Effect of Preparation Condition on Pore Structure and Heavy Oil Sorption of Charcoals

Charcoals were prepared under various conditions of carbonization from three kinds of plants: balsa (Ochroma lagopus Sw), giant ipil-ipil (Leucaena leucocephala (Lam.) de Wit) and mousou chiku (Phyllostachys pubescens). The pore structure of the various charcoals was observed on fractured cross-sections under SEM and was evaluated utilizing mercury porosimetry. The sorption capacity of the charcoals for A-grade heavy oil was determined by direct soaking in oil. It was found that the pore structure of the charcoals depended strongly on, not only, the precursor plants but also carbonization conditions, particularly heating rate. Balsa charcoals prepared with a heating rate of 50°C/min. under vacuum gave a relatively high sorption capacity for A-grade oil, approximately 30g/g of charcoal. The other two charcoals, derived from giant ipil-ipil and Mousou chiku, had a considerably lower capacity, approximately 1.5g/g-carbon. The dependence of pore occupancy, the ratio of volume of oil sorbed to total pore volume, on the average pore radius indicated that pores with a diameter above 1μm were largely responsible for heavy oil sorption.