Design of Advanced Materials for Application in Clean Energy and Carbon Capture and Utilization

Design of Advanced Materials for Application in

Clean Energy and Carbon Capture and Utilization

 

Peter C. Psarras

Energy Resources Engineering, Stanford University     Introduction This past half-century has brought much change to the landscape surrounding the chemical processes that sustain our global socio-economic framework. In the midst of this evolving climate, it has become increasingly apparent that new motivations, such as those for greater energy-efficiency and less carbon-intensive processes, are necessary to avert serious global consequences. Fortunately, this call to attention has re-energized the field of materials research, whereby promising new technologies can bridge the gap between out-of-date processes and those better-suited for consequence mitigation. Concurrent to this scientific revitalization has been a related emergence in its own right Ð the dawn of high performance computing environments; thus, theoretical methods represent a powerful approach to the design of materials aimed at resolving the shortcomings of essential industrial processes through revision and innovation. These methods are often favorable in situations where there exists a need to explore and screen a number of materials at low cost and risk, where conditions prove unsuitable or even unfeasible via conventional methods, or where an understanding is sought at molecular levels or timescales that are incompatible with experimental measurement. This presentation will introduce how different theoretical methods can be used to solve four issues related to climate change: nitrogen-selective membranes for indirect CO₂ capture, nitrogen-functionalized carbon sorbents for direct CO₂ capture, the assessment of carbon neutrality for irreplaceable industrial processes, and the effect of late-transition metal doping on methane selectivity in Fischer-Tršpsch (FT) catalysis.     Research Interests: Nitrogen-Functionalized Porous Carbons for Enhanced CO₂ Capture Traditional amine-based solvent technology is notoriously energy intensive, owing to high regeneration temperatures. Additionally, this process is water-intensive, a factor that is becoming increasingly important in drought-ridden states like California. Solid sorbents represent an alternative method for CO₂ capture, with liquid solvents replaced by (typically) large surface area, carbon-based porous frameworks. These sorbents are generally low-cost, easily fabricated, and are far less energy intensive in terms of regeneration. Further, their design can be customized through the inclusion of surface functional groups. Unfortunately, current sorbents display CO₂ loadings that are deemed too low to be cost-competitive with solvent-based scrubbing. Nitrogen-functionalization of these porous carbons could result in more efficient CO₂ capture through the introduction of surface charge heterogeneity which can selectively interact with the CO₂ quadrupole moment. Similar studies have examined the effects of oxygenated functional groups on CO₂ uptake and selectivity over N₂.   This study employs grand canonical Monte Carlo methods to explore the effect of quaternary, pyridinic, pyrrolic, oxidized-pyridinic, and pyridonic groups on CO₂ uptake in porous carbon sorbents. Doping amounts are varied to ascertain the optimum coverage for CO₂ capture. Additionally, gaseous mixtures of CO₂/N₂ and CO₂/N₂/H₂O are examined to assess CO₂ selectivity. Theoretical performance is validated through comparison with experimentally obtained CO₂ and N₂ isotherms over fabricated hierarchical micro/mesoporous N-doped carbon sorbents. The combination of these methods will inform on sorbent design by illustrating which groups are most important for enhanced CO₂ uptake. Design to include more of a particular functional group can be achieved through, for example, a change in carbonization temperature.   Assessment of the CO₂ Capture Potential from Irreplaceable Industrial Sources

In 2013, the US industrial sector emitted approximately 1.4 gigatonnes of carbon dioxide (Gt CO₂), or 21% of total US CO₂ emissions Ð the third highest figure for any economic sector behind transportation (27%) and electricity (31%).  These emissions can be further categorized as direct (fuel combustion accountable on-site, e.g., stationary combustion), indirect (assigned to electricity purchased for power and off-site steam generation) and process (CO₂ liberated as a reaction by-product). Direct and indirect emissions generally constitute ca. 80% of total emissions, with process emissions making up the balance, though the relative contribution of process emissions to total emissions is known to vary by industry.

  While these industrial process emissions constitute a smaller percentage of total US CO₂ emissions, they produce commodities like glass, cement, ammonia and steel Ð items that form the irreplaceable fabric of industrialized nations. Unlike the power sector, for example, where mitigation might be achieved through a transition to renewable forms of energy and adoption of best practice technologies, there are few CO₂-free alternative routes to product for most industrial commodities; thus, these irreplaceable industrial processes (IIPs) represent committed CO₂ emissions that remain largely unabatable. Further, these IIPs command attention for two important reasons: 1) there is a committed nature to these emissions by virtue of process chemistry, and perhaps more importantly 2) they can yield exhaust streams with higher CO₂ content when compared to the high volume flue exhausts of the power sector.  As the cost of CO₂ separation scales inversely with initial dilution of a mixed feed stream carbon capture technology retrofits have the potential to efficiently and economically divert emissions from industrial exhaust streams to viable CO₂ utilization opportunities, such as enhanced oil recovery (EOR), food processing, refrigeration, and fertilizer production. To assess the capture potential of these irreplaceable industries, it is necessary to geo-reference these sources alongside all current and potential future CO₂ sinks (utilization or market opportunities), with the goal of making economically sound linkages between source and markets of comparable scale. This entails a cost analysis of on-site capture, compression, and transport costs. Geographic information systems (GIS) mapping can assist in identifying regions of high CO₂ demand, geographically-logical source-sink partnerships, and viable routes of CO₂ transport. The aim is to classify these IIPs based on carbon-capture ÒreadinessÓ, which is ultimately a combination of the industry-specific and site-specific factors listed above.

    Vanadium-Ruthenium Alloys for Indirect CO₂ Capture Membranes represent a promising technology for carbon capture, yet several material challenges persist. Ideally, a membrane will need to demonstrate excellent CO₂ selectivity, strong mechanical and thermal stability, and high membrane flux. Here, investigate alloyed V/Ru membranes for selective nitrogen capture. In this technology, rather than separating out CO_₂ directly, nitrogen is separated from the flue stream. Nitrogen is far more efficient to separate, owing to its greater flue concentration and corresponding higher pressure differential across the membrane. Consequently, after N₂ separation the remaining exhaust components become more concentrated, CO₂ included, making all downstream capture points more efficient by the same virtue. This study will prepare 14 V/Ru alloys in concentrations spanning those considered in real application. Vanadium is known to bind nitrogen strongly, making it a good candidate for activation of the N-N triple bond. However, this tight binding inherently slows membrane diffusion. Nitrogen permeability can be represented as a product of its solubility and diffusivity. The former is sought by considering the effect of Ru concentration on relative binding energies and vibrational frequencies of interstitially-bound nitrogen, while diffusivity can be examined by calculating all potential TS-pathways, tabulating their rates, and employing kinetic Monte Carlo methods. Together, these results will combine to predict nitrogen permeability as a function of Ru content. These findings can inform on membrane design, whereby a theoretically optimal Ru composition can be validated experimentally.   The Effect of Late Transition Metal Doping on Methane Selectivity in Fischer-Tršpsch Catalysis (Dissertation Work) Fischer-Tršpsch synthesis has endured a long and industrious career as the premier chemical method for the synthesis of hydrocarbons from non-petroleum-based precursors. Historically, a collection of factors has dictated interest in the FT process, including foreign policy, availability of precursor(s), availability of alternate fuel sources and reserves, and environmental considerations. The effect of late transition metal substitution into Fe(100), Ni(111), and Co(0001) surface analogs is investigated using density functional theory (DFT) methods. The surface is modeled first using a 7-atom cluster, with perimeter atoms saturated with hydrogen atoms to approximate surface coordination and mitigate dangling bond artifacts, and next with plane-wave periodic models. Ab initio calculations are performed to predict adsorption energies and transition state geometries and energies for eight surface adsorbate species: *C + *H, *CH + *H, *CH₂ + *H, and *CH₃ + *H to represent the hydrogenating steps, while *C + *CH, *CH + *CH, *C + *CH₃, and *CH₂ + *CH₂ represent species involved in four competitive coupling pathways. A review of the effect of Cu, Ag, Au, and Pd on the reaction energies and barriers associated with these critical steps is discussed. Methane selectivity can be described by a single descriptor, the carbon binding strength; thus, a comparison of these energies over different surface/promoter analogs is an effective method to screen for promising candidates. In this representation, a lowering of carbon binding strength is equivalent to the lowering of methane selectivity.   Teaching Interests: My background in Chemistry has prepared me in the fundamentals of thermodynamics, quantum mechanics, catalysis, molecular simulations and adsorption. However, my research direction has forced me to become as proficient in the understanding of transport phenomena, fluid mechanics, and separations. I feel comfortable to instruct in any of these areas with confidence. Additionally, I plan to design a course centered around the fundamentals of electronic structure methods, tailored for application to climate change mitigation Ð suitable as a standalone course or special topic offering.   Additionally, I have experience teaching several undergraduate lecture courses, including Physical Chemistry I and Survey of Physical Chemistry, as well as several laboratory courses. I have also had the great privilege of mentoring several students, many who have since published in high impact journals such as Journal of Physical Chemistry C and Advanced Energy Materials. Through my experiences in teaching and mentoring, I have developed the valuable skill of balancing research and grant writing with class time and student development.