Pyrolysis of PC/ABS blends in gaseous ammonia

Polycarbonate/acrylonitrile–butadiene–styrene (PC/ABS) blends are important engineering plastics for electronic and automotive applications. This study investigates how gaseous ammonia (NH 3 ) affects the fixed-bed pyrolysis of a PC/ABS blend at 500 °C and atmospheric pressure. The NH 3 volume fraction in the carrier gas, x v , NH 3 , was varied between 0 and 0.4 while all other process parameters were kept constant. Complete mass balances were established and the liquid products were analyzed by gas chromatography with flame ionization detection (GC-FID) as well as comprehensive two-dimensional gas chromatography–mass spectrometry (GC × GC–MS). Increasing x v , NH 3 shifts the overall product distribution from gases and solids to liquids. The gas yield decreases from about 8 to below 1 wt%, and the solid yield from 10 to 3 wt%, whereas the condensate yield increases from roughly 70 to 90–100 wt%. Mass-balance evaluation reveals a systematic NH 3 deficit that is consistent with the capture of CO 2 as ammonium carbamate. Hydrogen yields increase monotonically with x v , NH 3 , indicating progressive NH 3 cracking, while CH 4 , CO, and especially CO 2 are strongly suppressed and approach plateaus at x v , NH 3 ≳ 0.2 . On the molecular level, NH 3 promotes depolymerization of PC toward bisphenol A (BPA) and suppresses multiple side reactions. The BPA yield rises from 26.5 wt% at x v , NH 3 = 0 to 35–40 wt% at x v , NH 3 = 0.4 , corresponding to an increase from 41 % to 59 % of the theoretical maximum based on the PC content, whereas phenol and styrene yields remain nearly unchanged. Targeted GC–FID and untargeted GC × GC–MS analyses combined with volcano plot analysis show that diverse PC-derived phenolics, including alkylphenols and species formed via isopropylidene cleavage, are suppressed. These results indicate that gaseous NH 3 may be used to tune PC pyrolysis toward higher BPA recovery and lower char formation and thus may offer a route toward more selective thermochemical recycling of PC.