Production
Rosin is the resinous constituent of the oleo-resin exuded by various species of pine, known in commerce as crude turpentine. The separation of the oleo-resin into the essential oil (spirit of turpentine) and common rosin is accomplished by distillation in large copper stills. The essential oil is carried off at a temperature of between 100° and 160°C, leaving fluid rosin, which is run off through a tap at the bottom of the still, and purified by passing through straining wadding. Rosin varies in color, according to the age of the tree from which the turpentine is drawn and the degree of heat applied in distillation, from an opaque, almost pitch-black substance through grades of brown and yellow to an almost perfectly transparent colorless glassy mass. The commercial grades are numerous, ranging by letters from A, the darkest, to N, extra pale, superior to which are W, window glass, and WW, water white varieties, the latter having about three times the value of the common qualities.
Tall oil rosin is produced during the distillation of crude tall oil, a by-product of the kraft paper making process.
Rosin may be obtained from aged pine stumps. This type of rosin is typically called wood rosin. In this process, stumps and roots are chipped and soaked in the light end of the heavy naphtha fraction (boiling between 90° C and 115° C) from a crude oil refinery. Multi-stage counter-current extraction is commonly used so fresh naphtha first contacts wood leached in intermediate stages and naphtha laden with rosin from intermediate stages contacts unleached wood before vacuum distillation to recover naphtha from the rosin, fatty acids, turpentine, and other constituents later separated through steam distillation. Leached wood is steamed for additional naphtha recovery prior to burning for energy recovery.
On a large scale, rosin is treated by destructive distillation for the production of rosin spirit, pinoline and rosin oil. The last enters into the composition of some of the solid lubricating greases, and is also used as an adulterant of other oils.
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