Membrane based gas separations are proven to be technically attractive because of their simplicity and low energy costs, although they are often limited by insufficient flux, selectivity and stability. During the past thirty years, major developments in this technology have been made by developing high flux asymmetric membranes, and large surface area membrane modules. Today, in the present market, the sales of the membrane gas separation equipments have grown to become a $150 million per year business, and substantial growth in the near future is likely. More than 90% of membrane gas separation business involves the separation of non-condensable gases, i.e. nitrogen from air, carbon dioxide from methane, and hydrogen from nitrogen, argon, or methane. However, a large potential market for membrane gas separation lies in refineries. The separations of hydrogen/hydrocarbon and olefin/paraffin are regarded as import processes (although challenging ones) in the petrochemical industry. The membrane based separation p~ocess to sepfirate olefins from paraffins is likely to be developed to the commercial state in the next few years. Industry's demands for increasing the separation effectiveness and productivity have encouraged conducting research into development of new membrane materials. Polyaniline is regarded as so far the best alternative for gas separations, since the molecular spacing of polymer chains can be controlled by its interesting doping/dedoping chemistry. A novel method to make reproducible defect-free dense self-supported polyaniline films with the thicknesses between 2 and 6 IJm, and polyaniline nanofilm membranes with selective polyaniline layer thicknesses between 300 and 800 nm supported on a porous polyvinylidene fluoride (PVDF) substrate is developed. (Continues...).

An experimental study was carried out into the effect of fluid properties upon mass transfer coefficients in packed distillation columns. A column consisting of 19 stainless steel discs supported in a vertical row, with each disc at right angles to its neighbour, was used for this purpose. This assembly was contained in a 1 in. diameter glass tube which allowed observation of the liquid running over the discs. Distillation runs were made with the systems ethanol/water, isopropanol/water, ethanol/benzene and benzene/n-heptane. With surface tension negative mixtures, sprays of droplets were emmitted from the liquid as it ran over the junctions between the discs. The phenomenon was filmed using high speed cine photography. In order to eliminate hydrodynamic effects in droplet formation the surface of a stationary sessile drop supported on a horizontal disc under total reflux conditions was also observed. Small droplets were seen to be ejected from the surface of the sessile drop with surface tension negative conditions, and again filmed using high speed cine photography. The additional interfacial area caused by droplet formation in the disc column was shown to be negligible. Experimental rashl ts, in the disc column wi th systems in which the vapour phase controls the mass transfer rate were used to establish correlations for the vapour side mass transfer coefficient.

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This thesis presents a novel methodology for synthesis of sequences separating ternary heterogeneous azeotropic mixtures employing distillation columns and decanters. Column design methods are developed for assessing feasibility of proposed separations and for identifying economically attractive designs of columns in sequences. Design methods for advanced and complex configurations of heterogeneous azeotropic columns exploit the boundary value method. The methods can be used for establishing product feasibility in a column and evaluating a column design on a basis of cost. A new design method is developed for columns with integrated decanters, in which the existence of two liquid phases is not limited to the decanter. For a column with multiple heterogeneous stages, multiple feasible designs can be generated, corresponding to different numbers of heterogeneous stages and various ratios of two liquid phases on the heterogeneous stages. The resulting feasible designs have different total numbers of stages and feed locations for a given set of product specifications and reflux ratio. The new design method is extended further for double-feed columns and columns with intermediate decanters. Case studies indicate that the presence of heterogeneous liquid in columns considerably improves the economic performance in some cases. The economic performance is also affected by the number of heterogeneous stages. The number of heterogeneous stages that leads to near-optimal designs can be determined using the new column design methods. For some mixtures, employing complex column configurations makes the separation feasible and provides significant cost savings. For other mixtures, the complex columns may not be as attractive as single-feed columns with integrated decanters. Column design details and other results form the column design methods are used successfully to initialise rigorous simulations and to facilitate simulation convergence.

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