Electrical grade ultra-clean polypropylene and process for its preparation

Abstract

The present application provides an electrical grade super-clean polypropylene and a preparation method thereof. The preparation method comprises material refining, slurry polymerization and post-treatment. The post-treatment comprises three times of washing of the solid polypropylene, the first time of which uses a dispersant, the second time of which uses a mixed solvent containing a metal ion complexing agent, and the third time of which uses an alcohol. The electrical grade super-clean polypropylene has an ash content of 20 ppm or less, an isotacticity of 98% or more, a mass average molecular weight of 350-425 thousand, a molecular weight distribution of 8-10.5, and a melt index of 3-4.5 g / 10 min. The preparation method of the electrical grade super-clean polypropylene has the advantages of simple process, low requirement for equipment, small energy consumption, low cost, small environmental pollution, etc. The raw material propylene can be reused after separation, and the dispersant and alcohol can also be reused after separation and purification, and the electrical grade super-clean polypropylene with excellent performance is prepared.

Description

TECHNICAL FIELD

[0001] The present application relates to an electrical grade ultra-clean polypropylene and a preparation method thereof, and belongs to the technical field of polypropylene. BACKGROUND

[0002] With the continuous expansion of the application range of polypropylene, low-ash polypropylene resin plays an important role in the fields of electronics, electrical appliances, textiles and medical treatment. Among them, the development and application of polypropylene capacitor film greatly improve the quality and performance of electronics and capacitors. The polypropylene ash refers to the metal and non-metal compounds remaining after the polypropylene sample is burned at a high temperature of 850±25℃, mainly including magnesium oxide, titanium dioxide, aluminum oxide, silicon dioxide, calcium oxide and phosphorus pentoxide. The ash content refers to the proportion of the mass of the remaining compounds to the total mass of the polypropylene sample, commonly expressed in %, ppm or mg / kg. In addition to the properties of ordinary polypropylene, the electrical grade ultra-clean polypropylene special material also has the advantages of high cleanliness, low ash content and low dielectric loss factor. The film processed from the polypropylene has the characteristics of good uniformity, high pressure resistance, high mechanical strength, high insulation resistance and high dielectric strength, and is widely used in low-voltage parallel power capacitors, capacitors for alternating current motors, direct current capacitors, power electronics, lamps, and anti-interference, filtering and power capacitors.

[0003] At present, the ash content of the product obtained by the existing polypropylene production technology is generally about 200-500 ppm, which is obviously higher than the ash content of polypropylene capacitor special resin, which is generally required to be below 100 ppm, and preferably below 30 ppm (CN102040690A). The polypropylene ash mainly comes from the catalyst, cocatalyst, external electron donor and various additives added in the granulation process. In the existing technology, the method for reducing the ash content of polypropylene mainly includes three aspects: first, strengthening the refining of propylene and other raw materials to reduce the content of harmful impurities such as water, oxygen, sulfur and arsenic, thereby increasing the activity of the catalyst and reducing the amount of alkyl aluminum used; second, using a high-activity catalyst to reduce the introduction of titanium-containing and magnesium-containing compounds, and to minimize the addition amount of cocatalyst alkyl aluminum and external electron donor; third, using organic compound additives that do not produce ash in the granulation process, and using a closed system in the production, processing and transportation process to avoid the introduction of external impurities (CN103965380A, CN111019025A, CN112979845A).

[0004] Zhongyuan Petrochemical prepared polypropylene by liquid bulk polymerization method using super-high activity catalyst (HA catalyst) on the 2nd generation loop process. Although the ash content of polypropylene is close to that of imported products, there is still a certain gap in the performance indicators such as molecular weight and its distribution, isotacticity, melting point, crystallinity, etc. compared with imported products (Science and Technology Innovation and Application, 2018, 18: 166-167; Insulating Materials, 2022, 55(10): 33-37.). Especially, the migration of small molecules during film forming process produces obvious smoking, which pollutes the clean production workshop and brings trouble to downstream film manufacturers. In addition, Zhongyuan Petrochemical produces capacitor film special resin (PPH-FC03) by direct polymerization method, but this product has not been mass-produced, and its processing performance, quality stability, electrical properties, etc. still need to be continuously improved (Petrochemical Technology and Application, 2021, 39(5), 365-370.).

[0005] CN109912734A reports a production method of low-ash polypropylene resin. The method washes and removes ash from the raw material polypropylene resin by heating four times, which is complicated and requires heating for each washing, resulting in high energy consumption. CN115124635A reports a method for removing ash from polyolefin materials. The method first impregnates and / or dissolves the polyolefin resin material to be treated in a hydrocarbon solvent, then adds an acidic reagent for impregnation and / or dissolution again, to obtain a pretreated mixture; then the pretreated mixture is subjected to metal complexation reaction with a complexing reagent, and then eluted with an eluent to obtain an ash-removed polyolefin resin material. Although this method has a certain ash removal effect, the use of multiple mixed solvents and the addition of a large amount of acidic solvents make it difficult to recycle the solvents and economically unsound.

[0006] Therefore, developing a new preparation method of electrical grade ultra-clean polypropylene is still one of the problems to be solved in the field. SUMMARY

[0007] To solve the above technical problems, the purpose of the present application is to provide an electrical grade ultra-clean polypropylene and a preparation method thereof. The method of the present application adopts the process flow of material refining, slurry polymerization and post-treatment, and can prepare electrical grade ultra-clean polypropylene with ash content below 20 ppm.

[0008] To achieve the above purpose, the first aspect of the present application provides a preparation method of electrical grade ultra-clean polypropylene, which comprises the following steps:

[0009] (1) Material refining: at least refining liquid propylene to obtain refined liquid propylene;

[0010] (2) slurry polymerization: polymerization is carried out in a slurry polymerization system, which comprises at least dispersant, catalyst system and the refined liquid propylene obtained in step (1), to obtain a slurry containing polypropylene, liquid propylene and dispersant;

[0011] (3) post-treatment: the slurry containing polypropylene, liquid propylene and dispersant is separated to obtain gas propylene, liquid system containing dispersant and solid polypropylene; the solid polypropylene is washed and dried to obtain the ultra-clean polypropylene for electrical engineering;

[0012] In step (3), the washing comprises:

[0013] first washing: the solid polypropylene is washed with dispersant for the first time, and the polypropylene after the first washing is obtained after solid-liquid separation;

[0014] second washing: the polypropylene after the first washing is washed with a mixed solvent containing metal ion complexing agent for the second time, and the polypropylene after the second washing is obtained after solid-liquid separation;

[0015] third washing: the polypropylene after the second washing is washed with alcohol for the third time, and the polypropylene after the third washing is obtained after solid-liquid separation.

[0016] In the above method, preferably, step (1) further comprises refining the dispersant, metal ion complexing agent and alcohol respectively. More preferably, the refining of the dispersant, metal ion complexing agent and alcohol respectively comprises dehydration and / or deoxygenation. The specific operation conditions of dehydration and deoxygenation can be routinely adjusted by those skilled in the art, and the present application does not particularly limit them. Further preferably, the water content and oxygen content of the refined dispersant, metal ion complexing agent and alcohol are each 1 mg / kg or less.

[0017] In the above method, preferably, in step (1), the refining of the liquid propylene comprises dehydration, desulfurization and decarbonation, dealcoholization, deoxygenation and decarboxylation to obtain the refined liquid propylene.

[0018] In the above method, preferably, in step (1), the water content, methanol content and oxygen content of the refined liquid propylene are each 0.5 mg / kg or less, and the total sulfur content, carbon monoxide content and carbon dioxide content are each 0.1 mg / kg or less.

[0019] In some embodiments of the present application, the liquid propylene is sequentially treated by a dehydration tower, a desulfurization and decarbon dioxide tower, a dealcoholization tower, a deoxygenation tower and a decarbon monoxide tower to obtain the refined liquid propylene which can be stored in a propylene metering tank. The operating conditions of the dehydration tower, the desulfurization and decarbon dioxide tower, the dealcoholization tower, the deoxygenation tower and the decarbon monoxide tower can be routinely adjusted by those skilled in the art as long as the water content, the methanol content, the oxygen content, the total sulfur content, the carbon monoxide content and the carbon dioxide content in the refined liquid propylene defined in the present application are met. The raw material liquid propylene is first treated by the dehydration tower to deeply remove the water in the raw material liquid propylene; then the raw material liquid propylene is treated by the desulfurization and decarbon dioxide tower to remove the organic sulfur, the inorganic sulfur and the carbon dioxide in the raw material liquid propylene; then the raw material liquid propylene is treated by the dealcoholization tower to remove the alcohol and other polar compounds in the raw material liquid propylene; then the raw material liquid propylene is treated by the deoxygenation tower to deeply remove the oxygen in the raw material liquid propylene; and finally the raw material liquid propylene is treated by the decarbon monoxide tower to deeply remove the carbon monoxide in the raw material liquid propylene.

[0020] In the above method, preferably, in step (2) and step (3), the dispersant comprises a combination of one or more of inert alkanes, inert cycloalkanes and inert aromatic hydrocarbons. More preferably, the dispersant comprises a combination of one or more of n-hexane, n-heptane and petroleum ether. Further preferably, the dispersant is n-hexane. According to embodiments of the present application, the dispersant used in step (2) and step (3) can be different or the same.

[0021] In the above method, preferably, in step (2), the polymerization reaction is carried out in a polymerization reactor, which comprises a tank reactor and / or a loop reactor. More preferably, the polymerization reactor comprises a tank reactor.

[0022] In the above method, preferably, in step (2), the catalyst system comprises a Ziegler-Natta catalyst system.

[0023] In some embodiments of the present application, the Ziegler-Natta catalyst system generally comprises a main catalyst, i.e. a solid catalyst, preferably a titanium-containing solid catalyst; a cocatalyst, which is generally an organic aluminum compound; and optionally an external electron donor, preferably an external electron donor.

[0024] In some embodiments of the present application, the procatalyst is a supported ultra-high-activity titanium-containing Ziegler-Natta procatalyst. Such supported ultra-high-activity titanium-containing solid catalysts can be those disclosed in the prior art, and the present application does not specially limit the specific composition and preparation method thereof. The "ultra-high-activity" refers to the activity of the catalyst being 50,000 times (i.e., 50,000 g PP / g Cat.) or more in the case of slurry polymerization process.

[0025] In some embodiments of the present application, the cocatalyst includes alkyl aluminum and / or halogenated alkyl aluminum, etc. Preferably, the cocatalyst includes one or a combination of several of triethyl aluminum, triisobutyl aluminum, and diethyl aluminum chloride, etc. More preferably, the cocatalyst is triethyl aluminum.

[0026] In some embodiments of the present application, the external electron donor includes organosilicon compounds, etc. Preferably, the external electron donor includes one or a combination of several of diisobutyl dimethoxysilane, cyclohexyl methyl dimethoxysilane, dicyclopentyl dimethoxysilane, diisopropyl dimethoxysilane, and n-propyl triethoxysilane, etc. More preferably, the external electron donor is cyclohexyl methyl dimethoxysilane.

[0027] In the above method, preferably, in step (2), the molar ratio of Al in the cocatalyst to Ti in the procatalyst in the catalyst system is Al:Ti = 800-100, for example, 600, 400, 200, etc.; and the molar ratio of Si in the external electron donor to Ti in the procatalyst is Si:Ti = 100-10, for example, 50, 25, 10, etc. In the above step (2), the amount of the dispersant in the reaction system can be routinely adjusted by those skilled in the art, and the present application does not specially limit it.

[0028] In the above method, preferably, in step (2), the reaction system further includes a molecular weight regulator. More preferably, the molecular weight regulator includes hydrogen. Further preferably, the amount of the molecular weight regulator added is 10-1 NL (normal liter), for example, 6 NL, 4 NL, 2 NL, based on a 5 L polymerization reactor.

[0029] In the above method, preferably, in step (2), the temperature of the polymerization reaction is 50-70°C, more preferably 70°C; the time of the polymerization reaction is 1-3 h, more preferably 2 h; and the pressure of the polymerization reaction is 2-4 MPa, more preferably 3.5 MPa.

[0030] In the above method, preferably, in step (3), the separation of the slurry containing polypropylene, liquid propylene and dispersant comprises: after vaporization of the liquid propylene, obtaining gaseous propylene and a slurry containing polypropylene and dispersant, and performing solid-liquid separation of the slurry containing polypropylene and dispersant under nitrogen pressure through a filter to obtain a liquid system containing dispersant and solid polypropylene. The nitrogen pressure can be routinely adjusted by those skilled in the art, and is generally below 0.8 MPa.

[0031] In some embodiments of the present application, the vaporization of liquid propylene is achieved through pressure relief of the polymerization reactor.

[0032] In some embodiments of the present application, the gaseous propylene can be reused after liquefaction.

[0033] In some embodiments of the present application, the liquid system containing dispersant can be separated and purified to obtain dispersant for reuse.

[0034] In the above method, preferably, in step (3), the mixed solvent containing metal ion complexing agent comprises a combination of dispersant, metal ion complexing agent and alcohol; in the combination, the volume ratio of dispersant to alcohol is (1-5): 1, more preferably 4: 1, and the content of metal ion complexing agent is 0.1%-2% of the total weight of dispersant and alcohol, more preferably 1%. The dispersant includes one or a combination of several of inert alkanes, inert cycloalkanes and inert aromatic hydrocarbons. More preferably, the dispersant includes one or a combination of several of n-hexane, n-heptane and petroleum ether. Further preferably, the dispersant is n-hexane.

[0035] In the above method, preferably, in step (3), the metal ion complexing agent includes one or a combination of several of crown ethers and derivatives thereof. More preferably, the metal ion complexing agent includes one or a combination of several of 12-crown-4, 15-crown-5 and 18-crown-6. Further preferably, the metal ion complexing agent is 15-crown-5.

[0036] In the above method, preferably, in step (3), the alcohol includes one or a combination of several of ethanol, propanol, isopropanol and n-butanol. More preferably, the alcohol is isopropanol.

[0037] In the above method, preferably, in step (3), all the three washes (i.e. the first wash, the second wash and the third wash) are performed under anhydrous and anaerobic conditions.

[0038] In the above method, preferably, in step (3), the weight ratio of the dispersing agent used in the first washing to the solid polypropylene is (2-10): 1, more preferably 3:1.

[0039] In the above method, preferably, in step (3), the operation conditions of the first washing include: adding the dispersing agent into the solid polypropylene, stirring under normal temperature and in a nitrogen atmosphere for 1-30 min, and then performing solid-liquid separation under nitrogen pressure through a filter to obtain the polypropylene after the first washing. The nitrogen pressure can be routinely adjusted by those skilled in the art, and is generally below 0.8 MPa.

[0040] In the above method, preferably, in step (3), the weight ratio of the mixed solvent containing metal ion complexing agent used in the second washing to the polypropylene after the first washing is (2-10): 1, more preferably 3:1.

[0041] In the above method, preferably, in step (3), the operation conditions of the second washing include: adding the mixed solvent containing metal ion complexing agent into the polypropylene after the first washing, stirring in a nitrogen atmosphere at 60-80°C (more preferably 70°C) for 1-3 h (more preferably 2 h), and then performing solid-liquid separation (i.e. centrifugal separation) through a centrifuge to obtain the polypropylene after the second washing.

[0042] In the above method, preferably, in step (3), the weight ratio of the alcohol used in the third washing to the polypropylene after the second washing is (2-10): 1, more preferably 3:1.

[0043] In the above method, preferably, in step (3), the operation conditions of the third washing include: adding the alcohol into the polypropylene after the second washing, and performing centrifugal washing and solid-liquid separation in a centrifuge under normal temperature and in a nitrogen atmosphere to obtain the polypropylene after the third washing.

[0044] In some specific embodiments of the present application, in step (3), the first washing can be performed in a polymerization reactor, and the first washing can remove excess cocatalyst and external electron donor. After the washing, solid-liquid separation is performed under nitrogen pressure through a filter to obtain the polypropylene after the first washing. The polypropylene after the first washing can be discharged under nitrogen pressure into a washing kettle for the second washing. After the washing, the temperature is lowered to room temperature, and the material is discharged under nitrogen pressure into a centrifuge for solid-liquid separation to obtain the polypropylene after the second washing. Then, the third washing is performed in a centrifuge under a nitrogen atmosphere, and solid-liquid separation is performed to obtain the polypropylene after the third washing. The nitrogen pressure can be routinely adjusted by those skilled in the art, and is generally below 0.8 MPa.

[0045] In the above method, preferably, step (3) further comprises: after the liquid obtained from the solid-liquid separation after the first washing, the second washing and the third washing is separated and purified, a dispersant and an alcohol are obtained and reused. The separation and purification of the liquid obtained from the solid-liquid separation can be performed by using the separation and purification method in the prior art, and the present application does not make special limitation thereto.

[0046] In step (3) of the above method, the temperature and the time of the drying can be routinely adjusted by those skilled in the art, and the present application does not make special limitation thereto. After the drying, an electric grade ultra-clean polypropylene powder can be obtained.

[0047] The second aspect of the present application provides an electric grade ultra-clean polypropylene, which is prepared by the above method for preparing an electric grade ultra-clean polypropylene. The ash content of the electric grade ultra-clean polypropylene is 20 ppm or less, the isotacticity is 98% or more, the mass average molecular weight is 350-425 thousand, the molecular weight distribution is 8-10.5, and the melt index is 3-4.5 g / 10 min.

[0048] The present application provides an electric grade ultra-clean polypropylene and a method for preparing the same. The technical scheme of the present application has at least the following beneficial effects:

[0049] (1) The method for preparing the electric grade ultra-clean polypropylene of the present application uses material refining and uses an ultra-high activity titanium-containing Ziegler-Natta main catalyst to reduce the introduction of ash in the polymer from the source; and, the slurry polymerization process is used to reduce the residues of the cocatalyst and the external electron donor in the polymer to a certain extent; the post-treatment process, especially the process of washing the polymer three times, further removes small molecules, oligomers, atactic polymers and residual ash, etc. in the polymer, and the addition of the metal ion complexing agent crown ether facilitates the efficient removal of residual metal ions in the polymer.

[0050] (2) The method for preparing the electric grade ultra-clean polypropylene of the present application has the advantages of simple process, low requirement for equipment, small energy consumption, low cost, small environmental pollution, etc., and the separated propylene can be reused, and the separated and purified dispersant and alcohol can also be reused.

[0051] (3) The electric grade ultra-clean polypropylene prepared by the present application has an ash content of less than 20 ppm, an isotacticity of 98% or more, a mass average molecular weight of 350-425 thousand, a molecular weight distribution of 8-10.5, and a melt index of 3-4.5 g / 10 min. The performance indicators of the electric grade ultra-clean polypropylene are excellent, and the key physical property parameters reach the technical indicators of imported resins (for example, Nordic Chemical HC300BF). The electric grade ultra-clean polypropylene has potential application prospects in the field of capacitor films. DETAILED DESCRIPTION

[0052] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present application, the technical solutions of the present application are described in detail as follows, but it should not be understood as a limitation to the implementable scope of the present application.

[0053] The experimental methods used in the following examples and comparative examples are all conventional methods unless otherwise specified.

[0054] The materials, reagents and the like used in the following examples and comparative examples can be obtained from commercial channels, and the specific information is as follows:

[0055] Hydrogen: Beijing HuanYuJingHuiJingcheng Gas Technology Co., Ltd;

[0056] High-purity nitrogen: Beijing HuanYuJingHuiJingcheng Gas Technology Co., Ltd;

[0057] Propylene: Beijing HuanYuJingHuiJingcheng Gas Technology Co., Ltd;

[0058] Polypropylene solid catalyst (i.e., main catalyst): HCAT catalyst (titanium content 3.3%), Renqiu City Lihe Science and Technology Development Co., Ltd;

[0059] Triethylaluminum: AR, Aldrich;

[0060] n-Hexane: AR, Inokai;

[0061] Isopropyl alcohol: AR, Inokai;

[0062] 15-crown-5: Inokai;

[0063] Cyclohexylmethyl dimethoxysilane: AR, Inokai;

[0064] Acetylacetone: AR, Aldrich;

[0065] Ethylene diamine tetraacetic acid (EDTA): AR, Bailingwei;

[0066] Citric acid: AR, National Pharmaceutical;

[0067] Filler for each column in the refining process of liquid propylene, dispersant, metal ion complexing agent and alcohol: Shanghai Lvqiang New Material Co., Ltd.

[0068] In the following examples, the polymer analysis characterization is measured according to national standards or industry standards:

[0069] The polymerization activity is calculated according to the following formula: polymerization activity = polymer mass / main catalyst dosage.

[0070] The ash content of the polymer was measured by inductively coupled plasma emission spectrometer (Thermo Scientific) (referring to SH / T 1829-2020) and platinum crucible calcination method (referring to GB / T 9345.1-2008).

[0071] The ash content in the polypropylene refers to the particulate impurities that cannot be volatilized after high-temperature calcination and are finally present in the form of metal oxides or non-metal oxides, and therefore the element content determined needs to be converted into the corresponding oxide content.

[0072] The theoretical ash content m = m(TiO2) + m(MgO) + m(Al2O3) + m(SiO2); the theoretical

[0073] Wherein m(PP) is the mass of the obtained polymer, m(Ti) is the added mass of titanium element, m(Mg) is the added mass of magnesium element, m(Al) is the added mass of aluminum element; m(Si) is the added mass of silicon element.

[0074] The measured ash content w = w(TiO2) + w(MgO) + w(Al2O3) + w(SiO2); the measured

[0075] Wherein w(Ti) is the measured content of titanium element, w(Mg) is the measured content of magnesium element, w(Al) is the measured content of aluminum element; w(Si) is the measured content of silicon element.

[0076] The isotacticity of the polymer was measured by n-heptane extraction method (referring to GB / T 2412-2008).

[0077] The molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the polymer were measured by PL-GPC220 gel permeation chromatograph at 150°C (referring to GB / T 36214.4-2018).

[0078] The melting point (Tm) of the polymer was measured by DSC (Q2000) differential scanning calorimeter (referring to GB / T 19466.3-2004).

[0079] The melt index (MFR) of the polymer was measured by melt index tester (MADSUR) (referring to GB / T 3682.1-2018).

[0080] The technical solutions of the present application will be described in detail in combination with examples and comparative examples, but the protection scope of the present application is not limited to the following examples.

[0081] Example 1

[0082] The embodiment provides a preparation method of an electrician-grade ultra-clean polypropylene, which comprises the following steps:

[0083] (1) Material refining:

[0084] The liquid propylene is sequentially subjected to treatment of a dehydration tower, a desulfurization and decarbon dioxide tower, a dealcoholization tower, a deoxygenation tower and a decarbon monoxide tower to obtain refined liquid propylene, which is used in a propylene metering tank;

[0085] The fillers and operating conditions of the dehydration tower, the desulfurization and decarbon dioxide tower, the dealcoholization tower, the deoxygenation tower and the decarbon monoxide tower are as follows:

[0086] The propylene dehydration tower is 3A molecular sieve (LQ 3A-EPG) and is operated at room temperature and 2.5 MPa;

[0087] The propylene desulfurization and decarbon dioxide tower is adsorbent (LQ AA-01Z) and is operated at room temperature and 2.5 MPa;

[0088] The propylene dealcoholization tower is adsorbent (LQ MS-13Z) and is operated at room temperature and 2.5 MPa;

[0089] The propylene deoxygenation tower is low-temperature deoxygenation agent (LQ 513-1-II) and is operated at room temperature and 2.5 MPa;

[0090] The propylene decarbon monoxide tower is low-temperature CO removal agent (LQ CZ-1) and is operated at room temperature and 2.5 MPa;

[0091] The refined liquid propylene has water content ≤0.5 mg / kg, total sulfur content ≤0.1 mg / kg, carbon dioxide content ≤0.1 mg / kg, methanol content ≤0.5 mg / kg, oxygen content ≤0.5 mg / kg and carbon monoxide content ≤0.1 mg / kg;

[0092] The dispersant is sequentially subjected to treatment of a dehydration tower and a deoxygenation tower, and the metal ion complexing agent and the alcohol are subjected to treatment of a dehydration tower respectively to obtain refined dispersant, metal ion complexing agent and alcohol for standby; the dispersant is n-hexane, the metal ion complexing agent is 15-crown-5 and the alcohol is isopropyl alcohol;

[0093] The fillers and operating conditions of the dehydration tower and the deoxygenation tower of the dispersant are as follows:

[0094] The dispersant dehydration tower is 3A molecular sieve (LQ 3A-EPG) and is operated at room temperature and 0.4 MPa;

[0095] The dispersant deoxygenation tower is low-temperature deoxygenation agent (LQ 513-1-II) and is operated at room temperature and 0.4 MPa;

[0096] The packing and operating conditions of the metal ion complexing agent and alcohol dehydration column are as follows:

[0097] Metal ion complexing agent dehydration column: 3A molecular sieve (LQ 3A-EPG), operating at room temperature, 0.1 MPa;

[0098] Alcohol dehydration column: 3A molecular sieve (LQ 3A-EPG), operating at room temperature, 0.1 MPa;

[0099] The water content of the refined dispersant, metal ion complexing agent and alcohol is all ≤1 mg / kg, and the oxygen content is all ≤1 mg / kg;

[0100] (2) Slurry polymerization:

[0101] First, the 5L reactor was vacuumed, and then replaced with nitrogen for 3 times, and finally replaced with propylene for 1 time, and kept a slight positive pressure of propylene atmosphere; when the temperature of the reactor was reduced to room temperature, 1.5L of n-hexane was added under the condition of opening the stirring (100r / min), and then 0.5mmol of cyclohexylmethyl dimethoxysilane (Si / Ti=50), 6mmol of triethylaluminum (Al / Ti=600) and 15mg of the main catalyst (0.01mmol Ti) were added in turn under the protection of propylene slight positive pressure, and then the catalyst tank was washed with 1.5L of n-hexane, the feeding valve was closed, and then 0.54g of hydrogen (6NL) was added and the valve was closed; the stirring speed was increased to 600r / min, the reactor was heated using circulating water, and when the temperature was close to the set temperature of 70℃, the propylene feeding valve was opened, and the polymerization reaction was started, the reaction pressure was 3.5MPa, and when the reaction was carried out for 2h, the propylene feeding valve was closed, and the polymerization reaction was completed, and a slurry containing polypropylene, liquid propylene and n-hexane was prepared;

[0102] (3) Post-treatment:

[0103] The circulating water of the reactor was set to the refrigeration mode, the reactor was cooled with circulating cold water, and when the temperature in the reactor was reduced to room temperature, the vent valve was slowly opened, the liquid propylene was vaporized, and the unreacted gaseous propylene was discharged, which could be reused after liquefaction; the reactor was replaced with nitrogen gas for 3 times; the slurry containing polypropylene and n-hexane was separated by a filter under the pressure of nitrogen, the solid polypropylene could not pass through the filter and remained in the reactor, and the liquid system containing n-hexane flowed out through the vent and was collected, which could be separated and purified to obtain n-hexane for reuse;

[0104] Then 3 L of n-hexane was added into the reactor, and after stirring for 10 min under nitrogen atmosphere, solid-liquid separation was carried out under nitrogen pressure through a filter to further remove the alkyl aluminum and external electron donor in the reaction system, to obtain the polypropylene after the first washing; then the polypropylene after the first washing was discharged into a 10 L washing kettle under nitrogen pressure, 4 L of n-hexane, 1 L of isopropyl alcohol and 34 g of 15-crown-5 were added, and stirring and washing were carried out under nitrogen atmosphere at 70°C for 2 h, and after being cooled to room temperature, centrifugal separation was carried out under nitrogen pressure to obtain the polypropylene after the second washing; then 3 L of isopropyl alcohol was added for further centrifugal washing, and finally solid-liquid separation was carried out to obtain the polypropylene after the third washing; the liquid obtained after solid-liquid separation after the first washing, the second washing and the third washing can be separated and purified to obtain n-hexane and isopropyl alcohol for reuse;

[0105] The polypropylene after the third washing (powder) was dried in a vacuum drying oven at 100°C to constant weight to obtain the electrical-grade ultra-clean polypropylene.

[0106] After weighing, 1.28 kg of polypropylene was obtained, with a polymerization activity of 85333 g PP / g Cat.; the theoretical ash content was 267.8 ppm (TiO2: 0.6 ppm; MgO: 4.7 ppm; Al2O3: 239.0 ppm; SiO2: 23.5 ppm); the measured ash content was 19.7 ppm (TiO2: 0.5 ppm; MgO: 2.4 ppm; Al2O3: 12.6 ppm; SiO2: 4.2 ppm); the melt index was 4.2 g / 10 min, the isotacticity was 98.0%, Mw= 3.51 x 10 5 g / mol, Mw / Mn = 10.3, Tm = 163.8°C.

[0107] Example 2

[0108] The present example provides a preparation method of electrical-grade ultra-clean polypropylene, which is basically the same as the preparation method provided in Example 1, except that:

[0109] During the slurry polymerization in step (2), 0.25 mmol of cyclohexylmethyldimethoxysilane (Si / Ti = 25), 4 mmol of triethyl aluminum (Al / Ti = 400) and 0.36 g of hydrogen gas (4 NL) were added.

[0110] The weighed amount was 1.65 kg of polypropylene, the polymerization activity was 110000 g PP / g Cat.; the theoretical ash content was 136.8 ppm (TiO2: 0.5 ppm; MgO: 3.7 ppm; Al2O3: 123.6 ppm; SiO2: 9.0 ppm); the measured ash content was 16.9 ppm (TiO2: 0.5 ppm; MgO: 3.0 ppm; Al2O3: 10.1 ppm; SiO2: 3.3 ppm); the melt index was 3.5 g / 10 min, the isotacticity was 98.4%, Mw= 3.92 x 10 5 g / mol, Mw / Mn = 9.8, Tm = 165.3 °C.

[0111] Example 3

[0112] This example provides a method for preparing an ultra-clean polypropylene for electrical engineering, which is basically the same as the method provided in Example 1, except that:

[0113] During the slurry polymerization in step (2), 0.10 mmol of cyclohexylmethyl dimethoxysilane (Si / Ti = 10), 2 mmol of triethylaluminum (Al / Ti = 200) and 0.18 g of hydrogen gas (2 NL) were added.

[0114] The weighed amount was 1.65 kg of polypropylene, the polymerization activity was 110000 g PP / g Cat.; the theoretical ash content was 136.8 ppm (TiO2: 0.5 ppm; MgO: 3.7 ppm; Al2O3: 123.6 ppm; SiO2: 9.0 ppm); the measured ash content was 16.9 ppm (TiO2: 0.5 ppm; MgO: 3.0 ppm; Al2O3: 10.1 ppm; SiO2: 3.3 ppm); the melt index was 3.5 g / 10 min, the isotacticity was 98.4%, Mw= 3.92 x 10 5 g / mol, Mw / Mn = 9.8, Tm = 165.3 °C.

[0115] Example 4

[0116] This example provides a method for preparing an ultra-clean polypropylene for electrical engineering, which is basically the same as the method provided in Example 1, except that:

[0117] During the slurry polymerization in step (2), 0.25 mmol of cyclohexylmethyl dimethoxysilane (Si / Ti = 25), 2 mmol of triethylaluminum (Al / Ti = 200) and 0.18 g of hydrogen gas (2 NL) were added, and the polymerization reaction time was 1 h.

[0118] The weight was measured to obtain 0.94 kg of polypropylene, the polymerization activity was 62667 g PP / g Cat.; the theoretical ash content was 131.9 ppm (TiO2: 0.9 ppm; MgO: 6.4 ppm; Al2O3: 108.5 ppm; SiO2: 16.1 ppm); the measured ash content was 15.3 ppm (TiO2: 0.7 ppm; MgO: 4.7 ppm; Al2O3: 8.7 ppm; SiO2: 1.2 ppm); the melt index was 3.1 g / 10 min, the isotacticity was 98.6%, Mw=4.23 x 10 5 g / mol, Mw / Mn=8.8, Tm=167.1 °C.

[0119] Comparative Example 1

[0120] This comparative example provides a preparation method of polypropylene, which is basically the same as the preparation method provided in Example 1, except that:

[0121] During the post-treatment of step (3), after the unreacted gas propylene was discharged, the slurry containing polypropylene and n-hexane was directly discharged into a stainless steel barrel, and then poured into a centrifuge for centrifugal separation, without any washing, and then dried in a vacuum drying oven at 100 °C to constant weight to obtain the polypropylene.

[0122] The weight was measured to obtain 1.32 kg of polypropylene, the polymerization activity was 88000 g PP / g Cat.; the theoretical ash content was 259.4 ppm (TiO2: 0.6 ppm; MgO: 4.3 ppm; Al2O3: 231.7 ppm; SiO2: 22.8 ppm); the measured ash content was 108.2 ppm (TiO2: 0.6 ppm; MgO: 4.1 ppm; Al2O3: 91.9 ppm; SiO2: 11.6 ppm); the melt index was 5.4 g / 10 min, the isotacticity was 96.4%, Mw=3.47 x 10 5 g / mol, Mw / Mn=11.5, Tm=162.6 °C.

[0123] Comparing the polypropylene prepared in this comparative example with the polypropylene prepared in Example 1, it can be seen that the polypropylene prepared in this comparative example has significantly lower performance in all aspects than the polypropylene prepared in Example 1, because the polypropylene in this comparative example is not subjected to washing post-treatment.

[0124] Comparative Example 2

[0125] This comparative example provides a preparation method of polypropylene, which is basically the same as the preparation method provided in Example 1, except that:

[0126] In the post-treatment process of step (3), 15-crown-5 is not added.

[0127] The weighed and metered polypropylene was obtained in an amount of 1.29 kg, with a polymerization activity of 86,000 g PP / g Cat.; a theoretical ash content of 265.7 ppm (TiO2: 0.6 ppm; MgO: 4.7 ppm; Al2O3: 237.1 ppm; SiO2: 23.3 ppm); a measured ash content of 75.5 ppm (TiO2: 0.6 ppm; MgO: 4.5 ppm; Al2O3: 61.7 ppm; SiO2: 8.7 ppm); a melt index of 4.3 g / 10 min, a degree of isotacticity of 97.2%, Mw= 3.61 x 10 5 g / mol, Mw / Mn = 10.6, Tm = 164.4 °C.

[0128] Comparing the polypropylene prepared in the present comparative example with the polypropylene prepared in Example 1, it can be seen that, in the post-treatment process of washing the polypropylene, the metal ion complexing agent 15-crown-5 used in Example 1 is not used in the present comparative example, and the properties of the polypropylene prepared in the present comparative example are all significantly lower than those of the polypropylene prepared in Example 1.

[0129] Comparative Example 3

[0130] The present comparative example provides a method for preparing polypropylene, which is basically the same as the method provided in Example 1, except that:

[0131] In the post-treatment process of step (3), after the unreacted gas propylene is discharged, the slurry containing the polypropylene and n-hexane is discharged into a 10 L washing kettle, 4 L of n-hexane and 1 L of isopropyl alcohol are added, and stirring and washing are performed at room temperature for 2 h, and then drying is performed in a 100 °C vacuum drying oven until a constant weight is obtained, to obtain the polypropylene.

[0132] The weighed and metered polypropylene was obtained in an amount of 1.29 kg, with a polymerization activity of 86,000 g PP / g Cat.; a theoretical ash content of 265.7 ppm (TiO2: 0.6 ppm; MgO: 4.7 ppm; Al2O3: 237.1 ppm; SiO2: 23.3 ppm); a measured ash content of 75.5 ppm (TiO2: 0.6 ppm; MgO: 4.5 ppm; Al2O3: 61.7 ppm; SiO2: 8.7 ppm); a melt index of 4.3 g / 10 min, a degree of isotacticity of 97.2%, Mw= 3.61 x 10 5 g / mol, Mw / Mn = 10.6, Tm = 164.4 °C.

[0133] Comparative Example 2 was compared with the polypropylene prepared in Example 1, and it was found that the polypropylene prepared in Comparative Example 2 was significantly inferior to the polypropylene prepared in Example 1 in all aspects.

[0134] It can be seen that the washing sequence is crucial in the present application. The excess alkyl aluminum and external electron donor are first removed by washing with n-hexane, because the excess alkyl aluminum in the slurry can react with alcohol to form metal alcoholate precipitate, which is difficult to separate from the polymer. Then the metal ion complexing agent-containing mixed solvent is used to further remove the metal ion efficiently. At the same time, the three washing steps in the present application are carried out under anhydrous and anaerobic conditions, which facilitates the removal of the metal ion. Otherwise, the alkyl aluminum will form an oxide upon contact with water and oxygen, which is extremely difficult to remove by using hydrocarbons, alcohol, weak acid, etc. Generally, the oxide can be removed only by adding a strong acid to form a salt.

[0135] Comparative Example 4

[0136] Comparative Example 2 provides a method for preparing polypropylene, which is basically the same as the method provided in Example 1, except that:

[0137] In Step (2), slurry polymerization is not used, but bulk polymerization process is used, i.e. no n-hexane dispersant is added in Step (2).

[0138] After weighing, 1.92 kg of polypropylene was obtained, with a polymerization activity of 128000 g PP / g Cat.; the theoretical ash content was 178.6 ppm (TiO2: 0.4 ppm; MgO: 3.2 ppm; Al2O3: 159.3 ppm; SiO2: 15.7 ppm); the measured ash content was 63.4 ppm (TiO2: 0.4 ppm; MgO: 3.1 ppm; Al2O3: 49.7 ppm; SiO2: 10.2 ppm); the melt index was 3.8 g / 10 min, the isotacticity was 97.4%, Mw=4.21 x 10 5 g / mol, Mw / Mn=11.2, Tm=166.2°C.

[0139] Comparative Example 2 was compared with the polypropylene prepared in Example 1, and it was found that the polypropylene prepared in Comparative Example 2 was significantly inferior to the polypropylene prepared in Example 1 in all aspects.

[0140] Comparative Example 5

[0141] The comparative example provides a preparation method of polypropylene, which is basically the same as the preparation method provided in Example 1, except that:

[0142] During the post-treatment of step (3), an equal mass of acetylacetone is added instead of 15-crown-5 as a metal ion complexing agent.

[0143] After weighing, 1.21 kg of polypropylene is obtained, the polymerization activity is 80667 g PP / g Cat.; the theoretical ash content is 283.3 ppm (TiO2: 0.7 ppm; MgO: 5.0 ppm; Al2O3: 252.8 ppm; SiO2: 24.8 ppm); the measured ash content is 45.6 ppm (TiO2: 0.6 ppm; MgO: 4.8 ppm; Al2O3: 31.3 ppm; SiO2: 8.9 ppm); the melt index is 4.0 g / 10 min, the isotacticity is 97.6%, Mw=3.31×10 5 g / mol, Mw / Mn=9.1, Tm=162.8℃.

[0144] Comparing the polypropylene prepared in the comparative example with the polypropylene prepared in Example 1, it can be seen that the polypropylene in the comparative example is not treated with the metal ion complexing agent 15-crown-5 in Example 1, but acetylacetone is used as the metal ion complexing agent, and the performance of the polypropylene prepared is significantly lower than that of the polypropylene prepared in Example 1.

[0145] Comparative Example 6

[0146] The comparative example provides a preparation method of polypropylene, which is basically the same as the preparation method provided in Example 1, except that:

[0147] During the post-treatment of step (3), an equal mass of EDTA is added instead of 15-crown-5 as a metal ion complexing agent.

[0148] After weighing, 1.30 kg of polypropylene is obtained, the polymerization activity is 86667 g PP / g Cat.; the theoretical ash content is 263.7 ppm (TiO2: 0.6 ppm; MgO: 4.7 ppm; Al2O3: 235.3 ppm; SiO2: 23.1 ppm); the measured ash content is 51.9 ppm (TiO2: 0.6 ppm; MgO: 4.7 ppm; Al2O3: 35.9 ppm; SiO2: 10.7 ppm); the melt index is 4.5 g / 10 min, the isotacticity is 97.8%, Mw=3.54×10 5 g / mol, Mw / Mn=10.2, Tm=163.4℃.

[0149] Comparing the polypropylene prepared in the present comparative example with the polypropylene prepared in Example 1, it can be seen that in the washing post-treatment process of the polypropylene in the present comparative example, the metal ion complexing agent 15-crown-5 in Example 1 is not used, but EDTA is used as the metal ion complexing agent, and the prepared polypropylene has significantly lower performance in all aspects than the polypropylene prepared in Example 1.

[0150] Comparative Example 7

[0151] The present comparative example provides a preparation method of polypropylene, which is basically the same as the preparation method provided in Example 1, and the difference is that:

[0152] In the post-treatment process after step (3), an equal amount of citric acid is added instead of 15-crown-5 as the metal ion complexing agent.

[0153] After weighing, 1.26 kg of polypropylene was obtained, the polymerization activity was 84000 g PP / g Cat.; the theoretical ash content was 272.0 ppm (TiO2: 0.6 ppm; MgO: 4.8 ppm; Al2O3: 242.8 ppm; SiO2: 23.8 ppm); the measured ash content was 63.6 ppm (TiO2: 0.6 ppm; MgO: 4.5 ppm; Al2O3: 47.3 ppm; SiO2: 11.2 ppm); the melt index was 4.3 g / 10 min, the isotacticity was 98.1%, Mw=3.64×10 5 g / mol, Mw / Mn=8.9, Tm=165.1℃.

[0154] Comparing the polypropylene prepared in the present comparative example with the polypropylene prepared in Example 1, it can be seen that in the washing post-treatment process of the polypropylene in the present comparative example, the metal ion complexing agent 15-crown-5 in Example 1 is not used, but EDTA is used as the metal ion complexing agent, and the prepared polypropylene has significantly lower performance in all aspects than the polypropylene prepared in Example 1.

[0155] The polymerization activity and performance parameters of the polypropylenes in Examples 1-4 and Comparative Examples 1-7 above are shown in Table 1 below.

[0156] Table 1

[0157]

[0158] Note: HC300BF is a product of North European Chemical, and PPH-FC03 is a product of Zhongyuan Petrochemical.

[0159] As shown in Table 1, by using the preparation method of the electrical-grade super-clean polypropylene provided by the application, through the process of material refining, slurry polymerization and post-treatment, especially the process of three times of washing of the polymer, small molecules, oligomers, random substances and residual ash in the polymer are removed, and especially the addition of the metal ion complexing agent crown ether can efficiently remove the residual ash in the polymer. The electrical-grade super-clean polypropylene prepared by the application meets the technical requirements of special resins for capacitor film.

[0160] The above has specifically described the embodiments of the application, but the application is not limited to the above-described embodiments. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A method for preparing an electrical grade ultra-clean polypropylene, comprising the following steps: (1) material refining: refining at least liquid propylene to obtain refined liquid propylene; the water content, methanol content and oxygen content of the refined liquid propylene are all 0.5 mg / kg or less, and the total sulfur content, carbon monoxide content and carbon dioxide content are all 0.1 mg / kg or less; (2) slurry polymerization: using a slurry polymerization method to make a reaction system polymerize, the reaction system at least comprises a dispersant, a catalyst system and the refined liquid propylene obtained in step (1), to prepare a slurry containing polypropylene, liquid propylene and dispersant; the catalyst system comprises a Ziegler-Natta catalyst system, the main catalyst of the Ziegler-Natta catalyst system is a supported ultra-high activity Ziegler-Natta main catalyst containing titanium, and the activity of the main catalyst is 50,000 g PP / g Cat. or more under the condition of using a slurry polymerization process; (3) post-treatment: separating the slurry containing polypropylene, liquid propylene and dispersant to obtain gaseous propylene, a liquid system containing dispersant and solid polypropylene; after washing and drying the solid polypropylene, the electrical grade ultra-clean polypropylene is obtained; wherein, in step (3), the washing comprises: first washing: using a dispersant to wash the solid polypropylene for the first time, and after solid-liquid separation, the polypropylene after the first washing is obtained; second washing: using a mixed solvent containing a metal ion complexing agent to wash the polypropylene after the first washing for the second time, and after solid-liquid separation, the polypropylene after the second washing is obtained; the metal ion complexing agent comprises one or a combination of several of crown ether and its derivatives; third washing: using an alcohol to wash the polypropylene after the second washing for the third time, and after solid-liquid separation, the polypropylene after the third washing is obtained. Step (1) further comprises: refining the dispersant, the metal ion complexing agent and the alcohol respectively. In step (1), the refining of the dispersant, the metal ion complexing agent and the alcohol respectively comprises dehydration and / or deoxygenation; the water content and oxygen content of the refined dispersant, the metal ion complexing agent and the alcohol are all 1 mg / kg or less. In step (1), the refining of the liquid propylene comprises dehydration, desulfurization and decarbonation, dealcoholization, deoxygenation, decarbon monoxide, to obtain the refined liquid propylene. In step (2) and step (3), the dispersant comprises one or a combination of several of inert alkanes, inert cycloalkanes and inert aromatic hydrocarbons. In step (2) and step (3), the dispersant comprises one or a combination of several of n-hexane, n-heptane and petroleum ether. In step (2) and step (3), the dispersant is n-hexane. In step (2), the polymerization reaction is carried out in a polymerization reactor, and the polymerization reactor comprises a tank reactor and / or a loop reactor. In step (2), the polymerization reactor comprises a tank reactor. ​ ​ ​ ​ ​ ​ ​ 2. The process for the preparation of electrotechnical grade ultra clean polypropylene according to claim 1 wherein, ​ 3. The method of producing an electrical grade ultra clean polypropylene according to claim 2, wherein, ​ 4. The process for the preparation of electrotechnical grade ultra clean polypropylene according to claim 1 wherein, ​ 5. The process for the preparation of electrotechnical grade ultra clean polypropylene according to claim 1 wherein, ​ 6. The method of producing an electrical grade ultra clean polypropylene according to claim 5, wherein, ​ 7. The method of producing an electrician grade ultra clean polypropylene according to claim 6, wherein, ​ 8. The method of producing an electrician grade ultra clean polypropylene according to claim 1, wherein, ​ 9. The method of producing an electrotechnical grade ultra clean polypropylene according to claim 8, wherein, ​ 10. The process for the preparation of electrotechnical grade ultra clean polypropylene according to claim 1 wherein, In step (2), the Ziegler-Natta catalyst system comprises a procatalyst, a cocatalyst and an external electron donor.

11. The method of producing an electrotechnical grade ultra clean polypropylene according to claim 10, wherein, In step (2), the cocatalyst comprises an aluminum alkyl and / or an aluminum halide alkyl.

12. The method of producing an electrical grade ultra clean polypropylene according to claim 11, wherein, In step (2), the cocatalyst comprises a combination of one or more of triethyl aluminum, triisobutyl aluminum and diethyl aluminum chloride.

13. The method of producing an electrotechnical grade ultra clean polypropylene according to claim 12, wherein, In step (2), the cocatalyst is triethyl aluminum.

14. The method of producing an electrical grade ultra clean polypropylene according to claim 10, wherein, In step (2), the external electron donor comprises an organosilicon compound.

15. The method of producing an electrician grade ultra clean polypropylene according to claim 14, wherein, In step (2), the external electron donor comprises a combination of one or more of diisobutyl dimethoxysilane, cyclohexylmethyldimethoxysilane, dicyclopentyl dimethoxysilane, diisopropyl dimethoxysilane and n-propyl triethoxysilane.

16. The method of producing an electrician grade ultra clean polypropylene according to claim 15, wherein, In step (2), the external electron donor is cyclohexylmethyldimethoxysilane.

17. The method of producing an electrical grade ultra clean polypropylene according to claim 10, wherein, In step (2), in the catalyst system, the molar ratio of Al in the cocatalyst to Ti in the procatalyst is Al:Ti = 800-100; the molar ratio of Si in the external electron donor to Ti in the procatalyst is Si:Ti = 100-10.

18. The method of producing an electrician grade ultra clean polypropylene according to claim 1, wherein, In step (2), the reaction system further comprises a molecular weight regulator.

19. The method of producing an electrician grade ultra clean polypropylene according to claim 18, wherein, In step (2), the molecular weight regulator comprises hydrogen.

20. The method of making an electrician grade ultra clean polypropylene according to claim 1, wherein, In step (2), the temperature of the polymerization reaction is 50-70℃, the time is 1-3h and the pressure is 2-4MPa.

21. The method of producing an electrician grade ultra clean polypropylene according to claim 1, wherein, In step (3), the separation of the slurry containing polypropylene, liquid propylene and dispersant comprises: after the liquid propylene is vaporized, gaseous propylene and a slurry containing polypropylene and dispersant are obtained; the slurry containing polypropylene and dispersant is subjected to solid-liquid separation by a filter under nitrogen pressure to obtain a liquid system containing dispersant and solid polypropylene.

22. A process for the preparation of an electrotechnical grade ultra clean polypropylene according to claim 1 or 21, wherein, In step (3), the gaseous propylene is reused after being liquefied.

23. A process for the preparation of an electrotechnical grade ultra clean polypropylene according to claim 1 or 21 wherein, In step (3), the dispersant is obtained after the liquid system containing dispersant is separated and purified, and is reused.

24. The method of producing an electrician grade ultra clean polypropylene according to claim 1, wherein, In step (3), the mixed solvent containing a metal ion complexing agent comprises a combination of dispersant, metal ion complexing agent and alcohol; in the combination, the volume ratio of dispersant to alcohol is (1-5):1, and the content of the metal ion complexing agent is 0.1%-2% of the total weight of the dispersant and alcohol.

25. A process for the preparation of an electrotechnical grade ultra clean polypropylene according to claim 1 or 24 wherein, In step (3), the metal ion complexing agent comprises a combination of one or more of 12-crown-4, 15-crown-5 and 18-crown-6.

26. The method of producing an electrician grade ultra clean polypropylene according to claim 25, wherein, In step (3), the metal ion complexing agent is 15-crown-5.

27. A process for the preparation of an electrotechnical grade ultra clean polypropylene according to claim 1 or 24 wherein, In step (3), the alcohol comprises a combination of one or more of ethanol, propanol, isopropanol and n-butanol.

28. The method of producing an electrician grade ultra clean polypropylene according to claim 27, wherein, In step (3), the alcohol is isopropanol.

29. The method of producing an electrician grade ultra clean polypropylene according to claim 1, wherein, In step (3), all the three times of washing are carried out under anhydrous and anaerobic conditions.

30. The method of producing an electrician grade ultra clean polypropylene according to claim 1, wherein, In step (3), the weight ratio of the dispersant used in the first time of washing to the solid polypropylene is (2-10):

1.

31. The method of producing an electrician grade ultra clean polypropylene according to claim 1, wherein, In step (3), the operation conditions of the first washing include: adding the dispersant into the solid polypropylene, stirring for 1-30 min under normal temperature and in nitrogen atmosphere, and then performing solid-liquid separation through a filter under nitrogen pressure to obtain the polypropylene after the first washing.

32. The method of producing an electrician grade ultra clean polypropylene according to claim 1, wherein, In step (3), the weight ratio of the mixed solvent containing the metal ion complexing agent used in the second washing to the polypropylene after the first washing is (2-10):

1.

33. The method of producing an electrician grade ultra clean polypropylene as claimed in claim 1, wherein, In step (3), the operation conditions of the second washing include: adding the mixed solvent containing the metal ion complexing agent into the polypropylene after the first washing, stirring for 1-3 h under 60-80℃ and in nitrogen atmosphere, and then performing solid-liquid separation through a centrifuge to obtain the polypropylene after the second washing.

34. The method of producing an electrician grade ultra clean polypropylene according to claim 1, wherein, In step (3), the weight ratio of the alcohol used in the third washing to the polypropylene after the second washing is (2-10):

1.

35. The method of producing an electrician grade ultra clean polypropylene according to claim 1, wherein, In step (3), the operation conditions of the third washing include: adding the alcohol into the polypropylene after the second washing, and performing centrifugal washing and solid-liquid separation in a centrifuge under normal temperature and in nitrogen atmosphere to obtain the polypropylene after the third washing.

36. The method of producing an electrician grade ultra clean polypropylene as claimed in claim 1, wherein, Step (3) further includes: separating and purifying the liquid obtained through the solid-liquid separation after the first, second and third washings to obtain the dispersant and alcohol, which are reused.

37. An electrically super-clean polypropylene with ash content of 20 ppm or less, isotacticity of 98% or more, mass average molecular weight of 350-425 thousand, molecular weight distribution of 8-10.5, and melt index of 3-4.5 g / 10 min, which is prepared by the method for preparing an electrically super-clean polypropylene according to any one of claims 1-36.

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