extração of cardanol

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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


l,C-17cardanol

83

3

2500.1

PolymericOH,alkanes,carboxylicacid,alkenes


l,C-17cardanol,cardol

76

4

3000.1

PolymericOH,alkanes,carboxylicacid,alkenes


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.

References

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