Page:EB1911 - Volume 20.djvu/811

Rh 0-770, constitutes the crude naphtha, and that up to a density of 0850 the burning oil. The remainder of the distillate, which solidifies at common temperatures, consists chiefly of lubricating oils and paraffin. These three fractions are delivered from the condensers into separate tanks. Although the crudeoil stiUs of Henderson may be employed for the continuous distillation of the once-run or other oils obtained in the process of refining, the inventor prefers another form of apparatus which he patented in 1883 (No. 540), and this is now generally used. This consists of three horizontal cylindrical stills, 7 ft. in diameter and 19 ft. in length. The oil enters through a pipe which passes through one end of the still and discharges at the opposite end, while the outlet-pipe is fitted below the inlet-pipe at the bottom of the end through which the latter passes, inlet and discharge being thus as far as possible from each other. The oil circulates as in the crude-oil stills. The burning oil is next treated with acid and alkali, and subsequently again fractionally distilled, the heavier portion yielding paraffin scale, while the residues are re distilled. The final chemical purification of the burning oil resembles that last referred to, but only half the quantity of acid is employed. The lighter products of these distillations form the crude shale naphtha, which is treated with acid and alkali, and re distilled, when the lightest fractions constitute the Scotch " gasoline " of commerce, and the remainder is known as " naphtha."

The solid paraffin, which is known in its crude state as paraffin scale, was formerly produced from the heavy oil obtained in the first, second and third distillations, that from the first giving " hard scale, " whOe those from the second and third gave " soft scale." The hard scale was crystallized out in shallow tanks, and the contained oil driven out by compression of the paraffin in filter bags. Soft scale was obtained by refrigeration, cooled revolving drums being caused to dip into trays containing the oil, when the paraffin adhered to the drums and was scraped off by a mechanical contrivance. Later improved appliances have aimed at the slow cooling of oil in bulk, whereby large crystals of paraffin are produced. Several processes have been invented, the most generally used being that patented by Henderson (No. 9557 of 1884). His cooler consists of a jacketed trough having a curved bottom, and divided into a series of transverse casings by metal disks, each consisting of two thin plates bolted together, but with a space between, in which, as also in the jacket surrounding the trough, cold brine is circulated. The paraffin crystallizes on the cold surfaces, from which it is constantly removed by scrapers, so that successive portions of the oil are cooled. The solid paraffin accumulates in a well or channel, where it is stirred up by rotary arms, so that it may be readily drawn away by a pump to the filter-press, whereby the solid paraffin is freed from oil. In the improved process of cooling employed at the works of the Oakbank Oil Company the oil to be cooled is pumped through coils submerged in the expressed oil from the filter-presses into the inner space of vertical coolers formed of two cast-iron tubes, and thence direct to the filter-presses. In the inner chamber of the coolers are fitted revolving scrapers, while in the outer annular space compressed ammonia is expanded.

The crude paraffin is then refined, for which purpose the " naphtha treatment " was formerly employed, but this has now given place almost entirely to the " sweating process." In the former the paraffin is dissolved in naphtha and then crystallized out. The sweating process consists in heating the crude wax to such a temperature that the softer portions are melted and flow away with the oil. In the process patented by N. M. Henderson (Nos. 1291 of 1887 and 11,799 of 1891), a chamber, 52 ft. by 13 ft. by 10 ft. high, heated by steam-pipes, and provided with large doors and ventilators for cooling, is fitted with a number of superimposed trays, 21 ft. by 6 ft. by 6 in. deep. These rest on transverse heating pipes, and each tray has a diaphragm of wire gauze. The bottoms communicate with short pipes fitted with swivel nozzles, worked on a vertical shaft. The diaphragms are covered with 5 in. of water, and the crude paraffin is melted and pumped through charging-pipes

on to its surface. When the paraffin has solidified, the water is drawn off, leaving the cake resting on the gauze. Doors and ventilators are then closed, and the chamber is heated, whereupon the liquefied impurities are drained off until the outflowing paraffin sets on a thermometer bulb at 130° F. The remainder is melted and decolonized by agitation with finely powdered charcoal. The charcoal is mainly separated by subsidence, and the paraffin drawn off into filters, whence, freed from the suspended charcoal, it runs into moulds, and is thus formed into cakes of suitable size for packing. The lubricating oils are refined by the use of sulphuric acid and alkali, substantially in the same manner as the burning oils.

The following table shows the average yield, in 1895, of the various commercial products from crude shale-oil at two of the principal Scottish refineries. The percentages are, however, often varied to suit market requirements:-

Young's Paraffin Light and Mineral Oil Co.

%

Gasoline and naphtha 6-09

Burning oils 31 '84

Intermediate and heavy oils 23 97

Paraffin scale '3'53

Total

Loss

Broxburn Oil Co.

Naphtha

Burning oil 30-0

Gas oil g-o

Lubricating oil

Paraffin

Loss

75-43

24-57

lOO-OO

3-0

39-0

i8-o

lO-O

30-0

From the ammonia cal liquor the ammonia is driven off by the application of heat in stills, the evolved vapour being conducted into " cracker-boxes, " which are now usually of circular form, from 5 to 8 in. in diameter, and 6 to 12 in. in depth. In these boxes the ammonia is brought into contact with sulphuric acid of about 50° Tw., and is thus converted into sulphate. Wilton's form of cracker-box, which is now generally in use, is provided with an arrangement for the automatic discharge on to a drying table of the sulphate of ammonia as it is deposited in the well of the box, and the process is worked continuously. For the heating of the ammonia cal liquor the ordinary horizontal boiler-stills formerly used have been superseded by " column stills, in which the liquor is exposed over a large area, as it passes from top to bottom of the still, to the action of a current of steam. (B. R.)

Paraffin, in chemistry, the generic name given to the hydrocarbons of the general formula C„H2r+2- Many of these hydrocarbons exist as naturally occurring products, the lower (gaseous) members of the series being met with as exhalations from decaying organic matter, or issuing from fissures in the earth; and the higher members of the series occur in petroleum (chiefly American) and ozokerite. They may be synthesized by reducing the alkyl halides (preferably the iodides) with nascent hydrogen, using either sodium amalgam, zinc and hydrochloric acid, concentrated hydriodic acid (Berthelot, Jour. prak. Chetn. 1868, 104, p. 103), aluminium amalgam (H. Wislicenus, ibid., 1896 (2), 54) or the zinc-copper couple (J. H. Gladstone and A. Tribe, Ber., 1873, 6, p. 202 seq.) as reducing agents.

They may also be derived from alkyl halides by heating to 120-140° with aluminium chloride in the proportion of three molecules of alkyl halide to one molecule of aluminium chloride (B. Kohnlein, Ber., 1 883, 16, p. 560); by heating with zinc and water to 150-160° C. (E. Frankland, A7m., 1849, 71, p. 203; 1850, 74, p. 41), 2 RI+2Zn-|-2HjO = 2RH-|-Znl2-|-Zn(OH)2; by conversion into zinc alkyls, which are then decomposed by water, ZnR2-|-2H20 = 2 RH-t-Zn(0H)2; by conversion into the Grignard reagent with metallic magnesium and decomposition of this either by water, dilute acids or preferably ammonium chloride (J. Houben, Ber., 1905, 38, p. 3019), RMgl-f-H20 = RH -f Mgl(OH); by the action of potassium hydride (H. Moissan, Comptes rendus, 1902, 134, p. 389); and by the action