REFINING AND MANUFACTURING PETROLEUM PRODUCTS
As has already been intimated, the Pennsylvania oil discoveries of
fifty years ago would have been relatively valueless if methods of
refining had not advanced sufficiently to develop the marketable
possibilities. If the reader has followed this narrative he will not
have failed to note that it was the optimism of experimental chemists,
who discerned in petroleum the possibilities of an illuminant which
would take the place of whale oil and other fats, which first suggested
to pioneer investors like Bissell the idea of developing America’s
oil fields by the boring system. Certain crude traditional methods
of refining petroleum had prevailed for centuries in the East, but
they had not produced an illuminant that would be acceptable to our
civilization.
The advancement of science, which gradually enabled the early American
refiners to produce a comparatively odourless, safe, and free-burning
oil from the crude, gave the necessary stimulus to the new industry.
The American refining system has since become one of the greatest
examples of standardized industry, fascinating in its minutiae,
and amazing in the efficiency and economy of its organization. The
pipe-line system has promoted the establishment of great central
refineries whither the crude travels distances of anywhere from five
hundred to fifteen hundred miles, and which, by treating it in vast
quantities, are enabled to provide the world with the products of
petroleum at the lowest possible cost.
It is the purpose of the refining process to produce from the crude
petroleum marketable products and this involves two stages. First:
The separation of the crude petroleum into its constituent parts,
corresponding in general to gasoline, kerosene, lubricating oil, etc.,
and, subsequently, the purification of each of these roughly separated
products to bring them into marketable condition.
The process might be best understood by likening the crude petroleum
to gravel scooped from out of the hillside. Such gravel would consist
of a mixture of sand, fine gravel, coarse gravel, rocks and boulders.
In this condition it would be unmarketable, except perhaps to fill up
marshy land. By analogy the crude petroleum consists of a mixture of
many different compounds and the mixture itself is unmarketable and of
no value except as a fuel, at once troublesome and dangerous.
To prepare the freshly mined or “crude” gravel for the market it would
be sifted through a series of screens which would separate it into its
component sizes. As a result of the sifting operation there would be
produced builders’ sand suitable for use in mortar, fine and coarse
gravel desirable for concrete, rough rock for road foundations, and
boulders for masonry structures.
The crude petroleum oil is a liquid and cannot be sifted on screens as
is the crude gravel, but nature has given it properties in consequence
of which it may be separated into its constituents almost as easily
as is the gravel. These properties are the different boiling points
of the several constituents. Thus, when water or any other single
liquid is heated it continues to increase in temperature until boiling
begins, after which its temperature remains the same, no matter how
rapidly the heat is applied, until all of the liquid has been boiled
away. When petroleum is heated, however, it begins to boil at a very
low temperature, a temperature hardly hot enough to injure the skin,
in some cases. It is not the whole of the petroleum which is boiling,
however, but only the very lightest part of it, that is, the gasoline
or naphtha. If the temperature were to be held constant for a short
length of time all of the gasoline would have been boiled off, and
although the liquid would be just as hot as it was before, the boiling
would cease entirely. If the heating is now continued, however, and the
temperature of the oil raised to some higher figure, it again begins
to boil and now it is the kerosene constituent of the crude petroleum
which is being converted into vapour and driven out of the liquid.
After a time all of this kerosene will be gone, and as before, the
liquid, although still at the same temperature at which it has just
previously been actively boiling, remains quiescent. In this fashion
the various constituents of the crude petroleum may be separated from
one another by a “sifting” operation somewhat similar to that used to
separate sand from gravel and gravel from rock, except that instead
of employing screens to effect the separation there is employed an
apparatus in which the heat of the oil can be gradually increased
and the products, which are successively driven off in this fashion,
separated from one another.
The apparatus commonly employed for this purpose is called a “still”
and consists merely of a steel receptacle, usually in the form of a
horizontal cylinder, much like a simple steam boiler. These stills
have been developed to large capacity, some of them holding upwards
of 50,000 wine gallons of oil at one time. The still is mounted over
a furnace which is usually heated by coal just as an ordinary steam
boiler. In this still the temperature of the crude petroleum is
gradually raised and with each elevation in temperature a different
product is boiled or driven off the mass of liquid until finally
nothing remains in the still except a small quantity of black residue
which is known as petroleum coke.
It remains, therefore, to cool and condense these vapours. This is
accomplished by an apparatus called a “condenser” which is connected to
each still. An elementary condenser consists merely of a coil of pipe
submerged in a tank of cold water. The vapour leaving the still passes
through the submerged coils in which the vapour by cooling is caused
to return to a liquid condition. Into one end of the condenser coil,
therefore, the vapour from the still enters and from the other end
there flows the condensed liquid.
The first and most important step in the process of refining all crude
petroleum is conducted in the fashion above described. A refinery
of large size will have perhaps 100 of those crude stills which are
generally arranged in groups or batteries, each battery containing
a dozen or more stills. From each still the condenser pipes are led
to a “receiving house” which is located in some central position. In
this manner it becomes possible for a single responsible supervisor
to observe and control the operation of a large number of stills.
The supervisor is called the “stillsman” and upon him rests the
responsibility for directing the initial process of separation or
sifting by which the crude petroleum received at the refinery is
roughly separated into different “fractions” or parts, each of which by
further refining becomes a marketable petroleum product. As generally
conducted, this first distillation process separates the crude
petroleum oil into four major fractions.
The fraction which has the lowest boiling point and is therefore the
first to be driven off from the crude petroleum in the still as the
latter is heated, is the naphtha or gasoline fraction. When all the
naphtha or gasoline from any particular still has been driven off,
the stillsman, stationed in the receiving house and able to observe
constantly the character of the condensed liquid, which is delivered
by the pipe from the condenser coil to the house, will change the
connections in the receiving house so that the next “distillate” to be
received will flow to a separate tank. This second distillate which
comes into the receiving house and is thus diverted to a separate tank
will be the illuminating oil distillate or, in refinery parlance, the
“refined oil distillate.” It is interesting to note that “refined oil”
to a petroleum refiner still means kerosene illuminating oil, since
in the original petroleum industry this illuminating product was the
only fraction of the crude oil which was highly purified or refined.
The entire remainder of the crude petroleum, including gasoline and
the lubricating oils and other products heavier than kerosene, were
either discarded wholly or else sold for whatever they would bring in
an unrefined or very poorly refined condition.
The next product which is driven off from the crude oil after all of
the kerosene has been removed is a somewhat heavy and discoloured, but
free flowing oil, known as “gas oil.” Gas oil is seldom sold at retail
and the general public has very little knowledge of it. Its main use
is for the manufacture of city gas, auxiliary to coal, the products of
which form the base of city gas.
The next product after the gas oil and the last important product of
crude petroleum is the lubricating oil distillate, which is known as
“paraffine distillate” for the reason that it contains the paraffine
wax.
With the exception of the gas oil, which by reason of the uses to which
it is put does not usually require any further treatment, the products
thus roughly separated from the crude petroleum each need not only
further separation, but actual chemical purification to prepare them
for the market.
Considering these products in the order in which they are derived
from the crude petroleum, the gasoline or naphtha fraction is often
subjected to a second distillation by which it is further “sifted” into
light, intermediate and heavy naphthas. It is customary to conduct this
second distillation process by steam heat instead of by fire, since
the gasoline or naphtha fraction boils at such a low temperature that
it is unnecessary to resort to a furnace and furthermore, the quality
of the product is thought to be better if the second distillation is
conducted with steam. Following this second distillation the naphtha
or gasoline is subjected to chemical purification which involves
treatment with sulphuric acid, with sodium hydrate, sodium plumate
and filtration through Fuller’s Earth--a species of clay which has
been found to have not only a mechanical but probably also a chemical
purifying and decolourizing action. There is a considerable variation
in the purification or refining method employed by the different
refiners, but the foregoing treatments are the principal ones now in
vogue. The marketable products produced from the crude gasoline or
naphtha distillate by this re-distillation and purification process
are principally as stated--light naphthas, intermediate naphthas and
heavy naphthas. The light naphthas range from petroleum ether, an
exceedingly sweet-smelling and volatile liquid to aviation gasoline,
especially suitable for use in aeroplane motors under extreme
conditions of temperature and power development. The intermediate
naphtha is the ordinary gasoline of commerce, principally used as fuel
for automobile engines. The heavy naphtha is that often sold under the
name of benzine, cleaners’ naphtha, solvent naphtha or varnish makers’
and painters’ naphtha. As these names indicate, the heavy naphtha
is principally used in the manufacture of paints and varnishes, for
dry-cleaning and as a solvent in the chemical industries.
The second fraction of the crude petroleum, the kerosene, illuminating
oil, or “refined oil,” is likewise ordinarily subjected to a second
distilling operation, the main purpose of which is to separate it from
any traces of gasoline which would tend to make it highly explosive
and dangerous when used in lamps. This re-distillation is followed by
a chemical purification, producing the kerosene of commerce, which is
not only so safe that it may be heated to a temperature well above
100° F. without danger of giving off any explosive vapour, but is also
water-white in colour, crystal clear, and of such purity that it may be
burned in a lamp in a closed room without producing offensive odours or
smoke.
The third major fraction of the crude petroleum is the gas oil which
has previously been referred to. In general this product may be
marketed without further treatment.
[Illustration: Lines for loading oil on vessels anchored from one to
two miles off shore. This is a regular practice in Mexico where a deep
harbour is not available]
[Illustration: Battery of crude stills at the Bayway Refinery, Linden,
N. J.]
The next and last major fraction is perhaps the most interesting of
all. It is from this fraction that the host of lubricating products
are obtained and also the paraffine wax which has almost entirely
superseded animal and vegetable waxes, not only for candles, but for
laundry use, for producing water-proof paper, for sealing preserve jars
and for a multitude of minor uses. The first step in the treatment of
this “paraffine distillate” or lubricating oil distillate fraction of
the crude petroleum is to separate from it the paraffine wax which
it carries in solution. This is accomplished by chilling the oil to
a very low temperature through the use of refrigerating apparatus.
When the oil is thus chilled the dissolved wax therein crystalizes so
that the mixture resembles nothing more than slush or mush ice. Having
caused the dissolved paraffine to freeze and come out in the form of
slush in this fashion, it remains to separate it from the oil. This is
accomplished by filtering the mush, still held at its low temperature,
through canvas cloths. The oily part of the mush passes freely through
the cloth while the solidified particles of wax remain on the face
of the fabric. The first two products separated by the chilling
and filtering processes are therefore a wax-free oil and an impure
paraffine wax.
The impure paraffine wax is known as “slack wax” and is melted and
poured in a liquid condition into shallow pans, where upon cooling, it
solidifies. The pans are then slowly and cautiously heated, and as the
temperature of the wax rises, the small quantity of oil which it still
carries sweats out of the wax, just as though the wax were actually
perspiring.
As a result of this sweating operation there is produced “crude scale
wax,” the ordinary wax of commerce. It is yellow to ivory in colour,
contains only a small proportion of oil and is almost odourless and
tasteless. The crude scale wax is very commonly further refined by the
general methods used throughout the oil industry, i.e. by treatment
with acid and alkali, and by filtration, to produce refined paraffine
wax of pure white colour, free from oil, and without odour or taste. It
is this refined grade of wax which is commonly met with in the retail
market.
Returning to the wax-free oil which passes through the canvas filters,
leaving behind the impure wax, we find that this is the product from
which lubricating oils are obtained. It is an oil of dark brown or
amber colour, considerably heavier than kerosene and has a very greasy
feeling which is indicative of its value for lubricating purposes.
Elaborate methods have been devised for accurately determining and
gauging this greasiness or viscosity, which is the property of the
oil upon which its lubricating value is most dependent. In general,
this oil is in part re-distilled, that is, it is charged into a still
and subjected to a temperature which is sufficient to drive off, in
the form of vapour, some portion, though not all of the oil under
treatment. This process, accurately described as “reducing” the
oil, serves to concentrate in the residue remaining in the still,
the heavier or more greasy or viscous constituents, the grade or
viscosity of the lubricating oil depending on the extent to which this
reduction is carried. As in the case of the other petroleum products,
it is customary to carry out a chemical purification process and to
filter the oil subsequent to the re-distillation. As a result of such
further chemical purification and filtration, the colour of the oil
is improved, any suspended solids or dirt which it may contain are
removed, and any chemical constituents which it may contain and which
may be detrimental to its use, are destroyed.
The refining process above described is that which is most largely
employed in this country, being a typical process for obtaining
gasoline, kerosene, gas oil, lubricating oils and paraffine wax from
the grade of crude petroleum produced from the central and central
western states of the United States. The process is considerably
varied, however, in dealing with crude petroleum of different
characteristics. For example--there is produced in Mexico and imported
into this country for refining in the plants located on the Atlantic
Coast a very large amount of petroleum oil which is little more than
thin asphalt. Oil of this character is not generally used for the
production of lubricating oils or wax, but is instead merely refined
for the production of gasoline, kerosene, and fuel oil, or for gasoline
and fuel oil only. It will be understood that the term “fuel oil”
merely indicates any heavy petroleum oil free from dirt and water, and
fluid enough to be readily pumped through a pipe, and containing no
constituents which would make it apt to give explosive mixtures with
air. Fuel oil of this description is largely replacing coal as a fuel
for steamships.
The State of California produces a considerable quantity of this
“asphalt base” crude petroleum, which, like the crude petroleum from
Mexico, is subjected to refining processes very much simpler and
yielding mainly gasoline, kerosene and fuel oil. It is usually also
from crude petroleum of this character that the artificial asphalts
which supplement the supply of natural asphalt for paving material
are produced. These artificial asphalts in general represent the
heavier constituents of crude petroleums, such as those of Mexico
and California. The term artificial asphalt is perhaps a misnomer,
for, although the properties of the asphalt are somewhat modified
by the refining operation, the asphalt exists as such in the crude
petroleum oil and the main purpose of the refining operation is merely
to separate it from the fluid constituents of the oil in which it is
dissolved.
There is also a large amount of oil produced in the United States,
mainly in Pennsylvania, which is of a character especially suited to
the production of high grade lubricants by a simple refining method.
With oil of this character the lubricating constituents do not require
distillation to separate them from impurities. The crude petroleum
may be directly reduced by distillation, taking off the three major
fractions, that is, gasoline, kerosene and gas oil, and leaving behind
in the still a very good grade of lubricating oil which, however,
contains paraffine wax. To separate this wax from the lubricating oil,
in which it is dissolved, an ingenious process called cold settling
is resorted to. According to this process, the mixture of lubricating
oil and wax is diluted with gasoline, enough gasoline being employed
to make a very thin liquid, and the mixture is then chilled to a low
temperature. From the chilled mixture the paraffine separates out in
the form of a thick grease which settles to the bottom of the chilling
tank. This grease is subsequently refined to produce the various grades
of petroleum jelly. The lubricating oil diluted with naphtha and
separated from the paraffine or grease as described is subjected to
re-distillation for the separation of the naphtha and forms a base for
the production of a wide variety of high grade lubricants.
Returning to the analogy by which we compared crude petroleum oil to
crude gravel mined from the hillsides, it will be noted as in the
case of the gravel, the various crude petroleums differ in character
considerably, according to their origin, and that the refining process
must be modified to suit the character of the oil.
The analogy may be pursued one step further to explain one of the most
interesting developments of the modern petroleum industry, i. e., the
manufacture of gasoline not naturally contained in crude petroleum.
This process of _manufacturing gasoline_ is called “cracking.”
Let us assume that we desire to obtain from crude gravel, mined from
the ground, a maximum amount of fine gravel. We would first use all of
the fine gravel which was naturally contained in the crude gravel and
then we might pass the remainder of the gravel, which is too large for
our use, through crushing rollers which would crush or crack it, thus
producing an additional quantity of fine gravel. An analogous process
has now been successfully developed for the treatment of petroleum
oils. According to this process, a heavier constituent of the crude
petroleum oil, for example, kerosene or gas oil, may be subjected to
distillation at high temperatures, and under high pressure in special
stills designed for this process, thus securing increased quantities
of gasoline. In this operation a certain proportion of the heavier oil
treated is caused to break down into gasoline. The U. S. Bureau of
Mines estimates that in 1919 some 15% of the country’s total gasoline
production was obtained by this process.