Engineering and Architecture
Francesc Medina Cabello
Universitat Rovira i Virgili
Nanoscience, Materials and Chemical Engineering
Conversion of plastic waste into fuel and added-value chemicals
1. Plastic waste is one of the most concerning environmental issues today, and efficient chemical processes to convert them into value added materials are scarce. One emerging area in this context is the use of olefin metathesis to break down polymers containing C=C double bonds in their structure. This research line may find economic solutions for the management of rubber waste, natural and synthetic alike. (For a review see: Monatsh. Chem., 2015, 146, 1081–1097.)
Chemical degradation of saturated polymers is a much more challenging problem. Polyethylene (PE) is the largest volume polymer product produced in the Chemical Industry, with over 100 million tons of yearly worldwide output. The chemical inertness of PE (strong, and non- or weakly polar C-C and C-H single bonds) is notable. Its natural degradation in the environment is extremely slow, and current technologies for its recovery, basically catalytic pyrolyses, are highly energy intensive, and non-selective. The research will address this problem of great relevance.
2. Herein we briefly outline two closely related strategies which will be applied towards the catalytic degradation of PE.
(i) As the first approach, both homogeneous and heterogeneous catalytic systems will be developed for the dehydrogenation of PE. Acceptorless dehydrogenation is preferred, but transfer hydrogenation of acceptors that lead to value added chemicals will also be examined. Once C=C double bonds have been formed in the backbone of the polymer, they will be cleaved by ethenolysis, or other reversed ADMET, using homogeneous and heterogeneous olefin metathesis catalysts. The process will ultimately yield alpha,omega-diolefins, or functionalized diolefins, depending on the structure of the smaller olefin reagent. The strategy first will be tested with isolated catalytic systems, but the final objective is to develop a one-pot, orthogonal tandem catalytic systems for the process.
(ii) Closely related to the previous suggestion, the application of catalytic cross alkane metathesis (CAM) to break down PE, using small C6-C10 alkanes as reagents, will also be applied. One of its possible mechanisms of CAM can be explained as the combination of three reactions: (a) dehydrogenation of the alkane reaction partners, followed by (b) olefin cross metathesis of the resulting alkenes, and then (c) conversion of the new alkenes into the corresponding alkanes by hydrogenation. (Science Advances, 2006, 312, 257-261) In the framework of the project economically and ecologically viable combinations of dihydrogenation/hydrogenation and olefin metathesis catalysts will be developed to perform CAM of saturated waste polymers towards C9-C20 linear alkanes, practically diesel fuel.
The above novel approaches would allow using chemically resistant plastic waste as an additional resource of fuel and building block chemicals, greatly contributing to the sustainability of human society.
37.5 hours a week
|This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 713679|