Separation of Hazardous Liquid Mixtures by Pervaporation
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1.4 CHEMICAL SCIENCES
Pervaporation is a membrane separation process used to separate liquid mixtures. Separation is achieved by establishing a concentration vapour-pressure gradient across the membrane. A number of membranes were examined for their potential use in pervaporation. A synthesised poly-4-methyl-1-pentene (TPX) membrane and a polyvinyl-alcohol membrane, and commercially available membranes such as Gesellschaft Fur Trenntecknik (GFT) 1000 ( a polyvinyl alcohol membrane) and GKSS Forschungszentrum “ Symplex” membrane ( a poly-electrolyte membrane) were used to separate water from ethyl acetate, methyl iso-butyl ketone, ethylene glycol, methyl ethyl ketone, iso-propyl alcohol, cyclohexanol, cyclohexanone and butyl acetate respectively. Synthesised membranes for example polyurethant (PU) and polydimethylsiloxane (PDMS) were used to separate iso-propyl alcohol, n-butanol, iso-butanol and cyclohexanol from water. All membranes were used in the temperature range 30 to 80°C/ Gas chromatography and Kark Fisher titration were used to analyse the resulting permeate and retentate samples. The separations were characterised by plotting feed concentration versus permeate concentration, feed concentration versus selectivity, permeante versus feed concentration, and cumulative time versus percentage of permeating component remaining. Flux values ranging from 0.096 kg/m2.hr for the separation of water from iso-propanol at a feed concentration of 5.02% w/w water and temperature of 40°C to 0.0006 kg/m2.hr for the separation of water from butyl acetate at a feed concentration of 0.91% w/w water and temperature of 50°C were obtained. Selectivity values ranging from 1.5x106 to 10 were obtained. The highest selectivity was recorded for the separation of water from methyl ethyl ketone using a GKSS membrane at 30°C with a value of 1.5x10(6) at a feed concentration of 1% w/w/ water. A plot of inverse temperature against natural log of flux allowed calculation of the activation energy of permeation. Values of 0.24 to 59.35 kJ/mole was obtained. Sorption experiments were carried out and the order of preferred sorption of components on to membranes was determined. The membranes were physically and chemically characterised by infra-red spectroscopy, NMR, mass spectroscopy, scanning electron microscopy, differential scanning calorimetry and sorption experiments. Glass transition temperatures were obtained. Aspen Model Manager Plus was used to calculate the energy requirements of distillation and liquid-liquid extraction to separate the above mixtures and compared to the energy requirements of pervaporation to separate the same mixtures. The energy requirements for pervaporation was 1.6 to 24 times less than other separation techniques. The experimental data obtained can be used to design a pervaporation of hybrid pervaporation system for the treatment and recovery of hazardous organic liquid waste.
Lakes, R.:Separation of Hazardous Liquid Mixtures by Pervaporation. Masters Thesis. Dublin Institute of Technology, 1999.
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