Drying process phases

For the organic contaminants, the required bromine product quality wilt also be site specific. If the catalytic oxidation unit is dedicated to a single bromination process, phase separation and drying may be the only purification required. Contaminants in the recovered bromine which are either the starting materials or products of the original bromination reaction should not present a problem if present in bromine recycled to the bromination reactor. In this case, the catalytic reactor would be operated to minimize the formation of undesirable brominated byproducts. For example, if phenol is present in the waste HBr from a tribromo-phenol manufacturing process, minor tribromophenol contamination of the bromine recycled to the reactor should not be a problem. Similarly, fluorobenzene in bromine recycled to a fluorobenzene bromination process should not present a problem. 

Decaffeination of green coffee beans is most usually carried out with a water/solvent partition system. The green coffee beans are first steamed until they are hot, wet, and swollen, to make the caffeine available. Solvent is then used to extract the caffeine out of the aqueous phase of the beans. Finally, the beans are steamed to drive off residual solvent. The coffee beans lose their wax surface covering in the process, as well as some flavor components. For this reason, the Robusta and Brazilian Arabica coffees that are dry-processed and have the most powerful flavors are usually the types that are decaffeinated. They become milder in the process. Mechanical polishing is used to improve the appearance of decaffeinated green coffee beans if they are not to be roasted immediately. Extra care is required, however, to store these decaffeinated beans since the loss of wax covering as well as caffeine renders them much more susceptible to fungal attack. 

The freeze-drying process is initiated by the freezing of the biopharmaceutical product in its final product containers. As the temperature is decreased, ice crystals begin to form and grow. This results in an effective concentration of all the solutes present in the remaining liquid phase, including the protein and all added excipients. For example, the concentration of salts may increase to... 

The next phase of the freeze-drying process entails the application of a vacuum to the system. When the vacuum is established, the temperature is increased, usually to temperatures slightly in excess of 0 °C. This promotes sublimation of the crystalline water, leaving behind a powdered cake of dried material. Once satisfactory drying has been achieved, the product container is sealed. 

Freeze drying or lyophilization is a drying process, in which the solvent and/or the medium of suspension is crystallized at low temperatures and thereafter sublimated from the solid state directly into the vapor phase. 

Freeze-drying is a layman s description, and acknowledges that external conditions may alter the conditions of a phase change, i.e. the drying process (removal of water) occurs at a temperature lower than 100°C. 

Vautaz, G. 2002. The phase diagram of milk A new tool for optimizing the drying process. Lait 82, 485-500. 

It should be noted that a column that has been deactivated with water no longer shows adequate separation properties. Restoring the activity of the column by pumping a large volume of dry mobile phase through the column is a slow and expensive process. Alternatively, reactivation can be accomplished chemically using the acid-catalyzed reaction between water and 2,2-dimethoxypropane, the products of which, acetone and methanol, are easily eluted from the column [14]. 

Therefore, product temperature should be monitored closely to control the fluidized bed drying process. During fluid-bed drying, the product passes through three distinct temperature phases (Fig. 21). At the beginning of the drying process, the material heats up from the ambient temperature to approximately the wet-bulb temperature of the air in the dryer. This temperature is maintained until the granule moisture content is reduced to the critical level. At this point, the material holds no free surface water, and the temperature starts to rise further. 

Fig. 15. 2-D slice sections through 3-D MR images of water distribution within an initially water-saturated packing of 500-pin glass spheres. Voxel resolution is 94 pm x 94 pm x 94 pm. Data are shown before drying commenced and at three time intervals during the drying process. Only the water within the inter-particle space of the bead packing was imaged (white pixels). No signal was obtained from the solid and gas phases present.

Other semi-2-IPNs [52] processed by the freeze-drying method included IPN from 4,4 -bismaleimido diphenylmethane (BMI) and linear BTDA/3,4 -ODA polyamic acid that were dissolved in 1,3,5-trioxane (Fig. 16). The resulting semi-2-IPNs exhibited higher Tgs and reduced phase separation, and contained no plasticizing solvent. A comparison of unidirectional properties of composites prepared by the freeze-dry process to those by traditional solvent evaporation process is presented in Table 13. The freeze-drying method for the preparation of IPNs appears to be superior to previous technology. 

The presence of sulfate ions markedly affects the nanopore structure of titania-sulfate aerogels. In Ti02-S042 materials, unlike in zirconia-sulfate aerogels, the larger sulfate load stimulates formation of a more consolidated structure. The XRD analysis shows that even a crystalline phase (anatase) may be present in fresh, dry aerogels, which, perhaps, is the first observation of this phase in sol-gel titania obtained from the low temperature drying process. 

As the gas flow rate increases beyond that at minimum fluidization, the bed may continue to expand and remain homogeneous for a time. At a fairly definite velocity, however, bubbles begin to form. Further increases in flow rate distribute themselves between the dense and bubble phases in some ways that are not well correlated. Extensive bubbling is undesirable when intimate contading between phases is desired, as in drying processes or solid catalytic reactions. In order to permit bubble formation, the... 

DRYING (Process). Frequently in the process industries, materials must be dried, i.e., liquid must be removed from a solid or gaseous phase. In most instances, the liquid to he removed is water, although in solvent... 

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