DE10361156A1 - Polymerizing olefinic monomer useful for producing polymers is carried out in a loop reactor at specific temperature and pressure, in a circulated suspension medium having specific average solids concentration - Google Patents

Abstract

Polymerization of at least one olefinic monomer is carried out in a loop reactor at 20 - 150[deg]C, but below the melting point of the polymer to be formed, and a pressure of 5 - 100 bar. The polymer formed is in a suspension in liquid or supercritical suspension medium, which is circulated by axial pump. Polymerization of at least one olefinic monomer is carried out in a loop reactor at 20 - 150[deg]C, but below the melting point of the polymer to be formed, and a pressure of 5 - 100 bar. The polymer formed is in a suspension in liquid or supercritical suspension medium, which is circulated by axial pump. The polymerization is carried out at an average solids concentrations of more than 53 wt.% of total mass of the contents, in the case of continuous product discharge, and at an average solids concentration of more than 45 wt.% in the case discontinuous product discharge, and at ethylene concentration of at least 10 mol%, of the suspension medium.

Description

object The present invention is a process for polymerization of at least one olefinic monomer in a loop reactor at temperatures of 20 to 150 ° C, but below the melting temperature of the polymer to be formed, and a pressure of 5 to 100 bar, wherein the polymer formed in a suspension in a liquid or supercritical Suspending agent is present and this suspension by means of an impeller pump led in a circle becomes.

suspension For the polymerization of olefins have long been known. Especially for the polymerization of ethylene, usually together with other comonomers, a suspension polymerization process has proven particularly useful in in which the polymerization is carried out in a loop reactor. In such loop reactors, the polymerization mixture becomes continuous pumped through a cyclic reactor tube. By pumping is on the one hand, a permanent one Mixing of the reaction mixture achieved while the dosed Catalyst and the monomers fed in the reaction mixture distributed. On the other hand, the pumping prevents sedimentation of the suspended polymer. The removal of the heat of reaction over the Reactor wall is favored by pumping The discharge of the polymer from the loop reactor is generally discontinuous in so-called settling legs. These settling legs are to branches perpendicular to the lower part of the reactor tube branches, in which the polymer particles can sediment. After the sedimentation of the polymer has reached a certain level, is short-lived a valve at the lower end of the settling legs open and the settled polymer discharged discontinuously.

There Loop reactors used for many years for production purposes have been numerous efforts the economic viability of these Rectors and the they carried out polymerization to increase. Particularly desirable is an increase in the space-time yield of Process. The space-time yield is particularly due to the removal the heat of reaction over the reactor wall and limited by the polymer content of the reaction suspension. By an increase the solids content in the reactor is in particular the discharge of the Polymers more effective and the average residence time of the polymers in Reactor higher.

In US-B1-6,239,235 describes a polymerization process in a loop reactor described in which by a continuous discharge system an increase the average solids content in the reactor is reached. With this continuous discharge system was an average Solids content in the reactor of 53 wt .-% achieved, whereas with the usual discontinuous discharge only an average solids concentration of 45 wt .-% was achieved. According to the conventional teaching if the document gives no indication of a varying reactor diameter, on the contrary should by gentle bows a trouble-free flow be achieved. Only in the area of the impeller pump seems apparently for reasons the impeller design a short extension of the reaction tube diameter to be present. Also the method described in this document leaves aside the solids concentration in the reactor still to be desired. Also confirms that Document the prevailing prejudice that it is generally not possible in suspension polymerization processes, polymer solids concentrations of more than 37 to 40 percent by weight.

task The present invention was therefore a method of polymerization of olefinic monomers in a loop reactor, which higher Solid concentrations in the reactor and higher space-time yields possible.

Accordingly, became found the method described above, which is characterized that the polymerization for the case of a continuous product discharge at an average solids concentration in the reactor of more than 53 wt .-%, based on the total mass of Reactor content, and for the case of a discontinuous product discharge at an average Solids concentration in the reactor of more than 45 wt .-%, based on the total mass of the reactor contents.

Furthermore, a process described above was found, which is characterized in that the polymerization in the case of a continuous product discharge at an average solids concentration in the reactor of more than 53 wt .-%, based on the total mass of the reactor contents, and in the case of a discontinuous Product discharge at an average solids concentration in the reactor of more than 45 wt .-%, based on the total mass of the reactor contents, and that the loop reactor comprises a cyclic reactor tube whose diameter varies by at least 10%, based on the prevailing reactor tube diameter, and wherein at least one Extension and constriction located in a different area than the impeller pump. It is also advantageous if, in addition, there is also an expansion and constriction of the reactor tube in the area of the impeller pump.

The inventive method is suitable for the polymerization of various olefinic monomers, in particular for the polymerization of ethylene, propylene and 1-butene as well as mixtures of these monomers. It can also be additional Monomers can be used as comonomers, e.g. further α-olefins such as 1-pentene, 1-hexene, 1-octene or 1-decene.

Especially preferred is a method which is characterized that as the monomer ethylene and as comonomer at least one α-olefin with 3 to 8 carbon atoms is used, preferably 1-butene, 1-witches or 1-octets. The amount of comonomer depends on the installation behavior of the respective catalyst with respect to the comonomer and of the desired Density of the copolymer from. The more comonomer incorporated into the polymer the lower the density of the copolymer becomes. After these considerations can The relationship from monomer to comonomer can be easily adjusted by the skilled person.

Provided the catalyst allows it also vinylaromatic comonomers such as styrene or polar comonomers such as vinyl acetate, vinyl alcohols, acrylic acid or acrylic acid esters be polymerized. Also cyclic monomers such as norbornene and Dienes such as butadiene, 1,5-hexadiene or 1,7-octadiene come as comonomers into consideration.

The inventive polymerization can be advantageously carried out at temperatures between 20 and 150 ° C, preferably at temperatures between 50 and 110 ° C, wherein the reaction temperature upwards through the melting temperature of the limited to forming polymers.

Of the Reaction pressure usually moves between 5 and 100 bar, preferably between 10 and 80 bar. Low pressures are generally associated with lower space-time yields, while higher pressures a higher one Capital expenditure and higher Energy costs for require the compression. In general, a reaction pressure Between 20 and 50 bar a good compromise between equipment expenditure and reaction yield. When using supercritical suspending agents like supercritical Propane can also be a higher Pressure above the critical pressure to be technically meaningful.

A preferred embodiment the method according to the invention is that the polymerization at a pressure of 43 to 80 bar, more preferably at a pressure of 45-75 bar he follows. Usually For example, polymerizations are loop-transferred at pressures 40 bar. An increase in pressure has a small effect. In the method according to the invention with high solids concentrations in the reactor has surprisingly an increase in pressure especially on pressures above 43 bar, a significant influence on the solids concentration, by the pressure increase can be further increased. This effect seems in it justified to be that at high solids concentrations, the proportion of Suspending agent on the reactor contents is so small that the process the solution of ethylene lens in the suspending agent has a marked influence on the Polymerization rate wins. A high ethylene pressure then leads to a higher one Concentration of dissolved Ethylene.

suitable Suspending agent for the inventive method are all means that are widely used in loop reactors are known. The suspending agent should be inert and under reaction conditions liquid or supercritical and should be one of the monomers and comonomers used have significantly different boiling point to a distillative To allow recovery of these feedstocks from the product discharge. Usual suspending agents are, for example, isobutane, butane, propane, isopentane, pentane and Hexane.

One important feature of the method according to the invention is that it allows polymerization at high ethylene concentrations. High solids content in the reactor, in this context also simple referred to as "reactor density" It goes without saying that the proportion of the suspending agent in the reactor accordingly is smaller. Due to the lower volume of the suspending agent In general, the amount of ethylene in the reactor is lower, which leads to a lower polymer formation. The inventive method allows however, an increase the ethylene concentration in the suspending agent and thus a higher polymer formation and a higher one Polymerization rate even at high reactor densities.

In a preferred embodiment, the inventive method is therefore characterized in that the polymerization at an ethylene concentration of at least 10 mol%, based on the Suspension agent, is made.

So were prepared by the method according to the invention Ethylene concentrations of 15 and even 17 mol%, based on the Suspensions, achieved.

there here is not the suspending agent used under the suspending agent like isobutane alone, but the mixture of this suspension medium used with the ones dissolved in it To understand monomers. The ethylene concentration can easily pass through Gas chromatographic examination of the suspending agent determined become.

As mentioned in the beginning the technology of loop reactors has been known for a long time. In general, these reactors essentially consist of one cyclic reactor tube with one or more ascending and one or more descending flanks of the cooling jackets for Removal of the heat of reaction are enclosed, and horizontal pipe parts which the vertical Connect flanks. In the lower part of the pipe are usually the impeller pump, the catalyst and monomer feed devices and as well the discharge, so usually the settling legs attached. The reactor may also have more than two vertical pipe parts, so that one serpentine Arrangement arises.

By The present invention makes possible a suspension polymerization process in a loop reactor at solids concentrations of more be carried out as 53 wt .-%, based on the total mass of the reactor contents, and thus the production capacity of the loop reactor to increase. These high solids concentrations can be achieved by various means be achieved.

In an embodiment The present invention is the high solids concentration achieved in that the cyclic reactor tube in its diameter by more than 10%, based on the prevailing reactor tube diameter, varied. A construction-related extension of the reactor tube In the area of the impeller pump should be disregarded, as a Such extension mainly the leadership of the impeller in the reaction tube serves and prevails in this area anyway a highly turbulent flow. The invention was based, inter alia, on the observation that that, contrary to the prevailing opinion, a specifically non-uniform flow of Polymerization mixture in the region of the reaction tube also outside the impeller area an increase allows the solids concentration in the reactor. This effect seems without being limited to this hypothesis to be on a more effective mixing of the heterogeneous Reaction mixture to be based. In particular, the monomer fed in, e.g. Ethylene, apparently spreads faster in the reaction mixture, dissolves faster in the suspending agent and is to a greater extent to the polymerization to disposal. Also, the removal of the heat of reaction seems to be relieved because of the disruption of the flow Movement across the flow direction, So in the direction of the cooled Reactor wall out, reinforced what happens with a uniform plug flow only very limited the case.

Around the flow conditions in this desired To be able to influence ways should the variation of the reaction tube diameter a certain Have measure. The diameter of the tube should be at least 10%, based on the predominantly prevailing diameter of the reactor tube, vary. Under the predominantly prevailing diameter of the reactor tube should In this case, the pipe diameter to be understood, over the longest Span of the reactor tube is constant. Preferably, the pipe diameter should at least 20%, better still at least 30% and especially preferably vary by at least 50%.

The conical expansion of the reactor diameter in the flow direction should have a cone angle of about 0.5-10 °, preferably 0.5-1.5 °, the cone angle at the narrowing of the pipe diameter for predominantly prevailing pipe diameter should be about 0.5-10 °, preferably 1-3 °.

The Length of Sections with extended pipe diameter is preferably at 2 to 30 times the predominantly prevailing pipe diameter, particularly preferred at 5 to 15 times this pipe diameter.

In a preferred embodiment the method according to the invention is in addition also an extension and constriction of the reaction tube in the area of Impeller pump. As already mentioned Such design-related extensions are already known. The effect of these extensions in the sense of the invention but can be reinforced Become stronger by expanding accomplished will and possibly also a longer one Pipe section concerns, as it required by the construction is.

The Effect of the present invention on the possibility of increasing the solids concentration in the reactor seems to be u.a. on a better mixing of the monomer to be based in the reaction mixture. It has been shown that this inventive effect can be exacerbated can, by the monomer, so for example ethylene, at several Spaces is fed into the reaction tube. An advantageous embodiment the method according to the invention is therefore that at least one olefinic monomer at least 2 points of the reactor tube is fed. As advantageous For example, a feed has 3 or 4 places along it the reactor tube proved. These feed points can be evenly along the reactor tube are mounted, it being advantageous if the feed points are mounted in front of the pipe extensions but not in the area of the last vertical flank before Produktaustragsbereich.

Out US-B1-6,239,235 is known that also a continuous discharge system may be suitable to increase the solids concentration in the reactor. These measure let yourself combine with the inventive method. Accordingly, the subject the present invention also a method described in the introduction, which is characterized in that the discharge of the formed Polymer from the reactor is carried out continuously.

The according to the invention high solids concentration in the reactor, as already explained by the above-mentioned measures be achieved. Particularly preferred is a method which characterized in that the polymerization at an average Solids concentration in the reactor of more than 53 wt .-%, based on the total mass of the reactor contents. Preferably lies this solids concentration over 55 wt .-%, more preferably above 58 wt .-% and particularly preferably above 60 wt .-%, wherein, as in The examples also show solid concentrations of more can be achieved as 62 wt .-%. As the average solids concentration while the solids concentration be understood in the reaction tube. In the discharge system, whether continuous or dis continuously even higher due to sedimentation Solid concentrations are observed.

The high solids concentrations can according to the invention also without continuous discharge of the polymer product can be achieved. A Variant of the method according to the invention is therefore that the discharge of the polymer formed from the reactor is discontinuous and that the polymerization at an average solids concentration in the reactor of more as 45 wt .-%, based on the total mass of the reactor contents, takes place. Preferably, the solids concentration is under these conditions in the reactor over 50 wt .-%, more preferably over 55% by weight.

The inventive method let yourself operate as a one-step process, but it can also be combined with further polymerization as a multi-stage cascade process carry out. An embodiment of the method according to the invention therefore exists in a process for the polymerization of at least one olefinic Monomer in a loop reactor, characterized in that this polymerization process before or after the polymerization in this loop reactor at least one further polymerization step in a loop reactor or a gas phase reactor. Such Cascade method, but without the specific features of Present invention, for example, in EP-A-517 868 and US-A-6,355,741.

Next the disorder described above the suspension flow in the reaction tube, a high reactor density can also by others activities be achieved, for example by selecting a particularly suitable Catalyst.

To the Use in the method according to the invention In principle, all catalysts that are otherwise suitable in loop reactors are suitable be used, so for example, chromium catalysts Phillips type, Ziegler catalysts, Ziegler-Natta catalysts or single-site catalysts such as metallocene catalysts. The Phillips catalysts are particularly popular in loop reactors experienced, which is particularly advantageous in the method according to the invention can be used. Among these catalysts are especially those preferred as described in patent applications WO-01/18069, WO-01/17675, WO-01/17676 and WO-01/90204. Surprisingly, it has become demonstrated that it is possible with these catalysts, very high solids concentrations reach in the reactor, even without the reactor tube of the loop reactor having a varying tube diameter.

The process according to the invention has numerous advantages over processes with a lower solids concentration in the reactor: the consumption of suspending agent is lower, the catalyst productivity is greater, the reactor throughput greater, the space-time yield greater, without significant additional Inves would be necessary. Since the process also makes products of particularly high molecular weight (ie, low melt flow rates) available, a higher activation temperature can be used to produce medium molecular weight products when using Phillips catalysts. The activation at higher activation temperature, in turn, usually leads to more active catalysts, so that the resulting polymers have a lower proportion of catalyst residues.

Also from the process of the invention resulting products have some advantages. In contrast to conventionally produced products they show less catalyst residues (ash), higher Bulk density, lower fines and thus better handling. Of the lower catalyst residue content usually also requires more homogeneous products with fewer product spots.

The explain the following examples the method according to the invention:

Examples

Preparation of catalyst A:

The preparation of the catalyst until activation took place according to the instructions given in WO 01/90204. Activation then took place at 520 ° C with air in a fluidized bed activator. The fluoride doping was carried out by using a mixture of the catalyst precursor with 2.5 wt .-% ammonium hexafluorosilicate (resulted in about 1 wt .-% fluoride content, based on the total mass of the catalyst) in the activation. For activation, this mixture was heated to 350 ° C within 1 hour, kept at this temperature for 1 hour, then heated to the desired activation temperature of 520 ° C, held for 2 hours at this temperature and then cooled, after cooling to 350 ° C. the further cooling was carried out under N ₂ .

polymerization:

In a loop reactor with a reactor volume of 0.18 m ³ , using the catalyst described above, ethylene was copolymerized with 1-hexene at a pressure of 39 bar and a temperature of 104 ° C. Ethylene was metered into the reactor at two points, one just before the impeller. The suspending agent was isobutane. The isobutane was metered into the reactor at 6 points, inter alia in the area of the impeller pump shaft and the catalyst metering. The impeller pump was operated at 1700-1900 rpm. The product discharge he followed discontinuously on conventional settling legs. Polymerizations were performed at slightly varied ethylene / isobutane ratios but the resulting product always had a density of about 0.949 g / cc and a high load melt index (21.6 / 190) of about 2.0. Further parameters of the polymerization are listed in the following Table A:

Table A: Polymerizations with chromium catalyst A

Preparation of catalyst B:

The Production was carried out that of the catalyst A, but was carried out the activation for 10 hours at 600 ° C without fluoride doping.

polymerization:

In a loop reactor with a reactor volume of 32 m ³ , using the catalyst B, ethylene was polymerized with 1-hexene at a temperature of 102 ° C. and further under the conditions given in Table B. Isobutene addition and circulation were as in Example A. The conditions were chosen to give a polymer having a density of 0.946 g / cm ³ and a High Load Melt Index (21.6 / 190) of about 6.0. From the experiments at different pressures it becomes clear that an increase in pressure has a significant influence on the solids concentration in the reactor.

Table B: Polymerizations with the chromium catalyst B

Preparation of catalyst C:

Of the Catalyst was prepared as described in EP-B1-589350, Example 2, but at an activation temperature of 520 ° C and an activation time of 5 hours.

polymerization:

In a loop reactor with a reactor volume of 32 m ³ , using the catalyst C, ethylene was polymerized with 1-hexene at a temperature of 106 ° C. in the presence of 0.13-0.14 ppm carbon monoxide and further under the conditions given in Table C. , Isobutanzugabe and circulation were carried out as described in Example A. The conditions were chosen so that a polymer having a density of 0.954 g / cm ³ and a high load melt index (21.6 / 190) is formed of about 2.0.

Table C: Polymerizations with the chromium catalyst C

Polymerization in the presence of catalyst D:

In a loop reactor with a reactor volume of 32 m ³ was using the catalyst D (catalyst 967 BWFL from Grace) ethylene with 1-hexene at a temperature of 106.7 ° C and further polymerized under the conditions given in Table C. Isobutanzugabe and circulation were carried out as in Example A. The conditions were chosen so that a polymer having a density of 0.954 g / cm ³ and a high load melt index (21.6 / 190) is formed of about 2.0.

Table D: Polymerizations with the chromium catalyst D

Polymerization in the presence of catalyst E:

In a loop reactor with a reactor volume of 32 m ³ was using the catalyst E (Ziegler catalyst Sylopol 5951 Grace) ethylene polymerized with 1-hexene at a temperature of 95 ° C and further under the conditions given in Table C. Isobutanzugabe and circulation were carried out as in Example A. The conditions were chosen so that a polymer having a density of 0.951 g / cm ³ and a Melt Index (2.16 / 190) is produced of approximately 6.0.

Table E: Polymerizations with the Ziegler catalyst E

Claims (9)

A process for the polymerization of at least one olefinic monomer in a loop reactor at temperatures of 20 to 150 ° C, but below the melting temperature of the polymer to be formed, and a pressure of 5 to 100 bar, wherein the polymer formed in a suspension in a liquid or supercritical Suspending agent is present and this suspension is circulated by means of an impeller pump, characterized in that the polymerization in the case of a continuous product discharge at an average solids concentration in the reactor of more than 53 wt .-%, based on the total mass of the reactor contents, and for the Case of a discontinuous product discharge at an average solids concentration in the reactor of more than 45 wt .-%, based on the total mass of the reactor contents, takes place. Method according to claim 1, characterized in that that the loop reactor comprises a cyclic reactor tube whose Diameter at least 10%, based on the predominant prevailing Reactor tube diameter varies, and wherein at least one Extension and narrowing in a different area than the impeller pump located. Method according to claim 1 or 2, characterized that in addition also an extension and narrowing of the reactor tube in the area the impeller pump is located. Method according to one of the preceding claims, characterized characterized in that the polymerization at a pressure of 43 to 80 bar. Method according to one of the preceding claims, characterized characterized in that the monomer is ethylene and as comonomer at least an α-olefin with 3 to 8 carbon atoms is used. Method according to one of the preceding claims, characterized in that at least one olefinic monomer is attached to at least 2 points of the reactor tube is fed. Method according to one of the preceding claims, characterized characterized in that the discharge of the polymer formed from the Reactor continuously. Method according to one of the preceding claims, characterized characterized in that the polymerization at an ethylene concentration of at least 10 mol%, based on the suspending agent becomes. Process for the polymerization of at least one olefinic monomer in a loop reactor according to one of the preceding Claims, characterized in that this polymerization process is before or after the polymerization in this loop reactor at least a further polymerization step in a loop reactor or a gas phase reactor.