The Liquefaction of Gases

INDUSTRIAL GASES, together with the Liquefaction of Gases. By various authors, including H. S. REDGROVE. (Crosby Lockwood, Second Impression, 1918, 9S. net.)... 

Equations of state (EOS) offer many rich enhancements to the simple pV = nRT ideal gas law. Obviously, EOS were developed to better calculate p, V, and T, values for real gases. The point here is such equations are excellent vehicles with which to introduce the fact that gases cannot be really treated as point spheres without mutual interactions. Perhaps the best demonstration of the existence of intermolecular forces that can also be quantified is the Joule-Thomson experiment. Too often this experiment is not discussed in the physical chemistry course. It should be. The effect could not exist if intermolecular forces were not real. The practical realization of the effect is the liquefaction of gases, nitrogen and oxygen, especially. 

Cryogenetic piston pumps are applied for the liquefaction of gases and for process applications at high-pressure [11] - and extremely low-temperature conditions. 

The temperatures on the envelope where pn = 0 are called inversion temperatures, Tt. At any given pressure, up to a maximum pressure, a given gas exhibits two inversion temperatures. The Joule-Thomson effect is important in refrigeration and in the liquefaction of gases. Modern refrigeration uses the larger effect of the evaporation of working fluids such as the chlorofluorocarbons. 

Problem 13 Mention the various methods that are adopted for producing cold and what is the lowest temperature hitherto attained How has it been reached Show how these have been used in the liquefaction of gases Mention the importance of liquefaction. What is inversion temperature. 

Oxygen was not obtained in the liquid state by Faraday m his classical investigations on the liquefaction of gases, because the refrigerating agents used by him did not suffice for the attainment of the critical temperature of the gas, above which it is impossible to effect liquefaction, no matter how great the pressure. 

In contrast to dipole-dipole forces, London Dispersion interactions are much weaker in nature since they involve nonpolar molecules that do not possess permanent dipole moments. The only modes for molecular attraction are through polarization of electrons, which leads to the creation of small dipole-dipole interactions and mutual attractive forces. Since electron polarization occurs much more readily for electrons farther from the nucleus, this effect is more pronounced for molecules that are larger with a greater number of electrons, especially positioned on atoms with a high atomic number, consisting of more diffuse orbitals. These induced dipole forces are responsible for the liquefaction of gases such as He and Ar at low temperatures and pressures. The relative strength of London Dispersion forces is described by Eq. 3 ... 

The marked fall of temperature accompanying adiabatic, or approximately adiabatic, expansion is used to some extent for cooling purposes in connection with the liquefaction of gases. 

The Joule-Thomson porous plug experiment has received an important technical application in that it is the basis of one of the methods used m the liquefaction of gases Cf infra... 

Kelvin) and performed by J. P. Joule to study departures from ideal gas behavior. The Joule-Thomson expansion, as it is called, is used in the liquefaction of gases and in refrigeration processes (see Chapter 5). ... 

Be able to.solve problems involving the liquefaction of gases... 

An important industrial process is the liquefaction of gases, such as natural gas (to produce LNG), propane, and refrigerant gases, to name a few. One way to liquefy a gas... 

Three terms are important in understanding the process of the liquefaction of gases by pressure critical point, critical temperature, and critical pressure. Critical point is the point at which a gas will exist as a gas or as a liquid. When a gas is heated to its critical temperature at its critical pressure, it becomes a liquid (see Figure 4.2). Critical temperature is the maximum temperature at which a liquid (in this case, a liquefied gas) can be heated and stiU remain a liquid. For example, for butane, the critical temperature is 305°F. As more heat is added, more of the liquid vaporizes. At the critical temperature, no amount of pressure can keep the liquid... 

Andrews experiment An investigation (1861) into the relationship between pressure and volume for a mass of carbon dioxide at constant temperature. The resulting isothermals showed clearly the existence of a critical point and led to greater understanding of the liquefaction of gases. The experiment is named for the Irish physical chemist Thomas Andrews (1813-1885). 

The solution to Problem 2.33 shows that the Joule-Thomson coefficient can be expressed in terms of the parameters representing the attractive and repulsive interactions in a real gas. If the attractive forces predominate, then expanding the gas will reduce its energy and hence its temperature. This reduction in temperature could continue until the temperature of the gas falls below its condensation point. This is the principle underlying the liquefaction of gases with the Linde refrigerator, which utilizes the Joule-Thomson effect. See Section 2.12 for a more complete discussion. 

Sioane, T. O. Liquid Air and the Liquefaction of Gases - Theory, History, Biography, Practical Applications Manufacture , Norman W. Henley Co. New York, NY, 1900 p 299, et seq. 

Linde process A process for the liquefaction of gases by the loule-Thomson effect. In this process, devised by Carl von Linde... 

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