Slow pyrolysis of polyethylene terephthalate: Online monitoring of gas production and quantitative analysis of waxy products

The slow pyrolysis of polyethylene terephthalate (PET) was investigated over a range of final temperatures from 410 degrees C to 480 degrees C yielding a wide variety of species. The objective of the current study was to provide thermal dependent evolution profile for mass loss and pyrolysis gas, in addition to the partial quantification of the waxy products. The polymer degradation was first characterized by thermogravimetric analysis. Many parameters were studied such as final temperature, heating rate, flow rate and the presence or not of a lid on the crucible. The slow pyrolysis of PET was then performed in a horizontal tubular reactor at 5 degrees C/min. The pyrolysis products were analysed, focusing especially on gaseous and waxy fractions. The gas emitted was monitored online by mu-GC which allowed establishing their real time evolution profile. Carbonyl species were analyzed using HPLC. As a result, the gas contained mainly acetaldehyde, CO and CO2, and to a smaller extent ethylene and benzene. Benzene profile exhibited two peaks, indicating that there may be two steps or two main reactions in the release of this compound. The waxy products were characterized by GC/MS-FID and FTIR techniques. FTIR showed that the main chemical moieties of the waxy products were carboxylic acids and esters. GC/MS-FID confirmed that these pyrolysates contained mainly benzoic acid and its derivatives and monovinyl terephthalate. The quantitative analysis showed that the highest production of benzoic acid was obtained at 430 degrees C. Its yield is 11% of initial PET mass.