214 † To whom correspondence should be addressed. E-mail: mnlotfollahi@semnan.ac.ir Korean J. Chem. Eng., 27(1), 214-217 (2010) DOI: 10.1007/s11814-009-0328-y RAPID COMMUNICATION Extraction of benzene from a narrow cut of naphtha via liquid-liquid extraction using pure-sulfolane and 2-propanol-sulfolane-mixed solvents Jafar Mahmoudi and Mohammad Nader Lotfollahi † School of Chemical, Gas and Petroleum Engineering, Semnan University, Semnan, Iran (Received 16 December 2008  accepted 9 July 2009) Abstract−The extraction of benzene from a narrow cut of naphtha produced by the Iranian petrochemical company has been studied at the operating temperatures of 40, 45 and 50 o C, and four solvent-to-feed ratios (S/F) varied over the range of 1-4. Two extraction solvents, sulfolane as a pure-solvent and (sulfolane containing 7 wt % 2-propanol) as a mixed-solvent have been investigated for selective removal of benzene from the naphtha cut. The experimental results demonstrated that the mixed-solvent at 40 o C is a suitable solvent to replace sulfolane for an industrial extraction process for the separation of benzene from the naphtha cut because of its lower price and energy savings. Key words: Liquid-liquid Extraction, Naphtha Cut, Benzene, Mixed Solvent INTRODUCTION Food grade n-hexane is used as a solvent for oil extraction from seeds. The main source of n-hexane is naphtha cut produced in the refinery and the petrochemical processes. However, this cut con- tains aromatic hydrocarbons, especially benzene. For example, the naphtha cuts from the Iranian crude oils contain about 2.5 to 5% by weight of benzene. Because benzene is carcinogenic, separation of benzene from the naphtha cut to reach the food grade specifica- tion is necessary [1]. In principle, the liquid-liquid extraction with solvents can be em- ployed to extract the aromatics from the naphtha cut. Solvents used for liquid extraction require high selectivity for aromatics, high capac- ity, capability to form two phase at reasonable temperatures, capa- bility of rapid phase separation, easy regeneration, good thermal stability and to be non-corrosive and non reactive [2]. Many investigators [3-10] have studied the liquid-liquid equilib- rium (LLE) of ternary systems containing solvent, aromatic and aliphatic hydrocarbons. Krishna et al. [11] separated aromatics from 63-69 o C naphtha fraction using sulfolane and NMP (n-methyl pyr- rolidone) as the solvents on a laboratory packed extraction column. Ali et al. [12] carried out the extraction of aromatics from the naphtha reformate with propylene carbonate as a solvent. Chen Dong Cho et al. [13] measured the liquid-liquid equilibrium of ternary sys- tems (heptane+NFM+aromatic hydrocarbon (benzene, toluene, and xylene)) over the temperature range of (298 to 353) K. Rappel et al. [14] reported liquid-liquid equilibrium data for the ternary sys- tems (sulfolane+p-xylene+cyclohexane), (sulfolane+p-xylene+n- hexane) and (sulfolane+toluene+n-hexane) at 308.15 and 323.15 K. Galie et al. [15] presented the optimal conditions of extraction of C6- C8 aromatic hydrocarbon from the reformate by triethylene glycol- sulfolane mixtures. Ko et al. [16] simulated the NFM (N-formyl- morpholine) extractive distillation process for the purpose of recov- ering aromatics from hydrocarbon mixtures using the NRTL equa- tion as the thermodynamic model. In this work, benzene was extracted from naphtha cut produced by the Iranian petrochemical company by using sulfolane and a mix- ture of sulfolane and 2-propanol as solvents. Based on the Bandar Imam Petrochemical Complex (BIPC) report, the narrow cut of naph- tha used in this work contained 2-methyl-pantane, 3-methyl-pan- tane, n-hexane, methyl-cyclo-pantane, benzene, cyclo-hexane, iso- pantane, n-pantane, cyclo-pantane, 2-methyl-hexane and 2,3-dime- thyl-pantane. EXPERIMENTAL 1. Materials Sulfolane, propanol, ethanol were obtained from Merck Com- pany (Germany), all with purity greater than 99.0%. All chemicals were used without further purification. The narrow cut of naphtha was from the Bandar Imam Petrochemical Complex (BIPC). 2. Procedure The benzene from naphtha cut was extracted by using the sul- folane as a pure-solvent and a mixed-solvent of sulfolaneco-solvent at temperatures 40, 45 and 50 o C and at solvent-to-feed ratios of 1, 2, 3 and 4 by weight. Experiments were carried out in equilibrium 250 ml glass cells. The cell temperature was regulated by a thermostatic bath (Grant instruments (Cambridge) ltd. (type SE 15, England)), accurate to ±0.2 o C. The mixture was prepared directly inside the cell, and the components were weighted on an analytical balance (A & D Company, GF-600, Japan) accurate to 0.001 g. The mix- ture was agitated with a magnetic stirrer (Stuart scientific SM 27, UK) for 1 h and then left for 8 h. Then the system split in two liquid phases that became clear and transparent at equilibrium, with a well defined interface. After decanting, samples from the two phases were taken for analysis. The samples were diluted in pure ethanol and analyzed by a gas chromatograph equipped with a helium ioniza- tion detector (HID). The analysis was repeated at least three times. The average of these readings was taken for the component com- positions. A good separation of the components was attained using a TRB-WAX capillary column (60 m×0.32 mm) with a poly eth-