100
J. Chem. Eng. Data 1988, 31, 100-102
Determination of Binary Gas-Phase Diffusion Coefficients Using Chromatographyt S. M. Ashraf,' R. Srlvastava,* and Asghar Hussalns Regional Research Laboratoty, Hyderabad 500 009, India Table I. Physical Constants of Purified Components
Blnary dlffudon coefflclents of 15 organlc vapors In nltrogen carrier gas were measured by udng the peak arrest technlque on a HewlettPackard 5840A gas chromatograph wlth a flame Ionization detector. The experiments were conducted at atmospheric pressure, above the normal boNlng polnt of the organlc vapors. The experhentally obtalned values were compared wlth those predlcted by utlng various correlations and reported In Ilterature. I n general, the observed values were In excellent agreement wlth the values predlcted by Fuller's correlation. Introductlon The binary dlffusion coefficients of gases are important parameters needed in the design of reactors where gas-phase reactions are involved. Several techniques have been reported for the measurement of dmLwlon coefflcients; however, evaiuation of quantitative resub is excessively time consuming in most of these techniques. Recent developments in the chromatographic theory have made it possible for rapid and accurate measurements of binary diffusion coefflcients. Several of these techniques have been reviewed by Choudhary (7). Among these, the peak arrest method of Knox and Mclaren (2) bypasses most of the experimental and theoretical difficulties encountered in the continuow elution methods. Several studies have been reported (3-8) recently using this technique for the measurement of binary diffusion coefflcients of gases and organic vapors. I n the present work, the peak arrest technique is employed to measure the diffusion coefflcients of 15 organic vapors with nitrogen as the carrier gas. The expertmentally obtained values are compared with the predicted values by using the correiations of Fuller et ai. (9), Chapman-Enskog (70), Siattery-Bird ( 7 7), Chen-Othmer ( 72),and Gliliiand et ai. ( 73). Experbnentai Procedure Studies were conducted using a microprocessor-controlled
gas chromawaph (HP5840A) wtth a flame ionizationdetector. Nitrogen was used as a carrier gas and as a component of gas-vapor binary system. Nitrogen was predried by passing it through a sulfuric acid trap and a molecular sieve trap before its entry into the column. A stainless steel unpacked helical cdumn of length 308 cm and Lntemal diameter of 2.16 mm was empbyed. The carrier gas coM1Bctkn was made tothe column through a three-way stopcuck, and the volumetric flow rate ( F ) was measured by means of a soap bubble flow meter with an accuracy of 1 s. The minimum time measured was around 300 s, whereas the maximum measured was 600 s. The output signal from the flame ionization detector was displayed by Presented at the World Chromatography/Spectroscopy Conference. London, lS83. *Present address: Department of Chemical Engineering, Washlngton Unlversky, St Louis. MO 63130. Present address: Department of Chemical Engineering, Unlverstty of Libya, Tripoli, Libya.
0021-9568/86/1731-0100$01.50/0
component 1-propanol 1-butanol 1-pentanol I-hexanol 1-heptanol 1-octanol nitrobenzene chlorobenzene bromobenzene o-nitrotoluene tetrachloroethane methyl isobutyl ketone
refractive index exptl lit. 1.3860 1.3854 (14) 1.4000 1.3993 (15) 1.4100 1.4099 (15) 1.4130 1.4133 (14) 1.4236 1.4233 (14) 1.4302 1.4304 (14) 1.5525 1.5524 (14) 1.5250 1.5251 (14) 1.5602 1.5604 (14) 1.5475 1.5474 (14) 1.4930 1.4921 (14) 1.3960 1.3959 (14)
exptl
density lit.
0.7955 0.8023 0.8075 0.8186 0.8223 0.8236 1.1932 1.0956 1.4814 1.1628 1.5950 0.8021
0.7960 (17) 0.8020 (17) 0.8076 (17) 0.8191 (15) 0.8219 (15) 0.8239 (15) 1.1936 (16) 1.0948 (16) 1.4815 (17) 1.1629 (17) 1.5953 (17) 0.8025 (17)
Table 11. Diffusion Coefficients of Organic Vapors in Nitrogen" DAB,cmz/s system N,-l-propanol Nz-1-butanol Nz-1-pentanol Nz-1-hexanol Nz-1-heptanol Nz-l-~tanol Nz-acetone Nz-methyl isobutyl ketone Nz-chloroform Nz-carbon tetrachloride Nz-nitrobenzene N2-chlorobenzene N2-bromobenzene Nz-o-nitrotoluene Nz-tetrachloroethane
temp, K 373 393 418 433 453 473 373 423 373 373 523 423 473 498 423
pred by exptl Fuller's correln 0.153 0.159 0.161 0.155 0.159 0.152 0.141 0.147 0.145 0.146 0.148 0.149 0.168 0.164 0.141 0.144 0.140 0.141 0.120 0.127 0.225 0.222 0.165 0.164 0.173 0.171 0.170 0.175 0.143 0.145
lit. valuesb
0.161 (20) 0.139 (20) 0.118 (20) 0.223 (7)
'Pressure = 1 atm. bCorrected to the experimental temperature.
means of variable-speed chart recorder; in order to get a broader peak the chart speed through out the investigation was maintained at 1 cm/mln. Among the chemicals used, acetone, carbon tetrachloride, and chloroform were of spectroscopic grade. The others were purified by doubly distining in a packed column; the first and last portions of the distillate were discarded and the rest was used in the measurements. Physical properties such as density and refractive index were measured at the temperature of referred literature value and compared in the chart given In Table I . A typical experimental run was started by maintaining a constant flow rate of the carrier gas for over an hour. MeanwMle the chromatogaph was tumed on and stabilized. A sharp band of organic IiquM (1 ML) was injected during the shortest possible time and eluted from the column at a known linear velocity, V (cm/s). The retention time was noted. I n the subsequent runs, when the band moved about half-way down the column, the flow was stopped by diverting the carrier gas outside the column using the three-way stopcock. The How of the carrier gas was stopped for an arrest time, t (s),during which band spreading occurred as a result of diffusion only. The band was eluted after the arrest time and its spreading recorded. Runs were repeated with dlffeent arrest times for the 0 1988 American Chemical Society
Journal of Chemlcal and Engineerlng Data, Vol. 31, No. 1, 1986
7
101
I -
NITROGEN CHLOROFOM SLOPE D 0 26 VELOCITY VELOCITY
8 4
i
-
NITROGEN METHYLISOBUTYL KETONE SLOPE :O 2 5
100 ILO
130
J
120
CMISEC
1 OL
1 - 4 0 CMISEC
I 2
i
90
VELOCITY
i
178
CMISEC
NITROGEN- BROMOBENZENE SLOPE = 0 2 3 123
VELOCITY;
CMISEC
I
/
