Solvent recirculation system

Abstract

The present invention relates to a solvent recycling system and comprises a solvent vessel outflow line configured to transport a solvent stream outflowing from a solvent vessel and connecting the solvent vessel and a buffer vessel, a buffer vessel outflow line configured to transport a feed stream outflowing from the buffer vessel, one or more feed supply lines connected with the solvent vessel outflow line, a densimeter arranged at a downstream end of the point of connection of the one or more feed supply lines, and a calculation unit receiving information on measured values of the densimeter and a material flow meter and configured to predict a composition of the feed stream transported via the buffer vessel outflow line using a state equation and a material balance, wherein the one or more feed supply lines and the buffer vessel outflow line each comprise the material flow meter.

Description

TECHNICAL FIELD

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Korean Patent Application No. 10-2021-0164957, filed on November 25, 2021, and Korean Patent Application No. 10-2022-0115830, filed on September 14, 2022, the entire contents of which are incorporated herein by reference as part of the specification. TECHNICAL FIELD

[0004] The present invention relates to a solvent recycling system, and more particularly, to a solvent recycling system capable of calculating in real time a composition of a feed stream supplied to a reactor of a polymerization process when a solvent separated and recovered in the polymerization process is reused in the polymerization process. BACKGROUND

[0005] In a conventional polymer polymerization method, according to a method of preparing a reaction product containing a desired product, purifying the desired product from the reaction product, and separating, recovering, and reusing a solvent used for polymerization, etc., raw material costs can be reduced and the price competitiveness of the product can be improved.

[0006] The feed stream supplied to the reactor can include a solvent and a raw material component, and the solvent can include fresh solvent and recycled solvent separated and recovered in the polymerization process. In this case, since it is difficult to measure the composition of the solvent recycled in the polymerization process, there is a problem that it is also difficult to determine the composition of the feed stream supplied to the reactor of the polymerization process.

[0007] Therefore, conventionally, the composition of the feed stream is not determined from the measured value of the feed stream. That is, conventionally, the composition of the feed stream is determined by calculation of a state equation and material balance in combination with information on conversion, temperature, pressure, and heat removal conditions of the reactor, and environmental information such as information on post-treatment flow rate, temperature, pressure, residence time, level, and operating condition information of a rotating device. However, since the sensitivity of the theory and the error margin according to the assumption are large, and the composition of the feed stream is calculated using environmental information, it is difficult to measure in real time to what extent changes applied to the polymerization process are reflected to the recycling unit, and it is difficult to apply when the process does not converge. SUMMARY

[0008] TECHNICAL PROBLEM

[0009] The present invention was made to solve the problems mentioned in the art as background of the invention, and the object thereof is to provide a solvent recycling system capable of optimizing the production conditions of a polymer by calculating in real time the composition of a feed stream supplied to a reactor of a polymerization process when a solvent separated and recovered in the polymerization process is reused in the polymerization process.

[0010] Technical Solution

[0011] To achieve this object, according to one aspect of the present application, there is provided a solvent recycling system including: a solvent container discharge line configured to transport a solvent stream discharged from a solvent container and connecting the solvent container and a buffer container; a buffer container discharge line configured to transport a feed stream discharged from the buffer container; one or more feed supply lines connected with the solvent container discharge line; a densimeter provided at a rear end of a point where the one or more feed supply lines are connected; and a calculation section receiving information on measured values of the densimeter and a material flow meter and configured to predict a composition of the feed stream transported through the buffer container discharge line using a state equation and material balance, wherein the feed supply line and the buffer container discharge line each include the material flow meter.

[0012] Advantageous Effects

[0013] According to the solvent recycling system of the present application, by calculating a composition of a feed stream containing recycled solvent in real time, and by calculating back a composition of recycled solvent, a composition of the entire process can be estimated.

[0014] Further, by estimating a composition of a feed stream in real time, polymer production conditions can be optimized to shorten a start-up, a grade change, and a shut-down. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 A process of operating a solvent recycling system according to one embodiment of the present application is explained. DETAILED DESCRIPTION

[0016] The terms or words used in the specification and claims of the present application should not be construed as being limited to the ordinary or dictionary meanings and should be interpreted to accord with the concept of the present application based on the principle that the inventor can properly define the concepts of the terms to best describe his or her application.

[0017] In the present application, the term "stream" can refer to a flow of fluid in a process, and can also refer to a fluid itself flowing in a line (pipe). Specifically, "stream" can refer to both a fluid itself and a flow of fluid flowing in a line connecting each device. Further, a fluid can include any one or more components of a gas, a liquid, and a solid.

[0018] Meanwhile, in the present invention, "downstream" can refer to the downstream of a specific point, and "upstream" can refer to the upstream of a specific point. For example, the "downstream" of a buffer vessel can refer to the downstream end discharged from the buffer vessel, and the "upstream" of the buffer vessel can refer to the upstream end introduced into the buffer vessel.

[0019] Hereinafter, the present invention will be described in detail with reference to Figure 1 The present invention will be described in more detail to help the understanding of the present invention.

[0020] According to the present invention, a solvent recycling system is provided. More specifically, a solvent recycling system is provided, which includes a solvent vessel discharge line 140 configured to transport a solvent stream discharged from a solvent vessel 100 and connecting the solvent vessel 100 and a buffer vessel 200, a buffer vessel discharge line 210 configured to transport a feed stream discharged from the buffer vessel 200, one or more feed supply lines connected to the solvent vessel discharge line 140, a density meter provided at the downstream of the point where the one or more feed supply lines are connected, and a calculation section receiving information on the measured values of the density meter and a material flow meter and configured to predict the composition of the feed stream transported through the discharge line of the buffer vessel 200, wherein the one or more feed supply lines and the buffer vessel discharge line 210 each include a material flow meter.

[0021] According to one embodiment of the present invention, the polymerization method of a polymer can include a preparation step and a post-treatment step. Specifically, the preparation step can be a step of preparing a reaction product containing a desired product by supplying a feed stream to a reactor, and the post-treatment step is a step of purifying the desired product from the reaction product and separating and recovering a solvent used for polymerization, etc.

[0022] According to one embodiment of the present invention, the reactor can be a continuous stirred tank reactor (CSTR), a plug flow reactor (PFR), or a loop reactor. Meanwhile, the polymerization method of a polymer is a method of producing a polyolefin by polymerizing a monomer in a solvent, and the solvent can be a fresh solvent or a mixture including paraffin, isoparaffin, and naphtha. Meanwhile, the monomer can include an α-olefin having 2 to 10 carbon atoms.

[0023] Meanwhile, the reaction product can be discharged from the reactor and subjected to a post-treatment step of separating and purifying a desired product, for example, a polyolefin, from unreacted monomers and solvents. That is, the post-treatment step can include a process of separating unreacted monomers and solvents as light components and a polyolefin as a heavy component by a separator and recovering the unreacted monomers and solvents. Here, the separator can be a gas-liquid separator or a liquid-liquid separator. The gas-liquid separator can be, for example, a devolatilizer such as a flash device.

[0024] When the separator is a gas-liquid separator, the stream discharged from the upper portion of the gas-liquid separator can include the solvent, and if necessary, the upper portion discharge stream can pass through the heat exchanger and the condensation buffer vessel. The solvent recovered from the upper portion discharge stream can be a liquid or a gas. In this case, the recovered liquid solvent and the gas solvent can be recycled to the solvent vessel 100 through the liquid solvent recycle line 120 and the gas solvent recycle line 130.

[0025] Meanwhile, when the separator is a liquid-liquid separator, the solvent is discharged from the upper portion of the liquid-liquid separator in a liquid state. In this case, the recovered liquid solvent can be recycled to the solvent vessel 100 through the liquid solvent recycle line 120.

[0026] Accordingly, the solvent recovered in the post-treatment step can include one or more than one of a gas solvent and a liquid solvent, and the solvent vessel 100 can include one or more than one of the liquid solvent recycle line 120 and the gas solvent recycle line 130 to receive one or more than one of the gas solvent and the liquid solvent recovered in the post-treatment step.

[0027] In this case, since the composition of the solvent recovered in the post-treatment step is continuously affected by the load of the separator that separates the solvent in the post-treatment step, the type of monomer, and the operating conditions, it is difficult to determine the composition in real time. In addition, when the solvent recovered in the post-treatment step is included as the solvent of the feed stream supplied to the reactor of the preparation step, it is also difficult to determine the composition of the feed stream.

[0028] Accordingly, conventionally, the composition of the feed stream is not determined from the measured value of the feed stream. That is, conventionally, the composition of the feed stream is determined by the calculation of the state equation and the material balance in combination with information on the conversion rate, temperature, pressure, and heat removal conditions of the reactor and environmental information such as information on the post-treatment flow rate, temperature, pressure, residence time, level, and operating condition information of the rotating device. However, since the phase separation and the reaction are assumed to cause a large error range and the composition of the feed stream is calculated using the environmental information, it is difficult to measure in real time to which extent the changes applied to the polymerization process are reflected to the circulating unit, and it is difficult to apply when the process does not converge.

[0029] On the contrary, in the present invention, by calculating the composition of the feed stream in real time using the solvent recycle system, it is possible to shorten the start-up period, the grade change period, and the shutdown period. In addition, it is possible to provide a solvent recycle system that can optimize the polymer production conditions by tracing back the composition of the recycled solvent and estimating the composition of the entire process through the material balance.

[0030] In addition to the liquid solvent recycle line 120 and the gas solvent recycle line 130, the solvent container 100 can include a solvent container supply line 110. The solvent container supply line 110 can include one or more of a solvent and a monomer supplied to a reactor through the solvent container 100 and a buffer container 200 described later. In this case, the solvent feed supply line 110 can include a material flow meter, and the material flow meter can transmit a measurement value of a material flow rate of a fresh solvent supplied through the solvent feed supply line 110 to the computing section. The fresh solvent can be appropriately selected according to a product required in a polymerization process.

[0031] An off gas discharge line for discharging off gas in the solvent container 100 can be provided at an upper portion of the solvent container 100.

[0032] The solvent container 100 can include a thermometer and a pressure gauge. Specifically, the thermometer and the pressure gauge can measure a temperature and a pressure of the solvent container 100, and the measurement values of the thermometer and the pressure gauge provided in the solvent container 100 can indicate a temperature and a pressure of a solvent stream discharged from the solvent container 100.

[0033] According to one embodiment of the present application, a solvent container discharge line 140 can be provided at a lower portion of the solvent container 100. That is, a liquid solvent stream containing a solvent present in the solvent container 100 (for example, a solvent recovered in a post-treatment step and a fresh solvent) is discharged and delivered through the solvent discharge line 140, and the solvent container discharge line 140 connects the solvent container 100 and the buffer container 200.

[0034] One or more feed supply lines can be connected to the solvent container discharge line 140. Specifically, components delivered through the feed supply lines can include one or more of a monomer and a solvent used to produce a desired product in a polymer polymerization process. Accordingly, a feed stream supplied to a reactor through the buffer container 200 described later can be formed. In addition, the number of the feed supply lines can be the same as the number of monomer components required to produce a desired product in a polymerization process.

[0035] A density meter can be provided at a rear end of a point at which one or more feed supply lines are connected. Specifically, the density meter is provided at a rear end of a point at which the feed supply lines are connected, and the density meter can measure a density of a stream in which a solvent stream delivered through the solvent container discharge line 140 and monomer components delivered through the feed supply lines are mixed, and transmit the density to the computing section.

[0036] The one or more feed supply lines include two feed supply lines, and when two or more feed supply lines are connected to the solvent vessel discharge line 140, the densimeter can be provided on all or a part of the points between the connected two or more feed supply lines and the buffer vessel discharge flow 210. For example, the densimeter can be provided between the two or more feed supply lines connected to the solvent vessel discharge line 140, and the densimeter provided at the rear end of the point where the last end feed supply line is connected can be provided in the buffer vessel discharge line 210.

[0037] Here, the rear end of the point where the respective feed supply lines are connected can refer to a portion between the connection point of the feed supply line to the solvent vessel discharge line 140 or the buffer vessel discharge line 210 and the connection point of another subsequent feed supply line after the feed supply line to the solvent vessel discharge line 140 or the buffer vessel discharge line 210 as the point where the densimeter is located.

[0038] By providing the densimeter as described above, the density of each section where the new component is combined with the solvent flow can be measured, and thus, the composition of the feed flow can be more accurately calculated.

[0039] As an example, when two monomers are used in the polymerization process of a polymer, the first feed supply line 141 and the second feed supply line 142 can be connected to the solvent vessel discharge line 140, the densimeter can be provided between the point where the first feed supply line 141 is connected to the solvent vessel discharge line 140 and the point where the second feed supply line 142 is connected to the solvent vessel discharge line 140, and the densimeter can be provided in the buffer vessel discharge line 210.

[0040] As another example, when three monomers are used in the polymerization process of a polymer, the first feed supply line 141, the second feed supply line 142, and the third feed supply line 143 can be connected to the solvent vessel discharge line 140, respectively, the densimeter can be provided between the point where the first feed supply line 141 is connected to the solvent vessel discharge line 140 and the point where the second feed supply line 142 is connected to the solvent vessel discharge line 140, the densimeter can be provided between the point where the second feed supply line 142 is connected to the solvent vessel discharge line 140 and the point where the third feed supply line 143 is connected to the solvent vessel discharge line 140, and the densimeter can be provided in the buffer vessel discharge line 210.

[0041] The one or more feed supply lines can include a material flow meter. The material flow meter can measure the material flow rate of the monomer component delivered through the respective feed supply line and transmit the measured value to the calculation part.

[0042] A temperature gauge and a pressure gauge can be provided at the front and rear ends of the point where the last end of the solvent container discharge line 140 is connected to the feed supply line, respectively. Specifically, the temperature gauge and the pressure gauge can be provided at the point where the last end of the solvent container discharge line 140 is connected to the feed supply line and the front end of the buffer container discharge line 210. Accordingly, the temperature and the pressure of the material stream can be measured at the front and rear ends of the point where the last end of the feed supply line is connected, and the measured values can be transmitted to the calculation unit.

[0043] A heat exchanger can be further provided between the point where the last end of the solvent container discharge line 140 is connected to the feed supply line and the buffer container 200. The heat exchanger can be used to completely dissolve the monomer components supplied through the one or more feed supply lines in the solvent stream delivered through the solvent container discharge line 140, and the heat exchange can improve the accuracy of the calculation unit in calculating the composition of the feed stream when the monomer components remain in a liquid phase.

[0044] The solvent container discharge line 140 can be provided with a pump 150. The pump 150 increases the pressure to a pressure lower than that of the last end of the feed supply line 143, thereby delivering the solution and forming a reaction pressure. For example, the pump 150 can be installed at the front end of the point where the last end of the feed supply line is connected in the solvent container discharge line 140, and the measured values of the temperature gauge, the pressure gauge, the viscosity gauge, and the material flow gauge at the rear end of the pump 150 can be transmitted to the calculation unit.

[0045] The buffer container 200 can include a temperature gauge and a pressure gauge like the solvent container 100. Specifically, the temperature gauge and the pressure gauge can measure the temperature and the pressure of the buffer container 200, and the measured values of the temperature gauge and the pressure gauge provided in the buffer container 200 can indicate the temperature and the pressure of the feed stream discharged from the buffer container 200.

[0046] According to one embodiment of the present application, the buffer container 200 can include a buffer container discharge line 210 for discharging and delivering the feed stream in which the solvent stream and the monomer components are mixed. The buffer container discharge line 210 can be connected to a reactor of a polymer polymerization process to supply the feed stream to the reactor.

[0047] The buffer container discharge line 210 can include a material flow gauge. The material flow gauge can measure the material flow rate of the feed stream delivered through the buffer container discharge line 210, and transmit the measured value to the calculation unit.

[0048] A pump 220 can also be provided in the buffer container discharge line 210. The pump 220 can be installed at the front end of the point where the material flow gauge is installed, thereby determining the final pressure of the reactor.

[0049] According to one embodiment of the present application, the solvent recirculation system can include a calculation section for calculating the composition of the feed stream by receiving the measurement values of the densimeter and the material flow meter provided in the solvent recirculation system. Specifically, the calculation section can receive information on the measurement values of each of the densimeter and the material flow meter, and calculate the composition of the feed stream delivered through the discharge line of the buffer vessel using the state equation of the steady state and the material balance. In addition, the calculation section can be used to calculate the composition of the feed stream by receiving the measurement values of the thermometer and the pressure gauge provided in the solvent recycing system.

[0050] In one embodiment of the present application, the calculation section can calculate the composition of the feed stream supplied to the reactor of the preparation step by the material balance using the measurement value of the material flow rate transmitted.

[0051] As an example, the method of calculating the composition of the feed stream in a polymer polymerization process using a solvent and two monomer components using the solvent recirculation system according to the present application can be exemplified.

[0052] Specifically, when the solvent is referred to as s, the monomer component delivered through the first feed supply line 141 is referred to as m1, the monomer component delivered through the second feed supply line 142 is referred to as m2, and the feed stream delivered through the discharge line of the buffer vessel 200 is referred to as the 8th stream. Also, the stream delivered through the solvent vessel discharge line 140 between the point at which the pump 150 and the third feed supply line 143 are connected is referred to as the 7th stream, and the composition of m2 in the eighth stream can be expressed as x m2 , the composition of m1 can be expressed as x m1 , and the composition of s can be expressed as x s , and in this case, since the sum of the compositions of m1, m2, and the solvent is 1, x s can be expressed as 1-x m1 -x m2 .

[0053] In addition, the composition of m2 in the 7th stream can be expressed as x' m2 , the composition of m1 can be expressed as x' m1 , the composition of s can be expressed as x' s , and the composition of the 7th stream can be expressed as the following relation 1 by the material balance of the m2 stream before the 8th stream is added.

[0054] [Relation 1]

[0055]

[0056] In relation 1, m7 is the total material flow rate of the 7th stream, m8 is the total material flow rate of the 8th stream, m m2 is the material flow rate of m2 in the 8th stream, and mm1 is the material flow rate of ml in the 8th stream, m s is the material flow rate of solvent s in the 8th stream, and m Fm2 is the total material flow rate of fresh m2 stream. Thus, the composition of ml, m2, and solvent s in the 7th stream can be expressed as a function of the 8th stream.

[0057] Meanwhile, the material density can be expressed by the following relation 2 from the relation of molar volume calculated by the equation of state and average molecular weight (mw).

[0058] [Relation 2]

[0059]

[0060] In relation 2, p is the material density, mw is the average molecular weight, Z is the compressibility factor, T is the temperature, P is the pressure, and R is the gas constant.

[0061] In this case, mw is a function of the composition, Z is a function of the composition and temperature calculated by the equation of state, and since the composition of the 7th stream can be expressed by replacing the composition of the 8th stream with relation 1, each stream can be expressed by the equations in the following relation 3.

[0062] [Relation 3]

[0063]

[0064] In relation 3, p7 is the material density of the 7th stream, p8 is the material density of the 8th stream, mw is the average molecular weight of the 8th stream, mw' is the average molecular weight of the 7th stream, Z is the compressibility factor of the 8th stream and is a function of the composition and temperature calculated by the equation of state, Z' is the compressibility factor of the 7th stream and is a function of the composition and temperature calculated by the equation of state, T8 is the temperature of the 8th stream, T7 is the temperature of the 7th stream, P8 is the pressure of the 8th stream, P7 is the pressure of the 7th stream, x m2 is the composition of m2, x m1 is the composition of ml, and R is the gas constant.

[0065] Since the temperature, pressure, and density values are measured in the 7th stream and the 8th stream, in order to obtain the composition of m2 and the composition of ml, the two equations in relation 3 can be combined to solve. In this way, the m2 composition and the ml composition of the 8th stream are obtained by relations 1 to 3, and thus, the composition of s can be obtained.

[0066] In addition, through the composition of the 8th stream, the composition of the solvent finally recovered in the post-treatment step can be inversely calculated by inversely calculating the stream composition at the front end of the points connecting the respective feed supply lines.

[0067] The calculation method in the calculation section can be applied in the same manner according to the number of feed supply lines, i.e., the number of monomer components required in the polymerization process.

[0068] By the composition of the feed stream calculated in the calculation section and the composition of the solvent recovered in the post-treatment step, the flow rates of the monomer components delivered through the feed supply lines and the operating conditions of the reactor are controlled to minimize off-spec products and to perform efficient separation process operation, and thus, the production conditions of the polymer can be optimized.

[0069] As described above, the solvent recycling system according to the present application is illustrated in the specification and the drawings, but the specification and the drawings only describe and illustrate the basic components for understanding the present application, and the methods and apparatuses that are not separately described and not illustrated other than the methods and apparatuses illustrated in the above-described specification and drawings can be appropriately applied and used to implement the solvent recycling system according to the present application. For the composition prediction of the examples, the same Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) equation of state was used.

[0070] Hereinafter, the present application will be described in more detail by examples. However, the following examples are intended to illustrate the present application, and it will be apparent to those skilled in the art that various changes and modifications can be made within the scope and spirit of the present application, and the scope of the present application is not limited thereto.

[0071] Examples and Comparative Examples

[0072] Comparative Example 1

[0073] As Figure 1 The process flow diagram as shown operates the solvent recycling system.

[0074] Specifically, fresh hexane (fresh C6) is supplied to the solvent container 100 through the solvent container supply line 110 without supplying the solvents and monomers recovered in the polyolefin polymerization process through the liquid solvent recycling line 120 and the gas solvent recycling line 130. In this case, a thermometer and a pressure gauge are installed in the solvent container 100, and a material flow meter is installed in the solvent container supply line 110.

[0075] The solvent stream is delivered through the solvent container discharge line 140 installed at the lower portion of the solvent container 100, octene (fresh C8) is supplied through the first feed supply line 141 connected to the solvent container discharge line 140, butylene (fresh C4) is not supplied through the second feed supply line 142, and ethylene (fresh C2) is supplied through the third feed supply line 143. In this case, material flow meters are installed in the first to third feed supply lines 141 to 143.

[0076] The heat exchanger is installed at the rear end of the point where the solvent container discharge line 140 is connected to the third feed supply line 143, and the stream containing hexene, octene and ethylene is subjected to heat exchange and then supplied to the buffer container 200.

[0077] The feed stream is delivered through the buffer container discharge line 210 installed at the lower portion of the buffer container 200, and the feed stream is supplied to the reactor of the polyolefin polymerization process. In this case, a pressure gauge and a thermometer are installed in the buffer container discharge line 210.

[0078] The mass fractions of hexene (C6), octene (C8), butene (C4) and ethylene (C2) in the 8th stream and the 7th stream are shown in Table 1 below.

[0079] Comparative Example 2

[0080] Comparative Example 2 is performed in the same manner as in Comparative Example 1, except that the solvent and monomers recovered in the polyolefin polymerization process are supplied through the liquid solvent recycle line 120 and the gas solvent recycle line 130, and the flow rates of fresh C6, fresh C8 and fresh C2 supplied through the solvent container supply line 110 and the first to third feed supply lines 141 to 143 are controlled in Comparative Example 1.

[0081] Comparative Example 3

[0082] Comparative Example 3 is performed in the same manner as in Comparative Example 1, except that the flow rates of fresh C6 and fresh C2 supplied through the solvent container supply line 110 and the third feed supply line 143 are different, and fresh C4 is supplied through the second feed supply line 142 instead of fresh C8 in Comparative Example 1. In addition, the mass fractions of hexene (C6), octene (C8), butene (C4) and ethylene (C2) in the 8th stream and the 7th stream are shown in Table 1 below.

[0083] Comparative Example 4

[0084] Comparative Example 4 is performed in the same manner as in Comparative Example 3, except that the solvent and monomers recovered from the polyolefin polymerization process are supplied through the liquid solvent recycle line 120 and the gas solvent recycle line 130, and the flow rates of fresh C6, fresh C4 and fresh C2 supplied through the solvent container supply line 110, the second feed supply line 142 and the third feed supply line 143 are controlled in Comparative Example 3.

[0085] Example 1

[0086] As Figure 1 shown in the process flow diagram, the solvent recycle system is operated.

[0087] Specifically, fresh hexane (fresh C6) is supplied to the solvent vessel 100 through the solvent vessel supply line 110, and a mixture of solvents and monomers recovered in the polyolefin polymerization process is not supplied through the liquid solvent recycle line 120 and the gas solvent recycle line 130. In this case, a thermometer and a pressure gauge are installed in the solvent vessel 100, and a material flow meter is installed in the solvent vessel supply line 110.

[0088] The solvent stream is delivered through the solvent vessel discharge line 140 installed at the lower portion of the solvent vessel 100, octene (fresh C8) is supplied through the first feed supply line 141 connected to the solvent vessel discharge line 140, butene (fresh C4) is not supplied through the second feed supply line 142, and ethylene (fresh C2) is supplied through the third feed supply line 143. In this case, material flow meters are installed in the first feed supply line 141 to the third feed supply line 143, a density meter is installed between the first feed supply line 141 and the second feed supply line 142, and a density meter is installed between the second feed supply line 142 and the third feed supply line 143.

[0089] A heat exchanger is installed at the rear end of the point where the third feed supply line 143 is connected in the solvent vessel discharge line 140, and the stream containing hexene, octene, and ethylene is subjected to heat exchange, and then supplied to the buffer vessel 200.

[0090] The feed stream is delivered through the buffer vessel discharge line 210 installed at the lower portion of the buffer vessel 200, and supplied to the reactor of the polyolefin polymerization process. In this case, a pressure gauge, a thermometer, and a density meter are installed in the buffer vessel discharge line 210.

[0091] In addition, the flow rates of fresh C6, fresh C8, and fresh C2 supplied through the solvent vessel supply line 110, the first feed supply line 141, and the third feed supply line 143 are controlled as in Comparative Example 1.

[0092] The measured values from the thermometer, the pressure gauge, the density meter, and the material flow meter are transmitted to a calculation section (not shown). In the calculation section, the material balance and the equation of state are combined and applied through Equations 1 to 3, the mass fractions of hexene (C6), octene (C8), butene (C4), and ethylene (C2) in the 8th stream and the 7th stream are calculated, and the results are shown in Table 1 below.

[0093] Example 2

[0094] Example 2 was performed in the same manner as in Example 1, except that in Example 1, the solvent and monomers recovered in the polyolefin polymerization process were supplied through the liquid solvent recycle line 120 and the gas solvent recycle line 130, and the flow rates of the fresh C6, fresh C8, and fresh C2 supplied through the solvent vessel supply line 110, the first feed supply line 141, and the third feed supply line 143 were controlled in the same manner as in Comparative Example 2.

[0095] The measured values from the thermometers, the pressure gauges, the densitometers, and the material flowmeters were transferred to a calculation section (not shown). In the calculation section, the material balances and the equation of state were combined and applied by the relations 1 to 3 to calculate the mass fractions of hexene (C6), octene (C8), butene (C4), and ethylene (C2) in the 8th stream and the 7th stream, the results of which are shown in Table 1 below.

[0096] Example 3

[0097] Example 3 was performed in the same manner as in Example 1, except that the flow rates of the fresh C6 and fresh C2 supplied through the solvent vessel supply line 110 and the third feed supply line 143 were different, and fresh C4 was supplied through the second feed supply line 142 instead of fresh C8 in Example 1. The measured values from the thermometers, the pressure gauges, the densitometers, and the material flowmeters were transferred to a calculation section (not shown). In the calculation section, the material balances and the equation of state were combined and applied by the relations 1 to 3 to calculate the mass fractions of hexene (C6), octene (C8), butene (C4), and ethylene (C2) in the 8th stream and the 7th stream, the results of which are shown in Table 1 below.

[0098] Example 4

[0099] Example 4 was performed in the same manner as in Example 3, except that the solvent and monomers recovered in the polyolefin polymerization process were supplied through the liquid solvent recycle line 120 and the gas solvent recycle line 130, and the flow rates of the fresh C6, fresh C4, and fresh C2 supplied through the solvent vessel supply line 110 and the second feed supply line 142 to the third feed supply line 143 were controlled in Example 3.

[0100] The measured values from the thermometers, the pressure gauges, the densitometers, and the material flowmeters were transferred to a calculation section (not shown). In the calculation section, the material balances and the equation of state were combined and applied by the relations 1 to 3 to calculate the mass fractions of hexene (C6), octene (C8), butene (C4), and ethylene (C2) in the 8th stream and the 7th stream, the results of which are shown in Table 1 below.

[0101] [Table 1]

[0102]

[0103] In Table 1, in the case of the composition of the 8th stream in Example 1, RMSE represents the root mean square error value of the calculated values compared to the measured values in Comparative Example 1, and in Example 3, RMSE represents the root mean square error value of the calculated values compared to the measured values in Comparative Example 3.

[0104] Referring to Table 1, in the case of Comparative Example 1 and Example 1, and Comparative Example 3 and Example 3, the composition of the 8th stream and the 7th stream was calculated using the solvent recirculation system according to the present application without using the recovered solvent. The results confirm that when fresh C8 monomer is used (Example 1), the RMSE is as low as 0.008, and when fresh C4 monomer is used (Example 3), the RMSE is as low as 0.0013.

[0105] Furthermore, in Comparative Examples 2 and 4, using the recovered solvent, it is not possible to measure the 8th stream, and therefore, it is not possible to retro calculate the composition of the 7th stream or the recovered solvent. In contrast, in the case of Example 2 and Example 4, the composition of the 8th stream can be calculated using the solvent recirculation system according to the present application, and therefore, the composition of the 7th stream or the composition of the recovered solvent can be retro calculated. This model for predicting the composition of the recirculated solvent can be improved by accumulation of operational data, and this model can be used universally in processes where the feed is a liquid.

Claims

1. A solvent recycling system, the solvent recycling system comprising: A solvent container discharge line, the solvent container discharge line being configured to deliver a flow of solvent discharged from a solvent container and connecting the solvent container and a buffer container; A buffer container discharge line, the buffer container discharge line being configured to deliver a feed stream discharged from the buffer container; One or more feed supply lines are connected to the solvent container discharge line; A densitometer, wherein the densitometer is disposed at the rear end of the point where the one or more feed supply lines are connected to the solvent container discharge line; as well as The calculation unit receives information about the measurements from the density meter and the material flow meter, and is configured to use equations of state and material balance to predict the composition of the feed flow delivered through the buffer container discharge pipeline. Wherein, each of the one or more feed supply lines and the buffer container discharge line includes the material flow meter. Wherein, the one or more feed supply lines include two or more feed supply lines, and The densitometer is located in all or part of the section between the two or more feed supply lines that connect to the solvent container discharge line, and in the buffer container discharge line.

2. The solvent recycling system according to claim 1, wherein, The solvent container includes one or more of a liquid solvent recirculation line and a gaseous solvent recirculation line.

3. The solvent recycling system according to claim 1, wherein, The solvent container includes a solvent container supply line, and the solvent container supply line includes the material flow meter.

4. The solvent recycling system according to claim 1, wherein, The solvent container includes a thermometer and a pressure gauge.

5. The solvent recycling system according to claim 1, wherein, The densitometer is located at the rear end of the point where the feed supply line at the end of the one or more feed supply lines connects to the solvent container discharge line.

6. The solvent recycling system according to claim 1, wherein, The one or more feed supply lines connected to the solvent container discharge line include a first feed supply line and a second feed supply line, and The densitometer is installed between the point where the first feed supply line connects to the solvent container discharge line and the point where the second feed supply line connects to the solvent container discharge line, and the densitometer is also installed in the buffer container discharge line.

7. The solvent recycling system according to claim 1, wherein, The one or more feed supply lines connected to the solvent container discharge line include a first feed supply line, a second feed supply line, and a third feed supply line, and The densitometer is installed between the point where the first feed supply line connects to the solvent container discharge line and the point where the second feed supply line connects to the solvent container discharge line, the densitometer is installed between the point where the second feed supply line connects to the solvent container discharge line and the point where the third feed supply line connects to the solvent container discharge line, and the densitometer is installed in the buffer container discharge line.

8. The solvent recycling system according to claim 1, wherein, A thermometer and a pressure gauge are installed at the front end of the point where the feed supply line is connected to the last end of one or more feed supply lines located in the solvent container discharge line, and the measured values ​​of the thermometer and the pressure gauge are transmitted to the calculation unit.

9. The solvent recycling system according to claim 1, wherein, A thermometer and a pressure gauge are installed in the discharge pipeline of the buffer container, and the measured values ​​of the thermometer and the pressure gauge are transmitted to the calculation unit.

10. The solvent recirculation system of claim 1, further comprising a heat exchanger disposed between the point where the feed supply line is connected to the one or more feed supply lines located at the last end of the solvent container discharge line and the buffer container.

11. The solvent recycling system according to claim 1, wherein, The calculation unit receives information about the measurements of the densitometer and the material flow meter, and uses the state equation and the material balance to calculate the composition of the feed flow delivered through the buffer container discharge pipeline.

Images