Activated carbons used in the Platinum Group Metals extraction industry are characterised by large internal surface areas and a great affinity for platinum, palladium and ruthenium. It is therefore necessary in this study to develop a method to produce an activated carbon that is suitable and yet cost effective, for use in the extraction of PGM's. The quality of the coal-based activated carbon may not prove to be as good as activated carbon produced from other traditional sources, but the production costs involved may make South African coal a feasible alternative feedstock. The purpose of this research is to prepare activated carbon from a South African based bituminous coal by physical activation. The activated carbon produced are characterised by BET surface area, activated carbon pH and phenol adsorption studies. The results of the different characterisation methods for the prepared activated carbons are compared to the results of a commercially available activated carbon, Norit RO 0.8 (control sample). Bituminous coals from various sources including Witbank Seam 4 and New Vaal are used. The preparation method chosen is raw material activation by means of physical activation with superheated steam. The effects of process variables such as activation time (1-3 hr) and temperature (600 - 800°C) are studied in order to optimise those preparation parameters. Activated carbon surface area is characterized by means of nitrogen adsorption isotherms at 77K. BET surface area analysis showed that Witbank Seam 4 coal activated at a temperature of 800°C and activation time of 3 hours, resulted in a surface area of 340m2/g. Quality control of each sample was performed by measuring the pH of a known amount of the prepared activated carbon in distilled water over time. Results showed that the pH of some of the prepared activated carbons reached a value of 11. Phenol adsorption results for the different activated carbons prepared corresponded well to the results obtained for the Norit RO 0.8 activated carbon sample. / Thesis (M. Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2008.

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The purpose of this thesis is to evaluate the performance and cost effectiveness of a Peroxone Groundwater Treatment Plant (PGTP) designed and operated by Montgomery Watson, in support of the Defense Evaluation Support Agency's independent analysis for the United States Army Environmental Center (USAEC). Many Department of Defense installations have sites that contain groundwater contaminated with explosive materials. Primary methods for the removal of explosive materials involve the use of Granular Activated Carbon (GAC). This process, however, requires additional waste disposal and treatment of explosive laden GAC, thereby incurring additional costs. An alternate method for the treatment of contaminated groundwater involves the use of hydrogen peroxide (H2O2) in conjunction with ozone (03). This method is referred to as the Peroxone oxidation process. A demonstration of the PGTP was conducted from 19 August to 8 November, 1996, at Cornhusker Army Ammunition Plant (CAAP), Grand Island, Nebraska using a small scale version with a maximum flow rate of 25 gallons per minute. The explosive contaminants analyzed during the demonstration include 2,4,6-Trinitrotoluene (TNT), 1,3,5-Trinitrobenzene (TNB), 1,3,5-Triazine (RDX), and Total Nitrobodies. Peroxone cost effectiveness was evaluated using a 30 year life cycle cost comparison to GAC and Ultraviolet/Ozone processes

This work concerns the functionalisation of a variety of carbon materials for the selective adsorption of carbon dioxide. A key challenge in post-combustion capture from gas fired power plants is related to the low CO2 concentration in the flue gas (4- 8%). Therefore highly selective adsorbents have the potential to improve the efficiency of the separation of carbon dioxide from gas mixtures. The study was performed in conjunction with the EPSRC funded project ‘Adsorption Materials and Processes for Carbon Capture from Gas-Fired Power Plants – AMPGas’. The carbon materials investigated included multi-walled carbon nanotubes, a microporous activated carbon, two types of mesoporous activated carbon and multi-walled carbon nanotube/polyvinyl alcohol composite aerogels. The uptake of carbon dioxide by these materials was enhanced through the addition of basic amine groups to the materials. The adsorption properties of the samples were tested by the zero-length column technique, thermal gravimetric analysis and breakthrough experiments. The materials were generally tested at conditions representative of those found in the flue gas of a fossil fuel power plant: 0.1 bar partial pressure of CO2. Two approaches were adopted for the chemical functionalization of the solid carbon supports. First, amine groups were covalently grafted directly to the surface and secondly amine molecules were physically adsorbed within the porous structure of the material by wet impregnation. It was seen that wet impregnation enabled the incorporation of a greater number of amine groups and the CO2 capacity of the materials was investigated with respect to the carbon support structure, the type of amine and the amount of amine loading. Larger pore volume mesoporous carbon materials were seen to provide a more efficient support for the amine to interact with the CO2. A greater than 12-fold increase in the CO2 capacity was observed when the amine impregnated carbon material was compared to the raw starting material. The extended zero-length column was introduced and fully characterized as a novel breakthrough experiment. It requires a small sample mass (~50 mg) and it allows binary selectivities to be calculated. It was shown, through multiple experiments and simulations that the breakthrough experiments were conducted under close to isothermal conditions which greatly simplifies the analysis of the breakthrough curves. In addition, a new zero-length column model was proposed to account for the reaction between the amine and the CO2 in the adsorbed phase and fitted to experimental data. An interesting double curvature was observed in the concentration profile during the desorption step which was attributed to the kinetics of the amine-CO2 reaction. A brief investigation was carried out into the binary separation of biogas (45% CO2: 55% CH4) by zeolite 13X, activated carbon and an amine impregnated activated carbon. Finally, initial investigations into the properties of low density carbon nanotube aerogels which have a large accessible pore volume, were carried out. Their potential as highly efficient supports for amine impregnation was investigated. It was found that amine functionalized carbons strongly interact with carbon dioxide and have the potential to be integrated as an adsorbent in a rapid temperature swing process that separates carbon dioxide from dilute gas streams.

Hydrogen sulphide is an environmentally hazardous gas which is present in many gas streams associated with oil and gas industry. Oxidation of H2S to sulphur in air produces no bulky or waste material and requires no further purification. Activated carbon is known as a catalyst for this reaction.<p> In this research, a coal-based precursor (luscar char) and a biomass-based precursor (biochar) were used for production of activated carbons by two common methods of activation: physical and chemical activation in which steam and potassium hydroxide (KOH), respectively, were used. Experiments were designed by the statistical central composite design method. Two models were developed for the BET surface area and reaction yield of each activation process. These models showed the effects of operating conditions, such as activation temperature, mass ratio of activating agent to precursor, activation time, and nitrogen flowrate on the BET surface area and reaction yield for each activation method for each precursor. The optimum operating conditions were calculated using these models to produce activated carbons with relatively large BET surface area (> 500 m2/g) and high reaction yield (> 50 wt %). The BET surface area and reaction yield for activated carbons produced at optimum operating conditions showed maximum 7 and 7.4 % difference, respectively, comparing to the values predicted by models.<p> The activated carbons produced at optimum operating conditions were used as the base catalysts for the direct oxidation of 1 mol % hydrogen sulphide in nitrogen to sulphur at the temperature range of 160-205 oC and pressure of 700 kPa. Originally activated carbons showed a good potential for oxidation of hydrogen sulphide by their selectivity for sulphur product and low amount of sulphur dioxide production. To improve the performance of steam-activated carbons, the catalysts were modified by acid-treatment followed by thermal desorption. This method increased the break-through times for coal-based and biomass-based catalysts to 115 and 141 minutes, respectively. The average amounts of sulphur dioxide produced during the reaction time were 0.14 and 0.03 % (as % of hydrogen sulphide fed to the reactor) for modified activated carbons prepared from biochar and luscar char, respectively. The effects of porous structure, surface chemistry, and ash content on the performances of these activated carbon catalysts were investigated for the direct oxidation reaction of hydrogen sulphide.<p> The acid-treatment followed by thermal desorption of activated carbons developed the porosity which produced more surface area for active sites and in addition, provided more space for sulphur product storage resulting in higher life time for catalyst. Boehm titration and temperature program desorption showed that the modification method increased basic character of carbon surface after thermal desorption in comparison to acid-treated sample. In addition, the effects of impregnating agents (potassium iodide and manganese nitrate) and two solvents for impregnation process were studied on the performance of the activated carbon catalysts for the direct oxidation of H2S to sulphur.<p> Sulphur L-edge X-ray near edge structure (XANES) showed that the elemental sulphur was the dominant sulphur species in the product. The kinetic study for oxidation reaction of H2S over LusAC-O-D(650) was performed for temperature range of 160-190 oC, oxygen to hydrogen sulphide molar ratio of 1-3, and H2S concentration of 6000-10000 ppm at 200 kPa. The values of activation energy were 26.6 and 29.3 kJ.gmol-1 for Eley-Rideal and Langmuir-Hinshelwood mechanisms, respectively.

Activated Carbon (AC) is an amorphous carbon-based material characterized with a large surface area (~ 1,000 m2/g) and consists primarily of graphitic (sp2 hybrid) layers. Its amphoteric chemical property results because of the chemical treatment of the surface of AC with oxidizing agents, reducing agents, and grafting agents. β-cyclodextrin (β-CD) is a very interesting carbohydrate oligomer that provides very strong binding ability for small organic guest molecules in its inner cavity (6.0 ~ 6.5 Å) by van der Waals interactions and hydrogen bond formation between the guest molecules and the host. <p>Surface modification of AC with β-CD was synthesized by chemical methods: oxidation with HNO3, reduction with LiAlH4, and grafting β-CD onto the surface of AC via organic linkers such as glutaraldehyde and 1,4-phenylene diisocyanate. This surface grafted AC with β-CD, then, was evaluated for its surface area and sorption performance by using a solution dye sorption method using dye adsorbates. <p>Surface functional groups produced from oxidation (carboxylic acid, lactone, quinine, phenol, and nitro groups), reduction (alcohol and amine groups), and grafting (imine, hemiacetal, and urethane bonds) methods including microscopy of untreated, surface modified, and grafted ACs were characterized by various surface characterization methods: Diffuse Reflectance Infra-red Fourier Transform Spectroscopy (DRIFTS), Scanning Electron Microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Thermogravimetric analysis (TGA), Differential thermogravimetry (DTG), Matrix Assisted Laser Desorption Ionization Time of Flight mass spectrometry (MALDI TOF MS), and Electron spin resonance (ESR) spectroscopy. A chemical method, the Boehm method, was used for identifying surface bound acidic and basic functional groups. Nitrogen porosimetry was used to analyze the surface area and pore structure characteristics of AC, surface modified ACs, and grafted ACs. <p>p-nitrophenol (PNP) and methylene blue (MB) were used as adsorbates for the dye sorption method. PNP and MB were used to measure the sorption performance of grafted ACs at equilibrium using UV-vis spectrophotometry in aqueous solution. Sorption capacity (Qe), surface area (m2/g), and binding affinity characteristics [KF (L/g), KL (g/mol), and KBET (L/g)] were determined at equilibrium conditions using fundamental sorption models such as Langmuir, Freundlich, and BET isotherms. The sorption performance of grafted ACs and granular AC were different according to the difference in surface area and pore structure characteristics of each material.

Activated Carbon (AC) is an amorphous carbon-based material characterized with a large surface area (~ 1,000 m2/g) and consists primarily of graphitic (sp2 hybrid) layers. Its amphoteric chemical property results because of the chemical treatment of the surface of AC with oxidizing agents, reducing agents, and grafting agents. β-cyclodextrin (β-CD) is a very interesting carbohydrate oligomer that provides very strong binding ability for small organic guest molecules in its inner cavity (6.0 ~ 6.5 Å) by van der Waals interactions and hydrogen bond formation between the guest molecules and the host. <p>Surface modification of AC with β-CD was synthesized by chemical methods: oxidation with HNO3, reduction with LiAlH4, and grafting β-CD onto the surface of AC via organic linkers such as glutaraldehyde and 1,4-phenylene diisocyanate. This surface grafted AC with β-CD, then, was evaluated for its surface area and sorption performance by using a solution dye sorption method using dye adsorbates. <p>Surface functional groups produced from oxidation (carboxylic acid, lactone, quinine, phenol, and nitro groups), reduction (alcohol and amine groups), and grafting (imine, hemiacetal, and urethane bonds) methods including microscopy of untreated, surface modified, and grafted ACs were characterized by various surface characterization methods: Diffuse Reflectance Infra-red Fourier Transform Spectroscopy (DRIFTS), Scanning Electron Microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Thermogravimetric analysis (TGA), Differential thermogravimetry (DTG), Matrix Assisted Laser Desorption Ionization Time of Flight mass spectrometry (MALDI TOF MS), and Electron spin resonance (ESR) spectroscopy. A chemical method, the Boehm method, was used for identifying surface bound acidic and basic functional groups. Nitrogen porosimetry was used to analyze the surface area and pore structure characteristics of AC, surface modified ACs, and grafted ACs. <p>p-nitrophenol (PNP) and methylene blue (MB) were used as adsorbates for the dye sorption method. PNP and MB were used to measure the sorption performance of grafted ACs at equilibrium using UV-vis spectrophotometry in aqueous solution. Sorption capacity (Qe), surface area (m2/g), and binding affinity characteristics [KF (L/g), KL (g/mol), and KBET (L/g)] were determined at equilibrium conditions using fundamental sorption models such as Langmuir, Freundlich, and BET isotherms. The sorption performance of grafted ACs and granular AC were different according to the difference in surface area and pore structure characteristics of each material.

Hydrogen sulphide is an environmentally hazardous gas which is present in many gas streams associated with oil and gas industry. Oxidation of H2S to sulphur in air produces no bulky or waste material and requires no further purification. Activated carbon is known as a catalyst for this reaction.<p> In this research, a coal-based precursor (luscar char) and a biomass-based precursor (biochar) were used for production of activated carbons by two common methods of activation: physical and chemical activation in which steam and potassium hydroxide (KOH), respectively, were used. Experiments were designed by the statistical central composite design method. Two models were developed for the BET surface area and reaction yield of each activation process. These models showed the effects of operating conditions, such as activation temperature, mass ratio of activating agent to precursor, activation time, and nitrogen flowrate on the BET surface area and reaction yield for each activation method for each precursor. The optimum operating conditions were calculated using these models to produce activated carbons with relatively large BET surface area (> 500 m2/g) and high reaction yield (> 50 wt %). The BET surface area and reaction yield for activated carbons produced at optimum operating conditions showed maximum 7 and 7.4 % difference, respectively, comparing to the values predicted by models.<p> The activated carbons produced at optimum operating conditions were used as the base catalysts for the direct oxidation of 1 mol % hydrogen sulphide in nitrogen to sulphur at the temperature range of 160-205 oC and pressure of 700 kPa. Originally activated carbons showed a good potential for oxidation of hydrogen sulphide by their selectivity for sulphur product and low amount of sulphur dioxide production. To improve the performance of steam-activated carbons, the catalysts were modified by acid-treatment followed by thermal desorption. This method increased the break-through times for coal-based and biomass-based catalysts to 115 and 141 minutes, respectively. The average amounts of sulphur dioxide produced during the reaction time were 0.14 and 0.03 % (as % of hydrogen sulphide fed to the reactor) for modified activated carbons prepared from biochar and luscar char, respectively. The effects of porous structure, surface chemistry, and ash content on the performances of these activated carbon catalysts were investigated for the direct oxidation reaction of hydrogen sulphide.<p> The acid-treatment followed by thermal desorption of activated carbons developed the porosity which produced more surface area for active sites and in addition, provided more space for sulphur product storage resulting in higher life time for catalyst. Boehm titration and temperature program desorption showed that the modification method increased basic character of carbon surface after thermal desorption in comparison to acid-treated sample. In addition, the effects of impregnating agents (potassium iodide and manganese nitrate) and two solvents for impregnation process were studied on the performance of the activated carbon catalysts for the direct oxidation of H2S to sulphur.<p> Sulphur L-edge X-ray near edge structure (XANES) showed that the elemental sulphur was the dominant sulphur species in the product. The kinetic study for oxidation reaction of H2S over LusAC-O-D(650) was performed for temperature range of 160-190 oC, oxygen to hydrogen sulphide molar ratio of 1-3, and H2S concentration of 6000-10000 ppm at 200 kPa. The values of activation energy were 26.6 and 29.3 kJ.gmol-1 for Eley-Rideal and Langmuir-Hinshelwood mechanisms, respectively.

Optical-electrical, rendering, paper-making, and sewage treatment plants emit odorous waste gases containing dimethyl sulfide (DMS) as one of the major odorous compounds. For the protection of ambient air quality and prevention of odor complaints, DMS should be eliminated from the gases before venting them into the atmosphere. This study aimed to develop a process for eliminating DMS in the waste gases by introducing an enough amount of chlorine gas to oxidize DMS therein to non-odorous dimethyl sulfone (DMSO2). The vented gas from the oxidation step is then contacted with a bed of granular activated carbon (GAC) to convert the residual chlorine to GAC-adsorbed hydrochloric acid and get a nearly odor-free gas. Both lab-scale and field tests were performed in this study. Results from the lab test indicate that the GAC had only an equilibrium DMS adsorption capacity of 4.30 mg/g GAC with 15-30 ppm DMS and no chlorine in the test gas. With an empty-bed gas-GAC contact time (EBCT) of around 0.49 s and no DMS in the test gas, 42 ppm gaseous chlorine could completely be reduced to HCl and the reduction product adsorbed to the GAC. The GAC had a minimum chlorine elimination capacity of around 110 mg/g GAC. Lab tests also indicate that with a molar Cl2/DMS ratio (R) of around 0.9 and a gas-phase reaction time of 5 s, and an EBCT of 0.58 s, the influent 22 ppm DMS could be removed to below detectable limits. Results from field tests in an optical-electrical wastewater plant show that by the developed process, < 1 ppm DMS in the plant¡¦s waste gas could be treated to an odor-free degree with a chlorine dose of 4-10 ppm.