{"title":"Chemical separation of polyurethane via acidolysis – combining acidolysis with hydrolysis for valorisation of aromatic amines†","authors":"","doi":"10.1039/d4gc00819g","DOIUrl":null,"url":null,"abstract":"<div><p>As the global production of polymers exceeded 400 million tons in 2022, it is imperative that recycling rates are increased to prevent the predominant end-of-life handling through landfilling and incineration processes. With an increasing reliance on polyurethane (PU), the 2022 global production of PU reached almost 26 million tons. As PU is mainly utilised as a thermoset material, the extensive cross-linked networks render melting and remolding processes known from thermoplastic materials incompatible. As such, the majority of PU that is recycled is processed through mechanical shredding and gluing processes or chemical recycling <em>via</em> glycolysis and acidolysis processes for polyol recovery, all providing a secondary material with properties different from the parent material. Here, we show that the well-established acidolysis process can be used to both depolymerise PU and separate the polyol and dianiline adducts with a specific focus on analysing and valorising the dianiline component arising from the hard segment of PU. By evaluation of the reaction outcome from acidolysis of flexible PU foam with succinic acid, adipic acid or phthalic acid under neat conditions, succinic acid was found to form the corresponding succinimide of toluene diamines that is readily separable from the polyol. The toluene diamine could in turn be reformed through ruthenium-catalysed hydrogenation or simple hydrolysis. Ultimately, the combined acidolysis/hydrolysis of a flexible PU foam yields the polyol and dianiline in a combined 83 wt% recovery. A similar recovery rate was achieved for a commercial rebonded flexible foam. As current PU recycling methods only target the polyol fraction often obtained in a low quality, this advancement shows that current industrially applied acidolysis could be altered so that both the diamines and polyol can be obtained from flexible PU foam. Preliminary results show that the process is applicable to rigid PU foams, a PU fraction that is difficult to recycle due to its molecular complexity. Finally, a mechanistic pathway is suggested to account for the observed product distributions.</p></div>","PeriodicalId":78,"journal":{"name":"Green Chemistry","volume":null,"pages":null},"PeriodicalIF":9.3000,"publicationDate":"2024-07-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Green Chemistry","FirstCategoryId":"92","ListUrlMain":"https://www.sciencedirect.com/org/science/article/pii/S1463926224006290","RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"CHEMISTRY, MULTIDISCIPLINARY","Score":null,"Total":0}
引用次数: 0
Abstract
As the global production of polymers exceeded 400 million tons in 2022, it is imperative that recycling rates are increased to prevent the predominant end-of-life handling through landfilling and incineration processes. With an increasing reliance on polyurethane (PU), the 2022 global production of PU reached almost 26 million tons. As PU is mainly utilised as a thermoset material, the extensive cross-linked networks render melting and remolding processes known from thermoplastic materials incompatible. As such, the majority of PU that is recycled is processed through mechanical shredding and gluing processes or chemical recycling via glycolysis and acidolysis processes for polyol recovery, all providing a secondary material with properties different from the parent material. Here, we show that the well-established acidolysis process can be used to both depolymerise PU and separate the polyol and dianiline adducts with a specific focus on analysing and valorising the dianiline component arising from the hard segment of PU. By evaluation of the reaction outcome from acidolysis of flexible PU foam with succinic acid, adipic acid or phthalic acid under neat conditions, succinic acid was found to form the corresponding succinimide of toluene diamines that is readily separable from the polyol. The toluene diamine could in turn be reformed through ruthenium-catalysed hydrogenation or simple hydrolysis. Ultimately, the combined acidolysis/hydrolysis of a flexible PU foam yields the polyol and dianiline in a combined 83 wt% recovery. A similar recovery rate was achieved for a commercial rebonded flexible foam. As current PU recycling methods only target the polyol fraction often obtained in a low quality, this advancement shows that current industrially applied acidolysis could be altered so that both the diamines and polyol can be obtained from flexible PU foam. Preliminary results show that the process is applicable to rigid PU foams, a PU fraction that is difficult to recycle due to its molecular complexity. Finally, a mechanistic pathway is suggested to account for the observed product distributions.
期刊介绍:
Green Chemistry is a journal that provides a unique forum for the publication of innovative research on the development of alternative green and sustainable technologies. The scope of Green Chemistry is based on the definition proposed by Anastas and Warner (Green Chemistry: Theory and Practice, P T Anastas and J C Warner, Oxford University Press, Oxford, 1998), which defines green chemistry as the utilisation of a set of principles that reduces or eliminates the use or generation of hazardous substances in the design, manufacture and application of chemical products. Green Chemistry aims to reduce the environmental impact of the chemical enterprise by developing a technology base that is inherently non-toxic to living things and the environment. The journal welcomes submissions on all aspects of research relating to this endeavor and publishes original and significant cutting-edge research that is likely to be of wide general appeal. For a work to be published, it must present a significant advance in green chemistry, including a comparison with existing methods and a demonstration of advantages over those methods.