What Is Solvent Distillation?
Purifying spent solvents by batch distillation is accomplished by putting the waste into the still. Heat is added to bring the solution to a boil. Only the constituents with a boiling point (BP) lower than the set point on the equipment will change into a vapor state. Constituents with a higher boiling point will remain in the bottom of the still (still bottoms). The solvent that has transitioned to the vapor phase comes in contact with refrigerated condensing coils that transform the vapor into a pure liquid solvent. The pure solvent is packaged and ready to go back to the industry for industrial uses.
For example, acetone boils at 132.8F, toluene boils at 231F, and isopropanol boils at 180F. If you have a blend of those three solvents and the recovery still has the max temperature set at 250F, only those three constituents will transform into a vapor state. Other constituents, such as Stoddard solvent, with a BP of 300F, oil with a BP of 800F, and solids, will become still bottoms.
When the maximum temperature of 250F is reached, the machine turns off, and the still bottoms are removed. The still bottoms go to the fuel blending area to be blended into an alternative fuel.
Everything is used; nothing is wasted.
