Browsing by Author "Amini, Shahriar"

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    Carbon Capture Utilization and Storage in Methanol Production Using a Dry Reforming-Based Chemical Looping Technology
    (American Chemical Society, 2022) Ugwu, Ambrose; Osman, Mogahid; Zaabout, Abdelghafour; Amini, Shahriar; Norwegian University of Science & Technology (NTNU); SINTEF; University of Alabama Tuscaloosa
    This further investigates the concept of gas switching dry reforming (GSDR) that efficiently converts the two major greenhouse gases (CO2 and CH4) into a valuable product (syngas) for gas-to-liquid (GTL) syntheses. The proposed GSDR is based on chemical looping technology but avoids external circulation of solids (metal oxides) by alternating the supply of reducing and oxidizing gas into a single fluidized bed reactor to achieve redox cycles. Each cycle consists of three steps where a metal oxide/catalyst is first reduced using GTL offgases to produce CO2 (and steam) that is supplied to the next reforming step to produce syngas for GTL processes. The metal oxide is then reoxidized in the third step associated with heat generation (through the exothermic oxidation reaction of the metal oxide and air) to provide the heat needed for the endothermic dry methane reforming step. Experimental demonstrations have shown that a syngas H-2/CO molar ratio between 1 and 2 suitable for methanol production could be achieved. A further demonstration shows that pressure has negative effects on gas conversion. Following the successful experimental campaign, process simulations were completed using ASPEN to show how the GSDR process can be integrated into a methanol (MeOH) production plant.
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    Combined Syngas and Hydrogen Production using Gas Switching Technology
    (American Chemical Society, 2021) Ugwu, Ambrose; Zaabout, Abdelghafour; Donat, Felix; van Diest, Geert; Albertsen, Knuth; Muller, Christoph; Amini, Shahriar; SINTEF; Swiss Federal Institutes of Technology Domain; ETH Zurich; University of Alabama Tuscaloosa; Norwegian University of Science & Technology (NTNU)
    This paper focuses on the experimental demonstration of a threestage GST (gas switching technology) process (fuel, steam/CO2, and air stages) for syngas production from methane in the fuel stage and H-2/CO production in the steam/ CO2 stage using a lanthanum- based oxygen carrier (La0.85Sr0.15Fe0.95Al0.05O3). Experiments were performed at temperatures between 750-950 degrees C and pressures up to 5 bar. The results show that the oxygen carrier exhibits high selectivity to oxidizing methane to syngas at the fuel stage with improved process performance with increasing temperature although carbon deposition could not be avoided. Co-feeding CO2 with CH4 at the fuel stage reduced carbon deposition significantly, thus reducing the syngas H-2/CO molar ratio from 3.75 to 1 (at CO2/CH4 ratio of 1 at 950 degrees C and 1 bar). The reduced carbon deposition has maximized the purity of the H-2 produced in the consecutive steam stage thus increasing the process attractiveness for the combined production of syngas and pure hydrogen. Interestingly, the cofeeding of CO2 with CH4 at the fuel stage showed a stable syngas production over 12 hours continuously and maintained the H-2/CO ratio at almost unity, suggesting that the oxygen carrier was exposed to simultaneous partial oxidation of CH4 with the lattice oxygen which was restored instantly by the incoming CO2. Furthermore, the addition of steam to the fuel stage could tune up the H-2/CO ratio beyond 3 without carbon deposition at H2O/ CH4 ratio of 1 at 950 degrees C and 1 bar; making the syngas from gas switching partial oxidation suitable for different downstream processes, for example, gas-to-liquid processes. The process was also demonstrated at higher pressures with over 70% fuel conversion achieved at 5 bar and 950 degrees C.
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    Development and Modelling of Self-Sufficient Wastewater Treatment with Near Zero Emissions
    (University of Alabama Libraries, 2022) Erguvan, Mustafa; Amini, Shahriar; University of Alabama Tuscaloosa
    A report published by the United Nations Water states that access to clean water will be a significant problem for more than 6 billion people by 2050 with population and water demand increasing. So as to mitigate water shortages, wastewater recovery with proper treatment can have an important contribution. Apart from water shortage, the water-energy-nexus (WEN) has been a key consideration owing to close connection and dependency of water and energy to each other. WEN also plays a key role in wastewater treatment plants (WWTPs), especially in developed countries, due to the fact that treatment of wastewater requires a significant amount of electricity usage. In this dissertation, two different models are developed to investigate the self-sufficiency of WWTPs in terms of energy with near-zero emissions. Chapter 1 discusses current and past studies involving the water energy nexus, wastewater treatment methods, activated sludge process, biomass conversion methods, anaerobic digestion, biogas utilization, self-sufficient WWTPs, CO2 capture techniques as well as oxy – fuel combustion processes. In the second chapter, a numerical model has been created to investigate the energetical self-sufficiency of a novel integrated energy system in a WWTP. The proposed system consists of an activated sludge process, an anaerobic digester, a Brayton cycle, and a Rankine cycle. In order to investigate energy and exergy efficiencies along with self-sufficiency ratio, several parametric studies have been conducted by varying some decision variables. While biological oxygen demand and dissolved oxygen level have been varied in the WWTP part, turbine inlet temperature, compression ratio, and preheater temperature have been used as decision variables in the power cycle. This work presented here suggests that up to 109% of the energy needed to treat wastewater can be provided using the proposed system. The optimum values and dominant parameters to achieve the highest self-sufficiency ratio have been determined as well. The highest exergy efficiencies for the WWTP, cogeneration system and overall system were found to be 58.36%, 44.59%, 36.6%, respectively. A subsequent study investigates the integration of activated sludge process, anaerobic digestion, and an oxyfuel combustion process in a WWTP in order to provide a plant which is not only energetically self-sufficient but also emission free. Several parametric studies have been conducted to investigate their effects on the thermodynamic efficiencies as well as self-sufficiency ratio. The most dominant factors were found to be wastewater strength and compression ratio. While the overall exergy efficiencies varied from 19.38 to 32.59%, self-sufficiency ratio changed from 82.29 to 132.4%. In addition, more than 95% of the CO2 has been captured and recycled in the combustion chamber. This study proves that an energetically self-sufficient WWTP with near zero emission is plausible.
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    Evaluation of the Environmental Impacts of Clean Hydrogen Production and CO2 Utilization from Carbon Capture and Direct Air Capture for Sustainable Chemical Synthesis
    (University of Alabama Libraries, 2025) Badger, Nicholas; Amini, Shahriar
    The transition to low-carbon industrial processes requires an understanding of the environmental trade-offs associated with emerging chemical conversion technologies. Life cycle assessment (LCA) provides a framework for evaluating these processes against decarbonization goals. This dissertation applies LCA to assess the impacts of methanol production, formic acid synthesis, and hydrogen production, incorporating both carbon capture (CC) and direct air capture (DAC), focused on greenhouse gas emissions. The first chapter establishes an LCA for DAC-based methanol production, showing that wind- and hydro-powered DAC lead to the most net-negative emissions of all energy sources, reaching as low as -2.53 kg CO2 eq per kg methanol. The findings highlight that DAC’s energy source determines the feasibility of CO2-derived methanol. The second chapter applies multi-objective optimization to balance competing stakeholder environmental and economic priorities relative to an LCA study. In the illustrative example, the DAC-to-methanol system is optimized between profit margin of methanol sale and climate change impacts, with the model predicting that the best business strategy is a mix of photovoltaic and wind energy cases. The third chapter examines formic acid synthesis from DAC-derived CO2 regenerated with waste heat. Results show up to a 110% global warming potential (GWP) reduction compared to fossil-based routes, but economic challenges remain, with electricity costs and CO2capture efficiency as key factors. The fourth chapter evaluates the environmental impacts of hydrogen production via gas switching reforming (GSR), a natural gas reforming process that integrates CO2 capture. The LCA results showed that compared to steam methane reforming (SMR), GSR reduces CO2 emissions by 73% and requires 94% less energy than proton exchange membrane (PEM)electrolysis. The final chapter assesses the environmental impacts of various hydrogen production routes for methanol production, showing that integrating renewable electrolysis-based hydrogen lowers emissions by 89% compared to steam methane reforming with CC, while methanol from GSR hydrogen reduces emissions by 30%.Together, these chapters provide a comprehensive assessment of decarbonization technologies, highlighting the interconnected roles of hydrogen production, DAC, carbon utilization, and synthetic fuel synthesis. This research quantifies key trade-offs, guiding the development of sustainable chemical conversion technologies to support climate change mitigation.
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    Experimental Investigation on CO2 Capture Technologies Under Microwave-Based Regeneration Conditions
    (University of Alabama Libraries, 2025) Boylu, Rahim; Amini, Shahriar
    In the United States (US), most (around 74%) human-caused greenhouse gas (GHG) emissions come from burning fossil fuels – coal, natural gas, and petroleum – for energy use. Today, burning fossil fuels accounted for 93% of total anthropogenic CO2 emissions. CO2 sources from other anthropogenic sources and activities were about 6% of total GHG emissions and 7% of total CO2 emissions. Economic growth and weather patterns that affect heating and cooling needs are the main factors that drive the amount of energy consumed. CO2 capture and storage (CCS) is a way of mitigating the contribution of fossil fuel emissions by capturing and subsequently storing the CO2. In 2015, countries agreed to limit warming – caused by such emissions – to below 2 °C and aim for 1.5 °C. According to International Energy Agency, CCS should contribute around 15% of effort in the pursuit of net-zero emissions by 2070. Various methods, such as temperature swing adsorption and pressure swing adsorption, have been used for CO2 regeneration. However, these approaches often struggle with challenges related to energy consumption and capital costs. In contrast, microwave heating-based CO2 capture technology emerges as a potential alternative, offering lower energy consumption and reduced costs.This study explores the necessity of CO2 capture and direct air capture (DAC) technologies, emphasizing their energy demands and heat transfer limitations using zeolite 13X as sorbent. Given these challenges, microwave-based heating emerges as a promising alternative due to its inherent advantages such as rapid and volumetric heating ability, which contributes to achieving homogeneous heat distribution. Experimental investigations were conducted at the Decarbonization Lab at the University of Alabama to evaluate microwave-assisted post-combustion CO2 capture and DAC under either dry or humid conditions. This study presents how the negative impact of humidity on zeolite 13X adsorption performance can be mitigated, ultimately enhancing its effectiveness in humid conditions. Experimental strategies in a fluidized bed reactor demonstrate that humidity effects can be mitigated through microwave-assisted direct air capture. The findings indicate that microwave-based CO2 capture enables lower energy consumption while achieving complete CO2 regeneration, even at low temperatures, positioning it as a viable alternative for sustainable carbon capture.