NH3 is an important chemical, mainly produced through the Haber-Bosch process. High temperature and pressure (&gt;400 °C, 150 bar) ) is required to obtain fast kinetics and to ensure high conversions. As a result, NH3 synthesis is known to be very complex and energy-intensive, accounting for three percent of CO2 emissions and up to 3% of world’s energy consumption. Overcoming this complication has led to a century of research to improve the catalyst. However, only slight improvements are achieved in the chemistry of the catalyst, and the catalyst is almost unchanged.<br/>To eliminate the dependency on fossil fuel and the carbon dioxide emissions, NH3 can be synthesized from wind-powered plants, and renewable resources: hydrogen from electrolysis of water and nitrogen from pressure swing adsorption of air. Here we make carbon-neutral NH3 in the UMN-WCROC plant, located in the agricultural region of Morris MN. Though working, the costs are twice that made conventionally, which is due to downscaling (40,000 scaled down process). Thus we are seeking a more efficient process to synthesize carbon-neutral NH3.<br/>In our proposed innovative process, we use the conventional catalyst and a solid absorber. With the reaction-absorption, NH3 can be synthesized at low pressure, with rates comparable to high-pressure conventional processes. The absorber enables us to remove NH3 from the reactor at high temperature, and remove the NH3 more completely, decreasing the concentration of NH3 in the recycle flow, which increases the driving force for the synthesis. In our low pressure reaction-absorption process, the work of compressing the fresh feed is significantly reduced, and the need for heat exchange also drops.<br/>In this talk, we discuss our recent findings of the reaction-absorption process. Our results indicate that the NH3 production rates can be sustained at pressures as low as 10-20 bar. Our studies show that the NH3 synthesis via reaction-absorption process is no longer controlled by the chemical kinetics or restricted by the reverse reaction, but governed by the absorption of NH3 and the recycle of unreacted hydrogen and nitrogen. I will also discuss some of the latest improvements in the supported absorbents design.<br/>This process suggests a strategy for making ammonia fertilizer locally, using wind-generated electricity. Alternatively, this NH3 made in rural areas, can be used as a fuel, or more advantageously, as a hydrogen carrier for fuel cell feed in more urban areas.

Lower pressure ammonia synthesis

254th National Meeting (2017)

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