Investigation of accessibility and reactivity of cellulose pretreated by ionic liquid at high loading

•Cellulose accessibilities are increased at high loading in the IL pretreatment.•Acid hydrolysis reactivity of pretreated cellulose also increases at high loading.•The reactivity enhancement is not observed when catalyzed by cellulase.•The key factor that differentiates the reactivity is found to be the catalyst size. High loading of cellulose in ionic liquid (IL) pretreatment is potentially a key technique for cellulose conversion to glucose in biorefining. In this work, to expand the potential use of this high loading technique, the accessibility of microcrystalline cellulose pretreated with an IL across a wide cellulose loading range (5–50mol%) and its relationship with the hydrolytic reactivity were comprehensively investigated. The results show that the estimated cellulose accessibility based on the crystallinity and specific surface area was notably higher in 25mol% loading than that for a conventional loading of 5mol%. Consistently, acid-catalyzed glucose conversion was faster at this high loading, showing that a higher cellulose loading improves the pretreatment efficiency. In contrast, enzymatic hydrolysis was not enhanced by a high cellulose loading. A key difference between the activities in these two hydrolytic reactions is the catalyst size.