The behavior of suspensions and macromolecular solutions in crossflow microfiltration

Membrane-based techniques for the separation and purification of proteins: an overview.

The potentials of using organic reaction media in biotechnological conversions have already been demonstrated in several experimental studies. Examples of possible advantages are: possibility of higher substrate and/or product concentrations, favorable shift of reaction equilibria, reduced substrate and/or product inhibition, and facilitated product recovery. Especially water/organic solvent two-phase systems seem to possess several of these advantages. The solvent type will highly affect kinetics and stability of the (immobilized) biocatalyst, solubility and partitioning of reactants/products, and product recovery. Therefore the solvent choice can have a large influence on the economics of the two-liquid-phase biocatalytic process. Immobilization of the biocatalyst may be useful to provide protection against denaturating solvent effects. The polarity of the employed support material will also be decisive for the partitioning of substrates and products among the various phases. A classification of biphasic systems, which is based on the possible types of theoretical concentration profiles and aqueous phase configurations, is discussed. Reversed micelles and aqueous two-liquid-phase systems can be considered as special cases. The design of two-liquid-phase bioreactors is dependent on the state of the biocatalyst, free or immobilized, and on the necessity for emulsification of one of the two liquid phases in the other. Many mass-transfer resistances, e.g. across the liquid/liquid interface, in the aqueous phase, across the liquid/solid interface, and in the biocatalyst phase, can limit the overall reaction rate. The epoxidation of alkenes in water/solvent two-phase systems is discussed to give an example of the scope of biotechnological processes that is obtained by using organic media. Finally, a design calculation of a packed-bed organic-liquid-phasel immobilized-biocatalyst reactor for the epoxidation of propene is given to illustrate some of the above aspects.

Biocatalysis in Organic Media

Ultrafiltration process has been applied widely in food processing industry for the last 20 years due to its advantages over conventional separation processes such as gentle product treatment, high selectivity, and lower energy consumption. Ultrafiltration becomes an essential part in food technology as a tool for separation and concentration. However, membrane fouling compromises the benefits of ultrafiltration as fouling significantly reduces the performance and hence increases the cost of ultrafiltration. Recent advances in this area show the various intensive studies carried out to improve ultrafiltration, focusing on membrane fouling control and cleaning of fouled membranes. Thus, this paper reviews recent developments in ultrafiltration process, focusing on fouling mechanisms of ultrafiltration membranes as well as the latest techniques used to counter membrane fouling.

Ultrafiltration in Food Processing Industry: Review on Application, Membrane Fouling, and Fouling Control

Immobilized cells : a review of recent literature

Mass transfer effects in fermentations using immobilized whole cells

A simple mathematical model was developed to predict the steady-state electroultrafiltration (a combination of ultrafiltration and electrophoresis) flux for processing bovine serum albumin (BSA) solutions at constant concentration. The assumption that the wall concentration is an exponential function of the electric field strength gave a linear dependence of flux on electric field strength. This dependence was experimentally confirmed for electroultrafiltration of 1–4 wt% BSA solutions at pH 7.4, using Amicon XM-50 membranes with a transmembrane pressure drop of 5 psig. The mathematical model uses the values of the solution and solvent fluxes for normal ultrafiltration plus the electrophoretic mobility of the solute to predict the electroultrafiltration flux. The difference between the model predictions and the measured performance was 7.5%.

Steady-State Modeling of Electroultrafiltration at Constant Concentration

An electrophoretic technique for controlling concentration polarization has been successfully applied to the ultrafiltration of charged macrosolutes-proteins and colloidal electrodeposition paints. The electric field controlled the build-up of retained macrosolutes at the membrane surface. Resultant fluxes were 75% to 500% higher than normal ultrafiltration fluxes. Selectivity was also improved as indicated by a 2 to 6 fold increase in the separation factor for solutions of proteins. These preliminary results are analyzed in terms of the important process variables.

Electrophoretic Techniques for Controlling Concentration Polarization in Ultrafiltration

The time required to concentrate various starting solutions of bovine serum albumin by ultrafiltration was compared to that by ultrafiltration with an electric field—electroultrafiltration. Diafiltration of bovine serum albumin solutions was also compared to diafiltration with an electric field In both cases the electric field improved the performance of the ultrafiltration or diafiltration process by increasing the flux through the membrane.

Concentration Ultrafiltration and Diafiltration of Albumin with an Electric Field

An exponential relationship between protein concentration and time is used to predict the solution flux when concentrating bovine serum albumin solutions with electroultrafiltration. The time constant can also be predicted from a plot of flux versus the logarithm of the bulk concentration. The limitations of this prediction are also discussed. The average flux during electrodiafiltration is used to predict the exponential relationship between salt concentration and time when using electrodiafiltration to remove NaCl from bovine serum albumin solutions. The processing time saved by using an electric field is easily calculated from these equations.

John M. Radovich

Papers

Mass transfer effects in fermentations using immobilized whole cells

Steady-State Modeling of Electroultrafiltration at Constant Concentration

Electrophoretic Techniques for Controlling Concentration Polarization in Ultrafiltration

Concentration Ultrafiltration and Diafiltration of Albumin with an Electric Field

A Semiempirical Model for Electroultrafiltration-Diafiltration