Sound waves and water droplets transform paper waste into higher-value chemical compound

Researchers at the University of Illinois Urbana-Champaign have discovered a groundbreaking method to convert lignin, a byproduct of the papermaking industry, into a valuable renewable chemical compound. Each year, over 50 million tons of kraft lignin is produced as a result of the pulp and paper manufacturing process. Traditionally, more than 90% of this lignin is incinerated to recover chemicals and generate energy.

However, scientists at Illinois have focused on harnessing the full potential of lignin, which has been challenging due to the need for catalysts and harsh reaction conditions in previous methods.

The team led by chemistry professor Joaquín Rodríguez-López and graduate student Supriya Das developed a novel approach using tiny water droplets energized by sound waves. This process, known as microdroplet chemistry, breaks down lignin in just 20 minutes at room temperature, without catalysts or harsh chemical conditions. The result is a dark-colored powder that transforms into a redox-active molecule with an orange color, indicating a significant chemical transformation.

In their study published in the journal Small, the Illinois researchers detail how their microdroplet method converted about 56% of the complex kraft lignin into a smaller molecule with potential applications in energy and chemical fields. The team named this unique molecule SEMILL-A (Sonicated Emulsive Microdroplet, SEM). The discovery was part of the DROPLETS project at the Beckman Institute for Advanced Science and Technology and involved collaboration with experts from Illinois, Princeton University, and Argonne National Laboratory.

The microdroplet method not only offers a high conversion rate but also has the potential to facilitate the nitration of lignin, making it a promising candidate for energy storage applications, such as redox flow batteries.