Browsing by Author "Langmi, Henrietta W."

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    Compaction of a zirconium metal–organic framework (UiO-66) for high density hydrogen storage applications
    (Royal Society of Chemistry, 2018) Bambalaza, Sonwabo E.; Langmi, Henrietta W.; Mokaya, Robert; Musyoka, Nicholas M.; Renad, Jianwei; Khotseng, Lindiwe E.
    We report a rare case whereby a metal–organic framework (MOF), namely UiO-66, is compacted at high pressure ( 700 MPa or 100 000 psi) resulting in densification and improved total volumetric hydrogen storage capacity, but crucially, without compromising the total gravimetric uptake attained in the powdered form of the MOF. The applied compaction pressure is also unprecedented for MOFs as most studies have shown the MOF structure to collapse when compacted at very high pressure. The UiO-66 prepared in this study retained 98% of the original surface area and microporosity after compaction at 700 MPa, and the densified pellets achieved a total H2 uptake of 5.1 wt% at 100 bar and 77 K compared to 5.0 wt% for the UiO-66 powder. Depending on the method used to compute the volumetric uptake, the densified UiO-66 attained unprecedented volumetric capacity at 77 K and 100 bar of up to 74 g L 1 (13 g L 1 at 298 K) compared to 29 g L 1 for the powder (6 g L 1 at 298 K) using a conventional method that takes into account the packing density of the adsorbents, or 43 g L 1 (compared to 35 g L 1 for the powder at 77 K and 100 bar) based on a method that uses both the single crystal and skeletal densities of MOFs. However, regardless of the difference in the calculated values according to the two methods, the concept of UiO-66 compaction for improving volumetric capacity without compromising gravimetric uptake is clearly proven in this study and shows promise for the achievement of hydrogen storage targets for a single material as set by the United States Department of Energy (DOE).
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    The production of hydrogen through the use of a 77 wt% Pd 23 wt% Ag membrane water gas shift Reactor
    (Elsevier, 2016) Baloyi, Liberty N.; North, Brian C.; Langmi, Henrietta W.; Bladergroen, Bernard J.; Ojumu, Tunde V.
    Hydrogen as an energy carrier has the potential to decarbonize the energy sector. This work presents the application of a palladium-silver (PdeAg) membrane-based reactor. The membrane reactor which is made from PdeAg film supported by porous stainless steel (PSS) is evaluated for the production of hydrogen and the potential replacement of the current two stage Water-Gas Shift (WGS) reaction by a single stage reaction. The permeability of a 20 mm PdeAg membrane reactor was examined at 320 _C, 380 _C and 430 _C. The effect of continuous hydrogen exposure on the PdeAg membrane at high temperature and low temperature was examined to investigate the thermal stability and durability of the membrane. During continuous operation to determine thermal stability, the membrane reactor exhibited stable hydrogen permeation at 320 _C for 120 h and unstable hydrogen permeation at 430 _C was observed. For the WGS reaction, the reactor was loaded with Ferrochrome catalyst. The membrane showed the ability to produce high purity hydrogen, with a CO conversion and an H2 recovery of 84% and 88%, respectively. The membrane suffered from hydrogen embrittlement due to desorption and adsorption of hydrogen on the membrane surface. SEM analysis revealed cracks that occurred on the surface of the membrane after hydrogen exposure. XRD analysis revealed lattice expansion after hydrogen loading which suggests the occurrence of phase change from a-phase to the more brittle b phase.
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    The production of hydrogen through the use of a 77 wt% Pd 23 wt% Ag membrane water gas shift reactor
    (Elsevier, 2016) Baloyi, Liberty N.; North, Brian C.; Langmi, Henrietta W.; Bladergroen, Bernard Jan; Ojumu, Tunde V.
    Hydrogen as an energy carrier has the potential to decarbonize the energy sector. This work presents the application of a palladium-silver (PdeAg) membrane-based reactor. The membrane reactor which is made from PdeAg film supported by porous stainless steel (PSS) is evaluated for the production of hydrogen and the potential replacement of the current two-stage Water-Gas Shift (WGS) reaction by a single stage reaction. The permeability of a 20 mmPdeAg membrane reactor was examined at 320° C, 380° C and 430° C. The effect of continuous hydrogen exposure on the PdeAg membrane at high temperature and low temperature was examined to investigate the thermal stability and durability of the membrane. During continuous operation to determine thermal stability, the membrane reactor exhibited stable hydrogen permeation at 320° C for 120 h and unstable hydrogen permeation at 430° C was observed. For the WGS reaction, the reactor was loaded with Ferrochrome catalyst. The membrane showed the ability to produce high purity hydrogen, with a CO conversion and an H2 recovery of 84% and 88%, respectively. The membrane suffered from hydrogen embrittlement due to desorption and adsorption of hydrogen on the membrane surface. SEM analysis revealed cracks that occurred on the surface of the membrane after hydrogen exposure. XRD analysis revealed lattice expansion after hydrogen loading which suggests the occurrence of phase change from a-phase to the more brittle b-phase.