室温离子液体中纤维素的溶解及改性研究

发布时间：2018-04-06 02:37

本文选题：纤维素　切入点：离子液体　出处：《南京林业大学》2017年硕士论文

【摘要】：目前,随着煤、石油等化石能源的日益枯竭以及环境污染问题的日益加剧,对绿色可再生资源的开发研究越来越多。纤维素在自然界中储量丰富、廉价易得、可再生,是一种可替代化石燃料的生物质资源。天然纤维素中含有大量的分子内和分子间的氢键,不溶于大多数常规溶剂,这成为扩展纤维素应用的最大障碍之一。而用于纤维素溶解的传统溶剂体系具有稳定性差、挥发性大、毒性大、污染环境等缺点,因此,开发新的纤维素溶剂体系是高效、绿色利用纤维素资源的良好途径。本研究先合成了6种对称型季胺盐离子液体和2种非对称型季胺盐离子液体,平均得率在85%左右。研究了阳离子结构、离子液体/助溶剂比例、溶解温度及纤维素原料对离子液体/助溶剂混合体系溶解纤维素的影响。结果显示,上述四个因素对纤维素的溶解均有重大影响:阳离子结构为非对称型的对纤维素的溶解优于对称型的;离子液体比例过低或者过多都不易于纤维素的溶解;溶解温度越高,纤维素原料聚合度越低,则溶解速率越快。合成的离子液体中四丁基醋酸铵(TBAA)溶解纤维素速率最快,四丁基醋酸铵(TBAA)/二甲基亚砜(DMSO)(WTBAA=0.15)混合体系在25 oC下溶解1 wt%滤纸仅需3.5 min。1-己基-三乙基醋酸铵(N2226CH3COO)溶解纤维素的量最多,N2226CH3COO/DMSO(WN2226CH3COO=0.35)混合体系在25 oC下最多可溶解11.37 wt%滤纸。此外,对比TBAA/DMSO与N2226CH3COO/DMSO这两个溶剂体系,溶解相同量纤维素时,后者得到的纤维素溶液黏度更低。本研究对离子液体TBAA/DMSO混合体系溶解纤维素机理进行了探讨。选用纤维二糖为纤维素模型物,微晶纤维素为纤维素原料,通过1H NMR、13C NMR、ATR-FTIR、电导率和黏度等方法对溶解过程进行表征,我们推测在TBAA/DMSO混合体系中,TBAA存在着“离子对”和“离子对分离”两种状态;当WTBAA=0.25~0.15时属于“离子对”状态,即醋酸根阴离子与四丁基铵阳离子结合较紧密;而WTBAA=0.15~0.05时属于“离子对分离”阶段,此状态有助于TBAA上的醋酸根阴离子与纤维素上的羟基作用形成强的氢键(阴离子)O···H-O(纤维素)。另外,DMSO在混合体系中不仅起到了降低体系黏度的作用,还与溶解的纤维素作用使其稳定存在于溶液中,促进纤维素的溶解。此外,我们对纤维素在TBAA/DMSO均相溶解体系中的无催化剂法丁二酸酐改性进行了研究。探讨了混合体系中TBAA含量、丁二酸酐比例,反应时间和反应温度对纤维素改性的影响,并用FTIR、TGA、XRD,固体CP/MAS 13C NMR光谱(CP/MAS 13C NMR)和SEM对改性纤维素进行了表征。结果表明通过对反应条件的控制可制备得到取代度范围在0.337~1.191之间的改性纤维素。改性纤维素可以用于重金属离子Cu2+和Cd2+的吸附。我们研究了改性纤维素取代度、金属溶液pH、吸附时间、吸附温度对吸附效果的影响。前两个因素对吸附效果影响最大,吸附温度次之。改性纤维素在室温下较短时间即可对Cu2+和Cd2+实现良好吸附。对Cu2+和Cd2+的最大吸附容量分别为51.92 mg/g和50.35 mg/g。
[Abstract]:At present, with the increasing depletion of coal, oil and other fossil energy and environmental pollution become increasingly serious, more and more research and development of green renewable resources. Cellulose in the nature reserves are abundant, cheap, renewable, is an alternative to fossil fuel raw material resources. Natural cellulose contains a large number of molecules and intermolecular hydrogen bonds, insoluble in most common solvents, it has become one of the biggest obstacle to expanding applications. For traditional cellulose dissolved cellulose solvent systems have poor stability, high volatile, high toxicity, environmental pollution and other shortcomings, therefore, the development of new cellulose solvent system is efficient, green with a good way of cellulose resources. This study first synthesized 6 kinds of symmetric quaternary ammonium ionic liquids and 2 asymmetric quaternary ammonium ionic liquid, the average yield is about 85%. The effects of cationic structure, The ionic liquid / solvent ratio, temperature and the effect of dissolved cellulose materials on ionic liquid / solvent mixture to dissolve cellulose. The results showed that the dissolution of these four factors have a significant impact on the cellulose cation structure is asymmetric type of cellulose dissolved in the ionic liquid symmetrical; dissolution ratio is too low or too many are not easy to dissolve cellulose; the higher the temperature is, the lower the degree of polymerization of cellulose material, then the dissolution rate more quickly. The ionic liquid in four Butyl Ammonium acetate (TBAA) dissolved cellulose rate, four Butyl Ammonium acetate (TBAA) / two dimethyl sulfoxide (DMSO) (WTBAA=0.15) only mixed the system was dissolved in 25 oC 1 wt% 3.5 min.1- three - ethyl hexyl Filterpaper ammonium acetate (N2226CH3COO) dissolved cellulose was highest in N2226CH3COO/DMSO (WN2226CH3COO=0.35) hybrid system under 25 oC the dissolved 11.37 wt% filter paper. In addition, compared with the TBAA/DMSO and N2226CH3COO/DMSO of the two solvent system, the same amount of dissolved cellulose, cellulose solution viscosity lower the latter. This study discusses the ionic liquid TBAA/DMSO mixed system selection mechanism. The dissolution of cellulose fiber two sugar as model cellulose, microcrystalline cellulose as cellulose raw materials, by 1H NMR, 13C NMR. ATR-FTIR, electrical conductivity and viscosity methods were used to characterize the dissolution process, we hypothesized that the TBAA/DMSO hybrid system, TBAA has "ion pair" and "ion of separation" two states; when WTBAA =0.25~0.15 belongs to the "ion pair", namely the acetate anion and four Butyl Ammonium Cation combination; WTBAA=0.15~0.05 when belong to the ion pair separation stage, the effect of hydroxy state contribute to TBAA on cellulose acetate anion and the formation of hydrogen bond (strong anion O) - H-O (cellulose). In addition, DMSO in the mixed system not only to reduce the viscosity of the system, and the stability and dissolution of cellulose in solution, promote the dissolution of cellulose. In addition, we in the TBAA/DMSO homogeneous dissolution system in cellulose fadin's two anhydride catalyst the modification was studied. To investigate the content of TBAA in the mixed system, Ding two anhydride ratio, reaction time and reaction temperature on the effect of modified cellulose, and FTIR, TGA, XRD, CP/MAS (CP/MAS 13C NMR spectra of solid 13C NMR) and SEM on the modified cellulose were characterized. The results showed that the prepared replace the modified cellulose in 0.337~1.191 concentration range by controlling the reaction conditions. Modified cellulose can be used for the adsorption of heavy metal ions Cu2+ and Cd2+. We study the degree of substitution of modified cellulose, metal solution pH, adsorption time, adsorption The influence of temperature on the adsorption effect. The first two factors have the greatest influence on the adsorption effect and the adsorption temperature is second. Modified cellulose can achieve good adsorption for Cu2+ and Cd2+ at room temperature for a short time. The maximum adsorption capacity for Cu2+ and Cd2+ is 51.92 mg/g and 50.35 mg/g., respectively.

【学位授予单位】：南京林业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O636.11

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