摘要:

AbstractA simple design technique for heterogeneous distillation columns has been developed. The underlying geometric conditions which govern minimum reflux are shown to share certain common features with homogeneous distillations, but differ in some important respects. It is shown that heterogeneous columns display some unusual sensitivities to the design parameters. The most notable being the drastic swings in the composition and temperature profiles with very small changes in the level of trace impurities in the product stream.

ISSN:0001-1541    

DOI:10.1002/aic.690351002

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractVarious strategies for sequencing heterogeneous azeotropic distillations have been explored. The design and optimization of these systems by simulation‐based methods is generally acknowledged to be a very difficult problem (Kingsley and Lucia, 1988). In this article, a simple and accurate design and optimization procedure has been developed. The method does not involve any recycle convergence loops and has been applied successfully to several test problems. Unlike the simulation‐based methods, our method is robust to changes in the system optimization variables (e.g., reflux ratio in the azeotropic column).In order to demonstrate the method, we present design and optimization results for the dehydration of ethanol using a benzene entrainer. Our optimal designs consume significantly less energy than state‐of‐the‐art designs reported in the l

ISSN:0001-1541    

DOI:10.1002/aic.690351003

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractA systematic method for synthesizing feedforward/state feedback controllers for a broad class of SISO nonlinear systems with measurable disturbances is presented. Depending on the structural characteristics of the system, the control law can be static or dynamic. The closed‐loop system is independent of the measurable disturbances and linear with respect to set point changes. The performance of the proposed control scheme is illustrated through an example of composition control in a system of three CSTR's in serie

ISSN:0001-1541    

DOI:10.1002/aic.690351004

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractUltrapyrolysis or ultrarapid pyrolysis is a hydrocarbon thermal cracking process which offers the promise of greater product selectivity, higher yield and feedstock flexibility. In this paper, ultrapyrolysis of propane in a spouted bed with a draft tube was used as a test system to demonstrate these advantages. Experiments, carried out on a 20‐cm‐diameter pilot‐scale reactor, illustrate the spouted bed to be capable of achieving the extremely high reactant heating rates of up to 105K/s and the short gas residence times of less than 500 ms necessary for this process. Moreover, reactant conversion and product yields can be enhanced by controlling the operating temperature of the bed. In addition, application of the propane pryolysis reaction scheme of Sundaram and Froment into a recently developed computer model indicates the ability to correctly simulate the spouted bed as an ultrapyrolysis re

ISSN:0001-1541    

DOI:10.1002/aic.690351005

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe final properties and end use of many organic solids often depends on their crystal‐size distribution (CSD), e.g., bioavailability for pharmaceutical solids. The objective of this study was to develop an alternate technology for crystallizing and manipulating size distribution of organic solids by crystallization from supercritical fluids. Such a technology might be superior to conventional‐size manipulation techniques, such as milling and recrystallization from organic solvents, which might contaminate the products and affect their physical‐chemical stability. Supercritical carbon dioxide was used as solvent to dissolve and then crystallize benzoic acid. A batch crystallizer was constructed and operated in the supercritical region. Seeded and unseeded crystallization experiments were performed. Different depressurization vs. time profiles for the supercritical fluid were used to produce crystals of various

ISSN:0001-1541    

DOI:10.1002/aic.690351006

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractCalculations of the ionization constant of H2O are presented for densities ranging from those of subcritical water to those of supercritical steam. A recently‐proposed semicontinuum model is used to calculate the standard‐state hydration properties for the ions, H3O+, and OH−(Tanger and Pitzer, 1989). Calculated ionization constants are in good agreement with reported measurements at pressures from vapor‐liquid saturation to 500 MPa and temperatures from 273 to 1,073 K. These measurements cover H2O densities ranging from ∼ 1,000 to 450 kg · m−3. At H2O densities less than 400 kg · m−3, our calculated ionization constants should be more reliable than those obtained from the commonly‐used equation of Marshall

ISSN:0001-1541    

DOI:10.1002/aic.690351007

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractSteel bars in reinforced concrete are protected from corrosion by the high pH environment of the surrounding concrete. This alkaline environment is destroyed by the reaction of atmospheric CO2with the Ca(OH)2of the concrete mass. When this process, called carbonation of concrete, reaches the reinforcing bars, corrosion of the latter may commence. In this paper, the physiochemical processes in this phenomenon are presented and modeled mathematically. The mathematical model is fairly complex, but certain simplifying assumptions are possible, which lead to the formation of a “carbonation front” and to a simple analytical expression for the evolution in time of this front, in terms of the composition parameters of cement and concrete and of the environmental conditions. This simple expression is in very good agreement with experimental results obtained in this and in previous studies. The effect of some parameters on the carbonation front propagation is also discus

ISSN:0001-1541    

DOI:10.1002/aic.690351008

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThis paper focuses on the problem of scale‐up of two‐phase (e.g., solid‐fluid) reactors. It outlines a class of such reactors which, for first‐order reactions, scale in the familiar single‐phase manner via an analog of the usual residence time distribution formula. The differences lie in the fact that the appropriate tracer experiment entering the formalism for this reactor class refers to a nonadsorbing tracer, and the analog of the plug flow solution is the solution for a fixed bed with fluid‐phase plug flow. Surprisingly, unlike single‐phase systems, there exist two‐phase reactors, outside of the class defined, that do not scale in this manner, even when, say, the true catalyst surface chemistry is purely first‐order. The paper discusses a few examples and implications for the design of two‐phase reactors, inclu

ISSN:0001-1541    

DOI:10.1002/aic.690351009

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractExperimental results are reported for equilibrium adsorption and diffusivities of CH4, C2H6and CO2in type A zeolite containing mixed Na and K cations ranging from 0 to 100% in composition, at two temperatures and 1 atm. Two simple theoretical solutions are given for the diffusivity. One is for diffusion with pore (aperture) blocking using the effective medium approximation, which is readily available from the literature on percolation theory. The other is a kinetic solution derived in this work for cavities containing heterogeneous sites, which is a case where the percolation theory is not applicable. The equilibrium adsorption results show that K+has a preference for the aperture (or pore‐blocking) sites (site type II), and these results are interpreted by the bond percolation theory. The diffusivity results are successfully interpreted by the poreblocking theory in zeolites containing less than 25% K+and by the kinetic theory for zeolites with higher K+content

ISSN:0001-1541    

DOI:10.1002/aic.690351010

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractA study was made of the effect of design and operating parameters on the regeneration of a fixed bed of activated carbon. Two adsorbed species were removed by a hot gas purge, making the study relevant to thermal swing cycles used commercially. The analysis utilized direct experimental results as well as simulated results using a model described earlier by the authors (Huang and Fair, 1988).Regeneration parameters studied were: type of purge gas, purge gas contact time and velocity, regeneration temperature, initial bed loading, and bed pressure. These were related to certain parameters influencing the adsorption step: type of carrier gas, feed concentration, contact time and velocity, pressure, and initial bed temperature. The results are summarized in the form of guidelines for optimal regeneration cycle specification.

ISSN:0001-1541    

DOI:10.1002/aic.690351011

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY