Charles Loney1, Ashley Graybill1, Cheyan Xu1, Julie Renner1*, Prashant Acharya2, David Suttmiller2, Lauren Greenlee2, Luke Wiles3, Katherine Ayers3, Wayne Gellett3
 Case Western Reserve University;  University of Arkansas; and  Proton OnSite, United States
NH3 Fuel Conference, Minneapolis, November 2, 2017
AIChE Annual Meeting, Topical Conference: NH3 Energy+
Today, most ammonia (NH3) manufacturing occurs via the Haber-Bosch process. This process consumes hydrogen from fossil fuels, and as a result NH3 contributes the highest amount of greenhouse gas emissions out of the top 18 large-volume chemicals made globally. Because the process is high temperature (400°–500°C) and pressure (150–300 atm) with a low (15%) single-pass conversion efficiency, the plants have to be very large to be economical. This means that ammonia is shipped from centralized locations, further increasing greenhouse gas emissions because of the fuel consumed in transportation. Additionally, their large size makes it difficult to integrate with renewable sources of hydrogen, such as electrolysis.
One promising alternative approach for NH3 manufacturing is to use electricity to drive the reaction, decreasing the need for high pressure and heat. This electrochemically driven process would be compatible with intermittent operation and enable utilization of renewable electricity, eliminating greenhouse gas emissions. Because electrochemical technologies are highly scalable, electrochemical ammonia production would enable distributed, near-point-of-use manufacturing. As megawatt (MW)-scale electrolysis systems are already being sold by companies such as Proton OnSite, localized ammonia production at relevant scales is feasible. There is also a natural synergy in using distributed wind power for fertilizer production. In the Plains and Upper Midwest, excess wind production capacity, transmission limitations, and high regional demand for nitrogen based fertilizers combine to create excellent economic drivers for this technology. Ammonia also has many other uses, including in chemical synthesis, refrigeration, or even has a fuel. It also features a high energy storage density. This flexibility in use makes ammonia an attractive renewable energy storage option.
While electrochemical ammonia generation is promising, the low-temperature and low-pressure testing to date has shown low efficiencies (<1%), highlighting the need for creative catalyst approaches. An ideal catalyst would facilitate the reduction of nitrogen to NH3 without undesired hydrogen evolution occurring. Meanwhile, the enzyme nitrogenase which reduces nitrogen in nature, operates at mild temperatures and pressures with high efficiency (75%). To address the need for efficient catalysts in electrochemical ammonia generation, Case Western Reserve University, the University of Arkansas, and Proton OnSite are collaborating to develop manufacturable, peptide-bound electrocatalysts inspired by the enzyme nitrogenase. Proton OnSite and their collaborators have spent the past few years developing an anion exchange membrane (AEM)-based technology, which is ideal for ammonia synthesis because the alkaline configuration allows the utilization of a wider array of low-cost catalysts. In this work, peptide-functionalized catalysts are developed, characterized and tested in and AEM-based system. The novel materials show promise compared to conventional catalyst approaches.
Read the abstract at the AIChE website.
Download this presentation [PDF, 3.2MB].
RELATED NH3 FUEL CONFERENCE PAPERS
2017: Design of Iron-Nickel Nanocatalysts for Low-Temperature Electrochemical Ammonia Generation
2017: Nitrogenase Inspired Peptide-Functionalized Catalyst for Efficient, Emission-Free Ammonia Production
2016: Developments in Electrochemical Ammonia Synthesis
2015: High Efficiency Low Cost Electrochemical Ammonia Production [PDF]