Gas-Solid Reaction Properties of Fluorine Compounds and Solid Adsorbents for Off-Gas Treatment from Semiconductor Facility

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 adsorb the fluorine compounds in the exhaust gases from the decomposition furnace by using two types of solid adsorbents: the calcium carbonate in the upper layer adsorbs HF and converts it to CaF2, and the sodium bicarbonate in the lower layer adsorbs HF and SiF4 and converts them to Na2SiF6. This paper describes the fluorine compound adsorption properties of both the solid adsorbents—calcium carbonate and the sodium compound—for the optimal design of the fixation furnace. 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. 1. Introduction 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 in order to achieve the requirements of the Kyoto Protocol. In the semiconductor industry, voluntary reduction goals for PFCs were set at the World Semiconductor Council held in April 1999 and ongoing reduction efforts have been made. However, since hydrofluorocarbons (HFCs) and PFCs are used in critical processes, including chamber cleaning and etching during the manufacturing of semiconductors such as LCDs and solar panels, the consumption of these chemicals increases every year. Therefore, in spite of the reduction efforts, the emission of fluorocarbons and PFCs has increased in recent years. The technology for the treatment of PFCs, which has been supplied in the semiconductor industries as an inexpensive process, is a combination of combustion to decompose PFCs into acid components such as HF and scrubbing to neutralize the acid components [1]. However, because the combustion method has a low decomposition ratio and the treatment of the resultant wastewater has a high energy load, a new dry treatment technology is desirable. Consequently, we are developing a new dry-type treatment technology for PFCs that consists of an electric furnace for decomposition of the PFCs and a dry-fixation furnace for adsorption of the acid components, which enables fluorine recycling. Fluorine is a precious resource for Japan, which imports most of its fluorine from China or Mexico [2]. This paper describes the details of the