Synthesis and performance evaluation of nanocomposite ceramic-sodalite membranes for pre-combustion CO2 capture

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science in Engineering. 9 February, 2017Global climate change and other environmental disasters have been attributed to continuous anthropogenic carbon dioxide (CO2) emission into the atmosphere. Today, researchers are constantly seeking measures to reduce anthropogenic CO2 emission. Traditionally, absorption technology with use of monoethanolamine (MEA) is used for separating / capturing of anthropogenic CO2. However, the use of MEA is associated with numerous shortcomings, including inefficient energy usage, high operating and capital cost, amine degradation, solvent loss and excessive equipment corrosion. Alternatively, zeolite based membrane systems are promising technique that prove handy and useful than the traditional processes (absorption with monoethanolamine). However, zeolitic membranes with zeolite coating on the supports (i.e. thin-film supported zeolite membranes) are susceptible to abrasion and thermal shock at elevated temperatures due to temperature mismatch between the supports and the membranes, making them to lose selectivity at early stages. On the contrary, nanocomposite architecture membranes, synthesized via pore-plugging hydrothermal route, are more thermally stable and membrane defects are controlled. Nanocomposite zeolite (sodalite) membranes have been proposed for gas separations, most importantly in the separation of H2/CO2, a major component in pre-combustion carbon capture. In addition, sodalite, a porous crystalline zeolite made up of cubic array of β-cages as primary building block having cage aperture in the range of 0.26 and 0.29 nm, is a potential candidate for the separation/purification of light molecules such as hydrogen which has a cage aperture of 0.27 nm under certain process conditions. In this work, nanocomposite architecture hydroxy sodalite membrane with sodalite crystals embedded within α-alumina tubes were successfully synthesized using the pore-plugging hydrothermal synthesis technique and characterized using techniques such as scanning electron microscopy (SEM) and X-ray diffraction (XRD). The morphology of the synthesized membranes shows that sodalite crystals were indeed grown within the porous structures of the support. Furthermore, Basic Desorption Quality Test (BDQT) and gas separation measurement were conducted to evaluate the quality of the as-synthesized membrane in industrial gas separation applications. The effects of operating variables such as pressure at 1.1 bar, 2.0 bar and 3.0 bar. Also, the effects of temperature were conducted on the nanocomposite membrane at 373 K, 423 K and 473 K. Finally, the gases permeation results were fitted with the well-known Maxwell-Stefan model. Results indicated that, the nanocomposite sodalite / ceramic membrane is a potential candidate for removal of H2 from H2/CO2 mixture. The gas permeation measurement from the one-stage nanocomposite membrane shows that the membrane displayed H2 and CO2 permeance of 3.9 x 10-7 mols-1m-2Pa-1 and 8.4 x 10-8 mols-1m-2Pa-1, respectively. However, the morphology of two-stage nanocomposite membrane shows that the support was more plugged with sodalite crystals and the permeance of H2 and CO2 were 7.4 x 10-8 mol.s-1.m-2.Pa-1 and 1.1 x 10-8 mol.s-1.m-2.Pa-1, respectively. Consequently, the H2/CO2 ideal selectivity for the one-stage nanocomposite membrane improved from 4.6 to 6.5 in the two-stage nanocomposite membrane. In conclusion, the two-stage synthesized membrane shows better improvement. The porous support was well plugged and separation performance was evaluated. However, occluded organic matters present in the cages of hydroxy sodalite could have adverse effect on the gas permeation performance of the membrane. It is expected that an organic-free sodalite supported membrane (such as silica sodalite supported membrane) could out-perform the hydroxy sodalite supported membrane reported in this work in term of membrane flux because there will be enough pore space for gas permeation.MT201

Microbial cell immobilization in biohydrogen production: a short overview

The high dependence on fossil fuels has escalated the challenges of greenhouse gas emissions and energy security. Biohydrogen is projected as a future alternative energy as a result of its non-polluting characteristics, high energy content (122 kJ/g), and economic feasibility. However, its industrial production has been hampered by several constraints such as low process yields and the formation of biohydrogen-competing reactions. This necessitates the search for other novel strategies to overcome this problem. Cell immobilization technology has been in existence for many decades and is widely used in various processes such as wastewater treatment, food technology, and pharmaceutical industry. In recent years, this technology has caught the attention of many researchers within the biohydrogen production field owing to its merits such as enhanced process yields, reduced microbial contamination, and improved homogeneity. In addition, the use of immobilization in biohydrogen production prevents washout of microbes, stabilizes the pH of the medium, and extends microbial activity during continuous processes. In this short review, an insight into the potential of cell immobilization is presented. A few immobilization techniques such as entrapment, adsorption, encapsulation, and synthetic polymers are discussed. In addition, the effects of process conditions on the performance of immobilized microbial cells during biohydrogen production are discussed. Finally, the review concludes with suggestions on improvement of cell immobilization technologies in biohydrogen production

Design and engineering of nanostructured liquid metal composites for catalytic applications

This thesis concentrated on the study of the room temperature liquid metal, gallium and its eutectics. The application of liquid metal-based alloys to new areas of catalysis was extended by encompassing energy and environmental applications. A significant advancement in the potential application of liquid metal-based alloys in electrocatalysis, photocatalysis and sonocatalysis has resulted from this research. Significantly, research conducted on carbon dioxide capture/conversion to metal carbonates during this graduate study is currently being explored for industrial waste management

Impacts Of Capital Flight On Economic Growth In Nigeria

This study examines the impacts of capital flight on economic growth in Nigeria between 1980 and 2012. The study used co-integration, Ordinary Least Square (OLS) and Error Correction Mechanism (ECM) as its main estimation techniques. The evidence, however, shows that capital flight, foreign reserve, external debt, foreign direct investment and current account balance co-integrate with Gross Domestic Product (GDP) in Nigeria within the year under study. It was also discovered that capital flight had negative impact on the economy. Based on the empirical findings, it is recommended that the government should create an enabling environment for profitable investment and offer foreign investors attractive incentives as this will reduce the occurrence of capital flight from Nigeria and lead to sustainable growth and development

Nanocomposite Architecture Hydroxy Sodalite/α-Alumina Membrane for CO2 Capture

The continuous anthropogenic carbon dioxide (CO2) emission into the atmosphere in the past decades with its associated global climate changes and other environmental disasters has received substantial attention worldwide. Other greenhouse gases (GHG) such as methane are likewise emitted but research findings indicated CO2 as the major pollutant, requiring urgent attention to combat climate change. Thus mitigating the climate change through reduction of CO2 emission constitutes a technological and scientific challenge [1]. However, numerous technologies (absorption, adsorption and membrane technology) for CO2 capture from power plants have been proposed and evaluated. Presently, the most advance and mature technique for CO2 capture is absorption technology using monoethanolamine (MEA), but this technology is considered cost and energy inefficient and the amine solvent (monoethanolamine) possesses low stability at elevated temperature [1]. The development of superior and advance materials with considerable lower energy and cost penalty is essential. Therefore one of the promising candidate is membrane technology and zeolite based membrane systems prove to handy and useful than the traditional processes [2] . Zeolite membranes have found tremendous uses in the industry for separation and purification application. For instance, hydroxy sodalite (SOD membranes are known to possess high chemical and thermal stability up to 450oC) [3]. However, commercial applications of zeolite based membranes are hampered by high cost of support and poor reproducibility. Moreover, zeolite membrane with zeolite coating on the support (i.e. thin-film supported zeolite membranes) are susceptible to abrasion and thermal shock at high temperature due to temperature mismatch caused by difference in thermal expansion of the zeolite material and the support, making them to lose selectivity very fast. On the contrary, nanocomposite architecture membranes obtained via pore-plugging hydrothermal synthesis protocol are more thermally stable and membrane defects are controlled [4, 5]. In this work, a nanocomposite architecture hydroxy sodalite membrane with zeolite crystals embedded within an α-alumina tube was synthesized using the pore-plugging hydrothermal synthesis technique and characterized. The as-prepared membrane was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM). The results obtained from these characterization techniques reveal that sodalite crystals were indeed grown within the porous structures of the support. In addition, the XRD analysis reveals the formation of sodalite crystals within the support. In addition, Small Angle X-Ray Scattering (SAXS) confirmed structural information such as particle size, shape and internal structure of SOD crystals. Since the average cage dimension of hydroxy sodalite is 0.265 nm, similar to the molecular size of an H2 (0.27 nm), the successfully synthesized membrane will be evaluated for removal of H2 from H2/CO2 mixture, a mixture that is obtained from pre-combustion after gasification in an Integrated Gasification Combined Cycle (IGCC) during power generation

Galvanic Replacement of Liquid Metal Galinstan with Copper for the Synthesis of Core-Shell Cuga-Cu2O Nanomaterials

Anthropogenic carbon dioxide (CO2), resulting from the world’s persistent reliance on fossil fuels as the principal source of energy, has perturbed and induced an imbalance in the natural carbon-cycle. This increased CO2 emission into the environment has been implicated in global warming and other environmental issues1. Therefore, coupling a sustainable energy system with carbon dioxide reduction to produce valuable chemical compounds is being thoroughly investigated1. Among the techniques developed for selective CO2 conversion, electrochemical CO2 reduction is regarded as one of the most appealing due to mild operating conditions and use of renewable energy to power the process. Theoretically, electrochemical CO2 reduction largely depends on the adsorption energies of intermediate species, therefore, metal-based catalysts (Pt, Au, Pd, Ag, Sn, Cu, In, and etc.) are commonly employed which can influence the overall system selectivity. In particular, Cu-based catalysts have shown reasonable activity and potential for selectivity for this reaction owing to moderate adsorption energy for intermediate species on Cu. In addition, Cu is one of the few inexpensive metals that can catalytically convert CO2 to a variety of useful chemicals under environmental conditions (room temperature and atmospheric pressure) via a multi-electron transfer process. Although Cu catalysts show interesting CO2 reduction properties, they still suffer from selectivity issues to generate a desired single product at scale 2. A recent development is in the area of room temperature liquid metals where the catalytic activity of liquid metal Galinstan has begun to be explored 3. Although in its infancy, we hypothesized that a multi-metallic electrocatalyst of galinstan (GaInSn) and Cu could be active for electrocatalytic and photocatalytic reactions such as CO2 reduction and dye degradation considering that Ga alloys with most metals and should therefore influence the electronic properties of Cu. Previous work has shown that the catalytic activity of multi-metallic electrocatalysts is superior to their mono and bimetallic electrocatalysts counterparts 4. Hence, multi-metallic electrocatalysts exhibit different electronic structures, crystallinity as a result of the interplay of geometric, ligand and electronic effects 5. To date, no report is available in the open literature reporting the alloying of liquid metal GaInSn and Cu via galvanic replacement. Herein, we report the simple synthesis of a multi-metallic nanostructure comprising of a CuGa core with trace In and Sn and a surface layer of Cu2O and Ga2O3. The material was characterized using Scanning Electron Microscopy (SEM), Grazing Incidence X-ray Diffraction (GIXRD), X-ray Photoelectron Spectroscopy (XPS), Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) and Transmission Electron Microscopy (TEM). The SAED and TEM images indicate that the core alloy is polycrystalline with well-defined lattice fringes with the presence of crystalline Cu2O and an amorphous region (resulting from gallium oxide). The presence of surface semiconducting oxides with an underlying metal core should in principle be an appropriate system for separating charge carriers under photoexcitation thereby facilitating organic molecule degradation studies. The multi-metallic nanostructure was therefore engineered towards electrochemical CO2 reduction and photocatalytic pollutant degradation. The preliminary investigation on the photocatalytic activity of this material using Toluidine Blue (TB) under visible light irradiation indicates excellent photocatalytic activity. References N. S. Lewis and D. G. Nocera, Proceedings of the National Academy of Sciences of the United States of America, 2006, 103, 15729-15735. H. Xie, T. Wang, J. Liang, Q. Li and S. Sun, Nano Today, 2018, 21, 41-54. F. Hoshyargar, H. Khan, K. Kalantar-zadeh and A. P. O'Mullane, Chemical Communications, 2015, 51, 14026-14029. E. A. Redekop, V. V. Galvita, H. Poelman, V. Bliznuk, C. Detavernier and G. B. Marin, ACS Catalysis, 2014, 4, 1812-1824. X. L. Tian, L. Wang, P. Deng, Y. Chen and B. Y. Xia, Journal of Energy Chemistry, 2017, 26, 1067-1076. Figure

Platinum-Gallium (PtGa) Nanoparticles Engineered via the Galvanic Replacement Reaction of the Liquid Metal Galinstan with Platinum

The world’s persistent reliance on fossil fuels as the principal source of energy has been linked with anthropogenic climate change and other environmental issues. Nowadays, developing and developed nations aim at improving their standards of living, which would simultaneously result in increased energy demand/consumption [1]. Renewal energy is a captivating alternative to non-renewal sources (fossil fuel) but they are intermittent. Alternatively, numerous technologies are being explored for the remediation of industrial pollutants which includes: heavy metal ion sensing, photoreduction of carbon dioxide (CO2) and etc. Advanced oxidation processes (AOPs) such as photocatalysis has been extensively studied, which has been widely applied to hydrogen evolution reactions (HER), alcohol oxidation reactions (AORs), as well as artificial photosynthesis. Traditionally, TiO2 is one of the most investigated catalysts, however, TiO2 cannot effectively absorb visible light owing to its large band gap, thus it is ineffective and unstable [2]. Recently, nanostructured materials are considered a potential candidate for AOPs due to their unconventional properties. For instance, gallium is a non-toxic liquid metal possessing excellent rheological properties (low-melting, high thermal & electrical conductivity). Although, gallium and its eutectic are known to passivate when exposed to over 1 ppm of oxygen [3]. Notwithstanding, engineering & surface modification could be used to enhance the efficiency of gallium-based alloys. However, few reports are available on alloying of catalytically active low-cost liquid metal galinstan and other precious metal, Pt. To the best of our knowledge, no such investigation has been carried out on galvanic replacement reaction of galinstan & Pt at room temperature. Herein, we report the synthesis of PtGa NPs, based on the galvanic replacement reaction of the liquid metal galinstan, such that gallium is embellished by PtGa NPs. A facile galvanic replacement technique was successfully applied for the synthesis of multi-metallic alloys composed mainly of Pt, Ga, and traces of In and Sn. The figure below depicts the galvanic replacement reaction process of Pt & Ga. The as-prepared PtGa NPs were characterized using scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy & transmission electron microscopy for a physiochemical characterization of this material. The results confirmed that an alloy of Pt & Ga is formed via the galvanic replacement reaction. TEM result suggests that the alloy is polydisperse with particle size ranging between 1.0 and 60.0 nm, while the HRTEM shows that the NPs are crystalline. Furthermore, alcohol oxidation of methanol and ethanol were carried out, the electrochemical experiments showed that the PtGa NPs have high activity for methanol than ethanol in alkaline media. This indicates a promising application of PtGa NPs in alkaline direct methanol fuel cells

Nanocomposite sodalite/ceramic membrane for pre-combustion CO2 capture: synthesis and morphological characterization

Carbon capture and storage (CCS) is amongst the possible options to reduce CO2 emission. In the application of CCS, CO2 capture techniques such as adsorption and membrane system have been proposed due to less energy requirement and environmental benign than the absorption process. However, membrane system has drawbacks such as poor membrane reproducibility, scale-up difficulty and high cost of the membrane supports. In this study synthesis and characterization of nanocomposite sodalite (HS)/ceramic membrane via “pore-plugging” hydrothermal synthesis (PPH) protocol for pre-combustion CO2 capture is reported. The morphology and crystallinity of the as-prepared membranes were checked with scanning electron microscopy and X-ray diffraction. Surface chemistry of the membrane was examined with Fourier Transform Infrared spectroscopy. In nanocomposite architecture membranes, zeolite crystals are embedded within the pores of the supports instead of forming thin-film layers of the zeolite crystals on the surface of the supports. Compared to the conventional in situ direct hydrothermal synthesis, membranes obtained from PPH possess higher mechanical strength and thermal stability. In addition, defect control with nanocomposite architecture membranes is possible because the zeolite crystals are embedded within the pores of the support, thereby limiting the maximum defect size to the pore size of the support. Furthermore, the nanocomposite architecture nature of the membranes safeguards the membrane from shocks or abrasion that could promote formation of defects. The aforementioned advantages of the nanocomposite architecture membranes could be beneficial in developing high performance and cost-effective membrane materials for pre-combustion CO2 capture.</p

Evaluation of highly active platinum-gallium (PtGa) nanoparticles, synthesized via the galvanic replacement reaction of the liquid metal galinstan with platinum

When considering the human quest for an improved standard of living, fossil fuel consumption has tremendously intensified and adversely depleted beyond the rate at which they are renewed within the earth crust. Besides, the combustion of fossil fuels has been directly implicated in the imbalance of the carbon cycle (anthropogenic CO2 emission) leading to global warming and environmental degradation. Hence, urgent attention is required to address the aforementioned challenges, such that a greener, sustainable, renewable, highly efficient energy conversion and storage system could serve as an alternative to fossil fuels. Renewable energy technologies which utilize energy sources such as solar, and biofuel (for example, bio-ethanol produced sustainably) are considered as a suitable alternative. Advanced Oxidation Processes (AOPs) including electrocatalysis and photoelectrocatalysis are currently topics of significant interest for fuel generation and energy conversion. To implement these technologies, many nanocatalysts have been engineered and evaluated. Precious metal (Platinum, Pt) based catalysts have been intensively investigated for alcohol oxidation reactions related to direct methanol and ethanol fuel cells, and they have shown excellent performance, nonetheless, Pt exhibits low resistance to carbon monoxide, leading to catalyst poisoning and degradation in performance. Furthermore, Pt is expensive and sparsely distributed in the earth crust. Incorporation of low-cost metals such as liquid metal galinstan could improve Pt utilisation and decrease cost. The catalytic activity of multi-metallic electrocatalysts are largely influenced by size, morphology, stabilizing agents, proportions of active sites and therefore exhibit different electronic structures, crystallinity as a result of the interplay of geometric, ligand and electronic effects. The catalytic activity of liquid metal-based composites is in its infancy but may be an opportunity to create new materials that are active for specific types of reactions. Therefore, engineering and surface modification of galinstan with platinum could provide synergy between Ga and Pt, and be a way to create a nanostructured PtGa catalyst. Till date, few reports are available on alloying liquid metal galinstan and other precious metals. To the best of our knowledge, no such investigation has been carried out on galvanic replacement reaction of galinstan with Pt at room temperature. Herein, we report the synthesis of PtGa nanoparticles (NPs), based on the galvanic replacement reaction of the liquid metal galinstan, such that gallium is surrounded by PtGa NPs. The as-prepared PtGa NPs were characterized using scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy for a physiochemical characterization. TEM result suggests that the alloy is polydisperse with particle sizes ranging between 1.0 and 60.0 nm, while the HRTEM shows that the NPs are crystalline. Furthermore, oxidation of methanol and ethanol were carried out, where the electro-oxidation experiments showed that the PtGa NPs have a higher activity for methanol than ethanol in alkaline media. This indicates a promising application of PtGa NPs in alkaline direct methanol fuel cells

Sonochemical synthesis of Ga/ZnO nanomaterials from a liquid metal for photocatalytic applications

The effective degradation of synthetic dyes via photocatalysis using abundant cheap materials is an ongoing challenge. Often photocatalysts are costly and employ complex fabrication processes that give limited efficiency which therefore inhibits widespread industrial proliferation. To address this issue, a simple room temperature alloying process followed by sonication for the preparation of photocatalytically active GaZnO nanosheets confined on a metallic GaZn core is reported. The material is characterized with X-ray diffraction, X-ray photoelectron spectroscopy, inductively coupled plasma optical emission spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, and electrochemical techniques. These analyses confirm the presence of a metallic GaZn core decorated with GaZnO nanosheets. The resultant GaZn/GaZnO catalyst exhibits excellent photocatalytic activity for the degradation of methyl orange. A high degradation efficiency of 73% is achieved under solar simulated conditions which is attributed to the GaZn core acting as an electron sink allowing for effective charge carrier separation at the surface confined GaZnO sheets and the production of reactive oxygen species.</p