Fabrication and Evaluation of a Forward Osmosis Water Purification System and The Synthesis of Boron Containing Nanomaterials
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2023
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Abstract
Global freshwater scarcity and shifting precipitation patterns brought about by naturaland anthropogenic climate change has spurned a plethora of research in the past decade
towards water desalination. Reverse osmosis (RO) is the most prevalent desalination
technique employed at the industrial scale, but it faces high operational costs due to frequent
membrane fouling and having to generate high hydraulic pressure. Forward osmosis
(FO) emerges as a potentially promising solution to these challenges. The core driving
force for the separation process relies on an osmotic pressure gradient. This gradient,
derived from a draw solution (DS) with a higher osmotic pressure relative to that of the
feed solution (FS), is utilized to induce a net flow of water through the semi-permeable
membrane. Because this natural osmotic process requires minimal external hydraulic
pressure, FO systems use significantly less energy than RO, and FO membranes have a
longer lifespan compared to RO membranes. One of the primary challenges impeding the
transition of FO systems from laboratory-scale prototypes to industrial applications lies
in the insufficient availability of draw solutions capable of efficient regeneration.
This current work will first introduce the theory and working principles governing the
FO process and then move into the design and fabrication of a lab scale FO test stand. To
determine the efficacy of the newly designed and fabricated test stand, evaluation trials
were performed to determine the accuracy and variance in the system and to reduce all
possible sources of errors. These trials were performed using an NH4Cl DS and deionized
(DI) water as the FS. The evaluation trials showed that the system has high accuracy. For
example, an initial water flux of 10.34 ± 0.28 LMH was measured which is inline with
the literature. Upon the completion of the evaluation trials, desalination experiments
were performed using novel DSs and seawater as the FS. The following DSs were tested:
potassium lacatate, potassium gluconate, 1-ethyl-3-methylimidazolium acetate, magnesium
1-ethyl-3-methylimidazolium acetate, zinc 1-ethyl-3-methylimidazolium acetate and glucose. Experimental conditions were kept constant throughout the DS testing experiments
having a flow rate of one LPM, temperature in the range of 20-22 °C and a cellulose
triacetate (CTA) membrane. Potassium lactate provided the best performance for the
desalination trials, transporting 329 ± 1.51 g of water over a 24-hour period. The experimental
findings offer insights into the impact of internal concentration polarization,
highlighting that the anion’s dimensions are critical in determining the efficacy of the FO
system.
Nanomaterials will play an important role in the future of the water-energy nexus,
and developing materials for hydrogen storage is crucial to a society not reliant on fossil
fuels. Magnesium borohydride (Mg(BH4)2) is a promising candidate for hydrogen storage
because of its high theoretical gravimetric and volumetric capacity being 14.9 wt % H2
and 145 g/L respectively. The enthalpy of desorption is also favorable, ΔH0 = 38 kJ/mol
H2, thus providing an opportunity to cycle MgB2 to Mg(BH4)2 at relatively moderate
pressures and temperatures.
Various methodologies in the literature demonstrate successful synthesis of MgB2
nanomaterials, employing both top-down and bottom-up techniques. This current work
aims to synthesize MgB2 via a top-down method starting with ball-milling to homogenize
bulk MgB2, followed by heat treatment in various solvents and finally ultra-sonication in
a target solvent. XPS of the synthesized products confirmed the presence of nanosized
MgB2 along with other impurity species of MgO and B2O3.
Description
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Mechanical engineering, Materials Science, Filtration, Forward Osmosis, Nanomaterial, Osmosis
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100 pages
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