Catalytic pyrolysis of mixed plastic wastes from public places to liquid oil: A case of Kathmandu Valley, Nepal

• Lab scale pyrolysis process of mixed plastic was successfully investigated. • Blended liquid oil was tested for its efficiency on a motorbike engine. • Use of catalyst increased yield and reduced retention time of the reaction. • PET plastics in the mixture hindered the production of liquid oil. This study addresses the challenge of plastic waste disposal by exploring its potential as an alternative fuel source. It investigates the conversion of a plastic waste mixture (20% LDPE, 40% HDPE, and 40% PET) into liquid fuel through catalytic pyrolysis. Using a custom-designed small-scale pyrolysis plant, the plastic samples were converted into liquid fuel with the aid of locally sourced bentonite powder as a catalyst, at temperatures ranging from 250°C to 450°C. Results demonstrate that the oil yield increases with both temperature and use of bentonite powder as a catalyst. At 450°C, 351±7.64 ml of liquid oil was produced with 10 g of catalyst, increasing to 355±4.17 ml with 15 g and 358±2.65 ml with 20 g, using 1 Kg of plastic waste sample. The retention time is reduced from 1.5 hours without a catalyst to 30 minutes with it. A 20% liquid oil and 80% gasoline blend demonstrated comparable power, torque, and engine temperature with respect to standard gasoline, achieving a mileage of 19.64±1.55 Km/L, engine torque of 1.37 Nm and engine temperature of 110°C at 3000 rpm, though higher blends show diminished performance. Key limitations include a low cetane number (43.8), use of old motorcycles, and lack of advanced chemical analysis (GC-MS/FTIR). Despite this, the study bridges lab research to practical application via intermediate-scale experiments and real-engine tests with a low-cost local catalyst. While further refining and emissions testing are needed, it highlights pyrolysis oil's potential as a sustainable fuel in the future.