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  • A trimethylamine–carbon dioxide draw solution for osmotic engines
    AlChE J. (IF 2.836) Pub Date : 2018-04-19
    Lingling Xia; Jason T. Arena; Jian Ren; Kevin K. Reimund; Amy Holland; Aaron D. Wilson; Jeffrey R. McCutcheon

    This study evaluates the pressure retarded osmosis performance of TMA–CO2 for potential use in osmotic heat engines. Power densities up to 18.6 W m−2 were achievable at relatively low pressure (10 bar) using 5 M TMA–CO2 draw solutions. Compared to NaCl control tests, the TMA–CO2 exhibited 20% lower water flux due in large part to its larger molecular size and associated higher solution viscosity and lower diffusion coefficient. Compared to the ammonia‐carbon dioxide draw solution, water flux was comparable but reverse solute flux of TMA–CO2 was nearly one order of magnitude lower. Larger solute size was found to create a performance tradeoff as reduced reverse solute flux improved water flux while higher viscosity and lower diffusion coefficient worsened water flux. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-04-20
  • Modeling granular material blending in a rotating drum using a finite element method and advection‐diffusion equation multiscale model
    AlChE J. (IF 2.836) Pub Date : 2018-04-19
    Yu Liu; Marcial Gonzalez; Carl Wassgren

    A multiscale model is presented for predicting the magnitude and rate of powder blending in a rotating drum blender. The model combines particle diffusion coefficient correlations from the literature with advective flow field information from blender finite element method simulations. The multiscale model predictions for overall mixing and local concentration variance closely match results from discrete element method (DEM) simulations for a rotating drum, but take only hours to compute as opposed to taking days of computation time for the DEM simulations. Parametric studies were performed using the multiscale model to investigate the influence of various parameters on mixing behavior. The multiscale model is expected to be more amenable to predicting mixing in complex geometries and scale more efficiently to industrial‐scale blenders than DEM simulations or analytical solutions. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-04-20
  • Residual film thickness following immiscible fluid displacement in noncircular microchannels at large capillary number
    AlChE J. (IF 2.836) Pub Date : 2018-04-17
    Yu Lu; Nina M. Kovalchuk; Mark J. H. Simmons

    An experimental study of the displacement of one immiscible fluid by another was performed in microchannels with circular, square and near‐semicircular cross‐sections, with hydraulic diameters from 100 to 200 μm. Experiments were performed over a range of capillary number, Ca, from 0.02 < Ca < 80, with viscosity ratios between the two fluids ranging from 20 to 100. The liquid film left on the channel wall following the advance of the displacing fluid was obtained from visual measurements and a method for the estimation of mean film thickness was shown to be in good agreement with existing correlations. The addition of a surfactant (Sodium Dodecyl Sulfate, SDS) dissolved in the displacing fluid led to a reduction in the thickness of the residual film. © 2018 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-04-17
  • Liquid‐bridge flow in the channel of helical string and its application to gas–liquid contacting process
    AlChE J. (IF 2.836) Pub Date : 2018-04-17
    Haifeng Cong; Zhenyu Zhao; Xingang Li; Hong Li; Xin Gao

    To solve the problems of the traditional packings, such as high pressure drop, mal‐distribution and short liquid residence time, a helical flow structured packings was proposed. Two different flow patterns, liquid‐bridge flow and liquid‐drop flow were identified when the width of the channel of the helical string was adjusted. Moreover, the characteristics of the helical liquid‐bridge flow including maximum liquid loading, mean thickness of liquid film, mean residence time and effective specific surface area, were examined. And the separation efficiency was studied by the lab‐scale distillation column. In comparison, the effective specific surface area of the helical flow type packings is almost as large as the traditional B1‐350Y structured packings, but with thinner liquid film, longer liquid residence time and finally higher separation efficiency. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-04-17
  • Co‐doped ZnO thin films grown by pulsed electron beam ablation as model nano‐catalysts in fischer‐tropsch synthesis
    AlChE J. (IF 2.836) Pub Date : 2018-04-16
    Asghar Ali; Redhouane Henda; James Aluha; Nicolas Abatzoglou

    A single‐step deposition of cobalt‐doped zinc oxide (Co‐ZnO) thin film nano‐composites on three different crystalline substrates, viz., Al2O3 (c‐sapphire), silicon (100) (Si), and SiO2 (quartz) is reported, using pulsed electron beam ablation (PEBA). The results indicate that the type of substrate has no effect on Co‐ZnO films stoichiometry, morphology, microstructure, and film thickness. The findings show the presence of hexagonal close‐packed metallic Co whose content increases in the films deposited on Al2O3 and Si substrates relatively to SiO2 substrate. The potential of the films as model nano‐catalysts has been evaluated in the context of the Fischer‐Tropsch (FT) process. Fuel fractions, which have been observed in FT liquid products, are rich in diesel and waxes. Specifically, Co‐ZnO/Al2O3 nano‐catalyst shows a selectivity of ∼4%, 31%, and 65% towards gasoline, diesel, and waxes, respectively, while Co‐ZnO/SiO2 nano‐catalyst shows a selectivity of ∼12%, 51%, and 37%, for gasoline, diesel, and waxes, respectively. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-04-17
  • Manganese‐containing redox catalysts for selective hydrogen combustion under a cyclic redox scheme
    AlChE J. (IF 2.836) Pub Date : 2018-04-16
    Ryan B. Dudek; Yunfei Gao; Junshe Zhang; Fanxing Li

    Selective hydrogen combustion (SHC) in the presence of light hydrocarbons was demonstrated with a series of Mn‐containing mixed oxide redox catalysts in the context of a chemical looping‐oxidative dehydrogenation scheme. Unpromoted and 20 wt % Na2WO4‐promoted Mg6MnO8, SrMnO3, and CaMnO3 exhibited varying SHC capabilities at temperatures between 550 and 850°C. Reduction temperature of unpromoted redox catalysts increased in the order Mg6MnO8 < SrMnO3 < CaMnO3. Promotion with 20 wt % Na2WO4 resulted in more selective redox catalysts capable of high‐temperature SHC. XPS analysis revealed a correlation between suppression of near‐surface Mn and SHC selectivity. Na2WO4/CaMnO3 showed steady SHC performance (89% H2 conversion, 88% selectivity) at 850°C over 50 redox cycles. In series with a Cr2O3/Al2O3 ethane dehydrogenation catalyst, Na2WO4/CaMnO3 combusted 84% of H2 produced while limiting COx yield below 2%. The redox catalysts reported can be suitable for SHC in a cyclic redox scheme for the production of light olefins from alkanes. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-04-17
  • Effect of fuel composition on NOx formation in high‐pressure syngas/air combustion
    AlChE J. (IF 2.836) Pub Date : 2018-04-11
    Nazli Asgari; Bihter Padak

    In this study, an experimental investigation of lean premixed syngas/air flames with H2/CO ratio of 1.0 and equivalence ratio of 0.5 has been conducted in a high‐pressure burner facility to investigate the effects of pressure and the presence of hydrocarbons on NOx speciation. Detailed NOx speciation measurements in the post‐flame region were conducted for various pressures up to 1.5 MPa (15 bar) using Fourier transform infrared (FTIR) spectroscopy. When the pressure is increased, NO concentration decreases while NO2 increases due to pressure dependence of NO to NO2 conversion. For a given pressure, the presence of hydrocarbons in syngas leads to an increase in NOx concentrations possibly due to prompt NO formation. Comparison of NO concentrations in presence of CH4 at different pressures shows that the effect of CH4 due to prompt NO formation is more dominant than the effect of pressure on NO. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-04-11
  • Morphology evolution and dynamics of droplet coalescence on superhydrophobic surfaces
    AlChE J. (IF 2.836) Pub Date : 2018-04-10
    Kai Wang; Qianqing Liang; Rui Jiang; Yi Zheng; Zhong Lan; Xuehu Ma

    In this work, the coalescence of two equal‐sized water droplets on superhydrophobic surfaces (SHSs) is experimentally investigated. The morphologies of droplet coalescence are observed from side‐view and bottom‐view using high‐speed camera system. The related morphology evolution and dynamics of droplet coalescence are explored. The dynamic behaviors of droplet coalescence on SHSs can be decomposed into liquid bridge growth, contact line evolution, and droplet jumping. The liquid bridge radius is proportional to the square root of time, whereas the dimensionless prefactor is decreased from 1.18 to 0.83 due to the transition of interface curvature. The retraction velocity of the contact line shows limited dependence on initial droplet radii as the retraction dynamics considered here are governed by the capillary–inertial effect. The coalesced droplet finally departs the substrate with a dimensionless jumping velocity of around 0.2. A heuristic argument is made to account for the nearly constant dimensionless jumping velocity. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-04-11
  • Near‐UV activated, photostable nanophosphors for in vitro dosimetry and dynamic bioimaging
    AlChE J. (IF 2.836) Pub Date : 2018-04-10
    Anastasia Spyrogianni; Peter Tiefenboeck; Fabian H. L. Starsich; Kerda Keevend; Frank Krumeich; Inge K. Herrmann; Jean‐Christophe Leroux; Georgios A. Sotiriou

    Luminescent rare earth nanoparticles exhibit superior optical stability over commonly‐used organic dyes and higher biocompatibility over quantum dots, rendering them advantageous as bioimaging nanoprobes. However, their typical excitation inhibits their broad employment with conventional fluorescence microscopes and, thus, solutions are sought to shift their activation in the long‐wavelength (near‐UV) spectral region. Here, we synthesize YVO4:Eu3+ nanophosphors by flame aerosol technology to systematically study the effect of Bi3+ codoping on their luminescence. That way, we identify an optimal Bi‐content for sufficient near‐UV activation. These nanophosphors are highly crystalline and appeared bright red under a conventional fluorescence microscope, facilitating bioimaging with HeLa cells and in vitro dosimetry correlations in the presence and absence of serum. The nanophosphor superiority over organic‐dye‐labeled silica nanoparticles is shown during dynamic imaging for 4 h without photobleaching for the former. These YVO4:Eu3+/Bi3+ nanophosphors can provide a non‐photobleaching tool for further dynamic nanoparticle‐cell interaction studies with conventional fluorescence microscopes. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-04-11
  • Design of active NiCo2O4‐δ spinel catalyst for abatement of CO‐CH4 emissions from CNG fueled vehicles
    AlChE J. (IF 2.836) Pub Date : 2018-04-06
    S. Trivedi; R. Prasad; S. K. Gautam

    Increasing number of CNG vehicles on road emits considerable amount of CO, a poisonous gas and CH4, a greenhouse‐gas. Highly active and oxygen‐deficient NiCo2O4‐δ spinel and its individual metal‐oxides were synthesized by calcination of precipitated/co‐precipitated basic‐carbonates followed by calcination under different strategies of stagnant air(s), flowing air(f) and reactive calcination(RC) for total oxidation of CO‐CH4 mixture. The catalysts were characterized by XRD, XPS, BET surface‐area, SEM‐EDX and TEM. The performance order of the catalysts for the oxidation of CO‐CH4 mixture was as follows: NiCoRC>NiCof>NiCos>CoRC>Cof>Cos>NiRC> Nif>Nis. The pairing of Ni and Co in spinel‐structure together with RC produced catalyst was oxygen‐deficient highly active for total oxidation of the mixture at the lowest temperature of 350°C. The NiCoRC was found stable under reaction‐conditions for 50h at 350°C and after four successive heating (350°C)‐cooling (35°C) cycles besides accelerated‐aging tests up to 600°C. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-04-10
  • The effect of mixing on Co‐precipitation and evolution of microstructure of Cu‐ZnO catalyst
    AlChE J. (IF 2.836) Pub Date : 2018-04-06
    Xin Jiang; Xiangfei Qin; Chen Ling; Zhiyong Wang; Jiangang Lu

    The influence of feeding point in conventional stirred tank reactor and flow characteristics in micro‐reactor on the microstructure of Cu‐ZnO catalyst was studied. Cu‐Zn distribution in co‐precipitate was characterized by EDS and Zn fraction in zincian malachite was estimated from the 20 peak shift in XRD pattern. The theory analysis and experimental results, combining with measurement of segregation index, show that the contact pattern and mixing of reactants in precipitation process determine the uniformity of Cu‐Zn distribution in initial co‐precipitates at the micro‐scale. The uniform Cu‐Zn distribution is favorable for the formation of zincian malachite with higher Zn fraction, whereas the uneven distribution could lead to either zincian malachite with lower Zn fraction or aurichalcite‐like nonmalachite. These differences in the precursor structure act on subsequent calcination and reduction, as well as their products. Along this path, mixing affects the evolution of the catalyst microstructure by means of Cu‐Zn distribution. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-04-10
  • Nano‐engineered nickel catalysts supported on 4‐channel α‐Al2O3 hollow fibers for dry reforming of methane
    AlChE J. (IF 2.836) Pub Date : 2018-03-30
    Zeyu Shang; Shiguang Li; Qingfa Wang; Xuehong Gu; Xinhua Liang

    A nickel (Ni) nanoparticle catalyst, supported on 4‐channel α‐Al2O3 hollow fibers, was synthesized by atomic layer deposition (ALD). Highly dispersed Ni nanoparticles were successfully deposited on the outside surfaces and the inside porous structures of hollow fibers. The catalyst was employed to catalyze the dry reforming of methane (DRM) reaction and showed a methane reforming rate of 2040 Lh−1gNi−1 at 800°C. NiAl2O4 spinel was formed when Ni nanoparticles were deposited on alpha‐alumina substrates by ALD, which enhanced the Ni‐support interaction. Different cycles (two, five, and ten) of Al2O3 ALD films were applied on the Ni/hollow fiber catalysts to further improve the interaction between the Ni nanoparticles and the hollow fiber support. Both the catalyst activity and stability were improved with the deposition of Al2O3 ALD films. Among the Al2O3 ALD coated catalysts, the catalyst with five cycles of Al2O3 ALD showed the best performance. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-31
  • Investigation mechanism of DEA as an activator on aqueous MEA solution for postcombustion CO2 capture
    AlChE J. (IF 2.836) Pub Date : 2018-03-30
    Helei Liu; Moxia Li; Xiao Luo; Zhiwu Liang; Raphael Idem; Paitoon Tontiwachwuthikul

    In this work, Diethanolamine (DEA) was considered as an activator to enhance the CO2 capture performance of Monoethanolamine (MEA). The addition of DEA into MEA system was expected to improve disadvantages of MEA on regeneration heat, degradation, and corrosivity. To understand the reaction mechanism of blended MEA‐DEA solvent and CO2, 13C nuclear magnetic resonance (NMR) technique was used to study the ions (MEACOO‐, DEACOO–, MEA, DEA, MEAH+, DEAH+, , ) speciation in the blended MEA‐DEA‐CO2‐H2O systems with CO2 loading range from 0 to 0.7 mol CO2/mol amine at the temperature of 301 K. The different ratios of MEA and DEA (MEA: DEA = 2.0:0, 1.5:0.5, 1.0:1.0, and 0:2.0) were studied to comprehensively investigate the role of DEA in the system of MEA‐DEA‐CO2‐H2O. The results revealed that DEA performs the coordinative role at the low CO2 loading and the competitive role at high CO2 loading. Additionally, the mechanism was also proposed to interpret the reaction process of the blended solvent with CO2. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-31
  • Novel aeration of a large‐scale flat sheet MBR: A CFD and experimental investigation
    AlChE J. (IF 2.836) Pub Date : 2018-03-30
    Bing Wang; Kaisong Zhang; Robert W. Field

    Having previously established that the hydrodynamic effect introduced by slug bubbles is more effective and economic in fouling amelioration in flat sheet MBRs (FSMBR) than conventional bubbling, this work is focused on its implementation in a commercial FSMBR. The overall objective is to enhance the hydrodynamic effect on fouling control through the use of two‐stage large‐sized bubble development (coalescence and split). Computational Fluid Dynamics (CFD) was used to predict hydrodynamic features and substantial agreement was observed with experimental measurements. The critical height for bubble development space was determined to be circa 250 mm. Slug bubbles could be introduced into 14 channels, resulting in six‐fold stronger shear stress than that from single bubbles. Energy demand could be reduced by circa 50% compared with industry average usage and the shear stresses developed would, for most applications, be sufficient to ameliorate fouling. Furthermore, the specific air demand per permeate would be halved. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-31
  • Machine learning for crystal identification and discovery
    AlChE J. (IF 2.836) Pub Date : 2018-03-30
    Matthew Spellings; Sharon C. Glotzer

    As computers get faster, researchers—not hardware or algorithms—become the bottleneck in scientific discovery. Computational study of colloidal self‐assembly is one area that is keenly affected: even after computers generate massive amounts of raw data, performing an exhaustive search to determine what (if any) ordered structures occur in a large parameter space of many simulations can be excruciating. We demonstrate how machine learning can be applied to discover interesting areas of parameter space in colloidal self‐assembly. We create numerical fingerprints—inspired by bond orientational order diagrams—of structures found in self‐assembly studies and use these descriptors to both find interesting regions in a phase diagram and identify characteristic local environments in simulations in an automated manner for simple and complex crystal structures. Utilizing these methods allows analysis to keep up with the data generation ability of modern high‐throughput computing environments. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-31
  • Scale‐dependent nonequilibrium features in a bubbling fluidized bed
    AlChE J. (IF 2.836) Pub Date : 2018-03-30
    Haifeng Wang; Yanpei Chen; Wei Wang

    We investigate experimentally the nonequilibrium features in a pseudo 2‐D bubbling fluidized bed. Velocities of individual particles are measured by using a particle tracking velocimetry (PTV) method, and void fractions are obtained with the Voronoi tessellation. A bimodal shape of probability density function (PDF) for particle vertical velocity is found in not only time‐averaged but also time‐varying statistics, which is caused by the transition between the dense and dilute phases and breaks the local‐equilibrium assumption in continuum modeling of fluidized beds. The results of time‐varying radial distribution function and voidage distribution also confirm this finding. Moreover, the analysis of voidage, particle velocity, granular temperature and turbulent kinetic energy of particles shows that there is no scale‐independent plateau over the interface, and it seems hard to find a scale‐independent plateau to separate the micro‐ and meso‐scales of fluidized beds, which require sub‐grid meso‐scale modeling for continuum or coarse‐graining methods of gas‐fluidized systems. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-30
  • Liquid‐to‐solid ratio control as an advanced process control solution for continuous twin‐screw wet granulation
    AlChE J. (IF 2.836) Pub Date : 2018-03-30
    Niels Nicolaï; Fien De Leersnyder; Dana Copot; Michiel Stock; Clara M. Ionescu; Krist V. Gernaey; Ingmar Nopens; Thomas De Beer

    Assuring compliance of intermediate and final quality attributes in a continuous pharmaceutical manufacturing campaign is of utmost importance. Application of corrective actions might be required in real‐time. This work exemplifies the steps needed to identify a linear pulse transfer function for the dynamic behavior of the granule liquid‐to‐solid ratio (%w/w) at the end of the granulation unit of a commercial ConsiGmaTM‐25 production line. Near‐infrared spectroscopy was used to monitor the granule composition in‐line. The outcome for both the tracking and regulator problem using either conventional or model predictive control was implemented and evaluated. Dynamic setpoints were correctly followed and an RMSE of 0.25%w/w with respect to the setpoint was obtained when inducing artificial disturbances. Important practical challenges were also tackled. Examples are fouling, computational limitations, and the limited flexibility of the automation software. Applying the proposed advanced process control solution offers an answer to upstream material flow rate deviations. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-30
  • Effect of Pickering stabilization on radical entry in emulsion polymerization
    AlChE J. (IF 2.836) Pub Date : 2018-03-26
    Barthélémy Brunier; Nida Sheibat‐Othman; Yves Chevalier; Élodie Bourgeat‐Lami

    The production of latexes stabilized by solid particles, so‐called Pickering stabilizers, has attracted considerable attention due to its benefits, including the enhanced mechanical properties of the polymer films. Clays for instance were found to enhance particle stabilization in emulsion polymerization, in a comparable way to conventional surfactants. Their concentration thus determines the polymer particles size and number, and consequently the reaction rate. In this work, we investigate the impact of the presence of such rigid and big platelets at the polymer particle's surface on radical exchange between the aqueous phase and the polymer particles. It was found for the system underhand that the average number of radicals per particle ( ) was independent of the stabilizer layer. Therefore, a radical capture model independent of the clay concentration could be used to simulate reactions involving different clay concentrations and predict the evolution of the monomer conversion, particle size, and . © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-27
  • Learning from the past: Are catalyst design principles transferrable between hydrodesulfurization and deoxygenation?
    AlChE J. (IF 2.836) Pub Date : 2018-03-25
    Sashank Kasiraju; Lars C. Grabow

    Molybdenum‐oxide (MoO3) is a promising catalyst candidate for hydrodeoxygenation (HDO) of pyrolysis vapor or liquefaction products to renewable fuels or value‐added chemicals. Density functional theory is used to study the mechanism and active site requirements for HDO of furan over the MoO3(010) facet and contrast our results with prior work on hydrodesulfurization (HDS) of thiophene over MoS2 model catalysts. The potential energy diagram for HDO over a realistically terminated MoO3(010) surface facet reveals that the elementary reaction steps for deoxygenation are facile, but the formation of oxygen‐vacancies is slow and endothermic. In general, HDO over MoO3 and HDS over MoS2 exhibit mechanistic similarities, which suggests that knowledge transfer from the mature HDS system to the emerging field of HDO catalysis is possible. For example, transition metal promotion of MoO3 resulted in an improvement of the kinetics and thermodynamics of oxygen vacancy formation, similar to Co and Ni promotion of MoS2. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-26
  • Effect of peptide linker length and composition on immobilization and catalysis of leucine zipper‐enzyme fusion proteins
    AlChE J. (IF 2.836) Pub Date : 2018-03-25
    Adam A. Caparco; Andreas S. Bommarius; Julie A. Champion

    Linkers are critical components of fusion proteins, as they physically separate individual domains to enable each to fold and retain function. The role of peptide linker properties was investigated for fusions of a leucine zipper immobilization domain (ZE) to a chimeric amine dehydrogenase (AmDH) or a formate dehydrogenase (cbFDH). A linker library was developed, which varied in length, orientation, and proline content, as a way to vary stiffness. Fusion proteins were characterized by melting temperature, immobilization ability, cofactor binding, and kinetic activity. The best linker candidate for each enzyme was tested in a dual‐functionality assay, where enzymatic activity of fusions immobilized in protein‐inorganic supraparticles was greater than 80% after washing. The best linker for AmDH was completely different than that for cbFDH. This work highlights the need to experimentally assess linker properties in the design of new fusion proteins and provides a linker library for this purpose. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-26
  • Analysis of volume‐to‐surface ratio effects on methane oxidative coupling using microkinetic modeling
    AlChE J. (IF 2.836) Pub Date : 2018-03-25
    V. I. Alexiadis; T. Serres; G. B. Marin; C. Mirodatos; J. W. Thybaut; Y. Schuurman

    The effect of the volume‐to‐surface (V/S) ratio on the catalytic performance of a La–Sr/CaO catalyst in a fixed bed reactor under oxidative coupling of methane (OCM) conditions is investigated by adjusting the amount of diluent in the catalyst bed. It was observed experimentally that the catalyst activity, C2 selectivity, and C2H4/C2H6 ratio are all favored at high V/S ratios. The total void volume, available in the intraparticle and the interstitial phase, was considered. A comprehensive OCM microkinetic model, explicitly distinguishing between these two phases, allowed accounting for the observed dependence of catalytic performance on V/S ratio. The major experimentally implemented variation in interstitial volume available for reaction, provoked also changes in radical concentration profiles in intraparticle phase. Given the high reaction rates occurring at this location, the experimentally observed effects with varying the V/S ratio, are attributed to concentration and, hence, reaction rate changes occurring mainly in the intraparticle phase. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-26
  • Validation study on spatially averaged two‐fluid model for gas–solid flows: I. A priori analysis of wall bounded flows
    AlChE J. (IF 2.836) Pub Date : 2018-03-25
    Simon Schneiderbauer

    In our prior study (Schneiderbauer, AIChE J, 2017;63(8):3544–3562), we presented a spatially averaged two‐fluid model, where closure models for the unresolved terms were derived. These closures require constitutive relations for the turbulent kinetic energies (TKEs) of the gas and solids phase as well as for the sub‐filter variance of the solids volume fraction (VVF). In this study, we have performed highly resolved TFM simulations of a set of three‐dimensional wall dominated periodic channels. An a priori analysis shows that these closures are able to correctly predict the wall profiles of the sub‐grid drag modification, the TKEs, the turbulent viscosities and the VVF without requiring special wall corrections. Solely the mixing lengths, which is required by the closures, has to be adapted in the vicinity of wall similar to single‐phase turbulence; in particular, the minimum of the filter size and the distance to the wall should be used. © 2018 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-26
  • New algorithm for the flexibility index problem of quadratic systems
    AlChE J. (IF 2.836) Pub Date : 2018-03-25
    Hao Jiang; Bingzhen Chen; Ignacio E. Grossmann

    A new flexibility index algorithm for systems under uncertainty and represented by quadratic inequalities is presented. Inspired by the outer‐approximation algorithm for convex mixed‐integer nonlinear programming, a similar iterative strategy is developed. The subproblem, which is a nonlinear program, is constructed by fixing the vertex directions since this class of systems is proved to have a vertex solution if the entries on the diagonal of the Hessian matrix are non‐negative. By overestimating the nonlinear constraints, a linear min–max problem is formulated. By dualizing the inner maximization problem, and introducing new variables and constraints, the master problem is reformulated as a mixed‐integer linear program. By iteratively solving the subproblem and master problem, the algorithm can be guaranteed to converge to the flexibility index. Numerical examples including a heat exchanger network, a process network, and a unit commitment problem are presented to illustrate the computational efficiency of the algorithm. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-26
  • Framework for work‐heat exchange network synthesis (WHENS)
    AlChE J. (IF 2.836) Pub Date : 2018-03-25
    Sajitha K. Nair; Harsha Nagesh Rao; Iftekhar A. Karimi

    Work and heat are the two predominant forms of energy in the process industry. Considerable savings can be achieved by synergizing the work and heat requirements of process streams. A generalized framework for integrating heat and work simultaneously is proposed based on a mixed‐integer nonlinear programing model for work‐heat exchange network synthesis. Starting with a set of streams with known flows, temperatures, and pressures, a network of single‐shaft‐turbine‐compressors with motors/generators, valves, heat exchangers, and utility heaters/coolers is synthesized for minimized total annualized cost. In contrast to existing works, (1) streams are not preclassified as hot/cold or high/low pressure, (2) pressure changes are allowed for streams with no net pressure change, (3) liquid‐vapor phase changes are allowed, and (4) phase‐based property correlations are used. Successful application of our approach to C3 splitting yields a nonintuitive configuration. Another application of an offshore natural gas liquefaction process is also studied. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-26
  • Controllable fabrication and catalytic performance of nanosheet HZSM‐5 films by vertical secondary growth
    AlChE J. (IF 2.836) Pub Date : 2018-03-22
    Yajie Tian; Hong Liu; Li Wang; Xiangwen Zhang; Guozhu Liu

    Nanosheet HZSM‐5 film vertically grown on the substrate with the tailorable macro‐ and meso‐pores between the layers of nanosheets is hydrothermally synthesized by seed‐assisted secondary growth method. The as‐prepared nanosheet HZSM‐5 film exhibits reaction rate enhancement up to 312% in catalytic cracking of n‐dodecane as well as twice light olefins selectivity, ascribed to the better mass transfer of reactants in the hierarchical porous structure and the ultra‐thin b‐axis pores of nanosheets. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-23
  • Direct numerical simulation of surfactant solution flow in the wide‐rib rectangular grooved channel
    AlChE J. (IF 2.836) Pub Date : 2018-03-22
    Chonghai Huang; Dongjie Liu; Jinjia Wei; Bo Yu; Hongna Zhang; Jianping Cheng

    The turbulent flow of surfactant solution in the wide‐rib rectangular grooved channels was studied by direct numerical simulation. Moreover, the variations of near‐wall streamwise vortices with time were discussed and the distributions of streamwise vortex radius, swirling strength and density were quantitatively investigated. It was found that the influence of microgrooves on the fluid mainly occurred within the buffer layer and microgrooves could induce numerous streamwise vortices with small size and swirling strength within the grooved valleys. The drag‐reducing enhancement mechanism of microgroove in the surfactant solution could be mainly considered as the competing results between the “restriction effect” and “tip effect” of microgroove, and the essential factor should be the numerous secondary streamwise vortices with small size and swirling strength within the grooved valleys. Furthermore, a predicted method for the optimal drag‐reducing size of microgroove was proposed, and the prediction values agreed well with the numerical results. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-23
  • The trail of perfumes
    AlChE J. (IF 2.836) Pub Date : 2018-03-22
    Joana Pereira; Patrícia Costa; Maria C. Coimbra; Alírio E. Rodrigues

    A methodology is proposed for modeling the diffusion of fragrances released from a moving source. First, we started with a one‐dimensional model considering molecular diffusion of α‐pinene in air as the only mass transport mechanism. The validation was performed in a diffusion tube, and a system was developed to move the scented source along the axial direction. Results showed that experimental data fitted well with the numerical simulation, suggesting this model as a valid tool to describe the trail of a fragrance released from a moving source for low Re of the order of 10. In the case of a person walking at the speed of 1.34 m/s in a room or corridor inside a building, three‐dimensional models are required and mass transport of the perfume to the surrounding air will be dominated by turbulent diffusion or eddy diffusion Dt which is two orders of magnitude higher than molecular diffusion. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-23
  • Product design: A pricing framework accounting for product quality and consumer awareness
    AlChE J. (IF 2.836) Pub Date : 2018-03-22
    Yuk C. Chan; Ka Y. Fung; Ka M. Ng

    A systematic framework has been developed to determine the optimal price of a completely new (or existing but improved) chemical product that is being launched (or relaunched) in the presence of a competing product. It has four elements. The first is a pricing model derived from a utility function with constant elasticity of substitution. It accounts for consumers' awareness of the product under consideration and consumer preferences. The second is a set of relationships relating the consumer preferences and the relevant sales data available to a relaunched product to the parameters of the pricing model. In the absence of sales data for a completely new product, the third element is a set of heuristics for choosing a pricing strategy and estimates of the pricing model parameters. The optimal price is finally determined in a profit maximization problem subject to the market size as well as any other constraints. This pricing framework allows simultaneous optimization of product quality and price using product specifications as design variables. It is illustrated with an example on energy drinks. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-23
  • Highly efficient methane reforming over a low‐loading Ru/γ‐Al2O3 catalyst in a Pd‐Ag membrane reactor
    AlChE J. (IF 2.836) Pub Date : 2018-02-01
    David S. A. Simakov; Yuriy Román‐Leshkov

    Natural gas can be reformed to syngas (CH4 + H2O = CO + 3H2), at temperatures above 850°C. Membrane catalytic reformers can provide high CH4 conversions at temperatures below 650°C, by separating H2 from the reactive mixture. Traditional Ni‐based catalysts suffer from low activity at low temperatures and deactivate rapidly by coking, particularly at low steam/carbon ratios. In this study, an ultralow loading (0.15 wt %) Ru/γ‐Al2O3 catalyst was implemented in a lab‐scale membrane reformer, using a supported 5μm Pd‐Ag film membrane. Methane conversions above 90% were achieved at 650°C, 8 bar, and H2O/CH4 = 2, 3 with contact times of ca. 10 s. The system generated up to 3.5 mol of ultrapure H2 per mol of CH4 fed, with a maximum power density of 0.9 kW/L. No significant deactivation was observed after 200 h time on stream, even when using low H2O:CH4 ratios. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • On the mechanisms of secondary flows in a gas vortex unit
    AlChE J. (IF 2.836) Pub Date : 2018-02-01
    Kaustav Niyogi; Maria M. Torregrosa; Guy B. Marin; Geraldine J. Heynderickx; Vladimir N. Shtern

    The hydrodynamics of secondary flow phenomena in a disc‐shaped gas vortex unit (GVU) is investigated using experimentally validated numerical simulations. The simulation using ANSYS FLUENT® v.14a reveals the development of a backflow region along the core of the central gas exhaust, and of a counterflow multivortex region in the bulk of the disc part of the unit. Under the tested conditions, the GVU flow is found to be highly spiraling in nature. Secondary flow phenomena develop as swirl becomes stronger. The backflow region develops first via the swirl‐decay mechanism in the exhaust line. Near‐wall jet formation in the boundary layers near the GVU end‐walls eventually results in flow reversal in the bulk of the unit. When the jets grow stronger the counterflow becomes multivortex. The simulation results are validated with experimental data obtained from Stereoscopic Particle Image Velocimetry and surface oil visualization measurements. © 2018 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • A square‐force cohesion model and its extraction from bulk measurements
    AlChE J. (IF 2.836) Pub Date : 2018-02-03
    Peiyuan Liu; Casey Q. LaMarche; Kevin M. Kellogg; Christine M. Hrenya

    Accurate modeling of interparticle forces in DEM is critical to predicting the rheology of cohesive particles. Rigorous cohesion models usually include parameters associated with particle surface roughness. However, both roughness measurement and its distillation into appropriate model parameters remain challenging. We propose a square‐force cohesion model, where cohesive force remains constant until a cutoff separation, above which cohesion vanishes. We demonstrate the square‐force model is a valid surrogate of more rigorous models. Specifically, when two parameters of square‐force model are chosen to match the two key quantities governing dense and dilute flows, namely maximum cohesive force and critical cohesive energy, respectively, DEM results using square‐force and more rigorous models show good agreement. For practical application of the square‐force model to lightly cohesive systems, a method is established to extract its parameters via defluidization, enabling determination of particle–particle cohesion from simpler bulk measurements than complicated and expensive scans on individual grains. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • Ecosystems as unit operations for local techno‐ecological synergy: Integrated process design with treatment wetlands
    AlChE J. (IF 2.836) Pub Date : 2018-02-03
    Varsha Gopalakrishnan; Bhavik R. Bakshi

    Despite the critical importance of ecological systems for sustaining all chemical and manufacturing processes, process design has kept nature outside its system boundary. Recent efforts for sustainable process design aim to reduce environmental impact, but no design method considers the capacity of ecosystems to supply the goods and services that are needed to sustain a process. Overcoming this deficiency of conventional process design is essential to transform the chemical industry into an activity that respects ecological constraints and results in a net positive societal impact. As an important step toward meeting this goal, this work expands the boundary of process design to include ecosystems as unit operations in traditional design. Similar to tasks performed by conventional unit operations, ecological processes perform ecosystem functions resulting in goods and services required by the technological system. The goal behind designing integrated techno‐ecological process flowsheets is to balance the ecosystem service demand of technological systems with the ecosystem service supply of ecological systems. Systems are optimized to balance the demand and supply subject to unit operation level constraints of technological and ecological systems, and interactions between detailed process level variables and ecological variables are explored. The Techno‐Ecological Synergy (TES) Design method is developed and applied to a biofuel production system, considering ecosystem services like water provisioning and water quality regulation provided by wetland ecosystems. Comparing the integrated TES design with conventional techno‐centric design shows that TES design can result in net positive impact manufacturing: a case where the ecosystem service supply is equal to or exceeds the demand, with little or no compromises in process profitability. These results should encourage close integration between technological and ecological systems while designing sustainable processes, and identify many challenges for developing TES of individual processes and across the life cycle. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • Continuous‐time formulations for the optimal planning of multiple refracture treatments in a shale gas well
    AlChE J. (IF 2.836) Pub Date : 2018-02-03
    Diego C. Cafaro; Markus G. Drouven; Ignacio E. Grossmann

    This work presents a continuous‐time optimization model for planning multiple refracture treatments over the lifespan of a shale gas well. We demonstrate that continuous‐time models can handle multiple restimulations very efficiently, increasing the net present value of the well development and refracturing plan. Well productivity is represented by a piecewise hyperbolic function, which accounts for when and how often the well has been refractured. We illustrate the application and effectiveness of the proposed approach for both the maximization of the total gas recovered and the maximization of the net present value. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • Method to estimate uncertainty associated with parcel size in coarse discrete particle simulation
    AlChE J. (IF 2.836) Pub Date : 2018-02-03
    Liqiang Lu; Sofiane Benyahia

    Coarse grained particle methods significantly reduce the computation cost of large‐scale fluidized bed simulation by lumping many real particles into a computation parcel. This research provides a method to estimate the errors associated with parcel size in large‐scale fluidized bed simulations. This uncertainty is first quantified in small scale domains by comparing results of discrete particle method with that employing coarse parcels of different sizes. Then, this uncertainty is correlated with parcel size and simulation domains consisting of a simple homogeneous cooling system and more complex bubbling and circulating fluidized beds. These correlations allow us to accurately estimate the uncertainty in large‐scale fluidized beds based solely on data obtained in smaller systems. The ability to estimate model‐related uncertainty in larger systems makes this method relevant for industrial applications. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • Metal nanoparticles in ionic liquid‐cosolvent biphasic systems as active catalysts for acetylene hydrochlorination
    AlChE J. (IF 2.836) Pub Date : 2018-02-03
    Lifeng Yang; Qiwei Yang; Jingyi Hu; Zongbi Bao; Baogen Su; Zhiguo Zhang; Qilong Ren; Huabin Xing

    Ionic liquid (IL)‐stabilized metal nanoparticles (NPs) have attracted increased attention as novel catalysts for various reactions due to their excellent stability and high activity. However, the high viscosity of ILs limits their applications. Here, for the first time, we reported an NPs@IL‐cosolvent liquid–liquid biphasic system for metal NPs catalysis. The NPs were successfully confined to IL phase, and abundant IL droplets containing NPs were generated under the reactant flow. The NPs@IL droplets served as microreactors for the catalysis; while the low viscosity organic phase enabled the rapid mass transfer of substances. The biphasic system exhibited improved performance for acetylene hydrochlorination than that of the pure IL system. An acetylene conversion of 98% and a selectivity of 99.5% were achieved along with a 90% decrease on IL usage. The tolerable gas hourly space velocity in the biphasic system for a satisfactory conversion was almost double that of the pure IL system. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • Preparation of high‐performance zeolite NaA membranes in clear solution by adding SiO2 into Al2O3 hollow‐fiber precursor
    AlChE J. (IF 2.836) Pub Date : 2018-02-03
    Nanke Ma; Rui Wang; Gaohong He; Zhengbao Wang

    Zeolite NaA membranes were prepared in a clear synthesis solution without the aid of nanoseeds. To improve the properties of the membranes formed in a clear solution, alumina hollow fibers were fabricated by adding silica powder to the conventional spinning slurry, resulting in hollow fibers with a mullite phase. Prior to the membrane synthesis, the hollow fibers were pretreated by dipping in an aged synthesis solution diluted with isopropanol. Dense zeolite NaA membranes on mullite‐containing alumina hollow fibers were successfully obtained at 100°C for 2 h without the aid of nanoseeds. The membranes have a good pervaporation performance with a high flux of 10.8 kg m−2 h−1 and a separation factor of over 10,000. The abundant mullite‐phase hydroxyl groups on the support surface promote the nucleation and growth of zeolite crystals on the support, resulting in dense membranes. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • Real‐time multivariable model predictive control for steam‐assisted gravity drainage
    AlChE J. (IF 2.836) Pub Date : 2018-02-06
    Sagar N. Purkayastha; Ian D. Gates; Milana Trifkovic

    Thermal recovery techniques, such as steam‐assisted gravity drainage (SAGD), are used to recover the majority of the crude bitumen, in Western Canada. However, suboptimal production techniques have led to a large carbon footprint and a subsequent search for more efficient extraction techniques, than open loop manual control. This article summarizes research on the comparison of performance of a novel multi‐input multioutput (MIMO) model predictive controller (MPC) with steam trap and oil rate controls with a multi‐input single output (MISO) MPC with only steam trap control. An appropriate system identification technique was also used for periodic model update in compliance with changing system behavior. The real‐time control study was made possible by establishing a bidirectional communication between computer modeling group STARSTM (virtual reservoir) and MATLAB (onsite controller) software. The results show a 171% improvement in oil recovery for the novel MIMO MPC over the MISO MPC. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • Nonspherical particles in a pseudo‐2D fluidized bed: Experimental study
    AlChE J. (IF 2.836) Pub Date : 2018-02-06
    Vinay V. Mahajan; Johan T. Padding; Tim M. J. Nijssen; Kay A. Buist; J. A. M. Kuipers

    Fluidization is widely used in industries and has been extensively studied, both experimentally and theoretically, in the past. However, most of these studies focus on spherical particles while in practice granules are rarely spherical. Particle shape can have a significant effect on fluidization characteristics. It is therefore important to study the effect of particle shape on fluidization behavior in detail. In this study, experiments in pseudo‐2D fluidized beds are used to characterize the fluidization of spherocylindrical (rod‐like) Geldart D particles of aspect ratio 4. Pressure drop and optical measurement methods (Digital Image Analysis, Particle Image Velocimetry, Particle Tracking Velocimetry) are employed to measure bed height, particle orientation, particle circulation, stacking, and coordination number. The commonly used correlations to determine the pressure drop across a bed of nonspherical particles are compared to experiments. Experimental observations and measurements have shown that rod‐like particles are prone to interlocking and channeling behavior. Well above the minimum fluidization velocity, vigorous bubbling fluidization is observed, with groups of interlocked particles moving upwards, breaking up, being thrown high in the freeboard region and slowly raining down as dispersed phase. At high flowrates, a circulation pattern develops with particles moving up through the center and down at the walls. Particles tend to orient themselves along the flow direction. © 2018 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • Impact of diversity of morphological characteristics and Reynolds number on local hemodynamics in basilar aneurysms
    AlChE J. (IF 2.836) Pub Date : 2018-02-06
    Marjan Rafat; Howard A. Stone; Debra T. Auguste; Mahsa Dabagh; Amanda Randles; Martin Heller; James D. Rabinov

    Morphological and hemodynamic parameters have been suggested to affect the rupture of cerebral aneurysms, but detailed mechanisms of rupture are poorly understood. The purpose of our study is to determine criteria for predicting the risk of aneurysm rupture, which is critical for improved patient management. Existing aneurysm hemodynamics studies generally evaluate limited geometries or Reynolds numbers (Re), which are difficult to apply to a wide range of patient‐specific cases. Association between hemodynamic characteristics and morphology is focused. Several two‐dimensional (2D) and three‐dimensional (3D) idealized and physiological geometries is assessed to characterize the hemodynamic landscape between flow patterns. The impact of morphology on velocity and wall shear stress (WSS) profiles were evaluated. Slight changes in aneurysm geometry is found or Re result in significant changes in the hemodynamic and WSS profiles. Our systematic mapping and nondimensional analysis qualitatively identify hemodynamic conditions that may predispose aneurysms to rupture. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • Hydrothermal pretreatment for deconstruction of plant cell wall: Part II. Effect on cellulose structure and bioconversion
    AlChE J. (IF 2.836) Pub Date : 2018-02-06
    Kun Yao; Qinfeng Wu; Ran An; Wei Meng; Mingzhu Ding; Bingzhi Li; Yingjin Yuan

    Influences of both ultrastructural modification of cellulose after hydrothermal pretreatment and products derived from lignin‐carbohydrate complex (LCC) on the subsequent enzymatic digestibility and fermentation were studied in this study. Under hydrothermal conditions, it was found that the rearrangement of hydrogen bonding pattern in cellulose via allomorph and conformational changes which was mainly severity‐dependent increased the numbers of water‐exposed glycosidic bond and the formation of “amorphous‐like” cellulose fibril facilitated enzymatic hydrolysis. Pseudo lignin, soluble xylo‐oligomers, phenols and degradation products from high severity impeded enzymatic digestion. LCC and phenols which were rich in pH‐controlled prehydrolyzate did not sufficiently inhibit yeast while furans and some aromatics which were rich in high‐severity prehydrolyzate might be potential inhibitors. Trade‐off phenomenon was solved by pH‐controlled operation and high yields in both glucose (83–93%) and xylose (75–80%) were simultaneously obtained. The final ethanol yield from cellulose to ethanol reached as high as 84–93%. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • A decomposition algorithm for simultaneous scheduling and control of CSP systems
    AlChE J. (IF 2.836) Pub Date : 2018-02-08
    Alexander W. Dowling; Tian Zheng; Victor M. Zavala

    We present a decomposition algorithm to perform simultaneous scheduling and control decisions in concentrated solar power (CSP) systems. Our algorithm is motivated by the need to determine optimal market participation strategies at multiple timescales. The decomposition scheme uses physical insights to create surrogate linear models that are embedded within a mixed‐integer linear scheduling layer to perform discrete (operational mode) decisions. The schedules are then validated for physical feasibility in a dynamic optimization layer that uses a continuous full‐resolution CSP model. The dynamic optimization layer updates the physical variables of the surrogate models to refine schedules. We demonstrate that performing this procedure recursively provides high‐quality solutions of the simultaneous scheduling and control problem. We exploit these capabilities to analyze different market participation strategies and to explore the influence of key design variables on revenue. Our results also indicate that using scheduling algorithms that neglect detailed dynamics significantly decreases market revenues. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • Scalar mixing in anisotropic turbulent flow
    AlChE J. (IF 2.836) Pub Date : 2018-02-08
    Quoc Nguyen; Dimitrios V. Papavassiliou

    While turbulent mixing has been studied extensively in homogeneous turbulence, chemical engineering processes where mixing is important are anisotropic. In anisotropic turbulence, the interplay between convection and diffusion is critical. Flow in an infinite channel is utilized here with clouds of scalars released instantaneously at different distances from the wall and at Schmidt numbers between 0.7 and 2400. Qualitative and quantitative measures of mixing efficiency and intensity are defined and the dynamics of mixing are explored. It is found that molecular diffusivity can even hinder mixing in some instances, because it affects the development of the cloud of the released scalars from regions within the viscous wall layer. Another finding is that while one would expect mixing to occur mostly in the space between two points of release, considerable amount of mixing could take place outside of this region and closer to the wall. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • Optimal design of batch‐storage network considering ownership
    AlChE J. (IF 2.836) Pub Date : 2018-02-09
    Gyeongbeom Yi; Gintaras V. Reklaitis

    This article develops a model of multi‐national supply chain activities, which incorporates currency storage units to manage currency flows associated with activities such as raw material procurement, processing, inventory control, transportation, and finished product sales. The core contribution of this model is that it facilitates the quantitative investigation of the influence of macroscopic economic factors such as ownership on supply chain operational decisions. The supply chain system is modeled as a batch‐storage network with recycle streams. The supply chain optimization problem is posed with the objective of minimizing the opportunity costs of annualized capital investments and currency/material inventories, while taking into account the benefit to stockholders in the numeraire currency. The major constraints on the optimization are that the material and currency storage units must not be depleted. A production and inventory analysis formulation (the periodic square wave model) provides useful expressions for the upper and lower bounds and for the average levels of the currency and material inventory holdings. The expressions for the Kuhn‐Tucker conditions of the optimization problem are reduced to a subproblem that allows development of analytical lot‐sizing equations. The lot sizes of procurement, production, transportation, and financial transactions can be determined in closed form once the average flow rates are known. The key result we obtain is that optimal value of the economic order quantity changes substantially with variation in ownership, thus showing quantitatively that ownership structure does impact plant operation. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • Removal of yield‐stress fluids from pipework using water
    AlChE J. (IF 2.836) Pub Date : 2018-02-10
    Ibrahim Palabiyik; Estefania Lopez‐Quiroga; Phillip T. Robbins; Kylee R. Goode; Peter J. Fryer

    The emptying of product from process plant is a significant multiphase flow problem in food and personal care industries, controlling both product recovery, and cleaning time. Product and operational losses can be significant, especially with viscous products. It is necessary to maximize product recovery while minimizing cleaning time and effluent volume. The removal of a range of products from fully filled pipework using water has been characterized and monitored by weighing pipes at intervals and by inline turbidity probe. Data is presented for a range of products (toothpaste, hand cream, apple sauce, yoghurt, and shower gel) that have been cleaned from two pipe systems. The data can be fitted by a linear relationship between a dimensionless cleaning time, and the ratio of the product yield stress to the surface shear stress. The effect of pipe fittings is to reduce cleaning times, reflecting increased shear/energy dissipation in the pipe. © 2018 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • An evaluation of the impact of SG1 disproportionation and the addition of styrene in NMP of methyl methacrylate
    AlChE J. (IF 2.836) Pub Date : 2018-02-12
    Stijn K. Fierens; Paul H. M. Van Steenberge; Florence Vermeire; Marie‐Françoise Reyniers; Guy B. Marin; Dagmar R. D'hooge

    A kinetic modeling study is presented for batch nitroxide mediated polymerization (NMP) of methyl methacrylate (MMA; nitroxide: N‐tert‐butyl‐N‐[1‐diethylphosphono‐(2,2‐dimethylpropyl)] (SG1)). Arrhenius parameters for SG1 disproportionation (A = 1.4 107 L mol−1 s−1; Ea = 23 kJ mol−1) are reported, based on homopolymerization data accounting for unavoidable temperature variations with increasing time, that is, nonisothermicity. For low targeted chain lengths (TCLs ≤ 300), this nonisothermicity is also relevant for NMP of MMA with a small amount of styrene. Parameter tuning to copolymerization data confirms a penultimate monomer unit effect for activation (sa2 = ka12/ka22=6.7; 363 K; 1: MMA; 2: styrene). To obtain, for a broad TCL range (up to 800), a dispersity well below 1.3 an initial styrene mass fraction of ca. 10% is required. An interpretation of the comonomer incorporation is performed by calculating the fractions of activation‐growth‐deactivation cycles with a given amount of monomer units and the copolymer composition distribution. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • Characterization of PVC‐soy protein nonwoven mats prepared by electrospinning
    AlChE J. (IF 2.836) Pub Date : 2018-02-12
    HeeRan Hong; Zachary C. Tronstad; Yi Yang; Matthew D. Green

    Poly(vinyl chloride) (PVC) is one of the most common polymers used in the water treatment industry due to outstanding hydrophobicity and mechanical strength. Generating eco‐friendly membranes derived from natural polymers has gained attention, particularly for water purification and producing potable water. In this study, nonwoven mats were prepared by electrospinning polymer solutions. Mats with a tailorable hydrophilicity were prepared by electrospinning solution mixtures containing PVC and an eco‐friendly, hydrophilic natural polymer: soy protein. As the viscosity of the solution decreased, the average fiber diameter, and average pore surface area reduced. However, when the PVC concentration remained constant and the soy protein concentration increased, the viscosity decreased and average fiber diameter became reduced, while the average pore diameter remained relatively constant. The mats with volumetric ratios of PVC:soy protein of 85:15 and 80:20 displayed optimal characteristics suitable for mat fabrication based on the fiber diameter and average pore surface area. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • Universal correlation for gas hydrates suppression temperature of inhibited systems: II. Mixed salts and structure type
    AlChE J. (IF 2.836) Pub Date : 2018-02-12
    Yue Hu; Bo Ram Lee; Amadeu K. Sum

    The first paper of this study discussed the development of the Hu‐Lee‐Sum (HLS) correlation and demonstrated the generality and universality of the correlation to predict structure I hydrates suppression temperature for any single salt system. However, natural gas commonly forms structure II hydrates, and mixed salts naturally occur in oil and gas production. Therefore, reliable prediction of structure II hydrates suppression temperature in presence of mixed salts over a wide range of pressure is considerably important. The contribution for each salt in salt mixtures is accounted for in the effective mole fraction to extend the HLS correlation for mixed salts systems. Moreover, a parameter (α) is introduced to account for the effect of hydrate structure on the hydrate suppression temperature. Herein, the HLS correlation is further shown to be universal and reliable to predict the hydrate suppression temperature for more complicated systems for mixed gases and mixed salts. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • Predicting NRTL binary interaction parameters from molecular simulations
    AlChE J. (IF 2.836) Pub Date : 2018-02-14
    Ashwin Ravichandran; Rajesh Khare; Chau‐Chyun Chen

    A predictive approach for calculating the binary interaction parameters ( ) of the nonrandom two liquid (NRTL) local composition model is developed, combining molecular simulations with the two‐fluid theory. The binary interaction parameters are determined for the following three sets of model binary mixtures: water + methanol, methanol + methyl acrylate, and water + methyl acrylate. For each binary mixture, the interaction parameters are expressed in terms of molecular size and strength of interactions, which are in turn, calculated from molecular simulations. We show that the binary interaction parameters determined from simulations are in qualitative agreement with those estimated from regressing experimental data. The major factors that determine the binary interaction parameters are outlined based on simple thermodynamic arguments for each mixture. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • Supra‐monolayer coverages on small metal clusters and their effects on H2 chemisorption particle size estimates
    AlChE J. (IF 2.836) Pub Date : 2018-02-14
    Abdulrahman S. Almithn; David D. Hibbitts

    H2 chemisorption measurements are used to estimate the size of supported metal particles, often using a hydrogen‐to‐surface‐metal stoichiometry of unity. This technique is most useful for small particles whose sizes are difficult to estimate through electron microscopy or X‐ray diffraction. Undercoordinated metal atoms at the edges and corners of particles, however, make up large fractions of small metal clusters, and can accommodate multiple hydrogen atoms leading to coverages which exceed 1 ML (supra‐monolayer). Density functional theory was used to calculate hydrogen adsorption energies on Pt and Ir particles (38–586 atoms, 0.8–2.4 nm) at high coverages (≤3.63 ML). Calculated differential binding energies confirm that Pt and Ir (111) single‐crystal surfaces saturate at 1 ML; however, Pt and Ir clusters saturate at supra‐monolayer coverages as large as 2.9 ML. Correlations between particle size and saturation coverage are provided that improve particle size estimates from H2 chemisorption for Pt‐group metals. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • Dynamics of pristine graphite and graphene at an air‐water interface
    AlChE J. (IF 2.836) Pub Date : 2018-02-16
    David M. Goggin; Joseph R. Samaniuk

    We examine the dynamics and morphology of graphitic films at an air‐water interface in a Langmuir trough by varying interfacial surface coverage, by observing in situ interfacial structure, and by characterizing interfacial structure of depositions on mica substrates. In situ interfacial structure is visualized with Brewster angle microscopy and depositions of the interface are characterized with atomic force microscopy and field‐emission scanning electron microscopy. Compression/expansion curves exhibit a monotonically decreasing surface pressure between consecutive compressions, but demonstrate a “rebound” of hysteretic behavior when the interface is allowed to relax between consecutive compressions. This dynamic results from a competition between consolidation of the interface via agglomeration of particles or the stacking of graphene sheets, and a thermally‐driven relaxation where nanometer‐thick particles are able to overcome capillary interactions. These results are especially relevant to applications where functional films with controlled conductivity and transparency may be produced via liquid‐phase deposition methods. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • Microfluidic synthesis of elastomeric microparticles: A case study in catalysis of palladium‐mediated cross‐coupling
    AlChE J. (IF 2.836) Pub Date : 2018-02-17
    Jeffrey A. Bennett; Andrew J. Kristof; Vishal Vasudevan; Jan Genzer; Jiri Srogl; Milad Abolhasani

    Palladium (Pd)‐loaded poly‐hydromethylsiloxane (PHMS) microparticles of tunable size and elasticity are prepared in a capillary‐based coaxial flow‐focusing microfluidic device constructed using off‐the‐shelf components. Simultaneous droplet formation and chemical cross‐linking processes are performed by tuning the dilution of the cross‐linking catalyst in the annular flow of the microreactor, resulting in PHMS microparticles synthesized in a single step. The size of the elastomeric microparticles can be tuned by adjusting the flow rate ratio of the polymer and cross‐linker mixture to water, while the elasticity can be tuned by the polymer to cross‐linker ratio as well as the flow rate ratio of the polymer mixture to cross‐linking catalyst mixture. Microparticle elasticity is characterized by the degree of solvent uptake. Application of the synthesized PHMS microparticles in organic synthesis is demonstrated by producing monodispersed Pd‐loaded microparticles and utilizing them as microreaction vessels for continuous Suzuki‐Miyaura cross‐coupling in a Pd‐loaded microparticle‐packed bed reactor. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • Hydrothermal pretreatment for deconstruction of plant cell wall: Part I. Effect on lignin‐carbohydrate complex
    AlChE J. (IF 2.836) Pub Date : 2018-02-17
    Kun Yao; Qinfeng Wu; Ran An; Wei Meng; Mingzhu Ding; Bingzhi Li; Yingjin Yuan

    Hydrothermal pretreatment with characteristic of green chemistry is considered as promising technology in the biorefineries. Using material balance and multiscale characterization techniques, the effects of process severity factor and pH on chemical behaviors of lignin‐carbohydrate complex (LCC) were systematically studied. During pretreatment, spatial relocation of lignin with covalently linked xylan facilitated local cell wall collapse. A kinetic model was established to describe the behaviors of LCC components changing with severity factor. It was found that cleavage of LCC linkage was strongly pH‐dependent. Low pH dominated cleavage of coumarate/ferulate esters which cross‐linking lignin with xylan and repolymerization of aromatics either from furfural or lignin into polymers such as pseudo lignin, while high pH which allowed the existence of soluble LCC dominated the aldol condensations from xylose to aromatics and depolymerizaton of lignin to phenols. Detailed reaction pathways concerned with LCC were finally established to elucidate the underlying mechanism. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • Reduction in greenhouse water usage through inlet CO2 enrichment
    AlChE J. (IF 2.836) Pub Date : 2018-02-20
    Neil Stacey; James Fox; Diane Hildebrandt

    Agriculture is mankind's single largest usage of water, comprising 70% of all water usage. Optimizing water usage in agriculture is therefore crucial to ensuring global water security. A greenhouse is quantitatively modeled as a bioreactor and it is shown that the bulk of the water supplied to a conventionally aspirated greenhouse is lost in the form of humidity. This implies that evaporative losses in agriculture comprise a clear majority of mankind's total water consumption. Inlet CO2 enrichment using existing membrane materials can minimize the air feed rate required to supply adequate CO2 for photosynthesis, thereby mitigating evaporative losses. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • Heat/mass transfer from a neutrally buoyant sphere by mixed natural and forced convection in a simple shear flow
    AlChE J. (IF 2.836) Pub Date : 2018-02-20
    Bing Yuan; Chao Yang; Zai‐Sha Mao; Xiaolong Yin; Donald L. Koch

    Building on the work of Yang et al. in 2011, the finite difference method and the Boussinesq approximation were applied to solve the time‐dependent Navier‐Stokes, convection diffusion and continuity equations in spherical coordinates. An idealized condition, the mass transfer from a neutrally buoyant sphere in a horizontal simple shear flow with natural convection was numerically simulated for the first time in this work. In the hybrid transfer case, the outwardly spiraling streamlines enhanced the transfer process, but the counter‐gravity spiraling streamlines near the sphere hindered the natural convection and the spatial dilution action weakened the natural convection transfer process. These competing effects led to nonmonotonic behavior of the Nusselt number with Reynolds number. Results from these previously undocumented cases were summarized into correlations for predicting Nusselt numbers at finite Reynolds numbers for various Grashof and Prandtl numbers. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • Hydrodynamics in a pilot‐scale cocurrent trickle‐bed reactor at low gas velocities
    AlChE J. (IF 2.836) Pub Date : 2018-02-22
    Puneet Kawatra; Srikanth Panyaram; Benjamin A. Wilhite

    Hydrodynamic data obtained from laboratory‐scale trickle‐beds often fail to accurately represent industrial‐scale systems with high packing aspect ratios and column‐to‐particle diameter ratios. In this study, pressure drop, liquid holdup, and flow regime transition were investigated in a pilot‐scale trickle‐bed column of 33 cm ID and 2.45 m bed height packed with 1.6 mm × 8.4 ± 1.4 mm cylindrical extrudates for air‐water mass superficial velocities of 0.0023 – 0.094 kg/m2s and 4.5 – 45 kg/m2s, respectively, at atmospheric pressure. Significant deviation was observed from pressure drop and liquid holdup correlations at low liquid flows rates, corresponding to gravity‐driven flow limit. Likewise, liquid saturation is overestimated by correlations at high liquid flow rates, owing to significantly reduced wall effects. Lastly, trickle‐to‐dispersed bubble flow and trickle‐to‐pulsing flow regime transitions are reported using a combination of visual observations and analysis of the magnitude of local pressure fluctuations within the column. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • A Numerical model of exchange chromatography through 3‐D lattice structures
    AlChE J. (IF 2.836) Pub Date : 2018-02-22
    Maher Salloum; David B. Robinson

    Rapid progress in the development of additive manufacturing technologies is opening new opportunities to fabricate structures that control mass transport in three dimensions across a broad range of length scales. We describe a structure that can be fabricated by newly available commercial 3‐D printers. It contains an array of regular three‐dimensional flow paths that are in intimate contact with a solid phase, and thoroughly shuffle material among the paths. We implement a chemically reacting flow model to study its behavior as an exchange chromatography column, and compare it to an array of 1‐D flow paths that resemble more traditional honeycomb monoliths. A reaction front moves through the columns and then elutes. The front is sharper at all flow rates for the structure with three‐dimensional flow paths, and this structure is more robust to channel width defects than the 1‐D array. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • Bilevel and parallel programing‐based operability approaches for process intensification and modularity
    AlChE J. (IF 2.836) Pub Date : 2018-02-22
    Juan C. Carrasco; Fernando V. Lima

    Process operability emerged in the last decades as a powerful tool for the design and control of chemical processes. Recent efforts in operability have been focused on the calculation of the desired input set for process design and intensification of natural gas utilization applications described by nonlinear models. However, there is still a gap in terms of problem dimensionality that nonlinear operability methods can handle. To fill this gap, in this article, the incorporation of bilevel and parallel programing approaches into classical process operability concepts is discussed. Results on the implementation of the proposed method show a reduction in computational time up to two orders of magnitude, when compared to the original results without parallelization. These results could be extrapolated for use in a supercomputer as presented in the computational time analysis performed. In terms of intensification, the proposed approach can produce a natural gas combined cycle plant modular design with a dramatic reduction in size, from the original 400 to 0.11 MW, while still keeping the high net plant efficiency. This approach thus provides a computationally efficient framework for process intensification of high‐dimensional nonlinear energy systems toward modularity. The proposed approach also enables the verification of a modular design and conditions that can be obtained according to economic and physical constraints associated with a specific natural gas well production. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • Concentrated slurry formation via drawdown and incorporation of wettable solids in a mechanically agitated vessel
    AlChE J. (IF 2.836) Pub Date : 2018-02-23
    Thomas Wood; Mark J. H. Simmons; Richard W. Greenwood; E. Hugh Stitt

    This article describes the effect of vessel configurations on the drawdown and incorporation of floating solids to prepare concentrated alumina slurries in stirred tanks. The impeller speed and power draw required to incorporate all dry powder within four seconds, NJI and PJI, are used to evaluate incorporation performance. The effect of impeller type is assessed, with pitched blade impellers proving to be the most effective across the full range of solid contents considered. At higher solids content the energy demand is shown to increase dramatically, with a 100‐fold increase in energy required to add 1% w/w more solid at 50% by weight compared to 1% by weight. Analysis of impeller power numbers show this coincides with a transition from constant power number to a region where power number increases linearly with decreasing Reynolds number. Contrary to studies at low solids content, the presence of baffles is shown to inhibit drawdown. © 2018 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • Experimental and numerical investigation of structure and hydrodynamics in packed beds of spherical particles
    AlChE J. (IF 2.836) Pub Date : 2018-02-23
    P. Lovreglio; S. Das; K. A. Buist; E. A. J. F. Peters; L. Pel; J. A. M. Kuipers

    In chemical industry, flows often occur in nontransparent equipment, for example in steel pipelines and vessels. Magnetic resonance imaging is a suitable approach to visualize the flow, which cannot be performed with classical optical techniques, and obtain quantitative data in such cases. It is therefore a unique tool to noninvasively study whole‐field porosity and velocity distributions in opaque single‐phase porous media flow. In this article, experimental results obtained with this technique, applied to the study of structure and hydrodynamics in packed beds of spherical particles, are shown and compared with detailed computational fluid dynamics simulations performed with an in‐house numerical code based on an immersed boundary method‐direct numerical simulation approach. Pressure drop and the radial profiles of porosity and axial velocity of the fluid for three packed beds of spheres with different sizes were evaluated, both experimentally and numerically, in order to compare the two approaches. © 2018 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
  • Experimental data for code validation: Horizontal air jets in a semicircular fluidized bed of Geldart Group D particles
    AlChE J. (IF 2.836) Pub Date : 2018-02-23
    William D. Fullmer; Casey Q. LaMarche; Allan Issangya; Peiyuan Liu; Ray Cocco; Christine M. Hrenya

    Experiments were conducted with 6 mm plastic beads (Geldart Group D) in a semi‐circular, gas‐fluidized bed with side jets. Attention was paid to particle characterization and bed measurements, making the resulting dataset ideal for CFD‐DEM validation and uncertainty quantification. The bed was operated slightly above and below the minimum fluidization velocity, with additional fluidization provided by one of two pairs of opposing jets located above the distributor near the flat, front face of the unit. Care is taken to report material properties and bed conditions with either measured distribution functions or uncertainty bounds. High‐speed video imaging and particle tracking velocimetry are used to extract bin‐averaged velocity profiles, which are used to extract jet penetration depths. The time‐averaged mean and standard deviation of the bed pressure drop is also reported. Finally, the lower jets are also inserted into the bed until the opposing jets merge to form a spout‐like pattern. © 2018 American Institute of Chemical Engineers AIChE J, 2018

    更新日期:2018-03-21
Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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