Solvent Dewaxing - Pour Point Control

Conventional solvent dewaxing is an energy- and cost-intensive process, and you therefore want to operate on the fewest number of moleeules consistent with a high product yield. Therefore you do extraction first to remove the non-lubes molecules and you do dewaxing last on the raffinate. But you optimize the total OPEX per volume through the entire process. If somehow it made better economics to do the DWX first, even though it is expensive, you would do it that way. 

The primary goal of solvent dewaxing is to make the pour and cloud point requirements. This is accomplished by paraffin separation by solubility of non-paraffins in cold solvent, fractional crystallization, and filtering the solid paraffins from the slurry. This may be done in ketone units which use MEK, MEK/MIBK, MEK/Toluene solvents or in propane units which use liquefied propane as the solvent. Secondary effects include viscosity increase, density increase, sulfur increase, and reduction in VI. 

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