Concurrent Production of Carbon Monoxide and Manganese(II) Oxide through the Reaction of Carbon Dioxide with Manganese

This study introduces the simultaneous production of manganese oxide (MnO (II)) and carbon monoxide (CO) from the reaction of carbon dioxide (CO₂) with manganese (Mn) at ambient pressures. The reaction results showed that Mn oxidation in the presence of CO₂ creates highly pure MnO (99.4 mol %) and a small portion of another manganese oxide (Mn₃O₄ (III)) with the evolution of CO. It is striking that the oxidation path of manganese under CO₂ environments is totally reverse compared to that under oxygen (O₂) environments, and it produces MnO at much lower temperature (around 700 °C) than the temperature (1700 °C) from the O₂ oxidation path. The different patterns of Mn oxidation by both CO₂ and O₂ can arise from the differences in thermodynamic stability and reactivity of CO₂ and O₂. Additionally, mass spectroscopic measurements revealed that CO generation originates from the CO₂ reduction. Above 700 °C, more CO was produced by the reverse Boudouard reaction occurring between the carbon deposited on the manganese oxide surface and CO₂. This Mn–CO₂ reaction system provides an opportunity for producing more valuable products such as MnO and CO by utilizing the greenhouse gas

Abnormal Proton Positioning of Water Framework in the Presence of Paramagnetic Guest within Ion-Doped Clathrate Hydrate Host

The unique host–guest interactions of ionic clathrate hydrates, as distinct from those of other nonionic clathrate hydrates, need to be investigated to understand their inherent physicochemical features, but direct observation of ionic host geometry has not yet been attempted. In this study, we first report the distortions of the water–water connection in the charged cages caused by orbital mixing between a paramagnetic guest and an ion-doped host, and by electrostatic repulsion between the cationic host and guest via the direct observation with using synchrotron high-resolution powder diffraction analysis. The present findings well explain the mechanisms of unique phenomena occurring in ionic clathrate hydrates with paramagnetic guests

Synergetic Effect of Ionic Liquids on the Kinetic Inhibition Performance of Poly(<i>N</i>‑vinylcaprolactam) for Natural Gas Hydrate Formation

To identify the synergetic inhibition effects of ionic liquids (ILs) containing tetrafluoroborate anion (BF₄^–), various ILs, poly­(<i>N</i>-vinylcaprolactam) (PVCap), commercially available polymeric hydrate inhibitor, and their mixtures, were tested as kinetic hydrate inhibitors (KHIs) for natural gas hydrate formation. The experimental results revealed that PVCap–IL mixtures exhibited significantly higher KHI performance. In particular, the mixture of PVCap and 1-hexyl-1-methylpyrrolidinium tetrafluoroborate (HMP-BF₄) showed the best hydrate inhibition effectiveness, even under higher pressures. As HMP-BF₄ also exhibited the highest hydrate-nucleation-inhibiting performance when it was used alone, further experiments were performed using the mixtures of PVCap and HMP-BF₄ at various combinational concentrations. As a result of the experiments, the combination of 1.0 wt % PVCap and 0.5 wt % HMP-BF₄ was found to provide the longest induction time. The excellent synergetic effect of the ILs on natural gas hydrate inhibition may arise from the prevention of methane-containing 5¹² cage formation by the ILs, inducing inhibition of metastable structure I hydrate formation

Tuning Behaviors of Methane Inclusion in Isoxazole Clathrate Hydrates

In this study, the inclusion of methane (CH₄) gas in isoxazole (C₃H₃NO) clathrate hydrates was investigated through spectroscopic observations, such as powder X-ray diffraction (PXRD) and Raman spectroscopy. PXRD patterns of isoxazole clathrate hydrates having two different mole fractions of water were analyzed, and Raman spectroscopy was used to understand the CH₄ inclusion behaviors in the hydrate cavities. Raman spectra indicated that CH₄ can be captured in both small and large cavities of structure II hydrate in the C₃H₃NO with 34H₂O system, while CH₄ can be entrapped in only small cavities of structure II hydrate in the C₃H₃NO with 17H₂O system. The PXRD result showed both clathrate hydrate samples exhibit the same cubic <i>Fd3m</i> structure II hydrate as expected. However, the structure II hydrate in the C₃H₃NO with 34H₂O system includes a small amount of hexagonal ice and structure I CH₄ hydrate. The phase equilibrium conditions of the binary (isoxazole + CH₄) clathrate hydrate were also identified through high-pressure micro differential scanning calorimetry (MicroDSC), and the equilibrium temperatures of the binary (isoxazole + CH₄) clathrate hydrate at given pressures are higher than those of the structure I CH₄ hydrate

Synergetic Effect of Ionic Liquids on the Kinetic Inhibition Performance of Poly(<i>N</i>‑vinylcaprolactam) for Natural Gas Hydrate Formation

To identify the synergetic inhibition effects of ionic liquids (ILs) containing tetrafluoroborate anion (BF₄^–), various ILs, poly­(<i>N</i>-vinylcaprolactam) (PVCap), commercially available polymeric hydrate inhibitor, and their mixtures, were tested as kinetic hydrate inhibitors (KHIs) for natural gas hydrate formation. The experimental results revealed that PVCap–IL mixtures exhibited significantly higher KHI performance. In particular, the mixture of PVCap and 1-hexyl-1-methylpyrrolidinium tetrafluoroborate (HMP-BF₄) showed the best hydrate inhibition effectiveness, even under higher pressures. As HMP-BF₄ also exhibited the highest hydrate-nucleation-inhibiting performance when it was used alone, further experiments were performed using the mixtures of PVCap and HMP-BF₄ at various combinational concentrations. As a result of the experiments, the combination of 1.0 wt % PVCap and 0.5 wt % HMP-BF₄ was found to provide the longest induction time. The excellent synergetic effect of the ILs on natural gas hydrate inhibition may arise from the prevention of methane-containing 5¹² cage formation by the ILs, inducing inhibition of metastable structure I hydrate formation

Active Control of Inertial Focusing Positions and Particle Separations Enabled by Velocity Profile Tuning with Coflow Systems

Inertial microfluidics has drawn much attention not only for its diverse applications but also for counterintuitive new fluid dynamic behaviors. Inertial focusing positions are determined by two lift forces, that is, shear gradient and wall-induced lift forces, that are generally known to be opposite in direction in the flow through a channel. However, the direction of shear gradient lift force can be reversed if velocity profiles are shaped properly. We used coflows of two liquids with different viscosities to produce complex velocity profiles that lead to inflection point focusing and alteration of inertial focusing positions; the number and the locations of focusing positions could be actively controlled by tuning flow rates and viscosities of the liquids. Interestingly, 3-inlet coflow systems showed focusing mode switching between inflection point focusing and channel face focusing depending on Reynolds number and particle size. The focusing mode switching occurred at a specific size threshold, which was easily adjustable with the viscosity ratio of the coflows. This property led to different-sized particles focusing at completely different focusing positions and resulted in highly efficient particle separation of which the separation threshold was tunable. Passive separation techniques, including inertial microfluidics, generally have a limitation in the control of separation parameters. Coflow systems can provide a simple and versatile platform for active tuning of velocity profiles and subsequent inertial focusing characteristics, which was demonstrated by active control of the focusing mode using viscosity ratio tuning and temperature changes of the coflows

Size-Dependent Inertial Focusing Position Shift and Particle Separations in Triangular Microchannels

A recent study of inertial microfluidics within nonrectangular cross-section channels showed that the inertial focusing positions changes with cross-sectional shapes; therefore, the cross-sectional shape can be a useful control parameter for microfluidic particle manipulations. Here, we conducted detail investigation on unique <i>focusing position shift</i> phenomena, which occurs strongly in channels with the cross-sectional shape of the isosceles right triangle. The top focusing positions shift along the channel walls to the direction away from the apex with increasing Reynolds number and decreasing particle size. A larger particle with its center further away from the side walls experiences shear gradient lift toward the apex, which leads to an opposite result with changes of Reynolds and particle size. The focusing position shift and the subsequent stabilization of corner focusing lead to changes in the number of focusing positions, which enables a novel method for microparticle separations with high efficiency (>95%) and resolution (<2 μm). The separation method based on equilibrium focusing; therefore, the operation is simple and no complex separation optimization is needed. Moreover, the separation threshold can be easily modulated with flow rate adjustment. Rare cell separation from blood cell was successfully demonstrated with spiked MCF-7 cells in blood by achieving the yield of ∼95% and the throughput of ∼10⁶ cells/min

Rollable Microfluidic Systems with Microscale Bending Radius and Tuning of Device Function with Reconfigurable 3D Channel Geometry

Flexible microfluidic system is an essential component of wearable biosensors to handle body fluids. A parylene-based, thin-film microfluidic system is developed to achieve flexible microfluidics with microscale bending radius. A new molding and bonding technique is developed for parylene microchannel fabrication. Bonding with nanoadhesive layers deposited by initiated chemical vapor deposition (iCVD) enables the construction of microfluidic channels with short fabrication time and high bonding strength. The high mechanical strength of parylene allows less channel deformation from the internal pressure for the thin-film parylene channel than bulk PDMS channel. At the same time, negligible channel sagging or collapse is observed during channel bending down to a few hundreds of micrometers due to stress relaxation by prestretch structure. The flexible parylene channels are also developed into a rollable microfluidic system. In a rollable microfluidics format, 2D parylene channels can be rolled around a capillary tubing working as inlets to minimize the device footprint. In addition, we show that creating reconfigurable 3D channel geometry with microscale bending radius can lead to tunable device function: tunable Dean-flow mixer is demonstrated using reconfigurable microscale 3D curved channel. Flexible parylene microfluidics with microscale bending radius is expected to provide an important breakthrough for many fields including wearable biosensors and tunable 3D microfluidics