A quantitative evaluation method for electrically enhanced catalytic effect in electrothermal catalysis

Abstract

The present invention discloses a quantitative evaluation method for electrically enhanced catalytic effects in electrothermal catalysis. This method regards the catalytic activity of a structured catalyst under the "internal resistance heating" reaction mode as consisting of two parts: a thermal contribution and an electrically enhanced contribution. The weight of the thermal contribution can be quantitatively measured by using the temperature distribution of the structured catalyst under electrical heating and the catalytic activity-temperature correlation under conventional external heating, thereby indirectly obtaining the electrically enhanced contribution. The method provided by the present invention provides a new quantitative indicator for analyzing the electrothermal catalytic reaction process, and is not limited by the catalyst type and reaction type. It can be used for comparative studies across catalytic material systems and across reaction systems, and has important guiding significance for the rational design of high-efficiency electrothermal catalysts.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysis, and in particular relates to a quantitative evaluation method for electrically enhanced catalytic effect in electrothermal catalysis. Background Art

[0002] Electricity is simple, flexible, and efficient to use. Furthermore, with the decreasing cost of renewable energy generation, electrification has become a key enabler for the green development of the chemical industry. In recent years, the technology of converting electrical energy into thermal energy to drive chemical reactions has begun to gain widespread attention. Compared with traditional thermal catalytic technologies where the heat source is external to the reactor, this type of technology often uses the catalyst directly as the electrothermal conversion carrier, meaning the catalyst itself is the heat source. This is known as "internal electric heating," and has the advantages of high thermal efficiency, freedom from heat transfer limitations, and strong controllability of reaction temperature. While various electrothermal conversion methods, such as resistance heating, microwave heating, and electromagnetic induction heating, can achieve "internal electric heating" of catalysts, resistance heating offers significant advantages in terms of energy efficiency, cost, and difficulty in industrial scale-up, and has therefore garnered increasing attention.

[0003] Among the catalytic technologies based on resistive heating, a new reaction method that combines "resistive internal heating" with structured catalysts has attracted much attention. It connects a structured catalyst with a conductive skeleton carrier as a resistive heating element to the circuit. The Joule heat generated by the current flowing through the skeleton carrier provides heat for the catalytic reaction. This is called "resistive internal heating" structured catalyst reaction technology. This reaction technology not only uses the heat generated inside the catalyst to control the reaction temperature, but also retains the process intensification characteristics of the structured catalyst to enhance mass transfer and heat transfer, making the temperature management of the catalyst bed more efficient, rapid and flexible. It has the potential for dynamic operation to directly drive the operation of the reactor using fluctuating and intermittent renewable electricity such as photovoltaic and wind power. Not only that, this method of applying electrical energy also brings the electric heat source into close contact with the catalytic active sites, allowing electrical energy to act on the surface catalytic active sites in various forms such as current, surface electric field, and thermal electrons, providing a new means of using electrical energy to regulate the reaction performance of the catalyst surface interface.

[0004] However, due to the strong coupling between electricity and heat under resistive heating, that is, the two are difficult to regulate independently, it is difficult to distinguish the weights between the electrical enhancement contribution and the thermal contribution in the reaction process, and there is a lack of basic knowledge and understanding of their synergistic relationship. To date, there is still a lack of effective experimental research methods to reasonably quantitatively evaluate the electrically enhanced catalytic effect under "resistive internal heating", and it is even more difficult to conduct systematic regularity research across catalytic material systems and catalytic reaction systems, which seriously restricts the development of the design theory of high-efficiency electrothermal catalysts. Summary of the Invention

[0005] The object of the present invention is to provide a method for quantitatively evaluating the electrically enhanced catalytic effect in electrothermal catalysis, wherein the method can quantitatively evaluate the electrically enhanced catalytic effect under the "resistance internal heating" structured catalyst reaction mode.

[0006] The present invention adopts the following technical solutions:

[0007] The basic idea of ​​the quantitative evaluation method of electrically enhanced catalytic effect in electrothermal catalysis provided by the present invention is to call the catalytic activity obtained by evaluating the catalyst under the "internal resistance heating" structured catalyst reaction mode as the apparent total catalytic activity, which is set to consist of two parts: thermal contribution and electrically enhanced contribution. The thermal contribution can be calculated based on the temperature of the structured catalyst and the conventional external heating catalytic activity data, and the electrically enhanced contribution is the difference between the apparent total catalytic activity and the thermal contribution.

[0008] The method provided by the present invention mainly includes:

[0009] Step 1: Power is applied to the first structured catalyst to drive the catalytic reaction using Joule heat, and the apparent total catalytic activity is measured under set reaction conditions (i.e., the composition, flow rate, and pressure of the reaction gas) and at a set current (or electric power);

[0010] Step 2: Dividing the first structured catalyst into a plurality of micro-regions that are easy to measure the temperature separately, and measuring the temperature of each micro-region under set reaction conditions and set current (or electric power);

[0011] Step 3: Based on the external heating reaction mode (the external heating reaction mode refers to a reaction mode in which the catalyst temperature is gradually increased from the surface to the inside through heating principles such as thermal radiation and convective heat transfer of an external flowing medium), a curve of the external heating catalytic activity of the second structured catalyst as a function of temperature under the set reaction conditions is obtained;

[0012] Step 4: Based on the results of the second and third steps, the thermal catalytic activity of each micro-region of the first structured catalyst is calculated according to the volume ratio of each micro-region of the first structured catalyst to the volume of the second structured catalyst;

[0013] Step 5: Accumulating the thermal catalytic activities of each micro-region of the first structured catalyst in Step 4 to obtain the overall thermal catalytic activity under a set current (or electric power);

[0014] Step 6: Divide the overall thermal catalytic activity obtained in step 5 by the apparent total catalytic activity obtained in step 1 to obtain the thermal contribution, and then subtract the thermal contribution from 1 to obtain the electrical enhancement contribution.

[0015] The first structured catalyst and the second structured catalyst are prepared using the same raw materials and the same method; the apparent total catalytic activity, external heating catalytic activity, micro-region thermal catalytic activity and overall thermal catalytic activity are uniformly expressed by one of the reactant conversion rate, reaction rate, product yield or product generation rate.

[0016] Preferably, an infrared thermal imager is used to perform imaging and temperature measurement on the first structured catalyst under power, and the temperature measurement principle based on a pixel array is utilized to realize micro-region division and separate temperature measurement of the first structured catalyst.

[0017] Furthermore, an infrared thermal image of the first structured catalyst that is cooled at a low temperature (i.e., below room temperature) and not powered is used to extract its contour (i.e., the corresponding pixel range) imaged in the pixel array, so as to accurately achieve micro-region division of the first structured catalyst.

[0018] Furthermore, the first structured catalyst is in the form of a thin sheet (thickness not greater than 1 cm), which is conducive to the consistency of its internal temperature and surface temperature, so that the infrared thermal imaging temperature measurement results can reflect the overall temperature distribution of the structured catalyst.

[0019] Preferably, an electric heating furnace is used to externally heat the second structured catalyst.

[0020] Preferably, the first structured catalyst and the second structured catalyst have the same macroscopic geometry and dimensions.

[0021] Preferably, the curve of the external heating catalytic activity changing with temperature is obtained by first experimentally measuring the catalytic activity at several discrete temperatures and then by numerical fitting.

[0022] The technical solution of the present invention has the following advantages:

[0023] (1) As a practical method to guide the development of efficient electrothermal catalysts, this method does not require the use of expensive material microstructure characterization equipment or complex catalytic reaction mechanism research. It has the advantages of being simple, low-cost, and time-saving.

[0024] (2) This method uses the experimentally easy-to-measure temperature as a scale to evaluate the contribution of thermal energy in the catalytic reaction process, and then indirectly obtains the contribution of the electrical enhancement effect, providing a new quantitative indicator for the analysis of the electrothermal catalytic reaction process.

[0025] (3) The application of this method is not limited by the type of structured catalyst and reaction type. It can carry out comparative studies across catalytic material systems and across reaction systems, which is conducive to establishing a systematic and regular understanding of electrically enhanced catalysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 are photos of the first structured catalyst (right) and the second structured catalyst (left);

[0027] Figure 2 Schematic diagram of a catalytic performance evaluation reactor, 11 is a quartz main pipe, 22 is a quartz branch pipe;

[0028] Figure 3 This is a schematic diagram of an infrared thermal imaging reactor, 1 main body, 2 ZnSe window, 3 gas inlet, 4 gas outlet;

[0029] Figure 4 This is a typical infrared thermal image of the first structured catalyst under low temperature cooling;

[0030] Figure 5 This is a typical infrared thermal image of the first structured catalyst under power supply;

[0031] Figure 6 is Figure 5 A temperature distribution map of the micro-regions (pixel points) divided on the first structured catalyst is obtained;

[0032] Figure 7 This is a curve showing the change of the external heating catalytic activity of the second structured catalyst (represented by (a) CO2 conversion rate, (b) CH4 reaction rate, (c) H2 yield and (d) CO production rate) with temperature, obtained by using the polynomial fitting method based on the data in Table 2. DETAILED DESCRIPTION

[0033] The present invention takes the foamed nickel-chromium-aluminum structured catalyst and methane dry reforming reaction as an example to specifically illustrate the application of the above-mentioned method for measuring the electrically enhanced catalytic effect.

[0034] (1) Preparation of structured catalysts

[0035] First, two cleaned and dried nickel-chromium-aluminum foam sheets (size 70 mm 4 mm The precursor was obtained by calcining in a H2 / Ar (volume ratio of 1:9) atmosphere at 750°C for 2 hours to obtain the catalyst.

[0036] like Figure 1 As shown, copper terminals are installed at both ends of a foamed nickel-chromium-aluminum structured catalyst as the first structured catalyst; and another foamed nickel-chromium-aluminum structured catalyst is directly used as the second structured catalyst.

[0037] (2) Introduction of key equipment

[0038] a) Catalytic performance evaluation reactor

[0039] The catalytic performance evaluations of the first structured catalyst under “internal resistance heating” and the second structured catalyst under external heating were both conducted using the same quartz tube reactor. Figure 2 As shown, the reactor consists of a quartz main pipe 11 with a length of 600 mm and an inner diameter of 11 mm and a quartz branch pipe 22 with a length of 200 mm and an inner diameter of 11 mm perpendicular to it. One end of the branch pipe is connected to the middle position of the main pipe. The main pipe is used to place the catalyst and the circulation of the reaction gas, and the branch pipe is used to insert a thermocouple to measure the temperature of the catalyst during external heating.

[0040] b) Infrared thermal imager

[0041] The temperature distribution of the first structured catalyst under "resistance internal heating" was measured using a Ti480PRO (FLUKE) infrared thermal imager. Its main technical indicators are:

[0042] Infrared spectrum: 7.5 μm to 14 μm

[0043] Detector resolution: 640×480 pixels

[0044] Temperature measurement range: -20 °C to +800 °C

[0045] Temperature measurement accuracy: ±2 °C or 2%

[0046] c) Infrared thermal imaging reactor

[0047] Since the infrared spectrum range required for infrared thermal imaging testing cannot penetrate the quartz material used in the catalytic performance evaluation reactor, an infrared thermal imaging reactor with an infrared window (ZnSe window 2) is used to measure the temperature distribution of the first structured catalyst under set reaction conditions and set current (or electric power). Figure 3 As shown, the main body 1 of the reactor is designed to be a rectangular structure, and the first structured catalyst is placed therein. The ZnSe window 2 serves as the upper surface reactor wall of the rectangular structure. Wires are connected to both ends of the first structured catalyst. The two wires are respectively led out of the reactor through the gas inlet 3 and the gas outlet 4 and then connected to the positive and negative poles of the power supply. The pulling force of the wires is used to make the catalyst suspended in the air and close to the lower surface reactor wall of the rectangular structure (direct contact between the two should be avoided to interfere with the temperature measurement). The surface to be measured temperature of the first structured catalyst is parallel to the ZnSe window 2 and there is a distance of about 10 cm between the two, which can avoid the adverse effects of high temperature generated by electric heating on the ZnSe material.

[0048] (3) Calculation of electrically enhanced catalytic effect

[0049] Step 1: The first structured catalyst was placed axially along the main quartz tube in the center of the catalytic performance evaluation reactor. Copper wires were connected to the positive and negative terminals of a high-precision constant-current DC power supply, extending from either end of the reactor. Current and voltage sensors were used to monitor the current flowing through the catalyst and the voltage across it in real time, thereby calculating the electrical power applied to the catalyst. The dry reforming reaction was conducted at atmospheric pressure. The feed gases (CO2: 49.7 ml / min, CH4: 30.3 ml / min) flowed into the main quartz tube of the catalytic performance evaluation reactor and out of the other end. The composition of the outflowing gas was monitored online by gas chromatography, yielding the apparent total catalytic activity of the first structured catalyst under various currents (electrical powers) during "resistance heating" (see Table 1).

[0050] Table 1

[0051]

[0052] Step 2: Place the first structured catalyst within the main structure of the infrared thermal imaging reactor. Connect copper wires to each end of the catalyst, extending from the reactor's two vents and then connecting to the positive and negative terminals of a high-precision constant-current DC power supply. The wires' pull maintains the catalyst suspended in mid-air, and the catalyst surface to be measured is aligned parallel to the ZnSe window 2. Mount the infrared thermal imager on a tripod, with the lens positioned directly above the ZnSe window 2. Adjust the lens focal length to ensure a clear image of the first structured catalyst. Set instrument parameters such as emissivity (0.7) and transmittance (99%). Feed gases (CO2: 49.7 ml / min, CH4: 30.3 ml / min) are introduced into the infrared thermal imaging reactor. Changes in the effluent gas composition are monitored in real time using an online gas mass spectrometer. Once the CO2 and CH4 mass spectrometer signals stabilize, infrared thermal imaging temperature measurement begins. First, when the first structured catalyst is not powered on, an ice pack is placed under the infrared thermal imaging reactor. After the catalyst temperature stabilizes, a thermal image is taken. The result is used to extract the outline of the first structured catalyst in the infrared thermal image (i.e., the corresponding pixel range). Figure 4 The typical result is then removed, the ice pack is kept, the relative position of the infrared thermal imager and the first structured catalyst is kept unchanged, different current intensities are passed through the first structured catalyst from low to high, and infrared thermal images are taken after the catalyst temperature stabilizes at each current. Figure 5 This is a typical infrared thermal image of the first structured catalyst under power (power is 20W). Figure 6 is Figure 5 The temperature distribution map of the divided micro-regions (pixel points) on the first structured catalyst is obtained.

[0053] Step 3: Place the catalytic performance evaluation reactor in an electric heating furnace for external heating and temperature increase. The second structured catalyst is placed in the middle of the catalytic performance evaluation reactor along the axial direction of the quartz main pipe, and is also located in the middle of the heating zone of the electric heating furnace (200 mm long, 80 mm in diameter). A K-type thermocouple is inserted from the quartz branch pipe and placed close to the surface in the middle of the catalyst. The measurement result is used to represent the catalyst temperature. The dry reforming reaction is carried out under normal pressure. The reaction raw gas (CO2: 49.7 ml / min, CH4: 30.3 ml / min) flows in from one end of the quartz main pipe of the catalytic performance evaluation reactor and flows out from the other end. The composition of the outflowing gas is detected online by a gas chromatograph, thereby obtaining the external heating catalytic activity results of the second structured catalyst at several discrete temperatures of external heating (as shown in Table 2). Appendix Figure 7 This is a curve showing the change of the external heating catalytic activity of the second structured catalyst (represented by (a) CO2 conversion rate, (b) CH4 reaction rate, (c) H2 yield and (d) CO production rate) with temperature, obtained by using the polynomial fitting method based on the data in Table 2.

[0054] Table 2

[0055]

[0056] Step 4: Calculate the micro-region volume V of the first structured catalyst corresponding to a single pixel in the infrared thermal imaging image. 像素 (0.0098mm 3 ), and then according to V 像素 The volume ratio of the second structured catalyst (3.5 10 -5 : 1) and the results of the third step, a curve of the micro-region thermal catalytic activity of the first structured catalyst changing with temperature is obtained, and finally, based on the curve and the temperature distribution results obtained in the second step, the thermal catalytic activity of each micro-region on the first structured catalyst under different currents can be obtained.

[0057] Step 5: The overall thermal catalytic activity at the same current (or power) was calculated by summing the thermal catalytic activities of all micro-regions on the first structured catalyst. Table 3 shows the overall thermal catalytic activity of the first structured catalyst under "resistance heating" at different currents (powers).

[0058] Table 3

[0059]

[0060] Step 6: Divide the overall thermal catalytic activity obtained in Step 5 by the apparent total catalytic activity obtained in Step 1 to obtain the thermal contribution. Subtract the thermal contribution from 1 to obtain the electrical enhancement contribution. Table 4 shows the electrical enhancement contribution results for the first structured catalyst under "resistance internal heating" at different currents (electrical powers).

[0061] Table 4

[0062]

[0063] The present invention is not limited to the above-mentioned embodiments. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A quantitative evaluation method for electrically enhanced catalytic effect in electrothermal catalysis, characterized in that: The catalytic activity of a catalyst under an electrothermal catalytic reaction is composed of two parts: a thermal contribution and an electrical enhancement contribution. The thermal contribution is estimated based on the catalyst temperature and its catalytic activity under an external heating reaction. The electrical enhancement contribution is estimated using the difference between the apparent total catalytic activity and the thermal contribution. The specific method is as follows: Step 1: applying electricity to the first structured catalyst to drive the catalytic reaction using Joule heat, and measuring the apparent total catalytic activity under set reaction conditions and at a set current or electric power; wherein the reaction conditions include the composition, flow rate, and pressure of the reaction gas; Step 2: dividing the first structured catalyst into a plurality of micro-regions, and measuring the temperature of each micro-region under the set reaction conditions and the set current or electric power; Step 3: obtaining a curve of the external heating catalytic activity of the second structured catalyst as a function of temperature under the set reaction conditions based on the external heating reaction mode; Step 4: Based on the results of the second and third steps, and according to the volume ratio of each micro-region of the first structured catalyst to the volume of the second structured catalyst, calculate the thermal catalytic activity of each micro-region of the first structured catalyst; Step 5: Accumulating the thermal catalytic activities of each micro-region of the first structured catalyst in the fourth step to obtain the overall thermal catalytic activity under the set current or electric power; Step 6: Divide the overall thermal catalytic activity by the apparent total catalytic activity to obtain the thermal contribution, and then subtract the thermal contribution from 1 to obtain the electrical enhancement contribution; The first structured catalyst and the second structured catalyst are prepared using the same raw materials and the same method; the apparent total catalytic activity, the externally heated catalytic activity, the micro-region thermal catalytic activity and the overall thermal catalytic activity are uniformly expressed by one of the reactant conversion rate, reaction rate, product yield or product generation rate.

2. The quantitative evaluation method according to claim 1, characterized in that An infrared thermal imager is used to image and measure the temperature of the first structured catalyst under power, and its temperature measurement principle based on a pixel array is used to achieve micro-region division and separate temperature measurement of the first structured catalyst.

3. The quantitative evaluation method according to claim 2, characterized in that: The infrared thermal image of the first structured catalyst that is cooled at low temperature and not powered is used to extract the contour of the first structured catalyst imaged in the pixel array, so as to accurately achieve micro-region division of the first structured catalyst.

4. The quantitative evaluation method according to claim 2, characterized in that The first structured catalyst is in a thin sheet type, which is conducive to the consistency of its internal temperature and surface temperature, so that the infrared thermal imaging temperature measurement result can reflect the overall temperature distribution of the first structured catalyst.

5. The quantitative evaluation method according to claim 1, wherein: The external heating reaction is carried out in an electric heating furnace.

6. The quantitative evaluation method according to claim 1, characterized in that The first structured catalyst and the second structured catalyst have the same macroscopic geometry and size.

7. The quantitative evaluation method according to claim 1, characterized in that The curve of the externally heated catalytic activity changing with temperature is obtained by first experimentally measuring the catalytic activity at multiple discrete temperatures and then by numerical fitting.

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