Sustainable, Energy-Efficient Process for Urea Synthesis

Urea, a vital element, is found in all things ranging from skincare commodities to fertilizers. Urea is a natural product of human urine; however, mass production of urea is a huge undertaking and accounts for around 2% of global emissions and energy utilized.

Engineers and scientists, for decades, were on the lookout to make urea production more energy-efficient as there is a huge demand for fertilizers with the growing population. A team of international researchers including engineers and scientists from the University of Texas at Austin developed a novel technique for producing urea that is eco-friendly than the process used to date.

They also focused on making the technology competitive enough to keep pace with the existing energy-intensive industrial processes.

The method currently used includes a two-step thermal process requiring greater amounts of pressure and heat under controlled, harsh environments. The newly devised method involves only a single step and is based on the concept known as electrocatalysis, which involves using electricity, along with sunlight, to activate chemical reactions in a solution at room temperature under ambient conditions.

Around the world, we need to lower emissions. That’s why we want to develop these more sustainable pathways to produce urea using electrocatalysis instead of this energy-intensive two-step process.

Guihua Yu, Associate Professor, Materials Science, Walker Department of Mechanical Engineering, Cockrell School of Engineering

Yu co-led the team, and their research findings have been published in the journal Nature Sustainability.

Currently, synthetic urea is mainly synthesized using the Haber-Bosch method, one of the most valued inventions of the 20^th century as it facilitated bulk production of fertilizer and contributed to an increase in food supply globally.

The conventional method combines hydrogen and nitrogen to make ammonia, which bonds with CO₂ to form urea. This dual-step process involves heating up to 400 or 500 °F for the reaction to occur, all the while taking in large amounts of energy and giving out emissions.

Urea production using electrocatalysis is a more sustainable, alternative process that saves energy. However, this method has not been employed enough to make it a viable alternative.

Also, the process produced many by-products and demanded more energy to disintegrate the bonds of the molecular building blocks to activate the reaction.

The initial challenge facing the researchers was to identify the right elements or catalysts to produce an efficient chemical reaction. The researchers employed nitrate rather than typical nitrogen to bond with CO₂. The catalyst solution comprised indium hydroxide nanomaterials.

According to Yu, the extremely efficient electrocatalyst has “high selectivity,” which means it creates only what the scientists intend to create and not a cluster of by-products. It produced more yields of urea when compared to the earlier attempts with electrocatalysis.

It takes much less energy to break the bonds of nitrate, compared to nitrogen, and that helps produce a lot higher yield of urea.

Guihua Yu, Associate Professor, Materials Science, Walker Department of Mechanical Engineering, Cockrell School of Engineering

Yu considers that this formula could be applied to both small- and large-scale applications. Electrocatalytic devices can be run by individuals and sold to individual farms so that they can produce urea by themselves. The researchers wish to equip large-scale industrial processes with an alternative solution to decrease energy use, which is crucial for a sustainable future because the population and demand for urea will rise in the coming years.

The further steps in this study involve improving the selectivity and yield, along with a prototype device that helps enhance production. The researchers are on the lookout for ways to power the process with solar energy instead of direct electricity.

The study is supported by grants from the U.S. Department of Energy and the Welch Foundation. The team included scientists from Nanyang Technological University in Singapore, the University of Science and Technology of China and the Harbin Institute of Technology.

Journal Reference:

Lv, C., et al. (2021) Selective electrocatalytic synthesis of urea with nitrate and carbon dioxide. Nature Sustainability. doi.org/10.1038/s41893-021-00741-3.

Source: https://news.utexas.edu/