Advanced Molecular sieve Membranes

FDA/PMDA-TMMDA (copoly(4,4'-methylenebis(2,6-dimethyl)-2,2-bis(3,4- dicarboxy- lphenyl) hexafluoro propane/pyromellitic) diimide), a new co-polyimide was synthesized and different solvents were utilized to alter the morphology of resultant membranes. Membranes were then pyrolyzed to produce Carbon Molecular Sieve membranes (CMSMs). The effects of the different morphologies of co-polyimide precursors and the pyrolysis temperatures (protocols) on the gas transport performance were studied. CMSMs were characterized with XRD, TGA-FTIR and gas permeation tests. It was found that higher pyrolysis temperature resulted in lower permeability and higher selectivity. Interestingly, CMSMs derived from precursors with different morphologies exhibited different permeabilities at the pyrolysis temperature of 550 °C. However, when the pyrolysis temperature was elevated to 800 °C, permeabilities become almost the same for all precursors. This result can be explained in terms of relationship bet...

Journal of Membrane Science, 2017

This study reports and analyzes gas transport and sorption properties between 35 C-50 C for polymeric and carbon molecular sieve (CMS) membranes derived from an in-house synthesized polyimide referred to as 6FDA/DETDA:DABA(3:2). The analysis of activation energies of permeation and diffusion and heats of sorption for CO 2 , CH 4 , O 2 , and N 2 in these membrane materials provides insights regarding the permeability and selectivity changes at increasing pyrolysis temperature between 550 C and 800 C. The diffusion selectivity is factored further into "energetic" and "entropic" selectivity contributions to show that higher permselectivity of CMS membranes compared to polymeric membrane arises from a larger than unity entropic selectivity. CMS membranes pyrolyzed at 800 o C are also shown to have significantly elevated entropic selectivity compared with membranes pyrolyzed at 550 o C. Analysis of the selectivity factors provides fundamental insights into the importance of entropic factors as tools to tailor membrane performance.

Lab on a Chip

In this issue of Lab on a Chip we are introducing a new regular series of minireviews that are tightly focused on recent research. These mini-reviews will cover trends in recent research, focus on potential new areas of research or even potential applications. The aim is to inform the reader about such recent trends, bring 'forgotten' papers back into the spotlight and perhaps most importantly, to provide a perspective of a particular subject as well as a critical evaluation of it that may help researchers to plan future research. Six mini-reviews will appear during the year.

Lab on a Chip, 2006

In this issue of Lab on a Chip we are introducing a new regular series of minireviews that are tightly focused on recent research. These mini-reviews will cover trends in recent research, focus on potential new areas of research or even potential applications. The aim is to inform the reader about such recent trends, bring 'forgotten' papers back into the spotlight and perhaps most importantly, to provide a perspective of a particular subject as well as a critical evaluation of it that may help researchers to plan future research. Six mini-reviews will appear during the year.

Microporous and Mesoporous Materials, 1998

Carbon molecular sieve (eMS) membranes with excellent separation performance and stability appear to be promising candidate for gas separation. In this work, eMS membranes were formed by a thin carbon layer obtained by pyrolysis of a coated polyetherimide solution onto porous disk support. The pyrolysis temperatures were varied under inert condition. Results showed that the pyrolysis temperature played an important role in determining the gas permeability of CMS membranes. The CMS membrane prepared at pyrolysis temperature of 700 DC shows high surface area and narrow PSD with well developed microporous carbon structures. The development oflarge pore occurs at higher pyrolysis temperature. The Oz/N z permselectivities of 2.86, 2.61 and 2.22, respectively were attained by CMS membranes prepared at pyrolyzed temperature of 700, 800 and 900°C.

The Journal of Physical Chemistry C, 2013

The development of the microstructure of carbon molecular sieve membranes (CMSMs) was examined using a variable monoenergy slow positron beam (VMSPB). To vary the structure of the CMSMs fabricated by pyrolyzing a Kapton precursor, different pyrolysis temperatures at a fixed heating rate under vacuum conditions and various periods of holding time at a given pyrolysis temperature were applied. The VMSPB was integrated with the platinum (Pt) capping technique, in which a layer of Pt was sputtered on the membrane surface to eliminate the back diffusion effect of positrons. On the basis of the depth profile obtained, the membranes carbonized at 800 and 900°C were demonstrated to exhibit asymmetric microstructures at the top layer. The analysis of positron annihilation spectroscopic data of the membranes using a VEPFIT program revealed three structural layers at the most: a dense top layer, a transition layer, and an underlying layer. At prolonged holding time, it was found that the decrease in the gas permeation was correlated not only to the reduction in the pore volume but also to the increase in the dense layer thickness.

Journal of Membrane Science, 2014

Carbon molecular sieve membranes (CMSM) were prepared on α-alumina supports by carbonization of a resorcinol-formaldehyde resin loaded with boehmite. Two series of carbon membranes produced at 500 ºC and 550 ºC carbonization end temperatures were prepared. The influence of the carbonization end temperature on the structure, morphology and performance of the membranes was examined by scanning electron microscopy, thermogravimetric analysis, CO2 adsorption and permeation to N2, O2, He, H2 and CO2 at temperatures from 25 ºC to 120 ºC. SEM photographs showed carbon membranes with a thin and very uniform layer and a thickness of ca. 3 m. Carbon dioxide adsorption isotherms revealed that all the produced carbon membranes have a welldeveloped microporous structure. Nevertheless, the membranes carbonized at 550 ºC have more ultramicropores and a narrower pore size distribution. The permselectivity of CMSM prepared at this temperature surpasses the Robeson upper bound for polymeric membranes, especially regarding ideal selectivities of pairs O2/N2 (O2 permeation rate: 9.85 x10-10 mol m-2 s-1 Pa-1 and ideal selectivity: >11.5), H2/N2 (H2 permeation rate: 5.04 x10-8 mol m-2 s-1 Pa-1 and ideal selectivity: >586) and He/N2 (He permeation rate: 4.68x10-8 mol m-2 s-1 Pa-1 and ideal selectivity: >544).

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2018

Two requirements of a porous filler for Mixed Matrix Membranes [MMMs] are a good adhesion to the polymer and the openness of its pores. The surface of SAPO-34 has been grafted with moieties containing amino groups, aromatic rings, and fluorinated chains, for a good adhesion to glassy polyimides, aromatic polymers and perfluoropolymers. The controlled excess of the modification agentpreferably trichlorosilanesin hydrophobic solvents and the strict control of moisture in the reaction environment prevent the growth of thick layers of grafts around the crystals. XPS confirms the success of the derivatizations and indicates a homogeneous and thin coverage of the surface. The negligible reduction of the surface area suggests that the modification of the surface does not plug the micropores. The counter-intuitive faster adsorption of n-heptane in silicalite-1 after modification with bulky fluorinated grafts indicates the openness of the pores even for large molecules, and the reduction of the resistance to the transport of mass across the surface of the molecular sieves, thanks to the reduced amount of water adsorbed on the hydrophobic outer surface of the crystals.

Springer eBooks, 1990

Advanced Science Institutes Series A series presenting the results of activities sponsored by the NA TO Science Committee, which aims at the dissemination of advanced scientific and technological knowledge, with a view to strengthening links between scientific communities.

Nature Communications, 2014

Organic open frameworks with well-defined micropore (pore dimensions below 2 nm) structure are attractive next-generation materials for gas sorption, storage, catalysis and molecular level separations. Polymers of intrinsic microporosity (PIMs) represent a paradigm shift in conceptualizing molecular sieves from conventional ordered frameworks to disordered frameworks with heterogeneous distributions of microporosity. PIMs contain interconnected regions of micropores with high gas permeability but with a level of heterogeneity that compromises their molecular selectivity. Here we report controllable thermal oxidative crosslinking of PIMs by heat treatment in the presence of trace amounts of oxygen. The resulting covalently crosslinked networks are thermally and chemically stable, mechanically flexible and have remarkable selectivity at permeability that is three orders of magnitude higher than commercial polymeric membranes. This study demonstrates that controlled thermochemical reactions can delicately tune the topological structure of channels and pores within microporous polymers and their molecular sieving properties.

Aiche Journal, 2004

Separation and Purification Technology, 2020

Enhancing the gas separation properties of mixed matrix membranes via impregnation of sieve phases with metal and nonmetal promoters, Separation and Purification Technology (2020), doi:

Carbon

Carbon molecular sieve (CMS) membranes separate penetrants using size and shape-selective pores. In this paper we report pyrolysis of a 6FDA:BPDA-DAM polyimide precursor between 500 and 800 C and measure gas evolution during the CMS structural development. The CMS materials were then characterized using combined transport properties, porosimetry, FTIR, Raman spectroscopy, TGA-FTIR, WAXD, and elemental analysis measurements to assess their resulting physical and chemical properties. The results support a previous vision that fragmentation of the polyimide precursor occurs to form aromatic strands that provide building blocks for the overall CMS cell structure. This fact notwithstanding, these new findings indicate that constituent strands appear to be more complicated than previously suggested. An ordering process of such strands can generate a bimodal morphology comprising larger micropores with irregular cell walls containing ultramicropores. Permeability and permselectivity of the CMS for the C 2 H 4 /C 2 H 6 pair are also correlated with CMS structures based on the above characterizations. The results of this work suggest that molecular probe-based transport measurements are by far the most useful tools to study these complex, amorphous materials for molecular separation applications.

Nature nanotechnology, 2017

Graphene and other two-dimensional materials offer a new approach to controlling mass transport at the nanoscale. These materials can sustain nanoscale pores in their rigid lattices and due to their minimum possible material thickness, high mechanical strength and chemical robustness, they could be used to address persistent challenges in membrane separations. Here we discuss theoretical and experimental developments in the emerging field of nanoporous atomically thin membranes, focusing on the fundamental mechanisms of gas- and liquid-phase transport, membrane fabrication techniques and advances towards practical application. We highlight potential functional characteristics of the membranes and discuss applications where they are expected to offer advantages. Finally, we outline the major scientific questions and technological challenges that need to be addressed to bridge the gap from theoretical simulations and proof-of-concept experiments to real-world applications.

AIChE Journal, 2004