Drying process data examples

Wiliemer, H. Freeze-drying process data determination for human blood derivates with factor VIII as example. PDA Fourth International Congress, p. 142-151, Vienna, 1996. Copyright 1996, PDA Inc. Bethesda, Maryland, USA... 

Unfortunately, to the best of our knowledge, there is no appropriate published experimental data on a 3D spray drying process for the pilot-scale spray chamber used here. However, the developed model of internal and external transport phenomena can be validated by experimental values available for a closely similar drying process, for example, pneumatic drying. For this purpose, the presented model, with slight modifications, has been utilized to perform steady-state numerical simulations of 3D pneumatic... 

Example ps at the sublimation front is 0.937 mbar (-21 °C) (see example in Table 1.9), in the chamber a pU20 = 0.31 mbar has been measured, resulting in a pressure difference of approx. 0.6 mbar. With these data, the water vapor permeability blp = 1.1 10 2 kg/h m mbar is calculated. With this data known, it is possible to calculate dp for different conditions, if the mass of frozen water miCL, the time /MD, the thickness (d) and the surface (F) are known. This dp depends from the amount vapor transported and thereby from the heat transfer (Table 1.9). In the examples given it changes between 0.17 mbar in a slow drying process (6 h) to 0.6 mbar for a shorter drying time, 2.5 h. 

The etch rate ratio of the resist to the Si02 reference is referred to as the resist process selectivity, and coupled with resist thermal stability data is representative of the overall resist process compatibility. The lower the selectivity ratio (i.e., 1), the better the resist polymer dry-process compatibility. PMMA, for example, has a marginal selectivity of 0.9-1.2, or etches at the undesirably same rate as Si02. In addition, PMMA is also very susceptible to thermally-induced image flow due to low tg and TGA parameters, and also undergoes surface "frying" phenomena (see Figure 2). Therefore, PMMA has very poor overall dry-process compatibility. 

As for the vinyl polymers, there appears to be no obvious correlation between resist thermal stability, as measured by the TGA parameter and resist image flow data, and PE rate ratio. It is obvious at this point however, that both thermal stability and low PE rate ratio are very desirable to achieve good overall dry-process compatibility. Based on the data of Table II, OFFR-800 and Hunt 204 are clearly examples of dry-process compatible resists. 

One key feature in this example is that we have conveniently separated the drying process into two systems. Whenever you have data on the humidity of air, it is convenient to separate it into two systems, as depicted in Fig. 7.27. In addition, as explained in the previous problems, we are not considering xh206 and xh207 as variables because they are equal to xh2os (due to the division). 

Consequently, a common effort should be made to establish and complete the data basis concerning the numerous thermodynamic, thermophysical, transport and rheological properties necessary for modeling and simulating the different steps of this complex mild drying process. Moreover, the methods available for the characterization of most of these end-use properties should be improved and additional characterization methods should be adapted from other research fields (material science, applied biochemistry, physical chemistry, etc.). Improved characterization methods promise a better description and a safer control of numerous end-use properties for existing freeze-dryers as well as for new machines with more possibilities to better comply with more and more severe quality requirements in the future. The use of non-invasive sensors or of rapid non-intrusive methods for on-line and in situ estimation of the main parameters of the process could also help to overcome the difficulties observed, for example, the artifacts resulting from invasive sensors inserted inside vials and presently commonly used. 

I have tried to show the interconnection between the property of the product, the goal to make it stable and the necessary processes to achieve this. The problems of the different process steps are discussed with examples and the parameters are described which influence each step. I have avoided following the many theoretical attempts describing one or more of the freeze-drying steps, but have restricted myself to a few equations which permit the calculation of process and product data with sufficient accuracy, or at least, allow an estimate, if some data is mentioned. 

Example 2 In a Pet Tabs (pet vitamin tablets) production, the pharmaceutical manufacturer is using milling and micronizing machines to pulverize raw materials into fine particles. These finished particles are combined and processed further in mixing machines. The mixed ingredients are then pressed into tablets, dried, and sealed in packages. A normally distributed quality characteristic, moisture content, is monitored. Samples of n = 4 tablets are taken from the manufacturing process every hour. The data after 25 samples have been collected are shown in Table 5. 

We have investigated the humification of straw, as an example, under constant conditions of humidity and temperature in a climatic chamber (4,18) and separated different fractions according to a modified method of Waksman s proximate analysis. The amount of nitrogen present in these processes is the factor limiting the rate of decomposition. Therefore we added nitrogen in form of ammonium nitrate in a quantity of 1% of straw dry weight to a nutrient solution in one experiment while the nutrient solution had no nitrogen in a parallel experiment. Table I shows the calculated data. 

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