Objectives, Applications and Mechanism of Drying Process : Pharmaguideline

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Objectives, Applications and Mechanism of Drying Process

A solid, semi-solid, or liquid is dried by evaporating water or another solvent from it.


A solid, semi-solid, or liquid is dried by evaporating water or another solvent from it. In the process of manufacturing or packaging pharmaceuticals, drying is often the final step. A product must be solid to be considered "dried", whether it is a sheet, piece, particle, or powder. Heat is used to dry the material, and vapors are removed at the end of the process. Water is the most common solvent removed from most pharmaceutical intermediates and finished products. Desiccation may be considered an extreme form of drying, or it may be synonymous with drying. Pharmaceutical products are always of the highest quality. As a result of microbial infection, oxidation, and thermal decomposition, contamination by metallic particles, or exposure to organic solvents, the product may degrade. It is imperative to remove these solvents as soon as possible.

It is best to use non-contaminating materials, such as stainless steel or enameled iron, for the construction of dryers. It is often useful to use closed dryers when removing moisture from organic solvents or their mixtures. Inert gas drying prevents oxidative decomposition. A vacuum or freeze-drying method can reduce thermal decomposition. Pharmaceuticals require expensive dryers because of all these requirements.

In pharmaceutical companies worldwide, a variety of different drugs are manufactured, and for that reason, dryers must be able to operate both batch and continuous modes. It is necessary to synthesize intermediate products, synthesize the drug, and then manufacture the dosage form in order to manufacture solid drug dosage forms such as tablets and capsules. These stages are then followed by drying. It is important to select the right dryer for these materials based on their characteristics. Controlling and adjusting moisture levels in solid materials is a critical aspect of product manufacturing. In the pharmaceutical industry, where powders and granules are handled and manufactured, it is common and important for solid materials to be dried.

A drying process' effectiveness plays a critical role in product quality and process efficiency. The drying process is a crucial step in the manufacturing of pharmaceuticals, for example. Following the drying process, such steps as tableting or encapsulation will have a negative impact on quality attributes of the final product. Other than drying solids to prepare them for further processing, it can also improve powder handling characteristics, for example powder flow and bulk filling.


The drying unit operation is widely used in the pharmaceutical industry, yet many factors, including moisture, environmental conditions, and the drying process parameters, have an impact on the quality of active pharmaceutical ingredients. This can cause challenges during product development, manufacture, storage, and usage. In order to achieve these objectives, drying should be carried out as follows:
  • For the purpose of overcoming common challenges facing pharmaceutical drying development, including material constraints for scale-up studies and equipment transfer to a variety of types and sizes of equipment.
  • Identify common development gaps in the drying development workflow that can be addressed by improving chemical and physical stability, drying kinetics, and powder properties through an understanding of drying development.
  • Research and technology advances should be encouraged to improve the drying process.
  • Furthermore, it is also necessary to reduce the outsize of the packaging, to prevent deterioration on storage, to reduce the amount of moisture in the tablet granules, to reduce the bulk and weight in order to reduce transportation expenses, in addition to certain preparations such as spray dried lactose.
  • To design and manufacture a dryer with minimal energy consumption, a low acquisition and operating cost, and optimum local content and flexibility.
  • Determine the impact of factors on product specifications and define residual solvents in accordance with regulations, along with the nature of these residual solvents.


The last stage of the manufacturing process is drying, which is done for at least one of the following purposes:
  • Various substrates and coatings are dried to remove moisture or other volatiles which may have accumulated.
  • Many materials are made using it to control and reduce moisture levels.
  • A high degree of thermolability is necessary for processing highly thermolabile products that aren't stable when liquid. As a result of lyophilization, thermolabile materials have a longer shelf life and can be stored and transported more easily. A few examples include drying of blood plasma, vaccines, enzymes, microbial cultures, hormones, and antibiotics
  • Material is dried in order to make it easier to handle and process. Drying is essential for free-flowing materials in bulk drugs and large-scale synthetic drug production. For example, spray-dried lactose, dried aluminum hydroxide, etc.
  • As a result, the product or drug is more stable, as moisture is prevented from causing corrosion and decreasing stability. To prevent the deterioration or contamination of crude drugs such as those originating from animals and plants, or synthetic or semi-synthetic drugs.
  • The process is used to improve and maintain the properties of a material, such as flowability and compressibility. For example, if you dry fresh plants like belladonna leaves, you can shrink them.
  • The purpose of this process is to improve tablet properties, especially how to compress viscous or sticky materials.
  • The physical form of materials can be modified by drying to improve their solubility. The dried extracts of milk and coffee are converted into instant soluble powders.
  • The purpose of drying is to make materials lighter in weight, which alleviates the cost of transporting large volumes of materials (liquids).
  • In evaporation, filtration, and crystallization, drying is used as the final step. It also protects materials against environmental factors.
  • Using drying, thermolabile and hydrolytic substances can be maintained and improved for a longer period of time. The degradation of blood products, skin, and tissues is prevented by preventing microbial decomposition.
  • Drying significantly helps improve stability by reducing enzymatic reactions, microbial attacks, and microbial growth.

Mechanism of Drying Process

In drying, the physical structure and appearance of the material must be preserved as well as the moisture is removed. Heat and mass transfer govern the process of drying. Moisture vaporizes at or near the surface of a moist solid when heated to the appropriate temperature. During the drying process, hot air or gas is used to evaporate moisture from the product. By evaporating from the surface, moisture is transferred into the surrounding medium in the course of drying. More moisture is transported from the bulk of the solid to the surface as some of the moisture vaporizes at the surface. Depending on the type and nature of the solid and the state of aggregation, diffusion of moisture occurs in a solid by various mechanisms. Drying is done on a wide range of solids, including crystalline, granular, beads, powders, sheets, slabs, and filters. Moisture is transported in the following ways:
  • Capillary action
  • Transport by liquid or vapour diffusion
  • Pressure-induced transport
It depends on the nature, pore structure, and rate at which a solid is dried as to the specific mechanism involved. At different stages of material drying, there may be multiple mechanisms at work.

When designing drying systems, a number of common terms are used. At the same temperature, bound moisture is achieved when the equilibrium vapors pressure of a substance exerts less pressure than the equilibrium vapors pressure of a pure liquid. At a given temperature, the amount of unbound moisture in solids exerting the same equilibrium vapour pressure as a pure liquid is the unbound moisture.
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Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of pharmaguideline.com, 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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