Method for the production of highly reactive polyisobutenes

Details Method for the production of highly reactive polyisobutenes Method for the production of highly reactive polyisobutenes

2002-03-19

2004-06-22

Lu, Caixia (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S209000, C526S210000, C526S212000, C526S348700, C585S510000, C585S525000

Reexamination Certificate

active

06753389

ABSTRACT:

The present invention relates to a process for the preparation of polyisobutene and to a binary nozzle formed for the process.
High molecular weight polyisobutenes having molecular weights of up to several 100,000 dalton have long been known. These polyisobutenes are in most cases prepared with the aid of Lewis acid catalysts, such as aluminum chloride, alkyl aluminum chlorides or boron trifluoride, and in most cases have less than 10 mol % of terminal double bonds (vinylidene groups) and a broad molecular weight distribution, characterized by a dispersity of from 2 to 5. The dispersity D is defined as the quotient formed by the weight-average molecular weight M
w
divided by the number-average molecular weight M
n
(D=M
w
/M
n
).
The highly reactive polyisobutenes which as a rule have average molar masses of from 500 to 5000 dalton and preferably contain more than 60 mol % of terminal vinylidene groups must be distinguished from these conventional polyisobutenes. In the context of the present application, terminal vinylidene groups or terminal double bonds are understood as meaning those double bonds whose position in the polyisobutene macromolecule is described by the formula
where R is a polyisobutene radical shortened by two isobutene units. The type and proportion of double bonds present in the polyisobutene can be determined with the aid of
13
C-NMR spectroscopy.
Such highly reactive polyisobutenes are used as intermediates for the preparation of additives for lubricants and fuels, as described, for example, in DE-A 27 02 604. The terminal vinylidene groups have the highest reactivity, whereas the double bonds present further toward the interior of the macromolecules have, depending on their position on the macromolecule, only little, if any, reactivity in the customary functionalization reactions. The proportion of terminal vinylidene groups in the molecule is therefore the most important quality criterion for this type of polyisobutene.
Highly reactive polyisobutenes are prepared by BF
3
-catalyzed, cationic polymerization of isobutene. The actual catalyst is a complex of boron trifluoride and at least one compound capable of forming a complex with BF
3
. This compound is as a rule selected from oxygen-containing compounds having at least one divalent oxygen atom, e.g. water, alcohols, ethers and carboxylic acids, and is referred to as a cocatalyst.
Further quality criteria for polyisobutenes are their average molecular weight and the molecular weight distribution (also referred to as dispersity) of the macromolecules contained in the polyisobutene. In general, polyisobutenes having average molecular weight (M
n
) of from 500 to 50,000 dalton are desirable. Molecular weights of from 500 to 5000, preferably from 600 to 3000, in particular from 700 to 2500, dalton are preferred for the preparation of polyisobutenes used as fuel additives, owing to their better activity.
Furthermore, a narrow molecular weight distribution of the polyisobutene molecules is desirable in order to reduce the proportion of undesired, relatively low molecular weight or high molecular weight polyisobutenes in the product produced and thus to improve its quality.
EP 0 481 297 A2 discloses a process for the preparation of polyisobutene. Isobutene and/or isobutene-containing hydrocarbons are prepared in the presence of a polymerization catalyst which consists of complex of BF
3
and of an alcohol. The complex is prepared separately from the polymerization reaction by introducing BF
3
, passing it as a gas or forcing it into the respective alcohol, if required in an inert solvent, and then feeding it to the polymerization of the isobutene. It has also been proposed to feed in additional complexing agent in a separate stream or in the solvent, in the isobutene or in the isobutene-containing hydrocarbons. However, the boron trifluoride complex catalyst is always prepared in a separate reaction and is therefore expensive. Owing to the exothermic nature of the complex formation, cooling apparatuses are additionally required.
EP 0 628 575 A1 describes a process for the preparation of highly reactive polyisobutenes. The polymerization takes place at from 0° C. to −60° C. in the presence of boron trifluoride and secondary alcohols of 3 to 20 carbon atoms. In addition to a separate preparation of the boron trifluoride complex with subsequent introduction into the reaction stream, production of the complex in situ is also proposed. For this purpose, the relevant secondary alcohol, if required together with a solvent and together with the isobutene, is fed into the polymerization apparatus and boron trifluoride is dispersed in the required amount in this mixture of the reactants, in which it reacts with the alcohol to give the boron trifluoride complex catalyst.
In the prior art process comprising in situ preparation of the boron trifluoride complex catalyst, the setting of a specific ratio of BF
3
to complexing agent (referred to below as cocatalyst) in the reaction mixture is problematic. Variations in the concentration of BF
3
or cocatalyst lead to variations in the catalyst activity and hence to variations in the molecular weight of the polyisobutenes prepared. The variations in the molecular weight and the resulting nonuniformity of the product (which is reflected in an increased dispersity value) adversely affect the product quality.
It was an object of the present invention to provide a process for the continuous preparation of polyisobutene by cationic polymerization of isobutene and/or isobutene-containing hydrocarbons in the liquid phase in the presence of a complex of BF
3
and a cocatalyst, the BF
3
/cocatalyst complex being produced in situ by adding BF
3
and cocatalyst to a reaction stream, in which more precise control of the course of the reaction in the reactor is possible.
We have found that this object is achieved, in a process of the generic type, by adding BF
3
and cocatalyst via a common binary nozzle having an outlet for BF
3
and an outlet for the cocatalyst.
Accordingly, the present invention relates to a process for the continuous preparation of polyisobutene by cationic polymerization of isobutene and/or isobutene-containing hydrocarbons in the liquid phase in the presence of a complex of BF
3
and at least one cocatalyst which is preferably selected from oxygen-containing compounds, the BF
3
/cocatalyst complex being produced in situ by adding BF
3
and cocatalyst to a reaction stream, wherein BF
3
and oxygen-containing cocatalyst are added to the reaction stream via a common binary nozzle having an outlet for BF
3
and outlet for the oxygen-containing cocatalyst.
In the novel process, the outlet orifices of the binary nozzle for boron trifluoride and cocatalyst are preferably arranged spatially directly adjacent to one another.
In contrast to the process of EP 0 628 575 A1, boron trifluoride and oxygen-containing cocatalyst are fed directly into the reaction mixture, also referred to below as reaction stream, and this is effected both separately from one another and separately from the feed of fresh isobutene or isobutene-containing hydrocarbons. If it is liquid under reaction conditions, the cocatalyst can fed in as such, otherwise it can be fed in as a liquid solution in an inert solvent.
According to the invention, the binary nozzle is preferably arranged in the polymerization reactor upstream of the inflow of the isobutene or of the isobutene-containing hydrocarbons, i.e. of the point at which isobutene or the isobutene-containing hydrocarbon mixture is introduced into the polymerization reactor. As a result of this arrangement, in each case fresh catalyst is produced at the point of the highest monomer concentration of the reactor, at and downstream of the isobutene inflow. This is particularly true if the addition of BF
3
and oxygen-containing cocatalyst is arranged adjacent to the isobutene inflow. In this arrangement, the fresh isobutene or the isobutene-containing hydrocarbons preferably flows in a flow cone generated by the BF
3
and cocatalyst infl

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