Conversion of natural gas to C2 hydrocarbons via cold plasma technology

The plasma technology served as a tool in unconventional catalysis has been used in natural gas conversion, because the traditional catalytic methane oxidative coupling reaction must be performed at high temperature on account of the stability of methane molecule. The focus of this research is to develop a process of converting methane to C2 hydrocarbons with non-equilibrium plasma technology at room temperature and atmospheric pressure. It was found that methane conversion increased and the selectivity of C2 hydrocarbons decreased with the voltage. The optimum input voltage range was 40-80 V corresponding to high yield of C2 hydrocarbons. Methane conversion decreased and the selectivity of C2 hydrocarbons increased with the inlet flow rate of methane. The proper methane flow rate was 20-40 ml/min (corresponding residence time 10-20 s). The experimental results show that methane conversion was 47% and the selectivity of C2 hydrocarbons was 40% under the proper condition using atmospheric DBD cold plasma technology. It was found that the breakdown voltage of methane VB was determined by the type of electrode and the discharge gap width in this glow discharge reactor. The breakdown voltage of methane VB,min derived from the Paschen law equation was established.     

Conversion of natural gas to C_2 hydrocarbons through dielectric-barrier discharge plasma catalysis

The experiments are carried out in the system of continuous flow reactors with dielectric-barrier discharge (DBD) for studies on the conversion of natural gas to C2 hydrocarbons through plasma catalysis under the atmosphere pressure and room temperature. The influence of discharge frequency, structure of electrode, discharge voltage, number of electrode, ratio of H2/CH4, flow rate and catalyst on conversion of methane and selectivity of C2 hydrocarbons are investigated. At the same time, the reaction process is investigated. Higher conversion of methane and selectivity of C2 hydrocarbons are achieved and deposited carbons are eliminated by proper choice of parameters. The appropriate operation parameters in dielectric-barrier discharge plasma field are that the supply voltage is 20-40 kV (8.4-40 W), the frequency of power supply is 20 kHz, the structure of (b) electrode is suitable, and the flow of methane is 20-60 ml · min-1. The conversion of methane can reach 45%, the selectivity of C2 hydrocarbons i     

Conversion of natural gas to C2 hydrocarbons through dielectric-barrier discharge plasma catalysis

The experiments are carried out in the system of continuous flow reactors with dielectric-barrier discharge (DBD) for studies on the conversion of natural gas to C₂ hydrocarbons through plasma catalysis under the atmosphere pressure and room temperature. The influence of discharge frequency, structure of electrode, discharge voltage, number of electrode, ratio of H₂/CH₄, flow rate and catalyst on conversion of methane and selectivity of C₂ hydrocarbons are investigated. At the same time, the reaction process is investigated. Higher conversion of methane and selectivity of C₂ hydrocarbons are achieved and deposited carbons are eliminated by proper choice of parameters. The appropriate operation parameters in dielectric-barrier discharge plasma field are that the supply voltage is 20–40 kV (8.4–40 W), the frequency of power supply is 20 kHz, the structure of (b) electrode is suitable, and the flow of methane is 20–60 mL · min⁻¹. The conversion of methane can reach 45%, the selectivity of C₂ hydrocarbons is 76%, and the total selectivity of C₂ hydrocarbons and C₃ hydrocarbons is nearly 100%. The conversion of methane increases with the increase of voltage and decreases with the flow of methane increase; the selectivity of C₂ hydrocarbons decreases with the increase of voltage and increases with the flow of methane increase. The selectivity of C₂ hydrocarbons is improved with catalyst for conversion of natural gas to C₂ hydrocarbons in plasma field. Methane molecule collision with radicals is mainly responsible for product formation.     

正压、低温脉冲微波等离子体裂解天然气直接转化 制C2烃的研究

利用脉冲微波强化、扩展丝光等离子体反应装置,在常压和正压条件下,对低温脉冲微波等离子体裂解甲烷和氢气混合气制C2烃的反应进行了研究。考察了压力、微波功率、脉冲通/断时间以及氢气/甲烷比例、流量等参数对反应的影响。结果表明,在脉冲微波的作用下,常规高压放电形成的在空间呈非连续分布的丝状等离子体被强化和扩展成为连续分布的伞状等离子体,等离子体利用率和活性均得以大幅度提高;利用这种低温等离子体可以获得高的甲烷转化率,而且产物纯净,只有乙烯和乙炔;通过改变压力,还可能调节产物中C2H2/C2H4的物质的量比值,当气体总流量为300mL/min、物质的量比n(H2)/n(CH4)=2:1、压力为0.13MPa、微波峰值功率为120W、脉冲通/断比=400/400ms时,甲烷转化率可达59.2%,C2烃单程收率可达52%,其中乙炔单程收率达42.7%。     

The conversion of natural gas to higher hydrocarbons using a microwave plasma and catalysts

Methane, the major constituent of natural gas, had been converted to higher hydrocarbons by a microwave plasma. The yield of C2+ products increased from 29.2% to 42.2% with increasing the plasma power and decreasing the flow rate of methane. When the catalysts were used in the plasma reactor, the selectivities of ethylene and acetylene increased while the yield of C2+ remained constant. Among the various catalysts used, the Fe catalyst showed the highest ethylene selectivity of 30%. When we introduced the actual natural gas, more C2+ products were obtained (46%). This is due to the ethane and propane in the natural gas. When an electric field inductance for evolving the high plasma was applied, a high yield in C2+ products of 63.7% was obtained for the Pd-Ni bimetal catalyst.     

Direct conversion of natural gas to higher hydrocarbons:A review

Direct conversion of methane to higher hydrocarbons is an effective process to solve the problem of natural gas utilization. Although remarkable progress has been achieved on the dehydro-aromatization of methane (DAM), low conversion caused by severe thermodynamic limitations,coke formation, and catalysis deactivation remain important drawbacks to the direct conversion process. Molybdenum catalysts supported on HZSM-5 type zeolite support are among the most promising catalysts. This review focuses on the aspects of direct methane conversion, in terms of catalysts containing metal and support, reaction conditions, and conversion in different types of reactors. The reaction mechanism for this catalytic process is also discussed.     

Direct conversion of natural gas to higher hydrocarbons: A review

Direct conversion of methane to higher hydrocarbons is an effective process to solve the problem of natural gas utilization. Although remarkable progress has been achieved on the dehydro-aromatization of methane (DAM), low conversion caused by severe thermodynamic limitations, coke formation, and catalysis deactivation remain important drawbacks to the direct conversion process. Molybdenum catalysts supported on HZSM-5 type zeolite support are among the most promising catalysts. This review focuses on the aspects of direct methane conversion, in terms of catalysts containing metal and support, reaction conditions, and conversion in different types of reactors. The reaction mechanism for this catalytic process is also discussed.     

Conversion of CH4, steam and O2 to syngas and hydrocarbons via dielectric barrier discharge

The conversion of CH4 with oxygen and steam in a dielectric barrier discharge (DBD) was studied in the paper to discuss the effects of different factors,such as the content of feed-in gas,the applied voltage and frequency.The results showed that a lower ratio of CH4 to O2 always resulted in a higher conversion of CH4.When it was 2,the conversion reached 32.43% without steam introduced into the system.The main effect of steam was increasing the selectivity to CO.The reaction was accelerated and the selectivities to CO and hydrocarbons were enhanced by increasing the applied voltage.It was also observed that a higher frequency led to a lower current and then restrained the reaction.     

Entrainment of cold gas into thermal plasma jets

There is increasing evidence that the entrainment of cold gas surrounding a turbulent plasma jet is more of an engulfment type process rather than simple diffusion. A variety of diagnostic techniques have been employed to determine the development of turbulence in a plasma jet and to measure concentration and temperatures of the cold gas entrained into atmospheric-pressure argon plasma jets in ambient argon or air. The results indicate that the transition to turbulence causes a rapid drop of the axial jet velocity due to entrainment of the cold gas surrounding the plasma jet. Dissipation of the cold engulfed gas bubbles by molecular diffusion is relatively slow if molecular gases (for example air) are entrained, as indicated by conditional sampling and CARS measurements. Temperature measurements using emission spectroscopy and enthalpy probes show strong discrepancies in the jet fringes.     

Conversion of methanol to hydrocarbons over metal-zeolite catalysts

Ni²⁺, Cr³⁺ and Pb²⁺ exchanged CaY zeolites including mixed forms like CrNiCaY and PbNiCaY were used to study methanol conversion. The selectivity of the reaction to olefin and paraffin formation depends on the type of samples, the activation of the catalyst and the reaction conditions.

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CaY , Ni²⁺, Cr³⁺ Pb²⁺- , CrNiCaY PbNiCaY, . - , .

     

Headspace gas chromatographic determination of aromatic hydrocarbons in natural and waste water

Summary The possibilities of using headspace analysis of aromatic hydrocarbon traces in aqueous solutions with changing values of the partition coefficients are discussed. A variant of headspace analysis of the simplest aromatic hydrocarbon in natural and waste water is described. It involves two-step gaseous extraction of a sample in vessels of varying volume before and after the equilibrium phase is replaced with a pure gas (air or nitrogen). This method permits to analyse 5–50 ml water samples with benzene and toluene contents varying from the ppb to the ppm range within an error not exceeding 155. The analysis time is about 1.5 h. The presence of non-volatile organic or mineral substances does not influence the determination. This method is unsuitable to heterogeneous systems (aqueous oil emulsions): before carrying out the analysis for the hydrocarbon content these systems have to be homogenized first.Presented at the Scientific Seminar on Headspace Gas Chromatography organized in cooperation with the Perkin-Elmer Corporation (Norwalk, CO, USA) in Leningrad, December 4–5, 1979.     

Conversion of Methane to C2 Hydrocarbons via Cold Plasma Reaction

Direct conversion of methane to C2 hydrocarbons via cold plasma reaction with catalysts has been studied at room temperature and atmospheric pressure. Methane can be converted into C2 hydrocarbons in different selectivity depending on the form of the reactor, power of plasma, flow rate of methane, ratio of N2/CH4 and nature of the catalysts. The selectivity to C2 hydrocarbons can reach as high as 98.64%, and the conversion of methane as high as 60% and the yield of C2 hydrocarbons as high as 50% are obtained. Coking can be minimized under the conditions of: proper selection of the catalysts, appropriate high flow rate of inlet methane and suitable ratio of N2 to CH4. The catalyst surface provides active sites for radical recombination.     

Conversion of 2-alkylcinnamaldehydes to 2-alkylindanones via a catalytic intramolecular Friedel-Crafts reaction

The preparation of indanones by the intramolecular acylation of 3-arylpropanoic acids or halides requires the use of noncatalytic acid promoters. In the presence of 5-10 mol % FeCl(3), in situ generated dimethyl acetals of (E)-2-alkylcinnamaldehydes cyclize to 1-methoxy-2-alkyl-1H-indenes in good-to-high yields. The 1-methoxyindenes were converted in high yield into 2-alkylindanones by treatment with triethylamine, to effect isomerization to the isomeric enol ethers, followed by acid-catalyzed hydrolysis. Thus, a catalytic, intramolecular Friedel-Crafts reaction leading to 2-alkylindanones from 2-alkylcinnamaldehydes was developed.     

Diffusion phenomena of a cold gas in a thermal plasma stream

The present study involves both experimental investigation and mathematical modeling of the diffusion process of a cold gas injected into a main plasma stream. The cold gas (nitrogen or helium) was injected axially through a water cooled tube located along the centerline of an induction plasma torch. The 2-D distribution of the temperature, velocity and concentration profiles in the plasma flow were measured using enthalpy probe techniques. The results are compared with the predictions of a 2-D, LTE, turbulent mathematical model. The effects of the nature (composition) of the injected gas and its mass flow rate are investigated. The enthalpy probe measurements and the predictions of the model are in good agreement. The effective (turbulent and molecular) transport properties are estimated from a comparison of the measured and calculated profiles of the temperature, velocity and concentration fields. This study sheds light on the basic diffusion mechanisms involved in a widely used configuration of induction plasma reactors, i.e. in which the material to be treated is injected axially into the plasma, through a central water cooled tube.     

Chromatographic determination of total hydrocarbons in ethanolamine employed in sweetening process of natural gas

Summary A rapid and easy gas chromatographic method is proposed for the determination of condensate content in monoethanolamine employed in the sweetening process of natural gas in the petroleum industry. This method covers a wide range of heavy hydrocarbons (condensate) content by using a short conventational column. A comparative study has been carried out and the advantages of the gas chromatographic technique have been demonstrated.     

Preparation of novel Ni-Ir/r-Al2O3 catalyst via high-frequency cold plasma direct reduction process

The novel Ni-Ir/γ-Al2O3 catalyst was prepared by high-frequency cold plasma direct reduction method (NIA-P) under ambient conditions without thermal treatment, and the conventional sample was prepared by impregnation, thermal calcination, and then by H2 reduction method (NIA-CR). The effects of reduction methods on catalysts for ammonia decomposition were studied, and the catalysts were characterized by XRD, N2 adsorption, XPS, and H2-TPD. It was found that the plasma-reduced NIA-P sample showed a better catalytic performance, over which ammonia conversion was 68.9%, at T = 450 ℃, P = 1 atm, and GHSV = 30, 000 h−1. It was 31.7% higher than that of the conventional NIA-CR sample. XRD results showed that the crystallite size decreased for the sample with plasma reduction, and the dispersion of active components was improved. There were more active components on the surface of the NIA-P sample from the XPS results. This effect resulted in the higher activity for decomposition of ammonia. Meanwhile, the plasma process significantly decreased the time of preparing catalyst.     

Control of the metal-support interface of NiO-loaded photocatalysts via cold plasma treatment

NiO-loaded semiconductors have been extensively used as the photocatalysts for water splitting. The metal-support interface is an important factor affecting the efficiency. In the present work, the pretreatment methods were studied to produce a more desirable metal-support interface using Ta2O5 and ZrO2 as the support. The traditional method includes a thermal decomposition, reduction at 773 K, and oxidation at 473 K (R773-O473). The thermal decomposition of Ni(NO3)2 makes the Ni atoms migrate into the bulk of the supports, resulting in a diffused interfacial region. Alternatively, a cold plasma treatment was used to replace the thermal decomposition. Metal salts are quickly decomposed by glow discharge plasma treatment at room temperature, avoiding the thermal diffusion of Ni atoms. With the sequent R773-O473 treatment, a clean metal-support interface is produced. Moreover, the metal particles have optimal shapes with a larger surface. In photocatalysis, the clean metal-support interface is more favorable for the charge separation and transfer, and the increased metal surface provides more active sites. NiO/Ta2O5 and NiO/ZrO2 prepared with the plasma treatment exhibit higher activity for photocatalytic hydrogen generation from pure water and methanol solution, respectively. This work shows the potential of cold plasma treatment in the preparation of metal-loaded catalysts and nanostructured materials.     

Mn-CaO催化剂上甲烷-二氧化碳共活化制C_2烃研究II.催化剂表征及反应机理研究

在Mn-CaO催化剂开展了一系列的表征,包括XRD,XPS,CO2-TPD.结合催化剂评价、表征结果,对催化反应机理进行了推测,指出Mn组分与催化剂的活性相关联而Ca组分的主要作用是提供吸附型的CO2(a)*,反应过程中形成的Mn3+/Mn2+离子对在CO2和CH4的活化过程中扮演了重要角色.