The results of the study of the evolution of the characteristics of dispersed carbon formed during the decomposition of liquid hydrocarbons in an electric arc are presented. It is shown that with an increase in the degree of decomposition of the raw material (assessed by the gas yield), along with a change in its group composition, the characteristics of soot change - the particle diameters increase and its structure increases, and the soot becomes less reactive. These changes need to be considered when designing the process.