摘要:

AbstractIgnition, extinction and autothermal behavior of surface and homogeneous oxidation reactions of CH4, NH3, and mixed NH3/CH4fuel systems in air over resistively heated Pt foils was studied in an atmospheric pressure flow reactor. Also examined were the effects of varying fuel concentration on the ignition, extinction, and autothermal surface temperatures. Heterogeneous ignition occurred at ∼200°C for NH3and at ∼600°C for CH4. The mixed fuel systems exhibited two surface ignitions (∼200°C and ∼600°C), implying a sequential ignition of the two fuels. The effects of removing one of the fuels during autothermal operation gave results consistent with this hypothesis.In homogeneous ignition, two types of flames were observed: a boundary layer flame associated with NH3systems and an independent flame observed in all systems. Homogeneous ignition of the two fuels and the mixtures occurred at surface temperatures ranging from 1,100°C to 1,600°C and appeared to be dominated by CH4in the mixed systems. A generic behavior is proposed for homogenous‐heterogeneous combustion of single

ISSN:0001-1541    

DOI:10.1002/aic.690370502

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractCondensation‐evaporation hysteresis associated with the internal wetting of catalyst particles is examined here by the Kelvin and Cohan equations. It is shown that in the absence of information on the thermal history, it is difficult to predict the extent of internal wetting and the associated reaction rate, for states with partial internal wetting, with the actual rate lying anywhere between the limits specified by the Kelvin and Cohan equations. Hysteresis effects arising from thermal cycling are discussed, and the predictions are shown to agree with the experimental data of Kim and Kim (1981a). Experimentally observed transitions between states with markedly different extents of internal wetting and with associated sudden evaporation or condensation are also rationalized by the theor

ISSN:0001-1541    

DOI:10.1002/aic.690370503

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractGorring (1973) reported a phenomenon, the “window effect,” whereby the diffusivities of normal paraffins within zeolite T do not decrease monotonically with increasing carbon number N, as would be expected intuitively. Rather, following an initial decrease with N, the diffusivities exhibit a local minimum at C8 followed by a pronounced local maximum at C12. This article presents a theoretical analysis of the window effect and related phenomena, based on an analogy of the configurational diffusion process with an “equivalent” one‐dimensional Brownian motion of a rod through a periodic sequence of potential barriers. Numerical calculations are found to be in reasonable agreement with Gorring's experimental data and quantify his qualitatively‐stated mechanism, namely that n‐alkanes longer than C8 are too large to fit entirely within the potential wells formed by erionite cages and therefore experience smaller energetic barriers

ISSN:0001-1541    

DOI:10.1002/aic.690370504

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractAdsorption of a strongly bound absorbate in a bidisperse‐pore system is modeled using a Turner pore structure. This idealized system leads to an analytical solution for the micropore uptake of adsorption that is valid for a part of the adsorption‐time profile. The analytical solution yields a well‐defined criterion that establishes the boundary between an adsorption process dominated by macropore resistance and one dominated by micropore resistance. The range of the analytical solution is extended to include the entire adsorption‐time profile using an approximate analytical solution and two asymptotic so

ISSN:0001-1541    

DOI:10.1002/aic.690370505

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractHigh‐surface‐area, Zr‐pillared, layered clays are synthesized and characterized for their adsorption properties. Although large free interlayer spacings are claimed in the literature (as also found in this work, 14.3 Å), the limiting pore size is the narrow interpillar spacing. The distribution of interpillar spacing is determined by molecular probing and adsorption data along with a theoretical framework available from the literature. Interpillar spacing can be tailored by controlling the number density of pillars inserted during the ion exchange (oligomer inserting) step. The following variables in the ion exchange solution result in lowering the pillar density: higher pH, lower oligomer concentration, and introduction of competitive cations. By changing these variables, peak interpillar spacing is shifted by nearly 2 Å (from 5 to 7 Å). The versatility of pillared clays as sorbents for kinetic separation (i.e., separation based on diffusivity differences) has been demonstrated by the separations of air and xylene

ISSN:0001-1541    

DOI:10.1002/aic.690370506

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractThe familiar batch concept of extent of reaction is reexamined for systems of reactions occurring in open systems. Because species concentrations change as a result of transport processes as well as reactions in open systems, the extent of reaction has been less useful in practice in these applications. It is shown that by defining the extent of the equivalent batch reaction and a second contribution to the extent of reaction due to the transport processes, it is possible to treat the description of the dynamics of flow through porous media accompanied by many chemical reactions in a uniform, concise manner. This approach tends to isolate the reaction terms among themselves and away from the model partial differential equations, thereby enabling treatment of large problems involving both equilibrium and kinetically controlled reactions. Implications on the number of coupled partial differential equations necessary to be solved and on numerical algorithms for solving such problems are discussed. Examples provided illustrate the theory applied to solute transport in groundwater flow.

ISSN:0001-1541    

DOI:10.1002/aic.690370507

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractConcentration profiles were determined in both phases for the system methyl isobutyl ketone (MIBK)—water‐acetic acid in a Kühni 72.45‐mm‐dia. Extraction column of 25 stages. Mass transfer and backmixing parameters were estimated numerically from the profiles in terms of the backflow model. The results indicated that backmixing of the continuous phase was appreciable, while that of the dispersed phase was negligible. Independent values of the continuous‐phase backmixing coefficient, αc, were also determined by both unsteady‐state and continuous tracer injection, in the former case both with and without mass transfer. The results indicated that αcis increased by mass transfer, and that the tracer values, both with and without mass transfer, are greater than those obtained from th

ISSN:0001-1541    

DOI:10.1002/aic.690370508

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractA major difficulty in control of distillation columns stems from their nonlinear behavior, especially of columns producing high‐purity products. Based on a previous development that adapted fixed‐bed theories to simple countercurrent processes, this study has established a nonlinear wave theory for the nonlinear and distributed dynamics of binary distillation columns by including the effects of reflux, reboil, and combination of sections. This theory clearly elucidates the intriguing dynamic behavior of distillation columns such as high steady‐state gains, large response lags, strong dependence of dynamics on the magnitudes and directions of disturbances, and asymmetric dynamics of the transitions between two steady states. It also underlines the inadequacy of conventional linearized models for high‐purity columns. With fairly simple mathematics, this nonlinear wave approach may be useful for model development, control system design, dual‐composition control, and feedforwar

ISSN:0001-1541    

DOI:10.1002/aic.690370509

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractA model of the process of polymer devolatilization in a heated slit is presented. Momentum, heat, and mass transfer in the slit are taken into consideration, and only one adjustable parameter is used. The model predicts pressure and temperature profiles, and residual volatile contents at the exit which are in good agreement with those measured in a single instrumented slit.

ISSN:0001-1541    

DOI:10.1002/aic.690370510

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractA mathematical model of the hydrocyclone, based on the physics of fluid flow, has been developed. The model equations are solved in a computer code that takes as input the hydrocyclone dimensions and feed slurry characteristics. The output of the computer code is the velocity profiles of the fluid and the separation efficiency curve. To validate the model, an LDV was used to measure the velocity profiles inside a 75‐mm hydrocyclone. Pure water and glycerol‐water mixture were used as the working media to simulate the increase of slurry viscosity in the presence of solid particles. The predicted velocity profiles agree well with the experimental measurements. Dilute limestone slurry was also classified with the same hydrocyclone, and predicted the separation efficiency curve shows good agreement with experimental observat

ISSN:0001-1541    

DOI:10.1002/aic.690370511

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY