Valorization of paper mill sludge using protic ionic liquids and deep eutectic solvents as a potential feedstock for biorefineries

Abstract

In this article, protic ionic liquids (PILs) and deep eutectic solvent (DESs) were explored to enrich the cellulose content of a paper mill sludge (PMS) received from a sanitary paper manufacturing plant. Compositional, morphological, physico-chemical, and thermal decomposition features of PMS were monitored using XRF, SEM, FTIR, XRD, and TGA. Triethylammonium hydrogen sulfate (TEAHSO₄), which functioned selectively for the elimination of mineralogical content and cellulose enrichment of PMS, enhanced the cellulose content of the material from 45% to 74% following the pretreatment at 150 °C. Though DESs such as choline chloride-urea behaved poorly toward demineralization relative to PILs, they preserved cellulose effectively in the structure and gave satisfactory saccharification yields that reached over 90%. In addition to integrating the sustainable benefits of PILs and DESs into the valorization of PMS for the first time in literature, this work highlighted the competency of PMS as a cellulose-rich feedstock for biorefinery applications.

Keywords:

• Paper mill sludge
• protic ionic liquid
• deep eutectic solvent
• cellulose
• demineralization

Acknowledgments

The authors would like to thank the Department of Chemical Engineering at Middle East Technical University (METU) for their support in HPLC analysis.

Disclosure statement

The authors declare no conflict of interest.

Additional information

Funding

This work is supported by The Scientific and Technological Research Council of Turkey (TUBITAK) under grant 120M386.