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

Abstract

Carbon reinforced composite plastic (CRCP) waste has been pyrolyzed under nitrogen atmosphere in a batch stainless steel autoclave between temperatures of 350°C and 500°C and reaction times of up to 60 minutes. 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 35MJ/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 darkbrownish oils, soluble in dichloromethane. The TGA/DTG 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.

A review on the recycling of waste carbon fibre/glass fibre-reinforced composites: fibre recovery, properties and life-cycle analysis

“…This process is limited to GF as no suitable study was found concerning CF. [65] further developed the process and successfully recycled CFRP waste-in which 98 wt% of the solid products (rCF) were recovered efficiently. The study stated that a reaction time increase could cause a decrease in the mechanical properties of the recycled CF.…”

“…The study found that chemical modification on the surface of recycled CF and GF could improve fibre properties. Additionally, both studies [61,65] used secondary combustion (SC) to oxidise minor resin impurities and char formation on the pyrolysed fibres. When comparing the results, oxidised fibres retained the most mechanical properties when compared to non-oxidised fibres.…”

Developing Polybenzoxazine Composites Based on Various Carbon Structures

“…Pyrolysis process of CF/PBZ composites was also investigated for CF and chemical recovery . The pyrolysis gases were mainly CO 2 , CO, CH 4 , H 2 , and small amounts of other hydrocarbons with high caloric values.…”

“…Pyrolysis process of CF/PBZ composites was also investigated for CF and chemical recovery. [70,71] The pyrolysis gases were mainly CO 2 , CO, CH 4 , H 2 , and small amounts of other hydrocarbons with high caloric values. A maximum surface area of 802 m 2 g −1 was observed for the activated CFs after heating process at 850 °C for 5 h. Nitrogen adsorptiondesorption isotherms revealed that the resultant activated CFs were mostly microporous.…”

Heterogeneous Thermoset/Thermoplastic Recycled Carbon Fiber Composite Materials for Second-Generation Composites

“…However, the resulting fiber often has inferior mechanical properties to virgin material and becomes very difficult to disperse into second-generation products. In addition, the amount of energy and chemicals required to obtain these products is considerable [9][10].…”