Fractionation and Characterization of Waxes A. K. Gupta a ; K. M. Agrawal a ;D. Severin b a

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1 This article was downloaded by: [CSIR ejournals Consortium] On: 25 May 2010 Access details: Access Details: [subscription number ] Publisher Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: Registered office: Mortimer House, Mortimer Street, London W1T 3JH, UK Petroleum Science and Technology Publication details, including instructions for authors and subscription information: Fractionation and Characterization of Waxes A. K. Gupta a ; K. M. Agrawal a ;D. Severin b a Indian Institute of Petroleum, Dehradun, India b Inst. Fuer Erdoel-Und Erdgasforschung, Clausthal, Germany To cite this Article Gupta, A. K., Agrawal, K. M. andseverin, D.(2006) 'Fractionation and Characterization of Waxes', Petroleum Science and Technology, 24: 1, 1 6 To link to this Article: DOI: /LFT URL: PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.

2 Petroleum Science and Technology, 24:1 6, 2006 Copyright Taylor & Francis Group, LLC ISSN: print/ online DOI: /LFT Fractionation and Characterization of Waxes A. K. Gupta and K. M. Agrawal Indian Institute of Petroleum, Dehradun, India D. Severin Inst. Fuer Erdoel-Und Erdgasforschung, Clausthal, Germany Abstract: By using short path molecular distillation (SPD) and supercritical fluid extraction (SFE) techniques, petroleum waxes have been fractionated into different fractions. These wax fractions were analyzed for their composition and phase transitions by gas chromatography (GC) and differential scanning calorimetry (DSC). GC data and the DSC thermograms indicated that the waxes vary significantly in their properties and composition. Keywords: DSC, fractionation, GC, waxes INTRODUCTION Petroleum waxes are complex mixtures of hydrocarbons. Their presence in crude oil leads to many problems during storage and transportation. Wax as a product has several applications, such as making candles, polishes, coating containers, impregnating paper, etc., but each application of wax requires specific properties. In some cases, the desired properties can be obtained by fractionation of wax. In the present study, wax fractions obtained by short path molecular distillation (SPD) and supercritical fluid extraction (SFE) have been characterized for their compositional properties. EXPERIMENTAL To fractionate petroleum wax samples by SPD and SFE on the basis of their volatility (Fischer, 1983) a short path distillation equipment model DISTACT, Leyboldt Heraeus, GmbH, was used. By fractionating a wax sample P (m.pt C) using this technique, five distillate fractions were obtained at five Address correspondence to A. K. Gupta, Indian Institute of Petroleum, Dehradun , India. 1

3 2 A. K. Gupta et al. wall temperatures ranging from C, and have been designated as AP1 to AP5. SFE using CO 2 as the supercritical fluid was also employed to carry out the fractionation of another wax (E) having m.pt. 60 C (different from that used for the short path distillation). SFE extracts were collected at an interval of 4 hr. These fractions have been designated as AE1 to AE3. Various wax fractions so obtained were analyzed for their composition and phase transition. Gas Chromatographic Analysis Gas chromatography (GC) analyses of the samples were carried out using a Perkin Elmer auto system XL Gas Chromatograph attached to a PC and equipped with a flame ionization detector. The column, SGE HT-5 alumina clad/fused silica, was used. Helium was employed as the carrier gas. Oven temperature programming covered the range of C. The injector was kept in oven program mode. Polywax 655 spiked with n-c 36 was used to identify the retention times of the n-alkane peaks of samples. Chromatographic data were acquired using turbochrom software. Differential Scanning Calorimetry Analysis The transitional temperatures and energies associated with each transition were recorded using a Dupont differential scanning calorimeter 9900 thermal analyzer. Calibration was performed using high purity Indium. A small quantity, approximately 10 mg of each sample, was taken and heated at a rate of 2 C/min to 120 C. RESULTS AND DISCUSSION Analysis of Wax and Its Fractions by Gas Chromatography Carbon number distribution for fractions obtained by SPD and SFE, along with the parent wax samples, are given in Table 1. In the case of short path distillate wax fractions, AP2, AP3, AP4, and AP5, C 27 remains the predominant alkane, as in the case of parent wax; while in the case of distillate fraction AP1, most predominant alkanes are C 24 C 25. All the SPD wax fractions have maximum concentration in the range of C 21 C 30 alkanes; however, concentration of the C 21 C 30 alkanes decreases from fractions AP1 to AP5. SFE fractions have maximum concentration in the range of C 21 C 30 alkanes. It was further observed that carbon number ranges of SFE fractions AE1, AE2, and AE3 are 19 59, 20 62, and 21 67, respectively. The carbon number range of SFE feed stock is Carbon number ranges of fractions

4 Table 1. Carbon number distribution of feed stocks and fractions Fractions Short path molecular distillation (SPD) Supercritical fluid extraction (SFE) C. Feed Feed No. wax wax range P AP1 AP2 AP3 AP4 AP5 E AE1 AE2 AE

5 4 A. K. Gupta et al. Table 2. Phase transition data of feed stocks and fractions Peak temperature, C Total energy Sample Solid solid Solid liquid (J/g) SPD feed wax Fraction AP Fraction AP Fraction AP Fraction AP Fraction AP SFE feed wax Fraction AE Fraction AE Fraction AE collected at different intervals of time (4, 8, 12 hr) have been shifted toward higher carbon numbers. So, SFE can also be used to alter the carbon number distribution of wax. Determination of Phase Transition of SPD and SFE Wax Fractions by Differential Scanning Calorimetry The various wax fractions obtained by SPD and SFE, along with the parent feed waxes, were also analyzed for their phase transition behavior by DSC. These results are given in Table 2. DSC thermograms of SPD feed wax and its fractions (AP1, AP2, and AP3) are shown in Figures 1 and 2, respectively. It was observed that in comparison to the parent wax used for fractionation by short path distillation, fraction AP1 shows considerably low solidliquid transition temperature. In the case of SFE fractions, it was observed that fractions AE1, AE2, and AE3 showed increasing trends in their solidliquid transition temperatures. SPD fractions did not show much difference in their total energy of transitions, whereas total energy for transitions, in the case of SFE fractions, varied considerably, particularly for fractions AE1 and AE3. CONCLUSION It can be concluded that short path molecular distillation (SPD) and supercritical fluid extraction (SFE) are good tools for wax characterization and fractionating of wax in order to gain various properties.

6 Fractionation and Characterization of Waxes 5 Figure 1. Thermogram of SPD feed wax P. Figure 2. Thermogram of SPD fractions.

7 6 A. K. Gupta et al. ACKNOWLEDGMENT The authors are thankful to DAAD for providing financial assistance for their study visit to Inst. Fuer Erdoelforschung, Germany. REFERENCE Fischer, W. (1983). Labor-distillation hoch sieden der mineralol anteile. Erdoel und Kohle-Erdgas Petrochemie 1:1.