Comparative assessment of liquid product from hydrothermal treatment of lignosulfonate in batch and nozzle reactors for aromatic compounds recovery

Lignosulfonate is one of the main by-products of the pulping process, with enormous potential for application as an alternative source of aromatic and bioactive compounds, especially in a closed-loop Circular Economy Concept. The lignin-derived bioactive compounds have attracted enormous interest in the scientific community due to their positive effects on human health. In the present paper, hydrothermal treatment technologies of the 10 wt% and 20 wt% lignosulfonate solutions i.e., slow HTL in batch reactor and fast HTL in continuous-flow (CF) reactor, are compared, and discussed, to assess their potential for obtaining bioactive and aromatic compounds. The hydrothermal liquefaction (HTL) in the two reactors was carried out at 275 degrees C at a pressure of 21.4 MPa, a 1:3 feed-to-water ratio. GC-MS and LC-MS-QTOF analyses were used to determine the chemical composition of the liquid products. According to the chromatogram integrated peak areas (PA), the fast HTL of the lignosulfonate produced the most isoeugenol (35.8-49.2%), eugenol (10.4-16.9%), and homovanillyl alcohol (13.8-18.4%). Slow HTL product, on the other hand, was rich in guiacol (62%) and apocynin (19.7%). LC-MS analysis of the product showed a similar composition to the liquid product in terms of heaviest compounds. Observed m/z values in the chromatograms indicated a presence of the compounds with masses between 121.159 and 934.021 u, possible configurations of the polycyclic phenolic compounds are presented.

Automated summary

Lignosulfonate, a by-product of the pulping process, has great potential as an alternative source of aromatic and bioactive compounds. This study compared and discussed the hydrothermal treatment technologies of 10% and 20% lignosulfonate solutions, namely slow HTL in a batch reactor and fast HTL in a continuous-flow reactor, to evaluate their potential for obtaining bioactive and aromatic compounds. The analysis of the liquid products using GC-MS and LC-MS-QTOF showed that fast HTL produced more isoeugenol, eugenol, and homovanillyl alcohol, while slow HTL was rich in guiacol and apocynin. LC-MS analysis confirmed the presence of polycyclic phenolic compounds.