Tailored Nucleophilic and Amphoteric Zeolites without Large Cavities for the Dehydration of Lactic Acid to Acrylic Acid

用于乳酸脱水为丙烯酸的无大空腔的定制亲核和两性沸石

• 批准号: 388060787
• 负责人: Professorin Dr. Yvonne Traa
• 金额: --
• 依托单位: Institut für Technische Chemie (ITC)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2020-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/388060787?language=en
• 关键词: Tailored; Nucleophilic; Amphoteric; Zeolites; without

Cation-exchanged zeolites can be seen as acid-base pairs. The cation works as a Lewis acid, the framework oxygen as Lewis base. The average charge on the framework oxygen can be calculated after Sanderson. Thus, cation-exchanged zeolites can be classified as nucleophilic, amphoteric or electrophilic. As suitable test reaction for nucleophilic and amphoteric zeolites, the dehydration of lactic acid to acrylic acid was chosen. This reaction is of economic importance for the raw materials change and the production of chemicals from renewables. Due to the two functional groups of lactic acid, there are other reactions possible besides the dehydration to acrylic acid. In order to avoid side reactions on electrophilic and nucleophilic sites, it would be desirable, if the dehydration of lactic acid would be an elimination via the E2 mechanism during which the lactic acid would be adsorbed on an electrophilic and a nucleophilic site at the same time. Thus, the elimination could be a concerted reaction. Since mainly protic sites favor the decarbonylation and polymerization of lactic acid, the catalyst for the dehydration of lactic acid should only have Lewis-acid electrophilic sites. In addition, the carboxyl group of the lactic acid should be masked by a sufficiently high concentration of nucleophiles. Since catalyst deactivation can only be avoided, if accumulation of acid hydrocarbons such as lactic acid, acrylic acid and open-chain lactic acid oligomers/polymers is minimized, the catalyst should have neither large cavities nor large pores. Hence, all zeolite framework types were screened, looking for non-electrophilic zeolites without large cavities. Therefore, the focus will be on the sodium forms of the following aluminum-rich zeolite framework types without large cavities: CAN, NAT, LAU, GME, MAZ and OFF. The balance between acid and basic active sites can furthermore be optimized by ion exchange with Li, K and Cs as well as by a variation of the aluminum content of the zeolites. By these measures, selectivities to acrylic acid of 90% or higher should be possible. The work should increase the understanding of the interaction between electrophilic and nucleophilic active sites in zeolite catalysts and enable the valorization of new non-Brønsted-acidic, aluminum-rich zeolite catalysts.

阳离子交换的沸石可以被视为酸-碱对。阳离子作为刘易斯酸，骨架氧作为刘易斯碱。骨架氧上的平均电荷可以在Sanderson之后计算。因此，阳离子交换的沸石可以被分类为亲核的、两性的或亲电子的。选择乳酸脱水制丙烯酸作为亲核和两性分子筛的适宜试验反应。该反应对于原材料的改变和从可再生能源生产化学品具有经济重要性。由于乳酸的两个官能团，除了脱水成丙烯酸之外，还可能有其他反应。为了避免在亲电和亲核位点上的副反应，如果乳酸的脱水是通过E2机理的消除，在此期间乳酸将同时吸附在亲电和亲核位点上，则将是期望的。因此，消除可能是一种协调一致的反应。由于主要的质子位点有利于乳酸的脱羰和聚合，因此用于乳酸脱水的催化剂应仅具有路易斯酸亲电位点。此外，乳酸的羧基应该被足够高浓度的亲核试剂掩蔽。由于只能避免催化剂失活，因此如果最大限度地减少乳酸、丙烯酸和开链乳酸低聚物/聚合物等酸性碳氢化合物的积累，则催化剂不应有大空腔或大孔隙。因此，筛选所有沸石骨架类型，寻找没有大空腔的非亲电沸石。因此，重点将放在以下没有大空腔的富铝沸石骨架类型的钠形式上：CAN、NAT、LAU、GME、MAZ和OFF。酸和碱活性位点之间的平衡还可以通过与Li、K和Cs的离子交换以及通过改变沸石的铝含量来优化。通过这些措施，90%或更高的丙烯酸选择性应该是可能的。这项工作将增加对沸石催化剂中亲电活性位点和亲核活性位点之间相互作用的理解，并使新的非布朗斯台德酸性富铝沸石催化剂的价值得到提高。