Investigation on the co-pyrolysis of waste rubber/plastics blended with a stalk additive

•When the rubber was 60 wt% in blending wastes of plastic and rubber, the oil yield rate reached the highest point.•Straw additive contributed to the oil production of co-pyrolysis.•The heating rate had clear effect on the oil yield of the co-pyrolysis.•With the oxygen-rich straw added, the content of alcohol, ester and ketone compounds in the pyrolysed oil increased.

This study presents an experimental investigation of co-pyrolysis of discarded rubber and plastics in a tube furnace. The properties of the pyrolysis oil and solid residue under various blending ratios of rubber and plastics were investigated. The impacts of the stalk additive and the heating rate on the pyrolysis oil yield and feedstock-to-oil energy conversion efficiency (FOECE) were studied. Compared with the pyrolysis of rubber or plastics separately, the co-pyrolysis of rubber and plastics produced a higher oil yield with a higher oil heating value. When the mass fraction of the rubber was 60 wt%, the pyrolysis oil yield and FOECE reached their maximum values. When adding 10% stalk additive at a rubber-to-plastics ratio of 4:1, a higher oil yield was achieved, and the oil yield increased by 10.3 wt%, where the heating value of the pyrolysis oil reached 39.93 MJ kg−1. The stalk additive only had a slight impact on the solid residue and the completeness of the pyrolysis reactions. The stalk additive increased the FOECE and postponed the highest yield point to the 80 wt% rubber blend because the greater volatility promoted the pyrolysis reaction and the production of condensable gaseous components. A higher heating rate improved the oil yield. According to the elemental analysis, a small fraction of sulfur existed in the oil. The stalk additive increased the H/C ratio in the oil. Through the GC–MS analysis, the primary components in the pyrolysis oil from the rubber and plastics blend were identified as alicyclic hydrocarbons and aromatics, whereas the oxygen-rich stalk additive increased the contents of alcohols, esters, and ketones. Overall, the stalk additive significantly improved the yield and the FOECE when co-pyrolysis of rubber/plastic blends was performed.