In recent years, spray drying technology has been widely used in the pharmaceutical industry. In the field of solid preparations, this technology is commonly used for the drying of easily decomposable drugs in high heat sensitive medicines and liquid concentration processes. Different APIs have different special requirements for spray drying during the application process. How to meet these requirements, should pay attention to what details are common concerns of both the device design producer and the user.
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â– Ensure cleanliness requirements Some of the main processes for the production of APIs need to be carried out in a clean environment of 100,000 grades. Spray drying is an important process for quality control. In order to ensure the quality of the medicine, the part of the spray dryer that contacts the material should be made of stainless steel. For materials with strong acid corrosion, 316L stainless steel is the best choice. The parts that directly contact the material such as the drying chamber, the cyclone separator, and the filter should be smooth inside the wall, have no dead angle, and are easy to disassemble for easy cleaning.
Due to the large size of the spray dryer, it cannot be placed in a clean area as a whole, and often only the part where the material is collected is placed in a clean area. In this case, the system is required to have a good sealing performance to prevent external contamination of the system.
■Avoiding sticking wall In the spray drying process of solid preparations (especially Chinese medicine), the sticking wall phenomenon is a prominent problem that hinders the normal operation of the spray dryer. The sticky wall of the material is not only unfavorable for the collection operation, but as time goes on, the sensitive sticky wall material will deteriorate into a non-conforming material. From a process point of view, the solution includes choosing the right solvent, adding excipients, and changing the process parameters. However, there is not much room for adjustment of these methods, so a fundamental solution must be sought from the perspective of the equipment. In recent years, domestic and foreign experts have studied the problem of sticking wall and agglomeration in the drying process. It is believed that the main cause of sticking wall is the wall temperature, which summarizes five measures to prevent sticking: using a wall drying tower. Cooling with air to keep the wall temperature below 50 °C; introducing a secondary air cooling tower wall through the tangential direction of the rotor wall; installing an air broom consisting of a row of nozzles near the wall of the tower and making it along the tower wall Slowly rotating; the air hammer is added to the tower wall, and the sticking material of the tower is forced to be detached by the hammering of the air hammer; the precision of the processing is increased, and the inner wall polishing of the tower can also reduce the sticking wall.
â– Improved self-control performance Spray drying is a continuous production process. The control points of the closed circulation system include: feed concentration, feed rate, inlet speed, inlet air temperature, system pressure, differential pressure of each component, gas purity detection, etc. Traditional manual adjustment is very difficult, so the system's self-control must be strengthened. A good automatic control system can make the whole spray drying system run smoothly, reduce the product's failure rate and reduce safety hazards.
â– Meeting different physical properties After the spray of the API, it is necessary to further complete the preparation process. Therefore, different production requirements may impose different requirements on the physical properties of the spray-dried product in terms of improving the effect of the preparation and the absorption effect of the final drug. .
The dispensing of drugs generally controls the volume according to the volume, which requires that the bulk density of the product is stable, the fluidity of the product is good, and the oral granules often require fast solubility. By varying the dispersion of the atomization or by appropriately changing the operating conditions to control the drying rate, products having different bulk densities can be produced, but the magnitude of the variation is limited.
Currently, there is a new technology in improving physical properties - foam spray drying, in which the feed liquid is first foamed and then spray dried. The method was originally proposed to improve thermal efficiency and was later used to adjust the physical properties of the product. It has been proved that the product prepared by foam spray drying has large particle size, is porous, has many depressions, has a rough surface, and has good fast solubility.
In addition, there are some special requirements for oral drug substances, such as particle shape. Production practice has shown that particles of different shapes can be obtained by changing the atomization method.
â– Safety measures are indispensable The specificity of certain drugs will place higher demands on the protection design of the equipment. Materials dissolved in organic solvents require the entire system to meet explosion-proof requirements during drying. At the same time, explosion-proof models must be selected for the design of motors, instruments, control valves and other accessories. In addition, in order to prevent the solvent and air from mixing into an explosive gas, the system must use a closed circulation system, and the carrier should use an inert gas such as nitrogen. In addition, some of the easy-to-oxide materials are dried, and a closed circulation system using nitrogen as a carrier is also used.
â– Environmental indicators must meet the standards Spray-dried products are fine particles, which are easy to form dust. In order to meet the requirements of environmental protection, it is not enough to separate the product and purify the exhaust gas by using the cyclone separator currently in the conventional configuration. It can also be cleaned with a bag filter to make the dust content of the exhaust gas less than 50 mg/cubic nanometer. Or use a wet scrubber to reduce the dust content of the exhaust gas to 15 ~ 35 mg / cubic nanometer of gas. When using nitrogen as a carrier, the system should pay attention to sealing.
The exhaust port should be led to the outside.
■Improving the heat utilization rate is the urgent hot air inlet temperature is 250 ° C ~ 500 ° C in the cocurrent operation, 200 ° C ~ 300 ° C in the countercurrent operation, the outlet temperature after atomization drying is generally controlled at 60 ° C ~ 100 ° C, its heat The lower utilization rate is also a disadvantage of spray drying.
At present, domestic industrial scale spray dryers generally have a thermal efficiency of 30% to 50%. Foreign spray dryers with waste heat recovery can achieve a thermal efficiency of 70%, but the equipment is economically significant only when the production capacity is greater than 100 kg (water) / hour. However, when a nitrogen carrier and an organic solvent are used, a closed circulation system can be used, and the nitrogen can be recycled, and the solvent can be condensed, thereby effectively reducing the production cost.
But in general, the cost of using spray drying requires equipment design and further research by producers to find better cost-reducing strategies.
(Lu Jinning Lin Zucong)
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Spray drying technology: refers to the method of spraying, the material is dispersed in the hot gas flow in the state of mist, the material is in full contact with the hot gas, and the heat transfer and mass transfer process is completed in an instant, so that the solvent is quickly evaporated into gas to achieve dryness. purpose. The technology can eliminate unit operations such as evaporation, crystallization, separation and pulverization, and can be continuously and automatically produced, and the operation is stable. With this drying method, the gas-solid two-phase contact surface area is large, and the drying time is short, generally 5 to 30 seconds, which is suitable for drying the heat sensitive material. The product obtained by drying has good performance, the obtained microparticles are small, and the product has good fluidity and fast solubility. The disadvantage is that the dryer has a large volume and a low heat transfer coefficient, resulting in low thermal efficiency and high power consumption.
The basic process of spray drying: the liquid is atomized by the atomizer, dispersed into fine mist into the drying chamber, and the heated gas is sent to the heater through the blower to heat up, and then enters the drying chamber. The liquid droplets are thoroughly mixed and contacted with the hot gas in the drying chamber. The droplets evaporate instantaneously into a gas, and the material is dried into fine particles. The mixed gas-solid two-phase is separated into the cyclone by the induced draft fan, and the solid material is settled to the bottom collector, and the gas phase is led to the dust filter to capture the escaped material. After the filtered gas phase is condensed by the condenser, the carried solvent becomes a liquid, which can be collected and used, and the gas as a carrier is dried and recycled in the system.
The main structures and components of the camera can be listed from the working principle of the camera:
1. LENS
Lens structure, consisting of several lenses, including plastic lens or glass lens
2. Image sensor
It can be divided into two categories:
CCD (charge couple device): charge coupled device
CMOS (complementary metal oxide semiconductor): complementary metal oxide semiconductor
3. Digital signal processing chip (DSP)
There are many DSP manufacturers, such as VIMICRO 301P/L, SONIX 102/120/128, ST (Logitech LOGITECH's DSP provider), SUNPLUS (SUN+focuses on the development of CIF and VGA for single chip, but the image quality is average), PIXART (original phase), PAC207, SQ930C, etc.
4. Power supply
Two working voltages are required inside the camera: 3.3V and 2.5V. The latest process chip can use 1.8V.
Some cameras also use video transmission lines for synchronous power supply without external power lines.