JP3724907B2 - Gas circulation method and equipment in gas phase polymerization - Google Patents

Description

BACKGROUND OF THE INVENTION
The present invention relates to a gas circulation method that does not cause adhesion of droplets, precipitation of solid foreign matters, and the like in a circulation pipe in a step of circulating a circulation gas containing condensable and reactive components. In particular, the present invention relates to a gas circulation method suitable for circulation of an unreacted gas in gas phase polymerization using a highly active metallocene catalyst.
[Prior art and problems to be solved by the invention]
Conventionally, circulation pipes for circulating gas containing condensable components are usually installed with steam traces, or heated to prevent condensation inside the pipe as a double pipe structure, It was raised in advance so that it would not condense even if the temperature dropped in the piping. It is also well known to keep the piping warm in order to keep this temperature drop to a minimum. This method was able to be carried out without any problem when the circulating gas was kept in an unreacted condition.
However, when the reactive gas and the solid catalyst component scattered from the reactor are contained in the circulating gas, the reaction tends to proceed inside the circulating gas pipe. In particular, when condensed components coexist, droplets are formed in the pipe, and if the liquid droplets are present, solid catalyst components and the like are likely to adhere to the wall surface of the pipe, and are attached to the pipe wall or taken into the liquid droplets. In this case, the polymerization reaction proceeded to produce a film-like or fiber-like polymer, which tended to be a cause of blockage of piping or a factor that would cause the polymerization vessel to become unstable.
A composition that does not condense at the entrance of the circulation pipe becomes a condensable component while moving through the circulation gas pipe, condenses to form droplets, and in some cases, a polymer is generated, which adheres to the wall of the circulation gas. There was something to do.
In such a condition that the components in the circulating gas are reactive, if the piping is heated or the temperature of the circulating gas is raised in advance, the reaction inside the piping is promoted, and deposits are deposited in the piping. There was also a risk that it would be generated or, in the worst case, blocked.
When such a problem occurs, resistance to the circulating gas is reduced and energy efficiency during gas circulation is reduced, and in some cases, a preliminary circulation line is installed to operate alternately, or the entire plant is stopped. In other words, it was likely to be necessary to clean the piping or to remove clogging.
In particular, in a gas phase polymerization facility using a highly active metallocene catalyst, the reaction pressure is higher than before, so the condensation temperature of the circulating gas rises, and in order to prevent condensation, the reaction pressure is further increased. It is necessary to heat. However, the more the temperature is increased, the more the reactivity is improved.
[Means to solve the problem]
In the process of circulating the circulating gas containing both condensable and reactive components at the same time, the present inventors diligently investigated the problems in the clogging of the pipes due to the adhesion of liquid droplets and the precipitation of solid foreign matters inside the circulation pipe. As a result, the inventors have found that it is possible to prevent these troubles by keeping the circulation pipe warm and defining the gas linear velocity, thereby completing the invention.
First, a method for keeping the piping warm will be described.
Any pipe insulation can be used as long as it is used for ordinary pipe insulation. For example, diatomite insulation, rock wool insulation, glass wool insulation, magnesium carbonate insulation, calcium silicate insulation, pearlite insulation. Materials, carbonized cork materials, foam polystyrene materials, rigid foam rubber materials, urethane foam materials, etc. Among these, a heat insulating material that is subjected to a treatment for reducing the intrusion of moisture, such as water-repellent pearlite, and has few components that corrode iron is preferable.
Since the insulation thickness of the insulation material depends on the climate of the installation area of each equipment, the insulation material thickness is such that the temperature in the circulating gas piping is less than 5 ° C from the heat exchanger outlet in each climate condition. Select the size.
The thickness is usually 25 mm or more and 80 mm or less in a region where the average annual temperature is 0 to 10 ° C., usually 25 mm or more and 70 mm or less in a region where the temperature is 10 to 20 ° C., and 25 mm or more and 60 mm or less.
Next, the gas linear velocity in the gas circulation pipe is usually 8 m / sec or more. Preferably they are 10 m / sec or more and 100 m / sec or less, More preferably, they are 10 m / sec or more and 50 m / sec or less.
When a piping facility for circulating gas containing condensable and reactive components has a heat exchange facility for temperature control at the inlet to the circulating piping, the temperature (TEout) at the outlet of the heat exchanger and the circulating gas Temperature difference at the reactor inlet (TRin) = TRin−TEout is −5 ° C. or higher and 3 ° C. or lower, preferably −3 ° C. or higher and 2 ° C. or lower.
Finally, the process before the gas circulation will be described. In the circulating gas having condensability and reactivity if the above-mentioned heat insulation is performed and the gas linear velocity is defined, clogging of the gas piping can be prevented, but if the following pretreatment is performed, it is more complete Achieved.
Immediately before starting the gas circulation, an inert gas having a temperature higher by 5 ° C. or more and 50 ° C. or less than the circulation gas temperature can be added by about 1% to 10% with respect to the circulation gas amount.
Accordingly, since the circulation pipe is heated in advance, there is no problem of condensation from the beginning of the circulation, the reaction inside the pipe is suppressed, and adhesion to the inside of the pipe can be prevented.
These circulating gas facilities are suitably used for an unreacted gas circulation step of gas phase polymerization using a highly active metallocene catalyst. In the olefin gas phase polymerization method according to the present invention, when the olefin is polymerized in the gas phase while continuously supplying the solid catalyst and the olefin to the polymerization reactor (fluidized bed reactor), The dry prepolymerization catalyst is supplied in a solid powder state to the polymerization reactor to polymerize the olefin. In the polymerization, the (D) organoaluminum compound as described above can be used together with the dry prepolymerization catalyst for olefin polymerization. (D) The organoaluminum compound is usually in an amount of 1 to 1000 mol, preferably 2 to 300 mol, per 1 mol of the transition metal atom in the transition metal compound (B) contained in the dry prepolymerization catalyst for olefin polymerization. It is desirable to be used.
The polymerization reaction can be carried out in any of batch, semi-continuous and continuous methods. Furthermore, the polymerization can be performed in two or more stages having different reaction conditions. In the present invention, it is preferable to employ a continuous fluidized bed gas phase polymerization method.
The polymerization temperature in the gas phase polymerization method is usually in the range of 50 to 120 ° C, preferably 60 to 100 ° C. The polymerization pressure is usually from normal pressure to 100 kg / cm @ 2, preferably from normal pressure to 50 kg / cm @ 2. The gas linear velocity is in the range of 0.4 to 1.5 m / sec, preferably 0.6 to 1.2 m / sec.
Here, the gas phase polymerization method of olefin according to the present invention will be described in detail with reference to FIG.
The dry prepolymerization catalyst (solid catalyst) for olefin polymerization as described above is continuously supplied to the fluidized bed reactor 2 in a solid powder state via, for example, the line 1.
The solid catalyst is usually 0.00001 to 1.0 mmol / hour, preferably 0.0001 to 0.1 mmol / hour in terms of transition metal atoms in the transition metal compound (A) per liter of polymerization volume. It is desirable to be used in an amount of.
Gaseous olefin is continuously blown into the fluidized bed reactor 2, for example in the lower part thereof, via a line 3 by a gas blower 5. The olefin is supplied from the olefin supply line 4 to the gas blower 5. The olefin blown into the lower part of the fluidized bed reactor 2 disperses the solid catalyst through a gas dispersion plate 6 such as a perforated plate to form a fluidized bed (reaction system) 7. In the fluidized bed 7, the olefin is (co) polymerized to form a particulate olefin (co) polymer. Thus, the olefin supplied to the reactor 2 also serves as a fluidizing gas that keeps the catalyst particles in the reaction system in a fluid state. It is also possible to use a gas mixture of an olefin and an inert gas such as nitrogen as the fluidizing gas. The produced polymer particles are continuously withdrawn from the fluidized bed reactor 2 through the polymer recovery line 8.
On the other hand, the gaseous unreacted olefin that has passed through the fluidized bed 7 is decelerated in the deceleration zone 2 a provided in the upper part of the fluidized bed reactor 2 and then comes out of the fluidized bed reactor 2. Unreacted olefin leaving the fluidized bed reactor 2 can be circulated through the circulation line 9 together with fresh olefin from the olefin feed line 4. The unreacted olefin is preferably removed from the polymerization heat by the heat exchanger 10 before being circulated. However, the heat of polymerization can also be used to heat fresh olefin before feeding it to the reactor 2.
As described above, the polymerization method of the present invention can be operated continuously.
The molecular weight of the resulting olefin polymer can be adjusted by the presence of a molecular weight regulator such as hydrogen in the polymerization system or by changing the polymerization temperature. Hydrogen can be supplied from any location in the gas phase fluidized bed reactor, such as line 4.
Here, the olefin used in the present invention is preferably an α-olefin having 2 to 18 carbon atoms, such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene. , 3-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene and the like.
Further, cyclopentene, cycloheptene, norbornene, 5-methyl-2-norbornene, tetracyclododecene, 2-methyl 1,4,5,8-dimethano-1,2,3,4,4a, 5,8,8a- Also included are monocyclic and polycyclic olefins such as octahydronaphthalene, and aromatic and alicyclic vinyl compounds such as styrene, vinyltoluene and vinylcyclohexane.
In addition to olefins, polyenes such as butadiene, isoprene, 1,4-hexadiene, dicyclopentadiene, and 5-ethylidene-2-norbornene can be copolymerized.
In the present invention, among these, it is preferable to produce linear low-density polyethylene (LLDPE) by copolymerizing ethylene and an α-olefin having 3 to 18 carbon atoms. In the present invention, among olefin polymers, a structural unit derived from ethylene is contained in a proportion of 75 to 98% by weight, preferably 80 to 97% by weight, and derived from an α-olefin having 3 or more carbon atoms. A low crystalline ethylene / α-olefin copolymer, so-called linear low density polyethylene (LLDPE), containing 3 to 25% by weight, preferably 3 to 20% by weight, is particularly preferable. Is done.
The highly active metallocene catalyst used in the present invention is a compound containing a ligand having a cyclopentadienyl skeleton represented by the following general formula (I) as the transition metal compound (B) of Group IVB of the periodic table Can be illustrated.
MLX (I)
In the formula, M represents one transition metal atom selected from group IVB transition metal atoms in the periodic table, and is preferably zirconium, titanium, or hafnium.
x is the valence of the transition metal atom M, and indicates the number of ligands L coordinated to the transition metal atom M.
L represents a ligand or group coordinated to the transition metal atom M, and at least one L is a ligand having a cyclopentadienyl skeleton, and the ligand having the cyclopentadienyl skeleton Other than L is a hydrocarbon group having 1 to 12 carbon atoms, an alkoxy group, an aryloxy group, a trialkylsilyl group, SO3R (wherein R is an optionally substituted carbon atom having 1 carbon atom) ˜8 hydrocarbon groups), a halogen atom, or a hydrogen atom. Two or more L may be the same as or different from each other.
Examples of the ligand having a cyclopentadienyl skeleton include cyclopentadienyl group; methylcyclopentadienyl group, dimethylcyclopentadienyl group, trimethylcyclopentadienyl group, tetramethylcyclopentadienyl group, penta Methylcyclopentadienyl group, ethylcyclopentadienyl group, methylethylcyclopentadienyl group, propylcyclopentadienyl group, methylpropylcyclopentadienyl group, butylcyclopentadienyl group, methylbutylcyclopentadienyl And an alkyl-substituted cyclopentadienyl group such as a hexylcyclopentadienyl group; an indenyl group; an alkyl-substituted indenyl group; a 4,5,6,7-tetrahydroindenyl group; and a fluorenyl group. These groups may be substituted with a halogen atom, a trialkylsilyl group or the like.
Among these ligands having a cyclopentadienyl skeleton, an alkyl-substituted cyclopentadienyl group is particularly preferable.
When the compound represented by the general formula (I) includes two or more ligands having a cyclopentadienyl skeleton, the ligands having two cyclopentadienyl skeletons are ethylene, propylene And a substituted alkylene group such as isopropylidene and diphenylmethylene; a silylene group; a dimethylsilylene group; and a substituted silylene group such as a diphenylsilylene group and a methylphenylsilylene group. In the present invention, as the transition metal compound (B), a transition metal compound in which the zirconium metal is replaced with titanium metal or hafnium metal in the above-described zirconium compound can also be used.
These transition metal compounds (B) may be used alone or in combination of two or more. Moreover, you may dilute and use for hydrocarbon or halogenated hydrocarbon.
In the present invention, as the transition metal compound (B), a zirconocene compound having a ligand having a central transition metal atom of zirconium and containing at least two cyclopentadienyl skeletons is preferably used.
Specific examples of the organoaluminum oxy compound (C) used in the present invention include conventionally known aluminoxanes and benzene-insoluble organoaluminum oxy compounds as exemplified in JP-A-2-78687.
A conventionally well-known aluminoxane can be manufactured from the (D) organoaluminum compound which is mentioned later by the following methods, for example.
(1) Compounds containing adsorbed water or salts containing water of crystallization, such as magnesium chloride hydrate, copper sulfate hydrate, aluminum sulfate hydrate, nickel sulfate hydrate, first cerium chloride hydrate, etc. A method in which an organoaluminum compound such as trialkylaluminum is added to a suspension in a hydrocarbon medium and reacted with adsorbed water or crystal water.
(2) A method of allowing water, ice or water vapor to act directly on an organoaluminum compound such as trialkylaluminum in a medium such as benzene, toluene, ethyl ether or tetrahydrofuran.
(3) A method in which an organotin oxide such as dimethyltin oxide or dibutyltin oxide is reacted with an organoaluminum compound such as trialkylaluminum in a medium such as decane, benzene, or toluene.
The aluminoxane may contain a small amount of an organometallic component. Further, after removing the solvent or unreacted organoaluminum compound from the recovered aluminoxane solution by distillation, it may be redissolved in a solvent or suspended in a poor aluminoxane solvent.
The olefin polymerization catalyst according to the present invention is a solid catalyst in which (B) a transition metal compound and (C) an organoaluminum oxy compound are supported on the above-mentioned (A) particulate carrier.
The prepolymerized catalyst is a solid catalyst in which an olefin is prepolymerized in the presence of the catalyst component.
The solid catalyst component can be prepared by bringing (B) a transition metal compound and (C) an organoaluminum oxy compound into contact with (A) a particulate carrier.
The above-mentioned components can be contacted in an inert hydrocarbon medium. Specific examples of such an inert hydrocarbon medium include propane, butane, pentane, hexane, heptane, octane, decane, dodecane, and kerosene. Aliphatic hydrocarbons such as cyclopentane, cyclohexane, methylcyclopentane, etc .; Aromatic hydrocarbons such as benzene, toluene, xylene; Halogenated hydrocarbons such as ethylene chloride, chlorobenzene, dichloromethane, etc. And the like.
In preparing the solid catalyst component, (B) the transition metal compound (in terms of transition metal atoms) is usually 0.001 to 1.0 mmol, preferably 0.01 to 0.5, per gram of (A) fine particle support. It is used in an amount of millimolar, and the (C) organoaluminum oxy compound is usually used in an amount of 0.1 to 100 millimolar, preferably 0.5 to 20 millimolar.
The solid catalyst component thus obtained may contain other components useful for olefin polymerization, such as an electron donor and a reaction aid, together with the above catalyst component.
As a method for prepolymerizing an olefin in the presence of the solid catalyst component, a conventionally known method is used, for example, by introducing the olefin into an inert hydrocarbon medium in the presence of the solid catalyst component. it can. Examples of the inert hydrocarbon medium used for the preparation of the prepolymerization catalyst are the same as those described above.
In the prepolymerization, the following organoaluminum compound (D) can be used together with the solid catalyst component.
【The invention's effect】
According to the method of the present invention, by maintaining the temperature of the circulation gas piping, the production of condensable and precipitateable compounds due to the reaction of the reactive circulation gas is suppressed, and further, the effect is enhanced by defining the gas linear velocity. Further, even if solids are mixed in the circulating gas, it is possible to achieve gas circulation without adhering to the pipe wall surface.
By treating with an inert gas before carrying out the gas circulation, it becomes possible to carry out the gas circulation smoothly and to further effectively prevent the blockage in the gas circulation pipe.
[Brief description of the drawings]
FIG. 1 shows a process of an olefin polymerization method according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Catalyst feed nozzle 2 ... Fluidized bed reactor 2a ... Deceleration zone 3 ... Gas supply line 4 ... Reactor supply line 5 ... Blower 6 ... Dispersion plate 7 ... Fluidized bed 8 ... Polymer extraction line 9 ... Circulation line 10 ... Condenser

Claims (2)

(A) a fine particle carrier made of an oxide of at least one element selected from Group II, Group III and Group IV of the Periodic Table, (B) a transition metal compound of Group IVB of the Periodic Table, and (C ) When circulating unreacted gas when gas phase polymerization is performed using a solid catalyst component in which an organoaluminum oxy compound is supported or a prepolymerized catalyst in which olefin is prepolymerized on the solid catalyst component, the gas circulation A gas phase polymerization method characterized in that the piping is kept warm in the piping, and the gas linear velocity inside the piping is set to 8 m / sec or more.   The gas phase polymerization method according to claim 1, wherein the gas circulation pipe is kept warm, and the gas linear velocity inside the pipe is set to 10 m / sec or more and 100 m / sec or less.

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