Method for preparing polyethylene by metallocene prepolymerization solution method

Abstract

The invention discloses a metallocene prepolymerization solution method polyethylene preparation method, which comprises the following steps: respectively introducing a mixture of a solvent and a second comonomer into a premixing zone of a reaction kettle and a reaction zone communicated with the premixing zone, respectively introducing a first comonomer into the premixing zone and the reaction zone, introducing a solution containing a catalyst into the pre-mixing zone, and carrying out a pre-polymerization reaction on the solution and the first comonomer and the second comonomer in the pre-mixing zone; a material obtained through the prepolymerization reaction continuously enters the reaction zone with stirring, and is subjected to a polymerization reaction with the first comonomer and the second comonomer in the reaction zone to prepare the metallocene polyethylene. According to the method, the catalyst and the polymer monomer are subjected to prepolymerization reaction in the prepolymerization area, so that the problems of poor reaction efficiency, low product yield and the like caused by high-temperature inactivation of the catalyst directly entering a reaction kettle can be effectively avoided, the yield of the prepared polyethylene is remarkably increased, the preparation cost can be reduced, and the method is suitable for industrial production. The method is suitable for large-scale industrial production.

Description

Technical Field

[0001] The invention relates to the technical field of solution-process polyethylene preparation, and in particular to a method for preparing polyethylene by a metallocene prepolymerization solution process. Background Art

[0002] Metallocene polyethylene is obtained by copolymerizing ethylene and α-olefins catalyzed by a single-active-center metallocene catalyst. It has the advantages of good rigidity, excellent resistance to stress cracking, good transparency, low heat-sealing temperature, and high heat-sealing strength. It is currently the fastest-growing metallocene polymer.

[0003] However, the production yield of metallocene polyethylene in the prior art is low and the production cost is high. Due to the high production cost and limited output, the market price of metallocene polyethylene is usually high, which limits its application in large-scale industrial production.

[0004] Therefore, there is an urgent need for a preparation method that can improve the production yield of metallocene polyethylene to solve the problem that its preparation cost is high and cannot be industrialized. Summary of the invention

[0005] The present invention provides a method for preparing polyethylene by metallocene prepolymerization solution process to solve the above problems.

[0006] In order to achieve the above object, the technical solution of the present invention is:

[0007] A method for preparing polyethylene by a metallocene prepolymerization solution process comprises the following steps:

[0008] A mixture of a solvent and a second comonomer is introduced into a premixing zone and a reaction zone connected to the premixing zone of the reactor respectively, and a first comonomer is introduced into the premixing zone and the reaction zone respectively, and a solution containing a catalyst is introduced into the premixing zone, and the solution is continuously stirred to allow the catalyst to undergo a prepolymerization reaction with the first comonomer and the second comonomer in the premixing zone;

[0009] The material containing the high temperature resistant catalyst obtained by the prepolymerization reaction is continuously introduced into the reaction zone with stirring, and undergoes polymerization reaction with the first comonomer and the second comonomer introduced into the reaction zone to prepare metallocene polyethylene.

[0010] Furthermore, the prepolymerization reaction is carried out at a temperature of -10°C to 50°C and a pressure of 10-14 MPa.

[0011] Furthermore, the polymerization reaction temperature is 140°C-207°C, and the pressure is 10-14MPa.

[0012] Further, the solvent in the solution containing the catalyst is an organic solvent toluene;

[0013] The catalyst comprises a main catalyst and a co-catalyst, wherein the main catalyst is a metallocene catalyst and the co-catalyst is an alkyl aluminum; the molar ratio of the main catalyst to the co-catalyst is 1:1;

[0014] The volume ratio of the mass of the catalyst to the volume of the organic solvent toluene is 0.0006295 g:1 ml;

[0015] The amount of the solution containing the catalyst introduced was 2.5 ml / min.

[0016] Furthermore, the amount of the first comonomer introduced into the premixing zone is 1 g / min, and the amount of the first comonomer introduced into the reaction zone is 29 g / min; and the first comonomer is ethylene.

[0017] Furthermore, the amount of the mixture introduced into the premixing zone is 54.67 g / min, and the amount of the mixture introduced into the reaction zone is 109.33 g / min.

[0018] Furthermore, the solvent is hexane, the second comonomer is octene, and the mass ratio of the solvent to the second comonomer in the mixture is 10:3.

[0019] Furthermore, the stirring rates in the premixing zone and the reaction zone are both 600 r / min.

[0020] The beneficial effects of the present invention are:

[0021] The invention discloses a method for preparing polyethylene by a metallocene prepolymerization solution method, wherein a catalyst and a polymer monomer are first subjected to a prepolymerization reaction in a prepolymerization zone, and then a material containing a high-temperature resistant catalyst generated by the prepolymerization reaction is subjected to a polymerization reaction with a comonomer in a reaction zone, thereby effectively avoiding the problem of high-temperature deactivation of the catalyst caused by direct stirring of the catalyst when the catalyst directly enters a reactor. The preparation method improves the high-temperature resistance of the catalyst and the reaction efficiency, thereby significantly improving the output of the prepared polyethylene, thereby reducing the polyethylene preparation cost, and is suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 The graph is a result of the product yield of the examples of the present invention and the comparative examples. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] Example:

[0026] The reactor used in this embodiment is provided with a premixing zone and a reaction zone, the reaction zone is provided on the upper side of the premixing zone and is connected with the premixing zone, the premixer is provided in the premixing zone of the reactor and at the feed port, the premixer is used to premix the catalyst with other materials in the premixing zone to improve the high temperature resistance of the catalyst, the bottom of the reactor body is provided with a first feed port, a second feed port and a third feed port connected with the premixing zone, the middle of the reactor body is provided with a fourth feed port and a fifth feed port connected with the reaction zone, the discharge port of the reactor is provided at the upper part of the reactor body and is connected with the reaction zone, a part of the solvent and the second comonomer are passed into the premixing zone through the first feed port through a pipeline, and the other part of the solvent and the second comonomer are passed into the premixing zone through a pipeline through the fourth feed port The first comonomer is passed into the reaction zone, and at the same time, a part of the first comonomer is passed into the premixing zone through the second feed port through one pipeline, and another part of the first comonomer is passed into the premixing zone through the fifth feed port through another pipeline, and the catalyst is passed into the premixing zone through the third feed port. The premixer can rotate continuously with the stirring paddle to stir the materials in the premixing zone, so that the catalyst continuously passed into the premixing zone and the first comonomer and the second comonomer continuously passed into the premixing zone are prepolymerized; the material containing the high temperature resistant catalyst obtained by the prepolymerization reaction is continuously entered into the reaction zone with the stirring of the stirring paddle, and is polymerized with the first comonomer and the second comonomer continuously passed into the reaction zone, and the prepared product flows out of the reactor through the discharge port.

[0027] A method for preparing polyethylene by a metallocene prepolymerization solution process comprises the following steps:

[0028] A solvent hexane and a second comonomer octene are mixed in a mass ratio of 3:1 to obtain a mixture, and 54.67 g / min of the mixture is introduced into a premixing zone of a reactor through a pipeline, and 109.33 g / min of the mixture is introduced into a reaction zone connected to the premixing zone through another pipeline, at which time a thermometer in the premixer displays the temperature of the mixture; a micro-regulating valve is used to control the introduction of 1 g / min of the first comonomer ethylene into the premixing zone through a pipeline, and at the same time, 29 g / min of the first comonomer ethylene is introduced into the reaction zone through another pipeline, and at this time the temperature in the premixer will drop by 2-3°C;

[0029] The catalyst is dissolved in toluene, an organic solvent, to obtain a solution containing the catalyst, wherein the catalyst comprises a main catalyst metallocene catalyst and a co-catalyst alkyl aluminum in a molar ratio of 1:1, and the mass and volume ratio of the catalyst to the organic solvent toluene is 0.0006295 g:1 ml (specifically, 0.0369 g of the metallocene catalyst and 0.089 g of the alkyl aluminum are dissolved in 200 ml of toluene); 2.5 ml / min of the solution containing the catalyst is introduced into the premixing zone through a catalyst delivery pump, and the catalyst is continuously stirred to perform a prepolymerization reaction with the first comonomer ethylene and the second comonomer hexane in the premixing zone, the prepolymerization reaction temperature is -10°C to 50°C, the pressure is 10-14 MPa, the stirring speed of the stirring paddle in the reactor is 600 r / min, and the starting temperature of the reactor is 140°C;

[0030] The material containing the high temperature resistant catalyst obtained by the prepolymerization reaction is continuously introduced into the reaction zone with stirring, and is polymerized with the first comonomer ethylene with an introduction amount of 29 g / min and the second comonomer octene with an introduction amount of 109.33 g / min into the reaction zone to prepare the generated metallocene polyethylene. The reaction pressure of the polymerization reaction is 10-14 MPa, the temperature is 140°C-207°C, and the stirring speed of the stirring paddle in the reactor is 600 r / min; the prepolymerization reaction and the polymerization reaction are carried out simultaneously and the reaction is continued for 40 minutes.

[0031] Comparative Example:

[0032] The only difference between this comparative example and the embodiment is that in this comparative example, the substances (solvent hexane, second comonomer octene, first comonomer ethylene, main catalyst and co-catalyst) are not passed to the premixing zone, but the substances with the same amount as in the embodiment are directly added to the reactor at the same rate to carry out the polymerization reaction, and the other reaction conditions and parameters are the same as in the embodiment, that is, the reaction temperature is 140°C-207°C, the pressure is 10-14MPa, the stirring speed of the stirring paddle in the reactor is 600r / min, and the reaction is continued for 40min.

[0033] The examples and comparative examples were sampled twice when the reaction had been going on for 10 min and 30 min, respectively, and recorded as sample No. 1 and sample No. 2. The duration of both samplings was 2 min, and the sampled samples were weighed and recorded.

[0034] The results are as follows Figure 1As shown, the experimental results of sample No. 1 show that the yield of metallocene polyethylene prepared by the method in the comparative example (without premixing step) is 35.86g, and the yield of metallocene polyethylene prepared by the present method (with premixing step) is 58.85g, which is about 64.1% higher than that of the comparative example; the experimental results of sample No. 2 show that the yield of metallocene polyethylene prepared by the method in the comparative example is 35.88g, and the yield of metallocene polyethylene prepared by the present method is 57.86g, which is about 61.3% higher than that of the comparative example; it can be seen that the present method can greatly increase the yield of the prepared metallocene polyethylene.

[0035] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing polyethylene by metallocene prepolymerization solution process, characterized in that: The following steps are involved: A mixture of a solvent and a second comonomer is introduced into a premixing zone and a reaction zone connected to the premixing zone of the reactor respectively, and a first comonomer is introduced into the premixing zone and the reaction zone respectively, and a solution containing a catalyst is introduced into the premixing zone, and the solution is continuously stirred to allow the catalyst to undergo a prepolymerization reaction with the first comonomer and the second comonomer in the premixing zone; The material containing the high temperature resistant catalyst obtained by the prepolymerization reaction is continuously introduced into the reaction zone with stirring, and undergoes polymerization reaction with the first comonomer and the second comonomer introduced into the reaction zone to prepare metallocene polyethylene.

2. The method for preparing polyethylene by metallocene prepolymerization solution method according to claim 1, characterized in that: The temperature of the prepolymerization reaction is -10°C to 50°C, and the pressure is 10-14MPa.

3. The method for preparing polyethylene by metallocene prepolymerization solution method according to claim 1, characterized in that: The polymerization reaction temperature is 140°C-207°C, and the pressure is 10-14MPa.

4. The method for preparing polyethylene by metallocene prepolymerization solution method according to claim 1, characterized in that: The solvent in the solution containing the catalyst is an organic solvent toluene; The catalyst comprises a main catalyst and a co-catalyst, wherein the main catalyst is a metallocene catalyst and the co-catalyst is an alkyl aluminum; the molar ratio of the main catalyst to the co-catalyst is 1:1; The volume ratio of the mass of the catalyst to the volume of the organic solvent toluene is 0.0006295 g:1 ml; The amount of the solution containing the catalyst introduced was 2.5 ml / min.

5. The method for preparing polyethylene by metallocene prepolymerization solution method according to claim 1, characterized in that: The amount of the first comonomer introduced into the premixing zone is 1 g / min, and the amount of the first comonomer introduced into the reaction zone is 29 g / min; the first comonomer is ethylene.

6. The method for preparing polyethylene by metallocene prepolymerization solution method according to claim 1, characterized in that: The amount of the mixture introduced into the premixing zone was 54.67 g / min, and the amount of the mixture introduced into the reaction zone was 109.33 g / min.

7. The method for preparing polyethylene by metallocene prepolymerization solution method according to claim 1, characterized in that: The solvent is hexane, the second comonomer is octene, and the mass ratio of the solvent to the second comonomer in the mixture is 10:

3.

8. The method for preparing polyethylene by metallocene prepolymerization solution method according to claim 1, characterized in that: The stirring rates in the premixing zone and the reaction zone are both 600 r / min.

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