DE10118634A1 - Propene production from mixture, comprising ethylene, hexenes, other olefins and optionally other inert hydrocarbons,contacted with a metathesis catalyst at high temperature - Google Patents

Abstract

Production of propene (Pr) from a mixture (M1) that comprises: (1) ethylene (E); (2) hexenes (H); (3) other olefins (K1a); and (4) optionally other inert hydrocarbons (K1b). The mixture is contacted with a metathesis catalyst (MC) at 20-350 deg C. Production of propene from a mixture (M1) that comprises: (1) ethylene (E); (2) hexenes (H); (3) other olefins (K1a); and (4) optionally other inert hydrocarbons (K1b). The mixture is contacted with a metathesis catalyst (MC) at 20-350 deg C. The mixture (M1) has: (i) a molar proportion of the sum of 2-hexene (H2) and 3-hexene (H3) in (H) of 4-99:1; (ii) a molar ratio of (E) to the sum of (H) and (K1a) of 1-100:1; and (iii) a ratio of (H2) to (H3) of at least 2:1, as long as (H3) is not simultaneously isomerized to increase the (H2) proportion correspondingly.

Description

The invention relates to a process for the flexible production of olefins, in particular pure C ₃ - / C ₄ - / C ₅ - and C ₆ -olefin streams from steam cracker and / or FCC-C ₄ streams, characterized in that the following process sequence is run through:

• Selective hydrogenation or extraction of butadiene in crude C _{4 cut} with subsequent selective hydrogenation, with the aid of which the isomer equilibrium between 1-butene and 2-butene ratio can be adjusted,
• Separation of isobutene from the remaining C ₄ stream by chemical, physico-chemical or physical methods, if necessary for its purification,
• - purification of the C ₄ stream thus obtained on adsorber materials to remove catalyst poisons,
• - Metathesis of the C ₄ stream thus obtained, if appropriate using ethylene, for the production of high-purity C ₃ / C ₅ / C ₆ olefin streams which can be further processed directly as such.
• - Metathesis of the C ₆ and / or C ₅ streams obtained under isomerizing conditions using ethene in order to obtain further propene

The advantage of the process sequence described lies in the flexibility of the discharge streams from steam crackers and FCC units in such a way that the added value of the C ₄ streams which are produced as a secondary yield can be optimized depending on the market situation and needs. In particular, with the last step it is possible to continue the ratio of the coupling products propene and 3-hexene, which is determined in the first metathesis stage by the 1-butene / 2-butene ratio prevailing in the feed, in the direction of the valuable propene.

Basics and background

Steam crackers are the main source of petrochemical basic chemicals such as ethylene, propylene, C ₄ -olefins and higher hydrocarbons. In the cracking process, it is necessary to transfer large amounts of energy at high temperatures in a time period which is sufficient on the one hand to carry out the cleavage and on the other hand but does not allow a further reaction of the fission products. When hydrocarbons are split, the yield of ethylene and propylene is therefore essentially determined by the

• - type of hydrocarbons used (naphtha, ethane, LPG, gas oil, etc.),
• - cracking temperature,
• - dwell  
• - and the partial pressures of the respective hydrocarbons

certainly.

The highest yield of ethylene and propylene is achieved at gap temperatures between 800 and 850 ° C and residence times of 0.2 to 0.5 s. The main product in this area is always ethylene, whereby the C ₃ / C ₂ discharge ratio can be increased to a small extent from about 0.5 to 0.7 by varying the cracking conditions. Worldwide, the demand for propylene is growing faster than for ethylene. One of the consequences of this is that processes for the downstream utilization of the higher hydrocarbons formed in the cracking process, such as, for. B. C ₄ , in terms of optimizing the propylene yield ge gain significant. With the metathesis reaction of raffinate II and ethylene, for example, the discharge ratio of propylene to ethylene can be increased from 0.5 to 0.7 as standard to values above 1. In addition to the availability of C ₄ olefins, the economy of such a metathesis stage depends primarily on the price difference between ethylene and propylene and is not guaranteed at all times.

In known methods according to the prior art, the olefin discharge from a steam cracker or an FCC unit can be controlled as required without structural or process engineering changes so that

• - The propylene yield with reduced discharge of functionalizable C5 / C6 olefins increased by a high 2-butene content in the feed and targeted addition of ethylene becomes,

or

• the yield of functionalizable C ₅ / C ₆ olefins is optimized at the expense of a lower propylene yield by a high 1-butene content in the feed without the addition of high-priced ethylene,

or

• - Any variant lying between the two described modes of operation is carried out.

In the processes known to date, the maximum possible yield of propylene determined by the 2-butene concentration in the feed.

Since the butadiene selective hydrogenation is particularly useful in the case of steam cracker streams is used to remove butadiene from the feed stream, the processes are limited regarding the maximum possible propylene output, since maximizing 2-butene only up to is possible to certain limits without over-hydrogenating the butadiene reach inert butanes.  

In both modes of operation, a pure pension and / or hexene olefin fraction, either as an inexpensive, alternative raw material ba sis can be used for plasticizer or surfactant alcohols, or as in the invention implemented according to the process under isomerizing conditions to further propylene can be.

In order to ensure the composition of the C ₄ feedstock optimized for the final method step metathesis, the raw C ₄ stream is preferably processed in the process according to the invention by the combination of the following process steps:

• 1. Selective hydrogenation of crude C _{4 cut} to remove 1,3-butadiene, 1,2-butadiene, 1-butyne (ethyl acetylene) and butenine (vinyl acetylene), or butadiene extraction with subsequent selective hydrogenation to remove residual amounts of 1 , 3-butadiene, 1,2-butadiene, 1-butyne (ethyl acetylene) and butenine (vinyl acetylene), in each case in the selective hydrogenation process step depending on the need for C ₅ - / C ₅ - / C ₆ -olefin discharge for the particular one Metathesis step optimized molar ratio 1-butene to 2-butene is set,
• 2. Separation of isobutene from the raffinate I stream thus obtained, preferably via Verethe tion with alcohols or hydration, using acid-catalyzed selective dimerization tion, oligomerization or polymerization of isobutene, by distillation using a so-called. Deisobutenizer column or by physical adsorption, if necessary for the purification of isobutene
• 3. Purification of the raffinate II stream obtained in this way on adsorber materials for removal tion of oxygenates, sulfur compounds, water, chlorides and other substances subsequent process step metathesis disruptive secondary components as well
• 4. one-stage metathesis reaction, possibly with ethylene feed, for the flexibly controllable production of pure C ₃ , C ₅ and C ₆ olefin streams
• 5. Introducing the C ₆ and / or C ₅ olefin stream obtained with the addition of ethene into a further metathesis stage under isomerizing conditions, and separating off the propylene produced and, if appropriate, recycling the unreacted olefins, either into the first or optionally into the second, isomerizing stage.

So far, a process has not been described whose flexibility allows the entire 3-hexene output to be additionally converted into propylene. Since the utilization of 3-hexene can vary in size depending on the market situation and, at the same time, there can be a great need for propylene, a process is desirable which allows the total C ₆ and / or C5 olefin output to be converted to propylene. The object is achieved according to the invention by the method described below:
The individual process steps are described in more detail below.

To 1.) Selective hydrogenation of crude C _{4 cut}

From the raw C ₄ fraction from a steam cracker or refinery, butadiene (1,2- and 1,3-butadiene) and alkynes or alkene nine contained in the C _{4 cut} are selectively hydrogenated in a two-stage process. According to one embodiment, the C ₄ stream originating from the refinery can also be fed directly into the second step of the selective hydrogenation.

The first step of the hydrogenation is preferably carried out on a catalyst which contains 0.1 to 0.5% by weight of palladium on aluminum oxide as a support. The reaction is carried out in the gas / liquid phase in a fixed bed (trickle mode) with a liquid circuit. The hydrogenation takes place at a temperature in the range from 40 to 80 ° C. and a pressure of 10 to 30 bar, a molar ratio of hydrogen to butadiene from 10 to 50 and a volume rate of LHSV of up to 15 m ³ fresh feed per m ³ catalyst per hour and a ratio of recycle to inflow operated from 5 to 20.

The second step of the hydrogenation is preferably carried out on a catalyst which contains 0.1 to 0.5% by weight of palladium on aluminum oxide as a support. The reaction is carried out in the gas / liquid phase in a fixed bed (trickle mode) with a liquid circuit. The hydrogenation takes place at a temperature in the range from 50 to 90 ° C. and a pressure of 10 to 30 bar, a molar ratio of hydrogen to butadiene from 1.0 to 10 and a volume rate LHSV of 5 to 20 m ³ fresh feed per m ³ catalyst per hour and operated with a recycle to inflow ratio of 0 to 15.

The hydrogenation is carried out as required under "low isom" conditions (for maximum hexene Production in the metathesis step) or under "high isom" conditions (for maximum propy len production in the metathesis step). The residual butadiene content can vary depending on Hydrogen sharpness be 0 to 50 ppm.

The reaction product thus obtained is referred to as raffinate I and has isobutene and n- / isobutane 1-butene and 2-butene in a molar ratio of 3 to 1 to 1 to 10 preferably from 2 to 1 to 1 to 7.

to 1.) alternatively: separation of butadiene from crude C _{4 cut} via extraction

The extraction of butadiene from crude C _{4 cut} is preferably carried out using N-methylpyrrolidone.

The reaction discharge of the extraction is according to one embodiment of the invention in the Selective hydrogenation described above, possibly in its second step, fed in Residual amounts of 1,3-butadiene, 1,2-butadiene, 1-butyne (ethyl acetylene) and butenine (vinyllace tylen) to remove, in this case also as required for the process step  Metathesis optimized molar ratio 1-butene to 2-butene from 3 to 1 to 1 to 10, preferably from 2 to 1 to 1 to 7.

to 2) separation of isobutene via etherification with alcohols

In the etherification stage, isobutene is mixed with alcohols, preferably with isobutanol, on egg acid catalyst, preferably on an acidic ion exchanger, to ether preferably implemented isobutyl tert-butyl ether. The implementation takes place according to an implementation Form of the invention in a three-stage reactor cascade, in the flooded fixed bed kata flow through the analyzers from top to bottom. In the first reactor, the on transition temperature 0 to 60 ° C, preferably 10 to 50 ° C; the initial temperature is between 25 and 85, preferably between 35 and 75 ° C, and the pressure is 2 to 50 bar, preferably 3 to 20 bar. With a ratio of isobutanol to isobutene of 0.8 to 2.0, preferably 1.0 to 1.5, the conversion is between 70 and 90%.

In the second reactor, the inlet temperature is 0 to 60 ° C, preferably 10 to 50 ° C; the initial temperature is between 25 and 85, preferably between 35 and 75 ° C, and the pressure is 2 to 50 bar, preferably 3 to 20 bar. The total sales over the two stages increases to 85 to 99%, preferably 90 to 97%.

In the third and largest reactor at the same inlet and outlet temperature from 0 to 60 ° C, preferably 10 to 50 ° C; the equilibrium turnover achieved. The ether cleavage follows the etherification and separation of the ether formed: the endothermic reaction is carried out on acidic catalysts, preferably on acidic heterogeneous contacts, for example phosphoric acid on an SiO _{2 support} , at an inlet temperature of 150 to 300 ° C., preferably at 200 to 250 ° C, and an initial temperature of 100 to 250 ° C, preferably at 130 to 220 ° C.

When using FCC-C ₄ cuts, it is to be expected that propane in amounts of around 1% by weight, isobutene in amounts of around 30 to 40% by weight and C ₅ hydrocarbons in amounts of around 3 to 10% will be introduced , which can impair the subsequent process sequence. Accordingly, the possibility of a distillative separation of the components mentioned is provided as part of the processing of the ether.

The reaction product thus obtained, referred to as raffinate II, has an isobutene Residual content of 0.1 to 3% by weight.

As further options for the separation of isobutene from raffinate I streams by retarding, the use of diols, such as, for. B. 1,2-propylene glycol, 1,4-butanediol or 1,6-hexanediol, for simplified phase separation between the corresponding ether and the residual C ₄ stream.

The subsequent metathesis step can also be carried out without restriction by the direct removal of isobutene from raffinate I by means of selective dimerization of isobutene over acidic fixed bed catalysts such as H ₃ PO ₄ / SiO ₂ , and the homogeneous or heterogeneously catalyzed acidic oligomerization or polymerization of isobutene in Presence of Brönstedt or Lewis acids such as B. BF ₃ , for the production of highly reactive polyisobutene.

With larger amounts of isobutene in the discharge, such as when using FCC-C ₄ fractions or when separating isobutene by acid-catalyzed polymerization to polyisobutene (partial conversion), the remaining raffinate stream can be prepared by distillation according to an embodiment of the invention before further processing ,

to 3) Purification of the raffinate II stream on adsorber materials

The raffinate II stream obtained after the etherification / polymerization (or distillation) is purified on at least one guard bed consisting of high-surface area aluminum oxides, silica gels, aluminosilicates or molecular sieves. The protective bed serves to dry the C ₄ stream and to remove substances which can act as a catalyst poison in the subsequent metathesis step. The preferred adsorbent materials are Selexsorb CD and CDO as well as 3Å and NaX molecular sieves (13X). The cleaning takes place in drying towers at temperatures and pressures which are chosen so that all components are in the liquid phase. If necessary, the cleaning step for feed preheating is used for the subsequent metathesis step.

For feed cleaning, the use of two adsorber beds is recommended, which are in the A / B Swing mode operation / regeneration are operated, whereby used adsorber material (Molecular sieves and high-surface aluminum oxides) can be regenerated.

The remaining raffinate II stream is almost free of water, oxygenates, organic Chlorides and sulfur compounds.

When performing the etherification step with methanol to produce MTBE, it can due to the formation of dimethyl ether as a minor component, several are required Combine cleaning steps or connect them in series.

to 4) single-stage metathesis reaction, possibly with ethylene feed, for flexible production of pure C ₃ -, C ₅ - and C ₆ -olefin streams

The raffinate II fraction thus obtained is, if necessary, in the context of a metathesis reaction Dosing of ethylene, on a homogeneous or preferably heterogeneous metath secondary catalyst implemented.

The following two borderline cases are distinguished:  

a) Maximum propylene yield with a reduced yield of C ₅ and / or C ₆ olefin mixture with targeted use of ethylene

In principle, by reaction of the C ₄ -olefins 1-butene, 2-butene and possibly isobutene contained in the raffinate II in the context of cross and self-metathesis reactions, the product mixture shown in the following equation, consisting of inert butanes, is not converted to 1- Butene, 2-butene and possibly isobutene and the metathesis products ethylene, propylene, 2-pentene, optionally 2-methyl-2-butene, 3-hexene and optionally 2-methyl-2-pentene are obtained:

The preferred variant a) in the case of low ethylene to propylene price difference provides a product mixture in which, through targeted addition of ethylene, the chemical equilibrium present between the components in the direction of propylene as the main product and a C ₅ containing 2-pentene and / or 3-hexene - or C ₆ fraction is shifted as a secondary yield. As a result of the targeted removal of C ₅ and / or C ₆ high boilers, the ethylene number used is from the theoretical value of 0.33 t ethylene per t propylene for the ethenolysis of 2-butene to 2 mol propylene

reduced to values below 0.30 t ethylene per t propylene.

The process diagram shown in simplified form in the following sketch includes a reactor unit which, according to conventional prior art, preferably consists of two reactors R operated in the swing mode synthesis / regeneration, and a three-stage distillation sequence which, in addition to the C ₄ purge stream, also removes pure C ₃ - , C ₅ - and / or C ₆ -olefin flows enables:

Fresh raffinate II, together with fresh ethylene and the recycled streams C ₂ ⁼ , C ₄ ^- / C ₄ ⁼ and possibly C ₅ ^=, enter the reactor R, which is preferably operated as a fixed bed. The latter consists of C ₂ -C ₆ olefins and butanes Existing discharge stream is separated in distillation D1 into a low boiler fraction consisting of ethylene and propylene, which can either be fed into the processing sequence of a cracker or preferably separated into the pure components ethylene and propylene in a further distillation column D3, and into a high boiler fraction, which consists of C ₄ olefins and butanes as well as 2-pentene and 3-hexene. Ethylene withdrawn overhead in D3 is at least partially returned to the metathesis reactor. The bottom draw from column D3 is separated into a further column D2, which can optionally be designed as a side draw column or dividing wall column, into a low boiler fraction consisting of C ₄ -olefins and butanes, which can be wholly or partly recycled to the metathesis step preferably a middle boiler fraction consisting of 2-pentene, which can be wholly or partly returned to the metathesis step, and into a 3-hexene in high purity of min. 99% existing valuable product fraction, which is preferably discharged.

In a special embodiment of the method according to the invention, the Ver reactor unit R and the distillation column D1 to a reactive distillation unit socialize.  

As catalysts in the metathesis step known heterogeneous rhenium catalysts, such as Re ₂ O ₇ on γ-Al ₂ O ₃ or on mixed supports, such as. B. SiO ₂ / Al ₂ O ₃ , B ₂ O ₃ / SiO ₂ / Al ₂ O ₃ or Fe ₂ O ₃ / Al ₂ O ₃ with different metal content is preferred. The Rheni umoxid content is regardless of the carrier chosen between 1 and 20%, preferably between 3 and 10%. The catalysts are used freshly calcined and need no further activation (e.g. by alkylating agents). Deactivated catalyst can be regenerated several times by burning off coke residues or polymer coatings at temperatures above 400 ° C in an air stream and cooling under an inert gas atmosphere. Homogeneous catalysts are comparatively less suitable, although they are sometimes more active, but in most cases they have a significantly shorter service life.

Pressure and temperature in the metathesis step are selected so that all reactants be in the liquid phase (T = 0-150 ° C, preferably 20-80 ° C; p = 2-200 bar). alternative However, it can be an advantage, especially with feed streams with a higher isobutene content, carry out the reaction in the gas phase and / or use a catalyst which has a lower acidity.

As a rule, the reactions are carried out after 1 s to 1 h, preferably after 30 s to 30 min ends.

Used catalyst can be burned off by oligomeric or polymeric deposits on the surface of the catalyst in an air stream at temperatures above 400 ° C be regenerated, with the use of two in the constant operation of the system Swing mode synthesis / regeneration operated reactors is preferred.

In a special embodiment of the method according to the invention, the Ver reactor unit R and the distillation column D1 to a reactive distillation unit socialize.

b) Maximum yield of C ₅ and / or C ₆ olefin fraction at the expense of a reduced propylene yield without the use of ethylene

The preferred variant b) with high ethylene to propylene price difference provides a product mixture in which, without the addition of ethylene, the chemical equilibrium present between the components in the direction of a C ₅ - or C ₆ containing 2-pentene and / or 3-hexene Fraction is shifted, propylene being formally obtained in a subsequent reaction from the ethylene and 2-butene formed in equimolar amounts in the self-metathesis of 1-butene to 3-hexene.

The simplified process diagram shown below corresponds to that of variant b) with the exception that no fresh ethylene is fed in and only that in the frame ethylene formed in the metathesis reaction is returned to the metathesis step.

The degree of branching of the C ₅ / C ₆ olefin fraction depends on the isobutene content in the C ₄ feed and is kept as low as possible in a preferred embodiment of the process. If there is no need for the C ₂ -olefin fraction, which contains mainly 2-pentene and is withdrawn as a side draw from column D2, the yield of the C ₆ -olefin fraction containing primarily 3-hexene can be increased by recycling the fraction mentioned into the metathesis reactor become. For subsequent reactions, such as B. the transition metal-catalyzed dimerization of 3-hexene to a C ₁₂ olefin mixture, the olefinic C ₆ bottom fraction obtained according to the above process scheme is of sufficiently high purity.

In a special embodiment of the method according to the invention, the Ver reactor unit R and the distillation column D1 to a reactive distillation unit socialize.

As catalysts in the metathesis step known heterogeneous rhenium catalysts, such as Re ₂ O ₇ on γ-Al ₂ O ₃ or on mixed supports, such as. B. SiO ₂ / Al ₂ O ₃ , B ₂ O ₃ / SiO ₂ / Al ₂ O ₃ or Fe ₂ O ₃ / Al ₂ O ₃ with different metal content is preferred. The Rheni umoxid content is between 1 and 20%, preferably between 3 and 10%, regardless of the carrier selected. The catalysts are used freshly calcined and need no further activation (e.g. by alkylating agents). Deactivated catalyst can be regenerated several times by burning off coke residues at temperatures above 400 ° C in an air stream and cooling under an inert gas atmosphere. Comparatively less suitable are homogeneous catalysts, which are partly more active, but in most cases have a significantly shorter service life.

Pressure and temperature in the metathesis step are selected so that all reactants be in the liquid phase (T = 0-150 ° C, preferably 20-80 ° C; p = 2-200 bar). alternative However, it can be an advantage, especially with feed streams with a higher isobutene content, carry out the reaction in the gas phase and / or use a catalyst which has a lower acidity.

As a rule, the reactions are carried out after 1 s to 1 h, preferably after 30 s to 30 min ends. It can be used continuously or discontinuously in reactors, such as pressure glass vessels, Flow tubes or reactive distillation devices are carried out, with Strö pipes are preferred.

Used catalyst can be burned off by oligomeric or polymeric deposits on the surface of the catalyst in an air stream at temperatures above 350 to 450 ° C can be regenerated.

The variants a) and b) presented correspond to the respective borderline cases. By feeding in different amounts of ethylene, the olefinic discharge streams C ₃ ⁼ and C ₅ ⁼ and / or C ₆ ⁼ can be adjusted as required when the 1-butene to 2-butene molar ratio in the raffinate II feed is adjusted. The preferred molar ratio of 1-butene to 2-butene is between 1 to 10 and 1 to 2 for increased propylene requirements, and between 1 to 2 and 3 to 1 for increased requirements for C ₅ and / or C ₆ olefin mixture.

Re 5.) Isomerizing metathesis of the C5 and / or C6 section obtained

In a further metathesis step, the C ₅ and / or C ₆ olefin stream obtained from step 4) is then reacted with the addition of ethylene over a homogeneous or heterogeneous metathesis catalyst. The reaction is carried out under isomerizing conditions in order to convert at least part of the olefin stream used to the corresponding 2-olefin. 2-Olefins produced in this way can react with ethylene to form further propylene. This is shown below using the example of 3-hexes:

The 1-olefins formed by ethenolysis can now be further isomerized and the 2-olefins formed, at least in portions, converted to further propylene become.

The isomerization can be achieved either by isomerization and Metathesis can be carried out in separate reactors, or preferably in one Reactor. Metathesis and isomerization catalysts can also be used in this reactor separates. The metathesis catalyst contains a compound of a metal Groups Vob, VIIb or VIII of the Periodic Table of the Elements. Preferably, the Metathesis catalyst is an oxide of a metal of group VIb or VIIb of the periodic table of the elements. In particular, the metathesis catalyst is selected from the group be consisting of Re2O7, WO3 and MoO3.

The isomerization catalyst contains a metal from groups Ia, Iia, IIIb, Ivb, Vb or VIII of the Periodic Table of the Elements or a combination thereof. Preferably, the Isomerization catalyst selected from the group consisting of RuO2, MgO and K2CO3.

The catalysts are generally based on the usual materials known to the person skilled in the art supported. Examples of suitable materials include SiO2, y-Al2O3, MgO or mixtures against these materials.

According to a variant of the invention, the isomerization of the olefins can be in the direction 2-olefins can also be achieved in that the metathesis on the above metaths is carried out, but special conditions with regard to pressure and Temperature can be selected. Carrying out the isomeri is particularly preferred metathesis reaction in the temperature range from 110 to 350 ° C and pressures of 1 up to 60 bar, particularly preferably at 150 ° and 5 bar with Re2O7 on Al2O3.

The isomerizing metathesis reaction can be continuous or discontinuous be performed.

The olefin mixture obtained after the isomerizing metathesis reaction is then added methods known to the person skilled in the art, for example distillation. Propylene will obtained as the main product, while other streams optionally in step 4) or also Step 5 can be traced back.  

In a particularly preferred embodiment of step S, that from step 4) is obtained tene 3-hexene fraction used to increase the propylene yield.

Claims (1)

Process for the flexible production of olefin streams from steam cracker and / or FCC-C ₄ streams, comprising the substeps

• a) Selective hydrogenation of crude C ₄ cuts with hydrogen in the presence of Pd / Al ₂ O ₃ as a catalyst, for removing 1,3-butadiene, 1,2-butadiene, 1-butyne (ethyl acetylene) and butenyne (vinyl acetylene) , or butadiene extraction using polar aprotic solvents with subsequent selective hydrogenation to remove residual amounts of 1,3-butadiene, 1,2-butadiene, 1-butyne (ethyl acetylene) and butenine (vinyl acetylene), in the process step selective hydrogenation depending on The need for C ₃ - / C ₅ - / C ₆ -olefin discharge for the respective metathesis step optimized molar ratio 1-butene to 2-butene can be set,
• b) separation of isobutene from the raffinate I stream thus obtained, preferably via Verethe tion with alcohols or diols, such as. B. methanol (to MTBE), isobutanol (to isobutyl tert-butyl ether IBTBE) or 1,2-propylene glycol (to propylene glycol tert-butyl ether), or by hydration to tert-butanol, by means of selective dimerization, oligomerization or polymerization of Isobutene, preferably in the presence of homogeneous and heterogeneous Brönsted or Lewis acids, or by distillation using a desiobutenizer distillation column
• c) Purification of the raffinate II stream obtained in this way on adsorber materials for removing impurities, such as oxygenates, chlorides, sulfur compounds, water, preferably on high-surface area aluminum oxides or molecular sieves, and
• d) metathesis reaction of the raffinate II stream thus obtained, optionally with ethylene feed, in the presence of a metathesis catalyst which contains at least one compound of a metal of VI.b, VII.b or VIII. subgroup of the Periodic Table of the Elements, for flexible use Production of pure C ₃ , C ₅ and C ₆ olefin streams.
• e) feeding the olefin streams obtained from step (d) into an isomerizing metathesis, optionally with the addition of ethylene, to produce further propylene-containing streams.