Conversion of biomass to biofuels and life cycle assessment: a review

Environmental Chemistry Letters (2021) 19:4075–4118 https://doi.org/10.1007/s10311-021-01273-0 REVIEW Conversion of biomass to biofuels and life cycle assessment: a review Ahmed I. Osman1 · Neha Mehta1,2 · Ahmed M. Elgarahy3,4 · Amer Al‑Hinai5 · Ala’a H. Al‑Muhtaseb6 · David W. Rooney1 Received: 6 May 2021 / Accepted: 9 July 2021 / Published online: 23 July 2021 © The Author(s) 2021 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. Keywords Biomass · Biofuel · Thermochemical · Biochemical · Life cycle assessment Introduction * Ahmed I. Osman * Amer Al‑Hinai * Ala’a H. Al‑Muhtaseb 1 School of Chemistry and Chemical Engineering, Queen’s University Belfast, Belfast, Northern Ireland BT9 5AG, UK 2 The Centre for Advanced Sustainable Energy, David Keir Building, Queen’s University Belfast, Stranmillis Road, Belfast, Northern Ireland BT9 5AG, UK 3 Environmental Science Department, Faculty of Science, Port Said University, Port Said, Egypt 4 Egyptian Propylene and Polypropylene Company (EPPC), Port‑Said, Egypt 5 Department of Electrical and Computer Engineering, College of Engineering, Sultan Qaboos University, Muscat, Oman 6 Department of Petroleum and Chemical Engineering, College of Engineering, Sultan Qaboos University, Muscat, Oman In recent decades, 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). Therefore, the necessary shift for exploring alternative options to overcome the world-scale looming energy crisis, considering the environmental concerns and its mitigation, while confronting the spiralling energy demand has become an urgent need of the hour. Biomass, 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). Thus, it is not feasible to substitute fossil-based fuels with the aforementioned sustainable energy sources; hence, biomass 13 Vol.:(0123456789) 4076 Environmental Chemistry Letters (2021) 19:4075–4118 utilisation to produce fuel and chemicals is required (Bharti et al. 2021). Biomass is classified as non-lignocellulosic or lignocellulosic in nature and exists in various forms such as woody, herbaceous, aquatic debris, farming manure and byproducts and other forms (Osman et al. 2019; Kaloudas 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). A recent review discussed integrating hydrothermal and biochemical routes in biomass utilisation from a circular bioeconomy approach (Song et al. 2021). The thermochemical methods usually involve a high energy intake along with solvent or catalyst addition. Meanwhile, the biochemical route has a lengthy cycle period and is less efficient in breaking down recalcitrant biomass materials. Thus, combining those two routes can be promising by incorporating the benefits of both methods in biofuel processing. They proposed a schematic route where hydrothermal routes are being used in the pretreatment stage to prepare the appropriate biomass feedstock for the following biological routes to improve the overall process efficiency and final product yields and vice versa, as shown in Fig. 1. There are unprecedented challenges with the integration of thermochemical and biochemical routes. For instance, the catalysts or solvent utilisation of the thermal routes may result in poisoning or kill the microorganism or generate various inhibitors that can affect the biological progress routes. Furthermore, this integration may lead to additional costs. Identifying sources of biofuels such as biodiesel and biochar can potentially reduce the environmental impacts of fossil fuels (Balajii and Niju 2019; Gunarathne et al. 2019). Biofuels can also counter the increasing use of fossil resources and prevent pressure on non-renewable sources (Peng et al. 2020; Hassan et al. 2020). However, it is important to use practical, scientific and robust tools to evaluate the real benefits of using biofuels over conventional energy sources (Chamkalani et al. 2020; Kargbo et al. 2021). Life cycle assessment (LCA) has been identified as a comprehensive evaluation approach (Astrup et al. 2015) to measure environmental impacts over the entire production chain of biofuels (Collotta et al. 2019). Therefore, this review aims to critically evaluate existing biomass to biofuel pathways and associated studies Fig. 1  Integration of hydrothermal and biochemical routes in biomass utilisation from a circular economy approach. Firstly, the biomass is pretreated using a biochemical process for the following thermochem- ical route or vice versa by thermochemical pretreatment for the following biochemical route and eventually producing biofuel or chemicals 13 Environmental Chemistry Letters (2021) 19:4075–4118 which evaluated environmental impacts for the entire life cycle. The main objectives were to: (1) critically review recent advan (...truncated)