Evolution of sulfur during fast pyrolysis of sulfonated Kraft lignin

Sulfonated Kraft lignin, the most available commercial lignin of today, has high sulfur content due to the extraction and the subsequent sulfonation processes. In this work, the evolution of sulfur during fast pyrolysis of sulfonated Kraft lignin has been studied. Fast Pyrolysis experiments have been done using Py-GC/MS. It is found that main sulfur-containing products in the pyrolytic vapors are present as the following small molecular compounds: H2S, SO2, CH3SH, CH3SCH3, and CH3SSCH3. This indicates that sulfur-containing radicals preferentially combine with the other small radicals such as center dot H and center dot CH3 during fast pyrolysis process. Sulfur is suggested to be mainly present as sulfite (-SO3-) and sulfide (-S-) in the sulfonated Kraft lignin. Sulfite that is incorporated into lignin during the sulfonation process mainly result in the formation of SO2. The nature of the sulfur links created during the Kraft pulping process is difficult to determine, but they are supposed to mainly exist in form of sulfide (S) bonds, which lead to the formation of H2S, CH3SH, CH3SCH3 and CH3SSCH3.