Kinetic study of the effect of in-situ mineral solids on pyrolysis process of oil sludge

Abstract

Oil sludge (OS) is composed of water, oil and inert solids (silica, clay minerals, etc.). Although solids were ubiquitous in oil sludge, its potential effects on altering pyrolysis characteristics had rarely been studied. Therefore, the role that solids played during the pyrolysis process of oil sludge was investigated by thermogravimetric analysis (TGA) in this study. The kinetic triplets of both OS (contained solids) and extracted oil (EO, solid-free) from OS during the pyrolysis processes were determined by a combined method, including the integral master-plots method and iso-conversional method. The activation energy values for OS pyrolysis varied between 28 and 107 kJ mol−1, and pre-exponential factor ranged from 10 to 104 s−1. Whereas, the activation energy values for EO pyrolysis ranged from 67 to 193 kJ mol−1, and its pre-exponential factor varied from 106 to 1010 s−1. These results suggested that inert solids had positive influences on the pyrolysis of OS because the activation energy for OS pyrolysis was obviously lower than that for EO pyrolysis. The comparison of kinetic models between OS and EO illustrated that solids not only provided sufficient surface for the devolatilization of hydrocarbon but also acted as nucleating agent in char formation.