Showing papers in "Aiche Journal in 2016"

Thermally induced phase separation and electrospinning methods for emerging membrane applications: A review

Abstract: In this review, thermally induced phase separation (TIPS) and electrospinning methods for preparation of fluoropolymer membranes are assessed, particularly for the polyvinylidene fluoride (PVDF) and polyethylene chlorotrifluoroethylene membranes. This review focuses on controlling the membrane morphology from the thermodynamic and kinetic perspectives to understand the relationship between the membrane morphology and fabrication parameters. In addition, the current status of the nonsolvent induced phase separation (NIPS) method and the combined NIPS-TIPS (N-TIPS) method, which is a new emerging fabrication method, are discussed. The past literature data are compiled and an upperbound curve (permeability vs. tensile strength) is proposed for the TIPS-prepared PVDF membranes. Furthermore, the key parameters that control and determine the membrane morphology when using the electrospinning method are reviewed. Exploiting the unique advantages of the electrospinning method, our current understanding in controlling and fine-tuning the PVDF crystal polymorphism (i.e., β-phase) is critically assessed. © 2015 American Institute of Chemical Engineers AIChE J, 62: 461–490, 2016

The Selectivity for Sulfur Removal from Oils: An Insight from Conceptual Density Functional Theory

Abstract: The selectivity for sulfur removal from oils is an important topic. In this work, the selectivity for different sulfur removal methods has been studied by conceptual density functional theory (CDFT) at the B3LYP/6-311++G(3df,2p) level of theory. In principle, the selectivity is directly related to the mechanisms of sulfur removal. It cannot be precisely elucidated until the mechanisms are totally known. However, current work shows that relationships can be constructed between CDFT and the selectivity. That is, for hydrodesulfurization, good descriptors will be ionization energy, hardness, and bond lengths of SC; for adsorptive desulfurization, the hardness is a good descriptor; for oxidative desulfurization, good descriptors are electron density and Fukui function. And for extractive desulfurization (nonmetal-based ionic liquids), electron affinity and electrophilicity may be good descriptors. In addition, structures and frontier orbitals of various sulfides have also been discussed. It is hoped that these relationships between CDFT and selectivity can give useful information to develop highly efficient sulfur removal methods for specific sulfides, like 4,6-dimethyldibenzothiophene, and 4-methyldibenzothiophene. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2087–2100, 2016

A review of the operating limits in slot die coating processes

Abstract: Slot die coating is a pre-metered process commonly used for producing thin and uniform films. It is an important film fabrication method for applications where precise coating is required. A major concern in slot die coating processes is how to determine the operating limits to set the appropriate range of operating parameters, including coating speed, flow rate, vacuum pressure, coating gap, liquid viscosity and surface tension, etc. Operating limits directly determine the effectiveness and efficiency of the process. In this article, the current state of academic research on operating limits in slot die coating processes is reviewed. Specifically, the theories, mechanisms, and empirical conclusions related to the limits on vacuum pressure, the low-flow limit, the limit of wet thickness for zero-vacuum-pressure cases, the limit of dynamic wetting failure, and the limits of coating speed for a specific flow rate are reviewed. The article concludes with some recommendations for future work. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2508–2524, 2016

Production of benzene, toluene, and xylenes from natural gas via methanol: Process synthesis and global optimization

Abstract: A systematic global optimization-based process synthesis framework is presented to determine the most profitable processes to produce aromatics from natural gas. Several novel, commercial, and/or competing technologies are modeled within the framework, including methanol-to-aromatics, toluene alkylation with methanol, selective toluene disproportionation, and toluene disproportionation and transalkylation with heavy aromatics, among others. We propose a stand-alone chemicals facility: the main products are aromatics with allowable by-products of gasoline, liquefied petroleum gas, and electricity. Several case studies are discussed that produce varying ratios of para-, ortho-, and meta-xylene across multiple refinery capacities. The results indicate that utilizing natural gas for the production of aromatics is profitable with net present values as high as $3800 MM dollars and payback periods as low as 6 years. The required investment for these refineries represents as much as a 65% decrease compared to published estimates of similar coal-based capacity plants. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1531–1556, 2016

Experimental study on the solvent regeneration of a CO2-loaded MEA solution using single and hybrid solid acid catalysts

Abstract: The performance of a hybrid solid acid catalyst consisting of a physical mixture of γ-Al2O3 and H-ZSM-5 in terms of the rate and heat duty for solvent regeneration (i.e., CO2 stripping) of a CO2-rich MEA solution was compared with the individual performance of γ-Al2O3, H-ZSM-5, and H-Y solid acid catalysts using MEA (2–7 mol/L), with initial CO2 loading of 0.5 mol CO2/mol MEA at 378 K. It was observed that any catalyst significantly decreased the energy required for CO2 regeneration. The performance of the catalysts investigated ranked as follows: γ-Al2O3/H-ZSM-5 = 2/1 > γ-Al2O3 > H-ZSM-5 > H-Y if the process is in the lean CO2 loading region whereas it was H-ZSM-5 > γ-Al2O3/H-ZSM-5 = 2/1 > γ-Al2O3 > H-Y if the process is in the rich CO2 loading region. These results highlight the joint dependence on Bronsted/Lewis acidity and mesopore surface area of heat duty for solvent regeneration. © 2015 American Institute of Chemical Engineers AIChE J, 2015

Size effects of graphene oxide on mixed matrix membranes for CO2 separation

Abstract: Graphene oxide (GO)-polyether block amide (PEBA) mixed matrix membranes were fabricated and the effects of GO lateral size on membranes morphologies, microstructures, physicochemical properties, and gas separation performances were systematically investigated. By varying the GO lateral sizes (100–200 nm, 1–2 μm, and 5–10 μm), the polymer chains mobility, as well as the length of the gas channels could be effectively manipulated. Among the as-prepared membranes, a GO-PEBA mixed matrix membrane (GO-M-PEBA) containing 0.1 wt % medium-lateral sized (1–2 μm) GO sheets showed the highest CO2 permeation performance (CO2 permeability of 110 Barrer and CO2/N2 mixed gas selectivity of 80), which transcends the Robeson upper bound. Also, this GO-PEBA mixed matrix membrane exhibited high stability during long-term operation testing. Optimized by GO lateral size, the developed GO-PEBA mixed matrix membrane shows promising potential for industrial implementation of efficient CO2 capture. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2843–2852, 2016

Poly(vinyl alcohol)/ZIF-8-NH2 mixed matrix membranes for ethanol dehydration via pervaporation

Abstract: Ethanediamine-modified zeolitic imidazolate framework (ZIF)-8 particles (ZIF-8-NH2) is synthesized and incorporated in the poly(vinyl alcohol) (PVA) matrix to fabricate novel PVA/ZIF-8-NH2 mixed matrix membranes (MMMs) for pervaporation dehydration of ethanol. The PVA/ZIF-8-NH2 MMMs exhibit enhanced membrane homogeneity and separation performance because of the higher hydrophilicity and restricted agglomeration of the particles, as compared to corresponding MMMs loaded with unmodified particles. The effect of ZIF-8-NH2 loading in the MMMs is studied and the MMM with a 7.5 wt % ZIF-8-NH2 loading shows the best pervaporation performance for ethanol dehydration at 40°C. Various characterization techniques (Fourier transform infrared, scanning electron microscope, contact angle, sorption test, etc.) are used to investigate the MMMs loaded with ZIF-8 and ZIF-8-NH2 particles. The impact of operation conditions on pervaporation performance is also performed. The performance benchmarking shows that the MMMs have superior separation factors and comparable flux to most other PVA hybrid membranes. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1728–1739, 2016

Ceramic tubular MOF hybrid membrane fabricated through in situ layer-by-layer self-assembly for nanofiltration

Abstract: Nanofiltration has been playing an important role in water purification, in which the developments of novel membrane materials and modules are among significant. Herein, a metal-organic framework (MOFs) hybrid membrane, ZIF-8/PSS was fabricated on a tubular alumina substrate through a layer-by-layer self-assembly technique. ZIF-8 particles in situ grow into PSS layers to improve their compatibility and dispersion, thereby getting high quality membrane, which was loaded into a steel tubular module for nano-filtrating dyes from water. Under optimized conditions, it shows outstanding nanofiltration properties toward methyl blue, with the flux of 210 Lm−2 h−1 MPa−1 and the rejection of 98.6%. Furthermore, the good pressure resistance ability and running stability of the membrane were revealed, which can be attributed to use the ceramic substrate and the inherent stability of ZIF-8. This work thus illustrates a simple approach for fabricating MOFs hybrid membranes on tubular ceramic substrates, having great potential for industrial applications. © 2015 American Institute of Chemical Engineers AIChE J, 62: 538–546, 2016

Catalytic dehydration of glucose to 5-hydroxymethylfurfural with a bifunctional metal-organic framework

Abstract: Glucose conversion to 5-hydroxymethylfurfural (HMF) generally undergoes catalytic isomerization reaction by Lewis acids followed by the catalytical dehydration to HMF with Bronsted acid. In this work, a sulfonic acid functionalized metal-organic framework MIL-101(Cr)-SO3H containing both Lewis acid and Bronsted acid sites, was examined as the catalyst for γ-valerolactone-mediated cascade reaction of glucose dehydration into HMF. Under the optimal reaction conditions, the batch heterogeneous reaction gave a HMF yield of 44.9% and selectivity of 45.8%. Reaction kinetics suggested that the glucose isomerization in GVL with 10 wt % water follows the second-order kinetics with an apparent activation energy of 100.9 kJ mol−1. Continuous reaction in the fixed-bed reactor showed that the catalyst is highly stable and able to provide a steady HMF yield. This work presents a sustainable and green process for catalytic dehydration of biomass-derived carbohydrate to HMF with a bifunctional metal-organic framework. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4403–4417, 2016

A systematic comparison of PCA-based statistical process monitoring methods for high-dimensional, time-dependent processes

Abstract: High-dimensional and time-dependent data pose significant challenges to Statistical Process Monitoring (SPM). Most of the high-dimensional methodologies to cope with these challenges rely on some form of Principal Component Analysis (PCA) model, usually classified as non-adaptive and adaptive. Non-adaptive methods include the static PCA approach and Dynamic PCA for data with autocorrelation. Methods, such as Dynamic PCA with Decorrelated Residuals, extend Dynamic PCA to further reduce the effects of autocorrelation and cross-correlation on the monitoring statistics. Recursive PCA and Moving Window PCA, developed for non-stationary data, are adaptive. These fundamental methods will be systematically compared on high-dimensional, time-dependent processes (including the Tennessee Eastman benchmark process) to provide practitioners with guidelines for appropriate monitoring strategies and a sense of how they can be expected to perform. The selection of parameter values for the different methods is also discussed. Finally, the relevant challenges of modeling time-dependent data are discussed, and areas of possible further research are highlighted. This article is protected by copyright. All rights reserved.

Predicting Effective Conductivities Based on Geometric Microstructure Characteristics

Abstract: Empirical relationships between effective conductivities in porous and composite materials and their geometric characteristics such as volume fraction e, tortuosity τ and constrictivity β are established. For this purpose, 43 virtually generated 3D microstructures with varying geometric characteristics are considered. Effective conductivities σeff are determined by numerical transport simulations. Using error-minimization the following relationships have been established: σeff=σ0e1.15β0.37τgeod4.39 and σeff=σ0eβ0.36τgeod5.17 (simplified formula) with intrinsic conductivity σ0, geodesic tortuosity τgeod and relative prediction errors of 19% and 18%, respectively. We critically analyze the methodologies used to determine tortuosity and constrictivity. Comparing geometric tortuosity and geodesic tortuosity, our results indicate that geometric tortuosity has a tendency to overestimate the windedness of transport paths. Analyzing various definitions of constrictivity, we find that the established definition describes the effect of bottlenecks well. In summary, the established relationships are important for a purposeful optimization of materials with specific transport properties, such as porous electrodes in fuel cells and batteries. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1834–1843, 2016

Direct numerical simulations of dynamic gas-solid suspensions

Abstract: Direct numerical simulation results for gas flow through dynamic suspensions of spherical particles is reported. The simulations are performed using an immersed boundary method, with careful correction for the grid resolution effect. The flow systems we have studied vary with mean flow Reynolds number, solids volume fraction, as well as particle/gas density ratio. On the basis of the simulation results, the effect of particle mobility on the gas-solid drag force is analyzed and introduced into the existing drag correlation that was derived from simulations of stationary particles. This mobility effect is characterized by the granular temperature, which is a result of the particle velocity fluctuation. The modified drag correlation is considered so-far the most accurate expression for the interphase momentum exchange in computational fluid dynamics models, in which the gas-solid interactions are not directly resolved. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1958–1969, 2016

Subspace identification for data‐driven modeling and quality control of batch processes

Abstract: In this Chapter, a novel data-driven, quality modeling and control approach for batch processes is presented. Specifically, subspace identification methods are adapted for use with batch data to identify a state-space model from available process measurements and input moves. The resulting LTI, dynamic, state-space model is shown to be able to describe the transient behavior of finite duration batch processes. Next, the terminal quality is related to the terminal value of the identified states. Finally, the resulting model is applied in a shrinking-horizon, model predictive control scheme to directly control terminal product quality. The theoretical properties of the proposed approach are studied and compared to state-of-the-art latent variable control approaches. The efficacy of the proposed approach is demonstrated through a simulation study of a batch polymethyl methacrylate (PMMA) polymerization reactor. Results for both disturbance rejection and set-point changes (that is, new quality grades) are demonstrated.

Effect of channel size on liquid-liquid plug flow in small channels

Abstract: The hydrodynamic properties of plug flow were investigated in small channels with 0.5-, 1-, and 2-mm internal diameter, for an ionic liquid/aqueous two-phase system with the aqueous phase forming the dispersed plugs. Bright field Particle Image Velocimetry combined with high-speed imaging were used to obtain plug length, velocity, and film thickness, and to acquire velocity profiles within the plugs. Plug length decreased with mixture velocity, while for constant mixture velocity it increased with channel size. Plug velocity increased with increasing mixture velocity and channel size. The film thickness was predicted reasonably well for Ca > 0.08 by Taylor's (Taylor, J Fluid Mech. 1961;10(2):161–165) model. A fully developed laminar profile was established in the central region of the plugs. Circulation times in the plugs decreased with increasing channel size. Pressure drop was predicted reasonably well by a modified literature model, using a new correlation for the film thickness derived from experimental values.

Ultrathin carbon molecular sieve membrane for propylene/propane separation

Abstract: Ultrathin (down to 300 nm), high quality carbon molecular sieve (CMS) membranes were synthesized on mesoporous γ-alumina support by pyrolysis of defect free polymer films. The effect of membrane thickness on the micropore structure and gas transport properties of CMS membranes was studied with the feed of He/N2 and C3H6/C3H8 mixtures. Gas permeance increases with constant selectivity as the membrane thickness decreases to 520 nm. The 520-nm CMS membrane exhibits C3H6/C3H8 mixture selectivity of ∼31 and C3H6 permeance of ∼1.0 × 10−8 mol m−2 s−1 Pa−1. Both C3H8 permeance and He/N2 selectivity increase, but the permeance of He, N2, and C3H6 and the selectivity of C3H6/C3H8 decrease with further decrease in membrane thickness from 520 to 300 nm. These results can be explained by the thickness-dependent chain mobility of the polymer film which yields thinner final CMS membranes with reduction in pore size and possible closure of C3H6-accessible micropores. © 2015 American Institute of Chemical Engineers AIChE J, 2015

Sustainability Decision Support Framework for Industrial System Prioritization

Abstract: A multicriteria decision-making methodology for the sustainability prioritization of industrial systems is proposed. The methodology incorporates a fuzzy Analytic Hierarchy Process method that allows the users to assess the soft criteria using linguistic terms. A fuzzy Analytic Network Process method is used to calculate the weights of each criterion, which can tackle the interdependencies and interactions among the criteria. The Preference Ranking Organization Method for Enrichment Evaluation approach is used to prioritize the sustainability sequence of the alternative systems. Moreover, a sensitivity analysis method was developed to investigate the most critical and sensitive criteria. The developed methodology was illustrated by a case study to rank the sustainability of five alternative hydrogen production technologies. The advantages of the developed methodology over the previous approaches were demonstrated by comparing the results determined by the proposed framework with those determined using the pervious approaches. © 2015 American Institute of Chemical Engineers AIChE J, 2015

A computational framework and solution algorithms for two-stage adaptive robust scheduling of batch manufacturing processes under uncertainty

Abstract: A novel two-stage adaptive robust optimization (ARO) approach to production scheduling of batch processes under uncertainty is proposed. We first reformulate the deterministic mixed-integer linear programming model of batch scheduling into a two-stage optimization problem. Symmetric uncertainty sets are then introduced to confine the uncertain parameters, and budgets of uncertainty are used to adjust the degree of conservatism. We then apply both the Benders decomposition algorithm and the column-and-constraint generation (C&CG) algorithm to efficiently solve the resulting two-stage ARO problem, which cannot be tackled directly by any existing optimization solvers. Two case studies are considered to demonstrate the applicability of the proposed modeling framework and solution algorithms. The results show that the C&CG algorithm is more computationally efficient than the Benders decomposition algorithm, and the proposed two-stage ARO approach returns 9% higher profits than the conventional robust optimization approach for batch scheduling. © 2015 American Institute of Chemical Engineers AIChE J, 62: 687–703, 2016

On the relation between flexibility analysis and robust optimization for linear systems

Abstract: Flexibility analysis and robust optimization are two approaches to solving optimization problems under uncertainty that share some fundamental concepts, such as the use of polyhedral uncertainty sets and the worst-case approach to guarantee feasibility. The connection between these two approaches has not been sufficiently acknowledged and examined in the literature. In this context, the contributions of this work are fourfold: (1) a comparison between flexibility analysis and robust optimization from a historical perspective is presented; (2) for linear systems, new formulations for the three classical flexibility analysis problems—flexibility test, flexibility index, and design under uncertainty—based on duality theory and the affinely adjustable robust optimization (AARO) approach are proposed; (3) the AARO approach is shown to be generally more restrictive such that it may lead to overly conservative solutions; (4) numerical examples show the improved computational performance from the proposed formulations compared to the traditional flexibility analysis models. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3109–3123, 2016

Particle-resolved direct numerical simulation of gas–solid dynamics in experimental fluidized beds

Abstract: Particle-resolved direct numerical simulations (PR-DNS) of a simplified experimental shallow fluidized bed and a laboratory bubbling fluidized bed are performed by using immersed boundary method coupled with a soft-sphere model. Detailed information on gas flow and individual particles’ motion are obtained and analyzed to study the gas–solid dynamics. For the shallow bed, the successful predictions of particle coherent oscillation and bed expansion and contraction indicate all scales of motion in the flow are well captured by the PD-DNS. For the bubbling bed, the PR-DNS predicted time averaged particle velocities show a better agreement with experimental measurements than those of the computational fluid dynamics coupled with discrete element models (CFD-DEM), which further validates the predictive capability of the developed PR-DNS. Analysis of the PR-DNS drag force shows that the prevailing CFD-DEM drag correlations underestimate the particle drag force in fluidized beds. The particle mobility effect on drag correlation needs further investigation. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1917–1932, 2016

Quantitative assessment of fine-grid kinetic-theory-based predictions of mean-slip in unbounded fluidization

Abstract: Significance The quantitative ability of a kinetic-theory-based, two-fluid model is demonstrated in a clustering (unstable) gas-solid system via highly resolved simulations Unlike previous works, this assessment is validated against ideal computational fluid dynamics-discrete element method data to minimize sources of discrepancy Overall, good agreement in mean-slip velocities is observed with relative errors less than 20% over a mean solids concentration range of 002–025 Local concentration gradient distributions are also studied, showing a distinct shift toward higher gradients at higher mean solids concentrations which is proposed as the bottleneck in obtaining grid-independence rather than the cluster length scale © 2015 American Institute of Chemical Engineers AIChE J, 2015

Hydrodynamics and mass transfer of oscillating gas‐liquid flow in ultrasonic microreactors

Abstract: Ultrasonic microreactors were used to intensify gas-liquid mass-transfer process and study the intensification mechanism. Fierce surface wave oscillation with different modes was excited on the bubble. It was found that for slug bubbles confined in smaller microchannel, surface wave oscillations require more ultrasound energy to excite due to the confinement effect. Cavitation microstreaming with two toroidal vortices was observed near the oscillating bubble by a streak photography experiment. Surface wave oscillation at the gas-liquid interface increases the specific surface area, while cavitation microstreaming accelerates the interface renewal and thus improves the individual mass-transfer coefficient. With these two reasons, the overall mass-transfer coefficient was enhanced by 3–20 times under ultrasonication. As for gas-liquid flow hydrodynamics, ultrasound oscillation disturbs the bubble formation process and changes the initial bubble length and pressure drop. © 2015 American Institute of Chemical Engineers AIChE J, 2015

Effects of Ga doping on Pt/CeO2-Al2O3 catalysts for propane dehydrogenation

Abstract: This paper describes catalytic consequencesThis paper describes catalytic consequences of Pt/CeO2-Al2O3 catalysts promoted with Ga species for propane dehydrogenation. A series of PtGa/CeO2-Al2O3 catalysts were prepared by a sequential impregnation method. The as-prepared catalysts were characterized employing N2 adsorption-desorption, X-ray diffrtaction, temperature programmed reduction, O2 volumetric chemisorption, H2-O2 titration, and transmission electron microscopy. We have shown that Ga3+ cations are incorporated into the cubic fluorite structure of CeO2, enhancing both lattice oxygen storage capacity and surface oxygen mobility. The enhanced reducibility of CeO2 is indicative of higher capability to eliminate the coke deposition and thus is beneficial to the improvement of catalytic stability. Density functional theory calculations confirm that the addition of Ga is prone to improve propylene desorption and greatly suppress deep dehydrogenation and the following coke formation. The catalytic performance shows a strong dependence on the content of Ga addition. The optimal loading content of Ga is 3 wt %, which results in the maximal propylene selectivity together with the best catalytic stability against coke accumulation. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4365–4376, 2016