Name: quantitative analysis by thermogravimetry-mass spectrum analysis for reactions with evolved gases
Uploaded: 2018-10-29T14:00:00
Description: Watch this Scientific Journal Video about Quantitative Analysis by Thermogravimetry-Mass Spectrum Analysis for Reactions with Evolved Gases at JoVE.com

The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China (Grant No. 51506199).

1. Calibration of ECSA for the TG-MS System
<ol>
	<li>Calibration of the characteristic spectrum
	<ol>
		<li>Prepare the evolved gases of CO2, H2O, CH4, He, etc. to be calibrated, modulating the gas pressure at 0.15 MPa.</li>
		<li>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.</li>
		<li>Monitor the mass spectrum of the individual gas. Carefully watch and c...

<ol>
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D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Study+on+pyrolysis+characteristics+of+pretreated+high-sodium+(Na)+Zhundong+coal+by+skimmer-type+interfaced+TG-DTA-EI/PI-MS+system.">Study on pyrolysis characteristics of pretreated high-sodium (Na) Zhundong coal by skimmer-type interfaced TG-DTA-EI/PI-MS system.</a> Fuel Processing Technology. 170, 79-87 (2018).</li><li>Li, C. Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Some+recent+advances+in+the+understanding+of+the+pyrolysis+and+gasification+behaviour+of+Victorian+brown+coal.">Some recent advances in the understanding of the pyrolysis and gasification behaviour of Victorian brown coal.</a> Fuel. 86 (12-13), 1664-1683 (2007).</li><li>Song, H. J., Liu, G. R., Zhang, J. Z., Wu, J. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pyrolysis+characteristics+and+kinetics+of+low+rank+coals+by+TG-FTIR+method.">Pyrolysis characteristics and kinetics of low rank coals by TG-FTIR method.</a> Fuel Processing Technology. 156, 454-460 (2017).</li><li>Kashimura, N., Hayashi, J., Li, C. Z., Sathe, C., Chiba, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evidence+of+poly-condensed+aromatic+rings+in+a+Victorian+brown+coal.">Evidence of poly-condensed aromatic rings in a Victorian brown coal.</a> Fuel. 83 (1), 97-107 (2004).</li><li>Li, C. Z., Sathe, C., Kershaw, J. 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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...

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. Real reaction behavior might not be affected, even though the concentration of a component in one complicated reaction is adjusted to a great extent since the other components might have a stronger influence on it. On the contrary, the flow rate of each component, as an absolute quantity, can give persuasive information to understand the characteristics of the reactions, especially very complicated ones.
At present, the TG-MS coupling system equipped with the electron ionization (EI) technique has been used as a prevalent tool for analyzing the features of reactions with evolved gases2,3,4. However, first, it should be noted that the ion current (IC) obtained from an MS system makes it difficult to directly reflect the flow rate or concentration of the evolved gas. The massive IC overlap, fragment, severe mass discrimination, and diffusion effect of gases in the furnace of a thermogravimeter can greatly hamper the quantitative analysis for TG-MS5. Second, EI is the most common and readily available strong ionization technique. An MS system equipped with EI easily results in fragments and does not often directly reflect some organic gases with a larger molecular weight. Therefore, MS systems with different soft ionization techniques (e.g., photoionization [PI]) are required simultaneously to be hyphenated to a thermobalance and applied to evolved gas analysis6. Third, the intensity of the IC at some mass-to-charge ratios (m/z) cannot be used to determine the dynamic characteristic of any reaction gas, because it is often affected by the other ICs for a complex reaction with multicomponent evolved gases. For example, the drop in the IC curve of a specific gas does not necessarily indicate a decrease in its flow rate or concentration; instead, maybe it is affected by the other gases in the complex system. Thus, it is important to take into account all gases&#39; ICs, certainly with a carrier gas and inert gas.
In fact, quantitative analysis based on mass spectrum greatly depends on the determination of the calibration factor and relative sensitivity of the TG-MS system. Maciejewski and Baiker7 investigated in a thermal analyzer-mass spectrometer (TA-MS) system, in which the TA is connected by a heated capillary to a quadrupole MS, the effect of experimental parameters, including the concentration of gases species, temperature, flow rate, and properties of the carrier gas, on the sensitivity of the mass spectrometric analysis. The evolved gases were calibrated by the decomposition of the solids via a well-known, stoichiometric reaction and injecting a certain amount of gas into the carrier gas stream with a constant rate. The experimental results show that there is a negative linear correlation of the MS signal intensity of evolved gas to that of the carrier gas flow rate, and the evolved gas MS intensity is not influenced by the temperature and the amount of analyzed gas. Further, based on the calibration method, Maciejewski et al.8 invented the pulse thermal analysis (PTA) method, which provides an opportunity to determine the flow rate by simultaneously monitoring the changes of the mass, enthalpy, and gas composition resulted from the reaction course. However, it is still hard to give persuasive information about the complicated reaction (e.g., coal combustion/gasification) by using the traditional TG-MS analysis or PTA methods.
In order to overcome the difficulties and disadvantages of the traditional measuring and analysis method for the TG-MS system, we developed the quantitative analysis method of ECSA9. The fundamental principle of ECSA is based on the TG-MS coupling mechanism. The ECSA can take into account all gases&#39; ICs, including the reaction gases&#39;, carrier gases&#39;, and inert gases&#39;. After building the calibration factor and relative sensitivity of some gas, the real mass or molar flow rate of each component can be determined by the calculation of the IC matrix (i.e., the mass spectrum of TG-MS). Compared with the other methods, ECSA for the TG-MS system can effectively separate the overlapping spectrum and eliminate the mass discrimination and the temperature-dependent effect of TG. The data produced by ECSA have proved to be reliable via a comparison between the mass flow rate of evolved gas and mass loss data by differential thermogravimetry (DTG). In this study, we used an advanced TG-DTA-EI/PI-MS instrument10 to carry out the experiments (Figure 1). This instrument consists of a cylindrical quadrupole MS and a horizontal thermogravimetry-differential thermal analyzer (TG-DTA) equipped with both EI and PI mode, and with a skimmer interface. ECSA for the TG-MS system determines the physics parameters of all evolved gases by utilizing the actual TG-MS coupling mechanism (i.e., an equal relative pressure) to implement the quantitative analysis. The overall analysis process includes a calibration, the test itself, and data analysis (Figure 2). We present two example experiments: (1) the decomposition of CaCO3 with only evolved gas of CO2 and the decomposition of hydromagnesite with evolved gas of CO2 and H2O, to evaluate the ECSA on a single-component system measurement and (2) the thermal pyrolysis of brown coal with evolved gases of inorganic gases CO, H2, and CO2, and organic gases CH4, C2H4, C2H6, C3H8, C6H14, etc., to evaluate the ECSA on a multi-component system measurement. ECSA based on the TG-MS system is a comprehensive solution method for quantitatively determining the amount of evolved gas in thermal reactions.

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

quantitative analysis by thermogravimetry-mass spectrum analysis for reactions with evolved gases

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.

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...

Watch this Scientific Journal Video about Quantitative Analysis by Thermogravimetry-Mass Spectrum Analysis for Reactions with Evolved Gases at JoVE.com

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

Precise determination of the evolved gases&#39; 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.

During energy conversion, material production, and metallurgy processes, reactions often have the features of unsteadiness, multistep, and ...

This method can help answer key questions in the energy, chemistry, and the metallurgy field about how to identify reaction kinetic parameters and evolved gas compositions. To me, an advantage of this technique is that the mass fluid of individual gases evolved from reactions can be qualitatively and quantitatively precisely determined. Through this method, can provide insight into reactions in the energy, chemistry, metallurgy system, and so on.It can also be applied to other systems such as food, pharmacy, or materials. To calibrate a characteristic spectrum, prepare the evolved gases to be calibrated, modulating the gas pressure at 0.15 megapascals. Use a stainless steel tube to connect each gas cylinder to the thermogravimetry mass spectrum, or TG-MS system, and purge all the evolved gases into the TG-MS system at a 100 milliliters per minute flow rate.Monitor the mass spectrum of each individual gas, carefully watching and comparing the characteristic peaks of the gases to be calibrated and any possible impurities within the gases. To calibrate the relative sensitivity of the gases, purge the reference gas at 300 milliliters per minute flow rate into the TG-MS system for 20 minutes to clean the system. Next, synchronously purge each of the calibrated gases with the reference gas into the TG-MS system at a 100 milliliter per minute flow rate.Then calculate the relative sensitivity of each gas according to the known flow rate and the mass spectrum as indicated in the equation. To prepare the samples, collect 10 grams of calcium carbonate with an average diameter of 15 micrometers, 10 grams of a white block of hydromagnesite or 20 grams of Zhundong coal. Break the hydromagnesite block into less than three millimeter pieces and grind the pieces with a machine stirred mill to approximately 10 micrometers.Then dry all of the samples for 24 hours in a 105 degree Celsius oven, breaking and grinding the coal in a mill the next day to obtain a particle size range of 180 to 355 micrometers. To test the thermal reactions of the samples, purge the TG-MS system with helium as the carrier gas for two hours to expel the air and moisture and heat the instrument to around 500 degree Celsius. When the system is cooled back to room temperature, use mass spectrometry to monitor the atmosphere for 20 minutes, carefully watching and comparing the characteristic carbon dioxide and helium peaks and the impurity peaks of the oxygen, nitrogen, and water gases.Weigh 10 milligrams of the sample of interest on a precision electronic balance, and add the weighed sample to an aluminum oxide crucible. Place the crucible with the sample into the TG system and close the furnace. Then set the appropriate operating parameters for the sample being tested.So a reference gas in the calibration must be the same as that in the sample testing process and must never react with the evolved gases. We recommend using helium as the carrier gas in both the calibration and the test. For qualitative and quantitative analysis of the sample data, load the 3D mass spectrum data onto the computer connected to the TG-MS system and use the equivalent characteristic spectrum analysis, ECSA, method to calculate the actual sample parameters based on the previously determined calibrated characteristic peak and the relative sensitivity of the sample.The thermal reaction can then be analyzed according to the actual sample parameters. After calibrating the characteristic peak and relative sensitivity of carbon dioxide to the carrier gas, helium, the actual mass flow rate of carbon dioxide evolved by thermal decomposition of calcium carbonate can be calculated by the ECSA method and compared with the actual mass loss. In this representative analysis, there was a good agreement between the mass flow rate of carbon dioxide and the mass loss data by digital thermogravimetry over the entire measurement process.Comparison of the thermal decomposition process of hydromagnesite by ECSA and the calibration of carbon dioxide and water revealed that these data were also in good agreement with the experimental digital thermogravimetry data. Combining both the electron ionization and photoionization measuring modes, this representative pyrolysis of Zhundong coal revealed the presence of 16 different volatile gases. After detailed determination of the mass spectrum and sensitivity of each identified gas to the carrier gas, the mass flow rate of each gas was calculated and used to compare the mass ion data for each gas based on the same operating parameters.While attempting this procedure, it's important to remember to build the composition fixture and the relative sensitivity of the gases before testing. Following this procedure, a method like differential thermal analysis combined ECSA can be performed to answer additional questions about the features of the reactions without evolved gases. After its development, this technique paved the way for the researchers in the field of energy, chemistry, metallurgy, and so on, to explore using gas reactions and mechanisms in energy conversion and advanced materials development.

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