Comprehensive quantitative analysis of polyolefin hydrogenolysis toward plastic waste management

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New methods for recovering the energy and value from polyolefin plastic waste must account for all the hydrocarbons formed during a deconstruction reaction. Analysis of the reaction mixture distribution is key to determining a catalyst’s performance (activity and selectivity) and evaluating the economic viability of a conversion process. The molecular species present in the reaction mixtures can range from H 2 and CH 4 to hyper-branched hydrocarbons above 100,000 g/mol and any hydrocarbon in between; therefore, multiple analytical techniques are required to quantify all of the products. Here we describe an optimized and validated workflow that uses integrated analytical gas chromatography for concurrent H 2 and gas-phase hydrocarbon quantification of the headspace; complementary gas chromatography, liquid chromatography and multi-nuclear magnetic resonance spectroscopy to quantify the composition of soluble products, as well as gel permeation chromatography to determine of the molecular weight distribution of the residual insoluble polymeric material. Using polyolefin hydrogenolysis in an autoclave reactor as an example, we describe how to specifically adapt these techniques to polymer deconstruction experiments and fully quantify the entire hydrocarbon population, while resolving and assigning specific species and characterizing structures. The information from this comprehensive analysis is needed to study reaction kinetics and to evaluate the intrinsic activity of a catalyst and reactivity of polymers in upcycling experiments, enabling mechanistic investigations and providing data to link experiment and theoretical models. The comprehensive quantitative analysis in this protocol can be completed within 4 d.

Polymer deconstruction is part of plastic waste management. These transformations generate multiphase mixtures of many products. Understanding these systems requires accurate quantitative measurement of the distributions, all species in the gas, liquid and solid phases.

The number-averaged molar mass ( M n ), obtained from the distributions, is used to calculate C, C bonds cleaved ( n cuts ). These fundamental data establish the basis for mechanistic models to develop better methods for recovery and upcycling.

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The authors declare that the data in examples supporting this protocol are available within the Protocol and its Supplementary Information and Supplementary Calculation Data 1, 7 files. NMR spectra and chromatography data that support the expected outcomes and are used in the representative Supplementary Calculation Data are available via DataShare at https://doi.org/10.25380/iastate.30943310 .

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We thank Dr. Jiaqi Yu for helping with the initial setup of the GC-FID/TCD system, Dr. Brett W. Boote for assistance with the TGA-DSC, and Reed Jensen for assistance with semi-flow reactor construction. The Protocol studies were supported by the Institute for Cooperative Upcycling of Plastics (iCOUP), an Energy Frontier Research Center funded by the US Department of Energy (DOE), Office of Basic Energy Sciences. Ames National Laboratory is operated by Iowa State University under contract no. DE-AC-02-07CH11358. The design and construction of the semibatch reactor were supported by DOE-EERE: BETO/AMMTO under award no. DE-EE0009300.

Department of Chemistry, Iowa State University, Ames, IA, USA

Chao Meng, Yi-Yu Wang, Xun Wu, Akalanka Tennakoon, Frédéric A. Perras, Aaron D. Sadow & Wenyu Huang