The Chemical Engineering Journal最新文献

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.

The calculation of temperature vs. time sequences to palliate catalyst deactivation in an integral reactor has been studied either by maintaining constant the conversion at the reactor outlet in a simple reaction or by maintaining constant the concentration of a given component at the outlet in a complex reaction system. The experimental systems studied, which are a simple one (dehydration of 2-ethylhexanol) and a complex one (isomerization of cis-butene), have kinetic models of the Langmuir-Hinshelwood-Hougen-Watson type for the main reaction and deactivation, with deactivation by coke dependent on the concentration of the reaction components. In the reaction of dehydration of 2-ethylhexanol deactivation occurs in parallel with the main reaction and in the isomerization of cis-butene deactivation occurs in series-parallel with the main reaction. A parametric study has been carried out for both reaction systems. The sequences calculated have been experimentally proven in an automated reaction apparatus.

Effects of adsorbent heterogeneity on the adsorption of cobalt phthalocyanine dye on activated carbon have been studied. Adsorption experiments were carried out by varying the temperature and adsorbent mass in batch adsorbers and, in addition, the adsorbent particle size and fluid flow rate in a continuous stirred tank reactor (CSTR)-type adsorber in order to investigate the equilibrium and the kinetics of adsorption.

The Brunauer-Emmett-Teller (BET), Langmuir with uniform distribution (LUD) and Langmuir-Freundlich equations are able to represent the equilibrium data with similar accuracy within the range of measurements. Reasonably large values of the heterogeneity parameter (2.69–2.86) show that the carbon surface is energetically heterogeneous.

A mathematical model that describes the adsorption dynamics, including film-, pore- and concentration-dependent surface diffusion on an energetically and structurally heterogeneous adsorbent, is presented here and fitted to the experimental concentration vs. time curves obtained in the continuously stirred tank adsorber.

Structural heterogeneity of the carbon, if not accounted for in the kinetic model, can be responsible for the very strong concentration dependence of the surface diffusion coefficient and for the variation in the parameter D_o with particle size and adsorber porosity as shown in this work.

Beer fermentation carried out in a cylindrical laboratory fermenter was used to study mixing characteristics. The evolution of the values of different

The extracellular enzyme dextransucrase was produced from Leuconostoc mesenteriodes NRRL B512F and purified by ultracentrifugation and cross-flow ultrafiltration for use in the biosynthesis of the macromolecule dextran by ion exchange chromatographic reaction—separation techniques. The two-stage purification process yielded over 90% pure dextransucrase with overall enzyme recovery of over 60%. A second stage of centrifugation was required to achieve complete cell removal. The purified enzyme contained 1–2 g l⁻¹ of solute ions, which affected the operation of the chromatographic system. Gel filtration removed over 93% of the remaining ions but resulted in high activity losses. Two-phase separation with polyethylene glycol (PEG) and purification by ion exchange chromatography were less successful in desalting the enzyme. PEG precipitation was successful in concentrating the enzyme, but the ions remained predominantly with the enzyme portion of the two phases. The purified enzyme was found to be unstable during storage.

Use of the enzyme in chromatographic reactor—separators for the production of dextran resulted in over 33% more high molecular weight dextran (the desired product) and a useful pure fructose byproduct being obtained than for a conventional reactor. Sodium and potassium ions in the enzyme hampered continuous operation by displacing calcium ions from the resin and thus reducing the separation efficiency of the system. Partial regeneration of the resin with calcium nitrate rather than complete enzyme desalting, which was very expensive and resulted in high activity losses, helped overcome this effect.

This paper illustrates how a neural net, a three-layered perceptron, can be trained to estimate viscosities for undefined crude oils and fractions. Three Saudi-Arabian crude oils were employed to illustrate the use of the neural net to approximate the relation in a very simple manner with no need for a priori knowledge of the system. This empirical correlation was accurate to 98.74% if tested on experimental data not used during training, which is a fivefold improvement on average results obtained by two recently-proposed equations to estimate the viscosity of hydrocarbons. Although the neural net equation seems to be less transparent than former correlations, a method called backward analysis is proposed to analyze the weight matrix of the neural net in order to gain valuable insight into the viscosity system.

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.