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Seawater desalination performance of MFI type membranes made by secondary growth

机译：二次生长制成的MFI型膜的海水淡化性能

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Seawater desalination is now commonly performed using membrane technology but new materials research is however needed to address issues such as membrane fouling. Ceramic materials such as zeolites are capable of providing the required desalination properties while being potentially tolerant to waters which readily foul polymer membranes and/or can withstand more cost effective cleaning methods. In this paper, we developed Silicalite and ZSM-5 zeolite membranes and tested desalination using the thermally based pervaporation, and more common reverse osmosis (RO) operation modes. Zeolite membranes were synthesised by the template-free secondary growth technique with varying Si/Al ratios. X-ray diffraction spectra of all membranes showed randomly oriented MFI structure. For intact membrane films, gas permeation was not measurable at room temperature until membrane was first heated to at least 125 °C under dry helium implying minimal defects and zeolite pore plugging by water. In pervaporation with 3.8 wt% seawater feed, zeolites containing alumina actively rejected ions, displaying equivalent rejections exceeding 99%. Flux typically decreased after introduction of seawater, but the membrane with Si/AI ratio of 100 uniquely showed a 30% increase in flux which could only be explained by an ion exchange/interaction mechanism which opened the zeolite structure to permeation. Optimal temperature for pervaporation was found to be 80℃, where high rejections persisted, and flux increased to 0.72 kg m~(-2) h~(-1). In RO, the Silicalite membrane achieved highest rejections, but had not reached steady state after 25 h of operation. Negative rejections were initially observed, but eventually crossed into positive values over time. Despite the complexity of water and multiple ion diffusion through molecular dimensioned zeolites with complex charged surfaces, MFI zeolite membranes with tailored Si/Al ratios are ideal candidates for desalination.
机译：现在通常使用膜技术进行海水淡化，但是需要新材料研究来解决膜污染等问题。陶瓷材料（例如沸石）能够提供所需的脱盐性能，同时潜在地耐受容易污染聚合物膜的水和/或可以承受更具成本效益的清洁方法。在本文中，我们开发了Silicalite和ZSM-5沸石膜，并使用基于热的全蒸发和更常见的反渗透（RO）操作模式对脱盐进行了测试。通过无模板二次生长技术以不同的Si / Al比合成了沸石膜。所有膜的X射线衍射光谱显示出随机取向的MFI结构。对于完整的薄膜薄膜，直到室温下将薄膜首先在干燥的氦气下至少加热到至少125°C之前，才能测量出气体的渗透性，这表明缺陷最少且沸石被水堵塞。在用3.8 wt％的海水进料进行全蒸发时，含氧化铝的沸石会主动排斥离子，表现出的等效排斥率超过99％。通入海水后通量通常会降低，但是Si / Al比率为100的膜独特地显示出通量增加了30％，这只能由离子交换/相互作用机制解释，该机制使沸石结构易于渗透。最佳的全蒸发温度为80℃，高截留率持续存在，通量增加到0.72 kg m〜（-2）h〜（-1）。在反渗透中，Silicalite膜的排斥率最高，但在运行25小时后仍未达到稳态。最初观察到负排斥，但随着时间的推移最终转化为正值。尽管水的复杂性和通过具有复杂电荷表面的分子尺寸沸石的多种离子扩散，具有定制Si / Al比的MFI沸石膜仍是脱盐的理想选择。

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