Crystallizers programme-cooled

Figure 7.4 Microcomputer programming of a hatch cooling crystallizer. A, crystallization vessel, B, control heater, C, control cooler. surrounding the draft-tube), D, contact thermometer, E, discharge plug and conical baffle), F, recorder, G, relay, H, temperature programmer, I, cooling water pump, J, cooling water reservoir, K, water inflow L, water outflow after Jones and Mullin, 1974)...

These liner exchange systems make feasible yet another analysis mode direct thermal desorption (DTD). Here the liner or an insert is packed with the solid sample. The liner exchange system can then be used in place of a conventional autosampler. The liner is automatically inserted into the PTV and the volatiles thermally desorbed onto the column. Some analysts may feel uneasy about such desorption from the solid phase how does one know that all of the volatile analytes have been released from the sample crystal lattice However, where applicable, this approach may not be as difficult to validate as one might imagine. For instance, the PTV can be cooled after the analyte transfer, and then, at the end of the chromatographic temperature programme, reheated to repeat the process. Ideally all of the analyte should transfer in the first cycle and none in the second, demonstrating that complete desorption occurs in the method. 

Figure 3. Kinetics of solidification illustrating how various cooling programmes (pathways 1 to 3) can affect the final inventory of phases which differ in their respective crystallization kinetics. The characteristic times are in the microsecond regime for metallic alloys but extend into the time-scales of days for compounds such as oxides.

V 0(H20)4S04]-S04-[H2N(C2H4)2NH2] [76], Na2S04, 2,2 -bipyridine and water in the molar ratio 1.25 5 2 278 were placed in a 23 ml Parr Teflon-lined autoclave which was subsequently heated for 48 hours in a programmable electric furnace maintained at 180°C. After cooling the autoclave at room temperature for 4 hours, brown crystals of [V 202(0H)2(S04)(2,2 -bipyridine)2] were filtered from mother liquor, carefully washed with water, and dried in the air at room temperature. The yield of the product was 55% (based on vanadium). 

Disodium tetraborate, or borax, containing 5 to 10 molecules of water is produced mainly from sodium-containing borate ores (International Programme on Chemical Safety 1998). Crushed and ground ore is mixed with hot recycled water containing some borax. Insoluble gangue (clay particles) is separated from the hot slurry to leave a clear concentrated borax solution. Evaporative cooling of the solution produces crystals of borax that are separated from the residual liquor and dried. 

Figure 9.13 demonstrates the benefits of employing programme-controlled cooling during a seeded batch crystallization of potassium sulphate in which... 

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