Understanding the Impacts of AFEX™ Pretreatment and Densification on the Fast Pyrolysis of Corn Stover, Prairie Cord Grass, and Switchgrass

Lignocellulosic feedstocks corn stover, prairie cord grass, and switchgrass were subjected to ammonia fiber expansion (AFEX (TM)) pretreatment and densified using extrusion pelleting and ComPAKco densification technique. The effects of AFEX (TM) pretreatment and densification were studied on the fast pyrolysis product yields. Feedstocks were milled in a hammer mill using three different screen sizes (2, 4, and 8 mm) and were subjected to AFEX (TM) pretreatment. The untreated and AFEX (TM)-pretreated feedstocks were moisture adjusted at three levels (5, 10, and 15 % wb) and were extruded using a lab-scale single screw extruder. The barrel temperature of the extruder was maintained at 75, 100, and 125 A degrees C. Durability of the extruded pellets made from AFEX (TM)-pretreated corn stover, prairie cord grass, and switchgrass varied from 94.5 to 99.2, 94.3 to 98.7, and 90.1 to 97.5 %, respectively. Results of the thermogravimetric analysis showed the decrease in the decomposition temperature of the all the feedstocks after AFEX (TM) pretreatment indicating the increase in thermal stability. Loose and densified feedstocks were subjected to fast pyrolysis in a lab-scale reactor, and the yields (bio-oil and bio-char) were measured. Bio-char obtained from the AFEX (TM)-pretreated feedstocks exhibited increased bulk and particle density compared to the untreated feedstocks. The properties of the bio-oil were statistically similar for the untreated, AFEX (TM)-pretreated, and AFEX (TM)-pretreated densified feedstocks. Based on the bio-char and bio-oil yields, the AFEX (TM)-pretreated feedstocks and the densified AFEX (TM)-pretreated feedstocks (pellets and PAKs) exhibited similar behavior. Hence, it can be concluded that densifying the AFEX (TM)-pretreated feedstocks could be a viable option in the biomass-processing depots to reduce the transportation costs and the logistical impediments without affecting the product yields.