Co-Pyrolysis Studies of Agricultural Residue and Plastics for Process Optimization in a Rotary Kiln Reactor System

This research mainly focuses on the co-pyrolysis of agricultural biomass, i.e., groundnut shell (GS) and different plastics such as low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP). Co-pyrolysis studies were conducted in a semi pilotscale rotary kiln reactor at 500 °C with different biomass to plastic ratios (90:10, 70:30, and 40:60). The maximum pyrolytic oil (Py-oil) yield of 49% was obtained with GS/HDPE in 40:60 ratio, while the maximum non-condensable gases (NCGs) yield of 36% was obtained with GS/LDPE (40:60). Maximum char yields of up to 38% were observed with pure GS. The yields of py-oil and NCGs. increased with increasing plastic ratio, whereas for char, the yield decreased with increasing plastic ratio. Elemental analysis of the py-oil showed an increase in the carbon and hydrogen content from 59 to 79% and from 7 to 12%, respectively, with increasing plastic content. The higher heating value (HHV) of py-oil increased from 25 to 43 MJ/kg with the addition of plastics to biomass. The chemical composition of the oil also varied significantly with different blend ratios and depended on the type of plastic. Overall, it was observed that by increasing the plastic ratio, there is a corresponding decrease in phenolics and improvement in aromatics (45%), alcohols (20%), and hydrocarbons (35%). The carbon content in char was found to increase moderately from 72 to 80% with an increase in plastic content.