DE10334001A1 - Polyisobutene production from hydrocarbon stream containing iso-, 1- and 2-butenes, including distillative separation into streams rich in different butenes to increase yields in useful by-product recovery - Google Patents

Abstract

Production of polyisobutene (I) from a starting 4C hydrocarbon stream (II), containing isobutene, 1-butene and 2-butene, includes: (a) distillatively separating (II) into a more volatile fraction (F1) (containing most of the isobutene and 1-butene in (II)) and a less volatile fraction (F2) (containing most of the 2-butene); and (b) subjecting the 1-butene in (F1) to chemically selective reaction and separating the reaction products from the remaining components of (F1).

Description

The present invention relates to a process for the preparation of performance products from a C ₄ hydrocarbon stream.

It is generally known that the constituents of a C ₄ fraction of a hydrocarbon mixture produced, for example, in a customary cracking process such as steam cracking of naphtha can serve as starting material for the preparation of various basic chemical products (see Industrielle Organische Chemie, K. Weissermel, H.- J. Arpe, Wiley-VCH, 1998, 5th edition, chapter 3.3.2.). From the C ₄ fraction is known before further reaction, the often contained therein 1,3-butadiene, usually either by selective hydrogenation or by extractive distillation, removed. The C ₄ -hydrocarbon mixture obtained in this process is commonly referred to as raffinate I. Usually, no further separation takes place by means of fractional distillation (compare loc cit cit P. 76), because this would be technically too complicated. Therefore, the individual components such as i-butene, 1-butene and 2-butene in the presence of other ingredients in chemical reactions are removed or refined to other products. Due to the sometimes lack of selectivity of the reaction, the conversion or the yield of the desired products is partly unsatisfactory.

at these reactions are e.g. to the production of witches by methathesis of 1-butene, the di- and oligomerization of 2-butene and the polymerization of i-butene to polyisobutylene.

The object of the present invention was therefore to provide a process for the preparation of the aforementioned performance products in high yield from a C ₄ -hydrocarbon fraction, in particular raffinate I.

• a) in Schritt (a) den Ausgangsstrom C₄ destillativ auftrennt in eine leichter flüchtige Fraktion (Fraktion I), die den größten Teil des in der Mischung von C₄-Kohlenwasserstoffen enthaltenen i-Buten und 1-Butens enthält und eine schwerer flüchtige Fraktion (Fraktion II), die den größten Teil der in der Mischungen von C₄-Kohlenwasserstoffen enthaltenen 2-Butene enthält, und
• b) in Schritt b) das in der Fraktion (I) enthaltene i-Buten in einer chemisch selektiven Reaktion umsetzt und das Umsetzungsprodukt von den verbleibenden Bestandteil der Fraktion (II) abtrennt.

Accordingly, a process for the preparation of polyisobutene from a C ₄ hydrocarbon stream containing i-butene, 1-butene and 2-butenes (starting stream C ₄ ) was found by

• a) in step (a), the starting stream C _{4 is} separated by distillation into a more volatile fraction (fraction I) containing most of the i-butene and 1-butene contained in the mixture of C ₄ hydrocarbons and a less volatile fraction (Fraction II), which contains most of the 2-butenes contained in the mixtures of C ₄ hydrocarbons, and
• b) in step b) the i-butene present in fraction (I) is reacted in a chemically selective reaction and the reaction product is separated from the remaining constituent of fraction (II).

In general, an output stream C _{4 is} used, which consists essentially of 2-butenes, 1-butene, i-butene, i-butane and butanes. In addition to the abovementioned components, the starting stream C ₄ may optionally be up to 10%, preferably up to 5 very particularly preferably up to 1% by weight of other unsaturated hydrocarbon compounds having 4 carbon atoms and optionally up to 10 preferably up to 5 and very particularly preferably up to 1% by weight. % Hydrocarbon compounds containing less than 4 or more than 4 carbon atoms.

The proportions of the main components in the output stream C ₄ are usually as follows: 15-60% Isobutene 20-60% 1-butene 10-40% 2-butene 2-30% n-butane 0.2-10% isobutane

at the other unsaturated Hydrocarbon compounds having 4 carbon atoms are generally butadienes, alkynes or allenes.

at the hydrocarbon compounds with less than 4 or more than 4 carbon atoms are generally propane, propene, Pentanes, pentenes, hexanes, or witches.

• – aus einem Kohlenwasserstoffstrom aus natürlichen Quellen oder erhältlich, indem man Naphtha oder sonstige Kohlenwasserstoffverbindungen enthaltende Ströme einem Steamcracking- oder FCC-Prozess unterwirft, zieht man eine C₄-Kohlenwasserstofffraktion (Strom Ca) ab,
• – aus Strom C₄ stellt man einen im wesentlichen aus Isobuten, 1,-Buten, 2-Buten und Butanen bestehender C₄-Kohlenwasserstoffstrom (Raffinat I) her, indem man mittels Selektivhydrierung die Butadiene und Butine zu C₄-Alkenen oder C₄- Alkanen hydriert oder die Butadiene und Butine durch Extraktivdestillation entfernt
• – das Raffinat I befreit man durch Behandlung mit Adsorbermaterialien von Katalysatorgiften und erhält auf diese Weise Ausgangsstrom Ca.

In general, the starting stream C _{4 is} prepared by carrying out the following sequence of steps:

• From a hydrocarbon stream from natural sources or obtainable by subjecting streams containing naphtha or other hydrocarbon compounds to a steam cracking or FCC process, a C ₄ hydrocarbon fraction (stream Ca) is withdrawn,
• From stream C ₄ , a C ₄ -hydrocarbon stream (raffinate I) consisting essentially of isobutene, 1-butene, 2-butene and butanes is prepared by selectively adding the butadienes and butynes hydrogenated to C ₄ alkenes or C ₄ - alkanes or removed the butadienes and butynes by extractive distillation
• - The raffinate I is freed by treatment with Adsorbermaterialien of catalyst poisons and obtained in this way output current Ca.

possibly Raffinate I can also without prior separation of catalyst poisons in step a) are used. In this case, the separation becomes the catalyst poisons are made immediately following step a).

Stream C ₄ is produced, for example, from LPG or LNG streams. LPG means liquefied petroleum gas. Such liquefied gases are defined for example in DIN 51 622. They generally contain the hydrocarbons propane, propene, butane, butenes and mixtures thereof, which are produced in oil refineries as by-products in the distillation and cracking of petroleum and in the natural gas treatment in the gasoline separation. LNG means Liquefied Natural Gas (natural gas). Natural gas consists mainly of saturated hydrocarbons, which, depending on their origin, have different compositions and are generally divided into three groups. Natural gas from pure natural gas deposits consists of methane and little ethane. Natural gas from oil deposits additionally contains even larger amounts of higher molecular hydrocarbons such as ethane, propane, isobutane, butane, hexane, heptane and by-products. Natural gas from condensate and distillate deposits not only contains methane and ethane, but also significantly higher boiling components with more than 7 carbon atoms. For a more detailed description of liquefied gases and natural gas, reference may be made to the relevant keywords in Römpp, Chemielexikon, 9th edition.

The LPG and LNG used as feedstock includes in particular so-called Feldbutane, as the C ₄ fraction of the "wet" shares of natural gas and the associated petroleum gases, which are separated by drying and cooling to about -30 ° C in liquid form from the gases , Cryogenic or pressure distillation yields the field butanes which vary in composition depending on the deposit, but which generally contain about 30% iso-butane and about 65% n-butane.

Furthermore, it is possible to recover the stream C ₄ by subjecting naphtha or other hydrocarbon compounds to a steam cracking or FCC process and separating off the stream C _{4 by} distillation from the hydrocarbon products formed thereby.

at the well-known FCC process (see Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH Verlag GmbH, Weinheim, Germany Sixth Edition, 2000 Electronic Release, Chapter Oil Refining, 3.2. Catalytic Cracking), the corresponding hydrocarbon is evaporated and in the gas phase with a catalyst at a temperature of 450 up to 500 ° C brought into contact. The particulate catalyst is passed through the counter-current Hydrocarbon stream fluidized. The catalyst is usually synthetic crystalline zeolites.

at the well-known steam cracking method (see. A. Chauvel, G. Lefebvre: Petrochemical Processes, 1 Synthesis Gas Derivatives and Major Hydrocarbons, 1989 Editions Technip 27 Rue Ginoux 75737 Paris, France, Chapter 2) becomes the hydrocarbon with water vapor mixed and depending on the residence time to temperatures of 700 to 1200 ° C in tubular reactors heated and then cooled quickly and separated by distillation into individual fractions.

The raffinate 1, can be obtained from the stream C ₄ by removal or partial hydrogenation of the dienes, alkynes and enynes.

The partial step of butadiene extraction from crude C _{4 cut} is preferably carried out using a butadiene-selective solvent selected from the class of polar aprotic solvents, such as acetone, furfural, acetonitrile, dimethylacetamide, dimethylformamide and N-methylpyrrolidone.

Preferably, the selective hydrogenation step of butadiene and acetylenic impurities present in stream C _{4 is} carried out in two stages by contacting the crude Ca cut in the liquid phase with a catalyst comprising at least one metal selected from the group consisting of nickel, palladium and platinum containing on a support, preferably palladium on alumina, at a temperature of 20 to 200 ° C, a pressure of 1 to 50 bar, a volume velocity of 0.5 to 30 m ³ Frischfeed per m ^{3 of} catalyst per hour and a ratio of Recycle to feed from 0 to 30 with a molar ratio of hydrogen to diolefins of 0.5 to 50 to obtain a reaction effluent in which in addition to isobutene, the n-butenes 1-butene and 2-butene in a molar ratio of 2: 1 to 1:10, preferably from 2: 1 to 1: 2, before lie substantially no diolefins and acetylenic compounds are included.

In step a) the column is preferably supplied in its central region of the C ₄ stream. The column is preferably operated at a top pressure in the range of 5 bar absolute, in particular from 3 bar to 15 bar absolute, thereby it is possible to condense with What water as a coolant at the top of the column, more expensive coolant are not required.

in the Column bottoms are temperatures in the range of about 35-90 ° C, especially 40-60 ° C, often from about 52 ° C one.

• • Die leichter flüchtige Fraktion (Fraktion I), die am Kopf entnommen wird, enthält vorwiegend terminale Butene (Isobuten, 1-Buten) und Isobutan. Bezogen auf den Feedstrom der Kolonne befindet sich im Kopfstrom der Kolonne: 90–100 bevorzugt 95–99,9 % des Isobutens, 90–100 % bevorzugt 95–99,9 % des 1-Butens, 0–2 % bevorzugt 0,1–1 % des 2-Butens, 1–40 % bevorzugt 3–35 % des n-Butans und 90–100 % bevorzugt 97–99,9 % des Isobutans.
• • Die schwerer flüchtige Fraktion (Fraktion II), die am Sumpf entnommen wird, enthält nicht terminale Butene (cis-Buten, trans-Buten) und n-Butan. Bezogen auf den Feedstrom der Kolonne befindet sich im Sumpfstrom der Kolonne: 0–5 % bevorzugt 0,05–2 % des Isobutens, 0–10 % bevorzugt 0,01–4 % des 1-Butens, 90–100 % bevorzugt 95–99,9 % des 2-Butens, 50–100 % bevorzugt 60–0 % des n-Butans und 0–5 % bevorzugt 0,0001–2 % des Isobutans.

Temperatures in the range of about 30-80.degree. C., in particular 35-50.degree. C., frequently of about 43.degree. C., occur in the top of the column.

• • The more volatile fraction (fraction I) taken from the top contains predominantly terminal butenes (isobutene, 1-butene) and isobutane. Based on the feed stream of the column is in the top stream of the column: 90-100 preferably 95-99.9% of isobutene, 90-100%, preferably 95-99.9% of 1-butene, 0-2%, preferably 0.1 -1% of the 2-butene, 1-40% prefers 3-35% of the n-butane and 90-100% prefers 97-99.9% of the isobutane.
• The less volatile fraction (fraction II) taken from the bottom contains non-terminal butenes (cis-butene, trans-butene) and n-butane. Based on the feed stream of the column is in the bottom stream of the column: 0-5%, preferably 0.05-2% of isobutene, 0-10%, preferably 0.01-4% of 1-butene, 90-100%, preferably 95- 99.9% of the 2-butene, 50-100% preferably 60-0% of the n-butane and 0-5%, preferably 0.0001-2% of the isobutane.

As a selective reaction for removing the i-butene from fraction I, for example, the reaction of the i-butene with an alkyl alcohol, in particular a C ₁ - to C ₄ -alkyl alcohol such as methanol or isobutanol to an alkyl tert-butyl ether or the polymerization polyisobutylene. The reactions are well known in their own right. The known methods can be applied analogously to fraction I.

The preparation of methyl tert-butyl ether (MTBE) from methanol and the isobutene-rich fraction I according to step b is generally carried out at 30 to 100 ° C and slight overpressure in the liquid phase over acidic ion exchangers. Usually one operates either in two reactors or in a two-stage shaft reactor in order to achieve an almost complete isobutene conversion (> 99%). The pressure-dependent azeotrope formation between methanol and MTBE requires a multistage pressure distillation to purify MTBE or, according to more recent technology, is achieved by adsorption of adsorbent resins on methanol. All other components of the C ₄ fraction remain unchanged.

to Polymerization of isobutene generally becomes acidic homogeneous and heterogeneous catalysts, e.g. Tungsten trioxide on titanium dioxide or boron trifluoride complexes used. In this way can be up to isobutene sales Be obtained 95% of a discharge stream, which has a residual amount of isobutene of maximum 5 wt .-% has.

The Preparation of high molecular weight polyisobutylene with molecular weights of 100,000 and more is e.g. from H. Güterbock: Polyisobutylene and Mixed polymers, pp 77 to 104, Springer Verlag, Berlin 1959 described.

low molecular weight Polyisobutylenes having a number average molecular weight of 500 to 5000 and a high content of terminal Vinylidene groups and their preparation are e.g. from DE-A-2702604, EP-A-628 575 and WO 96/40808 known.

there is e.g. so proceeded that the isobutene in the liquid phase using boron trifluoride as the catalyst in the presence of secondary alkanols having 3 to 20 carbon atoms polymerized at temperatures of 0 to -60 ° C polymerized. Further details are given in EP-A-628575.

The Separation of the formed polyisobutylene or MTBE from the non Reacted hydrocarbons are usually carried out by distillation.

at the unreacted hydrocarbons (fraction Ia) mainly 1-butene and iso-butane.

The fraction Ia is particularly suitable for the production of 3-hexene by metathesis. For this purpose is the fraction Ia at a temperature of 20 to 350 ° C with a conventional metathesis catalyst in contact. Such metathesis catalysts are well known and described for example in EP-A-1134271. These are in general compounds of a metal of the VIb, VIIb or VIII subgroup of the Periodic Table of the Elements.

Furthermore, the fraction Ia is suitable for the production of valeraldehyde. For this purpose, the fraction Ia is reacted together with synthesis gas. The embodiment of the process is well known and described, for example, in J. Falbe: New Syntheses with Carbon Monoxides, Springer Verlag, Berlin Heidelberg New York 1980, Chapter 1.3. As catalysts, especially co-complexes have been proven. Thus, in the so-called BASF process, the catalyst used is HCo (CO) ₄ in aqueous solution and reacted with the substrate in a loop reactor.

Fraction II consisting mainly of 2-butene and n-butane is preferred. In step b, in which the oligomerization of fraction IC _{4 is} carried out, it is preferred to prepare mainly octenes and dodecenes on nickel catalysts.

As Ni catalysts, especially those nickel-containing catalysts are used, which are known to cause a low oligomer branching, cf. eg DE 4339713 and WO 01/37989 to the prior art cited references, with particular reference to these references in terms of catalysts is hereby incorporated by reference. Particularly preferred are catalysts containing both sulfur and Ni as the active component.

Very particular preference is given to combining catalysts which differ in their S: Ni ratio. Advantageously, in the front reaction stage, a catalyst having an S: Ni ratio <0.5 mol / mol, preferably a catalyst according to WO 01/37989 or DE 4339713 and in the rear reaction stage, a catalyst having an S: Ni ratio> 0.5 mol / mol, preferably a catalyst according to EP 272970 . US 3959400 , FR 2641477 or US 4511750 with an S: Ni ratio> 0.8, more preferably 1.0 used.

The The above catalysts are e.g. used in processes, as they are e.g. in WO 99/25668 and WO 01/72670.

is the Ni catalyst is arranged in the reactor in several fixed beds, so the feed can be split and stored in several places, e.g. before a first fixed bed in the flow direction the reaction mixture and / or between individual Ni catalyst fixed beds, be introduced into the reactor. When using a reactor cascade for example, it is possible the feed completely to feed the cascade to the first reactor or over several Supply lines to the individual reactors of the cascade, as in the case of the single reactor described to distribute.

The Oligomerization reaction usually takes place at temperatures of 30 to 280, preferably from 30 to 190 and especially from 40 up to 130 ° C and a pressure of usually 1 to 300, preferably 5 to 100 and in particular from 10 to 50 bar instead. The pressure is there expediently so selected that the feed at the set temperature supercritical and in particular liquid is present.

Of the Reactor is usually one charged with the Ni catalyst cylindrical reactor; alternatively, a cascade can consist of several preferably two to three, one behind the other connected such Reactors are used.

In the reactor or the individual reactors of the reactor cascade can the Ni catalyst arranged in a single or in several Ni catalyst fixed beds be. Furthermore Is it possible, in the individual reactors of the cascade different Ni catalysts use. Furthermore you can different reaction conditions in the individual reactors of the reactor cascade in terms of pressure and / or temperature in the context of the above Pressure and temperature ranges are set.

The the front reaction stage should be> 50%, preferably> 70% and particularly preferably> 90% total olefin conversion to be operated while the rear reaction stage ensures the residual sales, so that in total a total olefin conversion of> 91 %, preferably> 95 % and more preferably> 97% results. This is basically also using the catalyst of the front reaction stage alone possible, but requires in comparison to the invention either high reaction temperatures, which lead to a relatively rapid catalyst deactivation, or size Catalyst volumes, the efficiency of the process in Would ask a question.

octenes or dodecenes are valuable intermediates, in particular by hydroformylation and subsequent hydrogenation to nonanol or Tridecanol can be implemented.

Experimental part

Examples 1 and 2:

The simulations according to Scheme 1 for the distillation of the raffinate I mixture was carried out on the basis of binary substance data sets. Raffinate I blends with two different compositions were considered:

Example 1: Use of Raffinate IB

The column was simulated with a pressure of 5 bar. The pressure was chosen so that there is a head temperature, which allows a condensation of the vapors with cooling water usual temperature. The column was built up from 55 theoretical stages, wherein the liquid-boiling feed (33 t / h, 48 ° C) takes place at stage 34. The feed is composed according to Raffinate 1B, see above. At the top of the column 25.4 t / h of vapor are withdrawn and 160 t / h liquid back to the column (reflux ratio = 6.3). The amount of heat extracted is 14.2 MW at a condensation temperature of 43 ° C. The following composition has the top stream: i-butene: 59.1% by weight 1-butene: 31.1% by weight 2-butene: 1.15% by weight n-butane: 4.2% by weight i-butane: 4.3% by weight butadiene: 0.15% by weight

7.6 t / h are withdrawn liquid at 51 ° C. at the bottom of the column. The amount of heat supplied to the sump is 16.4 MW. The following composition has the bottom stream: i-butene: 1% by weight 1-butene: 0.3% by weight 2-butene: 54.1% by weight n-butane: 44.6% by weight i-butane: 0% by weight butadiene: 0% by weight

Example 2: Use of Raffinate IA

The column was simulated with a pressure of 5 bar. The pressure was chosen so that there is a head temperature, which allows a condensation of the vapors with cooling water usual temperature. The column was built up from 55 theoretical stages, wherein the liquid-boiling feed (57.1 t / h, 49 ° C) takes place at stage 34. The feed is composed according to raffinate 1A, see above. At the top of the column 39.5 t / h are withdrawn in vapor form and 296 t / h liquid back to the column (reflux ratio = 7.5). The amount of heat withdrawn be 26.3 MW at a condensation temperature of 43 ° C. The following composition has the top stream: i-butene: 38.0% by weight 1-butene: 57.7% by weight 2-butene: 1.15% by weight n-butane: 1.6% by weight i-butane: 1.4% by weight butadiene: 0.15% by weight

17.6 t / h are withdrawn liquid at 52 ° C. at the bottom of the column. The amount of heat supplied to the sump is 29.7 MW. The following composition has the bottom stream: i-butene: 1% by weight 1-butene: 1.7% by weight 2-butene: 83.7% by weight n-butane: 13.6% by weight i-butane: 0% by weight butadiene: 0% by weight

Example 3: Dimerization from butenes

Example of advantageous Procedure with 1-butene-poor butane / butene mixture.

used catalysts

Catalyst I was a material which was shaped into 3 mm star strands according to DE-A-4339713 (composition in% by weight: 50% NiO, 12.5% TiO ₂ , 33.5% SiO ₂ , 4% Al ₂ O) ₃ ). Catalyst II was a material which according to WO 01/37989 was in the form of a 3 mm star strand (composition in% by weight: 8.9% Ni, 1.6% S, balance Al ₂ O ₃ ).

Feed:

• 1-butene-rich feed (comparable to raffinate II) in% by weight: 10.0 % i-butane, 42.8% n-butane, 24.5% 2-butene, 22.5% 1-butene, 0.2% i-butene
• 1-butene-poor feed (sump fraction of a raffinate I column) in% by weight: 9.8% i-butane, 42.7% n-butane, 44.8% 2-butene, 2.4 % 1-butene, 0.3% i-butene

Oligomerization of butenes, according to the invention and comparison

The reactions were carried out continuously using a thermostated fixed bed reactor (30mm clear width) under increased pressure compared to the autogenous pressure of the butane / butenes mixture. The pressure was generated via the reactor feed pump upstream of the reactor and controlled accordingly by means of a pressure maintenance after the reactor and after the reaction product cooling. The following conditions were kept constant in the experiments:
Catalyst pretreatment: filling of 250 ml catalyst, conditioning at 250 ° C for 24 h in a dry N ₂ stream (1500 Nl / h) under atmospheric pressure, then cooling to 20 ° C, metered addition of butane / butene mixture and pressure increase to 20bar with Help the pump or pressure maintenance, finally T-increase to 55 or 60 ° C (a 1-butene-rich feed is more reactive than a 1-butene poor feed, therefore, for setting a comparable sales at comparable load or Butene conc. In the feed a slightly different temperature necessary).
Reaction conditions: p = 20 bar, T = 55-60 ° C, load = 2.0 kg butane / butene mixture / (kg catalyst · hour).

Under the conditions mentioned were those in the table below 1 listed Results obtained.

Table 1: Oligomerization of butenes, according to the invention and comparison

It can be seen that at comparable butene conversion using 1-butene-poor feeds, the C ₈ selectivity is about 2% higher.

Example 4 Metathesis of Butenes to witches

example for advantageous Procedure with 1-butene-rich feed for the production of 3-hexene by the metathesis reaction of 1-butene. The 1-butene rich feed corresponds a raffinate-1 according to the invention Separation with subsequent Isobutene - removal e.g. by isobutene separation or polyisobutylene production.

The catalyst was used in the form of 4 mm strands. Composition in wt.%: 10% Re ₂ O ₇ , 90% Al ₂ O ₃ .

Feed:

• 1-butene-rich feed (top stream of the raffinate-I column with followed by Isobutene): 2% isobutane; 2% n-butane; 1.6% 2-butene; 93.4% 1-butene; 1% isobutene
• 1-butene-poor feed (comparable to raffinate II) 1.3% isobutane; 7% n-butane; 32.6% trans-2-butene; 58.1% 1-butene; 1 % isobutene

Metathesis of 1-butene, according to the invention and comparison

The reactions were carried out continuously using a thermostated fixed bed reactor (6mm clear width) under increased pressure compared to the autogenous pressure of the butane / butenes mixture. The pressure was generated via the reactor feed pump upstream of the reactor and controlled accordingly by means of a pressure maintenance after the reactor and after the reaction product cooling. The following conditions were kept constant in the experiments:
Catalyst preparation treatment: conditioning at 550 ° C for 24 h in a dry O ₂ / N ₂ stream (1500 Nl / h) under atmospheric pressure, then cooling to 20 ° C, metered addition of butane / butene mixture and pressure increase to 20 bar by means of the pump or pressure maintenance, finally T increase to 60 ° C.
Reaction conditions: p = 10 bar, T = 60 ° C, load = 12.5 g of butane / butene mixture / (g catalyst · hour).

Under the conditions mentioned were those in the 1 obtained results.

Claims (8)

Process for the preparation of polyisobutene from a C ₄ -hydrocarbon stream comprising i-butene, 1-butene and 2-butenes (starting stream C ₄ ) by a) in step (a) separating the starting stream Ca by distillation into a more easily volatile fraction ( Fraction I) containing most of the i-butene and 1-butene contained in the mixtures of C ₄ hydrocarbons and a less volatile fraction (fraction II) containing most of those contained in the mixtures of C ₄ hydrocarbons 2-butenes, and b) in step b) the i-butene present in fraction (I) is reacted in a chemically selective reaction and the reaction product is separated from the remaining constituents of fraction (II). Process according to one of the preceding claims, wherein an initial stream C _{4 is} used which consists essentially of 2-butenes, 1-butene, i-butene, i-butane and butanes. Method according to one of the preceding claims, wherein as a chemically selective reaction in step b) the i-butene with an alkyl alcohol to alkyl tert-butyl ether reacted or polymerized to polyisobutylene. Method according to one of the preceding claims, wherein the polymerization of the i-butene after step (b) of acidic homogeneous or heterogeneous catalysts. Method according to one of the preceding claims, wherein one from the remaining component of the fraction (II) stream one 3-hexene-containing stream is prepared by heating it at a temperature from 20 to 350 ° C with a metathesis catalyst in contact Method according to one of the preceding claims, wherein from the remaining constituent of the fraction (II) current through Hydroformylation produces isovaleraldehyde. A process according to any one of the preceding claims wherein the C ₄ olefins contained in fraction (I) are oligomerized to produce mainly octenes or dodecenes. Process according to claim 7, wherein the fraction (I) is contacted with a nickel catalyst.