An official website of the United States government
Zeolitic-imidazole framework-8 (ZIF-8) membranes have shown exceptional propylene/propane separation performances. Their commercial applications have, however, been impeded by several challenges. One such challenge is the difficulty of managing microstructural defects ( i.e. , grain boundary defects) in a consistent manner, leading to poor membrane performances and ultimately to a reproducibility issue. Herein, we introduce a new effective strategy to seal the microstructural defects of polycrystalline ZIF-8 membranes using post-synthetic surface polymerization which consists of two steps: (1) introduction of initiator ligands on the membrane surface by post-synthetic ligand exchange and (2) in situ polymerization of poly(methyl methacrylate) (PMMA) via atom transfer radical polymerization. The ZIF-8 membranes were fully covered with ultra-thin PMMA layers of sub-10 nm thickness, increasing the propylene/propane separation factor from ∼60 to ∼106 with unexpectedly increased propylene permeance, effectively improving the membrane reproducibility. The enhanced separation properties of the PMMA-coated ZIF-8 membranes were attributed to the ultra-thin PMMA layers as well as to the possible facilitated propylene transport by Cu ions in the PMMA layers.
more »
« less
Remarkably Selective Propylene–Propane Separation Using a Copper Scorpionate
Abstract Propylene is a crucial building block to produce many industrial‐scale chemicals including polypropylene. The separation of propylene from propane to reach the high‐purity levels needed for downstream applications is a difficult task due to the close similarities in their physical properties. The olefin/paraffin separation including that involving propylene mainly relies on highly energy‐intensive distillation processes and accounts for nearly 0.3% of the global energy consumption. The utility of a copper complex supported by a fluorinated bis(pyrazolyl)borate is demonstrated to accomplish the separation of propylene from propane repeatedly, under mild conditions with high selectivity. Complete characterization of a rare, copper(I) propylene complex is also reported including the molecular structure.
more »
« less
- Award ID(s):
- 1954456
- PAR ID:
- 10386012
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Small
- Volume:
- 19
- Issue:
- 11
- ISSN:
- 1613-6810
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Zeolitic Imidazolate Framework Membranes: Novel Synthesis Methods and Progress Toward Industrial UseIn the last decade, zeolitic imidazolate frameworks (ZIFs) have been studied extensively for their potential as selective separation membranes. In this review, we highlight unique structural properties of ZIFs that allow them to achieve certain important separations, like that of propylene from propane, and summarize the state of the art in ZIF thin-film deposition on porous substrates and their modification by postsynthesis treatments. We also review the reported membrane performance for representative membrane synthesis approaches and attempt to rank the synthesis methods with respect to potential for scalability. To compare the dependence of membrane performance on membrane synthesis methods and operating conditions, we map out fluxes and separation factors of selected ZIF-8 membranes for propylene/propane separation. Finally, we provide future directions considering the importance of further improvements in scalability, cost effectiveness, and stable performance under industrially relevant conditions.more » « less
-
null (Ed.)The use of alternative oxidants for the oxidative dehydrogenation of propane (ODHP) is a promising strategy to suppress the facile overoxidation to CO x that occurs with O 2 . Gaseous disulfur (S 2 ) represents a thermodynamically “softer” oxidant that has been underexplored and yet offers a potential route to more selective propylene formation. Here we describe a system for sulfur-ODHP (SODHP). We demonstrate that various metal sulfide catalysts generate unique reaction product distributions, and that propylene selectivities as high as 86% can be achieved at 450–550 °C. For a group of 6 metal sulfide catalysts, apparent activation energies for propylene formation range from 72–134 kJ mol −1 and parallel the corresponding catalyst XPS sulfur binding energies, indicating that M–S bond strength plays a key role in SODHP activity. Kinetic data over a sulfided ZrO 2 catalyst indicate a rate law which is first-order in propane and zero-order in sulfur, suggesting that SODHP may occur via a mechanism analogous to the Mars van Krevelen cycle of traditional ODHP. The present results should motivate further studies of SODHP as a route to the selective and efficient oxidative production of propylene.more » « less
-
Tandem catalysis couples multiple reactions and promises to improve chemical processing, but precise spatiotemporal control over reactive intermediates remains elusive. We used atomic layer deposition to grow In2O3over Pt/Al2O3, and this nanostructure kinetically couples the domains through surface hydrogen atom transfer, resulting in propane dehydrogenation (PDH) to propylene by platinum, then selective hydrogen combustion by In2O3, without excessive hydrocarbon combustion. Other nanostructures, including platinum on In2O3or platinum mixed with In2O3, favor propane combustion because they cannot organize the reactions sequentially. The net effect is rapid and stable oxidative dehydrogenation of propane at high per-pass yields exceeding the PDH equilibrium. Tandem catalysis using this nanoscale overcoating geometry is validated as an opportunity for highly selective catalytic performance in a grand challenge reaction.more » « less
-
Abstract The catalytic oxidative dehydrogenation of propane (ODHP) is a challenging reaction due to facile competing overoxidation to COx. The gaseous disulfur molecule, S2, is isoelectronic with O2and has been shown to act as an alternative, “soft oxidant” for the analogous process (SODHP) over bulk metal sulfide catalysts. However, these bulk catalysts suffer from low surface areas and ill‐defined active sites – issues that might be addressed with a supported catalyst. Here we investigate supported V/Al2O3materials for SODHP. We show that these catalysts are highly selective for propylene, far surpassing the yields of the prior bulk systems. Isolated sulfided vanadium species are found to be more active and selective than crystalline vanadium sulfide. Additionally, we compare the S2and O2oxidants over sulfided and calcined V/Al2O3materials, respectively, and find that the propylene selectivity is enhanced using S2as the oxidant. These results suggest that sulfur is a promising soft oxidant that can be used to achieve high propylene selectivities over supported metal sulfides.more » « less
