Dissolving lignocellulosic biomass in a 1-butyl-3-methylimidazolium chloride–water mixture

An ionic liquid (IL)–water mixture employed to treat lignocellulosic biomass is promising. The addition of water decreases viscosity and process cost so as to improve the IL practical application. In this work, effects of temperature (50–170 °C), water content (0–80 wt%), treating duration (0.5–4 h) and pressure (0.1–3.2 MPa) on treating legume straw process using a 1-butyl-3-methylimidazolium chloride ([C4mim]Cl)–water mixture were experimentally investigated. Legume straw was found to be partially dissolved, and the dissolved substances can be flocculated by adding the coagulating agent—water (equal to volume of the solution). For this process at 0.1 MPa, the maximum 29.1 wt% legume straw is dissolved in the [C4mim]Cl–water mixture with water content of 20 wt% at 150 °C during 2 h, which is much higher than 9.8 wt% using pure [C4mim]Cl. A hemicellulose-free lignin-rich material (64.0 wt% lignin and 35.3 wt% cellulose) is obtained by adding the water. Even for 0.5 h, 22.3 wt% of legume straw is dissolved in the case of water content of 20 wt%, 150 °C and 0.1 MPa. High pressure favors the dissolution of legume straw but lignin content in the residue has no obvious change. The addition of proper amount of water facilitates the dissolution of legume straw and a relative rapid dissolving rate can be achieved in a [C4mim]Cl–water mixture. There are great differences in chemical and physical properties between legume straw and the obtained samples (residue and floc) due to the dissolution and reconstitution.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Legume straw was found to be partially dissolved in 1-butyl-3-methylimidazolium chloride ([C4mim]Cl)–water mixture. ► A hemicellulose-free lignin-rich material is obtained from the solution by adding the coagulating agent—water. ► The temperature, water content and pressure greatly influence the dissolution of legume straw. ► Adding proper amount of water promotes cracking lignocellulosic network and a relative rapid dissolving rate can be achieved.