CN115612011B - Use of inert hydrocarbons in the solution polymerization of ethylene, alpha-olefins for maintaining the thermal stability of the reaction - Google Patents
Use of inert hydrocarbons in the solution polymerization of ethylene, alpha-olefins for maintaining the thermal stability of the reaction Download PDFInfo
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- 238000010528 free radical solution polymerization reaction Methods 0.000 title claims abstract description 48
- 229930195733 hydrocarbon Natural products 0.000 title claims abstract description 48
- 150000002430 hydrocarbons Chemical class 0.000 title claims abstract description 48
- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 title claims abstract description 47
- 239000005977 Ethylene Substances 0.000 title claims abstract description 47
- 239000004711 α-olefin Substances 0.000 title claims abstract description 47
- 238000006243 chemical reaction Methods 0.000 title claims abstract description 46
- 239000004215 Carbon black (E152) Substances 0.000 claims abstract description 41
- 238000000034 method Methods 0.000 claims abstract description 29
- 238000006116 polymerization reaction Methods 0.000 claims abstract description 24
- 230000002708 enhancing effect Effects 0.000 claims abstract description 4
- 229920000642 polymer Polymers 0.000 claims description 44
- 239000002904 solvent Substances 0.000 claims description 19
- KWKAKUADMBZCLK-UHFFFAOYSA-N 1-octene Chemical compound CCCCCCC=C KWKAKUADMBZCLK-UHFFFAOYSA-N 0.000 claims description 14
- VXNZUUAINFGPBY-UHFFFAOYSA-N 1-Butene Chemical compound CCC=C VXNZUUAINFGPBY-UHFFFAOYSA-N 0.000 claims description 10
- LIKMAJRDDDTEIG-UHFFFAOYSA-N 1-hexene Chemical compound CCCCC=C LIKMAJRDDDTEIG-UHFFFAOYSA-N 0.000 claims description 8
- TVMXDCGIABBOFY-UHFFFAOYSA-N n-Octanol Natural products CCCCCCCC TVMXDCGIABBOFY-UHFFFAOYSA-N 0.000 claims description 8
- 229920000089 Cyclic olefin copolymer Polymers 0.000 claims description 6
- QEMJIDSLEPYRLM-VMPITWQZSA-N (e)-3-ethylhex-2-ene Chemical compound CCC\C(CC)=C\C QEMJIDSLEPYRLM-VMPITWQZSA-N 0.000 claims description 4
- ZGEGCLOFRBLKSE-UHFFFAOYSA-N 1-Heptene Chemical compound CCCCCC=C ZGEGCLOFRBLKSE-UHFFFAOYSA-N 0.000 claims description 4
- FXNDIJDIPNCZQJ-UHFFFAOYSA-N 2,4,4-trimethylpent-1-ene Chemical compound CC(=C)CC(C)(C)C FXNDIJDIPNCZQJ-UHFFFAOYSA-N 0.000 claims description 4
- KKVVJQGDNYIIMN-SOFGYWHQSA-N 4-Methyl-3-heptene Chemical compound CCC\C(C)=C\CC KKVVJQGDNYIIMN-SOFGYWHQSA-N 0.000 claims description 4
- 150000001335 aliphatic alkanes Chemical class 0.000 claims description 4
- 150000001924 cycloalkanes Chemical class 0.000 claims description 4
- YWAKXRMUMFPDSH-UHFFFAOYSA-N pentene Chemical compound CCCC=C YWAKXRMUMFPDSH-UHFFFAOYSA-N 0.000 claims description 4
- 238000009825 accumulation Methods 0.000 claims description 3
- 239000012968 metallocene catalyst Substances 0.000 claims description 3
- OFKLSPUVNMOIJB-VMPITWQZSA-N (e)-3-methylhept-2-ene Chemical compound CCCC\C(C)=C\C OFKLSPUVNMOIJB-VMPITWQZSA-N 0.000 claims description 2
- RGYAVZGBAJFMIZ-UHFFFAOYSA-N 2,3-dimethylhex-2-ene Chemical compound CCCC(C)=C(C)C RGYAVZGBAJFMIZ-UHFFFAOYSA-N 0.000 claims description 2
- 239000011954 Ziegler–Natta catalyst Substances 0.000 claims description 2
- QQONPFPTGQHPMA-UHFFFAOYSA-N propylene Natural products CC=C QQONPFPTGQHPMA-UHFFFAOYSA-N 0.000 claims description 2
- 125000004805 propylene group Chemical group [H]C([H])([H])C([H])([*:1])C([H])([H])[*:2] 0.000 claims description 2
- 239000010409 thin film Substances 0.000 claims description 2
- 125000004122 cyclic group Chemical group 0.000 claims 1
- -1 dQ r /dT Chemical compound 0.000 abstract description 2
- 239000012071 phase Substances 0.000 description 12
- 238000000926 separation method Methods 0.000 description 12
- 239000003054 catalyst Substances 0.000 description 9
- VLKZOEOYAKHREP-UHFFFAOYSA-N hexane Substances CCCCCC VLKZOEOYAKHREP-UHFFFAOYSA-N 0.000 description 9
- 238000001704 evaporation Methods 0.000 description 8
- 230000008020 evaporation Effects 0.000 description 8
- 238000007334 copolymerization reaction Methods 0.000 description 6
- 238000005191 phase separation Methods 0.000 description 5
- 230000000694 effects Effects 0.000 description 4
- 239000007789 gas Substances 0.000 description 4
- 239000000178 monomer Substances 0.000 description 4
- 230000001105 regulatory effect Effects 0.000 description 4
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 3
- 229910052739 hydrogen Inorganic materials 0.000 description 3
- 239000001257 hydrogen Substances 0.000 description 3
- 239000007791 liquid phase Substances 0.000 description 3
- CPOFMOWDMVWCLF-UHFFFAOYSA-N methyl(oxo)alumane Chemical compound C[Al]=O CPOFMOWDMVWCLF-UHFFFAOYSA-N 0.000 description 3
- 125000004432 carbon atom Chemical group C* 0.000 description 2
- 239000012986 chain transfer agent Substances 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 239000012530 fluid Substances 0.000 description 2
- 229920001903 high density polyethylene Polymers 0.000 description 2
- 239000004700 high-density polyethylene Substances 0.000 description 2
- 230000001965 increasing effect Effects 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 238000011084 recovery Methods 0.000 description 2
- XDTMQSROBMDMFD-UHFFFAOYSA-N Cyclohexane Chemical compound C1CCCCC1 XDTMQSROBMDMFD-UHFFFAOYSA-N 0.000 description 1
- 229920010126 Linear Low Density Polyethylene (LLDPE) Polymers 0.000 description 1
- 239000004698 Polyethylene Substances 0.000 description 1
- 150000001336 alkenes Chemical class 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000009835 boiling Methods 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 230000001276 controlling effect Effects 0.000 description 1
- 229920001577 copolymer Polymers 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000001125 extrusion Methods 0.000 description 1
- 238000007701 flash-distillation Methods 0.000 description 1
- 238000009776 industrial production Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 150000005673 monoalkenes Chemical class 0.000 description 1
- JRZJOMJEPLMPRA-UHFFFAOYSA-N olefin Natural products CCCCCCCC=C JRZJOMJEPLMPRA-UHFFFAOYSA-N 0.000 description 1
- 239000012188 paraffin wax Substances 0.000 description 1
- 239000003208 petroleum Substances 0.000 description 1
- 229920000573 polyethylene Polymers 0.000 description 1
- 239000000376 reactant Substances 0.000 description 1
- 238000004064 recycling Methods 0.000 description 1
- 239000002002 slurry Substances 0.000 description 1
- 238000007613 slurry method Methods 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 229920001897 terpolymer Polymers 0.000 description 1
- 238000005979 thermal decomposition reaction Methods 0.000 description 1
Classifications
-
- 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
-
- 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
- C08F210/14—Monomers containing five or more carbon atoms
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/50—Improvements relating to the production of bulk chemicals
- Y02P20/54—Improvements relating to the production of bulk chemicals using solvents, e.g. supercritical solvents or ionic liquids
Abstract
The invention discloses an application of inert hydrocarbon in the solution polymerization of ethylene and alpha-olefin for maintaining the thermal stability of the reaction, wherein the inert hydrocarbon can increase the heat transfer rate of the operating point of the solution polymerization reactor of ethylene and alpha-olefin, namely dQ r /dT, thereby enhancing the thermal stability of the reactor; dQ r Refers to the heat transfer rate per unit time and unit volume of the reactor, and is in units of kJ/m 3 S; dT refers to the temperature change per unit time of the reactor, in units of ℃/s; inert hydrocarbons meet 0.21kJ/mol/K<Molar constant pressure specific heat<0.23kJ/mol/K; the molar constant pressure specific heat refers to the specific heat per unit mole of inert hydrocarbon at 25 ℃, 101325 Pa. The process according to the invention is particularly advantageous when the reaction rate in the polymerization reactor is relatively high, the reaction exotherm rate being large at high reaction rates, i.e.dQ g Relatively large/dT, relatively high possibility of uncontrolled thermal stability of the reaction, addition of inert hydrocarbon to make dQ r dT is equal to dQ g and/dT, maintaining the thermal stability of the polymerization reactor.
Description
Technical Field
The invention relates to the field of ethylene and alpha-olefin copolymerization, and aims at the reaction thermal stability during solution polymerization, in particular to the use of inert hydrocarbon in the solution polymerization of ethylene and alpha-olefin for maintaining the reaction thermal stability.
Background
In the solution polymerization of ethylene and alpha-olefins, the polymer product remains dissolved in the solvent under the reactor conditions to form a polymer solution, which, after leaving the reactor, is fed to a separation system to remove volatile components, such as solvent, monomers and comonomers, to obtain a polymer product.
Ethylene and alpha-olefin polymerization processes can be divided into three general categories, gas phase processes, slurry processes and solution processes. Compared with a gas phase method and a slurry method, the polyethylene process by the solution method has the characteristics that: the reaction temperature and pressure are higher, the reaction rate is faster, the residence time is shorter, and the polymer is dissolved in the solvent. The above-mentioned solution polymerization characteristics place higher demands on the stability of the reaction process, for example, the phase equilibrium stability and the thermal stability of the reaction. The composition, temperature, pressure changes within the reactor may lead to phase separation phenomena. Polymer solutions of a certain composition can phase separate into two liquid phases of different polymer content at a certain temperature and pressure, a phenomenon which is well known in the art. Phase separation generally results in reduced production efficiency, and thus it is necessary to avoid this phenomenon by controlling the operating conditions. The patent specification publication CN111630071a states that the critical temperature of the phase separation of a polymer solution can be increased by adding an inert hydrocarbon boiling in the range of 90 ℃ to 130 ℃. The patent specification publication WO 2002034795 A1 teaches the importance of selecting a suitable polymer solvent, such as octane, which maintains a homogeneous phase at a lower pressure.
The temperature and pressure are critical to maintaining the phase of the solution polymerization reactor and most solution polymerization processes for ethylene and alpha-olefins employ adiabatic reactors, such as the patent specification numbered CN 107614541B. The temperature control of the reactor is particularly important, particularly, the reaction rate of solution polymerization is high, and once the temperature is out of control, the polymer solution is easy to split phase, so that accidents such as stopping and the like are caused.
The invention aims to provide an ethylene and alpha-olefin solution polymerization method for improving the reaction thermal stability, and more particularly, to provide a solution polymerization method capable of better maintaining the reaction thermal stability when the temperature of a reactor deviates from the normal working condition.
The present invention has found that when ethylene and at least one alpha-olefin are copolymerized in a solution polymerization reactor, the polymerization reaction can be carried out by adding a catalyst satisfying 0.21kJ/mol/K<Molar constant pressure specific heat<Inert hydrocarbon at 0.23kJ/mol/K to increase the heat transfer rate at the operating point of the polymerization reactor, i.e., dQ r and/dT, thereby enhancing the thermal stability of the reactor and avoiding the scaling of the polymer caused by thermal splitting or polymer phase separation of the polymer due to the temperature runaway of the polymerization reactor. The invention also found that 0.21kJ/mol/K is satisfied<Molar constant pressure specific heat<The inert hydrocarbon of 0.23kJ/mol/K may be 2-cis-octene. Although 2-cis-octene has double bonds, 2-cis-octene is not copolymerized during polymerization. On the other hand, when the reaction rate in the solution polymerization reactor is relatively high, the reaction heat release rate is large at a high reaction rate, i.e., dQ g The process of the invention is particularly advantageous in that/dT is relatively large and the possibility of uncontrolled thermal stability of the reaction is relatively high.
Definition:
"alpha-olefin" refers to a mono-olefin having a double bond at the end of the molecular chain, such as 1-butene, 1-hexene, 1-octene, and the like.
"Polymer" is a polymer of ethylene with one or more alpha-olefin comonomers above C3, including terpolymers, and the like.
"adiabatic reactor" means that the reactor does not exchange heat with the outside. When the reaction materials are regulated to the specified temperature and fed into the reactor, the reaction temperature is only related to the feeding flow, the feeding temperature and the reaction heat and is not influenced by the external environment.
“dQ r "means the rate of heat transfer per unit time and unit volume (kJ/m) of the reactor 3 S) heat transfer means include, but are not limited to, heat transfer from a fresh feed at a lower temperature.
“dQ g "means the heat release rate per unit time (kJ/m) of the reactor 3 S) the reactor exotherm is the net thermal effect of all chemical reactions taking place within the reactor.
"dT" refers to the temperature change (DEG C/s) per unit time of the reactor.
Disclosure of Invention
The invention improves the copolymerization process of ethylene and alpha-olefin from the standpoint of thermal stability, and provides the use of inert hydrocarbon in the polymerization of ethylene and alpha-olefin solution for maintaining the thermal stability of the reaction.
Use of inert hydrocarbons to maintain thermal stability of reaction in ethylene, alpha-olefin solution polymerization, which inert hydrocarbons increase the rate of heat transfer at the operating point of the ethylene, alpha-olefin solution polymerization reactor, i.e., dQ r The dT is used for enhancing the thermal stability of the reactor, and avoiding the scaling caused by polymer thermal splitting or polymer phase splitting due to the temperature runaway of the polymerization reactor;
dQ r refers to the heat transfer rate per unit time and unit volume of the reactor, and is in units of kJ/m 3 /s；
dT refers to the temperature change per unit time of the reactor, in units of ℃/s;
the inert hydrocarbon satisfies 0.21kJ/mol/K < molar constant pressure specific heat <0.23kJ/mol/K;
the molar constant pressure specific heat refers to the specific heat per unit mole of the inert hydrocarbon at 25 ℃, 101325 Pa.
The inert hydrocarbon is preferably a paraffin having 7 or 8 carbon atoms and/or an olefin having 7 or 8 carbon atoms.
The inert hydrocarbon is further preferably at least one of 2-cis-octene, 2-trans-octene, 4-methyl-3-heptene, 3-methyl-2-heptene, 2, 3-dimethyl-2-hexene, 3-ethyl-2-hexene, 3, 4-dimethyl-trans-3-hexene, 2, 4-trimethyl-1-pentene.
The solvent in the solution polymerization of ethylene and α -olefin is preferably at least one of C4 to C6 chain alkane, C4 to C6 cycloalkane, more preferably at least one of C5 to C6 chain alkane, C5 to C6 cycloalkane, and α -olefin may be at least one of propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, and 1-octene, preferably at least one of 1-butene, 1-hexene, and 1-octene, most preferably 1-octene, and a catalyst known in the art for copolymerization of ethylene and α -olefin such as a metallocene catalyst or Ziegler-Natta catalyst may be used.
The reaction pressure for the solution polymerization of ethylene, alpha-olefins may be in the range of 30 to 200bar, preferably 35 to 100bar, more preferably 40 to 60bar, and the reaction temperature may be in the range of 120 to 220 ℃, preferably 140 to 200 ℃, more preferably 145 to 180 ℃.
The mode of realizing the application of the invention can be as follows: feeding the inert hydrocarbon to a solution polymerization reactor for the polymerization of ethylene with an alpha-olefin to obtain an intermediate polymer solution, and/or recycling the inert hydrocarbon during the polymerization.
Specifically, the inert hydrocarbon may be fed into the solution polymerization reactor by:
a. adding the inert hydrocarbon together with ethylene, alpha-olefin comonomer, and solvent and/or chain transfer agent to the solution polymerization reactor through a feed inlet;
b. the inert hydrocarbon is fed to the solution polymerization reactor through a separate inlet.
The chain transfer agent may be used in a solution polymerization reactor to control the molecular weight of the copolymer, such as hydrogen and the like.
The intermediate polymer solution preferably contains 0.05wt.% to 30wt.% of the inert hydrocarbon.
In a preferred embodiment, the intermediate polymer solution is withdrawn from the solution polymerization reactor, warmed by a heat exchanger, separated from the ethylene and alpha-olefin copolymer by a multi-stage flash separator, and the inert hydrocarbon is recovered and recycled back to the solution polymerization reactor to effect the recycle accumulation of the inert hydrocarbon during the polymerization reaction. By the above operations, little or no access to the inert hydrocarbon from an external storage tank or vessel is required.
Preferably, the ethylene and alpha-olefin copolymer exits the flash separator and enters a third separator, which may be a vacuum devolatilizer, a flash tank, a falling-strand evaporator, or a thin film evaporator.
The solution polymerization reactor is preferably an adiabatic reactor, the reactor having no gas phase space.
The heat exchanger may be a tube heat exchanger or a plate heat exchanger or the like.
The invention has the beneficial effects that:
the invention discovers for the first time that the addition meets 0.21kJ/mol/K<Molar constant pressure specific heat<Inert hydrocarbon of 0.23kJ/mol/L can increase the heat transfer rate of the operating point of the ethylene/alpha-olefin solution polymerization reactor, i.e., dQ r and/dT, the reaction thermal stability of the reactor is enhanced, and the scaling caused by thermal decomposition of polymer products or polymer split phase due to temperature runaway of the polymerization reactor is avoided. In particular, the process according to the invention is particularly advantageous when the reaction rate in the polymerization reactor is relatively high, the reaction exotherm rate being large at high reaction rates, i.e.dQ g The reaction thermal stability is relatively high and the possibility of losing control is relatively high, and the addition of the catalyst satisfies 0.21kJ/mol/K<Molar constant pressure specific heat<Inert hydrocarbon of 0.23kJ/mol/K gives dQ r dT is equal to dQ g and/dT, maintaining the thermal stability of the polymerization reactor.
Drawings
FIG. 1 is a schematic diagram of an ethylene and alpha-olefin solution polymerization system and process for maintaining thermal stability of the reaction as described in the examples of the present invention.
Detailed Description
The invention will be further elucidated with reference to the drawings and to specific embodiments. It is to be understood that these examples are illustrative of the present invention and are not intended to limit the scope of the present invention. The methods of operation, under which specific conditions are not noted in the examples below, are generally in accordance with conventional conditions, or in accordance with the conditions recommended by the manufacturer.
A specific method and system of an embodiment of the invention will be described below with reference to fig. 1, which shows an exemplary flow for using the method according to the invention. The system may add additional lines and/or additional equipment, such as a third separator, and/or other devices for operating the system, such as valves and pumps, as desired.
In fig. 1, ethylene, at least one alpha-olefin, and a solvent are fed into a solution polymerization reactor 1 through an inlet 5, and copolymerization occurs within the reactor. The effluent stream exits polymerization reactor 1 and passes through line 7, heat exchanger 2 and line 8 to first flash separator 3. At least a portion of the ethylene and alpha-olefin copolymer may be separated in the first flash separator 3 and withdrawn via line 9, fed to the second flash separator 4, and more ethylene and alpha-olefin copolymer may be separated in the second flash separator 4 and withdrawn via line 10. Inert hydrocarbons may be fed to the solution polymerization reactor 1 through inlet 5 along with ethylene, alpha-olefin comonomer and solvent, or may be fed directly to the solution polymerization reactor 1 through inlet 6. The inert hydrocarbon separated and recovered by the first flash separator 3 and the second flash separator 4 can be recycled to the solution polymerization reactor 1 through the pipelines 12 and 11.
The feed for this example comprises essentially ethylene monomer, alpha-olefin comonomer and solvent, inert hydrocarbons meeting the conditions defined in the description of the invention. As is known in the art, ethylene and alpha-olefin copolymerization is a process for producing polymers having different molecular weight, density, etc., such as ethylene and 1-octene for producing Linear Low Density Polyethylene (LLDPE), ethylene and 1-butene for producing High Density Polyethylene (HDPE). The solvent needs to be inert to the catalyst system and reactants and remain stable during the reaction, and the solvent does not perform exactly the same in the different polymerization processes, as is known in the art, solution polymerization requires a large amount of solvent to maintain the ethylene monomer, alpha-olefin comonomer, catalyst, molecular weight regulator, and polymer product in a single phase in the reactor. N-hexane, cyclohexane, isopar E are known in the art and widely used solvents.
As known in the art, the polymerization of ethylene and alpha-olefin is carried out with a catalyst, which may be any catalyst known in the art to be suitable for the solution copolymerization of ethylene with alpha-olefin comonomer, including Z-N catalysts and metallocene catalysts, such as a procatalyst which defines a geometry catalyst (CGC), and a cocatalyst which is Methylaluminoxane (MAO). As is known in the art, the addition of small amounts of a material having a large chain transfer constant can reduce the molecular weight of the polymer, and suitable chain transfer agents are various and commonly used, such as hydrogen.
The polymer solution is heated by a heat exchanger 2 before entering the separation system to obtain better separation effect, and volatile components in the polymer solution are removed, as known in the art, the heat exchanger 2 is a device for transferring heat from hot fluid to cold fluid to meet the process requirements, and plays an important role in chemical industry, petroleum, power, food and other industrial production, and has wide application. In the present invention, the heat exchanger 2 is used to control the temperature of the polymerization solution leaving the reaction unit so as to reach the specified temperature of the separation system. The patent specification CN 109563187B describes a method of using a spiral heat exchanger as a preheater for a polymer solution.
As is known in the art, polymer solution separation requires multiple separation and recovery steps, typically involving multiple flash distillation, rectification, recycle, extrusion, etc., with the primary purpose of devolatilizing the polymer solution to obtain a polymer that meets product requirements. Patent specification publication No. CN 114437253A discloses a polymer solution devolatilization method and device, comprising a first flash tank, a second flash tank and a heavy component devolatilization tower. Flash separation refers to the separation step that results in phase separation by pressure drop. In the process of devolatilizing a polymer solution, two-stage flash devolatilization is usually adopted, and patent specification with publication number of CN106414509A discloses a solution polymerization method comprising first-stage flash devolatilization and second-stage flash devolatilization, wherein a heated polymer solution from an outlet of a heat exchanger is fed into a first-stage flash tank for separation, a top gas phase stream is conveyed to a heat recovery unit, a bottom liquid phase stream is conveyed into a second-stage flash tank for continuous separation, and the temperature is regulated by a heat exchanger before the bottom liquid phase stream is conveyed into the second-stage flash tank.
The invention will be further described with reference to specific experiments and control groups, it being noted that the specific experiments are only illustrative of the invention and not limiting.
Experimental group 1, carried out according to the procedure described above, the reaction feed consisted of 12916.7kg/h ethylene monomer, 7916.67kg/h 1-octene comonomer, 58333.33kg/h solvent n-hexane, 4166.67kg/h 2-cis-octene inert hydrocarbon, 0.625kg/h procatalyst CGC, 6.25kg/h cocatalyst MAO, 2kg/h hydrogen as molecular weight regulator. The feed stream was split into two streams, one stream was temperature-regulated by a cooler to-28 ℃ and the other stream was temperature-regulated by a heater to 50 ℃, and after mixing the feed streams reached the established-25 ℃. The reactor adopts an adiabatic kettle reactor, a stirring part is arranged in the reactor, the reaction pressure is 40bar, the residence time is 10min, and the reaction temperature is 147 ℃. The reactor polymer solution contained 12500kg/h of polymer with a mass fraction of 15%.
The separation system adopts a three-stage flash evaporation mode, the first stage is medium-pressure flash evaporation, the pressure is 15bar, and the polymer solution is preheated to 200 ℃ before entering the first stage flash evaporation tank; the second stage is a low-pressure flash evaporation I, the pressure is 3bar, and the polymer solution is preheated to 190 ℃ before entering a second stage flash evaporation tank; the third stage is a low-pressure flash evaporation II, the pressure is 1bar, and the polymer solution is preheated to 190 ℃ before entering the second stage flash evaporation tank; after the third stage flash evaporation, the polymer solution enters an extruder to obtain a polymer. In an example 2500kg/h of 2-cis-octene inert hydrocarbon may be recovered during the first and second flash separation and recycled back to the solution polymerization reactor 1 via line 12 and line 11, respectively, to effect accumulation of inert hydrocarbon in the process. This has the advantage of reducing the addition of fresh inert hydrocarbon feed to the solution polymerization reactor 1 via line 6.
Experimental group 2 was conducted as per the method of experimental group 1, except that the reactor feed contained 54166.66kg/h solvent n-hexane, 8333.34kg/h 2-cis-octene inert hydrocarbon.
Experimental group 3 was conducted as per the method of experimental group 1, except that the reactor feed contained 45833.33kg/h solvent n-hexane, 16666.67kg/h 2-cis-octene inert hydrocarbon.
The control group was run as in experimental group 1, except that the reactor feed contained 62500kg/h solvent n-hexane, 0kg/h 2-cis-octene inerts, i.e., no 2-cis-octene inerts.
Table 1 shows the partial composition (wt.%) of the polymer solutions at the polymerization reactor outlets of the control group, the experimental group 1, the experimental group 2 and the experimental group 3. Table 1 also shows the dQ groups r dT (decimal place reserved) and dQ in percent r Change in/dT relative to control. As can be seen from Table 1, increasing the amount of 2-cis-octene, dQ r the/dT becomes larger, so that the thermal stability of the polymerization reactor is better, and the reactor operates more stably.
TABLE 1
Experimental groups 4 to 6 were conducted as in experimental group 3, except that 2-cis-octene in the reactor feed was replaced with equal mass of 4-methyl-3-heptene, 3-ethyl-2-hexene, 2, 4-trimethyl-1-pentene, i.e., 16666.67kg/h of 4-methyl-3-heptene, 3-ethyl-2-hexene, 2, 4-trimethyl-1-pentene, respectively, with the results shown in tables 2 to 4, respectively, wherein dQ r Each/dT retains decimal places to tenths of a digit.
TABLE 2
TABLE 3 Table 3
TABLE 4 Table 4
Further, it will be understood that various changes and modifications may be made by those skilled in the art after reading the foregoing description of the invention, and such equivalents are intended to fall within the scope of the claims appended hereto.
Claims (11)
1. Use of an inert hydrocarbon for maintaining the thermal stability of the reaction in the solution polymerization of ethylene, alpha-olefins, characterized in that said inert hydrocarbon increases the rate of heat transfer at the operating point of the ethylene, alpha-olefin solution polymerization reactor, i.e. dQ r /dT, thereby enhancing the thermal stability of the reactor;
dQ r refers to the heat transfer rate per unit time and unit volume of the reactor, and is in units of kJ/m 3 /s；
dT refers to the temperature change per unit time of the reactor, in units of ℃/s;
the inert hydrocarbon satisfies 0.21kJ/mol/K < molar constant pressure specific heat <0.23kJ/mol/K;
the molar constant pressure specific heat refers to the specific heat per unit mole of the inert hydrocarbon at 25 ℃ and 101325 Pa;
the inert hydrocarbon is at least one of 2-cis-octene, 2-trans-octene, 4-methyl-3-heptene, 3-methyl-2-heptene, 2, 3-dimethyl-2-hexene, 3-ethyl-2-hexene, 3, 4-dimethyl-trans-3-hexene, 2, 4-trimethyl-1-pentene.
2. The use according to claim 1, wherein the solvent in the solution polymerization of ethylene and alpha-olefin is at least one of C4-C6 chain alkane and C4-C6 cycloalkane, and the alpha-olefin is at least one of propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene and 1-octene, and a metallocene catalyst or a Ziegler-Natta catalyst is used.
3. The use according to claim 2, wherein the solvent in the solution polymerization of ethylene and α -olefin is at least one of a C5 to C6 chain alkane and a C5 to C6 cycloalkane.
4. Use according to claim 1, characterized in that the reaction pressure of the ethylene, α -olefin solution polymerization is between 30 and 200bar and the reaction temperature is between 120 and 220 ℃.
5. The process according to claim 4, wherein the reaction pressure for the solution polymerization of ethylene and alpha-olefins is between 35 and 100bar and the reaction temperature is between 140 and 200 ℃.
6. The process according to claim 5, wherein the reaction pressure for the solution polymerization of ethylene and alpha-olefins is 40-60bar and the reaction temperature is 145-180 ℃.
7. Use according to any one of claims 1 to 6, characterized in that the inert hydrocarbon is fed to a solution polymerization reactor for the polymerization of ethylene with an α -olefin to obtain an intermediate polymer solution and/or the inert hydrocarbon is accumulated cyclically during the polymerization.
8. Use according to claim 7, characterized in that the intermediate polymer solution contains 0.05-30 wt.% of the inert hydrocarbon.
9. Use according to claim 7, characterized in that the intermediate polymer solution, after exiting the solution polymerization reactor, is warmed by means of a heat exchanger, separated from ethylene and α -olefin copolymer by means of a multi-stage flash separator, while the inert hydrocarbon is recovered and recycled back to the solution polymerization reactor, achieving a cyclic accumulation of the inert hydrocarbon during the polymerization reaction.
10. Use according to claim 9, wherein the ethylene and α -olefin copolymer is withdrawn from the flash separator and passed to a third separator, which is a vacuum devolatilizer, a flash tank, a falling-strand evaporator or a thin film evaporator.
11. Use according to claim 9, characterized in that the solution polymerization reactor is an adiabatic reactor, the reactor being free of gas phase space;
the heat exchanger is a tubular heat exchanger or a plate heat exchanger.
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Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4769428A (en) * | 1985-10-17 | 1988-09-06 | Du Pont Canada Inc. | Solution process for the preparation of polymers of alpha-olefins |
| EP2848635A1 (en) * | 2013-09-16 | 2015-03-18 | Ineos Europe AG | Polymerization process |
| CN111630071A (en) * | 2018-01-10 | 2020-09-04 | 博里利斯股份公司 | Phase-stable ethylene alpha-olefin copolymerization process |
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Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4769428A (en) * | 1985-10-17 | 1988-09-06 | Du Pont Canada Inc. | Solution process for the preparation of polymers of alpha-olefins |
| EP2848635A1 (en) * | 2013-09-16 | 2015-03-18 | Ineos Europe AG | Polymerization process |
| CN111630071A (en) * | 2018-01-10 | 2020-09-04 | 博里利斯股份公司 | Phase-stable ethylene alpha-olefin copolymerization process |
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