Thermal conductivity, and flames

Catalysts were tested for oxidations of carbon monoxide and toluene. The tests were carried out in a differential reactor shown in Fig. 12.7-1 and analyzed by an online gas chromatograph (HP 6890) equipped with thermal conductivity and flame ionization detectors. Gases including dry air and carbon monoxide were feed to the reactor by mass flow controllers, while the liquid reactant, toluene was delivered by a syringe pump. Thermocouple was used to monitor the catalyst temperature. Catalyst screening and optimization identified the best catalyst formulation with a conversion rate for carbon monoxide and toluene at room temperature of 1 and 0.25 mmolc g min1. Carbon monoxide and water were the only products of the reactions. 

One major aspect of quantitative analysis is sensitivity and dynamic range of linearity. Such data have been reviewed (2) for the gas density, thermal conductivity, and flame ionization detectors. Since response is a function of molecular weight in the gas density detector, it is difficult to make comparisons in a simple manner. In general, however, the sensitivity of the gas density cell is about twice that of comparable thermal conductivity cells and about one-tenth that of flame ionization detectors (when bleed of the column is limiting). 

The catalytic hydrogenation of carbon dioxide was performed in a continuous fixed bed reactor. The catalyst was reduced in a flow of hydrogen at 723 K for 20 - 24 hr. After the reduction, the catalyst was brought to the following conditions 573 K, 10 atm, space velocity of 1900 h-i and H2/CO2 = 3. The activity data was taken after 24h of reaction. The products were analyzed by a gas chromatograph (Chrompack CP 9001) equipped with thermal conductivity and flame ionization detectors. Carbon monoxide, carbon dioxide and water were analyzed on a Porapak Q column and the hydrocarbons on a GS Q capillary column. 

The master gas chromatograph is a Varian 2760 instrument with thermal conductivity and flame ionization detection. A second Varian 2760 gas chromatograph (GC-2) serves for analysis of samples from two sources, pyrolysis products from the CDS 820 and from the structural determination function of the CDS 1200. The latter instrument (Chemical Data System) is a functional group and elemental analyzer which generates a vapor-phase thermolytic dissociation pattern for functional group analysis and also performs elemental analysis. The effluent from the master GC is split so that 10% of it is directed to the detector and 90% of it to the CDS 1200. A stop-flow valve admits one... 

On-line GC samples were taken at hourly intervals and analyzed for N, CO, CO, and C,-Cg hydrocarbons on a HP 5890 gas chromatograph equipped with thermal conductivity and flame ionization detectors. The space velocity was varied to give approx. 10% CO conversion. 

There are many kinds of detectors used for gas chromatography two common ones are thermal conductivity and flame ionization. In a thermal conductivity detector, there are two sets of hot filaments whose temperature depends on the composition of the gas flowing over them. The detector can be set to zero for pure carrier gas passing through the instrument over both filaments. As the components of the mixture elute over one set of filaments, their temperature will change and the current needed to bring them back to the zero point can be measured and plotted. A flame ionization detector measures the current induced by ions created as the effluent is burned. Again, a zero point for pure carrier gas is determined and deviations from zero are detected and plotted as the components of the mixture elute. 

Apparatus. Ayers et al used an Aerograph Model 1520-B equipped with thermal conductivity and flame ionization detectors and a Sargent SRI Millivolt range recorder with disc integrator. 

---