Kinetics of Deacetylation of Northeast Hardwood, 2017PEERS

Acetyl groups in wood hemicelluloses can be hydrolyzed to sodium acetate which is a precursor to acetic acid.  This deacetylation step can serve as the first stage in a two-stage kraft pulping process in which acetic acid is recovered in kraft pulp mills as part of a biorefinery concept (Patil, 2017). This paper summarizes data on the alkaline deacetylation of northeast hardwood using sodium hydroxide over the temperature range between 50 and 90 oC.  Data are presented for both wood meal and commercial chips.

Initially, a kinetic study was performed to determine the effect of time, temperature and sodium hydroxide concentration on the cleavage of acetyl groups using wood meal ground to minus 20 mesh size.  The sodium acetate formed from the cleavage of the acetyl groups was measured using high pressure liquid chromatography. Experiments using woodmeal minimizes diffusion effects and thus are thought to be chemical reaction rate controlling.  The kinetic data on the wood meal samples were fit to a first order kinetic model and compared to experimental results for the cleavage of acetyl groups from cottonwood hemicelluloses presented by Zanuttini and Marzocchi [1997]. In follow-up experiments, the data on milled wood were compared to similar deacetylation data obtained on commercial chips over the same temperature range.   Comparison of the data showed conclusively that deacetylation in hardwood chips is diffusion limiting.  Using commercial chips approximately 66% of the sodium acetate can be recovered by simply draining the extraction vessel following the deacetylation reaction and another 20% can be obtained by washing the chips for 1 hour by circulating wash water.  The deacetylation data obtained on wood chips were fit to multi-linear equations using time, temperature and the applied effective alkali as the independent variables.

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