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Application of spray drying technology in the production of oral solid preparation
Release time:2018-8-7     Viewed:
Spray Drying Technology is the method of spraying, so that the material is dispersed in the droplet state in the hot gas flow, the material and hot air full contact, in a moment to complete the process of heat transfer and mass transfer, so that solvents (including water and organic solvent) rapidly evaporated into a gas, to achieve the purpose of drying. Spray drying technology is widely used in the pharmaceutical industry in China, in the field of oral solid preparation, often for high-heat sensitive drugs and liquid concentration process of easy decomposition of the drug drying. The resulting product has fine particle size, uniformity, fluidity and quick-dissolving properties. Characteristics and Classification
of Spray dryers The spray dryer is a drying device that directly dries the solution or suspension as a solid particle.


Can be directly obtained from the liquid drying products, eliminating evaporation, crystallization, separation and crushing unit operation, can be continuous, automated production, stable operation. Using this drying method, the gas-solid two-phase contact surface area of the spray dryer is large, the drying time is short, the general drying time is 5~30s, which is suitable for drying thermal sensitive materials. The dried products have good quality and can obtain 30~50μm particles, and the product fluidity and quick-dissolving properties are good. The disadvantage is that the dryer has large volume, low heat transfer coefficient, resulting in low thermal efficiency and high power consumption. Spray Dryer Classification Method There are many, according to the gas-liquid flow can be divided into the flow, countercurrent and mixed flow type; According to the installation of atomizer can be divided into the spray-down type, under the spray-type; The structure of the atomizer can be divided into centrifugal type, pressure type and gas flow type
, according to whether the heating gas circulation can be divided into open, partial circulation and closed type. The basic process of spray drying (closed type)

is atomized by atomizer,

Dispersed into a small droplet into the drying chamber, at the same time, the heating gas through the blower into the heater heats up, and then into the drying chamber. The liquid droplet and the hot gas are fully mixed and contacted in the drying chamber. The liquid in the droplet evaporates instantaneously into a gas, and the material is dried into fine particles. The mixed gas-solid two-phase induced fan suction cyclone separator, two-phase separation, the solid material settles to the bottom collector, the gas phase is introduced to the dust filter, trapping the escaping material. After condensation of the filter gas phase through the condenser, the vapor-carrying solvent into a liquid, can be collected, as a carrier of the gas is dried in the system is recycled. The flowchart is as follows:


Process requirements

for oral APIs Oral solid preparation A wide range of specific process requirements are also different, in the spray dryer design and manufacture process, it is best for different varieties of the design, in order to achieve the equipment and technology to adapt to the best state. The production of solid preparation in the selection of spray drying machine, often put forward the following listed requirements:

1. Cleaning requirements (The following 7 small headings please change to italic)
The main process of raw material drug production needs to be carried out in a clean environment of level 100,000, spray drying is an important process of quality control. Spray dryer Contact parts of the material, to use stainless steel, for strong acid corrosion of materials, it is best to choose 316L Stainless steel. Dry cavity, cyclone separator, filter and other direct contact material parts, should be smooth inner wall, no dead angle, easy to clean, easy to disassemble, easy to clean. Spray dryer is often a large system, so can not be placed in clean areas, often only the part of the collection of materials in the clean area, which requires a good system of airtight performance, to prevent external pollution will not be system.
2
. To avoid sticking
wall phenomenon is still a prominent problem which hinders the normal operation of the spray dryer, especially the spray drying process of solid preparation (particularly traditional Chinese medicine). The material adhesion wall not only is not conducive to the collection operation, and with the extension of time, the sensitive adhesive wall material will deteriorate and become unqualified material. From the technological point of view, the solution includes the selection of suitable solvents, increase excipients, change the process parameters, but these methods can not be adjusted to a large extent, it must be from the point of view of the equipment to seek a fundamental solution. The problems of adhesion and caking in drying process were studied by experts at home and abroad, and it was agreed that the main cause of adhesion was wall temperature. The following list of five possible ways to prevent adhesion:
* Using a wall drying tower, during which air cooling, so that the wall temperature is kept below 50 ℃;
Two air cooling tower walls were introduced through the tangential direction of the tower wall.
* A gas broom consisting of a row of nozzles is installed near the wall of the tower and slowly rotates along the tower wall;
* Tower Wall added Air hammer , through the air hammer, forcing the adhesive wall material to disengage;
* Increase the precision of processing, the inner wall polishing can also reduce the adhesion wall.
3
. Self-control performance
Spray Drying is a continuous production process, control points more. For example, the control points of the closed circulatory system include: feed concentration, feed speed, inlet speed, air inlet temperature, system pressure, pressure difference of each component, gas purity detection, etc., relying on traditional manual adjustment is very difficult. A good set of automatic control system, can make the whole spray drying system smooth operation, reduce the product's unqualified rate, reduce safety hazards. At present, domestic products in the self-control is relatively backward, while some foreign advanced equipment, such as the Danish company's spray dryer, in self-control technology has been very mature.
4
. Drying effect
due to the need for oral API to further complete the preparation process, in improving the effect of the preparation and the final drug absorption effect, the spray drying products of the physical properties of different requirements. First of all, moisture content is the first indicator of drying products, generally requires control in a certain range, can not be too high or too low. Second, the drug's sub-assembly generally in accordance with the volume to control the volume, which requires the product's heap density stability, product mobility is better. Oral granules often require instant sex. Generally speaking, change the dispersion of atomization or appropriate change operating conditions to control drying rate, can be made with different heap density products, but the range of changes is limited. In the improvement of physical property is worth mentioning a technology is foam spray drying, will be the feed liquid first foam after the spray drying. The method was originally proposed for improving thermal efficiency and later used to adjust the physical property of the product. It has been proved that the foam spray drying products have large particle size, porous, concave and rough surface, and have good solubility. In addition, the oral API will have some special requirements, such as: particle shape. Some require spherical particles, particle size uniformity. In general, particles of different shapes can be obtained by changing the atomization mode. API manufacturers in the selection of spray dryer, preferably in the equipment manufacturing enterprises with the assistance of the parameter optimization experiment, to determine an optimal combination of parameters to ensure the drying effect of the injection of drugs.
5
. Protection measures
due to the different nature of the drug, the protection of the design of equipment also put forward some higher requirements. Materials dissolved with organic solvents require the entire system to meet explosion-proof requirements when drying. In the motor, instrument, control valve and other accessories design must choose the explosion-proof type. In addition, in order to prevent the mixture of solvents and air as explosive gas, the system can not be used open, but must use closed circulation system, and the carrier to select inert gas, such as nitrogen. In addition, some of the easy oxide drying, but also using nitrogen as a carrier of closed circulation system.
6
. Environmental protection
Spray Drying products for fine particles, in order to meet the requirements of environmental protection, spray drying system only with cyclone separator products, purification exhaust or not enough, generally also use bag filter purification, so that the dust content in the exhaust less than 50mg/ (NM) 3 gas, or wet scrubber, can reduce the dust content of exhaust gas to 15~35mg/(NM) 3 gas. The use of nitrogen as a carrier, the system should pay attention to airtight, exhaust port to lead to the outside.
7
. Lower the cost
of hot air inlet temperature in the 250~500℃ flow operation, countercurrent operation is 200~300℃, after atomizing drying outlet temperature general control in 60~100℃. Spray drying of low heat utilization, industrial-scale spray dryer, the thermal efficiency is generally 30%~50%. Abroad with waste heat recovery spray drying, thermal efficiency can reach 70%, but this equipment only in the production capacity of more than 100kg (water)/h is only economic significance. However, in the use of nitrogen carriers and organic solvents, the use of closed circulation system, nitrogen recycling can be used, solvent condensation applied, thereby effectively reducing the production cost. Domestic spray dryer manufacturers are constantly improving the technical level, to solve the spray drying in the field of oral pharmaceutical technology problems, I believe in the near future, will be able to produce more suitable, high quality and low price products,
So that our country's spray drying technology to reach the world's leading level. 
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