TG-FTIR, Py-two-dimensional GC–MS with heart-cutting and LC–MS/MS to reveal hydrocyanic acid formation mechanisms during glycine pyrolysis

摘要

To elucidate the formation process of HCN from the pyrolysis of glycine, the small molecule gaseous pyrolysates, H_2O, NH_3, CO_2, CO, HNCO, and HCN, were analyzed in real-time by TG-FTIR. The appearance of the volatile pyrolysis products and the solid residue was determined in real-time at their corresponding formation temperatures by online Py-two-dimensional GC–MS with heart-cutting and LC–MS/MS. The pyrolysis of 2,5-diketopiperazine, a thermolytic by-product of glycine pyrolysis, was also studied. The results showed that: (1) the pyrolysis of glycine can be divided into three temperature ranges 200–300, 300–440, and 440–900 ℃; HCN forms in each range with three peaks appearing at 273, 422, and 763 ℃, respectively. (2) The mechanistic pathways of HCN formation from glycine in the low- and high-temperature heating stages are different. Below 273 ℃, glycine undergoes a decarboxylation reaction to produce methylamine, which subsequently forms HCN by means of dehydrogenation. Above 300 ℃, glycine gives relatively large amounts of HCN via 2,5-diketopiperazine and subsequent HNCO or methylenimine formation.