WO2013120984A1

WO2013120984A1 - Method for producing high-molecular-weight polyisobutylene

Info

Publication number: WO2013120984A1
Application number: PCT/EP2013/053042
Authority: WO
Inventors: Thomas Wettling; Stefan Hirsch; Markus Brym; Markus Weis
Original assignee: Basf Se; Basf Schweiz Ag
Priority date: 2012-02-17
Filing date: 2013-02-15
Publication date: 2013-08-22
Also published as: CA2863836A1; JP2015507069A; MY168940A; CN104136470A; KR101974337B1; CA2863836C; CN104136470B; KR20140122757A; SG10201606861XA; EP2814851A1; JP2017186577A; JP6234382B2; SG11201403863YA

Abstract

The invention relates to the production of isobutylene homopolymers having a weight-average molecular weight of 75,000 to 10,000,000 by means of the polymerization of isobutylene by (a) performing the polymerization at -80°C to -190°C, (b) using optionally halogenated C₁ to C₅ hydrocarbons as an inert solvent, (c) using a Lewis acid complex as a polymerization catalyst, and (d) performing the polymerization in the presence of at least one reaction accelerator in the form of an ethylenically saturated hydrocarbon compound, which contains an oxygen atom and no proton that can be emitted, and performing the polymerization in the presence of at least one chain length regulator, which contains a tertiary olefinic carbon atom.

Description

Process for the preparation of higher molecular weight polyisobutylene

The present invention relates to an improved process for preparing isobutene homopolymers having a weight-average molecular weight of from 75,000 to 10,000,000 by polymerization of isobutene in the liquid phase in an inert solvent in the presence of a Lewis acid-based polymerization catalyst. Efficient and specification-specific production processes of higher molecular weight polyisobutenes usually require very low polymerization temperatures. A common process for the preparation of higher molecular weight polyisobutenes is the so-called "BASF belt process", in which liquid isobutene with boron trifluoride as a polymerization catalyst and a high excess of liquid ethene on an endless steel strip of 50 to 60 cm wide leads, which is designed trough-shaped by a suitable guide and is located in a gas-tight, cylindrical housing. By continuous evaporation of ethene at atmospheric pressure, a temperature of -104 ° C is established. The heat of polymerization is thereby completely dissipated. The vaporized ethene is collected, purified and recycled. The resulting polyisobutenes are freed from adhering ethene and residual monomers by degassing. The type of polymerization leads to a virtually complete isobutene conversion.

In the BASF strip process, the polymerization temperature may be due to the boiling-cooling, i. be controlled simply and safely by forming large vapor passages. However, it is a disadvantage of the BASF strip process that due to the lack of movement of the reaction mixture on the strip, there is no adequate mixing of the reaction mixture and thus no product surface renewal, which may adversely affect the product properties. This leads, for example, to an inhomogeneous distribution of the ethene used for the boiling cooling and, associated therewith, to a local overheating of the reaction mixture as soon as the ethene has evaporated. It can also become an explosive

Boiling of the reaction mixture come when overheated areas and ethenreiche cold areas contact each other, which then leads to contamination of the reactor wall by entrainment of polymerizing reaction mixture. Another disadvantage is that the inhomogeneous temperature distribution causes an undesirable broadening of the molecular weight distribution of the polymer, which is associated with unfavorable product properties. Another disadvantage of the BASF belt process is that the steel strip is subject to wear and thus causes high maintenance costs. Furthermore, it is disadvantageous in the BASF strip process that the reactor walls and the product feed are not cooled in the downstream working part (usually an extruder); Since polyisobutylene is highly tacky above its glass temperature, this leads to a marked adhesion of the reactor walls with polymers, which necessitates an increased cleaning effort. A further disadvantage of the BASF strip process is that boron trifluoride contained in the recirculated ethene stream at elevated temperatures. temperatures has a highly corrosive effect, which causes a high maintenance expense of the ethene processing cycle.

Another common method for the preparation of higher molecular weight polyisobutenes is the "Oxy-slurry process" in which the polymerization is carried out at -80 to -85 ° C. in a cooling jacket provided with cooling jacket which is charged with liquid ethene As a catalyst system, anhydrous aluminum chloride in methylene chloride is used, and as a result of very vigorous stirring, the polymer precipitates as a slurry consisting of small droplets, which flows via an intermediate vessel into a degassing vessel, where the slurry is steamed and treated with hot water so that the volatiles (substantially unreacted isobutene and methyl chloride) can be removed and subjected to reprocessing The remaining aqueous slurry of polymer particles is worked up by removing catalyst residues, solvent residues and isobutene residues.

Although intensive mixing and product surface renewal take place in the Exxon Breeding process, the polymerization temperature is difficult to control solely by jacket cooling. Since the adhesion of the polymer to the reactor and apparatus walls can not be completely prevented, the reactor and apparatus must be cleaned from time to time.

The BASF strip process and the Exxon Breeding process are described in more detail in Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition, Vol. A21, pages 555-561, under the heading "polyisobutylenes".

The object of the present invention was to provide an easy to carry out, efficient and economical process for the preparation of high molecular weight isobutene homopolymers, which allows a safe control of the polymerization with regard to the product parameters to be adjusted such as molecular weight, polydispersity and residual monomer content and an easily aufreininigendes and easy to handle, before In particular, a non-adhesive product before work-up supplies. Because of the more thorough mixing of the reaction product, the polymerization should be carried out in a conventional closed reactor and in the disperse phase in a non-miscible fluid or homogeneously mixed in a miscible fluid, i. in a suitable solvent or diluent.

The polymerization of isobutene to higher molecular weight isobutene homopolymers in conventional closed reactors in solvents or diluents is also known from other documents in addition to the described Exxon-Breiverfahren. For example, DE-OS 2 061 289 discloses an isobutene polymerization process in which isobutene is heated between 0 ° C. and -160 ° C. in an inert diluent such as ethylene, methane, ethane or propane using boron trifluoride as catalyst in the presence of a solution of formaldehyde in an alcohol such as isobutanol as a molecular weight regulator in a reaction flask polymerized to higher molecular weight polyisobutene. In the monograph "Polymerization and Polycondensation Processes, Advances in Chemistry Series 34" (1961) JP Kennedy and RM Thomas describe in their article "Cationic Polymerization at Ultralow Temperatures" on page 1 1 1 -1 19 the polymerization of isobutene in a propane. Isopentane mixture in a cooled reactor at -30 ° C to -190 ° C by means of an aluminum trichloride catalyst to higher molecular weight polyisobutene. Aluminum trichloride has the disadvantage that, as a non-volatile catalyst, it hinders the subsequent purification of the polyisobutene. Reaction accelerators or chain length regulators are not used.

It is known from the literature article "Fundamental Studies on Cationic Polymerization IV - Homo- and Combinations with Various Catalysts" by JP Kennedy and RG Squires in Polymer 6, pages 579-587, 1965, that isobutene catalyses boron trifluoride in alkyl chloride solvents polymerize at -30 ° C to -146 ° C in the presence of isoprene to higher molecular weight poly isobutene. Reaction accelerators are not included.

The object of the present invention has been achieved by a process for producing isobutene homopolymers having a weight-average molecular weight of from 75,000 to 10,000,000 by polymerizing isobutene in the liquid phase in an inert solvent in the presence of a Lewis acid-based polymerization catalyst is characterized in that in a polymerization reactor simultaneously

(A) the polymerization is carried out at temperatures of -80 ° C to -190 ° C, (b) as inert solvent one or more d- to Cs-hydrocarbons or one or more halogenated d- to Cs-hydrocarbons or a mixture thereof used and

(C) as a polymerization catalyst using a Lewis acid complex based on boron trifluoride, iron halides, aluminum trihalides or aluminum alkyl halides or a Lewis acid in combination with organic sulfonic acids as initiators, and further

(d) the polymerization in the presence of at least one reaction accelerator in the form

an ethylenically saturated hydrocarbon compound containing at least one oxygen atom and no abstractable proton, and / or (e) carrying out the polymerization in the presence of at least one chain length regulator containing at least one tertiary olefinic carbon atom.

In a preferred embodiment, the measures (d) and (e) are carried out simultaneously. In the context of the present invention, isobutene homopolymers are understood to mean those polymers which, based on the polymer, are composed of at least 98 mol%, preferably at least 99 mol%, of isobutene.

For the use of the isobutene or of the isobutene-containing monomer mixture as the monomer to be polymerized, the isobutene source is in particular pure isobutene, which generally contains at most 0.5% by volume of residual impurities such as 1-butene, 2 Butenes, water and / or C 1 to C 4 alkanols. In principle, however, it is also possible to use isobutene-containing technical C4 hydrocarbon streams, for example C4 raffinates, C4 cuts from isobutane dehydrogenation, C4 cuts from steam crackers and FCC crackers (fluid catalysed cracking), insofar as they are largely derived from 1, 3-butadiene contained therein are liberated. Suitable technical C4 hydrocarbon streams generally contain less than 500 ppm, preferably less than 200 ppm, butadiene. The isobutene from such technical C4 hydrocarbon streams polymerized here largely selectively to the desired isobutene homopolymer without significant amounts of other C4 monomers are incorporated into the polymer chain. Typically, the isobutene concentration in said C4 hydrocarbon commercial streams is in the range of 40 to 60 weight percent. However, in principle the process according to the invention can also be operated with isobutene-containing C 4 hydrocarbon streams which contain less isobutene, for example only 10 to 20% by weight. The isobutene-containing monomer mixture may contain small amounts of contaminants such as water, carboxylic acids or mineral acids, without resulting in critical yield or selectivity losses. It is expedient to avoid an accumulation of these impurities by removing such pollutants from the isobutene-containing monomer mixture, for example by adsorption on solid adsorbents such as activated carbon, molecular sieves or ion exchangers.

The according to measure (c) to be used as a polymerization catalyst Lewis acid complexes based on iron halides, aluminum trihalides or aluminum alkylalkylhalogeniden and used as a polymerization catalyst Lewis acids in combination with organic sulfonic acids as initiators are described in detail in WO 2012/072643 A2 , which is hereby incorporated by reference. The said iron halide, aluminum trihalide and aluminum alkyl halide complexes contain, in addition to the Lewis acid, a donor in the form of an organic compound having at least one ether function or one carboxylic ester function. The said combination of Lewis acids, in particular boron trifluoride, iron halides, aluminum trihalides or Aluminiumalkylhalogeniden, with organic sulfonic acids as initiators contain at least one organic sulfonic acid of the general formula Z-SO3H, in which Z is a Ci-C2o-alkyl radical, Ci-C2o Haloalkyl, Cs-Cs-cycloalkyl, C6-C20-aryl or C7-C20-aralkyl; a typical such organic sulfonic acid is methanesulfonic acid.

However, according to measure (c), a complex of boron trifluoride and a proton source is preferably used as the polymerization catalyst. As such proton sources, which the function of an activator or moderator in the catalyst complex are suitable, especially ethers, in particular C 1 to C ₄ dialkyl ethers such as diethyl ether, and alcohols, in particular low molecular weight monohydric aliphatic alcohols. In a particularly preferred embodiment, the polymerization catalyst used is a complex of boron trifluoride and a C 1 to C 3 alkanol, for example. Methanol, ethanol, n-propanol or isopropanol. It can be used as proton source and mixtures of said ethers and / or alcohols.

The boron trifluoride and the proton source can be premixed and already added as an action ready complex in the polymerization reactor. Alternatively, however, the boron trifluoride [gaseous, liquid or dissolved in an inert solvent or diluent, for example in an inert solvent according to measure (b)] and the proton source may also be supplied separately to the polymerization medium.

The amount of polymerization catalyst to be used depends essentially on the type of catalyst and on the reaction conditions, in particular the reaction temperature and the desired molecular weight of the polymer. It can be determined by means of fewer random tests for the respective reaction system. In general, the polymerization catalyst in amounts of 0.0001 to 1 wt .-%, in particular 0.0005 to 0.5 wt .-%, especially 0.001 to 0.1 wt .-%, each based on the Lewis acid Component or boron trifluoride portion in the catalyst complex and on isobutene used.

The proton source can be used in substoichiometric, stoichiometric or superstoichiometric amounts in relation to boron trifluoride. Typical molar ratios of proton source to boron trifluoride are in the range of 0.3: 1 to 3: 1, in particular 0.5: 1 to 2: 1, especially 0.7: 1 to 1, 3: 1 (in each case based on 1 Proton equivalent of the proton source). Like the amount of reaction accelerator according to measure (d) and chain length regulator according to measure (e), the amount of proton source according to measure (c) can also influence the adjustment of the molecular weight of the isobutene homopolymer to be achieved and with the targeted adjustment of its molecular weight serve.

The isobutene homopolymers prepared by the process according to the invention preferably have a weight-average molecular weight (M _w ) of from 150,000 to 8,000,000, in particular from 250,000 to 6,000,000, especially from 400,000 to 5,000,000. Alternatively, they preferably have a number average molecular weight (M _n ) (determined by gel permeation chromatography) of from 25,000 to 2,000,000, particularly preferably from 45,000 to 1,500,000, in particular from 55,000 to 1,000,000, especially from 65,000 to 750,000.

In general, the isobutene homopolymers produced by the process according to the invention have a polydispersity (PDI = M _w / M _n ) of from 2 to 20, in particular from 3 to 15, especially from 5 to 10.

In accordance with measure (a), the polymerization process according to the invention is carried out in the liquid polymerization medium at temperatures of -80.degree. C. to -190.degree. In a preferred Embodiment is carried out at temperatures near the lower limit of the above temperature range, and at -130 ° C to -190 ° C, especially at less than -160 ° C to -185 ° C, especially at - 165 ° C to -180 ° C, in a typical procedure at -168 ° C to -173 ° C. In an alternative preferred embodiment, the process is carried out at temperatures of -100 ° C to -150 ° C, preferably at -105 ° C to -147 ° C, especially at -1 10 ° C to -140 ° C, in particular at -1 15 ° C to -135 ° C, in a typical procedure at -120 ° C to -130 ° C, by. The controlled low polymerization temperatures have an advantageous effect on the product properties. The temperature setting during the precooling of the starting materials used, in particular the isobutene, may also influence the course of the polymerization and the results obtained; The isobutene to be used is usually cooled to temperatures of from -70.degree. C. to -140.degree. C., in particular to -70.degree. C. to -100.degree.

The cooling of the reaction medium to the above-mentioned temperatures is advantageously carried out by external cooling. In a preferred embodiment, therefore, to carry out measure (a), the polymerization medium is brought to the required cryogenic temperature by means of a separate cooling circuit and kept there during the polymerization. The separated cooling circuit, which is structurally usually implemented as an outer cooling jacket to the polymerization, is usually operated with liquid nitrogen or liquefied air as a coolant.

The polymerization is generally carried out at a pressure of 500 mbar to 5 bar, in particular at a pressure of 800 mbar to 2 bar. Most advantageously and most economically, the polymerization reactor is operated at or near the ambient pressure (normal pressure). A slight overpressure may provide benefits for some of the possible inert solvents. Although a procedure of polymerization with overpressure is possible in principle, bring higher pressures, especially those above 5 bar, in general, no additional advantages. According to measure (b), certain inert solvents or mixtures of such inert solvents are used in the liquid polymerization medium. In this case, inert solvents are understood to mean not only fluids in which isobutene dissolves homogeneously in the liquid phase, but also fluids with which isobutene is immiscible and is present in dispersed form. Suitable inert solvents are suitable for a C 1 to C 8 hydrocarbons, preferably C 1 to C 8 hydrocarbons, in particular C 2 to C 4 hydrocarbons, which are usually saturated or simply ethylenically unsaturated and are generally linear or slightly branched structure. Of course, if they are ethylenically unsaturated, they must not polymerize themselves under the reaction conditions of the present invention; they usually have only primary and / or secondary olefinic carbon atoms. Typical examples of such C to Cs-hydrocarbons are methane, ethane, ethene, propane, propene, n-butane, isobutane, n-pentane, 2-methylbutane, 2,3-dimethylbutane, 2-methylpentane, 3-methylpene tan, 3-ethylpentane, 2,2-dimethylpentane, 2,3-dimethylpentane, 2,4-dimethylpentane, 2-methyl-hexane, 3-methylhexane, 3-ethyl-2-methylpentane, 2,2-dimethylhexane, 2,3-dimethylhexane, 3,3-dimethylhexane, 4-methylheptane, 2,2,3-trimethylpentane and 3-methylheptane. As such inert solvents, on the other hand, halogenated C 1 to C 5 hydrocarbons, preferably halogenated C 1 to C 8 hydrocarbons, in particular fluorinated and / or chlorinated C 1 to C 8 or C 1 -hydrocarbons, such as methyl chloride, methyl fluoride, difluoromethane, dichloromethane , Fluoroethane, 1-fluoropropane, 1, 1, 1, 2,3,3,3-

Heptafluoropropane, octafluoropropane or 1-fluorobutane, suitable; in particular perfluorinated d- to Cs- or d- to Cs-hydrocarbons or such d- to Cs- or d- to Cs-hydrocarbons, in which at least half of the hydrogen atoms are replaced by fluorine atoms, come into consideration here. It is also possible to use mixtures of C.sub.1 to C.sub.s or C.sub.1 to C.sub.5 hydrocarbons, or mixtures of halogenated C.sub.1 to C.sub.s or C.sub.1 to C.sub.s

Hydrocarbons or mixtures of one or more d- to Cs or d- to Cs- hydrocarbons and one or more halogenated C to d or Cs or Cs hydrocarbons are used. In a preferred embodiment, the measure used as measure (b) as the inert solvent is ethane, ethene, propane, propene, n-butane, isobutane or a mixture thereof.

In an alternative preferred embodiment, the measure used as measure (b) as the inert solvent is 1,1,1,3,3,3,3-heptafluoropropane, octafluoropropane or a mixture thereof.

The weight ratio of isobutene to the inert solvents according to measure (b) in the polymerization reactor is generally 1: 0.1 to 1:50, preferably 1: 0.1 to 1:40, especially 0.1: 1 to 1: 20, in particular 1: 0.5 to 1: 10. According to measure (d), the polymerization is carried out in the presence of one or more reaction accelerators. Such a reaction accelerator is a compound which, under the chosen polymerization conditions, influences and thus controls the catalytic activity of the boron trifluoride in the desired manner. Such reaction accelerators are saturated hydrocarbon compounds which contain at least one oxygen atom, preferably as an ether oxygen atom or as part of a carbonyl function. In a preferred embodiment, the polymerization is carried out as measure (d) in the presence of at least one reaction accelerator selected from ketones, aldehydes, ethers, acetals and hemiacetals. Usually, such reaction accelerators are low molecular weight compounds having 1 to 40, in particular 1 to 16, especially 1 to 8 carbon atoms; their structure can be open-chain or cyclic; they may be aliphatic, aromatic or heteroaromatic in nature.

Typical representatives of such reaction accelerators are ketones such as acetone, butanone, cyclohexanone, acetophenone or benzophenone, aldehydes such as formaldehyde, trioxane, paraformaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, benzaldehyde, cyclohexylaldehyde or glyoxal, dialkyl ethers such as dimethyl ether, diethyl ether or di-n butyl ethers, cyclic ethers such as tetrahydrofuran or dioxane, as well as acetals and hemiacetals, which are prepared by reacting the abovementioned ketones and aldehydes with alcohols such as methanol, ethanol, n-propanol, isopropanol. nol, n-butanol, isobutanol, sec-butanol or part. Butanol are available. Very particular preference is given to formaldehyde as such a reaction accelerator.

The abovementioned reaction accelerators may most advantageously be used together with one or more medium-molecular weight alcohols, in particular monohydric aliphatic, cycloaliphatic or araliphatic alcohols, especially C ₄ -C 10 -alcohols, eg. n-butanol, isobutanol, sec-butanol, tert. Butanol, n-pentanol, n-hexanol, n-octanol, 2-ethylhexanol, n-decanol, 2-propylheptanol, cyclohexanol or benzyl alcohol. On the one hand, such medium molecular weight alcohols act similarly to the low molecular weight alcohols used as proton source according to measures (c) as activators or moderators in the catalyst complex, but usually with a weaker activating effect; on the other hand, they act as solvents for the reaction accelerators. If aldehydes or ketones are used as reaction accelerators, the abovementioned medium molecular weight alcohols as well as some of the low molecular weight alcohols mentioned can form with these acetals or hemiacetals or ketals (ketone acetals) which likewise act as reaction accelerators. If one uses formaldehyde as a reaction accelerator, a corresponding alcoholic solution, for. As formaldehyde in isobutanol, are used. If such medium molecular weight alcohols are used, their weight ratio to the reaction accelerator is generally 0.05: 1 to 15: 1, but preferably 0.1: 1 to 5: 1, in particular 0.5: 1 to 2.5: 1, especially 0.75: 1 to 1, 5: 1.

The reaction accelerator itself is normally used in amounts of from 0.0001 to 1% by weight, preferably from 0.0003 to 0.75% by weight, in particular from 0.0005 to 0.5% by weight, in particular from 0.001 to 0, 1 wt .-%, each based on isobutene used.

In accordance with measure (e), the polymerization is carried out in the presence of at least one chain length regulator which normally represents an ethylenically unsaturated system and contains one or more tertiary olefinic carbon atoms, optionally in addition to one or more primary and / or secondary olefinic carbon atoms. Most such chain length regulators are mono- or polyethylenically unsaturated hydrocarbons having 5 to 30, in particular 5 to 20, especially 5 to 16 carbon atoms; their structure can be open-chain or cyclic. Typical representatives of such chain length regulators are isoprene (2-methyl-1,3-butadiene), 2-methyl-2-butene, diisobutene, triisobutene, tetraisobutene and 1-methylcyclohexene. In a preferred embodiment, the polymerization is carried out as measure (e) in the presence of isoprene and / or diisobutene as chain length regulators. Diisobutene (isooctene) is usually understood to mean the mixture of isomers of 2,4,4-trimethyl-1-pentene and 2,4,4-trimethyl-2-pentene; Of course, the individually used isomers 2,4,4-trimethyl-1-pentene and 2,4,4-trimethyl-2-pentene also act as chain length regulators according to measure (e). The amount of chain length regulators used according to the invention allows the molecular weight of the isobutene homopolymers produced to be adjusted in a simple manner: the higher the amount of chain length regulators, the lower the molecular weight generally becomes. The chain length regulator controls Usually, the molecular weight is replaced by the fact that sooner or later it will be incorporated into the polymer chain, leading to chain termination at this point.

The chain length regulator is normally used in amounts of from 0.0001 to 2% by weight, in particular from 0.0005 to 1% by weight, in particular from 0.001 to 0.5% by weight, based in each case on isobutene used.

The process according to the invention for the preparation of isobutene homopolymers, including the subsequent work-up steps, can be carried out batchwise or continuously.

In principle, all batchwise or continuously operated reactor types suitable for such liquid-phase polymerizations, for example, stirred tanks, stirred tank cascades, kneaders, extruders, tube reactors or loop reactors, may be used as the polymerization reactor for the process according to the invention.

It is advantageous to carry out the process according to the invention at high conversions, if possible at full conversion or near full conversion, for example at a conversion of the isobutene used to the desired product of 85% to 100%, in particular 90% to 100%. But it is also possible - especially in continuous driving - the inventive method with partial conversion, for example, at a conversion of the isobutene used to the desired product of 10% to 85%, in particular from 30% to 60% to perform. In a preferred embodiment, the polymerization conditions for the process according to the invention are chosen such that the isobutene used in the polymerization onsreaktor with a conversion of at least 90%, in particular of at least 95%, especially of at least 99%, to isobutene homopolymers having a weight average molecular weight of 75,000 to 10,000,000 is implemented.

An advantageous embodiment of the inventive method is that in a separate vessel, the starting material isobutene or an isobutene-containing hydrocarbon mixture together with the proton source, in particular a C 1 to C 3 alkanol, and together with one or more reaction accelerators, in particular selected from Ketonen, aldehydes, ethers, acetals and hemiacetals, and / or one or more chain length regulators, in particular selected from isoprene and diisobutene, premixed and in the polymerization reactor to the cooled to the polymerization temperature inert solvent containing the boron trifluoride. It is also particularly advantageous to cool this mixture before it is added to the polymerization reactor. This isobutene-containing mixture is added to the polymerization reactor so that the desired polymerization temperature can be kept constant by the external cooling. A rapid and complete mixing of the isobutene in the continuous phase is crucial for an effective temperature control and thus for the success of the process. Evaporating nitrogen from the external cooling can then either be re-liquefied in a closed circuit or - without having to carry out a cleaning - be conducted into the environment. With renewed liquefaction of the recirculated nitrogen stream, the low temperature of the vaporized nitrogen can be used advantageously and thus recovered. Dispensing with the feedback, the cold energy of the gaseous nitrogen for other cooling purposes, for. B. for the cooling of the degassed end product can be used.

As an alternative to liquid nitrogen or liquefied air when working in the range of a polymerization temperature of -100 ° C to -150 ° C, other external coolants can also be used, for example based on halogenated hydrocarbons.

The workup of the isobutene homopolymers produced in the process according to the invention with a weight-average molecular weight of 75,000 to 10,000,000 is usually carried out by discharging the product from the polymerization reactor and - optionally after a suitable pretreatment - by thermal purification of the product. The discharge takes place advantageously at the lowest possible temperatures. The discharge from the reactor can be carried out, for example, by means of a mechanical discharge device such as a discharge screw. In a preferred embodiment, which is of particular importance in the case of the large-scale embodiment of the process according to the invention, the isobutene homopolymers produced in the polymerization reactor are discharged from the polymerization reactor at temperatures of less than -80 ° C. and subjected to a thermal purification process at temperatures of more as + 80 ° C. The thermal cleaning after discharge of the product from the polymerization reactor is advantageously carried out in the industrial scale of the inventive method by using one or more extruders. In this case, the isobutene homopolymers are heated to temperatures of more than 80 ° C., in particular more than 100 ° C. By mechanical action of the extruder shafts and, where appropriate, internals in the extruder, the inner surface is renewed again and again for better degassing of the volatile constituents in the product, such as residual monomers and solvents. The degassing and the purification of the product can be facilitated by applying a vacuum, in particular one works for this purpose at a pressure of less than 700 mbar, in particular less than 200 mbar, especially less than 100 mbar.

In principle, all customary single-shaft and two-shaft and multi-shaft extruders can be used for the thermal purification of the isobutene homopolymers produced. In twin- and multi-shaft extruders, the waves can work in the same direction or in opposite directions. The waves in single and multiple-shaft extruders are normally occupied by kneading and / or conveying elements. These appliances are usually self-cleaning. The speeds of rotation of the waves are generally in the range of 10 to 500, in particular 15 to 350 revolutions per minute. In a special design, the waves may be formed as worm shafts, whose gears are engaged with each other and whose inner shaft diameter preferably via the entire length is constant. Preferred building materials for the described extruders are steels or stainless steels. Advantageously, an inert gas, for example nitrogen, is introduced into one or more segments of the extruder in order to promote the degassing process.

The process according to the invention has the advantage that the isobutene homopolymers produced have only a low solubility in the solvents used (hydrocarbons and / or halogenated hydrocarbons) - and this applies to a greater extent at low temperatures - and thus largely precipitates as a solid. This precipitated solid has no tendency to stick at the low temperatures used, so that the crude product can be easily discharged and further processed, since in the region of collection of the product from the reactor in the workup at any point temperatures above the glass transition temperature of the polymer. The following examples are intended to illustrate the present invention without limiting it.

Examples 1 to 12

A 1 liter 3-necked flask with mechanical stirrer, dry nitrogen gaseous inert gas inlet tube, a temperature control thermocouple, and a coolable dropping funnel was placed after inerting with the aid of liquid nitrogen (in a half-shell dewar flask placed around the flask). 100 ° C pre-cooled. Subsequently, 300 ml of liquid propane were placed in the flask under nitrogen atmosphere and 0.1 g of gaseous boron trifluoride was introduced.

The dewar under the flask stood on a height-adjustable laboratory stage. By varying the fill level in the Dewar flask, the desired polymerization temperature T could be easily adjusted. 94.0 g (1.68 mol) of liquid isobutene were added to the dropping funnel cooled with dry ice (about -78 ° C.) or liquid nitrogen (about -130 ° C.). Subsequently, the respectively below indicated amounts of methanol, isobutanol, formaldehyde (which had been freshly produced from paraformaldehyde and was present dissolved in the methanol / isobutanol mixture) and diisobutene were metered in and mixed with the isobutene in the dropping funnel.

After reaching the desired polymerization temperature T in the flask, stirring was started with the dropping in of the dropping funnel contents. Each drop reacted immediately and increasingly gave a fine-grained solid. The desired reaction temperature T was kept constant during the entire dripping time by raising or lowering the dewar vessel by means of a lifting platform and adding liquid nitrogen. After the entire dropping funnel contents had dripped in, the contents of the flask were allowed to thaw, the solvent propane (boiling point: -42 ° C) evaporating. The crude product which had become tacky at room temperature was then removed and freed from the remaining solvent by heating in a drying oven (temperature: 160 ° C. at 30 mbar, duration: 2 h). Thereafter, the analytical data of the obtained isobutene homopolymer could be determined.

The following table indicates the temperatures, the amounts used and the analytical data of the products obtained in each case.

Example No. 1 2 3 4 5 6

Polymerisationstemp. T -170 ° C -170 ° C -170 ° C -170 ° C -170 ° C -170 ° C Pre-cooling isobutene -78 ° C -78 ° C -78 ° C -130 ° C -130 ° C -130 ° C

Quantity of methanol 0.15 ml 0.15 ml 0.15 ml 0.15 ml 0.15 ml 0.15 ml

Quantity of isobutanol 0.05 ml 0.05 ml 0.05 ml 0.05 ml 0.05 ml 0.05 ml

Amount of formaldehyde 0.05g 0.05g 0.05g 0.05g 0.05g 0.05g

Amount of diisobutene 0.01 ml 0.02 ml 0.05 ml 0 ml 0.01 ml 0.05 ml

Molecular weight M _w 824000 796000 483000 5157000 3831000 2055000

Molecular weight M _n 123000 1 17000 68000 586000 421000 221000

Polydispersity D 6.7 6.8 7.1 8.8 9.1 9.3

Example No. 7 8 9 10 1 1 12

Polymerisationstemp. T -150 ° C -140 ° C -130 ° C -120 ° C -1 10 ° C -100 ° C Pre-cooling isobutene -78 ° C -78 ° C -78 ° C -78 ° C -78 ° C -78 ° C

Amount of methanol 0.15 ml 0.15 ml 0.15 ml 0.15 ml 0.15 ml 0.15 ml amount isobutanol 0.05 ml 0.05 ml 0.50 ml 0.50 ml 0.05 ml 0, 05 ml amount of formaldehyde 0.05 g 0.05 g 0.05 g 0.50 g 0.50 g 0.50 g amount of diisobutene 0.01 ml 0.01 ml 0.01 ml 0.01 ml 0.01 ml 0.01 ml

Molecular weight M _w 823000 81 1000 803000 803000 766000 715000 Molecular weight M _n 121000 121000 1 10000 103000 88000 73000 Polydispersity D 6.8 6.7 7.3 7.8 8.7 9.8

Claims

claims

1 . Process for the preparation of isobutene homopolymers having a weight-average molecular weight of 75,000 to 10,000,000 by polymerization of isobutene in the liquid phase in an inert solvent in the presence of a polymerization catalyst based on Lewis acids, characterized in that simultaneously polymerization is carried out in a polymerization reactor at temperatures of -80.degree. C. to -190.degree. C., the inert solvent used is one or more C.sub.1- to C.sub.-hydrocarbons or one or more halogenated C.sub.1- to C.sub.-hydrocarbons or a mixture thereof and, as the polymerization catalyst, a Lewis Acid complex based on boron trifluoride, iron halides, aluminum trihalides or Aluminiumalkylhalogeniden or a Lewis acid used in combination with organic sulfonic acids as initiators, and further the polymerization in the presence of at least one reaction accelerator in the form of an ethy lenisch saturated hydrocarbon compound containing at least one oxygen atom and no abstractable proton, performs and / or

(e) carrying out the polymerization in the presence of at least one chain length regulator which contains at least one tertiary olefinic carbon atom.

A method according to claim 1, characterized in that one carries out the measures (d) and (e) simultaneously.

Process according to Claim 1 or 2, characterized in that, as measure (a), the polymerization is carried out at temperatures of less than -160 ° C to -185 ° C.

A method according to claim 1 or 2, characterized in that one carries out the polymerization at temperatures of -1 10 ° C to -140 ° C as measure (a).

Process according to Claims 1 to 4, characterized in that, to carry out measure (a), the polymerization medium is brought to the required low temperature by means of a separate cooling circuit and it is heated during the process Polymerization stops there.

6. Process according to claims 1 to 5, characterized in that one uses as measure (b) as the inert solvent ethane, ethene, propane, propene, n-butane, isobutane or a mixture thereof.

7. Process according to claims 1 to 5, characterized in that one uses as measure (b) as the inert solvent 1, 1, 1, 2,3,3,3-heptafluoropropane, octafluoropropane or a mixture thereof.

8. The method according to claims 1 to 7, characterized in that one uses as a measure (c) as a polymerization catalyst, a complex of boron trifluoride and a proton source. 9. The method according to Anspr8, characterized in that is used as measure (c) as the polymerization catalyst, a complex of boron trifluoride and a C 1 - to C ₄ - alkanol.

10. The method according to claims 1 to 9, characterized in that as a measure (d), the polymerization is carried out in the presence of at least one reaction accelerator selected from ketones, aldehydes, ethers, acetals and hemiacetals.

1 1. Process according to claims 1 to 10, characterized in that as a measure (e) the polymerization is carried out in the presence of isoprene and / or diisobutene as chain length regulators.

12. The method according to claims 1 to 1 1, characterized in that one selects the polymerization conditions so that the isobutene used in the polymerization sationsreaktor with a conversion of at least 90% to isobutene homopolymers having a weight average molecular weight of 75,000 to 10,000,000 is implemented ,

13. The method according to claims 1 to 12, characterized in that discharges the isobutene homopolymers produced in the polymerization reactor at temperatures of less than -80 ° C from the polymerization reactor and subjected to a thermal cleaning process at temperatures of more than + 80 ° C.

14. The method according to claim 13, characterized in that one or more extruders are used to carry out the thermal cleaning process.