摘要:

AbstractA gradientless reactor was used to study the xylene isomerization reaction over a series of cation‐exchanged (H+, Li+, Na+, and K+) ultrastable faujasite and on ZSM5 and silicalite to observe the effects of site modification on the reaction. Adsorption, diffusion, and kinetic parameters were determined in the presence of the reaction; the results generally agreed with the available literature data. The gradientless reactor and associated modeling techniques are shown to be effective tools in investigating catalyst behavior. Precise analytical techniques are required to directly measure the diffusion coefficient in the presence of reactio

ISSN:0001-1541    

DOI:10.1002/aic.690330802

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractThis paper addresses the question of the relative amounts of liquid removed during filtration and expression as a function of cake compressibility. As liq uid flows through a porous cake, the accumulative drag collapses the particulate structure, thereby increasing the solid content and displacing the liquid. The use of pump pressure in filtration represents the simplest hydraulic deliquoring process. In expression operations, pistons, membranes, rollers or belts are employed to squeeze the particulate cake after filtration is complete.Filtration followed by expression at constant pressures ranging from 0.6 to 24.7 MPa (6.1‐243.6 atm) was investigated theoretically and experimentally. During filtration and the early stages of expression, the flow rate and average liquid content of highly compressible attapulgite were virtually unaffected by increasing pressure in the range investigate

ISSN:0001-1541    

DOI:10.1002/aic.690330803

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractMany chemical engineering problems require the optimization of systems of differential and algebraic equations. Here a method is presented based on finite‐element collocation, which converts differential equations to algebraic residual equations with unknown coefficients. A nonlinear program is then formulated, with residuals incorporated as equality constraints and coefficients as decision variables. Also, adaptive knot placement is used to minimize the approximation error, with necessary and sufficient conditions for optimal knot placement incorporated as additional equality constraints in the nonlinear program. All equality constraints are then solved simultaneously with the optimization problem, thus requiring only a single solution of the approximated model. Finally, problems with discontinuous control profiles can be treated by introducing an extra level of elements (superelements) as decisions in the optimization problem. This approach is demonstrated on a simple optimal control problem as well as a reactor optimization problem with steep temperature profiles and state variable constraint

ISSN:0001-1541    

DOI:10.1002/aic.690330804

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractA theory for flow through permeable media with equilibrium precipitation/dissolution interactions is rigorously established. The general solution in terms of waves, which represent the propagation of concentration changes is developed, and the detailed structure of a precipitation/dissolution wave in the presence of dissipation (diffusion and dispersion) is derived; this structure plays a vital role in the general solution. The solution is based on Riemann invariants and thus exhibits certain similarities to wave solutions of related problems in gas dynamics and chromatography. However, a discontinuity peculiar to the precipitation/dissolution problem prevents unification of these similar solutions into a single, more general theory.

ISSN:0001-1541    

DOI:10.1002/aic.690330805

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractA multiloop control system and an on‐line reactor operability analysis were developed for the purpose of detecting and averting extinction of the autothermal state of a laboratory catalytic reactor. The reactor system consisted of a feed‐effluent heat exchanger and two packed beds in which the exothermic reaction between hydrogen and oxygen occurred.The strategy of control was based on the preservation of the relative stability of the autothermal steady state when the reactor experienced large changes in feed concentration and flow rate. Such a strategy involved a model‐based prediction of reactor conditions that so preserved stability, and a procedure to guide the process rapidly and smoothly to those new conditions. Experiments demonstrated the successful avoidance of extinction and the orderly attainment of new operating conditions in about three reactor‐system time constants. The procedures developed could serve as a component of an on‐line expert system for safe reactor o

ISSN:0001-1541    

DOI:10.1002/aic.690330806

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractExperimental measurements for an industrial azeotropic distillation tower that dehydrates secondary butyl alcohol (SBA) show erratic operation that only approaches a steady state. These are explained with steady‐state simulations which show that slight variations in the aqueous reflux rate cause many trays to shift from homogeneous to heterogeneous operation, accompanied by significant changes in the SBA purity, with water or entrainer contaminating the bottoms product. When other methods failed, an arc‐length homotopy‐continuation method made small adjustments in the reflux ratios to obtain close agreement with the measure

ISSN:0001-1541    

DOI:10.1002/aic.690330807

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractSince very high purity is sometimes required for health‐related (and other) products, it is useful to reexamine the common thermodynamic relations that describe the chemical potential of a solute at very high dilution. Because Stirling's approximation is not valid for small numbers, the usual thermodynamic relations must be reformulated for small systems, i.e., for a solute in a small bubble or drop. A simplistic analysis indicates that in a small bubble or drop, the chemical potential of a solute goes to a finite value as the mole fraction of solute goes to zero, in contrast to the conventional result, where that chemical potential goes to negative infinity. This simplistic analysis has profound implications for separation science; it implies that (in theory) ultrapurity may be attained by conventional diffusional methods. While serious objections can be raised to invalidate the simplistic analysis, it may nevertheless be useful for chemical engineers to consider separation methods using highly dispersed system

ISSN:0001-1541    

DOI:10.1002/aic.690330808

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractDry, electrostatic separation is a potentially efficient method of removing pyrites from coal. However, progress in the past was hampered by a lack of a quantitative analysis of the process. To help us design better separation equipment, we have developed a hydrodynamic model of separation of pyrites from coal in a batch electrofluidized bed. The simulations were done on a Cray‐2 computer. The input variables include the surface charge of the particles and the solids stress, which were measured.Realistic shapes and sizes of bubbles were computed with and without an applied electric field for a two‐dimensional bed with a central jet. The bubble sizes and the rising velocities were smaller with an applied field, consistent with observations. Computed electrophoretic mobilities in the fluidized bed will be useful for a better design of continuous b

ISSN:0001-1541    

DOI:10.1002/aic.690330809

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractA new unit operation is presented that utilizes a rapid feed pressure swing cycle in a bed packed with catalyst and adsorbent to effect both reaction and separation. This hybrid device combines features of a cyclic‐steady‐state pressure swing adsorber with those of a flow‐forced catalytic reactor. Feed sequences for the periodic separating reactor (PSR) are those of rapid, single‐bed pressure swing adsorbers (PSA). Only the case of extremely fast reactions is considered here. A perturbed reaction‐sorption equilibrium model is formulated and solved for isothermal operation for different equilibrium constants and reaction stoichiometries. The capacity and separation performance for an equilibrium‐limited PSR (EPSR) can be of the same order of magnitude as PSA alone. For reactions involving a single reactant or single product, the principal component in a particular exit stream depends upon both the reaction stoichiometry and feed fraction of the process cycle. The pressure dependency of the reaction equilibrium expression is the cause of separation reversals as parameters

ISSN:0001-1541    

DOI:10.1002/aic.690330810

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractThis paper is focused on the analysis of interaction of free convection and exothermic chemical reaction. As a consequence of the chemical reaction, free convection effects can result. It is difficult to perform an analytical bifurcation analysis of the full nonlinear governing equations; however, Fourier expansion combined with a Galerkin approximation results in a small set of ordinary nonlinear differential equations (initial‐value problem) that are amenable to analysis. Conditions for branching of the solution can be determined in an analytical way. A continuation algorithm makes it possible to calculate the branches of stability. The results of the approximative analysis are supported by the numerical integration of the full governing nonlinear equation

ISSN:0001-1541    

DOI:10.1002/aic.690330811

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY