Thermal Decomposition of Kraft Lignin under Gas Atmospheres of Argon, Hydrogen, and Carbon Dioxide

The behaviors of thermal decomposition of kraft lignin under three different gases (Ar, CO(2), or H(2)) were analyzed and compared using a temperature-programmed decomposition-mass spectrometry (TPD-MS) system. Experimental results indicated that Ar atmosphere produced the highest yield of solid chars, while H(2) atmosphere generated the highest yield of liquids and CO(2) atmosphere had the highest yield of gases. TPD-MS results showed that H(2) atmosphere was consumed at the temperature range from 205 to 810 °C and CO(2) atmosphere was consumed at the temperature range from 185 to 1000 °C. The H(2) promoted the cleavage of lignin side chains and significantly enhanced the formation of CH(4), C(6)H(6), HCHO, C(6)H(5)OH, CH(3)OH, and tars. The percentages of water in produced liquids were 90.1%, 85.3%, and 95.5% for Ar, H(2), and CO(2) as atmosphere, respectively. The H(2) yielded more organic chemicals in produced liquids compared to the other two gases. The observed organic chemicals were mainly acetic acid, phenols, ketones, alcohols, aldehydes, and esters. BET surface areas of solid products were 11.3, 98.5, and 183.9 m(2)/g for Ar., H(2), and CO(2) as the atmosphere, respectively. C–H–O–N–S elemental and morphology analyses on solid products indicated that the lowest carbon content and the highest oxygen content were obtained if Ar atmosphere was used, while H(2) and CO(2) yielded more carbon in final solid products. Solid products obtained under CO(2) or H(2) atmosphere contained sphere-shaped nanoparticles.