The refining operations consist of three distinct branches: (1) the distillation, (2) the extracting of paraffin and refining, and (3) the chemical treatment. When only a small percentage of the low boiling fractions has to be removed from the crude oil, the process is known as “topping,” and a convenient form of apparatus for the purpose is the tower still. This consists of a vertical cylinder fitted with perforated plates resting at intervals on pipes through which superheated steam travels. The pipes serve the double purpose of conveying the steam to its inlet and of heating the oil to be distilled. The steam, on entering the cylinder, ascends, meeting the crude oil, as it descends from plate to plate in a regulated stream, and carrying with it to the outlet the light fractions which the operation is intended to remove.

DIAGRAM SHOWING THE PRODUCTS OF PETROLEUM OBTAINED BY THE “CRACKING” PROCESS
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A few years ago, a Californian chemist invented an improvement of the principles of maximum heating and evaporating surfaces. His name was Trumble, and the process is known as the Trumble process. The crude oil is heated to the desired temperature in pipes or retorts set in a primary furnace, the hot gases of combustion from which are utilized to heat the distillation chamber proper. Entering the vertical cylinder at the top, the oil is spread over and through perforated plates falling on a cone-shaped plate to divert the continuous stream of oil to the sides of the still, down which it flows in a thin film. Other conical plates, arranged at intervals underneath, maintain the flow in the desired channel until it reaches the outlet at the bottom. When 60 or 70 per cent. (comprising the motor spirit series, the kerosenes, and perhaps the intermediate fractions) are to be removed, it is common practice to distil the crude oil in a series of stills, cylindrical in shape, connected continuously. The best-known system is that patented 35 years ago by Mr. Henderson, of the Broxburn Oil Company, Ltd., for the distillation of shale oil, and since adopted by many refiners of petroleum. In this system, the crude oil flows from a charging tank by gravity through a pre-heater, heated by the passage, from the second or other still, of distillates of suitable temperature, and thence into the first still. Here it is raised to distillation temperature, and the specific gravity of the distillate therefrom fixed. The feed of the crude oil is constant, the residue formed in the still passing through a connection at the bottom into the second still in the series, at the top, and led from back to front so that the inlet and outlet shall be as far apart as possible. It is here raised to a higher temperature, yielding a distillate of higher specific gravity, the residue passing on to the next still, and so on through the series of stills until it reaches the point where all the motor spirit (or benzine, as it is called), kerosene, and the intermediate distillates are removed.

The distillates obtained from the refining of the crude are usually purified by treatment successively with sulphuric acid and solution of caustic soda, this process of chemical treatment being necessary before the products are fit for the market.

The “cracking” process of distillation briefly consists in distilling the oils at a temperature higher than the normal boiling points of the constituents it is desired to decompose, and, in practice, the result is that the heavier oils are turned into lighter hydrocarbons of lower boiling points: thus the yield of the more valuable of the refined products is materially increased. The “cracking” process, which very largely obtains to-day, was quite accidentally discovered by a small refiner in America many years ago. The man in charge of the still left it with the intention of returning very shortly. He was, however, absent for several hours, and to his dismay found that; as the result of his neglect in attending to the still, a very light coloured distillate of much lower density than that which it was usual to obtain, was issuing from the condenser.

Upon investigation, it was found that a portion of the distillate had condensed upon the upper part of the still, which was cooler, and had dropped back into the still, where the temperature was sufficient to produce products of a lower boiling point—certainly a distinct improvement. As may be imagined, this “cracking” process does not commence until the lighter products of distillation have been removed, and is now so popular because by its use a greater yield can be obtained of those more valuable products for which there is an ever-increasing demand.

It is unnecessary here to enter into those various improvements which have been introduced from time to time, all of which have as their aim the production of larger quantities of refined oils, and it would likewise be invidious to enumerate even the more popular scientists to whose energies much of the resulting progress has been due, for the simple reason that it has ever been the aim of the petroleum chemist to turn his abilities in the direction indicated.

As may be imagined, the industry of petroleum refining has had to adapt itself to the altered conditions of to-day. For instance, prior to the advent of the internal combustion engine, which now is responsible for such a wide application of motor spirit, the demand for this, the lightest product of petroleum distillation, was non-existent. Consequently, when such spirit was produced, there was no market for it, and its production represented sheer loss to the refiners. Both in the Far East and in Russia, we have examples of the enormous loss which accrued to the refiners by reason of there being no market for this highly inflammable product. In the Far Eastern fields, in particular, this loss was very heavy, for in the earlier days of its operations, the “Shell” Company had to remove thousands of tons of this now valuable motor spirit from its refineries and burn it in the open fields. The successful introduction of the internal combustion engine, however, completely changed the aspect of petroleum refining, and the desire became general, not to see how little motor spirit could be produced, but to perfect methods by which the yield of the benzene series of hydrocarbons should be as large as possible. Even to-day progress is still being recorded in this direction, and each American refiner is vying with his neighbour as to how far that output of gasoline, as it is there called, can be increased.

Many and varied are the means which have been resorted to for this purpose, but most of them have reference to improvements in the processes for refining the crude oil. One, however, is worthy of being mentioned in this little treatise, inasmuch as it deals with quite another aspect of the problem of increased motor spirit supply.