Introduction to the application of spray drying technology in the production of solid preparations

Spray drying technology uses spray method to disperse the material in the hot gas stream in the droplet state The material is fully contacted with the hot gas, and the heat and mass transfer process is completed instantaneously, so that the solvent is rapidly evaporated into gas, so as to achieve the goal of drying Spray drying technology is widely used in the pharmaceutical industry In the field of solid preparations, it is often used to decompose drugs in the process of high heat sensitive drugs and liquid liquid thickening The particle size of the product is fine and uniform, and its fluidity and instant solubility are good The characteristics and classification of spray dryer are spray drying machines which directly dry the solution or suspension into solid particles It can save evaporation, crystallization, separation and smashing It can be continuously and automatically produced and operated stably With this drying method, the gas-solid two phase contact surface of the spray dryer is large, and the drying time is short It is generally 5 to 30s, and is suitable for drying heat sensitive materials The dried product has good performance, can obtain 30-50 mm particles, and has good fluidity and instant solubility The disadvantages of the dryer are its large volume, low heat transfer coefficient, low thermal efficiency and large power consumption There are many classifications of spray dryer According to gas liquid flow, they can be divided into parallel flow, counterflow and mixed flow According to the installation of nebulizer, they can be divided into upper and lower ones According to the structure of atomizer, they can be divided into centrifugal type, pressure type and airflow type According to whether the heating gas can circulate, it can be divided into open type, partial circulation type and closed type The basic process of spray drying (closed type) is atomized by atomizer, dispersed into fine droplets into the drying chamber Meanwhile, the heated gas is sent to the heater through the blower to heat up, and then enters the drying chamber The material liquid droplets and hot gas are fully mixed and contacted in the drying chamber The droplets evaporate into gas and the material is dried into fine particles The mixed gas-solid two-phase is sucked into the cyclone separator by the induced draft fan for separation, the solid material settles to the bottom collector, and the gas phase is led to the dust filter to catch the escaped material After the filtered gas phase is condensed by the condenser, the carried solvent becomes liquid, which can be collected and applied The carrier gas is dried and recycled in the system The flow chart is as follows: solid preparation process requires a wide variety of solid preparations and different processing requirements In the process of designing and manufacturing spray dryer, Zui aims at making different designs for different varieties so as to meet the Zui optimum condition of equipment and process The spray drying machine for solid pharmaceutical production should meet the following requirements: cleanliness requires that the main process of raw material production should be carried out in a clean environment of one hundred thousand levels, and spray drying is an important process of quality control The contact parts of spray dryer should be made of stainless steel 316L stainless steel is suitable for Zui with strong corrosiveness Dry chamber, cyclone separator, filter and other parts directly contacting with materials shall have smooth inner wall, no dead angle, easy to disassemble and clean Spray dryer often has large system, so it can not be put in the clean area as a whole It often only puts part of the collected material in the clean area, which requires that the system has good airtight performance to prevent the external pollution system Avoiding sticky wall sticking is a serious problem that hinders the normal operation of spray dryer The spray drying process of solid preparations (especially Chinese Medicine) is particularly obvious Material sticking to the wall is not only not conducive to the collection operation, but also with the extension of time, sensitive sticking materials will deteriorate into unqualified materials From the point of view of technology, the solutions include choosing suitable solvents, adding auxiliary materials and changing process parameters However, there is not much room for these methods to be adjusted Therefore, it is necessary to seek fundamental solutions from the perspective of equipment Experts at home and abroad have studied the problems of wall sticking and caking in the drying process, and they think that the main reason of wall sticking is the wall temperature Five possible ways to prevent wall sticking are listed as follows: a wall drying tower is used, in which air is used for cooling to keep the wall temperature below 50 ℃; secondary air is introduced into the tower wall through the tangential direction of the rotating air sheet on the tower wall to cool the tower wall; an air broom composed of a row of nozzles is installed near the wall of the tower, and it is rotated slowly along the tower wall Air hammer is added to the tower wall to force the wall sticking materials to separate through the impact of air hammer; the wall sticking can also be reduced by polishing the inner wall of the tower to increase the processing accuracy Automatic control performance spray drying is a continuous production process The control points of its closed loop system include: feed concentration, feed rate, intake speed, intake air temperature, system pressure, components pressure difference, 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 the hidden danger of safety The drying effect of the API still needs to be further completed In order to improve the preparation effect and the absorption and absorption effect of Zui final drugs, the physical properties of spray drying products are different First of all, the moisture content is the * index of dry products, which should be controlled in a certain range Secondly, the drug loading is generally controlled according to the volume, which requires that the bulk density of the product is stable and the fluidity of the product is good Oral granules are often required to be instant The products with different bulk density can be produced by changing the dispersion of atomization or operating conditions to control the drying rate, but the range of variation is limited One of the techniques to improve physical properties is foam spray drying, which is about to first foam and then spray dry The method Zui was first proposed to improve thermal efficiency, and later used to adjust the physical properties of products It has been proved that the products produced by foam spray drying are large, porous, concave and rough, and have good instant solubility In addition, oral APIs also have some special requirements, such as particle shape In general, particles of different shapes can be obtained by changing the atomization mode Before choosing the spray dryer, API Zui, with the help of equipment manufacturers, carries out parameter optimization experiments to determine the parameters combination of Zui and ensure the drying effect of the ejected drugs Protection measures the particularity of drugs also puts forward higher requirements for the protection design of equipment For materials dissolved in organic solvent, the whole system must meet the explosion-proof requirements when drying Explosion proof type shall be selected in the design of motor, instrument, control valve and other accessories In addition, in order to prevent the mixture of solvent and air into explosive gas, the system must adopt a closed circulation system, and the carrier should choose inert gas, such as nitrogen, etc In addition, the airtight circulation system with nitrogen as carrier should also be used for drying some easily oxidized materials Environmental protection spray drying products are fine particles In order to meet the requirements of environmental protection, it is not enough to separate products and purify exhaust gas by cyclone separators In general, the bag dust collector is used to purify the exhaust gas, and the dust content of the tail gas is lower than that of 50mg/nm3 gas Or the wet scrubber is used to reduce the dust content of the tail gas to 15 ~ 35mg/nm3 gas When nitrogen is used as carrier, the system shall be closed and the exhaust port shall be led to the outside To reduce the cost, the inlet temperature of hot air is 250-500 ℃ in parallel flow operation, 200-300 ℃ in reverse flow operation, and the outlet temperature after atomization drying is generally controlled at 60-100 ℃ The thermal efficiency of spray drying is low, and the thermal efficiency of the industrial scale spray dryer is generally 30% to 50% Foreign spray dryer with waste heat recovery can achieve 70% thermal efficiency, but the equipment has economic significance only when the production capacity is greater than 100kg (water) /h However, when nitrogen carrier and organic solvent are used, the closed circulation system can make nitrogen recycle and solvent condense, thus effectively reducing the production cost.