Abstract:

In recent years, a new route to acrylic acid (acrylate) production through the condensation reaction between formaldehyde and acetic acid (methyl acetate) received substantial attention from both academic and industrial communities. This reaction route is technically simpler and the feedstock can be obtained from natural gas and coal, which is economically favorable for sustainable acrylic acid production. So far, multifarious types of catalysts have been studied, including vanadium phosphorus oxide (VPO), supported alkali metal/alkaline earth metals, and ionic liquid, etc. This paper reviewed the recent achievements on the above catalysts and commented the advantages and disadvantages of the applied catalysts. The ionic liquid catalyst can be operated at rather low temperature with low energy consumption and high target product selectivity, whereas the nature of non-continuous homogeneous catalytic reaction causes the difficulties in product separation and catalyst recycling as well as the low process efficiency. The VPOs and alkali metal/alkaline earth metals are operated continuously at high temperatures (320—400℃), and the products can be readily separated from the system with higher catalytic efficiency. Compared to the VPOs, the alkali metal/alkaline earth metals involve less side reactions and thus show relatively higher product selectivity, though the overall efficiency could be lower, and the regeneration of deactivated catalyst is difficult. The latest study reveals that the typical fabrication of VPO precursor in an organic phase can be replaced by a more facile, lower-priced, and environmentally friendly approach operated one-pot in an aqueous phase. The activation of the precursor obtained in the new approach can be simply finished in air-atmosphere. The accomplishment not only greatly simplifies catalyst fabrication but also significantly enhances catalytic performance of laboratory scale, and lays a solid base for further application.

Key words: acetic acid, formaldehyde, condensation, catalyst, reactivity, selectivity, stability

摘要：

近年来，通过乙酸（酯）和甲醛缩合制备丙烯酸的新路线吸引了学术界和工业界的广泛关注。此新路线的优点是过程简单，原料可从天然气、煤化工产品中获得，成本低廉，对可持续生产丙烯酸具有十分重要的意义。国内外研究者针对这一反应开发了多种类型的催化剂，包括钒磷氧（VPO）类催化剂、负载型碱金属/碱土金属以及离子液体等。本文综述了不同种类催化剂近期的研究成果，总结了三类催化剂的优缺点。指出均相的离子液体催化剂具有反应温度低、能耗少、选择性高的特点，但反应为间歇操作，产物分离困难、催化剂较难重复利用，催化效率偏低。VPO类催化剂和碱金属/碱土金属类催化剂，反应温度较高（320～400℃），但可实现连续反应，产物分离方便，催化效率较高。相比于VPO类催化剂，碱金属/碱土金属类催化剂涉及的反应较少，对目标产物的选择性较高，但整体催化效能低于VPO类催化剂，且失活催化剂再生困难。最新的研究结果表明，经典的有机相法制备VPO前体可以被更加简便、经济与环境友好的一锅水相法取代。空气氛中简单焙烧即可完成催化剂前体的活化。不仅大大简化了催化剂制备，而且所得催化剂的小试性能优异，从而为后续应用奠定了重要基础。

关键词: 乙酸, 甲醛, 缩合, 催化剂, 活性, 选择性, 稳定性