CN114426616A - Method for synthesizing polyolefin and application thereof - Google Patents
Method for synthesizing polyolefin and application thereof Download PDFInfo
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- CN114426616A CN114426616A CN202011069407.1A CN202011069407A CN114426616A CN 114426616 A CN114426616 A CN 114426616A CN 202011069407 A CN202011069407 A CN 202011069407A CN 114426616 A CN114426616 A CN 114426616A
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F210/00—Copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
- C08F210/16—Copolymers of ethene with alpha-alkenes, e.g. EP rubbers
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F2/00—Processes of polymerisation
- C08F2/01—Processes of polymerisation characterised by special features of the polymerisation apparatus used
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- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
- C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
- C08L23/04—Homopolymers or copolymers of ethene
- C08L23/08—Copolymers of ethene
- C08L23/0807—Copolymers of ethene with unsaturated hydrocarbons only containing more than three carbon atoms
- C08L23/0815—Copolymers of ethene with aliphatic 1-olefins
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- C08L2205/00—Polymer mixtures characterised by other features
- C08L2205/02—Polymer mixtures characterised by other features containing two or more polymers of the same C08L -group
- C08L2205/025—Polymer mixtures characterised by other features containing two or more polymers of the same C08L -group containing two or more polymers of the same hierarchy C08L, and differing only in parameters such as density, comonomer content, molecular weight, structure
Abstract
The invention provides a method for synthesizing polyolefin, which comprises the following steps: providing a polymerization reaction system comprising a first reactor and a second reactor in communication, introducing a recycle stream comprising olefin monomer, molecular weight regulator, and at least two inert condensing media into the polymerization reaction system; regulating the proportion of at least two inert condensing media in the circulating material and the temperature of the circulating material to ensure that the circulating material is partially condensed; a part of the liquid material after partial condensation enters a first reactor, and the liquid material contacts with a catalyst in the first reactor to generate first polyolefin; the gas material, the residual liquid material and the first polyolefin after partial condensation enter a second reactor, and the gas material, the liquid material and the catalyst contact to generate second polyolefin in the second reactor; and regulating the ratio of the condensed liquid material entering the first reactor and the second reactor, so that the polymerization environment in the first reactor and the second reactor is changed. The method of the present invention can regulate the molecular weight distribution and branched chain distribution of polyolefin product in the reactor and lower the investment cost and production cost of the apparatus.
Description
Technical Field
The invention relates to a method for synthesizing polyolefin and application thereof.
Background
For polyolefin products, it is the molecular chain structure and the aggregate structure that determine their physical properties. The molecular chain structure comprises a structure of a repeating unit and a structure of a chain, wherein the chain structure comprises a chain length and a distribution thereof, a copolymerization composition and a distribution thereof, a sequence distribution of a copolymerization unit and the like. The condensed state structure includes a crystal structure, molecular orientation, and the like. From the polymerization mechanism, polyethylene generally belongs to coordination polymerization, that is, a process in which a carbon-carbon double bond (C ═ C) of an ethylenic monomer is first coordinated and activated on an active center of a transition metal initiator, and thereby monomer molecules are successively inserted into a transition metal-carbon bond to undergo chain propagation. In a polymerization environment in which liquid exists, the shielding effect of the liquid can control the active center to slowly release, and the active center can experience more different polymerization environments due to the lengthening of the polymerization period, so that polyethylene molecular chains with changeable structures are obtained, and the polyethylene molecular chains are mixed at a molecular level, so that the product performance is greatly improved. The polymerization environment with higher monomer concentration and lower molecular weight regulator concentration is beneficial to obtaining high molecular weight polymer, and vice versa is beneficial to obtaining low molecular weight polymer. It is known in the art that broadening the molecular weight distribution of polyolefins can achieve the goal of improving rheological properties while maintaining the mechanical properties of the final product; wherein the high molecular weight portion ensures the mechanical properties of the product and the low molecular weight portion contributes to improving the processability of the product.
In order to obtain a polyolefin having a specific molecular weight distribution and copolymerization composition distribution, the following five ways can be employed. (1) Parallel reactor processes or polymer melt blending. The polymer with specific chain structure can be conveniently prepared by blending polymers with different chain structures in a molten state. However, the physical blending method has difficulty in controlling the uniformity of the product quality. (2) The control of molecular weight distribution and branching degree distribution is realized by adopting a series reactor process and controlling polymerization reaction environments of different reactors. In practical applications, one or more reactors such as a stirred tank reactor, a loop reactor, a gas phase fluidized bed reactor, etc. may be combined in the series reactor process. Therefore, the method is flexible to operate, but the process flow is complex and the equipment investment cost is high. The series production process adopted in industrial production mainly comprises Borstar process of Borealis company, CX process of Mitsui chemistry, Unipol II process of Univation company, Spherilene process of Basell company and the like. Patent WO2006/022736 proposes a process for the production of propylene impact copolymers in series of two multizone circulating reactors. (3) The composite catalyst is used in a single reactor, and the regulation and control of molecular weight distribution and branching degree distribution are realized by changing the proportion of different catalysts such as a Ziegler-Natta catalyst, a metallocene catalyst, a late transition metal catalyst and the like. Chinese patent ZL 201310311017.4 adopts a cascade coordination metal catalytic system to prepare a broad peak/bimodal polyolefin product. The university company developed a Prodigy composite catalyst and applied to Unipol single gas phase reactors to produce bimodal HDPE. However, industrial catalysts are difficult to develop, and the regulation of the aggregation structure is limited. (4) A differentiated polymerization environment was constructed within a single reactor. WO00/02929A1 proposes a multi-zone circulating reactor process and apparatus for producing broad peak polyolefins by controlling the polymerization conditions in two reaction zones. The difficulty of controlling process conditions is higher than in a series reactor process due to operation in a single reactor. (5) Dynamically regulating and controlling the polymerization reaction environment in a single reactor. For example, by periodically varying the feed rates of a molecular weight regulator such as hydrogen and a comonomer such as an alpha-olefin, etc., so that the polyolefins produced at different times have different chain structures, the final product has a broader molecular weight distribution and branching degree distribution. This process is complicated to operate and requires a period of variation of the polymerization environment which is much shorter than the residence time of the polymer in the reactor. The process is therefore suitable for catalyst systems sensitive to chain transfer agents.
Disclosure of Invention
In view of the deficiencies of the prior art, the present invention provides a novel process for the polymerization of olefins.
An object of the present invention is to regulate the chain structure such as the molecular weight distribution and the branched chain distribution of polyolefin. The inventors of the present invention have found that different kinds of inert condensing media in the polymerization reaction system have different induced condensing efficiencies for the olefin monomer and the molecular weight modifier and different effects on the solubilities of the olefin monomer and the molecular weight modifier. Therefore, at least two inert condensing media are introduced into the reaction system, and the proportion of the olefin monomer and the molecular weight regulator in the liquid phase, the gas phase and the solid phase in the reactor can be flexibly regulated and controlled, so that the molecular weight distribution and the branched chain distribution of the final polyolefin product can be regulated and controlled.
It is another object of the present invention to combine the advantages of the tandem process and the condensation process, to introduce the polyolefin and the solvent produced in the former reactor directly into the latter reactor without separation, thereby reducing the equipment investment cost and the production cost.
A first aspect of the present invention provides a process for synthesizing a polyolefin, comprising the steps of:
s1: providing a polymerization reaction system comprising a first reactor and a second reactor in communication, introducing a recycle stream comprising olefin monomer, molecular weight regulator, and at least two inert condensing media into the polymerization reaction system;
s2: regulating the proportion of at least two inert condensing media in the circulating material and the temperature of the circulating material to ensure that the circulating material is partially condensed;
s3: a part of the liquid material after partial condensation enters a first reactor, and the liquid material contacts with a catalyst in the first reactor to generate first polyolefin;
s4: and feeding the partially condensed gas material, the residual liquid material and the first polyolefin into a second reactor, and contacting the gas material, the liquid material and the catalyst in the second reactor to generate second polyolefin.
According to some embodiments of the invention, the method further comprises regulating the distribution ratio of the liquid material in S3 and S4. According to the invention, the distribution ratio of the liquid materials in the S3 and the S4 can be realized by an industrial operation system or manual regulation.
According to some embodiments of the invention, the method further comprises step S5: the unreacted recycled material in the second reactor is continuously circulated in the polymerization reaction system, and the polyolefin is continuously or intermittently discharged from the outlet of the second reactor.
According to some embodiments of the present invention, the composition of the feed, such as the molar ratio of comonomer to ethylene (Cx/C), in the polymerization environment in the first and second reactors may be adjusted by adjusting one or more of the ratio of the at least two inert condensing media, the temperature of the recycled feed, and the distribution ratio of the liquid feeds in steps S3 and S42) Molar ratio of hydrogen to ethylene (H)2/C2). According to the invention, the comonomer refers to an alpha-olefin of 3 to 18 carbon atoms.
According to some embodiments of the present invention, the condensate content in the second reactor may be adjusted by adjusting one or more of the ratio of the at least two inert condensing media, the temperature of the recycled stream, and the distribution ratio of the liquid stream in steps S3 and S4.
According to some embodiments of the invention, the polymerization environment (e.g., Cx/C) of the first and second reactors is allowed for different comonomers2、H2/C2Equal material compositions) are the most different, and the compositions and proportions of the inert condensing media are also different.
According to the invention, the properties of product density, melt index, molecular weight distribution and the like are regulated and controlled by regulating and controlling the proportion of the at least two inert condensing media, the temperature of the circulating material and the distribution proportion of the liquid materials in the steps S3 and S4.
According to the invention, the first reactor is dominated by liquid material and solid material, and the second reactor is dominated by gaseous material and solid material, and a dense fluidized bed state is maintained. In the polymerization reaction process, unreacted circulating materials at the outlet of the second reactor are subjected to compression, condensation and gas-liquid separation in a circulating loop, wherein part of liquid-phase materials obtained by the gas-liquid separation enter the first reactor, reactants in the liquid materials in the first reactor are contacted with a catalyst to generate first polyolefin, the first polyolefin and the unreacted materials continuously discharged from the outlet of the first reactor enter the second reactor, and gas materials obtained by the gas-liquid separation and residual liquid materials return to the second reactor.
According to some preferred embodiments of the present invention, after the recycle stream is compressed, condensed and subjected to gas-liquid separation, the gaseous stream and the liquid stream are substantially in phase equilibrium with respect to each other. Because the boiling points, saturated vapor pressures, relative volatilities and the like of different components have obvious differences, the contents of olefin monomers in the circulating material, the gas material and the liquid material have larger differences. If the content of the olefin monomer and/or the molecular weight regulator in the liquid phase material or the gas phase material cannot meet the requirements of production load and the performance of the polyolefin product, the olefin monomer and/or the molecular weight regulator need to be supplemented into the two reactors.
According to some embodiments of the invention, the recycled material comprises at least two inert condensing media, wherein the mole percentage of any one inert condensing medium is between 0 and 99.99%.
According to some embodiments of the invention, the temperature of the recycled material is between 30 and 80 ℃.
In the present invention, the temperature of the recycled material is always below the lowest dew point of the at least two inert condensing media.
According to a preferred embodiment of the invention, the difference between the number of carbon atoms of the at least two inert condensing media is greater than or equal to 2. The inventor of the invention finds that the inert condensing medium realizes the regulation and control of the polymerization environment in the reactor by changing the induced condensing efficiency and the solubility of the inert condensing medium on olefin monomers and molecular weight regulators so as to indirectly regulate and control the product performance. If the difference between the boiling points of at least two condensing media is large, and the composition of the condensing media is changed, the solubility of various components in the circulating material is changed more, and the polymerization environment can be adjusted more flexibly, so that products with as wide molecular weight distribution as possible can be obtained in the same device.
According to some embodiments of the invention, the inert condensing media have different boiling points, for example the inert condensing media comprise a higher boiling condensing medium a and a lower boiling condensing medium B.
According to some embodiments of the invention, the inert condensing medium is selected from at least two of a linear alkane from C3 to C8, a branched alkane from C4 to C8, and a cyclic alkane from C4 to C8.
According to some embodiments of the invention, the inert condensing medium is selected from at least two of propane, n-butane, isobutane, isopentane, n-hexane and n-heptane.
According to some embodiments of the invention, the inert condensing medium comprises n-butane and n-hexane. To take into account product properties and reactor inlet temperatures of not less than 40 ℃ (45 ℃ in summer), butane is typically present in a molar fraction of 2% to 8%.
According to some embodiments of the invention, the inert condensing medium comprises propane and n-pentane.
According to some embodiments of the invention, the recycle feed, gaseous feed, and liquid feed comprise at least one olefin monomer.
According to some embodiments of the invention, at least two of the inert condensing medium, the promoter, the molecular weight regulator, and the inert gas are included in the recycled material, the gaseous material, and the liquid material.
According to some embodiments of the invention, the olefin monomer is selected from one or more of ethylene and an alpha-olefin of 3 to 18 carbon atoms.
According to some embodiments of the invention, the olefin monomer is selected from one or more of ethylene, propylene, 1-butene and 1-hexene.
According to some embodiments of the invention, the catalyst in the first and second reactors is the same or different.
According to some embodiments of the invention, the catalyst is selected from one or more of chromium based catalysts, ziegler-natta catalysts, metallocene catalysts and late transition metal catalysts, preferably from ziegler-natta catalysts.
According to some embodiments of the invention, the cocatalyst is a cocatalyst required for the use of the chromium-based catalyst in a reactor, such as an alkyl aluminum compound; preferably one or more selected from Triethylaluminium (TEA), Triisobutylaluminium (TIBA), Methylaluminoxane (MAO) and diethylaluminium ethoxide (DEAE); diethylaluminum ethoxide is preferred.
According to some embodiments of the invention, the co-catalyst is a co-catalyst required when the Ziegler-Natta catalyst is used in a reactor, such as one or more of an alkylaluminum compound, an alkyllithium compound, a dialkylaluminum oxy compound, an alkylzinc compound, and an alkylboron compound; preferably selected from alkyl aluminium compounds, more preferably one or more selected from triethyl aluminium, tri-isobutyl aluminium and tri-n-hexyl aluminium.
According to some embodiments of the invention, the cocatalyst is a cocatalyst required when the metallocene catalyst is used in a reactor, for example, one or more of an alkylaluminum compound, an alkylaluminum oxy compound, and a boron-based compound; preferably selected from alkylaluminum oxy compounds, more preferably one or more selected from methylaluminoxane, ethylaluminoxane and butylaluminoxane.
According to some embodiments of the present invention, the cocatalyst is a cocatalyst required when the late transition metal catalyst is used in the reactor, for example, one or more of an alkylaluminum compound, an alkylaluminum oxy compound, and a boron-based compound; preferably selected from alkylaluminum oxy compounds, more preferably one or more selected from methylaluminoxane, ethylaluminoxane and butylaluminoxane.
According to some embodiments of the invention, the molecular weight regulator is a conventional molecular weight regulator, and these compounds include hydrogen, metal alkyls or alpha-olefins, and the like, for example hydrogen.
According to some embodiments of the invention, the inert gas is a conventional inert gas, such as nitrogen.
According to some embodiments of the invention, the reaction pressure of the first reactor is between 1.0 and 10.0 MPa.
According to some embodiments of the invention, the reaction temperature of the first reactor is between 0 and 120 ℃.
According to some embodiments of the invention, the reaction pressure of the second reactor is between 1.0 and 10.0 MPa.
According to some embodiments of the invention, the reaction temperature of the first reactor is between 30 and 150 ℃.
According to some embodiments of the invention, the reaction pressure of the first reactor is higher than or equal to the reaction pressure of the second reactor.
According to some embodiments of the invention, the reaction temperature of the first reactor is lower than or equal to the reaction temperature of the second reactor.
According to some embodiments of the present invention, in the polymerization reaction system, at least two condensing media, a cocatalyst, a molecular weight regulator, and an olefin monomer may be directly introduced into the first reactor and the second reactor.
According to some embodiments of the present invention, in the polymerization reaction system, at least two condensing media, a cocatalyst, a molecular weight regulator, and an olefin monomer may be directly introduced into a circulation loop connecting the first reactor and the second reactor.
According to some embodiments of the present invention, in the polymerization reaction system, a portion of the at least two condensing media, the cocatalyst, the molecular weight regulator and the olefin monomer may be passed into the first reactor and the second reactor, and the others may be passed into a circulation loop connecting the first reactor and the second reactor.
According to a preferred embodiment of the present invention, in the polymerization reaction system, at least two inert condensing media, a cocatalyst, a molecular weight regulator and an olefin monomer are directly passed into a circulation loop connecting the first reactor and the second reactor.
A second aspect of the present invention provides a polymerization reaction system for the method of the first aspect, comprising a first reactor and a second reactor which are communicated, a gas material and liquid material conveying pipeline and equipment, a gas-liquid separation device, a heat exchange device, a catalyst storage device and a condensate storage device.
According to some embodiments of the invention, the type of the first reactor includes, but is not limited to, a stirred tank reactor or a loop reactor.
According to some embodiments of the invention, the gas-liquid separation device includes, but is not limited to, a surge tank separator or a cyclone separator.
According to some embodiments of the invention, the first reactor and the second reactor are connected to the pipeline by a material conveying device. Wherein, the first reactor mainly comprises liquid materials and solid materials. The second reactor is mainly composed of gas materials and solid materials and maintains a state of a dense-phase fluidized bed. In the polymerization reaction process, unreacted circulating materials at the outlet of the second reactor are subjected to compression, condensation and gas-liquid separation in a circulating loop, wherein part of liquid-phase materials obtained by the gas-liquid separation enter the first reactor, reactants in the liquid materials in the first reactor are contacted with a catalyst to generate first polyolefin, the first polyolefin and the unreacted materials continuously discharged from the outlet of the first reactor enter the second reactor, and gas materials obtained by the gas-liquid separation and residual liquid materials return to the second reactor.
A third aspect of the invention provides a use of the method according to the first aspect or the polymerization system according to the second aspect in the production of polyolefins.
The method is suitable for copolymerization systems such as homopolymerization, binary copolymerization, ternary copolymerization and the like. The method of the invention is based on a gas phase process and a condensation process, two reactors are connected end to end through a circulation loop, at least two inert condensation media are introduced into a system, and polymerization reaction environments of the two reactors are regulated by regulating the proportion of the inert condensation media, the temperature of circulating materials and the proportion of liquid materials respectively entering the first reactor and the second reactor, so that chain structures such as molecular weight distribution, branching degree distribution and the like of polyolefin in the two reactors are regulated, and the chain structure of a final product is regulated.
The invention is suitable for homopolymerization and copolymerization systems which take olefin as reaction raw material. The terms "homopolymerization" and "copolymerization" as used herein mean that the polymerization system comprises one polymerizable monomer and at least two polymerizable monomers, respectively. The term "inert condensing medium" as used herein refers to saturated hydrocarbons that do not chemically react with the olefin monomer, catalyst and cocatalyst at the reaction pressure and reaction temperature.
Compared with the prior art, the invention has the following advantages:
1) the polymerization reaction system comprises two reaction units of a first reactor and a second reactor which are communicated, the polymerization reaction environment and the production load of the first reactor and the second reactor can be adjusted in a large range, and the chain structure of a polyolefin final product can be regulated and controlled;
2) the mixture of the liquid removed from the first reactor and the first polyolefin is directly fed to the second reactor where the liquid is vaporized, thereby reducing the load on the devolatilization system and providing good economy.
Drawings
FIG. 1 is a schematic flow diagram of a binary copolymerization reaction system according to an embodiment of the present invention.
FIG. 2(a) shows the ratio of the mole fraction of hydrogen to the mole fraction of ethylene in two reactors versus the mole fraction of butane in the inert condensing medium according to one embodiment of the present invention.
FIG. 2(b) shows the ratio of the mole fraction of 1-butene to the mole fraction of ethylene in two reactors versus the mole fraction of butane in the inert condensing medium according to one embodiment of the present invention.
FIG. 3 shows a plot of mass fraction of condensate and temperature of recycled material versus mole fraction of butane in the inert condensing medium according to one embodiment of the present invention.
Figure 4(a) shows the molecular weight of a polyethylene according to one embodiment of the present invention as a function of the molar fraction of butane in the inert condensing medium.
Figure 4(b) shows the density of polyethylene as a function of the mole fraction of butane in the inert condensing medium according to one embodiment of the present invention.
Detailed Description
The present invention will be described in detail with reference to the following examples and drawings, which are only for illustrative purposes and are not intended to limit the scope of the present invention, and all reasonable variations and combinations included within the spirit and scope of the present invention are included in the scope of the present invention.
FIG. 1 is a simplified flow diagram of a binary polymerization reaction system according to one embodiment of the present invention, comprising:
a first reactor 1 for the polymerization of olefins;
a heat exchanger 2 for removing heat from the first reactor 1;
a distribution plate 3 for uniformly distributing gas at the bottom of the fluidized bed reactor;
a second reactor 4 for the polymerization of olefins;
a recycle gas compressor 5 for maintaining a recycle gas stream flowing in the line;
a heat exchanger 6 for cooling the gas material at the outlet of the second reactor 4;
a separation device 7 for separating the condensate from the partially condensed gas-liquid mixture at the outlet of the heat exchanger 6;
a storage tank 8 for storing the liquid material separated by the separation equipment 7;
a feed pump 9 for introducing the liquid material in the condensate storage tank 8 into the first reactor 1;
a recycle line 10 for recycling the gaseous feed from the outlet of the second reactor 4 to the gas phase distribution zone of the second reactor 4;
A fluid conduit 13 for introducing the first condensing medium into the circulation loop 10;
a fluid conduit 14 for introducing a second condensing medium into the circulation loop 10;
a fluid conduit 22 for introducing catalyst into the first reactor 1;
a fluid conduit 15 for introducing catalyst above the distribution plate 3;
a fluid line 16 for withdrawing solid phase polyolefin from the reactor;
a fluid conduit 17 for introducing a liquid feed into the first reactor 1;
a fluid conduit 18 for introducing slurry material from the reactor into the second reactor 4;
the outlet of the feed pump 9 is used to introduce part of the condensate directly into the flow line 19 of the second reactor 4.
Specifically, in a preferred embodiment of the present invention, the first reactor 1 and the second reactor 4 are connected end to end by means of material conveying means 5 and 9, and lines 10, 17 and 18. Wherein, the first reactor 1 mainly comprises liquid materials and solid materials. The second reactor 4 is mainly filled with gas materials and solid materials and maintains a dense-phase fluidized bed state. In the polymerization reaction process, unreacted circulating materials at the outlet of the second reactor 4 pass through a circulating gas compressor 5, a heat exchanger 6 and a gas-liquid separation device 7 in a circulating loop 10, wherein part of liquid-phase materials at the outlet of the gas-liquid separation device 7 enter the first reactor 1, reactants in the liquid materials in the first reactor 1 contact with a catalyst to generate polyolefin, the polyolefin and the unreacted materials continuously discharged from the outlet of the first reactor 1 enter the second reactor 4, and gas materials and residual liquid materials at the outlet of the gas-liquid separation device 7 return to the second reactor 4. By regulating the proportion of the first condensing medium and the second condensing medium in the circulating loop 10 in front of the heat exchanger 6 and the temperature of the outlet of the heat exchanger 6 (namely the temperature of the circulating material), the mol fractions of hydrogen, olefin monomer and comonomer in the solid phase and the liquid phase are regulated and controlled, and the aim of regulating and controlling the polyolefin chain structure is fulfilled.
FIGS. 2(a) and 2(b) show the composition in two reactors as a function of the mole fraction of one of the inert condensing media in the inert condensing medium according to one embodiment of the present invention. The first condensing medium is n-butane, the second condensing medium is n-hexane, the abscissa of fig. 2(a) is the mole fraction of n-butane in the inert condensing medium as the first condensing medium, and the ordinate is the ratio of the mole fraction of hydrogen to the mole fraction of ethylene in the first reactor and the second reactor. The abscissa of FIG. 2(b) is the molar fraction of n-butane in the inert condensation medium as the first condensation medium and the ordinate is the ratio of the molar fraction of 1-butene to the molar fraction of ethylene in the first and second reactor. As the n-butane content increases, the solubility of hydrogen, ethylene and 1-butene in the second reactor all decreases. The rate of change of solubility of the components in the second reactor is in order of magnitude 1-butene > ethylene > hydrogen with increasing n-butane content. Thus, as the n-butane content of the recycle increases, the ratio of the mole fractions of hydrogen and ethylene in the second reactor increases, while the ratio of the mole fractions of 1-butene and ethylene decreases. The ratio of the mole fractions of hydrogen and ethylene in the first reactor decreases while the ratio of the mole fractions of 1-butene and ethylene increases because the higher the n-butane content, the lower the temperature of the desired recycle, and the greater the proportion of molecular weight components condensed.
FIG. 3 shows the mass fraction of condensate and the temperature of the recycled material as a function of the mole fraction of one of the inert condensing media in the inert condensing medium according to one embodiment of the present invention. Wherein the abscissa is the mole fraction of the first condensation medium n-butane in the inert condensation medium, and the ordinate is the mass fraction of the condensate in the circulating material and the temperature of the circulating material respectively. Along with the increase of the n-butane mole fraction, the content of the second condensation medium n-hexane with a higher boiling point is reduced, the mass fraction of the condensation liquid in the circulating material is rapidly reduced, and the temperature of the circulating material is reduced in order to ensure the heat transfer capacity of the circulating material.
Fig. 4(a) and 4(b) show molecular weight and density of a polyethylene according to one embodiment of the present invention as a function of the mole fraction of one of the inert condensing media in the inert condensing medium. The reaction temperature of the first reactor and the second reactor were both 88 ℃. Wherein the abscissa is the mole fraction of n-butane in the first condensing medium in the inert condensing medium, the ordinate of FIG. 4(a) is the weight average molecular weight of the polyolefin, and the ordinate of FIG. 4(b) is the density of the polyolefin. Due to the effect of the condensing medium on the polymerization reaction environment in the liquid phase and the solid phase, the molecular weight and the density of the polyolefin obtained in the first reactor and the second reactor are greatly different, and are obviously influenced by the n-butane content of the first condensing medium.
The starting materials or components used in the present invention may be commercially or conventionally prepared unless otherwise specified.
In the Z-N catalyst system used in the examples of the present invention, the main catalyst is a Ziegler Natta catalyst, and the cocatalyst is triethylaluminum.
Example 1
Linear Low Density Polyethylene (LLDPE) is produced in a polymerization reaction system shown in figure 1, a first reactor 1 is used for carrying out binary copolymerization reaction on ethylene and 1-butylene in the first reactor under the action of a Z-N catalyst system, the polymerization reaction temperature is 88 ℃, the reaction pressure is 40.0bar, and reaction materials comprise hydrogen, nitrogen, ethylene, N-butane, 1-butylene and N-hexane. The second reactor 4 has a polymerization temperature of 88 ℃ and a pressure of 24.0bar under the action of a Z-N catalyst system, and reaction materials comprise hydrogen, nitrogen, ethylene, N-butane, 1-butene and N-hexane. The first condensing medium was n-butane, the second condensing medium was n-hexane, the molar fraction of n-butane in the recycle stream at the outlet of the second reactor was 0.0371, the molar fraction of n-hexane was 0.0638, the molar fraction of ethylene was 0.3000, the molar fraction of 1-butene was 0.06 and the molar fraction of hydrogen was 0.035. The temperature of the material at the outlet of the heat exchanger 6 was 54.89 ℃. The mass ratio of the stream flows in lines 17 and 19 is 1: 0. The mass ratio of the polyethylene produced in the first reactor and the second reactor was 3: 7.
The linear low density polyethylene produced according to example 1 had a density of 0.9246g/cm3And the weight average molecular weight is 162017. Wherein the first polyethylene obtained in the first reactor has a density of 0.9179 and a weight average molecular weight of 222745(ii) a The second polyethylene obtained in the second reactor had a density of 0.9275 and a weight average molecular weight of 141356.
Example 2
Linear Low Density Polyethylene (LLDPE) is produced in a polymerization reaction system shown in figure 1, a first reactor 1 is used for carrying out binary copolymerization reaction on ethylene and 1-butylene in the first reactor under the action of a Z-N catalyst system, the polymerization reaction temperature is 88 ℃, the reaction pressure is 40.0bar, and reaction materials comprise hydrogen, nitrogen, ethylene, N-butane, 1-butylene and N-hexane. The second reactor 4 has a polymerization temperature of 88 ℃ and a pressure of 24.0bar under the action of a Z-N catalyst system, and reaction materials comprise hydrogen, nitrogen, ethylene, N-butane, 1-butene and N-hexane. The first condensing medium was n-butane, the second condensing medium was n-hexane, the molar fraction of n-butane in the recycle at the outlet of the second reactor was 0.0478, the molar fraction of n-hexane was 0.0599, the molar fraction of ethylene was 0.3000, the molar fraction of 1-butene was 0.06 and the molar fraction of hydrogen was 0.035. The temperature of the feed at the outlet of the heat exchanger 6 was 52.01 ℃. The mass ratio of the stream flows in lines 17 and 19 is 1: 0. The mass ratio of the polyethylene produced in the first reactor and the second reactor was 3: 7.
The linear low density polyethylene produced according to example 2 had a density of 0.9249g/cm3And the weight average molecular weight is 15915. Wherein the first polyethylene obtained from the first reactor has a density of 0.9174 and a weight average molecular weight of 223918; the second polyethylene obtained in the second reactor had a density of 0.9281 and a weight average molecular weight of 137492.
Example 3
Linear Low Density Polyethylene (LLDPE) is produced in a polymerization reaction system shown in figure 1, a first reactor 1 has polymerization reaction temperature of 88 ℃ and reaction pressure of 40.0bar under the action of a Z-N catalyst system, ethylene and 1-hexene have binary copolymerization reaction in the first reactor, and reaction materials comprise hydrogen, nitrogen, ethylene, propane, isopentane and 1-hexene. The second reactor 4 has a polymerization temperature of 88 ℃ and a pressure of 24.0bar under the action of a Z-N catalyst system, and reaction materials comprise hydrogen, nitrogen, ethylene, propane, isopentane and 1-hexene. The first condensing medium was propane, the second condensing medium was isopentane, the mole fraction of propane in the recycle at the outlet of the second reactor was 0.0440, the mole fraction of isopentane was 0.0648, the mole fraction of ethylene was 0.3000, the mole fraction of 1-hexene was 0.06, and the mole fraction of hydrogen was 0.035. The temperature of the feed at the outlet of the heat exchanger 6 was 54.91 ℃. The mass ratio of the stream flows in lines 17 and 19 is 1: 0. The mass ratio of the polyethylene produced in the first reactor and the second reactor was 3: 7.
The linear low density polyethylene produced according to example 3 had a density of 0.9204g/cm3And the weight average molecular weight is 110940. Wherein the first polyethylene obtained in the first reactor has a density of 0.9199 and a weight average molecular weight of 158675; the second polyethylene obtained in the second reactor had a density of 0.9207 and a weight average molecular weight of 95166.
Comparative example 1
The gas phase fluidized bed is a polymerization reactor, Linear Low Density Polyethylene (LLDPE) is produced under the action of a Z-N catalyst system, the polymerization temperature is 88 ℃, the pressure is 24.0bar, and reaction materials comprise hydrogen, nitrogen, ethylene, N-butane and 1-butene. The first condensing medium was n-butane, the mole fraction of n-butane in the recycle at the outlet of the fluidized bed reactor was 0.1009, the mole fraction of ethylene was 0.3000, the mole fraction of 1-butene was 0.06 and the mole fraction of hydrogen was 0.035. The temperature of the feed at the outlet of the heat exchanger 6 was 33.72 ℃.
The linear low density polyethylene produced according to comparative example 1 had a density of 0.9301g/cm3And the weight average molecular weight is 125347.
Comparative example 2
The gas phase fluidized bed is a polymerization reactor, Linear Low Density Polyethylene (LLDPE) is produced under the action of a Z-N catalyst system, the polymerization temperature is 88 ℃, the pressure is 24.0bar, and reaction materials comprise hydrogen, nitrogen, ethylene, propane and 1-hexene. The first condensing medium was propane, the mole fraction of propane in the recycle at the outlet of the fluidized bed reactor was 0.1011, the mole fraction of ethylene was 0.3000, the mole fraction of 1-hexene was 0.06 and the mole fraction of hydrogen was 0.035. The temperature of the material at the outlet of the heat exchanger 6 was 42.35 ℃.
According to comparative example 2The density of the produced linear low-density polyethylene is 0.9198g/cm3And the weight average molecular weight is 109793.
It should be noted that the above-mentioned embodiments are only for explaining the present invention, and do not set any limit to the present invention. The invention has been described with reference to an exemplary embodiment, but the words which have been used herein are words of description and illustration, rather than words of limitation. The invention can be modified, as prescribed, within the scope of the appended claims, and changes can be made thereto without departing from the spirit and scope of the invention. Although the invention has been described herein with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein, but rather extends to all other methods and applications having the same functionality.
Claims (10)
1. A method of synthesizing a polyolefin comprising the steps of:
s1: providing a polymerization reaction system comprising a first reactor and a second reactor in communication, introducing a recycle stream comprising olefin monomer, molecular weight regulator, and at least two inert condensing media into the polymerization reaction system;
s2: regulating the proportion of at least two inert condensing media in the circulating material and the temperature of the circulating material to ensure that the circulating material is partially condensed;
s3: a part of the liquid material after partial condensation enters a first reactor, and the liquid material contacts with a catalyst in the first reactor to generate first polyolefin;
s4: and feeding the partially condensed gas material, the residual liquid material and the first polyolefin into a second reactor, and contacting the gas material, the liquid material and the catalyst in the second reactor to generate second polyolefin.
2. The method of claim 1, further comprising adjusting the ratio of the distribution of the liquid feed in S3 and S4.
3. The method according to claim 1 or 2, further comprising step S5: the unreacted recycled material in the second reactor is continuously circulated in the polymerization reaction system, and the polyolefin is continuously or intermittently discharged from the outlet of the second reactor.
4. The process of any one of claims 1 to 3, wherein the recycle stream comprises at least two inert condensing media, wherein the mole percent of any one inert condensing medium is from 0 to 99.99%; and/or the temperature of the recycled material is 30-80 ℃; preferably, the first and second electrodes are formed of a metal,
the inert condensing medium is selected from at least two of linear alkanes of C3-C8, branched alkanes of C4-C8 and cycloalkanes of C4-C8, and is preferably selected from at least two of propane, n-butane, isobutane, isopentane, n-hexane and n-heptane.
5. The process of any one of claims 1-4, wherein the recycled, gaseous, and liquid feeds include at least one olefin monomer; and/or
The circulating material, the gaseous material and the liquid material comprise at least two of inert condensing medium, cocatalyst, molecular weight regulator and inert gas.
6. The process according to any one of claims 1 to 5, characterized in that the olefin monomer is selected from one or more of ethylene and alpha-olefins of 3 to 18 carbon atoms, preferably from one or more of ethylene, propylene, 1-butene and 1-hexene; and/or
The catalyst in the first reactor and the second reactor is the same or different; preferably, the catalyst is selected from one or more of chromium based catalysts, ziegler-natta catalysts, metallocene catalysts and late transition metal catalysts.
7. The process according to any one of claims 1 to 6, wherein the reaction pressure of the first reactor is 1.0 to 10.0MPa and the reaction temperature is 0 to 120 ℃; and/or the reaction pressure of the second reactor is 1.0-10.0MPa, and the reaction temperature is 30-150 ℃; preferably, the reaction pressure of the first reactor is higher than or equal to the reaction pressure of the second reactor, and/or the reaction temperature of the first reactor is lower than or equal to the reaction temperature of the second reactor.
8. The process of any one of claims 1 to 7, wherein in the polymerization reaction system, the inert condensing medium, cocatalyst, molecular weight regulator and olefin monomer are directly passed into the first reactor and the second reactor; and/or the inert condensing medium, cocatalyst, molecular weight regulator and olefin monomer are passed directly into a circulation loop connecting the first reactor and the second reactor; and/or a portion of the inert condensing medium, cocatalyst, molecular weight regulator and olefin monomer is passed to the first reactor and the second reactor, the remaining portion being passed to a recycle loop connecting the first reactor and the second reactor.
9. A polymerization reaction system for use in the method of any one of claims 1-8, comprising connecting a first reactor and a second reactor, gaseous feed and liquid feed transfer lines and equipment, gas-liquid separation equipment, heat exchange equipment, catalyst storage equipment, and condensate storage equipment; preferably the type of the first reactor comprises a stirred tank reactor or a loop reactor; and/or the gas-liquid separation device comprises a buffer tank separator or a cyclone separator.
10. Use of the process according to any one of claims 1 to 8 or the polymerization system according to claim 9 in the production of polyolefins.
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| CN116072240A (en) * | 2023-03-21 | 2023-05-05 | 北京石油化工工程有限公司 | Method for confirming mole percentage and in-situ quantity of various monomers in gas phase and liquid phase in solution method olefin polymerization reaction system |
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