Showing papers in "Aiche Journal in 2007"
TL;DR: In this article, extensive lattice Boltzmann simulations were performed to obtain the drag force for random arrays of monodisperse and bidisperse spheres, and a new drag law was suggested for general polydisperse systems.
Abstract: Extensive lattice-Boltzmann simulations were performed to obtain the drag force for random arrays of monodisperse and bidisperse spheres. For the monodisperse systems, 35 different combinations of the Reynolds number Re (up to Re = 1,000) and packing fraction were studied, whereas for the bidisperse systems we also varied the diameter ratio (from 1:1.5 to 1:4) and composition, which brings the total number of different systems that we considered to 150. For monodisperse systems, the data was found to be markedly different from the Ergun equation and consistent with a correlation, based on similar type of simulations up to Re = 120. For bidisperse systems, it was found that the correction of the monodisperse drag force for bidispersity, which was derived for the limit Re = 0, also applies for higher-Reynolds numbers. On the basis of the data, a new drag law is suggested for general polydisperse systems, which is on average within 10% of the simulation data for Reynolds numbers up to 1,000, and diameter ratios up to 1:4
696 citations
TL;DR: In this paper, the role of feed and draw concentrations, membrane orientation, and membrane structural properties play in overall permeate flux performance and are linked to prevalence of external and internal concentration polarization.
Abstract: Osmotically-driven membrane processes, such as forward osmosis and pressure retarded osmosis, operate on the principle of osmotic transport of water across a semipermeable membrane from a dilute feed solution into a concentrated draw solution. The major hindrance to permeate water flux performance is the prevalence of concentration polarization on both sides of the membrane. This article evaluates the external and internal boundary layers, which decrease the effective osmotic driving force. By modeling permeate flux performance, the role that feed and draw concentrations, membrane orientation, and membrane structural properties play in overall permeate flux performance are elucidated and linked to prevalence of external and internal concentration polarization. External concentration polarization is found to play a significant role in the reduction of driving force, though internal concentration polarization has a far more pronounced effect for the chosen system conditions. Reduction of internal concentration polarization by way of membrane modification was found to improve the predicted flux performance significantly, suggesting that alteration of membrane design will lead to improved performance of osmotically driven membrane processes. 2007 American Institute of Chemical Engineers AIChE J, 53: 1736–1744, 2007
346 citations
TL;DR: In this paper, four new stripper configurations (matrix, internal exchange, flashing feed, and multipressure with split feed) have been evaluated with seven model solvents that approximate the thermodynamic and rate properties of 7m (30 wt %) monoethanolamine (MEA), potassium carbonate promoted by piperazine (PZ), promoted MEA, methyldiethanolamine (MDEA) promoted by PZ, and hindered amines.
Abstract: Aqueous absorption/stripping is a promising technology for the capture of CO2 from existing or new coal-fired power plants. Four new stripper configurations (matrix, internal exchange, flashing feed, and multipressure with split feed) have been evaluated with seven model solvents that approximate the thermodynamic and rate properties of 7m (30 wt %) monoethanolamine (MEA), potassium carbonate promoted by piperazine (PZ), promoted MEA, methyldiethanolamine (MDEA) promoted by PZ, and hindered amines. The results show that solvents with high heats of absorption (MEA, MEA/PZ) favor operation at normal pressure. The relative performance of the alternative configurations is matrix > internal exchange > multipressure with split feed > flashing feed. MEA/PZ and MDEA/PZ are attractive alternatives to 7m MEA. The best solvent and process configuration, matrix with MDEA/PZ, offers 22 and 15% energy savings over the baseline and improved baseline, respectively, with stripping and compression to 10 MPa. The energy requirement for stripping and compression to 10 MPa is about 20% of the power output from a 500 MW power plant with 90% CO2 removal. © 2007 American Institute of Chemical Engineers AIChE J, 2007
286 citations
TL;DR: In this article, a sintering model is formulated to describe the cyclic behavior of sorbents during cyclic calcination and carbonation, which explains the similar reversibility shown by Sorbents under different test conditions.
Abstract: The importance of calcium-based sorbents, especially natural limestones, for CO{sub 2} removal necessitates an investigation into the sotbent decay mechanism. This study starts from pore size distributions for samples from tests under various calcination/carbonation cycling conditions. A sintering model is formulated to describe the cyclic behavior of sorbents during cyclic calcination and carbonation. It explains the similar reversibility shown by sorbents under different test conditions. A balance between shorter cumulative sintering time and higher calcination rates appears to be responsible for the similar degrees of sintering and sorbent reversibility.
284 citations
TL;DR: In this paper, a computational study was performed on the adsorption separation of CO(sub 2) from flue gases (mixtures of CO{sub 2}/N{sub2}/O(sub2) ) in Cu-BTC metal-organic framework (MOF) to investigate the applicability of MOFs to this important industrial system.
Abstract: In this work, a computational study was performed on the adsorption separation of CO{sub 2} from flue gases (mixtures of CO{sub 2}/N{sub 2}/O{sub 2}) in Cu-BTC metal-organic framework (MOF) to investigate the applicability of MOFs to this important industrial system. The computational results showed that Cu-BTC is a promising material for separation of CO{sub 2} from flue gases, and the macroscopic separation behaviors of the MOF were elucidated at a molecular level to give insight into the underlying mechanisms. The present work not only provided useful information for understanding the separation characteristics of MOFs, but also showed their potential applications in chemical industry.
247 citations
TL;DR: In this article, scaling analysis of the convective mixing of CO2 in deep saline aquifers based on direct numerical simulations is presented, and three mixing periods are identified. And a criterion is developed that provides the appropriate numerical mesh resolution required for accurate modeling of convective mixed CO2.
Abstract: CO2 storage in deep saline aquifers is considered a possible option for mitigation of greenhouse gas emissions from anthropogenic sources. Understanding of the underlying mechanisms, such as convective mixing, that affect the long-term fate of the injected CO2 in deep saline aquifers, is of prime importance. We present scaling analysis of the convective mixing of CO2 in saline aquifers based on direct numerical simulations. The convective mixing of CO2 in aquifers is studied, and three mixing periods are identified. It is found that, for Rayleigh numbers less than 600, mixing can be approximated by a scaling relationship for the Sherwood number, which is proportional to Ra1/2. Furthermore, it is shown that the onset of natural convection follows tDc∼Ra−2 and the wavelengths of the initial convective instabilities are proportional to Ra. Such findings give insight into understanding the mixing mechanisms and long term fate of the injected CO2 for large scale geological sequestration in deep saline aquifers. In addition, a criterion is developed that provides the appropriate numerical mesh resolution required for accurate modeling of convective mixing of CO2 in deep saline aquifers. © 2007 American Institute of Chemical Engineers AIChE J, 2007
219 citations
209 citations
TL;DR: In this article, the mass transfer characteristics of immiscible fluids in the two kinds of stainless steel T-junction microchannels, the opposing-flow and the cross-flow Tjunction, are investigated experimentally.
Abstract: In this work, the mass transfer characteristics of immiscible fluids in the two kinds of stainless steel T-junction microchannels, the opposing-flow and the cross-flow T-junction, are investigated experimentally. Water-succinic acid-n-butanol is chosen as a typical example of liquid-liquid two-phase mass transfer process. In our experiments, the mixture velocities of the immiscible liquid-liquid two phases are varied in the range from 0.01 to 2.5 m/s for the 0.4 mm microchannel and from 0.005 to 2.0 m/s for the 0.6 mm microchannel, respectively. The Reynolds numbers of the two-phase mixture vary between 19 and 650. The overall volumetric mass transfer coefficients are determined quantitatively in a single microchannel, and their values are in the ranges of 0.067-17.35 s(-1), which are two or three orders of magnitude higher than those of conventional liquid-liquid contactors. In addition, the effects of the inlet configurations, the fluids inlet locations, the height and the length of the mixing channel, the volumetric flux ratio have been investigated. Empirical correlations to predict the volumetric mass transfer coefficients based on the experimental data are developed. (c) 2007 American Institute of Chemical Engineers AIChE J, 53:3042-3053, 2007.
207 citations
TL;DR: In this article, the phase equilibria of different ternary systems involving hydrocarbons present in gasoline formulations, thiophene, and [C8mim][BF4], were obtained experimentally.
Abstract: Increased reductions of statutory sulfur content on fossil fuels as gasoline or diesel have led to intense research into all possible methods of desulfurization. With the aim to study [C8mim][BF4] ionic liquid as extraction solvent for desulfurization, the phase equilibria of different ternary systems involving hydrocarbons present in gasoline formulations, thiophene, and [C8mim][BF4], were obtained experimentally. Potential interest of this ionic liquid for desulfurization was confirmed by the phase equilibria determined. As design of a multistage separation process requires knowledge of phase equilibria, simultaneous correlation of liquid-liquid equilibrium data was done using the nonrandom two liquid (NRTL) activity coefficient model. A gasoline formulation was simulated as a mixture of n-hexane, cyclohexane, iso-octane, and toluene with thiophene and dibezothiophene as sulfur-components, and its desulfurization was performed by multistage extraction using the ionic liquid in three successive stages. © 2007 American Institute of Chemical Engineers.
170 citations
TL;DR: In this paper, the authors propose a new paradigm that couples plant management with process feedback control to achieve economic optimal plant operation by regulating process variables at appropriate values, where the important task of plant monitoring and the incorporation of plant operator input take place at the plant management level.
Abstract: T he process industry is involved with the conversion of raw materials, through a series of chemical processing steps, to valued products and is a key economic sector in the U.S. and globally. The global market share and business performance of the process industry is heavily based on the value that can be generated from its assets which are comprised of process sites, people and materials, as well as intellectual property in the form of product knowledge, process expertise and physical properties of materials. While the range of valuable assets is large, nearly all the economic value in terms of operating profit in the process industry is a direct result of plant operations. This realization has motivated extensive research, over the last 40 years, on the development of advanced operation and control strategies to achieve economically optimal plant operation by regulating process variables at appropriate values. Figure 1 depicts the existing paradigm that couples plant management with process feedback control. This paradigm has been widely adopted by the process industries and extensively studied by the process systems engineering community. This paradigm features two distinct levels of plant operations: a plant management level and a process control level. At the plant management level, an optimization problem is solved on the basis of a (typically) steady state model of the plant to compute the economically optimal values for the process variables, while in the process control level, feedback control systems are used to regulate the process variables at the specified values. Additionally, the important task of plant monitoring — that is the determination of abnormal, potentially faulty plant behavior by proper analysis of plant sensor data — and the incorporation of plant operator input take place at the plant management level. While the paradigm of Figure 1 has undoubtedly been a successful one, over the last few years there have been numerous calls (e.g.,) for expanding this paradigm in a number of directions. Specifically, while economic prosperity has always Perspective
160 citations
TL;DR: In this paper, a novel silver ion-exchange treatment of zeolite was introduced to change the physical and chemical adsorption properties of penetrants in the zeolites, and the results showed that this type of composite membrane material is a superior candidate for the practical separation of natural gas.
Abstract: A novel silver ion-exchange treatment of zeolite was introduced in this work to change the physical and chemical adsorption properties of penetrants in the zeolite. EDX data confirm the complete replacement of sodium ion in zeolite NaA by silver ion, whereas XRD patterns and BET results show no changes in some physical properties of zeolite after the silver ion-exchange treatment. Polyethersulfone (PES)-zeolite NaA mixed matrix membranes (MMMs) and PES–zeolite AgA MMMs were fabricated at high processing temperatures with different zeolite loadings. Cross-sectional SEM images of these two types of MMMs indicate the interface between polymer and zeolite phases is comparable before and after the silver ion-exchange treatment. The effects of silver ion-exchange treatment of zeolite and zeolite loadings on the gas separation performance of these MMMs were investigated. CO2 permeability of PES–zeolite AgA MMMs is higher than that of PES–zeolite NaA MMMs, whereas their CH4 permeability is lower than that of PES–zeolite NaA MMMs. This trend is the result of the reversible reaction between silver ion and CO2 molecule. CO2 and CH4 permeability of PES–zeolite AgA MMMs decreases with increasing zeolite content arising from the effects of partial pore blockage of zeolite and polymer chain rigidification, whereas their CO2/CH4 selectivity increases with an increase in zeolite loadings and the highest value reaches 59.6 at 50 wt % zeolite loading because of a combined effect of the facilitated transport mechanism of silver ion and the molecular sieving mechanism of zeolite. Both CO2-induced plasticization test and CO2/CH4 mixed gas measurement were performed to examine the applicability of these developed PES–zeolite AgA MMMs in industry. Results prove that this type of composite membrane material is a superior candidate for the practical separation of natural gas. © 2007 American Institute of Chemical Engineers AIChE J, 2007
TL;DR: In this paper, a rate-based model for acid gas absorption was developed and validated against mass-transfer data obtained from a 3-month campaign in a laboratory pilot-plant absorber in which the experimental gas-liquid material balance was within an average of 6%.
Abstract: A rigorous rate-based model for acid gas absorption was developed and validated against mass-transfer data obtained from a 3-month campaign in a laboratory pilot-plant absorber in which the experimental gas–liquid material balance was within an average of 6%. The mass-transfer model is based on the penetration theory where the liquid film is discretized using an adaptive grid. The model was validated against all data and the deviation between simulated and averaged gas and liquid side experimental mass-transfer rates yielded a total variability of 6.26%, while the total average deviation was 6.16%. Simpler enhancement factor mass-transfer models were also tested, but showed slight over-prediction of mass-transfer rates. A sensitivity analysis shows that the accuracy of the equilibrium model is the single most important source of deviation between experiments and model, in particular at high loadings. Experimental data for the absorber in the integrated pilot plant are included. © 2007 American Institute of Chemical Engineers AIChE J, 2007
TL;DR: In this article, the core-annulus flow regime was used as a numerical benchmark to evaluate the sensitivity of gas-solids continuum models and boundary conditions to model formalisms and parameters.
Abstract: We use the well established core-annulus flow regime as a numerical benchmark to evaluate the sensitivity of gas–solids continuum models and boundary conditions to model formalisms and parameters. By using transient, 1D, grid-independent numerical solutions, we avoid the use of speculative closure terms and show that the kinetic theory of granular flow (KTGF) is sufficient to model core-annulus regime. That regime arises in the time-average solution as a consequence of the fluctuating motion of regions with high solids concentration. These fluctuations are most sensitive to the gravitational acceleration (g) and granular energy dissipation terms. The fluctuation frequency is α . The effect of fluctuations is so dominant that decreasing the restitution coefficient (KTGF parameter) actually increases the average granular temperature. The wall boundary conditions for solids momentum and granular energy equations dictate the core-annulus flow regime. They must cause a net dissipation of granular energy at the wall for predicting that regime. © 2007 American Institute of Chemical Engineers AIChE J, 2007
TL;DR: In this article, a mechanistic approach has been taken to enhance yield of a sonochemical reaction using those techniques, which influence the phenomenon of radical formation by the cavitation bubbles.
Abstract: In this study, a mechanistic approach has been taken to enhance yield of a sonochemical reaction. Formation of highly reactive free radicals due to the transient collapse of cavitation bubbles is the primary mechanism of a sonochemical reaction. A physical (reduction in dissolved gas concentration) and a chemical (increasing the reactant concentration) technique is used for enhancing yield of a sonochemical reaction using those techniques, which influence the phenomenon of radical formation by the cavitation bubbles. A bubble dynamics model is used for explaining the sonochemical phenomena. In a degassed medium, the ultrasound wave undergoes lesser attenuation; moreover, equilibrium size of a bubble shrinks due to rectified diffusion. Because of this, a bubble undergoes more violent collapse, resulting in greater production of radicals that give higher yield. On the other hand, increasing the initial reactant concentration shows an adverse effect on the sonochemical yield. This is ascribed to reduction in water vapor flux in the bubble due to reduction of vapor pressure of the medium. This study, therefore, demonstrates as how macroscopic manifestation (the sonochemical yield) of the microscopic phenomena (transient collapse of cavitation bubble) is a complicated function of several physical processes. The results of this study shed light on the complex and multifaceted physical mechanism of a sonochemical reaction, which may be useful in maximization of yield of other sonochemical systems. 2007 American Institute of Chemical Engineers AIChE J, 53: 1132–1143, 2007
TL;DR: In this article, the authors developed a bimetallic Co-Ni/Al2O3 oxygen carrier suitable for a fluidized bed chemical-looping combustion process, which showed that the addition of Co enhances the reducibility of the oxygen carrier by influencing the metal-support interactions helping the formation of reducible nickel species.
Abstract: This study deals with the development of a bimetallic Co-Ni/Al2O3 oxygen carrier suitable for a fluidized bed chemical-looping combustion process. Temperature programmed characterization shows that the addition of Co enhances the reducibility of the oxygen carrier by influencing the metal-support interactions helping the formation of reducible nickel species. Reactive characterization of the prepared oxygen carriers in a CREC fluidized riser simulator, using multiple reduction/oxidation cycles, demonstrates that the Co-Ni/Al2O3 particles display excellent reactivity and stability. The addition of Co in the bimetallic Co-Ni/Al2O3 influences the state of the surface minimizing the formation of nickel aluminate. The addition of Co also inhibits metal particle agglomeration by maintaining consistent metal dispersion during the cyclic oxidation/reduction processes. A solid-state kinetics for both reduction and oxidation cycles is established using a clarified Avrami-Erofeev model at nonisothermal conditions. This random nucleation model describes solid phase changes adequately. The activation energy for Co-Ni/Al2O3 reduction is found to be significantly lower than the activation energy for the unpromoted Ni/Al2O3 sample, with this observation confirming the positive influence of adding Co on the Ni-Al2O3 oxygen carrier. © 2007 American Institute of Chemical Engineers AIChE J, 2007
TL;DR: In this article, the van der Waals-Platteeuw model was applied to the measurements of the transient data and it is shown that the theory allows estimation of occupancies of each component during replacement.
Abstract: CH4–CO2 replacement in CH4 hydrate with high pressure CO2 was studied with in-situ laser Raman spectroscopy at 273.2 K and at initial pressures of 3.2, 5.4, and 6.0 MPa. Replacement rates increased with increasing pressures up to 3.6 MPa and did not change at higher pressures (∼6.0 MPa). These results showed that the replacement rates were dependent on pressure and phase conditions with the driving force being strongly related to fugacity differences of the two guest components between fluid and hydrate phases. When CH4 hydrate was contacted with CO2 under flow conditions, in-situ Raman measurements of the hydrate phase showed differences of cage decomposition rates between the Medium-cage (M-cage) and the Small-cage (S-cage) in the CH4 hydrate with decomposition of the M-cage being faster than that of the S-cage. The van der Waals–Platteeuw model was applied to the measurements of the transient data and it is shown that the theory allows estimation of occupancies of each component during replacement. © 2007 American Institute of Chemical Engineers AIChE J, 2007
TL;DR: In this article, a unified model for the calculation of diffusion coefficients of gas, liquid and supercritical states of nonpolar multicomponent mixtures is presented, where a new correlation is proposed for the binary infinite dilution-diffusion coefficients.
Abstract: Multicomponent diffusion is important in a variety of applications. In order to calculate diffusion flux, molecular diffusion coefficients are required, where fluid nonideality and the multicomponent nature of the mixture have a significant effect. A unified model for the calculation of diffusion coefficients of gas, liquid and supercritical states of nonpolar multicomponent mixtures is presented. A new correlation is proposed for the binary infinite dilution-diffusion coefficients. The generalized Vignes relation is used in multicomponent mixtures. Nonideality is rigorously described by the fugacity derivatives evaluated by the volume-translated Peng-Robinson equation of state. Predictions for highly nonideal gas and liquid multicomponent mixtures demonstrate the reliability of the proposed methodology. © 2007 American Institute of Chemical Engineers AIChE J, 2007
TL;DR: In this paper, the authors investigated the industrial scale SMB process from modeling, simulation, and optimization points of view, using experimentally measured xylene adsorption equilibrium and kinetics data on ion exchanged faujasite zeolite.
Abstract: One of the first applications of Simulated Moving Bed (SMB) technology was in p-xylene recovery from mixed xylenes. The three main industrial processes for p-xylene separation from mixed xylenes based on SMB technology are: UOP's Parex, IFP's Eluxyl, and Toray's Aromax. These units operate in liquid phase (T = 180°C and P = 9 bar), achieving high recovery of almost pure p-xylene with high on-stream efficiency and extended adsorbent life. In this work, the industrial scale SMB process is investigated from modeling, simulation, and optimization points of view, using experimentally measured xylene adsorption equilibrium and kinetics data on ion exchanged faujasite zeolite. The aim is to develop tools for training of SMB unit operators and choice of the best operating conditions. Useful studies for better understanding of the influence of the operating parameters, adsorbent packing, and separation requirements on unit productivity are presented. SMB unit revamping strategies and operative actions are proposed. The practical application of “separation volume” methodology in the selection of optimum operating conditions that lead to maximum p-xylene productivity with minimal desorbent consumption is described. © 2006 American Institute of Chemical Engineers AIChE J, 2007
TL;DR: In this paper, Zeolite 13X was employed for the capture and recovery of CO2 in a flow through system where the adsorbent was subjected to five adsorption-desorption cycles.
Abstract: The removal of carbon dioxide (CO2) from industrial emissions has become essential in the fight against climate change In this study, we employed Zeolite 13X for the capture and recovery of CO2 in a flow through system where the adsorbent was subjected to five adsorption-desorption cycles The influent stream contained 15% CO2 at standard conditions The adsorbent bed was 1 in in length and 1 in 3/8 in dia, and was packed with 10 g of the zeolite Temperature swing adsorption (TSA) was employed as the regeneration method through heating to approximately 135 °C with helium as the purge gas The adsorbent capacity at 90% saturation was found to decrease from 78 to 60gCO2/kgZeolite13X after the fifth cycle The CO2 capture ratio or the mass of CO2 adsorbed to the total mass that entered the system decreased from 63% to only 61% after the fifth cycle The CO2 recovery efficiency ranged from 82 to 93% during desorption, and the CO2 relative recovery, ie, CO2 desorbed for the nth cycle to CO2 adsorbed for the first cycle, ranged from 88 to 68% The service life of the adsorbent was determined to be equal to eleven cycles at a useful capacity of 40gCO2/kgZeolite13X © 2007 American Institute of Chemical Engineers AIChE J, 2007
TL;DR: In this article, the authors performed species segregation measurements in a fluidized bed composed of a binary Geldart B mixture, and three system types were explored: size segregation, density segregation, and combined size/density segregation with the smaller species denser and lighter.
Abstract: Species segregation measurements were performed in a fluidized bed composed of a binary, Geldart B mixture. Three system types were explored: size segregation, density segregation, and combined size/density segregation (with the smaller species denser and lighter). Glass and polystyrene mixtures were investigated, at various gas velocity, jetsam concentration, particle-size ratio, particle-density ratio, and bed-aspect ratio combinations. Axial and radial segregation profiles were obtained from frozen bed sectioning. Low-velocities were used in order to minimize the possibility of segregation during bed collapse. In size-segregating systems, coarse particles act as jetsam, with a nearly constant concentration of fines in the flotsam-rich section. For density segregation, heavier particles act as jetsam and segregation behavior is not monotonically dependent on bed composition. A slight radial segregation was observed at all gas velocities, with jetsam accumulating near the wall. In size-and-density-segregating systems, denser particles (smaller and lighter) act as jetsam, with a slightly higher jetsam accumulation near the core of the bed. At higher gas velocities, however, the bottom layers become richer in jetsam in the periphery. Collectively, the data provide a robust experimental data set for evaluating the ability of existing and new models to predict species segregation. © 2007 American Institute of Chemical Engineers AIChE J, 2007
TL;DR: A mathematical model that simulates temperature profiles during freezing process of standard pharmaceutical formulations (mannitol and BSA based) was set up in two-dimensional axsymmetric space, and the ice crystal mean sizes were semi empirically estimated from the resulting temperature profiles as mentioned in this paper.
Abstract: A mathematical model that simulates temperature profiles during freezing process of standard pharmaceutical formulations (mannitol and BSA based) was set up in two-dimensional axsymmetric space, and the ice crystal mean sizes were semi empirically estimated from the resulting temperature profiles. Water vapor mass transfer permeability values during sublimation step were also estimated from ice phase morphological parameters. All these numerical data were compared with experimental data, and a quite good agreement was observed that confirmed the adequacy of the present model calculations. It was confirmed that, for a given formulation, the mass transfer parameters during freeze-drying were strongly dependent on morphological textural parameters, and consequently, on the nucleation temperatures that fix the ice phase morphology. The influence of freezing rate was also predicted from the simulations, proving that an increase of cooling rates led to slower primary drying rates. © 2007 American Institute of Chemical Engineers AIChE J, 2007
TL;DR: In this article, the authors proposed a two-stage problem decomposition to find optimal trade-offs between design and control decisions, based on process dynamics and advanced control, to maximize performance in the face of operational and model uncertainty.
Abstract: Currently, chemical process design and process control are separate disciplines assisting process development at different stages. Design and control decisions are made separately despite the common objective of dissipating the impact of uncertainty to ensure robust plant operation. Experience suggests that designing processes for flexibility against disturbances or parameter variations without considering dynamics under actual control feedback does not guarantee robust performance. Thus, it appears advantageous to address process design and control decisions simultaneously for maximizing performance in face of operational and model uncertainty. Realistic high-performance processes should be optimal in their dynamic operation with realizable control. The lack of integration between design and control objectives at the conceptual level is addressed here. The proposed procedure finds optimal trade-offs between design and control decisions, based on process dynamics and advanced control. A major innovation is a novel embedded control optimization approach. It suggests a two-stage problem decomposition leading to a massive reduction of problem size and complexity. Integration of design and control is expected to have a broad impact on high-performance systems operated close to their limits. Two case studies demonstrate the suitability of the methodology. © 2007 American Institute of Chemical Engineers AIChE J, 2007
TL;DR: It is shown that a “novel” expression, previously presented in another form in the well known “Handbook of Mathematical Functions”, approximates very accurately the temperature integral and allows to obtain correct values of the activation energy.
Abstract: The kinetics of processes involving solids may be determined from experiments under non-isothermal conditions. On analyzing data by integral methods, it is necessary to calculate the temperature integral, which does not have an analytical solution. Instead of performing the numerical integration, most of the researchers prefer to circumvent the problem by using approximate expressions, not always adequate. The widespread use of inaccurate approximations does not contribute to a coherent growth of scientific knowledge. In the present article, a critical review of the known approximations is carried out and a clear ranking is established. Moreover, the deviations of the calculated activation energies relatively to the numerical solution are discussed, and some recommendations are proposed. Namely, it is shown that a “novel” expression, previously presented in another form in the well known “Handbook of Mathematical Functions”, approximates very accurately the temperature integral and allows to obtain correct values of the activation energy. © 2007 American Institute of Chemical Engineers AIChE J, 2007
TL;DR: In this article, the microstructure and interionic interaction in two selected amino-functionalized imidazolium ionic liquids, 1-aminoethyl-3methylimidazolate hexafluorophosphate and 1-aminopropyl-3-butylimidrazolium tetrafluoroborate, were studied both for bulk liquid by using molecular dynamics simulations and for isolated ion pair by using ab initio calculations.
Abstract: Imidazolium ionic liquids (ILs) can be functionalized by introducing -NH(2), which were found to be excellent solvents for CO(2) capture and electrophile separation, however, some disadvantages, e.g., the relatively high viscosities, limit their eventual large-scale applications. To understand the influences of amino addition on their properties and promote their applications, the microstructure and interionic interaction in two selected amino-functionalized imidazolium ILs, 1-aminoethyl-3-methylimidazolium hexafluorophosphate and 1-aminopropyl-3-butylimidazolium tetrafluoroborate, are studied both for bulk liquid by using molecular dynamics simulations and for isolated ion pair by using ab initio calculations. It is found that the amino addition does not remarkably affect the organization of anions around C2-site, C4-site, and C5-site on imidazolium ring, while it participates in the cation-anion interaction as a new strong site where anions strongly organize around -NH(2) and form strong ion-type hydrogen bonds. The condensed phase simulations indicate that their ionic self-diffusion coefficients are on the order of 10(-13) m(2) s(-1) at room temperature, roughly 2 order of magnitude lower than that of conventional imidazolium ILs without -NH(2); the isolated ion pair calculations show that such terminal amino-associated interaction reduces the flexibility of alkyl side chains and increases the cation-anion interaction; and these results are qualitatively consistent with their higher experimental viscosities. (c) 2007 American Institute of Chemical Engineers AIChE J, 53: 3210-3221, 2007.
TL;DR: In this article, an acid-base catalytic mechanism has been proposed to interpret the catalytic behavior based on the fact that acidbase hydroxyl group pairs on the activated LDH surface have a separation of 031 nm.
Abstract: Activated layered double hydroxides (LDHs) with high crystallinity, obtained by calcination/rehydration of LDH precursors synthesized by urea decomposition, have higher catalytic activity in acetone self-condensation and Knoevenagel reactions than less crystalline materials obtained from LDH precursors synthesized by titration co-precipitation The activated LDHs possess both basic and acidic sites High resolution transmission electron microscopy (HRTEM) confirms that the highly crystalline activated LDHs retain the lattice structure of the LDH precursors with lattice parameters a = b = 031 ± 001 nm and α = 60 ± 2° An acid-base catalytic mechanism has been proposed to interpret the catalytic behavior based on the fact that acid-base hydroxyl group pairs on the activated LDH surface have a separation of 031 nm It is proposed that the active sites are mainly located on the ordered array of hydroxyl sites on the basal surfaces rather than on the edges, as has been previously suggested © 2007 American Institute of Chemical Engineers AIChE J, 2007
TL;DR: In this paper, a mainframe is used for the control over composition distribution along the chain length in atom transfer radical copolymerization (CLRcoP) in a semibatch reactor with programmed comonomer feeding rates.
Abstract: Controlled/living radical copolymerization (CLRcoP) operated in a batch process is subject to composition drifting and thus produces spontaneous gradient copolymer. The composition distribution along the chain length of individual chains is solely determined by the reactivities of comonomers and the as-synthesized product is uncontrolled. Design of the composition vs. chain length profile provides a new route for developing polymer materials with tailor-made properties. Presented in this article is a theoretical mainframe used for the control over composition distribution along the chain length in atom transfer radical copolymerization. The control is based on a semibatch reactor technology with programmed comonomer feeding rates. Illustrated are three copolymerization model systems with representative reactivity ratios. The targeted composition distribution profiles are uniform, linear gradient, parabolic gradient, hyperbolic gradient, and di-block and tri-block distributions. © 2006 American Institute of Chemical Engineers AIChE J, 2007
TL;DR: In this article, porous Magnesium oxide (MgO) particles have been applied to generate mixed matrix membranes (MMM) for the dehydration of iso-propanol by pervaporation.
Abstract: For the first time, porous Magnesium oxide (MgO) particles have been applied to generate mixed matrix membranes (MMM) for the dehydration of iso-propanol by pervaporation. A modified membrane fabrication procedure has been developed to prepare membranes with higher separation efficiency. FESEM and DSC characterizations confirm that the MMMs produced have intimate polymer/particle interface; the nanosize crystallites on MgO surface may interfere with the polymer chain packing and induce chains rigidification upon the particle surface. It is observed that Matrimid 1 / MgO MMMs generally have higher selectivity, but lower permeability relative to the neat Matrimid 1 dense membrane. The highest selectivity is obtained with MMM containing 15 wt. % MgO. The selective sorption and diffusion of water in the MgO particles, and the polymer/particle interface properties combine to lead to the earlier phenomena. The investigation on the effect of feed water composition on the pervaporation performance reveals that the addition of MgO can show the selectivity-enhancing effects if the feed water concentration is lower than 30 wt. %. In the dehydration of isopropanol aqueous solution with 10 wt. % water, the selectivity of the MMMs is around 2,000, which is more than twice of 900 of neat polymeric membrane. This makes MMMs extremely suitable for breaking the azeotrops of water/iso-propanol. Gas permeation tests are also conducted using O2 and N2 to determine the microscopic structure of the MMMs, and to investigate the relationship between pervaporation and gas separation performance. 2007 American Institute of Chemical Engineers AIChE J, 53: 1745–1757, 2007
TL;DR: In this paper, a model has been developed to predict the flow and temperature fields inside a pilot scale (35 L) vessel during the pressure heating, holding and cooling stages of the process.
Abstract: High pressure high temperature processing is a candidate food sterilization process in which heat is generated volumetrically within the food as a result of rapid pressurization to 600 MPa or higher. For commercial viability the temperature profile in the process should be as uniform as possible. A model has been developed to predict the flow and temperature fields inside a pilot scale (35 L) vessel during the pressure heating, holding and cooling stages of the process. Simulations on the empty vessel show that thermal conduction causes excessive cooling. The model agrees well with experimental results in which thermocouples are used to measure temperature throughout a metallic composite carrier inserted into the vessel. The model is used to design a Polytetrafluoroethylene (PTFE) carrier which produces thermal uniformity within the carrier. Predicted variations of sterility resulting from a process are produced using the F0-value distribution. No significant reduction of spores was seen in the empty vessel, while more than 94.6% of the PTFE carrier volume achieved a reduction greater than 1012. © 2007 American Institute of Chemical Engineers AIChE J, 2007
TL;DR: In this paper, the impact on smooth solid substrates of drops formed by the drop-on-demand (DOD) method was investigated over a wide range of impaction speeds (U0 = 2.21-12.2 m/s), surface contact angles (θ = 6-107°), and drop diameters (D0 = 40.8-50.5 μm).
Abstract: Impaction on smooth solid substrates of drops formed by the drop-on-demand (DOD) method was investigated over a wide range of impaction speeds (U0 = 2.21–12.2 m/s), surface contact angles (θ = 6–107°), and drop diameters (D0 = 40.8–50.5 μm). The experimental results were compared with several existing equations for predicting maximum spreading. The dimensionless time to reach maximum spreading ratio, scaled by D0/U0, ranged from 0.6 to 2.99, depending on Weber number and contact angle. Micron and millimeter drop impactions were compared, and the results indicate that scaling based on three dimensionless numbers (We, Re or Oh, and cos θ) is valid, but spreading ratios of millimeter drops are usually slightly larger during the whole process. The difference is ascribed mainly to the effect of gravity. © 2007 American Institute of Chemical Engineers AIChE J, 2007
TL;DR: In this paper, a flame aerosol reactor (FLAR) system was used to deposit nanostructured photocatalytic films of titanium dioxide with well controlled morphologies.
Abstract: A flame aerosol reactor (FLAR) system was used to deposit nanostructured photocatalytic films of titanium dioxide with well controlled morphologies. Nanoparticles were generated in the aerosol phase and then deposited onto a water-cooled substrate via thermophoresis. Two important parameters that influenced film characteristics were the titanium precursor feed rate and substrate temperature, through their effect on particle sintering dynamics on the substrate. The size of the particles as they arrived at the substrate was controlled by varying the titanium precursor feed rate. When the size was below ∼8 nm, sintering was completed in the time available to obtain films with columnar nanostructures. Larger particle sizes resulted in granular, particulate films. The temperature of the substrate was also an important parameter as it controlled the sintering rate and the resultant crystal phase of the film. The thickness of the films was controlled by varying the precursor feed rate and deposition time. The performance of the as-synthesized photocatalytic films was established by measuring the resultant photocurrents. Well sintered columnar morphologies and thicker films (in the range of 40–900 nm) resulted in the largest photocurrents. © 2007 American Institute of Chemical Engineers AIChE J, 2007