A critical review of the effects of pretreatment methods on the exergetic aspects of lignocellulosic biofuels

Pretreatment process is the key technological step in lignocellulose bioconversion into biofuel owing to its robust molecular structure. This pivotal process can markedly affect the overall sustainability of lignocellulosic biofuel systems because of its energy-intensive, chemical-dependent, and time-consuming nature. More advanced methods should then be developed to evaluate the effects of pretreatment methods on the thermodynamic, economic, and environmental features of lignocellulosic biofuel systems. Among the various tools developed so far, exergetic approaches have attracted a great deal of interest for decision-making purposes because of their interdisciplinary character. Exergy-based methods could provide invaluable information regarding the technical characteristics, economic costs, and environmental impacts of lignocellulosic biofuel systems. Hence, this review is aimed at briefly summarizing the lignocellulose pretreatment methods as well as comprehensively reviewing and critically discussing their key effects on the exergetic aspects of the resulting biofuels. Overall, the hotspots of thermodynamic inefficiency, cost loss, and environmental burden of lignocellulosic biofuel systems could be reliably identified using exergetic methods. Much of the current literature on exergetic analysis of the lignocellulose pretreatment process has been particularly limited to dilute sulfuric acid, organosolv, and steam explosion pretreatment methods, while exergetic aspects of alkaline, liquid hot water, biological, and combined approaches have not been evaluated well enough. In addition, the majority of the published works have only focused on quantifying thermodynamic imperfections and determining exergetic efficiencies of the simulation-based lignocellulosic biofuel systems, while a limited number of studies have investigated exergy-based economic and environmental aspects of such biofuel systems. As a suggestion, future studies need to be concentrated on investigating exergetic aspects of the unexplored pretreatment strategies as well as applying exergoeconomic and exergoenvironmental methods for providing information regarding the formation processes of cost and environmental burden.