Enhancement of mass transfer using colloidal liquid aphrons: measurement of mass transfer coefficients in liquid-liquid extraction

Current applications of Colloidal Liquid Aphrons: Predispersed solvent extraction, enzyme immobilization and drug delivery

Colloidal Liquid Aphrons (CLAs) are micron sized discrete spherical solvent droplets formed by the dispersion of polyaphrons into a bulk aqueous phase at a low phase volume ratio where they can be kept homogenously suspended with only minimal agitation. CLAs have high stability due to the presence of a surfactant 'shell' surrounding the solvent core, and possess large surface areas per unit volume for mass transfer due to their small size. Therefore, CLAs are well suited for applications in pre-dispersed solvent extraction (PSE), enzyme immobilization, and have the potential to be used as a drug delivery system. Using PSE, CLAs have been used to remove metals such as Ni²⁺, Cu²⁺, Fe³⁺, Cr³⁺ and Mg²⁺ from dilute streams, separate organic dyes such as Yellow 1 from wastewater, extract succinic and lactic acid, reactively extract phenylalanine, and separate suspensions. CLAs have also been used to immobilize enzymes such as lipase, lysozyme and albumins with cases of superactivity being reported due to the influence of surfactant and solvent interactions with the enzyme. Furthermore, due to their similarity to current drug delivery systems such as microemulsions and hydrogels, and other advantages, CLA systems have the potential to be adapted for drug delivery systems also. This article provides a complete list of the current applications of Colloidal Liquid Aphrons (CLAs) in PSE and enzyme immobilization, and also presents insight into how CLAs can be utilized as a drug delivery method in the future. Finally, this review ends by summarizing potentially interesting research areas to pursue in this field.

Aphron applications--a review of recent and current research

Colloidal aphrons are multi-layered stable bubbles (CGAs) or droplets (CLAs), surrounded by a thin surfactant film. The small size of the aphrons creates a system with a high interfacial area which can be pumped like water without collapsing. The high stability of colloidal aphrons due to a thin soapy shell surrounding the core, and high interfacial area make them of interest in many processes such as mineral processing, protein recovery, drilling fluids, separation of organic dyes from waste water, predispersed solvent extraction of dilute streams, clarification and purification of suspensions, soil remediation, material synthesis and immobilization of enzymes. This article aims to provide a comprehensive database in generation, characterization and applications of colloidal gas and liquid aphrons from more than 140 published works so far. The article also reports scale up, industrial applications, technical limitation regarding aphrons application and important future research scopes.

Liquid-liquid mass transfer studies in various stirred vessel designs

A general review on correlations to evaluate mass transfer coefficients in liquid-liquid was conducted in this work. The mass transfer models can be classified into continuous and dispersed phase coefficients. The effects of drop size and interfacial area on mass transfer coefficient were investigated briefly. Published experimental results for both continuous and dispersed phase mass transfer coefficients through different hydrodynamic conditions were considered and the results were compared. The suitability and drawbacks of these correlations depend on the operating conditions and hydrodynamics. Although the results of these models are reasonably acceptable, they could not properly predict the experimental results over a wide range of designs and operating conditions. Therefore, proper understanding of various factors affecting mass transfer coefficient needs to be further extended.

Two-phase partitioning bioreactors for treatment of volatile organic compounds

Two-phase partitioning bioreactors (TPPBs) allow the biological removal of volatile organic compounds (VOCs) from contaminated gas streams at unprecedented rates and concentrations. TPPBs are constructed by adding a non-aqueous phase (e.g. hexadecane, silicone oil) to an aqueous phase that contains the microorganisms responsible for degrading the VOCs. Presence of a water-immiscible phase improves the transfer of hydrophobic substrates (e.g. hexane, oxygen) or reduces the toxicity of inhibitory substances (e.g. benzene, toluene) to the microorganisms present in the aqueous phase. The non-aqueous phase is selected based on cost, safety, good partitioning properties towards the target pollutants, biocompatibility, and non-biodegradability. TPPBs have hitherto been designed as laboratory-scale well-mixed stirred-tank reactors or as biofilters that contain a non-aqueous phase. Scale-up and industrial use of TPPBs require elucidation and modeling of the mechanisms of substrate transfer and uptake; understanding of the mechanisms of microbial selection; identification or synthesis of new inexpensive and robust non-aqueous phases; and generation of suitable guidelines for process design and control.

Measurement of bubble and pellet size distributions: past and current image analysis technology

Measurements of bubble and pellet size distributions are useful for biochemical process optimizations. The accuracy, representation, and simplicity of these measurements improve when the measurement is performed on-line and in situ rather than off-line using a sample. Historical and currently available measurement systems for photographic methods are summarized for bubble and pellet (morphology) measurement applications. Applications to cells, mycelia, and pellets measurements have driven key technological developments that have been applied for bubble measurements. Measurement trade-offs exist to maximize accuracy, extend range, and attain reasonable cycle times. Mathematical characterization of distributions using standard statistical techniques is straightforward, facilitating data presentation and analysis. For the specific application of bubble size distributions, selected bioreactor operating parameters and physicochemical conditions alter distributions. Empirical relationships have been established in some cases where sufficient data have been collected. In addition, parameters and conditions with substantial effects on bubble size distributions were identified and their relative effects quantified. This information was used to guide required accuracy and precision targets for bubble size distribution measurements from newly developed novel on-line and in situ bubble measurement devices.

Two-phase partitioning bioreactors in fermentation technology

The two-phase partitioning bioreactor concept appears to have a great potential in enhancing the productivity of many bioprocesses. The proper selection of an organic solvent is the key to successful application of this approach in industrial practice. The integration of fermentation and a primary product separation step has a positive impact on the productivity of many fermentation processes. The controlled substrate delivery from the organic to the aqueous phase opens a new area of application of this strategy to biodegradation of xenobiotics. In this review, the most recent advances in the application of two-liquid phase partitioning bioreactors for product or substrate partitioning are discussed. Modeling and performance optimization studies related to those bioreactor systems are also reviewed.