Micro Gas Analyzers

In addition to the need to process large quantities of samples that technology produces more and more prolihcally, the demand for faster analytical response is also borne from applications where analysis time is inherently critical, as with first-responders and held soldiers sampling the air to check for the presence of chemical warfare agents (CWA). DARPA (Defense Advanced Research Projects Agency), which commissions advanced research for the Department of Defense, is funding the development of micro gas analyzers (MGA) suitable for portable and virtually instant CWA detection. 

Fig. 9.3.7 MCA (micro gas analyzer) designed for sampling air and GC analysis after switch-over to Hj [3].

Although conventional GC/MS systems may not compete with the speed and sensitivity of these micro gas analyzers, the former s strength lies in their ability to resolve smaller analyte differences, which would be highly desirable for FAR reduction. The challenge of this research is to achieve a similar resolution using fast, more compact and multidimensional analysis approaches, such as pGC-pITMS and pGC-pITMS-MDD systems. 

U.Bonne, R. E. Higashi etal., PHASED Micro Gas Analyzer, DARPA-MTO webpage, 2004, at http //www.darpa.mil/ mto/mga/summaries/2004 summaries/ honeywell.html... 

The pH was maintained at 5.0 by the addition of 2 M NaOH (Micro DCU-300 B. Braun Biotech). The fermentation temperature was 30°C and the stirrer speed was 500 rpm (MCU-200 B. Braun Biotech). Cell mass was produced in an initial batch phase using a glucose concentration of 64 g/L. The concentrations of mineral salts, trace metals, vitamins, and Ergosterol/ Tween-80 were the same as in the fed-batch experiments. When the glucose in the batch medium was completely consumed, 1.9 L of dilute-acid hydrolysate was pumped into the reactor at maximum pump speed, by using a peristaltic pump (Ul-M Alitea AB). The ratio between batch volume and the final volume (i.e., after all the hydrolysate had been added) was similar to the ratio in the PDU fed-batch experiments, approx 1 4. The reactor medium was sparged with nitrogen (600 mL/min). The C02 content in the exhaust gas was measured with a gas analyzer (TanDem Adaptive Biosystems, Luton, UK). 

Cracking properties of a Si-VPl-5 (Si/Al=0.4 in the gel) and the reference catalyst were also investigated by Micro Activity Tests (MAT), using a short contact time MAT (SCT-MAT) which is a modified version of the ASTM MAT with better correlation to a commercial unit 1 g of atmospheric residue was fed to the reactor during 30 seconds at 524°C. Liquid products were collected at 0°C and analyzed on a HP 5880 Sim Dist GC, while gas products were collected over a saturated KCl-solution and injected on a HP 5880 Refinery Gas Analyzer. 

Catalytic reactions were carried out using a micro fixed bed flow type reactor. 60 to 400 mg of oxidized diamond-supported catalyst was used. The effluent was analyzed by an on-line micro gas chromatograph. 

Catalj tests were carried out in a fixed-bed flow reactor. The catalyst was tabletted pulverized into 10-22 mesh, and set in the reactor. The catalyst bed was heated to 500 C in a helium gas flow and held at that temperature for 30 min. Then, the reaction gas composed of 5,000 ppm N20,2% O2, and He balance was introduced to the catalyst bed at W/F = 0.3 g s cm. The effluent gases fixrm the reactor were analyzed every 5 min at 500 °C with an on-line micro-gas-chromatogr h (CP 2002, Chrompack, Netherlands) (columns 10 m molecular sieve 5A at 80 °C 10 m porapack Q at 40 °C). After the steady state was attained, reaction temperature was decreased Sum 500 °C to the temperature where the catalyst showed negli ble N2O conversion. The catalyst activity is expressed by the T50 value, which is defined as the temperature at which ftie catalyst exhibits 50 % N2O conversion under the above-mentioned conditions. 

Reaction products were analyzed using several chromatographs. Gas products were analyzed using a Flewlett-Packard Quad-Series Refinery Gas Analyzer Micro Gas Chromatograph (QRGA). The analysis of the aqueous phase collected beyond the reactor used a Hewlett-Packard 5790 GC with a thermal conductivity detector and a Porapak Q column. Oil and wax were combined and analyzed with a Hewlett-Packard 5890 GC with a flame ionization detector and a 60 m DB-5 column. The reactor wax was analyzed on a Hewlett-Packard 5890 High Temperature GC with an flame ionization detector and a 30 m alumina clad HT-5 column. 

Costamagna et al. [24] investigated design and part-load performance of a hybrid system based on a solid oxide fuel cell reactor and micro gas turbine. This study contains models of a centrifugal compressor and inflow expander. There is no ejector model analyzed in this paper. The hybrid system operated at 0.38 MPa and 800-1000°C, and generated about 290 kW at 60% efficiency. 

We consider the problem of liquid and gas flow in micro-channels under the conditions of small Knudsen and Mach numbers that correspond to the continuum model. Data from the literature on pressure drop in micro-channels of circular, rectangular, triangular and trapezoidal cross-sections are analyzed, whereas the hydraulic diameter ranges from 1.01 to 4,010 pm. The Reynolds number at the transition from laminar to turbulent flow is considered. Attention is paid to a comparison between predictions of the conventional theory and experimental data, obtained during the last decade, as well as to a discussion of possible sources of unexpected effects which were revealed by a number of previous investigations. 

One of the most far reaching analyzes along these lines of thought was given by Commenge [114] in the context of gas-phase reactions in continuous-flow processes. Specifically, he analyzed four different aspects of micro reaction devices, namely the expenditure in mechanical energy, the residence-time distribution, safety in operation, and the potential for size reduction when the efficiency is kept fixed. 

P 24] The nitration of naphthalene was carried out with dissolved or in situ generated N2O5 gas [37]. The temperatare was set to -10 to 50 °C and residence times to 15—45 s. The reaction mixtare processed in the micro reactor was quenched with water, extracted and analyzed by HPLC or GC with mass-selective detection. 

Liquid and gaseous products are analyzed by gas chromatography with respectively a Varian 3900 GC and a Varian 4900 micro GC. The identification of the liquid decomposition products is carried out by mass spectrometry on a GC/MS system (Shimadzu GC14A coupled with a Nermag/Quad service R10-10 C/U). 

After the activation period, the reactor temperature was decreased to 453 K, synthesis gas (H2 CO = 2 1) was introduced to the reactor, and the pressure was increased to 2.03 MPa (20.7 atm). The reactor temperature was increased to 493 K at a rate of 1 K/min, and the space velocity was maintained at 5 SL/h/gcat. The reaction products were continuously removed from the vapor space of the reactor and passed through two traps, a warm trap maintained at 373 K and a cold trap held at 273 K. The uncondensed vapor stream was reduced to atmospheric pressure through a letdown valve. The gas flow was measured using a wet test meter and analyzed by an online GC. The accumulated reactor liquid products were removed every 24 h by passing through a 2 pm sintered metal filter located below the liquid level in the CSTR. The conversions of CO and H2 were obtained by gas chromatography (GC) analysis (micro-GC equipped with thermal conductivity detectors) of the reactor exit gas mixture. The reaction products were collected in three traps maintained at different temperatures a hot trap (200°C), a warm trap (100°C), and a cold trap (0°C). The products were separated into different fractions (rewax, wax, oil, and aqueous) for quantification. However, the oil and wax fractions were mixed prior to GC analysis. 

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