PARAFFIN, the term given to a mineral wax and also used as a generic name for a particular series of hydrocarbons. Refined commercial paraffin is a white, translucent, waxy solid devoid of taste and smell and characterized by chemical indifference. The industry owes its origin to Dr. James Young, who in 185o applied for his patent "to obtain . . . paraffin from bituminous shales" by slow distillation. To-day, paraffin is obtained from the many crude petroleums that are designated "paraffin-base oils" because of their wax content. The wax-bearing crudes of America con tain on the average less than 5%, those of Galicia about 6%, the oils of Burma o% and Scottish shale oil about 13% of mer chantable wax.
Manufacture.—The manufacture of paraffin by modern methods falls under two heads. Firstly the distillation of the crude oil and secondly the extraction of wax from the distillate.
A process that has become almost conventional starts with crude oil and brings about by continuous distillation the removal of petrol and kerosene, leaving what may be called a "topped" oil.
In the majority of cases this topped oil contains heavy oil, such as gas oil, that is used for enriching water-gas in the gas works, lubricating oils, wax and pitch, as is clearly shown in the above diagram. This residue oil is again distilled con tinuously and run down to heavy kerosene, gas oil, wax distillates and pitch. In molt recent practice the distillation is carried out in a pipe-still through which the oil passes at high velocity under pressure and is discharged as vapour into a fractionating column. From the top of the column may be easily obtained an overhead distillate, e.g., petrol, and at various "decks" or trays at different distances from the top may be withdrawn fractions of higher and higher boiling point. But, in the majority of cases the wax dis tillates are of two kinds, known as crystalline or pressable and amorphous or non-pressable. As will be seen later, this difference is probably a function of the crystal size.
Crystalline (or Pressable) Wax Distillate.—This material in effect is a mixture of crude lubricating oils and crystalline paraffin hydrocarbons that possess no lubricating power what ever. It is necessary to remove the wax firstly because of this
lack of ability for lubrication and secondly because the high melt ing point of wax would render the lubricating oils solid or semi-solid at ordinary temperatures, and thirdly because of the market value of the wax. This wax distillate, then, is passed on to the paraffin sheds, as the extraction plant is usually termed, and is allowed to repose in tanks to promote thorough settling and the maximum reduction in temperature. It is then transferred to plant in which it can be cooled artificially to any particular temperature required. The refrigerating plants that achieve this cooling usually depend for their effect on the expansion of liquid ammonia or liquid carbonic acid gas. In modern practice heat exchangers are used so that the cold filtrate from the filter-presses can be employed further to chill the incoming wax distillate to the refrigerators. It is frequently convenient to cool the wax distillate in two stages, but this procedure depends largely on the content of wax and its nature. There have been devised many types of cooling apparatus of which that patented by James Bryson of Scottish Oils Ltd., is typical. This type consists of an inner cylinder in which the wax distillate passes and which is provided with a scraper. The cylinder is surrounded by a concentric casing through which cold brine is circulated after having been chilled by contact with pipes in which the refrigerant is being evaporated.