Principles of Gas Separation

In Fig. 6.8 note that the first condensation of this 80 mol % nitrogen-20 mol % helium mixture occurs at approximately 111 K. However, because of the widely differing boiling points between these two components, the concentration of helium in the condensate at this temperature is only 0.6 mol %. The concentration of the helium in the liquid attains a maximum when the temperature is lowered to approximately 103 K, and with further cooling the concentration of helium decreases as more of the nitrogen is condensed. Thus, simple condensation to 80 K makes it possible to recover a vapor product that has a helium concentration of nearly 94 mol % and a liquid product with a helium concentration of about 0.5 mol %. 

Example 6.6. A mixture of 79 mol % nitrogen and 21 mol % oxygen under a pressure of 0.101 MPa is cooled to 80 K. Does condensation occur and at what temperature If condensation occurs at 80 K, how much of the original mixture is condensed and what are the compositions of the liquid and vapor phases  

Solution. By interpolation Table 6.3 indicates that the dew-point temperature for a 79 mol % nitrogen-21 mol % oxygen mixture under a pressure of 0.101 MPa is 81.7 K. Thus, condensation does occur. Since the bubble-point temperature for this same mixture at the same pressure is 78.9 K, a two-phase mixture will be present at 80 K. The composition of the liquid phase can be obtained with the use of Eq. (6.22) and the equilibrium constants for nitrogen and oxygen from Table 6.2. Thus 

The fraction condensed may be obtained by making a component material balance 

Thus 41.4% of the mixture is condensed with a nitrogen mole fraction in the condensate of 0.654 while the vapor in equilibrium with the condensate has a nitrogen mole fraction of 0.886. Note that the liquid and vapor concentrations agree with those shown in Fig. 6.9. 

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Adsorption Chromatography. The principle of gas-sohd or Hquid-sohd chromatography may be easily understood from equation 35. In a linear multicomponent system (several sorbates at low concentration in an inert carrier) the wave velocity for each component depends on its adsorption equihbrium constant. Thus, if a pulse of the mixed sorbate is injected at the column inlet, the different species separate into bands which travel through the column at their characteristic velocities, and at the oudet of the column a sequence of peaks corresponding to the different species is detected. 

Ionisation processes in IMS occur in the gas phase through chemical reactions between sample molecules and a reservoir of reactive ions, i.e. the reactant ions. Formation of product ions in IMS bears resemblance to the chemistry in both APCI-MS and ECD technologies. Much yet needs to be learned about the kinetics of proton transfers and the structures of protonated gas-phase ions. Parallels have been drawn between IMS and CI-MS [277]. However, there are essential differences in ion identities between IMS, APCI-MS and CI-MS (see ref. [278]). The limited availability of IMS-MS (or IMMS) instruments during the last 35 years has impeded development of a comprehensive model for APCI. At the present time, the underlying basis of APCI and other ion-molecule events that occur in IMS remains vague. Rival techniques are MS and GC-MS. There are vast differences in the principles of ion separation in MS versus IMS. 

The principle of gas chromatography (GC) is similar to that of liquid chromatography or TLC, in that compounds in mixtures are separated from each other based on their affinity for a resin. GC is performed on volatile... 

Interestingly, research has started on single chamber SOFC (SC-SOFC) concepts. However, the SC-SOFC exhibits inherently low power density and is therefore primarily of academic interest. It has the potential to relax cell component requirements and probably to ease manufacture. The principle of SC-SOFC is that it is fed by an air fuel mixture which flows onto the PEN contained in a single compartment, avoiding the use of gas separator plates and high temperature sealants. The fluid may flow simultaneously or sequentially along the electrodes. Both electrodes are either built onto the same side of the electrolyte some distance apart or on opposite sides. Low temperature operation would apparently suppress direct combustion of the air fuel mixture provided the electrode materials chosen are highly selective towards their respective catalytic reactions. SC-SOFC stacks may hold prospects in specific applications where the reaction products are the prime focus. 

Conceptually, it is the atomic number and the electronic configuration of an element that define its position in the Periodic Table. Since they cannot be measured for the very heavy elements, information on its chemical behavior is often used to place an element in a chemical group. Unfortunately, with increasing nuclear charge the cross sections and the production rates drop so rapidly that such chemical information can be accessed only for elements with a half-life of the order of at least few seconds and longer. In this case, some fast chemistry techniques are used. They are based on the principle of chromatographic separations either in the gas phase exploiting the differences in volatility of heavy element compounds, or in the aqueous... 

A standard arrangement for sampling gaseous products downstream of the reactor is shown in Fig. 5. In a needle valve (or a similar device), the reactor effluent is depressurized and the flow rate is controlled. In the vast majority of cases, the analytical instrument of the choice will be a gas chromatograph equipped with a capillary column, because such an instrument often allows a good separation of the products and, if equipped with an appropriate detector, a reliable quantitative analysis of these products. The working principle of gas chromatography, however, is inherently... 

Mobile phase is gas and static phase is solid. The main principle of the separation by such method is adsorption on the static phase. 

The preceding discussion was provided to give a basic understanding of the principles of gas-liquid chromatography and of the various factors that contribute to the separations achieved on packed columns. Much of the discussion was drawn from a number of textbooks or monographs, to... 

The study of gas transport in membranes has been actively pursued for over 100 years. This extensive research resulted in the development of good theories on single gas transport in polymers and other membranes. The practical use of membranes to separate gas mixtures is, however, much more recent. One well-known application has been the separation of uranium isotopes for nuclear weapon production. With few exceptions, no new, large scale applications were introduced until the late 1970 s when polymer membranes were developed of sufficient permeability and selectivity to enable their economical industrial use. Since this development is so recent, gas separations by membranes are still less well-known and their use less widespread than other membrane applications such as reverse osmosis, ultrafiltration and microfiltration. In excellent reviews on gas transport in polymers as recent as 1983, no mention was made of the important developments of the last few years. For this reason, this chapter will concentrate on the more recent aspects of gas separation by membranes. Naturally, many of the examples cited will be from our own experience, but the general underlying principles are applicable to many membrane based gas separating systems. 

The product obtained from wells on petroleum, natural gas and gas-condensate fields is invariably a multi-phase, multimaterial produced needs to be processed before it can be transported by pipeline and delivered to gasoline plants, oil refineries, and fractionating plants. In this context, engineers widely employ technological processes based on the principle of division (separation) of the native mixture into liquid and gaseous phases as a result of the action of intrinsic forces such as gravity or inertia. 

At the present time, there is a great variety of separator designs (see Section 2.1). Nevertheless, they can be grouped into two basic dasses according to the physical principles of gas-liquid mixture separation gravitational and inertial separators. 

Many methods depend on the separation of a fluid mixture. Among these, gas chromatography (GC) stands out [8]. Suitable devices for on-line control were developed from laboratory gas chromatographs and operate very rehably. However, they can be expensive because of the associated program controls. The principle of gas chromatography is that a carrier gas (helium) is passed over a tubular column of a fine solid. A sample is injected into the carrier gas stream and the gas... 

They are based on the principle of chromatographic separations either in the gas phase exploiting differences in volatiUty of elements or their compounds, or in the aqueous phase by solvent extraction or ion-exchange separations using differences in the complex formation. Chemistry of elements 104 (Rf) through 108 (Hs), and of elements 112 (Cn) and 114 (llerovium, FI) has been successfully studied using these techniques (see Liquid-Phase Chemistry of Superheavy Elements and Gas-Phase Chemistry of Superheavy Elements ). 

In Section 3.3.8, the principle of particle separation via flotation in a gas-liquid system was briefly identified. Those particles whose surfaces are hydrophobic, and to which gas/air bubbles can be attached, will float to the surface of an aqueous suspension due to reduced density. Those particles whose surfaces are hydrophilic and wetted by the liquid (commonly, it is water) cannot become attached to gas/air bubbles and will not therefore float to the surface. Here, following Fuerstenau and Herrera-Urbina (1989), we will briefly iUusUate systems where such separations are achieved by converting particular mineral surfaces to a hydrophobic type via the adsorption of... 

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