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oil will freely burn in lamps without any refining treatment: in the vast majority of cases, however, the crude oil, as withdrawn from the producing wells, represents a liquid somewhat like molten tar.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.

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.

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.

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.

As I have mentioned in another chapter, enormous quantities of natural gas exude from the oil-wells, and this in the past has been for the most part allowed to go to waste in the air, causing an ever-present danger to oil-field operations on account of its liability to ignite. Being heavier than the air itself, for it is impregnated with oil gases, it remains for long periods in the lower air strata, and, consequently, not infrequently, has been the direct cause of great oil-field fires. This gas—casing-head gas, as it is termed—comes from the oil-wells between the casing and the tubing, and, in the case of numerous wells, the flow is remarkable, some wells giving forth 300,000 cubic feet of gas every 24 hours, and the only useful purpose that this vapour has served until recent years has been to light several towns situated comparatively near to the oil-producing fields. The great volume of the gas, however, has been allowed to go to waste.

But experiments have proved that the gas is capable of condensation into motor spirit, and the general yield of such spirit may be taken as fully 2 gallons per 1,000 cubic feet of natural gas treated. What wonderful possibilities lie in the direction of the conversion of this vapour into motor spirit! The oil-producers in the United States have not been slow to appreciate this, and to-day there are hundreds of plants in the United States which have been erected solely to condense these oil-well gas vapours. Some of these plants are dealing with as much as 3,000,000 cubic feet of gas a day. The most recent official returns available from the United States show that the production of gasoline (motor spirit) from this process of oil gas condensation is, approximately, 150,000,000 gallons per annum, and even this substantial figure is being steadily increased.

There is also another phase of the oil-refining industry which, during recent years, has materially altered. I refer to the production of solar oil during distillation. It is an apt saying that we can scarcely look to any section of our commercial or domestic life without being confronted with the fact that oil products play some part therein: there are few, however, who, without reflection, would agree that when they light their gas they are dependent upon petroleum for much of the light the gas gives. It is, nevertheless, a fact, as I will proceed to show.

Many years ago, the oil refiners in Baku were confronted with a problem which appeared for some time to be insurmountable. After the distillation of their kerosene, or illuminating oil, and before they could commence to take off the lubricating oil fractions, there was an intermediary product which, while being of no use for lamp oil, did not possess the necessary constituents of viscosity to make it acceptable as a lubricant. It was a fairly decent volume of something for which there was no market at the time.

Experiments were made, and with these the name of Dr. Paul Dvorkovitz will ever be associated, and it was found that by the passage of a current of gas over the surface of this intermediate product, the gas caught up as it were a richness which materially increased the lighting power of the gas. To cut a long, but highly interesting, story short, this solar or gas oil was subsequently introduced by Dr. Dvorkovitz to England for gas enrichment purposes, and the extent of its employment to-day may be judged from the fact that the United Kingdom regularly imports between 60,000,000 and 70,000,000 gallons per annum for the enrichment of the coal gas which finds useful employment in practically every home throughout the land. As is known, the gas companies have to produce gas of a certain lighting quality, and it is in the upholding of the lighting strength of the gas that solar oil to-day plays so important a part. At first, the oil came almost exclusively from Russia, but now the competition from the United States has secured for our American friends the vast bulk of the trade, which, as I have shown, has reached enormous proportions.

Solar oil is also largely utilized for the production of refined perfumery oils, which are quite colourless and inodorous, while the finest quality is used in pharmacy and known as paraffinum liquidum, and is in much demand, but in this connection it is the Russian petroleums that have gained distinction. It was held for many years that such tasteless and colourless oils could not be produced from the United States petroleums, but from the commencement of the European War, and the consequent closure of Russia’s export port, whereby all overseas trade in Russian petroleums was held up, much progress was made in the manufacture of tasteless medicinal petroleums in the United States, such articles having now become popular throughout the world.

One of the most important discoveries made during recent years has been the finding of large quantities of toluol in petroleum. This article is necessary for the manufacture of high explosives. In Borneo heavy petroleum, toluol exists to a very large extent, and it was its discovery and consequent use by the allies—thanks to the offer made to the Governments by Sir Marcus Samuel, Bart.—that almost unlimited quantities of high explosives were manufactured.

Vaseline is another useful commodity which is derived from the refining of crude petroleum, and this article is turned out of the American refineries as well as those of Russia and Galicia, in large quantities, but, beyond mentioning this fact, no useful purpose would here be served by relating the various processes employed.

With reference to the methods generally adopted in the refining of the products from the distillation of the Scottish oil shales, these are briefly dealt with in the chapter devoted to the Scottish oil industry.

It is safe to say that the past two or three decades have witnessed marked progress in perfecting the methods by which crude petroleums are refined into the innumerable common commodities of commerce, and it is doubtful whether in any branch of chemical research there has been such concerted energy shown as in regard to the refining of mineral oils. Signs, however, are not wanting to show that the zenith of this progress has by no means been reached.