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.
A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.