A theoretical model is derived to decide whether biphasic systems or single-phase aqueous systems are chosen as the media for microbial transformations. The yield ratio and product ratio at chemical equilibrium, which depend on the partition coefficients, equilibrium constants, activity coefficients and initial concentrations, are proposed as appropriate indices by the analysis of four common types of biochemical reaction under two extreme initial conditions.
An extension of the range of convergence of the classical Newton-Raphson method and modified forms of it by use of the functional transformation method is demonstrated herein by use of numerical examples of difficult-to-solve distillation problems. Variations of the Newton-Raphson method considered are as follows: (1) the 2N Newton-Raphson method with the Broyden modification; (2) the 2N Newton-Raphson method with the Broyden-Bennett modification; (3) the almost-band algorithm with the Broyden-Householder modification; (4) the almost-band algorithm with Schubert's modification; and (5) parametric continuation with step size selection by Gear's method.
In this work the problem of determining the feed rate policy of fresh enzyme into stirred bioreactors to offset the loss of activity due to enzyme deactivation is addressed. On the basis of a series-type deactivation mechanism with arbitrary deactivation kinetics, it is shown that the feed rate policy is a feedback function of the deactivation rate. From both the theoretical and the practical viewpoints, these results provide a useful tool in understanding enzyme deactivation, and in designing bioreactor operation.
Catalytic afterburners using short monoliths take advantage of the enhancement of the transfer coefficients in not fully developed flow. The correlations for Nu and Sh in laminar flow in the entrance region of a monolith available from the literature are evaluated and compared with experimental data. A one-dimensional model is proposed and solved using the orthogonal collocation method under stationary and transient conditions.The calculated results were compared with experimental data for the combustion of lean benzene-air mixtures in a short monolith.The model is able to describe the behaviour of the afterburner satisfactorily if local Nu and Sh values for simultaneously developing velocity, temperature and concentration profiles are employed. If the light-off occurs part way along the monolith channels, a new thermal entrance should be considered.
On the basis of the similarity of the shapes of the liquid heat capacity and vapour pressure curves, and the concept that a property such as heat capacity (energy storage capacity) should directly depend on the constitution and structure of the molecules, a corresponding state-type relation has been formulated and tested: CσL = RM(5.4571 − 0.3098TR − 1) where CσL (J mol−1 K−1) is the saturated liquid heat capacity, RM (cm3 mol−1) is the molar refraction and TR is the reduced temperature. The extension of the method, which predicts liquid heat capacities of pure non-polar liquids with an average absolute deviation of 5.5%, to polar liquids and several binary mixtures is also discussed.
Depending on the hydrodynamic conditions, a stirred tank reactor may be divided into two micromixing environments: maximum mixing followed by complete segregation (case 1), or vice versa (case 2). The Ng-Rippin two-environment model simulates case 1, whereas the Fan reversed two-environment model covers case 2. The micromixing concepts of Danckwerts and of Zwietering have been applied to both models in terms of the degree of segregation J to evaluate the influence of the order of micromixing-segregation effects on biological growth processes. The model predictions for both endogeneous and exogeneous cell metabolism show that case 2 gives more substrate conversion and cell production than does case 1, for the same extent of micromixing, particularly at low dilution rates. At high dilution rates, both models predict the same reactor performance, independent of the micromixing phenomenon. The substrate conversion and cell production decrease with increasing dilution rate, following a similar trend. Further, the effects of micromixing are found to be strong functions of dilution rate. At high dilution rates for case 2, the micromixing effects are pronounced only when the reactor approaches complete segregation. However, for case 1, the effects are appreciable when the reactor deviates slightly from perfect mixing. For some intermediate dilution rates, the Fan model, unlike the Ng-Rippin model, shows that the reactor output decreases linearly with increasing degree of segregation. Beyond a critical value of the dilution rate, the reactor output falls linearly with dilution rate for exogeneous cell metabolism (case 2). On the contrary, for case 1, the output decreases exponentially throughout the entire range of dilution rates.
Control of a fed-batch industrial-scale fermenter requires a large amount of ''finger-tip feeling'' on the part of operators, despite reasonably sophisticated instrumentation. The reason for this is that there are no applicable deterministic models giving aid to the control system in deciding the best operation strategies. This is a typical case of a heuristic experimental process, treating inexact knowledge that is excluded from deterministic and statistic modelling a priori. Essential parts of this problem can be solved by means of an expert system shell, capable of dealing with uncertain information, using the linguistic shell application. Knowledge was extracted from process records on fermentation batches producing baker's yeast on an industrial scale. A strategy for heuristically optimized yield and growth rate can be predicted using knowledge gained in previous runs and stored in the knowledge base of the expert system. The expert system, once built up, can also be used for experimental simulation of the effects of fundamental decision parameters: temperature, production rate, ethanol concentration and specific growth rate. The use of expert system consultations can be generally recommended as an efficient aid in fermentation control.
Optimization of batch distillation has been studied extensively over the last 30 years. Previously, the solution methods were basically derived or computed using short-cut models due to the lack of suitable computation techniques. In this study, a modified approach based on the work of Biegler and coworkers (L. T. Biegler, Comput. Chem. Eng., 8 (1984) 243; J. E. Cuthrell and L. T. Biegler, AIChE J., 8 (1987) 1257) was implemented to determine optimal constrained solutions for a ternary system with various objective functions, such as maximum product, minimum energy required and minimum end time, using a rigorous model. Unlike previous investigations, the optimal control solutions derived in this study were independent of the process model implemented. Therefore, no limitation on the distillation models exists, i.e. any rigorous model can be used to find solutions.The optimal control problem for the batch distillation of mixtures of benzene, toluene and o-xylene was solved. The solutions were assumed to be continuous or discontinuous polynomials. It was found that a discontinuous solution is superior to continuous results because of the discontinuous nature of the system itself.
Power consumption measurement of screw and helical ribbon agitators of efficient geometry which mixed pseudoplastic fluids in the creeping-flow regime, was performed. The values of the Metzner-Otto coefficient k and relations for its calculation were suggested on the basis of experimental results.
The results of anaerobic digestion in a fluidized bed reactor fed with municipal waste waters enriched with glucose are presented. Several process conditions have been tested by varying the influent chemical oxygen demand (COD) from 4 to 13 kg m−3 and the residence time from 5.0 to 68.2 h. The degradation efficiency and methane production rate are substantially affected by an increase in organic loading rate from 4 to 24 kgCODi m−3 day−1, suggesting a maximum operational value for this parameter. Using a Monod-type kinetic model, a maximum theoretical specific degradation rate of 1.76 kgCODr kgVSS−1 day−1 has been calculated, which is very similar to values calculated for other effluents from food industry activities.
One of the most essential problems in dealing with solid-liquid suspensions in stirred vessels is the determination of a reliable scale-up rule from small stirred tanks to large vessels on an industrial production scale. According to a new approach based on physical modelling of the complex fluid dynamics, the necessary power input in stirred suspensions can be calculated as a sum of the circulation power and the sinking power of a particle swarm. The following results, which are compared with a great variety of experimental data in the literature, reveal that there is no simple and constant scale-up rule applicable to describe the power input for a large range of suspension properties, tank size, geometrical conditions or comparable suspension criteria.
The fast Fourier transform technique was introduced as a calculational tool for the estimation of parameters in the time domain. A complex fixed bed enzymatic reactor was selected as the model example. The results show that this is a suitable and effective technique in this regard.
The intermittent initial period of crossflow microfiltration has been studied, and the nature of fouling-layer deposits ascertained by simple physical inspection. At low crossflow velocity, a visible solid deposit was formed on the inside of the tubular membrane, but at high velocities no such layer could be detected. In this regime, fouling was controlled by the concentration polarisation phenomenon. The initial flux in these cases was restored by stopping the apparatus for a few seconds. Cyclical stop-start operation as a way of increasing permeate production is discussed.
This paper deals with the experimental study of the axial dispersion phenomenon during flow through and by fixed beds packed with sheets of nickel foams. Its purpose is to characterize the hydrodynamic behaviour of a liquid flowing through different nickel foams according to configurations corresponding to the two working modes of volumic electrodes. A comparison of axial dispersion in liquid flow through various porous media determined by using the same procedure is presented. The axial dispersion is very low for flow through reticulated nickel foams, while tightly packed beds of very anisotropic flat plates show a very dispersive behaviour. For all other media a single correlation equation based on dimensionless numbers taking structural parameters into account is proposed.
The use of enzymes in waste treatment processes has been proposed by a number of investigators. However, most of this work has focused on demonstrating the disappearance of target pollutants and has not considered the engineering issues that will ultimately determine the process feasibility. The conditions that occur in most waste treatment situations are very different from the conditions that exist in chemical manufacturing processes, so the technical concerns in implementing enzyme technology cannot be extrapolated directly from experience in the manufacturing sector. The waste treatment situations that may be appropriate for enzyme technology are presented, along with criteria for enzymes that may be of near-term applicability. Previous work on the waste treatment applications of enzymes is reviewed and the technical issues that must be considered in feasibility determinations are discussed.
An invasive plate and frame capacitance probe was designed for dielectric constant measurements over a wide frequency range (10-5000 kHz) in a 5 1 stirred tank reactor. Preliminary measurements with polyethylene beads showed a linear variation of the effective permittivity with the volume fraction of the beads, in accordance with the Maxwell-Wagner theory. Results obtained by bubbling air under various agitation and aeration rates at 500 kHz in deionized water, and the effect of a non-ionic antifoam on permittivity variations, are shown and discussed; the technique is thought to allow precise local holdup measurements. Existing limitations and possible further improvements of the technique are discussed, especially in view of the information that can be gained from the standard deviation of the measurements.
The volumetric mass transfer coefficient kLa for a mechanically agitated gas—liquid contactor was measured by employing the dynamic method developed recently by Panja and Phaneswara Rao (Trans. Inst. Chem. Eng., 69 (1991) 302), which consists of bubbling pure CO2 into an aqueous solution and following the concentration of the bicarbonate ion continuously with the help of an electrical conductivity probe. A mathematical model was used which enabled the value of kLa to be determined by a non-linear least-squares method. In the present work the above method has been extended to study the effect of process variables such as temperature, solids concentration, viscosity and interfacial tension on kLa in a tank of diameter 16.4 cm with the standard tank configuration. The value of kLa was found to increase (1) with increasing temperature of the liquid, (2) with increasing amount of dissolved isopropanol and amyl alcohol, which cause a reduction in surface tension, (3) with increasing solids concentration in the range 0–6 wt.% and (4) with increasing ion concentration. However, the value of kLa was found to decrease (1) with increasing viscosity and (2) with increasing solids concentration above 6 wt.%. A new correlation for kL was obtained from the values of KL calculated from the present kLa data by knowing the value of interfacial area from the equation of Calderbank (Chem. Eng., 45 (1967) CE-209). The effect of the presence of an alcoholic compound (amyl alcohol) under miscible and immiscible conditions on gas holdup was also investigated experimentally. The gas holdup was found to first decrease and then increase in the miscible range of amyl alcohol, again decrease and finally increase at a higher volume fraction of amyl alcohol, when an immiscible phase of amyl alcohol also formed.
The mass balance equations for hollow fibre bioreactors have been solved for the zero-order limit of the Michaelis-Menten kinetics. As in the case of first-order reactions, the membrane and spongy matrix equations can be decoupled from the overall set of equations. For the case of the substrate remaining constant everywhere in the reactor a solution in terms of hypergeometric series is possible. For the substrate exhaustion case the extinction radius is a non-linear function of the system parameters and thus the equations have to be solved by numerical methods.
Mass transfer between an electrolyte and the inner core of an annular cell fitted with a tangential inlet is experimentally investigated using an electrochemical method. Attention is focused on the influence of the electrode length and position with respect to the tangential inlet to take into account both the development of the hydrodynamic and concentration boundary layers. According to the value of the ratio of the gap width e, to the inlet diameter Φe, two kinds of swirling motion are studied: pure swirl flow for e = Φe and contraction swirl flow when Φe >e. Depending on the geometric factors and the Reynolds number, enhancement in mass transfer of up to 550% is achieved in comparison with that obtained for fully developed axial flow. Two general correlations of the experimental data, taking into account the aforementioned parameters, are proposed for laminar and turbulent swirling flows.
Experiments were conducted to investigate the solid—liquid mass transfer behaviour in a non-newtonian liquid fluidized bed. The column diameter and height of the fluidized bed are 8 cm and 100 cm respectively. Carboxymethyl cellulose (CMC) solution was used as the non-newtonian fluid in this study. Dissolution of benzoic acid pellets into CMC solution was employed to obtain the solid—liquid mass transfer coefficient in the bed. The benzoic acid concentration in CMC solution was measured by titration. The in-bed benzoic acid concentration was examined to justify the use of an axial dispersion model in the evaluation of the mass transfer coefficient in this study. It was found that the mass transfer coefficient was essentially independent of the liquid velocity and particle size. However, it decreased as the CMC solution concentration was increased.
