Effect of Mechanical Pretreatment for Enzymatic Hydrolysis of Woody Residues, Corn Stover and Alfalfa

This work aimed to investigate the effects of biomass species on fermentable sugar production, with respect to both energy consumption and sugar yield, using the modified traditional mechanical system from Pulp & Paper Mills as a potential biorefinery step. The study explored four lignocellulosic biomass species including corn stover, alfalfa, white birch and black spruce during the pretreatment process with and without the addition of NaOH. This was followed by a disk refining pretreatment under various operating conditions of gap size and consistency through a pilot scaled disk refining system. The study characterized and analyzed the chemical components and sugar streams obtained from the biomasses using the thermochemical and refining pretreatment and also analyzed the energy consumption of the disk refining system. The results show that for all the biomasses, the thermochemical process mainly removed lignin and hemicelluloses through a steaming pretreatment. From low to high, the lignin contents of the four biomasses are shown as follows: corn stover, alfalfa, white birch and black spruce. With respect to the refining pretreatment, when the gap size remains constant, black spruce has the longest fibers while corn stover has the shortest. Moreover, using enzymatic hydrolysis to evaluate the sugar yield revealed that the thermochemical pretreatment increased the sugar yield in accordance with how much lignin was removed from each biomass as well as their final lignin content. However, the additional refining treatment had a greater effect on corn stover and alfalfa than on white birch and black spruce due to the reduction in fiber length. Therefore, with respect to existing mechanical refining equipment, the modified thermochemical disk refining pretreatment (TCDRP) has a greater effect on agricultural biomass and hardwood (white birch). Specifically, the sugar yield of the TCDRP corn stover was the highest (97.3%) when compared to the other biomasses, while its energy consumption was 196 kWh/ton.