University of Twente Student Theses
Volatile Fatty Acid Adsorption and Hyperthermia Regeneration of Magnetic Nanoparticle ImpregnatedResins
Nazari Khoorasgani, Ali (2023) Volatile Fatty Acid Adsorption and Hyperthermia Regeneration of Magnetic Nanoparticle ImpregnatedResins.
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| Abstract: | Strategically reducing anthropogenic greenhouse gas emissions involves leveraging circular economies through the utilization of wastestreams and green electrification. This thesis introduces a innovative methodology for valorizing volatile fatty acids, co-produced as by-products of anaerobic digestion in biowaste streams. The proposed approach involves the utilization of an adsorptive composite material with the capability of hyperthermia regeneration, activated by Neels and Brownian relaxation mechanisms. The composite material consists of Amberlite PS/DVB XAD1180N (hydrophobic polystyrene crosslinked with divinylbenzene) resins impregnated with superparamagnetic magnetite nanoparticles (Fe3O4 functionalised with oleic acid coating, MNP). The synthesis of MNP, capable of generating heat under alternating magnetic fields (hyperthermia), is achieved through the co-precipitation method. These nanoparticles are subsequently employed for impregnation into the resins by slowly evaporating the swell-inducing solvent toluene. This process occures over a span of five hours at vacuum conditions inside a rotary evaporator, under an oscillating pressure in the range of 230-290 mbar at a fixed temperature of 80°C, or very slowly within a 15-day timeframe under a fumehood at a slight under pressure and 20°C. The impregnation process, characterized by diffusional and capillary regimes, is elucidated through a developed and validated numerical model involving unsteady-state partial differential equations, providing insights into the diffusion of magnetite nanoparticles into the resin matrix. A comprehensive characterization strategy, encompassing scanning electron microscopy (SEM) and atomic absorption spectroscopy (AAS), coupled with numerical simulations, revealed that the magnetite nanoparticle content of the composite material is 15.2% for the 15-day trial and 5.0% for the 6-hour trial. In the latter case, the diffusivity of magnetite nanoparticles was approximately 2x10 -5 μm2/s during diffusional impregnation. Moreover, hyperthermic examinations of the composite material indicate that the embedded magnetite nanoparticles within the Amberlite series resins retain their hyperthermic capabilities. A maximum specific absorption rate of 3.5±0.7 kW/kg (rate of energy per kg of magnetite nanoparticles embedded) is achieved when exposed to an alternating magnetic field of 25 mT with a frequency of 52 kHz. Additionally, zero-length column adsorption and batch adsorption experiments, in combination with HPLC and IC analyses, demonstrated that the embedding process results in a reduction of active hydrophobic adsorptive sites and may have introduced steric hindrance in adsorption rates. Specifically, the initial adsorptive capacity of polymeric beads for capturing volatile fatty acids (VFAs) is diminished by a total of 22% when tested on artificially generated representation of fermented biowaste containing VFAs and commonly found salts in wastestreams. Further investigation using SEM revealed that the MNP primarily reside in the outer shell of the beads, introducing mass transfer limitations and active site blockage. SEM images demonstrated the penetration depth of the magnetite nanoparticles was approximately 1.5 μm. Observations revealed that the stability of the magnetite nanoparticle layer on the outer shell was compromised when immersed in sonification baths or when in contact with fluids characterized by a high Reynolds number. Accordingly, this proof of concept signifies viability within laminar flow conditions. |
| Item Type: | Essay (Master) |
| Faculty: | TNW: Science and Technology |
| Subject: | 35 chemistry |
| Programme: | Chemical Engineering MSc (60437) |
| Link to this item: | https://purl.utwente.nl/essays/97726 |
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