Paraffin

Paraffin (so called as being parum affinis—i.e. having little affinity—for an alkali) is a name given by Baron Reichenbach (q.v.) to a white transparent crystalline substance first obtained by him in 1830 from wood-tar. The honour of this discovery must be shared with Christison of Edinburgh, who independently and almost simultaneously obtained the same body in making a chemical examination of Rangoon petroleum, and which he named petroline. Dumas, a French chemist, obtained it also from coal-tar in 1835. But for twenty years after its discovery paraffin-wax remained a chemical curiosity only. It was not till 1850 that it began to be produced, by Mr James Young, in quantity sufficient to occupy the attention of manufacturers. Since then it has become of great importance commercially, and has for years been the principal material employed in the manufacture of candles in Great Britain and Germany, having for that purpose, to a large extent, superseded the use of beeswax, spermaceti, stearic acid, and tallow, besides being used in many other branches of the arts and manufactures, and in surgery.

The word paraffin, at first applied by Reichenbach to the solid body, is now used by chemists as a generic term for the series of saturated Hydrocarbons (q.v.), the higher members of which are paraffin-wax, lower members are liquid, and the lowest are gases; marsh-gas or firedamp being lowest of all. Paraffin-oil was the term first employed by Mr Young to denominate the mineral burning oils produced by him, and this name still applies in Britain to all the oils associated with the manufacture of paraffin. In these oils, however, the olefine series of non-saturated hydrocarbons is largely represented along with liquid paraffins. But Petroleum (q.v.) is the term in general use to designate the natural oils of America, Russia, and other countries, which are for the most part mixtures of these same two series of hydrocarbons. As the production of paraffin-wax and paraffin-oils has now become an industry of great importance to the world, it will be convenient to make some reference here to the history of its development, particularly in Scotland, which is now the seat of the industry. To a comparatively limited extent coal and shale or schist are made use of in Germany, in France, in Italy, and in Australia for the production of hydrocarbon oils.

In December 1847 Mr James Young received a letter from Dr (afterwards Lord) Playfair, calling his attention to a dark oily liquid found in a coal-mine at Alfreton in Derbyshire. On examining this oil Mr Young recognised the commercial importance of the products that could be obtained from it. He erected a refinery, and produced a light oil for burning, a heavy oil for lubricating, and paraffin-wax. This petroleum spring, at first producing about 300 gallons per day, had exhausted itself at the end of two years. Meanwhile, Mr Young, reflecting on the probable origin of the oil, and after a series of experiments, succeeded in distilling at a low heat an analogous oil from coal. This process became the subject of his celebrated patent obtained in 1850. Works were erected at Bathgate, in Scotland, in which neighbourhood a highly bituminous cannel coal was at that time being mined for gas-making. It was known as Torbanelhill Mineral or Boghead Coal (q.v.). This mineral was employed by Mr Young, and it yielded under distillation about 120 gallons of crude oil per ton. In 1851, when the Bathgate oil-works were started, the price of this coal was 13s. 6d. per ton, and it gradually rose, till in 1862 it stood at 90s. per ton, when the supply ceased. Mr Young's patent, which covered the distillation of oil from coal at a low red heat, ran from 1850 to 1864. In 1859, however, Mr Robert Bell erected oil-works at Broxburn (q.v.), in which he distilled oil from shale. He was the first in Scotland to use this material, although Du Buisson had obtained a patent in France previous to 1850 for the distillation of schist or shale. Since 1862 this mineral has been, and now is, the only mineral employed in Scotland for oil-making. Soon after Mr Young obtained his patent in 1850 he granted licenses for its use in the United States of America, where oil for several years was distilled from cannel-coal; but public attention being thereby directed to the natural petroleum which have since been found in such abundance, the use of cannel-coal was discontinued. Mr Young was thus the pioneer not only of the paraffin-oil manufacture, but also of the petroleum industries of the world.

During the progress of the shale-oil industry in Scotland it has been frequently subject to serious vicissitudes of fortune, more than once being threatened with extinction. During one of those periods of depression about 1872 the Welsh coal-oil trade collapsed entirely. The Scotch industry was saved from a similar fate by the energy and inventive resource of some of the persons engaged in it. The history of the trade naturally falls into various periods, and during these periods articles of manufacture that were considered by-products, and regarded of little value, or for which there was no market, and products which for years were even unknown came to be of prime importance in the life of the trade. The first period was a brief one (1848–50), when Mr Young utilised the petroleum-spring at Alfreton for the production mainly of lubricating oil, used in mills as a substitute for sperm-oil. The second period extended over the duration of Young's patent (1850–64), when the burning oil had become of the greatest importance to the manufacturer. The third period (1864–72) witnessed the great development of the petroleum trade in America, during which the price of burning oil fell so low that about half of the works in Scotland were closed. The fourth period (1872–78) was a period of severe struggle for existence. The smaller and weaker works disappeared. The production became concentrated in fewer hands with larger outputs. Burning oil being now less remunerative, the utmost attention was paid to the recovery of all waste-products and to the development of the by-products; paraffin-wax and sulphate of ammonia then becoming of chief importance to the manufacturer. Fortunately also the inventive genius, principally of N. M. Henderson, of William Young, and George T. Beilby, and others stimulated by necessity, culminated in the production of new and economical processes whereby manufacturing costs were reduced, and the yield of the products that had now become of most value were much increased. The fifth period (1878–87) was in consequence a time of much prosperity, ending, however, in a partial collapse by reason of over-production in Scotland combined with ever-increasing imports of wax from America. The sixth period, for a few years from 1887, was a period of combination, the Scotch and American producers having combined to restrict the supplies of paraffin-wax. After 1894 the Scotch companies suffered again from American (and also Russian) competition.

Geologically, the position of the shale in the east of Scotland is in the Lower Carboniferous series, but in the west of Scotland it is found in the ordinary coal-measures. There are some seven or eight different seams of shale, all varying in position and quality from each other; but the same shale also varies from its normal character in different districts, being thick and rich in one place, and thin and poor in another. The Broxburn seam of shale at its best is probably the richest and most profitable quality to work; but the Pumperston seams of shale, though poor in oil, have now become of value, because they are rich in ammonia. The shale is procured in the same manner as in coal-mining.

The following summaries will indicate the material facts in the history of the trade in Scotland, and the direction and extent to which the improved processes have tended—viz. diminished yield of burning oils, increased yield of lubricating oils, paraffin-wax, and sulphate of ammonia, together with reduction of loss in process of manufacture.

SHOWING PERCENTAGE OF PRODUCTS UNDER THE OLD AND NEW SYSTEMS OF WORKING.

The first most notable improvement was the Henderson retort, patented by N. M. Henderson in 1873. With this retort the spent shale off which the oil had been distilled, and which still contained about 12 per cent. of carbon, was allowed to descend into the furnace beneath the retort to serve as fuel in the distillation of fresh charges of shale. This effected a great saving of coal and labour, and, on account of mild temperature produced with regularity, there was increased yield of products of better quality and more easily refined.

In 1882 Mr William Young and Mr George T. Beilby, combining the results of their experiments, patented a new retort. It is a combination of two retorts; in the upper one the ordinary oil-products are distilled off, after which the shale is allowed to fall into a firebrick retort below, where a higher heat is employed and in which it is exposed to a current of steam and air; this method gives a greatly increased yield of ammonia; and it is therefore a form of retort of the utmost value in the case of shales rich in nitrogenous and poor in bituminous products.

This was followed in 1883 by Mr Henderson's continuous distillation process, in which the crude oil passes by gravitation through three stills. During the progress of the oil through these stills the fractionation or separation of the crude oil into naphtha, burning oil, and heavy or lubricating oil containing paraffin takes place automatically. In addition to these three stills there are two or more coking stills into which alternately the residue of the crude oil flows and where the distillation is completed, the dry coke being removed from each at regular intervals. The advantages obtained from this process are saving in first cost of plant, saving of labour, time, and fuel; less cost of maintenance; the fractionation of the oil is more perfect and uniform, and the distillates purer, giving less loss in refining. Mr Henderson also, by a patented process, greatly simplified and cheapened the cost of the production of sulphate of ammonia. And his new methods of refrigeration and refinement of the crude paraffin scale increased the yield of wax and improved the quality of the lubricating oils.

In the distillation of bituminous minerals for the production of gas a bright-red heat is employed in order to obtain as much incondensable vapour or permanent gas as possible. The aim of the oil-manufacturer on the contrary is to minimise the production of incondensable gas, and to obtain the highest percentage possible of the liquid and solid hydrocarbons. He therefore reduces the distillation temperature to the lowest practicable point—viz. from 600° to 800° F.

Crude oil is composed of a very wide range of hydrocarbons, each varying in specific gravity and boiling-point and in the percentage of carbon present; but in the practical operations of the refiner the fractionation of the oil is confined within certain definite limits which have been found of most convenience commercially—viz. Naphtha, specific gravity, 680 to 750 (water = 1000); volatile at ordinary temperatures; the highest portions are used for carburetting air gas; the heavier portions are principally used as solvents. Burning oils—(a) for domestic use; specific gravity, 800 to 805; flash-point, Abel test, about 100° F. (b) Lighthouse oil, specific gravity, 810 to 815; flash-point, Abel test, about 150° F. (c) High Test oils, specific gravity, 830 to 840; flash-point, Abel test, about 240° F.; used in special lamps for lighting railway-carrages and in ships. Lubricating oils: These are made of various standard specific gravities—viz. 865, 875, 885, 890–5. They are used principally for mixing with animal and vegetable oils in the preparation of lubricants. Paraffin-wax, with melting-points varying from 80° to 130° F. The soft wax from 80° to 100° is employed instead of sulphur in the preparation of ordinary safety-matches, while the harder qualities are manufactured into candles.

The operations in the production and refinement of mineral-oil products stated briefly are: The shale when taken from the pits is broken into small pieces and put into the retorts. In the retort the first chemical process, destructive distillation, takes place. The various products of the oil-works do not exist as such in the shale; they are all created by its destructive distillation. The shale, according to quality, yields from 20 to 40 gallons of crude oil per ton, and over 60 gallons of ammonia water. This water, now such a valuable product to the oil-manufacturer, was allowed for years to go to waste; but in 1864 was for the first time utilised by Mr Bell, who recovered ammonia from it in the form of sulphate.

The operations of the oil-refinery are: (1) distillation, (2) treatment with chemicals, (3) cooling and pressing the heavy oil containing paraffin so as to separate the solid hydrocarbons from the liquid. The oils are distilled several times and are fractionated into the various qualities required; and between each distillation the oil is treated with oil of vitriol and with caustic soda. After the finishing treatment with acid and soda some of the soda compounds are retained in solution by the oil; these have to be carefully removed by washing with water. The absence of acid and alkaline compounds, and thorough fractionation of the oil, are the great secrets in the refining of burning oils; and at some of the works in Scotland the best burning oils that can be obtained are now produced, and the safety of the Scotch oils can be relied upon. In lubricating oils the essential features are high viscosity, high flash-point, and low setting-point. The first two depend on proper fractionation; and the third is secured by careful refrigeration, so that the lowest forms of solid paraffin may be crystallised and separated from the oil.

The crude paraffin scale or wax is refined either by chemicals, by sweating, or by treatment with naphtha. The chemical treatment is seldom used, the greater portion being purified under the sweating process, which is simple and effective. The temperature of the sweating-chamber is raised from $2^\{\backslash circ\}$ to $3^\{\backslash circ\}$ above the setting-point of the paraffin required; the oil then drains off, carrying most of the other impurities with it. But the best qualities of refined paraffin require a treatment or two with shale naphtha. The paraffin is melted, and about 30 per cent. of spirit run in, and after careful stirring together the mixture is allowed to cool down; it is then pressed, when the naphtha runs out, taking the colouring matter with it. This pressed paraffin is again melted and steam blown through it, which carries off the remainder of the naphtha, and finally the melted paraffin is stirred with animal charcoal, settled, and then filtered through cloth and filter-paper, and run into pans to solidify into cakes of convenient size for the candle-maker. See CANDLE, HYDROCARBONS, WAX.