ETD Collection

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Subject: search.filters.subject.Nanotubes--Carbon content

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    Synthesis of carbon nanotubes - polyphenylene sulfone composite membranes for waste water treatment from petroleum sources
    (2017) Phasha, Motshamonyane Jacob
    Oil and gas operations produce high volumes of wastewater in the form of finely dispersed oil/ water (o/w) emulsions, which have detrimental effects on the environment. The current most feasible method used to mitigate the environmental impacts caused by the emulsion (produced water) from oil and gas operations is polymer membrane technology. However, polymer membranes are susceptible to fouling and concentration polarization, which leads to the necessity for frequent membrane replacement, thus loss of operating time and high operation cost. This motivates the need to investigate ways of modifying the polymer membrane in order to make it more resistant to fouling and concentration polarization. This study is concerned with circumventing the challenges experienced by polymer membrane during crude oil/ water mixture ultra-filtration by infusing the polymer membrane with nano particles. The aim of the research was to investigate the influence of addition of CNTs on the modified membranes in treatment of waste water from petroleum source. The Wet Impregnation method was used for the preparation of the bimetallic catalyst (Fe-Co catalyst supported on Zeolite), Chemical vapor deposition (CVD) method was used to prepare the carbon nanotubes (CNTs) and Phase inversion (PI) method was used for the preparation of the polymer nanocomposite membrane. The bimetallic catalyst was characterized using scanning electron microscope (SEM) and X-ray diffraction (XRD). The CNTs were characterized using Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and Transmission electron microscopy (TEM). The prepared polymer nanocomposite membranes were characterized using SEM, FTIR, goniometer (for contact angles) and TAXT plus texture analyzer (for tensile strength test). Functionalized carbon nanotubes were used as membrane fillers or modifiers to improve the filtration properties of the polymeric membrane, ultimately forming nanocomposite polymer membranes. This increased hydrophilicity, chemical, mechanical and physical properties of the polymer membrane, made them to perform better during filtration than pristine polymer membranes. The performance of the nanocomposite membranes were evaluated and it was determined that the nanocomposite polymer membrane with a loading 0.4 wt.% functionalized carbon nanotubes performed better than pristine membrane and other CNTs loaded nanocomposite polymer membranes. The pristine membrane (0 wt% CNTs) showed a higher contact angle (79o) which crosses ponds to the inability to soak up water. The 0.4 wt% nanocomposite polymer membrane showed the lowest contact angle of 72 o, this validated an improvement in the properties of the membrane, in particular hydrophilicity. The 0.4 wt% nanocomposite polymer membrane showed a superior mechanical strength, with a breaking force at 4 N relative to the other membranes of the same thickness. 0.4 wt% nanocomposite polymer membrane showed the highest permeate flux of 120 L/m2.h compared to the pristine membrane, which showed a permeate flux of 63 L/m2.h. The permeate flux of 0.4 wt% nano-composite polymer membrane increased with the operating pressure.
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    A CO2 capture technology using carbon nanotubes with polyaspartamide surfactant
    (2016-07-13) Ngoy, Jacob Masiala
    Technologies for the separation of CO2 from flue gas require a feat of engineering for efficient achievement. Various CO2 capture technologies, including absorption, adsorption, cryogenics and membranes, have been investigated globally. The absorption technology uses mainly alkanolamine aqueous solutions, the most common being monoethanolamine (MEA); however, further investigation is required to circumvent its weakness due to degradation through oxidation, material corrosion and high energy costs required for regeneration. Attractive advantages in adsorption technology, including the ability to separate the more diluted component in the mixture with a low energy penalty, have been a motivation for many researchers to contribute to the advancement of adsorption technology in CO2 capture. The challenge in CO2 adsorption technology is to design a hydrophobic and biodegradable adsorbent with large CO2 uptake, high selectivity for CO2, adequate adsorption kinetics, water tolerance, and to require low levels of energy for regeneration processes. The existing adsorbent such as activated carbon, silica gel, zeolites, metal organic frameworks and others, have been ineffective where moisture occurs in flue gas. This work provides an advanced adsorption technology through a novel adsorbent, MWNT-PAA, designed from the noncovalent functionalization of multi-walled carbon nanotubes (MWNTs) by polyaspartamide (PAA) as product of amine grafted to polysuccinimide (PSI). Three types of PAA were prepared using ethylenediamine (EDA), 1, 3 propanediamine (PDA) and monoethanolamine (MEA) drafted to PSI to give PSI-EDA, PSI-PDA and PSI-MEA respectively. The CO2 adsorption capacity was 13.5 mg-CO2/g for PSI-PDA and 9.0 mg-CO2/g for PSI-MEA, which decreased significantly from PSI where the CO2 adsorption capacity was 25 mg-CO2/g. PSIEDA was selected as PAA, because the CO2 adsorption capacity was 52 mg-CO2/g which doubled from PSI. The polymer polyethylenimine (PEI), the most commonly polymer used in CO2 capture, was found to be non-biodegradable, while the polymer PAA showed the presence of CONH as a biodegradable bond functionality, occurring in the MWNT-PAA, as confirmed through Fourier Transform Infrared (FTIR) analysis. The adsorbent MWNT-PAA was demonstrated to have a water tolerance in the temperature range 25-55 ℃, where CO2 adsorption capacity increased with the increase of water in the adsorbent. The highest CO2 adsorption capacity recorded was 71 mg-CO2/g for the moist MWNT-PAA using 100% CO2 and 65 mg-CO2/g for the mixture of 14% CO2 with air. Under the same conditions, the dry MWNT-PAA adsorbed 70 and 46 mg-CO2/g respectively (100%, 14% CO2). The 2 regenerability efficiency of the MWNT-PAA absorbent was demonstrated at 100 ᵒC; after 10 cycles of adsorption-desorption 99% of adsorbed gas was recovered in the desorption process. The heat flow for the thermal swing adsorption system resulted in the net release of heat over the complete cycle; a cycle includes adsorption (heat release) and desorption (heat absorbance). Thus, this MWNT-PAA adsorbent demonstrates an advantage in terms of overall energy efficiency, and could be a competitive adsorbent in CO2 capture technology.