ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Separation and characterization of products from thermal cracking of individual and mixed polyalkenes

E. Hájeková, L. Špodová, M. Bajus, and B. Mlynková

Faculty of Chemical and Food Technology, Slovak University of Technology, Radlinského 9, SK-812 37 Bratislava, Slovakia

E-mail: elena.hajekova@stuba.sk

Received: 27 September 2006  Revised: 13 March 2007  Accepted: 28 March 2007

Abstract: Low-density polyethylene (LDPE), polypropylene (PP), and their mixture in the mass ratio of 1: 1 (LDPE/PP) were thermally decomposed in a batch reactor at 450°C. The formed gaseous and oil/wax products were separated and analyzed by gas chromatography. The oils/waxes underwent both atmospheric and vacuum distillation. Densities, molar masses and bromine numbers of liquid distillates and distillation residues were determined. The first distillate fraction from the thermally decomposed LDPE contained mostly linear alkanes and alk-1-enes ranging from C₆ to C₁₃ (boiling point up to 180°C). The second distillate fraction was composed mostly of hydrocarbons C₁₁ to C₂₂ (boiling point up to 330°C). 2,4-Dimethylhept-1-ene was the major component of the first distillate fraction obtained from the product of PP decomposition, while in the 2nd distillate fraction it was 2,4,6,8-tetramethylundec-1-ene. The yields of some gaseous or liquid hydrocarbons obtained by distillation from thermally degraded LDPE/PP differed from the values corresponding to the decomposition of individual plastics due to the mutual influence of polyalkenes during their thermal cracking. Similarly, the yields of propene and methylpropene in the gaseous phase were higher in the case of mixture. Whereas the content of C₉ to C₁₇ alkanes and alkenes in the distillates separated from the liquid mixture obtained by the decomposition of LDPE/PP decreased, the formation of 2,4,6,8,10,12-hexamethylpentadec-1-ene remained unchanged. The corresponding mechanisms of thermal cracking were discussed.

Keywords: plastic waste - recycling - polyethylene - polypropylene - thermal cracking - GC analysis - physicochemical properties

Full paper is available at www.springerlink.com.

DOI: 10.2478/s11696-007-0031-6

Chemical Papers 61 (4) 262–270 (2007)