Pyrolysis study of waste cable hose with thermogravimetry/Fourier transform infrared/mass spectrometry analysis

Pyrolysis is considered as a promising method to recycle waste rubber material for fuel or chemical feedstock. In the present study, pyrolysis of one kind of typical waste cable hose with major composition of flame-retardant ethylene-propylene-diene monomer (EPDM) rubber is studied in inert atmosphere. Thermogravimetric analysis (TGA), in situ Fourier transform infrared (FTIR) and online TGA-FTIR-mass spectra (MS) analyses are employed. The activation energy and reaction mechanism are obtained employing three popular model-free methods and one typical model-fitting method. Results indicate that the pyrolysis of waste cable hose in inert atmosphere may be divided into three stages, wherein the aluminum hydroxide and magnesium hydroxide decompose at the first two stages and the decomposition of EPDM rubber and decabromodiphenyl ethane occurs in the third stage. The heating rate has little effect on the quantity of mass loss or conversion. The activation energy increases considerably in the first two stages, but remains almost constant in the third stage. The average values of the activation energy in the first, second and third stage are 130.81, 171.55 and 205.61 kJ/mol, respectively. It is also found that the 2-D diffusion model g(α)=(1-α)ln(1-α)+α may be the most suitable model to characterize the pyrolysis in the third stage and diffusion may be in charge of the pyrolysis in the third stage. Furthermore, volatile products including H₂O, aliphatic compounds, CO₂ and aromatic compounds mainly appear in the third stage. The specific gas species included in the aliphatic and aromatic compounds are presented. The maximum amount of the four volatile products in the order of most to least is aliphatic compounds >H₂O or aromatic compounds >CO₂. In particular, the maximum amount of aliphatic compounds outdistances that of the other three volatile products, which is extraordinarily useful for the recovery of waste cable hose for valuable gases either as fuel or chemical feedstock.