The Chemical Engineering Journal and the Biochemical Engineering Journal最新文献

Lysine is an essential amino acid in human nutrition and also widely used in animal feed formulations. It is produced on a large scale by fermentation in stirred tank bioreactors. In the present work lysine was produced by fed-batch fermentation with an industrial Brevibacterium flavum strain grown in a 115 m³ fermentor on a beet molasses based medium. The difficulties in on-line monitoring of substrate consumption and of product formation complicate real-time process control. We demonstrate that well-trained backpropagation multilayer neural networks can be employed to overcome such problems without detailed prior knowledge of the relationships of process variables under investigation. Neural network models programmed in MS-Visual C++ for Windows and implemented on a personal computer were constructed and applied to state estimation and multi-step-ahead prediction of consumed sugar and produced lysine on the basis of on-line measurable variables for process control purposes.

This work studies the optimum operating conditions in theoretical industrial acetifiers using computer simulation techniques. The fundamental part of the simulator is a global model for the growth of Acetobacter aceti in submerged culture compiled from the literature. The model is based on an expression which brings together a function for the specific rate of growth and another function for the specific rate of death, which reflects the combined influences of acetic acid, ethanol and oxygen. The kinetic parameters of the model are refitted by non-linear least-squares-type techniques, using data obtained from laboratory and industrial experimentation.

The optimum operating conditions have been calculated for two types of batch process: those with constant concentrations of dissolved oxygen and those with a constant rate of oxygen transfer to the fermentation medium. In both cases, the influence on the evolution of the process of different initial concentration levels of ethanol, acetic acid, biomass, dissolved oxygen and K_La has been studied.

The interactions between a turbulent flow field and discrete particles have numerous applications in biochemical engineering. On the one hand, flows have a strong influence on the particle motion, from which consequences for heat and mass transfer, mixing or even damage to particles are derived. On the other hand, the presence of the discontinuous (solid) phase is regarded as altering the turbulent field (two-way coupling). At present, no fully explained mechanism of this turbulence alteration is offered in the literature. However, the two-way coupling can no longer be considered when the particle concentration becomes sufficiently high. The dominant mechanism affecting the flow is then the particle—particle interaction. Until now, no clear definition of a demarcation between hydrodynamic (fluid—particle interaction) and viscous (particle—particle interaction) influences in liquid—solid or liquid—solid—gas systems has been given in the literature.

In this paper we present first a description of the forces acting on a particle in a flow and the most relevant parameters linked to the response of a particle to turbulent stimulations. Some illustrations are given for common biochemical applications. The second part is concerned with the action of the particles on the turbulence, the main trends observed and their significance in such applications being focused on. It is also demonstrated here that the transition between the hydrodynamic and the viscous regimes is located between 20% and 30% in solid volume concentration.

An experimental study of a membrane bioreactor has investigated the dynamics of the vortex wave as an effective aeration technique for application in high density mammalian cell culture. Gas transfer membranes have been employed in order to eliminate the potentially lethal gas3-liquid interface found in stirred tank and bubble columns. The diffusion-limited features of oxygen transfer through a membrane have been overcome by harnessing the excellent mixing characteristics of oscillatory flow and vortex formation.

The crucial hydrodynamic features of the vortex wave, in a relatively wide channel, have been classified in terms of deflector spacing, Reynolds number and Strouhal number. The dynamic gassing-in of oxygen from a gas phase, across the membrane, to a liquid phase has allowed us to quantify the mass transfer characteristics in terms of the Sherwood number. Significant mass transfer enhancement has been achieved under laminar flow conditions, without a major increase in power dissipation. The Sherwood number has been found to be dependent on both the Reynolds number and the Strouhal number. The Reynolds analogy has been employed to calculate shear rates. The low shear rates (about 300 s{sut-1}) and maximum theoretical hybridoma cell densities (about 1.0 sx 10{su9} cells ml{sut-1}) indicate that the vortex wave design may be an effective alternative to traditional bioreactors.

One method for economic planning and management of production processes is a balance of substrate mass and energy it contains. Theoretical assumptions and practical applications of mass and energy balances in the process of citric acid production by Aspergillus niger are discussed in the study.

In the calculation of biomass and product yields as well as the maintenance coefficients mechanistic values such as true biomass and citric acid yields Y^max_ATP,X(P) on ATP and specific ATP consumption m_ATP due to maintenance processes were used. A set of limitations imposed on theoretical and true yield coefficients in the linear growth equation is also presented.

The experimental measurements were performed in an air-lift bioreactor of 220 dm³ operating capacity, with external circulation loop. The sole carbon source for the cultivation of A. niger was sucrose at an initial concentration of 100 g l⁻¹.

The experimentally obtained yield coefficients relative to cell growth and citric acid production have reached 96% and 83% respectively of real maximum theoretical values. Calculated true biomass and citric acid yield coefficients were closely correlated with the values from the balance analysis of stoichiometric equations. Calculated value of specific maintenance requirements m_ATP was 0.015 mol ATP [mol C(dry mass)]⁻¹ h⁻¹.

Three pneumatically agitated reactors — a bubble column and two airlift devices — with identical rectangular cross-sections (0.456 m × 0.153 m), working heights (1.64 m) and equivalent gas sparging arrangements were compared in terms of the hydrodynamic and oxygen transfer performance. The two airlift reactors had identical riser-to-downcomer cross-sectional area ratios of 1.0, but differed in being sparged either in the central draft-tube or in the peripheral risers. The reactors produced comparable overall gas holdups for otherwise identical conditions in air—water or air—water—glass bead (0.069 mm particle diameter, 0%–5% (v/v) solids loading) systems. For the airlifts, irrespective of the sparging configuration or the solids loading, the same linear equation could relate the riser and the downcomer gas holdups. The velocity of the induced liquid circulation was not affected by solids loading, but the central draft-tube sparged design produced consistently higher velocities than did sparging in peripheral tubes. The bubble column had the poorest mixing performance. Complete suspension of solids occurred in all reactors in the range of superficial air velocities (0.01–0.08 m s⁻¹) tested; however, the distribution of solids was non-uniform in the bubble column. The airlift devices achieved homogeneous distribution. The oxygen transfer capability of the three reactors was comparable, with the bubble column performing slightly better.

Equilibrium studies on the distribution of penicillin G between aqueous solutions and Amberlite LA-2 (a secondary amine) in mixtures of n-butyl acetate and kerosene were made in the temperature range 288–308 K. Experiments were performed as a function of aqueous pH, penicillin G concentration in the aqueous phase, and amine concentration in the organic phase. The composition of the complex present in the organic phase and the equilibrium constant for the formation of this complex were numerically determined at different temperatures. In addition, the apparent enthalpy and entropy for complexation reaction were calculated.

An experimental investigation of dynamic liquid holdup and oxygen absorption mass transfer was carried out in a laboratory bioreactor packed with expanded clay balls. The column was operated with a cocurrent upflow of air and water at low Reynolds numbers.

The data obtained for dynamic liquid holdup have been represented by a modified Stiegel-Shah relation with a relative mean error of 0.7%.

For prediction of the oxygen mass transfer coefficient, an empirical correlation based on air and water mass superficial velocities has been proposed. It reproduced our experimental results with a relative mean error of 9%.

Both correlations proposed in this study are valid for small packing spheres around 2.7 mm in diameter and Reynolds numbers varying for gas and liquid from 0.197 to 0.593 and from 3.875 to 9.315 respectively.

In this work, a model was proposed to evaluate the effectiveness factor of a hollow-fiber biofilm reactor (HFBR) for optimum biofilm densities, to achieve a maximum substrate consumption rate. The effectiveness factor was calculated for selected lumen concentrations using a cell-density-dependent effective diffusion coefficient, Monod biokinetics adapted for maintenance, and a minimum substrate concentration concept for biofilm activity in the model, a different approach from that in the literature. The solution of the continuity equation revealed an optimum biofilm density and active biofilm thickness, corresponding to a maximum substrate consumption rate within the biofilm. The optimum biofilm density decreased with increasing lumen substrate concentrations, while the maximum substrate consumption rate and active biofilm thickness parabolically increased, as experimentally observed in the literature. Meanwhile, an interesting descending trend of the effectiveness factor at optimum biofilm density was observed at low lumen substrate concentration and biofilm thickness values for different radial flow rates.