Gas and soot products formed in the pyrolysis of acetylene mixed with methanol, ethanol, isopropanol or n-butanol

Abstract

The pyrolysis of acetylene-methanol, acetylene-ethanol, acetylene-isopropanol and acetylene-n-butanol mixtures has been studied in a flow reactor in the 975–1475 K temperature range. The purpose of this work is to analyze the effect of each alcohol on soot and gas products coming from the pyrolysis of the mixtures compared to the results observed in the pyrolysis of pure acetylene, taken as a reference. Results show that the presence of alcohols always reduces the formation of soot and that the lower the atomic carbon/oxygen (C/O) ratio in the reacting mixture, the higher the soot reduction achieved, mainly due to the enhancement of oxidation reactions by the presence of O in the fuel mixture. The experimental evolution of gas products at the reactor outlet is interpreted through a detailed gas phase chemical kinetic mechanism, which allows insight into the causes for soot reduction by the presence of the different alcohols. This analysis reveals that including methanol in the reacting mixture favours mainly the formation of CO, preventing most of the carbon coming from the alcohol to take part in soot formation and its precursors. The rest of the alcohols not only decompose into oxidation products but they can also form species that may contribute to soot formation. In particular, ethanol promotes the formation of CO and CH4, which come from competing reactions that prevent PAH formation, but also forms C2H4 that may contribute to soot precursors growth. Isopropanol contributes to disfavour PAH formation because it decomposes into CO and CH4, but it also forms C2 and C3 hydrocarbons that play an important role in PAH formation and growth. N-butanol enhances oxidation reactions to CO and CH4 formation in a lower degree than the rest of the alcohols and tends to decompose into small hydrocarbons, able to contribute to PAH formation and growth.