Date of Award

2009

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Science

First Advisor

Dr. Sayed Marzouk

Second Advisor

Dr. Fakhr Eldin Suliman

Third Advisor

Dr Muftah El Nass

Abstract

Sulfur dioxide (SO2) is considered one of the main contaminants in air because of its major contribution to acid rain and due to the major health concerns associated with exposure to high concentrations of SO2. Hence, there has been a great interest in the determination of SO2 because of continuous monitoring its impacts on the environment and public health. However, limited reports targeted SO2 in gas streams.

Therefore, the primary objective of the present work was to develop affordable gas analyzer for continuous monitoring of SO2 in gas streams. The principle of operation of the described analyzer was based on a gas diffusion scrubber (in the form of hollow fiber membrane module, HFMM) as a prior gas sampling unit which allowed the contact between the gas stream and a selected carrier solution. SO2, present in the gas stream diffuses to and dissolves in the flowing carrier solution. The concomitant changes of the carrier solution can be measured by means of a suitable flow-through detector placed downstream to produce analytical signal for the quantification of SO2 in the gas stream.

The selected detectors were limited to electrochemical detectors because of their simplicity and they do not usually require additional reagents or prior derivatization reactions. With regards to the chemical properties of SO2, pH, conductivity and amperometric detectors were selected as potential detectors for the construction of SO2 gas analyzers.

The first detector evaluated in the current project was based on potentiometric pH measurements. The obtained optimum experimental conditions for S02 detection were 0.1 M potassium oxalate buffer as carrier solution at flow rate 1.5 mL/min, gas flow rate 250 mL/min, using flat-bottom pH glass electrode and HFMM consisting of 60 PP fibers. Under the optimized conditions, a Nernestian slope up to 10000 ppm with a detection limit of 1.0 ppm SO2 was obtained. The response time varied from 20 to 200 seconds whereas the recovery time was 600 seconds when SO2 concentration decreased from 1000 ppm to zero. The pH-detector showed excellent selectivity. CO2 up to 500 folds did not exert significant interference and H2S up to 5 folds greater than that of SO2 was tolerated.

The second described detector was based on conductivity detection. The obtained optimum experimental conditions for S02 detection were 1.0 mM H2O2 as carrier solution at flow rate 2.0 mL/min, gas flow rate 200 mL/min, using commercial conductivity probe and HFMM consisting of 60 PP fibers. The favorable performance characteristics of the proposed SO2 analyzer was successfully applied in monitoring real experiment of removing SO2 from a gas stream. The optimized detector gave linear range up to 2500 ppm, a detection limit of 16 ppm for SO2 in nitrogen and 115 to 180 seconds for recovery time. In addition the conductometric detector showed no interference of CO2 up to 100 folds greater than that of SO2.

The third detector was based on a novel amperometric detection. The utilized electrode was based on an organic conducting salt (OCS) based on tetrathiafulvalenetetracyanoquinodimethane [TTF-TCNQ] complex. The TTF-TCNQ was mixed with silicone oil in 1:1.25 ratio. The formed paste was packed in Teflon cavity (12 mm in diameter). The obtained optimum experimental conditions for SO2 detection were 0.2 M potassium phosphate buffer pH 6.5 as carrier buffer at flow rate 5.0 mL/min, using commercial HFMM mini-module. The TTF-TCNQ electrode was polarized at 0.24 V vs. SCE. The obtained amperometric response was linear up to 500 ppm and can detect as small as 10 ppm of SO2 and showed no interference at very high levels of CO2 (3900 folds).

The advantages of the developed SO2 gas analyzers were manifold which include (i) the obtained performance characteristics of the described SO2 analyzer can be tuned for certain application requirements such as high sensitivity, wide linearity range, high selectivity towards a particular interfering gas, etc. (ii) low construction and operational cost, (iii) no special disposal required for the waste carrier, (iv) favorable response characteristics such as fast response, excellent reproducibility and signal stability, (v) the entire analyzer construction can be miniaturized to provide low-cost portable unit for industrial and/or environmental monitoring. This latter advantage presents some potential for commercialization of the described analyzer.

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