Some Further Drying Processes

In the past, numerous convective and contact drying processes have been developed and are successfully used to dry all kinds of prodncts such as particulate bulk material and powder, sheets and flnids. They are developed to cope with a wide variety of physicochemical and handling properties. Another reason for the manifold of processes is that most of these processes prodnce different product qualities 

Impinging jet dryers are employed in the case of sheet-like materials such as cardboard, folio, polymer film, paper, textile, and veneer. Hot gas impinges from an array of nozzles onto the good. This process creates high diying rates. Sometimes the good is transported on a substrate and heated from below as well. It may also be transported on air cushions. 

Agricultural goods like crop, silage and malt are dried in kiln and rotary kiln diy-ers, which lead the drying medium through or over the product. Often the drying 

Viscous solutions, polymers, and pastes are preferably dried by contaet diying on the surface of hot drams and belts. Also these processes offer a certain variety in possible product forms like flakes, chips, and pastilles. Also paddle dryers and kneaders are used in this case. 

Diying processes may be intensified by introduction of radiation energy. Infrared radiation is most common. In this case the applied heat is absorbed on the surface of the goods. Recently, microwave radiation is apphed for certain products. Micro-waves are absorbed by the water molecules of the drying good and thus penetrate into the diying good. 

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The trees are cleared of vines and smaller branches are cut off. These leaf-bearing branches are toasted momentarily over an open fire to reduce the moisture content, but with the avoidance of blackening . The process is known as supeco .1 Further drying is carried out by heating over a platform of poles suspended over an open fire for 12 to 24 h. An alternative procedure involves the use of a dome-shaped structure (barbaqua) over which the toasted branches are spread. Hot air is conducted through a tunnel from a fire some distance away. This procedure avoids direct smoke deposition on the leaf. The latter process requires 5 to 15 h. 

As the temperature is lowered further, the viscosity of the unfrozen solution increases dramatically until molecular mobility effectively ceases. This unfrozen solution will contain the protein, as well as some excipients, and (at most) 50 per cent water. As molecular mobility has effectively stopped, chemical reactivity also all but ceases. The consistency of this solution is that of glass, and the temperature at which this is attained is called the glass transition temperature Tg-. For most protein solutions, Tg- values reside between -40 °C and -60 °C. The primary aim of the initial stages of the freeze-drying process is to decrease the product temperature below that of its Tg- value and as quickly as possible in order to minimize the potential negative effects described above. 

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... 

From the process scheme of a C02-mineralization process (Figure P.15.7), in the meantime outdated, it appears that C02 needs to be compressed first, the feedstock needs to be ground to powder and mixed with water to a suspension and the reactor vessel produces a wet product and steam, that can be used to further dry the product. Keeping in mind that the process is meant to capture C02, what are some obvious questions to be raised ... 

Beyond some critical concentration in solid, aggregation of tactoids occurs undoubtedly. The critical concentration depends, obviously, on many factors, but at the present time we are not aware of any experimental studies on this matter, nor on the factors controlling the critical concentration. This further aggregation process yields larger objects with complicated texture and porous structure. Upon drying thick pastes, some kind of cards house structure has been reported (3). However, irregular stacks composed of tactoids with face to face aggregation have been commonly observed (9). 

Powders intended for nasal administration have to be optimized in terms of particle size and morphology as these properties are related to potential irritation in the nasal cavity [23], Certain procedures (e.g., spray drying process) can modify the particle size of the drug powder raw material, but in order to optimize the morphology and flowability properties of some pure drug powders, excipients need to be used. Sacchetti et al. [28] reported that the use of mannitol as a filler and hydroxy-propylmethyl cellulose (HPMC) as a shaper of spray-dried caffeine microparticles modified the typical needle shape of spray-dried caffeine to a more convenient roundish shape. Further addition of polyethylene glycol (PEG) resulted in increased... 

Note that aqueous flotation (with appropriate detergent eompounds) is used to separate the rare-earth-rich particles from the siliceous materials. After drying, the ore is calcinated (fired in air to form the oxides) and then treated with concentrated HCl. A cerium-rich concentrate is left after the other rare earths have dissolved. We have not shown how the cerium concentrate is processed since the main object is to obtain the more expensive oxides as a final product. The rare earth chloride solution is then adjusted to pH = 1.0, purified with activated carbon to remove some of the heavy metals and then extracted with DEHPA. The first extraction separates the "heavy" and "light" fractions of the rare earths. The resulting extracted solutions are then subjected to further extraction processes to produce the individual products, including La, Pr and Nd. 

Non-noble metals in dry air and at room temperature form a thin primary oxide film of different properties, structure, and thickness on the surface. If this oxide film is of low solubility, compact, and free of pores, then it is reducing the corrosion rate by orders of magnitude. This phenomenon is called passivity and the oxide film is called passive film. For some metals, like chromium, the passive film is very thin (some nanometers) and can become conducting. For another group of metals, like titanium, and aluminum, the so-called valve-metals, the oxide layer can get thicker (micrometers) and blocks further electrode processes. 

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