木质素模型物的氧化酯化反应研究

发布时间：2019-07-01 12:53

【摘要】：近年来,由于化石能源的不断枯竭和环境污染日益加剧,迫使人类寻找新型生物质能源。生物质包括纤维素、半纤维素和木质素等,其中木质素含量约占25%左右,目前每年以造纸工业废液等形式排放到自然界,不仅污染环境,而且木质素的高附加值化未能实现。本论文,以木质素模型化合物为研究对象,可以在一定程度上,探寻提高木质素附加值有效途径,因此,开展木质素模型化合物的催化转化研究具有重要的科学意义和应用价值。首先,以纳米金属作为催化剂,探究香草醛经氧化酯化合成香草酸甲酯产品的过程。采用沉积沉淀法制备了纳米金、铂、钯负载的固体催化剂,其中针对纳米金催化剂的制备,采用了三种不同方法合成Au/Al_2O_3,Au-R/Al_2O_3,Au-h/Al_2O_3催化剂,并将上述催化剂应用于催化香草醛与甲醇间的氧化酯化反应。研究发现,以Au-h/Al_2O_3为催化剂、氧气为氧化剂、140℃反应4小时后,香草醛的转化率为98.1%,主产物香草酸甲酯的选择性高达为99.1%。同时对Au-h/Al_2O_3催化剂做了5次循环实验,发现香草酸甲酯的收率仍保持96.1%以上,说明催化剂在该反应具有较高的稳定性。进而,考察在甲醇溶液中异香草醛、茴香醛、丁香醛、3,4,5-三甲氧基苯甲醛于氧气气氛下发生氧化酯化情况,发现纳米金负载三氧化二铝效果也较佳,对应芳香酯可达70.2-98.0%的收率。其次,还将不同制备方法的纳米金催化剂用于香草醇的氧化酯化过程,研究发现,在分子氧的存在下,经适当时间后香草醇和甲醇可以发生催化氧化酯化反应;其中,以Au-h/Al_2O_3为催化剂、氧气为氧化剂,在140℃反应4小时以后,香草醇转化率高达99.4%,不过,产物当中2-甲氧基-4-甲氧甲基苯酚的选择性为17.0%,香草醛的选择性为31.9%,香草酸甲酯的选择性为49.9%;继续延长反应时间至10、12小时,则香草醇接近全部转化,转化率分别为99.4%、99.9%,目标产物香草酸甲酯的选择性分别为94.8%、99.6%。结果表明,在Au-h/Al_2O_3催化剂促进下的氧化反应历程中,香草醇首先被氧化为香草醛,进而转化为香草酸甲酯。最后,通过对催化剂进行XRD、BET、TEM、SEM、TPD和NMR等表征测试,对反应数据做出了合理的解释。进而,基于实验现象和对比试验结果,在总结催化反应规律的基础上,提出了香草醇和甲醇的氧化酯化的反应机理。
[Abstract]:In recent years, due to the continuous depletion of fossil energy and environmental pollution, human beings are forced to look for new biomass energy. Biomass includes cellulose, hemicellulose and lignin, in which lignin content accounts for about 25%. At present, it is discharged into nature in the form of waste liquid from papermaking industry every year, which not only pollutes the environment, but also fails to realize the high addition value of lignin. In this paper, taking lignin model compounds as the research object, we can explore the effective ways to improve the added value of lignin to a certain extent. Therefore, it is of great scientific significance and application value to carry out the catalytic transformation of lignin model compounds. Firstly, using nano-metal as catalyst, the process of oxidative esterification of vanillin to methyl vanillic acid was studied. Solid catalysts supported on gold, platinum and palladium were prepared by deposition and precipitation method. Au/Al_2O_3,Au-R/Al_2O_3,Au-h/Al_2O_3 catalysts were synthesized by three different methods for the preparation of gold nanoparticles, and the catalysts were applied to the oxidative esterification of vanillin with methanol. It was found that the conversion of vanillin was 98.1% and the selectivity of methyl vanillic acid was 99.1% after reaction at 140 鈩，

本文编号：2508490