A low-isotactic polypropylene catalyst and a method for catalyzing propylene polymerization

Abstract

This invention discloses a low-isotactic polypropylene catalyst and a method for catalyzing propylene polymerization, aiming to provide a low-isotactic polypropylene catalyst with a greener and more environmentally friendly preparation process and good polymerization performance. The technical solution consists of a supported catalyst and a co-catalyst. The supported catalyst is composed of titanium tetrachloride and a composite support. The composite support is composed of any three of magnesium chloride, aluminum chloride, silica, alumina, and zeolite molecular sieves. The co-catalyst is an alkylaluminum with the structural formula AlR3 or an AlR... n Cl 3‑n It refers to one or any mixture of alkylaluminum chlorides; it belongs to the field of catalyst technology.

Description

Technical Field

[0001] This invention relates to a polypropylene catalyst, specifically a low isotactic polypropylene catalyst, and also to a method for catalyzing propylene polymerization; belonging to the field of catalyst technology. Background Technology

[0002] Low-isotactic polypropylene (LOP) is a type of propylene polymer that differs from isotactic polypropylene (iPP) and syndiotactic polypropylene (sPP). It is primarily composed of atactic polypropylene, block polymers consisting of atactic and isotactic polypropylene segments, and a small amount of low-molecular-weight isotactic polypropylene. Due to its low density, good low-temperature resistance, and excellent flowability, LOP is widely used in plastics processing, building materials, textiles, and printing.

[0003] Initially, polypropylene plants produced polypropylene containing a small amount of atactic polypropylene (aPP) byproducts due to insufficient catalyst orientation for propylene polymerization. Because the process required complex post-processing to separate aPP from the main product, iPP, catalysts with high orientation capabilities gradually replaced the earlier ones. However, due to its unique properties, aPP has been widely used in the market, and the application of new high isotactic polypropylene catalysts has significantly reduced the supply of aPP, leading to a shortage. Therefore, the development of specialized low isotactic polypropylene products has become a market necessity, and the key to polymer production lies in the catalyst.

[0004] Supported polypropylene catalysts primarily utilize TiCl4 supported on a support to catalyze propylene polymerization. The morphology of TiCl4 significantly influences the isotacticity of polypropylene. For catalysts targeting low-isotactic polypropylene, a large specific surface area on the support is advantageous, promoting the dispersion of TiCl4 as monotitanium on the support surface. MgCl2 is the primary material used as a TiCl4 support, with the δ-crystalline form being more suitable. This is because the δ-crystalline form has more structural defects and a larger specific surface area compared to the α-crystalline form, which is more conducive to the loading of TiCl4 on the surface. Unactivated MgCl2 is generally in the α-crystalline form with a small specific surface area. The conversion from α-crystalline to δ-crystalline can be achieved through chemical methods and physical milling. The chemical method typically uses a magnesium-containing reagent to generate MgCl2 in the system, which has a δ-crystalline form. The physical milling method utilizes the shear force of milling to change the crystal form of MgCl2 from α-crystalline to δ-crystalline.

[0005] Patent WO8809348 discloses a method for preparing a catalyst, which uses chlorine, hydrogen chloride, or other chlorides to chlorinate an organomagnesium compound to obtain a catalyst support. This support is then reacted with titanium tetrachloride under reflux to produce the catalyst, which can catalyze the slurry polymerization of propylene to obtain atactic (low isotactic) polypropylene. CN1124740A discloses a method for preparing a low isotactic polypropylene catalyst. This method uses magnesium chloride and silica as a two-component support, which reacts sequentially with an alcohol, then with alkylaluminum, and finally with titanium tetrachloride to obtain the catalyst. This catalyst is used in the slurry polymerization of propylene to obtain polypropylene with an isotacticity of 28-34%. CN1146461A discloses a method for preparing a catalyst, using aluminum trichloride or other compounds as chlorinating agents for organomagnesium compounds to obtain a catalyst support, which is then reacted with titanium tetrachloride to generate the catalyst. This catalyst exhibits good polymerization activity at an Al / Ti ratio of 500-900 and can yield low isotactic polypropylene. However, the aforementioned catalyst preparation methods all involve a series of reactions involving solvents, alkylaluminum, and titanium tetrachloride, generating large amounts of waste liquid and solid waste, which is detrimental to industrial production. Patent CN1315885C discloses a method for preparing a low-titanium-loading catalyst. This method uses magnesium chloride and aluminum chloride as a composite support and employs a milling method to prepare the catalyst. The resulting catalyst has a titanium content of 0.1-2%, and the prepared polypropylene has an isotacticity of 20-40%. This catalyst preparation method avoids the use of environmentally polluting solvents and alkylaluminum, but the resulting catalyst has low activity, below 10. 4 gPP / gTi·h. Therefore, developing green, simple, and high-performance catalyst synthesis methods remains a technological necessity for the industry. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the first objective of this invention is to propose a low-isotactic polypropylene catalyst with a greener and more environmentally friendly preparation process and excellent polymerization performance.

[0007] Therefore, the first technical solution adopted by the present invention is as follows:

[0008] A low isotactic polypropylene catalyst is composed of a supported catalyst and a co-catalyst, wherein the supported catalyst is composed of titanium tetrachloride and a composite support.

[0009] The composite carrier is composed of any three of the following: magnesium chloride, aluminum chloride, silicon dioxide, aluminum oxide, and zeolite molecular sieve.

[0010] In this case, a small amount of silica was added to prepare the polypropylene catalyst, forming a ternary composite support with magnesium chloride and aluminum chloride. The resulting catalyst exhibited superior polymerization performance compared to catalysts prepared using existing technologies. This polypropylene catalyst displayed high polymerization activity while yielding polypropylene with an isotacticity of less than 20%. It is speculated that the addition and dispersion of silica in the system not only gave magnesium chloride a larger specific surface area but also made it easier for magnesium chloride to form δ-crystals with crystal defects. This, in turn, facilitated the loading of titanium tetrachloride onto the support in the form of single titanium atoms, thus achieving the goal of preparing low-isotactic polypropylene.

[0011] The cocatalyst is an alkylaluminum with the structural formula AlR3 or an alkylaluminum with the structural formula AlR3. n Cl 3-n One or any mixture of alkylaluminum chlorides;

[0012] Where: R in AlR3 is -Me, -Et, or -Bu; AlRnCl 3-n In the case of n = 1, 1.5, 2;

[0013] The molar ratio of titanium in titanium tetrachloride to aluminum in the co-catalyst is 10-300:1;

[0014] The titanium content is 2-3.5% of the weight of the supported catalyst.

[0015] Furthermore, in the aforementioned low isotactic polypropylene catalyst, the composite support is composed of magnesium chloride, aluminum chloride, and silicon dioxide.

[0016] Furthermore, in the aforementioned low isotactic polypropylene catalyst, the molar ratio of magnesium chloride, aluminum chloride, and silicon dioxide is 10:0.2-4:0.5-3.

[0017] Furthermore, in the aforementioned low isotactic polypropylene catalyst, the molar ratio of magnesium chloride to titanium tetrachloride is 10:0.1-2.

[0018] Furthermore, in the aforementioned low isotactic polypropylene catalyst, the co-catalyst is trimethylaluminum (AlMe3), triethylaluminum (AlEt3), triisobutylaluminum (AliBu3), diethylaluminum chloride (AlEt2Cl), diethylaluminum chloride (AlEtCl2), or sesquiethylaluminum chloride (AlEt). 1.5 Cl 1.5 At least one of the following.

[0019] Furthermore, in the aforementioned low isotactic polypropylene catalyst, the co-catalyst is triethylaluminum or triisobutylaluminum.

[0020] Furthermore, in the aforementioned low isotactic polypropylene catalyst, the co-catalyst is composed of triethylaluminum and diethylaluminum chloride in a molar ratio of 10-90:90-10.

[0021] Furthermore, the aforementioned low-isotactic polypropylene catalyst, wherein the supported catalyst is prepared by the following method:

[0022] 1) Weigh each component;

[0023] 2) Under anhydrous and oxygen-free conditions, mix and grind the carrier weighed in step 1).

[0024] 3) Under anhydrous and oxygen-free conditions, titanium tetrachloride was added to the milled carrier and milling continued.

[0025] During the preparation of the supported catalyst, titanium tetrachloride can be added all at once, in batches, continuously dripped, or sprayed, with spraying being the preferred method.

[0026] The second technical solution provided by the present invention is the above-mentioned method for polymerizing propylene using a low isotactic polypropylene catalyst, wherein a supported catalyst and a co-catalyst are added to liquid propylene, and polymerization is carried out at a pressure of 0.1-5 MPa and a temperature of 0-120°C for 0.3-5 h. After the reaction is completed, the temperature is lowered, the remaining propylene is vented, and the resulting polymer is vacuum dried.

[0027] The weight ratio of the liquid propylene to the supported catalyst is 1000-5000:0.072;

[0028] The molar ratio of titanium in the supported catalyst to aluminum in the co-catalyst is 100:1.

[0029] More preferably, the pressure is 0.5-4 MPa; the temperature is 30-90℃; the polymerization time is 0.5-3 h; and the molar ratio of aluminum to titanium in the catalyst and co-catalyst is preferably 20-200:1, and more preferably 100:1.

[0030] More preferably, the catalyst used in propylene polymerization is applicable to a variety of processes, including but not limited to gas-phase polymerization, liquid-phase polymerization, solution polymerization and reasonable combinations thereof, with liquid-phase polymerization and solution polymerization being preferred.

[0031] The catalyst described above can be used in propylene polymerization in both batch and continuous polymerization methods.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The catalyst preparation method provided by the present invention does not use solvents when preparing the catalyst, which reduces the adverse impact on the environment and simplifies the processing steps in the catalyst preparation process.

[0034] 2. The catalyst preparation method provided by the present invention employs a composite of multiple supports, resulting in a catalyst with better catalytic activity during propylene polymerization;

[0035] 3. The catalyst provided by this invention can polymerize propylene over a wider temperature range and at a lower aluminum-titanium ratio to prepare low isotactic polypropylene, which not only facilitates industrial process control but also reduces the amount of organoaluminum used and lowers production costs. Detailed Implementation

[0036] The claims of the present invention will be further described in detail below with reference to specific embodiments, but this does not constitute any limitation on the present invention. Any limited modifications made by any person within the scope of the claims of the present invention are still within the protection scope of the claims of the present invention.

[0037] Unless otherwise specified, the following embodiments are all conventional experimental methods and operating procedures in the art.

[0038] Example 1 Preparation of supported catalyst

[0039] 14.3 g of magnesium chloride (baked and dried under a hydrogen chloride atmosphere), 1.5 g of anhydrous aluminum chloride, 0.9 g of baked and dried silica, 50 stainless steel balls with a diameter of 6 mm, and 30 stainless steel balls with a diameter of 7.5 mm were added to a grinding jar under a nitrogen atmosphere and after thorough drying. The mixture was ground at room temperature for 24 hours at a speed of 200 rpm. Then, 1.5 g of titanium tetrachloride was added to the grinding jar, and grinding continued at room temperature for another 24 hours to obtain the supported catalyst. The calculated titanium content of the catalyst was 2.08 wt%.

[0040] Example 2 Preparation of supported catalyst

[0041] Except for the addition of 2.0 g of aluminum chloride and 0.5 g of silicon dioxide, the other conditions were the same as in Example 1. The calculated titanium content of the catalyst was 2.07 wt%.

[0042] Example 3 Preparation of supported catalyst

[0043] Except for the addition of 3.0 g of aluminum chloride and 1.0 g of silicon dioxide, the other conditions were the same as in Example 1. The calculated titanium content of the catalyst was 2.12 wt%.

[0044] Example 4 Preparation of supported catalyst

[0045] Except for the addition of 5.0 g of aluminum chloride and 1.5 g of silicon dioxide, the other conditions were the same as in Example 1. The calculated titanium content of the catalyst was 2.10 wt%.

[0046] Example 5 Preparation of supported catalyst

[0047] Except for the addition of 7.2g of aluminum chloride and 2.5g of silicon dioxide, the other conditions were the same as in Example 1. The calculated titanium content of the catalyst was 2.15wt%.

[0048] Example 6 Preparation of Supported Catalyst

[0049] Except for the addition of 1.0 g of aluminum chloride and 1.4 g of silicon dioxide, the other conditions were the same as in Example 1. The calculated titanium content of the catalyst was 2.08 wt%.

[0050] Example 7 Preparation of Supported Catalyst

[0051] Except for the addition of 0.5g of aluminum chloride and 0.5g of silicon dioxide, the other conditions were the same as in Example 1. The calculated titanium content of the catalyst was 2.02wt%.

[0052] Example 8 Preparation of supported catalyst

[0053] Except for the addition of 1.0 g of titanium tetrachloride, the other conditions were the same as in Example 1. The calculated titanium content of the catalyst was 1.43 wt%.

[0054] Example 9 Preparation of supported catalyst

[0055] Except for the addition of 0.5 g of titanium tetrachloride, the other conditions were the same as in Example 1. The calculated titanium content of the catalyst was 1.08 wt%.

[0056] Example 10 Preparation of supported catalyst

[0057] Except for the addition of 2.4 g of titanium tetrachloride, the other conditions were the same as in Example 1. The calculated titanium content of the catalyst was 3.17 wt%.

[0058] Example 11 Preparation of supported catalyst

[0059] Except for the addition of 5.0 g of titanium tetrachloride, the other conditions were the same as in Example 1. The calculated titanium content of the catalyst was 5.85 wt%.

[0060] Example 12 Preparation of supported catalyst

[0061] Except for the addition of 7.8 g of titanium tetrachloride, the other conditions were the same as in Example 1. The calculated titanium content of the catalyst was 8.25 wt%.

[0062] Preparation of supported catalyst in Comparative Example 1

[0063] Except that no silica was added during catalyst preparation, the other conditions were the same as in Example 1. The calculated titanium content of the catalyst was 2.19 wt%.

[0064] Example 13 Propylene Polymerization Reaction

[0065] 5L (2.57kg) of liquid propylene was added to a 10L stainless steel reactor that had been vacuum-dried and returned to room temperature, and which had been replaced with a propylene atmosphere. Then, 3.1mL of triethylaluminum (1.0M hexane solution) was injected under nitrogen pressure. The stirring speed was set to 300 rpm, and the reactor was heated to 60°C. 72.0mg of the catalyst prepared in Example 1 was taken, and the Al / Ti ratio was adjusted to 100. The catalyst was dispersed in 10mL of hexane and injected under nitrogen pressure into the reactor to begin polymerization. After 1 hour, the reactor was cooled, and the remaining propylene was vented. The resulting polymer was vacuum-dried at 60°C. The polymerization results are listed in Table 1 below.

[0066] Example 14 Propylene Polymerization Reaction

[0067] Except that the catalyst prepared in Example 2 was used for propylene polymerization, and the amount of catalyst was adjusted to maintain Al / Ti = 100, the other conditions were the same as in Example 13. The polymerization results are listed in Table 1 below.

[0068] Example 15 Propylene Polymerization Reaction

[0069] Except that the catalyst prepared in Example 3 was used for propylene polymerization, and the amount of catalyst was adjusted to maintain Al / Ti = 100, the other conditions were the same as in Example 13. The polymerization results are listed in Table 1 below.

[0070] Example 16 Propylene Polymerization Reaction

[0071] Except that the catalyst prepared in Example 4 was used for propylene polymerization, and the amount of catalyst was adjusted to maintain Al / Ti = 100, the other conditions were the same as in Example 13. The polymerization results are listed in Table 1 below.

[0072] Example 17 Propylene Polymerization Reaction

[0073] Except that the catalyst prepared in Example 5 was used for propylene polymerization, and the amount of catalyst was adjusted to maintain Al / Ti = 100, the other conditions were the same as in Example 13. The polymerization results are listed in Table 1 below.

[0074] Example 18 Propylene Polymerization Reaction

[0075] Except that the catalyst prepared in Example 6 was used for propylene polymerization, and the amount of catalyst was adjusted to maintain Al / Ti = 100, the other conditions were the same as in Example 13. The polymerization results are listed in Table 1 below.

[0076] Example 19 Propylene Polymerization Reaction

[0077] Except that the catalyst prepared in Example 7 was used for propylene polymerization, and the amount of catalyst was adjusted to maintain Al / Ti = 100, the other conditions were the same as in Example 13. The polymerization results are listed in Table 1 below.

[0078] Example 20 Propylene Polymerization Reaction

[0079] Except that the catalyst prepared in Example 8 was used for propylene polymerization, and the amount of catalyst was adjusted to maintain Al / Ti = 100, the other conditions were the same as in Example 13. The polymerization results are listed in Table 1 below.

[0080] Example 21 Propylene Polymerization Reaction

[0081] Except that the catalyst prepared in Example 9 was used for propylene polymerization, and the amount of catalyst was adjusted to maintain Al / Ti = 100, the other conditions were the same as in Example 13. The polymerization results are listed in Table 1 below.

[0082] Example 22 Propylene Polymerization Reaction

[0083] Except that the catalyst prepared in Example 10 was used for propylene polymerization, and the amount of catalyst was adjusted to maintain Al / Ti = 100, the other conditions were the same as in Example 13. The polymerization results are listed in Table 1 below.

[0084] Example 23 Propylene Polymerization Reaction

[0085] Except that the catalyst prepared in Example 11 was used for propylene polymerization, and the amount of catalyst was adjusted to maintain Al / Ti = 100, the other conditions were the same as in Example 13. The polymerization results are listed in Table 1 below.

[0086] Example 24 Propylene Polymerization Reaction

[0087] Except that the catalyst prepared in Example 12 was used for propylene polymerization, and the amount of catalyst was adjusted to maintain Al / Ti = 100, the other conditions were the same as in Example 13. The polymerization results are listed in Table 1 below.

[0088] Comparative Example 2: Propylene Polymerization Reaction

[0089] Except for the catalyst prepared in Comparative Example 1, which was used for propylene polymerization, and the catalyst dosage was adjusted to maintain Al / Ti = 100, the other conditions were the same as in Example 13. The polymerization results are listed in Table 1 below.

[0090] Test methods

[0091] Catalytic efficiency: The ratio of polymer weight to catalyst weight, expressed in kgPP / gCat;

[0092] Melting point: Measured using differential scanning calorimetry (DSC), unit: °C;

[0093] Enthalpy of fusion: Measured using differential scanning calorimetry (DSC), in J / g;

[0094] Isotacticity: The percentage of the mass of the insoluble portion of 1.0g polypropylene extracted with boiling n-heptane is the polymer isotacticity.

[0095] Table 1

[0096]

[0097]

[0098] The test data from Examples 14-24 above show that the technical solution provided in this application has high catalytic efficiency, low melting enthalpy and isotacticity (below 20%), while the catalytic efficiency in Comparative Example 2 is significantly lower than that in Example 13, and the melting enthalpy and isotacticity are higher. This indicates that the technical solution provided in this application, by adding a small amount of silica, forms a ternary composite support with magnesium chloride and aluminum chloride, which has high polymerization activity, and the resulting catalyst has excellent polymerization performance.

Claims

1. A low-isotactic polypropylene catalyst, characterized in that, It consists of a supported catalyst and a co-catalyst, wherein the supported catalyst is composed of titanium tetrachloride and a composite support; The composite carrier is composed of magnesium chloride, aluminum chloride, and silicon dioxide in a molar ratio of 10:0.2-4:0.5-3; The cocatalyst is an alkylaluminum with the structural formula AlR3 or an alkylaluminum with the structural formula AlR3. n Cl 3-n One or any mixture of alkylaluminum chlorides; Where: R in AlR3 is -Me, -Et, or -Bu; AlR n Cl 3-n In the case of n=1, 1.5, 2; The molar ratio of titanium in titanium tetrachloride to aluminum in the co-catalyst is 10-300:1; The titanium content is 2-3.5% of the weight of the supported catalyst; The supported catalyst was prepared by the following method: 1) Weigh each component according to its weight. 2) Under anhydrous and oxygen-free conditions, mix and grind the carrier weighed in step 1); 3) Under anhydrous and oxygen-free conditions, titanium tetrachloride is added to the milled carrier and milled again.

2. The low isotactic polypropylene catalyst according to claim 1, characterized in that, The molar ratio of magnesium chloride to titanium tetrachloride is 10:0.1-2.

3. The low isotactic polypropylene catalyst according to claim 1, characterized in that, The co-catalyst is at least one of trimethylaluminum, triethylaluminum, triisobutylaluminum, diethylaluminum chloride, diethylaluminum chloride, and sesquiethylaluminum chloride.

4. The low isotactic polypropylene catalyst according to claim 1, characterized in that, The co-catalyst is triethylaluminum or triisobutylaluminum.

5. The low isotactic polypropylene catalyst according to claim 1, characterized in that, The co-catalyst is composed of triethylaluminum and diethylaluminum monochloro in a molar ratio of 10-90:90-10.

6. The method for propylene polymerization catalyzed by the low-isotactic polypropylene catalyst according to claim 1, characterized in that, A supported catalyst and a co-catalyst were added to liquid propylene, and polymerization was carried out at a pressure of 0.1-5 MPa and a temperature of 0-120 °C for 0.3-5 h. After the reaction was completed, the temperature was lowered, the remaining propylene was vented, and the resulting polymer was dried under vacuum. The weight ratio of the liquid propylene to the supported catalyst is 1000-5000:0.072; The molar ratio of titanium in the supported catalyst to aluminum in the co-catalyst is 10-300:

1.

7. The method for propylene polymerization catalyzed by the low-isotactic polypropylene catalyst according to claim 6, characterized in that, During polymerization, the pressure is 0.5-4 MPa; the temperature is 30-90℃; the polymerization time is 0.5-3 h; and the molar ratio of titanium in the supported catalyst to aluminum in the co-catalyst is 100:1.

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