Acetylene Production from Methane

The best acetylene yields obtained were 0.033 g/kJ. From the heat of the process 2 CH4 — C2H2 + 3 H2 — 360 kJ per one mole of acetylene, the thermodynamic yield is 

072 g/kJ. Consequently, the maximum yields represent 46% of the thermodynamic yield. The acetylene yield in the carbide process (obtained from calcium carbide) is 0.029 to 0.025 g/kJ, i.e. 40—35% of the thermodynamic yield. 

The mechanism of methane conversion to acetylene in electric discharge has not yet been sufficiently studied. The conversion of methane in arc discharge is suggested to occur in two steps. 

acetylene decomposition occurs in the discharge region in parallel to its formation. It has also been suggested that the increase in acetylene yield (per methane decomposed) observed upon dilution of methane with hydrogen is connected with a shift of the equilibrium C2H2 2C + H2 to the acetylene side, i.e. with eventual retardation of the second reaction step. 

Developing the concepts of a radical mechanism of the methane conversion in electric discharge [366], the dominant role in this reaction has been attributed to atomic hydrogen, uggesting that at low current densities, acetylene is formed mainly as a result of the dehydrogenation action of atomic hydrogen which is converted to methane CHg radicals are 

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Figure 9-6. Energy cost of acetylene production from methane in plasma , Babaritsky s microwave plasma experiments, p = 40 Torr , Babaritsky s microwave plasma experiments, p = 80 Torr o, a, experiments with thermal arc discharges. Curves represent calculations (1) quasi-equilibrium plasma modeling (2-5) non-equilibrium kinetic modeling at different values of the non-equilibrium factor y = (T, — To)/To = 0.1,0.2, 0.3, 0.5.

To determine the upper limits of energy efficiency of this quasi-eqttilibritun process, kinetic specifics of the Kassel mechanism should be taken into accormt. The total endothermic process (9-1) of acetylene production from methane (CH4 I/2C2H2 -I- 3/2H2) under qttasi-eqttilibriiun conditions corresponds to the first kinetic order and can be characterized by the reaction rate coefficient... 

Chains play an important part in all the mechanisms proposed for the acetylene production from methane in electric discharge. The composition of electrocracking products of various organic vapour in silent discharge resembles that of thermal cracking products (pyrolysis) of the same compounds. As the nature of active centers in these reactions is different, resembling product compositions would be expected only if the main amounts of these are generated by secondary processes this is only possible with chain mechanisms. 

Co-Production of Hydrogen Cyanide (HCN) and Acetylene (C2H2) from Methane and Nitrogen in Thermal Plasma Systems... 

Fig. 8. BASF burner for the production of acetylene from methane or light naphtha (14).

Like many singlet carbenes, nucleogenic, arc generated and chemically generated C atoms react with aliphatic C—H bonds by insertion. In the simplest case, reaction of chemically generated C atoms with methane yields ethylene and acetylene. When a mixture of CH4 and CD4 is used, product analysis indicates that the acetylene results from H abstraction followed by dimerization of the CH, while the ethylene results from C—H insertion followed by H migration in the carbene (Eq. 15). It seems probable that CH is formed in all reactions of carbon with hydrocarbons as acetylene is invariably produced in these reactions. 

Table III shows that gaseous product from the irradiation of less than 10 micron coal (micronized) showed higher methane and lower acetylene than coal from the cube. Other particle sizes will have to be investigated to determine if particle size is a parameter for maximum acetylene production.

The thermal reactions of dihydrobenzo[c]furan 258 were studied behind reflected shock waves in a single pulse shock tube over the temperature range 1050-1300 K to lead to products from a unimolecular cleavage of 258 <2001PCA3148>. Intriguingly, carbon monoxide and toluene were among the products of the highest concentration, while benzo[f]furan, benzene, ethylbenzene, styrene, ethylene, methane, and acetylene were the other products. Trace amounts of allene and propyne were also detected. 

A number of minor products including methane, acetylene, ethylene, ethane, methylcyclopentane, hexene, and cyclohexyl-hexene-1 have been reported (refs. 490, 492-495) with very low G-values, and probably arise from bond breaking of the cyclohexane ring. 

Rokstad, O. A., Olsvik, O., Jenssen, B. and Holmer, A., Ethylene, acetylene, and benzene from methane pyrolysis, in Novel Production Methods for Ethylene, Light Hydrocarbons and Aromatics (L. F. Albright, B. L. Cryness, and S. Nowak, Eds.), Marcel Dekker, New York, 1992, pp. 256-272. 

Since no water is formed under these circumstances, the process differs from that wherein ethylene is involved. Also, no methane appears in the products. From these results it may be concluded that no monohydroxy acetylene compound is formed as has been postulated for other hydrocarbons.96... 

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