Renewable and Sustainable Energy Reviews 13 (2009) 2003–2011

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Renewable and Sustainable Energy Reviews

journal homepage: www.elsevier.com/locate/rser

An energy analysis of ethanol from cellulosic feedstock–Corn stover

Lin Luo *, Ester van der Voet, Gjalt Huppes
Institute of Environmental Sciences (CML), Leiden University, P.O. Box 9518, 2300 RA, Leiden, The Netherlands

A R T I C L E I N F O A B S T R A C T

Article history: The shift from fossil resources to renewables for energy and materials production has been the driving
Received 17 November 2008 force for research on energy analysis and environmental impact assessment of bio-based production.
Accepted 20 January 2009 This study presents a detailed energy analysis of corn stover based ethanol production using advanced
cellulosic technologies. The method used differs from that in LCA and from major studies on the subject
Keywords: as published in Science in two respects. First, it accounts for all the co-products together and so mainly
Bioethanol
avoids the allocation problems which plague all LCA studies explicitly and other studies implicitly.
Corn stover
Second, the system boundaries only involve the content of the energy products used in the system but
Energy analysis
Net energy value
not the production processes of these energy products, like refining and electricity production. We
Co-product credits normalized the six Science studies to this unified method. The resulting values of the total energy
product use in both agricultural production and biomass conversion to ethanol are lower than these
literature values. LCA-type of values including energy conversion would systematically be higher, in our
case study around 45%. The net energy value of cellulosic ethanol production is substantially higher than
the ones of the corn-based technologies, and it is similar to incineration and gasification for electricity
production. The detailed analysis of energy inputs indicates opportunities to optimize the system. This
form of energy analysis helps establishing models for the analysis of more complex systems such as
biorefineries.
ß 2009 Elsevier Ltd. All rights reserved.

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2003
2. Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2004
2.1. System boundary and allocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2004
2.2. Data sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2004
2.3. Energy analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2004
2.3.1. Comparison with literature values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2004
2.3.2. Calculations of energy inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2005
3. Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2005
3.1. Results of energy use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2005
3.2. Survey of energy inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2007
4. Conclusions and recommendations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2010
Acknowledgements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2010
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2010

1. Introduction supplies, with biofuel as one of the options. Several studies on life
cycle assessment (LCA) of bioenergy have been conducted, focusing
Facing the threat of oil depletion and climate change, a shift from particularly on two main impacts: reduction of fossil resource
fossil resources to renewables is ongoing to secure long-term extraction and greenhouse gas (GHG) emissions. However, our
previous studies show that LCA as a tool supporting decision-making
has its limitations when multi-products are involved, requiring
* Corresponding author. Tel.: +31 71 5271497; fax: +31 71 5277434. some form of allocation. With the upcoming biorefineries, the
E-mail address: luo@cml.leidenuniv.nl (L. Luo). product systems involve variable multiple inputs and variable

1364-0321/$ – see front matter ß 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.rser.2009.01.016
2004 L. Luo et al. / Renewable and Sustainable Energy Reviews 13 (2009) 2003–2011

multi-outputs. Hence LCA in general cannot be applied. Therefore, an system, as usual in LCA, but an ‘energy products-to-gate’ analysis,
analysis methodology is needed in order to optimize integrated Primary energy conversion processes have been left out of account,
biorefineries with regard to energy conservation, environmental though an overall comparison is made to show the quantitative
impact and profitability. Since both the environmental impact and effect of this exclusion.
production costs are closely related to the amount of fossil fuels used There is no allocation involved in the foreground processes, as
in the life cycle of a product, energy analysis can give a key insight at all co-products are included there, making the outcomes
relatively low cost. Several studies have been conducted on the independent of arbitrary allocation choices which otherwise
energy analysis through the life cycle of corn-based (Zea mays, or would have to be made. Implicitly, allocation is involved in the
maize) ethanol [1–6]. Two studies stand out because they report data used for the background processes, with a limited quanti-
negative net energy values [1,2], requiring more fossil energy inputs tative effect on outcomes however. As there is no allocation, the
in the production processes than the energy contained in the systems compared involve differing amounts of the four main
bioethanol produced. The rest show positive net energy values to a products: corn, stover, electricity and ethanol.
varying extent. To permit a direct meaningful comparison of the data In order to make comparisons, we analyze these co-products
and assumptions across these six studies, Farrell et al. aligned from an energy content point of view. Other measures might be
methods and removed differences in underlying data. They indicate used, like economic value, adding broadness but not requiring
that calculations of net energy are highly sensitive to assumptions other types of modeling. Adding specific applications of corn,
about both system boundaries and key parameter values and, as to stover, ethanol and electricity will surely lead to different
content, conclude that large-scale use of fuel ethanol certainly outcomes of such more application focused studies. We leave
requires more sustainable practices in agriculture and advanced these out of account here, but they could easily be added.
technologies, shifting from corn to cellulosic ethanol production [7]. For the sake of simplicity, environmental effects have been left
The cellulosic ethanol production refers to the processes out of account as well, focusing on energy only. In the modeling
converting cellulosic feedstocks (i.e. corn stover, wheat and rice framework as applied, such effects can be specified in the usual
straw, sugarcane bagasse, wood or grass) to ethanol. A recent paper ways as have been developed in the realm of LCA.
on a comparative energy assessment of corn and stover based
ethanol concludes stover is a better feedstock than corn from a 2.2. Data sources
perspective of energy conservation [8]. In our study corn stover
was chosen as the feedstock for ethanol production. Aiming at Data used in this study are obtained from different sources. U.S.
giving an indication on the efficiency of the stover–ethanol life Life-Cycle Inventory Database [9] is the main source for agriculture
cycle and how to optimize the system in terms of energy data, and the data from Swiss Centre of Life Cycle Inventories
production, this study focuses on an energy analysis providing (Ecoinvent) [10] are used for adjustment when necessary. Data on
an overview of the total use of energy products, in all (sub-) transport of stover, ethanol and electricity production are from
processes or sections of the stover–ethanol life cycle. The results NREL report [11].
are used for comparison between different systems and optimiza-
tion of the corn agriculture and the fuel ethanol production. 2.3. Energy analysis

2. Methodology 2.3.1. Comparison with literature values

In order to compare the results with literature values, the energy
2.1. System boundary and allocation use in corn agriculture is calculated on a ‘per hectare’ basis for 14 cost
categories. The crop yield taken in this study is 8687 kg corn/ha [12],
All relevant processes in the biomass production (corn which means the annual yield of the harvested stover is 5112 kg/ha
agriculture producing corn and stover) and the conversion to [13]. In the other studies these data are slightly different and mostly
ethanol are included within the system boundaries of the ethanol stover is not specified. The total energy input in ethanol production
life cycle, as shown in Figs. 1 and 2. Capital goods production and is calculated based on producing 1 L of ethanol. Although the ethanol
wastes management are also included. It is not a ‘cradle-to-gate’ is produced from stover instead of corn, the results can provide an

Fig. 1. Corn and stover agriculture.

 L. Luo et al. / Renewable and Sustainable Energy Reviews 13 (2009) 2003–2011 2005

Fig. 2. Ethanol production from stover.

Fig. 3. The defined comparable systems.

indication on the scale of values, and more importantly, how production. When producing 1 kg of ethanol, 1.23 kWh of
efficient cellulosic technologies are as compared to corn based electricity is co-generated. All the sub-processes are indicated in
ethanol. Furthermore, net energy values without and with co- Figs. 1 and 2.
product credits were calculated and compared the literature values.
In the case of ethanol production from stover, electricity is the only 3. Results and discussion
co-product from the biorefinery.
3.1. Results of energy use
2.3.2. Calculations of energy inputs
In order to find out the energy intensive sub-processes and The results of energy use in corn agriculture and the total
improve process efficiency, a detailed analysis was performed. The energy use in ethanol production compared to the literature values
calculations of energy inputs are based on the production of 1 kg of are shown in Tables 1 and 2, respectively.
ethanol, which requires 3.97 kg of stover, while 6.62 kg of corn is It can be seen from Table 1 that the total energy use in
co-produced in agriculture. The agriculture process is divided into agriculture is in the same scale as the values in the literature,
two sections—production of agriculture inputs and agricultural although it lies on the low side. The major differences appear in
2006 L. Luo et al. / Renewable and Sustainable Energy Reviews 13 (2009) 2003–2011

Table 1
Comparison of energy use in corn agriculture with literature.

This study [1] Patzek [2] Pimentel [3] Shapouri [4] Graboski [5] de Oliviera [6] Wang

Corn production (kg/ha) 8,687 7,310 8,655 8,746 8,799 7,850 7,846
Stover harvest (kg/ha) 5,212 – – – – – –

Energy use in corn agriculture (MJ/ha year)

Fertilizer production 7,988 9,160 12,431 9,804 8,077 8,681 10,305
Lime production 1,067 583 1,318 – 369 445 –
Pesticide production 197 953 3,766 1,060 777 1025 970
Seed production 158a 1,968 2,176 228 215 2,048 –
Transport 398 400 707 73 738 – 168
Gasoline – 1,005 1,695 1,277 1,290 960 1,501
Diesel 3,071b 2,957 4,197 2,719 3,205 2,907 4,310
LPG – 1,205 – 765 1,357 1,512 1,072
Natural gas 116c 779 – 670 597 504 1,626
Electricity 382 688 143 820 1,571 657 225
Irrigation – – 1,339 49 – – –
Labour – 1,390 1,934 574 628 – –
Farm machinery 3,249d 6,050 4,259 – 320 – –
Input packaging – – – – 74 – –
Total 16,626 27,138 33,954 18,041 19,220 18,738 20,177

a
This value was taken from Ecoinvent database, as it is not provided in the U.S. database.
b
In the U.S. database, gasoline and LPG are used together with Diesel for the operation of agricultural machinery. However, Ecoinvent database was used to calculate the
energy inputs in all the agricultural operation, where only diesel is used as fuel.
c
Also calculated from Ecoinvent database.
d
Calculated by this study, as it is not provided in the U.S. database.

Table 2
Comparison of total energy use in ethanol production.

Energy use in ethanol production (MJ/L) This Study [1] Patzek [2] Pimentel [3] Shapouri [4] Graboski [5] de Oliviera [6] Wang

Total 9.5 17.0 17.0 15.2 16.6 14.1 12.5

pesticide production, gasoline and LPG consumption. Since the U.S. the values of the total energy use can be compared. Nevertheless,
database only provides the total amount of pesticides used without this gives an indication on how efficient the cellulosic process is.
specifying the energy type of herbicides and insecticides and the The net energy summaries compared to the literature values is
energy needed to produce the pesticides, the Ecoinvent database shown in Tables 3 and 4.
was used to estimate the energy engaged in the production, which The results show that when the co-products are not taken into
can be somewhat optimistic. In the U.S., it is common to use account, three literature studies results in a negative net energy
gasoline and LPG together with diesel for the operation of value. When the co-products are taken into account, all six studies
agricultural machineries. However, in Ecoinvent database the fuel give positive net energy values. This indicates that outcomes of net
for agriculture operation is mainly diesel, and total fuel consump- energy calculations depend on taking into account the energy
tion was lower than the data from the U.S. database. The major value of co-products. Farrell et al. only reckon with the co-products
reason why the U.S. life-cycle inventory database was used from biorefinery, and not the stover produced from agriculture. In
together with Ecoinvent database is to obtain a summary of energy our study all the co-products are included, also for the six literature
inputs in all the sub-processes in the agriculture, as shown in studies [1–6].
Section 3.2. The reason why the energy use per liter of ethanol in our study
For the total energy use in the stover based ethanol production, is the highest is that the yield of ethanol from stover is lower than
it takes 9.5 MJ of process energy to produce 1 L of ethanol. the one from corn. In order to produce 1 L of ethanol more stover is
Although the pretreatment of cellulosic feedstock is highly energy needed. While in our study the energy use for the biomass
intensive, the value of energy use is low compared to the literature conversion processes is substantially lower, due to its advanced
values for ethanol from corn. The reason for this result might be nature. In this study, the net energy value is much higher mainly
that we assumed the process to be highly optimized in terms of due to the co-product of corn, which is consumed in the ethanol
energy efficiency. Due to the incompleteness of the data in sub- production of the first generation to which the other studies refer.
processes in ethanol production provided by the literature, only Although the average ethanol yields in the six studies is 0.4 L

Table 3
Net energy summary excluding co-products, no allocation.

Energy Use (MJ/L) This Study [1] Patzek [2] Pimentel [3] Shapouri [4] Graboski [5] de Oliviera [6] Wang

Agriculture 10.0 9.9 10.0 5.3 5.6 6.3 6.6

Biorefinery 9.5 17.0 17.0 15.2 16.6 14.1 12.5
Total input 19.5 26.9 27.0 20.5 22.2 20.4 19.1
Ethanola 21.2 21.2 21.2 21.2 21.2 21.2 21.2
Total output 21.2 21.2 21.2 21.2 21.2 21.2 21.2
Net energy value 1.5 5.7 5.8 0.7 1.0 0.8 2.1
a
Normalized energy value for ethanol based on lower heating value (LHV).
 L. Luo et al. / Renewable and Sustainable Energy Reviews 13 (2009) 2003–2011 2007

Table 4
Net energy summary including co-products, no allocation.

Energy use (MJ/L) This study [1] Patzek [2] Pimentel [3] Shapouri [4] Graboski [5] de Oliviera [6] Wang

Agriculture 10.0 9.9 10.0 5.3 5.6 6.3 6.6

Biorefinery 9.5 17.0 17.0 15.2 16.6 14.1 12.5
Total input 19.5 26.9 27.0 20.5 22.2 20.4 19.1
Ethanola 21.2 21.2 21.2 21.2 21.2 21.2 21.2
Co-products in agricultureb 85.2 25.9 25.9 24.0 24.6 24.6 24.6
Co-products in biorefineryc 3.5 4.1 1.9 7.3 4.1 4.1 4.0
Total output 109.9 51.2 49.0 52.5 49.9 49.7 49.8
Net energy value 90.4 24.3 22.0 32.0 27.7 29.3 30.7
a
Normalized energy value for ethanol based on lower heating value (LHV).
b
In this study it refers to the corn as a co-product in the agriculture; in all the other six studies it refers to the harvested stover (60%, dry mass basis) as a co-product, and the
values are estimated in this study.
c
In this study it refers to electricity; in the literature studies it refers to a range of products from corn milling, such as dried distiller grains, corn gluten feed, corn oil, etc.

Table 5
Energy input, output and net energy values of the applications of stover.

Defined system Process energy Electricity generated Ethanol produced Net energy value
use (MJ/kg stover) (MJ/kg stover) (MJ/kg stover) (NEV)a (MJ/kg stover)

Stover–ethanol 3.04 1.12 7.46 5.54

Stover-electricity (direct fired boiler) 0.07 4.49 – 4.42
Stover-electricity (gasifier) 0.10 6.41 – 6.30
a
Net energy value (NEV) = ethanol produced + electricity produced process energy use.

ethanol/kg corn, while in our study the yield is only 0.3 L ethanol/ processes. This system boundary is different from the one in life
kg stover, cellulosic ethanol is more energy efficient. Moreover, it cycle assessment (LCA), which is ‘cradle to gate’. As we want to
can be seen that co-generation of electricity from wastes is a way to compare the results in this study with the literature values, the
increase energy efficiency. choice of the system boundary is also consistent with the one in the
One further question may then be raised, ‘Is it better to use literature studies.
stover for ethanol production or just burn it for power generation?’ How do our scores relate to the LCA-type cradle-to-gate
In order to answer this, two reference systems were defined to outcomes, with an expanded system definition? When the values
generate electricity, incinerating the same amount of stover as of the total energy input in the refinery and electricity production
required for the production of 1 kg of ethanol, that is 63.5 MJ are used instead of only the ones of the energy outputs, the
(3.97 kg) of stover. The energy use and the electricity generated in embodied energy is added to these flows. In this case the total
this system were calculated. The systems in comparison with the energy use in agriculture becomes 18,394.49 kJ for the production
stover–ethanol system are defined in Fig. 3 and the results are of 6.62 kg of corn and 3.97 kg of stover. The summary of the energy
shown in Table 5. use from the two comparable system definitions is given in Table 6.
Table 5 shows that in terms of net energy generation the The reason why the value for the biorefinery does not differ in
benefit of converting a given amount of stover to ethanol stands the two cases is that the energy use (mainly steam and electricity)
in between the ones for power generation from two electricity is supplied by the heat and power production within the refinery.
options, disregarding the further use of end products, here only Hence no external energy source is needed.
ethanol and electricity. The energy cost for stover–ethanol and In the corn-stover agriculture, fertilizer production, tillage and
electricity production is higher, but so are its energy proceeds. If harvesting are the most energy intensive processes. The reason
the application of ethanol and electricity is considered, the why fertilizer production contributes most to the energy use in
efficiency of ethanol use may be much lower than the one of agriculture is the large amount of natural gas used for steam
electricity use, as combustion process have a low energy reforming in the production of ammonia, which is then used in the
efficiency score. Also the possibility of using low temperature production of nitrogen fertilizers. Tillage and harvesting require a
steam for urban heating is not specified here. Creating more large amount of diesel, which is needed for the operation of
valuable products from lignocellulosic biomass than only energy agricultural machineries.
seems a promising option as well however, but then leaving the In Fig. 5 the total electricity consumed is 4217 kJ/kg ethanol,
domain of energy product analysis. With further optimization of and the co-generated electricity is 4433 kJ/kg ethanol. This
the ethanol production process, higher net energy value can be corresponds to the number 1.12 MJ/kg stover in Table 5, which
achieved. is not expressed per liter ethanol but per kg stover. The surplus of
216 kJ can be sold to the grid. In the ethanol production, the causes
3.2. Survey of energy inputs of the large energy inputs in pretreatment, product recovery and
enzyme production are the steam and electricity used. Steam is
The energy inputs in different sub-processes (sections) in needed for stover pre-hydrolysis due to the high temperature
agriculture and in ethanol production are shown in Figs. 4 and 5, requirement in hydrolysis reactor, and for condensation and the
respectively. The lower heating value (LHV) is the basis for the preparation of the boiler feed water. Since aerobic fermentation is
energy production analysis. used in the enzyme production, electricity is used to pump air into
In Fig. 4 the total energy use given (12646 kJ) refers to the sum the fermenter continuously.
of the energy content of the fuels used in agriculture, but not the After all the bottlenecks in the ethanol life cycle are defined,
primary energy—the energy sources (i.e. crude oil, coal, uranium, possible solutions are provided as follows for process optimization
biomass, etc.) in the oil refinery and electricity production to reduce energy consumption.
2008 L. Luo et al. / Renewable and Sustainable Energy Reviews 13 (2009) 2003–2011

Fig. 4. The energy inputs in corn-stover agriculture (unallocated).

 L. Luo et al. / Renewable and Sustainable Energy Reviews 13 (2009) 2003–2011 2009

Fig. 5. The energy inputs in stover biomass conversion to ethanol (unallocated).

2010 L. Luo et al. / Renewable and Sustainable Energy Reviews 13 (2009) 2003–2011

Table 6 of the energy inputs in all the energy intensive processes provides
Energy use in cradle-to-gate and in energy-product analysis.
the opportunity to optimize the system in terms of net energy
Energy use Methodology production.
The production of nitrogen fertilizer consumes more than 90%
Cradle-to-gate Energy-product
(MJ/kg ethanol) (MJ/kg ethanol) of the energy in fertilizer production, thus the possibilities of
reduction of nitrogen fertilizer use and improved production
Agriculture 18.39 12.65
processes require attention. For instance, organic farming repla-
Biorefinery 12.03 12.03
Total 30.42 24.68 cing synthetic fertilizers by green manure may result in less energy
use and lower environmental impact. Concerning agriculture
processes, optimization should focus on the design of the
machineries in order to achieve higher efficiency to reduce fuel
 To produce ammonia by nitrogen fixation instead of steam consumptions. Furthermore, stover might not be a good feedstock
reforming; option for cellulosic ethanol production due to its highly intensive
 To increase engine efficiency of the agricultural machines to agriculture. More promising feedstocks can be sugar cane and
reduce the fuel use; switchgrass.
 To use less energy intensive crops like sugarcane or grass instead In the ethanol production, advanced technologies involving two
of corn stover; steps pretreatment (dilute acid prehydrolysis and enzymatic
 To use non-thermal methods for pre-treatment, i.e. chemical or saccharification) and genetically modified organisms (GMO) for
mechanical methods; fermentation are engaged. The process has been conceptually
 To increase boiler efficiency of the distillation and rectification designed and optimized in terms of production yield and energy
columns; efficiency, but yet it needs to be established in practice. To further
 To apply anaerobic fermentation for cellulase production to optimize the system, strain development of microorganism to
prevent aeration. achieve a high yield and innovations of pretreatment and recovery
options can be the focus. It is worth noting the goal of energy
All the aforementioned means of improvement have their own conservation may bring side effects such as worse environmental
limitations comparing to the technologies engaged in the present performance, low profitability or unacceptable options by the
study. For instance, nitrogen fixation might be more costly than society. Therefore, it is crucial to develop a model for optimization
steam reforming; investment and initiatives need to be made to with a complete set of criteria, among which a reduced input of
increase the efficiency of machineries; the supply of different energy products can be an important one.
feedstocks depends on its regional availability and cost for The present study also indicates that in terms of net energy
transport; the application of anaerobic fermentation might bring value created, the incineration or gasification of cellulosic feed-
the yield of cellulase down. With all the incentives in reducing stocks is not better than ethanol and electricity production. There
energy consumption and the limitations mostly in process are opportunities to further increase the value derived from
economy, technology development shall be further investigated. biomass processing by coproducing high valued products next to
ethanol, especially using agricultural wastes as are available in
4. Conclusions and recommendations varying compositions. In such a complex multi-feedstocks and
multi-products biorefinery system, the production of high volume
This study presents a detailed energy analysis of stover based of low-value products (like fuels) and low volume of high-value co-
ethanol production using advanced cellulosic technologies. Unlike products (like pharmaceutical precursors) can be combined.
the ‘cradle to gate’ approach in LCA methodology, the system Together with collective feedstock supply, waste treatment and
boundaries defined in the present study as well as in the literature integrated power generation, a biorefinery complex could poten-
we compared our results with, only involve the energy content of tially maximize the total value derived from cellulosic feedstocks
the energy product but not the energy inputs to the production and minimize the energy consumption and environmental
processes of these energy products. Furthermore, for the calcula- impacts.
tion of net energy values, all the six studies as well as Farrell’s study
only reckon with the co-products from biorefinery but ignore the Acknowledgements
ones from agriculture, in their case stover. In this study this has
been corrected. The resulting values of the total energy use in both This project is financially supported by the Netherlands
agriculture and ethanol production are lower for the case of stover Ministry of Economic Affairs and the B-Basic partner organizations
based ethanol than the ones for corn based ethanol production. In (http://www.b-basic.nl) through B-Basic, a public-private NWO-
the corn agriculture the low energy use is mainly due to lower fuel ACTS program (ACTS = Advanced Chemical Technologies for
use in the operation of agriculture machineries. The reason for this Sustainability).
is that, the data provided by the U.S. Life-Cycle Inventory Database
have been optimized. In the second generation stover–ethanol References
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which shows ethanol production from cellulosic feedstocks is 2005;14:65–76.
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