of sulfur to nickel of less than 0.5 and in the last catalyst zone a catalyst is used which has a molar ratio of sulfur to nickel of 0.5 or more than 0.5. This process also does not yet lead to a completely satisfactory reaction of the alkene containing in the feed hydrocarbon mixture.
• the invention therefore provides a process for the oligomerization of alkenes, in which one provides an alkene-containing feed and an oligomerization in two subjected to reaction in the first reaction zone in the presence of a nickel-containing heterogeneous catalyst and the reaction in the second reaction zone in the presence of a nickel-free heterogeneous catalyst.
• oligomers includes dimers, trimers and higher products from the synthesis reaction of the alkenes used. Preferably, they are essentially dimers and / or trimers. The oligomers are themselves olefinically unsaturated. By suitable choice of the oligomerization catalysts used in the first and second reaction zones, as described below, branched oligomers can be obtained in very high yields to a low degree.
• the sum of the volumes of the nickel-containing heterogeneous catalyst in the first reaction zone and the nickel-free heterogeneous catalyst in the second reaction zone is 50% to 100%, more preferably 75% to 100%, especially 90% to 100%, especially 95% to 100%. , based on the total catalyst volume. In a specific embodiment, the sum of the volumes of the nickel-containing heterogeneous catalyst in the first reaction zone and the nickel-free heterogeneous catalyst in the second reaction zone is 100%.
• the volume ratio of the catalyst in the first reaction zone to catalyst in the second reaction zone is preferably in a range of 1: 1 to 20: 1, more preferably in a range of 5: 1 to 10: 1.
• one or more identical or different reactors can be used.
• a single reactor is used. If multiple reactors are used, they may each have the same or different mixing characteristics.
• the individual reactors can be subdivided one or more times by means of internals. Two or more reactors can be interconnected as desired, z. B. parallel or in row. In a preferred embodiment, two, three or four reactors connected in series are used.
• the entirety of the catalyst with which the alkene-containing feed or (for example when feeding the feed at two or more than two different points) a part thereof comes into contact, is also referred to as fixed catalyst bed in the context of this invention. If a reactor cascade is used, the fixed catalyst bed is usually distributed over all reactors of the cascade.
• a reaction zone is a section of the fixed catalyst bed in the flow direction of the feedstock.
• the fixed catalyst bed has a first reaction zone containing at least one nickel-containing heterogeneous catalyst and, downstream thereof, a second reaction zone containing at least one nickel-free heterogeneous catalyst.
• the fixed catalyst bed in its entirety can only consist of these two reaction zones or have further reaction zones. These include z. B. upstream, intermediate or downstream reaction zones, each having a different catalyst than the adjacent first and / or second reaction zone.
• the first reaction zone is characterized by the fact that a nickel-containing catalyst is used in it.
• the first reaction zone may also contain two or more than two nickel-containing catalysts, which may be in the form of defined sub-zones, as a mixture or in the form of a gradient.
• the second reaction zone is characterized by the fact that a nickel-free catalyst is used in it.
• the second reaction zone may also contain two or more than two nickel-free catalysts, which may be in the form of defined sub-zones, as a mixture or in the form of a gradient.
• a reaction zone may be located within a portion of a reactor, within a single reactor, or within two or more reactors.
• the catalysts of the first and second reaction zones are each arranged in a single reactor or in each case in a cascade of reactors.
• the alkene-containing feed can be fed to the fixed catalyst bed at a single point. It can also be divided and the partial streams thus obtained are fed to the fixed catalyst bed at different locations.
• the supply of the partial streams z. B. at locations which are arranged between the individual reactors.
• the process according to the invention is preferably carried out with continuous reaction.
• an alkene-containing feed is fed into the (first) reactor.
• this feed may also contain, in addition to fresh alkene, a recycle stream from the effluent of the oligomerization reaction or from the work-up of the reaction effluent.
• a discharge stream is taken from the first reaction zone and subjected to work-up to obtain a fraction enriched in oligomerization product and a fraction depleted in oligomerization product, the fraction depleted of oligomerization product can be at least partially recycled to the first reaction zone ,
• the recycle stream consists essentially of unreacted alkenes and saturated hydrocarbons.
• the recycle stream may optionally also contain portions of the oligomers formed.
• the control of the alkene conversion in the first and the second reaction zone or the content of the ionomer in the discharge from the first and the second reaction zone can (among other operating parameters, such as the catalyst used, the pressure and the temperature in the reaction zones and residence time) via the ratio of fresh alkene fed to the recycle stream.
• Suitable pressure-resistant reaction apparatuses for the oligomerization are known to the person skilled in the art. These include the commonly used reactors for gas-solid and gas-liquid reactions, such. B. tubular reactors, stirred tank, gas circulation reactors, bubble columns, etc., which may be subdivided by internals. Preference is given to using tube reactors or tube bundle reactors.
• the temperature in the oligomerization reaction is generally in a range of about 10 to 280 0 C, preferably from 20 to 200 0 C, in particular from 30 to 190 0 C and especially from 40 to 130 0 C. If more reactors are used have the same or different temperatures. Likewise, a reactor may have multiple reaction areas operating at different temperatures. Thus, for example, in a second reaction region of a single reactor, a higher temperature than in the first reaction region or in the second reactor of a reactor cascade, a higher temperature than in the first reactor can be set, for. B. to achieve the fullest possible sales.
• the temperature in the second reaction zone is preferably at most 30 0 C, particularly preferably at most 20 0 C, in particular at most 10 0 C higher than the temperature in the first reaction zone. If a reaction zone is operated at different temperatures or if both reaction zones are operated at different temperatures, a temperature averaged over the volume of the zone can be determined for this reaction zone (s). The averaged temperature is determined by measuring the temperature at a sufficient number of measuring points (eg 3, 4, etc.) in the respective reaction zone and subsequent averaging.
• a sufficient number of measuring points eg 3, 4, etc.
• the (average) temperature in the second reaction zone is preferably at most 30 0 C, particularly preferably at most 20 0 C, in particular at most 10 0 C higher than the (average) temperature in the first reaction zone. Due to the catalysts used according to the invention, it is often possible to operate the second reaction zone at approximately the same or a lower (averaged) temperature than the first reaction zone.
• the pressure in the oligomerization is generally in a range of about 1 to 300 bar, preferably from 5 to 100 bar and in particular from 10 to 50 bar.
• the reaction pressure may be different when using multiple reactors in the individual reactors.
• the temperature and pressure values used for the oligomerization are selected such that the olefin-containing feedstock is liquid or in the supercritical state.
• the reaction in the first and second reaction zone is preferably carried out adiabatically.
• This term is understood in the context of the present invention in the technical and not in the physico-chemical sense.
• the oligomerization reaction is usually exothermic, so that the reaction mixture undergoes an increase in temperature when flowing through the fixed catalyst bed.
• Adiabatic reaction is understood to mean a procedure in which the amount of heat liberated in an exothermic reaction is taken up by the reaction mixture in the reactor and no cooling by cooling devices is used.
• the reaction heat is removed with the reaction mixture from the reactor, except for a residual portion which is discharged by natural heat conduction and heat radiation from the reactor to the environment.
• the amount of heat generated in an exothermic reaction is removed by cooling by means of cooling or thermostating devices so that the temperature in the reactor is maintained substantially constant, ie, isothermal.
• the theoretical ideal case can not be fully realized.
• part of the heat of reaction is discharged with the reaction mixture.
• part of the heat of reaction is removed from the reaction mixture in the course of the first reaction zone and / or after leaving the first reaction zone and before entering the second reaction zone and / or in the course of the second reaction zone.
• a conventional heat exchanger can be used.
• the reaction product produced in the first reaction zone can be fed to the second reaction zone in a first embodiment without separation of the oligomers.
• a separation of the oligomerization product takes place neither in the course of the first reaction zone nor from the discharge of the first reaction zone.
• a discharge stream is taken from the first reaction zone, subjected to a work-up to obtain a fraction enriched in oligomerization product and a fraction which has been depleted of oligomerization product, and the fraction depleted of oligomerization product at least partly into the first and / or second fraction Reaction zone returned.
• the effluent stream may be the entire reaction mixture or a partial stream thereof.
• the discharge stream can be removed in the course of the first reaction zone or from the discharge of the first reaction zone. In a specific embodiment, the discharge stream is taken from the discharge of the first reaction zone.
• the entire reaction mixture is subjected to work-up in the course of the first reaction zone or as discharge from the first reaction zone to give a fraction enriched in oligomerization product and a fraction depleted in oligomerization product.
• the complete discharge from the first reaction zone is subjected to work-up to obtain a fraction enriched in oligomerization product and a fraction depleted of oligomerization product.
• the first reaction zone z. B. from two reactors connected in series, wherein the discharge from the first or the second reactor of a work-up to obtain an enriched oligomerization product fraction and a depleted in oligomerization product fraction is subjected.
• the depleted in oligomerization product fraction can be completely fed to the immediately downstream reactor. It may also be partially fed to a reactor located upstream of the withdrawal site of the effluent stream and partly to the immediately downstream reactor.
• the first reaction zone can also z. B.
• fraction depleted in oligomerization product can in turn be fed completely to the immediately downstream reactor. It may also be partially fed to a reactor located upstream of the withdrawal site of the effluent stream and partly to the immediately downstream reactor.
• the separation of the discharge stream into a fraction enriched in the oligomerization product and a fraction depleted in the oligomerization product can be carried out by customary methods known to the person skilled in the art. Preference is given to a distillative separation.
• the fraction enriched in the oligomerization product unless it is recycled to the oligomerization, can be further processed together with the oligomerization product from the second reaction zone or separately therefrom.
• the fraction depleted in the oligomerization product is fed completely into the second reaction zone in a specific embodiment.
• the heterogeneous nickel-containing catalysts used can have different structures. In principle, unsupported catalysts and supported catalysts are suitable. The latter are preferred.
• the support materials may, for. Silica, alumina, aluminosilicates, layered aluminosilicates and zeolites such as mordenite, faujasite, zeolite X, zeolite-Y and ZSM-5, zirconia treated with acids, or sulfated titania.
• Particularly suitable are precipitation catalysts obtained by mixing aqueous solutions of nickel salts and silicates, eg. Sodium silicate with nickel nitrate, and optionally aluminum salts, such as Aluminum nitrate, and calcination are available.
• catalysts can be used which are obtained by incorporation of Ni 2+ ions by ion exchange in natural or synthetic phyllosilicates, such as montmorillonites. Suitable catalysts may also be obtained by impregnating silica, alumina or aluminosilicates with aqueous solutions of soluble nickel salts, such as nickel nitrate, nickel sulfate or nickel chloride, followed by calcination.
• soluble nickel salts such as nickel nitrate, nickel sulfate or nickel chloride
• Preferred for use in the first reaction zone are catalysts having a molar ratio of sulfur to nickel in the range of 0 to 0.5: 1.
• sulfur-free and sulfur-containing catalysts such as those provided in WO 2004/005224 for use in the first catalyst zone are suitable.
• the reaction is carried out in the first reaction zone in the presence of a nickel-containing heterogeneous catalyst having a molar ratio of sulfur to nickel of at most 0.4: 1.
• nickel oxide-containing catalysts Preferred for use in the first reaction zone are nickel oxide-containing catalysts. Particular preference is given to catalysts which consist essentially of NiO, SiO 2, UO 2 and / or ZrO 2 and, if appropriate, Al 2 O 3. Such catalysts are particularly preferred when the process according to the invention is used for the oligomerization of butenes. They lead to a preference for the dimerization over the formation of higher oligomers and predominantly yield linear products. Most preferred is a catalyst containing as essential active ingredients 10 to 70 wt .-% nickel, 5 to 30 wt .-% titanium dioxide and / or zirconia, 0 to 20 wt .-% alumina and the balance silicon dioxide.
• Such a catalyst is comprises by precipitation of the catalyst composition at pH 5 to 9 by addition of a nickel nitrate aqueous solution to an alkali metal water glass solution containing titanium dioxide and / or zirconium dioxide, filtering, drying and annealing at 350 to 650 0 C available.
• a nickel nitrate aqueous solution to an alkali metal water glass solution containing titanium dioxide and / or zirconium dioxide, filtering, drying and annealing at 350 to 650 0 C available.
• nickel and sulfur containing catalysts having a molar ratio of sulfur to nickel of from 0.25: 1 to 0.38: 1.
• a nickel-free heterogeneous catalyst is used for the second reaction zone.
• a nickel-free catalyst is understood as meaning a catalyst which, except for unavoidable contaminations, does not contain nickel contains.
• Such catalysts generally have a nickel content of at most 0.01% by weight, more preferably of at most 0.001% by weight, based on the total weight of the catalyst.
• a catalyst which comprises alumina as the carrier.
• the support material is selected from gamma, eta or theta alumina and mixtures thereof. It is particularly preferred to use gamma-aluminum oxide as the carrier material.
• the catalysts used in the second reaction zone preferably have 1 to 15 wt .-%, based on the total weight of the catalyst, sulfur in oxidic form.
• Such a catalyst may, for. B. a support material with H2SO4 brought into contact, dried and then calcined.
• the catalysts used in the first and in the second reaction zone are preferably in particulate (particulate) form.
• the catalyst particles generally have an average value of the (largest) diameter of 1 to 40 mm, preferably 2 to 30 mm, in particular 3 to 20 mm.
• These include z. B. catalysts in the form of tablets, for. B. with a diameter of 2 to 6 mm and a height of 3 to 5 mm, rings with z. B. 5 to 7 mm outer diameter, 2 to 5 mm in height and 2 to 3 mm hole diameter, or strands of different lengths of a diameter of z. B. 1, 5 to 5 mm, before.
• Such forms are obtained in a manner known per se by tableting, extrusion or extrusion.
• the mass of the catalyst or a precursor thereof conventional aids, for.
• lubricants such as graphite or fatty acids (such as stearic acid) and / or molding aids and reinforcing agents, such as glass fibers, asbestos, silicon carbide or Kaliumtita- Nat added.
• Suitable alkene feedstocks for the process according to the invention are, in principle, all compounds which contain 2 to 6 carbon atoms and at least one ethylenically unsaturated double bond.
• Preferred are alkene feedstocks containing alkenes of 4 to 6 carbon atoms.
• the alkenes used for the oligomerization are preferably selected from linear (straight-chain) alkenes and alkene mixtures which contain at least one linear alkene. These include ethene, propene, 1-butene, 2-butene, 1-pentene, 2-pentene, 1-hexene, 2-hexene, 3-hexene and mixtures thereof.
• linear ⁇ -olefins and olefin mixtures containing at least one linear ⁇ -olefin are preferred. Particular preference is given to 1-butene, 1-pentene, 1-hexene, mixtures thereof and hydrocarbon mixtures which comprise at least one such alkene. Preferably, a technically available olefin-containing hydrocarbon mixture is used for the oligomerization.
• olefin mixtures result from hydrocarbon cracking in petroleum processing, for example by cat cracking, such as fluid catalytic cracking (FCC), thermocracking or hydrocracking followed by dehydrogenation.
• cat cracking such as fluid catalytic cracking (FCC), thermocracking or hydrocracking followed by dehydrogenation.
• FCC fluid catalytic cracking
• thermocracking thermocracking
• hydrocracking hydrocracking followed by dehydrogenation
• a suitable technical olefin mixture is the C4 cut.
• C4 cuts are available, for example, by fluid catalytic cracking or steam cracking of gas oil or by steam cracking of naphtha.
• raffinate I obtained after the separation of 1,3-butadiene
• raffinate II obtained after the isobutene separation technical olefin mixture
• Suitable olefin-containing hydrocarbon mixtures having 4 to 6 carbon atoms for use in step a) can furthermore be obtained by catalytic dehydrogenation of suitable industrially available paraffin mixtures.
• the production of C4-olefin mixtures from liquid gases (liquified petro- leum gas, LPG) and liquefied natural gas (LNG) is possible.
• the latter in addition to the LPG fraction, additionally comprise relatively large amounts of relatively high molecular weight hydrocarbons (light naphtha) and are thus also suitable for the preparation of Cs and C ⁇ -olefin mixtures.
• the preparation of olefin-containing hydrocarbon mixtures which contain monoolefins having 4 to 6 carbon atoms from LPG or LNG streams is possible by customary methods known to the person skilled in the art, which generally comprise one or more work-up steps in addition to the dehydrogenation. These include, for example, the separation of at least part of the saturated hydrocarbons contained in the aforementioned olefin feed mixtures. For example, these may be reused to produce olefin feeds by cracking and / or dehydrogenation.
• the olefins used in the process according to the invention may also contain a proportion of saturated hydrocarbons which are inert to the oligomerization conditions according to the invention.
• the proportion of these saturated components is generally at most 60 wt .-%, preferably at most 40 wt .-%, particularly preferably at most 20 wt .-%, based on the total amount of the olefin contained in the hydrocarbon feedstock and saturated hydrocarbons.
• a raffinate II suitable for use in the process according to the invention has, for example, the following composition:
• trans-2-butene From 20 to 40% by weight of trans-2-butene, from 10 to 20% by weight of cis-2-butene, From 25 to 55% by weight of 1-butene, from 0.5 to 5% by weight of isobutene
• trace gases such as 1, 3-butadiene, propene, propane, cyclopropane, propadiene, methylcyclopropane, vinyl acetylene, pentenes, pentanes, etc. in the range of not more than 1 wt .-%.
• a suitable raffinate II has the following typical composition:
• diolefins or alkynes are present in the olefin-rich hydrocarbon mixture, they may be removed from the same before the oligomerization to preferably less than 10 ppm by weight. They are preferably by selective hydrogenation, for. B. according to EP-81 041 and DE-15 68 542 removed, more preferably by a selective hydrogenation to a residual content of less than 5 ppm by weight, in particular less than 1 ppm by weight.
• Oxygen-containing compounds such as alcohols, aldehydes, ketones or ethers, are expediently also removed from the olefin-rich hydrocarbon mixture.
• the olefin-rich hydrocarbon mixture with advantage over an adsorbent such.
• a molecular sieve in particular one with a pore diameter of> 4 ⁇ to 5 ⁇ , are passed.
• the concentration of oxygen-containing, sulfur-containing, nitrogen-containing and halogen-containing compounds in the olefin-rich hydrocarbon mixture is preferably less than 1 ppm by weight, in particular less than 0.5 ppm by weight.
• the process according to the invention is preferably carried out such that the alkenes contained in the alkene-containing feed are reacted in the first reactor zone at from 75 to 99%, preferably from 85 to 99%, especially from 90 to 98%.
• the process according to the invention is preferably carried out such that the alkenes present in the discharge of the first reaction zone are reacted in the second reactor zone to 30 to 99%, preferably to 50 to 99%, especially to 70 to 98%.
• the oligomers formed are separated in a manner known per se from the unreacted hydrocarbons and if desired, are attributed to the process (cf., for example, WO-A 95/14647).
• the separation is usually carried out by fractional distillation.
• the process according to the invention is distinguished from the known processes of this type by the fact that it leads to a high alkene conversion with a simultaneously low degree of branching of the oligomers obtainable in this way.
• This effect could hitherto usually only be achieved by increasing the temperature in the rear part of the catalyst bed or using a more active catalyst in this area or by an overall increased volume of catalyst because of the decreasing content of alkene in the feed stream.
• Example 1 of DE 43 39 713 A1 a catalyst of the composition 50 wt .-% NiO, 37 wt .-% SiO 2 and 13 wt .-% TiO 2 is prepared.
• the catalyst powder is mixed with 3 wt .-% graphite and pressed into 3 x 3 mm tablets.
• a catalyst having a nickel content of 7.9% by weight and a sulfur content of 4.32% by weight, in each case based on the total weight of the catalyst, is prepared on a ⁇ -alumina support.
• the molar ratio of sulfur to nickel is 1.
• the carrier used was ⁇ -aluminum oxide of the "D10-21" type from BASF Aktiengesellschaft (2.3 mm extrudates, BET surface area 210 m 2 / g, water absorption capacity 0.77 ml / g, loss on ignition 0.8% by weight). used.
• a solution of 5.6 kg of 96% strength sulfuric acid in water (volume corresponding to the water absorption of the carrier) was added to 28 kg of this carrier at room temperature with stirring. sprayed. After 30 minutes of stirring, the so-impregnated support was dried for 2 hours at 120 0 C and then calcined for 5 h at 550 0 C in air.
• the catalyst thus obtained contains 5.5% by weight of sulfur in oxidic form.
• FIG. 1 shows the scheme of a device in which the inventive method is carried out continuously at 30 bar. All reactors R1 to R3 are operated adiabatically and each have a length of 4 m and a diameter of 0.8 m.
• the alkene-containing feed is fed via the feed line (F) to the first oligomerization reactor (R1).
• the discharge from (R1) is fed via an intermediate cooling (ZK1) to the reactor (R2).
• the effluent from reactor (R2) is separated by distillation in the column (K1) and the oligomeric reaction product is taken off as the bottom product via line (B1).
• the top product (H) of the column (K1) is fed to the third oligomerization reactor (R3).
• the effluent from reactor (R3) is separated by distillation in the column (K2) and the oligomeric reaction product is taken off as the bottom product via line (B2).
• the top stream of the column K2 is partially returned via the line (Z) in the reactor (R3), the remaining part of the top stream is discharged via the line (P) (purge stream) from the device.
• a raffinate II stream (76.4% butenes and 23.6% butanes) as alkene-containing feed is first subjected to oligomerization in the presence of the catalyst 1 a), as described in Example 5 of WO 99/25668 is described.
• 90.2% of the butenes were converted to oligomers; the Cs selectivity was 80.4%.
• the ISO index of the C 8 fraction was 0.99.
• the top product of the distillative separation was an alkenes depleted raffinate I Il stream having a butene content of 24%.
• the raffinate I II stream obtained after separation of the oligomers is then used for further reaction in the reactor R3.
• the nickel-containing catalyst 1 b) is used in the third reaction zone R3, in the inventive example the nickel-free catalyst 1 c).
• the relevant data of the oligomerization reaction and the results obtained are shown in Table 1 below:

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