Counter Flow Closed Cooling Tower
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Due to the very large product particle specific surface area and the extremely high heat exchange coefficient, spray drying is a very fast drying method. The large product particle specific surface area also allows drying to be carried out in moderate to low temperature environments. Rapid drying and moderate temperatures allow spray drying to be used for heat sensitive materials. The rapid drying and the fast stability of the attendant materials make spray drying very suitable for embedding and producing dry emulsions or amorphous materials. The possibility of particle engineering also includes powder performance characteristics such as aerodynamic size of the particles, particle geometry, particle size distribution, and powder flow characteristics.
Spray drying of nanoparticles involves drying nanoparticles that are suspended in a suitable liquid, such as water. After spray drying, the primary particles can be protected and new desirable powder properties can be obtained at the same time. That is, the powder has good flow properties and reduces the tendency to generate dust or has good powder flow properties and smaller aerodynamic particle sizes.
Micro-embedding can be achieved by using a spray drying and spray coagulation process. The spray-dried micro-embedded material is a liquid in which the drug is present in the package in a suspended or dissolved form. Suitable solvents can be water, alcohol, acetone, and the like. Another alternative is spray coagulation, where the packaging solution is replaced with a melt of the packaging material. By spray drying or spray coagulation, the particle size can be changed very easily to a controlled release shape that is suitable for commissioning and other desirable powder properties are obtained.
Dry emulsions are a variation of micro-embedding technology. In dry emulsions, it is necessary to embed micro-droplets, ie oily solutions containing oil-soluble drugs. The material needed to produce a dry emulsion by spray drying is an emulsion that contains a dissolved solid carrier. The spray-dried dry emulsion can be recombined to maintain the original droplet size to increase the bioavailability of the drug while obtaining other desirable powder properties.
Solid amorphous dispersants/solutions can be achieved using spray drying. The material used to produce the solid amorphous dispersant consists of a drug and a suitable solvent containing a stable material. Suitable solvents include alcohol, acetone, dichloromethane and the like. Spray-dried solid amorphous dispersants can increase the bioavailability of the drug and enhance the stability of the drug while obtaining other desirable powder properties, such as powder flowability and direct compression properties.
Drying When the drug behaves as a thermoplastic and has a high affinity for the solvent, it will cause the product to be difficult to dry. For drugs with high affinity for solvents, the residual solvent level in a certain product will require a higher drying temperature or a lower solvent vapor content in the exhaust gas, especially for those products that have both thermoplastic properties. It is a considerable challenge. For those drugs that behave like thermoplastics and have lower transition temperatures, the effective temperature range for drying is quite limited. Two contradictory factors determine the limited temperature range: The product temperature must be low enough to ensure product stability and non-stickiness; at the same time, the drying temperature must be high enough so that the material droplets/particles collide with the drying tower wall. Dry the material within the effective time. What's worse is that the solvent in the material behaves like a plasticizer, reducing the product's allowable temperature. Incorrect drying conditions can result in very low yields due to build-up of the tower walls, which can be caused by too low and too high drying temperatures.
For spray drying, it is important to distinguish between dryer inlet temperature, product temperature, drying temperature, and dryer outlet temperature. In a well-designed co-flow spray dryer, the drying temperature and the dryer outlet temperature are the same. Due to evaporation of the solvent in the product, the product temperature will be lower than the dryer outlet temperature, usually 5 to 20°C.
Drying of the pellets is first determined by the outlet temperature of the spray dryer and the solvent vapor content of the spray dryer exhaust. Higher spray dryer outlet temperatures or lower solvent vapor content of the spray dryer exhaust will affect product drying. For a fixed spray dryer outlet temperature and dry gas flow rate, lowering the inlet temperature of the dryer will result in a decrease in the feed volume, a decrease in evaporation, and a drop in the solvent vapor content of the spray dryer exhaust. Therefore, the parameters of the spray drying must be carefully balanced, and the answer can often be found in a window of opportunity.
The spray drying window may allow drying to be performed at a high yield, but it may also cause the final product to fail to meet the residual solvent level requirement. For many products, effective drying time is more important. When the residual solvent diffusion in the product is constrained, the single-stage dryer cannot be effectively dried, and in many cases additional drying stages must be added.
The thermoplasticity exhibited by some drugs will make them unsuitable for drying in conventional spray dryers. In this way, low pressure spray drying can be an option. Spray dryers operate at 0.5 to 0.7 bar, allowing significantly lower drying temperatures.
Dryer Forms Recently, Niro has introduced a series of dryers that can be used to accomplish these tasks. PHARMASD® (PSD) (Fig. 1, 2) and other necessary components are combined together to enable cGMP-compliant production at pharmaceutical companies.
The principle of PSD is to design a series of equipment with similar performance and different yields. Batches can range from a few grams to several tons of powder. The consistent performance of PSD equipment enables the scale-up process from early development to final scale production to be successfully implemented. PSD equipment is a combination of many modules used to meet specific requirements, regardless of operating temperature, operating pressure, solvent, production, or other factors. Therefore, dryers of the same output may be completely different in design, configuration and physical dimensions. PSD dryers are designed to use hot air or use nitrogen as a drying gas when drying non-water based materials (eliminating the risk of combustion). They can be used to dry a wide variety of acetone, dichloromethane, alcohol and other organic solvents. When using organic solvents and nitrogen, the dryer is usually operated in a closed loop system to minimize the loss of nitrogen and avoid the volatilization of organic solvents.
Summary By carefully selecting operating parameters, drugs that exhibit thermoplastic and solvent affinity can be produced using spray drying. Spray drying offers unparalleled advantages for the production of embedding, dry emulsions or amorphous materials with controlled release properties and/or pharmaceuticals that increase bioavailability.
Improve drug bioavailability and achieve controlled release by spray drying
Recently, for many dosing drugs, it has become extremely important to make drugs with good drug efficacy but poor solubility to control release drugs and to increase the drug's biopharmaceutical efficiency. This article focuses on the use of spray drying technology to produce products with controlled release and/or high drug bioefficacy. The main products include nanoparticles, microencapsulation, solid amorphous dispersions, and dry emulsions.