Current global plastics production is estimated to be of 332 million metric tons per year, which is expected to double in 2050.1
Consequently, an increase in plastic waste generation is expected, for which the most common disposal alternative is landfill storage that has the inconvenience of a limited capacity and public health issues related to it. Mechanical recycling is another important option for disposal but it reduces the quality and utility of the material every time it is processed. Thus, chemical recycling emerges as a promising alternative due to the possibility of producing fuels, chemicals, and monomers that can be used to produce new plastics or other industrial products. Pyrolysis of plastic has been widely studied at laboratory and pilot plant scales showing a wide range of products obtained at different temperature and reactor configurations. Although a deeper understanding on the effects of process variables and chemical mechanisms has been achieved, little information is available about the environmental and economic implications of this technology from an industrial scale. Therefore, in this study previously published data2
of waste High-Density Polyethylene (HDPE) pyrolysis at temperatures of 625, 650, and 675 °C over a range of vapor residence time is being used to design a process for the production monomers, aromatics, and aliphatic hydrocarbons. In the proposed process, waste HDPE is shredded into fine particles and introduced to a fluidized bed reactor using helium as the fluidizing gas and sand as the heating agent. This process is being simulated using Aspen Plus V. 8.8 and incorporates novel separation technologies and efficient integration of energy.
Techno-economic and life cycle assessment (TEA and LCA) are an essential component of this study and the results are going to be compared with production costs and environmental impacts from the current fossil-based pathways. As observed in previous waste refinery case studies, this process could potentially improve the environmental performance of the production of chemicals but with a possible increment in the cost. The results from the study will provide important information to guide future implementation of this technology from an industrial scale.
1. Plastics Europe. The plastic Industry. https://committee.iso.org/files/live/sites/tc61/files/The%20Plastic%20In... (accessed July 19, 2017).
2. Gracida-Alvarez, U.R.; Mitchell, M.K.; Sacramento-Rivero, J.C. & Shonnard, D.R. Effect of Temperature and Vapor Residence Time on the Micropyrolysis Products of Waste High Density Polyethylene. Industrial and Engineering Chemistry Research, 57, 1912-1923 (2018).