Solar Thermochemical Ammonia:
A More Sustainable Way to Feed the World
1,2,3Brian
Peterson, 2Ronny Michalsky, 2Peter Pfromm
REU Program, 2Kansas Brian
State University
PetersonCenter for Sustainable Energy
3Missouri University of Science and Technology Department of Chemical Engineering
1NSF
Introduction
Ammonia is critical as a source of fixed nitrogen
as fertilizer for agriculture globally. It has been
estimated that between one third and one half of
the world’s population could not be sustained
without chemical processes that synthetically
produce ammonia from nitrogen in the air. The
current standard for ammonia production is the
Haber-Bosch process. This 100-year-old process
consumes large quantities of fossil fuels and
requires large amounts of energy (accounts for
nearly 2% of energy usage globally). It is
imperative to study alternative, sustainable
processes to feed both the growing world
population and the growing biofuel industry.
Reduction of Magnesium Oxide
H 2O
In general, the Solar Ammonia process utilizes a
metal nitride which is corroded with a hydrogen
source (either H2 or H2O). When water is used,
the metal nitride corrodes very easily at room
temperature and atmospheric pressure, but a
rather unreactive metal oxide is formed. The
more difficult step is recycling the metal oxide
because it requires much higher temperatures
and a reducing agent such as carbon.
Tasks
Reduction of Magnesium Oxide
• Test effects of the addition of Iron(III) Oxide
and Chromium(III) Oxide at 1200 °C
• Analyze kinetics of best case mixtures
Corrosion of Calcium Nitride
Tab1: Percent of Magnesium atoms that left the
system at different reaction times which
correlates to Magnesium reduced.
Mg Nitride +CO ← Mg Oxide + C +N2
N2
C
(Biomass/Charcoal)
Goal
Molar Ratio
Mass % Mg Lost
MgO:C:FeO3:Cr2O3
30 min.
1:8:0:0
49.21%
1:8:1:0
-60.80%
1:8:0:1
7.09%
Reduce Magnesium Oxide into the form of
Magnesium Metal or Magnesium Nitride
Methods
Comparison
Process
Haber-Bosch Solar Ammonia
Pressure
300 bar
1 bar
Temperature
500 °C
400-1200 °C
Energy Source Natural Gas Solar Energy
Hydrogen Source Natural Gas Water or H3
Reaction
Catalyst
No Catalyst
• Higher ratios of Carbon to Magnesium Oxide
heavily influence Magnesium Nitride
• Chromium(III) Oxide appears to have a
stronger influence than Iron(III) Nitride on
the production of Magnesium Nitride
NH3.
Mg Nitride + H2O → Mg Oxide + NH3
CO
Corrosion of Calcium Nitride
Conclusions from Figure 1:
60 min.
120 min.
Fig1: Yield of 8 mixtures using Solar Concentrator
0.1
0.075
Magnesium Nitride Produced (g) per
50 mg Magnesium Oxide
0.05
0.025
Temp=1200 °C
0
• Identify composition of solids after reaction
• Analyze the kinetics at various H2 flow rates
Molar Ratio (MgO:C:Fe2O3:Cr2O3)
NH3.
Ca Nitride + H2 → “Ca solids”+ NH3
Ca Nitride ← “Ca solids” + N2
N2
Methods
• React Calcium Nitride with H2 at various
50.55% -43.35%
temperatures using an indoor reactor and
determine the composition of the solids
-74.01% -154.78%
•
Gather
kinetics
data
for
the
reaction
at
700°C
-24.82% 44.06%
• Make different molar combinations of 3 solid Conclusions from Table 1:
reactants
• Heavy error exists, most likely in the X-Ray
• React Nitrogen using Solar
Diffraction analysis of solid composition
Concentrator and reactor.
• Better analytical techniques might be
• Gather data on kinetics of 3
considered
mixtures, one with Iron(III)
Oxide added, one with
Fig3:
Mass
percent
of
Calcium
Hydride
in
the
Chromium
(III)
Oxide
solid
phase
after
reactions
at
various
temperatures
added, and a reference
25%
without additional oxides.
Percent of CaH2 in the Solid Phase
Run using an indoor
20%
Solar Concentrator
furnace and reactor
15%
Reaction Time=1 hr.
10%
Results and Conclusions
H2
5%
Goal
Maximize the production of Ammonia
Results and Conclusions
Fig2: Mol percent of Nitrogen atoms that left the
system, presumably as Ammonia at different
reaction temperatures
70%
Percent N Liberated to Gas Phase
60%
50%
Reaction Time=1 hr.
40%
30%
20%
0
500
1000
1500
Temperature (°C)
Conclusions from Figure 2:
0%
1500 • As expected, more Ammonia is produced
(Nitrogen liberated) at higher temperatures,
but levels off after 700 °C
Fig4: Mol percent of Nitrogen atoms liberated, • Flow rate experiments (Figure 4) should be
performed at 700 °C
likely as Ammonia at different Hydrogen flows
100%
Conclusions from Figure 3:
Percent N Liberated to the Gas Phase
• More Calcium Hydride is produced at higher
80%
temperatures
•
Also
Calcium
Hydride
is
vaporized
at
the
60%
higher temperatures and exits the system
Reaction Time=2 hr.
40%
Temp=700 °C
Conclusions from Figure 4:
• Hydrogen flow rate has little effect on
20%
Ammonia formation
0
0.5
1
1.5
2
2.5
• Thus this is likely a diffusion limited reaction
Hydrogen Flow Rate (L/min.)
0
500
1000
Temperature (°C)