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Pure ethane can undergo dehydrogenation reaction under the action of plasma plasma at low temperature and atmospheric pressure
Pure ethane can undergo dehydrogenation reaction under the action of plasma plasma at low temperature and atmospheric pressure: Under atmospheric pressure pulsed corona plasma conditions, the conversion rate of C2H6 and the yield of C2H2 increased with the increase of energy density, the yield of C2H4 increased slightly, but the yield of CH4 did not change much with the increase of plasma energy density. When the plasma energy density was 860 kJ/mol, the conversion of C2H6 was 23.2%, and the sum of the yields of C2H4 and C2H2 was 11.6%. It is generally believed that in a flow plasma reactor, when the flow rate of the reactant gas is constant, the high-energy electron density and its average energy in the system are mainly determined by the plasma energy density. The plasma power increases, the high-energy electron density and its average energy in the system increase, the elastic and inelastic collision probability between high-energy electrons and C2H6 molecules and the transmitted energy increase, and the CH bond and CC bond of C2H6 are more likely to break, and their breakage increases. The concentration of the free radicals formed also increases, and the probability of the free radicals to form products by recombination also increases. Therefore, the conversion rate of C2H6 and the yield of C2H2 tend to increase with the increase of plasma power. The insignificant upward trend of C2H4 yield and CH4 yield with the increase of plasma injection power may be related to the fact that C2H4 and CH4 are the primary reaction products of the reaction, and C2H2 is more stable. Chemical bond Dissociation energy/(kJ/mol) Dissociation energy/(eV/mol) CH3—CH3 367.8 3.8 C2H5—H 409.6 4.2 CH2=CH2 681.3 7.1 C2H3—H 434.7 4.5 CH≡CH 964.9 10.0 C2H—H 501.7 5.2 The main gas phase products of the conversion reaction of pure C2H6 under plasma conditions are: C2H4, C2H2, H2 and CH4, and the solid product is carbon deposition. In order to explore the possible mechanism of the conversion of pure ethane under the action of plasma, the conversion of pure ethylene was investigated under the same plasma conditions. The main products of the reaction were: C2H2, CH4 and a small amount of carbon deposits. According to the above experimental facts, combined with the mechanism of methane conversion reaction and plasma characteristics under the action of plasma, it is speculated that the process of C2H6 conversion reaction under plasma conditions is as follows. (1) The plasma field produces high-energy electrons. The free electrons are accelerated under the action of the electric field E to generate high-energy electrons e*: e + E → e* (3-26) (2) Initiates a free radical reaction. High-energy electrons collide elastically and inelastically with ethane molecules. Depending on the energy of the high (3-26) energy electrons, the collision leads to an increase in the kinetic energy or internal energy of the ethane molecule, which breaks the C-H and C-O bonds of ethane to generate various free radicals: C2H6 + e* → C2H5 + H + e (3-27) C2H6 + e* → 2CH3 + e (3-28) According to the chemical bond dissociation energy data in Table 3-1, the reaction formula (3-28) (C-C bond breaking) is more than the reaction Equation (3-27) (C-H bond cleavage) is easier to carry out. (3) Chain transfer reaction: H + C2H6 → C2H5 + H2 (3-29) CH3 + C2H6 → C2H5 + CH4 (3-30) CH3 + e* → CH2 + H (3-31) CH2 + e* → CH + H (3-32) CH + e* → C + H (3-33) (4) Chain termination reaction: CH3 + H → CH4 (3-34) CH2 + CH2 → C2H4 (3-35) CH3 + CH → C2H4 (3-36) CH + CH → C2H2 (3-37) Under the low temperature and normal pressure, pure ethane can undergo dehydrogenation reaction under the action of plasma to generate acetylene, ethylene, a small amount of methane and carbon deposits, but there are problems such as low conversion rate and the formation of carbon deposits on the reactor wall. According to the ethane dehydrogenation reaction mechanism under chemical catalytic conditions, for the ethane dehydrogenation reaction under plasma conditions, the CH bond of ethane is preferentially broken to form C2H5 radicals, and the C2H5 radicals are further dehydrogenated to ethylene. Key pathways for hydrogen reactions in practical applications. Therefore, the effect of the added gas and plasma on the ethane dehydrogenation reaction is particularly important.
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The effect of atmospheric plasma discharge voltage on the conversion reaction of plasma CH4 to H2
The effect of atmospheric plasma discharge voltage on the conversion reaction of plasma CH4 to H2: With the increase of the discharge voltage, the conversion rate of methane and the yield of C2 hydrocarbons showed an upward trend, and the selectivity of C2 hydrocarbons increased first and then decreased. When the atmospheric plasma discharge voltage was 16 kV, the selectivity of C2 hydrocarbons was large. According to literature reports, the emission intensity changes of CH active species under low temperature atmospheric plasma conditions are directly affected by the working pressure and discharge parameters. The degree of methane cracking in the plasma can be detected by the strength of the CH active species. Because the intensity of the same spectral line is proportional to the particle density of the component, the relative intensity of the spectral line can be inferred from the change of each process parameter. The number of particles varies with the corresponding process parameters. With increasing discharge voltage, the emission intensity of atmospheric plasmaCH active species increases with the increase of discharge voltage. The reason is that under the condition of constant gas flow rate, the energy obtained by the electrons accelerated by the electric field is low when the input voltage is low, and the total collision cross-sectional area in the low-energy state is also low, and the collision probability between CH4 and high-energy electrons is small, so This results in fewer active species being generated. With the increase of the discharge voltage, the ionization rate and electron density increase, and the cross-section of the collision between high-energy electrons and CH4 also increases, which means that the collision probability increases and the generated CH active species increase. It was also noticed that the coke deposits on the reactor walls increased with increasing voltage during the experiment.
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The performance of the modified catalyst by low temperature plasma treatment on Ni/Al2O3 catalyst for CO2 reforming methane
The performance of the modified catalyst by low temperature plasma treatment on Ni/Al2O3 catalyst for CO2 reforming methane: Low-temperature plasma is a system in a thermodynamically non-equilibrium state and has important applications in the field of catalysts. Plasma treatment has the performance of Ni/Al2O3 catalyst for catalyzing CO2 reforming methane. The catalyst surface after plasma treatment and then roasting has high low-temperature catalytic activity and strong anti-carbon deposition ability. Compared with conventional catalysts, the catalyst is prepared by plasma technology, and the dispersion of metal active species of the catalyst is obviously improved, and the catalyst activity is increased. Low-temperature plasma can be effectively used to directly synthesize ultrafine particle catalysts, improve the dispersion of catalyst active components, catalyst surface treatment, precipitation of active components into the matrix, and synergistic effect of catalysts, etc. The catalyst prepared or treated by low temperature plasma has the advantages of large specific surface area and fast reduction rate, thereby improving the catalytic activity of the catalyst. After the low temperature plasma modification, the structure of the solid base catalyst was changed in a friendly manner, the catalytic activity of the catalyst was effectively improved, and the thiol conversion rate was significantly improved. The morphology and particle size of the modified catalysts changed significantly. Compared with the unmodified catalyst, the treated catalyst has obvious particles, but part of it is still amorphous. Plasma-treated catalyst particles are distinct but non-uniform in particle size. The plasma-treated catalyst particles are elliptical and spherical, with uniform size and good dispersion, large porosity and no agglomeration. After the low temperature plasma modification, the average particle size of the catalyst components was reduced, and the particle dispersion of the catalyst was significantly improved. Activated carbon has the advantages of large adsorption capacity, good chemical stability, large specific surface area and large pores, etc. It can be used to adsorb mercaptans in air and liquid phase, and is a suitable catalyst carrier for desulfanization. The use of low-temperature plasma technology can destroy the original crystal structure of the catalyst and generate more holes to improve the activity of the catalyst. The specific surface area of ​​the low-temperature plasma-modified catalyst increases, and the number of micropores increases. Since it is the micropores that determine the adsorption of thiols, and the adsorption capacity also depends on the micropores, the modification of the low-temperature plasma can make the catalyst more active and the conversion rate of thiols higher. Under the action of plasma, a small amount of H2O and CO2 covered by the basic center of the catalyst are further removed, thereby reducing the possibility of reacting with MgO, and the basic center of the catalyst is exposed and enriched on the surface of the catalyst, which is beneficial to improve the reduction performance of the catalyst and adsorption performance, thereby improving catalyst activity.
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What are the consumption of vacuum plasma surface treatment machine metal polymer ceramic surface cleaning
What are the consumption of vacuum plasma surface treatment machine metal polymer ceramic surface cleaning: Vacuum plasma cleaner (plasmacleaner), also known as vacuum plasma surface processor, or vacuum plasma surface processor, is a brand-new high-tech technology that uses plasma to achieve effects that cannot be achieved by conventional cleaning methods. The consumption of vacuum plasma cleaning machine mainly has the following aspects. The loss is mainly in the maintenance of the vacuum pump. The vacuum pump needs to be fed and replaced on a regular basis. If you need to clean the product with reactive gas, the gas is also considered as one of the consumables of the vacuum plasma surface treatment machine. But not all processes use gas, and if the customer chooses to use a dry pump instead of an oil pump, there is no harm. Basically, it is inspected every three months, supplemented according to the condition, and other seals are used for one and a half years, and whether to replace it is determined according to the inspection aging condition. Generally speaking, according to the traditional cleaning method of water solvent, although it looks cheap, it costs a lot of energy and environmental costs. The drying process of this method is very slow and also requires a lot of energy. The vacuum plasma surface treatment machine can eliminate the various risks that may occur when cleaning with wet chemical methods, and no waste liquid is generated during the cleaning process. The use of chemical reagents with traditional cleaning skills will cause great harm to the environment. Plasma assisted cleaning It is a skill that can replace chemical cleaning and an environmentally friendly cleaning skill, which is both safe and environmentally friendly. Moreover, the consumables of the vacuum plasma surface treatment machine are almost insignificant compared with traditional washing methods. At present, plasma cleaning technology has been widely used in the cleaning of metal, polymer and ceramic surfaces, the removal of residual metals on the surface of hybrid circuits and printed circuit boards, the cleaning of biomedical implant materials, and the cleaning of silicon wafers. And the restoration of archaeological relics and other fields.
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The energy range of the plasma is very wide. There is no choice for the excitation or ionization of electrons
The energy range of the plasma is very wide. There is no choice for the excitation or ionization of electrons: Chemical reactions can only occur when the energy of the molecule exceeds the activation energy. In conventional chemistry, energy is transferred by collisions between molecules or between molecules and walls. In plasma, on the one hand, the vibrational energy is increased to a small response energy in a certain order; on the other hand, the collision of electrons and molecules can transfer more energy, which makes neutral molecules become multiple active components, or makes moderately active The components are ionized, and the new components mainly include super-active neutral particles, cations and anions. Traditional chemical reactions cannot produce many new components, but plasma has become a very powerful means of chemical manipulation, which is burdened with catalysis. Generally speaking, reactions with lower temperatures, and perhaps reactions with faster reaction speeds at a certain temperature, are all affected by the plasma. But in a plasma with a wide energy range, the excitation or ionization of electrons is not selective. In a plasma system, many different types of active particles can cause a large number of reactions. During the reaction process, it is almost impossible for the particularly important and significant particles to be manipulated. High-energy particles can destroy the covalent bonds of molecules in the plasma environment. The use of a strong local field to participate in the tail of the strong electron scattering function in high-energy electrons and non-equilibrium plasma may produce new chemical reactions. The plasma environment is conducive to many chemical reactions. Process parameters such as gas type, flow rate, pressure, input power, etc. determine whether a reaction can produce the primary input process parameters. There will also be multiple reactions between the border and the bottom. Ablation rate and accumulation rate are obtained through related surface treatment. When organic vapor is used as the working gas, polymerization and aggregation of plasma will occur. During the etching and accumulation process, the surface of the material reacts with the original or newly generated components in the plasma, that is, the surface conditions, such as pollutants, polymerization inhibitors, barrier layers, gas adsorption, etc., will affect the process dynamics and the accumulation of the film. Characteristics have an impact. The molecules in the plasma are decomposed into highly active components, which then react with organic matter. Hydrogen can be connected to double bonds and can be separated from other molecules. In oxygen-based plasma, there are many components of ionization and dissociation energies. Others can also constitute metastable components like O2(1△g). For the oxygen atom, the important reaction is to add a double bond, and the CH bond becomes a hydroxyl or carboxyl group. Nitrogen can react with saturated or unsaturated molecules. An interesting development of plasma chemistry is the decomposition of original simple molecules into chaotic molecular structures. Typical reactions include: isomerization, elimination of atoms or small groups, dimerization/polymerization, and destruction of original data, etc., for example, the mixture of methane, water, nitrogen, and oxygen through the glow discharge, and finally obtained from The substance of life-amino acids. There is cis-trans isomerization, ring formation, and ring-opening reactions in the plasma. In addition to single-molecule reactions, bimolecular reactions can also occur.
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Study on the experimental nucleation of plasma chemical vapor deposition diamond film
Study on the experimental nucleation of plasma chemical vapor deposition diamond film: The diamond film prepared by this technology is a technology with the ability of plasma chemical vapor accumulation. Because thin-film diamond is of great significance in super-hard maintenance coatings, light windows, heat sink data, microelectronics, etc., when mankind has mastered the preparation technology of diamond thin films, especially the preparation technology of single crystal diamond thin films, they rely on The history of data will quickly move from the age of silicon materials to the age of diamonds. However, the mechanism of plasma chemical vapor deposition of diamond films is still unclear, especially for heteroepitaxial single crystal diamond films. The difficulty lies in the fact that the low-temperature plasma is in a thermally unbalanced state, and the reaction gas used is also polyatomic molecules. , The reaction system is complex and lacks basic data support. However, after more than 20 years of theoretical and experimental research, people have not only developed many plasma chemical vapor deposition techniques for preparing diamond films, but also have a certain understanding of the factors affecting the growth of diamond films through the analysis and summary of experimental data. For the growth of polycrystalline diamond film, nucleation is the key, and there are many factors that affect nucleation, including plasma conditions, matrix data, and temperature. Using plasma chemical vapor deposition of diamond film, we must first understand the nucleation process of diamond, which is generally divided into two stages: carbon-containing groups reach the surface of the substrate, and then dispersed into the interior of the substrate; the second stage is the carbon reaching the surface of the substrate The nucleation and growth of atoms on the surface of the matrix centered on defects, diamond crystals, etc.; therefore, the factors that determine the diamond nucleation include: 1. Matrix data: because the nucleation depends on the saturation of the surface of the matrix and the amount of carbon reaching the core The critical concentration, therefore, the carbon dispersion coefficient of the matrix data has an important influence on nucleation. The larger the dispersion coefficient, the less likely it is to reach the critical concentration required for nucleation. It is very difficult for metal substrates such as iron, nickel, titanium to directly nucleate on this type of data; and for data with a lower carbon dispersion coefficient , Such as tungsten, silicon, etc., diamonds can quickly nucleate. 2. Surface grinding: Generally, the nucleation of diamond can be advanced by grinding the surface with diamond powder. Grinding using SiC, c-BN, Al2O3 and other data can also promote the formation of nucleation. There are two main mechanisms for grinding to promote nucleation formation: one is that after grinding, the diamond particles remain on the surface of the substrate and act as a seed; the other is that grinding can produce many tiny defects on the surface of the substrate. These defects are favorable directions for spontaneous nucleation. The closer the lattice point constant of the grinding data is to diamond, the better the effect of enhancing nucleation. Therefore, the general grinding data are diamond powder prepared by the high temperature and high pressure method. 3. Plasma parameters: In the early stage of diamond nucleation, due to the dispersion of carbon to the substrate, an interface layer was formed on the surface of the substrate. Therefore, the study pointed out that plasma parameters also have an important effect on the interface layer. For example, when a diamond film is deposited on the surface of a silicon substrate At this time, the methane concentration has a direct effect on the formation of the SiC interface layer. 4. Bias enhanced nucleation: In microwave plasma chemical vapor deposition, the substrate is generally negatively biased, that is to say, the potential of the substrate is related to the low potential of the plasma. The effect of the negative bias is to increase the ion concentration on the substrate surface. When the bias voltage is too high, because too many ions sputter the outer layer of the substrate and the precursor nuclei, a nucleation is formed. Therefore, when the bias voltage is enhanced, the size of the bias voltage is more appropriate.
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