Membrane emulsification and filtration for engineered particles

In many applications employing particles, the distribution of particle sizes has significant influence on the properties of the resultant material. Membrane emulsification (ME) is a method for manufacturing uniformly sized emulsion droplets where a dispersed phase is forced through a membrane into the continuous phase. It is the shear applied on the membrane surface that detaches the droplets thereby generating an emulsion. Formulation of the dispersed and the continuous phase influences the final droplet size of the emulsion. Therefore one of the aims of this research is to broaden the existing knowledge on particle production by membrane emulsification using nickel microengeneered disk membrane with cylindrical pores and the Dispersion Cell. The Dispersion Cell was successfully used to produce W/O/W emulsions (the oil phase was pumpkin seed oil). Also W/O emulsions (the water phase was acidified sodium silicate) were produced and additionally solidified in order to manufacture solid silica particles with high surface area and internal porosity. The particles were additionally functionalized using 3-aminopropyltrimethoxysilane and turned into ion exchange material capable to sorb copper. Since the silica particles do not swell such ion exchange material might be interesting for applications in nuclear industry. Having in mind an industrial application of membrane emulsification the Dispersion Cell cannot be used due to the problems with the scaling up. Therefore two novel systems: Oscillating and Pulsating were developed and reported for continuous production of the particles. Both systems were commissioned using sunflower oil for production of O/W emulsions. Additionally the Pulsating system was successfully used for production of complex coacervates. In the Oscillating system the nickel membrane was in the shape of a candle and the shear on the membrane surface was induced by vertical oscillations of the membrane. In the Pulsating system a tubular nickel membrane was used and the shear on the membrane surface was applied by oscillations of the continuous phase. The scaling up of both Oscillating and Pulsating system can be achieved by providing a larger membrane area (elongating the membrane) as well as connecting the membranes in parallel. It was successfully shown that a simple force balance can be used to model the size of emulsion droplets as a function of the shear stress. The average shear stress worked better when modelling the droplet sizes in the Dispersion Cell, but the correction for the droplet neck had to be taken into consideration when higher dispersed phase flow rates were used. In the Oscillating and Pulsating systems it was the maximal shear stress that gave the better prediction, but in both systems it was clear that additional forces were present which influenced the final droplet size. An alternative field of application for the Dispersion Cell, relevant to the tests of functionalized silica particles, was investigated. The Dispersion Cell was modified into a continuous flow stirred cell with a slotted nickel membrane on the bottom. The continuous flow stirred cell is shown to be an effective technique for both mass transfer kinetics as well as equilibrium data acquisition combining both into a single step, and simplifying ion exchange analysis. To commission the system the commercial ion exchange resin (Dowex 50W-X8) was used. Once determined, the design parameters can readily be used to model ion exchange contacting in a well mixed system, column operations or any process that requires ion exchange material. Using the continuous flow stirred cell it was shown that the silica particles produced using the Dispersion Cell and functionalized using 3-aminopropyltrimethoxysilane were capable to sorb copper. As a part of the collaboration within the DIAMOND (Decommissioning, Immobilisation And Management Of Nuclear wastes for Disposal) project a novel ion exchange material (copper hydroxide acetate suitable for iodide sorption) produced in the Department of Chemistry (Loughborough University) was successfully tested using the continuous flow stirred cell and equilibrium and mass transfer parameters were determined. The continuous flow stirred cell is particularly relevant to instances when the mass of ion exchange material available for the testing is low (less than 1g) and when dealing with hazardous or expensive materials. It is a technique employing microfiltration and ion exchange (or sorption), of the engineered particles that could be produced by membrane emulsification described in this thesis

Membrane emulsification for polymeric materials and sorption studies; and its process engineering

Membrane emulsification for polymeric materials and sorption studies; and its process engineerin

Oscillating membrane emulsification

Oscillating membrane emulsificatio

Combined ion exchange and microfiltration

The purpose behind this work is to produce polystyrene-divinylbenzene cation exchange resin particles at various sizes, smaller than are conventionally available, and to use them in a microfiltration process; comparing the results with conventional column operation. As a model system, for production of droplets using membrane emulsification, sunflower oil (discontinuous phase) and 2% Tween 20 solution (continuous phase) were used. By increasing the shear at the membrane surface the droplet size decreased from 185 to 50 μm. In the seeded microfiltration process, surface microfilters with slots without internal tortuosity were used to minimize fouling. A filtration flux rate of 3432 l m-2 h-1 was achieved. Rates of copper sorption on to ion exchange resin were found to be dependent on mass transport limitations due to aqueous film diffusion and internal particle diffusion. For prediction of copper sorption a model that takes into account both film and internal diffusion was used. Microfiltration combined with ion exchange has the advantage of very fast kinetics, when compared to column use, and may provide better utilization of the resin particle, depending on the internal diffusion coefficient of the transferring species within the particle

Novel oscillating membrane for production of W/O/W emulsions

Novel oscillating membrane for production of W/O/W emulsion

Recent developments in manufacturing multiple emulsions using membrane and micro fluidic devices

Membrane and microfluidic devices are new routes for controllable production of multiple emulsions with uniformly sized drops and accurate control of the internal drop structure. Membrane emulsification involves injecting single emulsion through a porous membrane into continuous phase in a stirred cell or cross-flow membrane module. In this work an alternative method to generate shear at the membrane surface was applied, based on the low frequency oscillation of the membrane at 10-90 Hz in a direction perpendicular to the flow of the injected phase. The advantage of oscillating membrane technique is that the risk of the drop breakage in the continuous phase is minimal, because the shear is generated only at the membrane surface. The oscillation signal was provided by an audio generator which fed a power amplifier driving the electro-mechanical oscillator on which the inlet manifold was mounted. The membrane was a microsieve-type membrane with regular pore spacing formed by Ni electroforming. At the constant maximal shear stress at the membrane surface the mean size of oil globules in W/O/W emulsions decreased with increasing the amplitude of oscillation. The most narrow drop size distribution with a span of 0.36 was obtained at 70 Hz and the peak amplitude of about 0.4 mm. A disadvantage of membrane emulsification is that the internal drop structure cannot be accurately controlled. Microfluidic devices with co-axial glass microcapillaries developed in Weitz Lab have been found convenient for controllable generation of both core-shell drops and multiple emulsion drops with a controlled number of inner drops in the outer drop. In this work core-shell drops with a size between 50 and 150 μm have been produced at the production rate ranging from 1,000 to 10,000 drops/s. The shell thickness was accurately controlled by adjusting the ratio of the middle fluid flow rate to the inner fluid flow rate and the drop size decreased with increasing the outer fluid flow rate

Novel method of producing highly uniform silica particles using inexpensive silica sources

Novel method of producing highly uniform silica particles using inexpensive silica source

Production of silica particles by membrane emulsification

Production of silica particles by membrane emulsificatio

Polycaprolactone multicore-matrix particle for the simultaneous encapsulation of hydrophilic and hydrophobic compounds produced by membrane emulsification and solvent diffusion processes

Co-encapsulation of drugs in the same carrier, as well as the development of microencapsulation processes for biomolecules using mild operating conditions, and the production of particles with tailored size and uniformity are major challenges for encapsulation technologies. In the present work, a suitable method consisting of the combination of membrane emulsification with solvent diffusion is reported for the production of multi-core matrix particles with tailored size and potential application in multi-therapies. In the emulsification step, the production of a W/O/W emulsion was carried out using a batch Dispersion Cell for formulation testing and subsequently a continuous azimuthally oscillating membrane emulsification system for the scaling-up of the process to higher capacities. In both cases precise and gentle control of droplet size and uniformity of the W/O/W emulsion was achieved, preserving the encapsulation of the drug model within the droplet. Multi-core matrix particles were produced in a post emulsification step using solvent diffusion. The compartmentalized structure of the multicore-matrix particle combined with the different chemical properties of polycaprolactone (matrix material) and fish gelatin (core material) was tested for the simultaneous encapsulation of hydrophilic (copper ions) and hydrophobic (α-tocopherol) test components. The best operating conditions for the solidification of the particles to achieve the highest encapsulation efficiency of copper ions and α-tocopherol of 99 (±4)% and 93(±6)% respectively were found. The multi-core matrix particle produced in this work demonstrates good potential as a co-loaded delivery system

Production of sunflower oil-in-water (O/W) emulsions using nickel microsieves

Uniform oil droplets can be used for encapsulation and controlled release of lipophilic active ingredients in various food, cosmetic, and pharmaceutical formulations. In these applications, uniform drops of controlled size are needed to achieve a controlled release at adjustable rates. In this work, O/W emulsions have been prepared by injecting sunflower oil through a flat disc nickel membrane into stirred continuous phase (aqueous solution of Tween® 20 or Pluronic® F-68). Three different membranes were used: 40μm whole membrane, 18 μm whole membrane and 18 μm ring membrane containing open pores only within a ring region. The effect of the paddle stirrer rotational speed, the transmembrane flux, the mean pore size and the membrane type (whole or ring) on the particle size distribution of prepared emulsions have been studied. It was found that stable emulsions could be produced using both Tween® 20 and Pluronic® F-68 but under the same conditions the emulsion droplets stabilized with Pluronic® F-68 are larger than the droplets prepared using Tween® 20. The final concentration of sunflower oil in the emulsions can be as high as 60 vol. % without any detrimental effect on the particle size distribution. The mean particle size was significantly effected by the rotational speed, the transmembrane flux, and the mean pore size and was varied between 76 and 281μm