Pyrolysis characteristics and gaseous product release properties of different livestock and poultry manures: Comparative study regarding influence of inherent alkali metals

Livestock and poultry manures are important biomass resources that can produce biogas by pyrolysis. Manures contain varied components and alkali metal contents, which may increase the complexity of pyrolysis. The influence of alkali metals in raw manure on the pyrolysis characteristics and the properties of the released gaseous product between different livestock and poultry manures were compared by thermogravimetric analysis coupled with Fourier-transform infrared spectroscopy and mass spectrometry (TGA-FTIR-MS). Five livestock and poultry manures showed different pyrolysis characteristics caused by the different components and alkali metal contents. The high alkali metal contents of swine manure (SM), broiler litter (BL), and layer chicken litter (LL), each of which showed one pyrolysis peak, catalytically reduced the activation energy; dairy manure (DM) and beef manure (BM) from cattle showed two overlapped pyrolysis peaks. The second release peaks of CH4 for SM, BL, and LL were more intense than those of DM and BM, corresponding to the lower absorption intensities of CO and COC/CC for SM, BL, and LL compared to those of DM and BM. The FTIR spectra of raw manures and biochars obtained at different final pyrolysis temperatures showed that the decreased absorptions of characteristic peaks in the biochars corresponded to the variations in the gaseous products. SM released the highest volume of H2 and a high CH4 yield, indicating that SM is more suitable for biogas production by pyrolysis gasification than other animal manures.