Cells for Gases

Infrared spectroscopy can be used to perform qualitative analysis of gases. Pierson et al. (1956) have given a chart to be used for this purpose. Also, infrared spectroscopy and gas chromatography are a useful combination for characterizing volatile substances (see Appendix 1). Sometimes fractions from a vapor fractometer are collected as vapors in a gas cell. White et al. (1959) have described a microgas cell of 1 m path for use with a beam condenser to observe the spectra of gas chromatographic fractions less than 0.05 % of the total charge. 

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Fig. 5.2 Cells for transmission measurements (a) UV/VIS liquid cell (b) flow cell for gases and liquids (c) demountable IR liquid cell.

Figure 14.10 Schematic of quasi-isostatic permeation cell for gases.

Practical separation techniques for gases dispersed in liquids are discussed. Processes and methods for dispersing gas in hquid have been discussed earlier in this section, together with information for predicting the bubble size produced. Gas-in-hquid dispersions are also produced in chemical reactions and elec trochemic cells in which a gas is liberated. Such dispersions are likely to be much finer than those produced by the dispersion of a gas. Dispersions may also be uninten-tionaUy created in the vaporization of a hquid. 

Since concentration variations have measurable effects on the cell voltage, a measured voltage cannot be interpreted unless the cell concentrations are specified. Because of this, chemists introduce the idea of standard-state. The standard state for gases is taken as a pressure of one atmosphere at 25°C the standard state for ions is taken as a concentration of 1 M and the standard state of pure substances is taken as the pure substances themselves as they exist at 25°C. The half-cell potential associated with a halfreaction taking place between substances in their standard states is called ° (the superscript zero means standard state). We can rewrite equation (37) to include the specifications of the standard states ... 

Electrochemical cells can be constructed using an almost limitless combination of electrodes and solutions, and each combination generates a specific potential. Keeping track of the electrical potentials of all cells under all possible situations would be extremely tedious without a set of standard reference conditions. By definition, the standard electrical potential is the potential developed by a cell In which all chemical species are present under standard thermodynamic conditions. Recall that standard conditions for thermodynamic properties include concentrations of 1 M for solutes in solution and pressures of 1 bar for gases. Chemists use the same standard conditions for electrochemical properties. As in thermodynamics, standard conditions are designated with a superscript °. A standard electrical potential is designated E °. 

Solid samples or solid extracts can be mixed and ground with potassium bromide (KBr),pressed to form a transparent pellet, and a spectrum obtained from the pellet (see C in Figure 14.3). There are gas cells for obtaining spectra of gases and many other methods for obtaining spectra from liquid and solid samples that are not as frequently used as these [13-17],... 

Another approach that has been reported is GC linked to IR spectroscopy linked to MS. The gas phase components from a GC analysis can easily be directed into an IR gas cell for analysis. Note that the carrier gases used in GC will not generally interfere with or be detected by IR spectroscopy and thus... 

Power systems that run on compressed gases such as propane, methane, or hydrogen are problematical. Range may be limited since distribution systems are not in place and each station pump could cost 30,000. So-called synthetic fuels could be used directly in engines or to generate electricity from fuel cells for electric motors. Other combustion engines such as the sterling motor may also become options. 

One of the most important factors in the selection of the sample handling technique is to attempt to analyze the sample, as it exists, without any form of chemical or physical modification. For gases and certain liquids, simple transmission cells, often with a flow-through configuration meet these requirements. 

An improved electrochemical cell for in situ studies is presented in Figure 14.2. In this method a platinized Pt electrode located in the anode compartment serves as the reference electrode. This cell can be installed in a test station. Such a station can have facilities for temperature and pressure control, humidification of reactant gases (e.g., hydrogen and oxygen), gas flow rate measurement, and measurement of half- and... 

Figure 3.4 Low temperature cell for HP IR spectroscopy in liquid noble gases (from Ref [10], reproduced by permission of The Royal Society of Chemistry).

In Figure 7 the selectivity to methane, ethane, ethylene, gases, gasoline (210°C), diesel (310°C), and coke at 65% level of conversion have been plotted for HYUS zeolites with 28, 21, 12, and 2 Al per unit cell for cracking gas-oil. It is apparent from the figures that thO selectivity to and C products decreases with a decreasing number of aluminum, up to 10- 0 Al per unit cell. With further dealumination the selectivity to and products... 

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