科研之友
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摘要
In this laboratory experiment, students performed thermogravimetric analysis (TGA) coupled with mass spectrometry (MS) of herbaceous materials (TGA-MS) and learned to analyze mass-loss curves, as well as identify common fragmentation ions. The experiment is the first one to present the application of TGA in a currently relevant topic: biomass conversion. A preweighed dry sample of herbaceous origin treated to 700 degrees C with a steady temperature increase rate exhibited the following mass-loss steps: desorption of adsorbed species (e.g., H2O and CO2) followed by char formation via emission of volatile organic compounds and small inorganic molecules. Next, when the process is carried out in the presence of oxygen, the formed char combusted leaving only the ash in the thermobalance crucible. The proportions of these mass losses are significant in the study of biomass for any potential application, such as in the production of energy in plants which already currently utilizes a mixture of coal and plant-based materials. A comparison of two TGA curves obtained from two portions of the same sample heated in an inert and oxygen-containing atmosphere enabled students to determine if and how the char-formation step is influenced by the presence of oxygen. Students also acquired mass spectrometry data from the gaseous stream that was emitted from the sample during the recorded mass-loss steps. Therefore, students were able to gain a basic understanding of what can happen to biomass upon heating, i.e., formation of H2O (m/z = 18) and CO2 (m/z = 44), and the release of simple organic molecules from complex organic matter, which is manifested in the MS spectrum by the presence of positively charged fragments (m/z = 29, 43, 77, 91, etc.).
- 出版日期2018-8
