**4.1. Life cycle of biomass hydro-fractionation**

For the conversion of the lignocellulosic biomass feedstock to bio-based products, there are several processes involved. Firstly, the agricultural plants are grown and harvested in which the agricultural residues and wastes could then be collected and transported for storage. The pretreatment and fractionation of the biomass are performed to prepare the material for some particular manufacturing processes. The obtained bio-based products are later on distributed to marketplaces and delivered to customers. The life cycle assessment (LCA) is known as a systematic method for evaluating the environmental impact of a product's entire life, starting from growing its feedstock to its disposal process [46]. For example, in case of the bio-based product, lignocellulosic biomass feedstock was generated from agricultural crops which require soil, fertilizers, water, and sunlight for its growth, while water, electricity, and heat are necessary for its manufacturing process. However, to make this chapter concise, only the pretreatment and fractionation process of the feedstock is emphasized.

In a study, Prasad and his team evaluated the life cycle of four different pretreatment methods including liquid hot water (or subcritical) extraction, organosolve extraction, dilute acid extraction, and steam explosion of milled corn stover [47]. The four environmental impacts in terms of climate change, eutrophication, water depletion, and acidification potential were predicted and compared among the four methods. For climate change, the CO2 emission was reported whereas subcritical water extraction gave the smallest amount of CO2 emission while almost 15 times of CO2

could be released from steam explosion due to higher energy consumption which required more electricity during the fractionation process. The second parameter, eutrophication or the nutrition enrichment of the Earth's surface, was determined by comparing nitrogen gas and phosphorus equivalents. The eutrophication took place mostly on the feedstock growth step; therefore, the efficiency of the fractionation process plays important roles on this part. Subcritical water extraction was found to show the smallest impact on eutrophication since less amount of feedstock is required for producing the same amount of the desired product. The subcritical water extraction also showed the smallest impact toward water depletion. In addition, the study indicated more than 90% of water in all four processes that was used in the feedstock growth step. The last parameter is acidification potential, where organosolve extraction and steam explosion showed smallest effects while diluted acid extraction had the highest impact on acidification potential.
