(14u) 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technologies can bridge the gap between out-of-date processes and those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.