NO144570B - CONTINUOUS PROCEDURE FOR VAPOR PHASE POLYMERIZATION OF A EVAPORABLE POLYMER, AND APPARATUS FOR CARRYING OUT THE PROCEDURE - Google Patents

Description

The present invention relates to a method and apparatus for the vapor phase polymerization of a polymerizable monomer or mixtures of polymerizable monomers to give normally solid polymeric products, and more particularly the invention relates to an apparatus for the polymerization of such monomers in the vapor phase by an essentially isobaric method using of a high-yield catalyst, possibly together with a co-catalyst, which apparatus is a horizontal, cooled, stirred-bed reactor, in which substantially all of the off-gas for the reactor is recycled.

Polymerization reactor for carrying out vapor phase polymerization

of a polymerizable monomer in vapor form, comprising a single-cylindrical, longitudinally extending horizontal reactor, a centrally arranged rotatable shaft extending longitudinally throughout the reactor, to which shaft is attached a number of adjacent and circularly offset agitators extending transversely inside the reactor and at a small distance from the reactor's inner surface, as well as drive devices for the aforementioned shaft, one or more inlets for introducing

ing a feed gas stream comprising monomer vapor to the polymerization zone in the reactor, one or more outlets for removing off-gas stream comprising monomer vapor from the polymerization zone in the reactor, as well as means for removing powdery, solid polymer from the reactor which is characterized in that the reactor contains at least one horizontal polymerization zone, that the stirring devices are flat, rectangular paddles, one or more inlets spaced along the bottom of the reactor for introducing the feed gas flow of monomer vapor to the polymerization zone, one or more in, the length of the reactor-

directionally arranged inlets for the introduction of catalyst to the polymerization ion zone, one or more separate inlets along the upper part of the reactor for the introduction of coolant to the polymerization ion zone, one or more separate outlets along the upper part of the reactor for removing an exhaust gas stream consisting of monomer vapor and coolant vapor from the polymerization zone, an execution zone containing at least one impeller, which execution zone is formed by a separation device at one end of the reactor, which separation device fills the entire internal cross-sectional area of the reactor and is provided with an opening in the upper part hence to permit the passage of gas and a controlled movement of the powdered solid polymer run between the polymerization zone and the run zone, which zone contains an outlet connected to means for removing the powdered polymer from the reactor without significant pressure drop." <: >One of the problems concerning dissolution - or suspension polymerization of monomers are the necessary investment costs for production. Monomer polymerization using a vapor phase process can be made substantially more economical if certain problems with which such a polymerization process is affected can be solved. These problems include conducting polymerization in a thermally controlled manner to avoid "hot spots", maintaining a proper product particle size distribution. as well as in cases where the catalyst used gives extremely high yields, but is very sensitive to poisoning, to reduce to a minimum the amount of starting material that is brought into contact with the catalyst per quantity unit of product that is formed.

Another problem relating to certain catalyst combinations is the narrow molecular weight distribution of the products obtained with these catalysts. A vapor phase reactor has now been invented which to a large extent or completely solves the problems mentioned above and which provides important economic benefits through savings in energy consumption, raw material and capital investments.

US Patent No. 2,502,953 describes a dammed, downwardly directed apparatus for bringing fluidized, solid particles into contact with gaseous fluids to flush or strip volatile constituents from such solids.

US patent no. 2,936,303 describes vapor phase polymerization of ethylene, propylene or mixtures thereof in a countercurrent, fluidized bed in the presence of an inert dilution gas. In the described method, the solid catalyst is fed down through the reactor, while, for example, ethylene mixed with the dilution gas is fed countercurrently up through a series of vertical fluidized bed reaction zones. With this method, the reaction in the different reaction zones can be controlled independently by removing the exhaust gas from the last reaction zone, cooling the gas and recirculating parts of this exhaust gas to each of the reaction zones. However, as a result of the dilution gas used and a fluidized layer, large quantities of gas must pass through the reactor per unit formed polymer.

US patent no. 3,023,203 shows a suspension gas phase polymerization of olefins using a reactor which has three concentric, overlapping, vertical sections, and where a finely divided catalyst is suspended in the entire amount of gas, and where temperature regulation is carried out by cooling of the gas. The shown process also includes removal of the polymer without pressure relief.

US patent no. 3,254,070 shows a method for gas-phase polymerization of ethylene using conventional kibling, and where a mixture of reaction products and solid or liquid catalysts is continuously finely divided mechanically. In this patent it is further described that the reacting components can be agitated through a number of stages, each with different polymerization conditions. In a further embodiment, it is described that the first few steps can be carried out using a liquid phase polymerization, and where the final polymerization is carried out in the vapor phase. Different polymerization temperatures can be used in separate reactors.

US patent no. 3,256,263 describes a method for removing heat and creating an intense movement in the polymeric product formed during gas phase polymerization of olefins in a reactor. vertical fluidized bed reactor, in which mechanical agitation is used and the introduction of polymerization monomers, immediately after extensive cooling, in the form of a moving gas or liquid jets. US patent no. 3,300,457 describes the polymerization of mono-olefins, especially ethylene and propylene in a fluidized bed using a stirred, vertical reactor. The catalysts and polymer in the reactor are moved in the flow direction of the mono-olefin by means of stirring, and heat is removed by cooling the walls of the chamber by heat transfer using a gas stream, or by introducing pre-liquefied mono-olefin.

In US patent no. 3,469,948, a horizontal paddle-stirred polymerization reactor is described, in which pulsating purge gases including the polymerizable olefin are used. This patent is aimed at the use of longitudinal vanes which are shaped in such a way that the solid polymer obtained by vapor phase polymerization is given a forward movement.

US patent no. 3,652,527 describes a method for gas phase polymerization of propylene in a vertical, stirred bed reactor, and where heat of evaporation is used to cool the reaction mixture. From this patent it appears that it is necessary that one component of the catalyst combination must be directly placed on the layer of solid polymer formed during the polymerisation, and that the other catalyst component must be introduced in the gas phase above the layer.

British patent no. 1,354,020 describes a vapor phase olefin polymerization process in which the heat generated during the polymerization process is removed by introducing the monomer and heat transfer agents in gaseous or liquid form into the polymerization zone. However, the use of several polymerization temperatures in the vertical, stirred fluidized bed reactor has not been described, and it is difficult to see how such individual control can be achieved with the described apparatus.

The attached drawings show:

fig. 1 a longitudinal section of an embodiment of the new reactor, fig. 2 a cross-section of such a reactor taken along the line 2-2 in fig. 1,

fig. 3 a second cross-section of the reactor according to fig. 1 taken along the line 3-3 in fig. 1,

fig. 4 an embodiment of an essentially isobaric process in which the described reactor is used, and where essentially all of the reactor exhaust gas is recycled.

Fig. 5 and 6 correspond respectively to fig. 1 and 4, but showing two horizontal polymerization zones instead of one.

The invention described in the following includes a horizontal reactor and a method for an essentially isobaric vapor phase polymerization of polymerizable monomers, where essentially all of the reactor exhaust gas is recycled, and where conditions are used that include forced cooling and stirred beds. The reactor is particularly suitable for the use of polymerization catalysts that provide a sufficiently high polymerization yield that the catalyst residues do not need to be removed from the polymerization product during the final polymerization process.

In general, the reactor uses a regulated introduction of the catalyst components and the cooling liquid in two or more of its polymerization ions, with both the catalyst components and the cooling liquid being applied directly to and in the stirred, subfluidized layer of polymer during formation and polymerization of the monomer from the vapor phase in and above such a layer. The polymer solid is continuously removed by passing it through a separation device which is generally arranged in one reactor and into a receiving vessel.

In the reactor, monomers or mixtures thereof, and possibly hydrogen are introduced essentially or completely under the polymer layer, and the cooling liquid is introduced on the surface of the layer.

The reactor comprises at least one polymerization zone generally divided

in two or more polymerization sections, and the different sections are separated from each other by means of dams or other suitably shaped separators to prevent substantial back-mixing between the sections. Each of the sections can be controlled individually with regard to polymerization temperature and polymerization rate, so that a polymeric product with a controlled dispersion in molecular weight and particle size can be easily produced.

Exhaust gas from the reactor is removed along the top of the reactor after

raised polymer fines are removed as completely as possible from the exhaust gases. The reactor off-gases are then fed to a separation zone in which the cooling liquid is at least partially removed together with any additional polymer fines, as well as some of the catalyst components from the polymerization monomer and hydrogen, if hydrogen is used,

after which the monomer and hydrogen are recycled to separate inlets along the various polymerization sections in the reactor, and which inlets are substantially completely arranged below the surface of the polymer layer.

A part of the dressing liquid including the additional polymer fines is removed from the separation zone and returned for a large part to the inlet which is arranged separately along the top of the reactor.

A smaller part of the cooling liquid, which is cleaned with regard to polymer fines and catalyst components, is fed to a catalyst refresh zone for catalyst dilution, so that it is not necessary to introduce new cooling liquid for this purpose. Opportunities can also be provided for in a multi-section reactor to introduce the catalyst components and the cooling liquid at different rates in the different sections of the reactor to aid individual control of the polymerization temperature and the polymerization production rate in the different sections. The catalyst components can be added in or on the stirred layer.

According to another feature of the invention, this comprises a compartmented, horizontal reactor and a method which is useful for vapor phase, essentially isobaric polymerization of polymerizable monomers, and where essentially all of the reactor off-gas is recycled, under conditions which includes forced cooling and stirred bed, and where at least one of the chambers has a vapor composition that differs from the others, and where at least one of the sections can be operated at a polymerization temperature and/or polymerization production rate that differs from the other sections.

The reactor is particularly suitable for polymerization using catalysts that give such a high polymerization yield that it is not necessary to remove the catalyst residues from the polymerization product during the final polymerization.

In general, a controlled introduction of catalysts and coolant in one or more sections contained in each chamber is used in the reactor? and then directly in or on the stirred, subfluidized layer of polymerized solid during formation and polymerization of monomer from the vapor phase in and above such a layer. The polymer solid is continuously removed by feeding it through a separation device which is generally arranged at one end of the reactor, after which the solid is fed to a receiving vessel.

In the reactor, monomers or mixtures thereof and possibly hydrogen are introduced wholly or partially under the polymer layer, and the cooling liquid is introduced on the surface of the layer. Each chamber has separate rudders for off-gas removal, a separate liquid separation zone and a separate vapor recirculation device. Each chamber of the reactor may be provided with one or more polymerization sections separated by partitions and, in a preferred embodiment, two or more of the sections in each chamber may be separated from each other by dams or other suitably shaped partitions to prevent substantial back-mixing between the sections. Each section can be individually controlled with regard to polymerization temperature and polymer production rate.

Two or more chambers may be separated by school structures such as

are constructed in such a way that they serve to regulate the vapor mixture between the chambers, but which allow the movement of free polymer particles from one chamber to another in a direction leading towards the outlet for the polymer. A polymeric product with a regulated dispersion in molecular weight, molecular weight distribution and particle size distribution can be more easily produced with the reactor described above.

The waste gases from each chamber are removed along the top of the reactor after the polymer fines have been removed as completely as possible from the waste gas. Such reactor exhaust gases are fed to a separate zone where the cooling liquid together with any further polymer fines and at least some of the catalyst components are removed from the polymerization monomer and any hydrogen used, after which the monomer and hydrogen are recycled to separate inlets along the various polymerization sections in the reactor chambers, these components generally being introduced under the surface of the polymer layer. A part of the cooling liquid including additional polymer fines is removed from the separation zone, and a significant part is fed back to separate inlets along the top of the reactor chamber. A second small part of the separated dressing liquid which has been freed from polymer fines and catalyst components is fed to a catalyst refreshing zone for catalyst dilution, so that for this purpose it is not necessary to introduce new dressing liquid.

It is also possible to introduce into the reactor the catalyst components and the cooling liquid at different rates into one or more of the polymerization sections in each of the reactor chambers to control the polymerization temperature and polymer production rate. The catalyst components can be added on the surface or below the surface of the layer.

The term vapor phase reactor or process respectively means a reactor or process where the monomer or monomers are present in vapor or gas phase under the conditions that exist in the reactor.

The recirculation system and the reactor are designed in such a way that they work essentially isobaric. This means that no more than the normal operating variations are present. Preferably, the pressure variations in the reactor and the recycling system are no more than 1.75 kg/cm, and more preferably no more than -0.7 kg/cm.

In one embodiment of the method, the reactor according to the present invention is used, which is shown in detail in fig. 4 which can roughly be divided into two parts, namely the reactor part and the part for treating the reactor off-gas (separation) and the reactor off-gas treatment (separation) and the catalyst refresh part.

As will be seen from fig. 4 or 6, the polymerization zone 405 in the horizontal polymerization reactor 401 is divided into several different stirred sections 467, 469, 471 and 473 to allow for the operation of the different conditions in the reactor at different temperatures and/or different polymer production rates. Polymerization takes place in each of said sections to provide a polymer layer distributed throughout the reactor, and the polymerization temperature in each of the sections can each be controlled by a combination of methods including agitation, the controlled differential introduction of recycled steam to each of the sections through the inlets 475, 477, 479 and 481 which are separated along the bottom of the reactor, and the introduction to each of the sections of an inert quench liquid and catalyst constituents at different rates through the quench liquid inlets 453, 455, 457 and 459 and the catalyst inlets 423, 425 , 427 and 429

which are arranged separately along the top of the reactor.

The reactor exhaust gases are removed through the outlets 48 3, 485, 487 and 489. As certain undesirable amounts of polymer dust can form in the reactor, these can advantageously be largely removed for the transfer of the reactor exhaust gases to the reactor exhaust gas treatment and the catalyst refresh section by using traps, filters , precipitation devices, cyclones or washing devices or combinations thereof.

Polymer solids are produced in each of the agitated sections 467 to 473, and as a result of the continuous production of such polymer, a certain amount of product will constantly be fed through the separator and out of the reactor to the polymer collection vessel 403.

The catalyst, either dissolved or suspended in the recirculating dressing liquid, is preferably introduced onto the surface of the bed in at least one of the various polymerization reaction sections through inlets 423, 425, 427 and 429. Correspondingly located inlets 453, 455, 457 and 459 are provided for the introduction of recirculating cooling liquid which may contain co-catalyst, on the layer in the individual reaction sections. However, depending on the type of catalyst, co-catalyst and monomer to be polymerized, the catalyst and/or co-catalyst can be sprayed or otherwise introduced into the reactor in its pure state or in another non-polymerizable carrier. Alternatively, for certain monomers, the catalyst and co-catalyst may be added to the refresh zone 445 and fed together to the reactor 401 .

In one mode of operation, it has been found advantageous to arrange the catalyst and the coolant inlets concentrically, so that the catalyst and the coolant are sprayed into the reactor and onto the surface of the polymer layer in such a way that a more even distribution of the catalysts on the polymer layer surface is achieved. However, the catalyst and dressing liquid inlets can be made separately, and the catalysts and dressing liquid are introduced separately to the bed. The reactor exhaust gases are fed out via the rudder line 431 to the washing tower 433, in which at least part of the coolant component in the waste gases, additional polymer fines and certain catalyst components are removed from the polymerizable monomer and any hydrogen used.

The polymerizable monomer and hydrogen together with some jacket liquid vapor are returned to the reactor 401 from the top of the wash tower 433, preferably after a passage through the heat exchanger 460

and the separator 461 to condense out additional cooling liquid via the blower 444 and vapor recycle piping 456 along with additional hydrogen and refresher monomers added via piping 463 and 465.

Alternatively, the monomer and hydrogen returned from the washing tower 433 to the reactor 401 can be fed outside the heat exchanger 460 and the separator 461. The amount of recirculation steam introduced into the individual sections of the reactor via the inlets 475, 477, 479 and 481 can be individually controlled using the valves 491, 493 , 495 and 497, whereby the layer can thereby be kept in a subfluidized state. The dressing liquid from the separator 461 is substantially free of polymer fines and the catalyst components and is suitable for use in the catalyst refresh zone 445.

Dress liquid, freed from the reactor exhaust gases, is cooled by means of the heat exchanger 454 and is returned in a significant part to the top of the washing tower 433, via the rudder line 438. A smaller part of the dress liquid is returned through the rudder line .437, the heat exchanger 443, the pump 439 and the dress liquid recycling rudder line 45 3 to the dress liquid inlets 453. catalyst is fed to the catalyst refresh zone 445, injected directly into the recirculating cooling liquid stream through the rudder line 447 or can be added directly in a non-polymerizable carrier to the reactor 401. A small part of the cooling liquid which is substantially freed of polymer fines and catalyst components is fed out from the separator 461 and fed again if the pipe line 434 and the pump 436 to the catalyst refresh zone 445 for cat-t aly s ator refresh ing sf orm 1.

Polymerization in the catalyst refresh zone 445 or the associated piping 449 and inlets 423 - 429 can cause serious resealing problems and can be controlled by keeping the co-catalyst concentration in the catalyst refresh zone 445 below a certain value, this value being dependent on the catalyst and co-catalyst used, and the monomer to be polymerized.

When refreshment co-catalyst is added to the catalyst refreshment zone 445, it may be necessary to take precautions to prevent polymerization taking place in the associated pipelines by cooling the refreshment zone, reducing the residence time of the catalyst components therein, etc. Alternatively, refreshment dressing liquid from the piping 440 can be used in the catalyst refreshment zone 445 instead of recirculating cooling liquid to prevent polymerization of the monomer in this zone.

The valve 499 is arranged in the catalyst refresh zone header line in order to be able to more easily vary the concentration of the catalyst in the refreshed catalyst which is introduced into the reactor. It has been found that the particle size of the polymer produced in the reactor 401 can be advantageously varied by varying the concentration of the catalyst introduced through inlets 423, 425, 427 and 429. Furthermore, it has been found advantageous to vary the catalyst concentration either by changing its concentration in the refresh zone 445, or in addition or alternatively to change its concentration by introducing cooling liquid into the catalyst dry pipe line 449 via the valve 499 close to the place where the catalyst is introduced into the catalyst inlets 42 3, 425, 427 and 429. Freshening catalyst is supplied through the pipe line 422.

The polymer solid which builds up in the stirred reactor 401 moves through the length of the reactor essentially as a result of the build-up of the polymer in the reactor bed, and not as a result of the stirring movement. This condition is ensured by the used vane construction which enables movement, but not a backwards or forwards movement of the layer. As a result of the stirring, the polymer particles in the layer adjacent to the extraction separation device are fed out through the extraction barrier opening which can be made of variable size and position using a number of devices to maintain different levels of polymer solids f in the reactor.

Dams, if used, can be attached to the drive shaft 405 by

with the help of drag rings or attached to the reactor walls and is advantageously oriented so that the top of the dam essentially coincides with the layer orientation during movement. This enables overflow along the entire length of the dam's upper part. However, the dams can also be oriented horizontally if this is desired. Other types of separation can be used instead of dams to prevent significant back-mixing between two or more of the sections in the reactor. For example, thin-walled partitions attached to the drive shaft 404 can be used, which fill the cross-section of the reactor and which are provided with one or more holes.

The polymer particles that pass through the withdrawal separator fall into a polymer collection tank 403. The discharged polymer solid can be treated with additives and melt extruded in a conventional manner, or the solid can be removed without any significant pressure drop in such a way that the solid is melted in the vessel 403 and where it is obtained molten polymer is treated with retarders and additives and freed of volatile constituents while the polymer is still in a molten state, after which the polymer is finished in a conventional manner into a commercial product.

Fig. 1 and 5 show in detail the reactor 401 in Fig. respectively. 4 and 6. It can be seen that the interior of the reactor 101 comprises a horizontal polymerization zone 105 divided into four individually adjustable polymerization sections 167 - 173 separated from each other

by means of dams 110 - 114, and where these dams extend somewhat upwards above the center point of the reactor and are oriented so that their upper surfaces will lie approximately in line with the polymer bed surface during agitation. In a preferred embodiment

the dams 110, 112 and 114 are constructed with such a height that the polymer layer fills approx. half the volume of the reactor. When the solid polymer exceeds the dam height, it falls into it

adjacent section and is moved in the direction of the lining device.

In a manufacturing method where it is desirable to operate with two

or several gas compositions (different hydrogen concentrations) as well as at different section temperatures, all the separation devices are constructed as indicated above except that one or more separation structures divide the reactor into chambers with different gas composition ions. The shell structures are thin-walled partitions which extend upwards and fill the entire cross-section of the reactor and are provided with an opening arranged below the level of the polymer layer for transport of solid polymer.

In this way, gas mixing between the chambers is controlled. When operating a reactor where different gas compositions are used, the individual chambers must be provided with separate reactor gas return treatments, as well as returns, and. may be provided with separate hydrogen and monomer refreshment devices.

In general, the separation structure is designed to prevent a significant mixing of the steam between the individual chambers, however, in a form of delivery where different hydrogen concentrations are used, the steam is deliberately mixed by passing steam from a chamber with a low hydrogen concentration to a chamber with a high hydrogen concentration and adding refreshment monomer essentially for the chamber with low hydrogen concentration and refreshment shy dr and one essentially for the chamber with high hydrogen concentration.

The interior of the reactor is provided with a rotating vane drive shaft 104 which extends longitudinally through the entire reactor 101, on which shaft are attached vanes which extend transversely from the shaft and form a small clearance between the inner wall of the reactor 110 for to ensure a sufficient layer mixture at the reactor wall. The vanes are preferably flat to maximize the layer movement for a given rotational speed and preferably two vanes are used per paddle wheel." The width of the paddles is such that there are between four and twelve paddle wheels (8 - 24 paddles) present in a reactor section with a length of about 1 m. The orientation of paddles on adjacent paddle wheels is about 90°. The paddles are designed to minimize any forward or backward movement of the bed during agitation and driven by the motor 102 at such a speed that the entire polymer bed in the reactor is given a slow and steady overturning. The speed of rotation of the paddle wheels should be sufficiently fast to bring about the desired heat and mass transfer between liquid, solid and gas, but not so quickly that the finer parts of the polymer layer are thrown up in large quantities in the space above the layer.

This means that the rotation speed is 5 - 30 rev/min, so that the integrity of the layer is maintained.

The space that follows the removal separation device and above the collection vessel is likewise provided with one or more corresponding paddle wheels 120, the number of which will depend on the amount of material removed. However, other extraction devices can also be used that can replace the extraction locking device, for example openings that are arranged in the end surface or on the side.

A number of catalyst and coolant inlets can be used in the reactor 101, and one or more pairs of catalyst and coolant inlets can be used in each reactor section 167 - 173. The catalyst and coolant inlets are preferably constructed so that the catalyst and coolant are distributed approximately at the same place on the upper part of the stirred layer. Such an introduction of the catalyst and the cooling liquid, combined with the slow movement, has been found to give a more uniform polymerization and prevents local coalescence of the polymer layer and consequently reduces the number of melted polymer plugs, which makes the operation of the reactor easier.

For a way of carrying out polymerization in the reactor, it is advantageous to arrange separately controlled addition of catalyst components and cooling liquid in the different sections, for example by means of valves. Such separately controlled addition in the reactor sections 167 - 173 enables separate control of the polymer in the season's temperature and the polymer production rate in the different sections and can be used to vary and control the molecular weight and particle weight distribution in the polymer.

The recirculation steam containing polymerisable monomer or monomers, as well as possibly hydrogen, is introduced through the recirculation steam line 156 to the recirculation steam inlets 175 - 181 at a rate adjusted to prevent fluidization of the bed. The rate at which the recirculating vapors or gases are introduced into the various sections 167 - 173 can be controlled by means of the valves 191 - 197, and such control can be used to assist in varying the polymerization temperatures and polymer production rates in the sections. .

In an important embodiment of the method using the described reactor, the polymerization temperature in one or more of the sections is maintained at a value different from

the temperature in a second section or sections (two-temperature operation or multi-temperature operation), and it is advantageous to vary the concentration of some or all of the catalyst components introduced into the different sections. The particle size distribution and molecular weight distribution can be advantageously influenced in this way. This can be achieved by varying the catalyst inputs to the individual sections. Even when operating at one temperature, it may be advantageous to feed one or more of the sections with the catalyst components in different concentrations than the catalyst components introduced into another section(s).

The overall reactor temperature range for the polymerization is dependent on the particular monomer being polymerized and the desired commercial product, as will be well known to one skilled in the art. In general, the temperature range will vary between approx. 40°C and up to the softening temperature of the layer. The total polymerization pressure is composed of the pressure for the polymerizable monomer, the vapor pressure for the cooling liquid and the pressure for any hydrogen used, and such a total pressure typically varies from atmospheric pressure to approx. 42 kg/cm 2. The individual partial pressures of the components which make up the total pressure determine the rate at which polymerization takes place, the molecular weight and the molecular weight distribution of the polymer to be produced. The polymerization temperature is controlled in a manner well known to a person skilled in the art.

False end plates which, due to the mechanical construction of the reactor 101, have been fitted into this are shown as 124 and 126.

In fig. 2 shows a section of the reactor 101 in fig. 1, taken along the line 2-2 in fig. 1. The drawing shows a 90° orientation of the blades on adjacent impellers, the adjustable discharge opening 218 in the discharge barrier device 216. Furthermore, the orientation of the dam 214 and the polymer layer in the reactor 201 is shown, as well as the direction of movement of the blades with regard to the layer orientation.

Fig. 3 shows a section of the reactor 101 in fig. 1 taken along the line 3-3 in fig. 1. Also shown is the discharge stop device 316 and the discharge opening 318 therein, as well as the direction of movement of the vanes with respect to the discharge stop opening 318 and the orientation of the polymer layer.

The described apparatus and method can be used for the polymerization of polymerizable monomers that are polymerizable below the softening point of their polymeric forms and include ethylene, propene, 4-methyl-pentene-1, butene-1, vinyl chloride, butadiene, styrene, and mixtures of such monomers. Spe-

particularly suitable is the polymerization of ethylene and propylene.

The dressing liquid used for temperature control is an easily volatile liquid that can be sprayed on the surface of the polymer layer in order to remove heat from the polymer layer by evaporation, and must therefore be inert to the monomer being polymerized, as well as inert to the catalyst components used in polymerization and have a high heat of vaporization compatible with

high volatility of the coolant in the reactor at the polymerization temperature. In general, alkanes can be used, such as propane, a butane, a pentane or a hexane or near-boiling mixtures thereof. The preferred quenching liquid for ethylene is isobutane or isopentane. It should be understood that in the case where the monomer to be polymerized is easily condensable, for example propene, the cooling liquid can be pre-liquefied monomer or a mixture of pre-liquefied monomer and an additional cooling liquid.

The rate of addition of the dressing liquid must be sufficiently low to keep the polymer layer dry, i.e. the partial pressure of the dressing liquid must be kept below its dew point, but still high enough to achieve the maximum cooling effect for the dressing liquid. In general, the dressing liquid will remove approx. 50% or more of the heat developed during the polymerization. For propene polymerization, it is advantageous that over 90% of the polymerization heat is removed by means of the cooling liquid. At a polymerization temperature of 93°C in the polymerization of ethylene, it is desirable that more than 70% of the heat of polymerization is removed using isobutane and that more than 50% of the heat is removed when using isopentane.

In general, the catalysts that are most useful in the described process are those that are very active and give a high yield based on the catalyst. Included in this group are co-catalysts composed of organometallic compounds of the metals within group IA, IIA and HIA of the periodic table, and catalysts that are based on compounds of the transition metals. Co-catalysts of aluminum alkyl compounds are particularly preferred and may be trialkyl aluminum or an alkyl aluminum halide, such as dialkyl aluminum chloride. The transition metal catalyst may be a compound of a metal of group IV or group V, such as a titanium or vanadium compound, a compound of a metal of group VI, such as chromium or molybdenum oxide, or may be one of the above-mentioned catalysts on

a magnesium-based support or on■ a support, such as alumina, silica or silica-alumina.

As previously mentioned, the preferred catalysts and co-catalysts are high-yield catalysts. By high-yield catalyst is meant catalyst and co-catalyst where it is not necessary to remove the remains of these from the product obtained by the method.

The preferred catalysts and co-catalysts for ethylene polymerization are a trialkyl aluminum co-catalyst with a catalyst which is a titanium compound supported on a magnesium-based support or chromium oxide on a support of alumina, silicon oxide or mixtures thereof. For propylene polymerization, it is preferred to use a dialkyl aluminum chloride co-catalyst and a catalyst which is an active titanium trichloride.

The following examples illustrate the invention.

EXAMPLE I

A supported titanium chloride catalyst was suspended in isoprene at a concentration of 30 mg/l and pumped continuously to the reactor at a rate of 300 ml/h. Triethylaluminum diluted with isoprene to 1000 mg/l was pumped in continuously at a rate to maintain the desired weight ratio of triethylaluminum/catalyst at 3:1 to 15:1. The ethylene was charged continuously at the rate of polymerization to maintain a pressure of 21 kg/cm 2 . A continuous gas stream in the amount of 8.5 l/h was removed from the reactor for chromatographic analysis. Hydrogen was added intermittently to maintain the hydrogen concentration in the reactor at 34 mole percent for polymer molecular weight control. The polymer layer in the reactor was kept at 71°c by continuous spraying with isopentane in a suitable amount on the polymer layer, which was stirred at 30 rpm. The evaporated isopentane was condensed and recycled. The non-condensed gas (2 - 10°C) was continuously recycled back into the bottom of the stirred polymer bed. The polymer layer level was maintained at the opening position in the retaining dam. The superfluid polymer dropped into a melter which was maintained at 177-205°C by a combination of polymerization heat and externally supplied electrical heat. The molten polymer that collected at the bottom was forced through a horizontal tube with a diameter of 1.9 cm and a length of 122 cm at a temperature of 205 - 260°C by means of the reactor pressure. Water was continuously injected into the polymer melt, at a rate of 10 ml/h, between the melter and the catalyst deactivator. The polymer melt was extruded from the catalyst deactivator through a 0.95 cm diameter orifice and was drawn through a water bath and cut up. The polymer was produced at a rate of 0.5 - 1.5 kg/h with a yield level of 100,000 g polymer/g catalyst. Physical properties of the polymer taken from the melter are shown in the following table I, and some properties of the polymer powder taken from the reactor are shown in table II.

EXAMPLE II

A carbon steel reactor with a diameter of approx. 60 cm and a length of 180 cm was used for continuous ethylene-propylene polymerization. The temperature was 82.8°C at one end of the reactor, 77.2°C in the center of the reactor and 82.8°C near the outlet end of the reactor, the total reactor pressure was 28 kg/cm . The ethylene was fed into the reactor at a rate of 9.33 kg/h and propylene was added at a rate of 0.13 kg/h. The recirculation gas rate was 64.8 l/min and the recirculation rate of the coolant, isopentane, was 1.1 Vmin. The supported titanium catalyst was added in an amount of 0.3 g/h as a dilute suspension in isopentane. The quantity of added suspension was 11.4 l/h. Triethylaluminum co-catalyst was added in a solution in isopene at a rate of 35 ml/h at a concentration of 0.025 g triethyleneamine/ml.

Gas analysis of the recirculating reactor gas was continuously performed and typical values were: hydrogen, 37 mol%; ethane, 0.3 mol%; propene, 1.1 mol%; isopentane, 1 mol % and ethylene, 60.6 mol %.

The product's melt index was 0.58 g/10 min.

EXAMPLE III

The ethylene was polymerized in the same way as described in example I. The catalyst used was 2.0% by weight chromium trioxide on

"W.R. Grace #952 Si02". The catalyst was calcined at 650°C with dry oxygen for 12 hours. The catalyst, triisobutylaluminum and ethylene were continuously added to the reactor at 99°c and a pressure of 21 kg/cm . Hydrogen was charged as needed to maintain 35 mol% H2 in the reactor. The molar ratio of Al(i-Bu)^/CrO^ was 3. The polymer yield calculated on catalyst was 4600 g/g. The polymer was removed continuously as a melt and exhibited the following physical properties:

EXAMPLE IV

Propylene was continuously polymerized in the gas phase using an active titanium chloride catalyst with diethyl aluminum chloride as co-catalyst under the conditions shown in Table IV. Propylene also served as a cooling fluid for removing heat. The polymer was intermittently removed as a powder through a lock chamber fitted with two ball valves connected to the withdrawal end of the reactor.

EXAMPLE V

Titanium chloride catalyst on a support and triethylaluminum catalyst were used in the same way as described in example 1 using approx. 3 mol% propylene in the reactor gas for copolymerization with ethylene. Liquid propylene was added continuously at a rate of 30 ml/h, maintaining its concentration of 3 mol% in the reactor gas. The copolymer was removed from a lock chamber fitted with two ball valves at the outlet end of the reactor in the form of a powder. The catalyst and.co -the catalyst was deactivated by treating the copolymer with steam at 121° C. A copolymer inhibitor package was added and the resulting product melt-extruded in the normal manner to give pellets. The conditions for two such trials are shown in Table V below.

EXAMPLE VI

Titanium chloride on a support and triethyl aluminum co-catalyst were used for the polymerization of ethylene in the same manner as shown in Example I. The polymer was removed in the form of a powder through the sluice provided with two ball valves. The catalyst was deactivated by treatment with steam at 121°C. A polymer inhibitor pack was added and the resulting mixture melt-extruded in the usual manner to give product in the form of pellets. Polymerization conditions and properties of the product obtained are shown for different trials in the following tables VI and VII.

EXAMPLE VII

The propylene was polymerized in substantially the same manner as described in Example I. The recycle gas and the cooling liquid were propylene. The temperature in the melter was 177°C, while the catalyst deactivation section was operated at 205°C. An active titanium chloride catalyst (33 mg) with diethyl aluminum chloride co-catalyst (77 mg), molar ratio Al/Ti = 3, was introduced into the reactor every half hour. Hydrogen was introduced as needed to maintain 2.9 mol% in the reactor gas. The reactor temperature was maintained at 71°C, and the reactor pressure was set at 21 kg/cm^ by regulating the temperature in the recirculation condenser to approx. 49°C. A polymer yield calculated on the catalyst of lOOOO g/g was obtained. The polymer was removed from the reactor as a melt. The polymer exhibited a melt flow rate of 16.4 g/10 min at 230°C at a load of 2060 g. n-hexane (68°C) extractables were 4% by weight.

EXAMPLE VIII

The ethylene was polymerized in the same manner as described in Example I with the exception that in this case the two sections of the reactor were kept at different temperatures. The first reactor section was operated at 71°C, while the second reactor section was operated at 99-110°C. This was made possible by varying the amount of added isopentane, as a cooling agent, to each of the sections. The catalyst used was a titanium compound on a support, and a triethyl aluminum co-catalyst was added in the weight ratio co-catalyst:catalyst = 3:1. The reactor pressure was set at 21 kg/cm and the hydrogen concentration was kept at 40 mol%. A polymer yield of 62 g polymer/g catalyst was obtained. The polymer melt index was measured to be 5.5 with a MF^Q/MF^ of approx. 40 and with a spiral current of 45.7 cm. A polymer with the same melt index prepared at single temperature conditions exhibited a MF^/MF^ value of approx. 34 and exhibited a spiral flow of approx. 41 cm.

Spiral flow is an empirical method for determining the processability of a polymer by measuring the length of flow in a particular form under particular pressure and temperature conditions. The longer the spiral flow, the better the processability of the polymer.-

The following examples illustrate the invention using

a reactor divided into two chambers.

EXAMPLES IX-XI

A carbon steel reactor with a diameter of approx. 60 cm and a length of approx. 180 cm was used. The dressing fluid was isopentane. The catalyst was a titanium compound with a magnesium compound as carrier, and the catalyst was triethylaluminum added in the weight ratio co-catalyst:catalyst approx. 6:1, and the catalyst was added in an amount of approx. 0.2 g/h. The production rate was approx. 60 kg polymer/h. The catalyst and co-catalyst were added separately to the first zone and the product was removed from the second zone of the reactor, the zones being separated from each other by a separation structure as previously described.

The melt indices and intrinsic viscosities were respectively measured according to ASTM D 1238-72 (Cond. E) and D 2857. The weight ratio of the average molecular weight to the number average molecular weight, Mw/fln, was measured by gel permeability chromatography.

Examples IX, X and XI shown in Table VIII show the effect on molecular weight of operating the two chambers at different hydrogen levels, compared to operating the reactor at a single hydrogen level. Example IX represents a product produced at a single hydrogen level o at a total pressure of 28 kg/cm 2 and where polymerization is carried out at 99°C and with 25 mol% hydrogen in the recirculating gas. The product obtained has an intrinsic viscosity, (VJ), of 2.0 dl/g, a melt index of 0.97 g/10 min and a relatively narrow molecular weight distribution Mw/Mn = 6. In a similar way when the reactor was operated at 99°C and with 5 mol % hydrogen, the product eg en skapene = 1.0 2 dl/g, melt index = 28.6 and Mw/Mn = 6. When the reactor was operated at 99°C and 57 mol % hydrogen, the product properties were (^) = 4.5 dl/g. At the latter high molecular weight, the melt index measurements are difficult and therefore not carried out.

In Example X in Table VIII, the results are given for polymerization where the first chamber in the reactor was kept at approx. 99°C and 26 mol% hydrogen, while the second chamber was kept at 99°C and 12 mol% hydrogen, and the relative polymer production in the first and second chambers was in the weight ratio 42:58. The product withdrawn from the reactor had an intrinsic viscosity of 2.1 dl/g and a melt index of 0.68. However, the measured Mw/Mn for the product had risen to approx. 9 with consequent improved rheological properties.

Example XI in Table VIII shows the results of a polymerization where the first chamber in the reactor is operated at 99°C and 57 mol% hydrogen, and the second chamber is operated at 99°C and 5 mol% hydrogen. By adjusting the relative weight ratio of the materials formed in the first and second chambers to 70:30, the product discharged from the reactor had an intrinsic viscosity of 1.99 dl/g, a melt index of 0.67 g/10 min. However, the measured Mw/Mn had risen to approx. 12. The changes in the rheological properties as a result of operating the reactor at different hydrogen levels are shown by the lowering of the apparent viscosity at 5 s<->^, 5.5 vs. 5.2 x 10 4 poise, an increase in the shear rate for incipient oscillating current, 650 vs. 1560 s~^~, and an increase in the shear rate for melt fracture [y(MF)], 2400 vs. 6900 s-1.

Claims (6)

1. Continuous process by dam<p>phase polymerization of at least one vaporizable, polymerizable monomer such as ethylene, propylene, butene-1, 4-methyl-l-pentene, butadiene, styrene or vinyl chloride, which method comprises polymerizing the monomer, introduced in vapor form, in a vapor phase in at least one elongated polymerization zone in the presence of a catalyst in a mechanically stirred , superfluidized powdery polymer layer in the zone, as well as extracting an off-gas stream comprising monomer vapor from the zone, characterized in that a feed stream comprising at least one monomer in vapor form is introduced below the surface of the layer of powdery solid polymer in the polymerization zone and in its upper part introducing an easily evaporable coolant such as ^"Cg aliphatic hydrocarbons, which coolant is sprayed onto the surface of the layer to regulate the polymerization temperature by evaporative cooling in the polymerization zone, performing an exhaust gas comprising monomer vapor and coolant vapor, which vapors are condensed isobarically to give a coolant recirculation stream and a gaseous recirculation stream comprising monomer vapor, which coolant recirculation stream, optionally with at least one catalyst component or additional fresh coolant, is returned to the upper part of the polymerization zone and where the gaseous recirculation stream is fed back to the polymerization zone together with newly added vaporized monomer. 2. Method according to claim 1 characterized in that ethylene or a mixture of ethylene and propylene is used as monomer and that isopentane is used as coolant. 3. Method according to claim 1, characterized in that propylene is used both as monomer and coolant. 4. Polymerization reactor for carrying out vapor phase polymerization of a polymerizable monomer in vapor form, comprising a cylindrical, longitudinally extended horizontal reactor, a centrally arranged rotatable shaft extending longitudinally through the entire reactor, to which shaft is attached a number of adjacent and circularly displaced stirring devices which extend transversely inside the reactor and at a small distance from the inner surface of the reactor, as well as drive devices for the aforementioned shaft, one or more inlets for introducing a feed gas flow comprising monomer vapor to the polymerization zone in the reactor, one or more outlets for removing off-gas flow comprising monomer vapor from the polymerization zone in the reactor, as well as means for removing powdery, solid polymer from the reactor, characterized in that the reactor (101) contains at least one horizontal polymerization zone (105), that the stirring devices are flat, rectangular vanes (106, 108, 132), one or more inlets (175, i77, 179, 181) separated along the bottom part of the reactor (101) for introducing the feed gas stream of monomer vapor to the polymerization zone (105), one or more inlets arranged in the longitudinal direction of the reactor (123, 125, 127, 129) for introducing catalyst to the polymerization zone (105), one or more inlets separated along the upper part of the reactor (153, 155, 157, 159) for introducing cooling liquid to the polymerization zone, one or more outlets separated along the upper part of the reactor (183, 185, 187, 189) for removing an exhaust gas stream consisting of monomer vapor and coolant vapor from the polymerization zone (105), a discharge zone (107) containing at least one vane wheel (120), which discharge zone (107) is formed by a separation device (116, 216) at one end of the reactor, which separator (116, 216) fills the entire internal cross-sectional area of the reactor (101) and is provided with an opening (118, 218) in the upper part thereof to allow the passage of gas and a regulated movement of that powder shaped solid polymer flow direction between the polymerization zone (105) and the discharge zone (107), which zone (107) contains an outlet (103) connected to devices for removing the powdered polymer from the reactor (101) without significant pressure drop. 5. Apparatus according to claim 4, characterized in that the polymerization zone (105) contains at least one overflow ning partition (110, 112, 114) to form at least two temperature controllable <p>polymerization sections (167, 169, 171, 173) therein. 6. Apparatus according to claim 4 or 5, characterized in that the reactor (101, 401) contains at least two adjacent polymerization zones (105, 405), -separated by means of a separation device (128, 428) which fills the internal cross-sectional area of the reactor (101 , 401), which separation device (128, 428) in the lower part is provided with an opening for the transfer of powdered solid between the polymerization zones (105, 405).