Developing Nanofiltration Composite Membrane With Ultra-thin And High Crosslinking Skin Layer Based On TMPIP

In order to overcome the "trade-off" phenomenon of traditional membrane performance improvement approaches and prepare nanofiltration composite membranes with balanced performance, a novel aqueous monomer trimesoyl piperazine(TMPIP) with branched triimine structure was designed and synthesized to regulate the interfacial polymerization(IP) process. The trimesoyl chloride (TMC)/TMPIP composite membrane supported by polysulfone ultrafiltration membrane was prepared via IP. Then the morphology, chemical structure and charging property of TMC/TMPIP composite membrane were characterized, and the mechanism of the membrane formation was proposed, and the reason improving membrane performance was analyzed. The separation performance for non-charged organic matter and varied salts as well as chlorine resistance was also investigated. Ultimately, the membrane preparation and operation conditions were studied. Mainly results of the dissertation include the following aspects:(1) The newly designed aqueous monomer TMPIP was synthesized with TMC and1-piperazinecarbaldehyde via functional group protection method. FTIR.’H NMR and XPS, etc. verified the structure of the synthetic product. Free-standing experiment manifested that TMPIP had excellent film-forming property just like PIP, and could form a fine and ultra-thin film with TMC, thus it could be used for subsequent composite membrane preparation.(2) The TMC/TMPIP composite membrane was prepared via IP on polysulfone substrate. The XPS and SEM characterizations demonstrated TMPIP could form thinner and denser skin layer than that of conventional TMC/PIP composite membrane. And as a result, the performance parameters of TMC/TMPIP composite membrane against PEG200aqueous solution(R=86.0%, F=35.8L m-2h-1) were both higher than that of TMC/PIP composite membrane(R=82.7%, F=27.4L m-2h-1). The separation tests against Na2SO4、MgSO4、NaCl and MgCl2manifested that the TMC/TMPIP composite membrane was a typical negatively charged poly(piperazine-amide) nanofiltration possessing same rejection sequence with TMC/PIP membrane, and the former also showed superior performance. Due to the same carbon skeleton structure, TMC/TMPIP membrane inherited the excellent chlorine resistance property of TMC/PIP membrane.(3) The preparation condition studies showed that the optimal monomer concentrations of TMC and TMPIP are0.1%(w/v) and1.3%(w/v) respectively and the optimal posttreatment temperature and aqueous solution pH are50-60℃and11-12. In addition, operation conditions such as operation pressure, concentration and pH of feed solution also affected the membrane performance. The selection of appropriate operation conditons made the nanofiltration process more economically.The research results listed above demonstrated that the aqueous monomer TMPIP with branched triimine structure and relatively large molecular size could regulate the relatively independent factors, namely thickness and crosslinking degree of skin layer during IP, and thus formed a much thinner and higher crosslinking skin layer. As a consequence, the flux and rejection were both enhanced due to the superimposition effect of the two factors. This research proved that the bifactor regulation was an feasible and effective membrane performance improvement approach.