Polyolefin recycling by C–C bond alumination

Efficient catalysis that simultaneously cleaves thermodynamically inert C–C bonds and generates functional moieties to stimulate chemical recycling of polyolefins is lacking. In this issue Chem, Kanbur et al. design an organozirconium catalyst combined with aluminum reagents enable a clever tandem cleavage carboalumination process yields value-added alkylaluminum products. With their ubiquitous almost irreplaceable functions, plastics are deeply ingrained in our daily life industrial activities. Polyolefins, including polyethylene (PE) polypropylene (PP), the most produced world occupy nearly 50% total plastic market 60% waste stream, reflecting single-use nature.1Geyer R. Jambeck J.R. Law K.L. Production, use, fate all ever made.Sci. Adv. 2017; 3: e1700782https://doi.org/10.1126/sciadv.1700782Crossref PubMed Scopus (3896) Google Scholar Indeed, solving challenge urgent given accumulation newly generated will double only 15 years as result exponential growth production. Polyolefins one least recycled because number challenges, lack product value secondary markets, difficulties sorting mixed contaminated waste, favorable depolymerization chemistry. Novel catalytic processes can break readily convert broken aliphatic chains value-enhanced chemicals feedstocks could shift current paradigm linear economy polyolefins. Chemical PE challenging inertness C–H bonds. be cleaved by high temperature, radicals, processes; each approach has different such energy cost little control composition (thus rendering it low value). Pyrolysis consumption been developed generate hydrocarbon gas, oil, wax, char without much composition.2Onwudili J.A. Insura N. Williams P.T. Composition products from pyrolysis polystyrene closed batch reactor: effects temperature residence time.J. Anal. Appl. Pyrolysis. 2009; 86: 293-303Crossref (268) A recent advance cross-alkane metathesis, involving dehydrogenation-hydrogenation Ir-based second Re2O7/γ-Al2O3 olefin metathesis catalyst, achieved highly efficient degradation under mild conditions.3Jia X. Qin C. Friedberger T. Guan Z. Huang selective polyethylenes into liquid fuels waxes conditions.Sci. 2016; 2: e1501591https://doi.org/10.1126/sciadv.1501591Crossref (111) Hydrogenolysis via surface-supported zirconium hydride cleave bond β-alkyl elimination, through which short-chain saturated oligomers, diesels, lower alkanes PP.4Dufaud V. Basset J.M. Catalytic hydrogenolysis at pressure diesels or supported on silica-alumina: step toward polyolefin microscopic reverse ziegler–natta polymerization.Angew. Chem. Int. Ed. 1998; 37: 806-810Crossref (177) Similar also accomplished noble-metal-nanoparticle catalysis.5Tennakoon A. Wu Paterson A.L. Patnaik S. Pei Y. LaPointe A.M. Ammal S.C. Hackler R.A. Heyden Slowing I.I. upcycling high-density processive mechanism.Nat. Catal. 2020; 893-901Crossref (60) Scholar,6Zhang F. Zeng M. Yappert R.D. Sun J. Lee Y.-H. Peters B. Abu-Omar M.M. Scott S.L. Polyethylene long-chain alkylaromatics hydrogenolysis/aromatization.Science. 370: 437-441Crossref (89) However, introduction groups, these catalytical routes limit conversion hydrocarbons have compete economics cheap fossil fuel Degradation chemistry tunable groups raise converted products, simulating recycling. Pifer Sen7Pifer Sen useful organic compounds oxidative degradation.Angew. 3306-3308Crossref (36) first utilized nitrogen oxides dioxygen 170°C sweep carboxylic acids radical-induced chain scission variety backbones. Microwave-assisted hydrothermal treatment (HDPE) effectively dicarboxylic used plasticizers for polylactide.8Bäckström E. Odelius K. Hakkarainen Designed recycled: turning covalently attached polylactide plasticizers.ACS Sustain. Eng. 2019; 7: 11004-11013https://doi.org/10.1021/acssuschemeng.9b02092Crossref (21) Similarly, hydroxyl-radical-induced PP, PE, polyvinyl chloride (PVC) was photocatalyst Nb2O5, turned CO2 then photoreduced acetic acid products.9Jiao Zheng Chen Q. Li Shao W. Xu Zhu Pan Xie Photocatalytic C2 simulated natural environment conditions.Angew. 59: 15497-15501Crossref (55) Nevertheless, strategies limited composition. inspired polybutadiene (containing unsaturated C bonds) deconstruction pathway,10Zheng Lin Liu Tan H. Wang Tang Controlled chain-scission Schwartz hydrozirconation.Chemistry. 2013; 19: 541-548Crossref (16) al.11Kanbur U. Zang G. Chatterjee P. Delferro Perras F.A. Sadow A.D. carbon–carbon carbon-element formation give new biodegradable surfactants.Chem. 2021; 1347-1362https://doi.org/10.1016/j.chempr.2021.03.007Abstract Full Text PDF (11) report novel method leads C–Al realizes flexibility installing versatile functionalities. The catenated benefits catalyst-controlled selectivity surface organometallic chemistry; subsequently form species further high-value fatty alcohols. authors propose following elementary reaction steps (Figure 1). presence surface-grafted Zr(CH2CMe3)2@SiAlOx Al 150°C–200°C over 12 h, methylene polymer backbone metalated alkylzirconium mid-chain polymerylzirconium. Through polymerylzirconium off terminal oligomerylzirconium surface. former undergoes hydroalumination reagents, creating Al–C bonds; latter heterobimetallic alkyl group hydridoaluminum species, transferring other half alkane forming bond. These shorter alcohols, acids, halides, addition appropriate quenching agent, streams This successful similar when converting isotactic PP supermarket bag made HDPE. By O2, methanol, I2, CO2, demonstrate versatility yielding hydrocarbons, iodides, affecting final product’s length. Another avenue characteristics accessible selecting transfer capabilities (i.e., AlH3 AliBu3). Such provide higher yield oils functionalized alcohols) than (AlEt3) aryl (AlPh3) counterparts, implied rules alkene polymerization. generating reactions, selected enhance rates activation thus impact subsequent β-elimination transfer. findings strongly imply advantageous opportunities offer optimization desired Via same mechanism, re-activate catalysts—supported either silica (Zr(CH2CMe3)2@SiO2) alumina (Zr(CH2CMe3)2@SiAlOx)—that previously oxygen impurities. alkoxylzirconium observed comparable results not purified pre-exposed oxygen. Thus, proposed system tolerate moisture impurities, providing robust option handling large quantities scale. summary, using reactants catalysts Earth-abundant non-toxic elements, combines elimination enables controlled installation pre-existing directing groups. optimization, theoretically applied centralized material-recovery facilities produce surfactants commercial surfactants. Future efforts include developing leverage mechanisms lead narrow distribution overcome preferential longer chains. carbon-carbon surfactantsKanbur al.ChemApril 9, 2021In BriefA transformation alumination investigated alcohols acids. Full-Text Open Access