On-line determination method and device for polymer concentration

Abstract

The invention relates to an online determination method and device for polymer concentration. The method comprises the following steps: measuring the overall density of a polymer slurry system; respectively determining the density of a liquid phase and the density of a polymer solid phase in the polymer slurry system; based on the overall density, the density of the liquid phase and the density of the solid phase of the polymer, the concentration of the polymer in the polymer slurry system is deduced through back calculation of a density mixing rule model, and therefore the concentration of the polymer slurry system can be obtained in real time and accurately.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of chemical engineering, in particular to a method and device for on-line determination of polymer concentration. BACKGROUND

[0002] There are many materials in the polymer device that are not homogeneous phases, and some may be in slurry state, for example, the process of producing polyethylene and polypropylene by slurry method, the polymerization system in the reactor is in a multi-phase (non-single phase) slurry state. During the production and operation of the polymer device, the proportion (concentration) of the polymer in the material is extremely important, because it affects the stability of the polymerization reaction state and the control of the polymerization reaction. The concentration of some polymers in the material relates to the amount of additives added in the polymer production process, and affects whether the final product quality is qualified or not. Therefore, in the polymer production process, it is very crucial to determine the concentration of the polymer in the material system in time.

[0003] However, the existing methods are mostly focused on inferring the concentration from the density based on rich experimental data or directly measuring according to the analysis instrument. For example, the patent with publication number CN120510959A discloses a method for constructing a concentration prediction model of a mixed solution and a concentration soft measurement method, which is based on data regression and uses AI algorithm to train the concentration prediction model. The premise of this method is to have a large amount of rich concentration analysis data, but for many scenarios of polymer production devices, there is no sampling point for concentration analysis. It is not that the operator does not want to analyze, but it does not have the conditions for sampling, for example, some polymerization reactions are carried out at ultra-low temperature below -90℃; there are components in the polymer system that are extremely volatile, which will introduce a large error in the sampling and analysis process; the patent with publication number CN111918716A discloses a method for monitoring and controlling the polymerization of polymers, which uses an online FTNIR probe to obtain the concentration of monomers in the solution polymerization process stream, but some polymerization reactions (such as cationic polymerization of butyl rubber) are carried out at ultra-low temperature below -90℃, and the sharp change of the reactor outlet temperature, low temperature and large temperature difference make it not suitable to use the probe. SUMMARY

[0004] (I) Technical problems to be solved

[0005] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present application provides a method and device for on-line determination of polymer concentration, which solves the technical problem that the concentration of the polymer cannot be directly obtained by sampling analysis or instrument measurement in the prior art.

[0006] (II) Technical solutions

[0007] In order to achieve the above-mentioned purposes, the main technical solutions adopted by the present application include:

[0008] In a first aspect, embodiments of the present application provide a method for online determination of polymer concentration, comprising:

[0009] measuring the overall density of the polymer slurry system;

[0010] determining the density of the liquid phase and the density of the polymer solid phase in the polymer slurry system, respectively;

[0011] inferred by a density mixing rule model based on the overall density, the density of the liquid phase and the density of the polymer solid phase, wherein the mathematical expression of the density mixing rule model is:

[0012]

[0013] wherein, represents the density of the polymer solid phase; x represents the concentration of the polymer in the polymer slurry system; represents the density of the liquid phase; represents the overall density.

[0014] In one possible embodiment, the overall density is achieved by an online density measuring instrument, which includes a nuclear density meter and a mass flow meter.

[0015] In one possible embodiment, the method for determining the density of the liquid phase includes the following steps: when the liquid phase is single-component, the density of the liquid phase at different temperatures is obtained, and the density of the liquid phase at different temperatures is processed by using a data fitting method or a data interpolation method to obtain the density of the liquid phase under the current process condition; when the liquid phase is a multi-component mixture, the PC-SAFT state equation method is used to determine the density of the liquid phase.

[0016] ​In one possible embodiment, the PC-SAFT equation of state is used to determine the density of the liquid phase, including: obtaining PC-SAFT model parameters of each pure component of the liquid phase mixture and binary interaction parameters between each component; calculating average parameters of the mixed components by using mixing rules according to the PC-SAFT model parameters of each pure component and the binary interaction parameters between each component; the average parameters include average chain segment number, dispersion energy cross term and chain segment diameter cross term; based on the average parameters, calculating total Helmholtz free energy at a hypothetical molar volume of the liquid phase mixture; wherein the total Helmholtz free energy is the sum of the Helmholtz free energy contributed by chain, the Helmholtz free energy contributed by dispersion and the Helmholtz free energy contributed by hard sphere; taking the molar volume as an iteration variable, calculating the predicted value of the system pressure through the partial derivative relationship of the total Helmholtz free energy with respect to the molar volume, and constantly adjusting the molar volume until the absolute value of the difference between the predicted value of the system pressure and the measured pressure is within a tolerance range, thereby determining the real molar volume of the liquid phase mixture; and calculating the density of the liquid phase according to the real molar volume and the molar mass of the liquid phase mixture.

[0017] In one possible embodiment, the method for determining the density of the polymer solid phase includes the following steps: for a system in which the polymer density remains stable, the density of the polymer solid phase is measured by a sampling analysis method; and for a system in which the apparent density of the polymer changes due to swelling of the polymer in the liquid phase, the density of the polymer solid phase is obtained by simultaneously solving material balance equations and a density mixing model.

[0018] In a second aspect, an embodiment of the present application provides an online determination device for polymer concentration, including:

[0019] A measurement module is configured to measure the overall density of the polymer slurry system.

[0020] A determination module is configured to determine the density of the liquid phase and the density of the polymer solid phase in the polymer slurry system, respectively.

[0021] An inference module is configured to infer the concentration of the polymer in the polymer slurry system by a density mixing rule model based on the overall density, the density of the liquid phase and the density of the polymer solid phase; and a mathematical expression of the density mixing rule model is as follows:

[0022]

[0023] In the formula, ρs represents the density of the polymer solid phase; x represents the concentration of the polymer in the polymer slurry system; ρl represents the density of the liquid phase; and ρ represents the overall density.

[0024] ​​​​In one possible embodiment, the overall density is achieved by an online density measurement instrument, which includes a nuclear density meter and a mass flow meter.

[0025] In one possible embodiment, the determining module is specifically configured to: when the liquid phase is single-component, acquire the density of the liquid phase at different temperatures, and perform corresponding processing on the density of the liquid phase at different temperatures by using a data fitting method or a data interpolation method to obtain the density of the liquid phase under current process conditions; and when the liquid phase is a multi-component mixture, determine the density of the liquid phase by using a PC-SAFT state equation method.

[0026] In one possible embodiment, the determining module is further specifically configured to: acquire PC-SAFT model parameters of each pure component of the liquid phase mixture and binary interaction parameters between components; calculate average parameters of the mixed components by using a mixing rule according to the PC-SAFT model parameters of each pure component and the binary interaction parameters between components; the average parameters include average segment number, dispersion energy cross term and segment diameter cross term; calculate total Helmholtz free energy under the assumed molar volume of the liquid phase mixture based on the average parameters; the total Helmholtz free energy is the sum of the Helmholtz free energy contributed by the chain, the Helmholtz free energy contributed by dispersion and the Helmholtz free energy contributed by hard sphere; take the molar volume as an iteration variable, calculate the predicted value of the system pressure through the partial derivative relationship of the total Helmholtz free energy with respect to the molar volume, and constantly iteratively adjust the molar volume until the absolute value of the difference between the predicted value of the system pressure and the measured pressure is within a tolerance range, thereby determining the real molar volume of the liquid phase mixture; and calculate the density of the liquid phase according to the real molar volume and the molar mass of the liquid phase mixture.

[0027] In one possible embodiment, the determining module is specifically configured to: for a system in which the density of the polymer is stable, measure the density of the polymer solid phase by a sampling analysis method; and for a system in which the apparent density of the polymer changes due to swelling of the polymer in the liquid phase, obtain the density of the polymer solid phase by simultaneously solving material balance equations and a density mixing model.

[0028] (Three) beneficial effects

[0029] The beneficial effects of the present application are:

[0030] Embodiments of the present application provide an online determination method and device for polymer concentration, which measure the overall density of a polymer slurry system, respectively determine the density of a liquid phase and the density of a polymer solid phase in the polymer slurry system, and deduce the concentration of the polymer in the polymer slurry system by a density mixing rule model based on the overall density, the density of the liquid phase and the density of the polymer solid phase, so that the concentration in the polymer slurry system can be obtained in real time and accurately.

[0031] In order to make the above-mentioned objects, features and advantages of the embodiments of the present application more apparent, the following will describe the preferred embodiments in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments of the present application. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation to the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0033] Figure 1 A flow chart of a method for determining the concentration of a polymer on-line according to an embodiment of the present application is shown;

[0034] Figure 2 A flow chart of a method for determining the density of the liquid phase using the PC-SAFT equation of state according to an embodiment of the present application is shown;

[0035] Figure 3 A schematic diagram of a halogenated butyl rubber glue buffer tank according to an embodiment of the present application is shown;

[0036] Figure 4 A schematic diagram of a polyethylene reactor according to an embodiment of the present application is shown;

[0037] Figure 5 A structural block diagram of a device for determining the concentration of a polymer on-line according to an embodiment of the present application is shown. DETAILED DESCRIPTION

[0038] In order to better explain the present application and facilitate understanding, the following will describe the present application in detail through specific embodiments with reference to the drawings.

[0039] In order to solve the problem that the concentration of a polymer cannot be directly obtained through sampling analysis or instrument measurement in the prior art, the embodiments of the present application provide a method and a device for determining the concentration of a polymer (or the mass ratio of the polymer in a slurry system) on-line. The overall density of a polymer slurry system is measured, and the density of the liquid phase and the density of the solid phase of the polymer in the polymer slurry system are determined respectively. Based on the overall density, the density of the liquid phase and the density of the solid phase of the polymer, the concentration of the polymer in the polymer slurry system is inferred through a density mixing rule model, so that the concentration of the polymer in the polymer slurry system can be obtained in real time and accurately.

[0040] For a better understanding of the above technical solutions, the exemplary embodiments of the present application will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present application are shown in the drawings, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present application can be more clearly, thoroughly understood and the scope of the present application can be completely conveyed to those skilled in the art.

[0041] In order to facilitate the understanding of the embodiments of the present application, the terms related to the present application are explained as follows:

[0042] Polymer slurry: It refers to a mixed system containing a polymer component, the polymer being in a solid phase and the others being in a liquid phase.

[0043] PC-SAFT (perturbed-chain Statistical Associating Fluid Theory) equation of state: a semi-empirical model based on statistical mechanics, which decomposes the dimensionless Helmholtz free energy (i.e. , where a is the dimensionless Helmholtz free energy, which is the normalized Helmholtz free energy eliminating the dimensional influence, A is the total Helmholtz free energy, N is the number of molecules, k B is the Boltzmann constant, and T is the temperature) into a hard sphere term, a chain term, and a dispersion term. The essence is based on the logic of "progressive fluid model from simple to complex", which first constructs the most basic hard sphere reference fluid, then superimposes the structural effect of chain molecules, and finally modifies the attractive force between molecules. These three terms correspond to the microscopic characteristics of fluids in different dimensions, and together describe the thermodynamic behavior of real fluids. The specific meanings are as follows: the hard sphere term is the core reference term of PC-SAFT, which describes the Helmholtz free energy of "hard sphere fluid with no attractive force and only rigid repulsive force"; the chain term describes the difference in free energy between "chain fluid formed by hard sphere segments connected by chemical bonds" and "single hard sphere fluid"; the dispersion term is the contribution of intermolecular van der Waals dispersion force (the main attractive force between nonpolar molecules, in addition to dipole-dipole interaction for polar molecules, but PC-SAFT is mainly for nonpolar / weakly polar fluids) to the free energy based on the "hard sphere chain fluid".

[0044] PC-SAFT pure component characteristic parameters: including chain segment number m i (describing the length of the molecular chain), chain segment diameter (characteristic size of molecules in hard sphere reference state, unit: angstrom Å, (1 Å = 10 -10 m), and interaction energy parameter (describing the strength of intermolecular attraction, unit: K, where K B is the Boltzmann constant, Energy parameter).

[0045] Binary interaction parameter k ij : correction for non-ideal interaction between different components, usually obtained by fitting the vapor-liquid equilibrium data of component i and component j.

[0046] Average chain length: the average number of segments contained in each molecule in the mixture, and this average chain length is used to describe the chain structure characteristics of the molecules in the mixture, which plays an important role in calculating the thermodynamic properties of the mixture. For example, this parameter is used in the calculation of hard sphere term, chain term and dispersion term Helmholtz free energy.

[0047] Dispersion energy cross term: it is used to describe the dispersion interaction energy between different component molecules in the mixture. In PC-SAFT, the dispersion energy parameter is usually related to the interaction between molecules, and for the mixture, the dispersion energy cross term can be calculated according to the Berthelot-Lorentz combination rule.

[0048] Segment diameter cross term: it is used to describe the interaction parameter of the segment diameter of different component molecules in the mixture. The segment diameter cross term has important application in the calculation of the packing fraction of the mixture, the intermolecular force, etc., and will affect the calculation results of the whole PC-SAFT model for the properties of the mixture.

[0049] Hard sphere packing fraction : the most basic parameter in PC-SAFT equation of state, used to quantify the "space occupation degree" of hard sphere molecules in the system, which is the premise for the subsequent calculation of radial distribution function g hs of chain contribution and dispersion correction function of dispersion contribution.

[0050] Hard sphere radial distribution function: a core function that describes the spatial distribution of molecules in a "hard sphere fluid with only repulsive interaction", on the one hand, it describes the "repulsive volume effect" between molecules, and on the other hand, it helps to calculate the thermodynamic properties of hard sphere fluid (including Helmholtz free energy).

[0051] Dispersion correction function: it is a key empirical or semi-empirical function, which is used to correct the difference in thermodynamic properties between "hard sphere reference fluid" and "real fluid" caused by intermolecular dispersion force (attractive force). And its core role is to quantify the influence of molecular density (packing fraction ) on the contribution of dispersion force, so that the model can more accurately describe the condensation characteristics (such as liquefaction, solubility, high pressure behavior, etc.) of real fluid.

[0052] It should be noted that the present application is applicable to the following situations: (1) the polymer concentration cannot be directly measured due to the limitations of process conditions (for example, the cationic polymerization reaction of butyl rubber), which is carried out at ultra-low temperature below -90℃, and the sharp change of the reactor outlet temperature, low temperature and large temperature difference make it not suitable to use the FTNIR probe; (2) the polymer concentration cannot be accurately obtained by the instrument or is obtained by the instrument but the cost is high; and (3) the AI data model is used to predict the density, but there is a lack of rich measured data support or the AI data model has poor generalization and extrapolation, so that the polymer concentration cannot be stably and accurately obtained.

[0053] Please refer to Figure 1 , Figure 1 A flow chart of an online determination method of polymer concentration provided by an embodiment of the present application is shown. It should be understood that the online determination method can be performed by an online determination device of polymer concentration, and the specific device of the online determination device can be set according to actual needs, and the embodiments of the present application are not limited thereto. Specifically, the online determination method comprises the following steps.

[0054] In step S110, the overall density of the polymer slurry system is measured.

[0055] Specifically, the overall density of the polymer mixture system can be measured online by a nuclear density meter, a mass flow meter or other instruments capable of obtaining density.

[0056] In step S120, the density of the liquid phase and the density of the polymer solid phase in the polymer slurry system are determined respectively.

[0057] It should be understood that the specific process of determining the density of the liquid phase in the polymer slurry system can be set according to actual needs, and the embodiments of the present application are not limited thereto.

[0058] Optionally, when the liquid phase is single-component, the density of the liquid phase at different temperatures is obtained, and a data fitting method or a data interpolation method is used to process the density of the liquid phase at different temperatures to obtain the density of the liquid phase under the current process condition.

[0059] That is to say, for a single-component liquid phase, the liquid phase density data at different temperatures can of course be obtained by looking up tables or literature and data (the liquid itself is difficult to compress, and the influence of pressure on the liquid phase density is usually small), and then the liquid phase density under specific process conditions (for example, specific temperature) can be obtained by using a data fitting or interpolation method, or can be calculated by a state equation method.

[0060] Optionally, when the liquid phase is a multi-component mixture, a PC-SAFT state equation method is used to determine the density of the liquid phase.

[0061] Specifically, for multi-component liquid phases involving the mixing of multiple components, it is necessary to consider intermolecular interactions and mixing effects, and the density of the multi-component liquid phase is calculated using the equation of state method. The equation of state method can calculate the density of both single-component and multi-component liquid phases. Here, we present the universal PC-SAFT equation of state method for calculating the density of multi-component liquid phases. The PC-SAFT equation of state is an advanced model based on statistical mechanics, and its prediction accuracy for liquid density is significantly higher than that of traditional cubic equations of state (such as SRK and PR).

[0062] The following is as follows Figure 2 The following are the specific steps and procedures for calculating liquid density using the PC-SAFT equation of state:

[0063] Step S210: Obtain the PC-SAFT model parameters of each pure component of the liquid mixture and the binary interaction parameters between each component.

[0064] Specifically, the PC-SAFT model parameters of the pure component, including the number of chain segments m, can be obtained by fitting literature or experimental data. i Chain segment diameter and interaction energy parameters The subscript i represents component i; the binary interaction parameter k between components is obtained by fitting data from literature or experimental data (e.g., gas-liquid equilibrium data (pressure-composition relationship)). ij , and k ij It is the binary interaction parameter between any two components (component i and component j) in the system.

[0065] Step S220: Based on the PC-SAFT model parameters of each pure component and the binary interaction parameters between the components, the average parameters of the mixed components are calculated using the mixing rules. The average parameters include the average number of chain segments, the dispersion energy cross term, and the chain segment diameter cross term.

[0066] Specifically, the formula for calculating the average number of chain segments is:

[0067] ;

[0068] In the formula, m avg x is the average number of chain segments; i Let m be the molar percentage of component i in the pure liquid phase of the slurry system; i This represents the number of chain segments.

[0069] Furthermore, the expression for calculating the dispersive energy cross term is:

[0070] ;

[0071] In the formula, For the dispersive energy cross term; kij is a binary interaction parameter; is an interaction energy parameter corresponding to component i; is an interaction energy parameter corresponding to component j.

[0072] and the calculation expression of the segment diameter cross term is:

[0073] ;

[0074] wherein, is a segment diameter cross term; is a segment diameter corresponding to component i; is a segment diameter corresponding to component j.

[0075] Step S230, based on the average parameters, calculate the total Helmholtz free energy under the assumed molar volume of the liquid phase mixture. Wherein, the total Helmholtz free energy is the sum of the Helmholtz free energy contributed by the chain, the Helmholtz free energy contributed by the dispersion, and the Helmholtz free energy contributed by the hard sphere.

[0076] Specifically, before calculating the hard sphere contribution term of the Helmholtz free energy, it is necessary to calculate the hard sphere packing fraction, the hard sphere volume of each component, the average hard sphere volume, and the total molecular number density.

[0077] wherein, the calculation expression of the hard sphere packing fraction of the pure component i is:

[0078] ;

[0079] wherein, is the hard sphere volume of component i; is the number of molecules of component i; m i is the number of segments of component i; is a segment diameter corresponding to component i.

[0080] and the calculation expression of the total hard sphere volume of the liquid phase mixture is:

[0081] ;

[0082] ;

[0083] wherein, is the total hard sphere volume; x i is the molar fraction of component i; N i is the number of molecules of component i; N total is the total number of molecules.

[0084] and the calculation expression of the total molecular number density is:

[0085] ;

[0086] where, is the total number density; N total is the total number of molecules; V is the molar volume.

[0087] And the calculation expression of the hard sphere packing fraction of pure component i is:

[0088] ;

[0089] where, is the hard sphere packing fraction of pure component i.

[0090] And when calculating the core items such as chain contribution and hard sphere contribution of the mixture using the PC-SAFT model, all components share the same mixing packing fraction that is .

[0091] And the calculation expression of the Helmholtz free energy of the hard sphere contribution is:

[0092] ;

[0093] where, is the Helmholtz free energy of the hard sphere contribution.

[0094] Then, the derivative of the Helmholtz hard sphere term with respect to the hard sphere packing fraction is:

[0095] .

[0096] And before calculating the chain contribution term of the Helmholtz free energy, the hard sphere radial distribution function needs to be calculated first:

[0097] ;

[0098] where, represents the hard sphere radial distribution function.

[0099] Then, the calculation expression of the Helmholtz free energy of the chain contribution is:

[0100] ;

[0101] where, is the Helmholtz free energy of the chain contribution.

[0102] Then, the derivative of the Helmholtz chain term with respect to the hard sphere packing fraction is:

[0103] .

[0104] And, before calculating the dispersion contribution term of Helmholtz free energy, the dispersion correction function and the dispersion average term need to be calculated first. Wherein, the calculation expression of dispersion correction function is:

[0105] ;

[0106] In the formula, is the dispersion correction function;

[0107] And the calculation expression of dispersion average term is:

[0108] ;

[0109] In the formula, is the energy parameter; is the segment diameter; x j is the mole fraction of component j; m j is the number of segments of component j. And the left side of the dispersion average term can be regarded as a symbol of a variable, which is the dispersion average term.

[0110] And the calculation expression of Helmholtz free energy of dispersion contribution is:

[0111] ;

[0112] In the formula, is the Helmholtz free energy of dispersion contribution; is the total molecular number density, that is, its total molecular number density ; m avg is the average segment number; k B is the Boltzmann constant; T represents the temperature of the system.

[0113] Then, the derivative of Helmholtz dispersion term with respect to hard sphere packing fraction is:

[0114] ;

[0115] And the calculation formula of total Helmholtz free energy is:

[0116] ;

[0117] In the formula, is the total Helmholtz free energy.

[0118] Step S240, taking the molar volume as the iteration variable, calculating the predicted value of the system pressure through the partial derivative relationship of the total Helmholtz free energy with respect to the molar volume, and constantly adjusting the molar volume until the absolute value of the difference between the predicted value of the system pressure and the measured pressure is within the tolerance range, thereby determining the true molar volume of the liquid mixture.

[0119] Specifically, the total pressure of the system (the pressure of the polymer slurry system) is calculated from the relationship between the Helmholtz free energy and the pressure of the system, and the total Helmholtz free energy is derived with respect to the volume V to obtain:

[0120] ;

[0121] In the formula, P is the total pressure, and the thermodynamic definition of P is the negative derivative of the total Helmholtz free energy A with respect to the macroscopic volume V; A is the total Helmholtz free energy of each component of the pure liquid phase of the slurry system; V is the total volume of the pure liquid phase; T is the temperature of the system; and N represents the number of molecules.

[0122] However, V is a function of the hard sphere packing fraction , so the derivative of the Helmholtz free energy with respect to the hard sphere packing fraction is obtained:

[0123] ;

[0124] That is, ;

[0125] In the formula, P is the left side of the formula obtained by the derivative of the Helmholtz free energy with respect to the hard sphere packing fraction, representing the total pressure of the system, and the right side is the result of the calculation of the Helmholtz free energy by PC-SAFT, where Pcal is the left side P obtained by the derivative.

[0126] And by iteratively adjusting the molar volume V, the hard sphere packing fraction is changed, causing the calculated pressure to change, and through continuous iteration, the calculated pressure is finally made to be within the tolerance range of the actual measured pressure (i.e. ), that is, the total molar volume of the liquid phase system is obtained.

[0127] Step S250, according to the true molar volume and the molar mass of the liquid mixture, the density of the liquid phase is calculated.

[0128] Specifically, the calculation expression of the molar mass of the multi-component liquid phase system (i.e. the liquid mixture) is:

[0129] ;

[0130] In the formula, is the molar mass of the liquid mixture; M i is the molar mass of component i in the liquid phase.

[0131] Subsequently, the density of the liquid phase can be calculated:

[0132] ;

[0133] In the formula, is the density of the liquid phase mixture (including each component), i.e. the density of the liquid phase . and m is the mass; V is the true molar volume determined in step S240.

[0134] It should also be understood that the specific process of determining the density of the polymer solid phase in the polymer slurry system can also be set according to actual needs, and the embodiments of the present application are not limited thereto.

[0135] Optionally, for a polymer density stable system, the density of the polymer solid phase is measured by a sampling analysis method. The polymer density stable system can be set according to actual needs, and the embodiments of the present application are not limited thereto.

[0136] For example, for a reactor for producing polyolefin by a slurry process, the density of the polyolefin (polyethylene or polypropylene) is mainly related to the amount of comonomer added, and the amount of comonomer added is constant when producing a certain brand product, so the density of the polymer can also be regarded as fixed, and therefore only a density test after sampling is required, and the density of the polymer can be regarded as stable. That is, for the polyolefin reaction system, the density of the polyolefin generally does not change greatly, and the density can be measured by a sampling analysis method.

[0137] Optionally, for a system in which the apparent density of the polymer changes due to swelling of the polymer in the liquid phase, the density of the polymer solid phase is obtained by simultaneously solving the material balance equation and the density mixing model. The system in which the apparent density of the polymer changes due to swelling of the polymer in the liquid phase can also be set according to actual needs, and the embodiments of the present application are not limited thereto.

[0138] For example, for a process for producing halogenated butyl rubber (brominated butyl rubber and chlorinated butyl rubber) by a solution method, the glue slurry cannot be installed with a flow meter due to its high viscosity, but a mass flow meter is installed at the outlet of the glue buffer tank because a certain amount of hexane is added to the tank, causing the halogenated butyl rubber to swell and dissolve to a certain extent in the tank. The glue in the glue slurry comes from the polymerization reaction, and the water is the residual water after dewatering by a vibrating screen. The liquid level L of the buffer tank is maintained stable, and the material balance equation is:

[0139] ;

[0140] In the formula, F in is unknown, and is the feed amount of the glue slurry; is the proportion of glue in the glue slurry, unknown, and needs to be calculated; F H is the amount of hexane added, known; Fout is the buffer tank outlet flow rate, known.

[0141] And the calculation expression of the density model of the mixed material (i.e., the density mixing model) is:

[0142]

[0143] In the formula, is the density of the glue in the buffer tank, unknown; is the density of water in the buffer tank, which can change with temperature, and can be obtained by the equation of state of water Figure 2 to obtain the density at different temperatures, and then corresponding data fitting is performed. Because water and hexane are divided into water phase and oil phase (two liquid phases) here, the water phase is pure water (the relationship between its density and temperature can be calculated by the steps of the equation of state of water Figure 2 ), and the oil phase is a hexane solution of glue (the glue is solid, and the hexane is liquid); is the density of hexane in the buffer tank, which can change with temperature, and can be obtained by the equation of state of hexane Figure 2 to obtain the density at different temperatures, and then corresponding data fitting is performed, or data is obtained by searching literature and then fitting; is the density of the buffer tank outlet, known, which can be obtained by a mass flow meter or a nuclear density meter.

[0144] For the device system, the amount of glue generated by the polymerization reaction should be consistent with the amount of glue after dehydration by the vibrating screen (because the amount of glue after dehydration by the vibrating screen comes from the polymerization reaction system), so:

[0145]

[0146] In the formula, is the amount of dry glue generated by the polymerization reaction; is the amount of mixed material of the polymerization reaction, known; conc is the monomer concentration in the polymerization mixture, known; d is the conversion rate of the polymerization reaction, known.

[0147] Therefore, by solving the above equations, the density of the glue in the buffer tank and the mass ratio of the glue in the glue-water slurry can be obtained, and the density of the glue is the density of the polymer solid phase.

[0148] In step S130, based on the overall density, the density of the liquid phase, and the density of the polymer solid phase, the concentration of the polymer in the polymer slurry system is inferred by a density mixing rule model.

[0149] The mathematical expression of the density mixing rule model is:

[0150] ;​​

[0151] wherein, represents the density of the polymer solid phase; x represents the concentration of the polymer in the polymer slurry system; represents the density of the liquid phase; represents the overall density.

[0152] Therefore, by means of the above technical solution, the polymer concentration in the polymer slurry system can be calculated in real time, thereby guiding the control of the real-time polymer concentration or the preparation of the specific polymer concentration.

[0153] In addition, the polymer concentration in the polymer slurry system can be determined without relying on expensive instrument equipment (such as a near-infrared spectrum analyzer).

[0154] In addition, the polymer concentration in the polymer slurry can be obtained by the method of the present application for occasions where sampling for testing cannot be performed (such as under specific process conditions (ultra-low temperature of -90°C or high-temperature high-pressure polymerization reactors)) or where the error of sampling for testing will be large (such as samples containing a large amount of components that are extremely volatile at room temperature and normal pressure).

[0155] For the convenience of understanding, the following will be described through specific examples.

[0156] Optionally, the halogenated butyl rubber is produced by a solution method, and before the halogenation reaction of the butyl rubber, a rubber solution with a certain concentration needs to be prepared, and the solvent is hexane. The aforementioned step of preparing the rubber solution with a certain concentration is Figure 3 as shown in the process, Figure 3 The process before the process shown in the above figure is a polymerization reaction process, and the key to preparing the rubber solution with a certain concentration is to determine the amount of rubber at the outlet of the buffer tank. After the amount of rubber is determined, the amount of hexane to be added is determined, and the preparation of the rubber solution with a certain concentration can be easily solved by using an APC controller. The process of determining the amount of rubber has been described in detail in step S120, and thus will not be described here.

[0157] Optionally, the polymer concentration (internal solid content) in the polyethylene reactor needs to be controlled. If the polymer concentration is too high, the efficiency of the axial flow pump will be affected, and if the polymer concentration is too low, the polymer yield will be too low, and thus the polymer concentration needs to be controlled within a suitable range. However, relevant instruments cannot be installed in the polymerization reactor to conveniently measure the polymer concentration, but the polymer concentration can be calculated by using the method of the present application. The polymerization reactor is as shown in Figure 4 The material in the reactor is in a slurry state, containing both polyethylene solids and a liquid phase mainly composed of isobutane. The composition of the liquid phase includes nitrogen, hydrogen, methane, ethylene, ethane, propane, butane, isobutane, butene, hexene, and hexane. The composition of the liquid phase can be analyzed by chromatography. The temperature and pressure of the reactor are also known.

[0158] For Figure 4 The polymer content in the loop polyethylene reactor shown in FIG. 1 can be obtained by the following steps:

[0159] First, the overall density of the material in the reactor is measured using a nuclear density meter ;

[0160] Subsequently, the density of the liquid phase in the polyethylene slurry can be calculated using the PC-SAFT equation of state method under the premise of known temperature, pressure and composition ;

[0161] Subsequently, the density of the polyethylene produced is mainly affected by the ratio of comonomer monomer, so the density of the polyethylene can be obtained by related sampling and analysis ;

[0162] Finally, the mixing model of the density is obtained based on the principle of material balance and material mixing:

[0163] ;

[0164] And the concentration of the polymer can be calculated according to the above formula:

[0165] .

[0166] It should be understood that the above-mentioned online determination method of the polymer concentration is only exemplary, and those skilled in the art can make various modifications according to the above-mentioned method, and the modified scheme also belongs to the protection scope of the present application.

[0167] Please refer to Figure 5 , Figure 5 FIG. 5 shows a structural block diagram of an online determination device 500 for polymer concentration provided by an embodiment of the present application. It should be understood that the online determination device 500 can perform each step in the above-mentioned method embodiment, and the specific functions of the online determination device 500 can be referred to the description in the above, and the detailed description is appropriately omitted here to avoid repetition. The online determination device 500 includes at least one software function module which can be stored in the memory in the form of software or firmware or solidified in the operating system (OS) of the online determination device 500. Specifically, the online determination device 500 includes:

[0168] The measurement module 510 is configured to measure the overall density of the polymer slurry system.

[0169] The determination module 520 is configured to determine the density of the liquid phase and the density of the polymer solid phase in the polymer slurry system, respectively.

[0170] The inference module 530 is configured to infer the concentration of the polymer in the polymer slurry system by a density mixing rule model based on the overall density, the density of the liquid phase, and the density of the polymer solid phase; and a mathematical expression of the density mixing rule model is as follows:

[0171] ;

[0172] wherein, represents the density of the polymer solid phase; x represents the concentration of the polymer in the polymer slurry system; represents the density of the liquid phase; represents the overall density.

[0173] In one possible implementation, the overall density is achieved by an online density measuring instrument, which includes a nuclear density meter and a mass flow meter.

[0174] In one possible implementation, the determination module 520 is specifically configured to: when the liquid phase is a single component, acquire the densities of the liquid phase at different temperatures, and perform corresponding processing on the densities of the liquid phase at different temperatures by using a data fitting method or a data interpolation method to obtain the density of the liquid phase under the current process condition; and when the liquid phase is a multi-component mixture, determine the density of the liquid phase by using a PC-SAFT state equation method.

[0175] In one possible implementation, the determination module 520 is further specifically configured to: acquire PC-SAFT model parameters of each pure component of the liquid phase mixture and binary interaction parameters between components; calculate average parameters of the mixed components by using a mixing rule according to the PC-SAFT model parameters of each pure component and the binary interaction parameters between components; the average parameters include average segment numbers, dispersion energy cross terms, and segment diameter cross terms; calculate total Helmholtz free energy under a hypothetical molar volume of the liquid phase mixture based on the average parameters; the total Helmholtz free energy is a sum of Helmholtz free energy contributed by chains, Helmholtz free energy contributed by dispersion, and Helmholtz free energy contributed by hard spheres; take the molar volume as an iteration variable, calculate a predicted value of the system pressure by a partial derivative relationship of the total Helmholtz free energy with respect to the molar volume, and constantly iteratively adjust the molar volume until an absolute value of a difference between the predicted value of the system pressure and a measured pressure is within a tolerance range, so as to stop iteration, thereby determining a real molar volume of the liquid phase mixture; and calculate the density of the liquid phase according to the real molar volume and a molar mass of the liquid phase mixture.

[0176] In one possible embodiment, the determining module 520 is specifically configured to: for a system in which the density of the polymer remains stable, measure the density of the polymer solid phase by a sampling analysis method; and for a system in which the apparent density of the polymer changes due to swelling of the polymer in the liquid phase, obtain the density of the polymer solid phase by simultaneously solving material balance equations and a density mixing model.

[0177] Since the apparatus described in the above embodiments of the present application is used for implementing the method described in the above embodiments of the present application, the specific structure and variations of the apparatus can be understood by those skilled in the art based on the method described in the above embodiments of the present application, and thus will not be described here again. Any apparatus used in the method described in the above embodiments of the present application belongs to the scope of the present application.

[0178] Those skilled in the art should understand that embodiments of the present application can be provided as a method, a system or a computer program product. Therefore, the present application can adopt a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer usable storage media containing computer usable program code (including but not limited to disk storage, CD-ROM, optical storage, etc.).

[0179] The present application is described with reference to flowcharts and / or block diagrams of the method, device (system) and computer program product according to embodiments of the present application. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of the flows and / or blocks in the flowcharts and / or block diagrams can be implemented by computer program instructions.

[0180] It should be noted that in the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of elements or steps not listed in the claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The application can be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the claims, the word "comprising" does not exclude the presence of other elements or steps than those listed in the claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The word "first", "second", "third" etc. does not imply any order. The use of relating terms can be understood as part of the name of the element.

[0181] Furthermore, it is to be understood that the use of "a" or "an", "the" or "said" employed throughout the present description, dependencies, abstract and claims, denotes a "single", "only" or "one and also any plurality whereas "the another" denotes "at least a second", or "at least one", unless otherwise clear from the context.

[0182] While the preferred embodiments of the application have been described, additional variations and modifications can be made to the preferred embodiments without departing from the spirit and scope of the application. Therefore, it is to be understood that the application shall not be limited to the specific examples set forth herein as the same can vary. The claims are to be interpreted broadly in accordance with the principles of the application and the specification.

[0183] It will be readily apparent to those skilled in the art that varying substitutions and modifications can be made to the application disclosed herein without departing from the scope and spirit of the application. Accordingly, unless limited by the claims set forth below, the application is to be understood as not limited by the disclosure provided herein.

Claims

1. A method for on-line determination of polymer concentration, characterized by, The method comprises the following steps: measuring the overall density of a polymer slurry system; determining the density of a liquid phase and the density of a polymer solid phase in the polymer slurry system respectively; inverting and inferring the concentration of the polymer in the polymer slurry system based on the overall density, the density of the liquid phase and the density of the polymer solid phase by a density mixing rule model; wherein the mathematical expression of the density mixing rule model is: ； wherein represents the density of the polymer solid phase; x represents the concentration of the polymer in the polymer slurry system; represents the density of the liquid phase; represents the overall density.

2. The online determination method of claim 1, wherein, The overall density is measured by an online density measuring instrument, and the online density measuring instrument comprises a nuclear density meter and a mass flow meter.

3. The online determination method of claim 1, wherein, The method for determining the density of the liquid phase comprises the following steps: when the liquid phase is a single component, the density of the liquid phase at different temperatures is obtained, and a data fitting method or a data interpolation method is used to process the density of the liquid phase at different temperatures to obtain the density of the liquid phase under the current process condition; when the liquid phase is a multi-component mixture, the PC-SAFT state equation method is used to determine the density of the liquid phase.

4. The online determination method of claim 3, wherein, The method for determining the density of the liquid phase by the PC-SAFT state equation method comprises the following steps: obtaining the PC-SAFT model parameters of each pure component of the liquid phase mixture and the binary interaction parameters between each component; calculating the average parameters of the mixed components according to the PC-SAFT model parameters of each pure component and the binary interaction parameters between each component; the average parameters include the average segment number, the dispersion energy cross term and the segment diameter cross term; based on the average parameters, calculating the total Helmholtz free energy under the assumed molar volume of the liquid phase mixture; wherein the total Helmholtz free energy is the sum of the Helmholtz free energy contributed by the chain, the Helmholtz free energy contributed by the dispersion and the Helmholtz free energy contributed by the hard sphere; taking the molar volume as an iteration variable, calculating the predicted value of the system pressure through the partial derivative relationship of the total Helmholtz free energy with respect to the molar volume, and continuously adjusting the molar volume until the absolute value of the difference between the predicted value of the system pressure and the measured pressure is within the tolerance range, and then stopping the iteration, so as to determine the real molar volume of the liquid phase mixture; calculating the density of the liquid phase according to the real molar volume and the molar mass of the liquid phase mixture.

5. The online determination method of claim 1, wherein, The method for determining the density of the polymer solid phase comprises the following steps: for a system with stable polymer density, the density of the polymer solid phase is measured by a sampling analysis method; for a system in which the apparent density of the polymer changes due to swelling in the liquid phase, the density of the polymer solid phase is obtained by simultaneously solving the material balance equation and the density mixing model.

6. An apparatus for on-line determination of polymer concentration, characterized by The method comprises the following steps: a measuring module for measuring the overall density of a polymer slurry system; a determining module for determining the density of a liquid phase and the density of a polymer solid phase in the polymer slurry system respectively; an inferring module for inverting and inferring the concentration of the polymer in the polymer slurry system based on the overall density, the density of the liquid phase and the density of the polymer solid phase by a density mixing rule model; wherein the mathematical expression of the density mixing rule model is: ； wherein represents the density of the polymer solid phase; x represents the concentration of the polymer in the polymer slurry system; represents the density of the liquid phase; represents the overall density.

7. The on-line determination apparatus according to claim 6, characterized in that The bulk density is achieved by an online density measuring instrument, which includes a nuclear density meter and a mass flow meter.

8. The on-line determination apparatus according to claim 6, characterized in that The determination module is specifically configured to: when the liquid phase is single-component, obtain the density of the liquid phase at different temperatures, and perform corresponding processing on the density of the liquid phase at different temperatures by using a data fitting method or a data interpolation method to obtain the density of the liquid phase under current process conditions; and when the liquid phase is a multi-component mixture, determine the density of the liquid phase by using a PC-SAFT state equation method.

9. The online determination method of claim 8, wherein, The determination module is further specifically configured to: obtain PC-SAFT model parameters of each pure component of the liquid phase mixture and binary interaction parameters between components; calculate average parameters of mixed components by using a mixing rule according to the PC-SAFT model parameters of each pure component and the binary interaction parameters between components; the average parameters include average segment numbers, dispersion energy cross terms and segment diameter cross terms; based on the average parameters, calculate total Helmholtz free energy under a hypothetical molar volume of the liquid phase mixture; wherein the total Helmholtz free energy is a sum of Helmholtz free energy contributed by chains, Helmholtz free energy contributed by dispersion and Helmholtz free energy contributed by hard spheres; take the molar volume as an iteration variable, calculate a predicted value of the system pressure by a partial derivative relationship of the total Helmholtz free energy with respect to the molar volume, and constantly iteratively adjust the molar volume until an absolute value of a difference between the predicted value of the system pressure and a measured pressure is within a tolerance range, thereby determining a real molar volume of the liquid phase mixture; and calculate the density of the liquid phase according to the real molar volume and a molar mass of the liquid phase mixture.

10. The on-line determination apparatus according to claim 6, wherein The determination module is specifically configured to: for a system in which the density of a polymer is stable, measure the density of the polymer solid phase by a sampling analysis method; and for a system in which the apparent density of a polymer changes due to swelling of the polymer in a liquid phase, obtain the density of the polymer solid phase by simultaneously solving material balance equations and a density mixing model.

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