Gases thennal conductivities

The thermal conductivity detector (TCD), which was one of the earliest detectors for gas chromatography, still finds wide application. This device consists of an electrically heated source whose temperature at constant electric power depends on the thermal conductivity of the surrounding gas. The heated element may be a fine platinum, gold, or tungsten wire (Figure 31 -9a) or, alternatively, a small thermistor. The electrical resistance of this element depends on the thermal conductivity of the gas. Twin detectors are ordinarily used, one located ahead of the sample injection chamber and the other immediately beyond the column alternatively, the gas stream can be split. The detectors are incorporated into two arms of a simple bridge circuit (see Figure 31 -9) such that the thennal conductivity of the carrier gas is... 

The catalytic oxidation of ethane at 573-648 K was carried out at atmospheric pressure in a fixed bed flow reactor. Mbftures of ethane (4 mol%), oxygen (4-12 mol%), and helium (balance) were fed to the reactor with a residence time of 38 g. h/mol C2H6, using a catalyst load of 0.36 g, (particle size 0.25-0.42 mm) mixed with SiC bits (dilution 1 4 vA) to reduce the heat release per imit volume. Reactants and products were analysed by gas chromatography on a Vaiian 3400, equ ped with a thennal conductivity detector, using Porapak QS (3 m) and molecular sieve 13X (1 m) columns. In all reaction conditions, the mass and carbon balances were within 10012 %. 

The experimental set up has been described in details in an earlier study [10]. Tlie kinetic measurements were performed at 300 C in differential flow reactor conditions by recycling the outlet gas mixture. The reactants (NO, CO) and reaction products (Nj, NjO, COj) were analysed by means of a chromatograph HP5850 equipped with a thennal conductivity detector. Their separation was achieved on a column CTRl supplied by Alltech. 

Figure 23.13. Effective thennal conductivity of the pore gas, Ag, of resorcinol-formaldehyde aerogels with different R/C ratios as a function of aerogel density at room temperature and ambient atmospheric pressure [24,31].

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