微波水热法碱活化降解木质素及木质素基酚醛树脂的制备

发布时间：2018-02-05 04:01

  本文关键词： 木质素 微波加热 碱活化 固体碱 酚醛树脂　出处：《福建农林大学》2017年硕士论文　论文类型：学位论文

【摘要】：木质素做为含量仅次于纤维素的天然高分子化合物,它的高值化利用对于新能源开发、化工原料替代和环境保护等方面都具有非常积极的意义,然而天然木质素结构复杂,分子量一般在几万到几十万之间,反应活性较低,因此长期以来无法对其进行充分利用,是一种极大的能源浪费。本论文以禾草类玉米芯木质素为研究对象,利用其分子中大量存在的醚键在不同碱性催化剂催化下的断裂反应,得到低分子量、多羟基官能团的活性降解产物,用以替代酚醇类物质制备木质素基酚醛树脂(LPF),实现木质素的资源化利用。首先,根据国内禾草类植物产量丰富的特点,选取玉米芯木质素为研究对象。采用元素分析、GPC、FT-IR、UV、1H-NMR、TG等分析手段分析了原料玉米芯木质素的元素组成、官能团结构、酚羟基数量、热分解性能等。研究结果表明原料木质素的分子量较大,分子量分布较为宽泛,难以直接用于酚醛树脂的合成。木质素中有着较高的苯环含量,同时由于氢、氧元素在木质素中所占相对比重较大,因此醚键、甲氧基、羟基等特征官能团的相对含量也较高。其次分别以NaOH、KOH传统碱为催化剂,在微波辅助下水热活化降解木质素。探究了微波与常规加热方法,反应温度、反应时间、木碱比等因素对木质素碱活化降解反应的影响规律。实验结果表明,木质素的碱活化降解反应主要发生的是醚键的水解断裂,生成了新的酚羟基衍生物,微波加热可以大幅度提高活化降解反应的速度与效率。同时确立了这两种不同碱微波水热降解木质素的最优工艺条件:反应温度160℃,反应时间45 min,木碱比1:1,在此条件下木质素的重均分子量分别降低到2100和1840,酚羟基含量分别增加58.4%和50.8%。采用浸渍法制备出负载型CaO/MgO和KOH/SBA-15固体碱催化剂,在微波辅助下采用固体碱活化降解木质素。优化了固体碱催化剂制备条件,同时考察了两种固体碱在不同的实验条件下的降解效率。实验发现,固体碱的碱度越大,催化效率越大,在最佳制备工艺条件下CaO/MgO固体碱的碱度最高可达29.2,KOH/SBA-15固体碱的碱度最高可达18.9。同时降解产物的表征结果表明,与玉米芯木质素相比,降解木质素的酚羟基含量明显升高,增长量最高分别可达78.2%和70.2%,甲氧基含量降低,分子量及其分布系数也有一定程度的降低,同时降解反应后木质素分子更加简单均一,木质素的活性官能团酚羟基数量提升,反应活性得到增强,使其更适用于制备木质素基酚醛树脂胶。最后使用降解改性后的玉米芯木质素替代和部分替代苯酚,合成LPF胶,并对LPF胶的基本性能进行检测。实验结果表明使用传统碱活化和固体碱活化的木质素合成的LPF胶都具有良好的性能,符合国家标准的要求,当改性木质素替代苯酚的量达到50%时,制备出的LPF胶工业化利用价值最高。
[Abstract]:Lignin, as a natural macromolecule, is second only to cellulose in content. Its high value utilization is of great significance for the development of new energy, the substitution of chemical raw materials and environmental protection. However, the structure of natural lignin is complex, the molecular weight is generally between tens of thousands and hundreds of thousands, the reaction activity is low, so it can not be fully utilized for a long time. It is a great waste of energy. In this paper, the low molecular weight was obtained by using the cleavage reaction of ether bond in gramineous corncob lignin under the catalysis of different basic catalysts. The active degradation products of polyhydroxyl groups are used to replace phenols to prepare lignin-based phenolic resin LPFs to realize the utilization of lignin. First of all. According to the rich yield of grasses in China, corncob lignin was selected as the research object, and the elemental analysis of GPC-FT-IRU UVN 1H-NMR was used. The elemental composition, functional group structure, phenolic hydroxyl content and thermal decomposition properties of the raw corn cob lignin were analyzed by TG and other analytical methods. The results showed that the molecular weight of the raw material lignin was high. The molecular weight distribution is relatively broad, it is difficult to be directly used in the synthesis of phenolic resin. Lignin has a higher benzene ring content, and because of the relatively large proportion of hydrogen and oxygen elements in lignin, so ether bond, methoxyl. The relative content of characteristic functional groups such as hydroxyl groups is also high. Secondly, the traditional NaOHHHOH base is used as catalyst to degrade lignin in water with microwave assisted thermal activation. The microwave and conventional heating methods are explored. The effects of reaction temperature, reaction time and ratio of lignin to alkali on the activation and degradation of lignin were studied. A new phenolic hydroxyl derivative was synthesized. Microwave heating can greatly improve the rate and efficiency of the activated degradation reaction. The optimum conditions of these two kinds of alkali microwave hydrothermal degradation of lignin were established: reaction temperature 160 鈩，

本文编号：1492062