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Catalytic Cracking of Polylactic Acid to Acrylic Acid
Yuchen Jiao, Meng Wang,* and Ding Ma*
Asa typical type of sustainable plastic, polyesters can be recycled or upcycledinto value-added chemicals in a variety of methods. However, excess reagentsare required for most of the depolymerization and upcycling processes, causingthe emission of environmental pollutants and the waste of chemical resources.Here we demonstrate a one-pot catalytic process to directly crack polylacticacid into acrylic acid by acid catalyst with the assistance of an ionic liquid,Bu4PBr. Polylactic acid is attacked by the Br- from Bu4PBrand the H+ from acid to form oligomers containing Br or acryloylgroup, and these oligomers serve as intermediates to produce acrylic acidduring their mutual transformation. The acrylic acid is vaporized directly fromthe reactor and obtained in a collector with a selectivity around of 90 % whenpolylactic acid is fully converted. This green process shows great advantagesin atom economy compared to the conventional recycling/upcycling methods forpolyesters, in addition, a better efficiency in converting the polymer than thecorresponding monomer could inspire new upcycle strategies for differentplastic wastes.
Polylactic acid | Acrylic acid | Atom economy | Upcycling | Ionic liquid | Commodity polymers | Plastics | Green chemistry
隨著塑料產(chǎn)量的逐漸擴大，塑料垃圾已經(jīng)逐漸成為除了化石燃料，二氧化碳和生物質(zhì)之外的最重要的碳資源之一。而傳統(tǒng)的廢塑料填埋、焚燒等處理方式一方面導致塑料垃圾大量堆積，嚴重危害自然環(huán)境和身體健康；另一方面也是對碳資源的浪費，帶來嚴重的經(jīng)濟損失。因此對廢塑料制品進行回收和轉(zhuǎn)化十分重要。近年來，北京大學馬丁/王蒙團隊在廢塑料升級轉(zhuǎn)化領(lǐng)域做出了系統(tǒng)性貢獻(J. Am. Chem. Soc. 2021, 143, 16358. Nat. Comm. 2022, 13,4809. Angew.Chem. Int. Edit. 2022, 61, e202117205. Chem. 2022,8, 892. Angew. Chem. Int. Edit. 2023, 62, e202304219. Nat.Sustain. 2023, 6, 712 )。
聚酯類廢塑料作為廢塑料組分之一，目前已經(jīng)開發(fā)出了多種降解回收方法，并可以轉(zhuǎn)化為其他高值化學品，實現(xiàn)升級循環(huán)。但是目前大多數(shù)的降解回收或轉(zhuǎn)化為其他高值化學品的過程（水解，胺解，醇解）都需要消耗其他化學品，或排放大量廢棄物。因此開發(fā)新的聚酯類塑料回收方法十分必要。
最近馬丁、王蒙等提出一種在較低溫度下一鍋法將聚乳酸裂化為丙烯酸的方法。在溶劑和催化劑的共同作用下，聚乳酸會先解聚為含溴寡聚體和丙烯酸酯等反應(yīng)中間體，之后丙烯酸酯解聚為丙烯酸并通過蒸餾進入吸收瓶中實現(xiàn)分離。與其他聚酯轉(zhuǎn)化方法不同，該方法對于乳酸單體的活性遠低于聚乳酸和其他寡聚體，且具有較高的原子利用率，為聚酯回收轉(zhuǎn)化為其他高值化學品提供了新思路。
上述研究結(jié)果作為Breaking Report發(fā)表于Chin. J. Chem. 2023, 41, 2071-2076, DOI: 10.1002/cjoc.202200752。該項工作得到了國家自然科學基金、中國石油天然氣集團公司-北京大學基礎(chǔ)研究戰(zhàn)略合作項目和騰訊基金會XPLORER獎支持。Left to Right: Yuchen Jiao, Meng Wang, Ding Ma
馬丁：北京大學化學與分子工程學院教授。長期在多相催化領(lǐng)域從事能源催化方面的研究，聚焦高效制氫過程，發(fā)展碳資源與氫氣轉(zhuǎn)化新路徑。實現(xiàn)水分子中O-H鍵在催化劑界面的低溫解離，開發(fā)了技術(shù)指標國際領(lǐng)先的低溫水中取氫、高效制氫催化新體系；揭示了鐵基費托合成催化劑最佳活性相，發(fā)展了合成氣高效轉(zhuǎn)化路徑；突破傳統(tǒng)途徑，以廢棄含碳物質(zhì)（廢塑料、二氧化碳）為碳資源構(gòu)建“碳-氫循環(huán)”催化新體系。
