A water gas shift (WGS) membrane reactor (MR) has been constructed using a MFI-type zeolite disk membrane packed with a cerium-doped ferrite catalyst. The WGS reaction was performed at high temperatures of 400−550 °C, and the effect of reaction pressure on the MR performance was investigated in a range from 2 to 6 atm with the permeate side swept by nitrogen at atmospheric pressure. Increasing temperature and pressure enhance both the reaction rate and the rate of H 2 membrane permeation that in turn significantly enhances the CO conversion. The equilibrium limit of CO conversion can be surpassed in the MR at high pressure and/or high temperature. It has been demonstrated in this study that membranes with moderate H 2 selectivity can be effective for enhancing CO conversion at high operation temperature and pressure with the cost of low H 2 concentration in the permeate stream. The timely removal of H 2 from the catalyst bed dramatically reduced the undesirable methane production because H 2 is a reactant for methanation reactions in the WGS system. Both the zeolite membrane and the Fe/Ce catalyst also exhibited good resistances to high concentration of H 2 S in WGS reactions.
Tissue engineering and regenerative medicine follow a multidisciplinary attitude to the expansion and application of new materials for the treatment of different tissue defects. Typically, proper tissue regeneration is accomplished through concurrent biocompatibility and positive cellular activity. This can be resulted by the smart selection of platforms among bewildering arrays of structural possibilities with various porosity properties (ie, pore size, pore connectivity, etc). Among diverse porous structures, zeolite is known as a microporous tectosilicate that can potentially provide a biological microenvironment in tissue engineering applications. In addition, zeolite has been particularly appeared promising in wound dressing and bone‐ and tooth‐oriented scaffolds. The wide range of composition and hierarchical pore structure renders the zeolitic materials a unique character, particularly, for tissue engineering purposes. Despite such unique features, research on zeolitic platforms for tissue engineering has not been classically presented. In this review, we overview, classify, and categorize zeolitic platforms employed in biological and tissue engineering applications.
Modified MFI-type zeolite membranes were investigated
as high-temperature water-gas shift (WGS) membrane reactors (MRs)
in combination with a nanocrystalline Fe/Ce WGS catalyst. The effects
of the MR operating conditions and the membrane separation performance
on the CO conversion (χCO) were studied experimentally
and by calculations using a simple one-dimensional plug-flow reactor
(PFR) model. The experimental results showed that, at high temperatures
(e.g., >500 °C), the zeolite MR with moderate H2 selectivity (e.g., αH2/CO2
∼ 31, and αH2/CO ∼ 25)
and permeance (P
m,H2
∼
0.9 × 10–7 mol s–1 m–2 Pa–1) was capable of overcoming
the limit of equilibrium CO conversion and χCO of
the MR could be further enhanced by increasing the reaction pressure
while keeping the permeate pressure unchanged. At high temperatures
and high reaction pressures, CO is rapidly consumed by a fast reaction
that minimizes the membrane permeation of unreacted CO; meanwhile,
the efficiency of H2 removal is improved as a result of
the increased H2 partial pressure difference across the
membrane. The model calculations have indicated that the current membrane
has the potential to achieve high CO conversion of χCO > 99% under practically meaningful operating conditions.
New membrane‐based molecular separation processes are an essential part of the strategy for sustainable chemical production. A large literature on “hybrid” or “mixed‐matrix” membranes exists, in which nanoparticles of a higher‐performance porous material are dispersed in a polymeric matrix to boost performance. We demonstrate that the hybrid membrane concept can be redefined to achieve much higher performance if the membrane matrix and the dispersed phase are both nanoporous crystalline materials, with no polymeric phase. As the first example of such a system, we find that surface‐treated nanoparticles of the zeolite MFI can be incorporated in situ during growth of a polycrystalline membrane of the MOF ZIF‐8. The resulting all‐nanoporous hybrid membrane shows propylene/propane separation characteristics that exceed known upper‐bound performance limits defined for polymers, nanoporous materials, and polymer‐based hybrid membranes. This serves as a starting point for a new generation of chemical separation membranes containing interconnected nanoporous crystalline phases.
We
demonstrate significantly enhanced conversion and selectivity
in high-temperature propane dehydrogenation (PDH) membrane reactors
via the synthesis and use of small-pore SAPO-34 zeolite membranes.
The reduction of SAPO-34 membrane thickness to ∼1 μm
levels while maintaining good H2 selectivity is challenging.
Initial reductions in membrane thickness were achieved using a single
structure-directing agent (SDA) and concentrated precursor solution,
leading to a large permeance increase and good H2/hydrocarbon
selectivity. We further show that thinner (∼1 μm) SAPO-34
membranes can be fabricated on a large area (∼18 cm2) tubular ceramic supports by the use of both base and salt forms
of the SDA to independently control the SDA concentration and pH.
EDX analysis and elemental mapping confirmed the formation of micrometer-thin
(∼1 μm) SAPO-34 zeolite membrane layers on α-alumina
tubular supports. Micrometer-thin SAPO-34 membranes reach propylene
selectivities greater than 80% as well as high propane conversions
(65–75% at weight hourly space velocities of 0.1–0.5
h–1), because of their efficient removal of hydrogen
generated in the PDH reaction.
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