Investigation of the effects of ion and water interaction on structure and chemistry of silicalite MFI type zeolite for its potential use as a seawater desalination membrane

Zhu, Bo; Zou, Linda; Doherty, Cara M.; Hill, Anita J.; Lin, Youzuo; Hu, Xiurong; Wang, Huanting; Duke, Mikel

doi:10.1039/b926455h

Cited by 43 publications

(59 citation statements)

References 44 publications

(54 reference statements)

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“…The potassium ions present as impurities in the structure directing agent, TPAOH, are the source of K + detected in the pure water permeates. It is common in zeolite synthesis that Na + and K + impurities come from the commercially available TPAOH solutions [25,48]. No Ca 2+ and Mg 2+ were detected in the permeates from the initial pure water testing as expected as there are no other sources of these ions other than what is provided in the seawater solution.…”

Section: Desalination Performancementioning

confidence: 97%

“…K + was found to be depleted from the material presumably due to the deionised water permeation which supports this theory. Na + however remained unchanged and because we have identified that K + and Na + uniquely enter the zeolite cage (while divalents cannot) [25,26], it sees that Na + preferred to remain in the zeolite cage due to the strong charges within the zeolite structure.…”

Section: Semmentioning

confidence: 99%

“…But this does not correlate with the gas permeation data where flux decreases and selectivity increase would indicate a better desalination membrane. It seems that the membrane experienced a disproportionate loss towards the larger pores of the membrane, which is mainly caused by the filling of the divalent ions into the grain boundaries [25]. So while they infiltrate the zeolite and open the pores thus reducing overall salt rejection, in gas permeation, they are dry and immobile, and instead block the pores to give a lower flux and high selectivity for small molecule gases.…”

Section: Gas Permeationmentioning

confidence: 99%

“…It was found from Figure 3 that some Na + and K + were detected in the permeate samples obtained from the initial pure water testing. Na + in the pure water permeate is likely due to the release of residual Na + from zeolite membrane preparation as NaOH was added in the synthesis precursor [6,25]. During the preparation of the zeolite membrane with the high concentration of NaOH and SiO 2 , significant amounts of Na + may have been trapped in the substrate and the zeolite intercrystal pores and formed some low-solubility sodium aluminosilicate compounds (e.g.…”

Section: Desalination Performancementioning

confidence: 99%

“…Several researchers have reported changes in the unit cell dimensions of MFI-type zeolite crystals during heat treatment [21][22][23][24]. Our recent studies [25,26] also showed that the interaction between MFI-type zeolites and the major cations in seawater causes changes not only in structure but also porosity, which is expected to affect diffusion properties of these materials when used as membranes for desalination. An easily modified feature of MFI-type zeolites is the Si/Al ratio which allows structures to be tailored to optimize the sorption uptake and species selectivity [27].…”

Section: Introductionmentioning

confidence: 99%

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Desalination of seawater ion complexes by MFI-type zeolite membranes: Temperature and long term stability

Zhu

Zhou

Milne

et al. 2014

Journal of Membrane Science

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Desalination of seawater ion complexes by MFI-type zeolite membranes: temperature and long term stability, Journal of Membrane Science, http://dx.doi.org/10.1016/j.memsci. 2013.10.071 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. 2 high rejection (>93%) for all major seawater ions including Na + (except for K + , 83%) at an applied pressure of 700 kPa and room temperature (22 °C), but showed a continuous decrease in ion rejection when increasing the temperature from 22 °C and 90 °C. Permeation flux of the zeolite membrane significantly increased with increasing in temperature. Upon closer observation of the major cations, size selective diffusion in the zeolite membrane was observed over the temperatures tested. Larger ions Ca 2+ and Mg 2+ were less responsive to temperature than smaller ions Na + and K + . No changes in membrane structure were observed by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) after 180 days seawater exposure. However, energy-dispersive X-ray spectroscopy (EDS) mapping on the surface of the membrane revealed a small quantity of tightly bound divalent cations present in the structure, which appear to have penetrated the zeolite, accelerated by temperature. They were suspected to have altered the permstructure, explaining why original high rejections at room temperature were not reversed after heat exposure. The work has shown that zeolite membranes can desalinate seawater, but other unusual effects such as ion selective diffusion as a function of temperature indicate a unique property for desalination membrane materials.

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Section: Desalination Performancementioning

confidence: 97%

Section: Semmentioning

confidence: 99%

Section: Gas Permeationmentioning

confidence: 99%

Section: Desalination Performancementioning

confidence: 99%