JPH02135205A - Method for reduction of sheeting when alpha-olefin is polymerized - Google Patents

Abstract

PURPOSE: To obtain a polymer while reducing sheeting by continuously passing a monomer, a comonomer, an inert gas and hydrogen to a fluidized bed reactor using Ti catalyst under a reaction condition, partially extracting this flow, mixing it with a feed gas followed by cooling, and then circulating it.

CONSTITUTION: A Ti catalyst or other catalyst tending to cause a sheeting during polymerization is supplied to the reaction band 12 of a fluidized bed reactor 10 from a storage tank 16, and a gas feed flow 42 consisting of monomer, comonomer, inert gas and hydrogen is continuously passed into the fluidized bed 10 under a reaction condition. A circulating flow consisting of polymer product, unreacted gas, and solid particle is extracted, mixed with the gas feed flow 42, introduced into a heat-exchanger 26 to cool it, then returned to the base 20 of the fluidized bed reactor 10, and directed into the reaction band 12 through a distributing plate 22, whereby α-olefins are polymerized while reducing the sheeting.

COPYRIGHT: (C)1990,JPO

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for reducing sheeting when polymerizing α-olefin, and more particularly to a method for reducing sheeting when polymerizing ethylene. Ru.

BACKGROUND OF THE INVENTION As is well known to those skilled in the art, low pressure high density or low density polyethylene is produced by a fluidized bed process using several catalysts to produce a full range of low density and high density products. Can be conveniently supplied at present. The appropriate selection of catalyst to utilize will depend in part on the type of end product desired (i.e., high density, high density, extruded plate, a BU grade resin) and other criteria, and generally No. 30, published in US Pat. No. 4,532,311.

Generally, the catalyst is introduced together with the polymerizable feedstock into a reactor with an enlarged section above the straight side section. The cycle gas enters the bottom of the reactor and passes through a gas distribution plate upwards into the fluidized bed located in the straight side section of the vessel. The gas distribution plate serves to ensure proper gas distribution and to support the resin bed when gas flow ceases.

The gas leaving the fluidized bed entrains the resin particles.

Most of these particles escape as the gas passes through the expansion section and reduces its velocity.

Unfortunately, the use of catalysts of the type shown in the above-mentioned US patent as Type IV catalysts as well as palladium-based catalysts has limited the use of sheeting in the production of polyolefins by polymerizing alpha-olefins in a fluidized bed process. have a tendency to cause

These types of catalysts (ie, Type IV catalysts) are used to satisfy a variety of end uses for ethylene resins, such as thin film, injection molding, and rotomolding applications. However, attempts to produce ethylene resins using type IV catalysts or vanadium-based catalysts supported on porous silica supports in fluidized bed reactors have not been completely satisfactory from a practical point of view. I can't do it. This is mainly due to the presence of [sheets] in the reactor after short periods of operation.
-J is formed. This "sheet" can be characterized as comprising a fused polymeric material.

These sheets vary widely in size but are similar in most respects. These are generally about 1/4 thick
~1/2 inch and about 1-5 feet long, with some samples being much longer. These have a width of about 3 inches to 18 inches or more. These sheets are
It has a core composed of a fused polymer oriented in the longitudinal direction of the sheet, the surface of which is covered with particulate resin fused to the core. , the edges of the sheet may have a hair-like appearance due to the strands of fused polymer.

After a relatively short period of time during polymerization, sheets 1~ begin to appear in the reactor, and these sheets block the product discharge system, leading to shutdown of the reactor.

It can therefore be seen that there is a current need to improve the polymerization techniques required to produce polyolefin products using titanium-based catalysts in fluidized bed reactors.

[Problems to be Solved by the Invention] Therefore, an object of the present invention is to provide a method for substantially reducing or eliminating the degree of sheeting that occurs during low-pressure fluidized bed polymerization of α-olefins using titanium-based compounds as catalysts. It is about providing.

These and other objects will become more apparent from the following description with reference to the accompanying drawings.

SUMMARY OF THE INVENTION Broadly speaking, the present invention provides a method for polymerizing α-olefins in the reaction zone of a fluidized bed reactor using titanium-based catalysts or other catalysts that have a tendency to produce sheeting during polymerization. During this process, a gas feed stream consisting of monomers, monomers, inert gas, and hydrogen is continuously passed through the fluidized bed under reaction conditions and sheet-forming conditions to remove polymer product, unreacted gas, and solid particles from the reaction zone. A method for polymerizing α-olefins, which comprises removing a circulating stream consisting of a comonomer, a comonomer and an inert gas, cooling the circulating stream and circulating the cooled circulating stream to the reaction zone. introducing said gas feed stream consisting of hydrogen into said circulating stream consisting of unreacted gas and solid particles at a point prior to cooling said circulating stream; and then cooling said circulating stream and said gas feed stream. and reducing or substantially eliminating sheeting in one reactor by directing the reaction mixture into the reaction zone.

The magnitude of electrostatic forces generated by impurity addition to a fluidized bed polymerization reactor is highly dependent on the point of impurity addition to the cycle. The point of impurity addition that causes the largest electrostatic response lies directly in the stagnation region of the fluid in the fluidized bed. If impurities are injected into this cycle far away from the fluidized bed (eg, upstream of the circulating gas cooler), the electrostatic charging effect that occurs is significantly attenuated. According to the invention, therefore, by locating the monomer, comonomer, nitrogen and hydrogen feed streams to the process (which optionally contain electrostatically generated impurities) upstream of the circulating gas cooler, Static charging is reduced. Reducing static charging in a fluidized bed results in better reactor performance by reducing the risk of sheet and junk formation, which is often a direct result of static electricity. The present invention minimizes sheeting and therefore eliminates the downtime required to remove these sheets.

With particular reference to the accompanying drawings, a conventional fluidized bed reaction system for polymerizing alpha-olefins comprises a reactor 10 consisting of a reaction zone 12 and a rate reduction zone 14.

Reaction zone 12 comprises a bed of increasing polymer particles, produced polymer particles and a small amount of catalyst particles, which bed contains a continuous stream of polymerizable and modifying gas components as make-up gas and cycle gas flowing through the reaction zone. Fluidized by currents. To maintain a usable fluidized bed, the mass gas flow rate to the bed is generally maintained above the minimum flow rate required for fluidization, preferably from about 1.5 to about 10 times Gmf, more preferably about It ranges from 3 to about 6 times. Gmf is used as an accepted symbol for the minimum gas flow rate required to achieve fluidization [C,Y.

Wen and Y. H. Nee [Mechanics of Fluidization],
Chemical Engineering Process Symposium Series, Volume 62, Pages 100-111 (1966
) ].

It is highly desirable that the bed always contain particles to prevent the formation of local "hot spots" and to entrain and distribute the particulate catalyst throughout the reaction zone. Upon starting,
The reactor is generally filled with a base of particulate polymer particles before starting the gas flow.

These particles can be the same as the polymer to be produced in Step 1, or they can be different. If different, these are collected together with the desired product polymer particles as the first product. Eventually, a fluidized bed of desired polymer particles replaces the starting bed.

Suitable catalysts used in the fluidized bed are preferably stored until use in reservoir 16 under a gas seal, the seal gas being a gas inert to the storage material, such as nitrogen or argon.

Fluidization is achieved by high flow rate gas circulation through the bed, typically on the order of about 50 times the make-up gas feed rate. A fluidized bed has the general appearance of a dense mass of usable particles in a free swirl that can be formed by the permeation of gas through the bed.

The pressure drop across the bed is equal to or slightly greater than the mass of the bed in cross-sectional area tJl'fi. This therefore depends on the geometry of the reactor.

Makeup gas is fed to the bed at a rate equal to the rate at which particulate polymer product is pumped. The makeup gas composition is determined by a gas analyzer 18 located above the bed. A gas analyzer measures the composition of the gas being circulated and the makeup gas composition is adjusted accordingly to maintain a near steady state gas composition within the reaction zone.

To ensure complete fluidization, part or all of the recycle gas and optionally make-up gas is returned to the reactor at the base 20 below the bed. A gas distribution plate 22 located above the return point ensures proper gas distribution and supports the resin bed when the gas flow stops.

The portion of the gas stream that does not react within the bed constitutes the recycle gas, which is preferably removed from the polymerization zone by being transferred above the bed into a velocity reduction zone 14 in which the entrained particles are You will be given the opportunity to fall back into the floor.

The circulating gas is then compressed by a compressor 24, passes through a heat exchanger 26, where the heat of reaction is removed, and then returned to the bed. Due to the constant removal of the heat of reaction, there appears to be no appreciable temperature gradient at the top of the bed.

A temperature gradient exists as a layer of about B to 12 inches at the bottom of the bed, with a temperature between the temperature of the incoming gas and the temperature of the remainder of the bed. The bed thus serves to almost instantaneously adjust the temperature of the circulating gas above the bottom layer of this bed zone to match the temperature in the remainder of the bed, thereby maintaining a nearly constant temperature under steady state conditions. was observed. The recycle stream is then returned to the reactor at its base 20 and distributed through the distribution plate 22.
to the fluidized bed. Compressor 24 can also be installed downstream of heat exchanger 26.

Hydrogen can be used as a chain extender in conventional polymerization reactions of the type contemplated in this invention.

If ethylene is used as the nanazuma, the hydrogen/ethylene ratio used is from about 0 to about 2 per mole of nanazuma in the gas stream.
．． Varies in the range of 0 moles of hydrogen.

According to the invention, a feed stream of hydrogen, nitrogen and co-monomer is introduced into the gas cycle stream before the point where the cycle gas stream enters the heat exchanger 26, for example via path 42. Introduce.

Any gas that is inert to the catalyst and reactants can also be present in the gas stream. The promoter is dispenser 28
is added to the gas cycle stream upstream of the connection with the reactor, such as via line 30.

As is well known, it is essential that fluidized bed reactors operate at temperatures below the sintering temperature of the polymer particles.

That is, an operating temperature lower than the sintering temperature is desirable to ensure that sintering does not occur. Preferably, an operating temperature of about 90-100°C is used to produce a product with a density of about 0.94-0.97, while about 0.91 A humidity of about 75-95°C is suitable for products with a density of ~0.94.

Fluidized bed reactors generally operate at pressures up to about 1000 psi, preferably between about 150 and 350 psi, with operation at higher pressures in this range being preferred for heat transfer. This is because an increase in pressure increases the unit volume heat capacity of the gas.

Catalyst is injected into the bed at a rate equal to its consumption at point 32 above distribution plate 22. The catalyst is introduced into the bed using a gas that is inert to the catalyst, such as nitrogen or argon.

An important feature is the injection of catalyst at a point above the distribution plate 22. Since the commonly used catalysts are very active, injection into the region below the distribution plate will initiate polymerization there, eventually leading to blockage of the distribution plate. Instead,
Injection into the usable bed helps distribute the catalyst throughout the bed and tends to eliminate the formation of localized areas of high catalyst concentration that can lead to the formation of "hot spots."

Under a given set of operating conditions, the fluidized bed is maintained at a substantially constant height by withdrawing a portion of the bed as product at a rate equal to the rate of formation of particulate polymer product.

Since the rate of heat evolution is directly related to product formation, the measurement of the temperature rise of the gas to the reactor (difference between inlet and outlet gas temperatures) is determined for the rate of particulate polymer formation at a constant gas velocity. It becomes a factor.

The particulate polymer product is preferably distributed at locations 34 on the distribution plate 22.
Or extract it from a place close to it.

Conveniently and preferably, the particulate polymer product is withdrawn via subsequent operation of a pair of timing valves 36 and 38 forming a separation zone 40. valve 3 while valve 38 is closed.
6 is opened to release a plug flow of gas and product into zone Vi 40 between this zone and valve 36, and then valve 36 is closed. Valve 38 is then opened to supply product to the external collection zone, and after delivery valve 38 is closed to await the next product collection operation.

Finally, the fluidized bed reactor should be equipped with an adequate exhaust system.
Evacuate the floor during startup and shutdown. The reactor does not require the use of stirring means and/or wall scraping means.

The reaction vessel is generally made of carbon steel and conditioned to the operating conditions described above.

Polymers that are primarily relevant to the present invention and which give rise to the above-mentioned seeding problems in the presence of titanium or vanadium catalysts are linear homopolymers or large mole % (≧90
%) of ethylene and a small mole % (<10%) of one or more C3-C8 alpha-olefins. The C3-C8 alpha-olefin must not have any branching on any carbon atom closer than the quaternary carbon atom.

Preferred C3-C8 α-olefins are propylene, butene-
1, hexene-1 and octene-1.

This description is not intended to preclude the use of the present invention for α-olefin homopolymer and copolymer resins in which ethylene is not present.

Homopolymers and copolymers have densities ranging from about 0.97 to 0.91. The density of the copolymer varies from 03 to C8 copolymerized with ethylene at a given melt index level.
It is mainly regulated by the amount of comonomer. That is, as the amount of comonomer added to the copolymer is gradually increased, the density of the copolymer is gradually reduced. The amount of each type of 03-C8 comonomer required to obtain the same result varies by a factor of 7 under the same reaction conditions. In the absence of comonomers, ethylene homopolymerizes.

The melt index of a homopolymer or copolymer reflects its molecular weight. Polymers with relatively high molecular weights have relatively high viscosities and low melt indexes.

EXAMPLES Having described the general nature of the invention, specific embodiments of the present invention will be further illustrated by the following examples. However, it will be understood that the present invention is not limited to these examples, and that various modifications can be made.

Examples 1 and 2 below are examples of opening operations, and were carried out in the fluidized bed reactor shown in the attached drawings, except that gas supply was a conventional method.
That is, the gas feed was introduced into the system via a route that fed into the bottom of the reactor after the heat exchanger.

Example 1 At operating conditions designed to produce a thin film plate low density ethylene copolymer product having a density of 0.918(]/CC, a null 1~ index of 1.OdMmm and a sticking temperature of 140°C. , the fluidized bed reactor was started. The reaction was initiated by feeding the catalyst into the reactor prefilled with a bed of granular resin similar to the product to be produced. The catalyst was A mixture of titanium chloride, 8.5 parts of magnesium chloride, and 14 parts of tetrahydrofuran was mixed with 100 parts of Davison grade 952 silica, which had been dehydrated at 800° C. and treated with 4 parts of triethylaluminum before deposition. 35 after deposition.
Activated with l-n-hexylaluminum.

The reactor and resin bed were brought to an operating temperature of 85° C. and nitrogen was circulated through the resin bed to purge impurities before starting the catalyst feed. The concentrations of ethylene, butene, and hydrogen are each 5
They were set at 3%, 24% and 11%. The cocatalyst was fed at a rate of 0.3 parts of triethyl aluminum per part of catalyst.

Reactor startup was normal. After producing the product for 29 hours and equaling 6,5 times the weight of the fluidized bed, the temperature change is 1-2 °C above the bed temperature at a height of 1 part 2 reactor diameters above the gas distribution plate. It was observed using a thermocouple installed inside the reactor wall. Conventional experience has shown that such temperature changes positively indicate that a sheet of resin is forming within the fluidized bed. At the same time, the bed voltage (measured using an electrostatic voltmeter connected to a 1/2 inch diameter spherical electrode placed 1 inch from the reactor wall at a height of 1 part 2 reactor diameters above the gas distribution plate) ) is +5 from the measured value of approximately +1500 to +2000 volts.
It increased to a reading of over 000 volts and then decreased to +2000 volts over a period of 3 minutes.

The temperature and voltage changes continued for approximately 12 hours and increased in frequency and amplitude. Over this period, sheets of fused polyethylene resin began to coalesce into the resin product. The occurrence of sheeting became more severe, the temperature changes rose to about 20°C higher than the bed temperature and remained high for a long time, and the voltage changes became more frequent. The reactor was stopped due to the occurrence of sheeting.

Example 2 The fluidized bed reactor used in Example 1 is started up and operated to produce a linear low density suitable for extrusion or rotomolding and having a density of 0.934, a melt index of 5 and a sticking temperature of 118°C. Manufactured Ejirenko Bolima. 28 part 1
The reaction was carried out by feeding a catalyst similar to that in Example 1, but activated with . I started it. The reactor and resin bed were brought to an operating temperature of 85° C. and purged of impurities with nitrogen before starting the catalyst feed. Ethylene (52%), butene (14%) and hydrogen (21%) were introduced into the reactor. The cocatalyst triethylaluminum was added at 0.0% per part of catalyst.
Supplied in 3 parts. The reactor was operated continuously for 48 hours, producing resin equal to nine times the amount of resin contained in the bed during this period. After this 48 hour smooth operation, sheets of fused resin began to emerge from the reactor with normal granular products. At this point, the voltage measured at a height one part two reactor diameters above the distribution plate averaged +2000 volts and ranged from O to +10,000 volts, while the skin thermocouple at the same height From temperature〉15
℃ showed a high change. Two hours after the first sheets were observed in the product from the reactor, it was necessary to stop feeding the catalyst and cocatalyst to the reactor to reduce the rate of resin production. This is because the sheet blocked the resin discharge system. After 1 hour, the catalyst and cocatalyst feeds were resumed. Formation of sheets continued and after 2 hours the feed of catalyst and cocatalyst was stopped again and the reaction was stopped by injecting carbon oxide. The voltage at this point was >12,000 volts, and the thermocouple temperature change continued until m was injected. In total, the reactor was operated for 53 hours and 10.5 bed volumes of resin were produced before the reaction was stopped for sheeting.

Example 3 Continuous polymerization of ethylene was maintained in a fluidized bed reactor. By feeding the catalyst and co-catalyst into the reactor, 0.918
A low-density copolymer in thin film plates with a density of (]/cm3 and a melt index of 2.Odg/min was prepared. The catalyst was composed of 5 parts TiCj.
DVICiC12 and 17th part! ~ lahydrofuran, deposited on 100 parts of Davison grade 955 silica, previously dehydrated at 600°C and treated with 5.5 parts of triethylaluminum before deposition,
And Shen Baojun was activated with 33 parts of tri-n-hexylaluminum and 11 parts of diethylaluminum chloride.

Triethylaluminum as cocatalyst is 40:1 A
j! :T! was fed in a sufficient proportion to maintain a molar ratio of . The fluidized bed was maintained at a temperature of 85°C. The concentrations of ethylene, butene, and hydrogen in the reactor are each 34 mol%,
They were 11 mol% and 8 mol%. The copolymer resin was periodically removed from the reactor to maintain a constant fluidized bed height within the reactor. The catalyst was fed directly into the fluidized bed and all other feeds were introduced into the gas circulation path upstream of both the heat exchanger and the compressor.

Water vapor of various rivers in nitrogen or oxygen were then simultaneously and continuously fed into the gas circulation path over several hours. The supply location was downstream of the compressor and upstream of the heat exchanger.

The rate of introduction of water or oxygen is given on a ppmw basis with respect to the rate of copolymer removal from the reactor. While introducing these
Both the circulating gas inlet temperature, measured below the fluidized bed, and the static voltage within the bed were monitored. A 1°C increase in inlet temperature showed a decrease in production rate of about 20%. The electrostatic voltage was measured by monitoring the voltage with a hemispherical Sudir probe installed in the fluidized bed at a position of 1 inch from the inner wall and 3 times the floor diameter of the distribution plate. Measurements of catalyst activity and electrostatic voltage are given below: Catalyst Activity Static Voltage Level Concentration Degree Change Impurity at Inlet Temperature Change in ppmw, °C Porto de 12
0 2.4 No change No change H2O4,
8+〇, 7° 50 H204, 1+〇, 4° 50 02 3.0 No change No change 02
7.8 +1.0' No change *Triethylaluminum was fed into the circulation path downstream of the heat exchanger.

Reactor operation remained smooth throughout these tests. This example shows that the introduction of impurity levels up to 7.8 ppmw created little or no static voltage when the impurities were introduced into the circulation path upstream of the heat exchanger.

Example 4 Again, continuous polymerization of ethylene was maintained in a fluidized bed reactor. By feeding the catalyst, co-catalyst and promoter to the reactor, a resin density of 0.946(]/cm3 and 9 parts g
/min flow index (190℃, 21.6k
A high-density copolymer with ( ) was produced.

The catalyst consisted of a mixture of 55 parts of VCj)3, 1.5 parts of diethylaluminum chloride, and 13 parts of tetrahydrofuran, which was deposited on 100 parts of pre-dehydrated Davison grade 953 silica at 600°C. . Triethylaluminum was fed in such a proportion as to maintain a molar ratio of AI1:v of 40:1. Trichlorofluoromethane is placed between the compressor and the heat exchanger at a ratio of 0.75:1.
of triethylaluminum. The temperature of the fluidized bed was maintained at 100°C. The concentrations of ethylene, hexene, and hydrogen in the reactor are each 73 mol%,
1 mol% and 1.6 mol%. Other fluidized bed operations were as in the previous example.

One concentration of water vapor and two concentrations of oxygen were then introduced into the reactor, each for several hours. These impurities were mixed with nitrogen and introduced into the cycle gas at a point immediately downstream of the compressor and upstream of the heat exchanger. As each of these impurities was being fed into the circulation path, catalyst activity and electrostatic voltage were monitored as described in the previous example. The results were as follows: Concentration impurity ppmw H204,0 025,0 029,0 Catalyst activity Degree of change in inlet temperature of electrostatic voltage level Change, °C Volts No change No change No change No change 10 No change 50 These impurities Reactor operation remained good during the feeding. The results show that impurities introduced upstream of the heat exchanger at levels up to 9 pI) mW, due to the different catalyst system and different resin properties than in the previous example, again have little or no effect on the electrostatic voltage. It shows that there is no.

Example 5 Continuous polymerization of ethylene was maintained in a fluidized bed reactor. By feeding the catalyst and cocatalyst into the reactor, 0.918
0 /cm3 density and 2. A thin film plate low density copolymer with a melt index of Odg/min was produced. The catalyst consisted of a mixture of 5 parts of T i Cj31/3A with 3 parts of C and 7 parts of M (JCj2 and 17 parts of tetrahydrofuran, which had been previously dehydrated at 600° C. and 5.5 parts of 1 treated with triethylaluminum
00 parts of Davison grade 955 silica and after deposition 33 parts of tri-low hexyl aluminum and 1
Activated with 1 part diethylaluminum chloride. The cocatalyst 1 to ethylaluminum is 30:1:1
! :Ti was supplied at a sufficient rate to maintain the molar ratio. The fluidized bed was maintained at 88°C. The concentrations of ethylene, butene, and hydrogen in the reactor are 37 mol% and 12 mol%, respectively.
and 9 mol%. The copolymer resin was periodically removed from the reactor to maintain a constant fluidized bed height within the reactor. The catalyst was fed directly into the fluidized bed and the raw feed was introduced into the gas circulation path upstream of both the heat exchanger and the compressor.

A stream of nitrogen saturated with water vapor was then fed to the reactor downstream of the compressor and upstream of the heat exchanger. The water addition rate is 20 parts per part of ethylene added to the circulation stream.
It was taken as the appearance of ppm of water. This water supply was carried out continuously for 2.5 hours, and no change in electrostatic voltage occurred within the fluidized bed over this period.

The electrostatic voltage was maintained at O volts during the period of water addition. 1 inch from the inner wall and 3 bed diameters from the distribution plate in the fluidized bed.
Static voltage was measured by monitoring the voltage with a hemispherical steel probe placed above the fold. The feed location of the saturated water stream was then moved to just downstream of the heat exchanger. The water addition to this position amounted to 81) t) m of water per m part of ethylene addition to the gas circulation. When water was introduced to this new location downstream of the heat exchanger, a negative static voltage of -250 volts immediately developed. Within 10 minutes of adding water downstream of the heat exchanger,
The temperature indicated by a thermocouple on the side wall of the polymerization reactor in the fluidized bed zone is up to 92°C, i.e. 4° below the bed temperature.
The temperature rose to ℃ higher. This measurement suggested sheet formation at this location on the wall within the fluidized bed.

Example 6 A copolymerization of ethylene and butene was maintained in a fluidized bed reactor. The resulting copolymer has a density of 0.918 (1/cm3 and 1
It was a thin film plate resin having a melt index of dol/min. The catalyst contains 5 parts of l'-i (,231/
3A12CL3 and 7 parts] M qCl! 2 To1721
i (7) 1-Lahydrofuran, which was first applied onto 100 parts of Guvin@955 silica).

The silica was pre-dehydrated at 600°C and treated with 5.7 parts of 1-helyethylaluminum before deposition, and activated with 32 parts of tri-lowhexylaluminum and 11 parts of diethylaluminum chloride after rough deposition. Ta. The catalyst triethylaluminum has an Aj! of 30:1. :rl molar ratio. The fluidized bed is 88
The temperature was maintained at ℃. The concentrations of ethylene, butene, and hydrogen in the reactor are 46 mol%, 16 mol%, and 14 mol%, respectively.
Expressed as mol%. Resin was periodically skimmed from the reactor to maintain a constant fluidized bed height within the reactor. The catalyst was fed directly into the fluidized bed and the raw feed was introduced into the recycle gas stream downstream of both the compressor and the heat exchanger.

Static voltage was measured in the fluidized bed by monitoring the voltage with a hemispherical steel probe placed one inch from the interior wall and one bed diameter above the distribution plate.

The water is then added to the ethylene feed at a rate of 0 to ethylene feed.
．． It was added in an amount of 6 ppm. This water addition produced an immediate electrostatic voltage response from O volts to 11600 volts within the fluidized bed.

The water addition point was then moved from downstream to upstream of the heat exchanger and the negative static voltage dissipated almost immediately to 0 volts.

Next, the water addition point was roughly fixed three times between the inlet and outlet of the heat exchanger. In each case of supplying water to the heat exchanger outlet, a negative voltage was generated, which immediately disappeared when water was supplied to the heat exchanger inlet. Water fed continuously to the heat exchanger inlet in a circulating flow for 3 hours at an amount of 8 ppm water per part of ethylene feed did not create a static voltage in the reactor.

Example 7 Using the same reactor producing the resin under the same conditions as in Example 6, the effect of the water supply point on the electrostatic voltage in another case was tested.

In this example, 0,31) p per part of ethylene feed
The water fed in a circulating stream to the heat exchanger outlet at a rate of 1,500 volts created a static voltage of 1,500 volts in the fluidized bed. When switching the feed point to the heat exchanger inlet, a water feed of up to IJppm per part of ethylene feed did not create a static voltage in the fluidized bed. 1.2 pp per part of ethylene feed
A continuous water feed rate of m over 4 hours did not create any static voltage within the fluidized bed.

Example 8 Using the same reactor producing the polymer resin in Examples 6 and 7 (under the same conditions as the pool), the effect of methanol feed point on electrostatic pressure and sheeting in the fluidized bed was investigated.

In this case, nitrogen saturated with methanol at 20° C. is first fed into the reactor circulation stream to the heat exchanger outlet at a rate of 1.3 ppm methanol per part of ethylene feed;
The electrostatic voltage within the reactor immediately rose to +4000 volts. At the same time, the temperature measured by the thermocouple on the inner wall of the reactor at a height 1 times the plate diameter above the distribution plate was 86°C to 94°C.
C, suggesting that a sheet has formed at this point.

At this point, the reactor temperature was 88°C, so 88°C
All wall thermocouple measurements above C suggest sheeting.

When the methanol supply was switched upstream of the heat exchanger, the static voltage dissipated almost immediately to O volts. Furthermore, when methanol was fed upstream of the heat exchanger, no wall thermocouple changes occurred above the temperature within the fluidized bed.

The methanol feed was stopped between the outlet and inlet of the heat exchanger a total of three times. In each case, a positive electrostatic voltage in the range of +700 volts to 14,000 volts immediately develops when methanol is fed downstream of the heat exchanger, and this electrostatic voltage increases when methanol is fed upstream of the heat exchanger. Even the bolts disappeared.

[Brief explanation of the drawing]

The drawing is a schematic flowchart showing a slightly modified typical gas phase fluidized bed polymerization process for producing high density and low density polyolefins to illustrate the process according to the present invention for reducing or eliminating sheeting. 10... Reactor 12... Reaction zone 14.
...Velocity reduction zone 1i0.16...Storage 18...Gas analyzer

Claims (7)

[Claims] (1) When polymerizing α-olefins in the reaction zone of a fluidized bed reactor using titanium-based catalysts or other catalysts that tend to produce sheeting during polymerization, monomers, comonomers, inert gases, and hydrogen continuous passage of a gas feed stream through said fluidized bed under reaction conditions, withdrawing from said reaction zone a recycle stream consisting of polymer product and unreacted gases and solid particles, cooling said recycle stream and cooling said recycle stream. A process for the polymerization of α-olefins comprising recycling a recycled stream of monomers, comonomers, an inert gas and hydrogen to the reaction zone, wherein the gas feed stream consisting of unreacted gas and solid particles is recycled to the reaction zone. A process for the polymerization of α-olefins, characterized in that the recycle stream is introduced into the stream at a point prior to cooling, and then the recycle stream and the gas feed stream are cooled and directed into the reaction zone. (2) directing a circulating stream of unreacted gas and solid particles exiting the reaction zone into a compressor, and directing a gas feed stream into said circulating stream at a point between the compressor and cooling of said circulating stream; 2. The method of claim 1, wherein: (3) Claim 1 in which one of the α-olefins is ethylene.
Method described. (4) The method according to claim 1, wherein the inert gas is nitrogen. (5) The method according to claim 1, wherein the catalyst having a tendency to cause sheeting is a vanadium-based catalyst. (6) alpha-olefin with large mol% (≧90%) of ethylene and small mol% (≦10%) of one or more C
2. The method according to claim 1, further comprising polymerizing a linear copolymer with α-olefins from _3 to C_8. (7) Polymer is propylene, butene-1, pentene-1
, hexene-1, 4-methylpentene-1, heptene-1
7. The method according to claim 6, wherein the polymer is a homopolymer or copolymer of octene-1 or octene-1.