Research on the Production of Hydrogen Fluoride from Silicon Tetrafluoride Using 2.45 GHz Microwave Plasma

Silicon tetrafluoride (SiF4), being a toxic gas, contains abundant fluorine and silicon resources. However, at present, the extraction of these resources from SiF4 remains a significant challenge for current technologies. Microwave plasma emerges as a promising technology with considerable potential in this area. Nevertheless, the majority of research endeavors concentrate on the silicon production through microwave plasma treatment of SiF4, while the resultant tail gas, rich in fluorine resources, is neglected and subsequently wasted. In this paper, a low-pressure microwave plasma is employed to process SiF4 and H2 for the one-step synthesis of hydrogen fluoride (HF). The microwave power reflection ratio, electron density, SF4 conversion rate, and produced HF concentration in varying microwave power levels and gas flow rates are obtained. The results demonstrate that all the processing parameters have a direct impact on the HF concentration. The maximum HF concentration of 11,200 ppm is achieved under the specific condition: an H2 flow rate of 2.5 sccm, a SiF4 flow rate of 2 sccm, and a microwave power level of 1100 W. Notably, this condition also results in the lowest energy cost. Moreover, the underlying reaction mechanism of the conversion from SiF4 to HF is thoroughly analyzed. This work presents fundamental process guidance for the production of HF using microwave plasma, facilitating the scalability of this technology in industry.