Enhanced delignification of cornstalk by employing superbase TBD in ionic liquids

Abstract

The delignification of cornstalk was efficiently accomplished by using 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as an additive in 1-allyl-3-methylimidazolium acetate ([Amim][OAc]). When 1.0 wt% TBD was added to [Amim][OAc], the cellulose and lignin contents of cellulose rich material (CRM) were achieved to be 39.12% and 6.74%, respectively. With the addition of 0.1 wt% TBD to [Amim][OAc], the lignin content of CRM could even be reduced to 2.06% without considering the cellulose content. There could be two possible reasons for the enhanced delignification of cornstalk by adding TBD in [Amim][OAc]. One is the alkalinity and exposed nitrogen atoms of TBD, which make it an efficient dibasic nucleophile and helpful for the lignin β-O-4 ether bond cleavage reaction. The other one is the decreased interaction energy of [Amim]⁺ and [OAc]⁻ from 99.1 kcal mol⁻¹ to 89.2 kcal mol⁻¹ with the addition of TBD, which makes the [Amim]⁺ and [OAc]⁻ easier to interact with the cornstalk components. Simultaneously, the CRM regenerated from the system of [Amim][OAc] + TBD was effectively hydrolyzed by cellulase with 98% enzymatic hydrolysis yield, which proved that the cellulose structures were highly disrupted and lignin was significantly removed in the CRM.