Preparation of halogen-free, reactive polyisobutene

Details Preparation of halogen-free, reactive polyisobutene Preparation of halogen-free, reactive polyisobutene

2001-01-31

2002-05-07

Teskin, Fred (Department: 1713)

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C526S088000, C526S096000, C526S101000, C526S103000, C526S104000, C526S107000, C526S113000, C526S172000, C526S290000, C526S348700, C585S526000, C585S530000, C585S531000

Reexamination Certificate

active

06384154

ABSTRACT:

The present invention relates to an improved process for preparing halogen-free, reactive polyisobutene having a terminal double bond content of more than 60 mol % and an average molecular weight M
n
of 800-3000 dalton by cationic polymerization in the liquid phase of isobutene over an acidic, essentially halogen-free heterogeneous catalyst, the increased terminal double bond content being obtained by partial conversion.
The polymerization of isobutene yields an inseparable mixture of polyisobutenes, in which the position of the double bond varies between the individual polyisobutenes. Polyisobutenes of formula I
where n is the degree of polymerization which in turn is derived from the average molecular weight M
n
of the polyisobutene prepared, contain terminal C—C double bonds of the vinylidene type which are herein also referred to as &agr;-olefinic double bonds owing to their position in the polyisobutene molecule. Accordingly, the double bonds in polyisobutenes of the formula II
are referred to as &bgr;-olefinic. If the polymerization of isobutene is carried out without taking special measures, a random mixture is formed which comprises polyisobutenes having &agr;-olefinic, i.e. terminal, double bonds, &bgr;-olefinic double bonds and double bonds located further toward the interior of the polyisobutene molecule. Both the terminal double bond content and the &bgr;-olefinic double bond content of a polyisobutene product prepared by a particular process are both reported in mol %.
The preparation of polyisobutenes is described, for example, in H. Güterbock, Polyisobutylene und Mischpolymerisate, p. 77-104, Springer-Verlag, Berlin, 1959. They are usually prepared by Lewis-acid-catalyzed isobutene polymerization employing aluminum chloride, alkylaluminum chloride or boron trifluoride as Lewis acids. However, the resulting polymers have a relatively low vinylidene-type terminal C—C double bond content of less than 10 mol %.
In contrast, reactive polyisobutene (PIB) having molecular weights of usually 500-5000 dalton has a high terminal vinylidene group content of, preferably, more than 50 mol %. These reactive polyisobutenes are used as intermediates in the preparation of additives for lubricants and fuels as described, for example, in DE-A 27 02 604. These additives are prepared by initially reacting polyisobutene with maleic anhydride. The preferred reactive sites for this reaction are terminal double bonds of the vinylidene type, whereas double bonds located further toward the interior of the macromolecule react to a lesser extent, if at all, depending on their position in the molecule. The polyisobutene/maleic anhydride adducts formed are then reacted with certain amines to give the corresponding additives. It is therefore absolutely necessary for polyisobutenes used as starting materials for the abovementioned additives to have a high terminal double bond content. The same applies to the preparation of the polyisobuteneamines of EP-A 244 616 which are also used as fuel additives and which are prepared by hydroformylation of the reactive polyisobutene and subsequent reductive amination of the resulting polyisobutene aldehyde. For this process, preference is likewise given to using polyisobutene having a high terminal double bond content, but &bgr;-olefinc polyisobutenes also give the desired product when the hydroformylation is carried out using cobalt catalysts, owing to their double bond isomerization activity.
Most prior art methods for the preparation of reactive polyisobutene involve the homogeneously catalytic polymerization of isobutene. According to DE-A 27 02 604, for example, a polyisobutene product having a terminal double bond content of up to 88% is obtained by reacting isobutene in the presence of boron trifluoride. EP-A 145 235 teaches the polymerization of isobutene in the presence of a complex of boron trifluoride and a primary alcohol at from −100° C. to +50° C. to give products having similarly high vinylidene double bond contents. According to U.S. Pat. No. 5,286,823, highly reactive polyisobutene can also be prepared using complexes of boron trifluoride and secondary alcohols as catalyst.
The disadvantages of this homogeneously catalyzed process are that the Lewis acid catalysts used are corrosive and that there is a risk that, in addition to the desired reactive polyisobutene, halogenated polymeric byproducts are formed which are virtually inseparable from PIB and adversely affect the product and further processing characteristics of the PIB. In these processes, the homogeneous catalyst is usually separated off by quenching with a nucleophile to destroy the catalyst and subsequently removing the PIB from the quenching mixture by extraction. These additional work-up steps are a further disadvantage of the homogeneously catalyzed process.
Furthermore, WO 94/28036 discloses the preparation of polyisobutene using heterogeneous Lewis acid-like catalysts. Catalysts used are salts of elements of transition groups III, IV, V and VI of the Periodic Table of the Elements which are insoluble in the reaction medium, preferably halides, sulfates, perchlorates, trifluoromethanesulfonates, nitrates and fluorosulfonates thereof. The polymerization is terminated by adding methanolic ammonia solution to the reaction medium to destroy or at least substantially inactivate the catalysts in question.
The preparation of PIB using heterogeneous, non-salt like catalysts is also known. For example, U.S. Pat. No. 4,288,649 describes a process for producing polyisobutene having an average molecular weight >1250 dalton by polymerizing C
4
-hydrocarbon mixtures comprising isobutene over halided alumina catalysts. The catalysts are prepared by treating the alumina with a haliding agent, preferably with a chloriding agent, in particular with carbon tetrachloride, at an elevated temperature. A disadvantage of this process is that some of the chlorine is transferred from the catalyst to the polymer which forms. For example, the polymerization of a mixture of n-butane, isobutane and isobutene over a chlorided alumina catalyst prepared in this manner gives, after a reaction time of 2 hours, a polyisobutene product having a chlorine content of 46 ppm.
U.S. Pat. No. 5,326,920 discloses a process for polymerizing isobutene employing as heterogeneous catalyst an oxidic support material, preferably silica, which has been activated with a metal chloride attached thereto, preferably with an aluminum chloride. Particular preference is given therein to an SiO
2
-AlCl
2
catalyst in which AlCl
2
groups are anchored on the SiO
2
support via oxygen linkages. The disadvantages of this process are that the polyisobutene products obtained have an extremely broad molecular weight distribution D of from 8 to 14, a low terminal double bond content and a chlorine content in the ppm range. Furthermore, this process requires the presence of promoters such as water, alcohols, alkyl halides or hydrogen chloride to achieve a catalyst activity which is sufficient for industrial operation. Similar catalyst systems for the polymerization of isobutene are described in WO 95/26815, WO 95/26816, WO 95/26814 and WO 96/26818.
JP-A 139 429/1981 utilizes heterogeneous zirconium dioxide and molybdenum oxide catalysts to prepare isobutene oligomers having a molecular weight of less than 300 dalton. These catalysts can be mixed with aluminum fluoride to increase their activity. According to this publication, for example, the reaction of an isobutene-comprising C
4
cut (composition: 46% of isobutene, 28% of 1-butene, 8% of 2-butenes, 12% of n-butane, 5% of isobutane, 1% of 1,3-butadiene) over an MoO
3
—ZrO
2
catalyst having a molybdenum content, calculated as MoO
3
, of 13% by weight at 120° C. yields an isobutene oligomer mixture comprising 29% of diisobutene, 49% of triisobutene and 19% of tetraisobutene.
EP-A 825 205 describes, inter alia, the continuous polymerization of pure isobutene over heterogeneous catalysts (heteropolyacids), but without giving any details about a specific reaction procedure

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