Synthesis of 2-methyl tetrahydrofuran from various lignocellulosic feedstocks Sustainability assessment via LCA

Resources, Conservation and Recycling 95 (2015) 174–182
Contents lists available at ScienceDirect
Resources, Conservation and Recycling
journal homepage: www.elsevier.com/locate/resconrec
Synthesis of 2-methyl tetrahydrofuran from various lignocellulosic
feedstocks: Sustainability assessment via LCA
Hsien H. Khoo ∗ , Loretta L. Wong, Jonathan Tan, Valerio Isoni, Paul Sharratt
Institute of Chemical and Engineering Sciences, 1 Pesek Road, Singapore 207683, Singapore
a r t i c l e
i n f o
Article history:
Received 9 July 2014
Received in revised form 2 December 2014
Accepted 29 December 2014
Available online 24 January 2015
Keywords:
Sustainability
Biomass
LCA
Land footprint
a b s t r a c t
This work highlights that bio-based chemicals may not automatically be synonymous with “green”, and
efforts to generate the quantitative environmental performance of bio-products via LCA are crucial in
ensuring their sustainable attributes. 2-Methyl tetrahydrofuran (2-MeTHF) is a new solvent derived
from natural product sources. A relative LCA comparing 2-MeTHF manufacture originating from different biomass resources was carried out to investigate the sustainability of each feedstock. The biofine
process was employed as a model for the production of levulinic acid from a mixture of C5 and C6 sugars
before the final synthesis of 2-MeTHF. A new perspective of LCA impact, land footprint (total land area
required), is proposed as a result of our evaluation, taking into account the viewpoint of competing land
use options in the LCAs of green chemicals.
© 2015 Elsevier B.V. All rights reserved.
1. Introduction
The chemical industry has grown in size and technological
maturity through the 20th century and is currently facing pressure to rethink its operations to adapt to a changing world. Amidst
concerns of global warming and decreasing fossil fuel reserves,
the manufacturing of environmentally friendly and green chemical
products has emerged (Clark, 2007). Some of the new bio-based
materials include new developments in the synthesis of chemicals
and cellulosic biofuels.
However, the transition from a petroleum-based economy to
one that exploits the potential of biomass requires new strategies
(Serrano-Ruiz et al., 2011). In order to be sustainable, biomass utilization demands the successful deployment of innovative, new
technologies now known as biorefineries. Large scale utilization
of biomass for the production of fuels and chemicals is associated
with a number of important environmental issues, namely land
footprint (area utilized), energy inputs and the application of fertilizers during the stage of agriculture (Dornburg et al., 2004; Luo
et al., 2009).
Along with the option to switch from fossil to bio-based chemicals comes the selection of biomass resources based on their
availability, sustainability and the available methods that can
be applied to process them into useful products. Lignocellulosic
∗ Corresponding author. +65 67967341.
E-mail address: khoo hsien [email protected] (H.H. Khoo).
http://dx.doi.org/10.1016/j.resconrec.2014.12.013
0921-3449/© 2015 Elsevier B.V. All rights reserved.
biomass is the target feedstock in this paper due to the fact that it
is an agriculture residue or crop by-product; hence no land competition for food is expected. This paper seeks to take into account
different biomass feedstocks: sugarcane bagasse, rice straw and
corn stover from different geographical locations.
1.1. Sugars (C5 /C6 ) from biomass
Lignocellulosic biomass has a variable content of cellulose,
hemicelluloses and lignin depending on the type of feedstock, country of origin and a number of other factors. However, the content of
cellulose is generally in the range of 29–45%, hemicellulose in the
range of 18–30%. These two polymers are among the most abundant
in nature, representing a form of renewable feedstock trapped in a
complex matrix, lignin (Yu et al., 2013a; Zhang et al., 2013; Gu et al.,
2013). The presence of lignin reduces the availability of such a great
energy reservoir dramatically since its complex phenolic polymeric
nature, prevents the direct access to hemicelluloses and cellulose.
Harsh conditions are generally required to breakdown lignin, such
as high temperature and high pressure or chemical treatment. After
separation of the solid residue (from lignin), the acidic solution containing a mixture of both hemicelluloses and cellulose is subject to
hydrolysis of the polysaccharides into monomeric C5 (pentoses)
and C6 (hexoses) sugars. Hexoses can be converted into levulinic
acid, whereas pentoses can undergo dehydration to form furfural.
Both levulinic acid and furfural can be converted to 2-MeTHF, but
in this work the effort was focused on the levulinic acid pathway.
H.H. Khoo et al. / Resources, Conservation and Recycling 95 (2015) 174–182
Three different types of non-edible biomass were considered for
the study: bagasse, rice straw and corn stover. The glucan contents
were extracted from various references (Yu et al., 2013a,b; Zhang
et al., 2013; Gu et al., 2013; Yang et al., 2013; Liu et al., 2013).
For each type of biomass the following parameters were
reported (Table 1):
• Glucan content in the corresponding biomass (expressed as
w/w%).
• Theoretical maximum yield of levulinic acid (assuming 100% conversion of glucan, expressed as w/w%) are calculated as:
- Mass of glucan/molecular weight of C6 sugar (C6 H12 O6 ) = moles
of C6 sugars.
- Moles of C6 sugars × molecular weight of LA = mass of levulinic
acid (assuming 100% yield).
• Yield of levulinic acid based on the biofine process (expressed as
w/w%) as 70% of theoretical as claimed by Hayes et al. (2005).
• Expected quantity of levulinic acid that could be produced in a
year per hectare of land (based on the biofine process) is estimated as: crop yield × biofine LA yield.
In this paper we focused on the production of levulinic acid and
2-MeTHF. Any additional information about side/undesired products (chars, combustible material, recycling of sulfuric acid) arising
from treatment of biomass, is not within the scope of the analysis.
2. Case study: bio-based 2-MeTHF
Three types of lignocellulosic biomass are introduced as a
renewable feedstock for the production of 2-methyl tetrahydrofuran (2-MeTHF). The non-edible biomass resources – corn stover,
sugarcane bagasse and rice straw – are selected with the consideration that they will not contribute to the social issues of limited food
supplies (Lal, 2005). The three top producers of stover, bagasse and
rice straw are the U.S. (USDA, 2013; Pikul et al., 2001; Shinners and
Binversie, 2007), Brazil (Sun et al., 2013) and China (CNGOIC, 2013)
respectively. The high variability of sugars content in the biomass is
affected by multiple factors such as location, land fertility, season
etc. In our study we based our conclusions on the representative
data summarized in Table 1.
The next section describes the conversion technology employed
to turn sugars into levulinic acid (LA), and subsequently into 2MeTHF. Life cycle assessment (LCA) – introduced in Section 3
– is employed to test the environmental impacts of the whole
cradle-to-gate system. LCA investigations are gaining momentum
for comparing the sustainability of processes, as well as, for quantifying the environmental impacts of different methods applied in
material production (Blengini et al., 2011; Klemeš et al., 2007).
To the best of our knowledge, no publications exist in peer
reviewed journals on the detailed LCA of 2-MeTHF.
2.1. Synthesis of 2MeTHF from biomass
In this work the overall conversion of biomass into 2-MeTHF
is considered as part of an ideal process, based on three known
industrial sequences described in the literature (Fig. 1) (Farone and
Cuzens, 1996; Fitzpatrick, 1997; Elliot and Frye, 1999; Kumar et al.,
2009).
It is worth noticing that the biofine process could be used for the
direct transformation of biomass into levulinic acid in one single
efficient process. However, the limited amount of details for such a
process (including different types of non-paper biomass), led us to
consider three different industrial procedures for the conversion of
cellulosic biomass into 2-MeTHF.
175
2.1.1. Step 1: From rice straw to C5 and C6 sugars
In the first step (acidic treatment of lignocellulosic material) the
biomass is treated with H2 SO4 (sulfuric acid) to furnish C5 (pentoses) and C6 (hexoses) sugars. For this transformation we referred
to an industrial process by Farone and Cuzens (1996) in which rice
straw is used as biomass and data from such a process were extrapolated (Fig. 2). Further reading on biomass pretreatment can be
found in Kumar et al. (2009).
Sulfuric acid is used at different stages of the process and its
concentration varies along the way, but it is possible to recover it,
at least partially. The C5 /C6 sugars are generally obtained as streams
(aqueous).
Side products of the hydrolysis process are:
• Si containing material (which can be either incinerated or
processed to produce silica gel).
• Combustible residue (which can be used to produce energy for
the process).
It was found that the energy used in pretreatment was essentially negligible compared with that required for isolation of
furfural or levulinic acid.
2.1.2. Step 2: Conversion of C5 sugars to furfural and C6 sugars to
levulinic acid
The mixture of C5 and C6 sugars can be treated in different
ways in order to favour the production of either furfural or levulinic acid (Fitzpatrick, 1997). Some processes targeted furfural as
intermediate to 2-MeTHF whereas others preferred levulinic acid
as intermediate (Hayes et al., 2005; Rackemann and Doherty, 2011;
Parton et al., 2012; Sabesan and Spado, 2013). The main issue in
those processes is the separation of C5 sugars from C6 sugars in
order to reduce undesired reactions, leading to an extra step to
purify/separate materials and eventually a lower yield.
However, to the best of our knowledge the biofine process seems
to be the only industrially relevant process able to favour the production of either levulinic acid or furfural starting from a mixture
of C5 and C6 sugars (Fitzpatrick, 1997). The typical yield claimed
for such process is around 50% by mass of C6 sugars into levulinic
acid (for example), 20% formic acid and 30% char. This means that
if the total sugars input is 0.51 kg (from Step 1), the expected levulinic acid output is 0.17 kg. The remainder mass consist of “solid
by-products or chars” and formic acid (from the C6 sugars) which
can be easily removed and sold as commodity chemical. The biofine
process is described in Fig. 3 (Hayes et al., 2005).
2.1.3. Step 3: Hydrogenation of levulinic acid
Finally, levulinic acid can be converted to 2-MeTHF via hydrogenation as explained in the Pacific Northwest Laboratory process
(Fig. 4) (Elliot and Frye, 1999). In this process the hydrogen is used
in excess (hydrogen/levulinic acid molar ratio = 5.9/1), yielding 2MeTHF (63% by mass).
The overall (mass) balance of all inputs and outputs to the process chain can be deduced from Table 1.
3. Method: relative LCA
Due to the increasing trend of the transition from a fossilbased to bio-based economy, the importance of carrying out an
environmental impact assessment of solvent production from a
systems-based perspective is becoming more apparent. LCA provides important additional information that can aid in the selection
of a synthesis pathway for a given material (Blengini et al., 2011;
Klemeš et al., 2007; Hellweg et al., 2004; Hatti-Kaul et al., 2007).
176
H.H. Khoo et al. / Resources, Conservation and Recycling 95 (2015) 174–182
Table 1
Comparison between different types of biomass (dry mass) to produce levulinic acid.
Type of biomass
Glucan content
(w/w%)
Theoretical yield of
LA (w/w%)
(calculated)
Biofine LA yield
(w/w%) (reported)g
Biomass (kg)
required for 1 kg LA
(calculated)
Potential Productivity of LA
from biofine (theoretical)
(kg/ha-yr)
Bagasse
45.2a
42.9b
29.1
27.7
20.4
19.4
4.90
5.17
4629
4394
Rice
straw
33.7c
35.9d
21.8
23.2
15.2
16.2
6.58
6.17
380
405
Corn
stover
31.7e
35.9f
20.5
23.2
14.3
16.2
6.99
6.17
501
567
a
b
c
d
e
f
g
Yu et al. (2013a).
Zhang et al. (2013).
Gu et al. (2013).
Liu et al. (2013).
Yang et al. (2013).
Yu et al. (2013b).
Hayes et al. (2005).
Fig. 1. Summary of the overall process to convert biomass into 2-MeTHF, combining three known processes.
Fig. 2. Details of the process to produce C5 /C6 streams of sugars from rice straw.
3.1. Goal and scope
each biomass feedstock selection, the system boundary starts with
agricultural practices in different locations: corn stover from U.S.,
sugarcane bagasse from Brazil, and rice straw from China. The entire
LCA flow diagram is illustrated in Fig. 5.
The functional unit, which ends at the “factory gate”, is defined
as 1 kg 2-MeTHF ready for use.
In the comparative or relative LCA system, the boundary starts
with agriculture activities (farm) where biomass is produced, and
next treated for the extraction of usable sugars. The sugars are
then sent to the biorefinery where 2-MeTHF is synthesized. For
CHO
H
O
HO
H
H
OH
H
OH
OH
CH2 OH
C6 sugars
O
O
HO
H
O
+
COO
OH
O
Hydroxy
H
meth
hylfurfural
F)
(HMF
Le
evulinic acid
H
OH
Formic acid
CHO
H
HO
O
H
OH
H
OH
CH2 OH
O
O
O
Furfural
+
H
OH
O
Formic acid
a
C5 sugars
Fig. 3. Biofine process chemical transformation.
Deecomposition
n
products
H.H. Khoo et al. / Resources, Conservation and Recycling 95 (2015) 174–182
for stover and rice straw, which are both left on the field after harvest. As for bagasse, mass allocation is made at the mill, where the
residual biomass is generated.
H2
0.05 Kg
H2
0.10 Kg
Pacific North
hwest
P
Laboratory
y
Levulinic acid
1.00 Kg
177
2-MeTHF
F
0.63 Kg
g
4. Results and discussions
4.1. Feedstock and land area
H 2O
0.31 Kg
g
O
3 H2
COOH
H
-2 H 2O
Lev
vulinic acid
O
2-Me
eTHF
Fig. 4. Hydrogenation of levulinic acid yields 2-MeTHF.
LCA studies are able to account for the material flows and fluctuations in the value chain of chemical production pathways. Based
on the yield of crops per land area (ton/ha-yr), ratio-of-biomass to
crop, amount of possible sugars extracted from each biomass feedstock (Table 1), conversion to LA and final synthesis of 2-MeTHF;
the amount of feedstock required can be easily derived from:
Feedstock total(kg/ha-yr) = [Yield(crop) in ton/ha-yr × 10−3 ]
× ratio(crop-to-residue) × %yield(sugars)
For all different biomass to material pathways, similar amounts
of sulfuric acid consumption and recovery were assumed. Therefore, there it was not necessary to carry out the LCA of H2 SO4 , nor,
compare the environmental impacts due to its consumption. Byproducts (Si, chars, formic acid) are not within the system boundary
of the LCA.
3.2. Inventory/data
LCA accounts for all input and output flows occurring along
the production chains, from planting and harvesting of crops,
collection of biomass residues, to the final conversion of levulinic acid from sugars and production of 2-MeTHF. Since for all
three cases, the biorefinery (biofine) employed are similar, energy
input and emissions from the final stage of production is omitted.
Taking into account different scenarios of each location (U.S.
and Brazil), the following are included in data collection and analysis: land use for agriculture; CO2 intake and emissions, yield of
crop, harvesting and crop-to-lignocellulosic biomass ratio. Details
of the data inventory are compiled from corn, sugarcane and rice
farms in U.S., Brazil and China respectively. They are presented in
Appendix A. Hydrogen supplied to the biorefinery is produced via
steam reforming of natural gas. The input-output data for the life
cycle of natural gas to hydrogen production is also contained in
Appendix A. The input–output inventories are allocated by mass
× %conversion(sugars-to-LA)
× %conversion(LA-to-2MeTHF)
(1)
The need to include the viewpoint of competing land use options
in the LCAs of green chemicals has been highlighted by Dornburg
et al. (2004). Impacts of land use have already been reported
LCA investigations. One such example can be found in de Baan
et al. (2013), where land use impacts are associated with loss of
biodiversity. The land use impacts are also segregated across biogeographic regions and taxonomic groups. In another example, the
multi-functionality of land use considering types of biodiversity
well as ecosystem services are modelled as environmental impacts
(Koellner et al., 2013).
In line with the need to measure the sustainability of bio-based
products, a different LCA land impact perspective, land footprint
(total land area required), is proposed. Land footprint is different
from the land use impact reported by Koellner et al. (2013) and
de Baan et al. (2013) since biodiversity and various types of ecosystem services are not considered. In addition to that, land use change
impacts are directed towards the production of crops rather than
its residual biomass (e.g. Davies-Barnard et al., 2014). Hence we
can reasonably assume that land use change impact investigations
are not applied to biomass residuals. However, since agricultural
land is cultivated primarily for growing crops, and the land footprint area is estimated from the amount of crop required as a
Fig. 5. Life cycle production stages of biomass cultivation to 2-MeTHF. (a) Amount of biomass feedstock per kg 2-MeTHF (only average values shown). (b) Land footprint (LF)
required per kg 2-MeTHF (only average values shown).
178
H.H. Khoo et al. / Resources, Conservation and Recycling 95 (2015) 174–182
Global Warming Potenal per kg 2-MeTHF
16
13.75
14
12.01
kg CO2-eq
12
10
8
6.64
6
5.62
4.95
4
3.05
2
2.57
1.70
1.74
0
stover
bagasse rice straw
stover
Biomass culvaon
bagasse rice straw
bagasse rice straw
stover
Conversion/producon
Total
Fig. 7. Global warming potential results (only average values are shown on graph).
Acidificaon Potenal per kg 2-MeTHF
0.05
0.041
0.04
0.039
0.035
kg SO2-eq
0.034
0.03
0.023
0.02
0.015
0.009
0.01
0.006
0.005
0
stover
bagasse rice straw
Biomass culvaon
Fig. 6. (a) Total lignocellulosic feedstock required; (b) corresponding amount of land
area required for the production of 1 kg 2-MeTHF.
prerequisite stage, before lignocellulosic biomass can be produced.
The following equation is introduced:
Land footprint(per kg 2-MeTHF) in total ha/yr
bagasse rice straw
stover
bagasse rice straw
Conversion/producon
Total
Fig. 8. Acidification potential results (only average values are shown on graph).
eutrophication (Fig. 9) and total energy use (Fig. 10). For all cases,
the potential impacts from agriculture are allocated by mass to the
biomass residual of stover, bagasse and rice straw.
4.2. Global warming potential
(2)
The results are displayed in Fig. 6a and b respectively.
From Fig. 6(a) the widest range of biomass feedstock amount
required seems to be stover, which is an indication of the potential amount of sugars that can be extracted from stover (refer to
Table 1); from these amount of feedstock consumed, the associated land footprint per product can be estimated. In terms of
land footprint (LF) per product (Fig. 6(b)), the order of preference
is sugarcane-bagasse, next rice straw and last of all, corn stover.
The most efficient crop (per land area utilized) is sugarcane, where
yields in the range of 60.11 ton/ha-yr to as high as 112.4 ton/ha-yr
have been reported (de Figuiredo and La Scala, 2011; Sun et al.,
2013). Comparatively, the highest recorded yields for the other
two crops are about 10 ton/ha-yr for both corn (Kim et al., 2009;
USDA, 2013) and rice (Xia and Yan, 2011; CNGOIC, 2013). This gives
sugarcane-bagasse a competitive edge as a choice of feedstock for
producing various types of biomass products. However, it should be
highlighted that the widespread promotion of bio-materials made
from sugarcane and its by-products come with an additional environmental burden – the demand for sugarcane-bagasse has led to
the clearing of forest areas for the expansion of sugarcane plantations in Brazil. It was reported that during the years 1996–2006
land conversions to grow more sugarcane led to more greenhouse
gas emissions due to deforestation (Sparovek et al., 2009).
The next sets of environmental impacts, from cradle-togate, are global warming potential (Fig. 7), acidification (Fig. 8),
As shown in Fig. 7, a significant portion of GWP results are from
agriculture, most notably from rice straw. China, the world’s major
rice producer, is a large contributor of nitrous oxide (N2 O) and
methane (CH4 ) – two significant greenhouse gases that are released
from rice paddy fields (Ahmad et al., 2009). The amount of CH4
generation is known to be affected by different farming practices
including fertilizer practices (Li et al., 2011) and tillage management (Cruvinel et al., 2011). Nitrogen related emissions are due to
N-fertilizer usage in the fields.
The GWP result shown for bagasse, which is slightly higher than
stover, is due to the emissions related to the transportation of sugarcane to the mill, where bagasse is generated as a by-product
Eutrophicaon per kg 2-MeTHF
0.008
0.007
0.007
0.007
0.007
0.006
kg phosphate-eq
= Feedstock total(kg/ha-yr) × [1/ratio(crop-to-residue) ]
× [1/Yield(crop) in ton/ha-yr × 10−3 ]
stover
0.004
0.004
0.003
0.002
0.001
6.45E-05
6.40E-05
0
stover
bagasse rice straw
Biomass culvaon
stover
bagasse rice straw
Conversion/producon
stover
bagasse rice straw
Total
Fig. 9. Aquatic eutrophication results (only average values are shown on graph).
H.H. Khoo et al. / Resources, Conservation and Recycling 95 (2015) 174–182
Total Energy consumpon per kg 2-MeTHF
20
19.45
19.65
18
16
179
Compared with agricultural stages of the LCA, other upstream
processes do not have any significant energy demands. According
to Hayes et al. (2005), the chars generated from the biofine process
can provide sufficient energy input for the biorefinery.
total MJ
14
12
11.48
11.28
10
8
5. Concluding remarks
9.22
9.02
6
4
2
0.20
0
stover
bagasse rice straw
Biomass culvaon
stover
0.20
0.20
bagasse rice straw
Conversion/producon
stover
bagasse rice straw
Total
Fig. 10. Energy use (only average values are shown on graph).
after sugarcane milling. Overall, in order to produce 1 kg 2-MeTHF,
rice straw resulted in about 52% and 60% higher global warming
potential results, compared to bagasse and stover respectively.
4.3. Acidification potential and eutrophication
Both stover and rice straw score about 41–44% higher than
bagasse in acidification and eutrophication impacts.
Emissions of NOx and NH3 are the consequences of N-fertilizer
applications in agricultural lands. Measured in LCA environmental
impact models as acidification potential (Fig. 8) and eutrophication (Fig. 9), these emissions are released from soil to atmosphere
after fertilizations, during the growing season, before and after harvesting (Yang et al., 2010). Both results show that the weights of
these environmental burdens fall mostly on the agriculture stages
of the production chain, with little contribution from the processes
employed to produce chemicals. Out of eight corn and stover production areas in the U.S. Corn Belt, Kim et al. (2009) reported that
nitrogen-related emissions from soil are major contributors to the
environment since large quantities of N-fertilizers are applied. The
environmental impacts of anthropogenic reactive nitrogen-related
emissions (NOx , NH3 ) are also evident from rice fields in China
(Yang et al., 2010; Xia and Yan, 2011).
Studies have been undergoing to control the use of N-fertilizers
which can result in tradeoffs with respect to eutrophication.
Improvements can be made by a combination of three farming
strategies: tillage, fertilizer practices and the use of buffer strips
to sequester nutrients (Xue et al., 2014).
4.4. Energy use
Of all three lignocellulosic biomass resources, bagasse has to be
collected after the processing of sugarcane at the sugar refinery. On
the contrary, stover and rice straw are collected directly from fields
after harvesting. The additional steps for bagasse include transportation from sugarcane plantations to the sugar mill, plus power
consumption during the processing sugarcane at the mills, resulted
in 53% and 42% more energy consumed than stover and rice straw
respectively (per 1 kg 2-MeTHF produced).
If bagasse – typically a by-product from sugarcane mills – is not
used for making bio-based materials, the by-product will be burned
on-site to power the mill itself. Assuming a traditional cogeneration
system employed in Brazilian sugarcane mills which operates on
Rankine Cycle processes (with overall efficiency 50%), along with a
heating value of bagasse as 7.5 MJ kg, about 3.75 MJ worth of steam
can be generated from 1 kg bagasse (Dias et al., 2011). Since about
8 kg of bagasse is required per kg 2-MeTHF (Fig. 6(a)), a total 30 MJ
would be made available to the sugar mills if bagasse is not utilized
to make other materials or chemicals.
Efforts to shift from fossil-based resource to renewable ones
have recently gained momentum. As fossil fuel depletion continues to be a global concern, various industries are exploring ways to
produce bio-based materials and chemicals. Three types of lignocellulosic biomass (stover, bagasse and rice straw) are introduced
as a renewable feedstock for the production of 2-methyl tetrahydrofuran (2-MeTHF). Life cycle assessment or LCA is applied for
each biomass feedstock selection, from their respective agricultural
production systems to biomass collection, sugars (C5 /C6 ) extraction, a biorefinery and ends at the “factory gate”, to produce 1 kg
2-MeTHF ready for use. The inventory data to support the LCA
for biomass cultivation for corn-stover, sugarcane-bagasse and rice
straw were extracted from the U.S., Brazil and China respectively.
However, the sugars content in all three biomass resources are
derived from various reports (summarized in Table 1). The biofine
process was employed as a model for the production of levulinic
acid from a mixture of C5 and C6 sugars before the final synthesis
of 2-MeTHF.
This work highlighted that alternative biomass resources should
be carefully selected based on their availability, sustainability and
the available technologies that can effectively convert them into
useful products. The LCA results demonstrated that bio-based
chemicals may not automatically be synonymous with “green”.
Such efforts to create more informed quantitative environmental
performance of bio-products have also been reported in other case
studies (e.g., Blengini et al., 2011).
Apart from GWP, acidification, eutrophication, energy use, a
new LCA impact, land footprint (total land area required), was
proposed. The order of preference for the results shown for land
footprint (LF) per kg 2-MeTHF is sugarcane-bagasse, followed
by rice straw and last of all, corn stover. All agriculture stages
score significantly higher in global warming potential, acidification, eutrophication and energy use, compared to the impacts from
the stages of processing biomass to 2-MeTHF. Rice straw resulted
in about 52% and 60% higher global warming potential results
compared to bagasse and stover respectively. Both stover and rice
straw score about 41–44% higher than bagasse in acidification and
eutrophication impacts.
Bagasse contributed the most to energy utilization, 53% higher
than stover and 42% higher than rice straw. This is due to the extra
stages of transportation from sugarcane plantations to the sugar
mill, and power consumption during the processing of sugarcane
at the mills. However, the overall observed environmental impact
of bagasse was much lower than those of stover and rice straw.
Besides being a valuable source of providing energy for (when
burned) sugar mills, bagasse seemed to be the most suitable candidate for producing bio-based chemicals. Apart from being the
most efficient crop per land footprint, a relatively higher glucan
content (up to 45 w/w%) provides a higher potential for levulinic
acid production.
Acknowledgement
The team would like to thank the GSK-Singapore Partnership
for Green and Sustainable Manufacturing for funding and supporting our work on A Multi-Disciplinary Assessment of Sustainable
Solvents.
180
H.H. Khoo et al. / Resources, Conservation and Recycling 95 (2015) 174–182
Table 4.A
Input and output data for rice production in China [12].
Appendix A.
The yields of crops are extracted from various country and
national reports from U.S., Brazil and China [1–8]. They are compiled in Table 1.A. The input–output datasets pertaining to various
agricultural practices within each country are also extracted from
literature [9–13]. Fertilizer use and other inputs, as well as the
associated emissions, are reported for sugarcane, corn and rice in
Tables 2.A, 3.A and 4.A respectively.
H2 gas is produced from steam reforming of natural gas. In
the process, the hydrocarbons are catalytically split in the presence of steam at temperatures of 800–900 ◦ C [14]. During the
Table 1.A
Yield of crops [1–8].
Yield
Range in ton/ha-yr
Sugarcane
Corn
Rice
60.11–112.4
5.75–10.16
3.6–10.0
Component
Amount
Comments
Input per 1 kg rice crop production
0.944 m3
Water
Energy used
0.78 MJ
Nitrogen fertilizer
1.71 × 10−3 kg
Phosphate fertilizer
4.73 × 10−3 kg
3.79 × 10−3 kg
Potassium fertilizer
3.53 × 10−5 kg
Pesticides
Substances
Amount
For pest prevention
Allocated to RS
in field
Output/emissions per 1 kg rice production
CO2
1.28 × 10−3 kg
8.96 × 10−2 kg
4.07 × 10−2 kg
2.85 × 10−2 kg
CH4
5.98 × 10−4 kg
4.19 × 10−4 kg
N2 O
6.42 × 10−7 kg
4.49 × 10−7 kg
NOx
a
NH3
1.28 × 10−3 kg
8.96 × 10−2 kg
0.7 kg
Rice straw
a
For irrigation
For traction
Fertilizers used in field
Comments
GHG emissions
from rice field
From N-fertilizers
Residual
biomass left on
field after rice
harvest
Extracted from EcoInvent [13].
Table 2.A
Input and output data for sugarcane production in Brazil [9].
Component
Amount
Comments
Input per 1 kg sugarcane production
0.043 m3
Water
0.103 MJ
Energy used
1.184 × 10−3 kg
Nitrogen fertilizer
9.686 × 10−4 kg
Phosphate fertilizer
3.239 × 10−3 kg
Potassium fertilizer
Lime
0.005 kg
For irrigation
For traction
Fertilizers used in field
For soil
treatment/condition
enhancer
For pest prevention
4.892 × 10−5 kg
Pesticides
Output/emissions per 1 kg sugarcane production
a
−1173 kg/ha-yr
CO2 -eq
Carbon sequestration
due to application of
green harvest
From manual
harvesting which
involves traditional
burning before harvest
From fertilizer
application
950 kg/ha-yr
1.560 × 10−5 kg
4.42 × 10−6
2.49 × 10−4
N2 O
NOx
NH3
Input per 1 kg bagasse production (at sugarcane mill)
Residual biomass
3.78 kg (26.4% bagasse
Sugarcane
per kg sugarcane)
0.567
kWh
Energy input
a
Extracted from De Figueiredo and La Scala [10].
Table 3.A
Input and output data for corn production in U.S. from seven corn producing states
in U.S. Corn Belt [11].
Component
Amount
Input per 1 kg whole corn production
0.5 MJ
Energy used
0.02 kg
Nitrogen fertilizer
Phosphate fertilizer
8.27 × 10−3 kg
8.18 × 10−2 kg
Potassium fertilizer
2.83 × 10−4 kg
Herbicides/insecticides
Substances
Amount
Allocated to
stover in field
Comments
For field operations
Fertilizers used in field
For pest prevention
Table 5.A
Input and output data for Hydrogen production from natural gas [15].
Component
Input per 1 kg H2 production
Natural gas
Energy used
Amount
4 kg
1.15 MJ
Output/emissions per 1 kg H2 production
9.155 kg
CO2
CO
0.04 g
N2 O
0.023 g
0.9 g
NOx
Comments
Steam reforming process
Water-gas shift reactor
Based on the
production capacity of
the hydrogen plant of
1.5 million Nm3/day
(57 million scfd)
Table 6.A
Input and output data for hydrogen production from natural gas [16–17].
Component
Amount
Input per 1 kg natural gas production
Oil
0.042 MJ
Natural gas
0.16 kg
Output/emissions per 1 kg natural gas production
70.9 g
CO2
0.25 g
CO
14.17 g
CH4
0.46 g
NOx
0.28 g
SOx
Comments
Process details from
Cetinkaya et al. [17],
page 3, Table 2
Gas losses due to
piping negligible
catalytic split, syngas is produced that mainly consists of H2 and
CO: Cn Hm + nH2 O → nCO + (n + m/2)H2 .
From there, CO from syngas is converted into CO2 and H2 :
CO + H2 O → CO2 + H2 .
The input–output data for H2 production is extracted from Spath
and Mann [15], and is compiled in Table 5.A. The inventory for natural gas production (Table 6.A) is compiled from Spath and Mann
[16]; and verified with process details from Cetinkaya et al. [17].
Comments
Output/emissions per 1 kg whole corn production
0.021 kg
0.012 kg
Net emissions
CO2 -eq
5 × 10−4 kg
2.9 × 10−4 kg
N2 O
From fertilizer
−3
0.0031
1.8 × 10 kg
NOx
application
0.58 kg
Left on field after corn harvest
Stover
References
[1] USDOA (U.S. Dept. of Agriculture). Crop Production 2012 Summary. U.S. Dept. of Agriculture; 2013. p. 1057–7823.
[2] Pikul Jr JL, Carpenter-Boggs L, Vigil M, Schumacher TE, Lindstrom MJ, Riedell WE. Crop yield and soil condition under ridge
H.H. Khoo et al. / Resources, Conservation and Recycling 95 (2015) 174–182
and chisel-plow tillage in the northern Corn Belt, USA. Soil Tillage
Res 2001;60(1–2):21–33.
[3] Kim S, Dale BE, Jenkins R. Life cycle assessment of corn grain
and corn stover in the United States. Int J LCA 2009;14(2):160–174.
[4] Sheehan J, Aden A, Paustian K, Killian K, Brenner J, Walsh M,
Nelson R. Energy and environmental aspects of using corn stover
for fuel ethanol. J Ind Ecol 2003;7(3–4):117–146.
[5] Shinners KJ, Binversie BN. Fractional yield and moisture of corn
stover biomass produced in the Northern US Corn Belt. Biomass
Bioenerg 2007;31(8):576–584.
[6] Sun XZ, Fujimoto S, Minowa T. A comparison of power generation and ethanol production using sugarcane bagasse from
the perspective of mitigating GHG emissions. Energy Policy
2013:57:624–629.
[7] Ministry of Agriculture. Price Policy for Sugarcane: the 2013–14
Sugar season. Commission for Agricultural Costs and Prices, Ministry of Agriculture, Government of India; 2012.
[8] China’s rice, wheat and soybean production. China National
Grain and Oils Information Centre (CNGOIC), State Administration
of Grain, Beijing, China; 2013.
[9] EcoInvent. Food industry/processing – sugarcane production:
BR, Materials Science and Technologies, EMPA – Swiss Center for
Life Cycle Inventories; 2006.
[10] de Figuiredo EB, La Scala Jr N. Greenhouse gas balance due to
the conversion of sugarcane areas from burned to green harvest in
Brazil. Agric Ecosys Environ 2011;141:77–85.
[11] Kim S, Dale BE, Jenkins R. Life cycle assessment of corn grain
and corn stover in the United States. Int. J. LCA 2009;14:160–174.
[12] Xia Y, Yan X. Life cycle evaluation of nitrogen-use in ricefarming systems: implications for economically-optimal nitrogen
rates. Biogeosciences 2011;8:3159–3168.
[13] EcoInvent. Food industry/processing – rice production: GLO,
Materials Science and Technologies, EMPA – Swiss Center for Life
Cycle Inventories; 2012.
[14] Koroneos C, Dompros A, Roumbas G, Moussiopoulos N. Life
cycle assessment of hydrogen fuel production processes. Int J
Hydrog Energy 2004;29:1443–1450.
[15] Spath PL, Mann MK. Life cycle assessment of hydrogen
production via natural gas steam reforming. Report No. DE-AC3699-GO10337. National Renewable Energy Laboratory (NREL), U.S.
Dept. of Energy Laboratory; 2001.
[16] Spath PL, Mann MK. Life Cycle Assessment of a Natural Gas
Combined-Cycle Power Generation System. Report No. NREL/TP570-27715. National Renewable Energy Laboratory (NREL), U.S.
Department of Energy Laboratory; 2000.
[17] Cetinkaya E, Dincer I, Naterer GF. Life cycle assessment
of various hydrogen production methods. Int J Hydrog Energy
2011;37:1–10.
References
Ahmad S, Li C, Dai G, Zhan M, Wang J, Pan S, et al. Greenhouse gas emission from
direct seeding paddy field under different rice tillage systems in central China.
Soil Tillage Res 2009;106:54–61.
Blengini GA, Brizio E, Cibrario M, Genon G. LCA of bioenergy chains in Piedmont
(Italy): a case study to support public decision makers towards sustainability.
Resour Conserv Recycl 2011;57:36–47.
Clark JH. Perspective: green chemistry for the second generation biorefinery – sustainable chemical manufacturing based on biomass. J Chem Technol Biotechnol
2007;82:603–9.
CNGOIC (China National Grain and Oils Information Centre). China’s rice, wheat and
soybean production. Beijing, China: China National Grain and Oils Information
Centre (CNGOIC), State Administration of Grain; 2013.
Cruvinel EBF, Bustamante MM, Kozovits AR, Zepp RG. Soil emissions of NO, N2 O and
CO2 from croplands in the savanna region of central Brazil. Agric Ecosys Environ
2011;144:29–40.
Davies-Barnard T, Valdes PJ, Singarayer JS, Jones CD. Climatic impacts of land-use
change due to crop yield increases and a universal carbon tax from a scenario
model. J Clim 2014;27:1413–24.
181
de Baan L, Alkemade R, Koellner T. Land use impacts on biodiversity in LCA: a global
approach. Int J LCA 2013;18:1216–30.
de Figuiredo EB, La Scala N Jr. Greenhouse gas balance due to the conversion of
sugarcane areas from burned to green harvest in Brazil. Agric Ecosys Environ
2011;141:77–85.
Dias MOS, Modesto M, Ensinas AV, Nebra SA, Filho RM, Rossell CEV. Improving
bioethanol production from sugarcane: evaluation of distillation, thermal integration and cogeneration systems. Energy 2011;36:3691–703.
Dornburg V, Lewandowski I, Patel M. Comparing the land requirements, energy
savings, and greenhouse gas emissions reduction of biobased polymers and
bioenergy. An analysis and system extension of life-cycle assessment studies.
J Ind Ecol 2004;7:93–116.
Elliot D, Frye JG. Hydrogenated 5-carbon compound and method of making. US
Patent 5883266; 1999.
Farone WA, Cuzens JE. Method of producing sugars using strong acid hydrolysis of
cellulosic and hemicellulosic materials. US Patent 5562777; 1996.
Fitzpatrick SW. Production of levulinic acid from carbohydrate-containing materials.
US Patent 5608105; 1997.
Gu F, Wang W, Jing L, Jin Y. Effects of green liquor pretreatment on the chemical composition and enzymatic digestibility of rice straw. Bioresour Technol
2013;149:375–82.
Hatti-Kaul R, Törnvall U, Gustafsson L, Börjesson P. Industrial biotechnology for
the production of bio-based chemicals – a cradle-to-grave perspective. Trends
Biotechnol 2007;25:119–214.
Hayes DJ, Ross J, Hayes MHB, Fitzpatrick S. The biofine process: production
of levulinic acid, furfural and formic acid from lignocellulosic feedstocks. Carbolea Research Group, University of Limerick; 2005, Available
from http://www.carbolea.ul.ie/files/HFHR Chapter%204 FINAL.pdf [accessed
07.07.14].
Hellweg S, Fischer U, Scheringer M, Hungerbühler K. Environmental assessment of
chemicals: methods and application to a case study of organic solvents. Green
Chem 2004;6:418–27.
Kim S, Dale BE, Jenkins R. Life cycle assessment of corn grain and corn stover in the
United States. Int J LCA 2009;14:160–74.
Klemeš J, Pierucci S, Worrell E. Sustainable processes thorough LCA, process integration and optimal design. Resour Conserv Recycl 2007;50:115–21.
Koellner T, de Baan L, Beck T, Brandão M, Civit B, Margni M, et al. UNEP-SETAC
guideline on global land use impact assessment on biodiversity and ecosystem
services in LCA. Int J LCA 2013;18:1188–202.
Kumar P, Barrett DM, Delwiche MJ, Stroeve P. Methods for pretreatment of lignocellulosic biomass for efficient hydrolysis and biofuel production. Ind Eng Chem
Res 2009;48:3713–29.
Lal R. World crop residues production and implications of its use as a biofuel. Environ
Int 2005;31:575–84.
Li D, Liu M, Cheng Y, Wang D, Qin J, Jiao J, et al. Methane emissions from doublerice cropping system under conventional and no tillage in southeast China. Soil
Tillage Res 2011;113:77–81.
Liu ZH, Qin L, Pang F, Jin MJ, Li BZ, Kang Y, et al. Effects of biomass particle
size on steam explosion pretreatment performance for improving the enzyme
digestibility of corn stover. Ind Crops Prod 2013;44:176–84.
Luo L, van der Voet E, Huppes G. An analysis of ethanol from cellulosic feedstock –
corn stover. Renew Sustain Energy Rev 2009;13:2003–11.
Parton RFMJ, Rijkers MPWM, Kroon JA. Continuous production of furfural and levulinic acid. Patent EP 2537841; 2012.
Pikul JL Jr, Carpenter-Boggs L, Vigil M, Schumacher TE, Lindstrom MJ, Riedell WE.
Crop yield and soil condition under ridge and chisel-plow tillage in the northern
Corn Belt, USA. Soil Tillage Res 2001;60:21–33.
Rackemann DW, Doherty WOS. The conversion of lignocellulosics to levulinic acid.
Biofuels Bioprod Bioref 2011;5:198–214.
Sabesan S, Spado CJ. Production of furfural from biomass. Patent WO 2013066541;
2013.
Shinners KJ, Binversie BN. Fractional yield and moisture of corn stover
biomass produced in the Northern US Corn Belt. Biomass Bioenerg 2007;31:
576–84.
Serrano-Ruiz JC, Luque R, Sepu Sepúlveda-Escribano A. Transformations of
biomass-derived platform molecules: from high added-value chemicals to fuels via aqueous-phase processing. Chem Soc Rev 2011;40:
5266–81.
Sparovek G, Barretto A, Berndes G, Martins S, Maule R. Environmental, land-use
and economic implications of Brazilian sugarcane expansion 1996–2006. Mitig
Adapt Strateg Glob Chang 2009;14:285–98.
Sun XZ, Fujimoto S, Minowa T. A comparison of power generation and ethanol
production using sugarcane bagasse from the perspective of mitigating GHG
emissions. Energy Policy 2013;57:624–9.
USDA (U. S. Dept. of Agriculture). Crop Production 2012 Summary. USA: U.S.
Dept. of Agriculture, National Agricultural Statistics Service; 2013, ISSN:
1949-0372.
Xia Y, Yan X. Life cycle evaluation of nitrogen-use in rice-farming systems:
implications for economically-optimal nitrogen rates. Biogeosciences 2011;8:
3159–68.
Xue X, Pang YL, Landis AE. Evaluating agricultural management practices to
improve the environmental footprint of corn-derived ethanol. Renew Energy
2014;66:454–60.
Yang L, Cao J, Mao J, Jin Y. Sodium carbonate–sodium sulfite pretreatment
for improving the enzymatic hydrolysis of rice straw. Ind Crops Prod
2013;43:711–7.
182
H.H. Khoo et al. / Resources, Conservation and Recycling 95 (2015) 174–182
Yang R, Hayashi K, Zhu B, Li F, Yan X. Atmospheric NH3 and NO2 concentration
and nitrogen deposition in an agricultural catchment of Eastern China. Sci Tot
Environ 2010;408:4624–32.
Yu Q, Zhuang X, Lv SL, He M, Zhang Y, Yuan Z, et al. Liquid hot water pretreatment of
sugarcane bagasse and its comparison with chemical pretreatment methods for
the sugar recovery and structural changes. Bioresour Technol 2013a;129:592–8.
Yu G, Li B, Liu C, Zhang Y, Wang H, Mu X. Fractionation of the main components of
corn stover by formic acid and enzymatic saccharification of solid residue. Ind
Crops Prod 2013b;50:750–7.
Zhang Z, Wong HH, Albertson PL, Doherty WO, O’Hara IM. Laboratory and pilot
scale pretreatment of sugarcane bagasse by acidified aqueous glycerol solutions.
Bioresour Technol 2013;138:14–21.