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Ammonia ranks among the most extensively manufactured substances globally, primarily utilized as fertilizer but also for generating various plastics, textiles, and other uses. Its manufacture, via processes that necessitate elevated heat and pressure, is responsible for nearly 20 percent of all greenhouse gases emitted by the chemical sector, prompting worldwide initiatives to discover methods for mitigating these emissions.
Currently, researchers at MIT have devised an innovative method that amalgamates two distinct techniques for producing ammonia, thereby minimizing waste products. When paired with additional straightforward enhancements, this could potentially decrease greenhouse gas emissions from production by up to 63 percent compared to the leading “low-emission” techniques currently in practice.
This novel strategy is outlined in the journal Energy & Fuels, in a study authored by MIT Energy Initiative (MITEI) Director William H. Green, graduate student Sayandeep Biswas, MITEI Director of Research Randall Field, and a couple of others.
“Ammonia has the highest carbon dioxide emissions of any chemical,” remarks Green, the Hoyt C. Hottel Professor in Chemical Engineering. “It’s a very vital chemical,” he asserts, due to its essential role as a fertilizer in supporting the global population’s nutritional needs.
Until the late 19th century, the prevalent source of nitrogen fertilizer was mined deposits of bat or bird droppings, mainly sourced from Chile. However, this supply started depleting, and there were forecasts indicating an imminent food shortage to sustain the growing population. Subsequently, a new chemical technique, recognized as the Haber-Bosch process—named after its inventors—enabled the creation of ammonia from nitrogen in the atmosphere and hydrogen, predominantly derived from methane. Unfortunately, both the combustion of fossil fuels for the necessary heat and the utilization of methane for hydrogen production resulted in significant climate-altering emissions from the process.
To address this challenge, two modern variations of ammonia synthesis have emerged: “blue ammonia,” in which greenhouse gases are captured directly at the production site and sequestered deep underground, and “green ammonia,” which is generated through an alternative chemical route employing electricity instead of fossil fuels to electrolyze water for hydrogen production.
Blue ammonia is already in the initial stages of implementation, with several facilities currently operating in Louisiana, according to Green, and the ammonia is primarily exported to Japan, “indicating that it’s somewhat commercially viable.” Other regions are beginning to explore green ammonia, particularly in areas rich in hydropower, solar, or wind energy to provide cost-effective electricity, including a large facility currently in development in Saudi Arabia.
However, in most regions, both blue and green ammonia still incur higher costs compared to the conventional fossil-fuel-derived version, prompting numerous teams globally to seek ways to minimize these expenses, ensuring that the discrepancy is manageable enough to be compensated through tax incentives or other support.
The issue is escalating, given that as the population expands and wealth increases, the demand for nitrogen fertilizers will grow steadily. Concurrently, ammonia serves as a promising alternative fuel to power hard-to-decarbonize transport modes like cargo vessels and heavy-duty trucks, potentially leading to even greater requirements for the chemical.
“It definitely functions” as a fuel for transportation, powering fuel cells that have been demonstrated for applications ranging from drones to barges, tugboats, and trucks, says Green. “People perceive that the most probable market for that would be shipping,” he remarks, “as ammonia’s drawbacks include its toxicity and odor, making it somewhat hazardous to handle and transport.” Thus, its optimal applications might be in high-volume scenarios located in relatively remote areas, such as the open seas. In fact, the International Maritime Organization will soon vote on new regulations that could significantly promote ammonia as a shipping alternative.
The essential aspect of the newly proposed system is to integrate the two existing methods within a single facility, placing a blue ammonia production plant adjacent to a green ammonia facility. The hydrogen generation process for the green ammonia plant produces a substantial quantity of excess oxygen, which is typically vented into the atmosphere. Conversely, blue ammonia necessitates a pure oxygen source through a process known as autothermal reforming; hence, a neighboring green ammonia factory can utilize this surplus oxygen.
“Placing them side by side has considerable economic benefits,” Green explains. This synergy could enable hybrid “blue-green ammonia” facilities to serve as a crucial stepping stone toward a future where green ammonia, the cleanest variant, may eventually prevail. However, that future is likely decades in the making, according to Green, thus emphasizing the significance of having the combined facilities as a progressive step.
“It might take a significant amount of time before [green ammonia] is economically appealing,” he notes. “At present, it’s far from that point, except in very unique circumstances.” Nevertheless, the co-located plants “could represent a highly attractive concept and perhaps a solid launchpad for the industry,” given that currently only small, standalone demonstration facilities of the green approach are being established.
“If green or blue ammonia is poised to become the preferred method for ammonia production, there’s a necessity to find methods to make it relatively economical across numerous countries, utilizing whatever resources are available,” he asserts. This newly proposed integration “appears to be an excellent idea that can help accelerate progress. Ultimately, a multitude of green ammonia plants will be needed in various locations,” and commencing with the combined plants, which could be comparatively affordable now, could facilitate that objective. The team has submitted a patent application for the process.
Although the team conducted a comprehensive study encompassing both the technology and economic aspects, demonstrating that the system holds significant promise, Green emphasizes, “No one has ever constructed one. Our analysis looks favorable, yet undoubtedly, when the first one is built, there will be peculiar details that require attention,” such as specific procedures for initiating or shutting down the process. “I would argue there’s ample additional work required to establish it as a legitimate industry.” However, the findings of this study, which reveal that costs are considerably lower than existing blue or green facilities in isolation, “definitely foster the likelihood of enabling substantial investments necessary to truly make this industry viable.”
This proposed amalgamation of the two methodologies “enhances efficiency, decreases greenhouse gas emissions, and reduces overall expenses,” comments Kevin van Geem, a professor in the Center for Sustainable Chemistry at Ghent University, who was not involved in this research. “The analysis is thorough, with validated process models, clear assumptions, and comparisons to benchmark literature. By merging techno-economic assessment with emissions accounting, the work offers a credible and balanced perspective on the trade-offs involved.”
He further notes, “Given the scale of global ammonia production, such a reduction could significantly contribute to decarbonizing one of the most emissions-intensive chemical sectors.”
The research team also included MIT postdoctoral researcher Angiras Menon and MITEI research leader Guiyan Zang. The project received support from IHI Japan via the MIT Energy Initiative and the Martin Family Society of Fellows for Sustainability.
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