(691g) Development of a Novel Process That Converts Waste Polyethylene Plastic to Ethylene

Ethylene is a key chemical compound in the petrochemical industry, with current global production reaching 225 million metric tons per year. Ethylene is primarily used in the production of polyethylene, which is the world's largest plastic resin based on production volume. Despite accounting for 34% of plastics production, polyethylene has a notably low recovery rate of less than 10%, with the majority ending up in landfills or the environment. These factors provide the motivation to consider the development of processes that convert waste plastics, notably polyethylene, to ethylene in an economical manner.

In this project, a novel process is developed to convert waste plastic into ethylene. Low-density polyethylene (LDPE, average molecular weight 4000) is used as the plastic source, obtained from Sigma-Aldrich without further treatment. The LDPE is mixed with a catalyst and then loaded into a reactor within a Sairem microwave system to generate a mixture of olefins. Preliminary experimental results indicate that at 400°C in microwave heating, the light olefin selectivity is about 60% with ethylene selectivity of 30% (by weight). Furthermore, the microwave process requires significantly less energy compared to the conventional thermal process. This experimental data is utilized with COMSOL modeling to design a suitable industrial-scale reactor and develop a conceptual flowsheet in the ASPENPlus environment. A separation scheme based on a train of distillation columns is developed to produce industrial quantities of polymer-grade ethylene and propylene. Heat integration tools are utilized to reduce the hot and cold utilities used in this process. This novel design is compared with the conventional process of making ethylene via ethane cracking. A technoeconomic analysis is conducted to demonstrate the economic feasibility of this process.