Pyrolysis and characterization of the kerogen from the Moroccan Youssoufia rock phosphate

Kerogen represents the main form of the trapped organic matter (85 wt.%) in the Youssoufia rock phosphate. It is highly aliphatic in nature and contains a substantial amount of oxygen. Its direct pyrolysis leads to a small amount of pyrolysate (0.4 wt.%) and large quantities of gases. Carbon-dioxide evolution proceeded in two waves centered on 300 and 420 °C, attributed to the cleavage of carboxylic and ester functions. Hydrogen production gives rise to a broad peak covering a wide temperature range (400 to 800 °C). The methane evolves in a single peak extending from 300 to 650 °C. It results from the conventional combination of H⋅ and (CH3)⋅ radicals. The evolution profiles of all the gases are similar to that observed when retorting directly the rock phosphate. n structure was also investigated by spectroscopic techniques and preparative pyrolysis in presence of tetramethyl ammonium hydroxide (thermochemolysis). The n-alkene/n-alkane doublets indicate the occurrence of cross-linked aliphatic chains, partly originating from preserved, resistant biopolyesters. Ester and probably ether groups are involved in the cross-linking of the matrix. Esterified C14–C28 fatty acids, cholestanol and 24-ethyl cholesterol are monosubstituents of the kerogen matrix. C29–C32 α,β hopanes indicate that the kerogen is at the diagenesis evolution stage.