ISSN:0001-1541    

DOI:10.1002/aic.690370602

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

ISSN:0001-1541    

DOI:10.1002/aic.690370603

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractThe electrical double‐layer free energy is computed numerically for a model colloidal suspension of charged, hexagonally‐packed monodisperse cylinders in a symmetric electrolyte solution using the Poisson‐Boltzmann equations. Comparison is made to the energies estimated from sums of pair interactions and from two versions of a radially‐symmetric cell model: one in which the outer boundary of the cylindrical cell is chosen to make the particle volume fraction Φ in the approximate model agree with that of the full lattice and the other in which the position of the outer boundary is chosen as half the nearest neighbor separation in the lattice. Calculations are performed for ranges of particle volume fractions from infinite dilution to 98% of closest packing, ionic strengths (in terms of the ratio of Debye length to particle radius λ/a) from 0.1 to 10.0, and dimensionless surface potentials and charge densities from 0.1 to 10.0.The pair approximation is valid only when typical interparticle spacings are greater than the Debye length. The first implementation of the cell model proves quite accurate, while the second is only qualitatively correct. The magnitude of particle surface charge density or potential has little effect on these co

ISSN:0001-1541    

DOI:10.1002/aic.690370604

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractA major difficulty affecting the control of product quality in industrial polymerization reactors is the lack of suitable on‐line polymer property measurements. In this article a scheme is developed to predict melt index and density in a fluidized‐bed ethylene copolymerization reactor. Theoretically‐based models are derived to predict quality variables from the available on‐line temperature and gas composition measurements. Adjustable parameters in these models are updated on‐line using infrequent laboratory measurements and a recursive parameter estimation technique. The application of this methodology is illustrated using operating data from an industrial reactor. It is shown that both melt index and density can be successfully predicted. Knowledge of product property deviations from desired targets is required so that manufacturers can take corrective actions to reduce the quantity of off‐grade material made and produce a consist

ISSN:0001-1541    

DOI:10.1002/aic.690370605

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractEquilibrium adsorption data for the N‐benzoyl derivatives of D‐ and L‐phenyl alanine in water/propanol solutions have been determined on a chiral‐selective stationary phase, bovine serum albumin immobilized on silica. These data are well accounted for by an isotherm equation resulting from the sum of two Langmuir terms. The first term corresponds to the chiral‐selective interactions, and the second to the nonselective molecular interactions between the enantiomers and the stationary phase. The individual band profiles of the two enantiomeric amino acids, either pure or in binary mixtures of various compositions, are predicted exactly by an equilibrium dispersive model using this bi‐Langmuir isotherm. A classical Langmuir isotherm fails to predict these band profiles, illustrating the importance to collect accurate adsorption data and to use a correct isotherm model when calculating chromatographic ba

ISSN:0001-1541    

DOI:10.1002/aic.690370606

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractThe catalytic activity, product selectivity, and coke deposition were studied during methylcyclopentane (MCP) reforming on bifunctional Pt/Al2O3Cl reforming catalysts with different metal loadings, but constant metal dispersion as well as constant Cl loading. Surprisingly, the overall conversion of MCP was found to decrease as the metal content of the catalyst increased. Analysis of the coke by temperature programmed oxidation (TPO) revealed two distinct peaks, one associated with coke on the metallic function and the other associated with coke on the acidic function. The change of activity of the metal and acid functions with time was monitored by following the rates of hydrogenolysis and hydrocracking, respectively. A mechanistically‐based dual‐site model for the kinetics of coke formation and the resulting deactivation was developed. The model successfully correlates the experimental data and is an improvement over existing models, since it explicitly accounts for the deactivation of both the metal and the acid func

ISSN:0001-1541    

DOI:10.1002/aic.690370607

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractExtractions using hollow fibers can be faster and more efficient than those in conventional equipment. These advantages, due to the large area per volume possible with fibers, can be compromised by accidental convection through the fibers' pores. When these pores are filled with gels of crosslinked polyvinyl alcohol, convection through the pores is stopped but the overall mass transfer is unaltered. The separations across these gel‐filled fiber walls provide excellent yield and purity, especially in the case of fractional extractio

ISSN:0001-1541    

DOI:10.1002/aic.690370608

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractTransport properties of various uncross‐linked and cross‐linked non‐Newtonian slurries in horizontal pipes are studied. Flow data are gathered in three long, different diameter, transparent horizontal pipes. Investigated are the effects of the pipe size, polymer concentration, fluid rheological properties, cross‐linking effects, particle size and density, solids concentration, fluid density, and slurry rate on the critical deposition velocities and particle resuspension velocities. It is found that critical deposition and resuspension velocities for the non‐Newtonian carrier fluids tested are significantly lower than those for water. Both velocities depend greatly on pipe size and particle density. Higher critical velocities are required to minimize settling (1) in larger pipe sizes and (2) for pumping solids denser than sand. For less viscous fluids, critical deposition and resuspension velocities increase slightly with increasing solids concentration. They are, however, independent of solids concentration for more visco

ISSN:0001-1541    

DOI:10.1002/aic.690370609

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractWaxy crude oils are highly non‐Newtonian materials known to cause handling and pipelining difficulties and whose flow properties are time‐ and history‐dependent. Experimental techniques are described that enable reproducible steady‐state flow property data to be obtained from rotational viscometers. The flow properties are shown to depend strongly on the shear rate applied during cooling (shear history effect). This leads to a definable minimum operating point below which flow in a waxy crude oil pipeline would cease. Modified pipeline design techniques are presented for both laminar and turbulent flow at temperatures below the pour point, and it is shown that existing techniques overestimate the flow rate in laminar flow by the order of 100%. The modified design techniques can be used to quantitatively assess the performance of flow improver (pour point depressant) additives under steady‐state c

ISSN:0001-1541    

DOI:10.1002/aic.690370610

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractOperational problems are of increasing importance as the process industries turn to the batch manufacture of high‐value specialty products. A method is presented to minimize stockout for multiunit plants where customer orders may constitute nonintegral batch multiples. Product‐ and unit‐dependent processing times and batch sizes, sequence‐dependent changeover times, and product‐to‐unit assignment constraints are modeled for nonidentical parallel processes. Arbitrary initial conditions are also modeled. The algorithm determines the number of production runs of each product, run length (lot sizing), the assignment of run to units, and run sequence on each unit.Scheduling with simultaneous lot sizing has not previously been addressed in the literature. The evolutionary method presented here obtains near‐optimal (and often globally optimal) solutions on industrial‐sized test problems. These results are significant since near‐optimal scheduling of many industrial process plants now becomes possible, although problems of this complexity are intractable us

ISSN:0001-1541    

DOI:10.1002/aic.690370611

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY