Experimental Study of Liquid Renewal on the Sheet of Structured Corrugation SiC Foam Packing and Its Dispersion Coefficients Chem. Eng. Sci. (IF 2.895) Pub Date : 2018-01-16 Hong Li, Zhiqiang Hao, Jaden Murphy, Xingang Li, Xin Gao
A new approach of studying mixed gas hydrates involving propane at non-equilibrium conditions and final state: An experimental study and modeling Chem. Eng. Sci. (IF 2.895) Pub Date : 2018-01-16 S. Maghsoodloo Babakhani, B. Bouillot, J. Douzet, S. Ho-Van, J.M. Herri
Metastable clathrate hydrates are a promising energy source in the shallow geosphere and present challenges in flow assurance, energy storage, and carbon capture sequestration. While they have been widely studied, little pertinent data is available for common propane hydrates concerning hydrate phase composition, nor its volume or the amount of converted water. This was the initial motivation for our work. Therefore, with a novel technique, propane hydrate composition and volume were measured dynamically at non-equilibrium conditions over time and at the final states for slow and quick rates of crystallization. Surprisingly, equilibrium pressure, hydrate volume and composition are different according to crystallization rate. The hydrate volume and water conversion in the quick crystallization process were larger. Moreover, at a slow crystallization rate, in a hydrocarbon mixture, enclathration of propane is more considerable and the hydrate crystals appear to be more homogeneous. Furthermore, the hydrate crystallization of a gas mixture is closer to the thermodynamic equilibrium at slow crystallization rates where the impact of kinetics is slight. A new compilation of propane Kihara parameters was presented. Unlike methane, ethane and carbon dioxide, for propane we strongly recommend two Kihara parameters, one for pure and the other for mixtures of propane. A thermodynamic model based on classical van der Waals and Platteuw model was also used to investigate the effects of kinetics. The simulation results have a satisfactory accordance with the experimental data from literature to predict the hydrate equilibrium pressure. The consequence of this research could have a substantial impact on design calculations in which the assumption of thermodynamic equilibrium are done. For instance, at present there would be excess hydrates volume estimations for pipe-lines, equilibrium conditions in energy storage and transportation or carbon capture sequestration and thus increase expenses or loss of productivity where propane is concerned.
Mechanistic and constrained thermochemical modelling in chemical reactor engineering: Ti(IV)Chloride oxidation revisited Chem. Eng. Sci. (IF 2.895) Pub Date : 2018-01-12 Pertti Koukkari, Eduardo Paiva
Solid-liquid suspension of microcarriers in stirred tank bioreactor - Experimental and numerical analysis Chem. Eng. Sci. (IF 2.895) Pub Date : 2018-01-11 Angélique Delafosse, Céline Loubière, Sébastien Calvo, Dominique Toye, Eric Olmos
Solid-liquid suspensions in stirred tank reactors are common operations in many processes, including bioprocesses such as animal or stem cell cultures. These cells are often anchorage-dependent, i.e. they need to adhere to a surface to grow. Typically, they are cultivated on the surface of small spherical microbeads, the so-called microcarriers, suspended in stirred-tank bioreactors. As far as we know, no extensive experimental characterization, and thus no validated simulation approach, of microcarrier suspensions in stirred-tank reactor exists in the literature. Therefore, the first aim of this work is to develop an experimental technique based on light attenuation to characterize the spatial distribution of particle concentration for various particle suspension states. The second aim is to determine the validity of Euler-Euler CFD simulations to predict the spatial distribution of low density particles, such as microcarriers, in a stirred tank bioreactor. Experiments and simulations were performed in a small hemispherical bottom bioreactor stirred with a down-pumping axial impeller. The particles used were Cytodex-1 microcarriers (dP d P = 162 μ μ m and ρS ρ S = 1020 kg m−3) at a solid concentration of 10 % in volume. The light attenuation technique enabled the characterization of the spatial distribution of the solid phase in the whole bioreactor, even for very dense suspensions by advantageously using the optical properties of the Cytodex-1 microcarriers. The analysis of the solid spatial distribution shows that the bioreactor volume can be divided in three distinct zones: a clear layer below the free surface where αS,layer α S , layer tends to 0, a bulk zone where the solid phase is homogeneously distributed (αS,bulk⩽〈αS〉 α S , bulk ⩽ α S ) and a packed bed of motionless particles at the bottom (αS,bed=αS,max α S , bed = α S , max ). One very interesting finding is that the evolution of the bulk solid concentration is directly proportional to the agitation rate and its value equals the averaged volume fraction αS,bulk=〈αS〉 α S , bulk = α S at N=Njs N = N js . Concerning the simulation results, the modeling approach presented in this work enables a reasonable estimation of the just-suspended agitation rate Njs N js . Nevertheless, the solid spatial distributions are not well predicted for agitation rates below or above Njs N js . The solid concentration at the vessel bottom is underestimated for N
Chemical-looping water splitting over ceria-modified iron oxide: performance evolution and element migration during redox cycling Chem. Eng. Sci. (IF 2.895) Pub Date : 2018-01-10 Xing Zhu, Mingyue Zhang, Kongzhai Li, Yonggang Wei, Yane Zheng, Jianhang Hu, Hua Wang
Color-PTV measurement and CFD-DEM simulation of the dynamics of poly-disperse particle systems in a pseudo-2D fluidized bed Chem. Eng. Sci. (IF 2.895) Pub Date : 2018-01-10 Zhaochen Jiang, Thomas Hagemeier, Andreas Bück, Evangelos Tsotsas
Impact of cellulose treatment with hydrotalcites in hydrothermal catalytic conversion. Chem. Eng. Sci. (IF 2.895) Pub Date : 2018-01-10 Carlos Guarín, Llorenç Gavilà, Magda Constantí, Francesc Medina
A Study on the Influence of the Tube Layout on Sub-channel Hydrodynamics in a Bubble Column with Internals Chem. Eng. Sci. (IF 2.895) Pub Date : 2018-01-09 F. Möller, Y.M. Lau, T. Seiler, U. Hampel, M. Schubert
Reactive absorption of CO2 in NaOH: An Euler-Euler simulation study Chem. Eng. Sci. (IF 2.895) Pub Date : 2018-01-09 Manuel Krauß, Roland Rzehak
Recently, a new model for the reactive mass transfer during absorption of CO2 in aqueous NaOH was developed, based on using a rather generally applicable expression for the enhancement factor and taking into account the reaction of CO2 with water in addition to that with hydroxide ions [Krauß and Rzehak, Chemical Engineering Science 166 (2017) 193–209]. By substituting the interfacial area concentration estimated from experimental data, good agreement was found for the pointwise measurement of time-dependent pH-value in a bubble column taken from the literature [Darmana et al., Chemical Engineering Science 62 (2007), 2556–2575]. In the present contribution, this mass transfer model is implemented in an Euler-Euler / RANS framework including also the hydrodynamic part of the problem. Hydrodynamic closures were taken the same as applied successfully for a range of different conditions in previous work. However, the accuracy of the coupled model in predicting the measured pH-value is seen to fall behind that of the simple pointwise approximation. This suggests that for the present application, the hydrodynamic part of the model requires further improvement. Possible directions to this end are discussed.
Coupled CFD-DEM simulation of oscillatory particle-laden fluid flow through a porous metal foam heat exchanger: mitigation of particulate fouling Chem. Eng. Sci. (IF 2.895) Pub Date : 2018-01-09 Sahan T.W. Kuruneru, Emilie Sauret, Suvash C. Saha, YuanTong Gu
A coupled finite volume-discrete element (FVM-DEM) numerical method is developed to investigate oscillating multiphase foulant-laden air (solid-gas) flow and particulate fouling in a porous heat exchanger channel comprising an array of circular cylinders. Oscillatory fluids serve as a steppingstone to advance existing conventional anti-fouling techniques and to yield optimum energy consumption. A performance evaluation criteria based on various amplitudes of pulsation and foulant injection rates is established. The fouling characteristics and pressure drop is compared against a non-oscillating steady flow. For the solid foulant particles considered in this study, the results show that the time-averaged deposition fraction is sensibly invariant with increasing foulant injection rate; however, the same observation is not realized for steady-flow cases. The 1 Hz case showed no significant disparity in terms of deposition fraction at high injection rates compared with the non-oscillating steady flow case. In addition, the 1 Hz case showed miniscule reduction of low-density foulants. The higher-frequency spectrum has superior fouling mitigation capabilities although comparatively higher pressure drop is generated. The 6-pore configuration outperforms the 3-pore under certain oscillatory flow conditions. An optimum frequency of 5 Hz exhibits superior fouling mitigation performance while achieving a low time-averaged pressure drop.
Emulsion behavior control and stability study through decorating silica nano-particle with dimethyldodecylamine oxide at n-heptane/water interface Chem. Eng. Sci. (IF 2.895) Pub Date : 2018-01-08 Caili Dai, Hao Li, Mingwei Zhao, Yining Wu, Qing You, Yongpeng Sun, Guang Zhao, Ke Xu
Emulsions have been widely applied in subterranean enhanced oil recovery processes, cosmetics and chemistry engineering fields, etc. Current research interests are focusing on improving the stability of emulsion by involving surfactants or colloidal materials. This work aims to enhance the emulsion stabilization by introducing silica nanoparticles (SNP) surface-hydrophobilized/hydrophilized by adding dimethyldodecylamine oxide (OA-12) and to reveal the dynamic behaviors of such composites on the liquid-liquid interface. The synergistic effect between SNPs and OA-12 in solution and on oil/water interface were studied by measuring the zeta potential, interfacial rheology and emulsion viscoelastic rheology, etc. It was found that the oil/water interface viscoelastic modulus are augmented by modified silica nano-particles and at the same time emulsions acquired significant long-time stability. Furthermore, phase transformation was induced with the increase of the concentration ratio between OA-12 and silica nano-particle, the emulsion type change from o/w, then to w/o and back to o/w. It is suggested that the inversions are induced by the mounting adsorption of OA-12 molecules on SNPs, which changes the hydrophilic-lipophilic balance of particle surfaces.
An Improved Meso-Scale Flow Model of Gas-Liquid-Solid Fluidized Beds Chem. Eng. Sci. (IF 2.895) Pub Date : 2018-01-08 Yongli Ma, Mingyan Liu, Yuan Zhang
Modeling of CO2 Diffusion into Water-Shielded Oil at Pore Scale Using Moving Mesh Technique Chem. Eng. Sci. (IF 2.895) Pub Date : 2018-01-08 Amir Fayazi, Apostolos Kantzas
During processes such as solvent-steam co-injection and tertiary CO2 flooding, oil may be prevented from direct contact with solvent by a water barrier which greatly affects microscopic displacement efficiency. As a result of diffusion through the water barrier, both oil and water phases swell progressively. If oil swelling displaces the blocking water completely, direct contact between solvent and oil can be achieved which results in high oil recovery. In this study, a moving mesh technique is applied to simulate swelling of a trapped oil blob by CO2 diffusion through a blocking water at pore scale. A moving interface between oil and water is considered to track the swelling process. The modelling results were validated with micromodel experiments on the recovery process of water-shielded oil in a dead-end pore. The water film rupture time for typical oil and water thicknesses (in micro scale) was calculated using experimental data for oil-water-CO2 system. Finally, a dimensionless rupture time was introduced and it was used to predict trapped oil recovery as a function of contact time for various pore body and throat size distributions. The results can be used to estimate the time scales necessary for having maximum trapped oil recovery.
Effects of obstacle lengths on the asymmetric breakup of a droplet in a straight microchannel Chem. Eng. Sci. (IF 2.895) Pub Date : 2018-01-08 Yunli Ma, Manman Zheng, Mohamed Gibril Bah, Jingtao Wang
Rheological behaviors of a droplet moving in the micro-channel with a linear obstacle off the channel axis are investigated numerically by employing Volume of Fluid methods. Five different hydrodynamic patterns of the rheological behaviors of the droplet have been observed. The effects of the length ratio L of the mother droplet to the linear obstacle on the critical capillary number of the droplet breakup have been particularly studied. When L is less than a critical value Lmin, the larger the droplet is, the smaller the critical capillary number Cacr is; when L is greater than Lmin, the larger the droplet is, the greater Cacr is. The curve of Cacr as a function of L has a minimum point at Lmin, which means that the droplet with L=Lmin could be broken up most easily. This is caused by the competition of the enhancing (positive) factors and the hindering (negative) factors on the droplet breakup, which has been analyzed carefully in this paper. When other parameters are fixed, it is very interesting to find out that the change of the obstacle length does not change the value of Lmin, which is fixed to 0.66 for the conditions discussed in this paper. The results obtained here might enlighten potential applications for the design of the micro-channel with obstacles and the packing rings in columns.
Deposition of polymer films by spin casting: A quantitative analysis Chem. Eng. Sci. (IF 2.895) Pub Date : 2018-01-08 José Danglad-Flores, Stephan Eickelmann, Hans Riegler
Spin casting of mixtures of nonvolatile polymeric solutes dissolved in volatile solvents is studied experimentally and theoretically. The final solute coverage, time-resolved film thinning, time-resolved solvent evaporation, and evolution of the solute concentration within the thinning film is investigated for various combinations of different polymers (PMMA, PS, PS-b-PMMA) and different solvents (toluene, ethyl-acetate) for a wide range of polymer concentrations and spin cast conditions. The comprehensive data unveil a clear picture of the spin cast process. The findings are translated into a concise theoretical description. Easily available bulk properties of the solvent/solute mixture plus a single ”calibration” experiment are sufficient for a quantitative description of the spin cast process including a prediction of the final solute coverage. This and the well-specified boundary conditions render the approach useful for practical applications.
Computational fluid dynamic studies of mixers for highly viscous shear thinning fluids and PIV validation Chem. Eng. Sci. (IF 2.895) Pub Date : 2018-01-08 Marti Cortada-Garcia, Weheliye Hashi Weheliye, Valentina Dore, Luca Mazzei, Panagiota Angeli
Agitation of highly viscous shear thinning fluids is normally conducted with complex impeller designs. Often, impellers almost as large as the tanks containing them and impeller blades equipped with holes are adopted in industry. In this work, we studied experimentally the main features of the flow generated by this type of impellers for a mixture of glycerol with a carbomeric gel by means of particle image velocimetry. The experiments were conducted at temperatures ranging from 40 to 60 °C and impeller speeds ranging from 40 to 140 rpm. In all cases, the flow regime was laminar or in the transition region. We also used computational fluid dynamics simulations to describe the behaviour of the mixer, validating the results experimentally with good agreement. We used the numerical results to obtain information on the performance of the mixer, determining the locations and size of vigorous agitation zones and the local effect of the holes present on the impeller blades. The power curves of the mixer were obtained, and the mixer efficiency in terms of power consumption was found to be similar to other impellers used to mix highly viscous non-Newtonian fluids.
Assessment of different coarse graining strategies to simulate polydisperse gas-solids flow Chem. Eng. Sci. (IF 2.895) Pub Date : 2018-01-07 Liqiang Lu, Yupeng Xu, Tingwen Li, Sofiane Benyahia
Enhanced C3H6/C3H8 separation performance in poly(vinyl acetate) membrane blended with ZIF-8 nanocrystals Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-29 Jian Yu, Chongqing Wang, Long Xiang, Yuanze Xu, Yichang Pan
The implementation of membrane-based separation for olefin/paraffin mixtures has the potential to significantly reduce energy consumption, but is limited by the lack of suitable membrane materials with desired performance and low cost. Here, mixed matrix membranes (MMMs) fabricated from incorporating ZIF-8 nanocrystals into the poly(vinyl acetate) (PVAc) matrix exhibit significant improvement of propylene/propane permeability and selectivity as well as the operating stability. On the 39 wt% ZIF-8/PVAc MMMs, both the C3H6 permeability and C3H6/C3H8 selectivity are about 10-fold increase over pure PVAc. The gas transportation mechanism through ZIF-8/PVAc MMMs was also evaluated. The favorable interfacial interaction between the H of the imidazole in the ZIF-8 and ester groups of PVAc enhances the mechanical strength and plasticization resistance of the neat polymer membrane. Therefore, the newly developed composite membrane may have great potential for industrial C3H6/C3H8 separation.
Optimal design of hybrid cryogenic flash and membrane system Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-27 Zuwei Liao, Yongxin Hu, Gaonv Tu, Jingyuan Sun, Binbo Jiang, Jingdai Wang, Yongrong Yang
Combining cryogenic flash units with membrane units is attractive for gas separation processes such as effluent gas recovery and CO2 capture. However, systematic design methodology for such hybrid systems have not been reported yet. The hybrid system is a complicated system that not only includes separation units, but also includes pressure manipulation units and heat exchangers. A two-step decomposition strategy is proposed to deal with the design of such complicated system. The separation sequence is first determined with energy consumption consideration in the first step. Subsequently, the remaining energy recovery units, the heat exchanger network and turbines are simultaneously synthesized with the separation flowsheet optimization. When applying the proposed strategy to recover the effluent gas from polyolefin plant, we find a novel flowsheet that avoid intensive capital and operating cost by tightly integration of process units.
Scale and causes of catalyst activity loss in enzymatic catalyzed reactive distillation Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-27 Torben Egger, Lisa S. Egger, Georg Fieg
Continuous enzymatic catalyzed reactive distillation (eRD) is a new process that can reduce product inhibition and the need for additional purification steps. However, the enzymatic catalyst is exposed to markedly different conditions than in conventional processes. The enzyme stability, a crucial cost factor, has not been investigated for the application in an eRD and the underlying mechanisms for catalyst deactivation are still unknown. This article presents for the first time a comprehensive study on the scale and causes of enzyme activity reduction in eRD processes. Pilot plant experiments with the transesterification of butyl acetate with hexanol catalyzed by Novozyme 435 confirm the existence of a process window with high reaction rates and low activity loss. The remaining activity after 320 h of operation is investigated in each reactive packing, leading to a new found cause of activity reduction that has so far not been considered for enzymatic catalyzed reactive distillation. The results allow for a better design and operation of eRD processes and the development of enzyme immobilisates that cater to the specific needs of integrated operation.
Solar thermal decoupled water electrolysis process II: An extended investigation of the anodic electrochemical reaction Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-26 S. Nudehi, C. Larson, W. Prusinski, D. Kotfer, J. Otto, E. Beyers, J. Schoer, R. Palumbo
We examined the kinetic and transport processes involved in the production of H2 from water with Co2+ as the electroactive species being oxidized at a Ni electrode in 40 weight percent KOH at 318 K. The relevant transport parameters such as electrochemical rate constants, transfer coefficients, diffusion coefficients, and adsorption coefficients were estimated from a combination of cyclic voltammetry experiments and numerical modeling. Fourteen parameters characterize the electrochemical reaction on a clean electrode, with the Butler-Volmer equation describing the electron transfer step to solution and to adsorption bound electroactive species. A Frumkin Isotherm describes the thermodynamics of the adsorption process. Experimentally realized anodic current densities at cell voltages below 1.23 V were circa 1 mA-cm-2, a hydrogen production level far too low for commercial viability of the solar thermal decoupled water electrolysis process. However, our 3-D finite element model of the electrochemical cell operating at 318 K, suggests that current densities approaching 20 mA-cm-2 can be reached in a cell with forced convection and a solvent that increases the solubility of CoO by a factor of 10 above that for KOH. Finally, the current density calculations from the perspective of industrial viability suggest producing porous metal anodes for which the actual surface area is 10 to 100 times larger than the electrode’s planar area.
Analysis of PIV measurements using modal decomposition techniques, POD and DMD, to study flow structures and their dynamics within a stirred-tank reactor Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-24 Anne de Lamotte, Angélique Delafosse, Sébastien Calvo, Dominique Toye
The present work is a comparative analysis of Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) computed on experimental turbulent velocity fields measured in a 20L-tank stirred by two Rushton impellers at two rotating speeds, N= N = 150 and 300 rpm. POD identifies flow structures that optimally capture the total kinetic energy of the flow, while DMD identifies structures that significantly contribute to the dynamics of the flow. The experimental data, i.e. the instantaneous velocity fields Ur(r,z,t) U r ( r , z , t ) and Uz(r,z,t) U z ( r , z , t ) , come from 2-D Particle Image Velocimetry (PIV). The flow motion is turbulent, and it occurs over a wide range of length and time scales, from equipment-dependent large-scale coherent structures to the smallest-scale eddies where energy dissipation takes place. It thus provides an interesting benchmark case for the comparison between POD and DMD, which are based on energy and dynamic analysis, respectively. POD analysis reveals that the most energetic structures are related to the inherent periodic unsteadiness due to the relative motion between the rotating impeller blades and the non-moving baffles. Apart from the mean field, the first most energetic group of modes is related to trailing vortices induced by the Rushton turbines and is associated to a frequency equivalent to the blade passage frequency and its overtones. The second most energetic group of modes is related to vortical structures in the impeller stream and is associated to a frequency equivalent to the rotating speed. DMD analysis identifies flow structures that are found similar to these most energetic modes, although differences appear due to the fact that DMD isolates structures associated to a single frequency and their corresponding growth/decay rate. As in POD, the relative importance of each DMD mode can be estimated using an appropriately defined energy criterion. Comparison of the results from both modal decomposition methods points out their complementarity and their potential for describing the spatial and time characteristics of the flow within a stirred tank.
Revisiting APOD accuracy for nonlinear control of transport reaction processes: a spatially discrete approach Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-24 Manda Yang, Antonios Armaou
This article addresses the problem of output feedback control of dissipative distributed parameter systems. The reduced order model used for controller and observer synthesis is recursively updated using a revised version of adaptive proper orthogonal decomposition (APOD), based on decomposing spatially descrete solution profiles. This approach eliminates the basis size oscillation resulting from the inaccuracy of estimation of energy in APOD when the sampling speed is too slow. The performance of this method is illustrated by applying it to regulate a diffusion-reaction process and a fluid flow system described by the Kuramoto-Sivashinsky equation.
Hydrodeoxygenation of fast pyrolysis oil with novel activated carbon-supported NiP and CoP catalysts Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-24 Cheng Guo, Kasanneni Tirumala Venkateswara Rao, Zhongshun Yuan, Sophia (Quan) He, Sohrab Rohani, Chunbao (Charles) Xu
Catalytic hydrodeoxygenation (HDO) has been considered as a promising technical route to upgrade fast pyrolysis oil to liquid transportation fuels. In this work, a series of active and inexpensive catalysts were synthesized for bio-oil HDO, i.e., activated carbon (AC)-supported nickel phosphide and cobalt phosphide catalysts, with a metal/P molar ratio varying from 5/2, 3/2, 1/1, 1/2, 1/3. For comparison, AC-support pure metal catalysts without P were also prepared. Effects of phosphorus content on HDO performance of the catalysts were investigated on a 100 mL bench-scale reactor system using a wood-derived pyrolysis oil at 300 °C and initial hydrogen pressure of 50 bar for 3 h. The results showed that the properties of the upgraded bio-oils were greatly affected by the phosphorus content in both Ni and Co catalysts. The best performance seemed to be achieved with the catalysts at a metal/P molar ratio of about 3/2. Moreover, 0.5 wt% of Ru was further added to the catalysts at a metal/P molar ratio of 3/2 and to the pure metal catalysts. The addition of a small amount of Ru was found to markedly decrease the relative molecular weight of the upgraded bio-oils, and achieved high quality bio-oil products similar to that obtained with an expensive commercially available 5wt% Ru/C catalyst.
Hydrodynamics of CO2-ethanol flow in a microchannel under elevated pressure Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-22 Alexandre Martin, Séverine Camy, Joëlle Aubin
Cross-flow structured packing for the process intensification of post-combustion carbon dioxide capture Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-22 Gianluca Lavalle, Mathieu Lucquiaud, Marc Wehrli, Prashant Valluri
We introduce novel insights into a cross-flow arrangement of structured packings specifically for post-combustion carbon dioxide capture. Gas-liquid dynamics are investigated numerically, with the liquid flowing under the action of the gravity and the gas driven by a horizontal pressure gradient crossing the liquid phase. An elementary packing cell consists of two connected channels: one depicting a co-current gas-liquid flow and the other depicting a counter-current two-phase flow. While flow reversal of the liquid phase can occur in the counter-flow channel at high gas flow rates, the overall flooding point is significantly delayed in comparison to a counter-current flow arrangement traditionally used for structured packings. Varying the gas flow rate and the tilting angle of the elementary cell, a detailed numerical analysis of the flow repartition between channels, the pressure drop, the gas and liquid velocities, and the onset of flooding is presented. The pressure drop is found to be smaller when tilting the cell with respect to the initial scenario at 45° 45 ° . Flow reversal instead is delayed when lowering the tilting angle, that is when the cell is tilted anti-clockwise. We also reveal the presence of long waves at the edge of the cell at low tilting angles. Finally, data of the wet pressure drop in the cross-flow cell are compared with different commercially available types of packing arranged in a conventional vertical counter-flow configuration, such as several versions of the Sulzer Mellapak™.
Decorating Platinum on Nitrogen-Doped Graphene Sheets: Control of the Platinum Particle Size Distribution for Improved Photocatalytic H2 generation Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-20 Hui Ling Tan, Aijun Du, Rose Amal, Yun Hau Ng
Emulsification of heavy crude oil in brine and its plugging performance in porous media Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-20 Long Yu, Mingzhe Dong, Boxin Ding, Yanguang Yuan
In this paper, heavy crude oil and formation brine collected from Xinjiang oilfield were used to prepare crude oil-in-water (O/W) emulsions. Emulsification tests were first conducted to screen suitable emulsifiers. Then stability test, droplet size distribution analysis, and rheological property measurements were carried out to investigate the physicochemical characteristics of the developed O/W emulsions. It was found that surfactants of Span 60 and Tween 80 combined with sodium hydroxide could reduce the oil/water interfacial tension and thereby emulsify the heavy crude oil in formation brine. A series of sandpack flow tests were conducted to evaluate the plugging performance of the heavy O/W emulsions, emulsified using 0.1 wt% Span 60 − 0.1 wt% Tween 80 − 0.025 wt% NaOH. The flow test results showed that heavy O/W emulsion can result in more than 99% permeability reductions in sandpacks. The permeability reduction by emulsion plugging increased greatly with an increase in oil quality and injected emulsion slug, but decreased with an increase in sandpack permeability and injection flow rate.
Coupled CFD-DEM with Heat and Mass transfer to Investigate the Melting of a Granular Packed Bed Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-20 Mehdi Baniasadi, Maryam baniasadi, Bernhard Peters
The eXtended Discrete Element Method (XDEM) platform which is a Coupled Eulerian-Lagrangian framework with heat and mass transfer, is extended for melting of granular packed beds. In this method, the fluid is simulated by computational fluid dynamics (CFD) and the soft-sphere discrete element approach (DEM) is used for the particle system. A four-way coupling accounts for solid-liquid interaction via drag and buoyancy forces and the collisions between the particles and the walls. The contact forces between the particles and wall-particle contacts have been calculated by the hertz-mindlin model. The particles heat up, melt and shrink due to heat and mass exchange, and the temperature distributions inside the particles are described. In order to validate the method, melting of a single ice particle and of a packed bed of ice in flowing water have been carried out. Very good agreement between the simulation and experiment has been achieved. The effects of the temperature and velocity of flowing water on melting rate are also discussed.
Damping Hydrodynamic Fluctuations in Microfluidic Systems Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-20 Ali Kalantarifard, Elnaz Alizadeh Haghighi, Caglar Elbuken
Modelling and numerical simulation of coupled transport phenomena with phase change: mixture evaporation from a rectangular capillary Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-19 Sebastian Rieks, Eugeny Y. Kenig
Understanding of transport phenomena in fluid-fluid two-phase systems is essential for many engineering applications. When evaporation or condensation is considered, there exists a two-way coupling of momentum, heat and species transfer, i.e. the fluid flow influences the heat and species transfer and vice versa. The CFD-based simulation of evaporating and/or condensing flows requires models and numerical solution techniques for two-way coupled transport equations and their boundary conditions. Most results on transport phenomena in systems with phase change available in the literature are restricted by either isothermal or one-component systems. Recently we have proposed an approach for modelling and simulation of two-way coupled transport phenomena in non-isothermal two-phase binary systems and performed a first validation using some one-dimensional problems (Rieks and Kenig, 2018). In the present work, a further, more sound validation of the new model and simulation code is accomplished to govern two-dimensional systems.
Synthesis of Yttrium Oxide Nanoparticles via a Facile Microplasma-assisted Process Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-19 Liangliang Lin, Sergey A. Starostin, Sirui Li, Saif A. Khan, Volker Hessel
Plasma electrochemistry is an emerging technique for nanomaterial synthesis. The present study reports the preparation of yttrium oxide nanoparticles via a simple, environmentally benign, microplasma-assisted process operated in pin-to-liquid configuration under ambient atmospheric conditions using yttrium nitrate aqueous solution as the precursor. The plasma-liquid interaction was monitored in-situ by optical emission spectroscopy. The morphology, structure and chemical composition of the obtained products were examined by complementary analytical methods. It was demonstrated that high purity crystalline Y2O3 nanoparticles with adjustable sizes can be fabricated via a two-step method: plasma electrodeposition of yttrium hydroxide followed by heat-treatment at various temperatures. A microplasma array design was proposed for the process upscaling towards industrial level production. Moreover, possible mechanisms for plasma-assisted yttrium hydroxide precipitation were discussed by correlating optical emission spectroscopic studies, plasma kinetic analysis and the precipitation equilibrium. As a proof-of-concept, this process offers a facile, environmental friendly and scalable route for rare-earth oxide nanomaterial synthesis.
Heats of adsorption on mixed-cation LiNa-LSX: Estimating SIII site occupancy by Li Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-19 Xiong Yang, Franklin E. Epiepang, Yingshu Liu, Ralph T. Yang
Li-LSX (low silica type-X) zeolite is the sorbent of choice for air separation by adsorption today. Li-LSX is obtained by ion exchange of Na-LSX. The occupancy of Site III (SIII, which is the open site in the supercage) by Li+ is crucially important for N2 adsorption. In this work, mixed-cation LiNa-LSX zeolites were prepared and N2 adsorption isotherms were measured. The isosteric heats of adsorption of N2 were obtained from the temperature dependence. The heats of adsorption remained at approximately 17.7 kJ/mol (i.e., that for pure Na-LSX) at Li+ exchange below approximately 70%, and increased upon further increase in Li+ exchange, to 22.6 kJ/mol (i.e., that for pure Li-LSX). The increase was not linear (i.e., concave shaped), however, which indicated that one N2 molecule could likely adsorb on two adjacent cation sites. The relationship between heat of adsorption and Li ion occupancy on site SIII was obtained. It is suggested that this relationship may be used to estimate the occupancy by Li+ on SIII of faujasite type of zeolites.
A Solvent ‘Squeezing’ Strategy to Graft Ethylenediamine on Cu3(BTC)2 for Highly Efficient CO2/CO Separation Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-19 Ruiqin zhong, Xiaofeng Yu, Wei Meng, Songbai Han, Jia Liu, Yunxing Ye, Changyu Sun, Guangjin Chen, Ruqiang Zou
CFD modeling of the influence of carrier thermal conductivity for structured catalysts in the WGS reaction Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-18 V. Palma, D. Pisano, M. Martino
Numerical study of fog formation around Ambient Air Vaporizers Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-18 Divyamaan Wadnerkar, Biao Sun, Ranjeet P. Utikar, Geoffrey Evans, Moses O. Tade, Neil Kavanagh, Solomon Faka, Vishnu K. Pareek
Ambient air vaporizers (AAVs) are used to re-gasify cryogenic industrial gases for distribution and use. Although AAVs have low carbon footprint, fog formation around the ambient air vaporizers is a common problem, thus often leading to reduced visibility. Moreover, since AAVs exchange the heat from the surrounding air, the efficiency of the process is also at stake due to possible recycling of exiting air. Thus, simulating fog formation, dispersion and dissipation around AAVs is of critical importance. So far most of the studies for AAV consider fog in single phase framework, which are incapable of simulating the dispersion and dissipation of fog accurately. In this study, multiphase model of fog formation and dissipation has been developed considering the thermodynamics and heat transfer effects. The models have been validated using available wind tunnel data for a velocity and temperature field around a sample obstacle. A parametric study has been also presented to demonstrate the effect of wind velocity, AAV inlet air velocity and number of AAV units on the ambient conditions. The study provides an in-depth insight of the process and presents an analysis of operating conditions suitable for AAVs.
An Empirical Model of the Wetted Wall Fraction in Separated Flows of Horizontal and Inclined Pipes Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-17 Taehwan Ahn, Jeongmin Moon, Byeonggeon Bae, Jaejun Jeong, Byounguhn Bae, Byongjo Yun
This study reports an experiment to investigate the wetted wall fraction (WWF), which represents the shape of the continuous interface of the air–water stratified and wavy flow regimes, in horizontal and inclined pipes with an inner diameter of 40 mm. Using the experimental data, a semi-empirical model to predict the WWF was developed based on the energy balance for the liquid phase in separated flows. The model used a relationship between the WWF and the center of gravity of the liquid phase with a concave interface that can describe continuous changes to the flow regime from a stratified to an annular. The coefficients of the model were empirically determined based on a wide range of experimental data from the literature obtained in the air and various liquids covering a void fraction of greater than 0.79, a pipe with inner diameter in the range 24–150 mm, density differences varying from 812 to 1,052 kg/m3, a range of liquid phase viscosity of 0.87–5.66 mPa-s, surface tension ranging from 27.9 to 72.7 mN/m, a wide range of inclination angles from -27° for a downward flow to +3° for an upward flow, and gas and liquid Reynolds numbers based on a superficial velocity of up to 219,000 and 7,500, respectively. This WWF model was tested using an extensive experimental database of the WWF and void fraction in the stratified and wavy flow regimes, and yielded the best agreement compared with existing models in the literature.
A multiscale DEM-PBM approach for a continuous comilling process using a mechanistically developed breakage kernel Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-16 Nirupaplava Metta, Marianthi Ierapetritou, Rohit Ramachandran
The population balance approach (PBM) is generally used in the literature to simulate a milling process. The formulation of a breakage kernel to represent particle breakage phenomenon is an important part of the model. This study proposes a methodology to estimate parameters of a breakage kernel that captures material property dependent particle level dynamics through discrete element method (DEM) simulations of a comill process. The DEM model takes into account a threshold impact energy that if exceeded, results in granule breakage. The impact energy distribution data for various size classes and impellor speeds is obtained from DEM. Comill experiments at various impeller speeds result in different observed size distributions and other process variables such as hold up amount, and time required for process to reach steady state. An iterative algorithm is proposed that uses mechanistic information from DEM and process variables from experiments to calibrate the breakage kernel through which material specific kernel parameters are estimated. A multi-scale modeling framework utilizing DEM, PBM as well as experimental data is developed. The framework is implemented to estimate material specific properties using milling experimental data at various impeller speeds. The milled particle size distribution predicted from the model with parameters estimated using this framework, demonstrated excellent agreement with experimental results.
Cellulose-based membranes via phase inversion using [EMIM]OAc-DMSO mixtures as solvent Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-16 Elif Nur Durmaz, P. ZeynepÇulfaz-Emecen
Efficient surface modification of thin-film composite membranes with self-catalyzed tris(2-aminoethyl)amine for forward osmosis separation Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-16 Liang Shen, Yan Wang
Prediction of fluid flow through and jet formation from a high pressure nozzle using Smoothed Particle Hydrodynamics Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-16 Gerald G. Pereira, Paul W. Cleary, Yoshihiro Serizawa
This paper reports on the development and evaluation of an SPH (Smoothed Particle Hydrodynamics) model for high pressure water flow through and from a nozzle and prediction of its break up into a spray of high speed water droplets. This appears to be the first application of the SPH technique to fully model a high pressure nozzle. The model predicts the internal flow and pressure distribution and enables exploration of the role of the internal geometric insert used in this design of the nozzle. It also predicts exit velocities from the nozzle as well as the pressure distribution generated by the nozzle and droplet size distribution of the resulting spray. Three different nozzle inflow rates were simulated and for all cases the numerical simulation of nozzle and spray gave generally good agreement with experiments, but complete agreement was not achieved. For better agreement, higher resolution for the SPH solution is required. The SPH simulations also show the role that the insert in the nozzle has on the flow and the resulting jet. It produces a flat inclined high velocity liquid jet within the second half of the nozzle which will generate turbulent eddies that may enhance the nucleation of the droplets in the fragmenting jet after it exits the nozzle. Overall, SPH has been shown to have a very good capacity to model high pressure nozzles and with further refinements of the technique should be able to yield accurate, quantitative data.
Corrective interface tracking approach to simulate finite-size bubbly flows Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-16 Hassan Badreddine, Nathan Lafferty, Bojan Ničeno, Horst-Michael Prasser
This work reports on the development and application of a new approach, corrective interface tracking, to simulate finite size bubbles. Finite-size bubbles, which are by definition bigger than the grid cell size but not well resolved, are not capable of being modeled with any standard two-phase flow approaches, such as interface tracking (IT), Euler-Euler (EE), or Lagrangian particle tracking (LPT). This poses a problem when simulating bubbly flows with different bubble sizes on the same computational grid. The Finite-size Lagrangian particle tracking (FSL) approach (Badreddine et al., 2015), aimed at simulating finite-size bubbly flows by inheriting features of IT and LPT approaches, simulated a single bubble with good accuracy. However, deficiencies with the FSL approach led to a newly developed approach based on interface tracking with the addition of a correcting force. The correcting force, derived from modeling the hydrodynamic forces on a bubble, attempts to correct for errors introduced when a coarse grid is used and the flow and pressure fields around the bubble are under-resolved. Therefore, as a finer grid is used the correcting force decreases. The corrective interface tracking approach is validated against a single bubble rising in stagnant and linear flow, and then results are compared to FSL and to finely resolved IT simulations.
Bridging the gap across scales: Coupling CFD and MD/GCMC in polyurethane foam simulation Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-16 Mohsen Karimi, Daniele Marchisio, Erik Laurini, Maurizio Fermeglia, Sabrina Pricl
This work presents a multi-scale approach to reacting and expanding polyurethane (PU) foams modeling and simulation. The modeling strategy relies on two pillars: an atomistic model (molecular dynamics (MD)/Grand Canonical Monte Carlo (GCMC)) that provides liquid mixture density and reactant solubility and a continuum model (CFD) in which the expansion characteristics of the foam is modeled exploiting the results of the atomistic simulations. The resulting coupled model is validated for two different PU systems applied in four batches with chemical and physical blowing agents. The results demonstrate the efficacy and reliability of the developed model in the simulation of different PU foam properties such as apparent density and temperature evolutions.
Hydrodynamics and kinetics in semi-batch stirred tank precipitation of L-glutamic acid based on pH shift with mineral acids Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-16 Ulla Ojaniemi, Johanna Puranen, Mikko Manninen, Elena Gorshkova, Marjatta Louhi-Kultanen
The precipitation process of L-glutamic acid from monosodium glutamate solution through acidification is studied by using hydrochloric acid and sulphuric acid. Both experimental and modelling methods are applied. The experiments have been carried out with a single feed semi-batch process applying two acid feed rates and two rotational mixing speeds. The method for computational fluid dynamics (CFD) modelling of the semi-batch process with a changing fluid volume is presented. The precipitation process including nucleation and crystal growth is modelled with CFD by using the kinetics presented in the literature for hydrochloric acid. A model for agglomeration presented in the literature and Eddy Dissipation Concept for micromixing are applied in the case of a lower rotational speed and hydrochloric acid. The particle size distribution is modelled with the simple number density model and with Quadrature Method of Moments. Micromixing was found to have an insignificant effect, but when including the model for agglomeration, the particle size distribution was in better agreement with the experiments. However, pH evolution of the system was captured better without the agglomeration model, indicating that the kinetic model may not describe the precipitation accurately. The pH and saturation ratio Sα were modelled based on thermodynamics. The significance of activities is highlighted in computing the thermodynamic equilibrium, and in precipitation kinetics. It was found that the applied acid had an effect on the chemical process, although the species concentrations were the same. The difference of the kinetic models between hydrochloric acid and sulphuric acid could be explained by the more complex dissociation of sulphuric acid. The greater computational ionic strength with sulphuric acid increased the nucleation rate, resulting in a difference in pH evolution in comparison with hydrochloric acid. Therefore, the kinetic parameters determined for the hydrochloric acid system are not applicable for other acid systems with different chemical compositions. For the modelling of the precipitating systems, more experimental work is needed for determining the kinetics.
A Three-Phase Solid-Liquid-Gas Slug Flow Mechanistic Model Coupling Hydrate Dispersion Formation with Heat and Mass Transfer Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-16 Carlos L. Bassani, Fausto A.A. Barbuto, Amadeu K. Sum, Rigoberto E.M. Morales
Pipe blockage due to gas hydrate formation is a main concern in the oil and gas industry due to the revenue losses caused by either production impairments or interruptions, and to the high costs associated to the elimination of such blockages. Assuming a hydrate formation rate in the gas-water interface based on the system subcooling, the present work models the transition from two-phase liquid-gas to three-phase solid-liquid-gas flows when hydrates form. The multiphase flow is assumed to be within the slug flow pattern region, as this is the prevailing flow regime in offshore production scenarios. The model couples mass, momentum and energy balances for the slug flow unit cell. The hydrate phase is assumed as homogeneously dispersed in the water. The gas and water consumption rates due to hydrate formation are modeled as source terms in the mass balance equations. The exothermic characteristic of the hydrate formation is taken into account in the energy conservation equation. The model provides analytic expressions for temperature and pressure distributions along the pipeline. However, the unit cell geometry is solved by numerical integration and the model closure is achieved only when empirical correlations for the slug frequency, the unit cell translational velocity and the slug aeration are used. The results from the numerical simulations are presented for the same input parameters for cases with and without hydrate formation. The discussion focuses on the influence of hydrate formation in the slug flow hydrodynamics and heat transfer. The main mechanisms affecting the mixture temperature and pressure distributions, the mixture heat transfer coefficient, the superficial velocities of the phases, the liquid loading, the slug flow frequency and the unit cell geometry are presented.
Impedance Spectroscopy and Membrane Potential Analysis of Microfiltration Membranes. The Influence of Surface Fractality Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-15 Darío Ramón Díaz, Francisco Javier Carmona, Laura Palacio, Nelio Ariel Ochoa, Antonio Hernández, Pedro Prádanos
Two-directional concurrent strategy of mode identification and sequential phase division for multimode and multiphase batch process monitoring with uneven lengths Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-15 Shumei Zhang, Chunhui Zhao, Furong Gao
In general, batch processes cover two-directional dynamics, in which the batch-wise dynamics are related to different operation modes, while the time-wise variations correspond to different phases within each batch. The problem of unevenness is common as a result of various factors, particularly in multimode batch processes. In order to address these issues, this paper proposes a two-directional concurrent strategy of mode identification and sequential phase division for multimode and multiphase batch process monitoring with the uneven problem. Firstly, pseudo time-slices are constructed in order to describe the process characteristics regarding the sample concerned, which can preserve the local neighborhood information within a constrained searching range and effectively prevent the synchronizing problem caused by uneven lengths. Secondly, mode identification is conducted along the batch direction and the phase affiliation is sequentially determined along time direction by determining the changes in variable correlations. The two-directional steps are implemented alternatively in order to identify the mode and phase information, which can also guarantee the time sequence within each mode. Thirdly, for online monitoring, the mode information and phase affiliation are simultaneously judged in real time for each new sample, from which the fault status is distinguished from the phase shift. The division results can indicate the critical-to-mode phases from which a certain mode begins to be separated into different sub-modes. In order to illustrate the feasibility and effectiveness of the proposed algorithm, it is applied to a multimode and multiphase batch process (namely an injection molding process) with the uneven problem.
Quantitative measurements of capillary absorption in thin porous media by the Automatic Scanning Absorptometer Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-14 C.J. Kuijpers, T.A.P. van Stiphout, H.P. Huinink, N. Tomozeiu, S.J.F Erich, O.C.G. Adan
A 1D model based on Darcy’s law is proposed to allow quantitative measurements of the penetration depth of water-glycerol-hexanediol mixtures in thin porous media using an Automatic Scanning Absorptometer (ASA). The limitations of this 1D model are discussed with respect to the nozzle dimensions and the liquid penetration depth. The penetration depth scales with liquid (viscosity and surface tension (η, σ)) and media parameters (average pore radius (r)) as predicted by Darcy’s law for Al2O3 disks that are inert to the liquid components. The penetration dynamics in PVDF and MCE filter membranes show a deviation from Darcy’s law, indicating specific liquid – media interaction with at least one of the liquid components. Furthermore a linear time regime is observed in the early stages of liquid penetration for time scales much larger than for which inertia effects are expected. This can on the one hand indicate that either, the liquid does not move into the fibrous samples as a homogenous liquid, or that the porous material deforms during the liquid imbibition process. On the other hand, it could be an effect resulting from the complexity of the porous structure itself and an indication of surface film flow formation.
Enhanced dehydration performance of hybrid membranes by incorporating fillers with hydrophilic-hydrophobic regions Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-14 Manru Wang, Hong Wu, Xiaotong Jin, Chen Yang, Xinyi He, Fusheng Pan, Zhongyi Jiang, Chengyang Wang, Mingming Chen, Peng Zhang, Xingzhong Cao
Synthesis of Mass Exchanger Networks in a Two-step Hybrid Optimisation Strategy Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-14 Michael Short, Adeniyi J. Isafiade, Lorenz T. Biegler, Zdravko Kravanja
We present a new method for the synthesis of mass exchanger networks (MENs) involving packed columns. Simultaneous synthesis of MENs is typically done through the use of mixed-integer nonlinear program (MINLP) optimization, with simplifications made in the mathematical representations of the exchangers due to computational difficulty in solving large non-convex mixed-integer problems. The methodology proposed in this study makes use of the stage-wise based superstructure MINLP formulation for the network synthesis. This stage-wise superstructure model incorporates fixed mass transfer coefficients, fixed column diameters, no pressure drops, and unequal compositional mixing for models. In this paper, the simplified MINLP model is further improved by including a detailed individual packed column design in a non-linear programming (NLP) sub-optimisation step, where orthogonal collocation is utilized for the partial differential equations, and optimal packing size, column diameter, column height, pressure drops, and fluid velocities. Detailed designs are then used to determine correction factors that update the simplified stage-wise superstructure models to more accurately portray the chosen design. Once the MINLP is updated with these correction factors, the model is re-run, with new correction factors obtained. This iterative procedure is repeated until convergence between the objective function of the MINLP and that of the NLP sub-optimisation is achieved, or until a maximum number of iterations is reached. The methodology is applied to two examples and is shown to be robust and effective in generating new topologies, and in finding superior networks that are physically realizable.
Gateway analysis for complex reaction mechanisms: Kinetic Informative Detachable (KID) sub-mechanisms Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-13 P. Daniel Branco, Gregory S. Yablonsky, Guy B. Marin, Denis Constales
In solving the kinetic model reduction problem for CSTR studies, a new procedure of decomposing the full mechanism was developed. In this procedure, the full mechanism was decomposed in two sub-mechanisms, Kinetic Informative Detachable (KID) mechanism and Feeding Mechanism (FEM) linked by a special bridging reaction via a single gateway substance which belongs to FEM. Requirements for such decomposition were formulated. This procedure allows to produce relationships which depend only on the kinetic coefficients of the KID mechanism and the gateway substance reaction. In a typical case, say for the mechanism A → k 1 B ⇄ k 2 - k 2 + C , the reciprocal space time value τ at the intersection of the B and C kinetic dependences is characterized by a simple relation 1 τ = k 2 + - k 2 - . In general, this or similar dependences can be used for extracting the kinetic coefficients. Mathematically, the procedure is grounded on a generalized eigenvalue problem. Decomposition of a given mechanism into sub-mechanisms can be done in multiple ways with different corresponding gateways, and, consequently, different kinetic coefficients can be extracted. Theoretical concepts are illustrated by many examples of mechanisms.
A Deterministic Model for Positional Gradients in Copolymers Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-13 Ivan Kryven, Yutian R. Zhao, Kimberley B. McAuley, Piet Iedema
Fluid dynamic evaluation of a 10 MW scale reactor design for chemical looping combustion of gaseous fuels Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-11 Michael Stollhof, Stefan Penthor, Karl Mayer, Hermann Hofbauer
The design of an efficient and scale-up ready reactor system is, together with development of a high performance oxygen carrier, one of the most important research topics in chemical looping combustion. The dual circulating fluidized bed (DCFB) concept is a reactor concept consisting of two interconnected circulating fluidized beds, air and fuel reactor, where the oxygen carrier is the bed material. In the present study a so-called cold flow model is used to investigate the fluid dynamic behavior of a next scale design based on the DCFB concept (10 MW fuel power input) in order to optimize the system design. Four different designs of the fuel reactor are investigated with focus on the solid distribution and general operating parameters and their influence on the operating range. For that purpose, several parameters like e.g. the amount of fluidization gas for both reactors, the total solid inventory, and the fuel power, are variated. Pressure profiles are used to get a comprehensive overview of the fluid dynamic behavior of the different reactor designs. Comparison of the fuel reactor designs shows that operation of the air reactor is not affected by changes of the fuel reactor design. In contrast significant changes, especially in the solid distribution, are recognizable for the different fuel reactor designs. These changes concern mainly the adapted sections of the fuel reactor. Two of the proposed fuel reactor designs are limited in their operating range due to unstable operating conditions, caused by fluid dynamic effects. At such unstable operating conditions the solid inventory distribution between both reactors fluctuates. This behavior is caused by the geometry of the fuel reactor. Further, due to variations in the geometry of the fuel reactor effects leading to the unstable operating conditions are identified. However, unstable operating conditions are caused by the shape of the conical form of the bottom part of the fuel reactor.
Dynamic Process Behavior and Model Validation of Reactive Dividing Wall Columns Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-11 Torben Egger, Georg Fieg
Reactive dividing wall columns (RDWC) are a highly integrated column type. The coupling of a reactive distillation and a dividing wall column leads to complex interactions between vapor-liquid mass transfer, chemical kinetics and component split around the dividing wall. In simulation studies such interactions have been shown to lead to complex dynamics and the occurrence of multiple steady states. However, experimental investigations are still missing to verify the theoretical findings. In this work the first comprehensive experimental study of the dynamic behavior of RDWCs is presented. The reference system of enzymatic catalyzed butyl acetate transesterification with hexanol has been employed to investigate the start-up and open loop behavior under different operating conditions. Two different start-up strategies are tested and compared. The experiments demonstrate the reliable and secure start-up and stable operation of a RDWC. Additionally, a developed rigorous dynamic RDWC model is presented that considers the dynamic influence on the vapor distribution in the dividing wall section. A detailed model validation is carried out using the obtained experimental data. The comparison of simulation results and experimental values show good agreement over a wide range of operating conditions.
Fischer-Tropsch synthesis in vertical, inclined and oscillating trickle-bed reactors for offshore floating applications Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-11 Ion Iliuta, Faïçal Larachi
Fischer-Tropsch synthesis performance in vertical, inclined and oscillating trickle-bed reactors for offshore floating applications was examined via a complex dynamic three-dimensional multiphase model based on volume-averaged mass, momentum, and species balance equations in liquid and gas phases and simultaneous diffusion and chemical reactions within the catalyst. Angular sinusoidal oscillatory motion of the trickle-bed reactor between vertical and an inclined position and between two inclined symmetrical/asymmetrical positions was examined. The behavior of inclined and oscillating Fischer-Tropsch trickle-bed reactors is atypical because the reactants in the main reactions originate from the gas phase and because a fraction of useful CO can be redirected in water gas-shift reaction. The performance of Fischer-Tropsch synthesis in the presence of water-gas shift reaction increases slightly with amplification of packed bed inclination even if the distortion of axial symmetry of liquid holdup and axial velocity radial distributions becomes considerable. Also, in asymmetric oscillating trickle-bed reactors the performance of Fischer-Tropsch synthesis is slightly improved. This enhancement is maximal for the reactor moving between vertical and an inclined position when the time-dependent waves of CO and H2 conversion develop around the steady-state solution of the middle inclination angle. The oscillatory Fischer-Tropsch performance moves towards the steady-state solution of the vertical state when the asymmetry between two inclined positions diminishes. Symmetric oscillating trickle-bed reactors generate an oscillatory Fischer-Tropsch performance around the steady-state solution of vertical state which is affected by the angular motion parameters of the reactor.
Pinch-off of liquid bridge during droplet coalescence under constrained condition Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-11 Leqin Peng, Zhengyuan Luo, Yi Y. Zuo, Gang Yan, Bofeng Bai
In this study, we perform an experimental investigation on the dynamical behaviors of a liquid bridge formed during droplet coalescence. Notably, the two droplets are constrained respectively by two vertically aligned needles. Of particular interest is the pinch-off of the liquid bridge under this constrained condition. We observe three typical behaviors of the liquid bridge: (1) reaching a stable shape after damped oscillations (regime I); (2) pinching off at both sides in the first necking stage with the largest oscillation amplitude (regime II); and (3) pinching off at only the upper side after once or twice necking (regime III). To indicate the condition when the pinch-off of the liquid bridge may occur, we develop a phase diagram based on the radius ratio of the droplet to the needle Rd/Rn and the Bond number Bo, which respectively characterizes the relative importance of surface tension to the constraint force from needles and that of gravity to surface tension. In general, the dynamical behavior of the liquid bridge transitions from regime II to regime I with Rd/Rn decreasing, and the critical value for this transition is 1.6. This transition indicates that the constraint force keeps the liquid bridge stable while the surface tension promotes its instability. Surprisingly, once the Bond number is sufficiently high (e.g., Bo > 0.05), regime III (i.e., pinch-off at only the upper side) is observed when Rd/Rn becomes around the regime II to I transition (i.e., Rd/Rn = 1.6). It is because the effect of gravity becomes predominant over the surface tension and the constrained force from needles. Moreover, we analyze the pinch-off characteristics of the liquid bridge lying in regimes II and III, including its pinch-off time (i.e., the time interval from the formation and pinch-off of the liquid bridge) and its neck shape at the instant of pinching off.
Engineering polymeric Janus Particles for Drug Delivery using Microfluidic Solvent Dissolution Approach Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-11 Pavithra Sundararajan, Jianbin Wang, Lawrence A. Rosen, Adam Procopio, Kenneth Rosenberg
Here we present the microfluidic approach to engineer polymeric Janus particles using solvent dissolution for potential drug delivery applications. Unlike the polymerization based particle generation techniques, this method does not suffer from potential toxicity concerns for drug delivery. This technique is based on dissolving away the solvent in the solution droplets containing designed concentration distribution of drug and polymer while preserving the concentration distribution during the transition of the droplet into a particle. We investigated the kinetics of solidification and concentration evolution in the droplets under different operational conditions. Our investigation demonstrated that the designed biphasic concentration of a drug surrogate introduced into two hemispheres of the droplets can be preserved in solidified particles. We conclude with practical guidelines for generating polymeric Janus particles using the dissolution technique.
Modeling of unmixed combustion based packed bed reactor system for heat transfer applications Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-09 Srinivas Krishnaswamy, Amol Deshpande, K.N. Ponnani
Unmixed Combustion (UMC), a novel variant of combustion, occurs when air and fuel alternately pass over an Oxygen Storage and Release Material (OSRM), usually metal/metal oxides, that undergoes oxidation and reduction reactions. The energy released during these reactions can potentially be utilized for various heat transfer applications. In this regard, a dynamic 2-D pseudo-homogeneous model has been developed for an UMC based annular packed bed reactor incorporating the phenomena of heat transfer across a surface to a representative coolant, i.e. air. A CFD software COMSOL MultiphysicsTM was used for model implementation and simulation. Cu/CuO on alumina was chosen as a representative OSRM, while zero air and methane (diluted with nitrogen) were used as reactive gases in the simulations. For prescribed operating conditions, the model predicts temperature profiles in the bed and total heat transfer. Model results for one cycle comprising of oxidation and reduction at 1.25 kg of OSRM loading and an operating temperature range of 823.15 – 973.15 K, were compared with those obtained from experimental data. Good agreement to within ± 2% for radial heat transfer to coolant and ± 9% for bed temperature profiles was found. The effect of varying reactive gas and coolant flowrate on the radial heat transfer was also simulated. This sensitivity analysis helped identify the limits of operating variables for optimal performance and confirm theoretical viability of operation. The results validate the use of a pseudo-homogeneous model in predicting the behaviour of dynamically operated UMC systems under the operating conditions in which the present study was carried out.
Dual effects of compatibilizer on the formation of oriented ribbon-like dispersed phase domains in polystyrene/polyamide 6 blends Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-06 Cai-Liang Zhang, Cong Li, Long Wang, Lian-Fang Feng, Tong Lin
Polymer blends with oriented ribbon-like dispersed phase were prepared via tape extrusion. Two specially designed compatibilizers, one being non-reactive and another reactive, were used to examine their influence on the formation of oriented ribbon-like dispersed phase in polystyrene (PS)/polyamide 6 (PA6) blend. Results show that both compatibilizers can decrease interfacial tension and produce vinculum effect to strengthen the deformation of dispersed phase. Moreover, the stretching force of tape extrusion pushes the compatibilizer molecules towards the tips of dispersed phase causing a non-uniform distribution along the surface of dispersed phase. At a low loading concentration of compatibilizer, the deformed dispersed phase particles can connect each other from their middle part and merge into long and even endless ribbons. However, when the loading of compatibilizer exceeds a certain level, the formation of ribbon-like dispersed phase will be impeded because all surfaces of dispersed phase are completely covered by the compatibilizer so that the coalescence of dispersed phase cannot occur.
Construction of thermo-tolerant yeast based on an artificial protein quality control system (APQC) to improve the production of bio-ethanol Chem. Eng. Sci. (IF 2.895) Pub Date : 2017-12-06 Ke Xu, Liping Yu, Wenxin Bai, Bing Xiao, Yueqin Liu, Bo Lv, Jun Li, Chun Li
A major challenge for the production of bio-ethanol is to develop yeast that can sustain growth under high temperature. Here, we show the application of an artificial protein quality control (APQC) system to an industrial Saccharomyces cerevisiae strain for improving thermo-tolerance, a key trait for a bio-ethanol fermentation program. All engineered strains exhibited a significantly higher growth rate and cell viability at 37°C, which conferred increased thermo-tolerance and more efficient glucose conversion to ethanol. Furthermore, the analysis of ubiquitination and the enzyme activities of pyruvate kinase (PK) and malate dehydrogenase (MDH) indicated strengthened protein quality, implying that proteostasis had been effectively improved at higher temperature. Industrial material fermentation results from yeast-RSP5-UBC4 (combined expression of ubiquitin conjugated enzyme E2 and ubiquitin ligase E3) showed a 2.4% increase in ethanol production. All these findings prove that APQC is suitable for improving yeast resistance to high temperature during industrial bio-ethanol production.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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