Changes in commercial wood charcoals by thermal treatments

As a continuation of a recent study of commercial wood charcoals as far as their potential production of carbon adsorbents is concerned, we have studied the influence of the final heating temperature (T) as carbonization variable in the range 250-1000 degrees C on the yield and on the characteristics of granular chars prepared from two very different charcoals: a holm-oak charcoal manufactured by partial combustion in a charcoal kiln and an eucalyptus charcoal industrially manufactured in a continuous furnace. Our study also includes the changes produced in both charcoals heated at 250 degrees C in air for 24 h, and their influences on the adsorption of water vapour at 25 degrees C. The samples were characterized by thermogravimetry, chemical analyses, Fourier transform infrared spectroscopy, densimetric measurements and mercury porosimetry. T affects the char yield, the chemical composition and the porosity of each char series differently. In particular, the total open pore volumes (to helium) ofthe starting charcoals, 0.475 and 1.044 cm 3 g(-1), increase to 0.872 and 1.293 cm(3) g(-1) heating up to 1000 and 500 degrees C, respectively. The changes by carbonization are mainly due to devolatilization; moreover, a moderate structural shrinkage occurs heating the eucalyptus charcoal at T > 500 degrees C. Concerning the air treatments, the yields do not present a significant difference; carbonyl groups are formed and the resulting pore structures depend on the starting charcoals. Water adsorption is larger for the eucalyptus carbons (approximately type V isotherms) than for the holm-oak carbons (type 11 isotherms). (C) 2007 Elsevier B.V. All rights reserved.