發(fā)布時間：2019-04-11 08:37

【摘要】：木質(zhì)素是自然界中來源最廣泛的芳香類多聚物,具有儲量豐富、可再生等優(yōu)點。由于當前木質(zhì)素提取工藝普遍存在著提取成本高、純度低、均一性差的特點,使其應用依舊停留在燃燒供能、減水劑等較初級的水平,無法被有效的用于高附加值產(chǎn)品的生產(chǎn)。為開發(fā)出適合高純木質(zhì)素的提取工藝,本論文以核桃殼為原料,開展了如下研究:首先,開發(fā)了水熱耦合高沸醇提取工藝并對其進行優(yōu)化,以解決高沸醇提取木質(zhì)素工藝效率低、含糖量過高而導致的品質(zhì)差等不足。核桃殼首先經(jīng)水熱預處理,半纖維素含量被脫除83.45%,木質(zhì)素含量則提高了 14.91%。隨后,將水熱預處理后的核桃殼用1,4-丁二醇提取木質(zhì)素,提取率達到44.66%,比單獨使用1,4-丁二醇提取高約14.66%左右。半纖維素的去除一方面使得后續(xù)高沸醇提取得到的木質(zhì)素產(chǎn)品多糖含量減少到0.15%-3.70%,相比于常規(guī)高沸醇提取的4.10%-5.47%有了較大的提高;同時,使提取后殘留在高沸醇中的糖分大大降低,為高沸醇的回收、循環(huán)利用提供了便利條件。其次,對堿法提取木質(zhì)素進行了優(yōu)化,同時將乙醇和堿相結(jié)合利用二者對木質(zhì)素溶解的疊加效應提高其溶出率,并探索木質(zhì)素沉淀過程中pH值對木質(zhì)素產(chǎn)量和品質(zhì)的影響規(guī)律。通過一系列實驗及分析,得到了堿法溶出木質(zhì)素的最佳條件為:NaOH用量12.5%(W/V),溫度為190℃,時間為3.0 h。在此條件下,木質(zhì)素的溶出率達到了 82.29%。通過乙醇和氫氧化鈉耦合提取木質(zhì)素的研究發(fā)現(xiàn)在180℃下經(jīng)含有15.0%(W/V)NaOH的15%(V/V)乙醇溶液處理3.0h后,可使核桃殼中98.98%的木質(zhì)素溶解。對溶解后的木質(zhì)素進行不同pH條件沉淀回收研究,結(jié)果表明隨pH值的減小,木質(zhì)素的純度越來越高。當pH達到1.00時,木質(zhì)素的純度可高達99.39%;通過掃描電鏡觀察發(fā)現(xiàn),在pH降低的過程中,木質(zhì)素亞微米顆粒之間接觸越來越緊密,顆粒之間的界限越來越模糊,最終在木質(zhì)素內(nèi)部形成孔道,形成多孔結(jié)構(gòu)。最后,對木質(zhì)素在酚醛樹脂合成中取代苯酚的應用進行了探索。通過將不同用量的木質(zhì)素與苯酚、甲醛進行酚醛樹脂合成試驗,結(jié)果表明,在木質(zhì)素添加量為10%時,泡沫壓縮強度最好,為0.10 MPa,較未添加木質(zhì)素的泡沫壓縮強度提高了 38.88%,達到了 GBT 20974-2014中對Ⅰ型、Ⅱ型硬質(zhì)酚醛泡沫的壓縮強度要求。此外,通過比較堿木質(zhì)素、堿醇木質(zhì)素、高沸醇木質(zhì)素所制備的酚醛樹脂泡沫,發(fā)現(xiàn)堿木質(zhì)素的表現(xiàn)較好,在添加量為10%時,壓縮強度為0.47 MPa,較未添加木質(zhì)素酚醛泡沫的提高了 571.42%,并能夠達到GBT 20974-2014中對Ⅰ型、Ⅱ型、Ⅲ型硬質(zhì)酚醛泡沫的壓縮強度要求;電鏡結(jié)果亦表明堿木質(zhì)素基酚醛泡沫泡孔最小,泡孔結(jié)構(gòu)均勻且完整。通過以上研究,得到了較高的木質(zhì)素溶出率和較高的木質(zhì)素品質(zhì),驗證了水熱耦合高沸醇和堿乙醇耦合提取高品質(zhì)木質(zhì)素的可行性。同時,經(jīng)過木質(zhì)素取代苯酚制備酚醛樹脂泡沫的研究,發(fā)現(xiàn)了木質(zhì)素基酚醛泡沫較未改性酚醛泡沫具有較好的品質(zhì)。所有這些都將會為木質(zhì)素的提取和應用提供理論基礎和實驗依據(jù)。
[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.
【學位授予單位】：中國科學院大學(中國科學院過程工程研究所)
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TQ328.0

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