Forming , solid-phase equipment

Liquids form solid phases on crystallization which are denser than the liquid (with the exception of water), and hence the freezing points are raised by increases in pressure. It is essential to avoid solidification because it can prevent a reaction from occurring and because possible damage to equipment may result. The freezing pressures of some common organic solvents at 25 °C are given in Table 7.2. 

Heterogeneous reactions of industrial significance occur between all combinations of gas, liquid, and solid phases. The solids may be inert or reac tive or catalysts in granular form. Some noncatalytic examples are listed in Table 7-11, and processes with solid catalysts are listed under Catalysis in Sec. 23. Equipment and operating conditions of heterogeneous processes are covered at some length in Sec. 23 only some highlights will be pointed out here. 

Rotating-drum-type and belt-type heat-transfer equipment forms granular products directly from fluid pastes and melts without intermediate preforms. These processes are described in Sec. 5 as examples of indirect heat transfer to and from the solid phase. When solidification results from melt freezing, the operation is known as flaking. If evaporation occurs, solidification is by diying. 

Solid phase is formed internally thus, only liquid streams enter and exit the column. Solid phase is formed in external equipment and fed as slurry into the purifier. 

In some circumstances, separation of solid from a liquid is better achieved by use of a centrifuge than by filtration, and a small, electrically driven centrifuge is a useful piece of equipment for an analytical laboratory. It may be employed for removing the mother liquor from recrystallised salts, for collecting difficultly filterable precipitates, and for the washing of certain precipitates by decantation. It is particularly useful when small quantities of solids are involved centrifuging, followed by decantation and re-centrifuging, avoids transference losses and yields the solid phase in a compact form. Another valuable application is for the separation of two immiscible phases. 

The study of carbon electrodeposition from carbonate and halide- carbonate melts was devoted a cycle of works [1 - 6]. It was found that under certain conditions carbon solid phase was formed on cathode with 100 % current yield. The questions of product morphology, structure and dispersity had remained not opened because of absence at that time analysis technical equipment with high-resolution. Different schools of the electrochemists offered various mechanisms of carbon phase formation ... 

In Sections III and IV, the principles of nucleation and growth were discussed separately. Now the crystallization process as a whole will be considered. In any practical application of crystallization, a stable solid phase must first be formed from the metastable liquid phase, and then additional molecules are deposited on the nucleus to form the macroscopic crystalline solid. Since nucleation and growth are taking place simultaneously, the theoretical principles discussed earlier are difficult to apply quantitatively to crystallization practice. Consequently, empirical expressions are still generally used in the design of equipment and prediction of its operation. 

This is a classical method for measurement of molecular weights of micromolec-ular species. The equipment is relatively simple. Problems include the elimination of supercooling and selection of solvents which do not form solid solutions with solutes and do not have solid phase transitions near their freezing temperatures. 

For the parallel synthesis of ureas based on amino acids, a solid-phase synthesis as well as a solution-phase synthesis were used (Scheme 5) [11]. Solution-phase synthesis gave the desired compounds 21 in yields ranging from 80-100% and purities in the range 71-97%. The work-up involved extraction of the benzotriazole formed in the coupling steps. An aqueous borax buffer (pH 9.2) was used and the separation of the CH2CI2 layer from the aqueous phase was performed in cartridges equipped with a PTFE frit. 

Solid phase is formed in external equipment and fed as slurry into the purifier. 

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