Supercritical carbon dioxide (SC-CO 2 ) extraction of 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, Japan b 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-CO 2 ) 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 at 353.2 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 (C 8 –C 14 ) were extracted at lower pressures of 20.7–27.6 MPa, and higher amounts of longer chain fatty acid constituents (C 16 –C 18:2 ) were extracted at higher pressures from 34.5 to 48.3 MPa. A simple correlation was developed based on a kinetic mass transfer model. From the correlation, the minimum amount of CO 2 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 oil industry 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 kernel and palm oil (PO) from the mesocarp layer differ greatly in their characteristics and properties (Goh, 1993). PKO is rich in lauric acid (C 12 ), containing about 50% C 12 and the remaining major fatty acids are myristic (C 14 ) and oleic acids (C 18:1 )(Tang & Teoh, 1985; Goh, 1993; Omar, Rah- man, & Hassan, 1998). PO is rich in palmitic acid (C 16 ) containing about 44% and about 36% C 18:1 . Other major fatty acids of PO are stearic acid (C 18:0 ) and linoleic acid (C 18:2 ). There are three types of conventional method are being used 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 followed by solvent extraction (MPOB, 2003). However, these meth- ods required much time, costly and organic solvent like hexane to obtain the refined, bleached and deodorized (RBD) palm kernel oil. Therefore, supercritical fluids have been suggested as attractive alternative solvents for many organic solvents by Saito (1995), who reviewed research activity. For exam- ple, CO 2 has been suggested as a replacement for n-hexane or toluene in desolventation of polymer solutions by Ino- mata, Honma, Imahori, and Arai (1999). In their super- critical states, CO 2 and water can be used in many extractions and reactions and have been recognized as earth compatible solvents (Arai & Adschiri, 1999). CO 2 has been proposed for use in a process for improving * Corresponding author. Present address: Department of Upland Agriculture, National Agricultural Research Center for Hokkaido Region, Shinsei, Memuro, Kasai, Hokkaido 082-0071, Japan. Tel.: +81 155 62 9278; fax: +81 155 62 2926. E-mail addresses: zaidul@naro.affrc.go.jp, zaidulsarker@yahoo.com (I.S.M. Zaidul).