Use of a Process Mass Spectrometer to Measure Rapid Changes of Gas Concentration
Abstract Experiments were conducted to investigate the suitability of a multistage in-situ reaction analyzer based on a micro fluidized bed (MFB-MIRA) for measuring rapid changes of gas concentration during gas-solid reactions. The results show that control of capillary temperature of a process mass spectrometer strongly influences the stability of on-line measurements. Based on observed regular patterns, the capillary temperature-control system was equipped with a precision controller that enabled a precision of ±0.2 °C to be achieved, and thereby guaranteed high stabilities of the sampling flow rate and chamber vacuum. Measurements using the modified gas-monitoring system showed that periodic fluctuations of the on-line measurement were eliminated and measurement stability significantly improved. The fluctuating range and relative standard deviation of the measured response to O 2 in air improved from 1.9% to 1.4% and 0.54% to 0.18%, respectively. A pressure-regulating device was also developed to control the absolute pressure at the gas sampling point. This achieved a control precision of ±0.02 kPa. The measured results showed that the response of the process mass spectrometer correlated positively with the absolute pressure at the sampling point, indicating the necessity for a pressure-regulating device. The accuracy and repeatability of the process mass spectrometer were improved. This work has enhanced the suitability of MFB-MIRA for studying rapid gas-solid reactions and broadened the scope of reliable applications of MFB-MIRA combined with a process mass spectrometer.