COMMENT

Chemistry challenges to enable a

sustainable bioeconomy
Nichole D. Fitzgerald
A bioeconomy — that is, an economy in which fuels, chemicals and other products are sourced
from biomass — can contribute to a sustainable and prosperous future. Realizing a bioeconomy
will necessitate new methods for processing the complex structure of biomass to produce
commodity chemicals. Many exciting opportunities are availing themselves to chemists brave
enough to tackle this challenging problem.

Implementing a bioeconomy involves deriving a portion and many are a part of the International Energy
of the world’s carbon requirements for fuels and Association Bioenergy Agreement, which provides a
chemicals from renewable, sustainable and biologically forum for collaborative studies to aid the international
derived carbon sources. As the only renewable liquid development of bioenergy.
transportation fuels that are compatible with our existing
infrastructure, biofuels are a major component of a US A paradigm shift
bioeconomy, which can contribute to more affordable Although the promise of a bioeconomy is clear, achieving
and reliable energy choices for American families. Yet a this goal will require us to overcome numerous tech-
bioeconomy includes much more than fuels — renewable nical hurdles, not least the chemistry challenges that
carbon streams will serve as precursors to many chemi- are outlined here. For example, the fledgling concept
cals and novel performance-advantaged materials, as well of biorefinery operation presents pressing challenges,
as a source of renewable power to supply the electricity making this topic fertile for research and development.
grid. Affordable access to these products will give us a By contrast, the petroleum industry has benefited from
bioeconomy that is truly environmentally friendly and over a century of research, shaping most synthetic
sustainable. chemistry and product development to be reliant on
fully saturated organic starting materials — a hydro­
The promise of a bioeconomy carbon paradigm. Without focused initiatives, develop-
The US Department of Energy has estimated that ing a bioeconomy as sophisticated and efficient as the
the US alone has the potential to sustainably produce petroleum industry will take decades. It will require a
one billion US tons of biomass per year by 2040. In paradigm shift away from starting with materials devoid
this context, sustainability is defined as “creating and of functionality and then painstakingly introducing
maintaining conditions under which humans and each heteroatom. Biomass-derived starting materials are
nature can exist in productive harmony, that permit already rich in oxygen, and in principle these materials
fulfilling the social, economic and other requirements can be converted to equally oxidized products. When
of present and future generations.” (REF. 1) The billion using biomass as a starting material, the primary chal-
tons of biomass includes agricultural waste residues, lenge shifts from adding functionality to instead remov-
forest residues, energy crops, algae and waste streams2. ing excess functionality. Developing these processes
A billion dry tons of sustainable biomass, or 2 × 1012 lb, will introduce exciting new challenges for chemists,
can serve as the feedstock for 50 billion gallons of bio- while enabling a bioeconomy for a sustainable future.
fuels, 75 × 109 kWh of electrical energy, and 50 × 1012 lb Sustainability will come sooner if chemists in research
Bioenergy Technologies Office, of bio-based chemicals and bioproducts3. The process laboratories work with those in industry to rapidly
Office of Energy Efficiency and of growing, harvesting, transporting and converting implement fundamental discoveries into commercial
Renewable Energy, a billion tons of biomass would create 1.1 million direct processes. Such cooperation is promoted by the US
U.S. Department of Energy,
Golden Field Office, Golden,
jobs in the US, many of which would be in rural areas. Department of Energy National Laboratories, which lead
Colorado 80401, USA. Domestically, developing this work is the remit of the the Bioprocessing Separations Consortium, ChemCatBio
nichole.fitzgerald@ee.doe.gov US Department of Energy Bioenergy Technologies and Agile BioFoundry — teams charged with
doi:10.1038/s41570-017-0080 Office. Internationally, numerous countries around the tackling separations, catalysis and biomanufacturing
Published online 20 Sep 2017 globe are pursuing their own version of a bioeconomy, challenges, respectively.

NATURE REVIEWS | CHEMISTRY VOLUME 1 | ARTICLE NUMBER 0080 | 1

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COMMENT

Unique feedstocks, unique challenges The complex nature of biomass feedstocks means that
Biomass feedstocks are complex. Lignocellulosic feed- many technologies that have been developed for petro-
stocks are composed of tightly wound cellulose, hemi­ leum feedstocks are not amenable to biomass feedstocks
cellulose and lignin polymers. The feedstocks have very or at least require significant modifications. Working with
high oxygen content (up to 50 wt%), which can be present in biomass feedstocks poses many chemistry challenges,
multiple reactive forms, including aldehydes, phenols and several of which are outlined in FIG. 1. On assessing
acids, depending on the severity of the biomass pretreat- the common issues that plague the development of bio­
ment and deconstruction. The complexity of this poten- refining, one can identify three prominent chemistry chal-
tially corrosive mixture can lead to undesired chemical lenges: catalyst development for selective deoxygenation
reactions. Water is a significant component of biomass and upgrading of oxygenated intermediates, separations
feedstocks, causing common catalyst support materials, and lignin utilization. At present, these processes con-
such as alumina, to undergo hydrolysis and decomposi- tribute substantially to the price of biofuel, and we have
tion. Biomass can contain elemental impurities, including much room for improvement on all three fronts. Analysis
alkali metals, S, N and Cl. In addition, the process of har- by the National Renewable Energy Laboratory has shown
vesting or acquiring the feedstock introduces many more that, for an unoptimized process, catalyst costs contribute
impurities, such as silica. Any single source of biomass is up to 23% of the cost of the conversion process4. Up to
heterogeneous, and sourcing biomass from many species 50% of the conversion costs are from separations, many
and regions adds even more complexity and heterogeneity. of which are unique to biological processes, such as the

Biomass Deconstruction Chemical Synthesis and Biofuels and

feedstocks and fractionation intermediates upgrading bioproducts

Feedstock, product Examples Related chemistry challenges

or process (listed in order of importance)

Biomass • Agricultural residues • Separations

feedstocks • Forest residues • Feedstock pretreatment
• Energy crops • Contaminant removal
• Organic waste streams • Understanding chemical composition
• Biogas and variability of feedstocks
• Algae

Deconstruction • Hydrolysis • Separations

and fractionation • Pyrolysis • Lignin valorization
• Hydrothermal liquefaction, • Robust and inexpensive catalytic processes
gasification • Improved enzymatic processes

Chemical • Syngas • Separations

intermediates • Bio-oil • Stabilization of chemical intermediates
• Sugars (including catalytic processes)
• Other biologically derived • Characterization of complex mixtures
chemical building blocks,
such as 5-(hydroxymethyl)furfural

Synthesis and • Catalytic chemical processes • Robust and inexpensive catalytic processes
upgrading • Biological processes • Separations
• Waste-stream valorization
(including lignin valorization)
• New biochemical processes
• Streamlined biological engineering
• Renewable and/or cost-effective
hydrogen generation

Biofuels and • Jet, gasoline or diesel fuel • Identification of target molecules

bioproducts • Drop-in chemical replacements • Product certification
• Functional replacements of • Refinery integration
existing products
• Novel bioproducts

Figure 1 | The chemical challenges associated with converting biomass, via value-addedNature
intermediates,
Reviews | Chemistry
to bio-based products. Biomass feedstocks are deconstructed and the products fractionated to afford chemical
intermediates. These intermediates can be further subjected to chemical or biochemical reactions to give biofuels
and bioproducts. Prominent challenges include those associated with developing efficient catalytic reactions and
separations.

2 | ARTICLE NUMBER 0080 | VOLUME 1 www.nature.com/natrevchem

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 COMMENT

isolation of products present at low concentrations in valorization strategies that use real biorefinery-derived
fermentation broths5. Finally, lignin accounts for about lignin streams instead of model compounds or ideal-
a third of biomass by weight and carbon content, such ized lignin streams. Numerous lignin deconstruction
that lignin valorization strategies could offset the cost strategies have been pursued, including homogeneous
of biofuel production by as much as US$2 per gallon if and heterogeneous catalysis, ionic-liquid solvolysis, bio-
transformed to useful chemicals, allowing for the sale of logical funnelling and thermochemical deconstruction.
a value-added co‑product alongside the biofuel. Despite the decades of research on lignin valorization,
existing biorefineries still divert lignin streams to com-
Catalysis bustion for the production of heat and power. As more
Virtually all pathways that convert biomass into a hydro- fuel plants producing cellulosic ethanol (and eventually
carbon fuel require a catalytic process. Catalysts for bio- hydro­carbons) come online, our lack of progress in lignin
energy applications need to be inexpensive and robust valorization will become problematic, because a plant
— that is, not susceptible to poisoning by the multiple that processes 2,000 tons of corn stover per day will pro-
impurities that are found in biomass and intermediates duce 70,000 tons of lignin per year 6–8. Burning a third of
en route to bio-based products. Although much of the a feedstock instead of converting it to useful products is
catalyst development for hydrocarbon fuel produc- a waste of a valuable resource.
tion has focused on catalysts for the bulk introduction
of hydrogen atoms into materials, there are many Outlook
opportunities to design better catalysts for the selective With contents that include heterogeneous polymers and
deoxygenation of highly oxygenated bio-derived inter- impurities, biomass is a varied and complex feedstock. The
mediates. For example, selective removal of a single unique properties of biomass feedstocks require unique
hydroxyl group from a sugar intermediate could pave chemistry solutions to convert biomass into useful hydro-
the way to novel, performance-enhanced bioproducts carbon biofuels and bioproducts. Finding these solutions
that are too costly to prepare from petroleum-derived will give chemists the opportunity to lay the groundwork
starting materials. As bio-derived products become for a sustainable bioeconomy across the globe.
more commercially prevalent, new catalytic reactions
1. Senate and House of Representatives of the United States of
for introducing hydrogen atoms into complex systems America in Congress. National Environmental Policy Act of 1969
will be necessary. Other pervasive challenges in catalysis Title I, Sec. 101a, https://energy.gov/nepa/downloads/national-
environmental-policy-act-1969 (1969).
for bioenergy include developing catalysts with longer 2. U.S. Department of Energy. Billion-Ton Report: Advancing Domestic
lifetimes, minimizing biogenic carbon loss to coke and Resources for a Thriving Economy Vol.1, https://energy.gov/sites/
prod/files/2016/12/f34/2016_billion_ton_report_12.2.16_0.pdf
aqueous waste streams, increasing fuel and product (2016).
yield, and controlling product selectivity and branching. 3. Rogers, J. N. et al. An assessment of the potential products and
economic and environmental impacts resulting from a billion ton
bioeconomy. Biofuels, Bioprod. Biorefin. 11, 110–128 (2017).
Separations 4. Dutta, A. et al. Process design and economics for the conversion of
lignocellulosic biomass to hydrocarbon fuels: thermochemical
Separations remain a pervasive challenge for biofuels research pathways with in situ and ex situ upgrading of fast pyrolysis
development. Contaminants are introduced at every vapors. National Renewable Energy Laboratory https://www.nrel.
gov/docs/fy15osti/62455.pdf (2015).
step of bioproduct synthesis, from the harvesting of the 5. Dunn, J. Biochemical conversion. U.S. Department of Energy https://
feedstock to the conversion process. Removing small www.energy.gov/sites/prod/files/2017/05/f34/Bioprocessing%20
Seperations%20Consortium_0.pdf (2017).
oxygen-containing molecules, such as alcohols and 6. Ragauskas, A. J. et al. The path forward for biofuels and
acids, from aqueous media without energy-intensive biomaterials. Science 311, 484–489 (2006).
7. Beckham, G. T., Johnson, C. W., Karp, E. M., Salvachua, D. &
techniques, such as distillation, is a common problem. Vardon, D. R. Opportunities and challenges in biological lignin
For example, the continuous removal of a dilute product valorization. Curr. Opin. Biotechnol. 42, 40–53 (2016).
8. Davis, R. et al. Process design and economics for the conversion of
from fermentation broths would be valuable for bio­ lignocellulosic biomass to hydrocarbons: dilute-acid prehydrolysis
energy applications. However, adding multiple sepa- and enzymatic hydrolysis deconstruction of biomass to sugars and
biological conversion of sugars to hydrocarbons. National
ration steps to a process can make it unviable from an Renewable Energy Laboratory https://www.nrel.gov/docs/
economic standpoint, and in order to produce cost- fy14osti/60223.pdf (2013).
competitive biofuels we must develop conversion pro- Acknowledgements
cesses, including catalytic reactions, that are tolerant to N.D.F acknowledges K. Craig and J. Male for helpful discussions.
diverse contaminants. Competing interests statement
The author declares no competing interests.
Lignin
Pretreating or deconstructing lignocellulosic biomass FURTHER INFORMATION
Agile BioFoundry: http://www.agilebiofoundry.org/
affords a lignin-rich stream, the nature of which depends Bioprocessing Separations Consortium: http://www.bioesep.org/
on the pretreatment strategy used. For example, acidic Bioenergy Technologies Office: http://www.energy.gov/eere/bioenergy/
bioenergy-technologies-office
pretreatments catalyse C–C bond formation across ChemCatBio: http://www.chemcatbio.org/
lignin polymers, and this crosslinking makes them more International Energy Association Bioenergy Agreement:
http://www.ieabioenergy.com/about/contracting-parties/
difficult to deconstruct. In this regard, we must develop

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