Researcher(s)
- Alexander Bregvadze, Chemical Engineering, University of Delaware
Faculty Mentor(s)
- Dionisios Vlachos, Chemical Engineering, University of Delaware
- Jessie Sun, Chemical Engineering, University of Delaware
Abstract
Plastics are used due to their low cost and chemical stability, but their prevalent use has led to unsustainable disposal methods; therefore, more sustainable solutions are needed to address the growing issue of plastic waste. Polyolefins (PO), such as low-density polyethylene (LDPE) plastic bags, constitute 57% of total municipal solid waste1 making them prime candidates for chemical upcycling. One promising method for upcycling PO is through hydrocracking which uses a bifunctional metal/zeolite catalyst to deconstruct long polymer chains into alkanes like naphtha.1
Previous works have utilized noble metals (Pt/Ru) supported on an acidic support including zeolites (ZSM-5/ Beta) to degrade POs into naphtha. Vance, B. et. al revealed the use of nickel, an earth-abundant metal, which is generally cheaper in comparison to noble metals, deposited on Beta Zeolite (Ni/BEA) catalyst.2 The 5Ni/BEA catalyst, though active, requires high hydrogen pressure and is highly susceptible to coke formation, thereby reducing its extended activity and reuse.2 Additionally, Wang, H. et al demonstrated that adding cerium (Ce) to a PtSn-based catalyst minimized coke formation and enhanced catalyst activity by increasing the concentration of BA sites for improved cracking efficiency.3 Therefore, we hypothesize that incorporating Ce into 5Ni/BEA would similarly decrease coke formation and improve catalyst performance.
Initial results indicate that increasing the incorporated Ce weight % in 5Ni/BEA enhances the conversion of LDPE without affecting the desired product selectivity for naphtha. Specifically, the catalyst with 20% Ce (5Ni20Ce/BEA) achieved the highest deconstruction with a product (C1-C16) yield of 86.8% whereas 5Ni/BEA achieved only 58.9%. Thermogravimetric Analysis (TGA) of the spent catalyst reveals lower mass loss attributed to the deposition of organic residues and coke species with the incorporation of Ce to Ni/BEA. This suggests Ce minimizes active site coking and rationalizes the higher catalytic performance. The 5Ni20Ce/BEA exhibits a lower coke content with a total mass loss of 19.8% compared to 5NiBEA 25.5%.
[1] Dong, Z., Chen, W., Xu, K., Liu, Y., Wu, J., & Zhang, F. (2022). Understanding the Structure–Activity Relationships in Catalytic Conversion of Polyolefin Plastics by Zeolite-Based Catalysts: A Critical Review. ACS Catalysis, 12(24), 14882–14901. https://doi.org/10.1021/acscatal.2c04915
[2] Vance, B. C., Yuliu, Z., Najmi, S., Selvam, E., Granite, J. E., Yu, K., Ierapetritou, M. G., & Vlachos, D. G. (2024). Unlocking naphtha from polyolefins using Ni-based hydrocracking catalysts. Chemical Engineering Journal, 487, 150468. https://doi.org/https://doi.org/10.1016/j.cej.2024.150468
[3] Wang, H., Yoskamtorn, T., Zheng, J., Ho, P.-L., Ng, B., & Tsang, S. C. E. (2023). Ce-Promoted PtSn-Based Catalyst for Hydrocracking of Polyolefin Plastic Waste into High Yield of Gasoline-Range Products. ACS Catalysis, 13(24), 15886–15898. https://doi.org/10.1021/acscatal.3c03996Top of Form