The name Hybrid Wiped-Film Distillation refers to a combination of the low thermal stress processing of Wiped-Film Distillation with the separation capabilities of a Packed Fractionating Column.
The Wiped-Film acts as a once-through, low thermal stress, low hold-up, partial reboiler for the distillation. The appropriate size and surface area of the Wiped Film Evaporator is determined by scale-up calculations based on distillation Pilot Plant trials.
The important parameters for operation of the Wiped-Film Evaporator are:
- Constant, controlled feed rate
- Steady vacuum level
- Steady evaporator temperature
The bottom of the Packed Fractionating Column is connected to the vapor arm of the Wiped-Film Evaporator, and is filled with column packing of a variety of commercially available distillation column packing types.
The diameter of the column is chosen based on the feed rate to the system, and the height of the packed column is chosen according to the number of theoretical plates needed for the desired separation. The diameter and column height are critical design parameters.
Sufficient theoretical plates, as determined by the depth of the packing in the column, must be used for a successful separation, but a large excess of column height will cause too much pressure drop, thereby raising the pressure in the reboiler, and thus require a higher reboiler temperature for the desired boil-up for the column. The higher required temperature can cause thermal degradation of the material being processed. A properly designed column balances the number of theoretical plates needed for the separation against the resulting pressure drop to enable the desired separation.
The column diameter needs to be appropriately designed to handle the desired boil-up. A column that is too small in diameter will flood at the desired distillation rate. A column that is too large in diameter will not allow sufficient contact between the vapor and liquid in the column and will give a very inefficient separation.
The condensed liquid from the overhead condenser is split into two streams by a three-way valve, using a timer to control the ratio of distillate take-off vs. reflux returned to the column. The proper reflux rate must be determined to allow the required energy exchange between vapor and liquid, and cause the enrichment of the light key component(s) at the top of the column.
A few examples of applications successfully developed on a Hybrid Wiped-Film Distillation System are:
- Omega-3 concentration and separation
- Flavor component purification
- Fragrance component purification
- Nutritional Supplement purification
- Fatty Acid fractionating
- Fatty Acid Ester fractionating
- Terpenoid separation from natural oils
- Many other temperature sensitive separations