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Journal ArticleDOI

Recent updates on different methods of pretreatment of lignocellulosic feedstocks: a review

18 Jan 2017-Bioresources and Bioprocessing (SpringerOpen)-Vol. 4, Iss: 1, pp 7-7
TL;DR: An extensive research is still required for the development of new and more efficient pretreatment processes for lignocellulosic feedstocks yielding promising results.
Abstract: Lignocellulosic feedstock materials are the most abundant renewable bioresource material available on earth. It is primarily composed of cellulose, hemicellulose, and lignin, which are strongly associated with each other. Pretreatment processes are mainly involved in effective separation of these complex interlinked fractions and increase the accessibility of each individual component, thereby becoming an essential step in a broad range of applications particularly for biomass valorization. However, a major hurdle is the removal of sturdy and rugged lignin component which is highly resistant to solubilization and is also a major inhibitor for hydrolysis of cellulose and hemicellulose. Moreover, other factors such as lignin content, crystalline, and rigid nature of cellulose, production of post-pretreatment inhibitory products and size of feed stock particle limit the digestibility of lignocellulosic biomass. This has led to extensive research in the development of various pretreatment processes. The major pretreatment methods include physical, chemical, and biological approaches. The selection of pretreatment process depends exclusively on the application. As compared to the conventional single pretreatment process, integrated processes combining two or more pretreatment techniques is beneficial in reducing the number of process operational steps besides minimizing the production of undesirable inhibitors. However, an extensive research is still required for the development of new and more efficient pretreatment processes for lignocellulosic feedstocks yielding promising results.

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Kumar and Sharma
Bioresour. Bioprocess. (2017) 4:7
DOI 10.1186/s40643-017-0137-9
REVIEW
Recent updates ondierent methods
ofpretreatment oflignocellulosic feedstocks:
a review
Adepu Kiran Kumar
*
and Shaishav Sharma
Abstract
Lignocellulosic feedstock materials are the most abundant renewable bioresource material available on earth. It is pri-
marily composed of cellulose, hemicellulose, and lignin, which are strongly associated with each other. Pretreatment
processes are mainly involved in effective separation of these complex interlinked fractions and increase the acces-
sibility of each individual component, thereby becoming an essential step in a broad range of applications particularly
for biomass valorization. However, a major hurdle is the removal of sturdy and rugged lignin component which is
highly resistant to solubilization and is also a major inhibitor for hydrolysis of cellulose and hemicellulose. Moreover,
other factors such as lignin content, crystalline, and rigid nature of cellulose, production of post-pretreatment inhibi-
tory products and size of feed stock particle limit the digestibility of lignocellulosic biomass. This has led to extensive
research in the development of various pretreatment processes. The major pretreatment methods include physical,
chemical, and biological approaches. The selection of pretreatment process depends exclusively on the application.
As compared to the conventional single pretreatment process, integrated processes combining two or more pretreat-
ment techniques is beneficial in reducing the number of process operational steps besides minimizing the produc-
tion of undesirable inhibitors. However, an extensive research is still required for the development of new and more
efficient pretreatment processes for lignocellulosic feedstocks yielding promising results.
Keywords: Pretreatment, Lignocellulosic biomass, Cellulose, Lignin, Reducing sugars
© The Author(s) 2017. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License
(
http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium,
provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license,
and indicate if changes were made.
Background
Lignocellulosic feedstock represents an extraordinar-
ily large amount of renewable bioresource available in
surplus on earth and is a suitable raw material for vast
number of applications for human sustainability. e
main composition of lignocellulosic feedstocks is cel
-
lulose, hemicellulose, and lignin (Table
1). However,
many obstacles are associated with effective utilization
of lignocellulosic materials. Some of the major factors
are the recalcitrance of the plant cell wall due to inte
-
gral structural complexity of lignocellulosic fractions
and strong hindrance from the inhibitors and byprod
-
ucts that are generated during pretreatment. In addition,
few more challenges still remain, like understanding the
physicochemical architecture of feedstock cell walls, suit
-
able pretreatment method and extent of cell wall decon-
struction for generation of value-added products etc.
ere are several criteria for the selection of a suitable
pretreatment method: (a) the selected method should
avoid the size reduction of biomass particles, (b) hemi
-
cellulose fraction must be preserved, (c) minimize the
formation of degradation products, (d) minimize the
energy demands and lastly, (e) should involve a low-cost
pretreatment catalyst and/or inexpensive catalyst recy
-
cle and regeneration of high-value lignin co-product
(Wyman
1999). e result of the pretreatment must
not only defend but also justify its impact on the cost of
downstream processing steps and the tradeoff between
operating costs, capital costs, biomass costs, etc. (Lynd
etal.
1996).
e pretreatment techniques for overcoming bio
-
mass recalcitrance are broadly divided into two classes:
Open Access
*Correspondence: kiranbio@gmail.com
Bioconversion Technology Division, Sardar Patel Renewable Energy
Research Institute, Vallabh Vidyanagar, Anand 388 120, Gujarat, India

Page 2 of 19
Kumar and Sharma
Bioresour. Bioprocess. (2017) 4:7
biochemical and thermochemical (Laser et al.
2009).
Based on the operating temperatures, thermochemical
pretreatment is again of two types: pyrolysis and gasifi
-
cation. e advantage of thermochemical conversion
is that it is a fast process with low residence time and is
able to handle a broad range of feedstock in a continuous
manner, but major drawback is its non-specific nature of
biomass deconstruction. On the other hand, biochemi
-
cal pretreatment is highly selective in biomass decon-
struction to their desired product formation. However,
biochemical conversion first uses low-severity thermo
-
chemical pretreatment to partially break down the cell
wall and expose the cellulose and hemicellulose fractions
for improving enzyme accessibility. Elucidating the phys
-
icochemical effects of the possible pretreatments upon
subsequent hydrolysis and fermentation of biomass has
been a significant challenge.
Although several reviews have been present which
describe the various categories of pretreatment processes
individually, however, a comprehensive review cover
-
ing different types of pretreatment processes along with
their advantages and disadvantages was the need of the
hour. erefore, this review covers all the techniques that
have been developed and used for pretreatment of ligno
-
cellulosic biomass, recent advancements in pretreatment
technology, their mechanism of action, and effect on var
-
ious lignocellulosic feedstocks.
Methods ofpretreatment
e pretreatment of lignocellulosic feedstocks is an
essential step and is required to alter the structure of bio
-
mass residues and expose the lignocellulosic fractions
for easy access to enzymes during enzymatic hydrolysis
and enhance the rate and yield of reducing sugars (Alvira
et al.
2010). Basically, the pretreatment processes are
classified into two major regimes viz. non-biological and
biological. A list of promising and most commonly used
pretreatment methods are listed in Fig.
1. Based on the
type of the treatment process involved, lignocellulosic
biomass pretreatment methods are broadly classified into
two groups: Non-biological and biological. Non-biolog
-
ical pretreatment methods do not involve any microbial
treatments and are roughly divided into different catego
-
ries: physical, chemical, and physico-chemical methods.
Here, we have reviewed the advances in few selective
treatment methods that are most commonly employed in
pretreatment process of a broad range of lignocellulosic
feedstocks.
Physical pretreatment
Mechanical extrusion
It is the most conventional method of biomass pretreat-
ment where the feedstock materials are subjected to
heating process (>300°C) under shear mixing. is pre
-
treatment process results mainly in production of gase-
ous products and char from the pretreated lignocellulosic
biomass residues (Shafizadeh and Bradbury
1979). Due
to the combined effects of high temperatures that are
maintained in the barrel and the shearing force generated
by the rotating screw blades, the amorphous and crystal
-
line cellulose matrix in the biomass residues is disrupted.
However, this method requires significant amount of
high energy making it a cost intensive method and dif
-
ficult to scale up for industrial purposes (Zhu and Pan
2010). Karunanithy etal. (2008) studied on the defibril
-
lation and shortening of the biomass fibers and concomi-
tant increase in the overall content of the carbohydrates
and its availability for enzymatic hydrolysis process.
Zheng and Rehmann (
2014) studied different process
parameters of mechanical extraction process and found
that the type of the screw design, compression ratio,
screw speed, and barrel temperature affected the bio
-
mass pretreatment. Similarly, Karunanithy and Muthu-
kumarappan (
2010) also studied the effect of temperature
Table 1 Cellulose, hemicellulose, and lignin content
incommon lignocellulosic feedstocks
Lignocellulosic
feedstocks
Cellulose (%) Hemicellulose (%) Lignin (%)
Sugar cane bagasse 42 25 20
Sweet sorghum 45 27 21
Hardwood 40–55 24–40 18–25
Softwood 45–50 25–35 25–35
Corn cobs 45 35 15
Corn stover 38 26 19
Rice Straw 32 24 18
Nut shells 25–30 25–30 30–40
Newspaper 40–55 25–40 18–30
Grasses 25–40 25–50 10–30
Wheat straw 29–35 26–32 16–21
Banana waste 13.2 14.8 14
Bagasse 54.87 16.52 23.33
Sponge gourd fibers 66.59 17.44 15.46
Agricultural residues 5–15 37–50 25–50
Hardwood 20–25 45–47 25–40
Softwood 30–60 40–45 25–29
Grasses 0 25–40 35–50
Waste papers from
chemical pulps
6–10 50–70 12–20
Newspaper 12 40–55 25–40
Sorted refuse 60 20 20
Leaves 15–20 80–85 0
Cotton seed hairs 80–95 5–20 0
Paper 85–99 0 0–15
Switch grass 45 31.4 12

Page 3 of 19
Kumar and Sharma
Bioresour. Bioprocess. (2017) 4:7
and screw speed on pretreatment of corn cobs with dif-
ferent cellulose degrading enzymes and their ratios.
When pretreatment was carried out at different temper
-
atures (25, 50, 75, 100, and 125°C) and different screw
speeds (25, 50, 75, 100, and 125rpm), maximum concen
-
trations of glucose (75%), xylose (49%), and combined
sugars (61%) were obtained at 75rpm and 125°C using
cellulase and β-glucosidase in the ratio of 1:4, which were
nearly 2.0, 1.7, and 2.0 times higher than the controls.
ese clearly indicated that optimization of the pretreat
-
ment process conditions and enzyme concentrations
had a synergetic effect on the overall yields of reducing
sugars.
Moreover, in another study, Karunanithy etal. (
2013)
selected different varieties of warm season grasses viz.
switch grass, big bluestem, and prairie cord grass and
studied the effect of different screw speeds (100, 150,
and 200 rpm), barrel temperatures (50, 75, 100, 150,
and 200 °C) and different concentrations of cellulase
with β-glucosidase (1:1 to 1:4). In all the experiments,
maximum reducing sugars were obtained when the ratio
of cellulase and β-glucosidase was maintained at 1:4. e
reducing sugar yields from the switchgrass pretreated
at screw speed of 200 rpm and barrel temperature of
75°C produced 28.2%, while big bluestem pretreated at
screw speed of 200 rpm and 150 °C barrel temperature
produced 66.2% and with prairie cord grass pretreated at
150rpm and 100°C produced 49.2%. Although the sugar
yields are high, mechanical extrusion cannot alone suffice
pretreatment of a range of lignocellulosic feedstocks with
varied cellulose, hemicellulose, and lignin contents. us,
it needs better pretreatment methods for higher sugar
yields. Besides, sugar recovery is also significantly influ
-
enced by the properties of the biomass.
Karunanithy and Muthukumarappan (
2010) studied the
effect of varying moisture contents (15, 25, 35, and 45%
wb) on the sugar recovery from switch grass and prairie
cord grass at compression ratio (2:1 and 3:1), screw speed
(50, 100 and 150rpm), and barrel temperature (50, 100,
and 150°C). After enzymatic hydrolysis of the pretreated
Fig. 1 Overview of different pretreatment processes

Page 4 of 19
Kumar and Sharma
Bioresour. Bioprocess. (2017) 4:7
biomass, maximum 45.2% sugar was recovered from
switch grass with 15% moisture content at screw speed
of 50 rpm and barrel temperature of 150 °C, whereas a
maximum of 65.8% sugar was recovered from prairie
cord grass with 25% moisture content at screw speed of
50rpm and barrel temperature of 50°C. Alongside, low
concentrations of glycerol and acetic acid in the range
of 0.02–0.18 g/L were also produced. It is well known
that glycerol and acetic acid are the byproducts that are
formed during the pretreatment of lignocellulosic feed
-
stocks. However, in this report, unlike hot compressed
hot water and acid hydrolysis, the byproduct formation
was significantly lower because in mechanical extraction
only physical interactions were observed between the
feedstock and the barrel blades. Similarly, Lamsal et al.
(
2010) also compared effects of grinding with extrusion
on wheat bran and soybean hull. Better sugar yield was
obtained in wheat bran through extrusion but not in
soybean hulls. e most plausible reason could be due
to the difference in the lignin contents between these
biomass residues. Soybean hulls contain nearly twofold
higher lignin content than the wheat bran. e residual
high-lignin bound to the pretreated biomass could have
shown a direct impact on the enzymatic hydrolysis. It is
well known that the cellulose degrading enzymes avidly
and irreversibly bind to lignin and thus not readily avail
-
able for effective cellulose disruption. e combination
of screw speed and barrel temperature maintained was
7Hz/150°C and 3.7Hz/110°C where highest sugar yield
was produced.
Moreover, particle size of biomass plays an important
role on the overall sugar recovery. Studies performed
by Karunanithy and Muthukumarappan (
2011) showed
maximum sugar recovery from big blue stem obtained
with 8-mm particle size, 20% wb moisture content at
a barrel temperature of 180 °C with screw speed of
150rpm, where 71.3% glucose, 78.5% xylose, and 56.9%
combined sugars were obtained. While with switch grass,
at similar particle size and moisture contents, but at a
barrel temperature of 176°C and screw speed of 155rpm,
maximum sugars of 41.4% glucose, 62.2% xylose, and
47.4% combined sugars were obtained. In another study,
Zhang et al. (
2012a, b) used a twin screw extruder for
sugar recovery from corn stover. At 27.5% moisture
content with a screw speed of 80rpm and enzyme dose
of 0.028 g enzyme/g dry biomass, glucose, xylose, and
combined sugar recovery were 48.79, 24.98, and 40.07%,
respectively. ese were 2.2, 6.6, and 2.6 times more
than that of untreated corn stover. Yoo (
2011) compared
a thermo-mechanical pretreatment process on soybean
hulls. Under optimum processing conditions at screw
speed of 350rpm, barrel temperature of 80°C and 40%
moisture content, 95% cellulose was converted glucose.
ese above studies clearly demonstrate that mechani
-
cal extrusion treatment had a significant effect on break-
down of cellulose and hemicelluloses fractions from a
wide variety of lignocellulosic feedstocks; however, when
combined with other pretreatment methods, mechanical
extrusion performs better and might enhance the overall
yields of the reducing sugars.
Milling
Mechanical grinding (milling) is used for reducing
the crystallinity of cellulose. It mostly includes chip
-
ping, grinding, and/or milling techniques. Chipping can
reduce the biomass size to 10–30mm only while grind
-
ing and milling can reduce the particle size up to 0.2mm.
However, studies found that further reduction of bio
-
mass particle below 0.4mm has no significant effect on
rate and yield of hydrolysis (Chang et al.
1997). Chip
-
ping reduces the heat and mass transfer limitations while
grinding and milling effectively reduce the particle size
and cellulose crystallinity due to the shear forces gener
-
ated during milling. e type and duration of milling and
also the kind of biomass determine the increase in spe
-
cific surface area, final degree of polymerization, and the
net reduction in cellulose crystallinity. Different milling
methods viz. two-roll milling, hammer milling, colloid
milling, and vibratory milling are used to improve the
digestibility of the lignocellulosic materials (Taherzadeh
and Karimi
2008). Compared to ordinary milling process,
vibratory ball milling is found to be more effective in
reducing cellulose crystallinity and improving the digest
-
ibility of spruce and aspen chips. Also, wet disk milling
has been a popular mechanical pretreatment because of
its low energy consumption. Disk milling enhances cel
-
lulose hydrolysis by producing fibers and is more effec-
tive as compared to hammer milling which produces
finer bundles (Zhua et al.
2009). Hideno et al. (2009)
compared the effect of wet disk milling and conventional
ball milling pretreatment method over rice straw. e
optimal conditions obtained were 60 min of milling in
case of dry ball milling while 10 repeated milling opera
-
tions were required in case of wet disk milling. Maximum
glucose (89.4%) and xylose (54.3%) were obtained with
conventional ball milling method as compared to 78.5%
glucose and 41.5% xylose with wet disk milling method.
However, wet disk milling had lower energy require
-
ment, high effectiveness for enzymatic hydrolysis, and
did not produce inhibitors. Lin et al. (
2010) found wet
milling better than dry milling for the pretreatment of
corn stover. e optimum parameters for milling were
particle size 0.5mm, solid/liquid ratio of 1:10, 20 number
of steel balls of 10mm dia each, ball speed of 350rpm/
min grounded for 30 min. Better results were obtained
when milling was combined with alkaline pretreatment

Page 5 of 19
Kumar and Sharma
Bioresour. Bioprocess. (2017) 4:7
method. As compared to wet milling process, alkaline
milling treatment increased the enzymatic hydrolysis
efficiency of corn stover by 110%. Sant Ana da Silva etal.
(
2010) performed a comparative analysis on effects of
ball milling and wet disk milling on treating sugarcane
bagasse and straw and found ball milling better pretreat
-
ment method than wet disk milling in terms of glucose
and xylose hydrolysis yields. Ball milling-treated bagasse
and straw produced 78.7 and 72.1 and 77.6 and 56.8%,
glucose and xylose, respectively. Kim et al. (
2013) com
-
pared three different milling methods i.e., ball, attrition,
and planetary milling. Attrition and planetary mills were
found more effective in reducing the size of biomass as
compared to ball milling. Planetary mill produced high
-
est amount of glucose and galactose than other milling
methods tested. It is to be noted that all the mill pretreat
-
ment methods do not produce any toxic compounds like
hydroxymethylfurfuraldehyde (HMF) and levulinic acid.
is makes milling pretreatment a good choice of prelim
-
inary pretreatment method for a wide variety of lignocel-
lulosic feed stocks. In another study, oil palm frond fiber
when pretreated through ball mill produced glucose and
xylose yields of 87 and 81.6%, respectively, while empty
fruit bunch produced glucose and xylose yields of 70 and
82.3%, respectively (Zakaria etal.
2014).
Microwave
Microwave irradiation is a widely used method for lig-
nocellulosic feedstock pretreatment because of vari-
ous reasons such as (1) easy operation, (2) low energy
requirement, (3) high heating capacity in short duration
of time, (4) minimum generation of inhibitors, and (5)
degrades structural organization of cellulose fraction.
Moreover, addition of mild-alkali reagents is preferred
for more effective breakdown. A study on microwave-
based alkali pretreatment of switch grass yielded nearly
70–90% sugars (Hu and Wen
2008). Microwave-based
alkali treatment of switchgrass and coastal bermudag
-
rass using different alkalis found sodium hydroxide as the
most suitable alkali. Under optimum conditions, switch
-
grass produced 82% glucose and 63% xylose while coastal
bermudagrass produced 87% glucose and 59% xylose
(Keshwani and Cheng
2010). Although not significant,
the authors have correlated the differences in reducing
sugars with the difference in the lignin content (19% in
bermudagrass vs 22% in switchgrass) in these lignocellu
-
losic feedstocks. Lu etal. (
2011) studied microwave pre-
treatment of rape straw at different powers for different
time durations. e higher power of microwave resulted
in higher glucose production but treatment time did
not have a significant effect at a specific power setting.
Chen etal. (
2011a, b) optimized the microwave heating
at 190°C for 5min for bagasse pretreatment in terms of
lignocellulosic structural disruption. In another investi
-
gation, Zhu etal. (
2015a, b, 2016) have extensively stud-
ied the effects of microwave on chemically pretreated
Miscanthus. Where, microwave treatment was applied
to NaOH- and H
2
SO
4
-pretreated Miscanthus and found
12-times high sugar yield in half the time as compared
to conventional heating NaOH and H
2
SO
4
pretreatment.
is was mainly due to the pre-disruption of crystalline
cellulose and lignin solubilization with the chemical pre
-
treatment. e maximum sugar yield obtained was 75.3%
and glucose yield was 46.7% when pretreated with 0.2M
H
2
SO
4
for 20 min at 180 °C. Similarly, Xu et al. (
2011)
developed an orthogonal design to optimize the micro
-
wave pretreatment of wheat straw and increased the
ethanol yield from 2.678 to 14.8%. Bonmanumsin et al.
(
2012) reported substantial increase in yield of mono
-
meric sugars from Miscanthus sinensis with microwave-
assisted ammonium hydroxide treatment. Microwave
pretreatment of oil palm empty fruit bunch fiber in the
presence of alkaline conditions showed 74% reduction in
lignin (Nomanbhay etal.
2013).
Ultrasound
Sonication is relatively a new technique used for the pre-
treatment of lignocellulosic biomass. However, studies
in the laboratory have found sonication a feasible pre
-
treatment option. Ultrasound waves produce both physi-
cal and chemical effects which alter the morphology of
lignocellulosic biomass. Ultrasound treatment leads to
formation of small cavitation bubbles which rupture the
cellulose and hemicellulose fractions thereby increasing
the accessibility to cellulose degrading enzymes for effec
-
tive breakdown into simpler reducing sugars. Yachmenev
et al. (
2009) reported that the maximum cavitation was
formed at 50°C which is also the optimum temperature
for many cellulose degrading enzymes. e ultrasonic
field is primarily influenced by ultrasonic frequency
and duration, reactor geometry and its type and solvent
used. Furthermore, biomass characteristics, reactor con
-
figuration, and kinetics also influence the pretreatment
through sonication (Bussemaker and Zhang
2013). Dura
-
tion of sonication has maximum effect on pretreatment
of biomass. However, prolonging sonication beyond a
certain limit has no additional effect in terms of delig
-
nification and sugar release (Rehman et al.
2013). Soni-
cation of corn starch slurry for 40s increased the sugar
yield by 5–6 times as compared to control (Montalbo
etal.
2010). Sonication of alkaline pretreated wheat straw
for 15–35 min increased delignification by 7.6–8.4% as
compared to control (Sun and Tomkinson
2002). Besides
duration, the frequency of sonication directly determines
the power of sonication, which is also an important fac
-
tor affecting the lignocellulosic feedstock pretreatment.

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TL;DR: This paper reviews process parameters and their fundamental modes of action for promising pretreatment methods and concludes that pretreatment processing conditions must be tailored to the specific chemical and structural composition of the various, and variable, sources of lignocellulosic biomass.

6,110 citations


"Recent updates on different methods..." refers methods in this paper

  • ...During this pretreatment, the hydrolysis of hemicellulose into glucose and xylose monomers is carried out by the acetic acid produced from the acetyl groups of hemicellulose; hence this process is also termed as autohydrolysis (Mosier et al. 2005)....

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TL;DR: Simultaneous saccharification and fermentation effectively removes glucose, which is an inhibitor to cellulase activity, thus increasing the yield and rate of cellulose hydrolysis, thereby increasing the cost of ethanol production from lignocellulosic materials.

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"Recent updates on different methods..." refers background in this paper

  • ...Although the biological pretreatment is highly intriguing, the rate of hydrolysis of lignocellulosic fractions is too slow which severely hampers to be foreseen as a potential pretreatment method at an industrial scale (Sun and Cheng 2002)....

    [...]

  • ...The temperature range is between 140 and 210 °C with a reaction time of 90 min and percolation rate is 5 mL/min after which the ammonia is recycled (Sun and Cheng 2002; Kim et al. 2008)....

    [...]

  • ...The temperature range is between 140 and 210 °C with a reaction time of 90 min and percolation rate is 5  mL/min after which the ammonia is recycled (Sun and Cheng 2002; Kim et  al....

    [...]

  • ...Although the biological pretreatment is highly intriguing, the rate of hydrolysis of lignocellulosic fractions is too slow which severely hampers to be foreseen as a potential pretreatment method at an industrial scale (Sun and Cheng 2002)....

    [...]

Journal ArticleDOI

3,909 citations


"Recent updates on different methods..." refers background in this paper

  • ...The complex anionic species are formed between X− and either a Lewis or Brønsted acid Y (z refers to the number of Y molecules that interact with the anion) (Smith et al. 2014)....

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Journal ArticleDOI
TL;DR: Steam pretreatment, lime pret treatment, liquid hot water pretreatments and ammonia based Pretreatments are concluded to be pretreatment with high potentials, providing an improved accessibility of the cellulose for hydrolytic enzymes.

3,618 citations


"Recent updates on different methods..." refers background in this paper

  • ...The vessel is heated to the required temperature and kept for several minutes at high temperatures (Hendricks and Zeeman 2009)....

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Journal ArticleDOI
TL;DR: This paper reviews the most interesting technologies for ethanol production from lignocellulose and it points out several key properties that should be targeted for low-cost and advanced pretreatment processes.

3,580 citations


"Recent updates on different methods..." refers background in this paper

  • ...ARP is capable of solubilizing hemicellulose but cellulose remains unaffected (Alvira et al. 2010)....

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