Saran charcoal, adsorption

Hydrogen, deuterium, neon, argon, and methane flow through saran charcoal by both Knudsen and surface flow. The latter is effected by the adsorbed molecules sliding from site to site across the surface. This is equivalent to a two-dimensional Knudsen flow where the adsorption site acts as the wall of the three-dimensional case, and a slide across the surface is the same as a flight across the pore. The activation energy for surface diffusion is 75 to 80% of the heat of adsorption. It is possible to calculate theoretically the relative contribution of each mechanism, while comparison with He, which does not adsorb, permits its experimental determination. The efficiency of surface flow is the ratio of the measured to the calculated value this decreases as the size of the molecule increases, being 80% for Ne and 12% for CH4. 

A pioneering investigation of the adsorption of water vapour by Saran charcoal (an ultramicroporous carbon) was carried out by Dacey et al., (1958). The isotherm at 55°C had the well-defined Type V character with a steep riser at p/p° 0.5-0.6. There was a small amount of low-pressure hysteresis, but the isotherm appeared to be completely reversible at p/p° > 0.55. 

FIGURE 2.5 Adsorption of iso-octane vapours on different Saran charcoal. 

FIGURE 2.6 Linear Langmuir plots for adsorption of iso-octane on different Saran charcoal [own work]. 

FIGURE 4.6 Adsorption of water vapor on Saran charcoal before and after pore blocking by deposition of sulphur. (After Bansal, R.C., Bala, S., and Sharma, N., Indian J. Technol., Tl, 206, 1989. With permission.)... 

FIGURE 4.9 Adsorption isotherms of heptane vapors on Saran charcoal before and aflerpore blocking by benzene pyrolysis. (After Sharma, N., Ph.D. thesis submitted to Panjab Univ.,... 

FIGURE 4.12 (a) Absorption isotherms of iso-octane vapours on Saran charcoal at different temperatures, (b) Absorption isotherms of iso-octane vapors on Saran-120 at different temperatures. (c) Absorption isotherms of a-pinene vapors on Saran charcoal at different temperatures, (d) Adsorption isotherms of a-pinene vapors on Saran-120 charcoal at different temperatures. (After Bansal, R.C. and Dhami, T.L., Carbon, 18, 207, 1980. With permission.)... 

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