Quantitative evaluation method for electrically enhanced catalytic action in electrothermal catalysis

Abstract

The invention discloses a quantitative evaluation method for an electrically enhanced catalytic action in electrothermal catalysis. According to the method, the catalytic activity of the structured catalyst in a'resistance internal heating 'reaction mode is considered to be composed of two parts, namely thermal contribution and electric strengthening contribution, and the weight of the thermal contribution can be quantitatively measured and calculated according to the temperature distribution of the structured catalyst under electric heating and the catalytic activity-temperature incidence relation under conventional external heating. And the electric strengthening contribution is indirectly obtained. The method provided by the invention provides a new quantitative index for analyzing the electro-thermal catalytic reaction process, is not limited by catalyst types and reaction types, can be used for comparative research of a cross-catalytic material system and a cross-reaction system, and has important guiding significance for rational design of an efficient electro-thermal catalyst.

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, and with the continuous reduction in the cost of renewable energy generation, electrification has become an important means of green development in the chemical industry. In recent years, the technical direction of converting electrical energy into thermal energy to drive chemical reactions has begun to receive widespread attention. Compared with traditional thermal catalytic technology where the heat source is outside the reactor, this type of technology often uses the catalyst directly as an electrothermal conversion carrier, that is, the catalyst itself is the heat source, which can be called "electrical internal heating". It has the advantages of high thermal utilization efficiency, no heat transfer restrictions, and strong controllability of reaction temperature. Although various electrothermal conversion methods such as resistance heating, microwave heating, and electromagnetic induction heating can achieve "electrical internal heating" of catalysts, resistance heating has more significant advantages in terms of energy efficiency, cost, and difficulty of industrial amplification, and has therefore received more and more attention.

[0003] In the catalytic technology based on resistance heating, the new reaction mode combining "resistance internal heating" with structured catalysts has attracted much attention. It connects the structured catalyst with a conductive skeleton carrier as a resistance heating element to the circuit, and the Joule heat generated by the current flowing through the skeleton carrier provides heat for the catalytic reaction. It is called "resistance 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 structured catalysts to enhance mass transfer and heat transfer, making the temperature management of the catalyst bed more efficient, fast and flexible, and has the potential for dynamic operation to directly drive the operation of the reactor using volatile and intermittent renewable electricity such as photovoltaics and wind power. Not only that, this way 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 for using electrical energy to regulate the reaction performance of the catalyst surface interface.

[0004] However, due to the strong coupling of 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 also a lack of basic knowledge and understanding of their synergistic relationship. To date, there is still a lack of effective experimental research methods that can reasonably quantitatively evaluate the electrical enhancement 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 efficient 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 estimated 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 comprises:

[0009] The first step is to energize the first structured catalyst, drive the catalytic reaction by Joule heat, and measure the apparent total catalytic activity under set reaction conditions (i.e., the composition, flow rate and pressure of the reaction gas) and under 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 is gradually heated from the surface to the inside through heating principles such as heat radiation and external flow medium convection heat transfer), a curve of the external heating catalytic activity of the second structured catalyst changing with temperature under 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 second structured catalyst;

[0013] Step 5: Accumulate 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 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] Among them, the first structured catalyst and the second structured catalyst are prepared by 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 image and measure the temperature of the first structured catalyst under power-on, and the temperature measurement principle based on a pixel array is used to achieve 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 on 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 size.

[0021] Preferably, the curve of the externally heated catalytic activity changing with temperature is first obtained by 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 the type of reaction. 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 photographs of the first structured catalyst (right) and the second structured catalyst (left);

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

[0028] Figure 3 It 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 on;

[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 generation 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 foams (size 70 mm 4 mm 1mm) was put into a hydrothermal kettle filled with 0.25mol / l urea aqueous solution, and the hydrothermal reaction was carried out at 110°C for 8 hours. The precursor was obtained after being taken out and dried; then, the catalyst was obtained by calcining at 750°C for 2 hours in a H2 / Ar (volume ratio of 1:9) atmosphere.

[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 thereto. 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 flow of 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 imager 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, and the ZnSe window 2 serves as the upper surface reactor wall of the rectangular structure. Both ends of the first structured catalyst are connected to wires, and 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 electrodes 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 effect of the high temperature generated by electric heating on the ZnSe material.

[0048] (3) Calculation of the electrocatalytic effect

[0049] Step 1: Place the first structured catalyst along the axis of the quartz main tube in the middle of the catalytic performance evaluation reactor, connect copper wires at both ends of the catalyst, lead out from both ends of the reactor and connect to the positive and negative electrodes of a high-precision constant current DC power supply, and use current sensors and voltage sensors to monitor the current flowing through the catalyst and the voltage at both ends in real time, thereby calculating the electric power applied to the catalyst. The dry reforming reaction is carried out at normal pressure, and the reaction raw gas (CO2: 49.7ml / min, CH4: 30.3ml / min) flows in from one end of the quartz main tube 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 apparent total catalytic activity results of the first structured catalyst under different currents (electric powers) of "internal resistance heating" (as shown in Table 1).

[0050] Table 1

[0051]

[0052] Step 2: Place the first structured catalyst in the main structure of the infrared thermal imaging reactor, connect copper wires at both ends of the first structured catalyst to the positive and negative electrodes of a high-precision constant current DC power supply, and use the pulling force of the wire to suspend the catalyst, and adjust the surface of the catalyst to be measured to be parallel to the ZnSe window 2. Install the infrared thermal imager on a tripod, with the lens directly above the ZnSe window 2, adjust the lens focal length to make the first structured catalyst image clear, and set the instrument parameters such as emissivity (0.7) and transmittance (99%). Introduce the reaction raw gas (CO2: 49.7ml / min, CH4: 30.3ml / min) into the infrared thermal imaging reactor, and use the online gas mass spectrometer to monitor the changes in the outflow gas components in real time. After the mass spectrometry signals of CO2 and CH4 are stable, start infrared thermal imaging temperature measurement. First, when the first structured catalyst is not powered on, an ice bag is placed under the infrared thermal imaging reactor, and a thermal image is taken after the catalyst temperature stabilizes. The result is used to extract the contour of the first structured catalyst in the infrared thermal imaging image (i.e., the corresponding pixel range). Figure 4 is a typical result; then, the ice pack is removed, 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-areas (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 (200mm long, 80mm 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 at normal pressure. The reaction raw gas (CO2: 49.7ml / min, CH4: 30.3ml / 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 generation 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 under the current (or electric power) is obtained by accumulating the thermal catalytic activities of all micro-regions on the first structured catalyst at the same current intensity (or electric power). Table 3 shows the overall thermal catalytic activity results of the first structured catalyst under "resistance internal heating" at different currents (electric 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, and then subtract the thermal contribution from 1 to obtain the electrical enhancement contribution. Table 4 shows the electrical enhancement contribution results of 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 implementation modes, and 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 the catalyst under the electrothermal catalytic reaction mode consists of two parts: thermal contribution and electrical enhancement contribution. The thermal contribution is calculated based on the catalyst temperature and its catalytic activity under the external heating reaction mode. The electrical enhancement contribution is calculated using the difference between the apparent total catalytic activity and the thermal contribution. The specific method is as follows: The first step is to energize the first structured catalyst, drive the catalytic reaction by Joule heat, and measure the apparent total catalytic activity under set reaction conditions and set current or electric power; wherein the reaction conditions are 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: Based on the external heating reaction mode, a curve of the external heating catalytic activity of the second structured catalyst changing with temperature under the set reaction conditions is obtained; Step 4: According to the results of the second step and the third step, 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 second 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: Dividing the overall thermal catalytic activity by the apparent total catalytic activity is the thermal contribution, and then subtracting the thermal contribution from 1 is the electrical enhancement contribution; Wherein, the first structured catalyst and the second structured catalyst are prepared by 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 calculation 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 the temperature measurement principle based on a pixel array is used to divide the first structured catalyst into micro-regions and measure the temperature separately.

3. The calculation 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 realize the micro-region division of the first structured catalyst.

4. The calculation method according to claim 2, characterized in that: The first structured catalyst is in the form of a thin sheet, 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 calculation method according to claim 1, characterized in that: The external heating reaction is carried out by using an electric heating furnace.

6. The calculation method according to claim 1, characterized in that: The first structured catalyst has the same macroscopic geometry and size as the second structured catalyst.

7. The calculation method according to claim 1, characterized in that: The curve of the externally heated catalytic activity changing with temperature is obtained by firstly experimentally measuring the catalytic activity at a plurality of discrete temperatures and then by numerical fitting.

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