Dewaxing is a process aimed at reducing the content of saturated hydrocarbons of predominantly normal structure in oil. Dewaxing can improve the performance properties of petroleum oils by lowering their viscosity and pour point.
A variety of dewaxing methods may be implemented:
- Low-temperature crystallization;
- Urea dewaxing;
- Adsorption dewaxing.
In most cases viscous oil dewaxing is conducted by means of low-temperature crystallization in selective solvents or binary solvents. They dissolve paraffins poorly and at the same time they dissolve other oil components rather well. For separation of solid hydrocarbons, oil filtration or centrifuging process is used, whereas the solvent is removed from hydrocarbons by distillation.
For dewaxing of low-viscosity oil, carbamide must be applied. It forms clathrates with normal paraffin hydrocarbons. They are separated by means of sedimentation, oil filtration or centrifugation, after which they are washed and decomposed into constituent components by heating in an aqueous medium. In order to distill the solvent, the product of dewaxing is fed into a special column.
Adsorption dewaxing is used mainly for kerosene gas-oil fractions. The process requires usage of the so-called molecular sieves (zeolites) capable of selective adsorption of normal paraffin hydrocarbons. For desorption of the absorbed components special propellants are used (H3, H2O, hexane, etc.).
Products that have been separated during dewaxing may be used in production of lubricating greases, packaging and insulating materials, additives, plasticizers, etc.
Dewaxing is also used in oil production in order to remove wax from pipes intended for pumping oil from reservoirs. In this case, removal of paraffin deposits is carried out by means of chemical agents, electric current, hot steam, etc.