Refrigerants cooling time

Fig. 2.21. Temperature of the shelf in a freeze drying plant as a function of cooling time, calculated for four different refrigerants.

C The cooling of a beef carcass from 37°C to 5 C with refrigerated air at 0 C in a chilling room takes about 48 h. To reduce the cooling time, it is proposed to cool the carcass with re frigeraled air at -10°C. How would you evaluate this proposal ... 

Crea.m Yeast. At a 5% soHds concentration in the fermentor, the yeast occupies about 12% of the fermentor volume. It is harvested by centrifugation in nozzle centrifuges and washed several times with water. The final centrifugate is cooled and stored in refrigerated tanks. This yeast cream (so called because of its off-white color) may be sold directly in this form, since in large baking faciHties, it may be piped directly to any desired location. 

The cooled mixture is transferred to a 3-1. separatory funnel, and the ethylene dichloride layer is removed. The aqueous phase is extracted three times with a total of about 500 ml. of ether. The ether and ethylene chloride solutions are combined and washed with three 100-ml. portions of saturated aqueous sodium carbonate solution, which is added cautiously at first to avoid too rapid evolution of carbon dioxide. The non-aqueous solution is then dried over anhydrous sodium carbonate, the solvents are distilled, and the remaining liquid is transferred to a Claisen flask and distilled from an oil bath under reduced pressure (Note 5). The aldehyde boils at 78° at 2 mm. there is very little fore-run and very little residue. The yield of crude 2-pyrrolealdehyde is 85-90 g. (89-95%), as an almost water-white liquid which soon crystallizes. A sample dried on a clay plate melts at 35 0°. The crude product is purified by dissolving in boiling petroleum ether (b.p. 40-60°), in the ratio of 1 g. of crude 2-pyrrolealdehyde to 25 ml. of solvent, and cooling the solution slowly to room temperature, followed by refrigeration for a few hours. The pure aldehyde is obtained from the crude in approximately 85% recovery. The over-all yield from pyrrole is 78-79% of pure 2-pyrrolealdehyde, m.p. 44 5°. 

The -toluenesulfonylhydrazide separates as fluffy, white platelets. The hydrazide, after cooling overnight in a refrigerator to complete crystallization, is filtered through a Buchner funnel. The filter cake is washed several times with petroleum ether (b.p. 35-60°), sucked dry, and then air-dried. / -Toluenesulfonyl-hydrazide (172-173 g., 90% yield) is obtained as a white, odorless, crystalline product, m.p. 101-104° (Note 7). 

A 500-ml, three-necked, round-bottom flask is fitted with a mechanical stirrer, a thermometer, and a wide-stern (powder) funnel. The flask is cooled in an ice-salt bath and charged with 125 ml (approx. 0.5 mole) of 15% sodium hydroxide solution. When the stirred solution reaches -10°, 30% hydrogen peroxide (57.5 g, 52.5 ml, approx. 0.5 mole) previously cooled to -10° is added in one portion. The pot temperature rises and is allowed to return to —10° whereupon 37.5 g (0.25 mole) of phthalic anhydride (pulverized) is added rapidly with vigorous stirring. Immediately upon dissolution of the anhydride, 125 ml (approx. 0.25 mole) of cooled (-10°) 20% sulfuric acid is added in one portion. (The time interval between dissolution of the anhydride and the addition of the cold sulfuric acid should be minimized.) The solution is filtered through Pyrex wool and extracted with ether (one 250-ml portion followed by three 125-ml portions). The combined ethereal extracts are washed three times with 75-ml portions of 40% aqueous ammonium sulfate and dried over 25 g of anhydrous sodium sulfate for 24 hours under refrigeration. 

After concentrating the filtrate to approximately 400 ml, solids started crystallizing out at which time the filtrate was cooled by refrigerating at 5°C for several hours. Filtration gave 1B.7 g of L-Dopa, MP 284° to 286°C (dec.) [oJd 8.81° (1% solution in aqueous 4% HCI). The infrared spectrum and paper chromatography indicated very good L-Dopa according to U.S. Patent 3,253,023. 

The above product was then recrystallized from 900 ml of 95% ethanol after filtering the hot solution through Celite. Crystallization was initiated and the mixture agitated occasionally while being cooled in the refrigerator. Yield of product 29 g, MP 253° to 259°C, Concentration of the filtrate to 125 ml yielded another 7.5 g of product, MP 253° to 259°C. The product was recrystallized another time in the manner described above. Total yield, first and second crops, 28.8 g (66%), MP 250° to 255°C. Product was dried at 80°C in a vacuum, according to U.S. Patent 3,360,518. 

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