Co-pyrolysis of beech wood and polyamide-6: Impact of plastic concentration and wood/plastic synergistic effects

Biomass residues and waste can be converted into bioliquids by pyrolysis, which can contribute to both the production of renewable fuels and the recycling of waste. In this paper, the catalytic co-pyrolysis of mixtures of beech wood (BW) and polyamide-6 (PA6) in different ratios was investigated to assess the effect of PA6 con-centration on the properties of bio-oils and on the catalyst performances in upgrading the bio-oils. The catalytic treatment was applied to the pyrolysis vapors that were driven across a H-ZSM-5 catalyst bed before their condensation into liquid products. Increasing the PA6 concentration in the BW+PA6 blends led to an increase in the average molar mass of bio-oils and to an increase in their N-content. Caprolactam and 5-cyano-1-pentene were the main products derived from PA6 pyrolysis, and their ratio also changed with the PA6 concentration. The production of fully deoxygenated compounds was strongly reduced in the presence of PA6, as the result of catalyst deactivation, also evidenced by the increase in sugars and decrease in furans concentrations. The amount of coke deposited on the catalyst decreased as the PA6 concentration increased, but this coke contained more nitrogen. Synergistic effects in the BW+PA6 pyrolysis were evidenced by the positive or negative deviation of different parameters (mass of gas, liquid, solid products, mass of coke on the catalyst, C, N, O composition of bio-oils) from a simple arithmetic combination of the same parameters for pure BW or pure PA6 weighted by their concentrations, in particular the N-content in the bio-oils was much higher than expected.