This document summarizes a study on optimizing the extraction of sandalwood oil using subcritical carbon dioxide compared to conventional techniques like steam distillation. Subcritical carbon dioxide extraction at 200 bars and 28°C yielded 4.11% oil in the first hour, higher than other methods and with higher quality as indicated by acid value and santalol content. Analysis found the oil extracted in each hour contained varying amounts of key constituents like α-santalene and β-santalol. The study demonstrates that subcritical carbon dioxide extraction is more efficient and yields higher quality sandalwood oil than conventional techniques like steam distillation.

1. Indian Journal of Chemical Technology
Vol. 21, July 2014, pp. 290-297
Process optimization of sandalwood (Santalum album) oil extraction by
subcritical carbon dioxide and conventional techniques
Omprakash H Nautiyal*
Department of Chemical Engineering, Institute of Chemical Technology (UDCT),
NM Parikh Marg, Matunga, Mumbai 400 019, India
Received 15 April 2013; accepted 28 March 2014
Sandalwood oil has been extracted using subcritical state carbon dioxide (SC-CO2) at 200 bars and 28oC using the two
experimental conditions, and the fractionation of the extract is analyzed intermittently. Comparative studies with regards to
extraction using steam distillation, hydro distillation, soxhlet extraction and pre-treatment studies have also been carried out.
All these studies reveal that the subcritical carbon dioxide extraction is much more efficient in terms of physical properties
of the oil as compared to commercial sandalwood oil. Acid value of the liquid CO2 extracted oil is found to be the best next
to the value of ethyl alcohol extracted oil. SC-CO2 yields 4.11% of oil in the first hour, 1.21% in second hour, 0.89% in third
hour and 0.30% finally in the fourth hour. The first hour gives α-santalene (0.55%), β-santalene (1.30%), α-santalol
(51.30%), β-santalene (27.94%); second hour gives 0.48, 1.08, 54.50, 28.16% third and fourth hour give 1.00, 1.92, 50.27,
26.18% and 1.14, 2.17, 51.99, 26.76% respectively. Benzene extraction yields 3.01% of an absolute out of 6.30 g of concrete,
diethyl ether yields 2.58% of an absolute out of 5.25 g of concrete, EtOH yields 3.70% of an absolute out of 10.90 g of concrete
(under the 5 hour of process time). Hydro distillation (alkaline treated) yields 2.68% of sandalwood oil in 48 h, steam
distillation gives 1.60% of sandalwood oil in 10 h of process time. Yield of 4.11% is obtained by SC-CO2 only.
Keywords: Carbon dioxide, Oil extraction, Sandalwood oil, Santalum album, Subcritical state
Sandalwood oil has a very good fixative properties
and applications in classic blender fixatives. It has a
delicate aroma and can be blended in small quantities
without altering the dominant fragrance. A minimum
of 90% santalol content is supposed to be present in
the sandalwood oil to make it saleable as premium
quality in market. Conventionally steam distillation is
employed for recovering sandalwood oil which yields
3.6% oil after 24 h of distillation, whereas subcritical
carbon dioxide (liquid CO2) extraction yields much
higher yield than that with steam distillation within
1 h of process time. Sub critical processed oil
contains high yield of santalol than that obtained
with steam distillation. In the light of high demand
of high quality sandalwood oil high-tech sub critical
CO2 extraction process was investigated. These
investigations were also compared with various
conventional techniques1,2.
The past few decades saw the emergence of
several noteworthy trends in processing products
from plant materials and their enhanced customer
concern for the quality such as flavour, fragrance,
odour, colour, stringent government regulations on
solvents and allowable solvent residues in food
and feed materials with increasing energy costs.
The future of many technology-oriented processes
including natural flavour and fragrance extraction
will be significantly affected by these issues.
Therefore SC-CO2 may play an important and lead
role as ecofriendly technology1,2.
Subcritical fluid extraction is an extraction process
utilizing a fluid as an extract temperature below
its critical temperature and pressures exceeding
its critical pressure. During the past three decades,
researchers have investigated the underlying
fundamentals and process applications of subcritical
fluid as solvents1,2. It is possible to separate a multi-component
mixture when a subcritical fluid is used
as an extractive solvent considering the differences
in volatilities of components (Salient features of
distillation) and the differences in specific interaction
between the mixture components and the subcritical
solvent (salient features of solvent extraction).
The application of subcritical solvents is based
on the experimental observations that many gases
exhibit enhanced solvating power when compressed
to conditions above and below the critical point1-3.
——————
*E-mail: opnautiyalus@yahoo.com

2. NAUTIYAL: PROCESS OPTIMIZATION OF SANDALWOOD OIL BY SC-CO2
291
The design of commercial super/subcritical plants
unit operations and designed specifications are important
for extractions of flavour materials like sandalwood oil.
Under subcritical conditions, the density and viscosity
of the solvent are comparatively high and essential
for the bulky mass materials like sandalwood oil. This
facilitates the contact time of the process to be as low as
2 h, as investigated in this study1-3.
Sandalwood oil, being precious oil, is in high
demand in the national and international markets.
It is usually steam distilled and its major constituents
α-santalols, β-santalols, α-santalenes and β-santalenes
are lost in the water during distillation, resulting in
inferior quality sandalwood oil. This study has been
undertaken to evaluate the quality and yield of oil
using subcritical carbon dioxide and the findings are
compared with those of the conventional techniques.
Sandalwood oil obtained by all the extraction
technology is subjected to an extensive physical
determination.
Experimental Procedure
Sandalwood chips were provided by the Malladi
Drugs & Pharmaceutical Limited along with the
commercial sandalwood oil for comparative details.
Equipments for the conventional processing were
purchased from the Indian suppliers of Borosil make,
including soxhlet extractor, Dean-Stark (moisture
contents), Clevenger apparatus for hydro distillation.
Steam distillation pilot plant of prototype was used.
Pilot plant for supercritical carbon dioxide extraction
was imported from UHDE, GmbH, Germany with
1 L capacity of extractor and separator each.
Pulverization of sandalwood
Sandalwood chips were pulverized in the pulveriser
to obtain powder of 40 mm in size. It was charged
into the extractor of SCF pilot plant and then operated
at subcritical state at 28°C to study the quality
and yield of the oil. Parallel experimental studies
were also performed using hydro distillation, steam-distillation,
solvent extraction (Soxhlet apparatus) to
study the evaluation of the extracted oil. Physical
properties of the extracted oil were determined
from the quality and fragrance point of view.
While extracting with solvents concrete of the
sandal was obtained, which was then hydro distilled
to obtain the essential oil.
Pilot scale steam-distillation, as commercially
used for the recovery of the oil, was also carried out.
The oil thus distilled was collected in the Florentine
container where the components get separated on
density basis. As oil is less dense, it floats over
the water surface and separated out on the gravity
basis.
Analysis of sandalwood oil
The oil extracted by all techniques was analyzed
by gas chromatography (Perkin-Elmer-8500).
Column specification and temperature programme
were column SE30(10%) on chromosorb W, column
material S.S, column length 4m, internal diameter
1/8 mm, injector temperature 300°C, FID temperature
300°C, flow rate of N2 38 mL/min, temperature
programming 100-250°C at 6°C/min. of temperature.
Its physical properties were determined using Bausch
Lomb refractometer for refractive index.
Theory of SC- CO2 technology and principle
Supercritical CO2 extraction means CO2 goes to
a supercritical phase after pressurization and
heating temperature above critical points. CO2 at
supercritical phase has solubility power similar to
liquid organic solvents, but with higher diffusivities,
higher transfer efficiency, lower viscosities, and
lower surface tension. With advantages of
non-toxic, colourless, odourless, incombustibility,
non-photochemical reaction, ecofriendly and easy
recycling, CO2 is now considered as the best solvent
for supercritical fluid extraction technology4,5.
Green environmental protection technology
Supercritical CO2 extraction has no disadvantages
of traditional extraction method. The biological
activity is easy to be damaged in high temperature
distillation extraction, the organic solvent left in
solvent extraction will influence the purity of extract,
and the aroma of esters is easy to vanish away in
expression extraction. Supercritical CO2 extraction
can extract high purity natural compounds easily.
There are no solvent residues and little thermal
degradation of sensitive compounds occurs.
Separation and purification of totally natural and
healthy compounds can also be achieved.
Supercritical CO2 extraction is the green and
epoch-making technology today and tomorrow4,5.
Advantages
The technology affects bioactive ingredients
extraction with lower viscosity and higher penetration
to the matrix. Low temperature extraction condition
results in less degradation of thermally-labile
components in the extracts. Green solvent with CO2

3. INDIAN J. CHEM. TECHNOL., JULY 2014
292
shows recovery rate over 95%. No solvent residue
is found in the extract. This means lower operating
costs for clean-up and the reduction in
post-processing steps. It is non-toxic, highly safe,
non-flammable and non-explosive. Selective
extraction is obtained by manipulating the
operating conditions, viz. temperature, pressures,
flow rate, batch time and ease of intermediate
fractionations4,5.
Thermodynamic state of supercritical fluid
The solvent power of supercritical fluid can be
related to the solvent density in the critical region.
This statement can be rationalized by considering the
density behaviour of a pure component, at a reduced
temperature (TR) ranging 0.8-1.55°C and pressure (PR)
ranging 0.1-10 mPas. The density of the solvent can
change from a value of about 0.1kg m-3 (gas like
density) to about 2.5 kg m-3 (a liquid like density).
As the reduced densities become liquid like, the
supercritical fluid begins to act as a liquid solvent.
When operating in the supercritical region both
temperature and pressure can be used to regulate
the density and therefore, the solvent power of
a supercritical fluid. In supercritical fluid extraction,
the supercritical fluid (SCF) region for a component
is strictly defined as that region of temperature and
pressure greater than or equal to critical temperature
and critical pressure respectively of the pure
component. The SCF region of interest for practical
considerations is considered less rigorously at
conditions bounded approximately by 0.9<TR<1.2 and
PR>1.0. In this region the SCF is highly compressible.
At constant TR of 1.1, increasing pressure from
PR<1.0 to PR>1.0 significantly increases the
density from relatively low values to liquid like
densities. At constant PR value of 1. 50, decreasing
temperature has a similar effect on density and
at higher reduced pressures, the density is less
sensitive to temperature changes. In the vicinity of
critical point, large density changes can be produced
with either relatively small pressure or temperature
changes4,5.
Results and Discussion
Sandalwood oil extraction with SC- CO2
Experiments were conducted employing liquid
carbon dioxide at 28oC temperature and 200 bars
pressure. Pulverized sandalwood of 40 mm size was
charged. Flow rate of solvent is 5 kg h-1 and batch
time 4 h. In the first set of experiments, the yield of
oil obtained was 3.76wt%. The peak areas of
α-santalene and β-sanatlene were 0.34 and 2.14%
respectively, whereas area per cents of α-sanatlol
and β-sanatlol were 43.78 and 22.81 respectively.
In another experiment, conditions were kept similar
but the oil was collected at the interval of 1 h. Hence,
in the first hour 4.11 g oil was extracted, 1.21 g in
the second hour, 0.89 g in the third hour, and 0.30 g
in the fourth hour. Thus, total 6.51 g of the oil was
extracted in batch time of 4 h. The oil obtained was
3.83wt% of the material charged6,7.
GC analysis shows that the peak areas of major
constituents, α-santalene and β-santalene extracted
in the first hour were 0.55 and 1.30% respectively,
whereas peak areas for α-santalol and β-santalol were
51.30 and 27.94% respectively. In the second hour,
the peak areas for α-santalene and β-santalene were
0.48 and 1.08%, and those of α-santalol and β-santalol
were 54.50 and 28.16%. In the third hour, the peak
areas of α-santalene and β-santalene were 1.00 and
1.92%, and those of α-santalol and β-santalol were
50.27 and 26.18% respectively. Finally, in the fourth
hour of extraction, the peak area of α-santalene,
β-santalene and α-santalol, β-santalol was 1.14,
2.17, 51.99 and 26.76% respectively. α-santalol
and β-santalol contents and the yields of the
sandalwood oil were found to be maximum in the
second hour (Table 1)7,8.
Hydro distillation
Yield of sandalwood oil with hydro distillation
Hydro distillation of sandalwood oil obtained from
pre immersed sandalwood in cold water for 72 h was
carried out for 36 h. The yield of the oil obtained was
found to be 1.71wt%. The colour of the oil was
Table1─Extraction of sandalwood oil by Liquid carbon dioxide (Subcritical state)
Time of collection Major constituents
h
Yield of oil
g α –Santalene β –Santalene α –Santalol β –Snatalol
1 4.11 0.55 1.30 51.30 27.94
2 1.21 0.48 1.08 54.50 28.16
3 0.89 1.00 1.92 50.27 26.18
4 0.30 1.14 2.17 51.99 26.76

4. NAUTIYAL: PROCESS OPTIMIZATION OF SANDALWOOD OIL BY SC-CO2
293
pale yellow with pleasant odour. The yield of the oil
was found to be less since the oil sacs remained
unexposed. In spite of softening the sandalwood
chips for a long time, it was difficult for the steam
to pierce through medullar ray cell, vessels, wood
fibres and wood parenchyma containing oil as it
was unpulverized. Gas chromatograph analysis
showed the presence of α-santalene and β-santalene
in trace amount, whereas the contents α-santalol
and β-santalol were 48.38 and 28.73% respectively9,10
(Table 2, Section 1).
Earlier hydro distilled sandalwood was dried,
pulverised and then extracted employing
Soxhlet apparatus. The powder was extracted
using toluene for 5.15 h in soxhlet apparatus.
5.33wt % of yellowish red concrete was obtained
and further yielded the absolute 0.37 wt %
(solvent extraction). α-santalene, β-santalene and
α-santalol, β-santalol were 0.36, 0.83, 39.71
and 19.76% respectively, as analyzed by GC.
The insoluble resinous mass left after the
extraction was then hydro distilled for 12 h. The yield
of the oil obtained was 1.05wt%. The oil obtained
was less odourant. α-santalene, β-sanatlene, α-sanatlol
and β-sanatlol were 3.98, 4.87, 38.47 and 20.42wt%
respectively. Hence, the net oil recovered
was 3.13% (refs 9,10).
In this case, sandalwood was pulverized to 40 mm
size (particle length 9 mm, diameter 3-4 mm) and
charged for the hydro distillation. Hydro distillation
was carried out for 30 h. The oil recovered was
1.86wt% which was found to be high in comparison
to that of unpulverized sandalwood chips. It was also
observed that pulverization exposed the sandalwood
vessels and hence the oil recovery was improved.
α-santalene and β-santalene were 2.17 and 1.26%
and α-santalol and β-santalol were 40.19 and 12.40%
respectively. The reduced extraction of α-santalol
and β-santalol could be because of these losses during
pulverization. The colour of the oil was pale yellow
and it had pleasant smell (refs 11,12).
Hydro distilled sandalwood powder was then
dried and charged for the solvent extraction using
benzene. The extraction was carried for 5 hrs.
The concrete obtained was 4.27% with dark red
colour. The absolute obtained was 1.25% in which
α-santalene, β-santalene and α-santalol, β-santalol
were 3.42, 4.99, 38.21 and 22.96% respectively.
The net oil recovered was 3.11 wt% (refs 11,12).
Effect of alkalinity on the yield of sandalwood oil using hydro
distillation
In this part of study, sandalwood powder
(40 mm size) was charged for hydro distillation,
utilizing alkaline water. The extraction was carried
out for 48 h. The oil recovered was 2.68wt%. The
yields of α-santalene and β-santalene were 4.25 and
3.01% and those of α-santalol and β-santalol were
41.90 and 19.89% respectively. α-santalene and
β-santalene extracted were high. The alkaline medium
was used since the pH of water during hydro
distillation plays a major role on composition of
essential oil. Acidity of water causes transformations
of thermo labile monoterpenes. Neutral or alkaline
medium minimizes the formation of artefacts during
distillation (Table 2, Section 2)13,14.
Yield of sandalwood oil from un pulverized sandalwood using
hydro distillation
In this study, extraction of sandalwood oil was
carried out for 38 h using preimmersed whole
sandalwood chips in hot water at 95oC for 24 h.
The yield of the oil obtained was 1.56wt% and the
colour of the oil was pale yellow with pleasant
odour with α-santalol 56.73%, β-santalol 27.10%,
α-santalene 0.30% and β-santalene 0.91%. Structures
of major constituents responsible for woody odour
and medicinal values are presented in Fig. 115,16.
Steam distillation
Effect of batch time on extraction of sandalwood oil using pilot
plant steam distillation
In this part of study, pulverized sandalwood
powder (2 mm size) was soaked in cold water for
48 h. It was then charged in the distillation still
along with the water. Steam pressure was 0.7 bar
Fig. 1 ─ Chemical structure of major constituents of sandalwood oil

5. INDIAN J. CHEM. TECHNOL., JULY 2014
294
Table 2─Extraction of sandalwood oil
Method of
extraction
Batch time
h
Physical/pre-treatment
% concrete
extracted
% oil/absolute
extracted
Major
constituents, %
Colour of
oil
Odour of
oil
Section 1
Hydro
distillation
36 Whole sandalwood
chips immersed in
cold water for 24 h
- 1.71 (i) traces (ii) traces
(iii) 48.38 (iv)28.73
Pale
yellow
Pleasant
Solvent
extraction
(toluene)
5.15 After hydro distillation
chips were finely
pulverized.
5.53
(yellowish
red concrete)
0.37 (i) 0.36 (ii) 0.83
(iii) 39.71 (iv)19.76
Pale
yellow
Less
pleasant
Hydro
distillation
of concrete
12 - - 1.05 (i) 3.98 (ii) 4.87
(iii) 38.47 (iv)20.42
Pale
yellow
Less
pleasant
Hydro
distillation
30 Pulverized coarse
powder
- 1.86 (i) 2.17 (ii) 1.26
(iii) 40.19 (iv).42
Pale
yellow
pleasant
Soxhlet
Extraction
(toluene)
10 Medium/coarse
pulverizing
7.56 2.59 (i) 3.98 (ii) 4.80
(iii) 29.22 (iv)30.54
Pale
yellow
Less
pleasant
Hydro
Distillation
48 0.3%alkaline water,
coarse/medium
pulverized
- 2.68 (i) 4.25 (ii) 3.01
(iii) 41.90 (iv)14.89
Pale
yellow
Pleasant
Hydro
distillation
38 Ungrounded chips
immersed in hot
water for 24 h
- 1.56 (i) 0.30 (ii) 0.91
(iii) 56.73 (iv)27.10
Pale
yellow
Pleasant
Section 2
Steam
distillation
10 Fine pulverized
powder
- 1.60 (i) 0.77 (ii) 1.80
(iii) 54.74 (iv)29.58
Pale
yellow
Pleasant
Soxhlet
Extraction
(benzene)
3 Steam distilled
powder
2.07 1.05 (i) 0.85 (ii) 1.70
(iii) 42.22 (iv)23.26
Pale
yellow
Pleasant
Soxhlet
Extraction
(ethyl alcohol)
6 Coarse pulverizing
immersed
10.90 3.70 (i) 0.96 (ii) 3.28
(iii) 50.03 (iv) 27.87
Pale
yellow
Less
pleasant
Soxhlet
Extraction
(diethyl ether)
5 Coarse pulverizing
immersed
5.23 2.58 (i) 0.57 (ii) 1.47
(iii) 48.82 (iv) 14.89
Pale
yellow
Less
pleasant
Soxhlet
Extraction
(benzene)
5 Previously hydro
distilled 30 hours
coarse powder
4.27 1.25 (i) 3.42 (ii) 4.99
(iii) 38.21 (iv) 23.37
Pale
yellow
Pleasant
Soxhlet
Extraction
(toluene)
12 Coarse pulverizing
immersed
4.98 2.45 (i) 3.84 (ii) 4.03
(iii) 37.04 (iv) 15.89
Pale
yellow
Less
pleasant
Soxhlet
extraction
(benzene)
5 Pulverized fine
powder
6.25
(dark red)
3.01 (i) 7.79 (ii) 5.12
(iii) 30.54 (iv) 15.98
Pale
yellow
Pleasant
(i) α-santalene, (ii) β –santalene, (iii) α-santalol, (iv) β –santalol.
gauge and the batch time was 10 h. About 8.1 g
oil was obtained from 500 g of sandalwood
powder; the recovered oil being 1.62wt%. The oil
was pale yellow in colour with pleasant odour.
In all six fractions were collected, each comprising
2 L of water. No oil was observed in the sixth
fraction GC analysis of the oil showed 54.74 and
29.58% of α-santalol and β-santalol. Steam distilled
powder was extracted using benzene for 3 h, yielding
2.07 wt% of the concrete. This was subjected to
hydro distillation for recovering 1.05wt% of the
absolute. Thus, total yield of the oil recovered
was 2.67wt%. GC analysis of the solvent extracted
oil showed 0.85% and 1.70% of α-santalene and
β-santalene, whereas 42.22% and 23.26% of
α-santalol and β-santalol respectively16,17.

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295
Table 3─Comparison of extracts of sandalwood oil obtained by different processes
Process of extraction Concrete extracted
wt%
Absolute extracted
wt%
Composition of oil
%
(i) (ii) (iii) (iv)
Liquid CO2 extraction (200 bars, 28°C, 4h) - 3.76 0.48 1.08 54.50 28.00
Solvent extraction
Benzene (5h) 6.30 3.01 7.86 1.63 30.81 12.18
Diethyl ether (5h) 5.23 2.58 0.57 1.47 48.82 23.37
Ethyl alcohol (5h) 10.90 3.70 1.14 0.42 54.55 29.01
Hydro distillation (30h) - 1.86 2.17 1.26 40.19 12.40
Hydro distillation, alkaline treated (48h) - 2.68 4.25 3.01 41.90 14.89
Steam-distillation, pilot plant (10h) - 1.60 0.77 1.80 54.74 29.58
(i) α-santalene, (ii) β –santalene, (iii) α-santalol, (iv) β –santalol
Sandalwood oil obtained by different processes is
summarized in Table 3. The major constituents
α-santalol and β-santalol were extracted in good amount
by liquid carbon dioxide as well as by ethyl alcohol.
Solvent extraction
Effect of batch time on extraction of sandalwood oil using
ethyl alcohol
Extraction of sandalwood oil was carried out
varying the batch time between 4 h to 7 h.
The extraction of the concrete was 6.67, 8.75, 10.90
and 10.91wt%. It was found that when ethyl alcohol
was employed as a solvent the per cent recovery
of the concrete was higher than that extracted by
benzene, toluene and diethyl ether. The absolute
extraction was 2.45, 2.80, 3.70 and 3.73wt%.
The peak areas of α-santalene and β-santalene at
4 h were 1.12 and 1.75% and that of α-santalol and
β-santalol were 43.80 and 24.87% respectively.
The extraction of α-santalene and β-santalene at
5 h were 0.96 and 3.28% and that of α-santalol
and β-santalol were 50.03 and 27.51% respectively.
Similarly the peak areas of α-santalene and
β-santalene were 1.14 and 0.42% and that of
α-santalol and β-santalol were 54.55 and 29.01%
respectively at 6 h. The content of α-santalene and
β-santalene were 0.54 and 1.25% and that of
α-santalol and β-santalol were 50.99 and 27.20%
respectively. Extraction of major constituents was
better18,19.
Effect of batch time on extraction of sandalwood oil using
diethyl ether
Major problem, using diethyl ether as an extractent,
was its high volatility due to its low boiling point.
The loss during the extraction was minimized by
circulating cold water at 10oC through the condenser.
However, the recovery of the solvent after extraction
was poor. Diethyl ether is a non-polar solvent.
The per cent recovery of the concrete was 4.20, 4.33,
5.23 and 5.74% for 3, 4, 5 and 6 h extraction time.
The per cent recovery of the absolute was 2.08, 2.14,
2.58 and 2.60% for the same batch time of extraction.
Although the recovery of the concrete at 6 h was
more compared to that at 5, the recovery of an
absolute at the same batch time was less than that of
5 h. This may be due to extraction of waxes and not
the resins which contain oil18,19.
Effect of batch time on extraction of sandalwood oil using
benzene
The composition of the sandalwood oil after 3
and 5 h batch time of extraction was analysed by
GC. Peaks of α-santalene, β-santalene, α-santalol and
β-santalol were taken to represent the quality of
sandalwood oil. It was found that higher quantities
of α-santalol and β-santalol were obtained when batch
time was increased from 3 h to 5 h. There was
an increase in the α-santalene and β-santalene
contents of the sandalwood oil. Sandalwood oil was
also extracted using toluene for the batch time of 12 h.
The yield of the concrete was 4.98 wt% and that
of the oil was 2.45 wt%18,19.
Extraction of sandalwood oil using Toluene
Sandalwood oil was extracted using Soxhlet
apparatus with toluene as a solvent for a batch time
of 12 h. The yield of the concrete was 4.98wt% and
the absolute obtained was 2.45wt%. The composition
of α-santalen, β-sanatlene, α-santalol and β-santalol
were 3.98, 4.80, 29.22 and 12.58% respectively. The
odour was less pleasant as compared to the extraction
with benzene19,20.

7. INDIAN J. CHEM. TECHNOL., JULY 2014
296
Table 4 ─ Physical properties of sandalwood oil
Method of extraction Pre treatment Refractive index Optical rotation Acid value
Hydro distillation Whole chips 1.500 -22.97 Nil
Soxhlet extraction
Pulverized coarse
(TOLUENE)
size powder
1.503 -19.14 4.67
Hydro distillation of concrete Nil 1.499 Nil 7.33
Hydro distillation Pulverized coarse size powder 1.499 -14.46 5.58
Hydro distillation Pulverized coarse size powder,
0.3% alkaline distilled water
1.502 -19.57 2.66
Steam distillation Pulverized powder immersed
in cold water (48 hrs)
1.503 -24.67 6.39
Soxhlet extraction (ethanol) Fine pulverized powder 1.504 -19.56 7.79
Soxhlet extraction (diethyl ether) Fine pulverized powder 1.503 -14.46 7.79
Soxhlet extraction (benzene) Pulverized fine powder 1.502 -28.07 6.95
Soxhlet extraction (toluene) Pulverized coarse size powder,
immersed in hot water
1.501 Nil 6.71
Liquid CO2 extracted Fine pulverized powder 1.505 -22.97 4.10
Commercial sandalwood oil Nil .504 -19.57 4.15
Required specification : Refractive index 1.499-1.506, Acid value 0.5-8, and Optical rotation 15° to -19.20°.
Comparison of the sandalwood oil obtained by different
separation methods
A comparison of extracts of sandalwood oil,
obtained by different methods, has shown that
the major constituents α-santalol and β-santalol were
extracted in good amount by liquid carbon dioxide
as well as by ethyl alcohol.
The physical properties of the sandalwood oil, such
as refractive index, optical rotation and acid values,
are presented in Table 4. The optical rotation value
obtained by hydro distillation, steam-distillation,
benzene extraction and liquid carbon dioxide extraction
were not within the required specification. However,
the refractive index and the acid value for all the
experiments were within the stipulated values for
sandalwood oil21-23.
Conclusion
It is evident from the results that the extraction
of sandalwood oil with subcritical state CO2 at
200 bars and 28oC yield 4.11wt% of sandalwood
oil in 1 h of batch time with maximum isolation
of major constituents - the price deciding factors
of the oil. Though the conventional techniques
(steam distillation and hydro distillation) are being
practiced commercially, but produces low yield of
oil and inferior quality due to lesser santalol and
santalene contents. This is because these processes
take longer extraction time, and the major constituents
are lost in distilled water. Though the cohobation
techniques, being used in the recovery of the
solubilised constituents may add up to the yield, it
also adds cost and time of processing. Moisture
minimization in sandalwood oil is quite essential so as
to maintain its quality and shelf life. Solvents usually
extracts concrete first and then recovery of an
absolute is made through alcohol selectively. But here
also the yield and quality may be down due to multi
processing techniques.
Hydro distillation yields 1.86wt% of oil in 30 h.
The yield of oil is found to increase when the
particle size is reduced. Pulverized sandalwood yields
2.68wt% of oil in 48 h when alkaline water is used
for hydro distillation. The yield as well as the colour
of the oil is found to be better when alkaline water
is used for hydro distillation. When fine pulverized
powder is charged for steam distillation using
steam pressure of 10 psi, the yield obtained by steam
distillation is 1.60wt%.
The best yields of absolute (3.70wt %) and
concrete (10.90wt %) are obtained when ethyl alcohol
is used as solvent. The major constituents of the
oil, viz. α-santalol and β-santalol are found 54.55
and 29.01% respectively. On the scale, the assigned
score is 9.5 for the best quality of sandalwood oil
extracted by subcritical carbon dioxide.
Physical properties of subcritical extracted
sandalwood oil are found to be superior to that of
conventional processing.

8. NAUTIYAL: PROCESS OPTIMIZATION OF SANDALWOOD OIL BY SC-CO2
297
Acknowledgement
Author is thankful to Dr N R Shastri (Director,
R&D, Malladi Drugs & Pharmaceutical Limited)
for funding the project and providing the raw
material and commercial sandalwood oil. Dr. K K
Tiwari, deserves special thanks for investigating
its commercial viablity.
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