Abstract
The behaviors of thermal decomposition of kraft lignin under three different gases (Ar, CO₂, or H₂) 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 H₂ atmosphere generated the highest yield of liquids and CO₂ atmosphere had the highest yield of gases. TPD-MS results showed that H₂ atmosphere was consumed at the temperature range from 205 to 810 °C and CO₂ atmosphere was consumed at the temperature range from 185 to 1000 °C. The H₂ promoted the cleavage of lignin side chains and significantly enhanced the formation of CH₄, C₆H₆, HCHO, C₆H₅OH, CH₃OH, and tars. The percentages of water in produced liquids were 90.1%, 85.3%, and 95.5% for Ar, H₂, and CO₂ as atmosphere, respectively. The H₂ 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 m²/g for Ar., H₂, and CO₂ 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 H₂ and CO₂ yielded more carbon in final solid products. Solid products obtained under CO₂ or H₂ atmosphere contained sphere-shaped nanoparticles.