Process for controlling production rate of propylene homo-or copolymers in gas phase reactor

Abstract

The present invention relates to a process for controlling the production rate of a propylene homopolymer or copolymer in a selected gas phase reactor of a multi-stage reactor system comprising a first reactor and one or more gas phase reactors downstream of the first reactor, wherein each gas phase reactor is equipped with a gas circulation line, a circulation gas compressor and a circulation gas cooler, and the circulation gas cooler comprises a cooling medium inlet, a cooling medium outlet and a cooling loop. The process comprises the steps of: a) polymerizing propylene and optionally a comonomer in a first reactor and one or more gas phase reactors, wherein the propylene homopolymer or copolymer is produced in each gas phase reactor by feeding a recycle gas into the gas phase reactor via a gas recycle line and simultaneously feeding a cooling medium (cm) via a cooling circuit of the recycle gas cooler, the cooling medium (cm) having a temperature Tin at the cooling medium inlet of the recycle gas cooler, a temperature Tout is provided at the coolant outlet of the recycle gas cooler, where the recycle gas comprises propylene and optionally a comonomer, and where the recycle gas is cooled by indirect heat exchange with the coolant (cm) in the cooling circuit of the recycle gas cooler, b) selecting one gas phase reactor from one or more gas phase reactors of the multi-stage reactor system as the selected gas phase reactor, c) calculating the production rate Z-X (kg / h) for producing the propylene homopolymer or copolymer in the selected gas phase reactor by formula (1), and d) controlling the production rate Z-X (kg / h) at which the propylene homopolymer or copolymer is produced in the selected gas phase reactor.

Description

[0001] This invention relates to a method for controlling the production rate of propylene homopolymers or copolymers in a gas-phase reactor of a multi-stage reactor system.

[0002] Removing heat from a gas-phase reactor requires a large gas flow and a suitable compressor to provide a sufficient pressure differential. To minimize gas recirculation, the temperature difference between the gas entering / exiting the reactor and arriving / exiting the reactor should be maximized, along with the gas fluidization rate and reactor operating pressure. Heat transfer agents are typically not added to reactors for polymerizing propylene to maximize the reactivity of monomers and comonomers.

[0003] However, the maximum operating temperature is limited by polymer grades with low melting points and high viscosity, such as propylene-ethylene copolymers containing 3-6 wt.% ethylene. These grades are typically produced at lower operating temperatures (typically 65°C to 75°C).

[0004] If one or more of the comonomers have a higher weight average molecular weight (Mw) than propylene, such as 1-butene or 1-hexene, the dew point of the circulating gas in the gas phase reactor will increase, further reducing the possible temperature difference in the reactor.

[0005] Condensation mode operation has been used to limit investment costs, at least when producing products with restricted operating temperatures and high dew point circulating gases. Calculating the heat of reaction based on polymerization reactor parameters is challenging when operating in condensation mode. When condensation occurs, a significant portion of the energy is removed over a narrow temperature range.

[0006] When only one reactor is operating, the process parameters for the reactor can be easily controlled and adjusted by utilizing mass balance. However, if more than one reactor is operating and the flow between reactors cannot be measured or determined, controlling and producing different polymer substances within the reactors becomes a challenge.

[0007] EP 0 241 947 discloses a method for controlling the temperature of a fluidized bed during polymer production in a fluidized bed reactor via an exothermic polymerization reaction, the method comprising: continuously introducing a gas stream cooled to below a desired maximum temperature within the bed into the bed, and simultaneously or separately introducing a liquid stream into the reactor under certain conditions, such that a substantially homogeneous two-phase mixture of gas and liquid is introduced into the bed at a level below the desired maximum temperature within the reactor.

[0008] One object of the present invention is to provide a method for determining and controlling the production rate of propylene homopolymers or copolymers in a gas-phase reactor, particularly in a cost-effective and easy manner.

[0009] A further object of the present invention is to provide a method for determining the degree of condensation in the gas phase reactor of a multi-stage reactor system.

[0010] Another object of the present invention is to provide a method for calculating the distribution between the gas phase reactor and the upstream reactor.

[0011] This invention is based on the discovery that the thermal balance of a gas-phase reactor can be calculated based on parameters of the cooling medium system associated with the gas-phase reactor. Furthermore, the production rate of polypropylene homopolymers or copolymers in the gas-phase reactor, as well as the distribution between the gas-phase reactor and previous reactors, can also be calculated and controlled.

[0012] Furthermore, the present invention provides a method for controlling the production rate of propylene homopolymer or copolymer in a selected gas-phase reactor of a multi-stage reactor system, the multi-stage reactor system comprising a first reactor and one or more gas-phase reactors downstream of the first reactor, wherein each gas-phase reactor is equipped with a gas circulation line, a circulating gas compressor, and a circulating gas cooler, wherein the circulating gas cooler includes a cooling medium inlet, a cooling medium outlet, and a cooling loop. The method includes the following steps: a) Polymerizing propylene and optional comonomers in a first reactor and one or more gas-phase reactors. In each gas-phase reactor, polypropylene homopolymer or copolymer is produced as follows: circulating gas is introduced into the gas-phase reactor via a gas circulation line, and simultaneously a cooling medium (cm) is introduced through a cooling loop of a circulating gas cooler, wherein the cooling medium (cm) has a temperature T at the cooling medium inlet of the circulating gas cooler. cm_in The outlet of the cooling medium in the circulating gas cooler has a temperature T. cm_out The circulating gas includes propylene and optional comonomers, and the circulating gas is cooled by indirect heat exchange with a cooling medium (cm) in the cooling loop of the circulating gas cooler. b) Select one gas phase reactor (GPR) from one or more gas phase reactors in the multi-stage reactor system as the selected gas phase reactor. c) Calculate the production rate Z–X (kg / h) of producing propylene homopolymer or copolymer in the selected gas-phase reactor using formula (1). , d) The production rate Z–X (kg / h) of propylene homopolymer or copolymer in the selected gas phase reactor (GPR) is controlled by using the production rate Z–X (kg / h) calculated in step c). in The total production of solid propylene homopolymer or copolymer Z (kg / h) = (feed to all reactors in the multistage reactor system) - (liquid and gas extracted from all reactors in the multistage reactor system). P=ΔT cm Cp cm MF cm T cm =T cm_out –T cm_in The cooling medium (cm) used in the circulating gas cooler of the selected gas phase reactor (GPR), in °C. Cp cm Specific heat capacity (J kg) of cooling medium (cm) -1 ℃ -1 ), MF cm The mass flow rate (kg / h) of the cooling medium (cm) in the cooling loop of the selected gas phase reactor (GPR). The production rate X (kg / h) of propylene homopolymer or copolymer transferred from the upstream reactor to the selected gas-phase reactor. The total feed rate Y (kg / h) from the upstream reactor to the selected gas phase reactor. The load R (kJ / h) is in addition to the feed from the upstream reactor. ΔH Y-X = Enthalpy change (kJ / kg) of liquid / gas transferred from the upstream reactor to the selected gas phase reactor. ΔH X = Enthalpy change (kJ / kg) of propylene homopolymer or copolymer transferred from the upstream reactor to the selected gas-phase reactor, and E is the average heat of reaction in the selected GPR, where E = heat of reaction (propylene). (Propylene content of the product produced in the selected gas-phase reactor) + Σ[(Heat of reaction (comonomer)) (The comonomer content of the product produced in the selected gas-phase reactor) and The upstream reactor is the reactor located directly upstream of the selected gas phase reactor.

[0013] This invention offers numerous advantages. The method of this invention not only allows for the determination of the production rate of propylene homopolymers or copolymers in a selected gas-phase reactor, but also allows for the adjustment or control of that production rate.

[0014] Another advantage is that this determination can be performed in a cost-effective and easy manner. Specifically, the heat balance can be calculated based on the parameters of the cooling medium system associated with the gas-phase reactor in which propylene homopolymers or copolymers are produced. Based on the heat balance, the production rate of polypropylene homopolymers or copolymers in the gas-phase reactor can be easily and reliably determined.

[0015] Another advantage is that the degree of condensation can be calculated based on the parameters of the cooling medium system associated with the gas phase reactor, thus allowing the gas phase reactor to be easily operated in condensation mode.

[0016] Another advantage is that the allocation between the selected gas phase reactor and the previous reactor can be calculated based on the parameters of the cooling medium system associated with the gas phase reactor.

[0017] In step a) of the method according to the invention, propylene and optional comonomers are polymerized in a first reactor and one or more gas-phase reactors of a multi-stage reactor system.

[0018] A multistage reactor system comprises, or consists of, a first reactor and one or more gas-phase reactors downstream of the first reactor. A multistage reactor system also implies that these reactors are arranged in series. In the case of a multistage reactor system with only one gas-phase reactor, that gas-phase reactor is designated as the first gas-phase reactor. In the case of a multistage reactor system with two gas-phase reactors, these are designated as the first gas-phase reactor and the second gas-phase reactor, where the second gas-phase reactor is downstream of the first gas-phase reactor. The same applies to the case of three gas-phase reactors, where the third reactor is downstream of the second gas-phase reactor.

[0019] Preferably, the multi-stage reactor system includes a first reactor and two or three gas-phase reactors downstream of the first reactor, or is composed of these reactors. In other words, the multi-stage reactor system includes a first reactor, a first gas-phase reactor downstream of the first reactor, a second gas-phase reactor downstream of the first gas-phase reactor, and optionally a third gas-phase reactor downstream of the second gas-phase reactor, or is composed of these reactors.

[0020] The preferred multistage reactor system is a “loop-gas phase” reactor system, such as those developed by Borealis (known as Borstar® technology) and described in patent literature (e.g., in EP 0 887 379, WO 92 / 12182, WO 2004 / 000899, WO 2004 / 111095, WO 99 / 24478, WO 99 / 24479 or WO 00 / 68315).

[0021] Preferably, the multi-stage reactor system further includes a prepolymerization reactor upstream of the first reactor. The prepolymerization reactor is preferably a loop reactor. Prepolymerization is known in the art.

[0022] Preferably, the first reactor is a slurry reactor. The slurry reactor is preferably a loop reactor or a continuous stirred tank reactor, more preferably a loop reactor. Loop reactors are generally known in the art, and examples are given, for example, in the following documents: US-A-4582816, US-A-3405109, US-A-3324093, EP-A-479186, and US-A-5391654. In such reactors, the slurry is circulated at high speed along a closed tube using a circulation pump.

[0023] Preferably, the second reactor is located downstream of the first reactor and upstream of one or more gas-phase reactors. The second reactor is preferably a slurry reactor. The slurry reactor is preferably a loop reactor.

[0024] The operation and operating conditions of slurry reactors (e.g., loop reactors) for the production of propylene homopolymers or copolymers are known in the art. The first and / or second reactors are typically operated at temperatures of 60 to 100°C (more preferably 65 to 90°C, most preferably 70 to 80°C) and / or preferably at pressures of 1 to 150 bar (more preferably 35 to 60 bar, even more preferably 40 to 55 bar, most preferably 43 to 52 bar). Hydrogen is typically introduced into the reactor to control the MFR2 of the produced propylene homopolymer or copolymer. Any catalyst suitable for the production of propylene homopolymers or copolymers can be used in this invention (e.g., metallocene catalysts).

[0025] Preferably, the multi-stage reactor system further includes means for feeding propylene and / or comonomers and / or hydrogen into the first reactor and / or the second reactor (if present).

[0026] One or more gas-phase reactors are located downstream of a first or second reactor (if present). Slurry from the first or second reactor (if present) is transferred to the gas-phase reactor located downstream of the first or second reactor. The slurry is preferably transferred between the first or second reactor and the gas-phase reactor via a direct feed line. The slurry comprises the produced propylene homopolymer or copolymer, unreacted monomers, and / or comonomers.

[0027] The gas-phase reactor used in the method of the present invention can be any suitable gas-phase reactor known in the art (e.g., preferably a fluidized bed gas-phase reactor).

[0028] The operation and operating conditions of gas-phase reactors (such as fluidized bed gas-phase reactors) are known in the art. Typically, the reaction temperatures used are in the range of 30 to 90°C, and the gas-phase reactor pressures are typically in the range of 10 to 40 bar. Any catalyst suitable for the production of propylene homopolymers or copolymers (e.g., metallocene catalysts) can be used.

[0029] Preferably, the one or more gas-phase reactors include means for feeding propylene and / or comonomers and / or hydrogen into the one or more gas-phase reactors. In addition, as is known in the art, the one or more gas-phase reactors include a recirculating gas outlet, a recirculating gas inlet, and a product outlet for extracting the produced propylene homopolymer or copolymer.

[0030] Each gas-phase reactor in the multi-stage reactor system is further equipped with a gas recirculation line, a recirculating gas compressor, and a recirculating gas cooler. Recirculating gas is introduced into the gas-phase reactor via the gas recirculation line, preferably via a recirculating gas inlet. The recirculating gas is preferably introduced into the recirculating gas line via recirculating gas line inlets upstream of the recirculating gas cooler and downstream of the gas-phase reactor. The recirculating gas flows through the gas-phase reactor in an upward direction.

[0031] In each gas-phase reactor, propylene homopolymers or copolymers are produced by polymerizing propylene and optional comonomers in the presence of a catalyst, with recirculated gas fed into the gas-phase reactor via a gas recirculation line. Simultaneously, a cooling medium (cm) is supplied through a cooling loop of a recirculated gas cooler, wherein the cooling medium (cm) has a temperature T at the cooling medium inlet of the recirculated gas cooler. cm_in The outlet of the cooling medium in the circulating gas cooler has a temperature T. cm_out .

[0032] The recycle gas includes propylene and optional comonomers. The comonomers preferably include or consist of ethylene, 1-butene, 1-hexene and / or 1-octene. The recycle gas typically further includes non-reactive gases (e.g., nitrogen or low-boiling hydrocarbons (e.g., propane and / or hydrogen)), and more preferably, the recycle gas further includes hydrogen.

[0033] The circulating gas cooler includes a cooling medium inlet, a cooling medium outlet, and a cooling circuit. The cooling circuit is preferably a closed-loop cooling circuit. The cooling medium can be circulated in the cooling circuit by a pump. The cooling medium is fed into the cooling circuit via the cooling medium inlet and passes through the circulating gas cooler, and exits via the cooling medium outlet. The circulating gas cooler further includes a circulating gas cooler gas inlet and a circulating gas cooler gas outlet.

[0034] Preferably, the circulating gas cooler is a heat exchanger, and more preferably an indirect heat exchanger. The heat exchanger is preferably a heat exchanger with a closed-loop cooling circuit.

[0035] Preferably, the circulating gas compressor is located downstream of the gas phase reactor, or the circulating gas compressor is located upstream of the gas phase reactor.

[0036] In the first embodiment, the circulating gas compressor is located downstream of the gas phase reactor, and the circulating gas cooler is located downstream of the circulating gas compressor. This is as follows: Figure 1 As shown in the figure. In this first embodiment, the gas circulation line transfers the circulating gas leaving the circulating gas outlet of the gas phase reactor to the circulating gas compressor, the circulating gas is further transferred from the circulating gas compressor to the circulating gas cooler, and then transferred back to the gas phase reactor via the circulating gas inlet of the gas phase reactor.

[0037] In the second embodiment, the circulating gas compressor is located upstream of the gas phase reactor, and the gas phase reactor is also equipped with a condensate separator. See also Figure 2 In this second embodiment, the circulating gas cooler is located downstream of the gas phase reactor, the condensate separator is located downstream of the circulating gas cooler, and the circulating gas compressor is located downstream of the condensate separator. The condensate separator causes at least a portion of the circulating gas leaving the circulating gas cooler to condense.

[0038] In this second embodiment, the gas circulation line transfers the circulating gas exiting the circulating gas outlet of the gas phase reactor to a circulating gas cooler. The circulating gas is further transferred from the circulating gas cooler to a condensate separator, and the condensate portion of the circulating gas exiting at the bottom outlet of the condensate separator is transferred back to the gas phase reactor. The circulating gas exiting the top outlet of the condensate separator is guided to a circulating gas compressor via a gas circulation line, and the compressed circulating gas is further returned to the gas phase reactor via the circulating gas inlet.

[0039] The arrangement of this second embodiment further reduces the amount of recirculated gas entering the recirculated gas compressor and provides the possibility of measuring condensation or the degree of condensation, for example, via a flow meter and a level controller to a container for controlling the liquid level. A portion of the condensate from the recirculated gas is returned to the gas phase reactor via a pump or by gravity through the recirculated gas inlet of the gas phase reactor.

[0040] The recirculating gas exiting the gas phase reactor is heated by the heat of polymerization generated within the gas phase reactor. The recirculating gas is then cooled through indirect heat exchange with the cooling medium (cm) in the cooling loop of the recirculating gas cooler. In other words, at least a portion of the heat of polymerization is transferred to the cooling medium (cm) in the recirculating gas cooler. Therefore, the cooling medium (cm) has a temperature T at the cooling medium outlet of the recirculating gas cooler. cm_out It is typically higher than the temperature T at the inlet of the cooling medium in the circulating gas cooler. cm_in Preferably, the cooling medium (cm) has a temperature T of 40°C to 60°C (more preferably 45°C to 55°C) at the cooling medium inlet of the circulating gas cooler. cm_in The cooled circulating gas is then redirected back into the gas-phase reactor. Therefore, indirect heat exchange provides effective temperature control for the gas-phase reactor.

[0041] Preferably, the cooling medium (cm) comprises water or is composed of water. In step b) of the method according to the invention, a gas-phase reactor is selected from one or more gas-phase reactors in a multi-stage reactor system. The selected gas-phase reactor is the one from which the operator wishes to determine and control the production rate of the propylene homopolymer or copolymer.

[0042] In step c) of the method according to the invention, the production rate Z–X (kg / h) of producing propylene homopolymer or copolymer in the selected gas-phase reactor is calculated according to formula (1). Furthermore, formula (1) can calculate the production rate Z–X (kg / h) of producing propylene homopolymer or copolymer in the selected gas-phase reactor, and this calculation allows for the desired control of the production rate ZX.

[0043] The calculation involves feeding the produced propylene homopolymer or copolymer, along with any excess gas and liquid from the upstream reactor, directly into the selected gas-phase reactor.

[0044] The upstream reactor is the reactor located directly upstream of the selected gas-phase reactor. If the upstream reactor is a slurry reactor, no additional heat input is required to evaporate or separate the liquid / gas from the polymer product. Instead, the liquid transferred from the slurry reactor to the gas-phase reactor acts as a cooling medium and removes some of the heat of reaction during evaporation. This heat removal reduces the need for condensation at the gas recirculation cooler.

[0045] If the upstream reactor is a gas-phase reactor, the gas flow from the upstream reactor can be directly fed into the selected gas-phase reactor. However, the gas flow between the reactors cannot be measured, and therefore the overall mass balance of the reactors cannot be calculated.

[0046] To control and calculate the production rate and degree of condensation, the heat balance and degree of condensation must be calculated based on the cooling medium circulation. The flow rate into the reactor is measured by a feed flow meter. The total output Z can be calculated by the mass balance across all reactors. The heat balance calculation for the gas-phase reactor will provide the production rate of the selected gas-phase reactor and its distribution among the preceding reactors and the gas-phase reactor.

[0047] The total yield Z (kg / h) of solid propylene homopolymer or copolymer is calculated based on (feed to all reactors in the multistage reactor system) - (liquid and gas extracted from all reactors in the multistage reactor system). Feed to all reactors in the multistage reactor system includes the sum of propylene feed (kg / h), comonomer feed (kg / h), and hydrogen feed (kg / h) (excluding catalyst feed) entering all reactors in the multistage reactor system. Liquid and gas extracted from all reactors in the multistage reactor system includes the sum of all liquid (kg / h) and gas (kg / h) extracted from all reactors.

[0048] This difference between the feed entering all reactors and the liquid / gas being drawn from all reactors forms the total yield Z (kg / h) of solid propylene homopolymer or copolymer exiting from the final or last reactor of the multi-stage reactor system.

[0049] The parameter P is calculated as P = ΔT cm Cp cm MF cm , where ΔT cm =T cm_out –T cm_in The cooling medium (cm) used at the circulating gas cooler of the selected gas phase reactor, in °C; Cp cm The specific heat capacity (J kg) of the cooling medium (cm) for the selected gas phase reactor (GPR) -1 ℃ -1 ); and MF cm It is the mass flow rate (kg / h) of the cooling medium (cm) in the cooling loop of the selected gas phase reactor.

[0050] The production rate X (kg / h) of propylene homopolymer or copolymer transferred from the upstream reactor to the selected gas-phase reactor is typically unknown or unmeasurable. The production rate X (kg / h) is the sum (kg / h) of all propylene homopolymers or copolymers produced in the reactor upstream of the selected gas-phase reactor, which are then transferred from the reactor directly upstream of the selected gas-phase reactor. Calculating and providing the production rate X (kg / h) of propylene homopolymer or copolymer transferred from the upstream reactor allows determination of the production rate Z–X (kg / h) of propylene homopolymer or copolymer produced in the selected gas-phase reactor, and consequently, control of the production rate ZX (kg / h).

[0051] The total feed rate Y (kg / h) is the rate at which all liquid, gaseous, and solid feeds enter the selected gas-phase reactor from the upstream reactor. Typically, this feed includes solid propylene homopolymer or copolymer produced in the upstream reactor, unreacted propylene, and unreacted hydrogen.

[0052] The load R (kJ / h) refers to the feed excluding the upstream reactor. Therefore, the load R (kJ / h) is the sum of all power quantities (energy per unit time) other than the feed from the upstream reactor. Preferably, the load R includes compressor heating load, heat loss from the reactor system to the atmosphere, and feed cooling / heating effects.

[0053] ΔH Y-X It is the enthalpy change (kJ / kg) of the liquid / gas transferred from the upstream reactor to the selected gas-phase reactor. The enthalpy change depends on pressure and temperature and can be determined by physical properties such as Redlich-Kwong-Soave (RKS) based on the gas composition in the reactor (by mass balance calculations and also by gas chromatography or other methods based on gas analysis) and the condensate composition.

[0054] ΔH X This is the enthalpy change (kJ / kg) of the propylene homopolymer or copolymer transferred from the upstream reactor to the selected gas-phase reactor. The enthalpy change depends on pressure and temperature. Since the propylene homopolymer or copolymer is typically transferred in powder form (i.e., in solid form), ΔH... X It is usually 0 kJ / kg.

[0055] The average heat of reaction E in the selected gas-phase reactor (GPR) is the heat of reaction (propylene). (Propylene content of the product produced in the selected gas-phase reactor) + Σ[(Heat of reaction (comonomer)) (Comonomer content of the product produced in the selected gas-phase reactor). The average heat of reaction can be found, for example, in the literature.

[0056] The heat of reaction of propylene depends primarily on the degree of crystallinity and reactor conditions (i.e., temperature and pressure), and is typically in the range of 2200 kJ / kg to 2500 kJ / kg. In the case of producing propylene copolymers, the heats of formation of the comonomers must also be considered. For example, when the propylene copolymer contains ethylene, 1-butene, and / or 1-hexene as comonomers, the heats of formation of these comonomers need to be considered: ethylene heat of formation = 3700 kJ / kg, 1-butene heat of reaction = 1545 kJ / kg, and 1-hexene heat of reaction = 988 kJ / kg. The heats of formation of other comonomers can be found in the literature.

[0057] The content of comonomers reacting with the final propylene copolymer can be assessed based on the overall mass balance of all reactors and powder samples.

[0058] Preferably, the selected gas-phase reactor operates in condensation mode. Condensation mode means that the degree of condensation of the circulating gas at the circulating gas cooler is in the range of >0 to 15%, preferably in the range of 5 to 15%. The degree of condensation is calculated according to formula (2): , in T cm =T cm_out –T cm_in The cooling medium (cm) used at the outlet and inlet of the circulating gas cooler of the selected gas phase reactor is expressed in °C. Cp cm Specific heat capacity (J kg) of cooling medium (cm) -1 ℃ -1 ), MF cm It is the mass flow rate (kg / h) of the cooling medium (cm) in the cooling circuit of the selected gas phase reactor. ΔT gas =T gas_in –T gas_out The circulating gas used at the gas inlet and gas outlet of the circulating gas cooler, in °C. Cp gas Specific heat capacity of the circulating gas (J kg) -1 ℃ -1 And measurements were taken on the circulating gas exiting the selected gas-phase reactor. MF gas This represents the mass flow rate (kg / h) of the circulating gas in the gas circulation pipeline. C gasIt is the heat of condensation of the circulating gas in the selected gas phase reactor (J / kg).

[0059] Condensation heat C gas It can be determined by physical property methods such as Redlich-Kwong-Soave (RKS).

[0060] Typically, monomeric propylene is the main condensation component in circulating gas coolers.

[0061] In step d), the production rate Z–X can be controlled in one or more ways. Preferably, the control in step d) is accomplished by adjusting the bed level in the selected gas-phase reactor and / or by adjusting the partial pressure of propylene in the selected gas-phase reactor and / or by adjusting the partial pressure of comonomers in the selected gas-phase reactor and / or the bed temperature of the gas-phase reactor.

[0062] The fluidized bed gas-phase reactor comprises a fluidized bed in which the polymerization catalyst is supported on an inert substrate. The level of this bed can be increased, which in turn increases the polymer mass and consequently the residence time. The residence time linearly affects the production rate. Furthermore, increasing the partial pressures of propylene and comonomers in the selected gas-phase reactor almost linearly affects the production rate. Additionally, the temperature of the bed in the selected gas-phase reactor can be increased, which in turn increases the productivity of the Ziegler-Natta catalyst, up to a certain catalyst-dependent temperature. Adjusting these parameters is well known in the art.

[0063] The invention is further described and illustrated in the following figures and non-limiting examples. The figures show... Figure 1 An embodiment of the invention illustrates that the selected gas-phase reactor includes a gas circulation line, a circulating gas compressor, and a circulating gas cooler, as well as... Figure 2 According to another embodiment of the invention, the selected gas phase reactor includes a gas circulation line, a circulating gas compressor, a circulating gas cooler, and a condensate separator.

[0064] The following figure references are used in the accompanying drawings: 1. Selected gas phase reactor 1a is used as the inlet for feeding from the previous reactor into the selected gas-phase reactor. 2. Circulating gas compressor 3. Circulating gas cooler 3a Cooling medium inlet 3b Cooling medium outlet 3C cooling circuit 4. Condensate Separator 5. Gas circulation pipeline 5a Gas circulation pipeline inlet.

[0065] exist Figure 1 In the first embodiment of the invention shown, a circulating gas compressor (2) is located downstream of the selected gas phase reactor (1), and a circulating gas cooler (3) is located downstream of the circulating gas compressor (2). In this first embodiment, a gas circulation line (5) transfers circulating gas from the circulating gas outlet of the gas phase reactor (1) to the circulating gas compressor (2), the compressed circulating gas is further transferred from the circulating gas compressor (2) to the circulating gas cooler (3), and the circulating gas is transferred back to the gas phase reactor (1) via the circulating gas inlet of the gas phase reactor (1). The circulating gas cooler (3) includes a cooling circuit (3c), into which a cooling medium, such as water, is introduced via a cooling medium inlet (3a). The cooling medium exits the cooling circuit (3c) via a cooling medium outlet (3b).

[0066] exist Figure 2 In the second embodiment of the invention shown, the circulating gas compressor (2) is located upstream of the selected gas phase reactor (1), and the gas phase reactor (1) is further equipped with a condensate separator (4). In this second embodiment, the circulating gas cooler (3) is located downstream of the gas phase reactor (1), the condensate separator (4) is located downstream of the circulating gas cooler (3), and the circulating gas compressor (2) is located downstream of the condensate separator (4). The condensate separator (4) condenses at least a portion of the circulating gas leaving the circulating gas cooler (3).

[0067] In this second embodiment, the gas circulation line (5) transfers the circulating gas exiting the circulating gas outlet of the gas phase reactor (1) to the circulating gas cooler (3), from which the circulating gas is further transferred to the condensate separator (4). The condensate portion of the circulating gas exiting at the bottom outlet of the condensate separator (4) is transferred back to the gas phase reactor (1) via a separate line. The circulating gas exiting the top outlet of the condensate separator (4) is guided to the circulating gas compressor (2) via the gas circulation line (5) for compression, and the compressed circulating gas is further returned to the gas phase reactor (1) via the circulating gas inlet. Also in this second embodiment, the circulating gas cooler (3) includes a cooling circuit (3c), into which a cooling medium, such as water, is introduced via a cooling medium inlet (3a). The cooling medium exits the cooling circuit (3c) via a cooling medium outlet (3b).

[0068] Example section In the following example, the Aspen Plus software is used to simulate a multi-stage reactor system, which includes a loop reactor as the first reactor and a subsequent gas-phase reactor (GPR) (see [link to example]). Figure 1 In this example, the circulating reactor operates at 70°C and 50 bar, and the selected GPR (1) operates at 70°C and 25 bar. The circulating gas composition is 1 mol% hydrogen, 2 mol% ethylene, and 10 mol% propane (impurities at the propylene feed, which accumulate in the process), with the remainder being propylene. The circulating gas is fed into the gas circulating line (5) upstream of the circulating gas cooler via the gas circulating line inlet (5a) at a rate of 10,000 kg / h. The circulating gas compressor (2) is used to circulate the circulating gas through the circulating gas line (5) through the circulating gas cooler (3) and to fluidize the polymer bed in the selected GRP (1). The inlet temperature of the cooling medium is T. cm_in The outlet temperature of the cooling medium is 50℃. cm-out The temperature is 57.7℃, and the mass flow rate of the cooling medium (cm) is MF. cm The initial load is 2,000,000 kg / h, and the other load R is 180,000 kJ / h. Water is used as the cooling medium (cm), and the specific heat capacity of water is Cp. cm It is 4.18 kJ / (kg) ℃).

[0069] The total yield Z of the propylene-ethylene copolymer produced is 60,000 kg / h. The enthalpy change of the liquid ΔH... Y-X The enthalpy change of the powder is ΔH, which is 242 kJ / kg. X The enthalpy change was 0 kJ / kg. The enthalpy change was determined using the Redlich-Kwong-Soave (RKS) physical property model included in the Aspen Plus software. The heat of polymerization in the selected GPR was 2400 kJ / kg, and the total feed Y from the previous reactor was 60000 kg / h. The previous reactor operated at 70°C and 50 bar.

[0070] The previous reactor production rate X (kg / h) can be calculated using formula (1) as follows: 60 000 kg / h - X = [(57.7 ℃ – 50 ℃) 4.18 kJ / (kg) ℃) 2 000 000 kg / h - (180 000 kJ / h + (60 000 kg / h - X) 242 kJ / kg + X 0 kJ / kg] / 2400 kJ / kg Solving the equations yields X (the production rate of the previous reactor) produced in the upstream circulating reactor at 30,000 kg / h. Therefore, the selected GPR production rate (Z–X) is 30,000 kg / h.

[0071] Total gas flow rate MF gas The flow rate is 1,400,000 kg / h, and the temperature T of the circulating gas is... cg_in The temperature T of the circulating gas from the cooler is 71.5℃. cg-out The temperature is 59.9℃. The degree of condensation can be calculated using formula (2) in this paper: Degree of condensation = [(57.7 ℃ - 50 ℃) × 4.18 kJ / (kg)] ℃) ×2 000 000 kg / h -1400 000 kg / h ×2.32 kJ / (kg ℃) × (71.5 °C – 59.9 ℃)] 100 / 240 kJ / kg / 1 400000 kg / h = 7.8%.

[0072] To calculate the degree of condensation according to formula (2), the specific heat capacity Cp of the circulating gas is first calculated using the "Aspen plus" software. gas It is 2.32 kJ / (kg) (℃), and then use the "Aspen Plus" software to calculate the condensation heat C of the circulating gas. gas It is 240 kJ / kg.

[0073] Therefore, operating the reactor under the above conditions results in a 7.8% condensation rate (i.e., the selected gas-phase reactor operates in condensation mode). The gas dew point is 60.1°C, making it impossible to track the condensation rate from the process side. Condensation in the recirculating gas cooler removes approximately 36% of the total heat, direct feed removes 10%, and cooling in the recirculating gas cooler removes 54% of the total heat.

[0074] The circulating gas velocity (m / s) is equal to the gas volumetric flow rate (m³ / s). 3 / s)) / [(diameter (m))^2 π / 4], where the gas volumetric flow rate (m³) 3 / s) is the mass flow rate (kg / s) / density (kg / m³) 3 Density (kg / m³) 3 The pressure (kPa) is calculated as [pressure]. [Molar mass (kg / mol)] / [Temperature (K) Compressibility gas constant (kg·m)] 2 / (s2 K The gas composition, pressure, and mass flow rate are known, and compressibility is determined using the "Aspen plus" software.

[0075] With this arrangement and the calculated circulating gas flow rate of 0.6 m / s inside a 4 m diameter gas-phase reactor, the selected GPR produces 30,000 kg / h of propylene-ethylene copolymer (random grade, 97 wt.% propylene and 3 wt.% ethylene as reactor products).

Claims

1. A method for controlling the production rate of propylene homopolymer or copolymer in a selected gas-phase reactor (1) of a multi-stage reactor system, the multi-stage reactor system comprising a first reactor and one or more gas-phase reactors located downstream of the first reactor, wherein each gas-phase reactor is equipped with a gas circulation line (5), a circulating gas compressor (2), and a circulating gas cooler (3), wherein the circulating gas cooler (3) comprises a cooling medium inlet (3a), a cooling medium outlet (3b), and a cooling loop (3c). The method includes the following steps: a) Polymerizing propylene and optional comonomers in the first reactor and the one or more gas-phase reactors. In each gas phase reactor, polypropylene homopolymer or copolymer is produced by feeding circulating gas into the gas phase reactor via the gas circulation line (5) and simultaneously feeding a cooling medium (cm) through the cooling loop (3c) of the circulating gas cooler (3), wherein the cooling medium (cm) has a temperature T at the cooling medium inlet (3a) of the circulating gas cooler (3). in The circulating gas cooler (3) has a temperature T at the cooling medium outlet (3b). out , The circulating gas comprises propylene and optional comonomers, and the circulating gas is cooled by indirect heat exchange with a cooling medium (cm) in the cooling circuit (3c) of the circulating gas cooler (3). b) Select one gas phase reactor (GPR) from one or more gas phase reactors of the multi-stage reactor system as the selected gas phase reactor (1). c) Calculate the production rate Z–X (kg / h) of producing propylene homopolymer or copolymer in the selected gas-phase reactor (1) using formula (1): d) The production rate Z–X (kg / h) of propylene homopolymer or copolymer in the selected gas-phase reactor (1) is controlled by using the production rate Z–X (kg / h) calculated in step c). in The total production of solid propylene homopolymer or copolymer Z (kg / h) = (feed to all reactors in the multistage reactor system) - (liquid and gas extracted from all reactors in the multistage reactor system). P=ΔT cm Cp cm MF cm , where ΔT cm =T cm_out –T cm_in The cooling medium (cm) used in the circulating gas cooler of the selected gas phase reactor (GPR), in °C. Cp cm The specific heat capacity (J kg) of the cooling medium (cm) in the cooling loop of the selected gas phase reactor (GPR) -1 ℃ -1 ), MF cm The mass flow rate (kg / h) of the cooling medium (cm) in the cooling loop of the selected gas phase reactor (GPR). The production rate X (kg / h) of propylene homopolymer or copolymer transferred from the upstream reactor to the selected gas-phase reactor. The total feed rate Y (kg / h) from the upstream reactor to the selected gas phase reactor. In addition to the feed from the upstream reactor, the load R (kJ / h) is also considered. ΔH Y-X = Enthalpy change (kJ / kg) of liquid / gas transferred from the upstream reactor to the selected gas phase reactor. ΔH X = Enthalpy change (kJ / kg) of propylene homopolymer or copolymer transferred from the upstream reactor to the selected gas-phase reactor, and E is the average heat of reaction in the selected GPR, where E = heat of reaction (propylene). (Propylene content of the product produced in the selected gas-phase reactor) + Σ[(Heat of reaction (comonomer)) (The comonomer content of the product produced in the selected gas-phase reactor) and The upstream reactor is the reactor located directly upstream of the selected gas phase reactor (1).

2. The method according to claim 1, wherein the first reactor is a slurry reactor, and the slurry reactor is preferably a loop reactor.

3. The method according to any one of the preceding claims, wherein the multi-stage reactor system comprises the first reactor and two or three gas-phase reactors downstream of the first reactor.

4. The method according to any one of the preceding claims, wherein the multi-stage reactor system includes a prepolymerization reactor located upstream of the first reactor, the prepolymerization reactor preferably being a loop reactor.

5. The method according to any one of the preceding claims, wherein the selected gas phase reactor (1) operates in condensation mode.

6. The method according to any one of the preceding claims, wherein the circulating gas further comprises hydrogen.

7. The method according to any one of the preceding claims, wherein the circulating gas further comprises a comonomer.

8. The method according to claim 7, wherein the comonomer comprises ethylene, 1-butene, 1-hexene and / or 1-octene.

9. The method according to any one of the preceding claims, wherein the control in step d) is accomplished by adjusting the bed level in the selected gas phase reactor and / or by adjusting the partial pressure of propylene in the selected gas phase reactor and / or by adjusting the partial pressure of comonomer in the selected gas phase reactor (1) and / or by adjusting the bed temperature of the selected gas phase reactor (1).

10. The method according to any one of the preceding claims, wherein the circulating gas compressor (2) is located downstream of the selected gas phase reactor (1), or wherein the circulating gas compressor (2) is located upstream of the selected gas phase reactor (1).

11. The method according to any one of the preceding claims, wherein the circulating gas cooler (3) is a heat exchanger, preferably a heat exchanger having a closed-loop cooling circuit.

12. The method according to any one of the preceding claims, wherein the one or more gas phase reactors include means for feeding propylene and / or comonomers and / or hydrogen into the one or more gas phase reactors.

13. The method according to any one of the preceding claims, wherein the first reactor includes means for feeding propylene and / or comonomer and / or hydrogen into the first reactor.

14. The method according to any one of the preceding claims, wherein the cooling medium (cm) has a temperature T between 40°C and 60°C at the cooling medium inlet (3a) of the circulating gas cooler (3). cm_in The preferred temperature is 45°C to 55°C.

15. The method according to any one of the preceding claims, wherein the cooling medium (cm) comprises water or is composed of water.

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