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Carbon-carbon bond forming reactions for bio-oil upgrading: heterogeneous catalyst and model compound studies.

机译：用于生物油提质的碳-碳键形成反应：非均相催化剂和模型化合物的研究。

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摘要

Development of a renewable liquid transportation fuel is likely to be one of the most important challenges faced by scientists during the 21 st century. As biomass provides a renewable source of carbon it is ideally situated to supply this alternative to the traditional petroleum derived feedstocks. While there have been a number of different techniques used to convert biomass to liquid fuels, fast pyrolysis is particularly promising as it can quite efficiently break down biomass directly into a liquid. This resulting liquid, called bio-oil, is a very complex mixture containing a large number of oxygen functionalized compounds. Unfortunately, this oil has a number of issues that must be resolved before it can be effectively utilized as a liquid transportation fuel including acidity, reactivity, and low energy density. With this in mind, heterogeneously catalyzed C-C bond forming reactions potentially valuable for the upgrading of bio-oil were investigated.;The aldol condensation is a well known reaction in organic chemistry usually promoted through the use of strong acid or bases. However, uses of these types of catalysts will likely cause undesirable side reactions. Ideally cooperative catalysis allows for weaker acids and bases to work in tandem to promote the reaction. Use of aluminum phosphate catalysts allowed for the tuning of the acidity and basicity of the materials through a nitridation process and hence probing of this cooperative catalysis. Through performing aldol condensations using model bio-oil compounds acetaldehyde, acetone, and MEK, it was found that acid and base sites were both needed to efficiently promote the cross condensation of the aldehyde and ketone. After reaction testing, a mechanism was proposed demonstrating the benefits of using heterogeneous catalysts as it allows for the coexistence of both acid and base sites.;Ketonization of carboxylic acids is also an ideal reaction for bio-oil upgrading as it removes acidity and oxygen as well as creates C-C bonds. However, this reaction is almost always performed in the vapor phase due to the high temperatures necessary to achieve significant conversions. In order to try to engineer a more active catalyst able to perform the reaction at lower temperatures, more must be understood about ketonization. Condensed phase ketonization was examined using ceria catalysts calcined at different temperatures. It was found that the reaction proceeded either through the formation of carboxylates in the bulk or on the surface of the catalyst depending on the temperature of calcination. Moreover, through in-situ XRD, this trend was found to be true in the vapor phase as well. Kinetic studies found that the mechanism for both these routes was likely the same.;As ketonization had been claimed to be sensitive to the surface structure of the ceria catalyst, shape selective ceria nanocrystals were synthesized and examined in acetic acid ketonization both in the vapor and condensed phases. It was found that in the condensed phase the catalysts underwent carboxylate formation in the bulk thus changing the crystal structure of the materials. However, in the vapor phase this did not occur but a clear trend with surface structure was not determined. Thus it is likely the surface structure of the ceria catalysts isn't of large influence in realistic ketonization conditions. Reaction condition influences were probed as well. It was found that the temperature of ketonization greatly influenced the reaction pathway with intermediate temperature reactions resulting in metal carboxylate formation in the bulk and high temperatures promoting the reaction on the surface. Discussion of these temperature regimes and a more detailed proposed mechanism are delivered.;Lastly, ketonization using mixed metal oxides was studied. It was found that mixing of ceria with another oxide greatly changed the catalyst properties. Coupled with reaction testing, experiments determined that metal carboxylate formation and decomposition are of supreme importance for ketonization and are influenced by mixing of oxides. Along with the work using pure ceria catalysts, this research into ketonization is a significant step forward into understanding of the reaction and how it can be applied to the upgrading of fast pyrolysis bio-oil.
机译：开发可再生液体运输燃料很可能是21世纪科学家面临的最重要挑战之一。由于生物质提供了可再生的碳源，因此它处于理想的位置，可以为传统的石油衍生原料提供这种替代品。尽管有许多不同的技术可用于将生物质转化为液体燃料，但是快速热解特别有希望，因为它可以将生物质直接有效地分解为液体。所得的液体称为生物油，是一种非常复杂的混合物，其中包含大量的氧官能化化合物。不幸的是，这种油具有许多必须解决的问题，才能有效地用作液体运输燃料，包括酸度，反应性和低能量密度。考虑到这一点，研究了可能对生物油的升级有价值的非均相催化的C-C键形成反应。醛醇缩合是有机化学中众所周知的反应，通常通过使用强酸或强碱来促进。但是，使用这些类型的催化剂可能会引起不良的副反应。理想情况下，协同催化可使弱酸和弱碱协同作用以促进反应。磷酸铝催化剂的使用允许通过氮化过程调节材料的酸度和碱度，并因此探测这种协同催化作用。通过使用模型生物油化合物乙醛，丙酮和MEK进行醛醇缩合，发现酸和碱位都需要有效促进醛和酮的交叉缩合。经过反应测试后，提出了一种机制，证明了使用多相催化剂的好处，因为它允许酸和碱位点同时存在。羧酸的酮化反应也是生物油提质的理想反应，因为它可以去除酸和氧气。以及创建CC债券。然而，由于实现显着转化所必需的高温，该反应几乎总是在气相中进行。为了尝试设计能够在较低温度下进行反应的更具活性的催化剂，必须对酮化有更多的了解。使用在不同温度下煅烧的二氧化铈催化剂检查了冷凝相的酮化作用。已经发现，取决于煅烧温度，反应通过在本体中或在催化剂表面上形成羧酸盐而进行。此外，通过原位XRD，发现这种趋势在气相中也是正确的。动力学研究发现，这两种途径的机理可能相同。由于酮化被认为对二氧化铈催化剂的表面结构敏感，因此合成了形状选择性的二氧化铈纳米晶体，并在乙酸酮的蒸气和气相中进行了研究。凝聚相。发现在冷凝相中，催化剂在本体中经历了羧酸盐的形成，因此改变了材料的晶体结构。然而，在气相中这没有发生，但是没有确定表面结构的明显趋势。因此，二氧化铈催化剂的表面结构很可能在现实的酮化条件下影响不大。还探讨了反应条件的影响。发现酮化的温度极大地影响了反应路径，而中间温度反应导致本体中形成金属羧酸盐，而高温促进了表面上的反应。讨论了这些温度范围，并提出了更详细的机理。最后，研究了使用混合金属氧化物的酮化作用。发现二氧化铈与另一种氧化物的混合极大地改变了催化剂性能。结合反应测试，实验确定金属羧酸盐的形成和分解对于酮化至关重要，并受氧化物混合的影响。除使用纯二氧化铈催化剂的工作外，对酮化的研究是对理解该反应以及如何将其应用于快速热解生物油升级的重要一步。

著录项

  • 作者

    Snell, Ryan William.;

  • 作者单位

    Iowa State University.;

  • 授予单位 Iowa State University.;
  • 学科 Chemistry Organic.;Engineering Chemical.
  • 学位 Ph.D.
  • 年度 2012
  • 页码 178 p.
  • 总页数 178
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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