supercritical carbon dioxide (sc-co2) extraction of palm kernel oil from palm kernel
TRANSCRIPT
Supercritical carbon dioxide (SC-CO2) extractionof palm kernel oil from palm kernel
I.S.M. Zaidul a,*, N.A. Nik Norulaini b, A.K. Mohd Omar c, R.L. Smith Jr. a
a Department of Chemical Engineering, Research Center of Supercritical Fluid Technology, Tohoku University,
Aoba-ku, Aoba-6-6-04, Sendai 980-8579, Japanb School of Distant Education, Universiti Sains Malaysia, 11800 P. Pinang, Malaysia
c School of Industrial Technology, Universiti Sains Malaysia, 11800 P. Pinang, Malaysia
Abstract
Extraction of palm kernel oil from dehulled ground palm kernel using supercritical carbon dioxide (SC-CO2) was studied at condi-tions of 313.2 and 353.2 K and at pressures from 20.7 to 48.3 MPa. The yield of PKO increased with pressure from 34.5 to 48.3 MPa at353.2 K and attained a value of 49 g oil/100 g palm kernel at 48.3 MPa and 353.2 K. Lower amounts of shorter chain triglycerides com-ponent in terms of fatty acid constituents (C8–C14) were extracted at lower pressures of 20.7–27.6 MPa, and higher amounts of longerchain fatty acid constituents (C16–C18:2) were extracted at higher pressures from 34.5 to 48.3 MPa. A simple correlation was developedbased on a kinetic mass transfer model. From the correlation, the minimum amount of CO2 usage for a given yield could be estimated.
Keywords: Supercritical extraction; Mass transfer; Palm kernel oil; Fatty acid constituents
1. Introduction
Palm kernel, which is a by-product of the palm oilindustry is obtained from the palm nut, Elaeis guineensis
and on a wet basis, contains about 45–50% oil (Tang &Teoh, 1985). Palm kernel oil (PKO) from palm kerneland palm oil (PO) from the mesocarp layer differ greatlyin their characteristics and properties (Goh, 1993). PKOis rich in lauric acid (C12), containing about 50% C12 andthe remaining major fatty acids are myristic (C14) and oleicacids (C18:1) (Tang & Teoh, 1985; Goh, 1993; Omar, Rah-man, & Hassan, 1998). PO is rich in palmitic acid (C16)containing about 44% and about 36% C18:1. Other major
* Corresponding author. Present address: Department of UplandAgriculture, National Agricultural Research Center for Hokkaido Region,Shinsei, Memuro, Kasai, Hokkaido 082-0071, Japan. Tel.: +81 155 629278; fax: +81 155 62 2926.
E-mail addresses: [email protected], [email protected](I.S.M. Zaidul).
fatty acids of PO are stearic acid (C18:0) and linoleic acid(C18:2).
There are three types of conventional method are beingused in Malaysia for extracting PKO from palm kernel e.g.(1) mechanical extraction using high pressure screw press,(2) direct solvent extraction and (3) pre-pressing followedby solvent extraction (MPOB, 2003). However, these meth-ods required much time, costly and organic solvent likehexane to obtain the refined, bleached and deodorized(RBD) palm kernel oil.
Therefore, supercritical fluids have been suggested asattractive alternative solvents for many organic solventsby Saito (1995), who reviewed research activity. For exam-ple, CO2 has been suggested as a replacement for n-hexaneor toluene in desolventation of polymer solutions by Ino-mata, Honma, Imahori, and Arai (1999). In their super-critical states, CO2 and water can be used in manyextractions and reactions and have been recognized asearth compatible solvents (Arai & Adschiri, 1999). CO2
has been proposed for use in a process for improving
the digestion properties of cellulosic material by Kim andHong (2001). Furthermore, CO2 in its supercritical statehas been used for fractionating thermally sensitive naturaloils (Suzuki, Chen, Adschiri, Inomata, & Arai, 1997) andhas the potential for refining the extracts to obtain RBDproducts.
Supercritical carbon dioxide (SC-CO2) has been used inthe extraction of oil from dehulled and undehulled groundpalm kernels (Hassan, Rahman, Anuar, Ibrahim, & Omar,2000; Rahman, Hassan, Anuar, Ibrahim, & Omar, 2001).Bharath, Inomata, Adschiri, and Arai (1992), and Bharath,Yamane, Inomata, Adschiri, and Arai (1993) fractionatedtriglycerides of fatty oil components of palm kernel basedon their carbon number using SC-CO2 at 313.2–353.2 Kand at pressures up to 30 MPa. Hassan et al. (2000), Rah-man et al. (2001), Zaidul (2003), Norulaini, Zaidul, Anuar,and Omar (2004a, 2004b), Zaidul, Norulaini, Omar, andSmith (2006) measured the solubility and extractability ofPKO in SC-CO2 at pressures from 20 to 48 MPa. Authorsalso extracted and fractionated oil from ground PK usingsupercritical CO2. In their studies it was found that solubil-ity of PKO in CO2 up to pressures of 34.5 MPa was higherthan that of non-lauric oils such as soybean oil, and cotton-seed oil as of the studies of Friedrich, List, and Heakin(1982), where pressures of at least 50 MPa were required.Bisunadan (1993) carried out SC-CO2 extraction of palmoil from palm but required high pressures (50 MPa) to highyields.
Conventional PKO extraction requires multi-stage pro-cessing and previous work has shown that SC-CO2 offersthe possibility of developing a complete process for oilextraction and purification that avoids the use of organicsolvents and large waste streams, besides producing oilhigh quality (Tang & Teoh, 1985). In this work, the objec-tives were to study mass transfer of PKO in SC-CO2 at dif-ferent pressures and temperatures and correlate the effectof extraction conditions of pressure, temperature andCO2 mass flow rate on the yield.
2. Materials and methods
2.1. Materials
Palm kernels were collected from Malpom Sdn. Bhd.,Nibong Tabal, Pinang. Commercial liquid carbon dioxide(purity, 99.9%), nitrogen (as carrier gas with the purity of99.9%), and auxiliary gases hydrogen (purity, 99.9%) andcompressed air (free from organic impurities) were pur-chased from Malaysian Oxygen Ltd., Pinang. The n-hex-ane, AR grade was obtained from R & M marketing(Kuala Lumpur). Reference standards of methyl ester ofcaprylic acid (C8), capric acid (C10), lauric acid (C12),myristic acid (C14), palmitic acid (C16), stearic acid (C18),oleic acid (C18:1) and linoleic acid (C18:2) that had a mini-mum purity of 99%, and sodium methoxide were obtainedfrom Sigma (St. Louis). A TC-wax column (30 m ·0.25 mm) purchased from Science Inc. (Tokyo).
2.2. Preparation of palm kernels for experiment
Palm kernels were prepared for the experiments bydehulling and grinding according to a procedure developedby Zaidul (2003) as briefly described here. About 500 g ofpalm kernels were soaked into 500 ml 12 M hydrochloricacid and then heated to 90 �C for 20 min. After heatingthe kernels for 30 min, they were kept for another 10 minat room temperature and then washed with water toremove the acid before minimum pressure was applied tothe kernels to remove the testa. The dehulled palm kernelswere ground into small pieces of 1.5 to 2.0 mm. The mois-ture content of ground palm kernel was determined accord-ing to PORIM Test Method no. p5.2 (1985) and was foundto be 4.9%.
2.3. Extraction of palm kernel oil using soxhlet method
Soxhlet extraction used for comparison with supercriti-cal extraction was carried out in duplicate for 15 g of palmkernel with 200 mL n-hexane for 6 h. The sample was thendried in the oven at 103 ± 1 �C for 2 h after which it wascooled in desiccators before reweighing. The total oil deter-mined in the dehulled ground palm kernel was found to be50.1 ± 0.2% (g oil extracted/100 g of dehulled ground palmkernel) on dry basis which is 47.7 g oil/100 g dehulledground palm kernel on a wet basis using hexane extractionmethod.
2.4. Supercritical carbon dioxide (SC-CO2) extraction
The experimental set-up for the SC-CO2 extraction pro-cess is shown in Fig. 1. It consisted of a pump (AmericanLewa, Massachusetts) with a maximum capacity of about69 MPa (10000 psi), an oven (S.C.S.I. instrument system),a chiller (B/L-730, Taipei), an extraction cell and a wetgas meter (WNK-1A, Sinagawa Corp., Tokyo).
Liquid carbon dioxide was pumped into the heatedextraction cell loaded with approximately 20 g (dry basis)of dehulled ground palm kernel. Pressures ranging from20.7 to 48.3 MPa and temperatures of 313.2 K and353.2 K were used. At each temperature–pressure combina-tion, extractions were run continuously for a total of 40 min.The oil was collected at the end of every 10 min giving a totalof four fractions. The CO2 flow (Table 1) was varied tomaintain the desired pressure and temperature of the extrac-tor and the volume of CO2 passed through the extractioncell was recorded at atmospheric pressure and temperatureat the end of each 10 min run using a wet gas meter. Yieldsof oil were defined on 100 g dry palm kernel basis. Densitiesof CO2 required to express total CO2 used were obtainedfrom the NIST database (no. 65), 2005.
Total oil yieldð%Þ
¼ Total oil yield ðgÞ of four successive fractions by SC-CO2
Total oil yield ðgÞ extracted by Soxhlet� 100%
A
B C
D
EF
G
H
I
J
K
T
Fig. 1. Schematic diagram of apparatus used in the extraction of palm kernel oil (PKO) from palm kernel with supercritical CO2 (A: CO2 cylinder; B:chiller; C: pump; D: back-pressure regulator; E: check valve; F: oven (T = temperature measured); G: extractor; H: pressure gauge; I: control valve; J:trap; K: wet test gas meter; L: vent).
Table 1Yield of PKO obtained at various pressures and flow rates of CO2 used at313.2 and 353.2 K
Pressure(MPa)
Flow rate of CO2
(g/min)Total amount ofCO2 used (g)
Yield ofPKO (%)
313.2 K 353.2 K 313.2 K 353.2 K 313.2 K 353.2 K
20.7 5.14 4.23 205.43 169.39 18.0 16.7227.6 4.90 4.41 196.06 176.60 34.33 33.4434.5 4.74 3.46 189.57 138.39 40.75 41.3141.4 3.26 2.54 130.46 101.63 42.85 44.3548.3 2.68 1.87 107.40 74.96 44.75 48.90
2.5. Methyl esterification of fatty acids
Oil samples were melted at 60–70 �C and homogenizedthoroughly before taking a test sample. A 100 lL of thetest sample was mixed with 1 ml n-hexane in a 2 ml vial.A 1 lL aliquot of sodium methoxide was added to the vial,which was mixed vigorously with a vortex mixer. The mix-ture first became clear and then turbid as sodium glycerox-ide was precipitated. After a few minutes, the clear upperlayer of methyl ester was pipetted off and injected intothe gas liquid chromatography (GLC) using external stan-dard method according to PORIM Test Method no. p3.4(1985).
2.6. Fatty acid profile analysis by gas liquid chromatograph
(GLC) standard
A GLC (Model, G-3000, HITACHI) was used to quan-tify fatty acid constituents of the samples. The methyl-esterified fatty acids mentioned above were analyzed to
determine fatty acid constituents. Standard of the fatty acidmethyl ester of C8 (9.84%), C10 (9.84%), C12 (24.6%), C14
(9.84%), C16 (14.76%), C18 (11.44%), C18:1 (9.84%) andC18:2 (9.84%) were prepared in hexane. A 1 lL sample ofthe fatty acid methyl ester standard mixture was injected.After elution, a 1 lL of the prepared solution (clear upperlayer) was injected separately onto the column (TC-wax,30 m · 0.25 mm). The oven temperature was set at 190 �Cand the detector and injector temperature were held con-stant at 250 �C. Carrier gas flow rate was 1 mL/min witha split ratio of 1:100. Chromato-integrator (HITACHI,D-2500) and an auto injector (Al-1000) were used accord-ing to PORIM Test Method no. p3.5 (1985).
2.7. Statistics
Experiments were the result of three runs that were aver-aged together. Standard deviations of the yields were onthe order of around ±1%. Standard deviations of the fattyacid constituents were on the order of about ±2%. Thestandard deviations were used as the basis for the errorbars shown in the figures.
3. Results and discussion
3.1. Characterisation of palm kernel
According to Snyder, Friedrich, and Christianson (1984)moisture content between 3% and 12% has very little effecton extractability of oils from seeds with supercritical car-bon dioxide. In the extraction of ground millet bran, Devit-tori et al. (2000) stated that if the moisture is reduced from
0
5
10
15
20
25
30
35
40
45
50
0 20 40 60 80 100 120 140 160 180 200 220
Total amount of CO2 used (g)
Yie
ld (
%)
Fig. 3. Cumulative yield of PKO (g oil/100 g palm kernel) versuscumulative amount of CO2 used at different pressures; m 20.7, n 27.6,d 34.5, s 41.4 and j 48.3 MPa at 353.2 K extracted for 40 min (Table 1shows the mass flow rate of CO2 at different pressures).
8 to 1%, it will not affect the extraction and the oil masstransfer in supercritical carbon dioxide (SC-CO2). On theother hand, Saldana, Carsten, Mohamed, and Brunner(2002) extracted caffeine from wet ground guarana seedsand achieved 98% removal. For our case, we did notobserve any noticeable effect of water on the extractionover the range of water content of the materials studied.
3.2. Effect of mass flow rate of SC-CO2 on the yield of PKO
Table 1 shows extraction yields of PKO at various pres-sures, temperatures and amount of CO2 used. The extrac-tion yields ranged from 16 to 49% depending on theconditions. Fig. 2 depicts the effect of pressure, CO2 flowrate, temperature and total amount of CO2 used on theyields of PKO 313.2 K. Fig. 3 shows results at 353.2 K.As expected, the yield increased as the total amount ofCO2 used increased for both temperatures, 313.2 K(Fig. 2) and 353.2 K (Fig. 3). Higher pressures gave higheryields for a given amount of CO2 used. The highest oil yieldwas 48.9% obtained at 48.3 MPa and 353.2 K with a CO2
flow rate of 1.87 g/min (Table 1). This value was close tothe oil yield obtained by soxhlet extraction. Lower CO2
flow rates applied usually result in lower amounts ofCO2 being required. Higher yields for lower amounts ofCO2 used reflect better economic advantage and can pro-vide similar final products (Saldana et al., 2002).
The flow rate has a large effect on the mass transfer ofthe extraction, which can be divided into a solubility con-trolled region and a diffusion controlled region. A lowersolvent flow improves the extraction performance, particu-
0
5
10
15
20
25
30
35
40
45
50
0 20 40 60 80 100 120 140 160 180 200 220Total amount of CO2 used (g)
Yie
ld (%
)
Fig. 2. Cumulative yield of PKO (g oil/100 g palm kernel) versuscumulative amount of CO2 used at different pressures; m 20.7, n 27.6,d 34.5, s 41.4 and j 48.3 MPa at 313.2 K extracted for 40 min (Table 1shows the mass flow rate of CO2 at different pressure).
larly during in the solubility controlled region, anddecreases the total solvent mass required to extract a givenamount of oil (McHugh & Krukonis, 1986). At lower pres-sures, the oil yield was directly proportional to the amountof CO2 needed as expected for extraction in the solubilitycontrolled region.
Similar trends on yield have been reported by Devittoriet al. (2000) in the extraction of oil from millet branthrough SC-CO2, whereby increasing the pressureincreased the oil extracted for a given amount of CO2. Theyfound that the kinetics of the oil mass transfer was high,that is up to 60–70% of the total oil present in the milletbeing extracted according to a linear relationship betweenthe mass of extracted oil and quantity of solvent used. Inthis experiment, linear relationships between pressure andthe oil extracted in the initial portions of each curve wereobserved (Figs. 2 and 3). After the free oil was extracted,the kinetics of the oil mass transfer slows down this iscalled diffusion period, whereby, the mass transfer is con-trolled by the resistance of the solid matrix to diffusion(Sovova, 2005). This period was mainly observed at thehighest pressures (Figs. 2 and 3).
Gomez and Martinez (2000) observed during wheatgerm oil extraction using SC-CO2 that the higher flow rategave a higher yield but with a much higher solvent con-sumption. Lower flow rates allowed the system to attainequilibrium in the later stages of the extraction processeven when the quantity of oil was very small. The findingsof this work concur with Gomez and Martinez (2000),where a lower flow rate of 1.87 g/min was applied at higherpressure to generate the highest PKO yield in this work.Higher flow rates can cause the sample to compactand restrict CO2 movement into and out of the sample,
Table 2Coefficients value of K for Eq. (2)
Coefficient Value
K0 �9.4840 · 10�2
KP 2.136 · 10�3
KF 5.611 · 10�3
KT 9.371 · 10�5
KTP 2.001 · 10�7
KTPP 4.274 · 10�10
KPP 4.561 · 10�6
300 320 340 360 380 40010
20
30
40
50
60
70
80
Pres
sure
[M
Pa]
Temperature [K]
50%
49%
48%
45%
40%
30%
20%
Fig. 4. Pressure and temperature conditions required for given yieldsbased on a flow rate of 5.14 g CO2/min calculated from Eq. (1).
reducing the amount of CO2 available for mass exchange asnoted by Tonthubthimthong, Chuaprasert, Douglas, andLuewisutthichat (2001). Likewise, similar arguments canbe made for the extraction of PKO from palm kernel, sincehigher flow rates did not achieve high PKO yield.
3.3. Effect of temperature and pressure on yield of PKO
Ooi et al. (1996) reported that SC-CO2 pressure affectsboth yield and solubility of PO. They observed that athigher pressures, the yield increased with temperature from323.2 to 338.2 K and they attributed this to the solubility ofPO increasing with increasing temperature, even thoughincreasing temperature causes the density of SC-CO2 todecrease. However, the rate of extraction with SC-CO2
can be enhanced by raising the temperature or pressureof the solvent (Brannolte, Mangold, & Stahl, 1983). In thiswork, an increase in temperature lead to an increase thetotal in the yield of PKO at a given mass flow rate and pres-sure. Norulaini et al. (2004a, 2004b) and Zaidul (2003) sta-ted that at pressures of 20.7 and 27.6 MPa, the increase invapour pressure of PKO due to an increase in temperatureappeared to compensate for the decrease in solubilitycaused by the decrease in SC-CO2 density at the highertemperatures. The amount of extracted oil as reported inthis work was higher at 313.2 K than at 353.2 K.
3.4. Mathematical model
According to Patel, Bandyopadhyay, and Ganesh (2006)there are many empirical models such as those of Chrastil(1982) model, kinetic model, intact-broken cells and othersthat have been proposed for extraction. In this work, weapplied the kinetic model of Subra, Castellani, and Jestin(1998) due to its simplicity. In their kinetic model, the rateof extraction is assumed to decrease exponentially and therate constant of the extraction related to mass transfer isdetermined by regressing experimental data. This modelis independent of matrix parameters. The kinetic modelwas developed in this study with the following assump-tions: (i) oil was uniformly distributed over the cell matrix,(ii) no axial dispersion, and (iii) uniform ground particlestructure. In the correlation, flow rate of supercritical fluid,system temperature and pressure were treated as constantswith respect to time and velocity gradients through theextractor were neglected. If C is mass fraction of solutein supercritical fluid over given period of time, and Cinf istotal amount of solute present in the solid phase, thenthe kinetic model can be expressed as:
C ¼ Cinfð1� expð�KtÞ ð1Þwhere K is a rate constant depending on extraction param-eters, t is time, and Cinf is the maximum obtainable yield of50.12 g/100 g sample (obtained by soxhlet extraction) forthe given sample. Through experimental studies, it hasbeen observed that the rate constant, K, depends on pres-sure, temperature and mass flow rate of the solvent and
therefore, we formed an expression in terms of the majorvariables including interactions between the variables:
K ¼ K0 þ KP � P þ KF � F þ KT � T þ KTP � T � Pþ KTPP � T � P � P þ KPP � P � P ð2Þ
In Eq. (2), P, F and T are pressure (MPa), mass flow rateof solvent (g/min) and temperature (K), respectively. Theconstant K0 has units of min�1. Eq. (2) was adopted fromthe equation of Patel et al. (2006) but with variable interac-tions for this case. Multiple linear regression for the param-eters in Eq. (2) was applied. The values of constant, K0 andthe coefficients of KP, KF, KT, KTP, KTPP and KPP areshown in Table 2. The positive values of KP, KT and KF,and the positive values of interaction between pressure–pressure and temperature–pressure indicate that withincreasing pressure and extraction time, the rate constantand hence the yield should increase with the amount ofCO2 used. This is in accordance with variation of PKOyield with pressure and mass flow rate of CO2 as shownin Figs. 2 and 3. As shown in Figs. 2 and 3, good correla-tion of the data could be obtained over a wide range oftemperatures (313.2 to 353.2 K), pressures (20.7 to48.3 MPa) and flow rates (5.14–1.87 g/min). Further, it ispossible to use Eq. (1) to interpolate or extrapolate the datawith temperature, pressure, or flow rate. As an example,Fig. 4 was calculated with the model using Eq. (1), which
0C8 C10 C12 C14 C16 C18:0 C18:1 C18:2
10
20
30
40
50
60
Fatty acid constituent
% F
atty
aci
d
Commercial PKO
20.7 MPa
48.3 MPa
0.3 0.1
was restricted to a given CO2 flow rate of 5.14 g/min toestimate conditions from 30% to 50% yield. From the fig-ure, it can be seen that for 20% yield, temperatures of 19to 22 MPa and 305 to 380 K are required. Similarly, it ispossible to achieve higher yields for the pressures and tem-perature ranges shown. These trends are similar to that ofour experimental and calculated yields that are shown inFigs. 2 and 3. It can be seen that a large increase in pressureis required to obtain 50% yield. This is due to the logarith-mic change of solubility with pressure.
3.5. Composition analysis of PKO extracts
The composition of the PKO extracts is also important,as certain fractions can have applications as cocoa butterreplacers (CBRs) blends as noted by Zaidul et al. (2006).Table 3 shows the triglycerides composition in terms offatty acid constituents in PKO extracted using SC-CO2
at different pressures (20.7–48.3 MPa) and temperature of313.2 K. Soxhlet extraction values are also shown. Atlower pressures from 20.7 to 27.6 MPa, it was found thatthe shorter chain fatty acid constituents (C8–C14) wereextracted with higher selectivity than the longer chain fattyacid constituents (C16–C18:2). At the higher pressures from34.5 to 48.3 MPa, the C8–C14 constituents started to reduceand the C16–C18:2 constituents increased. The trend wassimilar to that found at 353.2 K (Table 4). At 353.2 K,the increase of C8–C14 constituents and decrease of C16–C18:2 constituents at 20.7 and 27.6 MPa was higher thanthe 313.2 K. Similarly, at 34.5 to 48.3 MPa, the C8–C14
constituents decreased and C16–C18:2 constituents increased
Table 4Fatty acid constituents in palm kernel oil (PKO) extracted using Soxhletand SC-CO2 at different pressures at 353.2 K
Pressure (MPa) Fatty acids constituent (%)
C8 C10 C12 C14 C16 C18:0 C18:1 C18:2
20.7 7.0 6.0 52.8 16.6 8.8 0.3 8.4 0.127.6 6.4 5.6 52.9 16.3 7.3 0.8 10.1 0.734.5 5.0 4.9 50.0 14.4 10.0 1.4 12.9 1.441.4 4.1 4.0 48.0 12.7 11.9 2.1 14.5 2.848.3 3.3 3.1 42.9 9.1 14.9 2.5 19.0 5.1
Soxhlet extraction 4.0 3.7 48.0 15.4 7.5 2.0 15.1 2.7
Table 3Fatty acid constituents in palm kernel oil (PKO) extracted using Soxhletand SC-CO2 at different pressures at 313.2 K
Pressure (MPa) Fatty acids constituent (%)
C8 C10 C12 C14 C16 C18:0 C18:1 C18:2
20.7 6.9 6.0 52.6 16.5 8.5 0.5 8.9 0.127.6 6.2 5.4 52.1 16.0 8.1 0.9 10.5 0.834.5 5.9 5.3 51.1 15.5 8.9 1.0 11.8 0.841.4 5.3 5.0 51.6 14.6 9.8 1.1 11.9 0.948.3 4.6 4.0 48.2 13.1 11.2 1.9 13.7 3.4
Soxhlet extraction 4.0 3.7 48.0 15.4 7.5 2.0 15.1 2.7
more at 353.2 K than the 313.2 K, compared with the fattyacid constituents obtained from soxhlet extraction.
Fig. 5 shows a comparison of the extracted triglyceridescomposition in terms of fatty acid constituents of twoextractions of 20.7 MPa and 48.3 MPa at a given tempera-ture of 353.2 K of this work, and commercial PKO. At thegiven temperature, increasing pressure from 20.7 MPa and48.3 MPa, the solubility of the C8–C16 and C18:0–C18:2 fattyacid constituents tended to decrease and increase, respec-
Fig. 5. Fatty acid constituents in conventional PKO and SC-CO2 PKOextracted at lower (20.7 MPa) and higher pressures (48.3 MPa) at 353.2 K.
0C8 C10 C12 C14 C16 C18:0 C18:1 C18:2
10
20
30
40
50
60
Fatty acid constituent
% F
atty
aci
d
Commercial PKO
313.2 K
353.2 K
Fig. 6. Fatty acid constituents in conventional PKO and SC-CO2 PKOextracted at lower (313.2 K) and higher temperature (353.2 K) at48.3 MPa.
tively. Similarly, at the given pressure (48.3 MPa), increas-ing temperature from 313.2 to 353.2 K tended to decreasedand increased the solubility of the C8–C14 and C16–C18:2
fatty acid constituents, respectively (Fig. 6). However, thefindings of this work concur with our previous work ofSC-CO2 extraction and fractionation of PKO from palmkernel (Norulaini et al., 2004a, 2004b; Zaidul et al., 2006).
4. Conclusions
SC-CO2 extraction was applied to extraction of PKOfrom dehulled ground palm kernel. The yield of PKOincreased with pressures from 34.5 to 48.3 MPa at highertemperature (353.2 K). At lower pressures, the yield ofpalm kernel oil (PKO) was higher at 313.2 K than353.2 K. The yield of PKO increased with pressure from34.5 to 48.3 MPa at 353.2 K and attained a value of 49 goil/100 g palm kernel at 48.3 MPa and 353.2 K. Theshorter chain triglycerides component in terms of fatty acidconstituents (C8–C14) were extracted more than the longerchain fatty acid constituents (C16–C18:2) at lower pressuresup to 27.6 MPa at any temperature, whereas the C16–C18:2
constituents were extracted more than the C8–C14 constitu-ents at higher pressures. A kinetic model was developedthat could correlate the extraction yield of PKO withCO2 over the entire range of experimental conditions.The model provides the means for studying other pressure,temperature and flow rate combinations including temper-ature, pressure or flow rate programming.
Acknowledgement
This work was supported by the intensification of re-search in priority areas (IRPA) development grant no.305/PTEKIND/610636 of the ministry of science, technol-ogy and environment, Malaysian Government.
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