Collaborative Research: Modified Reverse Osmosis Membranes for Forward and Pressure Retarded Osmosis

McCutcheon/Freeman1160098/110069这项由化学和生物分离计划颁发的NSF奖支持Jeffrey McCutcheon教授和Benny Freeman教授开发一种新的方法，用于对商业反渗透膜进行化学修饰，用于正向渗透和压力减缓渗透应用。正向渗透(FO)和减压渗透(PRO)是同类技术，属于工程渗透(EO)的更广泛的区别。这个平台依靠通过膜的浓度差异引起的渗透流来净化水、脱水溶液和发电。FO最近被考虑用于海水淡化、废水再利用和食品加工，被认为是反渗透(RO)和蒸发方法的一种低成本替代方法。PRO被认为是用来在河流三角洲和“渗透引擎”系统中获取渗透势，以便通过水轮机发电。任何EO技术都需要一种量身定制的膜，不仅具有高度的选择性，而且还表现出促进渗透流的特性。今天的商业除盐膜是专门为反渗透而设计的。这些膜表现出良好的选择性和渗透性，但也使用了厚厚的多孔性支撑层。这些层对反渗透中的水力流动的阻力很小。然而，它们极大地影响了正向渗透过程中的传质，导致了通常所说的内部浓差极化。早期的工作表明，当在FO或PRO中进行评估时，反渗透膜的通量性能非常差。这项工作将证明用多巴胺及其类似物对反渗透膜支撑层进行化学修饰将通过增加支撑层的亲水性来提高渗透通量。一旦亲水，这些层就会饱和，从而提供必要的水相连续性，以减少传质阻力。早期的工作已经表明，在某些情况下，与未经修饰的膜相比，水通量可以增加10倍或更多。这种解决方案可能会提供一种替代方案，以使用难以规模化或需要多年开发才能达到与当今反渗透膜相似的性能的技术来构建新的膜。在对稀缺的水和能源资源的需求日益增长的世界里，像EO这样的新技术平台提供了新的可能性。利用环氧乙烷进行海水淡化和发电将通过开发新的、量身定制的膜来实现。然而，如果我们能够利用现有的膜技术进行简单的修改，我们就不需要开发一个全新的膜平台。事实上，提出的修改方法是可扩展的，因此很容易在现有的膜生产线上实现。如果不需要重建整个制造基础设施，薄膜制造商更有可能实施生产计划的改变。此外，这项研究将是首次考虑对反渗透膜支撑层进行改性以提高通量性能。为了实现我们的目标，有必要更好地了解涂层是如何在多孔材料(反渗透膜支撑层)内发生的。康涅狄格大学将评估涂层程序，以最大限度地提高性能，而德克萨斯大学将开发多多巴胺的模拟化学物质，这种化学物质可能更适合在多孔结构中沉积。最终，我们将了解化学和改性技术如何影响改性反渗透膜的渗透通量性能。根据美国国家工程院的说法，工程的重大挑战之一是为人类提供清洁的水。正向渗透等新兴水处理技术的发展可以重新激发人们对海水淡化和废水再利用的兴趣，因为它有望带来低成本的好处。因此，两家私人投资机构都将利用这项工作，在他们的教育和推广计划中激发人们对水的兴趣。在德克萨斯大学，弗里曼教授将为高中生和教师提供研究机会，提供宝贵的经验，帮助推动德克萨斯州高中的工程教育。在康涅狄格大学，麦卡钦教授将积极参与21世纪大学，这是一个促进跨学科和跨海洋的本科生研究的组织。23所成员大学为本科生提供展示他们的研究的程序，康涅狄格州大学是两所美国大学参与者之一。McCutcheon教授将帮助开发在康涅狄格州大学举办的暑期学校的规划，并指导计划参加年度会议和其他会议的康涅狄格州大学本科生。PIS将合作建立一个名为UCONNect2Texas的REU交换项目，该项目将让两所学校的本科生在夏季相互访问10周。

McCutcheon/Freeman1160098/110069This NSF award by the Chemical and Biological Separations program supports work by Professors Jeffrey McCutcheon and Benny Freeman to develop a new method for chemically modifying commercial reverse osmosis membranes for use in forward osmosis and pressure retarded osmosis applications. Forward osmosis (FO) and pressure retarded osmosis (PRO) are sibling technologies that fall under the broader distinction of engineered osmosis (EO). This platform relies on osmotic flow induced by concentration differences across a membrane to purify water, dewater solutions and generate electricity. FO has recently been considered for seawater desalination, wastewater reuse, and food processing and is considered a low cost alternative to reverse osmosis (RO) and evaporative approaches. PRO has been considered for harvesting osmotic potential at river deltas and within "osmotic engine" systems to generate electricity with a hydroturbine.Any EO technology requires a tailored membrane that not only is highly selective, but also exhibits properties that promote osmotic flow. Today's commercial desalting membranes are designed specifically for reverse osmosis. These membranes exhibit excellent selectivity and permeability, but also employ thick porous support layers. These layers provide little resistance to hydraulic flow in RO. However, they dramatically impact mass transfer in forward osmosis, causing what is commonly referred to as internal concentration polarization. Early work has shown that RO membranes have very poor flux performance when evaluated in FO or PRO. A significant amount of this resistance is caused by poor wetting of the support layers, which are comprised of hydrophobic polymers.This work will demonstrate that a chemical modification of reverse osmosis membrane support layers with polydopamine and its analogs will enhance osmotic flux by increasing the hydrophilicity of the support layers. Once hydrophilized, the layers will saturate, thereby providing the necessary continuity of the water phase to reduce mass transfer resistances. Early work has already shown that in some cases, water flux can be increased by a factor of 10 or more when compared to an unmodified membrane. This solution may provide an alternative to building new membranes using techniques that may be difficult to scale or will require years of development to achieve similar performance to today's RO membranes.In a world of ever increasing demand for scarce water and energy resources, new technology platforms, like EO, offer new possibilities. Desalination and power production using EO will be enabled through the development of new, tailored membranes. However, if we are able to use existing membrane technology with a simple modification, we do not need to develop an entirely new membrane platform. In fact, the proposed modification method is scalable and therefore easily implemented into existing membrane productions lines. Membrane manufacturers are more likely to implement changes to their production scheme if it doesn't require rebuilding their entire manufacturing infrastructure. Furthermore, this investigation will represent the first time that modification of a RO membrane support layer has been considered to increase flux performance.To achieve our goals, a better understanding of how the coating occurs within a porous material (the RO membrane support layer) will be necessary. The University of Connecticut will evaluate the coating procedure to maximize performance improvements while the University of Texas will develop analog chemistries to polydopamine that may be more appropriate for deposition within a porous structure. Ultimately, we will develop an understanding of how chemistry and modification technique impact osmotic flux performance across modified RO membranes.According to the National Academy of Engineering, one of the Grand Challenges for Engineering is providing access to clean water for mankind. The development of emerging water treatment technologies like forward osmosis could reinvigorate interest in desalination and wastewater reuse due to its promised benefits of low cost. As such, both PIs will use this work to stimulate interest in water within their educational and outreach programs. At the University of Texas, Professor Freeman will provide research opportunities for high school students and teachers, giving invaluable experience to help promote engineering education in Texas high schools. At the University of Connecticut, Professor McCutcheon will be an active participant in Universitas 21, an organization that promotes undergraduate research across disciplines and oceans. Twenty three member universities provide programming for undergraduates to present their research, and UCONN is one of two American university participants. Professor McCutcheon will help develop programming for a summer school to be held at UCONN as well as mentor the UCONN undergraduates who plan on attending the annual conference and other meetings. The PIs will collaborate in establishing an REU exchange program, called UCONNect2Texas, which will involve undergraduate students from each school visiting the other for a period of 10 weeks during the summer.