Drying process variables

FIGURE 57.1 Schematic diagram of drying-process variables. 

As stated previously, experimental measurements of the drying rate are usually preferred over using the equations for prediction. However, these equations are quite helpful to predict the effect of changing the drying process variables when limited experimental data are available. 

As drying proceeds, the point is reached where the evaporating surface is unsaturated. The point of evaporation moves into tne sohd, and the dry process enters the second faJhng-rate period. The drying rate is now governed by the rate of internal moisture movement the influence of external variables diminishes. This period usually predominates in determining the overall diying time to lower moisture content. 

Since drying occurs simultaneously with wetting, the effect of diy-ing can substantially modify the expected impacd of a given process variable and this should not be overlooked. In addition, simultaneously drying often implies that the dynamics of wetting are far more important than the extent. 

B. Lueckel, B. Helk, D. Bodmer, and H. Leuenberger, Effect of formulation and process variables on the aggregation of freeze dried interleukin-6 (IL-6) after lyophilization and storage, Pharm. Dev. Technol., 3, 337 (1998). 

Nevertheless, the acquisition of a sufficiently detailed body of physical information can allow a formulator to go far beyond the mere ability to cope with crises when they develop at unexpected times. For a well-understood system, it is theoretically possible to design an automated or semi-automated manufacturing scheme for which the processing variables would be appropriately controlled so as to minimize the possibility of batch failure. Materials passing the hurdles of physical test specifications would be totally predictable in their performance, and they could therefore be blended, granulated, dried, compressed, and delivered into containers without operator intervention. 

The program is written with two logical control variable flags, one takes the value of 1.0 to control the surface evaporation and the other a value of 1.0 to start the diffusional drying process. Array notation for the number of solid segments is used to allow plotting the concentration versus distance at any desired time. 

In the milling, blending, granulating and or drying processes, the operating principles of the equipment employed should be defined, and the variables determined. The impact and mechanism of measurement on in-process variables should be defined. Time, temperature, work input of equipment, blend/ granulation volume, and granulating rate should be determined. 

Prior to scaling up to production, pilot batches were manufactured at the 40 kg scale. In order to show the robustness of the process at the pilot scale, the lubricant level, and the water level, as well as processing variables such as drying temperature, granulating time, and compaction force, were varied as shown in Table 6. 

---