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 degrees 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 degrees 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 LOT and 30.12 +/- 0.01 CI values). Moreover, the reuse of [BMIM]BF4:DMS0 pretreatment in method B shows at least 70% cellulose conversion in the fourth round.

Automated summary

Ionic liquid pretreatment combined with dimethyl sulfoxide (DMSO) has been investigated in the delignification and cellulose hydrolysis of corncobs. Results showed that reusing the mixture of ionic liquid and DMSO can enhance cellulose conversion, and low temperature pretreatment can reduce lignin content.