Characterisation of cellulose pulps isolated from Miscanthus using a low-cost acidic ionic liquid

Abstract

The ionoSolv pretreatment generates a cellulose pulp by extracting hemicellulose and lignin using low-cost ionic liquids. In this study, cellulose pulp was obtained from Miscanthus × giganteus using the protic ionic liquid triethylammonium hydrogen sulfate [N2220][HSO4] with 20% water as a co-solvent and characterised in detail for its material properties as a function of pretreatment severity. We measured the particle size distribution, porosity and crystallinity of the unbleached pulps and the molar weight distribution of the cellulose contained within. We report that the surface area increased and the size of the pulp particles decreased as ionoSolv processing progressed. While the native cellulose I structure was maintained, the average degree of polymerisation of the cellulose was reduced to a DPn of around 300, showing the cellulose polymers are shortened. We correlate the pulp properties with enzymatic saccharification yields, concluding that enzymatic saccharification of the cellulose after ionoSolv pretreatment is mainly enhanced by removing hemicellulose and lignin. We also observed that overtreatment deteriorated saccharification yield and that this coincides with cellulose fibrils becoming coated with pseudolignin redeposited from the ionic liquid solution, as demonstrated by FT-IR spectroscopy. Pseudolignin deposition increases the apparent lignin content, which is likely to increase chemical demand in bleaching, suggesting that both glucose release and material use benefit from a minimum lignin content. Overall, this study demonstrates that cellulose pulps isolated with ionoSolv processing are not only a promising intermediate for high-yield release of purified glucose for biorefining, but also have attractive properties for materials applications that require cellulose I fibrils. Graphic abstract

Production of oligosaccharides and biofuels from Miscanthus using combinatorial steam explosion and ionic liquid pretreatment

“…Both SE and IL pretreatment itself and combinatorial SE + IL pretreatment of Mx2779 resulted in high recovery of residual glucan (~85 to 99 %) relative to initial glucan of untreated and SE pretreated Mx2779 , respectively, indicating that the applied pretreatment conditions preserved most of the glucan. [TEA][HSO 4 ] pretreatment of Mx2779 recovered ~85 % of the initial glucan ( Table 2 ) and similar amounts of glucan remaining in the pulp are well-documented for [TEA][HSO 4 ] pretreated Miscanthus × giganteus ( Mxg ) ( Brandt-Talbot et al, 2017 , Gschwend et al, 2016 , Tu et al, 2020 ). Sole SE and [C 2 mim][OAc] pretreatment or combinatorial [SE] + [C 2 mim][OAc] pretreatment resulted in glucan recovery of ~86 to 91 % due to the dissolution of glucan into gluco -oligosaccharides (GOS), based on HPAEC analysis of the SE hydrolysate and [C 2 mim][OAc] wash solution.…”

“…Each sole pretreatment resulted in significantly lower LOI values compared with untreated Mx2779 ( Table 3 ). The substantially lower LOI values for SE, [TEA][HSO 4 ] and [C 2 mim][OAc] are likely linked to shortened cellulose microfibrils or the allomorphic transformation of native parallel-packed arrays of cellulose microfibrils (cellulose I) to a mixture of antiparallel-packed fibrils of cellulose II and amorphous cellulose ( Cheng et al, 2011 , Tu et al, 2020 ). The little to no change in LOI values for combinatorial SE + ILs pretreatment may reflect evidence of remnant cellulose I or a paracrystalline regenerated cellulose II structure.…”

“…The HBI was significantly lower for SE and [SE] + [TEA][HSO 4 ] pretreated solids compared with untreated Mx2779 material ( Table 3 ). These findings may indicate that the SE and [SE] + [TEA][HSO 4 ] cellulose-rich pretreated pulp has a lower degree of intermolecular regularity or hydrogen bonds ( Oh et al, 2005 ), which might be attributed to disruption and shortened DP of the cellulose ( Tu et al, 2020 ). Pretreatment of Mx2779 with either [TEA][HSO 4 ], [C 2 mim][OAc] or [SE] + [C 2 mim][OAc] resulted in a higher HBI between neighbouring cellulose chains than untreated Mx2779 , indicative of an increase in the inter-and intra-chain hydrogen bonding or a more organised cellulose structure.…”

“…The negligible amounts of glucose and cellobiose released from SE, [TEA][HSO 4 ] and [SE] + [TEA][HSO 4 ] pretreated solids after endo -glucanase hydrolysis ( Fig. 1 ) suggests an inaccessible cellulose surface and that these pretreatments may have retained the native cellulose fibre orientation and crystalline cellulose I lattice structure ( Tu et al, 2020 ). These results further confirm that both ILs have a fundamentally different effect on the recovered cellulose properties, making the pulps potentially suitable for various biomaterial applications in the fields of packaging, food, cosmetics and medical products.…”

“…2 A). A recent [TEA][HSO 4 ] pretreatment study on Mxg achieved optimum glucose yields of 72 %, though after a longer enzymatic hydrolysis time (168 h) and a lower Cellic CTec2 dosage (~20 % w/w g enzyme/g glucan) ( Tu et al, 2020 ). Since cellulose crystallinity was shown to remain high for [TEA][HSO 4 ] and [SE] + [TEA][HSO 4 ] pretreated pulp ( Fig.…”