Changes in sulfite liquor composition while re-profiling mill from paper-grade to dissolving pulp production

Abstract

The re-profiling from paper-grade to dissolving pulp production is a common trend for acid sulfite cooking of wood. This provides substantial changes in the composition of the spent sulfite liquor (SSL) affecting its potentialities in subsequent processing within the biorefinery concept. In this work, a comparative analysis of the chemical composition of SSL was performed from the magnesium-based acid sulfite cooking of Eucalyptus globulus wood to produce the paper-grade and dissolving pulps. More severe pulping conditions required for dissolving pulp production led to a substantial increase in volatile compounds in SSL, such as acetic acid, methanol, and furfural. At the same time, the amounts of dissolved sugars and lignosulfonates (LS) were increased to a less extent. The main changes detected in LS were related to the increase of its molecular weight, degree of condensation, and sulfonation degree. The increased concentration of the sulfuric acid in SSL was one of the reasons for these changes.

Keywords:

• Acid sulfite pulping
• sulfite spent liquor
• lignosulphonates
• xylo-oligosaccharides
• biorefinery

Acknowledgments

This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020, UIDP/50011/2020 & LA/P/0006/2020, financed by national funds through the Portuguese Foundation for Science and Technology (FCT)/Ministry of Science, Technology and Higher Education (MCTES) and supported by FCT and the European Social Fund (ESF) within the framework of PORTUGAL2020, namely through the Programa Operacional Regional do Centro (Centro 2020) (PhD grant SFRH/BD/121275/2016). The NMR spectrometers are part of the National NMR Network (PTNMR) and are partially supported by Infrastructure Project N° 022161 (co-financed by FEDER through COMPETE 2020, POCI and PORL and by FCT through PIDDAC).

Disclosure statement

No potential conflict of interest was reported by the authors.

Supporting information

Supporting information contains the figures showing the lignin sulfonation (Figure S1) and condensation (Figure S2) reactions. Figure S3 represents the general scheme of the dissolving pulp production by Mg-based acid sulfite pulping, Figure S4 depicts the methodology for the preparation of the lignosulfonates-rich fractions LSG and LSF (including the lyophilized SSL denoted as SL_lyo), obtained from thick (THSL) and thin (SSL) liquors, respectively. Figure S5 shows the schematic representation of the multiple-effect evaporator system.

Additional information

Funding

This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020, UIDP/50011/2020 & LA/P/0006/2020, financed by national funds through the Portuguese Foundation for Science and Technology (FCT)/Ministry of Science, Technology and Higher Education (MCTES) and supported by FCT and the European Social Fund (ESF) within the framework of PORTUGAL2020, namely through the Programa Operacional Regional do Centro (Centro 2020) (PhD grant SFRH/BD/121275/2016). The NMR spectrometers are part of the National NMR Network (PTNMR) and are partially supported by Infrastructure Project N° 022161 (co-financed by FEDER through COMPETE 2020, POCI and PORL and by FCT through PIDDAC).