Matching Items (5)
Mixed-ionic electronic conducting (MIEC) oxides have drawn much attention from researchers because of their potential in high temperature separation processes. Among many materials available, perovskite type and fluorite type oxides are the most studied for their excellent oxygen ion transport property. These oxides not only can be oxygen adsorbent or O2-permeable membranes themselves, but also can be incorporated with molten carbonate to form dual-phase membranes for CO2 separation.
Oxygen sorption/desorption properties of perovskite oxides with and without oxygen vacancy were investigated first by thermogravimetric analysis (TGA) and fixed-bed experiments. The oxide with unique disorder-order phase transition during desorption exhibited an enhanced oxygen desorption rate during the TGA measurement but not in fixed-bed demonstrations. The difference in oxygen desorption rate is due to much higher oxygen partial pressure surrounding the sorbent during the fixed-bed oxygen desorption process, as revealed by X-ray diffraction (XRD) patterns of rapidly quenched samples.
Research on using perovskite oxides as CO2-permeable dual-phase membranes was subsequently conducted. Two CO2-resistant MIEC perovskite ceramics, Pr0.6Sr0.4Co0.2Fe0.8 O3-δ (PSCF) and SrFe0.9Ta0.1O3-δ (SFT) were chosen as support materials for membrane synthesis. PSCF-molten carbonate (MC) and SFT-MC membranes were prepared for CO2-O2 counter-permeation. The geometric factors for the carbonate phase and ceramic phase were used to calculate the effective carbonate and oxygen ionic conductivity in the carbonate and ceramic phase. When tested in CO2-O2 counter-permeation set-up, CO2 flux showed negligible change, but O2 flux decreased by 10-32% compared with single-component permeation. With CO2 counter-permeation, the total oxygen permeation flux is higher than that without counter-permeation.
A new concept of CO2-permselective membrane reactor for hydrogen production via steam reforming of methane (SRM) was demonstrated. The results of SRM in the membrane reactor confirm that in-situ CO2 removal effectively promotes water-gas shift conversion and thus enhances hydrogen yield. A modeling study was also conducted to assess the performance of the membrane reactor in high-pressure feed/vacuum sweep conditions, which were not carried out due to limitations in current membrane testing set-up. When 5 atm feed pressure and 10-3 atm sweep pressure were applied, the membrane reactor can produce over 99% hydrogen stream in simulation.
Global warming resulted from greenhouse gases emission has received widespread attention. Meanwhile, it is required to explore renewable and environmentally friendly energy sources due to the severe pollution of the environment caused by fossil fuel combustion. In order to realize a substantial adsorption process to resolve the environmental issues, the development of new adsorbents with improved properties has become the most critical issue. This dissertation presents the work of four individual but related studies on systematic characterization and process simulations of novel adsorbents with superior adsorption properties.
A perovskite oxide material, La0.1Sr0.9Co0.9Fe0.1O3-δ (LSCF1991), was investigated first for high-temperature air separation. The oxygen sorption/desorption behavior of LSCF1991 was studied by thermogravimetric analysis (TGA) and fixed-bed breakthrough experiments. A parametric study was performed to design and optimize the operating parameters of the high-temperature air separation process by pressure swing adsorption (PSA). The results have shown great potential for applying LSCF1991 to the high-temperature air separation due to its excellent separation performance and low energy requirement.
Research on using nanostructured zeolite NaX (NZ) as adsorbents for CO2 capture was subsequently conducted. The CO2/N2 adsorption characterizations indicated that the NZ samples lead to enhanced adsorption properties compared with the commercial zeolites (MZ). From the two-bed six-step PSA simulation, NZ saved around 30% energy over MZ for CO2 capture and recovery while achieving a higher CO2 purity and productivity.
A unique screening method was developed for efficient evaluation of adsorbents for PSA processes. In the case study, 47 novel adsorbents have been screened for coal bed methane (CBM) recovery. The adsorbents went through scoring-based prescreening, PSA simulation, and optimization. The process performance indicators were correlated with the adsorption selectivity and capacities, which provides new insights for predicting the PSA performance.
A new medium-temperature oxygen sorbent, YBaCo4O7+δ (YBC114), was investigated as an oxygen pumping material to facilitate solar thermochemical fuel production. The oxygen uptake and release attributes of YBC114 were studied by both TGA and a small-scale evacuation test. The study proved that the particle size has a significant effect on the oxygen pumping behavior of YBC114, especially for the uptake kinetics.
Carbon capture is an essential way to reduce greenhouse gas emissions. One way to decrease the emissions is through the use of adsorbents such as zeolites. Dr. Dong-Kyun Seo’s group (School of Molecular Sciences, Arizona State University) synthesized the nanostructured faujasite (NaX). The zeolite was characterized using Scanning Electron Microscopy (SEM) and the physisorption properties were determined using ASAP 2020. ASAP 2020 tests of the nano-zeolite pellets at 77K in a liquid N2 bath determined the BET surface area of 547.1 m2/mol, T-plot micropore volume of 0.2257 cm3/g, and an adsorption average pore width of 5.9 Å. The adsorption isotherm (equilibrium) of CH4, N2, and CO2 were measured at 25ºC. Adsorption isotherm experiments concluded that the linear isotherm was the best fit for N2, and CH4 and the Sips isotherm was a better fit than the Langmuir and Freundlich isotherm for CO2. At 25ºC and 1 atm the zeolite capacity for CO2 is 4.3339 mmol/g, 0.1948 mmol/g for CH4, and 0.3534 mmol/g for N2. The zeolite has a higher CO2 capacity than the conventional NaX zeolite. Breakthrough experiments were performed in a fixed bed 22in, 0.5 in packing height and width at 1 atm and 298 K with nano-zeolite pellets. The gas chromatographer tested and recorded the data every two minutes with a flow rate of 10 cm3/min for N2 and 10 cm3/min CO2. Breakthrough simulations of the zeolite in a fixed bed adsorber column were conducted on MATLAB utilizing varying pressures, flow rates, and fed ratios of various CO2, N2 and CH4. Simulations using ideal adsorbed solution theory (IAST) calculations determined that the selectivity of CO2 in flue gas (15% CO2 + 85% N2) is 571.79 at 1 MPa, significantly higher than commercial zeolites and literature. The nanostructured faujasite zeolite appears to be a very promising adsorbent for CO2/N2 capture from flue gas and the separation of CO2/N2.
This honors thesis is focused on two separate catalysis projects conducted under the mentorship of Dr. Javier Pérez-Ramírez at ETH Zürich. The first project explored ethylene oxychlorination over supported europium oxychloride catalysts. The second project investigated alkyne semihydrogenation over nickel phosphide catalysts. This work is the subject of a publication of which I am a co-author, as cited below.
Project 1 Abstract: Ethylene Oxychlorination
The current two-step process for the industrial process of vinyl chloride production involves CuCl2 catalyzed ethylene oxychlorination to ethylene dichloride followed by thermal cracking of the latter to vinyl chloride. To date, no industrial application of a one-step process is available. To close this gap, this work evaluates a wide range of self-prepared supported CeO2 and EuOCl catalysts for one-step production of vinyl chloride from ethylene in a fixed-bed reactor at 623 773 K and 1 bar using feed ratios of C2H4:HCl:O2:Ar:He = 3:3 6:1.5 6:3:82 89.5. Among all studied systems, CeO2/ZrO2 and CeO2/Zeolite MS show the highest activity but suffer from severe combustion of ethylene, forming COx, while 20 wt.% EuOCl/γ-Al2O3 leads to the best vinyl chloride selectivity of 87% at 15.6% C2H4 conversion with complete suppression of CO2 formation and only 4% selectivity to CO conversion for over 100 h on stream. Characterization by XRD and EDX mapping reveals that much of the Eu is present in non-active phases such as Al2Eu or EuAl4, indicating that alternative synthesis methods could be employed to better utilize the metal. A linear relationship between conversion and metal loading is found for this catalyst, indicating that always part of the used Eu is available as EuOCl, while the rest forms inactive europium aluminate species. Zeolite-supported EuOCl slightly outperforms EuOCl/γ Al2O3 in terms of total yield, but is prone to significant coking and is unstable. Even though a lot of Eu seems locked in inactive species on EuOCl/γ Al2O3, these results indicate possible savings of nearly 16,000 USD per kg of catalyst compared to a bulk EuOCl catalyst. These very promising findings constitute a crucial step for process intensification of polyvinyl chloride production and exploring the potential of supported EuOCl catalysts in industrially-relevant reactions.
Project 2 Abstract: Alkyne Semihydrogenation
Despite strongly suffering from poor noble metal utilization and a highly toxic selectivity modifier (Pb), the archetypal catalyst applied for the three-phase alkyne semihydrogenation, the Pb-doped Pd/CaCO3 (Lindlar catalyst), is still being utilized at industrial level. Inspired by the very recent strategies involving the modification of Pd with p-block elements (i.e., S), this work extrapolates the concept by preparing crystalline metal phosphides with controlled stoichiometry. To develop an affordable and environmentally-friendly alternative to traditional hydrogenation catalysts, nickel, a metal belonging to the same group as Pd and capable of splitting molecular hydrogen has been selected. Herein, a simple two-step synthesis procedure involving nontoxic precursors was used to synthesize bulk nickel phosphides with different stoichiometries (Ni2P, Ni5P4, and Ni12P5) by controlling the P:Ni ratios. To uncover structural and surface features, this catalyst family is characterized with an array of methods including X-ray diffraction (XRD), 31P magic-angle nuclear magnetic resonance (MAS-NMR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Bulk-sensitive techniques prove the successful preparation of pure phases while XPS analysis unravels the facile passivation occurring at the NixPy surface that persists even after reductive treatment. To assess the characteristic surface fingerprints of these materials, Ar sputtering was carried out at different penetration depths, reveling the presence of Ni+ and P-species. Continuous-flow three-phase hydrogenations of short-chain acetylenic compounds display that the oxidized layer covering the surface is reduced under reaction conditions, as evidenced by the induction period before reaching the steady state performance. To assess the impact of the phosphidation treatment on catalytic performance, the catalysts were benchmarked against a commercial Ni/SiO2-Al2O3 sample. While Ni/SiO2-Al2O3 presents very low selectivity to the alkene (the selectivity is about 10% at full conversion) attributed to the well-known tendency of naked nickel nanoparticles to form hydrides, the performance of nickel phosphides is highly selective and independent of P:Ni ratio. In line with previous findings on PdxS, kinetic tests indicate the occurrence of a dual-site mechanism where the alkyne and hydrogen do not compete for the same site.
This work is the subject of a publication of which I am a co-author, as cited below.
D. Albani; K. Karajovic; B. Tata; Q. Li; S. Mitchell; N. López; J. Pérez-Ramírez. Ensemble Design in Nickel Phosphide Catalysts for Alkyne Semi-Hydrogenation. ChemCatChem 2019. doi.org/10.1002/cctc.201801430
Carbon capture has been a highly sought-after technology for decades because of its<br/>capabilities to restore atmospheric damage done by greenhouse gasses. Thanks to evolving<br/>separation techniques, carbon capture is becoming more efficient with every new discovery in<br/>the field. Currently the biggest problems that carbon capture are facing is the cost of<br/>manufacturing material to aid the process and obtaining ideal conditions for removal of carbon<br/>from air and devising solutions for removal of CO2 in ambient and flue gas conditions.<br/>This Honors Thesis is a continuation of Dr. Shuguang Deng and Dr. Mai Xu’s research<br/>initiative to manufacture and test various zeolitic CO2 removal efficiencies. The goals of this<br/>Honors Thesis are to investigate the adsorption/desorption kinetics and isothermal equilibrium<br/>CO2 capacity of a NaX nanozeolite under ambient air conditions.<br/>What was determined from the following testing was that the zeolite of interest had a<br/>higher adsorption capacity of CO2 at lower temperatures, had a maximum equilibrium quantity<br/>adsorbed of 0.203 mmol/g for CO2 and 0.367 mmol/g of N2, had a maximum breakthrough CO2<br/>capacity of 0.101 mmol of CO2 per gram of zeolite at dry conditions and 298.15K and this<br/>linearly decreased to 0.040 mmol/g at 25% relative humidity.