Sensors for hydrocarbon monitoring

Amongst other developments, a gold-oxide composite has been developed as a sensor for hydrocarbon monitoring in automobile exhaust gases,119,120 and Au In2C>3 ceramics have been used for detection of ammonia and other reducing gases.121... 

Shmidt-Zhang, P. and Guth, U., A planar thick fihn sensor for hydrocarbon monitoring in exhaust gases. Sensors and Actuators B, Chem. 99 (2004) 258-263. 

A fiber-optic device has been described that can monitor chlorinated hydrocarbons in water (Gobel et al. 1994). The sensor is based on the diffusion of chlorinated hydrocarbons into a polymeric layer surrounding a silver halide optical fiber through which is passed broad-band mid-infrared radiation. The chlorinated compounds concentrated in the polymer absorb some of the radiation that escapes the liber (evanescent wave) this technique is a variant of attenuated total reflection (ATR) spectroscopy. A LOD for chloroform was stated to be 5 mg/L (5 ppm). This sensor does not have a high degree of selectivity for chloroform over other chlorinated aliphatic hydrocarbons, but appears to be useful for continuous monitoring purposes. 

Ishihara, T, Fukuyama, M., Dutta, A., Kabemura, K., Nishiguchi, H. and Takita, Y. (2003) Solid state amperometric hydrocarbon sensor for monitoring exhaust gas using oxygen pumping current. 7. Electrochem. Soc., 150 (10), H241-5. 

Barisci, J.N., G.G. Wallace, M.K. Andrews, A.C. Partridge, and P.D. Harris. 2002. Conducting polymer sensors for monitoring aromatic hydrocarbons using an electronic nose. Sens Actuators B Chem 84 252. 

Barisci, J. N. Wallace, G. G. Andrews, M. K. Partridge, A. C. Harris, P. D. Conducting polymer sensors for monitoring aromatic hydrocarbons nsing an electronic nose. Sens. 

The success of the O2 sensor has made the auto manufacturers, regulators, and environmentalists anxious to extend chemical sensing to a variety of tailpipe gases, notably CO, NO, and short-chain hydrocarbons. Considerable research and development is needed for these molecules to be monitored in the hostile exhaust system environment (36). 

Kastner J., Tacke M., Katzir A., Edl-Mizaikoff B., Gobel R. and Kellner R., Optimizing the modulation for evanescent-wave analysis with laser diodes (EWALD) for monitoring chlorinated hydrocarbons in wat, Sensors Actuators B 1997 38 163-170. 

The measurement technique was the crux of a paper by Acha et al.27 discussing the process of the dechlorination of aliphatic hydrocarbons. An ATR-FTIR sensor was developed to monitor parts per million (ppm) of trichloroethylene (TCE), tetrachloroethylene (PCE), and carbon tetrachloride (CT) in the aqueous effluent of a fixed-bed dechlorinating bioreactor. It was found that the best extracting polymer was polyisobutylene (PIB) as a 5.8 pm film. This afforded detection limits of 2, 3, and 2.5 mg/1 for TCE, PCE, and CT, respectively. The construction and operation of the measurement system are detailed in the paper. 

Cell components or metabolites capable of recognizing individual and specific molecules can be used as the sensory elements in molecular sensors [11]. The sensors may be enzymes, sequences of nucleic acids (RNA or DNA), antibodies, polysaccharides, or other reporter molecules. Antibodies, specific for a microorganism used in the biotreatment, can be coupled to fluorochromes to increase sensitivity of detection. Such antibodies are useful in monitoring the fate of bacteria released into the environment for the treatment of a polluted site. Fluorescent or enzyme-linked immunoassays have been derived and can be used for a variety of contaminants, including pesticides and chlorinated polycyclic hydrocarbons. Enzymes specific for pollutants and attached to matrices detecting interactions between enzyme and pollutant are used in online biosensors of water and gas biotreatment [20,21]. 

The aluminum oxide sensor is also used for moisture measurements in liquids (hydrocarbons). Because ot us low power usage, it is suitable lor use in explosion prool installations. These sensors are frequently used in petrochemical applications where low dew points are to he monitored on line and where the reduced accuracies and other limitations are acceptable. The advantages of the sensor must be weighted against the fact that... 

Table 2 summarizes the response of the different sensors to hydrogen and the various challenges, all expressed in equivalent volume fraction of hydrogen. Reported actual values are from the independent monitoring instruments, so for example the 130 pL/L reported as the actual fraction of propene is the value recorded from the NDIR hydrocarbon analyzer. 

Electrochemical sensors are also used to monitor the emissions from combustion processes. Because the oxidizer for most combustion processes is air, which contains 78% nitrogen, NO. gases are common components of the exhaust and their concentrations must be minimized [398, 399]. In addition, incomplete combustion can result in CO or hydrocarbon gaseous compounds in the exhaust gas, which both represent unconverted chemical energy and are hazardous to the environment. The use of sulfur-containing fuels can lead to the formation of SO gases [400], which have a detrimental impact on the environment, such as promoting acid rain. 

---