Two‐dimensional visualizations of point‐source liquid spills in porous media were performed in a flat rectangular packed bed, emplaced on a robotized hexapod, to emulate roll/pitch marine ...oscillations. The extent to which the directional modulation of liquid gravity and the moving‐bed inertial forces affect the liquid spills was the study's central aim. Spill morphology deviations were dictated by gravity force oscillations, while Coriolis/Euler/centrifugal forces were confined to secondary roles. Multiple gravity‐driven liquid branching with departures from the longitudinal direction, not only boosted wetting but also symmetrized the developing spills while suppressing the wall‐biased liquid influx, which impaired inclined beds. Wetting exhibited asymmetric sigmoidal deceleratory transients, reminiscent of many physicochemical transformations with skewed activation energy distribution. The parameters describing the dispersive kinetics and allied activation energy distribution of wetting—analogized to a phase change transition—were interpreted in terms of hexapod kinematic parameters.
Oxidation of n‐butane to produce maleic anhydride (MA) by the vanadium phosphorus oxide (VPO) catalyst is important for the fine chemical industry. However, the improvement in MA yield exceeding 60% ...is still a big challenge. In this article, a VPO catalyst with increased MA yield originated from the tailored structure of VPO precursor prepared in a rotating packed bed (RPB) reactor with excellent micro‐mixing efficiency. The activated VPO‐RPB catalyst displayed the coexistence of X1‐VOPO4 and αI‐VOPO4 phases and enhanced reducibility of V4+ state. Remarkably, the MA yield in n‐butane oxidation catalyzed by VPO‐RPB reached up to 66%, showing an increment by 14% compared with VPO‐STR prepared in a stirring tank reactor (STR). The VPO‐RPB showed the repeatable catalytic performance and achieved a promising scale‐up production. This work provides the experimental evidence of a dual‐phase (X1‐VOPO4 and αI‐VOPO4) mechanism for n‐butane oxidation, and reveals the structure–activity dependence of VPO catalyst.
The improvement of liquid dispersion by rotating wire mesh is one of the major causes for the mass transfer and micromixing intensification in rotating packed beds (RPBs). In particular, the initial ...dispersion region has been proved to have the greatest mass transfer and micromixing efficiency. However, the dispersion mechanism has not been revealed. This study investigated the dynamics of liquid dispersion in an RPB with single‐layer wire mesh. The liquid dispersion behaviors were obtained by high‐speed photography and numerical simulation. The liquid was found to stretch into ligaments and break into the main droplet and several satellite droplets. A new theoretical model was established to reveal the dispersion mechanism of these two stages. The stretching stage depends on the liquid initial momentum and acquired impulse, while the breakup stage was determined by the competition of ligaments recoil and pinch‐off behaviors. The model was validated in good agreement with the experimental and simulation results of the dispersion characteristics.
Liquid flow behaviors in the packing zone of a rotating packed bed reactor significantly affect the mass transfer performance. However, the interaction between the rotating packing and liquid is ...still not clear, due to packing's complex structure. In this work, liquid jet impaction on a rotating single‐layer wire mesh was investigated to clarify the interaction and liquid flow behaviors after the impaction was observed and analyzed by visualization and simulation methods. Visual experiments showed that the interaction could be divided into the shearing action generated by vertical fibers and carrying action generated by horizontal fibers of wire mesh. A dimensionless number β was introduced as a criterion to evaluate the influence of these actions on the liquid dispersion. Simulation results agreed well with the experimental results of liquid dispersion. Dynamic liquid film behaviors on the fiber surface were further simulated and the average film thickness was 21–32 μm.
Abstract
Dehydrochlorination of 1,3‐dichloropropanol with alkali is a key step to industrially produce epichlorohydrin. But there are many side reactions involved in the synthesis process. In this ...work, a complete mechanism and kinetics investigation of the related reaction network was constructed. Density functional theory simulation method was first used to simulate the possible reactions so as to confirm the reaction mechanism and simplify the reaction network. Based on the simulation results, the complex reaction network was simplified into a three‐step consecutive reaction. The kinetic parameters of the three consecutive steps, including the order of the reaction, the pre‐exponential factor, and activation energy, were experimentally determined by conductance and other methods. All the experimental results are basically consistent with the simulation. The obtained kinetics data provide a basis for epichlorohydrin synthesis process optimization.
Mixing of two immiscible liquids consists of two sections that are liquid‐liquid dispersion and mass transfer intraphase or interphase. It plays a crucial role in the liquid‐liquid heterogeneous ...reactions. Here, the liquid‐liquid heterogeneous mixing efficiency in RPB reactor is experimentally assessed by a consecutive‐competitive chemical probe system. The diameters of dispersed phase droplets in RPB were measured and a correlation to predict the mean diameters were obtained. Based on the dispersed phase size and mass transfer characteristic, a model for predicting the segregation index of liquid‐liquid heterogeneous mixing in RPB was established with a deviation <20%. Based on this model, the characteristic time of liquid‐liquid heterogeneous mixing in RPB is determined to be in the range of 0.01–1 s. RPB exhibits a great process intensification potential for heterogeneous mixing process.
A rotating packed bed (RPB) is recognized for its merits in chemical process intensification. In most studies of RPB mass transfer modeling, however, the effects of the end and cavity zones have not ...been taken into consideration, since it was very difficult to distinguish the end and bulk zones by hydrodynamics and mass transfer process. In this work, the radial thickness of the end zone was obtained by developing a probability method and imaging experiments to separate the end and bulk zones. A three‐zone model, including end, bulk, and cavity zones, of the overall gas‐side volumetric mass transfer coefficient (KGa)t was first established. Experiments of dissolved MEA chemisorption of CO2 were carried out to validate the proposed three‐zone mass transfer model. The results of the MEA‐CO2 absorption experiments showed that the experimentally obtained values of CO2 absorption efficiency were in agreement within ±20% with the model predictions.
•Grids were established based on the reconstructed information from CT scan.•RSM/Euler and LES/VOF model were applied for the simulations.•Droplet and film flow were predicted to develop inside ...packing’s microchannels.•Liquid microflow will help to optimize the packing structure.
The liquid holdup and microflow in a rotating packed bed (RPB) reactor with nickel foam packing were studied by computational fluid dynamics. We used X-ray computed micro-tomography (CT) to obtain the structural information characterizing the packing. The geometry and grids were established based on the space-resolved reconstructed information from the CT scans. The Reynolds stress model with Eulerian approach and the large eddy simulation with volume-of-fluid approach were implemented. Simulation results show that once the liquid was jetted into the packing zone, it would be quickly split and synchronized with the packing rotation. Two liquid flow patterns of droplet and film flow were predicted to develop inside the microchannels of the packing zone as these were experimentally observed and confirmed by a high-speed camera. The present investigation of liquid microflow will help to optimize the packing structure and to develop befitting mass transfer models.
A rotating trickle‐bed reactor (RTBR), having the advantage of mass transfer enhancement of 1–3 orders of magnitude higher than a packed column reactor, can intensify the apparent reaction rate of ...gas–liquid–solid catalytic reactions. However, studies of hydrodynamics like liquid holdup and wetting efficiency, which are essential for the RTBR design, are scarce. In this work, we have systematically, for the first time, investigated the liquid holdup and wetting efficiency in a RTBR packed with alumina spheres. The quantitative results revealed that the rotation reduced the static liquid holdup by about 80% at rotational speed from 0 to 2,400 r/min. The average wetting efficiency can reach 100% at rotational speed of 1,600 r/min and liquid superficial mass velocity of 3 kg/(m2·s). Correlations to predict the liquid holdup and wetting efficiency in the RTBR were developed, and deviations between experimental and calculated values were within ±15 and ±10%, respectively. The findings of the current work provided basic data for the potential catalytic reactions limited by mass transfer in the RTBR.
Postsynaptic NMDARs at spinal synapses are required for postsynaptic long-term potentiation and chronic pain. However, how presynaptic NMDARs (PreNMDARs) in spinal nociceptor terminals control ...presynaptic plasticity and pain hypersensitivity has remained unclear. Here we report that PreNMDARs in spinal nociceptor terminals modulate synaptic transmission in a nociceptive tone-dependent manner. PreNMDARs depresses presynaptic transmission in basal state, while paradoxically causing presynaptic potentiation upon injury. This state-dependent modulation is dependent on Ca
influx via PreNMDARs. Small conductance Ca
-activated K
(SK) channels are responsible for PreNMDARs-mediated synaptic depression. Rather, tissue inflammation induces PreNMDARs-PKG-I-dependent BDNF secretion from spinal nociceptor terminals, leading to SK channels downregulation, which in turn converts presynaptic depression to potentiation. Our findings shed light on the state-dependent characteristics of PreNMDARs in spinal nociceptor terminals on modulating nociceptive transmission and revealed a mechanism underlying state-dependent transition. Moreover, we identify PreNMDARs in spinal nociceptor terminals as key constituents of activity-dependent pain sensitization.
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