Development Of Photoionization Time-of-flight Mass Spectrometer And Its Application For Catalytic Reaction Monitoring

With the development of the society, the ascension of the economy and the growth of population, the industrial production develops rapidly to meet the growing consumer demands from various aspects of the current society. In order to improve the process flow, reduce the energy consumption, enhance the production efficiency and improve the products quality, people invested a lot of manpower and material resources to study and exploit new technologies and methods for industrial process monitoring. Online monitoring mass spectrometry, which is characterized with the soft ionization technique, is suitable for continuous online process monitoring for its advantages of rapid analysis speed, broad applicability, high sensitivity and resolution, and excellent ability for qualitative analysis.As an important and basic organic chemical raw materials, the light carbon olefin is indispensable in the field of resources and energy. With the shortage of the raw material in the global scope, MTO has gradually become the key technique in the coal to olefins route, and thus it is of great economic value and strategic significance. However, it is a great challenge for traditional analytical methods to realize real-time monitoring of the catalytic products during MTO catalytic reaction process, which makes it difficult to optimize the catalytic reaction conditions and explore the reaction mechanismsIn this thesis, a time-of-flight mass spectrometer (TOFMS) was designed, combined with a photoionization source using a commercialized vacuum ultraviolet (VUV) lamp, for real-time and online detection of MTO catalytic reaction process, which conquered the disadvantages of traditional detection methods. It was built using the structure of orthogonal acceleration and reflection, the field-free region was 348.5 mm, and the overall size of the TOFMS was 750×460×413 mm. The achieved mass resolution of TOFMS was 6409 at m/z 112, the limits of detection for typical VOCs (benzene, toluene, p-xylene) at ppb level were realized within 30s.A single photon ionization (SPI) and photoelectron ionization (PEI) combined ionization source was coupled to the TOFMS instrument, by which the molecular ions of analytes were obtained. As a result, a mass resolution of 3960 was achieved at m/z 28, and the mass peaks of N2+and C2H4+were baseline separated, which avoids the interference of the carrier gas N2 to the identification of the product C2H4 during MTO catalytic process. Under the condition of ionization region pressure 7 pa, the limits of detection down to 0.51,0.052, and 0.042 mL/m3 were obtained for ethylene, propylene and butylene within 5 s, respectively. The instrument has been successfully applied to the real-time, fast, and online analysis of gas-phase products during MTO catalytic process. The results indicate that this instrument has potential application value and broad application prospects in industrial process monitoring.