CN112250778B - Production method of propylene polymer - Google Patents
Production method of propylene polymer Download PDFInfo
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- CN112250778B CN112250778B CN202010961351.4A CN202010961351A CN112250778B CN 112250778 B CN112250778 B CN 112250778B CN 202010961351 A CN202010961351 A CN 202010961351A CN 112250778 B CN112250778 B CN 112250778B
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Abstract
The invention discloses a production method of a propylene polymer. Firstly, enabling a polymerization monomer, a polymerization catalyst system and hydrogen to enter a loop reactor for liquid-phase bulk polymerization, continuously taking out polymer particle slurry from the loop reactor, and enabling the polymer particle slurry to enter the front end of a first horizontal reaction kettle for continuing polymerization reaction; continuously taking out polymer particles from the first horizontal reaction kettle, and entering the front end of the second horizontal reaction kettle to continue polymerization reaction. The mass of the polymer particles obtained in the loop reactor accounts for less than 10% of the mass of the polymer particles in the discharge of the second horizontal reaction kettle; a separation device is arranged between the first horizontal reaction kettle and the second horizontal reaction kettle; the first horizontal reaction kettle adopts a mixing form of straight blade paddles and frame type paddles, and the second horizontal reaction kettle adopts frame type paddles. The invention solves the problem that a horizontal reaction kettle is easy to agglomerate in the prior art, and can realize the production of polypropylene products with higher impact resistance by improving the particle size uniformity of polymer particles.
Description
Technical Field
The invention belongs to the technical field of olefin polymerization, and particularly relates to a production method of a three-kettle series propylene polymer.
Background
The polypropylene is a variety which develops the fastest in synthetic resin, along with the rapid development of propylene polymerization and catalysis technologies, the variety and the brand of the polypropylene are continuously increased, the application range is continuously expanded, and the polypropylene becomes an important synthetic material.
The difference between the polypropylene production processes is mainly reflected in the difference of reactor types, and the uniformity of the particle size of the polymer corresponding to different reactor types is different, especially the uniformity of the particle size of the polymer in a horizontal reactor is better.
CN1228096 discloses a polymerization process using a series connection of double horizontal gas-phase stirred reactors, in which a material transfer device is arranged between two horizontal gas-phase kettles connected in series, so that different operating conditions can be adopted in the two reactors to produce polymers with better performance. The materials in the horizontal kettle are not in a fluidized state, and the stirring paddle does not produce forward or backward pushing action on the materials, so that the flowing state of the materials in the horizontal kettle reactor is close to a horizontal plug flow. Because the residence time distribution of materials in the horizontal reactor is narrowed, the back mixing and short circuit phenomena of the catalyst in the horizontal stirred reactor are less, and the method has the advantages of high catalyst utilization rate and uniform product properties.
However, the Ziegler-Natta catalyst used for propylene polymerization has high activity in the initial stage of the reaction, and has a reaction peak, and the exothermic amount is large. Because the residence time distribution of materials in the horizontal stirring reactor is close to plug flow and the initial concentration of the catalyst is higher, the reaction is particularly violent in the initial stage, so that local hot spots are easily formed in a bed layer, and if measures are not taken in time, polymer powder is likely to melt to form various lumps, thereby influencing the stable production of the device. The degree to which the reactor approaches plug flow varies with different stirrer designs, with better uniformity of particle size distribution but greater likelihood of creating the aforementioned localized "hot spots" with reactors closer to plug flow. Obviously, this contradiction cannot be resolved if the same stirring pattern is used.
Chinese patent CN108586644A provides a multistage polymerization method and device for propylene, which comprises introducing prepolymerization reaction, performing two-stage liquid-phase bulk polymerization to stabilize the catalyst activity, and performing two-stage gas-phase polymerization to obtain the final product polymer with wide molecular weight distribution, excellent mechanical properties and processability. One of the reactors is a gas phase horizontal stirred tank reactor, and the others are all full-mixing tank reactors, so that the technology has the problems of uneven product properties and the like.
Chinese patent CN87100218 proposes a polymerization method in which one section is a liquid phase bulk polymerization reactor and the other section is a horizontal stirred tank reactor. Wherein the liquid phase bulk polymerization reactor is a complete mixing flow reactor, the horizontal stirred tank reactor is a plug flow reactor, the proportion of the complete mixing flow reaction is usually higher or not optimized, and the particle size uniformity of the product is not high. In the method, a liquid-phase bulk polymerization product and a large amount of unreacted substances are directly injected into the horizontal kettle, so that the problem of local hot spots in the horizontal kettle is solved, but two different reaction conditions cannot be generated in two reactors, and a product with better performance cannot be obtained.
In a word, the prior art has the problems that the product has uneven particle size or low product performance, local 'hot spots' of a horizontal kettle are difficult to solve and the like, and still needs a perfect solution.
Disclosure of Invention
The invention finds that different stirring paddles cause different degrees of approach of the horizontal stirring kettle to the plug flow, so that the risk of local 'hot spots' generated when the high-activity polymerization catalyst is added into the reactor is different. The research of the invention shows that the horizontal stirring kettle adopting the straight blade paddle is equivalent to 3 to 4 full-mixing kettles, and the horizontal stirring kettle adopting the frame type paddle is equivalent to 7 to 8 full-mixing kettles. The invention further discovers that the addition of a full mixing kettle in front of the horizontal kettle not only affects the uniformity of the particle size of the product, but also affects the risk that the horizontal kettle generates local 'hot spots'. According to the invention, through optimizing the yield distribution of the full-mixing kettle and the two horizontal kettles, adopting a mixing-type stirring paddle design in the horizontal kettles, and arranging a separation device between the two horizontal kettles for realizing two independently adjustable reaction conditions, a polymer product with uniform particle size and high performance can be obtained, and meanwhile, the horizontal kettles do not generate local 'hot spots' and are not easy to agglomerate, so that the operation stability is better.
The invention provides a production method of a three-kettle series propylene polymer, which comprises the following steps:
step 1, firstly, a polymerization monomer, a catalyst, alkyl aluminum, an external electron donor and optional hydrogen enter a loop reactor to carry out liquid-phase bulk polymerization, and the loop reactor continuously produces polymer particle slurry; the polymerization monomer is propylene or propylene and one or more optional comonomers, and the comonomers comprise ethylene and C4-C6 alpha-olefin;
and 3, continuously taking out polymer particles from the first horizontal reaction kettle, and allowing the polymer particles to enter the front end of a second horizontal reaction kettle with a stirring paddle to continuously perform polymerization reaction.
According to the method, a polymerization monomer is added into the first horizontal reaction kettle and/or the second horizontal reaction kettle for polymerization reaction, wherein the polymerization monomer is propylene, or propylene and one or more optional comonomers; the mass of polymer particles obtained in the loop reactor is less than 10%, preferably less than 5% of the mass of polymer particles in the discharge of the second horizontal reactor.
According to the method of the invention, no separation equipment is arranged between the loop reactor and the first horizontal reaction kettle.
According to the method, a separation device is arranged between the first horizontal reaction kettle and the second horizontal reaction kettle.
According to the method, the first horizontal reaction kettle adopts a mixing mode of straight blade paddles and frame type paddles, and the second horizontal reaction kettle adopts frame type paddles.
According to the method, the straight blade paddle in the first horizontal reaction kettle is close to the feeding hole, and the length of the area where the straight blade paddle is located is less than one fourth of the length of the area of the rear-end frame type paddle.
According to the method, the gap between two adjacent straight blades is less than 0.1 time of the width of the straight blade.
According to the method, the gap between two adjacent frame-type paddles is 0.01-0.1 times the width of the frame-type paddles.
According to the method, the gap between the adjacent straight blade paddle and the frame paddle is less than 0.01 times of the width of the frame paddle
According to the method, the width of the frame type paddle is more than or equal to 2 times of the width of the straight blade paddle.
According to the method, 2n blades of the straight blade paddle and the frame paddle on the same circumference of the stirring shaft are uniformly distributed in 1 group (n is 2-6), and the included angle between two adjacent blades in each group is 360/2n degrees. The front section of the first horizontal reaction kettle is at most provided with 2n groups of straight blade paddles which are uniformly distributed on the front section of the stirring shaft; the rear section of the first horizontal reaction kettle is at least provided with 3n groups of frame-type paddles which are uniformly distributed on the rear section of the stirring shaft. 4n groups of frame type paddles are arranged in the second horizontal reaction kettle and are uniformly distributed on the stirring shaft.
According to a preferred embodiment of the method of the present invention, the straight blade paddle and the frame paddle have 1 group of 4 uniformly distributed blades on the same circumference of the stirring shaft, and the included angle between two adjacent blades in each group is 90 °. The front half section of the first horizontal reaction kettle is provided with 4 groups of straight blade paddles which are uniformly distributed on the front half section of the stirring shaft; the rear half section of the first horizontal reaction kettle is provided with 10 groups of frame-type paddles which are uniformly distributed on the rear half section of the stirring shaft. And 12 groups of frame-type paddles are arranged in the second horizontal reaction kettle and are uniformly distributed on the stirring shaft.
According to the method, in the step 1, the reaction temperature of the loop reactor is 30-70 ℃, and the reaction pressure is 2-5 MPa.
According to the method, in the step 2, the reaction temperature of the first horizontal reaction kettle is 50-80 ℃, and the reaction pressure is 2-3 MPa.
According to the method, in the step 3, the reaction temperature of the second horizontal reaction kettle is 50-80 ℃, and the reaction pressure is 2-3 MPa.
According to the method, the rotating speed of a stirring paddle of the first horizontal reaction kettle is 5-50 r/min; the rotating speed of the stirring paddle of the second horizontal reaction kettle is 5-50 r/min.
According to the method, the first horizontal reaction kettle and/or the second horizontal reaction kettle are/is provided with a circulation loop of reaction circulation gas; in the circulation loop, reaction circulation gas is sent out from the top of the reaction kettle to a condenser for condensation; after condensation and gas-liquid separation, liquid propylene (or propylene and comonomer) is sprayed in from the top of the reactor as quenching liquid through a circulating liquid pump, and polymerization reaction heat is taken away through monomer gasification; the non-condensable gas is introduced into the bed layer from the bottom of the reactor through a compressor, so that the whole bed layer is in a sub-fluidized state.
According to the method, the separation equipment arranged between the first horizontal reaction kettle and the second horizontal reaction kettle comprises a receiving tank and an isolation tank; the powder conveying and the gas phase isolation are completed through the receiving tank and the isolation tank, and two independently adjustable reaction conditions are realized.
Compared with the prior art, the technology has the following advantages: (1) the loop reactor is arranged to carry out liquid-phase bulk polymerization and control the polymerization amount, and then the slurry is directly injected into the front end of the first horizontal reaction kettle provided with the straight blade paddle to continue the polymerization reaction, so that the catalyst can be effectively prevented from being crushed, and the rapid dispersion of the catalyst is promoted, thereby avoiding the formation of hot spots and particle agglomeration and solving the problem that the horizontal reaction kettle is easy to agglomerate in the prior art; (2) in the first horizontal reaction kettle, a mixing paddle type of straight paddle and frame paddle is adopted, and the length of the straight paddle at the front end is controlled to be smaller than 1/4 of the length of the frame paddle at the rear end. Because the horizontal stirring kettle adopting the straight blade paddle is equivalent to 3 to 4 full-mixing kettles, the straight blade paddle used at the front end of the first horizontal reaction kettle can ensure that the catalyst is quickly dispersed; because the horizontal stirred tank that adopts frame oar is equivalent to 7 to 8 complete mixing cauldron, consequently the back end adopts frame oar in first horizontal reation kettle, and reduction granule that can the at utmost is back mixed, improves the particle diameter degree of consistency of polymer granule, has set up splitter simultaneously between two horizontal kettles and has been used for realizing two kinds of reaction conditions that can independently regulate and control, is favorable to producing the polypropylene product that shock resistance is higher.
Drawings
FIG. 1 is a schematic flow diagram of a three kettle series propylene polymer production system according to one embodiment of the present invention.
FIG. 2 is a schematic flow diagram of a two-pot series propylene polymer production system according to a comparative example of the present invention.
Detailed Description
The invention will be further illustrated and described with reference to specific embodiments. The technical features of the embodiments of the present invention can be combined correspondingly without mutual conflict.
The horizontal reaction kettle generally has the characteristic that the axial direction of the stirring shaft is parallel to the main propelling direction of materials in the reaction kettle. The invention makes the stirring paddle in the horizontal reaction kettle not generate the pushing action to the material forward or backward basically through the selection of the paddle shape, so the flowing state of the material in the horizontal reaction kettle is close to the plug flow, and compared with a single full mixing kettle with the same volume, the horizontal stirring reactor can realize the effect which is equal to the series operation of a plurality of full mixing kettles in a single reactor. The distribution of the residence time of the materials in the horizontal reactor is narrowed, so that the back mixing and short circuit of the catalyst in the horizontal stirred reactor are less, and the method has the advantages of high catalyst utilization rate and uniform product properties.
The straight blade paddle and the frame type paddle are in common stirring paddle forms and mainly generate radial force; the research of the invention finds that the horizontal stirring kettle adopting the straight blade paddle is equivalent to 3 to 4 full-mixing kettles; the horizontal stirred tank using frame paddle is equivalent to 7 to 8 complete mixing tanks.
In the first horizontal reactor of the present invention, the region where the straight blade paddle is installed is referred to as the front end of the stirring shaft, and the region where the frame paddle is installed is referred to as the rear end of the stirring shaft. Typically, but not by way of limitation, the ratio of the length of the front end to the rear end is, for example, 1/10, 1/8, 1/6, 1/5, 1/4.
The catalyst of the invention can be selected from Ziegler-Natta catalysts which are widely used in propylene polymerization methods. Ziegler-Natta catalysts typically comprise a solid Ziegler-Natta catalyst component comprising compounds of a group 1 to 3 metal and a group 4 to 6 transition metal, an internal electron donor, and optionally a group 13 metal as essential components.
The ziegler-natta catalysts used for the preparation of propylene polymers comprise, in addition to the catalyst component, a cocatalyst, usually an aluminium alkyl, and an external electron donor.
Typical examples of the co-catalyst comprise at least one compound selected from trialkylaluminums, dialkylaluminum chlorides, alkylaluminum dichlorides, alkylaluminum sesquichlorides or any mixture thereof. Preferably, the alkyl group is an alkyl group of 1 to 4C atoms, preferably ethyl or isobutyl. A commonly used cocatalyst is triethylaluminium.
External electron donors are well known in the art and include ethers, ketones, amines, alcohols, phenols, phosphines and silanes. The silane type external donors known in the art are generally organosilane compounds containing a Si-OCOR, Si-OR Si-NR2 bond, containing silicon as central atom, wherein R is an alkyl, alkenyl, aryl, aralkyl OR cycloalkyl group having from 1 to 20 carbon atoms. Diisobutyldimethoxysilane is preferred.
Example 1: the example 1 is a process flow for producing 45 ten thousand tons of homo-polypropylene annually. 0.7kg/h of alkyl aluminum catalyst, 2kg/h of mineral oil, 0.4kg/h of electron donor diisobutyldimethoxysilane, 3kg/h of cocatalyst triethyl aluminum and 3400kg/h of liquid phase propylene enter the loop reactor 1, the polymerization reaction of the propylene is carried out at 50 ℃ and 4.4MPaG, and the mass flow of the generated polypropylene is 1687 kg/h. No separation equipment is arranged between the loop reactor 1 and the first horizontal reaction kettle 2, and the material leaving the loop reactor 1 directly enters the front end of the first horizontal reaction kettle 2.
The first horizontal reaction kettle 2 is a polymerization kettle with central stirring, the diameter of the kettle body is 3.3m, the length of the kettle body is 18.5m, and the total volume of the kettle body is 180m3. The straight blade paddle and the frame type paddle in the polymerization kettle use 4 blades which are uniformly distributed on the same circumference of the stirring shaft as 1 group, and the included angle between every two adjacent blades in each group is 90 degrees. 4 groups of straight blade paddles are uniformly distributed on the front section of the stirring shaft, 10 groups of frame type paddles are uniformly distributed on the rear section of the stirring shaft, gaps do not exist between adjacent straight blade paddles and frame type paddles and between the straight blade paddles and the frame type paddles, and the stirring rotating speed is 20 revolutions per minute. 23200kg/h of propylene was charged into the feed tank, and homopolymerization of propylene was carried out at 66 ℃ under 2.2 MPaG. The reaction recycle gas is sent out from the dome 3 and 4 at the top of the reactor to the condenser 5 at the top of the first horizontal reaction kettle for condensation. Condensed by a condenser 5 and then enters a gas-liquid separator 6, liquid propylene is sprayed in from the top of the reactor 2 as a quenching liquid through a circulating liquid pump 7, and polymerization reaction heat is taken away through propylene gasification; the non-condensable gas is passed into the bed from the bottom of the reactor 2 via a compressor 8 so that the entire bed is in a "sub-fluidised" state. The mass flow of polypropylene produced in the first horizontal reaction vessel 2 was 37530 kg/h. A separation device is arranged between the first horizontal reaction kettle 2 and the second horizontal reaction kettle 11, and powder conveying and gas phase isolation are completed through a receiving tank 9 and an isolation tank 10. Polypropylene enters a second horizontal reaction kettle 11 through an isolation tank 10, and 17880kg/h gas phase propylene is obtained by separationThe alkene is sent to a condenser 5 at the top of the first horizontal reaction kettle, and continuously reacts in the first horizontal reaction kettle.
The second horizontal reaction kettle 11 is a polymerization kettle with central stirring, the diameter of the kettle body is 3.3m, the length of the kettle body is 18.5m, and the total volume of the kettle body is 180m3. 12 groups of frame-type paddles are uniformly distributed on the stirring shaft, no gap exists between adjacent frame-type paddles, and the stirring speed is 15 revolutions per minute. 15300kg/h of propylene was fed to the feed tank, and homopolymerization of propylene was carried out at 66 ℃ under 2.2 MPaG. The circulation process of the reaction circulating gas is the same as that of the first horizontal reaction kettle 2, the produced polypropylene product with the mass flow of 56300kg/h enters the post-treatment unit, and the obtained polypropylene product has a PDI (polymer dispersibility index) of 6.5.
Example 2: the example 2 is a process flow for the annual production of 45 ten thousand tons of atactic polypropylene. 0.7kg/h of alkyl aluminum catalyst, 2kg/h of mineral oil, 4kg/h of electron donor diisobutyl dimethoxysilane, 6kg/h of cocatalyst triethyl aluminum and 3400kg/h of liquid-phase propylene enter the loop reactor 1, the polymerization reaction of the propylene is carried out at 50 ℃ and 4.4MPaG, and the mass flow of the generated polypropylene is 1687 kg/h. No separation equipment is arranged between the loop reactor 1 and the first horizontal reaction kettle 2, and the material leaving the loop reactor 1 directly enters the front end of the first horizontal reaction kettle 2.
The first horizontal reaction kettle 2 is a polymerization kettle with central stirring, the diameter of the kettle body is 3.3m, the length of the kettle body is 18.5m, and the total volume of the kettle body is 180m3. The straight blade paddle and the frame type paddle in the polymerization kettle use 4 uniformly distributed blades on the same circumference of the stirring shaft as 1 group, and the included angle between two adjacent blades in each group is 90 degrees. The front section of the stirring shaft is uniformly distributed with 4 groups of straight blade paddles, the rear section is uniformly distributed with 10 groups of frame type paddles, no gap exists between the adjacent straight blade paddles, the adjacent frame type paddles and the gap between the straight blade paddles and the frame type paddles are 0.05 times of the width of the frame type paddles, and the stirring rotating speed is 25 revolutions per minute. 18140kg/h of propylene was charged into the feed tank, and polymerization of propylene was carried out at 66 ℃ under 2.2 MPaG. The reaction recycle gas is sent out from the dome 3 and 4 at the top of the reactor to the condenser 5 at the top of the first horizontal reaction kettle for condensation. Condensed by a condenser 5 and then enters a gas-liquid separator 6, liquid propylene is sprayed from the top of the reactor 2 as a quenching liquid through a circulating liquid pump 7 and passes through the propyleneThe alkene gasifies and takes away the heat of polymerization reaction; the non-condensable gas is passed into the bed from the bottom of the reactor 2 by means of a compressor 8 so that the entire bed is in a "sub-fluidised" state. The mass flow of the polypropylene generated in the first horizontal reaction kettle 2 is 34200 kg/h. A separation device is arranged between the first horizontal reaction kettle 2 and the second horizontal reaction kettle 11, and powder conveying and gas phase isolation are completed through a receiving tank 9 and an isolation tank 10. The polypropylene enters a second horizontal reaction kettle 11 through an isolation tank 10, 17960kg/h of gas-phase propylene obtained by separation is sent to a condenser 5 at the top of the first horizontal reaction kettle, and the reaction continues in the first horizontal reaction kettle 2.
The second horizontal reaction kettle 11 is a polymerization kettle with central stirring, the diameter of the kettle body is 3.3m, the length of the kettle body is 18.5m, and the total volume of the kettle body is 180m3. 12 groups of frame-type paddles are uniformly distributed on the stirring shaft, the gap between adjacent frame-type paddles is 0.05 times the width of the frame-type paddles, and the stirring speed is 20 revolutions per minute. To the feed tank, 13370kg/h of propylene was fed, and polymerization of propylene was carried out at 66 ℃ under 2.2 MPaG. The circulation process of the reaction circulating gas is the same as that of the first horizontal reaction kettle 2, and the produced polypropylene product with the mass flow of 56300kg/h enters the post-treatment unit. The product polypropylene PDI (Polymer Dispersion index) was 6.7.
Example 3: the process flow of example 3 is a 45 ten thousand ton annually produced high ethylene content impact polypropylene. 1kg/h of alkyl aluminum catalyst, 3kg/h of mineral oil, 1kg/h of electron donor diisobutyldimethoxysilane, 4kg/h of cocatalyst of triethyl aluminum and 3400kg/h of liquid phase propylene enter the loop reactor 1, and the polymerization reaction of the propylene is carried out at 50 ℃ and 4.4MPaG, and the mass flow of the generated polypropylene is 1687 kg/h. No separation equipment is arranged between the loop reactor 1 and the first horizontal reaction kettle 2, and the material leaving the loop reactor 1 directly enters the front end of the first horizontal reaction kettle 2.
The first horizontal reaction kettle 2 is a polymerization kettle with central stirring, the diameter of the kettle body is 3.3m, the length of the kettle body is 18.5m, and the total volume of the kettle body is 180m3. The straight blade paddle and the frame type paddle in the polymerization kettle use 4 blades which are uniformly distributed on the same circumference of the stirring shaft as 1 group, and the included angle between every two adjacent blades in each group is 90 degrees. The front section of the stirring shaft is uniformly distributed with 4 groups of straight blade paddles and the rear section is uniformly distributed with 10 groups of frame type paddlesAnd gaps do not exist between adjacent straight blades, adjacent frame type blades and gaps between the straight blades and the frame type blades are 0.1 time of the width of the frame type blades, and the stirring rotating speed is 30 revolutions per minute. 24430kg/h of propylene were fed to the feed tank, and polymerization of propylene was carried out at 66 ℃ under 2.2 MPaG. The reaction recycle gas is sent out from the dome 3 and 4 at the top of the reactor to the condenser 5 at the top of the first horizontal reaction kettle for condensation. Condensed by a condenser 5 and then enters a gas-liquid separator 6, liquid propylene is sprayed in from the top of the reactor 2 as a quenching liquid through a circulating liquid pump 7, and polymerization reaction heat is taken away through propylene gasification; the non-condensable gas is passed into the bed from the bottom of the reactor 2 via a compressor 8 so that the entire bed is in a "sub-fluidised" state. The mass flow rate of the polypropylene produced in the first horizontal reactor 2 was 38741 kg/h. A separation device is arranged between the first horizontal reaction kettle 2 and the second horizontal reaction kettle 11, and powder conveying and gas phase isolation are completed through a receiving tank 9 and an isolation tank 10. The polypropylene enters a second horizontal reaction kettle 11 through an isolation tank 10, 18040kg/h of gas-phase propylene obtained by separation is sent to a condenser 5 at the top of the first horizontal reaction kettle, and the reaction continues in the first horizontal reaction kettle 2.
The second horizontal reaction kettle 11 is a polymerization kettle with central stirring, the diameter of the kettle body is 3.3m, the length of the kettle body is 18.5m, and the total volume of the kettle body is 180m3. 12 groups of frame-type paddles are uniformly distributed on the stirring shaft, the gap between adjacent frame-type paddles is 0.1 time of the width of the frame-type paddles, and the stirring speed is 15 revolutions per minute. 5435kg/h of propylene and 8880kg/h of ethylene were charged into a feed tank, and copolymerization of propylene was carried out at 66 ℃ under 2.3 MPaG. The circulation process of the reaction circulating gas is the same as that of the first horizontal reaction kettle 2, a copolymer product with the mass flow of 56300kg/h is generated and enters a post-treatment unit, and the obtained product polypropylene PDI (polymer dispersity index) is 6.2.
Example 4: the process flow of example 4 is a 45 ten thousand ton annually produced impact polypropylene with low ethylene content. 2kg/h of alkyl aluminum catalyst, 4kg/h of mineral oil, 2kg/h of electron donor diisobutyl dimethoxysilane, 6kg/h of cocatalyst triethyl aluminum and 3400kg/h of liquid phase propylene enter the loop reactor 1 together, and the polymerization reaction of the propylene is carried out at 50 ℃ and 4.4MPaG, and the mass flow of the generated polypropylene is 1687 kg/h. No separation equipment is arranged between the loop reactor 1 and the first horizontal reaction kettle 2, and the material leaving the loop reactor 1 directly enters the front end of the first horizontal reaction kettle 2.
The first horizontal reaction kettle 2 is a polymerization kettle with central stirring, the diameter of the kettle body is 3.3m, the length of the kettle body is 18.5m, and the total volume of the kettle body is 180m3. The straight blade paddle and the frame type paddle in the polymerization kettle use 4 blades which are uniformly distributed on the same circumference of the stirring shaft as 1 group, and the included angle between every two adjacent blades in each group is 90 degrees. 4 groups of straight blade paddles of the anterior segment evenly distributed of the stirring shaft, 10 groups of frame type paddles of evenly distributed back segment, the gap between adjacent straight blade paddles is 0.01 times the width of the straight blade paddle, the gap between adjacent frame type paddles and the straight blade paddles and the frame type paddles is 0.05 times the width of the frame type paddles, and the stirring rotating speed is 25 revolutions per minute. 31310kg/h of propylene were charged into the feed tank, and polymerization of propylene was carried out at 66 ℃ under 2.5 MPaG. The reaction recycle gas is sent out from the dome 3 and 4 at the top of the reactor to a condenser 5 at the top of the first horizontal reaction kettle for condensation. Condensed by a condenser 5 and then enters a gas-liquid separator 6, liquid propylene is sprayed in from the top of the reactor 2 as a quenching liquid through a circulating liquid pump 7, and polymerization reaction heat is taken away through propylene gasification; the non-condensable gas is passed into the bed from the bottom of the reactor 2 via a compressor 8 so that the entire bed is in a "sub-fluidised" state. The mass flow rate of polypropylene produced in the first horizontal reaction vessel 2 was 47150 kg/h. A separation device is arranged between the first horizontal reaction kettle 2 and the second horizontal reaction kettle 11, and powder conveying and gas phase isolation are completed through a receiving tank 9 and an isolation tank 10. Polypropylene is fed into a second horizontal reaction vessel 11 through an isolation tank 10, 20630kg/h of gas-phase propylene obtained by separation is fed into a condenser 5 at the top of the first horizontal reaction vessel, and the reaction is continued in the first horizontal reaction vessel 2.
The second horizontal reaction kettle 11 is a polymerization kettle with central stirring, the diameter of the kettle body is 3.3m, the length of the kettle body is 18.5m, and the total volume of the kettle body is 180m3. 12 groups of frame-type paddles are uniformly distributed on the stirring shaft, the gap between adjacent frame-type paddles is 0.05 times the width of the frame-type paddles, and the stirring speed is 20 revolutions per minute. 320kg/h of propylene and 5680kg/h of ethylene were fed to a feed tank, and copolymerization of propylene was carried out at 66 ℃ and 2.5 MPaG. The circulation process of the reaction circulating gas is the same as that of the first horizontal reaction kettle 2, and the generated mass flow is 56300kg/h of copolymer product was passed to a work-up unit, giving a product polypropylene PDI (Polymer Dispersion index) of 6.6.
Comparative example 1: the comparative example 1 is a process flow for annual production of 45 ten thousand tons of homo-polypropylene. The first horizontal reaction kettle 1 is a polymerization kettle with central stirring, the diameter of the kettle body is 3.3m, the length of the kettle body is 18.5m, and the total volume of the kettle body is 180m3. 14 groups of straight blades are uniformly distributed on the stirring shaft, no gap exists between every two adjacent straight blades, and the stirring speed is 20 revolutions per minute. 0.7kg/h of alkyl aluminum catalyst, 2kg/h of mineral oil, 0.4kg/h of electron donor diisobutyldimethoxysilane, 3kg/h of cocatalyst triethyl aluminum and 44210kg/h of propylene enter the front end of the first horizontal reaction kettle 1 from a feeding tank, homopolymerization reaction of the propylene is carried out at 66 ℃ and 2.2MPaG, and the mass flow of the generated polypropylene is 37530 kg/h. The recycling process of the reaction recycle gas was the same as in example 1.
The second horizontal reaction vessel 10 is a polymerization vessel with a central stirring, the diameter of the vessel body is 3.3m, the length is 18.5m, and the total volume is 180m3. 12 groups of frame-type paddles are uniformly distributed on the stirring shaft, no gap exists between every two adjacent frame-type paddles, and the stirring speed is 15 revolutions per minute. 15500kg/h of propylene was charged into the feed tank, and homopolymerization of propylene was carried out at 66 ℃ under 2.2 MPaG. The circulation process of the reaction circulating gas is the same as that of the first horizontal reaction kettle 1, the produced polypropylene product with the mass flow of 56300kg/h enters the post-treatment unit, and the obtained polypropylene product PDI (polymer dispersibility index) is 7.1. Compared with example 1, the difference in product uniformity of the polymer product is more likely to cause agglomeration at the front part of the first horizontal reaction kettle of comparative example 1, and the first horizontal reaction kettle of example 1 does not cause agglomeration.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (8)
1. A process for the production of a propylene polymer, characterized in that it comprises:
step 1, firstly, a polymerization monomer, a catalyst, alkyl aluminum, an external electron donor and optional hydrogen enter a loop reactor to carry out liquid-phase bulk polymerization, and the loop reactor continuously produces polymer particle slurry; the polymerization monomer is propylene or propylene and one or more optional comonomers, and the comonomers comprise ethylene and C4-C6 alpha-olefin;
step 2, continuously taking out the particle slurry of the polymer from the loop reactor, and continuously carrying out polymerization reaction at the front end of a first horizontal reaction kettle with a stirring paddle; the first horizontal reaction kettle adopts a mixing mode of straight blade paddles and frame type paddles; the straight blade paddle in the first horizontal reaction kettle is close to the feed inlet, and the length of the area is less than one fourth of the length of the area of the rear end frame type paddle;
step 3, continuously taking out polymer particles from the first horizontal reaction kettle, and allowing the polymer particles to enter the front end of a second horizontal reaction kettle with a stirring paddle to continuously perform polymerization reaction; the second horizontal reaction kettle adopts a frame type paddle.
2. The method according to claim 1, characterized in that the first horizontal reaction kettle and/or the second horizontal reaction kettle is/are added with polymerization monomers to carry out polymerization reaction, wherein the polymerization monomers are propylene or propylene and one or more optional comonomers; the mass of the polymer particles obtained in the loop reactor accounts for less than 10% of the mass of the polymer particles in the discharge of the second horizontal reaction kettle.
3. The process according to claim 1, wherein no separation device is provided between the loop reactor and the first horizontal reactor.
4. The method according to claim 1, wherein a separation device is arranged between the first horizontal reaction kettle and the second horizontal reaction kettle.
5. The method according to claim 1, wherein the reaction temperature of the loop reactor is 30 to 70 ℃ and the reaction pressure is 2 to 5 MPa.
6. The method according to claim 1, wherein the reaction temperature of the first horizontal reaction kettle is 50-80 ℃ and the reaction pressure is 2-3 MPa.
7. The method according to claim 1, wherein the reaction temperature of the second horizontal reaction kettle is 50-80 ℃ and the reaction pressure is 2-3 MPa.
8. The method according to claim 1, characterized in that the first horizontal reaction kettle and/or the second horizontal reaction kettle is/are provided with a circulation loop of reaction circulation gas; in the circulation loop, reaction circulation gas is sent out from the top of the reaction kettle, after condensation and gas-liquid separation, liquid monomer is injected from the top of the reactor as quenching liquid, and polymerization reaction heat is taken away through gasification; the non-condensable gas is introduced into the bed layer from the bottom of the reactor.
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