Production of hydrogen and medium Btu gas via pyrolysis of a kraft lignin in a fixed-bed reactor

Lignins are generally used as a low grade fuel in the pulp and paper industry. In this work, pyrolysis of a Kraft lignin obtained from Westvaco was carried out in a fixed-bed reactor to produce hydrogen and gas with medium heating value. The effects of carrier gas (helium) now rate (13.4-33 ml/min/g lignin), heating rate (5-15 degrees C/min) and temperature (350-800 degrees C) on the Lignin conversion, product yield and the product gas composition were studied. At 800 degrees C and a constant heating rate of 15 degrees C/min, the carrier gas flow rate did not have any significant effect on the conversion. However, the volume of gas decreased from 820 to 736 ml/g of lignin with increase in carrier gas now rate from 13.4 to 33 ml/min/g lignin. The gaseous products mainly consisted of H-2, CO, CO2, CH4 and C2+. The production of hydrogen was high (66 mol%) at high carrier gas flow rate of 33 ml/min/g lignin. However, the product gas with maximum heating value of 437 Btu/scf was obtained at a helium now rate of 13.4 ml/min/g lignin. With increase in heating rate from 5 to 15 degrees C/min lignin conversion and hydrogen production increased from 52 to 57 wt % and 30 to 43 mol%, respectively. With increase in temperature, conversion of lignin as well as the production of hydrogen was further increased and the production of methane decreased. For example, with increase in temperature from 350 to 800 degrees C, the Lignin conversion was increased from 25 to 57 wt%, respectively. Maximum heating value of gas (491 Btu/scf) was obtained at 450 degrees C for Kraft lignin. From the kinetic study in a fixed-bed reactor the activation energy for Kraft lignin was obtained in the range of 17-89 kJ/mol.