Modern Gasworks Practice

HIGH TEMPERATURE CARBONIZATION OF COAL 403 bumed by itself it appears to show but poor light-giving properties, but when present in an admixture such as coal gas it undoubtedly accoimts for an increase in illumni-ating power out of proportion to that shown in the above table. Whatever its efiect as an. illuminant, however, methane—owing to its high calorific valne—is one of the most desirable constituents of modem gas. Fortunately, this hydro-carbon is the most stable of ihose present, and consequently suffers to a compara-tively slight extent from the degrading influences in the retort. One of the first investigators to tam his attention to the decomposition of gases was Bertlielot.1 wlio, in 1863, carried out a number of experiments with. the hydro-carbons. Previous to Berthelot’s work it had been shown by otter research that the ultimate resolution of a hydrocarbon into its elements, hydrogen, and carbon, can in no way be regarded as the immediate result of a single change, but that gradual brcaking down into molecules containing a smaller number of atoms takes place. Thus et hylene (C2H4) was considered to be resolved into free carbon and methane, and so on. (1) Ethylene, C2H4= C + CH4. (6) Ethane, C2H6=C2H4 (ethylene) +H2. The four hydrocarbons of chief interest to the gas engineer are the primary product ethane (which largely disappears at present-day temperatures), ethylene, acetylene and methane. Berthelot, as a result of his studies, was of the opinion that these hydrocarbons underwent decomposition in the following manner:— (a) Ethane, either (1) C2H6=C2H4 (ethylene) + H2, or (2) 2 C2H6= 2 CH4 (methane) + C2H2 (acetylene) + H2. (b) Ethylene, either (1) C2H4=C2H2 (acetylene) + H2, or (2) 2C2H4=C2H6 (ethane) + C2H2 (acetylene). (c) Acetylene. This be concluded was never resolved into its elements, but was capable of undergoing polymerization or condensation into benzene at high temperatures. Tlius 3 C2H2=CeHe. (d) Methane, either (1) 2 CH4= C2H2 (acetylene) + 3 H2, or (2) 2 CH4=CaH6 (ethane) +H2. In 1894, Lewes, in a number of experiments on the hydrocarbons, of which be chiefly studied ethylene, concluded that this compound is primarily decomposed into equal volumes of methane and acetylene on the following lines:—3 C2H4 = 2 CH4 + 2 C2H2. With regard to methane he agrees with Berthelot that this ie transformed into hydrogen and acetylene, but that the acetylene subsequently polymerizes or is resolved into its elements hydrogen and carbon. There is general agreement as to the marked stability of methane. But that degradation of this constituent does take place at higher temperatures and under certain couditions is shown by the manner in which the quantity has decreased in modem coal gas. 1 Ann. Chem. Phys., 1863, 1866, 1867, 1869.