A method and apparatus for pulsed laser driven flow phase methane dry reforming catalysis

Abstract

The application discloses a kind of pulse laser driven flow phase methane dry reforming catalytic method and device.The device includes laser module, and the lower side of laser module is equipped with reaction chamber;Reaction chamber is equipped with gas inlet and gas outlet at both ends respectively;The top of reaction chamber is equipped with the upper cover that is movably connected with reaction chamber.Catalyst is laid on catalyst carrier, and mixed gas containing methane and carbon dioxide is input into the gas inlet of reaction chamber, laser is focused on catalyst and reaction is carried out, and product gas is collected at gas outlet, to realize methane dry reforming catalysis.The application uses simple carbon molybdenum or tungsten carbide and other transition metal carbide as stable catalyst, and uses low-power laser as reaction source, and the device is simple, small in size and low in operation cost.The problems of traditional thermal catalytic equipment, such as complexity, large size, low conversion rate, low selectivity, high energy consumption and unstable transition metal carbide catalyst susceptible to oxidation and deactivation, are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of laser processing technology, in particular to a method and device for pulsed laser driven flow phase methane dry reforming catalysis. BACKGROUND

[0002] The massive emission of greenhouse gases such as methane (CH4) and carbon dioxide (CO2) is the main cause of global warming. Catalytic dry reforming of methane (DRM) provides an environmentally friendly and feasible way for large-scale utilization of greenhouse gases. In addition, the produced synthesis gas can be further used for the synthesis of oxygen-containing fuels and long-chain hydrocarbons through Fischer-Tropsch synthesis. Therefore, it is of great significance to convert two kinds of greenhouse gases into valuable chemical raw materials by using DRM. However, from the perspective of thermodynamics, DRM is an endothermic reaction. Traditional thermal catalysis requires a high temperature (700-1000℃) and high pressure to overcome the adverse kinetics and thermodynamics. Therefore, traditional thermal catalytic equipment requires an external heating system such as a radio frequency power supply, heating wires or coils, and a thick heat insulation system and a high-pressure resistant chamber; the thermal catalysis driven by the external heating source is limited by high temperature and high pressure, has high energy consumption and high cost. In addition, due to the high-temperature reaction, catalyst deactivation caused by sintering and carbon deposition is an inevitable problem in the DRM process, which requires the core catalyst in the traditional thermal catalytic system to be replaced frequently. Photothermal catalysis occurs at a relatively low temperature (about 600℃), but the DRM reaction efficiency of photothermal catalysis without an external heating source is very low. In order to improve the reaction efficiency, some photothermal catalytic equipment also requires an external heating system such as a radio frequency power supply, heating wires or coils, and a thick heat insulation system. For example, the patent with the application number 202010538772.6 discloses a method and device for plasma catalytic dry reforming of methane to produce synthesis gas. Although the application uses plasma for catalysis, the purpose is to make the entire reforming process occur at a lower reaction temperature and pressure, but it still must be carried out under the condition of electric heating insulation, otherwise the catalyst will be seriously carbonized. Therefore, the energy consumption of the patent has not been reduced, and the requirement for the equipment is still very high, and the use of an external heating furnace is required. Therefore, it is imperative to explore a new type of catalytic equipment that combines mild reaction conditions, high catalytic performance and low power consumption. SUMMARY

[0003] In view of the above prior art, the purpose of the present application is to provide a method and device for pulsed laser driven flow phase methane dry reforming catalysis. The present application uses simple carbon molybdenum (Mo2C) or tungsten carbide (WC) and other transition metal carbides as stable catalysts, and low-power laser as the reaction source. The device is simple, small in size and low in running cost. The problems of complex traditional thermal catalytic equipment, large size, low conversion rate, low selectivity, high energy consumption and unstable transition metal carbide catalysts prone to oxidation and deactivation are solved.

[0004] To achieve the above object, the application adopts the following technical solutions:

[0005] In the first aspect of the application, a device for pulsed laser driven flow phase methane dry reforming catalysis is provided, characterized in that the device comprises a laser module, a reaction chamber is arranged below the laser module, a gas inlet and a gas outlet are arranged at two ends of the reaction chamber respectively, and an upper cover is arranged at the top of the reaction chamber and movably connected with the reaction chamber.

[0006] Preferably, a sealing ring is arranged around the upper cover, and a catalyst carrier is arranged in the reaction chamber.

[0007] Preferably, the laser module is a fiber laser, and the materials of the reaction chamber, the upper cover and the catalyst carrier are all quartz.

[0008] The fiber laser is a low-power pulsed laser with a power of 16-20 W.

[0009] In the second aspect of the application, a method for pulsed laser driven flow phase methane dry reforming catalysis by using the above device is provided, the method being: laying a catalyst on a catalyst carrier, introducing a mixed gas containing methane and carbon dioxide into the gas inlet of the reaction chamber, focusing a laser on the catalyst and performing a reaction, collecting product gas at the gas outlet, and realizing methane dry reforming catalysis.

[0010] Preferably, the catalyst is a transition metal carbide.

[0011] Preferably, the catalyst is pure molybdenum carbide or tungsten carbide.

[0012] The preparation method of the Mo2C or WC nanosheet is as follows: placing MoO3 or WO3 oxide and the like on the upstream of a tubular CVD furnace, introducing a protective gas, heating the tubular CVD furnace from room temperature to 800-1000℃, introducing 50-100 sccm H2 / Ar mixed gas for 2 hours, naturally cooling the reaction, and collecting MoO2 or WO2 nanosheet at the end of the tubular CVD furnace system. Subsequently, the collected MoO2 or WO2 nanosheet is placed in a ceramic crucible of the tubular furnace, a protective gas such as 20 sccm Ar is introduced, heating is performed to 1000℃ at a heating rate of 10℃ / min, the Ar gas is closed when the temperature reaches 1000℃, and 20-80 sccm CH4 gas is introduced, the time lasts for 30 min, and then the tubular furnace is naturally cooled to room temperature in an argon atmosphere to obtain Mo2C or WC nanosheet.

[0013] Molybdenum carbide is prone to oxidation and deactivation in methane dry reforming, laser driven catalysis can make the reactant methane directly crack into CH*, avoid gradual dehydrogenation, establish a balance reaction between CO2 and CH4, realize balanced product ratio, and thus avoid oxidation and deactivation of molybdenum carbide.

[0014] Preferably, the mixed gas is a mixture of methane, carbon dioxide and argon, and the volume ratio of methane, carbon dioxide and argon is 45%:45%:10%.

[0015] Preferably, the gas hourly space velocity of the mixed gas is 30-120 L·gcat -1 ·h -1 Low gas hourly space velocity is conducive to obtaining higher CH4 conversion rate.

[0016] Preferably, the laser is emitted by a 1064 nm fiber laser; the repetition frequency of the laser is 16-20 kHz, the average laser power is 16-20 W, the single pulse energy is 0.8-1.3 mJ, the scanning interval is 0.01-0.05 mm, and the scanning speed is 1000-2000 mm / s -1 .

[0017] In a third aspect of the present application, the application of the above-mentioned pulsed laser driven flow phase methane dry reforming catalysis method in improving the catalytic efficiency of methane dry reforming or avoiding the oxidation deactivation of transition metal catalysts is provided.

[0018] The present application has the following beneficial effects:

[0019] (1) In the process of laser driven DRM reaction, the energy of the laser is localized and does not affect the surrounding medium, so the material requirements of the selected reactor are very low.

[0020] (2) Compared with traditional thermal catalytic equipment, the pulsed laser driven flow phase methane dry reforming device of the present application does not require high-temperature-resistant and heat-insulating materials, does not require a high-pressure-resistant chamber, has high energy utilization rate, and solves the problem of high energy consumption of traditional thermal catalysis. Under the action of the laser, not only a higher conversion rate is achieved, but also a more equal product ratio is achieved, and the ratio of hydrogen and carbon monoxide in the prepared synthesis gas is close to 1:1; it also has higher energy efficiency and more economical power cost efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a schematic diagram of the pulsed laser catalytic methane dry reforming equipment module of the present application; wherein 1 is a laser module, 201 is an upper cover, 202 is a reaction chamber, 203 is a sealing rubber ring, 301 is an air inlet, 302 is an air outlet, and 4 is a catalyst;

[0022] Figure 2 It is a schematic diagram of the principle of the pulsed laser enhanced catalytic methane dry reforming equipment of the present application;

[0023] Figure 3 It is a reactor physical map of the pulsed laser enhanced catalytic methane dry reforming equipment of the present application;

[0024] Figure 4 The movement of laser and gas in the flow phase system of the pulse laser enhanced catalytic dry reforming of methane equipment of the present application is shown in the schematic diagram.

[0025] Figure 5 In the same mass of Mo2C (120 mg), mass space velocity GHSV: 30 L g cat -1 h -1 Under the condition, the CH4 conversion rate (a) and selectivity (b) of laser catalytic DRM (16W) and traditional thermal catalytic DRM (800W, 800℃) are compared;

[0026] Figure 6 The catalytic stability of laser driven flow phase DRM reaction and traditional thermal catalytic flow phase DRM reaction is compared.

[0027] Figure 7 The total energy efficiency and cost efficiency of different catalytic systems. DETAILED DESCRIPTION

[0028] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0029] As introduced in the background section, the photo-thermal catalytic equipment in the prior art also needs an external heating system, such as a radio frequency power supply, a heating wire or a heating coil and a heavy thermal insulation system. Therefore, if the plasma catalytic methane dry reforming is not heated by an electric heating furnace and is not insulated, the catalyst will be seriously carbonized and the catalytic efficiency will still be very low. In addition, the low-temperature plasma reactor includes a high-voltage electrode, a grounding electrode and an insulating medium, which has a very high requirement for the reaction equipment. In the electric heating + plasma mode, due to the occurrence of the reverse water gas shift reaction, the CO2 conversion rate is always higher than the CH4 conversion rate, and the CO yield is higher than the H2 yield.

[0030] Based on this, the purpose of the present application is to provide a kind of pulse laser driven flow phase methane dry reforming catalytic method and device.The present application uses simple carbonized molybdenum (Mo2C) or tungsten carbide (WC) and other transition metal carbide as stable catalyst, with low-power laser as reaction source, device is simple, small in size, low in running cost.The present application uses low-power pulse laser (16W-20W) under the condition of no external heating source, laser passes through flowing carbon dioxide and methane gas and irradiates to the surface of transition metal carbide target material, and the synthesis gas with the ratio of hydrogen and carbon monoxide close to 1:1 is prepared, and the laser catalytic process makes the reactant methane directly crack into CH *, avoids step-by-step dehydrogenation, effectively solves the problem of poor catalytic methane cracking ability of transition metal carbide catalyst.In addition, pulse laser promotes the balance reaction between CO2 and CH4 in the process of methane cracking, prevents Mo2C from being deactivated due to excessive oxidation.The pulse laser catalytic dry reforming methane device in the present application does not need high-temperature and heat preservation materials, does not need high-pressure chamber compared with traditional thermal catalytic equipment, and has high energy utilization rate, solves the problem of high energy consumption of traditional thermal catalysis.In addition, the pulse laser enhanced catalytic methane dry reforming device not only realizes higher conversion rate, but also realizes more equal product ratio, and the ratio of CO and H2 in the prepared synthesis gas is close to 1:1;It also has higher energy efficiency and more economical power cost efficiency.Especially for flow phase methane dry reforming reaction, laser can realize rapid irradiation scanning, and by adjusting parameters, laser scanning speed can be higher than gas flow rate, and in addition to high catalytic activity of pulse laser, CO2 and methane conversion rate in flow phase DRM reaction is obviously improved, and the device has important significance for widening the application of flow phase DRM reaction.In addition, molybdenum carbide is prone to oxidation and deactivation in methane dry reforming, laser driven catalysis can realize balanced product ratio, thus avoiding oxidation and deactivation of molybdenum carbide, so that molybdenum carbide can be used for efficient catalysis in methane dry reforming.

[0031] In the process of laser driven DRM reaction, due to the energy localization of laser, there is no influence on the surrounding medium, so the material requirement of the selected reaction device is low, and any glass or even plastic reaction device can be used.No heating furnace, high-voltage electrode, insulating medium and other materials are needed.The device can effectively promote the methane cracking ability under the action of laser, realize more equal product ratio, and has higher energy efficiency and more economical power cost efficiency.

[0032] In order to enable those skilled in the art to more clearly understand the technical solutions of the present application, the technical solutions of the present application will be described in detail below in combination with specific embodiments.

[0033] The test materials used in the embodiments of the present application are all conventional test materials in the art, and can be purchased through commercial channels.

[0034] Example 1

[0035] A 120 mg Mo2C catalyst was used, and the corresponding gas hourly space velocity (GHSV) was controlled at 30 L·g cat -1 ·h -1 The laser device parameters were set to a repetition frequency of 20 kHz, a single pulse energy of 0.8 mJ, a scanning interval of 0.05 mm, and a scanning speed of 1000 mm s -1 of linear scanning mode to perform laser-driven DRM.

[0036] The specific preparation steps are as follows:

[0037] (1) Preparation of Mo2C nanosheets: Put MoO3 on the upstream of the tube CVD furnace, introduce the protective gas, and heat the tube CVD furnace from room temperature to 800°C; introduce 100 sccm H2 / Ar mixed gas for 2 hours, and collect MoO2 nanosheets at the end of the tube CVD furnace system after natural cooling. Then place the collected MoO2 nanosheets in the ceramic crucible of the tube furnace, introduce 20 sccm argon as a protective gas, heat to 1000°C at a rate of 10°C / min; when the temperature reaches 1000°C, turn off the argon gas and introduce 80 sccm CH4 gas, and the time lasts for 30 min, and then the tube furnace is naturally cooled to room temperature under argon atmosphere to obtain Mo2C nanosheets.

[0038] (2) The laser catalytic DRM reaction of the flow phase uses a quartz reactor as shown in Figure 3 , and the sealing of the reaction chamber is maintained by using a quartz cover and sealing silica gel. First, introduce argon gas from the gas inlet of the container to clean the container for at least 10 min to ensure that other gases in the container are exhausted, preventing impurity gases from affecting the methane dry reforming catalytic reaction;

[0039] (3) 120 mg Mo2C was fixed into a strip type and laid in the laser flow DRM reactor, and a flowable mixed gas (45% CH4 / 45% CO2 / 10% Ar) was introduced, and the corresponding gas hourly space velocity (GHSV) was controlled at 30 L·g cat -1 ·h -1 .

[0040] (4) A 1064 nm fiber laser was used to emit pulsed laser through the quartz cover plate and focus on the Mo2C strip, and the laser catalytic DRM was performed in linear scanning mode with a repetition frequency of 20 kHz, a single pulse energy of 0.8 mJ, a scanning interval of 0.05 mm, and a scanning speed of 1000 mm s -1 .

[0041] (5) Collect the gas after laser irradiation through the gas outlet, and analyze the conversion rate, yield and selectivity by gas chromatography.

[0042] Figure 3 The square reactor chamber shown has a volume of 5×5×0.3cm. 3 The reactor volume and catalyst strip length are adjusted according to the laser linear scanning parameters and gas flow rate.

[0043] like Figure 4 As shown, at 30 L·g cat -1 ·h -1 air velocity and 1000 mm / s -1 At laser scanning speeds of up to 1000 mm / s, the pulsed laser spot travels at an extremely high speed (1000 mm / s). -1 The laser beam extends into a stable line, passing through the reactor chamber perpendicular to the gas flow direction. By plotting the laser path, the laser beam travels at a speed of 20 mm / s on the Mo2C catalyst strip. -1 The laser beam moves along the direction of gas flow. Because the longitudinal velocity of the laser beam far exceeds the cross-sectional velocity of the CH4 / CO2 gas within the reaction chamber (1.33 mm / s),... -1 Therefore, the reactant gas passes through the Mo2C belt multiple times to carry out the laser-catalyzed DRM reaction.

[0044] like Figure 5 As shown, the laser line oscillates rapidly along the gas flow direction within the reactor, stabilizing the methane conversion rate of the DRM reaction at 50.5%. The conventional thermocatalytic DRM reaction was conducted in a fixed-bed mobile phase system (the temperature of the conventional thermocatalytic DRM reaction was 800°C, and the catalyst dosage and gas hourly space velocity were the same as in the laser catalytic system of Example 1: 120 mg Mo₂C, 45% CH₄ / 45% CO₂ / 10% Ar, gas hourly space velocity 30 L·g⁻¹). cat -1 ·h -1 The conversion rate and product molar ratio of the laser-catalyzed mobile phase DRM reaction were compared with those of the thermocatalytic system (methane conversion rate 2.6%, H2 / CO ≈ 0.46). Compared to the thermocatalytic system, laser-catalyzed DRM achieved not only a higher conversion rate (methane conversion rate 50.5%), but also a more uniform product molar ratio (H2 / CO ≈ 0.86). Figure 6 As shown, laser-driven catalysis achieves a balanced product ratio by establishing an equilibrium reaction between CO2 and CH4, thus avoiding the oxidation and deactivation of molybdenum carbide. It remains stable even after 500 min of continuous catalysis. In contrast, the performance of the fixed-bed thermocatalytic system drops to zero after 150 min of continuous catalysis due to the oxidation and deactivation of molybdenum carbide.

[0045] In addition, energy efficiency is also one of the key indicators of different DRM catalytic systems, as shown in Figure 7 Obviously, compared with the recently reported thermal catalytic work (thermal catalytic method, see: Exploiting two-dimensional morphology of molybdenum oxycarbide to enable efficient catalytic dry reforming of methane, Alexey Kurlov et al., nature communications, 11, 4920 (2020)) and photocatalytic work (photocatalytic method, see: Photocatalytic uphill conversion of natural gas beyond the limitation of thermal reaction systems, Shusaku Shoji et al., nature catalysis, 148-153 (2020)), laser catalytic DRM has higher energy efficiency (0.98 mmol kJ -1 ) and more economical power cost efficiency (46.8 mmol kw -1 h -1 ), which has practical application prospects. In addition, from the perspective of production application, the price of an industrial-grade medium-power nanosecond laser is less than 10,000 US dollars, which has high automation degree, is easy to adjust, has stable laser output performance, and has a long service life, generally up to 100,000 hours.

[0046] Example 2

[0047] A 120 mg WC catalyst was used, and the corresponding gas hourly space velocity (GHSV) was controlled at 30 L·g cat -1 ·h -1 . The laser equipment parameters were set as a linear scanning mode with a repetition frequency of 20 kHz, a single pulse energy of 0.8 mJ, a scanning interval of 0.05 mm, and a scanning speed of 1000 mms -1 . Laser-driven DRM was carried out.

[0048] (1) Preparation of WC nanosheet: Put WO3 and other oxides on the upstream of the tube CVD furnace, and pass in the protective gas, and heat the tube CVD furnace from room temperature to 1000 DEG C; pass in 50 sccm H2 / Ar mixed gas for 2 hours, and after the reaction is naturally cooled, collect WO2 nanosheet at the end of the tube CVD furnace system. Then place the collected WO2 nanosheet in the ceramic crucible of the tube furnace, pass in 20 sccm argon as a protective gas, and heat to 1000 DEG C, and the heating rate is 10 DEG C / min; when the temperature reaches 1000 DEG C, close the Ar gas, and pass in 20 sccm CH4 gas, and the time lasts for 30 min, and then the tube furnace is naturally cooled to room temperature under the argon atmosphere to obtain the WC nanosheet.

[0049] Steps (2)-(5) of the embodiment are the same as steps (2)-(5) of embodiment 1.

[0050] In summary, the pulse laser enhanced catalytic dry reforming of methane device of the present application uses low-power laser as a reaction source, and has simple device, small volume and low operation cost. Compared with the traditional thermal catalytic equipment, not only higher conversion rate is achieved, but also more equal product ratio is achieved; higher energy efficiency and more economical power cost efficiency are also achieved, and the problems of complex, large volume, low conversion rate, low selectivity, large energy consumption and unstable transition metal carbide catalysts prone to oxidation and deactivation of the traditional thermal catalytic equipment are solved.

[0051] The above only describes the preferred embodiments of the present application and is not used to limit the present application, and the present application can have various changes and variations for those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method of pulsed laser driven flow phase catalytic dry reforming of methane using a device for pulsed laser driven flow phase catalytic dry reforming of methane, characterized in that, The device for driving the catalysis of methane dry reforming by pulsed laser-driven flow phase includes a laser module, and a reaction chamber is arranged below the laser module; a gas inlet and a gas outlet are arranged at two ends of the reaction chamber, respectively; an upper cover is movably connected to the top of the reaction chamber; a sealing ring is arranged around the upper cover; a catalyst carrier is arranged in the reaction chamber; the laser module is a low-power fiber laser; and the reaction chamber, the upper cover and the catalyst carrier are all made of quartz. The method is as follows: the catalyst is laid on the catalyst carrier, a mixed gas containing methane and carbon dioxide is introduced into the gas inlet of the reaction chamber, the laser is focused on the catalyst to drive the methane dry reforming reaction, and the product gas is collected at the gas outlet to realize the catalysis of methane dry reforming.

2. The method of claim 1, wherein, The catalyst is a transition metal carbide.

3. The method of claim 2, wherein, The catalyst is simple molybdenum carbide or tungsten carbide.

4. The method of claim 1, wherein, The mixed gas is a mixed gas of methane, carbon dioxide and argon, and the volume fraction ratio of methane, carbon dioxide and argon is 45%:45%:10%.

5. The method of claim 1, wherein, The gas hourly space velocity of the mixed gas is 30-120 L.gcat -1 ·h -1 .

6. The method of claim 1, wherein, The laser is emitted by a 1064 nm fiber laser; the repetition frequency of the laser is 16-20 kHz, the average laser power is 16-20 W, the single-pulse energy is 0.8-1.3 mJ, the scanning pitch is 0.01-0.05 mm, and the scanning speed is 1000-2000 mm s −1 .

7. Use of the method according to any one of claims 1-6 in improving the catalytic efficiency of methane dry reforming or avoiding the oxidative deactivation of a transition metal catalyst.

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