阅读说明：本技术 生产聚乙烯聚合物的方法 (Process for producing polyethylene polymers ) 是由 C·L·布兰德尔 W·A·兰伯蒂 C·R·布勒尔 J·S·克莱门茨 H·W·德克曼 J·A 于 2018-02-07 设计创作，主要内容包括：提供了生产聚乙烯聚合物的方法,包括使乙烯和至少一种C<Sub>3</Sub>-C<Sub>8</Sub>α-烯烃共聚单体在流化床聚合反应器中与颗粒载体上的聚合催化剂在有效聚合至少一部分乙烯和共聚单体的条件下接触,和生产聚乙烯聚合物,其中所述载体具有通过激光衍射测量的至少18微米的d<Sub>10</Sub>粒度。(A process for producing a polyethylene polymer is provided comprising reacting ethylene and at least one C 3 ‑C 8 Contacting an alpha-olefin comonomer in a fluidized bed polymerization reactor with a polymerization catalyst on a particulate support under conditions effective to polymerize at least a portion of the ethylene and comonomer, and producing a polyethylene polymer, wherein the support has a d of at least 18 microns as measured by laser diffraction 10 Particle size.)

1. A process for producing a polyethylene polymer, said process comprising reacting ethylene and at least one C₃-C₈Contacting an alpha-olefin comonomer in a fluidized bed polymerization reactor with a polymerization catalyst on a particulate support having a d of at least 18 microns as measured by laser diffraction under conditions effective to polymerize at least a portion of the ethylene and comonomer, producing and recovering said polyethylene polymer₁₀Particle size.

2. The process of claim 1 wherein the polymerization catalyst comprises one or more metallocene catalysts.

3. The process of claim 1 or claim 2, wherein the particulate support comprises an inorganic oxide.

4. A process according to any one of the preceding claims wherein the particulate support comprises an oxide of silicon.

5. The process of any of the preceding claims, wherein the comonomer comprises propylene, 1-butene, 1-hexene, 1-octene, or mixtures thereof.

6. The method of any of the preceding claims, wherein the particles areThe particle carrier has a d of at least 40 microns as measured by laser diffraction₅₀Particle size.

7. A method according to any preceding claim, wherein the particulate carrier has a d of not more than 100 microns as measured by laser diffraction₉₀Particle size.

8. The process of any of the preceding claims, further comprising polymerizing at a temperature of 30 to 120 ℃ and a pressure of 790 to 3550 kPa-a.

9. The process of any of the preceding claims, wherein the polyethylene polymer has a density of at least 0.920 g/cc.

10. The process of any preceding claim, wherein the process comprises a sheeting rate, and a rate as measured using the same polymerization catalyst but with a d measured by laser diffraction₁₀The flaking rate is reduced compared to a substantially similar or identical process on a particulate carrier having a particle size of less than 18 microns.

11. The method of any of the preceding claims, wherein the polyethylene polymer has a density of less than 0.940 g/cc.

12. The method of any one of the preceding claims, wherein the method comprises a rate of distributor plate fouling, and a rate of fouling that is at the same superficial gas velocity and using the same polymerization catalyst but with a d measured by laser diffraction₁₀The rate of fouling of the distributor plate is reduced compared to a substantially similar or identical process on a particulate support having a particle size of less than 18 microns.

13. Process for reducing sheeting during ethylene and 1-hexene polymerization in a fluidized bed reactor to produce a polyethylene product having a gradient density of at least 0.940g/cc using a support having a d measured by laser diffraction₁₀Particle carrier having a particle size of at least 18 micronsA bulk polymerization catalyst.

14. The process of claim 13, wherein the polymerization catalyst comprises one or more metallocene catalysts.

15. The method of claim 13 or claim 14, wherein the particulate support comprises an inorganic oxide.

16. The method of claim 13 or claim 14, wherein the particulate support comprises an oxide of silicon.

17. The method of any one of claims 13-16, wherein the particulate support has a d of at least 40 microns as measured by laser diffraction₅₀Particle size.

18. The method of any one of claims 13 to 17, wherein the particulate carrier has a d of no greater than 100 microns as measured by laser diffraction₉₀Particle size.

19. A process for reducing distributor plate fouling at a constant superficial gas velocity during polymerization of ethylene and 1-hexene in a fluidized bed reactor to produce a polyethylene product having a gradient density of less than 0.940g/cc using a support having a d measured by laser diffraction₁₀A polymerization catalyst on a particulate support having a particle size of at least 18 microns.

20. The method of claim 19, wherein the polymerization catalyst comprises one or more metallocene catalysts.

21. The method of claim 19 or claim 20, wherein the particulate support comprises an inorganic oxide.

22. The method of claim 19 or claim 20, wherein the particulate support comprises an oxide of silicon.

23. The method of any one of claims 19-22, wherein the particulate carrier has a d of at least 40 microns as measured by laser diffraction₅₀Particle size.

24. The method of any one of claims 19-23, wherein the particulate carrier has a d of no greater than 100 microns as measured by laser diffraction₉₀Particle size.

Technical Field

The present invention relates to the production of polyethylene polymers in a gas phase polymerisation process.

Background

In a gas phase process for producing polyolefin polymers, such as polyethylene polymers, gaseous olefins (e.g., ethylene), hydrogen, comonomers (e.g., 1-hexene), and other feedstocks are converted to a solid polyolefin product. Generally, the gas phase reactor includes a fluidized bed reactor, a compressor and a cooler (heat exchanger). The reaction is maintained in a two-phase fluidized bed of particulate polyethylene polymer and gaseous reactants by a fluidizing gas which passes through a distributor plate near the bottom of the reactor vessel. The catalyst is injected into the fluidized bed while the heat of reaction is transferred to the recycle gas stream. The gas stream is compressed and cooled in an external recycle line and then reintroduced into the bottom of the reactor where it passes through a distributor plate. A make-up feed stream is added to maintain the desired reactant concentration.

For uniform reactor conditions, heat removal, and effective catalyst performance, the operation of most reactor systems is critically dependent on good mixing. The process must be controllable and must be capable of high production rates. Generally, the higher the operating temperature, the greater the ability to achieve high production rates. Since the polymerization reaction is generally exothermic, the transfer of heat from the reactor is critical to avoid problems such as particle agglomeration and runaway reactions. However, as the operating temperature approaches and exceeds the melting point of the polyolefin product, the polyolefin particles become tacky and melt. For example, uneven fluidization of the bed can create "hot spots", which in turn can cause newly formed polymer particles to become sticky due to the elevated temperatures in the hot spots.

The interaction of forces may cause the particles to agglomerate with adjacent particles and may lead to "sheeting" and other forms of reactor fouling. In agglomeration, the particles stick together, forming agglomerated particles that affect fluid flow, and may be difficult to remove from the system. In sheeting, sticky particles accumulate on the surfaces of the reactor system, such as the walls of the reactor vessel, to form a sheet of polymer particles. The progressive cycling in the process may eventually lead to the growth of the sheet and its falling into the fluidized bed. These sheets can disrupt fluidization, gas circulation, and product removal from the reactor, and may require reactor shutdown for removal.

Many factors affect sheeting tendencies and other fouling phenomena, one of which is the type of catalyst. For example, metallocene catalysts allow the production of polyolefins with unique properties such as narrow molecular weight distribution and narrow chemical composition. These properties in turn lead to improved structural properties of products made with these polymers, such as greater impact strength and clarity of the film. However, while metallocene catalysts produce polymers with improved properties, they present particular challenges when used in fluidized bed reactors, particularly with respect to sheeting and fouling in other parts of the reactor system, such as distributor plates and coolers.

Various methods have been developed for controlling sheeting. These processes generally involve monitoring the electrostatic charge near the reactor wall in a region known to suffer sheeting and introducing a static control agent into the reactor when the electrostatic charge level is outside a predetermined range. For example, U.S. Pat. nos. 4,803,251 and 5,391,657 disclose the use of various chemical additives in a fluidized bed reactor to control the electrostatic charge in the reactor. If the electrostatic charge is negative, then a positive charge generating additive is used; if the electrostatic charge is positive, an additive that generates a negative charge is used. Static voltage indicators, such as voltage or current probes or electrodes, are commonly used to measure the electrostatic charge in the reactor at or near the reactor wall at or below the location where sheet formation typically occurs. However, these approaches not only increase the cost of the process, but also increase the complexity of the process control.

Other methods rely on the addition of continuity additives to minimize aggregation and sheeting. One disadvantage of using continuity additives or antistatic agents is that they increase the cost of the polymerization reaction. Another disadvantage of using continuity additives or antistatic agents is that the gas phase reactor may require additional equipment to feed and monitor the levels of these additives. In addition, certain continuity aids can effectively act as mild catalyst poisons, thus leading to increased catalyst usage and cost. Accordingly, it is desirable to eliminate or reduce the need for continuity aids.

Another factor that has been shown to cause reactor fouling in gas phase fluidized bed processes for producing polyethylene polymers is the accumulation of polymer fines (defined as polymer particles having a particle size of less than 125 microns) in the reactor system. This problem is discussed, for example, in U.S. patent No.5,969,061, where a solution is proposed to introduce inert C in controlled amounts depending on the level of fines measured in the reactor₃-C₈The hydrocarbon is added to the fluidizing gas mixture. The goal is to reduce the amount of fines generated in the reactor without having to modify the catalyst. This solution relies on softening of the resin particles to promote agglomeration of the fines into larger particles by changing gas composition and adsorption, and to reduce formation of fines by reducing breakage of the larger particles. The proposed increased adsorption and particle softening also results in deleterious operating effects, i.e., a decrease in melting point and an increase in resin stickiness, which promotes increased resin sheeting (see, e.g., U.S. patent No.7,910,668). Furthermore, the solution methodIncreasing the complexity of the process monitoring system and the overall polymer cost.

Accordingly, there is a need for an improved process for producing polyethylene polymers in a gas phase fluidized bed reactor that reduces the likelihood of sheeting and/or agglomeration in the reactor system, and/or reduces or eliminates the need for continuity additives, gas composition changes, and/or antistatic agents.

Disclosure of Invention

Drawings

FIG. 1 is a flow diagram of a gas phase fluidized bed reaction system that can be used to produce polyethylene polymers.

FIG. 2 is a graph showing the change in superficial gas velocity required to maintain substantially stable distributor plate fouling during the polymerization of example 3.

FIG. 3 is a bar graph comparing the number of trays (pan) of polyethylene sheets produced in twelve hourly runs (shift) during the polymerization of examples 4 and 5.

Detailed Description

Before the present compounds, components, compositions, and/or methods are disclosed and described, it is to be understood that this invention is not limited to specific compounds, components, compositions, reactants, reaction conditions, ligands, metallocene structures unless otherwise specified, as such may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

Described herein is a process for producing a polyethylene polymer wherein ethylene and at least one C are reacted₃-C₈An alpha-olefin comonomer, preferably 1-hexene, is contacted with a particulate supported polymerization catalyst in a fluidized bed polymerization reactor under conditions effective to polymerize at least a portion of the ethylene and comonomer, and produce a polyethylene product. According to the invention, the particulate carrier is specifically selected to have a d of at least 18 microns, preferably at least 20 microns, more preferably at least 21 microns as measured by laser diffraction₁₀Particle size. By controlling d of the carrier₁₀Particle size, it was found that polymer fines (polymer particles having a particle size of less than 125 microns) can be significantly reduced during the polymerization processIs generated. This is an important advantage, since small polymer particles in the fluidized reactor bed are more likely to be entrained by the recycle gas and carried into the recycle gas conduit. The particles may then adhere to various components of the reactor system, such as the reactor walls, the recycle gas cooler, and the distributor plates, leading to fouling and eventually requiring shutdown and cleaning of the system. Thus, entrainment limits the Superficial Gas Velocity (SGV) at which the reactor can operate. Conversely, it is desirable to be able to operate at higher SGV because this increases the cooling rate in the recycle gas cooler so that the exothermic polymerization reaction can occur at higher production rates.

Except that it has a d of at least 18 microns₁₀In addition to particle size, the particulate support used in the present method may also have a d of at least 40 microns (e.g., at least 45 microns) as measured by laser diffraction₅₀Particle size and d of not more than 100 microns, e.g. not more than 95 microns, as measured by laser diffraction₉₀Particle size. In this regard, all carrier and polymer particle sizes referred to herein are measured on a Malvern Mastersizer 2000. As used herein, the term d_xFor example, where x is 10, 50 or 90, means that x% by weight of the relevant particulate material has a d less than the cited d_xThe particle size of the values, and (100-x) wt.% have d in the quoted_xParticle sizes above the value.

Any particulate material inert to the reagents and conditions used in the polymerization process may be used as the support. Preferably, the support material is an inorganic oxide. Suitable inorganic oxide materials include group 2, 4, 13 and 14 metal oxides such as silica, alumina and mixtures thereof. As used herein, unless otherwise indicated, all references to the periodic Table of the elements and groups thereof are to the New numbering scheme (NEW NOTIFION) published in Hawley's Condensed Chemical Dictionary, thirteenth edition, John Wiley & Sons, Inc, (1997), and reference to the previous IUPAC form designated by the Roman number (also shown therein). Other inorganic oxides that may be used alone or in combination with the silica or alumina are magnesia, titania, zirconia, clays, and the like. In a preferred embodiment, the particulate support material comprises at least in part a siliceous oxide, such as silica.

Silica particles having the desired particle size distribution can be produced by sieving commercially available or specially produced silicas having a broader particle size distribution. However, some commercial grades of silica also meet specifications.

In one class of embodiments, the silica support material should initially be dry, i.e., free of absorbed water or moisture. Drying of the silica support material may be carried out by heating or calcining at a temperature of from about 100 ℃ to about 1000 ℃, preferably at least about 200 ℃, preferably from about 200 ℃ to about 850 ℃, and most preferably about 600 ℃; and for a period of time of from about 1 minute to about 100 hours, from about 12 hours to about 72 hours, or from about 24 hours to about 60 hours. The calcined support material should have at least some reactive hydroxyl (OH) groups to produce a supported catalyst system. The calcined support material is then contacted with at least one polymerization catalyst comprising at least one catalyst compound and an activator.

A support material having reactive surface groups, typically hydroxyl groups, is slurried in a non-polar solvent and the resulting slurry is contacted with a solution of a catalyst compound and an activator. In some embodiments, the slurry of support material is first contacted with the activating agent for a period of time ranging from about 0.5 hours to about 24 hours, from about 2 hours to about 16 hours, or from about 4 hours to about 8 hours. The solution of catalyst compound is then contacted with the isolated support/activator. In some embodiments, the supported catalyst system is generated in situ. In alternative embodiments, the slurry of support material is first contacted with the catalyst compound for a period of time ranging from about 0.5 hours to about 24 hours, from about 2 hours to about 16 hours, or from about 4 hours to about 8 hours. The slurry of supported catalyst compound is then contacted with an activator solution.

The mixture of catalyst, activator and support is heated to a temperature of from about 0 ℃ to about 70 ℃, preferably from about 23 ℃ to about 60 ℃, preferably at room temperature. The contact time is typically from about 0.5 hours to about 24 hours, from about 2 hours to about 16 hours, or from about 4 hours to about 8 hours.

Suitable non-polar solvents are materials in which all or most of the catalyst system reactants, i.e. the activator and catalyst compound, are at least partially soluble and liquid at the reaction temperature. Preferred non-polar solvents are alkanes such as isopentane, hexane, n-heptane, octane, nonane and decane, but a variety of other materials including cycloalkanes such as cyclohexane and Tetrahydrofuran (THF), aromatics such as benzene, toluene and ethylbenzene may also be used.

The catalyst used in the process of the present invention generally comprises at least one metallocene compound or one or more metallocene catalysts. Metallocenes generally refer to compounds comprising one or more cyclopentadienyl (Cp) moieties bound to a transition metal. The Cp ring(s) may be similar or different, may be unsubstituted, substituted or derivatives thereof, for example, heterocyclic ring systems which may be substituted, and the substituents may be fused to form other saturated or unsaturated ring systems, for example tetrahydroindenyl, indenyl or fluorenyl ring systems. The active catalyst system should include not only the metallocene, but also an activator, such as an alumoxane or a derivative thereof (preferably, Methylalumoxane (MAO)), an ionizing activator, a non-coordinating anion, a lewis acid, or a combination thereof. Preferably, the catalyst system comprises a metallocene catalyst having a single or multiple cyclopentadienyl component reacted with a metal alkyl or alkoxy component or an ionic compound component. These catalysts may include partially and/or fully activated precursor compositions. The catalyst may be modified by prepolymerization or encapsulation. Specific metallocenes and catalyst systems useful are disclosed in WO 96/11961 and WO 96/11960. Other non-limiting examples of metallocene catalysts and catalyst systems are discussed in U.S. Pat. Nos. 4,808,561, 5,017,714, 5,055,438, 5,064,802, 5,124,418, 5,153,157, and 5,324,800. Other organometallic complexes and/or catalyst systems are described in Organometallics, 1999, 2046; WO 96/23010, WO 99/14250, WO98/50392, WO 98/41529, WO98/40420, WO 98/40374, WO 98/47933; EP 0881233 a and EP 0890581 a.

In several embodiments, the process of the present invention is generally carried out at a temperature of from 30 to 120 ℃, preferably from 60 to 115 ℃, more preferably from 70 to 110 ℃, most preferably from 70 to 100 ℃ and a pressure of from 790 to 3550kPa-a, preferably from 2100 to 2500 kPa-a. To produce a polyethylene polymer having a density of at least 0.940g/cc, such as 0.940 to 0.970g/cc, the preferred operating temperature is from about 90 ℃ to 100 ℃; and producing a product having a density of less than 0.940g/cc, for example, from about 0.910 to < 0.940g/cc, preferably a temperature of from about 75 ℃ to 95 ℃.

Referring now to FIG. 1, one example of a fluidized bed reaction system suitable for polymerizing ethylene and other alpha-olefins includes a reactor 10, the reactor 10 including a reaction zone 12 and a velocity reduction zone 14.

Reaction zone 12 comprises a bed of growing polymer particles, formed polymer particles and a minor amount of catalyst particles fluidized by the continuous flow of polymerizable and modifying gaseous components through the reaction zone in the form of make-up feed and recycle gas. To maintain a viable fluidized bed, the mass gas flow rate through the bed is generally maintained above the minimum flow required for fluidization, preferably G_mfAbout 1.5 to about 10 times of (A), more preferably G_mfAbout 3 to about 6 times of (a), wherein G_mfAn abbreviation is used in an acceptable form as the minimum gas flow required to achieve fluidization, see "Mechanics of fluidization", volume 62, page 100-111 (1966) of c.y.wen and y.h.yu.

It is highly desirable that the fluidized bed always contain particles to prevent the formation of localized "hot spots" and to entrain (entrap) and distribute the particulate catalyst throughout the reaction zone. At start-up, a base of particulate polymer particles (base) is typically added to the reactor prior to initiating the gas flow. Such particles may be the same or different in nature from the polymer to be formed. When different, they are discharged as a first product together with the polymer article desired to be formed. Eventually, a fluidized bed of the desired polymer particles replaces the start-up bed (start up bed).

Fluidization is achieved by gas circulation into and through the bed at a high rate, typically about 50 times the feed rate of the make-up gas. The general appearance of the fluidized bed is: possible free vortices are viable particles of dense quality due to 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 divided by the cross-sectional area. This is therefore dependent on the geometry of the reactor 10.

Make-up gas is fed to the bed at a rate equal to the rate at which particulate polymer product is withdrawn. The makeup gas composition is determined by a gas analyzer (not shown) located above the fluidized bed. The gas analyzer determines the composition of the gas being recycled and adjusts the composition of the make-up gas accordingly to maintain a substantially steady state gas composition within the reaction zone.

The portion of the gas stream which is not reacted in the fluidised bed constitutes recycle gas which is preferably removed from the polymerisation zone by passing it into a velocity reduction zone 14 above the bed, in which zone 14 entrained particles have the opportunity to fall back into the bed.

The recycle gas leaves the velocity reduction zone 14 via line 16 and is then compressed in compressor 18 and then passed through heat exchanger 20 where it strips the heat of reaction before returning to the bed. By continuously removing the heat of reaction, there appears to be no significant temperature gradient in the upper part of the bed. At the bottom of the bed, there will be a temperature gradient in a layer of about 6 to 12 inches between the temperature of the inlet gas and the temperature of the rest of the bed. It has therefore been observed that the role of the bed is to regulate almost immediately the temperature of the recycle gas above this floor of the bed region so as to coincide with the temperature of the rest of the bed, thereby maintaining itself in a stable condition at a substantially constant temperature. The compressor 18 may also be placed downstream of the heat exchanger 20.

To ensure complete fluidization, the recycle gas and, if desired, some or all of the make-up gas are returned to the reactor 10 at its bottom 22 below the fluidized bed. A gas distribution plate 24 located above the return point ensures proper gas distribution and also supports the resin bed when gas flow is stopped.

A suitable catalyst for use in the fluidized bed, in this case a metallocene catalyst on a particulate silica support, is preferably stored in reservoir 26 under a blanket of a gas inert to the material being stored, such as nitrogen or argon. The catalyst is injected into the fluidized bed at a rate equal to its consumption at a point 28 above said distributor plate 24. A gas inert to the catalyst, such as nitrogen or argon, may be used to carry the catalyst into the bed.

Will comprise ethylene monomer and any C₃-C₈A gaseous feed stream of alpha-olefin comonomer is introduced into the gas recycle stream and supplied to the reactor 10 at its bottom 22. Any gas inert to the catalyst and reactants may also be present in the gaseous feed stream.

The particulate polymer product is preferably discharged from the reactor 10 at a location 30 at or near the distributor plate 24.

In one embodiment, a fluidized bed reaction system as shown in FIG. 1 is used to polymerize ethylene and 1-hexene to produce a polyethylene product having a gradient density of at least 0.940 g/cc. In this case, it was found that by using a load having d measured by laser diffraction₁₀A metallocene catalyst on particulate silica having a particle size of at least 18 microns, and wherein the metallocene catalyst is supported on a support having a d as measured by laser diffraction₁₀The tendency to flake, particularly at the walls of the velocity reduction zone 14, is reduced compared to a substantially similar or identical process on particulate silica having a particle size of less than 18 microns.

In another embodiment, a fluidized bed reaction system as shown in FIG. 1 is used to polymerize ethylene and 1-hexene to produce a polyethylene product having a gradient density of less than 0.94 g/cc. In this case, it was found that by using a load having d measured by laser diffraction₁₀A metallocene catalyst on particulate silica having a particle size of at least 18 microns, operated at the same superficial gas velocity but wherein the metallocene catalyst is supported with a d as measured by laser diffraction₁₀The rate of fouling of the distributor plate 24 is reduced compared to a substantially similar or identical process on particulate silica having a particle size of less than 18 microns. OrBy increasing the apparent gas velocity, by using a load having a d measured by laser diffraction₁₀Metallocene catalysts on particulate silica having a particle size of at least 18 microns can increase reactor cooling rates and polymer production rates at constant distributor plate fouling rates.

Examples

It should be understood that while the invention has been described in conjunction with specific embodiments thereof, the foregoing description is intended to illustrate and not limit the scope of the invention. Other aspects, advantages, and modifications will be apparent to those skilled in the art to which the invention pertains.

Therefore, the following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description, and are not intended to limit the scope of what the inventors regard as their invention.