Methane plasma decomposition

DLC Films Prepared by Methane Plasma Decomposition and Their Presumed Structure... 

G s-Ph se Synthesis. A gas-phase synthesis route to making fine, pure SiC having controllable properties has been described (78,79). Methane was used as a carbon source if required, and the plasma decomposition of three feedstocks, siUcon tetrachloride [10026-04-7] SiCl, dimethyl dichi orosilane, and methyltrichlorosilane [75-79-6] CH Cl Si, into fine SiC powders was investigated. 

The plasma decomposition process is applicable to any hydrocarbon fuel, from methane to heavy hydrocarbons. Similar to oxidative plasma reforming, plasma decomposition processes fall into two major categories thermal and nonthermal plasma systems. 

Similar to the pyrolysis of ethane (10-5), effective plasma catalysis takes place in the direct plasma decomposition of methane with the production of soot and lydrogen ... 

A further paper on the cold-plasma decomposition of methane-water mixtures in the presence of apatite has appeared (see vol. 12, p. 6). Glucose 6-phosphate and ribose 5-phosphate were found among the products. ... 

Cold-plasma decomposition of methane-water mixtures produced simple organic compounds containing formaldehyde on apatite surfaces under u.v. irradiation and at various pH values erythrose, ribose, glucose, glucuronic acid, and cellobiose were obtained. Ammonia was found to favour the synthesis of sugars when used to create alkaline media. (The authors report all these sugars as D-enantiomers but no evidence for optical purity is presented.)... 

A thermal plasma system has been developed for the decomposition of methane. A schematic diagram of the experimental apparatus is shown in Fig. 1. The system consists primarily of D.C. plasma torch, plasma reactor and filter assembly. Plasma was discharged between a tungsten cathode and a copper anode using N2 gas. All the experiments were carried out at atmospheric pressure at 6 kW input electric power and N2 flow rate of 10 to 12 1/min. The feed gas (CH4) flow rates were varied from 3 to 15 1/min depending on the operating conditions, shown in Table. 1. 

Direct thermal decomposition of methane was carried out, using a thermal plasma system which is an environmentally favorable process. For comparison, thermodynamic equilibrium compositions were calculated by software program for the steam reforming and thermal decomposition. In case of thermal decomposition, high purity of the hydrogen and solidified carbon can be achieved without any contaminant. 

It could be concluded that thermal plasma process for methane decomposition is very effective for the production of high purity of the hydrogen as well as synthesis of the carbon black. 

Ogata, A., Mizuno, K., Kushiyama, S. and Yamamoto, T. (1998) Methane Decomposition in a Barium Titanate Packed-Bed Nonthermal Plasma Reactor, Plasma Chem. Plasma Process 18, 363-73. 

Gulyaev and Polak [Kinetics and Catalysis, 6 (352), 1965] have studied the kinetics of the thermal decomposition of methane with a view toward developing a method for the commercial production of acetylene in a plasma jet. The following differential equations represent the time dependence of the concentrations of the major species of interest. 

Schematics of thermal plasma reformer for decomposition of methane to hydrogen and carbon. 1 = Thermal plasma reactor, 2 = graphite electrodes, and 3 = hydrogen-carbon separation unit (cyclone).

In another paper, the authors advocated a plasma-assisted decomposition of methane into hydrogen and carbon.13 It was estimated that 1-1.9 kWh of electrical energy is consumed per normal cubic meter of hydrogen produced. The authors stated that plasma production of hydrogen is free of C02 emissions. However, since most of the electric energy supply in the world comes from fossil fuels, electricity-driven hydrogen production processes such as plasma and electrochemical processes, are C02 producers. 

Single pulse, shock tube decomposition of acetic acid in argon inv olves the same pair of homogeneous, molecular first-order reactions as thermolysis (19). Platinum on grapliite catalyzes the decomposition at 500—800 K at low pressures (20). Ketene, methane, carbon oxides, and a variety of minor products are obtained. Photochemical decomposition yields methane and carbon dioxide and a number of free radicals, wliich have complicated pathways (21). Electron impact and gamma rays appear to generate these same products (22). Electron cyclotron resonance plasma made from acetic acid deposits a diamond [7782-40-3] film on suitable surfaces (23). The film, having a polycrystalline stmcture, is a useful electrical insulator (24) and widespread industrial exploitation of diamond films appears to be on the horizon (25). 

CC-SiC can also be produced directly7 in the desired purity by the plasma gas-pliase reaction of species such as silane [7803-62-5j, SiH4, and methane /74-82-87, CH4 (7). P-SiC powders can be produced by7 the same gas-pliase reaction at lower temperature (1500—1600°C) or by polymer decomposition reactions (8). 

Szymanski96 has investigated the effect of plasma formed in the presence of a ferroelectric sample (BaTiOj ceramic) on the decomposition of methane. Gaseous end products were similar to those obtained in other types of electrical discharges suggesting similar mechanisms. However, atomic spectra of Ba and Ti were observed indicating that the ferroelectric sample had been activated by the plasma. 

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