Kinetics and product distribution of n-hexadecane pyrolysis

Pyrolysis experiments on n-hexadecane (n-C₁₆) were conducted at 673 - 723 K and n-C₁₆ concentrations of 0.07 - 1.47 mol/L by using batch type reactors. The main products of n-C₁₆ pyrolysis were n-alkanes and 1-alkenes at all the reaction conditions. The 1-alkene/n-alkane ratio decreased with increasing n-C₁₆ concentration at all the reaction temperatures. The rate of n-C₁₆ pyrolysis increased to a maximum and then decreased with increasing n-C₁₆ concentration. The activation energy of the overall rate constant of n-C₁₆ pyrolysis was 196 kJ/mol at 0.07 mol/L of n-C₁₆ concentration and 263 kJ/mol at 0.22 mol/L. To describe these phenomena, a mathematical model for the pyrolysis that expresses the radical network reaction, including initiation, isomerization, β-scission, H abstraction, and termination, was developed. The effect of radical size on the rates of bimolecular reactions (H abstraction and termination) was important for a correct quantitative description. Comparison between the experimental data and the model showed that the rates of bimolecular reactions were inversely proportional to the carbon number i of radical R(i). The model can predict product distribution and n-C₁₆ pyrolysis rate in a wide range of temperatures (603-893 K) and n-C₁₆ concentrations (6.86 x 10^-3 2.48 mol/L). Furthermore, the model can describe the pyrolysis kinetics of n-C₁₀ - n-C₂₅ by considering the carbon number of the hydrocarbon.