摘要:

AbstractAqueous polymer‐polymer two‐phase systems provide a powerful method for separating biomolecules by extraction. When a complex mixture of biomolecules (e.g., a fermentation broth or a solution of lysed cells) is added to such a system, biomolecules partition uniquely between the two phases, achieving separation.A thermodynamic framework is presented for optimizing extraction performance in biological separations. First, a molecular‐thermodynamic model, based on the osmotic virial equation, is proposed to describe phase equilibria for dilute aqueous mixtures containing polymers and protein. Second, experimental phase‐equilibrium data (protein partition coefficients) are reported for a number of model proteins including albumin, lysozyme, and α‐chymotrypsin. To interpret and correlate the experimental data, Low‐Angle Laser‐Light Scattering (LALLS) measurements were made to determine osmotic second virial coefficients for aqueous mixtures containing polymers, proteins, salts (KCl, KH2PO4and K2SO4at concentrations of 50 and 100 mM) and several combinations of polymer‐polymer and polymer‐protein pairs. Combined with electrochemical measurements (differences in potential between the two phases and protein net charge), these data provide parameters for the model to calculate the desired phase equilibria. A comparison of calculated and experimental results indicates that the virial‐equation model provides good prediction of binodals and a reliable basis for estimating infinite‐dilution protein partition coefficients for biote

ISSN:0001-1541    

DOI:10.1002/aic.690341002

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractTo obtain good representation in the liquid‐liquid critical region, a semitheoretical correction is added to a conventional expression (e.g., van Laar or NRTL) for the excess Gibbs energy of a binary or ternary system along the coexistence curve. This correction is an exponential function of a suitable distance from the critical point; it is significant in the critical region but not elsewhere. In the correction function, the preexponential factor is determined from stability considerations. In the exponential argument, two parameters are determined from theoretical power laws. While the coordinates of the critical point must be known (or estimated), no phase‐equilibrium data in the critical region are required to determine parameters. The correction presented here provides an excellent approximation for phase equilibria along the coexistence curve close to and remote from critical conditions. Further, the correction facilitates simultaneous representation of isothermal vapor‐liquid and liquid‐liquid equilibria including the liquid‐liquid critic

ISSN:0001-1541    

DOI:10.1002/aic.690341003

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe infiltration of an aqueous solution into a permeable medium generally results in the dissolution of some of the minerals initially present and the possible precipitation of others. When the infiltration velocities are small, as is the case for many natural processes, conditions of local equilibrium apply and the dissolution and precipitation processes exhibit a wave‐type behavior reminiscent of chromatogrphic fronts. Zones of constant composition (state) will be separated by narrow regions within which the aqueous and solid phase concentrations exhibit sharp changes. Because of this wave‐like structure, an algebraic solution of the coupled material balance equations exists, but in a form that involves a trial and error solution procedure which has heretofore discouraged its application. This paper describes the essence of a scheme which uses a combination of graph theory and heuristics to minimize trials and thereby render the algebraic solution practical. The scheme offers an alternative to time‐sequencing solutions (e.g., finite difference) of the set of partial differential equa

ISSN:0001-1541    

DOI:10.1002/aic.690341004

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe multicomponent equilibrium theory for ion‐exchange columns (chromatography) has been extended to systems accompanied by reactions in either or both phases. Based on the concept of coherence of concentration waves in the original theory, the proposed approach includes a systematic way to determine the thermodynamic variance and a general mathematical formulation to construct the composition path grid by means of numerical techniques. With proper adjustments, this approach can be applied as well to adsorption columns involving reactions. As a practical example, a comparison of predicted and observed effluent histories for an anion‐exchange system with dissociation‐association reactions is

ISSN:0001-1541    

DOI:10.1002/aic.690341005

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractA numerical computation is carried out to study the interaction of rotation and natural convection inside a finite horizontal cylinder. The natural convection is due to differential heating on the two ends, while the rotation is along the axis of the horizontal cylinder. The aspect ratio, length of the cylinder to its radius, is 2.0. The Grashof number is fixed at 1.43 × 106with air as a working fluid. The effect of rotation is examined withGr/Re2from 7.0 × 10−2to ∞, which covers the range from rotation dominated flow to buoyancy dominated flow. It is found that when rotational speed is relatively small orGr/Re2» 1, the effect of rotation is to render the spatial heat flux distribution more uniform. As the rotational speed increases, the heat transfer rate distribution on the end surfaces is more homogenous and its level is also reduced. When the rotational speed is sufficiently high (Gr/Re2« 1.0), heat transfer is by conduction only and the whole fluid inside the enclosure rotates as a rigid body. It is shown that there exists a rotation speed range in which one can have both relatively high and uniform heat transfer rates on the en

ISSN:0001-1541    

DOI:10.1002/aic.690341006

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractRigorous analytical methods for consistent modeling of control structures for multivariable processes are presented. The continuous distillation process is used to illustrate the methods, but the basic ideas, and more specifically the transformations and consistency relations derived, are valid in general.If steady‐state operating data and the process gains of an arbitrary control structure are known, it is possible to calculate the process gains of any feasible control structure. A general expression relating the process gaisn of different control structures is derived. In general, the process gains must also satisfy certain consistency relationships which can be derived from first principles, e.g., steady‐state material balances.The usefulness of the results is illustrated by control structure transformations and reconciliation of process gains, by an application to process dynamics, by synthesis of noninteracting control loops, and by derivation of analytical relationships useful in relative gain analy

ISSN:0001-1541    

DOI:10.1002/aic.690341007

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractForced‐convection mass transfer at the metal/bath interface during aluminum reduction from cryolitic melts was studied under reproducible convective conditions. A film of molten aluminum on a rotating molybdenum cylinder was the cathode. Concentration overpotential measured as a function of rotation rate, current density, and bath composition was converted to concentration differences between the bulk and the metal surface. Chosen as the basis for calculation of a mass transfer coefficient was the concentration of aluminum fluoride given by:\documentclass{article}\pagestyle{empty}\begin{document}$$ C_{{\rm AlF}_{\rm 3} } = \frac{{2\rho (100 - Al_2 {\rm O}_3 \%- {\rm CaF}_2 \%- IMP\%)}}{{100M_{{\rm AlF}_3} (CR + 2)}} $$\end{document}where the amounts of indicated compounds are in weight percent,IMPdesignates impurities,Mis molecular weight, ρ is the density of the melt, andCRis the cryolite ratio, the ratio of moles NaF to moles AlF3. Agreement with a correlation for mass transfer to a rotating cylinder allowed the calculation of effective diffusivities for aluminum fluoride species, in alumina‐saturated melts, of: 11.1 ± 1.1 × 10−5cm2/s at 1.8CR; 11.4 ± 1.7 × 10−5cm2/s at 2.3CR; 5.4 ± 0.8 × 10−5cm2/s at 3.0CR; and 4.4 ± 0.9 ×

ISSN:0001-1541    

DOI:10.1002/aic.690341008

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractPyrolysis and regeneration kinetics of 11 spent activated carbons were studied using a thermal balance and a fludized bed reactor. The adsorbates were aromatic compounds with different types and number of side groups, and most of the side groups were lost on pyrolysis, leaving a residue about equal to the weight of the aromatic portion of the adsorbate. The residues from alkyl phenols reacted with oxygen at 770‐920 K at rates up to 12 times the rate for the base carbon. There was a similar increase in oxygen chemisorption indicating increased number of active sites. The adsorption capacity of the carbons was mostly recovered by pyrolysis, even though the surface area and pore volume were reduced by the residue. Some oxidative regeneration is probably necessary to restore adsorption capacity for repeated us

ISSN:0001-1541    

DOI:10.1002/aic.690341009

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractA sudden reduction in the feed temperature of a packed‐bed reactor may lead to a transient temperature rise, referred to as a wrong‐way behavior. As expected, the axial dispersion of heat decreases the magnitude of the temperature excursion and prolongs the transient shift to a new steady state. In addition, the thermal dispersion may enable the wrong‐way behavior to ignite a low‐temperature steady state leading to a disastrous runaway of the reactor. Moreover, it may create a transient high‐temperature wave, which moves initially in the upstream direction. The axial dispersion of heat can lead to some behavioral features which are qualitatively different from those of a model which ignores it. The transient temperature excursion does not exceed a value, which can be estimated by a simple analytical e

ISSN:0001-1541    

DOI:10.1002/aic.690341010

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe planar‐flow melt‐spinning process which is used to rapidly solidify metals from the molten state is shown to be dominated by the fluid mechanics of the “puddle” region even though heat‐transfer limits the overall thickness of the metal ribbon product. The process is modeled to account for the hydrodynamical forces in the molten region with the influence of heat‐transfer entering through a parameter measuring solidification rate relative to wheel speed. It is shown that this parameterHcontrols the deviation of the flow behavior from classical coating flow solutions; these solutions are recovered in a limiting case of low solidification rate. A perturbation solution inHdistinguishes the melt spinning from the coating process and yields the ribbon thickness as a function of wheel‐speed and the other process parameters for a class of contact‐line conditions. Most interesting of these predictions is the result that under certain conditions there is a window of wheel‐speeds for which there is no steady solution. The relationship of predictions with the limited available data from experiment is

ISSN:0001-1541    

DOI:10.1002/aic.690341011

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY