Two-stage thermal and catalytic cracking of polypropylene using natural clinoptilolite in a catalytic step to petrochemicals and fuels

Raw natural clinoptilolite from the Slovak deposit in Nižný Hrabovec and clinoptilolite treated with solution of hydrochloric acid (0.1 M) were used to promote cracking of polypropylene (PP), as a representative of the second most common plastic in municipal waste, into valuable gaseous and liquid hydrocarbons. The influence of catalyst was studied using two-stage cracking apparatus. The process consisted of batch semiflow thermal cracking reactor connected to flow catalytic reactor operating at 450 °C. The cracking activity of fresh, unregenerated and regenerated clinoptilolite was studied. The cracking activity into gaseous hydrocarbons was the highest with fresh catalyst (28.1 % for raw and 53.4 % for acid-modified catalyst). It represented an increase of 11.3 % and 36.6 %, respectively, in comparison with thermal cracking. The content of valuable methylpropene in gas was markable (up to 27.1 wt %). It was confirmed that catalytic cracking of PP with unregenerated and regenerated catalyst was also effective although the cracking activity of those catalysts slightly decreased. All catalysts produced narrower range of C5-C14 hydrocarbons in the liquid fraction (mainly gasoline fraction) compared to thermal cracking (C5-C20 hydrocarbons).