The Study Of Lignin Model Compound Dissolution In Ionic Liquid-water Mixtures

With the depletion of fossil resources, to seek some kinds of energy alternatives is becoming more and more necessary. Development and utilization of renewable resources will be the main forms of energy in the future, especially lignocelluloses biomass which is an important resource with the advantages of carbon neutrality, storability and abundance, is attracting more and more researchers’ attention. Cellulose can be converted into fuels and fine chemicals through chemical and biotechnology process, and lignin which is only inferior to cellulose content in biomass is a natural macromolecular polymers with aromatic characteristics that can be utilized as raw materials for fuel and chemicals after deeply processed, or directly used as flame retardants, reinforcing agent, plastic packing etc.. Therefore, Biomass resources have broad prospects for development and application.How to effectively separate the component of biomass is a poser which comes first and always confused researchers. The traditional methods to extract lignin by the acid, alkali methods will destroy the structure of lignin, even affect the subsequent modification, and caused serious environmental pollution. Ionic liquids have been paid more attention by researchers after Rogers found that the room temperature ionic liquid [BMIM]Cl can dissolve the cellulose and the lignin in wood.The previous study of our group have found that the addition of water in ionic liquid can facilitate the dissolution of lignin, however, we have no idea about the mechanism of the dissolution which will hinder the further research of ionic liquid-water mixtures and lignin to some extent. Lignin is a kind of natural polymeric compound which consists of many functional groups, such as methoxy and hydroxyl, ether bond, double bond and so on. Thus, to explore the interaction between ionic liquid-water mixtures and lignin is of great difficulty. we have the principle of from simple to complex, so we choose lignin model compound in this study to explore its dissolution behavior in ionic liquid-water mixtures. We intend to put forward the mechanism of lignin dissolution in ionic liquid-water mixtures by analyzing the corresponding spectra.In this thesis, the main research contents include:1, preparation of different kinds and concentrations of ionic liquid solution, selected 2,6-dimethoxyp Henol as simple phenolic lignin model compound, and determine its solubility in ionic liquid-water mixtures; 2, probing the change of microenvironment of the system by UV; 3, detecting molecular interactions between 1-butyl-3-methylimidazolium chloride/water mixtures and lignin model compound by total reflectance infrared spectroscopy(ATR-IR).The results showed that: 1,different kinds of ionic liquid-water mixtures have different abilities to dissolve lignin model compound and the dissolving tendency showed various. The dissolving ability of alkaline ionic liquid-water mixtures were positively related to its concentration, and we believed that some chemical reaction may be occurred during the dissolving process according to the change of solution color. The neutral ionic liquid-water mixtures showed the similar property when used to dissolve lignin and lignin model compound(the solubility of lignin or lignin model compound achieve the peak when ionic content was about 70 wt%).2, The date of UV spectra showed that the micro polarities of ionic liquid-water mixtures have a maximum when XIL=0.1. and the micro polarity sharply decreased when XIL increased to 0.5, and became constant afterwards. The addition of lignin model compound mainly affect the solvent when XIL=0.1-0.5, and will lead to a lower micro polarity.3, The ATR spectrum of ionic liquid-water mixtures indicated that the state of ionic liquid maybe experienced the following process with the addition of ionic liquid: completely free hydrated ions, hydrated ion pairs, tight ion pairs and aggregated state of ionic liquid. Meanwhile, blue shifts of OH vibration indicated the state of water also changed. We speculated that the change of microstructure was the critical factor to influence lignin model compound solubility.