Study On Preparation And Characterization Of Glycolchitin/Polyacrylonitrile Composite Nanofiltration Membrane

Nanofiltration(NF), a new type of separation membrane technology developed since 1980's, is a pressure driven process that forms the transition between ultrafiltration and reverse osmosis, and NF supplied a gap between them.Chitin derivatives are excellent membrane materials with broad application prospects for their good abilities of moisture retention, filming performance, biocompatibility and being nontoxic. In this paper, two novel negatively charged composite membranes are prepared for the first time, whose active layer material is glycolchitin, cross-linking agents are epichlorohydrin (ECH) and diisocyanate (TDI), supporting layers is polyacrylonitrile(PAN) UF membrane. And also the application of the composite membrane in the treatment and recycling of textile wastewater is studied. The whole paper contains three parts:1. Preparation and characterization of glycolchitin/PAN composite membrane cross-linked by epichlorohydrinA novel composite nanofiltration membrane is fabricated by coating solution of glycolchitin onto PAN UF membrane and subsequently cross-linked by epichlorohydrin (ECH). Effects of membrane making and operating conditions on performances of the composite membrane are studied, and the structure of the membrane as well. The results suggest that the composite NF membrane with excellent rejection performance should be prepared while glycolchitin concentration is 1.5wt﹪, the membrane is dried for 2h at 50℃, ECH concentration is 1.0wt%, the acetone concentration is 75wt% while pH is 10, then cross-linked for 24h at 50℃, and heat treated for 20 min at 50℃.Rejections of the composite membrane of Na2SO4, K2SO4, MgSO4 , NaCl , KCl and MgCl2 solutions (1.0g?L) are 95.2﹪,91.5﹪,41.0﹪,31.1﹪,31.0﹪and 20.1﹪at 25℃under 1.0MPa;and permeation fluxes are 10.0,10.1 ,19.2,19.7,20.8 and 13.0 L?m2·h, respectively. The electro-osmotic trans- mission coefficient (β) of the negatively charged membrane is about -2mV/Mpa and the molecular weight cut-off is about 540,the pore size is about 0.73nm,the total roughness was 0.0191μm and the average roughness is 0.0108μm, the swelling degree is 46.6%.The results suggested that rejection performance is governed by Donnan effect.2. Preparation and characterization of glycolchitin/PAN composite membrane cross-linked by diisocyanate (TDI)A novel composite nanofiltration membrane is fabricated by coating solution of glycolchitin onto PAN UF membrane and subsequently cross- linked by diisocyanate (TDI).Effects of membrane making and operating conditions on performances of the composite membrane are studied, and the structure of the membrane as well. The results suggest that the composite NF membrane with excellent rejection performance should be prepared while glycolchitin concentration is 2.4wt﹪, the membrane is dried for 2h at 50℃,TDI concentration is 1.3wt%, the acetone concentration is 80wt% while pH is 8, then cross-linked with TDI for 15h at 50℃,and heat treated for 5min at 50℃. Rejections of the composite membrane of Na2SO4, K2SO4 , MgSO4, NaCl, KCl and MgCl2 solutions (1.0g?L) are 92.3﹪,90.6﹪,41.1﹪,21.7﹪,19.9﹪,19.6﹪and 18.6%;and permeation fluxes are 4.0,4.9,4.6,5.1,4.8,5.0 and 5.2 L?m2·h, respectively. The electro-osmotic transmission coefficient (β) of the negatively charged membrane is about -8mV/Mpa and the molecular weight cut-off is about 490,the pore size is about 0.67nm,the total roughness is 0.00985μm and the average roughness is 0.00934μm, the swelling degree is 32.8%.The results suggest that rejection performance is governed by Donnan effect.3. Study on treatment and recycling of textile wastewater by glycolchitin/PAN composite NF membraneGlycolchitin/PAN composite NF membrane cross-linked by ECH is used in the treatment and recycling of the textile wastewater, including removal of total phosphate,total soluble nitrogen in NO3- and NO2-,CODCr ,aniline,inorganic salt and chroma. The results suggest: when operating pressure is1.5MPa, flux is 40 L/h, the removal rate of inorganic salt,aniline and CODCr are 47.0%,67.9% and 85.2% ,respectively. The rejection to total phosphate and nitrogen in NO3- and NO2- are 97.8%and 29.7%, and the chroma removal rate is nearly 100%.In this way, the textile wastewater can be used again, which avoided the waste of water resource. The method of composite membrane preparation supply a new method for removal of organic matter,total phosphate ,total soluble nitrogen in NO₃^- and NO₂^- and chroma in the sewage. Which is hopeful to apply in water treatment.