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

Two petroleum residues of different composition were pyrolysed under differ ent experimental conditions to obtain semicokes with a range of aromaticity , mesophase content and optical texture. The X-ray diffraction patterns sho w the (002) peak, and a band (zone gamma) at lower values of 2 theta. In ge neral terms, the progress of carbonisation and the subsequent growth of mes ophase are paralleled by a slight decrease in d(002), an increase of the st ack height L-c of the lamellar structure, and a decrease of the intensity r egistered in zone gamma, due to the progressive transformation/elimination of the isotropic phase. Some semicokes have been extracted with heptane, to luene or 1-methyl-2-pyrrolidone to obtain soluble and insoluble fractions T he diffraction patterns of the insoluble fractions show that there is no si gnificant change in the value of L-c or in the position of the (002) peak, only a decrease in the zone gamma being detected; this indicates that the s olvent extracts isotropic material from the semicoke. On the other hand, th e diffractograms of the soluble fractions indicate that the mesophase is no t dissolved by heptane, but it is partially dissolved by toluene and especi ally by 1-methyl-2-pyrrolidone. (C) 1999 Elsevier Science Ltd. All rights r eserved.