Surface and bulk chemistry of charcoal obtained by vacuum pyrolysis of bark: influence of feedstock moisture content

Abstract

Samples of maple bark and softwood bark with moisture contents ranging from 6 to 42 wt% were pyrolyzed under vacuum at a temperature of 775 K. Vacuum pyrolysis of maple bark yields approximately 30 wt% wood charcoal on an anhydrous basis. For softwood bark the charcoal yield is smaller (23–28 wt%). The charcoal yield of maple bark pyrolysis depended only slightly on the bark moisture. The surface and bulk chemistry development of the charcoals was studied by electron spectroscopy for chemical analysis (ESCA), secondary ion mass spectroscopy (SIMS) and Raman spectroscopy, respectively. With decreasing bark moisture the charcoal surface becomes more graphite-like, whereas the bark moisture had only a limited influence on the bulk structure. The high specific surface area of the charcoals at 200–300 m 2/g makes these materials valuable feedstocks for the production of activated carbons.