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木质素高值化利用制备聚氨酯以及酚类的研究
其他题名Conversion of lignin to high value-added PUF and phenols
罗皓
学位类型工程硕士
导师徐建
2014-04
学位授予单位中国科学院研究生院
学位专业生物工程
关键词木质素   预处理   液化   puf   固体超强酸   酚类化合物
摘要木质素是自然界含量最丰富的芳香类化合物,具有资源量大,来源广,可再生等优点,然而由于木质素的复杂结构以及提取转化技术的限制,使其并未得到充分高值化利用。为提高木质素的品质,增强其在制备高分子化合物的共聚程度并开发木质素转化工艺,以提高其高值转化潜力,本论文开展了一下研究。 首先,针对木质素品质低的问题,选择了两种具有应用潜力的预处理技术,即湿法球磨(WBM)和离子液体预处理(ILP),对工业木质素进行了处理,并考察了预处理对木质素的平均分子量、分散性以及官能团的影响。结果表明,与WBM相比,ILP能更有效的降低木质素平均分子量和分散性,从而提高木质素的均一性。经[Emim][OAc]处理后的木质素样品粒径得到了显著下降,表面出现了明显的孔道结构,并且木质素样品的去甲基化程度达到45%。另外,与[Bmim]Cl相比, [Emim][OAc]处理后的木质素的酚羟基和羧基能维持在较高水平。这有利于提高其在后续转化过程中的反应活性,并在随后的催化转化制备酚类研究中得到了验证。 其次,针对木质素在制备高分子化合物的共聚程度低的问题,采用液化的方法将木质素转化为多元醇并制备了聚氨酯泡沫(PUF),对木质素液化工艺参数进行优化,考察了木质素基多元醇相关参数变化同时对制备的多元醇和聚氨酯进行了表征。结果表明,木质素液化制备多元醇的最佳条件为:PEG-400:甘油=4:1(w/w),催化剂浓H2SO4用量3%(相对于液化剂质量),固液比为1:5(w/w),反应温度T=140 ℃、时间t=1 h。在此基础上,以麦草木质素磺酸钠为原料,在通氮气条件下制备的多元醇较商业型的木质素基多元醇具有更高的羟值以及更低的水分含量。以不同比例混合的木质素基多元醇与商业型聚醚多元醇制备的聚氨酯比单独由商业聚醚多元醇合成的聚氨酯具有更高的抗压强度与密度,热稳定性也得以提高。以100%木质素基多元醇制备的聚氨酯,抗压强度为0.86 MPa,密度为109.36 Kg/m3, 较商业聚醚多元醇合成的聚氨酯分别提高了3.44倍和3.89倍,达到了国家标准(GB8813-88和GB/T6363-95)。 然后,针对浓硫酸催化木质素制备多元醇存在的中和、脱盐等问题,采用了固体超强酸替代浓硫酸液化木质素制备多元醇,并对制备的多元醇进行了聚氨酯的合成。从实验结果看,固体超强酸催化制备的木质素基多元醇具有更高的羟值、更低的分子量且无酸残留(酸值=0)。对其转化PUF的物性参数分析可知,固体超强酸催化液化得到的木质素基多元醇与二苯基甲烷二异氰酸酯(MDI)具有更好的反应活性、更好的发泡性能以及更规则的泡孔结构。 最后,对木质素催化降解制备芳香类化合物进行了探索。采用了双液相体系对木质素进行了催化转化的研究,并对预处理后的木质素转化效果进行了验证。研究表明,经离子液体预处理的木质素样品相对于其它样品催化转化为苯酚的得率明显上升,经过两轮循环后苯酚的收率接近8%。 另外,在中、高温双液相条件下,木质素催化降解的最佳条件为:初始pH=11,反应时间8h,其中初始pH和反应时间对香兰素和苯酚的得率具有显著影响(P<0.05)。 本论文的研究结果揭示了预处理对木质素结构参数的影响,且通过催化转化实验验证了离子液体预处理提高木质素品质的可行性。同时通过液化的方法将木质素转化为多元醇并制备成PUF的研究表明,液化后的木质素多元醇与MDI具有良好的共聚行为,而固体超强酸作为液化催化剂所得的多元醇具有更好的反应性能且聚氨酯发泡性能更优。预处理后的木质素更利于苯酚的生成。所有这些将会为木质素高值利用提供理论基础和实验依据。
其他摘要As the most abundant and renewable aromatic compounds in nature, lignin has attracted much effort to employ it as feedstock to produce bio-based chemicals, materials and fuels. However, there has been rather slow progress made on lignin conversion due to its poor quality, low copolymerization in preparing of macromolecular compounds, and low catalytic conversion rate. In order to improve the properties of lignin enhancing its utilization efficiency, the present study was carried out on the following aspects: (1) Two pretreatment technologies including wet ball milling (WBM) and ionic liquid pretreatment (ILP) were empolyed to pretreat industrial lignin in order to improve its quality. The average molecular weight, polydispersity, surface morphology, and functional group changes were compared before and after pretreatment. A dramatic decrease of 23% on polydipersity was observed with lignin pretreated by phosphoric acid WBM, the phenolic hydroxyl content was increased by 9% with the same pretreatment. Compared to phosphoric acid WBM, the ILP treated lignin showed significant reduction on the average molecular weight and polydispersity. The decrease on particle size and the emergence of porous structure were found when lignin was treated with [Emim][OAc]. In addition, the remarkable reductions of 50% and 45% were observed on methoxy groups from lignin treated by [Bmim]Cl and [Emim][OAc], respectively. This greatly helped increase lignin reaction activity which has been verified in the catalytic conversion of lignin to produce aromatic compounds. (2) To improve the copolymerization of lignin with other chemical compuonds, lignin was liquefied to produce polyol which was used to synthesize Polyurethane foam (PFU) subsequently. The liquefaction process was optimized and the properties of lignin based polyol and PFU were analyzed. The results indicate that the optimal liquefaction condition of lignin was : PEG-400 : Glycerol = 4:1 (w/w), H2SO4=3%, solid and liquid ratio=1:5 (w/w),T=140 ℃, t=1 h. With the protection of nitrogen, the polyol prepared from wheat straw ligninosulfonate (WS), showed higher hydroxyl value and lower moisture content compared to the commercial lignin-based polyol. In addition, the PUF synthesized with different proportion of lignin-based polyol to commercial polyether polyol presented some special properties such as better thermostability, higher cpmpressive stress and density compared to the PUF prepared from 100% commercial polyether polyol. The compressive stress and density of PUF from 100% lignin-based polyol were 0.86 Mpa and 109.36 Kg/m3 respectively, which can meet the standard of GB8813-88. (3) In order to improve the liquefaction process catalyzed by sulfuric acid (SA) which can cause corrosion of equipment and high acid value of polyol products, solid superacid (SSA) was used as catalyst. Compared to SA-catalyzed polyol, the polyol catalyzed by SSA showed higher hydroxyl value, smaller molecular weight and on acid residue. Additionally, the SSA catalyzed lignin-based polyol has been found to possess better reactivity with MDI which led to a unifrom structure on the foam formation and porosity size in the PUF synthesis. (4) Catalytic degradation of lignin to produce aromatic compounds in a biphatic aqueous system was carried out. The results demonstrate that ILP treated lignin enhanced phenol yield to about 8% significantly withtwo round cyclic reaction. In addition, the catalytic reaction condition of lignin was optimized at the medium temperature (180 ℃): initial pH=11, reaction time=8 h. Moreover, the initial pH and reaction time were observed to have significant effect on the yield of vanillin and phenol (P<0.05). This study revealed the effects of the pretreatment on the structural change of lignin, and the feasibility of ILP to improve the lignin quality in order to enhance its conversion efficiency to phenols was also verified. Meanwhile, the results obtained from the liquefaction of lignin to produce polyol and synthesize PUF showed that the liquefied lignin present good copolymerization with MDI and the lignin-based polyol was characterized with better reactivity and foam formation when catalyze by SSA. This will provide both practical experience and theoretical basis to the lignin industrialization.
语种中文
文献类型学位论文
条目标识符http://ir.ipe.ac.cn/handle/122111/15573
专题研究所(批量导入)
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罗皓. 木质素高值化利用制备聚氨酯以及酚类的研究[D]. 中国科学院研究生院,2014.
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