A method and apparatus for the production of acrylic acid from propylene using plasma in conjunction with catalysis

Abstract

The application discloses a method and device for preparing acrylic acid from propylene by plasma and catalysis, and the method comprises the following steps: feeding mixed reaction gas containing propylene, oxygen and dilution gas into a dielectric barrier discharge reactor filled with Mo-V-Te-Nb-O composite metal oxide catalyst in a discharge area; and directly preparing acrylic acid by one-step oxidation reaction at 100-200 DEG C under the synergistic action of discharge plasma and catalyst. The application also provides a special device for realizing the method, which comprises a gas feeding system, a dielectric barrier discharge reactor, a plasma power supply, a heating system and a product detection system. The application utilizes non-thermal plasma to generate high-energy active particles, activates propylene and oxygen molecules at low temperature, combines the directional conversion capacity of Mo-V-Te-Nb-O catalyst, realizes high-efficiency conversion of propylene and high-selectivity synthesis of acrylic acid, and has the advantages of low reaction temperature, reduced energy consumption, short process flow and excellent industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of acrylic acid synthesis, and more specifically to a method and apparatus for preparing acrylic acid from propylene by plasma-co-catalysis. Background Technology

[0002] Acrylic acid is an extremely important basic organic chemical raw material, widely used in the production of superabsorbent resins, coatings, adhesives, synthetic fibers, and plastic modifiers. With the rapid development of the global new materials industry, the market demand for acrylic acid is increasing year by year. Currently, the industrial production of acrylic acid mainly adopts the "two-step gas-phase oxidation process of propylene." Although this technology is relatively mature, it has the following significant drawbacks: (1) The process is long and the equipment investment is large. It requires two sets of reactors and separation systems in series, resulting in high fixed asset investment. (2) The reaction temperature is high and the energy consumption is huge. Both steps of the reaction need to be carried out at high temperature, which not only consumes a lot of energy, but also the high temperature easily causes propylene to undergo deep oxidation, generating CO and CO2, which reduces the yield of the target product. (3) The catalyst is easy to deactivate. Under high temperature environment, the active components on the catalyst surface are prone to sintering, volatilization or carbon deposition, which leads to a shortened catalyst life and increased operating costs.

[0003] To overcome the shortcomings of the two-step method, researchers have long been committed to developing the "one-step oxidation of propylene to acrylic acid" technology. For example, Chinese patent CN103285888B discloses a catalyst and its preparation method for the one-step oxidation of propylene to acrylic acid. Although the one-step method is achieved, the reaction temperature still needs to be maintained at around 400℃, and it is difficult to simultaneously achieve the single-pass conversion rate of propylene and the selectivity of acrylic acid. The problem of deep oxidation at high temperature is still serious, and there is still a large gap between it and industrial application.

[0004] In recent years, the application of nonequilibrium plasma technology in catalysis has attracted widespread attention. In nonequilibrium plasma, the electron temperature is extremely high (reaching 10⁴~10⁵ K), while the macroscopic temperature of the gas is close to room temperature. High-energy electrons can excite and dissociate reactive gas molecules through inelastic collisions, generating a large number of highly reactive free radicals, excited-state species, and ions (such as O*, propylene radicals, etc.). Combining plasma with solid catalysts (i.e., plasma-assisted catalysis) holds promise for overcoming traditional thermodynamic and kinetic limitations, enabling the directed transformation of difficult-to-activate molecules at extremely low macroscopic temperatures.

[0005] Therefore, designing a suitable plasma reactor and matching it with an efficient catalyst to achieve high propylene conversion and high selectivity of acrylic acid at low temperatures is a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method and apparatus for preparing acrylic acid from propylene using plasma-co-catalyzed processes, thereby solving the problems of high reaction temperature, high energy consumption, and low selectivity in the prior art.

[0007] This invention provides a method for plasma-co-catalyzed preparation of acrylic acid from propylene, wherein a mixed reaction gas containing propylene, oxygen and dilution gas is introduced into a dielectric barrier discharge reactor, and a solid catalyst is packed in the discharge region of the dielectric barrier discharge reactor; the solid catalyst is a Mo-V-Te-Nb-O composite metal oxide. Acrylic acid is directly produced by a one-step oxidation reaction at a reaction temperature of 100℃~200℃ under the synergistic effect of discharge plasma and the solid catalyst. The plasma is used to generate high-energy electrons in the gas phase to activate propylene and oxygen molecules to generate an active intermediate, and the solid catalyst is used to selectively catalytically convert the active intermediate into acrylic acid.

[0008] As an example, the general chemical formula of the solid catalyst is Mo1V. a Te b Nb c O x , where 0.1≤a≤0.4, 0.05≤b≤0.3, 0.05≤c≤0.2, and x is the number of oxygen atoms required to satisfy the valence balance of each element.

[0009] As an example, a=0.3, b=0.2, c=0.12.

[0010] As an example, the reaction temperature is 120℃~150℃.

[0011] As an example, the discharge power of the dielectric barrier discharge reactor is 10W~100W, and the discharge frequency is 5kHz~50kHz.

[0012] As an example, the discharge power of the dielectric barrier discharge reactor is 30W~50W; the discharge frequency is 10kHz~20kHz.

[0013] As an example, the dilution gas is nitrogen or argon.

[0014] As an example, in the mixed reaction gas, the volume concentration of propylene is 5% to 20%, the volume concentration of oxygen is 10% to 30%, and the balance is dilution gas; the volume hourly space velocity of the mixed reaction gas is 500 to 3000 h⁻¹.

[0015] The present invention also provides an apparatus for plasma-co-catalyzed preparation of acrylic acid from propylene, which is used to operate the method for plasma-co-catalyzed preparation of acrylic acid from propylene as described in any of the above contents, comprising: A gas feed system is used to provide a mixture of reactant gases, including propylene, oxygen, and dilution gas. A dielectric barrier discharge reactor includes a vertically arranged quartz dielectric tube, a high-voltage inner electrode coaxially arranged at the center of the quartz dielectric tube, and a grounded outer electrode tightly wrapped around the outer wall of the quartz dielectric tube; a discharge gap is formed between the high-voltage inner electrode and the grounded outer electrode; and a solid catalyst is filled in the discharge gap. A plasma power supply is electrically connected to the high-voltage internal electrode. Heating system is used to control the reaction temperature to a set value; A product detection system is connected to the outlet of the dielectric barrier discharge reactor and is used to analyze the reaction products.

[0016] As an example, the solid catalyst is loaded into the discharge gap as follows: catalyst particles are filled into the gap between the high-voltage inner electrode and the grounded outer electrode, and both ends are fixed with quartz wool.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. The reaction temperature of the method described in this invention is extremely low, and it can react efficiently at a low temperature of 120-150℃, which is more than 200℃ lower than that of traditional thermal catalysis (~400℃), thus saving energy consumption significantly.

[0018] 2. The method described in this invention has both high conversion rate and high selectivity. Under the most preferred conditions (Example 1), the propylene conversion rate can reach 92.5% and the acrylic acid selectivity can reach 88.5%.

[0019] 3. The process flow of the method described in this invention is short, realizing a true one-step direct synthesis of acrylic acid, eliminating the intermediate separation and secondary reaction devices of the two-step method.

[0020] 4. The method of the present invention avoids sintering and carbon deposition of active components during low-temperature operation. The active oxygen in the plasma helps to eliminate carbon deposit precursors, which is beneficial to extending the life of the catalyst.

[0021] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the description, claims, and drawings. Attached Figure Description

[0022] The accompanying drawings are provided to further understand the technical solutions of the present invention and constitute a part of the specification. They are used together with the embodiments of this application to explain the technical solutions of the present invention and do not constitute a limitation on the technical solutions of the present invention.

[0023] Figure 1 This is a schematic diagram of the apparatus for plasma-co-catalyzed preparation of acrylic acid from propylene according to the present invention.

[0024] Figure 2 yes Figure 1 A schematic diagram of the structure of a medium barrier discharge reactor.

[0025] The image is labeled as follows: 1-Gas cylinder, 2-Pressure reducing valve, 3-Mass flow controller, 4-Gas preheating mixer, 5-Heating jacket, 6-Temperature controller, 7-Gas chromatograph, 8-Condenser, 9-Gas inlet, 10-High-pressure internal electrode, 11-Plasma power supply, 12-Grounded external electrode, 13-Solid catalyst layer, 14-Quartz wool, 15-Quartz dielectric tube. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0027] like Figure 1-2 As shown, the plasma-co-catalyzed propylene-to-acrylic acid apparatus provided by the present invention mainly includes: a gas feed system, a dielectric barrier discharge reactor, a plasma power supply, a heating system, and a product detection system.

[0028] (a) Gas feeding system The gas feeding system includes multiple gas cylinders 1 ( Figure 1 Specifically, there are 3 cylinders (used for storing propylene gas, oxygen gas, and dilution gas respectively). Each gas cylinder 1 is connected to the gas preheating mixer 4 through its corresponding pressure reducing valve 2 and mass flow controller 3.

[0029] Specifically, propylene cylinders, oxygen cylinders, and dilution gas (nitrogen or argon) cylinders are each connected to pressure reducing valve 2 via independent pipelines to reduce the pressure of the high-pressure gas to the required pressure. Each pipeline is also equipped with a mass flow controller 3 to precisely control the flow rate of each gas. After being regulated by the mass flow controller 3, the gases converge into the gas preheating mixer 4. The gas preheating mixer 4 is a stainless steel pipeline or mixing tank with a heating device, which preheats the mixed gas to a temperature close to the reaction temperature (e.g., 100~150℃) while ensuring uniform gas mixing. The preheated mixed gas enters the dielectric barrier discharge reactor through inlet 9.

[0030] (II) Dielectric Barrier Discharge Reactor like Figure 2 As shown, the dielectric barrier discharge reactor has a coaxial cylindrical structure, including: a high-purity quartz dielectric tube 15, a high-voltage inner electrode 10 in the center, and a grounded outer electrode 12 on the outer periphery.

[0031] The quartz dielectric tube 15 is a high-purity quartz glass tube with excellent insulation and heat resistance properties. Its inner diameter is 12 mm and its outer diameter is 18 mm. The length of the quartz dielectric tube is 200 mm, matching the discharge power and gas space velocity. The quartz dielectric tube 15 is vertically arranged, with an inlet 9 at the top and an outlet at the bottom. Both the air inlet 9 and the air outlet use polyetheretherketone (PEEK) insulated connectors. It should be noted that the applicable temperature range for PEEK connectors is no higher than 250℃, and they can be used normally under the reaction conditions of 100℃~200℃ described in this invention. When simulating high-temperature thermocatalytic conditions of 350℃ in comparative experiments (with the plasma power supply off), the PEEK connectors must be replaced with high-temperature resistant nickel-based alloy connectors.

[0032] The high-voltage inner electrode 10 is a solid stainless steel rod with a diameter of 8 mm, which is set along the central axis of the quartz dielectric tube 15. Its upper end is connected to the high-voltage output terminal of the plasma power supply 11 through a high-voltage wire.

[0033] The grounding external electrode 12 is a stainless steel mesh (or metal sleeve) tightly wrapped around the middle of the outer wall of the quartz dielectric tube 15, with a length of 100 mm, and is grounded through a wire.

[0034] The radial distance between the high-voltage inner electrode 10 and the grounded outer electrode 12 constitutes the discharge gap, and the discharge gap width is set to 2 mm in the specific test. The wall of the quartz dielectric tube 15 serves as a dielectric barrier layer.

[0035] The solid catalyst layer 13 is loaded in the following manner: The aforementioned prepared Mo-V-Te-Nb-O catalyst particles (40~60 mesh) are filled into the annular discharge gap between the high-voltage inner electrode 10 and the inner wall of the quartz dielectric tube 15. The catalyst filling height is matched with the length of the grounded outer electrode 12. The upper and lower ends of the solid catalyst layer 13 are fixed with quartz wool 14 to prevent the catalyst particles from moving or being blown out.

[0036] In the specific test, the catalyst loading amount was about 6.0 g (corresponding to a volume of about 6 mL), and it was divided into two equal parts and loaded in sections, with a 1 mm high quartz wool interlayer in the middle.

[0037] (III) Plasma Power Supply and Monitoring System The plasma power supply 11 is a CTP-2000K high-frequency AC plasma power supply (Nanjing Suman Electronics Co., Ltd.), with an adjustable output frequency range of 5 kHz to 50 kHz, an output voltage of 0 to 30 kV, and an output power of 10 W to 100 W. The high-voltage output terminal of the power supply is connected to the high-voltage internal electrode 10, and the grounding terminal of the power supply is grounded together with the system.

[0038] To accurately measure the actual discharge power, this device is also equipped with an oscilloscope (such as the Tektronix TBS1102B model) and a high-voltage probe and a current probe. During measurement, the high-voltage probe is connected in parallel between the high-voltage inner electrode 10 and the grounded outer electrode 12, and its output is connected to one channel of the oscilloscope; the current probe is connected in series in the grounding circuit of the grounded outer electrode 12, and its output is connected to another channel of the oscilloscope.

[0039] Set the oscilloscope to XY mode, with the voltage signal as the X-axis and the current signal as the Y-axis, to obtain a Lissajous figure.

[0040] Discharge power P = Area of ​​the graphic × Proportional coefficient of voltage and current probe × Power supply frequency.

[0041] This method allows for real-time monitoring of the actual discharge power of the plasma.

[0042] (iv) Heating system The heating system includes a heating jacket 5 and a temperature controller 6. The heating jacket 5 is wrapped around the outside of the quartz dielectric tube 15 and adopts an open-type insulated tube furnace, which can achieve heating in the range of room temperature to 500°C. A thermocouple (not shown in the figure) is installed inside the heating jacket 5. The temperature sensing end of the thermocouple extends to the vicinity of the solid catalyst layer 13 for real-time monitoring of the reaction temperature. The temperature controller 6 is electrically connected to the heating jacket 5 and the thermocouple, and uses a PID control algorithm to precisely control the temperature of the solid catalyst layer 13 within ±1°C of a set value, which is 100°C to 200°C.

[0043] It should be noted that during plasma discharge, the inelastic collisions between high-energy electrons and gas molecules also generate heat. Therefore, the actual temperature of the solid catalyst layer 13 is determined by both the macroscopic heating provided by the heating jacket 5 and the heat release from the plasma. The temperature controller 6 automatically adjusts the heating power based on the feedback signal from the thermocouple to stabilize the bed temperature at the set value.

[0044] (v) Product detection system The product detection system includes insulated piping, a condenser 8, and a gas chromatograph 7.

[0045] The gaseous products after the reaction are discharged from the outlet at the lower end of the quartz media tube 15 and first enter the condenser 8 through an insulated pipeline (heated to approximately 170°C with a heating cable to prevent acrylic acid condensation). The condenser 8 uses an ice-water bath or circulating cooling water to rapidly cool the reaction tail gas to below room temperature, causing the acrylic acid to condense into a liquid state and be collected. The uncondensed gases (including unreacted propylene, oxygen, nitrogen, and CO, CO2, etc.) continue to enter the gas chromatograph 7 for online quantitative analysis.

[0046] The gas chromatograph 7 uses an Agilent 7890B model, equipped with a thermal conductivity detector (TCD) and a flame ionization detector (FID), and is equipped with a suitable packed column or capillary column (such as a Porapak Q column and a molecular sieve column) for the separation and quantitative analysis of the components in the reaction tail gas.

[0047] The formulas for calculating propylene conversion and acrylic acid selectivity are as follows: Propylene conversion rate (%) = (Amount of propylene consumed in the reaction / Total amount of propylene in the feed) × 100% Acrylic acid selectivity (%) = (Amount of acrylic acid produced / Amount of propylene consumed in the reaction) × 100% The above calculations are based on the carbon balance method, with nitrogen as the internal standard gas.

[0048] The Mo-V-Te-Nb-O catalysts used in the embodiments and comparative examples of this invention were all prepared by hydrothermal synthesis. Unless otherwise specified, all reagents or raw materials involved are commercially available products.

[0049] As an example, the general chemical formula of the Mo-V-Te-Nb-O catalyst is Mo1V. a Te b Nb c O x , where 0.1≤a≤0.4, 0.05≤b≤0.3, 0.05≤c≤0.2, and x is the number of oxygen atoms required to satisfy the valence balance of each element.

[0050] With Mo1V 0.3 Te 0.2 Nb 0.12 O x (For example, x represents the number of oxygen atoms required to achieve oxidation state balance among all elements.) The specific steps are as follows: (1) Weigh 17.66g of ammonium molybdate tetrahydrate ((NH4)6Mo7O 24 3.51 g of ammonium metavanadate (NH4VO3) and 4.59 g of telluric acid (H6TeO6) were added sequentially to 100 mL of deionized water at 80 °C and stirred continuously until completely dissolved to obtain a mixed solution.

[0051] (2) Weigh 6.46 g of niobium oxalate (Nb(HC2O4)5), dissolve it in 40 mL of deionized water, and stir at room temperature until completely dissolved to obtain niobium oxalate solution.

[0052] (3) Slowly add the niobium oxalate solution to the mixed solution using a dropper, stirring continuously during the addition process to form a suspension. After stirring for 30 minutes, transfer the suspension to a 200 mL stainless steel high-pressure reactor with a polytetrafluoroethylene liner (the volume of the reactants should be about 70% of the reactor volume).

[0053] (4) After sealing the reaction vessel, place it in a homogeneous reactor and carry out a hydrothermal reaction at 175°C for 48 hours.

[0054] (5) After the reaction is complete, allow it to cool naturally to room temperature. Centrifuge the precipitate, wash it three times alternately with deionized water and anhydrous ethanol, and then dry it in a vacuum drying oven at 80°C for 12 hours.

[0055] (6) The dried precursor powder was initially crushed and ground. The powder was placed in a quartz boat and then placed in a tube furnace. Under a flowing atmosphere of nitrogen and oxygen (95% N2, 5% O2), the temperature was increased to 550°C at a rate of 2°C / min, and calcined at this temperature for 2 hours. After cooling, the powder was ground, pressed into tablets, and sieved. Particles of 40-60 mesh were selected for use. This was designated as catalyst 1.

[0056] catalyst Mo1V a Te b Nb c O x The preparation methods remain basically the same regardless of the values ​​of a, b, and c; only the amount of raw materials used needs to be adjusted according to the values ​​of a, b, and c. Referring to the preparation process of catalyst 1, other catalysts 2-7 can be obtained simply by making the adjustments shown in Table 1.

[0057] Table 1

[0058] In the preparation of catalysts 2-7 above, except for the amount of raw materials listed in Table 1, the other process conditions are the same as those for catalyst 1.

[0059] To determine the optimal catalyst ratio, based on the above-mentioned apparatus, the propylene oxidation performance of catalysts 1-7 was evaluated under conventional thermocatalytic conditions of 350℃ without turning on the plasma power supply. The results are shown in Table 2.

[0060] Table 2

[0061] The results in Table 2 show that different element ratios have a significant impact on catalytic performance. A low V content (a<0.3) results in insufficient active sites, limiting the reaction; a high V content (a=0.4) leads to excessive oxidizing power, causing propylene to be over-oxidized to CO. xThis leads to selective collapse.

[0062] When the Te content is insufficient (b<0.2), a complete M1 crystal phase cannot be formed, and acrolein is mainly generated or deep oxidation occurs; when the Te content is too high (b=0.3), the active sites are covered, which inhibits side reactions but reduces the conversion rate.

[0063] When the Nb content is insufficient (c<0.12), the catalyst structure is unstable, Mo is easily volatilized and lost, and the active phase partially collapses; although the Nb content is too high (c=0.2), it can play a role in supporting the skeleton, but it has little effect on the main reaction kinetics.

[0064] Compared with catalyst 1, catalyst 7 uses a much larger amount of niobium oxalate, but its performance is not much improved and is similar to that of catalyst 1.

[0065] Taking both conversion rate and selectivity into account, catalyst 1 (Mo1V) 0.3 Te 0.2 Nb 0.12 O x Catalyst 1 exhibits the best overall catalytic performance. Subsequent plasma-assisted catalysis experiments all used catalyst 1.

[0066] In this invention, plasma and MoV 0.3 Te 0.2 Nb 0.12 O x The catalyst exhibited a strong synergistic effect, the microscopic mechanism of which is as follows: (1) Gas-phase activation: High-energy electrons (1~10 eV) in the plasma directly collide with O2 molecules, causing them to dissociate and generate highly reactive oxygen atoms (O*) and ozone (O3). At the same time, high-energy electrons collide with propylene molecules, causing their most vulnerable allyl CH bonds (bond energy about 3.8 eV) to break, generating allyl radicals. This process can occur in the gas phase, completely bypassing the activation energy barrier that requires high temperatures (>350℃) to overcome in traditional thermocatalysis.

[0067] (2) Surface reaction enhancement: The active oxygen species (O*, O3) generated in the gas phase due to the activation of the plasma reactor have a long lifetime and can migrate to the catalyst surface, rapidly replenishing the catalyst lattice oxygen consumed by the reaction and maintaining the high oxidation state of the catalyst surface. At the same time, the electric field generated by plasma discharge can change the electron distribution on the catalyst surface and reduce the reaction energy barrier for the conversion of intermediate products (such as acrolein) to acrylic acid.

[0068] (3) Low-temperature desorption: In a plasma environment, the micro-discharge and ion bombardment on the catalyst surface can promote the rapid desorption of the generated acrylic acid molecules from the acidic sites on the catalyst surface, avoiding the long-term residence of the product on the catalyst surface, thereby greatly inhibiting the deep oxidation side reaction (generating CO).x The occurrence of this process increases the selectivity of acrylic acid.

[0069] Using the above-mentioned apparatus and catalyst 1, the effects of different feed gas compositions and space velocities on reaction performance were investigated under the conditions of no plasma power supply and reaction temperature of 350°C, in order to determine the optimal operating window. The results are shown in Table 3 (experimental conditions with different gas ratios and space velocities) and Table 4 (evaluation results of catalytic performance under different conditions).

[0070] Table 3

[0071] Table 4

[0072] In Table 4, the space-time yield is calculated by dividing the amount of acrylic acid produced by the catalyst bed volume, in kg·h. -1 ·m -3 .

[0073] As can be seen from Tables 3 and 4: When the propylene content is low (condition 1), the required raw materials for the reaction are insufficient, the active sites of the catalyst are not fully utilized, the conversion rate is low, but the selectivity is less affected.

[0074] When the oxygen content is too low (condition 2, 10% O2), the oxidation capacity is insufficient. Although the conversion rate can reach 95.4%, a large amount of propylene undergoes deep cracking, and the selectivity is only 37.3%.

[0075] When the oxygen content is too high (condition 3, 30% O2), the conversion rate is at a high level, but the selectivity decreases significantly. The high oxygen concentration leads to side reactions. Increase airspeed (condition 4, GHSV = 3000 h) -1 Within a short period, the space-time yield rapidly increased due to the threefold increase in feed flow rate, reaching a maximum of 711.64 kg·h⁻¹·m⁻³. However, with the increase in space velocity, the contact time between propylene and the catalyst was drastically compressed, hindering the rate-determining step in the series reaction, namely the oxidation of acrolein to acrylic acid. This resulted in a large amount of intermediates escaping before reacting, leading to a rapid decrease in selectivity. Simultaneously, the exothermic deep oxidation intensified local hot spots, potentially causing catalyst coking. High temperature and high space velocity also accelerated the loss of the active phase, causing the catalyst activity to decrease rapidly within hours. The measured propylene conversion after 2 hours was 43%, the acrylic acid selectivity was 62.3%, and the space-time yield was 310 kg·h⁻¹. -1 ·m -3This also confirms the above theory. Furthermore, excessively high space velocities can disrupt the redox equilibrium of the composite oxide active phase on the catalyst—the rate at which gaseous oxygen replenishes lattice oxygen cannot keep up with the rate at which propylene consumes lattice oxygen, leading to a critical redox imbalance and irreversible over-reduction of the active crystalline phase. Therefore, under normal conditions, the experimental space velocity should not exceed 3000 h⁻¹. -1 .

[0076] In summary, the method of the present invention has a relatively wide operating window. The preferred gas composition is 5%~12% propylene, 20%~30% oxygen, and the balance being dilution gas, with a preferred GHSV of 1000~3000 h. -1 .

[0077] The following examples are used to verify the actual effect of plasma-co-catalysis of the present invention.

[0078] Using the above-mentioned device and catalyst 1, the plasma power supply is turned on to carry out the reaction under low temperature conditions. The specific operation method is as follows, and the process parameters of each embodiment are set respectively.

[0079] (1) Gas feeding: Open the pressure reducing valve 2 of each gas cylinder 1 for propylene, oxygen and nitrogen (or argon), and set the flow rate of each gas through the mass flow controller 3.

[0080] The feed gas composition is: propylene 12 vol%, oxygen 20 vol%, nitrogen (dilution gas) 68 vol%, total flow rate 100 mL / min, reaction pressure is atmospheric pressure, and gas hourly space velocity (GHSV) is approximately 1000 h⁻¹. -1 .

[0081] After the mixed gas is preheated to near the reaction temperature in the gas preheating mixer 4, it enters the dielectric barrier discharge reactor through the gas inlet 9.

[0082] (2) Heating and plasma excitation: Start the heating jacket 5 and the temperature controller 6 to heat the solid catalyst layer 13 to the set value. Turn on the plasma power supply 11 and adjust the output voltage and frequency to make the discharge power reach the set value. At this time, a stable dielectric barrier discharge is generated in the discharge gap between the high-voltage inner electrode 10 and the grounded outer electrode 12, forming a non-thermal plasma.

[0083] (3) Catalytic reaction: The mixed gas collides with high-energy electrons of the plasma in the discharge region, generating a large number of active oxygen species (O*, O3) and propylene radicals. These active species further interact with the surface of the Mo-V-Te-Nb-O catalyst, and under the selective catalysis of the catalyst, propylene is oxidized to acrylic acid in one step. The reaction products flow downward with the carrier gas and are discharged from the reactor through the gas outlet.

[0084] (4) Product collection and analysis: The reaction tail gas enters the condenser 8 through the insulated pipeline, where acrylic acid is condensed and collected. The non-condensable gas enters the gas chromatograph 7 for online analysis, and the propylene conversion rate and acrylic acid selectivity are calculated.

[0085] Example 1 Using the above-mentioned device and Mo1V 0.3 Te 0.2 Nb 0.12 O x The catalyst was used, and the reaction temperature was set to 150℃. The plasma power supply was turned on, the discharge voltage was adjusted to 15 kV, the discharge frequency to 10 kHz, and the discharge power was stabilized at 50 W. After the reaction stabilized for 1 hour, chromatographic sampling and analysis were performed, and the results are shown in Table 5.

[0086] Example 2 Using the above-mentioned device and Mo1V 0.3 Te 0.2 Nb 0.12 O x The catalyst was used, and the reaction temperature was set to 150℃. The plasma power supply was turned on, the discharge voltage was adjusted to 15 kV, the discharge frequency was 10 kHz, and the discharge power was stabilized at 30 W. After the reaction stabilized for 1 hour, chromatographic sampling and analysis were performed, and the results are shown in Table 5.

[0087] Example 3 Using the above-mentioned device and Mo1V 0.3 Te 0.2 Nb 0.12 O x The catalyst was used, the reaction temperature was set to 120℃, the plasma power supply was turned on, the discharge voltage was adjusted to 15 kV, the discharge frequency was 10 kHz, and the discharge power was stabilized at 50 W. After the reaction stabilized for 1 hour, chromatographic sampling and analysis were performed, and the results are shown in Table 5.

[0088] Comparative Example 1 Using the above-mentioned device and Mo1V 0.3 Te 0.2 Nb 0.12 O x The catalyst was used, the reaction temperature was set to 150℃, and the plasma power supply was turned off. After the reaction stabilized for 1 hour, chromatographic sampling and analysis were performed, and the results are shown in Table 5.

[0089] Comparative Example 2 The above-mentioned apparatus is used, but Mo1V is not installed in the reactor. 0.3 Te 0.2 Nb 0.12 O xInstead of a catalyst, an equal volume (6 mL) of quartz sand particles (40-60 mesh) was packed. The reaction temperature was set to 150℃. The plasma power supply was turned on, and the discharge power was set to 50 W. The results are shown in Table 5.

[0090] Comparative Example 3 Using the above-mentioned device and Mo1V 0.3 Te 0.2 Nb 0.12 O x The catalyst was used, but the plasma power supply was not turned on. To simulate conventional thermocatalysis, the temperature needed to be raised to 350°C, at which point the plasma power supply remained off. The heating system required a nickel-based high-temperature alloy connector. The results are shown in Table 5.

[0091] Table 5

[0092] The data analysis in Table 5 shows that: Compared with Example 1 and Comparative Example 1, at a low temperature of 150°C, the propylene conversion rate under conventional catalytic reaction is only 8.4%, with almost no reaction occurring, and the selectivity of acrylic acid is very low, with the product being mostly acrolein.

[0093] Compared with Example 1 and Comparative Example 2, only the plasma power supply was turned on, but the catalyst described in this invention was not placed. Although the conversion rate could be increased to 29.7%, due to the lack of directional guidance from the catalyst, the indiscriminate bombardment of high-energy electrons caused the propylene molecules to completely break down. The selectivity of the target product, acrylic acid, was only 4.4%. At this time, most of the product was a deeply oxidized product.

[0094] However, when the plasma interacts with Mo1V 0.3 Te 0.2 Nb 0.12 O x When the catalyst is combined, the propylene conversion jumps to 92.5%, and the acrylic acid selectivity reaches 88.5%. This fully demonstrates the perfect synergy between plasma gas-phase activation and catalyst surface-directed conversion. The plasma is responsible for breaking the CH bond activation energy, while the catalyst is responsible for guiding the intermediate to acrylic acid in a directional conversion.

[0095] Comparing Example 1 and Comparative Example 3, Comparative Example 3 represents the best performance (350°C) of conventional high-temperature thermocatalysis in existing "one-step" technologies. It can be seen that Example 1 of the present invention, at an extremely low temperature of only 150°C, exhibits higher propylene conversion (92.5% vs 90.3%) and acrylic acid selectivity (88.5% vs 80.2%) than the high-temperature thermocatalysis effect at 350°C. This high selectivity indicates that the accompanying significant reduction in reaction temperature leads to a significant suppression of deep oxidation side reactions. This not only fundamentally solves the high energy consumption problem but also improves the utilization rate of carbon atoms, demonstrating extremely significant technological advancements.

[0096] Comparing Example 1 and Example 2, at the same temperature, when the discharge power was increased from 30W to 50W, Example 1 showed higher conversion rate and selectivity, indicating that the higher power provided more reactive oxygen species and high-energy electrons, thus enhancing the reaction kinetics.

[0097] Comparing Examples 1 and 3, even when the temperature is further reduced to 120°C, with the assistance of 50W plasma, a high conversion rate of 88.2% and an excellent selectivity of 84.5% can still be maintained, demonstrating that the technology of the present invention has a wide operating window and good low-temperature adaptability.

[0098] While the embodiments disclosed in this invention are as described above, the content is merely for the purpose of facilitating understanding of the invention and is not intended to limit the invention. Any person skilled in the art to which this invention pertains may make any modifications and changes to the form and details of the implementation without departing from the spirit and scope disclosed herein; however, the scope of patent protection of this invention shall still be determined by the scope defined in the appended claims.

Claims

1. A method for preparing acrylic acid from propylene using plasma-co-catalyzed synthesis, characterized in that, A mixed reaction gas containing propylene, oxygen, and dilution gas is introduced into a dielectric barrier discharge reactor, wherein a solid catalyst is packed in the discharge region of the dielectric barrier discharge reactor; the solid catalyst is a Mo-V-Te-Nb-O composite metal oxide. Acrylic acid is directly produced by a one-step oxidation reaction at a reaction temperature of 100℃~200℃ under the synergistic effect of discharge plasma and the solid catalyst. The plasma is used to generate high-energy electrons in the gas phase to activate propylene and oxygen molecules to generate an active intermediate, and the solid catalyst is used to selectively catalytically convert the active intermediate into acrylic acid.

2. The method for preparing acrylic acid from propylene by plasma-co-catalysis according to claim 1, characterized in that, The chemical formula of the solid catalyst is Mo1V. a Te b Nb c O x , where 0.1≤a≤0.4, 0.05≤b≤0.3, 0.05≤c≤0.2, and x is the number of oxygen atoms required to satisfy the valence balance of each element.

3. The method for preparing acrylic acid from propylene by plasma-co-catalysis according to claim 2, characterized in that, a=0.3, b=0.2, c=0.

12.

4. The method for preparing acrylic acid from propylene by plasma-co-catalysis according to any one of claims 1-3, characterized in that, The reaction temperature is 120℃~150℃.

5. The method for preparing acrylic acid from propylene by plasma-co-catalysis according to any one of claims 1-3, characterized in that, The discharge power of the dielectric barrier discharge reactor is 10W~100W, and the discharge frequency is 5kHz~50kHz.

6. The method for preparing acrylic acid from propylene by plasma-co-catalysis according to claim 5, characterized in that, The discharge power of the dielectric barrier discharge reactor is 30W~50W; the discharge frequency is 10kHz~20kHz.

7. The method for preparing acrylic acid from propylene by plasma-co-catalysis according to claim 1, characterized in that, The dilution gas is nitrogen or argon.

8. The method for preparing acrylic acid from propylene by plasma-co-catalysis according to claim 1, characterized in that, In the mixed reaction gas, the volume concentration of propylene is 5%~20%, the volume concentration of oxygen is 10%~30%, and the remainder is dilution gas; the volume hourly space velocity of the mixed reaction gas is 500~3000 h⁻¹.

9. An apparatus for plasma-co-catalyzed preparation of acrylic acid from propylene, characterized in that, A method for operating a plasma-co-catalyzed propylene-to-acrylic acid production process as described in any one of claims 1-8, comprising: A gas feed system is used to provide a mixture of reactant gases, including propylene, oxygen, and dilution gas. A dielectric barrier discharge reactor includes a vertically arranged quartz dielectric tube, a high-voltage inner electrode coaxially arranged at the center of the quartz dielectric tube, and a grounded outer electrode tightly wrapped around the outer wall of the quartz dielectric tube; a discharge gap is formed between the high-voltage inner electrode and the grounded outer electrode; and a solid catalyst is filled in the discharge gap. A plasma power supply is electrically connected to the high-voltage internal electrode. The heating system is used to control the reaction temperature to a set value. A product detection system is connected to the outlet of the dielectric barrier discharge reactor and is used to analyze the reaction products.

10. The apparatus for plasma-co-catalyzed preparation of acrylic acid from propylene according to claim 9, characterized in that, The solid catalyst is loaded into the discharge gap by filling the gap between the high-voltage inner electrode and the grounded outer electrode with catalyst particles and fixing both ends with quartz wool.

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