Preparation and characterization of NF composite membrane

doi:10.1016/S0376-7388(02)00120-5

Journal of Membrane Science

Volume 210, Issue 1, 1 December 2002, Pages 3-11

https://doi.org/10.1016/S0376-7388(02)00120-5 Get rights and content

Abstract

With a view to be able to prepare high performance nanofiltration membranes, we made experiments where NF composite membranes were prepared by interfacial polymerization, using ultrafilitration membrane as substrate and their performances such as water flux, retention of Na₂SO₄ and PEG 600 were studied. The results show that under an operational pressure of 0.6 MPa, water fluxes of NF-1, NF-2 and NF-3 are 4.1, 6.0 and 26.5 l/m² h, respectively, while the retentions of Na₂SO₄ are 78, 94 and 94%, respectively. The chemical composition and the surface image of NF membranes are obtained by using IR and atomic force microscope Also explored are the prospects of their applications in the dyeing industry.

Introduction

Nanofiltration membrane is a kind of pressure-driven membrane between reverse osmosis and ultrafiltration membrane. Because of its advantages, such as low operation pressure, high flux, high retention of multivalent anion salt and organic molecular above 300, relatively low investment and low operation and maintenance cost, it has given rise to worldwide interest.

Great importance is attached to R&D work on nanofiltration membrane in many countries around the world. A large variety of nanofiltration membrane have been developed and used in different separation applications. Companies in US and Japan are particularly successful in the commercialization of nanofiltration membrane [1], [2].

Composite membrane technique is one of the most effective methods to prepare nanofiltration membranes. A composite membrane is obtained by forming an ultra-thin dense layer on a porous substrate. Several methods can be employed to prepare composite nanofiltration membrane. Interfacial polymerization is often used in the preparation. The conception of interfacial polymerization was put forward by P.W. Morgan [3]. Polymerization reaction takes place at the interface of the two liquids which are insoluble to each other. The key of this method is to select the right partition coefficient of the reactants in the two-phase solution and to set the appropriate diffusion speed of the reactants so as to achieve the ideal degree of densification of the membrane surface.

The NS-100 membrane was the first successful example of an interfacially formed membrane, which had high rejection of salts [4]. After NS-100, many commercial composite membranes have been developed [5], [6], [7], [8], such as NF series made by Filmtec Corporation, NTR series made by the Nitto Denko Company and the UTC series made by Toray Industries, ATF series by Advanced Membrane Technology Inc. and so on. They all exhibit good fluxes and rejections of salt at low operation pressure and are already in mass production. However, the development of nanofiltration membrane in China still remains at the stage of laboratory experimentation and there is a long way to go before it can be commercialized.

As we know, the controlling of the membrane surface morphology is very important to the performance. In 1988, Albrecht applied the atomic force microscope(AFM) in the observation of surface layer for the first time [9]. It opened a new door to the study on the membrane morphology. Bowen et al. [10] analyzed the pore size and its distribution in RO, UF, and NF membranes using AFM. Hirose et al. [11] found that the water flux increased as the roughness of membrane increased, when they were observing the surface of RO membrane. This theory was confirmed by the consequent researches [12].

Drawing on the experience of preparing UF membranes for many years, we prepared NF series membranes by the method of interfacial polymerization, using UF membranes as the substrate. SPES and PVDF ultrafiltration membranes were chosen as substrates and bisphenol-A (BPA) and isophthaloyl chloride and terephthaloyl chloride [13], [14], trimesoyl chloride, amine and/or piperazine were used to form three reaction systems for interfacial polymerization. Systematic research was carried out on the relationship between the performance of NF membranes and polymerization conditions. The performance of NF membrane was characterized and its dense layer’s chemical structure and image were observed by IR and AFM. The relationship between the dense layer’s chemical structure and the performance of NF membrane was explored, and at last, the prospect of NF membranes’ application in the dyeing industry was touched on.

Section snippets

Materials

BPA was provided by Mitsui Firm, Japan; isophthaloyl chloride (IC) and terephthaloyl chloride (TC) were obtained from Shanghai Celluloid Works; trimesoyl chloride was obtained from Shanghai Carbonization Works; metaphenylene diamine was obtained from Shanghai Wulian Chemical Works; piperazine hexahydrate was purchased from Shanghai Chemical Reagent Company; polyethylene glycol 600 of analytical purity grade was supplied by Shanghai No. 2 Detergent Works; toluene of chemical purity grade was

The factor of operation pressure

Under different operation pressures, the water flux and the retention of salts were measured. The concentration of Na₂SO₄ was 0.1%. The results were shown in Fig. 1, Fig. 2.

A conclusion could be reached from Fig. 1, Fig. 2. The flux of NF membrane increased as the operation pressure increased and the order was NF-3>NF-2>NF-1. But their desalination ratios were different. Their retention of salt for NF-2 and NF-3 increased as operation pressure increased while for NF-1, the retention decreased

The research on the application of NF membrane in dyeing industry

At present, large quantities of NaCl is generated during acidic dye synthesis processes. The presence of NaCl will lower the quality of dye. In traditional operation unit, ion exchange resins were used to remove NaCl. However, because of the large amount of NaCl being produced, the quantity of exchange resin as well as the energy consumption is large. An attempt to use NF-3 in treating dyeing waste water was made as part of our experiment and the data were shown in Table 5. Data were provided

Conclusion

NF series membranes were prepared by the way of interfacial polymerization and its performances were characterized systematically in our experiments. The results showed that NF series membranes all exhibited high rejection of electrolytes including divalent ions. NF-3 demonstrated high water flux and high rejection of electrolytes including divalent ions simultaneously. For NF-3 under 0.6 MPa, the water flux value of 27.0 l/m² h could be obtained, the retention of Na₂SO₄ could be 94%, and the

Acknowledgements

Xuemei Liang, Xiaodong Zhai, Bingfang Wang participated in this work, we thank for their help.

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Preparation and characterization of NF composite membrane

Abstract

Introduction

Section snippets

Materials

The factor of operation pressure

The research on the application of NF membrane in dyeing industry

Conclusion

Acknowledgements

J. Membr. Sci.

Polymer

J. Membr. Sci.

Composite reverse osmosis and nanofiltration membranes

J. Membr. Sci.

Nanofiltration extends the range of membrane filtration environmental progress