Sludge char-to-fuel approaches based on the catalytic pyrolysis II: heat release

The pyrolyzed sludge is concerned currently, while the produced higher heating value (HHV) is unclear yet. In this work, the effects of moisture content (MC), catalysts amount, and catalytic types on the HHV production were investigated. Based on the known fatty acids (FAs) and alcohol content, the heat release by catalytic and non-catalytic pyrolysis product was examined. A good correlation between the measured and calculated HHV in non-catalytic pyrolysis indicates that the method can effectively evaluate the pyrolysis effect. The results show that a higher HHV can be obtained by adding a catalyst when the MC was between 20 and 40% compared to the non-catalytic pyrolysis. In the catalytic pyrolysis, the maximum HHV produced by bentonite is 50.61 MJ kg^-1. Bentonite can rapidly initiate the decarboxylation but sand was a potential efficient catalyst because of the enrichment of large amounts of FAs C_16:0. If sand is used in combination with bentonite, C_16:0 may be enriched and further decarboxylated, eventually releasing more heat. Since sand is composed of SiO₂ and Al₂O₃, in the production of HHV, the addition of Al₂O₃ has a better catalytic effect than adding SiO₂. For the evaluation of catalytic pyrolysis products and HHV, it is proposed that the possibility of adding two types of catalysts for pyrolysis is of great significance for realizing sludge to the fuel.