【作者】 邓理；

【导师】 郭庆祥；

【作者基本信息】 中国科学技术大学 ， 可再生洁净能源， 2011， 博士

【摘要】 在资源逐渐匮乏的今天,可持续发展成为我们追求的目标,生物质资源作为唯一可再生的碳资源正得到越来越多的关注。纤维素作为自然界中总量最多的植物生物质,可以通过化学催化转化的方式得到人类需要的材料、燃料以及化学品。最新的研究显示通过水解、加氢、热解和脱水等反应可以有效地转化纤维制备葡萄糖、山梨糖醇、乙二醇、合成气、芳香烃以及呋喃化合物。上述化合物被称为未来生物精炼的“积木”(Building Blocks),是生物质基的平台化合物,能够衍生出更多的化学品或商品,有可能成为未来化学、材料和燃料的基础。乙酰丙酸也是来自纤维素的平台化合物之一,可以通过纤维素酸水解、脱水获得。它在燃料和高分子材料领域具有巨大的潜力,极有可能成为用途广泛的大宗化学品。从乙酰丙酸出发可以制备乙酰丙酸酯和γ-戊内酯,它们可以代替乙醇在汽油中作为添加剂使用。γ-戊内酯还可以通过各种化学催化的方法获得戊酸酯、5-壬酮、丁烯和长链烯烃,这些化合物具有更高的热值,可以作为高品位燃料的候选。在高分子材料领域,乙酰丙酸可以代替丙酮与苯酚反应,制备水溶性双酚A,这种单体在聚碳酸酯和环氧树脂生产方面应用前景广阔。而γ-戊内酯则可以用来生产α-亚甲基-γ-戊内酯,该单体聚合后制成的材料具有较高的玻璃化转化温度,可以在特殊场合代替聚丙烯酸酯。尽管乙酰丙酸和γ-戊内酯具有优良的性质和广泛的用途,但从纤维素原料出发制备上述两种化合物仍然存在一定的技术障碍,包括无机酸对设备的腐蚀性以及污染、缺乏高效地乙酰丙酸分离方法和γ-戊内酯及其衍生物制备过程中需要外部H2供给。本文针对乙酰丙酸和γ-戊内酯制备的技术障碍,提出了新的工艺路线,并在实验室规模开展了研究。在第1章中,我们简要介绍了目前生物质基化学品和生物燃料的发展状况,并介绍了生物质基平台化合物和“积木”的概念。详细综述了目前国内外纤维素化学催化转化、乙酰丙酸和γ-戊内酯合成与利用的最新研究进展。指出了生物质转化和绿色化学的关系。第2章介绍了介孔固体酸催化纤维素制备乙酰丙酸的研究内容。利用该催化剂,我们首次成功的实现了固体酸催化的纤维素到乙酰丙酸的转化,乙酰丙酸的产率高达50 mol%,并且通过在催化剂中引入磁性材料,完成了催化剂的循化使用。通过对比实验证明该固体酸的催化效率高于硫酸,结合催化剂的结构特征,我们对此给出了可能的解释:催化剂介孔孔道内具有很高的酸浓度,有助于碳水化合物脱水,生成乙酰丙酸。在接下来的两章中,我们将甲酸原位还原乙酰丙酸作为主要研究内容,首次提出在水相中利用当量的副产物甲酸还原乙酰丙酸的思路。该路线不仅体现了反应的原子经济性,避免了使用外部H2,还最大程度地降低了转化过程的分离能耗。研究结果表明,RuCl3/PPh3能够在水相条件下转化摩尔比1:1的甲酸和乙酰丙酸,高产率地得到γ-戊内酯。值得注意的是,甲酸原位生成的CO2可以促进疏水的膦配体PPh3在水相反应体系中发挥作用,解释了为什么RuCl3/PPh3在水相中拥有较高的催化效率,这也为廉价的PPh3替代水溶性膦配体提供了可能。另外,我们还提出了一种两步催化甲酸和乙酰丙酸制备γ-戊内酯的方法。该方法分别使用非均相催化剂Ru-P-SiO2和Ru/TiO2催化甲酸分解和乙酰丙酸加氢,成功地实现了催化剂的循环使用,为固定床连续法生产γ-戊内酯奠定了基础。综上所述,本文以纤维素制备乙酰丙酸和γ-戊内酯的绿色催化转化为研究内容,实现了固体酸催化制备乙酰丙酸的绿色过程;完成了甲酸作为还原剂制备γ-戊内酯过程中反应的耦合,解决了反应体系内部氢源的自给。更多还原

【Abstract】 With the aim of sustainable future, increasing attentions have been devoted tovarious routes for the production of biofuels and biochemicals via chemical andbiological catalysis. Taking amount of feedstock, food supply and processingcapacity into consideration, chemical transformation of cellulosic materials intobiofuels and biochemicals has to be emphasized. Current investigations show thatefficient conversion of cellulose to glucose, sorbitol, glycol, syngas, aromatics andfurans has been achieved via hydrolysis, hydrogenation, catalytic pyrolysis anddehydration. All of them are“building blocks”for biorefinery which is of greatpotentials to be the future chemicals, materials, and energy base.Levulinic acid, also a“building block”derived from cellulose, is a fascinatingcompound because it offers several promising routes for biofuels as well asbiochemicals. Starting from levulinic acid, levulinic esters andγ-valerolactone canbe obtained through addition of alkenes and hydrogenation respectively. Both can beblended with gasoline as ethanol. With regard to energy density, polarity and boilingpoint, the derivatives of levulinic acid orγ-valerolactone, such as valerate,5-nonanone, butene and C8+ alkenes, are more attractive in fuel applications.Moreover, levulinic acid andγ-valerolactone can also be converted to monomers.For instance, reaction with levulinic acid and phenol provides bisphenol A which isusually synthesized from acetone and plays important roles in polycarbonate andepoxy resin production. However, problems including the use of wasteful andcorrosive mineral acid, the efficient separation of levulinic acid and external H2supply, remain as bottleneck of the routes from cellulose to levulinic acid andγ-valerolactone.In chapter 1, we introduced the current state of the transformation of biomasstowards biofuels and biochemicals as well as the concept of“building blocks”brieflyThe chemical conversion of cellulose, synthesis and application of leculinic acid andγ-valerolactone were carefully reviewed. Besides,the relationship between biomassconversion and green chemistry were also commented.In chapter 2, levulinic acid was produced from cellulose by magnetic solid acidwith mesopores. The process may find important applications for the liquid fuels andvaluable chemicals production based on levulinic acid. By contrast with H2SO4, the catalysts are more efficient to convert microcrystalline cellulose into LA and catalyst separation can be readily achieved by magnetic force.The in-situ reduction of levulinic acid using by-product formic acid was reported in chapter 3 and 4. We creatively proposed the transformation of levulinic acid in water with equimolar formic acid toγ-valerolactone. The success of this new route not only improves the atom economy of the process, but also avoids the energy-costly step to separate LA from the aqueous solution mixture of LA and formic acid. We have demonstrated that by using inexpensive RuCl3/PPh3, 1:1 aqueous mixture of levulinic acid and formic acid can be catalytically converted toγ-valerolactone in high yields. A striking positive CO2 effect on Ru-catalyzed hydrogenation is also observed, which may be used to explain the good performance of aqueous hydrogenation using water insoluble ligand. Moreover, by using heterogeneous catalyst Ru-P-SiO2 for decomposition of fomic acid and Ru/TiO2 for hydrogenation of levulinic acid, an efficient two-step process forγ-valerolactone production has been developed. The two catalysts can be used repetitively for at least 8 times without deactivationIn summary, two key problems concerning levulinic acid andγ-valerolactone production has been solved. First, levulinic acid has been prepared from cellulosic feed via a“green”dehydration process using magnetic mesoporous solid acids. Second, levulinic acid formed in aqueous medium can be reduced toγ-valerolactone by robust catalysts without using external H2.更多还原