Polyethylene and Polypropylene Pyrolysis Using Fe³⁺-Modified Kaolin Catalyst for Enhanced Gas and Pyrolysis Oil...

Area of Science:

• Materials Science
• Catalysis
• Chemical Engineering

Background:

• Polypropylene (PP) and low-density polyethylene (LDPE) are abundant plastic wastes posing significant environmental challenges.
• Developing cost-effective and efficient catalytic processes for polyolefin valorization is crucial for sustainable waste management.
• Existing methods often require specialized catalysts or reactors, limiting their industrial applicability.

Purpose of the Study:

• To develop an inexpensive bifunctional catalyst for the simultaneous pyrolysis of PP and LDPE.
• To investigate the effect of catalyst loading on product distribution (gas, liquid, char, wax).
• To explore the catalytic mechanism involving in situ generation of active species.

Main Methods:

• Calcined and acid-leached kaolin was impregnated with iron(III) nitrate nonahydrate (Fe(NO3)3·9H2O) to achieve 6.6 wt.% Fe2O3.
• Slow fixed-bed pyrolysis experiments were conducted in a quartz tube reactor across a temperature range of 25–800 °C.
• Catalyst-to-plastic mass ratios of 1:4, 1:2, and 1:1 were employed for both PP and LDPE pyrolysis.

Main Results:

• For PP, increasing catalyst loading enhanced non-condensable gas yield (26–44 wt.%) and liquid aromatics (27.9–72.3%), while reducing paraffins, olefins, and wax.
• LDPE pyrolysis at a 1:4 ratio yielded 56 wt.% oil and 22 wt.% wax; higher catalyst ratios primarily boosted methane/CO-rich pyrolysis gas and char.
• Gas analysis indicated in situ generation of H2O, CO, and H2 via Fe2O3 reduction and kaolin de-hydroxylation.

Conclusions:

• The developed Fe/kaolin catalyst is an effective and inexpensive option for the pyrolysis of both PP and LDPE.
• The catalyst facilitates the production of valuable aromatics from PP and oil from LDPE, with tunable product selectivity.
• The process's scalability, catalyst regenerability, and ability to handle mixed polyolefins present a promising route for waste plastic valorization.