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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

SO2 and O2 separation by using ionic liquid absorption / S.L. Rabie

Rabie, Samuel Liversage January 2012 (has links)
In order to reduce the amount of pollution that is generated by burning fossil fuels alternative energy sources should be explored. Hydrogen has been identified as the most promising replacement for fossil fuels and can be produced by using the Hybrid Sulphur (HyS) cycle. Currently the SO2/O2 separation step in the HyS process has a large amount of knock out drums. The aim of this study was to investigate new technology to separate the SO2 and O2. The technology that was identified and investigated was to separate the SO2 and O2 by absorbing the SO2 into an ionic liquid. In this study the maximum absorption, absorption rate and desorption rate of SO2 from the ionic liquid [BMIm][MeSO4] with purities of 95% and 98% was investigated. These ionic liquid properties were investigated for pure O2 at pressures ranging from 1.5 to 9 bar(a) and for pure SO2 at pressures from 1.5 to 3 bar(a) at ambient temperature. Experiments were also carried out where the composition of the feed-stream to the ionic liquid was varied with compositions of 0, 25, 50, 75 and 100 mol% SO2 with O2 as the balance. For each of these compositions the temperature of the ionic liquid was changed from 30oC to 60oC, in increments of 10oC. The absorption rate of SO2 in the ionic liquid increased when the mole percentage SO2 in the feed stream was increased. When the temperature of the ionic liquid was decreased the maximum amount of SO2 that the ionic liquid absorbed increased dramatically. However, the absorption rate was not influenced by a change in the absorption temperature. The experimental results for the maximum SO2 absorption were modelled with the Langmuir absorption model. The model fitted the data well, with an average standard deviation of 17.07% over all the experiments. In order to determine if the absorption reaction was endothermic or exothermic the Clausius-Clapeyron equation was used to calculate the heat of desorption for the desorption step. The heat of desorption data indicated that the desorption of SO2 from this ionic liquid was an endothermic reaction because the heat of desorption values was positive. Therefore the absorption reaction was exothermic. From the pressure-change experiments the results showed that the mole percentage of O2 gas that was absorbed into the ionic liquid was independent of the pressure of the O2 feed.On the other hand, there was a clear correlation between the mole percentage SO2 that was absorbed into the ionic liquid and the feed pressure of the SO2. When the feed pressure of the SO2 was increased the amount of SO2 absorbed also increased, this trend was explained with Fick’s law. In the study the effect of the ionic liquid purity on the SO2 absorption capacity was investigated. The experimental results for the pressure experiments showed that the 95% and 98% pure ionic liquid absorbed about the same amount of SO2. During the temperature experiments the 95% pure ionic liquid absorbed more SO2 than the 98% pure ionic liquid for all but two of the experiments. However the 95% pure ionic liquid also absorbed small amounts of O2 at 30 and 40oC which indicated that the 95% pure ionic liquid had a lower selectivity than the 98% pure ionic liquid. Therefore, the 95% pure ionic liquid had better SO2 absorption capabilities than the 98% pure ionic liquid. These result showed that the 98% pure ionic liquid did not absorb more SO2 than the 95% pure ionic liquid, but it did, however, show that the 98% pure ionic liquid had a better selectivity towards the SO2. Hence, it can be concluded that even with the O2 that is absorbed it would be economically more advantageous to use the less expensive 95% pure ionic liquid rather than the expensive 98% pure ionic liquid, because the O2 would not influence the performance of the process negatively in such low quantities. / Thesis (MIng (Chemical Engineering))--North-West University, Potchefstroom Campus, 2013
42

Separation of SO2/O2 using membrane technology / Bongibethu Msekeli Hlabano-Moyo

Hlabano-Moyo, Bongibethu Msekeli January 2013 (has links)
The Hybrid Sulphur process is one technology out of a multitude of known technologies responsible for hydrogen production. Within the latter hydrogen production cycle, it is pivotal to recover O2 as a by-product from a sulphuric acid decomposition reaction that produces SO2, H2O and O2. It is assumed that a simple phase separation stage carried out on the reaction products would liberate SO2 and O2 as a gaseous mixture leaving behind H2O in the liquid state. Several separation technologies are available to effect SO2/O2 separation, but membrane technology has proved to be dearer due to simplicity of the technology, low capital and energy costs. It is a pity though that insignificant work has been done that considers the SO2/O2 binary system in the membrane technology context. Of the insignificant work done, non – commercial membranes were employed. It is on the latter background that the present study was proposed. Six commercial membranes were selected from literature, two (Udel Polysulfone and Teflon AF 2400) of which are currently used in gas separation applications and the remainder (Hyflon M, Hyflon F, Halar and Nafion 117) not necessarily used as gas separation membranes but present a potential of separating SO2/O2. The inclusion of the latter four membranes sought to unearth unknown gas separation potentials of the membranes based on hypothetical 1 μm thick membranes. A screening technique was employed to eliminate poor performing membranes through pure component permeation of SO2, O2, N2 and CO2. The use of the additional gases (N2 and CO2) was meant to allow the generation of a pool of data that would be used as a yardstick to compare to literature and thus validate the authenticity of the designed set up. The single permeation experiments were carried out at 25°C and at absolute gas feed pressures of 1 bar, 2 bar and 3 bar, with the exception of Hyflon F experiments that were carried out at 3.85 bar, 2.85 bar and 1.85 bar also at 25°C. The effect of pressure on gas permeability and ideal selectivity of all gases against O2 was investigated. Udel Polysulfone and Nafion 117 presented clearly evident pressure dependant SO2 permeabilities whilst CO2, N2 and O2 permeabilities were sluggishly dependant on pressure in all membranes. Gas flux in general increased with increasing pressure as pressure is essentially the driving force for permeability. Membrane screening for further investigation was then performed based on a compromise between SO2/O2 ideal selectivity and SO2 flux in hypothetical 1 μm thick membranes. Membranes that presented the best SO2/O2 selectivity include, Udel Polysulfone with SO2/O2 selectivities of 46, 58 and 314 at 1 bar, 2 bar and 3 bar respectively, Nafion 117 with SO2/O2 selectivities of 30, 35 and 40 at 1 bar, 2 bar and 3 bar respectively and Halar with a SO2/O2 selectivity of 17 at 3 bar. The best SO2 flux through hypothetical 1 μm thick membranes was manifested in Teflon AF 2400 with SO2 fluxes of 3.6 m3.m-2.hr-1, 5.9 m3.m-2.hr-1 and 9.9 m3.m-2.hr-1 at trans-membrane pressures of 1 bar, 2 Bar and 3 Bar respectively, Udel Polysulfone with SO2 fluxes of 0.13 m3.m-2.hr-1, 0.32 m3.m-2.hr-1 and 2.56 m3.m-2.hr-1 at trans-membrane pressures of 1 bar, 2 bar and 3 bar respectively and Nafion 117 with SO2 fluxes of 0.48 m3.m-2.hr-1, 1.03 m3.m-2.hr-1 and 1.79 m3.m-2.hr-1 at 1 bar, 2 bar and 3 bar trans-membrane pressures respectively. Despite Teflon AF 2400 presenting the highest SO2 flux, the poor SO2/O2 ideal selectivity ≈ 1 rendered the membrane unfit for further investigation. The low SO2 flux (0.02 m3.m-2.hr-1) presented by Halar also rendered the membrane unfit for further investigation despite the relatively fair SO2/O2 ideal selectivity of 17. Binary permeation experiments were then performed on Udel Polysulfone and Nafion 117 after passing the single permeation screening test. Gas mixture compositions of (25 wt %:75 wt %, SO2:O2), (50 wt %:50 wt %, SO2:O2) and (75 wt %:25 wt %, SO2:O2) were employed. The binary permeation experiments were carried out at a temperature range of 15°C to 55°C and a SO2 feed partial pressure range of 1.1 ± 0.1 bar to 2.3 ± 0.1 bar. The SO2 permeate composition increased with pressure and decreased with temperature in both Udel Polysulfone and Nafion 117. Udel Polysulfone presented a superior SO2/O2 separation potential, concentrating a (25 wt %:75 wt %, SO2:O2) gas mixture to (94 wt %:6 wt %, SO2:O2) in a single step at 15°C and 2.2 ± 0.1 bar SO2 feed partial pressure. Nafion 117 concentrated the same gas mixture to (87 wt %:13 wt %, SO2:O2) also in a single step at 15 °C and 2.4 ± 0.1 bar SO2 feed partial pressure. Based on hypothetical 1 μm thick membranes, Nafion 117 presented generally high SO2 molar fluxes in mixture with O2 of about a magnitude higher than the SO2 molar fluxes presented in Udel Polysulfone. Also, Nafion 117 proved to be less prone to plasticisation within the pressure range considered. Despite Udel Polysulfone presenting generally lower SO2 molar fluxes, Udel Polysulfone was deemed to be the ideal membrane for the current SO2/O2 separation application as thicknesses of 1 μm of Nafion the perfluorosulfonic acid based membrane are currently unknown and also Udel Polysulfone presented the best SO2/O2 separation capability. The latter findings are envisaged to prompt further research on the production of ultra-thin perfluoro-sulfonic acid based membranes for the current application. / Thesis (MIng (Chemical Engineering))--North-West University, Potchefstroom Campus, 2013
43

An advection-diffusion model of SO2 concentration for Hong KongIsland

Chung, Moon-kun, 鍾滿根 January 1977 (has links)
published_or_final_version / Mechanical Engineering / Master / Master of Philosophy
44

Metabolic, genetic and physiological responses to SO2 exposure and nutrient-limiting conditions in Brettanomyces bruxellensis

Louw, Marli 04 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Brettanomyces bruxellensis has become of increasing interest over the past few decades yet this complex red wine spoilage yeast is still poorly understood and strain variance also leads to the contradictory results reported in literature. This yeast is responsible for the production of phenolic compounds, associated with off-flavours that render wine unpalatable. Sulphur dioxide (SO2) is the most commonly used antioxidant and antimicrobial preservative instrumental in the control of spoilage yeasts such as B. bruxellensis. However, its diploid/triploid genome is enriched for genes that provide the yeast a fortuitous advantage, under conditions permissive for growth, with genotype-dependent SO2 tolerance phenotypes observed among numerous strains. This study investigates the metabolic, physiological and genetic responses associated with SO2 exposure. It also explores the environmental cues responsible for the onset of non-SO2 induced morphological characteristics. These morphological characteristics were investigated using fluorescent probes and microscopy in the presence of SO2 and in the absence thereof, in YPD media. Pseudohyphae formation was observed to be a highly strain dependent feature and less pronounced in the presence of 0.6 mg/L molecular SO2. This study also reports on the metabolic response observed over a 3-week period, following exposure to SO2, in a synthetic wine medium. The following metabolites were consistently monitored during the course of the experiment: acetic acid, acetaldehyde, D-glucose and D-fructose. Utilization of sugars was retarded in the presence of SO2 for up to 10 days in the presence of 1.2 mg/L molecular SO2 and overproduction of acetaldehyde was prominent, with a peak at day 10. The study further highlights the expression profiles observed for the SSU1 gene (referring to SO2 tolerance) and the PAD gene (referring to production of volatile compounds) under SO2 induced conditions in SWM, using qRT-PCR. The co-involvement of increased acetaldehyde production and elevated gene expression were indicative of B. bruxellensis yeast adapting to the presence of molecular SO2, allowing survival of this fascinating yeast. Sequencing of the SSU1 and PAD genes suggests the probable existence of different alleles of these genes that could explicate SO2 tolerance and phenolic compound production associated differences among strains of this species. / AFRIKAANSE OPSOMMING: Hoewel Brettanomyces bruxellensis oor die afgelope paar dekades toenemende belangstelling gewek het, word hierdie komplekse rooiwynbederfgis steeds swak verstaan en lei rasvariasie ook tot teenstrydige resultate in die literatuur. Hierdie gis is verantwoordelik vir die produksie van fenoliese verbindings, wat geassosieer word met afgeure, wat die wyn onsmaaklik laat. Swaweldioksied (SO2) is die algemeenste preserveermiddel wat, weens antioksidant- en antimikrobiese eienskappe, instrumenteel in die beheer van bederforganismes, soos B. bruxellensis, gebruik word. Nogtans is die diploïede/triploïede genoom vir gene verryk, wat die gis ‘n toevallige voordeel bied tydens ongunstige toestande, met genotipe-afhanklike SO2 weerstandbiedende fenotipes wat onder verskeie rasse waargeneem word. Hierdie studie ondersoek die metaboliese, fisologiese en genetiese reaksies tydens SO2-blootstelling. Dit bestudeer verder die omgewingsleidrade wat vir die aanvang van die nie-SO2 geassosiseerde morfologiese eienskappe verantwoordelik is. Hierdie morfologiese eienskappe is ondersoek met behulp van fluoresserende bakens en mikroskopie in die teenwoordigheid van molekulêre SO2 en, in die afwesigheid daarvan, in YPD-medium. Pseudohyphae-vorming is as ʼn baie rasspesifieke eienskap waargeneem en is minder prominent in die teenwoordigheid van molekulêre SO2. Hierdie studie rappoteer ook oor die metaboliese reaksies waargeneem oor ‘n 3-weke tydperk, na blootstelling aan SO2, in ‘n sintetiese wynmedium. Die volgende metaboliete was voordurend gemonitor tydens die verloop van die eksperiment: asynsuur, asetaldehied, D-glukose en D-fruktose. Benutting van die suikers is in die teenwoordigheid van SO2 vertraag en oorproduksie van asetaldehied is prominent waargeneem. Hierdie studie beklemtoon verder die uitdrukkingsprofiele vir die SSU1-geen (verwys na SO2-weerstandbiedendheid) en die PAD-geen (verwys na die produksie van vlugtige verbindings) in SO2-geïnduseerde toestande in SWM, met behulp van qRT-PCR. Die gesamentlike invloed van beide verhoogde asetaldehied produksie en verhoogde uitdrukking van gene, was beduidend van B. bruxellensis-gis wat aanpas in die teenwoordigheid van molekulêre SO2, wat die oorlewing van hierdie fassinerende gis verseker. Volgordebepaling van die SSU1- en PAD-geen dui daarop dat daar waarskynlik meer as een verskillende alleel vir dié gene bestaan, wat die SO2-verdraagsaamheid en produksie van fenoliese verbindings, wat tans tussen verskeie spesies teenwoordig is, kan verduidelik.
45

Study of nanofibrous membranes for application in post harvest technology

Harmzen, Elrika 04 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Grapes are lost annually due to spoilage by Botrytis cinerea. Botrytis cinerea is currently controlled using fungicides and SO2 fumigation in storage rooms but with limited success. Although these techniques have been used for decades they have been associated with numerous of disadvantages. Fungicides are restricted from being used during storage due to legislation and toxicity of the fungicides present on the surface of the berries. SO2 fumigation does not kill the dormant infections present inside the grape tissue and if the SO2 concentration is too high the berries are damaged. During this study two different polymer nanofibrous platforms was synthesized in an attempt to prevent the rotting effect of B. cinerea. The first polymer was modified to yield a polymer with a positively charged quaternized nitrogen moiety, which was subsequently reacted with sodium metabisulfite through an ion exchange process. The modified polymer was electrospun into nanofibrous mats for the benefit of the nanofibers’ high available surface area. A further functionalization was done to increase the quantity of sodium metabisulfite on the surface of the polymer nanofibers. Sodium metabisulfite salt released SO2 gas upon reaction with water vapour present in the atmosphere which resulted in the inhibition of conidial germination of B. cinerea. The second polymer was synthesized and then electrospun into polymer nanofibrous mats followed by chemical modification of the electrospun polymer nanofibers. This post-electrospun modification resulted in the covalent attachment of a fungicide-derivative to the surface of the polymer nanofibers. The fungicide-derivative showed excellent inhibition of B. cinerea mycelium growth. Anti-fungal studies were conducted using the two modified polymer nanofibrous mats against B. cinerea to evaluate these nanofibrous surfaces as B. cinerea inhibiting membranes. Results indicated that B. cinerea conidial germination and mycelium growth were successfully inhibited. / AFRIKAANSE OPSOMMING: Druiwe bederf jaarliks weens die verrottende effek van die fungi Botrytis cinerea. Botrytis cinerea word tans beheer deur gebruik te maak van swamdoders en swaweldioksied (SO2) besproeiings in stoorkamers, maar met beperkte sukses. Alhoewel hierdie tegnieke al vir dekades in gebruik is, word dit geassosieer met verskeie probleme. Die gebruik van swamdoders word in stoorkamers verbied, weens die moontlike skadelike inname daarvan deur die mens aangesien die swamdoders op die druiwe se oppervlakte teenwoordig is. SO2-gasbesproeiings maak nie dormante infeksies binne-in die druiwe self dood nie en indien SO2 -konsentrasies te hoog is kan dit die druiwe beskadig. Tydens hierdie studie is twee verskillende polimeer-nanoveselplatforms gesintetiseer met die doel om die verrottende effek van B. cinerea te voorkom. Die eerste polimeer is aangepas met ’n primêre amienverbinding met die doel dat dit deur ‘n opvolgende modifikasiereaksie verander om sodoende ’n polimeer met ‘n kwatenêre ammoniumgroep te verkry. Die doel van die kwatenêre eienskap is dat ioniese uitruiling plaasvind tussen die anioon van die polimeer en die natruimmetabisulfiet-anioon van die sout. Die voorbereide kopolimeer is geëlektrospin in nanoveselmatte deur middel van die enkelnaald-en-enkelbal-elektrospintegniek om SMI-qC12 nanovesels te lewer wat gefunksionaliseer is. Die nanoveselmatte is na die elektrospinproses verder aangepas om die hoeveelheid natruimmetabisulfiet op die oppervlak van die nanovesels te verhoog. Die natruimmetabisulfiet stel SO2-gas vry sodra dit in aanraking kom met waterdamp in die lug wat ’n beperkende effek op spoorontkieming van B. cinerea tot gevolg het. Die tweede polimeer is voor en na die elektrospinproses gefunksionaliseer met gesintetiseerde organiese verbindings (swamdoder). Die aanpassing van die polimeer met die organiese verbindings het plaasgevind op ‘n kovalente wyse om te verhoed dat die organiese verbinding vrygelaat word tydens gebruik. Die organiese verbindings het effektiewe beperking van miselium-groei getoon. Anti-swamstudies is uitgevoer tussen die twee gefunksionaliseerde polimeer platforms en B. cinerea om die oppervlaktes van die gefunksionaliseerde polimeer/nanovesels te evalueer as B. cinerea beperkende platforms. Resultate het aangetoon dat spoorontkieming en miselium groei van B. cinerea suksesvol beperk is.
46

Radial Growth of Oak and Aspen Near a Coal-Fired Station, Manitoba, Canada

Boone, Rachel, Tardis, Jacques, Westwood, Richard January 2004 (has links)
Eighteen stands of bur oak (Quercus macrocarpa Michx.) and trembling aspen (Populus tremuloides Michx.) were sampled and analyzed using dendrochronological methods to study the potential effects on tree growth of emissions from a 132 MW coal-fired generating station. Sixteen stands were sampled within a 16-km radius of the station, and two control stands were sampled outside of the range of influence, at distances . 40 km. All stands showed similar radial growth patterns from 1960-2001, regardless of distance from or direction relative to the generating station, and a number of stands, including the controls, had below average growth after 1970. Both species were significantly affected by climatic factors, showing decreased radial growth with increasing June temperature. The species differed in their growth responses to spring precipitation and temperature in the previous October. One bur oak site displayed marked radial growth decline beginning in the mid-1970s, strongly pronounced following 1977. This decline does not appear to be related to emissions from the station, but is suspected to be a result of poor site conditions (shallow soil developed over calcareous till), confounded by a change in drainage (a road was built adjacent to the stand in 1977, perpendicular to the direction of drainage). The below average growth seen in 1970-2001 across most stands is likely attributable to stand dynamics and age effects.
47

THE CONTRIBUTION OF LONG-RANGE TRANSPORT OF AIR POLLUTION TO THE SULPHUR BUDGET OF THE UNITED ARAB EMIRATES

Evans, Mary Yvonne 17 November 2006 (has links)
Student Number :8701745W - MSc research report - Faculty of Science / An air chemistry study over the United Arab Emirates revealed a high concentration of sulphur dioxide. SO2 and its resultant aerosols can have a significant effect on the atmospheric processes. These aerosols could both directly and indirectly affect the climate by scattering solar radiation and increasing the albedo of the atmosphere or by altering the cloud formation processes and characteristics. Sulphur dioxide and the resultant aerosols also have a damaging effect on the environment and on human health. Previous studies reviewed suggest that pollution can be transported for hundreds of kilometres from the source of the emission and affect the air chemistry of the receptor regions. The possibility that long-range transport of pollution to the UAE may have contributed to these high concentrations was also investigated. The possibility that the UAE is a receptor region of pollution transported over long distances is investigated with the intention of identifying the possible source regions of this pollution. In order to examine the import of pollution to the UAE it was important to analyse the background sulphur concentrations of the atmosphere over the UAE.
48

A Flue Gas Desulphurisation System Utilising Alumina Causticiser Residue

Leon Munro Unknown Date (has links)
The ever increasing global demand for materials has placed aluminium as the world’s second most used metal, with world annual production currently >24 million tons. Consequently, the global alumina industry is perpetually striving to meet demands in conjunction with research, development and implementation of more efficient and sustainable processes and practises. Of specific concern for many proponents within the industry is that increased alumina production inadvertently results in increased Bayer Process-derived alkaline solid and liquid waste loads. Furthermore, in-house power generation at all Australian alumina refineries contributes to acid gas emissions, particularly SOx and NOx, both of which have environmental and anthropogenic impacts of global concern. The focus of this work is SO2 emission. SOx emission control measures can be achieved before, during or after combustion; the latter is termed flue gas desulphurisation (FGD). Commercially available FGD systems are dominated by once-through wet processes whereby the flue gas passes up through an absorbtion tower. The most favourable medium for industrial use is seawater, followed by limestone, and in some cases, a combination of both. However, the ever-increasing stringency of environmental emission legislation continues to inflict tighter controls on power production and is forcing industry to investigate alternative cost-effective FGD mediums. Therefore much research is currently dedicated to the utilisation of high volume, alkaline waste streams over manufactured sorbents. Modern environmental engineering approaches to waste product minimisation, neutralisation and/or reuse have lead to many new processes which change the view of many materials from waste product to environmental resource. Subsequently, this work examines the application of an isolated Bayer Process waste product, tricalcium aluminate hexahydrate (TCA6), as a FGD medium. Initial research assessed the dissolution behaviour and performance of the proposed medium with sulphuric acid, followed by batch reactor trials with a simulated flue gas. Data derived from this research indicated the suitability of TCA6 as a FGD medium and was subsequently applied to a preliminary model and proposed design parameters required for further pilot scale investigations. This work provides strong support for an economically viable and more sustainable approach to FGD for the alumina industry.
49

Aqueous Phase Oxidation Of Sulfur Dioxide In Stirred Slurry Reactors

Gopala Krishna, K V January 1994 (has links)
Air pollution by sulfur dioxide is of great concern due to its harmful effects on environment, human beings, fauna and flora. Fossil-fuel-fired power plants are one of the major sources of SO2 emissions. Typically the concentration of SO2 in the flue gases of these plants is in the range of 2000 to 20000 ppm. Flue gas desulfurisation is one of the widely practiced strategies to control SO2 emissions. Aqueous phase oxidation of sulfur dioxide catalysed by carbonaceous particles is an attractive alternative to the conventional processes for flue gas desulfurisation because, amongst other reasons, sulfuric acid, the product of aqueous phase oxidation, finds extensive application in industry. In the literature it has been reported that sulfuric acid affects the solubility of sulfur dioxide and that activated carbon catalyses aqueous phase oxidation. However there is hardly any report on the systematic evaluation of the mechanism of the heterogeneous aqueous phase oxidation of sulfur dioxide which takes into account among other factors, the effect of sulfuric acid on the solubility of SO2 (particularly, at low levels of SO2 and sulfuric acid concentrations). Therefore the objective of the present work is to evaluate systematically the aqueous phase oxidation of SO2 in ppm levels with activated carbon as catalyst in a three-phase agitated slurry reactor and to model rigorously the solubility of SO2 in ppm levels in dilute sulfuric acid solutions and to estimate the concerned parameters experimentally. Strong effect of dilute concentrations of sulfuric acid on the solubility of SO2 is analyzed in terms of the influence of the acid on the equilibrium concentrations of the ionic species (HSO3¯ and SO4¯2 formed from the hydrolysis of SO2 (aq) and the dissociation of H2SO4 respectively) in SO2 - dil. H2SO4 systems. The analysis leads to a general expression relating the partial pressure of SO2 in the gas phase to the concentration of total dissolved SO2 and the concentration of sulfuric acid in the solution. Simple equations are obtained from the general expression for the cases of zero and high concentrations of sulfuric acid in the system, which in turn lead to direct experimental determination of the parameters, Henry's law constant and the equilibrium constant of hydrolysis of SO2 (aq). The developed model predicts the present experimental data as well as the data reported in the literature very closely. The dissolution of SO2, the hydrolysis of SO2 (aq) and the dissociation of H2SO4 are found to be instantaneous. From the dependency of the parameters on temperature, the heat of dissolution of SO2 is determined to be -31.47 kJ mol"1 and the heat of hydrolysis to be 15.69 kJ mol"1. The overall heat of solubility of sulfur dioxide is therefore -15.78 kJ mol"1. Preliminary reaction experiments have clearly indicated that SO2 (aq) does not react and HSO3¯ is the only reactant for aqueous phase oxidation of sulfur dioxide catalysed by activated carbon. The non-reactant SO2 (aq) deactivates the oxidation reaction by competing with HSO3¯ for adsorption on the active sites of the catalyst particles. However the catalyst particles become saturated with SO2 (aq) beyond a certain value of its concentration (saturation limit), which depends on temperature. A mechanism is proposed based on these observations to develop a rate model. The rate model also takes into account the effect of the concentration of the product sulfuric acid on the solubility of sulfur dioxide. The model predicts first order in HSO3¯ , half order in dissolved oxygen and a linear deactivation effect of 5O2(ag). The oxidation reaction is evaluated experimentally at various levels of the operating variables such as temperature and the concentrations of sulfur dioxide and oxygen in the inlet gas. In all experiments a pseudo steady-state region is observed where the gas phase concentration of SO2 reaches a steady value but the concentrations of HSO3¯ and total S (VI) in the liquid phase continue to change. Pseudo steady-state considerations lead to the determination of the initial estimates of the parameters of the rate model namely, the rate constant and the deactivation constant. These parameters are estimated from the transient profiles of the product (sulfuric acid) by solving the model equations by Runge-Kutta method along with Marquardt's non-linear parameter estimation algorithm. The predictions of the model with the estimated parameters match very well with the experimentally observed concentration profiles of S(VI) and HSO3 in the liquid phase and SO2 in the gas phase. The deactivation constant in the saturation range is independent of temperature and is 0.27, which indicates that the intrinsic rate constant is about four times greater than the observed rate constant. From Arrhenius equation-type dependency of the parameters on temperature, the activation energy for the oxidation reaction is determined to be 93.55 kJ mol"1 and for deactivation to be 21.4 kJ mol"1. The low value of activation energy for deactivation suggests a weak dependency of the deactivation on temperature, which perhaps is due to the weak nature of the chemisorption of SO2 (aq) on carbon.
50

The 1990 air pollution control regulation: a story of reducing the sulphur dioxide levels in ambient air in HongKong

Yan, Chun-man., 甄俊文. January 2010 (has links)
published_or_final_version / Public Health / Master / Master of Public Health

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