Inasmuch as the aim of this little volume is to interest other than those who are directly associated with the petroleum industry, I shall endeavour in this chapter to refer to the refining of petroleum in a manner which shall be readily understood by the reader, and shall, wherever possible, refrain from entering into those highly technical matters which do not lend themselves to popular expression.

The refining of crude oil as it is produced from the earth, consists in the classification of its various hydrocarbons by means of fractional distillation, into the various products which so largely enter into our commercial and domestic life of to-day. The refined products, in the order in which they are received by distillation, are: motor spirit, illuminating oils, solar oils, lubricating oils, fuel oils, residuum, etc.—the first mentioned being the lightest and the last the heaviest in specific gravity.

Almost simultaneously with the discovery of petroleum, there sprung up the first attempts to refine Nature’s product, and though these early experiments were of a most primitive character, they doubtless served their purpose admirably. In this respect, probably the most primitive oil refinery in the world was built near the Tigris, in Mesopotamia.

Crude petroleum varies in its character, for while certain crudes are pale in colour and almost transparent, others are almost black and viscid. Some, indeed, would appear to have undergone a course of refining by Nature itself, for in some fields the crude oil will freely burn in lamps without any refining treatment: in the vast majority of cases, however, the crude oil, as withdrawn from the producing wells, represents a liquid somewhat like molten tar.

The chemical composition of petroleum consists essentially of carbon and hydrogen, together with oxygen and varying amounts of nitrogen and sulphur. The crude from Pennsylvania—and this is the finest crude in the United States—consists chiefly of a large number of hydrocarbons of the paraffin series, whilst in the Russian petroleums, the predominant constituents are naphthenes or polymethylenes. Then the crude petroleum of the Dutch Indies and Burmah is of a different character from that found elsewhere, for in it aromatic hydrocarbons are largely present. The various series of hydrocarbons found in crude oils—the paraffins and naphthenes—readily lend themselves to conversion into other compounds of carbon and hydrogen by dissociation, and this conversion produces compounds of higher volatility, such as motor spirits, etc. When the compounds of hydrogen and carbon are submitted to distillation, certain chemical changes occur, as the result of which other series of hydrocarbons are formed, and, though it is not my intention here to dive into this comparatively new realm of chemical investigation, it is interesting to mention that, by carrying the treatment of the compounds still further, it is possible to obtain aromatic hydrocarbons, including trinitrotoluene (generally known as the explosive T.N.T.), in addition to various dye products.

In the earlier methods of refining, the stills usually consisted of a vertical cylinder in which the charge of crude oil was distilled almost to dryness, but this method was completely revolutionized many years ago, especially in the United States, by the introduction and immediate success of a principle known as the “cracking” process, and by the separation of the distillation into two portions, one for the removal of the more volatile constituents in the crude oil (such as motor spirit) and the other for the treatment of the heavier products.

DIAGRAM SHOWING THE PRODUCTS OF PETROLEUM BY FRACTIONAL DISTILLATION
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I will first deal with the method of refining known as the “straight” process, or the process which does not involve “cracking.” At one time, the refiner had to consider the saleability of his refined products before he commenced to refine them, but to-day, with the perfect system which prevails for the handling of huge quantities of refined products, and the transporting of them to the most distant markets, the one desire of the refiner is, naturally, to secure from his treatment of the crude oil, as many refined products as possible, always keeping an eye on the production of the largest quantities of the higher priced products than upon those which are of low value.

The process of refining to be applied to any particular oil naturally depends upon its composition as shown by analysis. It may be that the crude oil to be treated, apart from containing a small percentage of distillates with a low boiling point (motor spirit), is principally made up of residues of little value except as fuel, or, on the other hand, it may be that the crude oil is of high quality and contains all possible products. In the former case, the process of distillation is brief, and the plant inexpensive, as compared with the lengthy process of full refining necessitated in the latter case.