Porosity characteristics of chars derived from different lignocellulosic materials

Abstract

Sixteen agricultural waste products were subjected to pyrolysis at 550°C under a nitrogen atmosphere. The precursors which were treated in this manner were fruit stones and nut shells (peach, apricot and olive stones; date pits, almond, hazel nut and pistacio shells), fibrous materials (sugar cane bagasse, date palm branches and leaves, cotton stalks and wood meal), corn cobs, rice husks, alkali-washed rice hulls and barbecue charcoal. Low adsorption of nitrogen was observed at 77 K with low values being estimated for the corresponding BET surface areas and total pore volumes. The surface areas as determined from CO2 adsorption at 303 K were relatively higher and various micropore parameters were calculated from the Dubinin-Radushkevich equation. Iodine was adsorbed from aqueous solution in amounts higher than the apparent surface areas and Methylene Blue was also taken up in a similar fashion. Such behaviour was attributed to the surface chemical natures of the chars which contribute to the higher uptake from aqueous solution. Generally, microporous products exhibiting a predominant ultramicroporosity were obtained under pyrolysis conditions.