MXPA97008837A - Preparation of polyburgen of molecular weight, highly react - Google Patents

Abstract

The present invention relates to a process for the preparation of highly reactive low molecular weight polyisobutene, having an average molecular weight Mn of from 500 to 20,000 Dalton and containing more than 80 &mgr of terminal double bonds, by polymerization of isobutene or a stream of hydrocarbons containing isobutene in the liquid phase and with the aid of a boron trifluoride complex catalyst at a temperature of -40 to 0 ° C and at a pressure of from 1 to 20 bar, the process consists of in carrying out the polymerization reaction in at least two polymerization steps, the isobutene being added polymerized to a partial conversion of up to 98 & amp; in the first polymerization step, and the polymerization of the remaining isobutene is continued in one or more subsequent polymerization steps, without or after the previous isolation of the polyisobutene formed in the first subsequent polymerization stage, without or after the previous isolation of the polyisobutene formed in the first polymerization step, and carrying out the polymerization in the second polymerization stage at a polymerization temperature which is lower than that of the first stage of polymerization.

Description

PREPARATION OF MOLECULAR WEIGHT POLYISOBUTENUM, HIGHLY REACTIVE The present invention relates to a process for the preparation of low molecular weight polyisobutene, highly reactive, with an average molecular weight M "from 500 to 20,000 Dalton and containing more than 80 mol% of terminal double bonds, by polymerization of Isobutene or a stream of hydrocarbons containing isobutene, in liquid phase and with the aid of a boron trifluoride complex catalyst from 0 to -40 ° C and from 1 to 20 bar. Low molecular weight and high molecular weight polyisobutenes having molecular weights of up to some 100,000 Daltons have been known for a long time and their preparation is described, for example, in H. Güterbock: Polyisotubylen und Mischopolymerisate, pages 77-104, Springer , Berlin, 1959. The currently available polyisobutenes in this molecular weight range are usually prepared with the aid of Lewis acid catalysts such as aluminum chloride, aluminum alkyl chlorides or boron trifluoride and usually have less than 10 mol% of terminal double bonds (vinylidene groups) and a molecular weight distribution (dispersity) of 2 to 7. A difference must be made between these conventional polyisobutenes and the highly reactive polyisobutenes, which, as a rule, have molecular weights average from 500 to 5,000 Dalton and preferably contain substantially more than 60 mol% of vinylidene group. These 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. For the preparation of these additives, polyisobutene / maleic anhydride addition products, in particular polyisobutenyl succinic anhydrides, are produced by first reacting the terminal double bonds of the polyisobutene with maleic anhydride and then the addition products are reacted with certain amines to produce the finished additive. Since the formation of the addition products with maleic anhydride are mainly the vinylidene double bonds that react, depending on their position in the macromolecule, the double bonds present in addition to the interior of the macromolecules cause a conversion, if any, substantially low without the addition of halogens, the amount of terminal double bonds in the molecule is the most important quality criterion for this type of polyisobutene. The formation of the vinylidene double bonds and the isomerization of the terminal double bonds in the macromolecules of isobutene in the internal double bonds are, according to Puskas et al., J. Polymer Sci .: Symposium No. 56 81976), 191, based on the concepts shown in the following scheme: CH2 - displacement of gru 1, 3-methyl CH2 Three isomers with double bonds Three isomers with double bonds R = polyisobutene radical The polyisobutene cation I formed during the course of the polymerization reaction can be converted into the relevant polyisobutene as a result of the removal of a proton. The proton can be removed from one of the beta-methyl groups or the internal gamma-methylene group. Depending on which of these two positions the proton is removed, a polyisobutene having a vinylidene II double bond or having a tris substituted III double bond present near the end of the molecule is formed. The polyisobutene cation I is relatively unstable and attempts to achieve stability by rearrangement to form more highly substituted cations. It is possible to carry out the displacement of the 1,3-methyl group to give the cation polyisobutene IV and the successive or agreed group 1,2-hydride and the displacement of the 2,3-methyl group to give the cation polyisobutene V. Depending on the the position from which the proton is removed, in each case, 3 different isomers of polyisobutene with double bonds can be formed from cations IV and V. However, it is also possible that the IV and V cations have another rearrangement causing the double bond to migrate further into the polyisobutene macromolecule. All these deprotonations and rearrangements are equilibrium reactions and therefore reversible, but it is preferred, at the end of the formation of the most stable cations, more highly substituted and therefore the formation of the polyisobutenes with an internal double bond, the establishment of the equilibrium thermal. These deprotonations, protonations and rearrangements are catalyzed by any trace of acid present in the reaction mixture, but in particular by the real Lewis acid catalyst necessary to catalyze the polymerization. Due to these facts and since only the polyisobutenes with vinylidene double bonds according to formula II react very well with the maleic anhydride with formation of addition products, but the polyisobutenes of formula III have substantially lower reactivity in comparison and other Polyisobutenes with more highly substituted double bonds are almost non-reactive with maleic anhydride, the continuous efforts of many groups of researchers to understand improved processes for the preparation of highly reactive polyisobutenes with a higher and higher content of terminal double bonds are understandable. The preparation of low molecular weight polyisobutene, highly reactive, from isobutene hydrocarbon streams or isobutene-containing streams, in particular cuts or fractions of d, substantially free of a 1,3-butadiene originally present in them, from fractionators of steam, FCC fractionators (FCC: catalyzed fluid fractionation), ie refined C4 products, is known from a number of patents, for example, from EP-A-145 235, EP-A 481/297. DE-A-27 02 604, EP-A 628 575, EP-A-322 241 and WO 93/10063. All these processes refer to the polymerization of isobutene in a single polymerization stage. A disadvantage of these processes is that the fluorine-containing by-products are formed due to the use of the BFj complex catalyst. The fluorine content of the polyisobutenes prepared by these processes can be up to 200 ppm. When these polyisobutenes containing fluorine are subjected to thermal stresses, the result is the elimination of hydrogen fluoride, which is highly corrosive. This problem is particularly serious when cuts of C4 containing isobutene are used as starting materials, since, due to the content of n-butenes, this results in the formation of relatively stable secondary polyisobutene fluorides which, in other derivations of polyisobutene to give fuel additives and lubricating oil additives or during the subsequent use of these combustible additives in the engine, they can then be removed with formation of hydrogen fluoride and in this way cause corrosion damage. Another disadvantage of the one-step polymerization process in the use of C cuts is associated with the n-butenes contained in these hydrocarbon streams. As a result of its incorporation into the growing polymer chain, the polymerization can be terminated and the selectivity decreased with respect to the formation of highly reactive polyisobutene, ie, polyisobutene with a high content of vinylidene double bonds. In order to avoid these disadvantages, according to the process known up to now, the polymerization must be terminated at a still relatively high residual isobutene content of the C4 cut used in the polymerization. However, this leads to a large loss of initial material making the preparation of GDP from cuts of C4 through these conventional processes, not economic. An object of the present invention is to provide a process for the preparation of low molecular weight polyisobutene (PIB), highly reactive, whose fluorine content is substantially lower than the fluoride content of polyisobutene which is prepared by the known processes. The process should also allow, in particular, the preparation of PIB with a low content of fluorine and a high content of terminal double bonds from hydrocarbon stream of C * and must be economical. In addition, the PIB thus prepared must have a narrow molecular weight distribution D.

We have found that this objective is achieved by a process for the preparation of low molecular weight polyisobutene, highly reactive, with an average molecular weight M (l from 500 to 20,000 Dalton and containing more than 80 mol% of terminal double bonds, by the polymerization of isobutene or a stream of hydrocarbons containing isobutene in the liquid phase and with the aid of a boron trifluoride complex catalyst from -40 to 0 ° C and from 1 to 20 bar, which consists in carrying out the reaction of polymerization in at least two polymerization stages, the isobutene added being polymerized until a partial conversion of 95% in the first polymerization stage and the polymerization of the remaining isobutene is continued in one or more subsequent polymerization steps, without or after the pre-isolation of the polyisobutene formed in the first polymerization step.

The novel process is based on the knowledge obtained by the inventors in relation to the investigations in the formation of organic by-products containing fluorine in the preparation of PIB by means of complex BFI catalysts and that they interpreted according to the following scheme and used as a working hypothesis for the present invention. In this scheme, the BFj-alcohol complex used is representative of another complex BF catalyst. < .

I saw her VI II VII VIII R: organic radical The starting point in this scheme is the polyisobutyl cation which is formed during the course of the polymerization of isobutene and whose opposite ion is the anion [BF3OR] "A fluorine anion can be transferred from this anion to the polyisobutyl cation with the formation of polyisobutyl fluoride VI and BFOR In the presence of protons in the polymerization mixture, this polyisobutyl fluoride is in equilibrium with polyisobutene II and hydrogen fluoride The hydrogen fluoride formed can undergo an addition reaction with monomeric isobutene VII which is also present in the polymerization mixture and which, in the presence of protons, is in equilibrium with terbutyl fluoride ( VIII) thus formed By extracting or neutralizing the BFj complex catalyst or the polymerization mixture, it is possible to prevent this equilibrium from being established.When using isobutene-containing C4 cuts which also contain linear butenes, the sequence of the The reaction shown in the scheme is further complicated by virtue of the fact that the incorporation of 1-butene into the chain Increasing polyisobutene results in the formation of secondary cardenium ions in the polymer, which, in the case of the transfer of fluoride from the anion, can react to form secondary polyisobutyl fluorides, from which the fluoride only with difficulty under the polymerization conditions. The establishment of the equilibrium as shown in the scheme as well as the displacement of this depends on the reaction conditions used, in particular on the proportions of polymer and monomers present in the polymerization mixture, on the type of BFi complex catalyst and on the BFj / complexing agent ratio, and in addition to the established polymerization temperature. In view of these results, an object of the present invention is to design the reaction process for the polymerization of isobutene in such a way that the formation of organic by-products containing fluoride, in particular of polyisobutyl fluorides, is reduced to a minimum without affecting adversely the formation of low molecular weight polyisobutene with a high content of vinylidene double bonds. We have found that this objective is achieved by the measurement to carry out the polymerization of isobutene in at least two stages of polymerization, carrying out the second stage of polymerization or other subsequent polymerization steps at a temperature which as a general rule is lower to that of the first stage of polymerization. The novel process and some advantageous modalities of this process are illustrated below. In its simplest form, the novel process is operated in two stages of polymerization. Various methods can be adopted to obtain polyisobutene with high content of terminal double bonds and a low content of fluorine. For example, it is possible to establish an isobutene conversion from 5 to 98%, preferably from 50 to 95%, in particular from 50 to 90% in the first polymerization stage and to complete the polymerization in the second stage. The second polymerization stage is conveniently carried out at a lower polymerization temperature than the first polymerization stage, as a general rule, the temperature difference being from 1 to 20 ° C, preferably from 2 to 10 ° C. Since the polymerization of isobutene is exothermic, the polymerization temperature in the first polymerization stage is controlled, at a predetermined cooling temperature and as a function of the reactivity of the catalyst being used, by the addition of fresh isobutene at a rate such that the polymerization temperature remains essentially constant, independent of technically unavoidable fluctuations. The conversion of isobutene in the first stage of polymerization is controlled by establishing the reactivity of the catalyst complex through the dosage of the complexing agent, taking into account the aforementioned parameters, that is, the cooling temperature, the polymerization temperature and a time of average stay of the reaction mixture in the reactor.

The discharge of the first polymerization stage preferably is passed without further treatment to the second polymerization stage. In this, the polymerization is carried out without the addition of fresh isobutene, at a polymerization temperature lower than the first polymerization stage. This can be done by means of a lower cooling temperature or the use of a refrigerant at the same temperature as the first polymerization step, for example, using the cooling apparatus used, controlling the cooling in such a way that the amount of heat removed from the polymerization mixture is greater than the amount of heat that is released during the polymerization of the remaining isobutene. Under certain circumstances, it may be necessary or advantageous to replenish the deactivated catalyst during the use of the polymerization reaction by the addition of boron trifluoride or to increase the catalytic activity of the BFj complex catalyst by adding boron trifluoride, so that the polymerization does not stop prematurely This addition of boron trifluoride can be carried out before or after the introduction of the polymerization mixture in the second polymerization stage.

To obtain a conversion of isobutene from 50 to 90%, the residence time of the polymerization mixture in the first stage of polymerization is usually from 5 to 60 minutes, but it can be shorter or longer depending on the catalyst that is used. use if you are very active or less active. In the second stage of polymerization, a residence time is usually established from 1 to 180, preferably from 5 to 120 minutes. In the second polymerization step, the conversion of isobutene is generally established so that the total conversion of the isobutene in the first and second polymerization steps is generally from 80 to 100%, preferably from 90 to 100%, in particular from 95 to 100%. The discharge of the second polymerization stage can be treated in a conventional manner, for example by deactivating the catalyst by the addition of more complexing agent, for example water, alcohols, amines or nitriles, the extraction of deactivated catalyst from the polyisobutene and the isolation of GDP from the phase containing PIB eliminated the volatile components, such as solvents, volatile, low molecular weight, volatile isobutene oligomers and distillation byproducts. The PIB obtained by this process has a very high content of terminal double bonds and a very low fluorine content.

If the discharge of the second polymerization stage still contains relatively large amounts of unconverted isobutene, this isobutene can be separated from the polymerization discharge by distillation and then advantageously recycled to the first stage of polymerization if pure isobutene is used as starting material in the polymerization.

Otherwise, the unconverted isobutene can be fed, together with the polymerization discharge of the second polymerization stage, without further treatment, to a third polymerization stage and polymerized completely at a polymerization temperature which is lower than the second polymerization stage. In general, the polymerization temperature established in this third stage of polymerization is 1 to 20 ° C, preferably 2 to 10 ° C, lower than the polymerization temperature in the second polymerization stage above. The polymerization temperature can be established using the measures described in the above to set the polymerization temperature in the second polymerization stage. The residence time of the polymerization mixture that is established in the third stage of polymerization depends on the activity of the catalyst and the desired conversion and is generally from 5 to 180, preferably from 10 to 120 minutes. As mentioned in the explanation for carrying out the second polymerization step, it may be necessary or desirable to replenish the spent catalyst by the addition of boron trifluoride or increase the activity of the catalyst by adding boron trifluoride.

Although the use of second and third polymerization stages is also advantageous when pure isobutene is used in the polymerization, this proves to be particularly advantageous when currents of C4 hydrocarbons containing isobutene, such as refined C products or C4 cuts of the dehydrogenation of Isobutene, are used as starting materials in the novel process, since, as a result of hydrocarbon streams, the losses of isobutene are avoided, there is no increase in the level of undesirable hydrocarbons due to the recycling of unconverted isobutene containing other hydrocarbons in the first stage of polymerization and consequently a high quality PIB, almost without fluorine with a high content of terminal double bonds is obtained. The polymerization discharge of the third polymerization stage can be treated in the same manner as described for the treatment of the discharge of the second polymerization stage. The residual amounts of isobutene that are still present in the polymerization discharge after the second or, where relevant, after the third stage of polymerization and which is less than 2%, preferably up to 1%, of the isobutene originally present in the feed to the first polymerization stage, if an almost complete conversion of isobutene is desired, they can be completely polymerized in a resting vessel which is downstream of the second or third stage of polymerization and in this case performs the function of a third or fourth stage of polymerization. The standing vessel can be operated at the same polymerization temperature as the previous polymerization step, but in general, a higher temperature is established therein. In this way, the temperature of the polymerization mixture in the standing vessel can be from -40 to + 40 ° C, but the temperature in this is preferably increased to 0-40 ° C, preferably [SIC] 0- 30 ° C. The residence time of the polymerization mixture in the standing vessel can be from 0.1 to 3, preferably from 0.3 to 2 hours, this residence time is of course controlled according to the polymerization temperature in the resting vessel In general, no more recent catalyst is added to the polymerization discharge of the previous polymerization stage, which discharge also enters the rest tank without further treatment, except for the term polyisobutene of isobutene, the passage of the polymerization discharge to through the standing vessel results in further reduction in the fluorine content of the formed polyisobutene It is presumed that the hydrogen fluoride is removed in the standing vessel from the polyisobutyl fluoride still present in the polymerization discharge of the step of previous polymerization, with the establishment of a balance and with the formation of polyisobutene, and some fluoride Hydrogen oxide is trapped by the isobutene still present in the polymerization mixture with formation of readily volatile isobutyl or tert-butyl fluoride. Unless these readily volatile fluorides have been degraded during the treatment of the polymerization discharge leaving the standing vessel, which can be effected as described above, these can be easily removed from the PIB by absorption during other treatment by distillation and can be destroyed. Although the use of a resting vessel gives advantageous results, this is an optional measure of the novel process given that the efficiency in the cost of using this resting vessel depends essentially, of course, on factors such as the level of conversion of isobutene in the preceding polymerization steps and the fluorine content of the polyisobutene thus obtained. Figure 1 serves to further illustrate the novel process in which an embodiment of the novel process with 4 stages of polymerization for a single tubular reactor is shown., is schematically shown by way of example for the purpose of illustration. The isobutene or hydrocarbon stream containing isobutene, if necessary diluted with an inert solvent, is passed through feed 1 in reactor 2, with thermostat, by means of a cooling bath (not shown), the The reactor 2 is in the form of a tubular reactor circle in which the polymerization mixture is kept circulating by means of the pump 3. A high pumping capacity is advantageous for removing the heat from the reactor and ensures the mixing of the mixture. polymerization and consequently a constant concentration of isobutene in the steady state. The polymerization catalyst can be mixed with the feed before entering the polymerization reactor 2 or can be dosed at almost any point of the reactor 2 through feeds that are not shown. It is possible to introduce boron trifluoride complex catalyst that has been formed beforehand, ie, outside the polymerization reactor and to dose the complexing agent used and the boron trifluoride separately in the reactor, and to produce the in situ polymerization catalyst. in the reactor 2. In the latter case it must be ensured that there is not a high temporary concentration of boron trifluoride since this could have an adverse effect on the content of the terminal double bonds. In the case of the in situ production of the catalyst, it is advisable initially to take the complexing agent and dose the boron trifluoride only after the introduction of the complexing agent. After the desired steady-state equilibrium is established in reactor 2, the polymerization discharge of reactor 2 is withdrawn through line 4 and fed to the second polymerization stage, reactor 5, which is advantageously designed as a tubular reactor cycle in the same way as reactor 2, in which the polymerization mixture is circulated by means of pump 6. Reactor 5 is cooled by means of a cooling bath that is not shown. To increase the catalyst activity it is possible to subsequently measure more boron trifluoride through the intake ports in the feed line 4, or preferably, in the reactor cycle 5, whose inputs are not shown. After the desired steady-state polymerization equilibrium is established in reactor 5, the polymerization mixture of this reactor 5 is discharged through line 7 and fed to tubular reactor 8 which is present in a cooling bath ( not shown), it can also be designed as a tube bundle reactor and preferably operated as a continuous reactor. The residence time in this reactor can be established, for example, by adjusting the length of the reactor tube as a function of its diameter. If required, additional boron trifluoride can subsequently be metered through the intake orifices in the feed 7 or preferably into the reactor 8, whose inlets are not shown. The discharge of the reactor 8 is fed by line 9 to the resting vessel 10, which as a rule is not cooled and can be designed, for example, as a tank having an overflow or, in the same way, as a tubular reactor . If necessary, after the previous rest, the discharge of the reservoir is fed by line 11 to the treatment stage, which is carried out in a conventional manner, preferably by washing with a complexing agent by means of which deactivates the catalyst and the polymerization is terminated, particularly preferably by washing with water, the subsequent phase separation and the purification of the resulting PIB by distillation to remove the volatile components. The above statements are applied in a manner corresponding to the use of reactors with tubular bundles that are preferred when the process is carried out on an industrial scale. Of course, the novel process as shown in the figure, can be modified in various ways, for example, carrying out the polymerization only in two or three stages of polymerization. For example, the polymerization can be completed in the first two stages of the polymerization, corresponding to reactors 2 and 5 of Figure 1. It is also possible to carry out the polymerization in polymerization step 1 (reactor 2) at a conversion of relatively high isobutene and carry out the polymerization without the use of a reactor corresponding to reactor 5 of figure 1, in a reactor corresponding to reactor 8 in figure 1 and, if desired, additionally in a resting vessel. This embodiment also corresponds essentially to the novel process modality in which reactors 2 and 5 of FIG. 1 are practically combined in a single polymerization step, carrying out the reaction in a polymerization reactor corresponding to reactor 2 of FIG. 1 under almost identical polymerization conditions only for a conversion of isobutene, for example, from 4 to 10% and the discharge of this first reactor being fed, without further treatment, to the second reactor, corresponding to reactor 5 of figure 1 , wherein the polymerization is then continued to a higher conversion before the discharge of this second reactor is fed to a third reactor constituting the second polymerization stage, for example, a reactor corresponding to reactor 8 of Figure 1, in where the polymerization is complete or is very substantially complete. The option in relation to which of these modalities or what other possible modalities of the novel process are more advantageous in a specific case is made taking into account the initial material containing isobutene that is to be converted into the apparatus, the type of trifluoride catalyst of boron used, the quality of the desired PIB and the available cooling devices, etc., and it is routine work for a person skilled in the art to design the apparatus. If desired, the reaction of the isobutene can also be carried out until a partial conversion in which a high content of terminal double bonds in the polyisobutene is still ensured, after which the polymerization can be terminated by adding relatively large amounts of a complexing agent, for example water, the discharge containing the highly reactive PIB can be treated as described above and the mixture of hydrocarbons containing isobutene not converted and separated during the treatment can be further processed in a conventional manner to give the Low molecular weight polyisobutene with a lower content of terminal double bonds. The novel process is carried out using, as catalysts, complexes of boron trifluoride with complexing agents that include in the polymerization activity of boron trifluoride so that, on the one hand, the polymerization gives a low molecular weight polyisobutene and, on the other hand, the isomerization activity of boron trifluoride is reduced with respect to the isomerization of the terminal double bonds for the non-reactive or only slightly reactive double bonds within the polyisobutene molecule. Examples of suitable complexing agents are water, d-Cιo alcohols, C¿-CIÜ diols, C_-C2Ü carboxylic acids, C4-C carboxylic anhydrides? and dialkyl (of C, -C, 0) ethers. The complexing agents of the class consisting of Ci-C / alcohols, in particular C?-C 4 alcohols and of the class consisting of dialkyl (of C ?Cü) ethers are preferably used in the novel process, among which dialkyl ethers, in which oxygen from the ether is attached to the tertiary carbon atom of a tertiary alkyl group, are preferred, in particular the ethers described in WO 93/10063. Among alcohols, monohydric secondary alcohols [sic] C3-C20 alcohols, as described in EP-A 628 575 have, as complexing agents, a particularly advantageous effect on the polymerization activity and isomerization activity of the boron trifluoride catalyst, isopropanol and 2-butanol being particularly notable. The boron trifluoride complex catalysts in which the molar ratio of boron trifluoro to the complexing agent is less than 1, in particular from 0.4 to 0.95, particularly preferably from 0.5 to 0.8, are preferably used in the novel process. As mentioned above, the boron trifluoride complex catalysts can be preformed, as described, for example, in EP-A 145 235, before being used or they can be produced in situ in the polymerization reactor, as described in EP-A 628 575. Gaseous boron trifluoride is advantageously used as a raw material for the preparation of boron trifluoride complex catalysts and technical grade boron trifluoride which still contains small amounts of sulfur dioxide (purity: 96.5% by weight), but preferably highly pure boron trifluoride (purity: 99.5% by weight) can be used. Silicon tetrafluoride-free boron trifluoride is particularly preferably used for the preparation of the catalyst. The polymerization of isobutene can be carried out in the presence or absence of solvents which are inert under the reaction conditions, such as saturated hydrocarbons, for example, pentane, hexane or isooctane or halogenated hydrocarbons such as methylene chloride or chloroform. When C4 cutting is used as starting materials, the hydrocarbons present in the cut of C4 in addition to isobutene act almost as solvents. On an industrial scale, the polymerization to obtain PIB preferably takes place continuously. Conventional reactors, such as tubular reactors, reactors with tubular bundles or stirred kettles can be used for this purpose, the novel process preferably being carried out, in the first two stages of polymerization, using cyclic reactors, i.e. tubular reactors or of tubular bundles with continuous circulation of the reaction material, the ratio of the feed to circulation being, as a general rule, from 1: 1 to 1: 1000, preferably from 1:50 to 1: 200 v / v. Of course, the feed rate is equal to the speed of polymerization discharge after steady-state equilibrium has been established in the polymerization reactor. In order to avoid high local and steady state concentrations of the catalyst in the polymerization apparatus, which can lead to displacements of the double bonds, it is advantageous, during the introduction of the preformed catalyst complexes into the reactor and into the preparation itself. of the boron trifluoride complexes in the reactor, generate turbulent flow of the reaction material in the reactor for the perfect mixing of all the reagents, for which purpose the reactor can be provided, for example, with suitable screens such as plates of screens or cross sections of the tube can be dimensioned so that an adequate flow velocity is established. The residence time of the isobutene to be polymerized in the individual polymerization steps can be from 5 seconds to several hours, depending on the relevant polymerization stage, the residence time chosen being in the individual polymerization steps, preferably from 1 to 180, particularly preferably from 5 to 120 minutes, depending on the desired conversion of isobutene in these steps. As stated in the above, the time of stay in the resting vessel can be up to several hours. The reaction rate depends on the amount, especially the molar ratio of the catalyst that is used. As usual, the boron trifluoride / secondary alcohol and / or dialkyl ether catalyst is added in amounts from 0.05 to 1% by weight, based on the isobutene that is used or on the isobutene present in the hydrocarbon mixture. The polymerization is advantageously carried out below 0 ° C. Although isobutene can be successfully polymerized to highly reactive polyisobutene even at substantially lower temperatures, the reaction is generally carried out from 0 to 0 ° C, in particular from -4 to -30 ° C, particularly preferably -10 to -25 ° C. On the other hand, continuously higher temperatures can be used in the standing vessel, for example up to 40 ° C. The polymerization can be carried out at atmospheric pressure, the use of pressure above atmospheric up to 20 bar, as well as the autogenous pressure of the reaction system is advantageous, but as a general rule it is not important in relation to the result of the polymerization. The polymerization reaction is conveniently carried out under isothermal conditions and establishing a constant concentration of the monomer at the steady state in the reaction medium, in particular for a conversion of isobutene up to about 90%. The polymerization of the residual amounts of isobutene contained in the polymerization mixtures can be carried out with a decreasing concentration of isobutene. The concentration of isobutene in the steady state can, in principle, be chosen freely, as a general rule a monomer concentration from 0.1 to 50, preferably from 0.2 to 10% by weight, based on the total polymerization mixture, is established as advantageous. Since the polymerization reaction is exothermic, the heat of polymerization is usually removed with the aid of a cooling apparatus, which can be operated, for example, with liquid ammonia as a refrigerant. Another possibility to remove the polymerization heat is the evaporative cooling on the product side of the reactor. In this case, the heat that is released is eliminated by evaporation of isobutene and / or other easily volatile components of the isobutene feed or any easily volatile solvent, such as ethane, propane or butane, with the consequence that the temperature remains constant . Cooling can be done by internal or external cooling, depending on the type of reactor used. The tubular reactors are preferably cooled by means of external cooling, the reaction tubes being advantageously present in a cooling bath, and the kettle reactors with stirring and thermostat by external cooling, for example by means of cooling coils or by evaporative cooling , on the side of the product. For the treatment, the reaction discharge is advantageously passed to a medium which deactivates the polymerization catalyst and thus terminates the polymerization. For example, water, alcohols, acetonitrile, ammonia or aqueous solutions of mineral bases such as alkali metal and alkaline earth metal hydroxide solutions, carbonate solutions of these metals, etc., can be used for this purpose. In another course of the treatment, the polyisobutene is distilled off into C4 hydrocarbons, solvents, oligomers and polyisobutene, advantageously after a plurality of extractions to remove residual amounts of catalyst, usually by washing with methanol or water. In the case of washing with water, the hydrogen fluoride formed in the course of the polymerization is also removed in addition to the catalyst. If pure isobutene is used as starting material, it can be recycled to the polymerization, such as isobutene oligomers and solvents. When using C-cuts containing isobutene, unconverted isobutene and the other C4 hydrocarbons are usually not recycled and used for other purposes. The easily volatile by-products containing fluorine, such as terbutyl fluoride, can be removed from the polyisobutene together with the other hydrocarbons and can be separated from these hydrocarbons by distillation or extraction. The novel process ends the economic preparation of highly reactive polyisobutenes from pure isobutene and, in a particularly convenient form, from hydrocarbon streams containing isobutene. Very high terminal double bond contents of more than 8% mol in GDP are achieved and very good selectivities and very high conversions. The polyisobutenes thus prepared have average molecular weights M "from 500 to 20,000, preferably from 500 to 5,000 Daltons and a narrow molecular weight distribution D. Examples The average molecular weights (M ") of the polymers prepared according to the examples were determined by gel permeation chromatography (CPG) using the standardized polyisobutenes for calibration. The average molecular weight number M "was calculated from the resulting cro atograms according to the equation M " where Ci is the concentration of the individual polymeric species i in the resulting polymer mixture and Mi is the molecular weight of the individual polymeric species i. The molecular weight distribution, mentioned below as dispersity D, was calculated from the ratio of the weight average of the molecular weight (M to the average number of the molecular weight (M ") using the equation The average weight of molecular weight M "was determined from the resulting chromatograms with the help of the formula For the purpose of the present application, vinylidene double bonds or terminal double bonds are understood as those double bonds whose position in the polyisobutene macromolecule are described by the general formula wherein R is the relevant polyisobutylene radical. The type and amount of double bonds present in the polyisobutene prepared according to the invention was determined with the aid of the 13 C NMR spectroscopy method, in which the two carbon atoms labeled a and β Ha and associated with the terminal double bond are identifiable in the 1 * C NMR spectrum, by its signals in the chemical shift of 114.4 and 143.6 ppm, respectively, and the ratio of the terminal double bonds in relation to another type of double bonds is calculated by determining the peak areas of the signals in relation to the total integral of the olefin signals. For the NMR spectroscopy, deuterated chloroform was used as solvent and tetramethylsilane as internal standard. The fluorine content organically bound in the polymerization solution, as well as in the polyisobutene, was determined by the conventional methods of elemental analysis: for this purpose, the organic material was digested by combustion by the Wickbold or Schoniger method, the fluorine released it was absorbed in water and the fluorine content of the resulting aqueous fluorine solution was determined in potentiometric form with the aid of commercially available fluoride ion selective electrodes, using a calibration curve. The content of organically bound fluoride in the sample can be easily calculated from the fluoride content of the solution measured in this form and from the amount of sample used for combustion (literature: F. Ehrenberger: Quantitative Elementaranalyse; VCH Verlagsgesellschaft, Weinheim, page 436 et seq., Page 424 et seq., Page 617 et seq.). In addition to the pure isobutene, the cuts of C4 having the composition according to table 1 were used for the following examples.

Table 1 Cutting of C4 Dehydrogenase contains isobutane vapor (refined product I) Isobutane [% by 50.3 4.1 weight] n-butane [% by 0.5 9.3 weight] trans-but-2-ene [% 0.6 7.9 by weight] but-1 -eno [% by 0.1 28.8 weight] isobutene [% by 48.0 45.2 weight] cis-but-2-ene [% 0.3 4.5 by weight] butadiene [ppm] less than 50 87 Example 1 The reactor (= reactor 2 in the figure) consisted of a Teflon tube that had a length of 7.6 m and an internal diameter of 4 mm and through which 50 1 of the contents of the reactor was circulated by means of a mechanical pump. The tube and pump had a capacity of 100 ml. The Teflon tube and the pump head were in a cold bath at minus 19 ° C (cryostat). The refined product I (composition: Table 1) was used as feed, at a rate of 300 g / h. This product was dried on a 3 A molecular sieve to a water content of less than 3 ppm and fed to the reactor with circulation through a capillary having an internal diameter of 2 mm and pre-cooled to -19 ° C. The amounts of BFj and isopropanol were varied until a molecular weight M "of 1000 was obtained with an isobutene conversion of 80% PIB. The amount of BF¿ was 10 mol and that of isopropanol was 15 mol. The temperature of the reactor was -13 ° C. The conversion of isobutene was determined by gas chromatographic analysis of the outgoing gas. The feeds, the volumes of the reactor and the volumetric shrinkage due to the polymerization gave an average residence time of about 13 minutes. The polymerization was terminated with 15 ml / h of acetonitrile, immediately after the pressure regulating means in the discharge tube or in the sampling port. The pressure conditions of the reactor were determined by its geometry, the amount circulated, the viscosity of the reaction mixture and the regulation of the pressure. The pressure regulating medium directly at the reactor outlet on the pressure side of the pump was set at 7 bar and, under the prevailing concentration conditions, about 4 bar was measured at the suction side of the pump . The pressure loss of the system was thus 3 bar. After completion of the polymerization by acetonitrile, the reactor discharge was fed with 600 ml / h of hot water (60 ° C) in a one liter flask with stirring and the residual liquefied gas was evaporated. This liquefied gas contained 14.1% isobutene in addition to butanes and n-butenes. This was condensed in a dry ice condenser, and frozen water was azeotropically introduced onto the condenser surface. The level of the separating layer in the flask with stirring was maintained by means of a siphon and this phase mixed by means of a lateral overflow with a siphon. They were necessary about 2 hours before establishing the equilibrium in the steady state, after which a mixed sample was collected over a period of one hour, treated as described and taken in equal amounts of hexane, in addition water was separated . The fluorine content, organically bound, in the solution was 114 ppm. After removing the hexane by distillation, the residual volatile components such as water and oligomers were separated by distillation at 1 mbar absolute, the temperature was increased to 230 ° C. The polyisobutene remaining in the lower part of the rotary evaporator was then determined. The amount of terminal double bonds was 90 mol%. The viscosity, measured in an Ubbelohde viscometer was 198 mm2 / s, the average molecular weight M "was 1005 Dalton and the molecular weight distribution D was 1.5. The fluorine content was 65 ppm. The condensed salient gas was dried on a 3 A molecular sieve and then transferred to a pressure resistant vessel, heated to 50 ° C and passed through a riser tube with autogenous pressure in the reactor as described in FIG. the foregoing, wherein it was reacted with 2 mmol of BFj and 1 mmol of isopropanol at an isobutene concentration of the polymerization mixture of 0.6% by weight. After the treatment, a conventional polyisobutene with 28 mol% terminal double bonds and a viscosity (100 ° C) of 219 mm2 / s, an average molecular weight M "of 980 Dalton and a dispersity D of 1.8 was obtained. More information to carry out this example is provided in Table 2.

Example 2 A polymerization apparatus was used which consisted of 2 circulation reactors (* - reactors 2 and 5 in the figure), as described in Example 1. In contrast to this description, in this experiment the Teflon tubes were of 4.5 m long in the first reactor and 2.7 m long in the second reactor. The feeds of 150 g / h each of hexane and isobutene were dried in the manner described and fed to the reactor system separately, by capillaries with an internal diameter of 2 mm. The amounts of BFj and isopropane fed were varied to obtain polyisobutene with an average molecular weight M "of 1040 Dalton formed at a reactor temperature of -70 ° C and a 50% isobutene conversion. 15 mmol of BF3 and 27 mmol of isopropanol were necessary. The reactor discharge was passed, without further additions or treatment, to the second reactor, which was operated at a reactor temperature of -14 ° C. In this, isobutene was polymerized until the total conversion of 79% was reached. The discharge from this reactor was then treated as in Example 1 for the termination of the polymerization and for the treatment. The polyisobutene obtained contained 95 mol% of terminal double bonds, its viscosity (100 ° C) was 203 mmVs, the average molecular weight M "was 1040 Dalton and the dispersity D was 1.5. More information about this example is contained in Table 2. Example 3 A polymerization apparatus was used which consisted of 2 circulation reactors, as described in Example 1. Contrary to the description of Example 1, in this experiment, the tube Teflon in the first reactor was 0.7 m in length and the second reactor was 6.5 m in length. The initial material used was the refined product I (composition: Table 1), The feed of the refined product I was dried in the manner described. The amounts of BF3 and isopropanol fed were varied until a polyisobutene with an average molecular weight M "of 1000 Dalton was formed at a reaction temperature of -11 ° C in the first reactor and a conversion of isobutene of 6%. The discharge of the first reactor was passed to the second reactor without treatment. In the second reactor, whose temperature was brought to -13 ° C, the polymerization was continued until the total conversion of the isobutene contained in the feed of 90%. After the termination of the polymerization reaction by the addition of acetonitrile and the extraction with water of the deactivated BF¿ catalyst, the unconverted isobutene was removed by distillation, together with the other hydrocarbons contained in the refined product I. The polyisobutene residue was collected in the same amount of hexane and distilled again for the separation of the traces of water. The obtained polyisobutene solution contained 143 ppm of fluorine organically bound after the extraction and 3 ppm after the distillation treatment. The distillation treatment was carried out in written form. The PIB obtained after this treatment had an average molecular weight M "of 960 Dalton and a dispersity of 1.3 and contained 86 mol% of terminal double bonds. More information on this example is given in Table 2. EXAMPLE 4 150 g of dry hexane and isobutane respectively were introduced, as described in Example 2, into a reactor according to Example 1. BF.sup.-and isopropanol were fed. in the manner described, in the pre-cooled hexane stream, and the feed was varied to the polyisobutene formation with an average molecular weight M "of 1015 Dalton at an isobutene conversion of 90%. The temperature of the reactor was -13 ° C and the temperature of the cooling bath -19 ° C. After completion of the polymerization, extraction and distillation, a reactor discharge sample was analyzed: the organically bound fluorine content was 98 ppm, which decreased below 1 ppm after the distillation treatment. The content of the terminal double bonds was 88 mol% and the dispersity D was 1.5. The discharge of the first reactor (reactor 2 according to the figure) was transferred, without treatment, to another reactor (^ T reactor 8 in the figure) - a Teflon tube 50 cm long with an internal diameter of 4 mm - and passed through the latter in a single step. Reactor 8 was present in the same cooling bath as reactor 2, but, due to the lower conversion of isobutene, the reactor temperature decreased to -16 ° C. In this reactor 8 the residual isobutene was almost completely converted. A sample of the discharge from this reactor was analyzed: at a total isobutene conversion of more than 99%, the average molecular weight Mn of polyisobutene obtained was 1015 Dalton, the content of terminal double bonds was 88 mol%, the dispersity of 1.5 and the content of organically bound fluorine before distillation was 93 ppm and after distillation of 1 ppm. The discharge of this reactor 8 was passed, without treatment, to a resting vessel, where it was maintained at + 20 ° C for an average residence time of 3 hours. At the discharge of the standing vessel the isobutene was almost completely converted and the polyisobutene obtained was completely identical to the polyisobutene of the previous reactor in relation to its analytical data, but the content of organically bound fluorine before distillation was only 5 ppm. Further information on this example is given in Table 2. Example 5 Reactor 2 according to Example 1 was fed with a dry C cut from the dehydrogenation of isobutane (composition: see Table 1). With 12 mmol of BFj and 18 mmol of isopropanol an 80% isobutene conversion was obtained at a reactor temperature of -13 ° C. The resulting polyisobutene had an average molecular weight M "of 1030 Dalton and a dispersity D of 1.5 and contained 92% terminal double bonds. The organically bound fluorine content was 124 ppm before distillation and 15 ppm after distillation. The discharge of the rector 2 was passed, without further treatment, directly through a tubular reactor 8 consisting of a Teflon tube with a length of 1 m and an internal diameter of 4 mm. The temperature of the reactor was -21 ° C. After the mixture was passed through this reactor 8, the conversion of isobutene was increased to 99%. According to the analytical results, the polyisobutene obtained after the treatment was completely identical to that of the sample of the reactor 2. More information on this example is given in table 2.

Table 2 Example 1 2 3 4 5 combination of 2 + 5 2 + 5 2 + 5 2 + 8 + 10 2 + 8 reactor * feed product isobutene product isobutene dehydro refined I refined genation < -4 reactor 2 5 2 5 2 5 2 8 10 2 8 length of 7.6 7.6 4.5 2.7 0.7 6.5 7.6 0.5 - 7.6 1 tube [m] volume [mi] 100 100 61 39 14 87 100 11 1200 100 17 m Power 300 300 300 300 300 300 300 300 300 300 300 total [g] o Circulation / 100 100 100 100 100 100 100 - - 100 - feeding d Time of 13.6 12.6 8.4 5.7 1.7 12.1 14.9 - 180 14.5 - average stay at [min] 1 Temperature -13 -15 -7 -14 -11 -13 -13 -16 +20 -13 -21 [• C] i Pressure 4-7 5-6 5-6 4-7 5 4-7 4-7 1 1 5-6 1 [barat3] d BF3 [mmol] 10 2 15 10 11 12 to Isopropanol 15 1 27 14 17 18 [mmol] d Ratio 0.66 2 1 0.55 C 1.71 0.65 0 .66 molar BF3 / isopropanol Conversion 80 96 50 58 6 88.5 90 90 - 80 95 of isobutene [%] m? Conversion - 99 - 79 90 99 > 99 99 Isobutene or Content of 114 68 - 84 143 98 93 124 107 Fluorine d. and. [ppm] d Content of 65 35 - < 1 3 < 1 < 1 < 1 fluorine d. d. a [ppm] 1 Double 90 28 - 95 86 88 88 88 92 92 terminal links i [% mol] d Viscosity 198 219 - 203 200 210 210 210 217 217 100 ° c [mmVs] to Mr 1005 980 - 1040 - 960 1015 1015 1015 1030 1030 d D 1.5 1.8 - 1.5 1.6 1.5 1.5 1.5 1.5 * According to the numbering in figure 1. of: after extraction dd: after of distillation

Claims (1)

1. CLAIMS A process for the preparation of low molecular weight polyisobutene, highly reactive, with an average molecular weight M "from 500 to 20,000 Dalton and containing more than 80 mol% of terminal double bonds, by polymerization of isobutene or a stream of hydrocarbons that containing isobutene in liquid phase and with the help of a boron trifluoride complex catalyst from -40 to 0 ° C and from 1 to 20 bar, the process consists of carrying out the polymerization reaction in at least two stages of polymerization , the polymerized isobutene added up to a 95% partial conversion in the first polymerization step and the polymerization of the remaining isobutene is continued in one or more subsequent polymerization steps, without or after the previous isolation of the polyisobutene formed in the first stage of polymerization. The process according to claim 1, wherein the polymerization in the second polymerization stage is carried out at a polymerization temperature which is lower than that of the first polymerization stage. The process, according to claim 1 and 2, wherein the first polymerization step isobutene is polymerized at a conversion from 5 to 98% based on the amount of isobutene fed in the first polymerization step. The process according to claim 1 to 3, wherein the first polymerization step isobutene is polymerized at a conversion from 50 to 90% based on the amount of isobutene fed in the first polymerization step. The process, according to claim 1 to 4, wherein the discharge of the first polymerization stage is passed, without further treatment to the second or subsequent polymerization stage. The process, according to claim 1 and 5, wherein boron trifluoride is subsequently dosed in the second or subsequent polymerization step. The process according to any of claims 1 to 6, wherein the polymerization mixture obtained after passing to the second or subsequent polymerization stage is treated in a standing vessel which serves as a downstream reactor, at a temperature higher than that of the above polymerization steps, to polymerize the residual amounts of isobutene still obtained [sic] in the polymerization mixture. The process according to any one of claims 1 to 7, wherein the boron trifluoride complex catalyst used consists of a complex or complexes of boron trifluoride with a C?-C2ü alcohol, a tertiary alkyl ether or water. The process according to any of claims 1 to 8, wherein the boron trifluoride complex catalyst used is a complex of boron trifluoride with isopropanol or 2-butanol.