Desalination by reverse osmosis using MFI zeolite membranes

doi:10.1016/j.memsci.2004.06.045

Journal of Membrane Science

Volume 243, Issues 1–2, 1 November 2004, Pages 401-404

https://doi.org/10.1016/j.memsci.2004.06.045 Get rights and content

Abstract

This paper reports an experimental study on the reverse osmosis desalination of aqueous solutions using α-alumina-supported MFI-type zeolite membranes. A Na⁺ rejection of 76.7% with a water flux of about 0.112 kg m⁻² h⁻¹ was obtained for a 0.1 M NaCl feed solution under an applied pressure of 2.07 MPa. For a complex feed solution containing 0.1 M NaCl + 0.1 M KCl + 0.1 M NH₄Cl + 0.1 M CaCl₂ + 0.1 M MgCl₂, rejections of Na⁺, K⁺, NH₄⁺, Ca²⁺, and Mg²⁺ reached 58.1%, 62.6%, 79.9%, 80.7%, and 88.4%, respectively, with a water flux of 0.058 kg m⁻² h⁻¹, after 145 h of operation at an applied pressure of 2.4 MPa.

Introduction

Zeolite membranes have been studied extensively for more than 15 years, mainly focusing on gas separation and liquid pervaporation processes. Recently, molecular dynamic simulation has shown that zeolite membranes are theoretically suitable for ion removal from aqueous solutions by reverse osmosis (RO) processes [1]. The simulation revealed that 100% Na⁺ rejection could be achieved on a perfect (single crystal), all-Si, ZK-4 membrane through RO. The separation mechanism of the perfect ZK-4 zeolite membranes is the size exclusion of hydrated ions, which have kinetic sizes (0.8–1.0 nm for [Na(H₂O)_x]⁺) [2] significantly larger than the aperture of the ZK-4 zeolite (diameter 0.42 nm). Kumakiri et al. [3] reported using an A-type zeolite membrane in RO separation of water/ethanol mixtures. The hydrophilic A-type zeolite (pore size ∼0.4 nm) membranes showed 44% rejection of ethanol and a water flux of 0.058 kg m⁻² h⁻¹ under an applied feed pressure of 1.5 MPa. However, experimental demonstration of RO desalination on zeolite membranes has not been reported so far.

Results of the computer simulation and experimental RO separation of water/ethanol mixtures on A-type membranes indicate the possibility for zeolite membranes to simultaneously separate ions and dissolved organic compounds from aqueous solutions by RO processes. Zeolite membranes may be used as an alternative to polymeric membranes for desalination of complex wastewaters, which contain organic solvents and radioactive elements, or when high temperature operation is desired. However, existing zeolite membranes possess an imperfect polycrystalline structure [4] and may be of different types with various pore sizes and Si/Al ratios. [5] Therefore, experimental investigation of the effectiveness of RO desalination using real zeolite membranes is necessary. This work experimentally demonstrates RO separation using an α-alumina-supported MFI-type zeolite membrane for solutions containing a single cation and multiple cations.

Section snippets

Materials and apparatus

α-Alumina supported MFI-type zeolite membranes (thickness ∼3 μm) were synthesized through in-situ crystallization. The detailed synthesis procedure is available in the literature [6], [7]. The disc-shaped alumina substrates were 28 mm in diameter and 2 mm in thickness with an average pore size of 0.1 μm and porosity of about 35%. The composition of the synthesis solution was 20 g SiO₂ + 100 ml (1 M) TPAOH + 1.4 g NaOH + 3.2 g H₂O. Hydrothermal treatment was conducted in an autoclave at 180 °C with

Conclusions

Reverse osmosis of aqueous solutions on MFI zeolite membranes was experimentally demonstrated in this study. High rejection values were obtained for a concentrated solution containing five different types of cations, including Na⁺, K⁺, NH₄⁺, Ca²⁺, and Mg²⁺. Results of this work show that zeolite membranes have great potential for applications in RO desalination of complex mixtures. The zeolite membranes, due to their excellent chemical and thermal stabilities, may be particularly useful for

Acknowledgements

This research was sponsored under contract no. DE-FC26-00BC15326, through the US DOE's National Petroleum Technology Office (NPTO), within the National Energy Technology Laboratory. The research was also partially supported by SURP/Sandia. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the US DOE's National Nuclear Security Administration under contract DE-AC04-94AL85000. We thank Ms. Liz Bustamante for editing the manuscript.

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Desalination by reverse osmosis using MFI zeolite membranes

Abstract

Introduction

Section snippets

Materials and apparatus

Conclusions

Acknowledgements

Microporous Mesoporous Mater.

Microporous Mesoporous Mater.

J. Membr. Sci.

Biophys. Chem.

A computer simulation study of the separation of aqueous solution using thin zeolite membranes

Mol. Phys.

Molecular simulation of osmosis, reverse osmosis, and electro-osmosis in aqueous and methanolic electrolyte solutions

Mol. Phys.

Application of a zeolite A membrane to reverse osmosis process

J. Chem. Eng. Jpn.