BACKGROUND: Selection on proteins is typically measured with the assumption that each protein acts independently. However, selection more likely acts at higher levels of biological organization, requiring an integrative view of protein function. Here, we built a kinetic model for de novo pyrimidine biosynthesis in the yeast Saccharomyces cerevisiae to relate pathway function to selective pressures on individual protein-encoding genes. RESULTS: Gene families across yeast were constructed for each member of the pathway and the ratio of nonsynonymous to synonymous nucleotide substitution rates (dN/dS) was estimated for each enzyme from S. cerevisiae and closely related species. We found a positive relationship between the influence that each enzyme has on pathway function and its selective constraint. CONCLUSIONS: We expect this trend to be locally present for enzymes that have pathway control, but over longer evolutionary timescales we expect that mutation-selection balance may change the enzymes that have pathway control.

Thesis (PhD (Biochemistry))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: In the last decade a need arose to find a theoretical framework capable of gaining a quantitative understanding of ecosystems. Control analysis was proposed as a suitable candidate for the analysis of ecosystems with various theoretical applications being developed, i.e. trophic control analysis (TCA) and ecological control analysis (ECA). We set out to test the latter approach through experimental means by applying techniques akin to enzyme kinetics of biochemistry on a simple ecosystem between Saccharomyces cerevisiae and Gluconobacter oxydans. However, this exercise was far more complex than we originally expected due to the extra metabolic activities presented by both organisms. Nevertheless, we derived suitable kinetic equations to describe the metabolic behaviour of both organisms, with regards to the activities of interest to us, from pure culture experiments. We developed new techniques to determine ethanol and oxygen sensitivity of G. oxydans based on its obligately aerobic nature. These parameters were then used to build a simple kinetic model and a more complex model incorporating oxygen limited metabolism we observed at higher cell densities of G. oxydans. Our models could predict both situations satisfactorily for pure cultures and especially the more complex model could describe the lack of linearity observed between metabolic activity and cell density at higher cell densities of G. oxydans. Mixed populations of S. cerevisiae and G. oxydans reached quasi-steady states in terms of ethanol concentration and acetate flux, which was a positive indication for the application of control analysis on the ecosystem. However, the theoretical models based on parameters derived from pure culture experiments did not predict mixed culture steady states accurately. Careful analysis showed that these parameters were mostly under-estimated for G. oxydans and overestimated for S. cerevisiae. Hence, we calculated the kinetic parameters for mixed population assays directly from the experimental data obtained from mixed cultures. We could calculate the control coefficients directly from the experimental data of mixed population studies and compare it with those from theoretical models based on 3 different parameter sets. Our analysis showed that the yeast had all the control over the acetate flux while control over the steady-state ethanol was shared. The strength of our approach lies in designing our experiments with a control analysis approach in mind, but we have also shown that even for simple ecosystems this approach is non-trivial. Despite the various experimental challenges, this approach was very rewarding due to the extra information obtained especially regarding control structure with regards to the steady-state ethanol concentration. / AFRIKAANSE OPSOMMING: In die afgelope dekade het daar ’n behoefte ontstaan na ‘n teoretiese raamwerk om tot ‘n kwantitatiewe begrip van ekosisteme te kom. As kandidaat vir so tipe raamwerk is kontrole analise voorgestel gepaardgaande met die ontwikkeling van verskeie teoretiese toepassings, i.e. trofiese kontrole analise en ekologiese kontrole analise. In hierdie tesis het ons laasgenoemde aanslag eksperimenteel ondersoek op ‘n eenvoudige ekosisteem, tussen Saccharomyces cerevisiae en Gluconobacter oxydans, deur gebruik te maak van tegnieke vanuit ensiemkinetika van biochemie. Hierdie strategie was egter baie meer kompleks as wat oorspronklik verwag is as gevolg van verdere metabolise aktiwiteite aanwesig in beide organismes. Ons het egter steeds daarin geslaag om kinetiese vergelykings af te lei, vanuit suiwer kulture, wat die metaboliese gedrag van beide organismes beskryf vir die aktiwiteite van belang vir ons studie. Ons het nuwe tegnieke, gebaseer op die aerobiese natuur van G. oxydans, ontwikkel om die sensitiwiteit van G. oxydans vir etanol en suurstof te bepaal. Hierdie parameters is gebruik om eers ’n eenvoudige model en toe ‘n meer gevorderde model, wat die suurstof-beperkte metabolisme van G. oxydans by hoër biomassa te beskryf, op te stel. Beide modelle was baie effektief in die voorspelling van die situasies waarvoor hulle ontwikkel is vir die suiwer kulture waar veral die meer gevorderde model die gebrek aan ‘n linieêre verband tussen die metabolisme van G. oxydans en biomassa by hoër biomassa kon beskryf. ’n Bemoedigende aanduiding dat kontrole analise toegepas kon word op die ekosisteem was dat mengkulture van S. cerevisiae en G. oxydans het quasi-bestendige toestande bereik het in terme van etanol konsentrasies en asetaat-fluksie. Die teoretiese modelle gebaseer op die parameters afgelei vanaf suiwer kulture kon egter nie die bestendige toestande in mengkulture akkuraat voorspel nie. Nadere ondersoek het aangedui dat die parameters meesal onderskat is vir G. oxydans en oorskat is vir S. cerevisiae. Gevolglik het ons die kinetiese parameters vir mengkulture direk van eksperimentele data van die mengkulture bereken. Verder kon ons die kontrole koeffisiente ook direk vanaf die eksperimentele data van mengkulture bereken en vergelyk met dié bereken vanuit die teoretiese modelle gebaseer op drie verskillende paremeter-stelle. Ons analise het gewys dat die gis alle beheer op die asetaat-fluksie uitoefen en dat die beheer oor die etanol-konsnetrasie gedeel is tussen die twee organismes. Die krag van ons aanslag lê daarin dat die eksperimente ontwerp is met ‘n kontrole analise in gedagte, maar ons het ook bewys dat hierdie aanslag selfs vir eenvoudige ekosisteme nie triviaal is nie. Ten spyte van die eksperimentele uitdagings, was die aanslag baie waardevol as gevolg van die ekstra inligting verkry met spesifieke klem op die kontrole-struktuur met betrekking tot die etanol konsentrasie by bestendige toestand.

A pesquisa propôs avaliar o desempenho e o comportamento de reatores seqüenciais em batelada com biomassa suspensa e imobilizada, em escala de bancada, na remoção de compostos de nitrogênio. Tais sistemas foram testados como tratamento complementar de reatores sulfetogênico e metanogênico utilizados no tratamento de água residuária industrial com alta concentração de sulfato e amônia. Visou o desenvolvimento de uma estratégia de operação que viabilizasse o uso dos próprios constituintes da água residuária para a maximização da eficiência do tratamento. O estudo foi dividido em 3 etapas principais. Na etapa 1 (181 dias de operação), o reator com biomassa suspensa foi mantido com 4 fases alternadas aeróbio/anóxico e ciclo de 24 horas, e verificou-se a presença da desnitrificação endógena (eficiência de remoção de nitrogênio de 65 \'+ OU -\' 27%). Para a etapa 2 (127 dias de operação), o reator de biomassa suspensa foi submetido ao tempo de ciclo de 12 horas, com uma fase aeróbia (6 horas) e com posterior fase anóxica (6 horas). Nessa etapa adicionou-se efluentes dos reatores metanogênico e sulfetogênico, ricos em ácidos voláteis (ácido acético), com intuito de acelerar o processo desnitrificante. Os resultados obtidos foram baixos em termos de remoção de nitrogênio (42 \'+ OU -\' 21%). Para a etapa 3 (134 dias de operação), foram ensaiados vários meios suportes, através de técnica de microsensores de oxigênio dissolvido, a fim de verificar a formação de biofilme específico (nitrificante/desnitrificante) e optou-se pelo uso do carvão mineral no reator com biomassa imobilizada. Nesta última etapa, foi mantida a estratégia operacional adotada na etapa 2 (ciclo 12 horas), bem como a adição de parcela do afluente na fase anóxica. A remoção de nitrogênio, com períodos aeróbio e anóxico e ciclo de 12 horas, mostrou-se viável no reator com biomassa imobilizada (eficiência de remoção de nitrogênio de 72 \'+ OU -\' 13%). Ao final dos ensaios experimentais, realizaram-se modelagens cinéticas que permitiram a compreensão dos processos convencionais e não convencionais ocorridos nas várias etapas para remoção de nitrogênio, tais como desnitrificação em fase aeróbia e o processo ANAMMOX. / The purpose of this research was to evaluate the performance and the behavior of sequential batch reactors with suspended and immobilized biomass, in benches scale, for the nitrogen composite removal. Such systems had been tested as sulphetogenic and methanogenic reactors complementary treatment, used in an industrial waste water treatment with high sulphate and ammonia concentrations. The research aimed for the development of an operation strategy that could make possible the use of the proper waste water constituent for the improvement of the treatment efficiency. The study was divided into 3 main stages. In stage 1 (181 days of operation), the reactor with suspended biomass was kept with 4 alternating phases aerobic/anoxic and a 24-hour cycle was used, and the endogenous denitrification was verified (nitrogen removal efficiency of 65 \'+ OU -\' 27%). For stage 2 (127 days of operation), the suspended biomass reactor was submitted to a cycle of 12 hours, with an aerobic phase (6 hours) and posterior anoxic phase (6 hours). In this stage effluent of the methanogenic and sulphetogenic reactors, rich in volatile acid (acetic acid), was added to accelerate the denitrify process. The achieved results had been low in terms of nitrogen removal(42 \'+ OU -\' 21%). For stage 3 (134 days of operation), some supports media was tested through dissolved oxygen microsensors technique, in order to check the specific biofilm formation (nitrificant/denitrificant) and the mineral coal was opted to be used in the immobilized biomass reactor. In this last stage it was adopted an operational strategy similar in stage 2 (12 hours cycle), as well as the addition of part of the affluent in the anoxic phase. The nitrogen removal, with aerobic and anoxic periods and 12 hours cycle, revealed feasible in the reactor with immobilized biomass (nitrogen removal efficiency of 72 \'+ OU -\' 13%). In the end of the experimental tests, kinetic modelings were done and had allowed the understanding of conventional and not conventional processes occurred in the stages for nitrogen removal, such as desnitrification in aerobic phase and ANAMMOX process.

Devido à sua vasta biodiversidade, o Brasil dispÃe de uma grande variedade de resÃduos agrÃcolas e agroindustriais, cujo bioprocessamento à de grande interesse econÃmico e social. Entre os biocombustÃveis produzidos em todo o mundo, o etanol produzido no Brasil a partir da cana de aÃÃcar possui lugar de destaque, apresentando notÃvel evoluÃÃo durante as ultimas dÃcadas, alcanÃando assim maturidade e consistÃncia. Contudo, estima-se que a produÃÃo de etanol atravÃs dessa matÃria-prima nÃo seja suficiente para atender a demanda mundial. Neste contexto, o objetivo deste trabalho foi avaliar a produÃÃo de etanol a partir do suco de caju. Para tal fim, inicialmente, avaliou-se a necessidade de suplementaÃÃo do suco de caju para a sua posterior fermentaÃÃo. Nesta etapa, foi observado que nÃo se faz necessÃria a suplementaÃÃo do suco de caju com nutrientes, pois o mesmo in natura jà apresenta todos os nutrientes necessÃrios para o crescimento do microrganismo. Posteriormente, estudou-se o efeito da temperatura na produÃÃo de etanol, avaliando a fermentaÃÃo na faixa de 26 a 42ÂC. Os melhores resultados de rendimento (0,5 g.g-1), produtividade (4,9 g.L-1.h-1), eficiÃncia (92,8%) e produÃÃo mÃxima de etanol (49,3 g.L-1), foram obtidos quando se conduziu a fermentaÃÃo na faixa de 30 a 38ÂC. Os modelos de Monod e Arrhenius foram utilizados para descrever a dependÃncia dos parÃmetros cinÃticos com a temperatura, sendo os resultados obtidos satisfatÃrios. O potencial do suco de caju como fonte de aÃÃcares para a produÃÃo de etanol foi avaliado por diferentes cepas de leveduras dos gÃneros Saccharomyces e Kluyveromyces. Os resultados mostraram que as cepas de Saccharomyces foram bastante superiores quando comparadas Ãs Kluyveromyces quanto à produÃÃo mÃxima de etanol. A levedura que apresentou melhores resultados para os parÃmetros cinÃticos avaliados foi a Saccharomyces cerevisiae CCA008. Por ultimo, para determinar o efeito da concentraÃÃo inicial de substrato na produÃÃo de etanol, estudou-se a faixa de 70, 90, 110, 130 e 150 g.L-1 de substrato inicial. A concentraÃÃo que apresentou melhores resultados para os parÃmetros estudados foi 90 g.L-1. O modelo cinÃtico que conseguiu chegar mais prÃximos dos dados experimentais e assim descrever o processo mais fielmente foi o modelo proposto por Ghose & Thyagi. Com estes resultados, conclui-se que o uso do suco de caju como substrato para a produÃÃo de etanol trarà benefÃcios econÃmicos, pois estaremos utilizando um substrato de baixo custo, e ambientais, jà que o mesmo à um resÃduo agroindustrial proveniente da produÃÃo de castanha de caju. / Despite its big biodiversity, Brazil has a great variety of agriculturists and agroindustrials which its bioprocess has a lot of economic and social interest. Among all the ethanol produced all over the world, the ethanol produced in Brazil made of cane of sugar has great distinction. Its evolution on the last decade is remarkable reaching its maturity and consistency. Within all it is estimated that the ethanol produced with that material is not enough to be spread and supply worldwide. The object of this article is to evaluate the production of the ethanol made with cashew apple juice. In this stage, it was observed that it is not necessary to supplement the cashew apple juice to posterior fermentation because the juice already shows all the nutrients necessary for the growth of the microorganism. Later there was a study showing that the temperature in the production of ethanol evaluating its fermentation between 26 and 42ÂC. The best results of revenue (0,5 g.g-1), productivity (4,9 g.L-1.h-1), efficiency (92,8%) and the maximum production of ethanol (49,3 g.L-1), It was gained when the fermentation was conducted between 30 to 38ÂC. The models of Monod and Arrhenius were used to describe the dependence of the kinetic parameter with the temperature, showing the results to be satisfactory. The potential of the cashew apple juice being a source of sugar for the production of ethanol was evaluated by different sources of the genders Saccharomyces and Kluyveromyces. The results showed that the strains of Saccharomyces were higher when compared to the Kluyveromyces to the maximum production of ethanol. The strain that showed the best results for the kinetic parameter that was evaluated was Saccharomyces cerevisiae CCA008. At last, to determine the effect of the initial concentrate substratum in the production of ethanol, it was studied the range of 70, 90, 110, 130 and 170 g.L-1 of initial substratum. The one that showed the best results for the parameters studied was 90 g.L-1. The kinetic model that came closer to the ones experimented and could explain the process best was the model proposed by Ghose & Thyagi. In conclusion, with those results shows that the cashew apple juice used in the production of ethanol will bring great economic benefits because it is a product of low cost and economic as well as to the environment being a agroindustial product deriving from the production of the cashew nut.

Nanotubes have numerous potential applications in areas such as biotechnology, electronics, photonics, catalysis and separations. There are several challenges to be overcome in order to realize their potential, such as: (1) Synthesis of monodisperse (in diameter and in length) single-walled nanotubes; (2) Quantitative understanding of the mechanism of formation and growth of nanotubes; (3) Capability to engineer the nanotube size; (4) Low temperature synthesis process; and (5) Synthesis of impurity free nanotubes. Our investigation focuses on a class of metal oxide (aluminosilicate/germanate) nanotubes, which are; single walled nanotubes with monodisperse inner and outer diameters, can be synthesized in the laboratory by a low temperature (95ºC) process in mildly acidic aqueous solutions, and their formation timescales is hours, which makes it convenient as a model system to study the mechanisms of nanotube formation. This work is focused on obtaining a qualitative and quantitative understanding of the mechanism of formation of aluminosilicate and aluminogermanate nanotubes. In order to achieve this overall objective, this thesis consists of the following aspects: (1) A systematic phenomenological study of the growth and structural properties of aluminosilicate and aluminogermanate nanotubes. The constant size and increasing nanotube concentration over the synthesis time strongly suggest that these nanotubular are assembled through self-assembly process. (II) Investigation of the mechanism of formation of single-walled aluminogermanate nanotubes provided the central phenomena underlying the formation of these nanostructures: (1) the generation (via pH control) of a precursor solution containing chemically bonded precursors, (2) the formation of amorphous nanoscale (~ 6 nm) condensates via temperature control, and (3) the self-assembly of short nanotubes from the amorphous nanoscale condensates. (III) Synthesis of mixed metal oxide (aluminosilicogermanate) nanotubes with precise control of elemental composition, diameter and length of the product nanotubes. (IV) Preliminary work towards generalization of the kinetic model developed for aluminogermanate nanotubes to a larger class of metal oxide nanotubes. It was found that the size of nanotubes is dependent on the amount of precursors that can be packed in a single ANP and in turn depends on the size of the ANP.

The study combined photoelectrocatalytic technology (PEC) with electrical glassfiber filter (EGF) to decompose volatile organic compounds (VOCs). External electrical voltage was applied to retard the recombination of electron-electron hole pairs and increase the surface temperature of the photocatalysts coated on the electrical glassfiber filter, which could further decompose VOCs more effectively via photoelectrocatalytic technology. Acetone was selected as the gasous pollutant for this particular study. A commercial TiO2 photocatalyst (AG-160) was coated on GFF via impregnation to decompose acetone in a batch PEC reactor. Operation parameters investigated in this study included acetone concentration (50~400 ppm), electrical voltage (0~6,500V), water content (0~20,000 ppm), reaction temperature (40¢J~80¢J).The incident UV light of 365 nm wavelength was irradiated by three 15-wat low pressure mercury lamps (£f=365 nm) placing above the batch PEC reactor. The TiO2-coated EGF was placed at the center of the batch PEC reactor. Acetone was injected into the reactor by a gasket syringe to conduct the PEC decomposition test. Acetone was analyzed quantitatively by a gas chromatography with a flame ionization detector (GC/FID). Finally, a Langmuir-Hinshelwood kinetic (L-H) model was proposed to simulate the PEC reaction rate of acetone. Experimental results showed that the size range of the self-produced nano-sized photocatalyst prepared by sol-gel was 35~50 nm. Three duplicate tests of PC and PEC degradation of acetone indicated that TiO2 was not deactivated during the PC and PCE reactions, hence TiO2 can be reused in the experiments. Results obtained from the PC and PEC degradation experiments indicated that the PEC reaction rate was higher than the PC reaction rate.The PEC reaction rate increased with applied electrical voltage, and the highest decomposition efficiency occurred at 6,500 V. Electrical field generated by the differences of electrical voltage can effectively enhance the oxidation capability of TiO2 since electron (e-) can be conducted to retard the recombination of electron and electron hole pairs. Both PC and PEC technologies could be used to decompose acetone. Among them, PEC had highter decomposition efficiency of acetone than PC up to 34%. Rsults obtained from the operation parameter tests reaveled that raising electrical voltage could enhance the decomposition efficiency of acetone only for electrical voltages above 2,000 V. However, the decomposition efficiency of acetone tended to level off as electrical voltage became higher. Zero-order reaction rate of the PEC reaction was observed for initial acetone concentration of 100~400 ppm, while the PEC reaction decreased gradually for initial acetone concentration reaction below 100 ppm. It revealed that the PEC reaction was pseudo ozero-order for initial acetone concentration of 100~400 ppm, and pseudo first-order reaction for acetone concentration below 100 ppm. Additionally, the PC reaction rate increased with temperature at 45-80¢J. However the PEC reaction rate increased with temperature at 45-60¢J, and decreased with temperature at 60-80¢J. An adsorptive competition between acetone and water molecules at the active sites over TiO2 surface caused either promotion or inhibition of TiO2 decomposition depending on moisture content . For the PC and PEC reactions, the optimum operating condition of water vapor concentration was 10,000 ppm, but inhibition occurred when the water vapor concentration increased up to 20,000 ppm. Finally, the Langmuir-Hinshelwood kinetic model was applied to investiage the influences of reaction temperature, initial concentration of acetone, and water content on the photoelectrocatalytic reaction rate of acetone. Model simulation results showed that photoelectrocatalytic reaction rate constant of acetone(kLH) and adsorptive equilibrium constant(KA) increased with electrical voltage and acetone initial concentration. This study sevealed that experimental and simulated results were in good agreement. Thus, PEC reaction rate of acetone on the surface of TiO2 can be also succesfully simulated by the L-H kinetic model.

Adsorption/desorption behaviors of three volatile organic compounds (VOCs) emitted from the optoelectronics industry by Y-type and ZSM-5 zeolites were studied in this work. Target VOCs include acetone, isopropyl alcohol (IPA), and propylene glycol monomethyl ether acetate (PGMEA). Adsorption/desorption experiments were conducted in a fixed-bed column using various operating conditions to mimic the commercial ones. Also studied include the adsorption kinetics for single-component, two-component, and three-component cases. Experimental results of the single-adsorbate case by both model zeolites have shown that the amount of VOC adsorbed follows the order of PGMEA > IPA > Acetone. This is ascribed to the greatest molecular weight of PGMEA among three VOCs tested. The adsorption capacity of each zeolite for each target VOC was found to increase with its increasing initial concentration. Freundlich isotherm and Langmuir isotherm were found to be suitable for describing the adsorption behaviors for the single-adsorbate case. Results of the desorption experiments also showed that most of the target VOCs could be desorbed at 180¢J in 100 minutes. The adsorption capacities of the regenerated model zeolites were found to be decreasing as the regeneration times increased. As compared with the fresh ones, the regenerated zeolites had reduced specific surface areas, but increased pore sizes. In addition, the Yoon and Nelson equation was employed to study the kinetic behaviors of adsorbing the target VOCs by the model zeolites. A good agreement of the experimental results and predictions by the Yoon & Nelson model was obtained for the single-adsorbate case. However, the Yoon and Nelson model was found to be incompetent to simulate and predict all the multi-adsorbate cases including two-component adsorption and three-component adsorption in this work. Again, it is speculated that the displacement of lower-molecular-weight adsorbates (i.e., acetone and IPA) by PGMEA (an adsorbate of a much greater molecular weight) would be responsible for this finding. For the two-adsorbate case, nevertheless, the Yoon and Nelson equation was found to be capable of describing the adsorption behavior under the circumstance of C/C0 < 1.

The study of catalytic oxidation on the removal of NO was investigated over the Cu-catalysts . The Cu-catalysts , including Cu/TiO2 , Cu/Al2O3 and Cu/SiO2 , were prepared by impregnation method . Alougth NO2 , the product of this reaction , has higher toxicity than NO , but it might be removed completely by absorption with H2O or alkalinal solution for its high solubility . The experiments can be divided into three parts , i.e. , the screen of test catalysts , the effect of operating factors on the conversion of NO and the kinetic model . In the first part , the activity of test catalysts , which were prepared by mixing three various sources of Cu-ions¡]i.e., Cu(NO3)2 , Cu(CH3COO)2 , and CuSO4¡^with three different types of support¡]i.e., TiO2 , Al2O3 , and SiO2¡^, and were compared in form of conversion on NO to find the best catalyst . The results show that the mixture Cu(NO3)2 / TiO2 has the good performance on the conversion of NO , and also has more wider operating in range of temperature . In order to find the optimal loading of Cu on Cu(NO3)2 / TiO2 , additional test of various dosage over the catalysts was conduct in series . It is found that 8wt.% of Cu loading on Cu(NO3)2 / TiO2 is the most economic dosage . Therefore , we select this type of Cu oxide as the best catalyst in the following work . In the second part , the effect of NO inlet concentration , space velocity and humidity on the conversion of NO were performed . The results show that the conversion of NO decreases with the increasing of [NO]in when [NO]in is larger than 1000ppm¡Fthe conversion of NO is not changed with [NO]in when [NO]in is lower than 1000ppm . The better space velocity is 15000hr-1 , i.e.,the empty bed residence time is 0.24 second . The reaction on NO conversion would be restrained by higher humidity contenting in inlet gas stream , but the effect of inhibition on NO conversion is not significant . Finally , the kinetics of the oxidation of NO over 8wt.% Cu(NO3)2 / TiO2 was obtained by integral method .It is found that the oxidations of NO can be described by first order reversible reaction and the observed activation energy are 15.8 kcal/mole¡]forward reaction¡^and 25.9 kcal/mole¡]backward reaction¡^, respectively . By comparing the conversion of predicted NO with the experimentals , we can find the suitable operation conditions in application of the kinetic model : the inlet concentration of NO in a range of 300-1000ppm , the empty-bed residence time ranging from 0.12-0.48 second , and the absolute humidity ranging from 4854 to 42475ppm .

This study investigated the photocatalytic reduction of CO2 in a self-designed closed circulated batch reactor system and a bench-scale batch photocatalytic reactor. The photocatalysts tested included titanium dioxide (TiO2, Degussa P-25) and zirconium oxide (ZrO2). The reductants investigated included hydrogen (H2), water vapor (H2O), and hydrogen plus water vapor (H2+H2O). The wavelengths of incident near ultra-violet (UV) and UV lights for the photocatalysis of TiO2 and ZrO2 were 365 nm and 254 nm, respectively. The initial concentrations of CO2 ranged from 0.2-5.0% and the reaction temperature ranged from 35-95 ¡³C. The incident near-UV (or UV) light with wavelength of 365 nm (or 254 nm) was irradiated by a 15-watt low-pressure mercury lamp. The photocatalytic reaction was conducted continuously for approximately two hours. Reactants and products were analyzed by a gas chromatography with a flame ionization detector followed by a methanizer (GC/FID-methanizer). Experimental results indicated that glass pellets coated with TiO2 had better photoreduction efficiency than ZrO2. The highest yield rates of the photoreduction of CO2 were obtained using TiO2 with H2+H2O and ZrO2 with H2. Photoreduction of CO2 over TiO2 with H2+H2O formed CH4, C2H6, and CO in the yield of 32.95~94.60, 0.80~18.55, 1.12~21.78 £gmol/g, respectively, while the photoreduction of CO2 over ZrO2 with H2 formed CO in the yield of 0.34~4.99 £gmol/g. Results obtained from the operating parameter tests showed that the photoreduction rate increased with the initial concentration of carbon dioxide and resulted in more product accumulation. The photoreduction rate of carbon dioxide increased with reaction temperature, which promoted the formation of products. Concurred with previous researches, the reaction rate of major products over TiO2 and ZrO2 were higher than previous investigations of CO2 photoreduction. Furthermore, the spectra of FTIR showed that formic acid (HCOOHads), methanol (CH3OHads), carbonate (CO32−ads), bicarbonate (HCO32−ads), formate (HCOO−ads), formic acid (HCOOH ads), formaldehyde (HCOHads) and methyl formate (HCOOCH3 ads) formed on the surface of TiO2 and ZrO2 photocatalysts. The detected reaction products supported the proposal of two reaction pathways for the photoreduction of CO2 over TiO2 and ZrO2 with H2 and H2O, respectively. A modified bimolecular Langmuir-Hinshelwood kinetic model was developed to simulate the reaction temperature, CO2 initial concentration and relative humidity promotion and inhibition of the photoreduction of CO2. Additionally, the modified L-H kinetic model was successfully applied to simulate the photoreduction rate of CO2. The result showed that CO2 could be reduced by used solar light over TiO2 and ZrO2 photocatalysts. The reaction products of CO2 photoreduction over TiO2 were CH4, C2H6, and CO in the yield of 2.16~2.995, 0.057~0.128, 0.078~0.134 £gmol/g, respectively, while the photoreduction of CO2 over ZrO2 formed only CO in the yield of 0.023~0.051 £gmol/g. Furthermore, experimental results indicated that TiO2 gave the highest average photo energy efficiency (AEf) of ~4.13%, and apparent quantum efficiency (£pA) of ~1.05%. However, the ZrO2 gave the highest average photo energy efficiency (AEf) of 5.07¡Ñ10-3%, and apparent quantum efficiency (£pA) of ~1.54¡Ñ10-2%.

Acrylic resins, synthesized from a mixture of monomers selected from the methacrylate, acrylate and styrene families, are the base polymer components for many automotive coatings due to their excellent chemical and mechanical properties. The low molecular weight polymers with reactive functionalities are made via high-temperature starved-feed free-radical solution semibatch terpolymerization, operating conditions that greatly promote the importance of secondary reactions, such as methacrylate depropagation, and acrylate backbiting, chain scission and macromonomer propagation. In this work, a generalized model for styrene/methacrylate/acrylate terpolymerization has been developed and formulated in the PREDICI software package and poorly understood high temperature mechanisms have been studied. Unknown rate coefficients for methacrylate depropagation, reactivity of acrylate macromonomer and penultimate copolymerization kinetics were determined via separate kinetic experiments. The generality of the terpolymerization mechanistic model was verified against data obtained under a range of polymerization conditions, and provides an exclusive insight into the kinetic complexity of methacrylate/styrene/acrylate terpolymerization at high temperatures. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2010-04-28 19:56:36.906