Abstract
The global energy demand is projected to rise by almost 28% by 2040 compared to current levels. Biomass is a promising energy source for producing either solid or liquid fuels. Biofuels are alternatives to fossil fuels to reduce anthropogenic greenhouse gas emissions. Nonetheless, policy decisions for biofuels should be based on evidence that biofuels are produced in a sustainable manner. To this end, life cycle assessment (LCA) provides information on environmental impacts associated with biofuel production chains. Here, we review advances in biomass conversion to biofuels and their environmental impact by life cycle assessment. Processes are gasification, combustion, pyrolysis, enzymatic hydrolysis routes and fermentation. Thermochemical processes are classified into low temperature, below 300 °C, and high temperature, higher than 300 °C, i.e. gasification, combustion and pyrolysis. Pyrolysis is promising because it operates at a relatively lower temperature of up to 500 °C, compared to gasification, which operates at 800–1300 °C. We focus on 1) the drawbacks and advantages of the thermochemical and biochemical conversion routes of biomass into various fuels and the possibility of integrating these routes for better process efficiency; 2) methodological approaches and key findings from 40 LCA studies on biomass to biofuel conversion pathways published from 2019 to 2021; and 3) bibliometric trends and knowledge gaps in biomass conversion into biofuels using thermochemical and biochemical routes. The integration of hydrothermal and biochemical routes is promising for the circular economy.
Highlights
The biochemical route has a lengthy cycle period and is less efficient in breaking down recalcitrant biomass materials. Combining those two routes can be promising by incorporating the benefits of both methods in biofuel processing
Thermochemical and biochemical technologies are the two main routes employed to convert biomass into biofuels. The former route includes hydrothermal liquefaction, pyrolysis, torrefaction, gasification and combustion processes, while the latter route consists of fermentation and anaerobic digestion processes
Both routes have drawbacks: the former method usually involves a high energy intake along with solvent or catalyst addition. The latter route has a lengthy cycle period and is less efficient in breaking down recalcitrant biomass materials
Summary
Urbanisation, modernisation and industrialisation linked to energy production and utilisation have been a fundamental loop in various economic, scientific and social sectors (Ahmad Ansari et al 2020; Shrivastava et al 2019). The depletion of non-renewable fuel sources, accompanied with greenhouse gas emissions, has become a critical issue (Fawzy et al 2020; Osman et al 2021). Unlike other sustainable energy sources such as wind, solar, geothermal, marine and hydropower, can directly produce fuel along with chemicals (Quereshi et al 2021; Farrell et al 2019; Farrell et al 2020). It is not feasible to substitute fossil-based fuels with the aforementioned sustainable energy sources; biomass. Environmental Chemistry Letters (2021) 19:4075–4118 utilisation to produce fuel and chemicals is required (Bharti et al 2021). Various technologies are used to convert biomass into fuel or chemicals, such as gasification, combustion, pyrolysis, enzymatic hydrolysis routes and the fermentation processes (Abou Rjeily et al 2021; Peng et al 2020)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
