Pyrolytic carbons deposited in fluidized beds at 1200 to 1400°c from various hydrocarbons

Abstract

Pyrolytic carbons deposited in fluidized beds at 1200 to 1400°C from various hydrocarbon-helium mixtures using otherwise identical process parameters were compared. The trends of microstructure or density with increasing deposition rate were very similar at a given temperature. For each hydrocarbon investigated at 1400°C there was a minimum in the density vs. deposition rate curve. Pyrolytic carbons deposited at 1200°C at similar initial rates near 10 μ/hr from seven hydrocarbon-helium mixtures (methane, ethane, ethylene, acetylene, propane, cyclohexane and benzene) had very similar microstructures, densities, preferred orientations and apparent crystallite sizes. The results support the view that pyrolysis of hydrocarbons in fluidized beds involves dissociation into small fragments which then take place in polymerization-dehydrogenation reactions and indicate that the general mechanisms of pyrolytic carbon deposition in fluidized beds are independent of the hydrocarbon. The various microstructures were explained in terms of the extent of incorporation of gas-borne droplets or soot particles into the deposits or the variations of coating environment within the fluidized beds. The systematic variations of the properties of the pyrolytic carbons deposited from methanehelium mixtures at 1400, 1300 and 1200°C were investigated in detail and found to be consistent with a published model of pyrolytic carbon deposition in fluidized beds.