CHAPTER IV_Petroleum

THE REFINING OF PETROLEUM

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majority of cases, however, the crude oil, as withdrawn from the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.

CRUDE OIL

FRACTIONAL DISTILLATION

+--------------------+-----------------+--------------------+----+------------------+

| | | | |

Crude Naphtha Heavy Crude Natural +-------------+ Cylinder Stock

| Naphtha Lamp Oil | Lubricating | |

| Steam Distillation Distillate +-------------+ |

+-------+-----+ | Acid | Clay

| | | +-----+---+ Treatment Cold Pressing Percolation

| | Bottoms +------+---+ +----+------+ |

+------------+ | | | | | |

| Naphtha | +------------+ Sludge | Slack Wax +-------------+ |

| +------------+ | W W Oil | Process +-------------+ |

Acid Treatment +---------+ | | |

| +-----+----+ | +-------+---+

+------+---------+ | | | | |

Sludge Deodorized | Oil | +----------+

Naphtha | | | Cylinder |

+--------------+ | | Oil |

| Crude | | +----------+

| Paraffin Wax | Fractional

+--------------+ Distillation

| |

Clay +----+--------+

Percolation | |

| +------------+ +-----------+

+--------------+ | Gas & Fuel | | Neutral |

| Asphalt +------------+ +-----------+

+--------------+ |

| Paraffin Wax | Clay

+--------------+ Percolation

+----------+---+

| |

Asphalt |

+-------------+

| Neutral Oil |

+-------------+

DIAGRAM SHOWING THE PRODUCTS OF PETROLEUM BY FRACTIONAL DISTILLATION

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.

CRUDE OIL

CRACKING DISTILLATION

+-----------------------+----------------+---------------+---------+----------------------------------------------+

| | | | |

Crude Naphtha +---------+ Natural Cracked Distillate Tar

Steam Distillation | Heavy | Distillate Steam Distillation Mild Cracking

+------------+-----------+ +----+----+ Acid Treatment +---------+---------+ |

| | | | | | | +----------+----+----+-----------+

+------------+ | | | +------------+ +------------+ | +----------+

| +-----+-----+ | Acid | |

Acid Treatment | | | Treatment Acid +----------------------+

+----------+---+ | Naphtha | | +-------+--+ | +----------------------+

| | | Distillate | | | | +------+-----+ |

+------------+ Separated +----------+ Sludge | |

| Deodorized | by boiling | Gasoline | +------------+ +-------+----------+

+------------+ | +----------+ | Test | Slack Pressed Paraffin

+-----------+ | | Distillate | Wax Distillate

| | Steam +------------+ | |

+-----------+ Acid Distillation | Sweating Fractional

| Weak | Oil | Fractional Process Distillation

| Acid | | | | | | +-------+-------+

+-----------+ | Gasoline Bottoms +---------------+ | | |

Fractional | | | +------------+ +-----------+

+----------+ | White | | Fuel Oil | | +------------+ +-----------+

Acid Oil Asphalt +------------+ +----------+ +--------+ |

Distillate | | | |

Acid Treatment | Foots Acid

| | Oil Treatment

+-------------------+ | |

| | +----------+ +-----+-----+

+--------------------+ Sludge | Crude | | |

| Standard White Oil | | Paraffin | +----------+ Sludge

+--------------------+ | Wax | | Paraffin |

+----------+ | Oil |

| +----------+

Clay Percolation

+------+----+

| |

Asphalt +--------------+

| Paraffin Wax |

+--------------+

DIAGRAM SHOWING THE PRODUCTS OF PETROLEUM OBTAINED BY THE “CRACKING”

PROCESS

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.