Steam distillation is generally used for distillation at atmospheric pressure boiling point is relatively high, or at the boiling point of distillation easy to decompose the material, is also commonly used in the separation of volatile components and volatile components. Turpentine processing is the use of steam distillation, from the fat liquid evaporated volatile turpentine, and residual volatile rosin.
If direct distillation is used in rosin processing, when the boiling point of the rosin liquid is 179 ℃, the rosin content in the resin liquid is 70%; When the boiling point of the lipid liquid rises to 195 ℃, the rosin content in the lipid liquid reaches 85%. To distill the remaining turpentine from the lipid liquid, the distillation temperature must be greatly increased, which not only increases the cost, but also deepens the color of the produced rosin, even local cracking, quality is not guaranteed.
The use of steam distillation can reduce the distillation temperature, because turpentine and water are two immiscible liquids in the same distillation pot, heated by a closed steam pipe or jacket, the two liquids are heated and vaporized at the same time, then the total vapor pressure on the surface of the mixture is equal to the sum of the vapor pressures of the components at this temperature. If steam distillation is carried out at one atmospheric pressure, the mixture will boil as long as the sum of the vapor pressures of the two components in the mixture reaches one atmospheric pressure. At this time, its boiling point is lower than the boiling point of any component, I .e. lower than the boiling point of water at atmospheric pressure and lower than the boiling point of the main component in turpentine at atmospheric pressure.
In the processing of turpentine, dripping water or passing live steam is to produce water vapor and carry out water vapor distillation. In steam distillation, when the temperature of water and turpentine reaches 95.6 ℃, the sum of its vapor pressure is 760 mmHg, which is equal to the external pressure, and the mixture boils to evaporate turpentine. Therefore, steam distillation can reduce the distillation temperature, but also can steam out turpentine, to ensure the quality of the product, to avoid the shortcomings of direct steaming oil.