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The effect of CO2 addition on CH4 conversion reaction under the action of plasma

The effect of CO2 addition on CH4 conversion reaction under the action of plasma

The effect of CO2 addition on CH4 conversion reaction under the action of plasma:     In the O2 plasma methane oxidative coupling reaction, the amount of O2 added will directly affect the conversion rate of CH4 and the selectivity of C2 hydrocarbons. is COx(x=1, 2). For the CO2 oxidative CH conversion reaction under the action of plasma plasma, there is also a suitable amount of CO2 addition. The effect of CO2 addition on the conversion rate of CH4, CO2 and product yield can be seen from the results: when the CO2 concentration in the feed gas increases from 15% to 85%, the conversion rate of CH4 increases gradually, and the conversion rate of CO2 changes in a peak shape. When the CO2 concentration is 50%~65%, it reaches as high as about 24%. The research shows that the key step in the oxidation of CH4 by CO2 under the action of plasma plasma is the generation of active species, that is, the high-energy electrons generated by the plasma have elastic or inelastic collisions with CH4 and CO2 molecules, so that CH is successively broken. , generate CHx (x=1～3) free radicals; CO2 breaks C-0 bond to generate reactive oxygen species, which react with CH4 or methyl radicals to generate more CHx (x=1～3) free radicals. The higher the CO2 concentration in the feed gas, the higher the number of reactive oxygen species provided and the higher the CH conversion rate. Therefore, the CH conversion rate is related to two factors, the number of high-energy electrons in the system and the concentration of reactive oxygen species. The CO2 conversion rate is related to collisions between energetic electrons and CO2 molecules, which elastic or inelastic collisions promote: (1) C-O cleavage of CO2 generates CO and O: CO2 + e* → CO2 + O + e (4-1) The depletion of oxygen-reactive species by CH4 favors a rightward shift of the reaction. (2) The ground state CO2 molecules absorb energy and transform into excited state CO2 molecules. Obviously, the CO2 conversion mainly depends on the former. Under the same plasma conditions, the conversion rates of pure CH4 and pure CO2 were 10.9% and 9.4%, respectively. The conversion rates of CH4 and CO2 were higher than the above values ​​when CH4 and CO2 were co-fed, indicating that CH4 and CO2 were co-fed. It is favorable for the co-activation of the two. When the CO2 concentration in the system increased from 15% to 35%, the C2 hydrocarbon yield increased slightly; with the further increase of the CO2 concentration in the system, the C2 hydrocarbon yield gradually decreased. This is because at high CO2 concentration, too many reactive oxygen species in the system interact with CH4 molecules to generate oxidation products on the one hand, and on the other hand, they interact with the generated C2 hydrocarbon products to promote the conversion of C2H6, C2H4, and C2H2 into oxidation products. The CO yield increases with the increase of CO2 concentration, and becomes a constant value when the CO2 concentration is higher than 50%. At the same time, as the CO2 concentration in the system increased from 15% to 85%, the molar ratio of H2 and CO in the product decreased from 3.5 to 0.6. The above research results show that: under certain plasma conditions, in order to obtain a higher C2 hydrocarbon yield and a suitable H2/CO ratio, a lower amount of CO2 addition should be selected. Under the experimental conditions, its value should be 20% to 35%. The distribution of C2 hydrocarbons decreased with the increase of CO2 concentration in the system, and the mole fraction of C2H2 decreased; while the mole fractions of C2H6 and C2H4 showed a rising trend. The possible reasons are: 1. More and more CO2 molecules in the system will absorb more energy, reduce the number of high-energy electrons, and prevent the CH bond of the CH3(CH2) radical from being further broken, resulting in the concentration of CH3, CH2, and CH radicals. distribution changes. The free radical coupling reaction changes the distribution of C2 hydrocarbons in the system; 2. Just as inert gases such as N2 and He play a role in the methane coupling reaction under plasma plasma conditions, the CO2 molecules in the system also play a role as a diluent gas. effect. It is generally believed that methane generates acetylene through the following two paths under plasma conditions: 1. The coupling reaction of CH radicals; 2. The dehydrogenation reaction of C2H6 and C2H4. With the continuous increase of CO2 concentration in the system, a large number of high-energy electrons are consumed, and the collision probability between C2H6, C2H4 and high-energy electrons decreases continuously, further dehydrogenation reaction is hindered, and the generation of C2H4 is further reduced. Therefore, with the increase of CO2 concentration in the system, the mole fractions of C2H6 and C2H4 show a rising trend, while the mole fraction of C2H2 decreases.

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Plasma polymerization analysis of heat-sensitive polymer coating with low temperature plasma treatment technology

Plasma polymerization analysis of heat-sensitive polymer coating with low temperature plasma treatment technology

Plasma polymerization analysis of heat-sensitive polymer coating with low temperature plasma treatment technology: Plasma technology is more and more widely used in production, life and other fields. The surface modification of plasma materials is relatively convenient, clean, free from environmental interference, and has no restrictions on the types of materials. In plasma polymerization, N-isopropylacrylphthalamide monomer is carried, and enters into the reaction area to prepare N-isopropylacrylamide polymer on the surface of glass slide and polystyrene. Low temperature plasma mainly refers to a partially ionized gas generated by high temperature or gas discharge in industrial equipment or laboratories, which interacts with other substances. The plasma is mainly obtained by the gas discharge generated by the AC or DC power supply, and has a certain stability. The low temperature plasma is mostly generated in the form of gas discharge. In terms of the design of the plasma polymerization device, in order to promote the surface of the base material to obtain the N-isopropylacrylamide polymerized film, a solution bottle containing N-isopropylacrylamide was placed between the reaction chamber and the Ar gas cylinder. Monomer plasma polymerization can be achieved in a vacuum environment. At room temperature, N-isopropyl acrylphthalamide is white crystal, soluble in water, and the functional film produced has high temperature sensitivity, has a controlling effect on gel permeation chromatography and liquid chromatography packing, and can be used as temperature thickening agent, wound patch, resistive ink, anti-stain, etc. Poly-N-isopropylacrylophthalamide is a kind of heat-sensitive polymer material with good physiological compatibility and remarkable phase separation properties. It is widely used in substance separation and purification, drug controlled release and so on. Based on the atmospheric pressure environment, N-isopropyl acrylamide can be polymerized through dielectric barrier discharge, and the film is mainly obtained from the surface of the glass slide and polystyrene. During the polymerization process, a solution bottle containing N-isopropylpropene can be placed between the discharge area and the Ar gas bottle. When the gas in the Ar gas bottle is completely released, the solution is invaded through a long conduit (solution bottle), and then exported through a short conduit, and then N-isopropyl acrylic amine monomer is placed in the discharge area. The longer the polymerization time is, the thicker the film becomes, and the contact angle tends to increase, which is mostly due to the use of hydrophilic materials, which leads to an increase in the permeability of water droplets on its surface. In addition, nitrogen elements were introduced into the surface of the glass slide after polymerization treatment, and the components contained N-isopropylacrylamide monomer and polymer. The N-isopropyl acrylamide polymer film was obtained by plasma polymerization, and the thermal sensitivity of the polymer film was measured with the help of a temperature control device and a contact angle meter, which fully proved the spatial existence of poly-N-isopropyl acrylamide. The low-temperature plasma material processing technology has been fully applied in the fields of production and life, and it is believed that it will have a wider application space in other fields.

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The reaction mechanism of O2 oxidation of CH4 under the action of plasma cold plasma to prepare C2 hydrocarbon reaction

The reaction mechanism of O2 oxidation of CH4 under the action of plasma cold plasma to prepare C2 hydrocarbon reaction

The reaction mechanism of O2 oxidation of CH4 under the action of plasma cold plasma to prepare C2 hydrocarbon reaction: The free radical reaction induced by plasma plasma is very similar to the heterogeneous catalytic reaction, but plasma plasma is a very effective free radical initiation method. The current consensus on the reaction mechanism of CO2 oxidation of CH4 to prepare C2 hydrocarbons in one step is that CO2 decomposes under the action of plasma to generate CO and excited and metastable reactive oxygen species. These oxygen species react in the oxidative coupling reaction of methane. is very active, according to the main products of the reaction are C2H6, C2H4, C2H2, CO and H2, the possible reaction mechanism is as follows: (1) generate oxygen species CO2 + e → CO + 0- (4-9) CO2 + e → CO + 0 + e (4-10) (2) generate methyl radical CH4 + 0- → CH3∙ + 0H- (4-11) CH4 + O → CH3∙ + OH (4-12) (3) generate C2 hydrocarbons CH3 + CH3 → C2H6 (4-13) C2H6 + e → C2H5 + H + e (4-14) C2H6 + O → C2H5 +OH (4-15) 2C2H5 → C2H4 + C2H6 (4-16) C2H5 + CH3 → C2H4 + CH4 (4-17) (4) Generate CO CHX + O → HCHO + H (4-18) HCHO + O → OH +CHO (4-19) CHO + O → OH + CO (4-20) As an effective free radical initiation method, plasma cold plasma has been successfully used in CO2 oxidation of CH4 to produce C2 hydrocarbons in one step, and has achieved better experimental results than chemical catalysis. However, the selectivity of C2 hydrocarbon products is low, and the reaction mechanism is still unclear. Therefore, it is necessary to conduct in-depth research on the one-step preparation of C2 hydrocarbons from CO2 oxidation of CH4 under the action of plasma. Using the emission spectroscopy method, many kinds of excited state species in the plasma plasma can be effectively detected in the ultraviolet-visible band, without disturbing the plasma reaction system, and in-situ analysis can be realized. Therefore, in recent years, research reports on the application of emission spectroscopy in-situ diagnostic technology to plasma systems have been increasing, but they mainly focus on the research on the deposition system of CH4-H2 diamond thin film under plasma conditions. The in situ diagnostic technique of emission spectrometry was used to analyze the reactive species of CH4 in the CO2 oxidation CH reaction system under plasma conditions with different CO2 addition amounts.

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Plasma plasma and ten catalysts have different effects on the conversion of methane to carbon dioxide

Plasma plasma and ten catalysts have different effects on the conversion of methane to carbon dioxide

Plasma plasma and ten catalysts have different effects on the conversion of methane to carbon dioxide: Transition metal oxides are an important class of catalysts in industrial catalysts, and the heterogeneous catalytic reactions they participate in are usually carried out by the acid-base action or redox action of the catalyst. The research results of oxidative coupling of methane (OCM) under common catalytic conditions or under the combined action of plasma plasma catalysis show that most transition metal oxide catalysts have certain catalytic activity. Combined with previous studies on plasma plasma catalysis Working experience in methane dehydrogenation reaction under the action of selected transition metals such as Mn, Fe, Co, Ni and W to prepare their supported metal oxide catalysts, and research on CO2 oxidation under the combined action of supported transition metal oxide catalysts and plasma plasma Catalytic activity in the reaction of CH4 to C2 hydrocarbons. The order of methane conversion under the combined action of ten transition metal oxide catalysts such as NiO/Y-Al2O3 and plasma plasma is as follows: NiO/Y-Al2O3>ZnO/Y-Al2O3≈MoO3/Y-Al2O3>Re2Q7/Y-Al2O3>TiO2/7-Al2O3≈Cr2O3/Y-Al2O3≈Mn2O3/Y-Al2O3>Na2WO4/Y-Al2O3≈FeO3/ Y-Al2O3>Co2O2/Y-Al2O3. The order of carbon dioxide conversion rates is: Ni0/Y-Al2O3>TiO2/Y-Al2O3>Co2O3/Y-Al2O3> Na2WO4/Y-Al2O3≈Fe2O3/Y-Al2O3>Re2O7/Y-Al2O3≈Cr2O3/Y-Al2O3>Mn2O3/Y-Al2O3≈MoO3/ Y-Al2O3>ZnO/Y-Al2O3. It can be seen that under the same experimental conditions, the above ten catalysts and plasma plasma have different effects on the conversion of methane and carbon dioxide, and are different from the conversion of methane and carbon dioxide under the action of pure plasma (26.7% and 20.2%, respectively). NiO/Y-AL2O3 combined with plasma gave higher methane and carbon dioxide conversions (32.6% and 34.2%, respectively), while Co2O3/Y-Al2O3 and ZnO/Y-Al2O3 gave lower methane and carbon dioxide conversions rate (22.4% and 17.6%, respectively), the former is 10.2% and 16.6% higher than the latter, respectively. It shows that the catalysts participate in the C-H bond and C-O bond cleavage process of methane and carbon dioxide to different degrees.

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Catalytic activity of supported transition metal oxide catalysts under plasma plasma

Catalytic activity of supported transition metal oxide catalysts under plasma plasma

Catalytic activity of supported transition metal oxide catalysts under plasma plasma: According to the analysis results of the conversion reaction of CO2 oxidation of CH4 under the action of pure plasma plasma, refer to the relevant literature on the reaction of CO2 oxidation of CH4 to C2 hydrocarbons under the action of catalysis. It can be considered that in the plasma-catalyzed co-activated CO2 oxidation of CH4 to C2 hydrocarbons, the methane CH bond is broken mainly through the following pathways: 1. The inelastic collision of CH4 and high-energy electrons; 2. The activation of CH4 by reactive oxygen species; 3. The adsorption of CH4 by the catalyst Molecules, activate the C-H bond, causing the C-H bond to break. The conversion pathway of carbon dioxide is as follows: 1. The inelastic collision between CO2 molecules and high-energy electrons; 2. The active species such as CHx and H in the system activate CO2; 3. The catalyst adsorbs CO2 molecules, activates the C-0 bond, and promotes the cleavage of the CO bond to generate CO. and active O atoms. Obviously, pathway 3 is undoubtedly important for the conversion of CH4 and CO2 under the combined action of plasma catalysis. The activation of catalysts in plasma plasma mainly depends on collision with high-energy electrons. Due to the differences in the properties of catalysts, the catalysts have different activities, and have different adsorption and activation capabilities for methane and carbon dioxide. It can be seen from the above test results that NiO/Y-Al2O3 has strong adsorption, activation methane and carbon dioxide ability under the same plasma, so the conversion rate of CH and CO2 is high. On the contrary, Co2O3/Y-Al2O3 has weak ability to adsorb and activate methane, and the conversion rate of CH4 is low; Zn0/Y-Al2O has weak ability to adsorb and activate carbon dioxide, resulting in low CO2 conversion rate.  Under the action of plasma, according to the yield of C2 hydrocarbons, the catalytic activity sequence of supported transition metal oxides is: Na2WO4/Y-Al2O3>Cr2O3/Y-Al2O3≈Fe2O3/Y-Al2O3>TiO2/Y-Al2O3≈NiO/ Y-Al2O3≈Mn2O3/Y-Al2O3>Co2O3/Y-Al2O3>ZnO/Y-Al2O3≈MoO3/Y-Al2O3≈Re2O7/Y-Al2O3 According to the level of CO yield, the order of catalytic activity of supported transition metal oxides for: NiO/Y-Al2O3> TiO2/Y-Al2O3>Re2O3/Y-Al2O3≈Fe2O3/Y-Al2O3≈Co2O3/Y-Al2O3>MoO33/Y-Al2O3≈ZnO/Y-Al2O3≈Mn2O3/Y-Al2O3>Na2WO4/ Y-Al2O3≈Cr2O3/Y-A12O3. The experimental results show that the co-action of plasma plasma and supported transition metal oxide catalysts has different effects on the formation of C2 and CO. Na2WO4/Y-Al2O3 has higher C2 hydrocarbon yield (17.8%); NiO/Y-Al2O3 has higher CO yield (53.4%). Re2O7/Y-Al2O3 has a lower yield of C2 hydrocarbons (8.8%), and Cr2O3/Y-Al2O3 has a lower yield of CO (34.5%). Under the action of plasma catalysis, the reaction product is mainly formed by the recombination of active species on the surface of the third body, that is, C2 hydrocarbons are formed by the recombination of CHx on the surface of the third body, and CO is directly formed by the decomposition of carbon dioxide or C and O ( Oxygen-containing) actives are formed by recombining two pathways on the surface of the third body. Obviously, the adsorption capacity of the catalyst to various free radicals in the reaction system and whether the adsorption site is suitable will affect the yield of the reaction products C2 hydrocarbons and CO. For the Na2WO4/Y-Al2O3 catalyst, the yield of C2 hydrocarbons is much higher than other catalysts. The possible reason is that the surface of the catalyst is easy to attach CHx radicals, and the adsorption site is appropriate, which leads to the increased probability of CHx radicals coupling to generate C2 hydrocarbons. For NiO/Y-Al2O3, in addition to the higher CO2 conversion rate and the combination of C and O in the system, the CO2 yield is higher, and the active O2 adsorbed on the catalyst when the CHx radical is adsorbed on its surface. Atomic oxidation to generate CO is also a more important reason. The effect of NiO loading on the yields of 2 hydrocarbons and CO was investigated under the same experimental conditions. With the increase of NiO loading, the C2 hydrocarbon yield decreased and the CO yield increased. When the NiO loading was 40%, the reaction system had No C2 hydrocarbons can be detected, which confirms from the side that there is a CHx radical oxidation process on the surface of the catalyst in the reaction of CO2 oxidation of CH4 to C2 hydrocarbons when plasma plasma and NiO/Y-Al2O3 catalyst work together. Therefore, for the target product of the study, Na2WO4/Y-Al2O3 should be selected to generate C2 hydrocarbons, while NiO/Y-Al2O3 is more favorable for the formation of CO. The purpose of adding a catalyst for CO2 oxidation and CH4 conversion under the action of plasma is to improve the yield of C2 hydrocarbons with higher economic value. Therefore, improving the C2 hydrocarbon selectivity and C2 hydrocarbo

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Research on the modification of vanadium catalyst carrier diatomite performance index modified by plasma technology

Research on the modification of vanadium catalyst carrier diatomite performance index modified by plasma technology

Research on the modification of vanadium catalyst carrier diatomite performance index modified by plasma technology: The vanadium catalyst used in the production of sulfuric acid is a catalyst with vanadium oxide as active component, alkali metal oxide as co-catalyst and diatomaceous earth as carrier. The diatom shell in diatomite has a special microporous structure and a shell wall composed of amorphous silica. These small pores distributed on the shell wall can provide good conditions for uniform adsorption or coating of catalyst active components In addition, diatomite itself has good permeability, so that the fluid can pass through at a larger flow rate, so diatomite becomes an important carrier for vanadium catalysts. The reserves of diatomite in my country are very rich, but there are not many high-quality diatomite that can be used as vanadium catalyst carrier. In recent years, due to the protective mining measures adopted by the government, fewer and fewer high-quality diatomite mines are allowed to be mined. Many catalyst factories have begun to use imported diatomite to improve the quality of vanadium catalysts, but imported diatomite has gradually formed a monopoly in China. , the price is expensive, and the domestic catalyst factory is unbearable. How to improve the quality of domestic diatomite and make it meet or exceed the quality of imported diatomite has always been the direction of domestic catalyst factories. The pore size distribution of the carrier has an important relationship with the performance of the vanadium catalyst. In general, the important characteristics of good quality vanadium catalysts are large pore volume and reasonable pore size distribution. It is required that the number of pores with a pore size between 100 and 1000 nm accounts for more than 50% to ensure that there are enough internal diffusion channels for gas molecules in the catalytic reaction. Under the reaction conditions, the pores below 100 nm basically do not exist, and mainly become the storage unit of active substances, while the macropores with a pore size above 100 nm are not only unobstructed, but also provide an active surface. Domestic diatomite has a relatively large proportion of micropores with a pore diameter of less than 1 nm, and a relatively small proportion of mesopores with a pore diameter of 1 to 1000 nm and large pores above 1000 nm, resulting in a small pore volume and high bulk density of the vanadium catalyst, which is not conducive to the reaction. Diffusion of gases. Changing the pore size distribution of diatomite, increasing the pore volume and reducing the bulk density are important ways to improve diatomite in China. The diatomite is modified by plasma technology, the diatomite is treated by the active substance of the plasma, and the surface and internal impurities of the pore channel are cleaned by physical and chemical effects, so as to increase the pore size of the diatomite. Plasma bombardment of diatomite can make diatomite generate local high temperature, and the organic impurities in the pores are removed by high temperature pyrolysis, thus leaving more effective space, which is manifested as the increase of BJH adsorption pore volume. This also shows that plasma technology can be used as an effective method for diatomite modification. The increased pore volume of diatomite can make the reaction gas pass more smoothly and the catalytic efficiency is higher. Modified by plasma technology, a considerable number of micropores in diatomite may be converted into mesopores. The treatment has both physical effect (non-elastic collision effect) and chemical effect (active substance reacts with functional groups on the surface of diatomite), so as to achieve the effect of cleaning the surface of the pores and the internal organic impurities and some inorganic impurities.

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