Study Of Pretreatment On Water Hyacinth By Surfactant-free Ionic Liquid Microemulsion

Lignocellulosic biomass is a kind of renewable resource, and the key of its degradation and utilization is effective pretreatment. The ionic liquid(IL) surfactant-free microemulsion(denoted as SFME) was constructed. Water hyacinth(WH), a lignocellulose feedstock, was pretreated by the surfactant-free ionic liquid microemulsions(ILMs). The lignocellulosic composition of WH changed and the total crystallinity index(TCI) of cellulose decreased, which can improve the efficiency of enzymatic hydrolysis of WH.Surfactant-free ionic liquid microemulsion consisting of 1-ethyl-3-methylimidazolium acetate([Emim]Ac), toluene, and double-solvent ethanol( which can be dissolved in both polar phase and non-polar phase) was constructed successfully, and its properties and microstructures were characterized. The specific research contents and results are as follows.(1) The ternary phase diagram of [Emim]Ac/ethanol/ toluene was investigated. A single-phase microemulsion region and a multiphase region were observed in the ternary phase diagram, showing that [Emim]Ac can be used as the polar phase to prepare surfactant-free microemulsion.(2) The three types of microemulsion, IL-in-toluene(IL/O), biocontinuous(BC) and toluene-in-IL(O/IL), were examined by conductivity techniques.(3) The polarity of [Emim]Ac domains in the IL/O microemulsion was investigated by UV-visible spectroscopy using methylorange as probe. The experimental results showed that the micro-polarity increased with increasing of [Emim]Ac content.(4) The single-phase region area didn’t change while the temperature increasing from 30 °C to 70 °C. The good thermal stability of the microemulsion system is conductive to pretreat lignocellulosic biomass.The raw WH was pretreated by the constructed surfactant-free ionic liquid microemulsions. The experimental results were summarized as follows.(1) The surfactant-free ionic liquid microemulsions have stronger penetration ability than ethanol and toluene, resulting in a higher delignification rate. The rising of pretreatment temperature and the prolongation of pretreatment time could enhance delignification rate. After the pretreatment of WH with ILMa(mass ratio of toluene: ethanol: [Emim]Ac=0.35: 0.3: 0.35) under 70℃ for 12 h, the lignin could be removed by 63.6%, and the cellulose content of the pretreated sample increased from 21.3% in the untreated WH to 33.3%.(2) The crystallinity(CrI) of pretreated WH samples increased slightly since the enrichment of cellulose, the total crystallinity index(TCI) of cellulose decreased and the surface of pretreated WH particles became rougher, which can do contribution to the enzymatic saccharification of WH.(3) After being enzymatically hydrolyzed for 48 h, the maximum reducing sugar yield of the pretreated WH was 563.7 mg/g, and its hydrolysis yield(86.1%) was nearly four and a half times of that of the untreated one(20.2%).(4) Ionic liquid [Emim]Ac can be recycled by vacuum distillation and the chemical structure of recycled [Emim]Ac did not change.