Background: Identification of monomeric and oligomeric organic compounds in Organosolv process wastewater is of growing importance in the context of isolating high value chemicals and producing biofuels. There were many studies devoted to identification of such compounds in precipitated Organosolv lignin, all of them using demanding, mostly hyphenated techniques such as HPLC-MS/MS and two dimensional NMR spectroscopy. However, the resulting Organosolv wastewater has not been studied as intensively in this respect, even though the application of these techniques to identify the components of dried/lyophilized Organosolv wastewater would be straightforward.
Objective: The objective was to identify lignin-based breakdown products in Organosolv wastewater resulting from pulping of beech with aqueous ethanol solutions.
Method: Low resolution GC/MS analysis in combination with derivatization reactions using nonlabeled and isotopically labeled derivatization agents and retention index information (where available) were used.
Results: The application of isotopically labeled derivatization agents such as BSTFA-d9 (N,Obis( trimethylsilyl)trifluoracetamide-d9) turned out especially useful in structural identification work. In addition to monomers such as abundant syringaldehyde and vanillin, a multitude of dimeric products of the guaiacyl(syringyl) glycerol-β-guaiacyl(syringyl) ether-type, phenylcoumaran type and lignan-type could be detected, the most abundant surrogate being syringaresinol. Syringyl-type surrogates were more abundant compared to guaiacyl-type surrogates. Formation pathways of the monomeric breakdown products such as syringaldehyde and vanillin were proposed on the basis of the solvolytic cleavage of β-O-4 aryl ether linkages.
Conclusion: Solvolytic cleavage of β(α)-O-4, β-5 and β-β linkages within the macromolecular lignin network under Organosolv process conditions results in dimeric products. Further activities should be focused on the use of high resolution MS and the synthesis of authentic standards.