bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ca‐Mg acetate as dry SO2 sorbent: II. Sulfation of CaO in calcination product
Authors: Sohn Hong Yong , Han Dong Hoon 
Published: April 2004

AbstractThe sulfation rate of CaO contained in calcined calcium magnesium acetate CMA by SO2 and O2 was measured. Although calcined CMA contains CaO and MgO, only CaO reacts with SO2 above 950°C. The reaction occurs at a much greater rate than with other conventional desulfurization agents like calcined limestone, dolomite, or Ca(OH)2, the last of which yields one of the most reactive forms of CaO. The remarkable enhancement of sulfation rate of CaO in calcined CMA is due to its much larger pore size and porosity than those of other agents. Another consequence of this structure of calcined CMA is that the sulfation reaction proceeds to completion without the rate leveling off, unlike in the sulfation of most oxides.
Ca‐Mg acetate as dry SO2 sorbent: III. Sulfation of MgO+CaO
Authors: Sohn Hong Yong , Han Dong Hoon 
Published: April 2004

AbstractThe separate sulfation rate of MgO contained in calcined calcium magnesium acetate (CMA) by SO2 and O2 was measured, as well as the simultaneous sulfation of MgO and CaO in the temperature range where the sulfates of both oxides are stable. In the temperature range below 830°C in which MgO sulfation is thermodynamically possible the reaction produced CaSO4·3MgSO4, rather than MgSO4. The formation of the CaSO4·3MgSO4 phase at a reasonable rate during the sulfation of calcined CMA has a significant implication in that it allows the utilization of MgO for SO2 removal, whereas the sulfation of MgO from conventional sources is so slow that it is of no practical interest. Thus, the calcined CMA can remove SO2 at lower temperatures than conventional SO2 absorbent and at a greater capacity and rate, which presents a substantial competitive advantage of this material.
Inertial flow structures in a simple‐packed bed of spheres
Authors: Suekane Tetsuya , Yokouchi Yasuo , Hirai Shuichiro 
Published: April 2004

AbstractThe detailed characteristics of the interstitial velocity distributions in pores are critical to understanding heat and mass transfer in a Packed bed of granular material. The velocity distributions in a pore that models a simple‐packed bed were measured directly by a magnetic resonance imaging technique. With an increase in the Reynolds number from 12.17 to 59.78–204.74, the increase and decrease in main flow velocity did not correspond to the local pore geometry, as is the case with a creeping flow. This indicated that inertial forces dominate over viscous forces. For example, at the Reynolds number of 204.74, the fluid penetrated through the center of the pores like a jet with negligible change of velocity. Circulation in the surrounding stagnant spaces generated eight symmetrical eddies in the plane perpendicular to the main flow direction.
Mixing of power‐law fluids using anchors: Metzner‐Otto concept revisited
Authors: Shekhar S. Murthy , Jayanti S. 
Published: April 2004

AbstractIn 1957 Metzner and Otto proposed a simplified way of calculating the power consumption in impeller‐driven systems for power‐law type of fluids. Assuming a proportionality between the shear rate and rotational speed of the impeller, they reported that the proportionality constant was independent of the geometric and fluid properties of the mixing system. This was later contested by a number of researchers, and different correlations have been given to evaluate the proportionality constant. An in‐depth investigation of the Metzner–Otto concept is discussed with the help of computational fluid dynamics (CFD) techniques to calculate the flow field created by an anchor impeller. Fundamentally, both of the assumptions are broadly valid for typical operating parameters used in anchor‐driven impeller systems. A new correlation, based on the Metzner–Otto concept and making use of the present CFD simulations, was developed to calculate power consumption in anchor‐driven mixing systems.
Adaptive extremum seeking control of continuous stirred‐tank bioreactors
Authors: Zhang T. , Guay M. , Dochain D. 
Published: April 2004

AbstractAn adaptive extremum‐seeking control scheme for continuous stirred‐tank bioreactors is proposed which utilizes the structure information of the kinetics of bioreactors to construct a seeking algorithm that drives the system states to the desired setpoints that optimize the value of an objective function. Lyapunov's stability theorem is used in the design of the extremum‐seeking controller stucture and the development of the parameter learning laws. Numerical simulations illustrate the effectiveness of this approach.
Detecting abnormal process trends by wavelet‐domain hidden Markov models
Authors: Sun Wei , Palazoğlu Ahmet , Romagnoli Jose A. 
Published: April 2004

AbstractA novel method for detection of abnormal conditions during plant operation uses wavelet‐domain hidden Markov models (HMMs) as a powerful tool for statistical modeling of wavelet coefficients. By capturing the interdependence of wavelet coefficients of a measured process variable, a classification strategy is developed that can detect abnormal conditions and classify the process behavior on‐line. The method is extended to include multiple measured variables in detection and classification. Two case studies illustrate the potential of this method.
Hydroamination on homogeneous and heterogeneous catalysts: Kinetic study
Authors: Müller Thomas E. , Lercher Johannes A. , Van Nhu Nguyen 
Published: April 2004

AbstractThis kinetic analysis compares homogeneous and heterogeneous catalysts for the cyclization of 6‐aminohex‐1‐yne. The reaction was studied as a model for the direct addition of amine NH bonds to CC multiple bonds (hydroamination). Kinetic modeling showed that the metal‐catalyzed hydroamination reaction is followed by a proton‐catalyzed isomerization of the primary reaction product, 2‐methylene‐piperidine, to the thermodynamically more stable 2‐methyl‐1,2‐dehydropiperidine.
Dryout phenomena in a three‐phase fixed‐bed reactor
Authors: Cheng Zhen‐Min , Anter Abdulhakeim M. , Fang Xiang‐Chen , Xiao Qiong , Yuan Wei‐Kang , Bhatia Suresh K. 
Published: April 2004

AbstractUnderstanding the mechanism of liquid‐phase evaporation in a three‐phase fixed‐bed reactor is of practical importance, because the reaction heat is usually 7–10 times the vaporization heat of the liquid components. Evaporation, especially the liquid dryout, can largely influence the reactor performance and even safety. To predict the vanishing condition of the liquid phase, Raoult's law was applied as a preliminary approach, with the liquid vanishing temperature defined based on a liquid flow rate of zero. While providing correct trends, Raoult's law exhibits some limitation in explaining the temperature profile in the reactor. To comprehensively understand the whole process of liquid evaporation, a set of experiments on inlet temperature, catalyst activity, liquid flow rate, gas flow rate, and operation pressure were carried out. A liquid‐region length‐predicting equation is suggested based on these experiments and the principle of heat balance.
Nitrobenzene adsorption in activated carbon as observed by NMR
Authors: Pel L. , Valckenborg R. M. E. , Kopinga K. , Aarden F. B. , Kerkhof P. J. A. M. 
Published: April 2004

AbstractThe adsorption of nitrobenzene in activated carbon was investigated by nuclear magnetic resonance (NMR). Because of the short relaxation times and carbon is an electrically conducting material, a specially adapted NMR setup was used. It was found that during the adsorption process the nitrobenzene profiles can be scaled using the Boltzmann transformation and the overall effective diffusivity can be approximated by an exponential function of the nitrobenzene content.
Synthesis of silicalite tubular membranes by in situ crystallization
Authors: Lin Xiao , Chen Xiangshu , Kita Hidetoshi , Okamoto Kenichi 
Published: April 2004

AbstractSilicalite membrane preparation conditions related to membrane separation properties were studied focusing on in situ crystallization to prepare highly selective silicalite membranes on porous tubular supports by a single hydrothermal treatment. The membranes morphologies prepared under typical synthesis conditions were characterized by scanning electron microscopy. The silicalite membrane, well‐oriented with c axis normal to the support surface, could be prepared by in situ crystallization and a seeding method. The membrane separation properties were controlled by synthesis conditions such as seeding, temperatures, supports, and silica sources. Under certain conditions, such factors as tube pore size, played an important role. Silicalite membranes would be prepared better by in situ crystallization than by a seeding method under the same conditions. For example, the highest ethanol/water separation factor of 106 with a flux of 0.9 kg/m2·h for a feed concentration of 5 wt. % ethanol at 60°C was obtained for the silicalite membrane prepared on an unseeded mullite tube at 175°C for 16 h with colloidal silica, whereas the membranes prepared on the silicalite‐seeded tubes had separation factors up to 70. The higher separation selectivity for ethanol over water would be attributed to reduction in nonzeolitic pores, supported by gas permeations of n‐butane and i‐butane.
Multicomponent flash algorithm for mixtures containing polydisperse polymers
Authors: Behme Stefan , Sadowski Gabriele , Song Yuhua , Chen Chau‐Chyun 
Published: April 2004

AbstractAn algorithm called POLYMIX is introduced for flash calculations of multicomponent systems containing polydisperse polymers. The polydispersity of polymers is taken into account through the concept of pseudocomponents. In industrial practice, a relatively high number of pseudocomponents are often required to represent multimodal polymer molecular‐weight distributions. The algorithm formulation is independent of use of specific segment‐based polymer equations of state for computing thermodynamic properties of polymer mixtures. The algorithm further offers the advantage that the computing time for polymer flash calculations is independent of the number of pseudocomponents used to represent the polydisperse polymer. Applications to polymer mixtures containing polyethylene and polypropylene are presented.
Morphology of methane and carbon dioxide hydrates formed from water droplets
Authors: Servio Phillip , Englezos Peter 
Published: April 2004

AbstractMethane and carbon dioxide hydrate crystals were formed on nearly spherical water droplets at 274.6 K and 2,150 kPa or 1,000 kPa above the corresponding three‐phase hydrate equilibrium pressure. Each experiment was performed with two droplets 5 mm and 2.5 mm in diameter or three droplets with a diameter of 2.5 mm. At the higher pressure the water droplets quickly became jagged and exhibited many needlelike or hairlike crystals extruding from the droplet, whereas at the lower pressure the surface was smooth. In almost all experiments, a depression or collapse of the hydrate layer was observed to occur. This collapse was interpreted as evidence of a continuing hydrate formation after the droplet surface was covered by the hydrate layer. The type of hydrate‐forming gas and the size of the droplet was observed not to influence the macroscopic hydrate crystal morphology. The decomposition of the methane and carbon dioxide hydrate layers was also observed. Reformation was also experimented, and the effect of memory on the morphology of hydrate crystal growth was determined.
Mechanism for N2O formation from NO at ambient temperature
Authors: Wang Jinsheng , Jia Lufei , Anthony Edward J. 
Published: April 2004

AbstractN2O was reported to form in sample containers of flue gases containing NO and SO2. This could have significant implications for the evaluation of N2O buildup in the atmosphere. Existing models are based either on liquid‐phase reactions, which cannot account for N2O formation at low humidity, or on termolecular reactions, which are not likely to occur at low concentrations. In this work, we propose mechanisms for N2O formation based on gas‐phase reactions, which address the effect of SO2, O2, and moisture. Analytical expressions of the formation rate were derived and compared to reported rates, and rate constants were estimated for limiting cases. The current analyses suggest that N2O2 could be an important precursor for N2O formation from NO, and the mechanism may be important for N2O formation in power‐plant plumes.
Modeling heat and mass transfer in osmotic evaporation process
Authors: Romero J. , Rios G. M. , Sanchez J. , Bocquet S. , Savedra A. 
Published: April 2004

AbstractA model for the mass‐ and heat‐transfer phenomena in an osmotic evaporation process was developed based on the transfer of solvent from one aqueous solution to be concentrated to a second one separated by a macroporous hydrophobic membrane. The transfer is realized in vapor phase through the membrane porosity as a consequence of the gradient on water activity between both solutions. This technique has the major advantage to work at relatively low temperature and in nearly isothermal conditions, which is very useful to treat thermosensitive products such as fruits and vegetable juices, or other solutions from biotech industries. A series‐resistance model for mass and heat transfer was developed considering four regions, which include the membrane layers and different boundary regions at interfaces. The high values of flow measured in a previous experimental work are compared with those obtained by simulation. In addition, the relative importance of various resistances to overall process performance is established. Basic mechanisms that help optimize membrane structural characteristics, plant design and scale‐up are also discussed.
On‐line monitoring of a crystallization process
Authors: Mougin Patricia , Thomas Alistair , Wilkinson Derek , White Graeme , Roberts Kevin J. , Herrmann Norbert , Jack Robert , Tweedie Richard 
Published: April 2004

AbstractThe application of ultrasonic spectroscopy for particle‐size measurements was investigated during the batch crystallization of (L)‐glutamic acid α‐polymorph from an aqueous solution. The technique, based on measurements of the attenuation of ultrasonic waves through the suspension, was applied using a prototype ultrasonic spectrometer with a flow‐through cell. High‐precision measurements of ultrasonic attenuation in the frequency range 7–110 MHz were performed, the deconvolution of which enabled in‐process measurement of crystal size distribution and solid concentration throughout the crystallization process. In addition to evincing secondary nucleation, growth and crystal breakage on‐line in real time, the experimental results were used to obtain kinetic parameters essential for process design, including secondary nucleation rate and growth rate.
Disturbance models for offset‐free model‐predictive control
Authors: Pannocchia Gabriele , Rawlings James B. 
Published: April 2004

AbstractModel predictive control algorithms achieve offset‐free control objectives by adding integrating disturbances to the process model. The purpose of these additional disturbances is to lump the plant‐model mismatch and/or unmodeled disturbances. Its effectiveness has been proven for particular square cases only. For systems with a number of measured variables (p) greater than the number of manipulated variables (m), it is clear that any controller can track without offset at most m controlled variables. One may think that m integrating disturbances are sufficient to guarantee offset‐free control in the m controlled variables. We show this idea is incorrect and present general conditions that allow zero steady‐state offset. In particular, a number of integrating disturbances equal to the number of measured variables are shown to be sufficient to guarantee zero offset in the controlled variables. These results apply to square and nonsquare, open‐loop stable, integrating and unstable systems.
Optical and infrared imaging of growing polyolefin particles
Authors: Pater Jochem T. M. , Weickert Günter , van Swaaij Wim P. M. 
Published: April 2004

AbstractA method was developed that observes polymer particles during a polymerization reaction using optical‐ and infrared imaging. The yielding images give good insight into catalyst‐specific properties as shape replication, distribution of activity, and the activation. The advantage of this method is the possibility to link behavior of individual particles to its own specific properties. The infrared method measures surface temperatures of growing particles. Such data are useful to feed mathematical models describing the growth of single particles. The temperature–time curves showed maximum temperature to be reached after some minutes; a simple model was used to describe this effect qualitatively. The maximum particle temperature rise was 20 K, but depended strongly on reaction rate and particle size. Temperature, prepolymerization method, catalyst recipe, and catalyst activation time were varied for a fourth‐generation Ziegler‐Natta catalyst in polymerization of propylene and ethylene.
Development of fluidized‐bed catalyst for partial oxidation of n‐butane
Authors: Wen Xu , Yang Gong 
Published: April 2004

AbstractOptimization experiments were carried out for preparation of a catalyst precursor. Results show that the acid concentration and reaction temperature in precursor preparation exhibit strong effects on the catalyst behavior. For the catalysts prepared at higher concentrations of acid, the quantity of the V4+ phase (VO)2P2O7 is large, and the n‐butane conversions are all quite high. When decreasing the acid concentration in precursor preparation, the relative amount of the V5+ phase δ‐VOPO4 and the n‐butane conversion increase continuously; at the same time, the selectivity to maleic anhydride increases at the beginning, and then decreases after reaching a maximum value. The catalyst prepared at an acid concentration of 102.3% gave a maximum yield of maleic anhydride of 48.10% at an inlet n‐butane concentration of 4.0% and a space velocity of 500 h−1. The fine particle catalyst in this study offers great flexibility of operation.
Solidification in heat packs: I. Nucleation rate
Authors: Rogerson Mansel A. , Cardoso Silvana S. S. 
Published: April 2004

AbstractThe solidification of sodium acetate trihydrate in a commercial heat pack is investigated in a series of three articles. In the first work, the classic nucleation theory is used to predict the range of temperatures and pressures for which a subcooled solution of sodium acetate solidifies spontaneously. The nucleation temperature was determined experimentally and it was shown that it is insensitive to concentration, at atmospheric pressure. Using the theoretical results for high pressure and the experimental measurements at atmospheric pressure, an equation for the nucleation temperature was derived as a function of pressure. This relation takes into account heterogeneous nucleation on ever‐present impurities suspended in the solution.
Solidification in heat packs: III. Metallic trigger
Authors: Rogerson Mansel A. , Cardoso Silvana S. S. 
Published: April 2004

AbstractThe metallic trigger used in commercial heat packs initiates solidification by releasing minute crystals of solid sodium acetate trihydrate into the subcooled solution. These crystals are harbored in submicron cracks on the disk's surface and are released when the disk is flexed. Using scanning electron microscopy, such seed crystals are observed on the surface of a disk after flexing it. Classic nucleation theory is used to investigate the behavior of crystals residing in the cracks on the metallic disk's surface during heating and cooling. Sodium acetate trihydrate crystals are capable of surviving in a 1‐nm crack or smaller at regeneration temperatures of the order of 353 K. These seed crystals grow to the mouth of the crack at temperatures below the liquidus, but can only promote solidification of the whole solution surrounding the disk at temperatures below 256 K or when the disk is flexed.
Prediction of phase equilibria and excess properties for systems with sulfones
Authors: Wittig Roland , Lohmann Jürgen , Gmehling Jürgen 
Published: April 2004

AbstractThe group contribution method modified UNIFAC (Dortmund) has become very popular because of its broad applications, and reliable predictions for vapor‐liquid equilibria, solid‐liquid equilibria, liquid‐liquid equilibria, activity coefficients at infinite dilution, azeotropic data and excess enthalpies in a wide temperature range. Therefore, the existing parameter matrix for the modified UNIFAC method is continuously extended with the help of the Dortmund Data Bank and by carrying out systematic measurements. The new main group for sulfones, such as that required to describe systems with the selective solvent sulfolane, is introduced, as well as ten new pairs of group interaction parameters for modified UNIFAC.
Laminar mixing in different interdigital micromixers: I. Experimental characterization
Authors: Hessel V. , Hardt S. , Löwe H. , Schönfeld F. 
Published: April 2004

AbstractInterdigital‐type glass micromixers with alternating feed channels to periodically create liquid multilamellae, were fabricated for basic investigations of hydrodynamics for liquid mixing of two streams. Three interdigital designs developed, rectangular, triangular, and slit‐type, differed in their flow‐through mixing chamber. These designs are based on simple polygon geometries and their combinations. The flow patterns of an aqueous solution dyed with blue and uncolored water were investigated for different interdigital mixers. Since mixing in a nonfocused device, such as the rectangular mixer, was not completed, focusing techniques were applied. Geometric focusing was used to reduce lamellae width and to speed up mixing. In the special version of the triangular mixer, SuperFocus mixer, liquid mixing times are reduced to about 10 ms, as determined by iron‐rhodanide reaction imaging. In the latter case, the lamellae are compressed by a factor of 40, from a width of 160 to 4 μm. For both the triangular and slit‐type micromixer, flow patterns differed from regular multilamination ones. At high flow rates, lamellae tilted. When the flow cross‐sectional area was expanded, jet and associated eddies formed further improved mixing. Mixing investigations also helped develop imaging techniques. The rhodanide imaging complemented water blue contrasting.
Production of carbon nanotubes in a packed bed and a fluidized bed
Authors: Weizhong Qian , Fei Wei , Zhanwen Wang , Tang Liu , Hao Yu , Guohua Luo , Lan Xiang , Xiangyi Deng 
Published: April 2004

AbstractCarbon nanotubes (CNTs) prepared from ethylene decomposition over the Fe/Al2O3 catalyst are studied in a packed bed (PB) reactor and a nanoagglomerate fluidized bed reactor (NABR), respectively. CNTs sampled at different reaction times are characterized by TEM, Raman spectroscopy, and particle size analysis. The bulk density and agglomerate size of CNTs increase significantly with reaction time in a PB, while it remains at a stable level in NABR. Also, CNTs with good morphology, narrow diameter distribution, and fewer lattice defects are obtained in an NABR, rather than in a PB. In contrast to the unavoidable jamming due to volume increase of CNTs observed in a PB, a continuous CNT growth process is attained in an NABR, even though the amount of CNTs in an NABR is 6–7 times that in a PB. The flow dynamics, available space for growing, and mass and heat transfer can be controlled in an NABR, which favors the large‐scale production of CNTs with uniform properties.