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The production of chlorate, chlorine and sodium hydroxiderelies heavily on electrical energy, so that savings in thisarea are always a pertinent issue. This can be brought aboutthrough increased mass transfer of reacting species to therespective electrodes, and through increased catalytic activityand uniformity of current density distribution at theseelectrodes. This thesis will present studies involvingmathematical modelling and experimental investigations of theseprocesses. They will show the effect that hydrodynamicbehaviour has on the total current density and cell voltages,along with the effects on current density distributions andindividual overpotentials atthe respective electrodes. Primary, secondary and psuedo-tertiary current densitydistribution models of a chlor-alkali anode are presented anddiscussed. It is shown that the secondary model presentsresults rather similar to the pseudo-tertiary model, when thecurrent density distribution is investigated, although thepotential distribution differs rather markedly. Furthermore, itis seen that an adequate description of the hydrodynamicsaround the anode is required if the potential distribution, andthereby the prevalence of side-reactions, is to be reasonablepredicted. A rigorous tertiary current density distribution model ofthe chlorate cell is also presented, which takes into accountthe developing hydrodynamic behaviour along the height of thecell. This shows that an increased flowrate gives more uniformcurrent density distributions. This is due to the fact that theincreased vertical flowrate of electrolyte replenishes ioncontent at the electrode surfaces, thus reducing concentrationoverpotentials. Furthermore, results from the model lead to theconclusion that it is the hypochlorite ion that partakes in themajor oxygen producing side-reaction. A real-scale cross-section of a segmented anode-cathode pairfrom a chlorate cell was designed and built in order to studythe current density distribution in industrial conditions.These experiments showed that increased flowrate brought aboutmore even current density distributions, reduced cell voltageand increased the total current density. An investigation ofthe hydrodynamic effects on the respective electrodeoverpotentials shows the anode reactions being more favoured byincreased flowrate. This leads to the conclusion that theuniform current density distribution, caused by increasedflowrate, occurs primarily through decreasing the concentrationoverpotential at the anode rather than by decreasing thebubble-induced ohmic drop at the cathode. Finally, results from experiments investigating thebubble-induced free convection from a small electrochemicalcell are presented. These experiments show that Laser DopplerVelocimetry is the most effective instrument for investigatingthe velocity profiles in bubble-containing electrochemicalsystems. The results also show that the flow can transform fromlaminar to turbulent behaviour on both the vertical andhorizontal planes, in electrochemical systems where bubbles areevolved.

<p>The production of chlorate, chlorine and sodium hydroxiderelies heavily on electrical energy, so that savings in thisarea are always a pertinent issue. This can be brought aboutthrough increased mass transfer of reacting species to therespective electrodes, and through increased catalytic activityand uniformity of current density distribution at theseelectrodes. This thesis will present studies involvingmathematical modelling and experimental investigations of theseprocesses. They will show the effect that hydrodynamicbehaviour has on the total current density and cell voltages,along with the effects on current density distributions andindividual overpotentials atthe respective electrodes.</p><p>Primary, secondary and psuedo-tertiary current densitydistribution models of a chlor-alkali anode are presented anddiscussed. It is shown that the secondary model presentsresults rather similar to the pseudo-tertiary model, when thecurrent density distribution is investigated, although thepotential distribution differs rather markedly. Furthermore, itis seen that an adequate description of the hydrodynamicsaround the anode is required if the potential distribution, andthereby the prevalence of side-reactions, is to be reasonablepredicted.</p><p>A rigorous tertiary current density distribution model ofthe chlorate cell is also presented, which takes into accountthe developing hydrodynamic behaviour along the height of thecell. This shows that an increased flowrate gives more uniformcurrent density distributions. This is due to the fact that theincreased vertical flowrate of electrolyte replenishes ioncontent at the electrode surfaces, thus reducing concentrationoverpotentials. Furthermore, results from the model lead to theconclusion that it is the hypochlorite ion that partakes in themajor oxygen producing side-reaction.</p><p>A real-scale cross-section of a segmented anode-cathode pairfrom a chlorate cell was designed and built in order to studythe current density distribution in industrial conditions.These experiments showed that increased flowrate brought aboutmore even current density distributions, reduced cell voltageand increased the total current density. An investigation ofthe hydrodynamic effects on the respective electrodeoverpotentials shows the anode reactions being more favoured byincreased flowrate. This leads to the conclusion that theuniform current density distribution, caused by increasedflowrate, occurs primarily through decreasing the concentrationoverpotential at the anode rather than by decreasing thebubble-induced ohmic drop at the cathode.</p><p>Finally, results from experiments investigating thebubble-induced free convection from a small electrochemicalcell are presented. These experiments show that Laser DopplerVelocimetry is the most effective instrument for investigatingthe velocity profiles in bubble-containing electrochemicalsystems. The results also show that the flow can transform fromlaminar to turbulent behaviour on both the vertical andhorizontal planes, in electrochemical systems where bubbles areevolved.</p>

Submitted by Maria Medeiros (maria.dilva1@ufcg.edu.br) on 2018-07-06T13:50:36Z No. of bitstreams: 1 CARLOS THIAGO CÂNDIDO CUNHA - TESE (PPGCEMat) 2015.pdf: 3145702 bytes, checksum: bad9f1c620f682b0e77a37c797d9bc37 (MD5) / Made available in DSpace on 2018-07-06T13:50:36Z (GMT). No. of bitstreams: 1 CARLOS THIAGO CÂNDIDO CUNHA - TESE (PPGCEMat) 2015.pdf: 3145702 bytes, checksum: bad9f1c620f682b0e77a37c797d9bc37 (MD5) Previous issue date: 2015-06-22 / Capes / O hidróxido de sódio (NaOH) e o cloro estão entres os produtos químicos mais importantes na indústria e são produzidos simultaneamente pela eletrólise da salmoura. As células eletrolíticas são compostas de uma câmara catódica e uma anódica, separadas por um diafragma que permite a passagem dos íons por migração iônica. A maioria dos diafragmas se utilizam de amianto e as leis ambientais vigentes direcionam para extinção ou substituição deste material. Assim, foi realizado um estudo sobre o desenvolvimento de diafragmas alternativos à base de materiais poliméricos e aditivos que pudessem substituir o amianto e possibilitassem sua aplicação na indústria de cloro-soda. Para tanto, empregou-se fibras poliméricas, a exemplo do Polietileno de Ultra Alto Peso Molecular (PEUAPM), que resiste as condições severas do processo eletrolítico. Também se fez necessário o emprego da dopagem com carga inorgânica (argilas) para conferir menor permeabilidade aos diafragmas. Diante disso, foram desenvolvidos sistemas para deposição e caracterização dos diafragmas que possibilitam a reprodutividade e análises adequadas comparadas ao âmbito industrial. Partindo de um planejamento experimental de misturas com 5 diferentes fibras pode-se avaliar qual composição de diafragma favoreceu melhores resultados nos parâmetros da eletrólise. Os resultados se mostraram promissores, tendo em vista que dentre as 15 formulações testadas conseguiu-se chegar a uma composição cujas propriedades eletroquímicas atendem todas as especificações podendo inclusive ser aplicado em escala industrial. / Sodium hydroxide (NaOH) and chlorine are among the most important chemicals in industry and are produced simultaneously by the electrolysis of brine. Electrolyte cells are consisted by a cathodic and anodic chamber, separated by a diaphragm that allows the passage of ions by ion migration. Most diaphragms using asbestos and environmental laws in use direct to extinction or replacement of this material. In this way, it was done a study on the development of alternative diaphragm based on polymeric materials and additives that could replace the asbestos and could allow its application in chlorine-soda industry. So, polymeric fibres was used, such as, Ultra High Molecular Weight polyethylene (UHMWPE), resisting the harsh conditions of the electrolytic process. Also it was studied the use of doping with inorganic fillers (clays) to provide less permeability to the diaphragms. For this, systems were developed for deposition and characterization of diaphragms that make it possible the reproducibility and suitable analysis compared to the industrial scope. Starting from experimental planning of mixtures with 5 different fibers, it was evaluated which composition of diaphragm given best results in the electrolysis parameters. The results were promising, considering that among the 15 formulations, it was reached a composition whose electrochemical properties meet all specifications and can even be applied on an industrial scale.

Yes / The chlor-alkali industries produce caustic soda (NaOH), chlorine (Cl2 ), and hydrogen (H2 ) as primary products. In 2021, the global chlor-alkali market was valued at $63.2 billion. The article evaluates the global aspects of chlor-alkali industries and prospects for Bangladesh. The current production capacity of NaOH from the chlor-alkali industries in Bangladesh is around 282,150 metric tons/year (MT/y). The by-products, chlorine (Cl2 ) of 250,470 MT/y and hydrogen (H2 ) of 7055 MT/y, are produced domestically. The local demand of Cl2 is 68,779 MT/y. However, there are no systematic utilizations of the residual Cl2 and vented H2 , which threatens the sustainability of the chlor-alkali industries. The article prefigures that a 150,000 MT/y PVC plant can utilize 45.2 % of residual Cl2 of chlor-alkali plants, which would be an economical and environmental milestone for Bangladesh. The residual Cl2 can earn revenue of 908 million USD/y, which can be utilized to import ethylene. For the sustainable utilization of vented H2 , production of H2O2 , fuel cell electric vehicle (FCEV) and H2 fuel-cell-based power plant are the feasible solutions. Thus, for the long-term growth of the chlor-alkali industry in Bangladesh and other developing countries, systematic utilization of Cl2 and H2 is the only feasible solution. / This research was funded by ‘BUET Chemical Engineering Forum (BCEF), 001-2020.

The objectives of this study were to investigate the difference and interaction of mercury (Hg) and selenium (Se) among fish species and tissues. In addition, by comparing with the detected concentrations in other regions, it would be possible to evaluate the pollution status. In the meanwhile, this study analyzed the edibility of the fish, the interaction between Hg and Se as well as their impacts on fish growth. Ten species of fish, including tenpounder (Elops machnata), fourlined terapon (Pelates quadrilineatus), whipfin silverbiddy (Gerres filamentosus), common ponyfish (Leiognathus equulus), Hamilton's thryssa (Thryssa hamiltonii), tilapia (Orechromis niloticus), western Pacific gizzard shad (Nematalosa come), large-scaled mullet (Liza macrolepis), flathead mullet (Mugil cephalus) and milkfish (Chanos chanos), and 20 sediment samples were collected from September to October of 2003 at the reservoir adjacent to a chlor-alkali plant, which had been abandoned for 22 years in Tainan City. Total mercury (THg) and organic mercury (OHg) concentrations were determined in fish muscles, livers, kidneys, gonads, gills and sediment samples. Besides, Se concentrations were also analyzed in fish muscles and livers. Concentrations (mg/kg dry wt.) of THg and OHg in sediment were 43.2¡Ó23.4(mean¡Ósd) and 0.013¡Ó0.008, respectively. THg, OHg and Se concentrations (mg/kg wet wt.) in fish muscles were 0.432¡Ó0.360, 0.305¡Ó0.206 and 0.126¡Ó0.030, similar to the concentrations in other chlor-alkali polluted regions. With the diet habit of Taiwanese, the Hg concentrations of muscles in the seven fish species exceeded the limit of Hg which was allowed to be consumed by humans. THg and OHg concentrations in the fish muscles showed significant species difference. Obviously, the concentrations in carnivorous fishes were higher than those in omnivorous and herbivorous fishes. The OHg concentrations of fish livers and kidneys were highest in carnivorous fishes, but the THg concentrations were higher in omnivorous fishes than in that of carnivorous and herbivorous fishes. Besides, Se concentrations in fish muscles and livers also showed significant species difference, but did not show relation with the feeding habit of fishes. The Hg levels among fish tissues were highest in livers or kidneys, followed by gonads and muscles, lowest in gills. Generally speaking, Se levels were higher in livers than in muscles. The liver THg concentrations of tilapia reached 10 mg/kg wet wt. Their muscle THg concentrations decreased suddenly and maintained at a level about 0.4 mg/kg wet wt. Meanwhile, the liver inorganic Hg and Se concentrations increased with fish weight, while the liver OHg concentrations did not show such a trend but stay at a low level. High Hg concentrations in the fish tissues resulted in adverse effects on fish health. High Hg concentrations in muscles and livers caused heptasomatic index to decrease in western Pacific gizzard shad and milkfish, and condition factor declined in tilipia. Moreover, gonasomatic index remained low while the Hg concentrations of muscles, livers and gonads reached a threshold, which suggested that the growth of those fishes was likely inhibited in Hg polluted environment.

Submitted by Lucienne Costa (lucienneferreira@ufcg.edu.br) on 2018-04-24T00:19:47Z No. of bitstreams: 1 JULIANA ZEYMER AUAD PAFFER – DISSERTAÇÃO (PPGEQ) 2015.pdf: 2369945 bytes, checksum: 31ce517399cfe89bebdd0e7c02c68852 (MD5) / Made available in DSpace on 2018-04-24T00:19:47Z (GMT). No. of bitstreams: 1 JULIANA ZEYMER AUAD PAFFER – DISSERTAÇÃO (PPGEQ) 2015.pdf: 2369945 bytes, checksum: 31ce517399cfe89bebdd0e7c02c68852 (MD5) / Um dos efluentes gerados na indústria de cloro e soda é uma corrente ácida (água saturada de cloro). Esta corrente deve passar por um sistema de tratamento antes de ser descartado, devido ao potencial de dano que este pode causar à flora e à fauna marinha, além de infringir as regulamentações ambientais. Visando reduzir o consumo de energia e atender à especificação do efluente, o objetivo deste trabalho é realizar e avaliar a simulação dinâmica de um sistema de tratamento de efluente ácido. O sistema estudado é composto por uma coluna de stripper e um trocador de calor que pré aquece a corrente de alimentação. O estudo se concentrou em avaliar o comportamento do sistema no estado estacionário e dinâmico frente a alterações nas condições de operação do trocador de calor. As simulações foram realizadas no AspenTM e validados com dados da planta industrial. De acordo com os resultados, reduzindo a eficiência de troca de calor do trocador leva no aumento do consumo de energia e o efluente fica fora das especificações. Desta forma, é muito importante manter a eficiência do trocador de acordo com a de projeto e os controladores sintonizados. / One of the effluents generated by chlor-alkali plant is an acid stream (saturated water chlorine). This stream must pass through a treatment system before being discarded because of damage potential that this may cause to the flora and marine fauna, in addition to breaching environmental regulations. In order to reduce energy consumption and meet the effluent specification, the objective is to implement and evaluate the dynamic simulation of an acid wastewater treatment system. The system is composed of a column stripper and a heat exchanger that heats the pre feed stream. The study focused on evaluating the system behavior in the steady state and dynamic against changes in operating conditions of the heat exchanger. The simulations were accomplished by the simulator Aspen™ and validated with data from industrial plant. According to the results, reducing the efficiency of heat exchanger can make the power consumption increase and the effluent is out of specification. This way, it is very important to keep the heat exchange efficiency according to design and tuned controls.

Chlor-alkali electrolysis indicates significant demand response potential, accounting for over 2% of Germany’s total elec-tricity demand. To fully analyze this potential, digital models or digital twins are necessary. In this study, we use the IRPopt modeling framework to develop a digital model of an electrolysis process and examine the cost-optimal load shifting application in the day-ahead spot and balancing reserve market for various price scenarios (2019, 2030, 2040). We also investigate the associated CO2 emissions. Combined optimization at both markets results in greater and more robust cost savings of 16.1% but cannibalizes the savings that are possible through optimization separately at each market. In future scenarios, the shares of savings from spot and reserve market could potentially reverse. CO2 savings between 2.5% and 9.2% appear only through optimization at the spot market and could even turn negative if optimized solely at the reserve market.

In this work, the formation and effects of chlorate ion were studied over hydrogen evolution reaction (HER), focusing for the chlorine and alkalis production by diaphragm process, using a pilot and bench cells, respectively. Studies in pilot cell revealed that chlorate formation is dependent of NaOH concentration in liquor and brine dwelling time. It was also observed that the NaOH concentration increase in the cathodic side provoked decreasing of diaphragm structure lifetime. This phenomenon reduced the blockage efficiency to back migration and consequently, increasing NaOH concentration in the anodic chamber, further increase in the undesirable parallels reaction rate, for example, the chlorate formation. After formation of chlorate in the anodic chamber the migration to the cathodic side is inevitable. Therefore to complete the studies we decided to verify the influence the chlorate, in bench cell, in the cathodic side, specifically for HER process. Potential polarization experiments in presence of chlorate, evidenced effects of HER wave displacement over SAE1020 mild steel carbon steel plate employed in industrial cells for chlorine and alkalis production using diaphragm process. Alternatively to SAE1020, other duplex alloys like SAF2205, SAF2304 and SAF2507 were also investigated. SAF2205 alloy presented a very interesting electrocatalytic response for HER. Pilot cell results pointed for the problem detected with the NaOH migration to the anodic side of cell, and invoked the single possibility to solve this problem - the changing of diaphragm cell separator. Bench experiments revealed chlorate influence on HER over SAE1020 carbon steel, claiming for urgent developing of alternative materials/cathodes with chlorate-immune character. / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Esse trabalho estuda a formação e os efeitos de íon clorato sobre a reação de desprendimento de hidrogênio (RDH) com ênfase para a produção de cloro-soda por processo de diafragma, com a utilização de célula piloto e de bancada, respectivamente. Os estudos em célula piloto revelaram que a formação de clorato é dependente da concentração de hidróxido de sódio no licor de célula e do tempo de residência da salmoura. Observou-se também que o aumento da concentração de hidróxido de sódio no lado catódico provoca envelhecimento prematuro da estrutura do diafragma, e este fenômeno reduz a eficiência do bloqueio à back migration de forma mais intensa. Esta perda de eficiência promove uma maior alcalinização do anólito, e consequentemente, um aumento nas velocidades das reações paralelas indesejáveis, como por exemplo, a formação de clorato. Uma vez formado clorato no compartimento anódico, sua percolação para o lado catódico é inevitável. Por essa razão, optou-se por fazer estudos de bancada do processo catódico, particularmente na região de RDH. Os dados de polarização revelaram a dependência da RDH em presença de clorato sobre o aço carbono SAE1020, atualmente empregado nas células industriais no processo de diafragma para produção de cloro-soda. Alternativamente ao SAE1020, foram estudadas as ligas duplex SAF2205, SAF2304 e SAF2507. Os estudos de polarização mostraram a dependência da RDH para as ligas SAF2304 e SAF2507, por outro lado, a liga SAF2205 apresentou resposta eletrocatalítica para o desprendimento de hidrogênio. Os estudos em célula piloto mostram que a queda de rendimento de produção é observada de forma mais imediata na parte anódica do processo, e fica evidenciada a importância de otimização do separador de diafragma. Nos experimentos de bancada foi constatada a influência do clorato sobre a RDH para o SAE1020, mostrando a necessidade de materiais alternativos que não apresentem susceptibilidade em presença de clorato.