Two-step pyrolysis for waste HDPE valorization

Among the implemented strategies for recycling and reutilization of HDPE, pyrolysis process is considered an attractive alternative, because its potential to use waste materials to produce valuable chemical feedstock and high energy content hydrocarbons. Through pyrolysis transformation, plastics are thermally cracked in the absence of oxygen and the reaction parameters can be controlled to favor the production of specific compounds and liquid fractions. During this project, waste HDPE thermal decomposition was evaluated in a range of 450-550 degrees C, considering samples of 2 mm and 5 mm and a residence time of 30 min. A design of experiments was applied to find the optimal conditions to maximize the volatile fraction. Then the waste HDPE was transformed in a two-step pyrolysis in order to maximize the volatiles fraction and the intermediate and final products analyzed. According to results, A volatile fraction equivalent to the 97 % of HDPE mass was obtained at 500 degrees C, with a 5 mm particle size and a hold time of 30 min. The chemical analysis of wax and oil products showed that, although both blends are similarly made of alkanes, alkenes, and dienes, the compounds found in oil are shorter-chain and in a greater variety than those found in wax. (c) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.