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Separation and Purification Technology 55 (2007) 396–399

Short communication

Novel modified alumina: Synthesis, characterization andapplication for separation of hydrocarbons

Aslam Khan a,∗, Muhammad Riaz a, Shahid Bilal Butt b, J.H. Zaidi a

a Chemistry Division, PINSTECH, P.O. Nilore, Islamabad, Pakistanb Central Analytical Facility Division, PINSTECH, P.O. Nilore, Islamabad, Pakistan

Received 22 November 2006; received in revised form 8 March 2007; accepted 20 March 2007

bstract

Alumina surface was modified with Fe2O3 for improved separation of alkenes and alkanes. Scanning electron microscopy (SEM)-energyispersive X-ray analysis (EDXA) and XRD techniques were utilized to ascertain the desired modification. Various chromatographic parametersuch as height equivalent to theoretical plates (HETP), number of theoretical plates (N) and tailing factor (Tf) of bare and modified alumina columnslong with retention mechanism of hydrocarbon gases have been studied. The modified sorbent was applied for separation of alkenes and alkanesn a simulated mixture of coalmine gases to evaluate its qualitative performance. Modification of alumina with Fe2O3 improved the number of

heoretical plates along with tailing factor for better separation and quantification that enhanced selectivity of sorbent for studied light hydrocarbonsixture. GC column prepared from the proposed material ensured the elution of unsaturated hydrocarbons after the saturated hydrocarbons of the

ame carbon number. 2007 Elsevier B.V. All rights reserved.

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eywords: Modified alumina; Hydrocarbons; Gas chromatography; Coalmine

. Introduction

It is known that ethene and propene emitted from automo-ile exhaust possess genotoxic properties and ethene has beenonsidered as an important risk factor for the occurance of can-er in human in urban areas [1]. Both ethene and propene areseful indicator gases whose concentration profiles in coalmineir represent a mean of studying, the progress of low temper-ture coal oxidation that leads to spontaneous combustion [2].oncentration levels of alkenes change prior to the outbreak of

pontaneous combustion [3]. Monitoring of alkenes regardingheir environmental impact and for safety purpose of coalminesn the presence of alkanes forms the basis of an analytical methodor their efficient separation. Separation of low molecular weightydrocarbon gases by gas–liquid chromatography (GLC) is dif-cult due to the limited life of stationary phase because of the

olatility of the materials [4,5].

A number of modified column materials such as film-formingrganic polymer poly-[1-(trimethylsilyl)-1-propinel (PTMSP)]

∗ Corresponding author. Tel.: +92 51 2207277; fax: +92 51 9290275.E-mail address: aslamkhan@pinstech.org.pk (A. Khan).

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383-5866/$ – see front matter © 2007 Elsevier B.V. All rights reserved.oi:10.1016/j.seppur.2007.03.010

6], activated carbon modified with Apizone (L) [7], improvedurface area graphitized carbon black [8], molecular sieve, car-osieve [9] and geological materials such as serpentine ore haveeen studied for separation of light hydrocarbon gases in dif-erent matrices [10]. Gas sensors such as infra-red (IR) [11],coustic wave spectroscopy [12] and electron paramagnetic res-nance (EPR) [13] have also been reported for determinationf light hydrocarbon gases. However, the associated problemsre selectivity, high operating temperature and high noise level.ncorporating alumina into porous layer open tubular columnsPLOT) has improved separations of many small analytes andwo dimensional chromatography, using (PLOT) alumina capil-ary column in combination with methyl silicone and high purityilane using (trimethylsilylpropyne) liquid phases have beeneported for analysis of C1–C4 hydrocarbon gases [14–17] butolumns cost, requirement of operator expertise, special instal-ation arrangements in the gas chromatographic system and easyontamination with minor impurities [14] made the use of sucholumns very limited.

Gas–solid chromatography used in the present investigation,s capable to achieve separation of alkenes and alkanes, owningo the large surface area of the adsorbents used their insensitivityo oxygen, absence of column bleed, and the ability to tailor the

ification Technology 55 (2007) 396–399 397

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Fig. 1. XRD patterns of the modified alumina.

Fig. 2. shows the SEM image of the modified alumina.

A. Khan et al. / Separation and Pur

dsorbent with inorganic complex forming salts for improvederformance [18,19]. The choice of adsorbent depends on theroperties of analytes to be separated. Modification of adsorbenturface may substantially extend the usefulness of a number ofdsorbents. This can be achieved by bonding stationary phase tohe surface of the adsorbent, or in other cases by merely coatinghe surface.

There is a need to explore new low surface area sorbents suchs Fe2O3 modified alumina for efficient separation, removalnd analysis of environmental contaminants. Fe2O3 aluminamployed in the present investigation has been incorporated ascolumn material because it has a number of advantages such

s higher thermal stability, short conditioning time and longdsorbent lifetime. The present investigation involves surfaceodification of alumina with Fe2O3 and application of synthe-

ized material for alkenes and alkanes separation in a simulatedixture of coalmine gases.

. Experimental

.1. Reagents and chromatographic column

The column packing tube was made from nickel tub-ng 10 feet long and 1/8 in. of internal diameter purchasedrom Foxboro (USA). The alumina 100–120 mesh size wasbtained from sieving chromatographic grade (Aktivitatsstufe-) of 20–230 mesh size (E-Merck Germany). All other chemicalssed were of analar grade and solutions were prepared in dou-le distilled water. Standard hydrocarbon gases were suppliedy Matheson Gas Company (USA). An appropriate concentra-ion of gas mixture was prepared using International Standardrganization (ISO) volumetric method 6144-1987 (E).

.2. Preparation and characterization of modified alumina

Two hundred and fifty grams of alumina was placed in 400 ml.0 M ferric chloride solution in a 1 L beaker. After 30 min stir-ing to ensure adequate mixing, 3 M aqueous ammonia wasdded to the slurry until the completion of ferric hydroxide pre-ipitation. After 1 h constant stirring, the suspended material wasltered. The filtered material was washed several times with dis-

illed water, transferred into an evaporating dish, and placed inpreheated oven at 150 ◦C for 24 h as reported [20].

Scanning electron microscopy (SEM) has been used for char-cterization of GC column-packing materials [21]. A surfacetudy of the modified alumina was carried out using XRD alongith SEM/energy dispersive X-ray analysis (SEM/EDXA) to

nvestigate the presence of Fe3+. Fig. 1 shows, the XRD pat-erns of the modified alumina. It clearly indicates the presencef hematite iron on the alumina surface. Fig. 2 presents, theEM image of the modified alumina and its elemental analysis

s shown in Fig. 3 depicting Fe3+ on alumina matrix.

.3. Column packing procedure

A silanised glass wool plug was inserted into one side ofhe column, which was then connected to a vacuum pump. The Fig. 3. EDX Spectrum of modified alumina showing the Fek� and Fek� Peaks.

398 A. Khan et al. / Separation and Purification Technology 55 (2007) 396–399

Table 1Column efficiency data of modified and bare alumina columns

Chromatographic parameter Ethane Ethene Propane Propene Butane Butene

N 282, 199* 658, 429* 756, 558* 884, 758* 1420, 815* 1700, 823*H 11, 15.4* 4.6, 12.4* 4.0, 5.5* 3.5, 4.0* 2.2, 3.8* 1.8, 3.7*T 1.1, 1.4* 1.1, 1.3* 1.2, 1.5* 1.7, 2.3*

N Tf: tailing factor (measured at 10% of peak height); *values on bare alumina column.

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Fig. 4. Separation of a mixture of hydrocarbon gases on bare alumina column,chromatographic conditions: injector temperature, 100 ◦C; TCD temperature,150 ◦C; TCD current, 75 mA; column temperature, 70–150 ◦C, 10 ◦C min−1;fl4

rsterssfumn. Easy availability, low cost and easy in house preparationare additional advantages of such GC columns.

f 1.1, 1.0* 1.2, 1.2*

: number of theoretical plates; H: height equivalent to theoretical plates (mm);

acking material was introduced from the other end of the col-mn using a funnel and packed down by action of the pressureifferential with simultaneous vibration of column to ensureniformly distribution of the column material.

.4. Instrumentations and chromatographic conditions

The gas chromatograph was 263-70 series Hitachi (Japan)quipped with split/split less mode injection port and threeetectors, thermal conductivity (TCD), flame ionization (FID)nd electron capture (ECD). The chromatographic signals wereecorded on a Chromato-Integrator D-2500, Hitachi (Japan).

Modified and bare alumina adsorbent was packed into a col-mn of same material and size. These were used to separate therepared simulated standard gas mixture of hydrocarbon gasesy isothermal as well as temperature programming mode to opti-ize the separation parameters. The gas samples were injected

y means of airtight syringe (Precision Sampling (PS) Corpo-ation, USA). Detection of gases was achieved using a thermalonductivity detector (TCD).

. Results and discussion

A. Braithwaite and Cooper [2] have reported modified alu-ina with Na+ ion to improve the selectivity of alkenes/alkanes

air. The same authors used various alkali salts to modify alu-ina and the trend of increasing alkenes/alkanes separation

electivity with decreasing cation size in the following order+ > Li+ > Na+ > K+ > Cs+ [2]. Since the modifier cation size

ppears to have major impact on retention. We used Fe3+ iono incorporate in the alumina matrix since the Fe3+ ionic radius0.64 A) is smaller than that of Na+ (0.95 A) [22]. Because ofifferences in nuclear charge, atomic radii are not accurate mea-ures of electron attracting ability of atoms. Electronegativitys an atomic property associated with the ability of an atom tottract electrons. The electronegativity of Fe3+ (1.8) is greaterhan Na+ (0.9). The attraction of � electrons of alkenes towardse3+ will be more than Na+ and consequently result in improvedelectivity. Separation of alkenes and alkanes on Fe2O3 coatedolumn showed that alkenes were strongly retained than alka-es. This may be due to the interaction of pi electron systemf alkenes and dipole Lewis acid site of the aluminum ions ande3+ which also resides on the modified alumina surface. Var-

ous chromatographic parameters such as height equivalent to

heoretical plates (HETP), number of theoretical plates (N) andeak tailing factor (Tf) of hydrocarbons on bare and modifiedlumina columns were compared in Table 1. The Fe2O3 coatingn alumina has improved peak symmetry of eluting gases. The

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ow-rate He 10 ml min−1. Peak identification: 1, ethane; 2, ethene; 3, propane;, propene; 5, butane; 6, butene.

esolution between ethene and propane has also been improvedignificantly as shown in Figs. 4 and 5. The improved resolu-ion has been resulted from the interaction of Fe3+ ions with pilectron system of alkenes present on the modified matrix. Theesults indicate that the modified column is a better choice for theeparation of hydrocarbon gases. Moreover, analysis time washorter than two-dimensional column arrangement [16,17]. Iturther broadens the utility of the packed modified alumina col-

ig. 5. Separation of a mixture of hydrocarbon gases on modified aluminaolumn. Chromatographic conditions and peaks identification are same as inig. 4.

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A. Khan et al. / Separation and Pur

. Conclusion

Modified alumina has been found a good column packingaterial for separation of light hydrocarbon gases. By coat-

ng alumina with Fe2O3, the selectivity for alkenes/alkanes pairas been improved when compared with unmodified alumina.he number of theoretical plates along with tailing factor has

mproved for better separation and quantification. Moreover, theoating of adsorbent can produce tailor-made columns, whichay have potential to solve many analytical problems such as

he use of Fe2O3 as a modifying agent ensured that the activ-ty of the alumina surface was effective in eluting unsaturatedydrocarbons after the saturated hydrocarbons of the same car-on number. Modified alumina column is economically cheap,asy to install and operate. Easy in-house preparation saves a lotf down time of instrument and adsorbent column are not easilyontaminated.

cknowledgments

The authors are grateful to Physics Division and Mate-ial Division, PINSTECH for SEM/EDXA and XRD analysis,espectively.

eferences

[1] K.A. Persson, S. Berg, Automatic determination of selected C2–C4 hydro-carbons in urban air by solid sorbent sampling and gas chromatography,Chromatographia 27 (1989) 55.

[2] A. Braithwaite, M. Cooper, A study of surface modification of alumina forGC, Chromatographia 42 (1996) 77.

[3] M. Cooper, A. Braithwaite, Development of Methods for the Early Detec-tion of Spontaneous Combustion Using Specific Indicator Gases, BritishCoal and Nottingham Polytechnic ECSC Research Project 7258-02/08/120,1990.

[4] E.M. Fredricks, F.R. Brooks, Analysis of gaseous hydrocarbonsby gas–liquid partition chromatography, Anal. Chem. 28 (1956)297.

[5] T.A. Mckenna Jr., J.A. Idleman, Separation of C4 and lighter hydrocarbons

by gas chromatography, Anal. Chem. 31 (1959) 2000.

[6] V.G. Berezkin, A.A. Korolev, I.V. Malyukova, T.P. Popova, V.E. Shiryaeva,V.S. Khotimskil, Poly[1-(trimethylsilyl)-1-propine] as chromatographicadsorbent and prospects of its application in packed and capillary columns,J. Chromatogr. 960 (2002) 151.

[

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on Technology 55 (2007) 396–399 399

[7] L.A. Kulagina, I.I. Prusakova, T.A. Nekorkina, N.T. Karabanov, Modi-fied activated carbon for the determination of C1–C3 hydrocarbons by gaschromatography, J. Anal. Chem. 53 (1998) 829.

[8] A.R. Mastrogiacomo, E. Pierini, L. Sampaolo, F. Bruner, Evaluation ofnew graphitized carbon black employed in sampling volatile organic com-pounds, J. Chromatogr. 810 (1998) 131.

[9] Haunold, E. Rosenberg, M. Grasserbauer, An improved sampling strat-egy for the measurement of VOCs (volatile organic compounds) in airbased on cooled sampling and analysis by thermodesorption-GC–MS/FID,J. Environ. Anal. Chem. 67 (1997) 157.

10] B.N. Sing, B. Maiti, Separation of light hydrocarbons by gas chromatogra-phy using serpentine as stationary phase, J. Ind. Chem. Technol. 11 (2004)793.

11] J.J. Colman, A.L. Swanson, S. Meinardi, B.C. Sive, D.R. Blake, F.S.Rowland, Description of the analysis of a wide range of volatile organiccompounds in whole air samples collected during PEM-Tropics A and B,Anal. Chem. 73 (2001) 3723.

12] W. Rulin, W. Xia, L. Youngpin, Application of infrared spectrum in miningenvironmental inspection, in: Min. Sci. Technol, vol. 99, Proc. Int. Symp.,1999, p. 703.

13] S.G. Lunev, Acoustic monitoring of hazardous outbursts in coalminesNTTS promyshlennaya bezopasnost (Russ) Bezop, Tr. Prom-Stimul. (6)(2000) 40–42.

14] W.R. Betz, M.J. Keeler, J.H. Whitford, S.B. Cole, Alumina Plot Columnsfor Rapid and Consistent Separation of Light Hydrocarbons by Gas Chro-matography, vol. 15, Supelco, Supelco Bellefonte, PA, USA, 1996, p. 4.

15] M. Mohnke, D. Estel, A New Silica-Plot Column for Analyzing VolatileCompounds Chrompack R&D Labor Leipzig, D-04347, Leipzig, Germany,1997.

16] M.L. Wang, H.B. Cheng, Z.Y. Meng, G. Ding, Determination of volatilehydrocarbons in atmosphere by two dimensional capillary gas chromatog-raphy, Sepu. 20 (2002) 172.

17] V.A. Krytov, V.G. Berezkin, O.Yu. Chermova, Yu.M. Salganskii, A.Yu.sozin, Use of capillary gas chromatography for determining hydrocarbonsin high purity silane, J. Anal. Chem. 60 (2005) 851.

18] S. Bilal Butt, M. Riaz, E. Haq, Thermally treated charcoal: a substitute toporous polymer packing material for chromatographic analysis of perma-nent gases, J. Chem. Soc. Pak. 16 (1994) 12.

19] S. Bilal Butt, M. Riaz, E. Haq, S. Ahmad, F. Waqar, S. Ahmad, Evalua-tion and performance comparison of bare powdered graphite and coatedcolumns for gas chromatographic separation of halobenzenes and halocar-bons, Anal. Lett. 35 (2002) 1747.

20] E.H. Carter Jr., H.A. Smith, The separation of hydrogen, HD, TH, D TDand tritium mixtures by gas chromatography, J. Phys. Chem. 67 (1963)

1512.

21] D. Barcelo, M.T. Galceran, L. Eek, Scanning electron microscopy as anaid in gas chromatography, J. Chromatogr. 217 (1983) 109–123.

22] M.K. Synder, Chemistry Structure and Reactions, Holt Rinehart and Win-ston, Inc., New York, USA, 1966.