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Home > Wiped Film Stills |
| Wiped Film Stills |
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| The Molecular Background |
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Wiped-Film still technology takes advantage of the fact that each chemical substance has a characteristic vapor pressure. It is this relative difference in vapor pressures which dictates how easily a complex compound can be separated into its constituent components.
Since the molecules of all matter are in constant motion in varying degrees, depending upon the chemical composition of that matter and the temperature and pressure applied to it, molecules near the surface have a tendency to escape into the surrounding atmosphere. As temperature increases and pressure decreases, this escaping tendency usually increases and the substance is said to vaporize.
The force generated by these escaping molecules is referred to as the vapor pressure of that material at a particular temperature and pressure. It is the relative difference in vapor pressure of substances which dictates how easily a complex compound can be separated into its constituent compounds. |
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| Molecules Escaping from Solution |
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| Brief Operating Description |
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The Pope Wiped-Film Still consists of a heated body into which a fluid system requiring some degree of separation is continuously fed. The fluid is spread into a thin film by a rotating wiper blade assembly driven at a predetermined speed. The film, while being forced into turbulent flow by the wiper blades, progresses down the inside body wall aided by gravity and the slots in the wiper blades.
During the course of flow through the heater system, some degree of evaporation takes place depending upon the characteristics of the feed material and the inside wall temperature, in addition to the system pressure. The non evaporated fluid forming the bottom product flows out of the system continuously while the vapor is condensed either inside or outside the system depending on the type of design. |
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Basic evaporation and condensation |
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| Why Thin Films? |
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Thin films are created in Pope Wiped-Film Stills for a variety of reasons:
- Turbulence created by a rapidly moving wiper or controlled clearance blade greatly assists in heat
transmission, thereby lowering the temperature required on the inside evaporator wall for a given system pressure.
- A maximum surface area per unit volume of flow is generated facilitating rapid evaporation
- The liquid exposure time to the elevated wall temperature can be controlled within seconds or
less. This minimizes product degradation of heat sensitive materials by controlling the wiper assembly speed.
- High viscosity materials can be transported through the system for distillation or solvent stripping.
- Pope slotted wiper blades promote plug flow with little back mixing. This minimizes dwell time
distribution, ensuring that material flowing through the system has a uniform exposure to process conditions.
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| Wiper blade moves each plug of material downward |
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| Typical Applications |
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The thin film evaporator/molecular still technique has been successfully utilized since the 1940's. It remains a primary means of separation for many applications, including :
- Solvent stripping
- Stripping monomer from polymer
- Stripping free fatty acids from fats and oils
- Distilling fats and oils
- Concentrating or distilling heat-sensitive Pharmaceuticals, nutraceuticals and bio materials
- Distillation of polymers
- Distillation of petroleum fractions
- Reactive's from solid catalysts
- Concentration of fruit juices
- Isolation of aromatic compounds
- Deodorization of oils
- Removal of colors
- Separations of waxes or silicones
- Foods and flavors purifications
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