The pyridine vapor adsorption behavior and its influence on suppressing low-temperature cross-linking reactions during slow pyrolysis of lignite

A Chinese lignite, Yitai (YT) was pretreated by pyridine vapor and then purged by nitrogen gas to remove the pyridine which weakly interacted with coal. The effects of pyridine vapor treatment on the hydrogen bonds and the pyrolysis behavior of coal were studied by in situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFT) and TG-MS, respectively. The pyridine adsorption behavior of coal at room temperature was also studied. The results show that the pyridine vapor can break the hydrogen bonds in coal and form new stronger N–OH hydrogen bonds with oxygen function groups, resulting in N–OH hydrogen bonds slight increase and other hydrogen bonds decrease. When this swelled coal was pyrolyzed, the low-temperature cross-linking reactions that related to the hydrogen-bonded COOH–COOH and COOH-OH was suppressed due to the better thermal stability of the N–OH hydrogen bond in coal. This effect is reflected by the decrease in the yields of CO2 or H2O, and the larger weight loss difference between the raw and the pretreated coal during pyrolysis at the temperature below 400 °C.