Abatement of tetrafluoromethane by chemical absorption with molten aluminum

Abstract

Chemical absorption with molten aluminum to abate tetrafluoromethane (CF4) was investigated in this paper. The experiments were conducted at a series of different temperatures of 973 K, 1003 K, 1103 K, and 1188 K and the abatement rate of CF4 was calculated. It was found that CF4 can be adsorbed firstly and then react with molten aluminum automatically. The initial abatement rate of CF4 in molten aluminum was 3.10 × 10−2 mol·m−3·s−1 at 973 K, while it reached its maximum value of 1.08 × 10−1 mol·m−3·s−1 at the temperature of 1103 K. The highest abatement efficiency was 48.4%, reached at 1003 K. Higher temperatures up to 1188 K did not affect the abatement efficiency, however, they accelerated slightly the initial reaction rate. The products of the chemical absorption are white solid AlF3 and black graphite powder identified by XRD and SEM-EDS analysis. Due to density differences, solid AlF3 and graphite powder in the product tend to accumulate on the top of molten aluminum where they form two separate layers. This makes them recover more easily. The gas-liquid reaction process between CF4 and molten aluminum is accorded with the two-film theory model, diffusion process is considered to be the control step of the whole process.