Quantitative Analysis by Thermogravimetry-Mass Spectrum Analysis for Reactions with Evolved Gases

Summary

Precise determination of the evolved gases' flow rate is key to study the details of reactions. We provide a novel quantitative analysis method of equivalent characteristic spectrum analysis for thermogravimetry-mass spectrum analysis by establishing the calibration system of the characteristic spectrum and relative sensitivity, for obtaining the flow rate.

Abstract

During energy conversion, material production, and metallurgy processes, reactions often have the features of unsteadiness, multistep, and multi-intermediates. Thermogravimetry-mass spectrum (TG-MS) is seen as a powerful tool to study reaction features. However, reaction details and reaction mechanics have not been effectively obtained directly from the ion current of TG-MS. Here, we provide a method of an equivalent characteristic spectrum analysis (ECSA) for analyzing the mass spectrum and giving the mass flow rate of reaction gases as precise as possible. The ECSA can effectively separate overlapping ion peaks and then eliminate the mass discrimination and temperature-dependent effect. Two example experiments are presented: (1) the decomposition of CaCO₃ with evolved gas of CO₂ and the decomposition of hydromagnesite with evolved gas of CO₂ and H₂O, to evaluate the ECSA on single-component system measurement and (2) the thermal pyrolysis of Zhundong coal with evolved gases of inorganic gases CO, H₂, and CO₂, and organic gases C₂H₄, C₂H₆, C₃H₈, C₆H₁₄, etc., to evaluate the ECSA on multi-component system measurement. Based on the successful calibration of the characteristic spectrum and relative sensitivity of specific gas and the ECSA on mass spectrum, we demonstrate that the ECSA accurately gives the mass flow rates of each evolved gas, including organic or inorganic gases, for not only single but multi-component reactions, which cannot be implemented by the traditional measurements.

Introduction

Understanding in depth the real features of a reaction process is one critical issue for the development of advanced materials and the establishment of a new energy conversion system or metallurgy production process¹. Almost all reactions are carried out under unsteady conditions, and because their parameters, including the concentration and flow rate of reactants and products, always change with the temperature or pressure, it is difficult to clearly characterize the reaction feature by only one parameter, for instance through the Arrhenius Equation. In fact, the concentration implies only the relationship between the component and the mixture....

Protocol

1. Calibration of ECSA for the TG-MS System

1. Calibration of the characteristic spectrum
   1. Prepare the evolved gases of CO₂, H₂O, CH₄, He, etc. to be calibrated, modulating the gas pressure at 0.15 MPa.
   2. Connect the gas cylinder to the TG-MS system by stainless steel tube and purge the individual gas into the TG-MS system with a flow rate of 100 mL/min.
   3. Monitor the mass spectrum of the individual gas. Carefully watch and compare the characteristic peak of gases to be calibrated and the possible impurity gases in the mass spectrum by TG-MS to confirm the species and puri....

Results

The thermal decomposition of CaCO₃ is a relatively simple reaction, which was used to demonstrate the applicability of the ECSA method. After calibrating the characteristic peak and relative sensitivity of CO₂ to carrier gas He, the actual mass flow rate of CO₂ evolved by the thermal decomposition of CaCO₃ was calculated by the ECSA method and was compared with the actual mass loss (Figure 3). It is shown that there.......

Discussion

This protocol could be easily modified to accommodate other measurements for studying evolved gases and pyrolysis reactions by a TG-MS system. As we know, the evolved volatile from the pyrolysis of biomass, coal, or other solid/liquid fuel does not always include only the inorganic gases (e.g., CO, H₂, and CO₂) but also the organic ones (e.g., C₂H₄, C₆H₅OH, and C₇H₈). Moreover, massive fragments would result from the.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
CaCO3 and Ca(OH)2	Sinopharm Chemical Reagent
hydromagnesite	Bangko Coarea in Tibet
Zhundong coal	the coal field in the Mori Kazak Autonomous County, Junggar basin, Xinjiang province of China
ThermoMass Photo/H	Rigaku Corporation
The STA449F3 synchronous thermal analyzer and QMS403C quadrupole MS analyzer	NETZSCH