CN112980070B - Heat-resistant polyethylene, preparation method thereof and heat-resistant pipe - Google Patents
Heat-resistant polyethylene, preparation method thereof and heat-resistant pipe Download PDFInfo
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- 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
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- 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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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16L—PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL
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Abstract
The invention provides heat-resistant polyethylene, a preparation method thereof and a heat-resistant pipe. The preparation method comprises the following steps: carrying out a first polymerization reaction by taking a first part of ethylene as a raw material to obtain a first product system containing ethylene oligomer, wherein the melt flow rate of the product system of the first polymerization reaction is 50-65 g/10min; carrying out a second polymerization reaction by taking a second part of ethylene and a first comonomer as raw materials, wherein the melt flow rate of a product system of the second polymerization reaction is 0-0.1 g/10min, and then obtaining a second product system containing an ethylene copolymer; and carrying out a third polymerization reaction on the first product system, the second product system, the third part of ethylene and the second comonomer, wherein the melt flow rate of the product system of the third polymerization reaction is 0.5-0.95 g/10min, and then obtaining the heat-resistant polyethylene. The heat-resistant polyethylene prepared by the method has good heat resistance and processability, and is easy to control.
Description
Technical Field
The invention relates to the field of high polymer materials, and particularly relates to heat-resistant polyethylene, a preparation method thereof and a heat-resistant pipe.
Background
The heat-resistant polyethylene (PE-RT) is non-crosslinked polyethylene which can be used for cold and hot water pipes, the number and distribution of branched chains on a polyethylene molecular chain are properly controlled through polymerization reaction, so that the polyethylene molecular chain has good hydrostatic pressure resistance under high temperature, and the heat-resistant polyethylene (PE-RT) is mainly used for household cold and hot water conveying pipes, including floor heating, heating connection, heat exchanger plates, heat circulation systems and the like. The international standard ISO22391-2 2009 classifies PE-RT pipes into 2 types, i.e. type i and type ii. According to the standard requirements, the type I PE-RT pipe is allowed to have brittle failure under the temperature condition of below 110 ℃, namely, the hydrostatic curve can have an inflection point. The II type PE-RT pipe is not allowed to have brittle failure under the temperature condition below 110 ℃, namely, the hydrostatic pressure curve can not have inflection points.
The PE-RT polymerization process technology is developed from solution polymerization process technology to gas phase polymerization process technology and slurry polymerization process technology, the polymerization reaction is developed from a single reactor to a double reactor and a triple reactor, the comonomer is developed from the original octene to hexene and butene, and the types and the brands of PE-RT pipes are continuously increased.
The prior art provides methods for preparing heat resistant polyethylene copolymers by metallocene catalyzed copolymerization of ethylene and 1-hexene. Another prior document provides a process for the preparation of heat-resistant polyethylene copolymers and pipes. Two reaction kettles are connected in series in the polymerization process, and the polyethylene copolymer with excellent heat resistance can be obtained by changing the process conditions of the polymerization reaction, so that the polyethylene copolymer can be used as a heat-resistant pipe material in an extrusion molding mode. Another prior document adopts a slurry polymerization process with three reactors connected in series, which improves the defect that the PE-RT pipe produced by the slurry polymerization process with two reactors connected in series has insufficient long-term high-temperature creep property, and better meets the use requirements of heat-resistant polyethylene pipes.
The following drawbacks and deficiencies are common in current methods for preparing PE-RT copolymers and compositions thereof: (1) The polyethylene prepared by the metallocene catalyst has narrow molecular weight distribution, relatively poorer processability and higher cost of the metallocene catalyst; (2) The three-kettle series process is adopted, and the secondary hydrogen steaming process is adopted, so that the control is difficult.
Disclosure of Invention
The invention mainly aims to provide heat-resistant polyethylene, a preparation method thereof and a heat-resistant pipe, and aims to solve the problems of narrow polyethylene molecular weight distribution, poor processability and high process control difficulty in the conventional method for preparing the heat-resistant polyethylene.
In order to achieve the above object, according to an aspect of the present invention, there is provided a method for preparing heat resistant polyethylene, the method comprising: dividing the ethylene into three parts, wherein the weight ratio of the first part of ethylene to the second part of ethylene to the third part of ethylene is (45-60) to (10-25) to (15-30); under the action of a first catalyst, a first organic solvent and a first molecular weight regulator, carrying out a first polymerization reaction by taking a first part of ethylene as a raw material to obtain a first product system containing ethylene oligomer, wherein the melt flow rate of the product system of the first polymerization reaction is 50-65 g/10min; under the action of a second catalyst and a second organic solvent, a second part of ethylene and a first comonomer are used as raw materials for a second polymerization reaction, and a second product system containing an ethylene copolymer is obtained after the melt flow rate of the product system of the second polymerization reaction is 0-0.1 g/10min; and (3) carrying out a third polymerization reaction on the first product system, the second product system, a third part of ethylene and a second comonomer under the action of a second molecular weight regulator, wherein the melt flow rate of the product system of the third polymerization reaction is 0.5-0.95 g/10min, so as to obtain the heat-resistant polyethylene, wherein the first molecular weight regulator and the second molecular weight regulator are both hydrogen, and the heat-resistant polyethylene comprises an ethylene oligomer, an ethylene copolymer and a third polymer obtained through the third polymerization reaction.
Further, the preparation method comprises the following steps: and during the first polymerization reaction, obtaining a first product system after the melt flow rate of the first product system reaches 55-60 g/10min.
Furthermore, the weight ratio of the ethylene oligomer, the ethylene copolymer and the third polymer in the heat-resistant polyethylene is (48-55): 15-20): 20-30.
Furthermore, the reaction temperature of the first polymerization reaction is 80-85 ℃, the reaction pressure is 0.7-0.9 MPa, the partial pressure ratio of the first molecular weight regulator to the first part of ethylene is (3-4): 1, and the reaction time is 2-3 h.
Furthermore, the reaction temperature of the second polymerization reaction is 80-85 ℃, the reaction pressure is 0.2-0.3 MPa, the dosage of the first comonomer accounts for 8-15 wt% of the weight of the second part of the ethylene, and the reaction time is 1-2 h.
Further, the reaction temperature of the third polymerization reaction is 80-85 ℃, the reaction pressure is 0.2-0.3 MPa, the dosage of the second comonomer accounts for 8-15 wt% of the third part of ethylene, and the reaction time is 1-2 h.
Further, the first organic solvent and the second organic solvent are each independently selected from one or more of the group consisting of hexane, heptane, and octane.
Further, the first comonomer and the second comonomer are each independently selected from one or more of the group consisting of 1-butene, 1-hexene and 1-octene.
Further, the first catalyst and the second catalyst each comprise a ziegler-natta catalyst and an aluminum alkyl; preferably, the aluminum alkyl is selected from one or more of the group consisting of triethylaluminum, tri-n-butylaluminum, and triisobutylaluminum.
The application also provides heat-resistant polyethylene, and the heat-resistant polyethylene is prepared by the preparation method.
In another aspect, the present application provides a heat-resistant pipe made from the heat-resistant polyethylene.
By applying the technical scheme of the invention, under the action of a first catalyst and a first molecular weight regulator, ethylene is used as a raw material to synthesize low-molecular-weight oligomer; under the action of the second catalyst, the second polymerization process with ethylene and comonomer as material can form ultrahigh molecular weight polyethylene copolymer. The polyethylene copolymer with ultrahigh molecular weight, the ethylene oligomer, the ethylene and the 1-butene are subjected to a third polymerization reaction, so that the chain length and the molecular weight of a product can be effectively improved, and the hydrostatic strength of the product under a high-temperature condition is further improved, and the polyethylene prepared by the preparation method contains polymers (the ethylene oligomer, the ethylene copolymer and the third polymer) with three molecular weights, so that the processability of the polyethylene can be effectively improved. In addition, compared with the prior art, the preparation method has the advantages of simpler steps and easiness in control. On the basis, the heat-resistant polyethylene prepared by the method has good heat resistance and processability, and is easy to control.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:
fig. 1 shows a schematic configuration of a heat-resistant polyethylene production apparatus employed in an example according to the present invention.
Wherein the figures include the following reference numerals:
10. a, a reaction kettle; 20. b, a reaction kettle; 30. and C, a reaction kettle.
Detailed Description
As described in the background art, the existing methods for preparing heat-resistant polyethylene have problems of narrow molecular weight distribution of polyethylene, poor processability, and difficulty in process control. In order to solve the above technical problems, the present application provides a method for preparing heat-resistant polyethylene, comprising: dividing ethylene into three parts, wherein the weight ratio of the first part of ethylene to the second part of ethylene to the third part of ethylene is (45-60) to (10-25) to (15-30) in sequence; under the action of a first catalyst, a first organic solvent and a first molecular weight regulator, carrying out a first polymerization reaction by taking a first part of ethylene as a raw material to obtain a first product system containing ethylene oligomer, wherein the melt flow rate of the product system of the first polymerization reaction is 50-65 g/10min; under the action of a second catalyst and a second organic solvent, a second part of ethylene and a first comonomer are taken as raw materials to carry out a second polymerization reaction, and the melt flow rate of a product system of the second polymerization reaction is 0-0.1 g/10min; and under the action of a second molecular weight regulator, carrying out a third polymerization reaction on the first product system, the second product system, a third part of ethylene and a second comonomer, wherein the melt flow rate of the product system of the third polymerization reaction is 0.5-0.95 g/10min, so as to obtain the heat-resistant polyethylene, wherein the first molecular weight regulator and the second molecular weight regulator are both hydrogen, and the heat-resistant polyethylene comprises an ethylene oligomer, an ethylene copolymer and a third polymer obtained through the third polymerization reaction.
Synthesizing low molecular weight oligomer by using ethylene as a raw material under the action of a first catalyst and a first molecular weight regulator; under the action of the second catalyst, the second polymerization process with ethylene and comonomer as material can form ultrahigh molecular weight polyethylene copolymer. The polyethylene copolymer with ultrahigh molecular weight, the ethylene oligomer, the ethylene and the 1-butene are subjected to a third polymerization reaction, so that the chain length and the molecular weight of a product can be effectively improved, and the hydrostatic strength of the product under a high-temperature condition is further improved, and the polyethylene prepared by the preparation method contains polymers (the ethylene oligomer, the ethylene copolymer and the third polymer) with three molecular weights, so that the processability of the polyethylene can be effectively improved. In addition, compared with the prior art, the preparation method has the advantages of simpler steps and easiness in control. On the basis, the heat-resistant polyethylene prepared by the method has good heat resistance and processability, and is easy to control.
In another preferred embodiment, the above preparation method further comprises: under the action of a second molecular weight regulator and a third catalyst, performing a third polymerization reaction on a third part of ethylene and a second comonomer to obtain a third product system; mixing the first product system containing ethylene oligomer, the second product system containing ethylene copolymer and the third product system to obtain the heat resistant polyethylene. Compared with the first embodiment, the method enables the first product system, the second product system and the third product system to be prepared respectively without mutual influence, thereby being beneficial to shortening the production period; the heat-resistant polyethylene product obtained simultaneously also contains three ethylene polymers with different molecular weights, so that the heat-resistant polyethylene product has good processability.
In order to further improve the processability of the heat resistant polyethylene product, in a preferred embodiment, the preparation method comprises: and (3) during the first polymerization reaction, detecting the melt flow rate of the first product system to enable the melt flow rate to reach 55-60 g/10min, and obtaining the first product system.
In a preferred embodiment, the weight ratio of the ethylene oligomer, the ethylene copolymer and the third polymer obtained by the third polymerization reaction in the heat-resistant polyethylene is (48-55): (15-20): (20-30). The weight ratio of the three components is limited in the range, which is favorable for further improving the heat resistance and the mechanical property of the heat-resistant polyethylene.
In a preferred embodiment, the first polymerization reaction is carried out at a temperature of from 80 to 85 ℃ and a pressure of from 0.7 to 0.9MPa, the partial pressure ratio of the first molecular weight regulator to the first portion of ethylene is from (3 to 4): 1 and the reaction time is from 2 to 3 hours. The reaction temperature, reaction pressure, reaction time of the first polymerization reaction and the partial pressure ratio of the first molecular weight modifier to the first portion of ethylene include, but are not limited to, the above ranges, and the limitation thereof is not only advantageous for reducing the molecular weight of the ethylene oligomer but also advantageous for increasing the yield thereof.
Preferably, the first polymerization reaction further comprises: after the first polymerization reaction is finished, the product system of the first polymerization reaction is conveyed to a flash tank to flash off hydrogen. The hydrogen in the product system of the first polymerization reaction is removed, which is beneficial to better controlling the molecular weight distribution of the heat-resistant polyethylene in the third polymerization reaction. In order to further improve the overall performance of the heat-resistant polyethylene, the flash pressure is preferably 0.05 to 0.1MPa.
In a preferred embodiment, the second polymerization reaction is carried out at a temperature of 80 to 85 ℃ and a pressure of 0.2 to 0.3MPa, the first comonomer represents 8 to 15wt% of the second portion of ethylene, and the reaction time is 1 to 2 hours. The reaction temperature, reaction pressure, reaction time and weight percentage of the first comonomer of the second polymerization reaction include but are not limited to the above ranges, and limiting the ranges is not only beneficial to improving the molecular weight and chain length of the ethylene copolymer, and further improving the environmental stress cracking resistance, but also beneficial to improving the yield.
In a preferred embodiment, the third polymerization reaction is carried out at a temperature of 80 to 85 ℃ and a pressure of 0.2 to 0.3MPa, the second comonomer being present in an amount of 8 to 15wt% based on the weight of the third fraction of ethylene, and the reaction time being 1 to 2 hours. The reaction temperature, reaction pressure, reaction time of the third polymerization reaction and the weight percentage of the second comonomer include, but are not limited to, the above ranges, and the ranges are limited to the above ranges, which is advantageous for increasing the reaction rate of the third polymerization reaction process and the yield of the heat-resistant polyethylene.
The first molecular weight regulator and the second molecular weight regulator may be selected from those commonly used in the art. In a preferred embodiment, the first molecular weight regulator and the second molecular weight regulator are hydrogen. Compared with other molecular weight regulators, the regulator can control the molecular weight of the obtained polymer more accurately, and the molecular weight regulator is very simple and convenient to remove and low in cost after the reaction is finished.
In a preferred embodiment, the first comonomer and the second comonomer include, but are not limited to, one or more of the group consisting of 1-butene, 1-hexene, and 1-octene. Compared with other comonomers, the comonomers are adopted to further improve the heat resistance of finally obtained polyethylene.
The first organic solvent and the second organic solvent may be selected from those commonly used in the art. In a preferred embodiment, the first organic solvent and the second organic solvent are each independently selected from one or more of the group consisting of hexane, heptane, and octane.
The first catalyst and the second catalyst may be selected from those commonly used in the art. In a preferred embodiment, the first catalyst and the second catalyst each comprise a main catalyst and a cocatalyst. Preferably, the cocatalyst is selected from one or more of the group consisting of triethylaluminium, tri-n-butylaluminium and triisobutylaluminium. Compared with other catalysts, the adoption of the several cocatalysts is not only beneficial to improving the reaction rate, but also beneficial to reducing the process cost. Preferably, the molar ratio of the used amount of the first catalyst to the used amount of the second catalyst is (20-30): 1.
The application also provides heat-resistant polyethylene, and the heat-resistant polyethylene is prepared by the preparation method.
The heat-resistant polyethylene prepared by the preparation method contains polymers (polyethylene copolymer, ethylene oligomer and third polymer) with three molecular weights, so that the chain length and the molecular weight of the product can be effectively improved, the hydrostatic strength of the product under a high-temperature condition is further improved, and the processability of the polyethylene can be effectively improved. On the basis, the heat-resistant polyethylene prepared by the method has good heat resistance and processability, and is easy to control.
In yet another aspect, the present application further provides a heat-resistant pipe made from the heat-resistant polyethylene.
The heat-resistant polyethylene prepared by the method has good heat resistance and processability, and is easy to control. The heat-resistant pipe prepared from the high-temperature-resistant material has excellent application prospect.
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present invention will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.
In the examples, heat-resistant polyethylene was prepared by using the apparatus shown in FIG. 1.
Example 1
A Ziegler-Natta catalyst (Z501 catalyst) and aluminum alkyl (triethyl aluminum), ethylene and hydrogen are added into an A reaction kettle 10, the adding amount of the Z501 catalyst is 1.5mol/h, the mol ratio of the triethyl aluminum to Z501 (Ti) is 25, the adding amount of the ethylene accounts for 50% of the total adding amount (30 t/h) of the three-kettle ethylene, the temperature of a reactor is 80 ℃, the reaction pressure is 0.8MPa, the partial pressure ratio of the hydrogen to the ethylene is 4.0. After monitoring the melt flow rate of the first product system to 58g/10min, a first product system containing ethylene oligomers was obtained.
Adding a Ziegler-Natta catalyst (Z501 catalyst), aluminum alkyl (triethylaluminum), ethylene and 1-butene into a B reaction kettle 20, wherein the adding amount of the Z501 catalyst is 0.5mol/h, the molar ratio of the triethylaluminum to Z501 (Ti) is 25, the adding amount of the ethylene accounts for 25% of the total adding amount of the three-kettle ethylene, the adding amount of the 1-butene accounts for 10% of the total weight of the three-kettle ethylene, the temperature of the reactor is 80 ℃, the reaction pressure is 0.3MPa, and the reaction time is 1h. After monitoring the melt flow rate of the second product system to 0.05g/10min, a second product system containing ethylene copolymer was obtained.
Then discharging the slurry of the reaction kettle A10 and the slurry of the reaction kettle B20 into a reaction kettle C30, wherein the addition amount of ethylene in the reaction kettle C30 accounts for 25 percent of the total addition amount of ethylene in the three reaction kettles, the temperature of the reactor is 85 ℃, the pressure of the reactor is 0.2MPa, the addition amount of 1-butylene accounts for 15 percent of the total weight of ethylene in the three reaction kettles, the partial pressure ratio of hydrogen to ethylene is 0.03. After monitoring the melt flow rate of the third product system to 0.948g/10min, the desired heat resistant polyethylene was obtained.
Example 2
Adding a Ziegler-Natta catalyst (Z501 catalyst), aluminum alkyl (triethyl aluminum), ethylene and hydrogen into a reaction kettle A10, wherein the adding amount of the Z501 catalyst is 2.0mol/h, the molar ratio of the triethyl aluminum to Z501 (Ti) is 20. After monitoring the melt flow rate of the first product system to 55g/10min, a first product system containing ethylene oligomers was obtained.
A Ziegler-Natta catalyst (Z501 catalyst) and aluminum alkyl (triethyl aluminum), ethylene and 1-butene are added into a B reaction kettle 20, the adding amount of the Z501 catalyst is 0.6mol/h, the molar ratio of the triethyl aluminum to Z501 (Ti) is 20, the adding amount of the ethylene accounts for 10 percent of the total adding amount of the three reaction kettles of the ethylene, the adding amount of the 1-butene accounts for 10 percent of the total adding amount of the three reaction kettles of the ethylene, the temperature of the reaction kettle is 80 ℃, the reaction pressure is 0.2MPa, and the reaction time is 2h. After monitoring the melt flow rate of the second product system to 0.06g/10min, a second product system containing ethylene copolymer was obtained.
Then discharging the slurry of the reaction kettle A10 and the slurry of the reaction kettle B20 into a reaction kettle C30, wherein the addition amount of ethylene in the reaction kettle C30 accounts for 25 percent of the total addition amount of ethylene in the three reaction kettles, the temperature of the reactor is 85 ℃, the pressure of the reactor is 0.3MPa, the addition amount of 1-butylene accounts for 15 percent of the total weight of ethylene in the three reaction kettles, the partial pressure ratio of hydrogen to ethylene is 0.04. After monitoring the melt flow rate of the third product system to 0.947g/10min, the desired heat resistant polyethylene was obtained.
Example 3
Adding a Ziegler-Natta catalyst (Z501 catalyst), aluminum alkyl (triethylaluminum), ethylene and hydrogen into a reaction kettle (10) of A, wherein the adding amount of the Z501 catalyst is 1.8mol/h, the molar ratio of the triethylaluminum to Z501 (Ti) is 30. After monitoring the melt flow rate of the first product system to 60g/10min, a first product system containing ethylene oligomers was obtained.
Adding a Ziegler-Natta catalyst (Z501 catalyst), aluminum alkyl (triethyl aluminum), ethylene and 1-butene into a B reaction kettle 20, wherein the addition of the ethylene accounts for 20% of the total addition of the three kettles of ethylene, the addition of the 1-butene accounts for 10% of the total weight of the ethylene in the three reactors, the temperature of the reactors is 80 ℃, the reaction pressure is 0.3MPa, and the reaction time is 1h. After monitoring the melt flow rate of the second product system to 0.04g/10min, a second product system containing ethylene copolymer was obtained.
Then discharging the slurry of the reaction kettle A10 and the slurry of the reaction kettle B20 into a reaction kettle C30, wherein the addition amount of ethylene in the reaction kettle C30 accounts for 20 percent of the total addition amount of ethylene in the three reaction kettles, the temperature of the reactor is 85 ℃, the pressure of the reactor is 0.2MPa, the addition amount of 1-butylene accounts for 12 percent of the weight of ethylene in the three reaction kettles, the partial pressure ratio of hydrogen to ethylene is 0.03. After monitoring the melt flow rate of the third product system to 0.950g/10min, the desired heat resistant polyethylene was obtained.
Example 4
The differences from example 1 are: the melt flow rate of the first product system was 65g/10min and the melt flow rate of the second product system was 0.03g/10min.
Example 5
The differences from example 1 are: in the heat-resistant polyethylene, the weight ratio of the ethylene oligomer, the ethylene copolymer and the third polymer is 45.
Example 6
The differences from example 1 are: the reaction temperature of the first polymerization reaction was 80 ℃, the reaction pressure was 0.2MPa, the partial pressure ratio of the first molecular weight regulator to the first portion of ethylene was 3.0, and the reaction time was 2 hours.
Example 7
The differences from example 1 are: the reaction temperature of the second polymerization reaction is 85 ℃, the reaction pressure is 0.30MPa, the dosage of the first comonomer accounts for 10 percent of the weight of the second part of ethylene, and the reaction time is 1.5h.
Example 8
The differences from example 1 are: the reaction temperature of the third polymerization reaction is 80 ℃, the reaction pressure is 0.30MPa, the dosage of the second comonomer accounts for 12 percent of the weight content of the third part of the ethylene, and the reaction time is 1.5h.
Example 9
The differences from example 1 are: both the first comonomer and the second comonomer are 1-hexene.
Example 10
The differences from example 1 are: both the first comonomer and the second comonomer are 1-octene.
Comparative example 1
A Ziegler-Natta catalyst (Z501 catalyst) and aluminum alkyl (triethyl aluminum), ethylene and hydrogen are added into a reaction kettle (10) of A, the adding amount of the Z501 catalyst is 1.5mol/h, the mol ratio of the triethyl aluminum to Z501 (Ti) is 25, the adding amount of the ethylene accounts for 70 percent of the total adding amount (30 t/h) of the three kettles of ethylene, the temperature of a reactor is 85 ℃, the reaction pressure is 0.8MPa, the partial pressure ratio of the hydrogen to the ethylene is 4.0, the reaction time is 2.5h, and the flash evaporation pressure of the hydrogen is controlled to be 0.1MPa. After monitoring the melt flow rate of the first product system to 90g/10min, a first product system containing ethylene oligomers was obtained.
A Ziegler-Natta catalyst (Z501 catalyst) and aluminum alkyl (triethyl aluminum), ethylene and 1-butene are added into a B reaction kettle 20, the adding amount of the Z501 catalyst is 0.5mol/h, the molar ratio of the triethyl aluminum to Z501 (Ti) is 25, the adding amount of the ethylene accounts for 10 percent of the total adding amount of the three-kettle ethylene, the adding amount of the 1-butene accounts for 10 percent of the total weight of the three-kettle ethylene, the temperature of the reactor is 82 ℃, the reaction pressure is 0.35MPa, and the reaction time is 2.5h. After monitoring the melt flow rate of the second product system to 0.08g/10min, a second product system containing ethylene copolymer was obtained.
Then discharging the slurry of the reaction kettle A10 and the slurry of the reaction kettle B20 into a reaction kettle C30, wherein the addition amount of ethylene in the reaction kettle C30 accounts for 20 percent of the total addition amount of ethylene in the three reaction kettles, the temperature of the reactor is 82.5 ℃, the pressure of the reactor is 0.3MPa, the addition amount of 1-butylene accounts for 10 percent of the total weight of ethylene in the three reaction kettles, the partial pressure ratio of hydrogen to ethylene is 0.1, and the reaction time is 2 hours. After monitoring the melt flow rate of the third product system to 0.949g/10min, the desired heat resistant polyethylene was obtained.
100 parts of the copolymer, 0.05 part of zinc stearate, 0.05 part of calcium stearate, 0.8 part of antioxidant (1010), 0.4 part of antioxidant (168) and 0.1 part of fluoroelastomer processing aid are mixed, and then a double-screw extruder is utilized to extrude and granulate at the temperature of 220-270 ℃, so that the heat-resistant polyethylene resin is obtained.
Comparative example 2
The differences from example 1 are: the melt flow rate of the product system of the first polymerization reaction was 95g/10min, the melt flow rate of the product system of the second polymerization reaction was 0.07g/10min, and the melt flow rate of the product system of the third polymerization reaction was 0.950g/10min.
The high temperature creep resistance of the heat-resistant polyethylene resins prepared in examples 1 to 10 and comparative examples 1 to 2 is evaluated by a pipe hydrostatic test method, and the test method is shown in GB/T28799.2-2012, and the specific results are shown in Table 1.
TABLE 1
From the above description, it can be seen that the above-described embodiments of the present invention achieve the following technical effects: .
Comparing examples 1 to 10 and comparative examples 1 to 2, it can be seen that the overall performance of the heat-resistant polyethylene can be improved by the preparation method provided by the present application.
Comparing examples 1 and 4, it is seen that limiting the melt flow rates of the first and second product systems to the preferred ranges herein is beneficial to further improve the overall properties of the heat resistant polyethylene.
Comparing examples 1 and 5, it is understood that limiting the weight ratio of the ethylene oligomer, the ethylene copolymer and the third polymer in the heat-resistant polyethylene to the above range is advantageous for further improving the overall properties of the heat-resistant polyethylene.
It can be seen from comparison of examples 1, 6, 7 and 8 that limiting the ranges of the reaction temperature, reaction pressure and comonomer amount for the first polymerization reaction and the second polymerization reaction and the third polymerization reaction to the above ranges is advantageous for further improving the overall properties of the heat-resistant polyethylene.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (11)
1. A preparation method of heat-resistant polyethylene is characterized by comprising the following steps:
the ethylene is divided into three parts, and the weight ratio of the first part of ethylene to the second part of ethylene to the third part of ethylene is (45-60) to (10-25) to (15-30);
under the action of a first catalyst, a first organic solvent and a first molecular weight regulator, carrying out a first polymerization reaction by taking a first part of ethylene as a raw material to obtain a first product system containing ethylene oligomer, wherein the melt flow rate of the product system of the first polymerization reaction is 50-65 g/10min;
under the action of a second catalyst and a second organic solvent, a second part of ethylene and a first comonomer are used as raw materials for a second polymerization reaction, and a second product system containing an ethylene copolymer is obtained after the melt flow rate of a product system of the second polymerization reaction is 0-0.1 g/10min;
under the action of a second molecular weight regulator, carrying out a third polymerization reaction on the first product system, the second product system, a third part of the ethylene and a second comonomer, wherein the melt flow rate of the product system of the third polymerization reaction is 0.5-0.95 g/10min, so as to obtain the heat-resistant polyethylene, wherein the first molecular weight regulator and the second molecular weight regulator are both hydrogen, and the heat-resistant polyethylene comprises the ethylene oligomer, the ethylene copolymer and a third polymer obtained by the third polymerization reaction;
in the heat-resistant polyethylene, the weight ratio of the ethylene oligomer to the ethylene copolymer to the third polymer is (48-55) to (15-20) to (20-30).
2. The method of manufacturing according to claim 1, comprising: and (3) during the first polymerization reaction, obtaining the first product system after the melt flow rate of the first product system reaches 55-60 g/10min.
3. The process according to claim 1 or 2, wherein the first polymerization reaction is carried out at a reaction temperature of 80 to 85 ℃, a reaction pressure of 0.7 to 0.9MPa, a partial pressure ratio of the first molecular weight modifier to the first portion of ethylene is (3 to 4): 1, and a reaction time of 2 to 3 hours.
4. The preparation method according to claim 3, wherein the reaction temperature of the second polymerization reaction is 80-85 ℃, the reaction pressure is 0.2-0.3 MPa, the amount of the first comonomer accounts for 8-15 wt% of the weight of the second part of ethylene, and the reaction time is 1-2 h.
5. The preparation method according to claim 3 or 4, wherein the reaction temperature of the third polymerization reaction is 80-85 ℃, the reaction pressure is 0.2-0.3 MPa, the amount of the second comonomer accounts for 8-15 wt% of the third part of ethylene, and the reaction time is 1-2 h.
6. The method of claim 1 or 2, wherein the first organic solvent and the second organic solvent are each independently selected from one or more of the group consisting of hexane, heptane, and octane.
7. The process of any one of claims 1 to 6, wherein the first comonomer and the second comonomer are each independently selected from one or more of the group consisting of 1-butene, 1-hexene and 1-octene.
8. The method of claim 7, wherein the first catalyst and the second catalyst each comprise a Ziegler-Natta catalyst and an aluminum alkyl.
9. The method according to claim 8, wherein the alkyl aluminum is one or more selected from the group consisting of triethyl aluminum, tri-n-butyl aluminum, and triisobutyl aluminum.
10. A heat-resistant polyethylene, characterized in that it is obtained by the process according to any one of claims 1 to 9.
11. A heat resistant pipe, characterized in that it is made of the heat resistant polyethylene according to claim 10.
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| DE102005040390A1 (en) * | 2005-08-25 | 2007-03-01 | Basell Polyolefine Gmbh | Multi-modal polyethylene moulding material for production of pipes, e.g. water pipes, comprises low-mol. wt. ethylene homopolymer, high-mol. wt. ethylene copolymer and ultrahigh-mol. wt. ethylene copolymer |
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