Biofuels produced from cellulosic biomass can be used to replace petroleum-based transportation fuels. However, the manufacturing cost of cellulosic biofuels is still high, partly due to the low density of cellulosic feed-stocks. Pelleting of cellulosic feedstocks can increase their density, making their transportation and storage as well as biofuel conversion more efficient and, therefore, reducing the overall cost of biofuel manufacturing. It has been shown that ultrasonic-vibration-assisted (UV-A) pelleting, without using high-temperature steam and binder materials, can produce pellets with density comparable to that produced by conventional pelleting methods. Furthermore, the sugar yield of biomass (wheat straw) processed with UV-A pelleting is 20% higher than that of biomass pelleted without ultrasonic vibration. This paper reports an experimental investigation of UV-A pelleting of switchgrass. The influences of ultrasonic vibration on pellet density, stability, durability, and pelleting force are discussed. It is concluded that pellets processed with ultrasonic vibration had higher density and stability than those processed without ultrasonic vibration, they were more durable than those processed without ultrasonic vibration, and pelleting force with ultrasonic vibration was lower than that without ultrasonic vibration.
