Effects of potassium hydroxide on the catalytic pyrolysis of oily sludge for high-quality oil product

Oily sludge has received increasing attention for its hazardousness as well as its high potential as an energy resource. Previous studies have developed many methods for oil recovery from oily sludge. In this paper, the effect of KOH on improving the quality of oil product from different oily sludge through pyrolysis was studied. Gel permeation chromatography (GPC), rheometer and gas chromatography-mass spectrometry (GC-MS) were applied to characterize the pyrolysis oil products. The product yields along with possible reaction mechanisms and kinetic characteristics were discussed. It was found that the oil yield decreased while the gaseous yield and solid residues increased with the addition of KOH. The GPC results showed that hydrocarbon species in the pyrolysis oil were more pure and the average molecular weight could be reduced by 53% for the used sample when KOH was added, which could be possibly explained by the cracking reaction of heavy oil into light species. The viscosity of the oil product also showed a significant reduction while the heating value increased in the case of adding KOH. Additionally, SARA fractions were extracted from oil to obtain the asphaltenes content and to identify the detailed components of saturated compounds. Results showed that the concentration of asphaltenes was declined by half and more saturate hydrocarbons (such as C14H30 to C17H36) were produced when KOH ratio reached up to 10%. It revealed that quality of oil product was improved in terms of smaller average molecular weight, lower viscosity, higher heating value, less asphaltenes and more straight chain hydrocarbons.