Table 115. Engler Distillation

Other forms of fractionating columns, e.g. ring columns of various types, find application in the petroleum industry too, but, as much more intensive fractionating is employed in the coal-tar industry, the reader is referred to the section dealing with that subject for details of such columns.

In general, petroleum products are not required to conform to such rigid specifications as are demanded for pure toluene, benzine, etc., made from coal-tar. This is only natural as petroleum spirits are such complex mixtures of various hydrocarbons. It would not be commercially practicable to isolate pure hydrocarbons by distillation, nor, indeed, would it be possible in many cases owing to the formation of constant boiling point mixtures. Petroleum spirits of relatively narrow boiling point ranges, e.g. 90° to 110° C, 100° to 120° C, etc/are used as extraction spirits and cleaning spirits. The preparation of these by an efficient fractionating column presents no difficulty. The ordinary benzines or motor spirits have, however, much larger ranges of boiling point, e.g. from 35° C. up to 200° C, and so require little fractionating except in so far as it is necessary to obtain a sharp cut between the benzine and kerosene fractions.