By far the most extensive of the distillation industries is that of petroleum, not to mention the many individual industries distilling petrol eum products. The world's annual produc tion of crude petroleum is about 20,000,000,000 gallons, and except for a relatively small per centage used direct as fuel, practically the whole output passes twice through the still and con denser before it is fitted for use. In the United States alone nearly 14,000,000,000 gallons is thus twice distilled annually. In Scotland some 70, 000,000 gallons of crude oil are obtained annu ually from the oil shales by dry distillation.
The primary distillation of crude petroleum is commonly called refining. The oil is sepa rated by the first distillation into (1) benzine or naphtha, coming over up to a temperature of 300° F.; (2) kerosene, coming over above 300° and up to 570°; and (3) residuum, which in cludes lubricating oils, paraffin wax, vaseline, and pitch or asphalt, according to circumstances. These are again separated before marketing. From the naphtha is obtained gasoline, up to 160°; benzine between 160° and 250° ; and heavy benzine or ((turpentine substitute)) between 250° and 300°.
In the kerosene distillation, gas oil is first separated: it is used to enrich coal gas. After the principal part of the kerosene is distilled, the remainder is paraffin oil, also a burning oil, but with a higher flash-point. The lubricating oils are obtained by distilling the residuum in a vacuum with superheated steam. There are three degrees of these oils : light, medium and heavy. They are caught in three separate dephlegmating condensing tubes through which the vapors are made to pass, the heaviest oil condensing in the tube nearest the still, and the lightest traveling to the furthest tube before it condenses. Vaseline is obtained by carefully distilling certain kinds of crude petroleum in a vacuum still. Other products obtained from petroleum by distillation are paraffin wax, cere sine or earth wax, and a variety of asphalt, be sides pitch and coke.
The distillation of coal-tar is detailed under the title Cont-Tnit Pacmucrs.
The distillation process is employed in can dle-making for the purification of the fatty acids from which the candles are made. The operation takes place in a large copper still heated by a direct fire to about 500° F. Melted fats (after saponification) are run into the still as the operation progresses. Steam, superheated to from 500° to is blown through the liquid mass, and the fats distilled over into copper coils cooled by running water. The palmitic acid comes over first, followed by the stearic and oleic acids as the heat increases. These three fats constitute about 80 to 95 per cent of the whole. The distillate is allowed to cool very slowly for 10 or 12 hours during which time the stearic and palmitic acids crystallize in large crystals, with the oleic acid entangled among them in a liquid form. The °cakes' thus
obtained areput cold under hydraulic pressure of 250 atmospheres, and then again in the Mot') press (temperature, 140°) to remove the oleic acid. The candle fats are then ready for mold ing.
Another important application of the distilla tion process is in the recovery of glycerol (pure glycerine) following the saponification of fats in making soaps and candles. The glycerol re mains in a watery solution after the fatty acids are separated out, and is first concentrated by evaporation to about an 80 per cent solution. This crude glycerol is subjected in a still, in a vacuum of 28 inches, to blowing with dry steam at The first distillate contains volatile organic acids. These are neutralized with soda, and the product again distilled in vacuum. After concentration and reconcentration it is again distilled, and once more concentrated, this time to the standard specific gravity of 1.262. It is then ready for market as ((dynamite extensively used in making high explosives. For medical and food purposes the glycerol is again distilled and clarified.
The manufacture of natural perfumes and essential oils depends largely upon the distilla tion process. In preparing perfumes, the flowers are heated with water in stills, and the steam coming over carries the perfume oil with it. In some instances the perfume oil is dissolved out from the flowers by a volatile solvent like alcohol, ether or benzol, and the solvent then distilled off, leaving the heavier perfume oil. With the essential oils, extraction by pressure sometimes precedes the distillation, as with lemon and orange peel, and other citrus oils. The preliminary treatment with solvents is also used in gaining essential oils, as with celery from the seed), cinnamon, cloves, ginger, etc. The method of extraction by a solvent (bisul phide of or petroleum and sub sequent distillation, is finding favor in a much wider field than formerly. It has been found profitable by this process to extract the oils from the oil-cake residue of the cotton-seed and linseed oil presses, and it is used also at first hand in gaining the oils from poppy seed, rape seed, castor oil beans, copra, palm kernels, pumpkin seeds, grape seeds, and the like. It has also been successfully used to extract olive oil from the residuum of the olive oil presses. The solvent is used over and over again in a continuous still which is almost automatic, re quiring a minimum of attention, and in the case of the recovery of oil from oil-cake, the oil meal residue is as greedily eaten by cattle as the original oil-cake. This process has made it possible to recover much oil which has here tofore been sacrificed if not altogether wasted.