EP2212267A1

EP2212267A1 - Method for isomerizing olefins

Info

Publication number: EP2212267A1
Application number: EP08838846A
Authority: EP
Inventors: Stefan Iselborn; Thomas Heidemann
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2007-10-15
Filing date: 2008-10-15
Publication date: 2010-08-04
Also published as: KR20100075997A; WO2009050194A1; CN101827804A; JP2011500628A; US20100286458A1

Abstract

The present invention relates to a method for isomerizing olefins from olefin-containing hydrocarbon mixtures having (4) to (20) C atoms at temperatures from 20 to 200°C and pressures from 1 to 200 bar in the liquid phase in the presence of a heterogenic catalyst, characterized in that a catalyst is used comprising on an aluminum oxide carrier 1 to 20 weight % nickel in oxide form and 1 to 20 weight % of at least one element of the group VIB.

Description

Process for the isomerization of olefins

description

The present invention relates to a process for the isomerization of olefins from olefin-containing hydrocarbon mixtures having 4 to 20 C atoms, in particular a process for the isomerization of 1-butene to 2-butene.

For the double bond isomerization of olefins, numerous processes are known from the prior art, either at temperatures above 250 ^° C. or at lower temperatures in the range from 100 to 250 ^° C. or even below 100 ^° C. both with and without addition be carried out by hydrogen. The temperature level has a decisive influence on the isomer composition. Thus, at lower temperatures, the formation of olefins with internal double bonds is preferred, while at higher temperatures mainly 1-olefins are formed. The equilibrium composition is dependent not only on the temperature but also on the olefin used.

As u. a. from US Pat. No. 6,156,947, US Pat. No. 5,087,780 and US Pat. No. 4,417,089, the double bond isomerization can be carried out using hydrogen on noble metal-containing catalysts. These processes often take place in combination with a diolefin hydrogenation. As a side reaction of the isomerization it often comes to the formation of alkanes by overhydration.

In order to avoid overhydrogenation in the isomerization, therefore, processes for double bond isomerization are known, which can be carried out without the addition of hydrogen.

Suitable catalysts for such isomerization reactions are, for example, the alkaline earth oxides described in EP 0 718 036 A1 on alumina, and the mixed alumina / silica supports known from US 4,814,542, which are doped with oxides of alkaline earth metals, boron group metals, lanthanides or elements of the iron group, or with Alkali metals occupied γ-alumina, which is described in JP 51-108691.

Also suitable are catalysts of manganese oxide on alumina, described in US 4,289,919; Catalysts of magnesium, alkali and zirconium oxides dispersed on an alumina carrier described in EP 0 234 498 A1; and alumina catalysts additionally containing sodium oxide and silica described in US 4,229,610. However, the catalysts mentioned have the disadvantage that they have only ty at reaction temperatures above 250 ⁰ C a significant Isomerisierungsaktivi-. Therefore, superbasic catalysts based on alkali metal (suboxide) / carrier are used in the isomerization processes described in DE 23 36 138. These can also be used at temperatures below 100 ⁰ C. The disadvantage here is the high moisture sensitivity of the catalyst.

The invention therefore an object of the invention to provide a process for the isomerization of olefins, in particular for the isomerization of n-butenes, which selectively allows the formation of olefins with internal double bonds in high yields at low temperatures. Furthermore, the formation of undesired dienes, eg. B. 1, 3-butadiene can be avoided.

This object has been achieved by a process for the isomerization of olefins from olefin-containing hydrocarbon mixtures having 4 to 20 C atoms at temperatures of 20 to 200 ⁰ C and pressures of 1 to 200 bar in the liquid phase in the presence of a heterogeneous catalyst, characterized in that one uses a catalyst, on an alumina support 1 to 20 wt .-%, preferably 5 to 15 wt .-%, particularly preferably 7 to 12 wt .-% nickel in oxidic form and 1 to 20 wt. %, preferably 2 to 12 wt .-%, particularly preferably 3 to 9 wt .-% of at least one element of the group VIB contains, wherein the wt .-% information indicate the amounts of the respective metals, based on the total weight of the invention used catalyst.

The designation of the groups of the periodic system of the elements takes place according to the CAS nomenclature (chemical abstracts service).

As group VI B element tungsten or molybdenum or mixtures of tungsten and molybdenum are preferably used in each case in oxidic form, particularly preferably used tungsten in oxidic form.

The catalyst may moreover contain from 0.1 to 10% by weight, preferably from 0.3 to 5% by weight, particularly preferably from 0.5 to 2% by weight, of one or more elements of group VB in oxidic form, in particular Vanadium and / or 0.1 to 1 wt .-%, preferably 0.1 to 0.8 wt .-%, particularly preferably 0.1 to 0.5 wt .-% boron or phosphorus or a mixture of boron and phosphorus each contained in oxidic form.

The catalyst may further contain 0.01 to 0.5% by weight, preferably 0.1 to 0.4% by weight of sulfur in oxidic form, provided that the ratio of sulfur to nickel is in the range of 0, 01 to 0.1 mol / mol is to effectively suppress typical side reactions such as skeletal isomerization and oligomerization. The alumina used as support material for the catalysts used in the process according to the invention are preferably gamma-AbCh, theta-AbO ₃ or eta-AbO ₃ or mixtures thereof, as described, for example, by BASF, SASOL, Alcoa, Grace and Rhone Poulenc are commercially available. Particular preference is given to those alumina supports which consist predominantly of gamma-Al 2 O 3. Preferably, these aluminas have a water absorption capacity of from 0.2 to 1.5 ml / g of carrier material, preferably from 0.4 to 1.0 ml / g of carrier material and an inner surface, measured by BET, of from 100 to 600 m ² / g, preferably from 120 to 450 m ² / g, particularly preferably from 150 to 350 m ² / g. Also preferred are such aluminas having a content of less than 0.2% Na ₂ O, 0.2% Fe ₂ O ₃ and / or 0.1% SO ₃ .

The active components, additives and / or dopants contained in the catalyst can be applied to the support by any known method, for example by coating from the gas phase (chemical or physical vapor deposition) or impregnation of the support material in a solution containing the substances to be separated and / or compounds.

Impregnation processes for the separation of active components, additives and / or dopants on a support are known. In general, the carrier is impregnated with an aqueous or alcoholic solution of salts of the components to be separated, which convert in the course of further catalyst production in the substances to be deposited, the volume of the solution is so dimensioned that the solution is almost completely absorbed by the pore volume of the carrier becomes ("in- centip wetness" method).

Suitable VI B compounds are all compounds of the group VIB which, when heated in the presence of oxygen or oxygen-containing gas mixtures such as air, can be converted into an oxidic form of the metal under the calcining conditions. Preferably used as VI B compound water-soluble group VI B salts, especially ammonium tungstates, Ammoniummolybdate, molybdic acids, tungstic acids or heteropolyacids in H or NhU form.

Suitable nickel compounds are all compounds of nickel which can be converted into an oxidic form of the metal on heating in the presence of oxygen or oxygen-containing gas mixtures such as air under the calcination conditions. The nickel compound used is preferably water-soluble nickel salts, for example with an organic anion such as the formate, oxalate, acetylacetone or 2-ethylhexanoate and, in particular, optionally hydrated nickel nitrate.

The substances to be deposited can be removed individually and / or in partial quantities in several process steps or together and completely in one process step. to be divorced. Preferably, the co-deposition is in a impregnation step. The concentration of the salts in the solution is such that after impregnation and conversion of the supported catalyst to the finished catalyst, the components to be deposited are present in the desired concentration on the catalyst. The salts are chosen so as not to leave any residues which interfere with the preparation of the catalyst or its subsequent use.

Optionally, water-soluble compounds of sulfur, boron, phosphorus, vanadium and / or niobium, which may be converted to an oxidic form of the element upon heating in the presence of oxygen or oxygen-containing gas mixtures such as air under the calcination conditions, may also be added to the above impregnating solution become.

After soaking, the soaked carrier is dried in a conventional manner. This is generally carried out in the air stream at a temperature in the range from 60 to 300 ^° C., preferably in the range from 80 to 250 ^° C., more preferably in the range from 100 to 200 ^° C., very particularly preferably in the range from 110 to 180 ^° C. Drying is continued until substantially all of the water present in the impregnated catalyst has escaped, which is generally the case after a few hours. Typical drying times are in the range of 1 to 30 hours and depend on the set drying temperature, with a higher drying temperature shortening the drying time. The drying can be further accelerated by applying a negative pressure.

In a preferred embodiment of the method according to the invention, the drying of the impregnated catalyst is carried out with simultaneous movement of the impregnated support material, for example in a rotary kiln furnace.

In a further preferred embodiment of the method according to the invention, the air stream used for drying is passed in countercurrent through the rotary tube.

After drying, the catalyst is prepared in a conventional manner by calcination. This calcination essentially serves to convert the impregnated salts into the components or precursors of such components to be deposited. In the case of impregnation of metal nitrates, in this calcination, substantially the nitrates are decomposed into metals and / or metal oxides remaining in the catalyst and nitrous gases which escape.

During calcining, the catalytically active oxide nickel and group VI B-containing active composition is formed from the nickel compound and the VI B compound. The calcination temperature is generally 200 to 900 ^° C., preferably 280 to 800 ^° C., more preferably 300 to 600 ^° C. The calcination time is generally between 0.5 and 20 hours, more preferably between 0.5 and 10 hours preferably between 0.5 and 5 hours. The calcination is carried out in a conventional oven, for example in a rotary kiln, in a belt calciner or in a chamber furnace. The calcination may be followed directly by the drying without intermediate cooling of the supported and dried support.

In a particularly preferred embodiment of the process according to the invention, the drying and the calcination of the catalyst are combined in a rotary kiln.

Before being used as isomerization catalyst, the catalysts prepared in this way are expediently conditioned in the dry gas stream (eg dry nitrogen), eg. B. at atmospheric pressure and temperatures of 20 to 500 ⁰ C, preferably 100 to 250 ⁰ C to remove traces of moisture (such as from the air) from the catalyst.

For the isomerization process according to the invention, a fixed-bed reactor is preferably used. It can also be other types of reactors such. As a fluidized bed reactor, a moving bed reactor, tubular reactors or tube bundle reactors can be used. The reaction is slightly exothermic. The reaction can be carried out isothermally or adiabatically.

The isomerization is carried out at a temperature at which a shift of the double bond is ensured, skeleton isomerization and oligomerization, however, are largely avoided. The reaction temperature is therefore generally from 20 to 200 ⁰ C, preferably at 20 to 120 ⁰ C, particularly preferably at 30 to 110 ⁰ C. The pressure is adjusted so that the olefin is in liquid form. It is generally 1 to 200 bar, preferably 1 to 100 bar, more preferably 4 to 30 bar.

The loading of the catalyst is generally 0.01 to 20 kg, preferably 0.05 to 15 kg, particularly preferably 0.1 to 10 kg to be isomerized olefin per kg of catalyst per hour.

Suitable starting materials are olefins or olefin-containing hydrocarbon mixtures having 4 to 20 carbon atoms and a high proportion of 1-olefins. In particular, pure 1-butene as well as hydrocarbon mixtures with a high proportion of 1-butene can be used for the process according to the invention, for example C4 fractions, as obtained in steam or FCC cracking or in the dehydrogenation of butane. High in this sense is a salary that is higher than the salary in the thermodynamic equilibrium below the temperatures set in the reaction.

The isomerization process according to the invention can be carried out alone or else in combination with other chemical processes. Typical examples of combined process steps, which are not intended to limit the invention, are:

• Combination A:

Selective hydrogenation (eg of butadiene in a steamcracker-derived C4-olefin stream) and isomerization according to the invention;

• Combination B:

Inventive isomerization and olefin metathesis (eg, reaction of ethylene with 2-butenes to produce propylene);

Combination C: isomerization and olefin alkylation according to the invention (eg reaction of long-chain linear internal olefins with maleic anhydride to alkylsuccinic anhydrides);

• combination D:

Inventive isomerization and olefin oligomerization (for example for the preparation of alkylate (reaction of i-butene with n / i-butenes).

Preferred process combinations which comprise the isomerization process according to the invention are the combinations A and B.

Olefin metathesis has become an extremely valuable tool in organic synthesis in recent years. Also on an industrial scale, a number of applications have been established, for example, the process of Shell AG (SHOP process) for the production of internal olefins and in particular the Phillips process for the preparation of propene by ethenolysis (metathetic cleavage by ethene) of 2 But the metathesis step is an important building block.

The valuable scope of the metathesis reaction, however, is opposed by a crucial point that has long had a strong influence on the development of technical processes: metathesis catalysts deactivate relatively quickly in comparison with other technically used catalyst systems. Because of the often expensive transition metal catalysts used, which are methane active, it is desirable to reduce or avoid the deactivation due, for example, to feed contaminants.

The cause for the deactivation of metathesis catalysts has already been discussed extensively in the literature. Examples are J. Mol. Cat. 1991, 65, pages 39 to 50 (Commereuc et al.), Catalysis today 1999, 51, pages 289 to 299 (JC Mol) and J. Mol. Cat. 1991, 65, pages 219 to 235 (JC Mol).

In principle, two types of deactivation are postulated in the literature, namely an intrinsic pathway that is always present and a deactivation mechanism caused by certain impurities in the feed stream. These impurities in the feed stream can have a reversible effect or act as permanent poisons.

In particular, the deactivating substances mentioned in the literature are acetylenic compounds, isobutene and 1,3-butadiene, since they tend to form oligomers by cationic mechanisms, which act as a diffusion barrier. Furthermore, polar, basic components are mentioned as an important class of deactivating substances. This influence is known and is avoided in the prior art by the use of adsorptive feed cleaning - protective beds (eg molecular sieves). A detailed study of the influence of oxygen-containing compounds on metathesis catalysts can be found in J. A. K. du Plissis, J. Mol. Cat. A: Chemical, 1989, 133, pages 181 to 186. As adsorptive feed purification, in particular zeolites or aluminum oxides are suitable.

As a measure against the present in C4 feed 1, 3-dienes and acetylenic compounds, a selective hydrogenation is described in the prior art.

Thus, EP 0 742 195 A1 describes a process for converting C4 or C5 cuts into ethers and propylene. Starting from C4 cuts, the diolefins and acetylenic impurities initially contained are selectively hydrogenated, the hydrogenation being linked to an isomerization of 1-butene to 2-butene. The yield of 2-butenes should be maximized. The ratio of 2-butene to 1-butene after hydrogenation is about 9: 1. This is followed by etherification of the iso-olefins contained, the ethers being separated from the C4 cut. Then, oxygenate impurities are separated. The resulting effluent containing predominantly 2-butene besides alkanes is then reacted with ethylene in the presence of a metathesis catalyst to obtain a reaction effluent containing propylene as product. The metathesis is carried out in the presence of a catalyst containing rhenium oxide on a support.

DE-A 198 13 720 relates to a process for the preparation of propene from a C4 stream. First, butadiene and isobutene are removed from the C4 stream. Oxigenate impurities are then separated off and a two-stage metathesis of the butenes is carried out. First, 1-butene and 2-butene are converted to propylene and 2-pentene. Then, the obtained 2-pentene is further reacted with dosed ethylene to propylene and 1-butene. DE 100 13 253 A1 describes suitable pretreatments for C4 streams used for metathesis. The separation of 1, 3-butadiene and acetylenic compounds is achieved by extraction and / or selective hydrogenation. The limit value for the sum of dienes is defined as less than 10 ppm in DE 100 13 253 A1.

Olefin-containing hydrocarbon mixtures containing 1-butene and 2-butene and optionally isobutene, u. a. obtained in various cracking processes such as steam cracking or FCC cracking as C4 fraction. Alternatively, butene mixtures, as obtained in the dehydrogenation of butanes or by dimerization of ethene, can be used. Butanes contained in the C4 fraction are inert. Dienes, alkynes or enynes are removed before the metathesis step according to the invention by conventional methods such as extraction or selective hydrogenation.

The butene content of the C4 fraction used in the process is from 1 to 100% by weight, preferably from 50 to 90% by weight. The butene content refers to 1-butene, 2-butene and isobutene.

Preferably, a C4 fraction is used, as obtained in the steam or FCC cracking or in the dehydrogenation of butane.

Selective hydrogenation of crude C4 cut

In the crude C4 fraction originating from a steam cracker or a refinery, initially butadienes (1,2- and 1,3-butadiene) as well as alkynes or alkenines contained in the C4 cut are selectively hydrogenated in a generally two-stage process. The refinery derived C4 stream can also be fed directly to the second step of the selective hydrogenation.

The first step of the hydrogenation is preferably carried out on a catalyst containing 0.1 to 0.5 wt .-% palladium supported on alumina. The reaction is operated in gas / liquid phase in a fixed bed (trickle-flow mode) with a liquid circuit. The hydrogenation is carried out at a temperature in the range 40 to 80 ⁰ C and a pressure of 10 to 30 bar, a molar ratio of hydrogen to butadiene of 10 to 50 and a volume velocity LHSV of up to 15 m ³ Frischfeed per m ^{3 of} catalyst per hour and a Ratio of Recycle operated by 5 to 20 inflow.

The second step of the hydrogenation is preferably carried out on a catalyst containing 0.1 to 0.5% by weight of palladium on alumina as carrier. The reaction is carried out in gas / liquid phase in a fixed bed (trickle-bed method) with a liquid operated cycle. The hydrogenation is carried out at a temperature in the range of 50 to 90 ⁰ C and a pressure of 10 to 30 bar, a molar ratio of hydrogen to butadiene of 1, 0 to 10 and a volume velocity LHSV of 5 to 20 m ³ Frischfeed per m ^{3 of} catalyst operated per hour and a ratio of recycle to inflow from 0 to 15.

As a result of this hydrogenation, a C 4 -olefin mixture having a content of 1,3-butadiene of 100 to 500 ppm, preferably 110 to 400 ppm, particularly preferably 120 to 300 ppm, and a content of cumulated dienes such as propadiene, 1, 2-butadiene, 1, 2-pentadiene or 2,3-pentadiene of less than 10 ppm, preferably from 1 to 10 ppm, more preferably from 2 to 10 ppm.

The product stream obtained after the selective hydrogenation can then be used directly in the isomerization reaction already described above.

For example, the isomerization of n-butenes in the preparation of propylene from n-butenes and ethylene in the so-called metathesis process is a very important process step because, as stated in US Pat. No. 6,743,958, the selectivity to propylene and thus the product yield of propylene and the Energy consumption of the process is optimal, if as little as 1-butene, but as much as possible 2-butene in the feed mixture of the metathesis process is present.

Depending on the composition of the feed mixture used for the metathesis must often be preceded by a catalytic hydrogenation and an isomerization of the metathesis stage because, as already mentioned, some components of the mixture such. Butadienes are harmful to the metathesis stage (eg as a catalyst poison). According to the prior art, the catalytic hydrogenation stage is frequently constructed in such a way that, as far as possible, the hydroisomerization should also take place simultaneously in the hydrogenation reactor of the hydrogenation stage.

US 2006/0235254 A1 describes that in the hydroisomerization, the isomerization of 1-butene to 2-butene can be further increased by adding carbon monoxide CO to the starting material or to the hydrogen. In US 6,743,958 it is described that in the hydroisomerization, the isomerization can be increased by adding sulfur to the catalyst. However, in this case too, the degree of isomerization still remains limited.

There are also undesirable side reactions of the hydrogenation, for example the so-called overhydrogenation of the butenes to butane, which leads to a reduction in the product yield. Therefore, the hydrogenation process must be optimized so that the

Butadiene is hydrogenated, but not the butene. Experts call such hydrogenation processes selective hydrogenations. The implementation of these methods is very complex and / or not applicable everywhere. For example, the catalysts according to US Pat. No. 6,743,958 have to be prepared separately in a tedious complex production process. The use of CO according to US 2006/0235254 A1 is often out of the question because CO is poisonous and must be separated again in subsequent stages before the products of the process can be used.

If, on the other hand, selective hydrogenation and isomerization are carried out in separate process steps, each individual process step can be optimized so that it is optimally hydrogenated and, in the other process step, optimal 1-butene is isomerized to 2-butene. To carry out the hydrogenation step can be selected from catalysts that are offered by many manufacturers. These are usually Pd, Pt or Ni-containing catalysts, which are often applied to oxidic supports, preferably alumina supports. In the isomerization step, it is possible to use the catalyst according to the invention.

The selective hydrogenation step and the isomerization step can take place in separate process steps or separate reactors. However, it is also possible to drain the selective hydrogenation step and the isomerization step in the same reactor, for. Example, characterized in that the different catalysts are superimposed into the reactor, wherein preferably the hydrogenation catalyst is charged at the top and the amount of hydrogen is such that the hydrogen in the hydrogenation catalyst by reaction with the unsaturated hydrocarbons to less than 0.5 mol of hydrogen / moles of diene is abreacted.

Thus, with the new isomerization process according to the invention, it is possible to increase the ratio of 2-butene to 1-butene at the end of the isomerization stage to values above 10 and even above 20. In addition to these process improvements which are advantageous for the preparation of propylene by means of metathesis, moreover, only a very small number of undesired by-products, for example butadienes or oligomers, are formed.

Olefin metathesis

The metathesis reaction which can be used in combination with the isomerization process according to the invention can be carried out, for example, as described in WO 00/39058 or DE 100 13 253 A1.

Olefin metathesis (disproportionation), in its simplest form, describes the reversible metal-catalyzed transalkylidenation of olefins by breaking or reforming C = C double bonds according to the following equation:

In the specific case of the metathesis of acyclic olefins, a distinction is made between self-metathesis, in which an olefin is converted into a mixture of two olefins of different molar mass (for example: propene → ethene + 2-butene), and cross- or co-metathesis, which is a reaction of two describes different olefins (propene + 1-butene → ethene + 2-pentene). If one of the reaction partners is ethene, this is generally referred to as ethenolysis (for example, 2-butene + ethene → 2 propene).

Suitable metathesis catalysts are, in principle, homogeneous and heterogeneous transition metal compounds, in particular those of VI. to VIII. sub-group of the Periodic Table of the Elements and homogeneous and heterogeneous catalyst systems in which these compounds are contained.

Particularly preferred in the context of the present invention are those metathesis processes which start from C4 streams having a ratio of 2-butene to 1-butene of between 5 and 40.

For example, DE 199 32 060 A1 describes a process for preparing C ₅ - / C ₆ -olefins by reacting an initial stream which comprises 1-butene, 2-butene and isobutene to give a mixture of C 2-6 -olefins. In particular, propene is obtained from butenes. In addition, hexene and methylpentene are discharged as products. In the metathesis, no ethene is added. Optionally, ethene formed in the metathesis is recycled to the reactor.

The butene content of the C4 fraction used in the process can be in the range from 1 to 100% by weight, preferably 60 to 90% by weight. The butene content refers to 1-butene, 2-butene and isobutene.

The C 4 -olefin mixture used may, if appropriate, be treated prior to the metathesis reaction of a corresponding treatment on adsorber protection beds, preferably on high-surface area aluminas or molecular sieves, to remove interfering impurities.

The metathesis reaction is preferably carried out in the presence of heterogeneous, not or only slightly isomerization-active metathesis catalysts which are selected from the class of transition metal compounds applied to inorganic supports. fertilize metals of the VI. b, VII. b or VIII. Group of the Periodic Table of the Elements are selected.

Rhenium oxide is preferably used as a metathesis catalyst on a carrier, preferably on γ-aluminum oxide or on Al 2 O 3 / B 2 O 3 / SiO 2 mixed carriers.

In particular, Re2θ7 / γ-Abθ3 having a rhenium oxide content of 1 to 20 wt .-%, preferably 3 to 15 wt .-%, particularly preferably 6 to 12 wt .-% is used as the catalyst.

The metathesis is preferably carried out in the liquid way at a temperature of 0 to 150 ⁰ C, more preferably 20 to 80 ⁰ C and a pressure of 2 to 200 bar, particularly preferably 5 to 30 bar performed.

If the metathesis is carried out in the gas phase, the temperature is preferably 100 to 450 ^° C., more preferably 200 to 350 ^° C. The pressure in this case is preferably 1 to 40 bar, particularly preferably 1 to 30 bar.

The catalysts are used freshly calcined and require no further activation (eg by alkylating agents). Deactivated catalyst can be regenerated by burning off Coke residues at temperatures above 400 ⁰ C in the air stream and cooling under inert gas atmosphere several times.

In a special variant of today's metathesis processes, the so-called reverse Phillips triolefin process (see J. Mol Cat. A: Chemical 213 (2004) 39), an isomerization catalyst of MgO is used in the metathesis reactor in addition to the actual metathesis catalyst in order to obtain the To increase 2-butene content in the recycle stream. But the one -Butenanteil in the recycle stream is also quite high yet because the thermodynamic equilibrium at the used process temperature above 200 ⁰ C limits the possible principle 2-butene to 1 -Butenverhältnis to a value below the 10th

The present invention also provides a process for the preparation of propylene from n-butenes and ethylene

a) selective hydrogenation of a C4 mixture containing essentially a mixture of 1- and 2-butenes and butadiene; b) isomerization of 1-butene in the selectively hydrogenated C4 mixture at temperatures of 20 to 200 ⁰ C and pressures of 1 to 200 bar in the liquid phase in counter waiting a heterogeneous catalyst; c) Metathesis of ethylene with 2-butene to propylene in the selectively hydrogenated and isomerized C4 mixture in the presence of a metathesis catalyst, wherein at least equimolar amounts of ethylene are used on the butenes contained in the C4 mixture.

As a rule, all known isomerization catalysts can be used for the isomerization in process step b). A preferred embodiment of the abovementioned process is characterized in that, in process step b), a catalyst is used which comprises on an alumina support 1 to 20% by weight, preferably 5 to 15% by weight, particularly preferably 7 to 12% by weight .-% nickel in oxidic form and 1 to 20 wt .-%, preferably 2 to 12 wt .-%, particularly preferably 3 to 9 wt .-% of at least one element of group VIB contains, wherein the wt .-% information refer to the total weight of the catalyst used in the invention.

The catalyst may also be 0.01 to 0.5 wt .-%, preferably 0.1 to 0.4

Wt .-% sulfur in oxidic form, provided that the ratio of sulfur to nickel in the range of 0.01 to 0.1 mol / mol, to effectively suppress typical side reactions such as skeletal isomerization and oligomerization.

A preferred embodiment of the process according to the invention is characterized in that the C4 mixture used for the selective hydrogenation in process step a) additionally contains n-butane, isobutane or isobutene or mixtures thereof.

A further preferred embodiment of the process according to the invention is characterized in that the isomerization in process step b) is carried out without the addition of hydrogen, in contrast to the so-called hydroisomerization.

In current metathesis processes, the conversion in the actual metathesis reactor is not complete, which is why the unreacted butenes are very frequently separated from the product propylene by customary separation methods (eg separation columns or the like) and combined with the butenes of the starting material and in the metathesis report be returned. The recycle stream contains considerable amounts of 1-butene.

A resulting further preferred embodiment of the abovementioned process according to the invention is characterized in that

d) the product stream obtained by metathesis c) is first separated by distillation into a low-boiling fraction A containing C2-C3-olefins and high-boiling fraction B containing C4-C6-olefins and butanes; e) the low-boiling fraction A obtained from d) is then separated by distillation into a fraction containing ethylene and a fraction containing propylene, the ethylene-containing fraction being recycled to process step c) and the fraction containing propylene being discharged as product, and f) the from d) obtained high-boiling fraction B with the obtained according to process step a), selectively hydrogenated C4 mixture and re-used in the isomerization b).

A likewise preferred embodiment of the method according to the invention is characterized in that

d) the product stream obtained by metathesis c) is first separated by distillation into a low-boiling fraction A containing C2-C3-olefins and high-boiling fraction B containing C4-C6-olefins and butanes; e) the low-boiling fraction A obtained from d) is then separated by distillation into a fraction containing ethylene and a fraction containing propylene, the ethylene-containing fraction being recycled to process step c) and the fraction containing propylene being discharged as product, and f) the from d) obtained high-boiling fraction B with the obtained according to process step b), selectively hydrogenated and isomerized C4 mixture and re-used in the metathesis c).

The isomerization is carried out at a temperature at which a shift of the double bond is ensured, skeleton isomerization and oligomerization, however, are largely avoided. The reaction temperature is, therefore, generally at 20 to 200 ⁰ C, preferably at 20 to 120 ⁰ C, particularly preferably at 30 to 110 ⁰ C. The pressure is adjusted so that the olefin is in liquid form. It is generally 1 to 200 bar, preferably 1 to 100 bar, more preferably 4 to 30 bar.

A preferred embodiment of the process according to the invention is characterized in that the ratio of 2-butene to 1-butene in the exit of the isomerization stage b) is between 5 and 40, more preferably between 10 and 30. The selective hydrogenation and metathesis used together with the isomerization according to the invention are known to the person skilled in the art from the prior art and have already been described in more detail above with regard to the catalysts used therefor and the reaction conditions.

a) selective hydrogenation of a C4 mixture containing essentially a mixture of 1- and 2-butenes and butadiene; b) metathesis of ethylene with 2-butene to propylene in the selectively hydrogenated C4 mixture in the presence of a metathesis catalyst, based on the butenes contained in the C4 mixture at least equimolar amounts of ethylene are used, c) separation of propylene from the reaction mixture; d) isomerization of 1-butene in the liberated of propylene C4-reaction mixture at temperatures of 20 to 200 ⁰ C and pressures of 1 to 200 bar in the liquid phase in the presence of a heterogeneous catalyst and e) merging the streams from steps a) and d ) and reinstatement into the metathesis stage b),

characterized in that in process step d) a catalyst is used which contains on an alumina support 1 to 20 wt .-% nickel in oxidic form and 1 to 20 wt .-% of at least one element of group VIB.

A preferred embodiment of the process according to the invention is characterized in that the catalyst in process step d) additionally contains 0.1 to 10% by weight, preferably 0.3 to 5% by weight, particularly preferably 0.5 to 2% by weight. one or more elements of group VB, in particular vanadium in oxidic form.

A further preferred embodiment of the process according to the invention is characterized in that the catalyst in process step d) additionally contains 0.1 to 1 wt.%, Preferably 0.1 to 0.8 wt.%, Particularly preferably 0.1 to 0, 5 wt .-% boron or phosphorus or a mixture of boron and phosphorus in each case in oxidic form.

A further preferred embodiment of the process according to the invention is characterized in that the catalyst in process step d) additionally contains 0.01 to 0.5 wt .-%, preferably 0.1 to 0.4 wt .-% sulfur in oxidic form , with the Provided that the ratio of sulfur to nickel is in the range of 0.01 to 0.1 mol / mol.

A further preferred embodiment of the process according to the invention is characterized in that the C4 mixture used for the selective hydrogenation in process step a) additionally contains n-butane, isobutane or isobutene or mixtures thereof.

The isomerization is carried out at a temperature at which a shift of the double bond is ensured, skeleton isomerization and oligomerization, however, are largely avoided. The reaction temperature is therefore generally from 20 to 200 ⁰ C, preferably at 20 to 120 ⁰ C, particularly preferably at 30 to 1 10 ⁰ C. The pressure is adjusted so that the olefin is in liquid form. It is generally 1 to 200 bar, preferably 1 to 100 bar, more preferably 4 to 30 bar.

A further preferred embodiment of the process according to the invention is characterized in that the ratio of 2-butene to 1-butene at the exit of the isomerization stage is between 5 and 40, more preferably between 10 and 30.

The present invention will be explained in more detail with reference to the following examples.

Example 1 (Comparative Example 1) [NiO _x / Al ₂ O ₃ ]

200 g of an Al2O3 carrier material (1, 5 mm strands D10-10 BASF AG) were mixed with a solution consisting of 108 g of Ni (NO 3) 2 ^* 6H2θ filled with pressurized H2O to a volume of 160 ml in a rotating flask. After drying at 120 ^° C. in a drying oven overnight, the dried catalyst was calcined in a rotary tube while passing through 300 l of air / h over a period of 2 h at 500 ^° C. The elemental analysis showed a Ni content of 9.0 wt .-%. The catalyst strands were crushed and forced through a sieve with the upper mesh size 1, 0 mm and the lower mesh size 0.5 mm.

Example 2 (Comparative Example 2) [Ni ₃ SbO _x ZAI ₂ O ₃ ]

200 g of an Al2O3 carrier material (1, 5 mm strands D10-10 from BASF AG) were (with a solution consisting of 108 g of Ni (NO ₃₎ 2 ^* 6H ₂ O and 6.4 g of H ₂ SO ₄ 96% solution , calculated 100%) filled with H ₂ O to a volume of 160 ml in a rotating KoI ben applied. After drying at 120 ^° C. in a drying oven overnight, the dried catalyst was calcined in a rotary tube while passing through 300 l of air / h over a period of 2 h at 500 ^° C. Elemental analysis revealed a Ni content of 8.8 wt% and an S content of 0.8 wt%, which corresponds to an S: Ni ratio of 0.17 mol / mol. The catalyst strands were comminuted and pressed through a sieve with the upper mesh size 1, 0 mm and the lower mesh size 0.5 mm.

Example 3 (Inventive Example 1) [Ni _a WbO _x / Al ₂ θ3]

200 g of an Al2O3 carrier material (1, 5 mm strands D10-10 from BASF AG) were treated with a solution consisting of 108 g of Ni (NO 3) 2 ^* 6H2θ and 31 g of (NH ₄₎ 6 H ₂ _W-2 0 ₄ ι o - filled with H2O to a volume of 160 ml applied in the rotating flask. After drying at 120 ^° C. in a drying oven overnight, the dried catalyst was calcined in a rotary tube while passing through 300 l of air / h over a period of 2 h at 500 ^° C. The elemental analysis revealed a Ni content of 8.3 wt% and a W content of 8.8 wt%. The catalyst strands were crushed and forced through a sieve with the upper mesh size 1, 0 mm and the lower mesh size 0.5 mm.

Example 4 (Inventive Example 2) [Ni _a WbO _x / Al ₂ θ3]

200 g of an Al2O3 carrier material (1, 5 mm strands D10-10 BASF AG) were mixed with a solution consisting of 108 g of Ni (NO 3) 2 ^* 6H2θ and 15.4 g (NH ₄₎ 6 H ₂ W-ι ₂ 0 ₄ o filled with H2O to a volume of 160 ml applied in the rotating flask. After drying at 120 ^° C. in a drying oven overnight, the dried catalyst was calcined in a rotary tube while passing through 300 l of air / h over a period of 2 h at 500 ^° C. The elemental analysis revealed a Ni content of 8.3 wt% and a W content of 4.2 wt%. The catalyst strands were crushed and forced through a sieve with the upper mesh size 1, 0 mm and the lower mesh size 0.5 mm.

Example 5 (Inventive Example 3) [Ni ₃ SbWcOxZAI ₂ O ₃ ]

200 g of an Al2O3 carrier material (1, 5 mm strands D10-10 from BASF AG) were (with a solution consisting of 108 g of Ni (NO ₃₎ 2 ^* 6H ₂ O, 3.2 g H ₂ SO ₄ 96% solution , calculated 100%) and 15.4 g (NH ₄ ) GH ₂ Wi ₂ O ₄ O filled with H ₂ O applied to a volume of 160 ml in a rotating flask. After drying at 120 ^° C. in a drying oven overnight, the dried catalyst was calcined in a rotary tube while passing through 300 l of air / h over a period of 2 h at 500 ^° C. The elemental analysis showed a Ni content of 8.7 wt .-%, an S content of 0.3 wt .-% (S: Ni = 0.06) and a W content of 4.3 wt .-% , The catalyst strands were crushed and forced through a sieve with the upper mesh size 1, 0 mm and the lower mesh size 0.5 mm. Example 6 (Inventive Example 4) [Ni ₃ BbWcOxZAI ₂ O ₃ ]

200 g of an Al2O3 carrier material (1, 5 mm strands D10-10 BASF AG) were mixed with a solution consisting of 108 g of Ni (NO 3) 2 ^* 6H2θ, 4.1 g of H3BO3 and 15.4 g (NH4) 6H2Wi2θ4o filled with H2O applied to a volume of 160 ml in a rotating flask. After drying at 120 ^° C. in a drying oven overnight, the dried catalyst was calcined in a rotary tube while passing through 300 l of air / h over a period of 2 h at 500 ^° C. The elemental analysis revealed a Ni content of 8.7 wt%, a B content of 0.3 wt% and a W content of 4.3 wt%. The catalyst strands were crushed and forced through a sieve with the upper mesh size 1, 0 mm and the lower mesh size 0.5 mm.

Example 7 (Inventive Example 5) [Ni _a MθbW _c O _x / Al 2 O 3]

200 g of an Al2O3 carrier material (1, 5 mm strands D10-10 from BASF AG) were (with a solution consisting of 108 g of Ni (NO 3) 2 ^* 6H2θ, 10.4 g (NH ₄₎ eMθ7θ ₂₄ and 15.4 g NH4) 6H2Wi2θ4o filled up with H2O to a volume of 160 ml in the rotating piston. After drying at 120 ^° C. in a drying oven overnight, the dried catalyst was calcined in a rotary tube while passing through 300 l of air / h over a period of 2 h at 500 ^° C. The elemental analysis showed a Ni content of 8.4 wt .-%, a Mo content of 2.1 wt .-% and a W content of 4.2% by weight. The catalyst strands were crushed and forced through a sieve with the upper mesh size 1, 0 mm and the lower mesh size 0.5 mm.

Example 8 (Inventive Example 6) [Ni ₃ WcOxZAI ₂ O ₃ ]

200 g of an Al2O3 carrier material (1, 5 mm strands D10-10 BASF AG) were mixed with a solution consisting of 162.2 g of Ni (NO ₃₎ 2 ^* 6H ₂ O, and 30.7 g (NH ₄₎ ₆ H ₂ Wi ₂ O ₄₀ filled with H ₂ O applied to a volume of 160 ml in a rotating flask. After drying at 120 ^° C. in a drying oven overnight, the dried catalyst was calcined in a rotary tube while passing through 300 l of air / h over a period of 2 h at 500 ^° C. The elemental analysis showed a Ni content of 1 1, 4 wt .-% and a W content of 7.6 wt .-%. The catalyst strands were crushed and forced through a sieve with the upper mesh size 1, 0 mm and the lower mesh size 0.5 mm.

Example 9 (Inventive Example 7) [Ni _a W _c O _x / Al ₂ θ3]

200 g of an Al ₂ θ3 carrier material (1, 5 mm strands D10-10 BASF AG) were mixed with a solution consisting of 108 g of Ni (NO ₃₎ ₂ ^* 6H ₂ O, 46.1 g (NH ₄₎ ₆ H ₂ Wi ₂ O ₄₀ filled with H ₂ O applied to a volume of 160 ml in a rotating flask. After drying at 120 ^° C. in a drying oven overnight, the dried catalyst was dried. calcined in the rotary tube while passing through 300 l of air / h over a period of 2 h at 500 ⁰ C. The elemental analysis showed a Ni content of 7.6 wt .-% and a W content of 1 1, 5 wt .-%. The catalyst strands were crushed and forced through a sieve with the upper mesh size 1, 0 mm and the lower mesh size 0.5 mm.

Example 10 (Inventive Example 8) [Ni _a PbMo _c O _x / Al ₂ θ3]

200 g of an Al2O3 carrier material (1, 5 mm strands D10-10 BASF AG) were mixed with a solution consisting of 108 g of Ni (NO 3) 2 ^* 6H2θ and 18.9 g H3PM012O40 filled with H2O to a volume of 160 ml in the rotating Piston acted upon. After drying at 120 ^° C. in a drying oven overnight, the dried catalyst was calcined in a rotary tube while passing through 300 l of air / h over a period of 2 h at 500 ^° C. The elemental analysis showed a Ni content of 8.7 wt .-%, a P content of 0.1 wt .-% and a Mo content of 3.6 wt .-%. The catalyst strands were crushed and forced through a sieve with the upper mesh size 1, 0 mm and the lower mesh size 0.5 mm.

Example 1 1 (Inventive Example 9) [Ni _a VbMo _c O _x / Al ₂ θ3]

200 g of an Al2O3 carrier material (1, 5 mm strands D10-10 BASF AG) were mixed with a solution consisting of 108 g of Ni (NO 3) 2 ^* 6H2θ and 15.8 g H ₇ PV ₄ MOSO ₄ O filled up with H2O to a Volume of 160 ml applied in the rotating flask. After drying at 120 ^° C. in a drying oven overnight, the dried catalyst was calcined in a rotary tube while passing through 300 l of air / h over a period of 2 h at 500 ^° C. The elemental analysis revealed a Ni content of 8.7 wt%, a V content of 0.55 wt%, a P content of 0.09 wt% and a Mo content of 2.2 wt .-%. The catalyst strands were crushed and forced through a sieve with the upper mesh size 1, 0 mm and the lower mesh size 0.5 mm.

Example 12 (Inventive Example 10) [Ni ₃ VbWcOxZAI ₂ O ₃ ]

14.8 g of oxalic acid were dissolved in 83 ml of H ² O and heated to 50 ^° C. After addition of 5.6 g of V2O5, the solution was heated to 85 ⁰ C, to form a clear blue solution. After cooling to room temperature, 200 g of a carrier material AI2O3 (1, 5 mm strands D10-10 BASF AG) with a solution consisting of 108 g Ni (NO ₃ ) 2 ^* 6H ₂ O, 15.4 g (NH ₄ ). ₆ H ₂ Wi ₂ 0 ₄ o and above Vanadyloxalatlösung filled with H ₂ O applied to a volume of 160 ml in a rotating flask. After drying at 120 ⁰ C in an oven overnight, the dried catalyst was Rohr in turning while passing 300 l of air / h over a period of 2 hours at 500 ⁰ C calcined. The elemental analysis showed a Ni content of 8.7 wt .-%, a V content of 1, 2 wt .-% and a W content of 4.3 wt .-%. The catalyst strands were crushed and pressed through a sieve with the upper mesh size 1, 0 mm and the lower mesh size 0.5 mm.

Example 13

Catalyst Tests (Comparative Catalysts 1 and 2 vs. Inventive Catalysts 1 to 10)

The experiments were carried out in a laboratory facility with eight parallel tube reactors with a length of 25 cm and a width of 1 cm, which were installed in a circulating air oven for tempering. Each reactor was first filled with 5 ml of inert material and then with 15 g of catalyst in the form of 0.5 to 1 mm chippings. After activation of the catalysts in the ISb stream (10 NI / h per reactor, without pressure) at 250 ⁰ C over a period of 16 h, the reactors were cooled in the ISb stream to below 30 ⁰ C. After switching off the supply of nitrogen, the olefin starting material was pressed to 20 bar reaction pressure. Finally, the feed dosage was adjusted by HPLC pump to the desired value. To ensure adequate catalyst wetting and reproducible conditions (stirred tank characteristics), a circulating pump was additionally added to circulate the feed, which was operated in a ratio of approximately 20: 1 (recycle: feed).

In selected experiments, the circulation pump was turned off to simulate a tube characteristic in these examples.

On the one hand, raffinate II with the composition 42% 1-butene, 32% 2-butenes, 2% i-butene, 24% butanes, <100 ppm butadiene and 1-dodecene (96% pure) was used as the feed.

The analysis was carried out by means of on-line GC analysis (GC area percent).

Tables 1 and 2 below give the results obtained after 48 hours:

z. . See thermodynamic data GGW-2-butene: 1-butene ratio of 40 ⁰ C: 30; 60 ⁰ C: 23; 80 ⁰ C: 18; 100 ^° C: 16; 120 ⁰ C: 14; 250 ^° C; 8th

(from DR Stull, EF Westrum, GC Sinke, The Chemical Thermodynamics of Organic Compounds, John Wiley & Sons, New York 1969, and Table in US 5,177,281, p. 7) Table 1

Feed: Raffinate Il

Table 2

Feed: 1-dodecene

Example 14 - Metathesis reaction

14/1 - Catalyst preparation for the metathesis reaction:

Part A: 235.2 g of SiO 2 strands (BASF) with a diameter of 1, 5 mm were soaked in water uptake with an aqueous solution of 30.9 g of ammonium metatungstate and 635 g of water. After 15 minutes, the strands were pre-dried on a rotary evaporator at 80 ⁰ C and 50 mbar, then dried overnight at 120 ⁰ C in a vacuum oven and finally calcined at 600 ⁰ C in N ² stream. Part B: 400 g AbCh extrudates (BASF) with a diameter of 1.5 mm were soaked in water with an aqueous solution of 368.9 g magnesium nitrate hexahydrate and 8.1 g sodium nitrate, made up to 281 ml. The strands were dried overnight at 120 ⁰ C in a drying oven and finally calcined at 500 ⁰ C in N ² stream.

14/2 - Use of the catalyst from Example 14/1 in the metathesis reaction:

In a tubular reactor, 20 g of catalyst were incorporated as a mixture of 5 g of catalyst according to Example 14/1 - Part A and 15 g of catalyst according to Example 14/1 - Part B in the form of 1, 5 mm stranded. The catalyst was activated by passing air at 600 ⁰ C, inerting in N ² stream with cooling to 530 ⁰ C and passing a Raffinatstroms with simultaneous cooling to the reaction temperature. The feed consisted of ethylene and raffinate 2H. As raffinate 2H, a mixture of about 85% by weight of linear butenes, about 2.5% by weight of isobutene and butanes (remainder to 100% by weight) was used directly (experiment 1) or after enrichment with 2- Butene (experiment 2) used. The reaction was carried out at 300 ⁰ C and 25 bar. The input and output compositions were determined by online GC. Table 3 below shows the conversions and mass selectivities for metathesis for the two experiments with different 2-butene / 1-butene ratio in the raffinate. The mass selectivity indicates the mass fraction of propene in the product (propene plus olefins from C5). The higher 2-butene / 1-butene ratio in experiment 2 in this case corresponds to a feed as it is supplied from the isomerization according to the invention.

Table 3

It can be seen that with a higher proportion of 2-butene in the feed more propylene is formed, which is in an increase of the butene conversion and the Propenselektivi- tat shows in experiment 2 with higher 2-butene content.

Claims

claims

1. A process for the isomerization of olefins from olefin-containing hydrocarbon mixtures having 4 to 20 C-atoms at temperatures of 20 to 200 ⁰ C and pressures of 1 to 200 bar in the liquid phase in the presence of a heterogeneous catalyst, characterized in that a catalyst used, which contains on an alumina support 1 to 20 wt .-% nickel in oxidic form and 1 to 20 wt .-% of at least one element of the group VIB.

2. The method according to claim 1, characterized in that the catalyst additionally contains 0.1 to 10 wt .-% of one or more elements of group VB in oxidic form.

3. The method according to any one of claims 1 or 2, characterized in that the catalyst additionally contains 0.1 to 1 wt .-% boron or phosphorus or a mixture of boron and phosphorus in each case in oxidic form.

4. The method according to any one of claims 1 to 3, characterized in that the catalyst additionally contains 0.01 to 0.5 wt .-% sulfur in oxidic form, with the proviso that the ratio of sulfur to nickel in the range of 0, 01 to 0.1 mol / mol.

5. The method according to any one of claims 1 to 4, characterized in that one uses as a carrier material gamma, eta or theta-alumina or mixtures thereof.

6. The method according to claim 5, characterized in that gamma-alumina is used as the carrier material.

7. The method according to any one of claims 1 to 6, characterized in that one combines the isomerization with a selective hydrogenation.

8. The method according to any one of claims 1 to 6, characterized in that one combines the isomerization with an olefin metathesis.

9. The method according to any one of claims 1 to 6, characterized in that one combines the isomerization with a Olefinalkylierung

10. The method according to any one of claims 1 to 6, characterized in that one combines the isomerization with an olefin oligomerization.

1 1. A process for the preparation of propylene from n-butenes and ethylene by

a) selective hydrogenation of a C4 mixture containing essentially one

Mixture of 1- and 2-butenes and butadiene; b) isomerization of 1-butene in the selectively hydrogenated C4 mixture at temperatures of 20 to 200 ⁰ C and pressures of 1 to 200 bar in the liquid phase in the presence of a heterogeneous catalyst; c) Metathesis of ethylene with 2-butene to propylene in the selectively hydrogenated and isomerized C4 mixture in the presence of a metathesis catalyst, wherein based on the butenes contained in the C4 mixture at least equimolar amounts of ethylene are used.

12. The method according to claim 11, characterized in that one carries out the isomerization in step b) without the addition of hydrogen.

13. The method according to any one of claims 11 or 12, characterized in that one uses in step b) a catalyst which on an alumina support 1 to 20 wt .-% nickel in oxidic form and 1 to 20 wt .-% at least of an element of group VIB.

14. The method according to claim 13, characterized in that the catalyst additionally contains 0.1 to 10 wt .-% of one or more elements of group VB in oxidic form.

15. The method according to any one of claims 13 or 14, characterized in that the catalyst additionally contains 0.1 to 1 wt .-% boron or phosphorus or a mixture of boron and phosphorus in each case in oxidic form.

16. The method according to any one of claims 13 to 15, characterized in that the catalyst additionally contains 0.01 to 0.5 wt .-% sulfur in oxidic form, with the proviso that the ratio of sulfur to nickel in the range of 0, 01 to 0.1 mol / mol.

17. The method according to any one of claims 11 to 16, characterized in that the selective hydrogenation used in step a) C4 mixture additionally contains n-butane, isobutane or isobutene or mixtures thereof.

18. The method according to any one of claims 11 to 17, characterized in that one d) separating the product stream obtained by the metathesis c) first by distillation into a low-boiling fraction A containing C2-C3-olefins and high-boiling fraction B containing C4-C6-olefins and butanes; e) the low-boiling fraction A obtained from d) is then separated by distillation into an ethylene-containing fraction and a fraction containing propylene, wherein the ethylene-containing fraction is recycled to the process step c) and the fraction containing propylene is discharged as a product and f) from d ) received with the obtained according to process step a), selectively hydrogenated C4 mixture and recombined in the

Isomerization b) is used.

19. The method according to any one of claims 11 to 17, characterized in that one

d) separating the product stream obtained by the metathesis c) first by distillation into a low-boiling fraction A containing C2-C3-olefins and high-boiling fraction B containing C4-C6-olefins and butanes; e) the low-boiling fraction A obtained from d) is then separated by distillation into an ethylene-containing fraction and a fraction containing propylene, wherein the ethylene-containing fraction is recycled to the process step c) and the fraction containing propylene is discharged as a product and f) from d ) and combined with the selectively hydrogenated and isomerized C4 mixture obtained according to process step b) and reused in the metathesis c).

20. The method according to any one of claims 11 to 19, characterized in that the isomerization takes place at temperatures of 30 to 1 10 ⁰ C and pressures of 4 to 30 bar.

21. The method according to any one of claims 11 to 20, characterized in that the ratio of 2-butene to 1-butene in the output of the isomerization stage b) is between 5 and 40.

22. The method according to claim 21, characterized in that the ratio of 2-butene to 1-butene in the output of the isomerization is between 10 and 30.

23. A process for the preparation of propylene from n-butenes and ethylene by

a) selective hydrogenation of a C4 mixture containing essentially one

Mixture of 1- and 2-butenes and butadiene; b) Metathesis of ethylene with 2-butene to propylene in the selectively hydrogenated C4-

Mixture in the presence of a metathesis catalyst, wherein based on the butenes contained in the C4 mixture at least equimolar amounts of ethylene are used; c) separation of propylene from the reaction mixture; d) isomerization of 1-butene in the liberated of propylene C4-reaction rates mixed at temperatures of 20 to 200 ⁰ C and pressures of 1 to 200 bar in the liquid phase in the presence of a heterogeneous catalyst and e) merging the streams from steps a) and d) and reinstatement in the metathesis stage b),

24. The method according to claim 23, characterized in that the catalyst in step d) additionally contains 0.1 to 10 wt .-% of one or more elements of group VB in oxidic form.

25. The method according to any one of claims 23 or 24, characterized in that the catalyst in step d) additionally contains 0.1 to 1 wt .-% boron or phosphorus or a mixture of boron and phosphorus in each case in oxidic form.

26. The method according to any one of claims 23 to 25, characterized in that the catalyst in step d) additionally contains 0.01 to 0.5 wt .-% sulfur in oxidic form, with the proviso that the ratio of sulfur to nickel in the Range of 0.01 to 0.1 mol / mol.

27. The method according to any one of claims 23 to 26, characterized in that the selective hydrogenation used in step a) C4 mixture additionally contains n-butane, isobutane or isobutene or mixtures thereof.

28. The method according to any one of claims 23 to 27, characterized in that the isomerization in process step d) takes place at temperatures of 30 to 110 ⁰ C and pressures of 4 to 30 bar.

29. The method according to any one of claims 23 to 28, characterized in that the ratio of 2-butene to 1-butene in the exit of the isomerization stage is between 5 and 40.

30. The method according to claim 29, characterized in that the ratio of 2-butene to 1-butene in the exit of the isomerization is between 10 and 30.