Polyurethane Recycling: Conversion of Carbamates-Catalysis, Side-Reactions and Mole Balance

Area of Science:

• Polymer Chemistry
• Catalysis
• Sustainable Materials

Background:

• Diisocyanates are essential polyurethane monomers but are typically lost during recycling processes.
• Developing phosgene-free chemical recycling routes for polyurethanes is crucial for sustainability.

Purpose of the Study:

• To investigate the thermal and catalytic cracking of methyl N-phenyl carbamate (MPC) into phenyl isocyanate.
• To evaluate the effectiveness of various catalysts in this carbamate decomposition reaction.

Main Methods:

• Thermal and catalytic cracking of MPC in batch autoclaves at 160-200 °C.
• Utilized catalysts: ZnO, Bi2O3, Al2O3, and Montmorillonite K-10.
• Product analysis with high mole balance (≥90%) was performed.

Main Results:

• Thermal cracking of MPC was minimal at the tested temperatures.
• Catalytic cracking predominantly yielded aniline and urea, not phenyl isocyanate.
• The reaction appeared to be influenced by water adsorbed on the catalyst surfaces.

Conclusions:

• The catalytic cracking of carbamates to isocyanates is hindered by side reactions, likely water-mediated.
• Further research is needed to optimize catalysts and conditions for efficient phosgene-free isocyanate recovery from polyurethanes.