摘要:

Langmuir-Hinshelwood (or Hougen-Watson) type rate expressions are most often used in modeling reaction rate data. In cases when there are tens of possible rival models, effective discrimination between them requires that most of the inadequate models be discarded as early as possible in the discrimination process.

ISSN:0098-6445    

DOI:10.1080/00986449608936653

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

An unusual mode of operation of internal-loop airlift reactors is described as being of potential use in extending the range of practicable operating volumes or turndown ratios in wastewater treatment applications. Unlike normal operation, the new mode employs an inital static liquid level that is lower than the upper edge of the draft-tube or the splitting baffle. Hydrodynamics of the operation are analyzed using fundamental principles and an equation is developed for predicting the minimum required gas flow for attaining recirculation of the liquid. The equation is proven experimentally using data for air-water in split-cylinder reactors (aspect ratio = 7; volume = 0.08 m3; riser-to-downcomer cross-sectional area ratio = 2.44; − 0.03 <hc≤ 0.12, wherehcis the dimensionless clearance between the upper edge of the baffle and the static height of gas-free liquid), Effects of the clearance hc on gas holdup in the riser and downcomer, mixing behavior and liquid circulation rate are presented.

ISSN:0098-6445    

DOI:10.1080/00986449608936654

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Heat transfer in five air-lift and bubble column bioreactors has been investigated. Water (Newtonian) and xanthan solutions (non-Newtonian) were used. The effects of superficial gas velocity, liquid-phase viscosity and riser-to-downcomer cross-section area ratio have been studied. In air-lift slightly higher heat transfer coefficients were observed than in bubble column reactors. The superficial gas velocity and the effective liquid-phase viscosity influence strongly the heat transfer performance in all systems studied. Following the surface renewal concept, general correlations for heat transfer in Newtonian and non-Newtonian fermentation broth were developed. They describe precisely heat transfer coefficients in a wide range of operating and geometrical conditions.

ISSN:0098-6445    

DOI:10.1080/00986449608936655

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

An expression for premixed turbulent flame speed is presented, in which Reynolds numberRλbased on turbulent microlength scale λ and turbulent intensityú, and Damkohler number Da defined as the ratio of characteristic residence time of turbulent flame to that of laminar flame, are considered to be the two controlling parameters. The constants involved in that expression are detennined by regression with the available experimental data. It is found that the ratio of turbulent flame speed to laminar flame speed (Vs/Vl) increases withRλlinearly only when Da is kept fixed.

ISSN:0098-6445    

DOI:10.1080/00986449608936656

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A qualitative knowledge of how a continuous distillation column is expected to react to a physical parameter variation is often required, both in simulation and in practical operation. The topic is discussed in this paper with the aim to indicate some simple predictive rules concerning the steady-state variations, both under open- and closed-loop control. The binary distillation in conventional and non-conventional columns is examined in detail; some indications are also given for the multicomponent distillation in conventional columns. Geometrical constraints and asymptotic solutions are the basis for the adopted approach.

ISSN:0098-6445    

DOI:10.1080/00986449608936657

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Hydrogels, and particularly biopolymeric hydrogels, have recently received tremendous interest as controlled release systems for their peculiar features such as high biocompatibility, biodegradability, bioadhesivity, chemical and thermal resistance and good mechanical properties. Among biopolymers, the exocellular microbial polysaccharide scleroglucan appears to be particularly well suited for the formulation of monolithic hydrogel matrices for controlled drug release. In this work we studied the macroscopic factors influencing the kinetics of a model drug release (theophylline) from a scleroglucan hydrogel matrix (2%w/w) and modeled the relevant experimental results. The evidences for the release experiments indicate that the kinetics of the processes follow an apparently non-Fickian behavior under different active drug concentration, temperature and stirring speed. However, by considering the peculiar nature of the hydrogel matrix and the geometrical features of the experimental setup in the formulation of the appropriate initial and boundary conditions, data can be satisfactorily modeled with the classical Fick's law.

ISSN:0098-6445    

DOI:10.1080/00986449608936658

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The main disadvantage of the Claus process is that by introducing air as oxidant a large volume of tail gas is produced. This must be treated to reduce atmospheric emissions of sulfur-containing gases. The costs of the tail-gas unit are a significant fraction of the total capital and operating costs for sulfur recovery. A new process uses thermal decomposition of hydrogen sulfide in the presence of carbon dioxide instead of air oxidation. The products of this reaction are hydrogen, carbon monoxide, elemental sulfur, water vapor and carbonyl sulfide. Carbonyl sulfide is easily converted to H2S and C02by liquid- or vapor-phase hydrolysis. Unreacted H2S and C02are recovered by absorption and recycled to the reactor. Since no air is introduced, there is no tail gas and the tail-gas unit is eliminated, giving a substantial reduction in capital investment. The concentrations of sulfur-containing gases in the product streams depend only on the operation of the absorber and stripper units and can be controlled to very low levels by increasing stripper boil-up. Process operating costs depend on the level of sulfur recovery required and can also be much lower than those of the modified Claus Process.

ISSN:0098-6445    

DOI:10.1080/00986449608936659

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Causticizing is an important reaction in the kraft pulping process in which white liquor is regenerated from green liquor. In spite of its major significance to the pulp & paper mill, the kinetics of causticizing reaction is not yet well understood. A kinetic model for the causticizing reaction is developed in this study. The model doesn't take into account the mass transfer considerations as the experiments were done with analytical grade lime. The pseudo homogeneous kinetic model developed here is a stiff non-linear differential equation. The parameters involved in the model are solved using Differential Algebraic Optimization Technique. A systematic approach for solving the parameter estimation problem is outlined in this paper. The model predictions were found to be within 1 % of the observed values.

ISSN:0098-6445    

DOI:10.1080/00986449608936660

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Conversion of methane and monochtoromethane to acetylene, ethane, and ethylene via homogeneous oxidative pyrolysis is investigated in an isothermal continuous flow reactor employing steam and/or oxygen as oxidizing agents. The effects of monochloromethane to methane ratio in the feed (0.304−9.981), reactor temperature (973−1423 K), and reactor space time (0.0−3.76 s) on product distribution in the reactor effluent are studied. Steam is shown to be a more effective oxidizing agent than oxygen as far as production of C2species is concerned. Addition of steam in the feed suppresses formation of coke, carbon monoxide, and carbon dioxide. The efficacy of oxidative pyrolysis with steam is demonstrated by the substantially high selectivity of C2species (up to 74%).

ISSN:0098-6445    

DOI:10.1080/00986449608936661

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The capability of chain-of-rotalor group contribution equation of state (CORGC EOS) in prediction of vapour-liquid equilibria for electrolyte solutions is discussed. A new approach is considered in which salt is considered as a single component and therefore, there is no ion in the solution. The interaction parameters between water and 50 salts are determined and reported. The parameters are temperature dependent and thus, vapour-liquid equilibria calculations can be achieved at moderate temperature. The percent average absolute deviation for prediction of vapour pressure and osmotic coefficient for 50 aqueous solutions are equal to 0.89 and 16.7, respectively. Comparison between the calculated results and experimental data has been performed.

ISSN:0098-6445    

DOI:10.1080/00986449608936662

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor