The Study On Gas Permeation Characterization Of Poly Phosphazene Membrane And Its Bubbleless Aeration Efficiency In Water

Bubbleless aeration using membrane which is made of hydrophobic hollow fiber membrane to feed o_xygen into water. The fiber lumens were pressurized with pure o_xygen and water was pumped over the surface of the film, pure o_xygen was maintained at a pressure below the bubble point, so did the velocity of water. The high o_xygen concentration gradient encouraged the o_xygen to diffuse across the membrane wall, and to dissolve directly into the water without the formation of bubbles. Tthe mass transfer coefficient comes to optimization. Comparing to the traditional bubble aeration, the bubbleless aeration has advantages of high o_xygen transferring efficiency, no foam producing , good resistance to bacterial contamination and low energy e_xhaustion.Choose the right material is very important for bubbleless aeration. The advantage of polyphosphazenes such as e_xcellent durability and long-term stable are due to the specific main-chain structure, so it is a suitable membrane for gas separate. When the phosphorus atoms in polyphosphazenes with chain and ring structures are linked to various substituents, the polymers display versatile functions for corresponding changes of the physical and chemical properties, so it is hopeful to find a high o_xygen permeation material for bubbleless aeration to solve the hypo_xia in temporary-keeping of fish.Poly [(tetrafluoropropoxy)_2-x (trifluoroethoxy)] phosphazene and Poly[(hexafluoroisopropyloxy)_2-x(trifluoroethoxy)_x]phosphazene were synthesized via different substituent ratio nucleophilic substitution of polydichlorophosphazene(PDCP) which prepared by vacuum thermal ring-opening polymerization of he_xachlorocyclotriphosphazene(HCCP), The final substituted polyphosphazene products were purified through the THF - benzene precipitation to remove impurity. 31P NMR was used to assure the purification. The structure of this polymer was characterized by 1H NMR,FTIR,XRD,GPC and DSC. Gas permeability coefficient of N₂,O₂,CH₄,CO₂,He,H₂ in these polymers at 20℃were measured by permeate gas pressure method. The results shown that the O₂ permeability coefficient of poly[(tetrafluoropropo_xy)2-_x(trifluoroethoxy)_x]phosphazene was 20 barrer, while the O₂ permeability coefficient of Poly[(hexafluoroisopropyloxy)_2-x(trifluoroethoxy)_x]phosphazene was 27 barrer, these two polymers demonstrated to be a promising oxygen-rich material, and were suitable for membrane bubbleless aeration.The bubbleless aeration systerm which was made of hydrophobic hollow fiber membrane was equipped. The influence of water flow and oxygen pressure to the oxygen transfer efficiency in freshwater and seawater were researched. Finally, we found that, when controlled the oxygen below the bubble point, the oxygen transfer efficiency gradually increased with the increase of flux of water and also with the increase of oxygen pressure at the same. While the pressure above the bubble point, the oxygen transfer efficiency gradually increased with the increase of oxygen pressure, and came to the maximum for the initial stage. We also find that the oxygen transfer efficiency of seawater was better than freshwater.Finally, membrane bubbleless aeration was applied in high density temporary-keeping of fish, the result showed that it increased the oxygen concentration and the fish livability efficiently.