JP5322891B2 - Polypropylene production method and production apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for producing polypropylene for continuously achieving safe operation especially even in a condition where a supply flow rate of a liquid propylene is lowered by uniformly spraying the liquid propylene necessary for removing heat in a polypropylene polymerization reactor, wherein polymerization heat is removed by using evaporative latent heat of the liquid propylene, and preventing blockage of a nozzle. <P>SOLUTION: In the method and the like for producing polypropylene, propylene polymerization is carried out while removing polymerization heat by using evaporative latent heat of a condensate, when a mixed gas principally comprising unreacted propylene is taken out from the polymerization reactor and is introduced into a condenser to be separated into the condensate and a noncondensable gas, and a part of the separated noncondensable gas is returned to the polymerization reactor after being merged with the condensate to be a two-phase fluid. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a polypropylene production method and production apparatus for producing a polypropylene or propylene copolymer by a gas phase polymerization process using a solid catalyst containing a transition metal component. More specifically, a polypropylene polymerization reactor that mainly removes the heat of polymerization using the latent heat of vaporization of liquid propylene, uniformly sprays liquid propylene necessary for heat removal, and prevents clogging of the nozzle. The present invention relates to a polypropylene production method and a production apparatus capable of continuously achieving stable operation even under a condition where the supply flow rate of liquid propylene becomes small.

  A method for polymerizing olefins such as ethylene and propylene using a solid catalyst containing a transition metal component is widely known. These olefin polymerization methods include a slurry polymerization method in which polymerization is performed in an inert hydrocarbon solvent, a bulk polymerization method in which polymerization is performed in a liquefied monomer such as liquefied propylene, and a gas phase in the absence of a liquid phase. There is a gas phase polymerization method in which polymerization is performed in a phase. And, in addition to the fact that the improvement of the polymerization catalyst activity has been achieved, it is advantageous from the viewpoint of energy cost and plant construction cost, and furthermore, the amount of dangerous materials to be held is relatively low and preferable from the aspect of ensuring safety, The gas phase polymerization method has been awarded.

  In the gas phase polymerization process, in the state where there is substantially no liquid such as a monomer or a solvent, the monomer gas is continuously added to the vertical or horizontal stirred tank reactor or the reactor system of the fluidized bed reactor. Alternatively, hydrogen as a molecular weight regulator is fed and a solid catalyst component, a promoter component, or the like is continuously supplied into the reactor. The product obtained by the polymerization reaction is usually obtained in the form of powder, and is sequentially extracted from the reactor and sent to the next step. In order to control the properties of the product, the polymerization reaction may be so-called multistage polymerization in which a plurality of reactors are connected in series and desired polymerization conditions are used in each reactor.

  By the way, in the polymerization of olefins containing propylene, since the polymerization temperature and the melting point of the polymer are relatively close and the amount of heat of polymerization is relatively large, uniform heat removal is performed to achieve stable operation. This is an essential requirement. When the reaction is performed in the liquid phase, such as slurry polymerization or bulk polymerization, the heat transfer from the reaction heat to the liquid phase is relatively easy, so the problem is rarely revealed. Since the environment surrounding the polymer is a gas with a small heat capacity, it tends to lead to formation of heat spots and coalescence and formation of a lump. For these reasons, process considerations for achieving uniform heat removal are essential for stable operation, particularly in gas phase polymerization.

  Such gas phase polymerization processes can be roughly classified from heat removal systems into those that mainly use sensible heat and those that use latent heat. The former is a type often used in fluidized bed reactors, which circulates the reactor system without changing the phase of a large amount of monomer gas, and removes heat by cooling the gas in a heat exchanger on the circulation line. Is to do.

  On the other hand, in the heat removal method using latent heat, the monomer gas taken out from the reactor is condensed, the condensed liquid is returned to the reactor, and the reaction heat is removed as evaporation heat of this liquid. That is, the polymerization heat is removed by latent heat, and the reaction temperature is controlled. In general, the heat removal method using latent heat has many advantages such as a compact size of the reactor and the heat exchanger, and is widely put into practical use as a commercial process.

As a polymerization reactor having such a heat removal method by latent heat, a vertical reactor having a stirrer rotating around a vertical axis and a horizontal reactor having a stirrer rotating around a horizontal axis are known. Patent Document 1 describes a method for vapor-phase multistage polymerization of an ethylene / propylene copolymer using an apparatus in which two horizontal reactors are connected.
Generally, when a raw material such as propylene is supplied and a polymerization reaction is started, the catalyst particles gradually grow into polymer particles. When polymerization is carried out in a horizontal reactor, these particles progress along the axial direction of the reactor while gradually growing due to the two forces of formation of polypropylene by polymerization and mechanical stirring. For this reason, particles having a uniform growth rate, that is, a residence time are aligned with time from the upstream side to the downstream side of the reactor. That is, in the horizontal reactor, the flow pattern is a piston flow type, and the residence time distribution is narrowed to the same extent as when several complete mixing tanks are arranged in series. This is an excellent feature not seen in other polymerization reactors, and it is easy to achieve a solid degree of mixing equivalent to two, three or more reactors in a single reactor. This is economically advantageous. Therefore, there are many opportunities to use horizontal reactors.

When performing gas phase polymerization using a reactor that has a latent heat removal method, especially under operating reaction conditions where the heat of polymerization is small, the amount of liquid propylene that is the heat removal medium is reduced due to the above principle, so that the liquid is dispersed. There was a tendency that uniform heat removal in the reaction zone could not be obtained.
In other words, when the operation is started up or when the polymerization amount in the reactor itself is small in multistage polymerization, since the absolute amount of liquid propylene fed is small, uniform dispersion becomes difficult, resulting in unevenness. Reaction environment and associated lump formation. Further, since the liquid propylene feed nozzle is in an environment in contact with the catalyst and the polymer, there is a problem that the polymerization proceeds in the vicinity of the nozzle under a condition where the flow rate of the liquid propylene is small and this is blocked.

  In patent document 2, as a method of reducing the production | generation of the lump which inhibits a stable operation in continuous operation, it is proposed to make the recycle gas of the vaporization propylene supplied to a polymerization reactor into specific temperature. However, these methods cannot solve the fundamental problem that uniform spraying is difficult under the condition that the amount of liquid propylene feed is small, and it is not possible to completely eliminate the obstacles to stable operation. It was.

JP 59-23010 JP 2009-73890 A

  The problem to be solved by the present invention is that in view of the above-mentioned problems of the prior art, the liquid propylene required for heat removal is uniformly distributed in a polypropylene polymerization reactor that mainly removes the heat of polymerization using the latent heat of vaporization of liquid propylene. And a method for producing polypropylene and a production apparatus capable of continuously achieving stable operation even under conditions in which the supply flow rate of liquid propylene is reduced, in particular, while preventing nozzle clogging. It is in. In the present invention, a copolymer of propylene and α-olefin is also referred to as a propylene polymer or simply polypropylene.

  As a result of intensive studies on the above problems, the present inventor has taken out a multicomponent gas mainly composed of unreacted propylene from the polymerization reactor, introduced it into the condenser, and sometimes referred to as a condensate (mixed liquid). And non-condensable gas (sometimes referred to as mixed gas), and a part of the separated non-condensable gas is merged with the condensate to form a two-phase fluid and then returned to the polymerization reactor. Thus, by employing a specific process of polymerizing propylene while removing the heat of polymerization using the latent heat of vaporization of the condensate, the polymerization reactor can be continuously operated stably, and the present invention is completed. It came to.

  That is, according to the first invention of the present invention, in a method for producing a polypropylene or propylene-based copolymer by a gas phase polymerization process using a solid catalyst containing a transition metal component, unreacted propylene is produced from a polymerization reactor. Is taken out, introduced into the condenser, separated into condensate and non-condensable gas, a part of the separated non-condensable gas is merged with the condensate to form a two-phase fluid, and the polymerization reaction By returning to the vessel, a process for producing polypropylene is provided, in which propylene is polymerized while removing the heat of polymerization using the latent heat of vaporization of the condensate.

  According to the second invention of the present invention, in the first invention, the two-phase fluid has a non-condensable gas ratio of 0.01 or more as a mass flow rate ratio relative to the condensate (non-condensable gas / condensate). A method for producing polypropylene is provided.

  On the other hand, according to the third invention of the present invention, a polymerization reactor for producing a polypropylene or propylene copolymer by a gas phase polymerization process using a solid catalyst containing a transition metal component, and a polymerization reactor are taken out from the polymerization reactor. In the apparatus for producing polypropylene, comprising a condenser for separating the multi-component gas mainly composed of unreacted propylene into a condensed liquid and a non-condensed gas, and a mixed liquid line for returning the separated condensed liquid to the polymerization reactor, An apparatus for producing polypropylene comprising a mixed gas line for liquid dispersion assisting, wherein a part of a non-condensable gas separated by a condenser is joined to a condensate to form a two-phase fluid and then returned to the reactor. Provided.

According to a fourth aspect of the present invention, there is provided the apparatus for producing polypropylene according to the third aspect, wherein the polymerization reactor is a horizontal reactor having an agitator that rotates about a horizontal axis inside. Provided.
Furthermore, according to the fifth invention of the present invention, there is provided a polypropylene production apparatus characterized in that in the third or fourth invention, two or more polymerization reactors are connected.

  According to the method for producing polypropylene of the present invention, liquid propylene necessary for heat removal is mixed with non-condensable gas and supplied to the polypropylene polymerization reactor so that the liquid propylene necessary for heat removal is liquid. Since it does not become droplets but is atomized and sprayed uniformly in the reactor, the heat removal efficiency is improved. In addition, since the nozzles are prevented from being blocked, there is an effect that continuous and stable operation is possible. In particular, even under conditions where the supply flow rate of liquid propylene, which has heretofore been difficult to operate, becomes small, the heat removal efficiency is improved and a stable operation can be continuously achieved.

FIG. 1 is a schematic view of an apparatus including a horizontal reactor used in the method for producing polypropylene of the present invention. FIG. 2 is a schematic view of an apparatus including a vertical reactor used in the method for producing polypropylene of the present invention. FIG. 3 is a schematic view of an apparatus in which horizontal reactors used in the method for producing polypropylene of the present invention are connected in multiple stages.

  Below, the manufacturing method and manufacturing apparatus of the polypropylene of this invention are demonstrated concretely and in detail using drawing.

1. Polypropylene Production Method The polypropylene production method of the present invention is a method for producing polypropylene or a propylene-based copolymer by a gas phase polymerization process using a solid catalyst containing a transition metal component. Is taken out, introduced into the condenser, separated into condensate and non-condensable gas, a part of the separated non-condensable gas is merged with the condensate to form a two-phase fluid, and the polymerization reaction The propylene is polymerized while removing the heat of polymerization using the latent heat of vaporization of the condensate by returning to the vessel.

(1) Polymerization catalyst The type of the polymerization catalyst used in the production method of the present invention is not particularly limited as long as it is a solid catalyst containing a transition metal component, and a known catalyst can be used. For example, a so-called Ziegler-Natta catalyst in which a titanium compound and an organoaluminum compound are combined, or a metallocene catalyst can be used.
Ziegler-Natta catalyst is a titanium trichloride or titanium trichloride composition obtained by reduction with organoaluminum as a titanium compound, which is further activated by treatment with an electron donating compound. A so-called supported catalyst obtained by supporting titanium is included.

  Examples of the organoaluminum compound used as a promoter include trialkylaluminum such as trimethylaluminum, triethylaluminum, and triisobutylaluminum, alkylaluminum halide such as diethylaluminum chloride and diisobutylaluminum chloride, and alkylaluminum such as diethylaluminum hydride. Examples include hydrides, alkylaluminum alkoxides such as diethylaluminum ethoxide, alumoxanes such as methylalumoxane and tetrabutylalumoxane, and complex organoaluminum compounds such as dibutyl methylboronate and lithium aluminum tetraethyl. It is also possible to use a mixture of two or more of these.

Moreover, various polymerization additives can be used for the above-mentioned catalyst for the purpose of improving stereoregularity, controlling particle properties, controlling soluble components, controlling molecular weight distribution, and the like. For example, organosilicon compounds such as diphenyldimethoxysilane and tert-butylmethyldimethoxysilane, esters such as ethyl acetate, butyl benzoate, methyl p-toluate, and dibutyl phthalate, ketones such as acetone and methyl isobutyl ketone, diethyl ether And electron donating compounds such as ethers such as benzoic acid and propionic acid, and alcohols such as ethanol and butanol.
In the present invention, it is preferable that the addition polymerization catalyst is preliminarily polymerized before being used in the main polymerization. Prior to the polymerization process, a small amount of polymer is generated around the catalyst in advance, so that the catalyst becomes more uniform and the generation amount of fine powder can be suppressed.

(2) Polymerization conditions Polymerization conditions such as temperature, pressure and residence time in the present invention can be arbitrarily set as long as the effects of the present invention are not impaired. Specifically, the polymerization temperature is preferably 0 ° C. or higher, more preferably 30 ° C. or higher, and particularly preferably 40 ° C. or higher. However, the polymerization temperature must not be too high, preferably 100 ° C. or less, more preferably 90 ° C. or less, and particularly preferably 80 ° C. or less.
The polymerization pressure is not less than atmospheric pressure, preferably not less than 0.6 MPaG, more preferably not less than 1.0 MPaG, particularly preferably not less than 1.6 MPaG, but the polymerization pressure must not be too high, preferably not more than 4.2 MPaG More preferably, it is 3.5 MPaG or less, and particularly preferably 3.0 MPaG or less. Here, the polymerization temperature should not be set lower than the dew point of the reaction gas component at the polymerization pressure.
The residence time can be arbitrarily adjusted according to the configuration of the polymerization reactor (tank) and the product index, but is generally set within a range of 30 minutes to 10 hours.

  In the polymerization step in the present invention, a reaction process using latent heat of vaporization of liquid is employed as a main means for removing heat of polymerization. As a typical form of the reactor, a vertical or horizontal stirred tank type reactor can be mentioned, but these forms do not affect the effect of the present invention and are suitable in any case. Expect results. Hereinafter, according to the embodiment of the present invention, a case in which each reactor is used will be described in detail.

(3) Polymerization process employing a horizontal stirring tank reactor First, FIG. 1 shows a polymerization process employing a horizontal stirring tank reactor. A catalyst component is supplied from a catalyst component supply pipe 1 disposed at one end of the horizontal reactor 6 to which the raw material monomer is supplied. Here, the catalyst component is meant to include an organoaluminum compound as a promoter in addition to the solid catalyst, and can be supplied from one piping nozzle or performed from separate nozzles. The polymer produced by the start of polymerization in the horizontal reactor 6 is uniformly stirred by a stirring shaft provided with a stirring blade 7 which is built in the horizontal reactor and driven by the stirring motor 5.

  The heat generated by the polymerization is removed when the condensate (mixed liquid) supplied to the reactor via the condensate (mixed liquid) line 12 evaporates, and the inside of the reactor is controlled to a desired temperature. be able to. As the main component of the condensate (mixed liquid), it is possible to use easily liquefied monomers such as propylene and butene, propane and other inert hydrocarbon solvents. The unreacted gas vaporized by the polymerization heat is led to the condenser 9 via the unreacted gas extraction pipe 8. Here, a part of the gas is condensed and liquefied and separated into a condensed liquid (mixed liquid) and an uncondensed gas (mixed gas) in the gas-liquid separator 10.

An appropriate amount of raw material propylene is supplied to the gas-liquid separator 10 from the supply pipe 2 in order to supplement the propylene consumed in the polymerization. The condensed liquid (mixed liquid) separated by the gas-liquid separator 10 is circulated again to the reactor 6 by the mixed liquid pump 11 and used for heat removal. On the other hand, the non-condensed gas separated by the gas-liquid separator 10 is blown into the lower part of the reactor by the mixed gas compressor 13 via the mixed gas line 14 to help the diffusion of hydrogen and monomer gas components, and powder. Accelerate phase agitation. In the mixed gas line, a raw material gas supply pipe 3 is installed, and non-condensable monomer components such as hydrogen and ethylene for the purpose of adjusting the molecular weight can be supplied.
Furthermore, in the present invention, in addition to the above line configuration, a liquid dispersion assisting mixed gas line 15 is installed, and by the mixed liquid pump 11, the mixed liquid line 12, the mixed gas compressor 13, and the mixed gas line 14, A part of the non-condensable gas is joined to the condensate to form a two-phase fluid, and then returned to the polymerization reactor. The polymer (powder) polymerized in the reactor is extracted from the polymer extraction pipe 4.

  Here, the liquid dispersion assisting mixed gas line 15 will be described. As described above, since the polymerization reactor used in the present invention mainly uses the latent heat of vaporization of the condensate composed of liquid propylene as a heat removal means, the flow rate of the liquid mixture supplied by the pump 11 is generated in the reactor. It is closely related to the amount of heat of polymerization, that is, the polymerization rate. That is, when the polymerization is started up or when the reaction amount is controlled to be small in the reactor, the mixed liquid flow rate becomes very small. In general, when supplying these mixed liquids to the reactor, special nozzles are often devised to spray the polymerized powder more uniformly. I can't do enough.

  In this case, even if the polymerization amount of the reactor as a whole is small, local heat removal failure may cause poor temperature controllability, or may be a factor that hinders the continuation of operation from coalescence or lump formation due to melting of the polymer. . In the present invention, in order to solve these problems, by using the mixed gas line 15 for assisting liquid dispersion, a part of the gas from the mixed gas line 14 is joined to the condensed liquid circulated to the reactor, thereby supplying Even when the flow rate of the liquid mixture is small, more uniform liquid spraying is possible.

  The gas to be circulated through the liquid dispersion auxiliary mixed gas line 15 is taken out from the discharge gas at the outlet of the mixed gas compressor 13, but the object of uniformly dispersing the mixed liquid or preventing nozzle clogging is achieved. There is no limit to the flow rate as much as possible. However, for the former purpose, the mass flow rate ratio (non-condensed gas / condensate) in the merged pipe is preferably 0.01 or more, and more preferably 0.1 or more. Thereby, a liquid mixture can be disperse | distributed uniformly.

In the present invention, the method for supplying the mixed phase fluid of the condensed liquid and the non-condensed gas to the reactor is not limited as long as it is physically uniformly dispersed, but a nozzle for the purpose of liquid spray such as a so-called two-fluid nozzle If is used, more preferable results can be obtained. On the other hand, if the amount taken out from the discharge gas of the mixed gas compressor 13 to the liquid dispersion assisting mixed gas line 15 becomes excessive, the amount of non-condensed gas supplied to the lower part of the reactor becomes excessive, and stirring and gas in the reactor Consideration is required when selecting the operating conditions, since the effect of uniformizing the pressure decreases.
In order to grasp and control these liquid flow rate and gas flow rate, it is desirable to have a pressure gauge, a flow meter, and a control valve. For example, by monitoring the change in polymerization heat in the reactor, calculate the required liquid flow rate or gas flow rate according to the amount of polymerization heat, and adjust the supply amount to the reactor so that it becomes the optimum value. This is even more effective.

(4) Polymerization process using vertical stirring tank reactor Another mode of the polymerization process using latent heat of vaporization is a polymerization process using vertical stirring tank reactor. The basic process configuration is the same as when the horizontal reactor described above is used. As illustrated in FIG. 2, the catalyst component is supplied to the vertical reactor 6 provided with the stirrer 5 through the catalyst component supply pipe 1. Although gas phase polymerization is performed in the reactor, the heat of polymerization is removed by latent heat of vaporization that is lost when the condensate containing propylene vaporizes therein.

The unreacted gas evaporated here is guided to the compressor 13 through an unreacted gas extraction pipe at the top of the reactor. The mixed gas whose pressure has been increased here is separated into a condensate and an uncondensed non-condensed gas by the condenser 9.
Propylene, ethylene, and hydrogen are supplied into the system from the raw material propylene supply pipe 2 and the raw material gas supply pipe 3 to the condensed liquid mixture. The non-condensed gas is merged with the condensate by the liquid dispersion assisting mixed gas line 15 branched from a part of the mixed gas pipe 14. This makes it possible to assist the dispersion of the mixed solution in the reactor. The polymer (powder) obtained in these processes is extracted from the reactor 6 to the next step via the polymer extraction pipe 4.

  The range that can be taken as basic polymerization conditions such as temperature, pressure, residence time, and the like is the same as the contents using the horizontal stirred tank reactor. The same applies to the operating conditions of the liquid dispersion assisting mixed gas line 15.

(5) Multistage polymerization process using a plurality of horizontal stirred tank reactors The present invention is a process for producing a propylene polymer, not only by operating a single reactor, but also by a process in which a plurality of reactors are connected in series. It is also possible to apply to multistage polymerization in which continuous polymerization is performed.
For example, it is also suitable for the production of a so-called propylene block copolymer in which a homopolymer of propylene is produced in the first stage and a copolymer of propylene and an α-olefin is subsequently produced in the subsequent second stage.
In this multi-stage polymerization, it is required to grasp the polymerization ratio in each reaction stage and control it. However, in a reactor operated under a condition with a small polymerization amount ratio, the supply flow rate of the liquid medium becomes small and uniform. Dispersion may be difficult.

According to the method of the present invention, even in such a case, the mixed gas 28 mainly composed of unreacted α-olefin (ethylene) is taken out from the second-stage polymerization reactor 26 shown in FIG. After the introduction, the gas-liquid separator 30 separates the condensed liquid from the non-condensed gas, and a part of the non-condensed gas separated and discharged from the mixed gas compressor 33 is merged with the condensed liquid from the pump 31. After making the phase fluid, it is returned to the polymerization reactor 26.
The gas flowing through the liquid dispersion assisting mixed gas line 35 branches out from the discharge gas from the mixed gas compressor 33 and is taken out, but the object of uniformly dispersing the mixed liquid or preventing the nozzle from being blocked is achieved. There is no limit to the flow rate as much as possible. However, for the former purpose, the mass flow rate ratio (non-condensed gas / condensate) in the merged pipe is preferably 0.01 or more, and more preferably 0.1 or more. Thereby, a liquid mixture can be disperse | distributed uniformly.
As a result, when a copolymer of propylene and ethylene is produced while removing the heat of polymerization using the latent heat of vaporization of the condensate, uniform liquid dispersion and heat removal are possible, and a more stable operation is performed. Is possible.

2. Polypropylene production apparatus The polypropylene production apparatus of the present invention comprises a polymerization reactor for producing a polypropylene or propylene copolymer by a gas phase polymerization process using a solid catalyst containing a transition metal component, and the polymerization reactor is taken out of the polymerization reactor. In the apparatus for producing polypropylene having a condenser for separating a mixed gas mainly composed of unreacted propylene into a condensed liquid and a non-condensed gas, and a mixed liquid line for returning the separated condensed liquid to the polymerization reactor, A part of the non-condensable gas separated by the vessel is combined with the condensate to form a two-phase fluid and then returned to the reactor, and a liquid dispersion assisting mixed gas line is provided.

(1) Polymerization apparatus employing a horizontal stirring tank reactor FIG. 1 shows a polymerization apparatus employing a horizontal stirring tank reactor. The horizontal reactor 6 includes a stirring shaft equipped with a stirring blade 7 and includes a stirring motor 5 that uniformly stirs the polymer. A catalyst component supply pipe 1 for supplying a catalyst component is installed at one end of the reactor.

The mixed gas vaporized by the polymerization heat generated by the reaction of the raw material monomers is guided via the unreacted gas extraction pipe 8, and a part of the gas is condensed and liquefied by the condenser 9. A gas-liquid separator 10 that separates condensed liquid (mixed liquid) and uncondensed gas (mixed gas) is provided with a raw material propylene replenishment pipe 2 that supplements propylene consumed in polymerization.
The condensate separated by the gas-liquid separator 10 is circulated again to the reactor 6 by the mixed liquid pump 11 and used for heat removal. On the other hand, the non-condensed gas separated by the gas-liquid separator 10 is blown into the lower part of the reactor by the mixed gas compressor 13 via the mixed gas line 14 to help the diffusion of hydrogen and monomer gas components, and powder. Phase agitation is facilitated. In the mixed gas line, a raw material gas supply pipe 3 is installed for the purpose of supplying non-condensable monomer components such as hydrogen and ethylene for the purpose of molecular weight adjustment. The mixed liquid line 12 is provided to supply a condensate to the reactor, and heat is removed when the mixed liquid evaporates, so that the inside of the reactor can be controlled to a desired temperature. The polymer (powder) polymerized in the reactor is extracted by the polymer extraction pipe 4.

  Furthermore, in the present invention, in addition to the above line configuration, a liquid dispersion assisting mixed gas line 15 is provided. The liquid dispersion assisting mixed gas line 15 joins a part of the non-condensed gas separated by the condenser 9 to the condensed liquid to form a two-phase fluid and then returns it to the polymerization reactor 6. In order to uniformly disperse the mixed liquid, the mass flow rate ratio (non-condensed gas / condensed liquid) in the joining pipe is set to 0.01 or more, and more preferably 0.1 or more. Thereby, a liquid mixture can be disperse | distributed uniformly. Although not shown, it is desirable to install a calculator for calculating the flow rate of the non-condensable gas necessary for the heat of polymerization and a valve for flow rate control.

(2) Polymerization apparatus employing vertical stirring tank reactor As another aspect of the polymerization process utilizing latent heat of vaporization, a polymerization apparatus employing vertical stirring tank reactor is illustrated in FIG. Except for the change of the line due to the shape of the reactor, the basic equipment configuration is the same as when the horizontal reactor described above is used, and a part of the non-condensable gas separated by the condenser is joined to the condensate. In addition, a liquid dispersion assisting mixed gas line 15 is provided for returning to the reactor after making the two-phase fluid.
The vertical reactor 6 is provided with a stirrer 5 in the center, and a catalyst component is supplied through the catalyst component supply pipe 1. A raw material monomer is supplied from the lower side of the reactor to carry out gas phase polymerization, but a mixed liquid containing propylene and the like is supplied, and removal of heat of polymerization is achieved by latent heat of vaporization that is lost when vaporized therein.

The mixed gas evaporated here is guided to the compressor 13 through an unreacted gas extraction pipe. The unreacted gas whose pressure has been increased here is separated into a mixed liquid 12 and an uncondensed mixed gas 14 by a condenser 9.
Propylene, ethylene, and hydrogen are supplied to the condensed liquid mixture 12 from the raw material propylene supply pipe 2 and the raw material gas supply pipe 3. Branching from a part of the mixed gas 14, a liquid dispersion assisting mixed gas line 15 is installed, and this joins the mixed liquid 12 to assist the dispersion of the mixed liquid in the reactor. The polymer (powder) obtained in these processes is extracted from the reactor 6 to the next step via the polymer extraction pipe 4.

(3) Multistage continuous polymerization apparatus A multistage continuous polymerization apparatus is an apparatus in which a plurality of reactors are connected in series as shown in FIG. 3 in order to produce a propylene polymer.
For example, it can be suitably used for the production of a so-called propylene block copolymer in which a homopolymer of propylene is produced in the first stage and a copolymer of propylene and α-olefin is subsequently produced in the subsequent second stage. it can. As shown in FIG. 3, the polymer is supplied to the receiver via the polymer extraction pipe 4 of the first stage polymerization reactor 6 and introduced into the second stage polymerization reactor 26. Similarly to the first-stage polymerization reactor 6, the second-stage polymerization reactor 26 joins a part of the non-condensable gas separated by the condenser to the condensate to form a two-phase fluid and then to the reactor. A liquid dispersion assisting mixed gas line 35 is provided for return.

In the second stage polymerization reactor 26, the catalyst and the α-olefin are supplied, and the copolymerization of propylene and the α-olefin is performed. The mixed gas 28 mainly composed of unreacted α-olefin (ethylene) is introduced into a condenser 29 and then separated into a condensed liquid and a non-condensed gas by a gas-liquid separator 30. A part of the non-condensed gas 34 separated and discharged from the mixed gas compressor 33 is joined to the mixed liquid 32 from the pump 31 by the liquid dispersion assisting mixed gas line 35 to form a two-phase fluid, and then the polymerization reaction is performed. Return to vessel 26. The obtained polymer (powder) is extracted from the reactor via the polymer extraction pipe 24.
In this multi-stage polymerization, it is required to grasp the polymerization ratio in each reaction stage and control it. However, in a reactor operated under a condition with a small polymerization amount ratio, the supply flow rate of the liquid medium becomes small and uniform. Dispersion may be difficult. According to the apparatus configuration of the present invention, even in such a case, uniform liquid dispersion and heat removal are possible, and a more stable operation can be performed.

  The present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples. Methods for measuring various physical property values in Examples and Comparative Examples of the present invention are shown below.

[Measurement methods for various physical properties]
(1) Melt flow rate (MFR):
Measurement was performed under the conditions of 230 ° C. and 21.18 N (2.16 kgf) based on JIS K6921 using a melt indexer manufactured by Takara.
(2) Polymer bulk density (BD):
The bulk density of the powder sample was measured using an apparatus according to ASTM D1895-69. (3) Mass (% by weight) in the polymerization vessel:
After completion of the reaction, the propylene-based polymer in the polymerization vessel was recovered, and small lumps captured on a screen having an opening of 2.8 mm were separated, and the ratio was determined.

Example 1
A part of the non-condensable gas separated by the condenser in the horizontal reactor 6 shown in FIG. 1, a condenser, and a polypropylene production apparatus having a mixed liquid line for returning the separated condensate to the polymerization reactor. A liquid dispersion assisting mixed gas line 15 for joining the liquid to the condensate was attached. As the horizontal reactor 6, a horizontal polymerization reactor (L / D = 5.2) having an internal volume of 100 liters equipped with a stirrer was used.
Using this apparatus, gas phase polymerization of propylene was performed. While maintaining the stirring speed of 35 rpm, the magnesium-supported catalyst, raw material propylene, hydrogen, and solvent were supplied, and the operation was performed at a polymerization rate of 15 kg / h. At this time, the polymerization temperature is 65 ° C., the polymerization pressure is 2.1 MPaG, and the hydrogen concentration in the mixed gas is controlled to be 25 mol%. The product powder from the reactor has a level in the reactor of 50%. It was extracted out of the reactor to be retained.
The gas flowing through the liquid dispersion assisting mixed gas line 15 is taken out by branching from the gas discharged from the mixed gas compressor 13, but the purpose of uniformly dispersing the mixed liquid or preventing nozzle clogging is achieved. There is no limit to the flow rate as much as possible. However, for the former purpose, the mass flow rate ratio (non-condensed gas / condensate) in the junction pipe is preferably 0.01 or more, and more preferably 0.1 or more.
At this time, the total supply flow rate to the reactor of the condensate for removing the heat of polymerization was 66.3 kg / h, and this was sprayed by evenly distributing it with five nozzles. On the other hand, the total flow rate of the mixed gas taken out from the gas phase of the gas-liquid separator was 61.8 kg / h, and was supplied to the reactor powder layer. Here, 10 kg / h of the non-condensable gas is branched as the liquid dispersion assisting mixed gas line 15, and the operation is performed so that the five equally distributed gas lines are merged into the mixed liquid lines 12. It was. The flow rate of propylene supplied from the raw material propylene replenishment pipe was 6.7 kg / h.
The mass flow rate ratio (non-condensable gas / condensate) in the junction pipe is 0.15, which is a value obtained by dividing 10 kg / h by 66.3 kg / h, and the mixed liquid is sufficiently dispersed into fine particles by the non-condensable gas. Since it is sprayed, the heat removal effect in the reactor is remarkable.
After reaching the predetermined polymerization conditions, 100 hours of stable operation was performed. When the obtained polypropylene was analyzed, no small lumps captured on a screen with MFR = 250 g / 10 min, bulk density = 0.45 g / cm 3, and mesh size of 2.8 mm were observed. It was possible to remove the product from the factory very smoothly.

(Example 2)
The mass flow rate ratio (non-condensable gas / condensate) in the merged piping was set to 0.01 by setting the flow rate of the non-condensable gas to 0.663 kg / h using the apparatus of Example 1. Was polymerized in the same manner as in Example 1. Although a small amount (0.3% by weight) of small lumps captured on a screen having a mesh opening of 2.8 mm was generated, it was possible to smoothly remove the product from the reactor.

(Comparative Example 1)
The operation was started under the same conditions as in Example 1, and after stable conditions were obtained, the liquid dispersion assisting mixed gas line 15 was closed after 12 hours, and the merging of the non-condensed gas into the mixed liquid line 12 was stopped. did. The mass flow ratio (non-condensable gas / condensate) in the junction pipe is 0, and the mixed liquid is sufficiently dispersed in the non-condensable gas without being dispersed into fine particles, so that a more uniform heat removal effect in the reactor Cannot be expected.
As a result, small lumps were found in the product, and when analyzed, the amount of lumps captured on the screen having a mesh opening of 2.8 mm reached 3.2 wt% with respect to the product weight. .
Also, the extraction of the product during operation was unstable, and after 6 hours after closing the liquid dispersion assisting gas line 15, the extraction system was blocked and the operation was stopped. After that, when the reactor was opened, several centimeters of melt-like lumps were found, and it was confirmed that these were the main causes that blocked the extraction line.

"Evaluation"
As is clear from Example 1 above, in the method for producing polypropylene of the present invention, the mass flow ratio (non-condensable gas / condensate) in the joining pipe is as large as 0.1 or more, so the mixed liquid is sufficiently non-condensable gas. In this case, the heat removal effect in the reactor was remarkable.
As a result, it can be seen that the formation of small polymer in the reactor is remarkably small and the bulk density is high, so that the propylene-based polymer has high fluidity and long-term continuous operation is possible. Moreover, it turns out that the propylene-type polymer obtained by the manufacturing method of this invention has little production | generation of coarse powder. Further, in Example 2 in which propylene was polymerized in the same manner as in Example 1 except that the mass flow rate ratio (non-condensable gas / condensate) in the merged pipe was 0.01, a small lump was formed during the polymerization reaction. Although a small amount was generated, it can be seen that long-term continuous stable operation is possible.
On the other hand, in Comparative Example 1 in which the liquid dispersion assisting gas line is closed and the mass flow rate ratio (non-condensed gas / condensed liquid) in the merging pipe is 0, the heat removal effect in the reactor is the same as in the prior art. Since it cannot be expected, a large amount of bulk polymer is formed in the reactor, and a coarse powder of a propylene-based polymer is often generated.

The method for producing polypropylene according to the present invention is a method for producing polypropylene by a gas phase polymerization process in which heat removal is mainly performed by latent heat, in which a mixed liquid necessary for heat removal is uniformly dispersed, and nozzle blockage is prevented. It is possible to continuously achieve a stable operation, and the heat removal effect is particularly remarkable even under conditions where the supply flow rate of the liquid medium is small.
Moreover, the polypropylene production apparatus of the present invention can exhibit the above performance while having a relatively simple configuration. Thereby, the polypropylene resin which has the outstanding characteristic can be provided, and it is utilized for each field | areas, such as a film, a sheet | seat, a rope, a fiber, and an injection molded product, and industrial applicability is high.

1,21 Catalyst component supply pipe 2 Raw material propylene supply pipe 3, 23 Raw material gas supply pipe (hydrogen, ethylene, etc.)
4 Polymer extraction piping 5, 25 Agitator (motor)
6, 26 Reactor 7, 27 Stirring blade 8, 28 Unreacted gas extraction pipe 9, 29 Condenser 10, 30 Gas-liquid separator 11, 31 Mixed liquid pump 12, 32 Mixed liquid line 13 Mixed gas compressor 14, 34 Mixed gas line 15, 35 Liquid dispersion auxiliary mixed gas line 22 Raw material α-olefin supply pipe 40 Receiver

Claims (5)

In a method for producing a polypropylene or propylene-based copolymer by a gas phase polymerization process using a solid catalyst containing a transition metal component,
Take out the multi-component gas mainly composed of unreacted propylene from the polymerization reactor, introduce it into the condenser, separate it into condensate and non-condensable gas, and join a part of the separated non-condensable gas to the condensate A method for producing polypropylene, characterized in that propylene is polymerized while removing the heat of polymerization by utilizing the latent heat of vaporization of the condensate by returning to the polymerization reactor after making it into a two-phase fluid.   2. The method for producing polypropylene according to claim 1, wherein the two-phase fluid has a non-condensable gas ratio of 0.01 or more as a mass flow rate ratio relative to the condensate (non-condensable gas / condensate). A polymerization reactor for producing a polypropylene or propylene-based copolymer by a gas phase polymerization process using a solid catalyst containing a transition metal component, and a multi-component gas mainly composed of unreacted propylene taken out from the polymerization reactor. In a polypropylene production apparatus having a condenser that separates a condensed liquid and a non-condensed gas, and a mixed liquid line that returns the separated condensed liquid to a polymerization reactor,
An apparatus for producing polypropylene, comprising a mixed gas line for liquid dispersion assisting, wherein a part of the non-condensable gas separated by the condenser is joined to the condensate to form a two-phase fluid and then returned to the reactor. .   4. The apparatus for producing polypropylene according to claim 3, wherein the polymerization reactor is a horizontal reactor having an agitator rotating around a horizontal axis.   The apparatus for producing polypropylene according to claim 3 or 4, wherein two or more polymerization reactors are connected.

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