Nitrogen-enriched pyrolysis and catalytic pyrolysis of municipal sludge extract

Abstract

Municipal sludge (MS) extract obtained by degradative solvent extraction has the typical fuel characteristics of high nitrogen content, zero moisture, and low ash, which is suitable for producing valuable nitrogen-containing chemicals. This study compared the nitrogen-rich pyrolysis characteristic of MS extracts using thermogravimetric/thermogravimetric-mass spectrometry/pyrolysis-gas chromatography-mass spectrometry. The composition of bio-oil from catalytic pyrolysis of MS extracts with HZSM-5 was studied, and the pyrolysis kinetic models was established. The results show that different from the raw MS pyrolysis, the MS extracts pyrolysis all had two main peaks with similar values in the range of 140–530 °C (Stage L and Stage W). NH₃ is mainly released in the range of 140–370 °C (Stage L), and the nitrogen-containing compounds content in the bio-oil in this stage is 41.81%. After adding HZSM-5, the weight loss rate in Stage L decreased by 21.97%, while that in Stage W increased by 10.04%. An obvious weight loss peak (30.32%) appeared at the temperature of 530–900 °C, which is due to the increased fixed carbon content (increased by 16.07%) of the bio-oil from catalytic pyrolysis. The number of components in the nitrogen-containing compounds decreases much, however, its yield increases by 9.45% due to the transformation of nitrogen by the catalyst effect of HZSM-5 adding.