The 4th Doctoral Colloquium is an event dedicated to providing junior scientists an opportunity to network and have scientific exchanges with other universities and research institutions. These results form a part of Maximilian’s Doctoral project, and were shared with “Future researchers, industry leaders and policy makers”. In this article Maximilian shares a summary of this presentation:
In order to verify the feasibility of direct HTL of black liquor, we performed parameter studies in batch experiments using micro autoclaves. In this study we focused on the behavior of the sulfur-containing salts which are part of the black liquor. The product phases were separated and analyzed using different analytical methods. Our study shows that the typical depolymerisation products of lignin are found dependent on temperatures and residence times. The sulfur mass balance shows an increase of sulfur in the gas phase over time and temperature. In addition, dimethyl sulfide (DMS, H3C-S-CH3) and hydrogen sulfide (H2S) are found in significant concentration in the gas phase. This indicates that thiols are formed from hydrogen sulfide ions (HS-) during the process, but continue to react immediately due to their high reactivity.
For a deeper insight to these reactions, we prepared a model solution containing the lignin extracted from black liquor and the most important pulping salts. We used analytical data from the feedstock characterization of black liquor to prepare a representing salt concentration. The experiments with the model black liquor show that the typical reaction products after HTL are formed. Therefore, the model black liquor can be used to investigate the influence of the individual salts on HTL of lignin. Furthermore, we see an increase in the production of H2S and DMS with increasing concentration of sulfide (S2-). In contrast to this, only a minor influence of the salt concentrations on typical phenolic compounds in the product phase were detected.