OLEFIN POLYMERIZATION APPARATUS AND OLEFIN POLYMERIZATION PROCESS

Abstract

Provided in the present invention are an olefin polymerization apparatus and an olefin polymerization process. The following operations and effects can be realized by the apparatus or method provided in the present invention: the gas material discharged from the polymerization reactor is condensed, after the gas-liquid separation, the resulting gas portion is recycled to the reactor to form a circulation loop; the condensate can be selectively introduced to the polymerization reactor, in order to achieve the free switch between the homopolymerization reaction and the copolymerization reaction or between different copolymerization reactions, and at the same time the condensate can absorb the heat generated by the reaction. By using the apparatus and method provided in the present invention, polyolefin products having excellent mechanical properties and processability can be prepared as needed.

Claims

1. An olefin polymerization apparatus, comprising: a polymerization reactor for olefin homopolymerization and/or copolymerization reaction; a condensation unit for condensing a gas material discharged from the polymerization reactor; a gas-liquid separation unit for carrying out gas-liquid separation on the material from the condensation unit to generate a gas and a condensate; storage tanks for receiving the condensate discharged from the gas-liquid separation unit; and a control unit, wherein, the gas from the gas-liquid separation unit is introduced into the polymerization reactor, and the condensate from the storage tanks is selectively introduced into the polymerization reactor under the action of the control unit to achieve the switch between the olefin homopolymerization and copolymerization in the polymerization reactor.

2. The apparatus according to claim 1, characterized in that, the numbers of the storage tanks are 2 or more, preferably 2 to 4, and the storage tanks are respectively used for storing the condensate containing different comonomers.

3. The apparatus according to claim 2, characterized in that, the condensate in each of the storage tanks is selectively introduced into the polymerization reactor under the action of the control unit to achieve the switch between different copolymerization reactions in the polymerization reactor.

4. The apparatus according to any one of claims 1 to 3, characterized in that, the polymerization reactor is a fluidized bed reactor.

5. The apparatus according to any one of claims 1 to 4, characterized in that, the polymerization reactor comprises two or more, preferably 3 to 6 condensate inlets for receiving condensate; any two of the inlets are located in the same water level or in different water levels.

6. The apparatus according to any one of claims 1 to 5, characterized in that, the gas-liquid separation unit is a buffer tank type separator or a cyclone type separator.

7. The apparatus according to any one of claims 1 to 6, characterized in that, the apparatus further comprises a compression unit, and the gas material discharged from the polymerization reactor is firstly compressed by the compression unit and then enters into the condensation unit.

8. The apparatus according to any one of claims 1 to 7, characterized in that, pumps are connected between the storage tanks and the polymerization reactor.

9. The apparatus according to any one of claims 2 to 8, characterized in that, the apparatus can be controlled such that the switch frequency between the olefin homopolymerization and copolymerization in the polymerization reactor is at least 1 time/hour, preferably greater than or equal to 3 times/hour.

10. The apparatus according to any one of claims 2 to 9, characterized in that, the apparatus can be controlled such that the switch frequency between the different copolymerization reactions of olefins in the polymerization reactor is at least 1 time/hour, preferably greater than or equal to 3 times/hour.

11. An olefin polymerization process, includes the following steps: 1) reacting an olefin-containing reaction feedstock in a polymerization reactor and discharging a gas material from the polymerization reactor; 2) condensing the gas material, and then separating a gas and at least a portion of condensate through a gas-liquid separation unit; and 3) circulating the gas separated by the gas-liquid separation unit into the polymerization reactor, thereby forming a circulation loop, and introducing the condensate into storage tanks; wherein, the condensate in the storage tanks comprises a comonomer, and the condensate is controlled to be selectively introduced into the polymerization reactor to achieve switch between olefin homopolymerization and copolymerization in the polymerization reactor.

12. The process according to claim 11, characterized in that, the process is implemented on the apparatus according to any one of claims 1 to 10.

13. The process according to claim 11 or 12, characterized in that, the olefin is selected from ethylene and/or -olefins; the comonomer is selected from olefins with less that 18 carbon atoms, preferably selected from butene, hexene and octene.

14. The process according to any one of claims 11 to 13, characterized in that, the numbers of the storage tanks are 2 or more, preferably 2 to 4, which are respectively used for storing the condensate containing different comonomers; and the condensate in each of the storage tanks is controlled to be selectively introduced into the polymerization reactor to achieve switch between homopolymerization and copolymerization of olefins or the different copolymerization reactions of olefins in the polymerization reactor.

15. The process according to any one of claims 11 to 14, characterized in that, the switch frequency between the olefin homopolymerization and copolymerization is at least 1 time/hour, preferably greater than or equal to 3 times/hour.

16. The process according to claim 14 or 15, characterized in that, the switch frequency between different copolymerization reactions of olefins is at least 1 time/hour, preferably greater than or equal to 3 times/hour.

17. The process according to any one of claims 11 to 16, characterized in that, the operation time of each homopolymerization stage is maintained for 3-60 minutes, preferably 8-20 minutes: the operation time of each copolymerization stage is maintained for 5-60 minutes, preferably 8-20 minutes.

18. The process according to claim 17, characterized in that, when the comonomer is butene, the operation time of homopolymerization reaction is at least 18 minutes; when the comonomer is hexene, the operation time of homopolymerization reaction is at least 6 minutes; when the comonomer is octene or other olefins with higher molecular weights, the operation time of homopolymerization reaction is at least 3 minutes.

19. The process according to any one of claims 11 to 18, characterized in that, in the copolymerization reaction stage, the condensate content in the stream resulting from the condensation of the gas material is 5-50 wt %, preferably 10-30 wt % based on the weight of the stream.

20. The process according to any one of claims 11 to 19, characterized in that, 30-100 wt %, preferably 60-300 wt % of the total condensate entering the gas-liquid separation unit is separated by the gas-liquid separation unit.

21. The process according to any one of claims 11 to 20, characterized in that, in the polymerization process of the process, at least one of a cocatalyst, a polymeric monomer, an antistatic agent, a chain transfer agent, a molecular weight modifier, a condensing agent and an inert gas are introduced into the reactor and/or the circulation loop.

22. The process according to claim 21, characterized in that, the condensing agent is selected from at least one of C.sub.4-C.sub.7 saturated linear or branched alkanes, and C.sub.4-C.sub.7 cycloalkanes; preferably at least one of n-pentane, iso-pentane, hexane and heptane; most preferably iso-pentane and/or hexane.

23. The process according to any one of claims 11 to 22, characterized in that, the reaction pressure of the reaction in the step 1) is 0.5-10 MPa, preferably 1.5-5 MPa; and the reaction temperature is 40-150 C., preferably 50-120 C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0085] The drawings, which are intended to provide a further understanding of the present invention and form a part of the specification, are intended to be illustrative of the present invention in conjunction with the examples of the present invention and are not to be construed as limiting the present invention.

[0086] FIG. 1 is an olefin polymerization apparatus and a simplified operational flow chart in one particular embodiment of the present invention.

[0087] FIG. 2 is a schematic view showing the arrangement of condensate inlets above the polymerization distribution plate in one particular embodiment of the present invention, wherein FIGS. 2(a), (b), (c) and (d) show the conditions in which 1, 2, 3 and 4 condensate inlets are arranged, respectively.

[0088] FIG. 3 shows the change in the amount of liquid injected from the condensate inlets over time according to Example 4 disclosed herein.

SPECIFIC EMBODIMENTS

[0089] The embodiments of the present invention will be described in detail with reference to the drawings and examples, and how the technical solutions of the present invention can be applied to solve the technical problems and the realization of the technical effects can be fully understood and implemented. It is to be noted that the various examples of the present invention and the various features in the examples may be combined with each other as long as they are not conflicted, and the resulting technical solutions are within the scope of the present invention.

[0090] The partial performance parameters of the polyolefin products in the examples are determined by the following method.

[0091] (1) Melt flow rate (MFR): the melt flow rate is measured according to the conditions in GB/T 19466.3-2004 (190 C., load of 2.16 kg), and usually noted as MI2.16.

[0092] (2) Density: measured according to the method in GB/T 1033.2-2010.

[0093] (3) Tensile yield stress: measured in both machine direction (MD) and transverse direction (TD) according to ASTM D882.

[0094] (4) Elongation at break: the elongation at break is measured according to the method in GB/T 6344-2008.

[0095] (5) Free-falling dart impact value: the free-falling dart impact value is measured according to the A method in GB/T 9639.1-2008.

[0096] (6) Density: measured according to the method in GB/T 2410-2008.

[0097] FIG. 1 shows the olefin polymerization apparatus and the simplified operational flow according to one particular embodiment of the present invention. The shown olefin polymerization apparatus comprises the following components: [0098] a fluidized bed reactor 2 for homopolymerization reaction and copolymerization reaction, in which a distribution plate 1 is arranged; [0099] a gas circulation pipeline 10 for circulating the gas material from the outlet of the reactor 2 to the gas-phase distribution area of the reactor 2; [0100] a compression unit 3 for compressing the material in the circulation pipeline 10; [0101] a heat: exchanger 4 for cooling the material in the circulation pipeline 10; [0102] a gas-liquid separation unit 5; [0103] a first storage tank 6 and a second storage tank 8 (exemplary) for storing the condensate; [0104] fluid pipelines 11 and 12 (exemplary) for introducing the condensing agent into the reactor 2; [0105] a first feeding pump 7 and a second feeding pump 9 (exemplary) for introducing the condensate into the reactor 2; [0106] a pipeline 13 for introducing a polymerization catalyst into the reactor 2; [0107] a pipeline 14 for taking out the solid polyolefin from the reactor 2; [0108] fluid pipelines 15 and 16 (exemplary) for introducing the gas material into the reactor 2; and [0109] a fluid pipeline 1 (exemplary) for introducing the high-boiling-point comonomer and the condensing agent into the reactor 2.

[0110] Wherein, the circulation gas stream after the reaction flows out from the top of the fluidized bed reactor 2, enters the gas circulation pipeline 10, and flows through the compression unit 3 and the heat exchanger 4, and the partially condensed circulation stream flowing from the heat exchanger 4 enters the gas-liquid separation unit 5, the liquid material in the gas-liquid separation unit 5 is partially or completely separated and enters the first storage tank 6 and the second storage tank 8, and the unseparated liquid material enters the gas-phase distribution area of the reactor 2 with the circulation stream to complete one circulation.

[0111] In the homopolymerization reaction stage, the condensate in the first storage tank 6 and the second storage tank 8 is no longer introduced into the fluidized bed reactor 2; in the copolymerization reaction stage, the condensate in the first storage tank 6 and the second storage tank 8 is introduced to the position above the distribution plate 1 of the fluidized bed reactor 2 from the fluid pipeline 11 and 12 by the first feeding pump 7 and the second feeding pump 9, respectively. Wherein the first storage tank 6 and the second storage tank 8 may each contain the condensate containing different major comonomers; and certainly may also contain the same condensate. The condensate in one or more storage tanks may be controlled by the control unit (not shown) to be introduced into the reactor 2 as needed.

[0112] The fresh reaction feed gas required for the reaction is fed into the gas circulation pipeline 10 through the pipeline 15, the molecular weight modifier or the like can enter the gas circulation pipeline 10 through the pipeline 16, the high-boiling-point comonomer and the condensing agent can enter the gas circulation pipeline 10 through the pipeline 17, the catalyst intermittently or continuously enters the reactor 2 through the pipeline 13, and the solid-phase polymer produced in the polymerization reaction is intermittently or continuously discharged from the pipeline 14 and transported to the downstream stage for further processing.

[0113] At least one, preferably 3-6 liquid introduction points, i.e., condensate inlets, are distributed in the axial and radial directions of the reactor. FIG. 2 shows the distribution of the liquid introduction points in the radial direction of the reactor. FIGS. 2 (a)-(d) show the conditions in which 1-4 liquid introduction points are arranged in a plane, respectively. During the copolymerization reaction operation, the condensate in the first storage tank 6 and the second storage tank 8 are continuously fed into the reactor 2 from the liquid introduction points through the first feeding pump 7 and the second feeding pump 9.

EXAMPLE 1

[0114] The linear low density polyethylene (LLDPE) is produced in the fluidized bed polymerization reactor apparatus shown in FIG. 1. Under the action of a Ziegler-Natta (Z-N) catalyst system, the polymerization reaction temperature is 88 C., the pressure is 2.1 MPa, and the superficial velocity of the reactor is 0.61 m/s.

[0115] When the compolymerization reaction is switched into homopolymerization reaction, the circulation gas in the pipeline 10 includes hydrogen, nitrogen, methane, ethane, ethylene, butene, inert C.sub.4 and isopentane, the pressure is 2.1 MPa and the temperature is 90 C. After multiple circulations of the circulation gas, the circulation gas stream from the heat exchanger 4 contained no condensate, and the gas-phase density is 28.0 kg/m.sup.3; and gas-solid two-phase reaction is performed in the fluidized bed reactor, and ethylene is contacted with the continuously added catalyst to produce solid polyolefins.

[0116] When the homopolymerization reaction is switched into compolymerization reaction, the circulation gas in the pipeline 10 includes hydrogen, nitrogen, methane, ethane, ethylene, butene, inert C.sub.4 and isopentane. The circulation gas stream from the heat exchanger 4 contained 15 wt % of condensate, the condensate contained isopentane and -butene and the density is 593 kg/m.sup.3. When passing through the external gas-liquid separator 5, 80 wt % of the total condensate in the circulation gas stream entered the first storage tank 6, and the condensate not entering the first storage tank 6 entered the reactor 2 with the circulation gas stream. The condensate rich in the comonomer in the first storage tank 6 is introduced into the fluidized bed through the first feeding pump 7 for copolymerization reaction.

[0117] The above-mentioned copolymerization and homopolymerization reactions are switched repeatedly at 3 times/hour. The space-time yield of the system is 135 kg/m.sup.3.Math.hr; and the production capacity is increased by 50% compared to those of conventional gas-phase process.

[0118] The density of the linear low density polyethylene produced according to the example is 0.9210 g/cm.sup.3, the melt flow rate is 0.78 g/10 min, the tensile yield stress is up to 11.6 MPa, the elongation at break is 765%, the haze is 11.7%, and the free-falling dart impact damage weight is 114 g.

EXAMPLE 2

[0119] The linear low density polyethylene (LLDPE) is produced in the fluidized bed polymerization reactor apparatus shown in FIG. 1 by using a stepwise polymerization reaction process. Under the action of the Z-N catalyst system, the polymerization reaction temperature is 87 C., the pressure is 2.1 MPa, and the superficial velocity of the reactor is 0.72 m/s.

[0120] When the compolymerization reaction is switched into homopolymerization reaction, the circulation gas in the pipeline 10 includes hydrogen, nitrogen, methane, ethane, ethylene, isopentane and hexene, the pressure is 2.1 MPa and the temperature is 87 C. After multiple circulations of the circulation gas, the circulation gas stream from the heat exchanger 4 contained no condensate, and the gas-phase density is 28.8 kg/m.sup.3; and gas-solid two-phase reaction is performed in the fluidized bed reactor, and ethylene is contacted with the continuously added catalyst to produce the solid-phase polymer.

[0121] When the homopolymerization reaction is switched into the compolymerization reaction, the circulation gas in the pipeline included hydrogen, nitrogen, methane, ethane, ethylene, isopentane and hexene, the circulation gas stream from the heat exchanger 4 contained 30 wt % of condensate, the condensate contained isopentane and -hexene, the density is 601 kg/m.sup.3 and the gas-phase density is 29.1 kg/m.sup.3. After separation and enrichment of the gas-liquid separator 5, the condensate flowing into the second storage tank 8 can reach 50 wt % of the total condensate in the circulation gas stream, and is injected into the fluidized bed from three condensate inlets in different heights above the distribution plate through the second feeding pump 9. In this process, the pressure of the second feeding pump 9 is 3.5 MPa and the rate at which the liquid-phase material is injected into the fluidized bed reactor 2 is 60 t/hr. The condensate is atomized and injected into the fluidized bed through nozzles.

[0122] The above-mentioned copolymerization and homopolymerization reactions are switched repeatedly at 5 times/hour. The space-time yield of the system is 151 kg/m.sup.3.Math.hr; and the production capacity is increased by 68% compared to those of conventional gas-phase process.

[0123] The density of the linear low density polyethylene produced according to the example is 0.9175 g/cm.sup.3, the melt flow rate is 1.9 g/10 min, the tensile yield stress is up to 9.9 MPa, the elongation at break is 670%, the haze is 17.9%, and the free-failing dart impact damage weight is 142 g.

EXAMPLE 3

[0124] The linear low density polyethylene (LLDPE) is produced in the fluidized bed polymerization reactor apparatus shows in FIG. 1 by using a stepwise polymerization reaction process. Under the action of the Z-N catalyst system, the polymerization reaction temperature is 85 C., the pressure is 2.3 MPa, and the superficial velocity of the reactor is 0.70 m/s.

[0125] When the compolymerization reaction is switched into homopolymerization reaction, the circulation gas in the pipeline 10 includes hydrogen, nitrogen, methane, ethane, ethylene, hexene, hexane and the like, the pressure is 2.3 MPa and the temperature is 86 C. After multiple circulations of the circulation gas, the circulation gas stream from the heat exchanger 4 contained no condensate, and the gas-phase density is 29.1 kg/m.sup.3; and gas-solid two-phase reaction is performed in the fluidized bed reactor, and ethylene is contacted with the continuously added catalyst to produce the solid-phase polymer.

[0126] When the homopolymerization reaction is switched into the compolymerization reaction, the circulation gas stream from the heat exchanger 4 contained 10 wt % of condensate, and the condensate contained hexene and hexane, the density is 618.7 kg/m.sup.3 and the gas-phase density is 30.0 kg/m.sup.3. After separation and enrichment of the gas-liquid separator 5, the condensate entering the second storage tank 8 can reach 65 wt % of the total condensate in the circulation gas stream, and is injected into the reactor from three liquid introduction points in the same level through the second feeding pump 9. The distribution of the three liquid introduction points is shown in FIG. 2 (c). The flow rate of the introduced liquid material is 26 t/h, the temperature is 52 C., and the pressure is 3.6 MPa. The condensate is atomized and injected into the reactor through nozzles.

[0127] The above-mentioned copolymerization and homopolymerization reactions are switched repeatedly at 6 times/hour. The space-time yield of the fluidized bed reactor is 140 kg/m.sup.3.Math.hr; and the production capacity is increased by 56% compared to those of conventional gas-phase process.

[0128] The density of the linear low density polyethylene produced according to the example is 0.9218 g/cm.sup.3, the melt flow rate is 0.95 g/10 min, the tensile yield stress is up to 11.7 MPa, the elongation at break is 635%, the haze is 13.0%, and the free-falling dart impact damage weight is 168 g.

EXAMPLE 4

[0129] The linear low density polyethylene (LLDPE) is produced in the fluidized bed polymerization reactor apparatus shown in FIG. 1 by using a stepwise polymerization reaction process. Under the action of the Z-N catalyst system, the polymerization reaction temperature is 85 C., the pressure is 2.5 MPa, and the superficial velocity of the reactor is 0.67 m/s.

[0130] When the compolymerization reaction is switched into the homopolymerization reaction, the circulation gas in the pipeline 10 includes hydrogen, nitrogen, methane, ethane, ethylene, isopentane, hexene and the like, the pressure is 2.5 MPa and the temperature is 86 C. After multiple circulations of the circulation gas, the circulation gas stream from the heat exchanger 4 contained no condensate, and the gas-phase density is 28.9 kg/m.sup.3; and gas-solid two-phase reaction is performed in the fluidized bed reactor, and ethylene is contacted with the continuously added catalyst to produce the solid-phase polymer.

[0131] When the homopolymerization reaction is switched into the compolymerization reaction, the circulation gas stream from the heat exchanger 4 contained 28 wt % of condensate, the liquid phase is isopentane and hexene, the density is 620.4 kg/m.sup.3 and the gas-phase density is 31.2 kg/m.sup.3. After separation and enrichment of the gas-liquid separator 5, the condensate entering the second storage tank 8 can reach 70 wt % of the total condensate in the circulation gas stream, and is introduced into the reactor from four liquid introduction points in the same level on the sidewall of the reactor through the second feeding pump 9. The distribution of the four liquid introduction points is shown in FIG. 2 (d). The flow rate of the introduced liquid material is 56 t/h, and the pressure is 3.9 MPa. At the liquid introduction points, the condensate is atomized and injected into the reactor through nozzles.

[0132] The above-mentioned copolymerization and homopolymerization reactions are switched repeatedly at 4 times/hour. The space-time yield of the fluidized bed reactor is 165 kg/m.sup.3.Math.hr; and the production capacity is increased by 83%.

[0133] The density of the linear low density polyethylene produced according to the example 4 is 0.9119 g/cm.sup.3, the melt flow rate is 0.87 g/10 min, the tensile yield stress is up to 8.4 MPa, the elongation at break is 864%, the haze decreases to 10.3%, and the free-falling dart impact damage weight is 149 g.

[0134] FIG. 3 is a schematic view showing the change in the amount of liquid injected from the side wall of the reactor over time in the example. It can be seen from FIG. 3 that the copolymerization time is 10 minutes and the homopolymerization time is 15 minutes. It is to be noted that in the example, the separation efficiency of the gas-liquid separator 5 is 70 wt %, i.e., after the gas-liquid mixed stream discharged irons the heat exchanger 4 passes through the gas-liquid separator 5, the condensate accounting for 70 wt % of the condensate in the circulation gas stream enters the second storage tank 8 and enters the reactor 2 from the liquid introduction points on the sidewall through the second feeding pump 9.

[0135] In this example, the liquid is introduced from the sidewall of the reactor, so that the liquid accumulation on the distribution plate is avoided, the introduction amount of the condensate in the reactor can be increased and the space-time yield can be improved; and in addition, a plurality of low-temperature/comonomer enrichment areas and high-temperature areas are formed in the reactor, so that the products with wide molecular weight distribution can be produced.

EXAMPLE 5

[0136] The linear low density polyethylene (LLDPE) is produced in the fluidized bed polymerization reactor apparatus shown in FIG. 1 by using a stepwise polymerization reaction process. Under the action of the Z-N catalyst system, the polymerization reaction temperature is 80 C., the pressure is 2.3 MPa, and the superficial velocity of the reactor is 0.67 m/s.

[0137] When the compolymerization reaction is switched into the homopolymerization reaction, the circulation gas in the pipeline 10 includes hydrogen, nitrogen, methane, ethane, ethylene, butene, insert C.sub.4, a small amount of isopentane, a small amount of hexene and the like, the pressure is 2.3 MPa and the temperature is 80 C. After multiple circulations of the circulation gas, the circulation gas stream from the heat exchanger 4 contained no condensate; and gas-solid two-phase reaction is performed in the fluidized bed reactor, and ethylene is contacted with the continuously added catalyst to produce the solid-phase polymer.

[0138] When the homopolymerization reaction is switched into the compolymerization reaction, the circulation gas stream from the heat exchanger 4 contained 9 wt % of condensate, the liquid phase is butene and isopentane, the density is 580 kg/m.sup.3 and the gas-phase density is 30.9 kg/m.sup.3. After separation and enrichment of the gas-liquid separator 5, the condensate entering the first storage tank 6 can reach 65 wt % of the total condensate in the circulation gas stream, and is injected into the reactor from liquid introduction points shown in FIG. 2(b) through the first feeding pump 7. The flow rate of the liquid material introduced from the sidewall is 22 t/h, and the pressure is 3.7 MPa.

[0139] When the homopolymerization reaction is switched into the compolymerization reaction, the circulation gas stream from the heat exchanger 4 contained 22 wt % of condensate, the liquid phase is isopentane and hexene, the density is 616.8 kg/m.sup.3 and the gas-phase density is 28.3 kg/m.sup.3. After separation and enrichment of the gas-liquid separator 5, the condensate entering the second storage tank 8 can reach 65 wt % of the total condensate in the circulation gas stream, and is introduced into the reactor from four liquid introduction points in the same level through the second feeding pump 9. The distribution of the four liquid introduction points is shown in FIG. 2 (d). The flow rate of the liquid material introduced from the sidewall is 60 t/h, and the pressure is 3.9 MPa. At the liquid introduction points, the condensate is atomized and injected into the reactor through nozzles.

[0140] The above-mentioned copolymerization and homopolymerization reactions are switched repeatedly at 7 times/hour. The space-time yield of the fluidized bed reactor is 130 kg/m.sup.3.Math.hr; and the production capacity is increased by 44%.

[0141] The density of the linear low density polyethylene produced according to the example 5 is 0.9150 g/cm.sup.3, the melt flow rate is 0.91 g/10 min, the tensile yield stress is up to 8.6 MPa, the elongation at break is 870%, the haze decreases to 10.7%, and the free-felling dart impact damage mass is 210 g.

EXAMPLE 6

[0142] The medium density polyethylene (MDPE) is produced in the fluidized bed polymerization reactor apparatus shown in FIG. 1 by using a stepwise polymerization reaction process. Under the action of the Z-N catalyst system, the polymerization reaction temperature is 91 C., the pressure is 2.1 MPa, and the superficial velocity of the reactor is 0.65 m/s.

[0143] When the compolymerization reaction is switched into the homopolymerization reaction, the circulation gas in the pipeline 10 includes hydrogen, nitrogen, methane, ethane, ethylene, a small amount of isopentane, a small amount of hexene and the like, the pressure is 2.3 MPa and the temperature is 91 C. After multiple circulations of the circulation gas, the circulation gas stream from the heat exchanger 4 contained no condensate; and gas-solid two-phase reaction is performed in the fluidized bed reactor, and ethylene is contacted with the continuously added catalyst to produce the solid-phase polymer. In the example, the duration time of each homopolymerization reaction stage is about 8 minutes.

[0144] When the homopolymerization reaction is switched into the ethylene-hexene compolymerization reaction, the circulation gas stream from the heat exchanger 4 contained 26 wt % of condensate, the liquid phase is isopentane and hexene, the density is 604.4 kg/m.sup.3 and the gas-phase density is 28.6 kg/m.sup.3. After separation and enrichment of the gas-liquid separator 5, the condensate entering the second storage tank 8 can reach 70 wt % of the total condensate in the circulation gas stream, and is introduced into the reactor from four liquid introduction points two of which are located in the same level through the second feeding pump 9. The distribution of the four liquid introduction points is shown in FIG. 2 (d). The flow rate of the liquid material introduced from the side wall is 65 t/h, and the pressure is 3 MPa. At the liquid introduction points, the condensate is atomized and injected into the reactor through nozzles. In the example, the duration time of each homopolymerization reaction stage is about 12 minutes.

[0145] The above-mentioned copolymerization and homopolymerization reactions are switched repeatedly at 5 times/hour. The space-time yield of the fluidized bed reactor is 145 kg/m.sup.3.Math.hr; and the production capacity is increased by 60%.

[0146] The density of the medium density polyethylene produced according to the example 6 is 0.9300 g/cm.sup.3, the melt flow rate is 0.34 g/10 min, the tensile yield stress is up to 20.5 MPa, the elongation at break is 592%, the haze is 17%, and the free-falling dart impact damage mass is 75 g.

EXAMPLE 7

[0147] The high density polyethylene (HDPE) is produced in the fluidized bed polymerization reactor apparatus shown in FIG. 1 by using a stepwise polymerization reaction process. Under the action of the Z-N catalyst system, the polymerization reaction temperature is 100 C., the pressure is 2.1 MPa, and the superficial velocity of the reactor is 0.63 m/s. In the production process, the homopolymerization reaction is predominant in the fluidized bed reactor, the circulation gas stream in the pipeline 10 includes hydrogen, nitrogen, methane, ethane, ethylene, isopentane, a small amount of butene and the like, the pressure is 2.1 MPa and the temperature is 100 C. The circulation gas stream at the outlet of the heat exchanger 4 contained no condensate; and gas-solid two-phase reaction is performed in the fluidized bed reactor, and ethylene is contacted with the continuously added catalyst to produce the solid-phase polymer. The density of the high density polyethylene produced according to the example 7 is 0.9485 g/cm.sup.3, the melt flow rate is 1.1 g/10 min, the tensile yield stress is 21 MPa, the elongation at break is 500%, the haze is 21%, and the free-falling dart impact damage mass is 65 g.

[0148] From the results of the above examples, it can be seen that the olefin polymerization apparatus and the olefin polymerization process provided in the present invention can produce the polyolefin products having excellent mechanical properties and excellent processabilities, and have wide application space and high application value.