An apparatus and method for measuring the diffusion coefficient of a macromolecular compound in a porous medium

Abstract

The application provides a method for measuring the diffusion coefficient of macromolecular compounds, especially petroleum resin polymers, in a porous medium. An in-situ infrared spectrometer equipped with a high-precision MCT detector is used as an online concentration detection device to build a diffusion coefficient testing device suitable for macromolecular compounds such as DCPD petroleum resin, and the device is used to measure the adsorption curve of resin molecules in a porous medium with different pore diameters, and then the diffusion coefficient of the molecules in the porous medium with different pore diameters is calculated by combining a mathematical model. The method helps to solve the shortcomings that macromolecular compounds with high viscosity, poor fluidity and difficult gasification are difficult to test the diffusion coefficient by using traditional methods, and greatly widens the application range of the diffusion coefficient testing method. The device is easy to build, the testing process is simple to operate, and the measurement precision is high, so the method is an effective method for measuring the diffusion coefficient of macromolecular compounds in a porous medium.

Description

Technical Field

[0001] The invention relates to a device and a method suitable for measuring the diffusion coefficient of a macromolecular compound in a porous medium, and belongs to the field of chemical engineering. Background Art

[0002] Macromolecular polymers such as petroleum resin, nitrile rubber, and SBS are widely used in electronic chemicals, thermoplastics, adhesives, and other fields due to their excellent physical and chemical properties. However, due to the presence of a large number of unsaturated groups in the molecular structure of such polymers, they have deficiencies in optical properties, mechanical properties, and stability. In order to improve the above shortcomings and enhance product quality, catalytic hydrogenation is usually used to modify the polymers. For example, the unsaturated bonds in the resin molecules are hydrogenated and saturated, which can effectively improve their stability and antioxidant properties, improve their color, and enable them to be used in high-end fields.

[0003] However, for such molecules with large steric hindrance, the properties of the active components on the catalyst may not be the key factor. The diffusion (internal diffusion) process in the catalyst pores is often the rate-controlling step that determines the entire process. Therefore, it is very necessary to measure the diffusion coefficient of such molecules in the catalyst (porous medium). Although the current macroscopic test methods of diffusion coefficients (such as the ZLC method) have been able to meet most test requirements (Nat. Commun. 14, 1735 (2023); Chem. Eng. Sci. 258, 117733 (2022)), the detection instruments of the ZLC method are mostly gas chromatography or liquid chromatography, which cannot test fluids with high viscosity, poor fluidity, and high vaporization temperature. Therefore, this method is still limited to testing small molecule compounds, and there are fewer test devices that can be applied to polymers such as resins.

[0004] Therefore, improving the existing testing equipment so that it can meet the measurement of the diffusion coefficient of macromolecular compounds is of great significance for exploring the diffusion behavior of macromolecular compounds in catalysts. Summary of the Invention

[0005] In view of this, in order to solve the above problems, the present invention provides a device and method suitable for measuring the diffusion coefficient of macromolecular compounds in porous media. The present invention uses an in-situ infrared spectrometer as an online detection device for the concentration of the analyte, and builds a set of molecular diffusion coefficient testing devices, so that it can be applied to polymers with large molecular weight and high viscosity such as petroleum resin, thereby broadening the scope of application of the diffusion coefficient testing device.

[0006] To solve the above problems, the testing device provided by the present invention includes: a device suitable for measuring the diffusion coefficient of a macromolecular compound in a porous medium, characterized in that it includes: a first material storage tank, a second material storage tank, a three-way valve, a metering pump, a temperature control device, a fixed bed, an infrared light source, a liquid in-situ pool and an infrared detector, wherein the first material storage tank and the second material storage tank are respectively connected to the two inlets of the three-way valve through metal pipes, the outlet of the three-way valve is connected to the inlet of the metering pump through a metal pipe, the liquid outlet of the metering pump is connected to the fixed bed through a metal pipe, a thermocouple and a heating belt are installed in the fixed bed, and insulation cotton is wrapped around the periphery, the thermocouple and the heating belt are connected to the temperature control device through an electric wire, and the temperature of the fixed bed layer can be controlled in real time by the temperature control device; the outlet of the fixed bed is connected to the infrared in-situ pool through a metal pipe, and the outlet of the infrared in-situ pool is connected to a waste liquid bucket through a metal pipe; the infrared in-situ pool is placed between the infrared light source and the infrared detector, and the infrared light emitted from the infrared light source can be detected by the infrared detector through the infrared in-situ pool and the signal is processed and transmitted to the computer in real time.

[0007] The first material storage tank and the second material storage tank are any one of a glass container with a lid or an unsealed stainless steel tank, or a combination thereof; the three-way valve is any one of a manual stainless steel ferrule three-way ball valve, a solenoid valve, and a pneumatic valve; the metering pump is any one of a horizontal flow pump, a peristaltic pump, a plunger pump, a hydraulic pump, a mechanical diaphragm pump, or an electromagnetic metering pump; the liquid in-situ cell is any one of a liquid in-situ cell with a variable optical path or a fixed optical path, and the window used is any one of KBr, NaCl, CaF2, BaF2, ZnSe, KRS-5, CsI, and CsB; the infrared light source is a light source provided by any one of a far-infrared spectrometer, a mid-infrared spectrometer, and a near-infrared spectrometer; the detector is any one of a vacuum thermocouple detector, a pyroelectric detector, and a mercury cadmium telluride detector.

[0008] The first material storage tank and the second material storage tank are used to store the substance to be tested and the common solvent for the substance to be tested, respectively. Common substances to be tested include: DCPD petroleum resin, C5 petroleum resin, C9 petroleum resin, C5-C9 copolymer petroleum resin, etc. Common solvents include cyclohexane, benzene, acetone, etc.

[0009] The present invention is applicable to a method for measuring the diffusion coefficient of a macromolecular compound in a porous medium, and is characterized by the following specific steps:

[0010] (1) First, a certain amount of catalyst powder is filled into a fixed bed, and the catalyst powder is vacuum pretreated in advance to remove impurities adsorbed on the surface;

[0011] (2) The sample solution to be tested is placed in the first material storage tank, and the solvent corresponding to the sample to be tested is placed in the second material storage tank;

[0012] (3) Install the liquid in-situ pool in the corresponding position, turn on the infrared light source and infrared detector, and confirm that the material signal can be detected normally and displayed in real time on the computer;

[0013] (4) First switch the three-way valve to the channel connected to the second material storage tank;

[0014] (5) Turn on the metering pump, set the required flow rate and the maximum pressure allowed in the device, and allow the solvent to fill the entire device, exhaust the air, and wet the sample;

[0015] (6) After a period of time, the three-way valve is switched to the pipeline connected to the first material storage tank, so that the sample to be tested fills the entire device and is adsorbed in the porous medium in the fixed bed;

[0016] (7) When the infrared detector detects the signal of the object to be measured, it starts timing and collecting data;

[0017] (8) When the detected signal of the object to be tested does not change with time, stop the detection;

[0018] (9) Switch the three-way valve to the channel connected to the second material storage tank, keep the metering pump running, and flush the entire device pipeline with solvent;

[0019] (10) After a certain period of time, turn off the metering pump and the test is completed.

[0020] Steps (7) to (8) are used to collect the changes in the infrared spectrum of the molecular characteristics of the analyte over time.

[0021] The characteristic peak area of ​​the analyte molecule in the infrared spectrum obtained in steps (7) to (8) is integrated, and the change in the integrated area is used instead of the change in the analyte concentration to obtain the change in the analyte concentration over time, which is the adsorption curve.

[0022] The data obtained in steps (7) to (8) are fitted to the adsorption curve using the surface permeability formula and the diffusion coefficient formula, respectively. The surface permeability, internal diffusion coefficient, and apparent diffusion coefficient can be obtained by calculation. Processes (7) to (8) can collect the changes in the characteristic infrared spectrum of the analyte molecules over time. Then, the characteristic peak area of ​​the analyte molecules in the obtained infrared spectrum is integrated, and the change in the integrated area is used to replace the change in the analyte concentration to obtain the change in the analyte concentration over time, that is, the adsorption curve. The surface permeability formula and the diffusion coefficient formula are fitted to the adsorption curve, respectively. The surface permeability, internal diffusion coefficient, and apparent diffusion coefficient can be obtained by calculation.

[0023] The present invention uses an in-situ infrared spectrometer equipped with a high-precision MCT detector as an online concentration detection device. A diffusion coefficient testing device suitable for macromolecular compounds such as petroleum resin is built and used to measure their adsorption curves on porous media with different pore sizes. The diffusion coefficients of the molecules to be tested in catalysts with different pore sizes are then calculated using a mathematical model. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to make the above-mentioned objects, features and advantages of the present invention more clearly understood, preferred embodiments are specifically described below in detail with reference to the accompanying drawings.

[0025] Figure 1 Schematic diagram of the device for measuring the diffusion coefficient of a macromolecular compound in a porous medium according to the present invention;

[0026] Figure 2 The infrared spectra of the adsorption process of petroleum resin molecules in porous media with different pore sizes measured in the present invention;

[0027] Figure 3 Graph showing the relationship between the surface permeability coefficient, internal diffusion coefficient, and pore size obtained in the present invention. DETAILED DESCRIPTION

[0028] The present invention is suitable for a device for measuring the diffusion coefficient of a macromolecular compound in a porous medium, comprising: a first material storage tank 1, a second material storage tank 2, a three-way valve 3, a metering pump 4, a temperature control device 5, a fixed bed 6, an infrared light source 7, a liquid in-situ pool 8 and an infrared detector 9, wherein the first material storage tank 1 and the second material storage tank 2 are respectively connected to two inlets of the three-way valve 3 through metal pipes, the outlet of the three-way valve 3 is connected to the inlet of the metering pump 4 through a metal pipeline, the liquid outlet of the metering pump 4 is connected to the fixed bed 6 through a metal pipeline, and a liquid in-situ pool 8 is installed in the fixed bed 6. There are thermocouples and heating belts, and insulation cotton is wrapped around the outside. The thermocouples and heating belts are connected to the temperature control device 5 through electric wires, and the temperature of the fixed bed layer can be controlled in real time through the temperature control device; the outlet of the fixed bed 6 is connected to the infrared in-situ pool 8 through a metal pipeline, and the outlet of the infrared in-situ pool 8 is connected to the waste liquid bucket through a metal pipeline; the infrared in-situ pool 8 is placed between the infrared light source 7 and the infrared detector 9, and the infrared light emitted from the infrared light source 7 can pass through the infrared in-situ pool 8 and be detected by the infrared detector 9 and the signal is processed and transmitted to the computer in real time.

[0029] The first material storage tank 1 and the second material storage tank 2 are any one of a glass container with a lid or an unsealed stainless steel tank, or a combination thereof; the three-way valve 3 is any one of a manual stainless steel ferrule three-way ball valve, a solenoid valve, or a pneumatic valve; the metering pump 4 is any one of a horizontal flow pump, a peristaltic pump, a plunger pump, a hydraulic pump, a mechanical diaphragm pump, or an electromagnetic metering pump; the liquid in-situ cell 8 is any one of a liquid in-situ cell with a variable optical path or a fixed optical path, and the window used is any one of KBr, NaCl, CaF2, BaF2, ZnSe, KRS-5, CsI, or CsB; the infrared light source 7 is a light source provided by any one of a far-infrared spectrometer, a mid-infrared spectrometer, or a near-infrared spectrometer; the detector 9 is any one of a vacuum thermocouple detector, a pyroelectric detector, or a mercury cadmium telluride detector.

[0030] The first material storage tank 1 and the second material storage tank 2 are used to store the substance to be tested and the common solvent for the substance to be tested, respectively. Common substances to be tested include DCPD petroleum resin, which includes C5 petroleum resin, C9 petroleum resin or C5-C9 copolymer petroleum resin. Common solvents include cyclohexane, benzene or acetone.

[0031] The present invention is applicable to a method for measuring the diffusion coefficient of a macromolecular compound in a porous medium, and the specific steps are as follows:

[0032] 1. First, a certain amount of catalyst powder is filled into the fixed bed 6. The catalyst powder is vacuum pre-treated in advance to remove impurities adsorbed on the surface;

[0033] 2. The sample solution to be tested is placed in the first material storage tank 1, and the solvent corresponding to the sample to be tested is placed in the second material storage tank 2;

[0034] 3. Install the liquid in-situ pool 8 in the corresponding position, turn on the infrared light source 7 and the infrared detector 9, and confirm that the material signal can be detected normally and displayed in real time on the computer;

[0035] 4. First switch the three-way valve 3 to the channel connected to the second material storage tank 2;

[0036] 5. Turn on the metering pump 4, set the required flow rate and the maximum pressure allowed in the device, so that the solvent fills the entire device, exhausts the air and moistens the sample;

[0037] 6. After a period of time, the three-way valve 3 is switched to the pipeline connected to the first material storage tank 1, so that the sample to be tested fills the entire device and is adsorbed in the porous medium in the fixed bed 6;

[0038] 7. When the infrared detector 9 detects the signal of the object to be measured, it starts timing and collecting data;

[0039] 8. Stop testing when the detected signal of the object under test does not change over time;

[0040] 9. Switch the three-way valve 3 to the channel connected to the second material storage tank 2, keep the metering pump 4 working continuously, and use solvent to flush the entire device pipeline;

[0041] 10. After a certain period of time, turn off metering pump 4 and the test is completed.

[0042] Steps 7 and 8 are used to collect the changes in the characteristic infrared spectrum of the analyte molecules over time; the characteristic peak areas of the analyte molecules in the infrared spectrum obtained in steps 7 and 8 are integrated, and the changes in the integrated areas are used instead of the changes in the analyte concentration to obtain the changes in the analyte concentration over time, which is the adsorption curve; the data obtained in steps 7 and 8 are respectively fitted to the adsorption curve using the surface permeability formula and the diffusion coefficient formula, and the surface permeability, internal diffusion coefficient and apparent diffusion coefficient can be obtained by calculation.

[0043] Example 1

[0044] (1) A porous medium sample with an average pore size of 8.7 nm was treated in a vacuum oven at 80°C for 12 h. The sample was then cooled to room temperature, 30 mg was weighed, and slowly filled into a fixed bed and fixed.

[0045] (2) A 10% concentration of DCPD petroleum resin solution is placed in the first material storage tank, and analytically pure cyclohexane is placed in the second material storage tank, both to 2 / 3 of the maximum capacity.

[0046] (3) Connect all pipelines and install the liquid in-situ cell on the sample stage of the infrared spectrometer. Turn on the infrared light source and infrared detector to confirm that the material signal can be detected normally and displayed in real time on the computer.

[0047] (4) First switch the three-way valve to the channel connected to the second material storage tank.

[0048] (5) Turn on the metering pump and set the flow rate to 1 mL / min. Set the maximum pressure allowed in the device to 5 MPa. Press the start button to start the metering pump and fill the entire device with cyclohexane. When liquid drops are seen at the drain port, wait for 30 minutes to ensure that the air is completely exhausted and the sample is wetted. After the device is stable, collect the infrared spectrum test background.

[0049] (6) After the background acquisition is completed, the three-way valve is switched to the pipeline connected to the first material storage tank, so that the resin solution fills the entire device and is adsorbed in the porous medium in the fixed bed.

[0050] (7) When the infrared detector detects the signal of DCPD resin, it starts timing and continuously collects data with a data collection time interval of 4 seconds.

[0051] (8) When the signal of the detected DCPD resin does not change with time, stop the detection.

[0052] (9) Switch the three-way valve to the channel connected to the second material storage tank, keep the metering pump working continuously, and use cyclohexane solvent to flush the entire device pipeline to prevent the high viscosity resin from clogging the pipeline.

[0053] (10) After flushing for 30 minutes, turn off the metering pump and the test is complete.

[0054] After the test, the relationship between the infrared spectrum and time can be obtained, such as Figure 2 As shown in (a).

[0055] Example 2

[0056] (1) A porous medium sample with an average pore size of 11.6 nm was treated in a vacuum oven at 80 °C for 12 h. The sample was then cooled to room temperature, 30 mg was weighed, and slowly filled into a fixed bed and fixed.

[0057] Steps (2) to (10) are the same as those in Example 1. The data post-processing process is the same as that in Example 2. The relationship between the infrared spectrum and time is shown in FIG. Figure 2 (b).

[0058] Example 3

[0059] (1) A porous medium sample with an average pore size of 14.6 nm was treated in a vacuum oven at 80 °C for 12 h. The sample was then cooled to room temperature, 30 mg was weighed, and slowly filled into a fixed bed and fixed.

[0060] Steps (2) to (10) are the same as those in Example 1. The data post-processing process is the same as that in Example 2. The relationship between the infrared spectrum and time is shown in FIG. Figure 2 (c).

[0061] Example 4

[0062] (1) A porous medium sample with an average pore size of 19.1 nm was treated in a vacuum oven at 80 °C for 12 h. The sample was then cooled to room temperature, 30 mg was weighed, and slowly filled into a fixed bed and fixed.

[0063] Steps (2) to (10) are the same as those in Example 1. The data post-processing process is the same as that in Example 2. The relationship between the infrared spectrum and time is shown in FIG. Figure 2 (d).

[0064] Example 5

[0065] The characteristic peak of DCPD resin in the infrared spectrum obtained in Example 1 was integrated by area to obtain the relationship between the characteristic peak area of ​​DCPD resin and time. Then, the peak area was used to replace the signal intensity of DCPD resin molecules. The adsorption curve of DCPD resin molecules on the porous medium was obtained by plotting the time as the abscissa and the current signal intensity / saturation signal intensity as the ordinate. In equation (1), we can see that the relative concentration C t / C ∞ It is actually a quadratic function of the square root of the absorption time; and the quadratic coefficient depends only on the surface permeability α and the characteristic length of internal diffusion l. For a specific porous medium, l can be obtained and is fixed. Therefore, we can fit the initial stage of adsorption when t→0 to obtain the surface permeability α, as shown in Figure 3 (a); and the internal diffusion coefficient D can be obtained by fitting the adsorption curve as a whole according to equation (2), as follows: Figure 3 (b); When both the surface permeability and the internal diffusion coefficient are obtained, the apparent diffusion coefficient can be calculated by equation (3), which represents the result of the joint control of internal diffusion and surface resistance.

[0066]

[0067]

[0068]

[0069] The surface permeability and diffusion coefficient of DCPD resin on catalysts with different pore sizes can be calculated by the above method, such as Figure 3 As shown in the figure, as the pore size increases, the surface permeability and internal diffusion coefficient both increase, which means that the larger the pore size, the greater the tendency of DCPD resin molecules to diffuse from the surface to the pores and the diffusion rate in the pores.

Claims

1. A device for measuring the diffusion coefficient of a macromolecular compound in a porous medium, characterized in that: include: A first material storage tank (1), a second material storage tank (2), a three-way valve (3), a metering pump (4), a temperature control device (5), a fixed bed (6), an infrared light source (7), an infrared in-situ pool (8) and an infrared detector (9), wherein the first material storage tank (1) and the second material storage tank (2) are respectively connected to two inlets of the three-way valve (3) through metal pipes, the outlet of the three-way valve (3) is connected to the inlet of the metering pump (4) through a metal pipe, and the liquid outlet of the metering pump (4) is connected to the fixed bed (6) through a metal pipe, a thermocouple and a heating belt are installed in the fixed bed (6), and the outer periphery is wrapped with thermal insulation cotton, the thermocouple and the heating belt are connected to the temperature control device (5) through electric wires, and the temperature of the fixed bed layer can be controlled in real time through the temperature control device. The outlet of the fixed bed (6) is connected to the infrared in-situ pool (8) through a metal pipeline, and the outlet of the infrared in-situ pool (8) is connected to the waste liquid bucket through a metal pipeline; the infrared in-situ pool (8) is placed between the infrared light source (7) and the infrared detector (9), and the infrared light emitted from the infrared light source (7) can pass through the infrared in-situ pool (8) and be detected by the infrared detector (9) and the signal is processed and transmitted to the computer in real time; the first material storage tank (1) and the second material storage tank (2) are respectively used to store the substance to be tested and the common solvent of the substance to be tested, the substance to be tested is DCPD petroleum resin, DCPD petroleum resin includes C5 petroleum resin, C9 petroleum resin or C5-C9 copolymer petroleum resin, and the solvent is cyclohexane, benzene or acetone.

2. The device for measuring the diffusion coefficient of a macromolecular compound in a porous medium according to claim 1, characterized in that: The first material storage tank (1) and the second material storage tank (2) are any one of a glass container with a lid or an unsealed stainless steel tank or a combination thereof; the three-way valve (3) is any one of a manual stainless steel sleeve three-way ball valve, a solenoid valve or a pneumatic valve; the metering pump (4) is any one of a horizontal flow pump, a peristaltic pump, a plunger pump, a hydraulic pump, a mechanical diaphragm pump or an electromagnetic metering pump; the infrared in-situ cell (8) is any one of a liquid in-situ cell with a variable optical path or a fixed optical path, and the window used is any one of KBr, NaCl, CaF2, BaF2, ZnSe, KRS-5, CsI or CsB; the infrared light source (7) is a light source provided by any one of a far-infrared spectrometer, a mid-infrared spectrometer or a near-infrared spectrometer; the infrared detector (9) is any one of a vacuum thermocouple detector, a pyroelectric detector or a mercury cadmium telluride detector.

3. A method for using the device for measuring the diffusion coefficient of a macromolecular compound in a porous medium according to any one of claims 1 to 2, characterized in that: The specific steps are as follows: (1) First, a certain amount of catalyst powder is filled into the fixed bed (6), and the catalyst powder is vacuum pretreated in advance to remove impurities adsorbed on the surface; (2) The sample solution to be tested is placed in the first material storage tank (1), and the solvent corresponding to the sample to be tested is placed in the second material storage tank (2); (3) Install the infrared in-situ cell (8) at the corresponding position, turn on the infrared light source (7) and the infrared detector (9), and confirm that the material signal can be detected normally and displayed in real time on the computer; (4) First, switch the three-way valve (3) to the channel connected to the second material storage tank (2); (5) Turn on the metering pump (4), set the required flow rate and the maximum pressure allowed in the device, and allow the solvent to fill the entire device, exhaust the air, and wet the sample; (6) After a period of time, the three-way valve (3) is switched to the pipeline connected to the first material storage tank (1), so that the sample to be tested fills the entire device and is adsorbed in the porous medium in the fixed bed (6); (7) When the infrared detector (9) detects the signal of the object to be measured, it starts timing and collecting data; (8) When the detected signal of the object under test does not change with time, stop the detection; (9) Switch the three-way valve (3) to the channel connected to the second material storage tank (2), keep the metering pump (4) working continuously, and use solvent to flush the entire device pipeline; (10) After a certain period of time, turn off the metering pump (4) and the test ends.

4. The method for using the device for measuring the diffusion coefficient of a macromolecular compound in a porous medium according to claim 3, characterized in that: Steps (7) to (8) are used to collect the changes in the infrared spectrum of the molecular characteristics of the analyte over time.

5. The method for using the device for measuring the diffusion coefficient of a macromolecular compound in a porous medium according to claim 4, characterized in that: Integrate the characteristic peak areas of the analyte molecules in the infrared spectra obtained in steps (7) to (8), and use the change in the integrated area to replace the change in the analyte concentration to obtain the change in the analyte concentration over time, which is the adsorption curve.

6. The method for using the device for measuring the diffusion coefficient of a macromolecular compound in a porous medium according to claim 5, characterized in that: The data obtained in steps (7) to (8) are fitted to the adsorption curve using the surface permeability formula and the diffusion coefficient formula respectively. The surface permeability, internal diffusion coefficient and apparent diffusion coefficient can be obtained by calculation.

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