(7fw) Microporous Inorganic and Composite Membranes for Energy Efficient Separations

Membranes made of microporous inorganic materials, e.g., carbon molecular sieve (CMS), zeolite, metal organic framework (MOF) are capable of surpassing the performance limit of polymer membranes for separations of many important gas or liquid mixtures. Moreover, their exceptional thermal, chemical and mechanical stability make inorganic membranes well suited for separations under industrially relevant harsh conditions that polymeric materials can not handle. However, high cost per unit area of membrane has limited their implementation to only medium-sized industrial plants for the dehydration of organic solvents. At current permeance levels, large surface areas and correspondingly high capital investment are required for many applications. To overcome this challenge, further improvement of membrane performance and developing cost-effective membrane synthesis strategies are needed.

One way forward is to increase the membrane permeance by reducing membrane thickness, without the formation of non-selective defects. One of my graduate research projects focused on the fabrication of ultra-thin CMS membranes. Through deliberate design of the polymer precursors and the porous structure of substrate, the thickness of CMS membranes was decreased down to 300 nm, and gas permeance was considerably enhanced without compromising selectivity. The major share of the cost of inorganic membranes is actually imposed by the underlying porous ceramic support. One approach to reducing membrane cost is to use more cost-effective and scalable supports, such as polymeric hollow fibers, which can be easily made into membrane modules of high packing density. Another approach is to suspend nano-sized microporous materials into polymer matrix to form defect-free mixed matrix membranes (MMMs). These two research areas are the focuses of my current postdoc research. An innovative chemical vapor growth approach is being developed to fabricate MOF membranes on polymeric supports. Without the use of any solvents, this vapor phase growth eliminates the homogeneous nucleation/growth of MOFs and the dissolution of membrane materials during membrane synthesis, enabling the formation of conformal MOF membranes on solvent-sensitive polymer supports. Another focus of my current research is to in situ form MOF nano crystals inside the polymer matrix to produce MMMs free of any MOFs/polymer interface.

My future research interests are in design and synthesis of novel inorganic/polymeric composite materials/membranes for separation applications and understanding their fundamental synthesis-structure-property relationships. The combination of microporous inorganic materials (zeolite, MOFs and carbon-based molecular sieves) and polymer materials is likely to result in a scalable, cost effective and high performance membranes for energy-efficient separations. Building on my interdisciplinary background and expertise, my research will involve: (1) synthesis of new microporous materials with strong molecular sieving effect and/or preferential adsorption towards the targeted molecules, as well as excellent stability. (2) Understanding and improving the interface interaction between inorganic and polymeric phases; (3) developing innovative processing strategies for better structure and morphology control of the composites systems; and (4) Understanding the transport properties. MOFs will be the focus of the inorganic phase materials because of their high porosity, tunable pore structure and surface property. My goal is to develop novel hybrid materials as high-performing and cost-effective sorbents and membrane materials for the separations of gas or liquid mixtures, as well as water purification and desalination. Exploring these hybrid materials for other energy and environment related applications will also be pursued.

Research Experience:

My research experience has been a blend of chemistry, materials science and chemical engineering. Clean water technologies were the focuses of my undergraduate and master research. Novel functional polymers with powerful sorption capability to heavy metal ions were synthesized for water purification, and a new class of sensor based on an intrinsically conductive polymer was fabricated for efficient and reliable detection of leads ions in water. My PhD research was about membrane technology. Besides the aforementioned CMS membranes, I also worked on MOF-5, ZIF-8 and MFI zeolite membranes, with focuses on synthesis, structure characterization and studies on gas transport properties. I successfully developed positron annihilation spectroscopy (PAS) as an in-situ and non-destructive means to reveal the hierarchical microporous structure of zeolite membranes. This method is also applicable to other types of inorganic membranes materials, providing an opportunity to better understand the synthesis-structure-properties relationship of microporous inorganic membranes. My current research focuses on developing MOF/polymer composite membranes as the next-generation membranes for energy efficient separations.

Postdoctoral Project: “MOF-based membranes for gas separation”

Supervised by Dr. Michael Tsapatsis, Department of Chemical Engineering and Materials Science, University of Minnesota

PhD Dissertation: “Synthesis and characterization of microporous inorganic membranes for propylene/propane separation”

Supervised by Dr. Jerry Lin, School for Engineering of Matter, Transport and Energy, Arizona State University.

Teaching Interests:

I am interested in teaching heat and mass transfer, thermodynamics, transport processes, and materials related courses at both undergraduate and graduate levels. I am also interested in introducing and teaching a class at the interface between materials science and chemical engineering. This class will focus on the synthesis and characterization of materials that are particularly important to the field of chemical engineering, and the chemical engineering principles that can be used to develop and process novel materials.

Selected Publications:

X. L. Ma, X. T. Wei, J. Kniep, Y. S. Lin, Ultra-thin carbon molecular sieve membrane for propylene/propane separation, AIChE Journal, 2016, 62, 491–499.

X. L. Ma, H. Wang, H. B. Wang, J. O’Brien-Abrahama, Y. S. Lin, Pore structure characterization of supported polycrystalline zeolite membranes by positron annihilation spectroscopy, Journal of Membrane Science, 2015, 477, 41-48.

X. L. Ma, Jerry Y.S. Lin, Preparation Chemistry of Inorganic Membranes, Modern Inorganic Synthetic Chemistry, Elsevier, 2017.

D. F. Liu, X. L. Ma, H. X. Xi, Y. S. Lin, Gas transport properties and propylene/propane separation characteristics of ZIF-8 membranes, Journal of Membrane Science, 2014, 451, 85-93.

X. G. Li, X. L. Ma, J. Sun, M. R. Huang. Powerful reactive sorption of silver(I) and mercury(II) onto poly(o-phenylenediamine) microparticles. Langmuir, 2009, 25, 1675-1684.