Characterization and pyrolysis of post-consumer leather shoe waste for the recovery of valuable chemicals

Majority of post-consumer leather footwear currently ends up in landfill sites with adverse environmental impacts. Current waste recovery options have proven largely unsuccessful in minimizing this waste stream. This study investigates whether leather from post-consumer footwear can be pyrolyzed using gram-scale (fixed-bed) and microgram-scale (TGA) pyrolysis reactors. The investigation was conducted using final pyrolysis process temperatures between 450 and 650 °C and solid residence times of 5 to 15 minutes. The purpose of the experiments was to assess the waste recovery potential of leather pyrolysis products for valuable chemicals. The pyrolysis product fractions (solid, liquid, and gas) distribution were investigated, optimal pyrolysis conditions presented, and the product fractions characterized for their elemental and chemical composition using ultimate and GC-MS analysis. The distribution of the product fractions proved leather footwear pyrolysis was viable under the given conditions. The completion of leather footwear pyrolysis was evident at 650°C since the solid yield reached a constant value of approximately 25 wt.%. The liquid fraction was maximized within the temperature range of 550-650°C (Max= 54 wt.%), suggesting optimal pyrolysis conditions within this range. The higher heating values (HHVs) of the pyrolysis leather oil (33.6 MJ/kg) and char (25.6 MJ/kg) suggested their potential application for energy or fuel. The liquid fraction comprised predominantly of nitrogen derivatives and potential applications areas include use in the production of fertilizers, chemical feedstocks, or the pharmaceutical industry. This study proved that leather from post-consumer footwear can be pyrolyzed and provided valuable insight into its characterization and potential applications areas.