Bourbon production generates six to ten barrels of watery waste for every barrel of whiskey produced, but University of Kentucky chemists have found a way to transform that stillage into high-performance energy storage devices. Graduate student Josiel Barrios Cossio and professor Marcelo Guzman developed a method to convert bourbon distillery waste into supercapacitor electrodes that match the energy storage capacity of existing commercial devices.
Barrios Cossio was shocked to learn about the scale of bourbon waste when he began studying the industry. For every final barrel of bourbon produced, distilleries generate six to ten times that volume in leftover stillage — the watery used mash remaining after distillation.
"It's often sold to farmers as livestock feed or soil additives, but it's expensive to dry out and difficult to transport while wet," the researchers noted in their presentation at the American Chemical Society meeting in Atlanta.
The researchers worked directly with local distillery owners, who were happy to provide waste stillage samples. Using a high-intensity pressure cooking technique called hydrothermal carbonization, they converted the liquid waste into useful carbon materials.
The process involves pouring stillage into a reactor and using heat and pressure to transform it into black powder. That powder is then heated to 392°F (200°C) in a furnace to create hard carbon similar to graphite. In some cases, they added potassium hydroxide and heated the material to 1,472°F (800°C) to produce activated carbon.
Both hard carbon and activated carbon offer different advantages for energy storage applications. The team used activated carbon as electrodes to create double-layer capacitors, placing a liquid electrolyte between them. These proof-of-concept devices stored up to 48 watts per kilogram.
Encouraged by initial results, they built hybrid devices combining one activated carbon electrode with one hard carbon electrode, infusing both with lithium ions. The hybrid version achieved energy storage 25 times greater per kilogram than conventional supercapacitors.
While bourbon has been produced in the United States since the 18th century, particularly in Kentucky, commercial consumption and exports really expanded after World War II. Today it represents a multi-billion-dollar market, but the industry's waste stream has remained largely underutilized despite its volume.
The research team acknowledges significant work remains before their method could reach commercial scale. They plan to study the economic feasibility of scaling up production and assess the overall sustainability of their approach. Building larger versions of their supercapacitors will require further engineering and optimization.
Supercapacitors fill an important niche in energy storage, offering rapid charging and discharging capabilities that complement traditional batteries. While batteries excel at storing large amounts of energy for extended periods, supercapacitors can quickly absorb and release power, making them valuable for applications requiring burst energy delivery.
The bourbon industry's waste-to-energy potential extends beyond just stillage. Distilleries typically use charred new oak barrels that cannot be reused for bourbon production, though these are often recycled for aging beer, wine, and various sauces. The successful conversion of stillage into energy storage materials suggests similar approaches might work with other agricultural and food production waste streams.