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Principle, Construction, Working, Uses, Merits and Demerits of Vacuum Dryer

By creating a vacuum, moisture present in a wet solid is removed during vacuum drying.

Vacuum Dryer

Principle

By creating a vacuum, moisture present in a wet solid is removed during vacuum drying. In this process, there is an attempt to lower the pressure beneath the water's vapor pressure by creating a vacuum. Drying substances are made possible by reducing the pressure around them using vacuum pumps. Consequently, the boiling point of water inside of the product is lowered, increasing evaporation rates tremendously. It increases the drying rate significantly. Water boils at 25 – 30 °C at a pressure of 0.0296 –0.059 atmospheres in vacuum drying. This process involves drying an item in a batch at a reduced pressure and with a lower relative humidity than ambient pressure, enabling it to dry more quickly.

Constructions

The pharmaceutical industry also refers to vacuum dryers as vacuum ovens. Due to their high vacuum pressure, vacuum dryers are made of cast iron or stainless steel so they can withstand the pressure without deforming. Heat conduction is improved by the hollow trays that divide the oven. It's possible to reduce the pressure by connecting a vacuum pump to the oven door. Hot water and steam are supplied through a hollow shelf to provide heat.



Working

Vacuum dryers use trays to hold the materials to be dried, while the vacuum pump reduces the pressure. Steam is passed between trays and jackets through the tightly closed dryer door to transfer heat through conduction. In the condenser, vaporized water is collected from the feed. The vacuum pump is disconnected once the product has dried, and trays full of dried products are collected. It is possible to dry items faster if the pressure is lowered. During the drying process, you can regulate the temperature, and the wetting agent's boiling point is maintained largely throughout. There is a long drying time, usually between 12 and 48 hours. As the material contacts the heated surface of the dryer, heat is transferred, allowing the material to dry by conduction.

Uses

The following examples demonstrate how vacuum drying can be used.
  • Type of industries - Chemical, pharmaceutical, food, and plastic industries are just a few industries that use vacuum drying equipment.
  • Type of operation - The process typically involves removing and recovering solvents from moist material, or removing water from a moist material and recovering its solvents.
  • Changing physical state - Phase changes occur when a material's molecular and physical chemistry is modified by a chemical reaction or polymer solid state.
  • Separation - Vaporization of a material is typically used to separate volatile liquids from powders, cakes, slurries, or other moist materials.
  • Indirect-heat drying - Heating the surface of the dryer with indirect heat causes the material, which is in contact with the surface, to transfer heat, thereby drying the material.
  • Safety - It is safer to work near a vacuum dryer since there is no need for ventilation. During the drying process, the precipitated moisture that has been collected can also be utilized.
  • Drying pharmaceuticals - By wet granulation, it is used in the preparation of dental tablets and granules of crospovidone, camphor, and lactose. As a result of being exposed to vacuum, camphor is sublimated from its granules. Superior tablets are produced by compressing the porous granules.
  • Drying proteins - Protein vacuum-drying overcomes long processing times (typically 3 to 5 days) and instabilities associated with freeze-drying. During various freeze-drying processing steps, proteins tend to denature and aggregate irreversibly due to their complex structural properties. Using mannitol as bulking agent, proteins are vacuumed and dried as dry powders.
  • Drying bacteria - Dry-freezing bacteria is frequently used to preserve probiotic cultures and starter cultures until use. Some strains of bacteria cannot survive below 0°C due to the high energy consumption. The use of vacuum drying at moderate temperatures above 0°C can also be used to dry probiotics without compromising their cellular structure too much.
  • Vaccines and other injectables - Freeze-drying is used to produce vaccines and injectable pharmaceuticals. Vaccines and other injectables benefit from freeze-drying because it extends their shelf lives. The material can be packaged, shipped, and subsequently reconstituted to its original form by removing the water from the vial after it has been sealed under vacuum.

Merits

  • The vacuum dryer is designed to dry thermolabile materials at low temperatures as well as to recover solvents from solid products containing solvents.
  • By removing a large amount of moisture compared to typical dryers, materials can be dried in final containers or enclosures.
  • Typical dryers have lower average drying temperatures and the quality of dried material is superior to that of normal dryers.
  • A large surface area makes it easier for heat to be transferred throughout the dryer, thus providing faster drying action.
  • Its energy conservation is a major advantage. For storage, sale, or other purposes, drying a product requires less energy. This reduces economic and environmental costs.
  • Other drying methods take a lot longer than vacuum-drying, so the process takes less time.
  • Furthermore, this dryer has the advantage of less damaging materials during the drying process. It is generally believed that vacuum drying preserves the original item's integrity without damaging it with heat.
  • Generally, this operation is carried out in batches, but it is also possible to integrate it into a continuous process.
  • The equipment reduces the risk of workers being sick or having to wear protective clothing from vented fumes and particles.

Demerits

  • Drying by vacuum is typically a batch process that is inefficient.
  • There is a high cost associated with vacuum dryers, and skilled labor is needed to operate them.
  • Maintenance costs are relatively high.
  • In contrast to direct-heat dryers, its maximum temperature limit is lower (typically around 600 °F). As a result, a vacuum dryer's ability to raise material temperature is also limited. Inside a vacuum dryer, vacuum is maintained by a vacuum pump.
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Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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