Autoclave pyrolysis of carbon reinforced composite plastic waste for carbon fibre and chemicals recovery

Carbon reinforced composite plastic (CRCP) waste has been pyrolysed under nitrogen atmosphere in a batch stainless steel autoclave between temperatures of 350 and 500 degrees C and reaction times of up to 60 min. The reaction products were dominated by solid residue (72-77 wt-%), gas (2-4 wt-%) and liquid (22-25 wt-%). The solid residue consisted mainly of carbon fibre, giving up to 98 wt-% recovery. However, the mechanical properties of the recovered fibres were lower when compared with a sample of virgin carbon fibre. The gas products contained mainly carbon dioxide and some hydrocarbon gases. The proportion of the combustible gases gave calorific values of up to 35 MJ m(-3). The liquid products consisted of 15-20 wt-% water, possibly from the degradation of the amide/ester linkages in the resin, and the rest was dark brownish oils, soluble in dichloromethane. The thermal gravimetric/differential thermogravimetric analysis of the CRCP waste indicated that the primary resin present could be based on polybenzoxazine polymer. The major components of the oils included aniline, methyl aniline and phenols. Apparently, these chemical products could be regarded as the monomers for making the resin and its curing agents (e.g. bisphenol A). Hence, the autoclave pyrolysis allowed complete degradation of the resin fraction of the CRCP at moderately low temperature, along with the recovery of carbon fibre and chemical feedstocks.