In situ FTIR study on real-time changes of active groups during lignite reaction under low oxygen concentration conditions

Abstract

Coal spontaneous combustion is essentially the reaction of active groups, which usually occurs in low oxygen atmospheres. This paper studied the real-time changes of active groups during coal reaction at low oxygen concentrations by in situ FTIR. The results show that the active groups have different reactive activities and changing trends, i.e. continuously increase, continuously decrease, decrease at first and then increase. Both the quantity and changing trends are influenced by oxygen supply. The oxygen-containing groups having small reactive activity increase with temperature rise. The active groups having large reactive activity have two vibrational types. The bending vibration groups change with temperature rise as the same style, while the stretching vibration ones change in different styles. For the same group, the quantity and reactive activity of stretching vibration ones are greater than bending vibration ones. The active groups still can react with oxygen even under an oxygen atmosphere of 5%, but pyrolysis is the main reaction form under this condition. It will provide active groups or sites for coal self-heating. Therefore, it's better to control the oxygen concentration below 5% for fire prevention. The results will be helpful for further understanding the mechanism of coal self-heating.