How chemists turned bourbon waste into supercapacitors

The bourbon industry, a multi-billion-dollar sector, generates a significant amount of waste in the form of grain byproducts from distilleries. Researchers from the University of Kentucky have pioneered a groundbreaking technique to convert this byproduct, known as stillage, into valuable carbon electrodes. These electrodes are instrumental in the creation of supercapacitors that boast energy storage capabilities comparable to today’s leading commercial devices. This innovative research was recently showcased at a meeting of the American Chemical Society in Atlanta, Georgia. The bourbon-making tradition in the United States, particularly in Kentucky, dates back to the 18th century. However, it gained substantial traction in both consumption and exports post-World War II. For a whiskey to be classified as bourbon, its mash must contain at least 51% corn, with the remainder typically consisting of rye and barley. The production process begins with grinding the grains and mixing them with water, followed by the addition of a previous distillation’s mash to create a sour mash. After fermentation, the mash is distilled into a clear spirit known as “white dog,” which is then aged in charred new oak barrels for a minimum of two years. The aging process imparts bourbon with its signature dark color and rich flavor, thanks to the caramelized sugars and vanillin from the charred wood. While the barrels are often repurposed for products like barrel-aged beer and sauces, a large portion of the watery stillage produced during fermentation goes to waste. Graduate student Josiel Barrios Cossio was surprised to discover that for every barrel of bourbon produced, six to ten barrels of stillage are left over. Although some of this byproduct is sold as livestock feed or soil additives, the process of drying and transporting it can be costly and challenging. To address this issue, Barrios Cossio and his research advisor, Marcelo Guzman, explored the potential of transforming this liquid waste into useful carbon materials through a process known as hydrothermal carbonization, which utilizes high-pressure cooking techniques.