Small Angle Neutron Scattering to probe the mechanism of catalytic plastic cracking

Over 350 million metric tonnes of plastic are produced globally each year, with 55 % being discarded, Low-Density Polyethylene (LDPE), one of the most common polymers, takes centuries to decompose causing urban, and aquatic pollution. Whilst polymer recycling has been pushed for many decades, only 15 % of plastic is collected for recycling, with just 9 % actually being recycled. In the last 10 years processes such as polymer cracking with solid acid catalysts have been explored to form olefins, and aromatics, which would normally be synthesised from fossil fuels, thus establishing a “circular economy”, limiting waste, and lowering fossil fuel demand. Here we will perform SANS measurements on deuterated-eicosane/zeolite mixtures, to observe if this alkane (serving as a mimic for LDPE) can penetrate the pores of HZSM-5.

We will use a commercial high-silica HZSM-5 (Si/Al of 140, SLD of 3.4 x 10-6 Å-2 from previous studies). The high Si/Al ratio means fewer acid sites, and lower reactivity, allowing us to focus on the alkane’s accessibility, without reactions occurring. A blend of commercial deuterated and hydrogenated eicosane will be used for this study with the same SLD as the zeolite. Using the standard approximation, we anticipate C20 should have a radius of gyration of 2.8 Å, so should be able to diffuse into the pores of our HZSM-5 system. We anticipate this study will serve as a proof of principle work, leading to a further proposal using a LDPE system.