Polyethylene gas phase condensation state polymerization method

Abstract

The invention relates to a polyethylene gas phase condensation state polymerization method, which comprises the following steps of: modifying an aluminum-containing carrier by using alkyl aluminum and / or alkoxy aluminum, loading a chromium element and a titanium element, roasting at high temperature to obtain a catalyst, putting the catalyst into a reactor, introducing an ethylene monomer into the reactor, and reacting at high temperature to obtain the polyethylene gas phase condensation state. And carrying out polymerization reaction under the conditions that the temperature is 60-115 DEG C, the ethylene monomer pressure is 0.6-1.2 MPa and the gas phase condensation state is adopted to generate polyethylene. Compared with the prior art, the catalyst provided by the invention has the characteristic of fast activity excitation, can complete 90% of activity excitation within 30 minutes, and can be applied to gas phase condensation state operation.

Description

Technical Field

[0001] The present invention relates to the technical field of polyethylene synthesis, in particular to a polyethylene gas-phase condensed state polymerization method. Background Art

[0002] Gas-phase fluidized bed polymerization is a commonly used technology for ethylene polymerization. It requires no solvents and is environmentally friendly and clean. It operates at low temperatures and consumes minimal energy. It also allows for easy product separation and simplified post-processing. It also features continuous production and a high degree of automation. However, due to its low heat dissipation efficiency and limited production capacity, this technology can be used to conduct the reaction in a condensed gas phase to further improve production efficiency. Compared to the non-condensed phase, the condensed phase typically has a shorter reaction residence time. This improved heat transfer speeds up the reaction rate, resulting in higher yields per unit time and a narrower distribution of material residence times, thus producing high-performance, low-cost polyethylene products.

[0003] Chromium-based catalysts can produce polyethylene products with high molecular weights and broad molecular weight distributions. This results in final products with excellent mechanical and processing properties, and is widely used in high-performance products such as pipes and hollow parts. However, due to the long reaction induction time of conventional chromium-based catalysts, their activity is not fully exerted within the short residence time of the condensed state, resulting in low reaction activity. Therefore, the reaction induction time of chromium-based polyethylene catalysts used in the condensed state needs to be reduced. Summary of the Invention

[0004] The purpose of the present invention is to provide a polyethylene gas phase condensed state polymerization method to solve the problem that conventional chromium-based ethylene polymerization catalysts cannot be used in condensed state operation or the catalyst activity is low after being used in the condensed state.

[0005] The purpose of the present invention can be achieved by the following technical scheme: a method for gas-phase condensed state polymerization of polyethylene, which comprises modifying an aluminum-containing carrier with alkyl aluminum and / or alkoxy aluminum, loading chromium elements and titanium elements, and obtaining a catalyst by high-temperature calcination, placing the catalyst in a reactor, and introducing ethylene monomer into the reactor, and causing a polymerization reaction to occur under gas-phase condensed state conditions at a temperature of 60°C to 115°C, an ethylene monomer pressure of 0.6 to 1.2 MPa, to produce polyethylene.

[0006] Preferably, the polymerization activity peak time of the catalyst is 5 to 15 minutes.

[0007] Preferably, the time for the catalyst to be activated to 90% of its activity is 20 to 40 minutes, and the release of the catalytic activity is completed within 60 minutes.

[0008] More preferably, the time it takes for the catalyst to be activated to 90% of its activity is 30 minutes.

[0009] Preferably, the aluminum-containing carrier is kaolin (Al2Si2O5(OH)4), montmorillonite ((Na,Ca) 0.33 (Al,Mg)2(Si4O 10 )(OH)2·nH2O), alumina (Al2O3), aluminosilicate (SiO2-Al2O3), zeolite (SiO2-Al2O3), hydrotalcite (Mg6Al2(CO3)(OH) 16 ), calcium aluminate (CaO-Al2O3), aluminum sol (Al2O3), aluminum phosphate (Al2O3-P2O5), aluminum magnesium spinel (MgAl2O4), aluminum titanium composite oxide (Al2O3-TiO2), aluminum zirconium composite oxide (Al2O3-ZrO2) or at least one of the following:

[0010] Preferably, the alkylaluminum and / or alkoxyaluminum is at least one of triisobutylaluminum, tri-n-hexylaluminum, triisopropylaluminum, methyldiethylaluminum, trimethylaluminum, diethylaluminum ethoxide, diethylaluminum methoxide, dimethylaluminum ethoxide, diisopropylaluminum ethoxide, diethylaluminum propoxide, diisobutylaluminum ethoxide and methylethylaluminum ethoxide.

[0011] Preferably, the mass ratio of the addition amount of the alkyl aluminum and / or alkoxy aluminum to the aluminum-containing support is (0.1-10):100.

[0012] Preferably, the preparation method of the catalyst includes the following steps: after modifying an aluminum-containing carrier with alkyl aluminum and / or alkoxy aluminum, using a chromium salt solution to load chromium on the aluminum-containing carrier to obtain a carrier powder loaded with aluminum and chromium elements, then using an organic titanium compound solution to load titanium on the modified carrier powder loaded with aluminum and chromium elements to obtain a carrier powder simultaneously loaded with aluminum, chromium and titanium elements, and finally calcining the carrier powder simultaneously loaded with aluminum, chromium and titanium elements at a high temperature, the calcination temperature being 300 to 950°C and the calcination time being 0.5 to 48 hours to obtain the catalyst.

[0013] The present invention provides a chromium-based polyethylene catalyst applicable to gas-phase condensed state operation. The catalyst is obtained by modifying an aluminum-containing carrier with alkyl aluminum and / or alkoxy aluminum, simultaneously loading chromium and titanium compounds, and calcining at high temperature.

[0014] More preferably, the aluminum-containing support is modified with the aluminum alkyl and / or aluminum alkoxide by an impregnation method.

[0015] More preferably, the chromium salt comprises one or more of chromium acetate, dichromate, chromate, chromium nitrate or chromium oxide.

[0016] Further preferably, the content of chromium in the chromium salt is 0.1 to 5.0% of the mass of the aluminum-containing support after modification with alkyl aluminum and / or alkoxy aluminum.

[0017] More preferably, the organic titanium compound comprises at least one of tetraisopropyltitanium, tetraethyltitanium, tetrabutyltitanium, tetraisooctyl titanate, and n-butyl titanate.

[0018] Further preferably, the content of titanium in the organic titanium compound is 0.1 to 10% of the mass of the modified carrier powder loaded with aluminum and chromium elements.

[0019] Further preferably, the solvents of the chromium salt solution and the organic titanium compound solution are water, alcohol solvents or ketone solvents.

[0020] Preferably, the catalyst is placed in a polyethylene gas phase reactor, and the ethylene monomer feed gas is introduced into the reactor at a flow rate of 27 to 60 tons / h, the total pressure of the reactor is 1.6 to 2.4 MPa, the ethylene monomer partial pressure is 0.6 to 1.2 MPa, and the catalyst addition rate in the reactor is 1.5 to 20 kg / h.

[0021] More preferably, the ethylene monomer partial pressure is 0.6-0.8 MPa.

[0022] Preferably, n-hexane is further added into the reactor, and the concentration of n-hexane in the reactor is 11.5-25 wt % and the partial pressure is 0.23-0.575 MPa.

[0023] Preferably, nitrogen is further added into the reactor, and the partial pressure of nitrogen in the reactor is 1.0 to 1.2 MPa.

[0024] Preferably, a comonomer is further added into the reactor, and the comonomer partial pressure is 0.05 to 0.2 MPa.

[0025] Further preferably, the comonomer comprises hexene, butene or propylene.

[0026] Research has shown that by modifying an aluminum-containing support with aluminum alkyls and / or aluminum alkoxides and simultaneously loading them with chromium and titanium compounds, the gas-phase reaction induction time is significantly reduced. The choice of support is crucial. When the modified aluminum-containing support has a high aluminum content and is in the presence of aluminum, titanium, and chromium, the resulting catalyst exhibits a significantly reduced reaction induction time.

[0027] Furthermore, the present invention discovered that the chromium-based catalyst prepared based on the above characteristics can release catalytic activity within 60 minutes, with high catalytic activity, significantly enhancing polymerization activity in the gas-phase condensed state. Furthermore, rapid release of catalytic activity significantly reduces incomplete release of activity, which can lead to slow polymerization in the downstream system, resulting in oligomers and subsequent system agglomeration. Using an aluminum-free support, even if the support is modified with aluminum alkyls and / or aluminum alkoxides, will not achieve the desired short-term release of activity.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The catalyst of the present invention has a short reaction induction time, can be applied to polyethylene gas-phase condensed state polymerization process, and can achieve mass production;

[0030] 2. The present invention realizes the preparation of a chromium-based polyethylene catalyst capable of inducing a condensed state through an industrially feasible solution;

[0031] 3. The chromium-based polyethylene catalyst prepared by the present invention has the characteristic of rapid activation, and can complete 90% activation within 30 minutes, and can be applied to gas-phase condensed state operation;

[0032] 4. The present invention has a short reaction induction time, can still exert good activity in a short residence time in the condensed state, has high reaction activity, can be applied to gas phase condensed state operation, and can solve the problem that conventional chromium-based ethylene polymerization catalysts cannot be used in condensed state operation or the catalyst activity is low after being used in the condensed state. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a graph showing the relationship between ethylene flow and polymerization time for the comparative example and the catalyst of the present invention. DETAILED DESCRIPTION

[0034] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0035] Unless otherwise specified, the reagents, methods, instruments and equipment used in the present invention are conventional reagents, methods, instruments and equipment in the art. Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0036] Polyethylene vapor-phase condensed state industrial trial: A gas-phase polyethylene reactor with a designed capacity of 300,000 tons / year was loaded with an 80-120 ton seed bed. The seed bed was subjected to 3-6 cycles of pressure rise and fall and nitrogen flow displacement for over 36 hours. The water and oxygen content in the reactor was measured. Once the water and oxygen content fell below 5 ppm, 0.5-5 kg of alkyl aluminum was introduced for titration. After the reactor static electricity stabilized, ethylene, comonomer, and nitrogen were introduced, raising the reactor pressure to 1.6-2.4 MPa, with a nitrogen partial pressure of 1.0-1.2 MPa, an ethylene partial pressure of 0.6-0.8 MPa, and a comonomer partial pressure of 0.05-0.2 MPa. When the reactor pressure reached 1.6 MPa, the catalyst was added to the reactor via a catalyst feeder, the reaction was initiated, and polymerization evaluation was performed.

[0037] Catalyst activity test method: Calculate the catalyst activity curve based on ethylene consumption.

[0038] The silica gel used in the comparative example is silica gel 955 produced by GRACE Company. The specific properties are as follows: silica gel 955: particle size: 35-70μm, specific surface area: 280-300m 2 / g, pore volume: 1.65mL / g.

[0039] The specific properties of the K10 montmorillonite used in the examples are as follows:

[0040] K10 montmorillonite: particle size: <2μm, specific surface area: 220-270m 2 / g, pore volume: 0.3-0.4mL / g.

[0041] The specific properties of kaolin in the embodiment are as follows:

[0042] Kaolin: particle size: 0.1-4μm, specific surface area: 15-30m 2 / g, pore volume: 0.2-0.3mL / g.

[0043] Example 1

[0044] Triisobutylaluminum and K10 montmorillonite were blended at a mass ratio of 0.1:100 for modification. Ethanol and potassium dichromate were mixed at a mass ratio of 5:1 and then blended with the modified support. The chromium content in the potassium dichromate was 0.1% of the modified support's mass. After heating the mixture at 50°C and allowing it to stand for 10 hours, the mixture formed a dry powder.

[0045] The above powder was blended with tetraisopropyl titanium, ethanol, and triethylaluminum, with the titanium content of tetraisopropyl titanium accounting for 0.1% of the powder mass, the triethylaluminum accounting for 1% of the powder mass, and the powder mass accounting for 10% of the solvent mass. The above blend was allowed to stand at 0°C for 4 hours, then heated to 80°C and held for 1 hour until it became a dry powder.

[0046] The above dried powder was calcined at 300° C. for 0.5 hours to obtain a chromium-based polyethylene catalyst.

[0047] When the reaction temperature is 100°C, the catalyst is subjected to polymerization evaluation. The peak polymerization activity is 13 minutes after the catalyst is added, and the time for the activity to be excited to 90% is 35 minutes.

[0048] Example 2

[0049] Other conditions were consistent with those in Example 1, except that kaolin was used as the carrier. The treated dried powder was calcined at 950°C for 48 hours to obtain a chromium-based polyethylene catalyst. Polymerization evaluation of this catalyst revealed peak polymerization activity 14 minutes after catalyst addition, with 90% activity achieved at 30 minutes.

[0050] Example 3

[0051] Other conditions were the same as in Example 1, except that the mass ratio of triisobutylaluminum to K10 montmorillonite was adjusted from 0.1:100 to 10:100 for blending modification. The catalyst was evaluated for polymerization, and the peak polymerization activity occurred 5 minutes after catalyst addition, with 90% activity achieved at 27 minutes.

[0052] Example 4

[0053] Other conditions were the same as those in Example 1, except that the catalyst carrier was changed from K10 montmorillonite to kaolin. The catalyst was subjected to polymerization evaluation, and the polymerization activity peaked 14 minutes after the catalyst was added, and the time to 90% activation of the activity was 29 minutes.

[0054] Example 5

[0055] Other conditions were the same as in Example 1, except that kaolin was used as the carrier, and the titanium content of the tetraisopropyl titanium powder was adjusted from 0.1% to 10% by weight. Polymerization evaluation of the catalyst revealed peak polymerization activity 14 minutes after catalyst addition, with 90% activity achieved at 31 minutes.

[0056] Example 6

[0057] Other conditions were the same as in Example 1, except that the mass ratio of triisobutylaluminum to K10 montmorillonite was adjusted from 0.1:100 to 10:100 for blending and modification, and the titanium content of tetraisopropyltitanium was adjusted from 0.1% to 10% by weight of the powder. Polymerization evaluation of the catalyst revealed peak polymerization activity 5 minutes after catalyst addition, with 90% activity achieved at 24 minutes.

[0058] Comparative Example 1

[0059] A commercial chromium-based polyethylene catalyst, UCAT G(S2) from Professional Carbon, Inc. (USA), was used for evaluation. Polymerization evaluation of the catalyst at 100°C revealed peak polymerization activity 60 minutes after catalyst addition, with 90% activity achieved at 57 minutes.

[0060] Comparative Example 2

[0061] Other conditions were the same as those in Example 1, except that titanium loading was not performed during the preparation process of Example 1, to obtain a chromium-based polyethylene catalyst. The catalyst was evaluated for polymerization, and the peak polymerization activity occurred 40 minutes after the catalyst was added, and the time to 90% activation of the activity was 78 minutes.

[0062] Comparative Example 3

[0063] Other conditions were the same as in Example 1, except that the catalyst carrier was changed from K10 montmorillonite to silica gel 955. A chromium-based polyethylene catalyst was obtained. Polymerization evaluation of the catalyst revealed peak polymerization activity 17 minutes after catalyst addition, and 90% activity was achieved at 68 minutes.

[0064] Table 1 Key parameters and performance data of each embodiment and comparative example

[0065]

[0066]

[0067] From the above table and Figure 1 It can be seen that the specific chromium-based polyethylene catalyst of the present invention can induce activation in a very short time and release activity faster than traditional chromium-based polyethylene catalysts, and is suitable for ethylene polymerization production under conditions of short residence time in the gas phase condensed state.

[0068] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A polyethylene gas phase condensed state polymerization method, characterized in that: After modification with alkyl aluminum and / or alkoxy aluminum on an aluminum-containing carrier, chromium and titanium elements are loaded and a catalyst is obtained by high-temperature calcination. The catalyst is placed in a reactor, and ethylene monomer is introduced into the reactor. A polymerization reaction occurs at a temperature of 60°C to 115°C, an ethylene monomer pressure of 0.6 to 1.2 MPa, and a gas-phase condensed state to produce polyethylene.

2. The polyethylene gas phase condensed state polymerization method according to claim 1, characterized in that: The polymerization activity peak time of the catalyst is 5 to 15 minutes.

3. The polyethylene gas phase condensed state polymerization method according to claim 1, characterized in that: The time for the catalyst to be activated to 90% of its activity is 20 to 40 minutes, and the release of the catalytic activity is completed within 60 minutes.

4. The polyethylene gas phase condensed state polymerization method according to claim 1, characterized in that: The aluminum-containing carrier is at least one of kaolin, montmorillonite, alumina, aluminosilicate, zeolite, hydrotalcite, calcium aluminate, aluminum sol, aluminum phosphate, aluminum magnesium spinel, aluminum titanium composite oxide, and aluminum zirconium composite oxide.

5. The polyethylene gas phase condensed state polymerization method according to claim 1, characterized in that: The alkyl aluminum and / or alkoxy aluminum is at least one of triisobutyl aluminum, tri-n-hexylaluminum, triisopropyl aluminum, methyl diethyl aluminum, trimethyl aluminum, diethyl aluminum ethoxide, diethyl aluminum methoxide, dimethyl aluminum ethoxide, diisopropyl aluminum ethoxide, diethyl aluminum propoxide, diisobutyl aluminum ethoxide and methyl ethyl aluminum ethoxide.

6. The polyethylene gas phase condensed state polymerization method according to claim 1, characterized in that: The mass ratio of the added amount of the alkyl aluminum and / or alkoxy aluminum to the aluminum-containing carrier is (0.1-10):

100.

7. The polyethylene gas phase condensed state polymerization method according to claim 1, characterized in that: The preparation method of the catalyst comprises the following steps: modifying an aluminum-containing carrier with alkyl aluminum and / or alkoxy aluminum, loading chromium on the aluminum-containing carrier with a chromium salt solution to obtain a carrier powder loaded with aluminum and chromium elements, loading titanium on the modified carrier powder loaded with aluminum and chromium elements with an organic titanium compound solution to obtain a carrier powder loaded with aluminum, chromium and titanium elements simultaneously, and finally calcining the carrier powder loaded with aluminum, chromium and titanium elements simultaneously at a high temperature of 300 to 950° C. for 0.5 to 48 hours to obtain the catalyst.

8. The polyethylene gas phase condensed state polymerization method according to claim 7, characterized in that: The chromium salt comprises one or more of chromium acetate, dichromate, chromate, chromium nitrate or chromium oxide; The organic titanium compound comprises at least one of tetraisopropyl titanium, tetraethyl titanium, tetrabutyl titanium, tetraisooctyl titanate, and n-butyl titanate; The solvents of the chromium salt solution and the organic titanium compound solution are water, alcohol solvent or ketone solvent.

9. The polyethylene gas phase condensed state polymerization method according to claim 1, characterized in that: The catalyst is placed in a polyethylene gas phase reactor, and ethylene monomer raw gas is introduced into the reactor at a flow rate of 27 to 60 tons / h. The total pressure of the reactor is 1.6 to 2.4 MPa, the ethylene monomer partial pressure is 0.6 to 1.2 MPa, and the catalyst addition rate in the reactor is 1.5 to 20 kg / h.

10. The polyethylene gas phase condensed state polymerization method according to claim 1, characterized in that: Normal hexane is also added into the reactor. The concentration of normal hexane in the reactor is 11.5-25%, and the partial pressure is 0.23-0.575 MPa.

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