Application of highly stable biochar catalysts for efficient pyrolysis of plastics: a readily accessible potential solution to a global waste crisis

Biochar catalysts derived from corn stover and Douglas fir were employed for the catalytic pyrolysis of model low-density polyethylene (LDPE) and real waste plastics. The corn stover derived biochar resulted in a liquid yield of about 40 wt% without wax formation. The liquid product comprised about 60% of C8–C16 aliphatic, 20% of mono-aromatic, and 20% of C17–C23 aliphatic hydrocarbons. The gas yield was about 60 wt% with 60–80 vol% of H2. The corn stover derived biochar tended to generate more H2 gas, and by contrast, CH4 formation was favored when employing the Douglas fir derived biochar catalyst. As for the properties of reused biochars, the biochar catalyst derived from corn stover showed much better activity and longer lifetime than Douglas fir derived biochar, which might arise from the different contents of inherent minerals in biochar catalysts. After 20 times of experimental reuses and recycles, the corn stover derived biochar still possessed high activity in degrading LDPE without wax formation. And after 10 cycles of reuse of Douglas fir derived biochar, the catalyst was still active but its activity level sharply declined with the production of amounts of wax. Additionally, real packaging plastic wastes respectively consisting of LDPE, high-density polyethylene (HDPE), polypropylene (PP), polystyrene (PS) and polyethylene terephthalate (PET) also could be effectively converted into valuable hydrocarbons and gases through using biochar catalysts, which implied that biochar catalysts could be applied to the conversion of these common waste plastics. The current study demonstrated a new and efficient conversion of various waste plastics to jet fuels and H2 by using a powerfully simple, and long-life biochar catalyst.