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原位供氢条件下以糠醛为生物油模型化合物的加氢脱氧研究
伏朝林
学位类型硕士
导师林伟刚 ; 王泽  
2017-07
学位授予单位中国科学院研究生院
学位授予地点北京
学位专业化学工程
关键词供氢试剂 生物油 糠醛 2-甲基呋喃 加氢脱氧
摘要

随着能源短缺和环境污染问题变得越来越严峻,寻找和开发新的可持续的绿色能源迫在眉睫。生物质由于其来源广、储量大、成本低、可再生、CO2零贡献等优势而获得了各国的大量研究,同时由于其是唯一可提供碳源的可再生能源,故可用于生产平台化合物。生物质热解技术可以高产率的获得生物油,但是所得的生物油由于成分复杂、含氧量高、不稳定、热值低、酸性高而限制了其进一步应用,需要进一步处理。加氢脱氧技术由于液相收率高、脱氧程度大可用于生物油的提质,但是传统的加氢脱氧技术需要大量的外部氢气供给,给操作、运输、存储都带来了一定的安全风险,且往往氢气利用率低,故本论文利用供氢试剂替代传统H2,通过原位加氢脱氧技术来研究生物油的提质转化。通过以糠醛为生物油模型化合物的研究发现,糠醛是一种非常不稳定的物质,其水溶液在140oC就开始结焦,而通过向其中添加醇溶剂可以有效地抑制结焦现象,而甲醇的水溶液又正好是良好的供氢试剂。故以甲醇的水溶液为反应体系,考察了两类催化剂:金属氧化物(Fe2O3、ZnO、NiO、CuO)和负载型金属催化剂(Pd、Pt、Ru、Cu、Fe、Ni)催化糠醛转化的活性,发现金属氧化物对该反应体系基本没有催化活性,对于负载型金属催化剂,不同的金属表现出的催化性能不一样:Pd有很高的脱羰基能力,产物中呋喃产率达81mol%;Pt, Ru, Ni的催化性质类似,都对呋喃环和侧链羰基有催化活性,但Pt的催化活性更强,Ni其次,Ru最弱;Cu的催化活性低,但主要催化侧链羰基的还原;Fe基本没有表现出催化能力。以廉价的Ni为活性金属,通过对不同载体的考察(Al2O3、SiO2、MCM-41、SBA-15、ZSM-5)发现具有较大孔径和较多酸性位的介孔材料更有利于糠醛的转化以及呋喃和2-甲基呋喃的生成。对不同的反应条件的考察发现:升高温度有利于糠醛的转化,但产物以脱羰基生成的呋喃为主;增加Ni的负载量,糠醛的转化率提升不大,但是四氢呋喃的产率显著增加;增加甲醇的添加量,对糠醛的转化率影响也不大,但是可以显著地增加2-甲基呋喃的产率,推测甲醇除了以H2的形式供氢外,也以质子H的形式供氢;通过对反应时间的研究,发现反应主要发生在前4个小时,随后,糠醛的转化率和产物分配逐渐稳定。并基于该反应体系,对模型生物油进行了原位加氢脱氧研究,发现除苯酚外,其他物质均能高效地转化,利于提高生物油的热值和稳定性。当以甲酸为供氢试剂时,结合Ni金属的高活性和Cu金属对侧链羰基的高选择性,合成了双金属Ni-10%Cu/Al2O3催化剂,发现随着Ni的加入改变了催化剂的晶粒尺寸和分散度,同时出现了Ni-Cu合金态。Ni-Cu双金属催化剂对糠醛表现出了高催化活性和还原侧链羰基的高选择性,推测这主要是由于Ni本身具有的高内在活性以及Cu对于糠醛在催化剂表面的吸附构型的改变。同时在异丙醇为溶剂的反应体系中,异丙醇除了作为反应介质外,其本身还可以作为供氢试剂以质子H的形式通过转移加氢过程参与到糠醛侧链羰基的还原过程中去,但发现这种供氢方式对羰基的加氢很有作用,但是对随后的氢解作用不大,需要借助于更强的甲酸供氢。在经过7 h的反应后,糠醛的转化率能够达到100mol%,同时2-甲基呋喃的产率达92mol%。 

其他摘要

With the decrease of fossil fuel reserves and more seirous environment problems, it is urgent to search for sustainable energy sources. The research on biomass conversion has received rapid developments as it is regarded as a kind of abundant, cheap, stable and environmental friendly resource, as well as the only renewable carbon source. Therein, fast pyrolysis technology can efficiently convert biomass into bio-oil which can be a promising alternative to supply the fuels. However, due to the undesired poor natural properties of bio-oil, it has to be upgraded to reduce water content, acidity, oxygen content etc. and increase heat value and stability. A method named in-situ hydrodeoxygenation is employed to solve this problem with respect of reducing the operation, transporation, storage and safety problems, caused by the addition of a large amount of H2 in conventional hydrodeoxygenation process.In order to understand more basic and specific reaction mechanisms, furfural is selected as the model compound in the research as it can be the representative compound of furans and aldehydes in bio-oil. The preliminary experiment indicated that obvious coke formation of furfural aqueous solution started when the reaction temperature was higher than 140oC. However, by adding alcohol solvents into the system such as methanol, ethanol, isopropanol, the coke formation could be completely inhibited. Thus, methanol aqueous was selected as the solvent and hydrogen donor for this system. Two types of catalyst: metal oxide catalysts (Fe2O3, ZnO, NiO, CuO) and metal catalysts (Pd, Pt, Ru, Fe, Cu, Ni) were screened. The results showed that metal oxdie catalysts just had very low catalytic activity while the metal catalysts showed distinct performance. Pd was favorable for decarbonylation with a high 84mol% yield of furan; Pt, Ru, Ni all showed the catalytic activities for both carbonyl and furan ring with the ability ranking: Pt>Ni>Ru. Cu showed a low activity but a high selectivity for the reduction of carbonyl. Fe was hardly active in this system. Therefore, further researches were performed over Ni based catalyst to investigate the effect of support, reaction temperature, catalysts loading, feed ratio, residence time. The results indicated that the support with larger pore size and more acidities was preferable for the conversion of furfural and the formation of furan and 2-methylfuran. More decarbonylation product furan could be obtained by increasing temperature. More deep hydrogenated product tetrahydrofuran could be obtained by increasing metal loading and more 2-methylfuran could be obtained by increasing the fraction of methanol in the reaction medium. By studing the factor of reaction time, it was found that the primary reaction occurred in the first 4 hours and then the product distribution gradually turned stable. The in-situ HDO of synthetic bio-oil was also studied in this reaction system and it was found that except phenol, all the other compounds could be effectively converted for higher heat value and stability of bio-oil.When using formic acid as the hydrogen donor, the bimetallic Ni-10%Cu/Al2O3 catalyst was prepared by virtue of the high instinctive activity of Ni and high selectivity for carbonyl reduction of Cu. The characteristic results showed that the addition of Ni could change the dispersion and crystallite size of catalysts. The formation of Ni-Cu alloy was beneficial for the adsorption of carbonyl and the repulsion of furan ring. Thus, more 2-methylfuran could be generated with a highest yield 92mol% within 7 h. Moreover, the isopropanol solvent could contribute to the hydrogenation of carbonyl through transfer hydrogenation process while promoted slightly for the next hydrogenolysis, which required the participation of the stronger hydrogen donor formic acid. 

语种中文
文献类型学位论文
条目标识符http://ir.ipe.ac.cn/handle/122111/24210
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伏朝林. 原位供氢条件下以糠醛为生物油模型化合物的加氢脱氧研究[D]. 北京. 中国科学院研究生院,2017.
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