Method for controlling the production rate of propylene homo or copolymer in a gas-phase reactor.

Abstract

A method for controlling the production rate of propylene homo- or copolymer in a selected gas-phase reactor of a multi-stage reactor system, wherein the multi-stage reactor system includes a first reactor and one or more gas-phase reactors downstream of the first reactor, each gas-phase reactor comprising a gas circulation line, a circulating gas compressor, and a circulating gas cooler, the circulating gas cooler including a cooling medium inlet, a cooling medium outlet, and a cooling circuit, The method comprises the following steps: a) A step of polymerizing propylene and any comonomer in the first reactor and the one or more gas-phase reactors, In each gas-phase reactor, by supplying circulating gas to the gas-phase reactor via the gas circulation line and simultaneously supplying a cooling medium (cm) to the cooling circuit of the circulating gas cooler, a polypropylene homo- or copolymer is produced, The cooling medium (cm) has a temperature of T at the cooling medium inlet of the circulating gas cooler, in and a temperature of T at the cooling medium outlet of the circulating gas cooler, out and The circulating gas includes propylene and any comonomer, and the circulating gas is cooled by indirect heat exchange with the cooling medium (cm) in the cooling circuit of the circulating gas cooler; b) A step of selecting one of the one or more gas-phase reactors of the multi-stage reactor system as the selected gas-phase reactor; c) A step of calculating the production rate Z-X (kg / h) of the propylene homo- or copolymer produced in the selected gas-phase reactor according to formula (1), and d) A step of controlling the production rate Z-X (kg / h) of the propylene homo- or copolymer produced in the selected gas-phase reactor.

Description

[Technical Field]

[0001] The present invention relates to a method for controlling the production rate of propylene homo or copolymer in a gas-phase reactor of a multi-stage reactor system. [Background technology]

[0002] Removing heat from a gas-phase reactor requires a large gas flow rate and a suitable compressor to provide a sufficient pressure difference. To minimize gas circulation, the temperature difference between the gas entering and leaving the gas-phase reactor must be maximized, as well as the gas fluidization rate and reactor operating pressure. Typically, no heat transfer agents are added to propylene polymerization reactors to maximize monomer-comonomer reactivity.

[0003] However, for low-melting-point, viscous polymer grades such as propylene-ethylene copolymers containing 3-6% by weight of ethylene, the maximum operating temperature is limited. These grades are typically produced at lower operating temperatures of 65°C to 75°C.

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

[0005] Condensation mode operation has been used, at least to reduce investment costs, when producing products where the dew point of the circulating gas is high and the operating temperature is limited. When operating in condensation mode, it is difficult to calculate the heat of reaction from the polymerization reactor parameters. When condensation occurs, most of the energy is removed within a narrow temperature range.

[0006] The process parameters of a reactor can be easily controlled and adjusted by using mass balance when only one reactor is in operation. However, when multiple reactors are operating and the flow between these reactors cannot be measured or determined, it is difficult to control and produce different polymer materials in the reactors.

[0007] European Patent No. 0241947 discloses a method for controlling the temperature of a fluidized bed during polymer production in a fluidized bed reactor by means of an exothermic polymerization reaction, which comprises continuously introducing into the bed a gas stream cooled below the maximum desired temperature within the bed, and introducing a liquid stream into the reactor simultaneously or separately under conditions such that an essentially homogeneous two-phase mixture of the gas and the liquid is introduced into the bed at a level below the maximum desired temperature region within the reactor.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] An 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-reducing and easy manner.

[0010] A further object of the present invention is to provide a method for determining the degree of condensation in a gas-phase reactor of a multi-stage reactor system.

[0011] Another object of the present invention is to provide a method that enables the calculation of the distribution between a gas-phase reactor and an upstream reactor.

Means for Solving the Problems

[0012] This invention is based on the finding that the heat balance of a gas-phase reactor can be calculated based on the parameters of a cooling medium system coupled to the gas-phase reactor. Therefore, not only the distribution between the gas-phase reactor and the upstream reactor, but also the production rate of polypropylene homo or copolymer in the gas-phase reactor can be calculated and controlled.

[0013] Accordingly, the present invention relates to a method for controlling the production rate of a propylene homo or copolymer in a selected gas-phase reactor of a multistage reactor system, wherein the multistage reactor system comprises a first reactor and one or more gas-phase reactors downstream of the first reactor, each gas-phase reactor comprising a gas circulation line, a circulating gas compressor and a circulating gas cooler, the circulating gas cooler comprising a cooling medium inlet, a cooling medium outlet and a cooling circuit, and the following steps: a) A step of polymerizing propylene and an arbitrary comonomer in the first reactor and one or more gas-phase reactors, In each gas-phase reactor, circulating gas is supplied to the gas-phase reactor via the gas circulation line, and at the same time, a cooling medium (cm) is supplied to the cooling circuit of the circulating gas cooler, thereby producing polypropylene homo or copolymer. The cooling medium (cm) is defined as having a temperature of T at the cooling medium inlet of the circulating gas cooler. in Then, the temperature at the outlet of the cooling medium of the circulating gas cooler is T out And, The circulating gas comprises propylene and an optional comonomer, and the circulating gas is cooled by indirect heat exchange with the cooling medium (cm) in the cooling circuit of the circulating gas cooler. b) A step of selecting one gas-phase reactor (GPR) from the one or more gas-phase reactors of the multi-stage reactor system as the selected gas-phase reactor, c) A step of calculating the production rate ZX (kg / h) of the propylene homo or copolymer produced in the selected gas-phase reactor using formula (1):

number

[0014] The present invention offers numerous advantages. The method of the present invention not only enables the determination of the production rate of propylene homo or copolymer in a selected gas-phase reactor, but also enables the adjustment or control of this production rate.

[0015] A further advantage is that this decision can be made in a cost-effective and easy manner. Specifically, the heat balance can be calculated from the parameters of the cooling medium system coupled to the gas-phase reactor where the propylene homopolymer or copolymer is produced. From the heat balance, the production rate of the polypropylene homopolymer or copolymer in the gas-phase reactor can be easily and reliably determined.

[0016] A further advantage is that the degree of condensation can be calculated from the parameters of the cooling medium system coupled to the gas-phase reactor, allowing the gas-phase reactor to be easily operated in condensation mode.

[0017] Another advantage is that the distribution between the selected gas-phase reactor and the upstream reactor can also be calculated from the parameters of the cooling medium system coupled to the gas-phase reactor. [Brief explanation of the drawing]

[0018] The present invention is further described and illustrated by the following figures and non-limiting embodiments. These figures show: [Figure 1] Figure 1 shows one embodiment of a selected gas-phase reactor including a gas circulation line, a circulating gas compressor, and a circulating gas cooler. [Figure 2] Figure 2 shows another embodiment of the present invention, which includes a selected gas-phase reactor comprising a gas circulation line, a circulating gas compressor, a circulating gas cooler, and a condensate separator. [Modes for carrying out the invention]

[0019] In step a) of the method of the present invention, propylene and an optional comonomer are polymerized in a first reactor and one or more gas-phase reactors of a multi-stage reactor system.

[0020] A multistage reactor system includes or consists of a first reactor and one or more gas-phase reactors downstream of the first reactor. A multistage reactor system also means that the reactors are arranged in series. If a multistage reactor system has only one gas-phase reactor, this reactor is designated as the first gas-phase reactor. If a multistage reactor system has two gas-phase reactors, these two reactors are designated as the first gas-phase reactor and the second gas-phase reactor, with the second gas-phase reactor being downstream of the first gas-phase reactor. The same applies if there are three gas-phase reactors, with the third gas-phase reactor being downstream of the second gas-phase reactor.

[0021] Preferably, the multistage reactor system includes or comprises a first reactor and two or three gas-phase reactors downstream of the first reactor. That is, the multistage reactor system includes or comprises 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.

[0022] A preferred multistage reactor system is the "loop-gas phase" reactor system developed by, for example, Borealis (known as Borstar® technology), as described in patent documents such as European Patent No. 0887379, International Publication No. 92 / 12182, International Publication No. 2004 / 000899, International Publication No. 2004 / 111095, International Publication No. 99 / 24478, International Publication No. 99 / 24479, or International Publication No. 00 / 68315.

[0023] Preferably, the multistage 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.

[0024] Preferably, the first reactor is a slurry reactor. The slurry reactor is preferably a loop reactor or a continuous stirred tank reactor, and more preferably a loop reactor. Loop reactors are generally known in the art and are illustrated, for example, in U.S. Patent No. 4,582,816, U.S. Patent No. 3,405,109, U.S. Patent No. 3,324,093, European Patent No. 479,186 and U.S. Patent No. 5,391,654. In such reactors, the slurry is circulated at high speed along a closed pipe using a circulation pump.

[0025] 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.

[0026] The operation and operating conditions of slurry reactors, such as loop reactors, for producing propylene homo or copolymers are known in the art. The first and / or second reactors are typically operated at a temperature of 60–100°C, more preferably 65–90°C, most preferably 70–80°C and / or at a pressure of 1–150 bar, more preferably 35–60 bar, even more preferably 40–55 bar, most preferably 43–52 bar. Hydrogen is typically introduced into the reactor to control the MFR2 of the propylene homo or copolymer produced. In this invention, any catalyst suitable for producing propylene homo or copolymer, such as a metallocene catalyst, can be used.

[0027] Preferably, the multistage reactor system further includes means for supplying propylene and / or comonomers and / or hydrogen to the first reactor and / or, if present, to the second reactor.

[0028] One or more gas-phase reactors are located downstream of the first reactor or, if present, the second reactor. Slurry from the first reactor or, if present, slurry from the second reactor is transferred to a gas-phase reactor downstream of the first or second reactor. The slurry is preferably transferred via a direct supply line between the first or second reactor and the gas-phase reactor. The slurry contains the generated propylene homo- or copolymer, unreacted monomers and / or comonomers.

[0029] The gas-phase reactor used in the method of the present invention may be a suitable gas-phase reactor known in the art, for example, preferably a fluidized bed gas-phase reactor.

[0030] The operation and operating conditions of gas-phase reactors, such as fluidized bed gas-phase reactors, are known in the art. Typically, the reaction temperature used is generally in the range of 30 to 90°C, and the gas-phase reactor pressure is generally in the range of 10 to 40 bar. Any catalyst suitable for producing propylene homo or copolymers, such as metallocene catalysts, can be used.

[0031] Preferably, one or more gas-phase reactors include means for supplying propylene and / or comonomers and / or hydrogen to one or more gas-phase reactors. Separately, one or more gas-phase reactors include, as known in the art, a circulating gas outlet, a circulating gas inlet, and a product outlet for withdrawing the produced propylene homo or copolymer.

[0032] Each gas-phase reactor in a multi-stage reactor system further comprises a gas circulation line, a circulating gas compressor, and a circulating gas cooler. The circulating gas is supplied to the gas-phase reactor via the gas circulation line, preferably via a circulating gas inlet. The circulating gas is supplied to the circulating gas line, preferably via a circulating gas line inlet upstream of the circulating gas cooler and downstream of the gas-phase reactor. The circulating gas flows upward within the gas-phase reactor.

[0033] In each gas-phase reactor, circulating gas is supplied to the gas-phase reactor via a gas circulation line, and polypropylene homo or copolymer is produced by polymerizing propylene with an arbitrary comonomer in the gas-phase reactor in the presence of a catalyst. Simultaneously, a cooling medium (cm) is supplied to the cooling circuit of the circulating gas cooler, and the temperature of the cooling medium (cm) at the cooling medium inlet of the circulating gas cooler is T cm_in Therefore, the temperature at the outlet of the cooling medium of the circulating gas cooler is T cm_out That is the case.

[0034] The circulating gas contains propylene and any comonomer. The comonomers preferably include or consist of ethylene, 1-butene, 1-hexene and / or 1-octene. The circulating gas usually further contains an unreactive gas such as nitrogen, or a low-boiling hydrocarbon such as propane and / or hydrogen, and more preferably the circulating gas further contains hydrogen.

[0035] A 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 within the cooling circuit by a pump. The cooling medium is supplied to the cooling circuit through the cooling medium inlet, passes through the circulating gas cooler, and exits through the cooling medium outlet. The circulating gas cooler further includes a circulating gas cooler gas inlet and a circulating gas cooler gas outlet.

[0036] Preferably, the circulating gas cooler is a heat exchanger, and preferably an indirect heat exchanger. The heat exchanger is preferably a heat exchanger having a closed-loop cooling circuit.

[0037] Preferably, the circulating gas compressor is located downstream of the gas-phase reactor, or upstream of the gas-phase reactor.

[0038] 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 shown in Figure 1 below. In this first embodiment, the gas circulation line transfers the circulating gas from the circulating gas outlet of the gas-phase reactor to the circulating gas compressor, from where the circulating gas is further transferred to the circulating gas cooler, and the circulating gas is returned to the gas-phase reactor via the circulating gas inlet of the gas-phase reactor.

[0039] In the second embodiment, the circulating gas compressor is located upstream of the gas-phase reactor, and the gas-phase reactor further includes a condensate separator. See 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 condenses at least a portion of the circulating gas leaving the circulating gas cooler.

[0040] In this second embodiment, the gas circulation line transfers the circulating gas from the circulating gas outlet of the gas-phase reactor to a circulating gas cooler, from where the circulating gas is further transferred to a condensate separator, and finally the condensed portion of the circulating gas exiting the bottom outlet of the condensate separator is returned to the gas-phase reactor. The circulating gas exiting the top outlet of the condensate separator is transferred via the gas circulation line to a circulating gas compressor, and the compressed circulating gas is further returned to the gas-phase reactor via the circulating gas inlet of the gas-phase reactor.

[0041] The arrangement of this second embodiment further reduces the amount of circulating gas entering the circulating gas compressor and provides the possibility of measuring condensation or the degree of condensation, for example, via a flow meter and a level controller for a container for liquid level control. The condensed portion of the circulating gas is returned to the gas-phase reactor via the circulating gas inlet of the gas-phase reactor by pumping or gravity.

[0042] The circulating gas exiting the gas outlet of the gas-phase reactor is heated by the heat of polymerization generated within the gas-phase reactor. The circulating gas is then cooled indirectly by heat exchange with the cooling medium (cm) in the cooling circuit of the circulating gas cooler. That is, at least a portion of the heat of polymerization is transferred to the cooling medium (cm) of the circulating gas cooler. Therefore, the temperature of the cooling medium (cm) at the cooling medium outlet of the circulating gas cooler is typically T cm_out However, the temperature T at the cooling medium inlet of the circulating gas cooler cm_in Higher. Preferably, the cooling medium (cm) is at a temperature T at the cooling medium inlet of the circulating gas cooler. cm_in The temperature is 40°C to 60°C, more preferably 45°C to 55°C. The cooled circulating gas is returned to the gas-phase reactor. In this way, efficient temperature control is provided to the gas-phase reactor through indirect heat exchange.

[0043] Preferably, the cooling medium (cm) contains or consists of water. In step b) of the method of the present invention, one gas-phase reactor is selected from one or more gas-phase reactors of a multistage reactor system. This selected gas-phase reactor is the reactor in which the operator desires to determine and control the production rate of the propylene homo or copolymer.

[0044] In step c) of the method of the present invention, the production rate ZX (kg / h) of the propylene homo or copolymer produced in the selected gas-phase reactor is calculated according to formula (1). Thus, formula (1) makes it possible to calculate the production rate ZX (kg / h) of the propylene homo or copolymer produced in the selected gas-phase reactor, and this calculation then allows for desired control of the production rate ZX.

[0045] This calculation involves the direct supply of the produced propylene homo- or copolymer, as well as excess gases and liquids from the upstream reactor, to the selected gas-phase reactor.

[0046] 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 vaporize or separate the liquid / gas from the polymer product. Rather, the liquid from the slurry reactor, transferred to the gas-phase reactor, acts as a cooling medium, removing some of the reaction heat during vaporization. This heat removal reduces the need for condensation in the gas circulation cooler.

[0047] If the upstream reactor is a gas-phase reactor, the gas flow from the upstream reactor can be directly supplied to the selected gas-phase reactor. However, since the gas flow rate between reactors cannot be measured, it is not possible to calculate a comprehensive mass balance for that reactor.

[0048] To control and calculate the production rate and condensation, the heat balance and condensation must be calculated from the circulation of the cooling medium. The flow rate to the reactor is measured with a supply flow meter. The total production amount Z can be calculated from the mass balance across all reactors. By calculating the heat balance of the gas-phase reactor, the production rate of the selected gas-phase reactor and the distribution between the upstream reactor and the gas-phase reactor can be obtained.

[0049] The total production volume Z (kg / h) of solid propylene homopolymer is calculated as (supply to all reactors in a multistage reactor system) - (liquids and gases withdrawn from all reactors in a multistage reactor system). The supply to all reactors in a multistage reactor system includes the sum of the propylene supply (kg / h), comonomer supply (kg / h), and hydrogen supply (kg / h) to all reactors in a multistage reactor system (excluding the catalyst supply). The liquids and gases withdrawn from all reactors in a multistage reactor system include the sum of all liquids (kg / h) and gases (kg / h) withdrawn from all reactors.

[0050] This difference between the amount supplied to all reactors and the amount of liquid / gas withdrawn from all reactors gives the total production Z (kg / h) of solid propylene homopolymer from the final or last reactor in the multistage reactor system.

[0051] The parameter P is given by P = ΔT cm ·Cp cm ·MF cm It is calculated as (ΔTcm = T of the cooling medium (cm) in the circulating gas cooler of the selected gas-phase reactor (GPR) cm_out and T cm_in The difference (°C), Cp cm This is the specific heat capacity (Jkg) of the cooling medium (cm) of the selected gas phase reactor (GPR). -1 ℃ -1 ) and MF cm This is the mass flow rate (kg / h) of the cooling medium (cm) in the cooling circuit of the selected gas-phase reactor.

[0052] The production rate X (kg / h) of propylene homo- or copolymer transferred from an upstream reactor to a selected gas-phase reactor is usually unknown or unmeasurable. The production rate X (kg / h) is the sum of all propylene homo- or copolymer (kg / h) produced in the reactor upstream of the selected gas-phase reactor and subsequently transferred from the reactor directly upstream of the selected gas-phase reactor to the gas-phase reactor. By calculating and providing the production rate X (kg / h) of propylene homo- or copolymer transferred from the upstream reactor, the production rate ZX (kg / h) of propylene homo- or copolymer produced in the selected gas-phase reactor can be determined, and therefore the production rate ZX (kg / h) can also be controlled.

[0053] The total feed rate Y (kg / h) is the feed rate, including all liquids, gases, and solids, from the upstream reactor to the selected gas-phase reactor. Typically, this feed includes solid propylene homopolymer or copolymer produced in the upstream reactor, as well as unreacted propylene and unreacted hydrogen.

[0054] The load R (kJ / h) is everything except the supply from the upstream reactor. Therefore, the load R (kJ / h) is the sum of all power (energy per unit of time) other than the supply from the upstream reactor. Preferably, the load R includes the compressor heating load, heat loss from the reactor system to the atmosphere, and the supply cooling / heating effect.

[0055] ΔH Y-X This is the enthalpy change (kJ / kg) of the liquid / gas being transferred from the upstream reactor to the selected gas-phase reactor. The enthalpy change is pressure and temperature dependent and can be determined by physical property methods such as RKS (Redlich-Kwong-Soave) based on the gas composition in the reactor (calculated by mass balance and also analyzed by gas chromatography and other methods from the gas) and condensation composition.

[0056] ΔH XΔH is the enthalpy change (kJ / kg) of propylene homo- or copolymer transferred from an upstream reactor to a selected gas-phase reactor. The enthalpy change depends on pressure and temperature. Since propylene homo- or copolymer is usually transferred in powder form, i.e., solid form, ΔH X It is usually 0 kJ / kg.

[0057] The average heat of reaction E in a selected gas-phase reactor (GPR) is given by: heat of reaction (propylene) · (propylene content of the product produced in the selected gas-phase reactor) + Σ[(heat of reaction (comomeron)) · (comomeron content of the product produced in the selected gas-phase reactor)]. The average heat of reaction can be found, for example, in the literature.

[0058] 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. When propylene copolymers are produced, the heats of formation of the comonomers must also be considered. For example, if a propylene copolymer contains ethylene, 1-butene, and / or 1-hexene as comonomers, the heats of formation of these comonomers must be considered, with values ​​of 3700 kJ / kg for ethylene, 1545 kJ / kg for 1-butene, and 988 kJ / kg for 1-hexene. The heats of formation of other comonomers can be found in the literature.

[0059] The comonomer content reacting with the final propylene copolymer can be assessed from the overall mass balance across all reactors and powder samples.

[0060] Preferably, the selected gas-phase reactor is operated in condensation mode. Condensation mode means that the degree of condensation of the circulating gas in the circulating gas cooler is in the range of greater than 0% to 15%, preferably in the range of 5% to 15%. The degree of condensation is calculated according to equation (2):

number

[0061] C gas The heat of condensation can be determined using physical property methods such as RKS (Redlich-Kwong-Soave).

[0062] Typically, propylene, as a monomer, is the main condensate component in circulating gas coolers.

[0063] The production rate ZX in step d) can be controlled by one or more methods. Preferably, the control in step d) is carried out by adjusting the floor level of the selected gas-phase reactor and / or adjusting the propylene partial pressure of the selected gas-phase reactor and / or adjusting the comonomer partial pressure and / or the floor temperature of the gas-phase reactor.

[0064] A fluidized bed gas-phase reactor contains a fluidized bed on which a polymerization catalyst is supported on an inert substrate. The level of this bed can be increased, which increases the mass of the polymer and thus the residence time. Residence time has a linear effect on the production rate. Furthermore, increasing the partial pressure of propylene and comonomer in a selected gas-phase reactor has an almost linear effect on the production rate. In addition, the bed temperature of a selected gas-phase reactor can be increased, thereby raising the productivity of the Ziegler-Natta catalyst to a specific catalyst-dependent temperature. Adjusting the aforementioned parameters is well known in the art.

[0065] In the first embodiment of the present invention shown in Figure 1, a circulating gas compressor (2) is located downstream of a 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 the circulating gas from the circulating gas outlet of the gas-phase reactor (1) to the circulating gas compressor (2), from where the compressed circulating gas is further transferred to the circulating gas cooler (3), and the circulating gas is returned 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] In the second embodiment of the present invention shown in Figure 2, a circulating gas compressor (2) is located upstream of a selected gas-phase reactor (1), and the gas-phase reactor (1) further comprises a condensate separator (4). In this second embodiment, a 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 coming out of the circulating gas cooler (3).

[0067] In this second embodiment, the gas circulation line (5) transfers the circulating gas from the circulating gas outlet of the gas-phase reactor (1) to the circulating gas cooler (3), from where the circulating gas is further transferred to the condensate separator (4). The condensed portion of the circulating gas exiting the bottom outlet of the condensate separator (4) is returned to the gas-phase reactor (1) via another line. The circulating gas exiting the top outlet of the condensate separator (4) is compressed via the gas circulation line (5) towards the circulating gas compressor (2), and the compressed circulating gas is further returned to the gas-phase reactor (1) via the circulating gas inlet of the gas-phase reactor (1). In this second embodiment, the circulating gas cooler (3) also 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). [Examples]

[0068] In the following embodiment, a multistage reactor system (see Figure 1) including a loop reactor as the first reactor and a subsequent gas-phase reactor (GPR) was simulated using "Aspen Plus" software. In this embodiment, the loop reactor is operated at 70°C and 50 bar, and the selected GPR(1) is operated at 70°C and 25 bar. The circulating gas composition is 1 mol% hydrogen, 2 mol% ethylene, and 10 mol% propane (impurity during propylene supply, accumulation in the process), with the remainder being propylene. The circulating gas is supplied to the gas circulation line (5) upstream of the circulating gas cooler via the gas circulation line inlet (5a) at a supply rate of 10,000 kg / h. The circulating gas compressor (2) is used to circulate the circulating gas through the circulating gas line (5) to the circulating gas cooler (3) and to fluidize the polymer bed in the selected GPR(1). Cooling medium inlet temperature T cm_in is 50℃, coolant outlet temperature T cm_out The temperature is 57.7℃, and the cooling medium is (cm) with a mass flow rate of MF. cm The load R 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 Cp cm The value was 4.18 kJ / (kg·℃).

[0069] The total production volume Z of the propylene-ethylene copolymer produced is 60,000 kg / h. The enthalpy change ΔH of the liquid. Y-X The concentration is 242 kJ / kg, and the enthalpy change of the powder is ΔH X The heat of polymerization is 0 kJ / kg. The enthalpy change is determined using the Redlich-Kwong-Soave (RKS) material model included in the "Aspen Plus" software. The heat of polymerization of the selected GPR is 2400 kJ / kg, and the total feed rate Y from the upstream reactor is 60000 kg / h. The upstream reactor is operated at a temperature of 70°C and a pressure of 50 bar.

[0070] The upstream reactor production rate X (kg / h) can be calculated from equation (1) as follows: 60000kg / hX=[(57.7℃-50℃)・4.18kJ / (kg・℃)・2000000kg / h-(180000kJ / h+(60000kg / hX)・242kJ / kg+X・0kJ / kg)] / 2400kJ / kg

[0071] Solving the equation, we obtain X (upstream reactor production rate) as 30,000 kg / h, which is produced in the upstream loop reactor. Therefore, the production rate of the selected GPR (ZX) is 30,000 kg / h.

[0072] Total gas flow rate MF gas The flow rate is 1,400,000 kg / h, and the temperature of the circulating gas is T cg_in The temperature is 71.5°C, and the temperature of the circulating gas from the cooler is T cg_out The temperature is 59.9°C. The degree of condensation can be calculated according to formula (2) of this specification: Degree of condensation = [(57.7℃-50℃)*4.18kJ / (kg·℃)*2,000,000kg / h-1,400,000kg / h*2.32kJ / (kg·℃)*(71.5℃-59.9℃)]·100 / (240kJ / kg) / (1,400,000kg / h) = 7.8%

[0073] The calculation of the degree of condensation according to equation (2) first involves the specific heat capacity Cp of the circulating gas. gasThe heat of condensation C of the circulating gas was calculated to be 2.32 kJ / (kg·℃) using the "Aspen Plus" software. gas This was calculated to be 240 kJ / kg using the "Aspen Plus" software.

[0074] Therefore, when the reactor is operated under the above conditions, the degree of condensation is 7.8. In other words, the selected gas-phase reactor operates in condensation mode. Since the dew point of the gas is 60.1°C, the degree of condensation cannot be tracked from the process side. Of the total heat, approximately 36% is removed by condensation in the circulating gas cooler, 10% by direct supply, and 54% by cooling in the circulating gas cooler.

[0075] The circulating gas flow velocity (m / s) is equal to the gas volumetric flow rate (m³). 3 / s) / [(diameter (m)) 2 ·π / 4], where the gas volumetric flow rate (m 3 (kg / s) is calculated as mass flow rate (kg / s) / density (kg / m³). 3 ) is the density (kg / m³). 3 ) is [pressure (kPa) · molar mass (kg / mol)] / [temperature (K) · compressibility · gas constant (kg·m)] 2 / (s 2 It is calculated as (·K·mol). The gas composition, pressure, and mass flow rate are known, and the compressibility is determined using "Aspen Plus" software.

[0076] With this configuration and the calculated circulating gas flow rate of 0.6 m / s inside the 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). [Explanation of Symbols]

[0077] The following reference numerals are used in the diagram: 1. Selected gas-phase reactor 1a Inlet of the supply from the upstream reactor to the selected gas-phase reactor 2. Circulating gas compressor 3. Circulating gas cooler 3a Coolant inlet 3b Coolant outlet 3c cooling circuit 4. Condenser 5. Gas circulation line 5a Gas circulation line inlet

Claims

1. A method for controlling the production rate of propylene homo or copolymer in a selected gas-phase reactor (1) of a multi-stage reactor system, The multi-stage reactor system includes a first reactor and one or more gas-phase reactors downstream of the first reactor, each gas-phase reactor comprising a gas circulation line (5), a circulating gas compressor (2), and a circulating gas cooler (3), the circulating gas cooler (3) comprising a cooling medium inlet (3a), a cooling medium outlet (3b), and a cooling circuit (3c), The above method involves the following steps: a) A step of polymerizing propylene and an arbitrary comonomer in the first reactor and one or more gas-phase reactors, In each gas-phase reactor, circulating gas is supplied to the gas-phase reactor via the gas circulation line (5), and at the same time, a cooling medium (cm) is supplied to the cooling circuit (3c) of the circulating gas cooler (3), thereby producing polypropylene homo or copolymer. The cooling medium (cm) is such that the temperature at the cooling medium inlet (3a) of the circulating gas cooler (3) is T ｉｎ Then, the temperature at the cooling medium outlet (3b) of the circulating gas cooler (3) is T ｏｕｔ And, The circulating gas comprises propylene and an optional comonomer, and the circulating gas is cooled by indirect heat exchange with the cooling medium (cm) in the cooling circuit (3c) of the circulating gas cooler (3). b) A step of selecting one gas-phase reactor (GPR) from the one or more gas-phase reactors of the multi-stage reactor system as the selected gas-phase reactor (1), c) A step of calculating the production rate Z-X (kg / h) of the propylene homo or copolymer produced in the selected gas-phase reactor (1) using formula (1): [Math 1] d) A step of controlling the production rate Z-X (kg / h) of the propylene homo or copolymer produced in the selected gas-phase reactor (1) using the calculated production rate Z-X (kg / h) from step c), Includes, In the above formula, Total production of solid propylene homo or copolymer Z (kg / h) = (amount supplied to all reactors in the multi-stage reactor system) - (liquid and gas withdrawn from all reactors in the multi-stage reactor system) P = ΔT ｃｍ ・C ｐｃｍ MF ｃｍ (ΔT ｃｍ = The T of the cooling medium (cm) in the circulating gas cooler of the selected gas-phase reactor (GPR) ｃｍ＿ｏｕｔ and T ｃｍ＿ｉｎ The difference (°C), Cp ｃｍ is the specific heat capacity (J / kg －１ °C －１ ) of the cooling medium (cm) of the cooling circuit of the selected gas phase reactor (GPR), MF ｃｍ This is the mass flow rate (kg / h) of the cooling medium (cm) in the cooling circuit of the selected gas-phase reactor (GPR), The production rate X (kg / h) of propylene homopolymer transferred from the upstream reactor to the selected gas-phase reactor, The total supply rate Y (kg / h) from the upstream reactor to the selected gas-phase reactor, Load R (kJ / h) other than the supply 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 = The enthalpy change (kJ / kg) of the propylene homo or copolymer transferred from the upstream reactor to the selected gas-phase reactor, and E is the average heat of reaction of the selected GPR (E = 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 upstream reactor is a reactor located directly upstream of the selected gas-phase reactor (1), in this method.

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 claim 1 or 2, wherein the multi-stage reactor system includes the first reactor and two or three gas-phase reactors downstream of the first reactor.

4. The method according to any one of claims 1 to 3, wherein the multistage reactor system includes a prepolymerization reactor upstream of the first reactor, and the prepolymerization reactor is preferably a loop reactor.

5. The method according to any one of claims 1 to 4, wherein the selected gas-phase reactor (1) is operated in condensation mode.

6. The method according to any one of claims 1 to 5, wherein the circulating gas further contains hydrogen.

7. The method according to any one of claims 1 to 6, 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 claims 1 to 8, wherein the control in step d) is performed by adjusting the floor level of the selected gas-phase reactor and / or adjusting the propylene partial pressure of the selected gas-phase reactor and / or adjusting the comonomer partial pressure of the selected gas-phase reactor (1) and / or adjusting the floor temperature of the selected gas-phase reactor (1).

10. The method according to any one of claims 1 to 9, wherein the circulating gas compressor (2) is located downstream of the selected gas-phase reactor (1), or the circulating gas compressor (2) is located upstream of the selected gas-phase reactor (1).

11. The method according to any one of claims 1 to 10, 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 claims 1 to 11, wherein the one or more gas-phase reactors include means for supplying propylene and / or comonomers and / or hydrogen to the one or more gas-phase reactors.

13. The method according to any one of claims 1 to 12, wherein the first reactor includes means for supplying propylene and / or comonomer and / or hydrogen to the first reactor.

14. The cooling medium (cm) is at a temperature T at the cooling medium inlet (3a) of the circulating gas cooler (3). ｃｍ＿ｉｎ The method according to any one of claims 1 to 13, wherein the temperature is 40°C to 60°C, preferably 45°C to 55°C.

15. The method according to any one of claims 1 to 14, wherein the cooling medium (cm) contains water or consists of water.

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