REFINING. The refining of petroleum.i. based upon the separation of the component hydrocar bons by a process of fractional distillation. This is usually carried out in horizontal cylindrical iron stills, which are surmounted by a dome that connects with a vapor pipe. A common size of still is 30 feet long by feet in diameter. with a capacity of from 050 to 7(10 barrels of crude oil. When the latter is placed in the still and sub jected to increasing temperature, the oils pass off in the order of their volatility; the separation is not absolutely perfect, however• a. oils of lower boiling point may carry over some higher ones. As the vapor• rises it passes to the condenser, a series of iron pipes surrounded by cold water. The distillates are led off into their respective tanks. This process of distillation. which is known as the intermittent system, is the one commonly followed in the United States, and the still requires periodic refilling. In Russia a con tinuous system is employed, involving a series of stills, which are heated to successively higher temperatures. The crude oil then flows slowly from one 1.0 the other, and from each one there passes off the tailatilizing at the tempera ture to which the still is heated.
The process of fractional distillation can he di vided into two parts. In the first part of the process the more volatile products. such as gaso line and other naphthas, are evolved, The resi due is then transferred to another still in which the second part of the operation is carried OD, the oil being heated to a still higher temperature for the purpose of separating the uJunBoating and lubricating oils. The condensing apparatus ends in the tail hon.e, where the distillates are c•onductedl to their proper tanks. When the va rious fraction• of the distillation are to be kept separate, and of constant composition, a special form of condenser may be used. by means of is brought into contact with the surface of iron turning., thereby increasing the evaporation. If the oil contains sulphur it is
necessary tee redist il it in stills containing copper oxide, which removes the sulphr. Crocking is a term used to denote the pnwess of emidensing the heavier vapors in the still, causing them to become superheated and deeomposed, and thus ob taining a more complete separation of the frac tions. a. \Act] as increasing the percentage of illu minating oil. In the distillation 44 the oil the lightest eonstituents pass off first and the heav iest last. The fractions obtained in the their light mss: are the following 4 is the of all. and since its boning Ant is :t2 F.. it is a gas at ordinary tempera tore.. Rhiqolr ne. Boiling point, 6.5' F. tro b um Olu r, A higlrlv volatile product having a specific gravity of ftn:13. It has sometimes been called Sherwood oil. (bt.,o/ito.. This. properly -peaking. is the fraction following petroleum ether. although the name is often applied to a mixture of this and the three preyious ones. its gravity thus ranging. from 0.033 to 0.090. In prop( r the point from '90° to •'410 F, ..\lopiatila is at name broadly applied to all distillates. but more espeeially to those at so to 120' F., whose va ries !row low as 02 11, tip to 75' B. Bcoa:ine represents the least volatile product of time naphthas has a specific of about 0.73 (37' to (12' 11.I, and a point of 120° to ISO° F. Ligroine forms a spe'c'ial of solvent naphtha of a specific of 0.715. and a boil ing point of Int' to F. the naphthas come the oils, di vided into heavy and extra heavy naphthas: in the process of distillation these may either lie car ried separately or In the former case, the heavy naphthas may he redistilled and separated into benzine and distillate. The latter may then he mixed with the extra heart' naphthas in proportions to form white oil or export oil. There are many of do mestic. illuminating oil or kerosene, which differ chiefly in tire test.