Consequential improvement of reusing 1‑butyl‑3‑methylimidazolium tetrafluoroborate and dimethyl sulfoxide to enhance enzymatic hydrolysis

Ionic liquid pretreatment is a powerful technique that can deconstruct agricultural residues and remove lignin simultaneously to provide an easy access to fibers for lignocellulose-degrading enzymes. In this work, the effect of reusing a mixture of ionic liquid and dimethyl sulfoxide (DMSO) on the delignification of corncobs, followed by hydrolysis of cellulose, has been investigated. The solid lignin percentage of corncob sample pretreated at a low temperature for 3 h with the first round of reused 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) and added DMSO at 90 °C (method B) is 9.88 ± 0.17%,
much lower than 19.18 ± 0.10% solid lignin of raw corncob. After being reused for four rounds, [BMIM]BF4:DMSO of method B can enhance the cellulose conversion up to 70.43%. Meanwhile, when reusing [BMIM]BF4:DMSO of method A (DMSO added at room temperature before heating to 90 °C), the cellulose conversion is much less (46.54%). From the characterization of lignocellulose structure by Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) of the first reuse of [ BMIM]BF4 and DMSO of method B, it is found that the lateral order index (LOI) value is 1.07 ± 0.01 and the crystallinity index (CI) value is 24.84 ± 0.05. These values are lower than those of the reused combination [BMIM]
BF4 and DMSO in method A (1.12 ± 0.02 LOI and 30.12 ± 0.01 CI values). Moreover, the reuse of [BMIM]BF4:DMSO pretreatment in method B shows at least 70% cellulose conversion in the fourth round.