Study of treatments to remove water from petroleum sludge and evaluation of kinetic parameters by thermal analysis using isoconversional methods

Usually the water content of petroleum sludges is significantly high and its removal is of great importance due to the reduction of the amount of sludge to be treated, as well as of the respective needed energy. In this work, three different separation methods were used to decrease the water content of the studied sludge: filtration, centrifugation and simultaneous filtration and evaporation, the last of which was the most efficient. Pyrolysis kinetic data were obtained for each resulting product by thermal analysis in aluminum crucibles by using lids with a pinhole. Heating rates of 2, 5 and 10 °C min −1 from ambient temperature up to 600 °C were used under 100 mL min −1 nitrogen flow. Ozawa–Flynn–Wall with Doyle approximation, Kissinger–Akahira–Sunose and Błażejowski isoconversional methods were applied to calculate the activation energies of the initial evaporation and further pyrolysis stages. The samples with the highest residual water contents were the centrifuged and filtered ones, which show a similar discontinuity of their increasing activation energy, right after their first heating stage, during which water was totally released simultaneously to the lighter organic components, a fact that does not happen with the sludge resulting from filtration and natural evaporation, due to its very low water content. It was also noticed that for all studied conversion degrees, the activation energies of the centrifuged sludge were much higher than those of the other two treated samples, due to the sludge structure compaction during centrifugation, which caused the necessity of a much higher energy to vaporize or to pyrolyze its components.