The reaction of a lignocellulosic precursor with a strong chemical reagent, such as phosphoric acid (H3PO4), at temperatures up to 350 C or above, can lead to the formation of a porous carbon. Depending on the reagent, its concentration, and the carbon precursor material, the carbon will possess a highly developed internal pore structure and be an effective adsorbent for molecules in the gas or liquid phase.
The work presented here has focused on elucidating the fundamental processes involved in the synthesis of porous carbons from white oak (quercus alba) and yellow poplar (liriodendron tulipifera), by activation with phosphoric acid. The objectives were to improve the understanding of the relationship between activated carbon properties and the structure of the precursor, and to clarify the reaction chemistry and mechanisms.
With increasing reaction temperature, the wood initially contracts and subsequently dilates. At high temperatures there is a secondary contraction. The dimensional changes are related to the chemistry of activation and the development of porosity. Phosphoric acid is believed to function as an acid catalyst and as a phosphorylation agent for cellulose. The dual functions allow simultaneous formation of micropores by acid attack and crosslinking of amorphous biopolymers (lignin), and mesopores by the phosphorylation of crystalline cellulose that introduces bulk phosphate and polyphosphate side chains and bridging linkages, Detailed studies of the chemical and physical changes, and investigations with the individuals biopolymers and other reagents have provided insight into the process.
Part of the CAER's Internal Seminar Educational Series.
Featured Speaker: Dr. Marit Jagtoyen
Date: October 31, 1996, 9:00 a.m.
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