Condensation of mixed vapours

Condensation of mixed vapours is considered further in Volume 6, Chapter 12, where it is suggested that the local heat transfer coefficient may be expressed in terms of the local gas-film and condensate-film coefficients. For partial condensation where ... 

It is normal practice to assume that integral condensation occurs. The conditions for integral condensation will be approached if condensation is carried out in one pass, so that the liquid and vapour follow the same path as in a vertical condenser with condensation inside or outside the tubes. In a horizontal shell-side condenser the condensate will tend to separate from the vapour. The mean temperature difference will be lower for differential condensation, and arrangements where liquid separation is likely to occur should generally be avoided for the condensation of mixed vapours. 

Matsouka, M. in Jancic, S. J. and de Jong, E. J. (eds.) Industrial Crystallization 84 (Elsevier, Amsterdam 1984) 357-360. Rates of nucleation and growth of organic condensates of mixed vapours. 

Deo, P. V., Condensation of Mixed Vapours, Ph.D. Thesis in Chemical Engineering, University of Manchester, Institute of Science and Technology, Manchester, England, 1979. 

HCl gas dissolves in it to cause a sudden partial decrease in atmospheric pressure and the partial temperature may fall to some extent. This causes the condensation of water vapour in the saturated state to form another mist which absorbs the HCl gas again. This phenomenon spreads wider and wider in the damp air and creates a large volume of dense smoke. It is observed that the smoke is not created at the flame, but at a distance from the flame where the burnt gas and the air mix well together. 

The values of AG, AH and A/S obtained from K and its temperature dependence refer therefore to the following process [21] a solute in the gas phase, at temperature T, of unit molar concentration (m/F = = p/HT = 1) and ideal behaviour is transferred to solution in the liquid phase at T, with molar concentration equal to mity and intermolecular interactions characteristic of infinitely diluted solutions. Thus, solute vapotu s rather than liquid solute solve in the stationary phase. The overall process implies condensation of solute vapours followed by mixing the two liquids. A comparison of the thermodynamic properties of dissolution in the chromatographic column with the corresponding condensation properties (the vaporization properties of a single solute taken with minus sign) will supply infoimation on the difference between solute-solvent and solute-solute interactions. 

The material to be steam-distilled (mixed with some water if a solid compound, but not otherwise) is placed in C, and a vigorous current of steam blown in from D. The mixture in C is thus rapidly heated, and the vapour of the organic compound mixed with steam passes over and is condensed in E. For distillations on a small scale it is not necessary to heat C if, however, the flask C contains a large volume of material or material which requires prolonged distillation, it should be heated by a Bunsen burner, otherwise the steady condensation of steam in C will produce too great a volume of liquid. 

Dehumidification of air can be effected by bringing it into contact with a cold surface, either liquid or solid. If the temperature of the surface is lower than the dew point of the gas, condensation takes place and the temperature of the gas falls. The temperature of the surface tends to rise because of the transfer of latent and sensible heat from the air. It would be expected that the air would cool at constant humidity until the dew point was reached, and that subsequent cooling would be accompanied by condensation. It is found, in practice, that this occurs only when the air is well mixed. Normally the temperature and humidity are reduced simultaneously throughout the whole of the process. The air in contact with the surface is cooled below its dew point, and condensation of vapour therefore occurs before the more distant air has time to cool. Where the gas stream is cooled by cold water, countercurrent flow should be employed because the temperature of the water and air are changing in opposite directions. 

To evaluate the true temperature difference (driving force) in a mixed vapour condenser a condensation curve (temperature vs. enthalpy diagram) must be calculated showing the change in vapour temperature versus heat transferred throughout the condenser, Figure 12.48. The temperature profile will depend on the liquid-flow pattern in the condenser. There are two limiting conditions of condensate-vapour flow ... 

Aldol condensations were originally carried out in the liquid phase and catalysed homogeneously by acids or bases this way of operation is still predominant. Solid-catalysed aldol reactions can also be performed in the liquid phase (in trickle or submerged beds of catalyst), but in many cases vapour phase systems are preferred the factors determining the choice are the boiling points and the stability of the reactants at elevated temperatures. At higher temperatures, the formation of a, j3-unsaturated aldehydes or ketones [reactions (B) and (C)] is preferred to aldol (ketol) formation [reaction (A)]. A side reaction, which may become important in some cases, is the self-condensation of the more reactive carbonyl compound if a mixed condensation of two different aldehydes or ketones is occurring. The Cannizzaro reaction of some aldehydes or polymerisation to polyols or other resin-like products can also accompany the main reaction. 

The gas mixture escaping from the tower first of all enters a cooler to condense the water vapour. The dry mixture which contains less than 0.1% of water vapour is then mixed with oxygen and led to the oxidation reactor, where in the presence of a catalyst the following reaction is allowed to proceed at a temperature of 300 °C ... 

Condensation and Redistillation.—The condensation of the phosphorus vapour, mixed as it is with dust and furnace gases, presents special difficulties. The sketch (fig. 2) shows, diagrammatically only, how these have been overcome in the patent of Billandot et Cie.1... 

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