Revealing the local coke evolution under the pyrolysis and fuel-rich conditions by in-situ Raman microscopy

Coke is a harmful carbon substance formed on the hot pipeline of chemical equipment and supersonic aircraft, reducing heat transfer efficiency and overall performance. The structure evolution of coke on the specific and local position of the inner surface of the quartz flow reactor was studied by in-situ Raman microscopy during the acetylene pyrolysis. The in-situ Raman measurement method was put forward by combining the Raman microscopy and the quartz flow reactor. The Raman spectra of coke were continuously recorded to reveal the structure variation. The integrated intensity, band intensity ratio, and crystalline size were evaluated. A mechanism of coke evolution at a local position was proposed based on the in-situ Raman methods, including four stages, namely physical deposition, surface reaction, inside reaction, and inside maturity. The influence of temperature and the presence and amount of oxygen on the coke was studied. The high temperature and presence of certain oxygen could promote the progress of coke evolution, represented by the earlier transition time, and larger crystalline size of coke. This work achieves the in-situ observation of coke and provides a new perspective to reveal the local coke evolution. Investigations remain needed to further reveal the mechanism of local coke evolution, especially the physical deposition and inside reaction stages.