The physicochemical properties of liquid biofuel derived from the pyrolysis of low-quality rubber waste

Abstract

This research explores the potential of low-quality rubber waste as a feedstock for liquid biofuel production via pyrolysis, achieving a conversion rate of 65–70 %. The study presents a comprehensive analysis of waste rubber pyrolysis oil (WRPO) using FT-IR, ¹H and ¹³C NMR, and GC-MS techniques to identify its chemical composition and fuel properties. FT-IR analysis reveals a complex mixture of saturated and unsaturated hydrocarbons, aromatic rings, and oxygenated compounds, while NMR analysis confirms the diverse chemical structure of WRPO. GC-MS identifies key compounds, including d-Limonene, Dimethyl phthalate, Methyl hexadecanoate, and Oleic acid methyl ester, with 18.49 % saturated hydrocarbons and 81.51 % unsaturated hydrocarbons. The TGA results show that WRPO exhibits evaporation and thermal decomposition characteristics similar to B10 diesel, with evaporation beginning below 40 °C and complete decomposition at 300 °C, highlighting its potential as an efficient and environmentally friendly biofuel. Fuel property testing reveals WRPO has a kinematic viscosity of 1.47 cSt, a density of 785 kg/m³, and favorable low pour and cloud points (<−5 °C), making it suitable for cold climates. However, WRPO has a lower heating value of 9675 kcal/kg compared to B10 diesel (11083 kcal/kg) and a high acid number of 4.24 mg KOH/g, which may lead to oxidation and corrosion. In conclusion, WRPO shows considerable promise as a biofuel but would benefit from blending with higher-energy fuels, such as B10 diesel, palm oil biodiesel, or waste cooking oil biodiesel, to improve its stability, combustion efficiency, and heating value. This blending strategy enhances WRPO's potential for sustainable biofuel production and engine use.