| Pervaporation have been applied successfully in alcohols dehydration, removal of VOCs from water, and is particularly promising to application for azeotropic, near-boil, or isomeric compounds mixtures separation because of simple equipment, low energy consumptions, no pollution. It is considered as the third era membrane technology which will replace traditional distillation. Nowadays, increasingly energy crisis becomes a good chance to impulse the pervaporation membrane technology widespread industrial promotion. It becomes very important to prepare membrane and module with high separation properties, if we want to break the present state of few pervaporation membrane kinds, and gain large-scale application. The target of this paper is mainly focus on preparation high properties hollow fiber composite membrane and hollow fiber modules for alcohols aqueous dehydration.Firstly, viscometry and Fouier Transform Infrared (FTIR) and Scanning electro microscopes (SEM) investigated the range of blend compatibility of poly (vinyl alcohol) and sodium alginate. Blend ratio, kinds of crosslinking agent, content of crosslinking agent and layer thickness has remarkable effects on the separation properties. Experimental results showed that permeation flux increased and separation factor decrease with increasing PVA content in membrane. The separation factor increase, permeate flux decrease with increasing blend ratio of SA in blend membrane. The membranes crosslinked by maleic acid, citric acid and glutaraldehyde show different separation properties. The membrane crosslinked by maleic acid have 1400 g/m2h permeate flux, showing good permeate flux. While the membrane corsslinked by glutaraldehyde has 3250 separation factor, showing higher selectivity. With increasing content of crosslinking agent (maleic acid), permeate flux decreases, separation factor increases. The crosslinking mechanism of PVA-SA with maleic acid was analyzed by FTIR. Hydroxyls of PVA-SA were reacted by acid anhydride of maleic acid to form ester bond. Optimized preparation conditions of hollow fiber composite membrane were gained by experiments.PVDF hollow fiber membranes were prepared by dry-wet phase inversion. The effect on membrane structure of PVDF content, additive, take-up rate, bore fluid extrusion rate and crinkling were investigated. The optimizing preparation conditions were found. The effect of support membrane on separation properties were studied by comparison three kinds of hollow fiber membrane used as support membrane. It can provide gist of screening of hollow fiber support membrane. The separation properties of plate-frame module were compared with those of hollow fiber module which membrane modules have same membrane area. The results showed that permeate flux of the plate-frame module is bigger than that of hollow fiber module, while the separation factor is smaller.PVA-SA hollow fiber composite membranes were prepared by the optimizing preparation conditions. The dehydration of ethanol, isopropanol, n-butanol, ter-butanol and methanol aqueous were investigated with this membrane. The effects of alcohol concentration, operating temperature and feed velocity on separation properties were studied. Separation differences of four kinds of alcohols were explained by group contribution and viscometry. Membrane durability properties and batch dehydration were investigated. With alcohol concentration at 90 wt% in the feed at 45°C, the separation factors and permeation fluxes were 1727, 414 g/m2.h;606, 585 g/m2.h;725, 370 g/mlh;and 384, 384 g/m2.h for isopropanol, n-butanol, ter-butanol and ethanol water mixtures through the blended membranes, respectively.Different membrane area modules were prepared by coating PVA-SA on PAN hollow fiber outer surface. Scale-up effects of hollow fiber pervaporation were studied by testing separation properties of different membrane area module. The result showed that the permeate flux decreases, separation factor increase with increasing module membrane area. The bigger temperature drop and pressures decreasing of big module caused this phenomenon. The separation properties of big module were investigated at different operating temperature and feed concentration. According to large numbers of experimental data, model equation of water flux and alcohol flux and water concentration in permeate were gained with quadratic term fitting. The model equations were validated by the comparison the calculated valueand experimental value.Permeate flux equation were gained according to the solution-diffusion model, when the feed pass through the shell side, permeate flow through the bore side, mass balance, momentum balance and energy balance were established on feed side and permeate side, model equation of organics mixtures dehydration by hollow fiber membrane were established. By solving these equation numerically, the change conditions of feed concentration, temperature, permeate velocity, pressure of permeate and permeate flux along the axial of hollow fiber module were gained. Comparison calculated data with the experimental data;many conclusions can be used to instruct module design. |
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