核桃壳木质素提取及制备酚醛树脂泡沫的研究

发布时间：2019-04-11 08:37

【摘要】：木质素是自然界中来源最广泛的芳香类多聚物,具有储量丰富、可再生等优点。由于当前木质素提取工艺普遍存在着提取成本高、纯度低、均一性差的特点,使其应用依旧停留在燃烧供能、减水剂等较初级的水平,无法被有效的用于高附加值产品的生产。为开发出适合高纯木质素的提取工艺,本论文以核桃壳为原料,开展了如下研究:首先,开发了水热耦合高沸醇提取工艺并对其进行优化,以解决高沸醇提取木质素工艺效率低、含糖量过高而导致的品质差等不足。核桃壳首先经水热预处理,半纤维素含量被脱除83.45%,木质素含量则提高了 14.91%。随后,将水热预处理后的核桃壳用1,4-丁二醇提取木质素,提取率达到44.66%,比单独使用1,4-丁二醇提取高约14.66%左右。半纤维素的去除一方面使得后续高沸醇提取得到的木质素产品多糖含量减少到0.15%-3.70%,相比于常规高沸醇提取的4.10%-5.47%有了较大的提高;同时,使提取后残留在高沸醇中的糖分大大降低,为高沸醇的回收、循环利用提供了便利条件。其次,对碱法提取木质素进行了优化,同时将乙醇和碱相结合利用二者对木质素溶解的叠加效应提高其溶出率,并探索木质素沉淀过程中pH值对木质素产量和品质的影响规律。通过一系列实验及分析,得到了碱法溶出木质素的最佳条件为:NaOH用量12.5%(W/V),温度为190℃,时间为3.0 h。在此条件下,木质素的溶出率达到了 82.29%。通过乙醇和氢氧化钠耦合提取木质素的研究发现在180℃下经含有15.0%(W/V)NaOH的15%(V/V)乙醇溶液处理3.0h后,可使核桃壳中98.98%的木质素溶解。对溶解后的木质素进行不同pH条件沉淀回收研究,结果表明随pH值的减小,木质素的纯度越来越高。当pH达到1.00时,木质素的纯度可高达99.39%;通过扫描电镜观察发现,在pH降低的过程中,木质素亚微米颗粒之间接触越来越紧密,颗粒之间的界限越来越模糊,最终在木质素内部形成孔道,形成多孔结构。最后,对木质素在酚醛树脂合成中取代苯酚的应用进行了探索。通过将不同用量的木质素与苯酚、甲醛进行酚醛树脂合成试验,结果表明,在木质素添加量为10%时,泡沫压缩强度最好,为0.10 MPa,较未添加木质素的泡沫压缩强度提高了 38.88%,达到了 GBT 20974-2014中对Ⅰ型、Ⅱ型硬质酚醛泡沫的压缩强度要求。此外,通过比较碱木质素、碱醇木质素、高沸醇木质素所制备的酚醛树脂泡沫,发现碱木质素的表现较好,在添加量为10%时,压缩强度为0.47 MPa,较未添加木质素酚醛泡沫的提高了 571.42%,并能够达到GBT 20974-2014中对Ⅰ型、Ⅱ型、Ⅲ型硬质酚醛泡沫的压缩强度要求;电镜结果亦表明碱木质素基酚醛泡沫泡孔最小,泡孔结构均匀且完整。通过以上研究,得到了较高的木质素溶出率和较高的木质素品质,验证了水热耦合高沸醇和碱乙醇耦合提取高品质木质素的可行性。同时,经过木质素取代苯酚制备酚醛树脂泡沫的研究,发现了木质素基酚醛泡沫较未改性酚醛泡沫具有较好的品质。所有这些都将会为木质素的提取和应用提供理论基础和实验依据。
[Abstract]:Lignin is the most widely used aromatic polymer in nature, and has the advantages of rich reserves and renewable energy. The present lignin extraction process has the characteristics of high extraction cost, low purity and poor uniformity, and the application of the present lignin extraction process remains at a lower level such as the combustion energy supply and the water reducing agent, and can not be effectively used for the production of high-value-added products. In order to develop the extraction process suitable for high-purity lignin, the following research was carried out by using the walnut shell as the raw material: firstly, a hydrothermal coupling high-boiling alcohol extraction process is developed and the optimization is carried out to solve the problem that the high-boiling alcohol extraction lignin processing efficiency is low, And the quality difference caused by too high sugar content and the like is insufficient. The walnut shell was pretreated with hydrothermal method, the hemicellulose content was 83.45%, and the content of lignin increased by 14.91%. The lignin was then extracted with 1,4-butanediol, and the extraction rate was 44.66%, which was about 14.66% higher than that of using 1,4-butanediol alone. The removal of hemicellulose has the advantages that the content of the lignin product obtained by the subsequent high-boiling alcohol extraction is reduced to 0.15-3.70%, and compared with that of the conventional high-boiling-boiling alcohol, the content of the lignin product is greatly improved; meanwhile, the sugar content remaining in the high-boiling alcohol after extraction is greatly reduced, and the content of the high-boiling alcohol can be recovered, The cyclic utilization provides a convenient condition. Secondly, the alkali extraction lignin was optimized, and the effect of the pH value in the process of lignin precipitation on the yield and quality of the lignin was studied. By a series of experiments and analysis, the optimum conditions of the alkali-dissolved lignin were as follows: the dosage of NaOH was 12.5% (W/ V), the temperature was 190.degree. C. and the time was 3.0 h. In this condition, the dissolution rate of lignin was 82.29%. Studies on the extraction of lignin by coupling of ethanol and sodium hydroxide found that 98.98% of the lignin in the walnut shell was dissolved after 3.0 h treatment with a 15% (V/ V) ethanol solution containing 15.0% (W/ V) NaOH at 180.degree. C. The results show that the purity of the lignin is higher and higher with the decrease of the pH value. When the pH reaches 1.00, the purity of the lignin can be as high as 99.39%, and through the observation of the scanning electron microscope, the contact between the lignin sub-micron particles is more and more compact in the process of reducing the pH, and the boundary between the particles is more and more blurred, and finally, a pore canal is formed in the lignin to form a porous structure. Finally, the application of the substituted phenol in the synthesis of phenol-formaldehyde resin was explored. The results show that, when the content of lignin is 10%, the compression strength of the foam is the best, the compression strength of the foam with no lignin is increased by 38.88%, and the type I in GBT 20974-2014 is achieved. The compression strength requirement of type II rigid phenolic foam. In addition, by comparing the phenolic resin foam prepared by the alkali lignin, the alkali alcohol lignin and the high-boiling alcohol lignin, the performance of the alkali lignin is found to be better, when the addition amount is 10%, the compression strength is 0.47 MPa, and the increase of the lignin phenolic foam is increased by 571.42%, And the compression strength requirement of the type I, the type II and the type III hard phenolic foam can be achieved in the GBT 20974-2014, and the electron microscope result also indicates that the foam cells of the alkali lignin-based phenolic foam are the smallest, and the cell structure is uniform and complete. Through the above research, the high lignin dissolution rate and high lignin quality are obtained, and the feasibility of high quality lignin extraction by hydrothermal coupling high-boiling alcohol and alkali-ethanol coupling is verified. At the same time, the study of phenol-formaldehyde resin foam was prepared by lignin-substituted phenol, and it was found that the lignin-based phenolic foam had better quality than the unmodified phenolic foam. All of these will provide a theoretical basis and experimental basis for the extraction and application of lignin.
【学位授予单位】：中国科学院大学(中国科学院过程工程研究所)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ328.0

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