FR2749016A1 - OLEFIN (S) POLYMERIZATION PROCESS - Google Patents

Abstract

The present invention relates to a process for the polymerization of olefin (s) carried out in a reactor containing a liquid hydrocarbon polymerization medium at boiling point. According to the process, the polymerization reaction is carried out in the presence of an anti-foaming agent which can be chosen from polyoxyalkylene glycols or silicones. The process of the invention is particularly suitable for the manufacture of polybutenes or liquid polyisobutenes having a viscosity at 100 deg. C ranging from 20 to 50,000 cSt.

Description

 The present invention relates to a process for the polymerization of olefin (s) particularly suitable for the manufacture of polybutene or polyisobutene.

 It is known to polymerize a mixture of butenes in a boiling liquid hydrocarbon polymerization medium, in particular for manufacturing a liquid polybutene or polyisobutene. In general, the polymerization reaction is carried out in a reactor using a cationic type catalyst and optionally a cocatalyst. In such a process, reaction instability has very often been observed in the polymerization reactor. This instability can be characterized in particular by the manufacture of a polymer of irregular quality, for example having a distribution of molecular weights too wide, or catalytic residues or chlorine residues in too large a quantity. It can also be characterized by difficulties in controlling certain parameters of the polymerization, such as the polymerization temperature, the average residence time of the polymer in the reactor, or else the withdrawal of the polymer from the reactor.

 It has been surprisingly found, after long studies, that all of these problems are linked to the formation of a foam which occupies a large part or even the entire volume of the reactor.

 This foaming causes instability of the reaction as well as heterogeneity of the liquid hydrocarbon polymerization medium which is manifested in particular by a density gradient. These phenomena thus favor the obtaining of a poor quality polybutene or polyisobutene having in particular a width of the distribution of the molecular masses which is too wide and not compatible with certain applications. Furthermore, the operation of such a process is made difficult by disarming the pumps which convey the liquid hydrocarbon polymerization medium, in particular disarming the polymer withdrawal pump.

 A method has now been found which makes it possible to solve the problems mentioned above. In particular, the process makes it possible to manufacture, under conditions of improved reaction stability, a polybutene or polyisobutene of a stable and desired quality having in particular a narrow molecular weight distribution and a very low residual chlorine content.

 The process of the invention allows stabilization of the polymerization reaction and therefore better control of this reaction. Furthermore, taking into account that the polymerization reaction is stabilized, the liquid hydrocarbon polymerization medium is more homogeneous. Therefore, the average residence time of the polymer in the polymerization reactor can be reduced. Thus, the process of the invention can allow an increase in the polymer production capacity of the reactor.

 The present invention therefore relates to a process for the polymerization of olefin (s), for example C4, carried out in the presence of a catalytic system of the cationic type in a reactor containing a boiling liquid hydrocarbon polymerization medium, characterized in that the reaction of polymerization is carried out in the presence of an anti-foaming agent.

 The invention also relates to a process for increasing the reaction stability of a polymerization of olefin (s), for example C4, preferably carried out continuously, in a reactor containing a liquid hydrocarbon medium of boiling polymerization, in the presence of 'A cationic type catalytic system used under conditions liable to form foams in the reactor, characterized in that an anti-foaming agent is preferably introduced continuously into the reactor.

 The invention also relates to a process for narrowing the molecular weight distribution of a polyolefin obtained by polymerization of olefin (s), especially C4, preferably continuously, in a reactor containing a boiling liquid hydrocarbon polymerization medium, in presence of a cationic type catalytic system, characterized in that an anti-foaming agent is introduced into the reactor, preferably continuously.

 According to the invention, the polymerization reaction is carried out in the presence of an anti-foaming agent. Thus, any foaming phenomenon in the liquid hydrocarbon polymerization medium is avoided or stopped. In addition, it is then possible to conduct such a polymerization under stable conditions and to manufacture a polyolefin of a regular and even improved quality, in particular having a narrow distribution of molecular weights.

 Detection of any foaming can be done using pressure sensors by measuring, for example, the pressure variation between the top and bottom of the reactor and / or by absorption measurements of gamma radiation at different heights.

 The anti-foaming agent can be a known anti-foaming agent. It can be a polyoxyalkylene glycol, also called polyether, obtained by (co-) polymerization of one or more epoxides such as ethylene oxide, propylene oxide, butene oxide and having for example an average molecular weight by weight between 800 and 5000 dalton. The polyoxyalkylene glycol can be a polyoxyethylene glycol or preferably a polyoxypropylene glycol. Advantageously, a sequenced polyoxyalkylene glycol is used which comprises at least two different epoxide sequences. This block polyoxyalkylene glycol may include a pattern-based sequence.

derived from ethylene oxide and a sequence based on units derived from propylene oxide. It can in particular contain from 1 to 40% of units derived from ethylene oxide and from 60 to 99% of units derived from propylene oxide. The polyoxyalkylene glycol can be optionally fluorinated or perfluorinated. It can be a polyoxyalkylene glycol sold by
BP CHEMICALS Ltd (UK) under the brand BREOX @ or by
BASF under the brand PLURONIC Q.

 The best results are obtained when the anti-foaming agent is a silicone and more particularly a polysiloxane.

The term “silicone” generally means compounds corresponding to the general formula
R - SiO - R 'in which R and R', being identical or different, represent alkyl radicals for example from C1 to C12, especially from C1 to C6, aryl radicals for example from C6 to C10 or aralkyl radicals for example from C7 to C14.

dans laquelle R et R' sont définis comme précédemment. On préfère utilser un polysiloxane tel qu'un diphénylpolysiloxane ou un diméthylpolysiloxane. D'une manière très avantageuse, la silicone et en particulier le polysiloxane peuvent avoir une viscosité à 250C comprise entre 5 et 1 000 000 centiStokes (cSt), de préférence entre 5 000 et 7 000 000 cSt, et plus particulièrement entre 6 000 et 30 000 cSt.The term “polysiloxane” generally means polymers having a monomeric unit corresponding to the general formula

in which R and R 'are defined as above. It is preferred to use a polysiloxane such as a diphenylpolysiloxane or a dimethylpolysiloxane. Very advantageously, the silicone and in particular the polysiloxane can have a viscosity at 250C of between 5 and 1,000,000 centiStokes (cSt), preferably between 5,000 and 7,000,000 cSt, and more particularly between 6,000 and 30,000 cSt.

By way of example, it is possible to use a polysiloxane sold by General Electric Silicone (USA) in particular under the brand "VISCASIL", "SF 96", or "SF 97". We can also use a polysiloxane sold by
Wacker in particular under the brand "SRE" z or by Union
Carbide (USA) under the brand "SAG" 8.

 The concentration of defoaming agent in the liquid hydrocarbon polymerization medium can range from 0.01 to 100, preferably from 0.1 to 10 parts by weight per million (ppm).

 The anti-foaming agent can be used, as it is, or in the form of a solution in a hydrocarbon liquid at a concentration which can range from 2 to 50 by weight. This liquid can be a liquid hydrocarbon or a mixture of liquid hydrocarbons having for example from 3 to 25 carbon atoms. The hydrocarbon can be at least one reactive hydrocarbon such as one or more olefins such as butene or isobutene. The hydrocarbon can also be at least one inert hydrocarbon such as a linear, branched or cyclic alkane which can have from 3 to 12, preferably from 4 to 6 carbon atoms such as butane, pentane, hexane or cyclohexane. The liquid can be at least one light polymer, in particular an oligomer, or a mixture of light polymers for example of butene or isobutene which can originate from the polymerization reaction itself, optionally after being separated by distillation, and which may have a number average molecular weight, Mnr ranging from 100 to 300 dalton. The liquid may in particular be a liquid for supplying olefin (s) to the reactor, or the liquid hydrocarbon polymerization medium itself, especially when part of said medium is withdrawn from the reactor and reintroduced into the latter in order to ensure sufficient stirring of the reaction medium, or a liquid obtained by cooling and condensing condensable gas escaping through the upper part of the reactor and returned to the reactor.

The anti-foaming agent may preferably be introduced continuously into the reactor, in particular when the polymerization of olefin (s) is itself carried out continuously. Its introduction can be done at one or more points of the reactor. It can be done directly using a pipe which opens laterally into the reactor, or through the bottom or even through the top of the polymerization reactor. It can be done indirectly by introducing the anti-foaming agent into a supply line to the reactor, in particular into the supply line for olefins.
The anti-foaming agent can be introduced into the reactor directly into the liquid hydrocarbon polymerization medium and / or into the gas phase surmounting said liquid medium, for example by spraying.

 The anti-foaming agent can be introduced at a temperature preferably lower than that of the liquid hydrocarbon polymerization medium, in particular in order to avoid premature evaporation of the liquid used to form the solution of the anti-foaming agent. It can thus be introduced at a temperature of 2 to 300C, preferably 3 to 150C lower than that of the liquid hydrocarbon polymerization medium. It can also in certain cases be introduced at a temperature higher than that of the liquid hydrocarbon polymerization medium provided, however, that evaporation as mentioned above is avoided.

 The polymerization reaction can be carried out discontinuously or preferably continuously. The polymerization temperature is generally between - 300C and + 500C, preferably between - 200C and + 250C. The absolute pressure of the reactor is a function of the polymerization temperature and can range from 0.03 to 1, preferably from 0.05 to 0.5 MPa.

 The liquid hydrocarbon polymerization medium is boiling and in particular contains the olefin or olefins to be polymerized, the polymer being formed, the catalyst and optionally the cocatalyst and saturated hydrocarbons such as alkanes or cycloalkanes.

 An olefin (s) feed liquid containing the olefin (s) to be polymerized is preferably introduced into the reactor. The olefin to be polymerized is most often a C4 olefin, that is to say a butene, in particular isobutene. Therefore, the olefin feed liquid (s) generally consists of one or more C4 olefins, that is to say a butene or isobutene or a mixture of butenes and isobutene. The butene can be butene-1, butene-2 cis, butene-2 trans or more particularly isobutene. In practice, a mixture of butenes is used most often, in particular essentially based on isobutene. Such a mixture can comprise by weight from 1 to 40%, preferably from 3 to 30% of butene-1, from 5 to 20%, preferably from 10 to 15% of butene-2 cis, from 5 to 40%, preferably from 10 to 30% of butene-2 trans and from 15 to 60%, preferably from 20 to 50% of isobutene. Furthermore, the liquid for supplying olefin (s), in particular butenes, may also contain one or more alkanes or cycloalkanes such as butanes. Thus, for example, the olefin feed liquid (s) may contain from 60 to 95% by weight of a mixture of butenes such as those described above, and from 5 to 40 W of C 4 alkanes.

 The olefin (s) feed liquid for the reactor can advantageously be introduced directly into the polymerization medium. It can also be introduced into the liquid hydrocarbon polymerization medium by addition to any other liquid introduced into the reactor, in particular to a liquid obtained by cooling and condensing condensable gas escaping from the upper part of the reactor and returned to the reactor. Preferably, part or all of the liquid supplying olefin (s) can be introduced into the gas phase which surmounts the liquid hydrocarbon polymerization medium, laterally or through the top of the reactor, for example by spraying in the form of droplets .

 To carry out the polymerization, a catalytic system is used which is suitable for a cationic polymerization of olefins comprising a catalyst of the cationic type and optionally a cocatalyst. More particularly, the catalyst can be a halogenated boron compound such as boron trifluoride or an organoluminic compound for example of formula AlRnXn ~ 3 in which R is an alkyl radical having for example from 1 to 10 carbon atoms, X is chlorine or bromine and n a whole or fractional number ranging from 0 to 3. The cocatalyst can be hydrochloric acid, an alkyl halide such as tert-butyl chloride, water or an alcohol such as ethanol in particular when boron trifluoride is used as catalyst, in particular in the catalytic system of formula BF3, C2H5OH.

 The polymerization reaction can be carried out using an alkyl halide as cocatalyst according to the process described in European patent application EP-A-0 645 402, in particular with the catalytic system comprising ethyldichloroaluminum and tert-butyl chloride.

 The molar ratio between the cocatalyst and the catalyst is advantageously between 0.05 and 20, preferably between 1 and 10.

 The catalyst and the cocatalyst are preferably introduced into the reactor separately and in particular continuously. One of the components of the catalytic system can be introduced into the olefin (s) feed liquid. Part or all of the cocatalyst or catalyst can be introduced into the reactor in admixture with another hydrocarbon liquid, in particular with polymer, for example with part of the liquid hydrocarbon polymerization medium withdrawn from the reactor and reintroduced therein to ensure stirring of the reaction medium.

 The anti-foaming agent can be introduced into the reactor in the form of a mixture with the catalyst and / or the cocatalyst.

 The polymerization is advantageously carried out continuously. In this case, the feed liquid in olefin (s), the anti-foaming agent and the catalyst and optionally the cocatalyst are continuously introduced into the reactor. Furthermore, the liquid hydrocarbon polymerization medium containing the manufactured polymer is itself continuously withdrawn from the reactor, part of said medium being able to be returned to the reactor to maintain stirring in the reaction medium, and the defoaming agent being able to be added to this. part returned to the reactor. Likewise, at least part of a condensable gas escaping from the boiling liquid hydrocarbon polymerization medium can leave the reactor, and preferably be returned continuously to the reactor after cooling and condensation in the form of a liquid. To this liquid returned to the reactor, the anti-foaming agent and optionally the olefin supply liquid (s) can be added. The polymerization is preferably carried out with stirring, for example under mechanical stirring, or under stirring created by a force recirculation of part of the liquid hydrocarbon polymerization medium withdrawn from the reactor and reintroduced for example using a pump. . To this forced liquid recirculation, one can also add the anti-foaming agent.

 The process of the invention is particularly suitable for the manufacture of liquid polybutenes or polyisobutenes. These polybutenes or polyisobutenes can have a viscosity at 1000C ranging from 20 to 50,000 cSt, preferably from 100 to 5,000 cSt, a number-average molecular mass, Mnt of between 150 and 11,000, preferably between 500 and 5,500 dalton . They can contain between 3 and 200, preferably between 10 and 100 units derived from butene and / or isobutene. They contain approximately 1 unsaturation per mole and in particular between 0.02 and 0.95 unsaturation of vinylidene type and between 0.05 and 0.98 unsaturation of other types.

 One of the advantages of the process consists in that it makes it possible to manufacture polybutenes or polyisobutenes having a relatively narrow molecular weight distribution. For example, when the molecular weight of the polybutene or of the polyisobutene is between 500 and 5500 dalton, the width of the distribution of the molecular weights can be between 1.2 and 2.5, preferably between 1.4 and 2 and especially between 1.5 and 1.7.

Furthermore, the polybutenes or polyisobutenes obtained have a relatively low halogen content. They can for example contain less than 50 ppm of halogen such as chlorine.

 Figure 1 schematically shows an olefin polymerization device (s) comprising a reactor (1) essentially consisting of a cylindrical part (2). The reactor (1) is equipped with an olefin supply line (3) which opens into the cylindrical part (2). The olefin supply line (3) is equipped with a cocatalyst supply line (4) and a defoamer supply line (5). The reactor is also equipped with a polymer withdrawal line (6), a catalyst supply line (7) and a condensable gas outlet line (8) which can be cooled, condensed, and recycled in liquid form in the reactor.

Method for measuring the width of the molecular weight distribution of a polybutene or polyisobutene
In the present invention, the width of the molecular weight distribution of a polybutene or polyisobutene is calculated by the ratio of the weight average molecular weight, Mw, to the number average molecular weight, Mn, from a curve obtained by GPC WATERS Q equipment fitted with refractometric detection. The equipment includes a WATERS 717 Plus automatic injection system, a WATERS 610 Q pump and a set of 4 WATERS ULTRASTYRAGEL 3 columns.
o porosity 10 000, 1 000, 500 and 100 A, 25 cm long, mounted in series. The operating conditions are as follows
- solvent: tetrahydrofuran (THF)
- flow rate: 1 ml per minute
- temperature: 350C
- concentration of the analyzed sample: 4% in
weight
- injection volume: 40 p1
- calibration by polyisobutenes sold by BP CHEMICALS SNC (FRANCE) which are chosen according to the polybutene or polyisobutene to be analyzed. The number average molecular masses, Mn, of the standards used are most often between 500 and 5500 dalton.

The following examples illustrate the present invention.

Example 1
A polymerization reactor is used as shown diagrammatically in Figure 1 consisting of a cylindrical part (2).

 This reactor is supplied by line (3) by an olefin feed liquid containing, by weight, 29 W of butene-1, 8 W of butene-2 cis, 11 of butene-2 trans, 44 W d 'isobutene and 8 W of butanes. The olefin feed rate is 38 m3 / h.

 The anti-foaming agent "VISCASIL 12 M", having a viscosity at 250C of 12,500 cSt, is introduced into the pipe (5) at a flow rate of 110 g / h.

 The reaction temperature is + 100C; the total absolute pressure in the reactor is 0.15 MPa.

The catalytic system includes tert-butyl chloride as cocatalyst and ethyldichloroaluminum as catalyst in a molar ratio of 4.1: 1. The cocatalyst is introduced into the reactor through line (4) at a flow rate of 8 kg / h, and the catalyst is introduced through line (7).

 Under these conditions, after distillation, 10 t / h of a polyisobutene having a mass, Mn, of 1000 dalton, a molecular weight distribution width of 1.65 and a chlorine content of 25 ppm are obtained. Furthermore, no foaming phenomenon is observed and the polymerization takes place under stable conditions.

Example 2 (comparative)
The procedure is as in Example 1, except that no anti-foaming agent is introduced.

 Under these conditions, polymerization is carried out under unstable conditions, with in particular pump disarming problems (not shown in FIG. 1) on the draw-off line (6) of the polymer.

 After distillation, 10 t / h of a polybutene having a molecular weight distribution width of 1.85 and a chlorine content greater than 25 ppm are obtained. On the other hand, significant foaming of the liquid hydrocarbon polymerization medium is observed, which results in the presence of a foam which occupies the entire volume of the reactor, the density of which from the top to the bottom of the reactor ranges from 0.1 to 0, 5.

Claims (13)

1. Process for the polymerization of olefin (s) carried out in the presence of a catalytic system of the cationic type in a reactor containing a boiling liquid hydrocarbon polymerization medium, characterized in that the polymerization reaction is carried out in the presence of a defoaming agent. 2. Process for increasing the reaction stability of an olefin (s) polymerization carried out in a reactor containing a boiling liquid hydrocarbon polymerization medium, in the presence of a cationic catalytic system used under conditions capable of forming foams in the reactor, characterized in that an anti-foaming agent is introduced into the reactor. 3. Method according to claim 1 or 2, characterized in that the anti-foaming agent is a polyoxyalkylene glycol or a silicone. 4. Method according to any one of claims 1 to 3, characterized in that the anti-foaming agent is a silicone having a viscosity at 250C of between 5 and 1,000,000 cSt. 5. Method according to any one of claims 1 to 3, characterized in that the anti-foaming agent is a silicone having a viscosity at 250C of between 6,000 and 30,000 cSt. 6. Method according to any one of claims 1 to 5, characterized in that the concentration of defoaming agent in the liquid hydrocarbon polymerization medium is between 0.01 and 100 ppm. 7. Method according to any one of claims 1 to 6, characterized in that the anti-foaming agent is introduced continuously into the reactor. 8. Method according to any one of claims 1 to 7, characterized in that the anti-foaming agent is used in the form of a solution in a hydrocarbon liquid. 9. Method according to any one of claims 1 to 8, characterized in that the catalytic system comprises a catalyst chosen from boron compounds or organoluminic compounds having the formula AlRnXn ~ 3 in which R is an alkyl radical having from 1 with 10 carbon atoms, X is chlorine or bromine and n is a whole or fractional number ranging from 0 to 3, and optionally a cocatalyst chosen from hydrochloric acid, an alkyl halide, water or an alcohol. 10. Method according to claim 9, characterized in that the anti-foaming agent is introduced into the polymerization reactor in the form of a mixture with the catalyst and / or with the cocatalyst. 11. Method according to any one of claims 1 to 10, characterized in that the anti-foaming agent is introduced into the liquid hydrocarbon polymerization medium and / or into the gas phase surmounting said liquid medium. 12. Method according to any one of claims 1 to 11, characterized in that the olefin is a butene or isobutene or a mixture of butenes and isobutene. 13. Method according to any one of claims 1 to 12, characterized in that the method is used to manufacture liquid polybutenes or polyisobutenes having a viscosity at 1000C ranging from 20 to 50,000 cSt.