Optimization of the ionoSolv process for the preservation of pulp fibre dimensions

Abstract

The pulping industry, dominated by century-old technologies, is highly polluting, making imperative finding more environmentally friendly alternatives. The ionoSolv process, based on the use of low-cost protic ionic liquids, is one of the most promising methods to fractionate lignocellulose with low ecological impact. However, this process has been only optimized to produce sugar-derived chemicals, where fibre quality is not a key factor. Earlier studies have shown the detrimental effect of the standard ionoSolv conditions on fibre length, which renders them unsuitable for fibre applications, including the production of paper. For the first time, this study shows the optimization of the ionoSolv fractionation of Miscanthus to preserve key fibre properties of the pulps, namely fibre dimensions, degree of polymerization and relative molecular mass, while maintaining optimal purity. Different temperatures (150 ºC and 170 ºC), retention times (45–90 min), and acid:base ratios (a:b = 1.00 to a:b = 0.55) were investigated. Fractionation at 170 ºC for 45 min with a reduced acid:base ratio of a:b = 0.86 allowed for maximum delignification (lignin content of 4.4 %) and preservation of fibre length. Pulps recovered under optimal conditions were bleached using a single stage method based on H₂O₂ increasing pulp purity, achieving optimal decolorization and retaining fibre dimensions comparable to those obtained from a commercial process (Lc(l) = 0.509 mm and Lc(w) = 0.775 vs Lc(l) = 0.540 mm and Lc(w) = 0.975). This highlights the potential of the ionoSolv process as a greener fractionation alternative to produce cellulose fibre materials.