Exploration of new olefin production process: Effects of the addition of CO2 and H2O on n-heptane pyrolysis

Abstract

In order to study the new cracking process characteristics of hydrocarbon feedstock to light olefins by direct flue gas heating, the pyrolysis experiments of n-heptane in CO2 and H2O atmosphere were performed in pretreated STS316L flow reactor (ϕ10 mm × 2.5 mm × 700 mm) at a temperature range of 1073–1373 K, pressure range of 0.1–1.0 MPa. By changing the n-heptane flow and system pressure to adjust the residence time, results show that the latter is not conducive to olefin formation, but the residence time range about high olefin formation of the latter is wider than that of the former. Due to the promotion of CO and the high-temperature solubility of CO2, the types and contents of PAHs in tar under H2O&CO2 atmosphere are higher. Based on the analysis of n-heptane cracking products stream, the reactivity of H2O and CO2 gradually appears at high temperature and the reactivity of H2O is significantly higher than that of CO2, resulting in higher yields of H2 and CO. The mainstream of the process is the cracking of n-heptane, in which H2O is the supply source of •OH and •H, and CO2 acts as a coking agent. High olefin yields can be achieved in either H2O-rich or CO2-rich atmosphere, and the ratio of the two needs to be properly regulated.