Polymer Waste Treatment Using Rotating DC Arc Plasma Technology

Polymer has been widely used in industry and daily life,due to excellent properties.However,severe pollution problems accompany the wide use of polymer because of its high stability,large size and various additives.Polymer waste treatment is achieved nowadays by recycling,landfill and thermal degradation,which suffer from serious secondary pollution or generation of other toxic substances such as dioxin.This article proposed for the first time a new method of producing high-value gas(C2H2,CO)from polymer waste with a rotating direct current arc plasma technology,creating new opportunities for the utilization of polymer waste.Polyethylene was chosen as the representative material of linear polyolefin.Effects of input power,polyethylene feed rate,working gas flow rate and excitation current on the pyrolysis of polyethylene were systematically studied.The results show that product gas with C2H2 content higher than 10%can be obtained with proper input power,high feed rate and low working gas flow rate.The selectivity and yield of C2H2 can reach 85%and 75%,respectively,with the specific energy consumption of C2H2 as low as 15 kWh/kg-C2H2.The relationship between pyrolysis results and specific enthalpy(Ensp)as well as the ratio of H/C is revealed.Pyrolysis of polyolefins with alkyl side chains or aromatic side chains was studied,with polypropylene and polystyrene selected as representative materials.The results indicate that alkyl side chains has little influence on polymer pyrolysis,while aromatic structure tend to break C-C bond to form CH radical at low temperature and tend to be a coke precursor at high temperature.Polyethylene terephthalate(PET)is pyrolyzed to investigate the plasma pyrolysis of polymers with oxygen.The result shows that oxygen's presents in product gas is mainly in the form of CO,which would inhibits the formation of hydrocarbon products such as C2H2,C2H4 especially at high input power due to its stability at high temperature.The presence of oxygen favors a lower coke formation.For the materials with high O content,non-hydrogen plasma pyrolysis for the production of syngas is a promising method of utilization.Thermodynamic equilibrium calculation was carried out in single-phase equilibrium model and multi-phase equilibrium model based on the Gibbs energy law.The comparison between the calculated results and experimental results show that the single-phase model is better at predicting the gaseous product,while the multi-phase model takes the coking into account.The calculated results of less coking pyrolysis system is more accurate.The polymer waste pyrolysis equilibrium temperature is 3000-4000 K and side products(C2H4,CH4)do not exist at this temperature.But C2H2 content decreases during the quenching section and a small amount of side products will be produced.