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Measurement of binary gaseous diffusion coefficients of polar system Mian, Aziz Ahmed

Abstract

This investigation was undertaken primarily for the purpose of collecting reliable experimental data on binary gaseous diffusion coefficients of polar systems. The binary gas pairs investigated were the A - SO₂ , A - HCI , and SO₂ - HCI systems. Diffusion through, a porous solid in a flow apparatus was adopted for the diffusion measurement. The diffusion cell was standardized by making diffusion runs using the N₂ - CO₂ system at 5 different temperatures, room temperature, 70°C, 120°C, 200°C, and 250°C, and using also the N₂ - H₂ system at room temperature. Thermal conductivity cells and chemical methods, alone or in combination, were used for analysis of the gas streams. The results in all these three systems could be represented by straight lines on logarithmic plots of diffusion coefficient against temperatures from 20°C - 250°C. In the first two pas pairs, the experimental coefficients appeared to be 25.3% and 29.2% less at room temperature, and 20.0% and 12.1% less at about 250°C than the respectively predicted values obtained by using the Stockmeyer potential function in the Hirschfelder diffusion equation. The slopes of the lines were 1.988 and 2.42, respectively. It was found that the A - SO₂ system could be represented by a potential function of the Lennard-Jones type, although the molecular force parameters determined from the diffusion data did not agree with those calculated from the pure component values and the usual empriical combining rules. The system A - HCI could not be represented by a function of the Lennard-Jones type. The third system, SO₂ - HCI, was also found to behave more or less the same way as A - HCI system. However, the slope of the line obtained from a Log D vs Log T plot (2.22), was smaller than that of the A - HCI system, although still greater than that predicted by using the Monchick and Mason . (12-6-3) potential function. The magnitudes of the diffusion coefficients within the range of temperatures studied were found to be within 11.0% of the predicted ones. Nevertheless, the system did not conform completely to the Monchick and Mason model. Some qualitative reasons are given for the inadequacies of present potential functions and combining rules for use in predicting binary diffusion coefficients in mixtures containing polar molecules.

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