Effects Of Hydrogen On The Coking Of Heavy Hydrocarbon Feedstocks

The formation of carbon deposits in the volatilization of heavy hydrocarbon feedstocks and model compounds has been investigated in reactors at atmospheric pressure and others going up to 21 bar. Ny, and H» were used as Carrier gases and temperatures up to 650°C were employed. Cumulative weight losses with temperature were measured together with weights of residual carbon and compositions of effluent gases. Rates of weight loss were consistent with a model in which the feedstock evaporated into the carrier gas stream rather than one in which it boiled. Weight was lost more rapidly in H, than in Nos There was a linear correlation in both No and H, between carbon deposition and aromatic content of the feedstock. Change from a silica to a stainless steel crucible reduced deposits under all circumstances, H, reduced carbon deposition. In mixtures of anthracene and acenaphthylene, both anthracene and Hy were shown to inhibit carbon formation. Carbon formation was independent of the pressure or flow rate of carrier gas up to 21 bar. Methane, ethane and ethylene were the main product gases and change from Ny to Hy increased ethane and total gas output. Experiments on deasphalted feedstocks and asphaltenes indicated that in H carbon deposition was due to ’ hydrodealkylation i.e. asphaltene molecules to give gaseous Products from the side chains followed by condensation of the aromatic skeletons to give carbon. In No» hydrodealkylation did not occur and more carbon was de deposited. Carbon formed in the gas phase arose by a mechanism Similar to that of sooting or pyrolytic carbon.