滑动弧电极放电等离子体作用甲烷制C2烃的工艺

采用刀片式不锈钢电极放电反应器,以Ar气为稀释气,研究了等离子体作用下甲烷转化制C2烃的工艺条件。考察了CH4流量、高频电源输入电压和电极间距等参数对甲烷转化率、C2烃选择性、收率和反应表观能耗的影响。结果表明,增加CH4流量,表观能耗随之降低;当输入电压和电极间距较小时,甲烷转化率随输入电压和电极间距的增大而增大,但输入电压和电极间距过大时,C2烃收率明显下降,积碳严重。在CH4流量14 mL/min、Ar气流量60 mL/min、高频电源输入电压22 V、电流0.44 A、电极间距4 mm的优化条件下,甲烷最高转化率为43.1%,C2烃收率、选择性和表观能耗分别为40.1%、93.2%和2.41 MJ/mol。C2烃中不饱和烃的体积分数可达95%以上。     

Catalysis Conversion Methane into C2 Hydrocarbons via Electric Field Enhanced Plasma

In this paper the effect of catalyst and carrier in electric field enhanced plasma on methane conversion into C2 hydrocarbons was investigated. Methane coupling reaction was studied in the system of continuous flow reactor on Ni, MoO3, MnO2 catalysts and different ZSM-5 carriers. The per pass conversion of methane can be as high as 22%, the selectivity of ethylene can be as high as 23.8%, of acetylene 60.8%, of ethane 5.4% and of total C2 hydrocarbons was more than 90%. ZSM-5-25 was the better carrier and MnO2 was the better active component. The efficiency of energy was as high as 7.81%.     

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.     

冷等离子体作用下CH_4-CO_2转化制合成气

在常温常压条件下 ,利用电晕放电 ,使 CH4 - CO2 混合气转化生成合成气 .结果表明 ,该过程中 CH4 和 CO2 的转化率与反应体系能量密度、原料气配比和流速等有关 .在 0 .1MPa气压 ,能量密度为 10 50 k J/ mol(反应体系温度低于 50 0 K) ,n( CH4 )∶ n( CO2 ) =1∶ 2条件下 CH4 和 CO2 的转化率分别超过 60 %和 50 % ,超出了热力学平衡转化率的限制 .通过调配原料的配比 ,可以得到不同 n( H2 ) / n( CO)比值的产物 .对该体系的反应机理进行了探讨 .     

甲烷在微波等离子体下直接转化成C2烃

研究了非平衡微波等离子体中影响甲烷脱氢转化的几个因素，如功率、ＣＨ４／Ｈ２比和体系压力。在最佳条件下，甲烷转化率和乙炔的选择性分别达到７７．４６％和７４．０４％。     

常压辉光放电等离子体转化CH4制C2烃的研究

采用新型的旋转电极辉光放电反应器, 在常温常压下对辉光等离子体作用下的甲烷转化制C₂烃进行了研究. 在氢气共存条件下, 考察了反应器电极的结构、材料, 输入电场峰值电压和反应物流率等参数对甲烷转化率和C₂烃单程收率及其选择性的影响规律, 同时比较了不同反应器的能量效率. 结果表明: 在本实验条件下, 金属铜材料好于不锈钢, 螺旋形结构优于三排圆盘结构. CH₄转化率和C₂烃选择性和收率均随输入电场峰值电压的升高而增大, 随反应物流量的增加而减小. 从CH₄转化率、C₂烃的收率和选择性的指标来评价这些反应器, 采用旋转螺旋状铜电极反应器时最好, 当反应物流量为60 mL/min时, 甲烷最高转化率为77.31%, 对应的C₂烃收率和选择性分别为75.66%和97.88%; 当能量密度为800 kJ/mol时, 能效最高为13.5%.     

Conversion Natural Gas to Ci Hydrocarbons via Cold Plasma Reaction

Natural gas is not only an increasing important role in energy and chemicals supplies in 21st century but also the second most important of the greenhouse gases^[1]. For the past 200 years atmospheric methane concentrations have increased from 0.8 to 1.65ppm. This change in methane concentration had been led to an estimated increase in radiative forcing of climate of 0.47 W/m² compared to the increase of 1.56 W/m² due to the change in carbon dioxide concentration over a comparable time period^[2]. With large increases in natural gas reserves proven worldwide, it can be expected that natural gas will play an increasing important role in humanity future. Cold plasma chemical processing is a promising route for synthesis of chemicals that have high activation energies, because electric field can be excite reactant to the plasma and many kinds of reactive particles, electrons, free radicals, ions metastable species and photons are produced in a plasma chemical processing system.     

Distribution of Electrical Field Energy for Conversion of Methane to C2 Hydrocarbons via Dissymmetrical Electric Field Enhanced Plasma

Direct conversion of methane into C2 hydrocarbons through alternating current electric field enhanced plasma was studied under room temperature, atmospheric pressure and low power conditions. The distribution of electrical field intensity and distribution of energy were calculated with software that was developed by us according to the charge simulation method. The results indicated that the energy of tip of electrode was 0.36 J/mm3 and it was higher than the methane dissociation energy (0.0553 J/mm3). The methane located at this area can be activated easily. The higher-energy particles produced by dissociation collided with molecules around them and initiated consecutive reactions between free radicals and molecules. The method was proved to be valided and could be taken as a basis for the electrical field study concerned.     

Methane Decomposition and C2 Hydrocarbon Formation under the Condition of DC Discharge Plasma

The infrared emission spectra of methane, H, CH and C2 hydrocarbons in natural gas were measured. The processes of methane decomposition and formation of C2 hydrocarbons were studied. The experiment shows that methane decomposition can be divided into three periods as the reaction proceeds.In the first period, a large number of free radicals were formed. While in the last period, the formation of C2 hydrocarbons and the decrease of free radicals were observed. The time and conditions of methane decomposition and formation of C2 hydrocarbons are different.     

Platinum- and CuOx-Decorated TiO2 Photocatalyst for Oxidative Coupling of Methane to C2 Hydrocarbons in a Flow Reactor

Oxidative coupling of methane (OCM) is considered one of the most promising catalytic technologies to upgrade methane. However, C₂ products (C₂H₆/C₂H₄) from conventional methane conversion have not been produced commercially owing to competition from overoxidation and carbon accumulation at high temperatures. Herein, we report the codeposition of Pt nanoparticles and CuO_x clusters on TiO₂ (PC-50) and use of the resulting photocatalyst for OCM in a flow reactor operated at room temperature under atmospheric pressure for the first time. The optimized Cu_0.1Pt_0.5/PC-50 sample showed a highest yield of C₂ product of 6.8 μmol h⁻¹ at a space velocity of 2400 h⁻¹, more than twice the sum of the activity of Pt/PC-50 (1.07 μmol h⁻¹) and Cu/PC-50 (1.9 μmol h⁻¹), it might also be the highest among photocatalytic methane conversions reported so far under atmospheric pressure. A high C₂ selectivity of 60 % is also comparable to that attainable by conventional high-temperature (>943 K) thermal catalysis. It is proposed that Pt functions as an electron acceptor to facilitate charge separation, while holes could transfer to CuO_x to avoid deep dehydrogenation and the overoxidation of C₂ products.     

Screening of MgO- and CeO_2-Based Catalysts for Carbon Dioxide Oxidative Coupling of Methane to C_(2+) Hydrocarbons

The catalyst screening tests for carbon dioxide oxidative coupling of methane (CO2-OCM) have been investigated over ternary and binary metal oxide catalysts. The catalysts are prepared by doping MgO- and CeO2-based solids with oxides from alkali (Li2O), alkaline earth (CaO), and transition metal groups (WO3 or MnO). The presence of the peroxide (O2-2) active sites on the Li2O2, revealed by Raman spectroscopy, may be the key factor in the enhanced performance of some of the Li2O/MgO catalysts. The high reducibility of the CeO2 catalyst, an important factor in the CO2-OCM catalyst activity, may     

Zeolite-Enhanced Plasma Methane Conversion Directly to Higher Hydrocarbons Using Dielectric-Barrier Discharges

A zeolite-enhanced plasma methane conversion with pure methane feed using dielectric-barrier discharges (DBDs) at atmospheric pressure has been conducted. This plasma methane conversion over NaX has led to a selective production of light hydrocarbons. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of La2O3／γ—Al2O3 Catalyst on the Activation of CH4 and CO2 to C2 Hydrocarbons under Non—equilibrium Plasma

In the reaction of methane and carbon dioxide to C2 hydrocabons under non-equilibrium plasma, methane conversion was decreased,but selectivity of C2 hydroxarbons was increased when using La2O3/γ-Al2O3 as catalyst. So the yield of C2 hydrocarbons was higher than using plasma alone. The synergism of La2O3/γ-Al2O3 and plasma gave methane conversion of 24.9% and C2 yield of 18.1%. The distribution of C2 hydrocarbons changed when Pd-La2O3/γ-Al2O3 was used as catalyst,the major C2 product was ethylene.     

Oxidative Conversion of Methane/Natural Gas into Higher Hydrocarbons

Oxidative coupling of methane (OCM) to ethylene and ethane is a futuristic process of great practical importance for the effective utilization of methane/natural gas. A brief summary of the work carried out at National Chemical Laboratory (Pune) for the development of catalyst and catalytic process for OCM, particularly addressing the major issues/limitations of the OCM process and efforts made to overcome the problems is presented. This review particularly covers the development of a number of highly active/selective and stable unsupported and supported (using commercial catalyst carriers) catalysts for the OCM process and also the process of improvements/modifications to overcome most of the limitations of OCM.     

冷等离子体喷射流对甲烷二氧化碳重整用Ni/Al2O3催化剂的还原机制

采用理论计算与实验相结合的方法研究了常压冷等离子体喷射流还原Ni/Al2O3催化剂的机理.首先,在假设还原过程是H原子起主导作用的基础上,依据对冷等离子体喷射流的放电特性分析,计算得到H2的理论解离度和催化剂理论还原时间.其次,采用X射线衍射表征及活性评价的手段,考察了等离子体制得催化剂还原过程及实际还原时间.结果表明...     

Methane Conversion to Hydrogen and Higher Hydrocarbons by Double Pulsed Glow Discharge

Pulsed atmospheric glow plasma, sustained by corona discharge, was utilized to convert methane. Analysis by gas chromatography showed that hydrogen and C₂-products are the main constituents of outlet mixture while C₂₊-products with small concentrations were also detected. The chemical energy efficiency turned out to be about 9% for the best result obtained by this type of reactor. It has been shown that more improvement of energy efficiency is possible by increasing the pulse repetition rate.     

Kinetic Modeling of Plasma Methane Conversion Using Gliding Arc

Plasma methane (CH4) conversion in gliding arc discharge was examined. The result data of experiments regarding the performance of gliding arc discharge were presented in this paper. A simulation which is consisted some chemical kinetic mechanisms has been provided to analyze and describe the plasma process. The effect of total gas flow rate and input frequency refers to power consumption have been studied to evaluate the performance of gliding arc plasma system and the reaction mechanism of decomposition.Experiment results indicated that the maximum conversion of CH4 reached 50% at the total gas flow rate of 1 L/min. The plasma reaction was occurred at the atmospheric pressure and the main products were C (solid), hydrogen, and acetylene (C2H2). The plasma reaction of methane conversion was exothermic reaction which increased the product stream temperature around 30～50℃.     

Fe基催化剂上二氧化碳加氢制C2+烃的研究进展

将二氧化碳(CO₂)催化加氢转化为具有高附加值的烃类化合物,既可减缓大气中CO₂浓度的攀升速度,又符合可持续发展战略,对环境和社会均具有重要意义。本文综述了Fe基催化剂上CO₂加氢制C₂+烃的研究进展,着重介绍了反应路径及机理、催化剂研制及反应器设计,展望了CO₂制烃的研究前景。     

等离子体条件Cu/SiO2对甲烷偶联的催化作用

It has been reported that methane coupling by plasma techniques with catalysts, such as direct current corona discharge with a Sr/La2O3 catalyst[1], dielectric-barrier discharge with zeolites[2] and pulsed corona discharge with metal oxide catalysts[3], give C2 hydrocarbons under atmospheric pressure. But acetylene predominates over other C2 hydrocarbons in the products. Our recent work reported that good results can be obtained for methane coupling under a pulsed corona plasma in the presence of hydrogen[4]. The addition of hydrogen improves the conversion of methane and the yield of C2 hydrocarbons. A methane conversion of 57.1% and a yield of C2 hydrocarbons of 43.4% were obtained at lower power, but acetylene was inevitably the main product. With the introduction of a Ni/γ-Al2O3 catalyst prepared by a cold plasma into the plasma reaction, the distribution of C2 hydrocarbons changed, and the content of C2H4 was 66.1%[5].     

A High-Efficiency Reactor for the Pulsed Plasma Conversion of Methane

The authors recently developed a high-frequency pulsed plasma process for methane conversion to acetylene and hydrogen using a co-axial cylindrical (CAC) type of reactor. The energy efficiency represented by methane conversion rate per unit input energy has been improved so that such a pulsed plasma has potential for commercial acetylene production. A pulsed plasma consists of a pulsed corona discharge and a pulsed spark discharge. Most of energy is injected over the duration of the pulsed spark discharge. Methane conversion using this kind of pulsed plasma is a kind of pyrolysis enhanced by the pulsed spark discharge. In this study, a point-to-point (PTP) type of reactor that can produce a discharge channel over the duration of a pulse discharge was used for the pulsed plasma conversion of methane. The energy efficiency and carbon formation on electrodes have been improved. The influences of pulse frequency and pulse voltage on methane conversion rate and product selectivity were investigated. The features of methane conversion using PTP and CAC reactors were discussed.