Effective Interfacial Area Research Articles

Wetting Behavior of the Stainless Steel Wire Mesh with Al2O3 Coatings and Mass Transfer Intensification in a Rotating Packed Bed

An Al2O3-coated stainless steel wire mesh packing was prepared, aiming to serve as the monolithic catalyst support applied in a rotating packed bed (RPB) reactor. Before the application, the wetting behavior and gas–liquid mass transfer performance of Al2O3-coated wire mesh packing were investigated in this work. The results showed that the Al2O3-coated stainless steel fiber had on average 18.8% longer liquid spreading length compared with the uncoated stainless steel fiber. The gas–liquid effective interfacial area (ae) and the volumetric liquid-side mass transfer coefficient (kLae) of the RPB with Al2O3-coated wire mesh packing were on average 25.9 and 45.7% higher than those with uncoated wire mesh packing, respectively. The Al2O3-coated wire mesh packing has great prospects for the catalytic reactions in the RPB reactor by providing double functions of mass transfer intensification and the monolithic catalyst support.

Synthesis, structural and electrochemical properties of Mn-MoO4/graphene nanocomposite electrode material with improved performance for supercapacitor application

Abstract In this work a rapid and facile method has been adapted to synthesize Mn-MoO4/G nanocomposites through the self-limiting deposition of nanoscale Mn-MoO4 on the surface of graphene under hydrothermal conditions. The electrochemical performance of the nanostructured Mn-MoO4/G composite materials has been investigated. Mn-MoO4/G nanocomposite displays the specific capacitance as high as 302.08 Fg−1 at 0.1 Ag−1 which is significantly higher than that of GO (121.39 Fg−1) and Mn-MoO4 (201.81 Fg−1) in aqueous electrolyte Na2SO4. It has been observed that the capacitance retention ratio mainly depends on the current density with a maximum retention of 93.8% at 0.7 Ag−1. The energy density of 41.9 Wh kg−1 at the power density of 208 W kg−1 which is higher compared to pure Mn-MoO4. This is attributed to the higher operating voltage of the composite electrode. The improved electrochemical performance may be due to the increase in the electrode conductivity in the presence of graphene network, the increased effective interfacial area between Mn-MoO4 and the electrolyte, as well as the contact area between Mn-MoO4 and graphene.

Modelling of ammonia recovery from wastewater by air stripping in rotating packed beds

The processes of ammonia recovery from ammonia nitrogen containing wastewater by air stripping in the laboratory-scale and the pilot-scale rotating packed bed (RPB) were simulated by the Aspen with the module of RADFRAC. For a more accurate description of the model, a variety of correlations for the RPB were introduced into the Aspen by the FORTRAN, such as the gas-liquid mass transfer rate, the liquid holdup, the heat transfer rate and the effective gas-liquid interfacial area, etc. The predicted data of ammonia recovery rate were consistent with the experimental results. To further optimize the operating conditions of ammonia recovery, the research also covered the effects of high gravity factor, gas to liquid ratio, pH and temperature on ammonia recovery rate. The promising results had suggested the established model could serve as a powerful tool to simulate the processes of ammonia recovery from the ammonia nitrogen containing wastewater by air stripping in the laboratory-scale and the pilot-scale RPB.

Study of mass transfer correlations for rotating packed bed columns in the context of solvent-based carbon capture

The application of rotating packed beds (RPBs) in solvent-based carbon capture processes, will greatly reduce the physical footprint, capital and operating cost of the process. However, in designing RPBs, correlations for predicting mass transfer parameters are generally limited in literature and their prediction accuracies have not been demonstrated independently. In this paper, an RPB absorber model was developed in gPROMS ModelBuilder® and used to test and compare different correlations for predicting the effective interfacial area, liquid and gas film mass transfer coefficients. Our results showed that the modified packed column mass transfer correlations where the “g” term (i.e. gravitational acceleration) is replaced with “rw2” (i.e. centrifugal acceleration) commonly used in literature for RPBs generally give poor predictions compared to using correlations developed specifically for RPBs. Also, the Tung and Mah correlation has better predictive accuracy for the liquid film mass transfer coefficient in RPBs than more complex correlations. Finally, a set of new data for the gas film mass transfer coefficient for RPBs were also derived from overall volumetric mass transfer coefficient (KGa) experimental data from literature. This is the first report of gas film mass transfer data for RPBs. The results in this paper will guide researchers in selecting suitable correlations for predicting mass transfer parameters in RPBs.

Initial liquid dispersion and mass transfer performance in a rotating packed bed

Initial liquid dispersion significantly affects the liquid distribution and mass transfer performance in a rotating packed bed (RPB). However, investigation of initial liquid dispersion in the RPB by using a hydrophobic wire mesh was scarce. In this work, hydrophobic surface-modified stainless steel wire mesh (SSM) and non- surface-modified stainless steel wire mesh (NSM) were prepared and then used as the initial liquid disperser in a RPB. Compared with NSM, the liquid dispersion cone angle of SSM was much bigger after liquid jet impacted on the above rotating single-layer wire mesh, recorded by a high-speed camera. The effective interfacial area (ae) of the RPB with Packing A (single-layer SSM + multilayer NSM) and Packing B (single-layer NSM + multilayer NSM) was experimentally measured by a NaOH−CO2 absorption system. Results show that the values of ae in the RPB with Packing A were 22% higher than with Packing B at optimum operating conditions, which showed that a better initial liquid dispersion was beneficial for better mass transfer performance in the RPB.

Scale-up of a downflow bubble column: Experimental investigations

Co-current downflow bubble columns provide advantages like high gas phase residence time and small bubble diameters, which result in high gas-liquid interfacial area and high mass transfer rates. The precise knowledge of gas fraction, bubble size distribution, interfacial area (a_) and volumetric mass transfer coefficient (kLa_) data is essential for the design of such downflow bubble columns. The present work investigates the effect of superficial gas velocity, liquid velocity and gas sparging location on the volume averaged gas fraction, axial and chordal gas fraction profiles, Sauter-mean bubble size, kLa_, and a_ in a downflow bubble column modified to operate via an array of downward pointing micro-jets. Experiments were performed for air-water system with 20 PPM SDS in two-different scale downflow bubble columns: (1) volume of 5 L (Height (H) = 0.6 m, Diameter (D) = 0.1 m, aspect ratio (H/D) = 6) and (2) volume of 120 L (H = 1.5 m, D = 0.3 m, H/D = 5). The experimental results of axial and chordal gas fraction profiles and bubble size distributions are presented. Further, the empirical correlations have been proposed to predict the gas fraction (∈G), Sauter-mean bubble diameter (dB) and effective gas-liquid interfacial area a_ for better understanding the scale-up process.

A mesoscale 3D CFD analysis of the liquid flow in a rotating packed bed

Rotating packed beds (RPBs), as a type of process intensification technology, are promising to be employed as high-efficiency CO2 absorbers. However, the detailed understanding of the liquid flow in the RPB is still very limited. The complex and dense packing of the bed and the multiscale of the RPB make it very difficult to perform numerical simulations in detail, in particular for full 3D simulations. In this paper, a mesoscale 3D CFD modelling approach is proposed which can be used to investigate the liquid flow in both laboratory- and large-scale RPBs in detail and accuracy. A 3D representative elementary unit of the RPB has been built and validated with experimental observations, and then it is employed to investigate the gas–liquid flows at different locations, across a typical RPB, so that the overall characteristics of the liquid flow in the RPB can be assembled. The proposed approach enables the detailed prediction of the liquid holdup, droplets formation, effective interfacial area, wetted packing area and specific surface area of the liquid within real 3D packing structures throughout the bed. New correlations to predict the liquid holdup, effective interfacial area, and specific surface area of the liquid are proposed, and the sensitivities of these quantities to the rotational speed, liquid flow rate, viscosity and contact angle have been investigated. The results have been compared with experimental data, previous correlations and theoretical values and it shows that the new correlations have a good accuracy in predicting these critical quantities. Further, recommendations for scale-up and operation of an RPB for CO2 capture are provided. This proposed model leads to a much better understanding of the liquid flow behaviours and can assist in the RPB optimisation design and scaling up.

Insight into the experimental and modeling study of process intensification for post-combustion CO2 capture by rotating packed bed

The purpose of rotating packed bed is to intensify process conditions by using centrifugal forces. The effective interfacial area is a critical design factor and has a direct relationship with operational condition and mass transfer rate. Process intensification by the rotating packed bed is an emerging technology to improve the mass transfer rate in a high gravity system. Since there are limited modeling studies in order to control rotating packed bed parameters, in the present study, the multilayer perceptron artificial neural network (MLP) framework was successfully used to investigate the gas-liquid effective interfacial area in a rotating packed bed. In this regard, a number of 265 experimental data for the gas-liquid effective interfacial area was utilized by considering three groups including operational factors, physical dimension, and gas-liquid properties as the network’ inputs. The mean relative error and R-square as analogy factors for verification of the model accuracy obtained to be 8.2% and 0.97, respectively. Accordingly, the present model can be a huge value in the CO2-liquid system and it is introduced as a novel strategy to determine the gas-liquid effective interfacial area in a rotating packed bed.

Highly dispersed conductive polypyrrole hydrogels as sensitive sensor for simultaneous determination of ascorbic acid, dopamine and uric acid

Conductive polymer hydrogels (CPHs) have exhibited great potential as advanced material for sensing. Here, a facile approach to 3D networked polypyrrole (PPy) hydrogel is reported. This strategy relies on the doping of the azo dye molecule Tartrazine during the synthesis of nanostructured conductive PPy hydrogel. The prepared PPy hydrogel can be highly dispersible in the mixed solvent of isopropanol/H2O (4/1). The unique 3D network nanostructure endow PPy hydrogels with high electric conductivity and effective interface area for enhanced sensing performance towards the simultaneous determination of ascorbic acid, dopamine and uric acid with respective lower detection limits of 1.283, 0.044 and 0.046μmolL−1. The as-designed electrochemical sensor also exhibited excellent stability and reproducibility.

Enhanced Electron Collection and Light Harvesting of CH3NH3PbI3 Perovskite Solar Cells Using Nanopatterned Substrates

AbstractIn this study, a CH3NH3PbI3‐based perovskite solar cell (PSC) with high power conversion efficiency (PCE) has achieved by incorporating a nanopatterned fluorine‐doped tin oxide (FTO) substrate (NPFS). This NPFS‐PSC is prepared with different structural depths (100, 150, and 200 nm) using both self‐assembly and sphere lithography techniques. As determine through the optical and electrical analysis of different PSC devices, the NPFS‐PSCs not only display the enhanced light absorption (due to the 2D diffraction grating) but also improve the electron collection efficiency by increasing the FTO/electron transport layer (ETL) and ETL/perovskite effective interface area. Compared to a planar PSC, the photocurrent density of the 200 nm etched NPFS‐PSC is enhanced from 19.27 to 23.81 mA cm−2 leading to an increase in the PCE from 14.21% to 17.85%. These results indicate that introducing the NPFS into the TiO2‐based PSC can improve both light absorption ability and electron extraction and, therefore, represents a novel, promising, high‐performance photovoltaic device.

Role of Doped Nitrogen in Graphene for Flow‐Induced Power Generation

Flow‐induced power generation using nanomaterials, for example, graphene–water interface, has become an attractive energy harvesting mechanism. The effect of heteroatom doping of graphene on flow‐induced electricity is investigated by the authors. Nitrogen‐doped graphene is shown to generate 1.5 times higher power compared with pristine graphene due to surface charges and increase in effective interfacial area. Thus, doping‐induced surface tuning of graphene enhances output performance. The flow‐induced power generation using doped‐graphene allows relaxing the material selection constraints in the triboelectric series.

Reaction Kinetics of CO2 with Monoethanolamine in n-Propanol. 1. Reaction Kinetic Data and Comparison with Existing Rate Law Expressions

The reaction kinetics of CO2 with monoethanolamine is of industrial significance with respect to both CO2 sequestration applications and characterizing the effective interfacial mass transfer area of packed separation columns. Reaction kinetic data were previously, by necessity, only measured under pseudo-first-order conditions with respect to CO2. Furthermore, mass-transfer limitations encountered by the heterogeneous techniques restricted the validity range of the reaction kinetic models developed from the data. New reaction kinetic data, independent of mass-transfer limitations and outside pseudo-first-order conditions, are presented. The data, collected via a previously developed novel, in situ FTIR technique, were subsequently compared with the predictions of two widely accepted rate expressions, the power rate law and pseudo-steady-state hypothesis (PSSH) rate law. The expressions were modeled on the data using a novel multiobjective goal attainment algorithm also developed in this study. The PSSH r...

Gas-liquid mass-transfer behavior of packed-bed scrubbers for floating/offshore CO2 capture

The amine-based CO2 capture performance of packed bed scrubbers onboard offshore floating vessels was assessed in a systematic study using a hexapod robot with six-degree-of-freedom motions and an embarked column packed with structured elements (M500X) and Raschig rings. The potential bottlenecks stemming from ship tilts and oscillations on the mass transfer performance of the packed-bed scrubber were addressed in terms of effective gas-liquid interfacial area, CO2 removal efficiency, and overall volumetric mass-transfer coefficient. The results revealed that the CO2 absorption performance under offshore conditions would deviate from those measured with conventional vertical/stationary packed bed scrubbers. The effective gas-liquid interfacial area was found to decrease with incrementing tilt angle between 0° and 15° both for structured and random packings. Under column roll and roll + pitch oscillations, the interfacial area was also found to diminish monotonically with the oscillation period. Findings from this work indicate that the effect of offshore conditions and their influences on the packed-bed performance should be carefully considered in the design and scale-up of scrubber units subject to offshore floating perturbations since the mass transfer characteristics of packed beds onboard floating vessels are found to degrade with scrubber inclinations and oscillations.

Mass Transfer Studies in a Pilot Scale RPB with Different Packing Diameters

Rotating packed beds (RPBs) aim to intensify mass transfer processes by exploiting centrifugal forces. The limited use of RPBs in the chemical industry can be explained among others by missing comparative studies between state of the art equipment (e.g., packed columns) and RPBs to quantify the benefits that come along by the use of RPBs. The effective interfacial area, mainly dependent on the rotational speed, was found to be equal for both rotors (outer packing radii of 0.18 and 0.28 m, respectively) for rotational speeds larger than 20 s–1. The specific energy dissipation per provided interfacial area is newly introduced in order to link the pressure drop with the mass transfer. Compared to packed columns, the moles of CO2 absorbed per packing volume were found to increase by a factor of up to 3 in RPBs.

The Gas-absorption/Chemical-reaction Method for Measuring Air-water Interfacial Area in Natural Porous Media.

The gas-absorption/chemical-reaction (GACR) method used in Chemical Engineering to quantify gas-liquid interfacial area in reactor systems is adapted for the first time to measure the effective air-water interfacial area of natural porous media. Experiments were conducted with the GACR method, and two standard methods (x-ray microtomographic imaging and interfacial partitioning tracer tests) for comparison, using model glass beads and a natural sand. The results of a series of experiments conducted under identical conditions demonstrated that the GACR method exhibited excellent repeatability for maintaining constant water saturation and for measurement of interfacial area (Aia). Coefficients of variation for Aia were 3.5% for the glass beads and 11% for the sand. Estimated maximum interfacial areas (Am) obtained with the GACR method were statistically identical to independent measures of the specific solid surface areas of the media. For example, the Am for the glass beads is 29 (±1) cm-1, compared to 32 (±3), 30 (±2), and 31 (±2) cm-1 determined from geometric calculation, N2/BET measurement, and microtomographic measurement, respectively. This indicates that the method produced accurate measures of interfacial area. Interfacial areas determined with the GACR method were similar to those obtained with the standard methods. For example, Aias of 47 and 44 cm-1 were measured with the GACR and XMT methods, respectively, for the sand at a water saturation of 0.57. The results of the study indicate that the GACR method is a viable alternative for measuring air-water interfacial areas. The method is relatively quick, inexpensive, and requires no specialized instrumentation compared to the standard methods.

Feasibility studies of micromixing and mass-transfer in an ultrasonic assisted rotating packed bed reactor

Ultrasonic is well-known to be helpful for the improvement of chemical reactions due to its acoustic cavitation. This work reports for the first time the use of ultrasonic to enhance micromixing and mass-transfer in a rotating packed bed (RPB) reactor. The ultrasonic probes were installed as stators on the cover of the RPB reactor. Comparisons of micromixing efficiency, effective interfacial area, and volumetric liquid-side mass-transfer coefficient in the RPB reactor with and without ultrasonic were investigated systematically. A discussion for the micromixing and mass-transfer improvement in the RPB reactor was given. Feasibility studies indicated that the relative segregation index decreasing, the relative effective interfacial area increasing, and the relative volumetric liquid-side mass-transfer coefficient increasing are 13.8%, 3.7%, and 5.5%, respectively.

General mass-transfer model for gas phase in structured packings

Volumetric mass-transfer coefficient in the gas phase, kGa, for Mellapak 250.X and 250.Y structured packings has been measured by standard method of absorption of SO2 from carrier gas to aqueous solution of NaOH in the i.d. 150.6mm absorption column. Three carrier gases – He, N2 and SF6 – have been utilized providing wide range of ScG from 0.49 to 2.32. The gas-phase mass-transfer coefficient, kG, has been calculated from the experimental kGa data as the ratio of kGa and of the effective interfacial area, a, measured utilizing CO2/NaOH system. The experimental and literature kG data for Mellapak 250.X, 250.Y, 350.Y and 500.Y have been correlated by dimensionless correlation ShG=2.7+0.038⋅ReLG0.88⋅ScGβ with β=0.33+0.9⋅exp(−0.6⋅ScG). The correlation fits the data in the wide range of ReLG and ScG covering the process conditions of common absorption and distillation columns.

Study of Mass Transfer Correlations for Intensified Absorbers in Post-combustion CO2 Capture Based on Chemical Absorption

Process intensification (PI) technologies such as rotating packed beds (RPBs) could reduce the size of absorber used in post-combustion CO2 capture (PCC) based on chemical absorption processes by about 12 times compared to absorber with standard packed beds. However, mass transfer correlations for predicting effective interfacial area and liquid film mass transfer coefficient in RPBs are limited in literature and their prediction accuracy against experimental data is yet to be compared. This need is addressed in this study by evaluating the performances of different correlations through comparison with experimental data. Of all the correlations assessed, it is found that Lou et al. [1] and Tung and Mah [2] correlations give reliable estimate of the effective interfacial area and liquid film mass transfer coefficients respectively.

Mass-transfer characteristics in a rotating zigzag bed as a Higee device

Abstract A rotating zigzag bed, as a Higee device, has successfully achieved the industrialization of Higee in the commercial continuous distillation process. To increase applicability of rotating zigzag bed in the gas-liquid mass-transfer processes, the mass-transfer characteristics of the rotor of rotating zigzag bed were examined. The effective interfacial area ( a e ) and local liquid-side mass-transfer coefficient ( k L ) were measured using a chemical absorption of CO 2 in NaOH solution. Based on two-film theory, the local gas-side mass-transfer coefficient ( k G ) was obtained from the overall volumetric gas-side mass-transfer coefficient ( K G a e ) which was measured using a stripping of ethanol from an ethanol-water mixture by air. The effects of rotational speed, liquid volumetric flow rate and gas volumetric flow rate on these mass-transfer parameters were investigated. Compared to the conventional rotating packed bed, the k L of the rotor of rotating zigzag bed was as about 2.5 times higher as that of conventional RPB rotor, and the a e and k G of the rotor of rotating zigzag bed matched with those of the rotor of conventional rotating packed bed. Therefore, rotating zigzag bed has good mass-transfer performance with a great potential for the industrial application.

Absorption methods for the determination of mass transfer parameters of packing internals: A literature review

Methods for the determination of mass‐transfer coefficients and effective interfacial areas in packed absorption columns are reviewed. For each parameter, the methods are grouped into categories on the basis of their physical principle; the chemical systems used, experimental protocol, and the advantages and inconveniences are discussed. The treatment of end effects, the influence of packed bed height, and the recent efforts in standardization of measurement methods are also treated. The aim of the review is to give a broad overview of the methods used in literature in the last eight decades, some of which might be reconsidered in the light of modern measurement techniques and to evaluate them in relation to precision, practicality and hazardousness thereby to facilitate the search for reliable, precise, and convenient experimental practices. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3246–3275, 2017