WO2007113196A1

WO2007113196A1 - Process for preparing high molecular weight isobutene homopolymers by polymerization in an apparatus with mixing and conveying properties

Info

Publication number: WO2007113196A1
Application number: PCT/EP2007/053005
Authority: WO
Inventors: Thomas Wettling; Uwe Rachwalsky; Marco-Christian Volland; Werner Bochnitschek; Roland Kunklel; Markus JÄGGI; Pierre-Alain Fleury
Original assignee: Basf Se; List Holding Ag
Priority date: 2006-04-05
Filing date: 2007-03-29
Publication date: 2007-10-11

Abstract

Preparation of isobutene homopolymers with a weight-average molecular weight Mw of from 75 000 to 10 000 000 by polymerizing isobutene or isobutenic monomer mixtures in liquid phase in the presence of one or more Lewis acids as polymerization catalysts and of an inert solvent by performing the polymerization in an apparatus which simultaneously has mixing and conveying properties.

Description

Process for the preparation of higher molecular weight isobutene homopolymers by polymerization in an apparatus with mixing and conveying properties

description

The present invention relates to an improved process for the preparation of isobutene homopolymers having a weight-average molecular weight M _{w of} from 75,000 to 10,000,000 by polymerization of isobutene or isobutene-containing monomer mixtures in the liquid phase in the presence of one or more Lewis acids as polymerization catalysts and an inert solvent.

Efficient and specification-specific preparation processes of relatively high molecular weight polyisobutenes generally 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 vary due to the boiling-cooling, i. be controlled simply and safely by forming large vapor passages. A disadvantage of the BASF strip process, however, is that due to lack of movement of the reaction mixture on the belt no mixing and thus no product surface renewal takes place, which can adversely affect the product properties.

Another common method for producing higher molecular weight polyisobutenes is the "Exxon slurry process" in which the polymerization is carried out at -80 to -85 ° C. in a stirred tank equipped with a cooling jacket which is charged with liquid ethene is carried out. The catalyst system used is anhydrous aluminum chloride in methyl chloride. As a result of the very vigorous stirring, the polymer precipitates as a slurry consisting of small droplets, which flows over an intermediate vessel into a degassing vessel. Here, the slurry is treated with steam and hot water so that the volatiles (essentially unreacted isobutene and methyl chloride) can be removed and sent for reprocessing. The remaining aqueous slurry of Polymerisatteil- is worked up by removing catalyst residues, solvent residues and Isobutenresten.

Although intensive mixing and product surface renewal take place in the Exxon Breeding process, the polymerization temperature is difficult to control by jacket cooling alone. 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 belt process and the Exxon Breeding process are, for example, in

Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition, Vol. A21, pages 555-561, under the keyword "polyisobutylenes".

WO 02/090391 generally discloses the use of two-shaft kneading reactors for carrying out polymerization reactions in which a solvent is added only in a second stage, when the viscosity of the reaction mixture has already markedly increased due to the advanced polymerization. By this method, for example, methyl methacrylate in the presence of diethyl ether as a solvent and the initiator "Perkadox 16", which is based on di- (4-tert-butyl-cyclohexyl) peroxydicarbonate, in a temperature range of +5 to +60 ° C polymerized.

In DE-A 24 36 259 selbstabstreifende or self-cleaning two- or multi-shaft screw reactors for the bulk polymerization of alpha-olefins are recommended. Such screw reactors are positively conveying and ensure good mixing. The alpha-olefins used, for example butene-1, are polymerized at temperatures between -50 and + 180 ° C. and at pressures between 5 and 200 bar by means of organometallic mixed catalysts or catalysts comprising chromium oxide or molybdenum oxide.

Since it is known that high molecular weight isobutene homopolymers, in particular, can undergo undesired degradation reactions by shortening or cleavage of the polymer chains ("depolymerization") due to their branched structures at high mechanical energy inputs, as occurs in kneading and screw reactors, there was a prejudice, polymerization equipment With high mechanical energy inputs, so in particular equipment with conveying properties for the production of higher molecular weight isobutene homopolymers use.

The object of the present invention was to provide an easy to carry out, efficient and economical process for the preparation of higher molecular weight isobutene homopolymers, in particular those having a weight-average molecular weight M _w of 75,000 to 10,000,000, which on the one hand a safe Kon- trolle deep polymerization and on the other hand allows intensive mixing of the reaction mixture.

The object has been achieved by a process for the preparation of isobutene homopolymers having a weight-average molecular weight M _{w of} from 75,000 to

10,000,000 by polymerization of isobutene or isobutene-containing monomer mixtures in the liquid phase in the presence of one or more Lewis acids as polymerization catalysts and an inert solvent, which is characterized in that the polymerization is carried out in an apparatus which simultaneously and conveying properties.

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 the isobutene-containing monomer mixture as a monomer to be polymerized is suitable as an isobutene source in particular pure isobutene, which is usually at most 0.5 vol .-% of residual impurities such as 1-butene, 2-butenes , Butane, 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 appreciable amounts of other C4 monomers are incorporated into the polymer chain. Typically, the isobutene concentration in the stated C4 hydrocarbon streams is in the range from 40 to 60% by weight. However, in principle the process according to the invention can also be operated with isobutene-containing C4 hydrocarbon streams which contain less isobutene, for example only 10 to 20% by weight. The isobutene-containing mono-mersgemisch may contain small amounts of contaminants such as water, carboxylic acids or mineral acids, without there being any 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 polymerization catalysts used are heterogeneous or, in particular, homogeneous catalysts from the Lewis acid class. Lewis acids are electron-deficient compounds at their central atom and derive their catalytic properties from them Activity ago. In particular, these Lewis acids are compounds of elements of the 3rd main group of the Periodic Table, that is, boron, aluminum, indium, gallium and thallium. However, it is also possible to use halides, in particular chlorides, of tin, of titanium, of antimony or of iron. Such Lewis acids are often referred to as Friedel-Crafts catalysts.

Particularly preferred as polymerization catalysts are boron and aluminum compounds, in particular boron and aluminum halides, for example anhydrous aluminum chloride, boron trichloride, boron trifluoride, boron tribromide, boron triiodide and in particular boron trihalide complexes with activators such as boron trifluoride etherates, e.g. Boron trifluoride diethyl etherate, or boron trifluoride-alcohol complexes. If boron halides, in particular boron trifluoride, are used, it is advisable to use the additional activators in the complexes mentioned. A particularly preferred activator for boron trifluoride is here an alcohol, in particular a C 1 to C 4 alkanol, e.g. Methanol, ethanol, isopropanol, isobutanol or sec-butanol.

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 is used in amounts of 0.0001 to 1 wt .-%, in particular 0.0005 to 0.1 wt .-%, especially 0.001 to 0.01 wt .-%, each based on isobutene used ,

The isobutene homopolymers prepared by the process according to the invention preferably have a weight-average molecular weight M _{w of} from 100,000 to 8,000,000, in particular from 150,000 to 6,000,000, especially from 250,000 to 4,000,000.

In general, the isobutene homopolymers produced by the process according to the invention have a polydispersity (PDI = M _w / M _n ) of 1 to 20, in particular of

1 to 10, especially from 1 to 5 on.

In a preferred embodiment, the polymerization in the context of the present invention at temperatures below -60 ° C at a pressure of 10 mbar to 50 bar or preferably below -60 ° C at a pressure of 500 mbar to 5 bar or even more preferably below -60 ° C at a pressure of 800 mbar to

2 bar, in particular below -70 ° C at a pressure of 500 mbar to 5 bar or preferably below -70 ° C at a pressure of 800 mbar to 2 bar, especially at -80 to -120 ° C at one pressure from 800 mbar to 2 bar. Most advantageously and most economically, the polymerization apparatus is operated at or near the ambient pressure (normal pressure). A slight negative pressure may provide benefits for some of the possible inert solvents. Although a procedure of polymerization with overpressure in principle is possible, higher pressures generally bring no additional advantages. Of course, the optimum pressure also depends on the boiling point of the inert solvent used. The controlled low polymerization temperatures have an advantageous effect on the product properties.

The generally necessary low polymerization temperatures are preferably generated and controlled by the fact that the inert solvent acts as an internal coolant due to the boiling cooling caused by evaporation in the polymerization apparatus. Such solvents are, in particular, hydrocarbons or halogenated, in particular chlorinated or fluorinated, hydrocarbons each having 1 to 3 carbon atoms, for example methane, ethane, propane, methyl chloride, methyl fluoride, difluoromethane or ethene (ethylene). Ethene with a boiling point of -104 ° C at atmospheric pressure is particularly preferred. Although ethene contains an olefinic double bond, it is completely inert in the inventive polymerization of isobutene or isobutene-containing monomer mixtures. Furthermore, as is generally the case when working at low temperatures, it is generally advisable to use additional jacket cooling with double jacket construction with the same or a different cooling medium than in the case of the internal boiling-air cooling described above.

The weight ratio of isobutene or isobutene-containing monomer mixture to inert solvent in the polymerization apparatus is generally 1: 0.1 to 1:20, in particular 1: 0.5 to 1:10.

In a preferred embodiment, at least 50%, in particular at least 75%, especially at least 95%, of the total inert solvent to be fed into the polymerization apparatus is added before or at the beginning of the polymerization. Particularly preferred is the complete addition of the inert solvent before or at the start of polymerization in the polymerization apparatus together with the monomers to be polymerized and the polymerization catalyst. Contrary to the prejudice built up in WO 02/090391 that the presence of solvent makes a reaction slower and therefore that it can be done without solvent in the first phase, the complete or partial addition of solvent described above achieves good results from the beginning Successes.

Because of the rapid and highly exothermic polymerization of the isobutene or of the isobutene-containing monomer mixture, it is advantageous to distribute the substances supplied to the polymerization appliance to at least two separate streams, one of which contains the monomers to be polymerized and a second the preactivated or non-activated catalyst , Depending on the embodiment, it may also be advantageous be added together with the preactivated or non-activated catalyst with a portion or the total amount of the inert solvent and mix the monomers to be polymerized with or without admixture of a portion of the inert solvent in a separate stream. Furthermore, it may also be advantageous, at one or more other points of the polymerization apparatus, a portion of the inert solvent, which then preferably less than 50%, in particular less than 25%, especially less than 5% of the total amount to be fed into the polymerization of inert solvent is to meter in the already polymerized reaction.

The simultaneous mixing and conveying properties having polymerization works usually continuously. The amount of reaction material discharged by the conveying action in a certain direction at the outlet of the apparatus is replaced at the inlet or at the inlet by the corresponding amount of starting materials and solvent. Such apparatus are usually constructed substantially cylindrical or tubular, have inside mixing and conveying devices and normally have a length to diameter ratio of at least 2: 1, in particular from 2: 1 to 30: 1, especially 5: 1 to 10: 1.

In a preferred embodiment, the polymerization apparatus is a single-shaft or multi-shaft kneading reactor. Particularly preferred are single-shaft or twin-shaft kneading reactors. Also, three- and multi-shaft kneading reactors, which are structurally complex, can be used successfully. By "kneading reactors" are meant here continuously operating apparatus, usually such apparatuses are also referred to as mixing kneaders, extruders or screw machines.

In two- and multi-shaft kneading reactors, the waves can work in the same direction or in opposite directions. The waves in single and multi-shaft kneading reactors are normally filled with stirring elements. If possible, the stirring elements of the shafts should be arranged in such a way that thorough mixing, conveying action and, in addition, the best possible cleaning of the reactor interior and the other shaft (s) is ensured. This is especially necessary to ensure smooth continuous operation. The speeds of rotation of the waves are usually in the range of 20 to 150, in particular 40 to 120, especially 60 to 90 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 is preferably constant over the entire length. Preferred building material for the described kneading reactors are steels or stainless steels. For the expert it was surprising that in the kneading reactors described above, which are known in principle for polymerization reactions - for example, from WO 02/090391 and DE-A 24 36 259 -, against the background of the apparatus-structural conditions at such deep, preferably Isobutene or isobutene-containing monomer mixtures can be controlled by means of catalysts based on Lewis acids controlled by boiling heat, polymerized efficiently and economically to specification-compliant products.

The described polymerization reactor is preferably operated in such a way that its degree of liquid filling - with a preferably continuous mode of operation in the stationary state - is 30 to 90%, in particular 35 to 70%, especially 45 to 60% of the apparatus volume, i. the internal volume of the polymerization apparatus is. This ensures that a sufficiently large gas space is available for the buffering of evaporating internal coolant or, in other words, a sufficiently large surface area for the liquid / gas phase transition.

The average residence time of the polymerization mixture in the polymerization apparatus described is generally less than 100 minutes, in particular less than 60 minutes, especially 3 to 30 minutes.

In a preferred embodiment of the process according to the invention, the product is freed after successful or largely successful polymerization in a downstream apparatus with conveying properties by degassing residues of the inert solvent and / or unreacted monomers and / or other undesirable components in the product. As such a downstream equipment can be used, for example, a continuous screw machine or an extruder with one or more waves. In multi-wave machines, they can work equally or in opposite directions. The speeds of rotation of the waves are generally in the range of 50 to 500, in particular 150 to 350 revolutions per minute. These appliances are usually self-cleaning.

The ratio of length to diameter of the degassing apparatus described, which are usually constructed substantially cylindrical or tubular, is usually 10: 1 to 60: 1, in particular 20: 1 to 40: 1.

In a preferred embodiment, this downstream apparatus with conveying properties used for degassing is an extruder with at least two shafts, in particular with two shafts, and with a plurality of different temperature-controlled degassing zones. Preferably, this extruder is a self-cleaning, co-rotating twin-screw extruder. Depending on the concentration and vapor pressure of the components to be degassed, the number of degassing zones, which generally operate in stages, is determined; it is usually 1 to 8, in particular 2 to 6. Each degassing zone expediently has at least one degassing dome. In the successive degassing zones, the degassing pressure is expediently reduced in stages in the direction of product conveyance. For example, a typical pressure profile starts at 4000 mbar and ends in the vacuum range at, for example, 50 mbar.

Preferably, regardless of a reduction in the degassing pressure or in addition to a reduction in the degassing pressure, the degassing temperature in the said degassing zones is generally raised stepwise in the direction of product delivery. For example, a typical temperature profile starts at + 20 ° C, especially at + 50 ° C, and ends at, for example, + 230 ° C, especially + 200 ° C. At temperatures above + 230 ° C, a thermally induced unwanted degradation ("depolymerization") of the polymer chains can already occur.

With the described degassing, the residual concentrations of inert solvent and unreacted monomers and optionally other undesirable components in the product can be up to less than 5000 ppm by weight, in particular less than 500 ppm by weight, especially less than 100 wt. -ppm humiliate.

The weight-average molecular weight M _{w of} the product after carrying out the degassing described is generally less than 10% lower than the weight-average molecular weight M _{w of} the product at the outlet of the polymerisation apparatus.

The downstream degassing apparatus described is usually connected to the polymerization apparatus, in which a partial degassing of the product may have already taken place due to the boiling-cooling effect, usually by means of a discharge apparatus. The discharge apparatus may be a discharge screw or a discharge extruder. The discharge apparatus is usually self-cleaning as well. It can be single-wave or the same or opposite directions designed mehrwellig. A self-cleaning, co-rotating twin-screw extruder is preferred. The discharge apparatus is normally operated at the same low temperature as the polymerization apparatus, for this purpose the discharge extruder is expediently provided with a jacket jacket with double jacket construction, which is generally operated with the same coolant as the jacket cooling of the polymerization apparatus.

The arrangement of the polymerization apparatus, the discharge apparatus and the degassing apparatus is expediently chosen such that the lowest possible dead volumes occur during joint operation. A preferred arrangement of the three apparatuses provides that the polymerization apparatus is parallel to the degassing apparatus and both are connected by the horizontally extending at right angles thereto discharge apparatus, wherein the inlet of the discharge is connected to the bottom outlet of the polymerization and the outlet of the discharge is connected to the input housing of the degassing apparatus. The inlet housing of the degassing apparatus is usually located between the backward degassing zone and the degassing zones in the conveying direction.

The inert solvent released during the polymerization of the isobutene or of the isobutene-containing monomer mixtures and / or the subsequent work-up as inert gas may conveniently again be liquefied, if appropriate after a purification step, and recycled to the polymerization apparatus.

The following example is intended to illustrate the present invention without limiting it.

example

Into the inlet of a continuous two-shaft kneading reactor operating at standard pressure and a speed of 85 revolutions per minute (type ORP 80 Conti from List), the monomer to be polymerized, the catalyst components and the inert solvent were fed in by means of two separate lines. namely through the first line a mixture of 110 kg / h of ethene and 110 g / h boron trifluoride and through the second line a mixture of 16 kg / h of pure isobutene and 9 g / h of isobutanol. By evaporative cooling, a temperature of -104 ° C was established. The liquid level of the kneading reactor was about 50% of the volume of the apparatus. The crude product was obtained in the form of gritty particles floated in liquid ethene.

Due to the staggered arrangement of the two stirrer shafts in the kneading reactor, the crude product was moved to its outlet and by means of the connected jacket-cooled and operated at a speed of 65 revolutions per minute counter-rotating twin-screw discharge to run at a speed of 300 revolutions per minute degassing extruder with 6 degassing zones ( Type ZSK 70 from Coperion). At the inlet housing of the degassing extruder, the crude product had a temperature of -85 ° C. At a temperature profile of + 50 ° C to + 200 ° C and a pressure profile of 3500 mbar to 50 mbar ethene and unreacted isobutene were removed in the degassing extruder to a residual concentration of 250 ppm by weight. At the outlet of the vent extruder, 15.1 kg / hr of polyisobutene was withdrawn having a weight average molecular weight Mw of 3,000,000 (corresponding to a B value of 151 determined by solution viscosity measurement) and a polydispersity PDI of 4.5.

Claims

claims

1. A process for the preparation of isobutene homopolymers having a weight-average molecular weight M _{w of} from 75,000 to 10,000,000 by polymerization of isobutene or isobutene-containing monomer mixtures in the liquid phase in

Presence of one or more Lewis acids as polymerization catalysts and an inert solvent, characterized in that one carries out the polymerization in an apparatus which simultaneously has mixing and conveying properties.

2. The method according to claim 1, characterized in that the polymerization is carried out at temperatures below -60 ° C at a pressure of 10 mbar to 50 bar.

3. The method according to claim 1 or 2, characterized in that the inert solvent acts as an inert coolant due to the evaporation caused by evaporation in the polymerization apparatus Siedekühlung.

4. The method according to claim 3, characterized in that ethene is used as the inert solvent.

5. Process according to claims 1 to 4, characterized in that the polymerization catalyst used is at least one complex of boron trifluoride and an alcohol.

6. The method according to claims 1 to 5, characterized in that the Polymerisatonsapparatur is a single-shaft or multi-shaft kneading reactor.

7. Process according to claims 1 to 6, characterized in that at least 50% of the total amount of inert solvent to be fed into the polymerization apparatus is added before or at the start of the polymerization.

8. Process according to claims 1 to 7, characterized in that the liquid filling degree of the polymerization apparatus amounts to 30 to 90% of the apparatus volume.

9. Process according to claims 1 to 8, characterized in that the average residence time of the polymerization mixture in the polymerization apparatus is 3 to 30 minutes.

10. The method according to claims 1 to 9, characterized in that after successful or largely successful polymerization, the product freed in a downstream apparatus with conveying properties by degassing residues of the inert solvent and / or unreacted monomers and / or other unwanted in the product components becomes.

1 1. A method according to claim 10, characterized in that the downstream apparatus used for degassing with conveying properties is an extruder with at least two waves and with several different temperature-controlled degasification zones.