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.