Lignin, as a unique renewable resource for aromatics, keeps moving into the spotlight of industry and bio-economy. Highly altered, technical lignin, is produced in vast amounts as a by-product of pulp and paper industry. Therefore it still possesses a lot of potential to be exploited as it is mostly used thermally for its high calorific value at this stage. However, the term lignin, and even more so technical lignin, inadequately describes a group of polymers, which only share a similar set of monomers, but differ very much in their composition. This is highly dependent on the biomass they originate from and the process used to extract them. In terms of molecular structure that leaves us with high polydispersity and a variety of functional groups, such as hydroxyl, carboxyl, keto, thiol and sulfonic acid groups. The latter are introduced by the two major pulping processes, the kraft and the sulphite process, respectively. While so-called native or unaltered lignins and kraft lignins are rather well described in literature, lignosulfonates are underrepresented when it comes to structural investigation. Thus, in this study we want to provide a comparison of various lignosulfonate samples after extraction by two different methods which have been optimized towards the application on sulphite spent liquors. In-depth analysis of the samples by 2D NMR spectroscopy will be provided with a focus on distinct structural elements of lignosulfonates. The real-life samples will be compared to model compounds such as lignin dehydrogenation polymers. Additionally, methods for determination of the functional group content of technical lignins will be discussed. Typical approaches for sulfonic acid group determination will be compared to novel approaches such as gas chromatography. Finally, challenges of the highly polar sulfonic acid group and consequently the implications for sample preparation will be addressed in order to use established methods from lignin chemistry such as <sup>31</sup>P NMR.

Lignosulfonate analysis: Improving the toolset

251st National Meeting (2016)

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