熔盐水合物选择性水解纤维素制备葡萄糖

Glucose Production from Cellulose via Selective Hydrolysis in Molten Salt Hydrate

针对目前熔盐水合物(MSH)对纤维素的溶解、水解机理尚不明确这一问题,本文系统地研究了纤维素在Li^(+),Na^(+),K^(+),Zn^(2+)阳离子及Cl^(-),Br^(-),I^(-)阴离子所组成的MSH中水解的情况,筛选出对纤维素水解效果最佳的熔盐——LiBr,并研究了体系酸性对水解的影响规律.结果表明,MSH中阳离子Na^(+)和K^(+)在水中的有限溶解度导致没有足够的阳离子与纤维素中的氧原子配位,无法为糖苷键断裂提供足够的路易斯酸;MSH中的阴离子Cl^(-)的电负性不足以与纤维素中的羟基形成足够的新的氢键,纤维素溶解度不足导致水解效果较差.在非酸化体系中,130℃,5 h的反应条件下,纤维素在LiBr熔盐体系内可以被选择性水解为水溶性低聚糖和葡萄糖单糖,收率分别为57.2%和29.0%.在酸性环境下,MSH能有效催化纤维素糖苷键断裂,质量分数0.01%(HCl)LiBr熔盐体系于100℃水解纤维素30 min后,产物以寡聚葡萄糖为主,聚合度在4~13之间.酸性的提升可以提高糖苷键的断键效率;质量分数0.1%(HCl)LiBr在100℃,30 min条件下水解纤维素,葡萄糖得率可以达到90.9%.

To address the challenges of the unclear mechanism of cellulose dissolution and hydrolysis in molten salt hydrate(MSH).This work systematically studied the hydrolysis of cellulose in molten salts hydrate consisting of different cations(e.g.,Li^(+),Na^(+),K^(+),Zn2^(+)),and anions(e.g.,Cl^(‒),Br^(‒)and I^(‒)),and screened the best molten salt for cellulose hydrolysis,LiBr,and studied the effect of acidity on cellulose hydrolysis.The result indicated that the limited solubility of the cation Na^(+)and K^(+)resulted in the insufficient coordination between cations and oxygen atoms in the cellulose,which cannot provide sufficient Lewis acidity for glycosidic bonds cleavage.Additionally,the anion Cl^(‒)in MSH has limited electronegativity,which cannot form massive hydrogen bonds with the hydroxyl groups in cellulose,resulting in a limited solubility and thereby caused negative effect on hydrolysis.Under the reaction conditions of 130℃and 5 h in a non-acidified system,cellulose can be selectively hydrolyzed into water-soluble oligosaccharides and glucose with the yield of 57.2%and 29.0%,respectively.The results also show that the MSH can catalyze the cleavage of cellulose glycoside bonds and decrease the cellulose degree of polymerization(DP)in an 0.01%(HCl)dilute acidic MSH at 100℃for 30 min ranging from 4 and 13.Improvement of acidity can enhance the cleavage efficiency of glycosidic bond cleavage.When the acidity increased to 0.1%(HCl),a high yield of glucose at 90.9%can be achieved at 100℃for 30 min.