Name: Ammonia Synthesis at Low Pressure (Video) | JoVE Journal
Uploaded: 2017-08-23T13:00:00.000+00:00
Duration: 8 min 14 s
Description: Learn low-pressure ammonia synthesis using solid ammonia-selective absorbents to enhance reaction efficiency and reduce carbon emissions. This sustainable method enables safer, cost-effective production from renewable energy sources.

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5 minutes

This work was primarily supported by ARPA-E, a part of the US Department of Energy, by the Minnesota Environment and Natural Resources Trust Fund, as recommended the Legislative-Citizen Commission on Minnesota Resources, and by MNDRIVE, an initiative of the University of Minnesota. Additional support came from the Dreyfus Foundation.

1. Pilot Plant Start-up
<ol>
	<li>Nitrogen production system
	<ol>
		<li>Turn on the air dryer, the air compressor, and the nitrogen generator. Verify that there is at least 800 kPa of air in the air compressor tank. This keeps sending nitrogen to the buffer tank until there is no more than 0.004% (40 ppm) oxygen in the nitrogen.</li>
		<li>Turn on the nitrogen gas booster. The gas booster starts to fill the nitrogen supply tanks, at pressures as high as 17 MPa.</li>
	</ol>
	</li>
	<li>Hydrogen production system
	<ol>
		<li>Turn on the chiller, the water deionization unit, and the electrolyzer. The electrolyzer will not operate without a venting system, because there is a flow sensor that measures the negative pressure venting in order to let the electrolyzer start. The hydrogen is produced with a rate of 0.54 kg/h, and the discharge pressure will be about 1.5 MPa.</li>
		<li>Turn on the hydrogen gas booster. Verify that the chiller is operational and the cooling liquid is flowing through. The hydrogen supply tanks will be filled up to 17 MPa.</li>
	</ol>
	</li>
	<li>Ammonia skid start-up
	<ol>
		<li>Use the computer in the control room to do the following:
		<ol>
			<li>Verify the emergency exits for the building.</li>
			<li>Make sure that the oxygen, hydrogen, and ammonia concentrations in the building are less than 20%, 19 ppm, and 35 ppm, respectively.</li>
			<li>Verify that the hydrogen and nitrogen supply tanks are charged to 17 MPa.</li>
			<li>Make sure that the ammonia sampler and the weight tank valves are bypassed.</li>
			<li>Pressurize the skid with nitrogen by setting the skid&#39;s nitrogen inlet regulator to 2.5 MPa. Set the nitrogen pressure regulator to 300 psi and then open the nitrogen bypass valve to fill the skid with nitrogen to 300 psi. Then close the nitrogen valve when that pressure is reached. Set the hydrogen regular to 1,200 psi and open the hydrogen valve to allow the skid to fill to 1,200 psi. Then close the hydrogen bypass valve.</li>
			<li>Open the hydrogen inlet valve and set the skid&#39;s hydrogen inlet regulator to 10 MPa.</li>
			<li>Set the NH3 pressure regulator to 1 MPa.</li>
			<li>Use the GUI controlling software to close/open multiple bypass valves on the skid, the compressor, and the air valves.</li>
			<li>Use the GUI controlling software to turn a couple of the PID controllers to ensure that the skid is fed with a 1:3 ratio of N2:H2.</li>
			<li>From the control room, and using the master GUI controlling software, start the skid. The compressor starts to recirculate the gas in the skid, and inject the fresh feed.</li>
			<li>In the GUI controlling software, set the reaction and condensation temperature. The reactor and condenser temperatures are set at 440 &#176;C and -25 &#176;C, respectively. 
			NOTE: It takes up to 4 days for the reactor to get to the set point temperature and achieve a steady state condition.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>
2. Experimental Apparatus Start-up
<ol>
	<li>Reactor preparation and reduction
	<ol>
		<li>Weigh 3 g of the pre-reduced catalyst. Reduce the particle size of the catalyst particles to less than 1 mm using a mortar and pestle.</li>
		<li>Load the catalyst into 0.25 in tubing, and place quartz wool on both sides.</li>
		<li>Use a PID controller, and increase the reactor temperature to the reaction temperature (400 &#176;C) with appropriate ramps, while flowing hydrogen through the reactor with a flow rate of 500 standard cubic centimeters per minute (SCCM). Use the ramps (summarized in Table 1). 
		NOTE: The temperature increase should be very smooth in order to obtain the proper catalyst activity.</li>
		<li>Continue the reduction process for 24 h. Ensure that no air or impurity comes into contact with the catalyst. Always keep the reactor under a nitrogen blanket.</li>
	</ol>
	</li>
	<li>Absorber preparation
	<ol>
		<li>Load 80 g of the CaCl2 absorbent into the absorber column (ID: 2.3 cm, Length: 30 cm). According to different absorbent sizes, different absorber packing supports will be used on both sides of the absorber, in order to immobilize the packed bed.</li>
		<li>To remove any humidity, increase the absorber temperature to 350 &#176;C while flowing nitrogen with the flow rate of 200 SCCM for 24 h.</li>
	</ol>
	</li>
	<li>Starting reaction separation tests
	<ol>
		<li>Increase the reactor and absorber temperature to 400 &#176;C and 180 &#176;C, respectively. 
		NOTE: Use proper temperature ramps to increase the reactor temperature. Use transformers to make the temperature control smoother. Keep the system in idle mode under the nitrogen blanket. Before starting any test, charge the system with nitrogen to 5 MPa a few times, and then release the pressure.</li>
		<li>Use the GUI to control the hydrogen and nitrogen mass flow controllers.</li>
		<li>Charge the apparatus to the target pressures with nitrogen and hydrogen, with the ratio of 1:3.</li>
		<li>Once the target pressure is achieved, close the inlet valves, open the reactor outlet valve, and turn on the recirculating pump. Due to the exothermic reaction and absorption, the reactor and absorber temperatures might require more careful control at the beginning of the process.</li>
		<li>Continue the test for 5 h, until the point when the absorber starts to breakthrough.</li>
	</ol>
	</li>
	<li>Desorption of ammonia
	<ol>
		<li>Open the inlet and outlet valves.</li>
		<li>Reduce the system&#39;s pressure to atmospheric pressure and increase the temperature of the absorber while flowing nitrogen with a flow rate of 100 SCCM for 5 h to desorb ammonia from the absorbent material.</li>
	</ol>
	</li>
</ol>

<ol><li>Erisman, J. W., Sutton, M. A., Galloway, J., Klimont, Z., Winiwarter, W. <a target="_blank" href="http://www.nature.com/ngeo/journal/v1/n10/abs/ngeo325.html">How a century of ammonia synthesis changed the world.</a> Nat Geosci. 1 (10), 636-639 (2008).</li>
<li>Vojvodic, A., Medford, A. J., et al. <a target="_blank" href="http://www.sciencedirect.com/science/article/pii/S000926141400147X">Exploring the limits: A low-pressure, low-temperature Haber-Bosch process.</a> Chem Phys Lett. 598, 108-112 (2014).</li>
<li>Jennings, J. R. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aJennings%2C+JR+%22Catalytic+Ammonia+Synthesis%22">Catalytic Ammonia Synthesis</a>. , Springer Science and Business Media. Plenum Press. (1991).</li>
<li>Apodaca, L. E. Nitrogen (Fixed) - Ammonia. , Available from:
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 <a target="_blank" href="http://www.iea.org/w/bookshop/pricing.html">http://www.iea.org/w/bookshop/pricing.html</a> (2007).</li>
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 <a target="_blank" href="http://ateam.lbl.gov/PUBS/doc/LBNL-44314.pdf">http://ateam.lbl.gov/PUBS/doc/LBNL-44314.pdf</a> (2000).</li>
<li>Wojcik, A., Middleton, H., Damopoulos, I., Van herle, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Ammonia+as+a+fuel+in+solid+oxide+fuel+cells%5BTitle%5D)+AND+%22J+Power+Sources%22%5BJournal%5D)">Ammonia as a fuel in solid oxide fuel cells.</a> J Power Sources. 118 (1-2), 342-348 (2003).</li>
<li>Zamfirescu, C., Dincer, I. <a target="_blank" href="http://www.sciencedirect.com/science/article/pii/S0378775308004461">Using ammonia as a sustainable fuel.</a> J Power Sources. 185 (1), 459-465 (2008).</li>
<li>Christensen, C. H., Johannessen, T., Sørensen, R. Z., Nørskov, J. K. <a target="_blank" href="http://www.sciencedirect.com/science/article/pii/S0920586105007157">Towards an ammonia-mediated hydrogen economy?</a> Catalysis Today. 111 (1-2), 140-144 (2006).</li>
<li>Hummelshøj, J. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((reversible+high-density+hydrogen+storage+in+compact+metal+ammine+salts%5BTitle%5D)+AND+%22J+Am+Chem+Soc%22%5BJournal%5D)">reversible high-density hydrogen storage in compact metal ammine salts.</a> J Am Chem Soc. 130 (27), 8660-8668 (2008).</li>
<li>Ni, M., Leung, M. K. H., Leung, D. Y. C. <a target="_blank" href="http://onlinelibrary.wiley.com/doi/10.1002/er.1588/abstract">Ammonia-fed solid oxide fuel cells for power generation-A review.</a> Int J Energy Res. 33 (11), 943-959 (2009).</li>
<li>Zamfirescu, C., Dincer, I. <a target="_blank" href="http://www.sciencedirect.com/science/article/pii/S0378382009000241">Ammonia as a green fuel and hydrogen source for vehicular applications.</a> Fuel Process Technol. 90 (5), 729-737 (2009).</li>
<li>Ertl, G. <a target="_blank" href="http://www.tandfonline.com/doi/abs/10.1080/03602458008067533">Surface Science and Catalysis-Studies on the Mechanism of Ammonia Synthesis: The P. H. Emmett Award Address.</a> Catal Rev. 21 (2), 201-223 (2006).</li>
<li>Nielsen, A., Kjaer, J., Bennie, H. <a target="_blank" href="http://www.sciencedirect.com/science/article/pii/0021951764900946">Rate equation and mechanism of ammonia synthesis at industrial conditions.</a> J Catal. 3 (1), 68-79 (1964).</li>
<li>U.S. Department of Energy. DE-FOA-0001569 Sustainable Ammonia Synthesis. , Available from:
 <a target="_blank" href="https://science.energy.gov/~/media/grants/pdf/foas/2016/SC_FOA_0001569.pdf">https://science.energy.gov/~/media/grants/pdf/foas/2016/SC_FOA_0001569.pdf</a> (2016).</li>
<li>Chen, J., Miranda, R., Fitzsimmons, T., Stack, R. Sustainable Ammonia Synthesis - Exploring the scientific challenges associated with discovering alternative, sustainable processes for ammonia production. DOE Roundtable Report. , Available from:
 <a target="_blank" href="https://science.energy.gov/~/media/bes/pdf/reports/2016/SustainableAmmoniaReport.pdf">https://science.energy.gov/~/media/bes/pdf/reports/2016/SustainableAmmoniaReport.pdf</a> (2016).</li>
<li>Reese, M., Marquart, C., et al. <a target="_blank" href="http://pubs.acs.org/doi/abs/10.1021/acs.iecr.5b04909">Performance of a Small-Scale Haber Process.</a> Ind Eng Chem Res. 55 (13), 3742-3750 (2016).</li>
<li>Schlögl, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Catalytic+Synthesis+of+Ammonia-A+%22Never-Ending+Story%22%5BTitle%5D)+AND+%22Ange+Chemie+Int+Ed%22%5BJournal%5D)">Catalytic Synthesis of Ammonia-A "Never-Ending Story".</a> Ange Chemie Int Ed. 42 (18), 2004-2008 (2003).</li>
<li>Dyson, D. C., Simon, J. M. <a target="_blank" href="http://pubs.acs.org/doi/abs/10.1021/i160028a013">Kinetic Expression with Diffusion Correction for Ammonia Synthesis on Industrial Catalyst.</a> Ind Eng Chem Fund. 7 (4), 605-610 (1968).</li>
<li>Temkin, M., Pyzhev, V. <a target="_blank" href="http://pubs.acs.org/doi/abs/10.1021/ie051398g">Kinetics of ammonia synthesis on promoted catalysts.</a> Acta Physiochim USSR. 12, 327-356 (1940).</li>
<li>Annable, D. <a target="_blank" href="http://www.sciencedirect.com/science/article/pii/0009250952870113">Application of the Temkin kinetic equation to ammonia synthesis in large-scale reactors.</a> Chem Eng Sci. 1 (4), 145-154 (1952).</li>
<li>Guacci, U., Traina, F., Ferraris, G. B., Barisone, R. <a target="_blank" href="http://pubs.acs.org/doi/abs/10.1021/i260062a002">On the Application of the Temkin Equation in the Evaluation of Catalysts for the Ammonia Synthesis.</a> Ind Eng Chem Prod DD. 16 (2), 166-176 (1977).</li>
<li>Hummelshøj, J. S., Sørensen, R. Z., Kustova, M. Y., Johannessen, T., Nørskov, J. K., Christensen, C. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Generation+of+nanopores+during+desorption+of+NH3+from+Mg%28NH3%296Cl2%5BTitle%5D)+AND+%22J+Am+Chem+Soc%22%5BJournal%5D)">Generation of nanopores during desorption of NH3 from Mg(NH3)6Cl2.</a> J Am Chem Soc. 128 (1), 16-17 (2006).</li>
<li>Huberty, M. S., Wagner, A. L., McCormick, A., Cussler, E. <a target="_blank" href="http://onlinelibrary.wiley.com/doi/10.1002/aic.13744/abstract">Ammonia absorption at haber process conditions.</a> AIChE Journal. 58 (11), 3526-3532 (2012).</li>
<li>Himstedt, H. H., Huberty, M. S., McCormick, A. V., Schmidt, L. D., Cussler, E. L. <a target="_blank" href="http://onlinelibrary.wiley.com/doi/10.1002/aic.14733/abstract">Ammonia synthesis enhanced by magnesium chloride absorption.</a> AIChE Journal. 61 (4), 1364-1371 (2015).</li>
<li>Malmali, M., Wei, Y., McCormick, A., Cussler, E. L. <a target="_blank" href="http://pubs.acs.org/doi/abs/10.1021/acs.iecr.6b01880">Ammonia Synthesis at Reduced Pressure via Reactive Separation.</a> Ind Eng Chem Res. 55 (33), 8922-8932 (2016).</li>
<li>Wagner, K., Malmali, M., et al. <a target="_blank" href="http://onlinelibrary.wiley.com/doi/10.1002/aic.15685/abstract">Column absorption for reproducible cyclic separation in small scale ammonia synthesis.</a> AIChE Journal. , (2017).</li>
</ol>

The authors have nothing to disclose.

Critical Steps of the Reaction-absorption Experimental Apparatus:
Make sure that there is no impurity in the nitrogen and hydrogen system. The absorbent materials will change after each cycle. In most cases, at high temperature and in the presence of ammonia, the absorbent materials fuse and form a large solid concrete. According to the thermodynamic properties of each metal halide and ammine complex, the appropriate temperatures for absorption and desorption should be employed. Before each test,...

Ammonia is a key industrial chemical. It is produced through the Haber-Bosch process, which is known as one of the most important innovations of the 20th century1,2. Ammonia synthesis is carried out in the presence of a heterogeneous catalyst at elevated temperatures (&#62; 375 &#176;C) and pressures (&#62;100 bar)3. Such high temperature and pressure requirements make ammonia synthesis very energy- and capital-intensive. Approximately, 150 million tons of ammonia are produced each year4, which accounts for 1-3% of the world&#39;s energy consumption, 5% of the natural gas consumption, and up to 3% of the climate-changing gas emissions5,6,7.
Ammonia has two major potential uses. First, ammonia is a synthetic nitrogen fertilizer1. Without this fertilizer, half of the current population would not have access to sufficient food. Second, ammonia can serve as an energy vector, either as a carbon-neutral liquid fuel or as an indirect hydrogen carrier8,9,10,11. Typically, renewable resources (e.g. wind) are available in underpopulated rural areas, where it can be captured; this type of isolated wind and solar energy is called &#34;stranded&#34;. In this scenario, the electrical and thermal energies from the renewable energy source are converted to energy-dense carbon-neutral liquid ammonia. The liquid ammonia produced can then be shipped to urban centers, where it can be directly used in ammonia-based fuel cells12 and internal combustion engines13, or it can be decomposed into hydrogen and then be used in hydrogen fuel cells or hydrogen stations. As a result, we can move the wind of the U.S. prairies to the crowded urban areas of the U.S.
Mostly because of the fertilizer use, ammonia manufacture is a major industry. At room temperature, the ammonia synthesis reaction is exothermic and hence&#8212;at least, in principle&#8212;spontaneous14, however, achieving the reaction under ambient conditions is extremely difficult because of the strong nitrogen-nitrogen bond15. To overcome this, Fritz Haber famously used high temperatures to achieve fast kinetics, but these high temperatures meant that the reverse reaction inhibited the production. To reduce the inhibitions of this reverse reaction, Haber used high pressure to improve conversion. He carried out the large-scale reaction in a gun barrel, which still decorates the BASF plant in Ludwigshafen.
The necessity to use both high temperature and pressure when the reaction could potentially run under much more modest conditions has frustrated chemists for over a century2. Even after the process was commercialized, Karl Bosch and a huge cohort at BASF churned through the entire periodic table looking for better catalysts. While Bosch had little success, the search still continues. Even last year, a new research program aimed at seeking a new catalyst was initiated16,17. The detailed chemistry of ammonia synthesis is now well understood14, and if the search for the new catalyst is successful, it would certainly be worth the effort. However, in our view, the past failures reduce the chance of future success.
In the following text, small-scale ammonia synthesis process is described, and the motivation to investigate an alternative process is explained.
The Small-Scale Process:
Wind-Generated Ammonia 
We are improving the Haber-Bosch process for synthesizing ammonia, seeking a much smaller, simpler process which can be operated locally but produces negligible amounts of carbon dioxide. The feasibility of local ammonia manufacture from wind has already been demonstrated in a pilot plant located in Morris, MN, and shown in Figure 118. Morris sits on the Buffalo Ridge, a formation of sixty miles of rolling hills in the southwest corner of Minnesota. The ridge has unusually steady, strong wind, rolling across the prairie. As a result, it is a mecca for wind-generated electricity.
With this electricity, we already manufacture ammonia from wind, using this plant which is forty thousand times smaller than the existing commercial operations for fossil fuels. Some wind-generated electricity is used to make nitrogen from air by pressure swing adsorption, an established method for air separation used, for example, for patients with emphysema who need oxygen-enriched air. However, more of the electricity is used to make hydrogen by electrolysis of water. These gases are combined over a conventional catalyst in the process shown schematically in Figure 2. After the reaction, the gases are separated by chilling to condense the liquid ammonia. The unreacted gases, as well as the uncondensed ammonia, are recycled.
Details of the Pilot Plant 
In our pilot plant, the University of Minnesota Renewable Hydrogen and Ammonia Pilot Plant, the electric power is provided from a co-located 1.65 MW wind turbine. The pilot plant uses approximately 10% of the power generated, with the remaining power used at the University of Minnesota, Morris campus.
The hydrogen production system uses an electrolyzer, a booster compressor, and a thermal chiller. This system produces 0.54 kg of hydrogen gas per hour, which is stored at 2,400 psi using 24 kWh of electricity. Water from an on-site well is purified using a reverse osmosis and deionization system. The water is then supplied to the electrolyzer at a rate of up to 15 L/h. Nitrogen is generated using a nitrogen generator, a pre-air compressor, an air dryer, and a booster compressor. The nitrogen gas is stored at 2,400 psi using approximately 6 kWh of electricity.
The synthesis of ammonia uses a custom skid. It includes a compressor, a reactor, a refrigeration cooling loop, and a 20 kW electric heater. The skid uses approximately 28 kWh of electricity to produce 2.7 kg of ammonia per hour which is then stored at 150 psi. The ammonia production process is controlled with integrated PLC and HMI systems. The produced hydrogen and nitrogen are stored on site in 18 nitrogen storage tanks and 54 hydrogen storage tanks. The ammonia is also stored onsite within a 3,100-gallon vessel.
Wind Generation is Expensive 
The electricity for this process is made from wind, and so the fuel for making ammonia is free, without using any fossil fuel. However, the capital costs for this pilot plant are dominated by the investments for hydrogen production and for ammonia synthesis. The operations to date suggest that the cost of making small-scale ammonia are about twice that of conventional ammonia based on fossil fuels. While we continue to optimize our process, we believe that small-scale wind generated ammonia will not be competitive at the current natural gas prices. The capital costs per mass ammonia made could be reduced by a larger conventional process, or by an alternative process like that described next in this paper.
The Absorption Process:
Absorption Enhances Production 
The catalyst used for ammonia synthesis has remained almost unchanged during the last century19. As a result, we have carried out a different approach in this research. We apply the current catalyst and operating temperature, but absorb ammonia at modest pressures as soon as it is formed. We recycle any unreacted hydrogen and nitrogen. The process is schematically like that in Figure 3, similar to the conventional process, but with a packed bed absorber replacing the condenser.
Initial Reaction Kinetics Do Not Change 
Experiments with this system at low conversion show an initial reaction rate that is consistent with many of the earlier studies on this system3,14,15,20,21,22,23, as shown in Figure 4. The left panel shows the initial rates, which vary strongly with temperature. While these rates also vary with pressure, the variations are smaller, as shown in the right panel. In our new process, we use the same catalyst and similar operating conditions, but seek ways to improve ammonia production by using absorption at a lower pressure. We thus hope to reduce the capital costs for ammonia synthesis.
Absorption Enhances Conversion 
In our work, we replaced the condenser in the small process with a packed bed, which is a cylindrical vessel filled with small particles of the absorbent. We have emphasized absorbents made primarily of magnesium chloride and calcium chloride11,24. Such ammine absorbents have two effects. First, they reduce the ammonia concentration present in the recycled gases to near zero. Second, they effectively reduce the time for separation to near zero. This strategy is productive25,26,27. For example, in Figure 5, we show that the rate of making ammonia, which is proportional to the drop in the total pressure in the system, is much greater with absorption than without. In particular, the reaction at 90 bar, shown by the red circles, is less complete than the reaction with the absorbent, shown by the blue triangles27. This is true even though the reaction without absorbent takes place at a pressure almost twice that of the reaction with absorption. In earlier experiments (not shown here), we also showed that the eventual conversion of the process is about 20% without absorbent but over 95% with absorbent.
The rate of reaction varies much less with temperature with absorption than without. This is shown in Figure 6, which again reports ammonia synthesis as total pressure versus time27. Changing the reaction temperature by 60 &#176;C has little effect on the reaction rate. This contrasts with the initial rates in Figure 4, which shows a change of reaction rate of almost an order of magnitude. The results in Figure 4 and Figure 6 are different because the effect of the reverse reaction has been reduced, so the chemical kinetics are no longer the only step responsible for the overall rate.

<table><tbody><tr><td>&lt;strong&gt;Experimental Apparatus&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Magnesium Chloride</td><td>Sigma Aldrich</td><td>7786-30-3</td><td>St. Louis, MO</td></tr><tr><td>Calcium Chloride</td><td>Sigma Aldrich</td><td>10043-52-4</td><td>St. Louis, MO</td></tr><tr><td>Ultra Pure Hydrogen</td><td>Matheson</td><td>SG PHYF30050</td><td>New Brighton, MN</td></tr><tr><td>Ultra Pure Nitrogen</td><td>Matheson</td><td>SG G1881112</td><td>New Brighton, MN</td></tr><tr><td>Iron Based Catalyst</td><td>Clariant/Sud Chemie</td><td>-</td><td>Charlotte, NC</td></tr><tr><td>Variable Piston Pump</td><td>PumpWorks Inc.</td><td>PW2070N</td><td>Minneapolis, MN</td></tr><tr><td>Omega Ceramic Heater</td><td>Omega</td><td>CRFC-36/115-A</td><td>Stamford, CT</td></tr><tr><td>PID Controller</td><td>Omega</td><td>CN96211TR</td><td>Stamford, CT</td></tr><tr><td>Signal Conditioner</td><td>Omega</td><td>DRG-SC-TC</td><td>Stamford, CT</td></tr><tr><td>Pressure Transducer</td><td>WIKA</td><td>50426877</td><td>Lawrenceville, Georgia</td></tr><tr><td>Mass Flow Controller</td><td>Brooks Instruments</td><td>SLA5850</td><td>Hatefield, PA</td></tr><tr><td>&lt;strong&gt;Name&lt;/strong&gt;</td><td>&lt;strong&gt;Company&lt;/strong&gt;</td><td>&lt;strong&gt;Catalog Number&lt;/strong&gt;</td><td>&lt;strong&gt;Comments&lt;/strong&gt;</td></tr><tr><td>&lt;strong&gt;Pilot Plant&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Electrolyzer</td><td>Proton OnSite</td><td>H6 Series</td><td>Wallingford, CT</td></tr><tr><td>Gas Booster</td><td>PDC Machine</td><td>3 2500&amp;nbsp;</td><td>Warminster, PA</td></tr><tr><td>Wind Turbine</td><td>Vestas</td><td>V82</td><td>Portland, OR</td></tr><tr><td>Chiller</td><td>Thermal Care</td><td>SQ Series</td><td>Niles, IL</td></tr><tr><td>Water Purifier</td><td>Elga Pure Lab</td><td>S-15</td><td></td></tr><tr><td>Nitrogen Generator</td><td>Innovative Gas System</td><td>NS-10</td><td>Huoston, TX</td></tr><tr><td>Air Compressor</td><td>Hydrovane</td><td>HV05</td><td></td></tr></tbody></table>

ammonia synthesis at low pressure

Ammonia Synthesis at Low Pressure

Ammonia can be synthesized at low pressure by the use of an ammonia selective absorbent. The process can be driven with wind energy, available locally in areas requiring ammonia for synthetic fertilizer. Such wind energy is often called &#34;stranded,&#34; because it is only available far from population centers where it can be directly used.
In the proposed low pressure process, nitrogen is made from air using pressure swing absorption, and hydrogen is produced by electrolysis of water. While these gases can react at approximately 400 &#176;C in the presence of a promoted conventional catalyst, the conversion is often limited by the reverse reaction, which makes this reaction only feasible at high pressures. This limitation can be removed by absorption on an ammine-like calcium or magnesium chloride. Such alkaline metal halides can effectively remove ammonia, thus suppressing the equilibrium constraints of the reaction. In the proposed absorption-enhanced ammonia synthesis process, the rate of reaction may then be controlled not by the chemical kinetics nor the absorption rates, but by the rate of the recycle of unreacted gases. The results compare favorably with ammonia made from a conventional small scale Haber-Bosch process.

A pilot plant in Morris, MN has demonstrated the feasibility of using wind for local ammonia manufacture18, as shown in Figure 1. The wind generates electricity, which is used to make nitrogen and hydrogen through the pressure swing absorption of air and through the electrolysis of water, respectively. A reactor uses a conventional catalyst to combine the nitrogen and hydrogen gases, making ammonia. The ammonia is then separated using ...

Ammonia can be synthesized at low pressure by using a conventional catalyst and an ammonia selective absorbent.

Ammonia can be synthesized at low pressure by the use of an ammonia selective absorbent. The process can be driven with wind energy, available locally in ...

The overall goal of this procedure is to produce ammonia from air, water and wind-generated energy in a low-pressure process with negligible carbon dioxide emissions. This method can help address key issues in ammonia production such as reaction efficiency, product distribution and carbon dioxide emissions. The process uses a solid ammonia-selected absorbent rather than a condenser.Continually removing ammonia from the system decreases the occurrence of the reverse chemical reaction. The main advantage of this process is that it can performed at lower pressure which is safer and less expensive. Cory Marquart and I operate a plant for the conventional process that is 30, 000 times smaller than typical plants.This gives a standard for comparison with the absorbent process. Mike Reese and Cory Marquart are operating the conventional small-scale plant in Morris, Minnesota. Demonstrating the absorption-based process will be Mahdi Malmali, a post-doctoral fellow affiliated with our laboratory.Prior to beginning the process, start up the ammonia generation plant and ramp the catalytic reactor to 440 degrees Celsius. Set the condenser temperature to minus 18 degrees Celsius. Next, turn on the air dryer, the air compressor and the nitrogen generator.Turn on the nitrogen gas booster to fill the nitrogen supply tanks. Turn on the chiller, water deionization unit, electrolyzer and the hydrogen gas booster. Verify that the chiller is operational and cooling liquid is flowing through.Next set the nitrogen inlet regulator to 300 PSI. Open the nitrogen valve to begin pressurizing the process skid. Close the nitrogen bypass valve when the skid reaches 300 PSI.Then, set the hydrogen inlet regulator to 1, 200 PSI and open the hydrogen valve. Once the skid reaches 1, 200 PSI, close the hydrogen valve. Start the skid to begin cycling the one-to-three nitrogen-to-hydrogen gas mixture through the system.After the process has finished, store the condensed ammonia at 150 PSI. To prepare the reactor, use a mortar and pestle to grind the catalyst particles to less than one millimeter in size. Pack the ground catalyst into 0.25-inch tubing.To prepare the absorber, pack 80 grams of calcium chloride or an equivalent amount of another ammonia selective absorbent into a 30-centimeter column with an inner diameter of 2.3 centimeters. Plug the ends of the column with sufficient packing support material to immobilize the absorbent. Install the absorber and the reactor in the experimental apparatus.Heat the reactor to 450 degrees Celsius using the recommended activation temperature procedure while flowing hydrogen through the reactor at 500 SCCM to finish the catalyst activation. Keep the activated catalyst under a blanket of ultra-pure nitrogen gas when the system is idle. To begin the ammonia generation process, close the outlet valve and ramp the reactor to 400 degrees Celsius and the absorber to 180 degrees Celsius.Flush the system with ultra-pure nitrogen gas by repeatedly pressurizing and venting the system. Then, pressurize the system with a one-to-three mixture of nitrogen and hydrogen gases. Stop the nitrogen and hydrogen mass flow controllers.Close the reactor inlet valve. Open the reactor outlet valve and start the recirculation pump. Monitor the reactor and absorber temperatures as the reaction starts and adjust them as necessary to compensate for exothermic processes.Run the process for five hours or until the absorber starts to break through as indicated by a decrease in the change in system pressure over time. Open the nitrogen inlet valve and the ammonia outlet valve and reduce the system to atmospheric pressure. Flow nitrogen through the system at 100 SCCM while heating the absorber for five hours to release the ammonia.The high pressures used in the conventional method are necessary to favor the forward reaction at high temperatures. In the low-pressure separation method, the ammonia is more completely separated before it could undergo the reverse reaction. A significant increase in the rate of conversion was observed relative to the conventional method.The initial reaction rates of the separation method were consistent with published values and separate chemical kinetics experiments. Temperature variation was observed in the initial reaction rates of the reaction absorption method. The overall reaction rate showed much less temperature dependence indicating that the catalytic reaction rate is not a major limiting factor for the conversion rate in the separation method.The absorbent efficiently removed the ammonia from the system, but the capacity of the column decreased after each cycle. Investigation into prolonging the life of the absorbent column is underway. The absorption kinetics were not found to be a significantly limiting factor for ammonia production.The recirculation flow rate was found to correlate with the reaction rate indicating that it is the primary controlling step for the process. This process can make ammonia from air, water and wind. The air and water are sources of nitrogen and hydrogen by pressure-swing absorption and electrolysis respectively.The energy for the process comes from the wind. The Haber-Bosch process is a century-old reaction that feeds a large fraction of the world's population. Trying to improve it has high risk and potentially high reward.Our original idea for this work was to make family farms in rural Minnesota more self-sufficient for their nitrogen fertilizer. The promise of a fuel for energy-short cities by storing wind-based energy as liquid ammonia was an unexpected gain. The key to the absorption-based process is to develop a stable reusable absorbent that efficiently traps ammonia as it is produced.By replacing the conventional condenser with an absorbent bed, we are closer to a cheaper, safer ammonia generation process suitable for small-scale manufacturing.

Research

JoVE Journal

Bioengineering

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