Development of dry-type off-gas treatment technology of exhaust gases from the semiconductor industry for fluorine recycling

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Fluorocarbons and perfluoro compounds (PFCs) contribute to global warming and are used in large quantities in the semiconductor industry, which must reduce the emission of these gases to the atmosphere to achieve the requirements of the Kyoto Protocol. We have been developing a new dry-type off-gas treatment system for recycling fluorine from perfluoro compounds present in off-gases from the semiconductor industry. The feature of this system is to absorb the fluorine compounds in the exhaust gases from the decomposition furnace by using two types of solid absorbents: the calcium carbonate in the upper layer absorbs HF and converts it to CaF2, and the sodium bicarbonate in the lower layer absorbs HF and SiF4 and converts them to Na2SiF6. In this research, the fluorine compound adsorption properties of both the solid adsorbents-calcium carbonate and the sodium compound-for the optimal design of the fixation furnace are investigated. An analysis of the gas-solid reaction rate was performed from the experimental results of the breakthrough curve by using a fixed-bed reaction model, and the reaction rate constants and adsorption capacity were obtained for achieving an optimal process design.