Spray dryer technology uses the method of spraying to disperse the material in the hot air flow in the form of mist droplets. The material is in full contact with the hot gas, and the process of heat transfer and mass transfer is completed in an instant, so that the solvent (including water and organic solvent) can be quickly Evaporate into gas to achieve the purpose of drying. Spray drying technology is widely used in my country's pharmaceutical industry. In the field of oral solid preparations, it is often used for drying highly heat-sensitive drugs and easily decomposed drugs during the concentration of liquid. The resulting product has fine and uniform particle size, good fluidity and instant solubility.
Process requirements for oral raw materials
There are many kinds of oral solid preparations, and the specific process requirements are also very different. In the process of designing and manufacturing spray dryers, it is best to make different designs for different varieties to achieve the best state of equipment and process adaptation. When selecting a spray dryer for the production of solid preparations, some requirements listed below are often put forward:
1. Cleanliness requirements (please change the following 7 subtitles into italics)
The main process of API production needs to be carried out in a 100,000-class clean environment, and spray drying with a spray dryer is an important process for quality control. The part of the spray dryer in contact with the material should be made of stainless steel. For materials with strong acid corrosion, it is best to use 316L stainless steel. Drying chamber, cyclone separator, filter and other parts that directly contact with materials should have smooth inner walls, no dead angle, easy to clean, easy to disassemble and easy to clean. Spray dryers often have a large system, so they cannot be placed in a clean area as a whole, and often only the part that collects materials is placed in a clean area, which requires a good airtight system to prevent external contamination from entering the system.
2. Avoid sticking
Here are five possible ways to prevent sticking:
* Use a double wall drying tower, during which air cooling is used to keep the wall temperature below 50°C;
* The secondary air is tangentially introduced through the tower wall cyclone to cool the tower wall;
* An air broom consisting of a row of nozzles is installed near the wall of the tower, and it is slowly rotated along the tower wall;
* The air hammer is added to the wall of the tower, and the material sticking to the wall is forcibly separated by the blow of the air hammer;
* Increase the precision of processing, and the polishing of the inner wall of the tower can also reduce the sticking of the wall.
3. Self-control performance
Spray Dryer Spray drying is a continuous production process with many control points. For example, the control points of the closed circulation system include: feed concentration, feed speed, inlet air speed, inlet air temperature, system pressure, pressure difference of various components, gas purity detection, etc. It is very difficult to rely on traditional manual adjustment. A good automatic control system can make the whole spray drying system run smoothly, reduce the unqualified rate of products, and reduce potential safety hazards. the
4. Safeguard
Due to the different properties of medicines, some higher requirements are put forward for the protection design of equipment. For materials dissolved in organic solvents, the entire system must meet explosion-proof requirements when drying. When designing accessories such as motors, instruments, and control valves, explosion-proof types must be selected. In addition, in order to prevent the solvent and air from mixing into explosive gas, the system cannot be open, but a closed circulation system must be used, and the carrier should be an inert gas, such as nitrogen. In addition, the drying of some oxidizable materials also uses a closed circulation system with nitrogen as the carrier.
5. cut costs
The inlet temperature of the hot air is 250-500°C during co-current operation, 200-300°C during counter-current operation, and the outlet temperature after atomization and drying is generally controlled at 60-100°C. The heat utilization rate of spray drying is low, and the thermal efficiency of industrial-scale spray dryers is generally 30% to 50%. The thermal efficiency of spray drying with waste heat recovery in foreign countries can reach 70%, but this kind of equipment is only economically meaningful when the production capacity is greater than 100kg (water)/h. However, when nitrogen carrier and organic solvent are used, a closed circulation system can be used to allow nitrogen to be recycled and solvent to be condensed, thereby effectively reducing production costs.
6. environmental protection
The spray-dried products are fine particles. In order to meet the requirements of environmental protection, it is not enough for the spray-drying system to separate the products and purify the tail gas with a cyclone separator. Generally, it is also necessary to use a bag filter to purify the dust content in the tail gas. 50mg/(nm)3 gas; or use a wet scrubber to reduce the dust content of the tail gas to 15-35mg/(nm)3 gas. When nitrogen is used as the carrier, the system should be airtight, and the exhaust port should be led to the outside.
7. drying effect
Since oral raw materials need to further complete the preparation process, different requirements are put forward for the physical properties of the spray-dried product in terms of improving the preparation effect and the absorption effect of the final drug. First of all, the moisture content is the first index of dry products, and it is generally required to be controlled within a certain range, not too high or too low. Secondly, the dispensing of drugs is generally controlled according to the volume, which requires a stable bulk density of the product and good fluidity of the product. Oral granules often require instant dissolving. Generally speaking, products with different bulk densities can be obtained by changing the degree of dispersion of atomization or appropriately changing operating conditions to control the drying rate, but the range of change is limited.
A technology worth mentioning in terms of improving physical properties is foam spray drying, that is, the feed liquid is first foamed and then spray dried. This method was originally proposed to improve thermal efficiency, and was later used to adjust the physical properties of the product. In addition, there are some special requirements for oral raw materials, such as particle shape. Some require spherical particles with uniform particle size. Generally speaking, particles of different shapes can be obtained by changing the atomization method.
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