| The main trend of reverse osmosis (RO) technology is the development of the RO membrane with high permeation and reasonable rejection. The traditional composite membrane can improve certain property by physical or chemical modification, and the another property will be expensed as the trade-off phenomenon. The hyperbranced polymer (HP), due to its three-dimensional network structure, has been used as an additive or cross-linking agent in membranes preparation. However, because of the large steric hindrance, the as-prepared membrane is constrained to the nanofiltration composite membranes.In this work, in order to prepare the high performance RO membranes, two4-amino pyridine derivatives,4-pyrrolidinopyridine (4-PPY) and4-(dialkyamino) pyridine, were adopted to catalyze the interfacial polymerization between HPEA (hyperbranched aromatic polyesteramide)/TMC and PEI (hyperbranched aliphatic polyethyleneimine)/TMC, respectively. Scanning electron microscope (SEM), FTIR spectroscope (FTIR), atomic force microscope (AFM) and contacting angle test were carried out to study the structure and performance of composite membranes. The separation performances to Na2SO4, NaCl, MgSO4, MgCl2and PEG200aqueous were tested. In further, the preparation conditions, as well as the physicochemical characteristics of membranes were also investigated. Further’s more, according to the chemical structure, the catalytic mechanism of4-amino pyridine derivatives in this interfacial polymerization was given out.1. Study on the catalytic property of4-amino pyridine derivatives. Catalyzed by4-PPY, HPEA and TMC can crosslink into integrated and continuous RO composite membrane; Catalyzed by DMAP, the rejection of PEI/TMC composite membrane was doubled.2. Study on the separation performance of HPEA/TMC and PEI/TMC composite membranes. The4-PPY catalyzed HPEA/TMC composite membrane exhibits certain properties of ultra-low-pressure RO membrane. Under0.6Mpa, the rejections to Na2SO4, NaCl, MgSO4were up to90%, with the flux at30-40L-m-2·h-1. The rejection of PEG200was increased to98%, flux high to40L·m-2·h-1. The separation performance of PEI/TMC composite membrane catalyzed by DMAP was significantly increased. Apart from the doubles increase of the rejection to Na2SO4and NaCl, the rejection to MgSO4and MgCl2were also improved from80%to more than90%, with the flux at30-40L-m-2·h-1. The rejection of PEG200was high to93%, flux at38L-m-2·h-1.4. Study on the optimization of preparation conditions. The optical preparation conditions of HPEA/TMC composite membrane were as following: mass fraction of HPEA to4-PPY at8%,2.0%(w/v) HPEA in water,1.0%(w/v) TMC in hexane, reacting to30min. The optimal preparation conditions of PEI/TMC composite membrane were as following:mass fraction of PEI to DMAP at8%,1.0%(w/v)PEI in water,0.3%(w/v)TMC in hexane, reacting time at4min, curing temperature and time at60℃and20min, respectively.5. Study on the catalytic mechanism of4-amino pyridine derivatives in the HP-based interfacial polymerization. During the phase transfer reaction and acylation, by the ion pair between HPEA and the N-acylpyridinium salt with TMC,4-amino pyridine derivatives were effective to reduce the activation energy of this two reactions, remarkably enhancing the cross-linking of the active layer.6. HPEA/TMC composite membrane posses high resistance to active chloride, while PEI/TMC composite membrane still maintain stable properties under low/high pH or high temperature.From the above research results, it is reasonable to apply4-amino pyridine derivatives into HP based interfacial polymerization to prepare RO membrane of high performance. As the phase transfer catalyst and acylation catalyst,4-PPY and DMAP are able to overcome the large steric hindrance of hyperbranched polymers, thus increase the cross-linking degree of the three-dimensional network, which provides a possibility to prepare high performance composite membrane via interfacial chain propagation polymerization. |
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