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Extraction of cashew (Anacardium occidentale) nut shell liquidusing supercritical carbon dioxide
Rajesh N. Patel, Santanu Bandyopadhyay, Anuradda Ganesh *
Energy Systems Engineering, Indian Institute of Technology, Bombay, Powai, Mumbai 400 076, India
Received 7 August 2004; received in revised form 4 April 2005; accepted 6 April 2005
Available online 6 June 2005
Abstract
This work investigated the extraction of cashew nut shell liquid (CNSL) using supercritical carbon dioxide (SC-CO2). Effects of
process parameters such as extraction pressure, temperature and flow rate of SC-CO2 were investigated. The yield of CNSL
increased with increase in pressure, temperature and mass flow rate of SC-CO 2. However, under different operating conditions,
the composition of CNSL varied. The study of physical properties and chemical composition of the oil obtained through super crit-
ical fluid extraction (SCFE) showed better quality as compared to the CNSL obtained through thermal route. Experimental results
were compared with diffusion based mass transfer model. Based on this simple model, extraction time was optimized.
2005 Elsevier Ltd. All rights reserved.
Keywords: Cashew nut shell; Supercritical fluid extraction; Carbon dioxide; Mass transfer model; Optimum extraction time
1. Introduction
India is the largest producer and processor of cashews
(Anacardium occidentale) in the world (Das and Ganesh,
2003). In India, cashew cultivation covers a total area of
about 0.77 million hectares of land, with an annual pro-
duction of over 0.5 million metric tonnes of raw cashew
nuts. The average productivity per 100,000 m2 is around
760 kg. The world production of cashew nut kernel was
907,000 metric tonnes in 1998 (Smith et al., 2003). The
cashew nut shell liquid (CNSL) is reported to be
1520% by weight of the unshelled nut in Africa and
2530% by weight in India (Das and Ganesh, 2003).Considering the shell weight is about 50% of the weight
of the nut-in-shell (NIS), the potential of CNSL is about
450,000 metric tonnes per year. In India, processed cash-
ew dominates more than half the world cashew market.
The residue after extraction of CNSL is shell cake,
which is a very useful fuel and a substitute for fire wood.The innumerable applications of CNSL are based on the
fact that it lends itself to polymerization by various
means.
Various methods have been reported in literature for
the extraction of CNSL from CNS, which include, open
pan roasting, drum roasting, hot oil roasting, cold extru-
sion, solvent extraction, etc. The extraction through vac-
uum pyrolysis has been reported recently by Das et al.
(2004) and Tsamba (2004). The extraction of CNSL
using supercritical carbon dioxide (SC-CO2) has also
been reported by Shobha and Ravindranath (1991)
andSmith et al. (2003).Conventionally, both the quantity and quality (com-
position of CNSL) vary with the method of extraction of
CNSL. Various authors have reported varied composi-
tion of CNSL extracted. CNSL extracted by cold extru-
sion method is reported to contain approximately 70%
anacardic acid, 18% cardol and 5% cardanol and the
balance consisting of substituted phenols and less polar
substances (http://www.epa.gov/chemrtk/cnsltliq/c13793
tp.pdf). Das (2004) has also reported CNSL extracted
0960-8524/$ - see front matter 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.biortech.2005.04.009
* Corresponding author. Tel.: +91 22 25767886; fax: +91 22
25726875.
E-mail address: [email protected](A. Ganesh).
Bioresource Technology 97 (2006) 847853
mailto:[email protected]:[email protected] -
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by cold extrusion method with 90% anacardic acid and
nearly 10% cardol. According toTyman (1979), natural
CNSL contains nearly 64% anacardic acid, 11% cardol,
traces of cardanol, 23% of 2-methyl cardol and rest
polymeric material. About 52% cardanol, 10% cardol
and 30% polymeric material (Das, 2004) constitutes
the Technical Grade CNSL. A composition 64.8% card-anol, 20.5% cardol, 2.8% 2-methyl cardol, and rest as
non-volatile polymeric material have also been reported
(Tyman, 1975) for the Technical Grade CNSL. The
CNSL obtained through vacuum pyrolysis is cardanol
rich. It is reported to have cardol, substituted phenols,
di-n-octyl phthalate, bis(2-ethyl hexyl) phthalate, etc.
The use of this CNSL as a potential fuel in internal com-
bustion engine has also been suggested (Das, 2004).
However, the composition of CNSL obtained by SCFE
has not been reported in the literature.
SCFE, as mentioned by the authorsShobha and Rav-
indranath (1991) and Smith et al. (2003), has inherent
advantages over other extraction methods such as no
polymerization of CNSL, requirement of less amount
of solvent, and no extraction of undesirable coloured
compounds. In view of this, the present work is an at-
tempt to study the effect of operating parameters on
the yield and quality of CNSL extracted through SCFE
method. A simple mathematical model is also developed
for optimization of profit and energy/yield. The objec-
tive of the study is also to demonstrate the feasibility
of the component separation of CNSL using SCFE, par-
ticularly the higher molecular substances like cardanol.
2. Experimental procedure
Cashew nut shell (CNS) obtained from Pondicherry
was used for the present study. The shells were ground
to small particles (to pass through 8 mesh screen) and
weighed and then placed in the extractor. Carbon di-
oxide (99.9%) supplied by M/s Sicgil Corporation,
Bombay, was used as the supercritical fluid (SCF) for
extraction of oil from CNS.
SCFE unit supplied by M/s Deven Supercritical was
used for the present study. Carbon dioxide from the cyl-
inder passed through a pre-cooler, a positive displace-
ment pump, and a pre-heater before it entered the
bottom of the extraction vessel. (The extraction vessel
was maintained at a predefined temperature.) The flow
of carbon dioxide was controlled by a needle valve
and was measured by a gas flow meter with an accuracy
of 0.01 kg/h. A variable frequency drive pump con-
trolled the pressure in the vessel to an accuracy of
0.1 bar. Extracted oil was recovered by expansion of
the loaded solvent stream to ambient pressure in a glass
separator. Extract was collected and weighed at a fixed
time interval of 30 min (cumulatively) by closing the
needle valve. The needle valve was then opened and
extraction process continued for the next interval. Runs
were carried out for 6 h at the pressures ranging from
200 to 300 bar at 25 bar intervals. The extract of each
run was analysed by Gas Chromatograph Mass Spec-
troscopy (GC-MS) and Fourier Transform Infra-Red
Spectroscopy (FTIR).
3. Results and discussion
3.1. Effect of pressure on yield of CNSL
The total yield at various pressures from 200 bar to
300 bar, keeping other parameters constant, is shown
in Fig. 1. Temperature and mass flow rate of carbon
dioxide were kept constant at 333 K and 1.0 kg/h respec-
tively. Evidently total yield increased with increase in
pressure from 200 bar to 300 barthe yield being four
to five times higher at 300 bar than at 200 bar for the
same consumption of SC-CO2 (at the same flow rate
and temperature). This could be explained by the fact
that the extraction capacity of solvent at the supercriti-
cal state was density dependent. It was also observed
that the rate of extraction was high during initial phase
of extraction as the material is loaded with oil. The rate
of extraction decreased at later stages as shown inFig. 2.
The FTIR analysis was used to identify the components,
particularly cardanol.
3.2. Effect of pressure on the yield of cardanol
The samples were analysed by FTIR, GC-MS andUltraviolet (UV) spectroscopy. The FTIR and GC-MS
aided in identifying the functional groups present and
the components, respectively. The UV spectroscopy, cal-
ibrated for a commercial grade refined cardanol sample,
was used to determine the approximate percentage of
cardanol in the samples. The results of FTIR, GC-MS
and UV spectroscopy are summarized in Table 1. It
was interesting to note that acid group was traced by
Fig. 1. Variation in yield of CNSL and cardanol with extraction
pressure (extraction time 270 min, extraction temperature 333 0.5 K
and mass flow rate of SCF 1 0.01 kg/h).
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FTIR only for CNSL obtained above 225 bar. However,
GC-MS did not identify anacardic acid as a major
group and therefore, was assumed to be in traces.
GC-MS and FTIR analysis showed that at lower
pressure CNSL mainly consisted of cardanol. Amount
of cardanol in CNSL decreased with increase in pressure
from 86% at 200 bar and 333 K to 63% at 300 bar and
333 K.Fig. 1shows the CNSL yield, percentage carda-
nol in CNSL extracted and percentage cardanol ex-
tracted based on original CNS used. This percentage
cardanol was the product of the percentage yield of
CNSL with percentage cardanol in CNSL. The cardanol
yield, therefore, was higher at higher pressure.
3.3. Effect of temperature on yield of CNSL
It is known that the yield of extract depends on the
change in density and volatility of SCF. With increase
in temperature, the density of SCF decreased while vol-
atility increased (Mukhopadhyay, 2000). Hence experi-
ments were carried out at isochoric density by
modifying pressure. The effect of temperature on total
yield of CNSL is shown in Fig. 3.It could be seen that
with increase in temperature, total yield of CNSL in-
creased at a given mass flow rate and density.
3.4. Effect of mass flow rate of SCF on the
yield of CNSL
It is well understood that with increase in solvent to
solid ratio, the rate of extraction is enhanced, and hence
extraction time is reduced. The effect of mass flow rate
of SCF on total yield is shown in Fig. 4. It was observed
that with increase in flow rate of SCF, total CNSL yield
increased. However, due to lower retention time, load-
ing of SCF was lower, thereby reducing the capacity uti-
lization of the solvent. Table1
Effectofpressureontheyieldofcardanol(extractionparameters:extractiontemperature3330.5K,massflowrate1.00.01
kg/h)
Serialno.
Pressure(bar)
Function
algroups(FTIR)
Majorcomponentsidentified(GC-MS)
Cardanolpercentage
(UVspecroscopy)
1
2000.1
PolymericOH,alkanes,alkenes
C-13cardanol,3-(8-pentadecenyl)pheno
l,C-17cardanol
86
2
2250.1
PolymericOH,alkanes,alkenes
C-13cardanol,3-(8-pentadecenyl)pheno
l,C-17cardanol
83
3
2500.1
PolymericOH,alkanes,carboxylicacid,alkenes
C-13cardanol,3-(8-pentadecenyl)pheno
l,C-17cardanol,cardol
76
4
3000.1
PolymericOH,alkanes,carboxylicacid,alkenes
C-13cardanol,3-(8-pentadecenyl)pheno
l,C-17cardanol,dimethylanacardate
63
Fig. 2. Cumulative yield of CNSL at different extraction pressure.
Experimental conditions: mass flow of CO21.0 0.01 kg/h, extraction
temperature 333 0.5 K.
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3.5. Properties of oil extracted by SC-CO2
3.5.1. Physical properties of CNSL
The physical properties of the oil extracted at various
operating conditions were studied using standard test
procedures. It was observed that the calorific value of
the oil was almost same for all extraction conditions
while the density was in the narrow range of 0.92
0.934 kg/m3.
Table 2gives the comparison of physical properties of
oil extracted at 300 bar and 333 Kusing SCFE with
IS:840 (1964)and oil obtained through vacuum pyroly-
sis. It could be observed that the moisture content, den-
sity and viscosity of oil obtained through SCFE were
very close to IS:840 (1969) specifications, whereas these
properties were better as compared to CNSL obtained
through vacuum pyrolysis. Other properties of CNSL
extracted using SCFE were very close to that obtained
by vacuum pyrolysis. The comparison of this oil withoil obtained through vacuum pyrolysis was relevant in
terms of CNSL as a potential bio fuel.
3.5.2. Chemical composition of CNSL
The oil obtained at various operating parameters was
analysed for chemical compositions. Table 3shows the
main components present in CNSL obtained at various
operating parameters. It was noted that the main com-
ponent in CNSL was cardanol with side chain having
1317 carbon atoms; however, their concentration was
different at different operating parameters. This could
be attributed to the enhanced decarboxylation at higher
pressure (Hazen et al., 2002).
3.6. Residue analysis
The residue, after extracting oil from CNS at 300 bar
and 333 K in supercritical fluid extractor was pyrolysed
at 773 K under vacuum of 700 mm of Hg. The vapours
were condensed to find the condensates. The weight of
the condensed oil was hardly found 2% suggesting al-
most complete extraction of CNSL.
4. Mathematical model and optimization
In extraction, the solute from the cell matrix dis-
solved into the bulk fluid. Extraction of the solute be-
comes simple when it is free on the surface of solids.
On the other hand, as the solute interacts with cell ma-
trix its extraction becomes difficult. For natural material
with a high initial content of extractable, the rate of
extraction remains constant at the initial period. As
the outer surface of the solid is depleted of the extract-
able solute, solute from the core of the solid requires
more time to reach the fluidsolid interface. This results
in a drop in the rate of extraction with time (Ganga-
dhara Rao, 1990).
For extraction, several models have been proposed:
unsteady-state packed bed mass transfer model
(Mukhopadhyay, 2000), shrinking core leaching model
(Mukhopadhyay, 2000; Goto et al., 1996), empirical
models (Subra et al., 1998;Chrastil, 1982), etc. The un-
steady-state packed bed mass transfer model represents
the concentration profile of the SCF solvent phase in
the extractor with respect to time and length of bed.
In this model all constituents are clubbed together as a
solute, as it is believed that they would have similar mass
transfer characteristics (Mukhopadhyay, 2000). The
Fig. 4. Cumulative yield of CNSL at different extraction flow rates of
SC-CO2. Experimental conditions: pressure 250 0.1 bar, temperature
333 0.5 K.
Fig. 3. Cumulative yield of CNSL at different extraction temperatures.
Experimental conditions: mass flow of CO21.2 0.01 kg/h, density of
SCF 830 kg/m3.
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shrinkingcore leaching model accounts for intra-parti-
cle diffusion, external fluid film mass transfer and axial
dispersion. Several empirical models have been pro-
posed: Christil model, Kinetic model, etc. The Christil
model (Chrastil, 1982) provides yield as a function of
density of SCF and extraction temperature. It gives con-
stant rate of extraction and hence, only applicable for
the initial period of extraction. In kinetic model (Subra
et al., 1998) the rate of extraction is assumed to decrease
exponentially and the rate constant is determined by
regressing experimental data. This model is independent
of matrix parameters.
With the following assumptions, the kinetic model
was used in this study. Essential oil is assumed to be uni-
formly distributed over cell matrix. Axial dispersion is
neglected. Solid ground particles have uniform struc-
ture. Flow rate of SCF, system temperature and pres-
sure are constants and velocity of SCF through
extractor is negligible. If C is mass fraction of solute
in SCF over given period of time, Cinf is total amount
of solute present in solid, the kinetic model. This model
is expressed as:
C Cinf CinfexpKt 1
K is rate constant. Through experimental studies, it
has been observed that the rate constant, K, depends
on pressure, temperature and mass flow rate of the
solvent.
Table 2
Comparison of oil obtained by SCFE and thermal method
Properties CNSL (SCFE) CNSL specificationsIS:840 (1964) CNSL (pyrolysis method)
(Das and Ganesh, 2003)
Ash (%) (ASTM D482) 0.01 1.0 (max by wt.) 0.01
Moisture (%) (ASTM D1744) 0.747 1.0 (max by wt.) 3.5
Sp. Gr. at 301 K (ASTM D4052-86) 0.934 0.950.97 0.993
Absolute viscosity (cSt) at
303 K 95 550 CP(max) 159
333 K 27 33
353 K 14 16
(ASTM D445-88)
Flash point (K) (ASTM D93) 443 NR 453
Elemental composition (wt.% on dry basis) 77.85 NR 76.4
C 9.70 10.5
H 0.00
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K K0 KP P KF F KT T 2
where, P, F and T are pressure (bar), mass flow rate
of solvent (kg/h) and temperature (K) respectively. By
regressing the experimental results, following values
are obtained: K0= 0.004091, KP= 2.34 10(5), KF=
0.0030923, KT= 8.70563 10(6).
Positive values of KP and KF indicate that with in-crease in pressure and mass flow rate of solvent, the rate
constant and hence the yield increases. This is in accor-
dance with variation of CNSL yield with pressure and
mass flow rate of CO2 as shown in Figs. 2 and 4. The
negative value of temperature co-efficient in Eq.(2) sug-
gests that with increase in temperature, the yield of
CNSL decreases. However, its sensitivity on CNSL yield
is very low.
4.1. Optimum extraction time
The CNSL yield can be predicted using the kinetic
model for given operating parameters. It is well known
that the yield depends on extraction pressure, tempera-
ture, mass flow rate of the solvent and time of extrac-
tion. The operating parameters may be determined to
find maximum profit.
The pump, pre-cooler and pre-heater of SCFE pilot
plant consume the energy. The pump increased the pres-
sure of liquid CO2 from cylinder pressure to extraction
pressure. The energy required (WP) for driving a pump
depends on the density of CO2 (q), mass flow rate (F),
differential pressure (pressure difference between deliv-
ery pressure and cylinder pressure) and the mechanical
efficiency (gm,P) of the pump.
WP FP PC
36qgm;P3
It is to be ensured that CO2 must be in liquid phase
before it enters the pump. Carbon dioxide from cylinder
enters the pre-cooler and gets converted into liquid
phase. The energy required (WC) for driving the pre-
cooler is expressed as:
WC F
3600
CPfTsup Tsat hfg CPlTsat Tsub
COP
4
where CPfand CPl are specific heats of gaseous and li-
quid CO2 at cylinder pressure; hfg is the latent heat of
vaporization at cylinder pressure; Tsup is temperature
of CO2 at exit of cylinder; Tsat is saturated temperature
at cylinder pressure;Tsubis temperature of liquid CO2at
the exit of pre-cooler and COP is the coefficient of per-
formance of a pre-cooler.
Pre-heater increases the temperature of CO2 to
extraction temperature before it enters the extraction
vessel. If h1 and h2 are specific enthalpies of CO2 at
the entry and exit of pre-heater, the energy required
for pre-heater (WH) is expressed as:
WH Fh2 h1
3600 5
The specific energy (kW h/g m) required running
SCFE pilot plant for extraction time, t, is:
EWP WC WH t
C 6
Extraction of CNSL from CNS using SCFE is a semi-continuous process. At the end of each batch, the extrac-
tor is depressurized, fed with fresh raw material and
again pressurized for extraction period. There is a
non-productive down time between two consecutive
extraction batches. Moreover, the rate of extraction is
higher in the initial phase of extraction due to easily
available oil on the outer surface of the matrix. The rate
of extraction diminishes with time. Hence, it is also pos-
sible to determine the time of extraction of CNSL to get
maximum profit per day. Daily energy cost, cost for
recycling the CO2, revenues from selling of CNSL and
labor cost are considered for the formulation of profitfunction:
Daily profit revenues from CNSL
daily energy cost
cost of recycling of CO2 labor cost
The objective function (daily profit) is optimized with
following constraints:
190 bar< P
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regulated the total yield. It was also noticed that the sol-
ubility of supercritical fluid varied with extraction pres-
sure, temperature and mass flow rate of SCF. The yield
obtained was clear and with light yellow in colour. The
properties of CNSL obtained through SCFE were com-
pared with oil specifications mentioned inIS:840 (1964)
for CNSL. The moisture content, density and viscosityof the oil obtained through SCFE were very close to
CNSL specifications. The chemical analysis of CNSL ob-
tained in present study showed that it mainly contained
cardanol (7090%). It hardly contained anacardic acid,
while traces of cardol were found only at high pressures.
This suggested that selective separation of components
was possible by SCFE. The study of effect on percentage
yield of cardanol in CNSL at various pressures showed
that with increase in pressure concentration of cardanol
decreased due to extraction of components with higher
molecular weight along with cardanol at higher pressure.
However, total yield of the cardanol from CNS could be
predicted using the product of yield of CNSL from CNS
and yield of cardanol from CNSL in turn.
The study showed that the model developed could be
used to predict the yield of CNSL in the pressure range
of 190300 bar. Considering the down time for loading
and unloading of feed in each batch, the daily profit
optimization gave the optimum values for extraction
pressure, temperature, flow rate of solvent and also time
of extraction. The results of model suggested that in-
stead of complete extraction of CNSL from CNS, par-
tial extraction of CNSL would give more daily profit.
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