Distillates leaving the vacuum distillation unit contain such significant quantities of wax that they are solid at room temperature. Removal of the wax from the lubricating base oil is necessary for the base stocks to have the required low temperature properties. The Bechtel Hydrocarbon Technology Solutions (BHTS) solvent dewaxing process uses a mixture of MEK and toluene to aid in the crystallization and filtration of wax from the lube oil stocks.
Several recent developments have led to improved filtration rates, energy efficiency, water management, and operability of solvent dewaxing units. These include:
- Improved chilling and dilution techniques, including tailoring the chilling and dilution strategy for each individual stock
- Multiple effect evaporation for solvent recovery, significantly lowering the energy consumption of the process
- Use of inert gas instead of steam for stripping the dewaxed oil and wax products
- Automatic control of filter hot wash procedure
- Cold solvent backwashing to replace frequent hot solvent backwashing of the filters