Beneficial Use of Waste Tires: An Integrated Gasification and Combustion Process Design via Thermo-Gravimetric Analysis (TGA) of Styrene–Butadiene Rubber (SBR) and Poly-Isoprene (IR)

Currently, in the United States, nearly 58 million tires per year (∼640,000 tons) are discarded typically in landfills, which pose serious environmental issues because of their durability and strong tendency to leach toxic chemicals. A novel process intensification design (integrated combustion–gasification reactor) to convert waste tires to useful raw materials, such as syngas (CO and H2), has been investigated. This work will report on the findings from a series of thermogravimetric analyses (TGA) experiments at various heating rates on styrene–butadiene copolymer (SBR) and polyisoprene (IR) and the effects of various atmospheres (7% O2/N2, Air, 30%O2/N2, 3%H2/N2) on the combustion and gasification processes. The results indicate that oxygen enhanced atmospheres only have a significant effect on increasing combustion efficiency at low heating rates, such as 10°C/min. An unexpected result of the N2–O2 tests was the development of a plateau in mass-loss vs. temperature curves, at 700°C. Polyisoprene thermograms in 7% O2/N2 atmosphere, plateau was detected only at a low heating rate, such as 10°C/min. Furthermore, the amount of tar created is significantly different; polyisoprene generates much more tar. Measured data were used to obtain the kinetics of the significant reactions of waste tire conversion. That was combined with thermodynamic values from the literature and programmed into Aspen™ to simulate the integrated process. The results for a hypothetical reactor that consumes 10 million tires and 87,600 m3 of water (in the form of sewage sludge) per year, produces 18.9% H2, 16.6% CO, 6.0% H2O, 8.4% CO2, and 49.9% N2 of syngas. The total energy output is 28.6 MW of sensible heat and 103 MW of chemical energy.