Liquefaction and solidification

Methods of Liquefaction and Solidification. Carbon dioxide may be Hquefted at any temperature between its triple poiat (216.6 K) and its critical poiat (304 K) by compressing it to the corresponding Hquefaction pressure, and removing the heat of condensation. There are two Hquefaction processes. In the first, the carbon dioxide is Hquefted near the critical temperature water is used for cooling. This process requires compression of the carbon dioxide gas to pressures of about 7600 kPa (75 atm). The gas from the final compression stage is cooled to about 305 K and then filtered to remove water and entrained lubricating oil. The filtered carbon dioxide gas is then Hquefted ia a water-cooled condenser. 

Liquefaction and solidification of gases are obtained by compression of gas followed by cooling and throttling, leading to a change of phase for part of the fluid. 

The liquefaction of gaseous H2 occurs at 20.4 and solidification at 14.0 K. However, even in the solid state, H2 molecules have sufficient energy to rotate about a fixed lattice point and consequently the space occupied by each diatomic can be represented by a sphere. In the solid state, these spheres adopt an hep arrangement. 

Aggregation is not solely due to the strong chemical bonds described in Chapter 2. Even noble gas atoms experience weak interatomic forces that lead to liquefaction and, except for helium, solidification at low temperatures. Although these interactions are weak in terms of bond energy, they are of vital importance, especially in living organisms. They also lead to the formation of magnetic domains (Chapter 12) and should not be despised. 

Refrigerated liquids and gases, gases cooled to the point of liquefaction or solidification, such as methane which liquefies at -151 C. Refrigerated gases exert less pressure on their containers than do compressed gases. 

Manufacture Pure sulfur trioxide is industrially produced from oleum by distillation in stainless steel falling film evaporators or forced circulation evaporators and liquefaction of the vapor, in which a minimum temperature of 27 °C must be respected to prevent solidification of sulfur trioxide. The formation of solid sulfur trioxide modifications during longer transport times is hindered by the removal of water and the addition of stabilizers such as thionyl chloride or oxalyl chloride. 

Conversely, if a solid solution of the composition and at the temperature x is heated, liquefaction will begin at the temperature yielding a liquid of the composition d. On continuing to add heat, the temperature of the mass will rise, more of the solid will melt, and the composition of the two phases will change as represented by the curves da and cb. When the temperature has risen to a, complete liquefaction will have occurred. The process of solidification or of liquefaction is therefore extended over a temperature interval ac. 

In this case, as in the case of those systems where the pure components are deposited, a minimum freezing-point is obtained. In the latter case, however, there are two freezing-point curves which intersect at a eutectic point in the case where mixed crystals are formed there is only one continuous curve. On one side of the minimum point the liquid phase contains relatively more, on the other side relatively less, of the one component than does the solid phase while at the minimum point the composition of the two phases is the same. At this point, therefore, complete solidification and complete liquefaction will occur without change of temperature, and the solid solution will accordingly exhibit a definite melting-point. ... 

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