Green Chemistry
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EDITORIAL
Cite this: Green Chem., 2019, 21,
1168
DOI: 10.1039/c9gc90021g
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Green biorefinery technologies based on waste
biomass†
James H. Clark
Published on 07 March 2019. Downloaded on 2/2/2020 12:17:06 PM.
rsc.li/greenchem
Of the many factors threatening a more
sustainable society for future generations, those of increasing waste and
decreasing primary resources are among
the most important. Our 20th century
linear economic model of mine-processconsume-dispose was based on rapid
growth in consumer demand fed by a
rapidly growing industry, itself fed by
cheap and abundant mineral resources.
The model became auto-catalytic with
more consumer demand encouraging
more production and as that led to lower
costs and to a lower perceived value of
articles, so the practice of replacement
before redundancy became widely
adopted. This in turn led to a “throwaway society”, whereby an article that
had once been seen as useful and valuable quite quickly became something to
be disposed of. However, this model is
not and cannot be sustainable. Our traditional resources, at least in the foreseeable future, are from one planet and
they can only become more expensive
and more scarce, at least in the medium
term, especially as we have already
extracted most of the “easy” resources.
At the same time, our throwaway
items, which were not designed for endGreen Chemistry Centre of Excellence, University of
York, UK
† This paper is dedicated to the memory of Egid
Mubofu, a former student of mine who died
recently. Egid was a successful scientist in academic
and government circles, ending up as the Vice
Chancellor of the University of Dodoma. He was a
real champion for Green Chemistry, especially in
Africa, and a gentle and kind person. He will be
evergreen.
1168 | Green Chem., 2019, 21, 1168–1170
of-life, have been accumulating in landfill sites and more disturbingly, all over
the environment including seas and
rivers.
While there seems to be a real need
for people to review their attitudes about
resources and the value of articles, a successful transition from a linear to a
more circular economic model must be
driven by industry. This must be based
on the use of renewable resources, green
manufacturing and the production of
environmentally compatible, recyclable
products. Since the most widely useful
element in society is carbon and the
most widely used resource is fossil
carbon, it seems appropriate that we
place a lot of attention on more sustainable organic products and on their production from biomass. The choice of
biomass is critical – being renewable
does not guarantee being green and we
must learn from our experience of biofuels that the sourcing of the biomass is
critical. The use of non-food biomass is
vital and even better if we focus on bio
(mass)-waste. These can include agricultural waste, food processing waste,
municipal solid waste and sewage
sludge, although the organic components in these waste streams may not
be entirely bio-based, with ( petroleum
derived) plastic being an increasingly
common component of waste. By using
bio-waste feedstocks to make bio-based
products, we can help solve both
resource and waste problems and be
“double green”.
Bio-waste is rich in biodegradable
organic matter and is available in large
quantities worldwide. The utilization of
bio-waste helps reduce pollution but can
also provide renewable energy and biobased chemicals for the future.
Therefore, biomass waste resource utilization has attracted increasing attention
in scientific, industrial and government
communities. Anaerobic digestion is
probably the most established technology (other than composting) that is
widely applied to the utilization of biowaste, but the (bio) gas produced from
this process is of low value and the costs
of pre-treatment reduce the cost-effectiveness of the process. The chemical
potential of the bio-resource is also lost.
An increasing amount of new research is
focused on the application of different
technologies (including fermentation,
hydrothermal conversion, pyrolysis and
microwave treatment) to make chemicals
from bio-waste and thus improve
resource utilization. However, these
technologies can suffer from high cost
and secondary pollution. There is also a
concern about separation steps, since
these can represent up to 80% of the
total cost of many common chemical
processes and this is likely to increase
the cost for biomass based processes.1
This should be a driver for industry to
consider more the use of mixtures and
target properties and effects, rather than
always aiming for pure compounds
(which are then inevitably mixed into
formulations). The combination and
ultimately the integration of green
technologies is crucial for realising the
full potential of bio-waste as a truly sustainable chemical and energy resource.
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Green Chemistry
In this themed issue of the world’s
leading journal on green and sustainable
chemistry, we sought to address the
challenges and opportunities of biowaste utilization and in particular its use
for making chemicals. This follows on
from, and is informed by, a successful
workshop in China in December 2018
that brought together experts from universities and companies all over the
world to share their recent results and
progress on applying green technologies
in biomass utilization. The workshop
“Green Biorefineries for Biomass Waste
and the Environment” was organized by
Professors Buxing Han (a member of the
Green Chemistry editorial board) and
Shicheng Zhang from Fudan University.
It was held in Shanghai and was run as
part of the ISEH (International
Symposium on Environment and
Health). The workshop featured many
talks from speakers from China, Europe
and the USA. Topics included those
focused on common types of bio-waste,
including bio-energy production from
swine wastewater, bio-chemicals from
food waste, sludge processing, and the
valorization of cereal straws and forestry
residues. There were also more technology-focused presentations on solvothermal processing, microwave activation, solid acid catalysis, pyrolysis and
other bio-processing methods including
anaerobic digestion (AD) as well as membrane bio-reactors. Additionally, other
papers addressed the important issues
of biomass availability, integrated
technologies and bio-refineries. Overall
it was clear that the resource opportunity
is very large and multinational, and
that we can learn from traditional
( petroleum) refineries in aiming for a
range
of
products
including
(lower value) fuels and (higher value)
chemicals. We are still exploring a very
diverse range of valorization technologies. Only AD is currently widely
used and here the resource efficiency is
poor and the product range very
limited. More advanced technologies
offer a much more interesting range of
products and potentially higher resource
utilization, but separation will be a
major obstacle to their widespread
application.
This journal is © The Royal Society of Chemistry 2019
Editorial
The articles in this themed issue
largely reflect the topics and the key
messages from the workshop. Residues
and by-products from biorefinery operations are of particular interest. Biofuel
production
always
leaves
unused
biomass and this can be a rich source of
chemicals, as demonstrated by a group
of Chinese researchers working on algaebased biodiesel production, who also
used the CO2 by-product (DOI: http://dx.
doi.org/10.1039/C8GC03645D).
In
a
related article, Chinese and US research
groups led by the China Agricultural
University studied the organic content of
the often neglected aqueous phase from
the hydrothermal liquefaction of wet
biomass (DOI: http://dx.doi.org/10.1039/
C8GC02907E). In a joint paper from
groups in Belgium and Singapore,
microbial chain elongation is described
as a method for valorizing solid-free,
thin carbohydrate-containing wastes or
side-streams from food processing (DOI:
http://dx.doi.org/10.1039/C8GC03648A).
Lignin is the biggest bio-waste challenge and opportunity, being produced
in multi-million tonne quantities in
many existing processes, including
bioethanol and paper and pulp. In a
paper from the USA led by Princeton,
microbial electrochemical treatment is
used to treat biorefinery black liquors
and to make chemicals (DOI: http://dx.
doi.org/10.1039/C8GC02909A). Speed of
reaction can be essential to maximise
the conversion of lignin to small molecules (minimizing repolymerisation) and
this is demonstrated in a paper from
Spain on ultra-fast processing using
supercritical water (DOI: http://dx.doi.
org/10.1039/C8GC03989E). Once the
lignin is depolymerized and even if we
successfully prevent re-polymerisation,
we still have to deal with mixtures of products. In an article from several groups
at the University of Wisconsin-Madison,
microbes are used to metabolise such
mixtures, sometimes leading to excellent
selectivity to just one aromatic product
(DOI:
http://dx.doi.org/10.1039/
C8GC03504K). Downstream from such
processes, we will need clever green
chemistry to convert lignin decomposition products into more valuable
chemicals. Hydrodeoxygenation is a par-
ticularly important process in this
context and another American group, in
collaboration with Palacky University in
the Czech Republic, report new green
methods for achieving this (DOI: http://
dx.doi.org/10.1039/C8GC03951H).
Lignin itself may have a much wider
range of applications as a material than
those presently used: groups from
Hong Kong report a new functional
material based on a lignin-porphyrin
polymer (DOI: http://dx.doi.org/10.1039/
C8GC02904K). There are also important
papers on agro-food residues such as
corncobs from a group of Chinese universities led by the Guangzhou Institute of
Energy Conversion (DOI: http://dx.doi.org/
10.1039/C8GC02854K). A review on the
chemical potential of cashew nut shells
from a team of African chemists at
Universities including Dar es Salaam is
also featured in this special issue (DOI:
http://dx.doi.org/10.1039/C8GC02972E).
The application of green chemical
technologies to the valorization of biowaste is the main topic of a significant
number of the articles published here.
Catalysis is the most important of all of
these and in an article from a multinational collaboration between Hong Kong,
Thailand and Korea, aluminium biochar
is reported as a composite catalyst for
glucose isomerization (DOI: http://dx.doi.
org/10.1039/C8GC02466A). Catalysis is
also predominant in the article on corncobs, and in another article from Poland,
zinc oxide is used for oxidations under
ultrasonic activation (DOI: http://dx.doi.
org/10.1039/C8GC03131B).
Microwave activation of biomass is
becoming a very popular approach to
making bio-based chemicals, both in
terms of efficient heating but also for
more selective processes that minimize
run-away reactions to gases and small
molecules. Two papers from the York
Green Chemistry Centre of Excellence
describe different examples of how
microwaves can be used to help direct
biomass pyrolysis processes towards particular chemical products (DOI: http://dx.
doi.org/10.1039/C8GC03015D and http://
dx.doi.org/10.1039/C8GC02994F). This
special issue also contains a major
review on using microwaves to convert
biomass into chemicals and energy,
Green Chem., 2019, 21, 1168–1170 | 1169
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Editorial
which includes a feature on its combined use with alternative solvents that
interact strongly with microwave radiation (DOI: http://dx.doi.org/10.1039/
C8GC03908A).
Ethanol remains the most developed
biomass-derived chemical product. In a
review from groups in China, Spain,
Brazil and Azerbaijan, emerging techniques in bioethanol production are considered (DOI: http://dx.doi.org/10.1039/
C8GC02698J). The potential of adding
value to the main production by utilizing
biomass side-products like pectin is also
considered.
1170 | Green Chem., 2019, 21, 1168–1170
Green Chemistry
The future is very uncertain and we are
seeing almost daily examples of the
impact of climate change and political
turmoil. We are also being made increasingly aware of the harm to our planet and
to ourselves of waste and pollution.
Scarcity of resources is also a major threat
to a stable and sustainable society. As
Green Chemists we have the privilege to
be able to work on some of these problems and with that comes an opportunity
to “make a difference”. But we also have
the responsibility to use our skills and
knowledge effectively and wisely. Turning
waste streams from being environmental
threats into valuable resources, while also
reducing our dependency on virgin
resources, has multiple appeals and could
make a real difference to our ability to
provide a sustainable future for our planet
and those that live on it.
James Clark
Green Chemistry Centre of Excellence
University of York, UK
References
1 V. G. Zuin, Pure Appl. Chem., 2016, 88,
29.
This journal is © The Royal Society of Chemistry 2019