Sains Malaysiana 41(9)(2012): 1109–1116

Determination of Diffusion Coefficients and Activation Energy of Selected Organic

Liquids using Reversed-Flow Gas Chromatographic Technique

(Penentuan Pemalar Penyebaran dan Tenaga Pengaktifan bagi Cecair Organik Terpilih

Menggunakan Teknik Kromatografi Gas Aliran-Berbalik)

Khalisanni Khalid*, Rashid Atta Khan & Sharifuddin Mohd. Zain

Department of Chemistry, Faculty of Science, University of Malaya

50603 Kuala Lumpur, Malaysia

Received: 7 February 2011 / Accepted: 12 April 2012

ABSTRACT

Evaporation of vaporize organic liquid has ecological consequences when the compounds are introduced into both freshwater and marine environments through industrial effluents, or introduced directly into the air from industrial unit processes such as bioreactors and cooling towers. In such cases, a rapid and simple method are needed to measure physicochemical properties of the organic liquids. The Reversed-Flow Gas Chromatography (RF-GC) sampling technique is an easy, fast and accurate procedure. It was used to measure the diffusion coefficients of vapors from liquid into a carrier gas and at the same time to determine the rate coefficients for the evaporation of the respective liquid. The mathematical expression describing the elution curves of the samples peaks was derived and used to calculate the respective parameters for the selected liquid pollutants selected such as methanol, ethanol, 1-propanol, 1-butanol, n-pentane, n-hexane, n-heptane and n-hexadecane, evaporating into the carrier gas of nitrogen. The values of diffusion coefficients found were compared with those calculated theoretically or reported in the literature. The values of evaporation rate were used to determine the activation energy of respective samples using Arrhenius equation. An interesting finding of this work is by using an alternative mathematical analysis based on equilibrium at the liquid-gas interphase, the comparison leads to profound agreement between theoretical values of diffusion coefficients and experimental evidence.

Keywords: Diffusion coefficient; organic liquid; reversed-flow gas chromatography

ABSTRAK

Penyejatan cecair organik yang meruap adalah suatu ekologi berbahaya yang membawa maut dengan bahan dialirkan ke kawasan aliran air tawar dan air masin melalui bahan buangan industri, atau dialirkan secara terus ke udara daripada pemprosesan unit industri seperti bioreaktor dan menara penyejuk. Dalam kes yang demikian, suatu kaedah yang cepat dan ringkas diperlukan untuk mengkaji sifat fiziko-kimia cecair-cecair organik. Teknik pengsampelan Kromatografi Gas Aliran-berbalik adalah kaedah yang mudah, cepat dan tepat. Ia telah digunakan untuk mengukur pemalar penyebaran wap daripada cecair ke dalam gas pembawa dan dalam masa yang sama menentukan pemalar kadar bagi proses penyejatan bagi cecair yang terlibat. Ungkapan matematik yang menjelaskan puncak lengkungan elusi sampel yang diterbitkan dan digunakan untuk menaakul parameter berkaitan bagi cecair pencemar yang terpilih seperti metanol, etanol, 1-propanol, 1-butanol, n-pentana, n-heksana, n-heptana dan n-heksadesana yang tersejat ke dalam gas pembawa nitrogen. Nilai pemalar penyebaran eksperimen kemudiannya dibandingkan dengan nilai-nilai teori yang didapati secara kaedah pengiraan atau nilai-nilai yang telah dilaporkan di dalam jurnal, dan seterusnya nilai-nilai pemalar penyejatan ini digunakan bagi menentukan tenaga pengaktifan bagi setiap sampel menggunakan persamaan Arrhenius. Suatu penemuan yang menarik dalam penyelidikan ini ialah dengan menggunakan analisis matematik alternatif berdasarkan keseimbangan di fasa perantara cecair-gas, nilai-nilai teori pemalar penyebaran adalah selari dengan nilai eksperimen.

Kata kunci: Cecair organik; kromatografi gas aliran berbalik; pemalar penyebaran

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*Corresponding author; email: typhloids@gmail.com