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

The mathematical model previously developed in the Department of Chemical Engineering, Monash University for the metal uptake by living algal cells has been revised to take into account the actual surface area through which transfer occurs. Cadmium uptake data obtained using the three algal species Chlorella vulgaris, Chlorella pyrenoidosa and Chlamydomonas reinhardtii were able to be fitted satisfactorily by the revised model.

A new method is proposed to evaluate kinetic parameters and mass transfer coefficients for adsorption processes carried out in continuous stirred tank reactors. This method, employing a biphasic model, does not linearize nonlinear solute concentration versus time data, nor does it assume the existence of equilibrium in a typical nonequilibrium situation as is currently done. For a nonlinear adsorption isotherm, the coupled differential equations need to be solved numerically, but using an elegant analytical solution it is possible to determine rate constants and mass transfer coefficients in the case of nonlinear kinetics with a linear adsorption isotherm. This solution (biphasic model, linear isotherm) is obtained and compared with solutions incorporating (i) a linear model (linear isotherm) and (ii) a numerical solution (nonlinear isotherm) for recovery of the antibiotic novobicoin in stirred tank reactors. For novobiocin adsorption versus time data, use of the biphasic model results in a lower mean percentage error than either the linear model or the numerical simulation; further, it provides a far superior fit of short-time adsorption behavior. Hence, we strongly advocate that the biphasic model be routinely employed along with linear models and numerical simulations of Langmuir/Freundlich isotherms for interpretation of adsorption data.

Realistic mathematical models are essential for the scaling-up or the design of biofilters. However, the mathematical models which describe the steady-state and the transient operation of biofilters are very limited. Although some of these models are based on restrictive assumptions, they have been widely used in industry for designing actual biofilter units. This study gives detailed analysis and comparison between these models. The asymptotic behavior of recent models are presented. The results show that diffusion is an important phenomenon which should not be neglected in developing biofilter models, and that neglecting oxygen transport and its effects on growth kinetics will give unrealistic values for the effective as well as the actual film thickness.

Sinapine, a choline ester of sinapic acid and a main component of the phenolic fraction of rapeseed meals, was enzymatically transformed by an enzyme secreted by a white rot fungus Trametes versicolor. A model based on the Theorell-Chance Bi-Bi mechanism that describes the effect of pH, temperature, substrates and enzyme concentrations on the initial reaction rate was developed. The model parameters were estimated from the data regarding the effect of pH and temperature on initial reaction rates using a two-step estimation procedure that was developed in this work. The model predicts experimental data fairly well, and is valid for any pH and temperatures ranges. The optimum pH and temperature of reaction determined experimentally and confirmed by the model are 4.24 and 50 °C, respectively. However, when the effect of temperature on the oxygen solubility is not considered, i.e. oxygen is not the limiting substrate, the model shows that the optimum temperature of reaction is 60 °C. A relation between the temperature and the optimum pH of reaction was proposed. The developed model was used to predict the dynamics of sinapine transformation. The results showed that the investigated enzymatic system includes additional enzymatic reactions between oxygen and the products of sinapine transformation.

Glucose oxidase (GOD) was immobilized onto modified polymethylmethacrylate (PMMA) microspheres by covalent bonding. Monosize PMMA microbeads with 1.5 μm diameter were produced by dispersion polymerization of methylmethacrylate by using polyvinyl alcohol as a stabilizer. Hydroxyl groups on the microbeads were first converted to aldehyde groups by periodate oxidation. Three amino compounds, namely ammonium hydroxide, ethylene diamine and hexamethylene diamine were incorporated through the aldehyde groups. Then, GOD molecules were immobilized through the spacer-arms by using glutaraldehyde. The highest amount of immobilization and activity were obtained in which hexamethylene diamine was used as the spacer-arm with 14 atom length, and were 2.1 mg g⁻¹ polymer and 129 IU g⁻¹ polymer, respectively. The optimal conditions for GOD immobilization were obtained as follows: pH, 6.0; temperature, 30 °C; immobilization time, 60 min; and GOD initial concentration, 0.10 mg ml⁻¹. The optimal conditions for the GOD-immobilized PMMA microbeads were at pH 6.0 and at a temperature of 30 °C. The K_m and V_max values of the GOD-immobilized PMMA microbeads were, 13.79 mM and 26.31 mM min⁻¹ calculated by non-linear regression, respectively.

On the basis of the theory of affinity it is shown that enzyme-linked immunosorbent assay titres cannot increase as a result of proteolysis when all the antibody proteolytic fragments have approximately the same association constants as the intact antibody for the reaction with the antigen and with the enzyme-conjugated antibody. This finding was experimentally confirmed by proteolysis experiments carried out with a monoclonal IgM antibody against Lewis^b antigen using trypsin. The experimental results with this particular antibody confirmed that proteolysis cannot enhance ELISA titres in hybridoma cultures with serum-free medium or with serum-supplemented medium.

The geometry of the dead zone (stagnant solid) and of the spout zone in shallow cylindrical spouted beds of flat base has been studied using an optical fibre probe in a pilot plant unit. The angle formed by the dead zone-moving zone interface surface with the base of the contactor increases as the stagnant bed height and the particle diameter increase. The angle decreases as the ratio of the air velocity to the minimum spouting velocity increases and the ratio of the contactor inlet diameter to the column diameter increase. The influence of the geometric factors of the contactor, of the particle diameter and of the air velocity on the spout geometry have been analysed. The spout presents a neck whose position and magnitude depend on the geometric factors of the contactor and of the operating conditions. A correlation has been proposed for calculation of the mean spout diameter.