A study of drop size distribution was carried out in a spray column by photographing the drops either through a round column or through a short square column inserted into the round column. A close-up photography technique was used and optical distortion of the round column taken into account. The drops were assumed to be oblate spheroids and a preliminary study of drop shape was undertaken to find the limitations of the oblate spheroid hypothesis. Drop size frequency distribution curves were drawn up at start-up and steady-state conditions and for one set of flow rates. The distribution was analysed in terms of the shape of the curves, mean values with confidence limits and spread of values. Volume-surface diameters were calcu-lated, leading to the determination of interfacial area of contact between the two phases and the calculation of mass transfer coefficients without an included area factor. Throughout the work the drops were treated in terms of spheres of equal volume and the bulk of the calculations was carried out on a digital computer. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

The production of uniform-sized drops without small follower drops or "trailers" in liquid-liquid systems was studied using a periodic injection technique for dispersing one liquid through a sharp edged nozzle into the other. Previous investigators using a continuous flow technique found that uniform sized drops without trailers were limited to systems of higher interfacial tension. The effects of nozzle inside diameter, nozzle material, and of velocity-time profile of the dispersed fluid through a nozzle at drop formation were examined using two systems; n-butanol and water of very low interfacial tension, and methyl isobutyl ketone and water of low interfacial tension. These two systems were chosen so that the results of this study could be integrated with other work. The velocity-time profiles were obtained by using a positive displacement bellows pump, the stroke of which was controlled by a cam follower through a variable ratio linkage using three different cam profiles. The conditions under which uniform sized drops without trailers were formed, were located for both systems. The effects of surface active contaminants and the wetting of the nozzle tip by the dispersed phase were considered. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

A study has been made of sampling techniques in a liquid-liquid extraction spray column using first a bell-shaped and a hook-shaped probe for the dispersed phase and for the continuous phase respectively. Later a piston method was attempted for the dispersed phase. The main interest in this research was the point concentration inside the column. At first, the time to reach steady state was considered in the absence of sampling. Later on, the rate of purging and sampling was varied for the probes up to 14.2 cc./min. for the continuous phase and 28.2 cc./min. for the dispersed phase. These rates were not sufficient to disturb the steady state. The measured point concentration was studied as a function of rate of sampling. Coalescence at the dispersed phase (bell-shaped) probe entrance did not take place. Finally, a piston sampler was set up and used in conjunction with the continuous phase (hook-shaped) probe as a second way to obtain point concentrations of the dispersed phase to compare with the results obtained with the bell-shaped probe. From these experiments, it can be concluded that sampling rate, varied from zero to 34.0 cc./min. for the continuous phase and from zero to 28.0 cc./min. for the dispersed phase, does not influence the point concentrations measured for column flows of 54.8 ft³/hr.-ft² and 72.4 ft³/hr.-ft² for the water and ketone phases respectively. The point concentration of the dispersed phase measured with the piston do not check definitively the results obtained with the bell-shaped probe; they do indicate that such agreement is fairly probable. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

A study was made on the back mixing or circulation in the continuous phase of a spray type liquid-liquid extraction tower. Concentration profiles of both continuous and dispersed phases were obtained by internal sampling. Mass transfer data are presented for the transfer of acetic acid between water and methyl isobutyl ketone in the 1.5-in. I.D. columns of three different heights. Considerable circulation in the continuous water phase was observed which resulted in the reduction of the driving force for mass transfer. A driving force correction factor, F(m), was obtained from the H.T.U. data using a simplified picture of behaviour at the interface. The height of the tower did not seem to have any effect on F(m). The overall H.T.U. values, obtained from the experimental profiles, were correlated with the flow rates. The end effect due to the agitation and coalescence of the drops at the interface was measured. This end effect was correlated with the overall capacity coefficients and the dispersed phase flow rates. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

No description available.

Call number: LD2668 .T4 1962 G47

Pesticide residue analysis is very important both in agriculture and environmental protection. The effectiveness of the analytical method depends very much on the extraction and preconcentration of the analytes prior to the actual analysis, as these analytes occur in trace concentrations that may be lower than the detection limit of the instrument. Various methods of extraction and pre-concentration have been introduced in an effort to decrease costs and other negative environmental impacts without compromising efficiency. One such method is single-drop micro-extraction (SDME), whose benefits cannot be overemphasised. This method has been recently introduced in the pool of pre-concentration methods for pesticide and other organic residues. In this study, the SDME method has been developed using chloroform as a solvent for preconcentration of a ten-component mixture of triazine (TP619) herbicides, followed by analysis by gas chromatography and flame ionisation detector (ppm level detection) and mass spectrometry for detection at sub-ppb level. The developed method uses the simple introduction of an air bubble to the micro-litre droplet of the organic solvent used for extraction of the triazines. This air-bubble showed the increase in the extraction efficiency of the method by about 30% relative to the optimised extraction without the air bubble. The air bubble works very well with addition of the salt (10% NaCl) to the solution being extracted, with further extraction enhancements being observed. Traditionally, the solution being extracted is stirred to achieve good mass transfer. However, the present method does not require stirring as stirring makes the system unstable resulting in reduced precision. The optimum conditions for the newly developed method, named bubble-in-drop single-drop micro-extraction (BID-SDME) were found to be as follows: 1 μL chloroform, 0.5 μL air bubble, 10% NaCl and static equilibration for 20 minutes, while the sample volume is 1 mL. This method showed linearity in the region of 1 ppm to 0.05 ppb (about six orders of magnitude) as long as the instrumental settings were optimised for increased sensitivity. The RSD values observed in this method were better than those recorded in literature, being <10%. Some instrumental manipulations are necessary to realise the full potential of the instrument. Various settings were explored on the GC-MS to optimise its performance below the ppb level. It was observed that the configuration that gave the best sensitivity and the lowest limits of detection was the high-pressure and split-less injection mode. This improved the detection limits of the instrument by 2 orders of magnitude (from 1 ppb to below 0.05 ppb). The GC-MS performance was further improved by the use of selected ion monitoring (SIM) mode of analysis. This technique reduced the interferences from the co-extracted compounds that can compromise the precision and accuracy of the analytical method especially at low concentration applicable in trace analysis. The new BID-SDME method was applied to various samples (dam water, synthetic hard water, dam sediment, humic and sandy soil samples) giving unsurpassed efficiencies with very low RSD values. In these systems, NaCl addition (10% w/v) not only increased extraction efficiency but also had a matrix-normalising effect as the RSD values were reduced and the matrix effects somewhat diminished. The application of this method to orange juice required the addition of only 5% NaCl (not 10% like the other samples). The results obtained with the extraction of orange juice were better than those recorded in literature. The normalising effect was further observed as the RSD values with addition of the NaCl were reduced the RSD from 11.7 (salt-free solution) to 5.56 (5% NaCl). These application experiments were carried out at the 0.2 ppb level using spiked samples. The method was compared against the other extraction techniques used in trace analysis (especially SPME) and it performed better overall giving lower RSD values and much improved detection limits. The calculated detection limits for the ten triazines used in the mixture were in the region of parts per trillion (0.9-14 ppt) with RSD values of < 10% with the use of internal standard. / Prof. D.B.G. Williams Mr. R. Meyer

Thesis (M.Sc.)(Chemistry)--University of Pretoria, 2005. / Abstract in English. Includes bibliography. Available on the Internet via the World Wide Web.

Thesis (M.S.)--Virginia Polytechnic Institute, 1954. / Typewritten. Vita. Bibliography: leaves 191-199. Also available via the Internet.

This thesis summarizes an investigation into the need for removing extractives from herbaceous biomass feedstocks prior to their chemical characterization. Switchgrass (Panicum virgatum), was used in this study as a representative herbaceous biomass feedstock. The influence of extractives on the chemical analysis of switchgrass was done by comparing the composition of native switchgrass and solvent-extracted switchgrass preparations. Solvent-extracted switchgrass was prepared by extracting the native feedstock with either 95% ethanol, hot water or sequentially with ethanol and then water. Each of the feedstocks was analyzed for glycans, Klason lignin, acid soluble lignin, protein, ash, acetic acid and uronic acids. The results demonstrate that the extractives in native switchgrass significantly interfere with the analysis of Klason lignin. The lignin content of the feedstock was overestimated if the extractives were not removed prior to the analysis. The extractives in switchgrass did not affect glycan analyses. However, some soluble sugars are removed from the feedstock during the solvent extraction process. Total extractives removed by ethanol, water and ethanol/water amounted to 9.74%, 16.42%, and 19.11% of the feedstocks total solids, respectively. These amounts of extractives increased Klason lignin values by 4%, 4.5%, and 6.5% (on a wt percent of total solids), respectively. Most of the extractives in switchgrass are water-soluble and approximately one-quarter of these extractives measure as Klason Lignin. The removal of the water soluble extractives from the feedstock improved the mass closure values for the feedstock's summative analysis. Successive ethanol and hot water extraction has successfully removed most of the extractives in switchgrass yielding 100.4% mass balance. The recommended approach for the analysis of herbaceous biomass feedstocks will include sequential 95% ethanol and hot water extraction followed by chemical analysis on both the preextracted substrate and the extractives obtained from that substrate. / Graduation date: 1996