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of a fractionating column, endeavouring to carry out the fractionat- ing in one stage so that the one-bench stills would provide finished products. Similar considerations led to the development in Califor- nia of theTrumble process, introduced by M. J. Trumble, a California chemist, consisting of an elaborate series of heat interchanges. In this process, oil is heated in a tubular furnace. It is dropped down a tower where, by means of distributors, it is brought in contact with the hot side of the column still and so gives a film evaporation. A recent modification of stills is the Allan system, introduced by Hugh Allan, a British chemist, whereby the oil is vaporized in the ordinary kind of Henderson still, but in place of being subsequently redistilled, or being collected via a column, vapours are blown into a series of vertical pipes, getting a fractional condensation from member to member, the latent heat of the high boiling components being used to reeyaporate any condensed volatile oil, thus obtaining the fractions desired. Topping and skimming plants to raise the flash point and to dehydrate heavy oil have multiplied rapidly, particularly in the United States. The skimming industry is represented in all the major oil fields and has other purposes which give the plants practically a universal field in the oil industry, namely, to remove the lighter con- stituents of the oil for storage for a long period, thus reducing the losses from evaporation, to dehydrate or clean the oil and, in con- junction with a complete refinery, to remove the lighter fractions cheaply and quickly, leaving a residue to be re-run for lubricants, coke and other products.

Cracking Processes. The commercial development of the crack- ing process subsequent to 1913 marked an epoch in the petroleum industry. The growing importance of the internal-combustion engine made necessary a higher yield of motor fuel from the limited crude- oil supply, if the demands of this consuming agency were to be met. Modern cracking dates back to the patent obtained in 1889 by the late Sir Boverton Redwood and Prof. Dewar, British chemists (see 21.322), but commercial development followed the first patent of Dr. W. M. Burton, an American chemist, in 1913.

The following classification of oil cracking processes (represen- tative patents) is made by the Kansas City Testing Laboratory (Bul- letin No. 15) :

I. Cracking in the vapour phase.

A. Atmospheric pressure.

Oil gas plants, very high temperature.

Pintsch gas plants, very high temperature.

Blaugas plants, i,ooo-i,2ooF.

Parker (W. M.) process at 1,000" F. with or without

steam. Greenstreet Cherry red with steam.

B. Wjth increased pressure.

Rittman process above 950 F. and 200-300 Ib. pressure. W. A. Hall process i,iooF. and about 75 Ib. pressure.

II. Cracking in the liquid phase.

A. With distillation.

1 . At atmospheric pressure.

Luther Atwood (1860).

McAfee process with aluminium chloride.

Russian and American practice for ilium, oils.

2. Above atmospheric pressure.

Dewar and Redwood (1889).

Bacon and Clark at 100-300 Ib.

Burton (Standard Oil Co.) 650-850 F. and 60-85 Ib.

Dubbs, J. A., over 10 Ib. and over 300 F.

3. Very high pressure (over 27 atmospheres).

B. Without distillation and with high pressure.

1. Without vapour space for equilibrium (continuous

processes).

Benton (1860) 700-1,000 F. and 500 Ib. Goebel-Wellman. Mark (English).

2. With vapour space, (a) Intermittent.

Palmer (below 27 atmospheres for aromatics). (6) Continuous.

Dr. Burton's process is now extensively used in the United States. The development of this patent and the large-scale adaptation of the cracking process marked an era in the history of petroleum refining.

The following is a summary of an address made by Dr. Burton in May 1918, on the occasion of the presentation to him of the Wm. Gibbs medal by the American Chemical Society.

Dr. Burton pointed out that in 1910 the demand for gasoline created by automobiles began to grow so rapidly that it was obvious that something would have to be done to increase the supply of naphtha products. In those days the average yields of various products of petroleum were about as follows : naphtha products 1 8 %, kerosene or illuminating products 30%, lubricating products 10%, loss 3 %, leaving about 40% which was sold for gas-making or fuel in lieu of coal. The problem was to convert the high-boiling fractions existing in fuel and gas oil into low-boiling fractions needed by the internal-combustion engine. Dr. Burton and his associates worked for almost two years trying to devise a practical method, first by superheating and dissociation at high temperatures, but at atmos- pheric pressure; and, secondly, by the employment of various re-

agents, but their efforts were not successful. Having tried everything else that suggested itself these engineers decided to attack the prob- lem from the pressure distillation standpoint. In view of the fact that distillation must take place at temperatures ranging from 35OC. to 45OC., at which the tensile strength of steel begins to diminish very rapidly, and in view of the fact that steel at such temperatures, in the presence of carbonaceous matter (and even of free carbon, which often comes as the result of pressure distillation), is likely to absorb such carbon, become crystalline and lose its tensile strength, the practical refiner doubted the success and safety of this method.

The first large still built had a charging capacity of 6,000 gal. of heavy oil. Serious leaks were encountered, but this problem was finally solved, as the oil carbonized under the influence of the high temperature and the carbon deposits stopped the leaks. There were many puzzling problems to be solved, such as the devising of a safety valve that would operate freely in spite of the intense heat and the presence of carbonaceous matter. The entire apparatus had to be constructed in such a way as to insure ease of operation and freedom from excessive repairs. The production and disposition of the so- called " fixed gases " were troublesome. It was found that in some cases the heavy oil with which the operation began evolved more gas than was needed to maintain the desired pressure, whereas other oils evolved an insufficient amount of gas for this purpose. This ob- stacle was converted into an aid by arranging a large number of stills in parallel so that the superfluous gases from some stills were con- ducted to others that needed them. The plan gave a perfect method of securing uniform pressure and control.

By starting with fuel-oil products having boiling points ranging from 200 C. to 350 C., it was possible to secure a very substantial yield of a product having boiling points ranging from 50 C. to 200 C., and it was found that losses thus incurred were trifling, averaging less than 3 per cent. It was found that the high-boiling residues thus produced yielded a product almost identical with the natural asphalt.

Developed from the single 6,000 gal. still there were then (1918), Dr. Burton stated, over 500 stills of a larger capacity. During the preceding five years more than 20,000,000 bar. of gasoline or naphtha products had been produced by these stills in the United States.

It is estimated that cracked gasoline probably accounts for about '5% of all gasoline manufactured in the United States. Casing- head gasoline, manufactured from natural gas, the development of which ranks with cracked gasoline as one of the most important refining advances, is perhaps the source of from 12 % to 15 per cent.

Natural Gas. The United States and Canada produce all but a small fraction of the natural gas output of the world (see 21.321). The main areas of Pennsylvania, W. Virginia and Ohio have developed remarkable staying qualities, and these three states produced virtually two-thirds of the total production of the continent. The mid-continent field has shown a great increase in the natural gas production and the Wyoming field has proved productive. There is some natural gas production in Russia, Rumania, Persia, Galicia, India, Japan and "Mexico. The total production of natural gas in the United States in 1918 was 721,000,000,000,000 cubic feet. It is estimated that no less than 14,000,000 inhabitants of the United States are enjoying this fuel as a source of heat, light and power.

Natural Gas Gasoline. Although the foundation of the natural gas gasoline industry in the United States was laid in 1903 and 1904, the real expansion of this important phase of gasoline production began in 1909. In 1911, the first year for which statistics on the subject are available, 132 plants produced 7,425,839 gal. of raw gaso- line from natural gas. In 1918 the industry included 1,004 plants which produced 282,535,550 gal. of raw gasoline. Of the total, 865 were compression plants producing 219,767,207 gal. and 139 absorption plants producing 62,768,343 gallons. A canvass made in 1921 showed a total of 444 casing-head gasoline plants in Kansas, Oklahoma and northern and central Texas, having a daily output of 1,101,155 gal. of raw gasoline. Prior to 1916 the greatest proportion of gasoline production from natural gas was obtained from casing- head gas, oil-well gas or " wet " natural gas by the compression and condensation method. The development of the absorption process has extended the field of the natural gas gasoline industry to include practically all of the natural gas production in the United States, for there is but little gas production that does not contain an appreciable percentage of pentane and hexane, the hydrocarbons of the paraffin series that are the principal constituents of gasoline. Much of the so-called " wet " gas obtained from oil wells when they are first opened and from gas wells that produce no petroleum, has been sufficiently rich in gasoline vapours to warrant treatment by the absorption process, though excluded from successful treatment by compression and condensation. The following extracts are from Handbook of Casinghead Gas, by Henry P. Westcott :

" Casing-head gas received its name from the casing-head on the top of the casing through which it flows. It is the gas that flows from oil wells, coming out between the casing and the tubing. The volume varies from a few hundred cubic feet to several hundred thousand cubic feet per day. Invariably the gas becomes richer in gasoline content as the wells grow older. Generally a gasoline plant or property consists of a number of oil leases grouped around a main compressor station in which the actual making of gasoline takes place. The gas lines from different wells on each lease run to a main line in which is placed a meter to measure the gasoline from that