Preparation and Application of Zeolite and MOF Membranes from an Industrial viewpoint

Inorganic zeolites with well-defined pore network have received continuous worldwide interest, for fabricating membrane with molecular-sieving property. Despite the nearly 40 years of intense research on zeolite membranes, only the hydrophilic LTA membrane has been commercialized for industrial de-watering applications. The main features of state-of-the-art zeolite membranes are: 1. production capacity of a single plant is usually less than 10,000 tpy; 2. water content of the dewatered product is usually higher than 0.1 wt.%; 3. Only tubular type zeolite membrane is commercialized. To date, the annual market of zeolite membranes in China is around 15 million €. This is less than 1 percent of the market potential value. The main reasons are the high cost and the unsatisfied performance of the state-of-the-art zeolite membrane materials. A leap-forward development of zeolite membrane production is expected to be made in order to broaden the application of this technology.

Metal-organic frameworks (MOFs) possess not only zeolite-like topologies and properties, but also, more importantly, tunable pore sizes and well-designed functionalities, which makes them strong candidates for molecular sieve membranes. During the last 15 years, much progress in the development of MOF membranes has been witnessed. For example, numerous synthetic routes have been developed for preparing ZIF-8 membranes that demonstrate superior separation properties for propylene/propane mixture. However, the ZIF-8 membranes still face challenges in industrial applications. One of the biggest challenges is the unsatisfactory propylene flux when utilized in propylene/propane separation. Statistically, most of the reported ZIF-8 membranes have propylene flux of 0.1~0.2 kgm^-2h^-1, which is an order of magnitude lower than the water flux (1~5 kgm^-2h^-1) of commercialized LTA membrane for ethanol dehydration. Besides, the membrane stability under the real separation conditions needs further study.

In the presentation, we will report a continuous production line for zeolite membranes, with the aim to greatly increase the productivity and to reduce the membrane cost. Examples will be given in terms of ultra-deep dewatering of organic solvents. We will also talk about the possibility of continuous and scalable manufacture of ZIF-8 membranes. Compared with zeolite membranes, MOF membranes, endowed with simple preparation process, high separation efficiency and low manufacturing cost, offer enormous potential for scale-up preparation and commercial application. MOF membranes as a whole have an edge over zeolite membranes for commercialization in terms of the processing advantages. The application of MOF membranes in industrial gas separation can be reasonably expected for the next future.