Influence of AFEX™ pretreated corn stover and switchgrass blending on the compaction characteristics and sugar yields of the pellets

• AFEX™ samples achieved their maximum pellet unit density at 94.8 MPa pressure.
• AFEX™ pretreated switchgrass required relatively more energy for compaction.
• Blending and pelleting had no significant effect on sugar yields of AFEX™ samples.

The objective of this research was to investigate the impacts of Ammonia Fiber Expansion (AFEX™) pretreated corn stover and switchgrass blending ratio (25:75, 50:50 and 75:25 percent on dry weight), compressive pressure (31.6, 94.8, and 158.0 MPa), and screen size (2 and 4 mm) on pellet unit density, pellet hardness, specific energy consumption for pellets production, and the sugar yields. A single pelleting unit was employed in the study, and the untreated, AFEX™ pretreated, and AFEX™ pretreated blended samples were pelleted. The pellets produced from AFEX™ pretreated samples reached their maximum pellet unit densities at an applied pressure of 94.8 MPa. Pellet hardness was tested by applying the force to the pellets and recording the maximum force required to break. Results showed that the pellets produced from the small screen size sample at a higher applied pressure required more force to break. Besides, blend with higher proportion of AFEX™ pretreated corn stover produced harder pellets (711 N). Specific energy consumption for the pellets production varied from 11.4 to 57.9 kW h t−1, and due to low bulk density of switchgrass, blends with a higher proportion of switchgrass consumed more energy for pellet production. Glucose yields of the AFEX™ pretreated samples were enhanced by 4–4.5 times and the xylose yields by 2–2.5 times compared to the untreated samples. Pelleting and biomass blending had no significant effects on sugar yields of the AFEX™ pretreated corn stover and switchgrass samples.