Drying chambers

Fig. 10. Schematic of casting machine used to make microporous membranes by watervapor imbibition. A casting solution is deposited as a thin film on a moving stainless steel belt. The film passes through a series of humid and dry chambers, where the solvent evaporates from the solution, and water vapor is absorbed from the air. This precipitates the polymer, forming a microporous membrane that is taken up on a collection roU (25).

The second step is to disperse the core material being encapsulated in the solution of shell material. The core material usually is a hydrophobic or water-knmiscible oil, although soHd powders have been encapsulated. A suitable emulsifier is used to aid formation of the dispersion or emulsion. In the case of oil core materials, the oil phase is typically reduced to a drop size of 1—3 p.m. Once a suitable dispersion or emulsion has been prepared, it is sprayed into a heated chamber. The small droplets produced have a high surface area and are rapidly converted by desolvation in the chamber to a fine powder. Residence time in the spray-drying chamber is 30 s or less. Inlet and outlet air temperatures are important process parameters as is relative humidity of the inlet air stream. 

Active Dry Yeast (ADY). The production of active dry yeast is very similar to the production of compressed yeast. However, a different strain of yeast is used and the nitrogen content is reduced to 7% of soHds compared with 8—9% for compressed yeast. The press cake made with the active dry yeast strain is extmded through a perforated plate in the form of thin strands with a diameter of 2—3 mm and a length of 3—10 mm. The strands are dried on endless belts of steel mesh in drying chambers (a continuous process) or in roto-louvre dryers (a batch process), with the temperature kept below 40°C. Drying time in drying chambers is 3—4 h and in roto-louvre dryers is 6 h or more. The final moisture level attained is 7.5—8%. 

The agitated flash dryer (Fig. 12-106) consists of four major components feed system, drying chamber, heater, and exhaust air system. 

Syringe techniques have been developed for small volumes, while for large volumes or where much manipulation is required, dryboxes (glove boxes) or dry chambers should be used. 

It may be assumed that outlet gas composition from the coating and the dry chambers are independent of the entering gas compositions. 

Recrystallizatlon of the Crude Inosine 17.0 g of crude inosine are dissolved in 400 cc of 80% ethanol in a water bath, filtered while hot and brought to crystallization in an ice box. After standing overnight the crystalline material Is filtered off under suction and washed with ice water. The pure inosine is dried in a drying chamber at a temperature of 105°C. The yield of pure inosine is 15.0 g which is equal to 75%. The yield can be further increased by working up the mother liquor of the crystallization as set forth above. 

FIGURE 5.21 (a) Baron drying rack and (b) drying chamber for TLC plates. 

In freeze-drying, a solution is filled into vials, a special slotted stopper is partially inserted into the neck of the vial (Fig. 3), and trays of filled vials are transferred to the freeze-dryer. The solution is frozen by circulation of a fluid, such as silicone oil, at a temperature in the range of — 35 to about — 45°C through internal channels in the shelf assembly. When the product has solidified sufficiently, the pressure in the freeze-dry chamber is reduced to a pressure less that the vapor pressure of ice at the temperature of the product, and heat is applied to the... 

Liquid C02 from a siphon-tube tank is introduced into the chamber and used to replace 100% of the ethanol in the specimen. After the ethanol has been totally replaced by the C02, the critical point drying chamber (CPD) is brought above the critical point. The temperature is kept above the critical point, while the gaseous C02 is vented from the chamber. The process is finished when the CPD is returned to atmospheric pressure. After critical point drying, the specimen should be totally dry and it is ready to be introduced to the vacuum system of the sputter coater and SEM (Dykstra, 1993 Hayat, 1978). 

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