Investigations of Thermal Treatment of Softwood Kraft Lignin Under Fractional and Ablative Pyrolytic Conditions
Semester of Graduation
Master of Science in Biological and Agricultural Engineering (MSBAE)
Department of Biological & Agricultural Engineering
Lignin is second to cellulose in abundance among polymers in nature. Research studies on the development of new products and material combinations in which lignin degradation/conversion products are involved are still in their infancy, because fundamental knowledge about its structure, reactivity, and material and polymer behavior, is still lacking.
The objective of this research study was to investigate the complex thermal deconstruction and mechanistic behavior of a type of technical lignin, known as Kraft lignin, under depolymerization and to develop operating conditions for parameters influencing resulting product yields and operation of pyrolysis reactors.
Softwood Kraft lignin (s-KL) and methanol-fractionated (ex-KL) samples were thermally depolymerized via fractional (stepwise) pyrolysis at temperatures from 175 oC to 700 oC. An isothermal STDS (system for thermal diagnostic studies) reactor with a modified reaction chamber was used to obtain the distribution and the yields of pyrolysis products in five groups - the major tar products; guaiacols, vanillins, phenols, syringols, and sulfur-containing compounds. Sulfur-containing compounds, as intrinsic contaminants (both adsorbed and covalently bound to KL matrices), were found to strongly inhibit the formation of the major pyrolysis products. The yields of the major products were inversely correlated to the release of sulfur-containing compounds, i.e. the lesser the content of sulfur in the KL matrix, the higher the yields of major products. The initial pretreatment of ex-KL by Soxhlet extraction in methanol caused the high yields and early release of tar components at lower temperatures from ex-KL pyrolysis. No sulfur-containing bio-oil liquid products were detected from pyrolysis of both lignins indicating that sulfur-containing products were in the gas phase. A mechanistic explanation for the absence of sulfur-containing bio-oil products, and the inhibitory effect of sulfur-containing compounds, as well as the relatively high char content in depolymerization of both lignin substrates are presented.
Analytical techniques were subsequently used to compare the distribution of primary pyrolysis products from the fast pyrolysis of softwood Kraft lignin (s-KL) in the STDS and ablative IR CO2 laser reactors. Lesser transfer times and higher abundance of products were noticed from the IR CO2 laser ablative pyrolysis.
Daniel, Dideolu J., "Investigations of Thermal Treatment of Softwood Kraft Lignin Under Fractional and Ablative Pyrolytic Conditions" (2019). LSU Master's Theses. 5011.