T. A. Hatton

Liquid Emulsion Membranes and Their Applications in Biochemical Processing

Abstract The potential for liquid emulsion membrane (LEM) systems in biochemical applications and their advantages over conventional systems are discussed. Examples are cited where LEMs have been used to successfully separate organic acids, amino acids, and antibiotics. The use of LEMs to immobilize cells and enzymes to synthesize antibiotics and amino acids as well as decontaminate biological waste streams is described. Enzyme systems immobilized in LEMs are quantitatively evaluated via traditional engineering approaches. In light of the above analysis, the potential LEM process difficulties of membrane breakage, swell, and selectively are examined. New biological applications for LEMs are suggested.

Water transport mechanism in liquid emulsion membrane process for the separation of amino acids

Abstract The mechanism of swelling in liquid emulsion membrane processes was studied. Significant swelling was observed during the separation of L-phenylalanine and it was shown that the water transport was caused by the hydration of L-phenylalanine as well as mediated by the surfactant. The extraction scheme and extraction chemistry were also examined.

Extraction Behavior of Hemoglobin Using Reversed Micelles by Dioleyl Phosphoric Acid

A new surfactant, dioleyl phosphoric acid (DOLPA), has been applied to the extraction of hemoglobin using reversed micelles. The reversed micelles formed by DOLPA can easily extract hemoglobin from aqueous to reversed micellar solutions. DOLPA is the first surfactant to extract hemoglobin completely without using any cosurfactants. On the basis of the difference between DOLPA and AOT reversed micelles in the forward extraction behavior of hemoglobin, the nature of the interfacial complex that would be formed between surfactants and hemoglobin at the oil−water interface was found to be the dominant factor in determining the extraction efficiency of hemoglobin by reversed micelles. In addition, back‐transfer studies of hemoglobin from the DOLPA reversed micelles were also carried out by the phase transfer method. It was found that hemoglobin, once dissolved into the DOLPA reversed micelles, is not transferred to a fresh aqueous solution even when the conditions are adjusted to not allow the forward transfer of hemoglobin. However, the addition of several kinds of alcohol drastically improved the yield in the back‐transfer of hemoglobin. The efficiency in the back‐transfer of hemoglobin strongly depends on the aqueous conditions that are in contact with the reversed micelles, such as pH, ionic strength, and alcohol concentration. A pH higher than the pI of hemoglobin, a salt concentration lower than that of the water pool, and the proper concentration of alcohol are required for the recovery aqueous phase to ensure the back‐transfer of hemoglobin from the DOLPA reversed micelles.

Small-Angle Neutron Scattering Studies of Protein-Reversed Micelle Complexes

Enzymes solubilized in organic solvents, hosted within the polar cores of surfactant aggregates, known as reversed micelles, provide many unique opportunities for new biocatalytic synthesis and protein separation processes. Small‐angle neutron scattering (SANS) studies have shown that insertion of the protein cytochrome‐c in the reversed micelle polar core causes a significant reapportioning of the surfactants and water between the filled and unfilled micelles, leading to an increase in overall size of the filled micelles relative to their empty counterparts. The simple shell and core model assuming single occupancy of the reversed micelles has significant limitations in interpreting data for high protein loadings, and points to the need for more detailed characterization of the protein‐reversed micelle interactions.

Extraction and Activity of Chymotrypsin Using AOT−DOLPA Mixed Reversed Micellar Systems

Novel reversed micellar solutions formulated with a mixture of AOT (dioctyl sulfosuccinate) and DOLPA (dioleyl phosphoric acid) show good potential for use in reversed micellar protein extraction operations. Chymotrypsin is easily extracted from an aqueous phase into organic isooctane containing 10 mM AOT and DOLPA in a 4:1 ratio. The extraction ability of the mixed reversed micelles of 10 mM was higher than that of 200 mM AOT alone. The results of extraction indicated that the AOT−DOLPA mixed reversed micelles are very useful for separating and enriching chymotrypsin. Back‐extraction of chymotrypsin from the organic phase to a fresh aqueous phase is also accomplished by adding an alcohol to the organic phase. Although the back‐transfer of chymotrypsin from the reversed micelles formed by AOT alone is very slow and difficult, in the AOT−DOLPA mixed reversed micelles, the back‐extraction can be achieved completely by addition of 10% (v/v) isobutyl alcohol to the reversed micellar phase. The time to attain to the equilibrium of back‐extraction was reduced from more than 24 to 2 h by adding the alcohol. On the basis of the activity data, the best composition of AOT and DOLPA was a 4:1 ratio and the total surfactant concentration was 10 mM. The activity of chymotrypsin recovered from the mixed reversed micelles was higher than that of the initial protein before the forward‐transfer. This result means that the novel mixed reversed micellar solutions are useful not only in separation but also in purification of proteins.

Polydispersity and backmixing effects in diffusion controlled mass transfer with irreversible chemical reaction: An analysis of liquid emulsion membrane processes

Abstract The effects of polydispersity and backmixing on diffusion-controlled mass transfer with irreversible chemical reaction in liquid emulsion membrane processes have been analysed in terms of the “Advancing Front” model. Separation-of-variables is used to decouple the drop size and axial dependence effects to reduce the problem to a numerically-manageable form. In column-type contactors, it is shown that for constant Sauter mean radius, polydispersity effects arise primarily through the changes in dispersed phase hold-up caused by the distribution in globule rise velocities. For constant hold-up, an increase in Sauter mean radius causes an increase in performance despite a lowered total interfacial area, which can be attributed to the non-linear interaction between the fractional utilization of the internal reagent, the diffusional resistance to transport, and bypassing and segregation phenomena associated with the larger globules. The nonlinear dependence of the transport processes on fractional utilization of internal reagent is also responsible for the development of characteristically convex, rather than concave, concentration profiles in countercurrent operations. Polydispersity effects are evident in batch and mixer-settler operations only at large residence times, although even then they are not significant.

A simple phenomenological thermodynamic model for protein partitioning in reversed micellar systems

A simple thermodynamic model is developed for the partitioning of proteins between a bulk aqueous solution and a reversed micellar organic phase by assuming that a pseudo-chemical equilibrium is established when proteins in solution interact with a non-integral number of empty micelles to form the protein-micelle complex. From the equilibrium constant for this reaction, which is related to both the chemical and electrical free energy changes associated with the transfer of the proteins between the two phases, a simple expression is derived for the partition coefficient as a function of pH and surfactant concentration. Assumptions include a linear variation in protein net charge with pH, and a linear decrease in protein-micelle complex size with increasing protein charge. Results on the solubilization of ribonuclease-a and concanavalin-a in Aerosol-OT/isooctane organic solvents were well-correlated by the model equation, and the estimated parameters were of the expected order of magnitude as estimated based on the known physical properties of the system components.

Transient diffusional interactions between solid bodies and isolated fluids

Abstract A generalized Sturm-Liouville approach is used to provide an efficient solution procedure for the problem of one-dimensional diffusion accompanied by an irreversible first-order reaction in a body suddenly immersed in an isolated volume of moderately stirred fluid. Specific results are presented for the slab, solid and hollow cylinders, and the sphere. The non-reactive, non-adiabatic calorimeter problem is solved by reduction to a closely related adiabatic problem with first-order heat generation in the body, the solution to which is contained in the earlier developments of the paper.

A MODEL FOR LIQUID MEMBRANE EXTRACTION WITH INSTANTANEOUS REACTION IN CASCADED MIXERS

The Advancing Front Model for the description of extraction processes using liquid surfactant membranes has been invoked in the analysis and comparison of cascaded mixer systems with and without interstage settling. It is demonstrated that the extraction efficiency can be enhanced significantly if interstage settling is permitted.

On the significance of the dispersion coefficient in two-phase flow

Abstract A multiphase generalization of Taylor dispersion theory is used to show that the axial dispersion model for the design and analysis of countercurrent contactors for mass transfer should be used with some circumspection. The axial dispersion coefficients have been demonstrated to depend in a complex manner on the hydrodynamic, physicochemical and mass transfer conditions existing within the equipment. This casts considerable doubt on the significance of the dispersion coefficients as independent design variables, and on the utility of the axial dispersion model as a whole.