【作者】 龚艳；

【导师】 林鹿；

【作者基本信息】 华南理工大学 ， 制浆造纸工程， 2011， 博士

【摘要】 石化资源不可再生且储量有限。石化资源不断开采和转化利用以实现人类社会与经济的发展,其储量日益减少,同时也造成了严重的环境污染和极端气候,目前能源危机近在咫尺,环境保护迫在眉睫。而生物质是地球上含量最丰富的可再生资源,包括如纤维素、半纤维素、淀粉等等;它又是一种最方便,污染最小的能源,可以在很多领域取代其他能源。因此,探索从生物质转化为清洁燃料如乙醇、丁醇以及化学品以补充或替代石油化学品具有非常重要的意义。乙酰丙酸是生物质酸性水解的主要产物,其特殊的化学组成和空间结构使之成为一种重要的平台化合物。目前已经通过乙酰丙酸的酯化、氧化还原、卤化、缩合反应制取了多种有用的化合物和新型高分子材料,广泛应用于各个领域。但是将乙酰丙酸脱羧或氧化裂解的研究还很少。事实上,乙酰丙酸脱羧到丁酮是生物质基碳水化合物转化成各类燃料和化学品的关键步骤;乙酰丙酸还能氧化裂解形成其他高附加值的化学品如丁烯酮等。因此探索乙酰丙酸的氧化反应途径及其机理,可为生物质在能源和化工领域的应用提供理论基础。本文以生物质基乙酰丙酸为基础,探索了乙酰丙酸在不同反应体系不同反应条件下的脱羧途径及影响乙酰丙酸脱羧的因素,研究了反应前后催化剂的结构变化,并提出了反应机理;此外,还发现了乙酰丙酸氧化裂解形成丁烯酮、丁二酮的途径并探讨了反应的影响因素。作为γ酮酸的乙酰丙酸,γ位吸电子基团羰基的吸电子效应因为碳链的延长而减弱,不能像α羰基酸或α碳原子上带有吸电子基团的脂肪酸遵循羧酸负离子机理脱羧,也不能如β,γ不饱和烯酸或β酮酸脱羧经六元环过渡态脱羧。乙酰丙酸的热脱羧,即其碳链上的羧基在高温下发生断裂而脱去,但是研究发现,热脱羧的副反应较多,产物复杂,丁酮得率仅为15%左右。而氧化脱羧,即氧化铜和Ag（I）/S₂O₈^2-氧化乙酰丙酸脱羧的研究发现,氧化铜使乙酰丙酸脱羧得到的丁酮得率达到67.5%,乙酰丙酸基本被转化。氧化铜作为氧化剂参与反应,反应结束后氧化铜被还原成单质铜。而且研究发现,氧化铜的颗粒度越小,催化脱羧效果越好。而Ag（I）/S₂O₈^2-氧化乙酰丙酸脱羧的丁酮得率仅为44.2%,因为Ag（I）/S₂O₈^2-也能氧化产物丁酮,同时抑制了底物的氧化。两种氧化脱羧方法相比较,前者的脱羧效果较好,但是反应温度较高,时间较长。而后者的效率较差,但是条件温和,反应速度快。氧化铜负载于载体氧化铈和氧化铝上形成混合氧化物CuO/CeO₂和CuO/Al₂O₃,因为在混合物中氧化铜的还原温度降低了。在温度175℃、pH为3.2的KH₂PO₄ NaOH反应体系中反应2小时,CuO/CeO₂和CuO/Al₂O₃的氧化乙酰丙酸的HS GC–MS分析表明,丁烯酮的得率分别约为20%和6.5%。可以推测载体CeO₂和Al₂O₃也参与了反应或者促进了反应的进行,或者说,混合物中氧化铜与载体并不是独立存在,它们的结构发生了变化,从而导致反应结果的不同。载体CeO₂和Al₂O₃对乙酰丙酸氧化反应的研究表明,在氧化铜的量相同的情况下,CeO₂的量减小,而丁烯酮得率和乙酰丙酸转化率也逐渐减小。实验证明纯CeO₂可以直接催化氧化乙酰丙酸产生丁烯酮,但是得率很低;研究还发现,CuO/CeO₂的颗粒度越小,其对乙酰丙酸脱羧的效果更好。H₂O₂/O₂对乙酰丙酸的氧化反应表明, 2,3丁二酮是主产物。反应温度（180℃–260℃）、反应时间（0.25h–9h）、H₂O₂的量（H₂O₂和LA比率=1:2–2:1）和氧压（10bar–50bar）对乙酰丙酸氧化反应影响的研究表明,在水溶液中,反应温度220℃、氧气压为20bar,H₂O₂与摩尔LA比例为1.2:1的条件下反应1h,丁二酮的得率最高,达到32%。与其他丁二酮的生产方法相比,原料乙酰丙酸是来自生物质的水解,而非异丁醛、乙偶姻等石油化工产品。而且,H₂O₂/O₂氧化反应乙酰丙酸的制备工艺简单,丁二酮的得率较高,反应后H₂O₂/O₂转化为水,无污染。因此,这是一种环保又经济的丁二酮生产方法。更多还原

【Abstract】 Fossil resources are non renewable energy source and limited. As petroleum reserves decrease gradually, the exploitation increases rapidly for the development of economy. And the conversion and application of fossil resources are the principal cause for the serious environmental pollution and ecosystem damage. While, biomass is the most abundant and renewable organic substance in nature, which includes cellulose, semi cellulose and starch et al, and it’s the most convenient and the least polluted energy, which can replace other energy sources in many other areas. Therefore, replacing fossil resource with biomass is a trend of economic development and also a developing trend in chemical industry, and exploration for a feasible pathway to transform biomass into clean fuels （such as bio ethanol, butanol） and other chemicals to supplement or gradually replace the oil based chemicals or energy becomes increasingly significant.Levulinic acid is the main product from a series of hydrolysis of biomass. It is an important platform material due to its chemical constitution and spatial conformation. Currently, some chemicals and new functional polymer materials have been synthesized by means of esterification, halogenation, redox and condensation reactions of levulinic acid, which are widely applied in many fields. However, there are few studies relating to decarboxylation and oxidative degradation of levulinic acid. The decarboxylation of levulinic acid to form butanone is one of the key conversion steps from biomass derived carbohydrates to versatile fuels and chemicals; and levulinic acid can be oxidatively degraded into high valued chemicals such as methyl vinyl ketone et al. Consequently, the research with respect to pathways of LA oxidation and the mechanisms will provide the theoretical foundation for the application of biomass in the energy and chemical industries.The decarboxylation pathways of levulinic acid to butanone, the influence of react system and react conditions to the decarboxylation of levulinic acid and the structural change of catalysts during the reaction were explored; oxidative degradation pathways of levulinic acid to methyl vinyl ketone and 2,3 butandione were found out and the influence of react conditions were dealt with in detail in this paper.Levulinic acid is a kind ofγketone acids. Electron withdrawing effect of carbonyl group （electron withdraw group） decreases because of chain elongation. Thus, it cannot be decarboxylated by essentially anionic mechanisms likeαcarbonyl acids or fatty acids with a withdraw group carbonyl group connected inαcarbon atom; and it cannot experience the six member ring transition state to be decarboxylatd, likeβ,γunsaturated acids orβketone acids. The thermal decarboxylation of levulinic acid causes the cleavage of carbon chain with many side products for the yield of butanone was just about 15%. As to oxidative decarboxylation, it appeared from the research that CuO and Ag（I）/S₂O₈^2- could oxidize levulinic acid to be decarboxylated and form butanone as main product. The yield of butanone from the oxidative decarboxylation by CuO reaches 67.5% and levulinic acid is almost converted. The catalyst CuO involved in the reaction as a redox, that is, CuO is completely reduced to elemental form （Cu） after the reaction. Moreover, the smaller the CuO particles are, the better the effect of decarboxylation is. The LA decarboxylation oxidized by Ag（I）/S₂O₈^2- leads to butanone with a yield of about 44.2%. But Ag（I）/S₂O₈^2- also can oxidize the product butanone which results in a decrease in the yield of butanone and meantime inhibits the conversion of levulinic acid. The separation of butanone to avoid being oxidized is a main obstacle to increase the yield and conversion. Compared with these two kinds of oxidative decarboxylation, we find that the former has higher yield and higher conversion with relatively extreme react conditions; while, the latter is less effective but under milder conditions.The search of mild reactive conditions together with high catalytic efficiency is imperative for the future potential industrial applications and meaningful in organic synthesis. CuO/CeO₂ and CuO/Al₂O₃ were prepared because CuO in CuO modified compounds could be reduced at lower temperature for CeO₂ and Al₂O₃ could promote the hydrogen reduction activity of copper. The oxidation products of levulinic acid by CuO/CeO₂ and CuO/Al₂O₃ at 175°C for 2 h have been analyzed by HS GC–MS and the main product is MVK with the yields of about 20% and 6.5%, respectively. It was inferred that the support CeO₂ and Al₂O₃ involved in the reaction, or rather, structural change of modified compounds with respect to pure CuO resulted in the different catalytic behavior. The effect of CuO/CeO₂ and CuO/Al₂O₃ for the oxidation of levulinic acid in NaOH KH2PO4 solution has been studied. As the dosage of CeO₂ or Al₂O₃ increase, both the MVK yield and LA conversion increase on the condition of the same CuO dosage. Thereby CeO₂ was used in the reaction alone and it was revealed that levulinic acid is only marginally oxidized to MVK in the presence of CeO₂. Moreover, levulinic acid can be oxidized with a better MVK yield when CuO/CeO₂ and CuO/Al₂O₃ particles are smaller.The oxidation of levulinic acid by H₂O₂/O₂ in water solution has been studied and the result analyzed by HS GC–MS that 2,3 butandione formed as the main product. The effects of temperature （180°C–260°C）, retention time （0.25h–9 h）, dosage of H₂O₂ （the mol ratio of H₂O₂ and LA=1:2–2:1） and the pressure of O₂ （10bar–50bar） have been investigated. It indicated the reaction was carried out at the temperature of 220°C for 1h in the presence of H₂O₂ （the ratio of H₂O₂ and LA of 1.2:1） and O₂ （20bar）, the yield of 2,3 butandione reaches the maximum of 32%. Compared with other methods for the production of 2,3 butandione, raw material levulinic acid is degraded from hydrolysis of biomass, but not petrochemicals such as isobutylaldehyde and acetoin et al. In addition, the H₂O₂/O₂ oxidation can get better yield of 2,3 butandione with simple reaction processes; H₂O₂ is reduced to water after the reaction, which is economic and environment protected.更多还原