No description available.

No description available.

This thesis studies composite ionic liquid and polymer membranes (CILPMs} for gas separation and reactive separation membranes (RSMs) for reactive separation at elevated temperature. The aim of this investigation is to develop feasible CILPMs and RSM s, and optimize operating conditions to achieve high permeability and selectivity for gas separation. ClLPMs are composed of ionic liquids for facilitating gases through membranes and polymers as support. Ionic liquids: [C4mim][NTh], [C4mim j[PF6] , [C4mim][FAP] and polymers: PMDA-ODA PI, PBI were used to fabricate CILPMs in this project. A measurement rig was designed and built to measure permeabilities and selectivities of the CILPMs for H2, N2, CO, CO2 and CH4 at various pressures and temperatures. According to the results, gas permeability and selectivity of Cl l PMs were rarely changed with the pressure but greatly affected by the temperature. Normally, permeability increased and selectivity decreased with the rising of the temperature. The presence of ionic liquid in CILPMs had positive effect on CO2 permeation through the membranes, and therefore improved CO2 separation performance. However, H2 separation performance of the membranes was reduced by ionic liquids. RSMs combine the reaction and the separation in the membrane processes. In this project, RSMs were composed of CILPMs with dissolved catalysts for gas reaction. Ruthenium complexes were chosen as the catalyst for water gas shift reaction which transfers CO into H2 . The aim of reactive separation was increasing HJCO selectivity of the membranes and reducing the CO concentration in H2 stream to a very low level. A measurement rig for testing reactive separation was designed and built. According to the results, the water gas shift reaction occurred in RSMs increased the HJCO selectivity significantly under optimized conditions. A mathematical model was developed to simulate the reactive separation process and explain the results. CILPMs and RSMs showed improvements for gas separation and more research is required for optimizing these membranes.

No description available.

Due to the unique mechanism of oxygen permeation through dense ceramic membranes with the mixed ionic-electronic conducting property, these membranes have been widely studied for oxygen separation. It has been several decades since the use of a dense ceramic membrane reactor for methane conversion was proposed. One of the major reasons for persistent worldwide research efforts to develop such dense ceramic membrane reactors is the advantages that result from combining oxygen separation and catalytic reactions within a single unit. Besides the significant progress that has been made to date, more and more effort has been directed towards the development of more stable membrane materials with higher oxygen permeation, more advanced membrane micro-structures, membrane configurations with higher surface area per unit volume and better membrane reactor designs. By improving the aforementioned membrane and membrane reactor properties, lower operating temperatures, longer life time and reduced costs can be achieved. The evolution of membrane reactor designs has progressed through a number of stages, from an initial disk-type design to flat-sheet stack or tubular designs with higher surface areas. It is not until very recently that ceramic hollow fibre membrane with further increased surface area/volume ratios of up to 3000 m2/m3 has been developed. Although there has been a consistent progress in improving membrane configurations, the way that catalyst is employed in a membrane reactor is still based on packing catalyst particles on the membrane or inside the reactor. This occupies a considerable amount of space and as a consequence the actual surface area/volume ratio of a membrane reactor design is significantly lower than that of the membrane itself. In order to develop a highly compact membrane reactor design for partial oxidation of methane (POM) with the maximum possible surface area/volume ratio, this thesis focuses on the development of a functional ceramic hollow fibre membrane with a novel dual-layer structure. The outer layer is designed for oxygen separation while the inner layer can be considered as a catalytic substrate layer. Such dual-layer ceramic hollow fibre membranes can be fabricated by a novel single-step co-extrusion and co-sintering process. This new membrane fabrication process allows for the simultaneous formation of the dual-layer membrane structure with excellent adhesion between the two layers even at high operating temperatures. Moreover, as well as changes in the compositions of the membrane material, aspects of the membrane structure, such as the thickness of the outer oxygen separation layer, can be adjusted during the co-extrusion process, in order to achieve higher oxygen permeation and subsequently better reactor performance. Although the functional dual-layer ceramic hollow fibre membranes discussed in this thesis are designed for POM, there are generic advantages of such membrane structures and the membrane fabrication process. Therefore, membranes of this type can be transferred to other membrane processes of great importance, such as oxygen separation and solid oxide fuel cells (SOFC).

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.