The bond cleavage and radical coupling during pyrolysis of Huadian oil shale

Abstract

Pyrolysis of an oil shale starts with cleavage of covalent bonds to generate radical fragments which is followed by coupling of the radical fragments to form volatiles (shale oil and gas) and char. The radical’s reaction determines the distribution, composition and quality of pyrolysis products. However, information about the bond cleavage and the radicals’ reaction during oil shale pyrolysis is very limited in the literature. This paper studies the quantities of total radicals and bonds cleaved in pyrolysis of the organic matter in Huadian oil shale (HDOM) at 380–440°C. The kinetics of the bond cleavage is established and the behavior of radicals’ coupling is discussed. It is found that the quantities of cleavable bonds in HDOM are 0.62×10−2, 0.87×10−2, 1.10×10−2 and 1.33×10−2mol/g at 380, 400, 420 and 440°C, respectively. The bond cleavage can be described by the 1st-order reaction kinetics with an activation energy (Ea) of about 90.10kJ/mol and a pre-exponential factor of 5.23×105min−1. Since not all the bond cleavage yields a mass loss, the activation energy determined for the bond cleavage is different from that for the devolatilization reported in the literature. The number of stable radicals confined in the pyrolysis products shows a good linear relation with that of total radicals generated during pyrolysis and one stable radical is formed among around 2500 radicals generated from HDOM.