Experimental studies on n- heptane pyrolytic characteristics in CO2/H2O atmosphere

The pyrolysis experiments of n-heptane in the CO2/H2O atmosphere were carried out in a millimeter-sized tube reactor. Mass yields and molar concentrations of gaseous products, including C2H4, C3H6, H-2, CO, CH4, and C2H6, were obtained at a temperature range of 1073-1373 K, and atmospheric pressure. The pyrolysis characteristics of n-heptane under different reaction atmospheres and residence times were summarized. The results showed that the mass yields of ethylene and propylene in the mixed atmosphere of CO2 and H2O were 7.9 %-36.8 % higher than those in the single H2O atmosphere under low residence times. The yield and selectivity of olefin increased with increasing the temperature within narrow residence time range (less than 0.2 s). At 1173 K, the total mass yield of ethylene and propylene was more than 60 %, and the olefin selectivity was about 40 %, which was the peak value among all experimental temperature conditions. With a rise in temperature, there also occurred an interaction between pyrolysis and gasification processes as reported in the literature, and the gasification reaction rate increased, which led to the high production of CO and H-2. The overall studies in this paper show that reasonable and accurate control of reaction residence time in the CO2&H2O pyrolysis process is important to obtain higher olefin yield and selectivity, especially when the operating temperature is higher than 1173 K.