Studies On Separation Of Lignin From Corn Stalks

With the increasingly serious of environmental pollution and energy crisis, humans gradually began to realize the serious consequences brought by the deterioration of the harmonious relationship between man and nature. The renewability and biodegradability of lignocellulosic biomass has caused an increasing attention and lignin which is the abundant reserves of nature has become an important renewable resource. As a new type of "green solvents", ionic liquids have a relatively strong ability to dissolve lignin in corn stalks and so they will have a good application prospect in the utilization of biomass waste.In this paper, the lignin dissolution rate and the lignin selective dissolution capacity were used as the evaluation and the methods by ionic liquids and biology were respectively used to the dissolution and degradation of the lignin in corn stalks in order to study the optimum conditions and then compare and analyze their advantages and disadvantages.A synthesis method which uses anion exchange resin as an intermediary has been proposed to obtain high-purity ionic liquids in this article. Four kinds of anionic functionalized ionic liquids were designed and synthesized, such as [BMIM][HCOO],[BMIM][CH3COO],[BMIM][CH3CH2COO] and [BMIM][N(CN)2], and by means of ’H-NMR and13C-NMR the chemical structure of the ionic liquids were characterized and validated. The orthogonal experiment of [BMIM][CH3C00] which was carried on corn stalks shows that the reaction temperature is the most important factor to affect the lignin dissolution rate. By the single factor comparison experiment in which the four ionic liquids dissolve the corn stalks, we can get that in the solid-liquid ratio of5%, reaction time of24h and the reaction temperature of140℃,[BMIM][N(CN)2] under this condition has the highest lignin dissolution rate which is75.15%, and has the strongest lignin selective dissolution capacity, the highest selective dissolution coefficient η up to1.8073.The laccase can degradate the acid soluble lignin and acid insoluble lignin in corn stalks in different degrees, and the degradation specificity of the laccase on the acid-insoluble lignin are better than the acid-soluble lignin. In the laccase concentration of U·g-1, the reaction temperature of45℃, the reaction time of5h, the pH value of6.5and the solid-liquid ratio of1:25, the laccase under this condition has the highest lignin dissolution rate. Adding different volume percentage of the three kinds of fatty acid ionic liquids to the laccase can have a certain negative impact on the laccase activity. The greater the volume ratio is, the more significant the inhibition will be; in the volume ratio of10%, the ionic liquid completely inhibits the laccase activity and laccase is in a inactivated state;[BMIM][HCOO] has the most obvious inhibition effect on laccase activity.By a comparison of the ionic liquid method and the laccase method, the former has a strong ability to dissolve the lignin and the lignin dissolution rate is high, the latter has a strong lignin selective dissolution capacity but the lignin dissolution rate is low.