Polycyclic aromatic hydrocarbons (PAHs) are an important class of persistent organic pollutants (POPs) that are commonly found in the environment at low concentrations. POPs are long-lived organic compounds and originate almost entirely from anthropogenic activities such as chemical industries, combustion and agriculture activities. Owing to their potential carcinogenicity, mutagenicity and teratogenicity, PAHs have been determined in several matrices, particularly water, soil and sediment. Hazards associated with these compounds are owing to their hydrophobic character, persistence and bioaccumulation properties of several individual PAHs. Hence the primary goal of this research was to identify and determine PAHs in water and sediment samples, from rivers and dams in greater Johannesburg area, South Africa. In this work, three extraction techniques have been optimized for the extraction of PAHs in various samples. The extraction techniques based on hollow fiber liquid phase microextraction (HF-LPME) and solid phase extraction (SPE) were optimized for aqueous samples. Microwave assisted extraction technique (MAE) was optimized for solid samples. The optimized methods were applied to real water and sediment samples in and around Johannesburg area. HF-LPME and SPE techniques were compared with each other, while MAE was compared with Soxhlet (SE) in terms of their extraction efficiencies, enrichment factors, detection limits, relative standard deviations and concentrations of PAHs found in real samples. HF-LPME technique involved extraction of PAHs from a 20 mL sample containing 20% acetonitrile as a modifier. The PAHs were extracted into a 5 cm hollow fibre filled with heptane as organic solvent. At a stirring speed and extraction time of 600 rpm and 30 minutes, respectively, the acceptor solvent was collected to be analysed by GC-MS. The obtained enrichment factors ranged from 40 to 95 and the recoveries ranged from 3-8% depending on individual PAHs. The detection limits ranged from 23.0-95.0 ng L-1 while relative standard deviations for the recoveries were less than 5%, (n=3). The concentrations obtained in real water samples ranged from 30.3-213.8 ng L-1 and the relative standard deviations were between 0.8-11.9%, (n=3). SPE technique involved extraction of PAHs from a 100 mL sample containing 10% methanol as a modifier. The PAHs were extracted using C18 cartridges with 40% methanol in water as conditioning solvents and 3 mL acetone: THF (1:1) as eluting solvents. After eluting, the analyte is reduced to 1 mL under nitrogen and then analysed using GC-MS. The obtained enrichment factors ranged from 78-135 depending on the individual PAH. The detection limits ranged from 20.0-52.0 ng L-1. The relative standard deviations for the obtained enrichment factors were less than 6%. The obtained concentrations from real water samples ranged from 21.4-615.7 ng L-1 and the relative standard deviations were between 1.9-13.0%, (n=3). In MAE technique, the extraction was carried out with 20 mL of hexane: acetone (1:1, v/v) mixture with 1 g sample at 250 W for 20 minutes. After extraction, the extract was cleaned and reduced to 1 mL under nitrogen and then injected into an HPLC-Fluoresence system. The obtained recoveries ranged from 61-98% depending on the individual PAHs. The detection limits obtained ranged from 0.03-0.5 μg L-1 for HPLC-Fluorescence. The relative standard deviations were less than 6% for the obtained enrichment factors. The obtained concentrations in the sediments ranged from 61-45281μg kg-1 and the relative standard deviations ranged from 2.1-10.8%, (n=3). The possible major sources of PAHs pollution in rivers and dams in great Johannesburg area was suspected to be due to poor wastewater and solid waste management in informal settlements and a large oil spill accident that happened. This is supported by the large concentrations of PAHs found in sediments from Jukskei River which passes through one of the largest informal settlements. The pH in this river is also basic with large conductivity suggesting the presence of anions. The recipient dam of this river had also problems of algae and weeds growing in it. The influence of oil spill that happened is supported by decreasing concentrations of PAHs in the sediments with distance away from the accident area in the Blaauwpan dam. Other possible sources of PAHs are vehicle emission since studies have shown that from about 2005, the number of these in high ways in the city have been increasing by about 15-20% per year.

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 1996 / In present thesis the results of a study of the combined action of a solid catalyst and a gas-phase inintiator, hydrogen peroxide, in the methane partial oxidation and oxidative coupling reactions are presented. [Abbreviated Abstract. Open document to view full version] / MT2017

by Jimmy Siu-hung Tsang. / Bibliography: leaves 124-148 / Thesis (M.Ph.)--Chinese University of Hong Kong

Due to the combined heavy dependence on crude oil and the unpredictable nature of the associated markets, an alternative means to produce the required hydrocarbon based products is much desired. The Fischer-Tropsch synthesis provides a route to the production of synthetic crude oil by a catalytic reaction between carbon monoxide and hydrogen (collectively referred to as syngas) at moderate temperatures and pressures. First discovered in the early 1900's, the process results in a multitude of products which can supply a range of transportation fuels and petrochemicals. However, knowledge of the reaction process is still not completely understood due to the complex product distribution which is obtained. In order to gain better control over the process outputs, enhancing the understanding of the mechanistic routes which govern the overall reaction is key. A novel route was developed to monitor the number and length of hydrocarbon species which accumulate and grow on the catalyst surface during the reaction by implementing in situ quantitative FTIR spectroscopy. Initially molar absorption coefficients, required in order to quantify the adsorbed hydrocarbon species, were determined utilising a custom made thermogravimetric infrared cell. The resulting absorption coefficients values were then applied to data which was derived from infrared spectra collected for various catalysts during multiple Fischer-Tropsch reactions. The quantitative analysis of the catalyst surface was then compared with reaction data collected using gas chromatography (GC), in order to investigate if a link exists between the surface species and reaction products. Results showed that while no direct link was detected, the observed surface species could be attributed to oxygenate products of the Fischer-Tropsch reaction which are not produced in a detectable amount by GC. The species were shown to reside on both the metal and support material, with the transportation mechanism to the support also investigated.

No description available.

This research describes the production of hydrocarbons from acetone and isopropanol produced by the MixAlco process. The MixAlco process has two types of products: acetone and isopropanol. The effect of the temperature, weight hourly space velocity (WHSV), type of catalyst, feed composition, and pressure are studied. For the isopropanol reaction, the following conditions were used: HZSM-5 (280), 1 atm, 300–410°C, and 0.5–11.5 h–1, respectively. The temperature and WHSV affect the average carbon number of the reaction products. A product similar to commercial gasoline was obtained at T = 320 °C and WHSV= 1.3 to 2.7 h–1. Also, at these conditions, the amount of light hydrocarbons (C1–C4) is low. For the acetone reaction, the following conditions were used: HZSM-5 with silica alumina ratio (Si/Al) 80 and 280 mol silica/mol alumina, 1–7.8 atm, 305–415°C, 1.3–11.8 h–1, and hydrogen acetone ratio 0–1 mol H2 /mol acetone. The conversion on HZSM-5 (80) was higher than HZSM-5 (280); however, for HZM–5 (80) the production of light hydrocarbons (C1–C4) was more abundant than (280), and it formed less coke. For acetone, the effect of high pressure (P = 7.8 atm) was evaluated. At high pressure, the conversion was lower than at atmospheric pressure. HZSM-5 (280) rapidly deactivated, and the amount of light hydrocarbons (C1–C4) increased. For acetone, co-feeding hydrogen inhibited coke formation and decreased the amount of light hydrocarbons (C1–C4).

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Includes bibliographical references (leaves 210-217). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Environmental Sciences." Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 210-217). Available also in a digital version from Dissertation Abstracts.