(229f) Catalytic Co-Pyrolysis of Polyurethane Waste and Lignocellulosic Biomass with Two-Dimensional Zeolites

Continuous increase of plastic waste, without effective management, poses a threat not only to mankind but also to the environment. Upcycling of plastic wastes to new, valuable products is a promising but challenging alternative to address this issue. In the United States, for example, polyurethane is one of the most important and widely-used plastics. Polyurethane waste generally comes with others, such as biomass residues, while separation/purification of plastic wastes is difficult and costly. Herein, we investigated catalytic co-pyrolysis of polyurethane waste and lignocellulosic biomass in a fixed bed reactor with a variety of two-dimensional zeolites (e.g., different porosities and silica-to-alumina ratios) at varying reaction temperatures (400-600 °C), polyurethane-to-biomass ratios (1:5-5:1), and waste-to-catalyst ratios (1:2-2:1). Reaction temperature and polyurethane-to-biomass ratio were found to affect product yields and distribution significantly. Liquid product, i.e., bio-crude, was found to increase from 30 to 45 wt.% with reaction temperatures, while gas-phase product increased from 35 to 55 wt.% with increasing amount of catalysts. A solid product, i.e., biochar, was found to remain constant at approximately 20 wt.%. By gas chromatograph-mass spectrometry and (¹H and ¹³C) nuclear magnetic resonance, the resulting bio-crudes was shown to consist mainly of polycyclic aromatic hydrocarbons, nitrogen heterocycles, diols, ethers, esters, alcohols, and acids. Interestingly, with increased ratios of lignocellulosic biomass, toxic and harmful compounds (e.g., amino-, cyano-, and nitro-polycyclic aromatic hydrocarbons) in bio-crudes were decreased. Coking on the catalysts after use was also analyzed, using thermogravimetric analysis and positron annihilation lifetime spectroscopy. The extent of coking on the spent catalysts was observed to reduce in co-pyrolysis with higher ratios of polyurethane waste. Our findings pointed out that catalytic co-pyrolysis of plastic waste and biomass for productions of biofuels and/or biochemicals had a positive contribution on promoting plastic upcycling, waste management, energy security, and environmental protection.