Particle-scale modeling of asphaltene pyrolysis in thermal plasma

Thermal plasma technique is proposed as a potential approach to pyrolyze asphaltenes to useful chemicals at ultrahigh temperature. Thermal plasma pyrolysis experiments show that acetylene is the major gaseous product with concentration up to 45 wt.%, together with some hydrogen and methane as well as the solids residue as by-products. To predict such a millisecond process, a particle-scale heat transfer model coupled with a modified competition kinetic model has been proposed, in which the heat exchange between the plasma gas and the particles as well as the heat transfer inside the particles are taken into account. Typical results indicate that the pyrolysis temperature would remarkably increase the heating rate. The heating rate would exceed 107 K/s at 2000 K in H2 thermal plasma and the devolatilization process would complete in 0.4 ms for 50 μm asphaltene particles, H2 thermal plasma provides better heating exchange efficiency between the plasma and particles than He, N2 or Ar. Linear relationship is found between the heating rate and the devolatilization time under bi-logarithm coordinates at a certain temperature, regardless of the plasma gas compositions and pulverized sub-millimeter particle size, which gives powerful guidance for process optimization of the asphaltene pyrolysis.