Propane sensors

In a similar manner, Sahner et al. [76, 77] utilized a Pt-ZSM-5 layer to reduce the cross-sensitivity of a hydrocarbon (propane) sensor toward CO, propene, H2, and NO at 673 K. The zeolite layer was put on the sensor as a paste. The improved cross-sensitivity is attributed to selective oxidation of aU considered components except propane. Trimboli et al. [78] demonstrated the same concept by using a Pt-Y zeohte for the CO oxidation, maintaining the sensitivity for propane. 

Recently, development of a more accurate and robust propane sensor by replacing the fixed-wavelength He-Ne laser with a tunable diode laser was initiated. The strongest absorption of propane in the near-infrared region occurs near 1.68 /xm. Figure 10.4 shows the first known high-resolution spectral data of propane near 1.68 /xm, from which one can identify the optimum detection strategy. In this work, the diode laser was scanned across the absorption peak at 1.6837 /xm at 500 Hz to mecisure propane concentration. This sensor was applied to the head-end of the PDE at Stanford University, as shown in Fig. 10.5. The initial results of propane measurements are shown in Fig. 10.6. These results contain a wealth of information... 

Figure 10.5 Schematic of propane sensor applied to the Stanford PDE.

In contrast to this, sample presentation is thoroughly investigated. On behalf of the Ministry of Housing, Physical Planning and Environment, TNO investigated the influence of flow rate in relation to dilution factor, both analytically and sensorically. The flow rate varied from 6 to 35 1/min. Propane concentrations were measured at the back of the nose of an artificial head through which 20 1/min. was sucked continuously. Sensory measurements were carried out with butanol and ethylbutyrate. The results are summarized in figure 1. Based on this research 16 1/min. was recommended as the minimal sample flow rate. 

SiC capacitor sensors have demonstrated gas-sensitivity to gases such as hydrogen and hydrocarbons [21, 46, 68] up to a maximum temperature of 1,000°C [1, 68]. Devices that can be operated both as MOS capacitors (reverse bias) and as Schottky diodes at temperatures greater than 490°C have also been demonstrated (see Section 2.4.2) [10]. These devices showed sensitivity to combustible gases such as propane, propylene, and CO and were tested at temperatures up to 640°C. 

In order to clarify the resistivity characteristics of the specimens, we obtained the relationship between an equilibrium oxygen partial pressure and the oxygen excess ratio from both theoretical calculations and measurements using the oxygen sensor. The complete propane oxidation can be described by the following reaction. 

Fig. 11 Pumping current of the sensor of Fig. 10 as a function of X in a propane burner. X is defined as X —...

It was confirmed that this sensor was insensitive to methane (15000 ppm) and propane (7000 ppm) in air. 

Products obtained by propane-selective oxidation have been analyzed by gas sensor systems [19, 26]. Usually, several or multiple kinds of compounds are produced during the selective oxidation of propane. The formation of CO, C02, aldehydes such as acrolein, and ketone were observed over iron-silica catalysts [28, 29]. During the initial stage of catalyst investigation, the conversion of propane and the selectivity toward useful oxygenate products as chemical resources are of interest. Semiconductor-type gas sensors selective toward the oxygenate were employed to estimate the yield of oxygenate products, with a combination of the potentiometric CO sensor and the ND-IR C02 sensor [30]. 

Fig. 8.4 (a) shows the response of the oxygenate sensor-1 (Sn02 sensitized with Ti02) towards an alcohol (1-propanol), aldehyde (propanal), ketone (acetone), carbon monoxide (CO) and propane. The sensor is sensitive to the alcohol, aldehyde and ketone but not to CO and propane. Conversely, oxygenate sensor 2 (Sn02 sensitized with 13 wt% Si02/Al203) is less sensitive to the alcohol than aldehyde (Fig. 8.4b). Alcohol formation can thus be estimated from a comparison of the output signals of oxygenate sensors 1 and 2.

Fig. 8.6 Calibration plot of oxygenate sensor-1 for total oxygenate compounds produced by catalytic propane oxidation the yield of each oxygenate was determined with a conventional FID gas chromatograph (reproduced by permission of Elsevier from [19]).

Fig. 8.7 shows the product distributions determined by (a) a gas sensor system and (b) gas chromatography for propane oxidation over alkali Fe Si02 (=1 0.05 100). Since little alcohol was produced, there was no large difference between the signals from oxygenate sensors 1 and 2. When we compared the oxyge-... 

Oxidative dehydrogenation (ODH) is an important process for converting ethane or propane into more valuable ethylene or propylene. Ethylene has a specific IR absorption band around 950 cm4, which has been utilized by two research groups, using IR-based gas sensors, in the HTS of ethane ODH. Cong et al. at Symyx have used photothermal deflection [12, 13] and Johann et al. at the Max Planck Institute used a PAS sensor [24]. Johann et al. reported that position-sensi-... 

High-temperature stabilized NO-, zirconia potentiometric sensors are also being utilized [187], The electrochemical reactions on zirconia devices take place at the triple-phase boundary, that is, the junction between the electrode, electrolyte, and gas [186], It has been reported that sensors composed of a W03 electrode, yttria-stabilized zirconia electrolyte, and Pt-loaded zeolite filters demonstrate high sensitivity toward NO,, and are free from interferences from CO, propane, and ammonia, and are subject to minimal interferences from humidity and oxygen, at levels typically present in combustion environments [188], In this sensor, a steady-state potential arises when the oxidation-reduction reaction [186,188]... 

A final advantage of the vapor concentrator is that it can enhance the selectivity of the sensor. Clearly, the method is only effective for compounds that can be trapped on a sorbent polymer. Low molecular weight vapors such as methane, ethane, and propane are not readily trapped and thus will not be enriched. Likewise, very high molecular weight vapors will not be easily desorbed from the trap and thus will actually be diminished in concentration. 

In case of ethanol, the sensitivity of the sensor to ethanol-contained air is about 1/S of that of methanol. Because the SA molecular sieve is designed for the separation of the molecular size of methanol, ethane and propane or smaller, the SA molecular sieve coated sensor gives much less sensitivity with ethanol contained air. Unlike other solid particle coated sensor, such as activated carbon sensor, the molecular sieve coated sensor has selectivity to the molecular size of detecting material. The outcome presented in Fig. 3 indicates that the sensor coated with SA molecular sieve satisfactorily discern methanol vapor from bigger molecules, but it does not separate from small molecules. When 4 A molecular sieve coated sensor is implemented to detect methanol, the same result of measuring ethanol with S A molecular sieve sensor is yielded as shown in Fig. 4. In other... 

Optical temperature sensor (opt(r)odes) based on the viscosity-dependent intramolecular excimer formation of l,3bi(l-pyrenyl)propane in [C4mypr][Tf2N] have been developed [33], The relative intensity of the excimer emission was found to gain in intensity with higher temperature. This has been attributed to the generally low viscosity of the ionic liquid. The working temperature of this luminescence thermometer is between 25°C and about 150°C. 

Target signatures used were taken from a commercially available database of laboratory-measured absorption spectra and were convolved with the spectral response of the sensor (as were the atmospheric contributions described previously). Target species were determined from the ground truth listing of potential releases provided with the dataset. Species in the target library used were methane, propane, butane, ethane, sulfur dioxide, ethylene, propylene, and benzene. 

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