Harnessing the power of biorefining: paving the way for sustainable fuels and chemicals

George W. Huber

George Willis Huber is the Richard Antoine Professor of Chemical Engineering at the University of Wisconsin–Madison. His research focus is the design of disruptive technologies for the conversion of biomass, waste plastics and other waste resources into renewable fuels and chemicals. He is co-founder of Anellotech (https://www.anellotech.com) and Pyran (http://www.pyranco.com). He is the director of the $12.5 million Center on Chemical Upcycling of Waste Plastics (CUWP). Professor Huber has received visiting professorships from the Chinese Academy of Sciences in 2015 (at Dalian Institute of Chemical Physics), from the Royal Netherlands Academy of Arts and Sciences in 2019–20 and the ExxonMobil Visiting Chair Professor at the National University of Singapore in 2019. George did a post-doctoral stay with Avelino Corma at the Technical Chemical Institute at the Polytechnical University of Valencia, Spain (UPV-CSIC). He obtained his PhD in Chemical Engineering from the University of Wisconsin–Madison (2005). He obtained his B.S. (1999) and M.S. (2000) degrees in Chemical Engineering from Brigham Young University.

Muxina Konarova

Muxina Konarova is a Senior Lecturer at The University of Queensland (UQ) in the School of Chemical Engineering. She earned her PhD in Chemical Engineering from the Tokyo Institute of Technology, Japan in 2009. Dr Konarova has received Advance Queensland Research Fellowships (Early Career in 2016, Mid-Career in 2019), a Monash Engineering Women’s Leadership Award in Australia (2016) and represented Australian early/mid-career researchers at the VI World Materials Summit (2017) in Strasbourg, France. Dr Konarova’s research focuses on sustainable process development, specifically the conversion of agricultural biomass and low-value carbonaceous feedstock into carbon-neutral fuels and commodity chemicals. Her work centers around the design of advanced catalytic systems, enabling the production of desired products with high yields.

Jason Y. C. Lim

Jason Y. C. Lim heads the Sustainable Supramolecular Materials Group at the Institute of Materials Research and Engineering (IMRE), A*STAR in Singapore. Having trained in supramolecular chemistry, catalysis and polymer chemistry, he is currently active in sustainable chemistry, developing new catalytic processes for upcycling petroleum-based plastics into valuable chemicals and functional polymeric materials, as well as hydrogels for biomedical applications. He is also an Adjunct Assistant Professor at the Department of Materials Science and Engineering of the National University of Singapore.

Karen Wilson

Karen Wilson is a Sustainable Energy & Fuels Associate Editor and an Energy & Environmental Science Editorial Board member. She is a Professor of Catalysis in the Centre for Catalysis and Clean Energy at Griffith University, and a Distinguished Visiting Professor at Zhengzhou University, China. Her research focusses on the development of tunable porous heterogeneous catalysts for use in green and sustainable chemistry, and the valorisation of waste bio-derived feedstocks for biofuels and chemicals production.

As the world continues to confront the challenges of climate change and the imperative need to transition to cleaner energy sources, biorefining has emerged as a promising solution to improve the economic viability of biomass-based processes. Biorefining is the process of transforming biomass into numerous valuable products, such as renewable fuels and platform chemicals, akin to that in a petrochemical refinery. We are pleased to present the most recent Themed Collection of Sustainable Energy & Fuels on the topic of biorefining, which features a variety of articles highlighting innovative research in the fields of renewable energy and chemical production. This collection of articles highlights the remarkable advances being made in the development of novel catalysts, efficient conversion processes and novel biorefinery concepts for a range of feedstocks including lignocellulose, algae and food waste.

These articles provide a wealth of knowledge that not only demonstrates the potential of biorefining but also highlights our collective efforts to steer our energy landscape towards a greener and more sustainable future. Biomass uses carbon dioxide, water and sunlight as a feedstock. Our society must continue to find practical ways to use renewable biomass if we want to decrease our carbon emissions. Liquid hydrocarbon fuels have almost 100 times higher energy density than batteries, making them the practical energy source for vehicles that require a high-power requirement like aviation, heavy duty vehicles and shipping.

In the field of biorefining, it is crucial to address the concept of feedstock flexibility and explore methods to diversify the sources of biomass while minimizing competition with food production. This approach has been emphasized by Kim et al. (https://doi.org/10.1039/D2SE01345B). In their research, they highlighted the importance of sustainable sourcing practices and introduced novel ways of harnessing oil fractions from non-food alternatives, such as algae. One of the challenges with biomass conversion is how to deal with breaking down the biomass structure to make it suitable for further conversion. One notable technique to break down the biomass structure mentioned in the review article is electroporation. Electroporation relies on high-intensity electrical pulses to disrupt cell walls and introduce foreign molecules for the purpose of modifying existing genes. When applied to microalgae, electroporation enables the continuous reproduction of lipids, which are essential for biofuel production. By creating transient pores in the cell membrane, electroporation facilitates the sustained production of lipids.

In addition to exploring alternative biomass sources, utilizing waste materials as feedstock is another promising approach in ensuring long-term viability and providing environmental benefits. Cruz et al. (https://doi.org/10.1039/D3SE00188A) reported on a study where Tunisian date palm waste was used as feedstock for the production of renewable hydrocarbons (diesel and gasoline) through Fischer–Tropsch synthesis. This research demonstrated the potential of waste materials to be transformed into valuable resources. An interesting aspect highlighted by the authors is the integration of photovoltaic (PV) installations into the biorefinery. They presented a scenario in which a plant’s electricity demand could be met by a 10.7 MW PV system. This approach is particularly noteworthy because many industrial plants currently fulfill their electricity and heat demand by burning natural gas. By integrating PV technology, the biorefinery’s overall efficiency can be significantly improved, leading to a reduction in life-cycle greenhouse gas (GHG) emissions.

However, it is important to note that the large-scale deployment of PV systems would require minerals and the refining of ores, which can have adverse environmental impacts. The authors acknowledge this concern, highlighting the need to carefully consider the potential environmental consequences of such mineral extraction and refining processes.

Valorisation of lignocellulosic biomass is an important aspect of biorefinery due to its abundance and possibility of producing numerous useful chemicals and materials. However, the recalcitrance of lignin can hamper cellulose valorisation. To valorise the lignin component, Vinu and co-workers (https://doi.org/10.1039/D2SE01796B) demonstrated reductive catalytic fractionation (RCF) of lignin using activated charcoal-supported metal catalysts to simultaneously achieve high selectivity of aromatic propyl guaiacol, high degree of delignification and retention of carbohydrates. Notably, delignification and aromatic product selectivity could be enhanced through ultrasonic pre-treatment of the pinewood starting material. Separately, Meyer et al. (https://doi.org/10.1039/D3SE00111C) have shown that mechanocatalytic partial depolymerisation can also be used to achieve depolymerisation of lignocellulose towards oligomeric glycans that can potentially find applications in packaging.

The aviation sector is considered one of the challenging industries to decarbonize due to the limitations of using batteries and hydrogen as alternative fuels. Consequently, there is a growing focus on the synthesis of sustainable aviation fuels and jet fuel extenders to address this issue. An interesting study conducted by Ning Li (https://doi.org/10.1039/D3SE00069A) and his group explores the creosol condensation reaction in the presence of formaldehyde, which resulted in the successful achievement of phenol condensation through hydrodeoxygenation using Ru/H-ZSM-5 catalyst, leading to the production of C₁₄ and C₁₅ bicycloalkanes. In another work, Sharma and co-workers (https://doi.org/10.1039/D3SE00144J) demonstrated that an Fe-loaded silica–alumina solid acid catalyst could produce C₈–C₁₅ bio-jet fuel by low-pressure cracking of methyl oleate and other bio-oils with excellent selectivity under relatively mild conditions. These promising developments harbour great promise for sustainable aviation fuel production.

In line with the growing demand for sustainable transportation solutions, the article on “Ethanol to diesel: a sustainable alternative for the heavy-duty transportation sector” presents an intriguing approach to transforming ethanol into a viable diesel substitute. Ethanol is the most widely produced biofuel but can only be used in gasoline engines. This new approach was reported (https://doi.org/10.1039/D2SE01377K) by a team of researchers from the University of Wisconsin–Madison, USA and Princeton University, USA. The process combines experimental heterogeneous catalysis and process systems engineering to produce diesel with superior properties to its fossil counterparts. The produced fuels have a cetane number ∼70 and exceptional cold flow characteristics, making them a potential alternative to fossil-based diesel fuel. In addition, the process can be carried out with a net energy gain (EROI = 1.49 > 1) and reduced greenhouse gas emissions. This research highlights the need of collaborations across disciplines to accelerate key technological innovations, process optimization and integration strategies in biorefining. Such approach also allows for a far more in-depth analysis of sustainable fuel production.

Another collaborative research work between researchers from UK and Australia (https://doi.org/10.1039/D3SE90021E) is also featured in this collection. Here the authors engineered water-tolerant solid acid catalysts for inhibiting ester hydrolysis and achieving high turnover frequencies in fatty acid esterification in methanol. Such solid catalysts were synthesised by incorporating tungstated-zirconia into hydrophobic periodic mesoporous organosilicas (PMOs) to create Lewis acid sites. They also emphasise the significance of thin film deposition of zirconia to enhance WO_x-loading and generate Brønsted acid sites. The authors suggest that future work employing macroporous counterparts may offer enhanced performance for conversion of larger fatty acid molecules to avoid diffusion limitations. Development of water-tolerant catalysts is crucial considering that biomass contains a significant portion of carbohydrates, and many valuable fine chemicals syntheses may require inhibition of hydrolysis of intermediates.

This themed collection also emphasises the significance of sustainable power generation and wastewater treatment with an article (https://doi.org/10.1039/D3SE00237C) entitled “Phototrophic microbial fuel cells: a greener approach to sustainable power generation and wastewater treatment”. The authors present a method that utilises the power of photosynthetic microorganisms for simultaneous energy production and wastewater treatment, offering a potential solution to the ever-increasing demand for clean energy and water resources. On a smaller scale, there has also been considerable recent attention on converting mechanical energy (such as through human movements) into electricity that can be used to power battery-less nanodevices. In this regard, Li and co-workers (https://doi.org/10.1039/D2SE01715F) have demonstrated that self-assembly of a cyano-functionalised silyl ether on the surface of cellulose-based nanofibre films could function as a green triboelectric nanogenerator. This offers great potential for sustainable self-powered systems in wearable electronics.

These are just a few examples of the great studies highlighted in this collection on biorefining. Each article contributes valuable insights and novel solutions to the difficult challenges of achieving sustainability in energy and chemical production. We thank the authors for their outstanding contributions and commend their commitment to advancing the biorefining concept.

We hope that this compilation of articles will inspire additional research and collaboration among scientists, engineers, and industry professionals, thereby fostering the development of sustainable technologies and the realisation of a greener, more efficient future. We encourage our readers to examine the possibilities presented by these articles.

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