Development strategies for implementation of a piezoelectric gas monitor as a field device (SO2 and NO2 dynamic, real-time monitoring)
The environmental and physiological effects of the acid gases sulphur dioxide and nitrogen dioxide are surveyed. Particular attention is paid to diseases or malformations induced in plants, animals and man. A review of current analytical methods available for analysis of trace quantities [100ppm (V)] of both acid gases is reported. The past developments of the piezoelectric sorption technique are outlined in detail as a preview to the fundamentals, design, research and experimental work incorporated in this thesis. Current developments aimed at producing a working analytical system for the dynamic sampling of both gases are categorised under three general headings: (1) Chemistry of gas/liquid or gas solid reactions, (2) Design and construction of the gas mixing rigs and sampling cells, (3) Electronics Hardware associated with driving and measuring frequency responses from 9MHz piezoelectric crystals. Also the hardware involved with the incorporation of solid-state "Frigister" units for temperature control processing, thermal cycling temperature programmes, data recording and processing including multiplexing for direct rapid on-line results. The sorption isotherms of sulphur dioxide with three tertiary amines triethanolamine (TEA), tetrahydroxyethyl ethylenediamine (THEED), and N,N,N' ,N'-tetrakis (2-hydroxypropyl)ethylenediamine(Quadrol) were examined. The critical operating parameters of temperature, gas flow, coating area, gas strike area and product formation and coating age were evaluated. Simulated air profile analyses using the sulphur dioxide/triethanolamine system were achieved using both the initial reaction rate mode of operation (IRRMO) and the equilibrium shift mode of operation (ESMO). A simplified version of the laboratory Piezoelectric Gas Detector (P.G.D.) was set up as a field monitor and tested for the dynamic sampling of sulphur dioxide and other flue gases obtained from the burning of coal. This P.G.D. system utilized many of the features mentioned above. In the search for new and improved crystal coating materials with a specificity for a particular analyte gas the effect of humidity on selected gas/solid reactions was investigated e.g. N02/Mn02 N02/CU20, S02/Ni(0H)2). The novel use of bio-coating materials was investigated with a view to utilizing the specific and catalytic properties exhibited by specific enzymes. The micro-organism Azotobacter beijerinckii which produces nitrogenase and thus in nature fixes nitrogen was investigated as a model system for the use of bio-coatings. Finally work on the synthesis of an anchor polymer with reactive acceptor sites for sulphur dioxide was accomplished. This involved an organolithium preparation to incorporate reactive diene molecules on the surface of a divinylbenzene/styrene polymer.