Interaction between feedstocks, absorbers and catalysts in the microwave pyrolysis process of waste plastics

This work has selected high density polyethylene (HDPE), activated carbon (AC) and molecular sieves to form microwave pyrolysis system and studied the effects of reaction conditions and material mixing mode on the products. The mass ratio of HDPE and AC is between 100:60 and 100:330, and different heating power combinations (20–40% of the maximum power of 900 W) are used to meet the heat transfer requirements in different stages. The heating properties of the AC and the interaction between materials are also discussed. The results show that the temperature distribution of reaction system tends to be higher in the center, which makes the products discharge quickly. Therefore, adopting continuous heating, reducing the residence time and the amount of AC can promote wax formation and the maximum yield was 87.75 wt%. While adopting intermittent heating and complete mixing mode, increasing the residence time and the AC amount are beneficial to the liquid formation (mainly between C7 and C20) with the maximum yield of 82.36 wt%. The catalyst can enhance the break of long chain hydrocarbons and shorten the whole reaction time. However, the catalytic effect on the further pyrolysis of the product is limited due to the high heating speed of microwave field. [Display omitted] •The interaction mechanism among absorber, feedstock and catalyst has been proposed.•The effect of mixing mode of materials in microwave field on the product was studied.•Different heating strategies were proposed according to the different products.•Spherical activated carbon has dual functions of microwave absorption and catalysis.•Catalyst with big surface area and porous structure is easier to get catalytic effect.