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Chromatography Composition Measurement
Published in John G. Webster, Halit Eren, Measurement, Instrumentation, and Sensors Handbook, 2017
Behrooz Pahlavanpour, Mushtaq Ali, C.K. Laird
The gas chromatograph used for analysis of the gases is usually dual channel with FID and TCD detectors. A Porapak column is used for separation of hydrocarbons, and a methanizer is used for converting carbon oxides to methane followed by FID detector, while hydrogen, oxygen, and nitrogen are separated on a molecular sieve column and measured by TCD. Other arrangements such as column switching–backflushing should be used if a single detector is going to be used. In such cases, a TCD is usually used as a detector. IR detection of hydrocarbons followed by TCD is an alternative arrangement. A combination of Porapak and molecular sieve column is used for separation of hydrogen, oxygen, and nitrogen, followed by TCD detection. This arrangement requires a flash backflush system to prevent carbon dioxide from entering the molecular sieve column—where it would be so strongly adsorbed that it would require prolonged heating at a high temperature to remove it. The system is capable of detecting 1 ppm hydrocarbons and carbon oxides and 5 ppm hydrogen in the oil. Oxygen and nitrogen in the oil are usually present at high concentration, and therefore, their detection does not present any problem. High concentrations of acetylene gas in the oil may present some problems, such as poisoning the methanizer catalyst, and it may stay in the column for a long time. In such cases, a longer isothermal time and higher oven temperature for cleaning of the column is the recommended technique.
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Published in Leo M. L. Nollet, Dimitra A. Lambropoulou, Chromatographic Analysis of the Environment, 2017
Carolina Santamaría, David Elustondo, Esther Lasheras, Jesús Miguel Santamaría
In contrast to the aforesaid GC-TCD systems, FID is the favorite detector for sensitive determinations (Capasso and Inguaggiato, 1998; Juntarawijit et al., 2000; Ueta et al., 2013). When this detector is coupled to GC, carbon monoxide can first be reduced to methane by a methanizer. These methods are used in very specific determinations that usually require detection limits below 1 ppm. Kaminski et al. (2003) developed a method for determining trace amounts of CO, CH4, and CO2 in refinery hydrogen gases or in air. They modified GC-FID by adding a short molecular sieve 5A packed column to a Porapak Q column prior to reach the methanizer. This method reached detection limits of 0.15, 0.15, and 0.20 μg L−1 for CO, CH4, and CO2, respectively. Ueta et al. (2013) created a GC-FID system based on the introduction of a packed-capillary column and a methanizer to assess the photocatalytic properties of TiO2 for gaseous VOCs.
Gas Chromatography
Published in Thomas J. Bruno, Paris D.N. Svoronos, CRC Handbook of Basic Tables for Chemical Analysis, 2020
Thomas J. Bruno, Paris D.N. Svoronos
Another application in which the gas hold-up volume is needed is in the use of chromatographic retention parameters for solute identification. Chromatographic parameters include net retention volumes, relative retentions, specific retention volumes, and retention indices. Here, it is important to evaluate the applicability of a minimally retained marker in each case, since even a very light solute such as methane can show retentive behavior. It is usually best to use an extrapolative method to estimate the hold-up, although the chromatographic behavior of methane is often used in these procedures as well [2]. A convenient way to dispense the methane is with a permeation tube methanizer [3].
Experimental and Numerical Study of Ethyl Valerate Flat Flames at Low Pressure
Published in Combustion Science and Technology, 2018
Haddy Mbuyi Katshiatshia, Véronique Dias, Hervé Jeanmart
Two detectors have been used—a TCD: thermal conductivity detector and a FID: flame ionization detector. This GC is equipped with a methanizer before the FID, which allowed converting carbon monoxide (CO), carbon dioxide (CO2), and formaldehyde (CH2O) into methane (CH4). The conversion is due to the reduction reactions (heterogeneous catalyst reaction) between these molecules and the hydrogen in the methanizer. The CO, CO2, and CH2O FID signals were thus read as methane peaks but the retention times corresponded to the initial species (CO, CO2, or CH2O). The advantage of this technique is to measure CO, CO2, and CH2O concentrations with the FID, a detector more sensitive than the TCD. To check the good conversion of CO and CO2 into CH4, standard bottles have been used. As the ratio CO/CH4 in the standard bottle is 6.38 and the experimental ratio is 6.40, the agreement is considered excellent due to the standard deviation. Similarly, the ratio of CO2/CH4 is equal to 2.55 in the standard bottle, and the experimental value measured by the FID indicates a ratio of 2.50. Therefore, the methanizer showed a good chemical conversion of CO and CO2 into CH4. For CH2O, the same effect was assumed. Thanks to these results, only methane was calibrated.