Effect of $\rm CH_4{,}~\rm H_2{,}~\rm Ar$, carbon additives and the shape of a reactor on the porous structure of acetylene black formed during the decomposition of acetylene

The porous structure of acetylene black was studied depending on the conditions of its preparation in the decomposition of acetylene: at various pressures in a tubular reactor of limited volume, decomposition of acetylene in mixtures with $\rm CH_4{,}~\rm H_2$, or $\rm Ar$ and decomposition of acetylene in the presence of acetylene black and in reactors of various shapes. It has been found that the decomposition of pure acetylene with an increase in pressure from $2.35$ to $5$ bar increases the surface area of acetylene black from $75$ to $125$ m$^2$/g, and the average particle size decreases from $36$ to $22$ nm. Additives of $\rm CH_4{,}~\rm H_2$, or $\rm Ar$ inhibit the decomposition of acetylene, while the degree of inhibition decreases in the following sequence: $\rm H_2 > \rm CH_4 > \rm Ar$. Relatively small additions of hydrogen block the decomposition of acetylene, practically without affecting the size of acetylene black particles. On the contrary, addition of methane leads to a significant increase in the average size of acetylene black particles to $55$ nm and a corresponding decrease in the specific surface area to $57$ m$^2$/g. Addition of argon to acetylene qualitatively affects the porous structure of acetylene black in the same way as reducing the pressure of acetylene. During the decomposition of acetylene in the presence of acetylene black remaining in the reactor after the previous decomposition, a nonmonotonic change in the specific surface area and size of acetylene black particles was observed. It was shown in experiments with reactors different in shape but identical in volume that, with a decrease in the linear dimensions of the reaction vessel (length/diameter ratio), the surface area of the formed acetylene black increases rather significantly, and the average size of acetylene black particles decreases.