Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Removing and recycling removed material from an ongoing...
Reexamination Certificate
2002-04-25
2003-02-11
Teskin, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Removing and recycling removed material from an ongoing...
C526S068000, C526S237000, C526S348700
Reexamination Certificate
active
06518373
ABSTRACT:
The present invention relates to a process for the continuous preparation of polyisobutenes by polymerizing isobutene in the presence of a catalyst comprising boron trifluoride and at least one cocatalyst in an inert organic solvent.
High molecular weight polyisobutenes having molecular weights up to several 100,000 Dalton have long been known. These polyisobutenes are generally prepared with the aid of Lewis acid catalysts, such as aluminum chloride, alkylaluminum chlorides or boron trifluoride and generally have not less than 10 mol % of terminal double bonds (vinylidene groups) and a molecular weight distribution (dispersity) of from 2 to 5.
The highly reactive polyisobutenes, which as a rule have average molar masses of from 500 to 5,000 Dalton and contain more than 60, preferably more than 80, 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 the polyisobutene radical shortened by two isobutene units. The type and the proportion of the 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 exhibit in the usual functionalization reactions only very little reactivity, if any at all, depending on their position in the macromolecule. The proportion of terminal vinylidene groups in the molecule is therefore the most important quality criterion for this type of polyisobutene.
Further quality criteria for polyisobutene 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 weights (M
n
) of from 500 to 50,000 Dalton are desirable. Molecular weights of from 500 to 5,000, preferably from 600 to 3,000, in particular from 700 to 2,500, Dalton are preferred for the preparation of polyisobutenes used as fuel additives, owing to their better efficiency.
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.
Various polymerization reactions of isobutene under catalysis by various boron trifluoride complexes are known.
EP 0 807 641 A2 describes a process for the preparation of highly reactive polyisobutene having an average molecular weight of more than 5,000 and up to 80,000 Dalton and containing at least 50 mol % of terminal vinylidene groups. The cationic polymerization of isobutene or isobutene-containing hydrocarbons is carried out in the liquid phase in the presence of boron trifluoride complex catalysts at below 0° C. and from 0.5 to 20 bar, in one stage at a steady-state isobutene concentration of from 20 to 80% by weight. The boron trifluoride complex catalysts can be premolded before they are used or can be produced in situ in the polymerization reactor. The boron trifluoride concentration is from 50 to 500 ppm.
EP 0 628 575 A1 describes a process for the preparation of highly reactive polyisobutene containing more than 80 mol % of terminal vinylidene groups and having an average molecular weight of from 500 to 5,000 Dalton by cationic polymerization of isobutene or isobutene-containing hydrocarbons in the liquid phase in the presence of boron trifluoride and secondary alcohols of 3 to 20 carbon atoms. In addition to the separate preparation of the boron trifluoride complex with subsequent introduction into the reaction stream, production of the complex in situ is also proposed. The process is preferably operated with establishment of a steady-state monomer concentration in the reaction medium, which as a rule is set in the range from 0.2 to 50, preferably from 0.2 to 5, % by weight, based on the total polymerization mixture.
WO 99/31151 describes a process for the preparation of highly reactive low molecular weight polyisobutene, in which some of the boron trifluoride complex catalyst is recovered by separating the reactor discharge into a product-rich phase and a catalyst-rich phase and recycling the catalyst-rich phase to the polymerization reactor. However, this procedure makes it more difficult to carry out the reaction.
However, the reaction must be carried out precisely in order to ensure the product quality, in particular the uniformity of the molecular weight (i.e. for narrow molecular weight distribution) and a high content of vinylidene double bonds.
It is an object of the present invention to provide a continuous process for the preparation of polyisobutene having the generic features of the preamble of claim 1, in which the reaction can be carried out more precisely.
We have found that this object is achieved by a process for the continuous preparation of polyisobutene by polymerizing isobutene in the presence of a catalyst comprising boron trifluoride and at least one cocatalyst in an inert organic solvent,
a) a part of the reaction mixture obtained thereby being discharged continuously from the polymerization reactor,
b) the catalyst being separated from the discharge and/or being deactivated in the discharge and,
c) the solvent and any unconverted isobutene being separated from the discharge and recycled to the polymerization reactor,
wherein the recycled solvent and, if present, the isobutene are subjected to a wash with water before the recycling to the polymerization reactor and, if required, are then dried.
The separation of the solvent and of any unconverted isobutene from the discharge is effected as a rule by distilling off the solvent, isobutene and other volatile components also distilling off. As a result of the novel washing of the solvent with water before the recycling, the residues of water-soluble cocatalysts and traces of fluorine-containing decomposition products still present are removed in a simple manner and with high efficiency.
The washing of the solvent before recycling can be carried out in one stage or a plurality of stages. In a one-stage procedure, as a rule the solvent separated from the discharge is mixed with a sufficient amount of water in a mixer and a phase separation is then carried out in a separation vessel. For the multistage wash, these operations can be repeated several times in the manner of a cascade. Preferably, the multistage wash is carried out in an extraction column.
For washing the solvent, as a rule the solvent/water ratio of from 20:1 to 1:2, in particular from 10:1 to 1:1 (v/v) is chosen. In a one-stage wash, the ratio of solvent to water is particularly preferably about 1:1 (v/v); in a multistage wash or in the extraction using an extraction column, the solvent/water ratio is preferably not less than 2:1 and preferably from 2:1 to 1:10.
The wash is carried out as a rule at from 5 to 80° C., preferably from 10 to 50° C. A wash under superatmospheric pressure is also suitable.
The wash water produced during washing of the solvent (and of any unconverted isobutene) can be removed as wastewater. Since the pollution of the wash water with residues of water-soluble cocatalyst and fluorine-containing decomposition products is comparatively low, the wash water can advantageously be reused in the novel process before it is disposed of as wastewater. The wash water is, for example, suitable for deactivating the catalyst in the reaction discharge with simultaneous extraction of the catalyst decomposition products from the reaction discharge, as described in more detail further below. This second use of the wash water leads on the o
De Vree Eddy
Deyck Frans van
Hahn Dieter
Rath Hans Peter
Sandrock Gerhard
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