In 1887, a patent was granted in this country to Benton, of Titusville, Pa, for "improvements in the methods and means of refining crude and refuse petroleum and the like." The process consisted in pumping "the refuse of petroleum oil, tar oils, and other heavy mineral oils," under a pressure of 285 lbs. or more to the square inch, through a series of pipes heated in a furnace, and allowing the products to escape into a vapour chamber. The apparatus, which was said to produce lighter hydrocarbons from the products specified, is illustrated in Figs. 98 and 99. It consists of a series of pipes, B, heated by means of a furnace, A, and communicating on one side with a force-pump, 7, and on the other with a vapour chamber, C, which may be heated or partially exhausted. The pressure is regulated by a stop-valve, g, a weighted check-valve, q, being also provided. The un-volatilised liquid passes from the chamber, C, at h, and the vapour traverses a condenser, H.

The process patented by Dewar and Redwood in 1889,2 consists in the use of a suitable still and condenser in free communication with each

B

Fig. 99.

other-i.e., without any valve between them-the space in the still and condenser not occupied by liquid being charged with air, or carbonic acid gas, or other gas, under the required pressure, and the condenser being provided with a regulated outlet for condensed liquid. An objectionable feature of the system of allowing the vapour to escape from the still to the condenser through a loaded valve-viz., the irregularity of the distillation-is thus removed, and the benefits of regular vaporisation and condensation under high pressure are obtained. The ordinary process of cracking, which consists in allowing the less volatile portions of the vapour to become condensed in the stillhead, and fall back into the liquid below, is both slow and comparatively ineffective, besides involving considerable waste of heat, but if desired, the head of the still or retort employed in the DewarRedwood process may be so constructed as to produce partial condensation. The apparatus for carrying out the process may be arranged in various ways, one form being shown in Fig. 100. The lower portion of the figure is a sectional plan on the line XX. A is a fire1 Haddan's patent, No. 1,922. 2 No. 10,277.

place, with fire-door, A1, and ashpit door, 42, suited for regulating admission of air as required. Instead of a fireplace with grate for burning solid fuel, a burner for liquid or gaseous fuel may be employed. Above the combustion chamber, B, is placed a metal retort, C, which is enclosed within a refractory casing, C, to protect the metal from excessive local heating. The encased retort is situated in a heating chamber, B1, into which the hot products of combustion ascend by side

ports, B2, and from which they pass by central ports, B3, into a flue, B4, communicating with a chimney, B5. The front part of the retort, C', communicates freely with a stillhead, C2, provided with a pressuregauge, C3, and safety-valve, C4. The exposed end of the retort, C, is closed by a readily removable cover, C5, provided with a glass gauge to show the level of the liquid in the retort. D is a pipe-coil situated in a tank, D', in which circulation of water is maintained. The upper end of the coil, D, communicates by a pipe with the stillhead, C2, and its lower

end opens into a hollow column, D2, which is provided with a glass gauge, D3, and has at the bottom an outlet pipe, D4, furnished with a stopcock or valve. E is a pump for forcing the oil to be treated, by a pipe, E1, into the retort, C, this pipe preferably extending nearly to the further end of the retort. By another pipe, E2, furnished with a cock or valve, the contents of the retort can be drawn off, or this pipe may communicate with a second retort, which in like manner may be connected with a third, so as to form a series of any required number. F is an air-compressing pump, by which air or suitable gas is forced by a pipe, F1, into the stillhead, C2, or it might be into any other part of the apparatus which is in communication with the stillhead. The retort, C, being partly charged with oil by the pump, E; and the spaces in the retort, C, in the stillhead, C2, and in the condensing coil, D, and the column, D2, being charged with air or gas at the desired pressure; the retort is heated, vaporising the oil under pressure. The oil vapour is condensed in passing through the coil, D, and the liquid distillate collects in the column, D2, and is drawn off, either continuously or intermittently, into suitable receptacles, in which such gas as may be dissolved in the liquid is liberated and can be collected. By a pipe and cock, or a suitably loaded safety-valve, D5, gas may be withdrawn from the space above the liquid in the column, D2. Although only one retort and condenser are shown, there may be several sets of these in communication with the oil and gas pumps, or with each other, suitable cocks or valves being provided in the communicating pipes, so that the several retorts may be worked simultaneously, or in rotation. From time to time, the cover, C5, of the retort may be removed to clear out residue. During the distillation, such of the vapour as may be condensed in the stillhead, C2, or such liquid as may prime up into the stillhead, flows back into the body of liquid in the retort. By regulating the heat and pressure to which the retort is subjected, the character of the distillate may be varied. The proportions of the several parts of the apparatus may be altered, and if necessary, means of cooling may be applied to the stillhead, C2. With such an apparatus, intermediate and heavy oils may be readily converted to a considerable extent into lighter oils suitable for use in ordinary mineral-oil lamps, and even mineral spirit of low boiling point, capable of being employed for the carburetting of coal gas, may be produced.

Fig. 101 shows a cast-iron still used in Russia in carrying out the cracking process. It is in the form of a cast-iron cylinder with a hemispherical bottom, having an outlet, S, provided with a tap, through which the residue may be drawn off. In some cases, distillation is carried to dryness, the coke being then removed through a manhole, D. When superheated steam is employed in the distillation, as is often the case, the coke is of a somewhat soft nature, and does not adhere firmly to the still. The flame from the furnace, passes over a bridge, through a perforated block, N1, through a flue, Z1, round the lower part of the still and through a flue, Z2, round the upper part. By means of dampers, the heat may be diverted from the flue, Z. The crude oil, or residue from a previous distillation,

is placed in the still and heated, at first gently, to volatilise any water present and thus prevent "priming," and then more strongly to distil off the more volatile oils. Finally, the cracking process commences, the heating being regulated by the dampers according as lighter or heavier distillates are obtained. A suitable dephlegmator is used to collect and return or remove the heavy oils which are carried over during the distillation. To save room and time in the preliminary heating, it is usual, when the distillation is nearly completed, to refill the still without removing the residue; but this should not be done too often, or the coke incrustation may become excessive, the distillation being thus retarded, and the still injured by overheating. The dimensions of the still vary considerably, but the height is generally

two or two and a-half times the width.

When the best Scotch iron is used, the thickness of the bottom is 6 to 8 millimetres, while that of the sides is gradually diminished to about 5 millimetres, or less, at the upper edge.

It is only in very few works, and those of a primitive description, that the naphtha, kerosene, and lubricating oil are separated at one distillation. As already stated, it is usual to distil off the two former products, and then to subject the residue to a second distillation at another refinery.

In some cases, lubricating oil is obtained by simple filtration of the residue through steam-heated filters. Such oil is, however, only suitable, as a rule, for use in the lubrication of waggon axles, where

high viscosity, high volatilising point, and low cost are of importance, but its tarry constituents render it unfit for employment as a lubricant for steam engines, machinery, &c.

The use of mineral lubricating oils has only comparatively recently assumed its present importance, the objections formerly urged against this class of lubricants arising partly from prejudice, and partly from the inferior quality of the oils sold. In the earlier stages of develop, ment of the manufacture, the residues were distilled in cast-iron stills, and the lubricating properties of the products thus obtained were injured by over-heating.

The principal improvement consisted in aiding the distillation by the introduction of steam into the still, a device attributed by Veith to von Matscheko, of Austria-Hungary, and by Peckham to Merrill, of the Downer Kerosene Oil Company of America.

66

Although wet" steam may be employed in the distillation of kerosene from crude petroleum, it is useless for the treatment of the residue, because, in order to reach the temperature at which the distillation of this material commences, it would have to be produced at a higher pressure than any still could withstand. In practice, it is, therefore, necessary to employ superheated steam, which may be heated to any desired temperature without increase of pressure. The steam acts by carrying the vapours away to the condenser as fast as they are generated, the injury to the products resulting from their remaining in contact with the highly heated surface of the still being thus prevented.

The petroleum residue from which lubricating oils are prepared, is generally a thick fluid, sometimes semi-solid, dark green to dark brown in colour, and has an empyreumatic odour. It varies in specific gravity within wide limits, and usually has a boiling point of about 300° C. The thick, easily-congealed residues generally contain paraffin, though tarry products are sometimes the cause of their viscidity, while the more fluid residues are usually free from solid hydrocarbons.

On the completion of the first stage of the distillation of crude petroleum, it is not safe to draw off the residue and expose it to the air without preliminary cooling, as there is danger of spontaneous ignition. To avoid this risk, the residue may be run off through a worm passing through a water tank, or, as in Baku, through a crude oil feed-heater.

The cast-iron stills which at first were used in distilling lubricating oils, were found objectionable on account of the thickness of the metal, and have been almost entirely replaced by stills of wrought iron, and the horizontal form has been adopted in preference to the vertical.

In some cases, the air pressure in the still is reduced, in order that the distillation may be effected at the lowest possible temperature, and injury to the products by overheating be thus avoided.

Fig. 102 shows an arrangement adopted in Russia for distillation at atmospheric pressure. A is the oval still, B its dome, and C a condensing pipe formed into a coil, and having taps, at the points 1, 2, 3, for drawing off the condensed oils into three vessels, D, whence