Thermal conductivity detector performance

TEM observation and elemental analysis of the catalysts were performed by means of a transmission electron microscope (JEOL, JEM-201 OF) with energy dispersion spectrometer (EDS). The surface property of catalysts was analyzed by an X-ray photoelectron spectrometer (JEOL, JPS-90SX) using an A1 Ka radiation (1486.6 eV, 120 W). Carbon Is peak at binding energy of 284.6 eV due to adventitious carbon was used as an internal reference. Temperature programmed oxidation (TPO) with 5 vol.% 02/He was also performed on the catalyst after reaction, and the consumption of O2 was detected by thermal conductivity detector. The temperature was ramped at 10 K min to 1273 K. 

The activity tests of the catalyst were carried out in a microflow reactor set-up in which all the high temperature parts are constructed of hastelloy-C and monel. The reactor effluent was analyzed by an on-line gas chromatograph with an Ultimetal Q column (75 m x 0.53 mm), a flame ionization detector, and a thermal conductivity detector. The composition of the feed to the reactor can be varied, besides the temperature, pressure, and space velocity. The influence of the recycle components CHCIF2 and methane was tested by adding these components to the feed. In total five stability experiments of over 1600 hours were performed. In each... 

All reactions involving lactic acids were performed in 300 mL Parr Autoclave batch reactor. All reagents, including the resin catalyst, were charged into the reactor and heated up to the desired reaction temperature. Stirring was commenced once the desired temperature was reached this was noted as zero reaction time. Reaction sample were withdrawn periodically over the course of reaction and analysed for ester, water and alcohol using a Varian 3700 gas chromatograph with a thermal conductivity detector (TCD) and a stainless steel... 

TPO analyses were performed in a TPD/TPR 2900 (Micromeritics) equipment with a thermal conductivity detector a trap for sulfur compounds and a Pt/Silica bed for oxidation of CO and hydrocarbons to CO2. Eurthermore, it has a cold trap (isopropyl alcohol/liquid nitrogen) to condense CO2 and residual moisture. The combustion products are passed through the previous traps connected in series in order to remove other compounds different from O2 in the carrier gas. This ensures that the conductivity changes observed in the detector are attributed exclusively to changes in oxygen concentration in the carrier gas. 

Vapor-liquid equilibrium experiments were performed with an improved Othmer recirculation still as modified by Johnson and Furter (2). Temperatures were measured with Fisher thermometers calibrated against boiling points of known solutions. Equilibrium compositions were determined with a vapor fractometer using a type W column and a thermal conductivity detector. The liquid samples were distilled to remove the salt before analysis with the gas chromatograph the amount of salt present was calculated from the molality and the amount of solvent 2 present. Temperature measurements were accurate to 0.2°C while compositions were found to be accurate to 1% over most of the composition range. The system pressure was maintained at 1 atm. 1 mm... 

The purpose of the carrier is to transport the sample through the column to the detector. The selection of the proper carrier gas is very important because it affects both column and detector performance. Unfortunately, the carrier gas that gives the optimum column performance is not always ideal for the particular detector. The detector that is employed usually dictates the carrier to be used. For instance, an electron capture detector operating in the pulsed mode requires an argon-methane mixture a thermal conductivity detector works best with hydrogen or helium. The most common carrier gases are listed in Table 6.1. 

TPR of the samples in flowing He or H2 were performed in a Pyrex flow system which was also used for catalytic reactions. Acid properties of the samples were probed by TPD of NH3 preadsorbed at RT. The analysis of gaseous products was made by an on-line mass spectrometer or a thermal conductivity detector. Reactions of n-hexane in the presence of excess H2 were carried out at 623 K and atmospheric pressure. A saturator immersed in a constant temperature bath at 273 K was used to produce a reacting mixture of 6% n-hexane in H2. Reaction products were analyzed by an online gas chromatograph (HP-5890A) equipped with a flame ionization detector and an AT-1 (Alltech) capillary column. 

Ammonia TPD Measurement. The acidic properties of the catalysts were characterized using temperature programmed desorption (TPD) of ammonia. The experiments were carried out on a flow-type apparatus equipped with a fixed-bed and a thermal conductivity detector. The samples were activated in a helium flow of 5 L/h at 773 K for 1 hour. 300 mg of the H+-form of each dehydrated sample were used to perform the ammonia TPD. Pure ammonia, with a flow rate of 3 L/h, was then passed through the sample at 423 K for 30 min. The sample was subsequently purged with helium at the same temperature for 1.5 hours in order to remove the physisorbed ammonia. The TPD was performed under a helium flow of 6 L/h from 423 K to 873 K with a heating rate of 10 K/min and subsequently at the final temperature for 30 min. 

The TPR and chemisorption experiments were carried out in an apparatus described elsewhere [3] equipped with a thermal conductivity detector. The experiments were performed using a gas mixture of 7 vol% H2 in Ar and a heating rate of 10 G/min. Separate TPR experiments (not shown here) indicate that the degree of reduction of tin, based on the reaction Sn02 + 2 - Sn + 2H20, was about 50 % for the Pt-Sn catalyst. This indicates that most of the tin is in the Sn2+ state. 

Temperature programmed reduction (TPR) was performed using an equipment described in detail elsewhere [12]. Approximately 100 mg of catalyst was loaded in the quartz reactor tube and was heated at a rate of 0.167 K/s in a flow of 0,5 cm3(STP)/s of 66% hydrogen in argon. Hydrogen consumption was detected with a thermal conductivity detector (TCD). In order to prevent preliminary reduction of the catalyst, samples containing palladium were cooled to about 223 K during the time required to stabilize the detector. 

Temperature Programmed Oxidation. Determination of the amount of deposited carbon was performed by oxidation using 5% 02 in N2. Fractured catalyst samples (0.15-0.425 mm) were oxidized immediately after performing the test reaction using a heating rate of 3°C/mm. Carbon was detected as C02 in a gas chromatograph (Porapak Q column, 1/8", 2.5 m He carrier gas at 160°C) equipped with a thermal conductivity detector. 

Phillips and Timms [599] described a less general method. They converted germanium and silicon in alloys into hydrides and further into chlorides by contact with gold trichloride. They performed GC on a column packed with 13% of silicone 702 on Celite with the use of a gas-density balance for detection. Juvet and Fischer [600] developed a special reactor coupled directly to the chromatographic column, in which they fluorinated metals in alloys, carbides, oxides, sulphides and salts. In these samples, they determined quantitatively uranium, sulphur, selenium, technetium, tungsten, molybdenum, rhenium, silicon, boron, osmium, vanadium, iridium and platinum as fluorides. They performed the analysis on a PTFE column packed with 15% of Kel-F oil No. 10 on Chromosorb T. Prior to analysis the column was conditioned with fluorine and chlorine trifluoride in order to remove moisture and reactive organic compounds. The thermal conductivity detector was equipped with nickel-coated filaments resistant to corrosion with metal fluorides. Fig. 5.34 illustrates the analysis of tungsten, rhenium and osmium fluorides by this method. 

Gas chromatographic analyses were performed on a Hewlett Packard Model 5880 system equipped with a thermal conductivity detector with an injector temperature of 200°C, detector temperature of 250°C and an oven temperature of 35°C. All runs were isothermal. The columns used for the separation were 20 foot AgNOj-ethylene glycol columns. Absolute retention times were 1.15 min (trans 2-pentene), A.65 min (1-pentene), and 5.81 min (cis 2-pentene). Methods of automatic peak integration that were used during the analyses were peak height, peak area, area %, and internal standard experiments. 

The catalytic reaction was performed in a fixed bed flow glass reactor. A gas mixture of CO2 and H2 (1 4, volume ratio) was passed continuously on the catalyst with F/W = 5400 ml g- h-i, unless otherwise mentioned. After the reaction the gas mixture was analyzed using a Chrompac MicroGC CP2002 gas chromatograph equipped with a thermal conductivity detector. 

In TPD/TPR experiments, a mixture of H2/Ar (25%/75% v/v) was introduced at 30 ml/min lo reduce mg of calcined catalyst sample in a fixed bed reactor, while heating from 303 to 973K at 10 K/min. The effluent stream was monitored for hydrogen with a thermal conductivity detector after removal of moisture in a ice-acetone trap. After each TPR experiment, the catalyst was cooled in Ar from 973K to room temperature, and hydrogen adsorption was performed at room temperature for 1 hour. Argon was then used... 

Organic liquids were vaporized at 180°C and the vapor joined the helium carrier gas stream Immediately after Injection. The chromatography experiments were performed using either a Spectraphyslcs SP 7100 Model or a Varlan Aerograph Series 1400, both equipped with a thermal conductivity detector. 

Gas chromatographic methods measure the carbon monoxide content of blood. Y/hen blood is treated with potassium ferricyanide, carboxyhemoglobin is converted to methemoglobin, and the carbon monoxide is released into the gas phase. Measurement of the released carbon monoxide may be performed by GC using a molecular sieve column and a thermal conductivity detector. A lower detection limit is achieved by incorporating a reducing catalyst (e.g., nickel) between the GC column and the detector to convert... 

Gas chromatography was performed using a Hewlett-Packard 5700A Gas Chromatograph equipped with a thermal conductivity detector. Output was recorded and measured with a Hewlett-Packard 3380S Integrator. 

Catalysts were prepared from H-ZSM-5 obtained from Catal International, Sheffield, with a framework Si/Al ratio of 25, using conventional ion-exchange techniques [11]. Copper exchange levels ranged between 54% and 160%. Catalytic experiments were carried out using a fixed bed microreactor which has been described previously [11]. Product analysis was performed by a chemiluminescent NOx analyser (Signal Instruments Model 4000) and a gas chromatograph fitted with a thermal conductivity detector (Pye UNICAM PU 4550). 

The reaction was performed in a fixed bed micro-reactor interfaced with an on-line gas chromatograph equipped with a thermal conductivity detector. 0.05g of catalyst sample was taken and reduced at 450°C prior to the reaction temperature. The reaction temperature was varied from 275 to 450°C. The product analysis was carried out using a 30% squalene chw (HP) column (length lO, diameter Mi" and the identification of the product mixture was done by GC-MS (VG micro mass 7070 H, U.K, 30 eV, 100 pA, El... 

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