Valuable products from mineral waste oils containing heavy metals

The main objective of this paper is to study the conversion of mineral waste oils (MWO) containing heavy metals into valuable products via pyrolysis. The pyrolysis of the MWO has been carried out in a continuous-mode preparative scale pyrolysis unit containing a bed of char obtained from the Samca coal, a low-rank coal. Temperature of 625 degrees C and 700 degrees C and pressures of 0.1 and 1 MPa have been used. High yields of valuable light olefins as ethylene and propylene and light aromatics as BTX and naphthalene derivatives have been obtained. Special attention has been paid to the fate of the metals contained in the MWO during pyrolysis and their distribution into the pyrolysis products. in particular, the distribution of six metals (Cd, Ni, Pb, Cu, Cr, V) has been studied. The data show that the Samca coal chars used has the ability to take up some of the metals under study, but the behavior of each metal is different. So, while Pb and Cu are mostly retained in the coal char bed, V is not affected, and Cd, Ni, and Cr are even released from the char. The reduction of the Pb, Cu, and V contents from the MWO to the liquid pyrolysis products is very high, whereas the contents of Cd, Ni, and Cr in the liquids remain almost constant after the pyrolysis process. Variation of the distribution of the metals contained in MWO between the char bed and the liquid products recovered as a function of the pyrolysis conditions are discussed.