EP2029638A1

EP2029638A1 - Preparation of reactive, essentially halogen-free polyisobutenes from c4-hydrocarbon mixtures which are low in isobutene

Info

Publication number: EP2029638A1
Application number: EP07729909A
Authority: EP
Inventors: Richard J. Blackborow; Hans Peter Rath
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2006-06-06
Filing date: 2007-06-05
Publication date: 2009-03-04
Also published as: WO2007141277A1; CN101460530A; KR20090014372A; US20100234542A1

Abstract

The present invention relates to a process for preparing reactive and essentially halogen-free, especially fluorine-free, polyisobutenes from C<SUB>4</SUB>-hydrocarbon mixtures which are low in isobutene.

Description

Preparation of reactive, substantially halogen-free polyisobutenes from isobutene C4-hydrocarbon mixtures

The present invention relates to a process for preparing reactive and substantially halogen-free, especially fluorine-free polyisobutenes from low-isobutene C ₄ - hydrocarbon mixtures.

High molecular weight polyisobutenes having molecular weights of up to several 100,000 DaIton have long been known, see, for. B. Güterbock: Polyisobutylene and Mischpoly- merisate, pages 77 to 104, Springer Verlag, Berlin 1959. Of such conventional polyisobutenes, the so-called reactive polyisobutenes are to be distinguished. Reactive polyisobutenes differ from "lower reactive" in their higher content of terminal double bonds. As a rule, reactive polyisobutenes contain at least 50 mol%, e.g. at least 60 mol% of terminal double bonds, based on the total number of polyisobutene macromolecules. The terminal double bonds can be both 2-methyl-2-en groups [-CH = C (CH3) 2] (β-olefin) and vinylidene groups [-CH-C (= CH2) -CH3] (α Olefin). Such reactive polyisobutenes are used as intermediates for the preparation of additives for lubricants and fuels, as described, for example, in DE-A-2702604. The preparation of these additives includes, for example, the formation of polyisobutene-maleic anhydride adducts or the alkylation of, for example, phenols. With maleic anhydride mainly react the terminal vinylidene groups, whereas the lying further inside the macromolecules double bonds lead, depending on their position in the macromolecule without the addition of halogens to no or to a much lower conversion. The phenol alkylation is, however, less critical with respect to the end groups, since the alkylation with polyisobutenes, which are terminated with vinylidene groups, proceeds via the same cationic intermediate as in polyisobutenes terminated with 2-methyl-2-engroups. The proportion of terminal double bonds in the polyisobutene molecule is therefore an important quality criterion of the reactive polyisobutenes. For the use of reactive polyisobutenes as intermediates for the preparation of the abovementioned lubricating and fuel additives, the most uniform possible molecular weight distribution or dispersity is required since polyisobutenes having a relatively broad molecular weight distribution are as a rule unusable for the purposes mentioned.

The preparation of reactive polyisobutenes usually takes place by means of cationic polymerization of isobutene or isobutene-containing streams in the presence of suitable Lewis acids as catalyst. Particularly suitable catalysts are boron trifluoride and boron trifluoride complexes. In the polymerization reaction, for reasons of cost, no pure isobutene is often used, but technical C4 mixtures, ie mixtures of hydrocarbons having 4 carbon atoms (C4 feedstocks), which in addition to isobutene further C4 hydrocarbons, such as 1- and 2-butene, butane and isobutane , contain. However, the isobutene concentrations of conventional feedstocks are often in the range of 8 to 40 wt .-% isobutene or even less than 5 wt .-% isobutene and thus well below the optimum concentration range. So z. B. for the production of polyisobutene having an average molecular weight M _n of 1000, an isobutene concentration of 60 to 65 wt .-% in terms of achieving high space-time yields and high Isobutenumsätze desirable. Although it is known that the conversion of feedstocks can be increased with a suboptimal isobutene concentration, if you extend the reaction time or increases the proportion of BF3 in BF3 complexes; However, these measures are problematic because of the resulting organofluorine components. The CF bonds in the fluorinated polyisobutene molecules are labile, so that in the further reaction of the polyisobutenes, for example with maleic anhydride or with phenols, hydrogen fluoride is liberated, which can lead to considerable corrosion problems. In addition, the presence of HF upon combustion may favor the formation of (fluorinated) dioxins. Also, the HF formed can hardly be separated from the reaction products. Another problem is that many C4 feedstocks contain a not insignificant amount of 1-butene. A relatively high content of 1-butene is problematic in that, in the case of cationic polymerization of the isobutene-containing feedstock, the polymer chain is preferably terminated by copolymerized 1-butene at complete isobutene conversions. A 1-butene terminated polyisobutene molecule has a strong tendency to bind fluorine, eg from the boron trifluoride catalyst, so that the fluorine content of polyisobutenes from C4 feedstocks with a relatively high proportion of 1-butene is significantly higher compared to polyisobutenes from C4 feedstocks with a lower proportion of 1-butene. As already mentioned, a high fluorine content of the polyisobutenes makes them unattractive for many applications, for example in the fuel sector, due to the corrosive properties of HF or the formation of dioxins.

EP-A-0523838 describes a process for the isomerization of linear olefins to isoolefins, e.g. from n-butenes to isobutene, in the presence of zeolites as isomerization catalysts.

US Pat. No. 5,043,523 describes the isomerization of olefins, such as C4-olefins, in the presence of low-sodium siloxane-modified γ-aluminum oxide as isomerization catalyst. DE 3118199 describes a process for the isomerization of the C4 component in C3-C4 hydrocarbon mixtures using fluorinated aluminum oxide in the presence of water or steam.

US 4,436,949 describes the skeletal isomerization and disproportionation of olefins using acidic alumina as a catalyst in the presence of water.

EP 0192059 describes the dehydroisomerization of butane to isobutene using a zirconia-supported chromium oxide / niobium pentoxide catalyst.

H. Güterbock describes in "Polyisobutylene and Isobutylene Copolymers", Springer Verlag, 1959, the dehydroisomerization of butane to isobutene using aluminum oxide or aluminum silicates in porous form as catalysts. In addition, the isomerization of butenes to isobutene in the presence of various catalysts is described Furthermore, this document also describes the recovery of isobutene by depolymerization of isobutene oligomers.

EP-A-0671419 describes a process for the preparation of polyisobutene, in which a C4-hydrocarbon mixture is first subjected to a pretreatment to reduce the content of 1-butene and then polymerized, the pretreated hydrocarbon mixture.

US 4,435,609 describes a process for the hydroisomerization of 1-butene to 2-butenes using a metal of VIII. Subgroup as a catalyst in the presence of hydrogen.

EP-A-0288362 describes a process in which butadiene present in a C ₄ hydrocarbon mixture is hydrogenated and at the same time 1-butene is isomerized to 2-butene. The reaction takes place in the presence of two different catalysts, wherein the C4 feedstock first a hydrogenation catalyst (Pd in combination with Au and / or Pt, supported on alumina or silica) for the hydrogenation of butadiene and then an isomerization (on alumina or silica supported Pd) happened.

FR-A-2515171 describes the selective oligomerization of isobutene in a C ₄ hydrocarbon mixture. EP-A-0628575 and WO 99/64482 describe the preparation of reactive polyisobutenes by cationic polymerization of isobutene or isobutene-containing hydrocarbon streams in the presence of BF 3 in combination with alcohols or primary or secondary dialkyl ethers.

WO 97/06189 describes the preparation of halogen-free, reactive polyisobutenes by polymerization of isobutene or isobutene-containing hydrocarbon streams in the presence of a catalyst which comprises, in addition to an oxygen-containing zirconium compound, at least one oxygen-containing compound of at least one element from I, II, III, IV ., V., VII. Or VIII. Subgroup or from II., IM., IV., V. or VI. Main group contains and does not contain technically effective amounts of halogen.

It is an object of the present invention to provide a process for preparing reactive and substantially halogen-free, in particular fluorine-free, polyisobutenes which makes it possible to economically use isobutene-poor and optionally 1-butene-rich C 4 -hydrocarbon mixtures. In addition, the inventive method should allow the production of polyisobutenes with the narrowest possible molecular weight distribution.

The object was achieved by a process for preparing reactive and substantially halogen-free polyisobutenes, comprising the following steps:

(i) isomerization of a mixture I of C 4 hydrocarbons containing not more than 10% by weight of isobutene and not more than 0.5% by weight of butadiene, based in each case on the total weight of mixture I, to obtain a mixture Ia containing at least 5 wt .-% more isobutene than the mixture I;

(ii) optionally hydroisomerizing at least a portion of the mixture Ia obtained in step (i) to obtain a mixture Ib which contains at least 5% by weight less 1 -butene than the mixture Ia;

(iii) optionally recovering substantially pure isobutene from at least part of the mixture Ia obtained in step (i) or from at least part of the mixture Ib obtained in step (ii);

(iv) optionally mixing

(iv.1) the mixture Ia obtained in step (i) with the mixture Ib obtained in step (ii) or (iv.2) of the mixture Ia obtained in step (i) with the mixture obtained in step (iii) won isobutene or

(iv.3) the mixture Ib obtained in step (ii) with the isobutene obtained in step (iii) or

(iv.4) the mixture Ia obtained in step (i) with the mixture Ib obtained in step (ii) and the isobutene obtained in step (iii) or

(iv.5) the isobutene obtained in step (iii) with a mixture II of C 4 hydrocarbons other than mixtures Ia and Ib, or

(iv.6) the mixture Ib obtained in step (ii) with a mixture II of C4 hydrocarbons other than mixtures Ia and Ib; and

(v) reaction of the mixture Ia obtained in step (i) or the mixture Ib obtained in step (ii) or the mixture obtained in step (iv) or the isobutene obtained in step (iii) in a cationic polymerization in the presence of a BF 3 containing catalyst.

In the context of the present invention, reactive polyisobutenes are understood as meaning polyisobutenes which are at least 60 mol%, preferably at least 70 mol%, more preferably at least 80 mol% and in particular at least 90 mol%, e.g. about 95 mole percent, terminal double bonds based on the total number of polyisobutene macromolecules. The terminal double bonds can be both 2-methyl-2-engroups [-CH = C (CH3) 2] (β-olefin) and vinylidene groups [-CH-C (= CH2) -CH3] (α Olefin). Preferably, however, they are vinylidene groups.

In the context of the present invention, essentially halogen-free or fluorine-free means that the polyisobutene contains at most 50 ppm, preferably at most 20 ppm, more preferably at most 15 ppm and especially at most 10 ppm, for example at most 5 ppm or at most 2 ppm or at most 1 ppm halogen, specifically fluorine, based on the total weight of the polyisobutene. The ppm data here refer to ppm by weight, ie 1 ppm corresponds to 10 " ⁴ wt .-%.

According to the invention, in step (i), a mixture I of C 4 -hydrocarbons which has at most 10% by weight, based on the total weight of mixture I, of isobutene. Preferably, the mixture I at most 8 wt .-% and particularly preferably at most 5 wt .-%, based on the total weight of the mixture I, of isobutene. Suitable mixtures I of C 4 hydrocarbons result, for example, after one or more processing steps, in the hydrocarbon scale separation carried out on an industrial scale in the course of petroleum processing, for example by cracking such as fluid catalytic cracking (FCC), thermal cracking, hydroprocessing. Cracking or dehydration of isobutane. In this case fall, optionally after separation of higher or lower boiling hydrocarbons, referred to as C ₄ - cut technical olefin mixtures. C4 cuts are hydrocarbon mixtures whose main constituent are hydrocarbons having 4 carbon atoms, such as butane, isobutane, 1- and 2-butene and isobutene. C4 cuts can be obtained, for example, by fluid catalytic cracking or steam cracking of gas oil or by steam cracking of liquefied gas or naphtha or by dehydrogenation of isobutane or butane. Depending on the composition of the C _{4 cut, a} distinction is made between the total C ₄ cut (crude C ₄ cut) and the raffinate I obtained after the substantial removal of 1,3-butadiene, the raffinate obtained after extensive separation of isobutene II or IIP after additional separation of 1-butene and the raffinate IM obtained after extensive separation of olefins. Typical compositions of the aforementioned C4 raffinates can be found in the literature z. In EP-A-0671419 or Schulz, Homann "C4-Hydrocarbons and Derivatives, Resources, Production, Marketing", Springer Verlag 1989.

For raffinate II, the composition differs depending on whether the raffinate was recovered in a steam cracker or FC cracker, which methods of isobutene removal were used, and which feeds were used in the cracker.

Thus, raffinate II from steam crackers with naphtha as a feedstock and the removal of isobutene by etherification (e.g., to methyl tert-butyl ether) usually has substantially the following composition:

Isobutene: in the range of 1 to 10 wt .-%, preferably in the range of 1, 5 to 3 wt .-%, 1-butene: in the range of 40 to 60 wt .-%, preferably in the range of 45 to 55 wt %, cis-2-butene: in the range of 5 to 15% by weight, preferably in the range of 5 to 10% by weight, trans-2-butene: in the range of 10 to 20% by weight, preferably in the range from 12 to 18% by weight, n-butane: in the range from 10 to 20% by weight, preferably in the range from 12 to 20% by weight, Isobutane: in the range of 5 to 10% by weight, or preferably in the range of 6 to 10% by weight.

Raffinate II from FCC units is more dependent on the source of the crude oil and, after removal of isobutene by etherification, usually has essentially the following composition:

Isobutene: in the range of 0.5 to 3 wt .-%, preferably in the range of 1 to 2 wt .-%, 1-butene: in the range of 15 to 25 wt .-%, preferably in the range of 17 to 24 wt %, cis-2-butene: in the range of 10 to 25% by weight, preferably in the range of 12 to 33% by weight, trans-2-butene: in the range of 15 to 25% by weight, preferably in the range from 17 to 23% by weight, n-butane: in the range from 10 to 20% by weight, preferably in the range from 10 to 17% by weight, isobutane: in the range from 20 to 35% by weight. %. preferably in the range of 22 to 33% by weight.

As used herein, the term "substantially" means that the content of further components in the specified compositions is at most 5% by weight, preferably at most 1% by weight, based on the total weight of the raffinate compositions those skilled in the art, that when using technical hydrocarbon mixtures in particular also fractions of hydrocarbons having less or more than 4 carbon atoms can be contained as further components .In general, the content of other components in the raffinates used in the process according to the invention or Mixtures I of C4 hydrocarbons not more than 5 wt .-%, based on the total weight, amount.

A raffinate IIP usually has essentially the following composition:

Isobutene: in the range from 1 to 5% by weight, preferably in the range from 1 to 5% by weight,

1-butene: in the range of 1 to 5 wt.%, Preferably in the range of 2 to 4 wt.%, Cis-2-butene: in the range of 10 to 25 wt.%, Preferably in the range of 15 to 22% by weight, Trans-2-butene: in the range of 40 to 50 wt .-%, preferably in the range of 42 to 48 wt .-%, n-butane: in the range of 25 to 40 wt .-%, preferably in the range of 28 to 38% by weight,

Isobutane: in the range of 10 to 20% by weight, preferably in the range of 12 to 18% by weight.

A raffinate IM usually has substantially the following composition:

Isobutene: in the range of 0 to 3% by weight, preferably in the range of 0.1 to 1% by weight,

1-butene: in the range of 0 to 3 wt .-%, preferably in the range of 0.1 to 1 wt .-%, cis-2-butene: in the range of 1 to 5 wt .-%, preferably in the range of 1, 5 to 3 wt .-%, trans-2-butene: in the range of 5 to 30 wt .-%, preferably in the range of 8 to 20 wt .-%, n-butane: in the range of 40 to 70 wt .-%, preferably in the range of 45 to 65 wt .-%,

Isobutane: in the range of 10 to 30 wt .-%. preferably in the range of 15 to 25 wt .-%.

However, suitable mixtures I of C ₄ -hydrocarbon are also obtained from C ₄ sections which have been depleted in isobutene, for example by polymerization to polyisobutene. An example of this is the proportion of this C4 mixture remaining after the production of polyisobutene from raffinate I.

In step (i) of the process according to the invention, the mixture I used is preferably a raffinate II from a steam cracker or from an FCC unit or a raffinate II P or a raffinate III from a steam cracker. The cited raffinates in each case have in each case one of the abovementioned compositions.

According to the invention, the mixture I used has a content of not more than 0.5% by weight and preferably not more than 0.2% by weight, based on the total weight of the mixture I, of butadiene. Optionally required procedures and treatment steps to reduce the content of butadiene, eg. As a selective hydrogenation, are known in the art and for example in EP-A-0288362 and the cited therein, which is hereby incorporated by reference in its entirety.

In step (i) of the process according to the invention, an isomerization of at least part of the C4 hydrocarbons contained in the mixture I takes place. The isomerization is carried out under such conditions that the resulting mixture Ia contains at least 5% by weight more isobutene than the mixture I used (ie when mixture I × wt .-% isobutene, based on the total weight of the mixture I, contains, the mixture Ia obtained in step (i) contains at least (x + 5) wt .-% isobutene, based on the total weight of the mixture Ia). Preferably, the mixture Ia contains at least 10 wt .-%, more preferably at least 15 wt .-% and in particular at least 20 wt .-% more isobutene than the mixture used I.

The content of isobutene of the mixture Ia obtained in step (i) is preferably at least 10% by weight, more preferably at least 15% by weight and in particular at least 20% by weight, based on the total weight of the mixture Ia.

The isomerization reaction in step (i) is preferably a dehydroisomerization or a skeletal isomerization. Of course, under the given isomerization conditions, both isomerization forms can proceed side by side. In addition, under the isomerization conditions of step (i), dehydrations may also take place, e.g. from isobutane to isobutene.

In the context of the present invention, skeletal isomerization is understood as meaning a rearrangement reaction in which a methyl group formally migrates. An example of this is the rearrangement of 2-butene to isobutene.

In the context of the present invention, dehydroisomerization is understood as meaning the dehydrogenation of an alkane to the corresponding alkene, combined with skeletal isomerization, the latter taking place before, simultaneously with or after the dehydrogenation. An example of this is the dehydroisomerization of n-butane to isobutene.

These transformations, in order to increase the space / time yields, are generally carried out at comparatively high temperatures, typically in the range of 300 to 650 ° C. Preferably, the isomerization in step (i) is at a temperature in the range of 350 to 600 ° C. The dehydroisomerization takes place to avoid excessive dehydration, preferably in the presence of hydrogen. The skeletal isomerization preferably takes place in the presence of hydrogen and / or water vapor.

The isomerization can be carried out both under reduced pressure, at ambient pressure and under overpressure. The term pressure here refers to the total pressure which is composed of the pressure of the hydrocarbon mixture I and the pressure of the optionally present hydrogen and / or water vapor. Preferably, the isomerization is carried out under excess pressure, preferably at a pressure of 1, 5 to 20 bar, in particular 2 to 10 bar.

The isomerization preferably takes place in the gas phase or above the critical temperature.

The isomerization in step (i) is generally carried out in the presence of suitable catalysts.

Suitable catalysts for the skeleton isomerization are, for example, aluminum oxides, in particular γ-aluminum oxides, which are preferably distinguished by a low content of alkali metals and alkaline earth metals and which are optionally siloxane-modified, and zeolites. Zeolites are ordered porous crystalline aluminosilicates having a defined structure and cavities connected via channels. Suitable catalysts are described, for example, in EP 523838, US Pat. No. 5,043,523, US Pat. No. 4,436,949 and DE 31 18199 A1, to which reference is hereby fully made.

Suitable catalysts for the dehydroisomerization are, for example, aluminum oxides, in particular γ-aluminum oxides, aluminosilicates in porous form (eg bauxite, clay, kaolin), which are optionally supported and activated with phosphoric, boric or fluoric acid, and metal oxides of secondary group metals , eg

Chromium oxide, niobium oxide and the like, the latter preferably being supported, e.g. on zirconia. Suitable catalysts are described, for example, in EP 192059, US Pat. No. 4,704,497, US Pat. No. 4,806,624 and EP 51291 1, to which reference is hereby made in their entirety.

Dehydroisomerizations are known in principle and are described, for example, in US Pat. No. 4,806,624 and in particular in EP 512911, to which reference is hereby fully made. Examples of catalysts which are suitable for the dehydroisomerization, except in the two above-mentioned documents also in EP 192059 and US 4,704,497, which is hereby incorporated by reference.

Scaffold isomerizations are also known in principle and are described, for example, in EP 523838, US Pat. No. 5,043,523, US Pat. No. 4,436,949 and DE 31 18199 A1, to which reference is hereby fully made. Here you will find both information on the reaction conditions as well as suitable catalysts.

Whether one selects the isomerization conditions in step (i) in accordance with the conditions described above for a skeletal isomerization or rather for a hydroisomerization depends mainly on the hydrocarbon mixture I used in step (i). If this is relatively high in alkanes, it will be more likely to choose conditions favoring a dehydroisomerization reaction, while for mixtures I with a low level of alkanes, it would be desirable to select conditions that favor skeletal isomerization. On the other hand, the conditions which favor dehydroisomerizations or skeletal isomerizations do not differ so much from one another, that as a rule both types of isomerization proceed side by side.

If desired, the mixture Ia obtained in step (i) can be subjected to hydroisomerization. Hydroisomerization in the context of the present invention means the rearrangement of olefinic double bonds in which a hydrogen atom formally migrates. An example of this is the double bond rearrangement in the isomerization of 1-butene to 2-butene.

Hydroisomerization in step (ii) gives a mixture II whose content of 1-butene is at least 20% by weight, preferably at least 40% by weight, more preferably at least 60% by weight and in particular at least 80% % By weight, based on the 1 -butene contained in the mixture Ia.

Preferably, the mixture Ib obtained in step (ii) contains at most 10% by weight, more preferably at most 7% by weight, more preferably at most 5% by weight and especially at most 3% by weight, e.g. at most 2% by weight or at most 1% by weight of 1-butene, based on the total weight of the mixture Ib.

The hydroisomerization is carried out at comparatively low temperatures, preferably at 0 to 200 ° C, more preferably at 20 to 100 ° C. In addition, the hydroisomerization of step (ii) is usually carried out in the presence of hydrogen.

Preferably, it takes place under elevated pressure, e.g. at 2 to 50 bar, preferably at 5 to 30 bar. These pressure data relate to the total pressure of the reaction mixture, which is composed of the partial pressure of the hydrocarbon mixture Ia used in step (ii) and the partial pressure of the hydrogen which is generally present.

The hydroisomerization conditions are suitably chosen so that essentially only optionally present dienes (especially butadiene) and alkynes (especially acetylene and butynes) are hydrogenated and on the other hand isomerize 1-butene to 2-butene.

The hydroisomerization is preferably carried out in the presence of suitable catalysts. Suitable catalysts are, for example, transition metal catalysts, such as palladium or platinum. Preferably, the metal catalysts are supported, e.g. on alumina, silica or zirconia. Suitable catalysts are described, for example, in GB-A-2057006, which is hereby incorporated by reference. Some of the suitable catalysts, e.g. Palladium on alumina are commercially available (e.g., from Sudchemie).

The reaction is preferably carried out such that the mixture produced in step (i) is converted into a cooler reaction zone with a catalyst suitable for hydroisomerization, this reaction zone being arranged in the same reactor as the reaction zone for the isomerization reaction of step (i) can as well as in another reactor.

In the hydroisomerization in step (ii), especially 1-butene is converted to 2-butene. Accordingly, step (ii) is carried out above all when polyisobutenes with a low halogen content, especially fluorine content, are to be obtained and the content of 1-butene in the mixture Ia from step (i) is relatively large, for example at least 5% by weight. % or even at least 10 wt .-% is. The content of 1-butene in the mixture Ia is especially great when a hydrocarbon stream is used as the mixture I, which has a relatively high content of 1-butene, for example at least 5 wt .-% or at least 10 wt .-%, as is the case, for example, with raffinate II and / or when the content of 1-butene in mixture Ia increases as a result of the isomerization reaction of step (i) compared with mixture I, for example to at least 5% by weight or at least 10% by weight, for example because the isomerization conditions, especially higher temperatures, also favor the formation of 1-butene.

Accordingly, step (ii) is preferably carried out when in step (i) a mixture I containing at least 5% by weight of 1-butene, e.g. a mixture other than raffinate IIP or raffinate III, such as raffinate II, and / or when, in step (i), a mixture Ia containing at least 5% by weight of 1-butene is obtained.

On the other hand, step (ii) can be dispensed with despite a relatively high proportion of 1-butene in the mixture Ia obtained in step (i), if the optional step (iii) is carried out in which substantially pure isobutene is obtained, which is incorporated in the Polymerization reaction of step (v) is used or which is mixed in step (iv) with a isobutene-poorer mixture, eg with the mixture Ia obtained in step (i), which not only increases the isobutene content in this isobutene-poorer mixture, but at the same time decreases the proportion of 1-butene, and this mixture is then subjected to polymerization.

Suitable hydroisomerization reactions are known in principle and are described, for example, in EP-A-671419, US Pat. No. 4,435,609 and EP-A-0288362 and in particular in GB-A-2057006, to which reference is hereby fully made.

By "substantially pure isobutene", which is optionally obtained in step (iii), is meant in the context of the present invention an isobutene-containing mixture which is at least 75% by weight, preferably at least 85% by weight, especially preferred. at least 95 wt .-% isobutene, based on the total weight of the isobutene-containing mixture contains. Of course, the isobutene-containing mixture may also be pure isobutene, i. by at least 99% isobutene, act.

In a preferred embodiment of step (iii) substantially pure isobutene is recovered by a distillation of the mixture Ia or of the mixture Ib.

Suitable distillation devices and distillation conditions are known in the art and described for example in FR 2528033, which is incorporated herein by reference.

Because of the similar boiling points of isobutene and 1-butene (-6.8 ° C and -6.7 ° C, respectively), this separation variant is especially suitable for mixtures Ia and Ib which do not contain a high proportion of 1-butene, eg at most 10% by weight or at most 5% by weight of 1-butene. However, it is quite possible, this separation variant also with mixtures which are richer in 1-butene, if the mixture of the isobutene obtained from this separation variant is subsequently obtained in step (iv) in such a way that mixtures II are obtained with sufficiently low 1-butene contents, for example by mixing this relative to 1-butene Isobutene with a 1 Ib-enriched mixture Ib.

In an alternatively preferred embodiment of step (iii), the recovery of substantially pure isobutene comprises the following steps:

(iii.a) selective oligomerization of the isobutene contained in the mixture Ia or in the mixture Ib to give isobutene oligomers;

(iii.b) distillative removal of the volatiles from the isobutene oligomers; and

(iii.c) Cleavage of isobutene oligomers into isobutene monomers.

The selective oligomerization of isobutene in raffinate streams is basically known and described, for example, in FR 2515171, to which reference is hereby fully made. The removal of volatile constituents from the isobutene oligomers takes place by means of distillation in the conventional manner known to the person skilled in the art. Essentially pure isobutene can be obtained from the isobutene oligomers by cleavage. The depolymerization of isobutene oligomers is basically known and described, for example, in H. Güterbock, Polyisobutylene and isobutylene copolymers, Springer Verlag, 1959, pages 23-26, to which reference is hereby fully made. Thus, to obtain substantially pure isobutene from dimeric, trimeric and higher oligomers of isobutene, temperatures in the range from 200 to 450 ° C. and the presence of modified aluminum trioxide or silicon dioxide are suitable.

(iii.a) selective etherification of the isobutene mixture contained in the mixture Ia or in the mixture Ib with an aliphatic C 1 -C 6 -alcohol to give a tert-butyl ether of the aliphatic C 1 -C 6 -alcohol; (iii.b) distillative removal of the volatile constituents from the tert-butyl ether of the aliphatic C 1 -C 6 -alcohol; and

(iii.c) Cleavage of the tert-butyl ether of the aliphatic C 1 -C 6 -alcohol into isobutene monomers and the aliphatic C 1 -C 6 -alcohol.

Examples of suitable alcohols are methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, isobutanol (2-methylpropan-1-ol), n-pentanol, 2- and 3-pentanol, neopentanol, n-hexanol and Positional isomers thereof. Preferred alcohols are primary alcohols such as methanol, ethanol, n-propanol, n-butanol, isobutanol, n-pentanol and n-hexanol. Most preferably, methanol or isobutanol is used, with isobutanol (2-methylpropan-1-ol) being even more preferred.

The selective etherification of isobutene present in the mixture Ia or Ib is carried out by conventional etherification processes, as described, for example, in Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition on CD-ROM, Wiley-VCH, Chapter "Methyl tert-Butyl Ether", Chapter 4 " Production "and chapter" Butenes ", Chapter δ" Upgrading of butenene "are described, to which reference is hereby made in their entirety. The removal of volatile constituents from the resulting tert-butyl ethers is carried out by distillation in the usual manner known to those skilled in the art. The tert-butyl ethers can be split back into isobutene monomers and the alcohol used. This is usually carried out by conventional methods for the cleavage of ethers, as for example in Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition on CD-ROM, Wiley-VCH, chapter "Methyl tert-butyl ether", Chapter 4 "Production" and Chapter "Butene", Chapter 5 "Upgrading of Butene" or in US 4,287,379, to which reference is hereby made in its entirety.

The optional mixing step (iv) serves to optimize isobutene-containing mixtures with regard to their composition, in particular their isobutene and 1-butene content, for the polymerization. This avoids having to subject an entire suboptimal C4 hydrocarbon stream to the process steps (i) and, if necessary, (ii) and / or (iii) prior to the polymerization.

Thus, e.g. the mixture Ia obtained in step (i) is only partially subjected to step (ii) and then the mixture Ib obtained is mixed with the proportion of Ia not reacted in step (ii).

In addition, the mixture Ia obtained in step (i) or the mixture Ib obtained in step (ii) or both may be substantially pure with the product obtained in step (iii) Isobutene be mixed, for example, if the amount of isobutene contained in the mixtures Ia and / or Ib is not sufficiently high and / or if the 1-butene content present in one of the components (especially in the mixture Ia or in isobutene) is too high.

Furthermore, the essentially pure isobutene obtained in step (iii) or the mixture Ib obtained in step (ii) can be mixed with C ₄ hydrocarbon streams other than mixture Ia or Ib (mixture II). Suitable mixtures II are, for example, the mixture I used in step (i), raffinate I or C ₄ cuts of FCC units. Preferred mixtures II are Raffinate I and C ₄ cuts from FCC units.

The composition of raffinate I depends on whether liquefied petroleum gas, naphtha or mixtures thereof were used as the feedstock, with naphtha resulting in a raffinate I with higher isobutene contents.

The raffinate I obtained from steam crackers has essentially the following composition:

Isobutene: in the range of 35 to 55% by weight, preferably in the range of 35 to 48% by weight, 1-butene: in the range of 25 to 35% by weight, preferably in the range of 27 to 33% by weight. %, cis-2-butene: in the range of 2 to 10% by weight, preferably in the range of 3 to 8% by weight, trans-2-butene: in the range of 5 to 15% by weight, preferably in Range from 6 to 13% by weight, n-butane: in the range from 5 to 15% by weight, preferably in the range from 7 to 13% by weight, isobutane: in the range from 2 to 10% by weight, preferably in the range of 3 to 8% by weight,

The C _{4 cut} obtained from FCC units has essentially the following composition:

Isobutene: in the range of 10 to 20% by weight, preferably in the range of 12 to 18% by weight, 1-butene: in the range of 10 to 20% by weight, preferably in the range of 12 to 20% by weight. %, cis-2-butene: in the range of 10 to 20% by weight, preferably in the range of 12 to 18 wt%, trans-2-butene: in the range of 10 to 25 wt%, preferably in the range of 12 to 22 wt%, n-butane: in the range of 5 to 15 wt .-%, preferably in the range of 7 to 13 wt .-%, isobutane: in the range of 15 to 25 wt .-%, preferably in the range of 7 to 23 wt .-%.

Increasing the content of isobutene in isobutene-poor mixtures of C ₄ -

Hydrocarbons according to step (iv) of the process according to the invention increase the availability of isobutene, which can be fed to a polymerization for the preparation of reactive polyisobutenes. As a result, in particular those embodiments of the method according to the invention are made possible, which allow an economical utilization of C4 streams for the production of reactive polyisobutenes, without the isobutene having to be isolated from the entire amount of the C4 streams used. For this purpose, for example, the isobutene is obtained in substantially pure form from a portion of the C ₄ hydrocarbons used as mixture I after isomerization. This is done as described above by the separation of the isobutene from the mixture Ia or Ib (step (Ni)). The isobutene monomers thus obtained in substantially pure form can be used for the enrichment of available C ₄ - hydrocarbon mixtures. In this way, optimum isobutene concentrations in the reaction mixtures intended for polymerization can be adjusted in a simple manner. Thus, the pure isobutene separated off as described above can be blended directly with isobutene-rich C ₄ -hydrocarbon mixtures such as raffinate I or FCC-C ₄ cuts. C ₄ -Raffinatströme the comparatively low levels of isobutene of z. B. have less than 10 wt .-%, are also suitable for mixing with the isobutene monomers obtained as described above, if their content of isobutene was increased by means of the isomerization described above (for example, mixture Ia or Ib).

The individual mixture components used in step (iv) may be of the same or different origin.

In a preferred embodiment, essentially pure isobutene (from step (Ni)) is mixed in step (iv) with a mixture Ia (from step (i)) and / or a mixture Ib (from step (N)). Here, the mixture Ia, the mixture Ib and the substantially pure isobutene from the same or from different mixtures I of C ₄ hydrocarbons originate. In an alternatively preferred embodiment, in step (iv) substantially pure isobutene (from step (Ni)) is mixed with a relatively isobutene-rich C4 cut, for example with raffinate I.

For carrying out the process according to the invention, it has proved to be particularly advantageous to adjust the mixing ratio in step (iv) such that the resulting mixture has a content of isobutene of preferably at least 30% by weight, more preferably at least 40% by weight, in particular at least 50% by weight and especially at least 60% by weight, based in each case on the total weight of the mixture obtained in step (iv). In addition, it is preferable to adjust the mixing ratio so that the resulting mixture has a content of 1-butene of preferably at most 10% by weight, more preferably at most 5% by weight, especially at most 2% by weight and especially at most 1% by weight .-%, each based on the total weight of the mixture obtained in step (iv).

The reaction of isobutene to give reactive polyisobutenes in the presence of boron trifluoride complexes or boron trifluoride complexes as catalysts is known and described, for example, in EP-A-1095070 (WO 99/64482), EP-A-0628575 and EP-A-0671419, in which is hereby incorporated by reference in its entirety.

The catalyst used is boron trifluoride, often in combination with a suitable donor (cocatalyst, complexing agent). Suitable cocatalysts are alcohols, carboxylic acids, aldehydes, ketones, nitriles, phenols and dialkyl ethers. The resulting Lewis acceptor-donor complex has (also) Bronsted acid properties when using protic donors, such as alcohols or carboxylic acids. Particularly suitable complexes have both Lewis and Brönsted acid properties.

The polymerization is generally carried out at a temperature of -100 ° C to

100 ° C, preferably from -60 ° C to 40 ° C, and more preferably from -40 ° C to 20 ⁰ C.

Further suitable reaction conditions are described in EP-A-1095070 (WO 99/64482), EP-A-0628575 and EP-A-0671419, to which reference is hereby fully made.

In a preferred embodiment of the process, the components obtained in step (iii), from which the substantially pure isobutene is separated off, and / or the components obtained in step (v) after the polymerization, from which the formed polyisobutene is separated, are recycled back to step (i). These components obtained in step (iii) are largely C4 hydrocarbons other than isobutene. The components obtained in step (v) are, for the most part, unpolymerized C 4 -hydrocarbons (isobutene and C 4 -hydrocarbons different therefrom) and / or isobutene oligomers. The recycling is particularly preferably carried out when these components obtained in step (iii) or (v) have a low content of 1-butene, for example at most 5% by weight or at most 2% by weight, based on the total weight of the components so they do not need to be used in step (ii).

In a preferred embodiment, the method of the invention comprises step (i) and step (v), i. steps (i) and (v) are mandatory while steps (ii), (iii) and (iv) are optional.

In an alternatively preferred embodiment, the method according to the invention comprises step (i), step (ii), optionally step (iii), optionally step (iv) and step (v), i. steps (i), (ii) and (v) are mandatory while steps (iii) and (iv) are optional.

In an alternatively preferred embodiment, the process according to the invention comprises step (i), optionally step (ii), step (iii), optionally step (iv) and step (v), i. steps (i), (iii) and (v) are mandatory while steps (ii) and (iv) are optional.

In an alternatively preferred embodiment, the method according to the invention comprises step (i), optionally step (ii), step (iii), step (iv) and step (v), i. Steps (i), (iii), (iv) and (v) are mandatory while step (ii) is optional.

In an alternatively preferred embodiment, the method according to the invention comprises step (i), step (ii), step (iii), optionally step (iv) and step (v), i. steps (i), (ii), (iii) and (v) are mandatory while step (iv) is optional.

In an alternatively preferred embodiment, the method according to the invention comprises step (i), step (ii), step (iii), step (iv) and step (v), ie all 5 steps (i), (ii), (iii ), (iv) and (v) are mandatory. The statements made above on preferred embodiments of the individual method steps apply both individually taken alone and in combination.

The polyisobutenes prepared by the process according to the invention have a number average molecular weight M _n of preferably from 100 to 10,000, more preferably from 500 to 5000 and in particular from 800 to 3000, for example about 1000 or about 1500 or about 2000 or about 2500.

Furthermore, the polyisobutenes prepared by the process according to the invention have a dispersity (PDI = M _w / Mn; M _w = weight-average molecular weight) of preferably at most 3, for example from 1 to 3, particularly preferably at most 2.5, for example from 1 to 2 , 5, more preferably at most 2, for example from 1 to 2, and in particular at most 1, 8, for example from 1 to 1, 8 or 1, 2 to 1, 8.

The values given for M _n and M _w relate to values determined by gel permeation chromatography (GPC) using polyisobutene standards.

Preferably, the polyisobutenes prepared by the process of the present invention have at least 60 mole%, more preferably at least 70 mole%, more preferably at least 80 mole%, and most preferably at least 90 mole%, e.g. about 95 mole percent terminal double bonds based on the total number of polyisobutene macromolecules. The terminal double bonds are vinylidene groups (α-double bond) or 2-methyl-2-engroups (β-double bonds). Preferably, the terminal double bonds are vinylidene groups (α-double bond); i.e. the polyisobutenes prepared by the process of the present invention preferably have at least 60 mole%, more preferably at least 70 mole%, more preferably at least 80 mole%, and most preferably at least 90 mole%, e.g. about 95 mol%, terminally arranged vinylidene double bonds, based on the total number of polyisobutene macromolecules.

The proportion of terminal double bonds is determined by means of ¹ H-NMR spectroscopy.

Above all, however, the polyisobutenes prepared by the process according to the invention are distinguished by the fact that they are substantially halogen-free, especially essentially fluorine-free. Halogens such as fluorine may be present in particular in the form of fluoroorganic compounds. For use of the produced reactive Polyisobutenes for the preparation of lubricating and fuel additives, it is usually sufficient if the content of fluorine in the reactive polyisobutenes is at most 0.005 wt .-%. The halogen and especially the fluorine content in the polyisobutenes prepared according to the invention is preferably at most 0.005% by weight, more preferably at most 0.002% by weight, more preferably at most 0.0015% by weight, even more preferably at most 0.001% by weight. , for example, at most 5x10 " ⁴ wt .-% or at most 2x10 ^{" 4} wt .-%, and in particular at most 1x10 ^"4 wt .-%, based on the total weight of the polyisobutenes.

The fluorine content is determined by conventional methods, e.g. determined by combustion analysis with subsequent wet analysis.

The following experimental examples illustrate some aspects and embodiments of the present invention. They are in no way to be understood as limiting.

Examples

The determination of the M _n and M _w values was carried out by means of GPC (polyisobutene standards). The content of terminal vinylidene groups was determined by means of ¹ H-NMR. The fluorine content was determined by wet and combustion analysis.

example 1

A stream of a raffinate IM of the following composition:

1-Butene: 0.3% by weight of cis-2-butene: 1.9% by weight of trans-2-butene: 4.2% by weight of isobutene: 0.0% by weight of n-butane: 78.5% by weight

Isobutane: 15.1% by weight

was fed to a dehydroisomerization zone along with 100 ppm of water. The catalyst used here was a zirconium-based catalyst which was prepared in accordance with EP-A-192059, Example 1 b), the niobium content being 0.1 mol per mol of ZrO 2 and no chromium oxide being used. After calcining at 650 ° C. for two hours, the catalyst was obtained as a powder with 40 × 60 mesh and an oxygen surface area of 40 m ² / g. The dehydroisomerization zone was at an absolute Hydrogen pressure of 5 bar operated at 560 ° C. The load was 5 kg of reaction mixture per hour and kg of catalyst. After one hour, gas samples were taken and analyzed. The conversion of butanes to butenes was 58%, the selectivity 96%. The isobutene content was 33% and the 1-butene content was 13%. This reactor effluent was fed to a second lower temperature isomerization zone. 342 strand diameter 2 mm, strand length 2-6 mm, surface; in the second isomerization zone an alumina catalyst (was 95% alumina, 5% SiO 2, Siral ^® 5, Degussa, into a paste with formic acid, pelletized and 2 h at 350 ° C calcined m ² / g) are used. The second isomerization zone was operated at 70 ° C at a flow rate of 1 kg reaction mixture per hour and per kg of catalyst. The discharge of C4 hydrocarbons from the second isomerization zone had a content of isobutene of 39 wt .-% and a content of 1-butene of 5 wt .-%, each based on the total weight of the discharge on.

The polymerization was carried out analogously to EP-A-628575, Example 1. On the suction side of a loop reactor equipped with an integrated circulating pump (tube diameter 10 mm, volume 100 ml), 600 g of the discharge from the second isomerization zone was conducted for one hour to carry out the polymerization reaction. In this case, a catalyst was generated in situ from a BF3-2-butanol complex (22 mmol BF3, 37 mmol 2-butanol). The reactor was cooled so that the internal temperature was -13 ° C. The isobutene conversion was 60%, the average residence time 6.6 minutes. To terminate the polymerization, the reaction effluent in a stirred vessel was continuously admixed with 100 ml / h of 10% strength aqueous NaOH and the remaining liquid gas was evaporated at 40.degree. For further purification, the degassed product was dissolved in hexane and extracted three times with water. Removal of the solvent gave, after distillative separation of the oligomers at 3 mbar and 220 ° C., as residue a polymer having an average molecular weight M _n = 2207 and a dispersity Mw / M _n = 1.8. The polymer had a fluorine content of 9 ppm.

Example 2

A stream of a raffinate IIa of the following composition:

1-Butene 52.3 wt% cis-2-butene 8.1 wt% trans-2-butene 14 wt%

Isobutene 1, 8% by weight n-butane 16.6% by weight Isobutane 7.2% by weight

was fed to a skeletal isomerization zone along with 100 ppm of water. In this case, an alumina catalyst (95% alumina, 5% SiO 2, Siral ^® 5, Degussa, slurried in water, treated with 0.2% aqueous Na2CO3 solution, filtered off, dried overnight at 100 ° C, strand granulated and calcined at 350 ° C., strand diameter 2 mm, strand length 2-6 mm, surface area 327 m ² / g). The skeletal isomerization zone was operated at an absolute hydrogen pressure of 5 bar and a temperature of 425 ° C. The load was 2 kg of reaction mixture per hour and per kg of catalyst. The output from the skeleton isomerization zone had a content of isobutene of 22 wt .-% and a content of 1-butene of 12 wt .-%, each based on the total weight of the discharge on.

The effluent from the skeletal isomerization zone was fed to a reactor for conducting an etherification reaction. In the reactor, the reaction mixture was reacted with sec-butyl alcohol. The mixture thus obtained was subjected to fractional distillation. In this way, a fraction of pure sec-butyl tert-butyl ether could be obtained. This fraction was split back into sec-butyl alcohol and isobutene in a separate cracking reaction. The isobutene obtained in this case had a purity of 99% by weight.

The isobutene obtained in this way was used for the preparation of reactive polyisobutene. As the reactor, a circulation reactor was used, consisting of a 7.1 m long Teflon hose with an inner diameter of 6 mm, was passed over the 100 l / h reactor contents with a gear pump in a circle. Tube and pump had a capacity of 200 ml. Teflon tube and pump head were in a cooling bath cooled to -23.8 ° C via a cryostat. A mixture of 300 g / h of isobutene and 300 g / h of hexane was dried over a molecular sieve 3A to <3 ppm water, pre-cooled to 23.8 ° C and fed through a capillary with 2 mm inner diameter to the reactor. BF3 and isopropanol / diisopropyl ether as a complexing agent were fed into the Hexanzulauf. The BF3 feed was adjusted to 23.5 mmol and the total amount of feed of the mixture of hexane, isopropanol and diisopropyl ether was adjusted so that an isobutene conversion of 92% was achieved. The workup of the reactor effluent was carried out analogously to Example 1. It was a polymer with a mean molecular weight M _n = 11 10 and a dispersity Mw / M _n = 1, 6 was obtained. The polymer had a content of terminal vinylidene groups of 95%. The content of fluorine in the polymer was less than 1 ppm.

Example 3 A stream of raffinate Il P of the following composition:

1-butene 4.1% by weight cis-2-butene 16.2% by weight trans-2-butene 28.1% by weight isobutene 3.4% by weight n-butane 33.6% by weight -%

Isobutane 14.6% by weight

was fed to a dehydroisomerization zone along with 100 ppm of water. In the dehydroisomerization zone, a zirconium-based catalyst according to Example 1 was used. The dehydroisomerization zone was operated at 565 ° C and 5 bar absolute hydrogen pressure. The load was 5 kg of reaction mixture per hour and per kg of catalyst. The effluent from the dehydroisomerization zone contained 18% by weight of isobutene and 12% by weight of 1-butene. This discharge was brought into contact with an acidic fixed-bed catalyst according to Example 1 of EP 843688 at 10 ° C. The resulting discharge was subjected to fractional distillation. A bottoms fraction was obtained containing oligomers of isobutene and in particular dimers, trimers and tetramers of isobutene. This bottoms fraction was converted to substantially pure isobutene by cracking at 280 ° C over an aluminum / AIF3 based catalyst (fluorine content 7.8%).

The isobutene thus obtained was used analogously to Example 2 for the preparation of reactive polyisobutene. A polymer having an average molecular weight M _n = 1090 and a dispersity Mw / M _n = 1.6 was obtained. The polymer had a content of terminal vinylidene groups of 95 mol%. The fluorine content in the obtained polymer was less than 1 ppm.

Examples 4 to 7

The reaction mixture used for Examples 4 to 7 for the polymerization of isobutene monomers was obtained in each case by mixing or enriching different C4 streams with essentially pure isobutene. The mixed isobutene was obtained as described in Example 3.

The raffinate used for blending in Example 4 is a raffinate I from the C4 fraction of a predominantly naphtha-operated steam cracker having the following composition: 1-Butene 29.0% by weight cis-2-butene 4.5% by weight trans-2-butene 7.7% by weight isobutene 45.4% by weight n-butane 9.3% by weight -%

Isobutane 4.1% by weight

In Example 5, a C4 stream from the catalytic cracker of a refinery of the following composition was used for the mixing:

1-Butene 12.0 wt.% Cis-2-butene 10.9 wt.% Trans-2-butene 23.2 wt.% Isobutene 16.3 wt.% N-butane 15.8 wt. -%

Isobutane 21, 8% by weight

In example 6, a raffinate II P of a steam cracker of the following composition was obtained:

Isobutane 14.6% by weight

used for the blend, which was subjected to a Dehydroisomerisie- reaction according to Example 3.

In Example 7, a raffinate was IM of the following composition:

1-butene 0.3 wt% cis-2-butene 1, 9 wt% trans-2-butene 4.2 wt%

Isobutene 0.0% by weight n-butane 78.5% by weight

Isobutane 15.10% by weight used for the blend, which was subjected to a dehydro isomerization reaction according to Example 1.

In all Examples 4 to 7, the blend was made such that the reaction mixture intended for polymerization had an isobutene content of 60% by weight, based on the total weight of the reaction mixture. The polymerization of isobutene was carried out analogously to Example 2. This was adjusted to a flow rate of 600 g / h reaction mixture, 70 mmol BF3 / h, 40 mmol / h isopropanol and 80 mmol / h diisopropyl ether.

The following table shows the average molecular weight M _n , the dispersity PDI = Mw / M _n and the reactivity in%, ie the content of terminal vinylidene groups, for the particular polymer obtained.

Claims

claims

1. A process for the preparation of reactive and substantially halogen-free polyisobutenes, comprising the following steps:

(iv) optionally mixing

(iv.1) the mixture Ia obtained in step (i) with the mixture Ib obtained in step (ii) or

(iv.2) the mixture Ia obtained in step (i) with the isobutene obtained in step (iii) or (iv-3) the mixture Ib obtained in step (ii) with the isobutene obtained in step (iii) or

(iv.4) the mixture Ia obtained in step (i) with the mixture Ib obtained in step (ii) and the isobutene obtained in step (iii) or (iv.5) of the isobutene obtained in step (iii) with a mixture II of C4 hydrocarbons, which is different from the mixtures Ia and Ib, or

2. The process according to claim 1, wherein the isomerization in step (i) comprises a dehydro isomerization or skeletal isomerization of at least part of the C4 hydrocarbons contained in the mixture I.

3. The method according to any one of the preceding claims, wherein the mixture used in step (i) I contains at most 5 wt .-% isobutene.

4. The method according to any one of the preceding claims, wherein the mixture obtained in step (i) Ia contains at least 10 wt .-% isobutene more than the mixture I.

5. The method according to any one of the preceding claims, wherein in step (iii) in

Substantially pure isobutene is obtained by distillation of the mixture Ia or of the mixture Ib.

A process according to any one of claims 1 to 4, wherein the recovery of substantially pure isobutene comprises the steps of:

(iii.b) distillative removal of the volatiles from the isobutene oligomers; and

(iii.c) Cleavage of isobutene oligomers into isobutene monomers.

(iii.a) selective etherification of the mixture contained in the mixture Ia or in the mixture Ib

Isobutene with an aliphatic Ci-Cβ alcohol to give a tertiary

Butyl ether of the aliphatic Ci-Cβ-alcohol;

(iii.b) distillative removal of the volatile constituents from the tert-butyl ether of the aliphatic C 1 -C 6 -alcohol; and

8. The method of claim 7, wherein the aliphatic Ci-Cβ-alcohol is selected from methanol and 2-methyl-1-propanol.

9. The method according to any one of the preceding claims, wherein the mixture I as a raffinate Il from a steam cracker and / or from a fluid catalytic cracking unit and / or a raffinate Il P from a steam cracker and / or a raffinate IM from a steam cracker.

10. The method of claim 9, wherein

Raffinate II has essentially one of the following compositions:

a) isobutene: in the range of 1 to 10 wt .-%, 1-butene: in the range of 40 to 60 wt .-%, cis-2-butene: in the range of 5 to 15 wt .-%, trans-2 In the range of 10 to 20% by weight, n-butane: in the range of 10 to 20% by weight, isobutane: in the range of 5 to 10% by weight, or

b) isobutene: in the range of 0.5 to 3 wt .-%, 1-butene: in the range of 15 to 25 wt .-%, cis-2-butene: in the range of 10 to 25 wt .-%, trans 2-butene: in the range of 15 to 25 wt%, n-butane: in the range of 10 to 20 wt%, isobutane: in the range of 20 to 35 wt%, and

the raffinate II P has essentially the following composition:

Isobutene: in the range of 1 to 5% by weight,

1-butene: in the range of 1 to 5 wt%, cis-2-butene: in the range of 10 to 25 wt%, trans-2-butene: in the range of 40 to 50 wt%, n Butane: in the range of 25 to 40% by weight,

Isobutane: in the range of 10 to 20% by weight, and

the raffinate IM has essentially the following composition: Isobutene: in the range of 0 to 3% by weight,

1-butene: in the range of 0 to 3 wt .-%, cis-2-butene: in the range of 1 to 5 wt .-%, trans-2-butene: in the range of 5 to 30 wt .-%, n Butane: in the range of 40 to 70% by weight,

Isobutane: in the range of 10 to 30 wt .-%.

1 1. The method according to any one of the preceding claims, wherein the mixture II used as a raffinate I from a steam cracker or a C4 cut from a fluid catalytic cracking unit of a refinery.

12. The method of claim 11, wherein the raffinate I or the C4 cut has substantially one of the following compositions:

a) isobutene: in the range of 35 to 55% by weight, 1-butene: in the range of 25 to 35% by weight, cis-2-butene: in the range of 2 to 10% by weight, trans-2 In the range of 5 to 15% by weight, n-butane: in the range of 5 to 15% by weight, isobutane: in the range of 2 to 10% by weight, or

b) isobutene: in the range of 10 to 20% by weight, 1-butene: in the range of 10 to 20% by weight, cis-2-butene: in the range of 10 to 20% by weight, trans-2 In the range of 10 to 25% by weight, n-butane: in the range of 5 to 15% by weight, isobutane: in the range of 15 to 25% by weight.

13. The method according to any one of the preceding claims, wherein in step (iv) the mixing ratio between the mixture components adjusted so that the mixture obtained in step (iv) has a content of isobutene of at least 30 wt .-%, based on the total weight of obtained mixture having.

14. The method according to any one of the preceding claims, wherein polyisobutenes having a content of fluorine of less than 0.005 wt .-%, based on the weight of the polyisobutene molecule receives.