Effects of reactor severity on the gas-phase pyrolysis of cellulose- and kraft lignin-derived volatile matter

Abstract

Yields of permanent gases evolved by the gas-phase pyrolysis of cellulose- and lignin-derived voltatile matter cannot be correlated with a commonly used kinetic severity function. Instead, engineers explained the dependence of gas yields on temperature and residence time by a global mechanism composed of two competing reactions. The first creates permanent gases by cracking the volatile matter, whereas the second creates refractory condensable materials. For cellulose, the cracking reaction has an apparent activation energy of 49 kcal/g-mol, and the competing reaction 15 kcal/g-mol. The gas-phase cracking of cellulosic volatile matter involves competition between the dehydration (resulting in methane and ethylene formation) and decarboxylation reactions; the fraction of carbon atoms dedicated to carbon monoxide formation by the cracking reaction is not influenced by temperature. For lignin, competition exists between ethylene and carbon dioxide formation; the fraction of carbon atoms dedicated to carbon monoxide and methane formation is not influenced by temperature.