1. An apparatus for recovering propylene monomer and an inert diluent from a propylene polymer slurry comprising: the device comprises a first flash tank, a second flash tank, a first separation tower, a second separation tower and a washing tower, wherein a discharge hole in the top of the first flash tank is connected with a feed inlet of the first separation tower; the discharge port at the bottom of the first flash tank is connected with the feed port of the second flash tank, and the first flash tank is optionally connected with a first heat exchanger for adjusting the temperature of the propylene polymer slurry;

the first separation tower is provided with a first discharge hole, a second discharge hole and a third discharge hole, the first discharge hole is positioned at the top of the first separation tower, the second discharge hole is positioned at the position, with the distance from the bottom of the first separation tower to the tower being 1/10-4/5 of the height of the first separation tower, and the third discharge hole is positioned at the bottom of the first separation tower; the second discharge hole is connected with a feed inlet of a second separation tower, and the third discharge hole is connected with a feed inlet of a second flash tank;

the second separation tower is provided with a top discharge hole and a bottom discharge hole;

a discharge port at the top of the second flash tank is connected with a feed port of the washing tower, and a discharge port at the top of the washing tower is connected with the first separation tower through a first compressor;

the second flash tank is provided with a bottom discharge hole;

the first separation tower and the second separation tower are plate-type rectifying towers.

2. The apparatus of claim 1, wherein the feed inlet of the first separation column is located below the last tray at the bottom end of the first separation column;

and/or the second discharge outlet is spaced from the last tray at the bottom of the first separation tower by at least 2 trays, preferably at least 4 trays; the position of the second discharge port is separated from the first tower plate at the top of the first separation tower by at least 1 tower plate.

3. The apparatus according to claim 1 or 2, wherein the top discharge port and the bottom discharge port of the second separation column are respectively connected with a second heat exchanger, preferably the top discharge port of the second separation column is connected with the second heat exchanger through a second compressor, more preferably the second heat exchanger is also connected with the top and the bottom of the second separation column through a third heat exchanger and a fourth heat exchanger respectively;

or a top discharge hole of the second separation tower is directly connected with the top of the second separation tower through a third heat exchanger, and a bottom discharge hole of the second separation tower is directly connected with the bottom of the second separation tower through a fourth heat exchanger.

4. A process for recovering propylene monomer and inert diluent from a propylene polymer slurry using the apparatus of any one of claims 1 to 3, comprising the steps of:

(1) sending propylene polymer slurry from a propylene polymerization system into a first flash tank for flash evaporation and separation to obtain a first gas phase material and a first solid phase material;

(2) the first gas phase material obtained by separation in the step (1) enters a first separation tower through a discharge hole at the top of a first flash tank and a feed hole of the first separation tower for rectification separation, wherein a propylene gas material is obtained at the top of the first separation tower and is led out through a first discharge hole; obtaining a mixed liquid material of a propylene monomer and an inert diluent in the first separation tower, wherein part of the mixed liquid material of the propylene monomer and the inert diluent carries fine powder carried in the first gas-phase material to a tower kettle and enters a second flash tank through a third discharge hole, and the rest mixed liquid material of the propylene monomer and the inert diluent enters a second separation tower through a second discharge hole for separation, wherein the gas-phase material of the propylene monomer is obtained at the tower top of the second separation tower and is discharged and condensed through a discharge hole at the top of the second separation tower to obtain a propylene monomer enriched material, and the inert diluent enriched material is obtained at the tower kettle of the second separation tower and is discharged through a discharge hole at the bottom of the second separation tower;

(3) enabling the first solid-phase material obtained by separation in the step (1) to enter a second flash tank and carrying out flash separation on the material from a third discharge hole of a second separation tower together to obtain a second gas-phase material and a polypropylene material; and the second gas-phase material enters the washing tower to be washed, is discharged from a discharge port at the top of the washing tower, is compressed and then is conveyed to the first separation tower, and the polypropylene material is discharged from a discharge port at the bottom of the second flash tank.

5. The process according to claim 4, characterized in that the temperature of the propylene polymer slurry is 40-90 ℃, preferably 60-80 ℃; and/or the pressure of the first flash tank is 1.0-2.5 MPa; and/or the pressure of the second flash tank is 1-3bar, preferably 1-2 bar;

preferably, in step (1), the propylene polymer slurry is heated by a first heat exchanger at 0 to 30 ℃, preferably at 5 to 20 ℃, and then sent to a first flash tank.

6. The method according to claim 4 or 5, wherein in the step (2), the temperature of the top of the first separation tower is 30-60 ℃, preferably 40-50 ℃, and the temperature of the bottom of the first separation tower is 40-100 ℃, preferably 50-90 ℃;

and/or the top temperature of the second separation tower is 5-60 ℃, preferably 10-50 ℃, and the bottom temperature of the second separation tower is 40-150 ℃, preferably 50-120 ℃.

7. The method according to any one of claims 4 to 6, wherein when the temperature difference between the top and bottom of the second separation column is less than 45 ℃, the propylene monomer gas phase material extracted from the discharge port at the top of the second separation column is compressed by a second compressor, and then exchanges heat with the bottom material through a second heat exchanger, and is condensed to obtain the propylene monomer enriched material, and preferably, the propylene monomer gas phase material at the top of the second separation column and the inert diluent enriched material at the bottom of the column are respectively heated to the required temperature through a third heat exchanger and a fourth heat exchanger;

when the temperature difference between the top and the bottom of the second separation tower is more than 45 ℃, condensing the propylene monomer gas-phase material led out from the discharge hole at the top of the second separation tower to obtain the propylene monomer enriched material, and directly discharging the inert diluent enriched material obtained from the bottom of the second separation tower from the discharge hole at the bottom of the second separation tower;

preferably, a portion of the resulting propylene monomer-rich material is returned to the overhead first tray of the second separation column.

8. A process according to any one of claims 4 to 7, characterized in that the inert diluent comprises from 1% to 50% of the total molar fraction of liquid material in the propylene polymer slurry.

9. Process according to any one of claims 4 to 8, characterized in that the molar fraction of propylene in the gaseous feed of propylene is greater than 60%, preferably greater than 80%; and/or the molar fraction of inert diluent in the inert diluent-rich material obtained from the bottom of the second separation tower is more than 50%, preferably more than 70%, more preferably more than 90%; and/or the mass fraction of the polypropylene in the polypropylene material is 60-100 wt%.

10. A propylene polymerization process comprising the steps of:

(1) conveying a propylene monomer, a catalyst and an inert diluent into a prepolymerization reactor for prepolymerization reaction to obtain a prepolymer, and then carrying out polymerization reaction on the prepolymer in a polymerization reactor with the propylene monomer and optional hydrogen to obtain propylene polymer slurry;

(2) separating the resulting propylene polymer slurry by means of the apparatus of any one of claims 1-3 or the process of any one of claims 4-9 to obtain a propylene monomer rich aggregate and an inert diluent rich aggregate, and recycling the resulting propylene monomer rich aggregate and inert diluent rich aggregate to the prepolymerization reactor and/or the polymerization reactor, respectively.

Background

As is well known, loop reactors or loop reactors are common installations for the production of polyethylene and polypropylene. Generally, the material in the loop reactor is a liquid-solid mixture, wherein the liquid material includes polymerized monomers such as ethylene and propylene, inert solvents, chain transfer agents, co-catalysts, etc. may be used, and the solid material is catalyst and polymer. Heating and depressurizing and flashing the liquid-solid mixture discharged from the loop reactor, sending the separated solid material containing the catalyst to a gas phase reactor for further preparing the copolymer or sending the solid material to further flashing and devolatilizing to obtain a polymer, and returning the separated gas material to the loop reactor after separation, heavy component removal and other processes.

Generally, for a loop polymerization reactor, unreacted materials in the reaction system are directly recycled to the reaction unit as recycled materials. For example, chinese patent CN100531892 discloses a process for separating polymer and liquid materials, wherein a solid polymer obtained by two flash evaporation of a liquid-solid mixture discharged from a loop reactor is processed and pelletized, and gas materials at the top of a primary flash tank and a secondary flash tank are condensed and returned to the loop reactor. Although a cyclone is provided in the process for separating polymer fines, there may still be a portion of the active polymer fines entering the subsequent flow path with the gaseous feed, which may lead to problems with polymer fines deposition plugging of the transfer lines. Chinese patent CN102050900B discloses a process for degassing polymer and recycling propylene, wherein a liquid-solid mixture discharged from a loop reactor enters a first-stage flash tank, a gas material obtained by separation enters a high-pressure propylene washing tower, unreacted propylene in the high-pressure propylene washing tower is condensed and then returns to the reactor, and meanwhile, a strand of propylene material sends entrained polymer fine powder to a second-stage flash tank; and the solid material obtained by the separation of the first-stage flash tank enters a second-stage flash tank, and the gas material at the top of the second-stage flash tank passes through a low-pressure propylene washing tower and then is compressed to a high-pressure propylene washing tower. The process is also suitable for slurry polymerization using an inert diluent, but in this process both the diluent and unreacted monomer are returned to the reactor together from the top of the column, which is a waste of energy consumed by the high pressure propylene scrubber.

Therefore, it is important to develop a device and a method for efficiently separating and recovering the inert diluent and the reaction monomer, which have high operability, can reduce energy consumption and save cost.

Disclosure of Invention

In view of the problems in the prior art, the present invention provides an apparatus and method for recovering unreacted propylene monomer and an inert diluent from a propylene polymer slurry from a propylene polymerization system. The method can efficiently separate and recycle unreacted propylene monomers and the inert diluent from the propylene polymerization reaction system, has the advantages of high operability, energy consumption reduction and cost saving, and is particularly suitable for the polymerization reaction system with the inert diluent and a plurality of reactors.

To this end, a first aspect of the present invention provides an apparatus for recovering propylene monomer and an inert diluent from a propylene polymer slurry, comprising: the device comprises a first flash tank, a second flash tank, a first separation tower, a second separation tower and a washing tower, wherein a discharge hole in the top of the first flash tank is connected with a feed inlet of the first separation tower; the discharge port at the bottom of the first flash tank is connected with the feed port of the second flash tank, and the first flash tank is optionally connected with a first heat exchanger for adjusting the temperature of the propylene polymer slurry;

the first separation tower is provided with a first discharge hole, a second discharge hole and a third discharge hole, the first discharge hole is positioned at the top of the first separation tower, and the second discharge hole is positioned at 1/10-4/5, the distance from the first separation tower to the bottom of the first separation tower is the height of the first separation tower; the third discharge hole is positioned at the bottom of the first separation tower; the second discharge hole is connected with a feed inlet of a second separation tower, and the third discharge hole is connected with a feed inlet of a second flash tank;

the second separation tower is provided with a top discharge hole and a bottom discharge hole;

a discharge port at the top of the second flash tank is connected with a feed port of the washing tower, and a discharge port at the top of the washing tower is connected with the first separation tower through a first compressor;

the second flash tank is provided with a bottom discharge hole;

the first separation tower and the second separation tower are plate-type rectifying towers.

The "propylene polymer slurry" in the present invention means a liquid-solid mixture formed by unreacted materials and products in the propylene polymerization reaction system, which contains at least a polypropylene solid product, unreacted propylene monomers and an inert diluent, and may further contain hydrogen and other polymerization products such as oligomer components.

In the present invention, the "propylene monomer" is propylene or a mixture of propylene and at least one of α -olefins.

According to some embodiments of the invention, the alpha-olefin has the formula CH₂Wherein R is hydrogen or C₂-C₆In some preferred embodiments, the alpha-olefin is selected from at least one of ethylene, butene, hexene, and octene.

In the present invention, the "inert diluent" means a saturated hydrocarbon which does not chemically react with the propylene monomer, the catalyst and the cocatalyst at the reaction pressure and the reaction temperature, and may be either a single component or a mixture of a plurality of components.

According to some embodiments of the invention, the inert diluent is at least one of a C3-C7 alkane, preferably at least one of a C4-C6 alkane, more preferably at least one of n-butane, isobutane, n-pentane, isopentane, n-hexane, and cyclohexane.

"optionally" in the context of the present invention means either with or without the attachment, and may or may not mean through.

According to the invention, the specification and the plate spacing of the plate rectifying tower can be the conventional arrangement of the plate rectifying tower in the field. According to some embodiments of the invention, the number of trays of the first separation column and/or the second separation column is 10 to 35.

According to some embodiments of the invention, the feed inlet of the first separation column is located below the last tray at the bottom end of the first separation column.

According to some preferred embodiments of the present invention, the second outlet is spaced from the last tray at the bottom of the first separation column by at least 2 trays, preferably by at least 4 trays.

According to some preferred embodiments of the present invention, the second outlet is located at least 1 tray apart from the first tray at the top of the first separation column.

According to some preferred embodiments of the present invention, the top discharge port and the bottom discharge port of the second separation column are respectively connected to a second heat exchanger.

According to some preferred embodiments of the present invention, the top discharge port of the second separation column is connected to the second heat exchanger through a second compressor.

According to some embodiments of the invention, the second heat exchanger is further connected to the top and bottom of the second separation column via a third heat exchanger and a fourth heat exchanger, respectively.

According to some embodiments of the invention, the top discharge port of the second separation column is directly connected to the top of the second separation column through a third heat exchanger.

According to some embodiments of the invention, the bottom discharge port of the second separation column is directly connected to the bottom of the second separation column through a fourth heat exchanger.

In a second aspect, the present invention provides a process for recovering propylene monomer and an inert diluent from a propylene polymer slurry, using an apparatus according to the first aspect of the present invention, comprising the steps of:

(1) sending propylene polymer slurry from a propylene polymerization system into a first flash tank for flash evaporation and separation to obtain a first gas phase material and a first solid phase material;

(2) the first gas phase material obtained by separation in the step (1) enters a first separation tower through a discharge hole at the top of a first flash tank and a feed hole of the first separation tower for rectification separation, wherein a propylene gas material is obtained at the top of the first separation tower and is led out through a first discharge hole; obtaining a mixed liquid material of a propylene monomer and an inert diluent in the first separation tower, wherein part of the mixed liquid material of the propylene monomer and the inert diluent carries fine powder carried in the first gas-phase material to a tower kettle and enters a second flash tank through a third discharge hole, and the rest mixed liquid material of the propylene monomer and the inert diluent enters a second separation tower through a second discharge hole for separation, wherein the gas-phase material of the propylene monomer is obtained at the tower top of the second separation tower and is discharged and condensed through a discharge hole at the top of the second separation tower to obtain a propylene monomer enriched material, and the inert diluent enriched material is obtained at the tower kettle of the second separation tower and is discharged through a discharge hole at the bottom of the second separation tower;

(3) enabling the first solid-phase material obtained by separation in the step (1) to enter a second flash tank and carrying out flash separation on the material from a third discharge hole of a second separation tower together to obtain a second gas-phase material and a polypropylene material; and the second gas-phase material enters the washing tower to be washed, is discharged from a discharge port at the top of the washing tower, is compressed and then is conveyed to the first separation tower, and the polypropylene material is discharged from a discharge port at the bottom of the second flash tank.

According to the invention, the first gaseous feed comprises mainly unreacted propylene monomer and inert diluent, but it will be appreciated that, due to the propylene polymerization reaction, it is possible to adjust the molecular weight by adding hydrogen, for example, and that it is also possible to include other gases such as hydrogen and the like and inevitably carry some fine powder of propylene polymer.

According to the invention, the first solid phase material is mainly propylene polymer powder particles, but it will be understood that, due to incomplete flash separation, the first solid phase material may also contain propylene monomer, inert diluents and the like which have not flashed completely and/or are dissolved in the polymer powder particles.

According to the invention, the propylene gas feed comprises propylene monomer gas and optionally hydrogen and lower boiling inert components such as ethane and propane.

According to the present invention, the propylene monomer and inert diluent mixed liquid material comprises propylene and an inert diluent, but it is understood that the propylene monomer and inert diluent mixed liquid material may contain a small amount of hydrogen and inert components having a low boiling point such as ethane and propane, etc. due to the difficulty of 100% separation.

According to some embodiments of the present invention, the propylene gas feed obtained at the top of the first separation column may be recycled back to the reaction unit by methods known in the art, for example by means of a feed pump.

According to some embodiments of the invention, the process further comprises discharging a small amount of a non-condensable gas feed, such as hydrogen and lower boiling inert components such as ethane and propane, from the feed withdrawn from the top of the first separation column.

According to some embodiments of the present invention, the withdrawal of the mixed liquid feed of propylene monomer and inert diluent from the second discharge port located in the middle of the first separation column is controlled by the setting of a valve.

According to some embodiments of the invention, the temperature of the propylene polymer slurry is in the range of 40 to 90 ℃, preferably 60 to 80 ℃.

According to some embodiments of the invention, in step (1), the propylene polymer slurry is heated by a first heat exchanger at 0 to 30 ℃, preferably at 5 to 20 ℃ and then sent to a first flash tank. According to some embodiments of the invention, the pressure of the first flash tank is 1.0-2.5 MPa. According to the invention, by adjusting the temperature of the polypropylene slurry entering the first flash tank and the pressure of the first flash tank to be in the ranges, more than 90% of liquid materials and more than 70% of micromolecules dissolved in polymers in the first flash tank can be flash-removed, thereby reducing the workload and the energy consumption of the first compressor.

According to some embodiments of the invention, the pressure of the second flash tank is 1-3bar, preferably 1-2 bar. According to the invention, the temperature of the second flash tank is based on maintaining the temperature of the first solid phase feed entering it. According to some embodiments of the invention, the temperature of the second flash tank is between 50 ℃ and 90 ℃.

According to some embodiments of the invention, the wash column is a sieve plate column.

According to the invention, the second gas-phase feed comprises propylene monomer and diluent and oligomers and heavy components, if present.

According to some embodiments of the invention, a portion of the inert wash liquid at the bottom of the wash column is returned to the top of the wash column for reuse and the remainder is sent to a post-treatment unit.

According to some embodiments of the invention, the overhead temperature of the wash column is from 10 to 50 ℃.

According to some embodiments of the invention, the pressure of the wash column is 1-3 bar.

According to some embodiments of the invention, the overhead temperature of the first separation column is in the range of 30 to 60 ℃, preferably 40 to 50 ℃.

According to some embodiments of the present invention, since polymer fine powder is present in the first separation column, in order to avoid the problem of wall sticking, clogging, etc. caused by the dissolution of the polymer having a relatively low molecular weight in the liquid phase material, the temperature of the bottom of the first separation column is controlled to 40 to 100 ℃, preferably 50 to 90 ℃.

According to some embodiments of the invention, the overhead temperature of the second separation column is in the range of 5 to 60 ℃, preferably 10 to 50 ℃.

According to some embodiments of the invention, the still temperature of the second separation column is in the range of 40 to 150 ℃, preferably 50 to 120 ℃.

According to some embodiments of the present invention, the overhead material of the second separation column may be subjected to a pressure increase by a compressor to increase the temperature, so as to achieve heat exchange between the overhead material and the bottom material, i.e. to reduce the energy consumption of the second separation column by using heat pump rectification known in the art.

According to some preferred embodiments of the present invention, when the temperature difference between the top and bottom of the second separation column is less than 45 ℃, the propylene monomer gas phase material extracted from the discharge port at the top of the second separation column passes through the second compressor, and then exchanges heat with the bottom material through the second heat exchanger, and is condensed to obtain the propylene monomer enriched material.

According to some embodiments of the invention, the second separation column overhead propylene monomer gas phase feed and the bottoms inert diluent enrichment are brought to the desired temperature by a third heat exchanger and a fourth heat exchanger, respectively, when the difference between the overhead and bottoms temperatures of the second separation column is less than 45 ℃.

According to some embodiments of the present invention, the propylene monomer gas phase feed from the top of the second separation column is compressed by the second compressor to increase the temperature of the gas phase feed at the top of the second separation column, so that there is a sufficient temperature difference between the top feed and the bottom feed of the second separation column for heat exchange by the second heat exchanger.

According to some embodiments of the present invention, the gas phase feed of the propylene monomer at the top of the second separation column and the enriched feed of the inert diluent at the bottom of the column can be brought to the required temperature by the third heat exchanger and the fourth heat exchanger for the production conditions of different inert diluent concentrations. For example, if the heat provided by the gas phase material at the top of the second separation tower is insufficient, the tower bottom material is heated by the fourth heat exchanger. And if the heat provided by the gas phase material at the top of the second separation tower is excessive, cooling the material at the top of the second separation tower by a third heat exchanger.

According to some embodiments of the invention, when the temperature difference between the top and bottom of the second separation column is greater than 45 ℃, the propylene monomer gas phase feed from the top outlet of the second separation column is condensed to obtain the propylene monomer rich material, and the inert diluent rich material from the bottom outlet of the second separation column is directly discharged through the bottom outlet of the second separation column.

According to some embodiments of the invention, the propylene monomer rich material is partially returned to the first tray at the top of the second separation column and the remainder is returned to the polymerization reaction unit.

According to some embodiments of the invention, the propylene monomer rich material is returned to the polymerization reaction unit.

According to a preferred embodiment of the present invention, the inert diluent in the propylene polymer slurry is present in an amount of 1% to 50% based on the total molar fraction of liquid feed in the propylene polymer slurry.

According to some embodiments of the invention, the molar fraction of propylene in the gaseous feed of propylene is greater than 60%, preferably greater than 80%.

According to some embodiments of the invention, the molar fraction of inert diluent in the inert diluent rich aggregate obtained in the second separation column bottom is more than 50%, preferably more than 70%, more preferably more than 90%.

In a third aspect, the present invention provides a propylene polymerization process comprising the steps of:

(1) conveying a propylene monomer, a catalyst and an inert diluent into a prepolymerization reactor for prepolymerization reaction to obtain a prepolymer, and then carrying out polymerization reaction on the prepolymer in a polymerization reactor with the propylene monomer and optional hydrogen to obtain propylene polymer slurry;

(2) the resulting propylene polymer slurry is separated by means of the apparatus according to the first aspect of the invention to obtain a propylene monomer-rich material and an inert diluent-rich material, which are recycled to the prepolymerization reactor and/or the polymerization reactor, respectively.

According to some embodiments of the invention, the catalyst comprises at least one of a ziegler natta catalyst, a chromium based catalyst, a metallocene catalyst and a late transition catalyst, preferably at least one of a ziegler natta catalyst, a chromium based catalyst and a metallocene catalyst.

Compared with the prior art, the invention has the following advantages:

1) the invention can efficiently separate and recover the inert diluent and the unreacted monomer from the propylene polymerization reaction system, and the mole fraction of the recovered inert diluent is more than 85 percent, so that the inert diluent can be used for propylene polymerization reaction to more flexibly regulate the proportion of the inert diluent and the reaction monomer of each stream entering different polymerization reactors, regulate the concentration of the reaction monomer in the reactors, conveniently regulate the yield of different reactors, and further improve the operability of the device.

2) The separation of the liquid-solid mixture of the propylene polymer slurry and the separation of the solvent are coupled, and a strand of mixture of the propylene and the solvent is collected through the lateral line, so that on one hand, the entrainment of solid fine powder into the solvent is avoided, on the other hand, the energy consumption can be reduced, and the cost can be saved.

Drawings

FIG. 1 is a flow diagram of an apparatus for separating propylene monomer and inert diluent in accordance with one embodiment of the present invention.

FIG. 2 is a flow diagram of an apparatus for separating propylene monomer and inert diluent in accordance with another embodiment of the present invention.

Description of reference numerals: 1-a first heat exchanger; 2-a first flash tank; 3-a first separation column; 4-a second flash tank; 5-a washing tower; 6-a first compressor; 7-a first delivery pump; 8-a second separation column; 9-a second compressor; 10-a second heat exchanger; 11-a second delivery pump; 12-a third heat exchanger; 13-a fourth heat exchanger; 14-a polymer slurry; 15-first separation column feed inlet; 16-a first discharge port; 17-a second discharge port; 18-a third discharge port; 19-a discharge port at the top of the second separation tower; 20-a discharge port at the bottom of the second separation tower; 21-a discharge port at the bottom of the second flash tank; 22-, 23, 24, 25, 26, 27, 28, 29-lines.

Detailed Description

The invention aims to provide a device and a method for recovering unreacted propylene monomer and inert diluent from propylene polymer slurry, which are suitable for slurry polymerization processes of ethylene, propylene and the like in a loop reactor in the presence of the inert diluent, and are particularly suitable for polymerization processes using at least 2 slurry polymerization reactors. The term "loop reactor" as used in the present invention is a well-known loop reactor, in which the reaction mass flows rapidly in the circulation loop of the "tubular reactor" under the action of an axial pump and the polymerization reaction takes place. The present invention will be described in detail with reference to the following examples and drawings, which are only for illustrative purposes and are not intended to limit the scope of the present invention, and all reasonable variations and combinations included within the spirit and scope of the present invention are included in the scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used are not indicated by the manufacturer, and are conventional products which are commercially available or obtainable using conventional or published methods.

The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.

FIG. 1 is a flow chart of a separation and recovery device in an embodiment of the invention, which is particularly suitable for the working condition that the temperature difference between the top of a second separation tower and the bottom of the second separation tower is less than 45 ℃, and comprises the following main devices and units:

a first heat exchanger 1 for preheating a polymer slurry 14 discharged from a polymerization reactor;

a first flash tank 2 for preliminarily separating the polymer particle powder, the inert diluent and the unreacted monomer;

a first separation column 3 for removing polymer particle powder and recovering unreacted monomers;

a second flash tank 4 for separating the polymer pellet powder and the inert diluent, unreacted monomer, etc. dissolved in the polymer pellet powder;

a washing tower 5 for washing the gas phase material from the top of the second flash tank 4;

a first compressor 6 for conveying the gas phase material from the top of the washing tower 5 to the first separation tower 3 under pressure;

a first transfer pump 7 for returning the inert scrubbing liquid to the top of the scrubbing column 5 and sending part of the inert scrubbing liquid to the work-up via line 22;

a second separation column 8 for separating the unreacted monomer and the inert diluent;

a second compressor 9 for pressurizing and heating the propylene monomer gas-phase material extracted from the top of the second separation tower 8;

a second heat exchanger 10 used for exchanging heat between the material at the top of the second separation tower 8 and the material at the bottom of the tower;

a second conveying pump 11 for conveying the tower bottom material of the second separation tower 8;

a third heat exchanger 12 for cooling the overhead material from the second separation column 8.

A fourth heat exchanger 13 for heating the still material from the second separation column 8.

In the flow of the separation and recovery apparatus shown in FIG. 1, the propylene polymer slurry 14 discharged from the polymerization reactor is subjected to heat exchange in the first heat exchanger 1, then the temperature is raised, and then the propylene polymer slurry is sent to the first flash tank 2 for separation. The solubility of small molecules such as propylene, propane and inert diluents in polymer materials at the outlet of the first flash tank 2 is regulated and controlled by controlling the heating temperature of the first heat exchanger 1 and the pressure of the first flash tank 2. A first vapor phase feed comprising mainly unreacted monomer and inert diluent is obtained at the top of the first flash tank 2 and introduced into the first separation column 3 through a first separation column feed inlet 15 located at the bottom of the first separation column 3, wherein entrained fines are washed to the bottom of the column by the liquid. A propylene gas material mainly containing propylene gas is obtained at the top of the first separation column 3 and discharged through a first discharge port 16, and a part is recycled to the reaction unit through a line 25, and the other part is discharged to a recovery unit through a line 24 or directly sent to a combustion torch. The solid material washed from the bottom of the first separation column 3 is introduced into the second flash tank 4 through the third discharge port 18 along with a stream of liquid material. Through the arrangement of a valve, a mixed liquid material of the propylene monomer and the inert diluent which mainly comprises unreacted monomer and the inert diluent is led out from a second discharge hole 17 positioned in the middle of the first separation tower 3 and is guided into a second separation tower 8 to further separate and enrich the unreacted monomer and the inert diluent, wherein a propylene monomer gas phase material is obtained from the top of the second separation tower 8, is discharged from a discharge hole 19 at the top of the second separation tower and is condensed to obtain a propylene monomer enriched material, and an inert diluent enriched material is obtained from the bottom of the second separation tower and is discharged from a discharge hole at the bottom of the second separation tower. In order to reduce the energy consumption of the second separation column 8, a second compressor 9, a second heat exchanger 10, a third heat exchanger 12 and a fourth heat exchanger 13 are provided. The propylene monomer gas phase material led out from the top of the second separation tower is compressed by a second compressor 9 to improve the temperature of the gas phase material at the top of the second separation tower, so that the temperature difference between the material at the top and the material at the bottom of the second separation tower 8 is large enough to exchange heat through a second heat exchanger 10. In order to adapt to the production conditions of different diluent concentrations, the third heat exchanger 12 and the fourth heat exchanger 13 are reserved, and if the heat provided by the gas phase material at the top of the second separation tower 8 is insufficient, the tower bottom material is heated through the fourth heat exchanger 13. If the second separation column 8 provides too much heat to the gas phase feed at the top of the column, the top feed is cooled by a third heat exchanger 12.

The material which is drawn off from the bottom of the first flash tank 2 and introduced into the second flash tank 4 is polymer powder particles and possibly liquid material which is not completely flashed and reaction monomers, diluents and the like which are dissolved in the polymer powder particles. The absolute pressure of the second flash tank 4 is 1-3bar and the polymer powder particles containing the minor amount of reactive monomer and inert diluent are discharged through a discharge port 19 at the bottom of the second flash tank and transported to a granulation unit or a further devolatilization unit via line 23. The gaseous stream withdrawn from the top of the second flash tank 4 is passed to a scrubber 5 for removing oligomers and heavy components that may be present. The gas material at the top of the washing tower 5 is cooled and separated to obtain a liquid phase material, then the liquid phase material is compressed by a first compressor 6 and returns to the first separation tower 3, a part of inert washing liquid at the bottom of the washing tower 5 is sent to a first tower plate at the top of the washing tower 5 through a first conveying pump 7, and the rest part is continuously or intermittently discharged to a downstream working section, so that heavy components are prevented from accumulating in the washing tower 5. The material mainly containing unreacted monomers at the top of the second separation tower 8 is discharged from a discharge port at the top of the second separation tower, then passes through the second heat exchanger 10 and the third heat exchanger 12 to be completely condensed, part of the condensate is decompressed and returns to the second separation tower 8 through a pipeline 26, and the rest of the condensate is pressurized and returns to the polymerization reaction unit through a pipeline 27. The feed, based on inert diluent, at the bottom of the second separation column 8 is returned to the polymerization unit via the second transfer pump 11 via the line 28. The three streams 25, 27 and 28 returning to the polymerization unit can be fed to different polymerization reactors separately or after mixing different streams in a certain ratio.

The invention is economical in that the first separation tower 3 and the second separation tower 8 are directly separated to obtain materials meeting the requirements of different polymerization reactors.

According to some preferred embodiments of the present invention, the propylene polymer slurry 14 withdrawn from the polymerization reactor is subjected to heat exchange in the first heat exchanger 1, then the temperature is raised by 0 to 30 ℃ and then fed into the first flash tank 2.

According to some preferred embodiments of the present invention, the workload and energy consumption of the first compressor 6 can be reduced by increasing the temperature of the first heat exchanger and decreasing the pressure of the first flash tank to vaporize most of the liquid and flash remove most of the small molecule material dissolved in the polymer in the first flash tank 2.

FIG. 2 is a flow chart of a separation and recovery device of another embodiment of the invention, which is particularly suitable for the working condition that the temperature difference between the top of the second separation tower and the bottom of the second separation tower is more than 45 ℃, and comprises the following main devices and units:

a first heat exchanger 1 for preheating a polymer slurry 14 discharged from a polymerization reactor;

a first flash tank 2 for preliminarily separating polymer particle powder, a diluent and an unreacted monomer;

a first separation column 3 for removing polymer particle powder and recovering unreacted monomers;

a second flash tank 4 for separating the polymer pellet powder and the diluent, unreacted monomer, etc. dissolved in the polymer pellet powder;

a washing tower 5 for washing the gas phase material from the top of the second flash tank 4;

a first compressor 6 for conveying the top material from the washing column 5 to the first separation column 3 under pressure;

a first transfer pump 7 for returning the inert scrubbing liquid to the top of the scrubbing tower 5 and sending part of the inert scrubbing liquid to the post-treatment unit;

a second separation column 8 for separating the unreacted monomer and the inert diluent;

a second conveying pump 11 for conveying the tower bottom material of the second separation tower 8;

a third heat exchanger 12 for cooling the overhead material from the second separation column 8.

A fourth heat exchanger 13 for heating the still material from the second separation column 8.

The flow of the separation and recovery device shown in fig. 2 is different from that shown in fig. 1 only in that the propylene monomer gas-phase material led out from the discharge port at the top of the second separation tower is directly condensed by the third heat exchanger 12 to obtain the propylene monomer enriched material, part of the condensate is pressurized and returned to the second separation tower 8 through the pipeline 26, and the rest of the condensate is pressurized and returned to the polymerization reaction unit through the pipeline 27. The feed, based on inert diluent, at the bottom of the second separation column 8 is returned to the polymerization unit via the second transfer pump 11 via the line 28.

In the existing bulk polypropylene process, no diluent is used for regulating and controlling the yield of each reactor, and because the residence time of the reactors is a fixed value, the yields of two reactors are fixed values under the same catalyst and the same temperature. Compared with the prior patent, the invention can combine three materials obtained by two separation towers and fresh feed materials to respectively enter different reactors, thereby being capable of more flexibly regulating and controlling the yield of propylene polymers in different reactors. It is to be noted that the present invention is also particularly suitable for supported catalysts with high activity, such as supported metallocene catalysts, where the ratio of propylene to diluent entering the prepolymerization reactor can be controlled, thereby avoiding particle breakage due to high polymerization activity of the catalyst in the prepolymerization reactor.

Example 1

The method comprises the steps of conveying a propylene monomer, a metallocene catalyst and a diluent into a prepolymerization reactor to carry out prepolymerization reaction to obtain a prepolymer, and then carrying out polymerization reaction on the obtained prepolymer in a polymerization reactor with the propylene monomer and hydrogen to obtain a liquid-solid mixture of polypropylene, unreacted monomer and an inert diluent, wherein the mass flow rate of the polypropylene in the liquid-solid mixture is 9 tons/hour, and the output of the two reactors is 6.04t/h and 2.96t/h respectively. The diluent is isobutane. The resulting liquid-solid mixture was separated using the apparatus scheme shown in FIG. 1, and the molar fraction of diluent in the liquid-solid mixture based on the total liquid phase was 22.69%. The outlet of the first heat exchanger 1 had a temperature of 80 ℃. The number of the tower plates of the first separation tower 3 is 19, the tower top temperature is 44 ℃, the tower bottom temperature is 72 ℃, and the pressure is 1.85 MPa. A mixture of propylene and diluent is withdrawn from a second outlet of the first separation column 3 at a distance of 4 trays from the column bottom and introduced into a second separation column 8. The number of the tower plates of the second separation tower 8 is 16, the top temperature of the second separation tower 8 is 32 ℃, the top material of the second separation tower 8 is heated to 96 ℃ after being compressed by the second compressor 9, the bottom temperature of the tower is 73 ℃, and the pressure of the second separation tower is 1.3 MPa. The temperature of the second flash tank is 65 ℃, the pressure is 2bar, the washing tower is a sieve plate tower, the liquid phase material and the gas material are in reverse contact, the pressure of the washing tower is 2bar, and the temperature of the top of the tower is 25 ℃. The outlet pressure of the first compressor 6 is 1.9MPa, and the outlet pressure of the second compressor 9 is 3.5 MPa. The mass balance table is shown in table 1.

No fines and oligomers were detected in the feed to the second separation column. The heat load of the top of the first separation tower is 3110MJ/h, the heat load of the bottom of the first separation tower is 320MJ/h, the heat load of the top of the second separation tower is 1260+839MJ/h, and the heat load of the bottom of the second separation tower is 1621 MJ/h. The mole fraction of the inert diluent in the tower bottom is 90 percent. The first compressor has a power of 114.6MJ/h and the second compressor has a power of 364 MJ/h. The mass fraction of volatile components in the polypropylene at the outlet of the second flash tank is 1.21g/g polypropylene. And respectively recycling the separated propylene monomer material and the inert diluent material to the prepolymerization reactor or the polymerization reactor for reaction.

TABLE 1

Example 2

The method comprises the steps of conveying a propylene monomer, a metallocene catalyst and a diluent into a prepolymerization reactor to carry out prepolymerization reaction to obtain a prepolymer, and then carrying out polymerization reaction on the obtained prepolymer in a polymerization reactor with the propylene monomer and hydrogen to obtain a liquid-solid mixture of polypropylene, unreacted monomer and an inert diluent, wherein the mass flow rate of the polypropylene in the liquid-solid mixture is 9 tons/hour, and the output of the two reactors is 6.17t/h and 2.83t/h respectively. The diluent is isobutane. The resulting liquid-solid mixture was separated using the apparatus scheme shown in FIG. 1, with a mole fraction of liquid-solid mixture diluent in the total liquid phase of 41.83%. The outlet of the first heat exchanger 1 had a temperature of 80 ℃. The number of the tower plates of the first separation tower 3 is 19, the tower top temperature is 42 ℃, the tower bottom temperature is 80 ℃, and the pressure is 1.85 MPa. A mixture of propylene and diluent is withdrawn from a second outlet of the first separation column 3 at a distance of 4 trays from the column bottom and introduced into a second separation column 8. The number of the tower plates of the second separation tower 8 is 16, the temperature at the top of the second separation tower 8 is 34 ℃, the pressure is 1.3MPa, the material at the top of the second separation tower 8 is heated to 92 ℃ after being compressed by the second compressor 9, and the temperature of the tower kettle is 73 ℃. The temperature of the second flash tank is 67 ℃, the pressure is 2bar, the washing tower is a sieve plate tower, the liquid phase material and the gas material are in reverse contact, the pressure of the washing tower is 2bar, and the temperature of the top of the tower is 26 ℃. The outlet pressure of the first compressor 6 is 1.9MPa, and the outlet pressure of the second compressor 9 is 3.3 MPa. The mass balance table is shown in table 2.

No fines and oligomers were detected in the feed to the second separation column. 2640MJ/h of tower top heat load of the first separation tower, 154MJ/h of tower bottom heat load, 1260+1159MJ/h of tower top heat load of the second separation tower, 1830MJ/h of tower bottom heat load of the first separation tower and 90 percent of inert diluent mole fraction in the tower bottom. The power of the first compressor is 98.9MJ/h, and the power of the second compressor is 389 MJ/h. The mass fraction of volatile components in the polypropylene at the outlet of the second flash tank is 1.17g/g polypropylene. And respectively recycling the separated propylene monomer material and the inert diluent material to the prepolymerization reactor or the polymerization reactor for reaction.

TABLE 2

Example 3

The method comprises the steps of conveying a propylene monomer, a metallocene catalyst and a diluent into a prepolymerization reactor to carry out prepolymerization reaction to obtain a prepolymer, and then carrying out polymerization reaction on the obtained prepolymer in a polymerization reactor with the propylene monomer and hydrogen to obtain a liquid-solid mixture of polypropylene, unreacted monomer and an inert diluent, wherein the mass flow rate of the polypropylene in the liquid-solid mixture is 9.3 tons/hour, and the output of the two reactors is 6.29t/h and 3.01t/h respectively. The diluent is isopentane. The resulting liquid-solid mixture was separated using the apparatus scheme shown in FIG. 2, and the molar fraction of diluent in the liquid-solid mixture based on the total liquid phase was 13.57%. The outlet of the first heat exchanger 1 had a temperature of 80 ℃. The number of the tower plates of the first separation tower 3 is 19, the tower top temperature is 42 ℃, the tower bottom temperature is 81 ℃, and the pressure is 1.85 MPa. A mixture of propylene and diluent is withdrawn from a second outlet of the first separation column 3 at a distance of 4 trays from the column bottom and introduced into a second separation column 8. The number of the tower plates of the second separation tower 8 is 16, the temperature of the top of the second separation tower 8 is 30 ℃, the temperature of the bottom of the second separation tower is 114 ℃, and the pressure is 1.3 MPa. The outlet pressure of the first compressor 6 was 1.9 MPa. The temperature of the second flash tank is 61 ℃, the pressure is 2bar, the washing tower is a sieve plate tower, the liquid phase material and the gas material are in reverse contact, the pressure of the washing tower is 2bar, and the temperature of the top of the tower is 25 ℃. The mass balance table is shown in table 3.

No fines and oligomers were detected in the feed to the second separation column. The heat load of the top of the first separation tower is 3058MJ/h, the heat load of the bottom of the first separation tower is 354MJ/h, the heat load of the top of the second separation tower is 600MJ/h, the heat load of the bottom of the first separation tower is 630MJ/h, and the mole fraction of the inert diluent in the bottom of the first separation tower is 90 percent. The first compressor power is 140.2 MJ/h. The mass fraction of volatile components in the polypropylene at the outlet of the second flash tank is 1.93g/g polypropylene. And respectively recycling the separated propylene monomer material and the inert diluent material to the prepolymerization reactor or the polymerization reactor for reaction.

TABLE 3

Example 4

The process steps differ from example 1 only in that the propylene and diluent mixture is withdrawn from the first separation column 3 at a distance from the tray of column bottom 1 and introduced into the second separation column 8. In contrast to example 1, fines and oligomers were detected in the feed to the second separation column and these solvents containing fines and oligomers were returned to the reaction unit, thus risking plugging of equipment and piping between the second separation column and the reaction unit.

Example 5

The process steps are the same as in example 3, except that the second separation column 8 has a top temperature of 63 ℃ and a bottom temperature of 157 ℃. Example 5 has higher energy consumption than example 3. The second separation column had a top heat load of 685MJ/h, 14% higher than example 3 and a bottom heat load of 1018MJ/h, 62% higher than example 3.

Comparative example 1

The method comprises the steps of conveying a propylene monomer and a metallocene catalyst into a prepolymerization reactor to carry out prepolymerization reaction to obtain a prepolymer, and carrying out polymerization reaction on the prepolymer, the propylene monomer and hydrogen in a polymerization reactor to obtain a liquid-solid mixture of polypropylene and unreacted monomer, wherein the mass flow of the polypropylene in the liquid-solid mixture is 9 tons/h, and the output of the two reactors is 5.76t/h and 3.24t/h respectively. And (3) separating the liquid-solid mixture in the flow path of the device shown in the figure 2 but not comprising the second discharge port and the second separation tower. And recycling the separated propylene monomer material to the reaction unit for reaction. Compared with the embodiment, the concentration of propylene in the comparative example 1 is constant, and the residence time of the catalyst in different reactors can be regulated and controlled only by regulating and controlling the flow rate of propylene, so that the capacity of different reactors can be regulated and controlled, and the effect of regulating and controlling the capacity of different reactors is limited.

Comparative example 2

The method comprises the steps of conveying a propylene monomer, a metallocene catalyst and a diluent into a prepolymerization reactor to carry out prepolymerization reaction to obtain a prepolymer, and then carrying out polymerization reaction on the obtained prepolymer in a polymerization reactor with the propylene monomer and hydrogen to obtain a liquid-solid mixture of polypropylene, unreacted monomer and an inert diluent, wherein the mass flow of the polypropylene in the liquid-solid mixture is 9 tons/hour, and the output of the two reactors is 5.52t/h and 3.48t/h respectively. The diluent is isobutane. And (3) separating the liquid-solid mixture by using the device flow shown in the figure 2 but not comprising the second discharge port and the second separation tower. The separated mixed material of the unreacted monomer and the diluent is recovered from the top of the first separation column 3 and then returned to the reaction unit. In comparison with the examples, the unreacted propylene in comparative example 2 was returned to a different reactor together with the diluent. The same problem exists in comparative example 2 and comparative example 1, namely the flow rates of propylene and diluent entering different reactors cannot be independently regulated, so that the concentration of propylene in the two reactors in comparative example 2 has a narrow variation range and has a limited effect on regulating the capacity of different reactors.

Comparative example 3

In the device flow shown in the figure 1 but not comprising the second discharge port and the second separation tower, a liquid-solid mixture of polypropylene and unreacted monomers is separated. The pressure of the first flash tank 2 is 2.6MPa, and the heating power of the first heat exchanger 1 is 0. Other conditions were the same as in example 1. Compared with the example 1, the concentration of propylene in the comparative example 3 is constant, and the residence time of the catalyst in different reactors can be regulated and controlled only by regulating and controlling the flow rate of propylene, so that the capacity of different reactors can be regulated and controlled, and the effect of regulating and controlling the capacity of different reactors is limited. In addition, the first compressor power in comparative example 3 was 210MJ/h, 83% higher than that of example 1, and the mass fraction of volatiles in the polypropylene at the outlet of the second flash tank in comparative example 3 was 1.82g/g polypropylene, 50% higher than that of example 1.

It should be noted that the above-mentioned embodiments are only for explaining the present invention, and do not constitute any limitation to the present invention. The present invention has been described with reference to exemplary embodiments, but the words which have been used herein are words of description and illustration, rather than words of limitation. The invention can be modified, as prescribed, within the scope of the claims and without departing from the scope and spirit of the invention. Although the invention has been described herein with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein, but rather extends to all other methods and applications having the same functionality.