HIGH TEMPERATURE CARBONIZATION OF COAL 381
Gaseous Products. Liquids. Solids.
Humus bodies, yield . . | Carbon monoxide Carbon dioxide Methane Water Thin tar Free carbon
Resin bodies, yield . . Carbon monoxide Carbon dioxide Ethylene, and unsaturated hydrocarbons Water Rich tar Free carbon Pitch
Hydrocarbons, yield . Methane, ethane and other paraffins Heavier tars Free carbon Pitch
Carbon Residuum. TJnaffected by distiUation.
In the study of carbonization it is essential, in the first place, to distinguish between the primary and secondary products of distiUation, and to bear in mind that, in spite of the ultimate gas containing about 50 per cent, of hydrogen, this element, per se, is not necessarily evolved from the coal in the early stages, but results from the degradation of carbon and hydrogen compounds, and to some extent from the production of water gas. The lowest temperature at which car-bonization actively occurs varies between 300° and 400° C., when diiefly hydro-carbons of a considerable nature are evolved, the permanent gas yield being com-paratively small. At such temperatures primary products alone would be expected, but even at this stage some secondary decomposition will have occurred, so that a series of products of a purely primary nature will never be found. Low temperature distiUation in the absence of degradation would account for the following, which (according to Lewes) constitute the true primary gas :—
1. Water vapour.
2. Carbon dioxide and carbon monoxide.
3. Hydrocarbons of the paraffin series.
The bulk would be made up of these, whilst, in addition, there would be smaller quantities of:—
4. Unsaturated hydrocarbons.
5. Ammonia.
6. Sulphuretted hydrogen.
A large proportion of the paraffin hydrocarbons would be of a condensible nature, accounting for tar rieh in the methane hydrocarbons. From the above it will be seen that the water vapour and oxides of carbon are the first products to be evolved, and that of the primary constituents methane is by far the most important.