Effects of diammonium phosphate on the yields and composition of products from wood pyrolysis

The catalytic effects of diammonium phosphate on wood pyrolysis are investigated for applications in specialty chemical production and fire retardance. For a fixed-bed reactor operated at a temperature of 800 K, over a range of salt concentrations of 0-20%, the yields of char and water continuously increase (from 22 and 20%, respectively, to 45%), at the expense mainly of organic liquid products (from 43 to 6%) with only a small reduction in the yields of gases (percentages on a dry wood basis). As for the organic products, the yields of phenols, guaiacols, hydroxyacetaldehyde, hydroxypropanone, and some other minor carbohydrates rapidly attain low values. Major variations are undergone by levoglucosan only for mild treatments of wood, whereas levoglucosenone and 2-furaldehyde remain at the maximum values over a range of salt concentrations of roughly 2-5%. Diminution in the yields of acetic acid is generally slow. The same qualitative trends are preserved for a reactor temperature of 650 K. The ratio of the noncombustible to the combustible volatile products increases from 0.5 up to 5.5 already for a salt concentration of about 10%, thus confirming the fire-retardant action of diammonium phosphate in wood. Conversion times and global devolatilization rates are significantly affected by the modifications in the process energetics caused by salt addition.