Catalytic pyrolysis of spruce wood and swine manure in an auger reactor using NaCl and MgCl₂

This work investigates the catalytic pyrolysis of spruce wood (SW) and swine manure (SM) in a pilot-scale auger reactor using two alkali and alkaline earth metal (AAEM) catalysts, namely, NaCl and MgCl₂. Experiments evaluated the effects of temperature (400–600 °C), N₂ flow rate (4–8 L/min), and solid residence time (75–125 s) on product properties. Temperature proved to be the main process driver. Increasing it from 400 to 600 °C shifted yields toward syngas, producing carbon-rich aromatic biochars with lower O/C and H/C ratios, and gas richer in CO, H₂, and CH₄. Conversely, higher N₂ flow rates decreased oily phase yields and the water content. Under identical conditions, SM pyrolysis systematically yielded more biochar and aqueous phase but less oil and syngas than SW, due to its higher ash, AAEM, and nitrogen contents. For both feedstocks, NaCl and MgCl₂ impregnation increased char and ash yields while elevating the bio-oil water content, especially with MgCl₂, in line with the promotion of dehydration reactions induced by this catalyst. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) revealed that NaCl mildly affected the properties of SW-derived bio-oils, yielding slightly lower average m/z, O/C and unique compounds linked to lignin/hemicellulose degradation. Conversely, MgCl₂ promoted CHO-type species detected as [M + Cl]⁻ adducts with lower oxygen counts, stemming from cellulose and hemicellulose dehydration. Both catalysts induced chlorinated species in SW and SM bio-oils, with MgCl₂ triggering denitrogenation. Finally, both AAEM chlorides seemed to promote decarboxylation and water-gas shift reactions, increasing syngas CO₂ and H₂ production at the expense of CO.