Gas separations are often required in chemical processes, e.g. air separation, ethylene production, etc. These are often challenging and costly processes because of the low temperature and high pressure needed if vapour-liquid phase separations are involved. This thesis focuses on hybrid membrane-distillation separations as an opportunity to develop more energy-efficient separation processes. In a typical ethylene plant, recovery, the separation and purification of the cracked product are economically important. The focus of this thesis is on the ‘C2splitter’ which separates the desired product, ethylene, from ethane. Cryogenic distillation, which is currently used to separate the binary ethylene-ethane mixture, is extremely expensive in terms of both capital and operating costs, especially because of refrigerated cooling requirements. Hybrid membrane-distillation processes are able to effectively separate low-boiling compounds and close-boiling mixtures and to reduce energy consumption, relative to cryogenic distillation. However, hybrid membrane-distillation processes present challenges for process modelling, design and operation. There are two major challenges associated with the modelling of hybrid processes for low temperature separations: i) the complex interaction between the process and the refrigeration system and ii) the large number of structural options, e.g. conventional column, membrane unit or hybrid membrane-distillation separation, where the distillation column can be integrated with the membrane unit to form a sequential, parallel, ‘top’or ‘bottom’ hybrid scheme. This thesis develops a systematic methodology to design, screen, evaluate and optimise various design alternatives. Schemes are evaluated with respect to energy consumption, i.e. power consumption of process and refrigeration compressors, or energy costs. In the methodology, process options are screened first for feasibility, based on numerous simulations and sensitivity analyses. Then, the feasible options are evaluated in terms of energy consumption and compared to the performance of a conventional distillation column. Finally, economically viable schemes are optimised to identify the most cost-effective heat-integrated structure and operating conditions. The methodology applies models for multi-feed and multi-product distillation columns, the membrane, compressor and refrigeration system; heat recovery opportunities are systematically captured and exploited. For the separation of relatively ideal mixtures, modified shortcut design methods, based on the Fenske-Underwood-Gilliland method are appropriate because they allow fast evaluation without needing detailed specification of column design parameters (i.e. number of stages, feed and side draw stage locations and reflux ratio). The modifications proposed by Suphanit (1999) for simple column design are extended to consider multi-feed and/or multi-product columns. The complex column designs based on the approximate calculations method are validated by comparison with more rigorous simulations using Aspen HYSYS. To design the hybrid system, a reliable and robust membrane model is also needed. To predict the performance of the module model, this work applies and modifies detailed membrane model (Shindo et al., 1985) and approximate method (Naylor and Backer, 1955) to avoid the need for initial estimates of permeate purities and to facilitate convergence. Heat integration opportunities are considered to reduce the energy consumption of the system, considering interactions within the separation process and with the refrigeration system. A matrix-based approach (Farrokhpanah, 2009) is modified to assess opportunities for heat integration. The modified heat recovery model eliminates the need to design the refrigeration cycle and uses a new simple, linear model that correlates the ideal (Carnot) and a more accurately predicted coefficient of performance. This work develops a framework for optimising important degrees of freedom in the hybrid separation system, e.g. permeate pressure, stage cut, side draw molar flow rate and purity, column feed and side draw locations. Heat recovery options between: i) column feeds and products; ii) the membrane feed and products and iii) the associated refrigeration system are considered. A deterministic and a stochastic optimisation algorithm are applied and compared for their efficiency of solving the resulting nonlinear optimisation problem. The new approach is demonstrated for the design and optimisation of heat-integrated sequential and parallel hybrid membrane-distillation flowsheets. Case study results show that hybrid scheme can reduce energy cost by 11%, compared to distillation, and that parallel schemes have around 8% lower energy costs than sequential hybrid schemes. These results suggest hybrid membrane-distillation processes may be competitive with distillation when applied for ethylene-ethane separations, but that further development of suitable membranes may still be needed.

The combustion behavior of methane and ethane is important to the study of natural gas and other alternative fuels that are comprised primarily of these two basic hydrocarbons. Understanding the transition from methane-dominated ignition kinetics to ethane-dominated kinetics for increasing levels of ethane is also of fundamental interest toward the understanding of hydrocarbon chemical kinetics. Much research has been conducted on the two fuels individually, but experimental data of the combustion of blends of methane and ethane is limited to ratios that recreate typical natural gas compositions (up to ~20% ethane molar concentration). The goal of this study was to provide a comprehensive data set of ignition delay times of the combustion of blends of methane and ethane at near atmospheric pressure. A group of ten diluted CH4/C2H6/O2/Ar mixtures of varying concentrations, fuel blend ratios, and equivalence ratios (0.5 and 1.0) were studied over the temperature range 1223 to 2248 K and over the pressure range 0.65 to 1.42 atm using a new shock tube at the University of Central Florida Gas Dynamics Laboratory. Mixtures were diluted with either 75 or 98% argon by volume. The fuel blend ratio was varied between 100% CH4 and 100% C2H6. Reaction progress was monitored by observing chemiluminescence emission from CH* at 431 nm and the pressure. Experimental data were compared against three detailed chemical kinetics mechanisms. Model predictions of CH* emission profiles and derived ignition delay times were plotted against the experimental data. The models agree well with the experimental data for mixtures with low levels of ethane, up to 25% molar concentration, but show increasing error as the relative ethane fuel concentration increases. The predictions of the separate models also diverge from each other with increasing relative ethane fuel concentration. Therefore, the data set obtained from the present work provides valuable information for the future improvement of chemical kinetics models for ethane combustion.

Phase transitions and other intrinsic properties (shape, size, architecture) of molecularly structured aerosol particles are important for understanding their role in planetary atmospheres and for technical applications. By combining bath gas cooling with time resolved mid-infrared spectroscopy and modeling, information is obtained on dynamic processes and intrinsic properties of fluoroform and ethane aerosol particles. The distinct infrared spectral features of fluoroform aerosol particles make it a particularly suitable model system. Homogeneous crystallization rates of the sub-micron sized aerosol particles are determined (JV = 10⁸ - 10¹⁰ cm-³s-¹ or JS = 10³ – 10⁵ cm-²s-¹ at a temperature of T = 78 K), and the controversial question regarding volume versus surface nucleation in freezing aerosols is addressed. It is demonstrated that current state of the art measurements of droplet ensembles cannot distinguish between the two mechanisms due to inherent experimental uncertainties. The evolution of particle shape from spherical supercooled droplets to cube-like crystalline particles and eventually to elongated crystalline particles is recorded and analyzed in detail with the help of vibrational exciton model calculations. Phase behaviour of pure ethane aerosols and ethane aerosols formed in the presence of other ice nuclei under conditions mimicking Titan’s atmosphere provide evidence for the formation of supercooled liquid ethane aerosol droplets, which subsequently crystallize. The observed homogeneous freezing rates (JV = 10⁷ – 10⁹ cm-³s-¹) imply that supercooled ethane could play a similar role in ethane rich regions of Titan’s atmosphere as supercooled water does in the Earth’s atmosphere.

Phase transitions and other intrinsic properties (shape, size, architecture) of molecularly structured aerosol particles are important for understanding their role in planetary atmospheres and for technical applications. By combining bath gas cooling with time resolved mid-infrared spectroscopy and modeling, information is obtained on dynamic processes and intrinsic properties of fluoroform and ethane aerosol particles. The distinct infrared spectral features of fluoroform aerosol particles make it a particularly suitable model system. Homogeneous crystallization rates of the sub-micron sized aerosol particles are determined (JV = 10⁸ - 10¹⁰ cm-³s-¹ or JS = 10³ – 10⁵ cm-²s-¹ at a temperature of T = 78 K), and the controversial question regarding volume versus surface nucleation in freezing aerosols is addressed. It is demonstrated that current state of the art measurements of droplet ensembles cannot distinguish between the two mechanisms due to inherent experimental uncertainties. The evolution of particle shape from spherical supercooled droplets to cube-like crystalline particles and eventually to elongated crystalline particles is recorded and analyzed in detail with the help of vibrational exciton model calculations. Phase behaviour of pure ethane aerosols and ethane aerosols formed in the presence of other ice nuclei under conditions mimicking Titan’s atmosphere provide evidence for the formation of supercooled liquid ethane aerosol droplets, which subsequently crystallize. The observed homogeneous freezing rates (JV = 10⁷ – 10⁹ cm-³s-¹) imply that supercooled ethane could play a similar role in ethane rich regions of Titan’s atmosphere as supercooled water does in the Earth’s atmosphere.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-06-26T19:32:49Z No. of bitstreams: 1 marcelomoreiragoulart.pdf: 2141046 bytes, checksum: bdd7d61bbcebeeaf11dd6057dd1c0f99 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-06-26T19:53:12Z (GMT) No. of bitstreams: 1 marcelomoreiragoulart.pdf: 2141046 bytes, checksum: bdd7d61bbcebeeaf11dd6057dd1c0f99 (MD5) / Made available in DSpace on 2017-06-26T19:53:12Z (GMT). No. of bitstreams: 1 marcelomoreiragoulart.pdf: 2141046 bytes, checksum: bdd7d61bbcebeeaf11dd6057dd1c0f99 (MD5) Previous issue date: 2011-01-19 / CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico / Foram obtidos neste trabalho valores de Seção de Choque Total (SCT) do impacto de elétrons em metano e etano utilizando um aparelho desenvolvido no Laboratório de Espectroscopia Atômica e Molecular (LEAM) – DF – UFJF que emprega a técnica de transmissão linear. Estes dados traduzem a probabilidade total de espalhamento de elétrons incidentes que penetram em um meio gasoso, com uma enorme gama de aplicações, tais como desenvolvimento de "lasers", física de plasmas, eletrônica gasosa, astrofísica, estudos da atmosfera exterior terrestre e de semicondutores. Para a obtenção destas medidas foi construído um canhão de baixa energia que cobre continuamente a região de energia de 20 a 250 eV, com uma resolução em energia de 0,6 eV e intensidades de corrente da ordem de unidades a centenas de ƞA. As medidas foram realizadas para o metano e etano cobrindo as energias de 100, 110, 120, 130 e 150 eV e também 90eV para o etano. A partir das medias de atenuação do feixe eletrônico ao atravessar uma célula preenchida com o gás a ser estudado, a SCT foi obtida aplicando-se a Lei de Lambert-Beer. Os elétrons que não sofreram espalhamento pelos alvos foram discriminados daqueles espalhados por um analisador cilíndrico dispersivo 127º antes de serem detectados por um Coletor de Faraday. Os dados necessários à realização do cálculo de SCT para um valor de energia definido foram obtidos através de um processo estatístico envolvendo uma série de 5 a 10 seções de medidas. Além das medidas experimentais, determinou-se a SCT através da fórmula semi-empírica de García e Manero. Propôs-se, também, uma nova técnica de aquisição da SCT através da detecção do feixe de elétrons espalhado que atinge as paredes da célula de espalhamento. Os dados foram comparados com aqueles disponíveis na literatura e os calculados. Os valores de SCT obtidos neste trabalho apresentaram relativa concordância com a literatura. / Were obtained in this work values of total cross-section (TCS) of electron impact on methane and ethane using a device developed at the Atomic and Molecular Spectroscopy Laboratory (LEAM) - DF - UFJF employing the linear transmission technique. These data reflect the total scattering probability of incident electrons that penetrate a gaseous medium with a wide range of applications, such as the development of lasers, plasma physics, gaseous electronics, astrophysics, studies of Earth's outer atmosphere and semiconductors. A low-energy electron gun continuously covering the energy from 20 to 250 eV was built to obtain these measures with an energy resolution of 0.6 eV and current intensity of the order of units to hundreds of ƞA. The measurements were performed for methane and ethane covering the energies of 100, 110, 120, 130 and 150 eV and 90 eV also for ethane. Starting from mean attenuation of the electron beam that pass through a cell filled with gas to be studied, the SCT was obtained by applying the Beer-Lambert Law. The electrons that have not been scattered were discriminated from those scattered by a 127º cylindrical dispersive analyzer before being detected by a Faraday Cup. The necessary data to perform the calculation of TCS to a specific energy value was obtained through a statistical process involving a range from 5 to 10 acquisition turns. In addition to the experimental measurements, the SCT was determined by the semi-empirical formula of García and Manero. It was also proposed a new acquisition technique of SCT by detecting the scattered electron beam that reaches the walls of the scattering cell. The data were compared with those available in literature and the calculated ones. TCS values obtained in this study showed relative agreement with the literature.

Phase transitions and other intrinsic properties (shape, size, architecture) of molecularly structured aerosol particles are important for understanding their role in planetary atmospheres and for technical applications. By combining bath gas cooling with time resolved mid-infrared spectroscopy and modeling, information is obtained on dynamic processes and intrinsic properties of fluoroform and ethane aerosol particles. The distinct infrared spectral features of fluoroform aerosol particles make it a particularly suitable model system. Homogeneous crystallization rates of the sub-micron sized aerosol particles are determined (JV = 10⁸ - 10¹⁰ cm-³s-¹ or JS = 10³ – 10⁵ cm-²s-¹ at a temperature of T = 78 K), and the controversial question regarding volume versus surface nucleation in freezing aerosols is addressed. It is demonstrated that current state of the art measurements of droplet ensembles cannot distinguish between the two mechanisms due to inherent experimental uncertainties. The evolution of particle shape from spherical supercooled droplets to cube-like crystalline particles and eventually to elongated crystalline particles is recorded and analyzed in detail with the help of vibrational exciton model calculations. Phase behaviour of pure ethane aerosols and ethane aerosols formed in the presence of other ice nuclei under conditions mimicking Titan’s atmosphere provide evidence for the formation of supercooled liquid ethane aerosol droplets, which subsequently crystallize. The observed homogeneous freezing rates (JV = 10⁷ – 10⁹ cm-³s-¹) imply that supercooled ethane could play a similar role in ethane rich regions of Titan’s atmosphere as supercooled water does in the Earth’s atmosphere. / Science, Faculty of / Chemistry, Department of / Graduate

京都大学 / 新制・課程博士 / 博士(人間・環境学) / 甲第23976号 / 人博第1028号 / 新制||人||242(附属図書館) / 2022||人博||1028(吉田南総合図書館) / 京都大学大学院人間・環境学研究科相関環境学専攻 / (主査)教授 吉田 寿雄, 教授 田部 勢津久, 教授 中村 敏浩 / 学位規則第4条第1項該当 / Doctor of Human and Environmental Studies / Kyoto University / DFAM

The photocatalytic oxidation of trichloroethylene (TCE), ethylene. ethane and toluene on TiO2, Pt/TiO2 and Ag/TiO2 were investigated in a dedicated reactor set-up operated at room temperature and ambient pressure condition. The gas phase experiments were carried out for both single and binary mixtures of these chemicals to identify the role of Pt and Ag metallisation in the photocatalytic oxidation of different contaminants. In a single contaminant system, the presence of Pt enhanced the oxidation of ethylene, ethane and toluene but detrimental to the oxidation of TCE. In the oxidation of ethylene, Pt enhanced the oxidation by acting as catalyst and as electron sink. However, in ethane oxidation, the enhancement was solely associated to the ability of Pt to act as electron sink. The detrimental effect observed in TCE oxidation was attributed to Pt and Cl interaction, which formed a persistent inorganic chlorine species decreasing the overall Pt/TiO2 photocatalyst performance. Interestingly, Ag did not show any significant effect to the oxidation of any single system degradation. In binary system degradation, where TCE and another organic compound either ethylene, ethane or toluene were degraded simultaneously, Pt always caused a detrimental effect due to its strong interaction with Cl. However, the presence of Ag and Cl gives a more synergetic effect. Ag was found to provide sites to temporarily trap chlorine radicals as AgCl. Under illumination, electrons transferred from Cl to Ag forming chlorine radicals that could react with the surface contaminant enhancing its breakdown and mineralization.

<p>Polybrominated diphenyl ethers (PBDEs) are important chemical flame retardants, but also environmental pollutants. Their bromine substitution lends them a different bioaccumulation behaviour than the better studied organochlorines.</p><p>The contamination of a Swedish lake with lower brominated BDEs was assessed by a retrospective study of pike. The concentrations of tetra- to hexaBDEs increased exponentially up to the mid-1980s and then decreased slowly, possibly reflecting the voluntary reduction in production/usage of the chemicals. Methoxylated PBDEs were found to be present in similar concentrations to the PBDEs, but originated from different sources. The large size of the bromine atom was believed to result in negligible absorption of higher brominated BDEs in wildlife, thus explaining the low levels observed in fish despite high levels in e.g. sediment. However, it was shown that the fully brominated BDE, BDE209, was absorbed to a small extent via the diet. Once absorbed, it was reductively debrominated to lower brominated BDE congeners. Debromination was also observed in dairy cows exposed to higher brominated BDEs in their natural diet. Moreover, the molecular size restricted the transfer of higher brominated BDEs to milk. In contrast to PCBs and lower brominated BDEs, there was no equilibrium between adipose tissues and milk fat, and with increasing bromine substitution a progressively smaller fraction of the ingested PBDEs was transferred to the milk.</p><p>This thesis highlights differences in uptake, metabolism and excretion for PBDEs compared to the well characterized organochlorines. A knowledge that is useful for risk assessments given the ongoing use of these compounds. Furthermore, a representative of the next generation brominated flame retardants, decabromodiphenyl ethane, a replacement for the BDE209 technical product, was identified for the first time in the environment.</p>

Polybrominated diphenyl ethers (PBDEs) are important chemical flame retardants, but also environmental pollutants. Their bromine substitution lends them a different bioaccumulation behaviour than the better studied organochlorines. The contamination of a Swedish lake with lower brominated BDEs was assessed by a retrospective study of pike. The concentrations of tetra- to hexaBDEs increased exponentially up to the mid-1980s and then decreased slowly, possibly reflecting the voluntary reduction in production/usage of the chemicals. Methoxylated PBDEs were found to be present in similar concentrations to the PBDEs, but originated from different sources. The large size of the bromine atom was believed to result in negligible absorption of higher brominated BDEs in wildlife, thus explaining the low levels observed in fish despite high levels in e.g. sediment. However, it was shown that the fully brominated BDE, BDE209, was absorbed to a small extent via the diet. Once absorbed, it was reductively debrominated to lower brominated BDE congeners. Debromination was also observed in dairy cows exposed to higher brominated BDEs in their natural diet. Moreover, the molecular size restricted the transfer of higher brominated BDEs to milk. In contrast to PCBs and lower brominated BDEs, there was no equilibrium between adipose tissues and milk fat, and with increasing bromine substitution a progressively smaller fraction of the ingested PBDEs was transferred to the milk. This thesis highlights differences in uptake, metabolism and excretion for PBDEs compared to the well characterized organochlorines. A knowledge that is useful for risk assessments given the ongoing use of these compounds. Furthermore, a representative of the next generation brominated flame retardants, decabromodiphenyl ethane, a replacement for the BDE209 technical product, was identified for the first time in the environment.