Abstract
Pyrolysis is considered to be a promising method to dispose waste plastics by thermal cracking into chemicals. Previous studies focus on pyrolysis recycling of waste thermoplastics. The pyrolysis of waste thermosetting plastics, which may be different from that of waste thermoplastics, receives little attention. In order to provide guidance for reactor design and thermo-chemical process management for the pyrolysis recycling of waste thermosetting plastics, the pyrolysis kinetics, volatile products and reaction mechanisms of one typical waste thermosetting plastics namely phenolic fibre-reinforced plastic (phenolic FRP) are studied in the present study. Thermogravimetric analysis (TGA), in situ Fourier transform infrared (FTIR) and online TGA-FTIR-mass spectra (MS) analyses are employed. Results indicate that the pyrolysis of waste phenolic FRP in inert atmosphere may be divided into two stages with the threshold conversion rate of 0.2. The average values of activation energy in the first, second and whole pyrolysis process were 174.66 kJ/mol, 233.62 kJ/mol and 223.22 kJ/mol, respectively. The crosslinking between phenol derivatives and breakage of branched chain may result in the occurrence of the first stage, while the occurrence of the second stage may be due to the breakage of chain backbone and oxidation of methylene and hydroxymethyl. Four kinds of gases including H2O, alcohols, aliphatic compounds and carboxylic acids mainly constitute the volatile products in the first stage. The volatile products in the second stage mainly consist of CO, CO2, carboxylic acids and aromatic compounds. The amount of the volatile products in the second stage is much larger than that in the first stage. The maximum amount of these seven gases in the order of most to least is CO2 > CO > alcohols > carboxylic acids > aliphatic compounds > water vapour > aromatic compounds. It may be better to recover the waste phenolic FRP for valuable gases either as fuel or chemical feedstock in the first stage than the second stage.
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