Desire, sublimation

Ammonium bicarbonate is produced as both food and standard grade and the available products are normally very pure. Although purification is possible by sublimation at low temperatures, it is more economical to prepare the desired product directiy by using ammonia and carbon dioxide of high purity. 

Solveat extractioa (2,13—15,17) by freeze dryiag provides another means of maintaining chemical homogeneity ia solutioa-derived powders. Freezing solutioas or emulsions preveats chemical segregatioa and the desired salt is obtained by removing the solvent by sublimation. 

Preparation of 1 -(/3-D-arabinofuranosyl)-2-thiocytosine A solution of 2.0 g of 1 -(2, 3, 5 -0-triacetyl-/3-D-arabinofuranosyl)-2,4-dithiouracil in 100 ml of methanol is saturated with anhydrous ammonia at 0°C. The mixture, in a glass liner, is heated in a pressure bomb at 100°C for three hours. The reaction mixture is concentrated to a gum in vacuo, and most of the byproduct acetamide is removed by sublimation at 60°C/0.1 mm. The residue is chromatographed on 100 g of silica gel. Elution of the column with methylene chloride-methanol mixtures with methanol concentrationsof 2-25% gives fractions containing acetamide and a series of brown gums. The desired product is eluted with 30% methanol-methylene chloride to give a total yield of 0.386 g (30%), MP 175°-180°C (dec.). Recrystallization from methanol-iso-propanol furnishes an analytical sample, MP 180°-182°C (dec.). 

Parts of pyrazine-2arboxylic acid is heated in a reaction vessel provided with an intake for Inert gas. The reaction mixture is heated in a bath held at 220°C and nitrogen is introduced. The solid material melts and effervesces and sublimed pyrazinamide vapors are carried out of the reaction vessel in the nitrogen stream. They are introduced into a suitably cooled condenser, condensing in the form of a white sublimate. After the reaction is proceeding vigorously the bath temperature is raised to 255 C and then gradually and slowly allowed to drop to 190°C over a period of time sufficient to permit the reaction to go substantially to completion. The sublimed pyrazinamide, if desired, is further purified by recrystallization from water or alcohol. 

Sample analyses by metallography, x-ray diffraction and spectroscopy confirmed the desired solid compositions. These analyses revealed that only the small compositional variations expected due to the sublimation were encountered during the studies. 

For purification of the product, tubes A and B are cleaned, dried, and reassembled with a dry glass-wool insert in B. Tube C, containing the initially formed product, is attached to tube B as shown in Fig. 2. The system is evacuated and this time left open to the vacuum. The two furnaces are separated by ca. 1.5 cm. Furnace I is heated to 80° and furnace II to 130 to 140°. Sublimation is allowed to continue until all the titanium(IV) iodide has left tube C (12 to 16 hours). The purified product crystallizes in tube B at the separation of the two furnaces. The major impurity, iodine, crystallizes in tube A and in the liquid-nitrogen trap. A fluffy tan residue of negligible weight (0.04 to 0.06 g.) remains in tube C. If desired, further purification can be accomplished by moving tube B farther into furnace II, which results in a second sublimation of the product. 

With this information the maximum flow of energy can be estimated, which can be transported during freezing and main drying at a desired temperature difference between inlet and outlet temperature of the brine at the shelves, e. g. 2000 kj/h at a temperature difference of 3 °C. With this amount of energy approx. 0.7 kg ice could be sublimated per hour. (This estimate gives only the maximum possible sublimation-rate, whether it can be achieved or not depends from heat -and mass transfer conditions in the process (see Section 1.2.1 and Eq. (12)). 

However, the obscure choice of frequencies in the visible and UV regions in the original calculations may have been guided by a desire to fit experimental heats. In fact, the Debye rotational and translational crystal frequencies relate to sublimation energies of the lattice, and, together with internal molecular vibrations, can be used to calculate thermodynamic functions (16). An indirect connection between maximum lattice frequencies (vm) and heats of formation may hold because the former is inversely related to interatomic dimensions (see Section IV,D,1) ... 

The analytical expression for a given property can be reparametrized, if desired, to apply to a particular class of compounds. Our tendency is usually to have, as general, a database as possible. But for example, Byrd and Rice desired to optimize the heat of sublimation and heat of vaporization equations specifically for nitro derivatives [46]. They retained the dependence on surface area and vofot, but used a nitro compound database to obtain new coefficients for these quantities. 

Alchemy teaches this sublimation of desire under the metaphor of coins, metal monetary discs. The coin is a blind for the Pentacle, the magical tool representing the Earth of the wise and the world of Assiah. The Pentacle appears on the table of The Magician in Key I and is the last suit of cards in the Minor Arcana. The Pentacle is the symbol of... 

If it is desired to sublime larger amounts of substance, the upper watch-glass of the apparatus just described is replaced by a funnel, of which the diameter is somewhat less than that of the watch-glass. 

The term sublimation strictly refers to the phase change solid -> vapour, with no intervention of a liquid phase. In industrial applications, however, the term usually includes the reverse process of condensation or desublimation solid -> vapour -> solid. In practice, it is sometimes desirable to vaporise a substance from the liquid state and hence the... 

To model the solubility of a solute in an SCF using an EOS, it is necessary to have critical properties and acentric factors of all components as well as molar volumes and sublimation pressures in the case of solid components. When some of these values are not available, as is often the case, estimation techniques must be employed. When neither critical properties nor acentric factors are available, it is desirable to have the normal boiling point of the compound, since some estimation techniques only require the boiling point together with the molecular structure. A customary approach to describing high-pressure phenomena like the solubility in SCFs is based on the Peng-Robinson EOS [48,49], but there are also several other EOS s [50]. 

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