Chemical process monitoring devices

Fig. 15.14 Analytical techniques for time-resolved headspace analysis. An electronic nose can be used as a low-cost process-monitoring device, where chemical information is not mandatory. Electron impact ionisation mass spectrometry (EI-MS) adds sensitivity, speed and some chemical information. Yet, owing to the hard ionisation mode, most chemical information is lost. Proton-transfer-reaction MS (PTR-MS) is a sensitive one-dimensional method, which provides characteristic headspace profiles (detailed fingerprints) and chemical information. Finally, resonance-enhanced multiphoton ionisation (REMPI) TOFMS combines selective ionisation and mass separation and hence represents a two-dimensional method. (Adapted from [190])...

In in-line analysis, the chemical analysis is done in situ, directly in the main process stream or reactor, using a chemically sensitive probe. A condition is that the equipment has to be placed in the plant (with consequences for maintenance and safety aspects). In this case, there still is physical contact between probe and sample. Consequently, an in-Une process-monitoring device must often deal with hostile industrial processing conditions elevated p, T, fluctuating conditions, chemically aggressive environments, electrical noise, dust, and vibrational problems. Sampling delays are very short, or non-existent for in-Une devices. The feedback and control loop can be optimised in real-time manner. However, an in-line apparatus may interfere with the... 

Immunosensors promise to become principal players ia chemical, diagnostic, and environmental analyses by the latter 1990s. Given the practical limits of immunosensors (low ppb or ng/mL to mid-pptr or pg/mL) and their portabiUty, the primary appHcation is expected to be as rapid screening devices ia noncentralized clinical laboratories, ia iatensive care faciUties, and as bedside monitors, ia physicians offices, and ia environmental and iadustrial settings (49—52). Industrial appHcations for immunosensors will also include use as the basis for automated on-line or flow-injection analysis systems to analyze and control pharmaceutical, food, and chemical processing lines (53). Immunosensors are not expected to replace laboratory-based immunoassays, but to open up new appHcations for immunoassay-based technology. 

A calorimeter Is a device used to measure heat flows that accompany chemical processes. The basic features of a calorimeter include an Insulated container and a thermometer that monitors the temperature of the calorimeter. A block diagram of a calorimeter appears in Figure 6-15. In a calorimetry experiment, a chemical reaction takes place within the calorimeter, resulting in a heat flow between the chemicals and the calorimeter. The temperature of the calorimeter rises or falls in response to this heat flow. 

Recent developments in microsystems technology have led to the widespread application of microfabrication techniques for the production of sensor platforms. These techniques have had a major impact on the development of so-called Lab-on-a-Chip devices. The major application areas for theses devices are biomedical diagnostics, industrial process monitoring, environmental monitoring, drug discovery, and defence. In the context of biomedical diagnostic applications, for example, such devices are intended to provide quantitative chemical or biochemical information on samples such as blood, sweat and saliva while using minimal sample volume. 

Wireless data communications devices are used to enable transmission of data between computer systems and/or between a SCADA server and its sensing devices, without individual components being physically linked together via wires or cables. In industrial chemical processing systems, these devices are often used to link remote monitoring stations (i.e., SCADA components) or portable computers (i.e., laptops) to computer networks without using physical wiring connections. 

Future advances in precursor purity and manufacturing technology, real-time monitoring of chemical reactions, MOCVD reactor chamber design, computer-controlled epitaxial growth systems, detailed chemical process models, and real-time process control will lead to improved process efficiencies, reduced hazardous waste, and enhanced device reproducibility, yield, and performance. The future of MOCVD is certainly bright. We are on the frontier of a great expansion of the abilities of MOCVD to provide materials for products that improve and expand the human experience on earth, under the oceans, and in space. 

In this chapter, we explore the current and potential future applications of AW devices for materials characterization and process monitoring. Because of the limited mass of material that can be applied to the AW device surface, the majority of these applications deal with the chemical and physical characterization of thin-film properties. This thin film focus should not be thought of as a limitation of AW devices, but rather as a useful capability — the direct measurement of properties of materials in thin-film form. Since material properties can depend on the physical form (e.g., film, bulk) of the material (see Section 4.3.1.3), AW devices are uniquely suited to directly characterize thin-film materials. These considerations also indicate that even though it is possible to use AW thin-film data to predict bulk material properties, such extrapolations should be performed with care. 

Chemical sensors are small devices for the detection and quantification of gaseous or solvated species. This is an active research area based on the need to obtain increasing amounts of data in chemical and food process streams as well as environmental monitoring. Most sensors consist of an appropriate transduction principle such as the quartz-crystal-microbalancc (QCM) and a chemically sensitive layer that imparts the desired chemical response behaviour. Most often a chemically selective response is desirable. Zeolite molecular sieves offer size- and shape-selective adsorption behaviour that can be combined with appropriate transduction concepts in order to construct chemically selective sensor devices. 

In addition, since the SAW Is sensitive to minute perturbations occurring in thin films which are In Intimate contact with the surface, SAW devices can be used to monitor physical and chemical processes occurring In these overlayers. Based on this effect, SAW devices have recently found applications In the characterization of the properties of thin films (8-10). In this paper, we report on the utility of SAW devices to characterize (1) the surface area and pore size distribution of porous thin films based on Nj adsorption Isotherms and (2) diffusion coefficients (D) for thin polymer films based on absorption transients (l.e., mass absorbed as a function of time) as indicated by SAW velocity transients (l.e., SAW velocity... 

And we can also, to reduce uncertainty even further, take steps to secure our own society and our personal lives. All of us would like, to be sure, a simple quick fix to this situation. That s understandable. But the process of making ourselves more secure will not be simple. To be effective, security requires human intelligence. It can t rely solely on even the most advanced mechanical or electronic or any other kind of device to detect threats and remove them from our lives. It can t rely on software that automatically traps and counters invasive attacks. There is no computer or video surveillance or chemical or biological monitoring device that can, in and of itself, be substituted for informed and intelligent human watchfulness, analysis, and judgment. 

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