ARTICLE IN PRESS
Influence of pretreatment for deashing of sugarcane bagasse
on pyrolysis products
Piyali Dasa, Anuradda Ganesha,, Pramod Wangikarb
a
Energy Systems Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
Department of Chemical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
b
Abstract
This paper reports the studies made on the vacuum pyrolysis of deashed sugarcane bagasse, on the pyrolysis
products. The present work is with an objective to understand the change in the quantity and quality of the oil fraction
obtained from pyrolysis, upon pretreatment for deashing of original biomass. Ash, in the entrained char is believed to
be catalyzing the polymerization reaction in the oils and thereby increases the viscosity. Three different pre-treatment
processes used for deashing are water leaching, mild acid treatment with HCl and mild acid treatment with HF.1 The
study indicates the remarkable influence of pretreatment process for deashing, by enhancing the total energy
distribution in oil fraction of the pyrolysis products. This is attributed to selective removal of ash elements along with
removal of extractives and hemicellulose in different proportions. However, it was found that the pre-treatments do not
improve the stability of oil. The water leachate, as expected, showed potential of making ethanol via fermentation.
Keywords: Sugarcane bagasse; Leaching; Acid wash; Deashing; Stability; Vacuum pyrolysis
1. Introduction
Sugarcane bagasse—the residue left after juice
extraction is a waste available in abundance
worldwide. About 1.34 Gt of sugarcane was
produced globally in 1999, which equates to
approximately 375 MT of bagasse, 50% of which
is typically burned [1]. India is the second largest
producer of sugarcane next to Brazil with a
production of 300 MT of sugarcane in
1999–2000. In India, about 4 million hectares of
land is under sugarcane farming with an average
yield of 70 t ha 1. Besides Brazil and India,
Australia, South Africa, Cuba, China, tropical
and subtropical countries also are major contributors to world production of sugarcane. Thus,
446
sugarcane bagasse has a strong potential in
displacing fossil fuels and can be extensively used
in boilers, turbines and furnaces for power
generation.
Generating power by direct combustion of
sugarcane bagasse in boilers has a maximum
efficiency of about 26%. Combustion systems with
low efficiency are traditionally used in sugarcane
plants [2]. In populated areas, bagasse-fired boilers
can be one of the major health hazards due to
airborne fly ash. Recently, the overall efficiency of
the process is being greatly improved by cogeneration, wherein; the improvement comes from the
proper utilization of heat and effective waste heat
recovery. On the other hand, pyrolysis offers an
effective utilization of the ‘‘fuel energy’’ itself
giving energy-dense liquids (easier to handle, store
and transport), charcoal (improved solid fuel) and
gaseous fuel. The ability to decouple the fuel
production from the application is unique to
pyrolysis liquids and is a major advantage over
gasification and combustion, which must use the
energy products immediately and cannot store or
transport them. Thus, transformation of bagasse
into high-density renewable fuels, like charcoal
and bio-oil, can significantly increase the profitability of sugarcane plantations [3].
Fast pyrolysis at medium temperature and low
vapour residence times are known to be most
suitable conditions for maximizing liquid products
from biomass. To achieve the fast heating rates,
fluidized and entrained bed reactors have been
extensively used. In case of fluidized bed pyrolysis,
extensive particle entrainment with the vapours
has been reported. Vacuum pyrolyser—the low
turbulence inside moving and stirred-bed pyrolysis
reactors developed by Pyrovac [4,5] has been
reported to have reduced carryover of particles in
condensable products. The vacuum pyrolysis
provides the required low vapour residence time
with a slight compromise in the heating rate
achievable and thereby the reduction in liquid
products.
Sugarcane bagasse pyrolysis has been referred to
by many authors. The role of parameters like peak
temperature and tar yield has been investigated
[1,6]. Total condensates of the order of 40–60%
have been reported on dry bagasse basis. Vacuum
pyrolysis of sugarcane bagasse has been reported
first by Pakdel et al. [7]. The recent studies
reported by Perez et al. [2] gives a very elaborate
and extensive understanding about vacuum pyrolysis of sugarcane bagasse particularly in the
assessment of the yield and the product characteristics. The ageing tests reported therein are unique
and gives an insight into the ageing process of the
bagasse oil. This is of interest, particularly in its
application as a fuel. The major deterring factor in
the wide usage and acceptability of the bio oils are
its change of physico-chemical characteristics
during storage along with the corrosivity in the
commonly used storage medium. The oil undergoes polymerization thus resulting in an increase in
viscosity with time. During ageing etherification
and esterification reactions occur between hydroxyl, carbonyl and carboxyl group components
[8–11]. The presence of condensation reactions
during ageing is confirmed by increase in water
content in the oil with time [2]. It is also mentioned
in the literature [12,13] that this instability may be
attributed to the presence of alkali metals in the
ash, which are being carried over/entrained by the
char particles with the vapours. These alkali
metals catalyse the polymerization reactions and
thereby increase the viscosity. Moreover, these
alkali metals in ash, form deposits in combustion
applications, particularly in turbines, where the
damage potential is considerably high. Therefore,
the present study aims at understanding the
influence of this ash on the stability as well as
pyrolysis product yields upon vacuum pyrolysis of
sugarcane bagasse.
2. Materials and methods
2.1. Biomass properties
The properties of the sugarcane bagasse used for
the present study are given in Table 1.
2.2. Preparation of sample
The oven-dried bagasse sample ground to pass
through 60-mesh sieve (p250 mm particle size) has
been taken for the investigation.
447
Table 1
Properties of sugarcane bagasse
Proximate analysis
wt% (on dry basis)
Volatile matter
Fixed carbon
Ash
Table 2
Pretreatment processes and sugar analysis of leachates
Ultimate analysis
wt% (on dry basis)
84.83
13.28
1.89
C
H
N
O (By difference)
56.32
7.82
0.89
27.54
Treatment
no.
Leaching process
Soaking/leaching
time (h)
I
II
III
Water leachinga (WL1)
Water leachinga (WL2)
Special water leachingb
(WL3)
Leachinga with 5(M)
HCl solution
Leachinga with
(0.5–3)% HF solution
1
24
24
IV
V
2.2.1. Deashing treatments
Bagasse has been subjected to three different
types of treatments in this study. The selection of
the pretreatment processes is based on reported
literatures, wherein, leaching of biomass [14,15]
and coal/carbon deashing [16,17] processes have
been elaborated. The pretreatment processes are
aimed at maximum extraction of ash. The treatments are water leaching, leaching with 5(M) HCl
solution and leaching with HF solution ranging
between a concentration 0.5 and 3% of HF. The
details of proportion of leaching medium and
soaking time are given in Table 2. In case of HF
treatment, leaching with 3% HF solution was
finally selected (after studying different concentrations) based on minimum concentration of HF
solution required for the reduction of ash to a
fairly negligible limit.
For all the treatments, mixtures were leached
and occasionally stirred for predetermined time at
2572 1C after which the samples were filtered off
and washed with distilled water. The process of
washing was continued until the wash-water
remained neutral. Finally, the samples were dried
at 105 1C in oven. The leachates were collected and
stored in refrigerator and subsequently analysed
for sugar content.
2.2.1.1. Effect of different deashing treatments on
sugarcane bagasse—sample analysis. Each of the
deashing treatments is associated with the mass
reduction in the original biomass feedstock. The
degree of deashing as well as the mass reduction of
the original biomass associated with each process
is found to be different. The average mass
reduction on dry bagasse basis for treatments I,
a
1
1
150 ml leachate corresponds to 12.5 g of bagasse.
150 ml leachate corresponds to 25.0 g of bagasse.
b
II, and III was 18–20%, 26–27% and 26–27%,
respectively. The acid leaching caused higher mass
reduction with as high as 50 wt% with 5(M) HCl
treatment and an average mass reduction of
29–32% for treatment V. All biomass samplestreated and untreated, were ashed in a muffle
furnace to obtain ash, which is free of trapped or
unburnt carbon. The degree of deashing was also
found to be varying for different treatments. The
percentage ash in the untreated and the treated
bagasse are presented in Table 3. It shows that
treatment with HCl leads to an apparent increase
of ash percentage, which is attributed to the
relatively higher removal of other components in
bagasse. This also corresponds to the highest mass
reduction during 5 M HCl treatment. Water
leaching has a moderate effect on ash removal.
The best result is achieved with HF treatment, in
which case the ash percentage was reduced to as
low as 0.03% when treated with 3% HF solution.
The elemental composition of ash was obtained
by Inductively Coupled Plasma Atomic Emission
Spectra instrument (ICP-AES) and presented in
Table 4. In accordance to reported literature [18],
simple water leaching washes out the alkalis like
Na and K wherein, 5 M HCl leaching further
removes other alkali metals like Mg, Ca, Al etc.,
but HF treatment removes almost all the ash
elements.
To understand the nature of change in the
chemical composition in sugarcane bagasse due to
different pretreatments, the chemical composition
448
Table 3
Percentage of ash in untreated and treated sugarcane bagasse
Normal
bagasse
Ash (1.83)
a
Treated
bagasse
Water
leachinga at
2572 1C
(1 h)
Ash
(1.27)
Water
leachinga at
2572 1C
(24 h)
Ash
(1.02)
Water
leachingb at
2572 1C
(24 h)
Ash
(1.09)
5(M) HCl
leachinga at
2572 1C
(1 h)
Ash
(2.12)
0.5%HF
leachinga at
2572 1C
(1 h)
Ash
(0.5)
1% HF
leachinga at
2572 1C
(1 h)
Ash
(0.29)
2% HF
leachinga at
2572 1C
(1 h)
Ash
(0.08)
3% HF
leachinga at
2572 1C
(1 h)
Ash
(0.03)
150 ml leachate corresponds to 12.5 g of bagasse.
150 ml leachate corresponds to 25.0 g of bagasse.
b
Table 4
Elemental composition of untreated and treated sugarcane bagasse
Elements
Untreated bagasse (%
of biomass)
Water leached (1 h)
bagasse (% of biomass)
5(M) HCl-treated
bagasse (% of biomass)
3%HF-treated bagasse
(% of biomass)
Na
K
Ca
Mg
Al
Fe
Zn
Cr
Co
Cu
Mn
Ni
P
Si
S
0.012
0.175
0.087
0.437
0.003
0.004
0.001
0.004
ND
0.001
0.141
—
0.014
0.911
0.042
0.003
0.014
0.017
0.310
0.002
0.003
0.001
—
ND
0.001
—
ND
0.003
0.862
0.026
0.008
0.020
0.040
0.285
0.004
0.005
0.014
ND
0.001
0.030
ND
—
0.002
1.699
ND
—
—
0.020
0.002
—
—
—
—
—
—
—
—
—
—
—
ND: not determined.
(extractives, hemicellulose, cellulose and lignin) of
all biomass (untreated and treated) was also
carried out by Technical Association of Pulp and
Paper Industries (TAPPI) methods. Table 5 gives
the chemical composition and higher heating value
of some of the untreated and treated bagasse.
The investigations followed by the results and
discussion have been reported here in two parts—
A, B. Part A deals with the pyrolysis experiments,
product distribution and analysis of the pyrolysis
products. Fermentation of leachate for ethanol has
been discussed in part B.
Part A: pyrolysis of untreated and treated
sugarcane bagasse—product characteristics
3. Experimental
Pyrolysis experiments were carried out in a
packed-bed reactor of 3-in NB pipe made of
stainless steel. The reactor was electrically heated
at a maximum temperature of 500 1C under an
initial reactor vacuum of 5 kPA. At the end of each
pyrolysis run the reactor was cooled to room
449
Table 5
Chemical composition and higher heating value of untreated and treated sugarcane bagasse
Biomass
Untreated sugarcane
bagasse
Water-leached (1 h)
sugarcane bagasse
5(M) HCl (1 h)-treated
sugarcane bagasse
3% HF treated (1 h)sugarcane bagasse
a
Extractivesa
(alcohol–benzene–water
soluble) wt%
Chemical composition
HHV (Higher
heating value)
MJ/kg
Hemicellulosea
wt%
Cellulosea
wt%
Lignina wt%
25.8
23.3
31.0
21.8
20
13.1
22.2
43.4
21.2
18
14.0
4.4
61.8
19.9
18
14.6
16.2
40.4
23.3
20
TAPPY methods: T-9 m, 11 m, 13 m, 17 m and 201 m.
temperature under nitrogen flow and the char was
collected from the biomass basket hung inside the
reactor. The volatiles removed on pyrolysis are
gradually condensed in a pre-weighed condensing
train. The condensates with dew point 60–65 1C
were collected and the balance was condensed in
ice bath (5–71C). The total condensable collected
in the condensing train is termed as ‘total liquid’.
Among the ‘total liquid’, the condensate collected
having a dew point upto 60–65 1C, are termed as
‘bio-oil’ which have moisture content in the range
of 8–12% with a calorific value X20 MJ/kg and is
directly combustible without any further treatment
[19]. The condensate fractions other than the ‘biooil’ which are noncombustible, contain water and
light organics.
4. Results and discussion
4.1. Effect of deashing treatments on pyrolysis
product distribution of sugarcane bagasse
The effect of deashing treatments on sugarcane
bagasse pyrolysis product distribution (char, gas,
and total liquid including oil fraction), based on
treated bagasse basis, has been shown in Table 6
columns A. Columns B in Table 6 represent the
same on original bagasse basis, i.e. all values are
inclusive of mass reduction during leaching.
As expected, the pyrolysis product distribution
relates well to the chemical composition of bagasse
as follows. In case of water leaching, the extractives are being washed out and thereby reducing
the wt% of extractives from 25.8 to 13.3 (even for
1 h water leaching). This is attributed to the fact
that unlike woody biomass, extractives of sugarcane bagasse comprise largely of starch, sugars,
phenolic tannins, and are washed out in simple
water leaching. By virtue of above, though the
actual amount of cellulose is not changed, the
relative percentage of the same has increased in the
water leached bagasse. Leaching with 5(M) HCl
solution hydrolyses the hemicellulose fraction to a
large extent leading to a drastic reduction of
hemicellulose and extractives with a resultant
increase in the apparent cellulose percentage in
the treated bagasse. In this case, the percentage
mass reduction is so high (50%) that the
reduction in ash is not manifested; rather it
actually seems to be increasing. Therefore, the
percentage increase in the oil yield is marginal and
is not as high as it should have been, had the ash
been removed completely.
This aspect is confirmed by leaching with HF
solution. Leaching with HF not only increases the
relative percentage of cellulose in the treated
bagasse by removing extractives and hemicellulose, but also completely removes ash elements.
The increase in the oil percentage in this case is by
450
Table 6
Pyrolysis product distribution of untreated and treated sugarcane bagasse
Biomass
Product distribution
Total liquid
Normal bagassea
Leached bagassea (1 h)
Leached bagassea (24 h)
Leached bagasseb (24 h)
5MHCl-treated bagassea
HF(0.5%)-treated bagassea
HF(1%)-treated bagassea
HF(2%)-treated bagassea
HF(3%)-treated bagassea
Oil
Char
Gas
A
B
A
B
A
B
A
B
—
62.4
63.7
62.1
61.0
67.3
68.7
71.3
72.9
55.0
49.9
46.5
45.3
30.5
47.8
48.1
49.2
49.6
—
32.1
42.5
41.6
42.0
41.6
43.9
45.2
47.9
19.5
25.6
31.0
30.3
21.0
29.5
30.7
31.2
33.0
—
18.5
17.2
18.1
20.4
15.6
15.1
12.4
12.4
22.7
14.8
12.6
13.2
10.2
11.1
10.6
8.6
8.4
—
19.1
18.8
19.8
18.6
17.1
16.2
16.3
14.7
22.3
15.3
13.7
15.5
9.3
12.1
11.3
11.2
9.9
A: wt% on treated bagasse basis, B: wt% on original bagasse basis.
a
150 ml leachate corresponds to 12.5 g of bagasse.
b
150 ml leachate corresponds to 25.0 g of bagasse.
about 69% (based on original untreated biomass)
and by 145 (based on treated bagasse basis),
while in case of leaching with least possible water
and longer period (Treatment III) the increase is
by 55.4% (original basis) and by 113.3% (for
treated basis). A special reference has to be made
to explain the increase in the oil percentage for
treated bagasse. It is well reported that upon
deashing, both the amount of volatiles and the rate
of their evolution increase [20–23]. In the presence
of ash elements, the volatiles escaping undergo
secondary cracking and form a soot deposit on the
residual char. The oil fraction, which consists of
mainly the condensates of primary vapours from
cellulose, lignin etc., increases only when the
absolute values of cellulose and lignin increase
and/or when the secondary cracking of oil to give
lighter organic fraction occurs (catalysed by the
ash constituents). Thus, the increased devolatilization rates in combination with changed organic
chemical composition are responsible for the
increase in oil fraction as well as oil to total liquid
ratios. Similar increase in oil percentages has been
reported by Subbarayudu [19] for other biomass
also wherein reduction of ash is considerable
during pretreatment.
At this juncture, it is worth comparing the oil
percentages as well as the oil-to-liquid ratios for
two bagasse samples having similar composition.
It is well known that the bagasse composition changes with the source and origin. Same
composition may be arrived by pretreatment or
may occur naturally. The bagasse composition
used by Perez et al. [2] matches with the composition of 1 h water-leached bagasse in the present
study. The oil yield obtained in this study for the
above-mentioned pretreated bagasse is 32%,
which is nearly similar to the oil yield of 34.2%
reported by Perez et al. (see Table 7). Thus,
the removal of extractives and the higher percentage of cellulose are capable of giving high
yields of oil, which can be obtained by either
water leaching of the high extractive content
bagasse or by using a bagasse with high cellulose
content.
4.2. Effect of deashing treatments on pyrolysis
product characteristics of sugarcane bagasse
The products obtained on pyrolysis of untreated
and treated bagasse have been subjected to
different analysis for their properties. The
effect of deashing treatments on the pyrolysis
product characteristics is reported in the following
section.
451
Table 7
Comparison of oil and liquid yield by two processes
Biomass components
Total liquid
yield (% daf)
Oil yield
(% daf)
Ash (%
dry)
Hemicellulose+extractives
Cellulose
Lignin
(i) Present method (in situ
separation after
pretreatment)
35.3
43.4
21.2
62.4
32
1.89
(ii) Garcia Perez et al. [2]
(after processing of liquid)
35.8
43.1
21.1
62.0
34.2
1.6
Table 8
Properties of sugarcane bagasse pyrolysis oil
Biomass pyrolysis oil
HHV (Higher heating value) MJ/kg
pH
Moisture content
Normal bagasse pyrolysis oil
Water-leached bagasse pyrolysis oil
HCl-treated bagasse pyrolysis oil
HF-treated bagasse pyrolysis oil
23.3
22.2
21.6
23.2
2.6
2.5
2.3
2.4
12.0
11.2
8.3
7.4
4.2.1. Higher heating value (HHV), pH and
moisture content of sugarcane bagasse
pyrolysis oil
Higher heating value, moisture content and pH of
bagasse and treated bagasse oil, is given in Table 8.
There is no note-worthy variation in calorific value of
the oils, however, it is seen that moisture content of
the oil gradually decreases from untreated to waterleached and to acid-treated oil. This is supplementing
the observation discussed in Section 4.1, i.e. with
leaching, the oil content increases and the char
content decreases. It is appropriate to attribute this
to the removal of ash from bagasse, on pretreatment.
The removal or and absence of ash reduces the
occurrence of ash catalysed lignin decomposition
reactions forming char and water [20,21].
4.2.2. Miscibility characteristics of bagasse
pyrolysis oil
Characterization of pyrolysis oil in terms of polar
and non-polar fractions has been carried out by
means of solvent extraction. The percentage miscibility of untreated and pretreated bagasse pyrolysis oil in different solvents ranging from nonpolar hexane to highly polar methanol is presented
in Table 9. The comparative results of miscibility
show that moving from untreated to water leaching
the percentage solubility in non-polar solvents
decreases with gradual increase in solubility in
polar solvents. In case of acid-treated bagasse
pyrolysis oil, there is a drastic decrease in nonpolar fraction with an equal increase in the polar
fraction of oil. This may be attributed to the
formation of low molecular weight sugars, alcohols,
carboxylic acids resulting from the degradation of
cellulose and hemicellulose due to pretreatment.
Miscibility characteristics of bagasse pyrolysis
oil with diesel were also studied. It is seen that a
maximum of 15 g of diesel remain permanently
soluble when mixed with 100 g of bagasse oil in
5:5 wt ratios. For higher diesel-to-oil ratio the
miscibility was found to be broken down with time
with a clear separation of oil and diesel layer.
4.2.3. Stability characteristics of sugarcane
bagasse pyrolysis oil
The variation of viscosity was monitored for
untreated and treated bagasse pyrolysis oils, stored
both at room temperature (Fig. 1) as well as at 60 1C
(Table 10). The viscosity is measured at 60 1C for the
oils stored at room temperature, while for the oil
stored at 60 1C, viscosity was measured at three
452
Table 9
Solvent extraction of bagasse pyrolysis oil
Pyrolysis oil
% Solubility
Untreated bagasse
pyrolysis oil
1 h water-leached
bagasse pyrolysis oil
1 h HF-treated
bagasse pyrolysis oil
Hexane (Nonpolar aliphatic
and aromatic
compounds)
Benzene
(Aromatic
compounds)
Dichloromethane
(High proportion
of substituted
polar phenolic
compounds)
Ethyl acetate
(Phenolic
compounds+low
molecular wt.
carboxylic acids)
Methanol (Most
polar fractions
and difficult to
characterize.
Polyalcohols,
sugars and fatty
acids)
5.27
27.8
30.17
16.92
19.88
3.59
17.70
34.39
22.44
21.88
0.9
8.89
39
28
24
90
viscosity in cSt at 60˚C
80
70
untreated bagasse pyrolysis oil
60
50
1 hour water leached bagasse
pyrolysis oil"
40
1 hour HF treated bagasse
pyrolysis oil
30
20
10
0
0
1
5
7
14 21 30
time (days)
35
42
60 365
Fig. 1. Viscosity variation of untreated and treated bagasse pyrolysis oil with time (stored at room temperature).
Table 10
Viscosity of bagasse pyrolysis oil versus heating time and
heating temperature
Heating time H t H
Heating temperature (HT) 60 1C
Viscosity (cSt) (measured at)
0
1
24
168
30 1C
60 1C
80 1C
Thick
Thick
93.62
—
28.00
27.14
34.52
67.37
12.01
11.90
16.62
21.25
different temperatures like 30 1C, 60 1C and 80 1C. It
is seen that compared to untreated bagasse oil initial
viscosity as well as rate of change of viscosity of
pretreated bagasse oil is more. This is attributed to
the more polar fractions present in treated oils as
shown in Table 9. Pretreatment hydrolyses cellulose
and hemicellulose which results in the increase of
more acidic as well as polar fraction in the oil leading
to higher rate of increase of viscosity in the
pretreated oil compared to untreated pyrolysis oil.
The effect is more severe in case of acid pretreatment
which leads to accelerated polymerization giving
more viscous and more acidic oil having less water
content.
4.2.4. Chemical characterization of bagasse
pyrolysis oil
The bagasse pyrolysis oil, treated and untreated,
was analysed for their compounds using FTIR and
453
Table 11
BET surface area of sugarcane bagasse pyrolysis char
Pyrolysis char
BET surface area (m2/g)
HHV (Higher heating
value) MJ/kg
Iodine no. (mg/g)
Untreated bagasse pyrolysis char
Water-treated bagasse pyrolysis char
HCl-treated bagasse pyrolysis char
HF-treated bagasse pyrolysis char
98
115.77
153.72
242.73
28.64
26.27
27.32
28.22
264
332
—
538
GC/MS techniques. The oils were first separated
into five fractions according to polarity as mentioned in Section 4.2.2 and then analysed. There is
an increase in the oxygenated–polar (dichloromethane and ethylacetate-soluble fractions) as
shown for treated bagasse pyrolysis oil.
The major compounds present in the waterleached bagasse are very similar to that reported
by Perez et al. for vacuum pyrolysis of bagasse of
similar composition under same reaction conditions. The moisture content and the calorific
values are also comparable. Thus, it is seen that
not only the product distribution but the nature of
pyrolysis oil composition also depend largely on
the relative composition of bagasse feedstock. This
has been exploited and explained in detail by
Ravindran [20].
5. Introduction
As mentioned in Part A, pretreatment of
bagasse through leaching has been resorted to
for selective removal of ash. This is accompanied
by removal of other organic components like
sugars, extractives, hemicellulose etc. The leachate
has enough carbon to support the growth of
organisms and to convert this carbon source into
desired chemicals like ethanol. In view of this, the
following study investigates the potential of
ethanol production via fermentation of the leachates.
6. Experimental
6.1. Microorganism and culture media
4.2.5. Effect of deashing treatments on
pyrolysis char properties
BET surface area, Iodine number (ASTM D
4607-86) and higher heating value of untreated
and treated bagasse pyrolysis char is presented in
Table 11. It shows that in each of the deashing
treatments there is an increase of BET surface area
with a maximum increase in HF-treated bagasse
pyrolysis char. The leaching leads to the elimination of compounds containing metal cations. The
increase in surface area occurs as a result of
opening of silica pores previously blocked by metal
cations. The treatment with HF, which makes the
obtained material practically ash-less, leads to
elimination of silica causing a total increase of
surface area [17,24].
Part B: ethanol fermentation with leachates
In the present study, the leachates, which result
from different pretreatment processes of finely
powdered sugarcane waste, was fermented for
ethanol by yeast Saccharomyces cerevisiae Yeast
strain Saccharomyces cerevisiae (Distillers yeast)
provided by Burns Philip India Ltd (KegaonUran, India) was used for the study. The strain
was maintained on culture medium containing
glucose 20 g/l, peptone 5 g/l, yeast extract powder
5 g/l, and agar 25 g/l.
6.2. Ethanol fermentation with leachate
The ethanol fermentation was carried out in the
leachate medium. The water leachates (pH 3–4)
were first neutralized with 0.1 N NaOH solution.
Ethanol fermentation medium was prepared by
adding peptone (Nitrogen source) and yeast
454
extract powder, with a concentration of 5 g/l each,
in the neutralized leachate medium and was
autoclaved. The culture maintained on slants was
transferred to 100 ml (in 500 ml flask) of culture
media. This culture medium, containing 20 g/l
glucose, 5 g/l peptone, 5 g/l yeast extract powder),
was used to inoculate 50 ml (in 250 ml flask) of
fermentation media. This was used as a seed
culture for experimental work. All experiments
were carried out at 30 1C on an orbital shaker at
250 r.p.m. Biotransformation was initiated by
addition of 2 ml of seed culture to the fermentation
media and 1 ml of sample was withdrawn at
known time intervals for analysis.
Each of the samples taken in regular time
interval was then centrifuged at 6000 r.p.m. for
10 min. The supernatant was collected in Eppendorf tubes and stored at 4 1C for ethanol and
glucose estimation. The centrifuged organisms
were washed with saline water (0.9% aqueous
NaCl solution) and finally were resuspended in
saline water making the volume same as initial.
6.3. Estimation of cell concentration
Each sample (centrifuged organism suspended
in saline) was diluted with saline water to desired
concentration range and mixed in a vortex to make
homogeneous solution. Then, the absorbance was
measured at 600 nm on UV/visible spectrophotometer (Jasco model V-530). For calibration of
dry cell weight of yeast, 5 ml of cell suspensions
with known absorbance values were centrifuged
and dried in an oven at 80 1C to constant weight.
This procedure was repeated thrice and average
values were used for calibration.
6.4. Estimation of glucose concentration
For glucose estimation, 1 ml of each sample
(supernatant of each centrifuged sample diluted to
desired range of concentration) was added to 3 ml
of o-toluidine reagent (8% v/v o-toluidine in
glacial acetic acid). This was vortexed and placed
in a boiling water bath for 20 min. The resulting
solution was cooled and the absorbance was read
at 630 nm. A series of standards was made with
concentration of glucose (dextrose) in the range
0.05–0.25 g/l and absorbance was measured. Calibration curve was obtained by plotting absorbance
against concentration of standard samples. The
equation for the line of best fit for glucose
calibration found is given in the following section.
This method measures the reducing sugar glucose
exclusively among a mixture of saccharides. otoluidine in the presence of glacial acetic acid
reacts quantitatively with aldehyde [>CHO]
groups of aldohexoses to yield glycohexyl amines
and Schiff’s base. Aldopentoses, maltose and
lactose give similar reactions but are very less
reactive. A blue-green colour is obtained which is
estimated spectrophotometrically at 630 nm.
6.5. Estimation of ethanol concentration
Ethanol concentration was estimated using a
MAK series 911M Gas Chromatograph (GC) with
0.5 in steel Porapak Q column of 2 m length. The
column has a mesh size of 80/100. The GC
conditions are as follows: Oven temperature
180 1C (isothermal), Injector temperature 220 1C,
Flame Ionisation Detector (FID) temperature
220 1C. 3 ml sample (supernatant of each centrifuged sample) was injected for each run. Nitrogen
was used as the carrier gas with a flow rate of
30 ml/min. The calibration curve was obtained
using standard ethanol solutions of known concentration.
7. Results and discussion
All the leachates were analysed for glucose
content and the results are presented in Table 12.
It shows that, an average of 55% of total weight
loss of biomass during leaching process is contributed by glucose and the rest might be due to
pentoses like xylose and other sugars. The glucose
concentration of leachate being high (78%) in case
of pretreatment with higher biomass-to-water
ratio.
All the leachates were first neutralized with
0.1 N NaOH solution and tested for the viability of
cell growth. In case of 5 M HCl and HF
pretreatment leachate, there was no growth of
cell, which may be attributed to higher salinity of
455
Table 12
Sugar analysis of leachates
I
II
III
IV
V
Wt. of glucose (g/l)
in leachate
7.5
12.90
35.31
22.11
15.08
35
% Sugar (glucose)
loss w.r.t total wt.
loss in leaching
concentration (g/L)
Treatment
no.
40
50.00
57.30
78.00
53.06
56.55
30
25
cell(g/L)
20
glucose(g/L)
15
ethanol(g/L)
10
5
0
0
2
4
6
8 10 12 14 16 22 24 26 30 32 34 42
Time (h)
the leachate on neutralization with NaOH solution. On the other hand, NaF produced on
neutralizing HF-treated leachate inhibits the
TCA and glycolysis pathways, i.e. the central
metabolic pathways of cell growth. Finally,
leachate resulting from special 24-h water leaching
of bagasse was taken for fermentation study.
Fermentation tests were carried out with four
sets of substrates, viz. with control, 20 g/l glucose
solution, 24 h water leachate (Treatment II, WL2),
water leachate of special water treatment (Treatment III, WL3), and with the leachate of Treatment III supplemented with additional 20 g/l
glucose. The rate of production of ethanol as well
as the rate of consumption of glucose and rate of
cell growth for the leachate of Treatment III,
and with the leachate of Treatment III supplemented with additional glucose have been presented in Figs. 2 and 3, respectively. It is very
interesting to note that maximum conversion of
glucose to ethanol is 38–40% of original glucose
concentration.
8. Conclusion
Pre-treatment of bagasse with water, dilute HCl
solution and dilute HF solution shows a remarkable change in the pyrolysis product distribution
by virtue of a combination of a change in the
organic constituents and the selective removal of
inorganic ash elements. Mild HF solution is
effective in reducing the ash content of the biomass
to a negligible amount. Moreover, this treatment
effectively increases the oil yield by 69% (on the
basis of original wt of bagasse before treatment)
concentration (g/L)
Fig. 2. Kinetics of treatment 3-leachate fermentation.
50
40
cell(g/L)
glucose(g/L)
ethanol(g/L)
30
20
10
0
0 2 4 6 8 12 14 16 18 20 22 24 26 28 30
Time (h)
Fig. 3. Kinetics of mixture of treatment 3-leachate and 2%
Dextrose fermentation.
compared to oil obtained from untreated bagasse.
Thus, HF treatment removes the ash elements
completely, yet does not help in improving the
stability. Moreover, the leachates from this pretreatment, causing environmental concerns, are
not advisable to use. Similarly, treatment with 5 M
HCl leads to a marginal increase in oil yield but
results in an increase in viscosity of pyrolysis oil.
Acid pretreatment (both HF and HCl) hydrolyses
the hemicellulose and cellulose into smaller molecules resulting in the increase of acidic as well as
polar fractions in the oil and leads to higher rate of
increase of viscosity in case of pretreated oil
compared to untreated pyrolysis oil.
The leachates of both the acid pretreatment
processes have high sugar contents, yet ethanol
fermentation are not feasible in acid-treated
leachates due to high salinity of neutralized
leachates, which inhibits the TCA cycle and
glycolysis pathways of fermenting microorganism.
456
On the other hand, simple water leaching (with
least possible water) for longer period is effective
enough to reduce the extractives (function of
amount of extractives present originally, which in
turn depend on bagasse generation process) along
with some selected ash components in bagasse.
Water leaching, by virtue of selective removal of
ash and organic constituents increases the oil yield
(increase in the oil yield vary with the reduction in
extractives and total mass) by as much as 55.4%
(on original basis) on vacuum pyrolysis.
The calorific value of oil however is not affected
much and is in the range of 22–24 MJ/kg. The
pretreatment also produces char with a higher
adsorptive capacity, thereby adding value to the
char obtained from pyrolysis.
The high sugar content of water leaching
process carried with least possible water and for
longer period (24 h) shows promising result with a
maximum yield of ethanol 13.5 g/l and 38–40%
conversion of sugar. The fermentation process can
be made more economic by supplementing the
leachate with glucose or other ethanol making
substrate and hence increasing the ethanol concentration in the final product. The ethanol in
turn, can be used to stabilize the oil [20] produced
from pretreated (water-leached) bagasse. Technically based on simple calculations, i.e. if oil yield
from 24-h water-leached bagasse is 31% and 5%
ethanol is required for stabilizing the oil, the water
leachate when fermented produces enough ethanol
for stabilization of the oil. This shows the potential
of integrated loop-type approach for stable, less
viscous bio-oil product.
[5]
[6]
[7]
[8]
[9]
[10]
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[12]
[13]
[14]
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