Pretreatment of poplar wood for fast pyrolysis: rate of cation removal

It is well known that the presence of alkaline cations in biomass affect th e mechanism of thermal decomposition during fast pyrolysis causing primaril y fragmentation of the monomers making up the natural polymer chains rather than the predominant depolymerization that occurs in their absence. As a r esult, liquid products (bio-oil) of quite different compositions can be obt ained, and these bio-oils may be used for quite different purposes. A consi derable amount of research has been carried out on the changes in mechanism occurring due to the presence and absence of these cations during fast pyr olysis and the compositional changes, occurring in the bio-oil product as a result. However, if removal of such cations is to be practised as an indus trial process, it would be desirable to have some information on the rates of the exchange step and the degree of removal of a particular cation that can be economically achieved. The present work describes a preliminary stud y of the rates of removal of the indigenous alkaline cations in a poplar wo od (potassium and calcium mainly) by an ion exchange process using a dilute acid. The exchange process is rapid and potassium is more easily removed t han calcium. It is also shown that hot water washing alone is able to remov e a major amount of the alkaline cations from wood. The deionized wood can be used as the feed for a fast pyrolysis process for the thermal conversion of cellulose and hemicellulose to anhydrosugars for use in synthesis, or f or conversion to fermentable sugars in good yield. (C) 2001 Elsevier Scienc e B.V. All rights reserved.