Pyrolysis of petroleum residues: analysis of semicokes by X-ray diffraction Original Research Article

Two petroleum residues of different composition were pyrolysed under different experimental conditions to obtain semicokes with a range of aromaticity, mesophase content and optical texture. The X-ray diffraction patterns show the (002) peak, and a band (zone γ) at lower values of 2θ. In general terms, the progress of carbonisation and the subsequent growth of mesophase are paralleled by a slight decrease in d002, an increase of the stack height Lc of the lamellar structure, and a decrease of the intensity registered in zone γ, due to the progressive transformation/elimination of the isotropic phase. Some semicokes have been extracted with heptane, toluene or 1-methyl-2-pyrrolidone to obtain soluble and insoluble fractions. The diffraction patterns of the insoluble fractions show that there is no significant change in the value of Lc or in the position of the (002) peak, only a decrease in the zone γ being detected; this indicates that the solvent extracts isotropic material from the semicoke. On the other hand, the diffractograms of the soluble fractions indicate that the mesophase is not dissolved by heptane, but it is partially dissolved by toluene and especially by 1-methyl-2-pyrrolidone.