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Thesis (M. Tech. Chemistry, Dept. of Chemistry, Faculty of Applied and Computer Sciences)--Vaal University of Technology, 2010. / Membrane separation processes offer a promising alternative to energy-intensive separation processes such as distillation and solvent extraction. NF and RO are among the most investigated membrane processes with a potential use in the chemical industry. Carbon-carbon coupling reactions feature in the top ten most used reactions in the chemical industry. These reactions often use homogeneous palladium, nickel and other precious catalysts which are often difficult to separate from reaction products. This leads to potential product contamination and loss of active catalysts. This not only poses a threat to the environment but is also costly to the chemical industry. The purpose of this study was to investigate the efficiency of the recovery of the metal catalysts by selected membrane processes. Four commercial polymeric NF and RO membranes (NF90, NF270, BW30 and XLE) were selected for the study. Palladium catalysts commonly used in Heck and Suzuki coupling reactions were selected. These are Pd(OAc)2, Pd(OAc)2(PPh3)2, PdCl2 and Pd(PPh3)2Cl2. A range of organic solvents were also selected for the study. All the membranes were characterized for pure water permeability, pure solvent permeability, swelling, surface morphology and chemical structure. The chemical and catalytic properties of the catalysts were determined. Catalytic activity was investigated by performing coupling reactions. These catalysts generally performed well in the Heck coupling reaction with sufficient yields realized. The catalysts showed poor activities in the Suzuki and Sonogashira coupling reactions. These coupling reaction systems were affected by rapid palladium black formation. vi Catalyst retention studies showed the influence of membrane-solute interactions such as steric hindrance and size exclusion. The larger catalyst, Pd(OAc)2(PPh3)2 was rejected better by all the membranes irrespective of the solvent used. The smaller catalyst, Pd(OAc)2 was the most poorly rejected catalyst. This catalyst showed signs of instability in the selected solvents. An interesting finding from this study is that of higher rejections in water compared to other solvents for a particular catalyst. In this regard, the influence of solventsolute effects was evident. Generally, higher rejections were observed in solvents with higher polarity. This has been explained by the concept of solvation. It has been shown that solvents with different polarity solvate solutes differently, therefore leading to a different effective solute diameter in each solvent. Catalyst separation using NF90 membrane was attempted for the Heck coupling reaction system. The reaction-separation procedure was repeated for two filtration cycles with rapid activity decline evident. This was regarded as very poor showing of the catalyst separation efficiency of the membrane. Other authors in similar studies using SRNF membranes have reported reaction-separation processes of up to seven cycles. This observation shows the inferiority of polymeric membranes in organic solvent applications such as catalyst separation.

L’environnement géostationnaire autour de la Terre présente des conditions complexes influençant les performances ainsi que la durée de vie des satellites. En vol et au cours du temps, les polydiméthylsiloxanes se dégradent ce qui se manifeste par une perte de souplesse, de transparence, ou encore une dégradation de l'état de la surface. Dans ce contexte, le but de cette thèse consiste à étudier l’évolution de la stabilité des polydiméthylsiloxanes en environnement géostationnaire simulé et d’autre part à proposer des solutions qui permettent de limiter la dégradation des propriétés d’intérêts technologiques, optiques en particulier. La stabilisation des polydiméthylsiloxanes soumises aux irradiations UV par l’incorporation de différentes structures d’additifs (Hindered Amine Light Stabilizers, absorbeurs UV, nanocristaux de cellulose) a été étudiée. Une autre approche pour augmenter la stabilité des polydiméthylsiloxanes aux rayonnements UV a été envisagée avec le remplacement du système catalytique actuellement utilisé (catalyseur de Karstedt) par l’emploi de dérivés organométalliques à base de Rhodium ou de Platine. Des solutions concernant la stabilisation de ces polydiméthylsiloxanes aux irradiations H+, comme l’ajout d’additifs tels que le polystyrène, les silsesquioxanes ont également été proposées. / The geostationary environment around Earth is complex which strongly influences the satellites performances and lifetime. In flight and over time, polydimethylsiloxanes exhibit degradations like a loss of flexibility and transparency, or a deterioration of the surface state. In this context, the aim of this work was to study the evolution of polydimethylsiloxanes stability in geostationary environment to find solutions to limit the degradation of interest technological properties, in particular the optical one. The stabilization of silicone resins under UV irradiation has been performed by the incorporation of different additives such as Hindered Amine Light Stabilizers, UV Absorbers and cellulose nanocrystals into the PDMS matrix. Generally, polydimethylsiloxanes networks are obtained by hydrosilylation with highly active Karstedt catalyst. Various organometallics derivatives based on Rhodium and Platinum were studied as alternative catalysts for the cross-linking of polydimethylsiloxane in order to improve the UV stability. Finally, different solutions concerning the stabilization of polydimethylsiloxane to proton irradiation, such as the addition of various additives like polystyrene or silsesquioxanes have been investigated.

Submitted by Jos? Henrique Henrique (jose.neves@ufvjm.edu.br) on 2017-06-02T20:34:08Z No. of bitstreams: 2 camila_diana_lima.pdf: 4383425 bytes, checksum: a00aa24c475acb8858df11e235a0c29c (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Rodrigo Martins Cruz (rodrigo.cruz@ufvjm.edu.br) on 2017-06-14T19:40:25Z (GMT) No. of bitstreams: 2 camila_diana_lima.pdf: 4383425 bytes, checksum: a00aa24c475acb8858df11e235a0c29c (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2017-06-14T19:40:25Z (GMT). No. of bitstreams: 2 camila_diana_lima.pdf: 4383425 bytes, checksum: a00aa24c475acb8858df11e235a0c29c (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2017 / O presente trabalho descreve o estudo de novas metodologias para obten??o de ?steres benz?licos e ?steres met?licos de ?cidos graxos (biodiesel) utilizando o NbCl5 s?lido e catalisadores heterog?neos ?cidos. No estudo, o NbCl5 s?lido foi utilizado como reagente, e nos outros m?todos foi empregado um catalisador de ni?bio enxertado em s?lica e um catalisador de grupos sulf?nicos imobilizado em s?lica. Nos processos heterog?neos a SiO2 (507 m2g-1, ?rea espec?fica) utilizada como suporte dos catalisadores, foi produzida a partir de areia constru??o e carbonato. O NbCl5 e os grupos ?SO3H foram imobilizados diretamente ? temperatura ambiente na SiO2, formando respectivamente o SiO2-Nb, com 412 m2g-1 de ?rea espec?fica e o SiO2-SO3H, com 115 m2g-1 de ?rea espec?fica. Nas esterifica??es utilizando NbCl5 s?lido foi determinado que para a obten??o de rendimentos razo?veis de ?steres de benz?licos (>85%) e ?steres met?licos (>70%) em rea??es a temperatura ambiente, a propor??o m?nima em moles de NbCl5:?lcool benz?lico deve ser 1,5:1,0 e para obten??o dos ?steres met?licos a propor??o de 1,5:6,0. Nas metodologias aplicando os catalisadores heterog?neos foi utilizada uma quantidade de 7% (m/m) do catalisador SiO2-SO3H para catalisar a esterifica??o de diferentes ?cidos carbox?licos com ?lcool benz?lico. E para as mesmas rea??es com o catalisador SiO2-Nb foi utilizada uma raz?o de 10% (m/m) do catalisador. Ambos os processos foram realizados sob refluxo na aus?ncia de um solvente; rendimentos muito semelhantes foram obtidos apesar do catalisador SiO2-SO3H possuir uma ?rea superficial muito menor que o catalisador SiO2-Nb. / Disserta??o (Mestrado) ? Programa de P?s-gradua??o em Biocombust?veis, Universidade Federal dos Vales do Jequitinhonha e Mucuri, 2017. / The current work describes the study of new methodologies for obtaining benzyl esters and methyl esters of fatty acids (biodiesel) using solid NbCl5 and heterogeneous acid catalysts. In this study, solid NbCl5 was used as a reagent, and in the other methods a silica grafted niobium catalyst and a sulphonic group catalyst immobilized on silica were used. In the heterogeneous processes the SiO2 (507 m2g-1, specific area) used as support of the catalysts, was produced from sand building and carbonate. The NbCl5 and the -SO3H groups were directly immobilized at room temperature in SiO2, forming respectively SiO2-Nb, with 412 m2g-1 of specific area and SiO2 -SO3H, with 115 m2g-1 of specific area. In the esterifications using solid NbCl5 it was determined that in order to obtain reasonable yields of benzyl esters (>85%) and methyl esters (>70%) in reactions at room temperature, the minimum mole ratio of NbCl5/benzyl alcohol should be 1,5:1,0 and in the obtainment of the methyl esters at a ratio of 1,5:6,0. In the methodologies applying the heterogeneous catalysts to an amount of 7% (w/w) of the catalyst SiO2 -SO3H to catalyze an esterification of different carboxylic acids with benzyl alcohol. Both processes were performed under reflux in the absence of a solvent; very similar yields were obtained although the SiO2-SO3H catalyst had a much lower surface area than the SiO2-Nb catalyst.

<p dir="ltr">The recently developed in this group, new method of generating cobalt and nickel vinylidene complexes in situ from 1,1-dichloroalkenes and their catalytic transfer reactions has proven to be a fertile ground for discovery of many useful transformations. In this dissertation, further studies of their reactivity and mechanisms are discussed based on the findings from several methodology projects. The use of chiral ligand enables asymmetric vinylidene transfer reactions and with symmetrical (Z)-alkenes as substrates, the products are methylenecyclopropanes with axial chirality (Chapter 2). DFT studies unveil the unique model of asymmetric induction where the substituent on the vinylidene substrate plays a crucial role. These products were intriguing due to their potential applications in many fields as well as their chirality transfer reactions that can provide diverse building blocks, but they were previously unobtainable. In Chapter 3, the finding of a new reducing condition for these general transformations was discussed in detail, followed by the uncovering of previously unknown effects of routinely used metallic Zn powder. This study provided a window to view the vulnerabilities in the general mechanism of this novel type of net-reductive reaction when ran under Zn reduction and explains some of the previously mysterious ligand effects. The new reduction condition runs under photoexcitation and is a Lewis acid free medium that can allow the discovery of new reactions. In Chapter 4, the above alternative reduction condition was applied to address the yield problem of a [2+2+1] cycloaddition reaction of vinylidenes with 1,6-enynes. This reaction was also found to work successfully in an intermolecular manner with excellent regioselectivity. Overall, this doctoral research work further expands this manifold towards the direction of asymmetric reactions and more complex cycloaddition reactions.</p>