Separation and Purification Technology 19 (2000) 113 120

www.elsevier.com/locate/seppur

Simple fractionation through the supercritical carbon

dioxide extraction of palm kernel oil
M.N. Hassan a, N.N. Ab. Rahman b, M.H. Ibrahim c, A.K Mohd. Omar c,*
a
Uni6ersiti Teknologi MARA, Arau, 02600 Perlis, Malaysia
b
School of Distant Education, Uni6ersiti Sains Malaysia, Minden, 11800 Penang, Malaysia
c
School of Industrial Technology, Uni6ersiti Sains Malaysia, Minden, 11800 Penang, Malaysia

Received 16 November 1999; accepted 23 November 1999

Abstract

Supercritical carbon dioxide (SC-CO2) in the pressure range 20.7 48.3 MPa (3000 7000 psi) and temperatures
between 40 and 80C was used as a solvent in the extraction of palm kernel oil (PKO). At 20.7 and 27.6 MPa, the
solubility of PKO in SC-CO2 decreased with temperature. However, at higher pressures of 34.5, 41.4 and 48.3 MPa,
the solubility increased with temperature. The composition of the oil extracted varied with time. Earlier fractions were
rich in short-chain triglicerides, while the later fractions were rich in longer chain triglicerides and unsaturated
triglicerides. However, at higher pressures, the fractionation effect diminished and the oil could be considered as a
single component. At 48.3 MPa and 80C, the solubility of PKO in SC-CO2 of about 20% was relatively high
compared with that of soybean oil of about 3%. 2000 Elsevier Science B.V. All rights reserved.

Keywords: Palm kernel oil; Supercritical carbon dioxide; Extraction; Solubility; Fractionation

1. Introduction (15.6%) and oleic acids, C18:1 (15.1%) [13]. The

oil is conventionally extracted using screw press
Palm kernel is a by-product of the palm oil with 4043% (g oil/100 g kernel) yield or hexane
industry. It constitutes about 45% of the palm nut extracted with 44.546.5% yield [4]. In 1998,
of the palm oil Elaeis guineensis. On a wet basis, Malaysia produced about 2.4 million metric ton-
the kernel contains about 47 50% oil. Although it nes of palm kernel, of which about 1.1 million
lies within the palm nut, palm kernel oil and palm metric tonnes of crude palm kernel oil was ex-
oil differ greatly in their characteristics and prop- tracted [5].
erties. Palm kernel oil is rich in lauric acid, C12 Palm kernel oil (PKO) is regarded as a high-
(48.3%). Other major fatty acids are myristic, C14 quality oil for food use. It is a valuable compo-
nent of margarine formulation, giving rapid melt
* Corresponding author. Tel.: +6-4-6577888; fax: + 6-4-
down in the mouth characteristics. Its high solid
6573678. content at 1520C, together with rapid melt
E-mail address: akmomar@usm.my (A.K.M. Omar) down, makes it particularly useful in confec-

1383-5866/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved.
PII: S 1 3 8 3 - 5 8 6 6 ( 9 9 ) 0 0 0 8 2 - 9
114 M.N. Hassan et al. / Separation/Purification Technology 19 (2000) 113120

tionery products. It is commercially fractionated critical temperature of 31.1C, which are both
into liquid olein and solid stearin, the latter being easily achieved [1013].
a premium product. Fractionation increases the The fractionation effect of supercritical extrac-
lauric (C12) and myristic (C14) acid concentration tion of seed oil is caused by a large disproportion
in the resulting stearins, and leads to a corre- in solubilities of triglycerides in SC-CO2. Triglice-
sponding fall in the levels of short-chain (C6 rides with short chains and low polarity fatty
C10) and unsaturated (C18:1 and C18:2) fatty acids are more soluble in SC-CO2 and can be
acids. Normally, 20 40% stearin is produced. In easily removed from extracting materials. Gener-
these ways, a large number of fats become avail- ally, the solubility of triglicerides depends upon
able suitable for toffees, chocolate type coatings, the density of CO2, which can be manipulated
wafer filling, biscuit sprays, ice cream filled milk through the variation of pressure. Hence, with the
products and filling creams. Palm kernel stearins use of multiple separators, the pressure drops
are called cocoa butter substitute and are mainly from the extractor to the multiple separators can
used as total replacement for cocoa butter in be reduced gradually by adjusting the individual
special recipes [1,6]. back-pressure regulator of each separator [14].
Supercritical fluid extractions of oilseeds have Snyder et al. [15] found that fractionation of
been thoroughly studied by many researchers [7 soybean oil in SC-CO2 extraction at 8000 psi and
9]. At 48.3 MPa and 80C, the solubility of soy- 50C only occurred in the last 1015% of the oil
bean and cottonseed oil in supercritical carbon extracted in which the composition of fatty acid in
dioxide (SC-CO2) is about 3%, and rises dramati- triglycerides varied.
cally at pressures and temperatures above 55.7 In this study, carbon dioxide was used as a
MPa and 60C, respectively. Soybean triglycerides solvent in the extraction of palm kernel oil at a
become infinitely miscible with SC-CO2 at 81.1 pressure range of 20.748.3 MPa and tempera-
MPa and 70C [7]. SC-CO2 is the most common tures between 40 to 80C. Fractionation of PKO
gas used as a solvent. It is non-toxic, non- into various fractions were effected by collecting
flammable, easily available and relatively cheap. It the extracted oil at various time or volume
has a moderate critical pressure of 7.38 MPa and intervals.

Fig. 1. Schematic diagram of supercritical fluid extraction of palm kernel oil.

 M.N. Hassan et al. / Separation/Purification Technology 19 (2000) 113120 115

Fig. 2. Photograph of full-fat ground palm kernel.

2. Experimental pressure and temperature. The volume of CO2

passed through the extraction cell was recorded at
The set-up for the extraction process is shown atmospheric pressure and temperature immedi-
in Fig. 1. It consists of a pump (American Lewa, ately before the analyte receiver was replaced
Holistic, Massachusetts, USA) with a maximum using the wet gas meter.
capacity of 69.0 MPa (10 000 psi), an oven (C.C.S Solubility of PKO in SC-CO2 was calculated
Instrument System), a chiller (Yin Deer, B/L-730) based on the 40% (40g oil/100 g palm kernel) of
and a 50 cm3 extraction cell (Keystone), with 13 oil extracted from the kernel (actual oil content,
mm diameter and 320 mm height, and a wet gas 50.09 1.3%). Fatty acid (as fatty acid methyl
meter (WNK-1A; Sinagawa Corp., Tokyo, ester) compositions of PKO were analyzed ac-
Japan). cording to Palm Oil Research Institute of
Carbon dioxide gas (Malaysian Oxygen, Malaysia (PORIM) methods [16]. A gas chro-
Penang, Malaysia) from a gas cylinder was matograph (Hitachi, G-3000) with flame ioniza-
liquefied to a temperature below 5C and tion detector and a chromato-integrator (Hitachi
pumped into the heated extraction cell loaded D-2500), together with a 30 m0.25 mm 0.25
with about 18.5 g ground palm kernel, 92% of mm TC-Wax capillary column (GL Sciences Inc.,
Tokyo, Japan) at an isothermal temperature of
which passed through a sieve with a 2 mm open-
190C with nitrogen as a carrier gas, were used.
ing. Static extraction was performed for 5 min
before the pump was opened to stabilize the tem-
perature and another 5 min after the set pressure
was reached before the exit valve was opened. The 3. Results and discussion
oil receiver was replaced when about 20% of the
total oil content in the palm kernel matrices were Figs. 2 and 3 show pictures of the ground palm
extracted. Separation of the oil from the CO2 was kernel and the scanning electron micrograph of
effected by expanding the extract at atmospheric the oil cells after being extracted with SC-CO2,
116 M.N. Hassan et al. / Separation/Purification Technology 19 (2000) 113120

Fig. 3. Scanning electron micrograph of the oil cells of SC-CO2 extracted ground palm kernel.

Fig. 4. Solubility of palm kernel oil in SC-CO2 (80% yield) as a function of temperature at various pressures.
 M.N. Hassan et al. / Separation/Purification Technology 19 (2000) 113120 117

Fig. 5. Solubility of palm kernel oil in SC-CO2 (80% yield) as a function of pressure at various temperatures.

respectively. Figs. 4 and 5 show that at 27.6 MPa, respectively. At 34.5 MPa, the intensity of yellowish
the solubility of PKO decreases with an increase in colour increases with time or fraction collected,
temperature. At higher pressures of 34.5, 41.4 and while at 48.3 MPa, the intensity of yellowish colour
48.3 MPa, the solubility increases with tempera-
ture. At 48.3 MPa, the solubility of PKO in SC-CO2
almost tripled from about 7 to 20% as the temper-
ature was increased from 40 to 80C. At lower
pressures, the solvent strength of SC-CO2 is much
affected by the changes in density. However, at
higher pressures, the change in density with temper-
ature is less significant compared with the changes
caused by the increase in vapour pressure of the oil.
Physical observation showed that the colour of
the extracted oil was lighter than the oil extracted
from Soxhlet extraction using hexane as a solvent.
The colour of the extracted oil also varied with
extraction pressure and temperature. At room
temperature (ca. 25C), the oil collected at 20.7
MPa (3000 psi) and 40C were crystalline white in
colour as shown in Fig. 6. Figs. 7 and 8 show the
photographs of the PKO fractions collected at 34.5 Fig. 6. Photograph of palm kernel oil fractions extracted at
MPa (5000 psi) and 48.3 MPa (7000 psi) at 70C, 20.7 MPa (3000 psi) and 40C.
118 M.N. Hassan et al. / Separation/Purification Technology 19 (2000) 113120

Fig. 7. Photograph of palm kernel oil fractions extracted at 34.5 MPa (5000 psi) and 70C.
Fig. 8. Photograph of palm kernel oil fractions extracted at 48.3 MPa (7000 psi) and 70C.

does not change much with time. Fig. 9 shows the creased with time, while the percentage of C16,
variation of fatty acid composition of each frac- C18:0, C18:1 and C18:2 fatty acids increased with
tion of PKO collected in the extraction at 34.5 time. The percentage of C14 fatty acid remained
MPa (5000 psi) and 70C. It is apparent that the unchanged at about 16.2%. The variation of oil
percentage of C8, C10 and C12 fatty acids de- composition, and hence the characteristics such as
 M.N. Hassan et al. / Separation/Purification Technology 19 (2000) 113120 119

Fig. 9. Fatty acid composition of the fractions of palm kernel oil extracted at 34.5 MPa and 70C.

slip melting point and solid fat content, would time or mass intervals. At higher pressures, the
enable each fraction to be used for different end fractionation effect or selectivity of the solvent
products, such as in margarine formulation and as diminished and the oil composition does not
a cocoa butter substitute. At a higher pressure of change with time. A better and efficient extraction
48.3 MPa and 80C, the colour and composition and fractionation process is expected if the system
of each fraction did not change significantly, indi- is operated at higher pressures together with mul-
cating low selectivity of SC-CO2; however, the tiple pressure reduction collectors.
rate of extraction and solubility of PKO in SC-
CO2 were higher. The fraction of PKO, however,
could be achieved by multiple reduction of pres- Acknowledgements
sure of the extracted oil.
This work was supported by the Research and
Development grant No. 190/9609/2402 from the
4. Conclusions Malaysian Government.
The prospect of applying supercritical technol-
ogy in the extraction of palm kernel oil is better
compared with the non-lauric based oil such as References
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