Quantitative analysis of simultaneous multicomponent evolved gases in TG-MS

摘要

Thermal reactions are often such a complicated process in which their typical characteristic is unsteady since all evolved gases are unknown and vary with time or temperature of sample, even much multicomponent evolved gases occur at the same time. Although GC or FTIR can detect the concentration of different components, the concentration values cannot reflect the feature of reaction process because the total flow rate of evolved gas is always unknown and greatly change when the reactions start. On the contrary a new technique of equivalent characteristic spectrum analysis (ECSA) for TG-MS has precisely analyzed the mass flow rate of simultaneous multicomponent evolved gas which can directly describe the characteristic of reaction. This method eliminates the effect of temperature dependent, mass discrimination of mass spectrometer, overlap of mass spectra of different components [1]. Three typical experiments, which includes pure gases simulating test, NH4HCO3 thermal decomposition under different atmosphere and char gasification with CO2, had been conducted to verify the reliability and accuracy of ECSA. In the simulating test of three pure gases N2, CO2 and Ar which were purged with different and changing flow rate, the results calculated by ECSA correctly gave all flow rate values of different gases. The method of pure gases test can be applied to guarantee and monitor the working condition of any thermal reaction to satisfy all designing conditions, and to measure the consumption of reactive purged gas. In the test of NH4HCO3 thermal decomposition that simultaneously evolves NH3, H2O and CO2, ECSA analyzed the mass flow rates of three gases even if under CO2 atmosphere. But the data from the mass spectrum can hardly reflect real characteristic of thermal decomposition with multicomponent evolved gas. For char gasification with CO2, it is very difficult to distinguish the spectrum of CO from the intensive background CO2 since the spectrum of CO2 overlaps the whole fingerprint information of CO. ECSA could clearly separate the spectrum of CO and obtain its mass flow rate. All information from mass flow rate of all gases reasonably gave more reasonable understanding of char gasification characteristic.