Mariam Darestani

Enhanced water recovery in the coal seam gas industry using a dual reverse osmosis system

Mining of brines produced in the coal seam gas industry for water and salts is of major concern globally. This study focussed on the use of a dual stage reverse osmosis system to achieve high water recovery rates. It was our hypothesis that an intermediate nanofiltration stage was required to stabilize the performance of the second reverse osmosis stage. The second stage RO membrane was found to be fouled by silica and aluminosilicates when used with any intermediate brine treatment. Theoretical predictions using PHREEQC software supported the experimental outcomes in terms of identifying species with high scaling potential. Coagulation of the coal seam brine using aluminium chlorohydrate was found to remove up to 70.5% of dissolved silica and thus this method may be useful for prevention of fouling of downstream membranes. ROSA software was also employed to enable selection of possible nanofiltration membranes to treat the coal seam brine sample. Tighter membranes were found to exhibit significantly higher rejection of ions responsible for scale formation during brine concentration operations. Albeit, the flux rates were less than the looser membrane types. A pressure of 20 bar was suggested to be practical for the nanofiltration stage as the flux rate more than doubled from the flux estimated at 15 bar. An intermediate nanofiltration stage perhaps combined with a coagulation step is recommended for use in a dual stage RO system to concentrate coal seam brines.

Structure and electrochemical properties of polystyrene/CNT nanocomposites

The realization of the outstanding properties of CNTs (carbon nanotubes) is constrained by their inherent tendency to agglomerate. Emulsion polymerization was used for synthesizing poly(styrene)/CNT nanocomposites with functionalized CNTs. Chain transfer agents (CTAs) were incorporated to control polymer molar mass and end-use properties. Data from electrical impedance spectroscopy (EIS) at variable frequencies were analyzed to characterize and elucidate the electrical characteristics of poly(styrene) (PS)/CNT nanocomposites. The incorporation of CNT in the polymer matrix even at modest concentrations enhanced the electrical properties of the non-conductive poly(styrene) significantly as revealed by EIS spectra. The use of CTA enabled modulation of polymer molar mass and variation in the electrical properties for PS/CNT relative to composites with no CTA. The electrical behavior of PS/CNT dispersion has been shown to depend both on the CNT concentration and molecular weight of the substrate. The equivalent electrical circuit (EEC) analyses with the corresponding system parameters enabled determination of relative CNT arrangements for different types of PS/CNT composites. TEM images confirmed the CNT positions within the composites and helped support interpretation of EIS/EEC data.

Powering reversible actuators using forward osmosis membranes: feasibility study and modeling

ABSTRACT The aim was to determine the impact of membrane properties and operating conditions upon predicted performance of osmotically driven actuators. An actuator fitted with a forward osmosis membrane was studied, and significantly we examined the reversibility of the actuation process. It was discovered that the actuation-retraction cycle could be repeated for over 60 cycles before salt concentration became similar on both sides of the membrane. The cycle length and number of operative cycles were shown to be a dependent on membrane properties. It was demonstrated that issue of long actuation time can be addressed using membranes with high water permeability.