Principal component analysis for kinetic scheme proposal in the thermal and catalytic pyrolysis of waste tyres

• PCA is proposed as a method for the proposal of kinetic schemes in tyre pyrolysis.
• This tool provides criteria for lumping the products in the pyrolysis of polymers.
• The scheme proposed considers primary and secondary thermal cracking reactions.
• Catalytic pyrolysis requires additional reactions promoted by the catalysts used.

Principal component analysis is used as a pattern recognition method to find criteria for grouping into lumps the compounds formed in the thermal and catalytic pyrolysis of waste tyres. This information is the stating point for the proposal of simple kinetic schemes that efficiently describe the complex reactions that occur in the pyrolysis process. It has been proven that the kinetic scheme must consider a depolymerization step of the waste to give isoprene and styrene monomers and the dimer of the former (limonene), the formation of primary products (char, tar and gas) by thermal cracking of the original high molecular weight compounds, and the subsequent secondary reactions by thermal cracking of heavy primary fractions (tar) to form lighter fractions (gas, gasoline and C10− aromatics). The use of a catalyst prepared based on a HY zeolite selectively enhances the reactions of condensation and alkylation of limonene and gasoline to aromatics, whereas the one based on a HZSM-5 zeolite selectively enhances the cracking of tar to lighter fractions (gas and C10− aromatics), limonene cracking to isoprene and C5–C10 hydrocarbons or even the cracking of the latter to C1–C4 gases.