The Studies Of Proton Transfer And Its Effects On Other Ion Transport In Reverse Osmosis Composite Membrane

Aromatic polyamide contains amide groups (-CO-NH-). It has excellenthydrophilic property, mechanical stability, thermal stability and hydrolyticstability, and can be used in reverse osmosis process. Now, the aromaticpolyamide reverse osmosis membrane has become a leading membraneproduct, and it is used in desalination, water treatment of electric power plants,preparation of pure water and other fields. The application pH range of thearomatic polyamide membrane is generally 2-11 and its separationperformances are different under different pH. Most studies only took pH as acommon factor, there hasn't been in-depth, systematic research toward it,which has affected the proper use of the membrane. The proton transfer andits effects on other ion transport in reverse osmosis composite membranewere studied in this thesis.Under the conditions of 0.5MPa and 25℃, the zeta potential of themembrane in the pH range of 2-12 was investigated. The change ofswellability of the membrane with pH was also studied. When the pH waslow, the membrane surface was postively charged. When the pH was high, themembrane surface was negatively charged. The isoelectric point of membranewas about 4.3. At pH = 2 or 12, the membrane swellability increased, itsrejection of neutral solutes decreased.The rejection effect of H⁺ under different pH was investigated. For thehydrochloric acid system and sulfuric acid system, whether pure water or saltsolution, H⁺ was rejected negatively in the pH range, except pH = 2. Inaddition, the impact of negative rejection of H⁺ on membrane fouling wasresearched, the expriments proved that the negative rejection of H⁺ wouldincrease the membrane fouling.The pure water flux, water flux of 0.004mol / L of NaCl, KCl, CaCl₂, Na₂SO₄, and B(OH)₃solution and the rejection of various ions were measuredunder different pH. Because the electrical property and swellability ofmembrane were different, its separation performances of ions with differentradius, valence, electrical property, existence form were different. In addition,the solution flux also changed with pH.Finally, the pure water flux, water flux of KCl, CaCl₂, Na₂SO₄ solutionand the rejection of K⁺ , Ca²⁺ , SO₄^2- under the conditions of differenttemperature, pressure, concentration and compaction were measured at pH =3, 7 and 11 respectively. The combined effects of pH and other factors on themembrane separation were studied. The results showed that the effects ofpressure and pH or temperature and pH on membrane separation wereindependent, while concentration and pH or compaction and pH played across role in membrane separation performances.