Investigation of porous structure of activated carbon from rice husks

Abstract

One of possible ways of utilization of rice husks, by-producted in plants of the republic of the Union
of Myanmar is their processing into activated carbons by method of carbonization and activation with water
vapor. Characteristic changes of porous structure of the carbonized husks at the processing by water vapour
at 800°C for 0,25 hours, were estimated by the method of low-temperature nitrogen adsorption, the results of
which are processed according to the Dubinin-Radushkevich equation. Analysis of the isotherms of adsorption-desorption
of carbonization and activation products indicates, that at activation capable of chemisorption
acid centers on surface of the material partly disappear, and its primary and secondary porous structure
changes significantly. In particular, sorbing pores of the carbonizate, represented by ultramicro-, supermicroand
mesopores with distribution peaks of 0.68, 1.1 and 3 nm respectively, burn out in radial direction and
enlarge in size, forming micro- and mesopores. The differences of behaviour at activation at the same conditions
between the carbonizate of rice husks and that of coconut shells, forming predominantly micropores,
are shown. A significant (28 % of the volume of sorbing pores) proportion of mesopores in activated carbon
from rice husks predetermines feasibility of its use in processes of gas purification, that is illustrated by absorption
of n-butanol from its air-steam mixtures. The study of the kinetics and equilibrium of this process by
using a spring scale shows the benefits of activated carbon from rice husk compared to activated carbon, producted
from coconut shells: a higher adsorption capacity (145 mg/g) and less time of its achievement. Alternative
estimation of the volume of sorbing pores of these adsorbents by benzene vapor gives smaller volume
of sorbing pores due to unavailability of ultramicropores for molecules of adsorbate