Steam solution evaporation

It is frequently necessary to concentrate a filtrate in order to obtain a further crop of crystals, or it may be necessary to concentrate a solution to a smaller volume. If the solvent is water and the substance is not volatile in steam, simple evaporation on a large dish on a steam or water... 

Nicotinamide. Place 50 g. of pure ethyl nicotinate (Section V,23) in a 350 ml. bolt-head flask and add 75 ml. of concentrated aqueous ammonia saturated at 0°. Keep the flask loosely stoppered for 18 hours, after w)iich time the lower layer generally dissolves on shaking. Saturate the solution with ammonia and allow it to stand for a further 4 hours. Repeat the saturation with ammonia crystals of the amide commence to appear in the solution. Evaporate to drjmess in a dish on the steam bath and dry at 120°. The yield of nicotinamide, m.p. 130°, is usuallj quantitative. 

In the above example, 1 lb of initial steam should evaporate approximately 1 lb of water in each of the effects A, B and C. In practice however, the evaporation per pound of initial steam, even for a fixed number of effects operated in series, varies widely with conditions, and is best predicted by means of a heat balance.This brings us to the term heat economy. The heat economy of such a system must not be confused with the evaporative capacity of one of the effects. If operated with steam at 220 "F in the heating space and 26 in. vacuum in its vapor space, effect A will evaporate as much water (nearly) as all three effects costing nearly three times its much but it will require approximately three times as much steam and cooling water. The capacity of one or more effects in series is directly proportional to the difference between the condensing temperature of the steam supplied, and the temperature of the boiling solution in the last effect, but also to the overall coefficient of heat transfer from steam to solution. If these factors remain constant, the capacity of one effect is the same as a combination of three effects. 

Fit up the apparatus shown in Fig. 64. It consists of a large wide-necked bottle, in which the ammonia solution is placed The solution is stirred by a mechanical stirrer, rotated by means of a water-turbine. The solution of the chloracetic acid in 50 c.c. water, is dropped in from a tap-funnel. After standing 24 hours the liquid is poured into a flask, and the C lcess of ammonia is removed by passing in a current of steam, and evaporating at the same time on the water-bath until the last traces of ammonia disappear. The solution now contains gly-... 

The bomb tubes are returned to the dry ice-acetone bath. After cooling thusly, the tubes are drawn out to a fine capillary to allow the ammonia to escape, and the entire reaction mixture is immediately collected in an excess of dilute HCl acid solution. Evaporate the acidic solution to dryness on a steam bath, desiccate the residue, and extract in a soxhlet extractor for 12 hours using chloroform as the solvent (dry chloroform) and taking care to exclude all H2O. Distill off the chloroform and if separation is not important to you, then you can use the combination of all three amines in a synthesis calling for any one of the three. 

Dichloropurine (5 g, 25 mmol) was dissolved in 40% aq MeNH (150 mL). I he solution was heated on a steam bath for 2 h. Additional MeNH soln (100 mL) was added and the solution evaporated to dryness on the steam bath. The residue was dissolved in hot, dil HCl, treated with charcoal, and filtered, and the pH of the filtrate was adjusted to 7 with dil KOH. After refridgeration overnight, the light yellow product was filtered, washed with HjO and EtOH, and dried yield 0.9 g (19%). 

Methyl 2- 1,5-Dlmethylbicyclo [2.1.1] hexanyl-2-bromoacetate) (2).4 To a mixture of 1.5- nethylbfcyclo [2.1.1] hexane-2-acelic add 1 (2 92 g, 12.4 mmol) in PBr3 (7.94 g, 29 3 mmoO maintained for 1 h at room temperatura, was added Br2 (7.94 g, 57 mmol) in two batches under Ar. The reaction mixture was heated on a steam bath for 3 h, cooled, quenched with anh. MeOH. rSwed with EtjO and the organic layer was washed with 5% NaHCOs solution. Evaporation of the solvent and distillation of the residue gave 4.0 g of 2 (88%), bp 58-59-C (0.33 mm). 

A solution of 3 (1.0 g, 4 mmol) in CHCI3 (100 mL) was shaken with aqueous sodium dithiorete until the organic layer became coiortess. The glassy residue obtained after evaporation was dissolved in dk>xane TEA (1.1) (100 mL) by heating 12 h on a steam bath. Evaporation and chromatography (preparative TLC - PhH.MeOH 9 1) gave 0.6 g of 4 (89%), mp 77-7B.3 C. 

The previous discussion in this chapter has largely centred on crystallisation fouling under sensible heat transfer, but heat transfer under boiling conditions occurs in equipment such as steam boilers, evaporators for the concentration of solutions prior to crystallisation (e.g. sugar or table salt manufacture) or for the desalination of brackish or sea water. 

Fig. 7-10. Balance scheme to determine the solvent vapor flow and steam consumption (a) and heat flow diagram for single stage solution evaporation (b).

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