Continuous Zeolite MFI Membranes Fabricated from 2D MFI Nanosheets on Ceramic Hollow Fibers

Abstract

High-quality 2D MFI nanosheet coatings were prepared on a-alumina hollowf iber supports by vacuum filtration and then transformed into molecular sieving membranes by two sequential hydrothermal treatments.T his processing method eliminates the need for specially engineered silica-based support materials that have so far been necessary to allow the formation of functional membranes from 2D MFI nanosheets.T he sequential steps enhance adhesion of the membrane on the fiber support, fill in nanoscale gaps between the 2D nanosheets,a nd preserve the desirable (0k0) out-ofplane orientation without the need of any support engineering or modification. The membrane exhibits high performance for separation of n-butane from i-butane,a nd for other technologically important hydrocarbon separations.T he present findings have strong implications on strategies for obtaining thin, highly selective zeolite membranes from 2D zeolites in atechnologically scalable manner.Membrane-based separations have high potential for energy efficiency and cost reduction in chemical processes. Inorganic molecular sieving zeolite membranes [1] can offer anumber of advantages,such high permeability and selectivity as well as excellent thermal and chemical stability,inmany applications.However,the difficulty of low-cost and scalable fabrication of zeolite membranes is ak ey barrier to their widespread application. In the last few years,t he emergence of zeolitic membranes based upon two-dimensional (2D) zeolite nanosheets [2] has created an opportunity to overcome this barrier.Inprinciple,uniform and thin (0.1-1 mm) coatings of high-aspect ratio zeolite nanosheets can be deposited on nearly any kind of porous membrane substrate and then perform af inal zeolite growth step to close the nanoscopic gaps between the nanosheets,thereby creating very high-flux molecular sieving membranes.F or example,n anosheets (3-5nminthickness) of zeolite MFI have been synthesized both by exfoliation of 2D MFI layered stacks [2a, 3] as well as by seedassisted bottom-up methods. [2b] TheM FI nanosheets produced by the latter route offer particularly attractive structural features,s uch as av ery high aspect ratio favorable for thin coatings,v ery short diffusion pathways through the nanosheet, high-yield production without need for an exfoliation process,a nd good dispersibility in water. MFI membranes fabricated from these MFI nanosheets have shown high fluxes and excellent separation of xylene isomers and also of butane isomers. [2b, 4] Despite the excellent separation performance of the above MFI membranes,t heir current fabrication process faces considerable hurdles in practical feasibility and scalability.Atpresent the fabrication process is only possible on porous Stçber silica-derived disk-type supports.I th as been hypothesized that such as upport provides an optimal delivery of silicate reactants to the 2D MFI nanosheet coating and facilitates its growth into adefectfree membrane,a nd its properties are difficult to replicate with other types of silica-cont...

Recent Development in Composite Membranes for Flow Batteries

“…[56] Other OSs, that is, zeolitec omposite membranes with high stability,s how potentialf or long-term commercial applications. [47,51,57]…”

Highly Ordered Nanochannels in a Nanosheet‐Directed Thin Zeolite Nanofilm for Precise and Fast CO2 Separation

“…Crystalline zeolite/MOF nanosheets are attractive building blocks for the fabrication of oriented and thin nanofilms/membranes because they own very short nanochannels and are easily deposited at an oriented manner on various types of substrates. [ 1f,h,i,3b,c,5 ] Both the exfoliated [ 1f,h,5a ] and directly synthesized [ 1i,5b,6 ] zeolite/MOF nanosheets were used as building blocks for secondary growth of nanofilms/membranes. Ultrathin zeolite membranes after secondary growth of directly synthesized zeolite nanosheets with a thickness of 5 nm were first reported by Jeon et al [ 1i ] This b ‐oriented silicalite‐1 membrane [ 1i ] on disc substrate exhibited high separation performance for xylene isomers.…”

“…[ 3c ] However, there were only two publications that explored oriented zeolite membranes derived from nanosheet seed layers on tubular substrates. [ 5a,c ] The preparation of highly oriented and thin crystalline nanofilms/membranes on tubular substrate is more challenging but more compatible for practical applications.…”

“…The decrease trends of permeance and selectivity through the current oriented nanofilm along with temperature in the separation of CO 2 /CH 4 and CO 2 /N 2 mixtures were the same as those through the reported zeolite CHA [ 17 ] and AlPO‐18 membranes. [ 5c,18 ] In the case of 423 K, the current oriented SAPO‐34 nanofilm displayed CO 2 permeance as high as 4.4 × 10 −6 mol (m 2 s Pa) −1 and CO 2 /N 2 selectivity of 10 for an equimolar CO 2 /N 2 mixture.…”

“…Comparison of separation performance of our oriented SAPO‐34 nanofilms with other zeolite films/membranes presented in a) CO 2 /CH 4 selectivity versus permeance and b) CO 2 /N 2 selectivity versus permeance plots. AlPO‐18, [ 5c,15,18,21 ] ● DDR, [ 22 ] ▼ CHA, [ 17c,20b,23 ] ▽ SSZ‐13, [ 18a,b,24 ] △ MFI, [ 25 ] ▲ FAU, [ 26 ] SAPO‐17, [ 19 ] and ■ SAPO‐34 [ 10b,27 ] films/membranes.…”